Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury

*Roxana Rodrígez-Barrera, Adrián Flores-Romero, Julián García-Sánchez, Lisset Karina Navarro-Torres, Marcela Garibay-López and Elisa García-Vences*

## **Abstract**

The inflammatory response after a spinal cord injury (SCI) is a secondary mechanism of damage, this involves alterations at the local and systemic level, and it is mediated by cytokine participation that takes part actively. The excessive inflammatory response causes an autoreactive response that targets against components of the nervous tissue; this response lengthens the inflammatory process initiated during the acute phase. The participation of immune cells in acute phases is characterized by the arrival of neutrophils, macrophages, and microglia, as well as T lymphocytes, which express their peaks on different days post-injury (1st, 3rd, and 11th respectively). The chronic phase of the injury begins 14 days after it occurred, reaching its highest point at 60 days, and can still be detected the following 180 days. One of the outcomes of the inflammatory process and cytokine synthesis is the generation of glial scar. In this chapter, we will review the different cytokine mechanisms involved in the formation of glial scar in acute and chronic phases, as well as the modulating treatments of glial scar.

**Keywords:** spinal cord injury, immune cells, scar glial, modulating treatments

### **1. Introduction**

Spinal cord injury (SCI) causes catastrophic damaged to patients, and the incidence is getting higher each year. Most of them are occasioned by physical trauma from sports injuries, car accidents, falls, and more [1, 2]. This life-changing neurological condition also comes with socioeconomic implications for patients and their caregivers, besides the functional and sensitive consequences that are largely determined by the level and completeness of the injury [1, 3].

After SCI, the acute and focal inflammation triggers a multicellular and multifunctional complex response which induces resident and infiltrating cells to form the glial scar (GS) at the site of the lesion [3]. The GS is a complicated phenomenon which has been considered as one of the main causes of limited regenerative capacity by inhibiting axonal regeneration and preventing functional recovery [4]. It has been proven that the GS creates both a physical barrier for neural repair as well as a chemical inhibition by the secretion of inhibitory extracellular matrix

molecules [5]. At the present time, finding an effective treatment has shown to be challenging due to the lack of complete understanding about the multifactorial pathophysiology of SCI. Current medical treatment is confined to surgical procedures and anti-inflammatory drugs which aim to reduce the damage caused by the continuous inflammatory reactions and therefore increase the locomotor recovery. More importantly, recent studies have demonstrated that the GS can be both favorable or prejudicial depending on the evolution time of the SCI, being able to participate in tissue repair and functional recovery during the acute phase but later on establishing a recovery plateau due to the inhibition of axonal regeneration during the chronic phase [6, 7]. Therefore, in recent years there has been an increasing interest in developing new therapies that can modulate the immunological responses involved in the GS formation. Although there are many drugs that have been identified as potential treatments for SCI, there is currently no therapy that can effectively restore the neural function that is lost during this pathology. The purpose of this chapter is to describe the importance of cytokines in the immunological processes of GS formation as well novel therapies that could serve as potential treatments of SCI.

## **2. Inflammation in traumatic central nervous system**

Disorders in the homeostasis of the central nervous system (CNS) just as infection, trauma, ischemia, neurodegenerative diseases, and disturbances in general induce the beginning of neuroinflammatory responses that can be considered to consist principally of innate immune mechanisms [8, 9].

Inflammation is the way the human body acts in response to situations such as injury and infection. This mechanism involves several processes of the somatosensory, autonomic, immune, and vascular systems and more [10].

The immune and nervous system are capable of regulating physiological homeostasis and defending against infection and injury through inflammation. Both systems have improved many features for the recognition of alterations in the changing microenvironment to facilitate the protective responses. Although cells in each system (neurons and immune cells) have many differences, they can interact and communicate together to make a functional cooperation for the integral homeostasis [11].

Neuroinflammation is a localized inflammation in both CNS and peripheral nervous system (PNS), despite being distinct from the inflammation in peripheral tissues. There is also upregulation of several pro-inflammatory cytokines like IL-1β, IL-6, TNFα, and chemokines that affect the integrity of the blood brain barrier (BBB) resulting in local and systemic immune responses [9, 10, 12].

During these events, neural control plays an important role due to the fact that many immune molecules are detected by sensory neurons, which lead the system to generate immunoregulatory responses [13]. In general, the nervous system integrates biological functions to restore homeostatic function with the use of neurotransmitters and other regulatory molecules [11].

On the other hand, there are other cell types involved in the response, such as microglial and astrocytes. Microglial cells are made to deal with the harmful effects involving the activation of astrocytes, which are capable of modulating the activity of other immunocompetent cells in the site of the injury and also have an active role in the synaptic elimination, regeneration, cell elongation, and repair [8, 14, 15]. Many studies have reported that astrocytes participate in axonal regeneration by providing growth substrates and guidance structures [16]. They are also required in CNS repair, especially in the acute phase after injury but not

**77**

**Figure 1.**

*Inflammatory response after spinal cord injury.*

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

in the chronic phase, reducing GS formation and exacerbating the magnitude and

both to cell damage and tissue remodeling [12]. They are involved in reactive plasticity modulation of neuronal populations in different types of brain injuries, as well as in microglial cells and astrocytes, since they can activate and promote

as an important manipulable aspect of injury in animal and human studies to develop immunomodulatory therapies because it can be detrimental or beneficial;

however, it is necessary to understand the processes in a better way [19].

Nevertheless, it has been confirmed that inflammatory mechanisms contribute

Owing to the events explained before, neuroinflammation is taken into account

In the SCI there are two phases of the pathology: the primary one which consists in the initial accident-induced damage that can result from the compression of the spinal cord (SC), stretching of the nervous tissue, or disruption of local blood supply and the secondary one, which is characterized by the damage caused by inflammation and other biological mechanisms. These events can start at the moment of the injury and go on for days, and even weeks, after the event [2, 20] (see **Figure 1**). Inflammatory microenvironment after SCI involves activated microglia, astrocytes, and infiltrating macrophages that play a role in the development of the secondary injury, and it is the major target to combat SCI [1, 2]. Then, this environment following SCI is mediated by the activation of microglia and astrocytes and infiltrating macrophages that greatly contribute to the progression of secondary injury that is a compilation of complex events derived from the initial trauma. Some of the mechanisms in its pathogenesis includes neurodegeneration, gliosis, and apoptosis in nearby intact neural tissues [21–25]. Effective restraint of secondary injury is essential to minimize neurodegeneration and to improve significantly

It is important to know that a traumatic injury in the CNS begins with the disruption of the BBB and blood-spinal barrier (BSB), followed by the arrival of several cells and molecules of the immune system with the possibility of aggravating the situation, affecting subsequent events such as repair and regeneration [26].

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

duration of inflammatory activation [17, 18].

recovery and repair the neural circuits [8].

functional recovery [1].

**2.1 Inflammatory response after spinal cord injury**

#### *Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury DOI: http://dx.doi.org/10.5772/intechopen.93005*

in the chronic phase, reducing GS formation and exacerbating the magnitude and duration of inflammatory activation [17, 18].

Nevertheless, it has been confirmed that inflammatory mechanisms contribute both to cell damage and tissue remodeling [12]. They are involved in reactive plasticity modulation of neuronal populations in different types of brain injuries, as well as in microglial cells and astrocytes, since they can activate and promote recovery and repair the neural circuits [8].

Owing to the events explained before, neuroinflammation is taken into account as an important manipulable aspect of injury in animal and human studies to develop immunomodulatory therapies because it can be detrimental or beneficial; however, it is necessary to understand the processes in a better way [19].

#### **2.1 Inflammatory response after spinal cord injury**

In the SCI there are two phases of the pathology: the primary one which consists in the initial accident-induced damage that can result from the compression of the spinal cord (SC), stretching of the nervous tissue, or disruption of local blood supply and the secondary one, which is characterized by the damage caused by inflammation and other biological mechanisms. These events can start at the moment of the injury and go on for days, and even weeks, after the event [2, 20] (see **Figure 1**).

Inflammatory microenvironment after SCI involves activated microglia, astrocytes, and infiltrating macrophages that play a role in the development of the secondary injury, and it is the major target to combat SCI [1, 2]. Then, this environment following SCI is mediated by the activation of microglia and astrocytes and infiltrating macrophages that greatly contribute to the progression of secondary injury that is a compilation of complex events derived from the initial trauma. Some of the mechanisms in its pathogenesis includes neurodegeneration, gliosis, and apoptosis in nearby intact neural tissues [21–25]. Effective restraint of secondary injury is essential to minimize neurodegeneration and to improve significantly functional recovery [1].

It is important to know that a traumatic injury in the CNS begins with the disruption of the BBB and blood-spinal barrier (BSB), followed by the arrival of several cells and molecules of the immune system with the possibility of aggravating the situation, affecting subsequent events such as repair and regeneration [26].

**Figure 1.** *Inflammatory response after spinal cord injury.*

*Cytokines*

tial treatments of SCI.

homeostasis [11].

molecules [5]. At the present time, finding an effective treatment has shown to be challenging due to the lack of complete understanding about the multifactorial pathophysiology of SCI. Current medical treatment is confined to surgical procedures and anti-inflammatory drugs which aim to reduce the damage caused by the continuous inflammatory reactions and therefore increase the locomotor recovery. More importantly, recent studies have demonstrated that the GS can be both favorable or prejudicial depending on the evolution time of the SCI, being able to participate in tissue repair and functional recovery during the acute phase but later on establishing a recovery plateau due to the inhibition of axonal regeneration during the chronic phase [6, 7]. Therefore, in recent years there has been an increasing interest in developing new therapies that can modulate the immunological responses involved in the GS formation. Although there are many drugs that have been identified as potential treatments for SCI, there is currently no therapy that can effectively restore the neural function that is lost during this pathology. The purpose of this chapter is to describe the importance of cytokines in the immunological processes of GS formation as well novel therapies that could serve as poten-

**2. Inflammation in traumatic central nervous system**

consist principally of innate immune mechanisms [8, 9].

sory, autonomic, immune, and vascular systems and more [10].

(BBB) resulting in local and systemic immune responses [9, 10, 12].

neurotransmitters and other regulatory molecules [11].

Disorders in the homeostasis of the central nervous system (CNS) just as infection, trauma, ischemia, neurodegenerative diseases, and disturbances in general induce the beginning of neuroinflammatory responses that can be considered to

Inflammation is the way the human body acts in response to situations such as injury and infection. This mechanism involves several processes of the somatosen-

The immune and nervous system are capable of regulating physiological homeostasis and defending against infection and injury through inflammation. Both systems have improved many features for the recognition of alterations in the changing microenvironment to facilitate the protective responses. Although cells in each system (neurons and immune cells) have many differences, they can interact and communicate together to make a functional cooperation for the integral

Neuroinflammation is a localized inflammation in both CNS and peripheral nervous system (PNS), despite being distinct from the inflammation in peripheral tissues. There is also upregulation of several pro-inflammatory cytokines like IL-1β, IL-6, TNFα, and chemokines that affect the integrity of the blood brain barrier

During these events, neural control plays an important role due to the fact that many immune molecules are detected by sensory neurons, which lead the system to generate immunoregulatory responses [13]. In general, the nervous system integrates biological functions to restore homeostatic function with the use of

On the other hand, there are other cell types involved in the response, such as microglial and astrocytes. Microglial cells are made to deal with the harmful effects involving the activation of astrocytes, which are capable of modulating the activity of other immunocompetent cells in the site of the injury and also have an active role in the synaptic elimination, regeneration, cell elongation, and repair [8, 14, 15]. Many studies have reported that astrocytes participate in axonal regeneration by providing growth substrates and guidance structures [16]. They are also required in CNS repair, especially in the acute phase after injury but not

**76**

The inflammatory microenvironment after SCI involves activated microglia, astrocytes, and infiltrating macrophages that play a role in the development of the secondary injury, and it is the major target to combat SCI.

It has been demonstrated that there is a multiphasic response during the inflammation processes after SCI and a huge interaction between central and peripheral cellular and soluble components, which are influenced by some factors like patient age, sex, mechanism and degree of injury, therapeutic interventions, and genetic variability [9, 26].

In a study made by Beck et al. [26], they established two types of cellular inflammation phases. The early phase includes principally the infiltration of neutrophils which are polymorphonuclear leucocytes (PMNs), macrophages, and microglia, which inhibit recovery of the brain and SCI after the traumatic event. It was discovered that neutrophils are peaking 1 day of post-injury, macrophages/microglia 7 days of post-injury, and T cells 9 days of post-injury. The late phase was detected after 14 days of post-injury with its peak after 60 days of post-injury, and it also remained detectable throughout the 180 days of post-injury for all three cell types mentioned before. Moreover, the inhibition of the C5a-mediated inflammation after 14 days of injury reduced the locomotor recovery and myelination of the SC in the damaged site, suggesting that the late phase involves a restorative function [26].

Following this line, after the damage to the microvasculature, the presence of progressive edema and proapoptotic signaling begins. All of these events promote thrombosis and microvessel spasms causing hypoxia. Therefore, a relevant aspect to mention is that astrocytes are the first to act in the injury site, contributing to the formation of the GS, as well as preventing neurons to grow and heal [1, 20]. In the same way, neutrophils and macrophages are recruited from the periphery to the injured area, and, together with reactive astrocytes, microglia/macrophages will also contribute to the formation of a regeneration-inhibiting GS [27].

### **3. Cytokines and acute glial scar formation after spinal cord injury**

In the early phase, the formation of GS has a protective function, isolating potentially dangerous molecules of the rest of healthy tissue and controlling the spread of damage [28]. Accordingly with this, GS is considered as a mechanism of protection, developed by the organism against injuries that affect the CNS.

Overall, the GS is composed of two parts, the fibrotic and the glial. The fibrotic scar occupies the core of the injury with deposits of collagen matrix and is mainly composed of invading fibroblasts derived from meningeal and perivascular cells [29, 30]. The GS occupies the peripheral zone of the lesion and is composed mainly of astrocytes due to its evolution from a dynamic process known as reactive astrogliosis [30]. The glial limiting membrane is a specialized structure that is located close to the outer layer of the fibrotic scar and marks the division between these two parts [31]. Besides fibroblasts and astrocytes, the GS is also formed by NG2 + oligodendrocyte precursor cells (OPCs), microglia, pericytes, and ependymal cells [32].

A phenomenon that occurs simultaneously with the destruction of neuronal components is the activation of an inflammatory response characterized at first moment by the release of chemokines by endothelial cells and microglia cells [33]. These chemokines induce the migration of peripheral immunological cells to the affected tissue and promote the posterior establishment of inflammatory response [34]. The migration of macrophages and lymphocytes besides the activation of microglial cells is joined to the deficiency to control an inflammatory process in the CNS, thereby contributing with a destructive immunological response [35]. Both resident and

**79**

of the GS formation [36].

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

furtherly disrupt the BSB and increase vascular permeability [37].

key factor involved in the formation and maturation of GS [39].

to regulate the activity in neuronal synapsis [40].

infiltrating cells contribute to the GS formation, and the main characteristic of the inflammatory response at this time point is the sustained production of free radicals due to the continuous synthesis of pro-inflammatory cytokines like TNF-α, IL-1β, INF-γ, and enzymes that activate glial cells or disrupt the BSB [34, 36]. Moreover, activated macrophages produce and secrete matrix metalloproteinases (MMPs) to

Another phenomenon observed is the activation of inflammasome. The damage

Astrocyte is a specific cell residing only in the CNS that maintains the homeostasis, conforms the BBB, and keeps the concentration of ions and neurotransmitters

Reactive astrocytes (RAs) possess surface receptors for different cytokines just like the cells of the immune system, making them a target for products derived from the inflammatory environment. The pro-inflammatory cytokines induce the upregulation of inflammatory genes on astrocytes and the posterior secretion of various chemokines, including CXCL1, CCL2, CCL3, CCL4, and CXCL12, and cytokines like IL-1, transforming growth factor β (TGFβ), TNF-α, and INFγ. For example, INFγ interacts to modulate several facets of the gliotic response, and such interactions with growth factors may be important in creating the biochemical and physical properties of the GS; for this reason this cytokine is responsible for failed neuronal regeneration after SCI [41]. In this way, the astrocytes can contribute with the presence of a constant inflammatory response, affecting themselves and influencing other cell populations related with the formation of GS [41, 42].

Fibroblasts secrete extracellular matrix (ECM) components which include the chondroitin sulfate proteoglycans (CSPGs) family (neurocan, versican, brevican, phosphocan, and NG2) which is mainly secreted by astrocytes as well as fibronectin, collagen, and laminin which are produced by fibroblasts [36, 43]. Altogether, they contribute to the formation of GS and participate in developing its characteristic impermeability and the expression of molecules that impede the anatomical and functional restoration after the lesion [32, 44]. Fibroblasts also possess cytokine receptors on their surface which respond to high concentrations of pro-inflammatory cytokines and stimulate the activation of enzymatic machinery synthesized ECM protein. The inhibition of pericytes and fibroblasts by the application of different therapeutical strategies reduce the size and consolidation of GS, showing the importance of these types of cells in the GS formation. Of great importance is the presence of specific receptor for TGFβ on fibroblasts; the stimulation with this

molecule facilitates the synthesis and release of collagen type IV [45].

Generally speaking, after an injury to the CNS, there is a sequential phenotypic change in astrocytes called reactive astrogliosis, where naïve astrocytes (NAs) are transformed to RAs which eventually become scar-forming astrocytes (SAs) that can inhibit axonal regeneration and functional recovery [7]. Astrocytes are the most abundant glial cells within the CNS, and although they are not part of the immune system, they play a crucial role in the pathophysiology

Furthermore, RAs substantially upregulate their expression of GFAP, intermediate filaments, nestin, and vimentin and mobilize to the center of the injury

,

of cell membranes permits the release of molecules of ATP and the efflux of K<sup>+</sup>

stimulating the activation of the inflammasome and inducing the production of the pro-inflammatory cytokines, IL-1β and IL-18, which these cytokines have been related with neurodegenerative process [38]. Furthermore, studies in vitro have shown the direct relation of IL-1β with the overexpression of glial fibrillary acidic protein (GFAP) on astrocytes; for this reason the activation of inflammasome is a

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

#### *Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury DOI: http://dx.doi.org/10.5772/intechopen.93005*

infiltrating cells contribute to the GS formation, and the main characteristic of the inflammatory response at this time point is the sustained production of free radicals due to the continuous synthesis of pro-inflammatory cytokines like TNF-α, IL-1β, INF-γ, and enzymes that activate glial cells or disrupt the BSB [34, 36]. Moreover, activated macrophages produce and secrete matrix metalloproteinases (MMPs) to furtherly disrupt the BSB and increase vascular permeability [37].

Another phenomenon observed is the activation of inflammasome. The damage of cell membranes permits the release of molecules of ATP and the efflux of K<sup>+</sup> , stimulating the activation of the inflammasome and inducing the production of the pro-inflammatory cytokines, IL-1β and IL-18, which these cytokines have been related with neurodegenerative process [38]. Furthermore, studies in vitro have shown the direct relation of IL-1β with the overexpression of glial fibrillary acidic protein (GFAP) on astrocytes; for this reason the activation of inflammasome is a key factor involved in the formation and maturation of GS [39].

Astrocyte is a specific cell residing only in the CNS that maintains the homeostasis, conforms the BBB, and keeps the concentration of ions and neurotransmitters to regulate the activity in neuronal synapsis [40].

Reactive astrocytes (RAs) possess surface receptors for different cytokines just like the cells of the immune system, making them a target for products derived from the inflammatory environment. The pro-inflammatory cytokines induce the upregulation of inflammatory genes on astrocytes and the posterior secretion of various chemokines, including CXCL1, CCL2, CCL3, CCL4, and CXCL12, and cytokines like IL-1, transforming growth factor β (TGFβ), TNF-α, and INFγ. For example, INFγ interacts to modulate several facets of the gliotic response, and such interactions with growth factors may be important in creating the biochemical and physical properties of the GS; for this reason this cytokine is responsible for failed neuronal regeneration after SCI [41]. In this way, the astrocytes can contribute with the presence of a constant inflammatory response, affecting themselves and influencing other cell populations related with the formation of GS [41, 42].

Fibroblasts secrete extracellular matrix (ECM) components which include the chondroitin sulfate proteoglycans (CSPGs) family (neurocan, versican, brevican, phosphocan, and NG2) which is mainly secreted by astrocytes as well as fibronectin, collagen, and laminin which are produced by fibroblasts [36, 43]. Altogether, they contribute to the formation of GS and participate in developing its characteristic impermeability and the expression of molecules that impede the anatomical and functional restoration after the lesion [32, 44]. Fibroblasts also possess cytokine receptors on their surface which respond to high concentrations of pro-inflammatory cytokines and stimulate the activation of enzymatic machinery synthesized ECM protein. The inhibition of pericytes and fibroblasts by the application of different therapeutical strategies reduce the size and consolidation of GS, showing the importance of these types of cells in the GS formation. Of great importance is the presence of specific receptor for TGFβ on fibroblasts; the stimulation with this molecule facilitates the synthesis and release of collagen type IV [45].

Generally speaking, after an injury to the CNS, there is a sequential phenotypic change in astrocytes called reactive astrogliosis, where naïve astrocytes (NAs) are transformed to RAs which eventually become scar-forming astrocytes (SAs) that can inhibit axonal regeneration and functional recovery [7]. Astrocytes are the most abundant glial cells within the CNS, and although they are not part of the immune system, they play a crucial role in the pathophysiology of the GS formation [36].

Furthermore, RAs substantially upregulate their expression of GFAP, intermediate filaments, nestin, and vimentin and mobilize to the center of the injury

*Cytokines*

variability [9, 26].

The inflammatory microenvironment after SCI involves activated microglia, astrocytes, and infiltrating macrophages that play a role in the development of the

also contribute to the formation of a regeneration-inhibiting GS [27].

**3. Cytokines and acute glial scar formation after spinal cord injury**

protection, developed by the organism against injuries that affect the CNS.

In the early phase, the formation of GS has a protective function, isolating potentially dangerous molecules of the rest of healthy tissue and controlling the spread of damage [28]. Accordingly with this, GS is considered as a mechanism of

Overall, the GS is composed of two parts, the fibrotic and the glial. The fibrotic scar occupies the core of the injury with deposits of collagen matrix and is mainly composed of invading fibroblasts derived from meningeal and perivascular cells [29, 30]. The GS occupies the peripheral zone of the lesion and is composed mainly of astrocytes due to its evolution from a dynamic process known as reactive astrogliosis [30]. The glial limiting membrane is a specialized structure that is located close to the outer layer of the fibrotic scar and marks the division between these two parts [31]. Besides fibroblasts and astrocytes, the GS is also formed by NG2 + oligodendrocyte precursor cells (OPCs), microglia, pericytes, and ependymal cells [32]. A phenomenon that occurs simultaneously with the destruction of neuronal components is the activation of an inflammatory response characterized at first moment by the release of chemokines by endothelial cells and microglia cells [33]. These chemokines induce the migration of peripheral immunological cells to the affected tissue and promote the posterior establishment of inflammatory response [34]. The migration of macrophages and lymphocytes besides the activation of microglial cells is joined to the deficiency to control an inflammatory process in the CNS, thereby contributing with a destructive immunological response [35]. Both resident and

It has been demonstrated that there is a multiphasic response during the inflammation processes after SCI and a huge interaction between central and peripheral cellular and soluble components, which are influenced by some factors like patient age, sex, mechanism and degree of injury, therapeutic interventions, and genetic

In a study made by Beck et al. [26], they established two types of cellular inflammation phases. The early phase includes principally the infiltration of neutrophils which are polymorphonuclear leucocytes (PMNs), macrophages, and microglia, which inhibit recovery of the brain and SCI after the traumatic event. It was discovered that neutrophils are peaking 1 day of post-injury, macrophages/microglia 7 days of post-injury, and T cells 9 days of post-injury. The late phase was detected after 14 days of post-injury with its peak after 60 days of post-injury, and it also remained detectable throughout the 180 days of post-injury for all three cell types mentioned before. Moreover, the inhibition of the C5a-mediated inflammation after 14 days of injury reduced the locomotor recovery and myelination of the SC in the damaged site, suggesting that the late phase involves a restorative function [26]. Following this line, after the damage to the microvasculature, the presence of progressive edema and proapoptotic signaling begins. All of these events promote thrombosis and microvessel spasms causing hypoxia. Therefore, a relevant aspect to mention is that astrocytes are the first to act in the injury site, contributing to the formation of the GS, as well as preventing neurons to grow and heal [1, 20]. In the same way, neutrophils and macrophages are recruited from the periphery to the injured area, and, together with reactive astrocytes, microglia/macrophages will

secondary injury, and it is the major target to combat SCI.

**78**

to form a mesh-like structure of interlaced filamentous structures [46]. A high concentration of pro-inflammatory cytokines induces upregulation of GFAP on astrocytes and the development of hypertrophic prolongation. A certain study showed that genetically modified mice with deficiency of vimentin and GFAP produced a less dense GS which frequently conducted to constant bleeding, suggesting that vimentin and GFAP are part of the main cytoskeletal intermediate filaments that form the GS [47].

This astrocytic migration secludes inflammatory cells from the surrounding intact tissues and minimize the extension of secondary damage after CNS injury leading to tissue repair and functional improvement during the acute phase of GS formation [7, 48, 49]. In addition, the hemorrhagic flow into the CNS due to the rupture of the BBB exposes scar-forming cells to factors in plasma such as fibrinogen which has been proven to induce the expression of CSPGs in astrocytes through TGFβ/Smad2 signaling pathway [50].

Besides, in the acute phase of the GS formation, the overexpression of CSPGs (neurocan, versican, brevican, phosphocan, and NG2+) plays a beneficial role by modulating the inflammatory activity of resident microglia as well as the infiltration of monocytes through the CD44 receptor [51].

Moreover, to the featured RAs, the GS formation also requires the activation of ependymal cells, NG2+-expressing glia (including OPCs), meningeal- and vascular-derived fibroblasts, pericytes, and macrophages surrounding the injury area [52]. More importantly, some of these previously mentioned cells have the capacity to switch their phenotypes and become RAs to furtherly contribute in the GS formation [53]. Furthermore, there are several molecular mechanisms that contribute to the formation of the GS such as the upregulation of bone morphogenetic proteins (BMPs), MMPs, epidermal growth factor receptor (EGFR), eph/ ephrins, TGFβ, and signal transducer and activator of transcription and interleukin (STAT/IL) family (STAT3) [30, 54, 55]. The upregulation of BMP-4 has shown to promote astrocyte differentiation and to inhibit the production of oligodendrocytes and neurons [56]. In addition, the MMP family is involved in the ECM remodeling, and therefore, they are structurally and temporally involved in the GS formation [57]. The limitation of the extent of the GS was seen with the suppression of MMP-2 in mice, and MMP-9 has proven to be involved in the augmented migration of RAs to the injury site, therefore facilitating GS formation [58]. EGFR is upregulated in astrocytes following damage to the SC, leading to the activation of the Rheb-mToR signaling pathway which induces astrocytes to migrate and suffer hypertrophy to furtherly form the GS [59]. Moreover, EGFR ligands, such as transforming growth factor-alpha (TGF-alpha) and EGF, contribute to the formation of the GS by inducing astrocytes to secrete CSGPs [60]. In addition, TGFβ expression is upregulated immediately after SCI. It promotes the formation of the GS by simultaneously stimulating monocyte and lymphocyte activity as well as inducing the production and deposition of new ECM proteins (collagen, fibronectin, and proteoglycans) [61, 62]. The manipulation of TGFβ signaling in the injured CNS modulates the formation of the fibrotic scar in the lesion site. The administration of TGFβ1 to the injured CNS increases the deposition of ECMs in the lesion site [63, 64], while antibodies to TGFβ1 and TGFβ2 and the endogenous TGFβ inhibitor decorin, a small leucine-rich CSPG, conversely reduce the size of GS [64], which proposes the involvement of TGFβs in the formation of GS. In addition, RAs release TNF-α to inhibit oligodendrocyte progenitor cell (OPG) survival and prevent them from differentiating into mature oligodendrocytes, suggesting a mechanism for the failure of remyelination after SCI [65].

**81**

tissue [4, 5].

CNS [68].

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

RAs have been traditionally considered to be a unidirectional and irreversible

Even though GS formation in acute phases has proven to have beneficial effects, its evolution and persistence in chronic stages of the injury have shown to become a strong inhibitor for SC regeneration [3]. Therefore, there has been some attempts in

regulating the chronic phase of the GS to improve axonal outgrowth.

insult continues in most of the cases until the chronic phase [34].

necessary in chronic phases to inhibit, modulate, or remove the mature GS.

**5. Cytokines and chronic glial scar formation after spinal cord injury**

Through the years, it became clear that both the scar tissue and the immune system play important beneficial roles in axonal regeneration and healing of the

As mentioned before, SCI results in the disruption of the BBB, and the BSB increased inflammatory reactions such as the activation of the microglia and the production of various cytokines and augmented the activation of TGFβ and Smad2 signaling pathways [49]. The inflammatory microenvironment presented after the

Acute GS formation restricts inflammation and preserves neural tissue [28, 46, 69]. Nonetheless, at the chronic phase (>14 days after the injury in mice), RAs progressively transform into SAs that form astrocytic scars which compose the main impediment for axonal regeneration and functional recovery in the chronic phase of SCI [70, 71]. It has been suggested that after inflammation has resolved, chronic GS is expendable and detrimental because it continually prevents axon regeneration [6]. For this reason, it is

process; however, recent studies have proven to inhibit its progress and even revert the astrocyte's phenotype according to environmental cues [48, 49]. Over the past few years, there has been an increasing interest in modulating the GS formation; nevertheless, there has been a wide spectrum of results mainly due to the fact that the GS has many components and there are many different types of therapy strategies. Inclusive, recent studies have shown that the attenuation of RAs to prevent GS formation has resulted in a worse outcome in SCI and limited functional recovery [6, 7]. In transgenic mice where STAT3 selectively suppressed RAs showed reduced migration to the lesion epicenter, leading to an extensive area of injury with uncontrolled inflammatory cell filtration and limited functional recovery [7]. Another study showed a pronounced reduction of glial scarring in animals with conditional knockdown of STAT3, suggesting that this molecule is one of the most important factors involved in the formation of the GS [62]. A wide spectrum of molecules such as type I and II interferons and cytokines, growth factors including EGF, platelet-derived growth factor, IL-6, leukemia inhibitory factor, and ciliary neurotrophic factor (CNF) is able to activate STAT3 in order to cause variations in RAs and elicit GS formation [66, 67]. Similarly, a recent study used HSV1tk/GCV (a suicide system gene) to selectively kill proliferating RAs in SCI to avoid GS formation, resulting in a widespread infiltration of inflammatory cells and continuous involvement of healthy tissue surrounding the epicenter of the lesion as well as decreased neuronal survival and decreased locomotor recovery [5]. These findings furtherly support that reactive astrogliosis in acute-subacute phases plays beneficial roles in acute wound healing, remodeling processes, and isolating the injury to prevent the spread of cytotoxic molecules and inflammatory cells into the surrounding

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

**4. Modifications of the glial scar**

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury DOI: http://dx.doi.org/10.5772/intechopen.93005*

## **4. Modifications of the glial scar**

*Cytokines*

that form the GS [47].

TGFβ/Smad2 signaling pathway [50].

tion of monocytes through the CD44 receptor [51].

to form a mesh-like structure of interlaced filamentous structures [46]. A high concentration of pro-inflammatory cytokines induces upregulation of GFAP on astrocytes and the development of hypertrophic prolongation. A certain study showed that genetically modified mice with deficiency of vimentin and GFAP produced a less dense GS which frequently conducted to constant bleeding, suggesting that vimentin and GFAP are part of the main cytoskeletal intermediate filaments

This astrocytic migration secludes inflammatory cells from the surrounding intact tissues and minimize the extension of secondary damage after CNS injury leading to tissue repair and functional improvement during the acute phase of GS formation [7, 48, 49]. In addition, the hemorrhagic flow into the CNS due to the rupture of the BBB exposes scar-forming cells to factors in plasma such as fibrinogen which has been proven to induce the expression of CSPGs in astrocytes through

Besides, in the acute phase of the GS formation, the overexpression of CSPGs (neurocan, versican, brevican, phosphocan, and NG2+) plays a beneficial role by modulating the inflammatory activity of resident microglia as well as the infiltra-

Moreover, to the featured RAs, the GS formation also requires the activation of ependymal cells, NG2+-expressing glia (including OPCs), meningeal- and vascular-derived fibroblasts, pericytes, and macrophages surrounding the injury area [52]. More importantly, some of these previously mentioned cells have the capacity to switch their phenotypes and become RAs to furtherly contribute in the GS formation [53]. Furthermore, there are several molecular mechanisms that contribute to the formation of the GS such as the upregulation of bone morphogenetic proteins (BMPs), MMPs, epidermal growth factor receptor (EGFR), eph/ ephrins, TGFβ, and signal transducer and activator of transcription and interleukin (STAT/IL) family (STAT3) [30, 54, 55]. The upregulation of BMP-4 has shown to promote astrocyte differentiation and to inhibit the production of oligodendrocytes and neurons [56]. In addition, the MMP family is involved in the ECM remodeling, and therefore, they are structurally and temporally involved in the GS formation [57]. The limitation of the extent of the GS was seen with the suppression of MMP-2 in mice, and MMP-9 has proven to be involved in the augmented migration of RAs to the injury site, therefore facilitating GS formation [58]. EGFR is upregulated in astrocytes following damage to the SC, leading to the activation of the Rheb-mToR signaling pathway which induces astrocytes to migrate and suffer hypertrophy to furtherly form the GS [59]. Moreover, EGFR ligands, such as transforming growth factor-alpha (TGF-alpha) and EGF, contribute to the formation of the GS by inducing astrocytes to secrete CSGPs [60]. In addition, TGFβ expression is upregulated immediately after SCI. It promotes the formation of the GS by simultaneously stimulating monocyte and lymphocyte activity as well as inducing the production and deposition of new ECM proteins (collagen, fibronectin, and proteoglycans) [61, 62]. The manipulation of TGFβ signaling in the injured CNS modulates the formation of the fibrotic scar in the lesion site. The administration of TGFβ1 to the injured CNS increases the deposition of ECMs in the lesion site [63, 64], while antibodies to TGFβ1 and TGFβ2 and the endogenous TGFβ inhibitor decorin, a small leucine-rich CSPG, conversely reduce the size of GS [64], which proposes the involvement of TGFβs in the formation of GS. In addition, RAs release TNF-α to inhibit oligodendrocyte progenitor cell (OPG) survival and prevent them from differentiating into mature oligodendrocytes, suggesting a mechanism for the failure of remyelin-

**80**

ation after SCI [65].

RAs have been traditionally considered to be a unidirectional and irreversible process; however, recent studies have proven to inhibit its progress and even revert the astrocyte's phenotype according to environmental cues [48, 49]. Over the past few years, there has been an increasing interest in modulating the GS formation; nevertheless, there has been a wide spectrum of results mainly due to the fact that the GS has many components and there are many different types of therapy strategies. Inclusive, recent studies have shown that the attenuation of RAs to prevent GS formation has resulted in a worse outcome in SCI and limited functional recovery [6, 7]. In transgenic mice where STAT3 selectively suppressed RAs showed reduced migration to the lesion epicenter, leading to an extensive area of injury with uncontrolled inflammatory cell filtration and limited functional recovery [7]. Another study showed a pronounced reduction of glial scarring in animals with conditional knockdown of STAT3, suggesting that this molecule is one of the most important factors involved in the formation of the GS [62]. A wide spectrum of molecules such as type I and II interferons and cytokines, growth factors including EGF, platelet-derived growth factor, IL-6, leukemia inhibitory factor, and ciliary neurotrophic factor (CNF) is able to activate STAT3 in order to cause variations in RAs and elicit GS formation [66, 67]. Similarly, a recent study used HSV1tk/GCV (a suicide system gene) to selectively kill proliferating RAs in SCI to avoid GS formation, resulting in a widespread infiltration of inflammatory cells and continuous involvement of healthy tissue surrounding the epicenter of the lesion as well as decreased neuronal survival and decreased locomotor recovery [5]. These findings furtherly support that reactive astrogliosis in acute-subacute phases plays beneficial roles in acute wound healing, remodeling processes, and isolating the injury to prevent the spread of cytotoxic molecules and inflammatory cells into the surrounding tissue [4, 5].

Even though GS formation in acute phases has proven to have beneficial effects, its evolution and persistence in chronic stages of the injury have shown to become a strong inhibitor for SC regeneration [3]. Therefore, there has been some attempts in regulating the chronic phase of the GS to improve axonal outgrowth.

#### **5. Cytokines and chronic glial scar formation after spinal cord injury**

Through the years, it became clear that both the scar tissue and the immune system play important beneficial roles in axonal regeneration and healing of the CNS [68].

As mentioned before, SCI results in the disruption of the BBB, and the BSB increased inflammatory reactions such as the activation of the microglia and the production of various cytokines and augmented the activation of TGFβ and Smad2 signaling pathways [49]. The inflammatory microenvironment presented after the insult continues in most of the cases until the chronic phase [34].

Acute GS formation restricts inflammation and preserves neural tissue [28, 46, 69]. Nonetheless, at the chronic phase (>14 days after the injury in mice), RAs progressively transform into SAs that form astrocytic scars which compose the main impediment for axonal regeneration and functional recovery in the chronic phase of SCI [70, 71]. It has been suggested that after inflammation has resolved, chronic GS is expendable and detrimental because it continually prevents axon regeneration [6]. For this reason, it is necessary in chronic phases to inhibit, modulate, or remove the mature GS.

Certain factors present during the acute formation of the glial scar are also active during its chronic formation. The genetic suppression of BMPR1b (a subtype of the BMP type 1 receptor) resulted in the weakening of the GS in chronic stages of SCI, suggesting that BMPs play an important role in the acute formation of the GS as well as in its stabilization through the chronic stage [72].

Although the expression of CSPGs during acute glial scar formation participates in reducing the damage extent, the prolonged exposure of CSPGs is prejudicial for functional recovery for they are well-known to be the main inhibitors of GS axonal regeneration, sprouting, and remyelination during the chronic phase of SCI [3, 73]. The posterior formation of the GS traps on its core of GS, where they reside contributing with the chronic presence of an inflammatory response. The continual synthesis of pro-inflammatory cytokines like TNFα, IL1β, and INFγ promotes the aggregation of new elements and the modification of GS [74].

This is the main reason why astrogliosis may cause both beneficial and detrimental effects depending on its dynamic features and on its time course [50, 69]. Cytokines behave in a similar way. In the early stages of GS formation, pro-inflammatory cytokines such as TNF-α, IL-1β, and INF-γ help by recruiting and activating microglial cells, astrocytes, and other peripheral immunological cells to the injury site to prevent the extension of the injury [33, 35]. However, other acute-secreted cytokines such as IL-1β and IL-18 have been associated with neurodegenerative processes and activation of the inflammasome [37, 38]. On the other hand, during the chronic formation of the GS, cytokines contribute to impede axonal regeneration and functional recovery. Overall, cytokines may present both beneficial and detrimental effects depending on the stage of GS formation and depending on the process in which they are involved. Certain cytokines which are present in early stages and may present beneficial effects by increasing the production of CSPGs may become prejudicial as time progresses. Current pharmacological treatments


**83**

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

**6. Modulate, inhibit, or remove glial scar as therapeutic tool**

In this section we will review some modulating treatments of the GS. That should be able to counteract posttraumatic factors of inhibitory growth and pro-

In contrast with the pro-inflammatory cytokines produced after the injury, the application of anti-inflammatory therapies like the treatment with doses of methylprednisolone (MP) after the injury avoids the formation of the GS. The application of MP is helpful to reduce the expression of GFAP and reduce the deposition of

Combination therapy using MP and tranilast after SCI in rats significantly reduced posttraumatic SC edema and neutrophil infiltration and improved functional recovery better than single individual therapies, and it also significantly

Therapies that induce elevated concentrations of IL-10, a well-known antiinflammatory cytokine, reduce in an important way the presence of CSPG on GS [82]. Astrocytes also express the transcription nuclear factor (NF-kB). The selective inhibition of NF-kB induces a better neurological outcome and a reduction in size of the GS. In addition, the interference of NF-kB induces the reduction of pro-

Curcinum is a phytochemical compound that has an anti-inflammatory effect. This molecule inhibits pro-inflammatory cytokines (TNFα and IL-1β), which contribute to reduce the expression of GFAP through anti-inflammatory processes and help to suppress reactive gliosis [26]. Previous studies have also demonstrated to inhibit the generation of TGFβ1, TGFβ2, and SOX-9; as a result, there is a decreased deposition of CSPG, causing the inhibition of TGFβ and transcription factors. There is also evidence that curcinum reduces the amount of nestin and GFAP around de SCI, suggesting that

In addition, rapamycin is an immunosuppressant that inhibits the mTor pathway

Finally, TGFβ is involved in GS formation process, increasing the expression of neurocan, a CSPG that mediates GS formation and inhibits axon growth. Therefore, the use of antibodies against TGFβ1 and TGFβ2 is necessary; they mitigate the response of GFAP, causing the interruption of scar tissue and glial membrane

depend on cytokines to establish their mechanism of action and should be focused

The majority of SCI patients are those with lesions who may benefit insufficiently from therapeutic treatments designed for application in the chronic stage and focused on cytokines and other immunological processes. However, compared to treatments of acute experimental SCI, the efficacy of therapies promoting axonal regeneration seems impaired in chronic models. Therefore, GS formation can be improved if we combine treatments like stem cell transplants [75], iron chelators [76–78], and matrix biocompatible [16, 78]. **Table 1** summarizes some GS effects exerted by cytokines.

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

mote axonal and tissue recovery.

**6.1 Anti-inflammatory therapy**

CSPG and avoid the formation of the GS [80].

reduced the amount of GFAP expression at the injury site [81].

inflammatory cytokines, chemokines, and secretion of CSPG [83].

it inhibits astrogliosis improving the microenvironment to SC repair [27].

promotes angiogenesis and neuronal survival around the injury [2, 30].

selectively, and, it is considered neuroprotective because it increases the antiinflammatory microenvironment and reduces locomotor impairment and damage in neural tissue. Other outcomes have shown that reduced infiltrations of macrophages and neutrophils at the SCI also reduce microglial activation and secretion of TNFβ; the amount of cells expressing GFAP inhibits proliferation of astrocytes and

to develop further pharmacological strategies.

#### **Table 1.**

*Main cytokines involve in scar glial formation.*

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury DOI: http://dx.doi.org/10.5772/intechopen.93005*

depend on cytokines to establish their mechanism of action and should be focused to develop further pharmacological strategies.

The majority of SCI patients are those with lesions who may benefit insufficiently from therapeutic treatments designed for application in the chronic stage and focused on cytokines and other immunological processes. However, compared to treatments of acute experimental SCI, the efficacy of therapies promoting axonal regeneration seems impaired in chronic models. Therefore, GS formation can be improved if we combine treatments like stem cell transplants [75], iron chelators [76–78], and matrix biocompatible [16, 78]. **Table 1** summarizes some GS effects exerted by cytokines.

### **6. Modulate, inhibit, or remove glial scar as therapeutic tool**

In this section we will review some modulating treatments of the GS. That should be able to counteract posttraumatic factors of inhibitory growth and promote axonal and tissue recovery.

#### **6.1 Anti-inflammatory therapy**

*Cytokines*

Certain factors present during the acute formation of the glial scar are also active during its chronic formation. The genetic suppression of BMPR1b (a subtype of the BMP type 1 receptor) resulted in the weakening of the GS in chronic stages of SCI, suggesting that BMPs play an important role in the acute formation of the GS as

Although the expression of CSPGs during acute glial scar formation participates in reducing the damage extent, the prolonged exposure of CSPGs is prejudicial for functional recovery for they are well-known to be the main inhibitors of GS axonal regeneration, sprouting, and remyelination during the chronic phase of SCI [3, 73]. The posterior formation of the GS traps on its core of GS, where they reside contributing with the chronic presence of an inflammatory response. The continual synthesis of pro-inflammatory cytokines like TNFα, IL1β, and INFγ promotes the aggregation

This is the main reason why astrogliosis may cause both beneficial and detrimental effects depending on its dynamic features and on its time course [50, 69]. Cytokines behave in a similar way. In the early stages of GS formation, pro-inflammatory cytokines such as TNF-α, IL-1β, and INF-γ help by recruiting and activating microglial cells, astrocytes, and other peripheral immunological cells to the injury site to prevent the extension of the injury [33, 35]. However, other acute-secreted cytokines such as IL-1β and IL-18 have been associated with neurodegenerative processes and activation of the inflammasome [37, 38]. On the other hand, during the chronic formation of the GS, cytokines contribute to impede axonal regeneration and functional recovery. Overall, cytokines may present both beneficial and detrimental effects depending on the stage of GS formation and depending on the process in which they are involved. Certain cytokines which are present in early stages and may present beneficial effects by increasing the production of CSPGs may become prejudicial as time progresses. Current pharmacological treatments

**Cytokine Scar glial effect References**

[60] [45] [63, 64] [28]

[27]

[36]

[79] [78]

[18]

Inhibits the generation of TGFβ1, TGFβ2, and SOX-9 and as a result there is

Facilitates the synthesis and release of collagen type IV in fibroblast

IL-1β Increases overexpression of GFAP on astrocytes and maturation of GS [39]

differentiating into mature oligodendrocytes, suggesting a mechanism for

Reduces the expression of GFAP through anti-inflammatory processes and

interactions with growth factors may be important in creating modification

Transplantation with BMSCs was associated with significant increases in IL-4 and IL-13; these changes were associated with less scar tissue

INDP in combination with scar removal and DPY reduces pro-

IL-10 Activates beneficial M2 macrophages which were found to regulate scar

Increases the deposition of ECMs in the lesion site

TNFα RAs release TNF-α to inhibit OPCs survival and prevent them from

INFγ Promotes SG formation and modulates ECM which helps that the

well as in its stabilization through the chronic stage [72].

of new elements and the modification of GS [74].

TGFβ Induces the expression of CSPGs in astrocyte

a decreased deposition of CSPG

the failure of remyelination after SCI

inflammatory cytokines in chronic phase

helps to suppress reactive gliosis

in the GS

formation

resolution

*Main cytokines involve in scar glial formation.*

**82**

**Table 1.**

IL-4 and IL13 IL-4 and IL-10

In contrast with the pro-inflammatory cytokines produced after the injury, the application of anti-inflammatory therapies like the treatment with doses of methylprednisolone (MP) after the injury avoids the formation of the GS. The application of MP is helpful to reduce the expression of GFAP and reduce the deposition of CSPG and avoid the formation of the GS [80].

Combination therapy using MP and tranilast after SCI in rats significantly reduced posttraumatic SC edema and neutrophil infiltration and improved functional recovery better than single individual therapies, and it also significantly reduced the amount of GFAP expression at the injury site [81].

Therapies that induce elevated concentrations of IL-10, a well-known antiinflammatory cytokine, reduce in an important way the presence of CSPG on GS [82]. Astrocytes also express the transcription nuclear factor (NF-kB). The selective inhibition of NF-kB induces a better neurological outcome and a reduction in size of the GS. In addition, the interference of NF-kB induces the reduction of proinflammatory cytokines, chemokines, and secretion of CSPG [83].

Curcinum is a phytochemical compound that has an anti-inflammatory effect. This molecule inhibits pro-inflammatory cytokines (TNFα and IL-1β), which contribute to reduce the expression of GFAP through anti-inflammatory processes and help to suppress reactive gliosis [26]. Previous studies have also demonstrated to inhibit the generation of TGFβ1, TGFβ2, and SOX-9; as a result, there is a decreased deposition of CSPG, causing the inhibition of TGFβ and transcription factors. There is also evidence that curcinum reduces the amount of nestin and GFAP around de SCI, suggesting that it inhibits astrogliosis improving the microenvironment to SC repair [27].

In addition, rapamycin is an immunosuppressant that inhibits the mTor pathway selectively, and, it is considered neuroprotective because it increases the antiinflammatory microenvironment and reduces locomotor impairment and damage in neural tissue. Other outcomes have shown that reduced infiltrations of macrophages and neutrophils at the SCI also reduce microglial activation and secretion of TNFβ; the amount of cells expressing GFAP inhibits proliferation of astrocytes and promotes angiogenesis and neuronal survival around the injury [2, 30].

Finally, TGFβ is involved in GS formation process, increasing the expression of neurocan, a CSPG that mediates GS formation and inhibits axon growth. Therefore, the use of antibodies against TGFβ1 and TGFβ2 is necessary; they mitigate the response of GFAP, causing the interruption of scar tissue and glial membrane

formation that limit the edge of the injury. Astrocytes, OPCs, and NG2+ responses are diminished. This is possible by interrupting the Smad 3 signaling pathway in conjunction with TGFβ [2, 84].

In contrast, a study carried out by Kohta and colleagues showed that the inhibition of TGFβ1 with a neutralizing antibody resulted in the suppression of the GS formation resulting in a mild improvement of growth and/or preservation of axons in the injured GS caudal to the site of contusion [31]. Furthermore, rats treated with anti-TGFβ1 increased the activation of the microglia after injury, apparently providing a beneficial environment for the restoration and healing of the neural network [31].

The macrophages are immune cells with phagocytic capabilities. There are three subgroups, but now the focus goes towards M2 macrophages. When M2 macrophages infiltrate the SC, they may also secrete protective factors, such as the anti-inflammatory cytokine IL-10, and boosting the release of protective molecules would be advantageous. In addition, when MMP-2 is upregulated, it represents a beneficial effect for SCI recovery; however, when there is a deficiency in MMP-2 expression, an exacerbated lesion expansion, scar formation, vascular instability, and locomotor deficits are present [18, 85].

#### **6.2 Cell therapies**

#### *6.2.1 Schwann cells*

The SCs are the principal glia of the peripheral nervous system (PNS) [86], and in a SCI, they have shown to promote axonal regeneration through the formation of bridges across the injury. This bridge is a multicellular structure that crosses the lesion from the rostral to caudal part, providing an environment in which axons can grow and cover the GS to suppress axonal regeneration impediment [87, 88].

SC transplant provides a neuroprotective effect, preventing neural death by continuous inflammatory reaction caused by a SCI; moreover the neural peripheral grafts promote the expression of neurotrophins like BDNF and NGF, which is key for a successful regeneration as it delays the formation of the GS [89]. It is not advisable to transplant the SCs alone, because their regenerative capacity is limited by the secretion of myelin-associated and axonal growth inhibitors (CSPGs, semaphorins, and myelin-associated proteins) by the GS. Although many types of cells have been studied for transplantation, the SCs have always been considered as one of the best proposals for this treatment; however, they need to be co-transplanted with other molecules or cells such as OECs, MSCs, and NSCs, among other cells, in order to achieve its full therapeutic potential [88, 90].

#### *6.2.2 Bone marrow mesenchymal stem cells*

Bone marrow stem cells (BMSCs) are the most abundant cells in the bone marrow; they are hematopoietic and functional support cells [91]. The implantation of BMSCs has shown to have regenerative and immunomodulative properties that help to prevent the GS formation [91]. Furthermore, these cells are able to regulate CNTF-STAT3 signal transduction which reduces tissue scarring, inflammatory responses, and apoptosis [92]. Okuda et al. reported that BMSC sheets suppress the GS and provide a positive environment for axonal regeneration, causing changes in reactive astrocyte morphology [93]. Moreover, BMSCs can secrete different trophic factors (VEGF, BDNF, NGF, and hepatocyte growth factor) which increase positive results associated with BMSC transplantation [91, 94]. In addition, the transplant of BMSCs are associated with significant increases in IL-4 and IL-13; these changes were associated with less scar tissue formation [79].

**85**

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

be studied, such as their survival rate when transplanted.

With all that said, BMSCs possess many features that make them eligible for cell culture transplantation; however there are still many knowledge gaps that need to

Olfactory ensheathing cells (OECs) form the glial component of the primary olfactory system, and they reside both on CNS and PNS [87, 95]. Recent olfactory bulb (OB) transplants have shown to be able to infiltrate the scar tissue, through the environment of astrocytes thanks to their heparin profile [87]. They also provide a scaffold that promotes neuronal growth and angiogenesis and supply a bridge through the injury site that decreases the contusion area [96, 97]. OECs promote neural regeneration by promoting cell-to-cell interaction with sensorial axons and migrate ahead to the olfactory bulb, creating a favorable environment for axonal growth where cellular debris are phagocytized to increase restoration, neuroinflammation is modulated, neuroprotection is provided, and the expression of neurotrophic factors like BNDF, GDNF, NGF, and ECM molecules is augmented to provide a substrate for newly generated axons [98, 99]. These cells inhibits pro-inflammatory cytokines and induces the activation anti-inflammatory cytokines; they can activate neurotrophic factors. Neurotrophic factors secreted by OECs are capable of inhibiting scar formation and promote axonal regeneration, implying that they also are neuroprotective. The receptors of each neurotrophic factor are NGF/p75, BDNF/Trκβ, GDNF/GFR-1, NTN/GFR-2, and NRG-1/ErbB [43]. Also OECs reduce the expression of GFAP by an earlier shorter immune response by astrocytes and microglia, due to the attenua-

The chondroitinase ABC (ChABC) is a bacterial enzyme that catalyzes the removal of the CSPG and therefore digests them. The administration of ChABC has demonstrated to inhibit CSPG and deactivate their glycosaminoglycan chains, which promotes a significant regeneration of axons, and M2 macrophage phenotype

Certain studies have used ChABC in SCI models in rats to enzymatically degrade CSPGs and therefore reduce its inhibitory functions in axonal regeneration [35, 36]. The results of these experiments showed a significant improvement in locomotor and proprioceptive functions, demonstrating that the degradation of CSPGs is a promising strategy to avoid its long-term prejudicial effects in chronic SCI [36, 37]. It is also reported that the combination of glial-derived neurotrophic factor (GDNF) and transplanted SCs causes a reduction in astrogliosis (GFAP and CSPG) and is also responsible for promoting axon regeneration after SCI [102]. Another combination therapy with ChABC, acidic fibroblast growth factor (aFGF), and peripheral nerve graft bridge supports axon regeneration and functional recovery after chronic SCI like so bladder physiology outcomes associated with an invasive repair strategy. CSPG are significantly downregulated by the astroglial NF-kB inhibition [83]. Taken all together, these studies demonstrate that the degradation of CSPGs is a promising strategy to avoid its long-term prejudicial

Using iron chelators to inhibit collagen biosynthesis has been demonstrated to have beneficial effects by transient suppressing fibrous scarring in an acute SCI

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

tion of NF-κβ, which is involved in RAs [100].

**6.3 Chondroitinase ABC**

activation [2, 101].

effects in chronic SCI.

**6.4 Iron chelators to inhibit collagen biosynthesis**

*6.2.3 Olfactory ensheathing cells*

With all that said, BMSCs possess many features that make them eligible for cell culture transplantation; however there are still many knowledge gaps that need to be studied, such as their survival rate when transplanted.

## *6.2.3 Olfactory ensheathing cells*

*Cytokines*

conjunction with TGFβ [2, 84].

and locomotor deficits are present [18, 85].

achieve its full therapeutic potential [88, 90].

were associated with less scar tissue formation [79].

*6.2.2 Bone marrow mesenchymal stem cells*

**6.2 Cell therapies**

*6.2.1 Schwann cells*

formation that limit the edge of the injury. Astrocytes, OPCs, and NG2+ responses are diminished. This is possible by interrupting the Smad 3 signaling pathway in

In contrast, a study carried out by Kohta and colleagues showed that the inhibition of TGFβ1 with a neutralizing antibody resulted in the suppression of the GS formation resulting in a mild improvement of growth and/or preservation of axons in the injured GS caudal to the site of contusion [31]. Furthermore, rats treated with anti-TGFβ1 increased the activation of the microglia after injury, apparently providing a beneficial environment for the restoration and healing of the neural network [31]. The macrophages are immune cells with phagocytic capabilities. There are three subgroups, but now the focus goes towards M2 macrophages. When M2 macrophages infiltrate the SC, they may also secrete protective factors, such as the anti-inflammatory cytokine IL-10, and boosting the release of protective molecules would be advantageous. In addition, when MMP-2 is upregulated, it represents a beneficial effect for SCI recovery; however, when there is a deficiency in MMP-2 expression, an exacerbated lesion expansion, scar formation, vascular instability,

The SCs are the principal glia of the peripheral nervous system (PNS) [86], and in a SCI, they have shown to promote axonal regeneration through the formation of bridges across the injury. This bridge is a multicellular structure that crosses the lesion from the rostral to caudal part, providing an environment in which axons can

Bone marrow stem cells (BMSCs) are the most abundant cells in the bone marrow; they are hematopoietic and functional support cells [91]. The implantation of BMSCs has shown to have regenerative and immunomodulative properties that help to prevent the GS formation [91]. Furthermore, these cells are able to regulate CNTF-STAT3 signal transduction which reduces tissue scarring, inflammatory responses, and apoptosis [92]. Okuda et al. reported that BMSC sheets suppress the GS and provide a positive environment for axonal regeneration, causing changes in reactive astrocyte morphology [93]. Moreover, BMSCs can secrete different trophic factors (VEGF, BDNF, NGF, and hepatocyte growth factor) which increase positive results associated with BMSC transplantation [91, 94]. In addition, the transplant of BMSCs are associated with significant increases in IL-4 and IL-13; these changes

grow and cover the GS to suppress axonal regeneration impediment [87, 88]. SC transplant provides a neuroprotective effect, preventing neural death by continuous inflammatory reaction caused by a SCI; moreover the neural peripheral grafts promote the expression of neurotrophins like BDNF and NGF, which is key for a successful regeneration as it delays the formation of the GS [89]. It is not advisable to transplant the SCs alone, because their regenerative capacity is limited by the secretion of myelin-associated and axonal growth inhibitors (CSPGs, semaphorins, and myelin-associated proteins) by the GS. Although many types of cells have been studied for transplantation, the SCs have always been considered as one of the best proposals for this treatment; however, they need to be co-transplanted with other molecules or cells such as OECs, MSCs, and NSCs, among other cells, in order to

**84**

Olfactory ensheathing cells (OECs) form the glial component of the primary olfactory system, and they reside both on CNS and PNS [87, 95]. Recent olfactory bulb (OB) transplants have shown to be able to infiltrate the scar tissue, through the environment of astrocytes thanks to their heparin profile [87]. They also provide a scaffold that promotes neuronal growth and angiogenesis and supply a bridge through the injury site that decreases the contusion area [96, 97]. OECs promote neural regeneration by promoting cell-to-cell interaction with sensorial axons and migrate ahead to the olfactory bulb, creating a favorable environment for axonal growth where cellular debris are phagocytized to increase restoration, neuroinflammation is modulated, neuroprotection is provided, and the expression of neurotrophic factors like BNDF, GDNF, NGF, and ECM molecules is augmented to provide a substrate for newly generated axons [98, 99]. These cells inhibits pro-inflammatory cytokines and induces the activation anti-inflammatory cytokines; they can activate neurotrophic factors.

Neurotrophic factors secreted by OECs are capable of inhibiting scar formation and promote axonal regeneration, implying that they also are neuroprotective. The receptors of each neurotrophic factor are NGF/p75, BDNF/Trκβ, GDNF/GFR-1, NTN/GFR-2, and NRG-1/ErbB [43]. Also OECs reduce the expression of GFAP by an earlier shorter immune response by astrocytes and microglia, due to the attenuation of NF-κβ, which is involved in RAs [100].

## **6.3 Chondroitinase ABC**

The chondroitinase ABC (ChABC) is a bacterial enzyme that catalyzes the removal of the CSPG and therefore digests them. The administration of ChABC has demonstrated to inhibit CSPG and deactivate their glycosaminoglycan chains, which promotes a significant regeneration of axons, and M2 macrophage phenotype activation [2, 101].

Certain studies have used ChABC in SCI models in rats to enzymatically degrade CSPGs and therefore reduce its inhibitory functions in axonal regeneration [35, 36]. The results of these experiments showed a significant improvement in locomotor and proprioceptive functions, demonstrating that the degradation of CSPGs is a promising strategy to avoid its long-term prejudicial effects in chronic SCI [36, 37]. It is also reported that the combination of glial-derived neurotrophic factor (GDNF) and transplanted SCs causes a reduction in astrogliosis (GFAP and CSPG) and is also responsible for promoting axon regeneration after SCI [102]. Another combination therapy with ChABC, acidic fibroblast growth factor (aFGF), and peripheral nerve graft bridge supports axon regeneration and functional recovery after chronic SCI like so bladder physiology outcomes associated with an invasive repair strategy. CSPG are significantly downregulated by the astroglial NF-kB inhibition [83]. Taken all together, these studies demonstrate that the degradation of CSPGs is a promising strategy to avoid its long-term prejudicial effects in chronic SCI.

## **6.4 Iron chelators to inhibit collagen biosynthesis**

Using iron chelators to inhibit collagen biosynthesis has been demonstrated to have beneficial effects by transient suppressing fibrous scarring in an acute SCI

model [45, 77]. The iron chelation of α,α'-dipyridyl (DPY) has previously shown to decrease the collagen synthesis at a posttranscriptional level by inhibiting 4-prolyl hydroxylase, one of the key enzymes in collagen metabolism [103].

In a study with unilateral SC transection in adult and postnatal mice (14 days old) where DPY was applied at the injury site, it was observed that collagen type IV deposits and axons showed the expression of tyrosine hydroxylase and these axons extended through the site of injury by reinnervating the striatum [104]. Conversely, iron chelators suppress GS but do not degrade the existing scar, meaning that this treatment is not transferable to chronic SCI where a mature lesion scar is present, with a plethora of axon growth-inhibitory molecules attached [105, 106].

#### **6.5 Surgical resections**

Some studies have shown that the surgical removal of the GS promotes the development of axons in the injured portion of the SC, suggesting that axonal reconnection is feasible [16, 107]. Another study indicates that the use of surgical resection of the GS by itself does not offer positive results, because at the time of incising and removing the tissue healing, the same mechanisms that are activated during the acute phase are reactivated, generating a second lesion [75].

On the other hand, one study showed that careful surgical resection of the scar and filling cavity with biocompatible matrices promotes a functional improvement in a full-section model [16].

Therefore, the treatment of SCI can be improved if the behavior of the GS with the combination of transplants [75], iron chelators [45, 77], and matrices is biocompatible [16]. Furthermore, Rodriguez and colleagues explored whether INDP in combination with scar removal and DPY provided an appropriate microenvironment to promote neural restoration in chronic SCI. They found an increased activity in genes encoding for IL4, TGFβ, BDNF, IGF1, and GAP43, as well as a decreased activity in genes encoding for TNFα and IFNγ. Moreover, there was a significant increment in the number of serotonergic (5-HT-positive) and catecholaminergic (TH-positive) fibers at the caudal segment of the GS [78].

#### **7. Conclusions**

Cytokines are incredibly involved in GS formation during the acute and chronic phases of SCI, participating in either beneficial or detrimental effects. To achieve the best possible results, it is necessary to maintain the anti-inflammatory microenvironment for more extended periods of time in order to promote axonal regeneration, M2 phenotype macrophage activation, and secretion of neurotrophic factors that are capable of inhibiting the GS formation in the chronic phase. Several clinical trials have shown different therapeutic strategies to modulate the formation of GS. Although those experiments have had a significant therapeutic potential in patients with SCI, there are still enormous knowledge gaps which need further investigation in order to develop a potential cure for SCI.

#### **Acknowledgements**

We gratefully acknowledge the Universidad Anáhuac México for their support on this chapter.

**87**

**Author details**

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

Roxana Rodrígez-Barrera, Adrián Flores-Romero, Julián García-Sánchez, Lisset Karina Navarro-Torres, Marcela Garibay-López and Elisa García-Vences\* Centro de Investigación en Ciencias de la Salud (CICSA), Universidad Anáhuac

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

México Campus Norte, Huixquilucan, Estado de México, Mexico

\*Address all correspondence to: edna.garcia@anahuac.mx

provided the original work is properly cited.

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

The authors declare no conflict of interest.

**Conflict of interest**

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury DOI: http://dx.doi.org/10.5772/intechopen.93005*

## **Conflict of interest**

*Cytokines*

attached [105, 106].

**6.5 Surgical resections**

in a full-section model [16].

**7. Conclusions**

cure for SCI.

on this chapter.

**Acknowledgements**

model [45, 77]. The iron chelation of α,α'-dipyridyl (DPY) has previously shown to decrease the collagen synthesis at a posttranscriptional level by inhibiting 4-prolyl

In a study with unilateral SC transection in adult and postnatal mice (14 days old) where DPY was applied at the injury site, it was observed that collagen type IV deposits and axons showed the expression of tyrosine hydroxylase and these axons extended through the site of injury by reinnervating the striatum [104]. Conversely, iron chelators suppress GS but do not degrade the existing scar, meaning that this treatment is not transferable to chronic SCI where a mature lesion scar is present, with a plethora of axon growth-inhibitory molecules

Some studies have shown that the surgical removal of the GS promotes the development of axons in the injured portion of the SC, suggesting that axonal reconnection is feasible [16, 107]. Another study indicates that the use of surgical resection of the GS by itself does not offer positive results, because at the time of incising and removing the tissue healing, the same mechanisms that are activated

On the other hand, one study showed that careful surgical resection of the scar and filling cavity with biocompatible matrices promotes a functional improvement

Therefore, the treatment of SCI can be improved if the behavior of the GS with the combination of transplants [75], iron chelators [45, 77], and matrices is biocompatible [16]. Furthermore, Rodriguez and colleagues explored whether INDP in combination with scar removal and DPY provided an appropriate microenvironment to promote neural restoration in chronic SCI. They found an increased activity in genes encoding for IL4, TGFβ, BDNF, IGF1, and GAP43, as well as a decreased activity in genes encoding for TNFα and IFNγ. Moreover, there was a significant increment in the number of serotonergic (5-HT-positive) and catecholaminergic

Cytokines are incredibly involved in GS formation during the acute and chronic phases of SCI, participating in either beneficial or detrimental effects. To achieve the best possible results, it is necessary to maintain the anti-inflammatory microenvironment for more extended periods of time in order to promote axonal regeneration, M2 phenotype macrophage activation, and secretion of neurotrophic factors that are capable of inhibiting the GS formation in the chronic phase. Several clinical trials have shown different therapeutic strategies to modulate the formation of GS. Although those experiments have had a significant therapeutic potential in patients with SCI, there are still enormous knowledge gaps which need further investigation in order to develop a potential

We gratefully acknowledge the Universidad Anáhuac México for their support

during the acute phase are reactivated, generating a second lesion [75].

(TH-positive) fibers at the caudal segment of the GS [78].

hydroxylase, one of the key enzymes in collagen metabolism [103].

**86**

The authors declare no conflict of interest.

## **Author details**

Roxana Rodrígez-Barrera, Adrián Flores-Romero, Julián García-Sánchez, Lisset Karina Navarro-Torres, Marcela Garibay-López and Elisa García-Vences\* Centro de Investigación en Ciencias de la Salud (CICSA), Universidad Anáhuac México Campus Norte, Huixquilucan, Estado de México, Mexico

\*Address all correspondence to: edna.garcia@anahuac.mx

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **References**

[1] Sun X, Jones ZB, Chen XM, Zhou L, So KF, Ren Y. Multiple organ dysfunction and systemic inflammation after spinal cord injury: A complex relationship. Journal of Neuroinflammation. 2016;**13**(1):260

[2] Ahmed A, Patil AA, Agrawal DK. Immunobiology of spinal cord injuries and potential therapeutic approaches. Molecular and Cellular Biochemistry. 2018;**441**(1-2):181-189

[3] Alizadeh A, Dyck SM, Karimi-Abdolrezaee S. Traumatic spinal cord injury: An overview of pathophysiology, models and acute injury mechanisms. Frontiers in Neurology. 2019;**10**:282

[4] Ahuja CS, Wilson JR, Nori S, Kotter MRN, Druschel C, Curt A, et al. Traumatic spinal cord injury. Nature Reviews. Disease Primers. 2017;**3**:17018

[5] Gu Y, Cheng X, Huang X, Yuan Y, Qin S, Tan Z, et al. Conditional ablation of reactive astrocytes to dissect their roles in spinal cord injury and repair. Brain, Behavior, and Immunity. 2019;**80**:394-405

[6] Anderson MA, Burda JE, Ren Y, Ao Y, O'Shea TM, Kawaguchi R, et al. Astrocyte scar formation aids central nervous system axon regeneration. Nature. 2016;**532**(7598):195-200

[7] Okada S, Hara M, Kobayakawa K, Matsumoto Y, Nakashima Y. Astrocyte reactivity and astrogliosis after spinal cord injury. Neuroscience Research. 2018;**126**:39-43

[8] Liberman AC, Trias E, da Silva Chagas L, Trindade P, Dos Santos Pereira M, Refojo D, et al. Neuroimmune and inflammatory signals in complex disorders of the central nervous system. Neuroimmunomodulation. 2018;**25**(5-6):246-270

[9] Nizamutdinov D, Shapiro LA. Overview of traumatic brain injury: An immunological context. Brain Sciences. 2017;**7**(1):11

[10] Matsuda M, Huh Y, Ji RR. Roles of inflammation, neurogenic inflammation, and neuroinflammation in pain. Journal of Anesthesia. 2019;**33**(1):131-139

[11] Chavan SS, Pavlov VA, Tracey KJ. Mechanisms and therapeutic relevance of neuro-immune communication. Immunity. 2017;**46**(6):927-942

[12] Dzyubenko E, Manrique-Castano D, Kleinschnitz C, Faissner A, Hermann DM. Role of immune responses for extracellular matrix remodeling in the ischemic brain. Therapeutic Advances in Neurological Disorders. 2018;**11**:1756286418818092

[13] Pavlov VA, Chavan SS, Tracey KJ. Molecular and functional neuroscience in immunity. Annual Review of Immunology. 2018;**36**:783-812

[14] Shi Y, Wang Y, Li Q, Liu K, Hou J, Shao C. Immunoregulatory mechanisms of mesenchymal stem and stromal cells in inflammatory diseases. Nature Reviews. Nephrology. 2018;**14**(8):493-507

[15] Yang QQ, Zhou JW. Neuroinflammation in the central nervous system: Symphony of glial cells. Glia. 2019;**67**(6):1017-1035

[16] Estrada V, Brazda N, Schmitz C, Heller S, Blazyca H, Martini R, et al. Long-lasting significant functional improvement in chronic severe spinal cord injury following scar resection and polyethylene glycol implantation. Neurobiology of Disease. 2014;**67**:165-179

[17] Raposo C, Schwartz M. Glial scar and immune cell involvement

**89**

2016;**9**(1):48

2013;**2013**:945034

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

[26] Beck KD, Nguyen HX,

2010;**133**(Pt 2):433-447

2004;**24**(9):2143-2155

2013;**29**(4):421-435

[27] Bollaerts I, Van Houcke J, Andries L, De Groef L, Moons L. Neuroinflammation as fuel for axonal regeneration in the injured vertebrate central nervous system. Mediators of Inflammation. 2017;**2017**:9478542

Galvan MD, Salazar DL, Woodruff TM, Anderson AJ. Quantitative analysis of cellular inflammation after traumatic spinal cord injury: Evidence for a multiphasic inflammatory response in the acute to chronic environment. Brain.

[28] Faulkner JR, Herrmann JE, Woo MJ, Tansey KE, Doan NB, Sofroniew MV. Reactive astrocytes protect tissue and preserve function after spinal cord injury. The Journal of Neuroscience.

[29] Goritz C, Dias DO, Tomilin N, Barbacid M, Shupliakov O, Frisen J. A pericyte origin of spinal cord scar tissue.

Science. 2011;**333**(6039):238-242

[31] Matthews MA, St. Onge MF,

Faciane CL, Gelderd JB. Axon sprouting into segments of rat spinal cord adjacent to the site of a previous transection. Neuropathology and Applied Neurobiology. 1979;**5**(3):181-196

[32] Adams KL, Gallo V. The diversity and disparity of the glial scar. Nature Neuroscience. 2018;**21**(1):9-15

Akhmetzyanova ER, Martynova EV,

[34] Liu C, Shi Z, Fan L, Zhang C, Wang K, Wang B. Resveratrol improves

[33] Mukhamedshina YO,

Khaiboullina SF, Galieva LR, Rizvanov AA. Systemic and local cytokine profile following spinal cord injury in rats: A multiplex analysis. Frontiers in Neurology. 2017;**8**:581

[30] Yuan YM, He C. The glial scar in spinal cord injury and repair. Neuroscience Bulletin.

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

[18] Shechter R, Raposo C, London A, Sagi I, Schwartz M. The glial scarmonocyte interplay: A pivotal resolution phase in spinal cord repair. PLoS One.

[19] Jassam YN, Izzy S, Whalen M, McGavern DB, El Khoury J.

[20] Rouanet C, Reges D, Rocha E, Gagliardi V, Silva GS. Traumatic spinal cord injury: Current concepts and treatment update. Arquivos de Neuro-Psiquiatria. 2017;**75**(6):387-393

[21] Oyinbo CA. Secondary injury mechanisms in traumatic spinal cord injury: A nugget of this multiply cascade. Acta Neurobiologiae Experimentalis (Wars). 2011;**71**(2):281-299

[22] Zhou X, He X, Ren Y. Function of microglia and macrophages in secondary damage after spinal cord injury. Neural Regeneration Research.

[23] Wang X, Cao K, Sun X, Chen Y, Duan Z, Sun L, et al. Macrophages in spinal cord injury: Phenotypic and functional change from exposure to myelin debris. Glia. 2015;**63**(4):635-651

[24] Guo L, Rolfe AJ, Wang X, Tai W, Cheng Z, Cao K, et al. Rescuing macrophage normal function in spinal cord injury with embryonic stem cell conditioned media. Molecular Brain.

[25] Ren Y, Young W. Managing inflammation after spinal cord injury through manipulation of

macrophage function. Neural Plasticity.

2014;**9**(20):1787-1795

Neuroimmunology of traumatic brain injury: Time for a paradigm shift. Neuron. 2017;**95**(6):1246-1265

in tissue remodeling and repair following acute CNS injuries. Glia.

2014;**62**(11):1895-1904

2011;**6**(12):e27969

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury DOI: http://dx.doi.org/10.5772/intechopen.93005*

in tissue remodeling and repair following acute CNS injuries. Glia. 2014;**62**(11):1895-1904

[18] Shechter R, Raposo C, London A, Sagi I, Schwartz M. The glial scarmonocyte interplay: A pivotal resolution phase in spinal cord repair. PLoS One. 2011;**6**(12):e27969

[19] Jassam YN, Izzy S, Whalen M, McGavern DB, El Khoury J. Neuroimmunology of traumatic brain injury: Time for a paradigm shift. Neuron. 2017;**95**(6):1246-1265

[20] Rouanet C, Reges D, Rocha E, Gagliardi V, Silva GS. Traumatic spinal cord injury: Current concepts and treatment update. Arquivos de Neuro-Psiquiatria. 2017;**75**(6):387-393

[21] Oyinbo CA. Secondary injury mechanisms in traumatic spinal cord injury: A nugget of this multiply cascade. Acta Neurobiologiae Experimentalis (Wars). 2011;**71**(2):281-299

[22] Zhou X, He X, Ren Y. Function of microglia and macrophages in secondary damage after spinal cord injury. Neural Regeneration Research. 2014;**9**(20):1787-1795

[23] Wang X, Cao K, Sun X, Chen Y, Duan Z, Sun L, et al. Macrophages in spinal cord injury: Phenotypic and functional change from exposure to myelin debris. Glia. 2015;**63**(4):635-651

[24] Guo L, Rolfe AJ, Wang X, Tai W, Cheng Z, Cao K, et al. Rescuing macrophage normal function in spinal cord injury with embryonic stem cell conditioned media. Molecular Brain. 2016;**9**(1):48

[25] Ren Y, Young W. Managing inflammation after spinal cord injury through manipulation of macrophage function. Neural Plasticity. 2013;**2013**:945034

[26] Beck KD, Nguyen HX, Galvan MD, Salazar DL, Woodruff TM, Anderson AJ. Quantitative analysis of cellular inflammation after traumatic spinal cord injury: Evidence for a multiphasic inflammatory response in the acute to chronic environment. Brain. 2010;**133**(Pt 2):433-447

[27] Bollaerts I, Van Houcke J, Andries L, De Groef L, Moons L. Neuroinflammation as fuel for axonal regeneration in the injured vertebrate central nervous system. Mediators of Inflammation. 2017;**2017**:9478542

[28] Faulkner JR, Herrmann JE, Woo MJ, Tansey KE, Doan NB, Sofroniew MV. Reactive astrocytes protect tissue and preserve function after spinal cord injury. The Journal of Neuroscience. 2004;**24**(9):2143-2155

[29] Goritz C, Dias DO, Tomilin N, Barbacid M, Shupliakov O, Frisen J. A pericyte origin of spinal cord scar tissue. Science. 2011;**333**(6039):238-242

[30] Yuan YM, He C. The glial scar in spinal cord injury and repair. Neuroscience Bulletin. 2013;**29**(4):421-435

[31] Matthews MA, St. Onge MF, Faciane CL, Gelderd JB. Axon sprouting into segments of rat spinal cord adjacent to the site of a previous transection. Neuropathology and Applied Neurobiology. 1979;**5**(3):181-196

[32] Adams KL, Gallo V. The diversity and disparity of the glial scar. Nature Neuroscience. 2018;**21**(1):9-15

[33] Mukhamedshina YO, Akhmetzyanova ER, Martynova EV, Khaiboullina SF, Galieva LR, Rizvanov AA. Systemic and local cytokine profile following spinal cord injury in rats: A multiplex analysis. Frontiers in Neurology. 2017;**8**:581

[34] Liu C, Shi Z, Fan L, Zhang C, Wang K, Wang B. Resveratrol improves

**88**

*Cytokines*

**References**

[1] Sun X, Jones ZB, Chen XM, Zhou L, So KF, Ren Y. Multiple organ

inflammation after spinal cord injury: A complex relationship. Journal of Neuroinflammation. 2016;**13**(1):260

immunological context. Brain Sciences.

inflammation, and neuroinflammation

[11] Chavan SS, Pavlov VA, Tracey KJ. Mechanisms and therapeutic relevance of neuro-immune communication. Immunity. 2017;**46**(6):927-942

[13] Pavlov VA, Chavan SS, Tracey KJ. Molecular and functional neuroscience

in immunity. Annual Review of Immunology. 2018;**36**:783-812

[14] Shi Y, Wang Y, Li Q, Liu K, Hou J, Shao C. Immunoregulatory mechanisms of mesenchymal stem and stromal cells in inflammatory diseases. Nature Reviews. Nephrology.

2018;**14**(8):493-507

2014;**67**:165-179

[15] Yang QQ, Zhou JW.

Glia. 2019;**67**(6):1017-1035

Neuroinflammation in the central nervous system: Symphony of glial cells.

[16] Estrada V, Brazda N, Schmitz C, Heller S, Blazyca H, Martini R, et al. Long-lasting significant functional improvement in chronic severe spinal cord injury following scar resection and polyethylene glycol implantation. Neurobiology of Disease.

[17] Raposo C, Schwartz M. Glial scar and immune cell involvement

[10] Matsuda M, Huh Y, Ji RR. Roles of inflammation, neurogenic

in pain. Journal of Anesthesia.

[12] Dzyubenko E, Manrique-Castano D, Kleinschnitz C, Faissner A, Hermann DM. Role of immune responses for extracellular matrix remodeling in the ischemic brain. Therapeutic Advances in Neurological Disorders. 2018;**11**:1756286418818092

2019;**33**(1):131-139

2017;**7**(1):11

[2] Ahmed A, Patil AA, Agrawal DK. Immunobiology of spinal cord injuries and potential therapeutic approaches. Molecular and Cellular Biochemistry.

[3] Alizadeh A, Dyck SM, Karimi-Abdolrezaee S. Traumatic spinal cord injury: An overview of pathophysiology, models and acute injury mechanisms. Frontiers in Neurology. 2019;**10**:282

[4] Ahuja CS, Wilson JR, Nori S, Kotter MRN, Druschel C, Curt A, et al. Traumatic spinal cord injury. Nature Reviews. Disease Primers. 2017;**3**:17018

[5] Gu Y, Cheng X, Huang X, Yuan Y, Qin S, Tan Z, et al. Conditional ablation of reactive astrocytes to dissect their roles in spinal cord injury and repair. Brain, Behavior, and Immunity. 2019;**80**:394-405

[6] Anderson MA, Burda JE, Ren Y, Ao Y, O'Shea TM, Kawaguchi R, et al. Astrocyte scar formation aids central nervous system axon regeneration. Nature. 2016;**532**(7598):195-200

[7] Okada S, Hara M, Kobayakawa K, Matsumoto Y, Nakashima Y. Astrocyte reactivity and astrogliosis after spinal cord injury. Neuroscience Research.

[8] Liberman AC, Trias E, da Silva Chagas L, Trindade P, Dos Santos Pereira M, Refojo D, et al. Neuroimmune and inflammatory signals in complex disorders of the central nervous system. Neuroimmunomodulation.

[9] Nizamutdinov D, Shapiro LA. Overview of traumatic brain injury: An

2018;**126**:39-43

2018;**25**(5-6):246-270

dysfunction and systemic

2018;**441**(1-2):181-189

neuron protection and functional recovery in rat model of spinal cord injury. Brain Research. 2011;**1374**:100-109

[35] Rostami A, Ciric B. Role of Th17 cells in the pathogenesis of CNS inflammatory demyelination. Journal of the Neurological Sciences. 2013;**333**(1-2):76-87

[36] Cregg JM, DePaul MA, Filous AR, Lang BT, Tran A, Silver J. Functional regeneration beyond the glial scar. Experimental Neurology. 2014;**253**:197-207

[37] Noble LJ, Donovan F, Igarashi T, Goussev S, Werb Z. Matrix metalloproteinases limit functional recovery after spinal cord injury by modulation of early vascular events. The Journal of Neuroscience. 2002;**22**(17):7526-7535

[38] Hanamsagar R, Hanke ML, Kielian T. Toll-like receptor (TLR) and inflammasome actions in the central nervous system. Trends in Immunology. 2012;**33**(7):333-342

[39] Sticozzi C, Belmonte G, Meini A, Carbotti P, Grasso G, Palmi M. IL-1beta induces GFAP expression in vitro and in vivo and protects neurons from traumatic injury-associated apoptosis in rat brain striatum via NFkappaB/Ca2+ calmodulin/ERK mitogen-activated protein kinase signaling pathway. Neuroscience. 2013;**252**:367-383

[40] Miller SJ. Astrocyte heterogeneity in the adult central nervous system. Frontiers in Cellular Neuroscience. 2018;**12**:401

[41] DiProspero NA, Meiners S, Geller HM. Inflammatory cytokines interact to modulate extracellular matrix and astrocytic support of neurite outgrowth. Experimental Neurology. 1997;**148**(2):628-639

[42] Miljkovic D, Timotijevic G, Mostarica SM. Astrocytes in the tempest of multiple sclerosis. FEBS Letters. 2011;**585**(23):3781-3788

[43] Tang X, Davies JE, Davies SJ. Changes in distribution, cell associations, and protein expression levels of NG2, neurocan, phosphacan, brevican, versican V2, and tenascin-C during acute to chronic maturation of spinal cord scar tissue. Journal of Neuroscience Research. 2003;**71**(3):427-444

[44] Dias DO, Kim H, Holl D, Werne Solnestam B, Lundeberg J, Carlen M, et al. Reducing pericytederived scarring promotes recovery after spinal cord injury. Cell. 2018;**173**(1):153-165

[45] Klapka N, Muller HW. Collagen matrix in spinal cord injury. Journal of Neurotrauma. 2006;**23**(3-4):422-435

[46] Wanner IB, Anderson MA, Song B, Levine J, Fernandez A, Gray-Thompson Z, et al. Glial scar borders are formed by newly proliferated, elongated astrocytes that interact to corral inflammatory and fibrotic cells via STAT3-dependent mechanisms after spinal cord injury. The Journal of Neuroscience. 2013;**33**(31):12870-12886

[47] Pekny M, Johansson CB, Eliasson C, Stakeberg J, Wallen A, Perlmann T, et al. Abnormal reaction to central nervous system injury in mice lacking glial fibrillary acidic protein and vimentin. The Journal of Cell Biology. 1999;**145**(3):503-514

[48] Okada S, Nakamura M, Katoh H, Miyao T, Shimazaki T, Ishii K, et al. Conditional ablation of Stat3 or Socs3 discloses a dual role for reactive astrocytes after spinal cord injury. Nature Medicine. 2006;**12**(7):829-834

**91**

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

[57] Duchossoy Y, Horvat JC, Stettler O. MMP-related gelatinase activity is strongly induced in scar tissue of injured adult spinal cord and forms pathways for ingrowing neurites. Molecular and Cellular Neurosciences.

[58] Zhang H, Chang M, Hansen CN, Basso DM, Noble-Haeusslein LJ. Role of matrix metalloproteinases and therapeutic benefits of their inhibition in spinal cord injury. Neurotherapeutics.

[59] Codeluppi S, Svensson CI,

Hefferan MP, Valencia F, Silldorff MD, Oshiro M, et al. The Rheb-mTOR pathway is upregulated in reactive astrocytes of the injured spinal cord. The Journal of Neuroscience.

[60] Liu B, Neufeld AH. Activation of epidermal growth factor receptor causes astrocytes to form cribriform structures.

Yamashita T. Inhibition of TGF-beta1 promotes functional recovery after spinal cord injury. Neuroscience Research. 2009;**65**(4):393-401

[62] Herrmann JE, Imura T, Song B, Qi J, Ao Y, Nguyen TK, et al. STAT3 is a critical regulator of astrogliosis and scar formation after spinal cord injury. The Journal of Neuroscience.

2001;**17**(6):945-956

2011;**8**(2):206-220

2009;**29**(4):1093-1104

Glia. 2004;**46**(2):153-168

[61] Kohta M, Kohmura E,

2008;**28**(28):7231-7243

1996;**203**(2):97-100

[63] Hamada Y, Ikata T, Katoh S, Katoh K, Niwa M, Tsutsumishita Y, et al. Effects of exogenous transforming growth factor-beta 1 on spinal cord injury in rats. Neuroscience Letters.

[64] Logan A, Berry M, Gonzalez AM, Frautschy SA, Sporn MB, Baird A. Effects of transforming growth factor beta 1 on scar production in the injured

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

[50] Schachtrup C, Ryu JK, Helmrick MJ, Vagena E, Galanakis DK, Degen JL, et al. Fibrinogen triggers astrocyte scar formation by promoting the availability of active TGF-beta after vascular damage. The Journal of Neuroscience.

[51] Rolls A, Shechter R, London A, Segev Y, Jacob-Hirsch J, Amariglio N, et al. Two faces of chondroitin sulfate proteoglycan in spinal cord repair: A role in microglia/macrophage activation.

PLoS Medicine. 2008;**5**(8):e171

[52] Horky LL, Galimi F, Gage FH, Horner PJ. Fate of endogenous stem/ progenitor cells following spinal cord injury. The Journal of Comparative Neurology. 2006;**498**(4):525-538

[53] Meletis K, Barnabe-Heider F, Carlen M, Evergren E, Tomilin N, Shupliakov O, et al. Spinal cord injury reveals multilineage differentiation of ependymal cells. PLoS Biology.

[54] Sarafian TA, Montes C, Imura T, Qi J, Coppola G, Geschwind DH, et al. Disruption of astrocyte STAT3 signaling decreases mitochondrial function and increases oxidative stress in vitro. PLoS

[55] Smith GM, Strunz C. Growth factor and cytokine regulation of chondroitin sulfate proteoglycans by astrocytes.

[56] Xiao Q, Du Y, Wu W, Yip HK. Bone morphogenetic proteins mediate cellular response and, together with Noggin, regulate astrocyte differentiation after spinal cord injury. Experimental Neurology. 2010;**221**(2):353-366

2008;**6**(7):e182

One. 2010;**5**(3):e9532

Glia. 2005;**52**(3):209-218

[49] Nathan FM, Li S. Environmental

astrocytes after spinal cord injury. Neural Regeneration Research.

cues determine the fate of

2017;**12**(12):1964-1970

2010;**30**(17):5843-5854

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury DOI: http://dx.doi.org/10.5772/intechopen.93005*

[49] Nathan FM, Li S. Environmental cues determine the fate of astrocytes after spinal cord injury. Neural Regeneration Research. 2017;**12**(12):1964-1970

*Cytokines*

2011;**1374**:100-109

2013;**333**(1-2):76-87

2014;**253**:197-207

neuron protection and functional recovery in rat model of spinal cord injury. Brain Research.

[42] Miljkovic D, Timotijevic G,

[43] Tang X, Davies JE, Davies SJ. Changes in distribution, cell

associations, and protein expression levels of NG2, neurocan, phosphacan,

tenascin-C during acute to chronic maturation of spinal cord scar tissue. Journal of Neuroscience Research.

2011;**585**(23):3781-3788

brevican, versican V2, and

[44] Dias DO, Kim H, Holl D, Werne Solnestam B, Lundeberg J, Carlen M, et al. Reducing pericytederived scarring promotes recovery after spinal cord injury. Cell.

[45] Klapka N, Muller HW. Collagen matrix in spinal cord injury. Journal of Neurotrauma. 2006;**23**(3-4):422-435

[46] Wanner IB, Anderson MA, Song B, Levine J, Fernandez A, Gray-Thompson Z, et al. Glial scar borders are formed by newly proliferated, elongated astrocytes that interact to corral inflammatory and fibrotic cells via STAT3-dependent mechanisms after spinal cord injury. The Journal of Neuroscience.

2013;**33**(31):12870-12886

1999;**145**(3):503-514

[47] Pekny M, Johansson CB, Eliasson C, Stakeberg J, Wallen A, Perlmann T, et al. Abnormal reaction to central nervous system injury in mice lacking glial fibrillary acidic protein and vimentin. The Journal of Cell Biology.

[48] Okada S, Nakamura M, Katoh H, Miyao T, Shimazaki T, Ishii K, et al. Conditional ablation of Stat3 or Socs3 discloses a dual role for reactive astrocytes after spinal cord injury. Nature Medicine. 2006;**12**(7):829-834

2003;**71**(3):427-444

2018;**173**(1):153-165

Mostarica SM. Astrocytes in the tempest of multiple sclerosis. FEBS Letters.

[35] Rostami A, Ciric B. Role of Th17 cells in the pathogenesis of CNS inflammatory demyelination. Journal of the Neurological Sciences.

[36] Cregg JM, DePaul MA, Filous AR, Lang BT, Tran A, Silver J. Functional regeneration beyond the glial scar. Experimental Neurology.

[37] Noble LJ, Donovan F, Igarashi T,

metalloproteinases limit functional recovery after spinal cord injury by modulation of early vascular events. The Journal of Neuroscience.

[38] Hanamsagar R, Hanke ML, Kielian T. Toll-like receptor (TLR) and inflammasome actions in the central nervous system. Trends in Immunology.

[39] Sticozzi C, Belmonte G, Meini A, Carbotti P, Grasso G, Palmi M. IL-1beta induces GFAP expression in vitro and in vivo and protects neurons from traumatic injury-associated apoptosis in rat brain striatum via NFkappaB/Ca2+ calmodulin/ERK mitogen-activated protein kinase signaling pathway. Neuroscience. 2013;**252**:367-383

[40] Miller SJ. Astrocyte heterogeneity in the adult central nervous system. Frontiers in Cellular Neuroscience.

[41] DiProspero NA, Meiners S, Geller HM. Inflammatory cytokines interact to modulate extracellular matrix and astrocytic support of neurite outgrowth. Experimental Neurology.

1997;**148**(2):628-639

Goussev S, Werb Z. Matrix

2002;**22**(17):7526-7535

2012;**33**(7):333-342

**90**

2018;**12**:401

[50] Schachtrup C, Ryu JK, Helmrick MJ, Vagena E, Galanakis DK, Degen JL, et al. Fibrinogen triggers astrocyte scar formation by promoting the availability of active TGF-beta after vascular damage. The Journal of Neuroscience. 2010;**30**(17):5843-5854

[51] Rolls A, Shechter R, London A, Segev Y, Jacob-Hirsch J, Amariglio N, et al. Two faces of chondroitin sulfate proteoglycan in spinal cord repair: A role in microglia/macrophage activation. PLoS Medicine. 2008;**5**(8):e171

[52] Horky LL, Galimi F, Gage FH, Horner PJ. Fate of endogenous stem/ progenitor cells following spinal cord injury. The Journal of Comparative Neurology. 2006;**498**(4):525-538

[53] Meletis K, Barnabe-Heider F, Carlen M, Evergren E, Tomilin N, Shupliakov O, et al. Spinal cord injury reveals multilineage differentiation of ependymal cells. PLoS Biology. 2008;**6**(7):e182

[54] Sarafian TA, Montes C, Imura T, Qi J, Coppola G, Geschwind DH, et al. Disruption of astrocyte STAT3 signaling decreases mitochondrial function and increases oxidative stress in vitro. PLoS One. 2010;**5**(3):e9532

[55] Smith GM, Strunz C. Growth factor and cytokine regulation of chondroitin sulfate proteoglycans by astrocytes. Glia. 2005;**52**(3):209-218

[56] Xiao Q, Du Y, Wu W, Yip HK. Bone morphogenetic proteins mediate cellular response and, together with Noggin, regulate astrocyte differentiation after spinal cord injury. Experimental Neurology. 2010;**221**(2):353-366

[57] Duchossoy Y, Horvat JC, Stettler O. MMP-related gelatinase activity is strongly induced in scar tissue of injured adult spinal cord and forms pathways for ingrowing neurites. Molecular and Cellular Neurosciences. 2001;**17**(6):945-956

[58] Zhang H, Chang M, Hansen CN, Basso DM, Noble-Haeusslein LJ. Role of matrix metalloproteinases and therapeutic benefits of their inhibition in spinal cord injury. Neurotherapeutics. 2011;**8**(2):206-220

[59] Codeluppi S, Svensson CI, Hefferan MP, Valencia F, Silldorff MD, Oshiro M, et al. The Rheb-mTOR pathway is upregulated in reactive astrocytes of the injured spinal cord. The Journal of Neuroscience. 2009;**29**(4):1093-1104

[60] Liu B, Neufeld AH. Activation of epidermal growth factor receptor causes astrocytes to form cribriform structures. Glia. 2004;**46**(2):153-168

[61] Kohta M, Kohmura E, Yamashita T. Inhibition of TGF-beta1 promotes functional recovery after spinal cord injury. Neuroscience Research. 2009;**65**(4):393-401

[62] Herrmann JE, Imura T, Song B, Qi J, Ao Y, Nguyen TK, et al. STAT3 is a critical regulator of astrogliosis and scar formation after spinal cord injury. The Journal of Neuroscience. 2008;**28**(28):7231-7243

[63] Hamada Y, Ikata T, Katoh S, Katoh K, Niwa M, Tsutsumishita Y, et al. Effects of exogenous transforming growth factor-beta 1 on spinal cord injury in rats. Neuroscience Letters. 1996;**203**(2):97-100

[64] Logan A, Berry M, Gonzalez AM, Frautschy SA, Sporn MB, Baird A. Effects of transforming growth factor beta 1 on scar production in the injured central nervous system of the rat. The European Journal of Neuroscience. 1994;**6**(3):355-363

[65] Su Z, Yuan Y, Chen J, Zhu Y, Qiu Y, Zhu F, et al. Reactive astrocytes inhibit the survival and differentiation of oligodendrocyte precursor cells by secreted TNF-alpha. Journal of Neurotrauma. 2011;**28**(6):1089-1100

[66] Gris P, Tighe A, Levin D, Sharma R, Brown A. Transcriptional regulation of scar gene expression in primary astrocytes. Glia. 2007;**55**(11):1145-1155

[67] Regis G, Pensa S, Boselli D, Novelli F, Poli V. Ups and downs: The STAT1:STAT3 seesaw of interferon and gp130 receptor signalling. Seminars in Cell & Developmental Biology. 2008;**19**(4):351-359

[68] Shechter R, London A, Varol C, Raposo C, Cusimano M, Yovel G, et al. Infiltrating blood-derived macrophages are vital cells playing an antiinflammatory role in recovery from spinal cord injury in mice. PLoS Medicine. 2009;**6**(7):e1000113

[69] Sofroniew MV. Astrogliosis. Cold Spring Harbor Perspectives in Biology. 2014;**7**(2):a020420

[70] Karimi-Abdolrezaee S, Billakanti R. Reactive astrogliosis after spinal cord injury—Beneficial and detrimental effects. Molecular Neurobiology. 2012;**46**(2):251-264

[71] Silver J, Miller JH. Regeneration beyond the glial scar. Nature Reviews. Neuroscience. 2004;**5**(2):146-156

[72] Sahni V, Mukhopadhyay A, Tysseling V, Hebert A, Birch D, McGuire TL, et al. BMPR1a and BMPR1b signaling exert opposing effects on gliosis after spinal cord injury. The Journal of Neuroscience. 2010;**30**(5):1839-1855

[73] Pendleton JC, Shamblott MJ, Gary DS, Belegu V, Hurtado A, Malone ML, et al. Chondroitin sulfate proteoglycans inhibit oligodendrocyte myelination through PTPsigma. Experimental Neurology. 2013;**247**:113-121

[74] Trivedi A, Olivas AD, Noble-Haeusslein LJ. Inflammation and spinal cord injury: Infiltrating leukocytes as determinants of injury and repair processes. Clinical Neuroscience Research. 2006;**6**(5):283-292

[75] Rasouli A, Bhatia N, Dinh P, Cahill K, Suryadevara S, Gupta R. Resection of glial scar following spinal cord injury. Journal of Orthopaedic Research. 2009;**27**(7):931-936

[76] Klapka N, Hermanns S, Straten G, Masanneck C, Duis S, Hamers FP, et al. Suppression of fibrous scarring in spinal cord injury of rat promotes longdistance regeneration of corticospinal tract axons, rescue of primary motoneurons in somatosensory cortex and significant functional recovery. The European Journal of Neuroscience. 2005;**22**(12):3047-3058

[77] Schiwy N, Brazda N, Muller HW. Enhanced regenerative axon growth of multiple fibre populations in traumatic spinal cord injury following scar-suppressing treatment. The European Journal of Neuroscience. 2009;**30**(8):1544-1553

[78] Rodriguez-Barrera R, Flores-Romero A, Fernandez-Presas AM, Garcia-Vences E, Silva-Garcia R, Konigsberg M, et al. Immunization with neural derived peptides plus scar removal induces a permissive microenvironment, and improves locomotor recovery after chronic spinal cord injury. BMC Neuroscience. 2017;**18**(1):7

[79] Nakajima H, Uchida K, Guerrero AR, Watanabe S, Sugita D,

**93**

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury*

[87] Assinck P, Duncan GJ, Hilton BJ,

[88] Oudega M, Xu XM. Schwann cell transplantation for repair of the adult spinal cord. Journal of Neurotrauma.

[89] Kuo HS, Tsai MJ, Huang MC, Chiu CW, Tsai CY, Lee MJ, et al. Acid fibroblast growth factor and peripheral nerve grafts regulate Th2 cytokine expression, macrophage activation, polyamine synthesis, and neurotrophin expression in transected rat spinal cords. The Journal of Neuroscience.

[90] Do-Thi A, Perrin FE, Desclaux M, Saillour P, Amar L, Privat A, et al. Combination of grafted Schwann cells and lentiviral-mediated prevention of glial scar formation improve recovery of spinal cord injured rats. Journal of Chemical Neuroanatomy. 2016;**76**

[91] Lin L, Lin H, Bai S, Zheng L, Zhang X. Bone marrow mesenchymal

[92] Xiong LL, Liu F, Lu BT, Zhao WL, Dong XJ, Liu J, et al. Bone marrow mesenchymal stem-cell transplantation promotes functional improvement associated with CNTF-STAT3 activation after hemi-sectioned spinal cord injury in tree shrews. Frontiers in Cellular

stem cells (BMSCs) improved functional recovery of spinal cord injury partly by promoting axonal regeneration. Neurochemistry International. 2018;**115**:80-84

Neuroscience. 2017;**11**:172

[93] Okuda A, Horii-Hayashi N, Sasagawa T, Shimizu T, Shigematsu H, Iwata E, et al. Bone marrow stromal cell sheets may promote axonal regeneration and functional recovery with suppression of glial scar formation

Plemel JR, Tetzlaff W. Cell transplantation therapy for spinal cord injury. Nature Neuroscience.

2017;**20**(5):637-647

2006;**23**(3-4):453-467

2011;**31**(11):4137-4147

(Pt A):48-60

*DOI: http://dx.doi.org/10.5772/intechopen.93005*

Takeura N, et al. Transplantation of mesenchymal stem cells promotes an alternative pathway of macrophage activation and functional recovery after spinal cord injury. Journal of Neurotrauma. 2012;**29**(8):1614-1625

[80] Liu WL, Lee YH, Tsai SY, Hsu CY, Sun YY, Yang LY, et al. Methylprednisolone inhibits the expression of glial fibrillary acidic protein and chondroitin sulfate

Glia. 2008;**56**(13):1390-1400

2016;**59**(4):334-340

proteoglycans in reactivated astrocytes.

[81] Mbori NJ, Chuan XY, Feng QX, Alizada M, Zhan J. Evaluation of the combination of methylprednisolone and Tranilast after spinal cord injury in rat models. Journal of Korean Neurosurgical Association.

[82] Huang MQ, Cao XY, Chen XY, Liu YF, Zhu SL, Sun ZL, et al.

formation after sciatic nerve injury. Neural Regeneration Research.

[83] Brambilla R, Bracchi-Ricard V, Hu WH, Frydel B, Bramwell A,

nuclear factor kappaB reduces

Karmally S, et al. Inhibition of astroglial

inflammation and improves functional recovery after spinal cord injury. The Journal of Experimental Medicine.

[84] Li S, Gu X, Yi S. The regulatory effects of transforming growth factorbeta on nerve regeneration. Cell Transplantation. 2017;**26**(3):381-394

[85] Gaudet AD, Fonken LK. Glial cells shape pathology and repair after spinal cord injury. Neurotherapeutics.

[86] Nave KA. Myelination and support of axonal integrity by glia. Nature.

expression and inhibits scar

2018;**13**(9):1650-1656

2005;**202**(1):145-156

2018;**15**(3):554-577

2010;**468**(7321):244-252

Saikosaponin a increases interleukin-10

*Cytokines in Scar Glial Formation after an Acute and Chronic Spinal Cord Injury DOI: http://dx.doi.org/10.5772/intechopen.93005*

Takeura N, et al. Transplantation of mesenchymal stem cells promotes an alternative pathway of macrophage activation and functional recovery after spinal cord injury. Journal of Neurotrauma. 2012;**29**(8):1614-1625

*Cytokines*

1994;**6**(3):355-363

central nervous system of the rat. The European Journal of Neuroscience.

[73] Pendleton JC, Shamblott MJ, Gary DS, Belegu V, Hurtado A, Malone ML, et al. Chondroitin sulfate proteoglycans inhibit oligodendrocyte myelination through PTPsigma. Experimental Neurology.

[74] Trivedi A, Olivas AD, Noble-Haeusslein LJ. Inflammation and spinal cord injury: Infiltrating leukocytes as determinants of injury and repair processes. Clinical Neuroscience Research. 2006;**6**(5):283-292

[75] Rasouli A, Bhatia N, Dinh P, Cahill K, Suryadevara S, Gupta R. Resection of glial scar following spinal cord injury. Journal of Orthopaedic Research.

[76] Klapka N, Hermanns S, Straten G, Masanneck C, Duis S, Hamers FP, et al. Suppression of fibrous scarring in spinal

motoneurons in somatosensory cortex and significant functional recovery. The European Journal of Neuroscience.

[77] Schiwy N, Brazda N, Muller HW. Enhanced regenerative axon growth of multiple fibre populations in traumatic spinal cord injury following scar-suppressing treatment. The European Journal of Neuroscience.

cord injury of rat promotes longdistance regeneration of corticospinal

tract axons, rescue of primary

2005;**22**(12):3047-3058

2009;**30**(8):1544-1553

2017;**18**(1):7

[79] Nakajima H, Uchida K,

Guerrero AR, Watanabe S, Sugita D,

[78] Rodriguez-Barrera R, Flores-Romero A, Fernandez-Presas AM, Garcia-Vences E, Silva-Garcia R, Konigsberg M, et al. Immunization with neural derived peptides plus scar removal induces a permissive microenvironment, and improves locomotor recovery after chronic spinal cord injury. BMC Neuroscience.

2013;**247**:113-121

2009;**27**(7):931-936

[65] Su Z, Yuan Y, Chen J, Zhu Y, Qiu Y, Zhu F, et al. Reactive astrocytes inhibit the survival and differentiation of oligodendrocyte precursor cells by secreted TNF-alpha. Journal of Neurotrauma. 2011;**28**(6):1089-1100

[66] Gris P, Tighe A, Levin D,

[67] Regis G, Pensa S, Boselli D, Novelli F, Poli V. Ups and downs: The STAT1:STAT3 seesaw of interferon and gp130 receptor signalling. Seminars in Cell & Developmental Biology.

[68] Shechter R, London A, Varol C, Raposo C, Cusimano M, Yovel G, et al. Infiltrating blood-derived macrophages

[69] Sofroniew MV. Astrogliosis. Cold Spring Harbor Perspectives in Biology.

[71] Silver J, Miller JH. Regeneration beyond the glial scar. Nature Reviews. Neuroscience. 2004;**5**(2):146-156

[72] Sahni V, Mukhopadhyay A, Tysseling V, Hebert A, Birch D,

signaling exert opposing effects on gliosis after spinal cord injury. The Journal of Neuroscience.

2010;**30**(5):1839-1855

McGuire TL, et al. BMPR1a and BMPR1b

are vital cells playing an antiinflammatory role in recovery from spinal cord injury in mice. PLoS Medicine. 2009;**6**(7):e1000113

2008;**19**(4):351-359

2014;**7**(2):a020420

[70] Karimi-Abdolrezaee S, Billakanti R. Reactive astrogliosis after spinal cord injury—Beneficial and detrimental effects. Molecular Neurobiology. 2012;**46**(2):251-264

Sharma R, Brown A. Transcriptional regulation of scar gene expression in primary astrocytes. Glia. 2007;**55**(11):1145-1155

**92**

[80] Liu WL, Lee YH, Tsai SY, Hsu CY, Sun YY, Yang LY, et al. Methylprednisolone inhibits the expression of glial fibrillary acidic protein and chondroitin sulfate proteoglycans in reactivated astrocytes. Glia. 2008;**56**(13):1390-1400

[81] Mbori NJ, Chuan XY, Feng QX, Alizada M, Zhan J. Evaluation of the combination of methylprednisolone and Tranilast after spinal cord injury in rat models. Journal of Korean Neurosurgical Association. 2016;**59**(4):334-340

[82] Huang MQ, Cao XY, Chen XY, Liu YF, Zhu SL, Sun ZL, et al. Saikosaponin a increases interleukin-10 expression and inhibits scar formation after sciatic nerve injury. Neural Regeneration Research. 2018;**13**(9):1650-1656

[83] Brambilla R, Bracchi-Ricard V, Hu WH, Frydel B, Bramwell A, Karmally S, et al. Inhibition of astroglial nuclear factor kappaB reduces inflammation and improves functional recovery after spinal cord injury. The Journal of Experimental Medicine. 2005;**202**(1):145-156

[84] Li S, Gu X, Yi S. The regulatory effects of transforming growth factorbeta on nerve regeneration. Cell Transplantation. 2017;**26**(3):381-394

[85] Gaudet AD, Fonken LK. Glial cells shape pathology and repair after spinal cord injury. Neurotherapeutics. 2018;**15**(3):554-577

[86] Nave KA. Myelination and support of axonal integrity by glia. Nature. 2010;**468**(7321):244-252

[87] Assinck P, Duncan GJ, Hilton BJ, Plemel JR, Tetzlaff W. Cell transplantation therapy for spinal cord injury. Nature Neuroscience. 2017;**20**(5):637-647

[88] Oudega M, Xu XM. Schwann cell transplantation for repair of the adult spinal cord. Journal of Neurotrauma. 2006;**23**(3-4):453-467

[89] Kuo HS, Tsai MJ, Huang MC, Chiu CW, Tsai CY, Lee MJ, et al. Acid fibroblast growth factor and peripheral nerve grafts regulate Th2 cytokine expression, macrophage activation, polyamine synthesis, and neurotrophin expression in transected rat spinal cords. The Journal of Neuroscience. 2011;**31**(11):4137-4147

[90] Do-Thi A, Perrin FE, Desclaux M, Saillour P, Amar L, Privat A, et al. Combination of grafted Schwann cells and lentiviral-mediated prevention of glial scar formation improve recovery of spinal cord injured rats. Journal of Chemical Neuroanatomy. 2016;**76** (Pt A):48-60

[91] Lin L, Lin H, Bai S, Zheng L, Zhang X. Bone marrow mesenchymal stem cells (BMSCs) improved functional recovery of spinal cord injury partly by promoting axonal regeneration. Neurochemistry International. 2018;**115**:80-84

[92] Xiong LL, Liu F, Lu BT, Zhao WL, Dong XJ, Liu J, et al. Bone marrow mesenchymal stem-cell transplantation promotes functional improvement associated with CNTF-STAT3 activation after hemi-sectioned spinal cord injury in tree shrews. Frontiers in Cellular Neuroscience. 2017;**11**:172

[93] Okuda A, Horii-Hayashi N, Sasagawa T, Shimizu T, Shigematsu H, Iwata E, et al. Bone marrow stromal cell sheets may promote axonal regeneration and functional recovery with suppression of glial scar formation after spinal cord transection injury in rats. Journal of Neurosurgery. Spine. 2017;**26**(3):388-395

[94] Jeong SR, Kwon MJ, Lee HG, Joe EH, Lee JH, Kim SS, et al. Hepatocyte growth factor reduces astrocytic scar formation and promotes axonal growth beyond glial scars after spinal cord injury. Experimental Neurology. 2012;**233**(1):312-322

[95] Li Y, Decherchi P, Raisman G. Transplantation of olfactory ensheathing cells into spinal cord lesions restores breathing and climbing. The Journal of Neuroscience. 2003;**23**(3):727-731

[96] Gong S, Jin H, Zhang D, Zou W, Wang C, Li Z, et al. The therapeutic effects after transplantation of wholelayer olfactory mucosa in rats with optic nerve injury. BioMed Research International. 2018;**2018**:6069756

[97] Wright AA, Todorovic M, Tello-Velasquez J, Rayfield AJ, St. John JA, Ekberg JA. Enhancing the therapeutic potential of olfactory ensheathing cells in spinal cord repair using neurotrophins. Cell Transplantation. 2018;**27**(6):867-878

[98] Yao R, Murtaza M, Velasquez JT, Todorovic M, Rayfield A, Ekberg J, et al. Olfactory ensheathing cells for spinal cord injury: Sniffing out the issues. Cell Transplantation. 2018;**27**(6):879-889

[99] Khankan RR, Griffis KG, Haggerty-Skeans JR, Zhong H, Roy RR, Edgerton VR, et al. Olfactory ensheathing cell transplantation after a complete spinal cord transection mediates neuroprotective and Immunomodulatory mechanisms to facilitate regeneration. The Journal of Neuroscience. 2016;**36**(23):6269-6286

[100] Lopez-Vales R, Garcia-Alias G, Fores J, Vela JM, Navarro X, Verdu E. Transplanted olfactory ensheathing cells modulate the inflammatory response

in the injured spinal cord. Neuron Glia Biology. 2004;**1**(3):201-209

[101] Tsintou M, Dalamagkas K, Seifalian AM. Advances in regenerative therapies for spinal cord injury: A biomaterials approach. Neural Regeneration Research. 2015;**10**(5):726-742

[102] Deng LX, Hu J, Liu N, Wang X, Smith GM, Wen X, et al. GDNF modifies reactive astrogliosis allowing robust axonal regeneration through Schwann cell-seeded guidance channels after spinal cord injury. Experimental Neurology. 2011;**229**(2):238-250

[103] Ikeda H, Wu GY, Wu CH. Evidence that an iron chelator regulates collagen synthesis by decreasing the stability of procollagen mRNA. Hepatology. 1992;**15**(2):282-287

[104] Kawano H, Li HP, Sango K, Kawamura K, Raisman G. Inhibition of collagen synthesis overrides the age-related failure of regeneration of nigrostriatal dopaminergic axons. Journal of Neuroscience Research. 2005;**80**(2):191-202

[105] Davies JE, Tang X, Denning JW, Archibald SJ, Davies SJ. Decorin suppresses neurocan, brevican, phosphacan and NG2 expression and promotes axon growth across adult rat spinal cord injuries. The European Journal of Neuroscience. 2004;**19**(5):1226-1242

[106] Niclou SP, Ehlert EM, Verhaagen J. Chemorepellent axon guidance molecules in spinal cord injury. Journal of Neurotrauma. 2006;**23**(3-4):409-421

[107] Lu P, Jones LL, Tuszynski MH. Axon regeneration through scars and into sites of chronic spinal cord injury. Experimental Neurology. 2007;**203**(1):8-21

**95**

**Chapter 7**

**Abstract**

biomarkers.

**1. Introduction**

Polymorphisms

The Genetic Aspects of Behçet's

Disease: Role of Cytokine Genes

Behçet's disease (BD) is a complex, multisystemic inflammatory disorder characterized by recurrent oral aphthous ulcers, ocular symptoms, skin lesions, and genital ulcerations. The etiology of BD is not yet clear though various factors including environmental, genetic and immunological ones have been implicated. Genetic predisposition is a major factor in disease susceptibility and multiple host genetic factors have been suggested to be involved in the development of BD. In addition to the positive association of HLAB\*51, recent studies report additional independent associations in the non HLA loci. Single nucleotide polymorphisms (SNPs) in various genes including cytokines have been implicated in susceptibility to BD. However, the results are inconsistent and variation are found in several ethnic populations. Therefore, further genetic studies on BD patients of different ethnicity and genes associated with immunity are expected to elucidate BD pathogenesis and will contribute to the development of more targeted therapies and

**Keywords:** Behçet's disease, genetics, cytokines, TNF, interleukin, polymorphism

Behçet's disease (BD; MIM 109650) is a multisystemic inflammatory disorder characterized by recurrent oral aphthous ulcers, ocular symptoms, skin lesions, and genital ulcerations. BD has many features in common with systemic vasculitis. The prevalence of BD varies, it is more prevalent in the Far East, the Mediterranean and the Middle Eastern countries along the ancient Silk Road [1–3]. The highest prevalence has been reported in Turkey (80–420 cases per 100,000) followed by Israel (146.4), China (110), Iran (80), Korea (30.2), Japan (22), Saudi Arabia (20), Iraq

Clinical and immunological understandings of the disease suggest that BD is a cornerstone between autoimmune and inflammatory disease [5]. Due to effectiveness of immunosuppressives [6] and involvement of human heat-shock protein 60 (HSP60) [7], it is considered as an autoimmune disease. While on the basis of lack of antigen-specific T-cells or significant high-titer auto-antibodies, insignificant involvement of histocompatibility complex (MHC) class I molecules together with unprovoked recurrent inflammation episodes mainly caused by neutrophils [8], the association of the M694V MEFV mutation with its susceptibility and the therapeutic effectiveness of colchicine, BD is classified as an auto-inflammatory disease [4].

(17), Morocco (15), and Egypt (7.5) cases per 100,000 [1, 3, 4].

*Abdulrahman Al Asmari and Misbahul Arfin*

## **Chapter 7**

*Cytokines*

2017;**26**(3):388-395

2012;**233**(1):312-322

2003;**23**(3):727-731

2018;**27**(6):867-878

after spinal cord transection injury in rats. Journal of Neurosurgery. Spine.

in the injured spinal cord. Neuron Glia

Seifalian AM. Advances in regenerative

[103] Ikeda H, Wu GY, Wu CH. Evidence that an iron chelator regulates collagen synthesis by decreasing the stability of procollagen mRNA. Hepatology.

[104] Kawano H, Li HP, Sango K, Kawamura K, Raisman G. Inhibition of collagen synthesis overrides the age-related failure of regeneration of nigrostriatal dopaminergic axons. Journal of Neuroscience Research.

Biology. 2004;**1**(3):201-209

2015;**10**(5):726-742

2011;**229**(2):238-250

1992;**15**(2):282-287

2005;**80**(2):191-202

[105] Davies JE, Tang X,

2004;**19**(5):1226-1242

2006;**23**(3-4):409-421

2007;**203**(1):8-21

[106] Niclou SP, Ehlert EM,

Verhaagen J. Chemorepellent axon guidance molecules in spinal cord injury. Journal of Neurotrauma.

[107] Lu P, Jones LL, Tuszynski MH. Axon regeneration through scars and into sites of chronic spinal cord injury. Experimental Neurology.

Denning JW, Archibald SJ, Davies SJ. Decorin suppresses neurocan, brevican, phosphacan and NG2 expression and promotes axon growth across adult rat spinal cord injuries. The European Journal of Neuroscience.

[101] Tsintou M, Dalamagkas K,

therapies for spinal cord injury: A biomaterials approach. Neural Regeneration Research.

[102] Deng LX, Hu J, Liu N, Wang X, Smith GM, Wen X, et al. GDNF modifies reactive astrogliosis allowing robust axonal regeneration through Schwann cell-seeded guidance channels after spinal cord injury. Experimental Neurology.

[94] Jeong SR, Kwon MJ, Lee HG, Joe EH, Lee JH, Kim SS, et al. Hepatocyte growth factor reduces astrocytic scar formation and promotes axonal growth beyond glial scars after spinal cord injury. Experimental Neurology.

[95] Li Y, Decherchi P, Raisman G. Transplantation of olfactory ensheathing cells into spinal cord lesions restores breathing and

climbing. The Journal of Neuroscience.

[96] Gong S, Jin H, Zhang D, Zou W, Wang C, Li Z, et al. The therapeutic effects after transplantation of wholelayer olfactory mucosa in rats with optic nerve injury. BioMed Research International. 2018;**2018**:6069756

[97] Wright AA, Todorovic M,

Tello-Velasquez J, Rayfield AJ, St. John JA, Ekberg JA. Enhancing the therapeutic potential of olfactory ensheathing cells in spinal cord repair using neurotrophins. Cell Transplantation.

[98] Yao R, Murtaza M, Velasquez JT, Todorovic M, Rayfield A, Ekberg J, et al. Olfactory ensheathing cells for spinal cord injury: Sniffing out the issues. Cell Transplantation. 2018;**27**(6):879-889

Haggerty-Skeans JR, Zhong H, Roy RR,

ensheathing cell transplantation after a complete spinal cord transection mediates neuroprotective and Immunomodulatory mechanisms to facilitate regeneration. The Journal of Neuroscience. 2016;**36**(23):6269-6286

[100] Lopez-Vales R, Garcia-Alias G, Fores J, Vela JM, Navarro X, Verdu E. Transplanted olfactory ensheathing cells modulate the inflammatory response

[99] Khankan RR, Griffis KG,

Edgerton VR, et al. Olfactory

**94**
