**3. Function of extracellular vesicles in physiology**

### **3.1 Physiological role of extracellular vesicles**

EVs are connected to different physiological and pathological processes, such as tumor growth modulation, cytokine production, or cardiovascular disorders [22–24].

EVs contain lipids, and pools of proteins, some specific for the cell type generating them—MHC class I and II, and some which are present in most EVs—proteins from the plasma membrane, cytosol, and endosome. This latest feature suggests the shared biogenesis pathway for these EVs. On the surface of EVs, proteins similar with the ones from the originating cells can be found [25–28]. Different types of nucleic acids such as DNA, small RNA, ribosomal RNA (rRNA), microRNA (miRNA), long noncoding RNA (lncRNA), and mRNA are enclosed within the EVs, which transfer their content into recipient cells, inducing transient or persistent phenotypic changes, which will modify their cellular functions.

According to Barros et al. [25], there are at least four mechanisms by which the EVs can influence the target cells: (1) direct contact between the proteins from the target cell and EV membrane, which changes the intracellular signaling of the recipient cells; (2) cleavage of proteins on the EVs' surface and further interaction between the protein fragments and receptor-proteins on the recipient cell; (3) fusion between EVs and target cell membrane, followed by EV content release within the recipient cell; and (4) internalization of EVs by phagocytosis or endocytosis.

#### **3.2 Role of extracellular vesicles in immunological response**

The immune response involves participation of innate and adaptive immune system to regulation of body homeostasis, defense, and surveillance, thus maintaining the equilibrium between health and disease.

### *3.2.1 Activation of the helper T cells (CD4+)*

Molecules of MHC class II complex are specific to antigen-presenting cells (APCs), such as dendritic cells (DC), macrophages, and B lymphocytes, which present internalized exogenous peptides for the activation of CD4+ T cells. B cells release functional EVs with increased amounts of MHC class II molecules coupled with peptides, which are able to generate T helper cell response. T cells are strong stimulators of the EVs' synthesis by B cells due to activation of CD40, and IL-4 receptors [29–31], and the B cell-derived EVs also contain molecules of MHC class I, components of B cell receptor (BCR)—CD19, immunoglobulins, and tetraspanins [30, 31]. Content of EVs derived from DC, with MHC class II—peptide complexes, contributes to amplification of adaptive immune response [32–34].

#### *3.2.2 Activation of the cytotoxic T cells (CD8+)*

Because all nucleated cells express MHC class I molecules, the nucleated cellsderived EVs contain the MHC class I—endogenous/exogenous antigens complexes, thus giving the potential to activate the cytotoxic T cells [35]. These findings were confirmed for the first time by Admyre et al., who demonstrated that monocytederived DC released exosomes capable of inducing antigen-specific immune response from peripheral blood-isolated CD8+ T cells [36].

**115**

*Part One: Extracellular Vesicles as Valuable Players in Diabetic Cardiovascular Diseases*

The production and release of EVs presenting on the surface factors which are capable of triggering apoptotic pathways, such as Fas ligand or galectin 9, can induce immunosuppression. On the other hand, platelet-secreted EVs can induce secretion of pro-inflammatory cytokines, such as IL-8, IL-1β, and IL-6, thus trig-

**4. Extracellular vesicles as biological vectors modulating diabetic** 

Individuals with type 2 diabetes mellitus develop cardiovascular disorders, including coronary artery disease, more frequently than healthy controls, mainly through the chronic, damaging exposure of the vascular system to hyperglycemia. Therefore, it is important to understand the exact mechanisms through which diabetes contributes to the development and severity of these complications. EVs generated in patients with diabetes mellitus promote inflammation and contribute to the development of atherosclerotic lesions, stimulating monocyte adhesion and their infiltration in the subendothelial layer, promoting the migration and proliferation of vascular smooth muscle cells (VSMCs) and also the calcifica-

Recent studies have shown that atherosclerotic lesions of all stages contain MVs. Higher levels of circulating MVs have been discovered in individuals with cardiovascular risk factors, such as smoking [38], dyslipidemia [39], diabetes mellitus [40], and arterial hypertension [41], probably through activation or from apoptosis of different cells being exposed to a damaging stimulus. Data extracted from in vitro studies suggest that MVs can have both pro-inflammatory and antiinflammatory effects, depending on the stimulus that induces their formation [42]. MVs increase the release of proinflammatory cytokines, mainly interleukin-6 and -8 (IL-6 and IL-8), from ECs and leukocytes, promoting the adhesion of monocytes to the endothelium and their migration to the atherosclerotic plaque [42, 43]. Also, endothelial MVs can activate monocytes by transferring miR-10a and thus interfering with the nuclear factor-κB inflammatory pathway. Another effect of MVs is the decrease of the nitric oxide (NO) production by ECs, consequently impairing endothelial vasodilating properties [44]. Endothelial-derived MVs and platelet-derived MVs increase endothelial permeability by delivering two enzymes (caspase 3 and Rho-kinase) to target cells and inducing apoptosis [45]. MVs promote adhesion of monocytes to the endothelium by increasing endothelial expression of adhesion molecules, such as intercellular adhesion molecule-1 (ICAM-1), or adhesion molecule receptors, such as CD11a, on monocytes [46]. ICAM1 expression can also

Various MVs contribute to foam cell formation in the atherosclerotic plaque by stimulating lipid and cholesterol formation in macrophages. Macrophages and foam cells undergo afterward apoptosis, forming a core of extracellular lipids. Increased monocyte and macrophage apoptosis contributes to augmented MV release in the plaque. MVs of monocyte and macrophage origin are the largest population of MVs

**4.1 Role of extracellular vesicles in coronary artery disease**

*4.1.1 Extracellular vesicles and the coronary atherosclerotic plaque*

*DOI: http://dx.doi.org/10.5772/intechopen.85225*

*3.2.3 Immunomodulation induced by EVs*

**cardiovascular diseases**

tion of the atherosclerotic plaque.

be regulated by miR-222 in MVs [42, 47].

in human atherosclerotic lesions [48].

gering an inflammatory immune response [37].

*Part One: Extracellular Vesicles as Valuable Players in Diabetic Cardiovascular Diseases DOI: http://dx.doi.org/10.5772/intechopen.85225*

#### *3.2.3 Immunomodulation induced by EVs*

*Extracellular Vesicles and Their Importance in Human Health*

**3.1 Physiological role of extracellular vesicles**

[22–24].

functions.

endocytosis.

**3. Function of extracellular vesicles in physiology**

EVs are connected to different physiological and pathological processes, such as tumor growth modulation, cytokine production, or cardiovascular disorders

EVs contain lipids, and pools of proteins, some specific for the cell type generating them—MHC class I and II, and some which are present in most EVs—proteins from the plasma membrane, cytosol, and endosome. This latest feature suggests the shared biogenesis pathway for these EVs. On the surface of EVs, proteins similar with the ones from the originating cells can be found [25–28]. Different types of nucleic acids such as DNA, small RNA, ribosomal RNA (rRNA), microRNA (miRNA), long noncoding RNA (lncRNA), and mRNA are enclosed within the EVs, which transfer their content into recipient cells, inducing transient or persistent phenotypic changes, which will modify their cellular

According to Barros et al. [25], there are at least four mechanisms by which the EVs can influence the target cells: (1) direct contact between the proteins from the target cell and EV membrane, which changes the intracellular signaling of the recipient cells; (2) cleavage of proteins on the EVs' surface and further interaction between the protein fragments and receptor-proteins on the recipient cell; (3) fusion between EVs and target cell membrane, followed by EV content release within the recipient cell; and (4) internalization of EVs by phagocytosis or

The immune response involves participation of innate and adaptive immune system to regulation of body homeostasis, defense, and surveillance, thus maintain-

Molecules of MHC class II complex are specific to antigen-presenting cells (APCs), such as dendritic cells (DC), macrophages, and B lymphocytes, which present internalized exogenous peptides for the activation of CD4+ T cells. B cells release functional EVs with increased amounts of MHC class II molecules coupled with peptides, which are able to generate T helper cell response. T cells are strong stimulators of the EVs' synthesis by B cells due to activation of CD40, and IL-4 receptors [29–31], and the B cell-derived EVs also contain molecules of MHC class I, components of B cell receptor (BCR)—CD19, immunoglobulins, and tetraspanins [30, 31]. Content of EVs derived from DC, with MHC class II—peptide complexes,

Because all nucleated cells express MHC class I molecules, the nucleated cellsderived EVs contain the MHC class I—endogenous/exogenous antigens complexes, thus giving the potential to activate the cytotoxic T cells [35]. These findings were confirmed for the first time by Admyre et al., who demonstrated that monocytederived DC released exosomes capable of inducing antigen-specific immune

**3.2 Role of extracellular vesicles in immunological response**

contributes to amplification of adaptive immune response [32–34].

response from peripheral blood-isolated CD8+ T cells [36].

ing the equilibrium between health and disease.

*3.2.1 Activation of the helper T cells (CD4+)*

*3.2.2 Activation of the cytotoxic T cells (CD8+)*

**114**

The production and release of EVs presenting on the surface factors which are capable of triggering apoptotic pathways, such as Fas ligand or galectin 9, can induce immunosuppression. On the other hand, platelet-secreted EVs can induce secretion of pro-inflammatory cytokines, such as IL-8, IL-1β, and IL-6, thus triggering an inflammatory immune response [37].
