**4. Mesenchymal stem cell extracellular microvesicles (ExMV)**

Organ regeneration technologies attempt to restore the anatomical structure and original functionality of a damaged organ. Usually, the response is fibrosis and scar tissue formation and no regeneration. The strategies of IT and MR for the repair of organs/tissues allow restoration of normal functioning. The development of new products, derived from MSCs considered as active biological elements, has already started.

Preclinical and clinical studies with MSCs propose inducing endogenous repair, and this represents a new paradigm for the treatment of multiple diseases. The factors are produced from activated cells extracted from their physiological niches, aspirated BM or mobilized blood, such as peripheral blood mononuclear cells (PBMC), and these release biologically active paracrine factors that induce regeneration. The apoptotic secreted from PBMCs has been used successfully for the treatment of MI, chronic heart failure, spinal cord injury, stroke, and

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The EVs derived from the MSCs, exosomes, are powerful intercellular communication vehicles; composed of a lipid bilayer that contains transmembrane proteins, cytosolic proteins, and RNA; participate in diverse physiological and pathological functions of both receptor and parental cells; and transfer the information to other cells and influence the function of the recipient cell. The EVs transmit biomolecules (proteins, lipids, nucleic acids, and sugars) as a single information packet or deliver multiple messengers simultaneously to sites distant from the source EVs [37]. The EVs are between 100 and 1000 nm in diameter, and they are microvesicles, ectosomes, or microparticles, which sprout from the cellular plasma membrane. Other types of vesicles are exosomes, which are generated within multivesicular endosomes or multivesicular bodies (MVBs), secreted by fusing with the plasma membrane.) Exosomes are vesicles that are enriched with components derived from endosomes. They are targeted to the recipient cells and, once bound to a target cell, the EVs induce signaling through the receptor-ligand interaction or are internalized by endocytosis and/or phagocytosis, even fusing with the membrane of the target cell to release its cytosol content, which modifies the cellular receptor [38].

Exosomes of endocytic origin transmit different intercellular signals by surface interactions and by the displacement of functional RNA from one cell to another and are released by mast cells, dendritic cells, macrophages, epithelial cells, and tumor cells. Exosomes, released from mast cells exposed to oxidative stress, have the ability to communicate a protective signal to receptor cells exposed to oxidative stress to reduce cell death. Exosomes can influence the response of other cells to oxidative stress by providing resistance to oxidative stress to recipient cells and decreasing the loss of cell viability. The exosomal transfer of RNA is involved in cell-to-cell communication and influences the response of the recipient cells to an external stress stimulus. The mRNA content of the exosomes produced under oxidative stress differs both from the mRNA in the donor cell and in the exosomes produced by cells grown under normal conditions. [39]. Exosomes produced by cells exposed to oxidative stress have the ability to induce tolerance in other cells. This effect is associated with the change in the content of exosomal mRNA that is attenuated by the reduced activity of the RNA by exposure to ultraviolet light. This shows, for the first time, that exosomal RNA transfer can change the biological function of a recipient cell [40]. The encapsulation of biologically active ingredients of regeneration in carriers of nonliving exosomes offers advantages in the processing, manu-

Exosomes and ExMVs derived from MSCs influence tissue responses to lesions, infections, and diseases, and the exosomes of MSCs are not static, since they are the product of origin of MSCs, and they have actions with intercellular immediate neighbors. The MSCs, through paracrine action, activate the endogenous repair pathways, and the horizontal transfer of this load induces therapeutic changes; meanwhile, it has been demonstrated that microvesicles/ exosomes derived from MSCs repeat the therapeutic effects of the parental MSCs [42].

facturing, and regulation of MSC-based therapies [41].

wound healing [36].

The mechanisms of action of therapies with MSC have focused on paracrine actions, for the ability to generate regeneration without the application of cells. The primordial component, which creates a regenerative medium, is exosomes: intraluminal vesicles of 40–100 nm that transfer proteins and nucleic acids between cells and establish intracellular communication. The exosomes participate in organogenesis and regeneration and repeat the bioactivity of the SCs [29].

The extracellular space of multicellular organisms contains metabolites, ions, proteins, and polysaccharides. In the extracellular environment, a large number of mobile vesicles participate, and the term "extracellular vesicles or EVs" is suggested, which includes exosomes, microvesicles, microparticles (MV) and apoptotic bodies. The EVs comprise a heterogeneous population of lipid vesicles derived from cells containing exosomes and microvesicles. They are the mediators of the intercellular information transfer and can be vehicles for the administration of drugs of autologous cellular products. The therapeutic effects of cell therapies are mainly attributed to the EVs secreted by cells and directly involved in tissue regeneration processes [30].

Currently, interest focuses on EVs (exosomes and MV). Vesicles similar to exosomes have a common origin; however, they lack lipid-based microdomains; their size and sedimentation properties distinguish them from exosomes; and the term refers to an extracellular vesicle with a diameter of 40–150 nm and a density of 1.09–1.18 g/ml, proteins, nucleic acids, and membrane vesicles that generate a regenerative environment [31, 32].

Eukaryotic cells communicate with each other through direct interaction (juxtacrine contact dependent signaling) or by the secretion of factors such as hormones, GF, and cytokines, when they act in the cell itself (autocrine signaling) or act in neighboring cells (paracrine signaling) and distant cells (endocrine signaling). Tissue regeneration is related to the release of paracrine and autocrine substances and not only by cellular replication and differentiation. Eighty percent of the therapeutic effect of adult SCs is through paracrine actions. The molecules released by the SCs, the secretome, contain molecules (100), proteins, microRNA, GF, proteasomes, and exosomes, which generate paracrine activities. The composition of the different types of molecules depends on the stage and varies according to cell type, age, and environment. The secretory activity of cell-derived byproducts acts at a distance and is the main regenerative mechanism [33, 34].

In multicellular organisms, cells exchange information with signals from molecules in packages included in the EVs, which contain proteins, lipids, and nucleic acids. When released in the extracellular environment, exosomes interact with receptor cells by adhesion to the cell surface, by lipid-ligand receptor interactions, by endocytic uptake, or by direct fusion of the vesicles to the cell membrane [35].

Preclinical and clinical studies with MSCs propose inducing endogenous repair, and this represents a new paradigm for the treatment of multiple diseases. The factors are produced from activated cells extracted from their physiological niches, aspirated BM or mobilized blood, such as peripheral blood mononuclear cells (PBMC), and these release biologically active paracrine factors that induce regeneration. The apoptotic secreted from PBMCs has been used successfully for the treatment of MI, chronic heart failure, spinal cord injury, stroke, and wound healing [36].

**4. Mesenchymal stem cell extracellular microvesicles (ExMV)**

considered as active biological elements, has already started.

192 Stromal Cells - Structure, Function, and Therapeutic Implications

SCs [29].

processes [30].

Organ regeneration technologies attempt to restore the anatomical structure and original functionality of a damaged organ. Usually, the response is fibrosis and scar tissue formation and no regeneration. The strategies of IT and MR for the repair of organs/tissues allow restoration of normal functioning. The development of new products, derived from MSCs

The mechanisms of action of therapies with MSC have focused on paracrine actions, for the ability to generate regeneration without the application of cells. The primordial component, which creates a regenerative medium, is exosomes: intraluminal vesicles of 40–100 nm that transfer proteins and nucleic acids between cells and establish intracellular communication. The exosomes participate in organogenesis and regeneration and repeat the bioactivity of the

The extracellular space of multicellular organisms contains metabolites, ions, proteins, and polysaccharides. In the extracellular environment, a large number of mobile vesicles participate, and the term "extracellular vesicles or EVs" is suggested, which includes exosomes, microvesicles, microparticles (MV) and apoptotic bodies. The EVs comprise a heterogeneous population of lipid vesicles derived from cells containing exosomes and microvesicles. They are the mediators of the intercellular information transfer and can be vehicles for the administration of drugs of autologous cellular products. The therapeutic effects of cell therapies are mainly attributed to the EVs secreted by cells and directly involved in tissue regeneration

Currently, interest focuses on EVs (exosomes and MV). Vesicles similar to exosomes have a common origin; however, they lack lipid-based microdomains; their size and sedimentation properties distinguish them from exosomes; and the term refers to an extracellular vesicle with a diameter of 40–150 nm and a density of 1.09–1.18 g/ml, proteins, nucleic acids, and

Eukaryotic cells communicate with each other through direct interaction (juxtacrine contact dependent signaling) or by the secretion of factors such as hormones, GF, and cytokines, when they act in the cell itself (autocrine signaling) or act in neighboring cells (paracrine signaling) and distant cells (endocrine signaling). Tissue regeneration is related to the release of paracrine and autocrine substances and not only by cellular replication and differentiation. Eighty percent of the therapeutic effect of adult SCs is through paracrine actions. The molecules released by the SCs, the secretome, contain molecules (100), proteins, microRNA, GF, proteasomes, and exosomes, which generate paracrine activities. The composition of the different types of molecules depends on the stage and varies according to cell type, age, and environment. The secretory activity of cell-derived byproducts acts at a distance and is the

In multicellular organisms, cells exchange information with signals from molecules in packages included in the EVs, which contain proteins, lipids, and nucleic acids. When released in the extracellular environment, exosomes interact with receptor cells by adhesion to the cell surface, by lipid-ligand receptor interactions, by endocytic uptake, or by direct fusion of the

membrane vesicles that generate a regenerative environment [31, 32].

main regenerative mechanism [33, 34].

vesicles to the cell membrane [35].

The EVs derived from the MSCs, exosomes, are powerful intercellular communication vehicles; composed of a lipid bilayer that contains transmembrane proteins, cytosolic proteins, and RNA; participate in diverse physiological and pathological functions of both receptor and parental cells; and transfer the information to other cells and influence the function of the recipient cell. The EVs transmit biomolecules (proteins, lipids, nucleic acids, and sugars) as a single information packet or deliver multiple messengers simultaneously to sites distant from the source EVs [37].

The EVs are between 100 and 1000 nm in diameter, and they are microvesicles, ectosomes, or microparticles, which sprout from the cellular plasma membrane. Other types of vesicles are exosomes, which are generated within multivesicular endosomes or multivesicular bodies (MVBs), secreted by fusing with the plasma membrane.) Exosomes are vesicles that are enriched with components derived from endosomes. They are targeted to the recipient cells and, once bound to a target cell, the EVs induce signaling through the receptor-ligand interaction or are internalized by endocytosis and/or phagocytosis, even fusing with the membrane of the target cell to release its cytosol content, which modifies the cellular receptor [38].

Exosomes of endocytic origin transmit different intercellular signals by surface interactions and by the displacement of functional RNA from one cell to another and are released by mast cells, dendritic cells, macrophages, epithelial cells, and tumor cells. Exosomes, released from mast cells exposed to oxidative stress, have the ability to communicate a protective signal to receptor cells exposed to oxidative stress to reduce cell death. Exosomes can influence the response of other cells to oxidative stress by providing resistance to oxidative stress to recipient cells and decreasing the loss of cell viability. The exosomal transfer of RNA is involved in cell-to-cell communication and influences the response of the recipient cells to an external stress stimulus. The mRNA content of the exosomes produced under oxidative stress differs both from the mRNA in the donor cell and in the exosomes produced by cells grown under normal conditions. [39]. Exosomes produced by cells exposed to oxidative stress have the ability to induce tolerance in other cells. This effect is associated with the change in the content of exosomal mRNA that is attenuated by the reduced activity of the RNA by exposure to ultraviolet light. This shows, for the first time, that exosomal RNA transfer can change the biological function of a recipient cell [40]. The encapsulation of biologically active ingredients of regeneration in carriers of nonliving exosomes offers advantages in the processing, manufacturing, and regulation of MSC-based therapies [41].

Exosomes and ExMVs derived from MSCs influence tissue responses to lesions, infections, and diseases, and the exosomes of MSCs are not static, since they are the product of origin of MSCs, and they have actions with intercellular immediate neighbors. The MSCs, through paracrine action, activate the endogenous repair pathways, and the horizontal transfer of this load induces therapeutic changes; meanwhile, it has been demonstrated that microvesicles/ exosomes derived from MSCs repeat the therapeutic effects of the parental MSCs [42].

A new generation of drug delivery systems can be mediated by exosomes and ExMVs; because they have high administration efficiency and low immunogenicity, new therapies can be implemented, and standardization is achieved with isolation techniques, with high functional efficiency, solid performance, scalable production, adequate storage, and efficient loading methods, which do not damage its molecular integrity and the movement of the elements *in vivo* as novel "nano-vehicles" [43]. The elements derived from cells generate an endogenous mechanism for intercellular communication; they are vehicles with the capacity to transfer biological information and the potential use can be as means of drug delivery [44].

exosomes, and when fused with the plasma membrane, appear in the blood and urine, so they are easily accessible, and can be used as biomarkers, for the diagnosis and prognosis of

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Due to their cellular origin, exosomes express protein markers specific to the endosomal pathway, such as tetraspanins (CD63, CD9 and CD81), heat shock proteins (Hsp70), proteins of the Rab family, Tsg101 and Alix, which are not found in other vesicles of similar size. Their function is to eliminate damaged or aged cellular molecules, to protect cells from the accumulation of waste or drugs, participate in physiological and pathological processes, and have a wide variety of clinical applications, ranging from biomarkers to cancer therapy [49]. Proteomic and biochemical analysis of the purified exosomes revealed that the bilayer membrane of phospholipids is embedded with various proteins and lipids originating in the parental cells. These can serve as surface markers for the characterization and differentiation of exosomes from other types of microvesicles [50]. Exosomes contain various proteins, which express specific cellular functions, so they can serve as biomarkers for the diagnosis of liver, kidney, and cancer diseases [51]. Proteins in urinary exosomes are easily available through nontoxic means, are invasive, and are useful in diagnosis, especially for diseases of the urinary tract [52].

Exosomes contain exosomal RNAs, especially miRNAs that function as diagnostic biomarkers, are protected from RNase-dependent degradation, are detected in circulating plasma, and serve for the diagnosis of ovarian cancer [53, 54]. Nanostructure analysis and study of the transcriptome of exosomes that transport RNA are diagnostic and found in breast milk, saliva, blood, urine, malignant ascites, amniotic fluid, bronchoalveolar secretion, and synovial fluid [55, 56]. Urinary extracellular vesicles (uEV) are released in the nephron of the kidney and urinary tract. Specific proteomic and transcriptomic markers provide information on the cell of origin and are a reservoir for the discovery of biomarkers in kidney diseases. The uEV are a new means of cell signaling, renal tubular cells, and can provide exosomal markers not detectable in urine. Renal biopsy is an invasive technique with complications such as infection and hemorrhage. The analysis of proteomic and transcriptomic changes of uEV in different disease

In conclusion, the most important biomedical utility of exosomes is their application as biomarkers in clinical diagnosis. Compared with those detected in conventional samples, such as serum or urine, exosomal biomarkers provide comparable or superior sensitivity and specificity, attributed to their excellent stability, and the exosomal biomarkers of biofluids can be easily obtained. Recent technical advances in the isolation of exosomes will make diagnostics more beneficial.

**6. Stem cell therapeutics; exosomes as biomarkers in cardiovascular** 

The intercellular communication between cardiac, vascular, SCs, and progenitor cells with differentiated cardiovascular cells is a complex process, with a diversity of mechanisms in

malignant tumors and other pathologies [47, 48].

**5.2. Exosomal nucleic acids as diagnostic biomarkers**

states as a biomarker can be a noninvasive alternative to biopsy [57].

**diseases**
