**3. Intercellular communication through EVs**

EVs can carry a big amount of information within/on their surface to another cell, influencing physiological and pathological pathways [6]. For a better understanding,

in this chapter, some of these processes will be exemplified to illustrate the roles of EVs in intercellular communication.

#### **3.1 Implantation and embryonic development**

The implantation process refers to the development of the trophoblasts by the embryo, which then will adhere and invade the uterine wall. This is a crucial step in embryonic development, and any inaccuracy can have severe consequences [2]. EVs are secreted by both maternal and embryonic cells. In the first case, studies have shown that endometrial epithelial cells produce EVs that stimulate the activation of focal adhesion kinase (FAK), increasing the adhesion of trophoblasts to the uterine wall [52]. Regarding embryonic production of EVs, recent studies have shown the involvement of MVs. Laminin and fibronectin, two extracellular matrix proteins, found on the surface of MVs, are playing an important role in this case. MVs are transported to trophoblasts, where laminin and fibronectin activate integrins on the surface of the trophoblast, stimulating the activation of c-Jun N-terminal kinase (JNK) and FAK and thus promoting migration of trophoblastic cells and rates of implantation [53]. Embryonic development is influenced by communication between the cells of embryos, through the secretion of factors that are still not well known. Some studies have suggested that EVs could be involved in these processes. For example, a study conducted by P. Qu *et al*. on bovine cells has shown that embryos without replaced culture medium contain CD9 positive exosomes and have a better chance of a healthy pregnancy [54]. Another study conducted by I.M. Saadeldin *et al*. concluded that EVs are influencing the communication between embryos. They combined cloned embryos with embryos from an unfertilized egg cell and showed that the latter are secreting CD 9 positive exosomes and EVs containing RNA transcripts that encoded some pluripotency genes, improving the features of the cloned embryos if co-cultured [55].

The roles of the EVs in implantation and embryonic development are illustrated in **Figure 3**.

#### **3.2 Cancer development**

EVs are produced by stromal cells, which can be found, along with cancerous cells, as components of a tumor mass. In this case, EVs act like a bidirectional transferring mechanism between stromal cells and cancerous cells, influencing tumor evolution [6]. The biogenesis, release pathways, and the contents of EVs will be modified by the tumor microenvironment. Circulating DNA, contained by EVs will be transferred between apoptotic bodies (derived from apoptotic tumor cells) and other cells, leading to increased expression of oncogenes [56]. Tumor-derived EVs play a crucial role in all steps of cancer development, being more and more studied, to discover new treatment methods [57].

For a better understanding of the role of EVs in tumoral processes (cell proliferation, apoptosis resistance, angiogenesis, local invasion and metastasis, therapy resistance, etc.) we will discuss this with respect to some cancer types.

Some studies have shown that exosomes produced and released by ovarian cancer cells can carry RNAs and miRNAs, influencing cell transformation and tumor evolution. RNA-binding protein LIN 28, a marker of SCs, is associated with an unfavorable outcome when present in malignancies. Ovarian cancer cells which express high LIN 28 levels can secrete exosomes, which can further interact with noncancerous cells, leading to variations of gene expressions and cell behavior. This can lead

#### **Figure 3.**

*The roles of the EVs in embryo communication. (A) The uterine epithelium secretes EVs that stimulate the adhesion of trophoblastic cells to the uterus; (B) embryonic stem cells (ESCs) produce EVs that stimulate the trophoblasts to migrate and implant into the uterus; (C) the co-culturing of embryos increases (*↑*) embryo development (D), mediated by EVs. Created with BioRender.com (last accessed on September 22, 2021).*

to consequential amplification of genes responsible for epithelial to mesenchymal transition, human embryonic kidney 293 cells (HEK 293) invasion, and migration [58]. SKOV3, an ovarian cancer cell line, is also involved in cancer development by producing and releasing exosomes that can stimulate the M2 macrophage phenotype and consequently migration and proliferation of cancerous cells [6].

In breast cancer, studies have shown that EVs contain two extracellular matrix proteins, discoidin I-like domains 3 and epidermal growth factor-like repeats, that can activate FAK cascade and, along with an independent mechanism of microRNA biogenesis possessed by EVs, they play a crucial role in cancer development [59, 60].

In glioblastoma, EVs are transferring between cells the protein chloride intracellular channel-1, which stimulates the growth of the recipient cells, and the splicing factor RNA-binding motif protein 11, which increases survival [61, 62]. Moreover, the effect of EVs on angiogenesis, an important process in tumor growth, has been studied on glioma cells and it has been reported that EVs contain factors that promote angiogenesis by stimulating vascular endothelial growth factors [63].

In bladder and gastric cancer and melanoma, EVs are releasing platelet-derived growth factor receptor-beta, which is stimulating PI3K/AKT and MAP/ERK pathways, thus increasing cell proliferation and apoptosis resistance [64, 65].

The role of the EVs in intercellular communication and cancer development occurs not only locally but also remotely, leading to metastatic disease. The most studied components of EVs involved in this process are miRNAs that can influence angiogenesis, local invasion, colonization, immune modulation, etc., and annexin II, *Extracellular Vesicles as Intercellular Communication Vehicles in Regenerative Medicine DOI: http://dx.doi.org/10.5772/intechopen.101530*

a membrane-associated protein, by stimulating angiogenesis [66, 67]. Also, peritoneal metastases of ovarian cancer are accelerated by matrix metalloproteinase-1 from EVs [68].

Therapy response in cancer can be influenced by EVs, until the emergence of multidrug resistance, by transferring some drug resistance traits from cancer cells to recipient cells, like drug efflux pumps (decreasing drug concentrations in the cells by drug efflux), apoptotic regulators (simulating anti-apoptotic pathways), proteins involved in metal ion transportation (decreasing the effect of a metal-based therapy, as cisplatin), but also microRNAs, functional mRNAs and lncRNAs (long non-coding RNAs) [57, 69–71].

#### **3.3 Therapeutic potential of EVs**

As already mentioned, EVs have an important role in cell-cell communication and thus in physiological and pathological processes, leading to an increased interest in studying their ability to generate new therapeutic methods. Over time, several studies have tried to demonstrate the involvement of EVs in immunological modulation, tissue regeneration, bioengineering, transportation of therapeutic agents, etc. [4]. One focuses our attention on explaining some other therapeutic potential of EVs, while the role of EVs in tissue regeneration will be separately discussed.

One of the first studied therapeutic potentials of EVs has been in immunotherapy. EVs produced by mesenchymal stromal cells (MSCs), especially exosomes, can induce an M2-like phenotype (anti-inflammatory, regenerative) in monocytes *in vitro* and thus polarization of activated CD4 T-cells to regulatory T-cells [72]. Some experimental studies performed in rats have shown that allograft rejection can be decreased by regulatory T-cells (activated by exosomes) in kidney and intestinal transplantation in rats and by exosomes derived from immature dendritic cells in cardiac transplantation [73–75]. In ischemic events, MSCs are producing exosomes that are decreasing myocardial inflammation after 24 h, by secreting anti-inflammatory cytokines and MVs that are reducing renal inflammation and fibrosis [74, 75].
