In the past decade, extracellular vesicles (EVs) have been recognized as potent vehicles of intercellular communication, both in prokaryotes and eukaryotes. This is due to their capacity to transfer proteins, lipids and nucleic acids, thereby influencing various physiological and pathological functions of both recipient and parent cells. While intensive investigation has targeted the role of EVs in different pathological processes, for example, in cancer and autoimmune diseases, the EV-mediated maintenance of homeostasis and the regulation of physiological functions have remained less explored. Here, we provide a comprehensive overview of the current understanding of the physiological roles of EVs, which has been written by crowd-sourcing, drawing on the unique EV expertise of academia-based scientists, clinicians and industry based in 27 European countries, the United States and Australia. This review is intended to be of relevance to both researchers already working on EV biology and to newcomers who will encounter this universal cell biological system. Therefore, here we address the molecular contents and functions of EVs in various tissues and body fluids from cell systems to organs. We also review the physiological mechanisms of EVs in bacteria, lower eukaryotes and plants to highlight the functional uniformity of this emerging communication system.

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Biological properties of extracellular vesicles and their physiological functions

Mesenchymal stem cell transplantation is undergoing extensive evaluation as a cellular therapy in human clinical trials. Because MSCs are easily isolated and amenable to culture expansion in vitro there is a natural desire to test MSCs in many diverse clinical indications. This is exemplified by the rapidly expanding literature base that includes many in vivo animal models. More recently, MSC-derived extracellular vesicles (EVs), which include exosomes and microvesicles (MV), are being examined for their role in MSC-based cellular therapy. These vesicles are involved in cell-to-cell communication, cell signaling, and altering cell or tissue metabolism at short or long distances in the body. The exosomes and MVs can influence tissue responses to injury, infection, and disease. MSC-derived exosomes have a content that includes cytokines and growth factors, signaling lipids, mRNAs, and regulatory miRNAs. To the extent that MSC exosomes can be used for cell-free regenerative medicine, much will depend on the quality, reproducibility, and potency of their production, in the same manner that these parameters dictate the development of cell-based MSC therapies. However, the MSC exosome's contents are not static, but rather a product of the MSC tissue origin, its activities and the immediate intercellular neighbors of the MSCs. As such, the exosome content produced by MSCs appears to be altered when MSCs are cultured with tumor cells or in the in vivo tumor microenvironment. Therefore, careful attention to detail in producing MSC exosomes may provide a new therapeutic paradigm for cell-free MSC-based therapies with decreased risk. Stem Cells 2017;35:851-858.

https://stemcellsjournals.onlinelibrary.wiley.com/doi/epdf/10.1002/stem.2575

Concise Review: MSC-Derived Exosomes for Cell-Free Therapy

Extracellular vesicles (EVs), such as exosomes and microvesicles, are released by different cell types and participate in physiological and pathophysiological processes. EVs mediate intercellular communication as cell-derived extracellular signalling organelles that transmit specific information from their cell of origin to their target cells. As a result of these properties, EVs of defined cell types may serve as novel tools for various therapeutic approaches, including (a) anti-tumour therapy, (b) pathogen vaccination, (c) immune-modulatory and regenerative therapies and (d) drug delivery. The translation of EVs into clinical therapies requires the categorization of EV-based therapeutics in compliance with existing regulatory frameworks. As the classification defines subsequent requirements for manufacturing, quality control and clinical investigation, it is of major importance to define whether EVs are considered the active drug components or primarily serve as drug delivery vehicles. For an effective and particularly safe translation of EV-based therapies into clinical practice, a high level of cooperation between researchers, clinicians and competent authorities is essential. In this position statement, basic and clinical scientists, as members of the International Society for Extracellular Vesicles (ISEV) and of the European Cooperation in Science and Technology (COST) program of the European Union, namely European Network on Microvesicles and Exosomes in Health and Disease (ME-HaD), summarize recent developments and the current knowledge of EV-based therapies. Aspects of safety and regulatory requirements that must be considered for pharmaceutical manufacturing and clinical application are highlighted. Production and quality control processes are discussed. Strategies to promote the therapeutic application of EVs in future clinical studies are addressed.

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Applying extracellular vesicles based therapeutics in clinical trials - an ISEV position paper

Here, for the first time, we test a novel hypothesis that systemic treatment of stroke with exosomes derived from multipotent mesenchymal stromal cells (MSCs) promote neurovascular remodeling and functional recovery after stroke in rats. Adult male Wistar rats were subjected to 2 hours of middle cerebral artery occlusion (MCAo) followed by tail vein injection of 100 μg protein from MSC exosome precipitates or an equal volume of vehicle phosphate-buffered saline (PBS) (n=6/group) 24 hours later. Animals were killed at 28 days after stroke and histopathology and immunohistochemistry were employed to identify neurite remodeling, neurogenesis, and angiogenesis. Systemic administration of MSC-generated exosomes significantly improved functional recovery in stroke rats compared with PBS-treated controls. Axonal density and synaptophysin-positive areas were significantly increased along the ischemic boundary zone of the cortex and striatum in MCAo rats treated with exosomes compared with PBS control. Exosome treatment significantly increased the number of newly formed doublecortin (a marker of neuroblasts) and von Willebrand factor (a marker of endothelial cells) cells. Our results suggest that intravenous administration of cell-free MSC-generated exosomes post stroke improves functional recovery and enhances neurite remodeling, neurogenesis, and angiogenesis and represents a novel treatment for stroke.

https://journals.sagepub.com/doi/pdf/10.1038/jcbfm.2013.152

Systemic administration of exosomes released from mesenchymal stromal cells promote functional recovery and neurovascular plasticity after stroke in rats.

Mesenchymal stem cells (MSCs) have been considered as an attractive tool for the therapy of diseases. Exosomes excreted from MSCs can reduce myocardial ischemia/reperfusion damage and protect against acute tubular injury. However, whether MSC-derived exosomes can relieve liver fibrosis and its mechanism remain unknown. Previous work showed that human umbilical cord-MSCs (hucMSCs) transplanted into acutely injured and fibrotic livers could restore liver function and improve liver fibrosis. In this study, it was found that transplantation of exosomes derived from hucMSC (hucMSC-Ex) reduced the surface fibrous capsules and got their textures soft, alleviated hepatic inflammation and collagen deposition in carbon tetrachloride (CCl4)-induced fibrotic liver. hucMSC-Ex also significantly recovered serum aspartate aminotransferase (AST) activity, decreased collagen type I and III, transforming growth factor (TGF)-β1 and phosphorylation Smad2 expression in vivo. In further experiments, we found that epithelial-to-mesenchymal transition (EMT)-associated markers E-cadherin-positive cells increased and N-cadherin- and vimentin-positive cells decreased after hucMSC-Ex transplantation. Furthermore, the human liver cell line HL7702 underwent typical EMT after induction with recombinant human TGF-β1, and then hucMSC-Ex treatment reversed spindle-shaped and EMT-associated markers expression in vitro. Taken together, these results suggest that hucMSC-Ex could ameliorate CCl4-induced liver fibrosis by inhibiting EMT and protecting hepatocytes. This provides a novel approach for the treatment of fibrotic liver disease.

Exosomes Derived from Human Umbilical Cord Mesenchymal Stem Cells Alleviate Liver Fibrosis

Administration of bone marrow mesenchymal stem cells (MSCs) or secreted microvesicles improves recovery from acute kidney injury (AKI). However, the potential roles and mechanisms are not well understood. In the current study, we focused on the protective effect of exosomes derived from human umbilical cord mesenchymal stem cells (hucMSC-ex) on cisplatin-induced nephrotoxicity in vivo and in vitro. We constructed cisplatin-induced AKI rat models. At 24 h after treatment with cisplatin, hucMSC-ex were injected into the kidneys via the renal capsule; human lung fibroblast (HFL-1)-secreted exosomes (HFL-1-ex) were used as controls. All animals were killed at day 5 after administration of cisplatin. Renal function, histological changes, tubular apoptosis and proliferation, and degree of oxidative stress were evaluated. In vitro, rat renal tubular epithelial (NRK-52E) cells were treated with or without cisplatin and after 6 h treated with or without exosomes. Cells continued to be cultured for 24 h, and were then harvested for western blotting, apoptosis and detection of degree of oxidative stress. After administration of cisplatin, there was an increase in blood urea nitrogen (BUN) and creatinine (Cr) levels, apoptosis, necrosis of proximal kidney tubules and formation of abundant tubular protein casts and oxidative stress in rats. Cisplatin-induced AKI rats treated with hucMSC-ex, however, showed a significant reduction in all the above indexes. In vitro, treatment with cisplatin alone in NRK-52E cells resulted in an increase in the number of apoptotic cells, oxidative stress and activation of the p38 mitogen-activated protein kinase (p38MAPK) pathway followed by a rise in the expression of caspase 3, and a decrease in cell multiplication, while those results were reversed in the hucMSCs-ex-treated group. Furthermore, it was observed that hucMSC-ex promoted cell proliferation by activation of the extracellular-signal-regulated kinase (ERK)1/2 pathway. The results in the present study indicate that hucMSC-ex can repair cisplatin-induced AKI in rats and NRK-52E cell injury by ameliorating oxidative stress and cell apoptosis, promoting cell proliferation in vivo and in vitro. This suggests that hucMSC-ex could be exploited as a potential therapeutic tool in cisplatin-induced nephrotoxicity.

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Exosomes released by human umbilical cord mesenchymal stem cells protect against cisplatin-induced renal oxidative stress and apoptosis in vivo and in vitro

Circulating miR-17-5p and miR-20a (miR-17-5p/20a) have been demonstrated to be elevated in the plasma of gastric cancer patients. However, the clinical significance of the circulating levels of these microRNAs (miRNAs), the predictive power for prognosis and application for monitoring of chemotherapeutic effects remain unclear. To this end, we measured plasma miR-17-5p/20a levels in unpaired pre-operative (n=65), post-operative (n=16) and relapse (n=6) gastric cancer patient groups. The 3-year overall survival rate for the unpaired pre-operative patients was recorded. The circulating levels of miR-17-5p/20a were also tested in paired pre-operative and post-operative plasma from 14 gastric cancer patients. We found that the concentrations of miR-17-5p/20a were significantly associated with the differentiation status and TNM stages of gastric cancer. The miRNA levels in the different groups reflected pathological tumor progression. Kaplan-Meier curve analysis revealed that high expression levels of miR-17-5p/20a were significantly correlated with poor overall survival. Cox regression analysis demonstrated that the level of plasma miR-20a was an independent risk predictor for prognosis. An in vivo mouse tumor model was established and antagomirs against miR-17-5p/20a were applied as chemotherapeutics to perform tumor treatment. An assay of serum miR-17-5p/20a levels showed that the levels of serum miRNAs were notably reduced in post-treated mice with tumor volume regression. Taken together, the levels of circulating miR-17-5p/20a may be a promising non-invasive molecular marker for pathological progression, prediction of prognosis and monitoring of chemotherapeutic effects for gastric cancer.

https://www.spandidos-publications.com/10.3892/mmr.2012.828/download

Circulating miR-17-5p and miR-20a: molecular markers for gastric cancer.

miR-17-5p/20a are important markers for gastric cancer and murine double minute 2 participates in their functional regulation

The role of mesenchymal stem cells (MSCs) in kidney injury repair has been studied widely. However, the underlying molecular mechanism remains unclear. We profiled the altered microRNAs in renal tissues from cisplatin-induced acute kidney injury (AKI) rats treated with or without rat bone marrow MSCs (rMSCs). We observed that microRNA-146b (miR-146b) expression was considerably upregulated in renal tissues from AKI rats compared with that in healthy rats, and the expression decreased following MSC treatment after cisplatin administration. At the early stage of AKI, serum miR-146b levels exhibited a rapid increase that was even faster than that of two conventional renal function indexes: serum creatinine and blood urea nitrogen levels. Furthermore, the serum miR-146b levels in AKI patients were higher than those in healthy people. In vitro exposure to cisplatin also increased miR-146b expression in renal tubular epithelial cells (TECs). miR-146b knockdown protected renal TECs from cisplatin-induced apoptosis and promoted their proliferation. Moreover, ErbB4 was identified as a direct target of miR-146b, and miR-146b inhibition induced ErbB4 expression, resulting in enhanced proliferation of injured renal TECs. In addition, restoration by rMSCs could be controlled through ErbB4 downregulation. In conclusion, elevated miR-146b expression contributes to cisplatin-induced AKI, partly through ErbB4 downregulation. miR-146b might be an early biomarker for AKI, and miR-146b inhibition could be a novel strategy for AKI treatment. Significance The present study found that microRNA-146b (miR-146b) might be a novel biomarker for acute kidney injury and an indicator for its recovery after treatment with mesenchymal stem cells (MSCs). The results showed that in acute kidney injury induced by cisplatin, miR-146b in serum increased more quickly than did the usual indexes of kidney injury and decreased with restoration of MSCs. In addition, inhibition of miR-146b could ameliorate the apoptosis induced by cisplatin and potentially improve the proliferation by freeing ErbB4 and its downstream proteins.

https://stemcellsjournals.onlinelibrary.wiley.com/doi/pdf/10.5966/sctm.2015-0355

Yang Tao

Papers

Exosomes released by human umbilical cord mesenchymal stem cells protect against cisplatin-induced renal oxidative stress and apoptosis in vivo and in vitro

Circulating miR-17-5p and miR-20a: molecular markers for gastric cancer.

miR-17-5p/20a are important markers for gastric cancer and murine double minute 2 participates in their functional regulation

MicroRNA-146b, a Sensitive Indicator of Mesenchymal Stem Cell Repair of Acute Renal Injury