Membrane-derived microvesicles (MVs) are released from the cell surface and are implicated in cell-to-cell communication. We evaluated whether MVs derived from endothelial progenitor cells (EPCs) are able to trigger angiogenesis. We found that EPC-derived MVs were incorporated in endothelial cells by interaction with α4 and β1 integrins expressed on the MV surface. In vitro, MVs promoted endothelial cell survival, proliferation, and organization in capillary-like structures. In vivo, in severe combined immunodeficient (SCID) mice, MV-stimulated human endothelial cells organized in patent vessels. When incubated with RNase, despite their internalization into endothelial cells, MVs failed to induce in vitro and in vivo angiogenic effects. mRNA transfer was shown by transduction of GFP protein in endothelial cells by MVs containing GFP-mRNA and the biologic relevance by the angiogenic effect of MV-mRNA extract delivered by lipofectamine. Microarray ana-lysis and quantitative reverse transcription–polymerase chain reaction (RT-PCR) of MV-mRNA extract indicated that MVs were shuttling a specific subset of cellular mRNA, such as mRNA associated with the PI3K/AKT signaling pathway. Protein expression and functional studies showed that PI3K and eNOS play a critical role in the angiogenic effect of MVs. These results suggest that EPCs may activate angiogenesis in endothelial cells by releasing MVs able to trigger an angiogenic program.

Background. Several studies demonstrated that mesenchymal stem cells (MSCs) reverse acute kidney injury (AKI) by a paracrine mechanism rather than by MSC transdifferentiation. We recently demonstrated that microvesicles (MVs) released from MSCs may account for this paracrine mechanism by a horizontal transfer of messenger RNA and microRNA. Methods. MVs isolated from MSCs were injected intravenously in rats (30 μg/rat) immediately after monolateral nephrectomy and renal artery and vein occlusion for 45 min. To evaluate the MV effects on AKI induced by ischaemia–reperfusion injury (IRI), the animals were divided into different groups: normal rats (n = 4), sham-operated rats (n = 6), IRI rats (n = 6), IRI + MV rats (n = 6), and IRI + RNase-MV rats (n = 6), and all animals were sacrificed at Day 2 after the operation. To evaluate the chronic kidney damage consequent to IRI, the rats were divided into different groups: sham-operated rats (n = 6) and IRI rats (n = 6), IRI + MV rats (n = 6), and all animal were sacrificed 6 months after the operation. Results. We found that a single administration of MVs, immediately after IRI, protects rats from AKI by inhibiting apoptosis and stimulating tubular epithelial cell proliferation. The MVs also significantly reduced the impairment of renal function. Pretreatment of MVs with RNase to inactivate their RNA cargo abrogated these protective effects. Moreover, MVs by reducing the acute injury also protected from later chronic kidney disease. Conclusion. MVs released from MSCs protect from AKI induced by ischaemia reperfusion injury and from subsequent chronic renal damage. This suggest that MVs could be exploited as a potential new therapeutic approach.

Several studies demonstrated that treatment with mesenchymal stem cells (MSCs) reduces cisplatin mortality in mice. Microvesicles (MVs) released from MSCs were previously shown to favor renal repair in non lethal toxic and ischemic acute renal injury (AKI). In the present study we investigated the effects of MSC-derived MVs in SCID mice survival in lethal cisplatin-induced AKI. Moreover, we evaluated in vitro the effect of MVs on cisplatin-induced apoptosis of human renal tubular epithelial cells and the molecular mechanisms involved. Two different regimens of MV injection were used. The single administration of MVs ameliorated renal function and morphology, and improved survival but did not prevent chronic tubular injury and persistent increase in BUN and creatinine. Multiple injections of MVs further decreased mortality and at day 21 surviving mice showed normal histology and renal function. The mechanism of protection was mainly ascribed to an anti-apoptotic effect of MVs. In vitro studies demonstrated that MVs up-regulated in cisplatin-treated human tubular epithelial cells anti-apoptotic genes, such as Bcl-xL, Bcl2 and BIRC8 and down-regulated genes that have a central role in the execution-phase of cell apoptosis such as Casp1, Casp8 and LTA. In conclusion, MVs released from MSCs were found to exert a pro-survival effect on renal cells in vitro and in vivo, suggesting that MVs may contribute to renal protection conferred by MSCs.

Acute kidney injury (AKI) is an increasing health burden with high morbidity and mortality rates worldwide. AKI is a risk factor for chronic kidney disease (CKD) development and progression to end stage renal disease (ESRD). Rapid action is required to find treatment options for AKI, plus to anticipate the development of CKD and other complications. Therefore, it is essential to understand the pathophysiology of AKI to CKD transition. Over the last several years, research has revealed maladaptive repair to be an interplay of cell death, endothelial dysfunction, tubular epithelial cell senescence, inflammatory processes and more—terminating in fibrosis. Various pathological mechanisms have been discovered and reveal targets for potential interventions. Furthermore, there have been clinical efforts measures for AKI prevention and progression including the development of novel biomarkers and prediction models. In this review, we provide an overview of pathophysiological mechanisms involved in kidney fibrosis. Furthermore, we discuss research gaps and promising therapeutic approaches for AKI to CKD progression.