Stem cells and stem cell-derived extracellular vesicles in acute and chronic kidney diseases: mechanisms of repair.

Acute and chronic renal failure have long been described and now renamed as acute kidney injury (AKI) and chronic kidney disease (CKD). New concepts are emerging in the pathophysiology of kidney diseases. AKI is often caused by triggering factors (e.g., toxic, ischemic, immunologic) either individually or combined such as in sepsis (inflammation and hypoxia), and it is initiated at a defined time. Several experimental models of AKI have provided deep insight and have convincingly shown important proof-of-concepts of therapeutic relevance over the years. CKD is now considered a slowly developing disease with often an insidious course, lasting many years whereby co-morbidities (e.g., diabetes, hypertension, dysmetabolic syndrome) may act as worsening factors. It has become increasingly evident that even a single event of AKI may lead to a higher predisposition to develop a progressive CKD. In the present review, we will report studies on the renal protection by adult stem cells in different experimental models and clinical trials. The emerging role of extracellular vesicles (EVs) in cell-to-cell communication and their predominant effect in the paracrine mechanisms of stem cell-dependent actions have prompted several studies on their ability to attenuate both AKI and fibrosis occurring in CKD. We discuss several critical issues that need to be addressed before EVs may have a therapeutic application in humans.