Stem cells in kidney diseases.

Circulating bone marrow-derived endothelial progenitor cells (EPCs) seem to play a crucial role in both vasculogenesis and vascular homeostasis. Chronic kidney disease is a state of endothelial dysfunction, accelerated progression of atherosclerosis and high cardiovascular risk. As a consequence, cardiovascular disorders are the main cause of death in end-stage renal disease (ESRD). It has been shown that patients with advanced renal failure have decreased number of bone marrow-derived endothelial progenitor cells and impaired EPCs function. Moreover, in kidney transplant patients, renal graft function significantly correlated with EPC number. The reduced number of EPCs in patients with ESRD has been ascribed to the uremia. Therefore, therapies that improve the uremic status in dialysis patients such as nocturnal hemodialysis are associated with restoration of impaired EPCs number and migratory function. In fact, some of the common treatments for patients with chronic kidney disease such as erythropoietin, statins and angiotensin II receptor antagonist increase the number of EPCs. Nowadays, there is growing evidence indicating that, under pathophysiological conditions, stem cells (SCs) derived from bone marrow are able to migrate in the injured kidney, and they seem to play a role in glomerular and tubular regeneration. After acute tubular renal injury, surviving tubular epithelial cells and putative renal stem cells proliferate and differentiate into tubular epithelial cells to promote structural and functional repair. Moreover, bone marrow stem cells, including hematopoietic stem cells and mesenchymal stem cells can also participate in the repair process by proliferation and differentiation into renal lineages. For instance, mesenchymal SCs have been shown to decrease inflammation and enhance renal regeneration. The administration of ex vivo expanded bone marrow-derived mesenchymal SCs have been proved to be beneficial in various experimental models of acute renal failure. The mechanisms underlining this beneficial effect are still a matter of debate. Thus, therapeutic strategies aimed at correcting the regenerative potential of stem cells based on the administration of ex vivo expanded SCs or stimulating expansion and differentiation of local progenitor/SC populations are another exciting area of future research.