Contribution of stem cells to kidney repair.

The potential role of stem cells in the repair of glomerular and tubular injury is under intensive investigation. Several studies have addressed the role of endogenous bone-marrow (BM)-derived stem cells (SC) in the repair of renal injury. Some reports indicate that BM-derived SC are capable of engraftment into damaged nephrons, although the lineage of SC recruited has not been established. However, this issue remains highly controversial, and several studies point to a paracrine/endocrine action of endogenous SC rather than a direct repopulation of the injured nephron. Administration of exogenous mesenchymal SC in experimental acute kidney injury suggests that an SC-based therapy may improve functional and structural recovery of both glomerular and tubular compartments. A contribution of renal resident SC has also been postulated in the recovery after damage. However, several points still need to be clarified regarding the signals regulating homing of SC to injured tissue, the secreted factors underlying the paracrine/endocrine mechanisms, and in particular the long-term in vivo behavior of the administered SC. This review summarizes the current literature on the physiological role of endogenous SC in renal regeneration and on the potential therapeutic strategies based on the administration of exogenous SC.