Possible mechanisms of kidney repair

In most adult epithelia the process of replacing damaged or dead cells is maintained through the presence of stem/progenitor cells, which allow epithelial tissues to be repaired following injury. Existing evidence strongly supports the presence of stem cells in the adult kidney. Indeed, recent findings provide evidence in favour of a role for intrinsic renal cells and against a physiological role for bone marrow-derived stem cells in the regeneration of renal epithelial cells. In addition, recent studies have identified a subset of CD24+CD133+ renal progenitors within the Bowman's capsule of adult human kidney, which provides regenerative potential for injured renal epithelial cells. Intriguingly, CD24+CD133+ renal progenitors also represent common progenitors of tubular cells and podocytes during renal development. Chronic injury causes dysfunction of the tubular epithelial cells, which triggers the release of fibrogenic cytokines and recruitment of inflammatory cells to injured kidneys. The rapid interposition of scar tissue probably confers a survival advantage by preventing infectious microorganisms from invading the wound, but prevents subsequent tissue regeneration. However, the existence of renal epithelial progenitors in the kidney suggests a possible explanation for the regression of renal lesions which has been observed in experimental animals and even in humans. Thus, manipulation of the wound repair process in order to shift it towards regeneration will probably require the ability to slow the rapid fibrotic response so that renal progenitor cells can allow tissue regeneration rather than scar formation.