Retinoids and glomerular regeneration.

Retinoids are essential in the development and function of several organs, exerting potent effects on stem cell systems. All-trans retinoic acid, through binding to the retinoic acid response elements, alters transcription of numerous genes in stem cells, leading to an exit from the self-renewing state and promoting differentiation. In the kidney, retinoids protect against injury and ameliorate function in multiple experimental models of disease. Recent evidence suggests that retinoids act on renal progenitors by promoting their differentiation into mature podocytes and retinoic acid-induced podocyte differentiation is impaired by proteinuria because of sequestration of retinoic acid by albumin. However, retinoic acid administration can revert renal progenitor differentiation and promote podocyte regeneration. A more complete understanding of retinoid-dependent renal progenitor differentiation into podocytes should reward us with new insights into the mechanisms of progression toward glomerulosclerosis.