Stem cells and kidney diseases.

The role of the stem cell (SC) in physiology and physiopathology has recently attracted much interest. SCs may originate from embryos, aborted fetuses, umbilical cord blood, and adult organs and tissues. In the adult, SCs were first defined in tissues with a high cell turnover, like skin and gut. Today, SCs have also been identified in tissues with no or low regenerative potential and turnover. However, the SC concept is changing rapidly: adult SCs not only reside locally in specific niches, but may also be recruited from the circulation to actively participate in the regeneration of various tissues. Furthermore, reverse differentiation has been demonstrated. In the kidney, both glomerular and tubular cells may differentiate into a range of phenotypes during the remodelling process in response to injury. The glomerular and tubulointerstitial scarring processes involve primarily interactions between infiltrating inflammatory cells and resident renal cells that culminate in loss of renal cells and their replacement by extracellular collagenous matrix. Reverse embryogenesis is a key step in renal healing and scarring: intrinsic renal cells regress to primitive/embryonic mesenchymal phenotype. In addition, it is clear that renal remodelling in health and disease involves the migration of hematopoietic SCs into the kidneys. These cells assume various glomerular and tubular epithelial phenotypes. Therefore, a better understanding of some of these key events in renal remodelling may open the way to new interventions based on their manipulations. Cell-based therapy may be a more successful strategy by providing a dynamic and individualized therapeutic approach that responds to the physiopathological condition of the patient. In fact, SCs may provide innovative methods for drug delivery, immunotherapy, tissue regenerative or replacement engineering.