Chapter 15 - Stem Cell Niche in the Kidney

Abstract

The kidney is one of the few organs that undergo mesenchymaleepithelial transition during their development. Structures present in the adult kidney arise from reciprocal interactions between two discrete embryonic appendages: the ureteric bud and metanephric mesenchyme. The adult kidney contains more than 24 mature cell types arranged in distinct vascular, interstitial, glomerular, and tubular compartments. This unique organogenesis and structural complexity of the adult kidney is the cause of many challenges to the identification and characterization of kidney stem cells. Remission of disease and regression of renal lesions are widely observed in experimental animals and even in humans. The repair of injured renal tissue in mammals is not sustained by the generation of new nephrons and frequently leads to a non-functioning mass of fibrotic tissue. A large body of evidence has recently shown that the parietal epithelium of Bowman's capsule represents a reservoir of renal progenitors in adult kidney deputed to replacement and regeneration of podocytes, as well as of proximal tubular cells. This finding provides a new point of view for the understanding of renal physiology and pathophysiology. The first main outcome of the discovery of renal stem cells is that they encourage regeneration and promote functional repair of glomerular injury, and even prevention and treatment of glomerulosclerosis may be possible. The discovery that renal progenitors of Bowman's capsule can not only regenerate podocytes but also cause hyperplastic glomerular lesions in crescentic glomerulonephritis, collapsing glomerulopathy, FSGS or the tip lesion, suggests that glomerular disorders may at least in part result from abnormal or inefficient regenerative responses to podocyte injury.