The role of epithelial-to-mesenchymal transition in renal fibrosis.

Epithelial-to-mesenchymal transition (EMT) involving injured epithelial cells plays an important role in the progression of fibrosis in the kidney. Tubular epithelial cells can acquire a mesenchymal phenotype, and enhanced migratory capacity enabling them to transit from the renal tubular microenvironment into the interstitial space and escape potential apoptotic cell death. EMT is a major contributor to the pathogenesis of renal fibrosis, as it leads to a substantial increase in the number of myofibroblasts, leading to tubular atrophy. However, recent findings suggest that EMT involving tubular epithelial cell is a reversible process, potentially determined by the surviving cells to facilitate the repopulation of injured tubules with new functional epithelia. Major regulators of renal epithelial cell plasticity in the kidney are two multifunctional growth factors, bone morphogenic protein-7 (BMP-7) and transforming growth factor beta1 (TGF-beta1). While TGF-beta1 is a well-established inducer of EMT involving renal tubular epithelial cells, BMP-7 reverses EMT by directly counteracting TGF-beta-induced Smad-dependent cell signaling in renal tubular epithelial cells. Such antagonism results in the repair of injured kidneys, suggesting that modulation of epithelial cell plasticity has therapeutic advantages.