miR-200a Prevents Renal Fibrogenesis Through Repression of TGF-beta 2 Expression

OBJECTIVE-Progressive fibrosis in the diabetic kidney is driven and sustained by a diverse range of profibrotic factors. This study examines the critical role of microRNAs (miRNAs) in the regulation of the key fibrotic mediators, TGF-beta 1 and TGF-beta 2. RESEARCH DESIGN AND METHODS-Rat proximal-tubular epithelial cells (NRK52E) were treated with TGF-beta 1 and TGF-beta 2 for 3 days, and expression of markers of epithelial-to-mesenchymal transition (EMT) and fibrogenesis were assessed by RT-PCR and Western blotting. The expression of miR-141 and miR-200a was also assessed, as was their role as translational repressors of TGF-beta signaling. Finally, these pathways were explored in two different mouse models, representing early and advanced diabetic nephropathy. RESULTS-Both TGF-beta 1 and TGF-beta 2 induced EMT and fibrogenesis in NRK52E cells. TGF-beta 1 and TGF-beta 2 also downregulated expression of miR-200a. The importance of these changes was demonstrated by the finding that ectopic expression miR-200a downregulated smad-3 activity and the expression of matrix proteins and prevented TGF-beta-dependent EMT. miR-200a also downregulated the expression of TGF-beta 2, via direct interaction with the 3' untranslated region of TGF-beta 2. The renal expression of miR-141 and miR-200a was also reduced in mouse models representing early and advanced kidney disease. CONCLUSIONS-miR-200a and miR-141 significantly impact on the development and progression of TGF-beta-dependent EMT and fibrosis in vitro and in vivo. These miRNAs appear to be intricately involved in fibrogenesis, both as downstream mediators of TGF-beta signaling and as components of feedback regulation, and as such represent important new targets for the prevention of progressive kidney disease in the context of diabetes. Diabetes 60:280-287, 2011