Transforming Growth Factor β1 (TGF-β1) Enhances Expression of Profibrotic Genes through a Novel Signaling Cascade and MicroRNAs in Renal Mesangial Cells

Increased expression of transforming growth factor-beta 1 (TGF-beta 1) in glomerular mesangial cells (MC) augments extracellular matrix accumulation and hypertrophy during the progression of diabetic nephropathy (DN), a debilitating renal complication of diabetes. MicroRNAs (miRNAs) play key roles in the pathogenesis of DN by modulating the actions of TGF-beta 1 to enhance the expression of profibrotic genes like collagen. In this study, we found a significant decrease in the expression of miR-130b in mouse MC treated with TGF-beta 1. In parallel, there was a down-regulation in miR-130b host gene 2610318N02RIK (RIK), suggesting host gene-dependent expression of this miRNA. TGF-beta receptor 1 (TGF-beta R1) was identified as a target of miR-130b. Interestingly, the RIK promoter contains three NF-Y binding sites and was regulated by NF-YC. Furthermore, NF-YC expression was inhibited by TGF-beta 1, suggesting that a signaling cascade, involving TGF-beta 1-induced decreases in NF-YC, RIK, and miR-130b, may upregulate TGF-beta R1 to augment expression of TGF-beta 1 target fibrotic genes. miR-130b was down-regulated, whereas TGF-beta R1, as well as the profibrotic genes collagen type IV alpha 1 (Col4a1), Col12a1, CTGF, and PAI-1 were up-regulated not only in mouse MC treated with TGF-beta 1 but also in the glomeruli of streptozotocin-injected diabetic mice, supporting in vivo relevance. Together, these results demonstrate a novel miRNA-and host gene-mediated amplifying cascade initiated by TGF-beta 1 that results in the up-regulation of profibrotic factors, such as TGF-beta R1 and collagens associated with the progression of DN.