MicroRNA-196a/b Mitigate Renal Fibrosis by Targeting TGF-β Receptor 2

Organ-specific microRNAs have essential roles in maintaining normal organ function. However, the micro RNA profile of the kidney and the role of microRNAs in modulating renal function remain undefined. We performed an unbiased assessment of the genome-wide microRNA expression profile in 14 mouse organs using Solexa deep sequencing and found that nnicroRNA-196a (nniR-196a) and miR-196b are selectively expressed in kidney, with 74.37% of mouse total nniR-196a and 73.19% of mouse total miR-196b distributed in the kidneys. We confirmed the predominant expression of miR-196a/b in mouse and human kidney, particularly in the glomeruli and tubular epithelium, by quantitative RT-PCR and in situ hybridization assays. During unilateral ureteral obstruction (UUO)-induced mouse renal fibrosis, renal miR-196a/b levels rapidly decreased. Elevation of renal miR-196a/b expression by hydrodynamic-based delivery of a miR196a/b expressing plasmid before or shortly after UUO significantly downregulated profibrotic proteins, including collagen 1 and alpha-smooth muscle actin, and mitigated UUO-induced renal fibrosis. In contrast, depletion of renal nniR-196a/b by miR-196a/b antagomirs substantially aggravated UUO-induced renal fibrosis. Mechanistic studies further identified transforming growth factor beta receptor II (TGF beta R2) as a common target of miR-196a and nniR-196b. Decreasing miR-196a/b expression in human HK2 cells strongly activated TGF-beta-Smad signaling and cell fibrosis; whereas increasing miR-196a/b levels in mouse primary cultured tubular epithelial cells inhibited TGF-beta Smad signaling. In the UUO model, miR-196a/b silenced TGF-beta Smad signaling, decreased the expression of collagen 1 and a-smooth muscle actin, and attenuated renal fibrosis. Our findings suggest that elevating renal nniR-196a/b levels may be a novel therapeutic strategy for treating renal fibrosis.