miR-17/20a mitigates interstitial fibrosis by repressing Frmd6 expression in renal epithelia [PAR-CLIP]
In this study, we evaluated genetic mouse models of inducible renal epithelia-specific miR-17~92 loss-of-function and gain-of-function using unilateral ureteral obstruction. We utilized PAR-CLIP in HK2 cells to identify miR-17/-20a targets, which we subsequently validated in vitro. We examined expression of a novel miR-17/-20a target in human nephrectomy samples with varying degrees of fibrosis. We identify an activator of Hippo signaling, FERM domain-containing protein 6 (FRMD6, also known as Willin), as a novel miR-17/20a target. Frmd6 is upregulated in tubular epithelium of obstructed kidneys that lack miR-17~92, along with increased phosphorylation of Smad3 and STAT3, two known miR-17~92 profibrotic targets. Frmd6 overexpression is sufficient to result in elevated secretion of the extracellular matrix component collagen III in vitro. Finally, we demonstrate that FRMD6 expression is associated with collagen III expression in human nephrectomy samples.Our findings demonstrate that the miR-17~92 cluster in renal epithelia functions in an anti-fibrotic manner by regulating multiple pro-fibrotic pathways. We also identify Frmd6 as a novel miR-17/20a target in renal epithelia, which may drive renal fibrosis. Overall design: Identification of microRNA binding sites in RNAs from HK2 cells, in both control cells and cells treated with TGF-beta.