WNT/β‐catenin signal inhibitor IC‐2–derived small‐molecule compounds suppress TGF‐β1–induced fibrogenic response of renal epithelial cells by inhibiting SMAD2/3 signalling

Renal fibrosis compromises kidney function, and it is a risk factor for chronic kidney disease (CKD). CKD ultimately progresses to end-stage kidney disease that can be cured only by kidney transplantation. Owing to the increasing number of CKD patients, effective treatment strategies are urgently required for renal fibrosis. TGF-β is a well-established fibrogenic factor that signals through SMAD2/3 signaling pathway. It was shown that there is a cross-talk between TGF-β/SMAD and WNT/β-catenin signaling pathways in renal tubular epithelial cells, and that a WNT/β-catenin inhibitor, ICG-001, ameliorates TGF-β1induced renal fibrosis. IC-2, a derivative of ICG-001, has been shown to potently induce hepatocyte differentiation of human mesenchymal stem cells by inhibiting WNT/β-catenin signaling. In the present study, we examined the effect of ICG-001, IC-2, and IC-2 derivatives (IC-2-506-1, IC-2-506-2, IC-2-506-3, IC-2-Ar-Cl, IC-2-OH, IC-2-OTBS, and IC-2-F) on TGF-β1-induced SMAD activation and fibrogenic response in immortalized human renal tubular epithelial HK-2 cells. All these compounds inhibited LiCl-induced WNT/β-catenin reporter activation to a similar extent, whereas ICG-001, IC-2-OTBS, and IC-2-F almost completely suppressed TGF-β1-induced SMAD reporter activation without apparent cytotoxicity. Phosphorylation of SMAD2/3 by TGF-β1 was more potently inhibited by IC-2-OTBS and IC-2-F than by ICG-001 and IC-2. IC-2-F suppressed TGF-β1-induced COL1A1 protein expression, whereas IC-2-506-1 and IC-2-OTBS suppressed TGF-β1-induced epithelial-mesenchymal transition. These results demonstrated that IC-2 derivatives suppress the TGF-β1-induced fibrogenic response of tubular epithelial cells and thus could be promising therapeutic agents for the treatment of renal fibrosis.