RASAL1 prevents liver fibrosis by suppression TGF-β and PDGF signaling in hepatic stellate cells

[Purpose] RAS protein activator like-1 (RASAL1) is a member of the RAS-GTPase-activating proteins which inhibit RAS activity. We have reported that the decreased expression levels of RASAL1 are significantly related to liver fibrosis. In this study, we confirmed the role of RASAL1 in liver fibrosis by RASAL1 knockout mouse and searched for chemical compounds which increased RASAL1 levels by a knock-in reporter at the RASAL1 locus. [Method] 1) The experimentally induced liver fibrosis was examined in RASAL1 knockout mice. 2) Functional analyses were performed using LX-2 cells, human hepatic stellate cells (HSCs), under modifying the expression levels of RASAL1. 3) LX-2 cells with reporter knock-in at the RASAL1 locus by gene editing method using CRISPR were used for the comprehensive chemical compound library screening.[Result] 1) In RASAL1 knockout mice, CCl4-induced liver fibrosis was significantly reduced. 2) RASAL1-expressed LX-2 cells not only showed the decreased levels of α-SMA and collagen, which were associated with the inhibition of TGF-β signaling pathway, but also showed the reduced cell proliferation, which was associated with the inhibition of RAS-MAPK signaling pathway. 3) Chemical compound library screening using reporter knock-in cells identified significant compounds which could up-regulate endogenous RASAL1 gene expression levels. [Conclusion] RASAL1 in HSCs is a critical regulator of liver fibrosis. Chemical compounds identified here may be useful for the preventing liver fibrosis.