Liver fibrosis is driven by protease‐activated receptor‐1 expressed by hepatic stellate cells in experimental chronic liver injury

Abstract

BackgroundBlood coagulation protease activity is proposed to drive hepatic fibrosis through activation of protease‐activated receptors (PARs). Whole‐body PAR‐1 deficiency reduces experimental hepatic fibrosis, and in vitro studies suggest a potential contribution by PAR‐1 expressed by hepatic stellate cells. However, owing to a lack of specific tools, the cell‐specific role of PAR‐1 in experimental hepatic fibrosis has never been formally investigated. Using a novel mouse expressing a conditional PAR‐1 allele, we tested the hypothesis that PAR‐1 expressed by hepatic stellate cells contributes to hepatic fibrosis. MethodsPAR‐1flox/flox mice were crossed with mice expressing Cre recombinase controlled by the lecithin retinol acyltransferase (LRAT) promoter, which induces recombination in hepatic stellate cells. Male PAR‐1flox/flox/LRATCre and PAR‐1flox/flox mice were challenged twice weekly with carbon tetrachloride (CCl4, 1 mL/kg i.p.) for 6 weeks to induce liver fibrosis. ResultsPAR‐1 mRNA levels were reduced (>95%) in hepatic stellate cells isolated from PAR‐1flox/flox/LRATCre mice. Hepatic stellate cell activation was evident in CCl4‐challenged PAR‐1flox/flox mice, indicated by increased α‐smooth muscle actin labeling and induction of several profibrogenic genes. CCl4‐challenged PAR‐1flox/flox mice displayed robust hepatic collagen deposition, indicated by picrosirius red staining and type I collagen immunolabeling. Notably, stellate cell activation and collagen deposition were significantly reduced (>30%) in PAR‐1flox/flox/LRATCre mice. Importantly, the reduction in liver fibrosis was not a consequence of reduced acute CCl4 hepatotoxicity in PAR‐1flox/flox/LRATCre mice. ConclusionsThe results constitute the first direct experimental evidence that PAR‐1 expressed by stellate cells directly promotes their profibrogenic phenotype and hepatic fibrosis in vivo.