Fibromodulin, an Oxidative Stress-Sensitive Proteoglycan, Regulates the Fibrogenic Response to Liver Injury in Mice

Abstract

Collagen I deposition contributes to liver fibrosis, yet little is known about other factors that mediate this process. Fibromodulin is a liver proteoglycan that regulates extracellular matrix organization and is induced by fibrogenic stimuli. We propose that fibromodulin contributes to the pathogenesis of fibrosis by regulating the fibrogenic phenotype of hepatic stellate cells (HSCs). We analyzed liver samples from patients with hepatitis C-associated cirrhosis and healthy individuals (controls). We used a coculture model to study interactions among rat HSCs, hepatocytes, and sinusoidal endothelial cells. We induced fibrosis in livers of wild-type and Fmod(-/-) mice by bile duct ligation, injection of CCl(4), or administration of thioacetamide. Liver samples from patients with cirrhosis had higher levels of fibromodulin messenger RNA and protein than controls. Bile duct ligation, CCl(4), and thioacetamide each increased levels of fibromodulin protein in wild-type mice. HSCs, hepatocytes, and sinusoidal endothelial cells produced and secreted fibromodulin. Infection of HSCs with an adenovirus that expressed fibromodulin increased expression of collagen I and α-smooth muscle actin, indicating increased activation of HSCs and fibrogenic potential. Recombinant fibromodulin promoted proliferation, migration, and invasion of HSCs, contributing to their fibrogenic activity. Fibromodulin was sensitive to reactive oxygen species. HepG2 cells that express cytochrome P450 2E1 produced fibromodulin, and HSCs increased fibromodulin production in response to pro-oxidants. In mice, administration of an antioxidant prevented the increase in fibromodulin in response to CCl(4). Coculture of hepatocytes or sinusoidal endothelial cells with HSCs increased the levels of reactive oxygen species in the culture medium, along with collagen I and fibromodulin proteins; this increase was prevented by catalase. Fibromodulin bound to collagen I, but the binding did not prevent collagen I degradation by matrix metalloproteinase 13. Bile duct ligation caused liver fibrosis in wild-type but not Fmod(-/-) mice. Fibromodulin levels are increased in livers of patients with cirrhosis. Hepatic fibromodulin activates HSCs and promotes collagen I deposition, which leads to liver fibrosis in mice.