Fas Regulates Macrophage Polarization and Fibrogenic Phenotype in a Model of Chronic Ethanol-Induced Hepatocellular Injury

The role of Fas-mediated apoptosis and its effect on proinflammatory cytokine production in early alcoholic liver disease has not been addressed. Wild-type mice (C57Bl/6) or mice with a functional mutation in the Fas ligand (B6.gld) were given either high-fat control diet or ethanol diet by intragastric cannulation for 2 or 4 weeks. Liver injury, hepatic lipid accumulation, and proinflammatory cytokine production associated with chronic ethanol consumption were largely prevented in B6.gld mice compared with wild-type mice. Conversely, B6.gld mice given ethanol exhibited increases in collagen deposition, hepatic collagen gene expression, and profibrogenic cytokines (eg, transforming growth factor-β and IL-13) and alterations in matrix remodeling proteins (eg, matrix metalloproteinases and tissue inhibitor of metalloproteinases) compared with wild-type mice. Hepatic F4/80+ macrophage populations were increased significantly in B6.gld mice compared with wild-type mice; hepatic CD3+ cell populations were not significantly different. Importantly, a shift toward the expression of M2/Th2 cytokines (eg, IL-4 and IL-13) after ethanol exposure was observed in B6.gld mice compared with classical M1 cytokine expression in wild-type mice under similar conditions. In isolated macrophages, stimulation of Fas receptor minimally enhances lipopolysaccharide-induced M1 cytokine production and significantly limits M2 cytokine production. These data support the hypothesis that Fas-mediated signaling is important for an early ethanol-induced proinflammatory response but limits the profibrogenic response, regulating collagen production in response to chronic ethanol.