Microbiome and intestinal innate immune response in alcoholic liver disease

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Project Summary Alcohol abuse and alcohol-related diseases are a major medical burden in industrialized countries. Chronic alcoholism is associated with changes in the intestinal microbiome, increases in intestinal permeability, and elevated systemic levels of bacterial products. We have demonstrated quantitative (overgrowth) and qualitative dysbiotic changes in the intestinal microbiota in mouse models of chronic alcohol administration. A strong association exists between gut-derived bacterial products and progression of alcoholic liver diseases in several animal models, yet factors facilitating the onset of intestinal dysbiosis are unknown. Furthermore, how dysbiosis contributes to alcoholic liver disease beyond increasing intestinal permeability is also not known. Results from our laboratory suggest that suppression of gastric acid secretion and inhibition of the intestinal antimicrobial proteins regenerating-islet derived (Reg)-3b and Reg3g contribute to dysbiosis and liver disease following chronic ethanol feeding in mice. Furthermore, dysbiosis leads to deconjugation of intestinal bile acids in the proximal small intestine. Deconjugated bile acids are rapidly absorbed by nonionic diffusion in the jejunum, and a smaller amount of conjugated bile acids reaches the terminal ileum, which disrupts the enterohepatic circulation and results in increased hepatic bile acid synthesis. A larger bile acid pool contributes to more hepatocyte damage and alcoholic liver disease. The focus of this application is to characterize factors contributing to changes in the microbiota and to investigate how dysbiosis affects liver disease after chronic alcohol administration. We hypothesize that gastric acid suppression and alcohol-mediated inhibition of the antimicrobial Reg3 lectins modulate the intestinal microbiota. Dysbiosis in turn disrupts enterohepatic circulation of bile acids and increases the total bile acid pool, which enhances alcohol-induced liver damage. Our experimental approach is to use mouse models of chronic alcohol feeding to investigate the role of gastric acid in inducing intestinal dysbiosis and liver disease (Aim 1). We will also assess the functional contribution of the antimicrobial proteins Reg3b and Reg3g to changes in the microbiota composition, bacterial translocation and alcoholic liver disease (Aim 2). We will then determine the consequences of dysbiotic microbiome changes by focusing on bile acid metabolism (Aim 3). We believe these studies will provide novel insights into the contribution of the microbiota and its metabolites to alcoholic liver disease. New strategies will evolve to prevent or ameliorate alcoholic liver disease in patients.