The Commensal Microflora Suppresses Liver Fibrosis

描述（由申请人提供）： 肝纤维化是由各种病因引起的慢性肝损伤的结果，包括酗酒、肥胖或病毒性肝炎。慢性肝病可能进展为肝硬化，这是一种终末期疾病，是美国，特别是退伍军人发病率和死亡率的主要原因。慢性肝病患者表现为肠道细菌过度生长和生态失调。它们还表明肠道通透性增加，疾病严重程度与细菌产物的全身水平相关。虽然实验性肝纤维化依赖于肠道来源的细菌产物，但肠道微生物菌群对肝纤维化的确切贡献尚不清楚。由于病原体相关分子模式（PAMPs）与先天免疫系统的相互作用也可以赋予宿主保护作用，因此我们将无菌小鼠置于肝纤维化实验模型中。我们实验室的结果表明，与常规小鼠相比，无菌小鼠显示出加重的肝纤维化。无菌小鼠的肝脏具有抗氧化剂热休克蛋白（Hsp）-25的表达减少，更多的氧化应激和更高的细胞凋亡率。本申请的重点是进一步表征肠道微生物菌群与慢性肝病进展之间的关系。我们假设肠道菌群是氧化应激的重要抑制剂，因此在小鼠慢性肝损伤后纤维化。我们的实验方法是将毒素诱导和胆汁淤积性肝纤维化的小鼠模型应用于无菌和常规小鼠，并研究细菌微生物群对慢性肝病的贡献（目的1）。然后，我们将评估微生物群改善实验性肝纤维化的机制。重点将放在热休克蛋白25，这是低表达的肝细胞无菌小鼠相比，传统的小鼠，并具有抗氧化性能。我们将测试细菌产物或代谢产物在肝细胞中诱导Hsp25的新概念。我们还将关注肝星状细胞，以解释无菌条件下纤维化增加的表型（目的2）。然后，我们将用一种细菌代谢物补充无菌小鼠，或用吲哚-3-丙酸（IPA）合成细菌定植无菌小鼠，并使其经历实验性肝纤维化。将选择预防和治疗方法。细菌产物或代谢产物可能直接或通过诱导抗氧化分子进入肝脏而赋予抗氧化特性（目的3）。我们相信，这些研究将提供重要的见解的贡献，肠道微生物对肝纤维化。这将在目前的范式中建立一个新的转变，即所有易位的细菌及其产物都对肝损伤和慢性肝病有害。最终，这种方法可能会为慢性肝病患者带来新的治疗靶点和疗法。

DESCRIPTION (provided by applicant): Liver fibrosis is the result of chronic liver damage from various etiologies including alcohol abuse, obesity, or viral hepatitis. Chronic liver disease may progress to cirrhosis, an end stage disease and major cause of morbidity and mortality in the United States and in particular among Veterans. Patients with chronic liver disease show intestinal bacterial overgrowth and dysbiosis. They also demonstrate increased intestinal permeability, and disease severity correlates with systemic levels of bacterial products. Although experimental liver fibrosis is dependent on gut derived bacterial products, yet the exact contribution of the commensal microflora to liver fibrosis is unknown. Since the interaction of pathogen associated molecular patterns (PAMPs) with the innate immune system can also confer protection to the host, we subjected germfree mice to experimental models of liver fibrosis. Results from our laboratory demonstrate that germfree mice show exacerbated liver fibrosis as compared with conventional mice. Livers of germfree mice have a decreased expression of the antioxidant heat shock protein (Hsp)-25, more oxidative stress and a higher rate of apoptosis. The focus of this application is to further characterize the relationship between the intestinal microflora and the progression of chronic liver disease. We hypothesize that the commensal microflora is an important suppressor of oxidative stress and hence fibrosis upon chronic liver injury in mice. Our experimental approach is to apply mouse models of toxin-induced and cholestatic liver fibrosis to germfree and conventional mice and to investigate the contribution of the bacterial microflora to chronic liver disease (Aim 1). We will then assess the mechanism by which the microflora ameliorates experimental liver fibrosis. The focus will be on Hsp25 that is lower expressed in hepatocytes of germfree mice as compared with conventional mice and that has antioxidant properties. We will test the new concept that bacterial products or metabolites induce Hsp25 in hepatocytes. We will also focus on hepatic stellate cells to explain the phenotype with increased fibrosis under germ-free conditions (Aim 2). We will then supplement germfree mice with one bacterial metabolite or colonize germ-free mice with indole-3-propionic acid (IPA) synthesizing bacteria, and subject them to experimental liver fibrosis. A preventive and therapeutic approach will be chosen. Bacterial products or metabolites might confer antioxidant properties directly or via the induction of antioxidant molecules to the liver (Aim 3). We believe these studies will provide important insights into the contribution of the commensal microflora to liver fibrosis. This will establish a novel shift in the current paradigm that all translocated bacteria and their products are bad for liver injury and chronic liver disease. Eventually this approach might lead to new therapeutic targets and therapies for patients with chronic liver disease.