Project 4: Impact of the Gut Microbiome on Liver Innate Immunity and Skeletal Function

项目4--项目摘要 与生俱来的免疫反应有助于维持与共生肠道的平衡平衡关系。 微生物区系，但重要的是对寄主生理有强大的间接影响。肠道微生物区系免疫调节剂 行为影响骨重塑，但其机制尚不清楚。骨重建是一个持续的过程 其中骨骼通过骨吸收、破骨细胞和骨形成的动作动态更新 成骨细胞。当破骨细胞的作用超过成骨细胞时，就会发生骨骼退化。 幼年-成年无菌(GF)小鼠骨量增加，这种情况在肠道定植后被逆转 来自无特定病原体(SPF)小鼠的微生物区系。SPF小鼠体内共生微生物区系增强 破骨细胞生成和抑制成骨细胞生成，从而导致骨丢失。有趣的是，肠道微生物区系效应 对骨骼重塑的影响似乎不是由肠道内的免疫反应介导的，而是反映 肠道和肝脏之间的沟通。与GF小鼠相比，SPF小鼠的炎性反应增加 细胞因子在肝脏，但不在回肠。SPF小鼠肝脏引流中的炎性单核细胞也有增加 淋巴结，但不是肠系膜淋巴结。这些发现支持一种新的信号轴 调节骨骼重塑的肠道和肝脏。科学前提得到了初步数据的支持，这些数据表明 MyD88依赖的信号成分增加和肝细胞相关的先天免疫因子 在SPF小鼠的肝脏中表达上调，与GF小鼠相比。共生肠道微生物区系增加肝脏和 血清Lipocalin-2(Lcn2)水平，这是一种控制骨重建的候选先天免疫因子。 这项研究将检验循环肠道微生物区系衍生配体刺激肝细胞的总体假设。 MyD88依赖的调节骨重建的天然免疫血清因子的合成。肝细胞特异性 缺失和髓系特异性缺失小鼠将被安置在GF和SPF条件下，以及蛋白质组学、微生物组 将应用测序和骨免疫学研究技术。目标1将检验这一假设 肠道微生物区系通过MyD88刺激肝脏天然免疫及相关血清因子的合成 肝细胞和肝巨噬细胞中的依赖信号。目标2将检验肠道微生物区系的假设 刺激肝细胞来源的Lcn2增强破骨细胞生成，抑制成骨细胞生成。 拟议的研究将确定共生肠道微生物区系与肝脏天然免疫之间的关系。 反应和骨骼重塑。这项研究具有临床意义，因为驱动连续 年轻成人骨骼中的骨丢失是未知的。患有肠道和肝脏疾病的个体增加了 骨质疏松症的流行，这进一步强调了肠道、肝脏和骨骼之间的关系。

Project 4 – Project Summary The innate immune response helps maintain a balanced homeostatic relationship with the commensal gut microbiota, but importantly has potent indirect effects on host physiology. Gut microbiota immunomodulatory actions impact bone remodeling, but the mechanisms are unclear. Bone remodeling is the continuous process in which the skeleton is dynamically renewed by the actions of bone resorbing osteoclasts and bone forming osteoblasts. Skeletal deterioration occurs when the action of the osteoclasts exceeds those of the osteoblasts. Young-adult germfree (GF) mice have increased bone mass, which is reversed upon colonization with gut microbiota from specific pathogen free (SPF) mice. Commensal microbiota in SPF mice enhance osteoclastogenesis and suppress osteoblastogenesis, which drives bone loss. Intriguingly, gut microbiota effects on bone remodeling do not appear to be mediated by immune responses within the gut, but rather reflect communication between the gut and liver. When compared to GF mice, SPF mice have increased inflammatory cytokines in the liver, but not in the ileum. SPF mice also have enhanced inflammatory monocytes in liver draining lymph nodes, but not the mesenteric lymph nodes. These findings support a novel signaling axis between the gut and liver that regulates bone remodeling. The scientific premise is supported by preliminary data showing that Myd88-dependent signaling components were increased and hepatocyte-associated innate immune factors were upregulated in the livers of SPF compared to GF mice. Commensal gut microbiota increased liver and serum levels of lipocalin-2 (LCN2), which is a candidate innate immune factor that controls bone remodeling. This research will test the overall hypothesis that circulating gut microbiota-derived ligands stimulate liver cell MyD88-dependent synthesis of innate immune serum factors that regulate bone remodeling. Hepatocyte-specific null and myeloid-specific null mice will be housed under GF and SPF conditions, and proteomics, microbiome sequencing, and osteoimmunology research techniques will be applied. Aim 1 will test the hypothesis that the gut microbiota stimulates liver innate immunity and the synthesis of related serum factors through MyD88- dependent signaling in hepatocytes and liver macrophages. Aim 2 will test the hypothesis that gut microbiota stimulation of hepatocyte-derived LCN2 enhances osteoclastogenesis and suppresses osteoblastogenesis.!The proposed studies will determine the relationship between the commensal gut microbiota, liver innate immune response, and bone remodeling. This research is clinically relevant because the mechanisms driving continuous bone loss in the young adult skeleton are unknown. Individuals with gut and liver disorders have an increased prevalence of osteoporosis, which further underscores the relationship between the gut, liver and bone.