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

项目4 -项目摘要 先天性免疫反应有助于维持与肠道平衡的稳态关系 微生物群，但重要的是对宿主生理学有潜在的间接影响。肠道微生物群免疫调节 作用影响骨重建，但其机制尚不清楚。骨重建是一个持续的过程 其中骨骼通过骨再吸收破骨细胞和骨形成的作用而动态更新 成骨细胞当破骨细胞的作用超过成骨细胞的作用时，就会发生骨退化。 年轻成年无菌（GF）小鼠的骨量增加，这在肠道定植后逆转 来自无特定病原体（SPF）小鼠的微生物群。SPF小鼠的共生菌群增强 破骨细胞生成并抑制导致骨丢失的成骨细胞生成。有趣的是，肠道微生物群的影响 对骨重建的影响似乎不是由肠道内的免疫反应介导的，而是反映了 肠道和肝脏之间的沟通。与GF小鼠相比，SPF小鼠的炎症反应增加， 肝脏中的细胞因子，但回肠中没有。SPF小鼠在肝脏引流中也有增强的炎性单核细胞 淋巴结，但不是肠系膜淋巴结。这些发现支持了一个新的信号轴之间的 调节骨骼重塑的器官初步数据显示， Myd 88依赖性信号成分增加，肝细胞相关先天免疫因子 与GF小鼠相比，SPF小鼠的肝脏中表达上调。肠道菌群增加肝脏和 脂质运载蛋白-2（LCN 2）的血清水平，LCN 2是控制骨重建的候选先天免疫因子。 这项研究将测试循环肠道微生物衍生配体刺激肝细胞的总体假设， MyD 88依赖性合成调节骨重建的先天免疫血清因子。肝细胞特异性 无效和骨髓特异性无效小鼠将在GF和SPF条件下饲养，并进行蛋白质组学、微生物组学和免疫组化。 测序和骨免疫学研究技术将被应用。目标1将检验以下假设： 肠道微生物群通过MyD 88刺激肝脏先天免疫和相关血清因子的合成， 肝细胞和肝巨噬细胞中的依赖性信号传导。目标2将检验肠道微生物群 刺激肝细胞衍生的LCN 2增强破骨细胞生成并抑制成骨细胞生成。的 拟议的研究将确定肠道微生物群，肝脏先天免疫， 反应和骨重建。这项研究是临床相关的，因为驱动连续的机制 年轻成年人骨骼中的骨丢失是未知的。患有肠道和肝脏疾病的个体 骨质疏松症的患病率，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.