Neonatal Fc Receptor (FcRn) Trafficking of Immune Complexes to the Lysosome as a Driver of Glomerulonephritis

摘要/项目摘要 免疫介导的肾脏疾病引起大量的发病率，并经常导致进行性肾衰竭。 免疫复合物（IC）已被发现在足细胞在各种免疫介导的肾脏疾病，但它 目前尚不清楚足细胞如何处理免疫复合物，以及免疫复合物在足细胞中的运输是否 足细胞加重肾小球肾炎。新生儿Fc受体（FcRn）正确分类和运输IC， 包括足细胞在内的多种细胞。FcRn也是将免疫复合物运输到溶酶体所必需的， 树突状细胞用于蛋白水解加工和在MHC II上呈递。在初步研究中，我们发现， 足细胞特异性敲除FcRn在两种免疫介导的肾炎模型中具有保护作用， 不是由免疫介导的机制赋予的。虽然在免疫系统中没有任何差异， 通过检查参数，我们发现凋亡性细胞死亡显著减少， 用免疫复合物处理的FcRn敲除（KO）足细胞中的凋亡途径， 肾毒性血清诱导后足细胞特异性FcRn基因敲除小鼠肾小球凋亡减少 肾炎（NTS）。此外，我们还发现溶酶体激活显著减少， 用免疫复合物处理的FcRn KO足细胞中的溶酶体酶。由于需要FcRn来运输 我们假设在免疫介导的肾炎中，FcRn定向运输， ICs与溶酶体的结合导致溶酶体功能障碍，内源性凋亡途径的上调， 足细胞死亡为了验证这一假设，我们将直接检查WT和WT中的溶酶体结构和功能。 使用先进的成像技术和生物化学方法检测免疫激发后的FcRn KO足细胞 方法.我们还将研究FcRn介导的免疫复合物向溶酶体的运输是否导致了免疫复合物的死亡。 溶酶体渗透性增加和溶酶体组织蛋白酶渗漏到胞质溶胶中导致降解 线粒体膜完整性，细胞色素c的泄漏和内在凋亡途径的上调。 我们将测试FcRn的足细胞特异性敲除是否导致溶酶体活化降低和改善。 诱导免疫介导的肾病（NTS）后体内足细胞中的溶酶体功能，以及是否 这又导致较少的凋亡性细胞死亡、增加的存活足细胞数量和较轻的疾病 如通过功能和组织学参数评估的。由于溶酶体组织蛋白酶的上调与 在狼疮性肾炎较严重的患者中，我们还将检测足细胞是否特异性敲除FcRn 在狼疮性肾炎的自发小鼠模型中改善这种疾病。总体而言，拟议的工作 将为FcRn介导的足细胞中免疫复合物的运输提供新的见解， 创建靶向治疗以减缓或预防免疫介导的肾小球肾炎的进展。

Abstract/Project Summary Immune mediated kidney diseases cause substantial morbidity and often lead to progressive renal failure. Immune complexes (ICs) have been found in podocytes in a variety of immune mediated kidney diseases but it is not known how podocytes handle immune complexes and whether trafficking of immune complexes in podocytes exacerbates glomerulonephritis. The neonatal Fc receptor (FcRn) correctly sorts and traffics ICs in a variety of cells including podocytes. FcRn is also required to traffic immune complexes to the lysosome in dendritic cells for proteolytic processing and presentation on MHC II. In preliminary studies, we have found that podocyte specific knockout of FcRn protects in two models of immune mediated nephritis but that this protection is not conferred by an immune mediated mechanism. While there is no difference in any of the immune parameters examined, we have found that there is significantly less apoptotic cell death and upregulation of apoptotic pathways in FcRn knockout (KO) podocytes treated with immune complexes and significantly decreased apoptosis in the glomeruli of podocyte specific FcRn KO mice after induction of nephrotoxic serum nephritis (NTS). In addition, we have found significantly less lysosomal activation and less upregulation of lysosomal enzymes in FcRn KO podocytes treated with immune complexes. Since FcRn is required to traffic immune complexes to the lysosome, we hypothesize that in immune mediated nephritis, FcRn directed trafficking of ICs to the lysosome results in lysosomal dysfunction, upregulation of the intrinsic apoptotic pathway and podocyte death. To test this hypothesis we will directly examine lysosomal structure and function in WT and FcRn KO podocytes after an immune challenge using both advanced imaging techniques and biochemical methods. We will also examine whether FcRn mediated trafficking of immune complexes to the lysosome results in increased lysosomal permeability and leakage of lysosomal cathepsins into the cytosol causing degradation of mitochondrial membrane integrity, leakage of cytochrome c and upregulation of intrinsic apoptotic pathways. We will test whether podocyte specific knockout of FcRn results in decreased lysosomal activation and improved lysosomal function in podocytes in vivo after induction of immune mediated kidney disease (NTS) and whether this in turn results in less apoptotic cell death, an increased number of viable podocytes and less severe disease as assessed by functional and histologic parameters. Since upregulation of lysosomal cathepsins correlates with more severe lupus nephritis in patients, we will also examine whether podocyte specific knockout of FcRn ameliorates lupus nephritis in a spontaneous mouse model of this disease. Taken together, the proposed work will provide novel insights into FcRn mediated trafficking of immune complexes in podocytes and may allow for the creation of targeted therapies to slow or prevent progression of immune mediated glomerulonephritis.