Intracellular functions of APOL1 in the kidney

摘要 非裔美国人的慢性肾病(CKD)是美国最大的种族健康差距之一 各州。风险增加的原因被归因于等位基因变异的隐性遗传 载脂蛋白L1基因(APOL1)。这些被称为G1和G2的APOL1变体不会在其 自己的，但慢性肾脏病是由遗传遗传风险和暴露在触发环境中的组合引起的 应激源(一种基因-环境相互作用)。尽管CKD风险与APOL1变异体的关联超过 10年前，APOL1在肾脏中的生物学功能及其发病机制 疾病应激源的作用尚不清楚。我们的长期目标是了解遗传学和生物化学 这些APOL1基因多态性导致非裔美国人慢性肾脏病的机制。为了实现这一目标，我们 正在研究艾滋病毒相关性肾病(HIVAN)，这是CKD相关性最强的APOL1变体，以及 只有在已知环境应激源(艾滋病毒感染)的情况下，CKD才会发生。HIVAN是一种理想的解剖疾病模型 与APOL1功能、病毒感染和慢性肾脏病交叉的生化途径和细胞事件。我们最近 研究首次证明了常见的APOL1等位基因，即G0，在提供 在HIVAN中保护足细胞免受损失。由于APOL1风险是一种隐性遗传特征，这表明 CKD可能部分是由功能丧失过程(即G0缺失)引起的。在新的初步数据中，G0 似乎与含有HIV的细胞内囊泡中的Toll样受体(TLRs)有关，并促进信号转导 由干扰素调节因子(IRF)-3启动的事件，这些过程不存在APOL1风险 变种。方法将建立的HIV体外感染人足细胞系、体内HIVAN模型 以及复制内源性人APOL1表达的BAC-APOL1转基因小鼠。AIMS将审查这两个问题 足细胞对HIV感染的初步反应，以及HIVAN之间杂交的长期体内研究 并评价BAC-APOL1转基因小鼠对肾功能和病理的影响。这些研究也将 建立应激源诱导的APOL1表达的时间和幅度，以及先天改变的机制 通过TLRs对IRF-3/7信号的免疫激活及其对足细胞表型(存活和细胞)的影响 附着力)。G0保护作用对风险变异功能障碍的优势将在足细胞中进行测试 以及共同表达G0和风险变体的小鼠模型。这些研究应该会促进我们对 与APOL1风险等位基因隐性遗传相关的获得和功能丧失机制，以及 诱导APOL1表达以驱动应激反应的必要性。确定G0的贡献 功能与风险变异功能障碍将对进一步的治疗设计产生重要的临床影响，正如它将 确定替换G0或抑制风险变量是否为更有效的策略。

ABSTRACT Chronic kidney disease (CKD) in African Americans is one of the largest racial health disparities in the United States. The cause for the increased risk has been attributed to recessive inheritance of allelic variants in the gene for apolipoprotein L1 (APOL1). These APOL1 variants, known as G1 and G2, do not cause CKD on their own, but CKD is caused by a combination of the inherited genetic risk plus exposure to a triggering environmental stressor (a gene-environment interaction). Despite the association of CKD risk with APOL1 variants more than ten years ago, the biological function of APOL1 in the kidney and the mechanism of pathogenesis in the setting of a disease stressor remain unclear. Our long-term goal is to understand the genetics and biochemical mechanism of CKD in African Americans caused by these APOL1 polymorphisms. To accomplish this goal, we are studying HIV-associated nephropathy (HIVAN), the CKD most strongly associated APOL1 variants, and the only CKD where the environmental stressor is known (HIV infection). HIVAN is an ideal disease model to dissect biochemical pathways and cellular events intersected by APOL1 function, viral infection, and CKD. Our recent studies have demonstrated, for the first time, a function for the common APOL1 allele, known as G0, in providing protection against podocyte losses in HIVAN. Since APOL1 risk is a recessively inherited trait, this suggests CKD may be caused, in part, by a loss-of-function process (i.e. absence of G0). In new preliminary data, G0 appears to associate with Toll-like receptors (TLRs) in intracellular vesicles containing HIV and facilitate signaling events initiated by interferon regulatory factor (IRF)-3, and these processes were absent with the APOL1 risk variants. Methods will use established in vitro HIV infection of human podocyte cell lines, in vivo models of HIVAN and BAC-APOL1 transgenic mice that replicate endogenous human APOL1 expression. Aims will examine both initial response to HIV infection in podocytes, and long-term in vivo studies of intercrosses between the HIVAN and BAC-APOL1 transgenic mice evaluating effects on renal function and pathology. These studies also will establish temporal and magnitude of stressor-induced APOL1 expression, the mechanism of the altered innate immune activation through TLRs to IRF-3/7 signaling, and effect on podocyte phenotype (survival and cell adhesion). The dominance of the G0 protective effect over the risk variant dysfunction will be tested in podocytes and mouse models co-expressing G0 and the risk variants. These studies should advance our understanding of gain- versus loss-of-function mechanism associated with the recessive inheritance of APOL1 risk alleles, and the necessity of induced APOL1 expression to drive stress responses. Determining the contribution of G0 function versus risk variant dysfunction will have important clinical impact on further therapy design, as it will establish whether replacement of G0 or suppression of the risk variants would be the more effective strategy.