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异之一。 States.风险增加的原因归因于等位基因变异的隐性遗传， 载脂蛋白L1（APOL 1）基因。这些APOL 1变异体，称为G1和G2，在它们的染色体上不引起CKD。 但CKD是由遗传的遗传风险加上暴露于触发环境的组合引起的。 压力源（基因-环境相互作用）。尽管CKD风险与APOL 1变异的相关性超过 10年前，人们对APOL 1在肾脏中的生物学功能及其发病机制进行了研究， 疾病应激源的研究尚不清楚。我们的长期目标是了解遗传学和生物化学 这些APOL 1多态性引起的非裔美国人CKD的机制。为了实现这一目标，我们 正在研究HIV相关肾病（HIVAN），CKD最强相关的APOL 1变体，以及 只有环境应激源已知的CKD（HIV感染）。HIVAN是一种理想的疾病模型 生物化学途径和细胞事件由APOL 1功能、病毒感染和CKD引起。我们最近 研究首次证明了常见的APOL 1等位基因（称为G 0）的功能， 防止HIVAN中足细胞损失。由于APOL 1风险是一种重复遗传特征，这表明 CKD可能部分由功能丧失过程（即G 0缺失）引起。在新的初步数据中， 似乎与含有HIV的胞内囊泡中的Toll样受体（TLR）相关，并促进信号传导 干扰素调节因子（IRF）-3启动的事件，这些过程在APOL 1风险中不存在 变体。方法将利用体外建立的HIV感染人足细胞系，体内建立HIVAN模型 和复制内源性人APOL 1表达的BAC-APOL 1转基因小鼠。目标将检查两者 足细胞对HIV感染的初始反应，以及HIVAN之间交叉的长期体内研究。 和评估对肾功能和病理学的影响的BAC-APOL 1转基因小鼠。这些研究还将 建立应激诱导的APOL 1表达的时间和幅度，改变先天性免疫缺陷的机制， 通过TLR至IRF-3/7信号传导的免疫激活，以及对足细胞表型（存活和细胞 粘附性）。将在足细胞中测试G 0保护作用对风险变体功能障碍的优势 以及共表达G 0和风险变体的小鼠模型。这些研究应该促进我们对 与APOL 1风险等位基因隐性遗传相关的功能获得与功能丧失机制，以及 诱导APOL 1表达以驱动应激反应的必要性。确定G 0的贡献 功能与风险变异性功能障碍将对进一步的治疗设计产生重要的临床影响，因为它将 确定替代G 0或抑制风险变体是否是更有效的策略。

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.