Complement factor H modulates lipoprotein clearance in AMD

摘要 在发达国家，老年性黄斑变性(AMD)是导致不可逆性失明的主要原因 在老年人中，也有大多数患者没有治疗方法。早期AMD的特点是 形成富含蛋白质和脂肪的视网膜下色素上皮(RPE)沉积物。这些存款中含有 许多成分可归因于补体级联和脂蛋白的激活 新陈代谢。此外，补体和脂蛋白途径基因已经独立地与 AMD的多种方式，包括遗传风险关联和流行病学研究。努力了解如何 脂质代谢/运输和补体失调导致的AMD在一定程度上受到 缺乏与年龄相关的体内模型来忠实地概括疾病的这些致病方面。这个 拟议研究的目的是利用我们已有的AMD新动物模型得出的数据 发展起来的。这些模型引发了高龄、补体失调和血脂/胆固醇紊乱， 所有已知的人类AMD风险的贡献者。具体地说，我们基于大多数 与AMD风险相关的复制遗传风险变异，氨基酸中酪氨酸(Y)到组氨酸(H)的替换 替代补体的可溶性调节因子人补体因子H的402位(Y402H) 路径。只有表达人类H402 AMD风险变体(CFH-H/H)的小鼠才会出现AMD表型 与表达正常人类Y402 CFH变体的小鼠进行比较。值得注意的是，AMD的表型 与血液和RPE/Bruch膜(BRM)/脉络膜中脂蛋白水平的变化有关 很复杂。因此，我们首次在体内观察到Y402H多态的功能后果，即 促进类似AMD的病理，并影响老龄小鼠的脂蛋白水平。此外，我们还分析了载脂蛋白A-1 含有从老年人类捐赠者的BRM和血浆中分离出来的脂蛋白，发现它们具有非常 不同的蛋白质组成。最显著的区别是载脂蛋白B的浓度明显更高 和BRM中的ApoE，已知它们与糖胺多聚糖(GAG)结合并能促进脂蛋白 沉积在BRM GAG上；可能启动下游效应，导致RPE功能障碍/死亡。 基于这些观察和其他研究，我们假设异常的RPE衍生的高密度 脂蛋白(HDL)样脂蛋白的分泌有助于AMD的发展，并受CFH的调节。因此， 拟议研究的目标是使用我们新的AMD动物模型和人类诱导的多能性 干细胞来源的RPE：(1)阐明CFH调节AMD脂蛋白清除的机制 发病机制和(2)测试是否增加正常CFH和/或增强局部高密度脂蛋白清除 治疗AMD的可行策略。 这些研究的结果将机械地决定两个风险因素的相互作用，CFH和 并为这些因素作为AMD的治疗靶点建立概念证明。

ABSTRACT In developed countries, age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the elderly and there are no treatments for the majority of patients. Early AMD is characterized by the formation of protein- and lipid-rich, sub-retinal pigmented epithelium (RPE) deposits. These deposits contain many constituents that are attributable to both the activation of the complement cascade and lipoprotein metabolism. In addition, complement and lipoprotein pathway genes have been independently associated with AMD in multiple ways including genetic risk association and epidemiological studies. Efforts to understand how lipid metabolism/trafficking and complement dysregulation contribute to AMD have been limited in part by the lack of age-dependent in vivo models that faithfully recapitulate these pathogenic aspects of the disease. The aim of the proposed studies is to leverage data derived using novel animal models of AMD that we have developed. These models invoke advanced age, complement dysregulation and lipid/cholesterol perturbation, all known contributors to human AMD risk. Specifically, we generated mouse models based on the most replicated genetic risk variant associated with AMD risk, the tyrosine (Y) to histidine (H) substitution at amino acid position 402 (Y402H) of human complement factor H, the soluble regulator of the alternative complement pathway. Only mice expressing the human H402 AMD risk variant (CFH-H/H) develop an AMD phenotype compared to mice expressing the normal human Y402 CFH variant. Significantly, the AMD phenotype correlates with changes in lipoprotein levels in blood, and in the RPE/Bruch’s membrane (BrM)/choroid complex. Thus, we are the first to observe a functional consequence of the Y402H polymorphism in vivo, which promotes an AMD-like pathology and affects lipoprotein levels in aged mice. In addition, we analyzed ApoA-1 containing lipoproteins isolated from BrM and plasma of elderly human donors and found they have very different protein compositions. The most striking difference is the significantly higher concentration of ApoB and ApoE in BrM, which are known to bind to glycosaminoglycans (GAGs) and could promote lipoprotein deposition onto BrM GAGs; likely initiating downstream effects that contribute to RPE dysfunction/death. Based on these observations and other studies we hypothesize that aberrant RPE-derived high-density lipoprotein (HDL)-like lipoprotein secretion contributes to AMD development, and is modulated by CFH. Thus, the goals of the proposed studies are to use our novel animal models of AMD and human induced pluripotent stem cell-derived RPE to (1) elucidate the mechanism by which CFH modulates lipoprotein clearance in AMD pathogenesis and (2) to test whether augmenting normal CFH and/or enhancing local HDL clearance are viable strategies for treating AMD. Outcomes from these studies will mechanistically determine the interaction of two risk factors, CFH and lipoproteins in AMD and establish proof of concept for these factors as therapeutic targets for AMD.