Complement factor H modulates lipoprotein clearance in AMD

摘要 在发达国家，年龄相关性黄斑变性（AMD）是导致不可逆失明的主要原因 对于老年人来说，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质的视网膜下色素上皮（RPE）沉积物。这些沉积物包含 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/转运和补体失调导致 AMD 的部分原因是 缺乏忠实地概括该疾病的这些致病方面的年龄依赖性体内模型。的 拟议研究的目的是利用我们拥有的新型 AMD 动物模型获得的数据 开发的。这些模型涉及高龄、补体失调和脂质/胆固醇扰动， 所有已知的导致人类 AMD 风险的因素。具体来说，我们根据最 与 AMD 风险相关的复制遗传风险变异，氨基处酪氨酸 (Y) 替换为组氨酸 (H) 人补体因子 H 的酸位 402 (Y402H)，替代补体的可溶性调节剂 途径。只有表达人类 H402 AMD 风险变异体 (CFH-H/H) 的小鼠才会出现 AMD 表型 与表达正常人 Y402 CFH 变体的小鼠相比。值得注意的是，AMD 表型 与血液和 RPE/布鲁赫膜 (BrM)/脉络膜中脂蛋白水平的变化相关 复杂。因此，我们是第一个观察到 Y402H 多态性体内功能结果的人， 促进老年小鼠的 AMD 样病理学并影响脂蛋白水平。此外，我们还分析了 ApoA-1 含有从 BrM 和老年人类捐赠者血浆中分离出的脂蛋白，并发现它们具有非常 不同的蛋白质组成。最显着的差异是 ApoB 浓度显着升高 BrM 中的 ApoE 和 ApoE，已知它们可与糖胺聚糖 (GAG) 结合并可促进脂蛋白的形成 沉积到 BrM GAG 上；可能引发导致 RPE 功能障碍/死亡的下游效应。 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) 样脂蛋白分泌有助于 AMD 的发展，并受 CFH 调节。因此， 拟议研究的目标是使用我们的新型 AMD 动物模型和人类诱导多能性 干细胞衍生的 RPE (1) 阐明 CFH 调节 AMD 中脂蛋白清除的机制 (2) 测试增强正常 CFH 和/或增强局部 HDL 清除是否有效 治疗 AMD 的可行策略。 这些研究的结果将机械地确定两个风险因素 CFH 和 AMD 中的脂蛋白，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.