Department of Biomedical Engineering, Columbia University, New York, NY 10032, USA.
Jonas Children's Vision Care and the Bernard & Shirlee Brown Glaucoma Laboratory, Department of Ophthalmology, Columbia Stem Cell Initiative, Columbia University, New York, NY 10032, USA; Edward S. Harkness Eye Institute, New York-Presbyterian Hospital, New York, NY 10032, USA.
Am J Hum Genet. 2021 May 6;108(5):903-918. doi: 10.1016/j.ajhg.2021.04.006. Epub 2021 Apr 27.
Macular degeneration (MD) is characterized by the progressive deterioration of the macula and represents one of the most prevalent causes of blindness worldwide. Abnormal intracellular accumulation of lipid droplets and pericellular deposits of lipid-rich material in the retinal pigment epithelium (RPE) called drusen are clinical hallmarks of different forms of MD including Doyne honeycomb retinal dystrophy (DHRD) and age-related MD (AMD). However, the appropriate molecular therapeutic target underlying these disorder phenotypes remains elusive. Here, we address this knowledge gap by comparing the proteomic profiles of induced pluripotent stem cell (iPSC)-derived RPEs (iRPE) from individuals with DHRD and their isogenic controls. Our analysis and follow-up studies elucidated the mechanism of lipid accumulation in DHRD iRPE cells. Specifically, we detected significant downregulation of carboxylesterase 1 (CES1), an enzyme that converts cholesteryl ester to free cholesterol, an indispensable process in cholesterol export. CES1 knockdown or overexpression of EFEMP1, a variant of EGF-containing fibulin extracellular matrix protein 1 that is associated with DHRD and attenuated cholesterol efflux and led to lipid droplet accumulation. In iRPE cells, we also found that EFEMP1 has a hyper-inhibitory effect on epidermal growth factor receptor (EGFR) signaling when compared to EFEMP1 and may suppress CES1 expression via the downregulation of transcription factor SP1. Taken together, these results highlight the homeostatic role of cholesterol efflux in iRPE cells and identify CES1 as a mediator of cholesterol efflux in MD.
黄斑变性（MD）的特征是黄斑渐进性恶化，是全球最常见的致盲原因之一。视网膜色素上皮（RPE）中细胞内脂质滴的异常积累和富含脂质的物质的细胞周沉积物，称为玻璃膜疣，是不同形式的 MD 的临床标志，包括 Doyne 蜂窝状视网膜营养不良（DHRD）和年龄相关性 MD（AMD）。然而，这些疾病表型背后适当的分子治疗靶点仍难以捉摸。在这里，我们通过比较 DHRD 个体和其同基因对照的诱导多能干细胞（iPSC）衍生的 RPE（iRPE）的蛋白质组谱来解决这一知识空白。我们的分析和后续研究阐明了 DHRD iRPE 细胞中脂质积累的机制。具体来说，我们检测到羧酯酶 1（CES1）的显著下调，CES1 是将胆固醇酯转化为游离胆固醇的酶，胆固醇外排过程中必不可少。CES1 敲低或 EFEMP1 的过表达，EFEMP1 是一种与 DHRD 相关的 EGF 富含纤维连接蛋白细胞外基质蛋白 1 的变体，会减弱胆固醇外排并导致脂质滴积累。在 iRPE 细胞中，与 EFEMP1 相比，EFEMP1 对表皮生长因子受体（EGFR）信号具有超抑制作用，并且可能通过下调转录因子 SP1 来抑制 CES1 的表达。总之，这些结果突出了胆固醇外排在 iRPE 细胞中的稳态作用，并确定 CES1 是 MD 中胆固醇外排的介质。
