Impaired RPE Mitochondrial Energetics Leads Subretinal Fibrosis in Neovascular Age-related Macular Degeneration

Subretinal fibrosis permanently impairs the vision of patients with neovascular age-related macular degeneration. Despite emerging evidence revealing the association between disturbed metabolism in retinal pigment epithelium (RPE) and subretinal fibrosis, the underlying mechanism remains unclear. In the present study, single-cell RNA sequencing revealed, prior to subretinal fibrosis, genes in mitochondrial fatty acid oxidation are downregulated in the RPE lacking very low-density lipoprotein receptor (VLDLR), especially the rate-limiting enzyme carnitine palmitoyltransferase 1A (CPT1A). We found that overexpression of CPT1A in the RPE of Vldlr-/- mice suppresses epithelial-to-mesenchymal transition and fibrosis. Mechanistically, TGF2 induces fibrosis by activating a Warburg-like effect, i.e. increased glycolysis and decreased mitochondrial respiration through ERK-dependent CPT1A degradation. Moreover, VLDLR blocks the formation of the TGF receptor I/II complex by interacting with unglycosylated TGF receptor II. In conclusion, VLDLR suppresses fibrosis by attenuating TGF2-induced metabolic reprogramming, and CPT1A is a potential target for treating subretinal fibrosis. The RPE-choroid tissues of WT mice and Vldlr-/- mice at the age of 1 month and 2 months were used for scRNA seq.视网膜下纤维化会永久性损伤新生血管性年龄相关性黄斑变性患者的视力。尽管已有越来越多的研究证实，视网膜色素上皮（retinal pigment epithelium, RPE）代谢紊乱与视网膜下纤维化存在关联，但其潜在致病机制仍未明确。本研究通过单细胞RNA测序发现，在视网膜下纤维化发生前，缺失极低密度脂蛋白受体（very low-density lipoprotein receptor, VLDLR）的视网膜色素上皮细胞中，线粒体脂肪酸氧化相关基因的表达显著下调，其中限速酶肉碱棕榈酰转移酶1A（carnitine palmitoyltransferase 1A, CPT1A）的下调尤为突出。我们进一步发现，在Vldlr-/-小鼠的视网膜色素上皮细胞中过表达CPT1A，可有效抑制上皮间质转化（epithelial-to-mesenchymal transition, EMT）与纤维化进程。机制层面研究显示，TGF2可通过激活沃伯格样效应诱导纤维化：即通过ERK通路依赖的CPT1A降解，增强糖酵解水平并削弱线粒体呼吸功能。此外，VLDLR可通过与未糖基化的TGF受体II结合，阻断TGF受体I/II复合物的形成。综上，VLDLR可通过削弱TGF2诱导的代谢重编程抑制纤维化，而CPT1A或可成为治疗视网膜下纤维化的潜在药物靶点。本研究采用1月龄与2月龄野生型（WT）小鼠及Vldlr-/-小鼠的视网膜色素上皮-脉络膜组织开展单细胞RNA测序。