糖尿病视网膜病变(DR)患者数占糖尿病的1/3，是工作人群第一致盲眼病。临床发现控糖好的糖尿病人仍发生DR，葡萄糖外的代谢物能否诱发DR尚不清楚。前期代谢组检测发现DR早期小鼠视网膜和血清中琥珀酸等代谢物含量变化，单细胞测序显示代谢物波动伴随视网膜小胶质细胞表达促炎因子增加；琥珀酸干预小胶质细胞、体外培养视网膜和体内灌胃结果提示琥珀酸诱发视网膜小胶质细胞活化；同时，琥珀酸含量在视网膜、血清和肝脏代谢中联动，且肝脏特异性敲除Sdhaf4引发视网膜中琥珀酸增加和促炎因子表达升高。由此推测，Sdhaf4通过肝脏代谢物琥珀酸经血循环至视网膜，并活化小胶质细胞。本项目将通过细胞和动物水平发现琥珀酸活化视网膜小胶质细胞；运用Sdhaf4肝脏敲除小鼠揭示机体代谢循环琥珀酸连接肝脏-视网膜轴；并通过琥珀酸受体、ROS和蛋白琥珀酰化通路探究琥珀酸作用机制。本项目顺利开展将为肝脏代谢物调控DR研究提供新思路。

The amount of patients with diabetic Retinopathy (DR) accounts for 1/3 of diabetes and is the leading cause for blinding among working people. It is clinically found that diabetic patients with good blood glucose control still develop DR due to "metabolic memory", and it is unclear whether metabolic intermediates other than glucose could induce DR. Our preliminary metabolomic results revealed differential changes in metabolites, such as succinic acid, in the retina and serum of mice with early-stage DR. Single-cell sequencing showed that metabolic fluctuations accompanied with the expression of proinflammatory factors in retinal microglia cells. Succinic acid interfered with microglia cell line, retina culture in vitro and gavage experiments in vivo suggest that succinic acid induces the activation of retinal microglia and the production of pro-inflammatory factors. Interestingly, the content of succinic acid in retina was closely linked to its metabolism and transportation in liver and serum. Moreover, liver-specific knockout of succinate dehydrogenation enzyme assembly factor 4 (Sdhaf4) caused an increase of succinic acid in the retina, accompanied by an increase in the expression of pro-inflammatory factors in retina. According to these preliminary data, our hypothesis is that Sdhaf4 isolated by GWAS in diabetic patients has an effect on retina through liver metabolite succinic acid via blood circulation, which targets retinal microglia activation and produces inflammatory factors. This project is to discover and verify the abnormal increase of succinic acid could induce retinal microglia activation at cellular, animal, and clinical levels; and to reveal the how liver dispose of excess succinic acid and what outcomes might be caused in retina crosstalk; last but not least, to explore the mechanism of succinic acid function on microglia activation through GPR19, ROS or protein succinylation pathways. This project is to provide new ideas for the regulation of intermediate metabolite cycles on DR, and to provide new approach to predict DR development.