BCAT1 activation reprograms branched-chain amino acids (BCAAs) metabolism and epigenetically promotes inflammation in diabetic retinopathy

Branched-chain amino acids (BCAAs) metabolism is dysregulated in diabetic retinopathy. Retina Müller cells maintain various metabolic processes and immune homeostasis. Here, we found that branched-chain aminotransferase 1 (BCAT1), which catalyzes the first step of BCAAs metabolism, was predominantly expressed in retina Müller cells. Under diabetic conditions, BCAT1 showed increased enzymatic activity in Müller cells, which drove the remodeling of BCAAs catabolism, and upregulated the expression of inflammatory genes such as interleukin 6 (IL6) and tumor necrosis factor-a (TNF-a). Mechanistically, BCAT1 activity was negatively regulated by Polo-like kinase 4 (PLK4) via phosphorylation at threonine 333. Increased BCAT1 activity further reduced a-ketoglutarate (a-KG) levels, a critical substrate for histone demethylation, resulting in higher H3K4me3 levels at inflammatory gene promoters, and further upregulated inflammation genes. Treatment with chemical BCAT inhibitor significantly reduced inflammatory gene expression and vascular leakage in diabetic retinas in vivo. These findings reveal a crucial role of BCAT1 in metabolic remodeling and inflammatory regulation, which indicates that BCAT1 could be used as a target for diabetic retinopathy. Overall design: To investigate gene expression in the retinas of wild-type and db/db mice

支链氨基酸（Branched-chain amino acids, BCAAs）代谢在糖尿病视网膜病变中存在失调现象。视网膜穆勒细胞（Retina Müller cells）可维持多种代谢过程与免疫稳态。本研究发现，催化支链氨基酸代谢第一步反应的支链氨基酸转氨酶1（branched-chain aminotransferase 1, BCAT1）主要在视网膜穆勒细胞中表达。在糖尿病病理条件下，穆勒细胞内的BCAT1酶活性显著升高，推动支链氨基酸分解代谢发生重构，并上调白细胞介素6（interleukin 6, IL6）、肿瘤坏死因子-α（tumor necrosis factor-α, TNF-α）等炎症基因的表达。机制层面，Polo样激酶4（Polo-like kinase 4, PLK4）可通过对苏氨酸333位点的磷酸化修饰，负向调控BCAT1的活性。升高的BCAT1活性进一步降低了α-酮戊二酸（α-ketoglutarate, α-KG）的水平——而α-KG是组蛋白去甲基化的关键底物，这会导致炎症基因启动子区域的H3K4me3水平升高，进而进一步促进炎症基因的表达。体内实验显示，使用BCAT化学抑制剂可显著降低糖尿病小鼠视网膜组织中的炎症基因表达与血管渗漏情况。本研究揭示了BCAT1在代谢重构与炎症调控中的关键作用，表明BCAT1可作为糖尿病视网膜病变的潜在治疗靶点。整体实验设计：为探究野生型与db/db小鼠视网膜的基因表达特征。