BCAT1 Activation Reprograms Branched-Chain Amino Acid Metabolism and Epigenetically Promotes Inflammation in Diabetic Retinopathy.

Purpose: To investigate how branched-chain amino acid (BCAA) metabolism is remodeled and to determine its contribution to diabetic retinopathy progression.

Methods: We analyzed Bcat1 and Bcat2 expression in the retina using single-cell sequencing data and immunofluorescence. Bcat1-mediated remodeling of BCAA metabolism was assessed via targeted metabolomics in Müller cells. We performed chromatin immunoprecipitation (ChIP) to examine histone methylation at inflammatory gene promoters. Additionally, we utilized RNA sequencing and kinase screening assays to delineate phosphorylation regulation of Bcat1 activity. In vivo, we established diabetic mouse models and treated them with Bcat1-specific inhibitor to evaluate retinal inflammation and vascular leakage.

Results: Bcat1 was predominantly expressed in Müller cells and exhibited increased activity under diabetic conditions, leading to a remodeling of BCAA catabolism and upregulation of inflammatory genes (interleukin 6 [Il6] and tumor necrosis factor-α [Tnf-α]). Bcat1 activity was negatively regulated by polo-like kinase 4 (Plk4)-mediated phosphorylation at threonine 333. In high glucose-treated Müller cells, elevated Bcat1 activity reduced α-ketoglutarate (α-KG), a critical substrate for histone demethylation reactions, resulting in higher histone H3 lysine 4 trimethylation (H3K4me3) levels at inflammatory gene promoters, and further boosted retinal inflammation. Treatment with chemical Bcat1 inhibitors (BAY-069 and ERG240) significantly reduced inflammatory gene expression and vascular leakage in diabetic retinas in vivo.

Conclusions: Bcat1 activation mediates BCAA metabolism remodeling in Müller cells and epigenetically induces retinal inflammation, which offers a potential therapeutic target for diabetic retinopathy. Diabetes and diabetic retinopathy are potentially driven not only by hyperglycemia but also by dysregulated amino acid metabolism.