Endothelial histone deacetylase 9 promotes diabetic retinopathy in mice by regulating endothelial–mesenchymal transition

Diabetic retinopathy (DR) is a common and specific microvascular complication of diabetes and the leading cause of blindness in working-age adults. Endothelial-mesenchymal transition (EndoMT) underlies various chronic vascular diseases, while histone deacetylase 9 (HDAC9) is involved in the pathological process of cardiovascular diseases, cerebrovascular diseases, autoimmune diseases, and breast cancer. Recent evidence has shown that HDAC9 promotes EndoMT, thereby affecting the progression of atherosclerotic disease. In this study, we investigated the critical role of HDAC9 in DR and the underlying mechanism. DR model was established in mice by injecting streptozotocin (STZ, 50 mg/kg) for 5 consecutive days. Blood glucose was monitored regularly and DR experiments were performed 12 weeks after modeling. We showed that the expression levels of HDAC9 were significantly elevated in the vitreous fluid of diabetic patients and the retinal endothelial cells of DR model mice. Knockdown of endothelial HDAC9 reduced EndoMT and alleviated DR pathology in vivo, whereas overexpression of HDAC9 exacerbated EndoMT in DR model mice. To elucidate the downstream target genes of HDAC9 implicated in DR, we conducted integrated ChIP-seq and RNA-seq analysis of the retina in STZ-induced retinopathy and established that HDAC9 was involved in the transcriptional regulation of annexin A2 (ANXA2). We demonstrated that HDAC9 was bound to the promoter region of ANXA2, leading to the downregulation of ANXA2 expression in high glucose-treated human retinal microvascular endothelial cells and STZ-induced DR model mice. Overexpression of ANXA2 significantly reduced the EndoMT process in STZ-induced DR model mice. Collectively, our results demonstrate that HDAC9 promotes EndoMT by regulating ANXA2 transcription, thereby disrupting vascular homeostasis during DR. This study sheds light on the roles of HDAC9 and ANXA2 in DR pathology and provides a theoretical foundation for the potential therapeutic strategies to target DR.