Procyanidin Alleviates Diabetic Retinopathy by Activating the Expression of Activating Transcription Factor 1 Expression to Upregulate Synoviolin 1 and Inhibit the High Mobility Group Box 1/Toll‐Like Receptor 4 Pathway

Diabetic retinopathy (DR) remains a major cause of vision loss among working-age individuals, significantly impairing quality of life in diabetic patients. While no definitive cure exists, Procyanidin (PRO), a polyphenolic compound, has shown potential in mitigating diabetes-related complications. However, its mechanism of action in DR remains poorly understood. To explore this, we established an in vitro high glucose (HG) model using human retinal microvascular endothelial cells (hRMECs) and an in vivo diabetic rat model. Cells were cultured in normal glucose (NG, 5 mM) or HG (30 mM) for 48 h, followed by PRO treatment. Techniques including qRT-PCR, Western blotting, flow cytometry, histological staining, Transwell, tube formation, chromatin immunoprecipitation (ChIP), and dual-luciferase assays were employed. PRO treatment conferred protection against DR; however, this effect was reversed upon knockdown of activating transcription factor 1 (ATF1). Mechanistically, ATF1 enhanced transcription of synoviolin 1 (SYVN1), promoting HMGB1 degradation via ubiquitination and suppressing the HMGB1/toll-like receptor 4 (TLR4) signaling pathway. Findings from the in vitro model were validated in vivo. In conclusion, PRO alleviates DR by regulating the ATF1/SYVN1/HMGB1 axis and inhibiting pro-inflammatory signaling. These results provide novel insights into the molecular mechanism of PRO's protective role in DR and support its therapeutic potential.