OBJECTIVE: To elucidate the regulatory mechanism of circRNAs in diabetic retinopathy. METHODS: Next-generation sequencing (NGS) was employed to identify circRNAs that are abnormally expressed in endothelial progenitor cells (EPCs) under hyperglycemia (HG) conditions. The regulatory mechanism and predicted targets of this circRNA were also studied via bioinformatics analysis, luciferase reporter assays, angiogenic differentiation experiments, flow cytometry, and RT-qPCR. RESULTS: Circ-astrotactin 1 (circ-Astn1) expression was decreased in EPCs under HG conditions, and circ-Astn1 overexpression inhibited HG-induced endothelial damage. The miR-138-5p and silencing information regulator 2 related enzyme 1 (SIRT1) were identified as circ-Astn1 downstream targets, which were further verified through luciferase reporter assays. SIRT1 silencing or miR-138-5p overexpression reversed the protective effect of circ-Astn1 on HG-induced endothelial cell dysfunction, as evidenced by increased apoptosis, abnormal vascular differentiation, and inflammatory factor secretion. SIRT1 overexpression reversed miR-138-5p-induced endothelial cell dysfunction under HG conditions. In vivo experiments confirmed that circ-Astn1 overexpression promoted skin wound healing through the regulation of SIRT1. CONCLUSIONS: These findings suggest that circ-Astn1 promotes SIRT1 expression by sponging miR-138-5p. Circ-Astn1 overexpression suppresses HG-induced endothelial cell damage via miR-138-5p/SIRT1 axis.