The Janus tyrosine kinase and signal transducers and activators of transcription (JAK/STAT) pathway is involved in vascular endothelial growth factor (VEGF) expression, but the role of this pathway in diabetic retinopathy (DR) remains unclear. We investigated the role of the JAK/STAT pathway on DR and VEGF expression using a streptozotocin (STZ)-induced DR mouse model. Cultured ARPE-19 cells were exposed to high-glucose conditions and treated with JAK/STAT inhibitors (JAK inhibitor I [JAKiI], tofacitinib, STAT3 inhibitor [STAT3i]) for 48h. Reverse-transcription polymerase chain reaction, western blotting, and enzyme-linked immunosorbent assay were used to investigate p-JAK/STAT and VEGF expression. Diabetes was induced by intraperitoneal injection of STZ (50mg/kg) in C57BL/6 mice for 5days. DR development was evaluated every 4weeks. JAK/STAT inhibitors were administered for 8weeks. Immunofluorescence was used to measure the activation status of the JAK/STAT pathway and VEGF production in the retinal tissue. In ARPE-19 cells exposed to high-glucose conditions, the mRNA and secretory protein levels of VEGF, p-JAK1, p-JAK2, p-STAT3, and p-STAT5 levels were significantly increased. Treatment with JAKiI, tofacitinib, and STAT3i significantly suppressed VEGF to basal levels at both the mRNA and secretory levels in vitro. In STZ-induced mice, retinal vascular leakage, p-JAK1, p-JAK2, p-JAK3, p-STAT3, and VEGF were significantly increased after diabetes induction. Diabetes-induced retinal vascular leakage was significantly reduced by treatment with JAKiI and tofacitinib. Increased p-JAK1 and VEGF in STZ-induced mice were significantly reduced by JAKiI (p < 0.05, p < 0.001) and tofacitinib (p < 0.001, respectively). JAK1 may be more involved in VEGF production and DR progression in mice than JAK2, JAK3, and STAT3.

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