Purpose: Previous studies by the authors have shown that retinal levels of SERPINA3K, a serine proteinase inhibitor, are decreased in an animal model with diabetic retinopathy (DR). The purpose of this study was to investigate the function of SERPINA3K and its role in DR.
Methods: For the oxygen-induced retinopathy (OIR) model, newborn rats were exposed to 75% O(2) from postnatal day (P) 7 to P12. Cultured retinal cells were treated with CoCl(2) or 2% O(2) to induce hypoxia. CM-H2DCFDA was used to determine the intracellular reactive oxygen species (ROS) level. Inflammatory factors were measured using Western blot analysis or ELISA.
Results: Intravitreal injection of SERPINA3K significantly reduced retinal vascular leakage and leukostasis in the OIR model. SERPINA3K also prevented the hypoxia-induced decrease of occludin, a tight junction protein, in the OIR rat retina and in cultured retinal capillary endothelial cells and retinal pigment epithelial cells. Further, SERPINA3K blocked the overexpression of proinflammatory factors, such as VEGF, TNF-alpha, and ICAM-1, in the retina of the OIR model and in cultured retinal cells exposed to hypoxia. VEGF was downregulated by SERPINA3K at the transcriptional level. Knockdown of SERPINA3K by siRNA resulted in the overexpression of VEGF and TNF-alpha in cultured retinal cells. Moreover, SERPINA3K significantly decreased ROS generation and upregulated the expression and activity of manganese superoxide dismutase and glutathione levels, suggesting antioxidant activity.
Conclusions: SERPINA3K is an endogenous anti-inflammatory factor, and its anti-inflammatory effects may be mediated through antioxidant activity. Decreased retinal levels of SERPINA3K may contribute to retinal inflammation in DR.