The Mechanism Of α-melanocyte-stimulating Hormone Protects Diabetic Retinal Vascular Endothelial Cells

Aims:Oxidative stress and apoptosis are among the earliest lesions of diabetic retinopathy. The aim of this study was to examine anti-oxidative and anti-apoptotic effects of α-melanocyte-stimulating hormone (α-MSH) in early diabetic retina and explore the underlying mechanism in retinal vascular endothelial cells.Methods:Sprague Dawley rats were injected intravenously with streptozocin to induce diabetes, and injected intravitreally with α-MSH. At week5after diabetes, retinas were analyzed for gene expression and reactive oxygen species. One week later, eye cups were processed for transmission electron microscopy and terminal deoxynucleotidyl transferase dUTP nick end labeling staining. Retinal vascular endothelial cells were stimulated with high glucose with or without α-MSH, Forkhead box O proteins (FOXOs) expression was examined by real-time PCR. FOXO4gene was overexpressed in the endothelial cells by transient transfection prior to α-MSH and/or high glucose treatment, oxidative stress and apoptosis were analyzed by CM-H2DCFDA and annexin-V assav.Results:In diabetic retina, NO2-/NO3-and H2O2levels.were normalized, apoptotic cell number was substantially reduced, and ultrastructural injuries were ameliorated by α-MSH administration. Real-time PCR showed that eNOS expression was down-regulated, iNOS, ICAM-1, and TNF-α expression were up-regulated in diabetic retina, and this aberration was corrected by α-MSH. In the endothelial cells exposed to high glucose, α-MSH inhibited FOX04up-regulation and over-expression of FOX04abrogated anti-oxidative and anti-apoptotic effects of α-MSH.Conclusion:α-MSH normalizes oxidative stress, lessens apoptosis and ultrastructural impairments, and corrects gene expression in early diabetic retina. The protective effects of α-MSH in retinal vascular endothelial cells may be mediated by its inhibiting FOXO4up-regulation induced by high glucose. This study indicates the potential of α-MSH as an effective intervention approach to early diabetic retinopathy, and suggests a novel regulatory mechanism involving FOXO4.