Melatonin exerts protective effects on diabetic retinopathy via inhibition of Wnt/β-catenin pathway as revealed by quantitative proteomics.

Diabetic retinopathy (DR), the most common ocular complication resulting from diabetes in working-age adults, causes vision impairment and even blindness because of microvascular damage to the retina. Melatonin is an endogenous neurohormone possessing various biological properties, including the regulation of oxidative stress, inflammation, autophagy, and angiogenesis functions. To evaluate the effects of melatonin on DR, we first investigated the role of melatonin in retinal angiogenesis and inner blood-retina barrier (iBRB) under high glucose conditions in vitro and in vivo. Melatonin administration ameliorated high glucose-induced iBRB disruption, cell proliferation, cell migration, invasion and tube formation, and decreased the expression levels of VEGF, MMP-2, and MMP-9. Furthermore, melatonin treatment increased the level of autophagy but decreased the expression levels of inflammation-related factors under high glucose conditions. To further explore the underlying mechanism, we evaluated human retinal microvascular endothelial cells (HRMECs) via tandem mass tags (TMT)-labeled quantitative proteomics under high-glucose conditions with or without melatonin. Bioinformatics analysis results revealed that the main enrichment pathway of differentially expressed proteins (DEPs) was the Wnt pathway. We found that melatonin inhibited the activation of Wnt/β-catenin pathway following DR. These abovementioned protective effects of melatonin under hyperglycemia were blocked by lithium chloride (LiCl; activator of the Wnt/β-catenin signaling pathway). In summary, melatonin exerts protective effects on experimental DR via inhibiting Wnt/β-catenin pathway by, at least partially, alleviating autophagic dysfunction and inflammatory activation.