VEGF/Ang-2 imbalance: the crosslinking between methylglyoxal and vascular dysfunction in diabetic retinopathy

Abstract

Purpose Accumulation of methylglyoxal (MGO) in retinas of diabetic rats has been implicated in the formation of acellular capillaries, suggesting an important role for MGO in the vascular dysfunction observed in diabetes. In this study, we hypothesize that increased levels of MGO in retinal pigment epithelium (RPE) cells disturbs the balance VEGF/Ang2 secreted to the extracellular milieu, promoting apoptotis and low proliferation of endothelial cells. Methods ARPE19 cells were subjected both to hypoxia and MGO, two main features of diabetic retinopathy (DR). The levels of VEGF and Ang2 secreted into the culture medium were assessed by ELISA. Retinal endothelial cells were subsequently treated with the pre-conditioned media of the ARPE19 cells, as well as with different ratios of VEGF and Ang2 recombinant proteins. Apoptotic cell death was determined by immunoblot against Bax and Bcl2, while endothelial cell proliferation was assessed by BrdU-incorporation and fibrin gel angiogenic assays. Results MGO increases the levels of Ang2 and strongly decreases the levels of VEGF secreted by ARPE19 cells in response to hypoxia. VEGF downregulation appears to result from increased degradation of HIF103B1 and low HIF1 transcriptional activity. The VEGF/Ang2 imbalance generated by MGO significantly increases the expression of BAX and decreases the levels of Bcl2 of endothelial cells. Moreover, this imbalance also leads to decreased proliferation of the endothelial cells. Conclusion The VEGF/Ang2 imbalance induced by MGO activates the apoptotic cascade and induces low proliferation of retinal endothelial cells, possibly leading to vessels regression in pathologies that favour accumulation of MGO and where hypoxia is also present, such as DR.