Epigenetic control of early neurodegenerative events in Diabetic Retinopathy by the histone deacetylase SIRT6

Diabetic retinopathy (DR) is one of the common complications associated with diabetes mellitus (DM) and the leading cause of blindness worldwide. Recent research has demonstrated that DR is not only a microvascular disease but may be a result of neurodegenerative processes. Moreover, glucose-induced neuron and glial cell damage may occur shortly after the onset of diabetes which makes the disease hard to diagnose at early stages. SIRT6, a NAD-dependent sirtuindeacylase, modulates aging, energy metabolism and neurodegeneration. In previous studies we showed that SIRT6deficiency causes major retinal transmission defects, changes in the expression of glycolytic genes and elevated levels of apoptosis. Given the importance of glucose availability for retinal function and the critical role of SIRT6in modulating glycolysis, we aimed to analyze SIRT6participation in the molecular machinery that regulates the development of experimental DR. By using non-obese diabetic ( NOD) mice, we determined by Western blot that two weeks after the onset of the disease, high glucose concentrations induced retinal increase of a neovascularization promoting factor (VEGF) and the loss of a neuroprotective factor (BDNF) associated with reduced levels of SIRT6and increased acetylation levels of its substrates (H3K9 and H3K56) suggesting a deregulation of key neural factors. Noteworthy, retinas from CNS conditionally deleted SIRT6mice showed a resemblance to diabetic retinas exhibiting lower protein levels of BDNF and increased protein levels of VEGF. Moreover, cultured Muller glial cells subjected to high glucose concentrations exhibited decreased levels of SIRT6and increased levels of H3K56 acetylation. Additionally, the increment of VEGF levels induced by high glucose was reverted by the overexpression of SIRT6in this cell type. Accordingly, siRNA experiments showed that, when SIRT6was silenced, VEGF levels increased. Our findings suggest that epigenetically regulated neurodegenerative events may occur at an early diabetic stage prior to the characteristic proliferative and vascular changes observed at a later diabetic stage. This article is protected by copyright. All rights reserved.