Activation of Histone Deacetylase 6 (HDAC6) in the Diabetic Retina and in Retinal Endothelial Cells Exposed to Glucidic Stress, Promotes Oxidative Stress Through Suppression of the Thioredoxin System

Retinal microvascular dysfunction characterizes the pathophysiology of diabetic retinopathy (DR), a common complication of diabetes and a leading cause of blindness in the World. Oxidative stress and inflammation have been implicated as major pathogenic hubs for the induction and progression of DR. Reduced endogenous antioxidant activities within the retinal microvasculature can significantly contribute to oxidative stress in the diabetic retina. We have previously shown that diabetes inhibits the thioredoxin system (TrxS) and others have shown that the cytosolic histone deacetylase 6 (HDAC6) can promote oxidative stress in a not yet understood mechanism. Here we have investigated the role of HDAC6 in regulating the TrxS in the diabetic retinal microvasculature. HDAC6 expression and activity were assessed by immunoblotting and fluorimetric assay (respectively) in retinas of streptozotocin‐induced diabetic rats (STZ‐rats, 8 weeks of diabetes) and in primary culture of human retinal endothelial cells (HuREC) exposed to disease‐relevant glucose levels (HG=25mM D‐glucose) for 48 hours. Changes in TrxS were monitored by assessing the expression and activity of its functional unit, thioredoxin‐1 (Trx‐1), by immunoblotting and a commercially available fluorimetric assay, in STZ‐rats retinas and in HuREC exposed to HG. Some experiments in HuREC were conducted also in presence of 5μM of the specific HDAC6 inhibitor tubastatin A. CellROX assay and dot‐blot assessing 5‐nitrotyrosine (5‐NT) and 4 hydroxynonenal (4‐HNE) were used to measure oxidative stress in our experimental groups. HDAC6 expression and activity were found significantly elevated in retinas of STZ‐rats compared to normal age‐matched controls and in HuREC exposed to HG, but not to normal glucose (5mM D‐glucose) or the osmotic control L‐glucose (25mM). At the same time Trx‐1 expression was increased in diabetic retinas and in HuREC exposed to HG, whereas its activity was significantly decreased. Parallel to loss of Trx‐1 activity and increased HDAC6 expression and activity, we also found that oxidative stress parameters were also elevated. In HuREC, tubastatin A was able to block HG‐induced up‐regulation of oxidative stress parameters while up‐regulating Trx‐1 activity and normalizing its expression. In summary, our data confirm previous observations on the role of HDAC6 in promoting oxidative stress and disclose HDAC6 role in suppressing Trx‐1 activity. Therefore, our results, support HDAC6 pathogenic role in promoting oxidative stress in the diabetic retinal microvasculature and its implication in the pathogenesis of diabetic retinopathy.Support or Funding InformationEY022416This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.