Epigenetic Regulation of Endogenous Antioxidants in the Diabetic Retina

Abstract

Purpose: : Our group and other have previously shown that inhibition of the endogenous antioxidant system of the thioredoxins is potentially implicated in the pathogenesis of diabetic retinopathy (DR). More recently, epigenetic mechanisms have also been shown to be involved in maintenance of diabetes-induced cellular dysfunction. Here we studied whether modifications by acetylation of proteins within the thioredoxin system occur in the diabetic retina.

Methods: : Human post-mortem retinas from diabetic donors (Type1 and Type 2) and non diabetic (control) donors were obtained from Georgia Eye Bank. Retinas of STZ-rats, after 4 and 8 weeks of hyperglycemia were compared to age-matched normoglycemic rats (ND). Western blotting and immunopreciptation analyses were conducted to assess the protein levels and acetylation state of Trx-1 and TrxR1 and their interaction with histone deacetylase 6 (HDAC6). HDAC6 activity was assessed by measuring acetylated alpha-tubulin protein levels.

Results: : Hyperglycemic conditions stimulated a decrease in acetylation of Trx-1 and TrxR1 in the diabetic retina. This effect was correlated with decreases in acetylation of alpha-tubulin, a known target of the cytosolic HDAC6. Co-immunoprecipitation of HDAC6 with Trx-1 and TrxR1 revealed an increased interaction with these components of the antioxidant system of the thioredoxins.

Conclusions: : In conclusion, proteins within the thioredoxin system are post-translationally modified by acetylation. Furthermore, decreased acetylation of Trx proteins occur within the diabetic retina and correlate with their decreased activity and increased binding to HDAC6. These data suggest that deacetylation of endogenous antioxidants by HDAC6 could be involved in the pathogenesis of DR.

Keywords: diabetic retinopathy • antioxidants • retina