O-GlcNAcylation of 8-Oxoguanine DNA Glycosylase (Ogg1) Impairs Oxidative Mitochondrial DNA Lesion Repair in Diabetic Hearts.

Abstract Mitochondrial DNA (mtDNA) damage in cardiac myocytes resulting from increased oxidative stress is emerging as an important factor in the pathogenesis of diabetic cardiomyopathy. A prevalent lesion that occurs in mtDNA damage is the formation of 8-hydroxy-2-deoxyguanosine (8-OHdG), which can cause mutations if not repaired properly by 8-oxoguanine DNA glycosylase (Ogg1). Although the mtDNA repair machinery has been described in cardiac myocytes, the regulation of this repair has been incompletely investigated. Here, we report that the hearts of type 1 diabetic (T1D) mice, despite having increased Ogg1 protein levels, had significantly lower Ogg1 activity than the hearts of control, non-T1D mice. In diabetic hearts we further observed increased levels of 8-OHdG and an increased amount of mtDNA damage. Interestingly, Ogg1 was found to be highly O-GlcNAcylated in diabetic mice as compared to controls. In vitro experiments demonstrated that O-GlcNAcylation inhibits Ogg1 activity, which could explain the mtDNA lesion accumulation observed in vivo. Reducing Ogg1 O-GlcNAcylation in vivo by introducing a dominant negative O-GlcNAc transferase mutant (F460A) restored Ogg1 enzymatic activity and consequently reduced 8-OHdG and mtDNA damage, despite the adverse hyperglycemic milieu. Taken together, our results implicate hyperglycemia-induced O-GlcNAcylation of Ogg1 in increased mtDNA damage and therefore provide a new plausible biochemical mechanism for diabetic cardiomyopathy.