The Role of DNA Methylation in the Metabolic Memory Phenomenon Associated With the Continued Progression of Diabetic Retinopathy

Abstract

PurposeClinical and experimental studies have shown that diabetic retinopathy progression does not halt after termination of hyperglycemia, suggesting a “metabolic memory” phenomenon. DNA is highly dynamic, and cytosine methylation changes can last for several years. In diabetes, DNA methylation regulates expression of many genes associated with retinal mitochondrial homeostasis. Our aim was to investigate the role of DNA methylation in the metabolic memory.MethodsReversal of 4 days of 20 mM glucose by 4 to 8 days of 5 mM glucose, in the presence/absence of Dnmt inhibitor (5-aza-2′-deoxycytidine), was investigated on DNA methylation and its machinery in human retinal endothelial cells. The key parameters were confirmed in the retina from diabetic rats maintained in good glycemic control (glycated hemoglobin ∼6%) for 3 months after 3 months of poor control (glycated hemoglobin >10%).ResultsDNA methyltransferase 1 (Dnmt 1) remained active after 4 days of normal glucose that followed 4 days of high glucose, and mtDNA stayed hypermethylated with impaired transcription. Hydroxymethylating enzyme Tet2, and matrix metalloproteinase-9 (regulated by hydroxymethylation) also remained upregulated. But, 8 days of normal glucose after 4 days of high glucose ameliorated mtDNA methylation and MMP-9 hydroxymethylation. Direct Dnmt targeting by Aza during the reversal period benefited methylation status of mtDNA and MMP-9 DNA. Similarly, reinstitution of good control after 3 months of poor control in rats did not reverse diabetes-induced increase in retinal Dnmt1 and Tet2, and alter the methylation status of mtDNA and MMP-9.ConclusionsRetinal DNA methylation-hydroxymethylation machinery does not benefit immediately from reversal of hyperglycemia. Maintenance of good glycemic control for longer duration, and/or direct targeting DNA methylation ameliorates continuous mitochondrial damage, and could retard/halt diabetic retinopathy progression.

Epigenetics and Mitochondrial Stability in the Metabolic Memory Phenomenon Associated with Continued Progression of Diabetic Retinopathy

“…Retinal endothelial cells. Reversal of hyperglycemic insult fails to ameliorate diabetes-induced increase in Dnmt1 23 , and decrease in Mfn2 12 . Role of epigenetics in sustained decrease in Mfn2 was investigated by analyzing DNA methylation status of its promoter.…”

“…The dysfunctional mitochondria continue to fuel into the vicious cycle of free radicals 18,26,27 . Furthermore, the activation of the www.nature.com/scientificreports www.nature.com/scientificreports/ machinery responsible for DNA methylation does not benefit from re-institution of intensive glycemic control, and hypermethylation of mtDNA and hydroxymethylation of MMP-9 promoter continues [21][22][23] . Here, we provide convincing data showing the role of DNA methylation in sustained compromised mitochondrial structural and DNA stability.…”

“…Intervention of the reversal phase with the inhibitors of Dnmt restores mtDNA methylation, and prevents decrease in the transcription of mtDNA-encoded genes 23 . The effect of inhibition of Dnmts on restoration of mitochondrial dynamics and DNA stability was investigated.…”

Worsening of diabetic retinopathy with rapid improvement in systemic glucose control: A review

“…In another study using human retinal epithelial cells, the rapid achievement of good glycaemic control did not trigger an immediate effect on the retinal DNA methylation‐hydroxymethylation machinery associated with DR progression. In this study, good glycaemic control for a longer duration, and/or direct targeting of DNA methylation, improved mitochondrial damage and could therefore potentially slow DR progression (Table ) . The relationship between hypoglycaemia and ischaemic retinopathy was investigated in an in vivo study using Wistar rats.…”

“…In this study, good glycaemic control for a longer duration, and/or direct targeting of DNA methylation, improved mitochondrial damage and could therefore potentially slow DR progression (Table 3). 71 The relationship between hypoglycaemia and ischaemic retinopathy was investigated in an in vivo study using Wistar rats. In this study, reduced blood glucose levels or hypoglycaemia caused a significant (P < 0.001) reduction in vitreous glucose concentration, thereby exacerbating ischaemic retinal injury ( Table 3).…”