Purchase this article with an account.
Manish Mishra, Renu A Kowluru; Epigenetics- a molecular link between transcription of mitochondrial DNA and diabetic retinopathy. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5186.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Epigenetic modifications regulate gene transcription without altering the DNA sequence, and DNA methylation is a dynamic process which converts cytosine to 5-methyl cytosine (5mC) repressing the transcription. In the development of diabetic retinopathy, retinal mitochondria are dysfunctional, and their DNA is damaged with suboptimal transcription and compromised electron transport system. In diabetes, the activity of DNA methyl transferase (Dnmt), the enzymes responsible for methylation of cytosine is increased in the retina, and the enzyme responsible for mitochondrial DNA (mtDNA) biogenesis is hypermethylated. The goal of this study is to understand the role of methylation of mtDNA in the development of diabetic retinopathy.
Methylation of D-loop mtDNA region which contains transcriptional and regulatory elements, was analyzed in the retina from streptozotocin-induced diabetic rats by methylation specific PCR, and was confirmed by quantifying the levels of 5mC. The mitochondrial expression of Dnmt1, a tissue specific inducible isoform of Dnmt, was measured by western blot technique, and its binding at the D-loop region was quantified by chromatin immunoprecipitation technique. To validate the specific role of Dnmt1 in mtDNA methylation, retinal endothelial cells transfected with Dnmt1-siRNA were analyzed for D-loop methylation and quantification of mtDNA-encoded genes Cytochrome b and ND6.
Diabetes hypermethylated the D-loop region of mtDNA and increased 5mC levels by 2.5 fold. This was accompanied by a significant increase in Dnmt1 levels in the mitochondria, and its binding at the D-loop region. High glucose had similar effects on D-loop methylation in retinal endothelial cells. Regulation of Dnmt1 by its siRNA prevented glucose-induced increase in D-loop methylation, and decrease in mtDNA transcription.
Increased translocation of Dnmt1 to the mitochondria hypermethylates the D-loop region and due to hypermethylation of D-loop, transcription of mtDNA is decreased. This results in a dysfunctional electron transport system. Regulation of DNA methylation by pharmacological or genetic means could help restore the mitochondrial transcription and inhibit the development of diabetic retinopathy.
This PDF is available to Subscribers Only