Polycomb repressive complex 2 regulates MiR-200b in retinal endothelial cells: potential relevance in diabetic retinopathy.

Glucose-induced augmented vascular endothelial growth factor (VEGF) production is a key event in diabetic retinopathy. We have previously demonstrated that downregulation of miR-200b increases VEGF, mediating structural and functional changes in the retina in diabetes. However, mechanisms regulating miR-200b in diabetes are not known. Histone methyltransferase complex, Polycomb Repressive Complex 2 (PRC2), has been shown to repress miRNAs in neoplastic process. We hypothesized that, in diabetes, PRC2 represses miR-200b through its histone H3 lysine-27 trimethylation mark. We show that human retinal microvascular endothelial cells exposed to high levels of glucose regulate miR-200b repression through histone methylation and that inhibition of PRC2 increases miR-200b while reducing VEGF. Furthermore, retinal tissue from animal models of diabetes showed increased expression of major PRC2 components, demonstrating in vivo relevance. This research established a repressive relationship between PRC2 and miR-200b, providing evidence of a novel mechanism of miRNA regulation through histone methylation.

Oxidative-stress-induced epigenetic changes in chronic diabetic complications.

Oxidative stress plays an important role in the development and progression of chronic diabetic complications. Diabetes causes mitochondrial superoxide overproduction in the endothelial cells of both large and small vessels. This increased superoxide production causes the activation of several signal pathways involved in the pathogenesis of chronic complications. In particular, endothelial cells are major targets of glucose-induced oxidative damage in the target organs. Oxidative stress activates cellular signaling pathways and transcription factors in endothelial cells including protein kinase C (PKC), c-Jun-N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), forkhead box O (FOXO), and nuclear factor kappa-B (NF-κB). Oxidative stress also causes DNA damage and activates DNA nucleotide excision repair enzymes including the excision repair cross complimenting 1(ERCC1), ERCC4, and poly(ADP-ribose) polymerase (PARP). Augmented production of histone acetyltransferase p300, and alterations of histone deacetylases, including class III deacetylases sirtuins, are also involved in this process. Recent research has found that small noncoding RNAs, like microRNA, are a new kind of regulator associated with chronic diabetic complications. There are extensive and complicated interactions and among these molecules. The purpose of this review is to demonstrate the role of oxidative stress in the development of diabetic complications in relation to epigenetic changes such as acetylation and microRNA alterations.

MicroRNAs: the underlying mediators of pathogenetic processes in vascular complications of diabetes.

Diabetes mellitus causes chronic complications primarily affecting the vasculature of various organs, risking patients for renal failure, vision loss and heart failure. A newly discovered class of molecules, microRNAs, may be important in the genesis of these pathologic processes. microRNAs regulate gene expression at the post-transcriptional level by inhibiting target messenger RNA translation. In disease states, however, the expression of microRNAs often is altered, resulting in further altered expression (mostly overexpression) of downstream target genes. Interestingly, restoring microRNA expression to normal levels can correct downstream effects and prevent diabetes-associated changes. Investigations into microRNA involved in various pathogenetic processes mediating diabetic nephropathy, retinopathy and cardiomyopathy are highlighted in this review. Future directions of microRNA in therapeutics and diagnostics are also discussed. It is our intent to help the reader appreciate the diverse interactions microRNAs have in cellular signalling and how understanding epigenetic elements, such as microRNAs, potentially can yield new therapeutic strategies.