Insulin Gene Expression Is Regulated by DNA Methylation

Abstract

BackgroundInsulin is a critical component of metabolic control, and as such, insulin gene expression has been the focus of extensive study. DNA sequences that regulate transcription of the insulin gene and the majority of regulatory factors have already been identified. However, only recently have other components of insulin gene expression been investigated, and in this study we examine the role of DNA methylation in the regulation of mouse and human insulin gene expression.Methodology/Principal FindingsGenomic DNA samples from several tissues were bisulfite-treated and sequenced which revealed that cytosine-guanosine dinucleotide (CpG) sites in both the mouse Ins2 and human INS promoters are uniquely demethylated in insulin-producing pancreatic beta cells. Methylation of these CpG sites suppressed insulin promoter-driven reporter gene activity by almost 90% and specific methylation of the CpG site in the cAMP responsive element (CRE) in the promoter alone suppressed insulin promoter activity by 50%. Methylation did not directly inhibit factor binding to the CRE in vitro, but inhibited ATF2 and CREB binding in vivo and conversely increased the binding of methyl CpG binding protein 2 (MeCP2). Examination of the Ins2 gene in mouse embryonic stem cell cultures revealed that it is fully methylated and becomes demethylated as the cells differentiate into insulin-expressing cells in vitro.Conclusions/SignificanceOur findings suggest that insulin promoter CpG demethylation may play a crucial role in beta cell maturation and tissue-specific insulin gene expression.

Detection of β cell death in diabetes using differentially methylated circulating DNA

“…Our findings indicate that this method provides a biomarker for detecting β cell loss in prediabetic mice during progression of diabetes, and suggest it does the same in patients with new-onset T1D. Kuroda et al (26) previously identified demethylation of CpG sites in the insulin promoter, consistent with the notion that methylation of promoters is a mechanism for controlling tissuespecific gene expression. However, our analysis targeted differentially methylated CpG dinucleotides in the Ins1 gene in mice and the Ins gene itself in humans.…”

The ‘golden age’ of DNA methylation in neurodegenerative diseases

“…Aging, nutrition and sedentary lifestyle have been associated with epigenetic changes characteristic of type-2 diabetes [ 54 ]. DNA methylation have been shown to vary in diabetic vs. non-diabetic subjects, therefore this association strongly stresses for the existence of an epigenetic basis in the pathogenesis of type-2 diabetes [ 55 ].…”

Epigenetic regulation in obesity

“…Tissue-specific level of CpG methylation is found for example in promoters of leptin, pro-opiomelanocortin (precursor for melanocyte-stimulating hormone (a-MSH), ACTH and b-endorphine) and insulin correlating to the corresponding tissue-specific expression levels (for review, see McAllister). 39,40 That changes in DNA methylation can occur postnatally can be exemplified by increase in CpG methylation of the key metabolic transcriptional regulator peroxisome proliferator-activated receptor-a (Ppar-a) by folate supplementation in young rodents. 41 In fact, mice on high-fat diet developed hypomethylation in the satiety-receptor melanocortin-4 receptor, 42 whereas neonatal overfeeding rats, and rats obese because of overfeeding in small litters, developed hypermethylation of the satiety-mediator pro-opiomelanocortin in hypothalamus.…”