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Diabetologia. 2011 Feb;54(2):360-7. doi: 10.1007/s00125-010-1967-6. Epub 2010 Nov 23.

Insulin promoter DNA methylation correlates negatively with insulin gene expression and positively with HbA(1c) levels in human pancreatic islets.

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  • 1Department of Clinical Sciences, Lund University Diabetes Centre, Lund University, University Hospital Malmoe, 205 02 Malmoe, Sweden.

Abstract

AIMS/HYPOTHESIS:

Although recent studies propose that epigenetic factors influence insulin expression, the regulation of the insulin gene in type 2 diabetic islets is still not fully understood. Here, we examined DNA methylation of the insulin gene promoter in pancreatic islets from patients with type 2 diabetes and non-diabetic human donors and related it to insulin expression, HbA(1c) levels, BMI and age.

METHODS:

DNA methylation was analysed in 25 CpG sites of the insulin promoter and insulin mRNA expression was analysed using quantitative RT-PCR in pancreatic islets from nine donors with type 2 diabetes and 48 non-diabetic donors.

RESULTS:

Insulin mRNA expression (p = 0.002), insulin content (p = 0.004) and glucose-stimulated insulin secretion (p = 0.04) were reduced in pancreatic islets from patients with type 2 diabetes compared with non-diabetic donors. Moreover, four CpG sites located 234 bp, 180 and 102 bp upstream and 63 bp downstream of the transcription start site (CpG -234, -180, -102 and +63, respectively), showed increased DNA methylation in type 2 diabetic compared with non-diabetic islets (7.8%, p = 0.03; 7.1%, p = 0.02; 4.4%, p = 0.03 and 9.3%, p = 0.03, respectively). While insulin mRNA expression correlated negatively (p < 1 × 10(-6)), the level of HbA(1c) correlated positively (p ≤ 0.01) with the degree of DNA methylation for CpG -234, -180 and +63. Furthermore, DNA methylation for nine additional CpG sites correlated negatively with insulin mRNA expression (p ≤ 0.01). Also, exposure to hyperglycaemia for 72 h increased insulin promoter DNA methylation in clonal rat beta cells (p = 0.005).

CONCLUSIONS/INTERPRETATIONS:

This study demonstrates that DNA methylation of the insulin promoter is increased in patients with type 2 diabetes and correlates negatively with insulin gene expression in human pancreatic islets.

PMID:
21104225
[PubMed - indexed for MEDLINE]
PMCID:
PMC3017313
Free PMC Article
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