Insulin promoter DNA methylation correlates negatively with insulin gene expression and positively with HbA1c levels in human pancreatic islets

Abstract

Aims/hypothesisAlthough 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, HbA1c levels, BMI and age.MethodsDNA 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.ResultsInsulin 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 HbA1c 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/interpretationsThis 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.Electronic supplementary materialThe online version of this article (doi:10.1007/s00125-010-1967-6) contains supplementary material, which is available to authorised users.

Coordinate Changes in Histone Modifications, mRNA Levels, and Metabolite Profiles in Clonal INS-1 832/13 β-Cells Accompany Functional Adaptations to Lipotoxicity

“…These are chemical alterations of the DNA that affect gene function and expression without changing the DNA sequence (20 -22). Recent studies by our group and others' demonstrate that epigenetic modifications, including DNA methylation and histone modifications, in human pancreatic islets influence gene expression, islet function, and most likely the pathogenesis of T2D (23)(24)(25)(26)(27). To our knowledge, it has not yet been shown that FAs regulate histone modifications in pancreatic ␤-cells.…”

Regulation of core clock genes in human islets

“…For static measurements of insulin release, groups of 8 10 islets were incubated at 37 0 C for 1 h in 300 μl of the same buffer containing 3.3 or 16.7 mM glucose. Released insulin was measured in the buffer by radio immunoassay (RIA) as described [16]. Insulin content was extracted by acid ethanol and analyzed by RIA as previously described [16].…”

“…Released insulin was measured in the buffer by radio immunoassay (RIA) as described [16]. Insulin content was extracted by acid ethanol and analyzed by RIA as previously described [16].…”

Modulation of hyperglycemia and TNFα-mediated inflammation by helichrysum and grapefruit extracts in diabetic db/db mice

“…1 Insulin resistance (IR) is produced as soon as the pancreatic b-cells cannot compensate a reduced insulin function, leading to elevated circulating glucose levels. 2 Insulin inhibits gluconeogenesis in the liver and reduces lipolysis in adipose tissue.…”