title: Insulin promoter DNA methylation correlates negatively with insulin gene expression and positively with HbA(1c) levels in human pancreatic islets.
abstract: OBJECTIVE
  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
  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.
authors.affiliation: Department of Clinical Sciences, Lund University Diabetes Centre, Lund University, University Hospital Malmoe, 205 02 Malmoe, Sweden.
authors.forename: B T
authors.initials: BT
authors.lastname: Yang
authors.forename: T A
authors.initials: TA
authors.lastname: Dayeh
authors.forename: C L
authors.initials: CL
authors.lastname: Kirkpatrick
authors.forename: J
authors.initials: J
authors.lastname: Taneera
authors.forename: R
authors.initials: R
authors.lastname: Kumar
authors.forename: L
authors.initials: L
authors.lastname: Groop
authors.forename: C B
authors.initials: CB
authors.lastname: Wollheim
authors.forename: M D
authors.initials: MD
authors.lastname: Nitert
authors.forename: C
authors.initials: C
authors.lastname: Ling
mesh_terms: D000818:Animals; D002460:Cell Line; D019175:DNA Methylation / Q000235:genetics / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007328:Insulin / Q000235:genetics / Q000378:metabolism*; D050417:Insulin-Secreting Cells / Q000378:metabolism; D007515:Islets of Langerhans / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D051381:Rats
chemical_list: D007328:Insulin