title: DNA methylation of the glucagon-like peptide 1 receptor (GLP1R) in human pancreatic islets.
abstract: BACKGROUND
  Insulin secretion is enhanced upon the binding of Glucagon-like peptide-1 (GLP-1) to its receptor (GLP1R) in pancreatic β cells. Although a reduced expression of GLP1R in pancreatic islets from type 2 diabetic patients and hyperglycaemic rats has been established, it is still unknown if this is caused by differential DNA methylation of GLP1R in pancreatic islets of type 2 diabetic patients.
  
  
  METHODS
  In this study, DNA methylation levels of 12 CpG sites close to the transcription start site of GLP1R were analysed in pancreatic islets from 55 non-diabetic and 10 type 2 diabetic human donors as well as in β and α cells isolated from human pancreatic islets. DNA methylation of GLP1R was related to GLP1R expression, HbA1c levels and BMI. Moreover, mRNA expression of MECP2, DNMT1, DNMT3A and DNMT3B was analysed in pancreatic islets of the non-diabetic and type 2 diabetic donors.
  
  
  RESULTS
  One CpG unit, at position +199 and +205 bp from the transcription start site, showed a small increase in DNA methylation in islets from donors with type 2 diabetes compared to non-diabetic donors (0.53%, p=0.02). Furthermore, DNA methylation levels of one CpG site located 376 bp upstream of the transcription start site of GLP1R correlated negatively with GLP1R expression (rho=-0.34, p=0.008) but positively with BMI and HbA1c (rho=0.30, p=0.02 and rho=0.30, p=0.03, respectively). This specific CpG site is located in an area with known SP1 and SP3 transcription factor binding sites. Moreover, when we compared the DNA methylation of the GLP1R promoter in isolated human β and α cells, we found that it was higher in α- compared with β-cells (p=0.009). Finally, there was a trend towards decreased DNMT3A expression (p=0.056) in type 2 diabetic compared with non-diabetic islets.
  
  
  CONCLUSIONS
  Together, our study shows that while BMI and HbA1c are positively associated with DNA methylation levels of GLP1R, its expression is negatively associated with DNA methylation of GLP1R in human pancreatic islets.
authors.affiliation: Department of Clinical Sciences, Lund University Diabetes Centre, CRC, Lund University, Scania University Hospital, Malmö, Sweden.
authors.forename: Elin
authors.initials: E
authors.lastname: Hall
authors.forename: Tasnim
authors.initials: T
authors.lastname: Dayeh
authors.forename: Clare L
authors.initials: CL
authors.lastname: Kirkpatrick
authors.forename: Claes B
authors.initials: CB
authors.lastname: Wollheim
authors.forename: Marloes
authors.initials: M
authors.lastname: Dekker Nitert
authors.forename: Charlotte
authors.initials: C
authors.lastname: Ling
mesh_terms: D000368:Aged; D015992:Body Mass Index; D018899:CpG Islands; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics; D019175:DNA Methylation; D000090205:DNA Methyltransferase 3A; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics*; D005260:Female; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism; D000067757:Glucagon-Like Peptide-1 Receptor; D050416:Glucagon-Secreting Cells / Q000378:metabolism; D006442:Glycated Hemoglobin / Q000235:genetics*; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism; D008297:Male; D051783:Methyl-CpG-Binding Protein 2 / Q000235:genetics; D008875:Middle Aged; D018027:Receptors, Glucagon / Q000235:genetics* / Q000378:metabolism; D024363:Transcription Initiation Site; D000097584:DNA Methyltransferase 3B
chemical_list: D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; D000090205:DNA Methyltransferase 3A; D052216:Glucagon-Like Peptide 1; D000067757:Glucagon-Like Peptide-1 Receptor; D006442:Glycated Hemoglobin; D007328:Insulin; D051783:Methyl-CpG-Binding Protein 2; D018027:Receptors, Glucagon; D000097584:DNA Methyltransferase 3B; C000717967:DNMT3A protein, human; C000593833:GLP1R protein, human; C000593835:Glp1r protein, rat; C497392:MECP2 protein, human; C517652:hemoglobin A1c protein, human; C000619380:DNMT1 protein, human; C000619382:Dnmt1 protein, rat