title: Increased DNA methylation and decreased expression of PDX-1 in pancreatic islets from patients with type 2 diabetes.
abstract: Mutations in pancreatic duodenal homeobox 1 (PDX-1) can cause a monogenic form of diabetes (maturity onset diabetes of the young 4) in humans, and silencing Pdx-1 in pancreatic β-cells of mice causes diabetes. However, it is not established whether epigenetic alterations of PDX-1 influence type 2 diabetes (T2D) in humans. Here we analyzed mRNA expression and DNA methylation of PDX-1 in human pancreatic islets from 55 nondiabetic donors and nine patients with T2D. We further studied epigenetic regulation of PDX-1 in clonal β-cells. PDX-1 expression was decreased in pancreatic islets from patients with T2D compared with nondiabetic donors (P = 0.0002) and correlated positively with insulin expression (rho = 0.59, P = 0.000001) and glucose-stimulated insulin secretion (rho = 0.41, P = 0.005) in the human islets. Ten CpG sites in the distal PDX-1 promoter and enhancer regions exhibited significantly increased DNA methylation in islets from patients with T2D compared with nondiabetic donors. DNA methylation of PDX-1 correlated negatively with its gene expression in the human islets (rho = -0.64, P = 0.0000029). Moreover, methylation of the human PDX-1 promoter and enhancer regions suppressed reporter gene expression in clonal β-cells (P = 0.04). Our data further indicate that hyperglycemia decreases gene expression and increases DNA methylation of PDX-1 because glycosylated hemoglobin (HbA1c) correlates negatively with mRNA expression (rho = -0.50, P = 0.0004) and positively with DNA methylation (rho = 0.54, P = 0.00024) of PDX-1 in the human islets. Furthermore, while Pdx-1 expression decreased, Pdx-1 methylation and Dnmt1 expression increased in clonal β-cells exposed to high glucose. Overall, epigenetic modifications of PDX-1 may play a role in the development of T2D, given that pancreatic islets from patients with T2D and β-cells exposed to hyperglycemia exhibited increased DNA methylation and decreased expression of PDX-1. The expression levels of PDX-1 were further associated with insulin secretion in the human islets.
authors.affiliation: Department of Clinical Sciences, Unit of Epigenetics and Diabetes, Lund University Diabetes Centre, Scania University Hospital, 205 02 Malmoe, Sweden.
authors.forename: Beatrice T
authors.initials: BT
authors.lastname: Yang
authors.forename: Tasnim A
authors.initials: TA
authors.lastname: Dayeh
authors.forename: Petr A
authors.initials: PA
authors.lastname: Volkov
authors.forename: Clare L
authors.initials: CL
authors.lastname: Kirkpatrick
authors.forename: Siri
authors.initials: S
authors.lastname: Malmgren
authors.forename: Xingjun
authors.initials: X
authors.lastname: Jing
authors.forename: Erik
authors.initials: E
authors.lastname: Renström
authors.forename: Claes B
authors.initials: CB
authors.lastname: Wollheim
authors.forename: Marloes Dekker
authors.initials: MD
authors.lastname: Nitert
authors.forename: Charlotte
authors.initials: C
authors.lastname: Ling
mesh_terms: D019175:DNA Methylation; D003924:Diabetes Mellitus, Type 2 / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000494:pharmacology; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics*; D006801:Humans; D006943:Hyperglycemia / Q000378:metabolism; D007328:Insulin / Q000096:biosynthesis; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D010179:Pancreas / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics*
chemical_list: D018398:Homeodomain Proteins; D007328:Insulin; D012333:RNA, Messenger; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D005947:Glucose