Increased DNA methylation levels of the insulin-like growth factor binding protein 1 gene are associated with type 2 diabetes in Swedish men

Abstract

Background: Prospective studies have shown that low levels of circulating insulin-like growth factor binding protein-1 (IGFBP-1) are associated with the risk of type 2 diabetes. In the present study, we investigated DNA methylation in the IGFBP1 gene to evaluate its changes in relation to serum IGFBP-1 levels in type 2 diabetes.

Results: A total of 406 Swedish men, including age-matched normal glucose tolerance subjects and type 2 diabetes patients either newly diagnosed or undergoing treatment, were selected from the Stockholm Diabetes Prevention Program. IGFBP1 methylation levels in genomic DNA extracted from peripheral blood were analysed by bisulfite pyrosequencing. Serum IGFBP-1 levels were measured by radio-immunoassay. We found that IGFBP1 DNA methylation levels were higher in both newly diagnosed and treated type 2 diabetes patients with a mean diabetes duration of 3 years compared with subjects with normal glucose tolerance (19.8% and 20.2% vs. 16.9%, P < 0.001 for both). Serum levels of IGFBP-1 in newly diagnosed and in treated type 2 diabetes patients were lower compared with healthy individuals (18 μg/l both vs. 24 μg/l, P = 0.011, P < 0.001). IGFBP1 methylation levels but not serum IGFBP-1 levels in type 2 diabetes patients were independent of body mass index. Newly diagnosed patients with a family history of diabetes (FHD) had higher IGFBP1 methylation levels than those without FHD (20.3% vs. 18.6%, P = 0.017).

Conclusions: This study provides the first evidence that changes in DNA methylation of the IGFBP1 gene are associated with type 2 diabetes in Swedish men and suggests that increased IGFBP1 DNA methylation and decreased IGFBP-1 serum levels are features of type 2 diabetes with a short duration.

Figure 1

DNA methylation and serum levels of IGFBP1 in Swedish men with normal glucose tolerance and type 2 diabetes. (A)IGFBP1 DNA methylation levels at each of the six CpG sites in patients with newly diagnosed type 2 diabetes and in patients undergoing treatment were significantly higher compared with those in non-diabetic control subjects (P < 0.001 for all comparisons with non-diabetic subjects). (B) Combining all six CpG sites together as total, significantly increased DNA methylation levels of the IGFBP1 gene in newly diagnosed and treated type 2 diabetes patients in comparison with the controls were found (18.9%, 19.8% and 16.9%, respectively, P < 0.001 for both type 2 diabetes group vs. controls.) (C) Serum IGFBP-1 levels were significantly higher in non-diabetic control subjects than in both newly diagnosed and treated patients with type 2 diabetes. P values: * < 0.05, *** < 0.001. IGFBP-1, insulin-like growth factor binding protein-1; NGT, normal glucose tolerance; T2D, type 2 diabetes.

Figure 2

DNA methylation and serum levels of IGFBP1 according to family history of diabetes. Compared with those without a family history of diabetes (FHD) (0), non-diabetic control subjects with FHD (1) had similar IGFBP1 DNA methylation levels (16.9% vs. 17.0%, P = 0.895, A) but significantly lower serum protein levels (19 vs. 25 μg/L, P = 0.018) (B). Newly diagnosed type 2 diabetes patients with FHD had significantly increased IGFBP1 DNA methylation levels (20.3% vs. 18.6%, P = 0.014) (A), higher glucose (8.1 vs. 6.5 mmol/l, P = 0.007) and insulin (153.6 vs. 118.8 pmol/l, P = 0.022) levels compared to patients without FHD (B). There were no differences in levels of IGFBP1 DNA methylation, serum IGFBP-1, glucose or insulin between treated type 2 diabetes patients with and without FHD. P value: * < 0.05. FHD, family history of diabetes; NGT, normal glucose tolerance; T2D, type 2 diabetes.

Figure 3

DNA methylation and serum levels of IGFBP1 according to body mass index. (A) No differences were found in the IGFBP1 DNA methylation levels between lean and overweight/obese subjects in non-diabetic control subjects, newly diagnosed and treated type 2 diabetes patients. (B) However, lean individuals had significantly higher serum IGFBP-1, lower insulin and similar glucose levels compared with subjects who were overweight/obese. BMI, body mass index; IGFBP-1, insulin-like growth factor binding protein-1; NGT, normal glucose tolerance; T2D, type 2 diabetes.