Epigenetic analyses of the insulin-like growth factor binding protein 1 gene in type 1 diabetes and diabetic nephropathy

BACKGROUND: Clinical observations have demonstrated that high levels of circulating insulin-like growth factor binding protein-1 (IGFBP-1) are associated with type 1 diabetes (T1D), whereas low serum IGFBP-1 levels are associated with the risk of type 2 diabetes (T2D). Recently, we reported that increased DNA methylation levels in the IGFBP1 gene were associated with T2D. In the present study, we evaluated the epigenetic changes of IGFBP1 in T1D and diabetic nephropathy (DN). RESULTS: In total, 778 Swedish individuals, including T1D patients with or without DN and subjects with the normal glucose tolerance (NGT), were involved in the study. IGFBP1 methylation levels in genomic DNA extracted from peripheral blood were analyzed with bisulfite pyrosequencing. Serum IGFBP-1 levels were measured with radioimmunoassay. We found that DNA methylation levels in the IGFBP1 gene were decreased (15.6% versus 16.9%; P < 0.001), whereas serum IGFBP-1 levels were increased (31 versus 24 μg/L, P = 0.003) in T1D patients compared with NGT subjects. Furthermore, T1D patients with DN had increased circulating IGFBP-1 concentration compared with the patients without DN (52 versus 28 μg/L; P = 0.006). However, no difference of the IGFBP1 DNA methylation levels between T1D patients with and without DN was observed. CONCLUSIONS: This study shows for the first time that T1D patients had decreased DNA methylation levels in the IGFBP1 gene and further implies that increased circulating IGFBP-1 levels are associated with T1D and DN.