Correlation of CTGF gene promoter methylation with CTGF expression in type 2 diabetes mellitus with or without nephropathy

Increasing evidence shows that DNA methylation is involved in the development and progression of diabetes mellitus (DM) and its complications. Previous studies conducted by our group have indicated that high glucose levels may induce the demethylation process of the connective tissue growth factor (CTGF) gene promoter and increase the expression of CTGF in human glomerular mesangial cells. Based on these findings, the aim of the present study was to investigate the methylation level of genomic DNA and the CTGF promoter in patients with type 2 DM and to analyze its possible correlation with CTGF expression. Methylation levels of the whole genomic DNA were detected by high-performance liquid chromatography in a non-diabetes control (NDM) group (n=29), a diabetes without nephropathy (NDN) group (n=37) and a diabetes with nephropathy (DN) group (n=38). CTGF promoter methylation levels were detected by methylation-specific polymerase chain reaction and bisulfite sequencing. The levels of serum CTGF were assessed using the enzyme-linked immunosorbent assay. The methylation levels of the whole genomic DNA were not significantly different among the three groups. However, the CTGF methylation levels in the two diabetes groups were significantly lower than those in the NDM group (P<0.05), with the lowest methylation level in the DN group (P<0.05). The CTGF protein levels in the DN group were significantly higher than those in the NDM and NDN groups (P<0.05). Levels of CTGF were negatively correlated with the estimated glomerular filtration rate (eGFR) and the methylation level of the promoter, while they were positively correlated with age, urinary albumin-to-creatinine ratio (UACR), blood urea nitrogen, creatinine, fasting blood sugar and postprandial blood glucose. Multiple stepwise regression analysis showed that CTGF expression was associated with the UACR, CTGF methylation level and eGFR. DNA methylation is a regulatory mechanism of CTGF expression, which is decreased in patients with DM, particularly in those with DN, and may contribute to the pathogenesis of nephropathy.