In Utero Exposure to Gestational Diabetes Alters DNA Methylation and Gene Expression of CDKN2A/B in Langerhans Islets of Rat Offspring

DNA methylation, a major epigenetic reprogramming mechanism, contributes to the increased prevalence of type 2 diabetes mellitus (T2DM). Based on genome-wide association studies, polymorphisms in CDKN2A/B are associated with T2DM. Our previous studies showed that gestational diabetes mellitus (GDM) causes apoptosis in β-cells, leading to a reduction in their number in pancreatic tissue of GDM-exposed adult rat offspring. The aim of this study was to examine the impact of intrauterine exposure to GDM on DNA methylation, mRNA transcription, as well as protein expression of these factors in the pancreatic islets of Wistar rat offspring. Our hypothesis was that the morphological changes seen in our previous study might have been caused by aberrant methylation and expression of CDKN2A/B.

In this experimental study, we delineated DNA methylation patterns, mRNA transcription and protein expression level of CDKN2A/B in the pancreatic islets of 15-week-old rat offspring of streptozotocin-induced GDM dams. We performed bisulfite sequencing to determine the DNA methylation patterns of CpGs in candidate promoter regions of CDKN2A/B. Furthermore, we compared the levels of mRNA transcripts as well as the cell cycle inhibitory proteins P15 and P16 in two groups by qPCR and western blotting, respectively.

Our results demonstrated that hypomethylation of CpG sites in the vicinity of CDKN2A and CDKN2B genes is positively related to increased levels of CDKN2A/B mRNA and protein in islets of Langerhans in the GDM offspring. The average percentage of CDKN2A promoter methylation was significantly lower in GDM group compared to the controls (P<0.01).

We postulate that GDM is likely to exert its adverse effects on pancreatic β-cells of offspring through hypomethylation of the CDKN2A/B promoter. Abnormal methylation of these genes may have a link with β-cell dysfunction and diabetes. These data potentially lead to a novel approach to the treatment of T2DM.