Background: The visceral omental adipose tissues were closely associated with gestational diabetes mellitus (GDM). Till now, there had been few reports about genome-wide methylation profile in visceral omental adipose tissues of GDM.
Objective: To investigate the pathogenesis of GDM by measuring and comparing the genome-wide DNA methylation patterns in visceral omental adipose tissues between pregnant women with GDM and the normal pregnancies, in order to provide the clues for explaining the mechanism and process of GDM.
Methods: Pregnant women who accepted regular prenatal examination and hospital delivery in Department of Obstetrics and Gynecology, the First Affiliated Hospital of Kunming Medical University from January 2012 to May 2014 were enrolled. Three cases of GDM were enrolled as GDM group, while three cases of healthy pregnant women as control group. The visceral omental adipose tissues were obtained at time of term caesarean section. The genome-wide DNA of these tissues were extracted. The products were cleaved after degeneration and amplification. The DNA fragment were hybridized with Illumina Methylation Bead Chip chip. The methylation level of each gene sites were calculated according to Methylation Analysis Algorithms with deviation correction and infiltration. DAVID database was used to carry out Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) signaling pathway analysis in methylation gene with significant difference. Five cases of pregnant women with and without GDM in the same period were selected to verify the difference of methylation level of candidate gene promoter region.
Results: 1 298 genes were hypomethylated and 1 570 genes were hypermethylated in GDM group. Among them, the methylation of TMEM195, TCF7L2, IGF1 and IGF1R might be closely associated with regulation of blood glucose level. The methylation of DGKG and NRXN3 might be closely associated with BMI. The GO function analysis supported that the genes with hypomethylation were mainly involved in the biological processes, such as the regulation of cascade reaction activity, the regulation of cell apoptosis and protein transport, the cellular components were mainly extracellular matrix. The biological processes involved in the hypermethylated genes were mainly antigen processing and presentation, and antigen processing and presentation participated by major histocompatibility complex (MHC) Ⅱ. The main cellular components were muscle actin cytoskeleton proteins, MHC and so on. In the analysis of KEGG signal pathway, the pathway of enrichment ＞20.000 had antigen processing and presentation (23.142), PPAR (22.068). The different methylation gene HLA-G and PPARGC1A were respectively selected from antigen processing and presentation and PPAR signal pathway to validate. The methylation level of HLA-G promoter region in the visceral omental adipose tissues of GDM pregnant women was higher than non GDM pregnant women (t=4.968,P=0.001). There was no statistically significant difference in the methylation of PPARGC1A promoter region between GDM pregnant women and non GDM pregnant women (t=0.929,P=0.380).
Conclusion: There are statistically significant difference in gene methylation sites and levels between GDM and healthy pregnant women. The different methylation gene mainly involve in antigen processing and presentation and PPAR signaling pathway.