Associations between an integrated component of maternal glycemic regulation in pregnancy and cord blood DNA methylation

Cohort profile: the Genetics of Glucose regulation in Gestation and Growth (Gen3G) - a prospective prebirth cohort of mother-child pairs in Sherbrooke, Canada, 3-year and 5-year follow-up visits

PURPOSE

Initiated in 2010, the Genetics of Glucose regulation in Gestation and Growth (Gen3G) prospective cohort investigates the pathophysiology of impaired glycaemic regulation in pregnancy and evaluates its impact on both the mothers and her offspring health trajectory. Follow-up visits 3 and 5 years after delivery aimed to investigate pregnancy-related risk factors such as maternal obesity and gestational hyperglycaemia in relation to the mother's metabolic health after pregnancy, and with offspring health outcomes such as risk of obesity and neurodevelopmental problems in early childhood. We also investigated molecular mechanisms involved in the fetal programming of these later health outcomes.

PARTICIPANTS

Of the 1024 women originally recruited in the first trimester of pregnancy, we have targeted the 854 who had complete glucose tolerance test data and the 724 newborns who provided placenta and/or cord blood samples for follow-up recruitment. Of these, 695 mother-child dyads agreed to be contacted for the prospective follow-up visits. 448 and 521 mother-child dyads completed the research visits at 3 and 5 years after delivery respectively.

FINDINGS TO DATE

At both visits, we collected the mother's and child's medical history, lifestyle (using validated questionnaires), sociodemographic status, anthropometric measurements, mother's blood samples, child's saliva samples and growth charts. At the 5-year-old visit, we additionally collected the mother's and child's urine and stool samples and the child's blood samples; we performed a 75 g oral glucose tolerance test in the mothers and assessed the body composition in children using dual-energy X-ray absorptiometry. Using the Gen3G rich longitudinal data set, we have enhanced the understanding of the pathophysiology and characterisation of the heterogeneity of gestational diabetes mellitus, and we have shown that gestational hyperglycaemia and insulin resistance are associated with offspring epigenetics (DNA methylation) variations in the placenta, cord blood and blood at 5 years of age, as well as with offspring anthropometric, metabolic and neurodevelopmental outcomes in early childhood.

FUTURE PLANS

We are currently conducting a prospective follow-up of mothers and their children 12 years after delivery to study how prenatal and early-life metabolic factors may programme childhood adiposity and obesogenic dietary behaviours. This follow-up should be completed by the end of 2026.

Multigenerational diabetes mellitus

Gestational diabetes (GDM) changes the maternal metabolic and uterine environment, thus increasing the risk of short- and long-term adverse outcomes for both mother and child. Children of mothers who have GDM during their pregnancy are more likely to develop Type 2 Diabetes (T2D), early-onset cardiovascular disease and GDM when they themselves become pregnant, perpetuating a multigenerational increased risk of metabolic disease. The negative effect of GDM is exacerbated by maternal obesity, which induces a greater derangement of fetal adipogenesis and growth. Multiple factors, including genetic, epigenetic and metabolic, which interact with lifestyle factors and the environment, are likely to contribute to the development of GDM. Genetic factors are particularly important, with 30% of women with GDM having at least one parent with T2D. Fetal epigenetic modifications occur in response to maternal GDM, and may mediate both multi- and transgenerational risk. Changes to the maternal metabolome in GDM are primarily related to fatty acid oxidation, inflammation and insulin resistance. These might be effective early biomarkers allowing the identification of women at risk of GDM prior to the development of hyperglycaemia. The impact of the intra-uterine environment on the developing fetus, "developmental programming", has a multisystem effect, but its influence on adipogenesis is particularly important as it will determine baseline insulin sensitivity, and the response to future metabolic challenges. Identifying the critical window of metabolic development and developing effective interventions are key to our ability to improve population metabolic health.

Cross-Ancestry DNA Methylation Marks of Insulin Resistance in Pregnancy: An Integrative Epigenome-Wide Association Study

Although there are some epigenome-wide association studies (EWAS) of insulin resistance, for most of them authors did not replicate their findings, and most are focused on populations of European ancestry, limiting the generalizability. In the Epigenetics in Pregnancy (EPIPREG; n = 294 Europeans and 162 South Asians) study, we conducted an EWAS of insulin resistance in maternal peripheral blood leukocytes, with replication in the Born in Bradford (n = 879; n = 430 Europeans and 449 South Asians), Methyl Epigenome Network Association (MENA) (n = 320), and Botnia (n = 56) cohorts. In EPIPREG, we identified six CpG sites inversely associated with insulin resistance across ancestry, of which five were replicated in independent cohorts (cg02988288, cg19693031, and cg26974062 in TXNIP; cg06690548 in SLC7A11; and cg04861640 in ZSCAN26). From methylation quantitative trait loci analysis in EPIPREG, we identified gene variants related to all five replicated cross-ancestry CpG sites, which were associated with several cardiometabolic phenotypes. Mediation analyses suggested that the gene variants regulate insulin resistance through DNA methylation. To conclude, our cross-ancestry EWAS identified five CpG sites related to lower insulin resistance.