Mediation Analysis Supports a Causal Relationship between Maternal Hyperglycemia and Placental DNA Methylation Variations at the Leptin Gene Locus and Cord Blood Leptin Levels

Abstract

Changes in fetal DNA methylation (DNAm) of the leptin (LEP) gene have been associated with exposure to maternal hyperglycemia, but their links with childhood obesity risk are still unclear. We investigated the association between maternal hyperglycemia, placental LEP DNAm (25 5′-C-phosphate-G-3′ (CpG) sites), neonatal leptinemia, and adiposity (i.e., BMI and skinfold thickness (ST) (subscapular (SS) + triceps (TR) skinfold measures, and the ratio of SS:TR) at 3-years-old, in 259 mother–child dyads, from Gen3G birth cohort. We conducted multivariate linear analyses adjusted for gestational age at birth, sex of the child, age at follow-up, and cellular heterogeneity. We assessed the causal role of DNAm in the association between maternal glycemia and childhood outcomes, using mediation analysis. We found three CpGs associated with neonatal leptinemia (p ≤ 0.002). Of these, cg05136031 and cg15758240 were also associated with BMI (β = −2.69, p = 0.05) and fat distribution (β = −0.581, p = 0.05) at 3-years-old, respectively. Maternal glycemia was associated with DNAm at cg15758240 (β = −0.01, p = 0.04) and neonatal leptinemia (β = 0.19, p = 0.004). DNAm levels at cg15758240 mediates 0.8% of the association between maternal glycemia and neonatal leptinemia (p < 0.001). Our results support that DNAm regulation of the leptin pathway in response to maternal glycemia might be involved in programming adiposity in childhood.

Maternal glucose in pregnancy is associated with child's adiposity and leptin at 5 years of age

“…Our findings also showed that higher post‐load maternal glucose level, and not fasting glucose, in the second trimester was associated with greater total body fat percentage in children using DXA at 5 years of age. These findings are in line with some studies evaluating adiposity in 5 to 7 years' old children 5‐7 but not all studies are consistent with these observations 9,14‐16 . Previous studies that showed associations between 1 and 2 hours post‐OGTT glucose levels and childhood adiposity have reported findings using indirect adiposity measures such as BMI z ‐score 5 or sum of skinfolds in children exposed to GDM 6 .…”

“…The development of adipose tissue starts at 14 to 16 weeks of gestation, 31 and if relative hyperglycaemia was already present early in pregnancy, development of the pre‐adipocytes and the adipocytes in mid‐pregnancy might be impacted. In previous reports from our group, 15,18 Mendelian Randomization and mediation analyses supported causal relationship between maternal glucose in pregnancy and DNA methylation of leptin gene ( LEP ) in placenta and in cord‐blood samples. In line with this hypothesis, in a case‐control of young adults (26‐35 years‐old), pre‐adipocytes isolated from subcutaneous adipose tissue (SAT) biopsy and cultured in vitro showed a decrease in LEP methylation (in differentiation study), plus an increase in leptin secretion and expression in the GDM‐exposed or the T1D‐exposed compared to the control group 32 .…”

“…Little is known about the relationship between maternal glucose along the whole spectrum of glycaemia and leptin levels during childhood. A few studies reported associations between maternal glycaemia and leptin levels in cord blood 15,17‐19 . In later childhood, reports so far are limited to two case–control studies that investigated the level of leptin in children exposed to GDM or other type of diabetes in pregnancy.…”

“…Many cohort studies have observed that gestational diabetes mellitus (GDM) or maternal hyperglycaemia is associated with greater adiposity in childhood, 5‐13 despite some controversies when looking into specific periods of child development or using different methods of adiposity assessment such as body mass index (BMI) z ‐score, 5 skinfolds thicknesses 6‐9,14‐16 and dual‐energy X‐ray absorptiometry (DXA) 10‐13 . Fewer studies have investigated the link between maternal glycaemia and child leptin levels as part of potential mechanism for this ‘adiposity programming’ 15,17‐21 . A few studies investigated leptin levels at birth and have reported that higher fasting glucose in the second trimester was associated with higher cord blood leptin 15,17,18 .…”

“…Fewer studies have investigated the link between maternal glycaemia and child leptin levels as part of potential mechanism for this ‘adiposity programming’ 15,17‐21 . A few studies investigated leptin levels at birth and have reported that higher fasting glucose in the second trimester was associated with higher cord blood leptin 15,17,18 . In childhood, two case–control studies investigated the relationship between GDM exposure and leptin levels at 6 to 13 years old 20 and 9 to 16 years old 21 and reported weak or no association after adjustment for confounders including pre‐pregnancy BMI.…”