Leptin gene epigenetic adaptation to impaired glucose metabolism during pregnancy

Abstract

Objective: To verify whether the leptin gene epigenetic (DNA methylation) profile is altered in the offspring of mothers with gestational impaired glucose tolerance (IGT).

Research design and methods: Placental tissues and maternal and cord blood samples were obtained from 48 women at term including 23 subjects with gestational IGT. Leptin DNA methylation, gene expression levels, and circulating concentration were measured using the Sequenom EpiTYPER system, quantitative real-time RT-PCR, and enzyme-linked immunosorbent assay, respectively. IGT was assessed after a 75-g oral glucose tolerance test (OGTT) at 24-28 weeks of gestation.

Results: We have shown that placental leptin gene DNA methylation levels were correlated with glucose levels (2-h post-OGTT) in women with IGT (fetal side: ρ=-0.44, P≤0.05; maternal side: ρ=0.53, P≤0.01) and with decreased leptin gene expression (n=48; ρ≥-0.30, P≤0.05) in the whole cohort. Placental leptin mRNA levels accounted for 16% of the variance in maternal circulating leptin concentration (P<0.05).

Conclusions: IGT during pregnancy was associated with leptin gene DNA methylation adaptations with potential functional impacts. These epigenetic changes provide novel mechanisms that could contribute to explaining the detrimental health effects associated with fetal programming, such as long-term increased risk of developing obesity and type 2 diabetes.

Figure 1

Leptin gene CpG island proximal promoter region. The forward CpG island sequence is shown in italics and delimited by hyphens. The leptin exon 1 sequence is in bold type. Arrows indicate both PCR primer sequences. Underlined cytosines have already been associated with demethylation and leptin gene transcription activation (6). The sequence has been numbered relative to the first leptin gene codon (exon 2; Ensembl release 56 [September 2009]). The CpG sites have been numbered relative to the 3′ of the amplicon. The CpG no. 31 corresponds to −204 position in Melzner et al. (6).

Figure 2

DNA methylation levels for each CpG site and sample analyzed. *Cytosines that contributed to the summary statistic.

Figure 3

Correlations between leptin DNA methylation and 2-h post-OGTT glucose levels, within the IGT group (A and B), leptin DNA methylation and mRNA levels (C and D); and leptin mRNA levels and circulating concentrations measured at the end of the third trimester (between weeks 36 and 37) of pregnancy (E and F). IGT was defined as a 2-h glucose ≥7.8 mmol/l after a 75-g OGTT performed between 24 and 28 weeks of gestation. ‡Leptin DNA methylation n = 47 (NGT = 25 and IGT = 22). *Adjusted for first trimester BMI. †n = 43 (IGT [−] = 23 and IGT [+] = 20). AU, arbitrary units.