Epigenetic adaptation of the placental serotonin transporter gene (SLC6A4) to gestational diabetes mellitus

We tested the hypothesis that gestational diabetes mellitus (GDM) alters the DNA methylation pattern of the fetal serotonin transporter gene (SLC6A4), and examined the functional relevance of DNA methylation for regulation of the SLC6A4 expression in the human placenta. The study included 50 mother-infant pairs. Eighteen mothers were diagnosed with GDM and 32 had normal glucose tolerance (NGT). All neonates were of normal birth weight and born at term by planned Cesarean section. DNA and RNA were isolated from samples of tissue collected from the fetal side of the placenta immediately after delivery. DNA methylation was quantified at 7 CpG sites within the SLC6A4 distal promoter region using PCR amplification of bisulfite treated DNA and subsequent DNA sequencing. SLC6A4 mRNA levels were measured by reverse transcription D quantitative PCR (RT-qPCR). Functional SLC6A4 polymorphisms (5HTTLPR, STin2, rs25531) were genotyped using standard PCRbased procedures. Average DNA methylation across the 7 analyzed loci was decreased in the GDM as compared to the NGT group (by 27.1%, p = 0.037) and negatively correlated, before and after adjustment for potential confounder/s, with maternal plasma glucose levels at the 24th to 28th week of gestation (p0.05). The results suggest that DNA methylation of the fetal SLC6A4 gene is sensitive to the maternal metabolic state in pregnancy. They also indicate a predominant role of epigenetic over genetic mechanisms in the regulation of SLC6A4 expression in the human placenta. Longitudinal studies in larger cohorts are needed to verify these results and determine to which degree placental SLC6A4 changes may contribute to long-term outcomes of infants exposed to GDM

Placental <i>SLC6A4</i> mRNA levels according to maternal glucose tolerance status and <i>5-HTTLPR</i>/<i>rs25531</i> genotype.

<p>Shown are means and standard errors. p-values were 0.007, 0.316, and 0.176 for the main effect of diagnosis, main effect of genotype, and genotype x diagnosis interaction, respectively (two-way ANOVA). GDM, gestational diabetes mellitus; NGT, normal glucose tolerance; RER; relative expression ratio.</p

Association of placental <i>SLC6A4</i> methylation with categorical variables of the study population.

<p>Association of placental <i>SLC6A4</i> methylation with categorical variables of the study population.</p

Characteristics of newborns and their mothers stratified according to mother's glucose tolerance status.

<p>Characteristics of newborns and their mothers stratified according to mother's glucose tolerance status.</p

Placental <i>SLC6A4</i> methylation levels correlate with maternal fasting glucose concentrations and placental <i>SLC6A4</i> mRNA levels.

<p>Scatterplots depict correlation of placental <i>SLC6A4</i> methylation with (A) maternal fasting glucose levels in the 24th to 28th week of pregnancy, and (B) placental <i>SLC6A4</i> mRNA levels. n, number of subjects; r_p, Pearson's correlation coefficient; r_s, Spearman's correlation coefficient; RER, relative expression ratio.</p