Association of MAOA, 5-HTT, and NET promoter polymorphisms with gene expression and protein activity in human placentas.

Monoamine oxidase A (MAOA) and the transporters for serotonin (5-HTT) and norepinephrine (NET) may play important roles in regulating maternal monoamine neurotransmitters transferred across the placenta to the fetus. We investigated whether promoter polymorphisms in MAOA (uVNTR), 5-HTT (5-HTTLPR), and NET (NETpPR AAGG(4)) could influence gene expression and protein activity in human placentas. Normal term human placentas (n = 73) were collected, and placental MAOA, 5-HTT, and NET mRNA levels and protein activity were determined. The mRNA levels or protein activities were compared between different genotype groups. Placentas hemizygous (male fetus) or homozygous (female fetus) for MAOA uVNTR 4-repeat allele had significantly higher MAOA mRNA levels than those hemizygous or homozygous for the 3-repeat allele (P = 0.001). However, no significant difference in MAOA enzyme activity was found for these two groups of genotypes (P = 0.161). Placentas with the 5-HTTLPR short (S)-allele (S/S+S/L) had significantly lower 5-HTT mRNA levels and serotonin uptake rate than those homozygous for the long (L)-allele (L/L) (mRNA: P < 0.001; serotonin transporting activity: P < 0.001). Placentas homozygous for the NET AAGG(4) L(4) allele had significantly higher NET mRNA levels, as well as dopamine and norepinephrine uptake rates, than those with the S(4)/L(4) genotype (mRNA: P < 0.001; dopamine transporting activity: P = 0.012; norepinephrine transporting activity: P = 0.011). These findings suggest that the three promoter polymorphisms of MAOA, 5-HTT, and NET influence gene expression levels and protein activity of these genes in human placentas, potentially leading to different fetal levels of maternal monoamine neurotransmitters, which may have an impact on fetal neurodevelopment.