Placental miR-3940-3p Is Associated With Maternal Insulin Resistance in Late Pregnancy.

Context: An increase in maternal insulin resistance (IR) during pregnancy is essential for normal fetal growth. The mechanisms underlying this adaptation are poorly understood. Placental factors are believed to instigate and maintain these changes, as IR decreases shortly after delivery. Methylation of placental gene loci that are common targets for miRNAs are associated with maternal IR.

Objective: We hypothesized that placental miRNAs targeting methylated loci are associated with maternal IR during late pregnancy.

Methods: We collected placentas from 132 elective cesarean sections and fasting blood samples at delivery to estimate maternal homeostasis model assessment of insulin resistance (HOMA-IR). Placental miRNA expression was measured via whole genome small-RNA sequencing in a subset of 40 placentas selected by maternal pre-gravid body mass index (BMI) and neonatal adiposity. Five miRNAs correlated with maternal HOMA-IR and previously identified as targeting methylated genes were selected for validation in all 132 placenta samples via RT-qPCR. Multiple regression adjusted for relevant clinical variables.

Results: Median maternal age was 27.5 years, with median pre-pregnancy BMI of 24.7 kg/m2, and median HOMA-IR of 2.9. Among the 5 selected miRNA, maternal HOMA-IR correlated with the placental expression of miRNA-371b-3p (r = 0.25; P = 0.008) and miRNA-3940-3p (r = 0.32; P = 0.0004) across the 132 individuals. After adjustment for confounding variables, placental miRNA-3940-3p expression remained significantly associated with HOMA-IR (β = 0.16; P = 0.03).

Conclusion: Placental miRNA-3940-3p was associated with maternal IR at delivery. This placental miRNA may have an autocrine or paracrine effect-regulating placental genes involved in modulating maternal IR.