Placental Megalin and Cubilin Expression is Associated with Markers of Vitamin D Status but Not Fetal Bone Growth During Adolescent Pregnancy
Authors: Whisner Corrie M , Thomas Carrie E , O'Brien Kimberly O 
Published: June 2021

Megalin and cubilin are highly expressed in the human placenta and may be involved in modulating maternal‐fetal 25(OH)D status. Few studies have focused on the expression of these transporters and associations with vitamin D‐related outcomes during pregnancy. The purpose of this study was to characterize placental transcript expression of megalin and cubilin in a cohort of pregnant adolescents with suboptimal vitamin D status and evaluate their relationships with markers of maternal and neonatal vitamin D status and fetal bone growth. Placental tissue was obtained at delivery from pregnant adolescents (n=86; age ≤18 y) enrolled in a longitudinal study designed to assess maternal and fetal bone health in Rochester, New York. During pregnancy, teens completed up to three study visits during which maternal anthropometrics and bone quality (heel ultrasound) and standard fetal biometry measures (sonography) were obtained. Maternal serum obtained at mid‐gestation (MG; 26.2 ± 3.5 gestational weeks (GW)) and delivery (39.9 ± 1.2 GW) and cord blood collected at delivery were analyzed for 25(OH)D (Diasorin assay), 1,25(OH)2D (thymus receptor binding assay), PTH (ELISA), NTX (ELISA), osteoprotegerin (ELISA) and osteocalcin (RIA) concentrations. RNA was extracted from placental tissue and real‐time PCR reactions were performed in triplicate using megalin and cubilin‐specific primers (sequence ID numbers NM_004525.2 and NM_001081.3, respectively). Beta‐actin was used as an endogenous control (sequence ID NM_001101.2). Non‐parametric comparisons were completed using Wilcoxon rank sums and Chi‐square statistics, while two‐sample t tests and ANOVA were used for parametric comparisons. Pearson and Spearman correlations were used to assess associations between placenta transcript expression and maternal and fetal characteristics. This was a diverse cohort with 53 (61.6%) and 33 (38.4%) teens self‐reporting as African American and Caucasian, respectively; a total of 24 (27.9%) reported being Hispanic. Cubilin and megalin transcript expression were positively correlated with one another (r=0.294, p=0.006). Megalin and cubilin expression were not significantly associated with in utero fetal growth, infant birth weight and length, or measures of maternal heel bone quality. Significant positive associations were observed between placental cubilin expression and 1‐alpha hydroxylase (r=0.251, p<0.030) and 24‐hydroxylase (r=0.254, p=0.028) mRNA expression. Both megalin and cubilin mRNA levels were significantly negatively associated with maternal serum 1,25(OH)2D (r= −0.359, p=0.007 and r= −0.299, p=0.027, respectively) but not fetal 1,25(OH)2D or maternal and fetal 25(OH)D. Megalin transcript expression was also negatively associated with PTH concentrations in cord blood (r= −0.444, p=0.026) but not maternal PTH at MG or delivery. Pregnant teens with lower circulating 1,25(OH)2D had greater expression of megalin and cubilin mRNA suggestive of prenatal regulatory mechanisms to maintain maternal and fetal vitamin D status.Support or Funding InformationFunded by USDA/NIFA Grant No. 2012‐67012‐19815