Differential regulation of a placental SAM68 and sFLT1 gene pathway and the relevance to maternal vitamin D sufficiency.

OBJECTIVE The goal of this study was to determine if an axis of placental gene expression associated with early onset and severe preeclampsia (EOSPE) was operative in term pregnancy and correlated with vitamin D sufficiency. METHODS qPCR analysis of NKX2-5, SAM68, sFLT1 and membrane bound VEGFR1/FLT1 mRNA expression was conducted in placentas from 43 subjects enrolled in a vitamin D3 pregnancy supplementation trial. Pair-wise rank order correlations between patient-specific gene expression levels were calculated, and their relationship to maternal 25(OH)D status was assessed by a two-sample Wilcoxon test. Additionally, we probed the mechanistic link between SAM68 and sFLT1 using siRNA depletion in a human trophoblast cell line model. RESULTS Positive and highly significant correlations were found between SAM68 vs. sFLT1 and SAM68 vs. FLT1 expression levels, as were significant and differential correlations between the expression of these genes and perinatal 25(OH)D status. The variability when stratified by race/ethnicity was qualitatively distinct from those previously observed in EOSPE. Mechanistic studies confirmed a functional role for SAM68 protein in the regulation of sFLT1 expression. NKX2-5 expression was not significantly correlated with sFLT1 or SAM68 expression in these samples, suggesting that its expression may be significant at earlier stages of pregnancy or be restricted to pathological settings. CONCLUSIONS These data further support our overarching hypothesis that SAM68 expression is a key determinant of VEGFR1 isoform expression in the placenta, and provide additional insights into how this gene pathway may be differentially deployed or modified in normal and pathological pregnancies.