Placental HIF-1α, HIF-2α, membrane and soluble VEGF receptor-1 proteins are not increased in normotensive pregnancies complicated by late-onset intrauterine growth restriction

Inadequate trophoblast invasion and spiral artery remodeling leading to poor placental perfusion are believed to underlie the pregnancy pathologies preeclampsia (PE) and intrauterine growth restriction (IUGR). The main objective of this study was to investigate hypoxia-inducible transcription factor-α (HIF-α) and downstream genes (VEGF receptor-1) Flt-1 and soluble fms-like tyrosine kinase 1 (sFlt-1) proteins in IUGR placentas. Placentas from normal pregnant (NP; n = 18), PE ( n = 18), and IUGR ( n = 10) patients were investigated. Normotensive patients with IUGR delivered babies at ≥ 37 wk of gestation with birth weights of <10% and asymmetrical growth. HIF-1α, -2α, Flt-1, and sFlt-1 protein, and mRNA were assessed by Western and Northern blot analyses, respectively. The results are expressed as ratios of the densitometric values for each pair of pathologic and normal placentas, a ratio of 1.0 indicating no difference. Comparable to our earlier studies, the PE/NP ratios for HIF-1α, -2α, and Flt proteins were significantly increased by 50–100% (all P < 0.01 vs. 1.0). Unexpectedly, the IUGR/NP ratios for HIF-1α and -2α proteins were 1.03 ± 0.07 and 0.96 ± 0.16, respectively, and for Flt and sFlt were 1.14 ± 0.15 and 0.95 ± 0.12, respectively (all P = not significant vs. 1.0). Northern blot analysis revealed comparable levels of HIF-α mRNA in abnormal and normal placentas. In contrast to PE, HIF-α proteins and regulated genes are not increased in placentas from normotensive pregnant women delivering small, asymmetrically grown babies ≥ 37 wk of gestation. The absence of an increase in HIF-α protein is not due to insufficient HIF-α mRNA for protein synthesis. Thus, the placentas from women with PE and late IUGR are fundamentally different at the molecular level.