Preeclampsia, defined by the onset of
de novo
hypertension and proteinuria near the 20th week of gestation, is a major contributor to maternal and fetal morbidity and mortality worldwide. Preeclampsia is often preceded by placental ischemia and an imbalance in circulating angiogenic factors (e.g. VEGF - vascular endothelial growth factor, sFlt-1 - soluble VEGF receptor 1). Recent studies also report increased expression of endoplasmic reticulum (ER) stress products in preeclamptic placentas. Our laboratory recently reported 5-aminoimidazole-4-carboxamide-3-ribonuceloside (AICAR) reduces blood pressure and improves angiogenic balance (increased VEGF, decreased sFlt-1) in rats with placental ischemia-induced hypertension, but the mechanism is unclear. We hypothesized AICAR would decrease sFlt-1, increase AMPK phosphorylation, and decrease ER stress in hypoxic placental villous explants. On day 19 of pregnancy, placentas were isolated from four Sprague-Dawley rats and immediately dissected in ice-cold phosphate-buffered saline. Explants were cultured for 12 hours in physiologic normoxic (8% O2) and hypoxic (1.5% O2) conditions. All experiments were performed in triplicate. VEGF secretion was unaffected by AICAR treatment in both normoxic and hypoxic conditions. AICAR decreased sFlt -1 secretion in hypoxic villi (2147±116 vs. *1411±67, P<0.05). Additionally, AMPK activation ratio was increased with AICAR, and was hypoxic-dependent (8%: 2.9±0.3; 8%+A: 3.3±0.1; 1.5%: 3.5±0.1; 1.5%+A: *4.5±0.01;*P<.05). Moreover, markers of ER stress were increased with hypoxia, and decreased with AICAR treatment (BiP 8%: 1.2±0.2; 8%+A: 1.0±0.0; 1.5%: *8.3±0.7; 1.5%+A: 1.9±0.0.3;*P<.05), (CHOP 8%: 0.5±0.0; 8%+A: 0.3±0.1; 1.5%: *1.7±0.1; 1.5%+A: 0.7±0.1;*P<.05). ATF4 was not changed with hypoxia or AICAR treatment. The present data show that AICAR stimulates AMPK phosphorylation and decreases ER stress response proteins in hypoxic placental villi. Further, the present data support the hypothesis that AICAR restores angiogenic balance by decreasing sFlt-1 rather than increasing VEGF secretion from placental villi. These findings suggest AICAR may improve placental function during pregnancies complicated by placental-ischemia.
Cytological events involved in protein synthesis in cellular and syncytial trophoblast of human placenta. An electron microscope autoradiographic study of [3H]leucine incorporation.