Effect Of HIF-1 On Normal Pregnancy And Its Relation To Preeclampsia

Background: From the fertilization to the establishment of placenta-fetal blood circulation, the embryo and trophoblast undergo oxygen changing. The oxygen concentration is only 10—15mmHg when fertilized ovum implants into the endometnum, and the nutrition is supplied by endometrium glands. The oxygen concentration is up to 60mmHg when the sufficient placenta-fetal blood circulation sets up at around 12 weeks' gestation, and the oxygen and nutrition to the embryo relays on placenta-fetal blood exchanging. The embryo and the trophoblast are exposed in a hypoxic environment before 12 weeks' gestation, which is essential to the early embryonic development and makes embryo free from damage of oxygen free radicals. The hypoxic environment can induce angiogenesis and promote early development of some organs.The establishment of sufficient placenta-fetal blood circulation relys on trophoblast cells' invading into the uterine wall. The extravilloustrophoblast cells invade into spiral arteries where they replaces the vascular wall and converses the narrow caliber arteries into distented uteroplacental arteries, which can increase blood flow to the placenta and allow an adequate supply of oxygen and nutrition to the growing fetal. The invasive activity of the extravillous trophoblast cell is low before 8 weeks' gestation, increasing after 8 weeks', peaking at around 12 weeks' and declining thereafter. The invasive activity of the extravillous trophoblast cell is tempsrally and spatally regulated. If the invasive activity of the extravillous trophoblast cell is too low, it will make shallow invasion and lead to preeclampsia or intrauterine growth retardation. If the invasive activity of the extravillous trophoblast cell is too high, it maybe lead to gestational trophoblastic tumor.Preeclampsia is a major cause of maternal and fetal morbidity and mortality. The placenta plays an important role in pathogenesis of preeclampsia, and the placental ischemia/hypoxia may be the initial pathogenesis. Now the pathogenesis of preeclampsia is thought to be the shallow invading of trophoblast into the endometrium, which affects the establishment of sufficient placenta-fetal blood circulation and leads to placental ischemia/hypoxia. Hypoxic trophoblast can produce various vascular activity substances and release into maternal blood circulation to make vascular endothelial dysfuctions, which lead to hypertension, proteinuria and edema.The hypoxia inducible factor 1(HIF-1) is a transcription factor in mammal cells that can transfer the hypoxic signal and activate gene transcription in response to altering oxygen concentration of cells. HIF-1 is a member of bHLH-PAS supperfamily of proteins consistingof α and β subunits. Expression of the HIF-1α subunit is tightly regulated by the cellular oxygen concentration and determines the level of HIF-1 activity. The expression of HIF-la increases in hypoxic condition, and transposites into the nuclear, where the HIF-la integrates with HIF-1β to form activating HIF-1 that binds with the site of target gene to form transcriptional compound. The transcriptional compound can activate target gene transcription and increase biological protein's synthesis which make the cell adapting to hypoxia. The HIF-1 also participates in pathophysiology of many diseases.Whether the HIF-1 participates in embyo development and differentiation in hypoxia and the mechanism of inhibiting effect of hypoxia on the invasive activity of trophoblast are not fully elucidated, and the effect of HIF-1 on pathophysiology of preeclampsia is also not known.Objective: 1 To investigate the role of HIF-1 in the different stages of pregnancy and its modulation effect on the invasive activity of trophoblast. 2 To investigate the role of HIF-1 in the pathogenesis of preeclampsia.Methods: 1. The protein and mRNA expressions of HIF-la in the embryo, villous and normal term placentas are detected by histochemical analyses and PCR. 2. After the Be Wo cells and villous explants were interfered by sense or antisense oligonucleotide of HIF-1α under hypoxic condition, the level of HIF-1 α protein wasanalyzed by Western blot, and the level of HIF-1 α and TGF-3 β mRNA were measured with real time PCR. 3. Ten placental tissues of preeclampsia and 10 age-matched placental tissues of normal pregnancy were obtained. The level of HIF-1 α protein was analyzed by Western blot; The level of HIF-1 a and TGF-3β mRNA was determined by real time PCR; The location of HIF-1 a mRNA in preeclamptic placental was determined by in situ hybridization; The location of HIF-1α protein in preeclamptic placenta was detected by histochemical analyses.Results: 1. The protein and mRNA expression of HIF-1α were detected in human pre-implantation embryos, early pregnancy villous and normal term placentas as well. 2. Hypoxia increased expressions of HIF-1α and TGF-3β in BeWo cell and early pregnancy villous. After the HIF-1 α was downregulated by antisense oligonucleotide, the expression level of HIF-α and TGF-3β decreased. 3. The protein and mRNA expressions of HIF-1α were higher in preeclamptic placentas than in normal placentas; The expression of HIF-1α mRNA and protein were mainly located in the trophoblast and fetoplacental vascular endothelium in the preeclamptic placentas.Conclusions: 1. HIF-1α protein and mRNA are expressed in human pre-implantation embryo, early pregnancy villous and normal term placentas, and HIF-1α may participate in physiology of normal pregnancy. 2. hypoxia can induce TGF-3β expression to inhibit the...