Hypoxia plays an important role in normal placental development and its pathological processes. Cellular hypoxia leads to the expression of specific transcription factors including hypoxia inducible factor HIF- 1alpha and -2alpha which heterodimerized with constitutively expressed HIF-1beta and bind to the hypoxia response element of many genes. Recently, we documented the expression and ontogeny of HIF-1alpha and -2alpha mRNA, protein and DNA binding activity in placental villi. We showed regulation by hypoxia at the level fo protein, but not mRNA, as well as widespread and overlapping cellular distribution of HIF- 1alpha and -2alpha consistent with the physiological with the physiological hypoxia at that gestational stage. The main regulation of HIF-1alpha and -2alpha protein turnover has recently been shown to be through ubiquitin-proteasomal mediated degradation. Thus, we have begun investigating this pathway in the human placenta. Our preliminary data suggest impaired oxygen-dependent degradation of HIF-1alpha and -2alpha in villous explants from preeclamptic placentas. Thus, deficient degradation of HIF-1alpha and -2alpha contributes to exaggerated expression in preeclamptic placenta. Based on these findings five general hypotheses are proposed. Hypothesis 1 Proteasomal degradation of HIF-1alpha and -2alpha proteins is impaired in placental villi from women with preeclampsia, thereby contributing to deficient oxygen- dependent degradation and exaggerated placental expression. Hypothesis 2 Impaired uqiquitinylation of HIF-1alpha and -2alpha contributes to deficient proteasomal degradation of these transcription factors in placental villi of women with preeclampsia. Hypothesis 3 HIF-1alpha and -2alpha proteins are over-expressed by extravilous trophoblasts in the placental bed of women with preeclampsia. Hypothesis 4 HIF-1alpha and -2alpha regulated the expression of specific genes in the human placenta that are likewise inappropriately regulated in preeclampsia. Hypothesis 5 Deficient ubiquitin-proteasomal degradation of HIF-1alpha and-2alpha is a widespread abnormality occurring in other tissues of preeclamptic women and in their offspring. In summary, we propose to investigate the molecular mechanisms and consequences of HIF-1alpha and -2alpha over-expression in the preeclamptic placenta. These studies will likely advance our understanding of the placental contribution to the pathophysiology of preeclampsia.
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