Netrin-4 Expression and Regulation by Hypoxia in Human Placenta
Résumé
Netrin-4 is a well-known actor involved in axonal guidance. Recently we have reported the cellular localization of netrin-4 in human placenta. Furthermore we demonstrated its role in placental angiogenesis. Here we determined netrin-4 mRNA expression in first trimester placenta. First, we showed an increase in netrin-4 mRNA expression at 11-13 weeks of gestation (wg), suggesting a negative regulation of netrin-4 expression by hypoxia. In fact, the human placenta undergoes a transition from a low oxygenated to a highly oxygenated environment during the first trimester of pregnancy. This physiological switch in oxygen tension is a prerequisite for proper placental development and involves the hypoxia-inducible factor (HIF-1), a protein that is up-regulated under hypoxic conditions. Then, we used the trophoblast cell line BeWo to test this hypothesis. BeWo cells cultured under hypoxic conditions exhibited decreased levels of netrin-4 mRNA expression. Using siRNA strategy, hypoxia-inducible factor 1α (HIF-1α) knock-down induced a significant increase in netrin-4 mRNA expression. Altogether these results indicate that netrin-4 expression in the trophoblast cells is regulated by hypoxia via the HIF-1 pathway.
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