Mechanisms of oxygen sensing in human trophoblast cells

During pregnancy, changes in oxygen tension are essential for proper embryonic and placental development. Little is known about the mechanisms underlying mammalian cellular adaptations to changes in oxygen tension. Currently, we have explored putative mechanisms by which human trophoblast cells may sense oxygen. In order to investigate a role for hemoproteins in oxygen sensing, we cultured human villous explants of 5-8 weeks gestation under 20 per cent O(2) in the presence of either cobalt chloride or desferrioxamine, which interfere with the ability of iron (heme) to interact with oxygen. Treatment with these compounds mimicked hypoxia by stimulating the low oxygen effect on extravillous trophoblast outgrowth (EVT) and inducing HIF-1alpha expression, analogous to that observed in explants cultured at 3 per cent O(2). Addition of unhindered iron, in the form of iron chloride, to the treated-explants reversed the stimulatory effect on EVT outgrowth and HIF-1alpha expression. Subsequently, in order to probe into a mitochondrial role in trophoblast oxygen sensing, we cultured first trimester villous explants under 3 per cent O(2) in the presence of either diphenyleneiodonium or rotenone, known inhibitors of flavin-containing proteins. Treated-explants showed inhibition of the typical low oxygen-induced EVT outgrowth, when compared to untreated controls. Thus, this data supports a hypothesis that trophoblast cells may utilize mitochondria and/or hemoproteins as oxygen sensors to detect the critical changes in oxygen tension during pregnancy.