Reactive Oxygen Species Inhibit Polycystin-2 (TRPP2) Cation Channel Activity In Term Human Syncytiotrophoblast

Abstract 

Pregnancy is often associated with oxidative stress (OS) and lower antioxidant defences, which are both implicated in the pathophysiology of preeclampsia, free radical-induced birth defects, and abortions, as well as gestational diabetes mellitus (GDM), where products of lipid peroxidation are increased. The molecular target(s) of increased oxygen free radicals and consequent lipid peroxidation in the human placenta remains ill defined. The human syncytiotrophoblast (hST) expresses abundant polycystin-2 (PC2, TRPP2), a TRP-type Ca²⁺-permeable non-selective cation channel. Here, we explored the effect of reactive oxygen species (ROS) on PC2 channel activity of term hST. Apical membranes of the hST were reconstituted in a lipid bilayer chamber. Addition of either hydrogen-peroxide (H₂O₂) or tert-butyl hydroperoxide (tBHP) to the cis chamber (intracellular side) rapidly and completely inhibited PC2-mediated cation channel activity in reconstituted hST vesicles. A dose-response titration with increasing concentrations of H₂O₂ gave an IC₅₀=131nM. The effect of H₂O₂ on the isolated protein from in vitro transcribed/translated material was significantly different. H₂O₂ inhibited PC2 cation channel activity, with a much lower affinity (IC₅₀=193μM). To correlate these findings with H₂O₂-induced lipid peroxidation, TBARS where measured in hST apical membranes incubated with H₂O₂. Increased TBARS by exposure of hST apical membranes to H₂O₂ (625μM) returned to control value in the presence of catalase (167μg/ml). Taken together these data indicate that ROS affect PC2 channel function by targetting both membrane lipids and the channel protein. Thus, OS in human pregnancy may be linked to dysregulation of channels such as PC2, which allow the transport of Ca²⁺ into the placenta. Oxidative complications in pregnancy may implicate dysfunctional cation transfer between mother and fetus.

Keywords: TRP channels, Hydrogen peroxide, tert-butyl hydroperoxide, Oxygen free radicals, Placenta, TBARS, Lipid peroxidation