Post-Translational Modifications of the P2X₄ Purinergic Receptor Subtype in the Human Placenta are Altered in Preeclampsia

P2X₄ receptors are activated by extracellular ATP to raise intracellular calcium, thus altering cell signalling. ATP release occurs under pathophysiological, stress and adverse cell conditions; these are all increased in preeclampsia. Although P2X₄ is abundantly expressed in normal placenta neither the differences in the amount of protein nor its post-translational modifications have been studied in placentae from pregnancies complicated by preeclampsia. Thus we examined P2X₄ protein expression, localization and post-translational modifications in normotensive controls, term and preterm preeclamptic placentae. Densitometric analysis of Western blots showed a significant increase in P2X₄ protein expression in both term (p = 0.002) and preterm preeclamptic (p = 0.0008) placental samples compared to normotensive controls however the tissue localization of this receptor subtype was unaltered across the groups. Our data showed that P2X₄ is a nitrated protein in the placenta and this nitration is upregulated in preterm preeclamptic placenta compared to normotensive controls (p = 0.03). We also demonstrated that P2X₄ is heavily glycosylated in the placenta by deglycosylation with PNGase F which reduced the protein product size by 23 kDa. We propose that P2X₄ acts within the syncytiotrophoblast to alter intracellular calcium and subsequent signalling pathways thereby restoring placental cell homeostasis following ATP-induced changes during pathophysiological conditions such as preeclampsia. We also propose that the post-translational modifications of nitration and glycosylation are required for the normal functioning of P2X₄.