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.