Endothelin-1 Induces Endoplasmic Reticulum Stress by Activating the PLC-IP3 Pathway Implications for Placental Pathophysiology in Preeclampsia

Recent evidence implicates placental endoplasmic reticulum (ER) stress in the pathophysiological characteristics of preeclampsia. Herein, we investigate whether endothelin (ET)-1, which induces Ca2+ release from the ER, can induce placental ER stress. Loss of ER Ca2+ homeostasis impairs post-translational modification of proteins, triggering ER stress-response pathways. IHC confirmed the presence of both ET-1 and its receptors in the syncytiotrophoblast. Protein levels and immunoreactivity of ET-1 and the endothelin B receptor (ETBR) were increased in preeclamptic samples compared with normotensive controls. JEG-3 and BeWo choriocarcinoma cells treated with ET-1 displayed an increase in ER stress markers. ET-1 induced phospho-activation of the ETBR. Treating cells with BQ788, an ETBR antagonist, or small-interfering RNA knockdown of the receptor inhibited induction of ER stress. ET-1 also stimulated p-phospholipase C (PLC)gamma 1 levels. By using inhibitors of PLC activation, U73122, and the inositol 1,4,5-triphosphate (IP3) receptor, xestospongin-C, we demonstrated that ET-1 induces ER stress via the PLC-IP3 pathway. Furthermore, ET-1 levels increased in the syncytiotrophoblast of explants from normal placentas after hypoxia-reoxygenation in vitro. Conditioned medium from hypoxia-reoxygenation explants also contained higher ET-1 levels, which induced ER stress in JEG-3 cells that was abolished by an ET-1 neutralizing antibody. Collectively, the data show that ET-1 induced ER stress in trophoblasts via the ETBR and initiation of signaling through the PLC-IP3 pathway, with the potential for autocrine stimulation. (Am J Pathol 2012, 180:2309-2320; http://dx.doi.org/10.1016/j.ajpath.2012.03.005)