Upregulated GRP78 and sFlt-1 in preeclampsia induces IRE1 and ATF6 arms of UPR leading to ER stress in placental cells

IntroductionAmongst vivid and diversified stresses which placenta in preeclampsia undergoes, ER stress has been a hal of the fame which is an insinuation of ill-fated UPR. In our previous study, we have already reported activation of PERK arm due to sFlt-1 present in preeclamptic mothers. The present study is an attempt to interpret rest of the two arms (IRE1 and ATF6) of UPR and ER stress subsequently by in vitro study using BeWo cells after upregulation of master regulator of UPR (GRP78) in placental tissue. Materials and MethodsPart I: Serum analysis of circulating levels of GRP78 and sFlt-1 [in 50 pairs of preeclamptic and normotensive, non-proteinuric (control) pregnant women)] using ELISA. Part II: Correlation analysis of levels of GRP78 and sFlt-1 in preeclamptic and control groups. Part III: Status of expression of GRP78 in placentae (n=10 each, preeclamptic and control groups) was reported using immunofluorescence. Part IV: In vitro experiments using BeWo cells were carried out to analyse the effect of GRP78 and sFlt-1 on IRE1 and ATF6 arms of UPR at protein (immunofluorescence and western blot) and transcript (qRT-PCR) levels. ResultsProtein expressions of GRP78 and sFlt-1 were found significantly elevated in preeclamptic patients as compared to controls. Enhanced expression of master regulator of UPR (GRP78) in placental tissue of preeclamptic women was reported. Up-regulated expression of XBP1 (IRE1 arm) and ATF6 markers of UPR was observed in trophoblast cells. ConclusionThe upregulated expression of GRP78 in preeclamptic placentae and enhanced expression of XBP1 and ATF6 markers in BeWo cells at both protein and transcript levels connote role played by raised circulating levels of GRP78 and sFlt-1 in preeclampsia.