Calreticulin regulates syncytialization through control of the synthesis and transportation of E-cadherin in BeWo cells

Extracellularly Released Calreticulin Induced by Endoplasmic Reticulum Stress Impairs Syncytialization of Cytotrophoblast Model BeWo Cells

“…We also determined the CRT levels in the third-trimester placentas of the patients shown in Table 1 by using immunohistochemical analysis (normal placentas (n = 22) and preeclamptic placentas (n = 18); Figure 1e). In agreement with our previous report [16], the major site of CRT expression was the STB cytoplasm in both normal and preeclamptic placentas (Figure 1e). We also detected CRT in endothelial cells and villous macrophages (Hofbauer cells) in the villous cores, EVTs in the decidua and chorionic membrane, and connective tissue cells in the amnion layer of the external membranes in third-trimester placentas.…”

“…We successfully detected the 55-kDa CRT protein in placental and serum samples. We used cell lysates obtained from BeWo cells as the reference for the CRT protein band [ 16 ]. We noted no difference in the CRT levels in placentas from women with normal pregnancies and women with preeclampsia ( Figure 1 c), but the serum CRT levels were approximately 50% lower in nonpregnant women and 35% higher in preeclamptic women than the levels in women with normal pregnancies ( Figure 1 d).…”

“…We detected no alterations in the expression of these proteins including CRT after thapsigargin treatment ( Figure 3 b). We previously reported that genetic ablation of CRT expression resulted in reduced cell surface localization of E-cadherin and subsequent fusion of BeWo cells [ 16 ]. In our study here, we detected two bands that corresponded to E-cadherin, similar to bands for epithelial cells whose trafficking of E-cadherin was inhibited by cellular stress ( Figure 3 b) [ 34 ].…”

“…We used Mayer’s hematoxylin solution for counterstaining and scored the staining intensity as 0 = none, 1 = weak, 2 = moderate, and 3 = strong staining. We graded the percentage of positive cells as 0: no positive cells, 1: <30%, 2: 30–80%, or 3: >80% and then used the following equation to calculate the immunoreactive score (IRS): IRS = staining intensity × percentage of positive cells, according to previous reports [ 16 , 27 ].…”

“…Although inadequate placentation has been suggested to result in the induction of ER stress [ 12 ], how ER stress contributes to preeclampsia development is unknown. We previously showed that calreticulin (CRT), an ER-resident molecular chaperone that is ubiquitously expressed throughout the body including the placenta [ 13 , 14 ], is necessary for both adequate invasion of EVTs and syncytialization of CTBs [ 15 , 16 ]. Certain studies reported increases in CRT mRNA and protein levels in maternal blood and placentas from preeclamptic patients [ 12 , 13 ].…”