Involvement of the oncogene B-cell lymphoma 6 in the fusion and differentiation process of trophoblastic cells of the placenta

Abstract

The oncogene B-cell lymphoma 6 (BCL6) is associated with lymphomagenesis. Intriguingly, its expression is increased in preeclamptic placentas. Preeclampsia is one of the leading causes of maternal and perinatal mortality and morbidity. Preeclamptic placentas are characterized by various defects like deregulated differentiation and impaired fusion of trophoblasts. Its pathogenesis is however not totally understood. We show here that BCL6 is present throughout the cell fusion process in the fusogenic trophoblastic cell line BeWo. Suppression of BCL6 promotes trophoblast fusion, indicated by enhanced levels of fusion-related β-hCG, syncytin 1 and syncytin 2. Increased mRNA levels of these genes could also be observed in primary term cytotrophoblasts depleted of BCL6. Conversely, stable overexpression of BCL6 reduces the fusion capacity of BeWo cells. These data suggest that an accurately regulated expression of BCL6 is important for proper differentiation and successful syncytialization of trophoblasts. While deregulated BCL6 is linked to lymphomagenesis by blocking lymphocyte terminal differentiation, increased BCL6 in the placenta contributes to the development of preeclampsia by impairing trophoblast differentiation and fusion.

RITA Is Expressed in Trophoblastic Cells and Is Involved in Differentiation Processes of the Placenta

“…Nevertheless, the depletion of RITA is linked to a reduction of the fusion-associated genes GCM1, syncytin-1 (ERVW-1), and syncytin-2 (ERVFRD-1) as well as β-hCG (CBG3) and a decrease in cellular and secreted β-hCG in BeWo cells. Since PE is associated with impaired differentiation and fusion of CTBs [27,56], these data strengthen the concept of RITA's involvement in the development of PE.…”

“…Villous cytotrophoblast cell isolation and purification was carried out according to Petroff et al [26] and as specified [20,27]. In brief, approximately 50 g of villous placental tissue free of calcification or hematoma were finely minced within 30 min after delivery, rinsed with 0.9% NaCl, and digested with 0.25% trypsin (Thermo Fisher Scientific, Dreieich, Germany) and 300 U/mL DNase I (Sigma-Aldrich, Taufkirchen, Germany) for 20 min, shaking at 37 • C. After digestion, the supernatant was transferred into tubes containing 1.5 mL fetal bovine serum (Merck Millipore, Darmstadt, Germany) and centrifuged (1000× g, 15 min).…”

“…The fractions were pooled and diluted in pre-warmed medium for centrifugation (1000× g, 5 min). The cell pellet was resuspended in medium and the cells were cultured [20,27].…”

“…Fluorescence microscopy images of pan-cadherin (visualization of cell boundary) and DAPI (DNA) were merged for the quantification of cell fusion as described [27]. Percentages of fused cells were counted and calculated as follows: nuclei inside cell boundaries/total number of nuclei.…”

RNA-Seq reveals changes in human placental metabolism, transport and endocrinology across the first–second trimester transition

“…The BCL6 expression is significantly lower in the second trimester (-2.175-fold change, P adj. 0.018) and it has been previously shown to be required for proliferation of villous cytotrophoblast cells ( Muschol-Steinmetz et al, 2016 ), whilst BCL6 overexpression reduces trophoblast fusion and is increased in pre-eclamptic placentas ( Jasmer et al, 2017 ).…”