P 9 Involvement of B-cell lymphoma 6 in the fusion process of trophoblastic cells of the placenta

Abstract

Introduction Preeclampsia (PE) is one of the leading causes of maternal and perinatal mortality and morbidity and despite intensive research its pathogenesis is not totally understood. In a previous study, we evaluated the gene expression of placental samples from PE patients and controls using a self-designed gene array that targeted critical signaling pathways. Interestingly, the gene of B-cell lymphoma 6 (BCL6), a transcriptional repressor and key regulator of B-lymphocyte development, is increased in preeclamptic placentas. It is expressed in villous cytotrophoblasts (vCTBs), promotes proliferation and survival of trophoblastic cells and is a promising target to decipher the molecular mechanisms behind the pathogenesis of PE in more detail. Objectives The cell-cell fusion of mononuclear vCTBs forms the continuous syncytiotrophoblast (STB) layer. This process is critical for the placental development and is known to be deregulated in preeclamptic placenta. In this work, we have investigated the potential role of BCL6 in the fusion process of trophoblastic cells. Materials and methods Various molecular biological methods were used for this study including Western blotting, quantitative real-time PCR, immunofluorescence staining and ELISA to explore the function of BCL6 in the fusion process of trophoblastic cell lines and vCTBs isolated from term placentas. Cell lines were stimulated with forskolin to induce cell fusion. Results We show that BCL6 is present throughout the whole fusion process. We also demonstrate that the fusion capability of the investigated cells is affected by BCL6, as knockdown of BCL6 results in a considerable enhanced fusion rate of BeWo cells. Furthermore, increased mRNA expression of fusion-related proteins is also observable in JEG-3 cells as well as vCTBs. Conversely, stable overexpression of BCL6 impairs the process of fusion in BeWo cells. Conclusion Our data indicate that an accurately regulated expression of BCL6 is important for proper differentiation and successful syncytialization of trophoblasts in the placenta. Increased BCL6 impairs trophoblast fusion, contributing to the development of PE. Further work is required to detail the molecular mechanisms whereby BCL6 affects the fusion. It also warrants investigations in vivo and in vitro to clarify the correlation between elevated BCL6 and deregulated cytokines, hypoxia and oxidative stress in the preeclamptic placenta.