Date of Award
2024
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Microbiology and Molecular Genetics
First Advisor
Markus Thali
Abstract
Placental dysfunction is a root cause of poor birth outcomes, which are linked to lifelong illness for both mother and offspring. Critical to positive birth outcomes is the syncytiotrophoblast (ST), the placental barrier between maternal and fetal blood, which facilitates nutrient, gas, and waste exchange between mother and fetus, as well as synthesis of steroid and peptide hormones required in fetal development. ST formation occurs through the fusion of cytotrophoblast (CT) cells, a process which is mediated by two independently acquired endogenous retroviral envelope glycoproteins, syncytin-1 and syncytin-2. Syncytin-2 has been proposed to play a greater role in ST development than syncytin-1, however this is largely based on cell line data and this question has yet to be addressed in the much more physiologically relevant human trophoblast stem cells (hTSCs). hTSCs, which were originally derived from first trimester placenta and can be differentiated into any of the trophoblastic cell lineages, have recently become the state- of-the-art in vitro model for experiments on placental development.Cell-cell fusion is a fundamental and tightly regulated biological process, and one known regulatory mechanism involves tetraspanins, a family of transmembrane proteins. In HIV-1 infection, tetraspanins prevent excess fusion between HIV-1 infected and uninfected T cells. Both syncytin-mediated ST formation and HIV-1-induced fusion involve retroviral envelope glycoproteins, suggesting that similar processes may be involved in their regulation. Previous unpublished work showed that tetraspanin overexpression in two trophoblast cell lines, BeWo and JEG-3 cells, inhibited syncytin- mediated cell-cell fusion, but again this has not been studied in hTSCs. The primary aim of this study is to use hTSCs to better understand the differential role of syncytin-1 and syncytin-2 in ST formation, as well as the potential regulatory role of tetraspanins in this process. Characterizing the role of tetraspanins in syncytin-mediated ST formation will enhance our understanding of the complex regulatory mechanisms underlying placental development. Using split-luciferase cell-cell fusion assays, we demonstrate that a previously published syncytin-1 peptide inhibitor can effectively inhibit cell-cell fusion in 293T cells transfected with syncytin-1. However, the opposite effect was observed in hTSCs treated with syncytin-1 peptide inhibitor, where it instead significantly increased cell-cell fusion in a dose-dependent manner. A syncytin-2 peptide inhibitor reduced cell-cell fusion in both 293T cells transfected with syncytin-2 and hTSCs stimulated to differentiate into ST. Furthermore, treatment of hTSCs with a soluble ectodomain subunit of syncytin-2 (Syn- 2SU) also inhibited cell-cell fusion in a dose-dependent manner. No residual fusion activity was detected after maximal inhibition by Syn-2SU, suggesting that Syn-1 may not have a role in fusing hTSCs, possibly due to expression of the Syn-1 competitive inhibitor Suppressyn. Finally, experiments in hTSCs transduced to express tetrapanins CD9, CD63, or CD81 demonstrated no effect of tetraspanins on hTSC fusion compared to controls. Taken together, these data provide a basis for future work investigating the fusogenic activity of syncytins in ST formation and possible regulatory mechanisms that control this fundamental process.
Language
en
Number of Pages
89 p.
Recommended Citation
Carr, Madeline, "Evaluating the Role of Tetraspanins in Syncytin-Mediated Syncytiotrophoblast Formation" (2024). Graduate College Dissertations and Theses. 1944.
https://scholarworks.uvm.edu/graddis/1944