The trophoblast surface becomes refractory to adhesion by congenitally transmitted
Toxoplasma gondii
and
Listeria monocytogenes
during cytotrophoblast to syncytiotrophoblast development
Authors: da Silva Rafaela J. , Cabo Leah F. , George Jada L. , Cahoon Laty A. , Yang Liheng , Coyne Carolyn B. , Boyle Jon P. 
Published: May 2024

The placenta is a critical barrier against viral, bacterial, and eukaryotic pathogens. For most teratogenic pathogens, the precise molecular mechanisms of placental resistance are still being unraveled. Given the importance of understanding these mechanisms and challenges in replicating trophoblast-pathogen interactions using
in vitro
models, we tested an existing stem-cell-derived model of trophoblast development for its relevance to infection with
Toxoplasma gondii
. We grew human trophoblast stem cells (TS
CT
) under conditions leading to either syncytiotrophoblast (TS
SYN
) or cytotrophoblast (TS
CYT
) and infected them with
T. gondii
. We evaluated
T. gondii
proliferation and invasion, cell ultrastructure, as well as for transcriptome changes after infection. TS
SYNs
cells showed similar ultrastructure compared to primary cells and villous explants when analyzed by transmission electron microscopy and scanning electron microscopy (SEM), a resistance to
T. gondii
adhesion could be visualized on the SEM level. Furthermore, TS
SYNs
were highly refractory to parasite adhesion and replication, while TS
CYTs
were not. RNA-seq data on mock-treated and infected cells identified differences between cell types as well as how they responded to
T. gondii
infection. We also evaluated if TS
SC
-derived SYNs and CYTs had distinct resistance profiles to another vertically transmitted facultative intracellular pathogen,
Listeria monocytogenes
. We demonstrate that TS
SYNs
are highly resistant to
L. monocytogenes
, while TS
CYTs
are not. Like
T. gondii
, TS
SYN
resistance to
L. monocytogenes
was at the level of bacterial adhesion. Altogether, our data indicate that stem-cell-derived trophoblasts recapitulate resistance profiles of primary cells to
T. gondii
and highlight the critical importance of the placental surface in cell-autonomous resistance to teratogens.

IMPORTANCE

Congenital toxoplasmosis can cause a devastating consequence to the fetus. To reach the fetus’s tissues,
Toxoplasma gondii
must cross the placenta barrier. However, how this parasite crosses the placenta and the precise molecular mechanisms of placental resistance to this parasite are still unknown. In this study, we aimed to characterize a new cellular model of human trophoblast stem cells to determine their resistance, susceptibility, and response to
T. gondii
. Syncytiotrophoblast derived from trophoblast stem cells recapitulate the resistance profile similarly to placenta cells. We also showed that these cells are highly resistant to
Listeria monocytogenes
, at the level of bacterial adhesion. Our results suggest that resisting pathogen adhesion/attachment may be a generalized mechanism of syncytiotrophoblast resistance, and trophoblast stem cells represent a promising model to investigate cell-intrinsic mechanisms of resistance to pathogen adhesion and replication.