Growth control of Brucella abortus in human trophoblasts JEG-3 cells

Résumé

The intracellular Brucella pathogens cause a worldwide zoonosis named Brucellosis. They are facultative intracellular pathogens, able to replicate in several cell types, including trophoblasts of pregnant hosts. Indeed, Anderson et al. (1986) described that trophoblasts of pregnant goat contain numerous B. abortus at 5 days post-inoculation. This seems that trophoblasts are a natural site for B. abortus proliferation. In a study using HeLa cells or RAW 264.7 macrophages, Deghelt et al. (2014) showed that B. abortus blocks its growth and its cell cycle at the G1 stage during the first hours of infection in these cell types. Here, we found that in human trophoblast cell line JEG-3, a majority of B. abortus start already their growth at 2 hours post-infection (PI). We also found that G1-arrested bacteria are not the predominant infectious form of B. abortusin the infection to JEG-3 cells. This suggests that the entry of B. abortus into trophoblasts JEG-3 cells is different with HeLa cells and that trophoblasts cells provides a different growth-permissive environment compared to HeLa cells or RAW 264.7 macrophages.

A Tn-seq analysis was conducted to analyse the factors which are crucial for survival
until 5 hours post-infection in JEG-3 cells, that were not identified in RAW 264.7 macrophages at the same time post-infection. This analysis identified two potential regulators of cell cycle, a cyclic-di-GMP diesterase named PdeA (also called BpdA) and the histidine kinase PleC. Interestingly, both pde A and pleC mutants display a lower proportion of growing bacteria at 5h post-infection, compared to the wild type strain. This suggeststhat PdeA (and thus c-di-GMP level) and PleC could be involved in the control of B. abortus growth inside JEG-3 cells. In Caulobacter crescentus,
PdeA and PleC are involved in the control of the level of cyclic di-GMP, a second messenger molecule, since PdeA degrades c-di-GMP in the swarmer cells (flagellated cells) (Abel et al., 2011) and PleC is also required to lower c-di-GMP concentrations in the swarmer cells (Christen et al., 2010), among other functions. We thus propose that c-di-GMP concentrations could control growth of B. abortus inside JEG-3 cells.

Altogether, these data suggest that the differential adaptation of B. abortus within various host cells is part of the complexity of the infection process. Moreover, it suggests that conserved factors involved in cell cycle control, including cyclic-di-GMP, are involved in the control of cell cycle of B. abortus in these different intracellular niches. Among the future lines of investigation, synchronization of B. abortus cell cycle and a molecular study of the adaptation to starvation conditions could provide further insights into this research field.

la date de réponse	18 déc. 2017
langue originale	Anglais
L'institution diplômante	Universite de Namur
Sponsors	Fonds de la Recherche Scientifique F.R.S.-FNRS & Institut d’Astrophysique de Paris
Superviseur	Xavier De Bolle (Promoteur), Jean-Yves Matroule (Président), Laurence Van Melderen (Jury), Suzana P Salcedo (Jury), Johann Mignolet (Jury) & Xavier De Bolle (Promoteur)