Brucella abortus Infection of Placental Trophoblasts Triggers Endoplasmic Reticulum Stress-Mediated Cell Death and Fetal Loss via Type IV Secretion System-Dependent Activation of CHOP

Abstract

Subversion of endoplasmic reticulum (ER) function is a feature shared by multiple intracellular bacteria and viruses, and in many cases this disruption of cellular function activates pathways of the unfolded protein response (UPR). In the case of infection with Brucella abortus, the etiologic agent of brucellosis, the unfolded protein response in the infected placenta contributes to placentitis and abortion, leading to pathogen transmission. Here we show that B. abortus infection of pregnant mice led to death of infected placental trophoblasts in a manner that depended on the VirB type IV secretion system (T4SS) and its effector VceC. The trophoblast death program required the ER stress-induced transcription factor CHOP. While NOD1/NOD2 expression in macrophages contributed to ER stress-induced inflammation, these receptors did not play a role in trophoblast death. Both placentitis and abortion were independent of apoptosis-associated Speck-like protein containing a caspase activation and recruitment domain (ASC). These studies show that B. abortus uses its T4SS to induce cell-type-specific responses to ER stress in trophoblasts that trigger placental inflammation and abortion. Our results suggest further that in B. abortus the T4SS and its effectors are under selection as bacterial transmission factors. IMPORTANCE Brucella abortus infects the placenta of pregnant cows, where it replicates to high levels and triggers abortion of the calf. The aborted material is highly infectious and transmits infection to both cows and humans, but very little is known about how B. abortus causes abortion. By studying this infection in pregnant mice, we discovered that B. abortus kills trophoblasts, which are important cells for maintaining pregnancy. This killing required an injected bacterial protein (VceC) that triggered an endoplasmic reticulum (ER) stress response in the trophoblast. By inhibiting ER stress or infecting mice that lack CHOP, a protein induced by ER stress, we could prevent death of trophoblasts, reduce inflammation, and increase the viability of the pups. Our results suggest that B. abortus injects VceC into placental trophoblasts to promote its transmission by abortion.

Differential Secretion of Inflammatory Cytokines by Human Trophoblasts in the Presence of <b><i>Escherichia coli</i></b>, <b><i>Lactobacillus crispatus</i></b>, and <b><i>Lactobacillus jensenii</i></b>

“…Our study supports previous findings that suggest that the trophoblast may respond differently to different bacteria [46][47][48][49][50][51][52][53]. The results support the existence of separate mechanisms of bacterial recognition by trophoblasts, or the presence of bacterial products leading to alternative inflammatory/anti-inflammatory responses.…”

“…The degree to which trophoblasts participate in the control of potential placental-colonizing microbiota requires further study. Furthermore, previous studies have suggested that trophoblasts may respond differently to different bacteria [46][47][48][49][50][51][52][53]. In this paper, we compare the cytokine patterns exhibited by Swan 71 (Sw.71), immortalized human first trimester trophoblast cells [54], after in vitro interactions with E. coli (a common urogenital pathogen), L. jensenii (a vaginal commensal), and L. crispatus (a hypothesized mutualist and sentinel of the human vaginal ecosystem) [55,56].…”

Recombinant Treponema pallidum protein Tp0768 promotes proinflammatory cytokine secretion of macrophages through ER stress and ROS/NF-κB pathway

“…However, ER stress caused by microbial infection is usually long term. ER stress has been proven to be associated with inflammatory diseases caused by infections of various microorganisms, such as acute viral myocarditis, chronic hepatitis C virus, tuberculosis, and placental inflammation (Cai et al 2015;Dash et al 2019;Lim et al 2015;Byndloss et al 2019). In order to verify whether Tp0768 induces macrophages to produce ER stress, we observed the ultrastructure of ER using transmission electron microscopy Fig.…”

Brucella: Reservoirs and Niches in Animals and Humans

“…Once Brucella has impaired phagosome-lysosomal fusion, it replicates in the ER compartment, its replicative niche. Following replication, BCVs interact with host autophagic proteins Beclin1, ULK1, Atg14, and the IRE1α-UPR signaling axis for bacterial egress and the start of replication cycles within newly infected cells [ 64 , 65 , 66 , 67 ].…”