# BvrR From Brucella abortus Induces Neuroinflammation Through IRE1‐Mediated Activation of ATF2 and NF‐κB

## TL;DR

This study shows how a protein from Brucella bacteria causes brain inflammation by activating specific cellular pathways in microglial cells.

## Contribution

The study identifies a novel mechanism by which BvrR from Brucella abortus induces neuroinflammation via IRE1-mediated activation of ATF2 and NF-κB.

## Key findings

- BvrR expression in microglial cells activates IRE1, leading to ER expansion and phosphorylation of ATF2 and NF-κB p65.
- IRE1 inhibition blocks BvrR-induced cytokine production, while IRE1 activation mimics its effects.
- In vivo, BvrR expression in mouse hippocampus causes neuroinflammation and cognitive deficits.

## Abstract

Brucella‐induced neuroinflammation represents a key mechanism in the development of neurobrucellosis. The objective of this investigation was to clarify the molecular pathways through which the BvrR contributes to neuroinflammation and cognitive dysfunction. Human microglial clone 3 (HMC3) cells were transfected with pcDNA3.1‐BvrR‐His to examine the effects of BvrR from Brucella abortus on endoplasmic reticulum (ER) function and the activation of activating transcription factor 2 (ATF2) and nuclear factor kappa‐light‐chain‐enhancer of activated B cells (NF‐κB) p65. The role of phosphorylated inositol‐requiring enzyme 1 (p‐IRE1) in mediating BvrR‐induced activation of ATF2 and NF‐κB p65 was assessed by applying the IRE1 activator IXA4 and the IRE1 inhibitor GSK2850163, followed by evaluation with western blotting and RT‐qPCR. Interleukin‐6 (IL‐6) and tumor necrosis factor alpha (TNF‐α) concentrations in cell culture supernatants were quantified using ELISA. For in vivo analysis, HBAAV2/9‐IBA‐1‐BvrR‐6*HIS‐ZsGreen was stereotactically delivered into the right hippocampus of mice. Expression of BvrR in HMC3 cells induced phosphorylation of IRE1 and expansion of the ER. This activation enhanced ATF2 and NF‐κB p65 phosphorylation, facilitated their nuclear translocation, and significantly increased IL‐6 and TNF‐α expression at both the protein and mRNA levels. Inhibition of IRE1 with GSK2850163 suppressed these responses, whereas IRE1 activation with IXA4 reproduced the effects of BvrR. Findings indicate that BvrR from B. abortus activates IRE1, which subsequently stimulates ATF2 and NF‐κB p65, leading to increased expression of IL‐6 and TNF‐α and the induction of inflammatory responses in HMC3 cells.

This study demonstrates that the BvrR induces neuroinflammation. In microglial cells, BvrR expression localizes to the endoplasmic reticulum (ER), causing ER expansion and activating the stress sensor IRE1. Phosphorylated IRE1 subsequently drives the activation and nuclear translocation of transcription factors ATF2 and NF‐κB p65. This signaling cascade leads to the upregulated transcription and secretion of pro‐inflammatory cytokines IL‐6 and TNF‐α. The pivotal role of IRE1 was confirmed, as its activation mimicked, and its inhibition blocked, BvrR's effects. In vivo, microglia‐specific expression of BvrR in the mouse hippocampus recapitulated this IRE1/ATF2/NF‐κB pathway, resulting in neuroinflammation, neuronal damage, and cognitive deficits, elucidating a key mechanism in neurobrucellosis.