Innate immune sensing of ER stress during bacterial infection

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ABSTRACT Both pathogenic and non-pathogenic bacteria produce pathogen-associated molecular patterns (PAMPs) that stimulate innate immune responses in their eukaryotic hosts via pattern-recognition receptors such as toll-like receptors. Virulence factors of pathogens provide additional signals that allow the innate immune system to differentiate between harmless commensals and pathogens. These signals include virulence factors, such as Type III and Type IV secretion systems that translocate effector proteins into the host cell. Collectively, these processes are detected by the immune system as “patterns of pathogenesis” and can activate cytosolic signaling pathways. Brucella abortus is a stealthy pathogen expressing modified PAMPs that no longer serve as agonists for pattern recognition receptors. As a result, host responses generated during B. abortus infection are entirely dependent on detecting the function of its T4SS, as a pathogen-induced process. Here we propose to use this organism to interrogate novel innate immune signaling pathways linking perturbation of endoplasmic reticulum function to inflammation. The objectives of this application are to determine how activation of the IRE1α pathway of the host cell’s unfolded protein response influences the outcome of infection with intracellular bacteria, by eliciting inflammatory responses and providing inputs that drive survival or death of the infected cell. The proposed research will test the hypothesis is that in macrophages, a NOD1/NOD2-containing signaling complex detects perturbation of ER function during B. abortus infection to induce inflammatory responses and promote survival of infected macrophages, while in a secretory cell type infection-induced ER stress triggers immunogenic cell death, resulting in placentitis and abortion. Successful completion of this work will move the field forward by determining how cells detects pathogen-induced perturbation of ER function and how the resulting response drives cell survival vs cell death outcomes in different cell types. This concept has important ramifications not only for bacterial pathogenesis, but also for understanding host-virus interactions, innate immunity and the pathogenesis of inflammatory disorders associated with ER stress, such as type 1 diabetes, inflammatory bowel disease and neuroinflammatory disease.