The unfolded protein response is a critical mediator in Campylobacter jejuni pathogenesis and host defence

Campylobacter jejuni is the major bacterial cause of foodborne gastroenteritis worldwide. How this pathogen interacts with the host defence machinery of human intestinal epithelial cells (IECs) and is involved in pathogenesis remains elusive. Bacterial pathogens utilise strategies to gain access to the eukaryotic cell machinery that can involve subversion of biological processes in host. Unfolded protein response (UPR) is a highly conserved host cell stress response to the accumulation of misfolded proteins in the endoplasmic reticulum (ER) and is a conserved evolutionary response against invading pathogens. Several bacterial pathogens can induce the UPR for their own survival and thus design a dual scenario where UPR can both protect and facilitate pathogen evasion. Herein, we investigated whether UPR represents a virulence mechanism exploited by C. jejuni during bacterial invasion in human IECs. Our data show that following C. jejuni infection, we observe consistent upregulation of protein kinase R-like ER kinase (PERK), inositol-requiring enzyme 1α and (IRE1α), with activating transcription factor 6 (ATF6) activation occurring in a strain- and cell line-dependent manner. Chemical induction of UPR by thapsigargin in host cells reduced intracellular survival of C. jejuni while conversely pretreatment with UPR inhibitors increased intracellular survival of C. jejuni and attenuated IL-8 release. Finally, we show using C. jejuni mutants that the capsular polysaccharide and flagella contribute to UPR activation in IECs. Collectively, these findings provide observational insights into UPR activation during infections and how C. jejuni infection leads to UPR activation and inflammation, potentially contributing to downstream C. jejuni-mediated damage.