Outer membrane vesicles secreted by avian pathogenic Escherichia coli promote its survival within macrophages and systemic infection by inducing endoplasmic reticulum stress-mediated autophagy flux blockade

Avian pathogenic Escherichia coli (APEC) is an extraintestinal pathogenic Escherichia coli that primarily causes avian colibacillosis, leading to localized or systemic infections. Its persistent survival within host macrophages is a critical component of the systemic infection process. In this process, outer membrane vesicles (OMVs) secreted by APEC play an important role; however, the interactions between OMVs and macrophages and their effects on bacterial intracellular survival remain unclear. This study demonstrated that APEC-derived OMVs induced intracellular Ca(2+) release and reactive oxygen species (ROS) accumulation in macrophages, thereby activating all three branches of the protein kinase RNA-like ER kinase (PERK), inositol-requiring enzyme 1 (IRE1), and activating transcription factor 6 (ATF6) pathways of the unfolded protein response (UPR), leading to sustained endoplasmic reticulum stress (ERS). Additionally, OMVs disrupted the acidic environment of lysosomes, inhibiting autophagosome-lysosome fusion and leading to abnormal accumulation of autophagy marker proteins LC3-II and p62, resulting in ERS-mediated autophagy flux blockade (incomplete autophagy). Importantly, this ERS-dependent autophagy dysfunction significantly impaired the ability of macrophages to clear pathogens, thereby promoting intracellular proliferation and survival of APEC. Intervention with ERS inhibitors effectively alleviated ERS and restored autophagosome-lysosome fusion, significantly reducing APEC intracellular survival within macrophages (p < 0.01) and bacterial loads in chick tissues (trachea: p < 0.001, lungs: p < 0.001, liver: p < 0.05, spleen: p < 0.001). These results indicated that APEC triggers ERS in host macrophages by secreting OMVs, thereby causing autophagy flux blockade, escaping host immune clearance, achieving sustained intracellular survival, and ultimately leading to systemic infection. This study provides new insights into the role of OMVs in regulating the innate immune response of macrophages during APEC infection.