Map of Enteropathogenic Escherichia coli Targets Mitochondria and Triggers DRP-1-Mediated Mitochondrial Fission and Cell Apoptosis in Bovine Mastitis

Lycopene promoted M2 macrophage polarization via inhibition of NOTCH1-PI3K-mTOR-NF-κB-JMJD3-IRF4 pathway in response to Escherichia coli infection in J744A.1 cells

Escherichia coli (E. coli) can induce severe clinical bovine mastitis, which is to blame for large losses experienced by dairy farms. Macrophage polarization into various states is in response to pathogen infections. Lycopene, a naturally occurring hydrocarbon carotenoid, relieved inflammation by controlling M1/M2 status of macrophages. Thus, we wanted to explore the effect of lycopene on polarization states of macrophages in E. coli-induced mastitis. Macrophages were cultivated with lycopene for 24, before E. coli inoculation for 6 h. Lycopene (0.5 μmol/L) significantly enhanced cell viabilities and significantly reduced lactic dehydrogenase (LDH) levels in macrophages, whereas 2 and 3 μmol/L lycopene significantly enhanced LDH activities. Lycopene treatment significantly reduced the increase in LDH release, iNOS, CD86, TNF-α, IL-1β and phosphatase and tensin homolog (PTEN) expressions in E. coli group. 0.5 μmol/L lycopene significantly increased E. coli-induced downregulation of CD206, arginase I (ARG1), indoleamine 2,3-dioxygenase (IDO), chitinase 3-like 3 (YM1), PI3K, AKT, p-AKT, mammalian target of rapamycin (mTOR), p-mTOR, jumonji domain-containing protein-3 (JMJD3) and interferon regulatory factor 4 (IRF4) levels. Moreover, Ginkgolic acid C17:1 (a specific PTEN inhibitor), 740YPDGFR (a specific PI3K activator), SC79 (a specific AKT activator) or CHPG sodium salt (a specific NF-κB activator) significantly decreased CD206, AGR1, IDO and YM1 expressions in lycopene and E. coli-treated macrophages. Therefore, lycopene increased M2 macrophages via inhibiting NOTCH1-PI3K-mTOR-NF-κB-JMJD3-IRF4 pathway in response to E. coli infection in macrophages. These results contribute to revealing the pathogenesis of E. coli-caused bovine mastitis, providing the new angle of the prevention and management of mastitis.

Enteropathogenic E. coli infection co-elicits lysosomal exocytosis and lytic host cell death

IMPORTANCE

Enteropathogenic Escherichia coli (EPEC) infection is a significant cause of gastroenteritis, mainly in children. Therefore, studying the mechanisms of EPEC infection is an important research theme. EPEC modulates its host cell life by injecting via a type III secretion machinery cell death modulating effector proteins. For instance, while EspF and Map promote mitochondrial cell death, EspZ antagonizes cell death. We show that these effectors also control lysosomal exocytosis, i.e., the trafficking of lysosomes to the host cell plasma membrane. Interestingly, the capacity of these effectors to induce or protect against cell death correlates completely with their ability to induce LE, suggesting that the two processes are interconnected. Modulating host cell death is critical for establishing bacterial attachment to the host and subsequent dissemination. Therefore, exploring the modes of LE involvement in host cell death is crucial for elucidating the mechanisms underlying EPEC infection and disease.

Escherichia coli infection mediates pyroptosis via activating p53-p21 pathway-regulated apoptosis and cell cycle arrest in bovine mammary epithelial cells

Escherichia coli (E. coli) is a major environmental pathogen that causes mammary tissue damage and cell death, which results in substantial economic losses. Pyroptosis, a novel form of programmed cell death characterized by DNA fragmentation, chromatin condensation, cell swelling and leakage of cell contents, often occurs after inflammatory apoptotic pathways activation. Our objective was to investigate the intraction between E. coli infection and bovine mammary epithelial cells (bMECs) with pyroptosis and to explore the underlying regulatory mechanism. bMECs were infected with E. coli for 6 h. Lactic dehydrogenase activities, interleukin (IL)-10, IL-1β, IL-18 and tumor necrosis factor-α concentrations, total apoptosis indexes, and protein expressions of P-cdc25c, P-CDK1, cleaved caspase 9, cleaved caspase 3, cleaved PARP, P-NF-κB, NLRP3, ASC, caspase 1, gasdermin D N-terminal, IL-1β and IL-18 were significantly increased in E. coli infected bMECs. Whereas, cell membrane potential, protein levels of cdc25c, CDK1, cyclin B1, and Bcl-2/Bax level were markedly reduced. Furthermore, Ac-DEVD-CHO (specific inhibitor of apoptosis) dramatically suppressed pyroptosis in bMECs. Moreover, expressions of p53 and p21 promptly improved after E. coli infection, however, Pifithrin-α (specific inhibitor of p53) inhibited p53-p21 pathway, apoptosis, cell cycle arrest and pyroptosis. These results elaborated that E. coli infection of bMECs induced pyroptosis through activating the p53-p21 pathway-mediated apoptosis and cell cycle arrest. Taken together, inhibition of pyroptosis via suppressing of p53-p21 pathway may be an effective therapeutic approach for treating E. coli-induced mastitis, offering efficient theoretical support for the protection and treatment of bovine mastitis.

Attaching and effacing pathogens modulate host mitochondrial structure and function

Enteropathogenic and enterohemorrhagic Escherichia coli (EPEC and EHEC) are human enteric pathogens that contribute significantly to morbidity and mortality worldwide. These extracellular pathogens attach intimately to intestinal epithelial cells and cause signature lesions by effacing the brush border microvilli, a property they share with other "attaching and effacing" (A/E) bacteria, including the murine pathogen Citrobacter rodentium. A/E pathogens use a specialized apparatus called a type III secretion system (T3SS) to deliver specific proteins directly into the host cytosol and modify host cell behavior. The T3SS is essential for colonization and pathogenesis, and mutants lacking this apparatus fail to cause disease. Thus, deciphering effector-induced host cell modifications is critical for understanding A/E bacterial pathogenesis. Several of the ∼20-45 effector proteins delivered into the host cell modify disparate mitochondrial properties, some via direct interactions with the mitochondria and/or mitochondrial proteins. In vitro studies have uncovered the mechanistic basis for the actions of some of these effectors, including their mitochondrial targeting, interaction partners, and consequent impacts on mitochondrial morphology, oxidative phosphorylation and ROS production, disruption of membrane potential, and intrinsic apoptosis. In vivo studies, mostly relying on the C. rodentium/mouse model, have been used to validate a subset of the in vitro observations; additionally, animal studies reveal broad changes to intestinal physiology that are likely accompanied by mitochondrial alterations, but the mechanistic underpinnings remain undefined. This chapter provides an overview of A/E pathogen-induced host alterations and pathogenesis, specifically focusing on mitochondria-targeted effects.

Enteropathogenic Escherichia coli regulates host-cell mitochondrial morphology

The diarrheagenic pathogen enteropathogenic Escherichia coli is responsible for significant childhood mortality and morbidity. EPEC and related attaching-and-effacing (A/E) pathogens use a type III secretion system to hierarchically deliver effector proteins into host cells and manipulate epithelial structure and function. Subversion of host mitochondrial biology is a key aspect of A/E pathogen virulence strategy, but the mechanisms remain poorly defined. We demonstrate that the early-secreted effector EspZ and the late-secreted effector EspH have contrasting effects on host mitochondrial structure and function. EspZ interacts with FIS1, a protein that induces mitochondrial fragmentation and mitophagy. Infection of epithelial cells with either wildtype EPEC or an isogenic espZ deletion mutant (ΔespZ) robustly upregulated FIS1 abundance, but a marked increase in mitochondrial fragmentation and mitophagy was seen only in ΔespZ-infected cells. FIS1-depleted cells were protected against ΔespZ-induced fission, and EspZ-expressing transfected epithelial cells were protected against pharmacologically induced mitochondrial fission and membrane potential disruption. Thus, EspZ interacts with FIS1 and blocks mitochondrial fragmentation and mitophagy. In contrast to WT EPEC, ΔespH-infected epithelial cells had minimal FIS1 upregulation and exhibited hyperfused mitochondria. Consistent with the contrasting impacts on organelle shape, mitochondrial membrane potential was preserved in ΔespH-infected cells, but profoundly disrupted in ΔespZ-infected cells. Collectively, our studies reveal hitherto unappreciated roles for two essential EPEC virulence factors in the temporal and dynamic regulation of host mitochondrial biology.