Attaching and effacing bacterial pathogenesis: Characterisation of a severe disease model and the role of effector protein Map

Abstract

The mouse pathogen Citrobacter rodentium is commonly used to model colitis such as that caused by infection with enterohaemorrhagic E. coli (EHEC). The translocation of effector proteins into host cells via a type III secretion system (T3SS) is instrumental in the infectivity of C. rodentium, enteropathogenic E. coli (EPEC) and EHEC. Disease severity during infection with C. rodentium is dependent on host genetics. Whilst C. rodentium pathogenesis has been well characterised in the C57BL/6 mouse model, which exhibits mild self-limiting disease, less is known about infection in C3H/HeNCrl mice, which exhibit severe fatal colitis. To characterise C. rodentium infection in C3H/HeNCrl mice and elucidate the contribution of the multifunctional T3SS effector protein Map, in vivo monitoring and -omics techniques were employed. C. rodentium infection signatures were accelerated in C3H/HeNCrl mice with uniform colonisation of the colonic mucosa observed by 3 days post infection. The presence of either Map or EspF effectors was demonstrated to be essential for colonisation. In addition, a Map-dependent increase in colonic oxygenation upon infection was observed, likely due to Map-induced mitochondrial disruption. Global proteomic analysis of infection-induced changes in intestinal epithelial cells revealed a switch from mitochondrial metabolism to aerobic glycolysis and lactate fermentation characterised by higher abundance of SGLT4, LDHA and MCT4. In contrast to C57BL/6 mice, the pattern recognition receptors NLRP3 and ALPK1 were specifically induced in C3H/HeNCrl from 6 DPI at the transcriptional and translational level. Activation the ALPK1/TIFA axis, was demonstrated following in vitro infection of a TIFA-reporter cell line with C. rodentium. Activation was dependent on the ADP-heptose biosynthesis pathway, but independent of a functional T3SS. Together, this study reveals temporal IECs’ responses during severe infectious colitis including changes to cellular replication, innate immunity and metabolism.