Cecum gene expression signatures in germ-free WT mice colonized with microbiota from WT or Card9-/- mice and infected with Citrobacter rodentium induced colitis. Mus musculus

It is crucial to decipher the host-microbiota interactions as they are involved in intestinal homeostasis and diseases. Caspase Recruitment Domain 9 (Card9) is an inflammatory bowel disease (IBD) susceptibility gene coding for an adapter protein for innate immunity toward many microorganisms. Card9-/- mice are more susceptible to colitis induced by Citrobacter rodentium as a result of impaired of the IL-22 pathway. C. rodentium is a natural mouse pathogen widely used to model human infections with Enteropathogenic Escherichia coli and Enterohaemorrhagic E. coli. To explore the role of the gut microbiota in the susceptibility of Card9-/- mice to C. rodentium infection, we colonized WT germ-free (GF) mice with the microbiota of WT (WT-->GF) or Card9-/- (Card9-/- -->GF) mice and challenged them with C. rodentium. Card9-/- -->GF mice were more susceptible than WT-->GF mice to C. rodentium. To examine the mechanisms responsible for this defect, we compared the cecum transcriptomes of WT -->GF and Card9-/- -->GF mice before and during C. rodentium-induced colitis. The number of down-regulated and up-regulated genes on day 12 after C. rodentium infection was lower in Card9-/- -->GF mice than WT-->GF mice. Card9-/- -->GF mice showed a significant down-regulation of gut morphogenesis and wound healing pathways suggesting that recovery is impaired in Card9-/- -->GF mice after C. rodentium infection. Immune response and cell division pathways were up-regulated in WT-->GF mice but not in Card9-/- -->GF confirming the defect of global response to infection when only the Card9-/- microbiota was transferred. The most induced and differentially expressed genes between Card9-/- -->GF and WT-->GF mice on day 4 after C. rodentium infection were Reg3g (encoding REGIIIγ) and Reg3b (encoding REGIIIβ). Overall design: Germ-free (GF) C57BL/6 wild-type (WT) mice were inoculated by oral gavage with fresh stools from conventional WT (WT-->GF) or Card9-/- (Card9-/- -->GF) mice. Three weeks after the colonization, WT-->GF and Card9-/- -->GF mice were infected by oral gavage with 1x10^9 CFU of C. rodentium strain DBS100. 5 mice of each groups (WT-->GF and Card9-/- -->GF) were sacrified before infection. 6 mice of each group were sacrified 4 days after infection, 5 mice of each group were sacrified at day 12 and 3 WT-->GF mice and 5 Card9-/- -->GF mice were sacrified at day 22.