The absence of murine cathelicidin-related antimicrobial peptide impacts host responses enhancing Salmonella enterica serovar Typhimurium infection
Bescucci, D.M., Clarke, S.T., Brown, C.L.J., Boras, V.F., Montina, T., Uwiera, R.R.E., Inglis, G.D. (2020). The absence of murine cathelicidin-related antimicrobial peptide impacts host responses enhancing Salmonella enterica serovar Typhimurium infection. Gut Pathogens, [online] 12(1), http://dx.doi.org/10.1186/s13099-020-00386-1
Plain language summary
The progression of salmonellosis incited by Salmonella enterica serovar Typhimurium (ST) in mice with and without the murine-cathelicidin related antimicrobial peptide (mCRAMP) (i.e. mCRAMP+/+ and mCRAMP-/-) was evaluated by characterizing histopathologic changes, host immune responses, and alterations to the liver metabolome and enteric microbiota. The higher upregulation of pro-inflammatory genes and the higher concentration of immune proteins that we observed in SA+/ST-/mCRAMP-/- and SA+/ST+/mCRAMP-/- mice are clear indications of a higher susceptibility to salmonellosis when cathelicidin is absent. Moreover, the metabolic profiles of the livers of mice infected with S. Typhimurium differed between the mCRAMP-/- and mCRAMP+/+ genotypes. This evidence demonstrated that mCRAMP deficient mice were predisposed to Salmonella infection both locally and systemically. Additionally, we demonstrated that mCRAMP plays a role in host response to infection by S. Typhimurium by altering the microbiota. In this regard, the higher abundance of Akkermansia muciniphila that we observed in SA+/ST-/mCRAMP-/- and SA+/ST+/mCRAMP-/- mice could be an indicator of a disruption to the mucus layer resulting from the absence of mCRAMP. It is noteworthy that the two C57BL/6 genotypes using in the current study were housed separately but adjacent to one another in the LeRDC small animal facility, and we observed a difference between the two in the structure of their intestinal microbiota albeit subtle. Thus, future research to elucidate mechanisms of mCRAMP function should take steps to address this (e.g. select breeding of mCRAMP-/- and mCRAMP+/+ mice). Furthermore, research could involve studies in which mCRAMP is delivered to sites of intestinal inflammation incited by S. Typhimurium in mCRAMP-/- mice.
Background: Cathelicidins are a class of antimicrobial peptide, and the murine cathelicidin-related antimicrobial peptide (mCRAMP) has been demonstrated in vitro to impair Salmonella enterica serovar Typhimurium proliferation. However, the impact of mCRAMP on host responses and the microbiota following S. Typhimurium infection has not been determined. In this study mCRAMP−/− and mCRAMP+/+ mice (± streptomycin) were orally inoculated with S. enterica serovar Typhimurium DT104 (SA +), and impacts on the host and enteric bacterial communities were temporally evaluated. Results: Higher densities of the pathogen were observed in cecal digesta and associated with mucosa in SA+/mCRAMP−/− mice that were pretreated (ST+) and not pretreated (ST−) with streptomycin at 24 h post-inoculation (hpi). Both SA+/ST+/mCRAMP−/− and SA+/ST−/mCRAMP−/− mice were more susceptible to infection exhibiting greater histopathologic changes (e.g. epithelial injury, leukocyte infiltration, goblet cell loss) at 48 hpi. Correspondingly, immune responses in SA+/ST+/mCRAMP–/− and SA+/ST−/mCRAMP–/− mice were affected (e.g. Ifnγ, Kc, Inos, Il1β, RegIIIγ). Systemic dissemination of the pathogen was characterized by metabolomics, and the liver metabolome was affected to a greater degree in SA+/ST+/mCRAMP–/− and SA+/ST−/mCRAMP–/− mice (e.g. taurine, cadaverine). Treatment-specific changes to the structure of the enteric microbiota were associated with infection and mCRAMP deficiency, with a higher abundance of Enterobacteriaceae and Veillonellaceae observed in infected null mice. The microbiota of mice that were administered the antibiotic and infected with Salmonella was dominated by Proteobacteria. Conclusion: The study findings showed that the absence of mCRAMP modulated both host responses and the enteric microbiota enhancing local and systemic infection by Salmonella Typhimurium.