Abstract
The intestinal mucosa contributes to frontline gut defenses by forming a barrier (physical and biochemical) and preventing the entry of pathogenic microbes. One innate role of the human colonic epithelium is to secrete cathelicidin, a peptide with broad antimicrobial and immunomodulatory functions. In this study, the effect of cathelicidin in the maintenance of epithelial integrity, Toll-like receptor recognition, bacterial invasion and initiation of inflammatory response against Salmonella typhimurium is investigated in cultured human colonic epithelium. We found exogenous human cathelicidin restores the epithelial integrity in S. typhimurium-infected colonic epithelial (T84) cells by mostly post-translational effects associated with reorganization of zonula occludens (ZO)-1 tight junction proteins. Endogenous cathelicidin prevents S. typhimurium internalization as shown in colonic epithelial cells genetically deficient in the only human cathelicidin, LL-37 (shLL-37). Moreover, supplementation of shLL-37 cells with synthetic LL-37 reduces the grade of S. typhimurium internalization in a dose-dependent manner. Mechanistically, shLL-37 cells have lower gene expression of TLR4 and pro-inflammatory cytokine IL-1β in response to S. typhimurium. Thus, human cathelicidin aids in the early colonic epithelial defenses against enteric S. typhimurium by preventing bacterial invasion and maintaining epithelial barrier integrity, likely to occur due to the production of sensing TLR4 and pro-inflammatory cytokines.
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Acknowledgments
MM was supported by the National Scientific and Technical Research Council (CONICET; Argentina) and DD by the Markin Undergraduate Student Research Program (USRP) in Health and Wellness (University of Calgary). We thank Dr. John Kastelic (University of Calgary, Faculty of Veterinary Medicine) for revising and editing the manuscript.
Funding
This research was supported by the Natural Sciences and Engineering Research Council (NSERC) Discovery Grant (RGPAS-2017- 507827), Alberta Agriculture and Forestry (2018F050R) and University of Calgary URGC SEM Faculty Seed Grant (no. 1041449).
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Highlights
• Cathelicidin restores S. typhimurium induced epithelial integrity degradation.
• Cathelicidin decreases S. typhimurium colonic epithelial invasion.
• Endogenous cathelicidin promotes TLR4 and IL-1β production in response to S. typhimurium
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Supplementary Figure 1
Bar graph representing expression of LL-37 gene (normalized to sham control) in HT29 cells upon short-hairpin (Sh) RNA mediated silencing. (PNG 9 kb)
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Marin, M., Holani, R., Blyth, G.A.D. et al. Human cathelicidin improves colonic epithelial defenses against Salmonella typhimurium by modulating bacterial invasion, TLR4 and pro-inflammatory cytokines. Cell Tissue Res 376, 433–442 (2019). https://doi.org/10.1007/s00441-018-02984-7
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DOI: https://doi.org/10.1007/s00441-018-02984-7