Gut microbiota-derived indole-3-carboxylate influences mucosal integrity and immunity through the activation of the aryl hydrocarbon receptors and nutrient transporters in broiler chickens challenged with Eimeria maxima

Authors: PARK, INKYUNG - US Department Of Agriculture (USDA); NAM, HYOYOUN - US Department Of Agriculture (USDA); GOO, DOYUN - US Department Of Agriculture (USDA); WICKRAMASURIYA, SAMIRU - US Department Of Agriculture (USDA); ZIMMERMAN, NOAH - Arm & Hammer Animal And Food Production; SMITH, ALEXANDRA - Arm & Hammer Animal And Food Production; REHBERGER, THOMAS - Arm & Hammer Animal And Food Production; Lillehoj, Hyun

Submitted to: Frontiers in Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/2022
Publication Date: 6/23/2022
Citation: Park, I., Nam, H., Goo, D., Wickramasuriya, S.S., Zimmerman, N., Smith, A.H., Rehberger, T.G., Lillehoj, H.S. 2022. Gut microbiota-derived indole-3-carboxylate influences mucosal integrity and immunity through the activation of the aryl hydrocarbon receptors and nutrient transporters in broiler chickens challenged with Eimeria maxima. Frontiers in Immunology. 13:867754. https://doi.org/10.3389/fimmu.2022.867754.
DOI: https://doi.org/10.3389/fimmu.2022.867754

Interpretive Summary: There is limited information on the role of microbiota residing in the gut in poultry. With the help of modern genomics technologies, there is an enhanced understanding of their important role in gut health. In this paper, ARS scientists and their collaborating scientists from an animal health company report the importance of gut bacteria-secreted metabolites in maintaining gut health using poultry as a model. Especially, the authors identified several gut metabolites which were induced following dietary treatment with Bacillus subtilis probiotics using in-depth analysis of gut bacteria-secreted small molecular weight compounds. One of them is called indole-3-carboxylate which is detected by host pattern recognition receptors (PRRs) on intestinal epithelial cells. Recognition of these pathogen-associated molecular patterns via PRRs influence both the magnitude and the quality of host immune responses. The results of in vivo studies showed that indole can enhance innate immunity and improves gut integrity of host. Furthermore, in vitro testing of indole showed that indole increased the gene expression of gut proteins associated with intestinal integrity and reduced inflammatory cytokines in coccidiosis-infected chickens. In conclusion, these results demonstrate the beneficial effects of dietary indole on host intestinal immune response to E. maxima infection in broiler chickens. Therefore, indole-3-carboxylate is a potential postbiotic candidate to improve the growth and immunity of chickens afflicted with enteric diseases.

Technical Abstract: Two studies were conducted to evaluate the effects of indole-3-carboxylate (ICOOH) as a postbiotic on maintaining intestinal homeostasis against avian coccidiosis. In the first study, an in vitro culture system was used to investigate the effects of ICOOH on the proinflammatory cytokine response of chicken macrophage cells (CMC), gut integrity of chicken intestinal epithelial cells (IEC), differentiation of quail muscle cells (QMC) and primary chicken embryonic muscle cells (PMC), and anti-parasitic effect against Eimeria maxima. Cells to be tested were seeded in the 24-well plates and treated with ICOOH at concentrations of 0.1, 1.0, and 10.0 µg. CMC was first stimulated by lipopolysaccharide to induce an innate immune response, and QMC and PMC were treated with 0.5 and 2% fetal bovine serum, respectively before they were treated with ICOOH. After 18 h of incubation, cells were harvested and RT-PCR was performed to measure gene expression of proinflammatory cytokines of CMC, tight junction (TJ) proteins of IEC, and muscle cell growth markers of QMC and PMC. In the second study, in vivo trials were carried out to study the effect of dietary ICOOH on disease parameters in broiler chickens infected with E. maxima. One hundred and twenty male broiler chickens (0-day-old) were allocated into the following four treatment groups: (1) basal diet without infection (CON), (2) basal diet with E. maxima (NC), (3) ICOOH at 10.0 mg/kg feed with E. maxima (HI), and (4) ICOOH at 1.0 mg/kg feed with E. maxima (LO). Body weights (BW) were measured on days 0, 7, 14, 20, and 22. All groups except the CON chickens were orally infected with E. maxima on day 14. Jejunal samples were collected for lesion score, and the transcriptomic analysis of cytokines and TJ proteins. Data were analyzed using PROC MIXED in SAS. In vitro, ICOOH increased the expression of TJ proteins in IEC and decreased IL-1ß and IL-8 transcripts in the LPS-stimulated CMC. In vivo, chickens on HI diet showed reduced jejunal IL-1ß, IFN-', and IL-10 expression, and increased expression of genes activated by aryl hydrocarbon receptors and nutrient transporters in E. maxima-infected chickens. In conclusion, these results demonstrate the beneficial effects of dietary ICOOH on intestinal immune responses and barrier integrity in broiler chickens challenged with E. maxima. Furthermore, the present finding supports a notion to use microbial metabolites as novel feed additives to enhance resilience in animal agriculture.