Gastroenterology

Gastroenterology

Volume 145, Issue 2, August 2013, Pages 396-406.e10
Gastroenterology

Original Research
Full Report: Basic and Translational—Alimentary Tract
Short-Chain Fatty Acids Activate GPR41 and GPR43 on Intestinal Epithelial Cells to Promote Inflammatory Responses in Mice

https://doi.org/10.1053/j.gastro.2013.04.056Get rights and content

Background & Aims

Short-chain fatty acids (SCFAs), the most abundant microbial metabolites in the intestine, activate cells via G-protein−coupled receptors (GPRs), such as GPR41 and GPR43. We studied regulation of the immune response by SCFAs and their receptors in the intestines of mice.

Methods

Inflammatory responses were induced in GPR41−/−, GPR43−/−, and C57BL6 (control) mice by administration of ethanol; 2, 4, 6-trinitrobenzene sulfonic-acid (TNBS); or infection with Citrobacter rodentium. We examined the effects of C rodentium infection on control mice fed SCFAs and/or given injections of antibodies that delay the immune response. We also studied the kinetics of cytokine and chemokine production, leukocyte recruitment, intestinal permeability, and T-cell responses. Primary colon epithelial cells were isolated from GPR41−/−, GPR43−/−, and control mice; signaling pathways regulated by SCFAs were identified using immunohistochemical, enzyme-linked immunosorbent assay, and flow cytometry analyses.

Results

GPR41−/− and GPR43−/− mice had reduced inflammatory responses after administration of ethanol or TNBS compared with control mice, and had a slower immune response against C rodentium infection, clearing the bacteria more slowly. SCFAs activated intestinal epithelial cells to produce chemokines and cytokines in culture and mice after administration of ethanol, TNBS, or C rodentium. These processes required GPR41 and GPR43 and were required to recruit leukocytes and activate effector T cells in the intestine. GPR41 and GPR43 activated extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinase signaling pathways in epithelial cells to induce production of chemokines and cytokines during immune responses.

Conclusions

SCFAs activate GPR41 and GPR43 on intestinal epithelial cells, leading to mitogen-activated protein kinase signaling and rapid production of chemokines and cytokines. These pathways mediate protective immunity and tissue inflammation in mice.

Section snippets

Animals

All experiments with animals in this study were approved by the Purdue Animal Care and Use Committee. C57BL/6 mice were from Harlan Laboratories (Indianapolis, IN). CD45.1 C57BL/6 mice were from The Jackson Laboratory (Bar Harbor, ME). GPR43−/− C57BL/6 mice were from Deltagen (San Mateo, CA), and GPR41−/− C57BL/6 mice were described previously.14

Induction of Intestinal Inflammation with Ethanol and TNBS

Mice were starved overnight and received 100 μL 50% ethanol in the rectum using a round-tip needle. Intestinal inflammation with TNBS was induced as

Mice Deficient With GPR41 or GPR43 Are Defective in Mounting the Normal Inflammatory Response After an Ethanol-Induced Breach of the Gut Barrier Function

To determine the functions of SCFAs and their receptors in regulation of acute antibacterial responses, we temporarily breached the gut barrier function through rectal administration of ethanol into WT, GPR41−/−, and GPR43−/− mice. As expected, the ethanol treatment induced a transient decrease in the weight of WT mice at 24 h after the treatment (Figure 1A). However, the 2 knockout (KO) mouse strains were significantly less affected by the treatment. Gross examination revealed that only WT

Discussion

The mechanism of action for probiotics, prebiotics, and SCFAs to promote immunity in the gut is incompletely understood.29 We studied the roles of SCFA receptors in regulating immune responses in the intestine. The results identified positive roles of SCFAs and their receptors in preparing ECs to promptly mount immune responses during immunological challenges.

Our study demonstrated that SCFA signals are required for mounting acute inflammatory responses in the colon after ethanol treatment.

Acknowledgments

The authors thank B. Ulrich and F. Chu (Purdue University) for their excellent assistance and Dr. B. Vallance (University of British Columbia) for providing a C rodentium strain.

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    Author names in bold designate shared co-first authorship.

    Conflicts of interest The authors disclose no conflicts

    Funding This study was supported, in part, from grants from National Institutes of Health (R01AI074745, R01DK076616, 1R01AI080769 and 1S10RR028293) and National Multiple Sclerosis Society to CHK.

    The microarray data is deposited at: http://www.ncbi.nlm.nih.gov/geo (GSE36569).

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