Short-chain fatty acids activate GPR41 and GPR43 on intestinal epithelial cells to promote inflammatory responses in mice

Abstract

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.

Keywords: 2, 4, 6-trinitrobenzene sulfonic-acid; ATF2; C2; C3; C4; CFU; Colonic Inflammation; ECs; ERK; FITC; G-protein−coupled receptor; GPR; IL; Intestinal Barrier Leakage; KO; MAPK; Mouse Model; Pathogen; SCFAs; T-helper cell; TNBS; Th; WT; acetate; activating transcription factor 2; butyrate; colony-forming unit; epithelial cells; extracellular signal-regulated kinase; fluorescein isothiocyanate; interleukin; knock-out; mitogen-activated protein kinase; propionate; short-chain fatty acids; wild type.