Expression of FFAR2 by Dendritic Cells Prevents Their Expression of IL27 and is Required For Maintenance of Mucosal Barrier and Immune Response Against Colorectal Tumors in Mice

Abstract Background & Aims Intestinal microbes and their metabolites affect development of colorectal cancer (CRC). Short-chain fatty acids are metabolites generated by intestinal microbes from dietary fiber. We investigated the mechanisms by which free fatty acid receptor 2 (FFAR2), a receptor for short-chain fatty acids that affects the composition of the intestinal microbiome, contributes to the pathogenesis of CRC. Methods We performed studies with ApcMin/+ mice, ApcMin/+Ffar2-/- mice, mice with conditional disruption of Ffar2 in dendritic cells (DCs) (Ffar2fl/flCD11c-Cre mice), ApcMin/+Ffar2fl/flCD11c-Cre mice, and Ffar2fl/fl mice (controls); some mice were given dextran sodium sulfate to induce colitis, with or without a FFAR2 agonist or an antibody against interleukin 27 (IL27). Colon and tumor tissues were analyzed by histology, quantitative PCR, and 16S rRNA gene sequencing; lamina propria and mesenteric lymph node tissues were analyzed by RNA sequencing and flow cytometry. Intestinal permeability was measured following gavage with fluorescently labeled dextran. We collected data on colorectal tumors from the Cancer Genome Atlas. Results ApcMin/+Ffar2-/- mice developed significantly more spontaneous colon tumors than ApcMin/+ mice and had increased gut permeability before tumor development, associated with reduced expression of E-cadherin. Colon tumors from ApcMin/+Ffar2-/- mice had a higher number of bacteria than tumors from ApcMin/+ mice, as well as higher frequencies of CD39+CD8+ T cells and exhausted or dying T cells. DCs from ApcMin/+Ffar2-/- mice had an altered state of activation, increased death, and higher production of IL27. Administration of an antibody against IL27 reduced the numbers of colon tumors in ApcMin/+ mice with colitis. Frequencies of CD39+CD8+ T cells and IL27+ DCs were increased in colon lamina propria from Ffar2fl/flCD11c-Cre mice with colitis compared with control mice or mice without colitis. ApcMin/+Ffar2fl/flCD11c-Cre mice developed even more tumors than ApcMin/+Ffar2fl/fl mice, and their tumors had even higher numbers of IL27+ DCs. ApcMin/+ mice with colitis given the FFAR2 agonist developed fewer colon tumors, with fewer IL27+ DCs, than mice not given the agonist. DCs incubated with FFAR2 agonist no longer had gene expression patterns associated with activation or IL27 production. Conclusions Loss of FFAR2 promotes colon tumorigenesis in mice by reducing gut barrier integrity, increasing tumor bacterial load, promoting exhaustion of CD8+ T cells, and over-activating DCs, leading to their death. Antibodies against IL27 and agonists of FFAR2 reduce tumorigenesis in mice and might be developed for treatment of CRC.