SCFAs Induce Mouse Neutrophil Chemotaxis through the GPR43 Receptor

Abstract

Short chain fatty acids (SCFAs) have recently attracted attention as potential mediators of the effects of gut microbiota on intestinal inflammation. Some of these effects have been suggested to occur through the direct actions of SCFAs on the GPR43 receptor in neutrophils, though the precise role of this receptor in neutrophil activation is still unclear. We show that mouse bone marrow derived neutrophils (BMNs) can chemotax effectively through polycarbonate filters towards a source of acetate, propionate or butyrate. Moreover, we show that BMNs move with good speed and directionality towards a source of propionate in an EZ-Taxiscan chamber coated with fibrinogen. These effects of SCFAs were mimicked by low concentrations of the synthetic GPR43 agonist phenylacetamide-1 and were abolished in GPR43−/− BMNs. SCFAs and phenylacetamide-1 also elicited GPR43-dependent activation of PKB, p38 and ERK and these responses were sensitive to pertussis toxin, indicating a role for Gi proteins. Phenylacetamide-1 also elicited rapid and transient activation of Rac1/2 GTPases and phosphorylation of ribosomal protein S6. Genetic and pharmacological intervention identified important roles for PI3Kγ, Rac2, p38 and ERK, but not mTOR, in GPR43-dependent chemotaxis. These results identify GPR43 as a bona fide chemotactic receptor for neutrophils in vitro and start to define important elements in its signal transduction pathways.

Gut/brain axis and the microbiota

“…Fermentable carbohydrates such as acetate, propionate, and butyrate, which enter the colon and are converted into SCFAs, are a well-studied example of microbial-derived metabolites. Primary SCFAs have a number of physiologic effects, including reduction of food intake, improvement of glucose tolerance, modulation of lymphocyte and neutrophil function, and activation of epithelial cell signaling pathways (15,(123)(124)(125)(126)(127). Signaling through GPCRs, as well as transport of SCFAs by SLC5A8 and the resultant physiological effects, are affected by dietary intake of fermentable fiber (128).…”

The Therapeutic Potential of Allosteric Ligands for Free Fatty Acid Sensitive GPCRs

“…FFA2 agonists are reported to inhibit lipolysis and regulate plasma free fatty acid levels [95], enhance glucose uptake in adipocytes [85] and stimulate GLP-1 release [96]; all properties indicating that agonism of FFA2 may be beneficial for metabolic conditions. However, FFA2 agonists, including the allosteric compound 14, also promote neutrophil chemotaxis [93,97], a property potentially detrimental in inflammatory conditions. Indeed, FFA2 -/-mice were protected against tissue damage in a model of colitis [93], suggesting FFA2 antagonists, and not agonists, might be useful therapeutically for inflammation.…”

Use of Cellulose and Recent Research into Butyrate

“…Since more than 95% of SCFA is absorbed in the intestines, it is much too difficult to determine the concentration of SCFA [88].…”

“…Many studies have found physiological and pathological conditions of intestinal microorganisms and demonstrated that microorganisms and their products play an important role in the gastrointestinal tract, adipose tissue, immune system, and nervous system [20,59,87]. When the distribution of intestinal microorganisms is changed, the concentration of substances that are generated and secreted by microorganisms is changed, which contributes to conditions in which illnesses may break out, such as IBD, colon cancer, obesity, and type 1&2 diabetes [18,59,87,88]. The SCFA concentration in the gastrointestinal tract and blood is effective to prevent such diseases as IBD, cancer and diabetes [20,34,59,86].…”

“…Of SCFA's, butyrate coordinates the proliferation and differentiation of cells and is involved in immunity and inflammation reactions [89]. In vitro, SCFA induces the chemotaxsis of neutrophil and activates GPR109A, GPR41, and GPR43, which are receptors [16,43,53,58,76,88]. Anti-inflammation effects of butyrate include reducing the activities of NF-Kb, inhibiting the generation of interferon γ, increasing PPARγ (peroxisome proliferator-activated receptor-γ; multiplication and transcription factor for beta cells of the pancreas), inhibiting HDAC, and many others [35].…”