SCFAs Induce Mouse Neutrophil Chemotaxis through the GPR43 Receptor

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.短链脂肪酸（short chain fatty acids，SCFAs）近年来受到广泛关注，因其可作为肠道菌群调控肠道炎症的潜在介质。已有研究提示，部分此类调控效应可通过SCFAs直接作用于中性粒细胞表面的GPR43受体（GPR43 receptor）实现，但该受体在中性粒细胞激活中的确切作用仍不明晰。本研究证实，小鼠骨髓源中性粒细胞（bone marrow derived neutrophils，BMNs）可有效通过聚碳酸酯滤膜，向乙酸盐、丙酸盐或丁酸盐的浓度梯度源进行趋化运动。此外，在包被纤维蛋白原的EZ-Taxiscan趋化小室中，BMNs可向丙酸盐浓度梯度源以良好的速度和方向性迁移。SCFAs的上述效应可被低浓度的合成GPR43激动剂苯乙酰胺-1（synthetic GPR43 agonist phenylacetamide-1）模拟，且在GPR43基因敲除的BMNs中完全消失。SCFAs与苯乙酰胺-1同样可触发GPR43依赖的PKB、p38及ERK激活，且此类应答对百日咳毒素敏感，提示Gi蛋白参与了该信号通路。苯乙酰胺-1还可快速且一过性激活Rac1/2鸟苷三磷酸酶，并诱导核糖体蛋白S6磷酸化。通过遗传与药理学干预手段，本研究明确了PI3Kγ、Rac2、p38及ERK在GPR43依赖的中性粒细胞趋化过程中的关键作用，而雷帕霉素靶蛋白（mTOR）并未参与其中。上述结果证实GPR43是体外环境中中性粒细胞的功能性趋化受体，并初步阐明了其信号转导通路中的关键元件。