A Medium-chain Fatty Acid Receptor Gpr84in Zebrafish: Expression Pattern And Roles In Immune Regulation

Gpr84was recently identified as a receptor for medium-chain fatty acids, but its functionsremain to be clarified. We reported the identification of a zebrafish Gpr84homologue (zGpr84),which has a higher gene expression in the tissues of intestine, heart and liver. Duringembryogenesis, zGpr84is maternally expressed and a significant increase is observed atsegmentation period, and it is mainly restricted to the head region, pectoral fins, branchialarches, intestine and lateral line neuromast. Fasting or treatment with lipopolysaccharide (LPS)can induce significant up-regulation of zGpr84. We further demonstrated that zGpr84isinvolved in the accumulation of lipid droplets in cells. Moreover, undecanoic acid (UA) canamplify LPS induced production of the proinflammatory cytokine IL-12p40through zGpr84,supporting the proposal that Gpr84may play a role in directly linking fatty acid metabolism toimmunological regulation. The resulting data in fish lay a foundation for a comprehensiveexploration of the functions and evolution of Gpr84.