Protective effect of lodoxamide on hepatic steatosis through GPR35

Although GPR35 is an orphan G protein-coupled receptor, synthetic agonists and antagonists have been developed. Recently, cromolyn, a mast cell stabilizer, was reported as an agonist of GPR35 and was shown to exhibit antifibrotic effects through its actions on hepatocytes and stellate cells. In this study, the role of GPR35 in hepatic steatosis was investigated using an in vitro model of liver X receptor (LXR)-mediated hepatocellular steatosis and an in vivo model of high fat diet-induced liver steatosis. GPR35 was expressed in Hep3B human hepatoma cells and mouse primary hepatocytes. A specific LXR activator, T0901317, induced lipid accumulation in Hep3B cells. Lodoxamide, the most potent agonist of GPR35, inhibited lipid accumulation in a concentration-dependent manner. The protective effect of lodoxamide was inhibited by a specific GPR35 antagonist, CID2745687, and by siRNA-mediated knockdown of GPR35. The expression of SREBP-1c, a key transcription factor for lipid synthesis, was induced by T0901317 and the induction was inhibited by lodoxamide. Through the use of specific inhibitors of cellular signaling components, the lodoxamide-induced inhibition of lipid accumulation was found to be mediated through p38 MAPKs and JNK, but not through G_i/o proteins and ERKs. Furthermore, the protective effect of lodoxamide was confirmed in mouse primary hepatocytes. Lodoxamide suppressed high fat diet-induced fatty liver development, which suggested the protective function of GPR35 in liver steatosis. Therefore, the present data suggest that GPR35 may function to protect against fatty liver development.