Taurocholic acid improves hepatocyte lipid deposition by regulating macrophage polarization through TGR5

Abstract

Objective To investigate the effect of taurocholic acid (TLCA) regulating palmitic acid (PA)-induced macrophage polarization on hepatocyte lipid metabolism. Methods Mouse mononuclear macrophage (RAW264.7) cells, treated with TLCA and PA, were divided into control (CON), TLCA, PA and PA+TLCA groups. The conditioned medium (CM) was collected for culturing primary hepatocytes from C57 BL/6J and AML-12 liver cells. Triamterene was used to inhibit macrophage Takeda G-protein receptor 5(TGR5), which could investigate the role of TGR5 in regulating macrophage polarization and reducing lipid deposition in hepatocytes. BODIPY fluorescence staining was performed to detect lipid accumulation in hepatocytes; The mRNA levels of genes related to inflammatory factors and lipid metabolism were detected by RT-qPCR; Western blotting was performed to detect the level of protein expression of macrophage TGR5 and hepatic cell SREBP-1c. The expression of iNOS and CD206 were observed by immunofluorescence staining. Results BODIPY fluorescence staining showed that PA group displayed significantly increased lipid accumulation, compared with CON group, while TLCA treatment could reduce the PA-induced lipid accumulation(P < 0.05); Compared with the PA group, the PA+TLCA group had decreased mRNA levels of ACC1, FASN and SREBP-1c and protein expression of SREBP-1c (P < 0.05). However, there were no significant changes of expression of ACOX1 and CPT1A among these groups mentioned above. The outcome of RT-qPCR showed that PA stimulated RAW264.7 into M1-type polarization and significantly increased the levels of proinflammatory factors (iNOS, IL-6, IL-1β, TNF-α). PA combined with TLCA could reduce the levels of inflammatory factors and increased the mRNA expression levels of M2-type polarization-related genes, Arg1, IL-4 and IL-10 (P < 0.05). Compared with CON group, the PA group showed increased M1-type marker iNOS and decreased M2-type marker CD206, while TLCA could promote the protein expression of TGR5(P=0.0714). TGR5 inhibited by triamterene could suppress macrophage polarization regulated by TLCA and reduce hepatocyte lipid accumulation. Conclusion TLCA inhibits PA-induced M1-type polarization and promotes M2-type polarization via TGR5, which reduces proinflammatory factors, reduces hepatic lipogenesis and promotes hepatocyte lipid accumulation.

Keywords

• macrophages polarization
• taurocholic acid
• non-alcoholic fatty liver disease
• takeda g protein-coupled receptor 5