Arctiin activates CB2R to regulate the TRAF6-STAT1/6 pathway maintain macrophage M1/M2 homeostasis

Immune rejection after liver transplantation remains a major challenge impacting the long-term survival of liver transplant recipients. Inhibiting macrophage M1 polarization exerts a positive effect on alleviating post-transplant immune rejection. Arctiin, an active component derived from traditional Chinese medicine, may suppress macrophage M1 polarization by inhibiting the release of pro-inflammatory cytokines. This study employed experimental techniques including ELISA, double-label flow cytometry, Western blot analysis, and cellular immunofluorescence to investigate the potential mechanism underlying the effect of arctiin on macrophage M1/M2 phenotypic switching in vitro. Results demonstrated that arctiin promoted the conversion of M0 macrophages to the M2 phenotype, significantly downregulated the levels of pro-inflammatory cytokines IL-6 and TNF-α, inhibited the expression of the M1 macrophage marker inducible nitric oxide synthase (iNOS), and reduced the proportion of M1-type macrophages. Furthermore, arctiin notably enhanced STAT6 phosphorylation and TRAF6 protein expression in M1 macrophages while suppressing STAT1 phosphorylation. However, these beneficial effects of arctiin were significantly reversed by a CB2R antagonist. Additional experiments showed that a CB2R agonist exerted similar effects to arctiin. Treatment with a TRAF6 inhibitor abrogated the inhibitory effect of arctiin or the CB2R agonist on macrophage M1 polarization, increased STAT1 phosphorylation, and decreased STAT6 phosphorylation. In conclusion, this study indicates that arctiin can activate CB2R and exert anti-inflammatory effects through the TRAF6-STAT1/6 pathway, thereby promoting the phenotypic switch of macrophages from M1 to M2.