Cannabinoid receptor 1 mediates M1 type macrophage polarization by G(α)i/o/RhoA/NF-κB p65 signaling pathway in murine liver injury

Abstract

Abstract Macrophage, as an essential component of innate immunity, has emerged as a key role in liver injury. There are two main subtypes of macrophages in liver, referred to as tissue-resident Kupffer cells and bone marrow (BM)-derived monocyte/macrophages (BMMs). Macrophages are phenotypically heterogeneous and broadly characterized according to their polarization as M1/M2 types. Our previous research had demonstrated that cannabinoid receptor 1 (CB1) mediated infiltration and activation of BMMs in mouse liver injury. Here we investigated the role of CB1 in macrophage polarization. ICR mice were lethally irradiated and received BM transplants from enhanced GFP transgenic mice. Four weeks later, mice of BM reconstruction were subjected to carbon tetrachloride (CCl4)-induced liver injury. Expressions of M1 gene signatures (CD86, iNOS, IL-1b, IL-6, TNFa) in livers or cultured primary BMMs were measured by RT qPCR or Western blot. In the chimeric murine model, we found that amount of M1 type macrophages were increased from 1 to 28 days in CCl4 treatment with a maximal increase at 28 days by flow cytometry. Almost 70% of M1 type macrophages were from BMMs (CD86+EGFP+) and 30% of them were from Kupffer cells (CD86−EGFP+). Meanwhile, the dynamic changes of M1 gene signatures were consistent in injured livers by RT qPCR or Western blot. Blockage of CB1 by administration of its specific antagonist or siRNA in vivo decreased the amount of M1 type of BMMs origin, but showed little effect on that of Kupffer cells. Activation of CB1 by its agonist, ACEA, promoted M1 polarization of BMMs, depending on G(a)i/o/RhoA/NF-κB p65 signaling pathway. In conclusion, these data suggest that CB1 plays a crucial role in regulating M1 polarization of BMMs in liver injury.