The direct pro-fibrotic and indirect immune anti-fibrotic balance of blocking the cannabinoid CB2 receptor


Yosefa Avraham, Johnny Amer, Sarit Doron, Lina Abu-Tair, Mahmud Mahamid, Areej A.S Khatib, Elliot M. Berry, and Rifaat Safadi


Cannabinoid CB2-receptors expressed on immune cells are considered to be anti-fibrogenic. Hepatic stellate cells (HSCs) directly interact with, and phagocytose lymphocytes, but the nature of this interaction is obscure. Aims: To study the effects of CB2-receptors on hepatic-fibrosis via their role in mediating immunity. Methods: (I) Hepatic-fibrosis was induced by carbon-tetrachloride (CCl4) administration in C57BL/6 wild-type (WT) and CB2-knockout (CB2-/-) mice. (II) Irradiated-animals were reconstituted with WT or CB2-/- lymphocytes. (III) Lymphocytes from naïve/ fibrotic WT animals; and healthy/cirrhotic HCV were pre-incubated in-vitro with/without CB2-antagonist, evaluated for proliferation and apoptosis, and then co-cultured with primary mouse HSCs or a human HSCs line (LX2), respectively. Lymphocyte phagocytosis was then evaluated. Results: (I) Following CCl4-administration; CB2-/- mice develop significant hepatic-fibrosis but less necro-inflammation. WT mice harbored decreased liver CD4+ and NK+ cells but increased CD8+ subsets. Naïve CB2-/- mice had significantly decreased T-cell subsets. (II) Adoptive transfer of CB2-/- lymphocytes led to decreased fibrosis in the irradiated WT recipient as compared to animals receiving WT lymphocytes. Moreover, necro-inflammation also tended to decrease. (III) In-vitro, a CB2-antagonist directly increased human HSCs activation and increased apoptosis, decreased proliferation of mice/ human T-cells (healthy/ fibrotic) and their phagocytosis. Conclusions: CB2-/- lymphocytes exert an anti-fibrotic activity while lack of CB2-receptor in HSCs promotes fibrosis. These findings broaden our understanding of cannabinoid signaling in hepatic fibrosis beyond their activity solely in HSCs.