Cannabinoid receptor CB1 signaling has been implicated in atherogenesis, while underlying cell-specific effects are not understood. Here, we investigated the role of CB1 in myeloid cells, the main immune cells in atherosclerotic plaques. 

Myeloid Cnr1 (CB1 gene) knockout mice were generated on apolipoprotein E deficiency ( Apoe-/- ) background by crossing Cnr1flox/flox mice with transgenic mice carrying Cre recombinase under control of the lysozyme M promoter ( LysMCre ) for selective expression in myeloid cells. The resulting Apoe-/-LysMCreCnr1flox/flox mice as well as Apoe-/-Cnr1flox/flox and Apoe-/-LysMCre  controls were fed with WD (0.20% cholesterol) for 4 weeks or 16 weeks. Bone marrow-derived macrophages were isolated from baseline mice. Ldlr-/-mice fed with WD for 8 weeks received daily ip injections of CB1 antagonist JD5037 (3 mg/kg/day) or vehicle during the last 4 weeks of diet. Immunohistology, flow cytometry, qPCR, kinase array, bulk RNA sequencing, and seahorse metabolic flux assays were performed. Effects in male and female mice were compared throughout the study.

Male mice with myeloid-specific Cnr1 deficiency had significantly smaller lesions and necrotic cores compared to controls. In female mice, smaller necrotic cores and moderate effects on plaque progression were only observed at advanced stage (16 weeks WD). Atheroprotection in male mice was associated with reduced arterial monocyte recruitment, plaque macrophage proliferation and less inflammatory polarization. The sex-specific differences of CB1 signaling in murine macrophages were reproducible in vitro and blunted in male cells by estradiol treatment. Mechanistically, kinase activity profiling showed an implication of p53 signaling and cyclin-dependent kinases in CB1-mediated effects.Unbiased transcriptomic profiling further indicated a role for CB1 in macrophage oxidative metabolism, which was confirmed by metabolic flux assays. in particular, CB1 deficiency or antagonism resulted in improved oxidative energy metabolism. Chronic administration of the peripherally-restricted CB1 antagonist JD5037 prevented plaque progression in atherogenesis, which was again only observed in male mice. 

In conclusion, impaired CB1 signaling in macrophages is atheroprotective by limiting their arterial recruitment, local proliferation and inflammatory reprogramming. The biological effects of CB1 signaling in murine macrophages seem to be more pronounced in male mice, at least in early disease stage.