Aim: Cardiovascular diseases (CVDs) are the leading cause of death globally, claiming an estimated 17.9 million lives each year. Research into the mechanisms and signaling of endocannabinoids in atherosclerosis and related metabolic disorders might help finding novel treatments and reduce CVD deaths. Here, we aimed to clarify the myeloid-cell-specific effects of CB1 in atherosclerotic plaque formation and macrophage functions.

Methods: Myeloid CB1 knockout mice were generated on ApoE-/- background by crossing CB1flox mice with transgenic mice carrying Cre under control of the lysozyme M (LysM) promoter for selective expression in myeloid cells. Age - and sex-matched groups were analyzed at baseline, 4 and 16 weeks Western diet (0,15% cholesterol). For in vitro experiments, bone marrow-derived macrophages (BMDM) were generated from global CB1-/-ApoE-/- and ApoE-/- mice.

Results: Myeloid CB1 deficiency resulted in significantly smaller lesion formation after 4 weeks diet (ApoE-/-LysM Cre 37613 ± 3473 µm², n=15; ApoE-/-LysM Cre CB1flox 24600 ± 2793 µm², n=12; P<0.01) and less macrophage accumulation in the aortic roots of male mice, without effects on body weight and plasma cholesterol levels. In addition, male mice with myeloid CB1 deficiency showed reduced plaque progression after 16 weeks diet. No difference in plaque formation was observed in female mice. Myeloid CB1 deficiency led to increased myeloid cell frequencies in the circulation, which inversely correlated with plaque size, suggesting a reduced arterial monocyte recruitment. In vitro, CB1-/- male BMDM had lower proliferation rates compared to CB1+/+ macrophages (ApoE-/- 5.5% ± 0.3, n=11; ApoE-/-CB1-/- 3.0% ± 0.3, n=13; P<0.001). Likewise, plaques of male myeloid CB1 deficient mice contained less proliferating macrophages. This proliferation phenotype was only observed in male, but not female macrophages, supporting a sex-specific impact of CB1 signaling in myeloid cells.

Conclusion: This work reveals a pro-atherosclerotic role of myeloid CB1 in male mice. In addition to changes in cell proliferation, preliminary findings also suggest effects on monocyte recruitment/mobilization. Moreover, the biological function of CB1 signaling in macrophages seems to be sex-dependent.