Cannabinoid receptor type 2 (CB2) deficiency alters atherosclerotic lesion formation in hyperlipidemic Ldlr-null mice.

OBJECTIVE: To determine if cannabinoid receptor 2 (CB2) plays a role in atherosclerosis, we investigated the effects of systemic CB2 gene deletion on hyperlipidemia-induced atherogenesis in low density lipoprotein receptor-deficient (Ldlr(-/-)) mice. METHODS AND
RESULTS: Ldlr(-/-) and CB2/Ldlr double knockout (CB2(-/-)Ldlr(-/-)) mice were fed an atherogenic diet for 8 and 12 weeks. Morphometric analysis revealed no significant difference between the atherosclerotic lesion area in the proximal aortas of Ldlr(-/-) and CB2(-/-)Ldlr(-/-) mice after 8 or 12 weeks on the atherogenic diet. The macrophage and smooth muscle cell (SMC) content, as revealed by immunohistochemical staining, did not differ significantly between Ldlr(-/-) and CB2(-/-)Ldlr(-/-) lesions after 8 weeks. However, after 12 weeks, CB2(-/-)Ldlr(-/-) lesions displayed greater macrophage content (86.6 ± 4.1 versus 75.2 ± 7.5%, P<0.05) and SMC content (11.1 ± 5.1 versus 4.2 ± 2.4%, P<0.05) compared to controls. Lesional apoptosis, as determined by in situ TUNEL analysis, was reduced ~50% in CB2(-/-)Ldlr(-/-) lesions after 12 weeks. CB2(-/-)Ldlr(-/-) lesions displayed significantly reduced collagen content and increased elastin fiber fragmentation after 12 weeks, which was associated with an ~57% increase in matrix metalloproteinase 9 (MMP) levels. In vitro, CB2(-/-) macrophages secreted ~1.8-fold more MMP9 activity than CB2(+/+) macrophages.
CONCLUSIONS: CB2 receptor deficiency affects atherogenesis in Ldlr-null mice by increasing lesional macrophage and SMC content, reducing lesional apoptosis and altering extracellular matrix components, in part, by upregulating MMP9. These results suggest that pharmacological manipulation of CB2 receptors might exert multiple and complex effects on atherogenesis and plaque stability.