Type 2 Cannabinoid Receptor Deficiency is Associated with Atherosclerotic Lesion Calcification in Ldr-null Mice

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Background: Calcification of atherosclerotic plaques is associated with vulnerability to rupture and increased risk of myocardial infarction. The mechanism of plaque calcification is unclear, but has been shown to be a cell-mediated process involving complex signaling pathways affecting the osteogenic transcription factor Runt-related transcription factor 2 (Runx2). The type-2 cannabinoid receptor (CB2) modulates processes involved in bone remodeling and our prior studies determined that CB2 alters the composition of early lesions in hyperlipidemic Ldlr-/- mice; however, the function of CB2 in plaque calcification is unknown. Therefore, we tested the hypothesis that CB2 modulates plaque calcification by evaluating the effects of systemic CB2 gene deletion on lesion calcification and aortic expression of Runx2 in Ldlr-/- mice.

Results: Groups (n≥8) of 8-week old CB2+/+Ldlr-/- (WT) and CB2-/- Ldlr-/- (CB2-/-) mice were fed a high fat diet (HFD) for up to 24 weeks. Standard blood plasma analysis showed no difference in HFD-induced hyperlipidemia between WT and CB2-/- mice. Aortic levels of endocannabinoids, anandamide and 2-archidonylglycerol, were significantly elevated after 12 weeks of HFD feeding as determined by LC-MS/MS. En face analysis revealed the extent of atherosclerosis in the aortic arch and thoracic aorta did not differ between WT and CB2-/- mice, but was ~1.9-fold greater in the abdominal aortas of CB2-/- mice (17.0±1.3% vs 9.0±1.3%, p=0.002). Calcification of aortic root lesions was ~2.3 fold greater in CB2-/- mice compared to WT mice (12.9±1.1% vs 5.6±1.2%, p=0.002) as revealed by von Kossa staining. Western blot analysis showed significantly increased expression of Runx2 in aortas of WT mice compared to CB2-/- after 20 weeks of HFD (2.55±0.25 fold, p

Conclusion: Systemic CB2 deficiency enhances lesion calcification and is associated with altered aortic expression of Runx2. These results provide novel mechanistic insights into the function of CB2 signaling in the pathogenesis of atherosclerosis and vascular calcification that may lead to the development of therapies aimed at stabilizing calcified plaque.

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