Cannabinoid (CB2) receptor deficiency reduces the susceptibility of macrophages to oxidized LDL/oxysterol-induced apoptosis

Abstract

Macrophage apoptosis is an important process in the pathophysiology of atherosclerosis. Oxidized lowdensity lipoproteins (OxLDL) are a major component of lesions and potently induce macrophage apoptosis. Cannabinoid receptor 2 (CB2), the predominant macrophage cannabinoid receptor, modulates several macrophage processes associated with ongoing atherosclerosis; however, the role of CB2 in macrophage apoptosis is unknown. To determine if CB2 influences a macrophage apoptotic pathway relevant to atherosclerosis, we examined the effect of CB2 deficiency on OxLDL-induced macrophage apoptosis. In situ terminal transferase-mediated dUTP nick end labeling (TUNEL) analysis of resident peritoneal macrophages detected significantly fewer apoptotic CB2 2/2 macrophages than CB21/1 macrophages after incubation with OxLDL (27.9 6 4.7% vs. 61.9 6 8.5%, P , 0.001) or 7-ketocholesterol (7KC) (18.9 6 10.5% vs. 54.1 6 6.9%, P , 0.001), an oxysterol component of OxLDL. Caspase-3 activity; proteolytic conversion of procaspase-3; and cleavage of a caspase-3 substrate, PARP, were also diminished in 7KC-treated CB2 2/2 macrophages. Furthermore, the deactivation of the prosurvival kinase, Akt, in response to 7KC was impaired in CB2 2/2 macrophages. These results suggest that CB2 expression increases the susceptibility of macrophages to OxLDLinduced apoptosis, in part, by modulating the effect of oxysterols on the Akt survival pathway and that CB2 may influence atherosclerosis by modulating lesional macrophage apoptosis.

Cannabinoids and the immune system: An overview

“…CB2R activation by THC inhibits atherosclerotic plaque progression in mice by inhibiting macrophage recruitment and anandamide inhibits inflammatory gene expression in endothelial cells, and consequently monocyte adhesion (Mach and Steffens, 2008). CB2 may influence atherosclerosis by modulating lesional macrophage apoptosis (Freeman-Anderson et al, 2008). Endocannabinoids might also mediate pro-atherosclerotic effects by inducing platelet activation (Mach and Steffens, 2008).…”

The emerging role of the endocannabinoid system in cardiovascular disease

“…As described above, smooth muscle cells are crucially involved in the pathogenesis of atherosclerosis and restenosis. Moreover, there is evidence for a role of CB 2 receptors in macrophage apoptosis induced by oxidized LDL [147]. Oxidized LDL is a well-known trigger for atherosclerosis, which accumulates in macrophages within atherosclerotic lesions, resulting in foam cell formation [143].…”

“…Thus, macrophage apoptosis, at least in advanced lesions, could be considered as a proatherogenic factor triggering plaque instability and rupture [150]. Freeman-Anderson and colleagues investigated the effect of genetic CB 2 deficiency on oxidized LDL-induced apoptosis [147]. They found that the apoptosis rate was significantly reduced in peritoneal macrophages from CB 2 knockout mice as compared to wild-type animals.…”

Cannabinoid CB2 Receptors in Health and Disease

“…As reviewed recently by Buckley [67], several studies have shown that certain macrophage processes associated with the development and progression of atherosclerosis are modulated by CB 2 receptors [196,201,202]. In a more recent study Freeman-Anderson et al [203] detected fewer apoptopic resident peritoneal macrophages in CB 2 gene-deficient mice than in wildtype mice after incubation with oxidized LDL (OxLDL) and 7-ketocholesterol (7-KC) a component of OxLDL. Caspase-3 and cleavage of its substrate PARP, as well as deactivation of the prosurvival kinase, Akt in response to 7-KC, were all attenuated in CB 2 gene-deficient mouse macrophages.…”