Abstract
HMG-CoA reductase inhibitors (statins) decrease atherosclerosis by lowering low-density-lipoprotein cholesterol. Statins are also thought to have additional anti-atherogenic properties, yet defining these non-conventional modes of statin action remains incomplete. We have previously developed a novel mouse transplant model of atherosclerosis regression in which aortic segments from diseased donors are placed into normolipidemic recipients. With this model, we demonstrated the rapid loss of CD68+ cells (mainly macrophages) in plaques through the induction of a chemokine receptor CCR7-dependent emigration process. Because the human and mouse CCR7 promoter contain Sterol Response Elements (SREs), we hypothesized that Sterol Regulatory Element Binding Proteins (SREBPs) are involved in increasing CCR7 expression and through this mechanism, statins would promote CD68+ cell emigration from plaques. We examined whether statin activation of the SREBP pathway in vivo would induce CCR7 expression and promote macrophage emigration from plaques. We found that western diet-fed apoE-/- mice treated with either atorvastatin or rosuvastatin led to a substantial reduction in the CD68+ cell content in the plaques despite continued hyperlipidemia. We also observed a significant increase in CCR7 mRNA in CD68+ cells from both the atorvastatin and rosuvastatin treated mice associated with emigration of CD68+ cells from plaques. Importantly, CCR7-/-/apoE-/- double knockout mice failed to display a reduction in CD68+ cell content upon statin treatment. Statins also affected the recruitment of transcriptional regulatory proteins and the organization of the chromatin at the CCR7 promoter to increase the transcriptional activity. Statins promote the beneficial remodeling of plaques in diseased mouse arteries through the stimulation of the CCR7 emigration pathway in macrophages. Therefore, statins may exhibit some of their clinical benefits by not only retarding the progression of atherosclerosis, but also accelerating its regression.
Highlights
Atherosclerosis is responsible for more than half of all mortality in Western countries
Both atorvastatin and rosuvastatin were capable of lowering total cholesterol levels without affecting high density-lipoprotein cholesterol (HDL-C), and at the doses used, rosuvastatin appeared to be more effective in lowering total cholesterol than atorvastatin
Recent studies indicate that some of the cholesterol-independent or ‘‘pleiotropic’’ effects of statins involve improving endothelial function, enhancing the stability of atherosclerotic plaques, decreasing oxidative stress and inflammation, as well as inhibiting the thrombogenic response [22]. We describe another effect of statins, namely, their promotion of the depletion of CD68+ cells from plaques in a CCR7 dependent fashion
Summary
Atherosclerosis is responsible for more than half of all mortality in Western countries. As useful as statins may be in limiting progression of cardiovascular disease, there is likely to be a significant plaque burden remaining in the treated population. In spite of the clinical desirability to achieve regression and the success of statin treatment to achieve it in some patients [5,6], research into the factors that may be mediating this process has been hampered by the relative paucity of appropriate animal models. The similarities between atherosclerosis progression in humans and mice deficient either in apoE (apoE-/-) or the LDL receptor suggest that molecular mechanisms underlying regression in these mouse models could be relevant to the reduction in plaque burden in the human population (reviewed in [3,7])
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