Relation entre la structure et la fonction des artères cérébrales dans l’athérosclérose : impact des traitements cardioprotecteurs
Large artery stiffness and endothelial dysfunction are markers of atherosclerosis. Stiffening of the carotid arteries contrast with the paradoxical increase in distensibility of cerebral arteries that was reported in the presence of risk factors for cardiovascular diseases, such as hypertension. However, our knowledge concerning the influence of atherosclerosis on cerebrovascular compliance and structure remains incomplete. By targeting the endothelium, atherosclerosis induces a severe cerebral endothelial dysfunction affecting chronically the cerebral blood flow and potentially leading to cognitive dysfunctions. Few studies have shown that the paradoxical increase in cerebrovascular distensibility is consistently reported in animal model of risk factors for cardiovascular diseases exhibiting a cerebral endothelial dysfunction. That being said, we hypothesized that the compliance and structure of cerebral arteries is essentially controlled by the endothelium. To validate our hypothesis, in a first study, we selected three distinct therapeutic approaches that modulated the cerebral endothelial function and the mechanical stress imposed to the vascular wall by lowering heart rate in a mouse model of atherosclerosis, LDLr-/-; hApoB-100+/+ during three months. Ivabradine, metroprolol and voluntary physical training protected, with different efficiencies, the cerebral flow-mediated dilation and this was reflected by a prevention, or not, of the increase in compliance. A 13.5 % heart rate reduction with ivabradine and metoprolol limited carotid artery stiffening. Voluntary physical training did not induce an overall reduction of heart rate explaining the lack of effect on carotid mechanics and suggesting that carotids compliance is more influenced by the mechanical stress imposed to the vascular wall by the cardiac cycle.  In a second study, we confirmed our previous findings using a diatery approach that targeted more directly the endothelium, the polyphenol antioxidant catechin. Catechin was previously proven, by us and others, to reverse endothelial dysfunction, reduce inflammation and neutralize reactive oxygen species in diverse vascular beds from animal models of atherosclerosis. Accordingly, we found that catechin prevents adverse cerebral wall remodeling but, again, without a significant heart rate reduction, carotids remained stiff. We also integrated a new live imaging technology allowing us to confirm our findings in vivo and to demonstrate that endothelial, structural and mechanical protection by catechin can result in an improvement of basal cerebral blood flow.  Finally, both studies identified metalloproteinase -9 as a potential player in the process leading the weakening of the cerebral artery walls. Taken together, our studies highlight that structural and biomechanical alterations are genuinely triggered by endothelial dysfunction. In carotids, mechanicals stress seems to be the main factor controlling remodeling. In essence, indirect protection of the endothelium impedes in cerebral vessels the remodeling processes, such as the activation of metalloproteinase -9. Numerous studies have revealed that vascular, especially cerebral endothelial dysfunction is implicated in the pathogenesis of Alzheimer’s disease. When brain perfusion is compromised, the suboptimal energy delivery causes neuronal death. Deleterious cerebrovascular outcomes that promote the impairment of vasodilation and the encroachment of the lumen will limit cerebral blood flow in a chronic manner. Chronic treatment with ivabradine, voluntary physical training and catechin preserved the endothelial function, the structure and the mechanics of cerebral arteries, which guarantees a closer management of cerebral blow flow in atherosclerotic mice and a reduce propensity to develop cognitive deficiency.
Compliance Cerebral circulation Compliance Vascular remodeling Endothelial dysfunction Cerebral blood flow Metalloproteinases Heart rate Oxidative stress