Flore Mulhaupt

Increasing evidence supports the involvement of inflammation in the early phases of atherogenesis. Recruitment of leukocytes within the vascular wall, controlled by chemokines, is an essential process in the development of this common disease. In this study, we report that blocking a chemokine pathway in vivo with the CC chemokine antagonist Met-RANTES reduces the progression of atherosclerosis in a hypercholesterolemic mouse model. The reduction of lesions was correlated with a diminution of expression of several major chemokines and chemokine receptors, a decrease in leukocyte infiltration, and an increase of collagen-rich atheroma, features associated with stable atheroma. Treatment was well tolerated and serum lipid profiles were not affected. Whereas genetically engineered mice with deletion of either a CC chemokine or its receptor have demonstrated resistance to disease, to our knowledge, this is the first demonstration that treatment with a chemokine receptor antagonist limits the progression of atherosclerosis in vivo. Thus, our findings indicate that blockade of chemokine receptor/ligand interactions might become a novel therapeutic strategy to reduce the evolution of this common disease.

Paracrine cell-to-cell interactions are crucial events during atherogenesis. However, little is known about the role of direct intercellular communication via gap junctions during this process. We have investigated the expression pattern of 3 vascular gap junction proteins (connexins) in mouse and human atherosclerotic plaques. Low density lipoprotein receptor-deficient mice were fed a high-fat diet for 0, 6, 10, or 14 weeks to induce different stages of atherosclerosis. Connexin37 (Cx37) and Cx40 were detected in the endothelium, and Cx43 was detected in the media of nondiseased aortas. In early atheromas, endothelial and medial connexin expression remained unchanged, and "islets" of Cx43 in smooth muscle cells and Cx37 in macrophages were observed in the neointima. In advanced atheromas, Cx37 was detected in medial smooth muscle cells and in macrophages in the lipid core but not in the endothelium covering the plaques. Cx40 could also no longer be detected in the endothelium covering the plaques. Cx43, on the other hand, was detected in the endothelium covering the shoulder of the plaques and also sparsely in neointimal smooth muscle cells. Similar results were obtained for human carotid arteries. In conclusion, vascular connexins are differentially expressed by atheroma-associated cells within lesions. These observations suggest a role for gap junctional intercellular communication during atherogenesis.

BACKGROUND: Gap junctions allow the direct exchange of ions and small molecules between cells in contact, thus coordinating physiological processes such as cell growth and differentiation. We have recently demonstrated increased expression of the gap junction protein connexin43 (Cx43) in specific subsets of cells in atherosclerotic lesions. Because the development of atherosclerosis depends critically on paracrine cell-to-cell interactions, we hypothesized that direct intercellular communication via gap junctions may be another factor controlling atherogenesis. METHODS AND RESULTS: The role of Cx43 in atherogenesis was examined by use of both a genetic and a pharmacological approach. First, atherosclerosis-susceptible LDL receptor-deficient (LDLR-/-) mice with normal (Cx43+/+) or reduced (Cx43+/-) levels of Cx43 were fed a cholesterol-rich diet for 14 weeks. The progression of atherosclerosis was reduced by 50% (P<0.01) in the thoracoabdominal aorta and in the aortic roots of Cx43+/-LDLR-/- mice compared with Cx43+/+LDLR-/- controls. Atheroma in Cx43+/-LDLR-/- mice contained fewer inflammatory cells and exhibited thicker fibrous caps with more collagen and smooth muscle cells. Next, we observed that HMG-CoA reductase inhibitors, or "statins," lipid-lowering drugs well known for their pleiotropic antiatherogenic effects, reduced Cx43 expression in primary human vascular cells in vitro. Atheroma of LDLR-/- mice treated orally with pravastatin contained fewer inflammatory cells and exhibited thicker fibrous caps than controls. This was associated with reduced Cx43 expression in lesions of statin-treated mice. CONCLUSIONS: These data indicate a critical role for Cx43-mediated gap junctional communication in atherosclerotic plaque formation.

OBJECTIVE: HMG-CoA reductase inhibitors (statins) possess anti-inflammatory and immunomodulatory properties that are independent of their lipid-lowering action. As the CD40-CD40L signaling pathway is implicated in the modulation of inflammatory responses between vascular cells, involving adhesion molecules, pro-inflammatory cytokines, chemokines, we sought to investigate the potential role of statins in regulating the expression of CD40. METHODS AND RESULTS: Using Western blot, flow cytometry and immunohistochemistry analyses, we observed that four different statins reduced IFN-gamma-induced CD40 expression in human vascular cells (endothelial cells, smooth muscle cells, macrophages and fibroblasts). This effect was dose-dependent (from 5 microM to 80 nM) and reversed by addition of L-mevalonate. Activation of vascular cells by human recombinant CD40L, as measured by ELISA for IL-6, IL-8 and MCP-1, was strongly reduced when cells were treated with statins. Immunostaining of human carotid atherosclerotic lesions of patients subjected to statin treatment revealed less CD40 expression on a 'per vascular cell' basis compared to control patients. Although many pleiotropic effects of statins are mediated by nitric oxide synthase (NOS)- or peroxisome proliferator-activated receptor (PPAR)-dependent signaling pathways, we observed similar statin-induced reduction of CD40 expression using NOS inhibitors or different PPAR ligands. CONCLUSION: Statins decrease CD40 expression and CD40-related activation of vascular cells. These effects are partially reversed by the HMG-CoA reductase product L-mevalonate and are mediated by NOS- or PPAR-dependent pathways. Altogether, these findings provide mechanistic insight into the beneficial effects of statins on atherogenesis. They also provide a scientific rationale for the use of statins as immunomodulators after organ transplantation.