Background-Endothelial dysfunction is the initiating event of atherosclerosis. The expression of connexin40 (Cx40), an endothelial gap junction protein, is decreased during atherogenesis. In the present report, we sought to determine whether Cx40 contributes to the development of the disease. Methods and Results-Mice with ubiquitous deletion of Cx40 are hypertensive, a risk factor for atherosclerosis. Consequently, we generated atherosclerosis-susceptible mice with endothelial-specific deletion of Cx40 (Cx40del mice). Cx40del mice were indeed not hypertensive. The progression of atherosclerosis was increased in Cx40del mice after 5 and 10 weeks of a high-cholesterol diet, and spontaneous lesions were observed in the aortic sinuses of young mice without such a diet. These lesions showed monocyte infiltration into the intima, increased expression of vascular cell adhesion molecule-1, and decreased expression of the ecto-enzyme CD73 in the endothelium. The proinflammatory phenotype of Cx40del mice was confirmed in another model of induced leukocyte recruitment from the lung microcirculation. Endothelial CD73 is known to induce antiadhesion signaling via the production of adenosine. We found that reducing Cx40 expression in vitro with small interfering RNA or antisense decreased CD73 expression and activity and increased leukocyte adhesion to mouse endothelial cells. These effects were reversed by an adenosine receptor agonist. Key Words: atherosclerosis Ⅲ connexins Ⅲ endothelium Ⅲ gap junctions Ⅲ inflammation C ardiovascular diseases currently constitute the major cause of death in developed countries. 1 Atherosclerosis, an inflammatory disease of large and medium-sized arteries, 2 is the most important cause of cardiovascular diseases. The main consequences of atherosclerosis are myocardial infarction, cerebral infarction, and aortic aneurysm. 3 Conclusions-Cx40-mediated Clinical Perspective on p 131Atherosclerosis involves the formation of intimal lesions that are characterized by a dysfunctional endothelium, inflammation, lipid accumulation, cell death, and fibrosis. 2,3 The distribution of atherosclerotic plaques is highly characteristic in humans; the lesions develop predominantly near side branches of arteries where blood flow is disturbed. 4 A variety of substances mediating intercellular communication, including cytokines, chemokines, and growth factors, have been identified to induce, amplify, and modify the atherosclerotic inflammatory process. 5,6 In this context, connexins, a large family of proteins that form hemichannels and gap junction channels enabling transmembrane and intercellular coordination of tissue activity, 7,8 have been involved in atherogenesis. Three connexins are expressed in the vascular wall, namely connexin (Cx)37, Cx40, and Cx43, and important changes in their expression pattern have been reported in Received March 20, 2009; accepted October 28, 2009. From the Division of Cardiology (C.E.C., I.R., B.F., B.R.K.) and Department of Pediatrics (K.E.L.S., M.Z.R.S., M.B., B.F., T.D....

Abstract-We reported that smooth muscle cell (SMC) populations isolated from normal porcine coronary artery media exhibit distinct phenotypes: spindle-shaped (S) and rhomboid (R). R-SMCs are recovered in higher proportion from stent-induced intimal thickening compared with media suggesting that they participate in intimal thickening formation. Our aim was to identify a marker of R-SMCs in vitro and to explore its possible expression in vivo. S-and R-SMC protein extracts were compared by means of 2-dimensional polyacrylamide gel electrophoresis followed by tandem mass spectrometry. S100A4 was found to be predominantly expressed in R-SMC extracts. Using a monoclonal S100A4 antibody we confirmed that S100A4 is highly expressed by R-SMCs and hardly detectable in S-SMCs. S100A4 was colocalized with ␣-smooth muscle actin in stress fibers of several quiescent cells and upregulated during migration. PDGF-BB, FGF-2 or coculture with endothelial cells, which modulate S-SMCs to a R-phenotype, increased S100A4 expression in both S-and R-SMCs. Silencing of S100A4 mRNA in R-SMCs decreased cell proliferation, suggesting a functional role for this protein.In vivo S100A4 was absent in normal porcine coronary artery media, but highly expressed by SMCs of stent-induced intimal thickening. In humans, S100A4 was barely detectable in coronary artery media and markedly expressed in SMCs of atheromatous and restenotic coronary artery lesions. Our results indicate that S100A4 is a marker of porcine R-SMCs in vitro and of intimal SMCs during intimal thickening development. It is also a marker of a large population of human atheromatous and restenotic SMCs. Clarifying S100A4 function might be useful to understand the evolution of atherosclerotic and restenotic processes. Key Words: 2D-PAGE Ⅲ stent Ⅲ endothelial cells Ⅲ mts1 Ⅲ ␣-smooth muscle actin Ⅲ smoothelin T he concept of smooth muscle cell (SMC) phenotypic heterogeneity has been validated in several species including man (for review see 1 ). We have recently extended this notion to the porcine coronary artery (CA) and isolated from the normal media 2 distinct SMC populations: spindleshaped (S) with the classical "hills-and-valleys" growth pattern and rhomboid (R), which grows as a monolayer. 2 R-SMCs display enhanced proliferative, migratory and proteolytic activities as well as poor level of differentiation compared with S-SMCs. R-SMCs are recovered in higher proportion when SMCs are cultured from the intimal thickening (IT) induced after experimental stent implantation compared with the normal media, indicating that they are crucial for arterial repair, and could represent an atheromaprone phenotype.Our aim was to further characterize the phenotypic features of S-and R-SMCs, to identify them in vivo and possibly to verify their presence in atheromatous plaque and restenotic lesions. We have analyzed protein extracts by means of 2-dimensional polyacrylamide gel electrophoresis (2D-PAGE) followed by identification of differentially expressed proteins using tandem mass spectrometry (M...