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....

Transmigration of neutrophils through the microvascular endothelium is a cardinal event of acute inflammation. It has been suggested that gap junctions made of connexin43 (Cx43) may serve as a conducting pathway to spread inflammatory signals within the lung capillary network. To determine whether Cx43 contributes to neutrophil transmigration in vivo, the number of transmigrated neutrophils was monitored in lungs of Cx43 mouse models subjected to inflammation by intratracheal instillations of Pseudomonas aeruginosa lipopolysaccharide (LPS). Cx43 was detected in inflamed lungs independently of neutrophil recruitment, whereas Cx43 up-regulation was not detected in mice genetically protected from inflammation. Mice heterozygous for the Cx43 gene (gja1) showed a 56% (P < 0.01) reduction in airway neutrophil count. In contrast, increased (P < 0.05) neutrophil recruitment in response to LPS was observed in a mouse model expressing a mutant Cx43 with enhanced channel conductivity. In vitro adhesion assays showed that reduced conductivity of Cx43 channels with 43Gap26, a Cx43 blocking peptide, decreased adhesion of neutrophils to endothelial cells. Finally, we found that instillation of 43Gap26 in inflamed lungs reduced neutrophil transmigration by 65% (P < 0.05). These results indicate that inflammatory mediators up-regulate alveolar Cx43 to promote neutrophil recruitment to the airspace. Cx43 may therefore represent a pharmacological target in lung diseases characterized by excessive neutrophil recruitment to the airways.