Abstract 5064: Endothelial-Specific Deletion of Cx40 Promotes Atherosclerosis by Increasing CD73-Dependent Leukocyte Adhesion

Abstract

Endothelial dysfunction is the initiating event of atherosclerosis. The expression of connexin40 (Cx40), an endothelial gap junction protein, is decreased during atherogenesis. Here, we sought to determine whether Cx40 contributes to the development of the disease. 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 (Tie2CRE+ Cx40fl/fl ApoE−/− mice; EC-Cx40del mice). EC-Cx40del mice were indeed not hypertensive. The progression of atherosclerosis was increased in EC-Cx40del mice after 10 weeks high-cholesterol diet; lipid deposition in the thoracic-abdominal aortas was 21.4±3.5% (N=10, p<0.01) in EC-Cx40del mice as compared to 12.6±1.3% for Tie2CRE+ Cx40wt/wt ApoE−/− and 7.1±1.3% for Tie2CRE- Cx40fl/fl ApoE−/− controls. Moreover, spontaneous lesions were observed in the aortic sinuses of young EC-Cx40del mice without diet. These lesions showed monocyte infiltration into the intima, increased expression of VCAM-1 and decreased expression of the ecto-enzyme CD73 in the endothelium. The pro-inflammatory phenotype of EC-Cx40del mice was confirmed in another model of induced leukocyte recruitment from the lung microcirculation. The number of leukocytes that migrated to the alveolar space in response to intratracheal instillation of LPS was markedly enhanced (p<0.001) in EC-Cx40del mice compared to controls, both 3 and 6 hours after the treatment. Endothelial CD73 is known to induce anti-adhesion signaling via the production of adenosine. We found that reducing Cx40 expression in vitro with siRNA or anti-sense decreased CD73 expression and activity, and increased leukocyte adhesion to mouse endothelial cells (p<0.01). These effects were reversed by an adenosine receptor agonist. A control siRNA or Cx40 sense had no effect on leukocyte adhesion. We suggest that Cx40-mediated gap junctional communication contributes to a quiescent non-activated endothelium by propagating adenosine-evoked anti-inflammatory signals between endothelial cells. Alteration in this mechanism by targeting Cx40 promotes leukocyte adhesion to the endothelium, thus accelerating atherosclerosis.