Intercellular channels formed by connexins (Cx) have been shown to play a critical role in cardiovascular disease. For instance, vascular Cx43 influences atherosclerosis development and plaque stability, and cardiac Cx43 may determine the development of arrhythmias after myocardial infarction. In the heart, Cx40 is expressed in atrial cardiomyocytes, the conduction system and in endothelial cells, whereas Cx37 is only found in the endothelium. Here, we study the implication of the endothelial connexins during ischemia and reperfusion in mice.Methods and Results
We used the Cre-loxP system to create a mouse line in which Cx40 is deleted from the endothelium only. Immunostainings on Tie2Cre + Cx40fl/fl ApoE-/- mice confirmed the absence of Cx40 in the endothelium, whereas the protein was normally expressed in the atria and cardiac conduction system. Moreover, Cx40 was normally expressed in the endothelium, atria and conduction system of Tie2Cre + Cx40wt/wt ApoE-/- and Tie2Cre- Cx40fl/fl ApoE-/- control mice. Sixteen-week-old mice were subjected to in vivo left coronary artery occlusion for 30 minutes and sacrificed 24-hours after reperfusion for analysis of infarct size. Myocardial surfaces areas at risk and infarcted areas were measured from computed images using NIH Image software. Areas at risk, normalized to total left ventricle surfaces areas, were similar between the experimental groups, i.e Tie2Cre + Cx40wt/wt ApoE-/-: 29.2 ± 1.2% (N=11), Tie2Cre- Cx40fl/fl ApoE-/-: 33.7 ± 3.7% (N=9), and Tie2Cre + Cx40fl/fl ApoE-/- 31.7 ± 2.2% (N=11, n.s.). Interestingly, the infarct area, normalized to areas at risk, was significantly increased in Tie2Cre + Cx40fl/fl ApoE-/- (20.2 ± 3.1%, P < 0.05) mice as compared to controls (10.1 ± 2.0% and 11.3 ± 1.8%). To investigate the possible implications of another endothelial connexin in myocardial infarction, Cx37-/- ApoE-/- mice were submitted to the same protocol of in vivo ischemia-reperfusion. Areas at risks were similar between Cx37-/- ApoE-/- and control ApoE-/- mice (44.9 ± 3.3% (N=10), 38.4 ± 3.8% (N=12), n.s.), and the infarcted area appeared not affected by the deletion of Cx37 (Cx37-/- ApoE-/-: 13.8 ± 1.3%, ApoE-/-: 14.7 ± 2.7% n.s.).Conclusions
We conclude that endothelial Cx40, but not Cx37, is implicated in resistance of the heart to ischemia-reperfusion injury. These findings may point towards a specific novel therapeutic target to limit the cardiac injury after coronary interventions.