Biochemical and structural evidence for pig myocardium adherens junction disruption by cardiopulmonary bypass

Background-Given that cardiopulmonary bypass (CPB) is associated with edema and heart dysfunction and that adherens junctions may regulate vascular pe rmeability barrier integrity and cardiomyocyte function, we investigated ad herens junction protein steady-state levels in a pig model of CPB. Methods and Results-Pigs were subjected to normothermic CPB for 90 minutes, followed by post-CPB perfusion for 90 minutes. Atrial and ventricular myoc ardium tissue samples were harvested before institution of bypass (basal le vels) and at the end of post-CPB perfusion. Adherens junctions were analyze d by either total lysate or cadherin immunoprecipitates that were immunoblo tted for pan-cadherin, VE-cadherin, beta -catenin, and gamma -catenin. Adhe rens junction solubility was addressed with Triton X-100 extraction. Frozen tissue sections were labeled with the same antibodies, and adherens juncti ons were visualized by confocal microscopy. Immunoblotting of total lysates revealed an increase in smaller-molecular-weight fragments of VE-cadherin, beta -catenin, and gamma -catenin after post-CPB perfusion, indicating par tial protein degradation. Smaller-molecular-weight fragments recognized by VE-cadherin and beta -catenin antibodies were also obtained from VE-cadheri n immunoprecipitation, indicating degradation of endothelial cell adherens junctions. A prominent increase in adherens junction complex solubility was observed in post-CPB perfusion samples. Confocal microscopy of hearts obta ined before CPB showed a continuous, homogeneous pattern of cell-cell label ing that contrasted with an irregular, discontinuous, punctuate, or zigzag pattern observed in post-CPB perfusion samples, corroborating biochemical d ata. Conclusions-These results indicate that CPB is associated with signs of deg radation of endothelial and cardiomyocytes adherens junctions, pointing to a molecular mechanism leading to increased vascular permeability and cardio myocyte dysfunction.