Phosphorylation and translocation of heat shock protein 27 and αB-crystallin in human myocardium after cardioplegia and cardiopulmonary bypass

Objectives: Cardiac surgery using cardioplegia and cardiopulmonary bypass subjects myocardium to hypothermic reversible ischemic injury that can impair cardiac function. Research in animal and cell models demonstrates that acute myocardial ischemia/reperfusion injury causes phosphorylation of heat shock protein 27 and alpha B-crystallin. Phosphorylation of heat shock protein 27 and alpha B-crystallin is implicated in the regulation of both beneficial and detrimental responses to ischemic injury. The phosphorylation status of these proteins in human myocardium after ischemic insults associated with cardioplegia and cardiopulmonary bypass is unknown. Methods: Right atrial appendage and chest wall skeletal muscle samples were collected from patients before and after cardioplegia and cardiopulmonary bypass. Cardioplegia and cardiopulmonary bypass-induced changes in phosphorylation and localization of heat shock protein 27 and alpha B-crystallin were determined using immunoblot and confocal microscopy with total and phospho-specific antibodies. Results: Cardioplegia and cardiopulmonary bypass increased the phosphorylation of heat shock protein 27 on serine 15, 78, and 82, and alpha B-crystallin on serine 59 and 45, but not serine 19. The majority of heat shock protein 27 and alpha B-crystallin localized to I-bands of cardiac myofilaments and shifted to a detergent insoluble fraction after cardioplegia and cardiopulmonary bypass. Cardioplegia and cardiopulmonary bypass-induced phosphorylation of specific heat shock protein 27 and alpha B-crystallin residues were associated with additional subcellular locations. Increases in phosphorylation of heat shock protein 27 and alpha B-crystallin were negatively correlated with cardiac function after surgery. Conclusion: Cardiac surgery using cardioplegia and cardiopulmonary bypass is associated with phosphorylation and myotilament translocation of heat shock protein 27 and alpha B-crystallin in human myocardium. Phosphorylation of specific heat shock protein 27 and alpha B-crystallin serine residues is associated with distinct localization. Understanding the human myocardial small heat shock protein response may have significant implications for surgical myocardial protection.