Abstract 2526: Cardioplegia and Cardiopulmonary Bypass Induces Phosphorylation and Myofilament Localization of Heat Shock Protein 27 and αB-Crystallin in Human Myocardium
Evidence from cell culture and animal models indicates that HSP27 and αB-crystallin (cryAB) are dramatically regulated via phosphorylation in response to ischemic insults. The phosphorylation of these proteins is implicated in the regulation of diverse cellular processes including myocyte redox regulation, protein chaperone function, and depressed myocyte contractile function. Cardioplegia solutions used to arrest the heart during cardiac surgery are associated with ischemic insults including hypoxia and myocardial contractile deficits. It is unknown if HSP27 and cryAB play a role in the human myocardial response to ischemia in vivo. Therefore, we performed the following experiments to determine any changes in the phosphorylation and localization of HSP27 and cryAB in human myocardium following cardioplegia and cardiopulmonary bypass (CP/CPB). Right atrial appendage and chest wall skeletal muscle samples were collected from patients immediately before and after CP/CPB. CP/CPB induced a robust increase in the atrial phosphorylation of HSP27 at ser82 and cryAB at ser59. CP/CPB also induced phosphorylation of p38-MAPK, an upstream kinase of HSP27 and cryAB. Phosphorylation of HSP27 and cryAB associated with their movement to a Triton X100 insoluble protein pool, There was no change in phosphorylation of either protein in skeletal muscle, suggesting an ischemia specific response. Confocal microscopy of atrial tissue revealed translocation of HSP27 and cryAB from a diffuse/membrane localization with limited sarcomeric staining pre-CP/CPB to an almost entirely striated sarcomeric pattern after CP/CPB. Double labeling with an atrial specific myosin light chain 2a antibody revealed prominent staining of unphosphorylated, ser82, ser78, and ser15 phosphorylated HSP27 along I-bands of cardiomyocytes post CP/CPB. A similar pattern was observed for unphosphorylated, ser59, ser45, and ser19 phosphorylated cryAB. These results demonstrate that two members of the small HSP family, HSP-27 and cryAB, are phosphorylated and translocate to cardiac myofilaments following surgical ischemia associated with CP/CPB. Modulation of the HSP27 and cryAB response may have significant implications for cardioplegic protection during surgery.