Binding of the Stress ProteinαB-crystallin to Cardiac Myofibrils Correlates with the Degree of Myocardial Damage During Ischemia/Reperfusionin vivo

Stress proteins are assumed to protect cells against various kinds of stresses including ischemia. In this study, we focused on the behaviour of the most abundant myocardial stress protein,αB-crystallin, during ischemia and reperfusion of the pig heartin vivo.αB-crystallin constitutes 1–2% of the soluble protein pool and underwent, during severe but reversibly damaging ischemia (25 min), complete translocation to the Z-line area of myofibrils. Irreversibly damaging ischemia (60 min) was accompanied by extreme stretching of the majority of myofibrils, and by concomitant extension ofαB-crystallin localization from the Z-line area to I-bands. This I-band shift correlated with displacement of the T12epitope of titin from the vicinity of Z-lines into I-bands, indicating that the primary binding sites forαB-crystallin might also be located in juxtaposition to Z-lines and move into the I-bands during extreme sarcomeric stretching. During reperfusion after 25 min of ischemia,αB-crystallin disappeared rapidly from myofibrils; whereas reperfusion after irreversibly damaging ischemia (60 min) resulted in dissociation ofαB-crystallin only from those myofibrils and myocardiocytes that were still able to contract, andαB-crystallin remained bound to the overstretched, damaged myofibrils no longer capable of contraction. The time course of translocation ofαB-crystallin to myofibrils during ischemia correlated with phosphorylation of approximately 20% of the entireαB-crystallin pool. However, disappearance ofαB-crystallin from myofibrils during reperfusion was not accompanied by dephosphorylation, indicating that phosphorylation alone does not explain myofibrillar binding ofαB-crystallin. Ischemia-induced myofibrillar targeting ofαB-crystallin probably requires additional structural and posttranslational modifications of myofibrillar components in juxtaposition to I-bands.