Binding of the stress protein αB-crystallin to cardiac myofibrils correlates with the degree of myocardial damage during ischemia/reperfusion in 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, alpha B-crystallin, during ischemia and reperfusion of the pig heart in vivo. alpha B-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 of alpha B-crystallin localization from the Z-line area to I-bands. This I-band shift correlated with displacement of the T-12 epitope of titin from the vicinity of Z-lines into I-bands, indicating that the primary binding sites for B-crystallin might also be located in juxtaposition to Z-lines and more into the I-bands during extreme sarcomeric stretching, During reperfusion after 25 min of ischemia, alpha B-crystallin disappeared rapidly from myofibrils: whereas reperfusion after ii-reversibly damaging ischemia (60 min) resulted in dissociation of alpha B-crystallin only from those myofibrils and myocardiocytes that were still able to contract, and alpha B-crystallin remained bound to the overstretched, damaged myofibrils no longer capable of contraction. The time course of translocation of alpha B-crystallin to myofibrils during ischemia correlated with phosphorylation of approximately 20% of the entire alpha B-crystallin pool. However, disappearance of alpha B-crystallin from myofibrils during reperfusion was not accompanied by dephosphorylation. indicating that phosphorylation alone does not explain myofibrillar binding of alpha B-crystallin. Ischemia-induced myofibrillar targeting of alpha B-crystallin probably requires additional structural and posttranslational modifications of myofibrillar components in juxtaposition to I-bands. (C) 1999 Academic Press.