Binding of the stress protein alpha B-crystallin to cardiac myofibrils correlates with the degree of myocardial damage during ischemia/reperfusion invivo

Stress proteins are assumed to protect cells against various kinds of stres ses including ischemia. In this study, we focused on the behaviour of the m ost 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 m yofibrils. Irreversibly damaging ischemia (60 min) was accompanied by extre me stretching of the majority of myofibrils, and by concomitant extension o f alpha B-crystallin localization from the Z-line area to I-bands. This I-b and shift correlated with displacement of the T-12 epitope of titin from th e vicinity of Z-lines into I-bands, indicating that the primary binding sit es for B-crystallin might also be located in juxtaposition to Z-lines and m ore into the I-bands during extreme sarcomeric stretching, During reperfusi on after 25 min of ischemia, alpha B-crystallin disappeared rapidly from my ofibrils: 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-crystalli n 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 dep hosphorylation. indicating that phosphorylation alone does not explain myof ibrillar binding of alpha B-crystallin. Ischemia-induced myofibrillar targe ting of alpha B-crystallin probably requires additional structural and post translational modifications of myofibrillar components in juxtaposition to I-bands. (C) 1999 Academic Press.