alpha B-crystallin, a low-molecular-weight heat shock protein, acts as a regulator of platelet function

It has recently been reported that alphaB-crystallin, a low-molecular-weigh t heat shock protein, may be released from cells by mechanical stretch. We investigated a physiological role of alphaB-crystallin in platelet function . alphaB-crystallin inhibited platelet aggregation induced by thrombin or b otrocetin in hamsters and humans. These platelets had specific binding site s for alphaB-crystallin. Moreover, alphaB-crystallin significantly reduced thrombin-induced Ca2+ influx and phosphoinositide hydrolysis by phospholipa se C in human platelets. Additionally, plasma levels of alphaB-crystallin w ere markedly elevated in cardiomyopathic hamsters. Levels of alphaB-crystal lin in vessel walls after endothelial injury were markedly reduced. Therefo re, our results suggest that alphaB-crystallin, which is discharged from ve ssel walls in response to endothelial injury, acts intercellularly as a reg ulator of platelet function.