Abstract
Some low molecular mass heat shock proteins (HSPs) appear to act as molecular chaperones, but their exact physiological roles have not been fully elucidated. We reported the physiological roles of HSP20, HSP27, and alphaB-crystallin in platelet function in vitro and ex vivo. HSP20 and alphaB-crystallin dose-dependently inhibited the aggregation of human platelets induced by thrombin or botrocetin. On the other hand, HSP27, the other type of low molecular mass HSP, did not affect platelet aggregation. When HSP20 or alphaB-crystallin was injected intravenously as a bolus in hamsters, the development of thrombus after endothelial injury was prevented. Moreover, 9 amino acid sequences isolated from HSP20 or alphaB-crystallin significantly reduced platelet aggregation induced by TRAP, but not a PAR-4 agonist. These findings strongly suggest that HSP20 or alphaB-crystallin can act intercellularly to regulate platelet functions. Our results may provide the basis for a novel defense system against thrombus formation in vivo.
