The possibility of novel antiplatelet peptides: The physiological effects of low molecular weight HSPs on platelets

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 on a physiological role of HSP20, HSP27 and alpha B-crystallin on platelet function in vitro and ex vivo. HSP20 and alpha B-crystallin inhibited platelet aggregation using human Platelets dose-dependently 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 alpha B-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 alpha B-crystallin significantly reduced platelet aggregation induced by TRAP, but not a PAR-4 agonist. These findings strongly suggest that HSP20 or alpha B-crystallin can act intercellularly to regulate platelet functions. Our results may provide the basis for a novel defensive system to thrombus formation in vivo.