Platelet microparticles contain active caspase 3.
During storage, platelets undergo processes resembling apoptosis, including microparticle release, aminophospholipid exposure, and procaspase 3 processing. Recently, we showed that microparticles from endothelial cells contain caspase 3, one of the executioner enzymes of apoptosis. In this study we determined whether platelet-derived microparticles (PMP) contain caspase 3 in vitro (stored platelet concentrate) and ex vivo (plasma from healthy humans). In addition, we studied the underlying mechanism of caspase 3 formation in PMP, and the ability of such PMP to induce apoptosis in human macrophages (THP-1 cells). The presence of caspase 3 (antigen) was studied by Western blot and flowcytometry, and activity was determined by Ac-DEVD-pNA and ROCK I cleavage. In vitro, PMP numbers increased during storage. From day one onwards, PMP contained procaspase 3, whereas caspase 3 (antigen and activity) was detectable after 5-7 days of storage. PMP contained caspase 9 but not caspase 8, and the time course of caspase 9 formation paralleled procaspase 3 disappearance and caspase 3 appearance. In addition, PMP in human plasma also contained detectable quantities of caspase 3. Incubation of THP-1 cells with PMP induced apoptosis. Taken together, PMP contain caspase 3 in vitro and ex vivo. Our data implicate that procaspase 3 is likely to be processed by caspase 9 in PMP during storage. PMP induce apoptosis of human macrophages, but whether this induction is due to the transfer of caspase 3 remains to be determined.
Böing
Anita N
AN
Department of Clinical Chemistry, Academic Medical Center, Amsterdam, The Netherlands. A.N.Boing@amc.nl
Hau
Chi M
CM
Sturk
Auguste
A
Nieuwland
Rienk
R
D000813:Anilides / Q000737:chemistry; D017209:Apoptosis; D001792:Blood Platelets / Q000166:cytology / Q000201:enzymology*; D053148:Caspase 3 / Q000378:metabolism*; D053181:Caspase 8 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D008264:Macrophages / Q000166:cytology; D009842:Oligopeptides / Q000737:chemistry; D015539:Platelet Activation; D054460:rho-Associated Kinases / Q000378:metabolism
D000813:Anilides; D009842:Oligopeptides; C430230:acetyl-aspartyl-glutamyl-valyl-aspartic acid p-nitroanilide; C515851:ROCK1 protein, human; D054460:rho-Associated Kinases; D053148:Caspase 3; D053181:Caspase 8; D053453:Caspase 9