Platelets synthesize large amounts of active plasminogen activator inhibitor 1.
Previous studies have suggested that plasminogen activator inhibitor 1 (PAI-1) released from platelets convey resistance of platelet-rich blood clots to thrombolysis. However, the majority of PAI-1 in platelets is inactive and therefore its role in clot stabilization is unclear. Because platelets retain mRNA and capacity for synthesis of some proteins, we investigated if platelets can de novo synthesize PAI-1 with an active configuration. PAI-1 mRNA was quantified with real-time polymerase chain reaction and considerable amounts of PAI-1 mRNA were detected in all platelet samples. Over 24 hours, the amount of PAI-1 protein as determined by an enzyme-linked immunosorbent assay increased by 25% (P = .001). Metabolic radiolabeling with (35)S-methionine followed by immunoprecipitation confirmed an ongoing PAI-1 synthesis, which could be further stimulated by thrombin and inhibited by puromycin. The activity of the newly formed PAI-1 was investigated by incubating platelets in the presence of tissue-type plasminogen activator (tPA). This functional assay showed that the majority of the new protein was in an active configuration and could complex-bind tPA. Thus, there is a continuous production of large amounts of active PAI-1 in platelets, which could be a mechanism by which platelets contribute to stabilization of blood clots.
Clinical Experimental Research Laboratory, Department of Medicine, Sahlfrenska University Hospital/Ostra, Cardiovascular Institute, Göteborg, Sweden.
Helén
H
Brogren
Lena
L
Karlsson
Maria
M
Andersson
Lingwei
L
Wang
David
D
Erlinge
Sverker
S
Jern
D001483:Base Sequence; D001792:Blood Platelets / Q000378:metabolism*; D017931:DNA Primers; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000097:blood / Q000235:genetics; D012016:Reference Values; D014158:Transcription, Genetic
D017931:DNA Primers; D017395:Plasminogen Activator Inhibitor 1; D012333:RNA, Messenger