title: Mechanisms contributing to increased synthesis of plasminogen activator inhibitor type 1 in endothelial cells by constituents of platelets and their implications for thrombolysis.
abstract: We recently hypothesized that after pharmacologically induced coronary thrombolysis, increased activity of plasminogen activator inhibitor type 1 (PAI-1) retards recanalization, contributes to early reocclusion, or both. This hypothesis was based on the increased elaboration of PAI-1 that we observed in cultured liver cells exposed to growth factors releasable from platelets activated at sites of thrombosis in vivo. PAI-1 released locally is particularly likely to attenuate lysis of thrombi that are targets of thrombolytic drugs. Accordingly, the present study was performed to determine whether synthesis of PAI-1 by endothelial cells is augmented by products of platelets. Lysates from platelets (0.5-8.0 x 10(4)/mm3 media, i.e. less than 10% of the concentration of platelets in blood) increased synthesis and release of PAI-1 into both the extracellular matrix and conditioned media (by 2.8-fold and 3.3-fold within 6 and 24 hours, respectively). Synthesis of neither tissue-type plasminogen activator nor overall protein increased. Increased synthesis of PAI-1 was confirmed by immunoprecipitation of [35S]PAI-1 after metabolic labeling of cells. The increased elaboration of PAI-1 was consistent with increased transcription as reflected by the observed increase in PAI-1 mRNA of 2.2-fold in 4 hours. Effects of platelet lysates were simulated by transforming growth factor beta (TGF-beta), known to be present in platelet alpha-granules and released with platelet activation. Antibody to TGF-beta reduced the stimulation of PAI-1 synthesis by TGF-beta, as expected, by 82%.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Cardiovascular Division, Washington University School of Medicine, St. Louis, MO 63110.
authors.forename: S
authors.initials: S
authors.lastname: Fujii
authors.forename: W E
authors.initials: WE
authors.lastname: Hopkins
authors.forename: B E
authors.initials: BE
authors.lastname: Sobel
mesh_terms: D001792:Blood Platelets / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D066298:In Vitro Techniques; D015849:Plasminogen Inactivators / Q000378:metabolism*; D015539:Platelet Activation / Q000502:physiology; D011233:Precipitin Tests; D015912:Thrombolytic Therapy; D016211:Transforming Growth Factor alpha / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism
chemical_list: D015849:Plasminogen Inactivators; D016211:Transforming Growth Factor alpha; D016212:Transforming Growth Factor beta