Biomedical subjects

George L Dale

Publications and source records attributed to George L Dale.

6 recordsLinked to original sources

PubMed2006

Coated-platelets retain amyloid precursor protein on their surface.

Coated-Platelets are a subset of platelets produced by dual-agonist activation with collagen plus thrombin and are characterized by strong retention of several procoagulant, alpha-granule proteins on the cell surface. In this report we demonstrate that coated-platelets also retain full-length amyloid precursor protein (APP) on their surface in contrast to the cleavage of APP in platelets activated with a single agonist. In addition, western blot analysis indicated that APP is derivatized during coated-platelet synthesis. We subsequently measured coated-platelet production in patients with Alzheimer's disease (AD). Twenty-two AD patients showed a wide distribution of coated-platelet values; however the least impaired AD patients produced coated-platelets at a level significantly above that of aged controls (41.0 +/- 9.9 vs. 28.7 +/- 11.4%; mean +/- 1SD; p = 0.017). These findings suggest that coated-platelets may be a model of aberrant APP processing in early AD patients.

Age Factors↗

PubMed2004

Role of mitochondrial permeability transition pore in coated-platelet formation.

OBJECTIVE: Coated-platelets are a subset of cells observed during costimulation of platelets with collagen and thrombin. Important characteristics of coated-platelets include retention of multiple alpha-granule proteins and expression of phosphatidylserine on the cell surface. The mitochondrial permeability transition pore (MPTP) is a key step in apoptosis and is suggested to be involved in some forms of platelet activation. The objective of this study was to examine the role of MPTP in the synthesis of coated-platelets. METHODS AND RESULTS: Flow cytometric analysis of coated-platelet production was used to examine the impact of pharmacological effectors of MPTP formation. Cyclosporin A, coenzyme Q, and bongkrekic acid all inhibit MPTP formation as well as production of coated-platelets. Phenylarsine oxide and diamide, both potentiators of MPTP formation, stimulate coated-platelet synthesis. Atractyloside, another inducer of MPTP formation, does not affect the percentage of coated-platelets synthesized; however, it does increase the level of phosphatidylserine exposed on the surface of coated-platelets. CONCLUSIONS: These findings indicate that MPTP formation is an integral event in the synthesis of coated-platelets. Although the exact function of the MPTP remains to be determined, these data support a growing body of evidence that apoptosis-associated events are vital components of the platelet activation process. Formation of coated-platelets involves a complex set of activation events initiated by dual agonist activation. The mitochondrial permeability transition pore (MPTP) is a key intermediate in apoptosis and has been suggested to impact platelet activation. This report demonstrates that MPTP formation is essential to production of coated-platelets.

Adult↗

PubMed2004

Glycoprotein IIb/IIIa inhibitors increase COAT-platelet production in vitro.

Platelets activated simultaneously with thrombin and collagen reveal a subpopulation of cells that express on their surfaces high levels of several alpha-granule proteins, including factor V and fibrinogen; these COAT platelets (collagen and thrombin-activated platelets) represent roughly 30% of the total population. Evidence of enhanced stability of proteins on the COAT-platelet surface was provided by the observation that PAC-1, a mAB recognizing the activated form of glycoprotein (GP) IIb/IIIa, did not inhibit fibrinogen binding to COAT-platelets. We therefore undertook a systematic evaluation of the effects of other GP IIb/IIIa inhibitors on the production of COAT platelets. Not only did GP IIb/IIIa antagonists fail to inhibit the retention of fibrinogen on COAT-platelets, but several actually increased the absolute percentage of COAT platelets produced. The increases over control values in the presence of eptifibatide, tirofiban, and DMP-802 were 1.36-, 1.20-, and 1.05-fold, respectively (P <.01 for each comparison). COAT-platelet production in the presence of abciximab was not significantly affected. However, platelet activation with thrombin plus ALB6, an Fc-receptor agonist, produces a product, referred to as FcRT platelets, that is indistinguishable from COAT platelets; all 4 GP IIb/IIIa antagonists tested potentiated formation of FcRT platelets. These findings indicate that fibrinogen binding to COAT platelets and FcRT platelets is not affected by available GP IIb/IIIa inhibitors. More importantly, our study demonstrates a potentiation of COAT-platelet production by some GP IIb/IIIa antagonists that may be relevant to the observation that long-term administration of orally available GP IIb/IIIa inhibitors not only failed to protect patients but actually increased the frequency of acute coronary events.

Antibodies, Monoclonal↗

PubMed2003

COAT platelets.

PURPOSE OF REVIEW: COAT platelets are a recently described subpopulation of cells resulting from simultaneous activation with collagen and thrombin. The complete process by which COAT platelets are produced is still not clear, although significant recent progress has been made. RECENT FINDINGS: COAT platelets retain several procoagulant proteins on their surface by a previously unrecognized mechanism involving transglutaminase mediated conjugation of serotonin to released alpha-granule proteins. Fibrinogen and thrombospondin have been found to bind serotonin-conjugated proteins and thereby provide the requisite link for stabilization of serotonin-derivatized, procoagulant proteins on COAT platelets. SUMMARY: Multivalent interactions, resulting from traditional receptor interactions and binding of conjugated serotonin by fibrinogen and thrombospondin, result in exceptionally strong retention of procoagulant alpha-granule proteins on the surface of COAT platelets. The physiologic significance of this new subclass of platelets remains to be determined.

Blood Platelets↗

PubMed2002

Thrombospondin and fibrinogen bind serotonin-derivatized proteins on COAT-platelets.

Activation of platelets with 2 agonists, collagen and thrombin, reveals a subpopulation of cells referred to as COAT-platelets (collagen and thrombin activated). These cells are enriched in several membrane-bound, procoagulant proteins, including fibrinogen, thrombospondin, factor V, von Willebrand factor, and fibronectin. alpha-Granule proteins bound to COAT-platelets are derivatized with serotonin by a transglutaminase-mediated process, and the interaction of conjugated serotonins with unidentified serotonin binding sites on the platelet surface enhances retention of these proteins. We now demonstrate that both thrombospondin and fibrinogen provide the requisite serotonin binding sites. Thrombospondin and fibrinogen were identified using photoreactive cross-linking to an albumin-(serotonin)(6) conjugate during COAT-platelet production. We subsequently verified that biotin-albumin-(serotonin)(6) binds in vitro to thrombospondin, fibrinogen, and fibrinogen fragment D in a saturable manner. These data support a model for COAT-platelets where serotonin-derivatized procoagulant proteins interact with their respective receptors (eg, fibrinogen with glycoprotein IIb/IIIa or factor V with phosphatidylserine) as well as serotonin binding sites on fibrinogen and thrombospondin, resulting in a stable, multivalent complex on the cell surface.

Binding Sites↗

PubMed2002

Stimulated platelets use serotonin to enhance their retention of procoagulant proteins on the cell surface.

Activated platelets bind numerous adhesive and procoagulant proteins by receptor-mediated processes. Although there is little evidence to suggest that these processes are heterogeneous in platelets, we previously found that platelets co-stimulated with collagen and thrombin express functional alpha-granule factor V only on a subpopulation of cells. Here we show that these cells, referred to as 'COAT-platelets', bind additional alpha-granule proteins, including fibrinogen, von Willebrand factor, thrombospondin, fibronectin and alpha2-antiplasmin. These proteins are all transglutaminase substrates, and inhibitors of transglutaminase prevent the production of COAT-platelets. A synthetic transglutaminase substrate (CP15) also binds to COAT-platelets, and analysis by high performance liquid chromatography/mass spectrometry shows that a product is formed with a relative molecular mass (Mr) equal to CP15 plus 176. Serotonin, an abundant component of platelet-dense granules, has an Mr of 176, and fibrinogen isolated from COAT-platelets contains covalently linked serotonin. Synthetic bovine serum albumin-(serotonin)6 binds selectively to COAT-platelets and also inhibits the retention of procoagulant proteins on COAT-platelets. These data indicate that COAT-platelets use serotonin conjugation to augment the retention of procoagulant proteins on their cell surface through an as yet unidentified serotonin receptor.

Amino Acid Sequence↗