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Increased platelet activation and abnormal membrane glycoprotein content and redistribution in myeloproliferative
M K Jensen1, P de Nully Brown, B V Lund
1Department of Haematology, Rigshospitalet, University Hospital of Copenhagen, Denmark. mkj@rh.dk
Abstract:
Chronic myeloproliferative disorders (MPDs) are characterized by a high incidence of thrombohaemorrhagic complications, possibly caused by platelet dysfunction. In an attempt to define platelet functional abnormalities, we assessed the expression of activation-dependent membrane proteins in unstimulated and agonist [ADP and thrombin receptor-activating peptide (TRAP)]-stimulated platelets using quantitative whole blood flow cytometry in samples from 50 MPD patients and 30 controls. The receptor densities of activation markers and glycoproteins (GPs) were quantified using standardized fluorescent beads. Compared with controls, the mean percentage of P-selectin-positive (15.3% vs. 7.2%; P < 0.001) and thrombospondin (TSP)-positive (6.6% vs. 3.7%; P = 0.003) platelets was increased in unstimulated platelets from patients. Patients having experienced a thrombotic event had a higher mean percentage of TSP-positive non-stimulated platelets than patients without a history of thrombosis (9.0% vs. 4.6%; P = 0.02) and a higher GPIV molecules of equivalent fluorochrome (MEF) value (33113 vs. 24471 MEF; P = 0.02). Mean MEF values of monoclonal antibodies (mAbs) against GPIb (34055 vs. 38945 MEF; P < 0.001) and GPIIb/IIIa (1416 vs. 1648 MEF; P < 0. 001) were significantly reduced among patients, whereas surface expression of GPIV was increased in patients (28273 vs. 16258 MEF; P < 0.001). In TRAP (10 micromol/l) stimulated whole blood, the MEF of P-selectin (9611 vs. 13293 MEF; P = 0.004) and CD63 (2385 vs. 5177 MEF; P < 0.001) and the ratio of PAC-1/GPIIb/IIIa MEF (0.98 vs. 2. 00; P < 0.001) was reduced in patients, indicating either a reduced granule GP content or an intrinsic cellular defect in receptor-mediated granule secretion and activation of the GPIIb/IIIa complex. Expressed as the relative change of MEF compared with unstimulated platelets, TRAP induced decrease of GPIb (7.8% vs. 45%; P < 0.001) and increase of GPIIb/IIIa (49.1% vs. 95.7%; P < 0.001) and GPIV expression (17.8% vs. 55.2%; P < 0.001) was attenuated in patients.
Insights
Platelet dysfunction in myeloproliferative disorders (MPDs) is linked to increased P-selectin and thrombospondin expression. Patients with thrombosis history show higher thrombospondin and GPIV levels, indicating potential platelet activation abnormalities.
Area of Science:
- Hematology
- Oncology
- Platelet Biology
Background:
- Chronic myeloproliferative disorders (MPDs) are associated with a high risk of thrombohemorrhagic complications.
- Platelet dysfunction is a potential contributing factor to these complications in MPD patients.
Purpose of the Study:
- To investigate platelet functional abnormalities in MPD patients by assessing activation-dependent membrane protein expression.
- To compare protein expression in MPD patients with and without a history of thrombosis.
Main Methods:
- Quantitative whole blood flow cytometry was used to analyze unstimulated and agonist-stimulated platelets from 50 MPD patients and 30 controls.
- Expression of activation markers and glycoproteins (GPs) was quantified using standardized fluorescent beads and molecules of equivalent fluorochrome (MEF).
Main Results:
- Unstimulated MPD platelets showed increased P-selectin and thrombospondin (TSP) expression compared to controls.
- MPD patients with thrombosis history had higher TSP and GPIV expression.
- Reduced GPIb and GPIIb/IIIa, but increased GPIV, were observed in MPD patients.
- Stimulation with TRAP revealed reduced P-selectin, CD63, and PAC-1/GPIIb/IIIa ratio, indicating impaired granule secretion and GPIIb/IIIa activation.
Conclusions:
- MPD patients exhibit distinct platelet activation marker profiles, including increased TSP and GPIV, and reduced GPIb/IIIa.
- Impaired platelet activation and granule release mechanisms are evident in MPD, potentially explaining thrombohemorrhagic complications.