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Effect of thrombin on maturing human megakaryocytes
E M Cramer1, J M Massé, J P Caen
1INSERM U. 348 and Institut des Vaisseaux et du Sang, Hôpital Lariboisière, Paris, France.
The American Journal of Pathology
|November 1, 1993
Summary
Thrombin rapidly activates human megakaryocytes (MKs), inducing shape changes and alpha-granule secretion in both immature and mature cells. However, thrombin does not stimulate MK proliferation, indicating it is not mitogenic for these cells.
Area of Science:
- Hematology
- Cell Biology
- Biochemistry
Background:
- Thrombin is known to activate platelets and can be mitogenic in some nucleated cells.
- Human megakaryocytes (MKs) are precursors to platelets, and their response to agonists is crucial for hemostasis.
- Understanding MK responses to thrombin is important for insights into megakaryopoiesis and related pathologies.
Purpose of the Study:
- To investigate the response of human megakaryocytes (MKs) to thrombin.
- To determine if thrombin's effect on MKs is dependent on their maturation stage.
- To assess the mitogenic potential of thrombin on human MKs.
Main Methods:
- Human MKs were cultured from bone marrow precursors.
- Thrombin activation was studied using electron microscopy and immunoelectron microscopy.
- Mitogenic activity was assessed by flow cytometry to measure MK number and ploidy after thrombin exposure.
Main Results:
- Thrombin induced rapid morphological changes in MKs, including shape change and organelle centralization, in both immature and mature cells.
- MKs secreted alpha-granule proteins (thrombospondin, glycoprotein Ib) into the demarcation membrane system upon thrombin stimulation.
- Thrombin did not alter MK number or ploidy, indicating no mitogenic effect at the tested concentrations.
- MKs remained viable for over 24 hours after thrombin treatment.
Conclusions:
- Human megakaryocytes (MKs) respond rapidly to thrombin with activation and secretion, regardless of maturation stage.
- Mature MKs secrete alpha-granule proteins into the demarcation membrane system, which connects to the extracellular space.
- Thrombin is not mitogenic for human MKs, but its secretory effects may influence pathological conditions like myelofibrosis and autocrine regulation of megakaryopoiesis.