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Megakaryocyte colony growth-supporting activities in human plasma: modification by platelets and platelet membranes
K Yamasaki1, N Jamal, K G Mann
1Ontario Cancer Institute, University of Toronto, Canada.
Abstract:
Human megakaryocyte colonies are grown in methylcellulose with platelet-poor plasma and medium conditioned by phytohemagglutinin-stimulated leukocytes (PHA-LCM) as a source of megakaryocyte colony stimulating factor (MEG-CSF). The megakaryocyte colony growth-supporting activity in human plasma can be absorbed by intact platelets or degranulated platelet membranes. It was possible to recover the activity by solubilizing platelet membranes with cholic acid. Filtration of the solubilized platelet membrane preparations through a Sephadex G-100 column yielded at least two activity peaks. The molecular weight of these two activities differs from that of the growth-promoting activity in PHA-LCM.
Insights
Platelets contain factors that support human megakaryocyte colony growth. These factors can be extracted from platelet membranes and differ in molecular weight from those found in leukocyte-conditioned medium.
Area of Science:
- Hematology
- Cell Biology
- Biochemistry
Background:
- Megakaryocyte colony-stimulating factor (MEG-CSF) is crucial for megakaryocyte development.
- Human megakaryocyte colonies are typically cultured using phytohemagglutinin-stimulated leukocyte-conditioned medium (PHA-LCM).
Purpose of the Study:
- To investigate the source and characteristics of megakaryocyte colony growth-supporting activity in human plasma.
- To determine if platelets contribute to megakaryopoiesis by providing specific growth factors.
Main Methods:
- Human megakaryocyte colonies were cultured in methylcellulose with PHA-LCM.
- Platelet-poor plasma was used to assess growth-supporting activity.
- Activity was absorbed by intact platelets and degranulated platelet membranes.
- Platelet membranes were solubilized with cholic acid and fractionated using Sephadex G-100 chromatography.
Main Results:
- Megakaryocyte colony growth-supporting activity in plasma was absorbed by platelets.
- This activity was recovered from solubilized platelet membranes.
- Sephadex G-100 filtration revealed at least two distinct activity peaks from platelet membranes.
- The molecular weights of these platelet-derived activities differ from the growth factors in PHA-LCM.
Conclusions:
- Human platelets contain and release factors that support megakaryocyte colony formation.
- These platelet-derived factors possess distinct molecular weights compared to leukocyte-derived MEG-CSF.
- Platelets play a significant role in regulating megakaryopoiesis through specific growth-promoting activities.