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Regulation of megakaryocyte ploidy in vivo in the rat
1Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
Abstract:
The relationship between the bone marrow (BM) megakaryocyte and the circulating platelet was explored. Incremental changes in platelet count were made in rats by infusion of antiplatelet antibody or by platelet transfusion, and the response of megakaryocytes was measured by flow cytometry. Proportional changes in megakaryocyte ploidy were demonstrated: As the platelet count declined, ploidy increased; as the platelet count increased, ploidy decreased. Even moderate degrees of thrombocytopenia and thrombocytosis (48% and 177% of the normal platelet count) were associated with changes in ploidy. These changes were not the results of the technique used to alter the platelet count because reinfusion of platelets after 3 hours of thrombocytopenia prevented any ploidy change. These studies proved that the circulating platelet and the megakaryocyte constitute a classic feedback loop whose activity can be measured by the degree of ploidization of the megakaryocyte. The minimal duration of thrombocytopenia necessary to promote megakaryocyte ploidy changes was approximately 10 hours. Using a BM culture assay, we identified a plasma factor which induced alterations in megakaryocyte ploidy and whose level is inversely proportional to the platelet count.
Insights
Platelet counts regulate bone marrow megakaryocyte ploidy, forming a feedback loop. Lower platelet counts increase megakaryocyte ploidy, while higher counts decrease it, indicating a regulatory mechanism.
Area of Science:
- Hematology
- Cell Biology
- Physiology
Background:
- The bone marrow megakaryocyte is the progenitor of circulating platelets.
- Understanding the regulation of megakaryocyte function is crucial for platelet homeostasis.
Purpose of the Study:
- To investigate the relationship between circulating platelet count and bone marrow megakaryocyte ploidy.
- To elucidate the feedback mechanism regulating platelet production.
Main Methods:
- Platelet counts in rats were altered using antiplatelet antibodies or platelet transfusions.
- Megakaryocyte ploidy was measured using flow cytometry.
- Bone marrow culture assays were employed to identify plasma factors.
Main Results:
- A direct inverse relationship was observed between platelet count and megakaryocyte ploidy.
- Thrombocytopenia led to increased megakaryocyte ploidy, while thrombocytosis resulted in decreased ploidy.
- A plasma factor was identified that influences megakaryocyte ploidy, with levels inversely proportional to platelet count.
Conclusions:
- Circulating platelets and bone marrow megakaryocytes form a feedback loop regulated by ploidy.
- Megakaryocyte ploidy serves as a measurable indicator of this feedback loop's activity.
- This feedback loop is essential for maintaining platelet count homeostasis.