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Endocytosis and storage of plasma factor V by human megakaryocytes

Youko Suehiro1, Dragoslava Kika Veljkovic, Nola Fuller

  • 1Department of Pathology, McMaster University, Hamilton, Ontario, Canada.

Thrombosis and Haemostasis
|November 5, 2005
PubMed

Insights

Human megakaryocytes internalize plasma-derived Factor V (FV) and process it into alpha-granules. They also form Factor V-multimerin I complexes using both internal and external proteins.

Area of Science:

  • Hematology
  • Cell Biology
  • Biochemistry

Background:

  • Factor V (FV) is a crucial coagulation cofactor found in plasma and platelet alpha-granules.
  • Platelet FV is stored complexed with multimerin I (MMRN1).
  • The origin and processing of platelet FV and FV-MMRN1 complexes remain incompletely understood.

Purpose of the Study:

  • To investigate the origin and processing of human platelet Factor V (FV).
  • To understand the formation of Factor V-multimerin I (MMRN1) complexes within megakaryocytes.

Main Methods:

  • Cultured human megakaryocytes were used to study Factor V (FV) processing.
  • Detection of FV mRNA and protein.
  • Analysis of FV association with exogenous protein concentrations.
  • Study of FV proteolysis and complexation with MMRN1.
  • Megakaryocyte release studies using secretagogues.
  • Immunofluorescent and electron microscopy for FV uptake and trafficking.

Main Results:

  • Factor V (FV) mRNA was present in megakaryocytes, but FV protein required exogenous sources.
  • Megakaryocyte FV was proteolyzed and complexed with MMRN1, similar to platelet FV.
  • Megakaryocytes released FV, IgG, fibrinogen, and MMRN1 upon stimulation.
  • FV was confirmed to be taken up by endocytosis and trafficked to alpha-granules.

Conclusions:

  • Human megakaryocytes process plasma-derived Factor V (FV) and traffic it to alpha-granules.
  • Megakaryocytes synthesize MMRN1, contributing to FV-MMRN1 complex formation.
  • These findings elucidate the endogenous processing of plasma-derived FV in megakaryocytes.

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