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A role for the Fas/Fas ligand apoptotic pathway in regulating myeloid progenitor cell kinetics
Faris Q B Alenzi1, Stephen B Marley, John L Lewis
1LRF Centre For Adult Leukaemia, Department of Haematology, Faculty of Medicine, Imperial College of Science, Technology and Medicine, Hammersmith Campus, DuCane Road, London W12 0NN, UK.
Abstract:
Bone marrow from wild-type mice and mice with mutated Fas (lpr) or mutated Fas ligand (gld) was used to investigate the role of the Fas/FasL system in the regulation of myeloid progenitor cell kinetics.Granulocyte-macrophage colony-forming cells (CFU-GM) were measured by a standard colony assay and the proliferative activity of CFU-GM was measured by replating primary colonies and observing secondary colony formation. Fas expression was restored to lpr mouse bone marrow cells by retrovirus-mediated gene transfer and gld mouse marrow cells were treated with soluble FasL. Wild-type marrow cells were treated with YVAD (a caspase inhibitor) or anti-Fas monoclonal antibodies. There were greater frequencies of myeloid progenitor cells (CFU-GM) in lpr and gld mouse marrow compared to wild-type (WT) marrow (p = 0.0008). The proliferative capacity of CFU-GM was also significantly greater for lpr and gld CFU-GM compared to WT CFU-GM (p = 0.0003 and 0.0001, respectively). Retrovirus-mediated restoration of Fas into lpr marrow, and provision of soluble FasL (sFasL) to gld CFU-GM reduced CFU-GM proliferation to WT levels. Treatment of WT CFU-GM with YVAD or anti-FasL monoclonal antibody increased CFU-GM proliferation to the levels found in lpr and gld CFU-GM. YVAD significantly increased and anti-Fas significantly reduced the proliferative capacity of human CFU-GM (p = 0.015 and 0.04, respectively).Fas, FasL, and caspase activation may play an important role in regulating myeloid progenitor cell kinetics.
Insights
The Fas/FasL system regulates myeloid progenitor cell production. Inhibiting Fas or Fas ligand increases progenitor cell proliferation, while restoring Fas signaling normalizes it.
Area of Science:
- Immunology
- Hematology
- Cell Biology
Background:
- The Fas/FasL system is crucial for immune regulation and apoptosis.
- Its role in myeloid progenitor cell kinetics is not fully understood.
- Mutations in Fas (lpr) or Fas ligand (gld) affect immune homeostasis.
Purpose of the Study:
- To investigate the role of the Fas/FasL system in regulating myeloid progenitor cell kinetics.
- To determine how Fas signaling impacts granulocyte-macrophage colony-forming cells (CFU-GM) proliferation.
Main Methods:
- Utilized bone marrow from wild-type, lpr, and gld mice.
- Measured CFU-GM frequency and proliferative capacity using colony assays.
- Employed gene transfer (Fas restoration) and pharmacological inhibition (caspase inhibitor YVAD, anti-Fas antibodies, soluble FasL).
Main Results:
- lpr and gld mice exhibited significantly higher frequencies and proliferative capacity of CFU-GM compared to wild-type.
- Restoring Fas in lpr marrow and adding soluble FasL to gld marrow reduced CFU-GM proliferation to wild-type levels.
- Inhibition of caspase activation (YVAD) or Fas signaling (anti-Fas antibody) in wild-type cells mimicked the increased proliferation seen in lpr/gld models, affecting human CFU-GM as well.
Conclusions:
- The Fas/FasL pathway plays a critical role in controlling myeloid progenitor cell proliferation.
- Fas, FasL, and downstream caspase activation are key regulators of myeloid progenitor cell kinetics.
- Targeting this system could offer therapeutic avenues for myeloid disorders.