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Cellular source of human platelet secretory phospholipase A2
S Emadi1, M Mirshahi, I Elalamy
1Unité de Pharmacologie Cellulaire, Unité Associée Institut Pasteur-INSERM U285, Paris, France.
British Journal of Haematology
|March 6, 1998
Summary
This study confirms that human megakaryocytes express phospholipase A2 (sPLA2), supporting their role as the origin of platelet sPLA2. This finding clarifies the source of sPLA2 involved in inflammation.
Area of Science:
- Biochemistry
- Cell Biology
- Immunology
Background:
- Platelets release extracellular group II phospholipase A2 (sPLA2), a key mediator in inflammatory processes.
- While sPLA2 is known in platelets, its presence and origin within human megakaryocytes remain unestablished.
Purpose of the Study:
- To investigate the expression and release of sPLA2 in human megakaryocytes and megakaryoblastic cells.
- To determine if megakaryocytes are the cellular source of platelet-derived sPLA2.
Main Methods:
- Utilized an anti-sPLA2 monoclonal antibody (mAb BA11) and dot-blot detection.
- Employed spectrofluorescence assays to measure sPLA2 activity.
- Conducted double labeling with anti-GPIIb antiserum and reverse transcription-polymerase chain reaction (RT-PCR) with hybridization analysis.
Main Results:
- The human erythroleukaemia (HEL) cell line, with megakaryoblastic features, constitutively expresses sPLA2.
- HEL cells and platelets release sPLA2 upon thrombin stimulation, with activity confirmed by spectrofluorescence.
- sPLA2 was detected in human bone-marrow megakaryocytes, and sPLA2 mRNA was present in platelets and HEL cells.
Conclusions:
- Human megakaryocytes express sPLA2 at both transcriptional and post-translational levels.
- This strongly supports a megakaryocytic origin for platelet-derived sPLA2.
- The findings exclude the possibility of circulating platelets endocytosing sPLA2 from plasma.