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Tetraspanin CD9 is required for microparticle release from coated-platelets
George L Dale1, Gyula Remenyi, Paul Friese
1Department of Medicine, University of Oklahoma Health Sciences Center, Oklahoma, OK 73104, USA. george-dale@ouhsc.edu
Insights
The tetraspanin CD9 protein is essential for releasing microparticles from activated platelets. Blocking CD9 significantly inhibits this microparticle release process.
Area of Science:
- Biochemistry
- Cell Biology
- Hematology
Background:
- CD9 is a tetraspanin superfamily protein abundant on platelet surfaces.
- The precise function of CD9 in platelet biology is largely unknown.
- Platelets release microparticles upon activation, a process with implications in various physiological and pathological conditions.
Purpose of the Study:
- To investigate the role of CD9 in the release of microparticles from activated platelets.
- To determine if CD9 influences the membrane vesiculation process during platelet activation.
Main Methods:
- Utilized dual agonist activation (collagen and thrombin) to form coated-platelets.
- Assessed microparticle release using monoclonal antibodies targeting CD9 and integrin alpha(IIb)beta(3).
- Quantified the inhibition of microparticle release and determined IC(50) values for specific antibodies.
Main Results:
- CD9 was found to be required for microparticle release from coated-platelets.
- Four distinct anti-CD9 monoclonal antibodies inhibited microparticle release by 72-102%.
- The anti-alpha(IIb)beta(3) antibody AP2 also inhibited release, suggesting a cooperative role with CD9.
Conclusions:
- CD9 plays a critical role in the membrane vesiculation and microparticle release from activated platelets.
- The integrin alpha(IIb)beta(3) may also participate in this process, potentially in conjunction with CD9.
- These findings elucidate a novel function for CD9 in platelet biology and microparticle formation.
Abstract:
CD9, a member of the tetraspanin superfamily, is the third most abundant protein on the platelet surface, but its function remains unknown. In this report, we demonstrate that CD9 is required for the release of microparticles from coated-platelets. Coated-platelets are formed as a result of dual agonist activation with collagen and thrombin, and each coated-platelet releases 15-25 microparticles averaging 0.4 microm in diameter. We report here that four separate monoclonal antibodies against CD9 inhibited microparticle release from coated-platelets by 72-102% with an IC(50) of approximately 500 ng/mL for ALB6 and SN4. In addition, the anti-alpha(IIb)beta(3) monoclonal antibody AP2 also inhibited microparticle release although additional anti-alpha(IIb)beta(3) monoclonals did not. These data support participation of the tetraspanin CD9, together with the integrin alpha(IIb)beta(3), in the membrane vesiculation process associated with platelet microparticle release.
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