DIANNEXIN DOWN-MODULATES TNF-INDUCED ENDOTHELIAL MICROPARTICLE RELEASE BY BLOCKING MEMBRANE BUDDING PROCESS.
BACKGROUND
Microparticles are now recognised as true biological effectors with a role in immunopathology through their ability to disseminate functional properties. Diannexin, a homodimer of annexin V, binds to PS with a higher affinity and longer blood half-life than the monomer, inhibits prothrombinase complex activity thereby diminishing coagulation and reperfusion injury mediators and prevent microvesicle-mediated material transfer. Our aim was to determine if Diannexin could modulate microparticle production by endothelial cells by interacting with the phosphatidylserine exposure occurring during the release of these vesicles.


RESULTS
In this study we showed that fluorescently labelled Diannexin binds to calcimycin-activated endothelial cells but not to resting cells. After overnight incubation, Diannexin enters cells and their released MP carry Diannexin. Some Diannexin seems to be processed via early endosomes and later is found in lysosomes. Both unlabelled Diannexin and fluorescent Diannexin inhibit MP release from TNF-activated endothelial cells. However, Diannexin treatment does not prevent endothelial activation by TNF. In addition, the inhibitory effect of Diannexin on MP release could be observed when cells were pre-, concomitantly or post-treated with cytokines. Scanning electron microscopy showed differences in the numbers and types of protuberances at the cell surface when cells were treated or not with Diannexin. Finally, there is no apparent congruency between fluorescent Diannexin labelling and surface protuberances as shown by correlative microscopy.


CONCLUSIONS
Altogether these data suggest that Diannexin can inhibit endothelial vesiculation by binding PS present either at the cell surface or at the level of the inner leaflet of the plasma membrane.
Vascular Immunology Unit, Faculty of Medicine & Bosch Institute, The University of Sydney, Medical Foundation Building, 92-94 Parramatta Road, Camperdown NSW 2006, Australia; School of Life Sciences, The University of Technology, Sydney, Ultimo NSW 2007, Australia.
Valéry
V
Combes
Vascular Immunology Unit, Faculty of Medicine & Bosch Institute, The University of Sydney, Medical Foundation Building, 92-94 Parramatta Road, Camperdown NSW 2006, Australia.
Sharissa L
SL
Latham
Vascular Immunology Unit, Faculty of Medicine & Bosch Institute, The University of Sydney, Medical Foundation Building, 92-94 Parramatta Road, Camperdown NSW 2006, Australia.
Beryl
B
Wen
Alavita Inc, Palo Alto, California, United States of America.
Anthony C
AC
Allison
Vascular Immunology Unit, Faculty of Medicine & Bosch Institute, The University of Sydney, Medical Foundation Building, 92-94 Parramatta Road, Camperdown NSW 2006, Australia.
Georges E R
GE
Grau
Diannexin; Microparticles; TNF; cytokines; endothelium; inflammation; vesiculation