Endothelial microparticle uptake in target cells is annexin I/phosphatidylserine receptor dependent and prevents apoptosis.
OBJECTIVE
Endothelial microparticles (EMP) are released from activated or apoptotic cells, but their effect on target cells and the exact way of incorporation are largely unknown. We sought to determine the uptake mechanism and the biological effect of EMP on endothelial and endothelial-regenerating cells.


RESULTS
EMP were generated from starved endothelial cells and isolated by ultracentrifugation. Caspase 3 activity assay and terminal deoxynucleotidyl transferase dUTP nick end labeling assay showed that EMP protect target endothelial cells against apoptosis in a dose-dependent manner. Proteomic analysis was performed to identify molecules contained in EMP, which might be involved in EMP uptake. Expression of annexin I in EMP was found and confirmed by Western blot, whereas the corresponding receptor phosphatidylserine receptor was present on endothelial target cells. Silencing either annexin I on EMP or phosphatidylserine receptor on target cells using small interfering RNA showed that the uptake of EMP by human coronary artery endothelial cells is annexin I/phosphatidylserine receptor dependent. Annexin I-downregulated EMP abrogated the EMP-mediated protection against apoptosis of endothelial target cells. p38 activation was found to mediate camptothecin-induced apoptosis. Finally, human coronary artery endothelial cells pretreated with EMP inhibited camptothecin-induced p38 activation.


CONCLUSIONS
EMP are incorporated by endothelial cells in an annexin I/phosphatidylserine receptor-dependent manner and protect target cells against apoptosis. Inhibition of p38 activity is involved in EMP-mediated protection against apoptosis.
Department of Internal Medicine, University Hospital Bonn, University of Bonn, Bonn, Germany.
Felix
F
Jansen
Xiaoyan
X
Yang
Friedrich Felix
FF
Hoyer
Kathrin
K
Paul
Nadine
N
Heiermann
Marc Ulrich
MU
Becher
Nebal
N
Abu Hussein
Moritz
M
Kebschull
Jörg
J
Bedorf
Bernardo S
BS
Franklin
Eicke
E
Latz
Georg
G
Nickenig
Nikos
N
Werner
D017305:Annexin A1 / Q000502:physiology*; D017209:Apoptosis / Q000187:drug effects; D002166:Camptothecin / Q000494:pharmacology; D055252:Cell-Derived Microparticles / Q000502:physiology*; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000502:physiology*; D006801:Humans; D011956:Receptors, Cell Surface / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology
D017305:Annexin A1; D011956:Receptors, Cell Surface; C408123:phosphatidylserine receptor; D048051:p38 Mitogen-Activated Protein Kinases; D002166:Camptothecin