Down-regulation of monocyte apoptosis by phagocytosis of platelets: involvement of a caspase-9, caspase-3, and heat shock protein 70-dependent pathway.
Monocytes interact and cross-talk with platelets in many settings including inflammation, hemostasis, or vascular disorders. During inflammatory diseases, there is a rapid targeting of monocytes and platelets to points of inflammation and endothelial injury, where they lie side-by-side. In this in vitro study, we investigated different interactions between monocytes and platelets and elucidated whether platelets might affect monocyte apoptosis. Freshly isolated human monocytes were rendered apoptotic by serum deprivation or CD95 ligation and cocultured with platelets. Monocyte apoptosis was determined by flow cytometry, TUNEL staining, DNA electrophoresis, and transmission electron microscopy imaging. We could show that monocyte apoptosis was highly suppressed when platelets were added to the cultures. Transmission electron microscopy depicted that monocytes completely ingested thrombocytes by phagocytosis. Blocking thrombocyte uptake by the phagocytosis inhibitor cytochalasin D abrogated the enhanced monocyte survival and led to high apoptosis levels. Monocyte survival was paralleled by down-regulation of caspase-9 and -3 and up-regulation of heat shock protein 70 during uptake of platelets. Platelet supernatants and contents of platelet granules were ineffective in altering monocyte senescence. Also, ingestion of latex beads or zymosan by monocytes was ineffective to mimic platelet-dependent rescue from apoptosis. In conclusion, this study shows that platelets can suppress apoptosis of monocytes by a specific phagocytosis-dependent process with further consequences for atherosclerotic or inflammatory conditions.
Lang
Detlef
D
Department of Medicine and Institutes of Pathology and Immunology, University of Münster, Münster, Germany.
Dohle
Frank
F
Terstesse
Martin
M
Bangen
Philip
P
August
Christian
C
Pauels
Hans-Gerd
HG
Heidenreich
Stefan
S
D017209:Apoptosis / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology*; D053148:Caspase 3; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000502:physiology*; D002478:Cells, Cultured; D018920:Coculture Techniques; D015536:Down-Regulation / Q000276:immunology*; D006133:Growth Substances / Q000502:physiology; D018840:HSP70 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000502:physiology*; D006801:Humans; D009000:Monocytes / Q000166:cytology / Q000201:enzymology / Q000276:immunology*; D010587:Phagocytosis / Q000276:immunology*; D015539:Platelet Activation / Q000276:immunology; D015398:Signal Transduction / Q000276:immunology*; D015854:Up-Regulation / Q000276:immunology
D061945:Caspase Inhibitors; D006133:Growth Substances; D018840:HSP70 Heat-Shock Proteins; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases