title: Caspase-9 mediates the apoptotic death of megakaryocytes and platelets, but is dispensable for their generation and function.
abstract: Apoptotic caspases, including caspase-9, are thought to facilitate platelet shedding by megakaryocytes. They are known to be activated during platelet apoptosis, and have also been implicated in platelet hemostatic responses. However, the precise requirement for, and the regulation of, apoptotic caspases have never been defined in either megakaryocytes or platelets. To establish the role of caspases in platelet production and function, we generated mice lacking caspase-9 in their hematopoietic system. We demonstrate that both megakaryocytes and platelets possess a functional apoptotic caspase cascade downstream of Bcl-2 family-mediated mitochondrial damage. Caspase-9 is the initiator caspase, and its loss blocks effector caspase activation. Surprisingly, steady-state thrombopoiesis is unperturbed in the absence of caspase-9, indicating that the apoptotic caspase cascade is not required for platelet production. In platelets, loss of caspase-9 confers resistance to the BH3 mimetic ABT-737, blocking phosphatidylserine (PS) exposure and delaying ABT-737-induced thrombocytopenia in vivo. Despite this, steady-state platelet lifespan is normal. Casp9(-/-) platelets are fully capable of physiologic hemostatic responses and functional regulation of adhesive integrins in response to agonist. These studies demonstrate that the apoptotic caspase cascade is required for the efficient death of megakaryocytes and platelets, but is dispensable for their generation and function.
authors.affiliation: Cancer and Hematology Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: White
authors.forename: Simone M
authors.initials: SM
authors.lastname: Schoenwaelder
authors.forename: Emma C
authors.initials: EC
authors.lastname: Josefsson
authors.forename: Kate E
authors.initials: KE
authors.lastname: Jarman
authors.forename: Katya J
authors.initials: KJ
authors.lastname: Henley
authors.forename: Chloé
authors.initials: C
authors.lastname: James
authors.forename: Marlyse A
authors.initials: MA
authors.lastname: Debrincat
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Jackson
authors.forename: David C S
authors.initials: DC
authors.lastname: Huang
authors.forename: Benjamin T
authors.initials: BT
authors.lastname: Kile
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001713:Biphenyl Compounds / Q000494:pharmacology / Q000633:toxicity; D001792:Blood Platelets / Q000166:cytology* / Q000201:enzymology; D053453:Caspase 9 / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D019070:Cell Lineage; D006487:Hemostasis / Q000187:drug effects / Q000502:physiology; D006629:Hirudins / Q000494:pharmacology; D008099:Liver / Q000196:embryology; D016031:Liver Transplantation; D008533:Megakaryocytes / Q000166:cytology* / Q000201:enzymology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009596:Nitrophenols / Q000494:pharmacology / Q000633:toxicity; D010879:Piperazines / Q000494:pharmacology / Q000633:toxicity; D015539:Platelet Activation / Q000187:drug effects / Q000502:physiology; D011828:Radiation Chimera; D013449:Sulfonamides / Q000494:pharmacology / Q000633:toxicity; D013921:Thrombocytopenia / Q000139:chemically induced; D034061:Thrombopoiesis / Q000502:physiology*; D051028:bcl-2-Associated X Protein / Q000172:deficiency
chemical_list: C501332:ABT-737; C494827:Bax protein, mouse; D001713:Biphenyl Compounds; D006629:Hirudins; D009596:Nitrophenols; D010879:Piperazines; D013449:Sulfonamides; D051028:bcl-2-Associated X Protein; D053453:Caspase 9