title: Pertussis toxin promotes macrophage survival through inhibition of acid sphingomyelinase and activation of the phosphoinositide 3-kinase/protein kinase B pathway.
abstract: Apoptosis is an important mechanism involved in regulating the number of macrophages present at sites of inflammation. Several lines of evidence indicate that blocking macrophage apoptosis can increase atherosclerosis. We previously reported that oxidized LDL can inhibit apoptosis in cultured bone marrow-derived macrophages. We used pertussis toxin (PTX) to test whether G protein coupled receptors are activated by oxLDL. PTX is a bacterial toxin that inhibits Gi activation by ADP-ribosylating the alpha subunit of Gi, preventing the subunit from interacting with receptors. Unexpectedly, we found that PTX by itself selectively blocks macrophage apoptosis in a dose-dependent manner. PTX acts in part by inhibiting acid sphingomyelinase activity which in turn prevents generation of ceramide, which is required for macrophage apoptosis. A Gi activator peptide, mastoparan, increased ceramide levels in macrophage and induced apoptosis, but pre-treatment with PTX partially overrode mastoparan-induced apoptosis. The anti-apoptotic effect of PTX was found to require ADP-ribosylation. PTX failed to prevent A-SMase activation or apoptosis in macrophages lacking TLR4. The anti-apoptotic effect of PTX involved the same signaling pathways as those of oxidized LDL, in that both inhibited acid sphingomyelinase, and activated the phosphoinositide 3 kinase (PI3K)/protein kinase B (PKB) pathway which leads to nuclear localization of the transcription factor NFkappaB and up-regulation of Bcl-XL. These results indicate that Gi proteins, TLR4, A-SMase and the PI3K/PKB pathway are crucial components for regulation of macrophage apoptosis.
authors.affiliation: Department of Medicine, University of British Columbia, Vancouver, Canada.
authors.forename: Shih Wei
authors.initials: SW
authors.lastname: Wang
authors.forename: Kuljit
authors.initials: K
authors.lastname: Parhar
authors.forename: Kai Jen
authors.initials: KJ
authors.lastname: Chiu
authors.forename: Anthony
authors.initials: A
authors.lastname: Tran
authors.forename: Patricia
authors.initials: P
authors.lastname: Gangoiti
authors.forename: Jennifer
authors.initials: J
authors.lastname: Kong
authors.forename: Monika
authors.initials: M
authors.lastname: Gonzalez
authors.forename: Bill
authors.initials: B
authors.lastname: Salh
authors.forename: Vincent
authors.initials: V
authors.lastname: Duronio
authors.forename: Urs P
authors.initials: UP
authors.lastname: Steinbrecher
authors.forename: Antonio
authors.initials: A
authors.lastname: Gómez-Muñoz
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D005269:Femur / Q000166:cytology; D008264:Macrophages / Q000166:cytology / Q000187:drug effects*; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D037342:Pertussis Toxin / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000037:antagonists & inhibitors*; D013997:Time Factors
chemical_list: D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D013108:Sphingomyelin Phosphodiesterase