title: Involvement of Akt in preconditioning-induced tolerance to ischemia in PC12 cells.
abstract: The serine-threonine protein kinase Akt has been identified as an important mediator of cell survival able to counteract apoptotic stimuli. However, hibernation, a model of natural tolerance to cerebral ischemia, is associated with downregulation of Akt. We previously established a model of ischemic tolerance in a PC12 cell line and using this model we now addressed the question whether ischemic tolerance also downregulates Akt in PC12 cells. Kinetic studies showed decreased Akt phosphorylation in tolerized cells. Similarly, phosphorylated levels of three major targets of Akt and well-known proapoptotic factors, the glycogen synthase kinase 3 (GSK-3), a Forkhead family member, FoxO4, and the protein murine double minute 2 (MDM2), all inactivated upon phosphorylation by Akt, were decreased in preconditioned cells. In addition, pharmacological blockade of the phosphoinositide 3-kinase (PI3K)/Akt pathway reduced cell death induced by oxygen and glucose deprivation (OGD) and increased the protective effect of preconditioning (PC). Furthermore, decreasing availability of P-Akt by transfecting PC12 cells with constructs of inactive Akt also resulted in protection against OGD and potentiation of the protective effect of PC. Depending on the environment, GSK-3, FOXO-4, and MDM2 can trigger apoptotic responses or cell cycle arrest, and thus, in a situation of reduced energy, driving the cells into a state of quiescence might be neuroprotective. This work suggests that in the context of tolerance downregulation of Akt is beneficial.
authors.affiliation: 1Stroke Branch, Department of Health and Human Services, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4476, USA. jhilliol@jhmi.edu
authors.forename: Joëlle A
authors.initials: JA
authors.lastname: Hillion
authors.forename: YiXin
authors.initials: Y
authors.lastname: Li
authors.forename: Dragan
authors.initials: D
authors.lastname: Maric
authors.forename: Asako
authors.initials: A
authors.lastname: Takanohashi
authors.forename: Dace
authors.initials: D
authors.lastname: Klimanis
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Barker
authors.forename: John M
authors.initials: JM
authors.lastname: Hallenbeck
mesh_terms: D000818:Animals; D002545:Brain Ischemia / Q000378:metabolism / Q000473:pathology; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation / Q000235:genetics; D005947:Glucose / Q000494:pharmacology; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D019194:Ischemic Preconditioning; D051379:Mice; D009154:Mutation / Q000235:genetics; D010100:Oxygen / Q000494:pharmacology; D016716:PC12 Cells; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
chemical_list: C497208:Mdm2 protein, rat; D051736:Proto-Oncogene Proteins c-mdm2; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D005947:Glucose; D010100:Oxygen