title: Inhibition of apoptotic signaling cascades causes loss of trophic factor dependence during neuronal maturation.
abstract: During development, neurons are acutely dependent on target-derived trophic factors for survival. This dependence on trophic support decreases dramatically with maturation in several neuronal populations, including sympathetic neurons. Analyses of nerve growth factor deprivation in immature and mature sympathetic neurons indicate that maturation aborts the cell death pathway at a point that is mechanistically indistinguishable from Bax deletion. However, neither the mRNA nor protein level of BAX changes with neuronal maturation. Therefore, BAX must be regulated posttranslationally in mature neurons. Nerve growth factor deprivation in immature sympathetic neurons induces two parallel processes: (a) a protein synthesis-dependent, caspase-independent translocation of BAX from the cytosol to mitochondria, followed by mitochondrial membrane integration and loss of cytochrome c; and (b) the development of competence-to-die, which requires neither macromolecular synthesis nor BAX expression. Activation of both signaling pathways is required for caspase activation and apoptosis in immature sympathetic neurons. In contrast, nerve growth factor withdrawal in mature sympathetic neurons did not induce the translocation of either BAX or cytochrome c. Moreover, mature neurons did not develop competence-to-die with cytoplasmic accumulation of cytochrome c. Therefore, inhibition of both BAX-dependent cytochrome c release and the development of competence-to-die contributed to the loss of trophic factor dependence associated with neuronal maturation.
authors.affiliation: Department of Neurology, Department of Molecular Biology and Pharmacology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: G V
authors.initials: GV
authors.lastname: Putcha
authors.forename: M
authors.initials: M
authors.lastname: Deshmukh
authors.forename: E M
authors.initials: EM
authors.lastname: Johnson
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D020169:Caspases / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000187:drug effects / Q000502:physiology; D003574:Cytochrome c Group / Q000378:metabolism; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects / Q000502:physiology; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000737:chemistry / Q000378:metabolism; D009414:Nerve Growth Factors / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology* / Q000201:enzymology; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000032:analysis; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D017783:Superior Cervical Ganglion / Q000166:cytology; D051028:bcl-2-Associated X Protein
chemical_list: C494827:Bax protein, mouse; D003574:Cytochrome c Group; D009414:Nerve Growth Factors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D051028:bcl-2-Associated X Protein; D007770:L-Lactate Dehydrogenase; D020169:Caspases