Death commitment point is advanced by axotomy in sympathetic neurons.
Axotomized neurons have several characteristics that are different from intact neurons. Here we show that, unlike established cultures, the axotomized sympathetic neurons deprived of NGF become committed to die before caspase activation, since the same proportion of NGF-deprived neurons are rescued by NGF regardless of whether caspases are inhibited by the pan-caspase inhibitor Boc-Asp(O-methyl)-CH(2)F (BAF). Despite prolonged Akt and ERK signaling induced by NGF after BAF treatment has prevented death, the neurons fail to increase protein synthesis, recover ATP levels, or grow. Within 3 d, all the mitochondria disappear without apparent removal of any other organelles or loss of membrane integrity. Although NGF does rescue intact BAF-treated 6-d cultures after NGF deprivation, rescue by NGF fails when these neurons are axotomized before NGF deprivation and BAF treatment. Moreover, cytosolic cytochrome c rapidly kills axotomized neurons. We propose that axotomy induces signals that make sympathetic neurons competent to die prematurely. NGF cannot repair these NGF-deprived, BAF-treated neurons because receptor signaling (which is normal) is uncoupled from protein renewal, and the mitochondria (which are damaged) go on to be eliminated. Hence, the order of steps underlying neuronal death commitment is mutable and open to regulation.
Fletcher
G C
GC
Department of Biochemistry, University of Cambridge, Cambridge, CB2 1QW, United Kingdom.
Xue
L
L
Passingham
S K
SK
Tolkovsky
A M
AM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D019771:Axotomy; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival; D002478:Cells, Cultured; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D020932:Nerve Growth Factor / Q000494:pharmacology / Q000502:physiology*; D016501:Neurites / Q000502:physiology / Q000648:ultrastructure; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D017208:Rats, Wistar; D017783:Superior Cervical Ganglion / Q000166:cytology / Q000502:physiology
D061945:Caspase Inhibitors; D011518:Proto-Oncogene Proteins; C413643:benzyloxycarbonyl-aspartyl(O-methyl)fluoromethane; D001224:Aspartic Acid; D000255:Adenosine Triphosphate; D020932:Nerve Growth Factor; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020169:Caspases