ATP controls neuronal apoptosis triggered by microtubule breakdown or potassium deprivation.
BACKGROUND
Early loss of neurites followed by delayed damage of neuronal somata is a feature of several neurodegenerative diseases. Death by apoptosis would ensure the rapid removal of injured neurons, whereas conditions that prevent apoptosis may facilitate the persistence of damaged cells and favor inflammation and disease progression.


METHODS
Cultures of cerebellar granule cells (CGC) were treated with microtubule disrupting agents. These compounds induced an early degeneration of neurites followed by apoptotic destruction of neuronal somata. The fate of injured neurons was followed after co-exposure to caspase inhibitors or agents that decrease intracellular ATP (deoxyglucose, S-nitrosoglutathione, 1-methyl-4-phenylpyridinium). We examined the implications of energy loss for caspase activation, exposure of phagocytosis markers, and long-term persistence of damaged cells.


RESULTS
In CGC exposed to colchicine or nocodazole, axodendritic degeneration preceded caspase activation and apoptosis. ATP-depleting agents or protein synthesis inhibition prevented caspase activation, translocation of the phagocytosis marker, phosphatidylserine, and apoptotic death. However, they did not affect the primary neurite loss. Repletion of ATP by enhanced glycolysis restored all apoptotic features. Peptide inhibitors of caspases also prevented the apoptotic changes in the cell bodies, although the axodendritic net was lost. Under this condition cell demise still occurred 48 hr later in a caspase-independent manner and involved plasma membrane lysis at the latest stage.


CONCLUSIONS
Inhibition of the apoptotic machinery by drugs, energy deprivation, or endogenous mediators may result in the persistence and subsequent lysis of injured neurons. In vivo, this may favor the onset of inflammatory processes and perpetuate neurodegeneration.
Volbracht
C
C
Faculty of Biology, Department of Molecular Toxicology, University of Konstanz, Konstanz, Germany.
Leist
M
M
Nicotera
P
P
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000187:drug effects / Q000378:metabolism; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism; D003078:Colchicine / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003847:Deoxyglucose / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004734:Energy Metabolism; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005978:Glutathione / Q000031:analogs & derivatives / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D008840:Microfilament Proteins / Q000378:metabolism; D008870:Microtubules / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D018696:Neuroprotective Agents / Q000494:pharmacology; D009603:Nitroso Compounds / Q000494:pharmacology; D015739:Nocodazole / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D014176:Protein Biosynthesis; D026422:S-Nitrosoglutathione; D016559:Tacrolimus / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology; D013049:Spectrin
D000255:Adenosine Triphosphate; D000590:Amino Acid Chloromethyl Ketones; D002352:Carrier Proteins; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases; D003078:Colchicine; D016572:Cyclosporine; D015853:Cysteine Proteinase Inhibitors; D003847:Deoxyglucose; D016291:Dizocilpine Maleate; D004791:Enzyme Inhibitors; D005978:Glutathione; D008840:Microfilament Proteins; D018696:Neuroprotective Agents; D009603:Nitroso Compounds; D015739:Nocodazole; D009842:Oligopeptides; D017239:Paclitaxel; D011188:Potassium; D026422:S-Nitrosoglutathione; D016559:Tacrolimus; D014700:Verapamil; D013049:Spectrin; C108637:aspartyl-glutamyl-valyl-aspartal; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; C505409:Casp3 protein, mouse