Activation of calpain I converts excitotoxic neuron death into a caspase-independent cell death.
Glutamate receptor overactivation contributes to neuron death after stroke, trauma, and epileptic seizures. Exposure of cultured rat hippocampal neurons to the selective glutamate receptor agonist N-methyl-d-aspartate (300 microm, 5 min) or to the apoptosis-inducing protein kinase inhibitor staurosporine (300 nm) induced a delayed neuron death. In both cases, neuron death was preceded by the mitochondrial release of the pro-apoptotic factor cytochrome c. Unlike staurosporine, the N-methyl-d-aspartate-induced release of cytochrome c did not lead to significant activation of caspase-3, the main caspase involved in the execution of neuronal apoptosis. In contrast, activation of the Ca(2+)-activated neutral protease calpain I was readily detectable after the exposure to N-methyl-d-aspartate. In a neuronal cell-free apoptosis system, calpain I prevented the ability of cytochrome c to activate the caspase cascade by inhibiting the processing of procaspase-3 and -9 into their active subunits. In the hippocampal neuron cultures, the inhibition of calpain activity restored caspase-3-like protease activity after an exposure to N-methyl-d-aspartate. Our data demonstrate the existence of signal transduction pathways that prevent the entry of cells into a caspase-dependent cell death program after the mitochondrial release of cytochrome c.
Lankiewicz
S
S
Interdisciplinary Center for Clinical Research (IZKF), Research Group "Apoptosis and Cell Death," Westphalian Wilhelms University, D-48149 Münster, Germany.
Marc Luetjens
C
C
Truc Bui
N
N
Krohn
A J
AJ
Poppe
M
M
Cole
G M
GM
Saido
T C
TC
Prehn
J H
JH
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D002154:Calpain / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation; D006624:Hippocampus / Q000187:drug effects / Q000201:enzymology; D008856:Microscopy, Fluorescence; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D051381:Rats
D003574:Cytochrome c Group; D016202:N-Methylaspartate; D002154:Calpain; D020169:Caspases