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Death-signalling cascade in mouse cerebellar granule neurons
H Tanabe1, Y Eguchi, S Shimizu
1Department of Molecular Genetics, Biomedical Research Center, Osaka University Medical School, Suita, Japan.
Abstract:
Molecular mechanisms of neuronal cell death are still largely unknown. In the present study, the signal transduction pathway of cell death in cerebellar granule neurons was examined by employing various death-preventative agents. When death was induced by the depletion of serum and a depolarizing level of potassium, transient increase in active c-Jun, mitochondrial membrane potential (deltapsi) loss, activation of caspase-3 (-like) proteases, and nuclear condensation and fragmentation were observed. The protein synthesis inhibitor cycloheximide blocked all these phenomena, whereas RNA synthesis inhibitor actinomycin-D, survival factor such as insulin-like growth factor-1, brain-derived neurotrophic factor, high K+ (25 mM) and overproduced antiapoptotic protein Bcl-2, prevented deltapsi, loss, caspase activation, and nuclear change, but not an increase in active c-Jun. The caspase inhibitor z-Asp-CH2-DCB (carbobenzoxy-L-aspartyl-alpha-[(2,6-dichlorobenzoyl) oxy]methane) only inhibited activation of caspases and nuclear change. These results suggest that the death signal in cerebellar granule neurons is sequentially transduced in the order of c-Jun activation, de novo RNA synthesis, mitochondrial deltapsi loss, activation of caspase-3 (-like) proteases and nuclear change.
Insights
Neuronal cell death involves a sequence of events including c-Jun activation and mitochondrial changes. Understanding this pathway in cerebellar granule neurons is crucial for neuroprotection research.
Area of Science:
- Neuroscience
- Cell Biology
- Molecular Biology
Background:
- The molecular mechanisms underlying neuronal cell death remain largely unelucidated.
- Cerebellar granule neurons are a key model for studying neuronal survival and death pathways.
Purpose of the Study:
- To investigate the signal transduction pathway of cell death in cerebellar granule neurons.
- To identify the sequential molecular events leading to neuronal apoptosis.
Main Methods:
- Induction of cell death using serum depletion and potassium levels.
- Treatment with various agents including protein synthesis inhibitor cycloheximide, RNA synthesis inhibitor actinomycin-D, survival factors (IGF-1, BDNF), and caspase inhibitors (z-Asp-CH2-DCB).
- Assessment of molecular events: c-Jun activation, mitochondrial membrane potential (Δψm) loss, caspase-3 activation, and nuclear condensation/fragmentation.
Main Results:
- Serum and potassium depletion induced c-Jun activation, Δψm loss, caspase activation, and nuclear changes.
- Cycloheximide blocked all observed death phenomena.
- Actinomycin-D, survival factors, and Bcl-2 prevented Δψm loss, caspase activation, and nuclear changes, but not c-Jun activation.
- Caspase inhibitor z-Asp-CH2-DCB inhibited caspase activation and nuclear changes.
Conclusions:
- Neuronal cell death signaling in cerebellar granule neurons follows a sequential pathway.
- The sequence involves c-Jun activation, de novo RNA synthesis, mitochondrial dysfunction, caspase activation, and nuclear fragmentation.