Abstracts

Seizures whether brief or prolonged are capable of causing neuronal death. Apoptosis signaling pathways play a role is such neuronal loss. Previous studies have demonstrated that experimental seizures can activate the apoptotic intrinsic mitochondrial cell death pathway and that components of this pathway are altered in involved brain structures in patients with temporal lobe epilepsy.
We have developed a mouse model of seizure-induced neuronal death with features of programmed cell death. Presently, we examined the activation of the mitochondrial apoptotic pathway in this model and contrasted this to events within human epilepsy brain., The experimental methods used in this study included, a mouse seizure model: intraamygdala kainic acid injection in adult mice, terminated after 40 min by diazepam, human temporal lobe specimens: hippocampal resections obtained following surgery for intractable epilepsy compared to matched autopsy controls, Western blotting and Immunofuorescence., Seizures evoked by intraamygdala kainic acid in C57BL/6 mice caused ipsilateral death of CA1 and CA3 neurons within the hippocampus. Western blotting revealed seizures induced overexpression of Bax, cytochrome c release and activation of caspase-9 and -7. Analysis of hippocampi from patients with intractable epilepsy revealed cleaved caspases 9 and 7 were present. In searching for relevant anti-apoptotic proteins we found no changes to expression of Bcl-2 and Bcl-xl but a rapid decline in Bcl-w levels at both 0.5 (p [lt] 0.01) and 4 h following seizures. Reasoning that loss of Bcl-w may promote cell death after seizures we investigated hippocampal injury following seizures in mice lacking Bcl-w. Bcl-w knockout mice exhibited no obvious neuroanatomical differences to their wildtype littermates and expressed similar hippocampal levels of a range of apoptosis-associated proteins including Bcl-2 and similar amygdala levels of the kainic acid (KA) receptor GluR5-7. Seizures evoked by intraamygdala KA induced significantly more hippocampal neuronal loss and DNA fragmentation (terminal deoxynucleotidyl dUTP nick end labeling) in Bcl-w knockout mice compared to wildtype mice. Extending these data, we found higher cytoplasmic levels of Bcl-w in hippocampus from patients with TLE compared to autopsy controls., These data identify Bcl-w as an endogenous neuroprotective gene that may be a therapeutic target for the treatment of seizure-induced brain injury and temporal lobe epilepsy., (Supported by the Health Research Board, Ireland, Wellcome Trust, UK and NIH/NINDS, USA.)