Bim regulation may determine hippocampal vulnerability after injurious seizures and in temporal lobe epilepsy

Abstract

Programmed cell death pathways have been implicated in the mechanism by which neurons die following brief and prolonged seizures, but the significance of proapoptotic Bcl-2 family proteins in the process remains poorly defined. Expression of the death agonist Bcl-2-interacting mediator of cell death (Bim) is under the control of the forkhead in rhabdomyosarcoma (FKHR) transcription factors. This prompted us to examine the response of this pathway to experimental seizures and in hippocampi from patients with intractable temporal lobe epilepsy. A short period of status epilepticus in rats that damaged the hippocampus activated FKHR/FKHRL-1 and induced a significant increase in expression of Bim. Blocking of FKHR/FKHRL-1 dephosphorylation after seizures improved hippocampal neuronal survival in vivo, and Bim antisense oligonucleotides were neuroprotective against seizures in vitro. Inhibition of Akt increased the FKHR/Bim response and DNA fragmentation within the normally resistant cortex. Analysis of hippocampi from patients with intractable epilepsy revealed that Bim levels were significantly lower than in controls and FKHR was inhibited; we were able to reproduce these results experimentally in rats by evoking multiple brief, noninjurious electroshock seizures. We conclude that Bim expression may be a critical determinant of whether seizures damage the brain, and that its control may be neuroprotective in status epilepticus and epilepsy.Nonstandard abbreviations used: B cell lymphoma (Bcl); Bcl-2-associated death promoter (Bad); Bcl-2-associated X protein (Bax); Bcl-2-homologous antagonist/ killer (Bak); Bcl-2 homology domain 3 (BH3); Bcl-2-interacting mediator of cell death (Bim); BH3-interacting domain death agonist (Bid); cornu ammonis (CA); electroencephalogram (EEG); forkhead in rhabdomyosarcoma (FKHR); kainic acid (KA); 27-kDa Cdk-inhibitory protein 1 (p27 Kip1 ); lactate dehydrogenase (LDH); maximal electroshock seizure (MES); sodium orthovanadate (SOV).

Expression and localisation of brain-type organic cation transporter (BOCT/24p3R/LCN2R) in the normal rat hippocampus and after kainate-induced excitotoxicity

“…Although Bim has three major isoforms generated by alternative splicing, namely Bim EL (extra-long), Bim L (long) and Bim S (short) (O'Connor et al, 1998), only Bim EL was detected as a single band at 23kDa in the rat hippocampus, consistent with a previous study (Shinoda et al, 2004).…”

“…Importantly, double labelling showed that Bim positive neurons were also TUNEL-positive, consistent with the notion that Bim is a pro-apoptotic protein in hippocampal neurons undergoing excitotoxic injury. Previous studies have shown an increase in number of Fluoro-Jade positive and TUNEL-positive degenerating pyramidal neurons 1 day after KA administration (Korhonen et al, 2003, Shinoda et al, 2004, and presence of activated caspase 3 in the hippocampus, 1 day after excitotoxic injury in mice (Theofilas et al, 2009). The results suggest greater vulnerability of neurons than microglia to apoptosis.…”

Apoptosis signalling pathways in seizure-induced neuronal death and epilepsy

“…Upstream pro-apoptotic BH3 domain (Bcl-2 homology domain 3)-only members BAD (Bcl-2-associated death protein), Bid and Bim (Bcl-2-interacting mediator of cell death), can be activated via calcium-dependent mechanisms and each was found to be activated by seizures in vivo [11][12][13].…”

PI3Kγ deficiency enhances seizures severity and associated outcomes in a mouse model of convulsions induced by intrahippocampal injection of pilocarpine

“…SE induced Akt phosphorylation, a kinase that is regulated by PI3K, 30 min and 24 h after pilocarpine injection in WT, but not PI3Kγ −/− mice. Activation of Akt has been previously demonstrated in the hippocampus of patients with TLE and in the cortex of rats that received a kainic acid injection in the amygdala (Henshall et al, 2002;Shinoda et al, 2004). PI3Kγ is the only member of the family that can be activated by G protein coupled receptors.…”

“…Previous studies have shown an increased Akt phosphorylation in the hippocampus of patients with temporal lobe epilepsy (Shinoda et al, 2004) and in the cortex of rats injected with kainic acid into the basolateral nucleus of the amygdala (Henshall et al, 2002). However, the role of PI3K in seizures, as well as in postictal events, is still not fully understood.…”