Abstracts

Rationale: Temporal lobe epilepsy accompanied by hippocampal sclerosis (TLE-HS) is the single most common form of epilepsy that causes refractory seizures. Neuronal death in HS can be triggered by excitotoxic damage. However, the mechanisms which lead to this prominent neuronal loss and gliosis in hippocampus are poorly understood. The study of apoptosis-related genes is necessary to identify critical targets in epileptogenesis and to clarify the molecular physiopathology in TLE-HS.Methods: We studied three apoptosis-related genes to evaluate their mRNA expression by reverse transcription quantitative PCR (RT-qPCR): Platelet-activating factor acetylhydrolase 1b, regulatory subunit 1 (45kDa) (PAFAH1B1); Purkinje cell protein 4 (PCP4); and Semaphorin 5A (SEMA5A). Messenger RNA expression was quantified in the hippocampus of 13 TLE-HS refractory patients who underwent amygdalo-hippocampectomy for therapeutical reasons. Hippocampal tissues from five post mortem control subjects were used for gene expression comparison. Hypoxanthine phosphoribosyltransferase 1 (HPRT1) was used as the endogenous control.Results: We found that all target genes were upregulated in the TLE-HS patients (p<0.05).Conclusions: PAFAH1B1 is required for proper activation of Rho GTPases and actin polymerization at the leading edge of locomoting cerebellar neurons and post migratory hippocampal neurons in response to calcium influx triggered via NMDA receptors. Essentially, the control of neuronal activity involves the nerve-cell cytoskeleton. It has been believed that PAFAH1B1, as an actin and microtubule regulator, is the underlying cause of epileptic seizures in patients with cortical malformations and as a post-developmental role could contribute to the more temporary character of irregular neuronal activity. PCP4 plays a role as an endogenous negative regulator of calmodulin by repressing the connection of calmodulin with enzymes and other proteins. A recent study found that primary cortical neurons overexpressing PCP4 became resistant to glutamate-induced cell death, providing evidence that PCP4 upregulation intensifies resistance to Ca²⁺-mediated cytotoxicity. Moreover, endogenous PCP4 levels in neurons were significantly reduced following glutamate exposure. We hypothesize that PCP4 upregulation in TLE-HS patients is contributing to the prevention of neuronal apoptosis. SEMA5A is involved in axonal guidance during neural development. It has shown a comparative increase of endothelial expression of anti-apoptotic genes relative to pro-apoptotic genes in Sema5A-treated endothelial cells suggesting that Sema5A inhibits apoptosis through activation of Akt. Its upregulation indicates an anti-apoptotic effect in HS. Neuronal plasticity and survival mechanisms in response to necrosis and apoptosis in the sclerotic hippocampus appear to be contributing to the overexpression of these target genes, revealing a new understanding of signaling pathways in TLE-HS molecular physiopathology. This comprehension is essential for the development of new antiepileptic drugs.