RESUMEN
Transient brain insults, including status epilepticus (SE), can trigger a period of epileptogenesis during which functional and structural reorganization of neuronal networks occurs resulting in the onset of focal epileptic seizures. In recent years, mechanisms that regulate the dynamic transcription of individual genes during epileptogenesis and thereby contribute to the development of a hyperexcitable neuronal network have been elucidated. Our own results have shown early growth response 1 (Egr1) to transiently increase expression of the T-type voltage-dependent Ca2+ channel (VDCC) subunit CaV3.2, a key proepileptogenic protein. However, epileptogenesis involves complex and dynamic transcriptomic alterations; and so far, our understanding of the transcriptional control mechanism of gene regulatory networks that act in the same processes is limited. Here, we have analyzed whether Egr1 acts as a key transcriptional regulator for genes contributing to the development of hyperexcitability during epileptogenesis. We found Egr1 to drive the expression of the VDCC subunit α2δ4, which was augmented early and persistently after pilocarpine-induced SE. Furthermore, we show that increasing levels of α2δ4 in the CA1 region of the hippocampus elevate seizure susceptibility of mice by slightly decreasing local network activity. Interestingly, we also detected increased expression levels of Egr1 and α2δ4 in human hippocampal biopsies obtained from epilepsy surgery. In conclusion, Egr1 controls the abundance of the VDCC subunits CaV3.2 and α2δ4, which act synergistically in epileptogenesis, and thereby contributes to a seizure-induced "transcriptional Ca2+ channelopathy."SIGNIFICANCE STATEMENT The onset of focal recurrent seizures often occurs after an epileptogenic process induced by transient insults to the brain. Recently, transcriptional control mechanisms for individual genes involved in converting neurons hyperexcitable have been identified, including early growth response 1 (Egr1), which activates transcription of the T-type Ca2+ channel subunit CaV3.2. Here, we find Egr1 to regulate also the expression of the voltage-dependent Ca2+ channel subunit α2δ4, which was augmented after pilocarpine- and kainic acid-induced status epilepticus. In addition, we observed that α2δ4 affected spontaneous network activity and the susceptibility for seizure induction. Furthermore, we detected corresponding dynamics in human biopsies from epilepsy patients. In conclusion, Egr1 orchestrates a seizure-induced "transcriptional Ca2+ channelopathy" consisting of CaV3.2 and α2δ4, which act synergistically in epileptogenesis.
Asunto(s)
Canales de Calcio/metabolismo , Proteína 1 de la Respuesta de Crecimiento Precoz/metabolismo , Epilepsia del Lóbulo Temporal/metabolismo , Hipocampo/metabolismo , Convulsiones/metabolismo , Estado Epiléptico/metabolismo , Animales , Modelos Animales de Enfermedad , Epilepsia del Lóbulo Temporal/fisiopatología , Hipocampo/fisiopatología , Humanos , Ácido Kaínico , Masculino , Ratones , Red Nerviosa/metabolismo , Red Nerviosa/fisiopatología , Pilocarpina , Convulsiones/inducido químicamente , Convulsiones/fisiopatología , Estado Epiléptico/inducido químicamente , Estado Epiléptico/fisiopatologíaRESUMEN
Recently it was demonstrated that for the absence epilepsy characteristic spike-wave discharges initially emerge from the somatosensory cortex and quickly involve the rest of the cortex and cortico-thalamic network. This has led to the development of the focal theory of absence epilepsy. In this experiment, this theory was further investigated by studying the neuronal organization of the cortical focal zone, a non-focal zone in genetic epileptic WAG/Rij rats and functional related areas in non-epileptic age matched control rats. A classical Golgi staining technique was used to visualize whole cortical neurons with dendritic and axon arborisation. Apical dendrites of pyramidal cells in epileptic rats were often split, declined and were running in non-perpendicular directions. Quantitative differences between the strains were found for the length of neurons, between focal and control areas mainly for dendritic arborization. A significant "strain-zone" interaction was found for the maximal distance between two points of dendritic arborization, the mean length of a dendritic segment and the number of free terminations of apical dendrites. All this demonstrates that properties of dendrites in the cortical focal area of WAG/Rij rats were at variance with dendritic characteristics outside the focal area and with functional similar areas in non-epileptic controls. These features might reflect the hyperexcitability of somatosensory neurons, which underlie the initiation and spreading of spike-wave discharges in WAG/Rij rats. Finally, these results are in line with the cortical focus theory of absence epilepsy.