Expression of mutant β2 nicotinic receptors during development is crucial for epileptogenesis

Abstract

Autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) is a focal form of epilepsy characterized by seizures occurring during non-REM sleep. We have developed and characterized the first mouse model for ADNFLE type III carrying the V287L mutation of the beta2 subunit of neuronal nicotinic receptor. Mice expressing mutant receptors show a spontaneous epileptic phenotype by electroencephalography with very frequent interictal spikes and seizures. Expression of the mutant beta2 subunit is driven by a neuronal-specific tetracycline-controlled promoter, which allows planned silencing of transgene expression in a reversible fashion and tracking the involvement of mutant receptor in crucial phases of epileptogenesis. We found that restricted silencing during development is sufficient to prevent the occurrence of epileptic seizures in adulthood. Our data indicate that mutant nicotinic receptors are responsible for abnormal formation of neuronal circuits and/or long-lasting alteration of network assembly in the developing brain, thus leading to epilepsy.

Multi-electrode array study of neuronal cultures expressing nicotinic β2-V287L subunits, linked to autosomal dominant nocturnal frontal lobe epilepsy. An in vitro model of spontaneous epilepsy

“…We used the S3 and S5 lines of double transgenic mice [FVB-Tg(tTA: Chrnb2 V287L ], which express β2-V287L and the tetracycline-controlled transcriptional activator tTA (Manfredi et al, 2009). When the transgene is not silenced by doxycyclin, both lines show spontaneous seizures, more prolonged in S3 (25 s on average).…”

“…The neurophysiological evidence, although incomplete, points to alterations in release of neurotransmitters, especially GABA (Klaassen et al, 2006; Teper et al, 2007; Zhu et al, 2008). Recently, Manfredi et al (2009) developed murine strains which conditionally express the ADNFLE-linked β2-V287L subunit under control of the tetracycline promoter (TET-off system). Expression of β2-V287L can be silenced by doxycycline administration.…”

Genetic basis in epilepsies caused by malformations of cortical development and in those with structurally normal brain

“…There was a gene-dosage effect where higher transgene expression was correlated with more severe phenotypes. The authors were also able to demonstrate that silencing the transgene during early development only was enough to prevent the development of the epileptic phenotype, supporting the notion that this gene is involved with normal cortical development and connections or neuronal/synaptic function (Manfredi et al 2009). …”

Spontaneous epileptic seizures in transgenic rats harboring a human ADNFLE missense mutation in the β2-subunit of the nicotinic acetylcholine receptor

“…One is a conditional transgenic mouse strain, which displayed a spontaneous epileptic phenotype with frequent interictal spikes and seizures (Manfredi et al, 2009). However, the seizure phenotype in the conditional transgenic mouse may have been dependent on the overexpression of mutated ␤2 receptor.…”