Gene Expression Profiling of a Hypoxic Seizure Model of Epilepsy Suggests a Role for mTOR and Wnt Signaling in Epileptogenesis

Abstract

Microarray profiling was used to investigate gene expression in the hypoxic seizure model of acquired epilepsy in the rat, with the aim of characterizing functional pathways which are persistently activated or repressed during epileptogenesis. Hippocampal and cortical tissues were transcriptionally profiled over a one week period following an initial series of seizures induced by mild hypoxia at post-natal day 10 (P10), and the gene expression data was then analyzed with a focus on gene set enrichment analysis, an approach which emphasizes regulation of entire pathways rather than of individual genes. Animals were subjected to one of three conditions: a control with no hypoxia, hypoxic seizures, and hypoxic seizures followed by treatment with the AMPAR antagonist NBQX, a compound currently proposed to be a modulator of epileptogenesis. While temporal gene expression in the control samples was found to be consistent with known processes of neuronal maturation in the rat for the given time window, the hypoxic seizure response was found to be enriched for components of the PI3K/mTOR and Wnt signaling pathways, alongside gene sets representative of glutamatergic, synaptic and axonal processes, perhaps regulated as a downstream consequence of activation of these pathways. Wnt signaling components were also found enriched in the more specifically epileptogenic NBQX-responsive gene set. While activation of the mTOR pathway is consistent with its known role in epileptogenesis and strengthens the case for mTOR or PI3K pathway inhibitors as potential anti-epileptogenic drugs, investigation of the role of Wnt signaling and the effect of appropriate inhibitors might offer a parallel avenue of research toward anti-epileptogenic treatment of epilepsy.

The radial organization of neuronal primary cilia is acutely disrupted by seizure and ischemic brain injury

“…For example, Double-cortin domain containing 2 (DCDC2) is a cilia- and microtubule-localizing protein that interfaces between the primary cilium and the cytoskeleton to regulate Sonic hedgehog (Shh) and Wnt signaling (Massinen et al, 2011). Importantly, the Wnt/beta-catenin pathway has been shown to be induced by both seizure activity and hypoxia (Busceti et al, 2007; Theilhaber et al, 2013). Given the vital role that beta-catenin plays in the maintenance of neuronal structural integrity as well as synaptic plasticity (Maguschak and Ressler, 2012; Theilhaber et al, 2013), it is plausible that this pathway could be disrupted when primary cilia become compromised, as in the two pathological contexts we examined.…”

“…Importantly, the Wnt/beta-catenin pathway has been shown to be induced by both seizure activity and hypoxia (Busceti et al, 2007; Theilhaber et al, 2013). Given the vital role that beta-catenin plays in the maintenance of neuronal structural integrity as well as synaptic plasticity (Maguschak and Ressler, 2012; Theilhaber et al, 2013), it is plausible that this pathway could be disrupted when primary cilia become compromised, as in the two pathological contexts we examined. Still, it will be important to pinpoint the mechanisms by which neurological insult results in acute changes in cilia orientation and length, and to identify the functional consequences thereof.…”

mTOR inhibitors rescue premature lethality and attenuate dysregulation of GABAergic/glutamatergic transcription in murine succinate semialdehyde dehydrogenase deficiency (SSADHD), a disorder of GABA metabolism

“…5), which was unexpected despite our previous demonstration of glutamate increase in the CNS of aldh5a1 −/− mice (Gupta et al 2004). A link between glutamatergic signaling and mTOR activation is beginning to emerge (Weston et al 2012b; Theilhaber et al 2013; Chen et al 2015; Rosenberg et al 2015). These observations are relevant to aldh5a1 −/− embryonic mice, in which neurotransmitter imbalances are evident as early as E13, a developmental period in which GABAergic neurotransmission is still excitatory with the potential for development of a heightened excitatory state that may predispose neural networks to epilepsy in the embryonic period (Jansen et al 2008).…”

The Role of Wnt/β-Catenin Signaling Pathway in Disrupted Hippocampal Neurogenesis of Temporal Lobe Epilepsy: A Potential Therapeutic Target?

“…After ECS treatment, increased levels of Wnt-2 and associated activated bcatenin signaling in the DG were detected in newly born neurons [96]. Following advancements in gene expression profiling technology, hippocampal and cortical changes of genes for b-catenin signaling components, such as gene for b-catenin (CTNNB1), SFRP2, transducer DVL3 and genes for Frizzled ligands WNT2, WNT5A, and WNT10A, have been confirmed by microarray in response to hypoxic seizure in rodent models of epilepsy [97].…”