Chengwen Zhou, PhD - US grants

  Seizures affect almost 3 million peoples in US and in two thirds of patients, the causes are not known (possible genetic origins). Idiopathic generalized epilepsy(IGE) has been recognized as its genetic origins which include many single-nucleotide polymorphisms (SNPs) or mutation of ionotropic receptors, such as GABAergic receptor (GABAR) subunit mutations (Gabrg2Q390X and Gabra1A322D) linked to severe Dravet epilepsy syndrome and child absence epilepsy, and cognitive comorbidity in patients. In contrast to acquired seizures study, IGE seizure and epileptogenesis mechanism remains largely elusive. Moreover, seizures and sleep influence/interact with each other in their physiology mechanism, which imposes a challenge to IGE study and patient treatment. In one recent human patient study, sleep-like slow-wave oscillation has been shown to facilitate epileptic seizure activity. Therefore, we hypothesize that sleep-related slow-wave hyperpolarization-depolarization oscillation(SWO) can drive homeostatic potentiation(HSP) of excitatory synaptic currents, not inhibitory synaptic currents in cortical neurons of thalamocortical circuitry in IGE animal models with Gabrg2Q390X or Gabra1A322D mutation, and therefore create an escaped excitatory synaptic currents (without balancing from inhibitory synaptic currents) in cortical neurons during sleep and sleep-wake transition. This critical step of gabaergic current HSP impairment induced by SWOs can lead to seizure occurrence/initiation and also contribute to epileptogenesis in IGE models. This work will fill a critical void in our understanding of seizure mechanism, plus epileptogenesis, and potentially generate a new seizure therapy. First, we will study whether SWO-induced HSP of inhibitory GABAR-mediated currents is impaired, but not excitatory AMPAR-mediated currents in layer V-VI cortical neurons in vitro from heterozygous Gabrg2+/Q390X or Gabra1+/A322D knock-in mice and whether this impairment results in neuronal elevated firing. Second, we will determine whether light-induced SWOs in vivo causally initiate epileptic activity in cortex from mice expressing halorhodopsin (NpHR) and Gabrg2Q390X or Gabra1A322D mutation. Last, we will use a retinoid acid synthesis blocker DEAB to maintain the dynamic HSP balance between synaptic excitatory and inhibitory currents during SWOs in IGE models, which will provide a proof of principle for a potential seizure therapy. The information generated in these studies will substantially alter our view of seizure/epileptogenesis regarding its interaction with sleep waves and eventually lead to a new seizure therapy in IGE patients.

Seizures affect more than 3 million people in US, creating tremendous burdens to patients and their families/communities. Some intractable seizures with genetic causes (idiopathic generalized epilepsy, IGE) are resistant to conventional antiepileptic drugs. Although major progress has been made regarding mechanisms of acquired epilepsy, the causes for IGE remain elusive. We have not completely understood how the balance between synaptic/neuron excitation and inhibition is dynamically impaired under some conditions for IGE models. Moreover, functional MRI studies on seizures undeniably indicate that whole-brain networks (cortical and remote subcortical nodes) are involved during epileptic activity, suggesting that seizures are the emerging consequence of whole-brain epileptic network activity at the microscopic, mesoscopic, and macroscopic scales. However, it still remains challenging for clinical researchers to forecast how epileptic network nodes interact at network levels to generate the high-voltage spike-wave discharges (SWDs) during seizures. Specifically, no previous studies have ever focused on exactly how seizure onset and epileptic activity in IGE models are initiated through the interaction between epileptic network nodes at the network level, why seizures in human epileptic patients mostly occur during sleep-wake transition/quiet-awake period, and why seizure- presage conditions such as emotional prodromic aura phenomena can cause seizures in both acquired epilepsy and IGE patients. Thus, we hypothesize that subcortical nodes within epileptic network nodes, specifically anterior hypothalamus nucleus and medial amygdala, control cortical disfacilitation (neurons are hyperpolarized due to the absence of excitatory synaptic activity(Contreras et al., 1996; Timofeev et al., 1996; 2001)) during sleep-wake transition/quiet-awake period and other emotional prodromic auras. The resulting cortical disfacilitation prompts high-voltage slow-wave oscillations (SWOs), which hemostatically potentiate synaptic excitation (not inhibition) of epileptic neuron ensembles/engrams in the cortex. Eventually, these chain events lead to cortical neuron synchronous firing within epileptic network to trigger seizure onset and SWDs. It is the preceding cortical disfacilitation state in our IGE mouse models (present during sleep-wake transition/quiet-awake period and some emotion prodromic aura states) that consequently controls seizure onset and epileptic activity, which offers the network mechanism for IGE models. This proposal will use transgenic mice with neuron GFP expression (driven by activity dependent c-Fos promoter) to identify the epileptic network nodes in both cortex and subcortical structures in heterozygous Gabrg2Q390X or Gabra1A322D KI mice and determine whether the anterior hypothalamus and medial amygdala can cause cortical disfacilitation with optogenetic stimulation in vivo in these KI mice(neuron expressing ChR2/halorhodopsin driven by c-Fos promoter), which eventually induces SWOs and instigates epileptic SWDs in the cortex and generate seizures. New drugs for IGE treatment are proposed for a proof of principle study.