Gene Therapy for Epilepsy through Enhancing Inhibition with High-Frequency Activation of GABAergic Neurons in Mice

Description

Epilepsy is a chronic central nervous system disorder. Epilepsy patients may suddenly lose consciousness and have involuntary convulsive seizures. Seizures often cause physical injuries and psychological burdens; long-term seizures can impair patients' intelligence and directly cause deaths (1). More than 9 million people in China and about 1% of the Hong Kong population experience epileptic seizures (2, 3). Nearly a quarter of patients continue to have seizures after receiving antiepileptic drug treatment or surgery (4, 5). Epilepsy is related to the imbalance between inhibition and excitation of the brain (6). One of the strategies for the treatment of epilepsy is enhancing the inhibition. We recently found that high-frequency laser stimulation (HFLS) of GABAergic neurons enhanced the inhibition, reflecting from the suppressed auditory response under in-vivo preparation. We are aiming at manipulating the plasticity of inhibitory circuits to help cure epilepsy in mice. In this proposed project, we hypothesize that 1) high-frequency activation of GABAergic neurons enhances their inhibition on their output neurons, and 2) this enhancement of inhibition help rebalancing between inhibition and excitation of the brain, leading to the treatment of epilepsy in the long term. In the proposed study, we will test the above hypotheses by examining the enhanced inhibition using patch-clamp recording under in-vivo preparation. We have developed the viral vectors for gene therapy of optogenetics and chemogenetics and confirmed their permeability of the blood-brain barrier (BBB). We will deliver intravenously adeno-associated virus (AAV) carrying opsins or Gq‐coupled human muscarinic receptor hM3Dq (hM3D(Gq)) to approach the inhibitory neurons in our epileptic mouse model after injecting kainic acid (KA) into the mouse hippocampus. Once the mouse shows stably spontaneous seizures, we will apply HFLSto the brain or administrate hM3D(Gq)) agonist clozapine-N-oxide (CNO) to activate theGABAergic inhibitory neurons. We predict that the HFLS of GABAergic neurons will induce their high-frequency firing and thereby potentiate their inhibition to the postsynaptic-excitatory neurons while low-frequency laser stimulation (LFLS) not. This potentiation will generate a long-term inhibition effect on seizures. Likewise, oral CNO administration will activate theGABAergic neurons and suppress epileptic activities. The enhanced inhibition, eitheroptogenetically or chemogenetically, is supposedly long term; we expect that the suppression of epilepsy will last for a period after the treatment. The proposed gene therapies, if successful, will bring hopes to refractory epileptic patients who do not respond to current drugs.