kcna1a mutant zebrafish as a model of episodic ataxia type 1 and epilepsy

Abstract

ABSTRACTObjectiveKCNA1 mutations are associated with a rare neurological movement disorder known as episodic ataxia type 1 (EA1), with epilepsy as a common comorbidity. Current medications only provide partial relief to ataxia and/or seizures, making new drugs needed. Here, we investigate the utility of zebrafish kcna1a−/− as a model of EA1 with epilepsy by characterizing its phenotype and comparing the efficacy of the first-line therapy carbamazepine in kcna1a−/− zebrafish to Kcna1−/− rodents.MethodsWe used CRISPR/Cas9 mutagenesis to introduce a mutation in the sixth segment of the zebrafish Kcna1 protein. Behavioral and electrophysiological assays were performed on kcna1a−/− larvae to assess ataxia- and epilepsy-related phenotypes. We also carried out real-time qPCRs to measure the transcript levels of brain hyperexcitability markers and bioenergetic profiling of kcna1a−/− larvae to evaluate their metabolic health. Carbamazepine efficacy was tested using behavioral assessments in kcna1a−/− zebrafish and seizure frequency in Kcna1−/− mice.Resultskcna1a−/− zebrafish showed uncoordinated movements and locomotor deficits. The mutants also exhibited impaired startle responses when exposed to light-dark flashes and acoustic stimulation. Extracellular field recordings and upregulated fosab transcript levels showed hyperexcitability of the kcna1a−/− brain. Further, vglut2a and gad1b transcript levels were altered, indicative of neuronal excitatory/inhibitory imbalance in the kcna1a−/− brain. Metabolic health was also compromised in kcna1a−/− as seen by a significant reduction in measures of cellular respiration. Notably, carbamazepine reduced the impaired startle response in kcna1a−/− zebrafish but had no effect on the seizure frequency in Kcna1−/− mice, suggesting that this EA1 zebrafish model might better translate to human efficacy compared to rodents.SignificanceWe conclude that zebrafish kcna1a−/− larvae show ataxia and epilepsy-related phenotypes and that they are responsive to carbamazepine treatment, consistent with EA1 patients. This study supports the notion that these zebrafish disease models can be useful for drug screening as well as studying the underlying disease biology.KEY POINTSZebrafish kcna1a−/− larvae display dynamic behavioral changes, along with ataxia-like uncoordinated movements and brain hyperexcitabilitykcna1a−/− larvae have dysfunctional neuronal excitatory/inhibitory balance and perturbed metabolic healthSimilar to its effectiveness in patients, carbamazepine treatment improves behavioral deficits in kcna1a−/− larvae