kcna1a mutant zebrafish model episodic ataxia type 1 (EA1) with epilepsy and show response to first‐line therapy carbamazepine

Abstract

AbstractObjectiveKCNA1 mutations are associated with a rare neurological movement disorder known as episodic ataxia type 1 (EA1), and epilepsy is a common comorbidity. Current medications provide only partial relief for ataxia and/or seizures, making new drugs needed. Here, we characterized zebrafish kcna1a−/− as a model of EA1 with epilepsy and compared the efficacy of the first‐line therapy carbamazepine in kcna1a−/− zebrafish to Kcna1−/− rodents.MethodsCRISPR/Cas9 mutagenesis was used to introduce a mutation in the sixth transmembrane segment of the zebrafish Kcna1 protein. Behavioral and electrophysiological assays were performed on kcna1a−/− larvae to assess ataxia‐ and epilepsy‐related phenotypes. Real‐time quantitative polymerase chain reaction (qPCR) was conducted to measure mRNA levels of brain hyperexcitability markers in kcna1a−/− larvae, followed by bioenergetics profiling to evaluate metabolic function. Drug efficacies were tested using behavioral and electrophysiological assessments, as well as seizure frequency in kcna1a−/− zebrafish and Kcna1−/− mice, respectively.ResultsZebrafish kcna1a−/− larvae showed uncoordinated movements and locomotor deficits, along with scoliosis and increased mortality. The mutants also exhibited impaired startle responses when exposed to light–dark flashes and acoustic stimulation as well as hyperexcitability as measured by extracellular field recordings and upregulated fosab transcripts. Neural vglut2a and gad1b transcript levels were disrupted in kcna1a−/− larvae, indicative of a neuronal excitatory/inhibitory imbalance, as well as a significant reduction in cellular respiration in kcna1a−/−, consistent with dysregulation of neurometabolism. Notably, carbamazepine suppressed the impaired startle response and brain hyperexcitability in kcna1a−/− zebrafish but had no effect on the seizure frequency in Kcna1−/− mice, suggesting that this EA1 zebrafish model might better translate to humans than rodents.SignificanceWe conclude that zebrafish kcna1a−/− show ataxia and epilepsy‐related phenotypes and are responsive to carbamazepine treatment, consistent with EA1 patients. These findings suggest that kcna1−/− zebrafish are a useful model for drug screening as well as studying the underlying disease biology.