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

Abstract

Objective: KCNA1 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.

Methods: CRISPR/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.

Results: Zebrafish 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.

Significance: We 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.

Keywords: KCNA1; carbamazepine; epilepsy; episodic ataxia type 1; zebrafish.