Loss of glutamate transportereaat2aleads to aberrant neuronal excitability, recurrent epileptic seizures and hypoactivity

Abstract

Astroglial excitatory amino acid transporter 2 (EAAT2, GLT-1, SLC1A2) regulates the duration and extent of neuronal excitation by removing glutamate from the synaptic cleft. Human patients with altered EAAT2 function exhibit epileptic seizures, suggesting an important role for astroglial glutamate transporters in balancing neuronal excitability. To study the impact of EAAT2 function at the neural network levels, we generated eaat2a mutant zebrafish. We observed that eaat2a-/- mutant zebrafish larvae display recurrent spontaneous and light-induced seizures in neurons and astroglia, which coincide with an abrupt increase in extracellular glutamate levels. In stark contrast to this hyperexcitability, basal brain activity was surprisingly reduced in eaat2a-/- mutant animals, which manifested in decreased locomotion, neuronal and astroglial calcium signals. Our results reveal an unexpected key role of the astroglial EAAT2a in balancing brain excitability, affecting both neuronal and astroglial network activity.

Marigold: A machine learning-based web app for zebrafish pose tracking

“…Both head-and tail-stimulated slc1a2b tk57/tk57 embryos reach the maximum rostral-caudal angle later in the response than wild-type embryos, which could explain why no touch location differences were found for the maximum angle of slc1a2b tk57/tk57 responses. Although slc1a2b is not expressed in the Mauthner cell, slc1a2bexpressing glial cells surround the Mauthner array at 48 hpf (Hotz et al, 2022;McKeown et al, 2012). Based on the data presented here, we propose that the disrupted kinematic profile of slc1a2b tk57/tk57 embryos may be due to a reactivation of escape circuitry late into the response.…”

“…Interestingly, slc1a2b mutants harboring nonsense mutations are able to swim spontaneously at 5 dpf (Hotz et al, 2022), whereas the slc1a2b tk57/tk57 allele described here and in McKeown et al, 2012 is fully paralyzed by 96 hpf. This difference could be explained by the nature of the mutations; premature termination codons generated using CRISPR-Cas9 have been shown to trigger genetic compensation via transcriptional adaptation (El-Brolosy et al, 2019;Sztal & Stainier, 2020).…”

“…This mutant, henceforth referred to as slc1a2b tk57/tk57 , harbors a loss-of-function missense mutation in slc1a2b (Ensembl ID: ENSDARG00000102453) located on chromosome 25, which encodes Eaat2b, a glutamate transporter predominantly expressed in astroglia (Hotz et al, 2022;McKeown et al, 2012). We note that this gene and its protein product have also been referred to as slc1a2a and Eaat2a, respectively (Gesemann et al, 2010;Hotz et al, 2022); however, current genome databases indicate that these particular identifiers refer to a distinct gene found on chromosome 7 (Ensembl ID: ENSDARG00000052138), and its protein product (Breuer et al, 2019). slc1a2b tk57/tk57 embryos demonstrate a hyperactive response to touch by 48 hpf; however, the larvae are effectively paralyzed and shorter along the rostral-caudal axis by 96 hpf (McKeown et al, 2012).…”

“…Using Marigold, we investigated novel aspects of the techno trousers (tnt) locomotor phenotype (Granato et al, 1996;McKeown et al, 2012). This mutant, henceforth referred to as slc1a2b tk57/tk57 , harbors a loss-of-function missense mutation in slc1a2b (Ensembl ID: ENSDARG00000102453) located on chromosome 25, which encodes Eaat2b, a glutamate transporter predominantly expressed in astroglia (Hotz et al, 2022;McKeown et al, 2012). We note that this gene and its protein product have also been referred to as slc1a2a and Eaat2a, respectively (Gesemann et al, 2010;Hotz et al, 2022); however, current genome databases indicate that these particular identifiers refer to a distinct gene found on chromosome 7 (Ensembl ID: ENSDARG00000052138), and its protein product (Breuer et al, 2019).…”

A critical review of zebrafish schizophrenia models: Time for validation?

“…Although hyperlocomotor activity is a surrogate readout of seizure-like behaviour in zebrafish (validated usually with LFP recordings) (Afrikanova et al, 2013;Baraban, Dinday and Hortopan, 2013), a recent study found that larvae with seizure-like discharges were hypoactive in the locomotor test (Hotz et al, 2021). Suggesting that the type of seizures may inform the behavioural readout i.e.…”