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The ubiquitous volume-regulated anion channels (VRACs), which are composed of LRRC8 proteins, facilitate cell volume homeostasis, and contribute to many other physiological processes. Prior studies demonstrated that treatment with non-specific VRAC blockers, or brain-specific deletion of the essential VRAC subunit LRRC8A, are highly protective in rodent stroke. In this work, we tested the widely accepted idea that harmful effects of VRACs in the brain are mediated by pathological release of the excitatory transmitter glutamate. We used two molecular genetic strategies to ablate LRRC8A expression in either brain astrocytes only (inducible deletion ofLrrc8aflox/floxwithAldh1l1CreERT2) or the majority of brain cells (neurons, astrocytes, and oligodendrocytes withNestinCre). To produce stroke, genetically modified mice were subjected to a 40-minute occlusion of the middle cerebral artery. The inducible deletion of astrocytic LRRC8A yielded no histological or behavioral protection. In contrast, the brain-wide LRRC8A knockout reduced ischemic infarction by ~50% in both heterozygotes (Het) and the fullLrrc8aknockout (KO) as compared to the controlLrrc8aflox/+genotype. However, despite identical brain damage, Het and KO mice dramatically differed in their VRAC activities. Het mice had full swelling-activated glutamate release, while KO animals showed its virtual absence. These new findings refute the notion that VRAC-mediated glutamate release plays significant role in ischemic brain injury.

This is the final version of the manuscript accepted to FASEB Journal. DOI: 10.1096/fj.202002745R

This is a revised version of the previously registered manuscript https://osf.io/wcd2n

The leucine-rich repeat-containing family 8 member A (LRRC8A) is an essential subunit of the volume-regulated anion channel (VRAC). VRAC is critical for cell volume control, but its broader physiological functions remain under investigation. Recent studies in the field indicate that Lrrc8a disruption in brain astrocytes reduces neuronal excitability, impairs synaptic plasticity and memory, and protects against cerebral ischemia. In the present work, we generated the brain-wide conditional LRRC8A knock-out mice (LRRC8A bKO) using NestinCre-driven Lrrc8aflox/flox excision in neurons, astrocytes, and oligodendroglia. LRRC8A bKO animals were born close to the expected Mendelian ratio and developed without overt histological abnormalities, but, surprisingly, all died between 5 and 9 weeks of age with a seizure phenotype, which was confirmed by video and EEG recordings. Brain slice electrophysiology detected changes in the excitability of pyramidal cells and modified GABAergic inputs in the hippocampal CA1 region of LRRC8A bKO. LRRC8A-null hippocampi showed increased immunoreactivity of the astrocytic marker GFAP, indicating reactive astrogliosis. We also found decreased whole-brain protein levels of the GABA transporter GAT-1, the glutamate transporter GLT-1, and the astrocytic enzyme glutamine synthetase. Complementary HPLC assays identified reduction in the tissue levels of the glutamate and GABA precursor glutamine. Together, these findings suggest that VRAC provides vital control of brain excitability in mouse adolescence. VRAC deletion leads to a lethal phenotype involving progressive astrogliosis and dysregulation of astrocytic uptake and supply of amino acid neurotransmitters and their precursors.