LRRC8A/D-containing anion channels mediate swelling-activated taurine release in the mouse brain

Abstract

Volume-regulated anion channels (VRACs) are swelling-activated Cl- channels formed by heteromers of LRRC8 proteins (LRRC8A-E). VRACs mediate regulatory volume decrease by releasing Cl- and organic osmolytes, including taurine. In the brain, taurine functions as both an osmolyte and an inhibitory neuromodulator, acting as an agonist at glycine and GABAA receptors. Here, we used RNAi and genetically modified mice to (i) determine the contribution of LRRC8 subunits to swelling-activated taurine release, and (ii) test whether brain VRACs contribute to systemic osmoregulation. In astrocyte cultures lacking the essential VRAC subunit LRRC8A, swelling-activated [3H]taurine release was reduced by ~90%. Similarly, in vivo brain microdialysis revealed a [≥]90% reduction in swelling-activated taurine release in brain-wide LRRC8A knockout mice (bLRRC8A KO). RNAi experiments further confirmed LRRC8D as a key determinant of VRAC-mediated taurine release, with Lrrc8d knockdown reducing swelling activated [3H]taurine efflux by >50%. RNA-seq revealed enrichment of Lrrc8d in the hypothalamus, where astrocytic taurine release is proposed to inhibit magnocellular neurons and suppress arginine vasopressin secretion during hypoosmotic conditions. We therefore tested whether disrupting brain VRACs impairs recovery from systemic hypoosmotic stress. bLRRC8A KO mice and mice with gene trap-mediated LRRC8D depletion were challenged with an intraperitoneal injection of sterile water (7.5% body weight, under anesthesia), and serum osmolality was monitored over time. Unexpectedly, neither model showed impaired recovery from hypoosmotic challenge. Overall, this study identifies LRRC8A/D-containing VRACs as the primary conduit for swelling-activated taurine release in the brain, yet indicates that this pathway is not essential for maintaining systemic fluid-electrolyte homeostasis.