The LRRC8-mediated volume-regulated anion channel is altered in glaucoma

Xavier Gasull,Maria Isabel Canut,Marta Castany,Núria Comes,Aida Castellanos,Raúl Estévez,Alba Andrés-Bilbé,Mikel Rezola,Teresa Borrás

doi:10.1038/s41598-019-41524-3

Abstract

Regulation of cellular volume is an essential process to balance volume changes during cell proliferation and migration or when intracellular osmolality increases due to transepithelial transport. We previously characterized the key role of volume-regulated anion channels (VRAC) in the modulation of the volume of trabecular meshwork (TM) cells and, in turn, the aqueous humour (AH) outflow from the eye. The balance between the secretion and the drainage of AH determines the intraocular pressure (IOP) that is the major casual risk factor for glaucoma. Glaucoma is an ocular disease that causes irreversible blindness due to the degeneration of retinal ganglion cells. The recent identification of Leucine-Rich Repeat-Containing 8 (LRRC8A-E) proteins as the molecular components of VRAC opens the field to elucidate their function in the physiology of TM and glaucoma. Human TM cells derived from non-glaucomatous donors and from open-angle glaucoma patients were used to determine the expression and the functional activity of LRRC8-mediated channels. Expression levels of LRRC8A-E subunits were decreased in HTM glaucomatous cells compared to normotensive HTM cells. Consequently, the activity of VRAC currents and volume regulation of TM cells were significantly affected. Impaired cell volume regulation will likely contribute to altered aqueous outflow and intraocular pressure.

Highlights

Regulation of cellular volume is an essential process to balance volume changes during cell proliferation and migration or when intracellular osmolality increases due to transepithelial transport
Cell types were validated by quantifying Myocilin (MYOC) mRNA/protein in control HTM-5 cells treated with Dexamethasone (DEX) and the expression levels of glaucoma-related genes in glaucomatous HTM-3 cells
Previously demonstrated the participation of this channel in volume regulation of trabecular meshwork (TM) cells and aqueous outflow[5,6] but it was not until recently that LRRC8 proteins have been identified as the molecular components of VRAC15,16

Summary

Introduction

Regulation of cellular volume is an essential process to balance volume changes during cell proliferation and migration or when intracellular osmolality increases due to transepithelial transport. We previously characterized the key role of volume-regulated anion channels (VRAC) in the modulation of the volume of trabecular meshwork (TM) cells and, in turn, the aqueous humour (AH) outflow from the eye. Glaucoma is a chronic disease in which retinal ganglion cell degeneration leads to an optic nerve damage that results in visual field loss. This group of optic neuropathies represent a significant cause of blindness worldwide[1]. We and others have described how BKCa and VRAC ion channels can modulate aqueous outflow facility as a consequence of regulating the volume of trabecular cells[5,6,12]. The well-described electrophysiological properties of VRAC are outwardly rectification, inactivation at large depolarized potentials and iodide over chloride selectivity[13] while its molecular identity has been highly controversial for decades[14]

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Conclusion