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Yang J, Chen J, Liu Y, Chen KH, Baraban JM, Qiu Z. Ventral tegmental area astrocytes modulate cocaine reward by tonically releasing GABA. Neuron 2023; 111:1104-1117.e6. [PMID: 36681074 PMCID: PMC10079641 DOI: 10.1016/j.neuron.2022.12.033] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Revised: 11/30/2022] [Accepted: 12/27/2022] [Indexed: 01/21/2023]
Abstract
Addictive drugs increase ventral tegmental area (VTA) dopamine (DA) neuron activity through distinct cellular mechanisms, one of which involves disinhibition of DA neurons by inhibiting local GABA neurons. How drugs regulate VTA GABA neuron activity and drive addictive behaviors remains poorly understood. Here, we show that astrocytes control VTA GABA neuron activity in cocaine reward via tonic inhibition in mice. Repeated cocaine exposure potentiates astrocytic tonic GABA release through volume-regulated anion channels (VRACs) and augments tonic inhibition of VTA GABA neurons, thus downregulating their activities and disinhibiting nucleus accumbens (NAc) projecting DA neurons. Attenuation of tonic inhibition by either deleting Swell1 (Lrrc8a), the obligatory subunit of VRACs, in VTA astrocytes or disrupting δ subunit of GABAA receptors in VTA GABA neurons reduces cocaine-evoked changes in neuron activity, locomotion, and reward behaviors in mice. Together, our findings reveal the critical role of astrocytes in regulating the VTA local circuit and cocaine reward.
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Affiliation(s)
- Junhua Yang
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Jianan Chen
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Yongqing Liu
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Kevin Hong Chen
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Jay M Baraban
- Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Zhaozhu Qiu
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA; Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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2
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Ghouli MR, Jonak CR, Sah R, Fiacco TA, Binder DK. Regulation of the Volume-Regulated Anion Channel Pore-Forming Subunit LRRC8A in the Intrahippocampal Kainic Acid Model of Mesial Temporal Lobe Epilepsy. ASN Neuro 2023; 15:17590914231184072. [PMID: 37410995 PMCID: PMC10331354 DOI: 10.1177/17590914231184072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2023] [Revised: 05/22/2023] [Accepted: 06/07/2023] [Indexed: 07/08/2023] Open
Abstract
Volume-regulated anion channels (VRACs) are a group of ubiquitously expressed outwardly-rectifying anion channels that sense increases in cell volume and act to return cells to baseline volume through an efflux of anions and organic osmolytes, including glutamate. Because cell swelling, increased extracellular glutamate levels, and reduction of the brain extracellular space (ECS) all occur during seizure generation, we set out to determine whether VRACs are dysregulated throughout mesial temporal lobe epilepsy (MTLE), the most common form of adult epilepsy. To accomplish this, we employed the IHKA experimental model of MTLE, and probed for the expression of LRRC8A, the essential pore-forming VRAC subunit, at acute, early-, mid-, and late-epileptogenic time points (1-, 7-, 14-, and 30-days post-IHKA, respectively). Western blot analysis revealed the upregulation of total dorsal hippocampal LRRC8A 14-days post-IHKA in both the ipsilateral and contralateral hippocampus. Immunohistochemical analyses showed an increased LRRC8A signal 7-days post-IHKA in both the ipsilateral and contralateral hippocampus, along with layer-specific changes 1-, 7-, and 30-days post-IHKA bilaterally. LRRC8A upregulation 1 day post-IHKA was observed primarily in astrocytes; however, some upregulation was also observed in neurons. Glutamate-GABA/glutamine cycle enzymes glutamic acid decarboxylase, glutaminase, and glutamine synthetase were also dysregulated at the 7-day timepoint post status epilepticus. The timepoint-dependent upregulation of total hippocampal LRRC8A and the possible subsequent increased efflux of glutamate in the epileptic hippocampus suggest that the dysregulation of astrocytic VRAC may play an important role in the development of epilepsy.
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Affiliation(s)
- Manolia R. Ghouli
- Division of Biomedical Sciences, School of Medicine, University of California—Riverside, Riverside, CA, USA
- Center for Glial-Neuronal Interactions, University of California—Riverside, Riverside, CA, USA
| | - Carrie R. Jonak
- Division of Biomedical Sciences, School of Medicine, University of California—Riverside, Riverside, CA, USA
- Center for Glial-Neuronal Interactions, University of California—Riverside, Riverside, CA, USA
| | - Rajan Sah
- Department of Internal Medicine, Washington University School of Medicine, St. Louis, MO, USA
| | - Todd A. Fiacco
- Center for Glial-Neuronal Interactions, University of California—Riverside, Riverside, CA, USA
- Department of Cell Biology and Neuroscience, University of California—Riverside, Riverside, CA, USA
| | - Devin K. Binder
- Division of Biomedical Sciences, School of Medicine, University of California—Riverside, Riverside, CA, USA
- Center for Glial-Neuronal Interactions, University of California—Riverside, Riverside, CA, USA
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3
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Yamada K, Ding WG, Omatsu-Kanbe M, Toyoda F, Tsuji S, Katsura D, Kimura F, Matsuura H, Murakami T. Expression and functional maintenance of volume-regulated anion channels in myometrial smooth muscles of pregnant mice. Exp Anim 2022; 71:123-130. [PMID: 34789619 PMCID: PMC9130036 DOI: 10.1538/expanim.21-0111] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2021] [Accepted: 10/13/2021] [Indexed: 11/15/2022] Open
Abstract
Pregnancy causes changes in the uterus, such as increased cell volume and altered water content. However, the mechanisms that protect the structure and maintain the function of uterine smooth muscle cells against these changes during pregnancy have not been clarified. This study focused on the volume-regulated anion channel (VRAC), which opens with cell swelling under low osmotic pressure and releases Cl- ions and various organic osmolytes to resist cell swelling and regulates a wide range of biological processes such as cell death. In this study, myometrial smooth muscle (MSM) tissues and cells (MSMCs) were collected from non-pregnant and pregnant mice. Using western blotting and immunocytochemistry, leucine-rich repeat containing protein 8A (LRRC8A), an essential membrane protein that constitutes part of the VRAC, was determined to be diffused throughout MSMCs including in the cell membrane. Patch-clamp experiments were performed to investigate the electrophysiology of swelling-induced Cl- currents (ICl, swell) mediated by the VRAC. No significant changes between non-pregnancy and pregnancy groups were observed in either the expression density of LRRC8A or the current density of ICl, swell, however the presence of LRRC8A on the cell membrane was significantly increased in the third trimester of pregnancy compared to the non-pregnancy. This study suggests that the VRAC may play a role, such as maintaining cellular homeostasis in the pregnant MSM.
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Affiliation(s)
- Kazutaka Yamada
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
| | - Wei-Guang Ding
- Department of Physiology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga 520-2192, Japan
| | - Mariko Omatsu-Kanbe
- Department of Physiology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga 520-2192, Japan
| | - Futoshi Toyoda
- Department of Physiology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga 520-2192, Japan
| | - Shunichiro Tsuji
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
| | - Daisuke Katsura
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
| | - Fuminori Kimura
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
| | - Hiroshi Matsuura
- Department of Physiology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga 520-2192, Japan
| | - Takashi Murakami
- Department of Obstetrics and Gynecology, Shiga University of Medical Science, Setatsukinowa-cho, Otsu-shi, Shiga, 520-2192, Japan
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Rezola M, Castellanos A, Gasull X, Comes N. Functional Interaction Between Caveolin 1 and LRRC8-Mediated Volume-Regulated Anion Channel. Front Physiol 2021; 12:691045. [PMID: 34658903 PMCID: PMC8517123 DOI: 10.3389/fphys.2021.691045] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Accepted: 09/06/2021] [Indexed: 11/13/2022] Open
Abstract
Volume-regulated anion channel (VRAC), constituted by leucine-rich repeat-containing 8 (LRRC8) heteromers, is crucial for volume homeostasis in vertebrate cells. This widely expressed channel has been associated with membrane potential modulation, proliferation, migration, apoptosis, and glutamate release. VRAC is activated by cell swelling and by low cytoplasmic ionic strength or intracellular guanosine 5′-O-(3-thiotriphosphate) (GTP-γS) in isotonic conditions. Despite the substantial number of studies that characterized the biophysical properties of VRAC, its mechanism of activation remains a mystery. Different evidence suggests a possible effect of caveolins in modulating VRAC activity: (1) Caveolin 1 (Cav1)-deficient cells display insignificant swelling-induced Cl– currents mediated by VRAC, which can be restored by Cav1 expression; (2) Caveolin 3 (Cav3) knockout mice display reduced VRAC currents; and (3) Interaction between LRRC8A, the essential subunit for VRAC, and Cav3 has been found in transfected human embryonic kidney 293 (HEK 293) cells. In this study, we demonstrate a physical interaction between endogenous LRRC8A and Cav1 proteins, that is enhanced by hypotonic stimulation, suggesting that this will increase the availability of the channel to Cav1. In addition, LRRC8A targets plasma membrane regions outside caveolae of HEK 293 cells where it associates with non-caveolar Cav1. We propose that a rise in cell membrane tension by hypotonicity would flatten caveolae, as described previously, increasing the amount of Cav1 outside of caveolar structures interacting with VRAC. Besides, the expression of Cav1 in HEK Cav1- cells increases VRAC current density without changing the main biophysical properties of the channel. The present study provides further evidence on the relevance of Cav1 on the activation of endothelial VRAC through a functional molecular interaction.
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Affiliation(s)
- Mikel Rezola
- Neurophysiology Laboratory, Physiology Unit, Department of Biomedicine, Medical School, Institute of Neurosciences, University of Barcelona, Barcelona, Spain
| | - Aida Castellanos
- Neurophysiology Laboratory, Physiology Unit, Department of Biomedicine, Medical School, Institute of Neurosciences, University of Barcelona, Barcelona, Spain
| | - Xavier Gasull
- Neurophysiology Laboratory, Physiology Unit, Department of Biomedicine, Medical School, Institute of Neurosciences, University of Barcelona, Barcelona, Spain.,Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Núria Comes
- Neurophysiology Laboratory, Physiology Unit, Department of Biomedicine, Medical School, Institute of Neurosciences, University of Barcelona, Barcelona, Spain.,Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
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5
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Liu Y, Zhang H, Men H, Du Y, Xiao Z, Zhang F, Huang D, Du X, Gamper N, Zhang H. Volume-regulated Cl - current: contributions of distinct Cl - channels and localized Ca 2+ signals. Am J Physiol Cell Physiol 2019; 317:C466-C480. [PMID: 31242393 DOI: 10.1152/ajpcell.00507.2018] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The swelling-activated chloride current (ICl,swell) is induced when a cell swells and plays a central role in maintaining cell volume in response to osmotic stress. The major contributor of ICl,swell is the volume-regulated anion channel (VRAC). Leucine-rich repeat containing 8A (LRRC8A; SWELL1) was recently identified as an essential component of VRAC, but the mechanisms of VRAC activation are still largely unknown; moreover, other Cl- channels, such as anoctamin 1 (ANO1), were also suggested to contribute to ICl,swell. In this present study, we investigated the roles of LRRC8A and ANO1 in activation of ICl,swell; we also explored the role of intracellular Ca2+ in ICl,swell activation. We used a CRISPR/Cas9 gene editing approach, electrophysiology, live fluorescent imaging, selective pharmacology, and other approaches to show that both LRRC8A and ANO1 can be activated by cell swelling in HEK293 cells. Yet, both channels contribute biophysically and pharmacologically distinct components to ICl,swell, with LRRC8A being the major component. Cell swelling induced oscillatory Ca2+ transients, and these Ca2+ signals were required to activate both the LRRC8A- and ANO1-dependent components of ICl,swell. Both ICl,swell components required localized rather than global Ca2+ for activation. Interestingly, while intracellular Ca2+ was necessary and sufficient to activate ANO1, it was necessary but not sufficient to activate LRRC8A-mediated currents. Finally, Ca2+ transients linked to the ICl,swell activation were mediated by the G protein-coupled receptor-independent PLC isoforms.
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Affiliation(s)
- Yani Liu
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China.,Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao, China
| | - Huiran Zhang
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China.,Department of Pulmonary Medicine, the Second Hospital of Hebei Medical University, Shijiazhuang, China
| | - Hongchao Men
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China
| | - Yuwei Du
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China
| | - Ziqian Xiao
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China
| | - Fan Zhang
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China
| | - Dongyang Huang
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China
| | - Xiaona Du
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China
| | - Nikita Gamper
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China.,School of Biomedical Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, United Kingdom
| | - Hailin Zhang
- Department of Pharmacology, Hebei Medical University, The Key Laboratory of Neural and Vascular Biology, Ministry of Education, Shijiazhuang, China.,The Key Laboratory of New Drug Pharmacology and Toxicology, Shijiazhuang, China
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6
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Wilson CS, Bach MD, Ashkavand Z, Norman KR, Martino N, Adam AP, Mongin AA. Metabolic constraints of swelling-activated glutamate release in astrocytes and their implication for ischemic tissue damage. J Neurochem 2019; 151:255-272. [PMID: 31032919 DOI: 10.1111/jnc.14711] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2018] [Revised: 03/01/2019] [Accepted: 04/10/2019] [Indexed: 12/20/2022]
Abstract
Volume-regulated anion channel (VRAC) is a glutamate-permeable channel that is activated by physiological and pathological cell swelling and promotes ischemic brain damage. However, because VRAC opening requires cytosolic ATP, it is not clear if and how its activity is sustained in the metabolically compromised CNS. In the present study, we used cultured astrocytes - the cell type which shows prominent swelling in stroke - to model how metabolic stress and changes in gene expression may impact VRAC function in the ischemic and post-ischemic brain. The metabolic state of primary rat astrocytes was modified with chemical inhibitors and examined using luciferin-luciferase ATP assays and a Seahorse analyzer. Swelling-activated glutamate release was quantified with the radiotracer D-[3 H]aspartate. The specific contribution of VRAC to swelling-activated glutamate efflux was validated by RNAi knockdown of the essential subunit, leucine-rich repeat-containing 8A (LRRC8A); expression levels of VRAC components were measured with qRT-PCR. Using this methodology, we found that complete metabolic inhibition with the glycolysis blocker 2-deoxy-D-glucose and the mitochondrial poison sodium cyanide reduced astrocytic ATP levels by > 90% and abolished glutamate release from swollen cells (via VRAC). When only mitochondrial respiration was inhibited by cyanide or rotenone, the intracellular ATP levels and VRAC activity were largely preserved. Bypassing glycolysis by providing the mitochondrial substrates pyruvate and/or glutamine led to partial recovery of ATP levels and VRAC activity. Unexpectedly, the metabolic block of VRAC was overridden when ATP-depleted cells were exposed to extreme cell swelling (≥ 50% reduction in medium osmolarity). Twenty-four hour anoxic adaptation caused a moderate reduction in the expression levels of the VRAC component LRRC8A, but no significant changes in VRAC activity. Overall, our findings suggest that (i) astrocytic VRAC activity and metabolism can be sustained by low levels of glucose and (ii) the inhibitory influence of diminishing ATP levels and the stimulatory effect of cellular swelling are the two major factors that govern VRAC activity in the ischemic brain.
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Affiliation(s)
- Corinne S Wilson
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, New York, USA
| | - Martin D Bach
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, New York, USA
| | - Zahra Ashkavand
- Department of Regenerative and Cancer Cell Biology, Albany Medical College, Albany, New York, USA
| | - Kenneth R Norman
- Department of Regenerative and Cancer Cell Biology, Albany Medical College, Albany, New York, USA
| | - Nina Martino
- Department of Molecular and Cellular Physiology, Albany Medical College, Albany, New York, USA
| | - Alejandro P Adam
- Department of Molecular and Cellular Physiology, Albany Medical College, Albany, New York, USA
| | - Alexander A Mongin
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, New York, USA
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Netti V, Pizzoni A, Pérez-Domínguez M, Ford P, Pasantes-Morales H, Ramos-Mandujano G, Capurro C. Release of taurine and glutamate contributes to cell volume regulation in human retinal Müller cells: differences in modulation by calcium. J Neurophysiol 2018; 120:973-984. [PMID: 29790838 DOI: 10.1152/jn.00725.2017] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Neuronal activity in the retina generates osmotic gradients that lead to Müller cell swelling, followed by a regulatory volume decrease (RVD) response, partially due to the isoosmotic efflux of KCl and water. However, our previous studies in a human Müller cell line (MIO-M1) demonstrated that an important fraction of RVD may also involve the efflux of organic solutes. We also showed that RVD depends on the swelling-induced Ca2+ release from intracellular stores. Here we investigate the contribution of taurine (Tau) and glutamate (Glu), the most relevant amino acids in Müller cells, to RVD through the volume-regulated anion channel (VRAC), as well as their Ca2+ dependency in MIO-M1 cells. Swelling-induced [3H]Tau/[3H]Glu release was assessed by radiotracer assays and cell volume by fluorescence videomicroscopy. Results showed that cells exhibited an osmosensitive efflux of [3H]Tau and [3H]Glu (Tau > Glu) blunted by VRAC inhibitors 4-(2-butyl-6,7-dichloro-2-cyclopentylindan-1-on-5-yl)-oxybutyric acid and carbenoxolone reducing RVD. Only [3H]Tau efflux was mainly dependent on Ca2+ release from intracellular stores. RVD was unaffected in a Ca2+-free medium, probably due to Ca2+-independent Tau and Glu release, but was reduced by chelating intracellular Ca2+. The inhibition of phosphatidylinositol-3-kinase reduced [3H]Glu efflux but also the Ca2+-insensitive [3H]Tau fraction and decreased RVD, providing evidence of the relevance of this Ca2+-independent pathway. We propose that VRAC-mediated Tau and Glu release has a relevant role in RVD in Müller cells. The observed disparities in Ca2+ influence on amino acid release suggest the presence of VRAC isoforms that may differ in substrate selectivity and regulatory mechanisms, with important implications for retinal physiology. NEW & NOTEWORTHY The mechanisms for cell volume regulation in retinal Müller cells are still unknown. We show that swelling-induced taurine and glutamate release mediated by the volume-regulated anion channel (VRAC) largely contributes the to the regulatory volume decrease response in a human Müller cell line. Interestingly, the hypotonic-induced efflux of these amino acids exhibits disparities in Ca2+-dependent and -independent regulatory mechanisms, which strongly suggests that Müller cells may express different VRAC heteromers formed by the recently discovered leucine-rich repeat containing 8 (LRRC8) proteins.
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Affiliation(s)
- Vanina Netti
- Universidad de Buenos Aires, Facultad de Medicina. Departamento de Ciencias Fisiológicas, Laboratorio de Biomembranas , Buenos Aires , Argentina.,CONICET-Universidad de Buenos Aires. Instituto de Fisiología y Biofísica "Bernardo Houssay," Buenos Aires, Argentina
| | - Alejandro Pizzoni
- Universidad de Buenos Aires, Facultad de Medicina. Departamento de Ciencias Fisiológicas, Laboratorio de Biomembranas , Buenos Aires , Argentina.,CONICET-Universidad de Buenos Aires. Instituto de Fisiología y Biofísica "Bernardo Houssay," Buenos Aires, Argentina
| | - Martha Pérez-Domínguez
- Departamento de Medicina Genómica y Toxicología Ambiental, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Paula Ford
- Universidad de Buenos Aires, Facultad de Medicina. Departamento de Ciencias Fisiológicas, Laboratorio de Biomembranas , Buenos Aires , Argentina.,CONICET-Universidad de Buenos Aires. Instituto de Fisiología y Biofísica "Bernardo Houssay," Buenos Aires, Argentina
| | - Herminia Pasantes-Morales
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Gerardo Ramos-Mandujano
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad de México, México
| | - Claudia Capurro
- Universidad de Buenos Aires, Facultad de Medicina. Departamento de Ciencias Fisiológicas, Laboratorio de Biomembranas , Buenos Aires , Argentina.,CONICET-Universidad de Buenos Aires. Instituto de Fisiología y Biofísica "Bernardo Houssay," Buenos Aires, Argentina
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Rubino S, Bach MD, Schober AL, Lambert IH, Mongin AA. Downregulation of Leucine-Rich Repeat-Containing 8A Limits Proliferation and Increases Sensitivity of Glioblastoma to Temozolomide and Carmustine. Front Oncol 2018; 8:142. [PMID: 29868469 PMCID: PMC5949383 DOI: 10.3389/fonc.2018.00142] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2017] [Accepted: 04/18/2018] [Indexed: 12/18/2022] Open
Abstract
Background Glioblastoma (GBM) is the most common primary malignant brain tumor in adults. Ubiquitously expressed volume-regulated anion channels (VRAC) are thought to play a role in cell proliferation, migration, and apoptosis. VRAC are heteromeric channel complexes assembled from proteins belonging to the leucine-rich repeat-containing 8A (LRRC8A through E), among which LRRC8A plays an indispensable role. In the present work, we used an RNAi approach to test potential significance of VRAC and LRRC8A in GBM survival and sensitivity to chemotherapeutic agents. Methods Primary GBM cells were derived from a human surgical tissue sample. LRRC8A expression was determined with quantitative RT-PCR and downregulated using siRNA. The effects of LRRC8A knockdown on GBM cell viability, proliferation, and sensitivity to chemotherapeutic agents were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and Coulter counter assays. Cell cycle progression was further explored using fluorescence-activated cell sorting analysis of propidium iodide-stained cells. Results Temozolomide (TMZ), carmustine, and cisplatin reduced GBM cell survival with the IC50 values of ~1,250, 320, and 30 µM, respectively. Two of three tested gene-specific siRNA constructs, siLRRC8A_3 and siLRRC8A_6, downregulated LRRC8A expression by >80% and significantly reduced GBM cell numbers. The most potent siLRRC8A_3 itself reduced viable cell numbers by ≥50%, and significantly increased toxicity of the sub-IC50 concentrations of TMZ (570 µM) and carmustine (167 µM). In contrast, the effects of siLRRC8A_3 and cisplatin (32 µM) were not additive, most likely because cisplatin uptake is VRAC-dependent. The results obtained in primary GBM cells were qualitatively recapitulated in U251 human GBM cell line. Conclusion Downregulation of LRRC8A expression reduces GBM cell proliferation and increases sensitivity to the clinically used TMZ and carmustine. These findings indicate that VRAC represents a potential target for the treatment of GBM, alone or in combination with the current standard-of-care.
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Affiliation(s)
- Sebastian Rubino
- Department of Neurosurgery, Albany Medical Center, Albany, NY, United States.,Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, NY, United States
| | - Martin D Bach
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Alexandra L Schober
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, NY, United States
| | - Ian H Lambert
- Section for Cell Biology and Physiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Alexander A Mongin
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, NY, United States
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Gaitán-Peñas H, Pusch M, Estévez R. Expression of LRRC8/VRAC Currents in Xenopus Oocytes: Advantages and Caveats. Int J Mol Sci 2018; 19:ijms19030719. [PMID: 29498698 PMCID: PMC5877580 DOI: 10.3390/ijms19030719] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2018] [Revised: 02/25/2018] [Accepted: 02/28/2018] [Indexed: 12/26/2022] Open
Abstract
Volume-regulated anion channels (VRACs) play a role in controlling cell volume by opening upon cell swelling. Apart from controlling cell volume, their function is important in many other physiological processes, such as transport of metabolites or drugs, and extracellular signal transduction. VRACs are formed by heteromers of the pannexin homologous protein LRRC8A (also named Swell1) with other LRRC8 members (B, C, D, and E). LRRC8 proteins are difficult to study, since they are expressed in all cells of our body, and the channel stoichiometry can be changed by overexpression, resulting in non-functional heteromers. Two different strategies have been developed to overcome this issue: complementation by transient transfection of LRRC8 genome-edited cell lines, and reconstitution in lipid bilayers. Alternatively, we have used Xenopus oocytes as a simple system to study LRRC8 proteins. Here, we have reviewed all previous experiments that have been performed with VRAC and LRRC8 proteins in Xenopus oocytes. We also discuss future strategies that may be used to perform structure-function analysis of the VRAC in oocytes and other systems, in order to understand its role in controlling multiple physiological functions.
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Affiliation(s)
- Héctor Gaitán-Peñas
- Facultat de Medicina, Departament de Ciències Fisiològiques, Universitat de Barcelona-IDIBELL, C/Feixa Llarga s/n, L'Hospitalet de Llobregat, 08907 Barcelona, Spain.
- Centro de Investigación en red de Enfermedades Raras (CIBERER), Instituto de Salud Carlos III (ISCIII), 08907 Barcelona, Spain.
| | - Michael Pusch
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche (CNR), I-16149 Genova, Italy.
| | - Raúl Estévez
- Facultat de Medicina, Departament de Ciències Fisiològiques, Universitat de Barcelona-IDIBELL, C/Feixa Llarga s/n, L'Hospitalet de Llobregat, 08907 Barcelona, Spain.
- Centro de Investigación en red de Enfermedades Raras (CIBERER), Instituto de Salud Carlos III (ISCIII), 08907 Barcelona, Spain.
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Schober AL, Wilson CS, Mongin AA. Molecular composition and heterogeneity of the LRRC8-containing swelling-activated osmolyte channels in primary rat astrocytes. J Physiol 2017; 595:6939-6951. [PMID: 28833202 DOI: 10.1113/jp275053] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2017] [Accepted: 08/14/2017] [Indexed: 01/27/2023] Open
Abstract
KEY POINTS The volume-regulated anion channel (VRAC) is a swelling-activated chloride channel that is permeable to inorganic anions and a variety of small organic molecules. VRAC is formed via heteromerization of LRRC8 proteins, among which LRRC8A is essential, while LRRC8B/C/D/E serve as exchangeable complementary partners. We used an RNAi approach and radiotracer assays to explore which LRRC8 isoforms contribute to swelling-activated release of diverse organic osmolytes in rat astrocytes. Efflux of uncharged osmolytes (myo-inositol and taurine) was suppressed by deletion of LRRC8A or LRRC8D, but not by deletion of LRRC8C+LRRC8E. Conversely, release of charged osmolytes (d-aspartate) was strongly reduced by deletion of LRRC8A or LRRC8C+LRRC8E, but largely unaffected by downregulation of LRRC8D. Our findings point to the existence of multiple heteromeric VRACs in the same cell type: LRRC8A/D-containing heteromers appear to dominate release of uncharged osmolytes, while LRRC8A/C/E, with the additional contribution of LRRC8D, creates a conduit for movement of charged molecules. ABSTRACT The volume-regulated anion channel (VRAC) is the ubiquitously expressed vertebrate Cl- /anion channel that is composed of proteins belonging to the LRRC8 family and activated by cell swelling. In the brain, VRAC contributes to physiological and pathological release of a variety of small organic molecules, including the amino acid neurotransmitters glutamate, aspartate and taurine. In the present work, we explored the role of all five LRRC8 family members in the release of organic osmolytes from primary rat astrocytes. Expression of LRRC8 proteins was modified using an RNAi approach, and amino acid fluxes via VRAC were quantified by radiotracer assays in cells challenged with hypoosmotic medium (30% reduction in osmolarity). Consistent with our prior work, knockdown of LRRC8A potently and equally suppressed the release of radiolabelled d-[14 C]aspartate and [3 H]taurine. Among other LRRC8 subunits, downregulation of LRRC8D strongly inhibited release of the uncharged osmolytes [3 H]taurine and myo-[3 H]inositol, without major impact on the simultaneously measured efflux of the charged d-[14 C]aspartate. In contrast, the release of d-[14 C]aspartate was preferentially sensitive to deletion of LRRC8C+LRRC8E, but unaffected by downregulation of LRRC8D. Finally, siRNA knockdown of LRRC8C+LRRC8D strongly inhibited the release of all osmolytes. Overall, our findings suggest the existence of at least two distinct heteromeric VRACs in astroglial cells. The LRRC8A/D-containing permeability pathway appears to dominate the release of uncharged osmolytes, while an alternative channel (or channels) is composed of LRRC8A/C/D/E and responsible for the loss of charged molecules.
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Affiliation(s)
- Alexandra L Schober
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, NY, 12208, USA
| | - Corinne S Wilson
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, NY, 12208, USA
| | - Alexander A Mongin
- Department of Neuroscience and Experimental Therapeutics, Albany Medical College, Albany, NY, 12208, USA
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Platt CD, Chou J, Houlihan P, Badran YR, Kumar L, Bainter W, Poliani PL, Perez CJ, Dent SYR, Clapham DE, Benavides F, Geha RS. Leucine-rich repeat containing 8A (LRRC8A)-dependent volume-regulated anion channel activity is dispensable for T-cell development and function. J Allergy Clin Immunol 2017; 140:1651-1659.e1. [PMID: 28192143 DOI: 10.1016/j.jaci.2016.12.974] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Revised: 11/20/2016] [Accepted: 12/12/2016] [Indexed: 10/20/2022]
Abstract
BACKGROUND Leucine-rich repeat containing 8A (LRRC8A) is an ubiquitously expressed transmembrane protein with 17 leucine-rich repeats (LRRs) at its C-terminal end and is an essential component of the volume-regulated anion channel (VRAC), which controls cellular volume. A heterozygous mutation in LRRC8A that truncates the 2 terminal LRRs was reported in a patient with agammaglobulinemia and absent B cells and was demonstrated to exert a dominant negative effect on T- and B-cell development in mice. Lrrc8a-/- mice have severely defective T-cell development and function. It is not known whether the T- and B-cell defects caused by LRRC8A deficiency are caused by loss of VRAC activity. OBJECTIVE We sought to determine whether VRAC activity is required for normal T-cell development and function. METHODS VRAC activity was examined by using patch-clamp analysis. Flow cytometry was used to examine T-cell development. T-cell proliferation, cytokine secretion, and antibody titers were measured by using standard techniques. RESULTS We demonstrate that the spontaneous mouse mutant ébouriffé (ebo/ebo) harbors a homozygous 2-bp frameshift mutation in Lrrc8a that truncates the 15 terminal LRRs of LRRC8A. The Lrrc8aebo mutation does not affect protein expression but drastically diminishes VRAC activity in T cells. ebo/ebo mice share features with Lrrc8a-/- mice that include curly hair, infertility, reduced longevity, and kidney abnormalities. However, in contrast to Lrrc8a-/- mice, ebo/ebo mice have normal T-cell development and function and intact antibody response to T-dependent antigen. CONCLUSION LRRC8A-dependent VRAC activity is dispensable for T-cell development and function.
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Affiliation(s)
- Craig D Platt
- Division of Immunology, Boston Children's Hospital, Harvard Medical School, Boston, Mass
| | - Janet Chou
- Division of Immunology, Boston Children's Hospital, Harvard Medical School, Boston, Mass
| | - Patrick Houlihan
- Department of Cardiology, Boston Children's Hospital, Boston, Mass
| | - Yousef R Badran
- Division of Immunology, Boston Children's Hospital, Harvard Medical School, Boston, Mass
| | - Lalit Kumar
- Division of Immunology, Boston Children's Hospital, Harvard Medical School, Boston, Mass
| | - Wayne Bainter
- Division of Immunology, Boston Children's Hospital, Harvard Medical School, Boston, Mass
| | - P Luigi Poliani
- Department of Molecular and Translational Medicine, University of Brescia, Brescia, Italy
| | - Carlos J Perez
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas M. D. Anderson Cancer Center, Smithville, and the Graduate School of Biomedical Sciences at Houston, Houston, Tex
| | - Sharon Y R Dent
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas M. D. Anderson Cancer Center, Smithville, and the Graduate School of Biomedical Sciences at Houston, Houston, Tex
| | - David E Clapham
- Department of Cardiology, Boston Children's Hospital, Boston, Mass; Howard Hughes Medical Institute, Chevy Chase, Md
| | - Fernando Benavides
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas M. D. Anderson Cancer Center, Smithville, and the Graduate School of Biomedical Sciences at Houston, Houston, Tex
| | - Raif S Geha
- Division of Immunology, Boston Children's Hospital, Harvard Medical School, Boston, Mass.
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12
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Schober AL, Mongin AA. Intracellular levels of glutamate in swollen astrocytes are preserved via neurotransmitter reuptake and de novo synthesis: implications for hyponatremia. J Neurochem 2015; 135:176-85. [PMID: 26235094 DOI: 10.1111/jnc.13229] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Revised: 06/25/2015] [Accepted: 06/29/2015] [Indexed: 01/01/2023]
Abstract
Hyponatremia and several other CNS pathologies are associated with substantial astrocytic swelling. To counteract cell swelling, astrocytes lose intracellular osmolytes, including l-glutamate and taurine, through volume-regulated anion channel. In vitro, when swollen by exposure to hypo-osmotic medium, astrocytes lose endogenous taurine faster, paradoxically, than l-glutamate or l-aspartate. Here, we explored the mechanisms responsible for differences between the rates of osmolyte release in primary rat astrocyte cultures. In radiotracer assays, hypo-osmotic efflux of preloaded [(14) C]taurine was indistinguishable from d-[(3) H]aspartate and only 30-40% faster than l-[(3) H]glutamate. However, when we used HPLC to measure the endogenous intracellular amino acid content, hypo-osmotic loss of taurine was approximately fivefold greater than l-glutamate, and no loss of l-aspartate was detected. The dramatic difference between loss of endogenous taurine and glutamate was eliminated after inhibition of both glutamate reuptake [with 300 μM dl-threo-β-benzyloxyaspartic acid (TBOA)] and glutamate synthesis by aminotransferases [with 1 mM aminooxyacetic acid (AOA)]. Treatment with TBOA+AOA made reductions in the intracellular taurine and l-glutamate levels approximately equal. Taken together, these data suggest that swollen astrocytes actively conserve intracellular glutamate via reuptake and de novo synthesis. Our findings likely also explain why in animal models of acute hyponatremia, extracellular levels of taurine are dramatically elevated with minimal impact on extracellular l-glutamate. We identified mechanisms that allow astrocytes to conserve intracellular l-glutamate (Glu) upon exposure to hypo-osmotic environment. Cell swelling activates volume-regulated anion channel (VRAC) and triggers loss of Glu, taurine (Tau), and other cytosolic amino acids. Glu is conserved via reuptake by Na(+) -dependent transporters and de novo synthesis in the reactions of mitochondrial transamination (TA). These findings explain why, in acute hyponatremia, extracellular levels of Tau can be dramatically elevated with minimal changes in extracellular Glu.
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Affiliation(s)
- Alexandra L Schober
- Center for Neuropharmacology and Neuroscience, Albany Medical College, Albany, New York, USA
| | - Alexander A Mongin
- Center for Neuropharmacology and Neuroscience, Albany Medical College, Albany, New York, USA
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Milenkovic A, Brandl C, Milenkovic VM, Jendryke T, Sirianant L, Wanitchakool P, Zimmermann S, Reiff CM, Horling F, Schrewe H, Schreiber R, Kunzelmann K, Wetzel CH, Weber BH. Bestrophin 1 is indispensable for volume regulation in human retinal pigment epithelium cells. Proc Natl Acad Sci U S A 2015; 112:E2630-9. [PMID: 25941382 DOI: 10.1073/pnas.1418840112] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
In response to cell swelling, volume-regulated anion channels (VRACs) participate in a process known as regulatory volume decrease (RVD). Only recently, first insight into the molecular identity of mammalian VRACs was obtained by the discovery of the leucine-rich repeats containing 8A (LRRC8A) gene. Here, we show that bestrophin 1 (BEST1) but not LRRC8A is crucial for volume regulation in human retinal pigment epithelium (RPE) cells. Whole-cell patch-clamp recordings in RPE derived from human-induced pluripotent stem cells (hiPSC) exhibit an outwardly rectifying chloride current with characteristic functional properties of VRACs. This current is severely reduced in hiPSC-RPE cells derived from macular dystrophy patients with pathologic BEST1 mutations. Disruption of the orthologous mouse gene (Best1(-/-)) does not result in obvious retinal pathology but leads to a severe subfertility phenotype in agreement with minor endogenous expression of Best1 in murine RPE but highly abundant expression in mouse testis. Sperm from Best1(-/-) mice showed reduced motility and abnormal sperm morphology, indicating an inability in RVD. Together, our data suggest that the molecular identity of VRACs is more complex--that is, instead of a single ubiquitous channel, VRACs could be formed by cell type- or tissue-specific subunit composition. Our findings provide the basis to further examine VRAC diversity in normal and diseased cell physiology, which is key to exploring novel therapeutic approaches in VRAC-associated pathologies.
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Hisadome K, Koyama T, Kimura C, Droogmans G, Ito Y, Oike M. Volume-regulated anion channels serve as an auto/paracrine nucleotide release pathway in aortic endothelial cells. J Gen Physiol 2002; 119:511-20. [PMID: 12034759 PMCID: PMC2233868 DOI: 10.1085/jgp.20028540] [Citation(s) in RCA: 118] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mechanical stress induces auto/paracrine ATP release from various cell types, but the mechanisms underlying this release are not well understood. Here we show that the release of ATP induced by hypotonic stress (HTS) in bovine aortic endothelial cells (BAECs) occurs through volume-regulated anion channels (VRAC). Various VRAC inhibitors, such as glibenclamide, verapamil, tamoxifen, and fluoxetine, suppressed the HTS-induced release of ATP, as well as the concomitant Ca(2+) oscillations and NO production. They did not, however, affect Ca(2+) oscillations and NO production induced by exogenously applied ATP. Extracellular ATP inhibited VRAC currents in a voltage-dependent manner: block was absent at negative potentials and was manifest at positive potentials, but decreased at highly depolarized potentials. This phenomenon could be described with a "permeating blocker model," in which ATP binds with an affinity of 1.0 +/- 0.5 mM at 0 mV to a site at an electrical distance of 0.41 inside the channel. Bound ATP occludes the channel at moderate positive potentials, but permeates into the cytosol at more depolarized potentials. The triphosphate nucleotides UTP, GTP, and CTP, and the adenine nucleotide ADP, exerted a similar voltage-dependent inhibition of VRAC currents at submillimolar concentrations, which could also be described with this model. However, inhibition by ADP was less voltage sensitive, whereas adenosine did not affect VRAC currents, suggesting that the negative charges of the nucleotides are essential for their inhibitory action. The observation that high concentrations of extracellular ADP enhanced the outward component of the VRAC current in low Cl(-) hypotonic solution and shifted its reversal potential to negative potentials provides more direct evidence for the nucleotide permeability of VRAC. We conclude from these observations that VRAC is a nucleotide-permeable channel, which may serve as a pathway for HTS-induced ATP release in BAEC.
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Affiliation(s)
- Kazunari Hisadome
- Department of Pharmacology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan
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