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Wang J, Poliquin S, Mermer F, Eissman J, Delpire E, Wang J, Shen W, Cai K, Li BM, Li ZY, Xu D, Nwosu G, Flamm C, Liao WP, Shi YW, Kang JQ. Endoplasmic reticulum retention and degradation of a mutation in SLC6A1 associated with epilepsy and autism. Mol Brain 2020; 13:76. [PMID: 32398021 PMCID: PMC7218610 DOI: 10.1186/s13041-020-00612-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Accepted: 04/28/2020] [Indexed: 01/12/2023] Open
Abstract
Mutations in SLC6A1, encoding γ-aminobutyric acid (GABA) transporter 1 (GAT-1), have been recently associated with a spectrum of epilepsy syndromes, intellectual disability and autism in clinic. However, the pathophysiology of the gene mutations is far from clear. Here we report a novel SLC6A1 missense mutation in a patient with epilepsy and autism spectrum disorder and characterized the molecular defects of the mutant GAT-1, from transporter protein trafficking to GABA uptake function in heterologous cells and neurons. The heterozygous missense mutation (c1081C to A (P361T)) in SLC6A1 was identified by exome sequencing. We have thoroughly characterized the molecular pathophysiology underlying the clinical phenotypes. We performed EEG recordings and autism diagnostic interview. The patient had neurodevelopmental delay, absence epilepsy, generalized epilepsy, and 2.5–3 Hz generalized spike and slow waves on EEG recordings. The impact of the mutation on GAT-1 function and trafficking was evaluated by 3H GABA uptake, structural simulation with machine learning tools, live cell confocal microscopy and protein expression in mouse neurons and nonneuronal cells. We demonstrated that the GAT-1(P361T) mutation destabilizes the global protein conformation and reduces total protein expression. The mutant transporter protein was localized intracellularly inside the endoplasmic reticulum (ER) with a pattern of expression very similar to the cells treated with tunicamycin, an ER stress inducer. Radioactive 3H-labeled GABA uptake assay indicated the mutation reduced the function of the mutant GAT-1(P361T), to a level that is similar to the cells treated with GAT-1 inhibitors. In summary, this mutation destabilizes the mutant transporter protein, which results in retention of the mutant protein inside cells and reduction of total transporter expression, likely via excessive endoplasmic reticulum associated degradation. This thus likely causes reduced functional transporter number on the cell surface, which then could cause the observed reduced GABA uptake function. Consequently, malfunctioning GABA signaling may cause altered neurodevelopment and neurotransmission, such as enhanced tonic inhibition and altered cell proliferation in vivo. The pathophysiology due to severely impaired GAT-1 function may give rise to a wide spectrum of neurodevelopmental phenotypes including autism and epilepsy.
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Affiliation(s)
- Jie Wang
- Institute of Neuroscience and Department of Neurology of the Second Affiliated Hospital of Guangzhou Medical University; Key Laboratory of Neurogenetics and Channelopathies of Guangdong Province and the Ministry of Education of China, Guangzhou, 510260, China
| | - Sarah Poliquin
- The Neuroscience Program, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Felicia Mermer
- The Neuroscience Program, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Jaclyn Eissman
- The Neuroscience Program, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Eric Delpire
- Department of Anesthesiology, Vanderbilt University Department of Anesthesiology, Vanderbilt University, Nashville, TN, 37232, USA
| | - Juexin Wang
- Department of Electrical Engineering & Computer Science and Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA
| | - Wangzhen Shen
- Department of Neurology, Vanderbilt University Medical Center, Nashville, USA
| | - Kefu Cai
- Department of Neurology, Vanderbilt University Medical Center, Nashville, USA.,Department of Neurology, Affiliated Hospital, Nantong University, Nantong, 226001, Jiangsu, China
| | - Bing-Mei Li
- Institute of Neuroscience and Department of Neurology of the Second Affiliated Hospital of Guangzhou Medical University; Key Laboratory of Neurogenetics and Channelopathies of Guangdong Province and the Ministry of Education of China, Guangzhou, 510260, China
| | - Zong-Yan Li
- Institute of Neuroscience and Department of Neurology of the Second Affiliated Hospital of Guangzhou Medical University; Key Laboratory of Neurogenetics and Channelopathies of Guangdong Province and the Ministry of Education of China, Guangzhou, 510260, China
| | - Dong Xu
- Department of Electrical Engineering & Computer Science and Christopher S. Bond Life Sciences Center, University of Missouri, Columbia, MO, 65211, USA
| | - Gerald Nwosu
- Department of Neurology, Vanderbilt University Medical Center, Nashville, USA.,Neuroscience Graduate Program, Vanderbilt-Meharry Alliance, Vanderbilt University, Nashville, TN, 37235, USA
| | - Carson Flamm
- The Neuroscience Program, Vanderbilt University Medical Center, Nashville, TN, 37232, USA
| | - Wei-Ping Liao
- Institute of Neuroscience and Department of Neurology of the Second Affiliated Hospital of Guangzhou Medical University; Key Laboratory of Neurogenetics and Channelopathies of Guangdong Province and the Ministry of Education of China, Guangzhou, 510260, China
| | - Yi-Wu Shi
- Institute of Neuroscience and Department of Neurology of the Second Affiliated Hospital of Guangzhou Medical University; Key Laboratory of Neurogenetics and Channelopathies of Guangdong Province and the Ministry of Education of China, Guangzhou, 510260, China
| | - Jing-Qiong Kang
- Department of Neurology, Vanderbilt University Medical Center, Nashville, USA. .,Department of Pharmacology, Vanderbilt University, Vanderbilt Kennedy Center of Human Development, Vanderbilt Brain Institute, 6147 MRBIII, 465 21st Ave. South, Nashville, TN, 37232, USA.
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Myers SJ, Yuan H, Kang JQ, Tan FCK, Traynelis SF, Low CM. Distinct roles of GRIN2A and GRIN2B variants in neurological conditions. F1000Res 2019; 8:F1000 Faculty Rev-1940. [PMID: 31807283 PMCID: PMC6871362 DOI: 10.12688/f1000research.18949.1] [Citation(s) in RCA: 80] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 11/08/2019] [Indexed: 12/12/2022] Open
Abstract
Rapid advances in sequencing technology have led to an explosive increase in the number of genetic variants identified in patients with neurological disease and have also enabled the assembly of a robust database of variants in healthy individuals. A surprising number of variants in the GRIN genes that encode N-methyl-D-aspartate (NMDA) glutamatergic receptor subunits have been found in patients with various neuropsychiatric disorders, including autism spectrum disorders, epilepsy, intellectual disability, attention-deficit/hyperactivity disorder, and schizophrenia. This review compares and contrasts the available information describing the clinical and functional consequences of genetic variations in GRIN2A and GRIN2B. Comparison of clinical phenotypes shows that GRIN2A variants are commonly associated with an epileptic phenotype but that GRIN2B variants are commonly found in patients with neurodevelopmental disorders. These observations emphasize the distinct roles that the gene products serve in circuit function and suggest that functional analysis of GRIN2A and GRIN2B variation may provide insight into the molecular mechanisms, which will allow more accurate subclassification of clinical phenotypes. Furthermore, characterization of the pharmacological properties of variant receptors could provide the first opportunity for translational therapeutic strategies for these GRIN-related neurological and psychiatric disorders.
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Affiliation(s)
- Scott J Myers
- Center for Functional Evaluation of Rare Variants (CFERV), Emory University, Atlanta, GA, USA
- Department of Pharmacology and Chemical Biology, Emory University, Atlanta, GA, USA
| | - Hongjie Yuan
- Center for Functional Evaluation of Rare Variants (CFERV), Emory University, Atlanta, GA, USA
- Department of Pharmacology and Chemical Biology, Emory University, Atlanta, GA, USA
| | - Jing-Qiong Kang
- Department of Neurology, Vanderbilt Brain Institute, Vanderbilt Kennedy Center of Human Development, Vanderbilt University, Nashville, TN, USA
| | - Francis Chee Kuan Tan
- Department of Anaesthesia, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Stephen F Traynelis
- Center for Functional Evaluation of Rare Variants (CFERV), Emory University, Atlanta, GA, USA
- Department of Pharmacology and Chemical Biology, Emory University, Atlanta, GA, USA
| | - Chian-Ming Low
- Department of Anaesthesia, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
- Department of Pharmacology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
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