1
|
Curie A, Lion-François L, Valayannopoulos V, Perreton N, Gavanon M, Touil N, Brun-Laurisse A, Gheurbi F, Buchy M, Halep H, Cheillan D, Mercier C, Brassier A, Desnous B, Kassai B, De Lonlay P, Des Portes V. Clinical Characteristics, Developmental Trajectory, and Caregiver Burden of Patients With Creatine Transporter Deficiency ( SLC6A8). Neurology 2024; 102:e209243. [PMID: 38531017 DOI: 10.1212/wnl.0000000000209243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Accepted: 01/19/2024] [Indexed: 03/28/2024] Open
Abstract
BACKGROUND AND OBJECTIVES Creatine transporter deficiency (CTD) is a rare X-linked genetic disorder characterized by intellectual disability (ID). We evaluated the clinical characteristics and trajectory of patients with CTD and the impact of the disease on caregivers to identify relevant endpoints for future therapeutic trials. METHODS As part of a French National Research Program, patients with CTD were included based on (1) a pathogenic SLC6A8 variant and (2) ID and/or autism spectrum disorder. Families and patients were referred by the physician who ordered the genetic analysis through Reference Centers of ID from rare causes and inherited metabolic diseases. After we informed the patients and their parents/guardians about the study, all of them gave written consent and were included. A control group of age-matched and sex-matched patients with Fragile X syndrome was also included. Physical examination, neuropsychological assessments, and caregiver impact were assessed. All data were analyzed using R software. RESULTS Thirty-one patients (27 male, 4 female) were included (25/31 aged 18 years or younger). Most of the patients (71%) had symptoms at <24 months of age. The mean age at diagnosis was 6.5 years. Epilepsy occurred in 45% (mean age at onset: 8 years). Early-onset behavioral disorder occurred in 82%. Developmental trajectory was consistently delayed (fine and gross motor skills, language, and communication/sociability). Half of the patients with CTD had axial hypotonia during the first year of life. All patients were able to walk without help, but 7/31 had ataxia and only 14/31 could walk tandem gait. Most of them had abnormal fine motor skills (27/31), and most of them had language impairment (30/31), but 12/23 male patients (52.2%) completed the Peabody Picture Vocabulary Test. Approximately half (14/31) had slender build. Most of them needed nursing care (20/31), generally 1-4 h/d. Adaptive assessment (Vineland) confirmed that male patients with CTD had moderate-to-severe ID. Most caregivers (79%) were at risk of burnout, as shown by Caregiver Burden Inventory (CBI) > 36 (significantly higher than for patients with Fragile X syndrome) with a high burden of time dependence. DISCUSSION In addition to clinical endpoints, such as the assessment of epilepsy and the developmental trajectory of the patient, the Vineland scale, PPVT5, and CBI are of particular interest as outcome measures for future trials. TRIAL REGISTRATION INFORMATION ANSM Registration Number 2010-A00327-32.
Collapse
Affiliation(s)
- Aurore Curie
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Laurence Lion-François
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Vassili Valayannopoulos
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Nathalie Perreton
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Marie Gavanon
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Nathalie Touil
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Amandine Brun-Laurisse
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Fahra Gheurbi
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Marion Buchy
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Hulya Halep
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - David Cheillan
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Catherine Mercier
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Anaïs Brassier
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Béatrice Desnous
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Behrouz Kassai
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Pascale De Lonlay
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| | - Vincent Des Portes
- From the Child Neurology Department and Reference Centre of Rare Disease with Intellectual Disability (A.C., L.L.-F., M.G., A.B.-L., F.G., M.B., V.D.P.), Hospices Civils de Lyon, Lyon University Hospital; Lyon Neuroscience Research Centre (A.C., M.G., A.B.-L., F.G., M.B., V.D.P.), CNRS UMR5292, INSERM U1028; Lyon University (A.C., V.D.P.); Reference Centre for Inherited Metabolic Diseases (V.V., A.B., P.D.L.), Imagine Institute, Necker Enfants-Malades Hospital, Paris University Hospital, University of Paris Descartes; Clinical Investigation Center 1407/INSERM-Hospices Civils de Lyon (N.P., N.T., H.H., B.K.), Bron; Inborn Errors of Metabolism Unit (D.C.), Biochemistry and Molecular Biology Department; Department of Biostatistics (C.M.), Lyon University Hospital; and Reference Centre for Inherited Metabolic Diseases (B.D.), Department of Child Neurology, Marseille University Hospital, France
| |
Collapse
|
2
|
Ün D, Kovalchuk V, El-Kasaby A, Kasture A, Koban F, Kudlacek O, Freissmuth M, Sucic S. Breaking the rules of SLC6 transporters: Export of the human creatine transporter-1 from the endoplasmic reticulum is supported by its N-terminus. J Neurochem 2024. [PMID: 38419374 DOI: 10.1111/jnc.16088] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Revised: 02/13/2024] [Accepted: 02/15/2024] [Indexed: 03/02/2024]
Abstract
Mutations in the human creatine transporter 1 (CRT1/SLC6A8) cause the creatine transporter deficiency syndrome, which is characterized by intellectual disability, epilepsy, autism, and developmental delay. The vast majority of mutations cause protein misfolding and hence reduce cell surface expression. Hence, it is important to understand the molecular machinery supporting folding and export of CRT1 from the endoplasmic reticulum (ER). All other SLC6 members thus far investigated rely on a C-terminal motif for binding the COPII-component SEC24 to drive their ER export; their N-termini are dispensable. Here, we show that, in contrast, in CRT1 the C-terminal ER-export motif is cryptic and it is the N-terminus, which supports ER export. This conclusion is based on the following observations: (i) siRNA-induced depletion of individual SEC24 isoforms revealed that CRT1 relied on SEC24C for ER export. However, mutations of the C-terminal canonical ER-export motif of CRT1 did not impair its cell surface delivery. (ii) Nevertheless, the C-terminal motif of CRT1 was operational in a chimeric protein comprising the serotonin transporter (SERT/SLC6A4) and the C-terminus of CRT1. (iii) Tagging of the N-terminus-but not the C-terminus-with yellow fluorescent protein (YFP) resulted in ER retention. (iv) Serial truncations of the N-terminus showed that removal of ≥51 residues of CRT1 impaired surface delivery, because the truncated CRT1 were confined to the ER. (v) Mutation of P51 to alanine also reduced cell surface delivery of CRT1 and relieved its dependence on SEC24C. Thus, the ER-export motif in the N-terminus of CRT1 overrides the canonical C-terminal motif.
Collapse
Affiliation(s)
- Didem Ün
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Centre of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Vasylyna Kovalchuk
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Centre of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Ali El-Kasaby
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Centre of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Ameya Kasture
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Centre of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
- Department of Neuroscience and Developmental Biology, University of Vienna, Vienna, Austria
| | - Florian Koban
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Centre of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Oliver Kudlacek
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Centre of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Centre of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Sonja Sucic
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Centre of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
3
|
Ferrada E, Wiedmer T, Wang WA, Frommelt F, Steurer B, Klimek C, Lindinger S, Osthushenrich T, Garofoli A, Brocchetti S, Bradberry S, Huang J, MacNamara A, Scarabottolo L, Ecker GF, Malarstig A, Superti-Furga G. Experimental and Computational Analysis of Newly Identified Pathogenic Mutations in the Creatine Transporter SLC6A8. J Mol Biol 2024; 436:168383. [PMID: 38070861 DOI: 10.1016/j.jmb.2023.168383] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Revised: 11/26/2023] [Accepted: 12/01/2023] [Indexed: 12/24/2023]
Abstract
Creatine is an essential metabolite for the storage and rapid supply of energy in muscle and nerve cells. In humans, impaired metabolism, transport, and distribution of creatine throughout tissues can cause varying forms of mental disability, also known as creatine deficiency syndrome (CDS). So far, 80 mutations in the creatine transporter (SLC6A8) have been associated to CDS. To better understand the effect of human genetic variants on the physiology of SLC6A8 and their possible impact on CDS, we studied 30 missense variants including 15 variants of unknown significance, two of which are reported here for the first time. We expressed these variants in HEK293 cells and explored their subcellular localization and transport activity. We also applied computational methods to predict variant effect and estimate site-specific changes in thermodynamic stability. To explore variants that might have a differential effect on the transporter's conformers along the transport cycle, we constructed homology models of the inward facing, and outward facing conformations. In addition, we used mass-spectrometry to study proteins that interact with wild type SLC6A8 and five selected variants in HEK293 cells. In silico models of the protein complexes revealed how two variants impact the interaction interface of SLC6A8 with other proteins and how pathogenic variants lead to an enrichment of ER protein partners. Overall, our integrated analysis disambiguates the pathogenicity of 15 variants of unknown significance revealing diverse mechanisms of pathogenicity, including two previously unreported variants obtained from patients suffering from the creatine deficiency syndrome.
Collapse
Affiliation(s)
- Evandro Ferrada
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria.
| | - Tabea Wiedmer
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | - Wen-An Wang
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | - Fabian Frommelt
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | - Barbara Steurer
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | - Christoph Klimek
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | - Sabrina Lindinger
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | | | - Andrea Garofoli
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria
| | | | | | - Jiahui Huang
- Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | | | | | - Gerhard F Ecker
- Department of Pharmaceutical Sciences, University of Vienna, Vienna, Austria
| | - Anders Malarstig
- Pfizer Worldwide Research, Development and Medical, Stockholm, Sweden
| | - Giulio Superti-Furga
- CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria; Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria.
| |
Collapse
|
4
|
Clarke A, Farr CV, El-Kasaby A, Szöllősi D, Freissmuth M, Sucic S, Stockner T. Probing binding and occlusion of substrate in the human creatine transporter-1 by computation and mutagenesis. Protein Sci 2024; 33:e4842. [PMID: 38032325 PMCID: PMC10751730 DOI: 10.1002/pro.4842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2023] [Revised: 11/16/2023] [Accepted: 11/18/2023] [Indexed: 12/01/2023]
Abstract
In chordates, energy buffering is achieved in part through phosphocreatine, which requires cellular uptake of creatine by the membrane-embedded creatine transporter (CRT1/SLC6A8). Mutations in human slc6a8 lead to creatine transporter deficiency syndrome, for which there is only limited treatment. Here, we used a combined homology modeling, molecular dynamics, and experimental approach to generate a structural model of CRT1. Our observations support the following conclusions: contrary to previous proposals, C144, a key residue in the substrate binding site, is not present in a charged state. Similarly, the side chain D458 must be present in a protonated form to maintain the structural integrity of CRT1. Finally, we identified that the interaction chain Y148-creatine-Na+ is essential to the process of occlusion, which occurs via a "hold-and-pull" mechanism. The model should be useful to study the impact of disease-associated point mutations on the folding of CRT1 and identify approaches which correct folding-deficient mutants.
Collapse
Affiliation(s)
- Amy Clarke
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Clemens V Farr
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Ali El-Kasaby
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Daniel Szöllősi
- Department of Theoretical and Computational Biophysics, Max Planck Institute for Multidisciplinary Sciences, Göttingen, Germany
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Sonja Sucic
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Thomas Stockner
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
5
|
Koban F, Freissmuth M. The cell cycle protein MAD2 facilitates endocytosis of the serotonin transporter in the neuronal soma. EMBO Rep 2023; 24:e53408. [PMID: 37530743 PMCID: PMC10561363 DOI: 10.15252/embr.202153408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2021] [Revised: 06/23/2023] [Accepted: 07/14/2023] [Indexed: 08/03/2023] Open
Abstract
Monoamine transporters retrieve serotonin (SERT), dopamine (DAT), and norepinephrine (NET) from the synaptic cleft. Transporter internalization contributes to the regulation of their surface expression. Clathrin-mediated endocytosis of plasma membrane proteins requires adaptor protein-2 (AP2), which recruits cargo to the nascent clathrin cage. However, the intracellular portions of monoamine transporters are devoid of a conventional AP2-binding site. Here, we identify a MAD2 (mitotic arrest deficient-2) interaction motif in the C-terminus of SERT, which binds the closed conformation of MAD2 and allows for the recruitment of two additional mitotic spindle assembly checkpoint (SAC) proteins, BubR1 and p31comet , and of AP2. We visualize MAD2, BubR1, and p31comet in dorsal raphe neurons, and depletion of MAD2 in primary serotonergic rat neurons decreases SERT endocytosis in the soma. Our findings do not only provide mechanistic insights into transporter internalization but also allow for rationalizing why SAC proteins are present in post-mitotic neurons.
Collapse
Affiliation(s)
- Florian Koban
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and PharmacologyMedical University of ViennaViennaAustria
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and PharmacologyMedical University of ViennaViennaAustria
| |
Collapse
|
6
|
Li J, Xu S. Diagnosis and Treatment of X-Linked Creatine Transporter Deficiency: Case Report and Literature Review. Brain Sci 2023; 13:1382. [PMID: 37891751 PMCID: PMC10605349 DOI: 10.3390/brainsci13101382] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Revised: 09/18/2023] [Accepted: 09/25/2023] [Indexed: 10/29/2023] Open
Abstract
(1) Background: X-linked creatine transporter deficiency (CTD) (OMIM 300036) is a rare group of inherited metabolic disorders characterized by global developmental delay/intellectual disability (GDD/ID), seizures, autistic behavior, and movement disorders. Pathogenic variants in the SLC6A8 gene, located at Xq28, are causative of the disease, leading to impaired creatine transport into the brain. Supplementation with creatine and its precursors, glycine and arginine, has been attempted, yet the treatment efficacy remains controversial. (2) Methods: Here we report a de novo SLC6A8 variant in a boy aged 3 years 9 months presenting with GDD, autistic behavior, and epilepsy. Elevated urinary creatine/creatinine ratio and diminished creatine peak on brain MR spectroscopy suggested the diagnosis of CTD. Genetic sequencing revealed a de novo hemizygous frameshift variant (NM_005629: c.1136_1137del, p. Glu379ValfsTer85). Creatine supplementation therapy was initiated after definitive diagnosis. Electroencephalography and MR spectroscopy were monitored during follow-up in concurrence with neuropsychological evaluations. The clinical phenotype and treatment response of CTD were summarized by systematic view of the literature. (3) Results: In silico analysis showed this variant to be deleterious, probably interfering with substrate binding and conformational changes during creatine transport. Creatine supplementation therapy led to seizure cessation and modest cognitive improvement after half-year's treatment. (4) Conclusions: This case highlights the importance of MR spectroscopy and metabolic screening in males with GDD/ID, allowing for early diagnosis and therapeutic intervention. Mechanistic understanding and case-per-se analysis are required to enable precision treatment for the patients.
Collapse
Affiliation(s)
| | - Sanqing Xu
- Department of Pediatrics, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430074, China;
| |
Collapse
|
7
|
Lyons EL, Watson D, Alodadi MS, Haugabook SJ, Tawa GJ, Hannah-Shmouni F, Porter FD, Collins JR, Ottinger EA, Mudunuri US. Rare disease variant curation from literature: assessing gaps with creatine transport deficiency in focus. BMC Genomics 2023; 24:460. [PMID: 37587458 PMCID: PMC10433598 DOI: 10.1186/s12864-023-09561-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Accepted: 08/08/2023] [Indexed: 08/18/2023] Open
Abstract
BACKGROUND Approximately 4-8% of the world suffers from a rare disease. Rare diseases are often difficult to diagnose, and many do not have approved therapies. Genetic sequencing has the potential to shorten the current diagnostic process, increase mechanistic understanding, and facilitate research on therapeutic approaches but is limited by the difficulty of novel variant pathogenicity interpretation and the communication of known causative variants. It is unknown how many published rare disease variants are currently accessible in the public domain. RESULTS This study investigated the translation of knowledge of variants reported in published manuscripts to publicly accessible variant databases. Variants, symptoms, biochemical assay results, and protein function from literature on the SLC6A8 gene associated with X-linked Creatine Transporter Deficiency (CTD) were curated and reported as a highly annotated dataset of variants with clinical context and functional details. Variants were harmonized, their availability in existing variant databases was analyzed and pathogenicity assignments were compared with impact algorithm predictions. 24% of the pathogenic variants found in PubMed articles were not captured in any database used in this analysis while only 65% of the published variants received an accurate pathogenicity prediction from at least one impact prediction algorithm. CONCLUSIONS Despite being published in the literature, pathogenicity data on patient variants may remain inaccessible for genetic diagnosis, therapeutic target identification, mechanistic understanding, or hypothesis generation. Clinical and functional details presented in the literature are important to make pathogenicity assessments. Impact predictions remain imperfect but are improving, especially for single nucleotide exonic variants, however such predictions are less accurate or unavailable for intronic and multi-nucleotide variants. Developing text mining workflows that use natural language processing for identifying diseases, genes and variants, along with impact prediction algorithms and integrating with details on clinical phenotypes and functional assessments might be a promising approach to scale literature mining of variants and assigning correct pathogenicity. The curated variants list created by this effort includes context details to improve any such efforts on variant curation for rare diseases.
Collapse
Affiliation(s)
- Erica L Lyons
- Advanced Biomedical Computational Science, Frederick National Laboratory for Cancer Research, Frederick, MD, 21702, USA
| | - Daniel Watson
- Advanced Biomedical Computational Science, Frederick National Laboratory for Cancer Research, Frederick, MD, 21702, USA
| | - Mohammad S Alodadi
- Advanced Biomedical Computational Science, Frederick National Laboratory for Cancer Research, Frederick, MD, 21702, USA
| | - Sharie J Haugabook
- Division of Preclinical Innovation, Therapeutic Development Branch, Therapeutics for Rare and Neglected Diseases (TRND) Program, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Gregory J Tawa
- Division of Preclinical Innovation, Therapeutic Development Branch, Therapeutics for Rare and Neglected Diseases (TRND) Program, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Fady Hannah-Shmouni
- Division of Translational Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Forbes D Porter
- Division of Translational Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Jack R Collins
- Advanced Biomedical Computational Science, Frederick National Laboratory for Cancer Research, Frederick, MD, 21702, USA
| | - Elizabeth A Ottinger
- Division of Preclinical Innovation, Therapeutic Development Branch, Therapeutics for Rare and Neglected Diseases (TRND) Program, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, MD, 20892, USA.
| | - Uma S Mudunuri
- Advanced Biomedical Computational Science, Frederick National Laboratory for Cancer Research, Frederick, MD, 21702, USA.
| |
Collapse
|
8
|
Kasture AS, Fischer FP, Kunert L, Burger ML, Burgstaller AC, El-Kasaby A, Hummel T, Sucic S. Drosophila melanogaster as a model for unraveling unique molecular features of epilepsy elicited by human GABA transporter 1 variants. Front Neurosci 2023; 16:1074427. [PMID: 36741049 PMCID: PMC9893286 DOI: 10.3389/fnins.2022.1074427] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2022] [Accepted: 12/21/2022] [Indexed: 01/20/2023] Open
Abstract
Mutations in the human γ-aminobutyric acid (GABA) transporter 1 (hGAT-1) can instigate myoclonic-atonic and other generalized epilepsies in the afflicted individuals. We systematically examined fifteen hGAT-1 disease variants, all of which dramatically reduced or completely abolished GABA uptake activity. Many of these loss-of-function variants were absent from their regular site of action at the cell surface, due to protein misfolding and/or impaired trafficking machinery (as verified by confocal microscopy and de-glycosylation experiments). A modest fraction of the mutants displayed correct targeting to the plasma membrane, but nonetheless rendered the mutated proteins devoid of GABA transport, possibly due to structural alterations in the GABA binding site/translocation pathway. We here focused on a folding-deficient A288V variant. In flies, A288V reiterated its impeded expression pattern, closely mimicking the ER-retention demonstrated in transfected HEK293 cells. Functionally, A288V presented a temperature-sensitive seizure phenotype in fruit flies. We employed diverse small molecules to restore the expression and activity of folding-deficient hGAT-1 epilepsy variants, in vitro (in HEK293 cells) and in vivo (in flies). We identified three compounds (chemical and pharmacological chaperones) conferring moderate rescue capacity for several variants. Our data grant crucial new insights into: (i) the molecular basis of epilepsy in patients harboring hGAT-1 mutations, and (ii) a proof-of-principle that protein folding deficits in disease-associated hGAT-1 variants can be corrected using the pharmacochaperoning approach. Such innovative pharmaco-therapeutic prospects inspire the rational design of novel drugs for alleviating the clinical symptoms triggered by the numerous emerging pathogenic mutations in hGAT-1.
Collapse
Affiliation(s)
- Ameya S. Kasture
- Institute of Pharmacology, Medical University of Vienna, Vienna, Austria,Department of Neuroscience and Developmental Biology, University of Vienna, Vienna, Austria
| | - Florian P. Fischer
- Institute of Pharmacology, Medical University of Vienna, Vienna, Austria,Department of Epileptology and Neurology, University of Aachen, Aachen, Germany
| | - Lisa Kunert
- Department of Neuroscience and Developmental Biology, University of Vienna, Vienna, Austria
| | - Melanie L. Burger
- Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | | | - Ali El-Kasaby
- Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Thomas Hummel
- Department of Neuroscience and Developmental Biology, University of Vienna, Vienna, Austria
| | - Sonja Sucic
- Institute of Pharmacology, Medical University of Vienna, Vienna, Austria,*Correspondence: Sonja Sucic,
| |
Collapse
|
9
|
Experimental and Bioinformatic Insights into the Effects of Epileptogenic Variants on the Function and Trafficking of the GABA Transporter GAT-1. Int J Mol Sci 2023; 24:ijms24020955. [PMID: 36674476 PMCID: PMC9862756 DOI: 10.3390/ijms24020955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Revised: 12/27/2022] [Accepted: 12/31/2022] [Indexed: 01/06/2023] Open
Abstract
In this article, we identified a novel epileptogenic variant (G307R) of the gene SLC6A1, which encodes the GABA transporter GAT-1. Our main goal was to investigate the pathogenic mechanisms of this variant, located near the neurotransmitter permeation pathway, and compare it with other variants located either in the permeation pathway or close to the lipid bilayer. The mutants G307R and A334P, close to the gates of the transporter, could be glycosylated with variable efficiency and reached the membrane, albeit inactive. Mutants located in the center of the permeation pathway (G297R) or close to the lipid bilayer (A128V, G550R) were retained in the endoplasmic reticulum. Applying an Elastic Network Model, to these and to other previously characterized variants, we found that G307R and A334P significantly perturb the structure and dynamics of the intracellular gate, which can explain their reduced activity, while for A228V and G362R, the reduced translocation to the membrane quantitatively accounts for the reduced activity. The addition of a chemical chaperone (4-phenylbutyric acid, PBA), which improves protein folding, increased the activity of GAT-1WT, as well as most of the assayed variants, including G307R, suggesting that PBA might also assist the conformational changes occurring during the alternative access transport cycle.
Collapse
|
10
|
Angenoorth TJF, Maier J, Stankovic S, Bhat S, Sucic S, Freissmuth M, Sitte HH, Yang JW. Rescue of Misfolded Organic Cation Transporter 3 Variants. Cells 2022; 12:39. [PMID: 36611832 PMCID: PMC9818475 DOI: 10.3390/cells12010039] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Revised: 12/13/2022] [Accepted: 12/19/2022] [Indexed: 12/24/2022] Open
Abstract
Organic cation transporters (OCTs) are membrane proteins that take up monoamines, cationic drugs and xenobiotics. We previously reported novel missense mutations of organic cation transporter 3 (OCT3, SLC22A3), some with drastically impacted transport capabilities compared to wildtype. For some variants, this was due to ER retention and subsequent degradation of the misfolded transporter. For other transporter families, it was previously shown that treatment of misfolded variants with pharmacological and chemical chaperones could restore transport function to a certain degree. To investigate two potentially ER-bound, misfolded variants (D340G and R348W), we employed confocal and biochemical analyses. In addition, radiotracer uptake assays were conducted to assess whether pre-treatment with chaperones could restore transporter function. We show that pre-treatment of cells with the chemical chaperone 4-PBA (4-phenyl butyric acid) leads to increased membrane expression of misfolded variants and is associated with increased transport capacity of D340G (8-fold) and R348W (1.5 times) compared to untreated variants. We herein present proof of principle that folding-deficient SLC22 transporter variants, in particular those of OCT3, are amenable to rescue by chaperones. These findings need to be extended to other SLC22 members with corroborated disease associations.
Collapse
Affiliation(s)
- Thomas J. F. Angenoorth
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Währingerstraße 13A, 1090 Vienna, Austria
| | - Julian Maier
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Währingerstraße 13A, 1090 Vienna, Austria
| | - Stevan Stankovic
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Währingerstraße 13A, 1090 Vienna, Austria
| | - Shreyas Bhat
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Währingerstraße 13A, 1090 Vienna, Austria
- Department of Physics, Université de Montréal, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, QC H3T 1J4, Canada
- Department of Pharmacology and Physiology, Université de Montréal, 2960 Chemin de la Tour, Montréal, QC H3T 1J4, Canada
| | - Sonja Sucic
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Währingerstraße 13A, 1090 Vienna, Austria
| | - Michael Freissmuth
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Währingerstraße 13A, 1090 Vienna, Austria
| | - Harald H. Sitte
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Währingerstraße 13A, 1090 Vienna, Austria
| | - Jae-Won Yang
- Institute of Pharmacology, Center for Physiology and Pharmacology, Medical University of Vienna, Währingerstraße 13A, 1090 Vienna, Austria
| |
Collapse
|
11
|
Farr CV, El-Kasaby A, Erdem FA, Sucic S, Freissmuth M, Sandtner W. Cooperative Binding of Substrate and Ions Drives Forward Cycling of the Human Creatine Transporter-1. Front Physiol 2022; 13:919439. [PMID: 35837012 PMCID: PMC9273935 DOI: 10.3389/fphys.2022.919439] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 06/09/2022] [Indexed: 11/25/2022] Open
Abstract
Creatine serves as an ATP buffer and is thus an integral component of cellular energy metabolism. Most cells maintain their creatine levels via uptake by the creatine transporter (CRT-1, SLC6A8). The activity of CRT-1, therefore, is a major determinant of cytosolic creatine concentrations. We determined the kinetics of CRT-1 in real time by relying on electrophysiological recordings of transport-associated currents. Our analysis revealed that CRT-1 harvested the concentration gradient of NaCl and the membrane potential but not the potassium gradient to achieve a very high concentrative power. We investigated the mechanistic basis for the ability of CRT-1 to maintain the forward cycling mode in spite of high intracellular concentrations of creatine: this is achieved by cooperative binding of substrate and co-substrate ions, which, under physiological ion conditions, results in a very pronounced (i.e. about 500-fold) drop in the affinity of creatine to the inward-facing state of CRT-1. Kinetic estimates were integrated into a mathematical model of the transport cycle of CRT-1, which faithfully reproduced all experimental data. We interrogated the kinetic model to examine the most plausible mechanistic basis of cooperativity: based on this systematic exploration, we conclude that destabilization of binary rather than ternary complexes is necessary for CRT-1 to maintain the observed cytosolic creatine concentrations. Our model also provides a plausible explanation why neurons, heart and skeletal muscle cells must express a creatine releasing transporter to achieve rapid equilibration of the intracellular creatine pool.
Collapse
Affiliation(s)
| | | | | | | | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | | |
Collapse
|
12
|
Vats A, Xi Y, Feng B, Clinger OD, St Leger AJ, Liu X, Ghosh A, Dermond CD, Lathrop KL, Tochtrop GP, Picaud S, Chen Y. Non-retinoid chaperones improve rhodopsin homeostasis in a mouse model of retinitis pigmentosa. JCI Insight 2022; 7:153717. [PMID: 35472194 PMCID: PMC9220944 DOI: 10.1172/jci.insight.153717] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2021] [Accepted: 04/20/2022] [Indexed: 11/17/2022] Open
Abstract
Rhodopsin-associated (RHO-associated) retinitis pigmentosa (RP) is a progressive retinal disease that currently has no cure. RHO protein misfolding leads to disturbed proteostasis and the death of rod photoreceptors, resulting in decreased vision. We previously identified nonretinoid chaperones of RHO, including YC-001 and F5257-0462, by small-molecule high-throughput screening. Here, we profile the chaperone activities of these molecules toward the cell-surface level of 27 RP-causing human RHO mutants in NIH3T3 cells. Furthermore, using retinal explant culture, we show that YC-001 improves retinal proteostasis by supporting RHO homeostasis in RhoP23H/+ mouse retinae, which results in thicker outer nuclear layers (ONL), indicating delayed photoreceptor degeneration. Interestingly, YC-001 ameliorated retinal immune responses and reduced the number of microglia/macrophages in the RhoP23H/+ retinal explants. Similarly, F5257-0462 also protects photoreceptors in RhoP23H/+ retinal explants. In vivo, intravitreal injection of YC-001 or F5257-0462 microparticles in PBS shows that F5257-0462 has a higher efficacy in preserving photoreceptor function and delaying photoreceptor death in RhoP23H/+ mice. Collectively, we provide proof of principle that nonretinoid chaperones are promising drug candidates in treating RHO-associated RP.
Collapse
Affiliation(s)
- Abhishek Vats
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Yibo Xi
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Bing Feng
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Owen D Clinger
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Anthony J St Leger
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Xujie Liu
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Archisha Ghosh
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Chase D Dermond
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Kira L Lathrop
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| | - Gregory P Tochtrop
- Department of Chemistry, Case Western Reserve University, Cleveland, United States of America
| | - Serge Picaud
- Institut de la Vision, Sorbonne Université, Paris, France
| | - Yuanyuan Chen
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, United States of America
| |
Collapse
|
13
|
Disruption of the Ubiquitin-Proteasome System and Elevated Endoplasmic Reticulum Stress in Epilepsy. Biomedicines 2022; 10:biomedicines10030647. [PMID: 35327449 PMCID: PMC8945847 DOI: 10.3390/biomedicines10030647] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 03/05/2022] [Accepted: 03/07/2022] [Indexed: 02/06/2023] Open
Abstract
The epilepsies are a broad group of conditions characterized by repeated seizures, and together are one of the most common neurological disorders. Additionally, epilepsy is comorbid with many neurological disorders, including lysosomal storage diseases, syndromic intellectual disability, and autism spectrum disorder. Despite the prevalence, treatments are still unsatisfactory: approximately 30% of epileptic patients do not adequately respond to existing therapeutics, which primarily target ion channels. Therefore, new therapeutic approaches are needed. Disturbed proteostasis is an emerging mechanism in epilepsy, with profound effects on neuronal health and function. Proteostasis, the dynamic balance of protein synthesis and degradation, can be directly disrupted by epilepsy-associated mutations in various components of the ubiquitin-proteasome system (UPS), or impairments can be secondary to seizure activity or misfolded proteins. Endoplasmic reticulum (ER) stress can arise from failed proteostasis and result in neuronal death. In light of this, several treatment modalities that modify components of proteostasis have shown promise in the management of neurological disorders. These include chemical chaperones to assist proper folding of proteins, inhibitors of overly active protein degradation, and enhancers of endogenous proteolytic pathways, such as the UPS. This review summarizes recent work on the pathomechanisms of abnormal protein folding and degradation in epilepsy, as well as treatment developments targeting this area.
Collapse
|
14
|
Fischer FP, Kasture AS, Hummel T, Sucic S. Molecular and Clinical Repercussions of GABA Transporter 1 Variants Gone Amiss: Links to Epilepsy and Developmental Spectrum Disorders. Front Mol Biosci 2022; 9:834498. [PMID: 35295842 PMCID: PMC7612498 DOI: 10.3389/fmolb.2022.834498] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2021] [Accepted: 02/01/2022] [Indexed: 12/15/2022] Open
Abstract
The human γ-aminobutyric acid (GABA) transporter 1 (hGAT-1) is the first member of the solute carrier 6 (SLC6) protein superfamily. GAT-1 (SLC6A1) is one of the main GABA transporters in the central nervous system. Its principal physiological role is retrieving GABA from the synapse into neurons and astrocytes, thus swiftly terminating neurotransmission. GABA is a key inhibitory neurotransmitter and shifts in GABAergic signaling can lead to pathological conditions, from anxiety and epileptic seizures to schizophrenia. Point mutations in the SLC6A1 gene frequently give rise to epilepsy, intellectual disability or autism spectrum disorders in the afflicted individuals. The mechanistic routes underlying these are still fairly unclear. Some loss-of-function variants impair the folding and intracellular trafficking of the protein (thus retaining the transporter in the endoplasmic reticulum compartment), whereas others, despite managing to reach their bona fide site of action at the cell surface, nonetheless abolish GABA transport activity (plausibly owing to structural/conformational defects). Whatever the molecular culprit(s), the physiological aftermath transpires into the absence of functional transporters, which in turn perturbs GABAergic actions. Dozens of mutations in the kin SLC6 family members are known to exhort protein misfolding. Such events typically elicit severe ailments in people, e.g., infantile parkinsonism-dystonia or X-linked intellectual disability, in the case of dopamine and creatine transporters, respectively. Flaws in protein folding can be rectified by small molecules known as pharmacological and/or chemical chaperones. The search for such apt remedies calls for a systematic investigation and categorization of the numerous disease-linked variants, by biochemical and pharmacological means in vitro (in cell lines and primary neuronal cultures) and in vivo (in animal models). We here give special emphasis to the utilization of the fruit fly Drosophila melanogaster as a versatile model in GAT-1-related studies. Jointly, these approaches can portray indispensable insights into the molecular factors underlying epilepsy, and ultimately pave the way for contriving efficacious therapeutic options for patients harboring pathogenic mutations in hGAT-1.
Collapse
Affiliation(s)
- Florian P. Fischer
- Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
- Department of Epileptology and Neurology, University of Aachen, Aachen, Germany
| | - Ameya S. Kasture
- Department of Neuroscience and Developmental Biology, University of Vienna, Vienna, Austria
| | - Thomas Hummel
- Department of Neuroscience and Developmental Biology, University of Vienna, Vienna, Austria
| | - Sonja Sucic
- Institute of Pharmacology, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
15
|
Ponleitner M, Szöllősi D, El-Kasaby A, Koban F, Freissmuth M, Stockner T. Thermal Unfolding of the Human Serotonin Transporter: Differential Effect by Stabilizing and Destabilizing Mutations and Cholesterol on Thermodynamic and Kinetic Stability. Mol Pharmacol 2022; 101:95-105. [PMID: 34866045 DOI: 10.1124/molpharm.121.000413] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 11/21/2021] [Indexed: 11/22/2022] Open
Abstract
Folding-deficient mutants of solute carrier 6 (SLC6) family members have been linked to human diseases. The serotonin transporter [(SERT)/SLC6A4] is an important drug target in the treatment of depression, anxiety, and obsessive-compulsive disorders and-with structural information in several conformational states-one of the best understood transporters. Here, we surmised that thermal unfolding offered a glimpse on the folding energy landscape of SLC6 transporters. We carried out molecular dynamic (MD) simulations to understand the mechanistic basis for enhanced and reduced stability, respectively, of the thermostabilized variant SERT-Y110A/I291A/T439S, which had previously been used for crystallization of human SERT in the outward-facing state, and of the folding-deficient SERT-P601A/G602A. We also examined the hydrophobic mismatch caused by the absence of cholesterol to explore the contribution of cholesterol to protein stability. When compared with wild type SERT, the thermodynamic and kinetic stability of SERT-Y110A/I291A/T439S was enhanced. In the other instances, changes in these two components were not correlated: the mutations in SERT-P601A/G602A led to a drop in thermodynamic but an increase in kinetic stability. The divergence was even more pronounced after cholesterol depletion, which reduced thermodynamic stability but increased the kinetic stability of wild type SERT to a level comparable to that of SERT-Y110A/I291A/T439S. We conclude that the low cholesterol content of the endoplasmic reticulum facilitates progression of the folding trajectory by reducing the energy difference between folding intermediates and the native state. SIGNIFICANCE STATEMENT: Point mutations in solute carrier 6 (SLC6) family members cause folding diseases. The serotonin transporter [(SERT)/SLC6A4] is a target for antidepressants and the best understood SLC6. This study produced molecular dynamics simulations and examined thermal unfolding of wild type and mutant SERT variants to understand their folding energy landscape. In the folding-deficient SERT-P012A/G602A, changes in kinetic and thermodynamic stability were not correlated. Similarly, cholesterol depletion lowered thermodynamic but enhanced kinetic stability. These observations allow for rationalizing the action of pharmacochaperones.
Collapse
Affiliation(s)
- Markus Ponleitner
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Austria
| | - Daniel Szöllősi
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Austria
| | - Ali El-Kasaby
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Austria
| | - Florian Koban
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Austria
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Austria
| | - Thomas Stockner
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, Austria
| |
Collapse
|
16
|
Fernandes-Pires G, Braissant O. Current and potential new treatment strategies for creatine deficiency syndromes. Mol Genet Metab 2022; 135:15-26. [PMID: 34972654 DOI: 10.1016/j.ymgme.2021.12.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/13/2021] [Revised: 12/14/2021] [Accepted: 12/14/2021] [Indexed: 12/16/2022]
Abstract
Creatine deficiency syndromes (CDS) are inherited metabolic disorders caused by mutations in GATM, GAMT and SLC6A8 and mainly affect central nervous system (CNS). AGAT- and GAMT-deficient patients lack the functional brain endogenous creatine (Cr) synthesis pathway but express the Cr transporter SLC6A8 at blood-brain barrier (BBB), and can thus be treated by oral supplementation of high doses of Cr. For Cr transporter deficiency (SLC6A8 deficiency or CTD), current treatment strategies benefit one-third of patients. However, as their phenotype is not completely reversed, and for the other two-thirds of CTD patients, the development of novel more effective therapies is needed. This article aims to review the current knowledge on Cr metabolism and CDS clinical aspects, highlighting their current treatment possibilities and the most recent research perspectives on CDS potential therapeutics designed, in particular, to bring new options for the treatment of CTD.
Collapse
Affiliation(s)
- Gabriella Fernandes-Pires
- Service of Clinical Chemistry, University of Lausanne and Lausanne University Hospital, Lausanne, Switzerland
| | - Olivier Braissant
- Service of Clinical Chemistry, University of Lausanne and Lausanne University Hospital, Lausanne, Switzerland.
| |
Collapse
|
17
|
Chen S, Xiong J, Chen B, Zhang C, Deng X, He F, Yang L, Chen C, Peng J, Yin F. Autism spectrum disorder and comorbid neurodevelopmental disorders (ASD-NDDs): Clinical and genetic profile of a pediatric cohort. Clin Chim Acta 2022; 524:179-186. [PMID: 34800434 DOI: 10.1016/j.cca.2021.11.014] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 11/05/2021] [Accepted: 11/15/2021] [Indexed: 12/27/2022]
Abstract
BACKGROUND Autism spectrum disorder (ASD), a neurodevelopmental disorder, is featured by impaired social communication and restricted and repetitive behaviors and interests. ASD and comorbid neurodevelopmental disorders (ASD-NDDs), especially epilepsy and intellectual disability (ID)/global developmental delay (GDD) are frequently presented in genetic disorders. The aim of this study was to explore the clinical and genetic profile of ASD in combination with epilepsy or ID/GDD. METHODS We retrospectively analyzed the clinical characteristics, and genetic spectrum of pediatric patients presenting ASD-NDDs with proven genetic etiology. The pathogenicity of variants was conducted by molecular geneticists and clinicians complied with the guidelines of the American College of Medical Genetics and Genomics (ACMG). RESULTS Among 154 patients with ASD-NDDs, 79 (51.3%) patients gained a genetic diagnosis. Most patients (78/79, 98.7%) had comorbid ID or GDD, and 49 (49/79, 62.0%) had comorbid epilepsy. The clinical characteristics of those 79 patients were varied. 87 genetic variants were found among the 79 pedigrees. Most of the involved genes have roles in gene expression regulation (GER) and neuronal communication (NC). Most genes have been proven to be ASD-related genes, and some of them were not reported to contribute to ASD previously. CONCLUSION We summarized the genetic and clinical profile of 79 ASD-NDDs patients with proven genetic etiology. The genetic spectrum of ASD was expanded, and we highlighted a novel possible ASD candidate gene PRTG.
Collapse
Affiliation(s)
- Shimeng Chen
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Juan Xiong
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Baiyu Chen
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Ciliu Zhang
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Xiaolu Deng
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Fang He
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Lifen Yang
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Chen Chen
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Jing Peng
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China
| | - Fei Yin
- Department of Pediatrics, Xiangya Hospital of Central South University, Changsha, China; Hunan Intellectual and Developmental Disabilities Research Center, Changsha, China.
| |
Collapse
|
18
|
Chen HR, Zhang-Brotzge X, Morozov YM, Li Y, Wang S, Zhang HH, Kuan IS, Fugate EM, Mao H, Sun YY, Rakic P, Lindquist DM, DeGrauw T, Kuan CY. Creatine transporter deficiency impairs stress adaptation and brain energetics homeostasis. JCI Insight 2021; 6:e140173. [PMID: 34324436 PMCID: PMC8492331 DOI: 10.1172/jci.insight.140173] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 07/28/2021] [Indexed: 11/22/2022] Open
Abstract
The creatine transporter (CrT) maintains brain creatine (Cr) levels, but the effects of its deficiency on energetics adaptation under stress remain unclear. There are also no effective treatments for CrT deficiency, the second most common cause of X-linked intellectual disabilities. Herein, we examined the consequences of CrT deficiency in brain energetics and stress-adaptation responses plus the effects of intranasal Cr supplementation. We found that CrT-deficient (CrT–/y) mice harbored dendritic spine and synaptic dysgenesis. Nurtured newborn CrT–/y mice maintained baseline brain ATP levels, with a trend toward signaling imbalance between the p-AMPK/autophagy and mTOR pathways. Starvation elevated the signaling imbalance and reduced brain ATP levels in P3 CrT–/y mice. Similarly, CrT–/y neurons and P10 CrT–/y mice showed an imbalance between autophagy and mTOR signaling pathways and greater susceptibility to cerebral hypoxia-ischemia and ischemic insults. Notably, intranasal administration of Cr after cerebral ischemia increased the brain Cr/N-acetylaspartate ratio, partially averted the signaling imbalance, and reduced infarct size more potently than intraperitoneal Cr injection. These findings suggest important functions for CrT and Cr in preserving the homeostasis of brain energetics in stress conditions. Moreover, intranasal Cr supplementation may be an effective treatment for congenital CrT deficiency and acute brain injury.
Collapse
Affiliation(s)
- Hong-Ru Chen
- Department of Neurosciences, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - Xiaohui Zhang-Brotzge
- Department of Pediatrics, Division of Neurology, Emory University, Atlanta, Georgia, USA
| | - Yury M Morozov
- Department of Neuroscience, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Yuancheng Li
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, Georgia, USA
| | - Siming Wang
- Department of Chemistry, Georgia State University, Atlanta, Georgia, USA
| | | | - Irena S Kuan
- Department of Pediatrics, Division of Neurology, Emory University, Atlanta, Georgia, USA
| | - Elizabeth M Fugate
- Imaging Research Center, Department of Radiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Hui Mao
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, Georgia, USA
| | - Yu-Yo Sun
- Department of Neurosciences, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | - Pasko Rakic
- Department of Neuroscience, Yale University School of Medicine, New Haven, Connecticut, USA
| | - Diana M Lindquist
- Imaging Research Center, Department of Radiology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Ton DeGrauw
- Department of Pediatrics, Division of Neurology, Emory University, Atlanta, Georgia, USA
| | - Chia-Yi Kuan
- Department of Neurosciences, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| |
Collapse
|
19
|
Ghirardini E, Calugi F, Sagona G, Di Vetta F, Palma M, Battini R, Cioni G, Pizzorusso T, Baroncelli L. The Role of Preclinical Models in Creatine Transporter Deficiency: Neurobiological Mechanisms, Biomarkers and Therapeutic Development. Genes (Basel) 2021; 12:genes12081123. [PMID: 34440297 PMCID: PMC8392480 DOI: 10.3390/genes12081123] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 07/22/2021] [Accepted: 07/23/2021] [Indexed: 12/12/2022] Open
Abstract
Creatine (Cr) Transporter Deficiency (CTD) is an X-linked metabolic disorder, mostly caused by missense mutations in the SLC6A8 gene and presenting with intellectual disability, autistic behavior, and epilepsy. There is no effective treatment for CTD and patients need lifelong assistance. Thus, the research of novel intervention strategies is a major scientific challenge. Animal models are an excellent tool to dissect the disease pathogenetic mechanisms and drive the preclinical development of therapeutics. This review illustrates the current knowledge about Cr metabolism and CTD clinical aspects, with a focus on mainstay diagnostic and therapeutic options. Then, we discuss the rodent models of CTD characterized in the last decade, comparing the phenotypes expressed within clinically relevant domains and the timeline of symptom development. This analysis highlights that animals with the ubiquitous deletion/mutation of SLC6A8 genes well recapitulate the early onset and the complex pathological phenotype of the human condition. Thus, they should represent the preferred model for preclinical efficacy studies. On the other hand, brain- and cell-specific conditional mutants are ideal for understanding the basis of CTD at a cellular and molecular level. Finally, we explain how CTD models might provide novel insight about the pathogenesis of other disorders, including cancer.
Collapse
MESH Headings
- Animals
- Biomarkers/metabolism
- Brain Diseases, Metabolic, Inborn/metabolism
- Brain Diseases, Metabolic, Inborn/pathology
- Brain Diseases, Metabolic, Inborn/therapy
- Central Nervous System/pathology
- Creatine/deficiency
- Creatine/metabolism
- Disease Models, Animal
- Humans
- Mental Retardation, X-Linked/metabolism
- Mental Retardation, X-Linked/pathology
- Mental Retardation, X-Linked/therapy
- Mice
- Plasma Membrane Neurotransmitter Transport Proteins/deficiency
- Plasma Membrane Neurotransmitter Transport Proteins/metabolism
- Rats
Collapse
Affiliation(s)
- Elsa Ghirardini
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
| | - Francesco Calugi
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Giulia Sagona
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Federica Di Vetta
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Department of Biology, University of Pisa, I-56126 Pisa, Italy
| | - Martina Palma
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Roberta Battini
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Department of Clinical and Experimental Medicine, University of Pisa, I-56126 Pisa, Italy
| | - Giovanni Cioni
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Department of Clinical and Experimental Medicine, University of Pisa, I-56126 Pisa, Italy
| | - Tommaso Pizzorusso
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Department of Neuroscience, Psychology, Drug Research and Child Health NEUROFARBA, University of Florence, I-50135 Florence, Italy
| | - Laura Baroncelli
- Department of Developmental Neuroscience, IRCCS Stella Maris Foundation, I-56128 Pisa, Italy; (E.G.); (G.S.); (R.B.); (G.C.)
- Institute of Neuroscience, National Research Council (CNR), I-56124 Pisa, Italy; (F.C.); (F.D.V.); (M.P.); (T.P.)
- Correspondence:
| |
Collapse
|
20
|
Bonilla DA, Moreno Y, Rawson ES, Forero DA, Stout JR, Kerksick CM, Roberts MD, Kreider RB. A Convergent Functional Genomics Analysis to Identify Biological Regulators Mediating Effects of Creatine Supplementation. Nutrients 2021; 13:2521. [PMID: 34444681 PMCID: PMC8397972 DOI: 10.3390/nu13082521] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2021] [Accepted: 07/21/2021] [Indexed: 12/12/2022] Open
Abstract
Creatine (Cr) and phosphocreatine (PCr) are physiologically essential molecules for life, given they serve as rapid and localized support of energy- and mechanical-dependent processes. This evolutionary advantage is based on the action of creatine kinase (CK) isozymes that connect places of ATP synthesis with sites of ATP consumption (the CK/PCr system). Supplementation with creatine monohydrate (CrM) can enhance this system, resulting in well-known ergogenic effects and potential health or therapeutic benefits. In spite of our vast knowledge about these molecules, no integrative analysis of molecular mechanisms under a systems biology approach has been performed to date; thus, we aimed to perform for the first time a convergent functional genomics analysis to identify biological regulators mediating the effects of Cr supplementation in health and disease. A total of 35 differentially expressed genes were analyzed. We identified top-ranked pathways and biological processes mediating the effects of Cr supplementation. The impact of CrM on miRNAs merits more research. We also cautiously suggest two dose-response functional pathways (kinase- and ubiquitin-driven) for the regulation of the Cr uptake. Our functional enrichment analysis, the knowledge-based pathway reconstruction, and the identification of hub nodes provide meaningful information for future studies. This work contributes to a better understanding of the well-reported benefits of Cr in sports and its potential in health and disease conditions, although further clinical research is needed to validate the proposed mechanisms.
Collapse
Affiliation(s)
- Diego A. Bonilla
- Research Division, Dynamical Business & Science Society—DBSS International SAS, Bogotá 110861, Colombia;
- Research Group in Biochemistry and Molecular Biology, Universidad Distrital Francisco José de Caldas, Bogotá 110311, Colombia
- Research Group in Physical Activity, Sports and Health Sciences (GICAFS), Universidad de Córdoba, Montería 230002, Colombia
- kDNA Genomics, Joxe Mari Korta Research Center, University of the Basque Country UPV/EHU, 20018 Donostia-San Sebastián, Spain
| | - Yurany Moreno
- Research Division, Dynamical Business & Science Society—DBSS International SAS, Bogotá 110861, Colombia;
- Research Group in Biochemistry and Molecular Biology, Universidad Distrital Francisco José de Caldas, Bogotá 110311, Colombia
| | - Eric S. Rawson
- Department of Health, Nutrition and Exercise Science, Messiah University, Mechanicsburg, PA 17055, USA;
| | - Diego A. Forero
- Professional Program in Sport Training, School of Health and Sport Sciences, Fundación Universitaria del Área Andina, Bogotá 111221, Colombia;
| | - Jeffrey R. Stout
- Physiology of Work and Exercise Response (POWER) Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL 32816, USA;
| | - Chad M. Kerksick
- Exercise and Performance Nutrition Laboratory, School of Health Sciences, Lindenwood University, Saint Charles, MO 63301, USA;
| | - Michael D. Roberts
- School of Kinesiology, Auburn University, Auburn, AL 36849, USA;
- Edward via College of Osteopathic Medicine, Auburn, AL 36849, USA
| | - Richard B. Kreider
- Exercise & Sport Nutrition Laboratory, Human Clinical Research Facility, Texas A&M University, College Station, TX 77843, USA;
| |
Collapse
|
21
|
Duran-Trio L, Fernandes-Pires G, Simicic D, Grosse J, Roux-Petronelli C, Bruce SJ, Binz PA, Sandi C, Cudalbu C, Braissant O. A new rat model of creatine transporter deficiency reveals behavioral disorder and altered brain metabolism. Sci Rep 2021; 11:1636. [PMID: 33452333 PMCID: PMC7810893 DOI: 10.1038/s41598-020-80824-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Accepted: 12/28/2020] [Indexed: 11/10/2022] Open
Abstract
Creatine is an organic compound used as fast phosphate energy buffer to recycle ATP, important in tissues with high energy demand such as muscle or brain. Creatine is taken from the diet or endogenously synthetized by the enzymes AGAT and GAMT, and specifically taken up by the transporter SLC6A8. Deficit in the endogenous synthesis or in the transport leads to Cerebral Creatine Deficiency Syndromes (CCDS). CCDS are characterized by brain creatine deficiency, intellectual disability with severe speech delay, behavioral troubles such as attention deficits and/or autistic features, and epilepsy. Among CCDS, the X-linked creatine transporter deficiency (CTD) is the most prevalent with no efficient treatment so far. Different mouse models of CTD were generated by doing long deletions in the Slc6a8 gene showing reduced brain creatine and cognitive deficiencies or impaired motor function. We present a new knock-in (KI) rat model of CTD holding an identical point mutation found in patients with reported lack of transporter activity. KI males showed brain creatine deficiency, increased urinary creatine/creatinine ratio, cognitive deficits and autistic-like traits. The Slc6a8Y389C KI rat fairly enriches the spectrum of CTD models and provides new data about the pathology, being the first animal model of CTD carrying a point mutation.
Collapse
Affiliation(s)
- Lara Duran-Trio
- Service of Clinical Chemistry, University of Lausanne and University Hospital of Lausanne, Rue du Bugnon 46, 1011, Lausanne, Switzerland
| | - Gabriella Fernandes-Pires
- Service of Clinical Chemistry, University of Lausanne and University Hospital of Lausanne, Rue du Bugnon 46, 1011, Lausanne, Switzerland
| | - Dunja Simicic
- Centre d'Imagerie Biomedicale (CIBM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Jocelyn Grosse
- Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Clothilde Roux-Petronelli
- Service of Clinical Chemistry, University of Lausanne and University Hospital of Lausanne, Rue du Bugnon 46, 1011, Lausanne, Switzerland
| | - Stephen J Bruce
- Service of Clinical Chemistry, University of Lausanne and University Hospital of Lausanne, Rue du Bugnon 46, 1011, Lausanne, Switzerland
| | - Pierre-Alain Binz
- Service of Clinical Chemistry, University of Lausanne and University Hospital of Lausanne, Rue du Bugnon 46, 1011, Lausanne, Switzerland
| | - Carmen Sandi
- Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Cristina Cudalbu
- Centre d'Imagerie Biomedicale (CIBM), Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
| | - Olivier Braissant
- Service of Clinical Chemistry, University of Lausanne and University Hospital of Lausanne, Rue du Bugnon 46, 1011, Lausanne, Switzerland.
| |
Collapse
|
22
|
Bhat S, El-Kasaby A, Freissmuth M, Sucic S. Functional and Biochemical Consequences of Disease Variants in Neurotransmitter Transporters: A Special Emphasis on Folding and Trafficking Deficits. Pharmacol Ther 2020; 222:107785. [PMID: 33310157 PMCID: PMC7612411 DOI: 10.1016/j.pharmthera.2020.107785] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 12/02/2020] [Indexed: 01/30/2023]
Abstract
Neurotransmitters, such as γ-aminobutyric acid, glutamate, acetyl choline, glycine and the monoamines, facilitate the crosstalk within the central nervous system. The designated neurotransmitter transporters (NTTs) both release and take up neurotransmitters to and from the synaptic cleft. NTT dysfunction can lead to severe pathophysiological consequences, e.g. epilepsy, intellectual disability, or Parkinson’s disease. Genetic point mutations in NTTs have recently been associated with the onset of various neurological disorders. Some of these mutations trigger folding defects in the NTT proteins. Correct folding is a prerequisite for the export of NTTs from the endoplasmic reticulum (ER) and the subsequent trafficking to their pertinent site of action, typically at the plasma membrane. Recent studies have uncovered some of the key features in the molecular machinery responsible for transporter protein folding, e.g., the role of heat shock proteins in fine-tuning the ER quality control mechanisms in cells. The therapeutic significance of understanding these events is apparent from the rising number of reports, which directly link different pathological conditions to NTT misfolding. For instance, folding-deficient variants of the human transporters for dopamine or GABA lead to infantile parkinsonism/dystonia and epilepsy, respectively. From a therapeutic point of view, some folding-deficient NTTs are amenable to functional rescue by small molecules, known as chemical and pharmacological chaperones.
Collapse
Affiliation(s)
- Shreyas Bhat
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Ali El-Kasaby
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Michael Freissmuth
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria
| | - Sonja Sucic
- Institute of Pharmacology and the Gaston H. Glock Research Laboratories for Exploratory Drug Development, Center of Physiology and Pharmacology, Medical University of Vienna, A-1090 Vienna, Austria.
| |
Collapse
|
23
|
Ono K, Nakashima M. Sodium 4-phenylbutyrate inhibits protein glycation. Biomed Rep 2020; 13:61. [PMID: 33149906 DOI: 10.3892/br.2020.1368] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Accepted: 09/08/2020] [Indexed: 12/16/2022] Open
Abstract
The production and accumulation of advanced glycation end-products (AGEs) are hypothesized to have a causal role in the development of the complications associated with aging and lifestyle-related diseases, such as diabetes, atherosclerosis and hyperlipidemia. Therefore, it is important to reduce the production and accumulation of AGEs. In the present study, the ability of sodium 4-phenylbutyrate (PBA) on inhibition of glycation was assessed. In vitro, PBA inhibited the glycation of albumin and collagen by up to 42.1 and 36.9%, respectively. Furthermore, when spontaneously diabetic KK mice were administered PBA (20 mg/day) or vehicle orally, glycosuria developed rapidly in the control mice, but after 6 weeks, only one treated mouse was glycosuric. In addition, the weight gain and HbA1c levels were significantly lower in the treated mice compared with the untreated mice (weight gain, 36.0 g vs. 39.4 g, P<0.01; HbA1C level, 3.96 vs. 4.78%, P<0.01; respectively). These results suggested that PBA also inhibited glycation in vivo. Further studies are required to determine whether PBA may be effective for the therapy or prevention of aging or lifestyle-related diseases caused by the accumulation of AGEs. The method of administration and the side-effects of PBA have already been established as PBA is already used clinically. Therefore, the repurposing of PBA for reducing AGE levels may be a potential option to reduce complications associated with aging.
Collapse
Affiliation(s)
- Kazuhiko Ono
- Department of Drug Informatics and Translational Research, Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka 814-0180, Japan
| | - Manabu Nakashima
- Department of Immunological and Molecular Pharmacology, Faculty of Pharmaceutical Sciences, Fukuoka University, Fukuoka 814-0180, Japan
| |
Collapse
|
24
|
Farr CV, El-Kasaby A, Freissmuth M, Sucic S. The Creatine Transporter Unfolded: A Knotty Premise in the Cerebral Creatine Deficiency Syndrome. Front Synaptic Neurosci 2020; 12:588954. [PMID: 33192443 PMCID: PMC7644880 DOI: 10.3389/fnsyn.2020.588954] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 09/18/2020] [Indexed: 12/16/2022] Open
Abstract
Creatine provides cells with high-energy phosphates for the rapid reconstitution of hydrolyzed adenosine triphosphate. The eponymous creatine transporter (CRT1/SLC6A8) belongs to a family of solute carrier 6 (SLC6) proteins. The key role of CRT1 is to translocate creatine across tissue barriers and into target cells, such as neurons and myocytes. Individuals harboring mutations in the coding sequence of the human CRT1 gene develop creatine transporter deficiency (CTD), one of the pivotal underlying causes of cerebral creatine deficiency syndrome. CTD encompasses an array of clinical manifestations, including severe intellectual disability, epilepsy, autism, development delay, and motor dysfunction. CTD is characterized by the absence of cerebral creatine, which implies an indispensable role for CRT1 in supplying the brain cells with creatine. CTD-associated variants dramatically reduce or abolish creatine transport activity by CRT1. Many of these are point mutations that are known to trigger folding defects, leading to the retention of encoded CRT1 proteins in the endoplasmic reticulum and precluding their delivery to the cell surface. Misfolding of several related SLC6 transporters also gives rise to detrimental pathologic conditions in people; e.g., mutations in the dopamine transporter induce infantile parkinsonism/dystonia, while mutations in the GABA transporter 1 cause treatment-resistant epilepsy. In some cases, folding defects are amenable to rescue by small molecules, known as pharmacological and chemical chaperones, which restore the cell surface expression and transport activity of the previously non-functional proteins. Insights from the recent molecular, animal and human case studies of CTD add toward our understanding of this complex disorder and reveal the wide-ranging effects elicited upon CRT1 dysfunction. This grants novel therapeutic prospects for the treatment of patients afflicted with CTD, e.g., modifying the creatine molecule to facilitate CRT1-independent entry into brain cells, or correcting folding-deficient and loss-of-function CTD variants using pharmacochaperones and/or allosteric modulators. The latter justifies a search for additional compounds with a capacity to correct mutation-specific defects.
Collapse
Affiliation(s)
| | | | | | - Sonja Sucic
- Institute of Pharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| |
Collapse
|
25
|
Brecker M, Khakhina S, Schubert TJ, Thompson Z, Rubenstein RC. The Probable, Possible, and Novel Functions of ERp29. Front Physiol 2020; 11:574339. [PMID: 33013490 PMCID: PMC7506106 DOI: 10.3389/fphys.2020.574339] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Accepted: 08/14/2020] [Indexed: 12/16/2022] Open
Abstract
The luminal endoplasmic reticulum (ER) protein of 29 kDa (ERp29) is a ubiquitously expressed cellular agent with multiple critical roles. ERp29 regulates the biosynthesis and trafficking of several transmembrane and secretory proteins, including the cystic fibrosis transmembrane conductance regulator (CFTR), the epithelial sodium channel (ENaC), thyroglobulin, connexin 43 hemichannels, and proinsulin. ERp29 is hypothesized to promote ER to cis-Golgi cargo protein transport via COP II machinery through its interactions with the KDEL receptor; this interaction may facilitate the loading of ERp29 clients into COP II vesicles. ERp29 also plays a role in ER stress (ERS) and the unfolded protein response (UPR) and is implicated in oncogenesis. Here, we review the vast array of ERp29’s clients, its role as an ER to Golgi escort protein, and further suggest ERp29 as a potential target for therapies related to diseases of protein misfolding and mistrafficking.
Collapse
Affiliation(s)
- Margaret Brecker
- Cystic Fibrosis Center, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States
| | - Svetlana Khakhina
- Cystic Fibrosis Center, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States
| | - Tyler J. Schubert
- Cystic Fibrosis Center, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States
| | - Zachary Thompson
- Cystic Fibrosis Center, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States
| | - Ronald C. Rubenstein
- Cystic Fibrosis Center, The Children’s Hospital of Philadelphia, Philadelphia, PA, United States
- Department of Pediatrics, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, United States
- Division of Allergy and Pulmonary Medicine, Department of Pediatrics, Washington University in St. Louis School of Medicine, St. Louis, MO, United States
- *Correspondence: Ronald C. Rubenstein, ;
| |
Collapse
|
26
|
Sun WH, Zhuang DY, Wang Y, Xiao FF, Wu MY, Dong XR, Zhang P, Wang HJ, Zhou WH, Wu BB. [Clinical features and SLC6A8 gene mutations of cerebral creatine deficiency syndrome I: an analysis of two families]. ZHONGGUO DANG DAI ER KE ZA ZHI = CHINESE JOURNAL OF CONTEMPORARY PEDIATRICS 2020; 22:482-487. [PMID: 32434645 PMCID: PMC7389393 DOI: 10.7499/j.issn.1008-8830.2002012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Accepted: 03/30/2020] [Indexed: 06/11/2023]
Abstract
This article reports the clinical and genetic features of two cases of cerebral creatine deficiency syndrome I (CCDSI) caused by SLC6A8 gene mutations. Both children were boys. Boy 1 (aged 2 years and 10 months) and Boy 2 (aged 8 years and 11 months) had the clinical manifestations of delayed mental and motor development, and convulsion. Their older brothers had the same symptoms. The mother of the boy 1 had mild intellectual disability. The genetic analysis showed two novel homozygous mutations, c.200G>A(p.Gly67Asp) and c.626_627delCT(p.Pro209Argfs*87), in the SLC6A8 gene on the X chromosome, both of which came from their mothers. These two novel mutations were rated as possible pathogenic mutations and were not reported in the literature before. This study expands the mutation spectrum of the SLC6A8 gene and has great significance in the diagnosis of boys with delayed development, and epilepsy.
Collapse
Affiliation(s)
- Wei-Hua Sun
- Pediatric Research Institute, Children's Hospital, Fudan University, Shanghai 201102, China.
| | | | | | | | | | | | | | | | | | | |
Collapse
|
27
|
Salazar MD, Zelt NB, Saldivar R, Kuntz CP, Chen S, Penn WD, Bonneau R, Koehler Leman J, Schlebach JP. Classification of the Molecular Defects Associated with Pathogenic Variants of the SLC6A8 Creatine Transporter. Biochemistry 2020; 59:1367-1377. [PMID: 32207963 DOI: 10.1021/acs.biochem.9b00956] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
More than 80 loss-of-function (LOF) mutations in the SLC6A8 creatine transporter (hCRT1) are responsible for cerebral creatine deficiency syndrome (CCDS), which gives rise to a spectrum of neurological defects, including intellectual disability, epilepsy, and autism spectrum disorder. To gain insight into the nature of the molecular defects caused by these mutations, we quantitatively profiled the cellular processing, trafficking, expression, and function of eight pathogenic CCDS variants in relation to the wild type (WT) and one neutral isoform. All eight CCDS variants exhibit measurable proteostatic deficiencies that likely contribute to the observed LOF. However, the magnitudes of their specific effects on the expression and trafficking of hCRT1 vary considerably, and we find that the LOF associated with two of these variants primarily arises from the disruption of the substrate-binding pocket. In conjunction with an analysis of structural models of the transporter, we use these data to suggest mechanistic classifications for these variants. To evaluate potential avenues for therapeutic intervention, we assessed the sensitivity of these variants to temperature and measured their response to the proteostasis regulator 4-phenylbutyrate (4-PBA). Only one of the tested variants (G132V) is sensitive to temperature, though its response to 4-PBA is negligible. Nevertheless, 4-PBA significantly enhances the activity of WT hCRT1 in HEK293T cells, which suggests it may be worth evaluating as a therapeutic for female intellectual disability patients carrying a single CCDS mutation. Together, these findings reveal that pathogenic SLC6A8 mutations cause a spectrum of molecular defects that should be taken into consideration in future efforts to develop CCDS therapeutics.
Collapse
Affiliation(s)
- Martin D Salazar
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Nathan B Zelt
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Robert Saldivar
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Charles P Kuntz
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Sheng Chen
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Wesley D Penn
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| | - Richard Bonneau
- Center for Computational Biology, Flatiron Institute, Simons Foundation, New York, New York 10010, United States.,Department of Biology, New York University, New York, New York 10003, United States.,Department of Computer Science, New York University, New York, New York 10012, United States.,Center for Data Science, New York University, New York, New York 10011, United States
| | - Julia Koehler Leman
- Center for Computational Biology, Flatiron Institute, Simons Foundation, New York, New York 10010, United States
| | - Jonathan P Schlebach
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405, United States
| |
Collapse
|
28
|
How to rescue misfolded SERT, DAT and NET: targeting conformational intermediates with atypical inhibitors and partial releasers. Biochem Soc Trans 2019; 47:861-874. [PMID: 31064865 PMCID: PMC6599159 DOI: 10.1042/bst20180512] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2019] [Revised: 04/12/2019] [Accepted: 04/12/2019] [Indexed: 11/17/2022]
Abstract
Point mutations in the coding sequence for solute carrier 6 (SLC6) family members result in clinically relevant disorders, which are often accounted for by a loss-of-function phenotype. In many instances, the mutated transporter is not delivered to the cell surface because it is retained in the endoplasmic reticulum (ER). The underlying defect is improper folding of the transporter and is the case for many of the known dopamine transporter mutants. The monoamine transporters, i.e. the transporters for norepinephrine (NET/SLC6A2), dopamine (DAT/SLC6A3) and serotonin (SERT/SLC6A4), have a rich pharmacology; hence, their folding-deficient mutants lend themselves to explore the concept of pharmacological chaperoning. Pharmacochaperones are small molecules, which bind to folding intermediates with exquisite specificity and scaffold them to a folded state, which is exported from the ER and delivered to the cell surface. Pharmacochaperoning of mutant monoamine transporters, however, is not straightforward: ionic conditions within the ER are not conducive to binding of most typical monoamine transporter ligands. A collection of compounds exists, which are classified as atypical ligands because they trap monoamine transporters in unique conformational states. The atypical binding mode of some DAT inhibitors has been linked to their anti-addictive action. Here, we propose that atypical ligands and also compounds recently classified as partial releasers can serve as pharmacochaperones.
Collapse
|