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Zou S, Lan YL, Gong Y, Chen Z, Xu C. The role of ATP1A3 gene in epilepsy: We need to know more. Front Cell Neurosci 2023; 17:1143956. [PMID: 36866063 PMCID: PMC9972585 DOI: 10.3389/fncel.2023.1143956] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2023] [Accepted: 01/23/2023] [Indexed: 02/16/2023] Open
Abstract
The ATP1A3 gene, which encodes the Na+/K+-ATPase α3 catalytic subunit, plays a crucial role in both physiological and pathological conditions in the brain, and mutations in this gene have been associated with a wide variety of neurological diseases by impacting the whole infant development stages. Cumulative clinical evidence suggests that some severe epileptic syndromes have been linked to mutations in ATP1A3, among which inactivating mutation of ATP1A3 has been intriguingly found to be a candidate pathogenesis for complex partial and generalized seizures, proposing ATP1A3 regulators as putative targets for the rational design of antiepileptic therapies. In this review, we introduced the physiological function of ATP1A3 and summarized the findings about ATP1A3 in epileptic conditions from both clinical and laboratory aspects at first. Then, some possible mechanisms of how ATP1A3 mutations result in epilepsy are provided. We think this review timely introduces the potential contribution of ATP1A3 mutations in both the genesis and progression of epilepsy. Taken that both the detailed mechanisms and therapeutic significance of ATP1A3 for epilepsy are not yet fully illustrated, we think that both in-depth mechanisms investigations and systematic intervention experiments targeting ATP1A3 are needed, and by doing so, perhaps a new light can be shed on treating ATP1A3-associated epilepsy.
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Affiliation(s)
- Shuang Zou
- Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou, China
| | - Yu-Long Lan
- Department of Neurosurgery, Second Affiliated Hospital, School of Medicine, Zhejiang University, Hangzhou, Zhejiang, China,*Correspondence: Yu-Long Lan ✉
| | - Yiwei Gong
- Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou, China
| | - Zhong Chen
- Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou, China
| | - Cenglin Xu
- Key Laboratory of Neuropharmacology and Translational Medicine of Zhejiang Province, School of Pharmaceutical Science, Zhejiang Chinese Medical University, Hangzhou, China,Cenglin Xu ✉
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Schmid V, Wurzel A, Wetzel CH, Plössl K, Bruckmann A, Luckner P, Weber BHF, Friedrich U. Retinoschisin and novel Na/K-ATPase interaction partners Kv2.1 and Kv8.2 define a growing protein complex at the inner segments of mammalian photoreceptors. Cell Mol Life Sci 2022; 79:448. [PMID: 35876901 PMCID: PMC9314279 DOI: 10.1007/s00018-022-04409-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 05/05/2022] [Accepted: 05/30/2022] [Indexed: 11/28/2022]
Abstract
The RS1 gene on Xp 22.13 encodes retinoschisin which is known to directly interact with the retinal Na/K-ATPase at the photoreceptor inner segments. Pathologic mutations in RS1 cause X-linked juvenile retinoschisis (XLRS), a hereditary retinal dystrophy in young males. To further delineate the retinoschisin-Na/K-ATPase complex, co-immunoprecipitation was performed with porcine and murine retinal lysates targeting the ATP1A3 subunit. This identified the voltage-gated potassium (Kv) channel subunits Kv2.1 and Kv8.2 as direct interaction partners of the retinal Na/K-ATPase. Colocalization of the individual components of the complex was demonstrated at the membrane of photoreceptor inner segments. We further show that retinoschisin-deficiency, a frequent consequence of molecular pathology in XLRS, causes mislocalization of the macromolecular complex during postnatal retinal development with a simultaneous reduction of Kv2.1 and Kv8.2 protein expression, while the level of retinal Na/K-ATPase expression remains unaffected. Patch-clamp analysis revealed no effect of retinoschisin-deficiency on Kv channel mediated potassium ion currents in vitro. Together, our data suggest that Kv2.1 and Kv8.2 together with retinoschisin and the retinal Na/K-ATPase are integral parts of a macromolecular complex at the photoreceptor inner segments. Defective compartmentalization of this complex due to retinoschisin-deficiency may be a crucial step in initial XLRS pathogenesis.
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Affiliation(s)
- Verena Schmid
- Institute of Human Genetics, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany
| | - Alexander Wurzel
- Institute of Human Genetics, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany
| | - Christian H Wetzel
- Department of Psychiatry and Psychotherapy, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany
| | - Karolina Plössl
- Institute of Human Genetics, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany
| | - Astrid Bruckmann
- Institute of Biochemistry, Genetics and Microbiology, Protein Mass Spectrometry Group, University of Regensburg, Universitätsstraße 31, 93053, Regensburg, Germany
| | - Patricia Luckner
- Institute of Biochemistry, Genetics and Microbiology, Protein Mass Spectrometry Group, University of Regensburg, Universitätsstraße 31, 93053, Regensburg, Germany
| | - Bernhard H F Weber
- Institute of Human Genetics, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany.
- Institute of Clinical Human Genetics, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany.
| | - Ulrike Friedrich
- Institute of Human Genetics, University of Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany.
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Functional compartmentalization of photoreceptor neurons. Pflugers Arch 2021; 473:1493-1516. [PMID: 33880652 DOI: 10.1007/s00424-021-02558-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Revised: 03/15/2021] [Accepted: 03/22/2021] [Indexed: 12/16/2022]
Abstract
Retinal photoreceptors are neurons that convert dynamically changing patterns of light into electrical signals that are processed by retinal interneurons and ultimately transmitted to vision centers in the brain. They represent the essential first step in seeing without which the remainder of the visual system is rendered moot. To support this role, the major functions of photoreceptors are segregated into three main specialized compartments-the outer segment, the inner segment, and the pre-synaptic terminal. This compartmentalization is crucial for photoreceptor function-disruption leads to devastating blinding diseases for which therapies remain elusive. In this review, we examine the current understanding of the molecular and physical mechanisms underlying photoreceptor functional compartmentalization and highlight areas where significant knowledge gaps remain.
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Ropelewski P, Imanishi Y. RPE Cells Engulf Microvesicles Secreted by Degenerating Rod Photoreceptors. eNeuro 2020; 7:ENEURO.0507-19.2020. [PMID: 32376599 PMCID: PMC7242815 DOI: 10.1523/eneuro.0507-19.2020] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2019] [Revised: 04/10/2020] [Accepted: 04/24/2020] [Indexed: 01/11/2023] Open
Abstract
Rhodopsin is mislocalized to the inner segment plasma membrane (IS PM) in various blinding disorders including autosomal-dominant retinitis pigmentosa caused by class I rhodopsin mutations. In these disorders, rhodopsin-laden microvesicles are secreted into the extracellular milieu by afflicted photoreceptor cells. Using a Xenopus laevis model expressing class I mutant rhodopsin or Na+/K+-ATPase (NKA) fused to Dendra2, we fluorescently labeled the microvesicles and found retinal pigment epithelial (RPE) cells are capable of engulfing microvesicles containing rhodopsin. A unique sorting mechanism allows class I mutant rhodopsin, but not NKA, to be packaged into the microvesicles. Under normal physiological conditions, NKA is not shed as microvesicles to the extracellular space, but is degraded intracellularly. Those studies provide novel insights into protein homeostasis in the photoreceptor IS PM.
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Affiliation(s)
- Philip Ropelewski
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106
| | - Yoshikazu Imanishi
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106
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Disrupted Plasma Membrane Protein Homeostasis in a Xenopus Laevis Model of Retinitis Pigmentosa. J Neurosci 2019; 39:5581-5593. [PMID: 31061086 DOI: 10.1523/jneurosci.3025-18.2019] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 03/23/2019] [Accepted: 04/26/2019] [Indexed: 12/17/2022] Open
Abstract
Rhodopsin mislocalization is frequently observed in retinitis pigmentosa (RP) patients. For example, class I mutant rhodopsin is deficient in the VxPx trafficking signal, mislocalizes to the plasma membrane (PM) of rod photoreceptor inner segments (ISs), and causes autosomal dominant RP. Mislocalized rhodopsin causes photoreceptor degeneration in a manner independent of light-activation. In this manuscript, we took advantage of Xenopus laevis models of both sexes expressing wild-type human rhodopsin or its class I Q344ter mutant fused to Dendra2 fluorescent protein to characterize a novel light-independent mechanism of photoreceptor degeneration caused by mislocalized rhodopsin. We found that rhodopsin mislocalized to the PM is actively internalized and transported to lysosomes where it is degraded. This degradation process results in the downregulation of a crucial component of the photoreceptor IS PM: the sodium-potassium ATPase α-subunit (NKAα). The downregulation of NKAα is not because of decreased NKAα mRNA, but due to cotransport of mislocalized rhodopsin and NKAα to lysosomes or autophagolysosomes. In a separate set of experiments, we found that class I mutant rhodopsin, which causes NKAα downregulation, also causes shortening and loss of rod outer segments (OSs); the symptoms frequently observed in the early stages of human RP. Likewise, pharmacological inhibition of NKAα led to shortening and loss of rod OSs. These combined studies suggest that mislocalized rhodopsin leads to photoreceptor dysfunction through disruption of the PM protein homeostasis and compromised NKAα function. This study unveiled a novel role of lysosome-mediated degradation in causing inherited disorders manifested by mislocalization of ciliary receptors.SIGNIFICANCE STATEMENT Retinal ciliopathy is the most common form of inherited blinding disorder frequently manifesting rhodopsin mislocalization. Our understanding of the relationships between rhodopsin mislocalization and photoreceptor dysfunction/degeneration has been far from complete. This study uncovers a hitherto uncharacterized consequence of rhodopsin mislocalization: the activation of the lysosomal pathway, which negatively regulates the amount of the sodium-potassium ATPase (NKAα) on the inner segment plasma membrane. On the plasma membrane, mislocalized rhodopsin extracts NKAα and sends it to lysosomes where they are co-degraded. Compromised NKAα function leads to shortening and loss of the photoreceptor outer segments as observed for various inherited blinding disorders. In summary, this study revealed a novel pathogenic mechanism applicable to various forms of blinding disorders caused by rhodopsin mislocalization.
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Geneva II, Tan HY, Calvert PD. Untangling ciliary access and enrichment of two rhodopsin-like receptors using quantitative fluorescence microscopy reveals cell-specific sorting pathways. Mol Biol Cell 2016; 28:554-566. [PMID: 27974638 PMCID: PMC5305262 DOI: 10.1091/mbc.e16-07-0549] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 12/05/2016] [Accepted: 12/09/2016] [Indexed: 11/11/2022] Open
Abstract
Quantitative microscopy shows that protein-sorting signals have opposite effects on ciliary enrichment of G protein–coupled receptors in different cell types, revealing distinct ciliary trafficking mechanisms among ciliated cells. Resolution limitations of optical systems are major obstacles for determining whether proteins are enriched within cell compartments. Here we use an approach to determine the degree of membrane protein ciliary enrichment that quantitatively accounts for the differences in sampling of the ciliary and apical membranes inherent to confocal microscopes. Theory shows that cilia will appear more than threefold brighter than the surrounding apical membrane when the densities of fluorescently labeled proteins are the same, thus providing a benchmark for ciliary enrichment. Using this benchmark, we examined the ciliary enrichment signals of two G protein–coupled receptors (GPCRs)—the somatostatin receptor 3 and rhodopsin. Remarkably, we found that the C-terminal VxPx motif, required for efficient enrichment of rhodopsin within rod photoreceptor sensory cilia, inhibited enrichment of the somatostatin receptor in primary cilia. Similarly, VxPx inhibited primary cilium enrichment of a chimera of rhodopsin and somatostatin receptor 3, where the dual Ax(S/A)xQ ciliary targeting motifs within the third intracellular loop of the somatostatin receptor replaced the third intracellular loop of rhodopsin. Rhodopsin was depleted from primary cilia but gained access, without being enriched, with the dual Ax(S/A)xQ motifs. Ciliary enrichment of these GPCRs thus operates via distinct mechanisms in different cells.
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Affiliation(s)
- Ivayla I Geneva
- Center for Vision Research, Department of Ophthalmology, State University of New York Upstate Medical University, Syracuse, NY 13210.,Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY 13210
| | - Han Yen Tan
- Center for Vision Research, Department of Ophthalmology, State University of New York Upstate Medical University, Syracuse, NY 13210
| | - Peter D Calvert
- Center for Vision Research, Department of Ophthalmology, State University of New York Upstate Medical University, Syracuse, NY 13210 .,Department of Biochemistry and Molecular Biology, State University of New York Upstate Medical University, Syracuse, NY 13210.,Department of Neuroscience and Physiology, State University of New York Upstate Medical University, Syracuse, NY 13210
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