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Bianco L, Arrigo A, Antropoli A, Del Fabbro S, Mauro L, Pina A, Bandello F, Battaglia Parodi M. The Retinal Phenotype Associated with the p.Pro101Thr BEST1 Variant. Ophthalmol Retina 2024; 8:288-297. [PMID: 37717827 DOI: 10.1016/j.oret.2023.09.012] [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: 02/21/2023] [Revised: 08/29/2023] [Accepted: 09/11/2023] [Indexed: 09/19/2023]
Abstract
PURPOSE To describe the retinal phenotype associated with the p.Pro101Thr BEST1 variant. DESIGN Retrospective, observational case series. PARTICIPANTS Patients diagnosed with bestrophinopathies in which molecular genetic testing identified the p.Pro101Thr BEST1 as well as healthy carriers among their first-degree relatives. METHODS Medical records were reviewed to obtain data on family history and ophthalmic examinations, including retinal imaging. The imaging protocol included OCT and fundus autofluorescence using Spectralis HRA + OCT (Heidelberg Engineering). Genetic analysis was performed by next-generation sequencing. MAIN OUTCOME MEASURES Results of ophthalmic examinations and multimodal imaging features of retinal phenotypes. RESULTS The c.301C>A, p.Pro101Thr BEST1 missense variant was identified as the causative variant in 8 individuals (all men) from 5 families, accounting for 13% of cases (8/61) and 10% of pathogenic alleles (9/93) in our cohort of patients affected by bestrophinopathies. Seven individuals (14 eyes) had the variant in heterozygous status: all eyes had a hyperopic refractive error (median spherical equivalent of + 3.75 diopters [D]) and 4 individuals had a macular dystrophy with mildly reduced visual acuity (median of 20/25 Snellen), whereas the other 3 were asymptomatic carriers. On multimodal retinal imaging, 5 (36%) out of 14 eyes had subclinical bestrophinopathy, 4 (29%) had typical findings of adult-onset foveomacular vitelliform dystrophy (AOFVD), and the remaining 5 (36%) displayed a pattern dystrophy-like phenotype. Follow-up data were available for 6 subjects, demonstrating clinical stability up to 11 years, in both subclinical and clinical forms. An additional patient with autosomal recessive bestrophinopathy was found to harbor the p.Pro101Thr variant in homozygosity. CONCLUSIONS The p.Pro101Thr BEST1 variant is likely a frequent cause of bestrophinopathy in the Italian population and can result in autosomal dominant macular dystrophies with incomplete penetrance and mild clinical manifestations as well as autosomal recessive bestrophinopathy. The spectrum of autosomal dominant maculopathy includes the typical AOFVD and a pattern dystrophy-like phenotype. FINANCIAL DISCLOSURE(S) Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
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Affiliation(s)
- Lorenzo Bianco
- Department of Ophthalmology, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Alessandro Arrigo
- Department of Ophthalmology, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy.
| | - Alessio Antropoli
- Department of Ophthalmology, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Sebastiano Del Fabbro
- Department of Ophthalmology, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Luca Mauro
- Department of Ophthalmology, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Adelaide Pina
- Department of Ophthalmology, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Francesco Bandello
- Department of Ophthalmology, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
| | - Maurizio Battaglia Parodi
- Department of Ophthalmology, Istituto di Ricerca e Cura a Carattere Scientifico (IRCCS), San Raffaele Scientific Institute, Vita-Salute San Raffaele University, Milan, Italy
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Impaired Bestrophin Channel Activity in an iPSC-RPE Model of Best Vitelliform Macular Dystrophy (BVMD) from an Early Onset Patient Carrying the P77S Dominant Mutation. Int J Mol Sci 2022; 23:ijms23137432. [PMID: 35806438 PMCID: PMC9266689 DOI: 10.3390/ijms23137432] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Accepted: 07/01/2022] [Indexed: 01/25/2023] Open
Abstract
Best Vitelliform Macular dystrophy (BVMD) is the most prevalent of the distinctive retinal dystrophies caused by mutations in the BEST1 gene. This gene, which encodes for a homopentameric calcium-activated ion channel, is crucial for the homeostasis and function of the retinal pigment epithelia (RPE), the cell type responsible for recycling the visual pigments generated by photoreceptor cells. In BVMD patients, mutations in this gene induce functional problems in the RPE cell layer with an accumulation of lipofucsin that evolves into cell death and loss of sight. In this work, we employ iPSC-RPE cells derived from a patient with the p.Pro77Ser dominant mutation to determine the correlation between this variant and the ocular phenotype. To this purpose, gene and protein expression and localization are evaluated in iPSC-RPE cells along with functional assays like phagocytosis and anion channel activity. Our cell model shows no differences in gene expression, protein expression/localization, or phagocytosis capacity, but presents an increased chloride entrance, indicating that the p.Pro77Ser variant might be a gain-of-function mutation. We hypothesize that this variant disturbs the neck region of the BEST1 channel, affecting channel function but maintaining cell homeostasis in the short term. This data shed new light on the different phenotypes of dominant mutations in BEST1, and emphasize the importance of understanding its molecular mechanisms. Furthermore, the data widen the knowledge of this pathology and open the door for a better diagnosis and prognosis of the disease.
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Kamenarova K, Mihova K, Veleva N, Mermeklieva E, Mihaylova B, Dimitrova G, Oscar A, Shandurkov I, Cherninkova S, Kaneva R. Panel-based next-generation sequencing identifies novel mutations in Bulgarian patients with inherited retinal dystrophies. Mol Genet Genomic Med 2022; 10:e1997. [PMID: 35656873 PMCID: PMC9356554 DOI: 10.1002/mgg3.1997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2021] [Revised: 04/07/2022] [Accepted: 05/13/2022] [Indexed: 11/05/2022] Open
Abstract
BACKGROUND Next-generation sequencing (NGS)-based method is being used broadly for genetic testing especially for clinically and genetically heterogeneous disorders, such as inherited retinal degenerations (IRDs) but still not routinely used for molecular diagnostics in Bulgaria. Consequently, the purpose of this study was to evaluate the effectiveness of a molecular diagnostic approach, based on targeted NGS for the identification of the disease-causing mutations in 16 Bulgarian patients with different IRDs. METHODS We applied a customized NGS panel, including 125 genes associated with retinal and other eye diseases to the patients with hereditary retinopathies. RESULTS Systematic filtering approach coupled with copy number variation analysis and segregation study lead to the identification of 16 pathogenic and likely pathogenic variants in 12/16 (75%) of IRD patients, 2 of which novel (12.5%): ABCA4-c.668delA (p.K223Rfs18) and RР1-c.2015dupA (p.K673Efs*25). Mutations in the ABCA4, PRPH2, USH2A, BEST1, RР1, CDHR1, and RHO genes were detected reaching a diagnostic yield between 42.9% for Retinitis pigmentosa cases and 100% for macular degeneration, Usher syndrome, and cone-rod dystrophy patients. CONCLUSION Our results confirm the usefulness of targeted NGS approach based on frequently mutated genes as a comprehensive and successful genetic diagnostic tool for IRDs with significant impact on patients counseling.
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Affiliation(s)
- Kunka Kamenarova
- Molecular Medicine Center, Department of Medical Chemistry and Biochemistry, Medical Faculty, Medical University of Sofia, Sofia, Bulgaria.,Laboratory of Genomic Diagnostics, Department of Medical Chemistry and Biochemistry, Medical Faculty, Medical University of Sofia, Sofia, Bulgaria
| | - Kalina Mihova
- Molecular Medicine Center, Department of Medical Chemistry and Biochemistry, Medical Faculty, Medical University of Sofia, Sofia, Bulgaria.,Laboratory of Genomic Diagnostics, Department of Medical Chemistry and Biochemistry, Medical Faculty, Medical University of Sofia, Sofia, Bulgaria
| | - Nevyana Veleva
- Department of Ophthalmology, University Hospital "Alexandrovska", Medical University of Sofia, Sofia, Bulgaria
| | - Elena Mermeklieva
- Clinic of Ophthalmology, University Hospital "Lozenetz", Medical Faculty, Sofia University "St. Kliment Ohridski", Sofia, Bulgaria
| | | | - Galina Dimitrova
- Department of Ophthalmology, University Hospital "Alexandrovska", Medical University of Sofia, Sofia, Bulgaria
| | - Alexander Oscar
- Department of Ophthalmology, University Hospital "Alexandrovska", Medical University of Sofia, Sofia, Bulgaria
| | | | - Sylvia Cherninkova
- Department of Neurology, University hospital "Alexandrovska", Medical University of Sofia, Sofia, Bulgaria
| | - Radka Kaneva
- Molecular Medicine Center, Department of Medical Chemistry and Biochemistry, Medical Faculty, Medical University of Sofia, Sofia, Bulgaria.,Laboratory of Genomic Diagnostics, Department of Medical Chemistry and Biochemistry, Medical Faculty, Medical University of Sofia, Sofia, Bulgaria
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Self-organization and surface properties of hBest1 in models of biological membranes. Adv Colloid Interface Sci 2022; 302:102619. [PMID: 35276535 DOI: 10.1016/j.cis.2022.102619] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2021] [Revised: 02/19/2022] [Accepted: 02/20/2022] [Indexed: 11/22/2022]
Abstract
The transmembrane Ca2+ - activated Cl- channel - human bestrophin-1 (hBest1) is expressed in retinal pigment epithelium and mutations of BEST1 gene cause ocular degenerative diseases colectivelly referred to as "bestrophinopathies". A large number of genetical, biochemical, biophysical and molecular biological studies have been performed to understand the relationship between structure and function of the hBest1 protein and its pathophysiological significance. Here, we review the current understanding of hBest1 surface organization, interactions with membrane lipids in model membranes, and its association with microdomains of cellular membranes. These highlights are significant for modulation of channel activity in cells.
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Lee JH, Lew YJ, Kim JH, Kim JW, Kim CG, Lee DW. The Characteristics and the Clinical Courses of Best Disease in Korean Patients. JOURNAL OF THE KOREAN OPHTHALMOLOGICAL SOCIETY 2021. [DOI: 10.3341/jkos.2021.62.3.337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Sensing through Non-Sensing Ocular Ion Channels. Int J Mol Sci 2020; 21:ijms21186925. [PMID: 32967234 PMCID: PMC7554890 DOI: 10.3390/ijms21186925] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 09/17/2020] [Accepted: 09/18/2020] [Indexed: 12/12/2022] Open
Abstract
Ion channels are membrane-spanning integral proteins expressed in multiple organs, including the eye. In the eye, ion channels are involved in various physiological processes, like signal transmission and visual processing. A wide range of mutations have been reported in the corresponding genes and their interacting subunit coding genes, which contribute significantly to an array of blindness, termed ocular channelopathies. These mutations result in either a loss- or gain-of channel functions affecting the structure, assembly, trafficking, and localization of channel proteins. A dominant-negative effect is caused in a few channels formed by the assembly of several subunits that exist as homo- or heteromeric proteins. Here, we review the role of different mutations in switching a “sensing” ion channel to “non-sensing,” leading to ocular channelopathies like Leber’s congenital amaurosis 16 (LCA16), cone dystrophy, congenital stationary night blindness (CSNB), achromatopsia, bestrophinopathies, retinitis pigmentosa, etc. We also discuss the various in vitro and in vivo disease models available to investigate the impact of mutations on channel properties, to dissect the disease mechanism, and understand the pathophysiology. Innovating the potential pharmacological and therapeutic approaches and their efficient delivery to the eye for reversing a “non-sensing” channel to “sensing” would be life-changing.
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IMAGING OF VITELLIFORM MACULAR LESIONS USING POLARIZATION-SENSITIVE OPTICAL COHERENCE TOMOGRAPHY. Retina 2020; 39:558-569. [PMID: 29215532 DOI: 10.1097/iae.0000000000001987] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
PURPOSE To examine the involvement of the retinal pigment epithelium (RPE) in the presence of vitelliform macular lesions (VML) in Best vitelliform macular dystrophy (BVMD), autosomal recessive bestrophinopathy, and adult-onset vitelliform macular degeneration using polarization-sensitive optical coherence tomography (PS-OCT). METHODS A total of 35 eyes of 18 patients were imaged using a PS-OCT system and blue light fundus autofluorescence imaging. Pathogenic mutations in the BEST1 gene, 3 of which were new, were detected in all patients with BVMD and autosomal recessive bestrophinopathy. RESULTS Polarization-sensitive optical coherence tomography showed a characteristic pattern in all three diseases with nondepolarizing material in the subretinal space consistent with the yellowish VML seen on funduscopy with a visible RPE line below it. A focal RPE thickening was seen in 26 eyes under or at the edge of the VML. Retinal pigment epithelium thickness outside the VML was normal or mildly thinned in patients with BVMD and adult-onset vitelliform macular degeneration but was diffusely thinned or atrophic in patients with autosomal recessive bestrophinopathy. Patients with autosomal recessive bestrophinopathy showed sub-RPE fibrosis alongside the subretinal VML. Polarization-sensitive optical coherence tomography was more reliable in assessing the localization and the integrity of the RPE than spectral domain OCT alone. On spectral domain OCT, identification of the RPE was not possible in 19.4% of eyes. Polarization-sensitive optical coherence tomography allowed for definite identification of the location of VML in respect to the RPE in all eyes, since it provides a tissue-specific contrast. CONCLUSION Polarization-sensitive optical coherence tomography confirms in vivo the subretinal location of VML and is useful in the assessment of RPE integrity.
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Mutation-Dependent Pathomechanisms Determine the Phenotype in the Bestrophinopathies. Int J Mol Sci 2020; 21:ijms21051597. [PMID: 32111077 PMCID: PMC7084480 DOI: 10.3390/ijms21051597] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2019] [Revised: 02/21/2020] [Accepted: 02/24/2020] [Indexed: 12/11/2022] Open
Abstract
Best vitelliform macular dystrophy (BD), autosomal dominant vitreoretinochoroidopathy (ADVIRC), and the autosomal recessive bestrophinopathy (ARB), together known as the bestrophinopathies, are caused by mutations in the bestrophin-1 (BEST1) gene affecting anion transport through the plasma membrane of the retinal pigment epithelium (RPE). To date, while no treatment exists a better understanding of BEST1-related pathogenesis may help to define therapeutic targets. Here, we systematically characterize functional consequences of mutant BEST1 in thirteen RPE patient cell lines differentiated from human induced pluripotent stem cells (hiPSCs). Both BD and ARB hiPSC-RPEs display a strong reduction of BEST1-mediated anion transport function compared to control, while ADVIRC mutations trigger an increased anion permeability suggesting a stabilized open state condition of channel gating. Furthermore, BD and ARB hiPSC-RPEs differ by the degree of mutant protein turnover and by the site of subcellular protein quality control with adverse effects on lysosomal pH only in the BD-related cell lines. The latter finding is consistent with an altered processing of catalytic enzymes in the lysosomes. The present study provides a deeper insight into distinct molecular mechanisms of the three bestrophinopathies facilitating functional categorization of the more than 300 known BEST1 mutations that result into the distinct retinal phenotypes.
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Cordes M, Bucichowski P, Alfaar AS, Tsang SH, Almedawar S, Reichhart N, Strauß O. Inhibition of Ca 2+ channel surface expression by mutant bestrophin-1 in RPE cells. FASEB J 2020; 34:4055-4071. [PMID: 31930599 DOI: 10.1096/fj.201901202rr] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 12/09/2019] [Accepted: 12/31/2019] [Indexed: 01/11/2023]
Abstract
The BEST1 gene product bestrophin-1, a Ca2+ -dependent anion channel, interacts with CaV 1.3 Ca2+ channels in the retinal pigment epithelium (RPE). BEST1 mutations lead to Best vitelliform macular dystrophy. A common functional defect of these mutations is reduced trafficking of bestrophin-1 into the plasma membrane. We hypothesized that this defect affects the interaction partner CaV 1.3 channel affecting Ca2+ signaling and altered RPE function. Thus, we investigated the protein interaction between CaV 1.3 channels and bestrophin-1 by immunoprecipitation, CaV 1.3 activity in the presence of mutant bestrophin-1 and intracellular trafficking of the interaction partners in confluent RPE monolayers. We selected four BEST1 mutations, each representing one mutational hotspot of the disease: T6P, F80L, R218C, and F305S. Heterologously expressed L-type channels and mutant bestrophin-1 showed reduced interaction, reduced CaV 1.3 channel activity, and changes in surface expression. Transfection of polarized RPE (porcine primary cells, iPSC-RPE) that endogenously express CaV 1.3 and wild-type bestrophin-1, with mutant bestrophin-1 confirmed reduction of CaV 1.3 surface expression. For the four selected BEST1 mutations, presence of mutant bestrophin-1 led to reduced CaV 1.3 activity by modulating pore-function or decreasing surface expression. Reduced CaV 1.3 activity might open new ways to understand symptoms of Best vitelliform macular dystrophy such as reduced electro-oculogram, lipofuscin accumulation, and vision impairment.
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Affiliation(s)
- Magdalena Cordes
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a corporate member of Freie Universität, Humboldt-University, the Berlin Institute of Health, Berlin, Germany
| | - Piotr Bucichowski
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a corporate member of Freie Universität, Humboldt-University, the Berlin Institute of Health, Berlin, Germany
| | - Ahmad S Alfaar
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a corporate member of Freie Universität, Humboldt-University, the Berlin Institute of Health, Berlin, Germany
| | - Stephen H Tsang
- Jonas Children's Vision Care, and Bernard & Shirlee Brown Glaucoma Laboratory, Department of Ophthalmology, Columbia Stem Cell Initiative, Departments of Ophthalmology Pathology & Cell Biology, Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY, USA.,Edward S. Harkness Eye Institute, New York-Presbyterian Hospital, New York, NY, USA
| | - Seba Almedawar
- Center for Molecular and Cellular Bioengineering (CMCB), Center for Regenerative Therapies, Dresden (CRTD), Technische Universität Dresden, Dresden, Germany
| | - Nadine Reichhart
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a corporate member of Freie Universität, Humboldt-University, the Berlin Institute of Health, Berlin, Germany
| | - Olaf Strauß
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a corporate member of Freie Universität, Humboldt-University, the Berlin Institute of Health, Berlin, Germany
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Abstract
Bestrophinopathies are a group of clinically distinct inherited retinal dystrophies that lead to the gradual loss of vision in and around the macular area. There are no treatments for patients suffering from bestrophinopathies, and no measures can be taken to prevent visual deterioration in those who have inherited disease-causing mutations. Bestrophinopathies are caused by mutations in the Bestrophin1 gene (BEST1), a protein found exclusively in the retinal pigment epithelial (RPE) cells of the eye. Mutations in BEST1 affect the function of the RPE leading to the death of overlying retinal cells and subsequent vision loss. The pathogenic mechanisms arising from BEST1 mutations are still not fully understood, and it is not clear how mutations in BEST1 lead to diseases with distinct clinical features. This chapter discusses BEST1, the use of model systems to investigate the effects of mutations and the potential to investigate individual bestrophinopathies using induced pluripotent stem cells.
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Lima de Carvalho JR, Paavo M, Chen L, Chiang J, Tsang SH, Sparrow JR. Multimodal Imaging in Best Vitelliform Macular Dystrophy. Invest Ophthalmol Vis Sci 2019; 60:2012-2022. [PMID: 31070670 PMCID: PMC6735800 DOI: 10.1167/iovs.19-26571] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Purpose In patients diagnosed with Best vitelliform macular dystrophy (BVMD), quantitative fundus autofluorescence (qAF), near-infrared fundus autofluorescence (NIR-AF), and spectral-domain optical coherence tomography (SD-OCT) were used to elucidate pathogenic mechanisms. Methods Fourteen patients heterozygous for BEST1 mutations were recruited. qAF was analyzed using short-wavelength fundus autofluorescence (SW-AF) images. Mean gray levels (GL) were determined in nonlesion areas (7 to 9° eccentricity) and adjusted by GL measured in an internal fluorescent reference. NIR-AF images (787 nm; sensitivity of 96) were captured and saved in non-normalized mode. Horizontal SD-OCT images also were acquired and BVMD was staged according to the OCT findings. Results In the pre-vitelliform stage, NIR-AF imaging revealed an area of reduced fluorescence, whereas in the vitelliruptive stage, puncta of elevated NIR-AF signal were present. In both SW-AF and NIR-AF images, the vitelliform lesion in the atrophic stage was marked by reduced signal. At all stages of BVMD, nonlesion qAF was within the 95% confidence intervals for healthy eyes. Similarly, the NIR-AF intensity measurements outside the vitelliform lesion were comparable to the healthy control eye. SD-OCT scans revealed a fluid-filled detachment between the ellipsoid zone and the hyperreflectivity band attributable to RPE/Bruch's membrane. Conclusions NIR-AF imaging can identify the pre-vitelliform stage of BVMD. Mutations in BEST1 are not associated with increased levels of SW-AF outside the vitelliform lesion. Elevated SW-AF within the fluid-filled lesion likely reflects the inability of RPE to phagocytose outer segments due to separation of RPE from photoreceptor cells, together with progressive photoreceptor cell impairment.
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Affiliation(s)
- Jose Ronaldo Lima de Carvalho
- Department of Ophthalmology, Harkness Eye Institute, Columbia University, New York, New York, United States.,Department of Ophthalmology, Empresa Brasileira de Servicos Hospitalares (EBSERH) - Hospital das Clinicas de Pernambuco (HCPE), Federal University of Pernambuco (UFPE), Recife, Brazil.,Department of Ophthalmology, Federal University of São Paulo (UNIFESP), São Paulo, Brazil
| | - Maarjaliis Paavo
- Department of Ophthalmology, Harkness Eye Institute, Columbia University, New York, New York, United States
| | - Lijuan Chen
- Department of Ophthalmology, Harkness Eye Institute, Columbia University, New York, New York, United States.,Department of Ophthalmology, People's Hospital of PuTuo District, Shanghai, China
| | - John Chiang
- Department of Ophthalmology, Oregon Health and Science University, Portland, Oregon, United States
| | - Stephen H Tsang
- Department of Ophthalmology, Harkness Eye Institute, Columbia University, New York, New York, United States.,Department of Pathology and Cell Biology, Columbia University, New York, New York, United States
| | - Janet R Sparrow
- Department of Ophthalmology, Harkness Eye Institute, Columbia University, New York, New York, United States.,Department of Pathology and Cell Biology, Columbia University, New York, New York, United States
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Frecer V, Iarossi G, Salvetti AP, Maltese PE, Delledonne G, Oldani M, Staurenghi G, Falsini B, Minnella AM, Ziccardi L, Magli A, Colombo L, D'Esposito F, Miertus J, Viola F, Attanasio M, Maggio E, Bertelli M. Pathogenicity of new BEST1 variants identified in Italian patients with best vitelliform macular dystrophy assessed by computational structural biology. J Transl Med 2019; 17:330. [PMID: 31570112 PMCID: PMC6771118 DOI: 10.1186/s12967-019-2080-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2019] [Accepted: 09/21/2019] [Indexed: 11/18/2022] Open
Abstract
Background Best vitelliform macular dystrophy (BVMD) is an autosomal dominant macular degeneration. The typical central yellowish yolk-like lesion usually appears in childhood and gradually worsens. Most cases are caused by variants in the BEST1 gene which encodes bestrophin-1, an integral membrane protein found primarily in the retinal pigment epithelium. Methods Here we describe the spectrum of BEST1 variants identified in a cohort of 57 Italian patients analyzed by Sanger sequencing. In 13 cases, the study also included segregation analysis in affected and unaffected relatives. We used molecular mechanics to calculate two quantitative parameters related to calcium-activated chloride channel (CaCC composed of 5 BEST1 subunits) stability and calcium-dependent activation and related them to the potential pathogenicity of individual missense variants detected in the probands. Results Thirty-six out of 57 probands (63% positivity) and 16 out of 18 relatives proved positive to genetic testing. Family study confirmed the variable penetrance and expressivity of the disease. Six of the 27 genetic variants discovered were novel: p.(Val9Gly), p.(Ser108Arg), p.(Asn179Asp), p.(Trp182Arg), p.(Glu292Gln) and p.(Asn296Lys). All BEST1 variants were assessed in silico for potential pathogenicity. Our computational structural biology approach based on 3D model structure of the CaCC showed that individual amino acid replacements may affect channel shape, stability, activation, gating, selectivity and throughput, and possibly also other features, depending on where the individual mutated amino acid residues are located in the tertiary structure of BEST1. Statistically significant correlations between mean logMAR best-corrected visual acuity (BCVA), age and modulus of computed BEST1 dimerization energies, which reflect variations in the in CaCC stability due to amino acid changes, permitted us to assess the pathogenicity of individual BEST1 variants. Conclusions Using this computational approach, we designed a method for estimating BCVA progression in patients with BEST1 variants.
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Affiliation(s)
- Vladimir Frecer
- Department of Physical Chemistry of Drugs, Faculty of Pharmacy, Comenius University in Bratislava, Bratislava, Slovakia
| | - Giancarlo Iarossi
- Department of Ophthalmology, Bambino Gesù IRCCS Children's Hospital, Rome, Italy
| | - Anna Paola Salvetti
- Department of Biomedical and Clinical Sciences "Luigi Sacco", Sacco Hospital, University of Milan, Milan, Italy
| | | | - Giulia Delledonne
- Department of Biomedical and Clinical Sciences "Luigi Sacco", Sacco Hospital, University of Milan, Milan, Italy
| | - Marta Oldani
- Department of Biomedical and Clinical Sciences "Luigi Sacco", Sacco Hospital, University of Milan, Milan, Italy
| | - Giovanni Staurenghi
- Department of Biomedical and Clinical Sciences "Luigi Sacco", Sacco Hospital, University of Milan, Milan, Italy
| | - Benedetto Falsini
- Institute of Ophthalmology, Visual Electrophysiology Service, Fondazione Policlinico Gemelli/UniversitàCattolica del S. Cuore, Rome, Italy
| | - Angelo Maria Minnella
- Institute of Ophthalmology, Visual Electrophysiology Service, Fondazione Policlinico Gemelli/UniversitàCattolica del S. Cuore, Rome, Italy
| | - Lucia Ziccardi
- Neurophthalmology and Neurophysiology Unit, GB Bietti Foundation-IRCCS, Rome, Italy
| | - Adriano Magli
- Department of Ophthalmology, Orthoptic and Pediatric Ophthalmology, University of Salerno, Salerno, Italy
| | - Leonardo Colombo
- Department of Ophthalmology, San Paolo Hospital, University of Milan, Milan, Italy
| | - Fabiana D'Esposito
- Imperial College Ophthalmic Research Unit, Western Eye Hospital, Imperial College Healthcare NHS Trust, London, UK.,Eye Clinic, Department of Neurosciences, Reproductive Sciences and Dentistry, University of Naples Federico II, Naples, Italy.,MAGI Euregio, Bolzano, Italy
| | | | - Francesco Viola
- Department of Ophthalmology, Fondazione IRCCS Cà Granda, Clinica Regina Elena, Milan, Italy
| | | | - Emilia Maggio
- IRCCS-Ospedale Sacro Cuore Don Calabria, Negrar, VR, Italy
| | - Matteo Bertelli
- MAGI'S Lab S.R.L., Via Delle Maioliche 57/D, 38068, Rovereto, TN, Italy.,MAGI Euregio, Bolzano, Italy
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Lessons learned from quantitative fundus autofluorescence. Prog Retin Eye Res 2019; 74:100774. [PMID: 31472235 DOI: 10.1016/j.preteyeres.2019.100774] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 08/21/2019] [Accepted: 08/25/2019] [Indexed: 12/12/2022]
Abstract
Quantitative fundus autofluorescence (qAF) is an approach that is built on a confocal scanning laser platform and used to measure the intensity of the inherent autofluorescence of retina elicited by short-wavelength (488 nm) excitation. Being non-invasive, qAF does not interrupt tissue architecture, thus allowing for structural correlations. The spectral features, cellular origin and topographic distribution of the natural autofluorescence of the fundus indicate that it is emitted from retinaldehyde-adducts that form in photoreceptor cells and accumulate, under most conditions, in retinal pigment epithelial cells. The distributions and intensities of fundus autofluorescence deviate from normal in many retinal disorders and it is widely recognized that these changing patterns can aid in the diagnosis and monitoring of retinal disease. The standardized protocol employed by qAF involves the normalization of fundus grey levels to a fluorescent reference installed in the imaging instrument. Together with corrections for magnification and anterior media absorption, this approach facilitates comparisons with serial images and images acquired within groups of patients. Here we provide a comprehensive summary of the principles and practice of qAF and we highlight recent efforts to elucidate retinal disease processes by combining qAF with multi-modal imaging.
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14
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Milenkovic A, Schmied D, Tanimoto N, Seeliger MW, Sparrow JR, Weber BHF. The Y227N mutation affects bestrophin-1 protein stability and impairs sperm function in a mouse model of Best vitelliform macular dystrophy. Biol Open 2019; 8:bio.041335. [PMID: 31201163 PMCID: PMC6679414 DOI: 10.1242/bio.041335] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Human bestrophin-1 (BEST1) is an integral membrane protein known to function as a Ca2+-activated and volume-regulated chloride channel. The majority of disease-associated mutations in BEST1 constitute missense mutations and were shown in vitro to lead to a reduction in mutant protein half-life causing Best disease (BD), a rare autosomal dominant macular dystrophy. To further delineate BEST1-associated pathology in vivo and to provide an animal model useful to explore experimental treatment efficacies, we have generated a knock-in mouse line (Best1Y227N). Heterozygous and homozygous mutants revealed no significant ocular abnormalities up to 2 years of age. In contrast, knock-in animals demonstrated a severe phenotype in the male reproductive tract. In heterozygous Best1Y227N males, Best1 protein was significantly reduced in testis and almost absent in homozygous mutant mice, although mRNA transcription of wild-type and knock-in allele is present and similar in quantity. Degradation of mutant Best1 protein in testis was associated with adverse effects on sperm motility and the capability to fertilize eggs. Based on these results, we conclude that mice carrying the Best1 Y227N mutation reveal a reproducible pathologic phenotype and thus provide a valuable in vivo tool to evaluate efficacy of drug therapies aimed at restoring Best1 protein stability and function.
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Affiliation(s)
- Andrea Milenkovic
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
| | - Denise Schmied
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
| | - Naoyuki Tanimoto
- Division of Ocular Neurodegeneration, Centre for Ophthalmology, Institute for Ophthalmic Research, 72076 Tübingen, Germany.,Department of Ophthalmology, University of Kiel, 24105 Kiel, Germany
| | - Mathias W Seeliger
- Division of Ocular Neurodegeneration, Centre for Ophthalmology, Institute for Ophthalmic Research, 72076 Tübingen, Germany
| | - Janet R Sparrow
- Department of Ophthalmology, Harkness Eye Institute, Columbia University Medical Center, 10032 New York, USA
| | - Bernhard H F Weber
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
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Elorza-Vidal X, Gaitán-Peñas H, Estévez R. Chloride Channels in Astrocytes: Structure, Roles in Brain Homeostasis and Implications in Disease. Int J Mol Sci 2019; 20:ijms20051034. [PMID: 30818802 PMCID: PMC6429410 DOI: 10.3390/ijms20051034] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 02/15/2019] [Accepted: 02/17/2019] [Indexed: 12/29/2022] Open
Abstract
Astrocytes are the most abundant cell type in the CNS (central nervous system). They exert multiple functions during development and in the adult CNS that are essential for brain homeostasis. Both cation and anion channel activities have been identified in astrocytes and it is believed that they play key roles in astrocyte function. Whereas the proteins and the physiological roles assigned to cation channels are becoming very clear, the study of astrocytic chloride channels is in its early stages. In recent years, we have moved from the identification of chloride channel activities present in astrocyte primary culture to the identification of the proteins involved in these activities, the determination of their 3D structure and attempts to gain insights about their physiological role. Here, we review the recent findings related to the main chloride channels identified in astrocytes: the voltage-dependent ClC-2, the calcium-activated bestrophin, the volume-activated VRAC (volume-regulated anion channel) and the stress-activated Maxi-Cl−. We discuss key aspects of channel biophysics and structure with a focus on their role in glial physiology and human disease.
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Affiliation(s)
- Xabier Elorza-Vidal
- Unitat de Fisiologia, Departament de Ciències Fisiològiques, Genes Disease and Therapy Program IDIBELL-Institute of Neurosciences, Universitat de Barcelona, L'Hospitalet de Llobregat, 08907 Barcelona, Spain.
- Centro de Investigación en red de enfermedades raras (CIBERER), ISCIII, 08907 Barcelona, Spain.
| | - Héctor Gaitán-Peñas
- Unitat de Fisiologia, Departament de Ciències Fisiològiques, Genes Disease and Therapy Program IDIBELL-Institute of Neurosciences, Universitat de Barcelona, L'Hospitalet de Llobregat, 08907 Barcelona, Spain.
- Centro de Investigación en red de enfermedades raras (CIBERER), ISCIII, 08907 Barcelona, Spain.
| | - Raúl Estévez
- Unitat de Fisiologia, Departament de Ciències Fisiològiques, Genes Disease and Therapy Program IDIBELL-Institute of Neurosciences, Universitat de Barcelona, L'Hospitalet de Llobregat, 08907 Barcelona, Spain.
- Centro de Investigación en red de enfermedades raras (CIBERER), ISCIII, 08907 Barcelona, Spain.
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16
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Milenkovic A, Milenkovic VM, Wetzel CH, Weber BHF. BEST1 protein stability and degradation pathways differ between autosomal dominant Best disease and autosomal recessive bestrophinopathy accounting for the distinct retinal phenotypes. Hum Mol Genet 2019; 27:1630-1641. [PMID: 29668979 PMCID: PMC5905664 DOI: 10.1093/hmg/ddy070] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 02/19/2018] [Indexed: 12/21/2022] Open
Abstract
Mutations in bestrophin-1 (BEST1) are associated with distinct retinopathies, notably three forms with autosomal dominant inheritance and one condition with an autosomal recessive mode of transmission. The molecular mechanisms underlying their distinct retinal phenotypes are mostly unknown. Although heterozygous missense mutations in BEST1 reveal dominant-negative effects in patients with autosomal dominant Best disease (BD), heterozygous mutations associated with autosomal recessive bestrophinopathy (ARB) display no disease phenotype. Here we show that the recessive mutations trigger a strong and fast protein degradation process in the endoplasmic reticulum (ER), thereby favoring a decreased stoichiometry of mutant versus normal BEST1 subunits in the assembly of the homo-pentameric BEST1 chloride channel. In contrast, dominant mutations escape ER-associated degradation and are subjected to a slightly delayed post-ER degradation via the endo-lysosomal degradation pathway. As a result, increased formation of a non-functional BEST1 channel occurs due to a roughly equimolar incorporation of normal and mutant BEST1 subunits into the channel complex. Taken together, our data provide insight into the molecular pathways of dominantly and recessively acting BEST1 missense mutations suggesting that the site of subcellular protein quality control as well as the rate and degree of mutant protein degradation are ultimately responsible for the distinct retinal disease phenotypes in BD and ARB.
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Affiliation(s)
- Andrea Milenkovic
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
| | - Vladimir M Milenkovic
- Department of Psychiatry and Psychotherapy, Molecular Neurosciences, University of Regensburg, 93053 Regensburg, Germany
| | - Christian H Wetzel
- Department of Psychiatry and Psychotherapy, Molecular Neurosciences, University of Regensburg, 93053 Regensburg, Germany
| | - Bernhard H F Weber
- Institute of Human Genetics, University of Regensburg, 93053 Regensburg, Germany
- To whom correspondence should be addressed at: Institute of Human Genetics, University of Regensburg, Franz-Josef-Strauß-Allee 11, D-93053 Regensburg, Germany. Tel: +49 9419445400; Fax: +49 9419445402;
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17
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Clinical and Mutation Analysis of Patients with Best Vitelliform Macular Dystrophy or Autosomal Recessive Bestrophinopathy in Chinese Population. BIOMED RESEARCH INTERNATIONAL 2018; 2018:4582816. [PMID: 30498755 PMCID: PMC6220750 DOI: 10.1155/2018/4582816] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 08/21/2018] [Accepted: 09/19/2018] [Indexed: 12/18/2022]
Abstract
Mutations in the gene BEST1 usually cause bestrophinopathies, such as the rare progressive diseases Best vitelliform macular dystrophy (BVMD) and autosomal recessive bestrophinopathy (ARB). This study aimed to investigate the clinical characteristics of patients with BVMD or ARB carrying BEST1 mutations. A total of 12 probands including 9 patients with a clinical diagnosis of BVMD and 3 patients with a clinical diagnosis of ARB were recruited for genetics analysis. All patients underwent detailed ophthalmic examination. All coding exons of the BEST1 gene were screened by PCR-based DNA sequencing. Programs of PolyPhen-2, SIFT, and MutationTaster were used to analyze the potential pathogenicity of the mutations in BEST1. In the 9 unrelated patients with BVMD, one heterozygous BEST1 mutation was revealed in 8 patients and two compound heterozygous mutations in 1 patient. In the 3 unrelated patients with ARB, two compound heterozygous mutations were revealed in 2 patients and three compound heterozygous mutations in 1 patient. Molecular analyses identified a total of 15 mutations, including 3 novel mutations (c.424A>G p.S142G, c.436G>A p.A146T, and c.155T>C p.L52P). Antivascular endothelial growth factor (VEGF) drugs were given to two affected eyes, especially those also exhibiting choroidal neovascularization (CNV), and no serious adverse events occurred. Our study indicates that there is wide genotypic and phenotypic variability in patients with BVMD or ARB in China. The screening of BEST1 gene is significant for the precise diagnosis of BVMD and ARB.
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18
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Vaisey G, Long SB. An allosteric mechanism of inactivation in the calcium-dependent chloride channel BEST1. J Gen Physiol 2018; 150:1484-1497. [PMID: 30237227 PMCID: PMC6219684 DOI: 10.1085/jgp.201812190] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Accepted: 08/30/2018] [Indexed: 11/20/2022] Open
Abstract
Bestrophin proteins are calcium (Ca2+)-activated chloride channels. Mutations in bestrophin 1 (BEST1) cause macular degenerative disorders. Whole-cell recordings show that ionic currents through BEST1 run down over time, but it is unclear whether this behavior is intrinsic to the channel or the result of cellular factors. Here, using planar lipid bilayer recordings of purified BEST1, we show that current rundown is an inherent property of the channel that can now be characterized as inactivation. Inactivation depends on the cytosolic concentration of Ca2+, such that higher concentrations stimulate inactivation. We identify a C-terminal inactivation peptide that is necessary for inactivation and dynamically interacts with a receptor site on the channel. Alterations of the peptide or its receptor dramatically reduce inactivation. Unlike inactivation peptides of voltage-gated channels that bind within the ion pore, the receptor for the inactivation peptide is on the cytosolic surface of the channel and separated from the pore. Biochemical, structural, and electrophysiological analyses indicate that binding of the peptide to its receptor promotes inactivation, whereas dissociation prevents it. Using additional mutational studies we find that the "neck" constriction of the pore, which we have previously shown to act as the Ca2+-dependent activation gate, also functions as the inactivation gate. Our results indicate that unlike a ball-and-chain inactivation mechanism involving physical occlusion of the pore, inactivation in BEST1 occurs through an allosteric mechanism wherein binding of a peptide to a surface-exposed receptor controls a structurally distant gate.
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Affiliation(s)
- George Vaisey
- Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY.,Louis V. Gerstner, Jr. Graduate School of Biomedical Sciences, Memorial Sloan-Kettering Cancer Center, New York, NY
| | - Stephen B Long
- Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY
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Goldberg MF, McLeod S, Tso M, Packo K, Edwards M, Bhutto IA, Baldeosingh R, Eberhart C, Weber BHF, Lutty GA. Ocular Histopathology and Immunohistochemical Analysis in the Oldest Known Individual with Autosomal Dominant Vitreoretinochoroidopathy. Ophthalmol Retina 2018; 2:360-378. [PMID: 29774302 PMCID: PMC5950724 DOI: 10.1016/j.oret.2017.08.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
PURPOSE To assess the immunohistochemical and histopathological changes in a subject with Autosomal Dominant Vitreoretinochoroidopathy (ADVIRC). DESIGN Case study. PARTICIPANT Ninety two year-old Caucasian male with ADVIRC. METHODS The subject was documented clinically for 54 Years. The retina/choroid complex of the right eye was evaluated with cryosections stained with hematoxylin and eosin or periodic acid schiff reagent. Cryosections were also evaluated with immunofluorescence or alkaline phosphatase immunohistochemistry (IHC) using primary antibodies against bestrophin1, GFAP, PEDF, RPE65, TGFβ, VEGF, and vimentin. The left retina and choroid were evaluated as flat mounts using immunofluorescence. UEA lectin was used to stain viable vasculature. MAIN OUTCOME MEASURES The immunohistochemical and histopathological changes in retina and choroid from a subject with ADVIRC. RESULTS The subject had a heterozygous c.248G>A variant in exon 4 of the BEST1 gene. There was widespread chorioretinal degeneration and atrophy except for an island of spared RPE monolayer in the perimacula/macula OU. In this region, some photoreceptors were present, choriocapillaris was spared, and retinal pigment epithelial cells were in their normal disposition. There was a Muller cell periretinal membrane throughout much of the fundus. Bestrophin-1 was not detected or only minimally present by IHC in the ADVIRC RPE, even in the spared RPE area. Beyond the island of retained RPE monolayer on Bruch's membrane (BrMb), there was migration of RPE into the neuro-retina, often ensheathing blood vessels and producing excessive matrix within their perivascular aggregations. CONCLUSIONS The primary defect in ADVIRC is in RPE, the only cells in the eye that express the BEST1 gene. The dysfunctional RPE cells may go through epithelial/mesenchymal transition as they migrate from BrMb to form papillary aggregations in the neuro-retina, often ensheathing blood vessels. This may be the reason for retinal blood vessel nonperfusion. Migration of RPE from BrMb was also associated with attenuation of the choriocapillaris.
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20
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Caceres PS, Benedicto I, Lehmann GL, Rodriguez-Boulan EJ. Directional Fluid Transport across Organ-Blood Barriers: Physiology and Cell Biology. Cold Spring Harb Perspect Biol 2017; 9:a027847. [PMID: 28003183 PMCID: PMC5334253 DOI: 10.1101/cshperspect.a027847] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Directional fluid flow is an essential process for embryo development as well as for organ and organism homeostasis. Here, we review the diverse structure of various organ-blood barriers, the driving forces, transporters, and polarity mechanisms that regulate fluid transport across them, focusing on kidney-, eye-, and brain-blood barriers. We end by discussing how cross talk between barrier epithelial and endothelial cells, perivascular cells, and basement membrane signaling contribute to generate and maintain organ-blood barriers.
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Affiliation(s)
- Paulo S Caceres
- Margaret Dyson Vision Research Institute, Department of Ophthalmology, Weill Cornell Medical College, New York, New York 10065
| | - Ignacio Benedicto
- Margaret Dyson Vision Research Institute, Department of Ophthalmology, Weill Cornell Medical College, New York, New York 10065
| | - Guillermo L Lehmann
- Margaret Dyson Vision Research Institute, Department of Ophthalmology, Weill Cornell Medical College, New York, New York 10065
| | - Enrique J Rodriguez-Boulan
- Margaret Dyson Vision Research Institute, Department of Ophthalmology, Weill Cornell Medical College, New York, New York 10065
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21
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Johnson AA, Guziewicz KE, Lee CJ, Kalathur RC, Pulido JS, Marmorstein LY, Marmorstein AD. Bestrophin 1 and retinal disease. Prog Retin Eye Res 2017; 58:45-69. [PMID: 28153808 DOI: 10.1016/j.preteyeres.2017.01.006] [Citation(s) in RCA: 141] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2016] [Revised: 01/23/2017] [Accepted: 01/25/2017] [Indexed: 12/18/2022]
Abstract
Mutations in the gene BEST1 are causally associated with as many as five clinically distinct retinal degenerative diseases, which are collectively referred to as the "bestrophinopathies". These five associated diseases are: Best vitelliform macular dystrophy, autosomal recessive bestrophinopathy, adult-onset vitelliform macular dystrophy, autosomal dominant vitreoretinochoroidopathy, and retinitis pigmentosa. The most common of these is Best vitelliform macular dystrophy. Bestrophin 1 (Best1), the protein encoded by the gene BEST1, has been the subject of a great deal of research since it was first identified nearly two decades ago. Today we know that Best1 functions as both a pentameric anion channel and a regulator of intracellular Ca2+ signaling. Best1 is an integral membrane protein which, within the eye, is uniquely expressed in the retinal pigment epithelium where it predominantly localizes to the basolateral plasma membrane. Within the brain, Best1 expression has been documented in both glial cells and astrocytes where it functions in both tonic GABA release and glutamate transport. The crystal structure of Best1 has revealed critical information about how Best1 functions as an ion channel and how Ca2+ regulates that function. Studies using animal models have led to critical insights into the physiological roles of Best1 and advances in stem cell technology have allowed for the development of patient-derived, "disease in a dish" models. In this article we review our knowledge of Best1 and discuss prospects for near-term clinical trials to test therapies for the bestrophinopathies, a currently incurable and untreatable set of diseases.
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Affiliation(s)
- Adiv A Johnson
- Department of Ophthalmology, Mayo Clinic, Rochester, MN, USA; Nikon Instruments, Melville, NY, USA
| | - Karina E Guziewicz
- Department of Clinical Studies-Philadelphia, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - C Justin Lee
- Center for Neuroscience and Functional Connectomics, Brain Science Institute, Korea Institute of Science and Technology, Seoul, South Korea
| | - Ravi C Kalathur
- New York Structural Biology Center, New York Consortium on Membrane Protein Structure, New York, NY, USA
| | - Jose S Pulido
- Department of Ophthalmology, Mayo Clinic, Rochester, MN, USA
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Unravelling the Complexity of Inherited Retinal Dystrophies Molecular Testing: Added Value of Targeted Next-Generation Sequencing. BIOMED RESEARCH INTERNATIONAL 2016; 2016:6341870. [PMID: 28127548 PMCID: PMC5227126 DOI: 10.1155/2016/6341870] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Revised: 09/30/2016] [Accepted: 10/20/2016] [Indexed: 11/18/2022]
Abstract
To assess the clinical utility of targeted Next-Generation Sequencing (NGS) for the diagnosis of Inherited Retinal Dystrophies (IRDs), a total of 109 subjects were enrolled in the study, including 88 IRD affected probands and 21 healthy relatives. Clinical diagnoses included Retinitis Pigmentosa (RP), Leber Congenital Amaurosis (LCA), Stargardt Disease (STGD), Best Macular Dystrophy (BMD), Usher Syndrome (USH), and other IRDs with undefined clinical diagnosis. Participants underwent a complete ophthalmologic examination followed by genetic counseling. A custom AmpliSeq™ panel of 72 IRD-related genes was designed for the analysis and tested using Ion semiconductor Next-Generation Sequencing (NGS). Potential disease-causing mutations were identified in 59.1% of probands, comprising mutations in 16 genes. The highest diagnostic yields were achieved for BMD, LCA, USH, and STGD patients, whereas RP confirmed its high genetic heterogeneity. Causative mutations were identified in 17.6% of probands with undefined diagnosis. Revision of the initial diagnosis was performed for 9.6% of genetically diagnosed patients. This study demonstrates that NGS represents a comprehensive cost-effective approach for IRDs molecular diagnosis. The identification of the genetic alterations underlying the phenotype enabled the clinicians to achieve a more accurate diagnosis. The results emphasize the importance of molecular diagnosis coupled with clinic information to unravel the extensive phenotypic heterogeneity of these diseases.
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Distinct regions that control ion selectivity and calcium-dependent activation in the bestrophin ion channel. Proc Natl Acad Sci U S A 2016; 113:E7399-E7408. [PMID: 27821745 DOI: 10.1073/pnas.1614688113] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cytoplasmic calcium (Ca2+) activates the bestrophin anion channel, allowing chloride ions to flow down their electrochemical gradient. Mutations in bestrophin 1 (BEST1) cause macular degenerative disorders. Previously, we determined an X-ray structure of chicken BEST1 that revealed the architecture of the channel. Here, we present electrophysiological studies of purified wild-type and mutant BEST1 channels and an X-ray structure of a Ca2+-independent mutant. From these experiments, we identify regions of BEST1 responsible for Ca2+ activation and ion selectivity. A "Ca2+ clasp" within the channel's intracellular region acts as a sensor of cytoplasmic Ca2+. Alanine substitutions within a hydrophobic "neck" of the pore, which widen it, cause the channel to be constitutively active, irrespective of Ca2+. We conclude that the primary function of the neck is as a "gate" that controls chloride permeation in a Ca2+-dependent manner. In contrast to what others have proposed, we find that the neck is not a major contributor to the channel's ion selectivity. We find that mutation of a cytosolic "aperture" of the pore does not perturb the Ca2+ dependence of the channel or its preference for anions over cations, but its mutation dramatically alters relative permeabilities among anions. The data suggest that the aperture functions as a size-selective filter that permits the passage of small entities such as partially dehydrated chloride ions while excluding larger molecules such as amino acids. Thus, unlike ion channels that have a single "selectivity filter," in bestrophin, distinct regions of the pore govern anion-vs.-cation selectivity and the relative permeabilities among anions.
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24
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Mislocalisation of BEST1 in iPSC-derived retinal pigment epithelial cells from a family with autosomal dominant vitreoretinochoroidopathy (ADVIRC). Sci Rep 2016; 6:33792. [PMID: 27653836 PMCID: PMC5031956 DOI: 10.1038/srep33792] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 08/26/2016] [Indexed: 12/31/2022] Open
Abstract
Autosomal dominant vitreoretinochoroidopathy (ADVIRC) is a rare, early-onset retinal dystrophy characterised by distinct bands of circumferential pigmentary degeneration in the peripheral retina and developmental eye defects. ADVIRC is caused by mutations in the Bestrophin1 (BEST1) gene, which encodes a transmembrane protein thought to function as an ion channel in the basolateral membrane of retinal pigment epithelial (RPE) cells. Previous studies suggest that the distinct ADVIRC phenotype results from alternative splicing of BEST1 pre-mRNA. Here, we have used induced pluripotent stem cell (iPSC) technology to investigate the effects of an ADVIRC associated BEST1 mutation (c.704T > C, p.V235A) in patient-derived iPSC-RPE. We found no evidence of alternate splicing of the BEST1 transcript in ADVIRC iPSC-RPE, however in patient-derived iPSC-RPE, BEST1 was expressed at the basolateral membrane and the apical membrane. During human eye development we show that BEST1 is expressed more abundantly in peripheral RPE compared to central RPE and is also expressed in cells of the developing retina. These results suggest that higher levels of mislocalised BEST1 expression in the periphery, from an early developmental stage, could provide a mechanism that leads to the distinct clinical phenotype observed in ADVIRC patients.
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25
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Uggenti C, Briant K, Streit AK, Thomson S, Koay YH, Baines RA, Swanton E, Manson FD. Restoration of mutant bestrophin-1 expression, localisation and function in a polarised epithelial cell model. Dis Model Mech 2016; 9:1317-1328. [PMID: 27519691 PMCID: PMC5117222 DOI: 10.1242/dmm.024216] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2015] [Accepted: 07/21/2016] [Indexed: 01/13/2023] Open
Abstract
Autosomal recessive bestrophinopathy (ARB) is a retinopathy caused by mutations in the bestrophin-1 protein, which is thought to function as a Ca2+-gated Cl− channel in the basolateral surface of the retinal pigment epithelium (RPE). Using a stably transfected polarised epithelial cell model, we show that four ARB mutant bestrophin-1 proteins were mislocalised and subjected to proteasomal degradation. In contrast to the wild-type bestrophin-1, each of the four mutant proteins also failed to conduct Cl− ions in transiently transfected cells as determined by whole-cell patch clamp. We demonstrate that a combination of two clinically approved drugs, bortezomib and 4-phenylbutyrate (4PBA), successfully restored the expression and localisation of all four ARB mutant bestrophin-1 proteins. Importantly, the Cl− conductance function of each of the mutant bestrophin-1 proteins was fully restored to that of wild-type bestrophin-1 by treatment of cells with 4PBA alone. The functional rescue achieved with 4PBA is significant because it suggests that this drug, which is already approved for long-term use in infants and adults, might represent a promising therapy for the treatment of ARB and other bestrophinopathies resulting from missense mutations in BEST1. Summary: Chemical chaperone 4PBA fully restores Cl− conductance activity for mutant bestrophin-1 proteins associated with inherited retinal dystrophy, autosomal recessive bestrophinopathy.
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Affiliation(s)
- Carolina Uggenti
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Kit Briant
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Anne-Kathrin Streit
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Steven Thomson
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Yee Hui Koay
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Richard A Baines
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Eileithyia Swanton
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
| | - Forbes D Manson
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester M13 9PT, UK
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26
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Moshfegh Y, Velez G, Li Y, Bassuk AG, Mahajan VB, Tsang SH. BESTROPHIN1 mutations cause defective chloride conductance in patient stem cell-derived RPE. Hum Mol Genet 2016; 25:2672-2680. [PMID: 27193166 DOI: 10.1093/hmg/ddw126] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Revised: 04/13/2016] [Accepted: 04/18/2016] [Indexed: 12/20/2022] Open
Abstract
Bestrophin1 (BEST1) is expressed in human retinal pigment epithelium (RPE) and mutations in the BEST1 gene commonly cause retinal dysfunction and macular degeneration. BEST1 is presumed to assemble into a calcium-activated chloride channel and be involved in chloride transport but there is no direct evidence in live human RPE cells to support this idea. To test whether BEST1 functions as a chloride channel in living tissue, BEST1-mutant RPE (R218H, L234P, A243T) were generated from patient-derived induced pluripotent stem cells and compared with wild-type RPE in a retinal environment, using a biosensor that visualizes calcium-induced chloride ion flux in the cell. Calcium stimulation elicited chloride ion export in normal RPE but not in RPE derived from three patients with BEST1 mutations. These data, along with three-dimensional modeling, provide evidence that BEST1 assembles into a key calcium-sensing chloride channel in human RPE.
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Affiliation(s)
- Yasmin Moshfegh
- Barbara & Donald Jonas Laboratory of Regenerative Medicine, and Bernard & Shirlee Brown Glaucoma Laboratory, Department of Pathology & Cell Biology, Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA.,Edward S. Harkness Eye Institute, New York-Presbyterian Hospital, New York, NY 10032, USA
| | - Gabriel Velez
- Omics Lab.,Department of Ophthalmology and Visual Sciences.,Medical Scientist Training Program
| | - Yao Li
- Edward S. Harkness Eye Institute, New York-Presbyterian Hospital, New York, NY 10032, USA
| | | | - Vinit B Mahajan
- Department of Ophthalmology and Visual Sciences.,Medical Scientist Training Program
| | - Stephen H Tsang
- Barbara & Donald Jonas Laboratory of Regenerative Medicine, and Bernard & Shirlee Brown Glaucoma Laboratory, Department of Pathology & Cell Biology, Institute of Human Nutrition, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA .,Edward S. Harkness Eye Institute, New York-Presbyterian Hospital, New York, NY 10032, USA
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Strauß O, Reichhart N, Gomez NM, Müller C. Contribution of Ion Channels in Calcium Signaling Regulating Phagocytosis: MaxiK, Cav1.3 and Bestrophin-1. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2016; 854:739-44. [PMID: 26427483 DOI: 10.1007/978-3-319-17121-0_98] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Mutations in the BEST1 gene lead to a variety of retinal degenerations including Best's vitelliforme macular degeneration. The BEST1 gene product, bestrophin-1, is expressed in the retinal pigment epithelium (RPE). It is likely that mutant bestrophin-1 impairs functions of the RPE which support photoreceptor function and will thus lead to retinal degeneration. However, the RPE function which is influenced by bestrophin-1 is so far not identified. Previously we showed that bestrophin-1 interacts with L-type Ca²⁺ channels of the CaV1.3 subtype and that the endogenously expressed bestrophin-1 is required for intracellular Ca²⁺ regulation. A hallmark of Best's disease is the fast lipofuscin accumulation occurring already at young ages. Therefore, we addressed the hypothesis that bestrophin-1 might influence phagocytosis of photoreceptor outer segments (POS) by the RPE. Here, siRNA knock-down of bestrophin-1 expression as well as inhibition of L-type Ca²⁺ channel activity modulated the POS phagocytosis in vitro. In vivo CaV1.3 expression appeared to be diurnal regulated with a higher expression rate in the afternoon. Compared to wild-type littermates, Ca V 1.3 (-/-) mice showed a shift in the circadian POS phagocytosis with an increased activity in the afternoon. Thus we suggest that mutant bestrophin-1 leads to an impaired regulation of the POS phagocytosis by the RPE which would explain the fast lipofuscin accumulation in Best patients.
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Affiliation(s)
- Olaf Strauß
- Experimental Ophthalmology, Department of Ophthalmology, Charite University Medicine Berlin, Augustenburger Platz 1, 13353, Berlin, Germany.
| | - Nadine Reichhart
- Experimental Ophthalmology, Department of Ophthalmology, Charite University Medicine Berlin, Augustenburger Platz 1, 13353, Berlin, Germany.
| | - Nestor Mas Gomez
- Department of Anatomy and Cell Biology, School of Dental Medicine, University of Pennsylvania, Augustenburger Platz 1, 240 South 40th Street, 19104-6030, Philadelphia, PA, USA.
| | - Claudia Müller
- Department of Biological Sciences, Center for Cancer, Genetic Diseases and Gene Regulation, Fordham University Bronx, 10458, Bronx, NY, USA.
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Giblin JP, Comes N, Strauss O, Gasull X. Ion Channels in the Eye: Involvement in Ocular Pathologies. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2015; 104:157-231. [PMID: 27038375 DOI: 10.1016/bs.apcsb.2015.11.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology.
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Affiliation(s)
- Jonathan P Giblin
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Nuria Comes
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | | | - Xavier Gasull
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
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Johnson AA, Bachman LA, Gilles BJ, Cross SD, Stelzig KE, Resch ZT, Marmorstein LY, Pulido JS, Marmorstein AD. Autosomal Recessive Bestrophinopathy Is Not Associated With the Loss of Bestrophin-1 Anion Channel Function in a Patient With a Novel BEST1 Mutation. Invest Ophthalmol Vis Sci 2015. [PMID: 26200502 DOI: 10.1167/iovs.15-16910] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
PURPOSE Mutations in BEST1, encoding bestrophin-1 (Best1), cause autosomal recessive bestrophinopathy (ARB). Encoding bestrophin-1 is a pentameric anion channel localized to the basolateral plasma membrane of the RPE. Here, we characterize the effects of the mutations R141H (CGC > CAC) and I366fsX18 (c.1098_1100+7del), identified in a patient in our practice, on Best1 trafficking, oligomerization, and channel activity. METHODS Currents of Cl- were assessed in transfected HEK293 cells using whole-cell patch clamp. Best1 localization was assessed by confocal microscopy in differentiated, human-induced pluripotent stem cell-derived RPE (iPSC-RPE) cells following expression of mutants via adenovirus-mediated gene transfer. Oligomerization was evaluated by coimmunoprecipitation in iPSC-RPE and MDCK cells. RESULTS Compared to Best1, Best1 I366fsX18 currents were increased while Best1 R141H Cl- currents were diminished. Coexpression of Best1 R141H with Best1 or Best1 I366fsX18 resulted in rescued channel activity. Overexpressed Best1, Best1 R141H, and Best1 I366fsX18 were all properly localized in iPSC-RPE cells; Best1 R141H and Best1 I366fsX18 coimmunoprecipitated with endogenous Best1 in iPSC-RPE cells and with each other in MDCK cells. CONCLUSIONS The first 366 amino acids of Best1 are sufficient to mediate channel activity and homo-oligomerization. The combination of Best1 and Best1 R141H does not cause disease, while Best1 R141H together with Best1 I366fsX18 causes ARB. Since both combinations generate comparable Cl- currents, this indicates that ARB in this patient is not caused by a loss of channel activity. Moreover, Best1 I366fsX18 differs from Best1 in that it lacks most of the cytosolic C-terminal domain, suggesting that the loss of this region contributes significantly to the pathogenesis of ARB in this patient.
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Affiliation(s)
- Adiv A Johnson
- Department of Ophthalmology Mayo Clinic, Rochester, Minnesota, United States
| | - Lori A Bachman
- Department of Ophthalmology Mayo Clinic, Rochester, Minnesota, United States
| | - Benjamin J Gilles
- Department of Ophthalmology Mayo Clinic, Rochester, Minnesota, United States
| | - Samuel D Cross
- Department of Ophthalmology Mayo Clinic, Rochester, Minnesota, United States
| | - Kimberly E Stelzig
- Center for Regenerative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Zachary T Resch
- Center for Regenerative Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Lihua Y Marmorstein
- Department of Ophthalmology Mayo Clinic, Rochester, Minnesota, United States
| | - Jose S Pulido
- Department of Ophthalmology Mayo Clinic, Rochester, Minnesota, United States 3Department of Molecular Medicine, Mayo Clinic, Rochester, Minnesota, United States
| | - Alan D Marmorstein
- Department of Ophthalmology Mayo Clinic, Rochester, Minnesota, United States
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Wivestad Jansson R, Berland S, Bredrup C, Austeng D, Andréasson S, Wittström E. Biallelic Mutations in the BEST1 Gene: Additional Families with Autosomal Recessive Bestrophinopathy. Ophthalmic Genet 2015; 37:183-93. [PMID: 26333019 DOI: 10.3109/13816810.2015.1020558] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
PURPOSE To describe the genotype and phenotype of patients with autosomal recessive bestrophinopathy (ARB), and heterozygous carriers. METHODS The members of three unrelated ARB families were investigated. Molecular genetic analysis was performed on 11 members of these families. Ten members were examined clinically; including visual acuity, slit-lamp examination, biomicroscopy, fundus photography, and Goldmann applanation tonometry. Measurements were also made of the anterior chamber depth and axial length, and optical coherence tomography (OCT), electrooculography (EOG), and full-field electroretinography (full-field ERG) were performed. Multifocal electroretinography (mfERG) was performed on eight members of these families. RESULTS Two novel combinations of missense mutations in the BEST1 gene were identified: p.R141H/p.M325T in three patients with ARB in two unrelated Norwegian families, and p.R141H/p.I201T was found in an ARB patient in a Swedish family. All four patients with ARB had clinical and electrophysiological features of ARB. All the heterozygous carriers of the p.R141H mutation were clinically normal, and showed normal OCT, EOG and full-field ERG findings, but had mildly abnormal mfERG results. Only one heterozygous carrier of the p.M325T mutation was studied and he was clinically normal, showing normal OCT and full-field ERG results, but subnormal EOG and mfERG findings. The heterozygous carrier of the p.I201T mutation was clinically normal, showing normal OCT, EOG and full-field ERG results, but subnormal mfERG results. CONCLUSIONS We have shown that the two novel combinations of compound heterozygous mutations p.R141H/p.M325T and p.R141H/p.I201T in the BEST1 gene can also lead to the ARB phenotype.
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Affiliation(s)
- Ragnhild Wivestad Jansson
- a Department of Clinical Medicine , Section of Ophthalmology, University of Bergen , Bergen , Norway .,b Department of Ophthalmology , Haukeland University Hospital , Bergen , Norway
| | - Siren Berland
- c Department of Pathology , Section of Clinical Genetics, St. Olav's Hospital , Trondheim , Norway
| | - Cecilie Bredrup
- b Department of Ophthalmology , Haukeland University Hospital , Bergen , Norway
| | - Dordi Austeng
- d Department of Ophthalmology , Trondheim University Hospital , Trondheim , Norway , and
| | - Sten Andréasson
- e Department of Ophthalmology , Lund University , Lund , Sweden
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Bestrophin 1 is indispensable for volume regulation in human retinal pigment epithelium cells. Proc Natl Acad Sci U S A 2015; 112:E2630-9. [PMID: 25941382 DOI: 10.1073/pnas.1418840112] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
In response to cell swelling, volume-regulated anion channels (VRACs) participate in a process known as regulatory volume decrease (RVD). Only recently, first insight into the molecular identity of mammalian VRACs was obtained by the discovery of the leucine-rich repeats containing 8A (LRRC8A) gene. Here, we show that bestrophin 1 (BEST1) but not LRRC8A is crucial for volume regulation in human retinal pigment epithelium (RPE) cells. Whole-cell patch-clamp recordings in RPE derived from human-induced pluripotent stem cells (hiPSC) exhibit an outwardly rectifying chloride current with characteristic functional properties of VRACs. This current is severely reduced in hiPSC-RPE cells derived from macular dystrophy patients with pathologic BEST1 mutations. Disruption of the orthologous mouse gene (Best1(-/-)) does not result in obvious retinal pathology but leads to a severe subfertility phenotype in agreement with minor endogenous expression of Best1 in murine RPE but highly abundant expression in mouse testis. Sperm from Best1(-/-) mice showed reduced motility and abnormal sperm morphology, indicating an inability in RVD. Together, our data suggest that the molecular identity of VRACs is more complex--that is, instead of a single ubiquitous channel, VRACs could be formed by cell type- or tissue-specific subunit composition. Our findings provide the basis to further examine VRAC diversity in normal and diseased cell physiology, which is key to exploring novel therapeutic approaches in VRAC-associated pathologies.
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Kane Dickson V, Pedi L, Long SB. Structure and insights into the function of a Ca(2+)-activated Cl(-) channel. Nature 2014; 516:213-8. [PMID: 25337878 DOI: 10.1038/nature13913] [Citation(s) in RCA: 154] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 10/06/2014] [Indexed: 01/22/2023]
Abstract
Bestrophin calcium-activated chloride channels (CaCCs) regulate the flow of chloride and other monovalent anions across cellular membranes in response to intracellular calcium (Ca(2+)) levels. Mutations in bestrophin 1 (BEST1) cause certain eye diseases. Here we present X-ray structures of chicken BEST1-Fab complexes, at 2.85 Å resolution, with permeant anions and Ca(2+). Representing, to our knowledge, the first structure of a CaCC, the eukaryotic BEST1 channel, which recapitulates CaCC function in liposomes, is formed from a pentameric assembly of subunits. Ca(2+) binds to the channel's large cytosolic region. A single ion pore, approximately 95 Å in length, is located along the central axis and contains at least 15 binding sites for anions. A hydrophobic neck within the pore probably forms the gate. Phenylalanine residues within it may coordinate permeating anions via anion-π interactions. Conformational changes observed near the 'Ca(2+) clasp' hint at the mechanism of Ca(2+)-dependent gating. Disease-causing mutations are prevalent within the gating apparatus.
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Affiliation(s)
- Veronica Kane Dickson
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
| | - Leanne Pedi
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
| | - Stephen B Long
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York 10065, USA
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33
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Effects of alternative splicing on the function of bestrophin-1 calcium-activated chloride channels. Biochem J 2014; 458:575-83. [PMID: 24341532 DOI: 10.1042/bj20121546] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The proposed Ca2+-activated Cl- channel protein Best1 (bestrophin 1) is expressed and functionally important in the retina and in the brain. Human BEST1 has two known splice variants, Best1V1 and Best1V2, which arise from alternative splicing of two exons: exon 2 splicing results in a unique N-terminal domain, whereas alternative splicing of exon 11 produces two mutually exclusive C-termini. Prior studies were limited to Best1V1 and its clinically relevant mutations. In the present work, we cloned a novel splice variant of Best1V1 missing exon 2 (Best1V1Δex2) and differing from each of the two previously identified isoforms by one alternatively spliced domain. This finding allowed us to determine the role for alternative splicing of the Best1 N- and C-termini. We heteroexpressed Best1V1Δex2 in HEK (human embryonic kidney)-293 cells, and compared its properties with Best1V1 and Best1V2. Western blot analysis confirmed protein expression from all three splice variants. Both Best1V1 and Best1V1Δex2 successfully formed Ca2+-activated Cl- channels, demonstrating that the N-terminus encoded by exon 2 is not essential for channel function. In contrast, Best1V2-expressing cells had no detectable Ca2+-activated Cl- currents, pointing to a critical role for splicing of the C-terminus. Surface protein biotinylation demonstrated that Best1V1 and Best1V1Δex2 are trafficked to the plasma membrane, whereas Best1V2 is not. These results define the impact of alternative splicing on Best1 function, and should be taken into consideration in future modelling of the Best1 protein structure.
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Abstract
Human Bestrophin 1 (hBest1) is a calcium-activated chloride channel that regulates neuronal excitability, synaptic activity, and retinal homeostasis. Mutations in hBest1 cause the autosomal-dominant Best macular dystrophy (BMD). Because hBest1 mutations cause BMD, but a knockout does not, we wondered if hBest1 mutants exert a dominant negative effect through interaction with other calcium-activated chloride channels, such as hBest2, 3, or 4, or transmembrane member 16A (TMEM16A), a member of another channel family. The subunit architecture of Best channels is debated, and their ability to form heteromeric channel assemblies is unclear. Using single-molecule subunit analysis, we find that each of hBest1, 2, 3, and 4 forms a homotetrameric channel. Despite considerable conservation among hBests, hBest1 has little or no interaction with other hBests or mTMEM16A. We identify the domain responsible for assembly specificity. This domain also plays a role in channel function. Our results indicate that Best channels preferentially self-assemble into homotetramers.
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Moskova-Doumanova V, Pankov R, Lalchev Z, Doumanov J. Best1 Shot Through the Eye—Structure, Functions and Clinical Implications of Bestrophin-1 Protein. BIOTECHNOL BIOTEC EQ 2014. [DOI: 10.5504/bbeq.2012.0124] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Johnson AA, Lee YS, Chadburn AJ, Tammaro P, Manson FD, Marmorstein LY, Marmorstein AD. Disease-causing mutations associated with four bestrophinopathies exhibit disparate effects on the localization, but not the oligomerization, of Bestrophin-1. Exp Eye Res 2014; 121:74-85. [PMID: 24560797 PMCID: PMC4123461 DOI: 10.1016/j.exer.2014.02.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Revised: 01/31/2014] [Accepted: 02/07/2014] [Indexed: 01/11/2023]
Abstract
BEST1 encodes Bestrophin-1 (Best1), a homo-oligomeric, integral membrane protein localized to the basolateral plasma membrane of the retinal pigment epithelium. Mutations in BEST1 cause five distinct retinal degenerative diseases, including adult vitelliform macular dystrophy (AVMD), autosomal recessive bestrophinopathy (ARB), autosomal dominant vitreoretinochoroidopathy (ADVIRC), and retinitis pigmentosa (RP). The mechanisms underlying these diseases and why mutations cause one disease over another are, for the most part, unknown. To gain insights into these four diseases, we expressed 28 Best1 mutants fused to YFP in polarized MDCK monolayers and, via confocal microscopy and immunofluorescence, live-cell FRET, and reciprocal co-immunoprecipitation experiments, screened these mutants for defects in localization and oligomerization. All 28 mutants exhibited comparable FRET efficiencies to and co-immunoprecipitated with WT Best1, indicating unimpaired oligomerization. RP- and ADVIRC-associated mutants were properly localized to the basolateral plasma membrane of cells, while two AVMD and most ARB mutants were mislocalized. When co-expressed, all mislocalized mutants caused mislocalization of WT Best1 to intracellular compartments. Our current and past results indicate that mislocalization of Best1 is not an absolute feature of any individual bestrophinopathy, occurring in AVMD, BVMD, and ARB. Furthermore, some ARB mutants that do not also cause dominant disease cause mislocalization of Best1, indicating that mislocalization is not a cause of disease, and that absence of Best1 activity from the plasma membrane is tolerated. Lastly, we find that the ARB truncation mutants L174Qfs*57 and R200X can form oligomers with WT Best1, indicating that the first ∼174 amino acids of Best1 are sufficient for oligomerization to occur.
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Affiliation(s)
- Adiv A Johnson
- Physiological Sciences Graduate Interdisciplinary Program, University of Arizona, Tucson, AZ 85724, USA; Department of Ophthalmology, Mayo Clinic, Rochester, MN 55905, USA.
| | - Yong-Suk Lee
- Department of Ophthalmology, Mayo Clinic, Rochester, MN 55905, USA.
| | - Andrew J Chadburn
- Faculty of Life Sciences, Faculty of Medical and Human Sciences, The University of Manchester, Manchester M13 9PT, United Kingdom.
| | - Paolo Tammaro
- Faculty of Life Sciences, Faculty of Medical and Human Sciences, The University of Manchester, Manchester M13 9PT, United Kingdom.
| | - Forbes D Manson
- Manchester Centre for Genomic Medicine, Faculty of Medical and Human Sciences, The University of Manchester, Manchester M13 9PT, United Kingdom.
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Strauß O, Müller C, Reichhart N, Tamm ER, Gomez NM. The Role of Bestrophin-1 in Intracellular Ca2+ Signaling. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 801:113-9. [DOI: 10.1007/978-1-4614-3209-8_15] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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Pasquay C, Wang LF, Lorenz B, Preising MN. Bestrophin 1 – Phenotypes and Functional Aspects in Bestrophinopathies. Ophthalmic Genet 2013; 36:193-212. [DOI: 10.3109/13816810.2013.863945] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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39
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Guziewicz KE, Zangerl B, Komáromy AM, Iwabe S, Chiodo VA, Boye SL, Hauswirth WW, Beltran WA, Aguirre GD. Recombinant AAV-mediated BEST1 transfer to the retinal pigment epithelium: analysis of serotype-dependent retinal effects. PLoS One 2013; 8:e75666. [PMID: 24143172 PMCID: PMC3797066 DOI: 10.1371/journal.pone.0075666] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Accepted: 08/17/2013] [Indexed: 02/06/2023] Open
Abstract
Mutations in the BEST1 gene constitute an underlying cause of juvenile macular dystrophies, a group of retinal disorders commonly referred to as bestrophinopathies and usually diagnosed in early childhood or adolescence. The disease primarily affects macular and paramacular regions of the eye leading to major declines in central vision later in life. Currently, there is no cure or surgical management for BEST1-associated disorders. The recently characterized human disease counterpart, canine multifocal retinopathy (cmr), recapitulates a full spectrum of clinical and molecular features observed in human bestrophinopathies and offers a valuable model system for development and testing of therapeutic strategies. In this study, the specificity, efficiency and safety of rAAV-mediated transgene expression driven by the human VMD2 promoter were assessed in wild-type canine retinae. While the subretinal delivery of rAAV2/1 vector serotype was associated with cone damage in the retina when BEST1 and GFP were co-expressed, the rAAV2/2 vector serotype carrying either GFP reporter or BEST1 transgene under control of human VMD2 promoter was safe, and enabled specific transduction of the RPE cell monolayer that was stable for up to 6 months post injection. These encouraging studies with the rAAV2/2 vector lay the groundwork for development of gene augmentation therapy for human bestrophinopathies.
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Affiliation(s)
- Karina E. Guziewicz
- Section of Ophthalmology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * E-mail: (KEG); (GDA)
| | - Barbara Zangerl
- Section of Ophthalmology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Centre for Eye Health, University of New South Wales, Kensington, Australia
- * E-mail: (KEG); (GDA)
| | - András M. Komáromy
- Section of Ophthalmology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan, United States of America
| | - Simone Iwabe
- Section of Ophthalmology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Vincent A. Chiodo
- Department of Ophthalmology, University of Florida, Gainesville, Florida, United States of America
| | - Sanford L. Boye
- Department of Ophthalmology, University of Florida, Gainesville, Florida, United States of America
| | - William W. Hauswirth
- Department of Ophthalmology, University of Florida, Gainesville, Florida, United States of America
| | - William A. Beltran
- Section of Ophthalmology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Gustavo D. Aguirre
- Section of Ophthalmology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
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Doumanov JA, Zeitz C, Gimenez PD, Audo I, Krishna A, Alfano G, Diaz MLB, Moskova-Doumanova V, Lancelot ME, Sahel JA, Nandrot EF, Bhattacharya SS. Disease-causing mutations in BEST1 gene are associated with altered sorting of bestrophin-1 protein. Int J Mol Sci 2013; 14:15121-40. [PMID: 23880862 PMCID: PMC3742291 DOI: 10.3390/ijms140715121] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 07/02/2013] [Accepted: 07/04/2013] [Indexed: 01/03/2023] Open
Abstract
Mutations in BEST1 gene, encoding the bestrophin-1 (Best1) protein are associated with macular dystrophies. Best1 is predominantly expressed in the retinal pigment epithelium (RPE), and is inserted in its basolateral membrane. We investigated the cellular localization in polarized MDCKII cells of disease-associated Best1 mutant proteins to study specific sorting motifs of Best1. Real-time PCR and western blots for endogenous expression of BEST1 in MDCK cells were performed. Best1 mutant constructs were generated using site-directed mutagenesis and transfected in MDCK cells. For protein sorting, confocal microscopy studies, biotinylation assays and statistical methods for quantification of mislocalization were used. Analysis of endogenous expression of BEST1 in MDCK cells revealed the presence of BEST1 transcript but no protein. Confocal microscopy and quantitative analyses indicate that transfected normal human Best1 displays a basolateral localization in MDCK cells, while cell sorting of several Best1 mutants (Y85H, Q96R, L100R, Y227N, Y227E) was altered. In contrast to constitutively active Y227E, constitutively inactive Y227F Best1 mutant localized basolaterally similar to the normal Best1 protein. Our data suggest that at least three basolateral sorting motifs might be implicated in proper Best1 basolateral localization. In addition, non-phosphorylated tyrosine 227 could play a role for basolateral delivery.
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Affiliation(s)
- Jordan A. Doumanov
- Biological Faculty, Sofia University “Saint Kliment Ohridski”, 8 Dragan Tzankov str, Sofia 1164, Bulgaria; E-Mail:
- Author to whom correspondence should be addressed; E-Mail: ; Tel.: +359-2-8167-204; Fax: +359-2-8656-641
| | - Christina Zeitz
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMR_S 968, Paris F-75012, France; E-Mails: (C.Z.); (I.A.); (M.-E.L.); (J.-A.S.); (E.F.N.); (S.S.B.)
- Centre National de la Recherche Scientifique (CNRS), UMR_7210, Paris F-75012, France
- Centre de Recherche Institut de la Vision, Université Pierre et Marie Curie-Paris 6, 17 rue Moreau, Paris F-75012, France
| | - Paloma Dominguez Gimenez
- Andalusian Center of Molecular Biology and Regenerative Medicine, Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Avda. Americo Vespucio s/n, Parque Cientifico y Tecnologico, Isla de la Cartuja 41092, Sevilla, Spain; E-Mails: (P.D.G.); (A.K.); (M.L.B.D.)
| | - Isabelle Audo
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMR_S 968, Paris F-75012, France; E-Mails: (C.Z.); (I.A.); (M.-E.L.); (J.-A.S.); (E.F.N.); (S.S.B.)
- Centre National de la Recherche Scientifique (CNRS), UMR_7210, Paris F-75012, France
- Centre de Recherche Institut de la Vision, Université Pierre et Marie Curie-Paris 6, 17 rue Moreau, Paris F-75012, France
- Centre de Référence Maladies Rares/Centre d’Investigation Clinique (CMR/CIC), 503 INSERM, CHNO des Quinze-Vingts, Paris F-75012, France
| | - Abhay Krishna
- Andalusian Center of Molecular Biology and Regenerative Medicine, Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Avda. Americo Vespucio s/n, Parque Cientifico y Tecnologico, Isla de la Cartuja 41092, Sevilla, Spain; E-Mails: (P.D.G.); (A.K.); (M.L.B.D.)
| | - Giovanna Alfano
- Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK
| | - Maria Luz Bellido Diaz
- Andalusian Center of Molecular Biology and Regenerative Medicine, Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Avda. Americo Vespucio s/n, Parque Cientifico y Tecnologico, Isla de la Cartuja 41092, Sevilla, Spain; E-Mails: (P.D.G.); (A.K.); (M.L.B.D.)
| | - Veselina Moskova-Doumanova
- Biological Faculty, Sofia University “Saint Kliment Ohridski”, 8 Dragan Tzankov str, Sofia 1164, Bulgaria; E-Mail:
| | - Marie-Elise Lancelot
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMR_S 968, Paris F-75012, France; E-Mails: (C.Z.); (I.A.); (M.-E.L.); (J.-A.S.); (E.F.N.); (S.S.B.)
- Centre National de la Recherche Scientifique (CNRS), UMR_7210, Paris F-75012, France
- Centre de Recherche Institut de la Vision, Université Pierre et Marie Curie-Paris 6, 17 rue Moreau, Paris F-75012, France
| | - José-Alain Sahel
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMR_S 968, Paris F-75012, France; E-Mails: (C.Z.); (I.A.); (M.-E.L.); (J.-A.S.); (E.F.N.); (S.S.B.)
- Centre National de la Recherche Scientifique (CNRS), UMR_7210, Paris F-75012, France
- Centre de Recherche Institut de la Vision, Université Pierre et Marie Curie-Paris 6, 17 rue Moreau, Paris F-75012, France
- Centre de Référence Maladies Rares/Centre d’Investigation Clinique (CMR/CIC), 503 INSERM, CHNO des Quinze-Vingts, Paris F-75012, France
- Fondation Ophtalmologique Adolphe de Rothschild, Paris F-75019, France
| | - Emeline F. Nandrot
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMR_S 968, Paris F-75012, France; E-Mails: (C.Z.); (I.A.); (M.-E.L.); (J.-A.S.); (E.F.N.); (S.S.B.)
- Centre National de la Recherche Scientifique (CNRS), UMR_7210, Paris F-75012, France
- Centre de Recherche Institut de la Vision, Université Pierre et Marie Curie-Paris 6, 17 rue Moreau, Paris F-75012, France
| | - Shomi S. Bhattacharya
- Institut National de la Santé et de la Recherche Médicale (INSERM), UMR_S 968, Paris F-75012, France; E-Mails: (C.Z.); (I.A.); (M.-E.L.); (J.-A.S.); (E.F.N.); (S.S.B.)
- Centre National de la Recherche Scientifique (CNRS), UMR_7210, Paris F-75012, France
- Centre de Recherche Institut de la Vision, Université Pierre et Marie Curie-Paris 6, 17 rue Moreau, Paris F-75012, France
- Andalusian Center of Molecular Biology and Regenerative Medicine, Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Avda. Americo Vespucio s/n, Parque Cientifico y Tecnologico, Isla de la Cartuja 41092, Sevilla, Spain; E-Mails: (P.D.G.); (A.K.); (M.L.B.D.)
- Institute of Ophthalmology, University College London, 11-43 Bath Street, London EC1V 9EL, UK
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Johnson AA, Lee YS, Stanton JB, Yu K, Hartzell CH, Marmorstein LY, Marmorstein AD. Differential effects of Best disease causing missense mutations on bestrophin-1 trafficking. Hum Mol Genet 2013; 22:4688-97. [PMID: 23825107 DOI: 10.1093/hmg/ddt316] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Mutations in bestrophin-1 (Best1) cause Best vitelliform macular dystrophy (BVMD), a dominantly inherited retinal degenerative disease. Best1 is a homo-oligomeric anion channel localized to the basolateral surface of retinal pigment epithelial (RPE) cells. A number of Best1 mutants mislocalize in Madin-Darby canine kidney (MDCK) cells. However, many proteins traffic differently in MDCK and RPE cells, and MDCK cells do not express endogenous Best1. Thus, effects of Best1 mutations on localization in MDCK cells may not translate to RPE cells. To determine whether BVMD causing mutations affect Best1 localization, we compared localization and oligomerization of Best1 with Best1 mutants V9M, W93C, and R218C. In MDCK cells, Best1 and Best1(R218C) were basolaterally localized. Best1(W93C) and Best1(V9M) accumulated in cells. In cultured fetal human retinal pigment epithelium cells (fhRPE) expressing endogenous Best1, Best1(R218C) and Best1(W93C) were basolateral. Best1(V9M) was intracellular. All three mutants exhibited similar fluorescence resonance energy transfer (FRET) efficiencies to, and co-immunoprecipitated with Best1, indicating unimpaired oligomerization. When human Best1 was expressed in RPE in mouse eyes it was basolaterally localized. However, Best1(V9M) accumulated in intracellular compartments in mouse RPE. Co-expression of Best1 and Best1(W93C) in MDCK cells resulted in basolateral localization of both Best1 and Best1(W93C), but co-expression of Best1 with Best1(V9M) resulted in mislocalization of both proteins. We conclude that different mutations in Best1 cause differential effects on its localization and that this effect varies with the presence or absence of wild-type (WT) Best1. Furthermore, MDCK cells can substitute for RPE when examining the effects of BVMD causing mutations on Best1 localization if co-expressed with WT Best1.
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Gómez NM, Tamm ER, Strauβ O. Role of bestrophin-1 in store-operated calcium entry in retinal pigment epithelium. Pflugers Arch 2012. [PMID: 23207577 DOI: 10.1007/s00424-012-1181-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The retinal pigment epithelium (RPE) expresses bestrophin-1 where mutant bestrophin cause retinal degenerations. Overexpression of bestrophin-1 demonstrated Ca(2+)-dependent Cl(-) channel function, whereas the RPE in bestrophin-1 knockout or mutant bestrophin-1 knock-in mice showed no change in Cl(-) conductance. To account for these apparently mutually exclusive findings, we investigated the function of endogenously expressed bestrophin-1 in a short-time RPE cell culture system by means of immunocytochemistry, Ca(2+) imaging, and siRNA knockdown. Immunocytochemical quantification of bestrophin-1 localization demonstrated 2.5 times higher co-localization with the endoplasmic reticulum (ER) Ca(2+)-sensor protein, Stim-1, than with the membrane protein β-catenin, implicating it in store-operated Ca(2+) entry (SOCE). Ca(2+) release from ER stores under extracellular Ca(2+)-free conditions using thapsigargin (1 μM) to inhibit endoplasmic Ca(2+) ATPase (SERCA) followed by re-adjustment of extracellular Ca(2+) to physiological levels activated SOCE, which was insensitive to the blocker of numerous transient receptor potential channels and voltage-dependent Ca(2+) channels SKF96563 (1 μM). SOCE was augmented at 5 μM and inhibited at 75 μM by 2-aminoethoxydiphenyl borate which indicates the involvement Orai-1 channels. In confirmation, SOCE was decreased by siRNA knockdown of Orai-1 expression. SOCE amplitude was strongly reduced by siRNA knockdown of bestrophin-1 expression, which was due to neither changes in Stim-1/Orai-1 expression nor Stim-1/bestrophin-1 interaction. The amount of Ca(2+) released by SERCA inhibition was reduced after siRNA knockdown of bestrophin-1, but not of Orai-1. In conclusion we found that a proportion of bestrophin-1 is functionally localized to ER Ca(2+) stores where it influences the amount of Ca(2+) and therefore Ca(2+) signals which result from activation of Orai-1 via Stim-1.
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Affiliation(s)
- Néstor Más Gómez
- Experimental Ophthalmology, Eye Hospital, University Medical Center Regensburg, Franz-Josef-Strauss-Allee 11, 93053, Regensburg, Germany
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Anion-sensitive fluorophore identifies the Drosophila swell-activated chloride channel in a genome-wide RNA interference screen. PLoS One 2012; 7:e46865. [PMID: 23056495 PMCID: PMC3464265 DOI: 10.1371/journal.pone.0046865] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2012] [Accepted: 09/06/2012] [Indexed: 12/21/2022] Open
Abstract
When cells swell in hypo-osmotic solutions, chloride-selective ion channels (Cl(swell)) activate to reduce intracellular osmolality and prevent catastrophic cell rupture. Despite intensive efforts to assign a molecular identity to the mammalian Cl(swell) channel, it remains unknown. In an unbiased genome-wide RNA interference (RNAi) screen of Drosophila cells stably expressing an anion-sensitive fluorescent indicator, we identify Bestrophin 1 (dBest1) as the Drosophila Cl(swell) channel. Of the 23 screen hits with mammalian homologs and predicted transmembrane domains, only RNAi specifically targeting dBest1 eliminated the Cl(swell) current (I(Clswell)). We further demonstrate the essential contribution of dBest1 to Drosophila I(Clswell) with the introduction of a human Bestrophin disease-associated mutation (W94C). Overexpression of the W94C construct in Drosophila cells significantly reduced the endogenous I(Clswell). We confirm that exogenous expression of dBest1 alone in human embryonic kidney (HEK293) cells creates a clearly identifiable Drosophila-like I(Clswell). In contrast, activation of mouse Bestrophin 2 (mBest2), the closest mammalian ortholog of dBest1, is swell-insensitive. The first 64 residues of dBest1 conferred swell activation to mBest2. The chimera, however, maintains mBest2-like pore properties, strongly indicating that the Bestrophin protein forms the Cl(swell) channel itself rather than functioning as an essential auxiliary subunit. dBest1 is an anion channel clearly responsive to swell; this activation depends upon its N-terminus.
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