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Sechrest ER, Barbera RJ, Ma X, Dyka F, Ahn J, Brothers BA, Cahill ME, Hall I, Baehr W, Deng WT. Expression of red/green-cone opsin mutants K82E, P187S, M273K result in unique pathobiological perturbations to cone structure and function. Front Neurosci 2024; 18:1368089. [PMID: 38410159 PMCID: PMC10895044 DOI: 10.3389/fnins.2024.1368089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2024] [Accepted: 01/23/2024] [Indexed: 02/28/2024] Open
Abstract
Long-and middle-wavelength cone photoreceptors, which are responsible for our visual acuity and color vision, comprise ~95% of our total cone population and are concentrated in the fovea of our retina. Previously, we characterized the disease mechanisms of the L/M-cone opsin missense mutations N94K, W177R, P307L, R330Q and G338E, all of which are associated with congenital blue cone monochromacy (BCM) or color-vision deficiency. Here, we used a similar viral vector-based gene delivery approach in M-opsin knockout mice to investigate the pathogenic consequences of the BCM or color-vision deficient associated L-cone opsin (OPN1LW) mutants K82E, P187S, and M273K. We investigated their subcellular localization, the pathogenic effects on cone structure, function, and cone viability. K82E mutants were detected predominately in cone outer segments, and its expression partially restored expression and correct localization of cone PDE6α' and cone transducin γ. As a result, K82E also demonstrated the ability to mediate cone light responses. In contrast, expression of P187S was minimally detected by either western blot or by immunohistochemistry, probably due to efficient degradation of the mutant protein. M273K cone opsin appeared to be misfolded as it was primarily localized to the cone inner segment and endoplasmic reticulum. Additionally, M273K did not restore the expression of cone PDE6α' and cone transducin γ in dorsal cone OS, presumably by its inability to bind 11-cis retinal. Consistent with the observed expression pattern, P187S and M273K cone opsin mutants were unable to mediate light responses. Moreover, expression of K82E, P187S, and M273K mutants reduced cone viability. Due to the distinct expression patterns and phenotypic differences of these mutants observed in vivo, we suggest that the pathobiological mechanisms of these mutants are distinct.
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Affiliation(s)
- Emily R. Sechrest
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV, United States
| | - Robert J. Barbera
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV, United States
| | - Xiaojie Ma
- Department of Ophthalmology, University of Florida, Gainesville, FL, United States
| | - Frank Dyka
- Department of Ophthalmology, University of Florida, Gainesville, FL, United States
| | - Junyeop Ahn
- Department of Chemistry, University of Virginia, Charlottesville, VA, United States
| | - Brooke A. Brothers
- Department of Biochemistry, West Virginia University, Morgantown, WV, United States
| | - Marion E. Cahill
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV, United States
- Department of Biology, West Virginia University, Morgantown, WV, United States
| | - Isaac Hall
- Department of Natural Sciences, Fairmont State University, Fairmont, WV, United States
| | - Wolfgang Baehr
- Department of Ophthalmology, John A. Moran Eye Center, University of Utah Health Science Center, Salt Lake City, UT, United States
- Department of Neurobiology and Anatomy, University of Utah Health Science Center, Salt Lake City, UT, United States
- Department of Biology, University of Utah, Salt Lake City, UT, United States
| | - Wen-Tao Deng
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV, United States
- Department of Biochemistry, West Virginia University, Morgantown, WV, United States
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Sechrest ER, Ma X, Cahill ME, Barbera RJ, Wang Y, Deng WT. Structural and functional rescue of cones carrying the most common cone opsin C203R missense mutation. JCI Insight 2024; 9:e172834. [PMID: 38060327 PMCID: PMC10906232 DOI: 10.1172/jci.insight.172834] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2023] [Accepted: 12/05/2023] [Indexed: 01/24/2024] Open
Abstract
An arginine to cysteine substitution at amino acid position 203 (C203R) is the most common missense mutation in human cone opsin. Linked to color blindness and blue cone monochromacy (BCM), C203 is involved in a crucial disulfide bond required for proper folding. It has previously been postulated that expression of mutant C203R cone opsin exerts a toxic effect on cone photoreceptors, similar to some well-characterized missense mutations in rhodopsin that lead to protein misfolding. In this study, we generated and characterized a BCM mouse model carrying the equivalent C203R mutation (Opn1mwC198R Opn1sw-/-) to investigate the disease mechanism and develop a gene therapy approach for this disorder. Untreated Opn1mwC198R Opn1sw-/- cones phenocopied affected cones in human patients with the equivalent mutation, exhibiting shortened or absent cone outer segments and loss of function. We determined that gene augmentation targeting cones specifically yielded robust rescue of cone function and structure when Opn1mwC198R Opn1sw-/- mice were treated at early ages. Importantly, treated cones displayed elaborated outer segments and replenished expression of crucial cone phototransduction proteins. Interestingly, we were unable to detect OPN1MWC198R mutant opsin at any age. We believe this is the first proof-of-concept study exploring the efficacy of gene therapy in BCM associated with a C203R mutation.
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Affiliation(s)
- Emily R. Sechrest
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, West Virginia, USA
| | - Xiaojie Ma
- Department of Ophthalmology, University of Florida, Gainesville, Florida, USA
| | - Marion E. Cahill
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, West Virginia, USA
- Department of Biology and
| | - Robert J. Barbera
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, West Virginia, USA
| | - Yixiao Wang
- Department of Ophthalmology, University of Florida, Gainesville, Florida, USA
| | - Wen-Tao Deng
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, West Virginia, USA
- Department of Biochemistry and Molecular Medicine, West Virginia University, Morgantown, West Virginia, USA
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Sechrest ER, Chmelik K, Tan WD, Deng WT. Blue cone monochromacy and gene therapy. Vision Res 2023; 208:108221. [PMID: 37001420 PMCID: PMC10182257 DOI: 10.1016/j.visres.2023.108221] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Revised: 03/14/2023] [Accepted: 03/15/2023] [Indexed: 03/30/2023]
Abstract
Blue cone monochromacy (BCM) is a congenital vision disorder characterized by complete loss or severely reduced long- and middle-wavelength cone function, caused by mutations in the OPN1LW/OPN1MW gene cluster on the X-chromosome. BCM patients typically suffer from poor visual acuity, severely impaired color discrimination, myopia, and nystagmus. In this review, we cover the genetic causes of BCM, clinical features of BCM patients, genetic testing, and clinical outcome measurements for future BCM clinical trials. However, our emphasis is on detailing the animal models for BCM and gene therapy using adeno-associated vectors (AAV). We describe two mouse models resembling the two most common causes of BCM, current progress in proof-of-concept studies to treat BCM with deletion mutations, the challenges we face, and future directions.
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Affiliation(s)
- Emily R Sechrest
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV 26505, United States
| | - Kathryn Chmelik
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV 26505, United States; Department of Biochemistry, West Virginia University, Morgantown, WV 26505, United States
| | - Wendy D Tan
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV 26505, United States
| | - Wen-Tao Deng
- Department of Ophthalmology and Visual Sciences, West Virginia University, Morgantown, WV 26505, United States; Department of Biochemistry, West Virginia University, Morgantown, WV 26505, United States.
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