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Tam BM, Burns P, Chiu CN, Moritz OL. Synchronized Photoactivation of T4K Rhodopsin Causes a Chromophore-Dependent Retinal Degeneration That Is Moderated by Interaction with Phototransduction Cascade Components. J Neurosci 2024; 44:e0453242024. [PMID: 39089885 PMCID: PMC11376340 DOI: 10.1523/jneurosci.0453-24.2024] [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: 03/06/2024] [Revised: 06/29/2024] [Accepted: 07/24/2024] [Indexed: 08/04/2024] Open
Abstract
Multiple mutations in the Rhodopsin gene cause sector retinitis pigmentosa in humans and a corresponding light-exacerbated retinal degeneration (RD) in animal models. Previously we have shown that T4K rhodopsin requires photoactivation to exert its toxic effect. Here we further investigated the mechanisms involved in rod cell death caused by T4K rhodopsin in mixed male and female Xenopus laevis In this model, RD was prevented by rearing animals in constant darkness but surprisingly also in constant light. RD was maximized by light cycles containing at least 1 h of darkness and 20 min of light exposure, light intensities >750 lux, and by a sudden light onset. Under conditions of frequent light cycling, RD occurred rapidly and synchronously, with massive shedding of ROS fragments into the RPE initiated within hours and subsequent death and phagocytosis of rod cell bodies. RD was minimized by reduced light levels, pretreatment with constant light, and gradual light onset. RD was prevented by genetic ablation of the retinal isomerohydrolase RPE65 and exacerbated by ablation of phototransduction components GNAT1, SAG, and GRK1. Our results indicate that photoactivated T4K rhodopsin is toxic, that cell death requires synchronized photoactivation of T4K rhodopsin, and that toxicity is mitigated by interaction with other rod outer segment proteins regardless of whether they participate in activation or shutoff of phototransduction. In contrast, RD caused by P23H rhodopsin does not require photoactivation of the mutant protein, as it was exacerbated by RPE65 ablation, suggesting that these phenotypically similar disorders may require different treatment strategies.
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Affiliation(s)
- Beatrice M Tam
- Department of Ophthalmology & Visual Sciences, University of British Columbia, Vancouver, British Columbia V5Z 3N9, Canada
| | - Paloma Burns
- Department of Ophthalmology & Visual Sciences, University of British Columbia, Vancouver, British Columbia V5Z 3N9, Canada
| | - Colette N Chiu
- Department of Ophthalmology & Visual Sciences, University of British Columbia, Vancouver, British Columbia V5Z 3N9, Canada
| | - Orson L Moritz
- Department of Ophthalmology & Visual Sciences, University of British Columbia, Vancouver, British Columbia V5Z 3N9, Canada
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2
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Ferreira PA. Personal essay of a rookie's journey with Bill Pak and his legacy: tales and perspectives on PI-PLC, NorpA and cyclophilin, NinaA - William L. Pak, PhD., 1932-2023: in memoriam. J Neurogenet 2024:1-10. [PMID: 38913811 DOI: 10.1080/01677063.2024.2366455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2024] [Accepted: 05/30/2024] [Indexed: 06/26/2024]
Abstract
The neurogenetics and vision community recently mourned William L. Pak, PhD, whose pioneering work spearheaded the genetic, electrophysiological, and molecular bases of biological processes underpinning vision. This essay provides a historical background to the daunting challenges and personal experiences that carved the path to seminal findings. It also reflects on the intellectual framework, mentoring philosophy, and inspirational legacy of Bill Pak's research. An emphasis and perspectives are placed on the discoveries and implications to date of the phosphatidylinositol-specific phospholipase C (PI-PLC), NorpA, and the cyclophilin, NinaA of the fruit fly, Drosophila melanogaster, and their respective mammalian homologues, PI-PLCβ4, and cyclophilin-related protein, Ran-binding protein 2 (Ranbp2) in critical biological processes and diseases of photoreceptors and other neurons.
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Affiliation(s)
- Paulo A Ferreira
- Departments of Ophthalmology and Pathology, Duke University Medical Center, Durham, North Carolina, USA
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3
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Wang B, Arbuckle RK, Davoli KA, Clinger OD, Brown R, Sahel JA, Chen Y, Pi S. Compensation of inner retina to early-stage photoreceptor degeneration in a Rho P23H/+ mouse model of retinitis pigmentosa. Exp Eye Res 2024; 240:109826. [PMID: 38340947 PMCID: PMC10940204 DOI: 10.1016/j.exer.2024.109826] [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: 12/01/2023] [Revised: 02/05/2024] [Accepted: 02/07/2024] [Indexed: 02/12/2024]
Abstract
Retinitis pigmentosa (RP) is an inherited retinal disorder characterized by the degeneration of photoreceptors. RhoP23H/+ mice, which carry a Pro23His mutation in the RHODOPSIN (Rho) gene, are one of the most studied animal models for RP. However, except for the photoreceptors, other retinal neural cells have not been fully investigated in this model. Here, we record the temporal changes of the retina by optical coherence tomography (OCT) imaging of the RhoP23H/+ mice, from early to mid-phase of retinal degeneration. Based on thickness analysis, we identified a natural retinal thickness adaption in wild-type mice during early adulthood and observed morphological compensation of the inner retina layer to photoreceptor degeneration in the RhoP23H/+ mice, primarily on the inner nuclear layer (INL). RhoP23H/+ mice findings were further validated via: histology showing the negative correlation of INL and ONL thicknesses; as well as electroretinogram (ERG) showing an increased b-wave to a-wave ratio. These results unravel the sequential morphologic events in this model and suggest a better understanding of retinal degeneration of RP for future studies.
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Affiliation(s)
- Bingjie Wang
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; UPMC Vision Institute, University of Pittsburgh, Pittsburgh, PA, 15213, USA
| | - Riley K Arbuckle
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; UPMC Vision Institute, University of Pittsburgh, Pittsburgh, PA, 15213, USA; Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; Department of Human Genetics, University of Pittsburgh Graduate School of Public Health, Pittsburgh, PA, 15213, USA
| | - Katherine A Davoli
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; UPMC Vision Institute, University of Pittsburgh, Pittsburgh, PA, 15213, USA
| | - Owen D Clinger
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; UPMC Vision Institute, University of Pittsburgh, Pittsburgh, PA, 15213, USA
| | - Richard Brown
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; UPMC Vision Institute, University of Pittsburgh, Pittsburgh, PA, 15213, USA
| | - José-Alain Sahel
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; UPMC Vision Institute, University of Pittsburgh, Pittsburgh, PA, 15213, USA
| | - Yuanyuan Chen
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; UPMC Vision Institute, University of Pittsburgh, Pittsburgh, PA, 15213, USA; Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA, 15213, USA.
| | - Shaohua Pi
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA, 15213, USA; UPMC Vision Institute, University of Pittsburgh, Pittsburgh, PA, 15213, USA; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, 15213, USA.
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4
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Park JE, Lee J, Ok S, Byun S, Chang EJ, Yoon SE, Kim YJ, Kang MJ. Wg/Wnt1 and Erasp link ER stress to proapoptotic signaling in an autosomal dominant retinitis pigmentosa model. Exp Mol Med 2023:10.1038/s12276-023-01044-7. [PMID: 37464094 PMCID: PMC10394004 DOI: 10.1038/s12276-023-01044-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Revised: 04/11/2023] [Accepted: 04/17/2023] [Indexed: 07/20/2023] Open
Abstract
The endoplasmic reticulum (ER) is a subcellular organelle essential for cellular homeostasis. Perturbation of ER functions due to various conditions can induce apoptosis. Chronic ER stress has been implicated in a wide range of diseases, including autosomal dominant retinitis pigmentosa (ADRP), which is characterized by age-dependent retinal degeneration caused by mutant rhodopsin alleles. However, the signaling pathways that mediate apoptosis in response to ER stress remain poorly understood. In this study, we performed an unbiased in vivo RNAi screen with a Drosophila ADRP model and found that Wg/Wnt1 mediated apoptosis. Subsequent transcriptome analysis revealed that ER stress-associated serine protease (Erasp), which has been predicted to show serine-type endopeptidase activity, was a downstream target of Wg/Wnt1 during ER stress. Furthermore, knocking down Erasp via RNAi suppressed apoptosis induced by mutant rhodopsin-1 (Rh-1P37H) toxicity, alleviating retinal degeneration in the Drosophila ADRP model. In contrast, overexpression of Erasp resulted in enhanced caspase activity in Drosophila S2 cells treated with apoptotic inducers and the stabilization of the initiator caspase Dronc (Death regulator Nedd2-like caspase) by stimulating DIAP1 (Drosophila inhibitor of apoptosis protein 1) degradation. These findings helped identify a novel cell death signaling pathway involved in retinal degeneration in an autosomal dominant retinitis pigmentosa model.
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Affiliation(s)
- Jung-Eun Park
- Department of Pharmacology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, 05505, Republic of Korea
| | - Jiyoun Lee
- School of Biopharmaceutical and Medical Sciences, Sungshin University, Seoul, 01133, Republic of Korea
| | - Soonhyuck Ok
- Department of Pharmacology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, 05505, Republic of Korea
| | - Seunghee Byun
- Department of Pharmacology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, 05505, Republic of Korea
| | - Eun-Ju Chang
- Department of Biochemistry and Molecular Biology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, 05505, Republic of Korea
- Biomedical Research Center, Asan Institute for Life Sciences, Asan Medical Center, 88, Olympic-ro 43-gil, Songpa-gu, Seoul, 05505, Republic of Korea
| | - Sung-Eun Yoon
- Korea Drosophila Resource Center, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 61005, Republic of Korea
| | - Young-Joon Kim
- School of Life Sciences, Gwangju Institute of Science and Technology (GIST), 123 Cheomdangwagi-ro, Buk-gu, Gwangju, 61005, Republic of Korea
| | - Min-Ji Kang
- Department of Pharmacology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, 05505, Republic of Korea.
- Biomedical Research Center, Asan Institute for Life Sciences, Asan Medical Center, 88, Olympic-ro 43-gil, Songpa-gu, Seoul, 05505, Republic of Korea.
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5
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Zhao N, Li N, Wang T. PERK prevents rhodopsin degradation during retinitis pigmentosa by inhibiting IRE1-induced autophagy. J Cell Biol 2023; 222:e202208147. [PMID: 37022709 PMCID: PMC10082367 DOI: 10.1083/jcb.202208147] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2022] [Revised: 01/04/2023] [Accepted: 02/14/2023] [Indexed: 04/07/2023] Open
Abstract
Chronic endoplasmic reticulum (ER) stress is the underlying cause of many degenerative diseases, including autosomal dominant retinitis pigmentosa (adRP). In adRP, mutant rhodopsins accumulate and cause ER stress. This destabilizes wild-type rhodopsin and triggers photoreceptor cell degeneration. To reveal the mechanisms by which these mutant rhodopsins exert their dominant-negative effects, we established an in vivo fluorescence reporter system to monitor mutant and wild-type rhodopsin in Drosophila. By performing a genome-wide genetic screen, we found that PERK signaling plays a key role in maintaining rhodopsin homeostasis by attenuating IRE1 activities. Degradation of wild-type rhodopsin is mediated by selective autophagy of ER, which is induced by uncontrolled IRE1/XBP1 signaling and insufficient proteasome activities. Moreover, upregulation of PERK signaling prevents autophagy and suppresses retinal degeneration in the adRP model. These findings establish a pathological role for autophagy in this neurodegenerative condition and indicate that promoting PERK activity could be used to treat ER stress-related neuropathies, including adRP.
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Affiliation(s)
- Ning Zhao
- Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Ning Li
- College of Biological Sciences, China Agricultural University, Beijing, China
| | - Tao Wang
- Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
- College of Biological Sciences, China Agricultural University, Beijing, China
- Tsinghua Institute of Multidisciplinary Biomedical Research, Tsinghua University, Beijing, China
- National Institute of Biological Sciences, Beijing, China
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Oh JK, Levi SR, Kim J, Lima de Carvalho JR, Ryu J, Sparrow JR, Tsang SH. Differences in Intraretinal Pigment Migration Across Inherited Retinal Dystrophies. Am J Ophthalmol 2020; 217:252-260. [PMID: 32442431 DOI: 10.1016/j.ajo.2020.05.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Revised: 04/15/2020] [Accepted: 05/08/2020] [Indexed: 01/12/2023]
Abstract
PURPOSE To determine whether there are differences in the prevalence of intraretinal pigment migration (IPM) across ages and genetic causes of inherited retinal dystrophies (IRDs). DESIGN Retrospective cohort study. METHODS Patients were evaluated at a single tertiary referral center. All patients with a clinical diagnosis of IRD and confirmatory genetic testing were included in these analyses. A total of 392 patients fit inclusion criteria, and 151 patients were excluded based on inconclusive genetic testing. Patients were placed into 3 groups, ciliary and ciliary-related photoreceptor, nonciliary photoreceptor, and retinal pigment epithelium (RPE), based on the cellular expression of the gene and the primary affected cell type. The presence of IPM was evaluated by using slit lamp biomicroscopy, indirect ophthalmoscopy, and wide-field color fundus photography. RESULTS IPM was seen in 257 of 339 patients (75.8%) with mutations in photoreceptor-specific genes and in 18 of 53 patients (34.0%) with mutations in RPE-specific genes (P < .0001). Pairwise analysis following stratification by age and gene category suggested significant differences at all age groups between patients with mutations in photoreceptor-specific genes and patients with mutations in RPE-specific genes (P < .05). A fitted multivariate logistic regression model was produced and demonstrated that the incidence of IPM increases as a function of both age and gene category. CONCLUSIONS IPM is a finding more commonly observed in IRDs caused by mutations in photoreceptor-specific genes than RPE-specific genes. The absence of IPM does not always rule out IRD and should raise suspicion for disease mutations in RPE-specific genes.
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Affiliation(s)
- Jin Kyun Oh
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, New York, USA; College of Medicine, State University of New York at Downstate Medical Center, Brooklyn, New York, USA
| | - Sarah R Levi
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, New York, USA
| | - Joonpyo Kim
- Department of Statistics, Seoul National University, Seoul, South Korea
| | - Jose Ronaldo Lima de Carvalho
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, New York, USA; Department of Ophthalmology, Empresa Brasileira de Servicos Hospitalares, Hospital das Clinicas de Pernambuco, Federal University of Pernambuco, Recife, Pernambuco, Brazil; Department of Ophthalmology, Federal University of São Paulo, São Paulo, São Paulo, Brazil
| | - Joseph Ryu
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, New York, USA
| | - Janet R Sparrow
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, New York, USA; Department of Pathology and Cell Biology, and Columbia Stem Cell Initiative, Columbia University Irving Medical Center, New York, New York, USA; Department of Pathology & Cell Biology, and Columbia Stem Cell Initiative, Columbia University Irving Medical Center, New York, NY, USA
| | - Stephen H Tsang
- Department of Ophthalmology, Columbia University Irving Medical Center, New York, New York, USA; Department of Pathology and Cell Biology, and Columbia Stem Cell Initiative, Columbia University Irving Medical Center, New York, New York, USA; Department of Pathology & Cell Biology, and Columbia Stem Cell Initiative, Columbia University Irving Medical Center, New York, NY, USA.
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7
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Xiong L, Zhang L, Yang Y, Li N, Lai W, Wang F, Zhu X, Wang T. ER complex proteins are required for rhodopsin biosynthesis and photoreceptor survival in Drosophila and mice. Cell Death Differ 2019; 27:646-661. [PMID: 31263175 PMCID: PMC7206144 DOI: 10.1038/s41418-019-0378-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2018] [Revised: 06/11/2019] [Accepted: 06/13/2019] [Indexed: 12/17/2022] Open
Abstract
Defective rhodopsin homeostasis is one of the major causes of retinal degeneration, including the disease Retinitis pigmentosa. To identify cellular factors required for the biosynthesis of rhodopsin, we performed a genome-wide genetic screen in Drosophila for mutants with reduced levels of rhodopsin. We isolated loss-of-function alleles in endoplasmic reticulum membrane protein complex 3 (emc3), emc5, and emc6, each of which exhibited defective phototransduction and photoreceptor cell degeneration. EMC3, EMC5, and EMC6 were essential for rhodopsin synthesis independent of the ER associated degradation (ERAD) pathway, which eliminates misfolded proteins. We generated null mutations for all EMC subunits, and further demonstrated that different EMC subunits play roles in different cellular functions. Conditional knockout of the Emc3 gene in mice led to mislocalization of rhodopsin protein and death of cone and rod photoreceptor cells. These data indicate conserved roles for EMC subunits in maintaining rhodopsin homeostasis and photoreceptor function, and suggest that retinal degeneration may also be caused by defects in early biosynthesis of rhodopsin.
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Affiliation(s)
- Liangyao Xiong
- Peking University-Tsinghua University-National Institute of Biological Sciences Joint Graduate Program, School of Life Sciences, Peking University, Beijing, 100871, China.,National Institute of Biological Sciences, Beijing, 102206, China
| | - Lin Zhang
- Sichuan Provincial Key Laboratory for Human Disease Gene Study, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, Chengdu, Sichuan, 610072, China
| | - Yeming Yang
- Sichuan Provincial Key Laboratory for Human Disease Gene Study, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, Chengdu, Sichuan, 610072, China
| | - Na Li
- Southwest Jiaotong University, Chengdu, Sichuan, China
| | - Wenjia Lai
- CAS Key Laboratory of Standardization and Measurement for Nanotechnology, CAS Center for Excellence in Nanoscience, National Center for Nanoscience and Technology, Beijing, 100190, China
| | - Fengchao Wang
- National Institute of Biological Sciences, Beijing, 102206, China.,Tsinghua Institute of Multidisciplinary Biomedical Research, Tsinghua University, Beijing, 100871, China
| | - Xianjun Zhu
- Sichuan Provincial Key Laboratory for Human Disease Gene Study, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, Chengdu, Sichuan, 610072, China. .,Chengdu Institute of Biology, Chinese Academy of Sciences, Chengdu, China. .,Chinese Academy of Sciences Sichuan Translational Medicine Hospital, Chengdu, China. .,Department of Ophthalmology, First People's Hospital of Shangqiu, Shangqiu, Henan, China.
| | - Tao Wang
- National Institute of Biological Sciences, Beijing, 102206, China. .,Tsinghua Institute of Multidisciplinary Biomedical Research, Tsinghua University, Beijing, 100871, China.
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8
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Huang HW, Brown B, Chung J, Domingos PM, Ryoo HD. highroad Is a Carboxypetidase Induced by Retinoids to Clear Mutant Rhodopsin-1 in Drosophila Retinitis Pigmentosa Models. Cell Rep 2019; 22:1384-1391. [PMID: 29425495 PMCID: PMC5832065 DOI: 10.1016/j.celrep.2018.01.032] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2017] [Revised: 12/15/2017] [Accepted: 01/10/2018] [Indexed: 11/02/2022] Open
Abstract
Rhodopsins require retinoid chromophores for their function. In vertebrates, retinoids also serve as signaling molecules, but whether these molecules similarly regulate gene expression in Drosophila remains unclear. Here, we report the identification of a retinoid-inducible gene in Drosophila, highroad, which is required for photoreceptors to clear folding-defective mutant Rhodopsin-1 proteins. Specifically, knockdown or genetic deletion of highroad blocks the degradation of folding-defective Rhodopsin-1 mutant, ninaEG69D. Moreover, loss of highroad accelerates the age-related retinal degeneration phenotype of ninaEG69D mutants. Elevated highroad transcript levels are detected in ninaEG69D flies, and interestingly, deprivation of retinoids in the fly diet blocks this effect. Consistently, mutations in the retinoid transporter, santa maria, impairs the induction of highroad in ninaEG69D flies. In cultured S2 cells, highroad expression is induced by retinoic acid treatment. These results indicate that cellular quality-control mechanisms against misfolded Rhodopsin-1 involve regulation of gene expression by retinoids.
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Affiliation(s)
- Huai-Wei Huang
- Department of Cell Biology, New York University School of Medicine 550 First Avenue, New York, NY 10016, USA
| | - Brian Brown
- Department of Cell Biology, New York University School of Medicine 550 First Avenue, New York, NY 10016, USA
| | - Jaehoon Chung
- Department of Cell Biology, New York University School of Medicine 550 First Avenue, New York, NY 10016, USA
| | - Pedro M Domingos
- Instituto de Tecnologia Química e Biológica da Universidade Nova de Lisboa, Av. da República, Oeiras 2780-157, Portugal
| | - Hyung Don Ryoo
- Department of Cell Biology, New York University School of Medicine 550 First Avenue, New York, NY 10016, USA.
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9
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Wen RH, Stanar P, Tam B, Moritz OL. Autophagy in Xenopus laevis rod photoreceptors is independently regulated by phototransduction and misfolded RHO P23H. Autophagy 2019; 15:1970-1989. [PMID: 30975014 DOI: 10.1080/15548627.2019.1596487] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
We previously reported autophagic structures in rod photoreceptors expressing a misfolding RHO (rhodopsin) mutant (RHOP23H), suggesting that autophagy may play a role in degrading the mutant RHO and/or be involved in photoreceptor cell death. To further examine autophagy in normal and diseased rods, we generated transgenic Xenopus laevis tadpoles expressing the dually fluorescent autophagy marker mRFP-eGFP-LC3 in rods, which changes from green to yellow and finally red as autophagic structures develop and mature. Using transgenic lines with constitutive and inducible expression, we determined the time-course of autophagy in rod photoreceptors: autophagosomes last for 6 to 8 hours before fusing with lysosomes, and acidified autolysosomes last for about 28 hours before being degraded. Autophagy was diurnally regulated in normal rods, with more autophagic structures generated during periods of light, and this regulation was non-circadian. We also found that more autophagosomes were produced in rods expressing the misfolding RHOP23H mutant. The RHO chromophore absorbs photons to initiate phototransduction, and is consumed in this process; it also promotes RHO folding. To determine whether increased autophagy in light-exposed normal rods is caused by increased RHO misfolding or phototransduction, we used CRISPR/Cas9 to knock out the RPE65 and GNAT1 genes, which are essential for chromophore biosynthesis and phototransduction respectively. Both knockouts suppressed light-induced autophagy, indicating that although light and misfolded rhodopsin can both induce autophagy in rods, light-induced autophagy is not due to misfolding of RHO, but rather due to phototransduction. Abbreviations: CYCS: cytochrome c; bRHOP23H: bovine RHOP23H; Cas9: CRISPR associated protein 9; dpf: days post-fertilization; eGFP: enhanced green fluorescent protein; GNAT1: guanine nucleotide-binding protein G(t) subunit alpha-1 aka rod alpha-transducin; HSPA1A/hsp70: heat shock protein of 70 kilodaltons; LAMP1: lysosomal-associated membrane protein 1; LC3: microtubule-associated protein 1A/1B light chain 3; mRFP: monomeric red fluorescent protein; RHO: rhodopsin; RP: retinitis pigmentosa; RPE65: retinal pigment epithelium-specific 65 kDa protein: sfGFP: superfolding GFP; sgRNA: single guide RNA; WGA: wheat germ agglutinin; RHOp: the Xenopus laevis RHO.2.L promoter.
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Affiliation(s)
- Runxia H Wen
- Department of Ophthalmology and Visual Sciences, University of British Columbia , Vancouver , British Columbia , Canada
| | - Paloma Stanar
- Department of Ophthalmology and Visual Sciences, University of British Columbia , Vancouver , British Columbia , Canada
| | - Beatrice Tam
- Department of Ophthalmology and Visual Sciences, University of British Columbia , Vancouver , British Columbia , Canada
| | - Orson L Moritz
- Department of Ophthalmology and Visual Sciences, University of British Columbia , Vancouver , British Columbia , Canada
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10
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Deal SL, Yamamoto S. Unraveling Novel Mechanisms of Neurodegeneration Through a Large-Scale Forward Genetic Screen in Drosophila. Front Genet 2019; 9:700. [PMID: 30693015 PMCID: PMC6339878 DOI: 10.3389/fgene.2018.00700] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2018] [Accepted: 12/13/2018] [Indexed: 01/04/2023] Open
Abstract
Neurodegeneration is characterized by progressive loss of neurons. Genetic and environmental factors both contribute to demise of neurons, leading to diverse devastating cognitive and motor disorders, including Alzheimer's and Parkinson's diseases in humans. Over the past few decades, the fruit fly, Drosophila melanogaster, has become an integral tool to understand the molecular, cellular and genetic mechanisms underlying neurodegeneration. Extensive tools and sophisticated technologies allow Drosophila geneticists to identify and study evolutionarily conserved genes that are essential for neural maintenance. In this review, we will focus on a large-scale mosaic forward genetic screen on the fly X-chromosome that led to the identification of a number of essential genes that exhibit neurodegenerative phenotypes when mutated. Most genes identified from this screen are evolutionarily conserved and many have been linked to human diseases with neurological presentations. Systematic electrophysiological and ultrastructural characterization of mutant tissue in the context of the Drosophila visual system, followed by a series of experiments to understand the mechanism of neurodegeneration in each mutant led to the discovery of novel molecular pathways that are required for neuronal integrity. Defects in mitochondrial function, lipid and iron metabolism, protein trafficking and autophagy are recurrent themes, suggesting that insults that eventually lead to neurodegeneration may converge on a set of evolutionarily conserved cellular processes. Insights from these studies have contributed to our understanding of known neurodegenerative diseases such as Leigh syndrome and Friedreich's ataxia and have also led to the identification of new human diseases. By discovering new genes required for neural maintenance in flies and working with clinicians to identify patients with deleterious variants in the orthologous human genes, Drosophila biologists can play an active role in personalized medicine.
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Affiliation(s)
- Samantha L Deal
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX, United States
| | - Shinya Yamamoto
- Program in Developmental Biology, Baylor College of Medicine, Houston, TX, United States.,Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States.,Department of Neuroscience, Baylor College of Medicine, Houston, TX, United States.,Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, TX, United States
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11
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Kim BJ, Zack DJ. The Role of c-Jun N-Terminal Kinase (JNK) in Retinal Degeneration and Vision Loss. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1074:351-357. [PMID: 29721963 DOI: 10.1007/978-3-319-75402-4_43] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
c-Jun N-terminal kinase (JNK), a member of stress-induced mitogen-activated protein (MAP) kinase family, has been shown to modulate a variety of biological processes associated with neurodegenerative pathology of the retina. In particular, various retinal cell culture and animal models related to glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa indicate that JNK signaling may contribute to disease pathogenesis. This mini-review discusses the impact of JNK signaling in retinal disease, with a focus on retinal ganglion cells (RGCs), photoreceptor cells, retinal pigment epithelial (RPE) cells, and animal studies, with particular attention to modulation of JNK signaling as a potential therapeutic target for the treatment of retinal disease.
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Affiliation(s)
- Byung-Jin Kim
- The Wilmer Eye Institute, Johns Hopkins University, School of Medicine, Baltimore, MD, USA
| | - Donald J Zack
- The Wilmer Eye Institute, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.
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12
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Neuroprotective Strategy in Retinal Degeneration: Suppressing ER Stress-Induced Cell Death via Inhibition of the mTOR Signal. Int J Mol Sci 2017; 18:ijms18010201. [PMID: 28106827 PMCID: PMC5297831 DOI: 10.3390/ijms18010201] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Revised: 01/13/2017] [Accepted: 01/16/2017] [Indexed: 12/11/2022] Open
Abstract
The retina is a specialized sensory organ, which is essential for light detection and visual formation in the human eye. Inherited retinal degenerations are a heterogeneous group of eye diseases that can eventually cause permanent vision loss. UPR (unfolded protein response) and ER (endoplasmic reticulum) stress plays an important role in the pathological mechanism of retinal degenerative diseases. mTOR (the mammalian target of rapamycin) kinase, as a signaling hub, controls many cellular processes, covering protein synthesis, RNA translation, ER stress, and apoptosis. Here, the hypothesis that inhibition of mTOR signaling suppresses ER stress-induced cell death in retinal degenerative disorders is discussed. This review surveys knowledge of the influence of mTOR signaling on ER stress arising from misfolded proteins and genetic mutations in retinal degenerative diseases and highlights potential neuroprotective strategies for treatment and therapeutic implications.
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13
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Chow CY, Kelsey KJP, Wolfner MF, Clark AG. Candidate genetic modifiers of retinitis pigmentosa identified by exploiting natural variation in Drosophila. Hum Mol Genet 2015; 25:651-9. [PMID: 26662796 DOI: 10.1093/hmg/ddv502] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2015] [Accepted: 12/07/2015] [Indexed: 01/10/2023] Open
Abstract
Individuals carrying the same pathogenic mutation can present with a broad range of disease outcomes. While some of this variation arises from environmental factors, it is increasingly recognized that the background genetic variation of each individual can have a profound effect on the expressivity of a pathogenic mutation. In order to understand this background effect on disease-causing mutations, studies need to be performed across a wide range of backgrounds. Recent advancements in model organism biology allow us to test mutations across genetically diverse backgrounds and identify the genes that influence the expressivity of a mutation. In this study, we used the Drosophila Genetic Reference Panel, a collection of ∼200 wild-derived strains, to test the variability of the retinal phenotype of the Rh1(G69D) Drosophila model of retinitis pigmentosa (RP). We found that the Rh1(G69D) retinal phenotype is quite a variable quantitative phenotype. To identify the genes driving this extensive phenotypic variation, we performed a genome-wide association study. We identified 106 candidate genes, including 14 high-priority candidates. Functional testing by RNAi indicates that 10/13 top candidates tested influence the expressivity of Rh1(G69D). The human orthologs of the candidate genes have not previously been implicated as RP modifiers and their functions are diverse, including roles in endoplasmic reticulum stress, apoptosis and retinal degeneration and development. This study demonstrates the utility of studying a pathogenic mutation across a wide range of genetic backgrounds. These candidate modifiers provide new avenues of inquiry that may reveal new RP disease mechanisms and therapies.
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Affiliation(s)
- Clement Y Chow
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA and Department of Human Genetics, University of Utah School of Medicine, Salt Lake City, UT 84112, USA
| | - Keegan J P Kelsey
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA and
| | - Mariana F Wolfner
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA and
| | - Andrew G Clark
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA and
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The GTP- and Phospholipid-Binding Protein TTD14 Regulates Trafficking of the TRPL Ion Channel in Drosophila Photoreceptor Cells. PLoS Genet 2015; 11:e1005578. [PMID: 26509977 PMCID: PMC4624897 DOI: 10.1371/journal.pgen.1005578] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 09/15/2015] [Indexed: 01/04/2023] Open
Abstract
Recycling of signaling proteins is a common phenomenon in diverse signaling pathways. In photoreceptors of Drosophila, light absorption by rhodopsin triggers a phospholipase Cβ-mediated opening of the ion channels transient receptor potential (TRP) and TRP-like (TRPL) and generates the visual response. The signaling proteins are located in a plasma membrane compartment called rhabdomere. The major rhodopsin (Rh1) and TRP are predominantly localized in the rhabdomere in light and darkness. In contrast, TRPL translocates between the rhabdomeral plasma membrane in the dark and a storage compartment in the cell body in the light, from where it can be recycled to the plasma membrane upon subsequent dark adaptation. Here, we identified the gene mutated in trpl translocation defective 14 (ttd14), which is required for both TRPL internalization from the rhabdomere in the light and recycling of TRPL back to the rhabdomere in the dark. TTD14 is highly conserved in invertebrates and binds GTP in vitro. The ttd14 mutation alters a conserved proline residue (P75L) in the GTP-binding domain and abolishes binding to GTP. This indicates that GTP binding is essential for TTD14 function. TTD14 is a cytosolic protein and binds to PtdIns(3)P, a lipid enriched in early endosome membranes, and to phosphatidic acid. In contrast to TRPL, rhabdomeral localization of the membrane proteins Rh1 and TRP is not affected in the ttd14P75L mutant. The ttd14P75L mutation results in Rh1-independent photoreceptor degeneration and larval lethality suggesting that other processes are also affected by the ttd14P75L mutation. In conclusion, TTD14 is a novel regulator of TRPL trafficking, involved in internalization and subsequent sorting of TRPL into the recycling pathway that enables this ion channel to return to the plasma membrane. Protein trafficking in neurons occurs throughout the lifetime of a cell and includes the internalization and redistribution of plasma membrane proteins. Regulated protein trafficking controls the equipment of the plasma membrane with receptors and ion channels and thereby attenuates or enhances neuronal function. Defects in recycling of plasma membrane proteins can cause detrimental neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and Down´s syndrome. In Drosophila photoreceptors, the TRPL ion channel, together with the TRP channel, mediates vision and light-dependently shuttles between an endomembrane storage compartment and the apical plasma membrane. Here, we report the identification of a mutation in the ttd14 gene that inhibits TRPL-trafficking in both directions and also results in photoreceptor degeneration. The TTD14 protein contains a region with weak homology to a PX-domain, which is also found in proteins that sort cargo in the endosome and enable protein recycling. We characterize TTD14 as a new regulator of photoreceptor maintenance and ion channel trafficking that binds to GTP and PtdIns(3)P, a phospholipid enriched in early endosomes.
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15
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Dubos A, Castells-Nobau A, Meziane H, Oortveld MAW, Houbaert X, Iacono G, Martin C, Mittelhaeuser C, Lalanne V, Kramer JM, Bhukel A, Quentin C, Slabbert J, Verstreken P, Sigrist SJ, Messaddeq N, Birling MC, Selloum M, Stunnenberg HG, Humeau Y, Schenck A, Herault Y. Conditional depletion of intellectual disability and Parkinsonism candidate gene ATP6AP2 in fly and mouse induces cognitive impairment and neurodegeneration. Hum Mol Genet 2015; 24:6736-55. [PMID: 26376863 PMCID: PMC4634377 DOI: 10.1093/hmg/ddv380] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Accepted: 09/11/2015] [Indexed: 12/20/2022] Open
Abstract
ATP6AP2, an essential accessory component of the vacuolar H+ ATPase (V-ATPase), has been associated with intellectual disability (ID) and Parkinsonism. ATP6AP2 has been implicated in several signalling pathways; however, little is known regarding its role in the nervous system. To decipher its function in behaviour and cognition, we generated and characterized conditional knockdowns of ATP6AP2 in the nervous system of Drosophila and mouse models. In Drosophila, ATP6AP2 knockdown induced defective phototaxis and vacuolated photoreceptor neurons and pigment cells when depleted in eyes and altered short- and long-term memory when depleted in the mushroom body. In mouse, conditional Atp6ap2 deletion in glutamatergic neurons (Atp6ap2Camk2aCre/0 mice) caused increased spontaneous locomotor activity and altered fear memory. Both Drosophila ATP6AP2 knockdown and Atp6ap2Camk2aCre/0 mice presented with presynaptic transmission defects, and with an abnormal number and morphology of synapses. In addition, Atp6ap2Camk2aCre/0 mice showed autophagy defects that led to axonal and neuronal degeneration in the cortex and hippocampus. Surprisingly, axon myelination was affected in our mutant mice, and axonal transport alterations were observed in Drosophila. In accordance with the identified phenotypes across species, genome-wide transcriptome profiling of Atp6ap2Camk2aCre/0 mouse hippocampi revealed dysregulation of genes involved in myelination, action potential, membrane-bound vesicles and motor behaviour. In summary, ATP6AP2 disruption in mouse and fly leads to cognitive impairment and neurodegeneration, mimicking aspects of the neuropathology associated with ATP6AP2 mutations in humans. Our results identify ATP6AP2 as an essential gene for the nervous system.
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Affiliation(s)
- Aline Dubos
- Institut Clinique de la Souris, PHENOMIN, GIE CERBM, 1 rue Laurent Fries, 67404 Illkirch, France, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France, Centre National de la Recherche Scientifique, UMR7104, Illkirch, France, Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France and Université de Strasbourg, Illkirch, France
| | - Anna Castells-Nobau
- Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands
| | - Hamid Meziane
- Institut Clinique de la Souris, PHENOMIN, GIE CERBM, 1 rue Laurent Fries, 67404 Illkirch, France
| | - Merel A W Oortveld
- Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands
| | - Xander Houbaert
- Team Synapse in Cognition, Institut Interdisciplinaire de NeuroScience, Centre National de la Recherche Scientifique CNRS UMR5297, Université de Bordeaux, Bordeaux, France
| | - Giovanni Iacono
- Department of Molecular Biology, Radboud Institute for Molecular Life Sciences, Radboud University, Nijmegen, The Netherlands
| | - Christelle Martin
- Team Synapse in Cognition, Institut Interdisciplinaire de NeuroScience, Centre National de la Recherche Scientifique CNRS UMR5297, Université de Bordeaux, Bordeaux, France
| | - Christophe Mittelhaeuser
- Institut Clinique de la Souris, PHENOMIN, GIE CERBM, 1 rue Laurent Fries, 67404 Illkirch, France
| | - Valérie Lalanne
- Institut Clinique de la Souris, PHENOMIN, GIE CERBM, 1 rue Laurent Fries, 67404 Illkirch, France
| | - Jamie M Kramer
- Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands
| | - Anuradha Bhukel
- Genetics, Institute of Biology, Freie Universität Berlin, Berlin, Germany
| | - Christine Quentin
- Genetics, Institute of Biology, Freie Universität Berlin, Berlin, Germany, NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, Berlin, Germany
| | - Jan Slabbert
- VIB, Center for the Biology of Disease, Leuven, Belgium, KU Leuven, Center for Human Genetics and Leuven Institute for Neuroscience and Disease (LIND), Leuven, Belgium
| | - Patrik Verstreken
- VIB, Center for the Biology of Disease, Leuven, Belgium, KU Leuven, Center for Human Genetics and Leuven Institute for Neuroscience and Disease (LIND), Leuven, Belgium
| | - Stefan J Sigrist
- Genetics, Institute of Biology, Freie Universität Berlin, Berlin, Germany, NeuroCure Cluster of Excellence, Charité Universitätsmedizin Berlin, Berlin, Germany
| | - Nadia Messaddeq
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France, Centre National de la Recherche Scientifique, UMR7104, Illkirch, France, Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France and Université de Strasbourg, Illkirch, France
| | - Marie-Christine Birling
- Institut Clinique de la Souris, PHENOMIN, GIE CERBM, 1 rue Laurent Fries, 67404 Illkirch, France
| | - Mohammed Selloum
- Institut Clinique de la Souris, PHENOMIN, GIE CERBM, 1 rue Laurent Fries, 67404 Illkirch, France
| | - Henk G Stunnenberg
- Department of Molecular Biology, Radboud Institute for Molecular Life Sciences, Radboud University, Nijmegen, The Netherlands
| | - Yann Humeau
- Team Synapse in Cognition, Institut Interdisciplinaire de NeuroScience, Centre National de la Recherche Scientifique CNRS UMR5297, Université de Bordeaux, Bordeaux, France
| | - Annette Schenck
- Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands,
| | - Yann Herault
- Institut Clinique de la Souris, PHENOMIN, GIE CERBM, 1 rue Laurent Fries, 67404 Illkirch, France, Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch, France, Centre National de la Recherche Scientifique, UMR7104, Illkirch, France, Institut National de la Santé et de la Recherche Médicale, U964, Illkirch, France and Université de Strasbourg, Illkirch, France
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16
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Whole exome sequencing reveals genetic predisposition in a large family with retinitis pigmentosa. BIOMED RESEARCH INTERNATIONAL 2014; 2014:302487. [PMID: 25101269 PMCID: PMC4102027 DOI: 10.1155/2014/302487] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/16/2013] [Accepted: 05/22/2014] [Indexed: 12/19/2022]
Abstract
Next-generation sequencing has become more widely used to reveal genetic defect in monogenic disorders. Retinitis pigmentosa (RP), the leading cause of hereditary blindness worldwide, has been attributed to more than 67 disease-causing genes. Due to the extreme genetic heterogeneity, using general molecular screening alone is inadequate for identifying genetic predispositions in susceptible individuals. In order to identify underlying mutation rapidly, we utilized next-generation sequencing in a four-generation Chinese family with RP. Two affected patients and an unaffected sibling were subjected to whole exome sequencing. Through bioinformatics analysis and direct sequencing confirmation, we identified p.R135W transition in the rhodopsin gene. The mutation was subsequently confirmed to cosegregate with the disease in the family. In this study, our results suggest that whole exome sequencing is a robust method in diagnosing familial hereditary disease.
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17
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Wang S, Tan KL, Agosto MA, Xiong B, Yamamoto S, Sandoval H, Jaiswal M, Bayat V, Zhang K, Charng WL, David G, Duraine L, Venkatachalam K, Wensel TG, Bellen HJ. The retromer complex is required for rhodopsin recycling and its loss leads to photoreceptor degeneration. PLoS Biol 2014; 12:e1001847. [PMID: 24781186 PMCID: PMC4004542 DOI: 10.1371/journal.pbio.1001847] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Accepted: 03/21/2014] [Indexed: 12/22/2022] Open
Abstract
Rhodopsin recycling via the retromer, rather than degradation through lysosomes, can alleviate light-induced photoreceptor degeneration in Drosophila. Rhodopsin mistrafficking can cause photoreceptor (PR) degeneration. Upon light exposure, activated rhodopsin 1 (Rh1) in Drosophila PRs is internalized via endocytosis and degraded in lysosomes. Whether internalized Rh1 can be recycled is unknown. Here, we show that the retromer complex is expressed in PRs where it is required for recycling endocytosed Rh1 upon light stimulation. In the absence of subunits of the retromer, Rh1 is processed in the endolysosomal pathway, leading to a dramatic increase in late endosomes, lysosomes, and light-dependent PR degeneration. Reducing Rh1 endocytosis or Rh1 levels in retromer mutants alleviates PR degeneration. In addition, increasing retromer abundance suppresses degenerative phenotypes of mutations that affect the endolysosomal system. Finally, expressing human Vps26 suppresses PR degeneration in Vps26 mutant PRs. We propose that the retromer plays a conserved role in recycling rhodopsins to maintain PR function and integrity. Upon light exposure, rhodopsins—light-sensing proteins in the eye—trigger visual transduction signaling to activate fly photoreceptor cells. After activation, rhodopsins can be internalized from the cell surface into endosomes and then degraded in lysosomes. This mechanism prevents constant activation of the visual transduction pathway, thereby maintaining the function and integrity of photoreceptor cells. It is not known, however, whether these internalized rhodopsins can be recycled. Here, we show that the retromer, an evolutionarily conserved protein complex, is required for the recycling of rhodopsins. We find that loss of key retromer subunits (Vps35 or Vps26) causes rhodopsin mislocalization in the photoreceptors and severe light-induced photoreceptor degeneration. Conversely, gain of retromer subunits can alleviate photoreceptor degeneration in some contexts. Human retromer components can stand in for depleted fruit fly retromer, suggesting that this complex plays a role in recycling light sensors in both vertebrate and invertebrate photoreceptors.
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Affiliation(s)
- Shiuan Wang
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Kai Li Tan
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Melina A. Agosto
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Bo Xiong
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Shinya Yamamoto
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Human and Molecular Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas, United States of America
| | - Hector Sandoval
- Department of Human and Molecular Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Manish Jaiswal
- Department of Human and Molecular Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America
| | - Vafa Bayat
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Ke Zhang
- Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Wu-Lin Charng
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Gabriela David
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Lita Duraine
- Department of Human and Molecular Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America
| | - Kartik Venkatachalam
- Department of Integrative Biology and Pharmacology, University of Texas School of Medicine, Houston, Texas, United States of America
| | - Theodore G. Wensel
- Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Hugo J. Bellen
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Human and Molecular Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Jan and Dan Duncan Neurological Research Institute, Texas Children's Hospital, Houston, Texas, United States of America
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America
- Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
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18
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Proteomic survey reveals altered energetic patterns and metabolic failure prior to retinal degeneration. J Neurosci 2014; 34:2797-812. [PMID: 24553922 DOI: 10.1523/jneurosci.2982-13.2014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Inherited mutations that lead to misfolding of the visual pigment rhodopsin (Rho) are a prominent cause of photoreceptor neuron (PN) degeneration and blindness. How Rho proteotoxic stress progressively impairs PN viability remains unknown. To identify the pathways that mediate Rho toxicity in PNs, we performed a comprehensive proteomic profiling of retinas from Drosophila transgenics expressing Rh1(P37H), the equivalent of mammalian Rho(P23H), the most common Rho mutation linked to blindness in humans. Profiling of young Rh1(P37H) retinas revealed a coordinated upregulation of energy-producing pathways and attenuation of energy-consuming pathways involving target of rapamycin (TOR) signaling, which was reversed in older retinas at the onset of PN degeneration. We probed the relevance of these metabolic changes to PN survival by using a combination of pharmacological and genetic approaches. Chronic suppression of TOR signaling, using the inhibitor rapamycin, strongly mitigated PN degeneration, indicating that TOR signaling activation by chronic Rh1(P37H) proteotoxic stress is deleterious for PNs. Genetic inactivation of the endoplasmic reticulum stress-induced JNK/TRAF1 axis as well as the APAF-1/caspase-9 axis, activated by damaged mitochondria, dramatically suppressed Rh1(P37H)-induced PN degeneration, identifying the mitochondria as novel mediators of Rh1(P37H) toxicity. We thus propose that chronic Rh1(P37H) proteotoxic stress distorts the energetic profile of PNs leading to metabolic imbalance, mitochondrial failure, and PN degeneration and therapies normalizing metabolic function might be used to alleviate Rh1(P37H) toxicity in the retina. Our study offers a glimpse into the intricate higher order interactions that underlie PN dysfunction and provides a useful resource for identifying other molecular networks that mediate Rho toxicity in PNs.
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19
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Xiong B, Bellen HJ. Rhodopsin homeostasis and retinal degeneration: lessons from the fly. Trends Neurosci 2013; 36:652-60. [PMID: 24012059 DOI: 10.1016/j.tins.2013.08.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2013] [Revised: 08/02/2013] [Accepted: 08/12/2013] [Indexed: 11/16/2022]
Abstract
Rhodopsins (Rh) are G protein-coupled receptors that function as light-sensors in photoreceptors. In humans, Rh mutations cause retinitis pigmentosa (RP), a degenerative disease that ultimately results in blindness. Studies in Drosophila have provided many insights into basic Rh biology and have identified pathways that lead to retinal degeneration. It has been shown that, because Rh is very abundant in photoreceptors, its accumulation in numerous organelles induces severe stress and results in degeneration of these cells. Moreover, genetic lesions that affect proper activation of membrane-bound Rh lead to disruption in Ca(2+) homeostasis which also causes photoreceptor degeneration. We review here the molecular signals involved in Rh homeostasis and the mechanisms underlying retinal degeneration in flies, and discuss possible links to human diseases.
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Affiliation(s)
- Bo Xiong
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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20
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Ozaki T, Ishiguro SI, Hirano S, Baba A, Yamashita T, Tomita H, Nakazawa M. Inhibitory peptide of mitochondrial μ-calpain protects against photoreceptor degeneration in rhodopsin transgenic S334ter and P23H rats. PLoS One 2013; 8:e71650. [PMID: 23951212 PMCID: PMC3739725 DOI: 10.1371/journal.pone.0071650] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 07/01/2013] [Indexed: 11/23/2022] Open
Abstract
Mitochondrial μ-calpain and apoptosis-inducing factor (AIF)-dependent photoreceptor cell death has been seen in several rat and mouse models of retinitis pigmentosa (RP). Previously, we demonstrated that the specific peptide inhibitor of mitochondrial μ-calpain, Tat-µCL, protected against retinal degeneration following intravitreal injection or topical eye-drop application in Mertk gene-mutated Royal College of Surgeons rats, one of the animal models of RP. Because of the high rate of rhodopsin mutations in RP patients, the present study was performed to confirm the protective effects of Tat-µCL against retinal degeneration in rhodopsin transgenic S334ter and P23H rats. We examined the effects of intravitreal injection or topical application of the peptide on retinal degeneration in S334ter and P23H rats by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, electroretinogram (ERG), immunohistochemistry for AIF, and histological staining. In S334ter rats, we found that intravitreal injection or topical application of the peptide prevented photoreceptor cell death from postnatal (PN) 15 to 18 days, the time of early-stage retinal degeneration. Topical application of the peptide also delayed attenuation of ERG responses from PN 28 to 56 days. In P23H rats, topical application of the peptide protected against photoreceptor cell death and nuclear translocation of AIF on PN 30, 40, and 50 days, as the primary stages of degeneration. We observed that topical application of the peptide inhibited the thinning of the outer nuclear layer and delayed ERG attenuations from PN 30 to 90 days. Our results demonstrate that the mitochondrial μ-calpain and AIF pathway is involved in early-stage retinal degeneration in rhodopsin transgenic S334ter and P23H rats, and inhibition of this pathway shows curative potential for rhodopsin mutation-caused RP.
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Affiliation(s)
- Taku Ozaki
- Department of Ophthalmology, Hirosaki University Graduate School of Medicine, Hirosaki, Japan
- Department of Biochemistry and Molecular Biology, Hirosaki University Faculty of Agriculture and Life Science, Hirosaki, Japan
| | - Sei-ichi Ishiguro
- Department of Biochemistry and Molecular Biology, Hirosaki University Faculty of Agriculture and Life Science, Hirosaki, Japan
| | - Satoshi Hirano
- Department of Biochemistry and Molecular Biology, Hirosaki University Faculty of Agriculture and Life Science, Hirosaki, Japan
| | - Ayaka Baba
- Department of Biochemistry and Molecular Biology, Hirosaki University Faculty of Agriculture and Life Science, Hirosaki, Japan
| | - Tetsuro Yamashita
- Department of Biological Chemistry, Iwate University Faculty of Agriculture, Morioka, Japan
| | - Hiroshi Tomita
- Department of Chemistry and Bioengineering, Iwate University Graduate School of Engineering, Morioka, Japan
| | - Mitsuru Nakazawa
- Department of Ophthalmology, Hirosaki University Graduate School of Medicine, Hirosaki, Japan
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21
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Dourlen P, Bertin B, Chatelain G, Robin M, Napoletano F, Roux MJ, Mollereau B. Drosophila fatty acid transport protein regulates rhodopsin-1 metabolism and is required for photoreceptor neuron survival. PLoS Genet 2012; 8:e1002833. [PMID: 22844251 PMCID: PMC3405995 DOI: 10.1371/journal.pgen.1002833] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 06/05/2012] [Indexed: 01/16/2023] Open
Abstract
Tight regulation of the visual response is essential for photoreceptor function and survival. Visual response dysregulation often leads to photoreceptor cell degeneration, but the causes of such cell death are not well understood. In this study, we investigated a fatty acid transport protein (fatp) null mutation that caused adult-onset and progressive photoreceptor cell death. Consistent with fatp having a role in the retina, we showed that fatp is expressed in adult photoreceptors and accessory cells and that its re-expression in photoreceptors rescued photoreceptor viability in fatp mutants. The visual response in young fatp-mutant flies was abnormal with elevated electroretinogram amplitudes associated with high levels of Rhodopsin-1 (Rh1). Reducing Rh1 levels in rh1 mutants or depriving flies of vitamin A rescued photoreceptor cell death in fatp mutant flies. Our results indicate that fatp promotes photoreceptor survival by regulating Rh1 abundance.
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Affiliation(s)
- Pierre Dourlen
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
- * E-mail: (PD); (BM)
| | - Benjamin Bertin
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
| | - Gilles Chatelain
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
| | - Marion Robin
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
| | - Francesco Napoletano
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
| | - Michel J. Roux
- Translational Medicine and Neurogenetics, IGBMC, UMR7104 CNRS/Université de Strasbourg/Inserm U964, Strasbourg, France
| | - Bertrand Mollereau
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
- * E-mail: (PD); (BM)
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Looking into eyes: rhodopsin pathologies in Drosophila. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 723:415-23. [PMID: 22183360 DOI: 10.1007/978-1-4614-0631-0_53] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Dysmorphic photoreceptors in a P23H mutant rhodopsin model of retinitis pigmentosa are metabolically active and capable of regenerating to reverse retinal degeneration. J Neurosci 2012; 32:2121-8. [PMID: 22323724 DOI: 10.1523/jneurosci.4752-11.2012] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
This study evaluated the capacity of Xenopus laevis retina to regenerate photoreceptor cells after cyclic light-mediated acute rod photoreceptor degeneration in a transgenic P23H mutant rhodopsin model of retinits pigmentosa. After discontinuation of cyclic light exposure, we monitored histologic progression of retinal regeneration over a 3 week recovery period. To assess their metabolomic states, contralateral eyes were processed for computational molecular phenotyping. We found that retinal degeneration in the P23H rhodopsin mutation could be partially reversed, with regeneration of rod photoreceptors recovering normal morphology (including full-length rod outer segments) by the end of the 3 week recovery period. In contrast, retinal degeneration mediated by directly induced apoptosis did not recover in the 3 week recovery period. Dystrophic rod photoreceptors with truncated rod outer segments were identified as the likely source of rod photoreceptor regeneration in the P23H retinas. These dystrophic photoreceptors remain metabolically active despite having lost most of their outer segments.
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Ferreira PA, Orry A. From Drosophila to humans: reflections on the roles of the prolyl isomerases and chaperones, cyclophilins, in cell function and disease. J Neurogenet 2012; 26:132-43. [PMID: 22332926 DOI: 10.3109/01677063.2011.647143] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Despite remarkable advances in human genetics and other genetic model systems, the fruit fly, Drosophila melanogaster, remains a powerful experimental tool to probe with ease the inner workings of a myriad of biological and pathological processes, even when evolutionary forces impart apparent divergences to some of such processes. The understanding of such evolutionary differences provides mechanistic insights into genotype-phenotype correlations underpinning biological processes across metazoans. The pioneering work developed by the William Pak laboratory for the past four decades, and the work of others, epitomize the notion of how the Drosophila system breaks new fertile ground or complements research fields of high scientific and medical relevance. Among the three major genetic complementation groups produced by the Pak's laboratory and impairing distinct facets of photoreceptor neuronal function, the nina group (ninaA, …., ninaJ) selectively affects the biogenesis of G protein-coupled receptors (GPCRs), mediating the photoconversion and transduction of light stimuli. Among the nina genes identified, ninaA arguably assumes heightened significance for several reasons. First, it presents unique physiological selectivity toward the biogenesis of a subset of GPCRs, a standalone biological manifestation yet to be discerned for most mammalian homologues of NinaA. Second, NinaA belongs to a family of proteins, immunophilins, which are the primary targets for immunosuppressive drugs at the therapeutic forefront of a multitude of medical conditions. Third, NinaA closest homologue, cyclophilin B (CyPB/PPIB), is an immunophilin whose loss-of-function was found recently to cause osteogenesis imperfecta in the human. This report highlights advances made by studies on some members of immunophilins, the cyclophilins. Finally, it reexamines critically data and dogmas derived from past and recent genetic, structural, biological, and pathological studies on NinaA and few other cyclophilins that support some of such paradigms to be less than definite and advance our understanding of the roles of cyclophilins in cell function, disease, and therapeutic interventions.
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Affiliation(s)
- Paulo A Ferreira
- Department of Ophthalmology, Duke University Medical Center, Durham, NC 27710, USA.
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Haeri M, Knox BE. Rhodopsin mutant P23H destabilizes rod photoreceptor disk membranes. PLoS One 2012; 7:e30101. [PMID: 22276148 PMCID: PMC3261860 DOI: 10.1371/journal.pone.0030101] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Accepted: 12/09/2011] [Indexed: 11/19/2022] Open
Abstract
Mutations in rhodopsin cause retinitis pigmentosa in humans and retinal degeneration in a multitude of other animals. We utilized high-resolution live imaging of the large rod photoreceptors from transgenic frogs (Xenopus) to compare the properties of fluorescently tagged rhodopsin, Rho-EGFP, and RhoP23H-EGFP. The mutant was abnormally distributed both in the inner and outer segments (OS), accumulating in the OS to a concentration of ∼0.1% compared to endogenous opsin. RhoP23H-EGFP formed dense fluorescent foci, with concentrations of mutant protein up to ten times higher than other regions. Wild-type transgenic Rho-EGFP did not concentrate in OS foci when co-expressed in the same rod with RhoP23H-EGFP. Outer segment regions containing fluorescent foci were refractory to fluorescence recovery after photobleaching, while foci in the inner segment exhibited recovery kinetics similar to OS regions without foci and Rho-EGFP. The RhoP23H-EGFP foci were often in older, more distal OS disks. Electron micrographs of OS revealed abnormal disk membranes, with the regular disk bilayers broken into vesiculotubular structures. Furthermore, we observed similar OS disturbances in transgenic mice expressing RhoP23H, suggesting such structures are a general consequence of mutant expression. Together these results show that mutant opsin disrupts OS disks, destabilizing the outer segment possibly via the formation of aggregates. This may render rods susceptible to mechanical injury or compromise OS function, contributing to photoreceptor loss.
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Affiliation(s)
- Mohammad Haeri
- Center for Vision Research, Departments of Neuroscience and Physiology, Biochemistry and Molecular Biology and Ophthalmology, State University of New York Upstate Medical University, Syracuse, New York, United States of America
| | - Barry E. Knox
- Center for Vision Research, Departments of Neuroscience and Physiology, Biochemistry and Molecular Biology and Ophthalmology, State University of New York Upstate Medical University, Syracuse, New York, United States of America
- * E-mail:
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Gene delivery of wild-type rhodopsin rescues retinal function in an autosomal dominant retinitis pigmentosa mouse model. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 723:199-205. [PMID: 22183334 DOI: 10.1007/978-1-4614-0631-0_27] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Autosomal dominant retinitis pigmentosa (ADRP) is frequently caused by mutations within the gene for the opsin of rod photoreceptor cells. Studies on transgenic mice, carrying mutated rhodopsin (RHO) transgene on different genetic backgrounds suggested that that an increased amount of wild-type RHO in ADRP photoreceptors attenuated the impact of the mutant transgene. Therefore, we employed a gene therapy approach with a help of Adeno-associated virus (AAV) to treat mice expressing a P23H mutant human RHO transgene. Knowing that AAV5 primarily transduces photoreceptor cells, we designed “hardened” form of the rhodopsin gene (RHO301) that expressed normal rhodopsin and was specifically resistant to degradation by the previously tested siRNA301. AAV5 RHO301 was subretinaly injected into the right eyes of P23H RHO mice at post-natal day 15. Animals were analyzed monthly by electroretinography (ERG) for 6 months. Analysis of the full field scotopic electroretinogram (ERG) demonstrated that increased expression of opsin slowed the rate of retinal degeneration in P23H mice with increased amplitudes in both a-wave and b-wave amplitudes compared to control eyes. An increase in the ERG amplitudes was correlated with improvement of retinal structure. The thickness of the outer nuclear layer in AAV-RHO301 injected eyes was increased by 80% compared to control eyes. This finding indicates that wild -type RHO could rescue the retinal degeneration in transgenic mice carrying a dominant RHO mutation and that increased production of normal rhodopsin could suppress the effect of the mutant protein. These findings suggest that wild-type RHO can used as a therapeutic agent to retard retinal degeneration in ADRP caused by different mutations of RHO via increased production of normal rhodopsin protein.
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Abstract
Inherited retinal degeneration in Drosophila has been explored for insights into similar processes in humans. Based on the mechanisms, I divide these mutations in Drosophila into three classes. The first consists of genes that control the specialization of photoreceptor cells including the morphogenesis of visual organelles (rhabdomeres) that house the visual signaling proteins. The second class contains genes that regulate the activity or level of the major rhodopsin, Rh1, which is the light sensor and also provides a structural role for the maintenance of rhabdomeres. Some mutations in Rh1 (NinaE) are dominant due to constitutive activity or folding defects, like autosomal dominant retinitis pigmentosa (ADRP) in humans. The third class consists of genes that control the Ca ( 2+) influx directly or indirectly by promoting the turnover of the second messenger and regeneration of PIP 2, or mediate the Ca ( 2+) -dependent regulation of the visual response. These gene products are critical for the increase in cytosolic Ca ( 2+ ) following light stimulation to initiate negative regulatory events. Here I will focus on the signaling mechanisms underlying the degeneration in norpA, and in ADRP-type NinaE mutants that produce misfolded Rh1. Accumulation of misfolded Rh1 in the ER triggers the unfolded protein response (UPR), while endosomal accumulation of activated Rh1 may initiate autophagy in norpA. Both autophagy and the UPR are beneficial for relieving defective endosomal trafficking and the ER stress, respectively. However, when photoreceptors fail to cope with the persistence of these stresses, a cell death program is activated leading to retinal degeneration.
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Affiliation(s)
- Bih-Hwa Shieh
- Department of Pharmacology, Center for Molecular Neuroscience and Vision Research Center, Vanderbilt University, Nashville, TN USA.
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Lee J, Lee J, Ju BG. Drosophila arf72A acts as an essential regulator of endoplasmic reticulum quality control and suppresses autosomal-dominant retinopathy. Int J Biochem Cell Biol 2011; 43:1392-401. [PMID: 21693198 DOI: 10.1016/j.biocel.2011.06.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Revised: 05/25/2011] [Accepted: 06/06/2011] [Indexed: 11/27/2022]
Abstract
The eukaryotic endoplasmic reticulum operates multiple quality control mechanisms to ensure that only properly folded proteins are exported to their final destinations via the secretory pathway and those that are not are destroyed via the degradation pathway. However, molecular mechanisms underlying such regulated exportation to these distinct routes are unknown. In this article, we report the role of Drosophila arf72A--the fly homologue of the mammalian Arl1 - in the quality checks of proteins and in the autosomal-dominant retinopathy. ARF72A localizes to the Golgi membranes of Drosophila photoreceptor cells, consistent with mammalian Arl1 localization in cell culture systems. A loss of arf72A function changes the membrane character of the endoplasmic reticulum and shifts the membrane balance between the endoplasmic reticulum and the Golgi complex toward the Golgi complex, resulting in over-proliferated Golgi complexes and accelerated protein secretion. Interestingly, our study indicated that more ARF72A localized on the endoplasmic reticulum in the ninaE(D1) photoreceptor cell, a Drosophila model of autosomal-dominant retinitis pigmentosa, compared to that in the wild-type. In addition, arf72A loss was shown to rescue the ninaE(D1)-related membrane accumulation and the rhodopsin maturation defect, and suppress ninaE(D1)-triggered retinal degeneration, indicating that rhodopsin accumulated in the endoplasmic reticulum bypasses the quality checks. While previous studies of ARF small GTPases have focused on their roles in vesicular budding and transport between the specific organelles, our findings establish an additional function of arf72A in the quality check machinery of the endoplasmic reticulum distinguishing the cargoes for secretion from those for degradation.
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Affiliation(s)
- Jongwoo Lee
- Department of Biological Science, University of Notre Dame, Notre Dame, IN 46556, USA.
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29
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Griciuc A, Aron L, Ueffing M. ER stress in retinal degeneration: a target for rational therapy? Trends Mol Med 2011; 17:442-51. [PMID: 21620769 DOI: 10.1016/j.molmed.2011.04.002] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Revised: 04/07/2011] [Accepted: 04/13/2011] [Indexed: 10/18/2022]
Abstract
Mutations that cause rhodopsin misfolding and retention within the endoplasmic reticulum (ER) are a prominent cause of retinitis pigmentosa. Here, we discuss the hypothesis that the failure of photoreceptor neurons to adapt to the stress caused by rhodopsin accumulation in the ER leads to a global collapse of homeostasis and to retinal degeneration. We review the molecular mechanisms underlying the activity of local ER conformational sensors and stress-relaying modules and consider how ER-derived stress signals are amplified and implemented to impact on downstream processes, including rhodopsin clearance and cell fate control. The emerging view is that alterations to the systems responsible for the detection, transduction and implementation of ER stress might be used therapeutically to treat retinitis pigmentosa.
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Affiliation(s)
- Ana Griciuc
- Department of Protein Science, Helmholtz Zentrum Munich-German Research Center for Environmental Health, Neuherberg, Germany
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30
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Mao H, James T, Schwein A, Shabashvili AE, Hauswirth WW, Gorbatyuk MS, Lewin AS. AAV delivery of wild-type rhodopsin preserves retinal function in a mouse model of autosomal dominant retinitis pigmentosa. Hum Gene Ther 2011; 22:567-75. [PMID: 21126223 DOI: 10.1089/hum.2010.140] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Autosomal dominant retinitis pigmentosa (ADRP) is frequently caused by mutations in RHO, the gene for rod photoreceptor opsin. Earlier, a study on mice carrying mutated rhodopsin transgenes on either RHO + / + or RHO + /- backgrounds suggested that the amount of wild-type rhodopsin affected survival of photoreceptors. Therefore, we treated P23H RHO transgenic mice with adeno-associated virus serotype 5 (AAV5) expressing a cDNA clone of the rhodopsin gene (RHO301) that expressed normal opsin from the mouse opsin promoter. Analysis of the electroretinogram (ERG) demonstrated that increased expression of RHO301 slowed the rate of retinal degeneration in P23H mice: at 6 months, a-wave amplitudes were increased by 100% and b-wave amplitudes by 79%. In contrast, nontransgenic mice injected with AAV5 RHO301 demonstrated a decrease in the ERG, confirming the damaging effect of rhodopsin overproduction in normal photoreceptors. In P23H mice, the increase in the ERG amplitudes was correlated with improvement of retinal structure: the thickness of the outer nuclear layer in RHO301-treated eyes was increased by 80% compared with control eyes. These findings suggest that the wild-type RHO gene can be delivered to rescue retinal degeneration in mice carrying a RHO mutation and that increased production of normal rhodopsin can suppress the effect of the mutated protein. These findings make it possible to treat ADRP caused by different mutations of RHO with the expression of wild-type RHO.
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Affiliation(s)
- Haoyu Mao
- Department of Molecular Genetics and Microbiology, University of Florida, Gainesville, FL 32610, USA
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31
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Cook T, Zelhof A, Mishra M, Nie J. 800 facets of retinal degeneration. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2011; 100:331-68. [PMID: 21377630 DOI: 10.1016/b978-0-12-384878-9.00008-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
In today's world of genomics and large computational analyses, rapid progress has been made in identifying genes associated with human retinal diseases. Nevertheless, before significant advances toward effective therapeutic intervention is made, a clearer understanding of the molecular and cellular role of these gene products in normal and diseased photoreceptor cell biology is required. Given the complexity of the vertebrate retina, these advancements are unlikely to be revealed in isolated human cell lines, but instead, will require the use of numerous model systems. Here, we describe several parallels between vertebrate and invertebrate photoreceptor cell biology that are beginning to emerge and advocate the use of Drosophila melanogaster as a powerful genetic model system for uncovering molecular mechanisms of human retinal pathologies, in particular photoreceptor neurodegeneration.
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Affiliation(s)
- T Cook
- Department of Pediatric Ophthalmology, Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
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Griciuc A, Aron L, Roux MJ, Klein R, Giangrande A, Ueffing M. Inactivation of VCP/ter94 suppresses retinal pathology caused by misfolded rhodopsin in Drosophila. PLoS Genet 2010; 6:e1001075. [PMID: 20865169 PMCID: PMC2928793 DOI: 10.1371/journal.pgen.1001075] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Accepted: 07/20/2010] [Indexed: 11/30/2022] Open
Abstract
The most common Rhodopsin (Rh) mutation associated with autosomal dominant retinitis pigmentosa (ADRP) in North America is the substitution of proline 23 by histidine (Rh(P23H)). Unlike the wild-type Rh, mutant Rh(P23H) exhibits folding defects and forms intracellular aggregates. The mechanisms responsible for the recognition and clearance of misfolded Rh(P23H) and their relevance to photoreceptor neuron (PN) degeneration are poorly understood. Folding-deficient membrane proteins are subjected to Endoplasmic Reticulum (ER) quality control, and we have recently shown that Rh(P23H) is a substrate of the ER-associated degradation (ERAD) effector VCP/ter94, a chaperone that extracts misfolded proteins from the ER (a process called retrotranslocation) and facilitates their proteasomal degradation. Here, we used Drosophila, in which Rh1(P37H) (the equivalent of mammalian Rh(P23H)) is expressed in PNs, and found that the endogenous Rh1 is required for Rh1(P37H) toxicity. Genetic inactivation of VCP increased the levels of misfolded Rh1(P37H) and further activated the Ire1/Xbp1 ER stress pathway in the Rh1(P37H) retina. Despite this, Rh1(P37H) flies with decreased VCP function displayed a potent suppression of retinal degeneration and blindness, indicating that VCP activity promotes neurodegeneration in the Rh1(P37H) retina. Pharmacological treatment of Rh1(P37H) flies with the VCP/ERAD inhibitor Eeyarestatin I or with the proteasome inhibitor MG132 also led to a strong suppression of retinal degeneration. Collectively, our findings raise the possibility that excessive retrotranslocation and/or degradation of visual pigment is a primary cause of PN degeneration.
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Affiliation(s)
- Ana Griciuc
- Department of Protein Science, Helmholtz Zentrum Muenchen-German Research Center for Environmental Health, Neuherberg, Germany
| | - Liviu Aron
- Department of Molecular Neurobiology, Max-Planck-Institute of Neurobiology, Martinsried, Germany
| | - Michel J. Roux
- Department of Neurobiology and Genetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Illkirch, France
| | - Rüdiger Klein
- Department of Molecular Neurobiology, Max-Planck-Institute of Neurobiology, Martinsried, Germany
| | - Angela Giangrande
- Department of Cell and Developmental Biology, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Illkirch, France
| | - Marius Ueffing
- Department of Protein Science, Helmholtz Zentrum Muenchen-German Research Center for Environmental Health, Neuherberg, Germany
- Institute for Ophthalmic Research, Center for Ophthalmology, University of Tuebingen, Tuebingen, Germany
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Griciuc A, Aron L, Piccoli G, Ueffing M. Clearance of Rhodopsin(P23H) aggregates requires the ERAD effector VCP. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:424-34. [PMID: 20097236 DOI: 10.1016/j.bbamcr.2010.01.008] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2009] [Revised: 12/29/2009] [Accepted: 01/15/2010] [Indexed: 11/15/2022]
Abstract
Dominant mutations in the visual pigment Rhodopsin (Rh) cause retinitis pigmentosa (RP) characterized by progressive blindness and retinal degeneration. The most common Rh mutation, Rh(P23H) forms aggregates in the endoplasmic reticulum (ER) and impairs the proteasome; however, the mechanisms linking Rh aggregate formation to proteasome dysfunction and photoreceptor cell loss remain unclear. Using mammalian cell cultures, we provide the first evidence that misfolded Rh(P23H) is a substrate of the ERAD effector VCP, an ATP-dependent chaperone that extracts misfolded proteins from the ER and escorts them for proteasomal degradation. VCP co-localizes with misfolded Rh(P23H) in retinal cells and requires functional N-terminal and D1 ATPase domains to form a complex with Rh(P23H) aggregates. Furthermore, VCP uses its D2 ATPase activity to promote Rh(P23H) aggregate retrotranslocation and proteasomal delivery. Our results raise the possibility that modulation of VCP and ERAD activity might have potential therapeutic significance for RP.
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Affiliation(s)
- Ana Griciuc
- Department of Protein Science, Helmholtz Zentrum Muenchen-German Research Center for Environmental Health (GmbH), 85764 Neuherberg, Germany
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Krebs MP, Holden DC, Joshi P, Clark CL, Lee AH, Kaushal S. Molecular mechanisms of rhodopsin retinitis pigmentosa and the efficacy of pharmacological rescue. J Mol Biol 2009; 395:1063-78. [PMID: 19913029 DOI: 10.1016/j.jmb.2009.11.015] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Revised: 11/05/2009] [Accepted: 11/05/2009] [Indexed: 11/24/2022]
Abstract
Variants of rhodopsin, a complex of 11-cis retinal and opsin, cause retinitis pigmentosa (RP), a degenerative disease of the retina. Trafficking defects due to rhodopsin misfolding have been proposed as the most likely basis of the disease, but other potentially overlapping mechanisms may also apply. Pharmacological therapies for RP must target the major disease mechanism and contend with overlap, if it occurs. To this end, we have explored the molecular basis of rhodopsin RP in the context of pharmacological rescue with 11-cis retinal. Stable inducible cell lines were constructed to express wild-type opsin; the pathogenic variants T4R, T17M, P23A, P23H, P23L, and C110Y; or the nonpathogenic variants F220L and A299S. Pharmacological rescue was measured as the fold increase in rhodopsin or opsin levels upon addition of 11-cis retinal during opsin expression. Only Pro23 and T17M variants were rescued significantly. C110Y opsin was produced at low levels and did not yield rhodopsin, whereas the T4R, F220L, and A299S proteins reached near-wild-type levels and changed little with 11-cis retinal. All of the mutant rhodopsins exhibited misfolding, which increased over a broad range in the order F220L, A299S, T4R, T17M, P23A, P23H, P23L, as determined by decreased thermal stability in the dark and increased hydroxylamine sensitivity. Pharmacological rescue increased as misfolding decreased, but was limited for the least misfolded variants. Significantly, pathogenic variants also showed abnormal photobleaching behavior, including an increased ratio of metarhodopsin-I-like species to metarhodopsin-II-like species and aberrant photoproduct accumulation with prolonged illumination. These results, combined with an analysis of published biochemical and clinical studies, suggest that many rhodopsin variants cause disease by affecting both biosynthesis and photoactivity. We conclude that pharmacological rescue is promising as a broadly effective therapy for rhodopsin RP, particularly if implemented in a way that minimizes the photoactivity of the mutant proteins.
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Affiliation(s)
- Mark P Krebs
- Department of Ophthalmology and the Charlie Mack Overstreet Laboratories for Retinal Diseases, College of Medicine, University of Florida, Gainesville, FL 32610, USA
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35
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Malanson KM, Lem J. Rhodopsin-mediated retinitis pigmentosa. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2009; 88:1-31. [PMID: 20374723 DOI: 10.1016/s1877-1173(09)88001-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Retinitis pigmentosa (RP) is a genetically and phenotypically heterogeneous group of diseases that cause blindness. Mutations within the rhodopsin gene account for approximately 25% of autosomal dominantly inherited RP cases. Therefore, understanding the mechanisms causing rhodopsin-mediated RP has a significant health impact. To date, results from multiple labs indicate that rhodopsin-mediated RP pathogenesis does not share a common mechanism of degeneration. There is strong evidence that multiple mechanisms are involved, including protein misfolding, mislocalization, release of toxic products, and aberrant signaling. Development of effective treatments requires investigation of the mechanism involved in the different rhodopsin mutations. This chapter focuses on the mechanisms by which rhodopsin mutations cause retinal degeneration, as well as potential therapeutic strategies to treat the disease.
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Affiliation(s)
- Katherine M Malanson
- The Molecular Cardiology Research Institute, Tufts Medical Center, Boston, Massachusetts 02111, USA
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36
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Tiwari AK, Roy JK. Mutation in Rab11 results in abnormal organization of ommatidial cells and activation of JNK signaling in the Drosophila eye. Eur J Cell Biol 2009; 88:445-60. [PMID: 19473727 DOI: 10.1016/j.ejcb.2009.02.188] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Revised: 02/16/2009] [Accepted: 02/23/2009] [Indexed: 02/01/2023] Open
Abstract
Rab11(mo), a P insertion line of Rab11 showed degenerated ommatidia and excess cell death in larval/pupal eyes. Here, we demonstrate that Rab11 is essential for normal organization of ommatidial cells and their survival in Drosophila, and a mutation in this gene results in cytoskeleton disruption and activation of JNK signaling in the eye. The spatial organization of various cell types in compound eye, viz., cone, photoreceptor, pigment and bristle cells, were disrupted in Rab11 mutants as revealed by immunostaining of F-actin and adherens and septate junction proteins. Genetic interaction studies indicated that mutation in Rab11 upregulates Drosophila apoptotic genes, rpr, hid and grim. In order to study the pathway that causes excessive cell death in Rab11 mutants, the JNK pathway was chosen and genetic interaction analyses were carried out between Rab11 and candidates of the JNK signaling pathway. A downregulation of JNK signaling rescued the phenotype in Rab11 mutant eyes significantly while overexpression of JNK in the eyes using UAS-eiger, UAS-dtak1 or EP(2)0578, resulted in enhancement of the eye phenotype indicating a link between Rab11 and the JNK signaling pathway.
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Affiliation(s)
- Anand K Tiwari
- Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi 221005, India
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37
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Cellular responses to endoplasmic reticulum stress and apoptosis. Apoptosis 2009; 14:996-1007. [PMID: 19360473 DOI: 10.1007/s10495-009-0341-y] [Citation(s) in RCA: 285] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2009] [Accepted: 03/18/2009] [Indexed: 01/08/2023]
Abstract
The endoplasmic reticulum (ER) is the cell organelle where secretory and membrane proteins are synthesized and folded. Correctly folded proteins exit the ER and are transported to the Golgi and other destinations within the cell, but proteins that fail to fold properly-misfolded proteins-are retained in the ER and their accumulation may constitute a form of stress to the cell-ER stress. Several signaling pathways, collectively known as unfolded protein response (UPR), have evolved to detect the accumulation of misfolded proteins in the ER and activate a cellular response that attempts to maintain homeostasis and a normal flux of proteins in the ER. In certain severe situations of ER stress, however, the protective mechanisms activated by the UPR are not sufficient to restore normal ER function and cells die by apoptosis. Most research on the UPR used yeast or mammalian model systems and only recently Drosophila has emerged as a system to study the molecular and cellular mechanisms of the UPR. Here, we review recent advances in Drosophila UPR research, in the broad context of mammalian and yeast literature.
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Pathogenesis of retinitis pigmentosa associated with apoptosis-inducing mutations in carbonic anhydrase IV. Proc Natl Acad Sci U S A 2009; 106:3437-42. [PMID: 19211803 DOI: 10.1073/pnas.0813178106] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Missense mutations in the carbonic anhydrase IV (CA IV) gene have been identified in patients with an autosomal dominant form of retinitis pigmentosa (RP17). We used two transient expression systems to investigate the molecular mechanism by which the newly identified CA IV mutations, R69H and R219S, contribute to retinal pathogenesis. Although the R219S mutation drastically reduced the activity of the enzyme, the R69H mutation had a minimal effect, suggesting that loss of CA activity is not the molecular basis for their pathogenesis. Defective processing was apparent for both mutant proteins. Cell surface-labeling techniques showed that the R69H and R219S mutations both impaired the trafficking of CA IV to the cell surface, resulting in their abnormal intracellular retention. Expression of both CA IV mutants induced elevated levels of the endoplasmic reticulum (ER) stress markers, BiP and CHOP, and led to cell death by apoptosis. They also had a dominant-negative effect on the secretory function of the ER. These properties are similar to those of R14W CA IV, the signal sequence variant found in the original patients with RP17. These findings suggest that toxic gain of function involving ER stress-induced apoptosis is the common mechanism for pathogenesis of this autosomal-dominant disease. Apoptosis induced by the CA IV mutants could be prevented, at least partially, by treating the cells with dorzolamide, a CA inhibitor. Thus, the use of a CA inhibitor as a chemical chaperone to reduce ER stress may delay or prevent the onset of blindness in RP17.
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Cho KI, Yi H, Yeh A, Tserentsoodol N, Cuadrado L, Searle K, Hao Y, Ferreira PA. Haploinsufficiency of RanBP2 is neuroprotective against light-elicited and age-dependent degeneration of photoreceptor neurons. Cell Death Differ 2008; 16:287-97. [PMID: 18949001 DOI: 10.1038/cdd.2008.153] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Prolonged light exposure is a determinant factor in inducing neurodegeneration of photoreceptors by apoptosis. Yet, the molecular bases of the pathways and components triggering this cell death event are elusive. Here, we reveal a prominent age-dependent increase in the susceptibility of photoreceptor neurons to undergo apoptosis under light in a mouse model. This is accompanied by light-induced subcellular changes of photoreceptors, such as dilation of the disks at the tip of the outer segments, prominent vesiculation of nascent disks, and autophagy of mitochondria into large multilamellar bodies. Notably, haploinsufficiency of Ran-binding protein-2 (RanBP2) suppresses apoptosis and most facets of membrane dysgenesis observed with age upon light-elicited stress. RanBP2 haploinsufficiency promotes decreased levels of free fatty acids in the retina independent of light exposure and turns the mice refractory to weight gain on a high-fat diet, whereas light promotes an increase in hydrogen peroxide regardless of the genotype. These studies demonstrate the presence of age-dependent and RanBP2-mediated pathways modulating membrane biogenesis of the outer segments and light-elicited neurodegeneration of photoreceptors. Furthermore, the findings support a mechanism whereby the RanBP2-dependent production of free fatty acids, metabolites thereof or the modulation of a cofactor dependent on any of these, promote apoptosis of photoreceptors in concert with the light-stimulated production of reactive oxygen species.
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Affiliation(s)
- K-in Cho
- Department of Ophthalmology, Duke University Medical Center, Durham, NC, USA
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Xenopus laevis P23H rhodopsin transgene causes rod photoreceptor degeneration that is more severe in the ventral retina and is modulated by light. Exp Eye Res 2008; 86:612-21. [PMID: 18291367 DOI: 10.1016/j.exer.2008.01.005] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2007] [Revised: 12/21/2007] [Accepted: 01/03/2008] [Indexed: 11/20/2022]
Abstract
Rhodopsin transgenes carrying mutations that cause autosomal dominant retinitis pigmentosa in humans have been used to study rod photoreceptor degeneration in various model organisms including Xenopus laevis. To date, the only transgenes shown to cause rod photoreceptor degeneration in Xenopus laevis have been either mammalian rhodopsins or chimeric versions of rhodopsin based mainly on Xenopus laevis rhodopsin sequences but with a mammalian C-terminus. Since the C-terminal sequence of rhodopsin is highly conserved in mammals and divergent in Xenopus laevis, and mammalian and epitope-tagged rhodopsins may have unexpected properties as transgenes, we decided to test whether a Xenopus laevis rhodopsin transgene carrying only the P23H mutation could also cause rod photoreceptor degeneration. Xenopus laevis tadpoles expressing these transgenes indeed had shortened outer segments and, in severely affected animals, the loss of rod photoreceptors but not the loss of cone photoreceptors. RT-PCR analyses showed that less than 10% of mutant transgenic rhodopsin relative to wild-type endogenous rhodopsin mRNA was sufficient to produce severe rod photoreceptor degeneration. As observed in other animal models as well as humans carrying this particular rhodopsin mutation, the rod photoreceptor degeneration was most severe in the ventral retina and was modified by light. Thus, the rod photoreceptor degeneration produced in Xenopus laevis by the P23H mutation in an otherwise untagged Xenopus laevis rhodopsin is generally similar to that seen with mammalian rhodopsins and epitope-tagged versions of Xenopus laevis rhodopsin, though some differences remain to be explained.
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Tam BM, Moritz OL. Dark rearing rescues P23H rhodopsin-induced retinal degeneration in a transgenic Xenopus laevis model of retinitis pigmentosa: a chromophore-dependent mechanism characterized by production of N-terminally truncated mutant rhodopsin. J Neurosci 2007; 27:9043-53. [PMID: 17715341 PMCID: PMC6672211 DOI: 10.1523/jneurosci.2245-07.2007] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
To elucidate the molecular mechanisms underlying the light-sensitive retinal degeneration caused by the rhodopsin mutation P23H, which causes retinitis pigmentosa (RP) in humans, we expressed Xenopus laevis, bovine, human, and murine forms of P23H rhodopsin in transgenic X. laevis rod photoreceptors. All P23H rhodopsins caused aggressive retinal degeneration associated with low expression levels and retention of P23H rhodopsin in the endoplasmic reticulum (ER), suggesting involvement of protein misfolding and ER stress. However, light sensitivity varied dramatically between these RP models, with complete or partial rescue by dark rearing in the case of bovine and human P23H rhodopsin, and no rescue for X. laevis P23H rhodopsin. Rescue by dark rearing required an intact 11-cis-retinal chromophore binding site within the mutant protein and was associated with truncation of the P23H rhodopsin N terminus. This yielded an abundant nontoxic approximately 27 kDa form that escaped the ER and was transported to the rod outer segment. The truncated protein was produced in the greatest quantities in dark-reared retinas expressing bovine P23H rhodopsin and was not observed with X. laevis P23H rhodopsin. These results are consistent with a mechanism involving enhanced protein folding in the presence of 11-cis-retinal chromophore, with ER exit assisted by proteolytic truncation of the N terminus. This study provides a molecular mechanism for light sensitivity observed in other transgenic models of RP and for phenotypic variation among RP patients.
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Affiliation(s)
- Beatrice M. Tam
- Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, Canada V5Z 3N9
| | - Orson L. Moritz
- Department of Ophthalmology and Visual Sciences, Centre for Macular Research, University of British Columbia, Vancouver, British Columbia, Canada V5Z 3N9
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Wang T, Montell C. Phototransduction and retinal degeneration in Drosophila. Pflugers Arch 2007; 454:821-47. [PMID: 17487503 DOI: 10.1007/s00424-007-0251-1] [Citation(s) in RCA: 215] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Accepted: 03/05/2007] [Indexed: 01/05/2023]
Abstract
Drosophila visual transduction is the fastest known G-protein-coupled signaling cascade and has therefore served as a genetically tractable animal model for characterizing rapid responses to sensory stimulation. Mutations in over 30 genes have been identified, which affect activation, adaptation, or termination of the photoresponse. Based on analyses of these genes, a model for phototransduction has emerged, which involves phosphoinoside signaling and culminates with opening of the TRP and TRPL cation channels. Many of the proteins that function in phototransduction are coupled to the PDZ containing scaffold protein INAD and form a supramolecular signaling complex, the signalplex. Arrestin, TRPL, and G alpha(q) undergo dynamic light-dependent trafficking, and these movements function in long-term adaptation. Other proteins play important roles either in the formation or maturation of rhodopsin, or in regeneration of phosphatidylinositol 4,5-bisphosphate (PIP2), which is required for the photoresponse. Mutation of nearly any gene that functions in the photoresponse results in retinal degeneration. The underlying bases of photoreceptor cell death are diverse and involve mechanisms such as excessive endocytosis of rhodopsin due to stable rhodopsin/arrestin complexes and abnormally low or high levels of Ca2+. Drosophila visual transduction appears to have particular relevance to the cascade in the intrinsically photosensitive retinal ganglion cells in mammals, as the photoresponse in these latter cells appears to operate through a remarkably similar mechanism.
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Affiliation(s)
- Tao Wang
- Department of Biological Chemistry, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Ryoo HD, Domingos PM, Kang MJ, Steller H. Unfolded protein response in a Drosophila model for retinal degeneration. EMBO J 2007; 26:242-52. [PMID: 17170705 PMCID: PMC1782370 DOI: 10.1038/sj.emboj.7601477] [Citation(s) in RCA: 222] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Accepted: 11/06/2006] [Indexed: 12/15/2022] Open
Abstract
Stress in the endoplasmic reticulum (ER stress) and its cellular response, the unfolded protein response (UPR), are implicated in a wide variety of diseases, but its significance in many disorders remains to be validated in vivo. Here, we analyzed a branch of the UPR mediated by xbp1 in Drosophila to establish its role in neurodegenerative diseases. The Drosophila xbp1 mRNA undergoes ire-1-mediated unconventional splicing in response to ER stress, and this property was used to develop a specific UPR marker, xbp1-EGFP, in which EGFP is expressed in frame only after ER stress. xbp1-EGFP responds specifically to ER stress, but not to proteins that form cytoplasmic aggregates. The ire-1/xbp1 pathway regulates heat shock cognate protein 3 (hsc3), an ER chaperone. xbp1 splicing and hsc3 induction occur in the retina of ninaE(G69D)-/+, a Drosophila model for autosomal dominant retinitis pigmentosa (ADRP), and reduction of xbp1 gene dosage accelerates retinal degeneration of these animals. These results demonstrate the role of the UPR in the Drosophila ADRP model and open new opportunities for examining the UPR in other Drosophila disease models.
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Affiliation(s)
- Hyung Don Ryoo
- Department of Cell Biology, NYU School of Medicine, New York, NY, USA
- Howard Hughes Medical Institute, The Rockefeller University, New York, NY, USA
| | - Pedro M Domingos
- Howard Hughes Medical Institute, The Rockefeller University, New York, NY, USA
| | - Min-Ji Kang
- Department of Cell Biology, NYU School of Medicine, New York, NY, USA
| | - Hermann Steller
- Howard Hughes Medical Institute, The Rockefeller University, New York, NY, USA
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Iannaccone A, Man D, Waseem N, Jennings BJ, Ganapathiraju M, Gallaher K, Reese E, Bhattacharya SS, Klein-Seetharaman J. Retinitis pigmentosa associated with rhodopsin mutations: Correlation between phenotypic variability and molecular effects. Vision Res 2006; 46:4556-67. [PMID: 17014888 DOI: 10.1016/j.visres.2006.08.018] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2006] [Revised: 08/01/2006] [Accepted: 08/03/2006] [Indexed: 11/17/2022]
Abstract
Similar retinitis pigmentosa (RP) phenotypes can result from mutations affecting different rhodopsin regions, and distinct amino acid substitutions can cause different RP severity and progression rates. Specifically, both the R135L and R135W mutations (cytoplasmic end of H3) result in diffuse, severe disease (class A), but R135W causes more severe and more rapidly progressive RP than R135L. The P180A and G188R mutations (second intradiscal loop) exhibit a mild phenotype with regional variability (class B1) and diffuse disease of moderate severity (class B2), respectively. Computational and in vitro studies of these mutants provide molecular insights into this phenotypic variability.
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Affiliation(s)
- Alessandro Iannaccone
- Hamilton Eye Institute, Department of Ophthalmology, Retinal Degeneration and Ophthalmic Genetics Service, University of Tennessee Health Science Center, 930 Madison Avenue, Suit 731, Memphis, TN 38163, USA
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