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Kader MA, Devarajan B, Vijayan S, Ramakrishnan R, Sundaresan P, Uduman MS, Krishnadas SR, Kuppamuthu D. Myocilin Mutation N480K Leads to Early Onset Juvenile and Adult-onset Primary Open Angle Glaucoma in a Six Generation Family. J Glaucoma 2024; 33:218-224. [PMID: 37670504 DOI: 10.1097/ijg.0000000000002286] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Accepted: 07/29/2023] [Indexed: 09/07/2023]
Abstract
PRCIS A pathogenic autosomal dominant MYOC mutation N480K detected in 6 generations of an Indian family is primarily responsible for juvenile open angle glaucoma (JOAG) and adult-onset primary open angle glaucoma (POAG), emphasizing the importance of screening this mutation at a younger age. PURPOSE To screen myocilin mutations in a large South Indian family with early-onset JOAG and adult-onset POAG. METHODS In a large South Indian family with 20 members, 8 members diagnosed as JOAG, 7 members as POAG, 4 members as JOAG suspect, and 1 member as POAG suspect were screened for myocilin ( MYOC) mutations using Sanger sequencing. Whole exome sequencing was performed on clinically suspected JOAG/POAG individuals. RESULTS Myocilin gene mutation N480K (c.1440C>G) was detected in 20 family members, including proband, of whom 8 were JOAG and 7 were POAG patients, 3 were JOAG suspects, and 2 were unaffected. Among the unaffected carriers, 1 was less than 5 years old, and another was 25 years old. The earliest to develop the disease was a 10-year-old child. The penetrance of the mutation was 95% over 10 years of age. This family had JOAG/POAG suspects with no N480K MYOC mutation, and they were further screened for other mutations using whole-exome sequencing. Polymorphisms CYP1B1 L432V and MYOC R76K were detected in 3 JOAG/POAG suspects, and among these 3, one had another CYP1B1 polymorphic variant R368H. The presence of the CYP1B1 polymorphism along with an MYOC polymorphic variant among the JOAG/POAG suspects needs additional studies to explore their combined role in the onset of glaucoma. CONCLUSIONS This study reveals that MYOC mutation is primarily responsible for JOAG and adult-onset POAG in a family, emphasizing the importance of screening for this mutation at a younger age for early treatment.
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Affiliation(s)
| | | | - Saravanan Vijayan
- Department of Genetics, Aravind Medical Research Foundation, Madurai
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2
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Sazhnyev Y, Venkat A, Zheng JJ. Somatic Mutations within Myocilin due to Aging May Be a Potential Risk Factor for Glaucoma. Genes (Basel) 2024; 15:203. [PMID: 38397193 PMCID: PMC10887703 DOI: 10.3390/genes15020203] [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: 12/28/2023] [Revised: 01/17/2024] [Accepted: 01/29/2024] [Indexed: 02/25/2024] Open
Abstract
Glaucoma is a chronic optic neuropathy that leads to irreversible vision loss. Aging and family history are the two most important risk factors of glaucoma. One of the most studied genes involved in the onset of open-angle glaucoma is myocilin (MYOC). About 105 germline mutations within MYOC are known to be associated with glaucoma and result in endoplasmic reticulum (ER) stress, which leads to trabecular meshwork (TM) cell death and subsequent intraocular pressure (IOP) elevation. However, only about 4% of the population carry these mutations. An analysis of MYOC somatic cancer-associated mutations revealed a notable overlap with pathogenic glaucoma variants. Because TM cells have the potential to accumulate somatic mutations at a rapid rate due to ultraviolet (UV) light exposure, we propose that an accumulation of somatic mutations within MYOC is an important contributor to the onset of glaucoma.
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Affiliation(s)
- Yevgeniy Sazhnyev
- Department of Ophthalmology, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA; (Y.S.); (A.V.)
- Department of Ophthalmology, California Northstate University College of Medicine, 9700 West Taron Dr., Elk Grove, CA 95757, USA
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA
| | - Akaash Venkat
- Department of Ophthalmology, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA; (Y.S.); (A.V.)
- Department of Computer Science, Henry Samueli School of Engineering and Applied Science, University of California, Los Angeles, CA 90095, USA
| | - Jie J. Zheng
- Department of Ophthalmology, Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095, USA; (Y.S.); (A.V.)
- Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA
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3
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Saccuzzo EG, Mebrat MD, Scelsi HF, Kim M, Ma MT, Su X, Hill SE, Rheaume E, Li R, Torres MP, Gumbart JC, Van Horn WD, Lieberman RL. Competition between inside-out unfolding and pathogenic aggregation in an amyloid-forming β-propeller. Nat Commun 2024; 15:155. [PMID: 38168102 PMCID: PMC10762032 DOI: 10.1038/s41467-023-44479-2] [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: 02/14/2023] [Accepted: 12/14/2023] [Indexed: 01/05/2024] Open
Abstract
Studies of folded-to-misfolded transitions using model protein systems reveal a range of unfolding needed for exposure of amyloid-prone regions for subsequent fibrillization. Here, we probe the relationship between unfolding and aggregation for glaucoma-associated myocilin. Mutations within the olfactomedin domain of myocilin (OLF) cause a gain-of-function, namely cytotoxic intracellular aggregation, which hastens disease progression. Aggregation by wild-type OLF (OLFWT) competes with its chemical unfolding, but only below the threshold where OLF loses tertiary structure. Representative moderate (OLFD380A) and severe (OLFI499F) disease variants aggregate differently, with rates comparable to OLFWT in initial stages of unfolding, and variants adopt distinct partially folded structures seen along the OLFWT urea-unfolding pathway. Whether initiated with mutation or chemical perturbation, unfolding propagates outward to the propeller surface. In sum, for this large protein prone to amyloid formation, the requirement for a conformational change to promote amyloid fibrillization leads to direct competition between unfolding and aggregation.
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Affiliation(s)
- Emily G Saccuzzo
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, USA
| | - Mubark D Mebrat
- Biodesign Center for Personalized Diagnostics, Arizona State University, Tempe, USA
- School of Molecular Sciences, Arizona State University, Tempe, USA
| | - Hailee F Scelsi
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, USA
| | - Minjoo Kim
- Biodesign Center for Personalized Diagnostics, Arizona State University, Tempe, USA
- School of Molecular Sciences, Arizona State University, Tempe, USA
| | - Minh Thu Ma
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, USA
| | - Xinya Su
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, USA
| | - Shannon E Hill
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, USA
| | - Elisa Rheaume
- Interdisciplinary Graduate Program in Quantitative Biosciences, Georgia Institute of Technology, Atlanta, USA
| | - Renhao Li
- Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta and Department of Pediatrics, Emory University School of Medicine, Atlanta, USA
| | - Matthew P Torres
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, USA
| | - James C Gumbart
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, USA
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, USA
- School of Physics, Georgia Institute of Technology, Atlanta, USA
| | - Wade D Van Horn
- Biodesign Center for Personalized Diagnostics, Arizona State University, Tempe, USA.
- School of Molecular Sciences, Arizona State University, Tempe, USA.
| | - Raquel L Lieberman
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, USA.
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4
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Tirendi S, Domenicotti C, Bassi AM, Vernazza S. Genetics and Glaucoma: the state of the art. Front Med (Lausanne) 2023; 10:1289952. [PMID: 38152303 PMCID: PMC10751926 DOI: 10.3389/fmed.2023.1289952] [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: 09/06/2023] [Accepted: 11/28/2023] [Indexed: 12/29/2023] Open
Abstract
Glaucoma is the second leading cause of irreversible blindness worldwide. Although genetic background contributes differently to rare early-onset glaucoma (before age 40) or common adult-onset glaucoma, it is now considered an important factor in all major forms of the disease. Genetic and genomic studies, including GWAS, are contributing to identifying novel loci associated with glaucoma or to endophenotypes across ancestries to enrich the knowledge about glaucoma genetic susceptibility. Moreover, new high-throughput functional genomics contributes to defining the relevance of genetic results in the biological pathways and processes involved in glaucoma pathogenesis. Such studies are expected to advance significantly our understanding of glaucoma's genetic basis and provide new druggable targets to treat glaucoma. This review gives an overview of the role of genetics in the pathogenesis or risk of glaucoma.
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Affiliation(s)
- Sara Tirendi
- Department of Experimental Medicine, University of Genoa, Genoa, Italy
- Inter-University Center for the Promotion of the 3Rs Principles in Teaching & Research (Centro 3R), Genoa, Italy
| | - Cinzia Domenicotti
- Department of Experimental Medicine, University of Genoa, Genoa, Italy
- Inter-University Center for the Promotion of the 3Rs Principles in Teaching & Research (Centro 3R), Genoa, Italy
| | - Anna Maria Bassi
- Department of Experimental Medicine, University of Genoa, Genoa, Italy
- Inter-University Center for the Promotion of the 3Rs Principles in Teaching & Research (Centro 3R), Genoa, Italy
| | - Stefania Vernazza
- Department of Experimental Medicine, University of Genoa, Genoa, Italy
- Inter-University Center for the Promotion of the 3Rs Principles in Teaching & Research (Centro 3R), Genoa, Italy
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5
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Saccuzzo EG, Youngblood HA, Lieberman RL. Myocilin misfolding and glaucoma: A 20-year update. Prog Retin Eye Res 2023; 95:101188. [PMID: 37217093 PMCID: PMC10330797 DOI: 10.1016/j.preteyeres.2023.101188] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 05/18/2023] [Accepted: 05/19/2023] [Indexed: 05/24/2023]
Abstract
Mutations in the gene MYOC account for approximately 5% of cases of primary open angle glaucoma (POAG). MYOC encodes for the protein myocilin, a multimeric secreted glycoprotein composed of N-terminal coiled-coil (CC) and leucine zipper (LZ) domains that are connected via a disordered linker to a 30 kDa olfactomedin (OLF) domain. More than 90% of glaucoma-causing mutations are localized to the OLF domain. While myocilin is expressed in numerous tissues, mutant myocilin is only associated with disease in the anterior segment of the eye, in the trabecular meshwork. The prevailing pathogenic mechanism involves a gain of toxic function whereby mutant myocilin aggregates intracellularly instead of being secreted, which causes cell stress and an early timeline for TM cell death, elevated intraocular pressure, and subsequent glaucoma-associated retinal degeneration. In this review, we focus on the work our lab has conducted over the past ∼15 years to enhance our molecular understanding of myocilin-associated glaucoma, which includes details of the molecular structure and the nature of the aggregates formed by mutant myocilin. We conclude by discussing open questions, such as predicting phenotype from genotype alone, the elusive native function of myocilin, and translational directions enabled by our work.
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Affiliation(s)
- Emily G Saccuzzo
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA, 30332-0400, USA
| | - Hannah A Youngblood
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA, 30332-0400, USA
| | - Raquel L Lieberman
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA, 30332-0400, USA.
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6
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Scelsi HF, Hill KR, Barlow BM, Martin MD, Lieberman RL. Quantitative differentiation of benign and misfolded glaucoma-causing myocilin variants on the basis of protein thermal stability. Dis Model Mech 2023; 16:286212. [PMID: 36579626 PMCID: PMC9844228 DOI: 10.1242/dmm.049816] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Accepted: 11/28/2022] [Indexed: 12/30/2022] Open
Abstract
Accurate predictions of the pathogenicity of mutations associated with genetic diseases are key to the success of precision medicine. Inherited missense mutations in the myocilin (MYOC) gene, within its olfactomedin (OLF) domain, constitute the strongest genetic link to primary open-angle glaucoma via a toxic gain of function, and thus MYOC is an attractive precision-medicine target. However, not all mutations in MYOC cause glaucoma, and common variants are expected to be neutral polymorphisms. The Genome Aggregation Database (gnomAD) lists ∼100 missense variants documented within OLF, all of which are relatively rare (allele frequency <0.001%) and nearly all are of unknown pathogenicity. To distinguish disease-causing OLF variants from benign OLF variants, we first characterized the most prevalent population-based variants using a suite of cellular and biophysical assays, and identified two variants with features of aggregation-prone familial disease variants. Next, we considered all available biochemical and clinical data to demonstrate that pathogenic and benign variants can be differentiated statistically based on a single metric: the thermal stability of OLF. Our results motivate genotyping MYOC in patients for clinical monitoring of this widespread, painless and irreversible ocular disease.
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Affiliation(s)
- Hailee F. Scelsi
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA 30332-0400, USA
| | - Kamisha R. Hill
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA 30332-0400, USA
| | - Brett M. Barlow
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA 30332-0400, USA
| | - Mackenzie D. Martin
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA 30332-0400, USA
| | - Raquel L. Lieberman
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA 30332-0400, USA,Author for correspondence ()
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7
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Burdon KP, Graham P, Hadler J, Hulleman JD, Pasutto F, Boese EA, Craig JE, Fingert JH, Hewitt AW, Siggs OM, Whisenhunt K, Young TL, Mackey DA, Dubowsky A, Souzeau E. Specifications of the ACMG/AMP variant curation guidelines for myocilin: Recommendations from the clingen glaucoma expert panel. Hum Mutat 2022; 43:2170-2186. [PMID: 36217948 PMCID: PMC9771967 DOI: 10.1002/humu.24482] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Revised: 09/02/2022] [Accepted: 10/06/2022] [Indexed: 01/25/2023]
Abstract
The standardization of variant curation criteria is essential for accurate interpretation of genetic results and clinical care of patients. The variant curation guidelines developed by the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP) in 2015 are widely used but are not gene specific. To address this issue, the Clinical Genome Resource (ClinGen) Variant Curation Expert Panels (VCEP) have been tasked with developing gene-specific variant curation guidelines. The Glaucoma VCEP was created to develop rule specifications for genes associated with primary glaucoma, including myocilin (MYOC), the most common cause of Mendelian glaucoma. Of the 28 ACMG/AMP criteria, the Glaucoma VCEP adapted 15 rules to MYOC and determined 13 rules not applicable. Key specifications included determining minor allele frequency thresholds, developing an approach to counting probands and segregations, and reviewing functional assays. The rules were piloted on 81 variants and led to a change in classification in 40% of those that were classified in ClinVar, with functional evidence influencing the classification of 18 variants. The standardized variant curation guidelines for MYOC provide a framework for the consistent application of the rules between laboratories, to improve MYOC genetic testing in the management of glaucoma.
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Affiliation(s)
- Kathryn P. Burdon
- Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, Australia
| | - Patricia Graham
- Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, Australia
- Centre for Ophthalmology and Vision Sciences, Lions Eye Institute, University of Western Australia, Perth, WA, Australia
| | - Johanna Hadler
- Department of Ophthalmology, Flinders University, Flinders Medical Centre, Adelaide, SA, Australia
- SA Pathology, Adelaide, SA, Australia
| | - John D. Hulleman
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Francesca Pasutto
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Erin A. Boese
- Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, USA
| | - Jamie E. Craig
- Department of Ophthalmology, Flinders University, Flinders Medical Centre, Adelaide, SA, Australia
| | - John H. Fingert
- Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, USA
| | - Alex W. Hewitt
- Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, Australia
| | - Owen M. Siggs
- Department of Ophthalmology, Flinders University, Flinders Medical Centre, Adelaide, SA, Australia
- Garvan Institute of Medical Research, Darlinghurst, NSW, Australia
| | - Kristina Whisenhunt
- Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, Madison, WI, USA
| | - Terri L. Young
- Department of Ophthalmology and Visual Sciences, University of Wisconsin-Madison, Madison, WI, USA
| | - David A. Mackey
- Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, Australia
- Centre for Ophthalmology and Vision Sciences, Lions Eye Institute, University of Western Australia, Perth, WA, Australia
| | | | - Emmanuelle Souzeau
- Department of Ophthalmology, Flinders University, Flinders Medical Centre, Adelaide, SA, Australia
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8
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Das A, Imanishi Y. Drug Discovery Strategies for Inherited Retinal Degenerations. BIOLOGY 2022; 11:1338. [PMID: 36138817 PMCID: PMC9495580 DOI: 10.3390/biology11091338] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Revised: 08/31/2022] [Accepted: 09/07/2022] [Indexed: 12/03/2022]
Abstract
Inherited retinal degeneration is a group of blinding disorders afflicting more than 1 in 4000 worldwide. These disorders frequently cause the death of photoreceptor cells or retinal ganglion cells. In a subset of these disorders, photoreceptor cell death is a secondary consequence of retinal pigment epithelial cell dysfunction or degeneration. This manuscript reviews current efforts in identifying targets and developing small molecule-based therapies for these devastating neuronal degenerations, for which no cures exist. Photoreceptors and retinal ganglion cells are metabolically demanding owing to their unique structures and functional properties. Modulations of metabolic pathways, which are disrupted in most inherited retinal degenerations, serve as promising therapeutic strategies. In monogenic disorders, great insights were previously obtained regarding targets associated with the defective pathways, including phototransduction, visual cycle, and mitophagy. In addition to these target-based drug discoveries, we will discuss how phenotypic screening can be harnessed to discover beneficial molecules without prior knowledge of their mechanisms of action. Because of major anatomical and biological differences, it has frequently been challenging to model human inherited retinal degeneration conditions using small animals such as rodents. Recent advances in stem cell-based techniques are opening new avenues to obtain pure populations of human retinal ganglion cells and retinal organoids with photoreceptor cells. We will discuss concurrent ideas of utilizing stem-cell-based disease models for drug discovery and preclinical development.
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Affiliation(s)
- Arupratan Das
- Department of Ophthalmology, Eugene and Marilyn Glick Eye Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA
- Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, IN 46202, USA
- Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA
| | - Yoshikazu Imanishi
- Department of Ophthalmology, Eugene and Marilyn Glick Eye Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA
- Stark Neurosciences Research Institute, Indiana University School of Medicine, Indianapolis, IN 46202, USA
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, IN 46202, USA
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9
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Tanji T, Cohen E, Shen D, Zhang C, Yu F, Coleman AL, Zheng JJ. Age at Glaucoma Diagnosis in Germline Myocilin Mutation Patients: Associations with Polymorphisms in Protein Stabilities. Genes (Basel) 2021; 12:genes12111802. [PMID: 34828408 PMCID: PMC8623052 DOI: 10.3390/genes12111802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 11/08/2021] [Accepted: 11/10/2021] [Indexed: 12/02/2022] Open
Abstract
Glaucoma is the leading cause of irreversible blindness worldwide, with elevated intraocular pressure (IOP) as the only known modifiable risk factor. Trabecular meshwork (TM)-inducible myocilin (the MYOC gene) was the first to be identified and linked to juvenile and primary open-angle glaucoma. It has been suggested that mutations in the MYOC gene and the aggregation of mutant myocilin in the endoplasmic reticulum (ER) of TM may cause ER stress, resulting in a reduced outflow of aqueous humor and an increase in IOP. We selected 20 MYOC mutations with experimentally determined melting temperatures of mutated myocilin proteins. We included 40 published studies with at least one glaucoma patient with one of these 20 MYOC mutations and information on age at glaucoma diagnosis. Based on data from 458 patients, we found that a statistically significant but weak correlation was present between age and melting temperature based on various assumptions for age. We therefore conclude that genetic analysis of MYOC mutations alone cannot be used to accurately predict age at glaucoma diagnosis. However, it might be an important prognostic factor combined with other clinical factors for critical and early detection of glaucoma.
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10
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Scelsi HF, Barlow BM, Saccuzzo EG, Lieberman RL. Common and rare myocilin variants: Predicting glaucoma pathogenicity based on genetics, clinical, and laboratory misfolding data. Hum Mutat 2021; 42:903-946. [PMID: 34082484 DOI: 10.1002/humu.24238] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 05/07/2021] [Accepted: 05/31/2021] [Indexed: 12/12/2022]
Abstract
Rare variants of the olfactomedin domain of myocilin are considered causative for inherited, early-onset open-angle glaucoma, with a misfolding toxic gain-of-function pathogenic mechanism detailed by 20 years of laboratory research. Myocilin variants are documented in the scientific literature and identified through large-scale genetic sequencing projects such as those curated in the Genome Aggregation Database (gnomAD). In the absence of key clinical and laboratory information, however, the pathogenicity of any given variant is not clear, because glaucoma is a heterogeneous and prevalent age-onset disease, and common variants are likely benign. In this review, we reevaluate the likelihood of pathogenicity for the ~100 nonsynonymous missense, insertion-deletion, and premature termination of myocilin olfactomedin variants documented in the literature. We integrate available clinical, laboratory cellular, biochemical and biophysical data, the olfactomedin domain structure, and population genetics data from gnomAD. Of the variants inspected, ~50% can be binned based on a preponderance of data, leaving many of uncertain pathogenicity that motivate additional studies. Ultimately, the approach of combining metrics from different disciplines will likely resolve outstanding complexities regarding the role of this misfolding-prone protein within the context of a multifactorial and prevalent ocular disease, and pave the way for new precision medicine therapeutics.
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Affiliation(s)
- Hailee F Scelsi
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA
| | - Brett M Barlow
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA
| | - Emily G Saccuzzo
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA
| | - Raquel L Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, USA
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11
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Lieberman RL, Ma MT. Molecular Insights into Myocilin and Its Glaucoma-Causing Misfolded Olfactomedin Domain Variants. Acc Chem Res 2021; 54:2205-2215. [PMID: 33847483 DOI: 10.1021/acs.accounts.1c00060] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Numerous human disorders arise due to the inability of a particular protein to adopt its correct three-dimensional structure in the context of the cell, leading to aggregation. A new addition to the list of such protein conformational disorders is the inherited subtype of glaucoma. Different and rare coding mutations in myocilin, found in families throughout the world, are causal for early onset ocular hypertension, a key glaucoma risk factor. Myocilin is expressed at high levels in the trabecular meshwork (TM) extracellular matrix. The TM is the anatomical region of the eye that regulates intraocular pressure, and its dysfunction is associated with most forms of glaucoma. Disease variants, distributed across the 30 kDa olfactomedin domain (mOLF), cause myocilin to be sequestered intracellularly instead of being secreted to the TM extracellular matrix. The working hypothesis is that the intracellular aggregates cause a toxic gain of function: TM cell death is thought to lead to TM matrix dysfunction, hastening elevated intraocular pressure and subsequent vision loss.Our lab has provided molecular underpinnings for myocilin structure and misfolding, placing myocilin-associated glaucoma within the context of amyloid diseases like Alzheimer and diabetes. We have dissected complexities of the modular wild-type (WT) myocilin structure and associated misfolded states. Our data support the model that full-length WT myocilin adopts a Y-shaped dimer-of-dimers conferred by two different coiled-coil regions, generating new hypotheses regarding its mysterious function. The mOLF β-propellers are paired at each tip of the Y. Disease-associated variants aggregate because mOLFs are less stable, leading to facile aggregation under physiological conditions (37 °C, pH 7.2). Mutant myocilin aggregates exhibit numerous characteristics of amyloid in vitro and in cells, and aggregation proceeds from a partially folded state accessed preferentially by disease variants at physiological conditions. Interestingly, destabilization is not a universal consequence of mutation. We identified counterintuitive, stabilizing point variants that adopt a non-native structure and do not aggregate; however, these variants have not been identified in glaucoma patients. An ongoing effort is predicting the consequence of any given mutation. This effort is relevant to interpreting data from large-scale sequencing projects where clinical and family history data are not available. Finally, our work suggests avenues to develop disease-modifying precision medicines for myocilin-associated glaucoma.
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Affiliation(s)
- Raquel L. Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, Georgia 30332-0400, United States
| | - Minh Thu Ma
- School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, Georgia 30332-0400, United States
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12
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Gupta V, Somarajan BI, Gupta S, Walia GK, Singh A, Sofi R, Chaudhary RS, Sharma A. The mutational spectrum of Myocilin gene among familial versus sporadic cases of Juvenile onset open angle glaucoma. Eye (Lond) 2020; 35:400-408. [PMID: 32300215 DOI: 10.1038/s41433-020-0850-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 03/04/2020] [Accepted: 03/06/2020] [Indexed: 01/08/2023] Open
Abstract
PURPOSE Juvenile onset primary open angle glaucoma (JOAG) is a rare disorder associated with high IOP and progressive optic neuropathy in patients diagnosed before the age of 40 years. While in some populations it has primarily an autosomal dominant pattern of inheritance, in others it occurs in a primarily sporadic form. The main aim of the study was to assess the relative prevalence of Myocilin (MYOC) mutations in familial versus sporadic cases of JOAG. METHODS We screened 92 unrelated (sporadic) JOAG patients, and 22 affected families (70 affected members and 36 unaffected) for variations in the MYOC gene. We also analyzed the clinical features associated with these variations. RESULTS Three coding sequence variants were identified as mutations causing JOAG. Four families segregated distinct mutations at Gly367Arg, and two families at Gln337Arg, while only two sporadic JOAG cases harbored MYOC mutations (Gly367Arg and Gln48His). The frequency of MYOC mutations in familial cases (27%) was significantly higher than in sporadic JOAG cases (2%); p = 0.001. A 90% penetrance for the Gly367Arg variant was seen by the age of 40 years in our patients. Characteristic allele signatures, indicative of specific founder effects, were not observed for the Gly367Arg mutation that was looked for in 12 patients among 2 geographically close families, which harbored this mutation. CONCLUSION Our data demonstrated that genetic screening for MYOC mutations should be focused toward cases with familial rather than sporadically occurring JOAG.
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Affiliation(s)
- Viney Gupta
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India.
| | - Bindu I Somarajan
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Shikha Gupta
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | | | - Abhishek Singh
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Rayees Sofi
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Richard Sher Chaudhary
- Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India
| | - Arundhati Sharma
- Department of Anatomy, All India Institute of Medical Sciences, New Delhi, India
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13
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Aluri KC, Salisbury JP, Prehn JHM, Agar JN. Loss of angiogenin function is related to earlier ALS onset and a paradoxical increase in ALS duration. Sci Rep 2020; 10:3715. [PMID: 32111867 PMCID: PMC7048737 DOI: 10.1038/s41598-020-60431-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 02/12/2020] [Indexed: 12/11/2022] Open
Abstract
0.5-1% of ALS (Amyotrophic Lateral Sclerosis) and Parkinson's disease (PD) are associated with mutations in the angiogenin (ANG). These mutations are thought to cause disease through a loss of ANG function, but this hypothesis has not been evaluated statistically. In addition, the potential for ANG to promote disease has not been considered. With the goal of better defining the etiology of ANG-ALS, we assembled all clinical onset and disease duration data and determined if these were correlated with biochemical properties of ANG variants. Loss of ANG stability and ribonuclease activity were found to correlate with early ALS onset, confirming an aspect of the prevailing model of ANG-ALS. Conversely, loss of ANG stability and ribonuclease activity correlated with longer survival following diagnosis, which is inconsistent with the prevailing model. These results indicate that functional ANG appears to decrease the risk of developing ALS but exacerbate ALS once in progress. These findings are rationalized in terms of studies demonstrating that distinct mechanisms contribute to ALS onset and progression and propose that ANG replacement or stabilization would benefit pre-symptomatic ANG-ALS patients. However, this study challenges the prevailing hypothesis that augmenting ANG will benefit symptomatic ANG-ALS patients. Instead, our results suggest that silencing of ANG activity may be beneficial for symptomatic ALS patients. This study will serve as a call-to-arms for neurologists to consistently publish ALS and PD patient's clinical data-if all ANG-ALS patients' data were available our findings could be tested with considerable statistical power.
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Affiliation(s)
- Krishna C Aluri
- Barnett Institute of Chemical and Biological Analysis, Northeastern University, Boston, MA, 02115, USA
- Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts, 02115, United States
| | - Joseph P Salisbury
- Barnett Institute of Chemical and Biological Analysis, Northeastern University, Boston, MA, 02115, USA
- Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts, 02115, United States
| | - Jochen H M Prehn
- Department of Physiology and Medical Physics, SFI Future-Neuro Centre, Royal College of Surgeons in Ireland, Dublin, 2, Ireland
| | - Jeffrey N Agar
- Barnett Institute of Chemical and Biological Analysis, Northeastern University, Boston, MA, 02115, USA.
- Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts, 02115, United States.
- Department of Pharmaceutical Sciences, Northeastern University, 360 Huntington Avenue, Boston, Massachusetts, 02115, United States.
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14
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Different Grp94 components interact transiently with the myocilin olfactomedin domain in vitro to enhance or retard its amyloid aggregation. Sci Rep 2019; 9:12769. [PMID: 31484937 PMCID: PMC6726633 DOI: 10.1038/s41598-019-48751-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2019] [Accepted: 08/07/2019] [Indexed: 01/04/2023] Open
Abstract
The inherited form of open angle glaucoma arises due to a toxic gain-of-function intracellular misfolding event involving a mutated myocilin olfactomedin domain (OLF). Mutant myocilin is recognized by the endoplasmic reticulum (ER)-resident heat shock protein 90 paralog, glucose regulated protein 94 (Grp94), but their co-aggregation precludes mutant myocilin clearance by ER-associated degradation. When the Grp94-mutant myocilin interaction is abrogated by inhibitors or siRNA, mutant myocilin is efficiently degraded. Here we dissected Grp94 into component domains (N, NM, MC) to better understand the molecular factors governing its interaction with OLF. We show that the Grp94 N-terminal nucleotide-binding N domain is responsible for accelerating OLF aggregation in vitro. Upon inhibiting the isolated N domain pharmacologically or removing the Pre-N terminal 57 residues from full-length Grp94, OLF aggregation rates revert to those seen for OLF alone, but only pharmacological inhibition rescues co-aggregation. The Grp94-OLF interaction is below the detection limit of fluorescence polarization measurements, but chemical crosslinking paired with mass spectrometry analyses traps a reproducible interaction between OLF and the Grp94 N domain, as well as between OLF and the Grp94 M domain. The emerging molecular-level picture of quinary interactions between Grp94 and myocilin points to a role for the far N-terminal sequence of the Grp94 N domain and a cleft in the M domain. Our work further supports drug discovery efforts to inhibit these interactions as a strategy to treat myocilin-associated glaucoma.
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15
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Hill SE, Kwon MS, Martin MD, Suntharalingam A, Hazel A, Dickey CA, Gumbart JC, Lieberman RL. Stable calcium-free myocilin olfactomedin domain variants reveal challenges in differentiating between benign and glaucoma-causing mutations. J Biol Chem 2019; 294:12717-12728. [PMID: 31270212 PMCID: PMC6709634 DOI: 10.1074/jbc.ra119.009419] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2019] [Revised: 06/25/2019] [Indexed: 01/07/2023] Open
Abstract
Nonsynonymous gene mutations can be beneficial, neutral, or detrimental to the stability, structure, and biological function of the encoded protein, but the effects of these mutations are often not readily predictable. For example, the β-propeller olfactomedin domain of myocilin (mOLF) exhibits a complex interrelationship among structure(s), stability, and aggregation. Numerous mutations within mOLF are linked to glaucoma; the resulting variants are less stable, aggregation-prone, and sequestered intracellularly, causing cytotoxicity. Here, we report the first stable mOLF variants carrying substitutions in the calcium-binding site that exhibit solution characteristics indistinguishable from those of glaucoma variants. Crystal structures of these stable variants at 1.8-2.0-Å resolution revealed features that we could not predict by molecular dynamics simulations, including loss of loop structure, helix unwinding, and a blade shift. Double mutants that combined a stabilizing substitution and a selected glaucoma-causing single-point mutant rescued in vitro folding and stability defects. In the context of full-length myocilin, secretion of stable single variants was indistinguishable from that of the WT protein, and the double mutants were secreted to varying extents. In summary, our finding that mOLF can tolerate particular substitutions that render the protein stable despite a conformational switch emphasizes the complexities in differentiating between benign and glaucoma-causing variants and provides new insight into the possible biological function of myocilin.
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Affiliation(s)
- Shannon E. Hill
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332
| | - Michelle S. Kwon
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332
| | - Mackenzie D. Martin
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332
| | - Amirthaa Suntharalingam
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, University of South Florida, Tampa, Florida 33613
| | - Anthony Hazel
- School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332
| | - Chad A. Dickey
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, University of South Florida, Tampa, Florida 33613
| | - James C. Gumbart
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332,School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332
| | - Raquel L. Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332, To whom correspondence should be addressed:
School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Dr. NW, Atlanta, GA 30332-0400. E-mail:
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16
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Patterson-Orazem AC, Lieberman RL. Antibodies Used to Detect Glaucoma-Associated Myocilin: More or Less Than Meets the Eye? Invest Ophthalmol Vis Sci 2019; 60:2034-2037. [PMID: 31067323 PMCID: PMC6890424 DOI: 10.1167/iovs.19-26843] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Antibodies are key reagents used in vision research, indeed across biomedical research, but they often do not reveal the whole story about a sample. It is important for researchers to be aware of aspects of antibodies that may affect or limit data interpretation. Federal agencies now require funded grants to demonstrate how they will authenticate reagents used. There is also a push for recombinant antibodies, enabled by phage display technology awarded the 2018 Nobel Prize in Chemistry, which allow for thorough validation and a fixed DNA sequence. Here, we discuss how issues surrounding antibodies are pertinent to detecting myocilin, a protein found in trabecular meshwork and associated with a portion of hereditary glaucoma. Confirmation of myocilin expression in tissues and cell culture has been adopted as validation standard in trabecular meshwork research; thus, a discussion of antibody characteristics and fidelity is critical. Further, based on our basic structural understanding of myocilin architecture and its biophysical aggregation properties, we provide a wish list for the characteristics of next-generation antibody reagents for vision researchers. In the long term, well-characterized antibodies targeting myocilin will enable new insights into its function and involvement in glaucoma pathogenesis.
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Affiliation(s)
- Athéna C Patterson-Orazem
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
| | - Raquel L Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
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17
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Patterson-Orazem AC, Hill SE, Wang Y, Dominic IM, Hall CK, Lieberman RL. Differential Misfolding Properties of Glaucoma-Associated Olfactomedin Domains from Humans and Mice. Biochemistry 2019; 58:1718-1727. [PMID: 30802039 DOI: 10.1021/acs.biochem.8b01309] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Mutations in myocilin, predominantly within its olfactomedin (OLF) domain, are causative for the heritable form of open angle glaucoma in humans. Surprisingly, mice expressing Tyr423His mutant myocilin, corresponding to a severe glaucoma-causing mutation (Tyr437His) in human subjects, exhibit a weak, if any, glaucoma phenotype. To address possible protein-level discrepancies between mouse and human OLFs, which might lead to this outcome, biophysical properties of mouse OLF were characterized for comparison with those of human OLF. The 1.55 Å resolution crystal structure of mouse OLF reveals an asymmetric 5-bladed β-propeller that is nearly indistinguishable from previous structures of human OLF. Wild-type and selected mutant mouse OLFs mirror thermal stabilities of their human OLF counterparts, including characteristic stabilization in the presence of calcium. Mouse OLF forms thioflavin T-positive aggregates with a similar end-point morphology as human OLF, but amyloid aggregation kinetic rates of mouse OLF are faster than human OLF. Simulations and experiments support the interpretation that kinetics of mouse OLF are faster because of a decreased charge repulsion arising from more neutral surface electrostatics. Taken together, phenotypic differences observed in mouse and human studies of mutant myocilin could be a function of aggregation kinetics rates, which would alter the lifetime of putatively toxic protofibrillar intermediates.
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Affiliation(s)
- Athéna C Patterson-Orazem
- School of Chemistry & Biochemistry , Georgia Institute of Technology , Atlanta , Georgia 30332-0400 , United States
| | - Shannon E Hill
- School of Chemistry & Biochemistry , Georgia Institute of Technology , Atlanta , Georgia 30332-0400 , United States
| | - Yiming Wang
- Department of Chemical & Biomolecular Engineering , North Carolina State University , Raleigh , North Carolina 27695-7905 , United States
| | - Iramofu M Dominic
- School of Chemistry & Biochemistry , Georgia Institute of Technology , Atlanta , Georgia 30332-0400 , United States
| | - Carol K Hall
- Department of Chemical & Biomolecular Engineering , North Carolina State University , Raleigh , North Carolina 27695-7905 , United States
| | - Raquel L Lieberman
- School of Chemistry & Biochemistry , Georgia Institute of Technology , Atlanta , Georgia 30332-0400 , United States
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18
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Mouse model of ocular hypertension with retinal ganglion cell degeneration. PLoS One 2019; 14:e0208713. [PMID: 30640920 PMCID: PMC6331128 DOI: 10.1371/journal.pone.0208713] [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: 08/25/2018] [Accepted: 11/22/2018] [Indexed: 11/16/2022] Open
Abstract
Objectives Ocular hypertension is a primary risk factor for glaucoma and results in retinal ganglion cell (RGC) degeneration. Current animal models of glaucoma lack severe RGC cell death as seen in glaucoma, making assessment of physiological mediators of cell death difficult. We developed a modified mouse model of ocular hypertension whereby long-lasting elevation of intraocular pressure (IOP) is achieved, resulting in significant reproducible damage to RGCs. Results In this model, microbeads are mixed with hyaluronic acid and injected into the anterior chamber of C57BL/6J mice. The hyaluronic acid allows for a gradual release of microbeads, resulting in sustained blockage of Schlemm’s canal. IOP elevation was bimodal during the course of the model’s progression. The first peak occurred 1 hours after beads injection, with an IOP value of 44.69 ± 6.00 mmHg, and the second peak occurred 6–12 days post-induction, with an IOP value of 34.91 ± 5.21 mmHg. RGC damage was most severe in the peripheral retina, with a loss of 64.1% compared to that of untreated eyes, while the midperiphery exhibited a 32.4% loss, 4 weeks following disease induction. Conclusions These results suggest that sustained IOP elevation causes more RGC damage in the periphery than in the midperiphery of the retina. This model yields significant and reproducible RGC degeneration.
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19
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Wang H, Li M, Zhang Z, Xue H, Chen X, Ji Y. Physiological function of myocilin and its role in the pathogenesis of glaucoma in the trabecular meshwork (Review). Int J Mol Med 2018; 43:671-681. [PMID: 30483726 PMCID: PMC6317685 DOI: 10.3892/ijmm.2018.3992] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2018] [Accepted: 11/16/2018] [Indexed: 12/26/2022] Open
Abstract
Myocilin is highly expressed in the trabecular meshwork (TM), which plays an important role in the regulation of intraocular pressure (IOP). Myocilin abnormalities may cause dysfunction of the TM, potentially leading to increased IOP. High IOP is a well‑known primary risk factor for glaucoma. Myocilin mutations are common among glaucoma patients, and they are implicated in juvenile‑onset open‑angle glaucoma (JOAG) and adult‑onset primary open‑angle glaucoma (POAG). Aggregation of aberrant mutant myocilins is closely associated with glaucoma pathogenesis. The aim of the present review was to discuss the recent findings regarding the major physiological functions of myocilin, such as intra‑ and extracellular proteolytic processes. We also aimed to discuss the risk factors associated with myocilin and the development of glaucoma, such as misfolded/mutant myocilin, imbalance of myocilin and extracellular proteins, and instability of mutant myocilin associated with temperature. Finally, we further outlined certain issues that are yet to be resolved, which may represent the basis for future studies on the role of myocilin in glaucoma.
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Affiliation(s)
- Hongwei Wang
- Department of Ophthalmology, Jingjiang People's Hospital, Jingjiang, Jiangsu 214500, P.R. China
| | - Mingzhe Li
- Department of Ophthalmology, Shanghai Pudong Hospital, Fudan University Pudong Medical Center, Shanghai 201399, P.R. China
| | - Zhenzhen Zhang
- Department of Ophthalmology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, P.R. China
| | - Haifeng Xue
- Public Health School, Qiqihar Medical University, Qiqihar, Heilongjiang 161006, P.R. China
| | - Xing Chen
- Department of Science and Education, Jingjiang People's Hospital, Jingjiang, Jiangsu 214500, P.R. China
| | - Yong Ji
- Department of General Surgery, Jingjiang People's Hospital, Jingjiang, Jiangsu 214500, P.R. China
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20
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Progress toward development of a proteostasis drug for myocilin-associated glaucoma. Future Med Chem 2018; 10:1391-1393. [PMID: 29788763 DOI: 10.4155/fmc-2018-0073] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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21
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Huard DJE, Crowley VM, Du Y, Cordova RA, Sun Z, Tomlin MO, Dickey CA, Koren J, Blair L, Fu H, Blagg BSJ, Lieberman RL. Trifunctional High-Throughput Screen Identifies Promising Scaffold To Inhibit Grp94 and Treat Myocilin-Associated Glaucoma. ACS Chem Biol 2018; 13:933-941. [PMID: 29402077 PMCID: PMC6195314 DOI: 10.1021/acschembio.7b01083] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Gain-of-function mutations within the olfactomedin (OLF) domain of myocilin result in its toxic intracellular accumulation and hasten the onset of open-angle glaucoma. The absence of myocilin does not cause disease; therefore, strategies aimed at eliminating myocilin could lead to a successful glaucoma treatment. The endoplasmic reticulum Hsp90 paralog Grp94 accelerates OLF aggregation. Knockdown or pharmacological inhibition of Grp94 in cells facilitates clearance of mutant myocilin via a non-proteasomal pathway. Here, we expanded our support for targeting Grp94 over cytosolic paralogs Hsp90α and Hsp90β. We then developed a high-throughput screening assay to identify new chemical matter capable of disrupting the Grp94/OLF interaction. When applied to a blind, focused library of 17 Hsp90 inhibitors, our miniaturized single-read in vitro thioflavin T -based kinetics aggregation assay exclusively identified compounds that target the chaperone N-terminal nucleotide binding site. In follow up studies, one compound (2) decreased the extent of co-aggregation of Grp94 with OLF in a dose-dependent manner in vitro, and enabled clearance of the aggregation-prone full-length myocilin variant I477N in cells without inducing the heat shock response or causing cytotoxicity. Comparison of the co-crystal structure of compound 2 and another non-selective hit in complex with the N-terminal domain of Grp94 reveals a docking mode tailored to Grp94 and explains its selectivity. A new lead compound has been identified, supporting a targeted chemical biology assay approach to develop a protein degradation-based therapy for myocilin-associated glaucoma by selectively inhibiting Grp94.
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Affiliation(s)
| | - Vincent M. Crowley
- Emory Chemical Biology Discovery Center, Department of Pharmacology, Emory University
| | - Yuhong Du
- Department of Medicinal Chemistry, The University of Kansas
| | - Ricardo A. Cordova
- Byrd Alzheimer Institute, Department of Molecular Medicine, University of South Florida
| | - Zheying Sun
- Byrd Alzheimer Institute, Department of Molecular Medicine, University of South Florida
| | - Moya O. Tomlin
- School of Chemistry & Biochemistry, Georgia Institute of Technology
| | - Chad A. Dickey
- Byrd Alzheimer Institute, Department of Molecular Medicine, University of South Florida
| | - John Koren
- Byrd Alzheimer Institute, Department of Molecular Medicine, University of South Florida
| | - Laura Blair
- Byrd Alzheimer Institute, Department of Molecular Medicine, University of South Florida
| | - Haian Fu
- Department of Medicinal Chemistry, The University of Kansas
| | - Brian S. J. Blagg
- Emory Chemical Biology Discovery Center, Department of Pharmacology, Emory University
- Department of Chemistry and Biochemistry, The University of Notre Dame
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22
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Hill SE, Nguyen E, Donegan RK, Patterson-Orazem AC, Hazel A, Gumbart JC, Lieberman RL. Structure and Misfolding of the Flexible Tripartite Coiled-Coil Domain of Glaucoma-Associated Myocilin. Structure 2017; 25:1697-1707.e5. [PMID: 29056483 PMCID: PMC5685557 DOI: 10.1016/j.str.2017.09.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Revised: 08/07/2017] [Accepted: 09/18/2017] [Indexed: 01/15/2023]
Abstract
Glaucoma-associated myocilin is a member of the olfactomedins, a protein family involved in neuronal development and human diseases. Molecular studies of the myocilin N-terminal coiled coil demonstrate a unique tripartite architecture: a Y-shaped parallel dimer-of-dimers with distinct tetramer and dimer regions. The structure of the dimeric C-terminal 7-heptad repeats elucidates an unexpected repeat pattern involving inter-strand stabilization by oppositely charged residues. Molecular dynamics simulations reveal an alternate accessible conformation in which the terminal inter-strand disulfide limits the extent of unfolding and results in a kinked configuration. By inference, full-length myocilin is also branched, with two pairs of C-terminal olfactomedin domains. Selected variants within the N-terminal region alter the apparent quaternary structure of myocilin but do so without compromising stability or causing aggregation. In addition to increasing our structural knowledge of naturally occurring extracellular coiled coils and biomedically important olfactomedins, this work broadens the scope of protein misfolding in the pathogenesis of myocilin-associated glaucoma.
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Affiliation(s)
- Shannon E Hill
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Elaine Nguyen
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Rebecca K Donegan
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | | | - Anthony Hazel
- School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - James C Gumbart
- School of Physics, Georgia Institute of Technology, Atlanta, GA 30332, USA
| | - Raquel L Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA.
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23
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Laber JR, Dear BJ, Martins ML, Jackson DE, DiVenere A, Gollihar JD, Ellington AD, Truskett TM, Johnston KP, Maynard JA. Charge Shielding Prevents Aggregation of Supercharged GFP Variants at High Protein Concentration. Mol Pharm 2017; 14:3269-3280. [PMID: 28870080 DOI: 10.1021/acs.molpharmaceut.7b00322] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Understanding protein stability is central to combatting protein aggregation diseases and developing new protein therapeutics. At the high concentrations often present in biological systems, purified proteins can exhibit undesirable high solution viscosities and poor solubilities mediated by short-range electrostatic and hydrophobic protein-protein interactions. The interplay between protein amino acid sequence, protein structure, and solvent conditions to minimize protein-protein interactions is key to designing well-behaved pharmaceutical proteins. However, theoretical approaches have yet to yield a general framework to address these problems. Here, we analyzed the high concentration behavior of superfolder GFP (sfGFP) and two supercharged sfGFP variants engineered to have formal charges of -18 or +15. Under low cosolute conditions, sfGFP and the -18 variant formed a gel or phase separated at ∼10 mg/mL. Under conditions that screen surface charges, including formulations with high histidine or high NaCl concentrations, all three variants attained concentrations up to 250 mg/mL with moderate viscosities. Moreover, all three variants exhibited very similar viscosity-concentration profiles over this range. This effect was not mimicked by high sugar concentrations that exert excluded-volume effects without shielding charge. Collectively, these data demonstrate that charge shielding neutralizes not only long-range electrostatic interactions but also, surprisingly, short-range electrostatic effects due to surface charge anisotropy. This work shows that supercharged sfGFP behavior under high ionic strength is largely determined by particle geometry, a conclusion that is supported by colloid models and may be applicable to pharmaceutically relevant proteins.
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Affiliation(s)
- Joshua R Laber
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Barton J Dear
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Matheus L Martins
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Devin E Jackson
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Andrea DiVenere
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Jimmy D Gollihar
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Andrew D Ellington
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Thomas M Truskett
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Keith P Johnston
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
| | - Jennifer A Maynard
- Departments of †Chemical Engineering and ‡Molecular Biosciences, University of Texas at Austin , Austin, Texas 78712, United States
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24
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Zadoo S, Nguyen A, Zode G, Hulleman JD. A Novel Luciferase Assay For Sensitively Monitoring Myocilin Variants in Cell Culture. Invest Ophthalmol Vis Sci 2016; 57:1939-50. [PMID: 27092720 PMCID: PMC5110263 DOI: 10.1167/iovs.15-18789] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Purpose Primary open angle glaucoma–associated mutations in myocilin (MYOC) cause protein “nonsecretion,” rendering secreted MYOC difficult to detect using conventional techniques. This study focused on developing and using an assay that can quickly and easily detect mutant MYOC secretion. Methods We fused Gaussia luciferase (eGLuc2) to MYOC variants and expressed the constructs in HEK-293T and NTM-5 cells. Secreted and intracellular levels of MYOC eGLuc2 variants were evaluated by Western blotting and compared to untagged and FLAG-tagged MYOC constructs. Secreted and soluble intracellular MYOC eGLuc2 were measured by a GLuc assay. The secretion of nine additional MYOC mutants was assayed in conditioned media from transfected cells to test the applicability of the assay for monitoring other MYOC variants. Results Myocilin eGLuc2 behaved similarly to untagged and FLAG-tagged MYOC with respect to secretion, soluble intracellular levels, and in response to drug treatment. The GLuc assay could sensitively detect Y437H MYOC secretion 30 minutes after media change. Gaussia luciferase fused variants followed anticipated trends; nonpathogenic variants (D208E, G244V) were secreted at wild-type (WT) levels, whereas predicted disease-causing variants (C245Y, G246R, E300K, Y437H, I477N) demonstrated substantial secretion defects. Secretion defects caused by the C245Y, G246R, and Y437H mutations were partially rescued by permissive growth temperature. Interestingly, however, this increase in secretion was independent of newly synthesized protein. Conclusions Fusion of eGLuc2 to MYOC does not significantly change the behavior of MYOC. This newly developed MYOC reporter system can be used to study engineered MYOC variants and potentially to identify modulators of MYOC secretion and function.
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Affiliation(s)
- Serena Zadoo
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Annie Nguyen
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Gulab Zode
- Department of Cell Biology & Immunology and the North Texas Eye Research Institute, University of North Texas Health Science Center, Fort Worth, Texas, United States
| | - John D Hulleman
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States 3Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas, United States
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25
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Shen WC, Li HY, Chen GC, Chern Y, Tu PH. Mutations in the ubiquitin-binding domain of OPTN/optineurin interfere with autophagy-mediated degradation of misfolded proteins by a dominant-negative mechanism. Autophagy 2016; 11:685-700. [PMID: 25484089 DOI: 10.4161/auto.36098] [Citation(s) in RCA: 118] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
OPTN (optineurin) is an autophagy receptor and mutations in the OPTN gene result in familial glaucoma (E50K) and amyotrophic lateral sclerosis (ALS) (E478G). However, the mechanisms through which mutant OPTN leads to human diseases remain to be characterized. Here, we demonstrated that OPTN colocalized with inclusion bodies (IBs) formed by mutant HTT/huntingtin protein (mHTT) in R6/2 transgenic mice and IBs formed by 81QNmHTT (nuclear form), 109QmHTT (cytoplasmic form) or the truncated form of TARDBP/TDP-43 (TARDBP(ND251)) in Neuro2A cells. This colocalization required the ubiquitin (Ub)-binding domain (UbBD, amino acids 424 to 511) of OPTN. Overexpression of wild-type (WT) OPTN decreased IBs through K63-linked polyubiquitin-mediated autophagy. E50K or 210 to 410Δ (with amino acids 210 to 410 deleted) whose mutation or deletion was outside the UbBD decreased the IBs formed by 109QmHTT or TARDBP(ND251), as was the case with WT OPTN. In contrast, UbBD mutants, including E478G, D474N, UbBDΔ, 411 to 520Δ and 210 to 520Δ, increased accumulation of IBs. UbBD mutants (E478G, UbBDΔ) retained a substantial ability to interact with WT OPTN, and were found to colocalize with polyubiquitinated IBs, which might occur indirectly through their WT partner in a WT-mutant complex. They decreased autophagic flux evidenced by alteration in LC3 level and turnover and in the number of LC3-positive puncta under stresses like starvation or formation of IBs. UbBD mutants exhibited a weakened interaction with MYO6 (myosin VI) and TOM1 (target of myb1 homolog [chicken]), important for autophagosome maturation, in cells or sorted 109QmHtt IBs. Taken together, our data indicated that UbBD mutants acted as dominant-negative traps through the formation of WT-mutant hybrid complexes to compromise the maturation of autophagosomes, which in turn interfered with OPTN-mediated autophagy and clearance of IBs.
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Key Words
- ALS, amyotrophic lateral sclerosis
- Ab, antibody
- BafA1, bafilomycin A1
- CCD, coiled-coil domain
- Ef, FRET efficiency
- FT, filter-trap assay
- HD, Huntington disease
- IBs, inclusion bodies
- IP, immunoprecipitation
- K48, lysine 48
- K63, lysine 63
- LIR, LC3-interacting region
- MYO6, myosin VI
- OPTN, optineurin
- PBS, phosphate-buffered saline
- PFA, paraformaldehyde
- TARDBP/TDP-43
- TARDBP/TDP-43, TAR DNA-binding protein
- TBK1, TANK-binding kinase 1
- TUBA, alpha tubulin
- UPS, ubiquitin-proteasome system
- Ub, ubiquitin B/C/D
- UbBD, ubiquitin-binding domain
- WB, western blot
- WT, wild type
- autophagy
- dominant-negative
- huntingtin
- mHTT, mutant huntingtin
- optineurin
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Affiliation(s)
- Wen-Chuan Shen
- a Taiwan International Graduate Program in Molecular Medicine; National Yang-Ming University and Academia Sinica ; Taipei , Taiwan
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26
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Donegan RK, Lieberman RL. Discovery of Molecular Therapeutics for Glaucoma: Challenges, Successes, and Promising Directions. J Med Chem 2016; 59:788-809. [PMID: 26356532 PMCID: PMC5547565 DOI: 10.1021/acs.jmedchem.5b00828] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Glaucoma, a heterogeneous ocular disorder affecting ∼60 million people worldwide, is characterized by painless neurodegeneration of retinal ganglion cells (RGCs), resulting in irreversible vision loss. Available therapies, which decrease the common causal risk factor of elevated intraocular pressure, delay, but cannot prevent, RGC death and blindness. Notably, it is changes in the anterior segment of the eye, particularly in the drainage of aqueous humor fluid, which are believed to bring about changes in pressure. Thus, it is primarily this region whose properties are manipulated in current and emerging therapies for glaucoma. Here, we focus on the challenges associated with developing treatments, review the available experimental methods to evaluate the therapeutic potential of new drugs, describe the development and evaluation of emerging Rho-kinase inhibitors and adenosine receptor ligands that offer the potential to improve aqueous humor outflow and protect RGCs simultaneously, and present new targets and approaches on the horizon.
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Affiliation(s)
- Rebecca K Donegan
- School of Chemistry and Biochemistry, Georgia Institute of Technology , 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
| | - Raquel L Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology , 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
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27
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Itakura T, Peters DM, Fini ME. Glaucomatous MYOC mutations activate the IL-1/NF-κB inflammatory stress response and the glaucoma marker SELE in trabecular meshwork cells. Mol Vis 2015; 21:1071-84. [PMID: 26396484 PMCID: PMC4575906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2015] [Accepted: 09/15/2015] [Indexed: 11/14/2022] Open
Abstract
PURPOSE Activation of the IL-1/NF-κB inflammatory stress pathway and induction of SELE expression in the trabecular meshwork (TBM) is a marker for high-tension glaucomas of diverse etiology. Pathway activation stimulates aqueous outflow and protects against oxidative stress, but may be damaging in the long-term. MYOC mutations have been causally linked to high-tension forms of primary open angle glaucoma (POAG). This study investigated a possible link between MYOC mutations and activation of the IL-1/NF-κB pathway and expression of SELE. METHODS We constructed MYOC expression vectors with mutations at sites that cause POAG. Mutations (Q368X, Y437H, A427T) were selected to represent proteins with differing POAG-causing potency (Q368X > Y437H > A427T) and intracellular retention behavior (Q368X and Y437H retained, A427T released). The constructs were made in two different kinds of vectors; one a plasmid designed for transient transfection (pCMV6), and one a doxycycline-inducible lentiviral vector (pSLIK) for stable cell transduction. The immortalized human trabecular meshwork line TM-1 was used for all expression studies. Expression of IL1A mRNA was determined by reverse transcription (RT)-PCR, as well as a set of five other genes associated with signaling pathways linked to glaucoma: IL1B and IL6 (NF-κB pathway), TGFB2 and ACTA2 (TGF-β pathway) and FOXO1 (E2F1 apoptotic pathway). An ELISA was used to quantify IL1A protein released into culture media. To quantify intracellular NF-κB activity, we transiently transfected stably transduced cell lines with a luciferase expression vector under control of the IL8 promoter (containing an NF-κB response element). RESULTS Transiently expressed wild-type MYOC was released into cell culture media, whereas mutant MYOCs Q368X and Y437H remained within cells. Both mutant MYOCs activated the IL-1/ NF-κB pathway, significantly stimulating expression of IL1A and IL1B. However Y437H, which causes a severe glaucoma phenotype, was less effective than Q368X, which causes a moderate glaucoma phenotype. In addition, the retained mutants stimulated expression of stress response genes ACTA2 and FOXO1. Unexpectedly, wild-type MYOC significantly decreased expression of IL6 and TGFB2, to approximately half of the control levels, and expression of IL1B and ACTA2 was also slightly decreased. Induction of MYOC mutants Q368X and Y437H in stably transduced cell lines significantly stimulated the level of IL1A protein released into culture media. Once again however, the effect of the severe MYOC mutant Y437H was less than the effect of the moderate MYOC mutant Q368X. In contrast, induced expression of the intracellularly retained mutant MYOC A427T or wild-type MYOC did not change the amount of IL1A protein in culture media. Induction of Y437H MYOC plus IL1A treatment increased NF-κB activity by 25% over IL1A alone. In contrast, induction of Q368X or A427T plus IL1A treatment did not significantly affect NF-κB activity over IL1A alone. However, wild-type MYOC expression inhibited IL1A-stimulated NF-κB activity. We also observed that endogenous MYOC expression was induced by IL1A in TM-1 cells and primary TBM cell cultures. SELE was co-expressed with MYOC in the primary cell lines. CONCLUSIONS These results indicate that POAG-causing MYOC mutants activate the IL-1/NF-κB pathway, with activation levels correlated with intracellular retention of the protein, but not POAG-causing potency. Unexpectedly, it was also discovered that wild-type MYOC inhibits activation of the IL-1/NF-κB pathway, and that activation of the IL-1/NF-κB pathway stimulates expression of MYOC. This is the first evidence that glaucoma-causing MYOC mutants can activate the inflammatory response and that wild-type MYOC has anti-inflammatory activity.
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Affiliation(s)
- Tatsuo Itakura
- USC Institute for Genetic Medicine, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA
| | - Donna M. Peters
- Departments of Pathology & Laboratory Medicine and Ophthalmology & Visual Sciences, University of Wisconsin, Madison, WI
| | - M. Elizabeth Fini
- USC Institute for Genetic Medicine, USC Eye Institute, and Departments of Cell & Neurobiology and Ophthalmology, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA
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Stothert AR, Fontaine SN, Sabbagh JJ, Dickey CA. Targeting the ER-autophagy system in the trabecular meshwork to treat glaucoma. Exp Eye Res 2015; 144:38-45. [PMID: 26302411 DOI: 10.1016/j.exer.2015.08.017] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 07/23/2015] [Accepted: 08/18/2015] [Indexed: 12/19/2022]
Abstract
A major drainage network involved in aqueous humor dynamics is the conventional outflow pathway, which is gated by the trabecular meshwork (TM). The TM acts as a molecular sieve, providing resistance to aqueous outflow, which is responsible for regulating intraocular pressure (IOP). If the TM is damaged, aqueous outflow is impaired, IOP increases and glaucoma can manifest. Mutations in the MYOC gene cause hereditary primary open-angle glaucoma (POAG) by promoting the abnormal amyloidosis of the myocilin protein in the endoplasmic reticulum (ER), leading to ER stress-induced TM cell death. Myocilin accumulation is observed in approximately 70-80% of all glaucoma cases suggesting that environmental or other genetic factors may also promote myocilin toxicity. For example, simply preventing myocilin glycosylation is sufficient to promote its abnormal accretion. These myocilin amyloids are unique as there are no other known pathogenic proteins that accumulate within the ER of TM cells and cause toxicity. Moreover, this pathogenic accumulation only kills TM cells, despite expression of this protein in other cell types, suggesting that another modifier exclusive to the TM participates in the proteotoxicity of myocilin. ER autophagy (reticulophagy) is one of the pathways essential for myocilin clearance that can be impacted dramatically by aging and other environmental factors such as nutrition. This review will discuss the link between myocilin and autophagy, evaluating the role of this degradation pathway in glaucoma as well as its potential as a therapeutic target.
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Affiliation(s)
- Andrew R Stothert
- Department of Molecular Medicine, Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA
| | - Sarah N Fontaine
- Department of Molecular Medicine, Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA
| | - Jonathan J Sabbagh
- Department of Molecular Medicine, Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA
| | - Chad A Dickey
- Department of Molecular Medicine, Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA.
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29
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Hill SE, Donegan RK, Nguyen E, Desai TM, Lieberman RL. Molecular Details of Olfactomedin Domains Provide Pathway to Structure-Function Studies. PLoS One 2015; 10:e0130888. [PMID: 26121352 PMCID: PMC4488277 DOI: 10.1371/journal.pone.0130888] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Accepted: 05/26/2015] [Indexed: 11/18/2022] Open
Abstract
Olfactomedin (OLF) domains are found within extracellular, multidomain proteins in numerous tissues of multicellular organisms. Even though these proteins have been implicated in human disorders ranging from cancers to attention deficit disorder to glaucoma, little is known about their structure(s) and function(s). Here we biophysically, biochemically, and structurally characterize OLF domains from H. sapiens olfactomedin-1 (npoh-OLF, also called noelin, pancortin, OLFM1, and hOlfA), and M. musculus gliomedin (glio-OLF, also called collomin, collmin, and CRG-L2), and compare them with available structures of myocilin (myoc-OLF) recently reported by us and R. norvegicus glio-OLF and M. musculus latrophilin-3 (lat3-OLF) by others. Although the five-bladed β-propeller architecture remains unchanged, numerous physicochemical characteristics differ among these OLF domains. First, npoh-OLF and glio-OLF exhibit prominent, yet distinct, positive surface charges and copurify with polynucleotides. Second, whereas npoh-OLF and myoc-OLF exhibit thermal stabilities typical of human proteins near 55°C, and most myoc-OLF variants are destabilized and highly prone to aggregation, glio-OLF is nearly 20°C more stable and significantly more resistant to chemical denaturation. Phylogenetically, glio-OLF is most similar to primitive OLFs, and structurally, glio-OLF is missing distinguishing features seen in OLFs such as the disulfide bond formed by N- and C- terminal cysteines, the sequestered Ca2+ ion within the propeller central hydrophilic cavity, and a key loop-stabilizing cation-π interaction on the top face of npoh-OLF and myoc-OLF. While deciphering the explicit biological functions, ligands, and binding partners for OLF domains will likely continue to be a challenging long-term experimental pursuit, we used structural insights gained here to generate a new antibody selective for myoc-OLF over npoh-OLF and glio-OLF as a first step in overcoming the impasse in detailed functional characterization of these biomedically important protein domains.
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Affiliation(s)
- Shannon E. Hill
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Rebecca K. Donegan
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Elaine Nguyen
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Tanay M. Desai
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Raquel L. Lieberman
- School of Chemistry & Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States of America
- * E-mail:
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30
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Donegan RK, Hill SE, Freeman DM, Nguyen E, Orwig SD, Turnage KC, Lieberman RL. Structural basis for misfolding in myocilin-associated glaucoma. Hum Mol Genet 2014; 24:2111-24. [PMID: 25524706 DOI: 10.1093/hmg/ddu730] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Olfactomedin (OLF) domain-containing proteins play roles in fundamental cellular processes and have been implicated in disorders ranging from glaucoma, cancers and inflammatory bowel disorder, to attention deficit disorder and childhood obesity. We solved crystal structures of the OLF domain of myocilin (myoc-OLF), the best studied such domain to date. Mutations in myoc-OLF are causative in the autosomal dominant inherited form of the prevalent ocular disorder glaucoma. The structures reveal a new addition to the small family of five-bladed β-propellers. Propellers are most well known for their ability to act as hubs for protein-protein interactions, a function that seems most likely for myoc-OLF, but they can also act as enzymes. A calcium ion, sodium ion and glycerol molecule were identified within a central hydrophilic cavity that is accessible via movements of surface loop residues. By mapping familial glaucoma-associated lesions onto the myoc-OLF structure, three regions sensitive to aggregation have been identified, with direct applicability to differentiating between neutral and disease-causing non-synonymous mutations documented in the human population worldwide. Evolutionary analysis mapped onto the myoc-OLF structure reveals conserved and divergent regions for possible overlapping and distinctive functional protein-protein or protein-ligand interactions across the broader OLF domain family. While deciphering the specific normal biological functions, ligands and binding partners for OLF domains will likely continue to be a challenging long-term experimental pursuit, atomic detail structural knowledge of myoc-OLF is a valuable guide for understanding the implications of glaucoma-associated mutations and will help focus future studies of this biomedically important domain family.
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Affiliation(s)
- Rebecca K Donegan
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
| | - Shannon E Hill
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
| | - Dana M Freeman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
| | - Elaine Nguyen
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
| | - Susan D Orwig
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
| | - Katherine C Turnage
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
| | - Raquel L Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA
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31
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Han H, Kursula P. The olfactomedin domain from gliomedin is a β-propeller with unique structural properties. J Biol Chem 2014; 290:3612-21. [PMID: 25525261 DOI: 10.1074/jbc.m114.627547] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
All members of the olfactomedin (OLF) family have a conserved extracellular OLF domain, for which a structure has not been available. We present here the crystal structure of the OLF domain from gliomedin. Gliomedin is a protein expressed by Schwann cells in peripheral nerves, important for the formation of the nodes of Ranvier. Gliomedin interacts with neuronal cell adhesion molecules, such as neurofascin, but the structural details of the interaction are not known. The structure of the OLF domain presents a five-bladed β-propeller fold with unusual geometric properties. The symmetry of the structure is not 5-fold, but rather reveals a twisted arrangement. The conserved top face of the gliomedin OLF domain is likely to be important for binding to neuronal ligands. Our results provide a structural basis for the functions of gliomedin in Schwann cells, enable the understanding of the role of the gliomedin OLF domain in autoimmune neuropathies, and unravel the locations of human disease-causing mutations in other OLF family members, including myocilin.
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Affiliation(s)
- Huijong Han
- From the Faculty of Biochemistry and Molecular Medicine and Biocenter Oulu, University of Oulu, 90014 Oulu, Finland, the German Electron Synchrotron (DESY), 22607 Hamburg, Germany, and
| | - Petri Kursula
- From the Faculty of Biochemistry and Molecular Medicine and Biocenter Oulu, University of Oulu, 90014 Oulu, Finland, the German Electron Synchrotron (DESY), 22607 Hamburg, Germany, and the Department of Biomedicine, University of Bergen, N-5020 Bergen, Norway
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Williams SEI, Carmichael TR, Wainstein T, Hobbs A, Ramsay M. MYOCMutations in Black South African Patients with Primary Open-angle Glaucoma: Genetic Testing and Cascade Screening. Ophthalmic Genet 2014; 36:31-8. [DOI: 10.3109/13816810.2014.972520] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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33
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Stothert AR, Suntharalingam A, Huard DJE, Fontaine SN, Crowley VM, Mishra S, Blagg BSJ, Lieberman RL, Dickey CA. Exploiting the interaction between Grp94 and aggregated myocilin to treat glaucoma. Hum Mol Genet 2014; 23:6470-80. [PMID: 25027323 DOI: 10.1093/hmg/ddu367] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Gain-of-function mutations in the olfactomedin domain of the MYOC gene facilitate the toxic accumulation of amyloid-containing myocilin aggregates, hastening the onset of the prevalent ocular disorder primary open-angle glaucoma. Aggregation of wild-type myocilin has been reported in other glaucoma subtypes, suggesting broader relevance of misfolded myocilin across the disease spectrum, but the absence of myocilin does not cause disease. Thus, strategies aimed at eliminating myocilin could be therapeutically relevant for glaucoma. Here, a novel and selective Grp94 inhibitor reduced the levels of several mutant myocilin proteins as well as wild-type myocilin when forced to misfold in cells. This inhibitor rescued mutant myocilin toxicity in primary human trabecular meshwork cells. Mechanistically, in vitro kinetics studies demonstrate that Grp94 recognizes on-pathway aggregates of the myocilin olfactomedin domain (myoc-OLF), accelerates rates of aggregation and co-precipitates with myoc-OLF. These results indicate that aberrant myocilin quaternary structure drives Grp94 recognition, rather than peptide motifs exposed by unfolded protein. Inhibition of Grp94 ameliorates the effects of Grp94-accelerated myoc-OLF aggregation, and Grp94 remains in solution. In cells, when wild-type myocilin is driven to misfold and aggregate, it becomes a client of Grp94 and sensitive to Grp94 inhibition. Taken together, the interaction of Grp94 with myocilin aggregates can be manipulated by cellular environment and genetics; this process can be exploited with Grp94 inhibitors to promote the clearance of toxic forms of myocilin.
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Affiliation(s)
- Andrew R Stothert
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA
| | - Amirthaa Suntharalingam
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA
| | - Dustin J E Huard
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA and
| | - Sarah N Fontaine
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA
| | - Vincent M Crowley
- Department of Medicinal Chemistry, University of Kansas, Lawrence, KS 66049, USA
| | - Sanket Mishra
- Department of Medicinal Chemistry, University of Kansas, Lawrence, KS 66049, USA
| | - Brian S J Blagg
- Department of Medicinal Chemistry, University of Kansas, Lawrence, KS 66049, USA
| | - Raquel L Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA and
| | - Chad A Dickey
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA,
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Wu Y, Chen W, Guo M, He Q, Hu Y. Effects of transforming growth factor-β2 on myocilin expression and secretion in human primary cultured trabecular meshwork cells. INTERNATIONAL JOURNAL OF CLINICAL AND EXPERIMENTAL PATHOLOGY 2014; 7:4827-4836. [PMID: 25197353 PMCID: PMC4152043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 07/23/2014] [Indexed: 06/03/2023]
Abstract
High intraocular pressure (IOP) is a risk factor for primary open-angle glaucoma (POAG). The trabecular meshwork (TM), a reticular tissue in the outflow passage of the aqueous humor (AH), is a major contributor to intraocular outflow resistance. High levels of myocilin (MYOC), which is expressed in the TM, are associated with high IOP. Furthermore, transforming growth factor-β2 (TGF-β2) concentrations in human AH are significantly elevated in POAG patients. This study was designed to investigate the effects of TGF-β2 on MYOC expression and secretion in human primary cultured TM cells. Primary cultured human TM cells were treated with 0 (control group), 1, 10, and 100 ng/mL TGF-β2 for 12, 24, or 48 h. MYOC mRNA and protein expressions in TM cells and protein secretion in conditioned media were analyzed by semi-quantitative RT-PCR, Western blotting, and enzyme-linked immunosorbent assays (ELISA), respectively. TM cells treated with 1, 10, and, 100 ng/mL TGF-β2 for 48 h showed higher MYOC mRNA and protein expressions than those in the control group (0 ng/mL TGF-β2) (all P < 0.05). Treatment with TGF-β2 for 48 h also induced MYOC secretion in conditioned media in a dose-dependent manner (0 ng/mL: 7.107±1.163 pg/ml; 1 ng/mL: 7.879±1.894 pg/ml; 10 ng/mL: 8.063±1.181 pg/ml; 100 ng/mL: 8.902±0.699 pg/ml; all P < 0.05). In Conclusion, TGF-β2 induced MYOC expression and secretion in human primary cultured TM cells. Further investigations are required to confirm the involvement of these two factors in POAG pathogenesis.
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Affiliation(s)
- Yuyu Wu
- Department of Ophthalmology, The Second Affiliated Hospital of Fujian Medical University Quanzhou, China
| | - Wanzhu Chen
- Department of Ophthalmology, The Second Affiliated Hospital of Fujian Medical University Quanzhou, China
| | - Maosheng Guo
- Department of Ophthalmology, The Second Affiliated Hospital of Fujian Medical University Quanzhou, China
| | - Qin He
- Department of Ophthalmology, The Second Affiliated Hospital of Fujian Medical University Quanzhou, China
| | - Yan Hu
- Department of Ophthalmology, The Second Affiliated Hospital of Fujian Medical University Quanzhou, China
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35
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Orwig SD, Chi PV, Du Y, Hill SE, Cavitt MA, Suntharalingam A, Turnage KC, Dickey CA, France S, Fu H, Lieberman RL. Ligands for glaucoma-associated myocilin discovered by a generic binding assay. ACS Chem Biol 2014; 9:517-25. [PMID: 24279319 DOI: 10.1021/cb4007776] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Mutations in the olfactomedin domain of myocilin (myoc-OLF) are the strongest link to inherited primary open angle glaucoma. In this recently identified protein misfolding disorder, aggregation-prone disease variants of myocilin hasten glaucoma-associated elevation of intraocular pressure, leading to vision loss. Despite its well-documented pathogenic role, myocilin remains a domain of unknown structure or function. Here we report the first small-molecule ligands that bind to the native state of myoc-OLF. To discover these molecules, we designed a general label-free, mix-and-measure, high throughput chemical assay for restabilization (CARS), which is likely readily adaptable to discover ligands for other proteins. Of the 14 hit molecules identified from screening myoc-OLF against the Sigma-Aldrich Library of Pharmacologically Active Compounds using CARS, surface plasmon resonance binding studies reveal three are stoichiometric ligand scaffolds with low micromolar affinity. Two compounds, GW5074 and apigenin, inhibit myoc-OLF amyloid formation in vitro. Structure-activity relationship-based soluble derivatives reduce aggregation in vitro as well as enhance secretion of full-length mutant myocilin in a cell culture model. Our compounds set the stage for a new chemical probe approach to clarify the biological function of wild-type myocilin and represent lead therapeutic compounds for diminishing intracellular sequestration of toxic mutant myocilin.
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Affiliation(s)
- Susan D. Orwig
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
| | - Pamela V. Chi
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
| | - Yuhong Du
- Department
of Pharmacology, Emory University School of Medicine, 1510 Clifton
Road, Atlanta, Georgia 30322, United States
| | - Shannon E. Hill
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
| | - Marchello A. Cavitt
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
| | - Amrithaa Suntharalingam
- Department
of Molecular Medicine and Byrd Alzheimer’s Research Institute, University of South Florida, 4001 E. Fletcher Ave. Tampa, Florida 33613, United States
| | - Katherine C. Turnage
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
| | - Chad A. Dickey
- Department
of Molecular Medicine and Byrd Alzheimer’s Research Institute, University of South Florida, 4001 E. Fletcher Ave. Tampa, Florida 33613, United States
| | - Stefan France
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
| | - Haian Fu
- Department
of Pharmacology, Emory University School of Medicine, 1510 Clifton
Road, Atlanta, Georgia 30322, United States
| | - Raquel L. Lieberman
- School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive NW, Atlanta, Georgia 30332-0400, United States
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Li CM, Zhang YH, Ye RH, Yi CX, Zhong YM, Cao D, Liu X. Anticipation, anti-glaucoma drug treatment response and phenotype of a Chinese family with glaucoma caused by the Pro370Leu myocilin mutation. Int J Ophthalmol 2014; 7:44-50. [PMID: 24634862 DOI: 10.3980/j.issn.2222-3959.2014.01.08] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Accepted: 11/25/2013] [Indexed: 11/02/2022] Open
Abstract
AIM To describe the anticipation and anti-glaucoma drugs response of a Chinese family with juvenile-onset open angle glaucoma (JOAG) caused by the Pro370Leu myocilin (MYOC) mutation. METHODS Fifteen members of a three-generation Chinese family with JOAG were recruited to this study. They all underwent ophthalmic common examinations. Patients suspected to have JOAG got an assessment of visual field and optical coherence tomography. Intraocular pressures (IOPs) of four patients were measured at 8, 10, 12, 14, 17 o'clock respectively after using anti-glaucoma drugs. Mutation screening of all MYOC gene coding exons of the participants was performed by using direct sequencing of PCR products. RESULTS Clinical examinations and pedigree analysis revealed eight family members were suffered from JOAG. Apparent genetics anticipation phenomenon was observed in this family. Their clinical features included elevated IOP of 35-55mmHg, loss of visual field, thinning of retinal nerve fiber layer, and glaucomatous optic disc damage. Noticeably, their intraocular pressure levels could be controlled within normal range at 8 and 10 o'clock by anti-glaucoma drugs, but their IOPs would elevate >21mmHg after 12 o'clock. Seven patients received trabeculectomy produced thin-walled, pale, and saccate filtering blebs maintaining lower intraocular pressure efficiently. Mutation screening indentified a heterozygous C→T missense mutation in the MYOC gene at position 1 109 in exon 3, corresponding to a substitution of a highly conserved proline to leucine at codon 370 in the olfactomedin domain of MYOC. CONCLUSION The clinical characteristics of JOAG in this family were 1) genetics anticipation; 2) high IOP; 3) temporay response to anti-glaucoma drugs; 4) filtering surgery produced thin-walled and saccate filtering blebs, helping maintain lower IOP.
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Affiliation(s)
- Chun-Mei Li
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Yue-Hong Zhang
- First Municipal People's Hospital of Guangzhou, Guangzhou 510060, Guangdong Province, China
| | - Rong-Hua Ye
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Chang-Xian Yi
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Yi-Min Zhong
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Dan Cao
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
| | - Xing Liu
- State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou 510060, Guangdong Province, China
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Egorov VV, Grudinina NA, Lebedev DV, Shaldzhyan AA, Slita AV, Sirotkin AK, Vasin AV, Shavlovsky MM. Amyloidogenic peptide homologous to fragment 129-148 of human myocilin. Prion 2014; 7:248-52. [PMID: 23764838 DOI: 10.4161/pri.24239] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Myocilin is a protein with a molecular weight near 50 kDa. It is expressed in almost all organs and tissues. We showed that the peptide DQLETQTRELETAYSNLLRD corresponding to N-terminal Leucine zipper motif (LZM) of the protein is able to form amyloid-like fibrils. The possible role of this motif in myocilin aggregation is discussed.
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Affiliation(s)
- Vladimir V Egorov
- Research Institute of Influenza, Ministry of Healthcare of the Russian Federation, St. Petersburg, Russia.
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38
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Hill SE, Donegan RK, Lieberman RL. The glaucoma-associated olfactomedin domain of myocilin forms polymorphic fibrils that are constrained by partial unfolding and peptide sequence. J Mol Biol 2013; 426:921-35. [PMID: 24333014 DOI: 10.1016/j.jmb.2013.12.002] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Revised: 11/06/2013] [Accepted: 12/02/2013] [Indexed: 12/26/2022]
Abstract
The glaucoma-associated olfactomedin domain of myocilin (myoc-OLF) is a recent addition to the growing list of disease-associated amyloidogenic proteins. Inherited, disease-causing myocilin variants aggregate intracellularly instead of being secreted to the trabecular meshwork, which is a scenario toxic to trabecular meshwork cells and leads to early onset of ocular hypertension, the major risk factor for glaucoma. Here we systematically structurally and biophysically dissected myoc-OLF to better understand its amyloidogenesis. Under mildly destabilizing conditions, wild-type myoc-OLF adopts non-native structures that readily fibrillize when incubated at a temperature just below the transition for tertiary unfolding. With buffers at physiological pH, two main endpoint fibril morphologies are observed: (a) straight fibrils common to many amyloids and (b) unique micron-length, ~300 nm or larger diameter, species that lasso oligomers, which also exhibit classical spectroscopic amyloid signatures. Three disease-causing variants investigated herein exhibit non-native tertiary structures under physiological conditions, leading to a variety of growth rates and a fibril morphologies. In particular, the well-documented D380A variant, which lacks calcium, forms large circular fibrils. Two amyloid-forming peptide stretches have been identified, one for each of the main fibril morphologies observed. Our study places myoc-OLF within the larger landscape of the amylome and provides insight into the diversity of myoc-OLF aggregation that plays a role in glaucoma pathogenesis.
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Affiliation(s)
- Shannon E Hill
- School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive Northwest, Atlanta, GA 30332-0400, USA
| | - Rebecca K Donegan
- School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive Northwest, Atlanta, GA 30332-0400, USA
| | - Raquel L Lieberman
- School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive Northwest, Atlanta, GA 30332-0400, USA.
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39
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New direction for glaucoma therapeutics: focus on the olfactomedin domain of myocilin. Future Med Chem 2013. [PMID: 23190098 DOI: 10.4155/fmc.12.132] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
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40
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Kuchtey J, Chowdhury UR, Uptegraft CC, Fautsch MP, Kuchtey RW. A de novo MYOC mutation detected in juvenile open angle glaucoma associated with reduced myocilin protein in aqueous humor. Eur J Med Genet 2013; 56:292-6. [PMID: 23517641 DOI: 10.1016/j.ejmg.2013.03.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2012] [Accepted: 03/10/2013] [Indexed: 10/27/2022]
Abstract
MYOC mutations were originally identified in patients with juvenile open angle glaucoma (JOAG). Cell culture and mouse studies suggest that MYOC mutations cause glaucoma through a dominant-negative effect on myocilin protein secretion. We tested this hypothesis with patient samples in this study. Glaucoma and control patients underwent complete ocular examination. DNA samples from glaucoma patients, unaffected relatives and controls were used for DNA sequencing of MYOC. Aqueous humor (AH) samples from glaucoma and control patients were obtained at the time of surgery. Myocilin protein in AH was detected by quantitative Western blot analysis. A de novo Val251Ala mutation of MYOC was found to segregate with disease in a family with autosomal dominant JOAG. Myocilin protein was detected in all control AH samples but was nearly undetectable in AH samples from a patient heterozygous for the Val251Ala mutation. Our results using human patient samples are consistent with a dominant-negative effect of pathogenic MYOC mutations on myocilin secretion.
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Affiliation(s)
- John Kuchtey
- Vanderbilt Eye Institute, Vanderbilt University, 2311 Pierce Avenue, Nashville, TN 37232, USA.
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41
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Donegan RK, Hill SE, Turnage KC, Orwig SD, Lieberman RL. The glaucoma-associated olfactomedin domain of myocilin is a novel calcium binding protein. J Biol Chem 2012; 287:43370-7. [PMID: 23129764 DOI: 10.1074/jbc.m112.408906] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Myocilin is a protein found in the trabecular meshwork extracellular matrix tissue of the eye that plays a role in regulating intraocular pressure. Both wild-type and certain myocilin variants containing mutations in the olfactomedin (OLF) domain are linked to the optic neuropathy glaucoma. Because calcium ions are important biological cofactors that play numerous roles in extracellular matrix proteins, we examined the calcium binding properties of the myocilin OLF domain (myoc-OLF). Our study reveals an unprecedented high affinity calcium binding site within myoc-OLF. The calcium ion remains bound to wild-type OLF at neutral and acidic pH. A glaucoma-causing OLF variant, myoc-OLF(D380A), is calcium-depleted. Key differences in secondary and tertiary structure between myoc-OLF(D380A) and wild-type myoc-OLF, as well as limited access to chelators, indicate that the calcium binding site is largely buried in the interior of the protein. Analysis of six conserved aspartate or glutamate residues and an additional 18 disease-causing variants revealed two other candidate residues that may be involved in calcium coordination. Our finding expands our knowledge of calcium binding in extracellular matrix proteins; provides new clues into domain structure, function, and pathogenesis for myocilin; and offers insights into highly conserved, biomedically relevant OLF domains.
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Affiliation(s)
- Rebecca K Donegan
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, USA
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42
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Suntharalingam A, Abisambra JF, O'Leary JC, Koren J, Zhang B, Joe MK, Blair LJ, Hill SE, Jinwal UK, Cockman M, Duerfeldt AS, Tomarev S, Blagg BSJ, Lieberman RL, Dickey CA. Glucose-regulated protein 94 triage of mutant myocilin through endoplasmic reticulum-associated degradation subverts a more efficient autophagic clearance mechanism. J Biol Chem 2012; 287:40661-9. [PMID: 23035116 DOI: 10.1074/jbc.m112.384800] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND Mutant myocilin accumulates in the endoplasmic reticulum for unknown reasons. RESULTS Glucose-regulated protein (Grp) 94 depletion reduces mutant myocilin by engaging autophagy. CONCLUSION Grp94 triages mutant myocilin through ER-associated degradation, subverting autophagy. SIGNIFICANCE Treating glaucoma could be possible by inhibiting Grp94 and reducing its novel client, mutant myocilin. Clearance of misfolded proteins in the endoplasmic reticulum (ER) is traditionally handled by ER-associated degradation (ERAD), a process that requires retro-translocation and ubiquitination mediated by a luminal chaperone network. Here we investigated whether the secreted, glaucoma-associated protein myocilin was processed by this pathway. Myocilin is typically transported through the ER/Golgi network, but inherited mutations in myocilin lead to its misfolding and aggregation within trabecular meshwork cells, and ultimately, ER stress-induced cell death. Using targeted knockdown strategies, we determined that glucose-regulated protein 94 (Grp94), the ER equivalent of heat shock protein 90 (Hsp90), specifically recognizes mutant myocilin, triaging it through ERAD. The addition of mutant myocilin to the short list of Grp94 clients strengthens the hypothesis that β-strand secondary structure drives client association with Grp94. Interestingly, the ERAD pathway is incapable of efficiently handling the removal of mutant myocilin, but when Grp94 is depleted, degradation of mutant myocilin is shunted away from ERAD toward a more robust clearance pathway for aggregation-prone proteins, the autophagy system. Thus ERAD inefficiency for distinct aggregation-prone proteins can be subverted by manipulating ER chaperones, leading to more effective clearance by the autophagic/lysosomal pathway. General Hsp90 inhibitors and a selective Grp94 inhibitor also facilitate clearance of mutant myocilin, suggesting that therapeutic approaches aimed at inhibiting Grp94 could be beneficial for patients suffering from some cases of myocilin glaucoma.
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Affiliation(s)
- Amirthaa Suntharalingam
- Department of Molecular Medicine and Byrd Alzheimer's Research Institute, University of South Florida, Tampa, FL 33613, USA
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Orwig SD, Perry CW, Kim LY, Turnage KC, Zhang R, Vollrath D, Schmidt-Krey I, Lieberman RL. Amyloid fibril formation by the glaucoma-associated olfactomedin domain of myocilin. J Mol Biol 2011; 421:242-55. [PMID: 22197377 DOI: 10.1016/j.jmb.2011.12.016] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2011] [Revised: 12/02/2011] [Accepted: 12/07/2011] [Indexed: 12/30/2022]
Abstract
Myocilin is a protein found in the extracellular matrix of trabecular meshwork tissue, the anatomical region of the eye involved in regulating intraocular pressure. Wild-type (WT) myocilin has been associated with steroid-induced glaucoma, and variants of myocilin have been linked to early-onset inherited glaucoma. Elevated levels and aggregation of myocilin hasten increased intraocular pressure and glaucoma-characteristic vision loss due to irreversible damage to the optic nerve. In spite of reports on the intracellular accumulation of mutant and WT myocilin in vitro, cell culture, and model organisms, these aggregates have not been structurally characterized. In this work, we provide biophysical evidence for the hallmarks of amyloid fibrils in aggregated forms of WT and mutant myocilin localized to the C-terminal olfactomedin (OLF) domain. These fibrils are grown under a variety of conditions in a nucleation-dependent and self-propagating manner. Protofibrillar oligomers and mature amyloid fibrils are observed in vitro. Full-length mutant myocilin expressed in mammalian cells forms intracellular amyloid-containing aggregates as well. Taken together, this work provides new insights into and raises new questions about the molecular properties of the highly conserved OLF domain, and suggests a novel protein-based hypothesis for glaucoma pathogenesis for further testing in a clinical setting.
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Affiliation(s)
- Susan D Orwig
- School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA
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