1
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Liu H, Ghosh S, Vaidya T, Bammidi S, Huang C, Shang P, Nair AP, Chowdhury O, Stepicheva NA, Strizhakova A, Hose S, Mitrousis N, Gadde SG, Mb T, Strassburger P, Widmer G, Lad EM, Fort PE, Sahel JA, Zigler JS, Sethu S, Westenskow PD, Proia AD, Sodhi A, Ghosh A, Feenstra D, Sinha D. Activated cGAS/STING signaling elicits endothelial cell senescence in early diabetic retinopathy. JCI Insight 2023; 8:e168945. [PMID: 37345657 PMCID: PMC10371250 DOI: 10.1172/jci.insight.168945] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Accepted: 05/12/2023] [Indexed: 06/23/2023] Open
Abstract
Diabetic retinopathy (DR) is a leading cause of blindness in working-age adults and remains an important public health issue worldwide. Here we demonstrate that the expression of stimulator of interferon genes (STING) is increased in patients with DR and animal models of diabetic eye disease. STING has been previously shown to regulate cell senescence and inflammation, key contributors to the development and progression of DR. To investigate the mechanism whereby STING contributes to the pathogenesis of DR, diabetes was induced in STING-KO mice and STINGGT (loss-of-function mutation) mice, and molecular alterations and pathological changes in the retina were characterized. We report that retinal endothelial cell senescence, inflammation, and capillary degeneration were all inhibited in STING-KO diabetic mice; these observations were independently corroborated in STINGGT mice. These protective effects resulted from the reduction in TBK1, IRF3, and NF-κB phosphorylation in the absence of STING. Collectively, our results suggest that targeting STING may be an effective therapy for the early prevention and treatment of DR.
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Affiliation(s)
- Haitao Liu
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Sayan Ghosh
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Tanuja Vaidya
- GROW Laboratory, Narayana Nethralaya Foundation, Bengaluru, India
| | - Sridhar Bammidi
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Chao Huang
- Pharma Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., Basel, Switzerland
| | - Peng Shang
- Doheny Eye Institute, Los Angeles, California, USA
| | | | - Olivia Chowdhury
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Nadezda A Stepicheva
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Anastasia Strizhakova
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Stacey Hose
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Nikolaos Mitrousis
- Pharma Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., Basel, Switzerland
| | | | - Thirumalesh Mb
- GROW Laboratory, Narayana Nethralaya Foundation, Bengaluru, India
| | - Pamela Strassburger
- Pharma Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., Basel, Switzerland
| | - Gabriella Widmer
- Pharma Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., Basel, Switzerland
| | - Eleonora M Lad
- Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina, USA
| | - Patrice E Fort
- Kellogg Eye Center, University of Michigan School of Medicine, Ann Arbor, Michigan, USA
| | - José-Alain Sahel
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
- Institut De La Vision, INSERM, CNRS, Sorbonne Université, Paris, France
| | - J Samuel Zigler
- Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | | | - Peter D Westenskow
- Pharma Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., Basel, Switzerland
| | - Alan D Proia
- Department of Pathology, Duke University Medical Center, Durham, North Carolina, USA
- Department of Pathology, Campbell University Jerry M. Wallace School of Osteopathic Medicine, Lillington, North Carolina, USA
| | - Akrit Sodhi
- Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Arkasubhra Ghosh
- GROW Laboratory, Narayana Nethralaya Foundation, Bengaluru, India
| | - Derrick Feenstra
- Pharma Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., Basel, Switzerland
| | - Debasish Sinha
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
- Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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2
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Torm MEW, Dorweiler TF, Fickweiler W, Levine SR, Fort PE, Sun JK, Gardner TW. Frontiers in diabetic retinal disease. J Diabetes Complications 2023; 37:108386. [PMID: 36608490 PMCID: PMC10350338 DOI: 10.1016/j.jdiacomp.2022.108386] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Revised: 11/22/2022] [Accepted: 12/16/2022] [Indexed: 12/24/2022]
Abstract
Diabetic retinal disease (DRD) remains a leading cause of vision loss and blindness globally. Although treatments can be effective when given at vision-threatening stages of DRD, there is a lack of knowledge about the earliest mechanisms leading to the development of clinically evident DRD. Recent advances in retinal imaging methods for patients with diabetes allow a more precise and granular characterization of the different stages of DRD than is provided by the classic Diabetic Retinopathy Severity Scale based on fundus photographs. In addition, recent clinical studies have yielded more information on how to adjust blood glucose levels, lipid levels and blood pressure to minimize the risk of DRD. Given the incomplete success of current therapies, there is a critical need for better understanding of the mechanisms underlying DRD and novel treatment targets that address the entire neurovascular retina. Moreover, the causes for interindividual variability in the development of DRD in patients with similar glycemic history and other metabolic factors are not yet clarified either. Finally, greater focus on patients' experience with visual disabilities and treatment effects should be addressed in research in this field.
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Affiliation(s)
- Marie E Wistrup Torm
- Department of Ophthalmology, Rigshospitalet, Glostrup, Denmark; Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Tim F Dorweiler
- Department of Physiology, Michigan State University, East Lansing, MI, USA
| | - Ward Fickweiler
- Beetham Eye Institute, Joslin Diabetes Center, Boston, MA, USA; Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - S Robert Levine
- Mary Tyler Moore and S. Robert Levine, M.D. Charitable Foundation, Greenwich, CT, USA
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, MI, USA
| | - Jennifer K Sun
- Beetham Eye Institute, Joslin Diabetes Center, Boston, MA, USA; Department of Ophthalmology, Harvard Medical School, Boston, MA, USA
| | - Thomas W Gardner
- Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, MI, USA.
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3
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Liu H, Stepicheva NA, Ghosh S, Shang P, Chowdhury O, Daley RA, Yazdankhah M, Gupta U, Hose SL, Valapala M, Fitting CS, Strizhakova A, Shan Y, Feenstra D, Sahel JA, Jayagopal A, Handa JT, Zigler JS, Fort PE, Sodhi A, Sinha D. Reducing Akt2 in retinal pigment epithelial cells causes a compensatory increase in Akt1 and attenuates diabetic retinopathy. Nat Commun 2022; 13:6045. [PMID: 36229454 PMCID: PMC9561713 DOI: 10.1038/s41467-022-33773-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Accepted: 10/03/2022] [Indexed: 01/14/2023] Open
Abstract
The retinal pigment epithelium (RPE) plays an important role in the development of diabetic retinopathy (DR), a leading cause of blindness worldwide. Here we set out to explore the role of Akt2 signaling-integral to both RPE homeostasis and glucose metabolism-to DR. Using human tissue and genetically manipulated mice (including RPE-specific conditional knockout (cKO) and knock-in (KI) mice), we investigate whether Akts in the RPE influences DR in models of diabetic eye disease. We found that Akt1 and Akt2 activities were reciprocally regulated in the RPE of DR donor tissue and diabetic mice. Akt2 cKO attenuated diabetes-induced retinal abnormalities through a compensatory upregulation of phospho-Akt1 leading to an inhibition of vascular injury, inflammatory cytokine release, and infiltration of immune cells mediated by the GSK3β/NF-κB signaling pathway; overexpression of Akt2 has no effect. We propose that targeting Akt1 activity in the RPE may be a novel therapy for treating DR.
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Affiliation(s)
- Haitao Liu
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Nadezda A. Stepicheva
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Sayan Ghosh
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Peng Shang
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA ,grid.280881.b0000 0001 0097 5623Present Address: Doheny Eye Institute, Pasadena, CA USA
| | - Olivia Chowdhury
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Rachel A. Daley
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Meysam Yazdankhah
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA ,grid.443945.b0000 0004 0566 7998Present Address: Neural Stem Cell Institute, Rensselaer, NY USA
| | - Urvi Gupta
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Stacey L. Hose
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Mallika Valapala
- grid.411377.70000 0001 0790 959XSchool of Optometry, Indiana University, Bloomington, IN USA
| | - Christopher Scott Fitting
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Anastasia Strizhakova
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA
| | - Yang Shan
- grid.214458.e0000000086837370Kellogg Eye Center, University of Michigan School of Medicine, Ann Arbor, MI USA
| | - Derrick Feenstra
- grid.417570.00000 0004 0374 1269Pharma Research and Early Development, Roche Innovation Center Basel, F. Hoffmann-La Roche, Ltd., Basel, Switzerland
| | - José-Alain Sahel
- grid.21925.3d0000 0004 1936 9000Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA USA ,grid.462844.80000 0001 2308 1657Institut de la Vision, INSERM, CNRS, Sorbonne Université, Paris, France
| | | | - James T. Handa
- grid.21107.350000 0001 2171 9311The Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - J. Samuel Zigler
- grid.21107.350000 0001 2171 9311The Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Patrice E. Fort
- grid.214458.e0000000086837370Kellogg Eye Center, University of Michigan School of Medicine, Ann Arbor, MI USA
| | - Akrit Sodhi
- grid.21107.350000 0001 2171 9311The Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, MD USA
| | - Debasish Sinha
- Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA. .,The Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
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4
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Fort PE, Losiewicz MK, Elghazi L, Kong D, Cras-Méneur C, Fingar DC, Kimball SR, Rajala RVS, Smith AJ, Ali RR, Abcouwer SF, Gardner TW. mTORC1 regulates high levels of protein synthesis in retinal ganglion cells of adult mice. J Biol Chem 2022; 298:101944. [PMID: 35447116 PMCID: PMC9117545 DOI: 10.1016/j.jbc.2022.101944] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Revised: 03/17/2022] [Accepted: 03/18/2022] [Indexed: 02/02/2023] Open
Abstract
Mechanistic target of rapamycin (mTOR) and mTOR complex 1 (mTORC1), linchpins of the nutrient sensing and protein synthesis pathways, are present at relatively high levels in the ganglion cell layer (GCL) and retinal ganglion cells (RGCs) of rodent and human retinas. However, the role of mTORCs in the control of protein synthesis in RGC is unknown. Here, we applied the SUrface SEnsing of Translation (SUnSET) method of nascent protein labeling to localize and quantify protein synthesis in the retinas of adult mice. We also used intravitreal injection of an adeno-associated virus 2 vector encoding Cre recombinase in the eyes of mtor- or rptor-floxed mice to conditionally knockout either both mTORCs or only mTORC1, respectively, in cells within the GCL. A novel vector encoding an inactive Cre mutant (CreΔC) served as control. We found that retinal protein synthesis was highest in the GCL, particularly in RGC. Negation of both complexes or only mTORC1 significantly reduced protein synthesis in RGC. In addition, loss of mTORC1 function caused a significant reduction in the pan-RGC marker, RNA-binding protein with multiple splicing, with little decrease of the total number of cells in the RGC layer, even at 25 weeks after adeno-associated virus-Cre injection. These findings reveal that mTORC1 signaling is necessary for maintaining the high rate of protein synthesis in RGCs of adult rodents, but it may not be essential to maintain RGC viability. These findings may also be relevant to understanding the pathophysiology of RGC disorders, including glaucoma, diabetic retinopathy, and optic neuropathies.
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Affiliation(s)
- Patrice E Fort
- Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA; Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Mandy K Losiewicz
- Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Lynda Elghazi
- Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Dejuan Kong
- Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Corentin Cras-Méneur
- Internal Medicine (MEND Division), University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Diane C Fingar
- Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Scot R Kimball
- Cellular & Molecular Physiology, Penn State College of Medicine, Hershey, Pennsylvania, USA
| | - Raju V S Rajala
- Departments of Ophthalmology and Physiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA
| | - Alexander J Smith
- Centre for Gene Therapy and Regenerative Medicine, King's College London, England, United Kingdom
| | - Robin R Ali
- Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA; Centre for Gene Therapy and Regenerative Medicine, King's College London, England, United Kingdom
| | - Steven F Abcouwer
- Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA.
| | - Thomas W Gardner
- Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA; Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan, USA; Internal Medicine (MEND Division), University of Michigan Medical School, Ann Arbor, Michigan, USA
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5
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Fort PE, Rajendiran TM, Soni T, Byun J, Shan Y, Looker HC, Nelson RG, Kretzler M, Michailidis G, Roger JE, Gardner TW, Abcouwer SF, Pennathur S, Afshinnia F. Diminished retinal complex lipid synthesis and impaired fatty acid β-oxidation associated with human diabetic retinopathy. JCI Insight 2021; 6:e152109. [PMID: 34437304 PMCID: PMC8525591 DOI: 10.1172/jci.insight.152109] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Accepted: 08/25/2021] [Indexed: 12/22/2022] Open
Abstract
BACKGROUND This study systematically investigated circulating and retinal tissue lipid determinants of human diabetic retinopathy (DR) to identify underlying lipid alterations associated with severity of DR. METHODS Retinal tissues were retrieved from postmortem human eyes, including 19 individuals without diabetes, 20 with diabetes but without DR, and 20 with diabetes and DR, for lipidomic study. In a parallel study, serum samples from 28 American Indians with type 2 diabetes from the Gila River Indian Community, including 12 without DR, 7 with mild nonproliferative DR (NPDR), and 9 with moderate NPDR, were selected. A mass-spectrometry–based lipidomic platform was used to measure serum and tissue lipids. RESULTS In the postmortem retinas, we found a graded decrease of long-chain acylcarnitines and longer-chain fatty acid ester of hydroxyl fatty acids, diacylglycerols, triacylglycerols, phosphatidylcholines, and ceramide(NS) in central retina from individuals with no diabetes to those with diabetes with DR. The American Indians’ sera also exhibited a graded decrease in circulating long-chain acylcarnitines and a graded increase in the intermediate-length saturated and monounsaturated triacylglycerols from no DR to moderate NPDR. CONCLUSION These findings suggest diminished synthesis of complex lipids and impaired mitochondrial β-oxidation of fatty acids in retinal DR, with parallel changes in circulating lipids. TRIAL REGISTRATION ClinicalTrials.gov NCT00340678. FUNDING This work was supported by NIH grants R24 DK082841, K08DK106523, R03DK121941, P30DK089503, P30DK081943, P30DK020572, P30 EY007003; The Thomas Beatson Foundation; and JDRF Center for Excellence (5-COE-2019-861-S-B).
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Affiliation(s)
- Patrice E Fort
- Department of Ophthalmology and Visual Sciences.,Department of Molecular and Integrative Physiology
| | | | | | - Jaeman Byun
- Department of Internal Medicine-Nephrology, University of Michigan, Ann Arbor, Michigan, USA
| | - Yang Shan
- Department of Ophthalmology and Visual Sciences
| | - Helen C Looker
- Chronic Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Phoenix, Arizona, USA
| | - Robert G Nelson
- Chronic Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Phoenix, Arizona, USA
| | - Matthias Kretzler
- Department of Internal Medicine-Nephrology, University of Michigan, Ann Arbor, Michigan, USA
| | - George Michailidis
- Department of Statistics and the Informatics Institute, University of Florida, Gainesville, Florida, USA
| | - Jerome E Roger
- Paris-Saclay Institute of Neuroscience, CERTO-Retina France, CNRS, Université Paris-Saclay, Orsay, France
| | - Thomas W Gardner
- Department of Ophthalmology and Visual Sciences.,Department of Molecular and Integrative Physiology.,Department of Internal Medicine-Metabolism, Endocrinology and Diabetes, and
| | | | - Subramaniam Pennathur
- Department of Molecular and Integrative Physiology.,Department of Internal Medicine-Nephrology, University of Michigan, Ann Arbor, Michigan, USA.,Michigan Regional Comprehensive Metabolomics Resource Core, University of Michigan, Ann Arbor, Michigan, USA
| | - Farsad Afshinnia
- Department of Internal Medicine-Nephrology, University of Michigan, Ann Arbor, Michigan, USA
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6
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Phadte AS, Sluzala ZB, Fort PE. Therapeutic Potential of α-Crystallins in Retinal Neurodegenerative Diseases. Antioxidants (Basel) 2021; 10:1001. [PMID: 34201535 PMCID: PMC8300683 DOI: 10.3390/antiox10071001] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2021] [Revised: 06/12/2021] [Accepted: 06/15/2021] [Indexed: 11/18/2022] Open
Abstract
The chaperone and anti-apoptotic activity of α-crystallins (αA- and αB-) and their derivatives has received increasing attention due to their tremendous potential in preventing cell death. While originally known and described for their role in the lens, the upregulation of these proteins in cells and animal models of neurodegenerative diseases highlighted their involvement in adaptive protective responses to neurodegeneration associated stress. However, several studies also suggest that chronic neurodegenerative conditions are associated with progressive loss of function of these proteins. Thus, while external supplementation of α-crystallin shows promise, their potential as a protein-based therapeutic for the treatment of chronic neurodegenerative diseases remains ambiguous. The current review aims at assessing the current literature supporting the anti-apoptotic potential of αA- and αB-crystallins and its potential involvement in retinal neurodegenerative diseases. The review further extends into potentially modulating the chaperone and the anti-apoptotic function of α-crystallins and the use of such functionally enhanced proteins for promoting neuronal viability in retinal neurodegenerative disease.
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Affiliation(s)
- Ashutosh S. Phadte
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA; (A.S.P.); (Z.B.S.)
| | - Zachary B. Sluzala
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA; (A.S.P.); (Z.B.S.)
| | - Patrice E. Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA; (A.S.P.); (Z.B.S.)
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48105, USA
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7
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Zolov SN, Imai H, Losiewicz MK, Singh RSJ, Fort PE, Gardner TW. Insulin-like growth factor-2 regulates basal retinal insulin receptor activity. J Biol Chem 2021; 296:100712. [PMID: 33915127 PMCID: PMC8138762 DOI: 10.1016/j.jbc.2021.100712] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Revised: 04/15/2021] [Accepted: 04/23/2021] [Indexed: 11/14/2022] Open
Abstract
The retinal insulin receptor (IR) exhibits basal kinase activity equivalent to that of the liver of fed animals, but unlike the liver, does not fluctuate with feeding and fasting; it also declines rapidly after the onset of insulin-deficient diabetes. The ligand(s) that determine basal IR activity in the retina has not been identified. Using a highly sensitive insulin assay, we found that retinal insulin concentrations remain constant in fed versus fasted rats and in diabetic versus control rats; vitreous fluid insulin levels were undetectable. Neutralizing antibodies against insulin-like growth factor 2 (IGF-2), but not insulin-like growth factor 1 (IGF-1) or insulin, decreased IR kinase activity in normal rat retinas, and depletion of IGF-2 from serum specifically reduced IR phosphorylation in retinal cells. Immunoprecipitation studies demonstrated that IGF-2 induced greater phosphorylation of the retinal IR than the IGF-1 receptor. Retinal IGF-2 mRNA content was 10-fold higher in adults than pups and orders of magnitude higher than in liver. Diabetes reduced retinal IGF-2, but not IGF-1 or IR, mRNA levels, and reduced IGF-2 and IGF-1 content in vitreous fluid. Finally, intravitreal administration of IGF-2 (mature and pro-forms) increased retinal IR and Akt kinase activity in diabetic rats. Collectively, these data reveal that IGF-2 is the primary ligand that defines basal retinal IR activity and suggest that reduced ocular IGF-2 may contribute to reduced IR activity in response to diabetes. These findings may have importance for understanding the regulation of metabolic and prosurvival signaling in the retina.
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Affiliation(s)
- Sergey N Zolov
- Department of Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA; Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA; The Division of Pulmonary & Critical Care Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA.
| | - Hisanori Imai
- Department of Ophthalmology, Kobe University Medical School, Kobe, Japan
| | - Mandy K Losiewicz
- Department of Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | | | - Patrice E Fort
- Department of Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA; Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Thomas W Gardner
- Department of Ophthalmology & Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA; Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA; Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
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8
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Losiewicz MK, Elghazi L, Fingar DC, Rajala RVS, Lentz SI, Fort PE, Abcouwer SF, Gardner TW. mTORC1 and mTORC2 expression in inner retinal neurons and glial cells. Exp Eye Res 2020; 197:108131. [PMID: 32622801 DOI: 10.1016/j.exer.2020.108131] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2020] [Revised: 06/09/2020] [Accepted: 06/24/2020] [Indexed: 02/06/2023]
Abstract
The retina is one of the most metabolically active tissues, yet the processes that control retinal metabolism remains poorly understood. The mTOR complex (mTORC) that drives protein and lipid biogenesis and autophagy has been studied extensively in regards to retinal development and responses to optic nerve injury but the processes that regulate homeostasis in the adult retina have not been determined. We previously demonstrated that normal adult retina has high rates of protein synthesis compared to skeletal muscle, associated with high levels of mechanistic target of rapamycin (mTOR), a kinase that forms multi-subunit complexes that sense and integrate diverse environmental cues to control cell and tissue physiology. This study was undertaken to: 1) quantify expression of mTOR complex 1 (mTORC1)- and mTORC2-specific partner proteins in normal adult rat retina, brain and liver; and 2) to localize these components in normal human, rat, and mouse retinas. Immunoblotting and immunoprecipitation studies revealed greater expression of raptor (exclusive to mTORC1) and rictor (exclusive for mTORC2) in normal rat retina relative to liver or brain, as well as the activating mTORC components, pSIN1 and pPRAS40. By contrast, liver exhibits greater amounts of the mTORC inhibitor, DEPTOR. Immunolocalization studies for all three species showed that mTOR, raptor, and rictor, as well as most other known components of mTORC1 and mTORC2, were primarily localized in the inner retina with mTORC1 primarily in retinal ganglion cells (RGCs) and mTORC2 primarily in glial cells. In addition, phosphorylated ribosomal protein S6, a direct target of the mTORC1 substrate ribosomal protein S6 kinase beta-1 (S6K1), was readily detectable in RGCs, indicating active mTORC1 signaling, and was preserved in human donor eyes. Collectively, this study demonstrates that the inner retina expresses high levels of mTORC1 and mTORC2 and possesses active mTORC1 signaling that may provide cell- and tissue-specific regulation of homeostatic activity. These findings help to define the physiology of the inner retina, which is key for understanding the pathophysiology of optic neuropathies, glaucoma and diabetic retinopathy.
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Affiliation(s)
| | | | | | - Raju V S Rajala
- Departments of Ophthalmology and Physiology, University of Oklahoma Health Sciences Center, United States
| | - Stephen I Lentz
- Internal Medicine, Division of Metabolism, Endocrinology and Diabetes, United States
| | - Patrice E Fort
- Ophthalmology & Visual Sciences, United States; Molecular and Integrative Physiology, University of Michigan Medical School, United States
| | | | - Thomas W Gardner
- Ophthalmology & Visual Sciences, United States; Internal Medicine, Division of Metabolism, Endocrinology and Diabetes, United States; Molecular and Integrative Physiology, University of Michigan Medical School, United States.
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9
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Affiliation(s)
- Patrice E Fort
- Department of Ophathalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, United States
| | - Nan-Jie Xu
- Department of Anatomy and Physiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Wenbo Zhang
- Department of Ophthalmology & Visual Sciences, University of Texas Medical Branch, Galveston, TX, United States
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10
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Afshinnia F, Nair V, Lin J, Rajendiran TM, Soni T, Byun J, Sharma K, Fort PE, Gardner TW, Looker HC, Nelson RG, Brosius FC, Feldman EL, Michailidis G, Kretzler M, Pennathur S. Increased lipogenesis and impaired β-oxidation predict type 2 diabetic kidney disease progression in American Indians. JCI Insight 2019; 4:130317. [PMID: 31573977 PMCID: PMC6948762 DOI: 10.1172/jci.insight.130317] [Citation(s) in RCA: 62] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Accepted: 09/25/2019] [Indexed: 12/14/2022] Open
Abstract
BACKGROUNDIn this study, we identified the lipidomic predictors of early type 2 diabetic kidney disease (DKD) progression, which are currently undefined.METHODSThis longitudinal study included 92 American Indians with type 2 diabetes. Serum lipids (406 from 18 classes) were quantified using mass spectrometry from baseline samples when iothalamate-based glomerular filtration rate (GFR) was at least 90 mL/min. Affymetrix GeneChip Array was used to measure renal transcript expression. DKD progression was defined as at least 40% decline in GFR during follow-up.RESULTSParticipants had a mean age of 45 ± 9 years and median urine albumin/creatinine ratio of 43 (interquartile range 11-144). The 32 progressors had significantly higher relative abundance of polyunsaturated triacylglycerols (TAGs) and a lower abundance of C16-C20 acylcarnitines (ACs) (P < 0.001). In a Cox regression model, the main effect terms of unsaturated free fatty acids and phosphatidylethanolamines and the interaction terms of C16-C20 ACs and short-low-double-bond TAGs by categories of albuminuria independently predicted DKD progression. Renal expression of acetyl-CoA carboxylase-encoding gene (ACACA) correlated with serum diacylglycerols in the glomerular compartment (r = 0.36, and P = 0.006) and with low-double-bond TAGs in the tubulointerstitial compartment (r = 0.52, and P < 0.001).CONCLUSIONCollectively, the findings reveal a previously unrecognized link between lipid markers of impaired mitochondrial β-oxidation and enhanced lipogenesis and DKD progression in individuals with preserved GFR. Renal acetyl-CoA carboxylase activation accompanies these lipidomic changes and suggests that it may be the underlying mechanism linking lipid abnormalities to DKD progression.TRIAL REGISTRATIONClinicalTrials.gov, NCT00340678.FUNDINGNIH R24DK082841, K08DK106523, R03DK121941, P30DK089503, P30DK081943, and P30DK020572.
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Affiliation(s)
- Farsad Afshinnia
- Division of Nephrology, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Viji Nair
- Division of Nephrology, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Jiahe Lin
- Department of Statistics, University of Michigan, Ann Arbor, Michigan, USA
| | - Thekkelnaycke M. Rajendiran
- Michigan Regional Comprehensive Metabolomics Resource Core and
- Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Tanu Soni
- Michigan Regional Comprehensive Metabolomics Resource Core and
| | - Jaeman Byun
- Division of Nephrology, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Kumar Sharma
- Division of Nephrology, Department of Internal Medicine, University of Texas Health at San Antonio, San Antonio, Texas, USA
| | - Patrice E. Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Thomas W. Gardner
- Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Helen C. Looker
- Chronic Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, Phoenix, Arizona, USA
| | - Robert G. Nelson
- Chronic Kidney Disease Section, National Institute of Diabetes and Digestive and Kidney Diseases, Phoenix, Arizona, USA
| | - Frank C. Brosius
- Division of Nephrology, Department of Medicine, University of Arizona College of Medicine, Tuscan, Arizona, USA
| | - Eva L. Feldman
- Department of Neurology, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - George Michailidis
- Department of Statistics and
- Informatics Institute, University of Florida, Gainesville, Florida, USA
| | - Matthias Kretzler
- Division of Nephrology, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA
| | - Subramaniam Pennathur
- Division of Nephrology, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan, USA
- Michigan Regional Comprehensive Metabolomics Resource Core and
- Department of Molecular and Integrative Physiology, University of Michigan Medical School, Ann Arbor, Michigan, USA
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11
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Brignol TN, Fort PE. Reader response: Consensus-based care recommendations for adults with myotonic dystrophy type 1. Neurol Clin Pract 2019; 9:366. [DOI: 10.1212/cpj.0000000000000733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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12
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Eid S, Sas KM, Abcouwer SF, Feldman EL, Gardner TW, Pennathur S, Fort PE. New insights into the mechanisms of diabetic complications: role of lipids and lipid metabolism. Diabetologia 2019; 62:1539-1549. [PMID: 31346658 PMCID: PMC6679814 DOI: 10.1007/s00125-019-4959-1] [Citation(s) in RCA: 196] [Impact Index Per Article: 39.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Accepted: 05/21/2019] [Indexed: 02/07/2023]
Abstract
Diabetes adversely affects multiple organs, including the kidney, eye and nerve, leading to diabetic kidney disease, diabetic retinopathy and diabetic neuropathy, respectively. In both type 1 and type 2 diabetes, tissue damage is organ specific and is secondary to a combination of multiple metabolic insults. Hyperglycaemia, dyslipidaemia and hypertension combine with the duration and type of diabetes to define the distinct pathophysiology underlying diabetic kidney disease, diabetic retinopathy and diabetic neuropathy. Only recently have the commonalities and differences in the metabolic basis of these tissue-specific complications, particularly those involving local and systemic lipids, been systematically examined. This review focuses on recent progress made using preclinical models and human-based approaches towards understanding how bioenergetics and metabolomic profiles contribute to diabetic kidney disease, diabetic retinopathy and diabetic neuropathy. This new understanding of the biology of complication-prone tissues highlights the need for organ-specific interventions in the treatment of diabetic complications.
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Affiliation(s)
- Stephanie Eid
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
| | - Kelli M Sas
- Division of Nephrology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA
| | - Steven F Abcouwer
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, 1000 Wall Street, Ann Arbor, MI, 48105, USA
| | - Eva L Feldman
- Department of Neurology, University of Michigan, Ann Arbor, MI, USA
| | - Thomas W Gardner
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, 1000 Wall Street, Ann Arbor, MI, 48105, USA
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA
| | - Subramaniam Pennathur
- Division of Nephrology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, 1000 Wall Street, Ann Arbor, MI, 48105, USA.
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA.
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13
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Yoshitake S, Murakami T, Suzuma K, Yoshitake T, Uji A, Morooka S, Dodo Y, Fujimoto M, Shan Y, Fort PE, Ito S, Tsujikawa A, Yoshimura N. Anti-fumarase antibody promotes the dropout of photoreceptor inner and outer segments in diabetic macular oedema. Diabetologia 2019; 62:504-516. [PMID: 30488085 PMCID: PMC6441336 DOI: 10.1007/s00125-018-4773-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Accepted: 10/08/2018] [Indexed: 02/06/2023]
Abstract
AIMS/HYPOTHESIS In diabetic macular oedema (DMO), blood components passing through the disrupted blood-retinal barrier cause neuroinflammation, but the mechanism by which autoantibodies induce neuroglial dysfunction is unknown. The aim of this study was to identify a novel autoantibody and to evaluate its pathological effects on clinically relevant photoreceptor injuries. METHODS Biochemical purification and subsequent peptide fingerprinting were applied to identify autoantigens. The titres of autoantibodies in DMO sera were quantified and their associations with clinical variables were evaluated. Two animal models (i.e. passive transfer of autoantibodies and active immunisation) were characterised with respect to autoimmune mechanisms underlying photoreceptor injuries. RESULTS After screening serum IgG from individuals with DMO, fumarase, a Krebs cycle enzyme expressed in inner segments, was identified as an autoantigen. Serum levels of anti-fumarase IgG in participants with DMO were higher than those in diabetic participants without DMO (p < 0.001) and were related to photoreceptor damage and visual dysfunction. Passively transferred fumarase IgG from DMO sera in concert with complement impaired the function and structure of rodent photoreceptors. This was consistent with complement activation in the damaged photoreceptors of mice immunised with fumarase. Fumarase was recruited to the cell surface by complement and reacted to this autoantibody. Subsequently, combined administration of anti-fumarase antibody and complement elicited mitochondrial disruption and caspase-3 activation. CONCLUSIONS/INTERPRETATION This study has identified anti-fumarase antibody as a serum biomarker and demonstrates that the generation of this autoantibody might be a pathological mechanism of autoimmune photoreceptor injuries in DMO.
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Affiliation(s)
- Shin Yoshitake
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
| | - Tomoaki Murakami
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan.
| | - Kiyoshi Suzuma
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
| | - Tatsuya Yoshitake
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
| | - Akihito Uji
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
| | - Satoshi Morooka
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
| | - Yoko Dodo
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
| | - Masahiro Fujimoto
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
| | - Yang Shan
- Department of Ophthalmology and Visual Sciences, University of Michigan, Kellogg Eye Center, Ann Arbor, MI, USA
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Kellogg Eye Center, Ann Arbor, MI, USA
- Department of Molecular and Integrative Physiology, University of Michigan, Kellogg Eye Center, Ann Arbor, MI, USA
| | - Shinji Ito
- Medical Research Support Center, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Akitaka Tsujikawa
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
| | - Nagahisa Yoshimura
- Department of Ophthalmology and Visual Sciences, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaracho, Sakyo, Kyoto, 606-8507, Japan
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14
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Nahomi RB, Sampathkumar S, Myers AM, Elghazi L, Smith DG, Tang J, Lee CA, Kern TS, Nagaraj RH, Fort PE. The Absence of Indoleamine 2,3-Dioxygenase Inhibits Retinal Capillary Degeneration in Diabetic Mice. Invest Ophthalmol Vis Sci 2019; 59:2042-2053. [PMID: 29677366 PMCID: PMC5908388 DOI: 10.1167/iovs.17-22702] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Purpose Loss of retinal capillary endothelial cells and pericytes through apoptosis is an early event in diabetic retinopathy (DR). Inflammatory pathways play a role in early DR, yet the biochemical mechanisms are poorly understood. In this study, we investigated the role of indoleamine 2,3-dioxygenase (IDO), an inflammatory cytokine-inducible enzyme, on retinal endothelial apoptosis and capillary degeneration in the diabetic retina. Methods IDO was detected in human and mouse retinas by immunohistochemistry or Western blotting. Interferon-γ (IFN-γ) levels were measured by ELISA. IDO levels were measured in human retinal capillary endothelial cells (HREC) cultured in the presence of IFN-γ ± 25 mM D-glucose. Reactive oxygen species (ROS) were measured using CM-H2DCFDA dye and apoptosis was measured by cleaved caspase-3. The role of IDO in DR was determined in IDO knockout (IDO−/−) mice with streptozotocin-induced diabetes. Results The IDO and IFN-γ levels were higher in human diabetic retinas with retinopathy relative to nondiabetic retinas. Immunohistochemical data showed that IDO is present in capillary endothelial cells. IFN-γ upregulated the IDO and ROS levels in HREC. The blockade of either IDO or kynurenine monooxygenase led to inhibition of ROS in HREC. Apoptosis through this pathway was inhibited by an ROS scavenger, TEMPOL. Capillary degeneration was significantly reduced in diabetic IDO−/− mice compared to diabetic wild-type mice. Conclusions The results suggest that the kynurenine pathway plays an important role in the inflammatory damage in the diabetic retina and could be a new therapeutic target for the treatment of DR.
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Affiliation(s)
- Rooban B Nahomi
- Departments of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States.,Department of Ophthalmology, University of Colorado School of Medicine, Aurora, Colorado, United States
| | - Sruthi Sampathkumar
- Departments of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States
| | - Angela M Myers
- Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States
| | - Lynda Elghazi
- Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States
| | - Dawn G Smith
- Departments of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States
| | - Jie Tang
- Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States
| | - C Allen Lee
- Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States
| | - Timothy S Kern
- Departments of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States.,Medicine, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States
| | - Ram H Nagaraj
- Departments of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, Ohio, United States.,Department of Ophthalmology, University of Colorado School of Medicine, Aurora, Colorado, United States
| | - Patrice E Fort
- Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States
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15
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Brignol TN, Fort PE, Ventura DF, Tadayoni R, Rendon A. Cataract development associated with long-term glucocorticoid therapy in Duchenne muscular dystrophy patients. J AAPOS 2018; 22:483-484. [PMID: 30266609 PMCID: PMC6394826 DOI: 10.1016/j.jaapos.2018.07.347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 07/13/2018] [Accepted: 07/15/2018] [Indexed: 11/26/2022]
Affiliation(s)
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, and Molecular and Integrative Physiology, Kellogg Eye Center, Ann Arbor, Michigan
| | - Dora Fix Ventura
- Department of Experimental Psychology, Institute of Psychology, Universidade de São Paulo, Brazil
| | - Ramin Tadayoni
- Ophthalmology Department, Université Paris, Lariboisière, Saint Louis & Cochin Hospitals (AP-HP), OphtalmoPôle Paris, Académie Nationale de Chirurgie
| | - Alvaro Rendon
- Sorbonne Université, INSERM, CNRS, Institut de la Vision, Paris, France
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16
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Abstract
Heat shock proteins (Hsps) are a large family of molecular chaperones that are well-known for their roles in protein maturation, re-folding and degradation. While some Hsps are constitutively expressed in certain regions, others are rapidly upregulated in the presence of stressful stimuli. Numerous stressors, including hyperthermia and hypoxia, can induce the expression of Hsps, which, in turn, interact with client proteins and co-chaperones to regulate cell growth and survival. Such interactions must be tightly regulated, especially at critical points during embryonic and postnatal development. Hsps exhibit specific patterns of expression consistent with a spatio-temporally regulated role in neurodevelopment. There is also growing evidence that Hsps may promote or inhibit neurodevelopment through specific pathways regulating cell differentiation, neurite outgrowth, cell migration, or angiogenesis. This review will examine the regulatory role that these individual chaperones may play in neurodevelopment, and will focus specifically on the signaling pathways involved in the maturation of neuronal and glial cells as well as the underlying vascular network.
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Affiliation(s)
- David J Miller
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, United States.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, United States
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, United States.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, United States
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17
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Abstract
Crystallins are the predominant structural proteins in the lens that are evolutionarily related to stress proteins. There are two main crystallin gene families: α-crystallins and β/γ-crystallins. α- and β-crystallins were first considered to be lens-specific, but were recently recognized also as neuronal and retinal proteins. While in the ocular lens they are responsible for the maintenance of the transparency, their function in neurons is obviously different - regulating various protective mechanisms in degenerative conditions of the central nervous system. We recently reported the correlation between a gene conversion leading to a triple mutation in the betaB2-crystallin protein and a phenotype of familial congenital cataract with a high familial incidence also of primary open angle glaucoma. Congenital cataract is the leading cause of childhood blindness and progressive neuro degeneration of the optic nerve in glaucoma accounts as the leading cause of blindness worldwide. Altered solubility and stability of crystallin proteins cause cataract formation and are directly linked to a decrease in their protective function. Thus in this study, we evaluated the functional consequences of the mutations associated with this gene conversion on beta B2-crystallin protein biochemical properties in retinal neurons. We found that only the occurrence of the triple mutation leads to decreased solubility and formation of aggregates, which as we previously demonstrated, is associated with mislocalization to the mitochondria along with decreased mitochondrial function in retinal neurons and lens epithelial cells. Our data strongly support a significant role for beta B2-crystallin in both lenticular and retinal ocular tissues and warrant further analysis of its regulation and its impact not only in cataract formation but also in retinal neurodegenerative diseases.
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Affiliation(s)
- Anne Rübsam
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Jennifer E Dulle
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Sarah J Garnai
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Hermant S Pawar
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA
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18
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Abstract
Diabetic retinopathy is a common complication of diabetes and remains the leading cause of blindness among the working-age population. For decades, diabetic retinopathy was considered only a microvascular complication, but the retinal microvasculature is intimately associated with and governed by neurons and glia, which are affected even prior to clinically detectable vascular lesions. While progress has been made to improve the vascular alterations, there is still no treatment to counteract the early neuro-glial perturbations in diabetic retinopathy. Diabetes is a complex metabolic disorder, characterized by chronic hyperglycemia along with dyslipidemia, hypoinsulinemia and hypertension. Increasing evidence points to inflammation as one key player in diabetes-associated retinal perturbations, however, the exact underlying molecular mechanisms are not yet fully understood. Interlinked molecular pathways, such as oxidative stress, formation of advanced glycation end-products and increased expression of vascular endothelial growth factor have received a lot of attention as they all contribute to the inflammatory response. In the current review, we focus on the involvement of inflammation in the pathophysiology of diabetic retinopathy with special emphasis on the functional relationships between glial cells and neurons. Finally, we summarize recent advances using novel targets to inhibit inflammation in diabetic retinopathy.
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Affiliation(s)
- Anne Rübsam
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
| | - Sonia Parikh
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI 48105, USA.
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48105, USA.
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19
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Ruebsam A, Dulle JE, Myers AM, Sakrikar D, Green KM, Khan NW, Schey K, Fort PE. A specific phosphorylation regulates the protective role of αA-crystallin in diabetes. JCI Insight 2018; 3:97919. [PMID: 29467334 DOI: 10.1172/jci.insight.97919] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 01/17/2018] [Indexed: 12/19/2022] Open
Abstract
Neurodegeneration is a central aspect of the early stages of diabetic retinopathy, the primary ocular complication associated with diabetes. While progress has been made to improve the vascular perturbations associated with diabetic retinopathy, there are still no treatment options to counteract the neuroretinal degeneration associated with diabetes. Our previous work suggested that the molecular chaperones α-crystallins could be involved in the pathophysiology of diabetic retinopathy; however, the role and regulation of α-crystallins remained unknown. In the present study, we demonstrated the neuroprotective role of αA-crystallin during diabetes and its regulation by its phosphorylation on residue 148. We further characterized the dual role of αA-crystallin in neurons and glia, its essential role for neuronal survival, and its direct dependence on phosphorylation on this residue. These findings support further evaluation of αA-crystallin as a treatment option to promote neuron survival in diabetic retinopathy and neurodegenerative diseases in general.
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Affiliation(s)
- Anne Ruebsam
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, USA
| | - Jennifer E Dulle
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, USA
| | - Angela M Myers
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, USA
| | | | - Katelyn M Green
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, USA
| | - Naheed W Khan
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, USA
| | - Kevin Schey
- Department of Biochemistry and Ophthalmology and Visual Sciences, Vanderbilt University, Nashville, Tennessee, USA
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, USA.,Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, USA
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20
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Abramoff MD, Fort PE, Han IC, Jayasundera KT, Sohn EH, Gardner TW. Approach for a Clinically Useful Comprehensive Classification of Vascular and Neural Aspects of Diabetic Retinal Disease. Invest Ophthalmol Vis Sci 2018; 59:519-527. [PMID: 29372250 PMCID: PMC5786342 DOI: 10.1167/iovs.17-21873] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Accepted: 10/08/2017] [Indexed: 11/24/2022] Open
Abstract
The Early Treatment Diabetic Retinopathy Study (ETDRS) and other standardized classification schemes have laid a foundation for tremendous advances in the understanding and management of diabetic retinopathy (DR). However, technological advances in optics and image analysis, especially optical coherence tomography (OCT), OCT angiography (OCTa), and ultra-widefield imaging, as well as new discoveries in diabetic retinal neuropathy (DRN), are exposing the limitations of ETDRS and other classification systems to completely characterize retinal changes in diabetes, which we term diabetic retinal disease (DRD). While it may be most straightforward to add axes to existing classification schemes, as diabetic macular edema (DME) was added as an axis to earlier DR classifications, doing so may make these classifications increasingly complicated and thus clinically intractable. Therefore, we propose future research efforts to develop a new, comprehensive, and clinically useful classification system that will identify multimodal biomarkers to reflect the complex pathophysiology of DRD and accelerate the development of therapies to prevent vision-threatening DRD.
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Affiliation(s)
- Michael D. Abramoff
- Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, United States
- Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City, Iowa, United States
- Department of Electrical and Computer Engineering, University of Iowa, Iowa City, Iowa, United States
- Iowa City VA Health Care System, Iowa City, Iowa, United States
- Department of Biomedical Engineering, University of Iowa, Iowa City, Iowa, United States
| | - Patrice E. Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, United States
| | - Ian C. Han
- Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, United States
- Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City, Iowa, United States
| | - K. Thiran Jayasundera
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States
| | - Elliott H. Sohn
- Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, Iowa, United States
- Stephen A. Wynn Institute for Vision Research, University of Iowa, Iowa City, Iowa, United States
| | - Thomas W. Gardner
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, United States
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21
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Dulle JE, Rübsam A, Garnai SJ, Pawar HS, Fort PE. BetaB2-crystallin mutations associated with cataract and glaucoma leads to mitochondrial alterations in lens epithelial cells and retinal neurons. Exp Eye Res 2017; 155:85-90. [PMID: 28131617 DOI: 10.1016/j.exer.2017.01.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Revised: 01/19/2017] [Accepted: 01/22/2017] [Indexed: 11/17/2022]
Abstract
Crystallin proteins are the most prominent protein of the lens and have been increasingly shown to play critical roles in other tissues, especially the retina. Members of all 3 sub-families of crystallins, alpha-, beta- and gamma-crystallins have been reported in the retina during diabetes, traumatic injury and other retinal diseases. While their specific role in the retina is still unclear and may vary, beta-crystallin proteins have been shown to play a critical role in ganglion cell survival following trauma. We recently reported the correlation between a gene conversion in the betaB2-crystallin gene and a phenotype of familial congenital cataract. Interestingly, in half of the patients, this phenotype was associated with glaucoma. Taken together, these data suggested that the mutations we recently reported could have an impact on the role of betaB2-crystallin in both lens epithelial cells and retinal neurons. Consistent with this hypothesis, we show in the current study that the gene conversion leading to an amino acid conversion lead to a loss of solubility and a change of subcellular localization of betaB2-crystallin in both cell types. While the overall observations were similar in both cell types, there were some important nuances between them, suggesting different roles and regulation of betaB2-crystallin in lens cells versus retinal neurons. The data reported in this study strongly support a significant role of betaB2-crystallin in both lenticular and retinal ocular tissues and warrant further analysis of its regulation and its impact not only in cataract formation but also in retinal neurodegenerative diseases.
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Affiliation(s)
- Jennifer E Dulle
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Anne Rübsam
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Sarah J Garnai
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Hemant S Pawar
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI, USA; Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA.
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Kong D, Gong L, Arnold E, Shanmugam S, Fort PE, Gardner TW, Abcouwer SF. Insulin-like growth factor 1 rescues R28 retinal neurons from apoptotic death through ERK-mediated BimEL phosphorylation independent of Akt. Exp Eye Res 2016; 151:82-95. [PMID: 27511131 DOI: 10.1016/j.exer.2016.08.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2016] [Revised: 06/27/2016] [Accepted: 08/05/2016] [Indexed: 10/21/2022]
Abstract
Insulin-like growth factor 1 (IGF-1) can provide long-term neurotrophic support by activation of Akt, inhibition of FoxO nuclear localization and suppression of Bim gene transcription in multiple neuronal systems. However, MEK/ERK activation can also promote neuron survival through phosphorylation of BimEL. We explored the contribution of the PI3K/Akt/FoxO and MEK/ERK/BimEL pathways in IGF-1 stimulated survival after serum deprivation (SD) of R28 cells differentiated to model retinal neurons. IGF-1 caused rapid activation of Akt leading to FoxO1/3-T32/T24 phosphorylation, and prevented FoxO1/3 nuclear translocation and Bim mRNA upregulation in response to SD. IGF-1 also caused MAPK/MEK pathway activation as indicated by ERK1/2-T202/Y204 and Bim-S65 phosphorylation. Overexpression of FoxO1 increased Bim mRNA expression and amplified the apoptotic response to SD without shifting the serum response curve. Inhibition of Akt activation with LY294002 or by Rictor knockdown did not block the protective effect of IGF-1, while inhibition of MEK activity with PD98059 prevented Bim phosphorylation and blocked IGF-1 protection. In addition, knockdown of Bim expression was protective during SD, while co-silencing of FoxO1 and Fox03 expression had little effect. Thus, the PI3K/Akt/FoxO pathway was not essential for protection from SD-induced apoptosis by IGF-1 in R28 cells. Instead, IGF-1 protection was dependent on activation of the MEK/ERK pathway leading to BimEL phosphorylation, which is known to prevent Bax/Bak oligomerization and activation of the intrinsic mitochondrial apoptosis pathway. These studies demonstrate the requirement of the MEK/ERK pathway in a model of retinal neuron cell survival and highlight the cell specificity for IGF-1 signaling in this response.
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Affiliation(s)
- Dejuan Kong
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, Ann Arbor, MI, United States
| | - Lijie Gong
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, Ann Arbor, MI, United States
| | - Edith Arnold
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, Ann Arbor, MI, United States
| | - Sumathi Shanmugam
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, Ann Arbor, MI, United States
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, Ann Arbor, MI, United States
| | - Thomas W Gardner
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, Ann Arbor, MI, United States
| | - Steven F Abcouwer
- Department of Ophthalmology and Visual Sciences, University of Michigan Kellogg Eye Center, Ann Arbor, MI, United States.
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Gardner TW, Abcouwer SF, Losiewicz MK, Fort PE. Phosphatase control of 4E-BP1 phosphorylation state is central for glycolytic regulation of retinal protein synthesis. Am J Physiol Endocrinol Metab 2015; 309. [PMID: 26199279 PMCID: PMC4572451 DOI: 10.1152/ajpendo.00180.2015] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Control of protein synthesis in insulin-responsive tissues has been well characterized, but relatively little is known about how this process is regulated in nervous tissues. The retina exhibits a relatively high protein synthesis rate, coinciding with high basal Akt and metabolic activities, with the majority of retinal ATP being derived from aerobic glycolysis. We examined the dependency of retinal protein synthesis on the Akt-mTOR signaling and glycolysis using ex vivo rat retinas. Akt inhibitors significantly reduced retinal protein synthesis but did not affect glycolytic lactate production. Surprisingly, the glycolytic inhibitor 2-deoxyglucose (2-DG) markedly inhibited Akt1 and Akt3 activities, as well as protein synthesis. The effects of 2-DG, and 2-fluorodeoxyglucose (2-FDG) on retinal protein synthesis correlated with inhibition of lactate production and diminished ATP content, with all these effects reversed by provision of d-mannose. 2-DG treatment was not associated with increased AMPK, eEF2, or eIF2α phosphorylation; instead, it caused rapid dephosphorylation of 4E-BP1. 2-DG reduced total mTOR activity by 25%, but surprisingly, it did not reduce mTORC1 activity, as indicated by unaltered raptor-associated mTOR autophosphorylation and ribosomal protein S6 phosphorylation. Dephosphorylation of 4E-BP1 was largely prevented by inhibition of PP1/PP2A phosphatases with okadaic acid and calyculin A, and inhibition of PPM1 phosphatases with cadmium. Thus, inhibition of retinal glycolysis diminished Akt and protein synthesis coinciding with accelerated dephosphorylation of 4E-BP1 independently of mTORC1. These results demonstrate a novel mechanism regulating protein synthesis in the retina involving an mTORC1-independent and phosphatase-dependent regulation of 4E-BP1.
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Affiliation(s)
- Thomas W Gardner
- Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan; and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
| | - Steven F Abcouwer
- Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan; and
| | - Mandy K Losiewicz
- Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan; and
| | - Patrice E Fort
- Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan; and
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Eisma JH, Dulle JE, Fort PE. Current knowledge on diabetic retinopathy from human donor tissues. World J Diabetes 2015; 6:312-320. [PMID: 25789112 PMCID: PMC4360424 DOI: 10.4239/wjd.v6.i2.312] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2014] [Revised: 12/23/2014] [Accepted: 12/31/2014] [Indexed: 02/05/2023] Open
Abstract
According to the American Diabetes Association, diabetes was the seventh leading cause of death, and diabetic retinopathy the leading cause of blindness in working age adults in the United States in 2010. Diabetes is characterized by hyperglycemia associated with either hypoinsulinemia or insulin resistance, and over time, this chronic metabolic condition may lead to various complications including kidney failure, heart attacks, and retinal degeneration. In order to better understand the molecular basis of this disease and its complications, animal models have been the primary approach used to investigate the effects of diabetes on various tissues or cell types of the body, including the retina. However, inherent to these animal models are critical limitations that make the insight gained from these models challenging to apply to the human pathology. These difficulties in translating the knowledge obtained from animal studies have led a growing number of research groups to explore the diabetes complications, especially diabetic retinopathy, on tissues from human donors. This review summarizes the data collected from diabetic patients at various stages of diabetic retinopathy and classifies the data based upon their relevance to the main aspects of diabetic retinopathy: retinal vasculature dysfunction, inflammation, and neurodegeneration. This review discusses the importance of those studies to discriminate and establish the relevance of the findings obtained from animal models but also the limitations of such approaches.
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Dennis MD, Kimball SR, Fort PE, Jefferson LS. Regulated in development and DNA damage 1 is necessary for hyperglycemia-induced vascular endothelial growth factor expression in the retina of diabetic rodents. J Biol Chem 2014; 290:3865-74. [PMID: 25548280 DOI: 10.1074/jbc.m114.623058] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Vascular endothelial growth factor (VEGF) is considered a major role player in the pathogenesis of diabetic retinopathy, yet the mechanisms regulating its expression are not fully understood. Our laboratory previously demonstrated that diabetes-induced VEGF expression in the retina was dependent on the repressor of mRNA translation 4E-BP1. Interaction of 4E-BP1 with the cap-binding protein eIF4E regulates protein expression by controlling the selection of mRNAs for translation. The process is regulated by the master kinase mTOR in complex 1 (mTORC1), which phosphorylates 4E-BP1, thus promoting its disassociation from eIF4E. In the present study, we investigated the role of the Akt/mTORC1 repressor REDD1 (regulated in development and DNA damage) in diabetes-induced VEGF expression. REDD1 expression was induced by hyperglycemia in the retina of diabetic rodents and by hyperglycemic conditions in Müller cells concomitant with increased VEGF expression. In Müller cells, hyperglycemic conditions attenuated global rates of protein synthesis and cap-dependent mRNA translation concomitant with up-regulated cap-independent VEGF mRNA translation, as assessed by a bicistronic luciferase reporter assay. Hyperglycemic conditions also attenuated mTORC1 signaling and enhanced 4E-BP1 binding to eIF4E. Furthermore, ectopic expression of REDD1 in Müller cells was sufficient to promote both increased 4E-BP1 binding to eIF4E and VEGF expression. Whereas the retina of wild-type mice exhibited increased expression of VEGF and tumor necrosis factor alpha (TNF-α) 4 weeks after streptozotocin administration, the retina of REDD1 knock-out mice failed to do so. Overall, the results demonstrate that REDD1 contributes to the pathogenesis of diabetes in the retina by mediating the pathogenic effects of hyperglycemia.
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Affiliation(s)
- Michael D Dennis
- From the Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Scot R Kimball
- From the Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
| | - Patrice E Fort
- Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, Ann Arbor, Michigan 48105
| | - Leonard S Jefferson
- From the Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 and
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Abstract
Poorly controlled diabetes has long been known as a catabolic disorder with profound loss of muscle and fat body mass resulting from a simultaneous reduction in protein synthesis and enhanced protein degradation. By contrast, retinal structure is largely maintained during diabetes despite reduced Akt activity and increased rate of cell death. Therefore, we hypothesized that retinal protein turnover is regulated differently than in other insulin-sensitive tissues, such as skeletal muscle. Ins2(Akita) diabetic mice and streptozotocin-induced diabetic rats exhibited marked reductions in retinal protein synthesis matched by a concomitant reduction in retinal protein degradation associated with preserved retinal mass and protein content. The reduction in protein synthesis depended on both hyperglycemia and insulin deficiency, but protein degradation was only reversed by normalization of hyperglycemia. The reduction in protein synthesis was associated with diminished protein translation efficiency but, surprisingly, not with reduced activity of the mTORC1/S6K1/4E-BP1 pathway. Instead, diabetes induced a specific reduction of mTORC2 complex activity. These findings reveal distinctive responses of diabetes-induced retinal protein turnover compared with muscle and liver that may provide a new means to ameliorate diabetic retinopathy.
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Affiliation(s)
- Patrice E Fort
- Kellogg Eye Center, Departments of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI
| | - Mandy K Losiewicz
- Kellogg Eye Center, Departments of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI
| | - Subramaniam Pennathur
- Division of Nephrology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI
| | - Leonard S Jefferson
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA
| | - Scot R Kimball
- Department of Cellular and Molecular Physiology, Penn State College of Medicine, Hershey, PA
| | - Steven F Abcouwer
- Kellogg Eye Center, Departments of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI
| | - Thomas W Gardner
- Kellogg Eye Center, Departments of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI
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Cia D, Simonutti M, Fort PE, Doly M, Rendon A. Slight Alteration of the Electroretinogram in Mice Lacking Dystrophin Dp71. Ophthalmic Res 2014; 51:196-203. [DOI: 10.1159/000357272] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Accepted: 11/11/2013] [Indexed: 11/19/2022]
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Abstract
Diabetic retinopathy is the major ocular complication associated with diabetes, and represents the leading cause of legal blindness in the working-age population of developed countries. Although classically diagnosed based on abnormalities of the retinal microvasculature, diabetic retinopathy is now widely recognized as a neurovascular disease. While all patients with diabetes are at increased risk for eye disease including diabetic retinopathy, proactive measures, and timely intervention can prevent or delay subsequent vision loss. Systemic management of diabetes by combined control of glycemia, blood pressure, and serum lipid levels remains the most important method of preventing diabetic retinopathy onset and progression. Once detected, surgical and medical interventions including photocoagulation, vitrectomy, and intravitral drug injection can help preserve vision. However, the need for improved detection methods and therapies that will allow earlier diagnosis and treatment remains apparent. This review summarizes current techniques for the prevention and intervention for diabetic retinopathy, and examines ongoing developments in the search for new endpoints and therapies as they apply to preventing vision loss associated with diabetes.
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Affiliation(s)
- Lauren M Marozas
- Undergraduate Student, Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, US
| | - Patrice E Fort
- Assistant Professor, Department of Ophthalmology and Visual Sciences, Kellogg Eye Center, University of Michigan, US
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Heise EA, Marozas LM, Grafton SA, Green KM, Kirwin SJ, Fort PE. Strain-independent increases of crystallin proteins in the retina of type 1 diabetic rats. PLoS One 2013; 8:e82520. [PMID: 24349305 PMCID: PMC3862628 DOI: 10.1371/journal.pone.0082520] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Accepted: 10/25/2013] [Indexed: 12/18/2022] Open
Abstract
Diabetic retinopathy is the leading cause of vision loss in working-age individuals in the United States and is expected to continue growing with the increased prevalence of diabetes. Streptozotocin-induced hyperglycemia in rats is the most commonly used model for diabetic retinopathy. Previous studies have shown that this model can lead to different inflammatory changes in the retina depending on the strain of rat. Our previous work has shown that crystallin proteins, including members of the alpha- and beta/gamma-crystallin subfamilies, are upregulated in the STZ rat retina. Crystallin proteins have been implicated in a number of cellular processes, such as neuroprotection, non-native protein folding and vascular remodeling. In this current study, we have demonstrated that unlike other strain-dependent changes, such as inflammatory cytokines and growth factor levels, in the STZ rat, the protein upregulation of crystallins is consistent across the Brown Norway, Long-Evans and Sprague-Dawley rat strains in the context of diabetes. Taken together, these data illustrate the potential critical role played by crystallins, and especially alpha-crystallins, in the retina in the context of diabetes.
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Affiliation(s)
- Erich A. Heise
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Lauren M. Marozas
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Sean A. Grafton
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Katelyn M. Green
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Stefanie J. Kirwin
- Biological Science, Allergan Incorporated, Irvine, California, United States of America
| | - Patrice E. Fort
- Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States of America
- * E-mail:
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30
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Nahomi RB, Palmer A, Green KM, Fort PE, Nagaraj RH. Pro-inflammatory cytokines downregulate Hsp27 and cause apoptosis of human retinal capillary endothelial cells. Biochim Biophys Acta Mol Basis Dis 2013; 1842:164-74. [PMID: 24252613 DOI: 10.1016/j.bbadis.2013.11.011] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Revised: 10/25/2013] [Accepted: 11/12/2013] [Indexed: 01/10/2023]
Abstract
The formation of acellular capillaries in the retina, a hallmark feature of diabetic retinopathy, is caused by apoptosis of endothelial cells and pericytes. The biochemical mechanism of such apoptosis remains unclear. Small heat shock proteins play an important role in the regulation of apoptosis. In the diabetic retina, pro-inflammatory cytokines are upregulated. In this study, we investigated the effects of pro-inflammatory cytokines on small heat shock protein 27 (Hsp27) in human retinal endothelial cells (HREC). In HREC cultured in the presence of cytokine mixtures (CM), a significant downregulation of Hsp27 at the protein and mRNA level occurred, with no effect on HSF-1, the transcription factor for Hsp27. The presence of high glucose (25mM) amplified the effects of cytokines on Hsp27. CM activated indoleamine 2,3-dioxygenase (IDO) and enhanced the production of kynurenine and ROS. An inhibitor of IDO, 1-methyl tryptophan (MT), inhibited the effects of CM on Hsp27. CM also upregulated NOS2 and, consequently, nitric oxide (NO). A NOS inhibitor, L-NAME, and a ROS scavenger blocked the CM-mediated Hsp27 downregulation. While a NO donor in the culture medium did not decrease the Hsp27 content, a peroxynitrite donor and exogenous peroxynitrite did. The cytokines and high glucose-induced apoptosis of HREC were inhibited by MT and L-NAME. Downregulation of Hsp27 by a siRNA treatment promoted apoptosis in HREC. Together, these data suggest that pro-inflammatory cytokines induce the formation of ROS and NO, which, through the formation of peroxynitrite, reduce the Hsp27 content and bring about apoptosis of retinal capillary endothelial cells.
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Affiliation(s)
- Rooban B Nahomi
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Allison Palmer
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
| | - Katelyn M Green
- Kellogg Eye Center, University of Michigan, Ann Arbor, MI 48105, USA
| | - Patrice E Fort
- Kellogg Eye Center, University of Michigan, Ann Arbor, MI 48105, USA
| | - Ram H Nagaraj
- Department of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
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Heise EA, Fort PE. Impact of diabetes on alpha-crystallins and other heat shock proteins in the eye. J Ocul Biol Dis Infor 2011; 4:62-9. [PMID: 23264844 DOI: 10.1007/s12177-011-9073-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2011] [Accepted: 12/05/2011] [Indexed: 12/25/2022] Open
Abstract
Diabetes and its related complications represent a major growing health concern and economic burden worldwide. Ocular manifestations of diabetes include cataractogenesis and retinopathy, the latter being the leading cause of blindness in the working-age population. Despite numerous studies and recent progress, the exact pathophysiology of the disease remains to be fully elucidated and development of new and improved therapeutic strategies for this chronic condition are greatly needed. Heat shock proteins (Hsps) are highly conserved families of proteins, which are generally regarded as protective molecules that play a wide variety of roles and can be expressed in response to different types of cellular stresses. In recent years, numerous studies have reported their implication in various ocular diseases including diabetic retinopathy. The present review focuses on the potential implication of Hsps in ocular diabetic complications and discusses their specific mechanisms of regulation with respect to their expression, functions and alteration during diabetes. The review will conclude by examining the potential of Hsps as therapeutic agents or targets for the treatment of diabetic retinopathy.
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Affiliation(s)
- Erich A Heise
- Kellogg Eye Center, Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, MI USA
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Fort PE, Losiewicz MK, Reiter CEN, Singh RSJ, Nakamura M, Abcouwer SF, Barber AJ, Gardner TW. Differential roles of hyperglycemia and hypoinsulinemia in diabetes induced retinal cell death: evidence for retinal insulin resistance. PLoS One 2011; 6:e26498. [PMID: 22046295 PMCID: PMC3202547 DOI: 10.1371/journal.pone.0026498] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2011] [Accepted: 09/27/2011] [Indexed: 01/10/2023] Open
Abstract
Diabetes pathology derives from the combination of hyperglycemia and hypoinsulinemia or insulin resistance leading to diabetic complications including diabetic neuropathy, nephropathy and retinopathy. Diabetic retinopathy is characterized by numerous retinal defects affecting the vasculature and the neuro-retina, but the relative contributions of the loss of retinal insulin signaling and hyperglycemia have never been directly compared. In this study we tested the hypothesis that increased retinal insulin signaling and glycemic normalization would exert differential effects on retinal cell survival and retinal physiology during diabetes. We have demonstrated in this study that both subconjunctival insulin administration and systemic glycemic reduction using the sodium-glucose linked transporter inhibitor phloridzin affected the regulation of retinal cell survival in diabetic rats. Both treatments partially restored the retinal insulin signaling without increasing plasma insulin levels. Retinal transcriptomic and histological analysis also clearly demonstrated that local administration of insulin and systemic glycemia normalization use different pathways to counteract the effects of diabetes on the retina. While local insulin primarily affected inflammation-associated pathways, systemic glycemic control affected pathways involved in the regulation of cell signaling and metabolism. These results suggest that hyperglycemia induces resistance to growth factor action in the retina and clearly demonstrate that both restoration of glycemic control and retinal insulin signaling can act through different pathways to both normalize diabetes-induced retinal abnormality and prevent vision loss.
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Affiliation(s)
- Patrice E Fort
- Kellogg Eye Center, University of Michigan, Ophthalmology and Visual Sciences Department, Ann Arbor, Michigan, United States of America.
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Abstract
PURPOSE α-Crystallins are small heat shock proteins that regulate cellular damage and cell survival. Expression of the proteins of the crystallin superfamily in the retina and their role in neuronal cell survival were investigated in two animal models of diabetes and retinal neurons in culture. METHODS Crystallin expression was assessed in streptozotocin-induced and Ins2(Akita) diabetic mice using iTRAQ methodology and validated using immunoblotting. Protein-protein interactions, solubility properties, and subcellular localization of αA- and αB-crystallins were further analyzed in vivo and in a retinal neuronal cell model using immunoprecipitation and fractionation METHODS Survival of retinal neurons to metabolic stress after overexpression and knock-down of α-crystallins was used to measure their neuroprotective properties. RESULTS All 10 of the crystallins identified in retinal lysates from both models of type 1 diabetes were strongly upregulated, coinciding with increased retinal cell death and expression of proapoptotic proteins Bax and Bcl-Xs. Diabetes strongly reduces the chaperone function of α-crystallins by reducing their solubility and disrupting the normal interaction of α-crystallins with Bax. The same properties disrupted by diabetes were confirmed to be critical for the neuroprotective effect of the overexpression of α-crystallins in retinal neurons in culture. CONCLUSIONS Both chemically and genetically induced diabetic models are characterized by upregulation of α-, β-, and γ-crystallins in the retina. Despite being overexpressed, the molecular properties of α-crystallins are disrupted by diabetes and contribute to the loss of neuroprotective function. Identification and prevention of these alterations could lead to the emergence of new therapies for diabetic retinopathy.
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Affiliation(s)
- Mandy K Losiewicz
- Department of Ophthalmology, Penn State University, Hershey, Pennsylvania, USA
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Abstract
Diabetic retinopathy (DR) is a neurodegenerative and microvascular disease resulting in functional and structural changes of all cell types in the retina. Several mechanisms for neuroretinal homeostasis, including the blood-retinal barrier, normal metabolite delivery into the retina, and the effect of neurotrophins for the retina, are impaired in DR. However, it is still not clear which components are most important for the development of DR and which may be most useful as therapeutic targets. In this chapter, we summarize the evidence for the neurodegeneration in DR and review normal mechanisms for maintenance of postmitotic cells in the retina and alterations in normal maintenance pathways in DR with emphasis on 'neuroprotection'. Finally, we discuss current neuroprotective strategies and future directions for the treatment of DR.
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Sundstrom JM, Sundstrom CJ, Sundstrom SA, Fort PE, Rauscher RLH, Gardner TW, Antonetti DA. Phosphorylation site mapping of endogenous proteins: a combined MS and bioinformatics approach. J Proteome Res 2009; 8:798-807. [PMID: 19125583 DOI: 10.1021/pr8005556] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present a novel approach that combines MALDI-TOF profile analysis and bioinformatics-based inclusion criteria to comprehensively predict phosphorylation sites on a single protein of interest from limiting sample. It is technologically difficult to unambiguously identify phosphorylated residues, as many physiologically important phosphorylation sites are of too low abundance in vivo to be unambiguously assigned by mass spectrometry. Conversely, phosphorylation site prediction algorithms, while increasingly accurate, nevertheless overestimate the number of phosphorylation sites. In this study, we show that MODICAS, an MS data management and analysis tool, can be effectively merged with the bioinformatics attributes of residue conservation and phosphosite prediction to generate a short list of putative phosphorylation sites that can be subsequently verified by additional methodologies such as phosphospecific antibodies or mutational analysis. Therefore, the combination of MODICAS driven MS data analysis with bioinformatics-based filtering represents a substantial increase in the ability to putatively identify physiologically relevant phosphosites from limited starting material.
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Affiliation(s)
- Jeffrey M Sundstrom
- Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033, USA
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36
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Fort PE, Freeman WM, Losiewicz MK, Singh RSJ, Gardner TW. The retinal proteome in experimental diabetic retinopathy: up-regulation of crystallins and reversal by systemic and periocular insulin. Mol Cell Proteomics 2008; 8:767-79. [PMID: 19049959 DOI: 10.1074/mcp.m800326-mcp200] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Diabetic retinopathy is the leading cause of blindness in working age persons. Targeted studies have uncovered several components of the pathophysiology of the disease without unveiling the basic mechanisms. This study describes the use of complementary proteomic and genomic discovery methods that revealed that the proteins of the crystallin superfamily are increased dramatically in early diabetic retinopathy. Orthogonal methods confirmed that the amplitude of the up-regulation is greater than other changes described so far in diabetic retinopathy. A detailed time course study during diabetes showed differential up-regulation of the different isoforms of the crystallins superfamily. alpha- and beta-crystallins were regulated primarily at the translation level, whereas gamma-crystallins were also regulated transcriptionally. We also demonstrated cell-specific patterns of expression of the different crystallins in normal and diabetic rat retinas. In addition, systemic and periocular insulin treatments restored retinal crystallin protein expression during diabetes, indicating effects of phosphoinositide 3-kinase/Akt activity. Altogether this work shows the importance of proteomics discovery methods coupled with targeted approaches to unveil new disease mechanistic details and therapeutic targets.
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Affiliation(s)
- Patrice E Fort
- Department of Ophthalmology, Penn State College of Medicine, Hershey, Pennsylvania 17033, USA
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Fort PE, Sene A, Pannicke T, Roux MJ, Forster V, Mornet D, Nudel U, Yaffe D, Reichenbach A, Sahel JA, Rendon A. Kir4.1 and AQP4 associate with Dp71- and utrophin-DAPs complexes in specific and defined microdomains of Müller retinal glial cell membrane. Glia 2008; 56:597-610. [DOI: 10.1002/glia.20633] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Reiter CEN, Wu X, Sandirasegarane L, Nakamura M, Gilbert KA, Singh RSJ, Fort PE, Antonetti DA, Gardner TW. Diabetes reduces basal retinal insulin receptor signaling: reversal with systemic and local insulin. Diabetes 2006; 55:1148-56. [PMID: 16567541 DOI: 10.2337/diabetes.55.04.06.db05-0744] [Citation(s) in RCA: 131] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Diabetic retinopathy is characterized by early onset of neuronal cell death. We previously showed that insulin mediates a prosurvival pathway in retinal neurons and that normal retina expresses a highly active basal insulin receptor/Akt signaling pathway that is stable throughout feeding and fasting. Using the streptozotocin-induced diabetic rat model, we tested the hypothesis that diabetes diminishes basal retinal insulin receptor signaling concomitantly with increased diabetes-induced retinal apoptosis. The expression, phosphorylation status, and/or kinase activity of the insulin receptor and downstream signaling proteins were investigated in retinas of age-matched control, diabetic, and insulin-treated diabetic rats. Four weeks of diabetes reduced basal insulin receptor kinase, insulin receptor substrate (IRS)-1/2-associated phosphatidylinositol 3-kinase, and Akt kinase activity without altering insulin receptor or IRS-1/2 expression or tyrosine phosphorylation. After 12 weeks of diabetes, constitutive insulin receptor autophosphorylation and IRS-2 expression were reduced, without changes in p42/p44 mitogen-activated protein kinase or IRS-1. Sustained systemic insulin treatment of diabetic rats prevented loss of insulin receptor and Akt kinase activity, and acute intravitreal insulin administration restored insulin receptor kinase activity. Insulin treatment restored insulin receptor-beta autophosphorylation in rat retinas maintained ex vivo, demonstrating functional receptors and suggesting loss of ligand as a cause for reduced retinal insulin receptor/Akt pathway activity. These results demonstrate that diabetes progressively impairs the constitutive retinal insulin receptor signaling pathway through Akt and suggests that loss of this survival pathway may contribute to the initial stages of diabetic retinopathy.
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Affiliation(s)
- Chad E N Reiter
- Dept. of Cellular and Molecular Physiology, Juvenile Diabetes Research Foundation Diabetic Retinopathy Center, Penn State College of Medicine, Hershey, PA 17033, USA
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