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Vasović DD, Ivković S, Živanović A, Major T, Milašin JM, Nikolić NS, Simonović JM, Šutulović N, Hrnčić D, Stanojlović O, Vesković M, Rašić DM, Mladenović D. Reduced light exposure mitigates streptozotocin-induced vascular changes and gliosis in diabetic retina by an anti-inflammatory effect and increased retinal cholesterol turnover. Chem Biol Interact 2024; 394:110996. [PMID: 38593908 DOI: 10.1016/j.cbi.2024.110996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2024] [Revised: 04/02/2024] [Accepted: 04/04/2024] [Indexed: 04/11/2024]
Abstract
Diabetic retinopathy is not cured efficiently and changes of lifestyle measures may delay early retinal injury in diabetes. The aim of our study was to investigate the effects of reduced daily light exposure on retinal vascular changes in streptozotocin (STZ)-induced model of DM with emphasis on inflammation, Aqp4 expression, visual cycle and cholesterol metabolism-related gene expression in rat retina and RPE. Male Wistar rats were divided into the following groups: 1. control; 2. diabetic group (DM) treated with streptozotocin (100 mg/kg); 3. group exposed to light/dark cycle 6/18 h (6/18); 4. diabetic group exposed to light/dark cycle 6/18 h (DM+6/18). Retinal vascular abnormalities were estimated based on lectin staining, while the expression of genes involved in the visual cycle, cholesterol metabolism, and inflammation was determined by qRT-PCR. Reduced light exposure alleviated vasculopathy, gliosis and the expression of IL-1 and TNF-α in the retina with increased perivascular Aqp4 expression. The expression of genes involved in visual cycle and cholesterol metabolism was significantly up-regulated in RPE in DM+6/18 vs. DM group. In the retina only the expression of APOE was significantly higher in DM+6/18 vs. DM group. Reduced light exposure mitigates vascular changes and gliosis in DM via its anti-inflammatory effect, increased retinal cholesterol turnover and perivascular Aqp4 expression.
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Affiliation(s)
- Dolika D Vasović
- Eye Hospital, University Clinical Centre of Serbia, 11000, Belgrade, Serbia
| | - Sanja Ivković
- Department of Molecular Biology and Endocrinology, Vinca - Institute for Nuclear Sciences, National Institute of Republic of Serbia, University of Belgrade, 11000, Belgrade, Serbia
| | - Ana Živanović
- Department of Molecular Biology and Endocrinology, Vinca - Institute for Nuclear Sciences, National Institute of Republic of Serbia, University of Belgrade, 11000, Belgrade, Serbia
| | - Tamara Major
- Department of Pharmacology, Faculty of Pharmacy, University of Belgrade, 11000, Belgrade, Serbia
| | - Jelena M Milašin
- Department of Human Genetics, School of Dental Medicine, University of Belgrade, 11000, Belgrade, Serbia
| | - Nađa S Nikolić
- Department of Human Genetics, School of Dental Medicine, University of Belgrade, 11000, Belgrade, Serbia
| | - Jelena M Simonović
- Department of Human Genetics, School of Dental Medicine, University of Belgrade, 11000, Belgrade, Serbia
| | - Nikola Šutulović
- Laboratory for Neurophysiology, Institute of Medical Physiology "Richard Burian", Faculty of Medicine, University of Belgrade, 11000, Belgrade, Serbia
| | - Dragan Hrnčić
- Laboratory for Neurophysiology, Institute of Medical Physiology "Richard Burian", Faculty of Medicine, University of Belgrade, 11000, Belgrade, Serbia
| | - Olivera Stanojlović
- Laboratory for Neurophysiology, Institute of Medical Physiology "Richard Burian", Faculty of Medicine, University of Belgrade, 11000, Belgrade, Serbia
| | - Milena Vesković
- Institute of Pathophysiology "Ljubodrag Buba Mihailovic", Faculty of Medicine, University of Belgrade, 11000, Belgrade, Serbia
| | - Dejan M Rašić
- Eye Hospital, University Clinical Centre of Serbia, 11000, Belgrade, Serbia; School of Medicine, University of Belgrade, 11000, Belgrade, Serbia
| | - Dušan Mladenović
- Institute of Pathophysiology "Ljubodrag Buba Mihailovic", Faculty of Medicine, University of Belgrade, 11000, Belgrade, Serbia.
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Zhang S, Wei X, Bowers M, Jessberger S, Golczak M, Semenkovich CF, Rajagopal R. Increasing Energetic Demands on Photoreceptors in Diabetes Corrects Retinal Lipid Dysmetabolism and Reduces Subsequent Microvascular Damage. THE AMERICAN JOURNAL OF PATHOLOGY 2023; 193:2144-2155. [PMID: 37741454 PMCID: PMC10777362 DOI: 10.1016/j.ajpath.2023.09.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Revised: 08/14/2023] [Accepted: 09/01/2023] [Indexed: 09/25/2023]
Abstract
Mechanisms responsible for the pathogenesis of diabetic retinal disease remain incompletely understood, but they likely involve multiple cellular targets, including photoreceptors. Evidence suggests that dysregulated de novo lipogenesis in photoreceptors is a critical early target of diabetes. Following on this observation, the present study aimed to determine whether two interventions shown to improve diabetic retinopathy in mice-pharmacologic visual cycle inhibition and prolonged dark adaptation-reduce photoreceptor anabolic lipid metabolism. Elevated retinal lipid biosynthetic signaling was observed in two mouse models of diabetes, with both models showing reduced retinal AMP-activated kinase (AMPK) signaling, elevated acetyl CoA carboxylase (ACC) signaling, and increased activity of fatty acid synthase, which promotes lipotoxicity in photoreceptors. Although retinal AMPK-ACC axis signaling was dependent on systemic glucose fluctuations in healthy animals, mice with diabetes lacked such regulation. Visual cycle inhibition and prolonged dark adaptation reversed abnormal retinal AMPK-ACC signaling in mice with diabetes. Although visual cycle inhibition reduced the severity of diabetic retinopathy in control mice, as assessed by retinal capillary atrophy, this intervention was ineffective in fatty acid synthase gain-of-function mice. These results suggest that early diabetic retinopathy is characterized by glucose-driven elevations in retinal lipid biosynthetic activity, and that two interventions known to increase photoreceptor glucose demands alleviate disease by reversing these signals.
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Affiliation(s)
- Sheng Zhang
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri
| | - Xiaochao Wei
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri
| | - Megan Bowers
- Faculties of Medicine and Science, Laboratory of Neural Plasticity, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - Sebastian Jessberger
- Faculties of Medicine and Science, Laboratory of Neural Plasticity, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - Marcin Golczak
- Department of Pharmacology, Case Western Reserve University School of Medicine, Cleveland, Ohio
| | - Clay F Semenkovich
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, St. Louis, Missouri; Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri
| | - Rithwick Rajagopal
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, Missouri.
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Peng L, Ma W, Xie Q, Chen B. Identification and validation of hub genes for diabetic retinopathy. PeerJ 2021; 9:e12126. [PMID: 34603851 PMCID: PMC8445088 DOI: 10.7717/peerj.12126] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Accepted: 08/17/2021] [Indexed: 12/23/2022] Open
Abstract
Background Diabetic retinopathy (DR) is characterized by a gradually progressive alteration in the retinal microvasculature that leads to middle-aged adult acquired persistent blindness. Limited research has been conducted on DR pathogenesis at the gene level. Thus, we aimed to reveal novel key genes that might be associated with DR formation via a bioinformatics analysis. Methods The GSE53257 dataset from the Gene Expression Omnibus was downloaded for gene co-expression analysis. We identified significant gene modules via the Weighted Gene Co-expression Network Analysis, which was conducted by the Protein-Protein Interaction (PPI) Network via Cytoscape and from this we screened for key genes and gene sets for particular functional and pathway-specific enrichments. The hub gene expression was verified by real-time PCR in DR rats modeling and an external database. Results Two significant gene modules were identified. Significant key genes were predominantly associated with mitochondrial function, fatty acid oxidation and oxidative stress. Among all key genes analyzed, six up-regulated genes (i.e., SLC25A33, NDUFS1, MRPS23, CYB5R1, MECR, and MRPL15) were highly and significantly relevant in the context of DR formation. The PCR results showed that SLC25A33 and NDUFS1 expression were increased in DR rats modeling group. Conclusion Gene co-expression network analysis highlights the importance of mitochondria and oxidative stress in the pathophysiology of DR. DR co-expressing gene module was constructed and key genes were identified, and both SLC25A33 and NDUFS1 may serve as potential biomarker and therapeutic target for DR.
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Affiliation(s)
- Li Peng
- Department of Ophthalmology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China.,Department of Ophthalmology, Central South University Xiangya School of Medicine Affiliated Haikou Hospital, Haikou, Hainan, China
| | - Wei Ma
- Department of Ophthalmology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
| | - Qing Xie
- Department of Ophthalmology, Central South University Xiangya School of Medicine Affiliated Haikou Hospital, Haikou, Hainan, China
| | - Baihua Chen
- Department of Ophthalmology, The Second Xiangya Hospital of Central South University, Changsha, Hunan, China
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Rajagopal R, Sylvester B, Zhang S, Adak S, Wei X, Bowers M, Jessberger S, Hsu FF, Semenkovich CF. Glucose-mediated de novo lipogenesis in photoreceptors drives early diabetic retinopathy. J Biol Chem 2021; 297:101104. [PMID: 34425110 PMCID: PMC8445899 DOI: 10.1016/j.jbc.2021.101104] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2021] [Revised: 08/10/2021] [Accepted: 08/18/2021] [Indexed: 11/23/2022] Open
Abstract
Diabetic retinopathy (DR) is an increasingly frequent cause of blindness across populations; however, the events that initiate pathophysiology of DR remain elusive. Strong preclinical and clinical evidence suggests that abnormalities in retinal lipid metabolism caused by diabetes may account for the origin of this disease. A major arm of lipid metabolism, de novo biosynthesis, is driven by elevation in available glucose, a common thread binding all forms of vision loss in diabetes. Therefore, we hypothesized that aberrant retinal lipid biogenesis is an important promoter of early DR. In murine models, we observed elevations of diabetes-associated retinal de novo lipogenesis ∼70% over control levels. This shift was primarily because of activation of fatty acid synthase (FAS), a rate-limiting enzyme in the biogenic pathway. Activation of FAS was driven by canonical glucose-mediated disinhibition of acetyl-CoA carboxylase, a major upstream regulatory enzyme. Mutant mice expressing gain-of-function FAS demonstrated increased vulnerability to DR, whereas those with FAS deletion in rod photoreceptors maintained preserved visual responses upon induction of diabetes. Excess retinal de novo lipogenesis—either because of diabetes or because of FAS gain of function—was associated with modestly increased levels of palmitate-containing phosphatidylcholine species in synaptic membranes, a finding with as yet uncertain significance. These findings implicate glucose-dependent increases in photoreceptor de novo lipogenesis in the early pathogenesis of DR, although the mechanism of deleterious action of this pathway remains unclear.
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Affiliation(s)
- Rithwick Rajagopal
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, Missouri, USA.
| | - Beau Sylvester
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, Missouri, USA
| | - Sheng Zhang
- Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, Saint Louis, Missouri, USA
| | - Sangeeta Adak
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, Saint Louis, Missouri, USA
| | - Xiaochao Wei
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, Saint Louis, Missouri, USA
| | - Megan Bowers
- Laboratory of Neural Plasticity, Faculties of Medicine and Science, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - Sebastian Jessberger
- Laboratory of Neural Plasticity, Faculties of Medicine and Science, Brain Research Institute, University of Zurich, Zurich, Switzerland
| | - Fong-Fu Hsu
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, Saint Louis, Missouri, USA
| | - Clay F Semenkovich
- Division of Endocrinology, Metabolism, and Lipid Research, Washington University School of Medicine, Saint Louis, Missouri, USA; Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, Missouri, USA.
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Tonade D, Kern TS. Photoreceptor cells and RPE contribute to the development of diabetic retinopathy. Prog Retin Eye Res 2021; 83:100919. [PMID: 33188897 PMCID: PMC8113320 DOI: 10.1016/j.preteyeres.2020.100919] [Citation(s) in RCA: 88] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Revised: 10/27/2020] [Accepted: 10/31/2020] [Indexed: 12/26/2022]
Abstract
Diabetic retinopathy (DR) is a leading cause of blindness. It has long been regarded as vascular disease, but work in the past years has shown abnormalities also in the neural retina. Unfortunately, research on the vascular and neural abnormalities have remained largely separate, instead of being integrated into a comprehensive view of DR that includes both the neural and vascular components. Recent evidence suggests that the most predominant neural cell in the retina (photoreceptors) and the adjacent retinal pigment epithelium (RPE) play an important role in the development of vascular lesions characteristic of DR. This review summarizes evidence that the outer retina is altered in diabetes, and that photoreceptors and RPE contribute to retinal vascular alterations in the early stages of the retinopathy. The possible molecular mechanisms by which cells of the outer retina might contribute to retinal vascular damage in diabetes also are discussed. Diabetes-induced alterations in the outer retina represent a novel therapeutic target to inhibit DR.
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Affiliation(s)
- Deoye Tonade
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA
| | - Timothy S Kern
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH, USA; Veterans Administration Medical Center Research Service, Cleveland, OH, USA; Gavin Herbert Eye Institute, University of California Irvine, Irvine, CA, USA; Veterans Administration Medical Center Research Service, Long Beach, CA, USA.
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Ivanova E, Bianchimano P, Corona C, Eleftheriou CG, Sagdullaev BT. Optogenetic Stimulation of Cholinergic Amacrine Cells Improves Capillary Blood Flow in Diabetic Retinopathy. Invest Ophthalmol Vis Sci 2021; 61:44. [PMID: 32841313 PMCID: PMC7452855 DOI: 10.1167/iovs.61.10.44] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Purpose Disruption in blood supply to active retinal circuits is the earliest hallmark of diabetic retinopathy (DR) and has been primarily attributed to vascular deficiency. However, accumulating evidence supports an early role for a disrupted neuronal function in blood flow impairment. Here, we tested the hypothesis that selectively stimulating cholinergic neurons could restore neurovascular signaling to preserve the capillary circulation in DR. Methods We used wild type (wt) and choline acetyltransferase promoter (ChAT)-channelrhodopsin-2 (ChR2) mice expressing ChR2 exclusively in cholinergic cells. Mice were made diabetic by streptozotocin (STZ) injections. Two to 3 months after the last STZ injection, the rate of capillary blood flow was measured in vivo within each retinal vascular layer using high speed two-photon imaging. Measurements were done at baseline and following ChR2-driven activation of retinal cholinergic interneurons, the sole source of the vasodilating neurotransmitter acetylcholine. After recordings, retinas were collected and assessed for physiological and structural features. Results In retinal explants from ChAT-ChR2 mice, we found that channelrhodopsin2 was selectively expressed in all cholinergic amacrine cells. Its direct activation by blue light led to dilation of adjacent retinal capillaries. In living diabetic ChAT-ChR2 animals, basal capillary blood flow was significantly higher than in diabetic mice without channelrhodopsin. However, optogenetic stimulation with blue light did not result in flickering light-induced functional hyperemia, suggesting a necessity for a concerted neurovascular interaction. Conclusions These findings provide direct support to the utility and efficacy of an optogenetic approach for targeting selective retinal circuits to treat DR and its complications.
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Affiliation(s)
- Elena Ivanova
- Burke Neurological Institute, White Plains, New York, United States.,Department of Neuroscience, Weill Cornell Medicine, New York, United States
| | | | - Carlo Corona
- Burke Neurological Institute, White Plains, New York, United States
| | | | - Botir T Sagdullaev
- Burke Neurological Institute, White Plains, New York, United States.,Department of Ophthalmology, Weill Cornell Medicine, New York, United States
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7
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Abstract
Based on clinical findings, diabetic retinopathy (DR) has traditionally been defined as a retinal microvasculopathy. Retinal neuronal dysfunction is now recognized as an early event in the diabetic retina before development of overt DR. While detrimental effects of diabetes on the survival and function of inner retinal cells, such as retinal ganglion cells and amacrine cells, are widely recognized, evidence that photoreceptors in the outer retina undergo early alterations in diabetes has emerged more recently. We review data from preclinical and clinical studies demonstrating a conserved reduction of electrophysiological function in diabetic retinas, as well as evidence for photoreceptor loss. Complementing in vivo studies, we discuss the ex vivo electroretinography technique as a useful method to investigate photoreceptor function in isolated retinas from diabetic animal models. Finally, we consider the possibility that early photoreceptor pathology contributes to the progression of DR, and discuss possible mechanisms of photoreceptor damage in the diabetic retina, such as enhanced production of reactive oxygen species and other inflammatory factors whose detrimental effects may be augmented by phototransduction.
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Abstract
Vision loss, among the most feared complications of diabetes, is primarily caused by diabetic retinopathy, a disease that manifests in well-recognized, characteristic microvascular lesions. The reasons for retinal susceptibility to damage in diabetes are unclear, especially considering that microvascular networks are found in all tissues. However, the unique metabolic demands of retinal neurons could account for their vulnerability in diabetes. Photoreceptors are the first neurons in the visual circuit and are also the most energy-demanding cells of the retina. Here, we review experimental and clinical evidence linking photoreceptors to the development of diabetic retinopathy. We then describe the influence of retinal illumination on photoreceptor metabolism, effects of light modulation on the severity of diabetic retinopathy, and recent clinical trials testing the treatment of diabetic retinopathy with interventions that impact photoreceptor metabolism. Finally, we introduce several possible mechanisms that could link photoreceptor responses to light and the development of retinal vascular disease in diabetes. Collectively, these concepts form the basis for a growing body of investigative efforts aimed at developing novel pharmacologic and nonpharmacologic tools that target photoreceptor physiology to treat a very common cause of blindness across the world.
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Becker S, Carroll LS, Vinberg F. Rod phototransduction and light signal transmission during type 2 diabetes. BMJ Open Diabetes Res Care 2020; 8:8/1/e001571. [PMID: 32784250 PMCID: PMC7418690 DOI: 10.1136/bmjdrc-2020-001571] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Revised: 06/22/2020] [Accepted: 07/02/2020] [Indexed: 01/31/2023] Open
Abstract
INTRODUCTION Diabetic retinopathy is a major complication of diabetes recently associated with compromised photoreceptor function. Multiple stressors in diabetes, such as hyperglycemia, oxidative stress and inflammatory factors, have been identified, but systemic effects of diabetes on outer retina function are incompletely understood. We assessed photoreceptor physiology in vivo and in isolated retinas to better understand how alterations in the cellular environment compared with intrinsic cellular/molecular properties of the photoreceptors, affect light signal transduction and transmission in the retina in chronic type 2 diabetes. RESEARCH DESIGN AND METHODS Photoreceptor function was assessed in BKS.Cs-Dock7m+/+Lepr db/J mice, using homozygotes for Leprdb as a model of type 2 diabetes and heterozygotes as non-diabetic controls. In vivo electroretinogram (ERG) was recorded in dark-adapted mice at both 3 and 6 months of age. For ex vivo ERG, isolated retinas were superfused with oxygenated Ames' media supplemented with 30 mM glucose or mannitol as iso-osmotic control and electrical responses to light stimuli were recorded. RESULTS We found that both transduction and transmission of light signals by rod photoreceptors were compromised in 6-month-old (n=9-10 eyes from 5 animals, ***p<0.001) but not in 3-month-old diabetic mice in vivo (n=4-8 eyes from 2 to 4 animals). In contrast, rod signaling was similar in isolated retinas from 6-month-old control and diabetic mice under normoglycemic conditions (n=11). Acutely elevated glucose ex vivo increased light-evoked rod photoreceptor responses in control mice (n=11, ***p<0.001), but did not affect light responses in diabetic mice (n=11). CONCLUSIONS Our data suggest that long-term diabetes does not irreversibly change the ability of rod photoreceptors to transduce and mediate light signals. However, type 2 diabetes appears to induce adaptational changes in the rods that render them less sensitive to increased availability of glucose.
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Affiliation(s)
- Silke Becker
- Ophthalmology & Visual Sciences, John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA
| | - Lara S Carroll
- Ophthalmology & Visual Sciences, John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA
| | - Frans Vinberg
- Ophthalmology & Visual Sciences, John A. Moran Eye Center, University of Utah, Salt Lake City, Utah, USA
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Identification of the aberrantly methylated differentially expressed genes in proliferative diabetic retinopathy. Exp Eye Res 2020; 199:108141. [PMID: 32721427 DOI: 10.1016/j.exer.2020.108141] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 06/21/2020] [Accepted: 07/03/2020] [Indexed: 11/23/2022]
Abstract
Diabetic retinopathy (DR) is the most common complication of diabetes. Proliferative DR (PDR) is a more advanced stage of DR, which can cause severe impaired vision and even blindness. However, the precise pathological mechanisms of PDR remain unknown. DNA methylation serves an important role in the initiation and progression of numerous types of disease including PDR. The purpose of this study was to identify the aberrantly methylated differentially expressed genes (DEGs) as potential therapeutic targets of PDR. The gene expression microarray dataset GSE60436 and the methylation profiling microarray dataset GSE57362 were used to determine the aberrantly methylated DEGs in PDR, utilizing normal retinas as controls and fibrovascular membranes (FVMs) in patients with PDR as PDR samples. The functional term and signaling pathway enrichment analysis of the selected genes were subsequently performed. In addition, protein-protein interaction (PPI) networks were constructed to determine the hub genes, and the network of transcriptional factor (TF) and target hub genes was also analyzed. In total, 132 hypomethylated genes were found to be upregulated, whereas 172 hypermethylated genes were discovered to be downregulated in PDR. The hypomethylated upregulated genes were found to be enriched in the pathways, such as "cell-substrate adhesion", "adherens junction", "cell adhesion molecule binding" and "extracellular matrix receptor interactions". Meanwhile, the hypermethylated downregulated genes were enriched in the pathways, such as "visual perception", "presynapse" and the "synaptic vesicle cycle". Based on the PPI analysis, a total of eight hub genes were identified: CTGF, SERPINH1, LOX, RBP3, OTX2, RPE65, OPN1SW and NRL. It was hypothesized that the aberrant methylation of these genes might be related to the possible pathophysiology of PDR. An important transcriptional factor, TFDP1, was discovered to share the closest interactions with the hub genes from the gene-TF network. In conclusion, the present study identified an association among DNA methylation and gene expression in PDR using bioinformatics analysis, and identified the hub genes which might be potential methylation-based diagnosis and treatment targets for PDR in the near future.
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