A systematically derived overview of the non-ubiquitous pathways and genes that define the molecular and genetic signature of the healthy trabecular meshwork.

PURPOSE: The trabecular meshwork (TM) is situated in the most frontal part of the eye and is thought to play an important role in the regulation of the eye pressure. However, this tissue is rather difficult to harvest for research. The purpose of this study is therefore to integrate the existing gene expression data of the healthy TM to increase sample size and identify its signature genes and pathways. This provides a robust reference for the study of molecular disease processes and supports the selection of candidate target genes for new treatments. METHODS: A systematic search identified microarray data of healthy TM tissue. After quality control, datasets of low quality and deviating samples were excluded. Remaining individuals were jointly normalized and integrated into one database. The average gene expression of each tested gene over all individuals was calculated. The 25% genes with the highest average expression were identified as the most active genes in the healthy TM and used as input for pathway and network analysis. Additionally, ubiquitous pathways and genes were identified and excluded from the results. Lastly, we identified genes which are likely to be TM-specific. RESULTS: The gene expression data of 44 individuals, obtained from 18 datasets, were jointly normalized. Ubiquitous genes (n = 688) and ubiquitous pathways (n = 73) were identified and excluded. Following, 1882 genes and 211 pathways were identified as the signature genes and pathways of the healthy TM. Pathway analysis revealed multiple molecular processes of which some were already known to be active in the TM, for example extracellular matrix and elastic fiber formation. Forty-six candidate TM-specific genes were identified. These consist mainly of pseudogenes or novel transcripts of which the function is unknown. CONCLUSIONS: In this comprehensive meta-analysis we identified non-ubiquitous genes and pathways that form the signature of the functioning of the healthy TM. Additionally, 46 candidate TM-specific genes were identified. This method can also be used for other tissues that are difficult to obtain for study.

Vascular risk factors for optical coherence tomography-detected macular cysts: The Maastricht Study.

PURPOSE: To investigate whether higher blood pressure and greater arterial stiffness are associated with the presence of macular cysts and whether this association is already present in the absence of micro-aneurysms in individuals with and without type 2 diabetes. METHODS: Using spectral domain optical coherence tomography (OCT), we performed a macular volume scan in 2647 individuals (mean age 60 ± 8 years, 50% men, 27% type 2 diabetes). The association between macular cysts and 24-hour systolic and diastolic blood pressure, pulse pressure, mean arterial blood pressure, carotid-femoral pulse wave velocity and carotid distensibility was assessed by use of logistic regression. RESULTS: Twenty-four hours systolic blood pressure was associated with the presence of macular cysts [OR = 1.03 (95% CI 1.00-1.05) per 1 mmHg, p = 0.03]. 24 hr pulse pressure [OR = 1.61 (95% CI 1.11-2.34) per 10 mmHg, p = 0.01] and carotid-femoral pulse wave velocity [OR = 1.16 (95% CI 1.02-1.32) per 1 m/s, p = 0.02] were associated with macular cysts, while carotid distensibility was not [OR = 1.03 (95% CI 0.96-1.11) per 1.0*10-3 /kPa, p = 0.45]. Associations were similar in individuals with and without type 2 diabetes and were already present in the absence of micro-aneurysms. CONCLUSION: Twenty-four hours systolic blood pressure, 24 hr pulse pressure and carotid-femoral pulse wave velocity are associated with the presence of OCT-detected macular cysts in individuals with and without type 2 diabetes, even in the absence of micro-aneurysms. Therefore, blood pressure and aortic stiffness are potential factors contributing to macular cysts.

The Molecular Processes in the Trabecular Meshwork After Exposure to Corticosteroids and in Corticosteroid-Induced Ocular Hypertension.

Purpose: To identify processes that contribute to corticosteroid-induced ocular hypertension and candidate target genes for treatment. Methods: A systematic search identified five human microarray datasets investigating the effect of dexamethasone versus a control medium on trabecular meshwork (TM) tissue. After thorough quality control, samples of low quality were removed, and the datasets were integrated. Additionally, a bovine RNA-sequencing dataset allowed to investigate differences in gene expression profiling between cows with and without corticosteroid-induced ocular hypertension (responders vs. nonresponders). The obtained datasets were used as input for parallel pathway analyses. Significantly changed pathways were clustered into functional categories and the results were further investigated. A network visualizing the differences between the responders and nonresponders was created. Results: Seven functional pathway clusters were found to be significantly changed in TM cells exposed to dexamethasone versus a control medium and in TM cells of responders versus nonresponders: collagen, extracellular matrix, adhesion, WNT-signaling, inflammation, adipogenesis, and glucose metabolism. In addition, cell cycle and senescence were only significantly changed in responders versus nonresponders. The network of the differential gene expression between responders and nonresponders shows many connections between the identified processes via shared genes. Conclusions: Nine functional pathway clusters synthesize the molecular response to dexamethasone exposure in TM cells and are likely to be involved in the pathogenesis of corticosteroid-induced ocular hypertension.

Comprehensive bioinformatics analysis of trabecular meshwork gene expression data to unravel the molecular pathogenesis of primary open-angle glaucoma.

PURPOSE: Performing bioinformatics analyses using trabecular meshwork (TM) gene expression data in order to further elucidate the molecular pathogenesis of primary open-angle glaucoma (POAG), and to identify candidate target genes. METHODS: A systematic search in Gene Expression Omnibus and ArrayExpress was conducted, and quality control and preprocessing of the data was performed with ArrayAnalysis.org. Molecular pathway overrepresentation analysis was performed with PathVisio using pathway content from three pathway databases: WikiPathways, KEGG and Reactome. In addition, Gene Ontology (GO) analysis was performed on the gene expression data. The significantly changed pathways were clustered into functional categories which were combined into a network of connected genes. RESULTS: Ninety-two significantly changed pathways were clustered into five functional categories: extracellular matrix (ECM), inflammation, complement activation, senescence and Rho GTPase signalling. ECM included pathways involved in collagen, actin and cell-matrix interactions. Inflammation included pathways entailing NF-κB and arachidonic acid. The network analysis showed that several genes overlap between the inflammation cluster on the one hand, and the ECM, complement activation and senescence clusters on the other hand. GO analysis, identified additional clusters, related to development and corticosteroids. CONCLUSION: This study provides an overview of the processes involved in the molecular pathogenesis of POAG in the TM. The results show good face validity and confirm findings from histological, biochemical, genome-wide association and transcriptomics studies. The identification of known points of action for drugs, such as Rho GTPase, arachidonic acid, NF-κB, prostaglandins and corticosteroid clusters, supports the value of this approach to identify potential drug targets.

Risk Factors for the Development of Ocular Hypertension After Keratoplasty: A Systematic Review.

PURPOSE: To identify risk factors for the development of ocular hypertension after keratoplasty. METHODS: A systematic search in PubMed and Embase identified 67 relevant articles published between January 1990 and 2019. We preferentially searched for data on an intraocular pressure increase above 21 mmHg at 6 months or a threshold or time point close to that and reported whether the preoperative or intraoperative status of risk factors was defined. The results were presented in evidence tables, visualizing the direction of the association, whether univariate and/or multivariate analysis was performed, and the significance level (P < 0.05). Four researchers, blinded for the risk factors, independently assigned a level of evidence (definitely, probably, possibly, not associated). Consensus was met during group meetings. RESULTS: From the 110 studied risk factors, pre-existing glaucoma, high preoperative IOP and combined keratoplasty with removal or exchange of an intraocular lens (IOL) were definitely associated with an increased risk. In addition, if the pre-or postoperative lens status was undefined, aphakia and pseudophakia with the IOL in the anterior or posterior chamber were also definitely associated with an increased risk when compared to phakia. Glaucoma in the contralateral eye, indication of bullous keratopathy, African American descent, preoperative treatment with cyclosporine or olopatadine 0.1%, postoperative treatment with prednisolone acetate 1%, and combined surgery in general (ie, the type of surgeries undefined in primary studies) were probably associated. Multiple other identified risk factors lack sufficient evidence and need additional investigation. CONCLUSIONS: Risk factors with a definite association can help clinicians select patients at risk and adjust their follow-up and treatment. The other factors need further investigation.

Prevalence of optical coherence tomography detected vitreomacular interface disorders: The Maastricht Study.

PURPOSE: To calculate the prevalence of all vitreomacular interface (VMI) disorders and stratify according to age, sex and (pre)diabetes status. METHODS: The presence of VMI disorders was assessed in 2660 participants aged between 40 and 75 years from The Maastricht Study who had a gradable macular spectral-domain optical coherence tomography (SD-OCT) volume scan in at least one eye [mean 59.7 ± 8.2 years, 50.2% men, 1531 normal glucose metabolism (NGM), 401 prediabetes, 728 type 2 diabetes (DM2, oversampled)]. A stratified and multivariable logistic regression analysis was used. RESULTS: The prevalence of the different VMI disorders for individuals with NGM, prediabetes and DM2 was, respectively, 5.7%, 6% and 6.7% for epiretinal membranes; 6%, 9.6% and 6.8% for vitreomacular traction; 1.1%, 0.7% and 0.3% for lamellar macular holes; 0.1%, 0% and 0% for pseudoholes; 1.1%, 1.9% and 5.5% for macular cysts. None of the participants was diagnosed with a macular hole. The prevalence of epiretinal membranes, vitreomacular traction and macular cysts was higher with age (p < 0.001). Vitreomacular traction and lamellar macular holes were more frequent in women (p < 0.01). DM2 is positively associated [OR = 3.9 (95% CI 2.11-7.22, p < 0.001)] with macular cysts and negatively associated with lamellar macular holes [OR = 0.2 (95% CI 0.04-0.9, p = 0.036)] after adjustment for age and sex. The calculated prevalence of VMI disorders was 15.9%. CONCLUSIONS: The calculated prevalence of VMI disorders in individuals aged between 40 and 75 years is 15.9%. The prevalence depends on age, sex and glucose metabolism status for several types of VMI disorders.