Matrix metalloproteinases and their tissue inhibitors in aqueous humor of patients with primary open-angle glaucoma, exfoliation syndrome, and exfoliation glaucoma

Association of Matrix Metalloproteinases Polymorphisms with Glaucoma Risk, Glaucoma Phenotype, and Response to Treatment with Selective Laser Trabeculoplasty or Latanoprost

In open-angle glaucoma, the increase in intraocular pressure (IOP) is caused by an increased resistance to aqueous humour outflow in the trabecular meshwork. Since genetic variability of matrix metalloproteinase (MMP) genes may influence extracellular matrix remodelling, we investigated their association with glaucoma risk and/or response to treatment. The retrospective part of the study included patients with primary open-angle glaucoma and ocular hypertension (OHT); in the prospective part of the study, newly diagnosed patients with POAG or OHT were randomised to receive either latanoprost or selective laser trabeculoplasty (SLT) as the initial treatment. The reduction in IOP was measured 6 weeks after treatment. The following MMP single nucleotide polymorphisms were genotyped: MMP2 rs243865, rs243849, and rs7201; MMP3 rs3025058; MMP9 rs17576, rs17577, rs20544, and rs2250889; MMP14 rs1042704, rs1042704, and rs743257. Logistic regression was used to calculate odds ratios to assess the association between MMP polymorphism and risk of POAG or OHT, glaucoma phenotypes and response to treatment. Only carriers of the MMP3 rs3025058 TT genotype had a significantly higher risk of OHT, more advanced glaucoma, and a higher C/D ratio in the additive and dominant models. None of the investigated MMP polymorphisms were associated with response to treatment with latanoprost and SLT in our study population.

The relationship between intraocular pressure and glaucoma: An evolving concept

Intraocular pressure (IOP) is the most important modifiable risk factor for glaucoma and fluctuates considerably within patients over short and long time periods. Our field's understanding of IOP has evolved considerably in recent years, driven by tonometric technologies with increasing accuracy, reproducibility, and temporal resolution that have refined our knowledge regarding the relationship between IOP and glaucoma risk and pathogenesis. The goal of this article is to review the published literature pertinent to the following points: 1) the factors that determine IOP in physiologic and pathologic states; 2) technologies for measuring IOP; 3) scientific and clinical rationale for measuring diverse IOP metrics in patients with glaucoma; 4) the impact and shortcomings of current standard-of-care IOP monitoring approaches; 5) recommendations for approaches to IOP monitoring that could improve patient outcomes; and 6) research questions that must be answered to improve our understanding of how IOP contributes to disease progression. Retrospective and prospective data, including that from landmark clinical trials, document greater IOP fluctuations in glaucomatous than healthy eyes, tendencies for maximal daily IOP to occur outside of office hours, and, in addition to mean and maximal IOP, an association between IOP fluctuation and glaucoma progression that is independent of mean in-office IOP. Ambulatory IOP monitoring, measuring IOP outside of office hours and at different times of day and night, provides clinicians with discrete data that could improve patient outcomes. Eye care clinicians treating glaucoma based on isolated in-office IOP measurements may make treatment decisions without fully capturing the entire IOP profile of an individual. Data linking home blood pressure monitors and home glucose sensors to dramatically improved outcomes for patients with systemic hypertension and diabetes and will be reviewed as they pertain to the question of whether ambulatory tonometry is positioned to do the same for glaucoma management. Prospective randomized controlled studies are warranted to determine whether remote tonometry-based glaucoma management might reduce vision loss and improve patient outcomes.

Genome-wide RNA sequencing of ocular fibroblasts from glaucomatous and normal eyes: Implications for glaucoma management

Primary open angle glaucoma is a leading cause of visual impairment and blindness which is commonly treated with drugs or laser but may require surgery. Tenon's ocular fibroblasts are involved in wound-healing after glaucoma filtration surgery and may compromise a favourable outcome of glaucoma surgery by contributing to fibrosis. To investigate changes in gene expression and key pathways contributing to the glaucomatous state we performed genome-wide RNA sequencing. Human Tenon's ocular fibroblasts were cultured from normal and glaucomatous human donors undergoing eye surgery (n = 12). mRNA was extracted and RNA-Seq performed on the Illumina platform. Differentially expressed genes were identified using a bioinformatics pipeline consisting of FastQC, STAR, FeatureCounts and edgeR. Changes in biological functions and pathways were determined using Enrichr and clustered using Cytoscape. A total of 5817 genes were differentially expressed between Tenon's ocular fibroblasts from normal versus glaucomatous eyes. Enrichment analysis showed 787 significantly different biological functions and pathways which were clustered into 176 clusters. Tenon's ocular fibroblasts from glaucomatous eyes showed signs of fibrosis with fibroblast to myofibroblast transdifferentiation and associated changes in mitochondrial fission, remodeling of the extracellular matrix, proliferation, unfolded protein response, inflammation and apoptosis which may relate to the pathogenesis of glaucoma or the detrimental effects of topical glaucoma therapies. Altered gene expression in glaucomatous Tenon's ocular fibroblasts may contribute to an unfavourable outcome of glaucoma filtration surgery. This work presents a genome-wide transcriptome of glaucomatous versus normal Tenon's ocular fibroblasts which may identify genes or pathways of therapeutic value to improve surgical outcomes.

Relative ability of aqueous humor from dogs with and without primary angle-closure glaucoma and ADAMTS10 open-angle glaucoma to catalyze or inhibit collagenolysis

OBJECTIVE

The objective of the study was to compare the ability of aqueous humor (AH) from dogs with primary angle-closure glaucoma (CPACG), companion dogs without overt evidence of CPACG, and Beagles with and without ADAMTS10 open-angle glaucoma (ADAMTS10-OAG) to catalyze or inhibit collagenolysis.

ANIMALS STUDIED

Seventeen normal pet dogs, 27 dogs with CPACG, 19 Beagles with ADAMTS10-OAG, and 4 unaffected Beagles.

PROCEDURES

A fluorescein-based substrate degradation assay was used to assess AH proteolytic capacity. Samples were then assayed using the same substrate degradation assay, with recombinant activated matrix metalloproteinase-2 (MMP-2) added to measure protease inhibition effects.

RESULTS

For the protease activity assay, relative fluorescence (RF) for AH from normal pet dogs was 13.28 ± 2.25% of control collagenase while RF for AH from dogs with CPACG was 17.47 ± 4.67%; RF was 8.57 ± 1.72% for ADAMTS10-OAG Beagles and 7.99 ± 1.15% for unaffected Beagles. For the MMP-2 inhibition assay, RF for AH from normal dogs was 34.96 ± 15.04% compared to MMP-2 controls, while RF from dogs with CPACG was 16.69 ± 7.95%; RF was 85.85 ± 13.23% for Beagles with ADAMTS10-OAG and 94.51 ± 8.36% for unaffected Beagles. Significant differences were found between dogs with CPACG and both normal pet dogs and dogs with ADAMTS10-OAG and between normal pet dogs and both groups of Beagles.

CONCLUSIONS

AH from dogs with CPACG is significantly more able to catalyze proteolysis and inhibit MMP-2 than AH from normal dogs or dogs with ADAMTS10-OAG. Results suggest that pathogenesis may differ between CPACG and ADAMTS10-OAG.

Association between Oral Active-Matrix Metalloproteinase-8 Levels and Subretinal Fibrosis among Wet Age-Related Macular Degeneration Patients

PURPOSE

Periodontitis causes low-grade systemic inflammation and has been associated with elevated active-matrix metalloproteinase (aMMP-8) levels, blood-ocular barrier breakdown and a risk of wet age-related macular degeneration. To assess the association between aMMP-8 levels and macular status among patients with wet age-related macular degeneration (AMD).

METHODS

Patients on anti-VEGF treatment for wet AMD were enrolled for oral aMMP-8 rinse test in Mehiläinen Private Hospital, Helsinki, Finland. Macular status was examined from spectral-domain optical coherence tomography (SD-OCT) scans by a medical retina specialist and aMMP-8 levels were analyzed with chairside point-of-care oral rinse (PerioSafe®) test and real-time quantitated by a dentist using the ORALyzer®- reader with a 10 ng/ml cut-off for aMMP-8 activity.

RESULTS

Elevated aMMP-8 levels were found in 10 out of 32 patients. Age, gender, anti-VEGF (bevacizumab or aflibercept) distribution, cumulative number of anti-VEGF injections and treatment interval were comparable between patients with aMMP-8 levels below and above the point-of-care level. Macular status differed in regard to aMMP-8 activity; among patients with aMMP-8 levels below the point-of-care subretinal fibrosis was found in 6 out of 22 eyes, whereas among patients with aMMP-8 levels above the point-of-care subretinal fibrosis was found in 8 out of 10 eyes (p = 0.005). Respectively, the mean thickness of subretinal fibrosis at fovea was 19.5 ± 44.1 and 92.3 ± 78.3 µm (p = 0.018). No differences were found in the presence and in the area of geographic atrophy, or fluid distribution, whereas thicknesses of serous pigment epithelial detachment (65.5 ± 99.5 and 12.9 ± 27.9 µm, p = 0.038) and neuroretina (204.2 ± 57.8 µm and 143.0 ± 43.7 µm, p = 0.006) were greater in the eyes of patients with physiological aMMP-8 levels compared to those with elevated aMMP-8 levels.

CONCLUSION

Elevated aMMP-8 levels may account for subretinal fibrosis formation in wet AMD.

Matrix Metalloproteinases in Glaucoma: An Updated Overview

Matrix metalloproteinases (MMPs) are important regulators of the extracellular matrix (ECM) and are involved in many stages of cellular growth and development. An imbalance of MMP expression is also the basis of many diseases, including eye diseases, such as diabetic retinopathy (DR), glaucoma, dry eye, corneal ulcer, keratoconus. This paper describes the role of MMPs in the glaucoma and their role in the glaucomatous trabecular meshwork (TM), aqueous outflow channel, retina, and optic nerve (ON). This review also summarizes several treatments for glaucoma that target MMPs imbalance and suggests that MMPs may represent a viable therapeutic target for glaucoma.

Advances in targeting the extracellular matrix for glaucoma therapy: current updates

INTRODUCTION

Elevated intraocular pressure (IOP) is a well-recognized risk factor for development of primary open angle glaucoma (POAG), a leading cause of irreversible blindness. Ocular hypertension is associated with excessive extracellular matrix (ECM) deposition in trabecular meshwork (TM) resulting in increased aqueous outflow resistance and elevated IOP. Hence, therapeutic options targeting ECM remodeling in TM to lower IOP in glaucomatous eyes are of considerable importance.

AREAS COVERED

This paper discusses the complex process of ECM regulation in TM and explores promising therapeutic targets. The role of Transforming Growth Factor-β as a central player in ECM deposition in TM is discussed. We elaborate the key regulatory processes involved in its activation, release, signaling, and cross talk with other signaling pathways including Rho GTPase, Wnt, integrin, cytokines, and renin-angiotensin-aldosterone. Further, we summarize the therapeutic agents that have been explored to target ECM dysregulation in TM.

EXPERT OPINION

Targeting molecular pathways to reduce ECM deposition and/or enhance its degradation are of considerable significance for IOP lowering. Challenges lie in pinpointing specific targets and designing drug delivery systems to precisely interact with pathologically active/inactive signaling. Recent advances in monoclonal antibodies, fusion molecules, and vectored nanotechnology offer potential solutions.

Proposed Mechanism of Long-Term Intraocular Pressure Lowering With the Bimatoprost Implant

Purpose

The purpose of this study was to evaluate the effects of pharmacologically relevant bimatoprost and bimatoprost free acid (BFA) concentrations on matrix metalloproteinase (MMP) gene expression in cells from human aqueous outflow tissues.

Methods

MMP gene expression by human trabecular meshwork (TM), scleral fibroblast (SF), and ciliary muscle (CM) cells exposed to 10 to 1000 µM bimatoprost or 0.1 to 10 µM BFA (intraocular concentrations after intracameral bimatoprost implant and topical bimatoprost dosing, respectively) was measured by polymerase chain reaction array.

Results

Bimatoprost dose-dependently upregulated MMP1 and MMP14 mRNA in all cell types and MMP10 and MMP11 mRNA in TM and CM cells; in TM cells from normal eyes, mean MMP1 mRNA levels were 62.9-fold control levels at 1000 µM bimatoprost. BFA upregulated MMP1 mRNA only in TM and SF cells, to two- to three-fold control levels. The largest changes in extracellular matrix (ECM)-related gene expression by TM cells derived from normal (n = 6) or primary open-angle glaucoma (n = 3) eyes occurred with 1000 µM bimatoprost (statistically significant, ≥50% change for 9-11 of 84 genes on the array, versus 1 gene with 10 µM BFA).

Conclusions

Bimatoprost and BFA had differential effects on MMP/ECM gene expression. Dramatic upregulation in MMP1 and downregulation of fibronectin, which occurred only with bimatoprost at high concentrations observed in bimatoprost implant-treated eyes, may promote sustained outflow tissue remodeling and long-term intraocular pressure reduction beyond the duration of intraocular drug bioavailability. Variability in bimatoprost-stimulated MMP upregulation among cell strains from different donors may help explain differential long-term responses of patients to bimatoprost implant.

Glycosaminoglycans Influence Extracellular Matrix of Human Trabecular Meshwork Cells Cultured on 3D Scaffolds

Glaucoma is a multifactorial progressive optic neuropathy characterized by the loss of retinal ganglion cells leading to irreversible blindness. It is the leading cause of global irreversible blindness and is currently affecting over 70 million people. Elevated intraocular pressure (IOP) is considered the only modifiable risk factor and is a target of numerous treatment modalities. Researchers have assigned this elevation of IOP to accumulation of extracellular matrix (ECM) components in the aqueous humor (AH) outflow pathway. The major drainage structure for AH outflow is the trabecular meshwork (TM). The ECM of the TM is important in regulating IOP in both normal and glaucomatous eyes. In this work, we have studied the role of exogeneous glycosaminoglycans (GAGs), glucocorticoids, and culture conditions on the expression of the ECM gene and proteins by human TM (hTM) cells cultured on biomaterial scaffolds. Gene and protein expression levels of elastin, laminin, and matrix metalloproteinase-2 (MMP-2) were evaluated using quantitative PCR and immunohistochemistry. Pressure gradient changes in cell-laden scaffolds in perfusion cultures were also monitored. Our findings show that GAGs and dexamethasone play an influencing role in hTM ECM turnover at both transcriptional and translational levels by altering expression levels of elastin, laminin, and MMP-2. Understanding the role of exogeneous factors on hTM cell behavior is helpful in gaining insights on glaucoma pathogenesis and ultimately pivotal in development of novel therapeutics against the disease.

Matrix Metalloproteinases and Glaucoma

Matrix metalloproteinases (MMPs) are enzymes that decompose extracellular matrix (ECM) proteins. MMPs are thought to play important roles in cellular processes, such as cell proliferation, differentiation, angiogenesis, migration, apoptosis, and host defense. MMPs are distributed in almost all intraocular tissues and are involved in physiological and pathological mechanisms of the eye. MMPs are also associated with glaucoma, a progressive neurodegenerative disease of the eyes. MMP activity affects intraocular pressure control and apoptosis of retinal ganglion cells, which are the pathological mechanisms of glaucoma. It also affects the risk of glaucoma development based on genetic pleomorphism. In addition, MMPs may affect the treatment outcomes of glaucoma, including the success rate of surgical treatment and side effects on the ocular surface due to glaucoma medications. This review discusses the various relationships between MMP and glaucoma.

Scleral Cross-Linking in Form-Deprivation Myopic Guinea Pig Eyes Leads to Glaucomatous Changes

Purpose

To investigate the potential glaucomatous changes caused by scleral cross-linking (CXL) in a guinea pig form-deprivation (FD) myopia model.

Methods

Eighty 4-week-old tricolor guinea pigs were divided into four groups: FD only, genipin CXL only, FD plus CXL, and control. Refractive error, axial length (AL), intraocular pressure (IOP), and structural and vasculature optic disc changes in optical coherence tomography (OCT) and OCT angiography (OCTA) were measured at baseline and day 21. CXL efficacy was evaluated by scleral rigidity Young's modulus values. Histological and molecular changes in the anterior chamber angle, retina, and sclera were assessed.

Results

Baseline parameters were similar among groups (P > 0.05). The FD plus CXL group at day 21 had the least increase of AL (0.14 ± 0.08 mm) and highest IOP elevation (31.5 ± 3.6 mmHg) compared with the FD-only group (AL: 0.68 ± 0.17 mm; IOP: 22.2 ± 2.6 mmHg) and the control group (AL: 0.24 ± 0.09 mm; IOP: 17.4 ± 1.8 mmHg) (all P < 0.001). OCT and OCTA parameters of the optic disc in the FD plus CXL group at day 21 showed glaucomatous changes and decreased blood flow signals. Sclera rigidity increased in the CXL and FD plus CXL groups. Advanced glycation end products deposited extensively in the retina, choroid, and sclera of FD plus CXL eyes.

Conclusions

CXL causes increased IOP and subsequent optic disc, anterior segment, and scleral changes while inhibiting myopic progression and axial elongation in FD guinea pig eyes. Therefore, applying CXL to control myopia raises safety concerns.

The Role of Metalloproteinases and Their Tissue Inhibitors on Ocular Diseases: Focusing on Potential Mechanisms

Eye diseases are associated with visual impairment, reduced quality of life, and may even lead to vision loss. The efficacy of available treatment of eye diseases is not satisfactory. The unique environment of the eye related to anatomical and physiological barriers and constraints limits the bioavailability of existing agents. In turn, complex ethiopathogenesis of ocular disorders that used drugs generally are non-disease specific and do not act causally. Therefore, there is a need for the development of a new therapeutic and preventive approach. It seems that matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) have a significant role in the development and progression of eye diseases and could be used in the therapy of these disorders as pharmacological targets. MMPs and TIMPs play an important role in the angiogenesis, epithelial-mesenchymal transition, cell invasion, and migration, which occur in ocular diseases. In this review, we aim to describe the participation of MMPs and TIMPs in the eye diseases, such as age-related macular degeneration, cataract, diabetic retinopathy, dry eye syndrome, glaucoma, and ocular cancers, posterior capsule opacification focusing on potential mechanisms.

Functionally significant polymorphisms of the MMP9 gene are associated with primary open-angle glaucoma in the population of Russia

PURPOSE

The aim of this study was to investigate the role of functionally significant loci of the matrix metalloproteinases genes 1, 3, 9 (MMP1, MMP3, and MMP9) in the development of primary open-angle glaucoma (POAG) in Caucasians of the Central region of Russia.

METHODS

In total 604 participants were recruited for the study, including 208 patients with POAG and 396 healthy controls. They were genotyped at eight single nucleotide polymorphisms (SNPs) of the three MMP genes. The association was analyzed using logistic and log-linear regression. POAG-associated loci and their proxies were in silico assessed for their functional prediction.

RESULTS

Variant allele G*rs2250889 of MMP9 was significantly associated with higher risk of POAG (OR_cov = 1.57-1.71). Haplotype CCA [rs3918242-rs3918249-rs17576] of the MMP9 gene was associated with lower risk of POAG (OR_cov = 0.33). Allele А*rs3787268 of MMP9 was associated with the low intraocular pressure in the POAG patients (β_cov = -0.176 - -0.272), and so were haplotypes AA [rs17576-rs3787268] (β_cov = -0.577) and AAC [rs17576-rs3787268- rs2250889] (β_cov = -0.742) of the same gene, whereas allele 2G*rs1799750 of MMP1 was associated with the earlier onset of the disease (β_cov = -0.112 - -0.218). In silico analysis of the polymorphisms suggested the functionality of POAG-associated SNPs and their proxies (epigenetic potential, expression and alternative splicing effects for several genes).

CONCLUSIONS

The MMP9 gene polymorphisms are associated with POAG and intraocular pressure in POAG patients; rs1799750 of MMP1 was associated with the earlier age of manifestation of the disease symptoms.

Evaluation of matrix metalloproteinases and tissue inhibitors of metalloproteinases in aqueous humor of dogs with versus without naturally occurring primary angle-closure glaucoma

OBJECTIVE

To compare concentrations of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in aqueous humor from ophthalmologically normal dogs and dogs with naturally occurring primary angle-closure glaucoma (cPACG).

SAMPLE

Aqueous humor samples from 12 eyes with cPACG and 18 ophthalmologically normal eyes of dogs.

PROCEDURES

A multiplex fluorescence-based ELISA was used to measure concentrations of MMP-1, MMP-2, MMP-3, MMP-8, MMP-9, MMP-10, MMP-13, TIMP-1, TIMP-2, and TIMP-4. Results for eyes with versus without cPACG were compared.

RESULTS

Significantly higher mean concentrations of MMP-1 (45% higher), MMP-2 (55% higher), MMP-3 (39% higher), MMP-8 (79% higher), MMP-9 (29% higher), MMP-10 (60% higher), TIMP-1 (63% higher), and TIMP-2 (136% higher) were detected in aqueous humor from eyes with cPACG, compared with ophthalmologically normal eyes.

CLINICAL RELEVANCE

MMPs and TIMPs have pivotal roles in extracellular matrix turnover and homeostasis in the outflow pathways of the eye. Results of the present study documented higher concentrations of MMPs and TIMPs in aqueous humor samples from dog eyes with late-stage cPACG. Although, to our knowledge, TIMPs have not previously been evaluated in the context of cPACG, the markedly higher concentration of TIMPs in eyes with cPACG suggested that inhibition of proteolysis and extracellular matrix turnover might be a factor in the development of glaucoma in susceptible individuals. However, because the present study used samples from dogs with late-stage cPACG, further work is required to characterize the temporal relationship between MMP and TIMP concentration changes and onset or progression of disease.

Aqueous humor proteomic analysis of acute angle-closure glaucoma with visual field loss

Background

Acute angle-closure glaucoma (AACG) is an ophthalmic emergency that occurs over the course of hours or days and may cause irreversible blindness if not treated immediately. In most cases, optic nerve damage is the cause of visual field (VF) loss in AACG. There has been no reliable biomarker found to evaluate optic nerve damage to date. Aqueous humor (AH) proteome analysis might reveal the proteomic alterations in AACG and provide helpful clues in the search for an AH biomarker of optic nerve damage and VF loss.

Methods

In this study, we used the AH proteome to explore the functions of differentially expressed proteins (DEPs) during disease progression. The AH proteins from the early-stage group and late-stage group were extracted and analyzed by the data-independent acquisition (DIA) method. The DEPs functions were annotated, and parallel reaction monitoring (PRM) was used to validate the key DEPs.

Results

A total of 87 DEPs were found. Gene Ontology analysis showed that most DEPs were enriched in immunology, hemodynamics, and apoptosis. Ingenuity pathway analysis found that vascular endothelial growth factor (VEGF) signaling, the production of reactive oxygen species (ROS) in macrophages, and the nuclear factor erythroid 2-related factor 2 (NRF2)-mediated oxidative stress response were active pathways in the late stage of AACG. The mechanism of retinal ganglion cell (RGC) death was hypothesized on the basis of DEP functional analysis. A total of 20 DEPs were validated by using PRM, and prostaglandin-H2 D-isomerase was found to have the potential to evaluate optic nerve damage.

Conclusions

This study showed that AH proteomic analysis could reveal the proteomic alterations in the pathogenesis of VF loss in AACG and help to provide objective protein biomarkers to evaluate VF loss. These findings will benefit the application of the AH proteome to clinical research.

Establishment of appropriate glaucoma models using dexamethasone or TGFβ2 treated three-dimension (3D) cultured human trabecular meshwork (HTM) cells

To establish appropriate ex vivo models for a glaucomatous trabecular meshwork (TM), two-dimensional (2D) and three-dimensional (3D) cultures of human trabecular meshwork cells (HTM) were prepared in the presence of 250 nM dexamethasone (DEX) or 5 ng/mL TGFβ2, and characterized by the following analyses; transendothelial electrical resistance (TEER) measurements, FITC dextran permeability, scanning electron microscopy and the expression of the extracellular matrix (ECM) including collagen (COL)1, 4 and 6, and fibronectin (FN), α-smooth muscle actin (α-SMA), tissue inhibitor of metalloproteinase (TIMP)1–4, and matrix metalloproteinase (MMP)2, 9 and 14. DEX and TGFβ2 both caused a significant increase or decrease in the TEER values and FITC dextran permeability. During the 3D spheroid culture, DEX or TGFβ2 induced a mild and significant down-sizing and an increase in stiffness, respectively. TGFβ2 induced a significant up-regulation of COL1 and 4, FN, α-SMA, and MMP 2 and 14 (2D) or COL1 and 6, and TIMP2 and 3 (3D), and DEX induced a significant up-regulation of FN (3D) and TIMP4 (2D and 3D). The findings presented herein indicate that DEX or TGFβ2 resulted in mild and severe down-sized and stiff 3D HTM spheroids, respectively, thus making them viable in vitro HTM models for steroid-induced and primary open angle glaucoma.

Candidate Glaucoma Biomarkers: From Proteins to Metabolites, and the Pitfalls to Clinical Applications

Glaucoma is an insidious group of eye diseases causing degeneration of the optic nerve, progressive loss of vision, and irreversible blindness. The number of people affected by glaucoma is estimated at 80 million in 2021, with 3.5% prevalence in people aged 40-80. The main biomarker and risk factor for the onset and progression of glaucoma is the elevation of intraocular pressure. However, when glaucoma is diagnosed, the level of retinal ganglion cell death usually amounts to 30-40%; hence, the urgent need for its early diagnosis. Molecular biomarkers of glaucoma, from proteins to metabolites, may be helpful as indicators of pathogenic processes observed during the disease's onset. The discovery of human glaucoma biomarkers is hampered by major limitations, including whether medications are influencing the expression of molecules in bodily fluids, or whether tests to validate glaucoma biomarker candidates should include human subjects with different types and stages of the disease, as well as patients with other ocular and neurodegenerative diseases. Moreover, the proper selection of the biofluid or tissue, as well as the analytical platform, should be mandatory. In this review, we have summarized current knowledge concerning proteomics- and metabolomics-based glaucoma biomarkers, with specificity to human eye tissue and fluid, as well the analytical approach and the main results obtained. The complex data published to date, which include at least 458 different molecules altered in human glaucoma, merit a new, integrative approach allowing for future diagnostic tests based on the absolute quantification of local and/or systemic biomarkers of glaucoma.

Diverse effects of pan-ROCK and ROCK2 inhibitors on 2 D and 3D cultured human trabecular meshwork (HTM) cells treated with TGFβ2

A pan-ROCK-inhibitor, ripasudil (Rip), and a ROCK2 inhibitor, KD025, were used To study the effects of Rho-associated coiled-coil containing protein kinase (ROCK)1 and 2 on two-dimensional (2D) and three-dimensional (3D) cultures of a TGFβ2-treated human trabecular meshwork (HTM) cells. In the presence of 5 ng/mL TGFβ2, the effects of these inhibitors were characterized by transendothelial electrical resistance (TEER), FITC-dextran permeability, and the size and stiffness of 3D sphenoids, the expression of extracellular matrix (ECM) including collagen1, 4 and 6, and fibronectin, α-smooth muscle actin, a tissue inhibitor of metalloproteinase (TIMP)1–4, and matrix metalloproteinase (MMP)2, 9 and 14. TGFβ2 caused a significant increase in the TEER values, and decrease in FITC-dextran permeability, as well as a decrease in the sizes and stiffness of the 3D sphenoids. In the presence of ROCK inhibitors, the TGFβ2-induced effects of the TEER and FITC-dextran permeability were inhibited, especially by KD025. Rip induced a significant increase in sizes and a decrease in the stiffness of the TGFβ2-treated 3D sphenoids, although the effects of KD025 were weaker. Gene expressions of most of the ECMs, TIMP2 and MMP9 of 2D and 3D HTM cells were significantly up-regulated by TGFβ2. Those were significantly and differently modulated by Rip or KD025.

Normal and glaucomatous outflow regulation

Glaucoma remains only partially understood, particularly at the level of intraocular pressure (IOP) regulation. Trabecular meshwork (TM) and Schlemm's canal inner wall endothelium (SCE) are key to IOP regulation and their characteristics and behavior are the focus of much investigation. This is becoming more apparent with time. We and others have studied the TM and SCE's extracellular matrix (ECM) extensively and unraveled much about its functions and role in regulating aqueous outflow. Ongoing ECM turnover is required to maintain IOP regulation and several TM ECM manipulations modulate outflow facility. We have established clearly that the outflow pathway senses sustained pressure deviations and responds by adjusting the outflow resistance correctively to keep IOP within an appropriately narrow range which will not normally damage the optic nerve. The glaucomatous outflow pathway has in many cases lost this IOP homeostatic response, apparently due at least in part, to loss of TM cells. Depletion of TM cells eliminates the IOP homeostatic response, while restoration of TM cells restores it. Aqueous outflow is not homogeneous, but rather segmental with regions of high, intermediate and low flow. In general, glaucomatous eyes have more low flow regions than normal eyes. There are distinctive molecular differences between high and low flow regions, and during the response to an IOP homeostatic pressure challenge, additional changes in segmental molecular composition occur. In conjunction with these changes, the biomechanical properties of the juxtacanalicular (JCT) segmental regions are different, with low flow regions being stiffer than high flow regions. The JCT ECM of glaucomatous eyes is around 20 times stiffer than in normal eyes. The aqueous humor outflow resistance has been studied extensively, but neither the exact molecular components that comprise the resistance nor their exact location have been established. Our hypothetical model, based on considerable available data, posits that the continuous SCE basal lamina, which lies between 125 and 500 nm beneath the SCE basal surface, is the primary source of normal resistance. On the surface of JCT cells, small and highly controlled focal degradation of its components by podosome- or invadopodia-like structures, PILS, occurs in response to pressure-induced mechanical stretching. Sub-micron sized basement membrane discontinuities develop in the SCE basement membrane and these discontinuities allow passage of aqueous humor to and through SCE giant vacuoles and pores. JCT cells then relocate versican with its highly charged glycosaminoglycan side chains into the discontinuities and by manipulation of their orientation and concentration, the JCT and perhaps the SCE cells regulate the amount of fluid passage. Testing this outflow resistance hypothesis is ongoing in our lab and has the potential to advance our understanding of IOP regulation and of glaucoma.

TGFβ1, MMPs and cytokines profiles in ocular surface: Possible tear biomarkers for pseudoexfoliation

Purpose

Pseudoexfoliation (PXF) is a unique form of glaucoma characterized by accumulation of exfoliative material in the eyes. Changes in tear profile in disease stages may give us insights into molecular mechanisms involved in causing glaucoma in the eye.

Methods

All patients were categorized into three main categories; pseudoexfoliation (PXF), pseudoexfoliation glaucoma (PXG) and cataract, which served as control. Cytokines, transforming growth factor β1 (TGFβ1), matrix metalloproteases (MMPs) and fibronectin (FN1) were assessed with multiplex bead assay, enzyme-linked immunosorbent assay (ELISA), gelatin zymography, and immunohistochemistry (IHC) respectively in different ocular tissues such as tears, tenon’s capsule, aqueous humor (AH) and serum samples of patients with PXF stages.

Results

We found that TGFβ1, MMP-9 and FN1 protein expression were upregulated in tears, tenon’s capsule and AH samples in PXG compared to PXF, though the MMP-9 protein activity was downregulated in PXG compared with control or PXF. We have also found that in PXG tears sample the fold change of TGF-α (Transforming Growth Factor-α), MDC (Macrophage Derived Chemokine), IL-8 (Interleukin-8), VEGF (Vascular Endothelial Growth Factor) were significantly downregulated and the levels of GM-CSF (Granulocyte Macrophage Colony Stimulating Factor), IP-10 (Interferon- γ produced protein-10) were significant upregulated. While in AH; IL-6 (Interleukin-6), IL-8, VEGF, IFN-a2 (Interferon- α2), GRO (Growth regulated alpha protein) levels were found lower and IL1a (Interleukin-1α) level was higher in PXG compared to PXF. And in serum; IFN-a2, Eotaxin, GM-CSF, Fractalkine, IL-10 (Interleukin-10), IL1Ra (Interleukin-1 receptor antagonist), IL-7 (Interleukin-7), IL-8, MIP1β (Macrophage Inflammatory Protein-1β), MCP-1 (Monocyte Chemoattractant Protein-1) levels were significantly upregulated and PDGF-AA (Platelet Derived Growth Factor-AA) level was downregulated in the patients with PXG compared to PXF.

Conclusions

Altered expression of these molecules in tears may therefore be used as a signal for onset of glaucoma or for identifying eyes at risk of developing glaucoma in PXF.

Matrix metalloproteinases and their inhibitors in Fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) is characterized by a progressive loss of corneal endothelial cells (CECs) and an abnormal accumulation of extracellular matrix in Descemet's membrane leading to increased thickness and formation of excrescences called guttae. Extracellular matrix homeostasis is modulated by an equilibrium between matrix metalloproteinases (MMPs) and their endogenous tissue inhibitors (TIMPs). This study aimed to investigate MMPs and TIMPs profile in FECD, taking into account cell morphology. Populations of FECD and healthy CECs were cultured and their conditioned media collected for analysis. The presence of proteases in the conditioned media was studied using a semi-quantitative proteome profiler array, and MMPs levels were assessed using quantitative assays (ELISA and quantitative antibody array). MMP activity was determined by zymography and fluorometry. The expression pattern of the membrane type 1-MMP (MT1-MMP, also known as MMP-14) was examined by immunofluorescence on ex vivo FECD and healthy explants of CECs attached to Descemet's membrane. Finally, MMPs and TIMPs protein expression was compared to gene expression obtained from previously collected data. FECD and healthy CEC populations generated cultures of endothelial, intermediate, and fibroblastic-like morphology. Various MMPs (MMP-1, -2, -3, -7, -8, -9, -10, and -12) and TIMPs (TIMP-1 to -4) were detected in both FECD and healthy CECs culture supernatants. Quantitative assays revealed a decrease in MMP-2 and MMP-10 among FECD samples. Both these MMPs can degrade the main extracellular matrix components forming guttae (fibronectin, laminin, collagen IV). Moreover, MMPs/TIMPs ratio was also decreased among FECD cell populations. Activity assays showed greater MMPs/Pro-MMPs proportions for MMP-2 and MMP-10 in FECD cell populations, although overall activities were similar. Moreover, the analysis according to cell morphology revealed among healthy CECs, both increased (MMP-3 and -13) and decreased (MMP-1, -9, -10, and -12) MMPs proteins along with increased MMPs activity (MMP-2, -3, -9, and -10) in the fibroblastic-like subgroup when compared to the endothelial subgroup. However, FECD CECs did not show similar behaviors between the different morphology subgroups. Immunostaining of MT1-MMP on ex vivo FECD and healthy explants revealed a redistribution of MT1-MMP around guttae in FECD explants. At the transcriptional level, no statistically significant differences were detected, but cultured FECD cells had a 12.2-fold increase in MMP1 and a 4.7-fold increase in TIMP3. These results collectively indicate different, and perhaps pathological, MMPs and TIMPs profile in FECD CECs compared to healthy CECs. This is an important finding suggesting the implication of MMPs and TIMPs in FECD pathophysiology.

Proteomic analysis of Exosomes derived from the Aqueous Humor of Myopia Patients

Objectives: Myopia is the most common refractive vision disorder. In recent years, several studies have suggested that the alteration of the exosomal protein levels in the aqueous humor (AH) is associated with the development of several eye diseases. Therefore, we aimed to explore the exosomal protein profile of the AH from myopia patients. Methods: Exosomes were isolated from the AH. The quality, concentration, and size distribution of exosomes for each patient were measured using nanoparticle tracking analysis system. Then, the exosomal proteins were purified and digested by trypsin for liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Results: There was no significant difference observed between the myopia and control when comparing the concentration and size distribution of exosomes in the AH for each sample. Based on LC-MS/MS analysis, myopia patients had higher and more complex exosomal peptide content. We found two proteins that were common in AH exosomes and eight proteins that were highly expressed in the myopia group. Conclusions: Our results provide pioneering findings for the exploration of the exosomal protein profile in myopia development. Further studies may provide significant information for the diagnosis, clinical treatment, and prognosis of myopia.

The Constitutive Proteome of Human Aqueous Humor and Race Specific Alterations

Aqueous humor (AH) is the fluid in the anterior and posterior chambers of the eye that contains proteins regulating ocular homeostasis. Analysis of aqueous humor proteome is challenging, mainly due to low sample volume and protein concentration. In this study, by utilizing state of the art technology, we performed Liquid-Chromatography Mass spectrometry (LC-MS/MS) analysis of 88 aqueous humor samples from subjects undergoing cataract surgery. A total of 2263 unique proteins were identified, which were sub-divided into four categories that were based on their detection in the number of samples: High (n = 152), Medium (n = 91), Low (n = 128), and Rare (n = 1892). A total of 243 proteins detected in at least 50% of the samples were considered as the constitutive proteome of human aqueous humor. The biological processes and pathways enriched in the AH proteins mainly include vesicle mediated transport, acute phase response signaling, LXR/RXR activation, complement system, and secretion. The enriched molecular functions are endopeptidase activity, and various binding functions, such as protein binding, lipid binding, and ion binding. Additionally, this study provides a novel insight into race specific differences in the AH proteome. A total of six proteins were upregulated, and five proteins were downregulated in African American subjects as compared to Caucasians.

Novel Data about Association of the Functionally Significant Polymorphisms of the MMP9 Gene with Exfoliation Glaucoma in the Caucasian Population of Central Russia

AIM

This study aimed to investigate the role of functionally significant polymorphisms of the MMP1, MMP3, and MMP9 genes in the development of exfoliation glaucoma (XFG) in the Caucasian population of Central Russia.

METHODS

The study sample consisted of 724 participants, including 328 patients with XFG and 396 individuals in the control group. The participants were of Russian ethnicity (self-reported) born in Central Russia. The participants were genotyped at 8 functionally significant polymorphisms of the MMP genes (rs3918242, rs3918249, rs17576, rs3787268, rs2250889, rs17577 MMP9, rs679620 MMP3, and rs1799750 MMP1). The association analysis was performed using logistic regression. Two polymorphisms, which were associated with XFG, and 12 polymorphisms linked to them (r2 ≥ 0.8) were analyzed for their functional significance in silico.

RESULTS

Allele C of rs3918249 MMP9 was associated with XFG according to the additive model (OR = 0.75, 95% CI: 0.56-0.93, pperm = 0.015), and allele G of the rs2250889 MMP9 locus was associated with XFG according to the additive (OR = 1.59, 95% CI: 1.10-2.29, pperm = 0.013) and dominant (OR = 1.68, 95% CI: 1.11-2.56, pperm = 0.016) models. Two XFG-associated loci of the MMP9 gene and 12 SNPs linked to them had a significant regulatory potential (they are located in the evolutionarily conserved regions, promoter and enhancer histone marks, the DNAase-hypersensitivity regions, a region binding to regulatory protein, and a region of regulatory motifs) and may influence the expression of 13 genes and alternative splicing of 4 genes in various tissues and organs related to the pathogenesis of XFG.

CONCLUSION

Allele C rs3918249 MMP9 decreased risk for XFG (OR = 0.75), and allele G of the rs2250889 MMP9 locus increased risk for XFG (OR = 1.59-1.68) in the Caucasian population of Central Russia.

Matrix Metalloproteinases and Glaucoma Treatment

Matrix metalloproteinases (MMPs) are a family of proteolytic enzymes that degrade extracellular matrix (ECM) components such as collagen and have important roles in multiple biological processes, including development and tissue remodeling, both in health and disease. The activity of MMPs is influenced by the expression of MMPs and tissue inhibitors of metalloproteinase (TIMPs). In the eye, MMP-mediated ECM turnover in the juxtacanalicular region of the trabecular meshwork (TM) reduces outflow resistance in the conventional outflow pathway and helps maintain intraocular pressure (IOP) homeostasis. An imbalance in the MMP/TIMP ratio may be involved in the elevated IOP often associated with glaucoma. The prostaglandin analog/prostamide (PGA) class of topical ocular hypotensive medications used in glaucoma treatment reduces IOP by increasing outflow through both conventional and unconventional (uveoscleral) outflow pathways. Evidence from in vivo and in vitro studies using animal models and anterior segment explant and cell cultures indicates that the mechanism of IOP lowering by PGAs involves increased MMP expression in the TM and ciliary body, leading to tissue remodeling that enhances conventional and unconventional outflow. PGA effects on MMP expression are dependent on the identity and concentration of the PGA. An intracameral sustained-release PGA implant (Bimatoprost SR) in development for glaucoma treatment can reduce IOP for many months after expected intraocular drug bioavailability. We hypothesize that the higher concentrations of bimatoprost achieved in ocular outflow tissues with the implant produce greater MMP upregulation and more extensive, sustained MMP-mediated target tissue remodeling, providing an extended duration of effect.

Higher TGF-β1, TGF-β2, MMP-2, and TIMP-1 Levels in the Aqueous Humor of Patients with Acute Primary Angle Closure

PURPOSE

To assess the quantitative differences in the levels of members of the transforming growth factor (TGF-β), matrix metalloproteinase (MMP), and tissue inhibitor of MMP (TIMP) families in the aqueous humor (AH) between patients with acute primary angle closure (APAC) and those with cataract only.

METHODS

AH samples were collected from 26 patients with APAC and cataract as well as 26 patients with age-related cataract only. Multiplex assays were used to measure the concentrations of TGF-β1, TGF-β2, and TGF-β3; MMP-1, MMP-2, MMP-7, MMP-9, and MMP-10; and TIMP-1 and TIMP-2.

RESULTS

The concentrations of TGF-β1, TGF-β2, MMP-2, (p < 0.001), and TIMP-1 were significantly higher (all p < 0.001) in AH samples from patients with APAC versus cataract only. Conversely, the AH concentrations of MMP-7 (p = 0.524), MMP-9 (p = 0.103), MMP-10 (p = 0.111), and TIMP-2 (p = 0.059) did not significantly differ between the groups. The concentrations of TGF-β3 and MMP-1 were below the respective detection limits in most AH samples.

CONCLUSION

The AH levels of TGF-β1, TGF-β2, MMP-2, and TIMP-1 were elevated in APAC eyes. Such altered protein levels could induce abnormal deposition of extracellular matrix in the trabecular meshwork, resulting in an increase in aqueous outflow resistance and, thereby, providing a possible explanation of the mechanism of residual glaucoma after cataract surgery.

Imbalance of Matrix Metalloproteinases and Their Inhibitors Is Correlated With Trabeculectomy Outcomes in Acute Primary Angle Closure

PURPOSE

To analyze matrix metalloproteinases (MMPs), tissue inhibitors of metalloproteinases (TIMPs), and their molar ratios in the aqueous humor in previous acute primary angle closure (APAC) patients and their correlations with trabeculectomy outcomes.

DESIGN

Prospective cohort study.

METHODS

Aqueous humor samples were collected from a total of 78 eyes, including 52 previous APAC eyes and 26 cataract eyes. TIMP-1, 2, 3, and 4 and MMP-1, 2, 3, 7, 8, 9, 12, and 13 analyte concentrations were measured using multiplexed immunoassay kits. Patient follow-up occurred at 1 week and 1, 3, 6, 12, and 18 months.

RESULTS

In the previous APAC group, 11 MMP/TIMP molar ratios were significantly lower. APAC eyes were then followed for up to 18 months after trabeculectomy and divided into success (37 eyes) and failure (15 eyes) groups. Five out of the 11 molar ratios were significantly lower in the failure group than in the success group. In multiple logistic regression analysis, failed filtration surgery was more likely in APAC eyes with lower MMP-2/TIMP-2 (P = .040, odds ratio = 44.499) and MMP-13/TIMP-1 (P = .034, odds ratio = 37.947) ratios. Previous APAC eyes were divided according to MMP-2/TIMP-2 and MMP-13/TIMP-1 ratios. Compared to eyes with high ratios, eyes with low MMP-2/TIMP-2 and MMP-13/TIMP-1 ratios had significantly higher failure rates.

CONCLUSIONS

In previous APAC eyes, changes in MMP and TIMP levels resulted in MMP and TIMP imbalance. Lower MMP-2/TIMP-2 and MMP-13/TIMP-1 ratios in aqueous humor are risk factors for trabeculectomy failure. Modulating specific MMP/TIMP ratios may have potential clinical applications for filtration surgery.

Gelatin Nanoparticles-HPMC Hybrid System for Effective Ocular Topical Administration of Antihypertensive Agents

The increment in ocular drug bioavailability after topical administration is one of the main challenges in pharmaceutical technology. For several years, different strategies based on nanotechnology, hydrogels or implants have been evaluated. Nowadays, the tolerance of ophthalmic preparations has become a critical issue and it is essential to the use of well tolerated excipients. In the present work, we have explored the potential of gelatin nanoparticles (GNPs) loaded with timolol maleate (TM), a beta-adrenergic blocker widely used in the clinic for glaucoma treatment and a hybrid system of TM-GNPs included in a hydroxypropyl methylcellulose (HPMC) viscous solution. The TM- loaded nanoparticles (mean particle size of 193 ± 20 nm and drug loading of 0.291 ± 0.019 mg TM/mg GNPs) were well tolerated both in vitro (human corneal cells) and in vivo. The in vivo efficacy studies performed in normotensive rabbits demonstrated that these gelatin nanoparticles were able to achieve the same hypotensive effect as a marketed formulation (0.5% TM) containing a 5-fold lower concentration of the drug. When comparing commercial and TM-GNPs formulations with the same TM dose, nanoparticles generated an increased efficacy with a significant (p < 0.05) reduction of intraocular pressure (IOP) (from 21% to 30%) and an augmentation of 1.7-fold in the area under the curve (AUC)(0-12h). On the other hand, the combination of timolol-loaded nanoparticles (TM 0.1%) and the viscous polymer HPMC 0.3%, statistically improved the IOP reduction up to 30% (4.65 mmHg) accompanied by a faster time of maximum effect (tmax = 1 h). Furthermore, the hypotensive effect was extended for four additional hours, reaching a pharmacological activity that lasted 12 h after a single instillation of this combination, and leading to an AUC(0-12h) 2.5-fold higher than the one observed for the marketed formulation. According to the data presented in this work, the use of hybrid systems that combine well tolerated gelatin nanoparticles and a viscous agent could be a promising alternative in the management of high intraocular pressure in glaucoma.

Effect of prostaglandin analogs: Latanoprost, bimatoprost, and unoprostone on matrix metalloproteinases and their inhibitors in human trabecular meshwork endothelial cells

Bimatoprost, latanoprost, and unoprostone are prostaglandin F_2α analogs (PGAs) and are used to lower intraocular pressure. We investigated the free acid effects of these three prostaglandin analogs: bimatoprost, latanoprost, and unoprostone on human matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMP) in the trabecular meshwork (TM) cells. Immunoblot results show that all three PGAs generally increased MMPs-1,9 and TIMPs-4. Additionally, bimatoprost and latanoprost both increased MMP-3 and TIMP-2, while unoprostone had an indeterminate effect on both. Zymography results show that all three PGAs except unoprostone increased intermediate MMP-1 activity while bimatoprost and latanoprost increased MMP-9 activity. Together, these data suggest that the balance between MMPs and TIMPs correlate to the relative intraocular pressure lowering effectiveness observed in clinical studies of these PGAs.

Hyperlipidemia Affects Tight Junctions and Pump Function in the Corneal Endothelium

Hyperlipidemia impacts on various diseases, such as atherosclerosis, hypertension, and diabetes mellitus. However, its influence, if any, on ocular tissues is largely unknown. Herein, we developed hyperlipidemic murine models by feeding 4-week-old male wild-type mice with a high-fat diet and apolipoprotein E knockout (ApoE^-/-) mice with a high-fat diet or standard diet to investigate the corneal endothelial change under hyperlipidemic conditions. Oil Red O staining showed an accumulation of lipid droplets in corneal endothelial cells (CECs) of hyperlipidemic mice. Other manifestations included a reduced cell density and distorted cell morphology, a disruption of the endothelial cell tight junctions and adhesion junctions, a reduced number of surface microvilli, down-regulation of Na⁺-K⁺-ATPase expression and function, activation of oxidative stress, changes in mitochondrial ultrastructure, and increased apoptosis. CEC recovery after injury, moreover, was diminished in hyperlipidemic mice; and high palmitate levels were found in the aqueous humor. In vitro hyperlipemia model, moreover, was found to be associated with dose-dependent CEC cytotoxicity, altered cell morphology, reduced pump function, and an induction of oxidative stress, leading to functional and pathologic changes in the corneal endothelium.

Role of matrix metalloproteinase-9 gene polymorphisms in glaucoma: A hospital-based study in Chinese patients

Background

Glaucoma is the irreversible vision loss and contributes second leading cause of blindness worldwide. Matrix metalloproteinase‐9 (MMP‐9) is involved with remodeling and destruction of extracellular matrix. Elevated MMP‐9 levels and various functional variants of MMP‐9 have been associated with glaucoma in different population. In the current investigation, we tested association of MMP‐9 common variants with different clinical categories of glaucoma in Chinese population.

Materials and Methods

We enrolled total of 396 glaucoma patients those reported to hospital comprising of 212 primary angle closure glaucoma (PACG) cases and 184 primary open‐angle glaucoma POAG patients. In addition, 329 normal individuals from similar geographical areas were enrolled as healthy controls. Five common single nucleotide polymorphisms (rs3918242, rs3918254, rs2250889, rs3918249, and rs17576) were genotyped by PCR‐RFLP. Plasma levels of MMP‐9 were quantified by ELISA.

Results

Heterozygotes (GC) and allele “G” for rs2250889 polymorphism were more frequent in PACG cases compared with healthy controls (GC: P < .0001, OR = 2.26; G: P < .0001, OR = 1.19). Similarly, heterozygous mutant and minor allele for rs3918242 polymorphism were more prevalent in POAG in comparison with healthy controls. Interestingly, distribution of rs17576 variant was statistically higher in both PACG and POAG cases than healthy controls. Furthermore, analysis of plasma MMP‐9 with MMP‐9 polymorphisms revealed significant association of rs2250889, rs3918242, and rs17576 with plasma levels of the protein.

Conclusions

MMP‐9 mutants are associated with elevated plasma MMP‐9 and predisposed to development of glaucoma.

Thrombospondin-2 is up-regulated by TGFβ2 and increases fibronectin expression in human trabecular meshwork cells

Elevated intraocular pressure (IOP) is a major risk factor for the development of primary open-angle glaucoma (POAG). This is from an increased aqueous humour (AH) outflow resistance through the trabecular meshwork (TM). The pathogenic mechanisms leading to the increase in TM outflow resistance are poorly understood but are thought to be from a dysregulation of the TM extracellular matrix (ECM) environment. ECM modification and turnover are crucial in regulating the resistance to aqueous outflow. ECM turnover is influenced by a complex interplay of growth factors such as transforming growth factors (TGFβ) family and matrix metalloproteinases (MMPs). Elevated TGFβ2 levels result in an increase in ECM deposition such as fibronectin leading to increased resistance. Fibronectin is a major component of TM ECM and plays a key role in its maintenance. Thrombospondins (TSP)-1 and -2 are important regulators of the ECM environment. TSP-1 has been implicated in the pathogenesis of POAG through activation of TGFβ2 within the TM. TSP-2 does not contain the catalytic domain to activate latent TGFβ, but is able to mediate the activities of MMP 2 and 9, thereby influencing ECM turnover. TSP-2 knock out mice show lower IOP levels compared to their wild type counterparts, suggesting the involvement of TSP-2 in the pathogenesis of POAG but its role in the pathogenesis of POAG remains unclear. The purpose of this study was to investigate the role of TSP-2 in trabecular meshwork ECM regulation and hence the pathogenesis of POAG. TSP-1 and TSP-2 expressions in immortalised glaucomatous TM cells (GTM3) and primary human non-glaucomatous (NTM) and glaucomatous cells (GTM) were determined by immunocytochemistry, immuno-blot analysis and qPCR following treatment with TGFβ2 and Dexamethasone. The level of ECM protein fibronectin was determined in TM cells using immuno-blot analysis following treatment with TSP-1 or -2. TM cells secrete TSP-1 and -2 under basal conditions at the protein level and TSP-2 mRNA and protein levels were increased in response to TGFβ2 three days post treatment. Exogenous treatment with TSP-2 up-regulated the expression of fibronectin protein in GTM3 cells, primary NTM and GTM cells. TSP-1 did not affect fibronectin protein levels in GTM3 cells. This suggests that the role of TSP-2 might be distinct from that of TSP-1 in the regulation of the TM cell ECM environment. TSP-2 may be involved in the pathogenesis of POAG and contribute to increased IOP levels by increasing the deposition of fibronectin within the ECM in response to TGFβ2.

Human aqueous humor proteome in cataract, glaucoma, and pseudoexfoliation syndrome

Twenty-nine human aqueous humor samples from patients with eye diseases such as cataract and glaucoma with and without pseudoexfoliation syndrome were characterized by LC-high resolution MS analysis. In total, 269 protein groups were identified with 1% false discovery rate including 32 groups that were not reported previously for this biological fluid. Since the samples were analyzed individually, but not pooled, 36 proteins were identified in all samples, comprising the constitutive proteome of the fluid. The most dominant molecular function of aqueous humor proteins as determined by GO analysis is endopeptidase inhibitor activity. Label-free protein quantification showed no significant difference between glaucoma and cataract aqueous humor proteomes. At the same time, we found decrease in the level of apolipoprotein D as a marker of the pseudoexfoliation syndrome. The data are available from ProteomeXchange repository (PXD002623).

Associations between matrix metalloproteinase gene polymorphisms and glaucoma susceptibility: a meta-analysis

Background

Matrix metalloproteinases (MMPs) polymorphisms have been implicated in the pathogenesis of glaucoma risk. However, the results were controversial. We performed a meta-analysis to evaluate the precise associations between MMPs polymorphisms and glaucoma risk.

Methods

Related studies were reviewed by searching electronic databases within four databases. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the association between the most common polymorphisms of MMPs and glaucoma risk. Heterogeneity, publication bias and sensitivity analysis were conducted to guarantee the statistical power.

Results

Overall, 11 selected articles involving 2,388 cases and 2,319 controls were included in this meta-analysis. Significant associations were only found between MMP-9 rs17576 G > A polymorphism (GA vs. GG: OR = 0.80, 95%CI = 0.67-0.97, P = 0.02, I² = 0%), MMP-9 rs3918249 C > T polymorphism (TT vs. CC + CT: OR = 0.71, 95%CI = 0.51-0.98, P = 0.04, I² = 0%) and glaucoma risk in the general population. Subgroup analysis also suggested that MMP-9 rs17576 G > A was related to glaucoma in the Caucasian population (GA vs. GG: OR = 0.67, 95%CI = 0.45-1.00, P = 0.05; GA + AA vs. GG: OR = 0.66, 95%CI = 0.45-0.97, P = 0.03, I² = 0%).

Conclusions

Our meta-analysis demonstrates that MMP-9 rs17576 G > A polymorphism might be a protective factor against the development of glaucoma in Caucasian population.

Induction of MMP‑1 and ‑3 by cyclical mechanical stretch is mediated by IL‑6 in cultured fibroblasts of keratoconus

In order to understand the effect of mechanical stretch on corneal extracellular matrix remodeling, human keratoconus fibroblasts (HKCFBs) were subjected to cyclic stretch in vitro and the expression of matrix metalloproteinases (MMPs), tissue inhibitor of metalloproteinases (TIMPs), and inflammatory cytokines were evaluated. HKCFBs were seeded into a flexible membrane base and subjected to a cyclic stretch regimen of 10% equibiaxial stretch at a stretching frequency of 1 Hz for 6 h using a Flexcell tension unit. An antibody directed against interleukin‑6 (IL‑6 Ab) was used to investigate the roles of IL‑6 on mechanical stretch mediated regulation of MMP in HKCFBs. Culture supernatants were assayed using an enzyme‑linked immunosorbent assay for MMP‑1 and ‑3, TIMP‑1 and ‑2, and IL‑6. Total RNA from the cells was extracted, and quantitative polymerase chain reaction was used to determine mRNA for MMP‑1 and ‑3, TIMP‑1 and ‑2, and IL‑6. In stretched cells, levels of MMP‑1 and ‑3 demonstrated an increase compared with unstretched cells, but levels of TIMP‑1, and ‑2 revealed a decrease. Mechanical stretch significantly increased the mRNA expression and protein synthesis of IL‑6 compared with unstretched cells. IL‑6 induced MMP‑1 and ‑3 expression, whereas no significant effects were observed in levels of TIMP‑1 and ‑2 compared with the untreated control groups. Additionally, the IL‑6 Ab markedly inhibited the stretch‑induced increase in MMP‑1 and ‑3 in culture supernatants in a dose‑dependent manner. No significant differences in TIMP‑1 and ‑2 protein levels were detected between stretched cells treated with IL‑6 Ab and stretched cells without IL‑6 Ab treatment. These results indicate that cyclical mechanical stretch augments IL‑6 production and MMP expression, and reduces levels of TIMP in HKCFBs. Thus, it is suggested that IL‑6 mediates the stretch‑induced MMP expression.

The potential impact of recent insights into proteomic changes associated with glaucoma

INTRODUCTION

Glaucoma, a major ocular neuropathy, is still far from being understood on a molecular scale. Proteomic workflows revealed glaucoma associated alterations in different eye components. By using state-of-the-art mass spectrometric (MS) based discovery approaches large proteome datasets providing important information about glaucoma related proteins and pathways could be generated. Corresponding proteomic information could be retrieved from various ocular sample species derived from glaucoma experimental models or from original human material (e.g. optic nerve head or aqueous humor). However, particular eye tissues with the potential for understanding the disease's molecular pathomechanism remains underrepresented. Areas covered: The present review provides an overview of the analysis depth achieved for the glaucomatous eye proteome. With respect to different eye regions and biofluids, proteomics related literature was found using PubMed, Scholar and UniProtKB. Thereby, the review explores the potential of clinical proteomics for glaucoma research. Expert commentary: Proteomics will provide important contributions to understanding the molecular processes associated with glaucoma. Sensitive discovery and targeted MS approaches will assist understanding of the molecular interplay of different eye components and biofluids in glaucoma. Proteomic results will drive the comprehension of glaucoma, allowing a more stringent disease hypothesis within the coming years.

The role of alkyl chain length of monothiol-terminated alkyl carboxylic acid in the synthesis, characterization, and application of gelatin-g-poly(N-isopropylacrylamide) carriers for antiglaucoma drug delivery

To improve ocular bioavailability and extend pharmacological response, this study aims to investigate the role of alkyl chain length of monothiol-terminated alkyl carboxylic acids in the synthesis, characterization, and application of gelatin-g-poly(N-isopropylacrylamide) (GN) biodegradable in situ gelling carriers for antiglaucoma drug delivery. In the presence of mercaptoacetic acid (MAA), mercaptopropionic acid (MPA), mercaptobutyric acid (MBA), or mercaptohexanoic acid (MHA) as a chain transfer agent, the carboxylic end-capped poly(N-isopropylacrylamide) samples were prepared by free radical polymerization technique. Our results showed that with increasing alkyl chain length, the hydrophobicity of thermo-responsive polymer segments significantly increased, mainly due to an increase in CH stretching frequencies. In addition, the greater hydrophobic association favored the decrease in both phase transition temperature and weight loss of GN copolymers, thereby accelerating their temperature-triggered gelation process and retarding the degradation progress under physiological conditions. The benefits from these features allowed the pilocarpine carriers to increase drug payload and extend drug release. Irrespective of carbon number of monothiol-terminated alkyl carboxylic acid, the synthesized GN materials exhibited high tolerance to corneal endothelial cells without any evidence of inhibited proliferation, viability loss, inflammatory stimulation, and functional abnormality, indicating good biocompatibility. Results of clinical observations and histological examinations demonstrated that the therapeutic efficacies in treating glaucomatous damage are in response to in vivo drug release profiles from various intracamerally injected GN carriers. The research findings suggest the influence of alkyl chain length of chain transfer agent-mediated polymer hydrophobicity and degradability on pharmacological bioavailability and action of pilocarpine in a glaucomatous rabbit model.

STATEMENT OF SIGNIFICANCE

Considering that glaucoma is a chronic disease that requires long-term medical therapy to preserve vision in patients, it is highly desirable to augment pharmacological bioavailability and govern release profile by tuning the properties of drug delivery carriers. For the first time, the present study provide striking evidence that the alkyl chain length of monothiol-terminated alkyl carboxylic acid related to the synthesis of biodegradable in situ gelling copolymers plays a key role in molecular functionalization of intracameral delivery systems for ocular administration and controlled release of antiglaucoma medications. The therapeutic efficacies in treating glaucomatous damage are in response to in vivo pilocarpine release profiles modulated by the carbon number of thermo-responsive polymer segment-mediated carrier hydrophobicity and degradability.

Major review: Exfoliation syndrome; advances in disease genetics, molecular biology, and epidemiology

Exfoliation syndrome (XFS) is a common age-related disorder that leads to deposition of extracellular fibrillar material throughout the body. The most recognized disease manifestation is exfoliation glaucoma (XFG), which is a common cause of blindness worldwide. Recent developments in XFS genetics, cell biology and epidemiology have greatly improved our understanding of the etiology of this complex inherited disease. This review summarizes current knowledge of XFS pathogenesis, identifies gaps in knowledge, and discusses areas for future research.

Definition, Classification, and Pathophysiology of Canine Glaucoma

Glaucoma is a common ocular condition in humans and dogs leading to optic nerve degeneration and irreversible blindness. Primary glaucoma is a group of spontaneous heterogeneous diseases. Multiple factors are involved in its pathogenesis and these factors vary across human ethnic groups and canine breeds, so the clinical phenotypes are numerous and their classification can be challenging and remain superficial. Aging and oxidative stress are major triggers for the manifestation of disease. Multiple, intertwined inflammatory and biochemical cascades eventually alter cellular and extracellular physiology in the optic nerve and trabecular meshwork and lead to vision loss.

iTRAQ-Based Proteomics Investigation of Aqueous Humor from Patients with Coats' Disease

Background

Coats' disease is an uncommon form of retinal telangiectasis, and the identification of novel proteins that contribute to the development of Coats' disease is useful for improving treatment efficacy. Proteomic techniques have been used to study many eye diseases; however, few studies have used proteomics to study the development of Coats' disease.

Methods

Isobaric tagging for relative and absolute protein quantification (iTRAQ) was employed to screen differentially expressed proteins (DEPs) in the aqueous humor (AH) between stage 3A patients (n = 8), stage 3B patients (n = 14), stage 4 patients (n = 2) and control patients (n = 20). Differentially co-expressed proteins (DCPs) were present in all three stages of Coats' disease and were considered disease-specific proteins. These proteins were further analyzed using Gene Ontology (GO) functional annotations.

Results

A total of 819 proteins were identified in the AH, 222 of which were significantly differentially expressed (fold change > 2 and P < 0.05) in the samples from at least one stage of Coats' disease. Of the DEPs, 46 were found among all three stages of Coats' disease and the controls; therefore, they were considered Coats' disease-specific proteins (DCPs). A GO classification analysis indicated that the DCPs were closely related to structural molecule activity, cell adhesion molecule binding and receptor binding. Western blotting confirmed the expression levels of haptoglobin and apolipoprotein C-I were significantly up-regulated in Coats’ disease.

Conclusions

The 46 Coats' disease-specific proteins may provide additional insights into the mechanism of Coats' disease and represent potential biomarkers for identifying individuals with Coats' disease.

Association of MMP-9 Gene Polymorphisms with Glaucoma: A Meta-Analysis

The aim of this study was to evaluate the associations between matrix metalloproteinase-9 (MMP-9) gene polymorphisms (rs17576 and rs3918249) and glaucoma risk. All eligible studies were searched in PubMed, Embase, the Cochrane Library and the China Knowledge Resource Integrated Database. Pooled odds ratios and 95% confidence intervals were used to assess associations between MMP-9 gene polymorphisms and glaucoma. Seven studies on rs17576 (1,357 cases and 1,432 controls) and 3 studies on rs3918249 (550 cases and 794 controls) were included. The results suggest that rs17576 was not associated with glaucoma risk based on current publications. However, stratification analyses indicated that GG genotypes increased the risk of primary open-angle glaucoma in a recessive model (GG vs. AA + AG). The rs3918249 polymorphism was also associated with a decreased risk of glaucoma, especially for Caucasian patients. To sum up, our data indicate that rs17576 polymorphism is not related to glaucoma and rs3918249 polymorphism might be a protective factor against glaucoma.

Augmentation of Lysosomal Phospholipase A2 Activity in the Anterior Chamber in Glaucoma

AIM

The lysosomal enzyme in the anterior chamber has a crucial role in the digestion of the insoluble materials in the aqueous humor (AH). The dysfunction of AH filtration in the trabecular meshwork (TM) causes increasing AH outflow resistance in the TM. Those insoluble objects, including phospholipids, should be digested in the TM for normal outflow. The present study was conducted to explore the involvement of lysosomal phospholipase A2 (LPLA2), a phospholipid-degrading enzyme, of the AH in glaucoma using clinical AH specimens.

MATERIALS AND METHODS

One hundred and twenty-five AH specimens were collected from patients. The measurement of LPLA2 activity in the AH was carried out using liposomes consisting of phosphatidylglycerol and N-acetylsphingosine (NAS). The correlation between the LPLA2 activity in the AH and ocular diseases was investigated.

RESULTS

The human AH showed both transacylation of NAS and the release of fatty acids under acidic conditions but not at a neutral pH, which is consistent with the known properties of LPLA2. The LPLA2 activity in the AH was not affected by age or systemic disease. A comparison between ocular diseases showed that the AH specimens obtained from patients with glaucoma had significantly higher LPLA2 activity than the other ocular disease groups.

DISCUSSION

The present findings suggest that the ascended level of LPLA2 activity in the AH of glaucoma patients is associated with the development of glaucoma.

Altered Expression Levels of MMP1, MMP9, MMP12, TIMP1, and IL-1β as a Risk Factor for the Elevated IOP and Optic Nerve Head Damage in the Primary Open-Angle Glaucoma Patients

The aim of presented work was to analyze the impact of particular polymorphic changes in the promoter regions of the -1607 1G/2G MMP1, -1562 C/T MMP9, -82 A/G MMP12, -511 C/T IL-1β, and 372 T/C TIMP1 genes on their expression level in POAG patients. Blood and aqueous humor samples acquired from 50 patients with POAG and 50 control subjects were used for QPCR and protein levels analysis by ELISA. In vivo promoter activity assays were carried on HTM cells using dual luciferase assay. All studied subjects underwent ophthalmic examination, including BCVA, intraocular pressure, slit-lamp examination, gonioscopy, HRT, and OCT scans. Patients with POAG are characterized by an increased mRNA expression of MMP1, MMP9, MMP12, and IL-1β genes as compared to the control group (P < 0.001). Aqueous humor acquired from patients with POAG displayed increased protein expression of MMP1, MMP9, MMP12, and IL-1β compared to the control group (P < 0.001). Allele -1607 1G of MMP1 gene possesses only 42,91% of the -1607 2G allele transcriptional activity and allele -1562 C of MMP9 gene possesses only 21,86% of the -1562 T allele. Increased expression levels of metalloproteinases can be considered as a risk factor for the development of POAG.

Evaluation of genetic polymorphisms in clusterin and tumor necrosis factor-alpha genes in South Indian individuals with pseudoexfoliation syndrome

PURPOSE

The aim of this study was to explore the potential association of genetic variants across clusterin (CLU) and tumor necrosis factor-alpha (TNF-α) genes in South Indian individuals with pseudoexfoliation syndrome (PEXS) and pseudoexfoliation glaucoma (PEXG).

MATERIALS AND METHODS

A total of 523 individuals including 299 unrelated cases (150 PEXS and 149 PEXG) and 224 age- and ethnically-matched healthy controls were recruited for genetic analysis. Six single-nucleotide polymorphisms (SNPs) including, five CLU SNPs (rs11136000, rs2279590, rs9331888, rs9331931, rs3087554) and one promoter SNP (rs1800629) of TNF-α were genotyped in all study subjects. Genotyping of CLU SNPs were performed using the TaqMan allelic discrimination assay while TNF-α SNP was genotyped using polymerase chain reaction (PCR)-based restriction fragment length polymorphism (RFLP) analysis. Association analysis was performed by determining the distributions of genotype and allele frequencies, Hardy-Weinberg equilibrium, and chi-square p values and odds ratios as implemented in the Golden Helix SNP & Variation Suite (SVS).

RESULTS

Five CLU SNPs did not show any significant differences in allele frequencies between patients and control subjects (rs3087554, p = 0.919, OR = 1.01, 95% CI: 0.77-1.33; rs2279590, p = 0.432, OR = 1.12, 95% CI: 0.84-1.51; rs9331931, p = 0.310, OR = 1.24, 95% CI: 0.81-1.89; rs11136000, p = 0.072, OR = 1.31, 95% CI: 0.97-1.76; rs9331888, p = 0.911, OR = 1.01, 95% CI: 0.78-1.31). The investigation of TNF-α SNP established a significant association with PEXS and PEXG (p = 0.042, OR = 0.61, 95% CI: 0.38-0.99). However, this association did not remain significant after Bonferroni correction.

CONCLUSIONS

Our data suggest that genetic variants in CLU and TNF-α genes do not play a major role in the development of PEXS and PEXG in the South Indian population.

Ocular and systemic manifestations of exfoliation syndrome

Exfoliation syndrome is an age-related disease characterized by the production and progressive accumulation of a fibrillar extracellular material in many ocular tissues. It leads to the most common identifiable cause of open-angle glaucoma worldwide, comprising the majority of glaucoma in some countries. The material in the eye appears as white deposits on the anterior lens surface and/or pupillary border. During pupillary movement, the iris scrapes exfoliation material from the lens surface, while the material on the lens causes rupture of iris pigment epithelial cells, with concomitant pigment dispersion into the anterior chamber and its deposition on anterior chamber structures. Exfoliation material can be found in many different organs. It is an ischemic disease and is associated with elevated serum homocysteine. Systemic associations include transient ischemic attacks, hypertension, angina, myocardial infarction, cerebrovascular and cardiovascular disease, aortic aneurysm, Alzheimer disease, and hearing loss. The discovery in 2007 of nonsynonymous single nucleotide polymorphisms in the LOXL1 (lysyl oxidase-like 1) gene are expected to make a major impact not only in understanding exfoliation syndrome, but in leading to new avenues of therapy.

Matrix metalloproteinase-2, tissue inhibitor of matrix metalloproteinase-2, and transforming growth factor beta 1 in the aqueous humor and serum of patients with pseudoexfoliation syndrome

Purpose

The aim of the study reported in this article was to determine the presence and quantitative differences of matrix metalloproteinase-2 (MMP-2), its tissue inhibitor (TIMP-2) and transforming growth factor beta 1 (TGF-β1) in the aqueous humor and serum samples of patients with pseudoexfoliation (PEX) syndrome.

Methods

Aqueous humor and serum samples were collected from 32 patients with PEX syndrome (with and without glaucoma) and a control group, who underwent routine cataract surgery. Levels of MMP-2, TIMP-2, and TGF-β1 were determined by specific immunoassays (enzyme-linked immunosorbent assay).

Results

MMP-2, TIMP-2, and TGF-β1 were identified in aqueous humor and serum samples from all groups of patients. The aqueous and serum samples of MMP-2, TIMP-2, and TGF-β1 showed no significant differences between PEX syndrome and control groups. Serum levels of MMP-2, TIMP-2, and TGF-β1 were statistically greater than their aqueous levels (P<0.05), except for TIMP-2 levels in the control group.

Conclusion

No statistically significant difference among mean MMP-2, TIMP-2, and TGF-β1 levels in both aqueous humor and serum samples was found between patients with PEX syndrome and the control group. It is important to simultaneously evaluate serum and aqueous samples from patients with PEX syndrome, which is related to an impaired blood–aqueous barrier.