Activation of αvβ3 Integrin Alters Fibronectin Fibril Formation in Human Trabecular Meshwork Cells in a ROCK-Independent Manner

The Identification of New Pharmacological Targets for the Treatment of Glaucoma: A Network Pharmacology Approach

Background: Glaucoma is a progressive optic neuropathy characterized by the neurodegeneration and death of retinal ganglion cells (RGCs), leading to blindness. Current glaucoma interventions reduce intraocular pressure but do not address retinal neurodegeneration. In this effort, to identify new pharmacological targets for glaucoma management, we employed a network pharmacology approach. Methods: We first retrieved transcriptomic data from GEO, an NCBI database, and carried out GEO2R (an interactive web tool aimed at comparing two or more groups of samples in a GEO dataset). The GEO2R statistical analysis aimed at identifying the top differentially expressed genes (DEGs) and used these as input of STRING (Search Tool for the Retrieval of Interacting Genes/Proteins) app within Cytoscape software, which builds networks of proteins starting from input DEGs. Analyses of centrality metrics using Cytoscape were carried out to identify nodes (genes or proteins) involved in network stability. We also employed the web-server software MIRNET 2.0 to build miRNA-target interaction networks for a re-analysis of the GSE105269 dataset, which reports analyses of microRNA expressions. Results: The pharmacological targets, identified in silico through analyses of the centrality metrics carried out with Cytoscape, were rescored based on correlations with entries in the PubMed and clinicaltrials.gov databases. When there was no match (82 out of 135 identified central nodes, in 8 analyzed networks), targets were considered "potential innovative" targets for the treatment of glaucoma, after further validation studies. Conclusions: Several druggable targets, such as GPCRs (e.g., 5-hydroxytryptamine 5A (5-HT5A) and adenosine A2B receptors) and enzymes (e.g., lactate dehydrogenase A or monoamine oxidase B), were found to be rescored as "potential innovative" pharmacological targets for glaucoma treatment.

The Role of αvβ3 Integrin in Lamina Cribrosa Cell Mechanotransduction in Glaucoma

Purpose: Glaucoma, one of the leading causes of irreversible blindness, is a common progressive optic neuropathy characterised by visual field defects and structural changes to the optic nerve head (ONH). There is extracellular matrix (ECM) accumulation and fibrosis of the lamina cribrosa (LC) in the ONH, and consequently increased tissue stiffness of the LC connective tissue. Integrins are cell surface proteins that provide the key molecular link connecting cells to the ECM and serve as bidirectional sensors transmitting signals between cells and their environment to promote cell adhesion, proliferation, and remodelling of the ECM. Here, we investigated the expression of αVβ3 integrin in glaucoma LC cell, and its effect on stiffness-induced ECM gene transcription and cellular proliferation rate in normal (NLC) and glaucoma (GLC) LC cells, by down-regulating αVβ3 integrin expression using cilengitide (a known potent αVβ3 and αVβ5 inhibitor) and β3 integrin siRNA knockdown. Methods: GLC cells were compared to age-matched controls NLC to determine differential expression levels of αVβ3 integrin, ECM genes (Col1A1, α-SMA, fibronectin, vitronectin), and proliferation rates. The effects of αVβ3 integrin blockade (with cilengitide) and silencing (with a pool of four predesigned αVβ3 integrin siRNAs) on ECM gene expression and proliferation rates were evaluated using both reverse transcription quantitative polymerase chain reaction (RT-qPCR) and Western blotting in the human NLC cells cultured on soft (4 kPa) and stiff (100 kPa) substrate and in GLC cells grown on standard plastic plates. Results: αVβ3 integrin gene and protein expression were enhanced (p < 0.05) in GLC cells as compared to NLC. Both cilengitide and siRNA significantly reduced αVβ3 expression in GLC. When NLC were grown in the stiff substrate, cilengitide and siRNA also significantly reduced the increased expression in αVβ3, ECM components, and proliferation rate. Conclusions: Here, we provide evidence of cilengitide- and siRNA-mediated silencing of αVβ3 integrin expression, and inhibition of ECM synthesis in LC cells. Therefore, αVβ3 integrin may be a promising target for the development of novel anti-fibrotic therapies for treating the LC cupping of the ONH in glaucoma.

Estrogen dysregulation, intraocular pressure, and glaucoma risk

Characterized by optic nerve atrophy due to retinal ganglion cell (RGC) death, glaucoma is the leading cause of irreversible blindness worldwide. Of the major risk factors for glaucoma (age, ocular hypertension, and genetics), only elevated intraocular pressure (IOP) is modifiable, which is largely regulated by aqueous humor outflow through the trabecular meshwork. Glucocorticoids such as dexamethasone have long been known to elevate IOP and lead to glaucoma. However, several recent studies have reported that steroid hormone estrogen levels inversely correlate with glaucoma risk, and that variants in estrogen signaling genes have been associated with glaucoma. As a result, estrogen dysregulation may contribute to glaucoma pathogenesis, and estrogen signaling may protect against glaucoma. The mechanism for estrogen-related protection against glaucoma is not completely understood but likely involves both regulation of IOP homeostasis and neuroprotection of RGCs. Based upon its known activities, estrogen signaling may promote IOP homeostasis by affecting extracellular matrix turnover, focal adhesion assembly, actin stress fiber formation, mechanosensation, and nitric oxide production. In addition, estrogen receptors in the RGCs may mediate neuroprotective functions. As a result, the estrogen signaling pathway may offer a therapeutic target for both IOP control and neuroprotection. This review examines the evidence for a relationship between estrogen and IOP and explores the possible mechanisms by which estrogen maintains IOP homeostasis.

Role of integrins in the development of fibrosis in the trabecular meshwork

Primary open angle glaucoma (POAG) is a progressive and chronic disease exhibiting many of the features of fibrosis. The extracellular matrix (ECM) in the trabecular meshwork (TM) undergoes extensive remodeling and enhanced rigidity, resembling fibrotic changes. In addition, there are changes associated with myofibroblast activation and cell contractility that further drives tissue fibrosis and stiffening. This review discusses what is known about the integrins in the TM and their involvement in fibrotic processes.

Evaluation of trabecular meshwork-specific promoters in vitro and in vivo using scAAV2 vectors expressing C3 transferase

AIM

To evaluate the potential of two trabecular meshwork (TM)-specific promoters, Chitinase 3-like 1 (Ch3L1) and matrix gla protein (MGP), for improving specificity and safety in glaucoma gene therapy based on self-complementary AAV2 (scAAV2) vector technologies.

METHODS

An scAAV2 vector with C3 transferase (C3) as the reporter gene (scAAV2-C3) was selected. The scAAV2-C3 vectors were driven by Ch3L1 (scAAV2-Ch3L1-C3), MGP (scAAV2-MGP-C3), enhanced MGP (scAAV2-eMGP-C3) and cytomegalovirus (scAAV2-CMV-C3), respectively. The cultured primary human TM cells were treated with each vector at different multiplicities of infections. Changes in cell morphology were observed by phase contrast microscopy. Actin stress fibers and Rho GTPases/Rho-associated protein kinase pathway-related molecules were assessed by immunofluorescence staining, real-time quantitative polymerase chain reaction and Western blot. Each vector was injected intracamerally into the one eye of each rat at low and high doses respectively. In vivo green fluorescence was visualized by a Micron III Retinal Imaging Microscope. Intraocular pressure (IOP) was monitored using a rebound tonometer. Ocular responses were evaluated by slit-lamp microscopy. Ocular histopathology analysis was examined by hematoxylin and eosin staining.

RESULTS

In TM cell culture studies, the vector-mediated C3 expression induced morphologic changes, disruption of actin cytoskeleton and reduction of fibronectin expression in TM cells by inhibiting the Rho GTPases/Rho-associated protein kinase signaling pathway. At the same dose, these changes were significant in TM cells treated with scAAV2-CMV-C3 or scAAV2-Ch3L1-C3, but not in cells treated with scAAV2-eMGP-C3 or scAAV2-MGP-C3. At low-injected dose, the IOP was significantly decreased in the scAAV2-Ch3L1-C3-injected eyes but not in scAAV2-MGP-C3-injected and scAAV2-eMGP-C3-injected eyes. At high-injected dose, significant IOP reduction was observed in the scAAV2-eMGP-C3-injected eyes but not in scAAV2-MGP-C3-injected eyes. Similar to scAAV2-CMV-C3, scAAV2-Ch3L1-C3 vector showed efficient transduction both in the TM and corneal endothelium. In anterior segment tissues of scAAV2-eMGP-C3-injected eyes, no obvious morphological changes were found except for the TM. Inflammation was absent.

CONCLUSION

In scAAV2-transduced TM cells, the promoter-driven efficiency of Ch3L1 is close to that of cytomegalovirus, but obviously higher than that of MGP. In the anterior chamber of rat eye, the transgene expression pattern of scAAV2 vector is presumably affected by MGP promoter, but not by Ch3L1 promoter. These findings would provide a useful reference for improvement of specificity and safety in glaucoma gene therapy using scAAV2 vector.

Fibronectin-targeted FUD and PEGylated FUD peptides for fibrotic diseases

Tissue fibrosis is characterized by excessive deposition of extracellular matrix (ECM) molecules. Fibronectin (FN) is a glycoprotein found in the blood and tissues, a key player in the assembly of ECM through interaction with cellular and extracellular components. Functional Upstream Domain (FUD), a peptide derived from an adhesin protein of bacteria, has a high binding affinity for the N-terminal 70-kDa domain of FN that plays a crucial role in FN polymerization. In this regard, FUD peptide has been characterized as a potent inhibitor of FN matrix assembly, reducing excessive ECM accumulation. Furthermore, PEGylated FUD was developed to prevent rapid elimination of FUD and enhance its systemic exposure in vivo. Herein, we summarize the development of FUD peptide as a potential anti-fibrotic agent and its application in experimental fibrotic diseases. In addition, we discuss how modification of the FUD peptide via PEGylation impacts pharmacokinetic profiles of the FUD peptide and can potentially contribute to anti-fibrosis therapy.

Glaucoma - 'A Stiff Eye in a Stiff Body'

Glaucoma is a progressive, age-related optic neuropathy, whereby the prevalence increases sharply over the age of 60 and is associated with increased systemic tissue stiffness. On a molecular basis, this is associated with increased deposition of collagen and loss of elastin structure, resulting in aberrant biomechanical compliance and reduced tissue elasticity. Increased tissue stiffness is a known driver of myofibroblast activation and persistence, especially in chronic cellular injuries via mechanotransduction pathways mediated by integrins and focal adhesion kinases. Evidence from histological and imaging studies plus force measurements of glaucomatous eyes show that several ocular tissues are stiffer than normal, healthy age-matched controls including the trabecular meshwork, Schlemm's canal, cornea, sclera and the lamina cribrosa. This is associated with increased extracellular matrix deposition and fibrosis. This review reports on the evidence to support the concept that glaucoma represents 'a stiff eye in a stiff body' and addresses potential mechanisms to attenuate this.

Estimating 3D spatiotemporal point of regard: a device evaluation

This paper presents and evaluates a system and method that record spatiotemporal scene information and location of the center of visual attention, i.e., spatiotemporal point of regard (PoR) in ecological environments. A primary research application of the proposed system and method is for enhancing current 2D visual attention models. Current eye-tracking approaches collapse a scene's depth structures to a 2D image, omitting visual cues that trigger important functions of the human visual system (e.g., accommodation and vergence). We combined head-mounted eye-tracking with a miniature time-of-flight camera to produce a system that could be used to estimate the spatiotemporal location of the PoR-the point of highest visual attention-within 3D scene layouts. Maintaining calibration accuracy is a primary challenge for gaze mapping; hence, we measured accuracy repeatedly by matching the PoR to fixated targets arranged within a range of working distances in depth. Accuracy was estimated as the deviation from estimated PoR relative to known locations of scene targets. We found that estimates of 3D PoR had an overall accuracy of approximately 2° omnidirectional mean average error (OMAE) with variation over a 1 h recording maintained within 3.6° OMAE. This method can be used to determine accommodation and vergence cues of the human visual system continuously within habitual environments, including everyday applications (e.g., use of hand-held devices).

A Novel Technique Identifies Valve-Like Pathways Entering and Exiting Schlemm’s Canal in Macaca nemestrina Primates With Similarities to Human Pathways

Purpose: The aim of the study was 1) to describe a novel combination of techniques that permit immunohistochemistry imaging of Schlemm’s canal inlet (SIV) and outlet (SOV) valve-like structures, 2) to identify tissue-level SIV adhesive relationships linking the trabecular meshwork (TM) to hinged collagen leaflets at the Schlemm’s canal (SC) external wall, and 3) to determine whether the SIV lumen wall’s adhesive vascular markers are similar to those of the SC inner wall endothelium.

Materials and Methods: Anterior segments of 16 M. nemestrina primates underwent immunohistochemistry (IHC) labeling. We perfused fluorescent microspheres into 12 of the eyes. Limbal tissues were divided into quadrants, viscoelastic introduced into SC, tissues fixed, immunohistochemistry performed, radial segments cut, tissues clarified, and confocal microscopy performed. Finally, we generated ImageJ 3D projections encompassing the TM, SC, and distal pathways.

Results: IHC imaging identified 3D relationships between SIV, collector channel ostia, collector channels (CC), SOV, and intrascleral channels. Imaging depth increased 176.9%, following clarification (p < 0.0001). Imaging demonstrated CD31, collagen type 1 and 4 in the walls of the SIV lumen and more distal pathways. In eight eyes, 384 segments were examined, 447 SIV identified, and 15.4% contained microspheres.

Conclusion: Our technique’s imaging depth permitted the identification of SIV linkage between the TM and SOV. We found comparable cell–cell adhesion molecules (CD31) and basement membrane components in the SC inner wall and SIV lumen walls. Recent OCT studies have suggested that SIV tensional relationships may control CC entrance dimensions that regulate distal resistance. Cellular adhesive properties sustain SIV tensional relationships. These SIV cell–cell and cell-basement membrane properties warrant further study because abnormalities could be a factor in the IOP elevation of glaucoma.

Integrin Crosstalk and Its Effect on the Biological Functions of the Trabecular Meshwork/Schlemm’s Canal

Integrins are a family of heterodimeric receptors composed of an α- and β-subunit that mediate cell-adhesion to a number of extracellular matrix (ECM) proteins in the Trabecular Meshwork/Schlemm’s canal (TM/SC) of the eye. Upon binding an ECM ligand, integrins transmit signals that activate a number of signaling pathways responsible for regulating actin-mediated processes (i.e phagocytosis, cell contractility, and fibronectin fibrillogenesis) that play an important role in regulating intraocular pressure (IOP) and may be involved in glaucoma. An important function of integrin-mediated signaling events is that the activity of one integrin can affect the activity of other integrins in the same cell. This creates a crosstalk that allows TM/SC cells to respond to changes in the ECM presumably induced by the mechanical forces on the TM/SC, aging and disease. In this review, we discuss how integrin crosstalk influences the function of the human TM/SC pathway. In particular, we will discuss how different crosstalk pathways mediated by either the αvβ3 or α4β1 integrins can play opposing roles in the TM when active and therefore act as on/off switches to modulate the cytoskeleton-mediated processes that regulate the outflow of aqueous humor through the TM/SC.

Pathogenesis of glaucoma: Extracellular matrix dysfunction in the trabecular meshwork-A review

The trabecular meshwork regulates aqueous humour outflow from the anterior chamber of the eye. It does this by establishing a tunable outflow resistance, defined by the interplay between cells and their extracellular matrix (ECM) milieu, and the molecular interactions between ECM proteins. During normal tissue homeostasis, the ECM is remodelled and trabecular cell behaviour is modified, permitting increased aqueous fluid outflow to maintain intraocular pressure (IOP) within a relatively narrow physiological pressure. Dysfunction in the normal homeostatic process leads to increased outflow resistance and elevated IOP, which is a primary risk factor for glaucoma. This review delineates some of the changes in the ECM that lead to gross as well as some more subtle changes in the structure and function of the ECM, and their impact on trabecular cell behaviour. These changes are discussed in the context of outflow resistance and glaucoma.

Membrane cholesterol regulates TRPV4 function, cytoskeletal expression, and the cellular response to tension

Despite the association of cholesterol with debilitating pressure-related diseases such as glaucoma, heart disease, and diabetes, its role in mechanotransduction is not well understood. We investigated the relationship between mechanical strain, free membrane cholesterol, actin cytoskeleton, and the stretch-activated transient receptor potential vanilloid isoform 4 (TRPV4) channel in human trabecular meshwork (TM) cells. Physiological levels of cyclic stretch resulted in time-dependent decreases in membrane cholesterol/phosphatidylcholine ratio and upregulation of stress fibers. Depleting free membrane cholesterol with m-β-cyclodextrin (MβCD) augmented TRPV4 activation by the agonist GSK1016790A, swelling and strain, with the effects reversed by cholesterol supplementation. MβCD increased membrane expression of TRPV4, caveolin-1, and flotillin. TRPV4 did not colocalize or interact with caveolae or lipid rafts, apart from a truncated ∼75 kDa variant partially precipitated by a caveolin-1 antibody. MβCD induced currents in TRPV4-expressing Xenopus laevis oocytes. Thus, membrane cholesterol regulates trabecular transduction of mechanical information, with TRPV4 channels mainly located outside the cholesterol-enriched membrane domains. Moreover, the biomechanical milieu itself shapes the lipid content of TM membranes. Diet, cholesterol metabolism, and mechanical stress might modulate the conventional outflow pathway and intraocular pressure in glaucoma and diabetes in part by modulating TM mechanosensing.

USP10 Promotes Fibronectin Recycling, Secretion, and Organization

Purpose

Integrins play a central role in myofibroblast pathological adhesion, over-contraction, and TGFβ activation. Previously, we demonstrated that after corneal wounding, αv integrins are protected from intracellular degradation by upregulation of the deubiquitinase USP10, leading to cell-surface integrin accumulation. Because integrins bind to and internalize extracellular matrix (ECM), we tested whether extracellular fibronectin (FN) accumulation can result from an increase in integrin and matrix recycling in primary human corneal fibroblasts (HCFs).

Methods

Primary HCFs were isolated from cadaver eyes. HCFs were transfected with either USP10 cDNA or control cDNA by nucleofection. Internalized FN was quantified with a FN ELISA. Recycled extracellular integrin and FN were detected with streptavidin-488 by live cell confocal microscopy (Zeiss LSM 780). Endogenous FN extra domain A was detected by immunocytochemistry. Cell size and removal of FN from the cell surface was determined by flow cytometry.

Results

USP10 overexpression increased α5β1 (1.9-fold; P < 0.001) and αv (1.7-fold; P < 0.05) integrin recycling, with a concomitant increase in biotinylated FN internalization (2.1-fold; P < 0.05) and recycling over 4 days (1.7–2.2-fold; P < 0.05). The dependence of FN recycling on integrins was demonstrated by α5β1 and αv integrin blocking antibodies, which, compared with control IgG, decreased biotinylated FN recycling (62% and 84%, respectively; P < 0.05). Overall, we established that extracellular FN was composed of approximately 1/3 recycled biotinylated FN and 2/3 endogenously secreted FN.

Conclusions

Our data suggest that reduced integrin degradation with a subsequent increase in integrin/FN recycling after wounding may be a newly identified mechanism for the characteristic accumulation of ECM in corneal scar tissue.

Overexpression and Activation of αvβ3 Integrin Differentially Affects TGFβ2 Signaling in Human Trabecular Meshwork Cells

Studies from our laboratory have suggested that activation of αvβ3 integrin-mediated signaling could contribute to the fibrotic-like changes observed in primary open angle glaucoma (POAG) and glucocorticoid-induced glaucoma. To determine how αvβ3 integrin signaling could be involved in this process, RNA-Seq analysis was used to analyze the transcriptomes of immortalized trabecular meshwork (TM) cell lines overexpressing either a control vector or a wild type (WT) or a constitutively active (CA) αvβ3 integrin. Compared to control cells, hierarchical clustering, PANTHER pathway and protein-protein interaction (PPI) analysis of cells overexpressing WT-αvβ3 integrin or CA-αvβ3 integrin resulted in a significant differential expression of genes encoding for transcription factors, adhesion and cytoskeleton proteins, extracellular matrix (ECM) proteins, cytokines and GTPases. Cells overexpressing a CA-αvβ3 integrin also demonstrated an enrichment for genes encoding proteins found in TGFβ2, Wnt and cadherin signaling pathways all of which have been implicated in POAG pathogenesis. These changes were not observed in cells overexpressing WT-αvβ3 integrin. Our results suggest that activation of αvβ3 integrin signaling in TM cells could have significant impacts on TM function and POAG pathogenesis.

Dexamethasone and Glucocorticoid-Induced Matrix Temporally Modulate Key Integrins, Caveolins, Contractility, and Stiffness in Human Trabecular Meshwork Cells

Purpose

To determine the temporal effects of dexamethasone (DEX) and glucocorticoid-induced matrix (GIM) on integrins/integrin adhesomes, caveolins, cytoskeletal-related proteins, and stiffness in human trabecular meshwork (hTM) cells.

Methods

Primary hTM cells were plated on plastic dishes (TCP), treated with vehicle (Veh) or 100 nM DEX in 1% serum media for 1, 3, 5, and 7 day(s). Concurrently, hTM cells were also plated on vehicle control matrices (VehMs) and GIMs for similar time points; VehMs and GIMs had been generated from chronic cultures of Veh-/DEX-stimulated hTM cells and characterized biochemically. Subsets of cells prior to plating on TCP or VehMs / GIMs served as baseline. Protein expression of mechanoreceptors, cytoskeletal-related proteins, and elastic moduli of hTM cells were determined.

Results

Compared with Veh, DEX temporally overexpressed αV, β3, and β5 integrins from day 3 to day 7, and integrin linked kinase at day 7, in hTM cells. However, DEX decreased β1 integrin at day 1 and day 7, while increasing Cavin1 at day 7, in a time-independent manner. Further, DEX temporally upregulated α-smooth muscle actin(α-SMA) and RhoA at day 7 and day 5, respectively; while temporally downregulating Cdc42 at day 3 and day 7 in hTM cells. Conversely, GIM showed increased immunostaining of fibronectin extra-domain A and B isoforms. Compared with VehM, GIM temporally increased αV integrin, Cavin1, and RhoA from day 3 to day 7, at day 3 and day 7, and at day 5, respectively, in hTM cells. Further, GIM overexpressed α-SMA at day 3 and day 7, and stiffened hTM cells from day 1 to day 7, in a time-independent fashion.

Conclusions

Our data highlight crucial mechanoreceptors, integrin adhesomes, and actin-related proteins that may temporally sustain fibrotic phenotypes precipitated by DEX and/or GIM in hTM cells.

Adenosine A3 receptor activated in H2O2 oxidative stress of primary open-angle glaucoma

Background

Primary open-angle glaucoma (POAG), as one of the leading reasons for blindness, is mainly due to trabecular meshwork (TM) dysfunction. Bioinformatics analysis was used to find related genes involved in TM oxidative stress, which is a major cause of TM fibrosis.

Methods

A total of three datasets from the Gene Expression Omnibus (GEO) database were used to identify differentially expressed genes (DEGs). Gene expression relationships were enriched by the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway and Gene Ontology (GO) pathways. The interaction network was listed by the protein-protein interaction (PPI) network. The expression of adenosine A3 receptor (ADORA3) was validated in POAG tissue and human trabecular meshwork cells (HTMCs) by western blot (WB) and reverse transcription polymerase chain reaction (RT-PCR). Additionally, WB and RT-PCR were used to measure oxidative stress injury relative protein and gene expression, respectively, such as fibronectin (FN), collagen-I (Col-I), and α-smooth muscle actin (α-SMA). Cell migration function and vitality were tested via transwell migration assay and Cell Counting Kit-8 (CCK-8). The cell vitality was measured using CCK-8.

Results

A total of 61 significant DEGs among the three data sources were analyzed. Among all three different datasets, two significant DEGs [ADORA3 and DNA damage-inducible transcript 4 protein (DDIT4)] were identified. The dataset ADORA3 was selected for further analysis. In the POAG TM tissue, ADORA3 was overexpressed at transcriptional and post-transcriptional levels. Overexpression of ADORA3 reduced TMC viability and migration but upregulated the extracellular matrix (ECM) proteins (FN, Col-I, and α-SMA) expression. It was found that ADORA3 can exacerbate oxidative stress injury in normal TMCs. These results indicated that ADORA3 might play an essential role in the occurrence and progression of POAG.

Conclusions

A total of 61 novel common DEGs identified are related to the development and prognosis of POAG. In the POAG, ADORA3 was verified as overexpressed; therefore, it may be associated with an oxidative stress injury in TMCs.

Disruption of fibronectin fibrillogenesis affects intraocular pressure (IOP) in BALB/cJ mice

Increased deposition of fibronectin fibrils containing EDA+fibronectin by TGFβ2 is thought to be involved in the reduction of aqueous humor outflow across the trabecular meshwork (TM) of the eye and the elevation in intraocular pressure (IOP) observed in primary open angle glaucoma (POAG). Using a fibronectin-binding peptide called FUD that can disrupt fibronectin fibrillogenesis, we examined if disrupting fibronectin fibrillogenesis would affect IOP in the TGFβ2 BALB/cJ mouse model of ocular hypertension. BALB/cJ mice that had been intravitreally injected with an adenovirus (Ad5) expressing a bioactive TGFβ2226/228 showed a significant increase in IOP after 2 weeks. When 1μM FUD was injected intracamerally into mice 2 weeks post Ad5-TGFβ2 injection, FUD significantly reduced IOP after 2 days. Neither mutated FUD (mFUD) nor PBS had any effect on IOP. Four days after FUD was injected, IOP returned to pre-FUD injection levels. In the absence of TGFβ2, intracameral injection of FUD had no effect on IOP. Western blotting of mouse anterior segments expressing TGFβ2 showed that FUD decreased fibronectin levels 2 days after intracameral injection (p<0.05) but not 7 days compared to eyes injected with PBS. mFUD injection had no significant effect on fibronectin levels at any time point. Immunofluorescence microscopy studies in human TM (HTM) cells showed that treatment with 2ng/ml TGFβ2 increased the amount of EDA+ and EDB+ fibronectin incorporated into fibrils and 2μM FUD decreased both EDA+ and EDB+ fibronectin in fibrils. An on-cell western assay validated this and showed that FUD caused a 67% reduction in deoxycholate insoluble fibronectin fibrils in the presence of TGFβ2. FUD also caused a 43% reduction in fibronectin fibrillogenesis in the absence of TGFβ2 while mFUD had no effect. These studies suggest that targeting the assembly of fibronectin fibrillogenesis may represent a way to control IOP.

Role of Fibronectin in Primary Open Angle Glaucoma

Primary open angle glaucoma (POAG) is the most common form of glaucoma and the 2nd most common cause of irreversible vision loss in the United States. Nearly 67 million people have the disease worldwide including >3 million in the United States. A major risk factor for POAG is an elevation in intraocular pressure (IOP). The increase in IOP is believed to be caused by an increase in the deposition of extracellular matrix proteins, in particular fibronectin, in a region of the eye known as the trabecular meshwork (TM). How fibronectin contributes to the increase in IOP is not well understood. The increased density of fibronectin fibrils is thought to increase IOP by altering the compliance of the trabecular meshwork. Recent studies, however, also suggest that the composition and organization of fibronectin fibrils would affect IOP by changing the cell-matrix signaling events that control the functional properties of the cells in the trabecular meshwork. In this article, we will discuss how changes in the properties of fibronectin and fibronectin fibrils could contribute to the regulation of IOP.