Functional properties of fibronectin in the trabecular meshwork

In vitro comparison of human and murine trabecular meshwork cells: implications for glaucoma research

The trabecular meshwork (TM) is crucial for regulating intraocular pressure (IOP), and its dysfunction significantly contributes to glaucoma, a leading cause of vision loss and blindness worldwide. Although rodents are commonly used as animal models in glaucoma research, the applicability of these findings to humans is limited due to the insufficient understanding of murine TM. This study aimed to compare primary human TM (hTM) and murine TM (mTM) cells in vitro to enhance the robustness and translatability of murine glaucoma models. In this in vitro study, we compared primary hTM and mTM cells under simulated physiological and pathological conditions by exposing both cell types to the glucocorticoid dexamethasone (DEX) and Transforming Growth Factor β (TGFB2), both of which are critical in the pathogenesis of several ophthalmological diseases, including glaucoma. Phagocytic properties were assessed using microbeads. Cells were analyzed through immunocytochemistry (ICC) and Western blot (WB) to evaluate the expression of extracellular matrix (ECM) components, such as Fibronectin 1 (FN1) and Collagen IV (COL IV). Filamentous-Actin (F-Act) staining was used to analyze cross-linked actin network (CLAN) formation. Additionally, we evaluated cytoskeletal components, including Vimentin (VIM), Myocilin (MYOC), and Actin-alpha-2 (ACTA2). Our results demonstrated significant similarities between human and murine TM cells in basic morphology, phagocytic properties, and ECM and cytoskeletal component expression under both homeostatic and pathological conditions in vitro. Both human and murine TM cells exhibited epithelial-to-mesenchymal transition (EMT) after exposure to DEX or TGFB2, with comparable CLAN formation observed in both species. However, there were significant differences in FN1 and MYOC induction between human and murine TM cells. Additionally, MYOC expression in hTM cells depended on fibronectin coating. Our study suggests that murine glaucoma models are potentially translatable to human TM. The observed similarities in ECM and cytoskeletal component expression and the comparable EMT response and CLAN formation support the utility of murine models in glaucoma research. The differences in FN1 and MYOC expression between hTM and mTM warrant further investigation due to their potential impact on TM properties. Overall, this study provides valuable insights into the species-specific characteristics of TM and highlights opportunities to refine murine models for better relevance to human glaucoma.

Simvastatin Attenuates Glucocorticoid-Induced Human Trabecular Meshwork Cell Dysfunction via YAP/TAZ Inactivation

PURPOSE

Impairment of the trabecular meshwork (TM) is the principal cause of increased outflow resistance in the glaucomatous eye. Yes-associated protein (YAP) and transcriptional coactivator with PDZ binding motif (TAZ) are emerging as potential mediators of TM cell/tissue dysfunction. Furthermore, YAP/TAZ activity was recently found to be controlled by the mevalonate pathway in non-ocular cells. Clinically used statins block the mevalonate cascade and were shown to improve TM cell pathobiology; yet, the link to YAP/TAZ signaling was not investigated. In this study, we hypothesized that simvastatin attenuates glucocorticoid-induced human TM (HTM) cell dysfunction via YAP/TAZ inactivation.

METHODS

Primary HTM cells were seeded atop or encapsulated within bioengineered extracellular matrix (ECM) hydrogels. Dexamethasone was used to induce a pathologic phenotype in HTM cells in the absence or presence of simvastatin. Changes in YAP/TAZ activity, actin cytoskeletal organization, phospho-myosin light chain levels, hydrogel contraction/stiffness, and fibronectin deposition were assessed.

RESULTS

Simvastatin potently blocked pathologic YAP/TAZ nuclear localization/activity, actin stress fiber formation, and myosin light chain phosphorylation in HTM cells. Importantly, simvastatin co-treatment significantly attenuated dexamethasone-induced ECM contraction/stiffening and fibronectin mRNA and protein levels. Sequential treatment was similarly effective but did not match clinically-used Rho kinase inhibition.

CONCLUSIONS

YAP/TAZ inactivation with simvastatin attenuates HTM cell pathobiology in a tissue-mimetic ECM microenvironment. Our data may help explain the association of statin use with a reduced risk of developing glaucoma via indirect YAP/TAZ inhibition as a proposed regulatory mechanism.

Absorption, metabolism, and functions of hyaluronic acid and its therapeutic prospects in combination with microorganisms: A review

Hyaluronic acid (HA) is key to the stability of the internal environment of tissues. HA content in tissues gradually decreases with age, causing age-related health problems. Exogenous HA supplements are used to prevent or treat these problems including skin dryness and wrinkles, intestinal imbalance, xerophthalmia, and arthritis after absorption. Moreover, some probiotics are able to promote endogenous HA synthesis and alleviate symptoms caused by HA loss, thus introducing potential preventative or therapeutic applications of HA and probiotics. Here, we review the oral absorption, metabolism, and biological function of HA as well as the potential role of probiotics and HA in increasing the efficacy of HA supplements.

Toll-Like Receptor 4 Signaling in the Trabecular Meshwork

Primary open-angle glaucoma is one of the leading causes of blindness worldwide. With limited therapeutics targeting the pathogenesis at the trabecular meshwork (TM), there is a great need for identifying potential new targets. Recent evidence has implicated Toll-like receptor 4 (TLR4) and it is signaling pathway in augmenting the effects of transforming growth factor beta-2 (TGFβ2) and downstream extracellular matrix production. In this review, we examine the role of TLR4 signaling in the trabecular meshwork and the interplay between endogenous activators of TLR4 (damage-associated molecular patterns (DAMPs)), extracellular matrix (ECM), and the effect on intraocular pressure.

Fibronectin extra domain A (FN-EDA) causes glaucomatous trabecular meshwork, retina, and optic nerve damage in mice

BACKGROUND

Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of primary open angle glaucoma and is due to trabecular meshwork (TM) damage. Here, we investigate the role of an endogenous Toll-like receptor 4 (TLR4) ligand, FN-EDA, in the development of glaucoma utilizing a transgenic mouse strain (B6.EDA+/+) that constitutively expresses only FN containing the EDA isoform.

METHODS

Eyes from C57BL6/J (wild-type), B6.EDA+/+ (constitutively active EDA), B6.EDA-/- (EDA null) mice were processed for electron microscopy and consecutive images of the entire length of the TM and Schlemm's canal (SC) from anterior to posterior were collected and montaged into a single image. ECM accumulation, basement membrane length, and size and number of giant vacuoles were quantified by ImageJ analysis. Tlr4 and Iba1 expression in the TM and ONH cells was conducted using RNAscope in situ hybridization and immunohistochemistry protocols. IOP was measured using a rebound tonometer, ON damage assessed by PPD stain, and RGC loss quantified in RBPMS labeled retina flat mounts.

RESULTS

Ultrastructure analyses show the TM of B6.EDA+/+ mice have significantly increased accumulation of ECM between TM beams with few empty spaces compared to C57BL/6 J mice (p < 0.05). SC basement membrane is thicker and more continuous in B6.EDA+/+ mice compared to C57BL/6 J. No significant structural differences are detected in the TM of EDA null mice. Tlr4 and Iba1 expression is increased in the TM of B6.EDA+/+ mice compared to C57BL/6 J eyes (p < 0.05). IOP is significantly higher in B6.EDA+/+ mice compared to C57BL/6 J eyes (p < 0.001), and significant ON damage (p < 0.001) and RGC loss (p < 0.05) detected at 1 year of age. Tlr4 mRNA is expressed in mouse ONH cells, and is present in ganglion cell axons, microglia, and astrocytes. There is a significant increase in the area occupied by Iba-1 positive microglia cells in the ONH of B6.EDA+/+ mice compared to C57BL/6 J control eyes (p < 0.01).

CONCLUSIONS

B6.EDA+/+ mice have increased ECM accumulation in the TM, elevated IOP, enhanced proinflammatory changes in the ONH, loss of RGCs, and ONH damage. These data suggest B6.EDA+/+ mice recapitulate many aspects of glaucomatous damage.

Vitamin D and Ocular Diseases: A Systematic Review

The contributory roles of vitamin D in ocular and visual health have long been discussed, with numerous studies pointing to the adverse effects of vitamin D deficiency. In this paper, we provide a systematic review of recent findings on the association between vitamin D and different ocular diseases, including myopia, age-related macular degeneration (AMD), glaucoma, diabetic retinopathy (DR), dry eye syndrome (DES), thyroid eye disease (TED), uveitis, retinoblastoma (RB), cataract, and others, from epidemiological, clinical and basic studies, and briefly discuss vitamin D metabolism in the eye. We searched two research databases for articles examining the association between vitamin D deficiency and different ocular diseases. One hundred and sixty-two studies were found. There is evidence on the association between vitamin D and myopia, AMD, DR, and DES. Overall, 17 out of 27 studies reported an association between vitamin D and AMD, while 48 out of 54 studies reported that vitamin D was associated with DR, and 25 out of 27 studies reported an association between vitamin D and DES. However, the available evidence for the association with other ocular diseases, such as glaucoma, TED, and RB, remains limited.

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.

Fundamental Biomaterial Considerations in the Development of a 3D Model Representative of Primary Open Angle Glaucoma

Glaucoma is a leading cause of irreversible blindness globally, with primary open angle glaucoma (POAG) being the most common subset. Raised intraocular pressure is an important risk factor for POAG and is caused by a reduction in aqueous humour (AqH) outflow due to dysfunctional cellular and matrix dynamics in the eye’s main drainage site, the trabecular meshwork (TM) and Schlemm’s canal (SC). The TM/SC are highly specialised tissues that regulate AqH outflow; however, their exact mechanisms of AqH outflow control are still not fully understood. Emulating physiologically relevant 3D TM/S in vitro models poses challenges to accurately mimic the complex biophysical and biochemical cues that take place in healthy and glaucomatous TM/SC in vivo. With development of such models still in its infancy, there is a clear need for more well-defined approaches that will accurately contrast the two central regions that become dysfunctional in POAG; the juxtacanalicular tissue (JCT) region of the TM and inner wall endothelia of the Schlemm’s canal (eSC). This review will discuss the unique biological and biomechanical characteristics that are thought to influence AqH outflow and POAG progression. Further consideration into fundamental biomaterial attributes for the formation of a biomimetic POAG/AqH outflow model will also be explored for future success in pre-clinical drug discovery and disease translation.

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.

Cell-Matrix Interactions in the Eye: From Cornea to Choroid

The extracellular matrix (ECM) plays a crucial role in all parts of the eye, from maintaining clarity and hydration of the cornea and vitreous to regulating angiogenesis, intraocular pressure maintenance, and vascular signaling. This review focuses on the interactions of the ECM for homeostasis of normal physiologic functions of the cornea, vitreous, retina, retinal pigment epithelium, Bruch's membrane, and choroid as well as trabecular meshwork, optic nerve, conjunctiva and tenon's layer as it relates to glaucoma. A variety of pathways and key factors related to ECM in the eye are discussed, including but not limited to those related to transforming growth factor-β, vascular endothelial growth factor, basic-fibroblastic growth factor, connective tissue growth factor, matrix metalloproteinases (including MMP-2 and MMP-9, and MMP-14), collagen IV, fibronectin, elastin, canonical signaling, integrins, and endothelial morphogenesis consistent of cellular activation-tubulogenesis and cellular differentiation-stabilization. Alterations contributing to disease states such as wound healing, diabetes-related complications, Fuchs endothelial corneal dystrophy, angiogenesis, fibrosis, age-related macular degeneration, retinal detachment, and posteriorly inserted vitreous base are also reviewed.

Updates on Genes and Genetic Mechanisms Implicated in Primary Angle-Closure Glaucoma

Primary angle-closure glaucoma (PACG) is estimated to affect over 30 million people worldwide by 2040 and is highly prevalent in the Asian population. PACG is more severe and carries three times the higher risk of blindness than primary open-angle glaucoma, thus representing a significant public health concern. High heritability and ethnic-specific predisposition to PACG suggest the involvement of genetic factors in disease development. In the recent past, genetic studies have led to the successful identification of several genes and loci associated with PACG across different ethnicities. The precise cellular and molecular roles of these multiple loci in the development and progression of PACG remains to be elucidated. Nonetheless, these studies have significantly increased our understanding of the emerging cellular processes and biological pathways that might provide more significant insights into the disease’s genetic etiology and may be valuable for future clinical applications. This review aims to summarize and update the current knowledge of PACG genetics analysis research.

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.

Human trabecular meshwork cell behavior is influenced by collagen scaffold pore architecture and glycosaminoglycan composition

Glaucoma is a degenerative eye disease in which damage to the optic nerve leads to a characteristic loss of vision. The primary risk factor for glaucoma is an increased intraocular pressure that is caused by an imbalance of aqueous humor generation and subsequent drainage through the trabecular meshwork (TM) drainage system. The small size, donor tissue limitations, and high complexity of the TM make it difficult to research the relationship between the TM cells and their immediate environment. Thus, a biomaterial-based approach may be more appropriate for research manipulations and in vitro drug development platforms. In this work, human TM (hTM) cells were cultured on various collagen scaffolds containing different glycosaminoglycans (GAGs) and different pore architectures to better understand how hTM cells respond to changes in their extracellular environment. Cellular response was measured by quantifying cellular proliferation and expression of an important extracellular matrix protein, fibronectin. The pore architecture of the scaffolds was altered using freeze-casting technique to make both large and small pores that were aligned or with a non-aligned random structure. The composition of the scaffolds was altered with the addition of chondroitin sulfate and/or hyaluronic acid. It was found that the hTM cells grown on large pore scaffolds proliferate more than those grown on small pores. There was an increase in the fibronectin expression with the incorporation of GAGs, and its morphology was changed by the underlying pore architecture. This work will help provide an insight into the behavior of hTM cells when introducing changes in their microenvironment.

Low systemic vitamin D as a potential risk factor in primary open-angle glaucoma: a review of current evidence

Currently, intraocular pressure is the only modifiable risk factor for glaucoma; thus, identifying other modifiable determinants may have far-reaching outcomes. There has been increasing interest in vitamin D status and glaucoma pathogenesis as low vitamin D has been identified by some studies as an independent risk factor for glaucoma. Although the exact mechanism of vitamin D in glaucoma remains uncertain, there is sufficient evidence to continue research in this area. There is a potential physiological role for vitamin D as an anti-inflammatory agent in the oxidative stress-driven pathogenesis of primary open-angle glaucoma, and further studies are required to evaluate the temporal and causal relationship. Ocular vitamin D status in the tear, aqueous and vitreous fluid is a prospective gap in research.

Fibronectin extra domain A (FN-EDA) elevates intraocular pressure through Toll-like receptor 4 signaling

Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of primary open angle glaucoma and is due to trabecular meshwork (TM) damage, which leads to impaired aqueous humor outflow. Here, we explore a novel molecular mechanism involved in glaucomatous TM damage. We investigated the role of an endogenous Toll-like receptor 4 (TLR4) ligand, fibronectin-EDA (FN-EDA), in TGFβ2-induced ocular hypertension in mice. We utilized transgenic mouse strains that either constitutively express only FN containing the EDA isoform or contain an EDA-null allele and express only FN lacking EDA, with or without a mutation in Tlr4, in our inducible mouse model of ocular hypertension by injection of Ad5.TGFβ2. IOP was measured over time and eyes accessed by immunohistochemistry for total FN and FN-EDA expression. Constitutively active EDA caused elevated IOP starting at 14 weeks of age. Ad5.TGFβ2 induced ocular hypertension in wildtype C57BL/6J mice and further amplified the IOP in constitutively active EDA mice. TLR4 null and EDA null mice blocked Ad5.TGFβ-induced ocular hypertension. Total FN and FN-EDA isoform expression increased in response to Ad5.TGFβ2. These data suggest that both TLR4 and FN-EDA contribute to TGFβ2 induced ocular hypertension.

Electrospinning of natural polymers for the production of nanofibres for wound healing applications

Wound healing is a highly regulated process composed of four overlapping phases: (1) coagulation/haemostasis, (2) inflammation, (3) proliferation and (4) remodelling. Comorbidities such as advanced age, diabetes and obesity can impair natural tissue repair, rendering the wound in a pathological state of inflammation. This results in significant discomfort for patients and considerable financial costs for healthcare systems. Due to the complex nature of wound healing, current treatments are ineffective at dealing with delayed healing. With flexible properties that can be tailored, nanomaterials have emerged as alternative therapeutics for many biomedical applications. A nanofibrous network can be made via electrospinning polymers using a high electric field to create a responsive meshwork that can be used as a medical dressing. A nanofibrous device has properties that can overcome the limitations of traditional dressings, such as: (1) adaptability to wound contour; (2) controlled drug delivery of therapeutics; (3) gaseous exchange; (4) exudate absorption and (5) surface functionalisation to further enhance the biological activity of the dressing. This review details emerging trends in nanotechnology to specifically target wound healing applications. Particular focus is given to the most common natural polymers that could address many unmet healthcare needs.

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

Purpose

Fibronectin fibrillogenesis is an integrin-mediated process that may contribute to the pathogenesis of primary open-angle glaucoma (POAG). Here, we examined the effects of αvβ3 integrins on fibrillogenesis in immortalized TM-1 cells and human trabecular meshwork (HTM) cells.

Methods

TM-1 cells overexpressing wild-type β3 (WTβ3) or constitutively active β3 (CAβ3) integrin subunits were generated. Control cells were transduced with an empty vector (EV). Deoxycholic acid (DOC) extraction of monolayers, immunofluorescence microscopy, and On-cell western analyses were used to determine levels of fibronectin fibrillogenesis and fibronectin fibril composition (EDA+ and EDB+ fibronectins) and conformation. αvβ3 and α5β1 Integrin levels were determined using fluorescence-activated cell sorting (FACS). Cilengitide and an adenovirus vector expressing WTβ3 or CAβ3 integrin subunits were used to examine the role of αvβ3 integrin in HTM cells. The role of the canonical α5β1 integrin–mediated pathway in fibrillogenesis was determined using the fibronectin-binding peptide FUD, the β1 integrin function-blocking antibody 13, and the Rho kinase (ROCK) inhibitor Y27632.

Results

Activation of αvβ3 integrin enhanced the assembly of fibronectin into DOC-insoluble fibrils in both TM-1 and HTM cells. The formation of fibronectin fibrils was dependent on α5β1 integrin and could be inhibited by FUD. However, fibrillogenesis was unaffected by Y27632. Fibrils assembled by CAβ3 cells also contained high levels of EDA+ and EDB+ fibronectin and fibronectin that was stretched.

Conclusions

αvβ3 Integrin signaling altered the deposition and structure of fibronectin fibrils using a β1 integrin/ROCK-independent mechanism. Thus, αvβ3 integrins could play a significant role in altering the function of fibronectin matrices in POAG.

Generating cell-derived matrices from human trabecular meshwork cell cultures for mechanistic studies

Ocular hypertension has been attributed to increased resistance to aqueous outflow often as a result of changes in trabecular meshwork (TM) extracellular matrix (ECM) using in vivo animal models (for example, by genetic manipulation) and ex vivo anterior segment perfusion organ cultures. These are, however, complex and difficult in dissecting molecular mechanisms and interactions. In vitro approaches to mimic the underlying substrate exist by manipulating either ECM topography, mechanics, or chemistry. These models best investigate the role of individual ECM protein(s) and/or substrate property, and thus do not recapitulate the multifactorial extracellular microenvironment; hence, mitigating its physiological relevance for mechanistic studies. Cell-derived matrices (CDMs), however, are capable of presenting a 3D-microenvironment rich in topography, chemistry, and whose mechanics can be tuned to better represent the network of native ECM constituents in vivo. Critically, the composition of CDMs may also be fine-tuned by addition of small molecules or relevant bioactive factors to mimic homeostasis or pathology. Here, we first provide a streamlined protocol for generating CDMs from TM cell cultures from normal or glaucomatous donor tissues. Second, we document how TM cells can be pharmacologically manipulated to obtain glucocorticoid-induced CDMs and how generated pristine CDMs can be manipulated with reagents like genipin. Finally, we summarize how CDMs may be used in mechanistic studies and discuss their probable application in future TM regenerative studies.

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 Trabecular Meshwork Progenitors

Trabecular meshwork (TM) cells are a group of progenitors that have the ability to become adipocytes, chondrocytes and endothelial cells. Therefore, those adult corneal progenitors may be used as an effective therapy for trabecular meshwork diseases such as glaucoma, corneal endothelial dysfunctions such as blindness due to corneal endothelial dysfunction, and similar diseases. In order to promote the understanding of human trabecular meshwork progenitors, this article reviews human trabecular meshwork progenitor therapy and discusses its potential applications for curing human eye blindness.

Novel fibronectin mutations and expansion of the phenotype in spondylometaphyseal dysplasia with "corner fractures"

Heterozygous pathogenic variants in the FN1 gene, encoding fibronectin (FN), have recently been shown to be associated with a skeletal disorder in some individuals affected by spondylometaphyseal dysplasia with "corner fractures" (SMD-CF). The most striking feature characterizing SMD-CF is irregularly shaped metaphyses giving the appearance of "corner fractures". An array of secondary features, including developmental coxa vara, ovoid vertebral bodies and severe scoliosis, may also be present. FN is an important extracellular matrix component for bone and cartilage development. Here we report five patients affected by this subtype of SMD-CF caused by five novel FN1 missense mutations: p.Cys123Tyr, p.Cys169Tyr, p.Cys213Tyr, p.Cys231Trp and p.Cys258Tyr. All individuals shared a substitution of a cysteine residue, disrupting disulfide bonds in the FN type-I assembly domains located in the N-terminal assembly region. The abnormal metaphyseal ossification and "corner fracture" appearances were the most remarkable clinical feature in these patients. In addition, generalized skeletal fragility with low-trauma bilateral femoral fractures was identified in one patient. Interestingly, the distal femoral changes in this patient healed with skeletal maturation. Our report expands the phenotypic and genetic spectrum of the FN1-related SMD-CF and emphasizes the importance of FN in bone formation and possibly also in the maintenance of bone strength.

The Association of Serum Vitamin D Levels with Pseudoexfoliation Glaucoma/Syndrome

Results:

PEX glaucoma group consisted of 17 males and 14 females, PEX syndrome group of 27 males and 7 females, and the control group of 27 males and 16 females. The mean age was 70.9±8.9 years, 72.1±7.3 years, and 67.9±9.1 years in PEX glaucoma, syndrome and control group, respectively. Mean vitamin D levels were 9.4±7.7 ng/mL, 7.9±6,1 ng/mL, 11.5±14.2 ng/mL in PEX glaucoma, syndrome and control group, respectively (p>0.05). The mean serum vitamin D level was 8.04±4.7 ng/mL in those who underwent glaucoma surgery and 10.1±8.7 ng/mL in those who didn't undergo glaucoma surgery in PEX glaucoma group (p>0.05). No difference was found between the PEX glaucoma subgroups in terms of the mean deviation when classified according to vitamin D levels (<10 ng/mL, ≥10 ng/mL) (p>0.05).

Conclusion:

Although we found no statistically significant difference between the PEX syndrome/ glaucoma, and control group in terms of serum vitamin D levels, serum vitamin D levels were lower in PEX syndrome and glaucoma group than control group. Our results indicate that serum vitamin D levels have no effect on the development of PEX glaucoma/syndrome or the control of the disorder in cases with PEX glaucoma. However, these results need to be supported with further studies on a larger number of patients and with longer follow-up.

Human stem cells home to and repair laser-damaged trabecular meshwork in a mouse model

Glaucoma is the leading cause of irreversible vision loss, and reducing elevated intraocular pressure is currently the only effective clinical treatment. The trabecular meshwork is the main resistance site for aqueous outflow that maintains intraocular pressure. In this study, we transplanted human trabecular meshwork stem cells (TMSCs) intracamerally into mice that received laser photocoagulation over a 180° arc of the trabecular meshwork. TMSCs preferentially homed and integrated to the laser-damaged trabecular meshwork region and expressed differentiated cell markers at 2 and 4 weeks. Laser-induced inflammatory and fibrotic responses were prevented by TMSC transplantation with simultaneous ultrastructure and function restoration. Cell affinity and migration assays and elevated expression of CXCR4 and SDF1 in laser-treated mouse trabecular meshwork suggest that the CXCR4/SDF1 chemokine axis plays an important role in TMSC homing. Our results suggest that TMSCs may be a viable candidate for trabecular meshwork refunctionalization as a novel treatment for glaucoma.

Hongmin Yun et al. show that implanted human stem cells can accurately home to and repair damaged trabecular meshwork tissue in the mouse eye via a chemokine axis defined by CXCR4 and SDF1. The study suggests that stem cells from the trabecular meshwork could be used to refunctionalize the outflow pathway as a treatment for glaucoma.

Glaucomatous cell derived matrices differentially modulate non-glaucomatous trabecular meshwork cellular behavior

Ocular hypertension is a causal risk-factor to developing glaucoma. This is associated with stiffening of the trabecular meshwork (TM), the primary site of resistance to aqueous-humor-outflow. The mechanisms underlying this stiffening or how pathologic extracellular matrix (ECM) affects cell function are poorly understood. It is recognized that mechanotransduction systems allow cells to sense and translate the intrinsic biophysical properties of ECM into intracellular signals to control gene transcription, protein expression, and cell behavior. Using an anterior segment perfusion model, we document that there are significantly more low flow regions that are much stiffer, and fewer high flow regions that are less stiff in glaucomatous TM (GTM) when compared to non-glaucomatous TMs (NTM). GTM tissue also has fewer cells overall when compared with NTM tissue. In order to study the role of pathologic ECM in glaucoma disease progression, we conducted studies using cell derived matrices (CDM). First, we characterized the mechanics, composition and organization of fibronectin in ECM deposited by GTM and NTM cells treated with glucocorticosteroids. Then, we determined that these GTM-derived ECM are able to induce stiffening of normal NTM cells, and alter their gene/protein expression to resemble that of a glaucomatous phenotype. Further, we demonstrate that GTM-derived ECM causes endoplasmic reticular stress in NTM. They also became resistant to being reorganized by these NTM cells. These phenomena were exacerbated by ECMs obtained from steroid treated glaucoma model groups. Collectively, our data demonstrates that CDMs represent a novel tool for the study of bidirectional interactions between TM cells and their immediate microenvironment.

STATEMENT OF SIGNIFICANCE

Extracellular matrix (ECM) changes are prevalent in a number of diseases. The precise mechanisms by which changes in the ECM contribute to disease progression is unclear, primarily due to absence of appropriate models. Here, using glaucoma as a disease model, we document changes in cell derived matrix (CDM) and tissue mechanics that contribute to the pathology. Subsequently, we determine the effect that ECMs from diseased and healthy individuals have on healthy cell behaviors. Data emanating from this study demonstrate that CDMs are a potent tool for the study of cell-ECM interactions.

Disruption of fibronectin matrix affects type IV collagen, fibrillin and laminin deposition into extracellular matrix of human trabecular meshwork (HTM) cells

Fibronectin fibrils are a major component of the extracellular matrix (ECM) of the trabecular meshwork (TM). They are a key mediator of the formation of the ECM which controls aqueous humor outflow and contributes to the pathogenesis of glaucoma. The purpose of this work was to determine if a fibronectin-binding peptide called FUD, derived from the Streptococcus pyogenes Functional Upstream Domain of the F1 adhesin protein, could be used to control fibronectin fibrillogenesis and hence ECM formation under conditions where its expression was induced by treatment with the glucocorticoid dexamethasone. FUD was very effective at preventing fibronectin fibrillogenesis in the presence or absence of steroid treatment as well as the removal of existing fibronectin fibrils. Disruption of fibronectin fibrillogenesis by FUD also disrupted the incorporation of type IV collagen, laminin and fibrillin into the ECM. The effect of FUD on these other protein matrices, however, was found to be dependent upon the maturity of the ECM when FUD was added. FUD effectively disrupted the incorporation of these other proteins into matrices when added to newly confluent cells that were forming a nascent ECM. In contrast, FUD had no effect on these other protein matrices if the cell cultures already possessed a pre-formed, mature ECM. Our studies indicate that FUD can be used to control fibronectin fibrillogenesis and that these fibrils play a role in regulating the assembly of other ECM protein into matrices involving type IV collagen, laminin, and fibrillin within the TM. This suggests that under in vivo conditions, FUD would selectively disrupt fibronectin fibrils and de novo assembly of other proteins into the ECM. Finally, our studies suggest that targeting fibronectin fibril assembly may be a viable treatment for POAG as well as other glaucomas involving excessive or abnormal matrix deposition of the ECM.

Open-angle glaucoma: therapeutically targeting the extracellular matrix of the conventional outflow pathway

INTRODUCTION

Ocular hypertension in open-angle glaucoma is caused by a reduced rate of removal of aqueous humour (AH) from the eye, with the majority of AH draining from the anterior chamber through the conventional outflow pathway, comprising the trabecular meshwork (TM) and Schlemm's Canal. Resistance to outflow is generated, in part, by the extracellular matrix (ECM) of the outflow tissues. Current pressure-lowering topical medications largely suppress AH production, or enhance its clearance through the unconventional pathway. However, therapies targeting the ECM of the conventional pathway in order to decrease intraocular pressure have become a recent focus of attention. Areas covered: We discuss the role of ECM of the TM in outflow homeostasis and its relevance as a target for glaucoma therapy, including progress in development of topical eye formulations, together with gene therapy approaches based on inducible, virally-mediated expression of matrix metalloproteinases to enhance aqueous outflow. Expert opinion: There remains a need for improved glaucoma medications that more specifically act upon sites causative to glaucoma pathogenesis. Emerging strategies targeting the ECM of the conventional outflow pathway, or associated components of the cytoskeleton of TM cells, involving new pharmacological formulations or genetically-based therapies, are promising avenues of future glaucoma treatment.

Role of ID Proteins in BMP4 Inhibition of Profibrotic Effects of TGF-β2 in Human TM Cells

Purpose

Increased expression of TGF-β2 in primary open-angle glaucoma (POAG) aqueous humor (AH) and trabecular meshwork (TM) causes deposition of extracellular matrix (ECM) in the TM and elevated IOP. Bone morphogenetic proteins (BMPs) regulate TGF-β2–induced ECM production. The underlying mechanism for BMP4 inhibition of TGF-β2–induced fibrosis remains undetermined. Bone morphogenic protein 4 induces inhibitor of DNA binding proteins (ID1, ID3), which suppress transcription factor activities to regulate gene expression. Our study will determine whether ID1and ID3 proteins are downstream targets of BMP4, which attenuates TGF-β2 induction of ECM proteins in TM cells.

Methods

Primary human TM cells were treated with BMP4, and ID1 and ID3 mRNA, and protein expression was determined by quantitative PCR (Q-PCR) and Western immunoblotting. Intracellular ID1 and ID3 protein localization was studied by immunocytochemistry. Transformed human TM cells (GTM3 cells) were transfected with ID1 or ID3 expression vectors to determine their potential inhibitory effects on TGF-β2–induced fibronectin and plasminogen activator inhibitor-I (PAI-1) protein expression.

Results

Basal expression of ID1-3 was detected in primary human TM cells. Bone morphogenic protein 4 significantly induced early expression of ID1 and ID3 mRNA (P < 0.05) and protein in primary TM cells, and a BMP receptor inhibitor blocked this induction. Overexpression of ID1 and ID3 significantly inhibited TGF-β2–induced expression of fibronectin and PAI-1 in TM cells (P < 0.01).

Conclusions

Bone morphogenic protein 4 induced ID1 and ID3 expression suppresses TGF-β2 profibrotic activity in human TM cells. In the future, targeting specific regulators may control the TGF-β2 profibrotic effects on the TM, leading to disease modifying IOP lowering therapies.

Therapeutic potential of AAV-mediated MMP-3 secretion from corneal endothelium in treating glaucoma

Intraocular pressure (IOP) is maintained as a result of the balance between production of aqueous humour (AH) by the ciliary processes and hydrodynamic resistance to its outflow through the conventional outflow pathway comprising the trabecular meshwork (TM) and Schlemm's canal (SC). Elevated IOP, which can be caused by increased resistance to AH outflow, is a major risk factor for open-angle glaucoma. Matrix metalloproteinases (MMPs) contribute to conventional aqueous outflow homeostasis in their capacity to remodel extracellular matrices, which has a direct impact on aqueous outflow resistance and IOP. We observed decreased MMP-3 activity in human glaucomatous AH compared to age-matched normotensive control AH. Treatment with glaucomatous AH resulted in significantly increased transendothelial resistance of SC endothelial and TM cell monolayers and reduced monolayer permeability when compared to control AH, or supplemented treatment with exogenous MMP-3.Intracameral inoculation of AAV-2/9 containing a CMV-driven MMP-3 gene (AAV-MMP-3) into wild type mice resulted in efficient transduction of corneal endothelium and an increase in aqueous concentration and activity of MMP-3. Most importantly, AAV-mediated expression of MMP-3 increased outflow facility and decreased IOP, and controlled expression using an inducible promoter activated by topical administration of doxycycline achieved the same effect. Ultrastructural analysis of MMP-3 treated matrices by transmission electron microscopy revealed remodelling and degradation of core extracellular matrix components. These results indicate that periodic induction, via use of an eye drop, of AAV-mediated secretion of MMP-3 into AH could have therapeutic potential for those cases of glaucoma that are sub-optimally responsive to conventional pressure-reducing medications.

Modulatory effects of 1,25-dihydroxyvitamin D3 on eye disorders: A critical review

Many studies have shown that the presence of 1,25-dihydroxyvitamin D3 in the eye is able to modulate inflammatory responses. In fact, it has been demonstrated that topical administration of vitamin D3 inhibits Langerhans cells migration from the central cornea, corneal neovascularization, and production of cytokines (i.e., interleukin-1-6-8) in experimental animals. Moreover, both in vitro and in vivo studies have demonstrated that vitamin D is a potent inhibitor of retinal neovascularization. It has been shown that calcitriol, the biologically active form of vitamin D, inhibits angiogenesis both in cultured endothelial cells and in retinas from guinea pigs with retinoblastoma or oxygen-induced ischemic retinopathy. In addition, it seems that this compound is able to prevent the progression from early to neovascular age-related macular degeneration (AMD) and, at the same time, to down-regulate the characteristic inflammatory cascade at the retinal pigment epithelium-choroid interface due to its anti-inflammatory and immunomodulatory capabilities. Furthermore, 1,25-dihydroxyvitamin D3 and its analogue, 2-methylene-19-nor-1,25-dihydroxyvitamin D3, are able to modulate intraocular pressure (IOP) through gene expression. Several studies have suggested a role in glaucoma and diabetic retinopathy therapies for vitamin D3. In conclusion, this review summarizes our current knowledge on the potential use of vitamin D3 in the protection and treatment of ocular diseases in ophthalmology.

Effect of benzalkonium chloride on trabecular meshwork cells in a new in vitro 3D trabecular meshwork model for glaucoma

PURPOSE

To validate a new culture model of primary human trabecular meshwork cells (p-hTMCs) using Matrigel®, in order to mimic in vitro 3D-TM organization, and to investigate the proinflammatory effect of benzalkonium chloride (BAK) in 3D p-hTMC cultures.

METHODS

p-hTMCs, seeded onto Matrigel®-coated inserts were stimulated with BAK (10^-4%), dexamethasone (DEX) (10^-6M) or transforming growth factor-beta 2 (TGF-β2) (5ng/ml) for 48h and observed with confocal microscopy. The BAK effect at 10^-4% or 5.10^-3% on the gene expressions of interleukin-6 (IL-6), interleukin-8 (IL-8) and matrix metalloproteinase (MMP-9) was investigated using qRT-PCR in 2D and 3D p-hTMC cultures.

RESULTS

p-hTMCs seeded in Matrigel® were able to organize themselves in a 3D-spatial conformation in the different conditions tested with cross-linked actin network (CLAN) formation in presence of DEX or TGF-β2 and intercellular space contraction with TGF-β2. IL-6 and IL-8 gene expressions increased in presence of BAK in 2D and in 3D p-hTMC cultures. BAK 10^-4% only showed a tendency to stimulate MMP-9 expression in p-hTMCs after 24h-recovery.

CONCLUSIONS

We investigated this new 3D-TM in vitro model in Matrigel^® matrix for pathophysiological and toxicological purposes. It appears as a new promising tool for a better understanding of TM behavior in physiological and stress conditions, as well as toxicological evaluations of antiglaucoma eyedrops and preservatives.

Differential response and withdrawal profile of glucocorticoid-treated human trabecular meshwork cells

The goal of the study was to examine secreted protein response and withdrawal profiles from cultured human trabecular meshwork (HTM) cells following short- and long-term glucocorticoid treatment. Primary cultures of five human HTM cell strains isolated from 5 different individual donor eyes were tested. Confluent HTM cells were differentiated in culture media containing 1% FBS for at least one week, and then treated with Dexamethasone (Dex, 100 nM) 3 times/week for 1 or 4 weeks. Cell culture supernatants were collected 3 times per week for 8 weeks. Secretion profiles of myocilin (MYOC), matrix metalloproteinase-2 (MMP2) and fibronectin (FN) were determined by Western blot analysis and MMP2 activity by zymography. Dex treatment reduced MMP2 expression and activity, returning to normal levels shortly after Dex withdrawal in 5 HTM cell strains. All five cell strains significantly upregulated MYOC in response to Dex treatment by an average of 17-fold, but recovery to basal levels after Dex withdrawal took vastly different periods of time depending on cell strain and treatment duration. Dex treatment significantly increased FN secretion in all strains but one, which decreased FN secretion in the presence of Dex. Interestingly, secretion of FN and MYOC negatively correlated during a 4 week recovery period following 4 weeks of Dex treatment. Taken together, the time course and magnitude of response and recovery for three different secreted, extracellular matrix-associated proteins varied greatly between HTM cell strains, which may underlie susceptibility to glucocorticoid-induced ocular hypertension.

Functional Anatomy of the Outflow Facilities

In order to understand the pathophysiology, select optimal therapeutic options for patients and provide clients with honest expectations for cases of canine glaucoma, clinicians should be familiar with a rational understanding of the functional anatomy of the ocular structures involved in this group of diseases. The topographical extension and the structural and humoral complexity of the regions involved with the production and the outflow of aqueous humor undergo numerous changes with aging and disease. Therefore, the anatomy relative to the fluid dynamics of aqueous has become a pivotal yet flexible concept to interpret the different phenotypes of glaucoma.

Extracellular matrix in the trabecular meshwork: intraocular pressure regulation and dysregulation in glaucoma

The trabecular meshwork (TM) is located in the anterior segment of the eye and is responsible for regulating the outflow of aqueous humor. Increased resistance to aqueous outflow causes intraocular pressure to increase, which is the primary risk factor for glaucoma. TM cells reside on a series of fenestrated beams and sheets through which the aqueous humor flows to exit the anterior chamber via Schlemm's canal. The outer trabecular cells are phagocytic and are thought to function as a pre-filter. However, most of the outflow resistance is thought to be from the extracellular matrix (ECM) of the juxtacanalicular region, the deepest portion of the TM, and from the inner wall basement membrane of Schlemm's canal. It is becoming increasingly evident that the extracellular milieu is important in maintaining the integrity of the TM. In glaucoma, not only have ultrastructural changes been observed in the ECM of the TM, and a significant number of mutations in ECM genes been noted, but the stiffness of glaucomatous TM appears to be greater than that of normal tissue. Additionally, TGFβ2 has been found to be elevated in the aqueous humor of glaucoma patients and is assumed to be involved in ECM changes deep with the juxtacanalicular region of the TM. This review summarizes the current literature on trabecular ECM as well as the development and function of the TM. Animal models and organ culture models targeting specific ECM molecules to investigate the mechanisms of glaucoma are described. Finally, the growing number of mutations that have been identified in ECM genes and genes that modulate ECM in humans with glaucoma are documented.

Inhibition of NF-κB signaling ablates the invasive phenotype of glioblastoma

Glioblastoma multiforme, the most common primary brain tumor, is highly refractory to therapy, mainly due to its ability to form micrometastases, which are small clusters or individual cells that rapidly transverse the brain and make full surgical resection impossible. Here, it is demonstrated that the invasive phenotype of glioblastoma multiforme is orchestrated by the transcription factor NF-κB which, via metalloproteinases (MMP), regulates fibronectin processing. Both, cell lines and tumor stem cells from primary glioblastoma multiforme, secrete high levels of fibronectin which when cleaved by MMPs forms an extracellular substrate. Subsequently, forming and interacting with their own microenvironment, glioblastoma multiforme cells are licensed to invade their surroundings. Mechanistic study revealed that NF-κB inhibition, either genetically or pharmacologically, by treatment with Disulfiram, significantly abolished the invasive phenotype in the chick chorioallantoic membrane assay. Furthermore, having delineated the underlying molecular mechanism of glioblastoma multiforme invasion, the potential of a disulfiram-based therapy was revealed in a highly invasive orthotrophic glioblastoma multiforme mouse model.

IMPLICATIONS

This study defines a novel therapeutic approach that inhibits micrometastases invasion and reverts lethal glioblastoma into a less aggressive disease.

Cellular fibronectin expression in human trabecular meshwork and induction by transforming growth factor-β2

PURPOSE

Levels of TGF-β2 are higher in POAG aqueous humor, causing deposition of extracellular matrix (ECM) proteins, including fibronectin (FN), in the glaucomatous human trabecular meshwork (HTM) that may be responsible for elevated IOP. The purpose of this study was to identify the expression of cellular FN (cFN) isoforms (EDA and EDB) in HTM cells and tissues, and to determine whether TGF-β2 can induce cFN expression and fibril formation in cultured HTM cells.

METHODS

Expression of cFN mRNA isoforms and induction by recombinant TGF-β2 (5 ng/mL) were determined by quantitative RT-PCR. The TGF-β2 induction of EDA isoform protein expression and FN fibril formation were analyzed using Western immunoblots and immunocytochemistry (ICC), respectively. Immunohistochemistry (IHC) analysis was used to examine total FN and EDA isoform expression in normal (NTM) and glaucomatous (GTM) trabecular meshwork (TM) tissues.

RESULTS

Both cFN mRNA isoforms were expressed in cultured HTM cells and were induced by TGF-β2 after 2, 4, and 7 days (P < 0.05). Similarly, EDA isoform protein and fibril formation were increased after 4 and 7 days of TGF-β2 treatment. Finally, GTM tissues had significantly greater EDA isoform protein levels (1.7-fold, P < 0.05) compared to NTM tissues.

CONCLUSIONS

This study demonstrated that cFN isoforms are expressed and induced in HTM cells by TGF-β2. Also, increased EDA isoform protein levels were seen in GTM tissues. Our findings suggest that induction of cFN isoform expression in the TM ECM may be a novel pathologic mechanism involved in the TM changes associated with glaucoma.

Dexamethasone increases αvβ3 integrin expression and affinity through a calcineurin/NFAT pathway

The purpose of this study was to determine how dexamethasone (DEX) regulates the expression and activity of αvβ3 integrin. FACS analysis showed that DEX treatment induced expression of an activated αvβ3 integrin. Its expression remained high as long as DEX was present and continued following DEX removal. FACS analysis showed that the upregulation of αvβ3 integrin was the result of an increase in the expression of the β3 integrin subunit. By real time qPCR, DEX treatment induced a 6.2-fold increase (p<0.04) in β3 integrin mRNA by day 2 compared to control and remained elevated for 6days of treatment and then an additional 10days once the DEX was removed. The increase in β3 integrin mRNA levels required only 1day of DEX treatment to increase levels for 4days in the absence of DEX. In contrast, DEX did not alter β1 integrin mRNA or protein levels. The DEX-induced upregulation of β3 integrin mRNA was partly due to an increase in its half-life to 60.7h from 22.5h in control cultures (p<0.05) and could be inhibited by RU486 and cycloheximide, suggesting that DEX-induced de novo protein synthesis of an activation factor was needed. The calcineurin inhibitors cyclosporin A (CsA) and FK506 inhibited the DEX induced increase in β3 integrin mRNA. In summary, the DEX-induced increase in β3 integrin is a secondary glucocorticoid response that results in prolonged expression of αvβ3 integrin and the upregulation of the β3 integrin subunit through the calcineurin/NFAT pathway.

New therapeutic targets for intraocular pressure lowering

Primary open-angle glaucoma (POAG) is a leading cause of irreversible and preventable blindness and ocular hypertension is the strongest known risk factor. With current classes of drugs, management of the disease focuses on lowering intraocular pressure (IOP). Despite of their use to modify the course of the disease, none of the current medications for POAG is able to reduce the IOP by more than 25%-30%. Also, some glaucoma patients show disease progression despite of the therapeutics. This paper examines the new described physiological targets for reducing the IOP. The main cause of elevated IOP in POAG is thought to be an increased outflow resistance via the pressure-dependent trabecular outflow system, so there is a crescent interest in increasing trabecular meshwork outflow by extracellular matrix remodeling and/or by modulation of contractility/TM cytoskeleton disruption. Modulation of new agents that act mainly on trabecular meshwork outflow may be the future hypotensive treatment for glaucoma patients. There are also other agents in which modulation may decrease aqueous humour production or increase uveoscleral outflow by different mechanisms from those drugs available for glaucoma treatment. Recently, a role for the ghrelin-GHSR system in the pathophysiology modulation of the anterior segment, particularly regarding glaucoma, has been proposed.

The Juxtacanalicular Region of Ocular Trabecular Meshwork: A Tissue with a Unique Extracellular Matrix and Specialized Function

The trabecular meshwork (TM) is a filter-like tissue located in the anterior segment of the eye. It is composed of a series of fenestrated beams through which aqueous humor flows to exit the anterior chamber via Schlemm's canal. The primary function of the TM is to regulate the flow of aqueous humor in order to establish intraocular pressure (IOP). Dysregulated aqueous humor outflow causes elevated IOP, which is a primary risk factor for glaucoma. The region of the TM implicated in establishing IOP lies adjacent to Schlemm's canal and is called the juxtacanalicular tissue (JCT) or cribriform region. Recent advanced light microscopy studies suggest that the JCT can be subdivided into inner and outer zones based on the localization of certain extracellular matrix (ECM) molecules. By comparing the ECM of the JCT to other connectives tissues and disease processes, this review outlines the evidence for two new concepts in TM biology: (1) continuous maintenance ECM remodeling, which may be critical in order to preserve open aqueous humor flow channels by releasing trapped debris and associated ECM fragments from the outflow pathways; (2) the JCT ECM as a barrier to functionally isolate the aqueous outflow channels. The ECM surrounding the outflow channels in the JCT may function to sequester small active regulatory molecules and prevent them from aberrantly modulating outflow resistance. These adaptations point to a distinctive tissue that has evolved transient ECM remodeling processes in order to regulate aqueous humor outflow and maintain rigorous control of IOP.

Integrins in trabecular meshwork and optic nerve head: possible association with the pathogenesis of glaucoma

Integrins are a family of membrane-spanning proteins that are important receptors for cell adhesion to extracellular matrix proteins. They also provide connections between the extracellular environment and intracellular cytoskeletons and are responsible for activation of many intracellular signaling pathways. In vitro and in vivo data strongly indicate that integrin-mediated signaling events can modulate the organization of the actin cytoskeleton in trabecular meshwork (TM) cells and are associated with astrocyte migration and microglia activation of the optic nerve head in patients with primary open angle glaucoma. Consequently, increase in resistance in the TM outflow pathways and remodeling of the optic nerve head occur, which in turn increases intraocular pressure (IOP), adds additional mechanical stress and strain to optic nerve axons, and accelerates damage of axons initially caused by optic nerve head remodeling. Integrins appear to be ideal candidates for translating physical stress and strain into cellular responses known to occur in glaucomatous optic neuropathy.

Inhibition of hyaluronan synthesis reduces versican and fibronectin levels in trabecular meshwork cells

Hyaluronan (HA) is a major component of the extracellular matrix (ECM) and is synthesized by three HA synthases (HAS). Similarities between the HAS2 knockout mouse and the hdf mutant mouse, which has a mutation in the versican gene, suggest that HA and versican expression may be linked. In this study, the relationship between HA synthesis and levels of versican, fibronectin and several other ECM components in trabecular meshwork cells from the anterior segment of the eye was investigated. HA synthesis was inhibited using 4-methylumbelliferone (4MU), or reduced by RNAi silencing of each individual HAS gene. Quantitative RT-PCR and immunoblotting demonstrated a reduction in mRNA and protein levels of versican and fibronectin. Hyaluronidase treatment also reduced versican and fibronectin levels. These effects could not be reversed by addition of excess glucose or glucosamine or exogenous HA to the culture medium. CD44, tenascin C and fibrillin-1 mRNA levels were reduced by 4MU treatment, but SPARC and CSPG6 mRNA levels were unaffected. Immunostaining of trabecular meshwork tissue after exposure to 4MU showed an altered localization pattern of HA-binding protein, versican and fibronectin. Reduction of versican by RNAi silencing did not affect HA concentration as assessed by ELISA. Together, these data imply that HA concentration affects synthesis of certain ECM components. Since precise regulation of the trabecular meshwork ECM composition and organization is required to maintain the aqueous humor outflow resistance and intraocular pressure homeostasis in the eye, coordinated coupling of HA levels and several of its ECM binding partners should facilitate this process.

Genomic characteristics of adhesion molecules in patients with symptomatic pulmonary embolism

The aim of this study was to identify the differences in the expression of cell adhesion molecule-related mRNAs between symptomatic pulmonary embolism (PE) and a control group, and to investigate the interactions among activated leukocytes, platelets and endothelial cells. Whole human gene chip was applied to detect the expression of cell adhesion molecule-related mRNAs in symptomatic PE and in the control group, and statistical analysis was performed. In patients with PE, the expression of the majority of integrin mRNAs located on leukocytes and platelets was significantly upregulated. The expression of mRNAs related to L-selectin and P-selectin glycoprotein ligand was significantly upregulated, while the expression of mRNA related to E-selectin was significantly downregulated. The expression of mRNAs related to classic cadherins and protocadherins was downregulated, and the expression of mRNAs related to vascular endothelial cadherin was significantly downregulated; the expression of mRNAs related to the immunoglobulin superfamily had no obvious difference between the 2 groups. In conclusion, we demonstrated that, in symptomatic PE patients, the adhesion of leukocytes and platelets was enhanced; the activation of endothelial cells was obviously weakened; the adherens junctions among endothelial cells were weakened, with the endothelium becoming more permeable.

Natural and Genetically Engineered Proteins for Tissue Engineering

To overcome the limitations of traditionally used autografts, allografts and, to a lesser extent, synthetic materials, there is the need to develop a new generation of scaffolds with adequate mechanical and structural support, control of cell attachment, migration, proliferation and differentiation and with bio-resorbable features. This suite of properties would allow the body to heal itself at the same rate as implant degradation. Genetic engineering offers a route to this level of control of biomaterial systems. The possibility of expressing biological components in nature and to modify or bioengineer them further, offers a path towards multifunctional biomaterial systems. This includes opportunities to generate new protein sequences, new self-assembling peptides or fusions of different bioactive domains or protein motifs. New protein sequences with tunable properties can be generated that can be used as new biomaterials. In this review we address some of the most frequently used proteins for tissue engineering and biomedical applications and describe the techniques most commonly used to functionalize protein-based biomaterials by combining them with bioactive molecules to enhance biological performance. We also highlight the use of genetic engineering, for protein heterologous expression and the synthesis of new protein-based biopolymers, focusing the advantages of these functionalized biopolymers when compared with their counterparts extracted directly from nature and modified by techniques such as physical adsorption or chemical modification.

1α,25-Dihydroxyvitamin D(3) and its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), suppress intraocular pressure in non-human primates

Ocular hypertension is the greatest known risk factor for glaucoma that affects an estimated 70 million people worldwide. Lowering intraocular pressure (IOP) remains the mainstay of therapy in the management of glaucoma. By means of microarray analysis, we have discovered that 1α,25-dihydroxyvitamin D(3) (1α,25-(OH)(2)D(3)) regulates genes that are known to be involved in the determination of intraocular pressure (IOP). Topical administration of 1α,25-(OH)(2)D(3) or its analog, 2-methylene-19-nor-(20S)-1α,25-dihydroxyvitamin D(3) (2MD), markedly reduces IOP in non-human primates. The reduction in IOP is not the result of reduced aqueous humor formation, while a 35% increase in aqueous humor drainage by 1α,25-(OH)(2)D(3) was found but this increase did not achieve significance. Nevertheless, our results suggest that 1α,25-(OH)(2)D(3), or an analog thereof, may present a new approach to the treatment of glaucoma.

Comparison of fibronectin in human marginal gingiva and interdental papilla using immunohistochemistry

BACKGROUND

The differences between marginal gingiva and interdental papilla may be due to variation in the molecular composition of these two different anatomical structures. The aim of this study was to evaluate the staining intensity of fibronectin in human marginal gingiva and interdental papilla.

MATERIALS AND METHODS

In a prospective analytical study, 16 healthy subjects needing crown lengthening surgery were selected. All participants were medically healthy, non-smokers, with no medication intake, and a healthy periodontium. During surgery, facial/buccal marginal gingiva and interdental papilla were separately harvested. The specimens were subjected to hematoxylin and eosin, histochemical (Masson' strichorom, reticulin, and elastic), and immunohistochemical staining for evaluation of morphology and inflammation; assessment of connective tissue fibers (collagen, reticulin, and elastic); and determination of fibronectin staining intensity. The data were analyzed by Spsssoftware, Wilcoxon, and Spearman tests. P<0.05 was considered to be statistically significant.

RESULTS

From a total of 32 specimens, 21 specimens were found to be normal or having mild inflammation, while the remaining specimens had moderate to severe inflammation in some parts. Collagen fibers were found to be dense in reticular connective tissue and degenerated in the region of inflammation. Reticulin fibers strongly stained near epithelium. Elastic fibers were sparsely found. Mean fibronectin staining intensity between marginal gingiva and interdental papilla was not statically significant (P=0.44). There is no statistically significant correlation between tissue inflammation and fibronectin staining intensity (P=0.76 for marginal gingival and P=0.20 for interdental papilla). Considering all specimens, fibronectin staining intensity of connective tissue adjacent to Sulcular/Junctional epithelium was higher than reticular connective tissue (P=0.003) and higher than connective tissue adjacent to oral epithelium (P<0.001).

CONCLUSION

This study did not show any difference in interdental papilla and marginal gingival with respect to fibronectin composition. More studies in this context are needed.

Myocilin, a glaucoma-associated protein, promotes cell migration through activation of integrin-focal adhesion kinase-serine/threonine kinase signaling pathway

The MYOCILIN gene encodes a secreted glycoprotein which is highly expressed in eye drainage structures. Mutations in this gene may lead to juvenile open-angle glaucoma and adult onset primary open-angle glaucoma, one of the leading causes of irreversible blindness in the world. Functions of wild-type myocilin are still unclear. We have recently demonstrated that myocilin is a modulator of Wnt signaling and may affect actin cytoskeleton organization. Here we report that myocilin and its naturally occurring proteolytic fragments, similar to Wnt3a, are able to stimulate trabecular meshwork, NIH3T3, and FHL124 cell migration with the N-terminal proteolytic fragment of myocilin lacking the olfactomedin domain producing the highest stimulatory effect. Stimulation of cell migration occurs through activation of the integrin-focal adhesion kinase (FAK)-serine/threonine kinase (AKT) signaling pathway. Inhibition of FAK by siRNA reduced the stimulatory action of myocilin by threefold. Activation of several components of this signaling pathway was also demonstrated in the eyes of transgenic mice expressing elevated levels of myocilin in the eye drainage structures. These data extend the similarities between actions of myocilin and Wnt proteins acting through a β-catenin-independent mechanism. The modification of the migratory ability of cells by myocilin may play a role in normal functioning of the eye anterior segment and its pathology including glaucoma.

Anterior segment dysgenesis and early-onset glaucoma in nee mice with mutation of Sh3pxd2b

PURPOSE

Mutations in SH3PXD2B cause Frank-Ter Haar syndrome, a rare condition characterized by congenital glaucoma, as well as craniofacial, skeletal, and cardiac anomalies. The nee strain of mice carries a spontaneously arising mutation in Sh3pxd2b. The purpose of this study was to test whether nee mice develop glaucoma.

METHODS

Eyes of nee mutants and strain-matched controls were comparatively analyzed at multiple ages by slit lamp examination, intraocular pressure recording, and histologic analysis. Cross sections of the optic nerve were analyzed to confirm glaucomatous progression.

RESULTS

Slit lamp examination showed that, from an early age, nee mice uniformly exhibited severe iridocorneal adhesions around the entire circumference of the eye. Presumably as a consequence of aqueous humor outflow blockage, they rapidly developed multiple indices of glaucoma. By 3 to 4 months of age, they exhibited high intraocular pressure (30.8 ± 12.5 mm Hg; mean ± SD), corneal opacity, and enlarged anterior chambers. Although histologic analyses at P17 did not reveal any indices of damage, similar analysis at 3 to 4 months of age revealed a course of progressive retinal ganglion cell loss, optic nerve head excavation, and axon loss.

CONCLUSIONS

Eyes of nee mice exhibit anterior segment dysgenesis and early-onset glaucoma. Because SH3PXD2B is predicted to be a podosome adaptor protein, these findings implicate podosomes in normal development of the iridocorneal angle and the genes influencing podosomes as candidates in glaucoma. Because of the early-onset, high-penetrance glaucoma, nee mice offer many potential advantages as a new mouse model of the disease.

Evidence for a role of angiopoietin-like 7 (ANGPTL7) in extracellular matrix formation of the human trabecular meshwork: implications for glaucoma

The trabecular meshwork tissue controls the drainage of the aqueous humor of the eye. A dysfunctional trabecular meshwork leads to an altered fluid resistance, which results in increased intraocular pressure (IOP). IOP is the major risk factor of glaucoma, the second-leading cause of blindness in the developed world. In the search for genes altered by glaucomatous insults, we identified angiopoietin-like7 (ANGPTL7), a member of the ANGPTL family. Although structurally related to the angiopoietins, ANGPTL7's function is poorly understood. Because ANGPTL7 is secreted and because extracellular matrix (ECM) deposition and organization is critical for aqueous humor resistance, we investigated the effect of ANGPTL7 on relevant trabecular meshwork ECM genes and proteins. We find that overexpression of ANGPTL7 in primary human trabecular meshwork cells altered the expression of fibronectin, collagens type I, IV & V, myocilin, versican, and MMP1. ANGPTL7 also interfered with the fibrillar assembly of fibronectin. Finally, we find that silencing ANGPTL7 during the glucocorticoid insult significantly affected the expression of other steroid-responsive proteins. These results indicate that ANGPTL7 modulates the trabecular meshwork's ECM as well as the response of this tissue to steroids. Together with previous findings, these properties strengthen ANGPTL7's candidacy for the regulation of IOP and glaucoma.