Digital spatial profiling of segmental outflow regions in trabecular meshwork reveals a role for ADAM15

In this study we used a spatial transcriptomics approach to identify genes specifically associated with either high or low outflow regions in the trabecular meshwork (TM) that could potentially affect aqueous humor outflow in vivo. High and low outflow regions were identified and isolated from organ cultured human anterior segments perfused with fluorescently-labeled 200 nm FluoSpheres. The NanoString GeoMx Digital Spatial Profiler (DSP) platform was then used to identified genes in the paraffin embedded tissue sections from within those regions. These transcriptome analyses revealed that 16 genes were statistically upregulated in high outflow regions and 57 genes were statistically downregulated in high outflow regions when compared to low outflow regions. Gene ontology enrichment analysis indicated that the top three biological categories of these differentially expressed genes were ECM/cell adhesion, signal transduction, and transcription. The ECM/cell adhesion genes that showed the largest differential expression (Log2FC ±1.5) were ADAM15, BGN, LDB3, and CRKL. ADAM15, which is a metalloproteinase that can bind integrins, was upregulated in high outflow regions, while the proteoglycan BGN and two genes associated with integrin signaling (LDB3, and CRKL) were downregulated. Immunolabeling studies supported the differential expression of ADAM15 and showed that it was specifically upregulated in high outflow regions along the inner wall of Schlemm's canal and in the juxtacanalicular (JCT) region of the TM. In addition to these genes, the studies showed that genes for decorin, a small leucine-rich proteoglycan, and the α8 integrin subunit were enriched in high outflow regions. These studies identify several novel genes that could be involved in segmental outflow, thus demonstrating that digital spatial profiling could be a useful approach for understanding segmental flow through the TM. Furthermore, this study suggests that changes in the expression of genes involved in regulating the activity and/or organization of the ECM and integrins in the TM are likely to be key players in segmental outflow.

NFATc1 Regulation of Dexamethasone-Induced TGFB2 Expression Is Cell Cycle Dependent in Trabecular Meshwork Cells

Although elevated TGFβ2 levels appear to be a causative factor in glaucoma pathogenesis, little is known about how TGFβ2 expression is regulated in the trabecular meshwork (TM). Here, we investigated if activation of the cytokine regulator NFATc1 controlled transcription of TGFβ2 in human TM cells by using dexamethasone (DEX) to induce NFATc1 activity. The study used both proliferating and cell cycle arrested quiescent cells. Cell cycle arrest was achieved by either cell-cell contact inhibition or serum starvation. β-catenin staining and p21 and Ki-67 nuclear labeling were used to verify the formation of cell-cell contacts and activity of the cell cycle. NFATc1 inhibitors cyclosporine A (CsA) or 11R-VIVIT were used to determine the role of NFATc1. mRNA levels were determined by RT-qPCR. DEX increased TGFβ2 mRNA expression by 3.5-fold in proliferating cells but not in quiescent cells or serum-starved cells, and both CsA and 11R-VIVIT inhibited this increase. In contrast, the expression of other DEX/NFATc1-induced mRNAs (myocilin and β3 integrin) occurred regardless of the proliferative state of the cells. These studies show that NAFTc1 regulates TGFβ2 transcription in TM cells and reveals a previously unknown connection between the TM cell cycle and modulation of gene expression by NFATc1 and/or DEX in TM cells.

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.

The Effects of Mechanical Stretch on Integrins and Filopodial-Associated Proteins in Normal and Glaucomatous Trabecular Meshwork Cells

The trabecular meshwork (TM) is the tissue responsible for regulating aqueous humor fluid egress from the anterior eye. If drainage is impaired, intraocular pressure (IOP) becomes elevated, which is a primary risk factor for primary open angle glaucoma. TM cells sense elevated IOP via changes in their biomechanical environment. Filopodia cellular protrusions and integrin transmembrane proteins may play roles in detecting IOP elevation, yet this has not been studied in detail in the TM. Here, we investigate integrins and filopodial proteins, such as myosin-X (Myo10), in response to mechanical stretch, an in vitro technique that produces mechanical alterations mimicking elevated IOP. Pull-down assays showed Myo10 binding to α5 but not the β1 subunit, αvβ3, and αvβ5 integrins. Several of these integrins colocalized in nascent adhesions in the filopodial tip and shaft. Using conformation-specific antibodies, we found that β1 integrin, but not α5 or αvβ3 integrins, were activated following 1-h mechanical stretch. Cadherin -11 (CDH11), a cell adhesion molecule, did not bind to Myo10, but was associated with filopodia. Interestingly, CDH11 was downregulated on the TM cell surface following 1-h mechanical stretch. In glaucoma cells, CDH11 protein levels were increased. Finally, mechanical stretch caused a small, yet significant increase in Myo10 protein levels in glaucoma cells, but did not affect cellular communication of fluorescent vesicles via filopodia-like tunneling nanotubes. Together, these data suggest that TM cell adhesion proteins, β1 integrin and CDH11, have relatively rapid responses to mechanical stretch, which suggests a central role in sensing changes in IOP elevation in situ.

Consensus Recommendation for Mouse Models of Ocular Hypertension to Study Aqueous Humor Outflow and Its Mechanisms

Due to their similarities in anatomy, physiology, and pharmacology to humans, mice are a valuable model system to study the generation and mechanisms modulating conventional outflow resistance and thus intraocular pressure. In addition, mouse models are critical for understanding the complex nature of conventional outflow homeostasis and dysfunction that results in ocular hypertension. In this review, we describe a set of minimum acceptable standards for developing, characterizing, and utilizing mouse models of open-angle ocular hypertension. We expect that this set of standard practices will increase scientific rigor when using mouse models and will better enable researchers to replicate and build upon previous findings.

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.

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.

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.

Fibronectin in the Tumor Microenvironment Activates a TLR4-dependent Inflammatory Response in Lung Cancer Cells

The microenvironment of solid tumors plays an essential role in tumor progression. In lung cancer, the stromal cells produce a fibronectin rich extracellular matrix which is known to contribute to both tumor metastasis and drug resistance. Due to its conformational lability, fibronectin is considerably remodeled by the contractile forces of the fibrotic microenvironment within the tumor stroma. As a result, the secondary structure of fibronectin's Type III domains is disrupted and the molecule becomes highly stretched. The contribution/impact of these strained forms of fibronectin on tumor growth and metastasis is not known. In the current study we show that the partially unfolded first Type III domain of fibronectin, III-1c, activates a toll-receptor/NF-κB pathway leading to an increase in the expression of IL-8. Using a 3-D model of tumor-associated extracellular matrix, we demonstrate that lung cancer cells seeded onto this matrix activate a TLR4/NF-κB signaling pathway leading to a robust increase in the release of IL-8. Cytokine release by these cells is completely dependent on the presence of fibronectin in the extracellular matrix. These findings suggest that paracrine signaling between the tumor and the stromal myofibroblasts causes a remodeling of the matrix fibronectin into a strained conformation which supports the activation of a TLR4/NF-κB signaling pathway resulting in the upregulation of fibro-inflammatory cytokines.

α5β1 Integrin Promotes Anchoring and Integration of Transplanted Stem Cells to the Trabecular Meshwork in the Eye for Regeneration

Stem cell-based therapy to restore the function of abnormal trabecular meshwork (TM) and decrease intraocular pressure (IOP) provides a novel approach to treat open-angle glaucoma. However, molecular mechanism for stem cells homing and anchoring to the TM remains unclear. This study aimed to discover the function of integrins in homing and integration of exogenous TM stem cells (TMSCs) to the TM. Integrin expression in TMSCs and fibroblasts was evaluated by quantitative real-time PCR (qPCR), flow cytometry, immunofluorescent staining, and western blotting. Expression of integrin ligand fibronectin was detected in cultured TM cells and murine TM tissue by immunostaining. Cell affinity to TM cells or fibronectin matrix was examined to compare TMSCs with TMSCs functionally blocked with an α5β1 integrin antibody. TMSCs and TMSCs with α5β1 integrin-blocking were intracamerally injected into wild-type mice. Wholemounts and cryosections were analyzed to discover cell distribution and integration at 3 days and 1 month. IOP was measured to detect possible changes. We discovered that human TMSCs expressed a higher level of α5β1 integrin than fibroblasts, but similar levels of αvβ3 and αvβ5 integrin. Upregulation of fibronectin was found in both TM cells treated with dexamethasone for 14 days and murine TM tissues damaged by laser photocoagulation. TMSCs were able to attach to the TM cells and fibronectin matrix in vitro. When the surface α5β1 integrin was blocked, the attached cell numbers were significantly reduced. Both TMSCs and TMSCs incubated with an α5β1 integrin-blocking antibody could home to the mouse TM after injection. TMSCs blocked with the α5β1 integrin-blocking antibody were not retained in the TM tissue at 1 month. The injected cells did not affect mouse IOP. In conclusion, highly expressed α5β1 integrin participates in maintaining TMSCs anchored and integrated to the TM, which would be crucial for stem cell-based therapy for glaucoma.

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.

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.

Effect of αvβ3 Integrin Expression and Activity on Intraocular Pressure

Purpose

To determine the effects of αvβ3 integrin expression and activation on intraocular pressure (IOP).

Methods

Cre^+/−β3^flox/flox mice were treated with topical tamoxifen eye drops for 5 days to activate Cre and excise the β3 integrin gene from the anterior segment. IOP was measured weekly for 11 weeks using rebound tonometry. Mice were then killed and changes in expression of the β3 integrin subunit in Cre^+/− β3^flox/flox mice were determined using Western blotting analysis and immunofluorescence microscopy. To determine the effect of αvβ3 integrin activation on outflow facility, porcine organ culture anterior segments (POCAS) were perfused with the αvβ3 integrin-activating antibody AP5 or an isotype IgG control for 21 hours. The effect of αvβ3 integrin activation on IOP was measured over 7 days in C57BL/6J mice intracamerally infused with AP5, AP3, IgG, or PBS.

Results

Deletion of the β3 integrin subunit using the tamoxifen-inducible Cre-loxP system resulted in a decrease in expression of the β3 integrin subunit in the trabecular meshwork and ciliary muscle. Morphologically no gross changes in the anterior segment were detected. Deletion of the β3 integrin subunit resulted in a significantly (P < 0.05) lower IOP in mice within 2 weeks following the tamoxifen treatment and persisted for 11 weeks. Activating the αvβ3 integrin with the AP5 antibody resulted in a significant (P < 0.05) increase in IOP in C57BL/6J mice and a decrease in outflow facility in 42% of the POCAS.

Conclusions

These studies demonstrate a role for αvβ3 integrin signaling in the regulation of IOP.

Genomic/proteomic analyses of dexamethasone-treated human trabecular meshwork cells reveal a role for GULP1 and ABR in phagocytosis

Purpose

The purpose of this study is to examine the expression profile of genes related to integrin-mediated phagocytosis that are altered by dexamethasone (DEX) and/or αvβ3 integrin signaling to gain a better understanding of the molecular basis of phagocytosis and the pathophysiology of glucocorticoid-induced ocular hypertension.

Methods

RNA and cell lysates were obtained from human trabecular meshwork (HTM) cells incubated with and without DEX for 4-5 d. The relative level of gene expression was evaluated using the Affymetrix Gene Chip® human gene microarray and quantitative PCR (qPCR). Changes in protein expression were validated using western blots or FACS analyses. The involvement of proteins in phagocytosis was determined using siRNA to knock down the expression of these proteins in an immortalized TM-1 cell line. Changes in the phagocytic activity were measured using pHrodo™-labeled S. aureus bioparticles followed by immunofluorescence microscopy. The effect of αvβ3 integrin expression and activity on GULP1 mRNA levels was measured using qPCR in TM-1 cells overexpressing wild type or constitutively active αvβ3 integrin.

Results

Gene microarrays revealed statistically significant differences (>2 fold) in the expression of seven genes known to be involved in phagocytosis. Three genes (CD36, ABR, and GULP1) were downregulated, while four genes (ITGB3, CHN1, PIK3R1, and MFGE8) were upregulated. The genes were either associated with modulating RAC1 activity (ABR and CHN1) or integrin signaling (CD36, GULP1, ITGB3, PIK3R1, and MFGE8). Another gene, SIRPA, was also downregulated (1.6 fold) but only in one cell strain. qPCR and western blot analyses verified that DEX caused a decrease in SIRPA and GULP1 mRNA and their protein levels, while levels of CHN1 mRNA and its protein were upregulated by DEX. qPCR showed that although ABR mRNA was downregulated compared to non-treated controls after 5 d of treatment with DEX, no change at the protein level was detected. qPCR analysis also revealed that DEX caused an increase in MFGE8 mRNA levels. The levels of CD36 mRNA and protein varied between cell strains treated with DEX and were not statistically different compared to controls. The knockdown of GULP1 and ABR using siRNAs decreased phagocytosis by 40%. Interestingly, GULP1 mRNA levels were also decreased by 60% when αvβ3 integrin was overexpressed in TM-1 cells.

Conclusion

The DEX-induced inhibition of phagocytosis may be caused by the downregulation of ABR and GULP1 disrupting the αvβ5 integrin/RAC1-mediated engulfment pathway. The downregulation of GULP1 by αvβ3 integrin further suggests that this integrin may be a negative regulator of phagocytosis by transcriptionally downregulating proteins needed for phagocytosis. In summary, these results represent new insights into the effects of glucocorticoids and integrin signaling on the phagocytic process in the TM.

Characterization of the PEGylated Functional Upstream Domain Peptide (PEG-FUD): a Potent Fibronectin Assembly Inhibitor with Potential as an Anti-Fibrotic Therapeutic

PURPOSE

To develop PEGylated variants of pUR4/FUD (FUD), a fibronectin assembly inhibitor, using 10 kDa, 20 kDa, and 40 kDa PEGs to evaluate their binding affinity and inhibitory potency.

METHODS

The FUD peptide was recombinantly expressed, purified, and PEGylated at the N-terminus using 10 kDa, 20 kDa, and 40 kDa methoxy-PEG aldehyde. The PEGylates were purified and fractionated using ion-exchange chromatography. The molecular weight and degree of PEGylation of each conjugate was verified using MALDI-TOF. The binding affinity of each PEG-FUD conjugate was studied using isothermal titration colorimetry (ITC) and their inhibitory potency was characterized by a cell-based matrix assembly in vitro assay.

RESULTS

The 10 kDa, 20 kDa, and 40 kDa PEG-FUD conjugates were synthesized and isolated in good purity as determined by HPLC analysis. Their molecular weight was consistent with attachment of a single PEG molecule to one FUD peptide. The binding affinity (Kd) and the fibronectin fibrillogenesis inhibitory potency (IC50) of all PEG-FUD conjugates remained nanomolar and unaffected by the addition of PEG.

CONCLUSIONS

Retention of FUD fibronectin binding activity following PEGylation with three different PEG sizes suggest that PEG-FUD holds promise as an effective anti-fibrotic with therapeutic potential and a candidate for further pharmacokinetic and biodistribution studies.

Consensus recommendations for trabecular meshwork cell isolation, characterization and culture

Cultured trabecular meshwork (TM) cells are a valuable model system to study the cellular mechanisms involved in the regulation of conventional outflow resistance and thus intraocular pressure; and their dysfunction resulting in ocular hypertension. In this review, we describe the standard procedures used for the isolation of TM cells from several animal species including humans, and the methods used to validate their identity. Having a set of standard practices for TM cells will increase the scientific rigor when used as a model, and enable other researchers to replicate and build upon previous findings.

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.

Involvement of Tiam1, RhoG and ELMO2/ILK in Rac1-mediated phagocytosis in human trabecular meshwork cells

We previously demonstrated that an αvβ5 integrin/FAK- mediated pathway regulated the phagocytic properties of human trabecular meshwork (HTM) cells. Here we demonstrate that this process is mediated by Rac-1 and a previously unreported signaling pathway that utilizes the Tiam1 as well as a novel ILK/RhoG/ELMO2 signaling pathway. Phagocytosis in both a TM-1 cell line and normal HTM cells was mediated by Rac1 and could be significantly decreased by >75% using the Rac1 inhibitor EHop-016. Knockdown of Rac1 in TM-1 cells also inhibited phagocytosis by 40% whereas overexpression of a constitutively active Rac1 or stimulation with PDGF increased phagocytosis by 83% and 32% respectively. Tiam1 was involved in regulating phagocytosis. Knockdown of Tiam1 inhibited phagocytosis by 72% while overexpression of Tiam1 C1199 increased phagocytosis by 75%. Other upstream effectors of Rac1 found to be involved included ELMO2, RhoG, and ILK. Knockdowns of ELMO2, ILK, and RhoG caused a reduction in phagocytosis by 51%, 55% and 46% respectively. In contrast, knockdown of Vav2 and Dock1 or overexpression of Vav2 Y159/172F did not cause a significant change in phagocytosis. These data suggest a novel link between Tiam1 and RhoG/ILK /ELMO2 pathway as upstream effectors of the Rac1-mediated phagocytic process in TM cells.

Glaucomatous MYOC mutations activate the IL-1/NF-κB inflammatory stress response and the glaucoma marker SELE in trabecular meshwork cells

PURPOSE

Activation of the IL-1/NF-κB inflammatory stress pathway and induction of SELE expression in the trabecular meshwork (TBM) is a marker for high-tension glaucomas of diverse etiology. Pathway activation stimulates aqueous outflow and protects against oxidative stress, but may be damaging in the long-term. MYOC mutations have been causally linked to high-tension forms of primary open angle glaucoma (POAG). This study investigated a possible link between MYOC mutations and activation of the IL-1/NF-κB pathway and expression of SELE.

METHODS

We constructed MYOC expression vectors with mutations at sites that cause POAG. Mutations (Q368X, Y437H, A427T) were selected to represent proteins with differing POAG-causing potency (Q368X > Y437H > A427T) and intracellular retention behavior (Q368X and Y437H retained, A427T released). The constructs were made in two different kinds of vectors; one a plasmid designed for transient transfection (pCMV6), and one a doxycycline-inducible lentiviral vector (pSLIK) for stable cell transduction. The immortalized human trabecular meshwork line TM-1 was used for all expression studies. Expression of IL1A mRNA was determined by reverse transcription (RT)-PCR, as well as a set of five other genes associated with signaling pathways linked to glaucoma: IL1B and IL6 (NF-κB pathway), TGFB2 and ACTA2 (TGF-β pathway) and FOXO1 (E2F1 apoptotic pathway). An ELISA was used to quantify IL1A protein released into culture media. To quantify intracellular NF-κB activity, we transiently transfected stably transduced cell lines with a luciferase expression vector under control of the IL8 promoter (containing an NF-κB response element).

RESULTS

Transiently expressed wild-type MYOC was released into cell culture media, whereas mutant MYOCs Q368X and Y437H remained within cells. Both mutant MYOCs activated the IL-1/ NF-κB pathway, significantly stimulating expression of IL1A and IL1B. However Y437H, which causes a severe glaucoma phenotype, was less effective than Q368X, which causes a moderate glaucoma phenotype. In addition, the retained mutants stimulated expression of stress response genes ACTA2 and FOXO1. Unexpectedly, wild-type MYOC significantly decreased expression of IL6 and TGFB2, to approximately half of the control levels, and expression of IL1B and ACTA2 was also slightly decreased. Induction of MYOC mutants Q368X and Y437H in stably transduced cell lines significantly stimulated the level of IL1A protein released into culture media. Once again however, the effect of the severe MYOC mutant Y437H was less than the effect of the moderate MYOC mutant Q368X. In contrast, induced expression of the intracellularly retained mutant MYOC A427T or wild-type MYOC did not change the amount of IL1A protein in culture media. Induction of Y437H MYOC plus IL1A treatment increased NF-κB activity by 25% over IL1A alone. In contrast, induction of Q368X or A427T plus IL1A treatment did not significantly affect NF-κB activity over IL1A alone. However, wild-type MYOC expression inhibited IL1A-stimulated NF-κB activity. We also observed that endogenous MYOC expression was induced by IL1A in TM-1 cells and primary TBM cell cultures. SELE was co-expressed with MYOC in the primary cell lines.

CONCLUSIONS

These results indicate that POAG-causing MYOC mutants activate the IL-1/NF-κB pathway, with activation levels correlated with intracellular retention of the protein, but not POAG-causing potency. Unexpectedly, it was also discovered that wild-type MYOC inhibits activation of the IL-1/NF-κB pathway, and that activation of the IL-1/NF-κB pathway stimulates expression of MYOC. This is the first evidence that glaucoma-causing MYOC mutants can activate the inflammatory response and that wild-type MYOC has anti-inflammatory activity.

Viral Vector Effects on Exoenzyme C3 Transferase-Mediated Actin Disruption and on Outflow Facility

PURPOSE

Purified Clostridium botulinum exoenzyme C3 transferase (C3) effects on the actin cytoskeleton in human trabecular meshwork cells (HTM) and on the outflow facility response in monkey organ-cultured anterior segments (MOCAS) were determined in the presence or absence of viral vectors.

METHODS

Human adenovirus type 5 (AdV) and feline immunodeficiency virus (FIV) vectors were produced using kits. Cell soluble purified C3 (C3cs) was purchased commercially. Recombinant C3 (C3rec) cDNA was overexpressed in Escherichia coli and purified. The HTM cells were incubated with up to 10 μg/mL C3cs or with 5 μg of C3rec and/or viral vector (multiplicity of infection [MOI] = 25). Cells then were fixed and stained for actin. Outflow facility in MOCAS was measured at baseline, 4 hours, 24 hours, and 3 to 4 days following bolus injection of AdV (1.6 × 107 transducing units) and/or 2.5 μg C3rec.

RESULTS

The HTM cells treated for 4 hours with C3cs (all doses) or for 24 hours with C3rec developed a rounded morphology and lost stress fibers. Cells transduced with vectors alone showed no changes at any time point. Cells exposed to C3rec and cotransduced with either viral vector showed significant disruption of the actin cytoskeleton within 4 hours after exposure, which persisted at 24 hours. In MOCAS, the AdV vector alone had no effect on outflow facility, but enhanced the response to C3rec at 4 hours.

CONCLUSIONS

Coadministration of viral vectors enhances the ability of C3 transferase to disrupt actin stress fiber formation in HTM cells and increase outflow facility in MOCAS. Viral vectors potentially could be used to increase the bioavailability of proteins for cells that are difficult to transfect.

NFATc1 activity regulates the expression of myocilin induced by dexamethasone

Mutations in the myocilin gene (MYOC) account for 10% of juvenile open-angle glaucoma cases and 3-4% of adult onset primary open-angle glaucoma cases. It is a secreted glycoprotein found in many ocular and non-ocular tissues and has been linked to elevated intraocular pressure. In human trabecular meshwork (HTM) cells, MYOC expression can be induced by the glucocorticoid dexamethasone (DEX). In this study we examined the role of the calcineurin/NFATc1 (Nuclear Factor of Activated T-cells) pathway in the DEX induction of MYOC in HTM cells. In post-confluent HTM cells treated with either 500 nM DEX or 0.1% ethanol (EtOH; vehicle control) for 0-6 days both protein and mRNA levels of MYOC were increased while DEX was present. The protein and mRNA levels remained elevated for an additional 12 days after the removal of DEX. Only 1 day of DEX treatment was sufficient to trigger a sustained increase in MYOC mRNA that lasted for 4 days after the removal of DEX. Similar to other studies, myocilin protein expression was not seen until the second day of DEX treatment while mRNA increased within one day of DEX indicating that this is a secondary glucocorticoid response. To determine if MYOC gene expression was regulated by calcineurin/NFATc1, HTM cells were pre-treated for 1 h with the calcineurin inhibitors cyclosporin A or INCA-6 prior to the addition of DEX or EtOH for 2 days. NFATc1 siRNA was used to determine if NFATc1 was required for MYOC mRNA expression. Cells were also treated with the ionophone ionomycin to determine if increased cytosolic calcium affected MYOC expression. These studies showed that the DEX induced increase in MYOC mRNA could be inhibited with either cyclosporin A or INCA-6 or by transfection with NFATc1 siRNA and that ionomycin was unable to increase MYOC mRNA. Immunofluorescence microscopy was also performed to determine if DEX caused the nuclear translocation of NFATc1. Immunostaining showed that NFATc1 relocated to the nucleus within 15 min of DEX treatment and remained there for up to 2 h. The data suggest that the DEX-induced increase in MYOC expression activates a calcineurin and NFATc1 pathway in a calcium independent mechanism.

A syndecan-4 binding peptide derived from laminin 5 uses a novel PKCε pathway to induce cross-linked actin network (CLAN) formation in human trabecular meshwork (HTM) cells

In this study, we examined the role(s) of syndecan-4 in regulating the formation of an actin geodesic dome structure called a cross-linked actin network (CLAN) in which syndecan-4 has previously been localized. CLANs have been described in several different cell types, but they have been most widely studied in human trabecular meshwork (HTM) cells where they may play a key role in controlling intraocular pressure by regulating aqueous humor outflow from the eye. In this study we show that a loss of cell surface synedcan-4 significantly reduces CLAN formation in HTM cells. Analysis of HTM cultures treated with or without dexamethasone shows that laminin 5 deposition within the extracellular matrix is increased by glucocorticoid treatment and that a laminin 5-derived, syndecan-4-binding peptide (PEP75), induces CLAN formation in TM cells. This PEP75-induced CLAN formation was inhibited by heparin and the broad spectrum PKC inhibitor Ro-31-7549. In contrast, the more specific PKCα inhibitor Gö 6976 had no effect, thus excluding PKCα as a downstream effector of syndecan-4 signaling. Analysis of PKC isozyme expression showed that HTM cells also expressed both PKCγ and PKCε. Cells treated with a PKCε agonist formed CLANs while a PKCα/γ agonist had no effect. These data suggest that syndecan-4 is essential for CLAN formation in HTM cells and that a novel PKCε-mediated signaling pathway can regulate formation of this unique actin structure.

Prospects for lentiviral vector mediated prostaglandin F synthase gene delivery in monkey eyes in vivo

Currently, the most effective outflow drugs approved for clinical use are prostaglandin F2α analogues, but these require daily topical self-dosing and have various intraocular, ocular surface and extraocular side effects. Lentiviral vector-mediated delivery of the prostaglandin F synthase (PGFS) gene, resulting in long-term reduction of intraocular pressure (IOP), may eliminate off-target tissue effects and the need for daily topical PGF2α self-administration. Lentiviral vector-mediated delivery of the PGFS gene to the anterior segment has been achieved in cats and non-human primates. Although these results are encouraging, our studies have identified a number of challenges that need to be overcome for prostaglandin gene therapy to be translated into the clinic. Using examples from our work in non-human primates, where we were able to achieve a significant reduction in IOP (2 mm Hg) for 5 months after delivery of the cDNA for bovine PGF synthase, we identify and discuss these issues and consider several possible solutions.

The role of integrins in the trabecular meshwork

Integrins are a family of heterodimeric transmembrane receptors that mediate adhesion to the extracellular matrix (ECM). However, integrins are not just adhesion receptors. They can act as "bidirectional signal transducers" that coordinate a large number of cellular activities in response to the extracellular environment and intracellular signaling events. Among the activities regulated by integrins are cell adhesion, assembly of the ECM, growth factor signaling, apoptosis, organization of the cytoskeleton, and cytoskeleton-mediated processes such as contraction, endocytosis, and phagocytosis. Integrins regulate these activities through a complex network of intracellular signaling kinases and adaptor proteins that associate with the transmembrane and cytoplasmic domains of the integrin subunits. In this review, we will discuss how some of the known integrin-mediated activities can control the function of the trabecular meshwork. We will also discuss how integrin activity is a tightly regulated process that involves conformation changes within the heterodimer which are mediated by specific integrin-binding proteins.

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.

Activated αvβ3 integrin regulates αvβ5 integrin-mediated phagocytosis in trabecular meshwork cells

PURPOSE

To investigate the roles of αvβ3 and αvβ5 integrins in phagocytosis in human trabecular meshwork (HTM) cells.

METHODS

Immunofluorescence microscopy and FACS analysis were used to determine levels of αvβ3 and αvβ5 integrins in TM tissue and cultures of normal and immortalized TM cells. Phagocytosis was measured using pHrodo-labeled S. aureus bioparticles followed by FACS analysis. The role of αvβ5 integrin in phagocytosis was evaluated by knocking down αvβ5 integrin expression with siRNA against the human β5 gene. Signaling from focal adhesion kinase (FAK) was blocked using FAK inhibitor 14. The role of αvβ3 integrins in phagocytosis was determined by treating HTM cells with dexamethasone (DEX) or ethanol (EtOH) and by generating stable cell lines that overexpressed either wild type (WT) or constitutively active (CA) β3 integrin subunit.

RESULTS

Both TM tissue and cell lines expressed αvβ3 and αvβ5 integrins. Knockdown of αvβ5 integrin reduced phagocytosis by ∼60% and FAK inhibition significantly reduced phagocytosis up to 84%, in a dose-dependent manner. DEX treatment increased αvβ3 integrin expression in HTM cells but reduced phagocytosis by ∼50% compared with untreated and EtOH-treated cells. The CA β3 integrin-expressing cell line showed increased αvβ3 integrin levels and decreased phagocytosis by ∼50% compared with the control.

CONCLUSIONS

The αvβ5 integrin-FAK-mediated pathway regulates phagocytosis in TM cells and this pathway is inhibited by activation of αvβ3 integrins. This suggests that changes in integrin expression and activity may be responsible for alterations in phagocytosis observed in steroid induced glaucoma.

The effectiveness of local child weight management programmes: an audit study

BACKGROUND

  Many different child weight management programmes exist, with varying degrees of evaluation to provide evidence of their success. The purpose of this research was to use a standardized approach to audit the effectiveness of weight management intervention programmes in the West Midlands region of the UK, specifically to assess the benefits to participating children in terms of health improvement and behaviour change.

METHODS

  An audit of seven family-based intervention programmes currently in place in the West Midlands. Programmes were audited against the Standard Evaluation Framework.

RESULTS

  The programmes provided a partial data set relating to a change in weight from the baseline to the end of the programme; none of the programmes provided all of the measures indicated by the Standard Evaluation Form as being essential for evaluation. Weight change ranged from an increase in group mean of 0.4 kg to a decrease of 0.9 kg. Body Mass Index SD decreased by 0.1-0.2 points in four programmes and remained unchanged in two programmes. Four programmes collected long-term follow-up data at 6 months. This was often limited because of participant dropout. Improvement in diet and exercise were reported by participants in all programmes which measured these behaviours.

CONCLUSIONS

  Ongoing evaluation of all programmes, using a standard approach, is essential in order to improve the evidence base and support future commissioning.

Comparative genomic and proteomic analysis of cytoskeletal changes in dexamethasone-treated trabecular meshwork cells

Changes in the actin cytoskeleton, especially the formation of cross-linked actin networks (CLANs) are thought to contribute to the increased intraocular pressure observed in primary open-angle and steroid-induced glaucoma. To better understand the effects of glucocorticoids, we employed a shotgun method to analyze global changes in the cytoskeleton and integrin signaling pathways following dexamethasone (DEX) treatment of human trabecular meshwork (HTM) cells. RNA and cell lysates were obtained from HTM cells incubated with or without DEX. Changes in protein expression were determined by mass spectrometry (MS) following differential centrifugation of cell lysates to enrich for low-abundance cytoskeletal and signaling proteins, proteolytic digestion, and a titanium dioxide column to enrich for phosphopeptides. Results were validated by Western blots. Changes in RNA levels were determined with gene arrays and RT-PCR. Overall, MS identified 318 cytoskeleton associated proteins. Five of these proteins (PDLIM1, FGFR1OP, leiomodin-1, ZO-2 and LRP16A) were only detected in DEX-treated cells by MS. However, only PDLIM1 showed a statistically significant increase at the RNA level. Other proteins with differences at both the RNA and protein levels included β3 integrin, caveolin-1, Borg2, raftlin1, PI-3 kinase regulatory subunit α, transgelin, and filamin B. By immunofluorescence microscopy filamin B and PDLIM1 showed enhanced expression in human trabecular meshwork cells, but only PDLIM1 demonstrated significant localization within CLANs. Finally, MS showed that some of the cytoskeleton proteins (Borg2, leiomodin-1, LRP16A, raftlin1 and CKAP4) contained phosphorylated residues. This study suggests that DEX affects the expression of cytoskeleton proteins at the transcriptional and translational level and shows that a combined genomic and proteomic approach can be used for rapid analysis of proteins in the TM. It also shows that DEX altered the expression of components (PDLIM1 and β3 integrins) involved in CLAN formation and provides new findings into the effects of glucocorticoids on the cytoskeleton.

Dexamethasone-associated cross-linked actin network formation in human trabecular meshwork cells involves β3 integrin signaling

PURPOSE

To determine whether cross-linked actin networks (CLANs) formed in dexamethasone (DEX)-treated human trabecular meshwork (HTM) cells are structurally similar to those formed after β3 integrin activation and involve αvβ3 integrin signaling.

METHODS

Two HTM cell strains and an αvβ3 integrin-overexpressing immortalized TM cell line were used. DEX- or ethanol-pretreated HTM cells were plated on fibronectin with or without β3 integrin-activating mAb AP-5. Immunofluorescence microscopy was used to identify phalloidin-labeled CLANs and to ascertain the presence of α-actinin, PIP(2), and syndecan-4 within them. β3 Integrin signaling involvement was determined using a PI3-kinase (LY294002) or Rac1 (NSC23766) inhibitor. αvβ3 Integrin expression levels and the β3 integrin activation state were determined by fluorescence-activated cell sorter analysis and immunofluorescence microscopy.

RESULTS

CLANs associated with either DEX treatment or β3 integrin activation contained syndecan-4, PIP(2), and α-actinin. In the absence of mAb AP-5, LY294002 did not affect DEX-associated CLAN formation, whereas NSC23766 decreased the percentage of CLAN-positive cells by 80%. In the presence of mAb AP-5, both inhibitors decreased DEX-associated CLAN formation. DEX pretreatment increased β3 integrin-induced CLAN formation nearly sixfold and the level of αvβ3 integrin expression and activation threefold compared with control cells. Activated β3 integrin-positive adhesions increased nearly fivefold in DEX-treated cells. αvβ3 Integrin overexpression in TM-1 cells increased CLAN formation twofold.

CONCLUSIONS

DEX-associated CLANs were structurally similar to those induced by mAb AP-5 and involved both increased expression and activation of αvβ3 integrins. Thus, glucocorticoid-induced CLAN formation may involve enhanced β3 integrin signaling in HTM cells, possibly by an inside-out signaling mechanism.

The impact of school-day variation in weight and height on National Child Measurement Programme body mass index-determined weight category in Year 6 children

BACKGROUND

In England, the National Child Measurement Programme (NCMP) annually measures the weight and height of Year 6 schoolchildren (age 10-11 years). While measurement protocols are defined, the time of measurement within the school day is not. This study examined the impact of school-day variation in weight and height on NCMP body mass index (BMI)-determined weight category in Year 6 children.

METHODS

Standing height and weight were measured in morning and afternoon sessions in 74 children, boys (n= 34; height: 141.16 ± 7.45 cm; weight: 36.48 ± 9.46 kg, BMI: 18.19 ± 3.98 kg/m(2) ) and girls (n= 40; height: 144.58 ± 7.66 cm; weight: 42.25 ± 11.29 kg; BMI: 19.97 ± 3.98 kg/m(2) ) aged 11 ± 0.3 years.

RESULTS

In the whole sample, height decreased (Mean =-0.51 cm, 95% CI: -0.39 to -0.64 cm, P= 0.01), weight did not change (Mdn = 36.40 to 36.35, P= 0.09) and BMI increased (Mdn = 18.04 to 18.13, P= 0.01). In girls weight increased (Mdn = 41.40 to 41.60, P= 0.01). BMI percentile increased (Mdn = 57th to 59.5th centile, P= 0.01). One girl increased in BMI category from morning to afternoon according to the clinical cut-offs (≤2nd, >91st and >98th) and three girls increased BMI category according to the population monitoring cut-offs (≤2nd, ≥85th, ≥95th).

CONCLUSIONS

School-day variation in height (and in girls alone, weight) impact upon increased BMI and BMI percentile in afternoon versus morning measurements in Year 6 children. Although not reaching statistical significance, resultant variation in categorization at the individual level may lead to unwarranted follow-up procedures being initiated. Further research with larger samples is required to further explore the impact of daily variability in height and weight upon both clinical and population monitoring BMI-determined weight status categorization in the NCMP.

Integrin-linked kinase regulates integrin signaling in human trabecular meshwork cells

PURPOSE

To determine whether integrin-linked kinase (ILK) controls the organization of the actin cytoskeleton in the trabecular meshwork (TM) by regulating integrin co-signaling.

METHODS

The cell binding domain and the Heparin II (Hep II) domain of fibronectin were used to activate α5β1 and α4β1 integrin signaling, respectively, in differentiated human TM (HTM) cells. The role of ILK was determined using either ILK small interfering RNA (siRNA) to knockout ILK expression or the ILK inhibitors, KP392 and QLT0267. The knockdown of ILK expression was verified by Western blot analysis. The presence of actin stress fibers and focal adhesions was determined by labeling cultures with phalloidin and anti-talin or ILK antibodies, respectively.

RESULTS

Cell spreading in differentiated HTM cells required ILK, since ILK siRNA and the ILK inhibitors significantly reduced cell spreading, actin polymerization, and the localization of talin and ILK in focal adhesions (FAs). Both cell spreading and the localization of talin and ILK to FAs in differentiated HTM cells could be rescued by inducing α4β1 integrin signaling with a recombinant Hep II domain of fibronectin, even though α4β1 integrins were not found in FAs. In the absence of ILK inhibition, the Hep II domain had minimal effect on α5β1 integrin-mediated spreading.

CONCLUSIONS

This study suggests that cooperative α5β1/α4β1 integrin signaling may be regulated by ILK trans-dominantly and that alterations in ILK activity may affect actin cytoskeleton organization and contractility in the TM.

Sodium orthovanadate effect on outflow facility and intraocular pressure in live monkeys

Sodium orthovanadate (Na(3)VO(4)) is reported to reduce IOP by affecting aqueous formation, but whether it also affects outflow facility (OF) is unclear. We tested the effect of Na(3)VO(4) on OF and intraocular pressure (IOP) in live cynomolgus monkeys, and on actin and cell adhesion organization in cultured human trabecular meshwork (HTM) cells. Total OF (n = 12) was measured by 2-level constant pressure perfusion of the monkey anterior chamber (AC) before and after exchange with 1 mM Na(3)VO(4) or vehicle in opposite eyes. Topical 1% Na(3)VO(4) or vehicle only was given twice daily (each 2 × 20 μL drops) for 4 days to opposite eyes (n = 8), and Goldmann IOP was measured before and hourly after treatment for 6 h on Days 1 and 4. Filamentous actin and vinculin-containing cell adhesions were examined by epifluorescence microscopy after the cells had been incubated with 1 mM Na(3)VO(4) for 24 h. A) In monkeys, Na(3)VO(4) increased OF by 29.3 ± 8.8% (mean ± s.e.m.) over the perfusion interval when adjusted for baseline and contralateral eye washout (p = 0.01; n = 12). B) Day 1 baseline IOP was 16.2 ± 1.5 mmHg in treated eyes and 15.9 ± 1.3 mmHg in the contralateral control eyes. Following treatment on Day 1, IOP was no different (p > 0.05) between treated eyes and control eyes at any time-point or compared to baseline. Day 4 mean IOP averaged over hours 2-6 was 13.5 ± 0.8 mmHg in treated eyes and 16.1 ± 0.2 mmHg in control eyes. Treated eye IOP was lower than its Day 4 baseline (p < 0.005), lower than control eyes for the same Day 4 interval (p = 0.009), and lower than the Day 1 baseline (p = 0.0000). Control eye IOP on Day 4 was not significantly different from baseline on Day 1. C) Incubation of HTM cells with 1 mM Na(3)VO(4) for 24 h caused a loss of actin stress fibers and vinculin-containing adhesions. Cell retraction and separation was also observed in vanadate-treated cultures. Reformation of actin stress fibers, vinculin-containing adhesions and confluent monolayers occurred within 24 h after Na(3)VO(4)-containing culture medium was replaced with Na(3)VO(4)-free medium. Ocular administration of Na(3)VO(4) to live monkeys significantly increases OF and reduces IOP. Na(3)VO(4) reversibly disrupts actin and cell adhesion organization and causes retraction and separation of cultured HTM cells. Na(3)VO(4) increases pressure-dependent outflow in live monkeys. Altered actin architecture in the TM may play a part in this increased OF.

Heparin II domain of fibronectin mediates contractility through an alpha4beta1 co-signaling pathway

In the trabecular meshwork (TM) of the eye, regulation of tissue contractility by the PPRARI sequence within the Heparin II (HepII) domain of fibronectin is believed to control the movement of aqueous humor and dictate the level of intraocular pressure. This study shows that the HepII domain utilizes activated alpha4beta1 integrin and collagen to mediate a co-signaling pathway that down-regulates contractility in TM cells. siRNA silencing of alpha4beta1 integrin blocked the actin disrupting effects of both PPRARI and the HepII domain. The down-regulation of the actin cytoskeleton and contractility did not involve syndecan-4 or other heparan sulfate proteoglycans (HSPGs) since siRNA silencing of syndecan-4 expression or heparitinase removal of cell surface HSPGs did not prevent the HepII-mediated disruption of the actin cytoskeleton. HepII-mediated disruption of the cytoskeleton depended upon the presence of collagen in the extracellular matrix, and cell binding studies indicated that HepII signaling involved cross-talk between alpha4beta1 and alpha1/alpha2beta1 integrins. This is the first time that the PPRARI sequence in the HepII domain has been shown to serve as a physiological alpha4beta1 ligand, suggesting that alpha4beta1 integrin may be a key regulator of tissue contractility.

COCH transgene expression in cultured human trabecular meshwork cells and its effect on outflow facility in monkey organ cultured anterior segments

Purpose. To determine the effects of COCH transgene expression on cultured human trabecular meshwork (HTM) cell morphology and on outflow facility (OF) in monkey organ cultured anterior segments (MOCAS). Methods. An adenoviral (Ad) vector expressing both cochlin (COCH) and green fluorescent protein (GFP) (AdCOCHGFP) or GFP alone (AdGFP) was used to transduce cultured HTM cells (multiplicity of transduction, 2.8 and 28). COCH transgene expression in transduced HTM cells and the culture medium was verified by Western blot analysis and immunofluorescence detection 5 days after transduction. MOCAS were used to test the effect of Ad vectors (2.8 x 10(10) viral particles per segment) on OF. The morphology of transduced MOCAS was evaluated by light microscopy. Results. Western blot analysis showed a viral vector dose-dependent expression of cochlin in transduced cells and the culture medium. There was no notable morphologic change in transduced cells. In MOCAS, cochlin expression was detectable in the medium by 3 days after transduction. A 35% decrease in OF in AdCOCHGFP-transduced MOCAS was detected after 3 days, decreasing by 76% after 12 days when compared to control segments injected with AdGFP. Anterior segment pressure (ASP) more than doubled (P < 0.05) in segments injected with AdCOCHGFP at 12 days after transduction. Light microscopy revealed normal angle structures in transduced segments. Conclusions. Ad vector delivery of the COCH transgene resulted in cochlin expression in HTM cells and MOCAS. Cochlin expression was effective in decreasing OF and increasing ASP in MOCAS, suggesting possible involvement of cochlin in IOP elevation in vivo. COCH gene delivery has potential for use in developing a glaucoma model.

Regulation of cross-linked actin network (CLAN) formation in human trabecular meshwork (HTM) cells by convergence of distinct beta1 and beta3 integrin pathways

PURPOSE

To determine the beta1/beta3 integrin-mediated pathways that regulate cross-linked actin network (CLAN) formation in human trabecular meshwork (HTM) cells. CLANs form in glaucomatous and steroid-treated TM cells, which may contribute to reducing outflow facility through the TM.

METHODS

Expression of CD47 (an alphavbeta3 integrin coreceptor/thrombospondin-1 receptor) and integrins alphavbeta3 and beta1 was assessed by FACS. CLANs were induced by plating cells on fibronectin (a beta1 integrin ligand) in the absence or presence of the beta3 integrin-activating mAb AP-5 and were identified by phalloidin labeling. The role of Src kinases, PI-3 kinase (PI-3K), Rac1, and CD47 was determined by incubating cells with the inhibitors PP2 and EPA (Src kinases), LY294002 (PI-3K), or NSC23766 (Rac1). Tiam1 and Trio siRNAs and dominant-negative Tiam1 were used to determine which Rac1-specific guanine nucleotide exchange factor was involved. The role of CD47 was determined using the thrombospondin-1-derived agonist peptide 4N1K and the CD47 function blocking antibody B6H12.2.

RESULTS

HTM cells expressed CD47 and integrins alphavbeta3 and beta1. beta3 Integrin or CD47 activation significantly increased CLAN formation over beta1 integrin-induced levels, whereas anti-CD47 mAb B6H12.2 inhibited this increase. PP2, NSC23766, and Trio siRNA decreased beta3-induced CLAN formation by 72%, 45%, and 67%, respectively, whereas LY294002 and dominant negative Tiam1 had no effect. LY294002 decreased beta1 integrin-mediated CLAN formation by 42%, and PP2 completely blocked it.

CONCLUSIONS

Distinct beta1 and alphavbeta3 integrin signaling pathways converge to enhance CLAN formation. beta1-Mediated CLAN formation was PI-3K dependent, whereas beta3-mediated CLAN formation was CD47 and Rac1/Trio dependent and might have been regulated by thrombospondin-1. Both integrin pathways were Src dependent.

Functional properties of fibronectin in the trabecular meshwork

Fibronectin plays a number of important roles in the extracellular matrix (ECM) including providing structural support and signaling cues for cell survival, migration, differentiation, gene expression, growth factor signaling, and cell contractility. In this review, we examine recent findings about the biological and structural properties of fibronectin and discuss how these properties could contribute to the regulation of aqueous humor (AH) outflow in the trabecular meshwork (TM).

Identification of the active site in the heparin II domain of fibronectin that increases outflow facility in cultured monkey anterior segments

PURPOSE

To determine the active site in the Heparin II (HepII) domain of fibronectin that regulates outflow facility in cultured anterior segments and disrupts the actin cytoskeleton in transformed human trabecular meshwork (TM-1) cells.

METHODS

Outflow facility was determined by two-level, constant-pressure perfusion in cultured anterior segments of rhesus and cynomolgus monkey eyes. One segment from each pair was exchanged with either the HepII domain or an integrin/syndecan binding peptide (IDAPS or PPRARI) from the HepII domain. To assay changes in the actin cytoskeleton, TM-1 cells were incubated for 24 hours with or without the HepII domain, PPRARI, or IDAPS. Changes were monitored with phase and immunofluorescence microscopy.

RESULTS

HepII domain (100 microg/mL) and PPRARI (500 microg/mL) increased outflow facility by 31% +/- 13% (n = 9, P < 0.05) and 24% +/- 9% (n = 8, P < 0.05), respectively in cultured anterior segments after an overnight infusion. Perfusion with IDAPS (500 microg/mL) had no effect on outflow facility. In TM-1 cultures, 250 microg/mL of the HepII domain or 4 mg/mL of PPRARI disrupted the assembly of actin filaments. A lower concentration of PPRARI (2 mg/mL) disrupted the actin cytoskeleton when used in combination with a nondisrupting concentration of the HepII domain (30-60 microg/mL). In contrast, IDAPS did not disrupt the actin cytoskeleton under any condition tested.

CONCLUSIONS

The active site in the HepII domain that regulates outflow facility in cultured anterior segments and disrupts the actin cytoskeleton in TM-1 cells is the syndecan/integrin binding sequence, PPRARI.

Magnetic resonance imaging of abdominal adiposity in a large cohort of British children

OBJECTIVE

To describe abdominal adipose tissue distribution in a large sample of contemporary British children; to determine the influence of gender, stage of maturation and body mass index (BMI) on abdominal adipose tissue distribution; and to compare the ability of BMI and waist circumference to predict abdominal adipose tissue.

SUBJECTS AND METHODS

A total of 74 boys (mean age 13.4+/-0.4 years) and 96 girls (mean age 13.5+/-0.5 years) were selected from volunteer children enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC). Height, weight and waist circumference were measured and BMI calculated. Stage of sexual maturation was available for 113 children using a self-report questionnaire based on Tanner's criteria. Magnetic resonance imaging was used to assess subcutaneous abdominal adipose tissue (SAAT) and intra-abdominal adipose tissue (IAAT) volumes and patterning.

RESULTS

Boys had lower levels of IAAT (P=0.036) and SAAT (P=0.003) than girls. IAAT and SAAT were higher in overweight and obese boys and girls when compared with normal weight children (P<0.0001). This pattern was also reflected in waist circumference groups. Boys had higher IAAT/SAAT ratios than girls, indicating proportionately more adipose tissue deposited intra-abdominally (P=0.002). However, both boys and girls deposited less than 10% of their abdominal fat as internal adipose tissue. WC predicted 67.4% of the variance in IAAT (P<0.001), and BMI predicted 84.8% of the variance in SAAT (P<0.001). However, BMI as the best single predictor explained only 8.4% of the variance in the IAAT/SAAT ratio (P<0.001).

CONCLUSIONS

At this age and stage of sexual maturation, the amount of IAAT remains relatively small. WC and BMI offer a feasible alternative to the MRI estimation of IAAT and SAAT, respectively, in a population-based sample of boys and girls. International Journal of Obesity (2008) 32, 91-99; doi:10.1038/sj.ijo.0803780; published online 27 November 2007.

Potential role for heparan sulfate proteoglycans in regulation of transforming growth factor-beta (TGF-beta) by modulating assembly of latent TGF-beta-binding protein-1

Latent transforming growth factor-beta-binding proteins (LTBPs) are extracellular matrix (ECM) glycoproteins that play a major role in storage of latent TGF-beta in the ECM and regulate its availability. We have previously identified fibronectin as a key molecule for incorporation of LTBP1 and TGF-beta into the ECM of osteoblasts and fibroblasts. Here we provide evidence that heparan sulfate proteoglycans may mediate binding between LTBP1 and fibronectin. We have localized critical domains in the N terminus of LTBP1 that are required for co-localization with fibronectin in osteoblast cultures and have identified heparin binding sites in the N terminus of LTBP1 between residues 345 and 487. Solid-phase binding assays suggest that LTBP1 does not bind directly to fibronectin but that the binding is indirect. Heparin coupled to bovine serum albumin (heparin-BSA) was able to mediate binding between fibronectin and LTBP1. Treatment of primary osteoblast cultures with heparin or heparin-BSA but not with chondroitin sulfate impaired LTBP1 deposition onto fibronectin without inhibiting expression of LTBP1. Inhibition of LTBP1 incorporation was accompanied by reduced incorporation of latent TGF-beta into the ECM, with increased amounts of soluble latent TGF-beta. Inhibition of attachment of glycosaminoglycans to the core proteins of proteoglycans by beta-d-xylosides also reduced incorporation of LTBP1 into the ECM. These studies suggest that heparan sulfate proteoglycans may play a critical role in regulating TGF-beta availability by controlling the deposition of LTBP1 into the ECM in association with fibronectin.

The heparin III-binding domain of fibronectin (III4-5 repeats) binds to fibronectin and inhibits fibronectin matrix assembly

Fibronectin matrix assembly involves interactions among various regions of the molecule, which contribute to elongation and stabilization of the fibrils. In this study, we examined the possible role of the heparin III domain of fibronectin (repeats III4-5) in fibronectin fibrillogenesis. We show that a recombinant fragment comprising these repeats (FNIII4-5 fragment) blocked fibronectin fibril formation and the incorporation of 125I-fibronectin into cell layers. Binding assays using a biosensor revealed that FNIII4-5 bound fibronectin and the amino-terminal 70 kDa and 29 kDa fragments. It also bound to itself, indicating a previously unidentified self-association site in repeats III4-5. These interactions were specific since FNIII4-5 did not bind to the FNIII7-10 fragment, representing a central region in fibronectin. The fibronectin-binding property of the III4-5 domain, but not its matrix assembly inhibitory function, was apparently cryptic in larger fragments. By mutating the arginine residues in the WTPPRAQITGYRLTVGLTRR proteoglycan-binding sequence (HBP/III5 site) of FNIII4-5 [Moyano, J.V., Carnemolla, B., Albar, J.P., Leprini, A., Gaggero, B., Zardi, L., Garcia-Pardo, A., 1999. Cooperative role for activated alpha4beta1 integrin and chondroitin sulfate proteoglycans in cell adhesion to the heparin III domain of fibronectin. Identification of a novel heparin and cell binding sequence in repeat III5. J. Biol. Chem. 274, 135-142.], we found that the first two arginine residues in HBP/III5 were involved in the fibronectin-binding property of FNIII4-5, while the last two arginine residues in HBP/III5 were required for inhibition of matrix assembly and the binding of 125I-fibronectin to cell layers. Both properties appear to function independently from each other, depending on the conformation of the fibronectin dimer.

Effect of heparin II domain of fibronectin on actin cytoskeleton and adherens junctions in human trabecular meshwork cells

PURPOSE

To determine whether the heparin II (HepII) domain of fibronectin previously shown to increase outflow facility affects the formation and assembly of actin cytoskeleton and adherens junctions in human trabecular meshwork (HTM) cells.

METHODS

Normal HTM cells and two transformed HTM cell lines were treated for 24 hours with increasing concentrations of the HepII domain. Disruptions in adherens junctions and the actin cytoskeleton were determined using immunofluorescence microscopy and Western blot analysis of immunoprecipitated cadherin/catenin complexes. Actin filaments were detected with phalloidin. Catenin (alpha and beta) and cadherin antibodies were used to detect adherens junctions.

RESULTS

Treatments of cultures with the HepII domain caused cadherin/beta-catenin complexes in adherens junctions and actin filaments to disassemble. The disruption of adherens junctions and actin filaments occurred in a dose-dependent and temporal fashion. The disassembly of actin filaments occurred first, followed by the disassembly of adherens junctions. Dissociation of adherens junctions, but not actin filaments, was reversible if the HepII domain was removed. Reassembly of actin filaments required the addition of serum. Serum, however, could not trigger the reassembly of actin filaments if the HepII domain was present, suggesting that the HepII domain acted downstream of the serum stimulated RhoA activity.

CONCLUSIONS

The exposure of HTM cells to the HepII domain triggers the disassembly of actin filaments and the subsequent destabilization of adherens junctions in HTM cells. This suggests that the HepII domain may increase outflow facility in cultured anterior segments by altering the organization of the TM cytoarchitecture.

Crossvalidation of anthropometry against magnetic resonance imaging for the assessment of visceral and subcutaneous adipose tissue in children

BACKGROUND

The study of the relationship between anthropometry and visceral adipose tissue (VAT) is of great interest because VAT is associated with many risk factors for noncommunicable diseases and anthropometry is easy to perform in clinical practice. The studies hitherto available for children have, however, been performed on small sample sizes.

DESIGN

Pooling of the data of studies published from 1992 to 2004 as indexed on Medline.

AIMS

To assess the relationship between anthropometry and VAT and subcutaneous adipose tissue (SAT) as measured by magnetic resonance imaging (MRI) in children and to analyze the effect of age, gender, pubertal status and ethnicity.

SUBJECTS AND METHODS

Eligible subjects were 7-16 year-old, with availability of VAT and SAT, gender, ethnicity, body mass index (BMI) and waist circumference (WC). A total of 497 subjects were collected from seven different investigators and 407 of them (178 Caucasians and 229 Hispanics) were analyzed.

RESULTS

Despite ethnic differences in MRI data, BMI, WC and age, no difference in VAT was found between Caucasians and Hispanics after correction for SAT and BMI. Univariate regression analysis identified WC as the best single predictor of VAT (64.8% of variance) and BMI of SAT (88.9% of variance). The contribution of ethnicity and gender to the unexplained variance of the VAT-WC relationship was low (< or =3%) but significant (P < or =0.002). The different laboratories explained a low (< or =4.8%) but significant (P < 0.0001) portion of the unexplained variance of the VAT-WC and SAT-BMI relationships. Prediction equations for VAT (VAT (cm(2)) = 1.1 x WC (cm)-52.9) and SAT (SAT (cm(2)) = 23.2 x BMI (kg/m(2))-329) were developed on a randomly chosen half of the population and crossvalidated in the remaining half. The pure error of the estimate was 13 cm(2) for VAT and 57 cm(2) for SAT.

CONCLUSIONS

WC can be considered a good predictor of VAT as well as BMI of SAT. The importance of ethnicity and gender on VAT estimation is not negligible.

Beta1 and beta3 integrins cooperate to induce syndecan-4-containing cross-linked actin networks in human trabecular meshwork cells

PURPOSE

To characterize the molecular composition of cross-linked actin networks (CLANs) and the regulation of their formation by integrins in normal human trabecular meshwork (TM) cells. CLANs have been observed in steroid-treated and glaucomatous TM cells and have been suggested to contribute to decreased outflow facility by altering the contractility of the TM.

METHODS

Immunofluorescence microscopy was used to identify molecular components of CLANs and quantitate CLAN formation in HTM cells plated on coverslips coated with various extracellular matrix (ECM) proteins (fibronectin, types I and IV collagen, and vitronectin), vascular cell adhesion molecule (VCAM)-1, or activating antibodies against beta1, beta3, or alpha2beta1 integrins. These integrin antibodies were also used as soluble ligands.

RESULTS

CLAN vertices contained the actin-binding proteins alpha-actinin and filamin and the signaling molecules syndecan-4 and PIP2. CLANs lacked Arp3 and cortactin. CLAN formation was dependent on the ECM substrate and was significantly higher on fibronectin and VCAM-1 compared with vitronectin, types I or IV collagen. Adsorbed beta1 integrin antibodies also induced CLANs, whereas adsorbed beta3 or alpha2beta1 integrin antibodies did not. Soluble beta3 integrin antibodies, however, induced CLANs and actually enhanced CLAN formation in cells spread on fibronectin, VCAM-1, type I or type IV collagen, or beta1 integrin antibodies.

CONCLUSIONS

CLANs are unique actin-branched networks whose formation can be regulated by beta1 and beta3 integrin signaling pathways. Thus, integrin-mediated signaling events can modulate the organization of the actin cytoskeleton in TM cells and hence could participate in regulating cytoskeletal events previously demonstrated to be involved in controlling outflow facility.

The effect of C3 transgene expression on actin and cellular adhesions in cultured human trabecular meshwork cells and on outflow facility in organ cultured monkey eyes

PURPOSE

To determine the effects of adenovirus-delivered exoenzyme C3 transferase (C3) gene expression on cultured human trabecular meshwork (HTM) cells and on outflow facility in organ cultured monkey anterior segments.

METHODS

An adenoviral (Ad) vector expressing both C3 and green fluorescent protein (GFP) was used to transduce cultured HTM cells. Changes in cell morphology and the organization of actin, vinculin, and beta-catenin were assessed using immunofluorescence. Cultured monkey eye anterior segments were used to test the effects of AdC3GFP on outflow facility.

RESULTS

Treatment of HTM cells with AdC3GFP resulted in dose-dependent morphological changes 3 or 4 days post-transduction. The AdC3GFP-transduced cells were either partially retracted, rounded, or very elongated compared to non-transduced cells. Compared to AdGFP-transduced cells, AdC3GFP-transduced cells demonstrated disrupted actin cytoskeleton, reduced vinculin-positive focal adhesions, and loss of beta-catenin staining. Cells transduced with AdGFP did not round up or retract. In organ culture studies, outflow facility was increased by 90+/-21% (n=15, p<0.001) in AdC3GFP-transduced eyes compared to baseline and corrected for AdGFP-transduced control eye washout on days 3-6 after transduction.

CONCLUSIONS

C3 transduction is effective in disrupting actin filaments, cytoskeleton, and cellular adhesions in HTM cells and in increasing outflow facility in organ cultured monkey anterior segments, suggesting that expressing the C3 gene in the trabecular meshwork may be an effective approach for glaucoma therapy.

Fibronectin regulates latent transforming growth factor-beta (TGF beta) by controlling matrix assembly of latent TGF beta-binding protein-1

Latent transforming growth factor-beta-binding proteins (LTBPs) are extracellular matrix (ECM) glycoproteins that play a major role in the storage of latent TGF beta in the ECM and regulate its availability. Here we show that fibronectin is critical for the incorporation of LTBP1 and transforming growth factor-beta (TGF beta) into the ECM of osteoblasts and fibroblasts. Immunolocalization studies suggested that fibronectin provides an initial scaffold that precedes and patterns LTBP1 deposition but that LTBP1 and fibronectin are later localized in separate fibrillar networks, suggesting that the initial template is lost. Treatment of fetal rat calvarial osteoblasts with a 70-kDa N-terminal fibronectin fragment that inhibits fibronectin assembly impaired incorporation of LTBP1 and TGFbeta into the ECM. Consistent with this, LTBP1 failed to assemble in embryonic fibroblasts that lack the gene for fibronectin. LTBP1 assembly was rescued by full-length fibronectin and superfibronectin, which are capable of assembly into fibronectin fibrils, but not by other fibronectin fragments, including a 160-kDa RGD-containing fragment that activates alpha5beta1 integrins. This suggests that the critical event for LTBP1 assembly is the formation of a fibronectin fibrillar network and that integrin ligation by fibronectin molecules alone is not sufficient. Not only was fibronectin essential for the initial incorporation of LTBP1 into the ECM, but the continued presence of fibronectin was required for the continued assembly of LTBP1. These studies highlight a nonredundant role for fibronectin in LTBP1 assembly into the ECM and suggest a novel role for fibronectin in regulation of TGF beta via LTBP1 interactions.

Heparin II domain of fibronectin uses alpha4beta1 integrin to control focal adhesion and stress fiber formation, independent of syndecan-4

Co-signaling events between integrins and cell surface proteoglycans play a critical role in the organization of the cytoskeleton and adhesion forces of cells. These processes, which appear to be responsible for maintaining intraocular pressure in the human eye, involve a novel cooperative co-signaling pathway between alpha5beta1 and alpha4beta1 integrins and are independent of heparan sulfate proteoglycans. Human trabecular meshwork cells isolated from the eye were plated on type III 7-10 repeats of fibronectin (alpha5beta1 ligand) in the absence or presence of the heparin (Hep) II domain of fibronectin. In the absence of the Hep II domain, cells had a bipolar morphology with few focal adhesions and stress fibers. The addition of the Hep II domain increased cell spreading and the numbers of focal adhesions and stress fibers. Cell spreading and stress fiber formation were not mediated by heparan sulfate proteoglycans because treatment with chlorate, heparinase, or soluble heparin did not prevent Hep II domain-mediated cell spreading. Cell spreading and stress fiber formation were mediated by alpha4beta1 integrin because soluble anti-alpha4 integrin antibodies inhibited Hep II domain-mediated cell spreading and soluble vascular cell adhesion molecule-1 (alpha4beta1 ligand)-induced cell spreading. This is the first demonstration of the Hep II domain mediating cell spreading and stress fiber formation through alpha4beta1 integrin. This novel pathway demonstrates a cooperative, rather than antagonistic, role between alpha5beta1 and alpha4beta1 integrins and suggests that interactions between the Hep II domain and alpha4beta1 integrin could modulate the strength of cytoskeleton-mediated processes in the trabecular meshwork of the human eye.

Myocilin binding to Hep II domain of fibronectin inhibits cell spreading and incorporation of paxillin into focal adhesions

Myocilin, a novel matricellular protein found in the human eye, can modify signaling events mediated by the Heparin II domain of fibronectin. Using myocilin produced in sf9 insect cells, myocilin inhibited spreading of cycloheximide-treated human skin fibroblasts plated on substrates co-coated with myocilin and either fibronectin or its Heparin II domain. Cell spreading could be rescued by adding back either substrate adsorbed or soluble Heparin II domains. Myocilin did not inhibit cell attachment to fibronectin even in the presence of a 2400 M excess of myocilin. Myocilin impaired focal adhesion formation and specifically blocked the incorporation of paxillin, but not vinculin, into focal adhesions. The Heparin II domain mediated the incorporation of paxillin into focal adhesions, since paxillin was not assembled into focal adhesions unless the Heparin II domain was present. The effect of myocilin on focal adhesions could be overcome by treating cells with either phorbol 12-myristate (PMA) or oleoyl-L-alpha-lysophosphatidic acid (LPA). Myocilin bound to the fibroblast cell surface, but its binding could not be competed with excess fibronectin, suggesting that myocilin does not compete for cell surface binding sites of fibronectin. Myocilin therefore appears to specifically block functions mediated by the Heparin II domain possibly through direct interactions with it.

Distribution of syndecans 1-4 within the anterior segment of the human eye: expression of a variant syndecan-3 and matrix-associated syndecan-2

Control of the actomyosin network plays a role in regulating the movement of aqueous humor through the anterior segment of the eye. Receptors that could control its activity are unknown. In this study, we show that all four members of the syndecan family, which can regulate the actomyosin network, are present within the anterior segment. In both sections of human anterior segments and cultures of human trabecular meshwork (HTM), Schlemm's canal (HSC) and the ciliary muscle (HCM) cells from the anterior segment, syndecans-3 and -4 were the predominant family members. They were widely distributed throughout the anterior segment. Syndecan-3 within the anterior segment was a novel, recently described variant 55 kDa form. Low levels of syndecans-1 and -2 were also observed in situ and in all three cultures. Their expression was weaker and more localized than that observed for syndecans-3 and -4. Staining for syndecan-1 in HCM cultures was variable. In HTM and HSC cultures, syndecan-2 also co-distributed with fibronectin, laminin and type IV collagen suggesting that it was shed and associated with the extracellular matrix. Western blots supported this idea and showed syndecan-2 ectodomains in lysates from anterior segments.

In vitro localization of TIGR/MYOC in trabecular meshwork extracellular matrix and binding to fibronectin

PURPOSE

To determine whether trabecular meshwork-inducible glucocorticoid response/myocilin (TIGR/MYOC) protein associates with the extracellular matrix (ECM) of human trabecular meshwork (HTM) cells.

METHODS

The extracellular localization of TIGR/MYOC was examined by immunofluorescence microscopy in HTM cultures treated with and without dexamethasone and ascorbate and in a transformed HTM cell line, TM-1, transiently transfected with TIGR/MYOC cDNA. Antibodies to TIGR/MYOC, fibronectin, laminin, type IV collagen, or thrombospondin were used to determine the extracellular localization of TIGR/MYOC. Solid phase binding assays using 125I-recombinant TIGR/MYOC and types I and IV collagens, fibronectin, and laminin were done to examine the association of TIGR/MYOC with these proteins and to identify a specific TIGR/MYOC binding site within fibronectin. The domains of fibronectin tested were the fibrin/collagen binding domain, the RGD domain, and the Heparin II (Hep II) domain.

RESULTS

TIGR/MYOC colocalized with fibronectin, laminin, and type IV collagen, but not thrombospondin in both dexamethasone and dexamethasone/ascorbate-treated HTM cultures and in TM-1 cultures transfected with TIGR/MYOC cDNA. In solid phase binding assays, 125I-TIGR/MYOC bound fibronectin but not laminin or type IV collagen. Binding to fibronectin could be competed with excess TIGR/MYOC or fibronectin. Specific binding was found for the Hep II domain of fibronectin.

CONCLUSIONS

TIGR/MYOC can associate with components of the ECM via interactions with the Hep II domain of fibronectin. The interactions with the Hep II domain of fibronectin could alter cell-matrix interactions in the TM and provides an interesting lead to explore the role(s) of TIGR/MYOC in both steroid-induced and primary open angle glaucoma.