Trabecular cells express the TGF-beta 2 gene and secrete the cytokine

Ferroptosis in Glaucoma: A Promising Avenue for Therapy

Glaucoma, a blind-leading disease largely since chronic pathological intraocular high pressure (ph-IOP). Hitherto, it is reckoned incurable for irreversible neural damage and challenges in managing IOP. Thus, it is significant to develop neuroprotective strategies. Ferroptosis, initially identified as an iron-dependent regulated death that triggers Fenton reactions and culminates in lipid peroxidation (LPO), has emerged as a focal point in multiple tumors and neurodegenerative diseases. Researches show that iron homeostasis play critical roles in the optic nerve (ON) and retinal ganglion cells (RGCs), suggesting targeted treatments could be effective. In glaucoma, apart from neural lesions, disrupted metal balance and increased oxidative stress in trabecular meshwork (TM) are observed. These disturbances lead to extracellular matrix excretion disorders, known as sclerotic mechanisms, resulting in refractory blockages. Importantly, oxidative stress, a significant downstream effect of ferroptosis, is also a key factor in cell senescence. It plays a crucial role in both the etiology and risk of glaucoma. Moreover, ferroptosis also induces non-infectious inflammation, which exacerbate glaucomatous injury. Therefore, the relevance of ferroptosis in glaucoma is extensive and multifaceted. In this review, the study delves into the current understanding of ferroptosis mechanisms in glaucoma, aiming to provide clues to inform clinical therapeutic practices.

Aqueous Humor TGF-β2 and Its Association With Intraocular Pressure in a Naturally Occurring Large Animal Model of Glaucoma

Purpose

Transforming growth factor (TGF)-β2 has been widely implicated in human glaucoma pathology. The purpose of this study was to determine the source of TGF-β2 in aqueous humor (AH) and its relationship with intraocular pressure (IOP) in an inherited large animal model of glaucoma.

Methods

Sixty-six glaucomatous cats homozygous for LTBP2 mutation, and 42 normal cats were studied. IOP was measured weekly by rebound tonometry. AH was collected by anterior chamber paracentesis from each eye under general anesthesia, and serum samples collected from venous blood concurrently. Concentrations of total, active and latent TGF-β2 in AH and serum samples were measured by quantitative sandwich immunoassay. For comparisons between groups, unpaired t-test or Mann Whitney test were used, with P < 0.05 considered significant. The relationships between TGF-β2 concentrations and IOP values were examined by Pearson's correlation coefficient and generalized estimating equation.

Results

IOP and AH TGF-β2 concentrations were significantly higher in glaucomatous than in normal cats. AH TGF-β2 showed a significant, robust positive correlation with IOP in glaucomatous cats (r = 0.83, R2 = 0.70, P < 0.0001). Serum TGF-β2 did not correlate with AH TGF-β2 and was not significantly different between groups. TGF-β2 mRNA and protein expression were significantly increased in local ocular tissues in glaucomatous cats.

Conclusions

Enhanced, local ocular production of TGF-β2 with a robust positive association with IOP was identified in this spontaneous feline glaucoma model, providing a foundation for preclinical testing of novel therapeutics to limit disease-associated AH TGF-β2 elevation and signaling in glaucoma.

CHIR99021 balance TGFβ1 induced human corneal endothelial-to-mesenchymal transition to favor corneal endothelial cell proliferation

Corneal endothelial cells (CECs) play a major role in the maintenance of stromal hydration via the barrier and pump function for clear vision. Adult CEC cannot regenerate after injury. CECs cultured in vitro can undergo mitosis but may undergo corneal endothelial-to-mesenchymal transition (EnMT) and lose their endothelial characteristics. In this study, we examined the effects of CHIR99201 on transforming growth factor beta-1(TGFβ1)-induced EnMT in human CEC (hCECs) lines. CHIR99021 kept hCECs in the hexagonal shape and could downregulate the EnMT markers alpha-smooth muscle actin (α-SMA) and fibronectin (FN1), meanwhile maintained the hCECs function markers Na⁺/K⁺-ATPase and zonula occludens-1 (ZO-1) at levels comparable to those in the normal control. Interestingly, we found that the combination of CHIR99021 and TGFβ1 at appropriate concentrations would significantly promote the proliferation and migration of hCECs. These effects may be related to the inhibition of RhoA or Rac1, as well as the activation of Wnt and Erk pathway, with a calcium homeostasis. Our findings indicate that CHIR99021 inhibit EnMT and that the combination of CHIR99021 and TGFβ1 may provide new ideas for corneal endothelial regeneration and wound healing.

Lysophosphatidic Acid and IL-6 Trans-signaling Interact via YAP/TAZ and STAT3 Signaling Pathways in Human Trabecular Meshwork Cells

Purpose

Lysophosphatidic acid (LPA) and soluble interleukin-6 receptor (sIL6R) are elevated in primary open angle glaucoma (POAG). LPA and IL6 modulate in response to biomechanical stimuli and converge on similar fibrotic phenotypes. Thus, we determined whether LPA and IL6 trans-signaling (IL6/sIL6R) interact via Yes-associated protein (YAP)/Transcriptional coactivator with a PDZ-binding motif (TAZ) or Signal transducer and activator of transcription 3 (STAT3) pathways in human trabecular meshwork (hTM) cells.

Methods

Confluent primary hTM cells were serum starved for 24 hours, and treated with vehicle, LPA (20 µM), IL6 (100 ng/mL)/sIL6R (200 ng/mL), or both (LPA + IL6/sIL6R) for 24 hours, with or without a YAP inhibitor (verteporfin; 2 µM) or STAT3 inhibitor (2 µM). Expression of key receptors and ligands, signaling mediators, actomyosin machinery, cell contractility, and extracellular matrix (ECM) targets of both signaling pathways was determined by immunocytochemistry, RT-qPCR, and Western blotting.

Results

LPA and IL6 trans-signaling coupling overexpressed/activated receptors and ligands, glycoprotein-130, IL6, and autotaxin; signaling mediators, YAP, TAZ, Pan-TEAD, and phosphorylated STAT3 (pSTAT3); actomyosin and contractile machinery components, myosin light chain 2 (MLC2), phosphorylated MLC2, rho-associated protein kinase 1, filamentous actin, and α-smooth muscle actin; and fibrotic ECM proteins, collagen I and IV, fibronectin, laminin, cysteine-rich angiogenic inducer 61, and connective tissue growth factor in hTM cells; mostly beyond LPA or IL6 trans-signaling alone. Verteporfin inhibited YAP, TAZ, and pSTAT3, with concomitant abrogation of aforementioned fibrotic targets; the STAT3 inhibitor was only partially effective.

Conclusions

These data suggest synergistic crosstalk between LPA and IL6 trans-signaling, mediated by YAP, TAZ, and pSTAT3. By completely inhibiting these mediators, verteporfin may be more efficacious in ameliorating LPA and/or IL6 trans-signaling–induced ocular hypertensive phenotypes in hTM cells.

Inflammation in Glaucoma: From the back to the front of the eye, and beyond

The pathophysiology of glaucoma is complex, multifactorial and not completely understood. Elevated intraocular pressure (IOP) and/or impaired retinal blood flow may cause initial optic nerve damage. In addition, age-related oxidative stress in the retina concurrently with chronic mechanical and vascular stress is crucial for the initiation of retinal neurodegeneration. Oxidative stress is closely related to cell senescence, mitochondrial dysfunction, excitotoxicity, and neuroinflammation, which are involved in glaucoma progression. Accumulating evidence from animal glaucoma models and from human ocular samples suggests a dysfunction of the para-inflammation in the retinal ganglion cell layer and the optic nerve head. Moreover, quite similar mechanisms in the anterior chamber could explain the trabecular meshwork dysfunction and the elevated IOP in primary open-angle glaucoma. On the other hand, ocular surface disease due to topical interventions is the most prominent and visible consequence of inflammation in glaucoma, with a negative impact on filtering surgery failure, topical treatment efficacy, and possibly on inflammation in the anterior segment. Consequently, glaucoma appears as an outstanding eye disease where inflammatory changes may be present to various extents and consequences along the eye structure, from the ocular surface to the posterior segment, and the visual pathway. Here we reviewed the inflammatory processes in all ocular structures in glaucoma from the back to the front of the eye and beyond. Our approach was to explain how para-inflammation is necessary to maintain homoeostasis, and to describe abnormal inflammatory findings observed in glaucomatous patients or in animal glaucoma models, supporting the hypothesis of a dysregulation of the inflammatory balance toward a pro-inflammatory phenotype. Possible anti-inflammatory therapeutic approaches in glaucoma are also discussed.

Trabecular meshwork cells are a valuable resource for cellular therapy of glaucoma

Trabecular meshwork (TM) contains a subset of adult stem cells or progenitors that can be differentiated into corneal endothelial cells, adipocytes and chondrocytes, but not osteocytes or keratocytes. Accordingly, these progenitors can be utilized as a cell‐based therapy to prevent blindness caused by glaucoma, corneal endothelial dysfunction and other diseases in general. In this review, we review in vitro expansion techniques for TM progenitors, discuss their phenotypic properties, and highlight their potential clinical applications in various ophthalmic diseases.

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.

The Role of Wnt/β-Catenin Signaling and K-Cadherin in the Regulation of Intraocular Pressure

Purpose

Wnt/β-catenin signaling in the trabecular meshwork (TM) is required for maintaining normal intraocular pressure (IOP), although the mechanism(s) behind this are unknown. We hypothesize that Wnt/β-catenin signaling regulates IOP via β-catenin's effects on cadherin junctions.

Methods

Nonglaucomatous primary human TM (NTM) cells were treated with or without 100 ng/ml Wnt3a, 1 μg/ml sFRP1, or both for 4 to 48 hours. Cells were immunostained for β-catenin, total cadherins, or cadherin isoforms. Membrane proteins or whole-cell lysates were isolated for Western immunoblotting and probed for cadherin isoforms. RNA was extracted for cDNA synthesis and qPCR analysis of cadherin expression. Some NTM cells were cultured on electric plates for cell impedance assays. Ad5.CMV recombinant adenoviruses encoding K-cadherin, and/or sFRP1 were injected into eyes of 4- to 6-month-old female BALB/cJ mice (n = 8–10). Conscious IOPs were assessed for 35 days.

Results

Upon Wnt3a treatment, total cadherin expression increased and β-catenin accumulated at the TM cell membrane and on processes formed between TM cells. qPCR showed that Wnt3a significantly increased K-cadherin expression in NTM cells (P < 0.01, n = 3), and Western immunoblotting showed that Wnt3a increased K-cadherin in NTM cells, which was inhibited by the addition of sFRP1. Cell impedance assays showed that Wnt3a treatment increased transcellular resistance and anti-K-cadherin siRNA decreased transcellular resistance (P < 0.001, n = 4–6). Our in vivo study showed that K-cadherin significantly decreased sFRP1-induced ocular hypertension (P < 0.05, n = 6). Western immunoblotting also showed that K-cadherin alleviated sFRP1-induced β-catenin decrease in mouse anterior segments.

Conclusions

Our results suggest that cadherins play important roles in the regulation of TM homeostasis and IOP via the Wnt/β-catenin pathway.

Growth Factors, Oxidative Damage, and Inflammation in Exfoliation Syndrome

Exfoliation syndrome (XFS) produces deleterious ocular aging and has protean systemic manifestations. Local ocular production of TGFβ1 is of central importance in XFS. TGFβ1 appears to induce the expression of LOXL1 and the production of other extracellular matrix components which are known to be present in exfoliation material. Furthermore, results from several studies find that the aqueous humor of exfoliation glaucoma patients exhibits a decreased antioxidant defense and increased oxidative stress systems. Finally, studies show that the levels of interleukin-6 and interleukin-8 in the aqueous humor of XFS patients were 3-fold higher than in controls. Overall TGFβ1, as well as a prooxidative and proinflammatory environment seems to play an important role in XFS.

BMP and Activin Membrane Bound Inhibitor Regulates the Extracellular Matrix in the Trabecular Meshwork

Purpose

The trabecular meshwork (TM) has an important role in the regulation of aqueous humor outflow and IOP. Regulation of the extracellular matrix (ECM) by TGFβ2 has been studied extensively. Bone morphogenetic protein (BMP) and activin membrane-bound inhibitor (BAMBI) has been shown to inhibit or modulate TGFβ2 signaling. We investigate the role of TGFβ2 and BAMBI in the regulation of TM ECM and ocular hypertension.

Methods

Mouse TM (MTM) cells were isolated from B6;129S1-Bambitm1Jian/J flox mice, characterized for TGFβ2 and dexamethasone (DEX)-induced expression of fibronectin, collagen-1, collagen-4, laminin, α-smooth muscle actin, cross-linked actin networks (CLANs) formation, and DEX-induced myocilin (MYOC) expression. MTM cells were transduced with Ad5.GFP to identify transduction efficiency. MTM cells and mouse eyes were transduced with Ad5.Null, Ad5.Cre, Ad5.TGFβ2, or Ad5.TGFβ2 + Ad5.Cre to evaluate the effect on ECM production, IOP, and outflow facility.

Results

MTM cells express TM markers and respond to DEX and TGFβ2. Ad5.GFP at 100 MOI had the highest transduction efficiency. Bambi knockdown by Ad5.Cre and Ad5.TGFβ2 increased fibronectin, collagen-1, and collagen-4 in TM cells in culture and tissue. Ad5.Cre, Ad5.TGFβ2, and Ad5.TGFβ2 + Ad5.Cre each significantly induced ocular hypertension and lowered aqueous humor outflow facility in transduced eyes.

Conclusions

We show for the first time to our knowledge that knockdown of Bambi alters ECM expression in cultured cells and mouse TM, reduces outflow facility, and causes ocular hypertension. These data provide a novel insight into the development of glaucomatous TM damage and identify BAMBI as an important regulator of TM ECM and ocular hypertension.

A Review of Nitric Oxide for the Treatment of Glaucomatous Disease

Glaucoma is the leading cause of irreversible blindness worldwide, affecting 64.3 million people. An estimated 60.5 million people are affected by primary open angle glaucoma globally, and this will increase to 111.8 million by 2040. The definition of glaucoma has evolved greatly over time. Although multiple risk factors such as ischemia, inflammation, myopia, race, age and low ocular perfusion pressure may play a role, intraocular pressure (IOP) is still the main risk factor we can easily identify and modify. Currently, both medical and surgical interventions aim to reduce IOP. Effective IOP reduction controls and prevents the progression in many cases of glaucoma. Although this multifactorial disease's true pathophysiology is difficult to elucidate, physiologic mediators including nitric oxide (NO) are being evaluated as novel ways to impact progression by both lowering IOP and improving optic nerve head perfusion. Latanoprostene bunod 0.024% is an emerging therapeutic agent that has shown promise in clinical trials. As a nitric oxide-donating prostaglandin F2-alpha receptor agonist, it has proven to effectively, and with good tolerability, reduce IOP in glaucoma and ocular hypertensive patients. Latanoprostene bunod capitalizes on NO's ability to modulate the conventional aqueous humor outflow system, directly improving outflow through the trabecular meshwork, Schlemm's canal and distal scleral vessels. Importantly, targeting the conventional outflow tissues with NO-donating drugs represents an opportunity to restore outflow function, which will most likely have a beneficial consequence of additional IOP-lowering effects with dampening of diurnal and other IOP fluctuations, the benefit of a healthy trabecular meshwork.

Active transforming growth factor-β2 in the aqueous humor of posterior polymorphous corneal dystrophy patients

Purpose

Posterior polymorphous corneal dystrophy (PPCD) is characterized by abnormal proliferation of corneal endothelial cells. It was shown that TGF-β2 present in aqueous humor (AH) could help maintaining the corneal endothelium in a G1-phase-arrest state. We wanted to determine whether the levels of this protein are changed in AH of PPCD patients.

Methods

We determined the concentrations of active TGF-β2 in the AH of 29 PPCD patients (42 samples) and 40 cadaver controls (44 samples) by ELISA. For data analysis the PPCD patients were divided based on either the molecular genetic cause of their disease as PPCD1 (37 samples), PPCD3 (1 sample) and PPCDx (not linked to a known PPCD loci, 4 samples) or on the presence (17 samples) or absence (25 samples) of secondary glaucoma or on whether they had undergone penetrating keratoplasty (PK, 32 samples) or repeated PK (rePK, 7 samples).

Results

The level of active TGF-β2 in the AH of all PPCD patients (mean ± SD; 386.98 ± 114.88 pg/ml) in comparison to the control group (260.95 ± 112.43 pg/ml) was significantly higher (P = 0.0001). Compared to the control group, a significantly higher level of active TGF-β2 was found in the PPCD1 (P = 0.0005) and PPCDx (P = 0.0022) groups. Among patients the levels of active TGF-β2 were not significantly affected by gender, age, secondary glaucoma or by the progression of dystrophy when one or repeated PK were performed.

Conclusion

The levels of active TGF-β2 in the AH of PPCD patients are significantly higher than control values, and thus the increased levels of TGF-β2 could be a consequence of the PPCD phenotype and can be considered as another feature characterizing this disease.

TGF-β induces phosphorylation of phosphatase and tensin homolog: implications for fibrosis of the trabecular meshwork tissue in glaucoma

Fundamental cell signaling mechanisms that regulate dynamic remodeling of the extracellular matrix (ECM) in mechanically loaded tissues are not yet clearly understood. Trabecular meshwork (TM) tissue in the eye is under constant mechanical stress and continuous remodeling of ECM is crucial to maintain normal aqueous humor drainage and intraocular pressure (IOP). However, excessive ECM remodeling can cause fibrosis of the TM as in primary open-angle glaucoma (POAG) patients, and is characterized by increased resistance to aqueous humor drainage, elevated IOP, optic nerve degeneration and blindness. Increased levels of active transforming growth factor-β2 (TGF-β2) in the aqueous humor is the main cause of fibrosis of TM in POAG patients. Herein, we report a novel finding that, in TM cells, TGF-β-induced increase in collagen expression is associated with phosphorylation of phosphatase and tensin homolog (PTEN) at residues Ser380/Thr382/383. Exogenous overexpression of a mutated form of PTEN with enhanced phosphatase activity prevented the TGF-β-induced collagen expression by TM cells. We propose that rapid alteration of PTEN activity through changes in its phosphorylation status could uniquely regulate the continuous remodeling of ECM in the normal TM. Modulating PTEN activity may have high therapeutic potential to alleviating the fibrosis of TM in POAG patients.

Definition, Classification, and Pathophysiology of Canine Glaucoma

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

The many faces of the trabecular meshwork cell

With the combined purpose of facilitating useful vision over a lifetime, a number of ocular cells have evolved specialized features not found elsewhere in the body. The trabecular meshwork (TM) cell at the irido-corneal angle, which is a key regulator of intraocular pressure, is no exception. Examination of cells in culture isolated from the human TM has shown that they are unique in many ways, displaying characteristic features of several different cell types. Thus, these neural crest derived cells display expression patterns and behaviors typical of endothelia, fibroblasts, smooth muscle and macrophages, owing to the multiple roles and two distinct environments where they operate to maintain intraocular pressure homeostasis. In most individuals, TM cells function normally over a lifetime in the face of persistent stressors, including phagocytic, oxidative, mechanical and metabolic stress. Study of TM cells isolated from ocular hypertensive eyes has shown a compromised ability to perform their daily duties. This review highlights the many responsibilities of the TM cell and its challenges, progress in our understanding of TM biology over the past 30 years, as well as discusses unanswered questions about TM dysfunction that results in IOP dysregulation and glaucoma.

Rho GTPase signaling promotes constitutive expression and release of TGF-β2 by human trabecular meshwork cells

Elevated intraocular pressure (IOP) is causally implicated in the pathophysiology of primary open-angle glaucoma (POAG). The molecular mechanisms responsible for elevated IOP remain elusive, but may involve aberrant expression and signaling of transforming growth factor (TGF)-β2 within the trabecular meshwork (TM). Consistent with previously published studies, we show here that exogenous addition of TGF-β2 to cultured porcine anterior segments significantly attenuates outflow facility in a time-dependent manner. By comparison, perfusing segments with a TGFβRI/ALK-5 antagonist (SB-431542) unexpectedly elicited a significant and sustained increase in outflow facility, implicating a role for TM-localized constitutive expression and release of TGF-β2. Consistent with this thesis, cultured primary or transformed (GTM3) quiescent human TM cells were found to constitutively express and secrete measurable amounts of biologically-active TGF-β2. Disrupting monomeric GTPase post-translational prenylation and activation with lovastatin or GGTI-298 markedly reduced constitutive TGF-β2 expression and release. Specifically, inhibiting the Rho subfamily of GTPases with C3 exoenzyme similarly reduced constitutive expression and secretion of TGF-β2. These findings suggest that Rho GTPase signaling, in part, regulates constitutive expression and release of biologically-active TGF-β2 from human TM cells. Localized constitutive expression and release of TGF-β2 by TM cells may promote or exacerbate elevation of IOP in POAG.

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.

The role of TGF-β in the pathogenesis of primary open-angle glaucoma

Transforming growth factor-β2 (TGF-β2) is found in increasing amounts in aqueous humor and reactive optic nerve astrocytes of patients with primary open-angle glaucoma (POAG), a major cause of blindness worldwide. The available data strongly indicate that TGF-β2 is a key player contributing to the structural changes in the extracellular matrix (ECM) of the trabecular meshwork and optic nerve head as characteristically seen in POAG. The changes involve an induction in the expression of various ECM molecules and are remarkably similar in trabecular meshwork cells and optic nerve head astrocytes. The ECM changes in the trabecular meshwork most probably play a role in the increase of aqueous humor outflow resistance causing higher intraocular pressure (IOP). In the optic nerve head, TGF-β2-induced changes might contribute to deformation of the optic nerve axons causing impairment of axonal transport and neurotrophic supply and leading to their continuous degeneration. The increase in IOP further adds mechanical stress and strain to optic nerve axons and accelerates degenerative changes. In addition, high IOP might induce the expression of activated TGF-β1 in trabecular meshwork cells and optic nerve head astrocytes; this again might significantly lead to the progress of axonal degeneration. The action of TGF-β2 in POAG is largely mediated through the connective tissue growth factor, whereas the activities of TGF-β1 and -β2 are modulated by the blocking effects of bone morphogenetic protein-4 (BMP-4) and BMP-7, by gremlin that inhibits BMP signaling and by several species of microRNAs.

Exploring anti-TGF-β therapies in cancer and fibrosis

Transforming growth factor-β (TGF-β) is a multifunctional cytokine, with important roles in maintaining tissue homeostasis. TGF-β signals via transmembrane serine/threonine kinase receptors and intracellular Smad transcriptional regulators. Perturbed TGF-β signaling has been implicated in a large variety of pathological conditions. Increased TGF-β levels have been found in patients with cancer, fibrosis, and systemic sclerosis, and were correlated with disease severity. In cancer, TGF-β mediates tumor invasion and metastasis by affecting both tumor cells and the tumor microenvironment including fibroblast activation and immune suppression. Furthermore, TGF-β is a strong stimulator of extracellular matrix deposition. On the basis of these observations, small molecule inhibitors of the TGF-β receptor kinases, neutralizing antibodies that interfere with ligand?receptor interactions, antisense oligonucleotides reducing TGF-β expression, and soluble receptor ectodomains that sequester TGF-β have been developed to intervene with excessive TGF-β signaling activity in the aforementioned disorders. Here, we review the current state of anti-TGF-β therapy in clinical trials.

Role of TGFbeta/Smad signaling in gremlin induction of human trabecular meshwork extracellular matrix proteins

PURPOSE

The bone morphogenic protein (BMP) antagonist gremlin is elevated in glaucomatous trabecular meshwork (TM) cells and tissues and elevates intraocular pressure (IOP). Gremlin also blocks BMP4 inhibition of transforming growth factor (TGF)-β2 induction of TM extracellular matrix (ECM) proteins. The purpose of this study was to determine whether Gremlin regulates ECM proteins in cultured human TM cells.

METHODS

Human TM cells were treated with recombinant gremlin to determine the effects on ECM gene and protein expression. Expression of the ECM genes FN, COL1, PAI1, and ELN was examined in cultured human TM cells by quantitative RT-PCR and Western immunoblot analysis. TM cells were pretreated with TGFBR inhibitors (LY364947, SB431542 or TGFBR1/TGFB2 siRNAs), inhibitors of the Smad signaling pathway (SIS3 or Smad2/3/4 siRNAs), or CTGF siRNA to identify the signaling pathway(s) involved in gremlin induction of ECM gene and protein expression.

RESULTS

All ECM genes analyzed (FN, COL1, PAI1, and ELN) were induced by gremlin. This gremlin induction of ECM genes and protein expression was blocked by inhibitors of TGFBR and the canonical Smad2/3/4 and CTGF signaling pathways.

CONCLUSIONS

Gremlin employs canonical TGFβ2/Smad signaling to induce ECM genes and proteins in cultured human TM cells. Gremlin also induces both TGFβ2 and CTGF, which can act downstream to mediate some of these ECM changes in TM cells.

Influence of race and age on aqueous humor levels of transforming growth factor-beta 2 in glaucomatous and nonglaucomatous eyes

PURPOSE

To evaluate the influence of race and age on aqueous humor levels of transforming growth factor-beta 2 (TGF-β2).

METHODS

Patients >40 years of age and undergoing cataract or glaucoma surgery without associated significant intraocular pathology were selected for this study. In bilateral cases, only the first operated eye was included for evaluation. At the time of surgery, a small amount of aqueous was withdrawn. The concentration of total TGF-β2 was measured by enzyme-linked immunosorbent assay in duplicate by a masked observer.

RESULTS

Fifty-five aqueous humor samples were analyzed from subjects with an average age of 68.05 ± 10.94 years. Overall median TGF-β2 concentration was 247.03 pg/mL. The median concentration of TGF-β2 was higher in eyes with glaucoma than in eyes without glaucoma (269.39 vs. 165.56 pg/mL, respectively; P = 0.001). Subgroup analysis found no significant difference between African American and Caucasian American subjects in the nonglaucomatous or glaucomatous subgroups. Age showed positive correlation with TGF-β2 in nonglaucomatous eyes (r(2) = 0.44, P = 0.019). No correlation between age and TGF-β2 was noted in the glaucoma group (r(2) = 0.02, P = 0.343).

CONCLUSION

The aqueous humor concentration of TGF-β2 was significantly higher in eyes with glaucoma than in eyes without glaucoma. No significant difference between the aqueous humor levels of TGF-β2 from African American and Caucasian American subjects could be measured. However, a significant and positive correlation between age and aqueous humor concentration of TGF-β2 in the eyes of nonglaucomatous subjects was measured. These results are consistent with the idea that elevated levels of TGF-β2 within the anterior segment contribute to the development of glaucoma. In addition, the increased risk for developing glaucoma as one ages may in part be related to the rise of this cytokine.

Modulation of extracellular matrix turnover in the trabecular meshwork

Intraocular pressure (IOP) is the most critical risk factor for primary open angle glaucoma (POAG). In most cases of POAG, IOP is increased because of an abnormally high aqueous humor outflow resistance in the juxtacanalicular region of the trabecular meshwork. A distinct structural change in the trabecular meshwork of patients with POAG is the increase in fibrillar extracellular matrix in the juxtacanalicular region of the trabecular meshwork. Our knowledge on the molecular factors that govern turnover of the extracellular matrix in the trabecular meshwork has increased considerably in recent years. It has become clear that quality and quantity of the extracellular matrix in the trabecular meshwork are regulated by several signaling molecules that interact with each other to promote its synthesis, degradation, or extracellular modification. Transforming growth factor-beta1 and beta2 (TGF-beta1 and TGF-beta2) which derive from the aqueous humor or may be locally expressed induce in cultured trabecular meshwork cells the expression of a variety of extracellular matrix molecules. The action of TGF-betas very likely requires local activation by thrombospondin-1 and is partly mediated by its downstream mediator connective tissue growth factor, both of which are constitutively expressed in the trabecular meshwork. Bone morphogenetic proteins (BMP)-7 and -4 effectively antagonize the effects of TGF-beta2 on matrix deposition. The antagonizing effects of BMP-7 are mediated in trabecular meshwork cells through Smad7. Smad7 is a key molecular switch to inhibit TGF-beta2 signaling in the trabecular meshwork.

Decreased active TGF-beta2 levels in the aqueous humour during immune reactions following penetrating keratoplasty

PURPOSE

The secretion of transforming growth factor (TGF)-beta (2) into the aqueous humour is important for maintaining the immunological privilege of the anterior ocular segment that promotes corneal allograft survival. Levels of total TGF-beta (2), however, were similar in eyes with and without immune reactions following penetrating keratoplasty (PK). In this study, we tested the hypothesis whether the activated form of TGF-beta (2) is decreased in eyes with immune reactions following PK.

METHODS

Anterior chamber puncture was performed in 38 cataract patients without PK (group I), in 10 patients without immune reaction following PK (group II), and in 10 patients following PK with newly diagnosed endothelial immune reaction (group III). About 0.05-0.1 ml of aqueous humour were harvested from each patient. Analysis of active TGF-beta (2) was started via ELISA within 3 h following puncture.

RESULTS

Average active TGF-beta (2) concentration was 38.9 pg/ml+/-24.3 in group I, 47.4 pg/ml+/-23.1 in group II, and 12.7+/-26.0 pg/ml in group III. The differences between groups I and III (P=0.005) and groups II and III (P=0.008) were statistically significant.

CONCLUSION

The lowest levels of active TGF-beta (2) were measured in eyes with newly diagnosed endothelial immune reactions. This suggests that TGF-beta (2) has a protective effect on corneal grafts following PK. Further (prospective) studies are being carried out to discover whether active TGF-beta (2)--determined prior to PK--might serve as a predictive parameter for the occurrence of immune reactions.

Effect of excess synthesis of extracellular matrix components by trabecular meshwork cells: possible consequence on aqueous outflow

The extracellular matrix (ECM) of the trabecular meshwork (TM) is an important determinant of its functional properties. This study was performed to investigate whether overexpression of ECM components, laminin (LM) and collagen type IV (Col) by TM cells may play a role in the development of outflow resistance. To determine the effect of excess LM and Col expression on cell monolayer permeability, an in vitro cell culture model was used in which overexpression of the two ECM components, LM and Col, was induced by high glucose (HG) (30 mM) or 0.1 microM dexamethasone (D) in bovine and human trabecular meshwork (BTM and HTM) cells. Western blot analysis and immunofluorescence staining confirmed increased LM and Col synthesis in cells exposed to HG or D. Increased level of LM and Col protein resulted in reduced cell monolayer permeability. Transfection with antisense oligos (AS-oligos) targeted against LM or Col inhibited HG- or D-induced LM and Col gene overexpression in TM cells with concomitant increase in permeability. The AS-oligo strategy was effective in reducing LM or Col level in the TM cells in all conditions tested in this study. These findings suggest that increased LM and Col deposition in the outflow pathway may cause resistance to aqueous outflow and contribute to the development of primary open angle glaucoma (POAG).

Changes in aqueous humor dynamics with age and glaucoma

Changes in aqueous humor dynamics with age and in glaucoma have been studied for several decades. More recently, techniques have been developed which confirm earlier studies showing that outflow facility decreases with age and in glaucoma and add the newer finding that uveoscleral outflow also decreases. Morphologic studies in aging and glaucoma eyes have shown an increase in accumulation of extracellular material in both the trabecular meshwork and ciliary muscle and a loss of trabecular meshwork cells, which contribute to this reduction in outflow and result in an increase in intraocular pressure. A reduction in hyaluronic acid and increases in fibronectin and thrombospondin contribute to the change in the extracellular environment. Imbalances in responses to age-related stresses such as oxidative damage to long-lived molecules, protein cross-linking and loss of elasticity could trigger excess production of factors such as transforming growth factor beta, interleukin-1 and CD44S that could stimulate pathways leading to increases in fibronectin, transformation of trabecular meshwork cells to a myoepithelial state and decrease the breakdown in extracellular matrix material, allowing excess to accumulate. Ultimately trabecular outflow and uveoscleral outflow are reduced and intraocular pressure becomes elevated, adding more stress and perpetuating the pathological condition. Future research to identify additional factors and clarify their roles in these processes could lead to alternative therapies for age and glaucoma related changes in the eye.

Innervation of the porcine ciliary muscle and outflow region

The porcine eye serves as a model to study various functions of the aqueous outflow system. To compare these data with the primate eye, a detailed investigation of the distribution of contractile properties and of the innervation of the outflow region was conducted in the porcine eye. In all quadrants of the anterior eye segment, elastic fibres connected the ciliary muscle (CM) with the well-developed scleral spur (ScS) and also partly with the corneoscleral trabecular meshwork (TM) and the loops of the collecting outflow channels. Immunohistochemistry with antibodies against smooth muscle alpha-actin revealed intense staining of the CM and some myofibroblasts in the ScS and outer TM. In addition to a few cholinergic and aminergic nerve fibres in the outflow region, numerous substance P- and calcitonin-gene related peptide-positive nerve fibres and nerve endings were found near the outflow loops of the porcine TM. Although the porcine CM serves rather as a tensor choroideae muscle than as a muscle for accommodation, the innervation and morphology of the collecting outflow channel loops and of the expanded TM between the ScS and the cornea showed close similarities to the primate eye.

Growth factors in the anterior segment: role in tissue maintenance, wound healing and ocular pathology

A number of growth factors and their associated receptors, including epidermal growth factor, transforming growth factor-beta, keratinocyte growth factor, hepatocyte growth factor, fibroblast growth factor and platelet-derived growth factor have been detected in the anterior segment of the eye. On binding to cellular receptors, these factors activate signalling cascades, which regulate functions including mitosis, differentiation, motility and apoptosis. Production of growth factors by corneal cells and their presence in the tear fluid and aqueous humour is essential for maintenance and renewal of normal tissue in the anterior eye and the prevention of undesirable immune or angiogenic reactions. Growth factors also play a vital role in corneal wound healing, mediating the proliferation of epithelial and stromal tissue and affecting the remodelling of the extracellular matrix (ECM). These functions depend on a complex interplay between growth factors of different types, the ECM, and regulatory mechanisms of the affected cells. Imbalances may lead to deficient wound healing and various ocular pathologies, including edema, neovascularization and glaucoma. Growth factors may be targeted in therapeutic ophthalmic applications, through exogenous application or selective inhibition, and may be used to elicit specific cellular responses to ophthalmic materials. A thorough understanding of the mechanism and function of growth factors and their actions in the complex environment of the anterior eye is required for these purposes. Growth factors, their function and mechanisms of action as well as the interplay between different growth factors based on recent in vitro and in vivo studies are presented.

Functional dichotomy: glutathione and vitamin E in homeostasis relevant to primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a complex chronic neurological disease that can result in blindness. The goal of understanding the aetiology of POAG is to be able to target effective treatment to individuals who will eventually go blind without it. Epidemiological studies of POAG have not specifically addressed the possibility that nutrition may play a role in the development of POAG. A handful of papers have considered that nutrition may have an impact on POAG patients. POAG is not believed to be a 'vitamin-deficiency disease'. The concept of 'vitamin-deficiency diseases' and the recommended daily allowances have not kept pace with the growing understanding of the cellular and molecular functions of vitamins and other micronutrients. The aetiology of POAG remains a mystery. Discoveries in cell physiology can be assimilated from the literature and applied to known homeostatic mechanisms of the eye. In this way the possible roles of nutritional components involved in the aetiology of POAG can be described. The mechanisms may be subject to many influences in ways that have yet to be defined. Two distinct changes in the trabecular meshwork can be identified: trabecular meshwork changes that cause intra-ocular pressure to increase and trabecular meshwork changes that are directly correlated to optic nerve atrophy. Compelling evidence suggests that collagen trabecular meshwork extracellular matrix (ECM) remodelling is correlated to increased intraocular pressure in POAG. Elastin trabecular meshwork ECM remodelling is correlated to POAG optic nerve atrophy. There appear to be two different pathways of ECM remodelling and apoptosis induction in POAG. The pathway for collagen remodelling and apoptosis induction seems to be exogenously influenced by water-soluble antioxidants, for example, glutathione. The pathway for elastin remodelling and apoptosis induction seems to be influenced by endogenous lipid-soluble antioxidants, for example, vitamin E. Roles can be defined for antioxidants in the two different pathways of ECM remodelling and apoptosis induction. This suggests that antioxidants are important in maintaining cellular homeostasis relevant to the aetiology of POAG.

Influence of argon laser trabeculoplasty on transforming growth factor-beta 2 concentration and bleb scarring following trabeculectomy

BACKGROUND

The purpose of this study was to evaluate the influence of previous argon laser trabeculoplasty (ALT) on transforming growth factor-beta 2 (TGF-beta 2) concentration of the aqueous humor and its influence on bleb scarring after trabeculectomy.

METHODS

Fifty-one patients with primary open-angle glaucoma (POAG) and 29 patients with exfoliation (XFS) glaucoma were recruited for this prospective study before undergoing trabeculectomy. Sixty to 200 micro l of aqueous humor were analyzed for total and biologically active TGF-beta 2 concentrations (R and D Systems). TGF-beta 2 levels and a standardized bleb assessment were compared between the ALT- and non-ALT-treated groups.

RESULTS

POAG eyes without ALT showed significantly higher total TGF-beta 2 levels (2,317.7+/-1,041.1 pg/ml) than eyes with previous ALT (1,621.6+/-899.6 pg/ml; P=0.026). No significant difference was found for active TGF-beta 2 levels (ALT: 238.1+/-119.0 pg/ml; no ALT: 220.1+/-96.9 pg/ml; P=0.585). In XFS patients ALT did not alter total TGF-beta 2 levels (ALT: 1,524.9+/-624.9 pg/ml, no ALT: 1,220+/-499.1 pg/ml; P=0.20), but active TGF-beta 2 was significantly higher in the ALT-treated (237.0+/-99.7 pg/ml) than in the non-ALT-treated (140.0+/-95.3 pg/ml, P=0.028) group. Bleb grading revealed no statistical difference between the ALT- and non-ALT-treated groups in POAG (P=0.545, Fisher's exact test), whereas XFS patients with ALT were at increased risk for scarring compared to non-ALT-treated patients (P=0.053).

CONCLUSIONS

ALT appears to increase the risk of scarring in XFS patients because of increased levels of activated TGF-beta 2.

Hyaluronan synthase in trabecular meshwork cells

BACKGROUND/AIMS

Hyaluronan is present in the trabecular meshwork where it is involved in the pathophysiology of aqueous outflow environment. In this study, the expression and regulation of hyaluronan synthase (HAS), which is the enzyme synthesising hyaluronan, in trabecular meshwork cells were investigated.

METHODS

Cultured bovine trabecular meshwork cells (BTMCs) were used. HAS expression in BTMCs was examined by RT-PCR. The effects of transforming growth factor beta (TGF-beta) and platelet derived growth factor BB (PDGF-BB) on HAS expression in BTMCs were examined by quantitative RT-PCR. The HAS2 expression by TGF-beta and PDGF-BB at the protein level was also confirmed immunohistochemically. The production of hyaluronan from BTMCs was detected by high performance liquid chromatography (HPLC).

RESULTS

Three HAS isoforms were expressed in BTMCs at the mRNA level. Among HAS isoforms, only the expression of HAS2 mRNA was increased by the administration of TGF-beta or PDGF-BB. HAS2 upregulation by these growth factors was also confirmed at the protein level. Further, hyaluronan production from BTMCs was stimulated by TGF-beta or PDGF-BB.

CONCLUSION

Expression of HAS in trabecular meshwork may maintain the hyaluronan content in the aqueous outflow pathway. Its production is regulated by TGF-beta and PDGF-BB. The regulation of the expression of HAS in trabecular meshwork might be useful for modulating the aqueous outflow environment.

Transporters/receptors in the anterior chamber: pathways to explore ocular drug delivery strategies

Membrane transporters/receptors are involved in drug transport processes and play a key role in intestinal absorption, tissue distribution and elimination. Drug targeting to specific transporters and receptors using carrier-mediated absorption has immense clinical significance. Ocular drug delivery is a challenging task since it involves drug transport across various barriers in the eye. Specialised transport processes exist at these barriers, which control the entry of drugs and xenobiotics. Ocular drug therapy involving topical or systemic administration of drugs has various limitations. Transport processes in the eye have been targeted in an effort to increase ocular bioavailability of drugs following topical instillation. This review discusses various transport processes in the eye and drug delivery strategies utilising these transporters/receptors.

Novel antisense oligonucleotides targeting TGF-beta inhibit in vivo scarring and improve surgical outcome

The scarring response is an important factor in many diseases throughout the body. In addition, it is a major problem in influencing results of surgery. In the eye, for example, post-operative scarring can determine the outcome of surgery. This is particularly the case in the blinding disease glaucoma, where several anti-scarring regimens are currently used to improve glaucoma surgery results, but are of limited use clinically because of severe complications. We have recently identified transforming growth factor-beta (TGF-beta) as a target for post-operative anti-scarring therapy in glaucoma, and now report the first study of novel second-generation antisense phosphorothioate oligonucleotides against TGF-beta in vivo. Single applications of a TGF-beta OGN at the time of surgery in two different animal models closely related to the surgical procedure performed in glaucoma patients, significantly reduced post-operative scarring (P<0.05) and improved surgical outcome. Our findings suggest that TGF-beta antisense oligonucleotides have potential as a new therapy for reducing post-surgical scarring. Its long-lasting effects after only a single administration at the time of surgery make it particularly attractive clinically. Furthermore, although we have shown this agent to be useful in the eye, it could have widespread applications anywhere in the body where the wound-healing response requires modulation.

Differential effects of transforming growth factor-beta2 on corneal endothelial cell proliferation-A role of serum factors

PURPOSE

To determine the influence of serum on transforming growth factor (TGF)-beta2 mediated effects on the proliferation of corneal endothelial cells (CE).

METHODS

Rat CE were grown in explant culture and the proliferation of CE was measured by [(3)H]thymidine bioassay. Subconfluent cells were synchronized in the G0 (quiescent) phase of the cell cycle by serum starvation for 24hr. Serum and [(3)H]thymidine were then added to the cells in the presence or absence of a physiological concentration (5ngml(-1)) of exogenous active TGF-beta2. Radioactivity was measured at various time points to detect DNA synthesis. These experiments were repeated without adding serum after serum starvation. Preincubation of exogenous TGF-beta2 with neutralizing antibody was used to test the cytokine specificity.

RESULTS

Without TGF-beta2, a linear increase in [(3)H]thymidine incorporation, indicating S-phase, began approximately 16hr after serum addition, then plateaued at approximately 24hr. Serum promoted DNA synthesis of CE in a dose-dependent manner at concentrations of 0.5-10%. In cultures with 10% serum, TGF-beta2 (0.5, 1, 5, and 20ngml(-1)) suppressed CE growth dose-dependently. The growth amplitude decreased and the time before S-phase entry, G1 phase, was prolonged to 24hr. In culture with 1% serum, TGF-beta2 (5ngml(-1)) suppressed the CE proliferation by delaying S-phase entry without suppressing growth amplitude. In cultures without serum, TGF-beta2 promoted CE growth to a level similar to that of cultures supplemented with 0.5% serum.

CONCLUSIONS

Responses of cultured CE to exogenous TGF-beta2 depended on the concentration of serum in the medium. This result implies a possibility that in vivo serum influx through a compromised blood-ocular barrier could influence the CE growth by changing the responses of these cells to TGF-beta2 in aqueous humor.

Circadian variations of transforming growth factor-beta2 and basic fibroblast growth factor in the rabbit aqueous humor

PURPOSE

To compare levels of transforming growth factor-beta2 (TGF-beta2) and basic fibroblast growth factor (bFGF) in the ocular fluids of rabbits at various times of the day.

METHODS

Seventy-two young adult New Zealand albino rabbits were entrained to a daily 12-hour light (6 AM to 6 PM) and 12-hour dark cycle. Eight rabbits were sacrificed at each of 6 time points: 4 AM, 8 AM, noon, 4 PM, 8 PM, and midnight. Under an acute 24-hour constant dark condition, 8 additional rabbits were sacrificed at each of 3 time points in the accustomed light period (8 AM, noon, and 4 PM). Samples of aqueous humor and vitreous humor were collected from both eyes. Using enzyme immunoassay, samples from one eye were assayed for total TGF-beta2 and active form of TGF-beta2 and samples from the other eye were assayed for bFGF. Concentrations at various time points were analyzed using one-way ANOVA and post-hoc Bonferroni t-test for multiple comparisons.

RESULTS

Aqueous humor levels of total TGF-beta2, active TGF-beta2, and bFGF changed during the 24-hour period. Total TGF-beta2 and bFGF levels increased between 4 AM and 8 AM. Active TGF-beta2 level increased between 8 PM and midnight. Similar patterns of changes were found when considering aqueous humor samples collected under the acute constant dark condition. In the vitreous humor, total TGF-beta2, active TGF-beta2, and bFGF remained unchanged throughout the 24 hours.

CONCLUSIONS

Endogenous circadian rhythms of total TGF-beta2, active TGF-beta2, and bFGF occur in the rabbit aqueous humor. These two extracellular signaling molecules may be associated with specific physiological functions in the anterior segment according to the time of the day.

Beyond Mitomycin: TGF-beta and wound healing

The introduction of the anti-cancer drugs Mitomycin and 5-fluorouracil as anti-scarring agents within the last decade, has greatly improved surgical results of glaucoma filtration surgery. However, a number of problems associated with their use have emerged. At the same time, the transforming growth factor-beta (TGF-beta) has been identified as an important component of wound healing, particularly in the conjunctival scarring response. Recent developments in molecular therapy offer exciting prospects for the modulation of wound healing, specifically those targeting TGF-beta. As TGF-beta is such a potent stimulant of scarring, this review examines its biology and role in ocular wound healing and repair, and discusses promising new approaches to modifying its activity.

Advances in glaucoma diagnosis and therapy for the next millennium: new drugs for trabecular and uveoscleral outflow

Advances in our understanding of the physiology and molecular biology of the trabecular and uveoscleral outflow pathways of the eye will lead to the development of new approaches for glaucoma therapy. Therapies of the future will target the structures and enzymes involved in maintaining cell shape and cell-cell and cell-extracellular matrix interactions. Altering the extracellular matrix in the ciliary muscle has been important in the intraocular pressure lowering effects of prostaglandins and will be developed further as an approach to enhancing outflow through the trabecular meshwork. Gene therapy may be used to enhance or suppress the endogenous targets that are ultimately responsible for the outflow enhancement triggered by these agents.

TGF-beta2 inhibits growth of uveal melanocytes at physiological concentrations

The effect of TGF-beta2 on growth of uveal melanocytes in vitro was studied and the dose-dependent inhibitory effect of TGF-beta2 was compared with the known concentration of TGF-beta2 in aqueous humor. Uveal melanocytes were isolated and cultured with medium supplemented with cAMP elevating agents and basic fibroblast growth factor. The uveal melanocytes were plated into multi-well plates. After 24 hr, TGF-beta2 was added to the medium in various concentrations. After 5 days, the cells were detached, counted and compared to the controls. The effect of TGF-beta2 on DNA synthesis (as evaluated by uptake of bromodeoxyuridine) were also tested. TGF-beta2 inhibited growth and DNA synthesis of cultured uveal melanocytes in a dose-dependent manner at concentrations from 0.03-10.0 ng ml-1. The growth-inhibition of TGF-beta2 was present even in serum-free medium. TGF-beta2 had little or no effect on melanogenesis of cultured uveal melanocytes. The serum used for cultivation did not contain active TGF-beta1 or TGF-beta2 as measured by immunoassay. The known amount of active TGF-beta2 in aqueous humor (0.2-0.4 ng ml-1) is sufficient to inhibit the growth of uveal melanocytes. It indicates that TGF-beta2 is a potent growth inhibit factor of uveal melanocytes and may play an important role in maintaining the non-proliferative, relatively quiescence status of uveal melanocytes in vivo.

Increased level of vascular endothelial growth factor in aqueous humor of patients with neovascular glaucoma

PURPOSE

This study aimed to quantitate and compare the concentration of vascular endothelial growth factor (VEGF) in aqueous humor samples from patients with neovascular glaucoma (NVG), primary open-angle glaucoma (POAG), and cataract, as well as in serum samples of healthy human subjects.

METHODS

The authors collected aqueous humor samples by using their previously published technique of limbal paracentesis. The authors determined the concentration of VEGF by using a competitive enzyme immunoassay system and four-parameter logistic curve fitting and performed statistical analysis by using the Mann-Whitney-Wilcoxon test.

RESULTS

The authors detected VEGF in 12 of 12 samples from patients with NVG (mean +/- standard error of the mean, 29.267 +/- 7.350 ng/ml), 15 of 28 samples from patients with POAG (0.726 +/- 0.204 ng/ml), 4 of 20 aqueous humor samples from patients with cataract (0.257 +/- 0.043 ng/ml), and 16 of 16 human serum samples (20.246 +/- 1.568 ng/ml). The mean concentration of VEGF in aqueous humor of patients with NVG was 40- and 113-fold higher than that in patients with POAG and cataract, respectively, and the difference was statistically significant (P < 0.01). The VEGF level in patients with POAG was elevated compared with that in patients with cataract (P < 0.05). Although the mean concentration of VEGF in aqueous humor of patients with NVG was approximately 1.45-fold higher than that in serum, the difference was not significant (P > 0.05).

CONCLUSION

The authors' findings show that patients with NVG had a significantly increased level of VEGF in the aqueous humor and implicate VEGF as an important factor in the pathogenesis of intraocular neovascularization in these patients. The authors discuss the possible role of the ciliary epithelium, in addition to retina, in the production of VEGF and the complementary function of basic fibroblast growth factor and other growth factors.

Expression of TGF-beta type I and type II receptors in rat eyes

Transforming growth factor beta (TGF-beta) transduces signals through mediation of type I and type II serine/threonine kinase receptors. The expression of TGF-beta type I (T beta R-I) and II (T beta R-II) receptors in rat eyes was investigated immunohistochemically. T beta R-I and T beta R-II immunoreactivity was detected in corneal and conjunctival epithelial cells, corneal endothelial cells, ciliary epithelial cells, lens epithelial cells, retinal pigment epithelial cells, and choroidal vessels. This co-expression of T beta R-I and T beta R-II indicates that the above cells respond to TGF-beta and, because TGF-beta is reported to be produced in ocular tissues, that it may have important autocrine and/or paracrine roles in the growth and metabolism of ocular tissues in situ.

The extracellular matrix and its modulation in the trabecular meshwork

The extracellular matrix (ECM) in the trabecular meshwork is is believed to be essential for maintenance of the normal outflow system. Excessive, abnormal accumulations of ECM materials have been noted in the trabecular meshwork of eyes obtained from patients with primary open angle glaucoma. This review summarizes the current knowledge regarding the composition of this matrix and the receptors for ECM proteins in the trabecular meshwork. Modulations of the ECM elements by constituents in the aqueous humor after phagocytic challenges and by glucocorticoids are also described. The ECM is known to regulate cell differentiation and cell behavior in a number of systems. It will thus be of particular interest to establish the relationship between the modulated ECM and the functional status of trabecular meshwork cells and to examine the possible relevance of such modulation to outflow resistance.