High total TGF-beta 2 levels in normal human tears

Inflammation mechanism and anti-inflammatory therapy of dry eye

Dry eye is a widespread chronic inflammatory disease that causes fatigue, tingling, burning, and other symptoms. Dry eye is attributed to rheumatic diseases, diabetes, hormone disorders, and contact lenses, which activate inflammatory pathways: mitogen-activated protein kinases (MAPK) and nuclear factor-B (NF-κB), promote macrophage inflammatory cell and T cell activation, and inflammation factors. Clinicians use a combination of anti-inflammatory drugs to manage different symptoms of dry eye; some of these anti-inflammatory drugs are being developed. This review introduces the dry eye inflammation mechanisms and the involved inflammatory factors. We also elucidate the anti-inflammatory drug mechanism and the detection limits.

TGF-β Isoforms Affect the Planar and Subepithelial Fibrogenesis of Human Conjunctival Fibroblasts in Different Manners

Three highly homologous isoforms of TGF-β, TGF-β-1~3, are involved in the regulation of various pathophysiological conditions such as wound healing processes in different manners, despite the fact that they bind to the same receptors during their activation. The purpose of the current investigation was to elucidate the contributions of TGF-β-1 ~3 to the pathology associated with conjunctiva. For this purpose, the biological effects of these TGF-β isoforms on the structural and functional properties of two-dimensional (2D) and three-dimensional (3D) cultured human conjunctival fibroblasts (HconF) were subjected to the following analyses: 1) transendothelial electrical resistance (TEER), a Seahorse cellular metabolic measurement (2D), size and stiffness measurements of the 3D HTM spheroids, and the qPCR gene expression analyses of extracellular matrix (ECM) components (2D and 3D). The TGF-β isoforms caused different effects on the proliferation of the HconF cell monolayer evaluated by TEER measurements. The differences included a significant increase in the presence of 5 ng/mL TGF-β-1 and -2 and a substantial decrease in the presence of 5 ng/mL TGF-β-3, although there were no significant differences in the response to the TGF-β isoforms for cellular metabolism among the three groups. Similar to planar proliferation, the TGF-β isoforms also induced diverse effects toward the mechanical aspects of 3D HconF spheroids, where TGF-β-1 increased stiffness, TGF-β-2 caused no significant effects, and TGF-β-3 caused the downsizing of the spheroids and stiffness enhancement. The mRNA expression of the ECMs were also modulated in diverse manners by the TGF-β isoforms as well as the culture conditions for the 2D vs. 3D isoforms. Many of these TGF-β-3 inducible effects were markedly different from those caused by TGF-β1 and TGF-β-2. The findings presented herein suggest that the three TGF-β isoforms induce diverse and distinctly different effects on cellular properties and the expressions of ECM molecules in HconF and that these changes are independent of cellular metabolism, thereby inducing different effects on the epithelial and subepithelial proliferation of human conjunctiva.

FGF-2 Differentially Regulates Lens Epithelial Cell Behaviour during TGF-β-Induced EMT

Fibroblast growth factor (FGF) and transforming growth factor-beta (TGF-β) can regulate and/or dysregulate lens epithelial cell (LEC) behaviour, including proliferation, fibre differentiation, and epithelial–mesenchymal transition (EMT). Earlier studies have investigated the crosstalk between FGF and TGF-β in dictating lens cell fate, that appears to be dose dependent. Here, we tested the hypothesis that a fibre-differentiating dose of FGF differentially regulates the behaviour of lens epithelial cells undergoing TGF-β-induced EMT. Postnatal 21-day-old rat lens epithelial explants were treated with a fibre-differentiating dose of FGF-2 (200 ng/mL) and/or TGF-β2 (50 pg/mL) over a 7-day culture period. We compared central LECs (CLECs) and peripheral LECs (PLECs) using immunolabelling for changes in markers for EMT (α-SMA), lens fibre differentiation (β-crystallin), epithelial cell adhesion (β-catenin), and the cytoskeleton (alpha-tropomyosin), as well as Smad2/3- and MAPK/ERK1/2-signalling. Lens epithelial explants cotreated with FGF-2 and TGF-β2 exhibited a differential response, with CLECs undergoing EMT while PLECs favoured more of a lens fibre differentiation response, compared to the TGF-β-only-treated explants where all cells in the explants underwent EMT. The CLECs cotreated with FGF and TGF-β immunolabelled for α-SMA, with minimal β-crystallin, whereas the PLECs demonstrated strong β-crystallin reactivity and little α-SMA. Interestingly, compared to the TGF-β-only-treated explants, α-SMA was significantly decreased in the CLECs cotreated with FGF/TGF-β. Smad-dependent and independent signalling was increased in the FGF-2/TGF-β2 co-treated CLECs, that had a heightened number of cells with nuclear localisation of Smad2/3 compared to the PLECs, that in contrast had more pronounced ERK1/2-signalling over Smad2/3 activation. The current study has confirmed that FGF-2 is influential in differentially regulating the behaviour of LECs during TGF-β-induced EMT, leading to a heterogenous cell population, typical of that observed in the development of post-surgical, posterior capsular opacification (PCO). This highlights the cooperative relationship between FGF and TGF-β leading to lens pathology, providing a different perspective when considering preventative measures for controlling PCO.

Role of Decorin in the Lens and Ocular Diseases

Decorin is an archetypal member of the small leucine-rich proteoglycan gene family and is involved in various biological functions and many signaling networks, interacting with extra-cellular matrix (ECM) components, growth factors, and receptor tyrosine kinases. Decorin also modulates the growth factors, cell proliferation, migration, and angiogenesis. It has been reported to be involved in many ischemic and fibrotic eye diseases, such as congenital stromal dystrophy of the cornea, anterior subcapsular fibrosis of the lens, proliferative vitreoretinopathy, et al. Furthermore, recent evidence supports its role in secondary posterior capsule opacification (PCO) after cataract surgery. The expression of decorin mRNA in lens epithelial cells in vitro was found to decrease upon transforming growth factor (TGF)-β-2 addition and increase upon fibroblast growth factor (FGF)-2 addition. Wound healing of the injured lens in mice transgenic for lens-specific human decorin was promoted by inhibiting myofibroblastic changes. Decorin may be associated with epithelial-mesenchymal transition and PCO development in the lens. Gene therapy and decorin administration have the potential to serve as excellent therapeutic approaches for modifying impaired wound healing, PCO, and other eye diseases related to fibrosis and angiogenesis. In this review, we present findings regarding the roles of decorin in the lens and ocular diseases.

TGF-β Superfamily Signaling in the Eye: Implications for Ocular Pathologies

The TGF-β signaling pathway plays a crucial role in several key aspects of development and tissue homeostasis. TGF-β ligands and their mediators have been shown to be important regulators of ocular physiology and their dysregulation has been described in several eye pathologies. TGF-β signaling participates in regulating several key developmental processes in the eye, including angiogenesis and neurogenesis. Inadequate TGF-β signaling has been associated with defective angiogenesis, vascular barrier function, unfavorable inflammatory responses, and tissue fibrosis. In addition, experimental models of corneal neovascularization, diabetic retinopathy, proliferative vitreoretinopathy, glaucoma, or corneal injury suggest that aberrant TGF-β signaling may contribute to the pathological features of these conditions, showing the potential of modulating TGF-β signaling to treat eye diseases. This review highlights the key roles of TGF-β family members in ocular physiology and in eye diseases, and reviews approaches targeting the TGF-β signaling as potential treatment options.

Association of TGFB -509C>T promoter polymorphism with primary angle closure glaucoma in a North Indian Punjabi cohort

PURPOSE

Transforming growth factor beta (TGFB) is an important candidate gene implicated in glaucoma pathogenesis because it affects retinal ganglionic cell survival. The present study assessed the genetic association of -509C > T variant in the TGFB promoter region with primary open angle glaucoma (POAG) and primary angle closure glaucoma (PACG) in a North Indian Punjabi population.

METHOD

A total of 867 subjects (307 POAG, 133 PACG cases and 427 controls) were recruited from the targeted population. Genotyping was done by PCR-RFLP method and the data was analyzed using PLINK software (v1.07). Logistic regression under different genetic models was applied and genotype phenotype correlation was assessed by one-way ANOVA.

RESULT

A statistically significant difference in the frequency of heterozygotes among PACG cases (53.16%) and controls (30.07%) (p = 0.0002) was observed. Genetic model analysis revealed that mutant "TT" genotype conferred 2-fold risk towards PACG development under recessive model (p = 0.0019) while dominant model and co-dominant model provided 0.62 and 0.37 fold protection against PACG (p = 0.025 and p = 0.0001, respectively). Data segregation based on sex revealed a strong protective effect of heterozygous 'CT' genotype against progression of PACG among females (p = 0.002, OR = 0.37, 95% CI = 0.19-0.70), but conferred 2.14-fold risk among female POAG subjects (p = 0.013).

CONCLUSION

The study revealed a strong genetic association of -509C > T variant in TGFB with PACG in females. There is a need to replicate the results in a larger PACG cohort in other populations and further assess the contribution of sex specific factors in modifying genetic susceptibility to PACG.

TGFβ1 and TGFβ2 proteins in corneas with and without stromal fibrosis: Delayed regeneration of apical epithelial growth factor barrier and the epithelial basement membrane in corneas with stromal fibrosis

The purpose of this study was to investigate the expression and localization of transforming growth factor (TGF) β1 and TGFβ2 in rabbit corneas that healed with and without stromal fibrosis, and to further study defective perlecan incorporation in the epithelial basement membrane (EBM) in corneas with scarring fibrosis. A total of 120 female rabbits had no surgery, -4.5D PRK, or -9D PRK. Immunohistochemistry (IHC) was performed at time points from unwounded to eight weeks after surgery, with four corneas at each time point in each group. Multiplex IHC was performed for TGFβ1 or TGFβ2, with Image-J quantitation, and keratocan, vimentin, alpha-smooth muscle actin (SMA), perlecan, laminin-alpha 5, nidogen-1 or CD11b. Corneas at the four-week peak for myofibroblast and fibrosis development were evaluated using Imaris 3D analysis. Delayed regeneration of both an apical epithelial growth factor barrier and EBM barrier function, including defective EBM perlecan incorporation, was greater in high injury -9D PRK corneas compared to -4.5D PRK corneas without fibrosis. Defective apical epithelial growth factor barrier and EBM allowed epithelial and tear TGFβ1 and tear TGFβ2 to enter the corneal stroma to drive myofibroblast generation in the anterior stroma from vimentin-positive corneal fibroblasts, and likely fibrocytes. Vimentin-positive cells and unidentified vimentin-negative, CD11b-negative cells also produce TGFβ1 and/or TGFβ2 in the stroma in some corneas. TGFβ1 and TGFβ2 were at higher levels in the anterior stroma in the weeks preceding myofibroblast development in the -9D group. All -9D corneas (beginning two to three weeks after surgery), and four -4.5D PRK corneas developed significant SMA + myofibroblasts and stromal fibrosis. Both the apical epithelial growth factor barrier and/or EBM barrier functions tended to regenerate weeks earlier in -4.5D PRK corneas without fibrosis, compared to -4.5D or -9D PRK corneas with fibrosis. SMA-positive myofibroblasts were markedly reduced in most corneas by eight weeks after surgery. The apical epithelial growth factor barrier and EBM barrier limit TGFβ1 and TGFβ2 entry into the corneal stroma to modulate corneal fibroblast and myofibroblast development associated with scarring stromal fibrosis. Delayed regeneration of these barriers in corneas with more severe injuries promotes myofibroblast development, prolongs myofibroblast viability and triggers stromal scarring fibrosis.

Biological functions of tear film

Tears have a vital function to protect and lubricate the ocular surface. Tear production, distribution and clearance is tightly regulated by the lacrimal functional unit (LFU) to meet ocular surface demands. The tear film consists of an aqueous-mucin layer, containing fluid and soluble factors produced by the lacrimal glands and mucin secreted by the goblet cells, that is covered by a lipid layer. The array of proteins, glycoproteins and lipids in tears function to maintain a stable, well-lubricated and smooth optical surface. Tear factors also promote wound healing, suppress inflammation, scavenge free radicals, and defend against microbial infection. Disease and dysfunction of the LFU leads to tear instability, increased evaporation, inflammation, and blurred and fluctuating vision. The function of tear components and the consequences of tear deficiency on the ocular surface are reviewed.

Application of autologous serum eye drops after pterygium surgery: a prospective study

PURPOSE

The study aims to determine the effect of 50% autologous serum drops (ASD) on corneal healing and patient comfort following pterygium surgery.

METHODS

Fifty eyes of 50 patients who underwent pterygium excision combined with autologous conjunctival graft were included in this prospective randomized study: in 25 eyes, 50% ASD. In the remaining 25 eyes, conventional artificial tears (CAT) were applied postoperatively until corneal epithelium had completely epithelialized. Corneal epithelium healing speed, visual analog scale (VAS) for postoperative pain assessment, conjunctival inflammation, and recurrences were evaluated. Patients were followed up for 6 months.

RESULTS

Mean corneal epithelium closure time was 3.16 ± 0.37 days (range 3 and 4 days) in ASD group and 4.96 ± 0.84 days in CAT group (range 4 and 6 days), and the difference was statistically significant (p < 0.001). VAS scores were significantly lower in ASD group than CAT group in the first 5 days after surgery. In 9 of 50 eyes, moderate conjunctival inflammation continued 1 month: 4 (16%) in ASD group and 5 (20%) in CAT group (p = 0.713). In total, pterygium recurrence was seen in 5 (10%) eyes: 2 eyes (8%) in ASD group and 3 eyes (12%) in CAT group (p = 0.637).

CONCLUSION

ASD accelerated corneal epithelial healing following pterygium surgery. ASD group had lesser pain that was seem to be related with accelerated corneal epithelial healing.

Serum components and clinical efficacies of autologous serum eye drops in dry eye patients with active and inactive Sjogren syndrome

PURPOSE:

Autologous serum eye drops are considered safe and efficient for the treatment of various ocular surface disorders, including dry eye diseases (DED) caused by the primary and secondary Sjogren syndrome (SS). However, the serum components in patients of SS may be different from those of normal patients and can thus lead to unpredictable therapeutic effects. This study divided the SS patients into active and inactive types based on the erythrocyte sedimentation rate and the presence or absence of active rheumatoid arthritis.

METHODS:

We compared the serum components of these two groups with standard and multiplex enzyme linked immunosorbent assay arrays and predicted the therapeutic effects of topical autologous serum for the treatment of DED with ocular surface disease index (OSDI) and Oxford Schema scale (OSS).

RESULTS:

Hyaluronic acid and transforming growth factor b1 levels were significantly higher in the active SS group compared to the inactive SS group (P < 0.01), whereas epidermal growth factors, insulin growth factor 1, and fibroblast growth factor b had no significant differences between these two groups. Active SS group had significantly higher expressions of interleukin (IL) 1 beta, IL 6, and tumor necrosis factor alpha compared to inactive SS patients (P < 0.05). There were no statistical differences in therapeutic effects between these two groups, as measured with the OSDI or OSS.

CONCLUSION:

Dividing the Sjogren dry eye patients into active and inactive groups may appear as a reasonable method to predict the quality of autologous serum eye drops, but there seems to be no significant predictability to the therapeutic effects.

Conjunctival TGF-B Level in Primary Augmented Trabeculectomy

Purpose :

To compare the levels of conjunctival transforming growth factor beta (TGF-β) between glaucoma and control patients and to determine conjunctival TGF-β levels before and 3 months after augmented primary trabeculectomy.

Methods :

Patients with primary open angle glaucoma (POAG) or primary angle closure glaucoma (PACG) admitted for mitomycin (MMC) augmented primary trabeculectomy due to failure in achieving target pressure after maximum medical therapy were selected. Age-matched non-glaucoma patients were controls. Impression cytology of the conjunctiva was obtained twice from glaucoma patients (1 week before augmented primary trabeculectomy and 3 months after surgery) and once from controls. Conjunctival cells were tagged with an anti-TGF-β antibody and analyzed by flow cytometry.

Results :

Eighteen patients (11 POAG and 7 PACG patients) and 18 age-matched control patients were included. Conjunctival TGF-β levels were significantly different between glaucoma (35.21% ± 14.12%) and control patients (14.96% ± 6.34%) (p = 0.001). There was a significant reduction in conjunctival TGF-β levels after augmented trabeculectomy (23.0% ± 13.8%) (p < 0.001). A significantly greater reduction in conjunctival TGF-β levels (61.6% ± 17.9%) was associated with complete success of trabeculectomy at 3 months (83.3%) after surgical intervention (p = 0.029).

Conclusion :

The reduction of TGF-β on the conjunctival post primary augmented trabeculectomy may suggest TGF-β as potential predicting marker of short term trabeculectomy success. However, the result may be affected by site of impression, topical pressure lowering drugs and small sample size.

Evaluation of the efficacy of 50% autologous serum eye drops in different ocular surface pathologies

PURPOSE

This study evaluated the efficacy of 50% autologous serum eye drops in ocular surface diseases not improved by conventional therapy.

METHODS

We analyzed two groups: (1) acute eye pathologies (e.g., chemical burns) and (2) chronic eye pathologies (e.g., recurrent corneal erosion, neurotropic keratitis, and keratoconjunctivitis sicca). The patients were treated for surface instability after conventional therapy. The patients received therapy 5 times a day until stabilization of the framework; they then reduced therapy to 3 times a day for at least 3 months. We analyzed the best corrected visual acuity, epithelial defects, inflammation, corneal opacity, and corneal neovascularization. We also analyzed symptoms such as tearing, burning, sense of foreign body or sand, photophobia, blurred vision, and difficulty opening the eyelids.

RESULTS

We enrolled 15 eyes in group 1 and 11 eyes in group 2. The average therapy period was 16 ± 5.86 weeks in group 1 and 30.54 ± 20.33 weeks in group 2. The epithelial defects all resolved. Signs and symptoms improved in both groups. In group 2, the defect recurred after the suspension of therapy in 2 (18%) patients; in group 1, no defects recurred.

CONCLUSIONS

Autologous serum eye drops effectively stabilize and improve signs and symptoms in eyes previously treated with conventional therapy.

Biomarkers in primary open angle glaucoma

Glaucoma, a leading cause of blindness worldwide, is currently defined as a disturbance of the structural or functional integrity of the optic nerve that causes characteristic atrophic changes in the optic nerve, which may lead to specific visual field defects over time. This disturbance usually can be arrested or diminished by adequate lowering of intraocular pressure (IOP). Glaucoma can be divided roughly into two main categories, ‘ open angle ’ and ‘ closed angle ’ glaucoma.Open angle, chronic glaucoma tends to progress at a slower rate and patients may not notice loss of vision until the disease has progressed significantly. Primary open angle glaucoma(POAG) is described distinctly as a multifactorial optic neuropathy that is chronic and progressive with a characteristic acquired loss of optic nerve fibers. Such loss develops in the presence of open anterior chamber angles, characteristic visual field abnormalities, and IOP that is too high for the healthy eye. It manifests by cupping and atrophy of the optic disc, in the absence of other known causes of glaucomatous disease. Several biological markers have been implicated with the disease. The purpose of this study was to summarize the current knowledge regarding the non-genetic molecular markers which have been predicted to have an association with POAG but have not yet been validated.

Interleukin 11 expression in the normal canine eye

OBJECTIVES

The purpose of this study was to characterize the expression of interleukin-11 (IL-11), a cytokine with anti-inflammatory, cytoprotective, and immune-modulating characteristics, in the canine eye.

PROCEDURES

Normal canine eyes were collected from clinically healthy dogs that had been euthanized for reasons unrelated to this study. The distribution of IL-11 expression in the different ocular layers was evaluated by immunofluorescence (eight eyes). Expression levels were quantified (based on fluorescence intensity) using pixel density analysis. Primary cell cultures were derived from all three corneal cell layers. IL-11 mRNA expression was assessed in these cultures using quantitative RT-PCR before and after treatment with TGF-β1, a known inducer of IL-11 expression. IL-11 protein expression was also assessed in the media of these cells by Western blot analysis.

RESULTS

IL-11 protein was detected in the corneal epithelium, keratocytes, and the corneal endothelium of the normal canine eyes examined using immunofluorescence. Baseline IL-11 mRNA expression was noted in the corneal epithelium, fibroblasts, and endothelium using quantitative RT-PCR. Treatment of canine corneal cell lines with TGF-β1 resulted in statistically significant increases in IL-11 expression in the corneal epithelium, endothelial and fibroblast cell lines with strongest induction noted in the fibroblasts and endothelium.

CONCLUSION

This is the first description of IL-11 expression in the canine eye. The protein and mRNA appear to be constitutively present throughout all layers of the cornea and are increased by TGF-β1, a cytokine important in ocular inflammation and disease.

Treatment of corneal defects with delayed re-epithelization with a medical device/drug delivery system for epidermal growth factor

BACKGROUND

  Human recombinant epidermal growth factor has been shown to be effective in corneal healing when applied topically. The purpose of this preliminary study was to observe whether re-epithelization occurred in patients with non-healing corneal defects treated with a bandage contact lenses impregnated with epidermal growth factor.

DESIGN

  Prospective non-comparative interventional case series study. Epidermal growth factor-impregnated bandage contact lenses (created through passive transfer of epidermal growth factor into hydrogel contact lenses of high water content) were used to passively release epidermal growth factor to the corneal surface of the damaged eye.

PARTICIPANTS

  Nine clinical patients who presented for tertiary care at the University of British Columbia Eye Care Centre at Vancouver General Hospital.

METHODS

  All patients had clinically significant delayed corneal re-epithelization that had not healed despite standard treatments including conventional bandage contact lenses and topical medications. Causes of delayed re-epithelization varied from corneal injuries (e.g. alkali burns, recurrent corneal erosions) to recent corneal surgery (photorefractive keratectomy, phototherapeutic keratectomy, penetrating keratoplasty).

MAIN OUTCOME MEASURES

  Closure of wounds.

RESULTS

  Re-epithelialization was seen in the corneas of seven of the nine patients within 8 days after insertion of the epidermal growth factor-treated bandage contact lens into the damaged eye. The drug delivery system appeared to be most effective in non-inflamed corneas.

CONCLUSIONS

  Preliminary results indicate that bandage contact lenses impregnated with epidermal growth factor may be helpful in promoting re-epithelization in corneas with delayed healing. Efficacy appears to be reduced for vascularized and significantly inflamed corneas.

Stability of epitheliotrophic factors in autologous serum eye drops from chronic Stevens-Johnson syndrome dry eye compared to non-autoimmune dry eye

PURPOSE

To compare the concentrations of epitheliotrophic factors in autologous serum eye drops (ASE) prepared from sera of chronic Stevens-Johnson syndrome (SJS) patients with dry eyes to those prepared from non-autoimmune dry eye controls and to study the stability of the epitheliotrophic factors in different storage conditions.

METHODS

Twenty-percent ASE were prepared from 10 chronic SJS patients with dry eyes and 10 age-matched non-autoimmune dry eye controls. The concentrations of major epitheliotrophic factors comprising epidermal growth factor (EGF), transforming growth factor-beta1 (TGF-β1), transforming growth factor-beta2 (TGF-β2), and fibronectin in those ASE preparations were determined by enzyme-linked immunosorbent assay (ELISA) at baseline and after different storage conditions: at 4 °C for 1 week and 1 month; and at -20 °C for 1, 3 and 6 months.

RESULTS

There were no significant differences in the concentrations of EGF, TGF-β1, TGF-β2 and fibronectin in 20% ASE between the SJS and control groups (EGF: 176.9 ± 40.9 vs. 185.5 ± 36.9 pg/mL, TGF-β1: 9.5 ± 2.1 vs. 9.5 ± 1.9 ng/mL, TGF-β2: 55.3 ± 30.0 vs. 63.91 ± 45.6 pg/mL and fibronectin: 70.5 ± 20.2 vs. 62.2 ± 21.3 µg/mL, respectively). These factors were stable at 4 °C for up to 1 month. Storage at -20 °C for up to 6 months resulted in a slight decrease in TGF-β1 (SJS: from 9.5-8.4 ng/mL, p < 0.01 and control: from 9.5-8.1 ng/mL, p < 0.01).

CONCLUSIONS

The results suggested that the epitheliotrophic capacity of ASE from chronic SJS should be comparable to those from non-autoimmune dry eye patients, and that ASE should be sufficiently stable for up to 6 months, if stored properly at -20 °C.

Cytokine and chemokine levels in tears from healthy subjects

PURPOSE

There is growing evidence for the existence of an 'immune tone' in normal tears. The aim of this study was to determine the levels of a large panel of cytokines and chemokines in tears obtained from healthy subjects. These levels can then serve as baseline values for comparison with patients suffering from ocular surface diseases.

SUBJECTS AND METHODS

Nine healthy subjects participated in this study, and normal ocular surface health was documented by the results of a dry eye questionnaire, Schirmer strip wetting, and vital staining of the cornea. Four microliters of tears were collected from each eye and analysed separately with multiplex bead-based assays for the concentration of 30 cytokines and chemokines.

RESULTS

Twenty-five cytokines/chemokines were detected. CCL11/Eotaxin1, GM-CSF, G-CSF, IFN-γ, IL-2, IL-3, IL-4, IL-5, IL-10, IL-13, IL-12p70, IL-15, CX3CL1/Fractalkine, TNF-α, epidermal growth factor, and CCL4/MIP-1β were present at 5-100 pg/ml. IL-1β, IL-6, IL-7A, CXCL8/IL-8, and CCL2/MCP-1 were present at 100-400 pg/ml. IL-1Ra, CXCL10/IP-10 and vascular endothelial growth factor were present at more than 1000 pg/ml.

CONCLUSION

Multiplex bead-based assays are convenient for cytokine/chemokine detection in tears. Fracktalkine has been detected in human healthy tears for the first time. The knowledge of cytokine/chemokine concentrations in tears from normal subjects is an important reference for further comparison with patients suffering from ocular surface diseases. Variability in their levels can reflect a phenomenon of potential importance for the understanding of the ocular surface cytokine pattern.

Immunohistochemical Localization of EGF, TGF-α, TGF-β, and Their Receptors in Rat Corneas During Healing of Excimer Laser Ablation

PURPOSE

Members of the epidermal growth factor (EGF) and transforming growth factor beta (TGF-beta) families of growth factors and receptors are known to regulate key aspects of corneal wound healing, including epithelial migration and scar formation. To further understand their roles, mRNA levels were measured and proteins were immunolocalized in rat corneas at multiple time points during healing of excimer laser ablation injury.

METHODS

Excimer laser photoablation was performed to a depth of 50 microm on rat corneas. Levels of mRNAs for EGF, TGF-alpha, TGF-beta isoforms 1, 2, and 3, and their receptors (EGF-R and TGFbeta-IIR) were measured by quantitative RT-PCR on days 0, 1.5, 7, 21, 42, and 91 after ablation. Immunohistochemical localization of the growth factors and their receptors was performed on days 0, 7, and 21 in corneal sections.

RESULTS

Levels of EGF mRNA remained stable in rat corneas after ablation (68 +/- 12 copies/cell, mean +/- SD), whereas levels of TGF-alpha mRNA progressively increased sixfold to a maximum at day 42 (300 copies/cell) then slightly decreased on day 91. Levels of EGF-R mRNA rapidly increased 60-fold on day 7 compared with day 0 (571 vs. 9 copies/cell) then decreased sixfold above baseline at day 91. Levels of TGF-beta1 mRNA remained stable (36 +/- 10 copies/cell), whereas levels of TGF-beta2 and TGF-beta3 mRNAs peaked on day 21 (300-fold and 25-fold increase) and remained elevated through day 91. Levels of TGFbeta-IIR mRNA showed a similar pattern. Immunostaining of all the growth factors and receptors was primarily in basal layers of epithelial cells in uninjured cornea and during healing. Intensity of immunostaining for TGF-beta1, TGFbeta-IR, and TGFbeta-IIR increased appreciably in the basal epithelial layers after ablation.

CONCLUSIONS

Levels of mRNAs for several key members of the EGF and TGF-beta systems increase during corneal wound healing. In addition, the proteins are primarily localized in basal layers of epithelial cells, which suggest these cells are active in synthesizing autocrine and paracrine growth factors that modulate corneal wound healing.

Growth Factors in the Tear Film: Role in Tissue Maintenance, Wound Healing, and Ocular Pathology

Numerous biologically active growth factors are secreted by the lacrimal gland and distributed via the tears over the ocular surface, where they affect cellular proliferation, migration, differentiation, and survival. The role of growth factors and their receptors in maintenance of tissue homeostasis and wound healing continues to be elucidated, and the effect of growth factor imbalances in ocular surface diseases is just beginning to be understood. For instance, in eyes with ocular surface diseases, including conjunctivitis, corneal erosion, keratitis, and corneal ulcers, epidermal growth factor release rates have been shown to be significantly lower than in normal eyes during reflex tearing. Future research into the mechanisms of dry eye disease will focus on reasons for decreased tear and growth factor production in the neuronal reflex loop or the acinar lacrimal gland cells. Animal models to test therapeutic approaches must be developed.

Transforming growth factor-beta levels in human aqueous humor of glaucomatous, diabetic and uveitic eyes

Purpose

Transforming growth factor-β₂ is known to be present at elevated levels in the aqueous humor of patients with primary open angle glaucoma (POAG) and diabetes but not in uveitis-related secondary glaucoma. We investigated total TGF-β₂ levels and levels of the active form of TGF-β₂ in the aqueous humor of eyes with different types of glaucoma.

Methods

The concentration of the total and active form of TGF-β₂ was measured in 63 patients with primary open angle glaucoma, neovascular glaucoma complicated with diabetes (NVG), and secondary open angle glaucoma complicated with uveitis (SOAG) using a double antibody 'sandwich-indirect' ELISA method.

Results

The levels of total TGF-β₂ in the aqueous samples of POAG, NVG, and SOAG were elevated. The levels of active TGF-β₂ in the aqueous samples of POAG, and NVG were also elevated, whereas the level of active TGF-β₂ was within the normal range in the aqueous samples of SOAG.

Conclusions

These results suggest that the level of TGF-β₂ may play a role in the pathology of various types of glaucoma.

TGFbeta pathobiology in the eye

Transforming growth factor beta (TGFbeta), a multifunctional growth factor, is one of the most important ligands involved in the regulation of cell behavior in ocular tissues in physiological or pathological processes of development or tissue repair, although various other growth factors are also involved. Increased activity of this ligand may induce unfavorable inflammatory responses and tissue fibrosis. In mammals, three isoforms of TGFbeta, that is, beta1, beta2, and beta3, are known. Although all three TGFbeta isoforms and their receptors are present in ocular tissues, lack of TGFbeta2, but not TGFbeta1 or TGFbeta3, perturbs embryonic morphogenesis of the eyes in mice. Smads2/3 are key signaling molecules downstream of cell surface receptors for TGFbeta or activin. Upon TGF binding to the respective TGF receptor, Smads2/3 are phosphorylated by the receptor kinase at the C-terminus, form a complex with Smad4 and translocate to the nucleus for activation of TGFbeta gene targets. Moreover, mitogen-activated protein kinase, c-Jun N-terminal kinase, and p38 modulate Smad signals directly via Smad linker phosphorylation or indirectly via pathway crosstalk. Smad signals may therefore be a critical threrapeutic target in the treatment of ocular disorders related to fibrosis as in other systemic fibrotic diseases. The present paper reviews recent progress concerning the roles of TGFbeta signaling in the pathology of the 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.

Relationship between posterior capsule opacification and intraocular lens biocompatibility

The type of healing process that occurs in response to cataract surgery and intraocular lens (IOL) implantation is dependent on a complex set of variables. Their interactions determine whether or not optical clarity is restored as a result of this procedure. In this process, wound healing entails cells undergoing either epithelial-mesenchymal transition, resulting in the generation of fibroblastic cells and accumulation of extracellular matrix, or lenticular structure formation. Such desperate cellular behaviors are regulated by the localized release of different cytokines, including transforming growth factor beta and fibroblast growth factors, which can result in post-operative capsular opacification. Other factors affecting the biological and mechanical outcome of IOL implantation are its composition, surface properties and shape.

Transforming growth factor-beta2 inhibition of corneal endothelial proliferation mediated by prostaglandin

PURPOSE

To determine the influence of Prostaglandin (PG) E2 on transforming growth factor (TGF)-beta2-mediated inhibitory effects on the proliferation of corneal endothelial cells (CE).

METHODS

The PGE2 and cell proliferation assays were performed using cultured rabbit corneal endothelium. A PGE2-specific enzyme immunoassay was used to check PGE2 synthesis in supernatants of cells cultured with and without added TGF-beta2 and/or indomethacin. To evaluate the inhibitory effects of PGE2 and TGF-beta2 on CE proliferation, the number of cells grown with exogenous PGE2, or TGF-beta2 with or without indomethacin pretreatment was determined.

RESULTS

TGF-beta2, 0.5 to 50 ng/ml, increased the PGE2 secretion of CE dose-dependently in a time-dependent manner. Indomethacin (> or =0.1 microg/ml) inhibited this PGE2 secretion to a low level (around 5-10 ng/ml) in the presence or absence of exogenous TGF-beta2. Both exogenous TGF-beta2 and PGE2 inhibited CE proliferation dose-dependently over a wide range of concentrations. Indomethacin reversed the inhibitory effects of TGF-beta2 but not those of exogenous PGE2. In the medium supplemented with indomethacin, even in the presence of 50 ng/ml of TGF-beta2, CE growth did not differ from control cultures.

CONCLUSIONS

TGF-beta2 stimulates PGE2 synthesis in CE and inhibits CE proliferation in a dose-dependent manner. Indomethacin extinguishes the inhibitory effects of TGF-beta2 on CE proliferation but not the effect of exogenous PGE2. These data suggest that the antiproliferative effects of TGF-beta2 on CE may be possibly due to TGF-beta2-induced synthesis of PG, most likely PGE2.

SUMMARY

Inhibition of endogenous prostaglandins synthesis by indomethacin extinguished the inhibitory effects of Transforming Growth Factor-beta2 on corneal endothelium proliferation but not exogenous prostaglandin E2. It suggesting that TGF-beta2-induced autocrine synthesis of PGs, most likely PGE2, may be responsible for the anti-proliferative effects of TGF-beta2 on corneal endothelium.

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.

Interactions of corneal cells with transforming growth factor β2-modified poly dimethyl siloxane surfaces

The downgrowth of corneal epithelial cells at the interface of an artificial cornea and the host eye tissue poses a significant problem to be overcome in developing a successful implant. As a means of inhibiting the proliferation of corneal epithelial cells on the stromal surface of the implant, we examined the immobilization of transforming growth factor beta-2 (TGF-beta2) via a bifunctional poly ethylene glycol (PEG) spacer to poly dimethyl siloxane (PDMS) surfaces. Growth factor immobilization was confirmed by modification with (125)I-labeled TGF-beta 2. The modified surfaces were also characterized by advancing water contact angles, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Although the amount of growth factor covalently bound to the surface was difficult to quantify apparently due to strong interactions between the growth factor and the PEG layer and high levels of adsorption, differences in the modified surfaces, suggestive of the presence of a significant amount of TGF-beta 2, were found. In vitro interactions of the modified surfaces with human corneal epithelial and stromal cells were examined. Growth factor surface concentrations as well as culture in the absence and presence of serum and other adhesive proteins were examined. Corneal stromal and epithelial cells cultured on the TGF-beta 2-modified surfaces consistently gave results opposite to those expected. Likely, the most notable and surprising result was the almost complete lack of adhesion of the stromal cells, with coverage averaging between 3 and 5%. In comparison, corneal epithelial cell growth appeared to be promoted by the presence of the immobilized growth factor, with cell coverage averaging 50-60% at 7 days of culture. A TGF-beta 2 concentration effect was noted with both cell types in the absence of serum, with increases in the coverage at higher TGF-beta 2 concentrations. The observed cell growth appeared to be the result of interactions between the cells and active growth factor, because the addition of anti-TGF-beta 2 to the culture medium reduced cell coverage to levels similar to those noted on control surfaces. Therefore, although TGF-beta 2-modified surfaces may not be suitable as corneal epithelial cell inhibiting surfaces, interactions of surface immobilized growth factor and corneal cells are complex and should be further examined.

Lens epithelial cell death after cataract surgery

PURPOSE

To determine whether lens epithelial cells (LECs) undergo apoptosis during healing after cataract surgery to further characterize the healing process of the postoperative lens capsule.

SETTING

Department of Ophthalmology, Wakayama Medical University, Wakayama, Japan.

METHODS

Apoptotic cells were detected in human postoperative lens capsules using the terminal deoxynucleotidyl transferase deoxy-UTP nick-end labeling (TUNEL) method. The effect of exogenous transforming growth factor-beta2 (TGF-beta2) on mouse LEC apoptosis was also examined in an organ-culture system.

RESULTS

Three of 17 postoperative specimens contained TUNEL-positive cells. In 2 lens capsules obtained earlier than 10 days, many TUNEL-positive cells, presumably apoptotic LECs, were observed beneath the residual anterior capsule. In cell multilayers in capsule opacification extracted later than 10 days, a few TUNEL-positive cells were seen in 1 specimen; most cells remained negative. In mouse lenses organ-cultured with 1.0 ng/mL TGF-beta2 for 48 hours, TUNEL-positive cells were detected beneath the lens capsule.

CONCLUSIONS

Lens epithelial cells undergo apoptosis during healing after cataract surgery, especially in the early phase. Transforming growth factor-beta2 may be a factor inducing apoptosis in in vivo LECs.

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.

Comparison of TGF-β1 in Tears Following Laser Subepithelial Keratomileusis and Photorefractive Keratectomy

PURPOSE

To compare the release of tear fluid transforming growth factor-beta1 (TGF-beta1) of 15 patients who underwent photorefractive keratectomy (PRK) in one eye and laser subepithelial keratomileusis (LASEK) in the other eye.

METHODS

Tear fluid samples were collected with scaled microcapillary tubes preoperatively (day 0) and on the first, second, and seventh postoperative days. We calculated the release of TGF-beta1 (tear fluid flow-corrected concentrations of TGF-beta1) by multiplying the concentration by capillary tear fluid flow and also evaluated corneal haze at 1, 3, and 6 months after PRK or LASEK.

RESULTS

The median TGF-beta1 release values were: Day 0: 50.6 pg/min (range 0 to 101.6 pg/min) for PRK and 56.7 pg/min (range 0 to 121.8 pg/min) for LASEK (P=.496); Day 1: 240.6 pg/min (range 56.6 to 1120.2 pg/min) for PRK and 155.2 pg/min (range 45.1 to 480.4 pg/min) for LASEK, which showed a significant difference between the two procedures (P=.041); Day 2: 395.7 pg/min (range 92.3 to 1150.7 pg/min) for PRK and 185.2 pg/min (range 41.4 to 872.5 pg/min) for LASEK (P=.004); and Day 7: 91.3 pg/min (range 0 to 225.4 pg/min) for PRK and 74.3 pg/min (range 0 to 187.1 pg/min) for LASEK, (P=.244). The mean corneal haze score at 1 month after PRK was 0.88 +/- 0.50 and 0.53 +/- 0.29 after LASEK, and a statistically significant difference was noted between the two groups (P=.005). At 3 months (P=.083) and 6 months (P=.157) after the procedures, there were no statistically significant differences.

CONCLUSIONS

A lower amount of tear fluid transforming growth factor-beta1 was released in the early postoperative days following LASEK than in PRK. The lower grade of corneal haze seen in LASEK than PRK in the early postoperative period may come from a decreased release of TGF-beta1, which may have a role in wound healing.

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.

Characteristics of the human ocular surface epithelium

An appreciation of the biological characteristics of the human ocular surface epithelium affords us a great insight into the physiology of the human ocular surface in health and disease. Here, we review five important aspects of the human ocular surface epithelium. First, we recognize the discovery of corneal epithelial stem cells, and note how the palisades of Vogt have been suggested as a clinical marker of their presence. Second, we introduce the concept of the gene expression profile of the ocular surface epithelium as arrived at using a new strategy for the systematic analysis of active genes. We also provide a summary of several genes abundantly or uniquely expressed in the human corneal epithelium, namely clusterin, keratin 3, keratin 12, aldehyde dehydrogenase 3 (ALDH3), troponin-I fast-twitch isoform, ssig-h3, cathepsin L2 (cathepsin V), uroplakin Ib, and Ca(2+)-activated chloride channel. Genes related to limbal and conjunctival epithelia are also described. Third, we touch upon the genetic abnormalities thought to be involved with epithelial dysfunction in Meesmann's dystrophy, gelatinous drop-like corneal dystrophy, and the ssig-h3-mutated corneal dystrophies. Fourth, we provide an update regarding the current state of knowledge of the role of cytokines, growth factors and apoptosis in relation to ocular surface homeostasis and tissue reconstruction; the main factors being epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), transforming growth factor-ss (TGF-ss), and some inflammatory cytokines. Fifth, corneal epithelial barrier function and dysfunction as measured by fluorophotometry is remarked upon, with an explanation of the FL-500 fluorophotometer and its ability to detect corneal epithelial dysfunction at a subclinical level. The research described in this review has undoubtedly generated a complete understanding of corneal epithelial pathophysiology-an understanding that, directly or indirectly, has helped advance the development of new therapeutic modalities for ocular surface reconstruction.

Smad translocation and growth suppression in lens epithelial cells by endogenous TGFbeta2 during wound repair

To determine whether endogenous TGFbeta affects lens epithelial cells during repair after an anterior capsule injury in mice, we studied translocation of Smad proteins, which carry the TGFbeta signal from cell surface receptors to promoters in nuclei. We immunolocalized Smads in murine lenses at intervals up to 8 weeks following capsular injury. Effects of injecting TGFbeta neutralizing antibodies on Smad4 location and cell proliferation were examined at 24 hr after injury. Finally, we examined whether exogenous TGFbeta2 induced Smad nuclear translocation in murine lenses in organ culture. Cell proliferation was quantitated by 5-bromo-2'-deoxyuridine (BrdU) labelling. In uninjured lenses, Smads were located in the cytoplasm. In injured lenses, nuclear localization of Smads was observed in cells next to the capsular break from 8 to 24 hr after the injury, and was observed peripheral to the break at 48 hr. Nuclear Smads then continued to be observed occasionally in a minority of cells. Injection of antibodies neutralizing TGFbeta2, but not TGFbeta1 or TGFbeta3, inhibited Smad4 nuclear translocation and resulted in the appearance of BrdU-positive anterior epithelial cells. With the lenses in culture, transient nuclear localization of Smads occurred between 3 and 24 hr in response to continuous exposure to TGFbeta2. No nuclear translocation was seen at 48 hr. Endogenous TGFbeta2 affects lens cells during wound repair after anterior capsule injury, inhibiting lens cell proliferation during the early phase. Nuclear translocation of Smads in lens epithelial cells is transient even with continuous exposure to TGFbeta2.

Transforming growth factor-beta isoform proteins in cell and matrix deposits on intraocular lenses

PURPOSE

To determine whether the cells that adhere to poly(methyl methacrylate) (PMMA) posterior chamber intraocular lenses (PC IOLs) implanted in human eyes produce transforming growth factor-beta (TGF-beta) isoforms and whether the acellular proteinaceous deposits on these IOLs contain TGF-beta.

SETTING

Department of Ophthalmology, Wakayama Medical College, Japan.

METHODS

Thirty-two PMMA PC IOLs explanted from Japanese patients were immunostained for TGF-beta1, -beta2, or -beta3, and observed under light microscopy.

RESULTS

Cell deposits were observed on 12 IOLs and proteinaceous deposits on 16. Components of the cell deposits were mainly of macrophage origin. The cell and matrix deposits tested positive for each isoform of TGF-beta.

CONCLUSION

The cells that adhered to implanted PMMA PC IOLs produced TGF-beta, and the extracellular matrix that accumulated on the surface of the IOLs contained TGF-beta. Transforming growth factor-beta from the cells on IOLs may influence the healing process of residual lens capsules after cataract surgery with IOL implantation.

Growth factors: importance in wound healing and maintenance of transparency of the cornea

The mechanism of corneal wound healing has not been clarified yet. However, evidence has accumulated that various kinds of growth factor such as epidermal growth factor (EGF), fibroblast growth factor (FGF), transforming growth factor (TGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF) play a key role in corneal wound healing. For example, these growth factors are expressed in the corneal epithelial cells, keratocytes and endothelial cells, and their receptors are expressed in the corneal cells. Furthermore, these growth factors promote the proliferation of corneal cells and induce the migration of corneal cells. In addition to the growth factors, inflammatory cytokines such as interleukin (IL)-1, IL-6 and TNF-alpha are involved in corneal wound healing. These cytokines are expressed in the normal and inflammatory cornea after infections, alkaliburn, etc. where they control the growth of corneal cells and induce the migration of corneal cells. Thus, a number of growth factors and cytokines function in the regulation of corneal cell proliferation and in the maintenance of corneal transparency.

Corneal cell proteins and ocular surface pathology

The cornea is a transparent and avascular tissue that functions as the major refractive structure for the eye. A wide variety of growth factors, chemokines, cytokines and their receptors are synthesized by corneal epithelial and stromal cells, and are found in tears. These molecules function in corneal wound healing and in inflammatory responses. Proteoglycans and glycoproteins are essential for normal corneal function, both at the air-epithelial interface and within the extracellular matrix. The ocular MUC mucins may play roles in forming the mucus layer of the tear film, in regulating tear film spread, and in inhibiting the adhesion of pathogens to the ocular surface. Lumican, keratocan and mimecan are the major keratan sulfate proteoglycans of the corneal stroma. They are essential, along with other proteoglycans and interfibrillar proteins, including collagens type VI and XII, for the maintenance of corneal transparency. Corneal epithelial cells interact with a specialized extracellular matrix structure, the basement membrane, composed of a specific subset of collagen type IV and laminin isoforms in addition to ubiquitous extracellular matrix molecules. Matrix metalloprotein-ases have been identified in normal corneal tissue and cells and may play a role in the development of ulcerative corneal diseases. Changes in extracellular matrix molecule localization and synthesis have been noted in other types of corneal diseases as well, including bullous keratopathy and keratoconus.

Transforming growth factor-beta suppresses proliferation of rabbit corneal endothelial cells in vitro

Corneal endothelial cells in vivo appear to be inhibited in G1 phase of the cell cycle. Studies were carried out to determine whether cultured rabbit corneal endothelium expresses transforming growth factor-beta (TGF-beta) receptor types I, II, and III, suggesting they would be sensitive to a TGF-beta-induced signal. In addition, we explored if TGF-beta might mediate this G1 phase inhibition by implementing flow cytometry and 5-bromo-2'-deoxyuridine (BrdU) immunofluorescence. Reverse transcription-polymerase chain reaction (RT-PCR) products of the expected size were obtained for all three TGF-beta receptor types. Flow cytometry revealed a dose-dependent suppression in the percentage of S phase cells in cultures treated with TGF-beta1 or TGF-beta2. The lowest percentage of S phase cells was found for 10 ng/ml TGF-beta1 and 0.1 ng/ml TGF-beta2. BrdU, an S phase marker, was immunolocalized, and semiquantitative analysis of stained cells showed a maximum suppression of S phase entry at 18 h for 10 ng/ml of TGF-beta11 and 24 h for 10 ng/ml of TGF-beta2. In rabbit, the corneal endothelium expresses TGF-beta receptor types I, II, and III, permitting a TGF-beta signal to be transduced. Flow cytometry reveals a dose-dependent response to both TGF-beta1 and TGF-beta2, and the cells are more sensitive to TGF-beta2. At optimal TGF-beta concentrations, the percentage of S phase cells is comparable to that of a non-proliferating culture, suggesting TGF-beta prevents the cells from proceeding through the G1/S phase transition. This suppression was also seen with BrdU labeling. Together, these results indicate that TGF-beta could be one of the pathways that leads to G1 phase arrest in corneal endothelial cells.

Effect of transforming growth factor-beta1 and -beta2 on in vitro rabbit corneal epithelial cell proliferation promoted by epidermal growth factor, keratinocyte growth factor, or hepatocyte growth factor

Corneal epithelial wound healing is intimately controlled by a variety of growth factors, such as epidermal growth factor (EGF), keratinocyte growth factor (KGF), hepatocyte growth factor (HGF), and transforming growth factor-betas (TGF-betas). In this study, we investigate the effects of TGF-beta1 and TGF-beta2 on cultured rabbit corneal epithelial cell proliferation promoted by EGF, KGF, or HGF. Both TGF-beta1 and -beta2 dose-dependently inhibited corneal epithelial cell proliferation promoted by KGF (40 ng ml-1) and HGF (40 ng ml-1), and weakly inhibited cell proliferation promoted by EGF (4 ng ml-1). Furthermore, the inhibitory effect tended to be stronger with TGF-beta2 than TGF-beta1. These findings suggest that TGF-beta1 and -beta2 play important roles as negative modulators against the cell proliferation effect of EGF, KGF and HGF.