Transforming growth factor-beta1 expression in cultured corneal fibroblasts in response to injury

Management of Stromal Corneal Dystrophies; Review of the Literature with a Focus on Phototherapeutic Keratectomy and Keratoplasty

Corneal dystrophies are a group of non-inflammatory inherited disorders of the cornea. This review considers treatment options for epithelial-stromal and stromal corneal dystrophies: namely Reis–Bücklers, Thiel–Behnke, lattice, Avellino, granular, macular and Schnyder corneal dystrophies. Where there is visual reduction, treatment options may include either phototherapeutic keratectomy (PTK) or corneal transplantation. Due to the anterior location of the deposits in Reis-Bücklers and Thiel–Behnke dystrophies, PTK is considered the treatment of choice. For lattice, Avellino, granular and macular corneal dystrophies, PTK provides temporary visual improvement; however, with recurrences, repeat PTK or a corneal transplant would be needed. For Schnyder dystrophy, should treatment be required, PTK may be the preferred option due to the potential for recurrence of the disease in corneal transplantation. This review discusses the literature and evidence base for the treatment of corneal dystrophies in terms of visual outcomes and recurrence rate.

Role of Bone Morphogenetic Protein 7 (BMP7) in the Modulation of Corneal Stromal and Epithelial Cell Functions

In the cornea, healing of the wounded avascular surface is an intricate process comprising the involvement of epithelial, stromal and neuronal cell interactions. These interactions result to the release of various growth factors that play prominent roles during corneal wound healing response. Bone morphogenetic proteins (BMPs) are unique multi-functional potent growth factors of the transforming growth factor-beta (TGF-β) superfamily. Treatment of corneal epithelial cells with substance P and nerve growth factor resulted to an increase in the expression of BMP7 mRNA. Since BMP7 is known to modulate the process of corneal wound healing, in this present study, we investigated the influence of exogenous rhBMP7 on human corneal epithelial cell and stromal cell (SFs) function. To obtain a high-fidelity expression profiling of activated biomarkers and pathways, transcriptome-wide gene-level expression profiling of epithelial cells in the presence of BMP7 was performed. Gene ontology analysis shows BMP7 stimulation activated TGF-β signaling and cell cycle pathways, whereas biological processes related to cell cycle, microtubule and intermediate filament cytoskeleton organization were significantly impacted in corneal epithelial cells. Scratch wound healing assay showed increased motility and migration of BMP7 treated epithelial cells. BMP7 stimulation studies show activation of MAPK cascade proteins in epithelial cells and SFs. Similarly, a difference in the expression of claudin, Zink finger E-box-binding homeobox 1 was observed along with phosphorylation levels of cofilin in epithelial cells. Stimulation of SFs with BMP7 activated them with increased expression of α-smooth muscle actin. In addition, an elevated phosphorylation of epidermal growth factor receptor following BMP7 stimulation was also observed both in corneal epithelial cells and SFs. Based on our transcriptome analysis data on epithelial cells and the results obtained in SFs, we conclude that BMP7 contributes to epithelial-to-mesenchymal transition-like responses and plays a role equivalent to TGF-β in the course of corneal wound healing.

Effects of TGFβ1, PDGF-BB, and bFGF, on human corneal fibroblasts proliferation and differentiation during stromal repair

In an effort to improve the regenerative nature of corneal repair, this study reports the use of an in vitro human corneal fibroblasts (HCFs) wound model after treatment with three of the main growth factors (GFs) involved in corneal healing: transforming growth factor beta 1 (TGFβ1), platelet-derived growth factor BB-isoform (PDGF-BB), and basic fibroblast growth factor (bFGF) in order to delve in cell proliferation and differentiation processes. HCFs were mechanically wounded. The individual effect of TGFβ1, PDGF-BB, and bFGF on cell proliferation and differentiation during the repair process was studied at different time points until wound closure. Wound dimensions and morphological changes were evaluated by microscopy. Cell proliferation and myofibroblast differentiation were analyzed by immunofluorescence cytochemistry. Changes in cell morphology were apparent at Day 4. PDGF-BB- and bFGF-treated cells had fibroblast-like morphology. TGFβ1 stimulated proliferation in the wound edge and surrounding area, induced myofibroblast differentiation and inhibited cellular migration. PDGF-BB induced rapid wound closure due to proliferation, high motility, and late myofibroblast differentiation. The time course of closure induced by bFGF was similar to that for PDGF-BB, but was mostly due to proliferation in the wound area, and inhibited myofibroblast differentiation. Each of the GFs induced increases in responses promoting stromal repair differently. This study provides insight regarding how to optimize the outcome of stromal repair following corneal injury.

Contribution of TGFβ1 codon 10 polymorphism to high myopia in an ethnic Kashmiri population from India

This study looks at novel variants of the TGFβ1 gene and their potential association with high myopia in an ethnic population from Kashmir, India. Allele frequencies of 247 Kashmiri subjects (from India) with high myopia and 176 ethnically matched healthy controls were tested for Hardy-Weinberg disequilibrium. The genotype and allele frequencies were evaluated using chi-square or Fisher's exact tests. One of the three SNPs in codon 10 showed a significant difference between patients and control subjects (rs1982073: p genotype = 0.003, p allele = 0.001). There were no statistically significant differences between patients and control subjects for the other two SNPs, rs1800471 at codon 25 and a novel variant at codon 52. SNP rs1982073, substituting proline with leucine, appeared to be significantly associated with high myopia (p < 0.05). In silico predictions show that substitutions are likely to have an impact on the structure and functional properties of the protein, making it imperative to understand their functional consequences in relation to high myopia.

JNK1/2 siRNA inhibits transforming-growth factor-beta1-induced connective tissue growth factor expression and fibrotic function in THSFs

Transforming-growth factor-beta1 (TGF-beta1) plays an important role in fibrosis by inducing connective tissue growth factor (CTGF) expression. In cornea, however, signaling pathway in the process is unclear. In this paper, real-time RT-PCR and Western blot analysis were used to examine the expression and TGF-beta1-induced upregulation of CTGF in telomerase-immortalized human cornea stroma fibroblast cells (THSFs). A detailed molecular mechanism for TGF-beta1-mediated cell proliferation and collagen I production was then investigated by detecting the activation of JNK pathway in TGF-beta1-stimulated THSFs and blocking the JNK pathway using JNK1/2 siRNA. Both TGF-beta1 and CTGF clearly induced cell proliferation in THSFs which was inhibited by functional blocking CTGF by anti-CTGF antibody. Blocking JNK pathway by JNK1/2 siRNA significantly inhibited induction of CTGF by TGF-beta1. Taken together, the data indicate that CTGF is critical to the fibrosis process in wounded human cornea, acting via upregulation and activation of JNK signaling pathway.

VEGF regulates FGF-2 and TGF-beta1 expression in injury endothelial cells and mediates smooth muscle cells proliferation and migration

BACKGROUND

Vascular endothelial growth factor (VEGF) is implicated in the development of restenosis after percutaneous transluminal coronary angioplasty (PTCA) as well as atherosclerosis. The purpose of our study was: 1) to evaluate the expression of endothelial cell (EC) fibroblast growth factor 2 (FGF-2) and transforming growth factor beta1 (TGF-beta1) mRNA expression following vascular injury and VEGF modulation and 2) to assess whether VEGF indirectly stimulates smooth muscle cell (SMC) migration and proliferation via growth factors released by injured EC.

METHODS

Bovine aortic endothelial cells (BAEC) were cultured to near confluency and were serum starved. Linear wounds were made in medium with and without VEGF. FGF-2 and TGF-beta1 mRNA expression were evaluated. Bovine aortic organ culture experiments were also carried out and growth factor expression was assessed. SMC proliferation and migration was assessed in response to EC injury medium with/without VEGF.

RESULTS

EC injury in the presence of VEGF increased FGF-2 mRNA. EC injury also induced TGF-beta1 mRNA expression; however VEGF inhibited TGF-beta1 mRNA expression in both injured and noninjured ECs. VEGF increased FGF-2 mRNA stability and did not alter TGF-beta1 mRNA stability. SMC proliferation and migration was found to be induced by injured EC media and injury EC medium with VEGF, respectively

CONCLUSIONS

The results demonstrate that 1) VEGF indirectly stimulates SMC proliferation and migration through stimulation of the expression of FGF-2 and 2) VEGF inhibits the expression of TGF-beta1 released by EC. Theses data further suggest an integral role for FGF-2 and TGF-beta1 in wound repair.

Exacerbation of granular corneal dystrophy type II (Avellino corneal dystrophy) after LASEK

PURPOSE

To report cases of granular corneal dystrophy type II (Avellino corneal dystrophy) that were exacerbated by uncomplicated laser epithelial keratomileusis (LASEK) for myopia.

METHODS

Eight patients (15 eyes) with granular corneal dystrophy type II who underwent LASEK were examined by DNA sequencing, slit-lamp microscopy, and confocal microscopy.

RESULTS

The number and density of the opacities increased after LASEK. Best spectacle-corrected visual acuity decreased after LASEK as the density of the opacities increased. In three patients, mitomycin C was used intraoperatively, but corneal deposits also worsened in these patients.

CONCLUSIONS

LASEK is contraindicated in patients with granular corneal dystrophy type II because vision may be reduced from an increase in the density of corneal opacities postoperatively.

Homozygous granular corneal dystrophy type II (Avellino corneal dystrophy): natural history and progression after treatment

PURPOSE

To describe the clinical features of homozygous granular corneal dystrophy type II (GCDII) with age and with several kinds of treatment in 18 homozygous patients in several different conditions.

METHODS

Eighteen homozygous GCDII patients, confirmed with DNA analysis, of 13 families were enrolled. Their clinical features that include age at detection by parents, visual acuity, and disease progression were evaluated. We also studied the recurrence patterns for the 13 patients who underwent phototherapeutic keratectomy, penetrating keratoplasty, lamellar keratoplasty, or deep lamellar keratoplasty.

RESULTS

The age at detection by the parents ranged from 3 to 5 years; visual loss begins in childhood with progression into the 20s. All of the patients who had undergone surgeries acquired better vision immediately after surgery. Corneal deposits reappeared soon after treatments. Recurrences became progressively more rapid and severe with treatments.

CONCLUSIONS

The clinical features of homozygous GCDII are characterized by a severe granular type of corneal dystrophy with an early onset and rapid progression. After surgical treatment, recurrence is rapid and severe.

Exclusion of Transforming Growth Factor-b1 as a Candidate Gene for Myopia in the Japanese

PURPOSE

To determine whether single-nucleotide polymorphisms (SNPs) within the transforming growth factor-beta1 (TGF-beta1) gene are associated with high myopia in Japanese. Previous studies have indicated that the gene expression products, regulators of the TGF-beta1 gene, are involved in high myopia.

METHODS

Genomic DNA samples were obtained from 330 Japanese patients with high myopia and 330 Japanese controls without high myopia who were chosen at random. SNPs were genotyped by the TaqMan system, using primer extension and polymerase chain reaction amplification.

RESULTS

Ten SNPs were identified in the high-myopia patients and controls, with four of the ten SNPs having nonsynonymous changes. However, no statistical differences in the SNPs were detected between the high-myopia cases and the controls.

CONCLUSIONS

Sequence variants of the TGF-beta1 gene were not associated significantly with high myopia, and further studies are needed to identify which genes are responsible for high myopia.

Ocular delivery of nucleic acids: antisense oligonucleotides, aptamers and siRNA

Nucleic acids have gained a lot of interest for the treatment of ocular diseases. The first to enter in clinic has been Vitravene an antisense oligonucleotide for the treatment of cytomegalovirus (CMV) infection and more recently, research on aptamers have led to the marketing of anti-vascular endothelial growth factor (VEGF) inhibitor (Macugen) for the treatment of age-related macular degeneration (AMD). The siRNAs appear very promising as they are very potent inhibitors of protein expression. Despite their potential, nucleic acids therapeutic targets of nucleic acid-based drugs are mainly located in the posterior segment of the eye requiring invasive administration which can be harmful if repeated. Their intracellular penetration in some cases needs to be enhanced. This is the reason why adequate delivery systems were designed either to insure cellular penetration, protection against degradation or to allow long-term delivery. A combination of both effects was also developed for an implantable system. In conclusion, the intraocular administration of nucleic acids offers interesting perspectives for the treatment of ocular diseases.

Exacerbation of Avellino corneal dystrophy after LASIK in North America

PURPOSE

To report the first case of Avellino corneal dystrophy exacerbation after LASIK in a white or North American patient.

METHODS

Case report and literature review.

RESULTS

A 25-year-old white female developed progressive corneal opacities after LASIK. Preoperative examination had revealed only subtle white corneal opacities in each eye. The patient's mother had similar corneal opacities. DNA analysis of the patient revealed a heterozygous mutation at the R124H location in the BIGH3 gene.

CONCLUSIONS

LASIK can exacerbate Avellino corneal dystrophy and should be avoided in patients with this condition. A careful history and genetic analysis can identify affected patients and those at risk.

Effects of topical tranilast on corneal haze after photorefractive keratectomy

PURPOSE

To determine whether topical tranilast might reduce corneal haze through suppression of transforming growth factor (TGF)-beta1 synthesis in keratocyte after photorefractive keratectomy.

SETTING

Department of Ophthalmology, Korea University College of Medicine, Seoul, Republic of Korea.

METHODS

Photorefractive keratectomy was performed on 48 eyes of 28 white rabbits and 24 eyes in a tranilast group were treated with tranilast solution, and the other 24 eyes in control group were treated with saline after laser ablation. The grades of corneal haze at 1, 2, 4, and 8 weeks after surgery were evaluated in 10 eyes of each group for comparison. Immunohistochemistry was performed on 10 eyes of each group, and Western blot analysis was done on 4 eyes of each group for studying TGF-beta1 expression at postoperative day 7.

RESULTS

There was no statistically significant difference in corneal haze between 2 groups from week 1 to week 4 after surgery, but a significant difference was found at week 8 after photorefractive keratectomy (P=.02). The mean number of keratocytes that expressed TGF-beta1 in the tranilast group was 58.3 (+/-17.2), which showed significant difference, compared with that of the control group, 104.5 (+/-23.0) (P<.01). Western blot analysis also revealed that the amount of TGF-beta1 in tranilast group was slightly less than the control group.

CONCLUSIONS

Topical tranilast could reduce corneal haze by suppressing TGF-beta1 expression in keratocytes after photorefractive keratectomy.

Cellular injury induces activation of MAPK via P2Y receptors

Wound healing is a complex process that involves cell communication, migration, proliferation, and changes in gene expression. One of the first events after injury is the rapid release of Ca(2+) that propagates as a wave to neighboring cells (Klepeis et al. [2001]: J. Cell. Sci. 114:4185-4195). Our goal was to examine the signaling events induced by cellular injury and identify extracellular molecules that induce the activation of extracellular signal responsive kinase (ERK) (p42/44). In this study we demonstrated that injury induced ERK1/2 activation occurred within 2 min and was negligible by 15 min. Treatment of unwounded cells with wound media caused activation of ERK that could be inhibited by apyrase III. Stimulation with epidermal growth factor (EGF) did not mimic the injury response and it was not detected in the wound media. To identify the active component, size fractionation was performed and factor(s) less than 3 kDa that induced the release of Ca(2+) and activation of ERK1/2 were identified. Activity was not altered by heat denaturation, incubation with proteinase K but it was lost by treatment with apyrase. Adenosine triphosphate (ATP), uridine triphosphate (UTP), adenosine diphosphate (ADP), and uridine diphosphate (UDP) promoted activation by 2 min with similar profiles as that generated by injury. Preincubation with phospholipase C inhibitor, U73122, inhibited activation that was induced by injury and/or nucleotides. Lack of activation by alpha-beta-methylATP (alpha, beta-MeATP) and beta-gamma-methylATP (beta, gamma-MeATP) to purinergic (P)2X receptors further indicated that activation occurs via P2Y and not P2X purinergic receptors. These results indicate that injury-induced activation of ERK1/2 is mediated by a P2Y signaling pathway.

PAI-1 expression is required for epithelial cell migration in two distinct phases of in vitro wound repair

Several proteases and their specific inhibitors modulate the interdependent processes of cell migration and matrix proteolysis as part of the global program of trauma repair. Expression of plasminogen activator inhibitor type-1 (PAI-1), a serine protease inhibitor (SERPIN) important in the control of barrier proteolysis and cell-to-matrix adhesion, for example, is spatially-temporally regulated following epithelial denudation injury in vitro as well as in vivo. PAI-1 mRNA/protein synthesis was induced early after epidermal monolayer scraping and restricted to keratinocytes comprising the motile cohort closely recapitulating, thereby, similar events during cutaneous healing. The time course of PAI-1 promoter-driven PAI-1-GFP fusion "reporter" expression in wound-juxtaposed cells approximated that of the endogenous PAI-1 gene confirming the location-specificity of gene regulation in this model. ERK activation was evident within 5 min after injury and particularly prominent in cells residing at the scrape-edge (suggesting a possible role in PAI-1 induction and/or the motile response) as was myosin light chain (MLC) phosphorylation. Indeed, MEK blockade with PD98059 or U0126 attenuated keratinocyte migration (by > or =60%), as did transient transfection of a dominant-negative ERK1 construct (40% decrease in monolayer repair), and completely inhibited PAI-1 transcript expression. Anti-sense down-regulation of PAI-1 synthesis (by 80-85%), or addition of PAI-1 neutralizing antibodies also inhibited injury site closure over a 24 h period establishing that PAI-1 was required for efficient long-term planar motility in this system. PAI-1 anti-sense transfection or actinomycin D transcriptional blockade, in contrast, did not affect the initial migratory response suggesting that residual PAI-1 protein levels (at least in transfectant cells and actinomycin D-treated cultures) may be sufficient to support early cell movement. Pharmacologic inhibition of keratinocyte MEK signaling effectively ablated scrape-induced PAI-1 mRNA expression but failed to attenuate wound-associated increases in cellular PAI-1 protein levels soon after monolayer injury. Collectively, these data suggest that basal PAI-1 transcripts may be mobilized for initial PAI-1 synthesis and, perhaps, the early motile response while maintenance of the normal rate of migration requires the prolonged PAI-1 expression that typically accompanies the repair response. To assess this possibility, scrape site closure studies were designed using keratinocytes isolated from PAI-1-/- mice. PAI-1-/- keratinocytes, in fact, had a significant wound healing defect evident even within the first 6 h following monolayer denudation injury. Addition of active PAI-1 protein to PAI-/- keratinocytes rescued the migratory phenotype that that approximating wild-type cells. These findings validate use of the present keratinocyte model to investigate injury-related controls on PAI-1 gene regulation and, collectively, implicate participation of PAI-1 in two distinct phases of epidermal wound repair.

Overexpression of HER2 (erbB2) in Human Breast Epithelial Cells Unmasks Transforming Growth Factor β-induced Cell Motility

We have examined overexpression of the human epidermal growth factor receptor 2 (HER2) to determine if it modifies the anti-proliferative effect of transforming growth factor (TGF)-beta against MCF-10A human mammary epithelial cells. Exogenous TGF-beta inhibited cell proliferation and induced Smad-dependent transcriptional reporter activity in both MCF-10A/HER2 and MCF-10A/vector control cells. Ligand-induced reporter activity was 7-fold higher in HER2-overexpressing cells. In wound closure and transwell assays, TGF-beta induced motility of HER2-transduced, but not control cells. The HER2-blocking antibody trastuzumab (Herceptin) prevented TGF-beta-induced cell motility. Expression of a constitutively active TGF-beta type I receptor (ALK5(T204D)) induced motility of MCF-10A/HER2 but not MCF-10A/vector cells. TGF-beta-induced motility was blocked by coincubation with either the phosphatidylinositol 3-kinase inhibitor LY294002, the mitogen-activated protein kinase (MAPK) inhibitor U0126, the p38 MAPK inhibitor SB202190, and an integrin beta(1) blocking antibody. Rac1 activity was higher in HER2-overexpressing cells, where both Rac1 and Pak1 proteins were constitutively associated with HER2. Both exogenous TGF-beta and transduction with constitutively active ALK5 enhanced this association. TGF-beta induced actin stress fibers as well as lamellipodia within the leading edge of wounds. Herceptin blocked basal and TGF-beta-stimulated Rac1 activity but did not repress TGF-beta-stimulated transcriptional reporter activity. These data suggest that 1) overexpression of HER2 in nontumorigenic mammary epithelial is permissive for the ability of TGF-beta to induce cell motility and Rac1 activity, and 2) HER2 and TGF-beta signaling cooperate in the induction of cellular events associated with tumor progression.

Isoform-specific Changes in Scleral Transforming Growth Factor-β Expression and the Regulation of Collagen Synthesis during Myopia Progression

The development of high myopia is associated with altered scleral extracellular matrix biochemistry. Previous studies highlight the importance of collagen turnover in this process, yet it is unclear which factors control scleral remodeling. This study used a mammalian model of myopia to investigate the capacity of TGF (transforming growth factor)-beta1, -beta2, and -beta3 to influence scleral remodeling in myopia. RT-PCR confirmed the presence of all mammalian TGF-beta isoforms in scleral tissue and scleral fibroblasts. Myopia was experimentally induced via monocular deprivation of pattern vision, and animals were allocated to two groups depending on the duration of treatment (1 or 5 days). Down-regulation of each isoform was apparent after only 1 day of myopia development (TGF-beta1, -32%; TGF-beta2, -27%; TGF-beta3, -42%). Whereas the decrease in TGF-beta1 and -beta3 expression was relatively constant between the two time points, differential down-regulation of TGF-beta2 was found between days 1 (-27%) and 5 (-50%). In vitro experiments, using primary scleral fibroblasts, demonstrated the capacity of all isoforms to increase collagen production in a dose-dependent manner. Changes in TGF-beta levels, which mimicked those during myopia induction, caused an approximately 15% reduction in collagen synthesis, which is qualitatively similar to those previously reported in vivo. These data represent the first demonstration of TGF-beta3 expression in the sclera and implicate all three TGF-beta isoforms in the control of scleral remodeling during myopia development. In addition, the early alterations in TGF-beta expression levels may reflect a role for these cytokines in mediating the retinoscleral signal that controls myopic eye growth.

Insulin-like growth factor-I (IGF-I) and transforming growth factor-beta (TGF-beta) modulate tenascin-C and fibrillin-1 in bullous keratopathy stromal cells in vitro

PURPOSE

Pseudophakic bullous keratopathy (PBK) is a major indication for corneal transplantation. Previous studies showed that PBK corneas had increased levels of insulin-like growth factor-I (IGF-I), bone morphogenetic protein-4 (BMP-4), transforming growth factor-beta (TGF-beta), interleukin-1alpha (IL-1alpha) and IL-8. The PBK corneas also had accumulations of tenascin-C (TN-C), fibrillin-1 (Fib-1), matrix metalloproteinase-2 (MMP-2), inflammatory cells but not myofibroblasts. Our goal is to determine if the growth factors/cytokines that are elevated in PBK corneas alter the expression of extracellular matrix (ECM) and/or degradative enzymes in vitro.

METHODS

Stromal cell cultures from normal and PBK human corneas were established and treated for 6 days with IGF-I, BMP-4, IL-1alpha, IL-8 or TGF-beta1/beta2. Immunostaining, Western blot and dot blot analyses for TN-C, Fib-1, alpha-smooth muscle actin (alpha-SMA, a marker for myofibroblasts) or tissue inhibitor of metalloproteinase-1 (TIMP-1) were performed. RNAs were collected and analyzed with Northern blots for TN-C, Fib-1 and beta(2)-microglobulin. Culture media were analyzed using gelatin zymography with or without ethylenediaminetetraacetic acid (EDTA). Some samples were activated with p-aminophenylmercuric acetate (APMA) and reduction/alkylation, and the degradative activities were measured by the MMP-gelatinase activity assay kit.

RESULTS

The IGF-I and TGF-beta1/TGF-beta2 increased (a) TN-C protein deposition, and (b) Fib-1 protein and RNA levels, but (c) had no significant affect on TIMP-1, matrix metalloproteinase-2 (MMP-2) or gelatinase activities. TGF-beta1/TGF-beta2 induced alpha-SMA protein (myofibroblasts) while IGF-I did not. BMP-4, IL-1alpha and IL-8 had little affect on the cells.

CONCLUSIONS

Based upon our data, the fibrotic markers, TN-C and Fib-1, found in PBK corneas may be accounted for by IGF-I and TGF-beta. These growth factors promote fibrosis and ECM deposition without promoting proteolysis. While the other growth factors/cytokines are elevated in PBK corneas, their role(s) in PBK pathogenesis are not clear. In addition, exogenous IGF-I most closely elicited a response that was most similar to the characteristics of the PBK/ABK corneas, i.e. accumulation of TN-C and Fib-1 proteins in the absence of myofibroblasts.

Role of epidermal growth factor and epidermal growth factor receptor on hemidesmosome complex formation and integrin subunit beta4

Epidermal growth factor (EGF) stimulates integrin beta4 expression and synthesis in corneal epithelium through ligand binding to the EGF receptor, receptor dimerization and activation of the intracellular domain. We hypothesized that inhibition of EGF receptor messenger RNA (mRNA) would block integrin beta4 expression, which is induced by EGF. We also tested the hypothesis that EGF would cause the degradation of hemidesmosomes in control and injured corneal organ cultures. Primary rabbit corneal epithelial cell cultures or corneas were cultured in keratinocyte medium in the presence or absence of an antisense 20-mer phosphorothioate oligonucleotide complementary to the initiation codon region of EGF receptor mRNA. Cells were also cultured in the presence or absence of EGF. Sense and scrambled oligonucleotides similarly modified were used as controls. The concentration of EGF receptor mRNA was semiquantitatively determined by reverse transcriptase/polymerase chain reaction (RT-PCR). We found that transfection did inhibit EGFR expression and migration of epithelial cells and also demonstrated that EGFR mediated expression of integrin beta4 mRNA. Injury induced a decrease in hemidesmosomes that was enhanced with EGF but was not caused by the presence of growth factor in unwounded tissue. These results indicate that injury causes the activation of EGFR but that EGF alone is not responsible for the degradation of hemidesmosomes and that other growth factors play a role in the complex repair of wounds in an avascular tissue.

Macrophages and post-burn immune dysfunction

The activation of a pro-inflammatory cascade after burn injury appears to be important in the development of subsequent immune dysfunction, susceptibility to sepsis and multiple organ failure. Macrophages are major producers of pro-inflammatory mediators and their productive capacity for these mediators is markedly enhanced following thermal injury. Thus, macrophage hyperactivity (as defined by increased productive capacity for pro-inflammatory mediators) appears to be of critical importance in the development of post-burn immune dysfunction. This review will focus on the current state of knowledge with regards to the role of macrophages in the development of post-burn immune dysfunction. Particular areas of discussion include: nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems, macrophages and the T-helper (Th)-1/Th-2 cytokine responses, alterations in macrophages signal transduction and a potential role for gamma/delta T-cells in the development of macrophage hyperactivity following thermal injury. A more comprehensive understanding of the relationship between macrophage activity and post-burn immune dysfunction will hopefully provide the basis for improved therapeutic regimes in the treatment of burn patients.

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.

Epithelial monolayer wounding stimulates binding of USF-1 to an E-box motif in the plasminogen activator inhibitor type 1 gene

Several proteases and their co-expressed inhibitors modulate the interdependent processes of cell migration and matrix proteolysis during wound repair. Transcription of the gene encoding plasminogen activator inhibitor type 1 (PAI-1), a serine protease inhibitor important in the control of barrier proteolysis and cell-to-matrix adhesion, is spatially-temporally regulated following epithelial denudation injury in vitro as well as in vivo. Using a well-defined culture model of acute epidermal wounding and reepithelialization, PAI-1 mRNA/protein synthesis was induced early after monolayer scraping and restricted to cells comprising the motile cohort. PAI-1 levels in locomoting cells remained elevated (relative to the distal, contact-inhibited monolayer regions) throughout the time course of trauma repair. Targeted PAI-1 downregulation by transfection of antisense PAI-1 expression constructs significantly impaired keratinocyte migration and monolayer scrape wound closure. Injury-induced PAI-1 transcription closely paralleled growth state-dependent controls on the PAI-1 gene. An E-box motif (CACGTG) in the PAI-1 proximal promoter (located at nucleotides -160 to -165), previously shown to be necessary for serum-induced PAI-1 expression, was bound by nuclear factors from wound-stimulated but not quiescent, contact-inhibited, keratinocytes. UV crosslinking approaches to identify E-box-binding factors coupled with deoxyoligonucleotide affinity chromatography and gel retardation assays confirmed at least one major E-box-binding protein in both serum- and wound-activated cells to be USF-1, a member of the helix-loop-helix family of transcription factors. An intact hexanucleotide E-box motif was necessary and sufficient for USF-1 binding using nuclear extracts from both serum- and wound-simulated cells. Two species of immunoreactive USF-1 were identified by western blotting of total cellular lysates that corresponded to the previously characterized phosphorylated and non-phosphorylated forms of the protein. USF-1 isolated by PAI-1 promoter-DNA affinity chromatography was almost exclusively phosphorylated. Only a fraction of the total cellular USF-1 in proliferating cultures, by comparison, was phosphorylated at any given time. PAI-1 E-box binding activity, assessed by probe mobility shift criteria, increased within 2 hours of monolayer scrape injury, a time frame consistent with wound-stimulated increases in PAI-1 transcription. Relative to intact cultures, scrape site-juxtaposed cells had significantly greater cytoplasmic and nuclear USF-1 immunoreactivity correlating with the specific in situ-restricted expression of PAI-1 transcripts/protein in the wound-edge cohort. USF-1 immunocytochemical staining declined significantly with increasing distance from the denudation site. These data are the first to indicate that binding of USF-1 to its target motif can be induced by 'tissue' injury in vitro and implicate USF-1 as a transcriptional regulator of genes (e.g. PAI-1) involved in wound repair.

Fibrodysplasia ossificans progressiva and corneal keloid

PURPOSE

To report on the formation of a corneal keloid in a patient with fibrodysplasia ossificans progressiva after excision of a pterygium-like lesion.

METHODS

Clinical and pathophysiological observations and hypothesis concerning pathophysiological mechanisms.

RESULTS

An 11-year-old boy with fibrodysplasia ossificans progressiva presented with progressive development of a growing white scar in the central part of the left cornea after excision of a pterygium-like lesion.

DISCUSSION

To the best of our knowledge, this is the first case report of a corneal keloid formation in a patient with fibrodysplasia ossificans progressiva. Pathophysiological mechanisms are considered. Therapeutic options are discussed.

TGF-beta1 regulates TGF-beta1 and FGF-2 mRNA expression during fibroblast wound healing

AIMS

To evaluate the expression of transforming growth factor beta1 (TGF-beta1) and fibroblast growth factor 2 (FGF-2) mRNA in stromal cells in response to injury in the presence of either TGF-beta1 or FGF-2. It has been shown previously that heparan sulfate proteoglycans and FGF-2 are present transiently during wound repair in vivo and that an increase in TGF-beta1 mRNA is detected rapidly after injury.

METHODS

Primary corneal fibroblasts were cultured to confluency, serum starved, and linear wound(s) were made in medium containing TGF-beta1 or FGF-2. TGF-beta1 and FGF-2 mRNA expression were evaluated using both northern blot analysis and in situ hybridisation. Both dose dependent and time course experiments were performed. Whole eye organ culture experiments were also carried out and growth factor expression was assessed.

RESULTS

Injury and exogenous TGF-beta1 increased TGF-beta1 mRNA values. The increase in expression of FGF-2 mRNA was not detected until wound closure. In contrast, FGF-2 inhibited the expression of TGF-beta1. TGF-beta1 increased TGF-beta1 mRNA stability but did not alter that of FGF-2. Migration assay data demonstrated that unstimulated stromal cells could be activated to migrate to specific growth factors.

CONCLUSIONS

TGF-beta1 specifically enhances cellular responsiveness, as shown by increased stability after injury and the acquisition of a migratory phenotype. These data suggest that there is an integral relation during wound repair between TGF-beta1 and FGF-2.

Approaches to studying cellular signaling: a primer for morphologists

Many research projects will lead to understanding tissue and/or cell responses to extracellular influences either from soluble factors or the surrounding extracellular matrix. These types of investigations will require the understanding of signal transduction. This particular cell biological field has literally exploded with information and new technical approaches in the past 10 years. This article is directed toward investigators interested in using these new approaches to study their systems. An overview of the general principles of signal transduction events including the types of receptors and intracellular signaling events is followed by an introduction to methods for visualizing signal transduction. This is followed by an introduction to biochemical analysis and an example of combining several approaches to understanding a tissue response to extracellular matrix stimulus.

Growth factors but not gap junctions play a role in injury-induced Ca2+ waves in epithelial cells

This paper characterizes the early responses of epithelial cells to injury. Ca2+ is an important early messenger that transiently increases in the cytoplasm of cells in response to external stimuli. Its elevation leads to the regulation of signaling pathways responsible for the downstream events important for wound repair, such as cell migration and proliferation. Live cell imaging in combination with confocal laser scanning microscopy of fluo-3 AM loaded cells was performed. We found that mechanical injury in a confluent region of cells creates an elevation in Ca2+ that is immediately initiated at the wound edge and travels as a wave to neighboring cells, with [Ca2+]i returning to background levels within two minutes. Addition of epidermal growth factor (EGF), but not platelet-derived growth factor-BB, resulted in increased [Ca2+]i, and EGF specifically enhanced the amplitude and duration of the injury-induced Ca2+ wave. Propagation of the Ca2+ wave was dependent on intracellular Ca2+ stores, as was demonstrated using both thapsigargin and Ca2+ chelators (EGTA and BAPTA/AM). Injury-induced Ca2+ waves were not mediated via gap junctions, as the gap-junction inhibitors 1-heptanol and 18α-glycyrrhetinic acid did not alter wave propagation, nor did the cells recover in photobleaching experiments. Additional studies also demonstrated that the wave could propagate across an acellular region. The propagation of the injury-induced Ca2+ wave occurs via diffusion of an extracellular mediator, most probably via a nucleotide such as ATP or UTP, that is released upon cell damage.

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Proteoglycan expression during transforming growth factor beta -induced keratocyte-myofibroblast transdifferentiation

Keratocytes of the corneal stroma secrete a unique population of proteoglycan molecules considered essential for corneal transparency. In healing corneal wounds, keratocytes exhibit a myofibroblastic phenotype in response to transforming growth factor beta (TGF-beta), characterized by expression of alpha-smooth muscle actin. This study examined proteoglycan and collagen expression by keratocytes in vitro during the TGF-beta-induced keratocyte-myofibroblast transition. TGF-beta-treated primary bovine keratocytes developed myofibroblastic features, including actin stress fibers anchored to paxillin-containing focal adhesions, cell-associated fibronectin, alpha(5) integrin, and alpha-smooth muscle actin. Collagen I and III protein and mRNA increased in response to TGF-beta. Secretion of [(35)S]sulfate-labeled keratan sulfate proteoglycans decreased markedly in response to TGF-beta. Dermatan sulfate proteoglycans, however, increased in size and abundance. Protein and mRNA transcripts for normal stromal proteoglycans (lumican, keratocan, mimecan, and decorin) all decreased in response to TGF-beta, but protein expression and mRNA for biglycan, a proteoglycan present in fibrotic tissue, was markedly up-regulated. These results show that TGF-beta in vitro induces a proteoglycan expression pattern similar to that of corneal scars in vivo. This altered proteoglycan expression occurred coordinately with transdifferentiation of keratocytes to the myofibroblastic phenotype, implicating these cells as the source of fibrotic tissue in nontransparent corneal scars.

TGF-β1-induced PAI-1 gene expression requires MEK activity and cell-to-substrate adhesion

The type-1 inhibitor of plasminogen activator (PAI-1) is an important physiological regulator of extracellular matrix (ECM) homeostasis and cell motility. Various growth factors mediate temporal changes in the expression and/or focalization of PAI-1 and its protease target PAs, thereby influencing cell migration by barrier proteolysis and/or ECM adhesion modulation. TGF-β1, in particular, is an effective inducer of matrix deposition/turnover, cell locomotion and PAI-1 expression. Therefore, the relationship between motility and PAI-1 induction was assessed in TGF-β1-sensitive T2 renal epithelial cells. PAI-1 synthesis and its matrix deposition in response to TGF-β1 correlated with a significant increase in cell motility. PAI-1 expression was an important aspect in cellular movement as PAI-1-deficient cells had significantly impaired basal locomotion and were unresponsive to TGF-β1. However, the induced migratory response to this growth factor was complex. TGF-β1 concentrations of 1-2 ng/ml were significantly promigratory, whereas lower levels (0.2-0.6 ng/ml) were ineffective and final concentrations ≥5 ng/ml inhibited T2 cell motility. This same growth factor range progressively increased PAI-1 transcript levels in T2 cells consistent with a bifunctional role for PAI-1 in cell migration. TGF-β1 induced PAI-1 mRNA transcripts in quiescent T2 cells via an immediate-early response mechanism. Full TGF-β1-stimulated expression required tyrosine kinase activity and involved MAPK/ERK kinase (MEK). MEK appeared to be a major mediator of TGF-β1-dependent PAI-1 expression and T2 cell motility since PD98059 effectively attenuated both TGF-β1-induced ERK1/2 activation and PAI-1 transcription as well as basal and growth factor-stimulated planar migration. Since MEK activation in response to growth factors is adhesion-dependent, it was important to determine whether cellular adhesive state influenced TGF-β1-mediated PAI-1 expression in the T2 cell system. Cells maintained in suspension culture (i.e., over agarose underlays) in growth factor-free medium or treated with TGF-β1 in suspension expressed relatively low levels of PAI-1 transcripts compared with the significant induction of PAI-1 mRNA evident in T2 cells upon stimulation with TGF-β1 during adhesion to a fibronectin-coated substrate. Attachment to fibronectin alone (i.e., in the absence of added growth factor) was sufficient to initiate PAI-1 transcription, albeit at levels considerably lower than that induced by the combination of cell adhesion in the presence of TGF-β1. T2 cells allowed to attach to vitronectin-coated surfaces also expressed PAI-1 transcripts but to a significantly reduced extent relative to cells adherent to fibronectin. Moreover, newly vitronectin-attached cells did not exhibit a PAI-1 inductive response to TGF-β1, at least during the short 2 hour period of combined treatment. PAI-1 mRNA synthesis in response to substrate attachment, like TGF-β1-mediated induction in adherent cultures, also required MEK activity as fibronectin-stimulated PAI-1 expression was effectively attenuated by the MEK inhibitor PD98059. These data indicate that cellular adhesive state modulates TGF-β1 signaling to particular target genes (i.e., PAI-1) and that MEK is a critical mediator of the PAI-1+/promigratory phenotype switch induced by TGF-β1 in T2 cells.

Altered expression of growth factors and cytokines in keratoconus, bullous keratopathy and diabetic human corneas

The purpose of this study was to identify the growth factors and cytokines present in normal and diseased corneas. Total RNA was isolated from normal and diseased corneas. cDNA was synthesized from individual corneas and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was performed with primers to IL-1alpha, 1IL-8, PDGF-B, BMP-2, BMP-4, IGF-I, TGF-beta2, FGF-2, and VEGF. After normalization to beta2-microglobulin, several factors were identified that were significantly different from normal. Antibodies to IGF-I, BMP-2, VEGF and TGF-beta2 were used for immunohistochemistry. A total of 93 corneas were used for this study including 31 normal, 20 keratoconus, 19 bullous keratopathy (pseudophakic and aphakic, PBK/ABK), and 23 diabetic corneas. The VEGF RNA levels were significantly decreased in the keratoconus and PBK/ABK corneas but increased in the diabetic corneas. BMP-2 gene expression was lower than normal in the PBK/ABK and diabetic corneas. IGF-I and BMP-4 RNA levels were increased in PBK/ABK. In the immunohistochemical studies, the protein patterns paralleled those found at the mRNA level. The only exception was IGF-I in diabetic corneas that showed increased staining in the epithelium and its basement membrane without a significant increase in mRNA levels. TGF-beta2 mRNA and protein levels were similar to normal in all diseased corneas. Thus, no alterations in the tested growth factors/cytokines were unique to keratoconus corneas. In contrast, PBK/ABK corneas had specific significant elevations of BMP-4 and IGF-I. Diabetic corneas were unique in their increased VEGF mRNA levels. These data suggest that while some growth factor/cytokine alterations are non-specific and can be found in multiple corneal diseases, there are others that are unique to that disease.

Injury and EGF mediate the expression of alpha6beta4 integrin subunits in corneal epithelium

Our goal was to evaluate the role of epidermal growth factor and injury on the expression of integrin subunits alpha6(alpha6) and beta4(beta4). An in vitro wound model was used to evaluate corneal wound repair and cellular migration. Primary rabbit corneal epithelial cell cultures were serum-starved and injured in the presence or absence of EGF or tyrphostin AG1478, an inhibitor of EGF receptor kinase activity. Repair was monitored morphologically and expression was analyzed using in situ hybridization and immunohistochemistry accompanied by confocal microscopy. The addition of EGF to cell cultures induced a dose-dependent increase in beta4 mRNA expression but the constitutive expression of alpha6 was several fold greater. In the wounded cultures there was a rapid change in expression at the edge of the wound that was enhanced with EGF. In our model there was an increase in beta4 and alpha6 protein in migrating cells. Changes in integrin expression were accompanied by a transient increase in activation of the EGF receptor. The addition of tyrphostin inhibited migration of cells and wound repair, the activation of the EGF receptor and phosphorylation of beta4 in the cytoplasm. These data indicate that the activation of the EGF receptor plays a critical role in the regulation of integrin receptors and the mediation of cellular migration.

Antisense targeting of c-fos transcripts inhibits serum- and TGF-beta 1-stimulated PAI-1 gene expression and directed motility in renal epithelial cells

Plasminogen activator inhibitor type-1 (PAI-1), the major regulator of pericellular plasmin generation, and the c-FOS transcription factor are expressed by migrating cells in response to monolayer wounding. Induced c-fos and PAI-1 transcripts were evident within 30 min and 2 h, respectively, of scrape injury to confluent, growth-arrested, cultures of NRK epithelial cells. Since c-FOS/AP-1 DNA-binding activity modulates both basal and inducible modes of PAI-1 gene control, and AP-1 motif binding factors were present in quiescent as well as stimulated NRK cells, a model of directionally regulated cell movement (migration into scrape-denuded "wounds") was used to assess the consequences of c-fos transcript targeting on PAI-1 expression and cell motility. This in vitro model of epithelial injury closely approximated in vivo wound repair with regard to the spatial and temporal emergence of cohorts of cells involved in migration, proliferation, and PAI-1 expression. Stable cell lines (NRKsof) were generated by transfection of parental NRK cells with a c-fos antisense expression vector. Serum-inducible c-fos transcripts and PAI-1 protein levels were significantly attenuated in NRKsof transfectants relative to parental controls or cells transfected with a neo(R) vector without the sof insert. NRKsof cells had a markedly impaired ability to repair scrape-generated monolayer wounds under basal, serum-stimulated, or TGF-beta 1-supplemented culture conditions. Since injury closure and PAI-1 induction were attenuated in c-fos antisense cells, it was important to clarify the role of specific AP-1 sites in serum-mediated PAI-1 transcription. PAI-1 "promoter"-driven CAT reporter expression was assessed within the real time of serum-stimulated PAI-1 induction. A segment of the PAI-1 promoter corresponding to nucleotides -533 to -764 upstream of the transcription start site functioned as a prominent serum-responsive region (SSR). The 9-fold increase in CAT mRNA levels attained with the -533 to -764 bp PAI-1 SRR ligated to a minimal PAI-1 promoter (i.e., 162 bp of 5' flanking sequence containing the basal transcription complex) closely approximated the serum-induced transcriptional activity of a fully responsive (1,230 bp) PAI-1 promoter construct as well as the endogenous PAI-1 gene. AP-1-like, CTF/NF-1-like, and AP-2 sites were identified in the SRR. The SRR AP-1 motif was homologous to the sequence TGACACA that mapped between nucleotides -740 and -703 in the human PAI-1 gene, a region essential for growth factor-inducible PAI-1 transcription. While the functionality of this AP-1 site in wound-regulated PAI-1 synthesis remains to be determined, antisense c-fos transcripts effectively attenuated PAI-1 induction and basal as well as growth factor-stimulated cell locomotion, indicating that expression of both the PAI-1 and c-fos genes is necessary for wound-initiated NRK cell migration.

Blockade of TGF-beta by in vivo gene transfer of a soluble TGF-beta type II receptor in the muscle inhibits corneal opacification, edema and angiogenesis

Accumulating evidence suggests the involvement of TGF-beta in the process of corneal opacity, which is one of the serious causes of visual loss. However, whether TGF-beta is indeed critical for the pathogenesis remains unknown. We constructed an adenovirus expressing an entire ectodomain of the human type II TGF-beta receptor fused to Fc portion of human IgG (AdTbeta-ExR): this soluble receptor is secreted from AdTbeta-ExR-infected cells, binds to TGF-beta and inhibits TGF-beta signaling. When AdTbeta-ExR was injected into the femoral muscle of Balb/c mice, a high level of the soluble receptor protein (2.0-3.5 x 10(3) pM) was detectable in the serum and in the ocular fluid for at least 10 days. In the mice subjected to corneal injury with silver nitrate and to intramuscular injection with either saline or a control adenovirus expressing beta-galactosidase (AdLacZ), corneal opacification composed of extracellular matrix (ECM) accumulation, of infiltration of neutrophils and monocytes/macrophages, and of angiogenesis were all induced. In contrast, they were markedly reduced in the mice injected with AdTbeta-ExR. Immunohistochemical analysis revealed that TGF-beta, fibronectin, macrophage chemoattractant protein-1, and vascular endothelial growth factor were densely stained in the edge of wounded cornea, but they were scarcely present in the injured-cornea of AdTbeta-ExR-treated mice. Our results demonstrate that TGF-beta indeed plays a critical role in the process of cornea opacification, and that adenovirus-mediated expression of a soluble TGF-beta receptor can be therapeutically useful.