Growth factor-induced proliferation in corneal epithelial cells is mediated by 12(S)-HETE

PURPOSE

Previous studies in our laboratory have shown that 12(S)-hydroxyeicosatetraenoic acid (12(S)-HETE), a product of 12-lipoxygenase (12-LOX) activity, is the predominant metabolite formed in rabbit corneas after injury. The present study was undertaken to investigate the effects of epidermal growth factor (EGF), hepatocyte growth factor (HGF), and keratinocyte growth factor (KGF) on 12-LOX expression and activity. We also investigated whether 12(S)-HETE mediated the growth factor-induced proliferation of corneal epithelial cells.

METHODS

Rabbit corneas were stimulated with EGF, HGF, and KGF (10 ng ml(-1)) for different times. 12-LOX activity was assayed by incubating corneal microsomal preparations with radiolabeled arachidonic acid (AA) as substrate. For inhibitor studies, the microsomes were pretreated with 12-LOX-specific inhibitors baicalein (BC) or cinnamyl 3,4-dihydroxy-(alpha)-cyanocinnamate (CDC). Lipid extracts were injected onto an Ultramex 5 microm C(18) column and radioactivity was monitored online by a Radiomatic Flo-One Beta detector. Stereochemical analysis of 12-HETE product was determined by chiral-phase HPLC. To evaluate the effects of growth factors on 12-LOX mRNA expression, mRNA was extracted at several time points (12, 24, 36, 48 hr) and subjected to real-time PCR. For 12-LOX protein expression, microsomal preparations from 24- and 48-hr incubations were analyzed by Western blot. In cell-proliferation studies, epithelial cells treated with EGF, HGF, or KGF for 24, 48, and 72 hr were measured with a CyQUANT cell-proliferation assay kit. To determine the role of growth factor-induced 12(S)-HETE synthesis on corneal epithelial cell proliferation, cells were pretreated with 12-LOX-specific inhibitors BC or CDC prior to growth-factor supplementation.

RESULTS

Stimulation with EGF, HGF, or KGF for 12 hr induced 12-LOX mRNA expression in rabbit corneal epithelial cells. This gene induction was followed by an increase in protein expression at 24 and 48 hr and a marked increase in 12(S)-HETE synthesis when compared to untreated controls. At 24-hr incubations, KGF showed a greater capacity than did EGF and HGF to stimulate microsomal 12-LOX activity, while at 48 hr 12(S)-HETE synthesis was significantly greater in EGF-treated cells as compared to that of HGF- and KGF-treated cells. Pretreatment with 12-LOX inhibitors blocked the growth factor-induced increase in 12(S)-HETE synthesis. Stimulation with growth factors or 12(S)-HETE for 24, 48, and 72hr produced a significant increase in corneal epithelial proliferation, which was partially inhibited by pretreatment of cells with 12-LOX-specific inhibitors.

CONCLUSION

These findings suggest that EGF, HGF, and KGF stimulate 12(S)-HETE production in rabbit corneal epithelial cells through gene induction of 12-LOX. Furthermore, 12(S)-HETE may play a role in regulating epithelial cell proliferation and the rate of corneal re-epithelialization following an injury.

Human corneal epithelial cells require MMP-1 for HGF-mediated migration on collagen I

PURPOSE

To investigate the potential regulation of matrix metalloproteinases (MMPs) by hepatocyte growth factor (HGF), and to identify individual MMPs essential for migration of human corneal epithelial cells.

METHODS

Migration of human corneal epithelial cells (HCECs) was measured with a colony dispersion assay in response to concentrations of HGF (0-50 ng/mL). MMP activity in the conditioned media collected from the dispersion assay was assessed by zymography. The broad-spectrum MMP inhibitor ilomastat (1-100 microM) or an MMP-9-neutralizing antibody (1-10 microg/mL) were included in the dispersion assay to determine their effects on HCEC migration. Immunocytochemistry and in situ hybridization were used to localize MMP-1 in HCECs in the colony dispersion assay and in a human ex vivo corneal wound-healing model, respectively. ELISA for MMP-1 was performed on conditioned medium from migrating HCECs. Neutralizing antibodies to MMP-1 and -9 were added to an in vitro scratch-wound model to assess the effect on HCEC healing.

RESULTS

HCEC migration (P < 0.05) and MMP-2 and -9 released into the medium increased in response to HGF in a dose-dependent manner up to 20 ng/mL. Broad-spectrum MMP inhibition significantly reduced HCEC migration (P < 0.05). In contrast, neutralization of MMP-9 increased migration (P < 0.05). MMP-1 was found in association with HCECs at the migratory leading edge in both the dispersion and the ex vivo wound-healing experiments, and was found to be stimulated above basal levels by HGF. Neutralization of MMP-1 significantly decreased (P < 0.05), whereas neutralization of MMP-9 significantly increased (P < 0.05), scratch-wound closure.

CONCLUSIONS

This study provided novel data regarding HCEC migration in response to HGF and highlighted the importance of MMPs, particularly MMP-1 in migration and possibly reepithelialization in vivo. MMP-9 and/or -2 may be released by HCECs to remodel matrix behind the leading migratory front. Studies such as this are essential to assist in the safe and efficacious design of MMP inhibitors for therapeutic use in the eye.

Corneal neovascularization after excimer keratectomy wounds in matrilysin-deficient mice

PURPOSE

Matrilysin, matrix metalloproteinase (MMP)-7, is upregulated in the corneal epithelium during wound healing after excimer keratectomy wounds. The purpose of this study was to determine the role of matrilysin in maintaining corneal avascularity during wound healing.

METHODS

Matrilysin-deficient mice (n = 17) and their age-matched wild-type littermates (n = 18) were treated with 193 nm argon-fluoride excimer keratectomy (experiment I). The percentage of corneal surface occupied by neovascularization was measured with a computer image-analysis program adjusted for parallax. In another experiment (experiment II), epithelial closure was monitored with slit lamp biomicroscopy and fluorescein staining, and corneal neovascularization was confirmed by india ink perfusion, electron microscopy, and immunolocalization of CD31 and type IV collagen. Corneal micropocket assays were performed to compare the area of corneal neovascularization in matrilysin-deficient mice and wild-type littermates (experiment III). To determine whether the differences in corneal neovascularization were related to differences in angiogenic factors, the levels of basic fibroblast growth factor (bFGF) were compared with those of vascular endothelial growth factor (VEGF) in matrilysin-deficient and wild-type mouse corneas (experiment IV).

RESULTS

The percentages of the corneal surface occupied by neovascularization after excimer laser keratectomy in the matrilysin-deficient mice measured 21.3% +/- 5.2% and 18.7% +/- 5.8% at days 3 and 7, respectively, compared with 5.3% +/- 2.4% and 5.5% +/- 3.4% in the wild-type littermates at days 3 (P < 0.01) and 7, respectively (P < 0.05; experiment I). No significant differences in the rates of epithelial closure of corneal wounds were observed between matrilysin-deficient and wild-type mice after wounding. Corneal neovascularization in the matrilysin-deficient mice was confirmed by india ink present in the corneal stromal blood vessels (extending from the limbus to the wound), immunohistochemical staining, and electron microscopy. Gram, Giemsa, calcofluor white, and acridine orange stains and electron microscopy showed no evidence of corneal infection (experiment II). The area of corneal neovascularization in matrilysin-deficient mice was not significantly different from that of wild-type littermates after implantation of bFGF pellets (0.91 +/- 0.55 mm(2) and 0.77 +/- 0.34 mm(2), respectively; experiment III). The levels of bFGF and VEGF (VEGF, VEGF-B, and VEGF-C) in corneal epithelial cells were not elevated in matrilysin-deficient mice compared with the wild-type mice (experiment IV).

CONCLUSIONS

Matrilysin may play an important role in maintaining corneal avascularity during wound healing. The differences in corneal neovascularization between matrilysin-deficient mice and wild-type littermates seem unrelated to the bFGF and VEGF levels in the corneal epithelium.

Evaluation of peculiarities of the acetylcholinesterase-positive nerve plexus and its length in the cornea

The objective of this study was to evaluate age-related peculiarities of acetylcholinesterase-positive nerve plexus and its length in the dog cornea.

MATERIAL AND METHODS

Nine mixed breed dogs (male and female) of 1.8-20 kg weight were used. They were divided into three age groups: young (until 1 year), adult (1-7 years) and old (8 and more years). Acetylcholinesterase-positive nerve plexus was identified using acetylcholinesterase method of M. J. Karnowsky and L. A. Roots (1964) modified by D. H. Pauza et al. (1996). The length of nerve bundles was measured by mm in 1 mm(2) of cornea.

RESULTS AND CONCLUSIONS

Branching thick, medium and thin nerve bundles form acetylcholinesterase-positive nerve plexus in dog cornea. The average of the length of nerve bundles between the left and the right corneas was similar in different age groups (p>0.05). The length of acetylcholinesterase-positive nerve bundles in 1 mm(2) of the cornea in the group of adult dogs (10.32+/-0.11 mm) was higher than in the groups of young (9.42+/-0.02 mm) and old dogs (7.75+/-0.14 mm) (p<0.001).

EGF-induced ERK phosphorylation independent of PKC isozymes in human corneal epithelial cells

PURPOSE

To investigate the role of protein kinase C (PKC) isozymes in epithelial growth factor (EGF)-induced activation of extracellular signal-regulated kinase (ERK) and cell proliferation in cultured human corneal epithelial cells.

METHODS

Simian virus (SV)40 stably transfected human corneal epithelial (THCE) cells were cultured in keratinocyte growth medium. PKC isozymes and phosphorylation of ERK in THCE cells were assessed by Western blot analysis. Translocation of the PKC isozyme was determined by subcellular fractionation followed by Western blot analysis. Cell proliferation was measured by incorporation of [(3)H]-thymidine into DNA.

RESULTS

Six PKC isozymes-PKC-alpha, -betaI, -betaII, -delta, - epsilon, and - micro -were found in THCE cells. Phorbol 12-myristate 13-acetate (PMA) caused PKC-alpha, -betaI, and - epsilon, initially present in the cytoplasm, to be translocated to the membrane and nuclear subcellular fractions and PKC-delta to be depleted from the cytoskeleton. The PKC inhibitor GF109203X inhibited PMA-induced, but not basal or EGF-induced, phosphorylation of ERK, whereas the EGF receptor inhibitor tyrphostin AG1478 blocked basal and EGF-, but not PMA-, induced phosphorylation of ERK. Depletion of PMA-sensitive PKC isozymes including PKC-alpha, -betaI, -betaII, -delta, and - epsilon, inhibited PMA-, but not EGF-, induced phosphorylation of ERK. Depletion of these PKC isozymes blocked PMA-, but not EGF-, induced cell proliferation.

CONCLUSIONS

Although activation of PKC by PMA results in activation of ERK, EGF-induced phosphorylation of ERK and/or cell proliferation is independent of the conventional and novel isozymes PKC-alpha, -betaI, -betaII, -delta, and - epsilon in human corneal epithelial cells.

The role of nitric oxide in ocular surface cells

The role of nitric oxide (NO) in the ocular surface remains unknown. We investigated the conditions leading to an increase of NO generation in tear and the main sources of NO in ocular surface tissue. We evaluated the dual action (cell survival or cell death) of NO depending on its amount. We measured the concentration of nitrite plus nitrate in the tears of ocular surface diseases and examined the main source of nitric oxide synthase (NOS). When cultured human corneal fibroblast were treated with NO producing donor with or without serum, the viabilities of cells was studied. We found that the main sources of NO in ocular surface tissue were corneal epithelium, fibroblast, endothelium, and inflammatory cells. Three forms of NOS (eNOS, bNOS, and iNOS) were expressed in experimentally induced inflammation. In the fibroblast culture system, the NO donor (SNAP, S-nitroso-N-acetyl-D, L-penicillamine) prevented the death of corneal fibroblast cells caused by serum deprivation in a dose dependent manner up to 500 micrometer SNAP, but a higher dose decreased cell viability. This study suggested that NO might act as a double-edged sword in ocular surface diseases depending on the degree of inflammation related with NO concentration.

Platelet-activating factor induces the gene expression of TIMP-1, -2, and PAI-1: imbalance between the gene expression of MMP-9 and TIMP-1 and -2

Previous studies in the laboratory have shown that platelet-activating factor (PAF), a potent inflammatory mediator that accumulates rapidly in the cornea after an injury, stimulates the expression of urokinase (uPA) and matrix metalloproteinase-1 (MMP-1) and -9 (MMP-9). Tissue inhibitors of MMPs (TIMPs) and plasminogen activator inhibitor (PAI-1) are produced in conjunction with these enzymes and are important regulators of their activity. Here, the authors investigated how PAF affects the expression of PAI-1, TIMP-1 and -2 relative to that of uPA, MMP-1, and -9 in rabbit corneal epithelial cells. Rabbit corneas were incubated in MEM medium containing 100 nM cPAF. To block the effects of PAF in some studies, corneas were preincubated for 1 hr in the presence of the PAF antagonist BN50730 (10 microM). At several time intervals, mRNA was extracted from epithelial cells and the levels of gene expression for the enzymes and their inhibitors were determined by real-time PCR. All quantitations were normalized to the 18s rRNA values (endogenous control) and changes in gene expression were reported as fold increase relative to untreated controls. PAF produced a 20-fold increase in the gene expression of PAI-1 at 8 hr, while similar fold increases in uPA mRNA expression occurred at 2 hr. PAF treatment also stimulated the expression of TIMP-1 and -2 genes, with a six-fold increase in TIMP-1 expression occurring at 36 hr and a four-fold increase in TIMP-2 expression at 24 hr. Maximal induction of MMP-1 and -9 mRNA, on the other hand, occurred at 4 and 8 hr, respectively. Induction of MMP-1 gene expression was similar to that of its inhibitors TIMP-1 and -2, while MMP-9 mRNA induction exceeded that of these inhibitors by 100-fold. The PAF-induced expression of PAI-1, TIMP-1 and -2 mRNAs was abolished by pre-treatment with BN50730. These data indicate that PAF activates the gene expression of TIMP-1, -2, and PAI-1 in corneal epithelium by a receptor-mediated mechanism. Furthermore, PAF induced overexpression of MMP-9 mRNA relative to that of TIMP-1 and -2, suggesting an imbalance between the expression of this proteolytic enzyme and its inhibitors, which may contribute to changes in the wound-healing process and ultimately lead to corneal ulcer development.

Differentiation-dependent increases in lactate dehydrogenase activity and isoenzyme expression in rabbit corneal epithelial cells

Lactate dehydrogenase (LDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) activities were studied during corneal epithelial growth and differentiation in cell culture. LDH and G-6-PDH activities increased up to 60 and 150-fold, respectively, when corneal epithelial cells constituted a differentiated four to five layered epithelium; these increases showed a similar time-course to the expression of K3 keratin. Immunostaining experiments showed that in growing colonies, LDH staining is stronger in those cells that are K3 positive; in contrast, in confluent four to five layered epithelia LDH and K3 were located in all cell layers, similar to the pattern found in frozen sections from rabbit central cornea. During growth and differentiation, the LDH isoenzyme set from corneal epithelial cells did not change; and it was different from those observed in cultured conjunctival, esophageal and epidermal cells. The augment in LDH activity was due to a 25-fold increase in the LDH-H mRNA and a 12-fold augment in LDH-M mRNA. A computer-assisted search led to identify AP2 and Sp1 binding sites in the LDH and G-6-PDH promoters, suggesting that their expression might share common regulatory mechanisms with the regulation of the differentiation-linked keratins. It is proposed that LDH may be an early marker of corneal epithelial differentiation, and its isozyme pattern could be distinctive from other epithelial cell lineages.

An immunohistochemical study of endothelin-1 converting enzyme in the human eye

PURPOSE

The important role of ET-1 in vasoconstriction has been shown for the vasoregulation in the retina, choroid and optic nerve. ET-1 induced vaso-constriction, however, can be treated effectively at the level of endothelin-1 converting enzyme (ECE-1) by ECE-1 inhibitors because ECE-1 converts biologically almost inactive big endothelin to endothelin-1 (ET-1), the most potent vasoconstrictor known. The purpose of this study was to clarify the anatomical distribution of ECE-1 in the human eye.

METHODS

11 post-mortem eyes were fixed in 4% formalin and embedded in paraffin. 4 microm thin sections were analyzed immuno-histochemically using a self-produced monoclonal primary antibody against human ECE-1 and a polyclonal alpha-actin antibody for comparison.

RESULTS

ECE-1 -IR was demonstrated in the corneal epithelium, vascular smooth muscle and endothelial cells, and in the non-vascular smooth muscle cells of the ciliary body, the dilator and sphincter muscle of the iris.

CONCLUSIONS

A strong immunoreactivity for ECE-1 can be found in the blood vessels of the retina, optic nerve and choroid. Therefore, it should be possible to treat ET-1-induced vaso-constriction in the eye using ECE-1 inhibitors, especially in diseases like hypertensive vasculopathy, vasospasm, vaso-occlusions or low tension glaucoma.

Platelet-activating factor (PAF) enhances apoptosis induced by ultraviolet radiation in corneal epithelial cells through cytochrome c-caspase activation

PURPOSE

To examine the role of platelet-activating factor (PAF) on apoptosis of corneal epithelial cells exposed to radiation.

METHODS

Rabbit corneal epithelial (RCE) and human corneal epithelial (HCE) cells were exposed to UVC radiation and then to carbamyl PAF (cPAF) for different increments of time. The PAF antagonist BN50739 was added 30 min before cPAF. The caspase inhibitors Ac-DEVD-CHO and Ac-YVAD-CHO were added 1 h before, and the phospholipase A(2) (PLA(2)) inhibitor MAFP was added 3 h before UVC irradiation. FITC-dUTP TUNEL and DAPI staining were performed to assess the percentage of apoptotic cells. DNA ladder analysis was used to investigate apoptosis induced by different intensities of UVC (50-600 J/m(2)) with or without cPAF. Caspase activation and release of cytochrome c from mitochondria to cytosol were determined by Western blot.

RESULTS

While only 2.7% of RCE cells were DAPI positive in controls incubated for 12 h, 44% of cells were stained positive 4 h after irradiation; these values increased to 63% in the presence of cPAF. Cells incubated with cPAF alone were similar to controls. TUNEL staining and DNA laddering showed also increased in apoptosis after PAF treatment of UV-irradiated cells and BN50739 blocked the effect of cPAF. cPAF increased caspase-3 activation induced by UV irradiation in HCE cells. Cytochrome c release from mitochondria to cytosol was observed 30 min after irradiation. cPAF almost doubled the release of cytochrome c at 30 min and 1 h. Here, too, BN50739 blocked the PAF effect. No release of cytochrome c by PAF was seen in non-irradiated cells, even at higher concentrations. MAFP caused a decrease in cytochrome c release from UV-treated cells, and caused an even greater inhibition of cytochrome c release in cells stimulated with PAF.

CONCLUSIONS

PAF increases RCE and HCE apoptosis caused by UV irradiation by stimulating PLA(2), producing an early release of cytocrome c from mitochondria and activating caspase-3 by a receptor-mediated mechanism. This accelerating effect of PAF on the apoptotic cascade only occurred when corneal epithelial cells had been previously damaged by UV radiation.

Regulation of MMP-9 production by human corneal epithelial cells

The matrix metalloproteinases, MMP-2 and MMP-9, are known to be critical extracellular-remodeling enzymes in wound healing and other diseases of the ocular surface. This study investigated the regulation of MMP-2 and MMP-9 in human corneal epithelial cells by growth factors and pro-inflammatory cytokines (IL-1beta and TNF-alpha) they are exposed to, and by doxycycline, a medication used to treat ocular surface disease. Primary human corneal epithelial cell cultures were treated with one of the following cytokines (IL-1alpha, IL-1beta, IL-6, IL-8, TNF-alpha) or growth factors (EGF, HGF, KGF, PDGF-BB, TGF-alpha, TGF-beta), with or without their corresponding inhibitors. The conditioned media were collected after 24 hr for gelatin zymography and MMP-9 activity assay. Total RNA was extracted from the cells treated for 6 hr and was subjected to RT-PCR and Northern hybridization. Between the two gelatinases, MMP-2 and MMP-9, detected by zymography, the 92 kDa MMP-9 in the conditioned medium was markedly up-regulated by the pro-inflammatory cytokines, IL-1beta and TNF-alpha. The MMP-9 protein and activity were dose-dependently stimulated by IL-1beta or TNF-alpha at 0.1, 1.0 and 10 ng ml(-1). This up-regulation was nearly abolished by neutralizing antibodies (IL-1beta and TNF-alpha) and by IL-1 receptor antagonist. Semi-quantitative RT-PCR and Northern hybridization disclosed that the MMP-9 transcript was also markedly up-regulated in a dose-dependent manner by IL-1beta and TNF-alpha. Doxycycline (10 microg ml(-1)) suppressed MMP-9 protein level and activity, but not its mRNA, that was stimulated by IL-1beta and TNF-alpha (1 ng ml(-1)). In contrast, the 72 kDa MMP-2 was not significantly modulated by any of these cytokines. In conclusion, production of MMP-9 is stimulated by the pro-inflammatory cytokines, IL-1beta and TNF-alpha. These factors may play a role in the pathogenesis of MMP-9 mediated corneal matrix degradation. The efficacy of doxycycline in treating ocular surface diseases may be related to its ability to suppress MMP-9 production in the corneal epithelium.

Lens lactate dehydrogenase inactivation after UV-B irradiation: an in vivo measure of UVR-B penetration

PURPOSE

To elucidate the spatial distribution of inactivation of lactate dehydrogenase (LDH) in ultraviolet-B radiation (UVR-B)-exposed eyes. To determine the in vivo penetration depth of UVR-B in the lens.

METHODS

LDH activity in cornea and lens was investigated with an enzyme histochemical technique. Thirty rats were exposed in vivo to UVR-B of approximately 300 nm, and the eyes were enucleated and frozen at 0, 2, and 6 hours after exposure. LDH activity in frozen sections was determined quantitatively in the corneal epithelium and four different regions in the lens. UVR-B penetration depth was estimated by using a calculated Lambertian absorption coefficient.

RESULTS

The LDH activity was decreased in the cornea and the outer anterior lens cortex at all three time points. The average decrease in enzyme activity in the time range was 35% in the cornea and 20% in the outer anterior lens cortex. UVR-B inhibition of LDH was immediate and not dependent on an inflammatory reaction within the eye. Penetration depth, corresponding to 1/e(2) ( approximately 14%) residual UVR-B intensity, was 0.45 mm.

CONCLUSIONS

UVR-B does not exhibit any significant effect on LDH activity in the major part of the lens, and this is attributed to the shallow penetration (0.45 mm) of UVR-B into the anterior parts of the lens.

Treatment of recalcitrant recurrent corneal erosions with inhibitors of matrix metalloproteinase-9, doxycycline and corticosteroids

PURPOSE

To review the efficacy of inhibitors of matrix metalloproteinase-9, corticosteroids, and doxycycline for treatment of recalcitrant recurrent corneal erosion.

METHODS

Retrospective, clinic-based, interventional case series. The medical records of seven consecutive patients who were treated between January 1995 to January 2000 for recurrent corneal erosion who had not responded to conventional therapy were reviewed. Treatment of seven eyes of seven patients consisted of oral doxycycline (50 mg, two times a day) for 2 months along with a topical corticosteroid (either methylprednisolone 1%, prednisolone acetate 1%, or fluoromethalone 0.1%) three times a day, for 2 to 3 weeks. The effects of doxycycline and methylprednisolone on metalloproteinase-9 activity in human corneal epithelial cultures were evaluated by gelatin zymography and a commercial metalloproteinase-9 activity assay kit.

RESULT

Fingernail injury in three of the seven eyes was the most common form of corneal injury. There was no evidence of epithelial basement membrane or corneal stromal dystrophy in any of the patients, although epithelial microcysts were observed in the involved area in three patients. One eye had intact elevated corneal epithelium that showed abnormal diffuse staining with fluorescein dye, and six eyes had a corneal epithelial defect at the time of presentation. In all seven eyes, pain resolved and epithelial defects healed within 2 to 10 days after initiation of therapy. No recurrence was observed during an average follow-up period of 21.9 months (range, 1.5 to 60 months). Methylprednisolone and doxycycline each produced a statistically significant decrease in amount and activity of metalloproteinase-9 in conditioned media of human corneal epithelial cultures.

CONCLUSIONS

Therapy with a combination of medications that inhibit metalloproteinase-9 produced rapid resolution and prevented further recurrence of cases of recurrent corneal erosions that were unresponsive to conventional therapies.

Peroxiredoxin in bovine ocular tissues: immunohistochemical localization and in situ hybridization

Peroxiredoxins are widely distributed in nature and constitute a molecular family of antioxidant enzymes which decompose hydrogen peroxide and alkyl hydroperoxides. We have previously characterized a peroxiredoxin from bovine ciliary body and deduced its amino acid sequence from analysis of cDNA clones encoding the protein. In this work, we investigated the immunolocalization of this novel antioxidant enzyme and its mRNA expression in bovine eye tissues. High levels of immunoreactivity and mRNA for the enzyme were detected in corneal epithelium. Distinct immunoreactivity and mRNA expression for peroxiredoxin were also detected in uveal tissues, some of the retinal cell layers and ocular vasculature.

Upregulation of phospholipase Cgamma1 activity during EGF-induced proliferation of corneal epithelial cells: effect of phosphoinositide-3 kinase

PURPOSE

Previously, the authors showed that epidermal growth factor (EGF) stimulates phospholipase Cgamma1 (PLCgamma1) and phosphoinositide-3 kinase (PI3K) activities in confluent rabbit corneal epithelial cells (RCECs). The purpose of this study was to investigate whether PLCgamma1 activity is upregulated during EGF-induced proliferation of RCECs and to determine whether there is any cross-talk between PLCgamma1 and PI3K in these cells.

METHODS

Simian virus (SV)-40-immortalized RCECs were cultured in the presence and absence of EGF and other agents. At prescribed time intervals, the cultures were terminated and the cells counted. PLCgamma1 activity in intact cells was assessed by measuring the production of [(3)H]IP(3) in [(3)H]myoinositol-labeled cells. The in vitro enzyme activity was assayed using immunoprecipitated PLCgamma1 and [(3)H]PI(4,5)P(2) as substrate. [(3)H]IP(3), the product of PLCgamma1, was analyzed by anion-exchange chromatography. The changes in protein content and level of phosphorylation of PLCgamma1 were determined by Western immunoblot analysis, with the appropriate antibodies.

RESULTS

Addition of EGF (50 ng/ml) caused a time-dependent increase in proliferation of RCECS. The effect of EGF peaked at approximately 36 hours. Under the same experimental conditions, EGF stimulated PLCgamma1 activity with a time course similar to that of cell proliferation. Data from Western immunoblot analysis revealed that the EGF-stimulated PLCgamma1 activity was due to increased synthesis of the enzyme. Furthermore, during cell proliferation, tyrosine phosphorylation of PLCgamma1 increased in a time-dependent manner that corresponded closely with the expression of PLCgamma1. EGF exerted its effects both on cell proliferation and PLCgamma1 activation in a dose-dependent manner. Treatment of the cells with U-73122, a PLC inhibitor, or myr-GLYRKAMRLRY, a myristoylated PLCgamma1 inhibitor peptide, caused attenuation of both the EGF-stimulated cell proliferation and PLCgamma1 activity. Treatment of the cells with the PI3K inhibitors, wortmannin or LY294002, caused inhibition of both EGF-stimulated cell proliferation and PLCgamma1 activation. Addition of PI(3,4,5)P(3) to the in vitro PLCgamma1 assay mixture stimulated the enzyme activity in a dose-dependent manner.

CONCLUSIONS

The data suggest a positive correlation between EGF-stimulated PLCgamma1 activation and cell proliferation in RCECS. The EGF-stimulated PLCgamma1 activity was mirrored by increased synthesis and tyrosine phosphorylation of the enzyme. The data also show that PLCgamma1 activation and cell proliferation were inhibited by PI3K inhibitors, suggesting a role for PI3K in EGF-stimulated proliferation of corneal epithelial cells.

Different expression patterns for ubiquitous calpains and Capn3 splice variants in monkey ocular tissues

The purpose of the present investigation was to compare the expression of ubiquitous and tissue-specific calpains in ocular tissues from the Macaca fascicularis monkey. Calpain isoforms in retina and corneal epithelium from adult M. fascicularis monkeys were characterized by RT-PCR, cDNA cloning and sequencing. Calpain isoform activities in ocular tissues were investigated by fractionation on DEAE-HPLC, immunoblotting, and casein zymography. Capn3 splice variants in the ocular tissues from rat, rabbit and monkey were compared after RT-PCR. RT-PCR analysis revealed that numerous splice variants of Capn3 were expressed in the epithelium from monkey cornea. The variants contained deletions or insertions in or around the IS1, IS2, and NS regions. The cDNAs for Capn3 variants were highly conserved, yet the expression patterns of the Capn3 isoforms were widely different among the mammalian species. In contrast, the expression patterns of ubiquitous calpains in ocular tissues were conserved among the mammalian species, and similarities between monkey and human cDNAs for Capn1 (mu-calpain) and Capn2 (m-calpain) were 98 and 99%, respectively. These results suggested that differences in expression patterns of Capn3 variants might be related to the function of each variant in a particular tissue or species.

Regulation of a Rho-associated kinase expression during the corneal epithelial cell cycle

PURPOSE

It has been recognized that an increased expression of the Rho-associated kinase (ROCK-I), a downstream target of Rho (a Ras-related small guanosine triphosphatase [GTPase]), is associated with limbal-to-corneal epithelial transition. The purpose of the present study was to determine whether the expression of ROCK-I is regulated during the cell cycle of corneal epithelial cells.

METHODS

Rabbit corneal epithelial cells in culture were subjected to different culture conditions to enrich them in the G0, G1, and S phases of the cell cycle. Indirect immunofluorescence staining and western blot techniques were used for analyzing the changes in the relative intracellular concentrations of ROCK-I. Northern blot analysis of the isolated cellular RNA was performed to estimate the relative concentrations of ROCK-I mRNA.

RESULTS

Serum deprivation did not cause all the corneal epithelial cells in culture to be arrested in the G0 phase of the cell cycle. However, the cells could be arrested in G0 by treating them with culture medium supplemented with transforming growth factor (TGF)-beta1. The relative concentration of ROCK-I in the G0-arrested cells was higher than in the corresponding control untreated cultures. G0-arrested cells were induced to enter G1, followed by the S phase of the cell cycle, by refeeding them with the medium devoid of TGF-beta1. The total intracellular concentration of ROCK-I significantly decreased during the G1 phase of the cell cycle and increased again during the S phase. The decrease in intracellular ROCK-I during the G1 phase was confirmed by arresting the cells in G1 with isoleucine deprivation and thymidine-mimosine treatments. ROCK-I mRNA levels were also found to be decreased during the G1 phase of the cell cycle.

CONCLUSIONS

The levels of ROCK-I in the corneal epithelial cells were significantly lower in the G1 phase than those in the S and G0 phases of the cell cycle. Therefore, a Rho signaling pathway(s) involving ROCK-I may be regulated during the corneal epithelial cell cycle. The downregulation of ROCK-I during the G1 phase, at least in part, is due to the decreased levels of its mRNA. Based on these findings, ROCK-I may have a role in the progression of the cell cycle in the corneal epithelial cells as they migrate centripetally from the limbal to the corneal surface.

Reactive oxygen species (ROS)-generating oxidases in the normal rabbit cornea and their involvement in the corneal damage evoked by UVB rays

The corneas of albino rabbits were irradiated (5 min exposure once a day) with UVB rays (312 nm) for 4 days (shorter procedure) or 8 days (longer procedure). The eyes were examined microbiologically and only the corneas of sterile eyes or eyes with non-pathogenic microbes were employed. Histochemically, the activities of reactive oxygen species (ROS)-generating oxidases (xanthine oxidase, D-amino acid oxidase and alpha-hydroxy acid oxidase) were examined in cryostat sections of the whole corneas. Biochemically, the activity of xanthine oxidoreductase/xanthine oxidase was investigated in the scraped corneal epithelium. UVB rays significantly changed enzyme activities in the corneas. In comparison to the normal cornea, where of ROS-generating oxidases only xanthine oxidase showed significant activity in the corneal epithelium and endothelium, D-amino acid oxidase was very low and alpha-hydroxy acid oxidase could not be detected at all, in the cornea repeatedly irradiated with UVB rays, increased activities of xanthine oxidase and D-amino acid oxidase were observed in all corneal layers. Only after the longer procedure the xanthine oxidase and D-amino acid oxidase activities were decreased in the thinned epithelium in parallel with its morphological disturbances. Further results show that the xanthine oxidase/xanthine oxidoreductase ratio increased in the epithelium together with the repeated irradiation with UVB rays. This might suggest that xanthine dehydrogenase is converted to xanthine oxidase. However, in comparison to the normal corneal epithelium, the total amount of xanthine oxidoredutase was decreased in the irradiated epithelium. It is presumed that xanthine oxidoreductase might be released extracellularly (into tears) or the enzyme molecules were denatured due to UVB rays (particulary after the longer procedure). Comparative histochemical and biochemical findings suggest that reactive oxygen species-generating oxidases (xanthine oxidase, D-amino acid oxidase) contribute to the corneal damage evoked by UVB rays.

Tear film MMP accumulation and corneal disease

BACKGROUND/AIMS

Matrix metalloproteinases (MMPs) accumulate in the tears of patients with active peripheral ulcerative keratitis (PUK) but it is unknown whether these enzymes have a central role in disease progression. The aims of the present investigation were to determine the source of these enzymes and to ascertain whether their accumulation in tears is a phenomenon specific to PUK or a general feature of other anterior segment diseases.

METHODS

The experimental samples were obtained from the culture media of conjunctival and corneal epithelial cells, from fractionated blood plasma and leucocytes of healthy subjects and patients with rheumatoid arthritis, and from the tears of healthy subjects and patients with a variety of anterior segment diseases. The MMPs of all samples were visualised by zymography and tear samples were assayed using nitrophenol acetate and an MMP-9 susceptible quenched fluorescent peptide as substrate.

RESULTS

The major MMPs that accumulate in the tears of patients with rheumatoid arthritis with active ocular disease are MMP-9 and a species of M(r) 116,000. By comparing the zymographic activity profiles of the gelatinases present in the samples obtained, it was deduced that the main source of these MMPs was granulocytes. Their accumulation in tears was not unique to patients with PUK; detectable amounts of the enzymes also occurred in the tears of patients with keratoconus with associated atopic disease, patients undergoing treatment for herpetic eye disease, and patients with systemic and non-systemic dry eye disease.

CONCLUSION

The MMPs that accumulate in tears are mainly derived from granulocytes. This may be effected by autoimmune diseases that involve ocular tissue or by ocular diseases that induce an inflammatory response.

Membrane-type matrix metalloproteinases in mice intracorneally infected with Pseudomonas aeruginosa

PURPOSE

To establish the presence of membrane-type matrix metalloproteinases (MT-MMPs) in the cornea and their expression in naive and immunized mice intracorneally infected with Pseudomonas aeruginosa.

METHODS

Naive (unimmunized) and immunized C57BL/6J mice were infected with P. aeruginosa, and gene expression of MT-MMPs were detected by RT-PCR. Immunoblot analysis and immunostaining were also used to characterize the MT-MMP response in both sets of animals.

RESULTS

Expression of MT1-MMP, MT2-MMP, and MT3-MMP (MMP 14, 15, and 16) was detected by RT-PCR and immunoblot analysis. Of the three MT-MMPs detected, MT1-MMP exhibited the greatest expression at protein levels. In general, a bell-shaped curve was obtained for each of the MT-MMPs in naive mice, but all of them showed much less expression in the immunized mice. MT1-MMP was localized in the epithelial tissue of the cornea, whereas MT2-MMP and MT3-MMP were mainly found in the interface between the epithelium and substantia propria.

CONCLUSIONS

MT1-MMP was detected and expressed to a greater extent in naive mice than MT2-MMP and MT3-MMP. Peak expression of all three MT-MMPs showed a good correlation with the overall inflammatory response.

Transketolase gene expression in the cornea is influenced by environmental factors and developmentally controlled events

PURPOSE

Transketolase (TKT) has been proposed to be a corneal crystallin, and its gene and protein are abundantly expressed in the corneal epithelium of several mammals. A marked up-regulation of TKT gene expression coincides with the time of eyelid opening in the mouse. Here, we examined whether exposure to incident light contributes to the up-regulation of TKT gene expression during cornea maturation.

METHODS

Mice were raised in either standard light/dark cycling conditions or total darkness. In some cases, subcutaneous injections of epidermal growth factor (EGF) were given beginning on the day of birth to induce early eyelid opening. RNA was prepared from the corneas of mothers and pups and subjected to Northern blot analyses. In addition, the relative levels of TKT mRNA and/or enzyme activity were examined in the corneas of human, bovine, rat, chicken, and zebrafish.

RESULTS

TKT mRNA levels were 2.1-fold higher in the corneas of 25-day-old mouse pups ( 12 days after eyelid opening) that had been born and raised in light/dark conditions compared to pups born and raised in total darkness. By contrast, the level of TKT mRNA in the mature corneas of adult mice maintained in the dark for 2-8 weeks did not vary greatly from those of mice maintained in light/dark conditions. Interestingly, TKT mRNA levels in the corneas of dark-raised mice, although reduced, did exhibit the increase characteristically observed before and after eyelid opening. In addition, TKT mRNA levels were elevated fivefold in the corneas of 28-day-old mice raised in darkness and injected with EGF compared to uninjected mice also deprived of light. The EGF-injected mice opened their eyes 3 days early, and their corneal epithelium did not grossly differ from that of control mice. TKT mRNA and/or enzyme activity was found to be much higher in the corneas than in other tissues of humans, bovines, and rats but was extremely low in the corneas of chicken and zebrafish.

CONCLUSION

Our studies suggest that both exposure to incident light and events surrounding the process of eyelid opening play a role in the up-regulation of TKT gene expression observed during corneal maturation in mice. Light appears to play a less important role in the mature cornea in maintaining high levels of TKT gene expression. The low levels of TKT in the cornea of chicken and zebrafish support the notion that TKT acts as a taxon-specific enzyme-crystallin in mammals. The involvement of environmental signals for this putative, mammalian cornea crystallin contrasts with the purely developmental signals involved in the up-regulation of the crystallin genes of the lens.

Plasminogen activator activity in tears after excimer laser photorefractive keratectomy

PURPOSE

To quantify changes of plasminogen activator activity in tear fluid during corneal re-epithelialization after excimer laser photorefractive keratectomy (PRK).

METHODS

Tear samples were collected with glass capillaries from 77 eyes of 42 patients immediately before and immediately after PRK treatment and on postoperative days 3 and 5. In 20 patients, the contralateral eye was similarly sampled to serve as control. Plasminogen activator activity in the tear samples was measured by a spectrophotometric method using human plasminogen and chromogenic peptide substrate, D-valyl-L-leucyl-L-lysine-p-nitroanilide (S-2251).

RESULTS

In tears of all eyes that underwent PRK, the plasminogen activator activities were lower immediately after PRK than were the preoperative values. For patient eyes with normal wound healing, tear plasminogen activator activities were significantly elevated above the preoperative level on the third postoperative day and then returned to the preoperative level by the fifth postoperative day. In contrast, tear plasminogen activator activities remained low through the third postoperative day in all (six) eyes in which haze developed after 3 to 6 months. The contralateral control eyes showed no appreciable change in plasminogen activator activity over the 5-day period.

CONCLUSIONS

Plasminogen activator activity levels measured in tears of excimer laser PRK-treated eyes may serve as a predictor of wound healing. Extended low levels of plasminogen activator activity through the third postoperative day correlate with the development of corneal healing abnormalities (haze). The low plasminogen activator activity could be not only an accompanying sign but also a cause of defective corneal wound healing.

Changes of superoxide dismutase, catalase and glutathione peroxidase in the corneal epithelium after UVB rays. Histochemical and biochemical study

In this study, the effects of UVA and UVB rays on antioxidant enzymes (superoxide dismutase, glutathione peroxidase, catalase) were examined in the corneal epithelium. The corneas of albino rabbits were irradiated with a UV lamp generating UVA (365 nm wavelength) or UVB rays (312 nm wavelength), 1 x daily for 5 min, from a distance of 0.03 m, over 4 days (shorter procedure) or 8 days (longer procedure). In contrast to UVA rays, which did not evoke significant disturbances, UVB rays changed the activities of antioxidant enzymes. The longer repeated irradiation with UVB rays was performed, the deeper the observed decrease in antioxidant enzymes. The shorter procedure evoked a more profound decrease of glutathione peroxidase and catalase (the enzymes cleaving hydrogen peroxide) than of superoxide dismutase, an enzyme scavenging superoxide radical and producing hydrogen peroxide during the dismutation reaction of a superoxide free radical. This may contribute to an insufficient hydrogen peroxide cleavage at the corneal surface and danger to the cornea from oxidative damage. After the longer procedure (UVB rays), the activities of all antioxidant enzymes were very low or completely absent. In conclusion, repeated irradiation of the cornea with UVB rays evokes a deficiency in antioxidant enzymes in the corneal epithelium, which very probably contributes to the damage of the cornea (and possibly also deeper parts of the eye) from UVB rays and the reactive oxygen products generated by them.

The effect of sodium hyaluronate on the expression of gelatinases in rabbit corneal epithelial wound healing

PURPOSE

We investigated the effect of sodium hyaluronate (Na-HA) on the expression of gelatinases in a rabbit model with corneal epithelial defects.

METHODS

Topical administration of Na-HA or phosphate-buffered saline (PBS) was carried out in the experimental eyes after surgical removal of the corneal epithelium. At 0, 6, 24, 48, and 72 hours after wounding, mRNA expression of 72 kDa type gelatinase (MMP-2), 92 kDa type gelatinase (MMP-9), and tissue inhibitor of matrix metalloproteinases-1 (TIMP-1) were analyzed by reverse transcription polymerase chain reaction in those corneas. In addition, gelatinolytic activities were investigated using gelatin zymography.

RESULTS

The levels of constitutive expression of MMP-2 and TIMP-1 mRNA persisted, whereas MMP-9 mRNA in the PBS-treated side was expressed temporarily after surgical removal. In the Na-HA-treated side, at 6 hours after wounding, a much higher expression of MMP-9 mRNA was reproducibly observed compared with that in the PBS-treated side. In zymography, the levels of gelatinolytic activity corresponding to proMMP-9 were significantly higher in the Na-HA-treated side than in the PBS-treated side at 6 hours after wounding.

CONCLUSIONS

These results suggest a novel participation of Na-HA in the expression of MMP-9 in rabbit corneal epithelial wound healing.

Differential expression of MT1-MMP (MMP-14) and collagenase III (MMP-13) genes in normal and wounded rat corneas

PURPOSE

Several members of the matrix metalloproteinase (MMP) group have been identified in the rat cornea during corneal wound healing. The aim of the present study was to identify additional members of the MMP gene family in the rat cornea and localize the expression of membrane type-1 matrix metalloproteinase (MT1-MMP; MMP-14) and collagenase III (MMP-13) in normal and wounded corneas.

METHODS

Adult rats underwent laser keratectomy on the right eye. Unwounded left eyes were normal controls. Corneas were collected and processed at different times post-wounding. Reverse transcription-polymerase chain reaction (RT-PCR) and DNA sequencing were used to discover the MMP genes expressed in the corneas. In situ hybridization was performed to localize the mRNA expression of MMP-14 and MMP-13.

RESULTS

MMP-13 mRNA was detected in epithelial cells of wounded corneas, but not in normal controls; MMP-14 was found in both normal and wounded corneas. MMP-14 mRNA was expressed predominantly in the stromal keratocytes and rarely in the basal epithelial cells in normal and wounded corneas. MMP-13 mRNA was localized exclusively to basal cells of the epithelium at the wounded area from 6 hours to 3 days after wounding.

CONCLUSIONS

MMP-14 and MMP-13 expression in rat corneas parallels that of gelatinases A and B, respectively. MMP-13 may play an important role in the gelatinase B-associated proteolytic cascade that allows rapid turnover of the extracellular matrix (ECM) components during corneal wound healing. MMP-14 may contribute to removing abnormal ECM components through activation of gelatinase A in rat corneas.