Expression of HGF, KGF, EGF and receptor messenger RNAs following corneal epithelial wounding

Direct inhibition of EGF receptor activation in vascular endothelial cells by gefitinib ('Iressa', ZD1839)

The development of gefitinib ('Iressa', ZD1839) by targeting the EGFR tyrosine kinase is a recent therapeutic highlight. We have reported that gefitinib is antiangiogenic in vitro, as well as in vivo. In this study, we asked if the anti-angiogenic action of gefitinib is due to a direct effect on activation of vascular endothelial cells by EGF. EGF, as well as VEGF, caused pronounced angiogenesis in an avascular area of the mouse cornea, and i.p. administration of gefitinib almost completely blocked the response to EGF, but not to VEGF. Immunohistochemical analysis demonstrated phosphorylation of EGFR by EGF in the neovasculature, and gefitinib markedly reduced this effect. Gefitinib also inhibited downstream activation of ERK 1/2 via EGFR in cultured microvascular endothelial (HMVE) cells. These findings suggest that the anti-angiogenic effect of gefitinib in the vascular endothelial cells of neo-vasculature is partly attributable to direct inhibition of EGFR activation, and that endothelial cells in malignant tumors play a critical role in the cancer therapeutic efficacy of gefitinib.

Wound-induced HB-EGF ectodomain shedding and EGFR activation in corneal epithelial cells

PURPOSE

Epithelial wound healing is, at least in part, mediated in an autocrine fashion by epidermal growth factor (EGF) receptor (EGFR)-ligand interactions. This study sought to identify the endogenous EGFR ligand and the mechanism by which it is generated in response to wounding in cultured porcine corneas and human corneal epithelial cells.

METHODS

Epithelial debridement wounds in cultured porcine corneas and scratch wounds in an epithelial monolayer of SV40-immortalized human corneal epithelial (THCE) cells were allowed to heal in the presence of tyrphostin AG1478 (an EGFR inhibitor), GM6001 (a matrix metalloproteinase [MMP] inhibitor), or CRM197 (a diphtheria toxin mutant), with or without HB-EGF. The activation of EGFR and extracellular signal-regulated kinase (ERK) was analyzed by immunoprecipitation using EGFR antibodies and Western blot analysis with phosphotyrosine antibody. Wound induced HB-EGF shedding was assessed by isolation of secreted HB-EGF from wounded THCE cells and by measuring the release of alkaline phosphatase (AP) in THCE stable cell lines expressing HB-EGF-AP.

RESULTS

In THCE cells, wound-induced EGFR phosphorylation and ERK activation. In both organ and cell culture models, epithelial wounds were healed in basal media and inhibition of EGFR activation by AG1478 blocked wound closure with or without exogenously added HB-EGF. GM6001 delayed wound closure. Its effects diminished in the presence of exogenous EGF or HB-EGF, suggesting that the MMP inhibitor primarily blocks the release of EGFR ligands. CRM197, a highly specific antagonist of HB-EGF, impaired epithelial wound closure, suggesting that HB-EGF is an endogenous ligand released on epithelial wounding. Consistent with the effects on epithelial migration, all inhibitors as well as HB-EGF function-blocking antibodies retarded wound-induced EGFR phosphorylation in cultured THCE cells. The release of HB-EGF in response to wounding was demonstrated by the fact that heparin-binding proteins isolated from wounded, but not control, THCE-conditioned medium stimulated EGFR and ERK phosphorylation and by the expression of HB-EGF-AP in THCE cells, in which wounding induced the release of AP activity in an MMP-inhibitor-sensitive manner.

CONCLUSIONS

HB-EGF released on wounding acts as an autocrine-paracrine EGFR ligand. HB-EGF shedding and EGFR activation represent a critical event during corneal epithelial wound healing, suggesting a possible manipulation of wound healing during the early phases.

Keratocyte activation and inflammation in diffuse lamellar keratitis after formation of an epithelial defect

PURPOSE

To examine the inflammatory reaction in acute or late-onset post-laser in situ keratomileusis (LASIK) diffuse lamellar keratitis (DLK) associated with an epithelial defect.

SETTING

Department of Ophthalmology, Helsinki University Central Hospital, Helsinki, Finland.

METHODS

Six consecutive LASIK patients presented with stage 2 to 3 unilateral DLK 1 to 4 days after formation of an epithelial detachment (intraoperatively or up to 19 months postoperatively). Five corneas of 5 DLK patients, 1 eye twice, were examined by corneal in vivo confocal microscopy 1 to 8 days after the appearance of the epithelial defect. Confocal microscopy of conjunctival venules was performed in 2 of 6 DLK patients to quantify leukocyte rolling and extravasation. Corneas of 5 patients and conjunctival venules of 4 patients who had uneventful LASIK served as controls.

RESULTS

Two of the 4 patients examined 0 to 1 day after the onset of DLK presented with small objects, presumably inflammatory cells (diameter 6.0 to 10.0 microm), in the LASIK flap interface. A third patient examined 1 day after the onset of DLK had larger objects (approximately 13.0 microm in diameter) in the interface. Three other cases (1 to 7 days after the onset of DLK) showed changes typical of keratocyte activation and altered extracellular matrix. All cases healed completely following treatment with steroids. Control LASIK subjects showed some keratocyte activation on day 5.

CONCLUSIONS

Neither uneventful LASIK nor DLK induced an inflammatory reaction displaying leukocyte rolling in conjunctival venules or extravasation into the conjunctival stroma. Diffuse lamellar keratitis related to an epithelial defect does not always lead to the appearance of inflammatory cells in the flap interface. The corneal manifestations of epithelial defect-related DLK may originate from sterile epithelial-stromal or inflammatory cell-stromal cell interactions, leading to alteration of the keratocyte phenotype.

Epidermal growth factor receptor regulates normal urothelial regeneration

Members of the epidermal growth factor (EGF) family and their receptors are involved in many cellular processes, including proliferation, migration, and differentiation. We have previously reported that these growth factors are expressed and have specific regulatory functions in an organ-like culture model of normal human urothelial cells. Here, we used this model to investigate the involvement of EGF receptor (EGFR) in human urothelial regeneration. Three 4-mm-diameter damaged areas were made in confluent normal human urothelial cell cultures with a biopsy punch. Regeneration was measured, on fixed stained cultures, with an image analyzer, at 4, 24, and 48 hours after injury. Cell proliferation was assessed by 5-bromo-2-deoxyuridine incorporation. To identify EGF family factors potentially involved in the healing process, we studied the effect of these factors on damaged confluent cultures and the level of expression of mRNAs extracted from these cultures. EGFR inhibition of the proliferation and migration of urothelial cells was tested with (1). a specific tyrosine kinase inhibitor (AG1478) and (2). a blocking anti-EGFR antibody (LA22). Exogenously added amphiregulin, EGF, transforming growth factor-alpha and heparin-binding EGF (HB-EGF) stimulated urothelial regeneration. The damaged areas were repaired by regrowth within 48 hours. Both AG1478 and LA22 inhibited the repair (by 50% and 30%, respectively), as well as proliferation and migration. This regeneration was accompanied by increased HB-EGF mRNA expression in cultures of cells from four of six subjects, but no corresponding change in EGFR protein level was observed. These results indicate that the EGFR signaling pathway is involved in urothelial regeneration. Our data support an autocrine role of HB-EGF in this process and suggest that the EGFR pathway is a potential therapeutic target for modulating urothelial cell proliferation.

Corneal cells: chatty in development, homeostasis, wound healing, and disease

PURPOSE

To provide an overview of cell-cell interactions in the cornea that have a critical role in corneal development, homeostasis, wound healing, and disease.

DESIGN

Review.

METHODS

Review of the literature. RESULTS; Cell-cell interactions make critical contributions to development, homeostasis, and wound healing in the cornea. Many of these interactions are mediated by cytokines, growth factors, and chemokines. The best characterized are stromal-epithelial interactions between epithelial cells and stromal cells such as keratocytes, keratoblasts, and myofibroblasts. However, interactions also occur between corneal nerves and epithelial cells and between corneal cells (epithelial cells and stromal cells) and corneal immune cells. Although investigations are limited, it is likely that there are interactions between corneal endothelial cells and keratocytes in the posterior stroma.

CONCLUSIONS

Cellular communications in the cornea are critical during development, homeostasis, and wound healing. Disorders of cellular communication likely contribute to many corneal diseases.

p38 and ERK1/2 coordinate cellular migration and proliferation in epithelial wound healing: evidence of cross-talk activation between MAP kinase cascades

One important action of growth factors is their participation in tissue repair; however, the signaling pathways involved are poorly understood. In a model of corneal wound healing, we found that two paracrine growth factors, hepatocyte growth factor (HGF) and keratinocyte growth factor (KGF), induced rapid and marked activation and prompt nuclear accumulation of phospho-p38 (p-p38) and -ERK1/2 (p-ERK1/2), but not of JNK (p-JNK1/2), in corneal epithelial cells. Interruption of p38 and ERK1/2 signaling pathways by pretreatment with inhibitors SB203580 and PD98059 and subsequent stimulation with HGF or KGF abolished the activation and nuclear localization. Inhibition of either one of these mitogen-activated protein kinases, p38 or ERK1/2, induced a robust cross-activation of the other. In immunofluorescence studies of wounded cornea, p-p38, unlike p-ERK1/2, was immediately detectable in epithelium after injury. Inhibition of p38 by SB203580 blocked migration of epithelial cells almost completely. In contrast, PD98059 seemed to slightly increase the migration, through concomitant activation of p38. Unlike ERK1/2, p38 did not significantly contribute to proliferation of epithelial cells. Inhibition of either the ERK1/2 or p38 pathway resulted in delayed corneal epithelial wound healing. Interruption of both signaling cascades additively inhibited the wound-healing process. These findings demonstrate that both p38 and ERK1/2 coordinate the dynamics of wound healing: while growth factor-stimulated p38 induces epithelial migration, ERK1/2 activation induces proliferation. The cross-talk between these two signal cascades and the selective action of p38 in migration appear to be important to corneal wound healing, and possibly wound healing in general, and may offer novel drug targets for tissue repair.

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.

Histological and immunohistochemical findings after laser in situ keratomileusis in human corneas

PURPOSE

To describe histopathological and immunohistochemical findings in human corneas after myopic laser in situ keratomileusis (LASIK) followed by iatrogenic keratectasia and after hyperopic LASIK.

SETTING

Department of Ophthalmology, University of Innsbruck, Innsbruck, Austria.

METHODS

Clinical, histological, and immunohistochemical investigations were performed of 1 human cornea with iatrogenic keratectasia following myopic LASIK and 1 human cornea with irregular astigmatism and central scar formation after hyperopic LASIK. Corneal buttons were obtained during penetrating keratoplasty in both patients.

RESULTS

Histopathological examination showed thinning of the central stroma with a posterior residual thickness of 190 microm in the patient with iatrogenic keratectasia after myopic LASIK and significant midperipheral thinning in the patient who had hyperopic LASIK. However, this characteristic ablation profile of the stroma after hyperopic LASIK was partially mitigated and compensated by the epithelium, which was significantly thinned in the center and markedly thickened in the midperiphery. Traces of wound healing with minimal scar tissue were present at the flap margin after myopic and hyperopic LASIK. In a few sections of the cornea with keratectasia after myopia LASIK, only a few collagen lamellae were visible crossing between the posterior residual stroma and the superficial flap. Immunohistochemical examination revealed minimally increased staining of dermatan sulfate proteoglycan within the stroma adjacent to the interface of the microkeratome incision. Increased staining of hepatocyte growth factor was found on keratocytes/fibroblasts at the flap margin in both corneas.

CONCLUSIONS

The wound-healing response is generally poor after LASIK, which may result in significant weakening of the tensile strength of the cornea after myopic LASIK, probably due to biomechanically ineffective superficial lamella. After LASIK in patients with high hyperopia, compensatory epithelial thickening in the annular midperipheral ablation zone might be partly responsible for regression.

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

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

Injury-elicited differential transcriptional regulation of phospholipid growth factor receptors in the cornea

The phospholipid growth factors (PLGFs), including lysophosphatidic acid (LPA), have been implicated in corneal wound healing. PLGF concentrations and activities are elevated after corneal injury. Using real-time PCR, we quantified receptor mRNA levels in the healing rabbit cornea. In intact corneas, transcripts for S1P(1), LPA(1), and LPA(3) receptor subtypes were detected, as was lipid phosphate phosphatase 1 (LPP1). After wounding, the trend for endothelium and keratocytes was for significant decreases in transcript numbers for the three receptor subtypes, whereas epithelial cells showed increased transcript numbers, except for an S1P(1) decrease in healing cells. LPP1 transcript numbers were decreased in keratocytes and endothelium, although LPP-specific activity was unchanged. LPA-elicited Ca(2+) transients were significantly reduced in the healing endothelium. Consistent with reduced LPA(3) receptor numbers, dioctylglycerol pyrophosphate, a selective antagonist, reduced LPA-induced Ca(2+) transients 2.7-fold in nonwounded epithelium but only 1.5-fold in wound-healing endothelium. These data for the first time establish physiologically relevant differential changes in the expression of PLGF receptor subtypes and provide evidence for the changing role of LPA(3) receptors in endothelial cells.

The role of platelet-activating factor in the corneal response to injury

Platelet-activating factor (PAF) is a potent bioactive lipid that is generated in the cornea after injury and whose actions are mediated through specific receptors. Studies from our laboratory have shown that PAF interactions with its receptor activate several transmembrane signals involved in inflammation, wound healing, and apoptosis. The wide variety of responses to PAF implicate this lipid as a central player in many responses of the cornea after a pathologic stimulus. An exciting facet of PAF is that it induces the expression of specific genes involved in the remodeling of components of the extracellular matrix, such as some metalloproteinases, urokinase plasminogen activator, and selective inhibitors of metalloproteinases. These enzymes, when overexpressed, could lead to corneal ulceration. Continuous exposure to PAF during prolonged inflammation produces increase keratocyte apoptosis and inhibition of epithelial adhesion to the basement membrane. As a consequence, there is a marked delay in wound healing, which is not countered by the actions of growth factors. In this review, we present data mainly from our laboratory showing actions of PAF in corneal epithelium in vivo and in vitro in corneal models of injury as well as in cells in culture. We also discuss the signal-transduction mechanisms involved in the different actions of PAF. A therapeutic role for PAF antagonists in blocking the effects of PAF is guaranteed in the future.

Corneal haze after photorefractive keratectomy for myopia: role of collagen IV mRNA typing as a predictor of haze

PURPOSE

To develop a test based on the individual expression of collagen type IV synthesis in corneal epithelial cells to identify patients who have the potential for significant corneal haze after myopic photorefractive keratectomy (PRK).

SETTING

Department of Ophthalmology and the Institute of Microbiology, University of Regensburg, Germany.

METHODS

The individual synthesis of collagen type IV alpha3 mRNA was quantitatively measured in corneal epithelial cells of 34 eye (34 patients) with myopia ranging from -1.5 to -10.0 diopters (D) by a polymerase chain reaction (PCR) test. The corneal epithelial cells were collected before the PRK procedure. Collagen type IV alpha3 mRNA levels were correlated to postoperative haze and regression at 12 months.

RESULTS

In all samples, collagen type IV alpha3 mRNA was detected; the mean was 1.47 (range 0.11 to 6.42). There was a correlation between haze and the amount of collagen type IV alpha3 mRNA; that is, eyes with haze had more collagen IV expression. In contrast, no correlation was observed between regression and the amount of collagen type IV alpha3 mRNA.

CONCLUSIONS

The results show that collagen type IV alpha3 is an important factor in the development of corneal haze after PRK. Based on a quantitative PCR test, the individual collagen IV mRNA concentration in corneal epithelial cells could be measured. Further development could establish a screening test by which eyes with pronounced synthesis of collagen IV could be identified as being at high risk for haze after PRK.

Growth factors in corneal wound healing following refractive surgery: A review

The first part of this review article aims to provide important basic definitions of growth factor terminology, and to put forward a model for understanding the role of growth factors in a wound healing context. In the second part of the paper, we review the literature on growth factors in the cornea, including that on changes associated with wound healing following refractive surgery in the epithelial, stromal, and endothelial layers. The role of growth factors in stromal removal, corneal neovascularization, corneal innervation and wound healing is considered. The importance of the epithelial-stromal interaction is discussed, including the role of growth factors in keratocyte apoptosis. In the final section, we review the current literature on endogenous and exogenous modulation of growth factors in corneal wound healing. This includes important in vitro work but aims to emphasize clinically relevant results. Photorefractive keratectomy (PRK) may have short-term complications such as pain and haze, whereas laser in situ keratomilieusis (LASIK) may have longer-term adverse effects on corneal biomechanics. The emerging technique of laser epithelial keratomilieusis (LASEK) provides an interesting alternative wound which may be less susceptible to the inherent complications of PRK and LASIK. At present, the phenomenon of iatrogenic keratectasia following LASIK is not fully understood, but these features of wound healing following PRK may be amenable to growth factor modulation.

Characteristics of the human ocular surface epithelium

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

Regeneration of rabbit cornea following excimer laser photorefractive keratectomy: a study on gap junctions, epithelial junctions and epidermal growth factor receptor expression in correlation with cell proliferation

Corneal wound repair was investigated in rabbits following excimer laser ablation of a 6 mm diameter and 90 microm deep disc. In the healing process particular attention was focused on the epithelium where gap junction expression and the rearrangement of desmosomes and hemidesmosomes were correlated with cell proliferation and epidermal growth factor receptor expression. Immunofluorescence-based confocal laser scanning microscopy, semithin resin section morphology and electron microscopy were utilized. In resting cornea two isotypes of gap junctions, confined to different regions in the same basal epithelial cells, were detected. Particulate connexin43 (alpha1) immunostaining was concentrated on the apical while the connexin26 type (beta2) in the baso-lateral cell membranes. This is the first report of connexin26 in the cornea. Connexin43 was found also in corneal keratocytes and endothelial cell. Since the two connexins do not form functioning heteromeric channels and have selective permeabilities they may serve alternative pathways for direct cell-cell communication in the basal cell layer. During regeneration both connexins were expressed throughout the corneal epithelium including the migrating cells. They also showed transient up-regulation 24 hr after wounding in the form of overlapping relocation to the upper cell layers. At this time, basal epithelial cells at the limbal region, adjacent to the wound and those migrating over the wounded area all expressed membrane bound epidermal growth factor receptor and they were highly proliferating. In conclusion, like in other stratified epithelia connexin26 is also expressed in the cornea. Transient up-regulation and relocation of connexins within the regenerating epithelium may reflect the involvement of direct cell-cell communication in corneal wound healing. Mitotic activity in the migrating corneal epithelial cells is also a novel finding which is probably the sign of the excessive demand for new epithelial cells in larger wounds not met alone by the proliferating limbal stock.

HGF- and KGF-induced activation of PI-3K/p70 s6 kinase pathway in corneal epithelial cells: its relevance in wound healing

In this study we have investigated the involvement of PI-3K and its downstream target p70 S6K in the signaling response of corneal epithelial cells after HGF and KGF stimulation. HGF induced three- to five-fold increase in PI-3K activity in 5-10 min, whereas KGF stimulation resulted in two- to three-fold increase in activity in 2-10 min. Both growth factors also caused the phosphorylation of p70 S6K and stimulation of its activity. HGF increased p70 S6K activity by 300% and KGF by about 200%. Protein kinase C (PKC) activator TPA also induced the phosphorylation of p70 S6K. Both the PI-3K inhibitor wortmannin and PKC inhibitor calphostin C blocked the phosphorylation of p70 S6K mediated by the growth factors. However, the mitogen-activated protein kinase (p42/44 MAPK) cascade inhibitor PD98059 had no effect on p70 S6K activation. Furthermore, HGF and KGF increased the rate of corneal epithelial wound healing in an organ culture model, and wortmannin and rapamycin (the p70 S6K inhibitor) blocked corneal epithelial wound healing promoted by the growth factors. These studies suggest that PI-3K and p70 S6K are important signal transducers in the stimulation of corneal epithelial cells by HGF and KGF. PKC is involved in the PI-3K-dependent activation of p70 S6K but not MAPK. Inhibition of wound closure by PI-3K and p70 S6K inhibitors suggests these enzymes play a significant role in corneal wound repair stimulated by HGF and KGF.

Diffuse Lamellar Keratitis Associated With Recurrent Corneal Erosions After Laser in situ Keratomileusis

PURPOSE

Diffuse lamellar keratitis (DLK) is marked by the presence of diffuse or multifocal infiltrates confined to the laser in situ keratomileusis (LASIK) interface. These infiltrates are culture-negative, and the etiology is thought to be noninfectious. Most cases of DLK occur within the first week or two following surgery.

METHODS

We describe one case of diffuse lamellar keratitis that occurred 3 months after LASIK. The patient developed a spontaneous corneal erosion in one eye. Over the next 2 days while the erosion was being treated, there was rapid development of DLK. Slit-lamp biomicroscopy and in vivo scanning slit confocal microscopy were performed. The patient was treated with intensive topical corticosteroids.

RESULTS

Scanning slit confocal microscopy revealed numerous, highly-reflective round bodies consistent with a polymorphonuclear infiltrate located at the flap interface. Treatment with topical 1.0% prednisolone acetate was instituted, with rapid improvement in patient symptoms, visual acuity, and slit-lamp biomicroscopy.

CONCLUSIONS

Diffuse lamellar keratitis may occur months after LASIK as a result of a spontaneous recurrent corneal epithelial erosion.

Corneal epithelial wound healing

One of the important functions of the cornea is to maintain normal vision by refracting light onto the lens and retina. This property is dependent in part on the ability of the corneal epithelium to undergo continuous renewal. Epithelial renewal is essential because it enables this tissue to act as a barrier that protects the corneal interior from becoming infected by noxious environmental agents. Furthermore, the smooth optical properties of the corneal epithelial surface are sustained through this renewal process. The rate of renewal is dependent on a highly integrated balance between the processes of corneal epithelial proliferation, differentiation, and cell death. One experimental approach to characterize these three aspects of the renewal process has been to study the kinetics and dynamics of corneal re-epithelialization in a wound-healing model. This effort has employed in vivo and in vitro studies. From such studies it is evident that the appropriate integration and coordination of corneal epithelial proliferation, adhesion, migration, and cell demise is dependent on the actions of a myriad of cytokines. Our goal here is to provide an overview into how these mediators and environmental factors elicit control of cellular proliferation, adhesion, migration, and apoptosis. To this end we review the pertinent literature dealing with the receptor and the cell signaling events that are responsible for mediating cytokine control of corneal epithelial renewal. It is our hope that a better appreciation can be obtained about the complexity of the control processes that are responsible for assuring continuous corneal epithelial renewal in health and disease.

Hepatocyte growth factor is increased in the aqueous humor of glaucomatous eyes

PURPOSE

To assess the concentrations of hepatocyte growth factor (HGF) in the aqueous humor of eyes with glaucoma compared with control eyes with cataract only.

METHODS

Concentrations of HGF were measured in aqueous humor aspirates taken during anterior segment surgery from 84 patients, of whom 72 had glaucoma (38 cases of primary open-angle glaucoma, 17 angle-closure glaucoma, and 17 exfoliative glaucoma) and 12 had cataract only, using a sandwich enzyme-linked immunosorbent assay kit.

RESULTS

Hepatocyte growth factor was detected in all samples. The concentration in eyes with cataract only was 563.3 +/- 178.8 pg/mL (mean +/- standard deviation), which was significantly lower than that in eyes with glaucoma (967.1 +/- 514.7 pg/mL, P < 0.01). Eyes with exfoliative glaucoma had significantly higher HGF concentrations (1,425.5 +/- 586.7 pg/mL) than did eyes with primary open-angle glaucoma (855.0 +/- 341.5 pg/mL) and angle-closure glaucoma (759.4 +/- 511.4 pg/mL) (P < 0.01). There was no effect of age, sex, or history of medical, laser, or surgical treatment on the aqueous humor HGF concentration (P > 0.05). Aqueous humor and plasma HGF concentrations were measured and compared in 28 patients. The aqueous humor HGF concentration (908 +/- 586.2 pg/mL) was significantly higher (P < 0.01) than the plasma concentration (521.3 +/- 183.1 pg/mL). No significant correlation could be found between aqueous humor and plasma HGF concentrations.

CONCLUSIONS

The relatively high concentration of HGF in human aqueous humor suggests that HGF may play an important role in ocular physiology and disease. The higher concentration in patients with glaucoma may indicate a response to injury.

Expression of the receptor tyrosine kinases, epidermal growth factor receptor, ErbB2, and ErbB3, in human ocular surface epithelia

PURPOSE

To investigate the distribution and relative level of expression of the receptor tyrosine kinases, epidermal growth factor receptor (EGFR), ErbB2 and ErbB3, in human ocular surface epithelia.

METHODS

Immunofluorescent staining was performed to identify expression of the EGFR, ErbB2 and ErbB3 in the corneal, limbal and conjunctival epithelium in tissue sections and impression cytologies taken from normal human eyes. Western blotting was undertaken to confirm the results of immunofluorescent staining.

RESULTS

The three receptor tyrosine kinases, EGFR, ErbB2 and ErbB3, were detected in human corneal, limbal and conjunctival epithelia by immunofluorescent staining. Strong staining for the EGFR was observed in the basal epithelial cells at all 3 sites and throughout the corneal epithelium. Minimal or no staining for the EGFR was observed in the superficial conjunctival and limbal epithelia. The strongest staining for ErbB2 and ErbB3 was observed in the superficial ocular surface epithelium. All three receptors were detected in the corneal, limbal and conjunctival epithelium by western blot.

CONCLUSION

EGFR, ErbB2 and ErbB3 are expressed by the ocular surface epithelia. EGFR is preferentially expressed by the basal epithelial cells that have the greatest proliferative potential. In contrast, ErbB2 and ErbB3 are preferentially expressed by the superficial differentiated ocular surface epithelia.

Postoperative Inflammation, Microbial Complications, and Wound Healing Following Laser in situ Keratomileusis

Although the biology of corneal wound healing is only partly understood, healing after photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) differs in many respects, and the mechanisms appear to be differently controlled. There is less of an inflammatory and healing response after LASIK, but a longer period of sensory denervation. The cellular, molecular, and neural regulatory phenomena associated with postoperative inflammation and wound healing are likely to be involved in the adverse effects after LASIK, such as flap melt, epithelial ingrowth, and regression. Interface opacities in the early postoperative period include diffuse lamellar keratitis (DLK), microbial keratitis, epithelial cells, and interface opacities. Diffuse lamellar keratitis (sands of the Sahara syndrome) describes an apparently noninfectious diffuse interface inflammation after lamellar corneal surgery probably caused by an allergic or a toxic inflammatory reaction. Noninfectious keratitis must be distinguished from microbial keratitis to avoid aggressive management and treatment with antimicrobial drugs. Microbial keratitis is a serious complication after LASIK, but a good visual outcome can be achieved following prompt and appropriate treatment.

The hepatocyte growth factor/Met pathway in development, tumorigenesis, and B-cell differentiation

This article summarizes the structure, signal transduction and physiologic functions of the HGF/Met pathway, as well as its role in tumor growth, invasion, and metastasis. Moreover, it highlights recent studies indicating a role for the HGF/Met pathway in antigen-specific B-cell development and B-cell neoplasia.