Molecular and cellular responses of the corneal epithelium to wound healing

In Vivo confocal microscopic changes of the corneal epithelium and stroma in patients with herpes zoster ophthalmicus

PURPOSE

To analyze the density and morphology of corneal epithelial cells and keratocytes by in vivo confocal microscopy (IVCM) in patients with herpes zoster ophthalmicus (HZO) as associated with corneal innervation.

DESIGN

Prospective, controlled and masked cross-sectional study.

METHODS

setting: Single-center study.

PATIENTS

Thirty eyes with the diagnosis HZO and their contralateral clinically unaffected eyes, 15 eyes of 15 normal controls. intervention procedures: In vivo confocal microscopy and corneal esthesiometry of the central cornea.

MAIN OUTCOME MEASURES

Changes in morphology and density of the superficial and basal epithelial cells and stromal keratocytes, and correlation with corneal sensation.

RESULTS

The density of superficial epithelial cells in HZO eyes with severe sensation loss (766.5 ± 25.2 cells/mm(2)) was significantly lower than both healthy control eyes (1450.23 ± 150.83 cells/mm(2)) and contralateral unaffected eyes (1974.13 ± 298.24 cells/mm(2)) (P = .003). Superficial epithelial cell size (1162.5 μm(2)) was significantly larger in HZO eyes with severe loss of sensation, as compared to contralateral (441.46 ± 298.14) or healthy eyes (407.4 ± 47.2μm(2); all P < .05). The density of basal epithelial cells, anterior keratocytes, and posterior keratocytes did not show statistical significance between patients, controls, and contralateral unaffected eyes. Changes in superficial epithelial cell density and morphology correlated strongly with corneal sensation.

CONCLUSIONS

In vivo confocal microscopy reveals profound HZO-induced changes in the superficial epithelium, as demonstrated by increase in cell size, decrease in cell density, and squamous metaplasia. We demonstrate that these changes strongly correlate with changes in corneal innervation in eyes affected by HZO.

A comparison of epithelial-to-mesenchymal transition and re-epithelialization

Wound healing and cancer metastasis share a common starting point, namely, a change in the phenotype of some cells from stationary to motile. The term, epithelial-to-mesenchymal transition (EMT) describes the changes in molecular biology and cellular physiology that allow a cell to transition from a sedentary cell to a motile cell, a process that is relevant not only for cancer and regeneration, but also for normal development of multicellular organisms. The present review compares the similarities and differences in cellular response at the molecular level as tumor cells enter EMT or as keratinocytes begin the process of re-epithelialization of a wound. Looking toward clinical interventions that might modulate these processes, the mechanisms and outcomes of current and potential therapies are reviewed for both anti-cancer and pro-wound healing treatments related to the pathways that are central to EMT. Taken together, the comparison of re-epithelialization and tumor EMT serves as a starting point for the development of therapies that can selectively modulate different forms of EMT.

Cellular changes of the corneal epithelium and stroma in herpes simplex keratitis: an in vivo confocal microscopy study

PURPOSE

To analyze the morphologic features of corneal epithelial cells and keratocytes by in vivo confocal microscopy in patients with herpes simplex keratitis (HSK) as associated with corneal innervation.

DESIGN

Prospective, cross-sectional, controlled, single-center study.

PARTICIPANTS

Thirty-one eyes with the diagnosis HSK and their contralateral clinically unaffected eyes were studied and compared with normal controls (n = 15).

METHODS

In vivo confocal microscopy (Confoscan 4; Nidek Technologies, Gamagori, Japan) and corneal esthesiometry (Cochet-Bonnet; Luneau Ophthalmologie, Chartres, France) of the central cornea were performed bilaterally in all patients and controls. Patients were grouped into normal (>5.5 cm), mild (>2.5-5.5 cm), and severe (<2.5 cm) loss of sensation.

MAIN OUTCOME MEASURES

Changes in morphologic features and density of the superficial and basal epithelial cells, as well as stromal keratocytes, were assessed by 2 masked observers. Changes were correlated to corneal sensation, number of nerves, and total length of nerves.

RESULTS

There was a significant and gradual decrease in the density of superficial epithelial cells in HSK eyes, with 852.50 ± 24.4 cells/mm(2) in eyes with severe sensation loss and 2435.23 ± 224.3 cells/mm(2) in control eyes (P = 0.008). Superficial epithelial cell size was 2.5-fold larger in HSK eyes (835.3 μm(2)) compared with contralateral or normal eyes (407.4 μm(2); P = 0.003). A significant number of hyperreflective desquamating superficial epithelial cells were present in HSK eyes with normal (6.4%), mild (29.1%), and severe (52.2%) loss of sensation, but were absent in controls. The density of basal epithelial cells, anterior keratocytes, and posterior keratocytes did not show statistical significance between patients and controls. Changes in superficial epithelial cell density and morphologic features correlated strongly with total nerve length, number, and corneal sensation. Scans of contralateral eyes did not show any significant epithelial or stromal changes compared with controls.

CONCLUSIONS

In vivo confocal microscopy reveals profound HSK-induced changes in the superficial epithelium, as demonstrated by increase in cell size, decrease in cell density, and squamous metaplasia. This study demonstrated that these changes correlate strongly with changes in corneal innervation.

Roughness of Excimer Laser Ablated Corneas With and Without Smoothing Measured With Atomic Force Microscopy

PURPOSE

To analyze the surface roughness of porcine corneas after excimer laser ablation with and without the smoothing procedure by means of atomic force microscopy.

METHODS

Excimer laser photorefractive keratectomy (PRK) was performed on eight porcine corneas. Immediately following the procedure, smoothing was performed on four corneas using a viscous solution of 0.25% sodium hyaluronate. The corneas were examined in balanced salt solution after fixation in 2.5% glutaraldehyde solution using atomic force microscopy. Quantitative analysis of the ablated stromal surface topography was performed using the section analysis module of the atomic force microscopy software. Repeated measurements were made over small areas (< or =50 microm2) near the center of each ablation, with a vertical resolution of <1 nm.

RESULTS

Images of the ablated stromal surface showed undulations and granule-like features on the ablated surface of the specimens. The specimens on which the smoothing procedure was performed (root-mean-square [RMS] rough: 0.152 +/- 0.014 microm) were more regular (P < .001) than those on which PRK alone was performed (RMS rough: 0.229 +/- 0.018 microm).

CONCLUSIONS

Atomic force microscopy analysis requires a simpler preparation of the specimens with respect to that necessary for scanning electron microscopy; for this reason, atomic force microscopy techniques are more reliable for the study of biological surfaces and prove to be a feasible method to establish the differences when comparing different laser techniques. Our investigations highlight that although the laser cut of scanning-spot excimer laser systems is precise in removing even the smallest amounts of tissue, the smoothing technique may still be useful to reduce post-ablation roughness.

Insulin, not leptin, promotes in vitro cell migration to heal monolayer wounds in human corneal epithelium

PURPOSE

To investigate the effects of insulin and leptin on in vitro wound healing of transformed human corneal epithelial cell monolayers and to identify cellular (migration versus proliferation) and intracellular signaling mechanisms.

METHODS

Scratch wounds were created in monolayers of an immortalized human corneal epithelial cell (HCEC) line. The wounded monolayers were exposed to insulin and leptin. Wound areas were measured every hour after wounding for up to 8 hours. Phosphoinositide 3-kinase (PI3-kinase) and mitogen-activated protein (MAP)-kinase signaling was analyzed with Western blot. The actions of insulin were also examined after incubation with inhibitors to extracellular signal regulated kinase (ERK 1/2) and PI3-kinase.

RESULTS

The presence of insulin, but not leptin facilitated closure of wounds created in corneal epithelial cell monolayers. Phosphorylation of ERK 1/2 and Akt was stimulated after exposure of the monolayers to insulin. Inhibitors of PI3-kinase and ERK 1/2 prevented or reduced insulin-induced corneal wound healing, respectively.

CONCLUSIONS

Exposure of corneal epithelium to insulin facilitated closure of in vitro small wounds through enhanced cell migration instead of proliferation, which depended on ERK 1/2 and PI3-kinase signaling. These data suggest a mechanism by which insulin may influence corneal wound healing in vitro. In vivo, disruptions to the insulin signaling pathway observed in diseases such as diabetes might account for the delayed wound healing and corneal defects.

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.

Trefoil peptides promote restitution of wounded corneal epithelial cells

The ocular surface shares many characteristics with mucosal surfaces. In both, healing is regulated by peptide growth factors, cytokines, and extracellular matrix proteins. However, these factors are not sufficient to ensure most rapid healing. Trefoil peptides are abundantly expressed epithelial cell products which exert protective effects and are key regulators of gastrointestinal epithelial restitution, the critical early phase of cell migration after mucosal injury. To assess the role of trefoil peptides in corneal epithelial wound healing, the effects of intestinal trefoil factor (ITF/TFF3) and spasmolytic polypeptide (SP/TFF2) on migration and proliferation of corneal epithelial cells were analyzed. Both ITF and SP enhanced restitution of primary rabbit corneal epithelial cells in vitro. While the restitution-enhancing effects of TGF-alpha and TGF-beta were both inhibited by neutralizing anti-TGF-beta-antibodies, trefoil peptide stimulation of restitution was not. Neither trefoil peptide significantly affected proliferation of primary corneal epithelial cells. ITF but not SP or pS2 mRNA was present in rabbit corneal and conjunctival tissues. In summary, the data indicate an unanticipated role of trefoil peptides in healing of ocular surface and demand rating their functional actions beyond the gastrointestinal tract.

Immunolocalization of transcription factor AP1 in human ocular surface epithelia

PURPOSE

The present study examined whether normal human ocular surfcae epithelia express AP1 components. Changes in expression patterns of these components in a case of ocular surface epithelial dysplasia was also evaluated before and after topical mitomycin C treatment.

METHODS

Specimens of normal corneas (n = 2) and conjunctiva (n = 4) were obtained from 4 patients during cataract surgery or post mortem, while specimens of dysplastic epithelial tissue from the limbus were obtained from one patient. Specimens were immunohistochemically studied using antibodies against components of AP1.

RESULTS

The normal corneal epithelium showed no staining with antibodies against c-Fos, Fra-2, FosB, c-Jun or JunB, whereas the limbal and bulbar conjunctival epithelia were positive for c-Fos, Fra-2, and c-Jun. Anti-FosB and -JunB antibodies reacted weakly with the conjunctival epithelium. JunD was absent in normal corneal and conjunctival epithelia. The dsyplastic epithelium showed positive labelling for c-Fos, Fra-2, c-Jun, and JunD throughout its thickness. Fra-1 was present in all specimens of epithelia examined. The dysplastic epithelium treated with mitomycin C was not labeled by anti-c-Fos or -Fra-2 antibody.

CONCLUSION

Individual AP1 components show specific expression patterns in normal ocular surface epithelia and a case of dysplastic epithelium before and after topical MMC treatment, implying that these factors may play important roles in modulating epithelial cell function, e.g., proliferation and differentiation.

Expression of fos family and jun family proto-oncogenes during corneal epithelial wound healing

PURPOSE

While transformation of epithelial cells to a motile form is the first step in wound healing of the corneal epithelium, the migratory mechanism in these cells is not fully understood. We studied the expression of proto-oncogene mRNAs: c-fos; c-jun; fos B; jun B; jun D in injured corneal epithelium using in situ hybridization. Moreover, we examined immunolocalization of c-Fos and c-Jun protein products to elucidate the transcriptional activation prior to the onset of migration in corneal epithelium.

METHODS

An epithelial defect was made on one cornea of 60 Wistar rats. The affected eye was enucleated immediately (within 5 min) or was allowed to heal for 15, 30, 60, 90, 120 and 180 min. Frozen sections were processed for in situ hybridization with c-fos, c-jun, fos B, jun B and jun D mRNAs or were stained with anti-c-fos and anti-c-jun antibodies.

RESULTS

Fifteen min after the epithelial ablation, weak signals for c-fos and c-jun mRNAs were detected in the corneal epithelium surrounding the wound. These signals reached a peak 30 to 60 min after ablation, but were no longer evident at 120 min. Immunoreactivities for these proteins were also detected in the same area at 60 to 120 min after the epithelial ablation. Fos B mRNA was detected in the same region at 30 min after the ablation, and reached its peak after 30 to 60 min, but was no longer evident at 120 min. Jun B mRNA was detected in the epithelium around the defect 60 min after the ablation, later than the other proto-oncogenes, and reached its peak after 90 min. The message for jun D was detected in normal epithelium, and was not affected by wounding.

CONCLUSIONS

These findings indicate that transcriptional activation of epithelial cells is initiated in the early phase after epithelial ablation, before the cells start to migrate, and that these proto-oncogene products may play important roles in wound healing in corneal epithelium. The time lag of the peak of expression of these proto-oncogenes in this process.

Expression of c-Fos and c-Jun in the cornea, lens, and retina after ultraviolet irradiation of the rat eye and effects of topical antisense oligodeoxynucleotides

AIMS

Immunohistochemical techniques were used to investigate c-Fos and c-Jun proto-oncogene expression in the cornea, lens, and retina after ultraviolet irradiation of the rat eye.

METHODS

Eyes of anaesthetised rats were exposed to 1.5 J/cm2 of ultraviolet radiation (280-380 nm). Animals were perfused 1, 6, or 24 hours after irradiation and tissue sections were incubated with specific antiserum to c-Fos and c-Jun, respectively.

RESULTS

Non-irradiated contralateral eyes displayed no c-Fos and c-Jun immunoreactivity. One and 6 hours after ultraviolet exposure numerous c-Fos and c-Jun immunopositive nuclei were observed mainly in the epithelial cell layers of the cornea and the lens epithelium. Scattered labelled nuclei were detectable in the retinal ganglion cell layer and the inner nuclear layer. Twenty four hours after irradiation c-Fos and c-Jun protein expression returned to near control levels. Histological signs of ultraviolet damage (for example, chromatin condensation, nuclear fragmentation) were first recognisable in the corneal epithelium 6 hours after irradiation and became more apparent at later times.

CONCLUSION

Thus, the rapid and sustained activation of c-Fos and c-Jun expression in the eye after single ultraviolet exposure may represent the molecular mechanism underlying ultraviolet induced photodamage and initiation of cell death. Furthermore, topical application of a c-fos antisense oligodeoxynucleotide to the ultraviolet exposed rat eye inhibited the increase in c-Fos expression in the cornea, suggesting therapeutic activity of antisense drugs in corneal malignant and infectious diseases.

Effect of topical beta blockers on corneal epithelial wound healing in the rabbit

Topical beta adrenergic receptor blocking agents (beta blockers) are among the most frequently prescribed ophthalmic drugs. It has been suggested that some of these agents have a toxic effect on the corneal epithelium. In the present study, four beta blockers in common therapeutic concentrations, as well as their vehicles, were applied to rabbit corneas that had undergone mechanical removal of epithelium from a 6 mm diameter corneal wound. The tested drugs (0.25% timolol, 0.25% levobunolol, 0.25% betaxolol, and 0.3% metipranolol) were found significantly to accelerate wound closure, compared with saline treatment in controls. Eyes treated with two of the vehicles (betaxolol vehicle and metipranolol vehicle) also demonstrated more rapid healing than controls, but the magnitude of the effect was not as great as that seen with the drugs. Only the beta blockers were responsible for wound closure before 60 hours, whereas the saline treated controls and vehicle treated eyes required longer times for wound closure. In this model of wound healing, beta blockers appear to have no deleterious effect on corneal epithelial wound healing.