Nerve growth factor and corneal wound healing in dogs

An eye on the dog as the scientist's best friend for translational research in ophthalmology: Focus on the ocular surface

Preclinical animal studies provide valuable opportunities to better understand human diseases and contribute to major advances in medicine. This review provides a comprehensive overview of ocular parameters in humans and selected animals, with a focus on the ocular surface, detailing species differences in ocular surface anatomy, physiology, tear film dynamics and tear film composition. We describe major pitfalls that tremendously limit the translational potential of traditional laboratory animals (i.e., rabbits, mice, and rats) in ophthalmic research, and highlight the benefits of integrating companion dogs with clinical analogues to human diseases into preclinical pharmacology studies. This One Health approach can help accelerate and improve the framework in which ophthalmic research is translated to the human clinic. Studies can be conducted in canine subjects with naturally occurring or noninvasively induced ocular surface disorders (e.g., dry eye disease, conjunctivitis), reviewed herein, and tear fluid can be easily retrieved from canine eyes for various bioanalytical purposes. In this review, we discuss common tear collection methods, including capillary tubes and Schirmer tear strips, and provide guidelines for tear sampling and extraction to improve the reliability of analyte quantification (drugs, proteins, others).

Nerve growth factor in dogs: Assessment of two immunoassays and selected ocular parameters following a nicergoline challenge per os

Impairment of corneal nerves can result in the development of ocular surface diseases such as aqueous tear deficiency and neurotrophic keratopathy. This study investigates oral nicergoline, an α-adrenoceptor antagonist shown to enhance endogenous secretion of nerve growth factor (NGF) by the lacrimal gland, as a potential therapy for these conditions. Five female spayed Beagle dogs received a 2-week course of oral nicergoline (10 mg twice daily). Drug safety was evaluated with ophthalmic and physical examinations, blood pressure monitoring, bloodwork, and urinalysis. The effect of nicergoline on the ocular surface was assessed with corneal esthesiometry, Schirmer tear test-1, and tear film breakup time. Drug effect on NGF levels was assessed by collecting tears and blood at baseline and completion of therapy using a bead-based immunoassay and an enzyme-linked immunosorbent assay. Although nicergoline was well tolerated in all dogs, it did not have a significant impact on corneal sensitivity, tear production, or tear stability. Of note, NGF was below the limit of quantification in all tear samples and was only detected in 8/20 serum samples with no significant difference between levels at baseline (189.4 ± 145.1 pg/mL) and completion of therapy (149.4 ± 79.4 pg/mL). Further validation of NGF analytical assays is warranted before nicergoline is investigated in clinical patients.

Molecular markers for corneal epithelial cells in larval vs. adult Xenopus frogs

Corneal Epithelial Stem Cells (CESCs) and their proliferative progeny, the Transit Amplifying Cells (TACs), are responsible for maintaining the integrity and transparency of the cornea. These stem cells (SCs) are widely used in corneal transplants and ocular surface reconstruction. Molecular markers are essential to identify, isolate and enrich for these cells, yet no definitive CESC marker has been established. An extensive literature survey shows variability in the expression of putative CESC markers among vertebrates; being attributed to species-specific variations, or other differences in developmental stages of these animals, approaches used in these studies and marker specificity. Here, we expanded the search for CESC markers using the amphibian model Xenopus laevis. In previous studies we found that long-term label retaining cells (suggestive of CESCs and TACs) are present throughout the larval basal corneal epithelium. In adult frogs, these cells become concentrated in the peripheral cornea (limbal region). Here, we used immunofluorescence to characterize the expression of nine proteins in the corneas of both Xenopus larvae and adults (post-metamorphic). We found that localization of some markers change between larval and adult stages. Markers such as p63, Keratin 19, and β1-integrin are restricted to basal corneal epithelial cells of the larvae. After metamorphosis their expression is found in basal and intermediate layer cells of the adult frog corneal epithelium. Another protein, Pax6 was expressed in the larval corneas, but surprisingly it was not detected in the adult corneal epithelium. For the first time we report that Tcf7l2 can be used as a marker to differentiate cornea vs. skin in frogs. Tcf7l2 is present only in the frog skin, which differs from reports indicating that the protein is expressed in the human cornea. Furthermore, we identified the transition between the inner, and the outer surface of the adult frog eyelid as a key boundary in terms of marker expression. Although these markers are useful to identify different regions and cellular layers of the frog corneal epithelium, none is unique to CESCs or TACs. Our results confirm that there is no single conserved CESC marker in vertebrates. This molecular characterization of the Xenopus cornea facilitates its use as a vertebrate model to understand the functions of key proteins in corneal homeostasis and wound repair.

Contact lens wear and the diabetic corneal epithelium: A happy or disastrous marriage?

Diabetes mellitus is an epidemic in the US and abroad. With the advent of new contact lens technology, the use of contact lenses as glucose sensors in lieu of the traditional finger stick is quickly becoming realized. This has the potential to rapidly expand the contact lens market into this growing patient population. The independent cellular and physiological effects of contact lens wear and diabetes on the corneal epithelium have been described. However, little evidence exists to date to support whether there is increased risk associated with contact lens wear in diabetes. The focus of this review is to discuss what is known about the cellular effects of contact lenses on the corneal epithelium, the pathophysiological changes in the corneal epithelium that occur in diabetes, and whether an increased risk for corneal epithelial damage and/or infection may negatively impact safety in diabetic contact lens wearers. Available data indicates that there are inherent risks associated with contact lens wear in diabetics. Importantly, eye care practitioners fitting contact lenses in the diabetic patient need to carefully consider the duration of disease, the level of glycemic control, the presence of retinopathy, and the patient's overall health.

Shifting the IGF-axis: An age-related decline in human tear IGF-1 correlates with clinical signs of dry eye

OBJECTIVE

The human corneal epithelium expresses both the insulin-like growth factor type 1 receptor (IGF-1R) and the IGF-1R/insulin receptor (INSR) hybrid. Despite the previous identification of IGF-1 in human tear fluid, little is known regarding the regulation of IGF-1 in tear fluid and its role in corneal epithelial homeostasis. In the present study, we investigated the impact of biological parameters on the concentration of human tear levels of IGF-1.

DESIGN

Tear levels of IGF-1 were measured in 41 healthy, human volunteers without any reported symptoms of dry eye. All volunteers underwent standard biomicroscopic examination of the cornea and tear film. In a subgroup of volunteers, corneal staining with sodium fluorescein, tear film break up time and tear production using a Schirmer's test strip were measured to assess clinical signs of dry eye. Tears were collected from the inferior tear meniscus using glass microcapillary tubes and IGF-1 levels were measured using a solid phase sandwich ELISA.

RESULTS

Tear levels of IGF-1 were highest in young adults and significantly decreased in older adults (P = 0.003). There were no differences in tear IGF-1 between males and females (P = 0.628). Tear IGF-1 levels were correlated with tear film break up time (R = 0.738) and tear production (R = 0.826).

CONCLUSIONS

These data indicate that there is a progressive decline in tear IGF-1 due to aging that is associated with clinical signs of dry eye. This effect is likely due to age-related changes in the lacrimal gland.

Effects of topically applied heterologous serum on reepithelialization rate of superficial chronic corneal epithelial defects in dogs

OBJECTIVE To assess the effects of topical application of undiluted heterologous serum on time to corneal reepithelialization in dogs with superficial chronic corneal epithelial defects (SCCEDs). DESIGN Multicenter, randomized, double-masked, controlled clinical trial. ANIMALS 41 client-owned dogs. PROCEDURES After collection of baseline clinical and historical data, dogs were randomly assigned to receive topically applied undiluted heterologous serum (n = 22) or isotonic saline (0.9% NaCl) solution (19) along with tobramycin and atropine. Epithelial debridement (at all visits) and grid keratotomy (at visits 2, 3, and 4) of SCCEDs were performed. Ophthalmic examination including fluorescein application was performed once weekly for 4 weeks or until corneal reepithelialization. Clinicians and owners were masked to treatment group. RESULTS No differences in baseline data were detected between treatment groups. No difficulties with medication administration, noncompliance, or adverse reactions were noted. All SCCEDs in both groups healed by 4 weeks after treatment began. Median time to reepithelialization (2 weeks) was not significantly different between serum-treated and placebo-treated eyes. Irrespective of treatment group, median time to reepithelialization was not significantly different for Boxers versus non-Boxer breeds. Direct correlations were detected between time to reepithelialization and vascularization score at study entry, vascularization score at time of reepithelialization, and ulcer area at study entry in both groups. Time to reepithelialization was not correlated with age, sex, or duration of signs in either group. CONCLUSIONS AND CLINICAL RELEVANCE Topical application of undiluted heterologous serum was well tolerated by dogs with SCCEDs but, as an adjunct to standard treatment, did not reduce time to corneal reepithelialization.

Age-Related Changes in Murine Corneal Nerves

PURPOSE

The aim of this study is to determine age-related morphological changes in the corneal subbasal nerve plexus (SNP) in two inbred mouse strains.

MATERIALS AND METHODS

The corneal SNP was investigated by in vivo confocal laser scanning microscopy (CLSM) in 0.5-, 1-, 1.5-, and 2-year-old C57BL/6J mice and in 0.5- and 1-year-old BALB/c mice (n = 4 per age category and strain; 10 images per mouse). Fixed corneal samples from C57BL/6J mice were also analyzed after PGP9.5 staining. Nerve fiber density (NFD) was determined using the semi-automated NeuronJ program. In addition, a new custom-designed, fully automated computerized technique based on oriented multiscale matched filtering was tested to objectify and accelerate image analysis.

RESULTS

C57BL/6J mice showed low NFD (11.7 ± 0.5 mm/mm²). Aging from 0.5 to 1, 1.5, and 2 years resulted in significant reductions in subbasal NFD by 34%, 49%, and 66%, respectively. The decline in nerve fibers revealed by in vivo CLSM together with NeuronJ quantification was confirmed by ex vivo immunohistochemical analyses. Subbasal NFD in BALB/c mice (30.0 ± 1.4 mm/mm²) was 3-fold higher than in C57BL/6J mice. Aging from 0.5 to 1 year resulted in a significant 17% reduction in NFD. With the automated approach, NFD of 22.6 ± 2.9 mm/mm² and a 45% reduction during aging was determined from the same images.

CONCLUSIONS

An age-related reduction in subbasal corneal nerve fibers was observed. The differing extent of reduction in the two mouse strains may be accounted for by genetic factors. Automated NFD quantification of corneal nerve fibers in mice appears to be a useful, reliable, objective, and time-saving tool.

Nerve growth factor regulates neurolymphatic remodeling during corneal inflammation and resolution

The cellular and physiologic mechanisms that regulate the resolution of inflammation remain poorly defined despite their widespread importance in improving inflammatory disease outcomes. We studied the resolution of two cardinal signs of inflammation–pain and swelling–by investigating molecular mechanisms that regulate neural and lymphatic vessel remodeling during the resolution of corneal inflammation. A mouse model of corneal inflammation and wound recovery was developed to study this process in vivo. Administration of nerve growth factor (NGF) increased pain sensation and inhibited neural remodeling and lymphatic vessel regression processes during wound recovery. A complementary in vivo approach, the corneal micropocket assay, revealed that NGF-laden pellets stimulated lymphangiogenesis and increased protein levels of VEGF-C. Adult human dermal lymphatic endothelial cells did not express canonical NGF receptors TrkA and p75^NTR or activate downstream MAPK- or Akt-pathway effectors in the presence of NGF, although NGF treatment increased their migratory and tubulogenesis capacities in vitro. Blockade of the VEGF-R2/R3 signaling pathway ablated NGF-mediated lymphangiogenesis in vivo. These findings suggest a hierarchical relationship with NGF functioning upstream of the VEGF family members, particularly VEGF-C, to stimulate lymphangiogenesis. Taken together, these studies show that NGF stimulates lymphangiogenesis and that NGF may act as a pathogenic factor that negatively regulates the normal neural and lymphatic vascular remodeling events that accompany wound recovery.

A fully caninised anti-NGF monoclonal antibody for pain relief in dogs

Background

Monoclonal antibodies are a major class of biological therapies in human medicine but have not yet been successfully applied to veterinary species. We have developed a novel approach, PETisation, to rapidly convert antibodies for use in veterinary species. As an example, anti-nerve growth factor (anti-NGF) monoclonal antibodies (mAbs) which are effective in reducing acute and chronic pain in rodents and man are potentially useful for treating pain in dogs but a fully caninised mAb is required in order to avoid an immune response. The aim of this study was to determine the optimal properties of a caninised anti-NGF mAb for safe, repeated administration to dogs, to determine its pharmacokinetic properties and to evaluate its efficacy in a model of inflammatory pain in vivo.

Results

Starting with a rat anti-NGF mAb, we used a novel algorithm based on expressed canine immunoglobulin sequences to design and characterise recombinant caninised anti-NGF mAbs. Construction with only 2 of the 4 canine IgG heavy chain isotypes (A and D) resulted in stable antibodies which bound and inhibited NGF with high-affinity and potency but did not bind complement C1q or the high-affinity Fc receptor gamma R1 (CD64). One of the mAbs (NV-01) was selected for scale-up manufacture, purification and pre-clinical evaluation. When administered to dogs, NV-01 was well tolerated, had a long serum half-life of 9 days, was not overtly immunogenic following repeated dosing in the dog and reduced signs of lameness in a kaolin model of inflammatory pain.

Conclusions

The combination of stability, high affinity and potency, no effector activity and long half-life, combined with safety and activity in the model of inflammatory pain in vivo suggests that further development of the caninised anti-NGF mAb NV-01 as a therapeutic agent for the treatment of chronic pain in dogs is warranted.

The TFOS International Workshop on Contact Lens Discomfort: report of the subcommittee on neurobiology

This report characterizes the neurobiology of the ocular surface and highlights relevant mechanisms that may underpin contact lens-related discomfort. While there is limited evidence for the mechanisms involved in contact lens-related discomfort, neurobiological mechanisms in dry eye disease, the inflammatory pathway, the effect of hyperosmolarity on ocular surface nociceptors, and subsequent sensory processing of ocular pain and discomfort have been at least partly elucidated and are presented herein to provide insight in this new arena. The stimulus to the ocular surface from a contact lens is likely to be complex and multifactorial, including components of osmolarity, solution effects, desiccation, thermal effects, inflammation, friction, and mechanical stimulation. Sensory input will arise from stimulation of the lid margin, palpebral and bulbar conjunctiva, and the cornea.

Nerve growth factor promotes corneal epithelial migration by enhancing expression of matrix metalloprotease-9

PURPOSE

Nerve growth factor (NGF) is a neuropeptide essential for the development, survival, growth, and differentiation of corneal cells. Its effects are mediated by both TrkA and p75 receptors. Clinically relevant use of NGF was introduced to treat neurotrophic ulcerations in patients. Herein, we examine the mechanisms by which NGF enhances epithelial wound healing both in vivo and in vitro.

METHODS

An animal model using adult hens was implemented for the in vivo experiments. Laser ablation keratectomy was performed and animals were observed for up to 7 days. Epithelial healing was measured with fluorescein. In addition, proliferation was measured using BrdU incorporation and both TrkA and matrix metalloprotease-9 (MMP-9) expression were measured by immunohistochemistry (IHC) and Western blot (WB). In vitro experiments were carried out with telomerase-immortalized human corneal epithelial cells (HCLE). The rate of proliferation was measured using a colorimetric assay and BrdU incorporation. Real-time migration was evaluated with an inverted microscope. MMP-9 expression was evaluated by immunocytochemistry (ICC), WB, zymography, and RT-PCR. Finally, beta-4 integrin (β4) expression was assessed by ICC and WB.

RESULTS

Faster epithelial healing was observed in NGF-treated corneas compared with controls (P < 0.01). These corneas showed increased proliferation, TrkA upregulation, and enhanced MMP-9 presence (P < 0.01). In vitro, faster spreading and migration were observed in response to NGF (P < 0.01). Enhanced proliferation, as well as enhanced TrkA and MMP-9 expression, and decreased β4 levels were observed after adding NGF (P < 0.01).

CONCLUSIONS

NGF plays a major role during the epithelial healing process by promoting migration, a process that is accelerated by cell spreading. This effect is mediated by both the upregulation of MMP-9 and cleavage of β4 integrin.

An NGF mimetic, MIM-D3, stimulates conjunctival cell glycoconjugate secretion and demonstrates therapeutic efficacy in a rat model of dry eye

The aim of this study was to evaluate the efficacy of MIM-D3, a small molecule nerve growth factor (NGF) peptidomimetic, as a therapeutic agent in rats with scopolamine induced dry eye. NGF plays an important role in ocular surface maintenance and corneal wound healing and was recently shown to have mucin secretagogue activity in conjunctival cells. We investigated whether MIM-D3 increased glycoconjugate secretion in conjunctival cells in vitro and in rat tear fluids in vivo. Primary rat conjunctival cell cultures were treated with increasing concentrations of MIM-D3 and evaluated for glycoconjugate secretion, proliferation and MAPK1/2 activation. Glycoconjugates were quantitated in tear fluids from normal rats treated topically with increasing doses of MIM-D3 (0.4%, 1% and 2.5%). Dry eye was induced in rats by subcutaneous scopolamine treatment, administered by surgically implanted osmotic pumps for 14 or 28 days. Aqueous tear production, tear clearance, fluorescein corneal staining and tear break-up time (tBUT) were evaluated. Glycoconjugates and NGF were quantitated in the tear fluids by enzyme-linked lectin assay (ELLA) and enzyme-linked immunosorbant assay (ELISA), respectively. We found that 50 μM MIM-D3 statistically significantly induced a 1.3-fold increase in glycoconjugate secretion and a 2.3-fold increase in MAPK1/2 activation without increasing proliferation from conjunctival cell cultures. Application of 2.5% MIM-D3 in normal rat eyes statistically significantly increased tear glycoconjugate concentration by 2.3-fold. In the experimental dry eye model, application of 1% MIM-D3 to rat eyes for either 1 or 17 consecutive days, followed by 1 week of no dosing produced a statistically significant decrease in corneal staining (p < 0.001), a slight increase in tBUT, and increases in tear glycoconjugates (p < 0.05) compared to vehicle. Scopolamine treatment also caused a statistically significant increase of endogenous NGF in tears (p < 0.005). We concluded that the increase in glycoconjugate concentration by the 1% MIM-D3 dose may have improved the quality and stability of the tear film, and thereby improved healing on the ocular surface in dry eye. Therefore, MIM-D3 may have therapeutic potential as a topical agent for the treatment of dry eye.

New therapeutic approaches in the treatment of diabetic keratopathy: a review

The cornea is densely innervated, and the integrity of these nerve fibres is critical in maintaining the refractive and protective functions of the cornea. Many ocular and systemic diseases can adversely affect corneal sensory nerves and consequently impair their function, with vision loss being the inevitable consequence of severe corneal neurotrophic ulceration. However, current standard treatments regimens are often ineffective. Over the past three decades, the role of growth factors in maintaining the normal structure and function of the cornea, and in corneal epithelial healing, has become increasingly evident. Many preclinical and clinical trials have shown that growth factors and cytokines can significantly enhance epithelialization (epithelial proliferation and migration) and consequently accelerate wound healing. More recently, local/topical administration of insulin, naltrexone (opioid antagonist) and nicergoline (ergoline derivatives) were found to improve, and significantly increase, the corneal wound healing rate. This report reviews the major attributes of these growth factors and therapeutic agents that may be used in ameliorating impaired corneal wound healing, and presents a perspective on the potential clinical use of these agents as a new generation of ophthalmic pharmaceuticals for the treatment of diabetic keratopathy.

Topical administration of adrenergic receptor pharmaceutics and nerve growth factor

Topical application of nerve growth factor (NGF) and adrenergic receptor pharmaceutics are currently in use for corneal ulcers and glaucoma. A recent interest in the neuroprotective abilities of NGF has led to a renewed interest in NGF as a therapeutic for retinal and choroidal diseases. NGF can promote cell proliferation through actions of the TrkA receptor or promote apoptosis through receptor p75^NTR. This understanding has led to novel interest in the role of NGF for diseases of the posterior eye. The role of β-adrenergic receptor agonists and antagonists for treatments of glaucoma, diabetic retinopathy, and their potential mechanisms of action, are still under investigation. This review discusses the current knowledge and applications of topical NGF and adrenergic receptor drugs for ocular disease.

Expression of semaphorin 3A in the rat corneal epithelium during wound healing

The neural guidance protein semaphorin 3A (Sema3A) is expressed in corneal epithelial cells of the adult rat. We have now further investigated the localization of Sema3A in the normal rat corneal epithelium as well as changes in its expression pattern during wound healing after central corneal epithelial debridement. The expression pattern of Sema3A was compared with that of the tight-junction protein zonula occludens-1 (ZO-1), the gap-junction protein connexin43 (Cx43), or the cell proliferation marker Ki67. Immunofluorescence analysis revealed that Sema3A was present predominantly in the membrane of basal and wing cells of the intact corneal epithelium. The expression of Sema3A at the basal side of basal cells was increased in the peripheral epithelium compared with that in the central region. Sema3A was detected in all layers at the leading edge of the migrating corneal epithelium at 6h after central epithelial debridement. The expression of Sema3A was markedly up-regulated in the basal and lateral membranes of columnar basal cells apparent in the thickened, newly healed epithelium at 1 day after debridement, but it had largely returned to the normal pattern at 3 days after debridement. The expression of ZO-1 was restricted to superficial epithelial cells and remained mostly unchanged during the wound healing process. The expression of Cx43 in basal cells was down-regulated at the leading edge of the migrating epithelium but was stable in the remaining portion of the epithelium. Ki67 was not detected in basal cells of the central epithelium at 1 day after epithelial debridement, when Sema3A was prominently expressed. Immunoblot analysis showed that the abundance of Sema3A in the central cornea was increased 1 day after epithelial debridement, whereas that of ZO-1 or Cx43 remained largely unchanged. This increase in Sema3A expression was accompanied by up-regulation of the Sema3A coreceptor neuropilin-1. Our observations have thus shown that the expression of Sema3A is increased markedly in basal cells of the newly healed corneal epithelium, and that this up-regulation of Sema3A is not associated with cell proliferation. They further suggest that Sema3A might play a role in the regulation of corneal epithelial wound healing.

Localization of the low-affinity nerve growth factor receptor p75 in human limbal epithelial cells

Biological effects of nerve growth factor (NGF) are mediated through receptors known as nerve growth factor receptors (NGFR), which include p75 and TrkA. This study was initiated after identifying NGFR as an up-regulated gene in the limbus by cDNA microarray analysis and we postulate that its expression may be indicative of a stem/progenitor cell phenotype. Immunohistochemistry was performed on normal human adult (n= 5) and foetal (n= 3) corneal tissue using antibodies directed against p75, TrkA, NGF, p63, ABCG2 and CK3/12. Limbal, conjunctival and pterygium tissue was obtained from patients (n= 10) undergoing pterygium resection and used for immunohistochemical assessment. Paraffin-embedded archival human skin specimens (n= 4) were also evaluated. In vitro expression of NGFR was determined in limbal, conjunctival and pterygium-derived epithelial cells. p75 was selectively expressed by basal epithelial cells in pterygia, conjunctiva and limbus, but was absent in the central cornea. These results were confirmed with two additional p75 specific antibodies. In contrast, TrkA was found in full-thickness pterygium, conjunctival, limbal and corneal epithelium in both adult and foetal eyes. p75 expression was identified in a small percentage, while TrkA was found on the entire population of cultured conjunctival, limbal and pterygium-derived epithelial cells. This receptor was also observed in selective regions of the human epidermis and hair follicle bulge. Our results illustrate the selective expression of p75 in basal pterygium, conjunctival and limbal epithelium, while staining was absent in adult and foetal central cornea. p75 may represent an additional ocular surface epithelial stem/progenitor cell signature gene.

Corneal innervation in mesocephalic and brachycephalic dogs and cats: assessment using in vivo confocal microscopy

OBJECTIVE

To determine the density of the canine and feline corneal neural network in healthy dogs and cats using in vivo confocal microscopy (IVCM). ANIMALS EXAMINED: A total of 16 adult dogs (9 Mesocephalic breeds, 7 Brachycephalic breeds) and 15 cats (9 Domestic Short-haired cats (DSH), 6 Persian cats) underwent IVCM.

PROCEDURE

Animals were examined with a confocal corneal microscope (HRTII/RCM; Heidelberg Retina Tomograph II/Rostock Cornea Module, Heidelberg Engineering, Dossenheim, Germany). The investigations focused on the distribution of the corneal nerves and quantification of central subepithelial and subbasal nerve plexus.

RESULTS

The corneal stromal nerve trunks, subepithelial and subbasal nerve plexus were observed. The nerve fiber density (NFD) quantified in nerve fiber length in mesocephalic dogs were 12.39 +/- 5.25 mm/mm(2) in the subepithelial nerve plexus and 14.87 +/- 3.08 mm/mm(2) in the subbasal nerve plexus. The NFD of the subepithelial nerve plexus in DSH cats was 15.49 +/- 2.7 and 18.4 +/- 3.84 mm/mm(2) in the subbasal nerve plexus. The subbasal NFD of DSH cats was significantly higher than in mesocephalic dogs (P = 0.037). The subepithelial NFD in brachycephalic dogs, and Persian cats were 10.34 +/- 4.71 and 9.50 +/- 2.3 mm/mm(2), respectively. The subbasal NFD measured 11.80 +/- 3.73 mm/mm(2) in brachycephalic dogs, and 12.28 +/- 4.3 mm/mm(2) NFD in Persian cats, respectively. The subepithelial and subbasal NFD in Persian cats were significantly lower than in DSH cats (P = 0.028, respectively, P = 0.031), in contrast to brachycephalic vs. mesocephalic dogs.

CONCLUSION

The noninvasive IVCM accurately detects corneal innervation and provides a reliable quantification of central corneal nerves.

Control of patterns of corneal innervation by Pax6

PURPOSE

Corneal nerves play essential roles in maintaining the ocular surface through provision of neurotrophic support, but genetic control of corneal innervation is poorly understood. The possibility of a neurotrophic failure in ocular surface disease associated with heterozygosity at the Pax6 locus (aniridia-related keratopathy [ARK]) was investigated.

METHODS

Patterns of corneal innervation were studied during development and aging in mice with different Pax6 dosages and in chimeras. Immunohistochemistry and ELISA-based assays were used to determine the molecular basis of defects seen in Pax6 mutants, and wound healing assays were performed.

RESULTS

In adults, the Pax6(+/-) epithelium was less densely innervated than the wild-type epithelium, and radial projection of epithelial nerves was disrupted. Neurotrophic support of the corneal epithelium appeared normal. Directed nerve projection correlated with patterns of epithelial cell migration in adult wild-types, but innervation defects observed in Pax6(+/-) mice were not fully corrected in wound healing or chimeric models where directed epithelial migration was restored.

CONCLUSIONS

Pax6 dosage nonautonomously controls robust directed radial projection of corneal neurons, and the guidance cues for growth cone guidance are not solely dependent on directed epithelial migration. There is little evidence that ARK represents neurotrophic keratitis.

Immune-mediated canine and feline keratitis

Although the normal cornea is devoid of vasculature and lymphatics, there are still several immune-mediated corneal conditions that can occur in dogs and cats. An overview of corneal immunology is presented. Diseases of dogs, including chronic superficial keratitis, superficial punctate keratitis, and canine adenovirus endotheliitis, as well as feline diseases, including eosinophilic keratitis and herpesvirus-related conditions, are discussed.

Expression of matrix metalloproteinase 2 and 9 in experimentally wounded canine corneas and spontaneous chronic corneal epithelial defects

PURPOSE

To determine matrix metalloproteinase (MMP) 2 and MMP 9 expression in acute and chronic experimentally wounded canine corneas and keratectomy samples from canine patients with spontaneous chronic corneal epithelial defects (SCCEDs).

METHODS

Mechanical debridement was performed unilaterally in 25 healthy dogs for the acute wound study. Twenty-four hours (n = 8), 48 hours (n = 5), 72 hours (n = 3), or 1 week (n = 9) after wounding, the dogs were euthanized. Debridement was performed once weekly for 8 weeks for the chronic study (n = 8). Therapeutic superficial keratectomies (n = 16) were performed on SCCED patients. Gelatin zymography and immunohistochemistry were performed.

RESULTS

Acute wounds showed upregulation of MMP 9 at all time points. At 7 days after wounding, values diminished markedly but remained elevated above those of unwounded controls. SCCED and chronic wound samples showed a significant increase in MMP 9 compared with controls but were less than that of acute wounds. There was no significant difference between chronic wounds versus SCCED samples. Fellow control eyes showed significant upregulation of MMP 9 in tandem with wounded eyes. There was no significant difference in values for MMP 2 in wounded corneas or SCCED compared with those of controls. Immunhistochemistry localized MMP 9 to predominantly the epithelium with some staining of keratinocytes and stroma.

CONCLUSIONS

The dog exhibits similar MMP expression during corneal wound healing to that of other species. The lack of significant difference in MMP expression between SCCED and chronic wounds suggest that MMP 2 and 9 are not involved in the pathophysiology of SCCED and are more likely altered secondary to a chronic epithelial defect.