Substance P released from sensory nerve endings influences tear secretion and goblet cell function in the rat

Substance P promotes transforming growth factor-β-induced collagen synthesis in human corneal fibroblasts

Corneal fibroblasts maintain homeostasis of the corneal stroma by mediating the synthesis and degradation of extracellular collagen, and these actions are promoted by transforming growth factor-β (TGF-β) and interleukin-1β (IL-1β), respectively. The cornea is densely innervated with sensory nerve fibers that are not only responsible for sensation but also required for physiological processes such as tear secretion and wound healing. Loss or dysfunction of corneal nerves thus impairs corneal epithelial wound healing and can lead to neurotrophic keratopathy. The sensory neurotransmitter substance P (SP) promotes corneal epithelial wound healing by enhancing the stimulatory effects of growth factors and fibronectin. We have now investigated the role of SP in collagen metabolism mediated by human corneal fibroblasts in culture. Although SP alone had no effect on collagen synthesis or degradation by these cells, it promoted the stimulatory effect of TGF-β on collagen type I synthesis without affecting that of IL-1β on the expression of matrix metalloproteinase-1. This effect of SP on TGF-β-induced collagen synthesis was accompanied by activation of p38 mitogen-activated protein kinase (MAPK) signaling and was attenuated by pharmacological inhibition of p38 or of the neurokinin-1 receptor. Our results thus implicate SP as a modulator of TGF-β-induced collagen type I synthesis by human corneal fibroblasts, and they suggest that loss of this function may contribute to the development of neurotrophic keratopathy.NEW & NOTEWORTHY This study investigates the role of substance P (SP) in collagen metabolism mediated by human corneal fibroblasts in culture. We found that, although SP alone had no effect on collagen synthesis or degradation by corneal fibroblasts, it promoted the stimulatory effect of transforming growth factor-β on collagen type I synthesis without affecting that of interleukin-1β on the expression of matrix metalloproteinase-1.

GP2-expressing cells: a new guardian with divergent functions in the intestine, eyes, and nose

GP (glycoprotein)-2, originally identified as a predominant membranous component of pancreatic acinar cells, has attracted the interest of researchers in mucosal immunology for its role as a functional molecule specific for antigen-sampling cells in the intestinal Peyer's patches. GP2 is involved in the detection of pathological bacteria and is also histologically useful for the identification of the M cell lineage and their differentiation in lymphoid tissues. Subsequent immunohistochemistry for GP2 has revealed a broad distribution of M cells and related cells in the nasopharyngeal lymphoid tissues, conjunctiva, tear duct, and airway. Especially, GP2 cells in the paranasal sinuses and tear duct have been identified as novel types of epithelial cells. The systematic administration of RANKL can induce extra-M cells in conventional epithelia of body. The production and release of GP2 by conjunctival goblet cells and several mucous glands suggests leading roles for mucous cells in protection, including the entrapment of microorganisms for infections. The ocular surface and conjunctiva are connected to the lacrimal sac, nasolacrimal duct, and further nasal cavity, comprising another canal that passes through the body. The broad distribution of GP2-expressingcells may indicate its function as a new guardian in the intestine, eyes, and nose, all of which are exposed to external milieu.

A synthetic tear protein resolves dry eye through promoting corneal nerve regeneration

Corneal architecture is essential for vision and is greatly perturbed by the absence of tears due to the highly prevalent disorder dry eye. With no regenerative therapies available, pathological alterations of the ocular surface in response to dryness, including persistent epithelial defects and poor wound healing, result in life-long morbidity. Here, using a mouse model of aqueous-deficient dry eye, we reveal that topical application of the synthetic tear protein Lacripep reverses the pathological outcomes of dry eye through restoring the extensive network of corneal nerves that are essential for tear secretion, barrier function, epithelial homeostasis, and wound healing. Intriguingly, the restorative effects of Lacripep occur despite extensive immune cell infiltration, suggesting tissue reinnervation and regeneration can be achieved under chronic inflammatory conditions. In summary, our data highlight Lacripep as a first-in-class regenerative therapy for returning the cornea to a near homeostatic state in individuals who suffer from dry eye.

Currently, there are no regenerative treatments for ocular pathologies due to dry eye. Efraim et al. demonstrate the synthetic tear peptide Lacripep as a regenerative therapy capable of restoring the damaged, dysfunctional ocular surface to a near homeostatic state through promoting nerve regeneration in the presence of chronic inflammation.

Immunomodulatory Role of Neuropeptides in the Cornea

The transparency of the cornea along with its dense sensory innervation and resident leukocyte populations make it an ideal tissue to study interactions between the nervous and immune systems. The cornea is the most densely innervated tissue of the body and possesses both immune and vascular privilege, in part due to its unique repertoire of resident immune cells. Corneal nerves produce various neuropeptides that have a wide range of functions on immune cells. As research in this area expands, further insights are made into the role of neuropeptides and their immunomodulatory functions in the healthy and diseased cornea. Much remains to be known regarding the details of neuropeptide signaling and how it contributes to pathophysiology, which is likely due to complex interactions among neuropeptides, receptor isoform-specific signaling events, and the inflammatory microenvironment in disease. However, progress in this area has led to an increase in studies that have begun modulating neuropeptide activity for the treatment of corneal diseases with promising results, necessitating the need for a comprehensive review of the literature. This review focuses on the role of neuropeptides in maintaining the homeostasis of the ocular surface, alterations in disease settings, and the possible therapeutic potential of targeting these systems.

A Single Administration of OC-01 (Varenicline Solution) Nasal Spray Induces Short-Term Alterations in Conjunctival Goblet Cells in Patients with Dry Eye Disease

INTRODUCTION

Dry eye disease is characterized by a persistently unstable or deficient tear film causing discomfort or visual impairment. Varenicline is a small-molecule nicotinic acetylcholine receptor agonist recently approved for use as a preservative-free nasal spray (OC-01 [varenicline solution] nasal spray [OC-01 VNS]) to treat signs and symptoms of dry eye disease, but its effect on conjunctival goblet cells has not been studied.

METHODS

In this phase 2, single-center, vehicle-controlled study, patients aged 18 years or more with a diagnosis of dry eye disease and Ocular Surface Disease Index© score of at least 23 were randomized 2:1 to receive a 50-µL single dose of OC-01 0.06 mg VNS or vehicle nasal spray in each nostril. Image assessments for area and perimeter were performed pre and 10 min post treatment for goblet cells by in vivo confocal microscopy and for meibomian glands by infrared meibography. Non-parametric Wilcoxon signed-rank test compared pre- and post-treatment measurements for each treatment group. Treatment-emergent adverse events (TEAEs) were assessed.

RESULTS

The study randomized 18 patients (mean age 61 years); 6 received vehicle (3/6 [50%] female) and 12 patients received OC-01 VNS (11/12 [92%] female). OC-01 VNS treatment decreased mean goblet cell area (pre-treatment, 106.4 µm2; post-treatment, 67.6 µm2; p = 0.02) and perimeter (pre-treatment, 38.9 µm; post-treatment, 31.2 µm; p = 0.03) but not vehicle did not (p = 0.25). There were no significant changes in mean meibomian gland area with either treatment (p ≥ 0.05). All TEAEs were non-ocular, non-serious, and mild.

CONCLUSIONS

This study demonstrated that a single administration of OC-01 0.06 mg VNS in patients with dry eye disease reduced conjunctival goblet cell area and perimeter, suggesting goblet cell degranulation and associated release of lubricating mucin. By activating the natural tear film, OC-01 VNS may provide benefits over topical medications.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT03688802.

Neuroimmune crosstalk in the cornea: The role of immune cells in corneal nerve maintenance during homeostasis and inflammation

In the cornea, resident immune cells are in close proximity to sensory nerves, consistent with their important roles in the maintenance of nerves in both homeostasis and inflammation. Using in vivo confocal microscopy in humans, and ex vivo immunostaining and fluorescent reporter mice to visualize corneal sensory nerves and immune cells, remarkable progress has been made to advance our understanding of the physical and functional interactions between corneal nerves and immune cells. In this review, we summarize and discuss recent studies relating to corneal immune cells and sensory nerves, and their interactions in health and disease. In particular, we consider how disrupted corneal nerve axons can induce immune cell activity, including in dendritic cells, macrophages and other infiltrating cells, directly and/or indirectly by releasing neuropeptides such as substance P and calcitonin gene-related peptide. We summarize growing evidence that the role of corneal intraepithelial immune cells is likely different in corneal wound healing versus other inflammatory-dominated conditions. The role of different types of macrophages is also discussed, including how stromal macrophages with anti-inflammatory phenotypes communicate with corneal nerves to provide neuroprotection, while macrophages with pro-inflammatory phenotypes, along with other infiltrating cells including neutrophils and CD4⁺ T cells, can be inhibitory to corneal re-innervation. Finally, this review considers the bidirectional interactions between corneal immune cells and corneal nerves, and how leveraging this interaction could represent a potential therapeutic approach for corneal neuropathy.

Modulating the tachykinin: Role of substance P and neurokinin receptor expression in ocular surface disorders

Substance P (SP) is a tachykinin expressed by various cells in the nervous and immune systems. SP is predominantly released by neurons and exerts its biological and immunological effects through the neurokinin receptors, primarily the neurokinin-1 receptor (NK1R). SP is essential for maintaining ocular surface homeostasis, and its reduced levels in disorders like diabetic neuropathy disrupt the corneal tissue. It also plays an essential role in promoting corneal wound healing by promoting the migration of keratocytes. In this review, we briefly discuss the structure, expression, and function of SP and its principal receptor NK1R. In addition, SP induces pro-inflammatory effects through autocrine or paracrine action on the immune cells in various ocular surface pathologies, including dry eye disease, herpes simplex virus keratitis, and Pseudomonas keratitis. We provide an in-depth review of the pathogenic role of SP in various ocular surface diseases and several new approaches developed to counter the immune-mediated effects of SP either through modulating its production or blocking its target receptor.

The Role of Neuropeptides in Pathogenesis of Dry Dye

Neuropeptides are known as important mediators between the nervous and immune systems. Recently, the role of the corneal nerve in the pathogenesis of various ocular surface diseases, including dry eye disease, has been highlighted. Neuropeptides are thought to be important factors in the pathogenesis of dry eye disease, as suggested by the well-known role between the nervous and immune systems, and several recently published studies have elucidated the previously unknown pathogenic mechanisms involved in the role of the neuropeptides secreted from the corneal nerves in dry eye disease. Here, we reviewed the emerging concept of neurogenic inflammation as one of the pathogenic mechanisms of dry eye disease, the recent results of related studies, and the direction of future research.

The two-faced effects of nerves and neuropeptides in corneal diseases

Corneal nerves are instrumental to maintain cornea integrity through regulation of key physiological functions such as tear secretion, blink reflex, and neuropeptide turnover. Corneal nerve injury/stimulation can follow many insults including mechanical/chemical trauma, infections and surgeries. Nerve disruption initiates a process named neurogenic inflammation which leads to edema, pain, and recruitment and activation of leukocytes. Interestingly, leukocyte influx in the cornea can further damage nerves by releasing inflammatory mediators-including neuropeptides. The clinical outcome of neuroinflammation can be beneficial or detrimental to corneal integrity. On one side, it ensures prompt wound healing and prevents infections. On the other, prolonged and/or deranged neuroinflammation can permanently disrupt corneal integrity and impair vision. The cornea is an ideal site to study peripheral neuroinflammation and neurogenic inflammation since it receives the highest density of sensory nerves of the entire body. We will review the corneal nerve anatomy and neurochemistry, discuss the beneficial and detrimental effects of neurogenic inflammation in corneal wound healing, inflammatory processes, and pain. We will also examine the emerging remote impact of corneal nerve disruption on the trigeminal ganglion and the brain, highlighting the key role of neuropeptide Substance P. Finally, we will discuss the clinical relevance of such neuroinflammatory network in the context of severe and highly prevalent ocular diseases, including potential treatments.

Immunohistochemical study on the expressions of neuropeptides in the superficial and deep gland of the third eyelid of pigs

The superficial gland of the third eyelid (SGTE) and deep gland of the third eyelid (DGTE) are classified as accessory lacrimal glands. The aim of the present study was to immunohistochemically investigate the expression of vasoactive intestinal peptide (VIP), dopamine beta-hydroxylase (DβH), substance P (SP), galanin, neuropeptide Y (NPY), pituitary adenylate cyclase-activating peptide (PACAP), somatostatin and calcitonin gene-related peptide (CGRP) in the porcine SGTE and DGTE. We demonstrated the distribution patterns of VIP, DβH, SP, NPY and galanin in the nerve fibres in the SGTE and DGTE. None of somatostatin-, PACAP- and CGRP-immunoreactive (IR) nerve fibres were found in the SGTE and DGTE. The majority of VIP- and DβH-IR nerves fibres were found near to glandular acini, tubules, secretory ducts and blood vessels in the SGTE and DGTE. VIP-IR nerve fibres were found in external connective tissue in SGTE and DGTE and only in interlobular connective tissue in the SGTE. DβH-IR nerve fibres were found in interlobular and external connective tissue in the DGTE but not in the SGTE. Single galanin-, SP- and NPY-IR nerve fibres were observed in close proximity to acini and tubules in the SGTE and DGTE. Single galanin-, SP-, NPY-IR nerve fibres were found in close proximity to the secretory ducts in the DGTE, however only SP-IR nerve fibres were found near to the secretory ducts in SGTE. In conclusion, our research aims to highlight some aspects of SGTE and DGTE innervation in pigs and may also be a source of basic knowledge for further studies.

Neuroanatomy and neurochemistry of rat cornea: Changes with age

PURPOSE

To characterize the entire rat corneal nerve architecture, the changes that occur with aging, and its sensory, sympathetic, and parasympathetic fiber distribution.

METHODS

Sprague-Dawley rats (aged 1 day to 2 years old) of both sexes were euthanized, and the whole corneas were immunostained with protein gene product 9.5 (PGP9.5). The specimens were double-labeled with antibodies against calcitonin gene-related peptide (CGRP) and substance P (SP) as sensory nerve markers, vasoactive intestinal peptide (VIP) as a parasympathetic nerve marker, and neuropeptide Y (NPY) and tyrosine hydroxylase (TH) as markers of sympathetic fibers. Relative nerve density positive for each antibody was assessed by computer-assisted image analysis.

RESULTS

Thick nerve trunks enter the cornea in the middle of the stroma and run towards the anterior stroma, subsequently dividing into smaller branches that penetrate upwards into the epithelium to form the subbasal nerve bundles. There was no significant difference in corneal innervation between sexes. CGRP and SP were the major sensory neuropeptides with 47.6% ± 3.5% and 34.9% ± 5.1%, respectively, of the total nerves. VIP was 18.4% ± 5.7%, and NPY and TH positive fibers took up 6.92% ± 2.66% and 2.92% ± 1.52%, respectively. Epithelial nerve density increased with age, reached full development at 5 weeks, and decreased at 120 weeks.

CONCLUSION

This study provides a complete nerve architecture and content of components of sensory, parasympathetic, and sympathetic nerves in the rat cornea. The normal innervation pattern described here will provide an essential baseline for investigators who use the rat model for assessing corneal pathologies that involve nerve alterations.

Tear neuromediators in eyes on chronic topical antiglaucoma therapy with and without BAK preservatives

PURPOSE

To evaluate tear neuropeptides (NPs) (vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), calcitonin gene-related peptide (CGRP), substance P (SP), nerve growth factor (NGF)) in chronic ocular topical hypotensive therapy with and without benzalkonium chloride (BAK) preservative.

METHODS

A comparative, open label, cross-sectional study of patients using antiglaucoma medications for >6 months with BAK (group I), without BAK (group II) and controls was done. Tear NPs (ELISA), ocular surface evaluation tests (tear breakup time (TBUT), Schirmer's test, corneal and conjunctival staining score) and confocal central corneal subbasal nerve fibre layer (SBNFL) imaging was done.

RESULTS

Of 153 eyes evaluated, group 1 (82 eyes (41 patients; mean age 48±14.5 years)) and group 2 (71 eyes (36 patients; mean age 43.11±15 years)) were on therapy for a mean duration of 10.05±2.0 and 9.67±2.3 months, respectively. Tear analysis showed elevated SP and NGF (p<0.01); decreased CGRP (p=0.03), VIP and NPY (p<0.01) compared with controls (n=30, mean age 29.33±5.7 years). Tear NP levels (SP (p=0.1), NGF (p=0.33), CGRP (p=1), VIP (p=0.87), NPY (p=0.83)) and SBNFL (p=0.09) were comparable in both groups. There was no correlation seen between tear NP levels and clinical tests and SBNFL.

CONCLUSION

Our study analysis points towards altered tear NP levels in eyes on chronic topical hypotensive therapy in comparison with controls with no significant difference in tear NP levels and central corneal SBNFL density between the BAK preservative and BAK-free antiglaucoma therapy.

Mapping the entire nerve architecture of the cat cornea

OBJECTIVE

To provide a complete nerve architecture and neuropeptide distribution in the cat cornea.

ANIMALS STUDIED

Two adult domestic cats.

PROCEDURE

The cat corneas were stained with protein gene product (PGP) 9.5 antibody-a pan marker for nerve fibers-and then divided into four quarters and double labeled with calcitonin gene-related peptide (CGRP) or substance P (SP) antibodies. Relative corneal nerve fiber densities and nerve terminals were evaluated in whole mount images by computer-assisted analysis.

RESULTS

An average of 21.5 ± 2.1 thick stromal nerves enters the cornea around the limbus where they split into many branches going up to the anterior stroma. Some branches link to each other, but most of them penetrate the basement membrane in the periphery to give origin to subbasal bundles, which run centripetally and merge to form a whirl-like structure (vortex) at the center. These nerve bundles send out many fine terminals that innervate the epithelial cells. Subbasal nerve density and nerve terminals were greater in the center than in the periphery of the cornea. Additionally, CGRP-positive central epithelial nerve fibers and terminals were more abundant than SP-positive nerves and terminals.

CONCLUSION

The architecture of cat corneal nerves shows similarities to human and mouse cornea innervation. This study provides useful data for researchers who use the cat model to assess corneal nerve pathological alterations, as well as in the veterinary field where corneal opacities, ulcerations, and infections damage the nerves and decrease sensitivity.

Reconsidering the central role of mucins in dry eye and ocular surface diseases

Mucins are key actors in tear film quality and tear film stability. Alteration of membrane-bound mucin expression on corneal and conjunctival epithelial cells and/or gel-forming mucin secretion by goblet cells (GCs) promotes in ocular surface diseases and dry eye disease (DED). Changes in the mucin layer may lead to enhanced tear evaporation eventually contributing to tear hyperosmolarity which has been associated with ocular surface inflammation. Inflammatory mediators in turn may have a negative impact on GCs differentiation, proliferation, and mucin secretion. This sheds new light on the position of GCs in the vicious circle of DED. As contributor to ocular surface immune homeostasis, GC loss may contribute to impaired ocular surface immune tolerance observed in DED. In spite of this, there are no tools in routine clinical practice for exploring ocular surface mucin deficiency/dysregulation. Therefore, when selecting the most appropriate treatment options, there is a clear unmet need for a better understanding of the importance of mucins and options for their replacement. Here, we comprehensively revisited the current knowledge on ocular surface mucin biology, including functions, synthesis, and secretion as well as the available diagnostic tools and treatment options to improve mucin-associated homeostasis. In particular, we detailed the potential link between mucin dysfunction and inflammation as part of the uncontrolled chronic inflammation which perpetuates the vicious circle in DED.

Role of Substance P Neuropeptide in Inflammation, Wound Healing, and Tissue Homeostasis

Substance P (SP) is an undecapeptide present in the CNS and the peripheral nervous system. SP released from the peripheral nerves exerts its biological and immunological activity via high-affinity neurokinin 1 receptor (NK1R). SP is also produced by immune cells and acts as an autocrine or paracrine fashion to regulate the function of immune cells. In addition to its proinflammatory role, SP and its metabolites in combination with insulin-like growth factor-1 are shown to promote the corneal epithelial wound healing. Recently, we showed an altered ocular surface homeostasis in unmanipulated NK1R^-/- mice, suggesting the role of SP-NK1R signaling in ocular surface homeostasis under steady-state. This review summarizes the immunobiology of SP and its effect on immune cells and immunity to microbial infection. In addition, the effect of SP in inflammation, wound healing, and corneal epithelial homeostasis in the eye is discussed.

Recovery of Corneal Sensitivity and Increase in Nerve Density and Wound Healing in Diabetic Mice After PEDF Plus DHA Treatment

Diabetic keratopathy decreases corneal sensation and tear secretion and delays wound healing after injury. In the current study, we tested the effect of treatment with pigment epithelium-derived factor (PEDF) in combination with docosahexaenoic acid (DHA) on corneal nerve regeneration in a mouse model of diabetes with or without corneal injury. The study was performed in streptozotocin-induced diabetic mice (C57BL/6). Ten weeks after streptozotocin injection, diabetic mice showed significant decreases of corneal sensitivity, tear production, and epithelial subbasal nerve density when compared with age-matched normal mice. After diabetic mice were wounded in the right eye and treated in both eyes with PEDF+DHA for 2 weeks, there was a significant increase in corneal epithelial nerve regeneration and substance P-positive nerve density in both wounded and unwounded eyes compared with vehicle-treated corneas. There also was elevated corneal sensitivity and tear production in the treated corneas compared with vehicle. In addition, PEDF+DHA accelerated corneal wound healing, selectively recruited type 2 macrophages, and prevented neutrophil infiltration in diabetic wounded corneas. These results suggest that topical treatment with PEDF+DHA promotes corneal nerve regeneration and wound healing in diabetic mice and could potentially be exploited as a therapeutic option for the treatment of diabetic keratopathy.

Corneal Nerve Morphology, Sensitivity, and Tear Neuropeptides in Contact Lens Wear

PURPOSE

To determine tear neuropeptide levels in contact lens wearers and non-wearers, and to examine relationships with indices of corneal innervation, tear function, and ocular discomfort.

METHODS

A cross-sectional, single-visit, investigator-masked pilot study. Assessments included Ocular Comfort Index (OCI), central and mid-peripheral corneal nerve density and morphology (HRT-Rostock), corneal sensitivity (Cochet-Bonnet aesthesiometer), tear Substance P and calcitonin gene-related peptide (CGRP) concentration (ELISA), in situ tear osmolarity (TearLab), tear secretion (Phenol Red Thread), and noninvasive tear break-up time (NITBUT; Keeler Tearscope). Groups were compared using independent t-test or Mann-Whitney U test, and regional differences assessed using paired t-tests. Associations were analyzed using Pearson or Spearman correlation. Significance was determined at P < .05.

RESULTS

Twenty contact lens wearers (7M:13F, 32 ± 5 years) and 20 non-wearers (7M:13F, 31 ± 5 years) completed the study. OCI score was numerically higher in lens wearers (32.27 ± 5.33) than non-wearers (27.66 ± 9.94). Tear osmolarity was higher [298.0 (IQR 291.0-309.8) vs. 288.5 (282.3-298.3) mOsmol/L; P = .01] whereas NITBUT was lower (9.8 ± 3.4 vs. 13.8 ± 5.6 s; P = .01) in lens wearers compared with non-wearers. Tear neuropeptide concentrations were not different between groups [Substance P 4.29 ng/ml (IQR 1.57-6.05), CGRP 14.89 ng/ml (5.08-59.26)], and there were no differences in nerve morphology or ocular surface sensitivity. Higher nerve density, interconnections, and tortuosity were observed in the central cornea than mid-peripherally (P < .05). OCI score was moderately associated with nerve tortuosity (r = 0.42, P = .01). CGRP was associated with central nerve density (ρ = 0.38, P = .02), as was tear secretion (r = -0.37, P = .02). Nerve interconnections were strongly associated with corneal sensitivity (ρ = 0.64, P < .001).

CONCLUSIONS

Relationships were demonstrated between nerve density, tear CGRP, and corneal sensitivity. Markers of corneal neurobiology and sensory function do not appear to be altered in contact lens wear despite worse tear function (osmolarity and stability) in lens wearers. This suggests that mechanisms other than overt changes in corneal innervation regulate tear function during lens wear. The relationship between nerve tortuosity and ocular discomfort requires elucidation.

Neuroanatomy and Neurochemistry of Mouse Cornea

Purpose

To investigate the entire nerve architecture and content of the two main sensory neuropeptides in mouse cornea to determine if it is a good model with similarities to human corneal innervation.

Methods

Mice aged 1 to 24 weeks were used. The corneas were stained with neuronal-class βIII-tubulin, calcitonin gene–related peptide (CGRP), and substance P (SP) antibodies; whole-mount images were acquired to build an entire view of corneal innervation. To test the origin of CGRP and SP, trigeminal ganglia (TG) were processed for immunofluorescence. Relative corneal nerve fiber densities or neuron numbers were assessed by computer-assisted analysis.

Results

Between 1 and 3 weeks after birth, mouse cornea was mainly composed of a stromal nerve network. At 4 weeks, a whorl-like structure (or vortex) appeared that gradually became more defined. By 8 weeks, anatomy of corneal nerves had reached maturity. Epithelial bundles converged into the central area to form the vortex. The number and pattern of whorl-like structures were different. Subbasal nerve density and nerve terminals were greater in the center than the periphery. Nerve fibers and terminals that were CGRP-positive were more abundant than SP-positive nerves and terminals. In trigeminal ganglia, the number of CGRP-positive neurons significantly outnumbered those positive for SP.

Conclusions

This is the first study to show a complete map of the entire corneal nerves and CGRP and SP sensory neuropeptide distribution in the mouse cornea. This finding shows mouse corneal innervation has many similarities to human cornea and makes the mouse an appropriate model to study pathologies involving corneal nerves.

GP2-expressing cells in the conjunctiva and tear ducts of mice: identification of a novel type of cells in the squamous stratified epithelium

GP2 is a membrane-associated secretory protein originally identified in zymogen granules of pancreatic acinar cells. Recently, this glycoprotein has attracted attention as a marker substance of M cells of Peyer's patches and for its involvement in the selective uptake of pathological bacteria via M cells. When we stained the conjunctiva and tear ducts of mice using a GP2 antibody, all goblet cells in the squamous stratified epithelium of the conjunctiva were intensely immunolabeled, while goblet cells in the intestine and airway were devoid of the immunoreactivity, indicating that the conjunctiva contains a special type of goblet cell. Further immunostaining for GP-2 labeled dispersed cells of peculiar shapes within the stratified squamous epithelium in the lacrimal canaliculi, lacrimal sac, and nasolacrimal duct. The GP2-immunoreactive cells in the tear duct projected arched or branched processes toward the basement membrane. Electron-microscopically, immunogold particles for GP2 outlined the basolateral plasma membrane of both the conjuntival goblet cells and the peculiarly shaped cells in the tear duct. Intracellularly, GP2 products of the goblet cells were localized around secretory granules in the apical cytoplasm and those of the tear duct cells inside the vesicles. The luminal contents close to apical plasma membrane were heavily labeled with immunogold particles, suggesting an exocytosis-based targeting of GP2 to the plasma membrane and its release into the lumen. The possible function of GP2 in tear ducts is discussed in relation to a defense system against invasive microoranisms and antigens.

Conjunctival and corneal sensitivity in patients under topical antiglaucoma treatment

The purpose of the study is to measure corneal and conjunctival sensitivity in patients under glaucoma topical treatment as compared to a control group. It is a case-control study. Corneal and conjunctival esthesiometry were carried out through a Cochet-Bonnet esthesiometer. We took healthy individuals as controls, who did not use any type of ophthalmic topical medications and without history of ocular surface pathology or irritation. The study group was subdivided per number of applications (1, 2, and 3 or more applications). From a total 182 eyes from 91 patients, of which 26 (28.57 %) were controls and 65 (71.43 %) were in the study group, a mean corneal sensitivity of 58.98 ± 2.25 mm was found in the control group and 52.97 ± 6.41 mm in patients using topical medication. Mean conjunctival sensitivity was 18.80 ± 5.40 mm in the control group and 11.76 ± 5.45 mm in the study group. There was no statistically significant difference among groups when separated by 1, 2, and 3 or more applications. Eyes under use of timolol-containing medications showed lower sensitivity values as compared to other topical antiglaucoma medications. Corneal and conjunctival sensitivities are diminished in patients with chronic use of topical hypotensive medications and these results can explain the lack of correlation between signs and symptoms that is typically found in patients treated for glaucoma or ocular hypertension.

The cellular mechanisms of dry eye: from pathogenesis to treatment

Dry eye is a complex disease characterized by changes in the ocular surface epithelia related to reduced quality and/or quantity of tears, inflammatory reaction, and impairment of ocular surface sensitivity. It has recently been proposed that increased tear osmolarity represents a main trigger to the altered cellular mechanisms leading to epithelial damage in dry eye. However, dry eye pathogenesis is multifactorial, with cytotoxic inflammatory mediators, altered lacrimal gland secretion and nerve function, squamous metaplasia of the conjunctival epithelium and decrease of goblet cells density, all playing a role in a detrimental loop that perpetuates and worsens damage to the corneal and conjunctival epithelia. Current topical treatments for dry eye patients include the use of lubricants and anti-inflammatory drugs. However, lubricants only improve symptoms temporarily, and chronic use of topical steroids is associated to severe ocular side effects such as cataract and glaucoma. The deeper understanding of the cellular mechanisms that are altered in dry eye is opening novel perspectives for patients and physicians, who are seeking treatments capable not only of improving symptoms but also of restoring the homeostasis of the ocular surface. In this review, we will focus on novel anti-inflammatory agents and on nerve growth factor, a neurotrophin that is altered in dry eye and has been suggested as a main player in the neuroimmune cross-talk of the ocular surface as well as in the stimulation of corneal sensitivity, epithelial proliferation and differentiation, and stimulation of mucin production by goblet cells. J. Cell. Physiol. 228: 2253-2256, 2013. © 2013 Wiley Periodicals, Inc.

Retinal pigment epithelium, age-related macular degeneration and neurotrophic keratouveitis

Age-related macular degeneration (AMD) is the leading cause of impaired vision and blindness in the aging population. The aims of our studies were to identify qualitative and quantitative alterations in mitochondria in human retinal pigment epithelium (RPE) from AMD patients and controls and to test the protective effects of pigment epithelium-derived factor (PEDF), a known neurotrophic and antiangiogenic substance, against neurotrophic keratouveitis. Histopathological alterations were studied by means of morphometry, light and electron microscopy. Unexpectedly, morphometric data showed that the RPE alterations noted in AMD may also develop in normal aging, 10-15 years later than appearing in AMD patients. Reduced tear secretion, corneal ulceration and leukocytic infiltration were found in capsaicin (CAP)-treated rats, but this effect was significantly attenuated by PEDF. These findings suggest that PEDF accelerated the recovery of tear secretion and also prevented neurotrophic keratouveitis and vitreoretinal inflammation. PEDF may have a clinical application in inflammatory and neovascular diseases of the eye.

Corneal and conjunctival sensitivity in patients with dry eye: the effect of topical cyclosporine therapy

PURPOSE

: To evaluate changes in mechanical sensitivity of cornea and conjunctiva in patients with dry eye disease unresponsive to artificial tears therapy and to investigate the effect of topical cyclosporine therapy on sensitivity of the ocular surface.

METHODS

: Thirty-seven patients with dry eye disease and 35 healthy control subjects were enrolled to this prospective study. All patients included in the study completed a 3-month run-in period of using nonpreserved artificial tear supplements, but all failed to achieve adequate subjective or objective improvement. Patients were then instructed to use topical cyclosporine A 0.05% twice a day. Pre- and posttreatment (1, 3, and 6 months) evaluations included, corneal and conjunctival sensitivity testing with the Cochet-Bonnet esthesiometer, subjective symptom scoring, fluorescein and lissamine green staining, Schirmer test, and tear breakup time (BUT).

RESULTS

: Conjunctival and corneal sensitivities were significantly lower in patients with dry eye compared with controls (P < 0.0001). In patients with dry eye, corneal sensitivity correlated positively with conjunctival sensitivity and negatively with ocular surface staining scores. Conjunctival sensitivity correlated negatively with the duration of dry eye disease, the total symptom severity score, and the severity of dryness symptom and positively with Schirmer test and tear BUT. Corneal and conjunctival sensitivities did not change significantly after artificial tear therapy (P > 0.05). After topical cyclosporine, statistically significant improvements from baseline were observed in corneal sensitivity at 3- and 6-month visits (P < 0.001). For conjunctival sensitivity, statistically significant improvements from baseline were seen at all follow-up visits (P < 0.0001). Topical cyclosporine treatment also led to significant improvements in symptom scores, Schirmer test, tear BUT, and ocular surface staining scores (P < 0.0001).

CONCLUSIONS

: The mechanical sensitivity of cornea and conjunctiva to tactile stimulus is reduced in patients with dry eye. Our findings suggest that topical cyclosporine may be effective in improving this reduced mechanical sensitivity of the ocular surface.

Nerve growth factor localization in the nasal mucosa of patients with persistent allergic rhinitis

BACKGROUND AND OBJECTIVES

Nerve growth factor (NGF) and NGF receptors have been shown to be expressed by structural and infiltrating inflammatory cells in the human allergic bronchial mucosa and conjunctiva. In the nose, a positive immunostaining for NGF was recently reported in biopsies of subjects undergoing surgery for refractory nasal obstruction. This study was aimed at studying by immunohistochemistry NGF expression and localization in the nasal mucosa from subjects with moderate/severe persistent allergic rhinitis and natural allergen exposure.

METHODS

Immunostaining for NGF, tryptase and eosinophil cationic protein was performed in human nasal turbinate sections of 25 patients affected by persistent allergic rhinitis and sensitization to Dermatophagoides pteronyssinus.

RESULTS

NGF was consistently expressed in the epithelium and in the submucosa of allergic rhinitic subjects, preferentially localized in eosinophils and mast cells. A strong NGF immunostaining was found in mucous cells of the epithelial lining and in the submucosal glands.

CONCLUSIONS

As previously shown for allergic asthma and allergic conjunctivitis, NGF is also detectable in the nasal mucosa of patients with persistent allergic rhinitis. The preferential NGF localization in mucous cells of the epithelial lining and in the submucosal glands suggests a possible role for NGF in modulating secretion in allergic rhinitis and possibly other allergic diseases.

Surface chemistry and in situ spectroscopy of a lysozyme langmuir monolayer

Surface pressure and surface potential-area isotherms were used to characterize a lysozyme Langmuir monolayer. The compression-decompression cycles and stability measurements showed a homogeneous and stable monolayer at the air-water interface. Salt concentration in the subphase and pH of the subphase were parameters controlling the homogeneity and stability of the Langmuir monolayer. In situ UV-vis and fluorescence spectroscopies were used to verify the homogeneity of the lysozyme monolayer and to identify the chromophore residues in the lysozyme. Optimal experimental conditions were determined to prepare a homogeneous and stable lysozyme Langmuir monolayer.

Investigation of the effects of PACAP on the composition of tear and endolymph proteins

Pituitary adenylate cyclase activating polypeptide (PACAP) is widely distributed in ocular tissues, including the lacrimal gland. PACAP has been shown to influence the activity of several exocrine glands, but its effects on the composition of the tear film are not known yet. Similarly, the presence of PACAP has already been shown in the inner ear, but it is not known whether PACAP influences the composition of the endolymph. The aim of the present study was to investigate whether systemic injection of PACAP has any modulatory effects on the protein composition of the tear film and endolymph using chip electrophoresis and mass spectrometry analysis. Tear and endolymph samples were collected from rats and chickens, respectively, at various time points after systemic injection of PACAP. Fluid samples were further processed for chip electrophoretic studies. No difference was found in the protein composition of the endolymph between control and PACAP-treated animals. In contrast, tear samples showed a marked difference after PACAP treatment. Proteins in the molecular range 50-70 kDa, which showed a different chip electropherogram profile in every PACAP-treated sample, were further analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. PACAP treatment induced a repression in certain keratins, while others were induced after PACAP injection. Furthermore, PACAP treatment decreased aldehyde dehydrogenase expression. The present study provides a base for further studies on the in vivo effects of PACAP on the composition of tear film. These investigations may have important clinical relevance because of the noninvasive sample collection, the correlation between tear proteins and ocular diseases, and the possible presence of biomarkers for both ophthalmological and systemic pathological conditions.

Mucins and TFF peptides of the tear film and lacrimal apparatus

The three-dimensional organization of the tear film, which is produced and drained by the different structures of the ocular adnexa, is essential for maintainance and protection of the ocular surface. This is facilitated by a class of large, highly glycosylated, hydrophilic glycoproteins, the mucins, which are usually expressed in association with a class of peptides having a well-defined, structurally conserved trefoil domain, the mammalian trefoil factor family (TFF) peptides. In this review, the latest information regarding mucin and TFF peptide function and regulation in the human lacrimal system, the tear film and the ocular surface is summarized with regard to mucous epithelia integrity, rheological and antimicrobial properties of the tear film and tear outflow, age-related changes and certain disease states such as dry eye, dacryostenosis and dacryolith formation.