Mucin deficiency causes functional and structural changes of the ocular surface

Topical naltrexone increases aquaporin 5 production in the lacrimal gland and restores tear production in diabetic rats

Diabetes mellitus is a prevalent disease that is often accompanied by ocular surface abnormalities including delayed epithelial wound healing and decreased corneal sensitivity. The impact of diabetes on the lacrimal functional unit (LFU) and the structures responsible for maintaining tear homeostasis, is not completely known. It has been shown that the Opioid Growth Factor Receptor (OGFr), and its ligand, Opioid Growth Factor (OGF), is dysregulated in the ocular surface of diabetic rats leading to overproduction of the inhibitory growth peptide OGF. The opioid antagonist naltrexone hydrochloride (NTX) blocks the OGF-OGFr pathway, and complete blockade following systemic or topical treatment with NTX restores the rate of re-epithelialization of corneal epithelial wounds, normalizes corneal sensitivity, and reverses dry eye in diabetic animal models. These effects occur rapidly and within days of initiating treatment. The present study was designed to understand mechanisms related to the fast reversal (<5 days) of dry eye by NTX in type 1 diabetes (T1D) by investigating dysregulation of the LFU. The approach involved examination of the morphology of the LFU before and after NTX treatment. Male and female adult Sprague-Dawley rats were rendered hyperglycemic with streptozotocin, and after 6 weeks rats were considered to be a T1D model. Rats received topical NTX twice daily to one eye for 10 days. During the period of treatment, tear production and corneal sensitivity were recorded. On day 11, animals were euthanized and orbital tissues including conjunctiva, eyelids, and lacrimal glands, were removed and processed for histologic examination including immunohistochemistry. Male and female T1D rats had significantly decreased tear production and corneal insensitivity, significantly decreased number and size of lacrimal gland acini, decreased expression of aquaporin-5 (AQP5) protein and decreased goblet cell size. Thus, 10 days of NTX treatment restored tear production and corneal sensitivity to normal values, increased AQP5 expression, and restored the surface area of goblet cells to normal. NTX had no effect on the number of lacrimal gland acini or the number of conjunctival goblet cells. In summary, blockade of the OGF-OGFr pathway with NTX reversed corneal and lacrimal gland complications and restored some components of tear homeostasis confirming the efficacy of topical NTX as a treatment for ocular defects in diabetes.

Probiotic potential of Saccharomyces cerevisiae GILA with alleviating intestinal inflammation in a dextran sulfate sodium induced colitis mouse model

Recently, several probiotic products have been developed; however, most probiotic applications focused on prokaryotic bacteria whereas eukaryotic probiotics have received little attention. Saccharomyces cerevisiae yeast strains are eukaryotes notable for their fermentation and functional food applications. The present study investigated the novel yeast strains isolated from Korean fermented beverages and examined their potential probiotic characteristics. We investigated seven strains among 100 isolates with probiotic characteristics further. The strains have capabilities such as auto-aggregation tendency, co-aggregation with a pathogen, hydrophobicity with n-hexadecane,1,1-diphenyl-2-picrylhydrazyl scavenging effect, survival in simulated gastrointestinal tract conditions and the adhesion ability of the strains to the Caco-2 cells. Furthermore, all the strains contained high cell wall glucan content, a polysaccharide with immunological effects. Internal transcribed spacer sequencing identified the Saccharomyces strains selected in the present study as probiotics. To examine the effects of alleviating inflammation in cells, nitric oxide generation in raw 264.7 cells with S. cerevisiae showed that S. cerevisiae GILA could be a potential probiotic strain able to alleviate inflammation. Three probiotics of S. cerevisiae GILA strains were chosen by in vivo screening with a dextran sulfate sodium-induced colitis murine model. In particular, GILA 118 down-regulates neutrophil-lymphocyte ratio and myeloperoxidase in mice treated with DSS. The expression levels of genes encoding tight junction proteins in the colon were upregulated, cytokine interleukin-10 was significantly increased, and tumor necrosis factor-α was reduced in the serum.

The protective role of conjunctival goblet cell mucin sialylation

Gel-forming mucins secreted by conjunctival goblet cells have been implicated in the clearance of allergens, pathogens, and debris. However, their roles remain incompletely understood. Here we show that human and mouse conjunctival goblet cell mucins have Alcian blue-detectable sialic acids, but not sulfates in the steady state. Interestingly, Balb/c mouse strain lacks this sialylation due to a point mutation in a sialyltransferase gene, St6galnac1, which is responsible for sialyl-Tn synthesis. Introduction of intact St6galnac1 to Balb/c restores the sialylation of conjunctival goblet cell mucus. Sialylated mucus efficiently captures and encapsulates the allergen particles in an impenetrable layer, leading to the protection of mice from the development of allergic conjunctivitis. Expression of ST6GALNAC1 and sialyl-Tn is upregulated in humans under conditions with chronic stimuli. These results indicate that the sialylated glycans on the ocular mucins play an essential role in maintaining the conjunctival mucosa by protecting from the incoming foreign bodies such as allergen particles.

Immune regulation of the ocular surface

Despite constant exposure to various environmental stimuli, the ocular surface remains intact and uninflamed while maintaining the transparency of the cornea and its visual function. This 'immune privilege' of the ocular surface is not simply a result of the physical barrier function of the mucosal lining but, more importantly, is actively maintained through a variety of immunoregulatory mechanisms that prevent the disruption of immune homeostasis. In this review, we focus on essential molecular and cellular players that promote immune quiescence in steady-state conditions and suppress inflammation in disease-states. Specifically, we examine the interactions between the ocular surface and its local draining lymphoid compartment, by encompassing the corneal epithelium, corneal nerves and cornea-resident myeloid cells, conjunctival goblet cells, and regulatory T cells (Treg) in the context of ocular surface autoimmune inflammation (dry eye disease) and alloimmunity (corneal transplantation). A better understanding of the immunoregulatory mechanisms will facilitate the development of novel, targeted immunomodulatory strategies for a broad range of ocular surface inflammatory disorders.

Characterisation of Gel-Forming Mucins Produced In Vivo and In Ex Vivo Conjunctival Explant Cultures

One key element to the health of the ocular surface encompasses the presence of gel-forming mucins in the pre-ocular tear film. Conjunctival goblet cells are specialized epithelial cells that secrete mucins necessary for tear film stability and general homeostasis. Their dysfunction can be linked to a range of ocular surface inflammation disorders and chronic injuries. To obtain new perspectives and angles to tackle mucin deficiency, the need for an accurate evaluation of their presence and corresponding mucin secretion in ex vivo conjunctival cultures has become a requisite. In vitro, goblet cells show a significant decrease in the production and secretion of gel-forming mucins, accompanied by signs of dedifferentiation or transdifferentiation. Explant cultures on laminin-treated CLP-PEG hydrogels can, however, support the production of gel-forming mucins. Together, we challenge the current paradigm to evaluate the presence of cultured goblet cells solely based on their general mucin (MUC) content through imaging analyses, showing the need for additional techniques to assess the functionality of goblet cells. In addition, we broadened the gel-forming mucin profile of in vivo goblet cells with MUC5B and MUC6, while MUC2 and MUC6 is added to the profile of cultured goblet cells.

Autoimmunity in dry eye disease - An updated review of evidence on effector and memory Th17 cells in disease pathogenicity

The classic Th1/Th2 dogma has been significantly reshaped since the subsequent introduction of several new T helper cell subsets, among which the most intensively investigated during the last decade is the Th17 lineage that demonstrates critical pathogenic roles in autoimmunity and chronic inflammation - including the highly prevalent dry eye disease. In this review, we summarize current concepts of Th17-mediated disruption of ocular surface immune homeostasis that leads to autoimmune inflammatory dry eye disease, by discussing the induction, activation, differentiation, migration, and function of effector Th17 cells in disease development, highlighting the phenotypic and functional plasticity of Th17 lineage throughout the disease initiation, perpetuation and sustention. Furthermore, we emphasize the most recent advance in Th17 memory formation and function in the chronic course of dry eye disease, a major area to be better understood for facilitating the development of effective treatments in a broader field of autoimmune diseases that usually present a chronic course with recurrent episodes of flare in the target tissues or organs.

Role for Mucin-5AC in Upper and Lower Airway Pathogenesis in Mice

Mucin-5AC (MUC5AC) is a major secreted mucin in pathogenic airways. To determine its role in mucus-related airway disorders, Muc5ac-deficient (Muc5ac^-/-) and wild-type (Muc5ac^+/+) mice were compared in bleomycin-induced pulmonary fibrosis, respiratory syncytial virus (RSV) disease, and ozone toxicity. Significantly greater inflammation and fibrosis by bleomycin were developed in Muc5ac^-/- lungs compared to Muc5ac^+/+ lungs. More severe mucous cell metaplasia in fibrotic Muc5ac^-/- lungs coincided with bronchial Muc2, Muc4, and Muc5b overexpression. Airway RSV replication was higher in Muc5ac^-/- than in Muc5ac^+/+ during early infection. RSV-caused pulmonary epithelial death, bronchial smooth muscle thickening, and syncytia formation were more severe in Muc5ac^-/- compared to Muc5ac^+/+. Nasal septal damage and subepithelial mucoserous gland enrichment by RSV were greater in Muc5ac^-/- than in Muc5ac^+/+. Ozone exposure developed more severe nasal airway injury accompanying submucosal gland hyperplasia and pulmonary proliferation in Muc5ac^-/- than in Muc5ac^+/+. Ozone caused periodic acid-Schiff-positive secretion only in Muc5ac^-/- nasal airways. Lung E-cadherin level was relatively lower in Muc5ac^-/- than in Muc5ac^+/+ basally and after bleomycin, RSV, and ozone exposure. Results indicate that MUC5AC is an essential mucosal component in acute phase airway injury protection. Subepithelial gland hyperplasia and adaptive increase of other epithelial mucins may compensate airway defense in Muc5ac^-/- mice.

In vitro and ex vivo expression of serum amyloid A3 in mouse lung epithelia

BACKGROUND AND PURPOSE

Serum amyloid A (SAA), an acute-phase protein whose level tracks infection and inflammation, is the precursor protein of amyloid A (AA) fibrils that is thought to cause AA amyloidosis in human and animals. SAA protein has several isoforms based on the difference of amino acid sequence, such as SAA1 to SAA4 in mice. AA fibrils are associated with chronic inflammation and are mainly originated from SAA1 produced in the liver. SAA3 reportedly contributes to the innate immune response in epithelia; however, little is known about its role at the lung epithelia. Therefore, we investigated SAA3 expression in the lung epithelium activated by bacterial antigens.

MATERIALS AND METHODS

The expressions of SAA3 and SAA1 mRNA were investigated using quantitative real-time PCR, in vitro using mouse Clara (Club) cells and ex vivo using surgically removed mouse lungs, after their stimulation by using either lipopolysaccharide (LPS), the major outer membranous antigen of gram-negative bacteria, or lipoteichoic acid (LTA), the major outer membranous antigen of gram-positive bacteria. In addition, SAA3 and SAA1/2 proteins in treated lung samples were detected by immunohistochemistry (IHC).

RESULTS

SAA3 mRNA expression increased in cells and lungs treated with either LPS or LTA. SAA3 mRNA was more sensitively expressed in LPS than LTA treatment. In contrast, SAA1 mRNA expression did not increase by either LPS or LTA treatment. Furthermore, SAA3 mRNA expression increased in a dose-dependent manner in cells treated with tumor necrosis factor-alpha. By IHC, SAA3 protein was highly expressed in the luminal side of the bronchial epithelium, while SAA1/2 was not expressed.

CONCLUSION

These results obtained from in vitro and ex vivo experiments suggest that SAA3 plays an important role in the innate immune response to bacterial infection in the lung epithelia.

Contribution of Mucins towards the Physical Properties of the Tear Film: A Modern Update

Instability of the tear film (TF) protecting the ocular surface results in dry eye syndrome (DES), the most prevalent public health ophthalmic disease affecting the quality of life of 10 to 30% of the human population worldwide. Although the impact of the tear film lipid layer (TFLL) and of the aqueous tears (AT) to the TF stability is extensively studied, in contrast the contribution of the secretory mucins (SM) and of the membrane-associated mucins (MAM), i.e., one of the most abundant molecular classes in AT and in the corneal epithelium respectively, remains poorly defined. However, it is well known that in DES both types of mucins are quantitatively or qualitatively deficient. Numerous studies since the 1990s until now have proposed direct involvement of SM and MAM in the material properties (viscoelasticity, hydration, and protection of the ocular surface; synergistic cooperation with the rest of the TF layers; etc.) and stability of TF. These theories will be reviewed here in the context of the classical and modern in vitro and in vivo results that allow their reappraisal and in view of the novel mucin secretion enhancing pharmaceuticals, which have opened innovative routes for the therapy of DES.

Lipopolysaccharide and lipoteichoic acid enhance serum amyloid A3 mRNA expression in murine alveolar epithelial cells

Serum amyloid A (SAA) is an acute-phase protein indicative of inflammation. In murine colonic epithelial cells, lipopolysaccharide (LPS), a gram-negative bacterial antigen, strongly enhanced mRNA expression of SAA3, but not SAA1 or SAA2, suggesting that SAA3 might respond to bacterial infection in other epithelia. We examined SAA1/2 and SAA3 mRNA expression in murine alveolar epithelial cells exposed to LPS or the gram-positive bacterial antigen, lipoteichoic acid (LTA), using real-time PCR. LPS enhanced SAA3 mRNA expression at lower concentrations than did LTA, whereas SAA1/2 mRNA expression was not enhanced by either LPS or LTA. These results suggest that SAA3 expression is enhanced in lung epithelium upon bacterial infection as part of innate immunity, with higher sensitivity to LPS than to LTA.

Ocular mucins in dry eye disease

Dry eye disease is a common and multifactorial disease with a high prevalence worldwide. Water loss, reduced expression of glycocalyx mucins, and loss of goblet cells secreting gel-forming mucins are hallmarks of dry eye disease. Mucins are large and complex heavily glycosylated proteins. Their organization in the tear film remains unclear, but they play a key role to protect and maintain integrity of the ocular surface. Mice have been extremely valuable mammalian models with which to study ocular physiology and disease, and to evaluate eye therapies. Genetically modified mice and spontaneously occurring mutants with eye defects have proven to be powerful tools for the pharmaceutical industry, clinicians, and basic researchers investigating dry eye disease. However, ocular mucins remain relatively under-studied and inadequately characterized. This review aims to summarize current knowledge about mucin production at the ocular surface in healthy individuals and in dry eye disease, and to compile an overview of mouse models available for the study of mucins in dry eye disease.

Secreted Mucins on the Ocular Surface

Mucins, which play important roles on the ocular surface in wettability, lubrication, and barrier function, are classified into two categories: secreted mucins and membrane-associated mucins. The most important secreted mucin on the ocular surface is MUC5AC, which is secreted by the conjunctival goblet cells. In the human conjunctiva, goblet cells are present in higher concentrations in the fornix, inferior nasal bulbar, and the lid wiper on the lid margin. The number of conjunctival goblet cells and MUC5AC expression/secretion are decreased in a patient with dry eye. In Japan, drugs that stimulate mucin secretion or increase the number of conjunctival goblet cells are commercially available. A P2Y2 receptor, diquafosol, stimulates tear fluid secretion from conjunctival epithelial cells and promotes mucin secretion from conjunctival goblet cells. Rebamipide was marketed originally as an oral therapeutic drug to treat gastritis in Japan. Topical rebamipide increases numbers of goblet cells in the bulbar conjunctiva and the lid wiper area of palpebral conjunctiva. Many researchers have reported decreases in the ocular surface mucin expression including MUC5AC secreted by goblet cells in patients with dry eye. However, it is unknown whether changes in mucin expression on the ocular surface cause or result from dry eye. Further study is needed to determine the true mechanism of dry eye disease.

Ramifications of secreted mucin MUC5AC in malignant journey: a holistic view

Heavily glycosylated secreted mucin MUC5AC, by the virtue of its cysteine-rich repeats, can form inter- and intramolecular disulfide linkages resulting in complex polymers, which in turn craft the framework of the polymeric mucus gel on epithelial cell surfaces. MUC5AC is a molecule with versatile functional implications including barrier functions to epithelial cells, host-pathogen interaction, immune cell attraction to sites of premalignant or malignant lesions and tumor progression in a context-dependent manner. Differential expression, glycosylation and localization of MUC5AC have been associated with a plethora of benign and malignant pathologies. In this era of robust technologies, overexpression strategies and genetically engineered mouse models, MUC5AC is emerging as a potential diagnostic, prognostic and therapeutic target for various malignancies. Considering the clinical relevance of MUC5AC, this review holistically encompasses its genomic organization, domain structure, glycosylation patterns, regulation, functional and molecular connotation from benign to malignant pathologies. Furthermore, we have here explored the incipient and significant experimental tools that are being developed to study this structurally complex and evolutionary conserved gel-forming mucin.

Context-Dependent Regulation of Conjunctival Goblet Cell Function by Allergic Mediators

In the eye, goblet cells responsible for secreting mucins are found in the conjunctiva. When mucin production is not tightly regulated several ocular surface disorders may occur. In this study, the effect of the T helper (Th) 2-type cytokines IL4, IL5, and IL13 on conjunctival goblet cell function was explored. Goblet cells from rat conjunctiva were cultured and characterized. The presence of cytokine receptors was confirmed by Reverse Transcription-Polymerase Chain Reaction (RT-PCR). Changes in intracellular [Ca2+], high molecular weight glycoconjugate secretion, and proliferation were measured after stimulation with Th2 cytokines with or without the allergic mediator histamine. We found that IL4 and IL13 enhance cell proliferation and, along with histamine, stimulate goblet cell secretion. We conclude that the high levels of IL4, IL5, and IL13 that characterize allergic conjunctivitis could be the reason for higher numbers of goblet cells and mucin overproduction found in this condition.

Mucus models to evaluate the diffusion of drugs and particles

Mucus is a complex hydrogel that acts as a natural barrier to drug delivery at different mucosal surfaces including the respiratory, gastrointestinal, and vaginal tracts. To elucidate the role mucus plays in drug delivery, different in vitro, in vivo, and ex vivo mucus models and techniques have been utilized. Drug and drug carrier diffusion can be studied using various techniques in either isolated mucus gels or mucus present on cell cultures and tissues. The species, age, and potential disease state of the animal from which mucus is derived can all impact mucus composition and structure, and therefore impact drug and drug carrier diffusion. This review provides an overview of the techniques used to characterize drug and drug carrier diffusion, and discusses the advantages and disadvantages of the different models available to highlight the information they can afford.

Efficacy and safety of retinol palmitate ophthalmic solution in the treatment of dry eye: a Japanese Phase II clinical trial

Purpose

The purpose of this study was to investigate the efficacy and safety of the administration of retinol palmitate (VApal) ophthalmic solution (500 IU/mL) for the treatment of patients with dry eye.

Patients and methods

This study included 66 patients with dry eye. After a 2-week washout period, patients were randomized (1:1) into either a VApal ophthalmic solution or a placebo group, and a single drop of either solution was administered six times daily for 4 weeks. Efficacy measures were 12 subjective symptoms, rose bengal (RB) and fluorescein staining scores, tear film breakup time, and tear secretion. Safety measures included clinical blood and urine analyses and adverse event recordings.

Results

In comparisons of the two groups, the mean change in RB staining score from baseline was significantly lower in the VApal group at 2 and 4 weeks (P<0.05 and P<0.01, respectively). Furthermore, the fluorescein clearance rate (fluorescein staining score) was significantly higher in the VApal group at 4 weeks (P<0.05). The VApal group showed a significant improvement in blurred vision at 1 and 2 weeks (P<0.01 and P<0.05, respectively), and the mean change in the total score for subjective symptoms from baseline was significantly lower in the VApal group at 1 week (P<0.05). In before- and after-intervention comparisons, the fluorescein and RB staining scores showed improvement in both groups. Improvement was noted for 11 subjective symptoms in the VApal group and for seven symptoms in the placebo group. No significant differences in adverse events and reactions were found between the groups.

Conclusion

VApal ophthalmic solution (500 IU/mL) is safe and effective for the treatment of patients with dry eye.

In vivo imaging of the Muc5b gel-forming mucin

Gel-forming mucins are macromolecules produced by goblet cells and responsible for the mucus gel formation. Changes in goblet cell density and in gel-forming mucin production have emerged as sensitive indicators for mucosal diseases. A Muc5b-GFP tagged reporter mouse was used to assess Muc5b production in mouse tissues by immunofluorescence microscopy and fluorescent activity using stereromicroscopy and probe-based confocal laser endomicroscopy. Muc5b production was followed longitudinally by recording the fluorescent activity in vagina and in embryonic lung explants under stimulation by interleukin 13. We show that the GFP is easily visualized in the mouse adult ear, nose, trachea, gallbladder, and cervix. Live Muc5b is also easily monitored in the nasal cavity, trachea and vagina where its production varies during the estrus cycle with a peak at the proestrus phase and in pregnant mice. Explant culture of reporter mouse embryonic whole lung shows that interleukin 13 stimulates Muc5b production. The transgenic Muc5b-GFP mouse is unique and suitable to study the mechanisms that regulate Muc5b production/secretion and mucous cell differentiation by live imaging and can be applied to test drug efficacy in mucosal disease models.

Efficacy and safety of a cationic emulsion in the treatment of moderate to severe dry eye disease: a randomized controlled study

PURPOSE

To evaluate the efficacy and safety of a preservative-free cationic emulsion (CE) with a 0.18% hyaluronate sodium (HS) solution in patients with moderate to severe dry eye disease (DED) with keratitis or keratoconjunctivitis.

METHODS

Eighty-five patients were randomized (1:1) in this multicenter, prospective, reference-controlled, parallel-group, investigator-masked study to receive CE (n = 44) or HS (n = 41). Clinical signs and symptoms were assessed over 3 months. The primary efficacy endpoint was noninferiority of CE to HS in change from baseline of ocular surface staining (OSS) score at 1 month.

RESULTS

In the per protocol (PP) set and full analysis set (FAS), CE showed a similar and noninferior (p&lt;0.0001) improvement in OSS scores compared with HS at 1 month (PP: -2.5 ± 1.3 vs -1.9 ± 1.6; FAS: -2.2 ± 1.5 vs -2.0 ± 1.8 for CE vs HS). Other clinical signs of DED similarly improved in both groups. In the FAS, global symptoms score of ocular discomfort was significantly better with CE compared with HS at 1 month (-14.8 ± 17.3 vs -7.6 ± 14.2; p = 0.0469), including greater alleviation of itching (-14.8 ± 21.2 vs -1.7 ± 19.7; p = 0.0100) and eye dryness (-21.9 ± 28.3 vs -8.4 ± 21.4; p = 0.0016). Similar trends were observed at 3 months for itching and eye dryness. Investigator global efficacy assessment and quality of life scores for eye pain and driving favored CE at 3 months. Incidence of adverse events was low in both treatment groups.

CONCLUSIONS

CE was similar to HS with regards to safety and efficacy for objective signs but was superior to HS in improving DED symptoms in patients with moderate to severe DED.

Interaction of IFN-γ with cholinergic agonists to modulate rat and human goblet cell function

Goblet cells populate wet-surfaced mucosa including the conjunctiva of the eye, intestine, and nose, among others. These cells function as part of the innate immune system by secreting high molecular weight mucins that interact with environmental constituents including pathogens, allergens, and particulate pollutants. Herein, we determined whether interferon gamma (IFN-γ), a Th1 cytokine increased in dry eye, alters goblet cell function. Goblet cells from rat and human conjunctiva were cultured. Changes in intracellular [Ca(2+)] ([Ca(2+)](i)), high molecular weight glycoconjugate secretion, and proliferation were measured after stimulation with IFN-γ with or without the cholinergic agonist carbachol. IFN-γ itself increased [Ca(2+)](i) in rat and human goblet cells and prevented the increase in [Ca(2+)](i) caused by carbachol. Carbachol prevented IFN-γ-mediated increase in [Ca(2+)](i). This cross-talk between IFN-γ and muscarinic receptors may be partially due to use of the same Ca(2+)(i) reservoirs, but also from interaction of signaling pathways proximal to the increase in [Ca(2+)](i). IFN-γ blocked carbachol-induced high molecular weight glycoconjugate secretion and reduced goblet cell proliferation. We conclude that increased levels of IFN-γ in dry eye disease could explain the lack of goblet cells and mucin deficiency typically found in this pathology. IFN-γ could also function similarly in respiratory and gastrointestinal tracts.

Ocular surface mucins and local inflammation--studies in genetically modified mouse lines

Mucins locate to the apical surfaces of all wet-surfaced epithelia including ocular surface. The functions of the mucins include anti-adhesive, lubrication, water retention, allergens and pathogen barrier function. Ocular surface pathologies, i.e. dry eye syndrome or allergic conjunctivitis, are reportedly associated with alteration of expression pattern of mucin components. Recent investigations indicated anti-bacterial adhesion or anti-inflammatory effects of members of mucins in non-ocular tissues, i.e., gastrointestinal tracts or airway tissues, by using genetically modified mouse lines that lacks an expression of a mucin member. However, examination of ocular phenotypes of each of mucin gene-ablated mouse lines has not yet fully performed. Muc16-dficient mouse is associated with spontaneous subclinical inflammation in conjunctiva. The article reviews the roles of mucin members in modulation of local inflammation in mucous membrane tissues and phenotype of mouse lines with the loss of a mucin gene. Analysis of ocular surface of mucin-gene related mutant mouse lines are to be further performed.

Protective Role of Surfactant Protein D in Ocular Staphylococcus aureus Infection

Staphylococcus aureus is one of the most common pathogens causing keratitis. Surfactant protein D (SP-D) plays a critical role in host defense and innate immunity. In order to investigate the role of SP-D in ocular S. aureus infection, the eyes of wild-type (WT) and SP-D knockout (SP-D KO) C57BL/6 mice were infected with S. aureus (10⁷ CFU/eye) in the presence and absence of cysteine protease inhibitor(E₆₄).Bacterial counts in the ocular surface were examined 3, 6, 12, 24 hrs after infection. Bacterial phagocytosis by neutrophils and bacterial invasion in ocular epithelial cells were evaluated quantitatively. S. aureus-induced ocular injury was determined with corneal fluorescein staining. The results demonstrated that SP-D is expressed in ocular surface epithelium and the lacrimal gland; WT mice had increased clearance of S. aureus from the ocular surface (p<0.05) and reduced ocular injury compared with SP-D KO mice. The protective effects of SP-D include increased bacterial phagocytosis by neutrophils (p<0.05) and decreased bacterial invasion into epithelial cells (p<0.05) in WT mice compared to in SP-D KO mice. In the presence of inhibitor (E₆₄), WT mice showed enhanced bacterial clearance (p<0.05) and reduced ocular injury compared to absent E₆₄ while SP-D KO mice did not. Collectively, we concluded that SP-D protects the ocular surface from S. aureus infection but cysteine protease impairs SP-D function in this murine model, and that cysteine protease inhibitor may be a potential therapeutic agent in S. aureus keratitis.

A role for ELOVL4 in the mouse meibomian gland and sebocyte cell biology

PURPOSE

The meibum lipidome contains lipids with extremely long chain fatty acid (ELCFA) residues, longer than C28. Particular lipids based on extremely long chain (O-acyl)-ω-hydroxy fatty acids (OAHFA) are found in all mammal meibum and are proposed to stabilize the tear film by forming the interphase between its lipid and aqueous sublayers. The enzyme ELOVL4 is required for synthesis of ELCFA. We investigated whether Stgd3 mice, harboring mutations in ELOVL4 that have been shown to decrease the levels of its biosynthetic lipid products, would represent a model system in which to define the role of such lipids in meibum.

METHODS

Ocular phenotypes of wild-type mice were compared with those of Stgd3 mice. ELOVL4 expression in eyelid and back skin was characterized by immunohistochemical analysis. Anatomical changes within the eyelids of mutant mice were examined by hematoxylin and eosin staining of paraffin-embedded tissue.

RESULTS

Mutant mice had increased eyelid blink rates, a reluctance to maintain their eyes fully open, protruding meibomian gland (MG) orifices, and anatomical changes within the MG. In wild-type mice, ELOVL4 was strongly expressed within the holocrine meibomian and sebaceous glands. The enzyme localized to structures encircling lipid deposits within cells in both the early and late stages of differentiation. No ELOVL4 was detected within the central meibomian duct.

CONCLUSIONS

Stgd3 mice show changes that resemble clinical findings in patients with the evaporative type of dry eye disease, suggesting that further studies in this mouse model will provide a basis for better understanding of the causes of human dry eye.

The ocular surface phenotype of Muc5ac and Muc5b null mice

PURPOSE

Recent development of mice null for either Muc5ac or Muc5b mucin allows study of their specific roles at the mouse ocular surface. A recent report indicated that Muc5ac null mice show an ocular surface phenotype similar to that seen in dry eye syndrome. The purpose of our study was to determine the effect of lack of Muc5ac or Muc5b on the ocular surface, and to determine if environmental desiccating stress exacerbated a phenotype.

METHODS

Muc5ac null and Muc5b null mice, and their wild-type controls were examined for ocular surface defects by fluorescein staining. The number of goblet cells per area of conjunctival epithelium was counted, and levels of mucin gene expression and genes associated with epithelial stress, keratinization, and differentiation, known to be altered in dry eye syndrome, were assayed. To determine if the null mice would respond more to desiccating stress than their wild-type controls, they were challenged in a controlled environment chamber (CEC) and assessed for changes in fluorescein staining, tear volume, and inflammatory cells within the conjunctival and corneal epithelia.

RESULTS

Unlike the previous study, we found no ocular surface phenotype in the Muc5ac null mice, even after exposure to desiccating environmental stress. Similarly, no ocular surface phenotype was present in the Muc5b null mice, either before or after exposure to a dry environment in the CEC.

CONCLUSIONS

Our results indicate that deleting either the Muc5ac or Muc5b gene is insufficient to create an observable dry eye phenotype on the ocular surface of these mice.

Tear film mucins: front line defenders of the ocular surface; comparison with airway and gastrointestinal tract mucins

The ocular surface including the cornea and conjunctiva and its overlying tear film are the first tissues of the eye to interact with the external environment. The tear film is complex containing multiple layers secreted by different glands and tissues. Each layer contains specific molecules and proteins that not only maintain the health of the cells on the ocular surface by providing nourishment and removal of waste products but also protect these cells from environment. A major protective mechanism that the corneal and conjunctival cells have developed is secretion of the innermost layer of the tear film, the mucous layer. Both the cornea and conjunctiva express membrane spanning mucins, whereas the conjunctiva also produces soluble mucins. The mucins present in the tear film serve to maintain the hydration of the ocular surface and to provide lubrication and anti-adhesive properties between the cells of the ocular surface and conjunctiva during the blink. A third function is to contribute to the epithelial barrier to prevent pathogens from binding to the ocular surface. This review will focus on the different types of mucins produced by the corneal and conjunctival epithelia. Also included in this review will be a presentation of the structure of mucins, regulation of mucin production, role of mucins in ocular surface diseases, and the differences in mucin production by the ocular surface, airways and gastrointestinal tract.