Mucin genes expressed by the ocular surface Epithelium

Allogenic Cultured Limbal Epithelial Transplantation and Cultivated Oral Mucosal Epithelial Transplantation in Limbal Stem Cells Deficiency: A Comparative Study

INTRODUCTION

This study compared the clinical outcomes of allogenic cultured limbal epithelial transplantation (ACLET) and cultivated oral mucosal epithelial transplantation (COMET) in the management of limbal stem cell deficiency (LSCD).

METHODS

Forty-one COMET procedures in 40 eyes and 69 ACLET procedures in 54 eyes were performed in the Corneoplastic Unit of Queen Victoria Hospital, East Grinstead. Data were examined for demographics, indications, ocular surface stability, absence of epithelial defect, ocular surface inflammation, visual outcomes, and intra- and postoperative complications.

RESULTS

Kaplan-Meier analysis showed that patients in the ACLET group with longer follow-up had a significantly higher graft survival rate (81.7%, n = 56) than the COMET group (60.7%, n = 25) and the difference was statistically significant (p = 0.01). In the COMET group, there was no statistically significant improvement in the visual acuity (VA) while in the ACLET group there was statistically significant improvement in the final VA. Elevated intraocular pressure (IOP) developed in 9 eyes (22.0%) in the COMET group and in 18 eyes (26.1%) in the ACLET group; infection developed in 4 eyes (9.8%) in the COMET group and in 10 eyes (14.5%) in the ACLET group; and perforation or melting happened in 4 eyes (9.8%) in the COMET group and in 1 eye (1.4%) in the ACLET group. Postoperative immunosuppression complications were noted in 9 eyes (13.0%) in the ACLET group. No graft rejection was observed in either group.

CONCLUSION

Both ACLET and COMET are effective therapeutic procedures for managing advanced and bilateral cases of LSCD. Although COMET has lower graft survival rate than ACLET, it does not mandate systemic immunosuppression therapy to protect against potential graft rejection.

Lactobacilli and Their Probiotic Effects in the Vagina of Reproductive Age Women

In the present narrative review, the probiotic effects of vaginal Lactobacillus spp. are described in detail, covering the importance of the differential production of lactic acid, the lactic acid D/L isoforms, the questionable in vivo effect of hydrogen peroxide, as well as bacteriocins and other core proteins produced by vaginal Lactobacillus spp. Moreover, the microbe–host interaction is explained with emphasis on the vaginal mucosa. To understand the crucial role of Lactobacillus spp. dominance in the vaginal microbiota, different dysbiotic states of the vagina are explained including bacterial vaginosis and aerobic vaginitis. Finally, this review takes on the therapeutic aspect of live lactobacilli in the context of bacterial vaginosis. Until recently, there was very low-quality evidence to suggest that any probiotic might aid in reducing vaginal infections or dysbiosis. Therefore, clinical usage or over the counter usage of probiotics was not recommended. However, recent progress has been made, moving from probiotics that are typically regulated as food supplements to so-called live biotherapeutic products that are regulated as medical drugs. Thus, recently, a phase 2b trial using a Lactobacillus crispatus strain as a therapeutic add-on to standard metronidazole showed significant reduction in the recurrence of bacterial vaginosis by 12 weeks compared to placebo. This may constitute evidence for a brighter future where the therapeutic use of lactobacilli can be harnessed to improve women’s health.

Corneal Epithelial Stem Cells-Physiology, Pathophysiology and Therapeutic Options

In the human cornea, regeneration of the epithelium is regulated by the stem cell reservoir of the limbus, which is the marginal region of the cornea representing the anatomical and functional border between the corneal and conjunctival epithelium. In support of this concept, extensive limbal damage, e.g., by chemical or thermal injury, inflammation, or surgery, may induce limbal stem cell deficiency (LSCD) leading to vascularization and opacification of the cornea and eventually vision loss. These acquired forms of limbal stem cell deficiency may occur uni- or bilaterally, which is important for the choice of treatment. Moreover, a variety of inherited diseases, such as congenital aniridia or dyskeratosis congenita, are characterized by LSCD typically occurring bilaterally. Several techniques of autologous and allogenic stem cell transplantation have been established. The limbus can be restored by transplantation of whole limbal grafts, small limbal biopsies or by ex vivo-expanded limbal cells. In this review, the physiology of the corneal epithelium, the pathophysiology of LSCD, and the therapeutic options will be presented.

Ex vivo cultivated oral mucosal epithelial cell transplantation for limbal stem cell deficiency: a review

Destruction or dysfunction of limbal epithelial stem cells (LESCs) leads to unilateral or bilateral limbal stem cell deficiency (LSCD). Fifteen years have passed since the first transplantation of ex vivo cultivated oral mucosal epithelial cells (COMET) in humans in 2004, which represents the first use of a cultured non-limbal autologous cell type to treat bilateral LSCD. This review summarizes clinical outcomes from COMET studies published from 2004 to 2019 and reviews results with emphasis on the culture methods by which grafted cell sheets were prepared.

Conjunctival Goblet Cells, the Overlooked Cells in Glaucoma Treatment

Glaucoma is the leading cause of irreversible blindness worldwide. Although no definitive cure exists, lowering of the intraocular pressure decreases the rate of progression in the majority of patients with glaucoma. Antiglaucomatous treatment modalities consist predominantly of chronic use of eye drops. It has become increasingly evident that long-term exposure to eye drops has a significant impact on the ocular surface, and thereby on patient compliance and quality of life. Maintenance of the ocular surface is highly dependent on a stable tear film. Conjunctival goblet cells (GCs) of the ocular surface play an important role in providing the innermost mucin layer of the tear film and are essential for maintaining the ocular surface homeostasis. Recent studies have reported severe side effects of antiglaucomatous drops on GCs. In particular, a preservative containing antiglaucomatous drops have been shown to affect the viability and functions of the GCs. Furthermore, GC density has been suggested as a potential predictor of surgical outcome after filtration surgery. The present review provides an overview of the current literature on the impact of antiglaucomatous eye drops on GCs as well as the impact on the ocular surface. Moreover, the existing evidence of a possible association between GC density and glaucoma filtration surgery outcome is summarized. We conclude that prostaglandin analogs spare the conjunctival GCs more compared with other antiglaucomatous drops and that GCs may be a good predictor of surgical outcome after filtration surgery. Overall, given the multiple functions of GCs in the ocular surface homeostasis, dedicated strategies should be adopted to preserve this cell population during the course of glaucoma.

Generation of 13C-Labeled MUC5AC Mucin Oligosaccharides for Stable Isotope Probing of Host-Associated Microbial Communities

Stable isotope probing (SIP) has emerged as a powerful tool to address key questions about microbiota structure and function. To date, diverse isotopically labeled substrates have been used to characterize in situ growth activity of specific bacterial taxa and have revealed the flux of bioavailable substrates through microbial communities associated with health and disease. A major limitation to the growth of the field is the dearth of biologically relevant "heavy" labeled substrates. Mucin glycoproteins, for example, comprise an abundant source of carbon in the gut, oral cavity, respiratory tract, and other mucosal surfaces but are not commercially available. Here, we describe a method to incorporate a ¹³C-labeled monosaccharide into MUC5AC, a predominant mucin in both gastrointestinal and airway environments. Using the lung adenocarcinoma cell line, Calu-3, polarized cell cultures grown in ¹³C-labeled d-glucose resulted in liberal mucin production on the apical surface. Mucins were isolated by size-exclusion chromatography, and O-linked glycans were released by β-elimination, permethylated, and analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) techniques. We demonstrate a 98.7% incorporation of ¹³C in the heterogeneous O-linked oligosaccharides that make up >80% of mucin dry weight. These "heavy" labeled glycoproteins represent a valuable tool for probing in vivo activity of host-associated bacterial communities and their interactions with the mucosal barrier. The continued expansion of labeled substrates for use in SIP will eventually allow bacterial taxa that degrade host compounds to be identified, with long-term potential for improved health and disease management.

Mucins: Structural diversity, biosynthesis, its role in pathogenesis and as possible therapeutic targets

Mucins are the main structural components of mucus that create a selective protective barrier for epithelial surface and also execute wide range of other physiological functions. Mucins can be classified into two types, namely secreted mucins and membrane bounded mucins. Alterations in mucin expression or glycosylation and mislocalization have been seen in various types of pathological conditions such as cancers, inflammatory bowel disease and ocular disease, which highlight the importance of mucin in maintaining homeostasis. Hence mucins can be used as attractive target for therapeutic intervention. In this review, we discuss in detail about the structural diversity of mucins; their biosynthesis; its role in pathogenesis; regulation and as possible therapeutic targets.

Physicochemical properties of mucus and their impact on transmucosal drug delivery

Mucus is a selective barrier to particles and molecules, preventing penetration to the epithelial surface of mucosal tissues. Significant advances in transmucosal drug delivery have recently been made and have emphasized that an understanding of the basic structure, viscoelastic properties, and interactions of mucus is of great value in the design of efficient drug delivery systems. Mucins, the primary non-aqueous component of mucus, are polymers carrying a complex and heterogeneous structure with domains that undergo a variety of molecular interactions, such as hydrophilic/hydrophobic, hydrogen bonds and electrostatic interactions. These properties are directly relevant to the numerous mucin-associated diseases, as well as delivering drugs across the mucus barrier. Therefore, in this review we discuss regional differences in mucus composition, mucus physicochemical properties, such as pore size, viscoelasticity, pH, and ionic strength. These factors are also discussed with respect to changes in mucus properties as a function of disease state. Collectively, the review seeks to provide a state of the art roadmap for researchers who must contend with this critical barrier to drug delivery.

Vitamin D Replacement Improves Tear Osmolarity in Patients with Vitamin D Deficiency

BACKGROUND

Vitamin D deficiency is a common health problem worldwide. Many parts of the human eye, including the epithelium of the cornea, lens, ciliary body, and retinal pigment epithelium, as well as the corneal endothelium, ganglion cell layer, and retinal photoreceptors, contain vitamin D receptor (VDR). Dry eye is also a common health problem. An adequate tear film is required for maintaining health and function of the eye. Tear hyperosmolarity is considered to be the cause of ocular surface inflammation, symptoms, and tissue damage. It is well-documented that vitamin D has an anti-inflammatory action. We aimed to investigate the effect of vitamin D replacement on tear osmolarity in patients with vitamin D deficiency.

METHODS

A total of 44 patients (38 females, six males, mean age:43.5 ± 12.8 years) with vitamin D deficiency currently managed by the Endocrinology and Metabolism Department of Diskapi Training and Research Hospital in Turkey were enrolled in the study. Patients were given 50,000 units of 25(OH)D₃ intramuscularly, once weekly, over a period of eight weeks. All of the patients underwent tear function osmolarity (TFO) measurement initially and eight weeks after vitamin D replacement. Demographic, anthropometric, and biochemistry data of patients were recorded.

RESULTS

The mean TFO was significantly decreased (313.7 ± 17.3 mOsm/L; 302.7 ± 14.2 mOsm/L, p<0.001) at the end of the second month; 25(OH)D₃ concentrations increased from 8.3 ± 3.5 ng/mL to 68.8 ± 22.3 ng/mL (p<0.001). The mean levels of hsCRP, FPG, P were 2.5 ± 2.5 mg/L, 5.09 ± 0.48 mmol/L, 1.06 ± 0.16 mmol/L initially, and 3.8 ± 5.9 mg/L, 5.11 ± 0.68 mg/dL, 1.09 ± 0.16 mmol/L after vitamin D replacement, respectively (p>0.05). The mean Ca level was 2.37 ± 0.07 mmol/L initially and 2.35 ± 0.07 mmol/L after vitamin D replacement (p<0.05). The change of TFO was negatively correlated with the variation of 25(OH)D₃ before and after replacement in patients with dry eye disease (r=-0.390, p=0.049).

CONCLUSIONS

As a consequence of the presence of VDR and 1α-hydroxylase in different parts of the eye, vitamin D replacement improves tear hyperosmolarity that is considered to be induced by ocular surface inflammation.

The tear ferning test: a simple clinical technique to evaluate the ocular tear film

A healthy tear film is very important for many major functions of the ocular surface. Dry eye disease is a significant clinical problem that needs to be solved but the poor correlation between clinical signs and reported symptoms makes it difficult for the clinician to apply a scientific basis to his clinical management. The problem is compounded by the difficulties of evaluating the tear film due to its transparency, small volume and complex composition. Practical insight into tear film composition would be very useful to the clinician for patient diagnosis and treatment but detailed analysis is restricted to expensive, laboratory-based systems. There is a pressing need for a simple test. The tear ferning test is a laboratory test but it has the potential to be applied in the clinic setting to investigate the tear film in a simple way. Drying a small sample of tear fluid onto a clean, glass microscope slide produces a characteristic crystallisation pattern, described as a 'tear fern'. This test is currently not widely used because of some limitations that need to be overcome but several studies have demonstrated its potential. Such limitations need to be resolved so that tear ferning could be used in the clinic setting to assess the tear film.

Evaluation of the adhesive properties of the cornea by means of optical coherence tomography in patients with meibomian gland dysfunction and lacrimal tear deficiency

Objective

The aim was to determine the influence of meibomian gland dysfunction (MGD) and aqueous tear deficiency dry eye (ADDE) on the adhesive properties of the central cornea by means of optical coherence tomography (OCT), and to investigate the relationship between corneal adhesiveness and classical tear tests, as well as the reliability of results, in these lacrimal functional unit disorders.

Design

Prospective, case-control study.

Methods

Twenty-eight patients with MGD and 27 patients with ADDE were studied. A group of 32 healthy subjects of similar age and gender distribution served as a control group. The adhesive properties of the anterior corneal surface were measured by OCT, based on the retention time of adhesion marker above it, in all participants.

Results

An excellent (≥5 minutes), borderline (within 3–5 minutes), fair (within 1–3 minutes) and poor (<1 minute) values of corneal adhesiveness were found, respectively, in 0%, 7.1%, 64.3% and 28.6% of MGD, in 0%, 7.4%, 63% and 29.6% of ADDE, and in 31.3%, 65.6%, 3.1% and 0% of healthy patients. The differences in time of corneal adhesiveness between MGD and healthy patients, as well as between ADDE and healthy patients, were found to be statistically significant (p<0.001; p<0.001; respectively). Conversely, no statistical significant differences between MGD and ADDE were found (p = 0.952). Data analysis revealed a statistically significant correlation between corneal adhesiveness and clinical tests of dry eye, as well as an excellent degree of inter-rater reliability and reproducibility for OCT measurements (p<0.001).

Conclusion

ADDE and MGD share similar abnormalities on OCT imaging. Decreased adhesive properties of the anterior cornea were identified as a common feature of MGD and ADDE. This simple OCT approach may provide new clues into the mechanism and evaluation of dry eye syndrome.

Nanoparticles based on naturally-occurring biopolymers as versatile delivery platforms for delicate bioactive molecules: an application for ocular gene silencing

Nanoparticles based on naturally-occurring biopolymers, most of them endogenous macromolecules, were designed as a versatile generation of delivery platforms for delicate bioactive molecules. The design of these nanosystems was specifically based on our recent finding about the ability of endogenous polyamine spermine (SPM) to interact with anionic biopolymers (ABs) generating ionically cross-linked nanosystems. The initial first generation of these delivery platforms, based on glycosaminoglycans and other polysaccharides, showed a very high association capacity for some delicate bioactive proteins such as growth factors, but a limited capacity to associate negatively charged molecules, such as pDNA and siRNA. However, the versatility of these nanosystems in terms of composition allowed us to customise the association of active ingredients and their physicochemical characteristics. Concretely, we prepared and incorporated gelatine cationized with spermine (CGsp) to their composition. The resulting modified formulations were characterised by a nanometric size (150-340 nm) and offer the possibility to modulate their zeta potential (from -35 to 28 mV), providing an efficient association of nucleic acids. The biological evaluation of these optimised nanosystems revealed that they are able to be internalised in vivo into corneal and conjunctival tissues and also to provide a significant siRNA gene silencing effect.

Sex hormones and the dry eye

The greater prevalence of dry eye in women compared to men suggests that sex hormones may have a role in this condition. This review aims to present evidence for how sex hormones may affect the ocular structures involved in the production, regulation and maintenance of the normal tear film. It is hypothesised that hormone changes alter the homeostasis of the ocular surface and contribute to dry eye. Androgens impact on the structure and function of the meibomian and lacrimal glands and therefore androgen deficiency is, at least in part, associated with the aetiology of dry eye. In contrast, reports of the effects of oestrogen and progesterone on these ocular structures and on the conjunctiva are contradictory and the mechanisms of action of these female-specific sex hormones in the eye are not well understood. The uncertainty of the effects of oestrogen and progesterone on dry eye symptoms is reflected in the controversial relationship between hormone replacement therapy and the signs and symptoms of dry eye. Current understanding of sex hormone influences on the immune system suggests that oestrogen may modulate a cascade of inflammatory events, which underlie dry eye.

Lamellar structures of MUC2-rich mucin: a potential role in governing the barrier and lubricating functions of intestinal mucus

Mucus is a ubiquitous feature of mammalian wet epithelial surfaces, where it lubricates and forms a selective barrier that excludes a range of particulates, including pathogens, while hosting a diverse commensal microflora. The major polymeric component of mucus is mucin, a large glycoprotein formed by several MUC gene products, with MUC2 expression dominating intestinal mucus. A satisfactory answer to the question of how these molecules build a dynamic structure capable of playing such a complex role has yet to be found, as recent reports of distinct layers of chemically identical mucin in the colon and anomalously rapid transport of nanoparticles through mucus have emphasized. Here we use atomic force microscopy (AFM) to image a MUC2-rich mucus fraction isolated from pig jejunum. In the freshly isolated mucin fraction, we find direct evidence for trigonally linked structures, and their assembly into lamellar networks with a distribution of pore sizes from 20 to 200 nm. The networks are two-dimensional, with little interaction between lamellae. The existence of persistent cross-links between individual mucin polypeptides is consistent with a non-self-interacting lamellar model for intestinal mucus structure, rather than a physically entangled polymer network. We only observe collapsed entangled structures in purified mucin that has been stored in nonphysiological conditions.

Sialylated glycans and mucins in the lacrimal gland and eyelid of man and pig. Potential receptors for pathogenic microorganisms

The conjunctiva of the eyelid is coated by secretion products from the lacrimal and eyelid glands, and by mucins produced by conjunctival goblet cells, which together form a glycoprotein-rich layer that lubricates and protects the surface of the eye. However, these ocular carbohydrates may also act as adhesives for viruses and bacteria and thereby facilitate their colonization. This paper provides histochemical demonstration of the in situ localization of such carbohydrate receptors in the form of sialylated glycans and mucins in the lacrimal and eyelid glands and conjunctiva from both humans and pigs. The pig is included in this study because viruses of swine origin may be capable of transmission to humans. We found that the human and pig ocular surfaces contain receptors for bacteria and viruses in the form of mucins (both membrane bound and secreted) and carbohydrates terminating in Sialylα2-6Gal epitopes and to a lesser degree in Sialylα2-3Gal. The glycosylation of the human soft palate could indicate a mucinous route for the spread of microorganisms from the eye via the nasolacrimal duct to the nasopharynx and thus to the upper part of the respiratory tract.

Distribution of goblet cells and MUC5AC mRNA in the canine nictitating membrane

This study evaluated the distribution of goblet cells and the expression of MUC5AC mRNA in the canine nictitating membrane. The distribution of goblet cells in the nictitating membrane and temporal bulbar conjunctiva of beagle dogs was examined by histochemical analysis of impression cytology specimens and frozen sections. MUC5AC mRNA was detected by the reverse transcription polymerase chain reaction (RT-PCR). The distribution of MUC5AC mRNA was also examined by in situ hybridization using digoxigenin-labeled antisense and sense RNA probes. Histochemical analysis showed that the canine nictitating membrane epithelium contained many more periodic acid-Schiff positive goblet cells, particularly on the palpebral side, compared with the temporal bulbar conjunctiva. RT-PCR revealed that MUC5AC was expressed in both the nictitating membrane and in conjunctival tissue. When the distribution of MUC5AC mRNA was assessed by in situ hybridization, its expression was high on the palpebral side of the nictitating membrane and low in the temporal bulbar conjunctiva. MUC5AC mRNA expression corresponded with the distribution of goblet cells by histochemical examination. In conclusion, there were numerous goblet cells in the canine nictitating membrane epithelium, particularly on the palpebral side, and MUC5AC mRNA was expressed in the nictitating membrane epithelium at locations corresponding to the goblet cells.

Significance of lipid mediators in corneal injury and repair

Corneal injury induces an inflammatory reaction and damages the sensory nerves that exert trophic influences in the corneal epithelium. Alterations in normal healing disrupt the integrity and function of the tissue with undesirable consequences, ranging from dry eye and loss of transparency to ulceration and perforation. Lipids play important roles in this complex process. Whereas lipid mediators such as platelet activating factor (PAF) and cyclooxygenease-2 metabolites contribute to tissue damage and neovascularization, other mediators, such as the lipoxygenase (LOX) derivatives from arachidonic acid, 12- and 15-hydroxy/hydroperoxyeicosatetraenoic acids, and lipoxin A4, act as second messengers for epidermal growth factor to promote proliferation and repair. Stimulation of the cornea with pigment epithelial derived factor in the presence of docosahexaenoic acid gives rise to the synthesis of neuroprotectin D1, a derivative of LOX activity, and increases regeneration of corneal nerves. More knowledge about the role that lipids play in corneal wound healing can provide insight into the development of new therapeutic approaches for treating corneal injuries. PAF antagonists, lipoxins, and neuroprotectins can be effective therapeutic tools for maintaining the integrity of the cornea.

Mucins in the mucosal barrier to infection

The mucosal tissues of the gastrointestinal, respiratory, reproductive, and urinary tracts, and the surface of the eye present an enormous surface area to the exterior environment. All of these tissues are covered with resident microbial flora, which vary considerably in composition and complexity. Mucosal tissues represent the site of infection or route of access for the majority of viruses, bacteria, yeast, protozoa, and multicellular parasites that cause human disease. Mucin glycoproteins are secreted in large quantities by mucosal epithelia, and cell surface mucins are a prominent feature of the apical glycocalyx of all mucosal epithelia. In this review, we highlight the central role played by mucins in accommodating the resident commensal flora and limiting infectious disease, interplay between underlying innate and adaptive immunity and mucins, and the strategies used by successful mucosal pathogens to subvert or avoid the mucin barrier, with a particular focus on bacteria.

MUC19 expression in human ocular surface and lacrimal gland and its alteration in Sjögren syndrome patients

This study investigated the expression of MUC19, a newly discovered gel-forming mucin gene, in normal human lacrimal functional unit components and its alteration in Sjögren syndrome patients. Real-time PCR and immunohistochemistry were performed to determine the expression of MUC19 and MUC5AC in human cornea, conjunctiva, and lacrimal gland tissues. Conjunctival impression cytology specimens were collected from normal control subjects and Sjögren syndrome patients for Real-time PCR, PAS staining, and immunohistochemistry assays. In addition, conjunctiva biopsy specimens from both groups were examined for the expression differences of MUC19 and MUC5AC at both mRNA and protein level. The MUC19 mRNA was found to be present in cornea, conjunctiva and lacrimal gland tissues. The immunohistochemical staining of mucins showed that MUC19 was expressed in epithelial cells from corneal, conjunctival, and lacrimal gland tissues. In contrast, MUC5AC mRNA was only present in conjunctiva and lacrimal gland tissues, but not in cornea. Immunostaining demonstrates the co-staining of MUC19 and MUC5AC in conjunctival goblet cells. Consistent with the significant decrease of mucous secretion, both MUC19 and MUC5AC were decreased in conjunctiva of Sjögren syndrome patients compared to normal subjects. Considering the contribution of gel-forming mucins to the homeostasis of the ocular surface, the decreased expression of MUC19 and MUC5AC in Sjögren syndrome patients suggested that these mucins may be involved in the disruption of the ocular surface homeostasis in this disease.

Adherence of nontypeable Streptococcus pneumoniae to human conjunctival epithelial cells

Conjunctivitis outbreaks have occurred in the US in which nontypeable (NT) Streptococcus pneumoniae (Pnc) strains have been identified as the etiologic agent; however, the pathogenesis of Pnc conjunctivitis has not been extensively evaluated. Here we assessed the adhesive and invasive properties of 13 NT US conjunctivitis outbreak strains (cPnc) using an immortalized human conjunctival epithelial cell (HCjE) line expressing high or low levels of mucin as a surrogate for in vivo ocular surface events. Studies reveal differential binding efficiencies (up to 18-fold) among cPnc strains to HCjE cells and reduced or little adherence efficiency to high mucin-expressing (HME-HCjE). Additionally, in the presence of exogenous mucin there is considerable inhibition (20% to approximately 100%) of bacterial binding to the HCjE cells. Invasion assays suggest that the cPnc are internalized in HCjE, and less in HME-HCjE cells. Microarray analysis of cPnc isolates revealed an up-regulation of Pnc neuraminidases, and treatment of HME-HCjE cells with exogenous neuraminidase resulted in a 2-13-fold enhancement in cPnc binding. The results indicate that mucin acts as a protective barrier in vitro and that neuraminidases, which can degrade mucin, may be contributing factors leading to bacterial adherence, a first step in the pathogenesis of this transmissible infection.

Mucins and contact lens wear

PURPOSE

This study was designed to determine whether long-term tolerant contact lens (CL) wear causes changes in the expression of mucin mRNA by the conjunctival epithelium and mucin protein content in tears and to determine whether specific mucins adhere to contact lenses.

METHODS

Twenty long-term (> or = 5 years ) and tolerant CL wearers (2 with hard and 18 with soft contact lenses) were compared with 23 non-CL wearers. One hour after CL removal, tear fluid was collected after instillation of 60 microL of sterile water onto the ocular surface, and protein concentration was determined. Impression cytology was performed on the bulbar temporal region of conjunctiva to collect cells for RNA isolation. Real-time polymerase chain reaction was performed using TaqMan primer and probes for MUC1, 4, 5AC, and 16. ELISA was performed on the collected tears to detect MUC5AC and the mucin carbohydrate epitope H185. For the analysis of adherent mucins on CL, discarded daily-wear contact lenses were collected, rinsed, and incubated overnight at 4 degrees C in mucin isolation buffer. Immunoblot analysis of adherent mucins was performed to detect MUC1, 4, 5AC, 16, and H185.

RESULTS

No significant changes in the levels of mucin mRNA from impression cytology samples were detected when comparing CL and non-CL wearers. The amount of total protein in tears collected from CL wearers (39.9 +/- 27.2 microg) was significantly less than that from non-CL wearers (95.1 +/- 73.8 microg, P = 0.001). The level of MUC5AC mucin and the H185 epitope in tears per unit protein in CL wearers was not significantly different from non-CL wearers. Low levels of membrane-associated mucins, the secreted mucin MUC5AC, and the carbohydrate epitope, H185, were detected in protein extracts from discarded CLs. Compared with MUC1, 4, and 5AC, there was less MUC16 adherent to the CLs.

CONCLUSION

Neither mucin mRNA expression by conjunctival epithelia nor mucin content per unit protein in tears was altered by long-term tolerant CL wear; however, the amount of protein in the tears was significantly less. Shed membrane-associated mucins and the goblet cell mucins adhere to CLs.

The surface activity of purified ocular mucin at the air-liquid interface and interactions with meibomian lipids

PURPOSE

Ocular mucins are thought to contribute to the stability of the tear film by reducing surface tension. The purpose of this study was to compare the effect of different mucins and hyaluronic acid (HA) alone and mixed with meibomian lipids on the surface pressure at an air-liquid interface.

METHODS

A Langmuir trough and Wilhelmy balance were used to measure and compare the surface activity of bovine submaxillary gland mucin (BSM), purified BSM, purified bovine ocular mucin and HA, and mixtures of these with meibomian lipids, phosphatidylcholine, and phosphatidylglycerol. Their appearance at the surface of an air-buffer interface was examined using epifluorescence microscopy.

RESULTS

Purified ocular mucin had no surface activity even at concentrations that were 100 times more than normally occur in tears. By contrast, commercial BSM caused changes to surface pressure that were concentration dependent. The surface pressure-area profiles showed surface activity with maximum surface pressures of 12.3-22.5 mN/m depending on the concentration. Purified BSM showed no surface activity at low concentrations, whereas higher concentrations reached a maximum surface pressure of 25 mN/m. HA showed no surface activity, at low or high concentrations. Epifluorescence showed that the mucins were located at the air-buffer interface and changed the appearance of lipid films.

CONCLUSION

Purified bovine ocular mucin and HA have no surface activity. However, despite having no surface activity in their own right, ocular mucins are likely to be present at the surface of the tear film, where they cause an increase in surface pressure by causing a compression of the lipids (a reorganization of the lipids) and alter the viscoelastic properties at the surface.

Interaction of Pseudomonas aeruginosa with human tear fluid components

PURPOSE

Reflex human tears bind Pseudomonas aeruginosa bacteria and prevent them from invading corneal epithelial cells. In this study, we assessed the effect of eye closure and the role of sialoglycoprotein (SG) in tears on bacterial binding and invasion.

METHODS

Human tears (reflex and closed-eye) were collected using a microcapillary tube. Reflex tears were separated into 13 fractions by high-performance liquid chromatography while high-molecular-weight components from closed-eye tears were separated into an SG/mucin fraction and a nonmucin fraction. Bacterial binding was quantified by viable counts and bacterial invasion was tested using the gentamicin survival technique.

RESULTS

Closed-eye tears bound significantly more bacteria than open-eye tears. Fractionation of reflex tears showed that 11 out of the 13 fractions bound bacteria, while all 13 fractions significantly reduced bacterial invasion of corneal epithelial cells. Surprisingly, the SG/mucin component of closed-eye tears resisted bacterial binding and had no significant effect on bacterial invasion.

CONCLUSIONS

P. aeruginosa bacteria bind more efficiently to closed-eye tears than to open-eye tears. The mechanism by which tears bind bacteria and protect against invasion does not require SG/mucin, as this fraction of closed-eye tears does not contain either activity.

Heterogeneity in the ultrastructure of the mucous (goblet) cells of the rabbit palpebral conjunctiva

AIM

The purpose of this study was to assess objectively the ultrastructure of the secretory granules in rabbit conjunctival mucin-producing 'goblet' cells.

METHOD

The upper eyelids from five young adult dioestrous female rabbits were dissected out, stretched onto a cardboard support and prepared for transmission electron microscopy by repeated application of an isotonic two per cent glutaraldehyde fixative at room temperature. Post-fixation treatment included osmium tetroxide and staining with uranyl acetate and lead citrate. Low magnification micrographs were taken of the goblet cells of the conjunctiva, printed at a magnification of approximately 6,000 and the number, size and features of the secretory granules assessed.

RESULTS

Across the entire palpebral conjunctiva of all five rabbits, the majority of mucous cells displayed a goblet shape and the secretory granules were uniformly pale in staining. The average width of the goblet cells was 10.8 +/- 1.1 microm and the diameter of the secretory granules was 0.82 +/- 0.16 microm. However, in localised regions across the palpebral conjunctiva of two of the rabbits, some goblet cells were different in that the secretory granules had either a denser-staining core, in which some of the granules were densely staining (while others were pale) or most of the granules were densely staining. These mucous cells had an average diameter of 10.3 +/- 1.7 microm and the granule diameters averaged 0.88 +/- 0.01 microm. For these abnormal goblet cells, inflammatory cells were found in their immediate vicinity. Occasionally, goblet cells were seen to be in the process of degranulation with associated apparent cell necrosis and the mucin granule diameter was close to 1 microm.

CONCLUSIONS

The ultrastructure of the mucin-containing secretory granules of the conjunctival mucous cells is not necessarily homogeneous in character and further attention needs to be given to the effects of localised inflammation in the tissue and to possible hormonal influences.

Changes in the tear film and ocular surface from dry eye syndrome

Dry eye syndrome (DES) refers to a spectrum of ocular surface diseases with diverse and frequently multiple aetiologies. The common feature of the various manifestations of DES is an abnormal tear film. Tear film abnormalities associated with DES are tear deficiency, owing to insufficient supply or excessive loss, and anomalous tear composition. These categorizations are artificial, as in reality both often coexist. DES disrupts the homeostasis of the tear film with its adjacent structures, and adversely affects its ability to perform essential functions such as supporting the ocular surface epithelium and preventing microbial invasion. In addition, whatever the initial trigger, moderate and severe DES is characterized by ocular surface inflammation, which in turn becomes the cause and consequence of cell damage, creating a self-perpetuating cycle of deterioration. Progress has been made in our understanding of the aetiology and pathogenesis of DES, and these advances have encouraged a proliferation of therapeutic options. This article aims to amalgamate prevailing ideas of DES development, and to assist in that, relevant aspects of the structure, function, and production of the tear film are reviewed. Additionally, a synopsis of therapeutic strategies for DES is presented, detailing treatments currently available, and those in development.

Molecular adsorption: early stage surface exploration

In this study, the atomic force microscope has been employed in force spectroscopy mode to gain information on the interaction between long mucin molecules and a positively charged surface during the first few seconds of interaction. Recent studies have revealed that negatively charged mucin molecules introduced to a positively charged surface are kinetically trapped and bind very rapidly, assuming non-equilibrium conformations. This systematic study of surface dwell times has revealed that significant differences exist in mucin adsorption during the first three seconds of introduction to the surface and provides direct evidence of molecular rearrangement for several seconds before trapping occurs. Limited interactions were recorded at dwell times of less than one second, with increased molecular rearrangement observed between 1.5 and 2.25 s. Increasing the surface dwell time beyond this critical limit caused rupture of the tip-tethered mucin molecules during the retract cycle of the cantilever. All subsequent recorded events, at increased dwell times up to 3s, revealed events at much reduced distances from the point of contact between the mucin functionalised-cantilever and the positively charged surface.

The tear film and ocular mucins

The trilaminar tear film, composed of the lipid, aqueous and mucin layers, has many functions including defending the ocular surface. The aqueous layer has several soluble antimicrobial factors that protect the ocular surface. Ocular mucins have recently been studied with regard to their role in the defense of the eye as well as in dry eye syndromes. To date, 15 mucin genes have been identified, and six of these mucin genes are localized to or secreted by ocular glands or epithelia. Understanding the production, secretion and function of ocular mucins will aid in the treatment of dry eye syndromes and ocular surface microbial infections.

Human epithelium from conjunctival impression cytology expresses MUC7 mucin gene

PURPOSE

To prove that noninvasive methods of obtaining conjunctival tissue, such as conjunctival impression cytology (CIC), could be valid alternatives that are simpler, faster, and more convenient for patients than biopsy to analyze mRNA levels of mucin genes.

METHODS

Using the semiquantitative reverse-transcriptase polymerase chain reaction, we studied the presence of the mucin genes described on the ocular surface thus far and attempted to detect the presence of MUC7 in CIC samples from 10 healthy donors.

RESULTS

Conjunctival cells recovered by CIC expressed all the genes studied. There were no statistically significant differences between male and female subjects, and there was a significant correlation between the two eyes of the same donor only in the expression of MUC7.

CONCLUSION

CIC is a valid, noninvasive technique to detect the mRNAs of ocular genes in healthy individuals. MUC1, MUC2, MUC4, MUC5AC, and MUC7 mucin genes could be all detected in each CIC sample. This technique may be a useful tool to study the expression of some genes in ocular diseases.

The role of calcium in mucin packaging within goblet cells

Recent reports hypothesize that calcium plays an important role in providing cationic shielding to keep negatively charged mucins condensed and tightly packed within mucus granules of goblet cells. Vitamin D controls mineral ion homeostasis and intestinal calcium absorption, which is mediated by the nuclear vitamin D receptor (VDR). Hypocalcemia is observed in mice in which the VDR has been ablated. The purpose of this study was to test the hypothesis that normal levels of calcium are required for the physiological packaging of mucins, by comparing the morphology and mucin extractability of conjunctival goblet cells of VDR-ablated to wild-type control mice. Whole eyes from C57/129/sv hybrid wild-type, VDR-ablated, and VDR-ablated mice fed a diet high in calcium to normalize serum ionized calcium levels were fixed in situ and processed for light and transmission electron microscopy (TEM). Mucin extractability from sections of mouse eyes was assessed by lectin-blot, using helix pomatia agglutinin (HPA), and mucin content within goblet cells was assessed by immunohistochemistry, using an antibody specific to the goblet cell mucin Muc5AC. Altered mucin packaging in the goblet cells of VDR-ablated mice as compared to control mice was observed by both light and electron microscopy. In the VDR-ablated mice, the mucin packets varied in size and staining. In contrast, in the controls, the secretory granules appeared regular and uniform. By TEM, mucin packets in the VDR-ablated mice showed dispersed fibrillar and less electron-dense material compared to the homogeneous and more electron-dense packets in wild type. The appearance of mucin packets in the VDR-ablated mice with restored calcium levels was comparable to those of the wild-type control mice. HPA binding to mucin extracted from sections of VDR mouse eyes was reduced when compared to that from wild type. By immunohistochemistry, there was markedly less binding of the antibody to the mucin Muc5AC to goblet cells of VDR-ablated mice compared to controls.VDR-ablated mice presented altered conjunctival mucin packaging. There were lower levels of extractable and immunohistochemically localizable mucin in VDR-ablated mouse conjunctivas than in the wild-type controls. Restoration of ionized calcium levels in the VDR-ablated mice prevented altered mucin packaging, supporting the hypothesis that calcium is required for the physiological packaging of mucins in goblet cells.

Mucin gene expression is not regulated by estrogen and/or progesterone in the ocular surface epithelia of mice

PURPOSE

Dry eye syndrome is prevalent in post-menopausal women, and post-menopausal women secrete less mucus in their reproductive tracts. Using a mouse model, the purpose of this study was to determine if estrogen and/or progesterone regulates Muc4 and Muc5AC gene expression in the ocular surface epithelia, as the hormones do in reproductive tract epithelia.

METHODS

Adult C57BL/6 mice were ovariectomized, and 19 days later, pellets containing estrogen, progesterone, or a combination were inserted subcutaneously. Ocular surface and reproductive tract tissues were harvested following seven days of hormone treatment. A control group consisted of ovariectomized mice that received no hormone treatment. Real-time reverse transcription-polymerase chain reaction was used to determine the tissue expression levels of mucin mRNA of each treatment group relative to the control. Muc4 mRNA expression levels were determined for the reproductive tract, and both Muc4 and Muc5AC expression levels were determined for the ocular surface epithelia. Muc4 and Muc5AC gene expression in ocular surface and Muc4 in reproductive tract epithelia was demonstrated by In Situ hybridization, and Muc4 and Muc5AC protein was demonstrated in the epithelia of animals in the experimental groups.

RESULTS

The mRNA expression levels of Muc4 and Muc5AC and the immunofluorescence localization pattern in the ocular surface epithelia were not significantly different in any hormone treatment group when compared to the control ovariectomized group. By comparison, mice that were administered estrogen had a significant increase of Muc4 mRNA in the reproductive tract epithelia, progesterone given in combination with estrogen antagonized the upregulatory effects of estrogen in the reproductive tract, and the amount of Muc4 mRNA in the reproductive tract of progesterone-treated animals was not different from ovariectomized controls. Immunofluorescence localization of Muc4 in the reproductive tract epithelia of the experimental groups correlated to message levels, with lack of Muc4 protein detected in the control and progesterone groups.

CONCLUSION

In comparison to reproductive tract epithelia, Muc4 and Muc5AC are not hormonally regulated by estrogen or progesterone in the ocular surface epithelia of mice. These data demonstrate that regulation of epithelial mucin genes is tissue specific.

Human glands of Moll: histochemical and ultrastructural characterization of the glands of Moll in the human eyelid

The function of the human gland of Moll of the eyelid is not exactly known. We studied the secretory and cytoskeletal components of these apocrine glands in males and females by immunohistochemical methods, and the ultrastructural organization of the glandular cells with an electron microscope. The glands of Moll are exclusively located at the margin of the eyelids and their ducts empty into the lash follicle. Immunohistochemical staining for actin and cytokeratins CK19 and CK7 points to the involvement of actin in the pinching-off mechanism of the apical cell protrusion during apocrine secretion and to a stabilizing role for the cytokeratins in this apical region of the glandular cells. The presence of the bacteriolytic enzyme lysozyme, the membrane-associated mucin 1, and the immunoglobulin A and its secretory component within the gland suggest a function in local immune defense. The presence of a variety of sugar components in the secretory product was verified by lectin histochemistry and periodic acid Schiff and Alcian blue stain. We suppose that these apocrine glands are active from birth in producing agents against pathogenic microorganisms in the eyelid shaft and on the ocular surface.

Impact of brief exposure to balanced salts solution or cetylpyridinium chloride on the surface appearance of the rabbit corneal epithelium--a scanning electron microscopy study

PURPOSE

To examine the surface of pre-corneal mucous layer by scanning electron microscopy (SEM) with the view to assessing whether it was an amorphous, fibrous or porous structure.

METHODS

Healthy female albino rabbits (2 kg) were euthanised at 15.00 h and the corneal surface immediately fixed with buffered glutaraldehyde fixative pH 7.2 to 7.4 at 35 degrees C, carefully rinsed with balanced salts solution (BSS) and then fixed, or treated with the same fixative containing 0.05 to 0.25% w/v cetylpyridinium chloride (CPC). The corneas were critical point dried and gold-palladium coated, prior to examination at 1000x or 15000x magnification.

RESULTS

Buffered glutaraldehyde fixation resulted in an SEM image of polygonal cells, with very contrasting electron reflexes (light, medium and dark) and distinct cell surface microplicae and large crater-like features (average diameter 2.8 +/- 0.9 microm). Along the cell-cell borders was a distinct line (referred to as "caulking"), perhaps composed of mucous. Rinsing of the corneal surface with BSS just before fixation reduced the cell contrast, the surface was then covered with very short strands or small clumps of presumed mucus, the cell-cell border features were changed, but the crater-like features were largely unchanged (average diameter 2.5 +/- 0.7 microm). Fixation in the presence of 0.05% or 0.1% CPC resulted in the appearance of very short fine strands and occasional coarse mucous strands or even small plaques of mucous on the cell surfaces. The microplicae and craters were still often evident. Fixation with 0.2 or 0.25% CPC however yielded a surface with a uniform grey reflex that included numerous ultramicroscopic debris particles (average diameter of 72 nm) and was punctuated by numerous pores. No microplicae or craters were evident. The average pore diameter was 70 nm, their density averaged 59/5 microm(2), but a radial distribution analysis indicated no substantial pattern.

CONCLUSIONS

The pre-corneal mucous layer can be dispersed, by careful rinsing with a divalent cation containing solution, into small fibrils or clumps, but the cell surface craters are unaffected. After precipitation with a low concentrations of a polycation, some coarse fibrils are also formed. The use of high concentrations of a polycation in the fixative transforms the more superficial aspects of the pre-corneal mucous layer into a pore-like gel. The crater-like features therefore do not appear to be mucous, but the pore-like structure may be indicative of the organisation of the mucous layer on the surface of the living eye.

Cell type specific expression of secretory TFF peptides: colocalization with mucins and synthesis in the brain

The "TFF domain" is an ancient cysteine-rich shuffled module forming the basic unit for the family of secretory TFF peptides (formerly P-domain peptides and trefoil factors). It is also an integral component of mosaic proteins associated with mucous surfaces. Three mammalian TFF peptides are known (i.e., TFF1-TFF3); however, in Xenopus laevis the pattern is more complex (xP1, xP4.1, xP4.2, and xP2). TFF peptides are typical secretory products of a variety of mucin-producing epithelial cells (e.g., the conjunctiva, the salivary glands, the gastrointestinal tract, the respiratory tract, and the uterus). Each TFF peptide shows an unique expression pattern and different mucin-producing cells are characterized by their specific TFF peptide/secretory mucin combinations. TFF peptides have a pivotal role in maintaining the surface integrity of mucous epithelia in vivo. They are typical constituents of mucus gels, they modulate rapid mucosal repair ("restitution") by their motogenic and their cell scattering activity, they have antiapoptotic effects, and they probably modulate inflammatory processes. Pathological expression of TFF peptides occurs as a result of chronic inflammatory diseases or certain tumors. TFF peptides are also found in the central nervous system, at least in mammals. In particular, TFF3 is synthesized from oxytocinergic neurons of the hypothalamus and is released from the posterior pituitary into the bloodstream.

Significance of mucin on the ocular surface

PURPOSE

To review the significance of mucin in the tear film and the ocular surface epithelium.

METHODS

Summary of the information on how mucin derived from the corneal and conjunctival epithelia and from goblet cells plays a role in the stability of the tear film over the ocular surface. The change in mucin expression derived from the ocular surface epithelium is also discussed with reference to ocular surface disease.

RESULTS

The corneal and conjunctival epithelia produce transmembrane mucins such as MUC1, MUC2, and MUC4. In contrast, goblet cells produce the gel-forming secretory mucin, MUC5AC. The lacrimal gland produces MUC7. On the ocular surface, cooperation between transmembrane mucin and secretory mucin is necessary for the stability of the tear film. The expression of mucin from the ocular surface epithelium is coordinated from the time of eyelid opening and is altered in conditions such as squamous metaplasia and dry eye. This alteration may result in instability of the tear film. CONCLU SION: The induction of mucin from the ocular surface may facilitate the stability of the tear film, and increased knowledge may lead to the development of a new modality for the treatment of dry eye.