Secreted human conjunctival mucus contains MUC5AC glycoforms

An Unexpected Alteration Colonic Mucus Appearance in the Constipation Model via an Intestinal Microenvironment

Due to the lack of research between the inner layers in the structure of colonic mucous and the metabolism of fatty acid in the constipation model, we aim to determine the changes in the mucous phenotype of the colonic glycocalyx and the microbial community structure following treatment with Rhubarb extract in our research. The constipation and treatment models are generated using adult male C57BL/6N mice. We perform light microscopy and transmission electron microscopy (TEM) to detect a Muc2-rich inner mucus layer attached to mice colon under different conditions. In addition, 16S rDNA sequencing is performed to examine the intestinal flora. According to TEM images, we demonstrate that Rhubarb can promote mucin secretion and find direct evidence of dendritic structure-linked mucus structures with its assembly into a lamellar network in a pore size distribution in the isolated colon section. Moreover, the diversity of intestinal flora has noticeable changes in constipated mice. The present study characterizes a dendritic structure and persistent cross-links have significant changes accompanied by the alteration of intestinal flora in feces in models of constipation and pretreatment with Rhubarb extract.

Human ocular mucins: The endowed guardians of sight

Mucins are an ancient group of glycoproteins that provide viscoelastic, lubricating and hydration properties to fluids bathing wet surfaced epithelia. They are involved in the protection of underlying tissues by forming a barrier with selective permeability properties. The expression, processing and spatial distribution of mucins are often determined by organ-specific requirements that in the eye involve protecting against environmental insult while allowing the passage of light. The human ocular surface epithelia have evolved to produce an extremely thin and watery tear film containing a distinct soluble mucin product secreted by goblet cells outside the visual axis. The adaptation to the ocular environment is notably evidenced by the significant contribution of transmembrane mucins to the tear film, where they can occupy up to one-quarter of its total thickness. This article reviews the tissue-specific properties of human ocular mucins, methods of isolation and detection, and current approaches to model mucin systems recapitulating the human ocular surface mucosa. This knowledge forms the fundamental basis to develop applications with a promising biological and clinical impact.

Abnormal Spontaneous Brain Activities of Limbic-Cortical Circuits in Patients With Dry Eye Disease

Whether brain function is altered in patients with dry eye disease (DED) remains unclear. Twenty patients with DED and 23 healthy controls (HCs) were scanned using resting-state functional magnetic resonance imaging. Regional homogeneity (ReHo) and support vector machine (SVM) were used to analyze the imaging data. Relative to the HCs, the patients with DED showed significantly increased ReHo values in the left inferior occipital gyrus (IOG), left superior temporal gyrus, and right superior medial prefrontal cortex, and significantly decreased ReHo values in the right superior frontal gyrus/middle frontal gyrus and bilateral middle cingulum (MC). SVM results indicated that the combination of ReHo values in the left MC and the left IOG in distinguishing patients with DED from HCs had a sensitivity of 95.00%, a specificity of 91.30%, and an accuracy of 93.02%. The present study found that the patients with DED had abnormal ReHo values in the limbic-cortical circuits. A combination of ReHo values in the left MC and the left IOG could be applied as a potential imaging biomarker to distinguish patients with DED from HCs. The dysfunction of limbic-cortical circuits may play an important role in the pathophysiology of DED.

The Interaction of the Gut Microbiota with the Mucus Barrier in Health and Disease in Human

Glycoproteins are major players in the mucus protective barrier in the gastrointestinal and other mucosal surfaces. In particular the mucus glycoproteins, or mucins, are responsible for the protective gel barrier. They are characterized by their high carbohydrate content, present in their variable number, tandem repeat domains. Throughout evolution the mucins have been maintained as integral components of the mucosal barrier, emphasizing their essential biological status. The glycosylation of the mucins is achieved through a series of biosynthetic pathways processes, which generate the wide range of glycans found in these molecules. Thus mucins are decorated with molecules having information in the form of a glycocode. The enteric microbiota interacts with the mucosal mucus barrier in a variety of ways in order to fulfill its many normal processes. How bacteria read the glycocode and link to normal and pathological processes is outlined in the review.

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.

TFOS DEWS II pain and sensation report

Pain associated with mechanical, chemical, and thermal heat stimulation of the ocular surface is mediated by trigeminal ganglion neurons, while cold thermoreceptors detect wetness and reflexly maintain basal tear production and blinking rate. These neurons project into two regions of the trigeminal brain stem nuclear complex: ViVc, activated by changes in the moisture of the ocular surface and VcC1, mediating sensory-discriminative aspects of ocular pain and reflex blinking. ViVc ocular neurons project to brain regions that control lacrimation and spontaneous blinking and to the sensory thalamus. Secretion of the main lacrimal gland is regulated dominantly by autonomic parasympathetic nerves, reflexly activated by eye surface sensory nerves. These also evoke goblet cell secretion through unidentified efferent fibers. Neural pathways involved in the regulation of meibomian gland secretion or mucin release have not been identified. In dry eye disease, reduced tear secretion leads to inflammation and peripheral nerve damage. Inflammation causes sensitization of polymodal and mechano-nociceptor nerve endings and an abnormal increase in cold thermoreceptor activity, altogether evoking dryness sensations and pain. Long-term inflammation and nerve injury alter gene expression of ion channels and receptors at terminals and cell bodies of trigeminal ganglion and brainstem neurons, changing their excitability, connectivity and impulse firing. Perpetuation of molecular, structural and functional disturbances in ocular sensory pathways ultimately leads to dysestesias and neuropathic pain referred to the eye surface. Pain can be assessed with a variety of questionaires while the status of corneal nerves is evaluated with esthesiometry and with in vivo confocal microscopy.

Vascular-Associated Muc4/Vwf Co-Localization in Human Conjunctival Malignant Melanoma Specimens-Tumor Metastasis by Migration?

PURPOSE

To investigate whether vascular differentiation marker von Willebrand factor (vWf) and proliferation marker KI67 expression correlate with MUC4 localization around stromal tumor vascularization in human conjunctival malignant melanoma (CMM).

MATERIALS AND METHODS

For the purposes of this study, we analyzed samples from human CMMs (n = 4), conjunctival compound nevi (n = 7), and samples from healthy conjunctiva (n = 7) for MUC1, 4, and 16 by immunohistochemistry. To test CMM vessel association of MUC4, we investigated the co-localization of MUC4 with vWf or KI67 in human CMM specimens (n = 10) by immunohistochemistry. Also, we investigated the MUC4 localization around vessels of healthy conjunctiva (n = 10).

RESULTS

The immunohistochemical analysis demonstrated membrane-associated mucin expression in epithelia of CMM, nevi and healthy conjunctiva, whereas only MUC4 was localized perivascular in CMM tissue in this preliminary analysis. Co-staining analysis with vWf and KI67 demonstrated MUC4 localization around stromal vessels in human CMM specimens. In contrast, no MUC4 localization has been seen around healthy conjunctiva stroma vessels.

CONCLUSIONS

MUC4 was detected around vWf/KI67-positive CMM stromal vascular tissue, but not around healthy conjunctival stroma vessels. Therefore, we assume that MUC4 might play a role in tumor cell migration toward vessels inducing metastasis.

Effect of rebamipide ophthalmic suspension on the success of lacrimal stent intubation

PURPOSE

To evaluate the effect of the postoperative administration of rebamipide ophthalmic suspension on the success rate of lacrimal stent intubation (LSI) for the treatment of primary acquired nasolacrimal duct obstruction (PANDO).

METHODS

This comparative interventional cohort study investigated 110 consecutive patients with PANDO who were treated with LSI and followed up for 12 months postoperatively at one institution. LSI was performed by one surgeon, and all patients received identical postoperative care. Among the total 110 patients, 71 underwent LSI with postoperative administration of rebamipide ophthalmic suspension, and 39 underwent LSI without administration of the suspension. Data related to patient age, gender, laterality, and postoperative administration of rebamipide ophthalmic suspension were collected and used as independent variables, and logistic regression analyses were performed to compare the anatomical success rate at 12 months postoperatively between patients with and without postoperative administration of the suspension.

RESULTS

The anatomical success rate of LSI in patients with and without postoperative administration of rebamipide ophthalmic suspension was 90.1 and 69.2 %, respectively. A comparison of these success rates showed statistical significance, in that the rate of treatment success was higher in PANDO patients who underwent LSI with postoperative administration of the suspension [odds ratio (OR), 3.37; P < 0.05].

CONCLUSIONS

The findings of this study show that postoperative administration of rebamipide ophthalmic suspension increases the rate of anatomical success in patients who undergo LSI for the treatment of PANDO.

Glycomic characterization of basal tears and changes with diabetes and diabetic retinopathy

As a secreted fluid, the state of tear glycosylation is particularly important in the role of immunity of the ocular surface. Tears are a valuable source of non-invasive biomarkers for disease and there are continued efforts to characterize their components thoroughly. In this study, a small volume of basal tears (5 μL) was collected from healthy controls, patients with diabetes without retinopathy and patients with diabetes and retinopathy. The detailed N- and O-linked tear protein glycome was characterized and the relative abundance of each structure determined. Of the 50 N-linked glycans found, 89% were complex with 50% containing a bisecting N-acetylglucosamine, 65% containing a core fucose whilst 33% were sialylated. Of the 8 O-linked glycans detected, 3 were of cores 1 and 5 of core 2 type, with a majority of them being sialylated (90%). Additionally, these glycan structures were profiled across the three diabetic disease groups. Whilst the higher abundant structures did not alter across the three groups, only five low abundance N-linked glycans and 1 O-linked glycan did alter with the onset of diabetes mellitus and diabetic retinopathy (DR). These results suggest the conservation of glycan types on basal tear proteins between individuals and point to only small changes in glycan expression on the proteins in tears with the development of diabetes and DR.

Ocular drug delivery - a look towards nanobioadhesives

IMPORTANCE OF THE FIELD

A major challenge emanating in the design of topical ophthalmic preparations is their short precorneal residence time. Retention of a drug delivery system in the front of the eye is thus desirable. One solution identified to address this concern is a retentive system that can preferably be delivered in a liquid drop form and ultimately remain attached to the corneal tissue owing to incorporation of a bioadhesive component. Forward-thinking approaches are required to achieve advancements in this approach for the attainment of an effective drug concentration at the site of action. Accordingly, several investigators have identified the benefits of nanotechnology-based drug delivery systems for ophthalmic drug delivery.

AREAS COVERED IN THIS REVIEW

A concerted effort was made to review critically all 'nanobioadhesives', that is, nanosystems designed for ocular drug delivery with the goal of attaining prolonged ocular retention, in a systematic, chronological manner, from their reported point of inception to the present.

WHAT THE READER WILL GAIN

A perspective on possible future trends in this growing field of ocular drug delivery is formulated.

TAKE HOME MESSAGE

The importance of and need for new developments in the field of ocular nanobioadhesives is emphasized.

Expression profiles of MUC mucins and trefoil factor family (TFF) peptides in the intrahepatic biliary system: physiological distribution and pathological significance

Mucin secreted by mucosal epithelial cells plays a role in the protection of the mucosal surface and also is involved in pathological processes. So far, MUC1-4, 5AC, 5B, 6-8, 11-13 and 15-17 genes coding the backbone mucin core protein have been identified in humans. Their diverse physiological distribution and pathological alterations have been reported. Trefoil factor family (TFF) peptides are mucin-associated molecules co-expressed with MUC mucins and involved in the maintenance of mucosal barrier and the biological behavior of epithelial and carcinoma cells. Intrahepatic biliary system is a route linking the bile canaliculi and the extrahepatic bile duct for the excretion of bile synthesized by hepatocytes. Biliary epithelial cells line in the intrahepatic biliary system, secreting mucin and other molecules involved in the maintenance and regulation of the system. In this review, the latest information regarding properties, expression profiles and regulation of MUC mucins and TFF peptides in the intrahepatic biliary system is summarized. In particular, we focus on the expression profiles and their significance of MUC mucins in developmental and normal livers, various hepatobiliary diseases and intrahepatic cholangiocarcinoma.

The isolated MUC5AC gene product from human ocular mucin displays intramolecular conformational heterogeneity

Atomic force microscopy (AFM) has been used to show that human ocular mucins contain at least three distinct polymer conformations, separable by isopycnic density gradient centrifugation. In this work we have used affinity purification against the anti(mucin peptide core) monoclonal antibody 45M1 to isolate MUC5AC gene products, a major component of human ocular mucins. AFM images confirm that the affinity-purified polymers adopt distinct conformations that coidentify with two of those observed in the parent population, and further reveal that these two different conformations can be present within the same polymer. AFM images of the complexes formed after incubation of 45M1 with the parent sample reveal different rates of binding to the two MUC5AC polymer types. The variability of gene products within a mucin population was revealed by analyzing the height distributions along the polymer contour and periodicities in distances between occupied antibody binding sites. AFM analysis of mucin polymers at the single molecule level provides new information about the genetic origins of individual polymers and the contributions of glycosylation to the physicochemical properties of mucins, which can be correlated with information obtained from biochemistry, antibody binding assays, and molecular biology techniques.

The adhesion of Pseudomonas aeruginosa to high molecular weight human tear film species corresponds to glycoproteins reactive with Sambucus nigra lectin

Pseudomonas aeruginosa is a pathogen gaining prevalence in contact lens-related corneal ulcers. Tear outflow protects the ocular surface, where high molecular weight tear glycoproteins bind bacteria for removal from the eye. The purpose of the present study was to identify glycoproteins in human tears involved in the adhesion of ocular P. aeruginosa isolates. Basal human tears were applied to a bacterial adhesion assay involving electrophoretic separation of tear components, transfer to nitrocellulose and incubation with biotin-labelled bacteria. Glycoproteins were further characterised using lectin profiling. The results showed large-dimension agarose gels were imperative for the detection of at least four glycoproteins with a migration >200 kDa, including species not previously identified. P. aeruginosa 6294 preferentially bound to a well-defined glycoprotein near the origin of the gel that, unlike other glycoproteins >200 kDa, reacted with Sambucus nigra lectin (sialic acid alpha2-6) but not WGA lectin (N-acetylglucosamine, sialic acid alpha2-3). Adhesion did not involve free biotin label or hydrophobic interactions. Also, the pre-incubation of separated tear glycoproteins with S. nigra lectin increased subsequent adhesion of 6294 to this tear glycoprotein. The less virulent Paer1 strain showed diffuse adhesion in the S. nigra-reactive region at the gel origin. In conclusion, an overlay adhesion assay was developed that identified slow-migrating sialylated glycoprotein species in human tears preferentially bound by P. aeruginosa ocular strains, and S. nigra lectin seemed to enhance the interaction. The study provides a basis for direct investigation of bacterial adhesion to glycoproteins with an apparent migration >200 kDa in tear fluid.

Identification of 9-O-acetyl-N-acetylneuraminic acid in normal canine pre-ocular tear film secreted mucins and its depletion in Keratoconjunctivitis sicca

O-Acetylated sialic acids have been reported in many sialoglycoproteins where they mediate a variety of immune and other biological events. We have previously demonstrated that the protective mucus barrier on the surface of the canine eye contains sialoglycoproteins. We have also investigated the occurrence of O-acetylated sialic acids in these ocular mucins. Mucus aspirated from the surface of normal dog eyes and those with keratoconjunctivitis sicca (KCS) was fractionated into three pools by density gradient centrifugation. Sialic acids comprised 0.6-0.9% of the dry weight of the mucins isolated. The sialic acid profile in these pools was examined using HPLC. O-Acetylated sialic acids, mainly Neu5,9Ac2, were detected in normal animals and made up 10-30% of the total sialic acids detected. A doubling of the sialic acid content was found in KCS mucins, but the level of 9-O-acetylated sialic acid was reduced below 4% of total. Histological analysis of conjunctival tissue from normal and KCS dogs showed the presence of sialic acids, detected with the alpha(2-6) sialic acid-specific lectin Sambucus nigra, in the goblet cells and corresponding to the staining pattern for MUC5AC, the major ocular-secreted mucin gene product. In KCS animals a disruption of the normal pattern of conjunctival goblet cells was seen with preservation of the pattern of lectin binding observed in normal animals. Thus the data demonstrate the presence of mono-O-Acetylated sialic acids in normal canine ocular mucins and a loss of this population of sialic acids in dry eye disease in spite of a significant increase in total sialic acids in KCS mucin.

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.

Glycomics analyses of tear fluid for the diagnostic detection of ocular rosacea

A Glycomics approach to detect disease is illustrated in the analyses of human tear fluid for rosacea. The diagnosis of ocular rosacea is particularly challenging in a subgroup of patients that do not present with typical facial skin findings but have ocular signs and symptoms. Indeed, up to 90% of patients with ocular rosacea may have neither obvious roseatic skin changes nor a previous diagnosis of rosacea. Tear fluid was collected from 37 subjects (21 controls and 16 patients with ocular rosacea) after conjunctival stimulation with filter (Schirmer) paper. O-linked oligosaccharides were released from tear fluid by beta-elimination and then purified using solid-phase extraction. Mass spectra were recorded on an external source HiResMALDI with a 7.0 T magnet. Mass spectra were obtained in both the positive and negative modes. However, signals were stronger in the negative mode. Tear fluid samples from rosacea patients yielded distinctive clusters of peaks that extend to higher masses. Patients with rosacea presented several oligomeric series that were not found in the controls. To discriminate the ocular rosacea cases from the normal controls, the sum of absolute intensities of 13 series corresponding to nearly 50 identified mass spectrum peaks was used. Thirty-six out of the 37 samples were correctly classified. This yields a sensitivity of 100% (95% CI 79.5-100) and specificity of 95.2% (95% CI 76.2-99.9). The high abundance of oligosaccharides in the tear fluid of patients with rosacea may lead to an objective diagnostic marker for the disease.

Cell and molecular biology of human lacrimal gland and nasolacrimal duct mucins

The old concept that the lacrimal gland is only a serous gland has been superseded by the finding that lacrimal acinar cells are able to produce mucins--high-molecular-weight proteins--the major mass being carbohydrates with the common feature of tandem repeats of amino acids rich in serine, threonine, and proline in the central domain of the mucin core peptide. At the ocular surface, maintenance of the tear film, lubrication, and provision of a pathogen barrier on the epithelia, conjunctiva, and cornea have been shown to be facilitated by mucins that are present in membrane-anchored (lining epithelial cells) or secreted (goblet cells) form. Also in the lacrimal gland, both membrane-anchored (MUCs 1, 4, and 16) and secreted (MUCs 5B and 7) mucins have been identified. The lacrimal gland is the main contributor to the aqueous portion of the tear film. It is part of the lacrimal apparatus that comprises, together with the lacrimal gland, the paired lacrimal canaliculi, the lacrimal sac, and the nasolacrimal duct, which collects the tear fluid and conveys it into the nasal cavity. In this review, the latest information regarding mucin function in the human lacrimal gland and the human efferent tear ducts 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 the pathogenesis of dry eye, dacryostenosis, and dacryolith formation.

Normal but not altered mucins activate neutrophils

Interactions between leucocytes and their surroundings are mediated through oligosaccharide epitopes, some of which are also expressed on ocular mucins. Neutrophils represent the majority of immune cells in the proinflammatory environment of the ocular surface during sleep. We have tested whether changes in mucin glycosylation, as occur in dry eyes, influence the phenotype and activation of neutrophils. Peripheral blood leucocytes were circulated over equal concentration mats of ocular surface mucins purified from normal volunteers and dry-eye patients, and in sequence over normal and pathological mucins in all combinations. Non-adherent cells were tagged with monoclonal fluorescent antibodies to leucocyte determinants and analysed by flow cytometry. Oxidative burst, assessed with dihydrorhodamine, was followed in cells and supernatant. At a speed similar to that of leucocyte traffic in the retina, normal mucins caused a decrease in neutrophil cathepsin G fluorescence, a decrease that was not observed with mucins from patients with Meibomian gland disease or Sjogren syndrome. No effect was detected at a higher flow. Supernatant and cells collected after circulation over normal mucin showed increased rhodamine fluorescence, indicative of oxidative burst. Fluorescence could also be observed in intact cells adherent to dry-eye mucins. Non-adherent cells could be activated with phorbol 12-myristate 13-acetate after flow over any mucin or combination of mucins. Differences in neutrophil activation after exposure to normal and pathological mucins highlight reciprocal influences at the interface between local and systemic immunity.

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 preocular mucins reflect changes in surface physiology

BACKGROUND/AIMS

Mucin function is associated with both peptide core and glycosylation characteristics. The authors assessed whether structural alterations occurring during mucin residence in the tear film reflect changes in ocular surface physiology.

METHODS

Ocular surface mucus was collected from normal volunteers as N-acetyl cysteine (NAcCys) washes or directly from the speculum after cataract surgery. To assess the influence of surface health on mucins, NAcCys washings were also obtained from patients with symptoms, but no clinical signs of dry eye (symptomatics). Mucins were extracted in guanidine hydrochloride (GuHCl) with protease inhibitors. Buoyant density of mucin species, a correlate of glycosylation density, was followed by reactivity with anti-peptide core antibodies. Mucin hydrodynamic volume was assessed by gel filtration on Sepharose CL2B.

RESULTS

Surface fluid and mucus contained soluble forms of MUC1, MUC2, MUC4, and MUC5AC and also the same species requiring DTT solubilisation. Reactivity with antibodies to MUC2 and MUC5AC peaked at 1.3-1.5 g/ml in normals, while dominated by underglycosylated forms in symptomatics. Surface mucins were predominantly smaller than intracellular species. MUC2 size distributions were different in symptomatics and normals, while those of MUC5AC were similar in these two groups.

CONCLUSIONS

A reduction in surface mucin size indicates post-secretory cleavage. Dissimilarities in surface mucin glycosylation and individual MUC size distributions in symptomatics suggest changes in preocular mucin that might precede dry eye signs.

Glycopolymer charge density determines conformation in human ocular mucin gene products: an atomic force microscope study

Atomic force microscopy (AFM) has been applied to the study of heterogeneity in the structure and function of individual biopolymers with complex structures such as glycoproteins, polysaccharides and nucleic acids. In this work we describe experiments which shed light on the heterogeneity of human ocular mucin gene products. By separating samples of native human ocular mucins on a caesium chloride density gradient, at least three populations consisting predominantly of products of the gene MUC5AC can be identified. Separation on the caesium chloride density gradient is governed by molecular architecture and charge density, and thus provides a route to the discrimination between different glycoforms within a glycoprotein sample. AFM images of these populations show that each is characterised by different conformational properties and polymer diameters, both of which can be attributed to differences in the degree and nature of glycosylation. These differences in glycosylation are likely to be the result of post-translational processing and may also have functional consequences. The AFM's ability to examine the composition of a predominantly single gene product population at the level of the single molecule allows the consequences of post-translational process heterogeneity to be examined at high resolution.

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.

Isolation of conjunctival mucin and differential interaction with Pseudomonas aeruginosa strains of varied pathogenic potential

The purpose of the study was to investigate the adhesion of Pseudomonas aeruginosa strains with varying pathogenic potential to purified ocular mucin. Bovine conjunctival mucin was purified by three sequential density gradient centrifugation steps. Immobilised mucin was probed with biotin-labelled bacteria isolated from different contact lens events and quantified by densitometry. Bacterial pili were identified by electron microscopy. The results indicate that purified ocular mucin consisted of a polydisperse high molecular weight population containing at least one species of goblet cell origin and was associated with a 97 kDa mucin-associated protein. Three pathogenic P. aeruginosa strains, Paer1 (57.5 +/- 10.8x10(6) CFU ml(-1); contact lens induced acute red eye (CLARE)), 6294 (127.0 +/- 4.7x10(6) CFU ml(-1); microbial keratitis) and Paer25 (60.5 +/- 11.3x10(6) CFU ml(-1); CLARE) exhibited a significantly higher level of adhesion to mucin than the negative control, E. coli (14.3 +/- 9.6x10(6) CFU ml(-1)) (p<0.005). The remaining P. aeruginosa isolates, Paer3 (asymptomatic patient), Paer12 (microbial keratitis) and ATCC 15442 (standard environmental strain) did not significantly differ in their mucin adhesion from the negative control. The majority of bacterial strains tested contained pili; thus differences in mucin adhesion observed could not be solely explained by pili status. In conclusion, P. aeruginosa isolates exhibit differential adhesion patterns to purified ocular mucin. It is proposed that more avid mucin-adhering strains are given the opportunity to adhere and subsequently penetrate the mucous layer of the tear film to initiate pathogenesis.

Mucin degradation mechanisms by distinct Pseudomonas aeruginosa isolates in vitro

Pseudomonas aeruginosa has emerged as an important causative agent of bacterial keratitis, a rapidly progressive ocular condition that may result in blindness. Secretory mucin forms the main constituent of the precorneal tear film, a three-layer film on the ocular surface protecting the underlying corneal epithelium from potential pathogens. The purpose of the present study was to compare mucin degradation mechanisms between ocular P. aeruginosa strains. Mucin degradation was assessed by agarose electrophoresis, lectin blotting, and size exclusion chromatography. The results indicate that certain P. aeruginosa strains (Paer12, ATCC 15442, 6294, and Paer25) had depleted mucin from the culture supernatant and that this was contingent on the inherent ability of these isolates to produce proteases. Non-protease-producing strains (Paer1 and Paer3) did not appreciably degrade mucin. Further, galactosidase, N-acetylglucosaminidase, and N-acetylgalactosaminidase activities were detected in some strains, suggesting the operation of further mechanisms of mucin degradation by P. aeruginosa. Mucin degradation by P. aeruginosa also seemed to be for the acquisition of nutrients, as a growth advantage was observed in mucin-depleting strains over nondepleting strains in the long term. It is postulated that the degradation of mucin serves to collapse the mucin barrier and its associated network containing antibacterial tear components and to provide energy for sustained bacterial growth.

Optimisation of sample preparation methods for air imaging of ocular mucins by AFM

The addition of cations to the imaging buffer for AFM has been previously shown to improve the binding of biological molecules to mica. Investigations were carried out to find the concentration of NiCl(2) required to immobilize mucin molecules on a freshly cleaved mica surface, for imaging using intermittent contact in air. Drop-deposition of samples prepared in HEPES buffer with 1, 2 and 5mM NiCl(2) revealed the sensitivity of the mucin molecules to salt. Dialysis of the mucin solutions dramatically reduced the amount of salt present and allowed single molecules to be imaged, revealing a variation in thickness along their length. Spray deposition of the same mucin solutions produced single molecules that, although less affected by co-adsorbed salt, showed a degree of self-folding. This shows the sensitive balance between HEPES and NiCl(2) required for successful imaging of the sub-molecular features of individual mucin molecules.

Exploring the molecular adhesion of ocular mucins

Mucins have been ascribed both pro- and anti-adhesive functions. To clarify how both functions can be embodied in the same molecule we studied the interaction of human ocular mucins with mica and with mucins deposited on mica. Adhesion energy and forces of interaction were evaluated as a function of speed of approach, dwell time at maximum extension, and presence of divalent cations in the imaging buffer. Mucins were tethered to an AFM gold-coated tip. Repeated cycles of approach and retract to mica revealed a large number of adhesions in each cycle. Adhesion energy (0.2-48 aJ) and detachment forces (0.1-4 nN) increased with the addition of Ni(II) ions, and with lengthening dwell time. Speed of approach made little difference to the interactions. Most detachments occurred less than 40 nm from the surface. Inter-detachment distances reflected the major periodicities of the mica basal plane. Short distances of interaction, magnitude of detachment forces, and imaging of mucins on SAM all suggest deformable compact mucin aggregates on the AFM tip. Inter-detachment distances suggest a large degree of interpenetration between neighboring molecules. Tip-tethered mucins did not adhere to mucins deposited on mica. This phenomenon is analogous with the nonadherence of the mucin gels on lids and on cornea during blinking.

Role of Mucins in the Function of the Corneal and Conjunctival Epithelia

The surface of the eye is covered by a tear film, which is held in place by a wet-surfaced, stratified, corneal and conjunctival epithelia. Both are vital for light refraction and protection of vision. Maintenance of tear film on the ocular surface, lubrication, and provision of a pathogen barrier on this wet surface is facilitated by a class of large, highly glycosylated, hydrophilic glycoproteins--the mucins. In the past 15 years, a number of mucin genes have been cloned, and based on protein sequence, categorized as either secreted or membrane associated. Both types of mucins are expressed by ocular surface epithelia. Goblet cells intercalated within the stratified epithelium of the conjunctiva secrete the large gel-forming mucin MUC5AC, and lacrimal gland epithelia secrete the small soluble mucin MUC7. Apical cells of the stratified epithelium of both corneal and conjunctival epithelium express at least three membrane-associated mucins (MUCs 1, 4, and 16), which extend from their apical surface to form the thick glycocalyx at the epithelium-tear film interface. The current hypothesis regarding mucin function and tear film structure is that the secreted mucins form a hydrophilic blanket that moves over the glycocalyx of the ocular surface to clear debris and pathogens. Mucins of the glycocalyx prevent cell-cell and cell-pathogen adherence. The expression and glycosylation of mucins are altered in drying, keratinizing ocular surface diseases.

Commensal ocular bacteria degrade mucins

BACKGROUND/AIMS

Antimicrobial activity in tears prevents infection while maintaining a commensal bacterial population. The relation between mucin and commensal bacteria was assessed to determine whether commensals possess mucinolytic activity, how degradation depends on mucin integrity, and whether mucins affect bacterial replication.

METHODS

Bacteria were sampled from healthy eyes and contact lenses from asymptomatic wearers. Intracellular mucins were extracted and purified from cadaver conjunctivas, and surface mucins from extended wear contact lenses. After exposure to bacteria, changes in mucin hydrodynamic volume (proteolytic cleavage) and subunit charge (oligosaccharide degradation) were assayed by size exclusion and ion exchange chromatography. The effect of mucin on bacterial replication was followed for up to 24 hours from the end of incubation with purified ocular mucins.

RESULTS

Ocular bacteria decreased the hydrodynamic volume of intracellular and contact lens adherent mucins, irrespective of glycosylation density. A decrease in mucin sialylation was observed after exposure to commensal bacteria. Subunit charge distributions were generally shifted to lesser negative charge, consistent with loss of charged epitopes. Subunits with high negative charge, observed after digesting lightly adhering contact lens mucins with bacteria, suggest preferential cleavage sites in the mucin molecule. The presence of purified ocular mucin in the medium inhibited bacterial growth.

CONCLUSION

Bacteria in the healthy ocular surface possess mucinolytic activity on both intact and surface processed mucins, targeted to discrete sites in the mucin molecule. Inhibition of bacterial growth by ocular mucins can be seen as part of the mucosal control of microbiota.

Identification of two highly sialylated human tear-fluid DMBT1 isoforms: the major high-molecular-mass glycoproteins in human tears

Human open eye tear fluid was separated by low-percentage SDS/PAGE to detect high-molecular-mass protein components. Two bands were found with apparent molecular masses of 330 and 270 kDa respectively. By peptide-mass fingerprinting after tryptic digestion, the proteins were found to be isoforms of the DMBT1 gene product, with over 30% of the predicted protein covered by the tryptic peptides. By using gradient SDS/agarose/polyacrylamide composite gel electrophoresis and staining for glycosylation, it was shown that the two isoforms were the major high-molecular-mass glycoproteins of >200 kDa in human tear fluid. Western blotting showed that the proteins expressed sialyl-Le(a). After the release of oligosaccharides by reductive beta-elimination from protein blotted on to PVDF membrane, it was revealed by liquid chromatography-MS that the O-linked oligosaccharides were comprised mainly of highly sialylated oligosaccharides with up to 16 monosaccharide units. A majority of the oligosaccharides could be described by the formula dHex(0-->2)NeuAc(1-->)(x)Hex(x)HexNAc(x)(-ol), x=1-6, where Hex stands for hexose, dHex for deoxyhexose, HexNAc for N-acetylhexosamine and NeuAc for N-acetylneuraminate. The number of sialic acids in the formula is less than 5. Interpretation of collision-induced fragmentation tandem MS confirmed the presence of sialic acid and suggested the presence of previously undescribed structures carrying the sialyl-Le(a) epitopes. Small amounts of neutral and sulphated species were also present. This is the first time that O-linked oligosaccharides have been detected and described from protein variant of the DMBT1 gene.

Heterogeneity and persistence length in human ocular mucins

Atomic force microscopy (AFM) has been used to investigate the heterogeneity and flexibility of human ocular mucins and their subunits. We have paid particular attention, in terms of theory and experiment, to the problem of inducing the polymers to assume equilibrium conformations at a surface. Mucins deposited from a buffer containing Ni(2+) ions adopt extended conformations on mica akin to those observed for DNA under similar conditions. The heterogeneity of the intracellular native mucins is evident from a histogram of contour lengths, reflecting, in part, the diversity of mucin gene products expressed. Reduction of the native mucin with dithiothreitol, thereby breaking the S==S bonds between cysteine residues, causes a marked reduction in polymer length. These results reflect the modes of transport and assembly of newly synthesized mucins in vivo. By modifying the worm-like chain model for applicability to two dimensions, we have confirmed that under the conditions employed mucin adsorbs to mica in an equilibrated conformation. The determined persistence length of the native mucin, 36 nm, is consistent with that of an extended, flexible polymer; such characteristics will influence the properties of the gels formed in vivo.