Membrane-associated mucins of the human ocular surface in health and disease

Bioengineered bilayered grafts for structural and functional posterior lamellar eyelid reconstruction

Eyelid defects involving posterior lamella loss pose significant challenges in reconstructive surgery due to their functional-anatomical complexity. While our previous autologous auricular chondrocyte-derived tissue-engineered cartilage (TEC) grafts successfully maintained normal eyelid morphology, they lacked functional epithelium. This study develops bioengineered bilayered mucosa-cartilage (BMC) grafts through coculture of TEC with oral mucosal explants. The resulting BMC grafts demonstrated a stratified epithelium with barrier integrity and MUC1-producing capacity and a cartilage layer with surgical-grade tensile modulus (1.68 MPa). Upon transplantation into rabbit tarsoconjunctival defects, BMC grafts surpassed both untreated controls and TEC grafts. All grafts demonstrated integration by 2 weeks post-implantation, with transient inflammatory infiltration resolving by 8 weeks. BMC and TEC grafts better preserved eyelid morphology and blinking function than controls throughout the 8-week study. Crucially, BMC-reconstructed eyelids developed continuous stratified epithelia with 5.8-layer MUC1-secreting epithelial cells as early as 2 weeks, progressing to MUC5AC+ goblet cell-rich epithelia by 8 weeks post-implantation. In contrast, TEC counterparts formed thinner epithelia with a lower density of goblet cells. These results confirm the structural integrity and secretory functions of BMC grafts, advancing clinical translation of functional eyelid substitutes.

MUC4 O-GlcNAcylation Regulates the Epithelial Phenotype in Conjunctival Epithelial Cells

In the present study, our aim was to explore the role of MUC4 in IL-4-stimulated conjunctival epithelial cells and the underlying mechanisms. Human recombinant IL-4 was employed in human conjunctival epithelial cells (HConEpic) cells, and MUC4 shRNA (sh-MUC4) was constructed to explore the functional role of MUC4. The protein level of MUC4, O-GlcNAc transferase (OGT), O-GlcNAc hydrolase (OGA), zonula occludens 1 (ZO-1), gap junction protein beta 2 (GJB2), claudin-8 (CLDN8), and E-cadherin were detected by Western blot in HConEpic cells, the interaction between MUC4 and OGT/OGA was assessed by co-immunoprecipitation (IP) and Western blot in 293T cells. Our results showed that IL-4 significantly up-regulated MUC4 and OGT protein levels in HConEpic cells, while down-regulated OGA protein level. Also, IL-4 down-regulated ZO-1, GJB2, CLDN8, and E-cadherin protein levels in HConEpic cells, while which was markedly reversed by sh-MUC4. Additionally, OGT inhibitor significantly reduced MUC4 protein level, and elevated ZO-1, GJB2, CLDN8, and E-cadherin protein levels in HConEpic cells, while OGA inhibitor resulted in the opposite results. Furthermore, in addition to the interaction between OGT/OGA and MUC4, Co-IP and Western blot also revealed the alteration of MUC4 O-GlcNAcylation in 293T cells treated with OGT/OGA inhibitor. Above findings suggested that OGT/OGA inhibitor regulated MUC4 protein level by affecting MUC4 O-GlcNAcylation to regulate ZO-1, GJB2, CLDN8, and E-cadherin protein levels in HConEpic cells, which was achieved via inhibiting the interaction between OGT/OGA and MUC4. This study may provide a better understanding of the pathogenesis of allergic conjunctivitis (AC).

Mucin1 N-domain variant contributes to dry eye syndrome in diabetes by increasing immature mucus secretory granules

BACKGROUND

Diabetes-associated dry eye syndrome (DMDES) affects 20-54 % of diabetes, leading to ocular irritation and blurry vision. Decreased conjunctival goblet cell mucus secretion is one of the major pathological processes of DMDES. This study aims to investigate the mechanism of mucus granule maturation and secretion disturbance in DMDES.

METHODS

Tear samples from diabetic patients with and without dry eye syndrome were analyzed by mass spectrometry to identify proteins associated with ocular mucous layer reduction. The N-terminal domain fragment of Mucin1 (MUC1-ND) was transfected into the mouse conjunctiva to investigate alterations in goblet cell mucus secretion. Protein localization and granule morphology were explored through transmission electron microscopy with colloidal gold labeling and immunohistochemistry. Immunofluorescence, co-immunoprecipitation, and integrative computational modeling of protein interactions were employed to explore protein-protein interactions.

RESULTS

Tear proteomic analysis revealed significantly elevated MUC1-ND levels in tears from DMDES patients, which correlated with reduced goblet cell mucus secretion and tear film instability. Upregulation of MUC1-ND in mice conjunctiva inhibited the maturation of secretory mucus granules, contributing to tear mucous layer reduction. Protein docking and co-immunoprecipitation analysis demonstrated that the binding of MUC1-ND and Syntaxin6 prevents granule fusion and maintains the immature state of secretory granules, which leads to reduced mucus secretion.

CONCLUSION

In DMDES, MUC1-ND binds with Syntaxin6 to disrupt the fusion and maturation of secretory mucus granules in conjunctival goblet cells, which provides a new insight into DMDES pathophysiology.

Androgens suppress the sialyltransferases ST3GAL1 and ST3GAL4 and modulate mucin 10 glycosylation in the submandibular gland, related to sex differences in commensal microbiota composition in mice

Sex differences exist in the commensal microbiota that impact on multiple physiological processes in the host. Here, we examined the mechanism by which the sex differences are formed. In addition to the epithelial ductal cell, the acinar cell mass in the submandibular gland was associated with androgen-androgen receptor (AR) signaling. Sex differences in the formation of submandibular mucin 10 (MUC10) were identified using SDS-PAGE. Neuraminidase treatment, which hydrolyzes terminal sialic acid, influenced the mobility shift of MUC10. Androgen-AR signaling negatively regulated ST3 β-galactoside α-2,3-sialyltransferase 1 (St3gal1) and St3gal4 in the submandibular gland. There was a trend and significant sex differences in α-diversity (Shannon, P = .09) and β-diversity (unweighted UniFrac) in oral microbiota composition, respectively. Some female-preferring bacteria including Akkermansia muciniphila can assimilate mucin by degrading terminal sialic acids. Our results indicate that androgen-AR signaling suppresses ST3GAL1 and ST3GAL4, which can influence sex differences in commensal microbiota composition.

A hyaluronic acid-modified cyclodextrin self-assembly system for the delivery of β-carotene in the treatment of dry eye disease

Dry eye disease (DED) is a multifactorial ocular disease, the core mechanism of which is the tear film instability caused by ocular oxidative stress damage and inflammation. Although various pharmaceutical agents are available for DED treatment, their effectiveness is often limited by the eyes' unique biological barriers, and the long-term use of steroid hormones can lead to several adverse effects. This study reported a nano-supramolecular delivery system consisting of a polycyclodextrin (PCD), hyaluronic acid (HA) and the natural compound β-carotene (BC) for the DED treatment. Our findings indicate that the HA/PCD@BC eye drops effectively distribute on the ocular surface, retain BC, and significantly enhance the corneal penetration of BC. The excellent biocompatibility of HA/PCD@BC was demonstrated through viability testing on different cell lines, the Draize eye test, as well as the hematoxylin-eosin staining (H&E) sections of cornea and conjunctiva. Both in vitro oxidative stress assays and in vivo DED model evaluations demonstrated that the HA/PCD@BC delivery system significantly reduced abnormal oxidative stress levels on the ocular surface, inhibited the secretion of inflammatory factors, and increased the secretion of tear film stabilizing mucin. These effects collectively improved pathological changes in eye tissues and minimized damage to the ocular surface. It is of particular importance to note that HA/PCD@BC eye drops showed superior efficacy in comparison to cyclosporine A (CsA), an FDA-approved first-line drug. To sum up, the HA/PCD@BC nanodelivery system provides a natural, safe and effective therapeutic strategy for the treatment of DED and various ocular diseases.

The Pax transcription factor EGL-38 links EGFR signaling to assembly of a cell type-specific apical extracellular matrix in the Caenorhabditis elegans vulva

The surface of epithelial tissues is covered by an apical extracellular matrix (aECM). The aECMs of different tissues have distinct compositions to serve distinct functions, yet how a particular cell type assembles the proper aECM is not well understood. We used the cell type-specific matrix of the C. elegans vulva to investigate the connection between cell identity and matrix assembly. The vulva is an epithelial tube composed of seven cell types descending from EGFR/Ras-dependent (1°) and Notch-dependent (2°) lineages. Vulva aECM contains multiple Zona Pellucida domain (ZP) proteins, which are a common component of aECMs across life. ZP proteins LET-653 and CUTL-18 assemble on 1° cell surfaces, while NOAH-1 assembles on a subset of 2° surfaces. All three ZP genes are broadly transcribed, indicating that cell type-specific ZP assembly must be determined by features of the destination cell surface. The paired box (Pax) transcription factor EGL-38 promotes assembly of 1° matrix and prevents inappropriate assembly of 2° matrix, suggesting that EGL-38 promotes expression of one or more ZP matrix organizers. Our results connect the known signaling pathways and various downstream effectors to EGL-38/Pax expression and the ZP matrix component of vulva cell fate execution. We propose that dedicated transcriptional networks may contribute to cell-appropriate assembly of aECM in many epithelial organs.

The Role of Scanning Electron Microscopy in the Evaluation of Conjunctival Microvilli as an Early Biomarker of Ocular Surface Health: A Literature Review

Microvilli are bristle-like protuberances of the plasma membrane, which express the vitality of mucous and epithelial cells; their alteration indicates a condition of cellular suffering in a predictive sense, making it possible to establish how much an inflammatory state or toxic conditions affect cellular functionality. In this article, the authors evaluate the applications of scanning electron microscopy (SEM) examination to impression cytology (IC) of the bulbar conjunctiva for the assessment of microvillar alteration as an early ultrastructural indicator of ocular surface health. This method offers several advantages, starting with its simplicity: it involves the non-invasive application of a strip of bibulous paper to the bulbar or tarsal conjunctiva. Unlike conjunctival or corneal biopsies, which are surgical procedures, this technique is far less invasive and more comfortable for the patient. It also provides a more clinically relevant in vivo assessment compared to studies on cultured cell lines, which are mostly limited to scientific research and may not accurately reflect real-world conditions. This makes it an effective, repeatable, and patient-friendly option for detecting early pathological alterations of the ocular surface. It also represents a useful tool for evaluating the efficacy of topical drugs and the toxic effects of external factors and ophthalmic or systemic diseases. Finally, it allows for obtaining accessory information relating to goblet cells, the presence of inflammatory infiltrate, or any pathogens.

MUC1‑ND interacts with TRPV1 to promote corneal epithelial cell proliferation in diabetic dry eye mice by partly activating the AKT signaling pathway

Although both mucin1 (MUC1) and transient receptor potential cation channel subfamily V member 1 (TRPV1) have been reported to be associated with dry eye (DE) disease, whether they interact and their regulatory roles in diabetic DE disease are unknown. Diabetic DE model mice were generated by streptozotocin induction and assessed by corneal fluorescein staining, tear ferning (TF) tests, phenol red thread tests, hematoxylin and eosin staining of corneal sections and periodic acid Schiff staining of conjunctival sections. Cell proliferation was measured by CCK8 assay. Western blotting was performed to measure protein expression. Primary mouse corneal epithelial cells (MCECs) were cultured after enzymatic digestion. Immunofluorescence staining of MCECs and frozen corneal sections was conducted to assess protein expression and colocalization. Coimmunoprecipitation was performed to detect protein‑protein interactions. It was found that, compared with control mice, diabetic DE mice exhibited increased corneal epithelial defects, reduced tear production, poorer TF pattern grades and impaired corneal and conjunctival tissues. In vivo and in vitro experiments showed that hyperglycemia impaired cell proliferation, accompanied by decreased levels of the MUC1 extracellular domain (MUC1‑ND) and TRPV1. Additionally, it was found that capsazepine (a TRPV1 antagonist) inhibited the proliferation of MCECs. Notably, MUC1‑ND was shown to interact with the TRPV1 protein in the control group but not in the diabetic DE group. It was also found that the AKT signaling pathway was attenuated in the diabetic DE mice and downstream of TRPV1. MUC1‑ND interacted with TRPV1, partly activating the AKT signaling pathway to promote MCEC proliferation. The present study found that the interaction of MUC1‑ND with TRPV1 promotes MCEC proliferation by partly activating the AKT signaling pathway, providing new insight into the pathogenesis of corneal epithelial dysfunction in diabetic DE disease.

TRPV4 activation in human corneal epithelial cells promotes membrane mucin production

Given that the corneal epithelium is situated on the outermost part of the eye, its functions can be influenced by external temperatures and chemical substances. This study aimed to elucidate the expression profile of chemosensory receptors in corneal epithelial cells and analyze their role in eye function regulation. A comprehensive analysis of 425 chemosensory receptors in human corneal epithelial cells-transformed (HCE-T) revealed the functional expression of TRPV4. The activation of TRPV4 in HCE-T cells significantly increased the expression of membrane-associated mucins MUC1, MUC4, and MUC16, which are crucial for stabilizing tear films, with efficacy comparable to the active components of dry eye medications. The present study suggests that TRPV4, which is activated by body temperature, regulates mucin expression and proposes it as a novel target for dry eye treatment.

Ag/Cu nanoparticles-loaded glycocalyx biomimetic corneal bandage lenses for combatting bacterial keratitis

Bacterial keratitis is a major cause of blindness, hindered by the rising threat of antibiotic resistance. Although corneal bandage lenses (CBLs) are widely utilized in ophthalmic treatment, their effectiveness in treating bacterial keratitis remains limited due to risks of secondary infections, patient discomfort, and complications. In this study, we developed a novel biomimetic coating on CBLs by grafting Ag/Cu bimetallic nanoparticles (Ag/Cu-NPs) and thiol-functionalized heparin (Hep-SH) using a rapid polydopamine (PDA) deposition technique, effectively mimicking the ocular surface glycocalyx structure. The resulting Ag/Cu-NPs/Hep-SH coated CBLs (PNH-CBLs) exhibited significant antibacterial activity, with over 80 % reduction in Staphylococcus aureus (S. aureus) and 70 % in Escherichia coli (E. coli) due to the sustained release of Ag+ and Cu2+, along with displaying favorable in vitro biocompatibility. Animal experiments conducted on New Zealand white rabbits with bacterial keratitis demonstrated successful treatment therapeutic outcomes, with PNH-CBLs leading to a significant decrease in clinical score. These biomimetic lenses also exhibited selective anti-protein adsorption properties, minimizing inflammation and promoting surface lubrication. Overall, this innovative approach addresses critical challenges in antibiotic resistance and offers a promising therapeutic strategy for managing ophthalmic infectious diseases.

Evolution of therapeutic strategy based on oxidant-antioxidant balance for fuchs endothelial corneal dystrophy

Fuchs endothelial corneal dystrophy (FECD) stands as the most prevalent primary corneal endothelial dystrophy worldwide, posing a significant risk to corneal homeostasis and clarity. Corneal endothelial cells exhibit susceptibility to oxidative stress, suggesting a nuanced relationship between oxidant-antioxidant imbalance and FECD pathogenesis, irrespective of FECD genotype. Given the constrained availability of corneal transplants, exploration into non-surgical interventions becomes crucial. This encompasses traditional antioxidants, small molecule compounds, biologics, and diverse non-drug therapies, such as gene-related therapy, hydrogen therapy and near infrared light therapy. This review concentrates on elucidating the mechanisms behind oxidant-antioxidant imbalance and the evolution of strategies to restore oxidant-antioxidant balance in FECD. It provides a comprehensive overview of both conventional and emerging therapeutic approaches, offering valuable insights for the advancement of non-surgical treatment modalities. The findings herein might establish a robust foundation for future research and the therapeutic strategy of FECD.

The Pax transcription factor EGL-38 links EGFR signaling to assembly of a cell-type specific apical extracellular matrix in the Caenorhabditis elegans vulva

The surface of epithelial tissues is covered by an apical extracellular matrix (aECM). The aECMs of different tissues have distinct compositions to serve distinct functions, yet how a particular cell type assembles the proper aECM is not well understood. We used the cell-type specific matrix of the C. elegans vulva to investigate the connection between cell identity and matrix assembly. The vulva is an epithelial tube composed of seven cell types descending from EGFR/Ras-dependent (1°) and Notch-dependent (2°) lineages. Vulva aECM contains multiple Zona Pellucida domain (ZP) proteins, which are a common component of aECMs across life. ZP proteins LET-653 and CUTL-18 assemble on 1° cell surfaces, while NOAH-1 assembles on a subset of 2° surfaces. All three ZP genes are broadly transcribed, indicating that cell-type specific ZP assembly must be determined by features of the destination cell surface. The paired box (Pax) transcription factor EGL-38 promotes assembly of 1° matrix and prevents inappropriate assembly of 2° matrix, suggesting that EGL-38 promotes expression of one or more ZP matrix organizers. Our results connect the known signaling pathways and various downstream effectors to EGL-38/Pax expression and the ZP matrix component of vulva cell fate execution. We propose that dedicated transcriptional networks may contribute to cell-appropriate assembly of aECM in many epithelial organs.

Imaging assessment of conjunctival goblet cells in dry eye disease

Dry eye disease (DED) is a widespread, multifactorial, and chronic disorder of the ocular surface with disruption of tear film homeostasis as its core trait. Conjunctival goblet cells (CGCs) are specialised secretory cells found in the conjunctival epithelium that participate in tear film formation by secreting mucin. Changes in both the structure and function of CGCs are hallmarks of DED, and imaging assessment of CGCs is important for the diagnosis, classification, and severity evaluation of DED. Existing imaging methods include conjunctival biopsy, conjunctival impression cytology and in vivo confocal microscopy, which can be used to assess the morphology, distribution, and density of the CGCs. Recently, moxifloxacin-based fluorescence microscopy has emerged as a novel technique that enables efficient, non-invasive and in vivo imaging of CGCs. This article presents a comprehensive overview of both the structure and function of CGCs and their alterations in the context of DED, as well as current methods of CGCs imaging assessment. Additionally, potential directions for the visual evaluation of CGCs are discussed.

Ectoine Enhances Mucin Production Via Restoring IL-13/IFN-γ Balance in a Murine Dry Eye Model

Purpose

This study aimed to explore protective effects and potential mechanism of ectoine, a natural osmoprotectant, on ocular surface mucin production in dry eye disease.

Methods

A dry eye model was established in C57BL/6 mice exposed to desiccating stress (DS) with untreated (UT) mice as controls. DS mice were topically treated with 2.0% ectoine or PBS vehicle. Corneal epithelial defects were assessed by Oregon Green Dextran (OGD) fluorescent staining. Conjunctival goblet cells, ocular mucins, and T help (Th) cytokines were evaluated by immunofluorescent staining or ELISA, and RT-qPCR.

Results

Compared with UT mice, corneal epithelial defects were detected as strong punctate OGD fluorescent staining in DS mice with vehicle, whereas ectoine treatment largely reduced OGD staining to near-normal levels. Conjunctival goblet cell density and cell size decreased markedly in DS mice, but was significantly recovered by ectoine treatment. The protein production and mRNA expression of two gel-forming secreted MUC5AC and MUC2, and 4 transmembrane mucins, MUC1, MUC4, MUC16, and MUC15, largely decreased in DS mice, but was restored by ectoine. Furthermore, Th2 cytokine IL-13 was inhibited, whereas Th1 cytokine IFN-γ was stimulated at protein and mRNA levels in conjunctiva and draining cervical lymph nodes (CLNs) of DS mice, leading to decreased IL-13/IFN-γ ratio. Interestingly, 2.0% ectoine reversed their alternations and restored IL-13/IFN-γ balance.

Conclusions

Our findings demonstrate that topical ectoine significantly reduces corneal damage, and enhances goblet cell density and mucin production through restoring imbalanced IL-13/IFN-γ signaling in murine dry eye model. This suggests therapeutic potential of natural osmoprotectant ectoine for dry eye disease.

Mucin Expression Profiles in Ulcerative Colitis: New Insights on the Histological Mucosal Healing

A structural weakness of the mucus barrier (MB) is thought to be a cause of ulcerative colitis (UC). This study aims to investigate the mucin (MUC) composition of MB in normal mucosa and UC. Ileocolonic biopsies were taken at disease onset and after treatment in 40 patients, including 20 with relapsing and 20 with remitting UC. Ileocolonic biopsies from 10 non-IBD patients were included as controls. Gut-specific MUC1, MUC2, MUC4, MUC5B, MUC12, MUC13, MUC15, and MUC17 were evaluated immunohistochemically. The promoters of mucin genes were also examined. Normal mucosa showed MUC2, MUC5B, and MUC13 in terminal ileum and colon, MUC17 in ileum, and MUC1, MUC4, MUC12, and MUC15 in colon. Membranous, cytoplasmic and vacuolar expressions were highlighted. Overall, the mucin expression was abnormal in UC. Derangements in MUC1, MUC4, and MUC5B were detected both at onset and after treatment. MUC2 and MUC13 were unaffected. Sequence analysis revealed glucocorticoid-responsive elements in the MUC1 promoter, retinoic-acid-responsive elements in the MUC4 promoter, and butyrate-responsive elements in the MUC5B promoter. In conclusion, MUCs exhibited distinct expression patterns in the gut. Their expression was disrupted in UC, regardless of the treatment protocols. Abnormal MUC1, MUC4, and MUC5B expression marked the barrier dysfunction in UC.

Effects of particulate matter exposure on the expression of the SARS-CoV-2 ACE2 receptor in ocular surface tissues and cells

Particulate matter (PM) has been reported to be one of the risk factor for COVID-19 caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, although the ocular surface is deeply affected by both PM exposure and SARS-COV-2 infection, no studies have investigated the effects of PM exposure on the ocular route of SARS-COV-2 infection. To this end, we explored the effects of PM on the expression of SARS-COV-2-associated receptors and proteins in ocular surface. Herein, short- and long-term PM-exposed rat models were established by topically administering PM for 3 and 10 days, respectively. Immortalized human corneal epithelial cells (HCECs) and human conjunctival epithelial cells (HCjECs) were exposed to PM. ACE2, TMPRSS2, CD147, and ADAM17 expression levels were measured by western blot analysis. Our results show that short-term PM exposure had little effect on the expressions of ACE2, TMPRSS2, and CD147 in ocular surface tissues. However, long-term PM exposure decreased the ACE2 expression in conjunctival tissues and increased the CD147 expression in corneal or conjunctival tissues. PM exposure reduced the ACE2 expression by increasing the ADAM17 expression and ACE2 shedding level in HCECs and HCjECs. Our findings suggest that long-term PM exposure down-regulate the expression of the SARS-CoV-2 receptor ACE2 in conjunctival tissues through ADAM17-dependent ACE2 shedding. However, long-term PM exposure up-regulates the expression of another SARS-CoV-2 receptor CD147 in ocular surface tissues, accompanied by ocular surface damage and cytotoxicity. This study provides a new insight into uncovering potential risk factors for infection with SARS-CoV-2 via the ocular route.

Design, preparation, and characterization of lubricating polymer brushes for biomedical applications

The lubrication modification of biomedical devices significantly enhances the functionality of implanted interventional medical devices, thereby providing additional benefits for patients. Polymer brush coating provides a convenient and efficient method for surface modification while ensuring the preservation of the substrate's original properties. The current research has focused on a "trial and error" method to finding polymer brushes with superior lubricity qualities, which is time-consuming and expensive, as obtaining effective and long-lasting lubricity properties for polymer brushes is difficult. This review summarizes recent research advances in the biomedical field in the design, material selection, preparation, and characterization of lubricating and antifouling polymer brushes, which follow the polymer brush development process. This review begins by examining various approaches to polymer brush design, including molecular dynamics simulation and machine learning, from the fundamentals of polymer brush lubrication. Recent advancements in polymer brush design are then synthesized and potential avenues for future research are explored. Emphasis is placed on the burgeoning field of zwitterionic polymer brushes, and highlighting the broad prospects of supramolecular polymer brushes based on host-guest interactions in the field of self-repairing polymer brush applications. The review culminates by providing a summary of methodologies for characterizing the structural and functional attributes of polymer brushes. It is believed that a development approach for polymer brushes based on "design-material selection-preparation-characterization" can be created, easing the challenge of creating polymer brushes with high-performance lubricating qualities and enabling the on-demand creation of coatings. STATEMENT OF SIGNIFICANCE: Biomedical devices have severe lubrication modification needs, and surface lubrication modification by polymer brush coating is currently the most promising means. However, the design and preparation of polymer brushes often involves "iterative testing" to find polymer brushes with excellent lubrication properties, which is both time-consuming and expensive. This review proposes a polymer brush development process based on the "design-material selection-preparation-characterization" strategy and summarizes recent research advances and trends in the design, material selection, preparation, and characterization of polymer brushes. This review will help polymer brush researchers by alleviating the challenges of creating polymer brushes with high-performance lubricity and promises to enable the on-demand construction of polymer brush lubrication coatings.

Mucin1 as a potential molecule for cancer immunotherapy and targeted therapy

Mucin1 is a highly glycosylated type 1 transmembrane mucin that ranks second among 75 tumor-related antigens published by the National Cancer Institute, and has been identified as a possible therapeutic target over the past 30 years. MUC1 plays an important role in malignant transformation and disease evolution, including cell proliferation, survival, self-renewal, and metastatic invasion. MUC1 has been shown to interact with diverse effectors such as β-catenin, receptor tyrosine kinases, and cellular-abelsongene, which are of importance in the pathogenesis of various malignant tumors. Targeting MUC1 has been shown to be an effective way to induce tumor cell death in vivo and in vitro models. In recent years, a number of therapeutic strategies targeting MUC1 have been developed and their value for tumor therapy have been demonstrated experimentally. This review summarizes recent findings on the structure of MUC1, its expression in different tumors and its involved mechanism pathways, with emphasis on new progress in cancer therapy which related MUC1 in the past decade and evaluates their therapeutic effect.

The Efficacy and Safety of Rebamipide Ophthalmic Suspension (OPC-12759) in Patients with Dry Eye Disease: A Systematic Review of Randomized Controlled Trials

The aim of this paper is to evaluate the efficacy and safety of Rebamipide (REB) ophthalmic suspension in dry eye disease (DED). A systematic review that only included full-length randomized controlled studies (RCTs) reporting the effects of REB ophthalmic suspension in three databases, PubMed, Scopus and Web of Science, was performed according to the PRISMA statement. The Cochrane risk of bias tool was used to analyze the quality of the studies selected. A total of seven studies were included in this systematic review. Although the overall risk of bias was low, most studies were sponsored by the manufacturer. REB ophthalmic suspension treatment achieved higher improvement than the control group in all reported variables. The mean differences between both groups were in favor of the REB group and were as follows: dry eye-related quality of life score (DEQS) -3.5 ± 2.9 points, tear film break-up time (TBUT) of 0.7 ± 0.6 s, Schirmer test (ST) without anesthesia of 0.3 ± 0.6 mm and total corneal fluorescein staining (tCFS) of -1.2 ± 0.7 points. Adverse events (AEs) were 5.2 ± 7.6% superior in the REB group, with an overall compliance > 95%. Therefore, REB ophthalmic suspension is a safe and effective treatment that could be recommended in patients with DED.

Investigation of Conjunctival Goblet Cell and Tear MUC5AC Protein in Patients With Graves' Ophthalmopathy

Purpose

The aim of this study was to investigate conjunctival goblet cell density (GCD) and tear mucin-5AC (MUC5AC) protein levels in patients with Graves' ophthalmopathy (GO) and their association with dry eye indicators.

Methods

A total of 99 patients with GO (54 active, 45 inactive) and 40 healthy controls were recruited. Comprehensive ophthalmic examinations, including the external eye, ocular surface, GCD, and tear MUC5AC ELISA, were performed. The GCD examination was performed in temporal bulbar conjunctiva, including IVCM GCD by in vivo confocal microscopy (IVCM) and filled GCD of cytokeratin-7 and MUC5AC-positive co-immunomarkers by impression cytology. Tear MUC5AC protein was detected using samples extracted from Schirmer strips.

Results

The GO group showed a significant decrease in IVCM GCD, filled GCD, and normalized tear MUC5AC protein compared to controls, with the active GO group showing the greatest decrease (all P < 0.05). Tear MUC5AC protein levels in GO correlated with those of IVCM GCD (r = 0.40, P < 0.001) and filled GCD (r = 0.54, P < 0.001, respectively). Higher ocular surface disease index (r = -0.22, P < 0.05; r = -0.20, P < 0.05; r = -0.21, P < 0.05) and lisamine green staining (r = -0.23, P < 0.05; r = -0.38, P < 0.001; r = -0.42, P < 0.001) were associated with lower tear MUC5AC protein levels, IVCM GCD, and filled GCD, respectively, which decreased with increasing clinical activity score (r = -0.24, P < 0.05; r = -0.28, P < 0.01; r = -0.27, P < 0.01) and conjunctival congestion score (r = -0.27, P < 0.01; r = -0.33, P < 0.001; r = -0.42, P < 0.001).

Conclusions

The goblet cell count and tear MUC5AC protein in GO eyes were decreased, possibly due to ocular surface inflammation.

Translational Relevance

This study observed the change of tear film mucin in GO patients.

Roles unveiled for membrane-associated mucins at the ocular surface using a Muc4 knockout mouse model

Membrane-associated mucins (MAMs) are proposed to play critical roles at the ocular surface; however, in vivo evidence has been lacking. Here we investigate these roles by phenotyping of a Muc4 KO mouse. Histochemical analysis for expression of the beta-galactosidase transgene replacing Muc4 revealed a spiraling ribbon pattern across the corneal epithelium, consistent with centripetal cell migration from the limbus. Depletion of Muc4 compromised transcellular barrier function, as evidenced by an increase in rose bengal staining. In addition, the corneal surface was less smooth, consistent with disruption of tear film stability. While surface cells presented with well-developed microprojections, an increase in the number of cells with fewer microprojections was observed. Moreover, an increase in skin-type keratin K10 and a decrease in transcription factor Pax6 was observed, suggesting an incipient transdifferentiation. Despite this, no evidence of inflammatory dry eye disease was apparent. In addition, Muc4 had no effect on signaling by toll-like receptor Tlr4, unlike reports for MUC1 and MUC16. Results of this study provide the first in vivo evidence for the role of MAMs in transcellular barrier function, tear film stability, apical epithelial cell architecture, and epithelial mucosal differentiation at the ocular surface.

Comparison of mucin levels at the ocular surface of visual display terminal users with and without dry eye disease

BACKGROUND

The long-term use of visual display terminals (VDT) is linked to an increased risk of dry eye disease (DED). Numerous studies have indicated that ocular mucins play a vital role in the pathogenesis of DED. Therefore, we aimed to evaluate (1) whether mRNA levels of membrane-associated mucins (MAMs), including MUC1, MUC4, MUC16, and MUC20, as well as MUC5AC are altered in conjunctival cells of VDT users with and without DED and (2) the relationship between mucin levels and subjective and objective tests of DED in VDT users.

METHODS

Seventy-nine VDT users were enrolled and divided into DED (n = 53) and control (n = 26) groups. All participants were evaluated for parameters of DED using the Ocular Surface Disease Index (OSDI) questionnaire, tear breakup time (TBUT), corneal fluorescein staining (CFS), lissamine green (LG) staining, and tear meniscus height (TMH). Based on the conjunctival impression cytology (CIC) method, differences in MUC1, MUC4, MUC16, MUC20, and MUC5AC mRNA expression levels were observed between the DED and control groups, and between symptomatic and asymptomatic participants.

RESULTS

The DED group showed significantly decreased MUC1, MUC16, and MUC20 expressions (all P < 0.05) compared to the control group. In addition, these mucin levels were lower in subjects with frequent ocular symptoms (foreign body sensation, blurred vision and painful or sore eyes) than in asymptomatic participants (all P < 0.05). Correlation analysis revealed that MUC1, MUC16, and MUC20 levels in VDT users were positively correlated with TBUT or TMH, or both. However, no significant relationship was found between MUC4 and MUC5AC levels and the DED parameters.

CONCLUSION

VDT users with an increased frequency of ocular discomfort or a diagnosis of DED had a decreased MUC1, MUC16 and MUC20 mRNA expression in their conjunctival cells. MAMs deficiency in the conjunctival epithelium may be one of the mechanisms leading to tear film instability and DED in VDT users.

Transmembrane Mucin Response in Conjunctival Epithelial Cells Exposed to Wall Shear Stresses

Human conjunctival epithelium cells (HCEC) line the inner surface of the eyelid and cover the sclera and are continuously subjected to wall shear stresses (WSS). The effects of external forces on the conjunctival epithelium are not fully known. The conjunctival epithelium contains stratified squamous cells that synthesize the membrane-spanning mucins MUC1 and MUC16, which play important roles in protecting the ocular surface. Alterations in both gel-forming and membrane-tethered mucins occur in drying ocular surface diseases. The aim of this study was to explore the mechanobiological characteristics of transmembrane mucin secretion and cellular alterations of primary HCEC exposed to airflow-induced WSS perturbations. We exposed the HCEC to a steady WSS of 0.5 dyne/cm2 for durations of 15 and 30 min. Cytoskeletal alterations and MUC1 secretions were studied using immunohistochemically fluorescent staining with specific antibodies. We investigated for the first time an in vitro model of membrane-tethered mucin secretion by HCEC in response to WSS. The exposure of HCEC to WSS increased the polymerization of F-actin, altered the cytoskeletal shape and reduced the secretion of membrane-tethered MUC1.

View from the Biological Property: Insight into the Functional Diversity and Complexity of the Gut Mucus

Due to mucin's important protective effect on epithelial tissue, it has garnered extensive attention. The role played by mucus in the digestive tract is undeniable. On the one hand, mucus forms "biofilm" structures that insulate harmful substances from direct contact with epithelial cells. On the other hand, a variety of immune molecules in mucus play a crucial role in the immune regulation of the digestive tract. Due to the enormous number of microorganisms in the gut, the biological properties of mucus and its protective actions are more complicated. Numerous pieces of research have hinted that the aberrant expression of intestinal mucus is closely related to impaired intestinal function. Therefore, this purposeful review aims to provide the highlights of the biological characteristics and functional categorization of mucus synthesis and secretion. In addition, we highlight a variety of the regulatory factors for mucus. Most importantly, we also summarize some of the changes and possible molecular mechanisms of mucus during certain disease processes. All these are beneficial to clinical practice, diagnosis, and treatment and can provide some potential theoretical bases. Admittedly, there are still some deficiencies or contradictory results in the current research on mucus, but none of this diminishes the importance of mucus in protective impacts.

Single cell RNA-seq of human cornea organoids identifies cell fates of a developing immature cornea

The cornea is a protective and refractive barrier in the eye crucial for vision. Understanding the human cornea in health, disease, and cell-based treatments can be greatly advanced with cornea organoids developed in culture from induced pluripotent stem cells. While a limited number of studies have investigated the single-cell transcriptomic composition of the human cornea, its organoids have not been examined similarly. Here, we elucidated the transcriptomic cell fate map of 4-month-old human cornea organoids and human donor corneas. The organoids harbor cell clusters that resemble cells of the corneal epithelium, stroma, and endothelium, with subpopulations that capture signatures of early developmental states. Unlike the adult cornea where the largest cell population is stromal, the organoids contain large proportions of epithelial and endothelial-like cells. These corneal organoids offer a 3D model to study corneal diseases and integrated responses of different cell types.

Advances in MUC1-Mediated Breast Cancer Immunotherapy

Breast cancer (BRCA) is the leading cause of death from malignant tumors among women. Fortunately, however, immunotherapy has recently become a prospective BRCA treatment with encouraging achievements and mild safety profiles. Since the overexpression and aberrant glycosylation of MUC1 (human mucin) are closely associated with BRCA, it has become an ideal target for BRCA immunotherapies. In this review, the structure and function of MUC1 are briefly introduced, and the main research achievements in different kinds of MUC1-mediated BRCA immunotherapy are highlighted, from the laboratory to the clinic. Afterward, the future directions of MUC1-mediated BRCA immunotherapy are predicted, addressing, for example, urgent issues in regard to how efficient immunotherapeutic strategies can be generated.

Ocular microbiota promotes pathological angiogenesis and inflammation in sterile injury-driven corneal neovascularization

Microbiota promotes or inhibits the pathogenesis of a range of immune-mediated disorders. Although recent studies have elucidated the role of gut microbiota in ocular disease, the effect of ocular microbiota remains unclear. Herein, we explored the role of ocular commensal bacteria in non-infectious corneal inflammation and angiogenesis in a mouse model of suture-induced corneal neovascularization. Results revealed that the ocular surface harbored a microbial community consisting mainly of Actinobacteria, Firmicutes and Proteobacteria. Elimination of the ocular commensal bacteria by oral broad-spectrum antibiotics or topical fluoroquinolone significantly suppressed corneal inflammation and neovascularization. Disease amelioration was associated with reduced numbers of CD11b⁺Ly6C⁺ and CD11b⁺Ly6G⁺ myeloid cells, not Foxp3⁺ regulatory T cells, in the spleen, blood, and draining lymph nodes. Therapeutic concentrations of fluoroquinolone, however, did not directly affect immune cells or vascular endothelial cells. In addition, data from a clinical study showed that antibiotic treatment in combination with corticosteroids, as compared with corticosteroid monotherapy, induced faster remission of corneal inflammation and new vessels in pediatric patients with non-infectious marginal keratitis. Altogether, our findings demonstrate a pathogenic role of ocular microbiota in non-infectious inflammatory disorders leading to sight-threatening corneal neovascularization, and suggest a therapeutic potential of targeting commensal microbes in treating ocular inflammation.

Epithelial barrier dysfunction in ocular allergy

The epithelial barrier is the first line of defense that forms a protective barrier against pathogens, pollutants, and allergens. Epithelial barrier dysfunction has been recently implicated in the development of allergic diseases such as asthma, atopic dermatitis, food allergy, and rhinitis. However, there is limited knowledge on epithelial barrier dysfunction in ocular allergy (OA). Since the ocular surface is directly exposed to the environment, it is important to understand the role of ocular epithelia and their dysfunction in OA. Impaired epithelial barrier enhances allergen uptake, which lead to activation of immune responses and development of chronic inflammation as seen in allergies. Abnormal expression of tight junction proteins that helps to maintain epithelial integrity has been reported in OA but sufficient data not available in chronic atopic (AKC) and vernal keratoconjunctivitis (VKC), the pathophysiology of which is not just complex, but also the current treatments are not completely effective. This review provides an overview of studies, which indicates the role of barrier dysfunction in OA, and highlights how ocular barrier dysfunction possibly contributes to the disease pathogenesis. The review also explores the potential of ocular epithelial barrier repair strategies as preventive and therapeutic approach.

Dry eye disease and proteomics

Dry eye disease (DED) is a highly prevalent disease worldwide mostly associated with age, though other factors such as screen use and contact lens wear explain why it is increasingly diagnosed in younger people. DED also disproportionately affects women. Symptoms include eye dryness, burning, pain and sensitivity to light that can significantly affect quality of life. This condition may progress to cause lasting damage to the ocular surface if left untreated. Currently, diagnosis is through assessment of signs and symptoms determined by clinical tests and questionnaires. However, there is considerable overlap between normal and DED result distributions of currently available metrics as signs and symptoms fluctuate over time and with disease severity. Importantly, the non-targeted approach of proteomics means that significant changes in novel proteins may be discovered. Proteomics is a powerful tool that has been applied to the field of DED to understand changes at a biochemical level, uncover new disease biomarkers and determine the success of clinical interventions. While individual proteins may not be sensitive enough when used as single biomarkers, proteomics opens the possibility to uncover several relevant proteins that may be combined in a panel to provide more accurate diagnostic value i.e. parallel testing. In this review we discuss the use of proteomics in DED research and the potential for application of proteomic results in the clinic. We also identify shortcomings and future avenues for research.

Secreted Ly-6/uPAR-related protein-1 (SLURP1) is a pro-differentiation factor that stalls G1-S transition during corneal epithelial cell cycle progression

PURPOSE

Previously we demonstrated that the secreted Ly-6/uPAR related protein-1 (SLURP1), abundantly expressed in the corneal epithelium (CE) and secreted into the tear fluid, serves as an anti-inflammatory and anti-angiogenic molecule. Here we describe the Slurp1-null (Slurp1X-/-) mouse corneal phenotype for the first time.

METHODS

We compared the 10-week-old wild type (WT) and Slurp1X-/- mouse corneal (i) histology by hematoxylin-eosin and periodic acid-Schiff's reagent staining, (ii) cell proliferation by immunostaining for Ki67, (iii) cell adhesion molecules by immunostaining for desmosomal and tight junction proteins, (iv) barrier function by fluorescein staining and (v) wound-healing by epithelial debridement. Effect of SLURP1 on cell cycle was quantified in human corneal limbal epithelial (HCLE) cells engineered to express SLURP1 (HCLE-SLURP1).

RESULTS

WT and Slurp1X-/- corneal histology was largely comparable, other than a few loosely attached superficial cells in Slurp1X-/- corneas. Compared with the WT, Slurp1X-/- corneas displayed (i) increase in Ki67+ cells, (ii) altered expression and/or localization of tight junction proteins Tjp1 and Pard3, and desmosomal Dsp, (iii) increased superficial fragility and (iv) slower CE wound healing. HCLE-SLURP1 cells displayed (i) decrease in Ki67+ cells, (ii) increased cell number doubling time, (iii) stalling in G1-S phase transition during cell cycle, and (iv) downregulation of cyclins CCNE and CCND1/D2, cyclin-dependent kinases CDK4 and CDK6, and upregulation of CDK inhibitor p15/CDKN2B.

CONCLUSIONS

Collectively, these results elucidate that Slurp1X-/- CE cell homeostasis is altered and suggest that SLURP1 is a pro-differentiation factor that stalls G1-S transition during cell cycle progression by downregulating cyclins and upregulating p15/CDKN2B.

Transcriptome Analysis of Pterygium and Pinguecula Reveals Evidence of Genomic Instability Associated with Chronic Inflammation

Solar damage due to ultraviolet radiation (UVR) is implicated in the development of two proliferative lesions of the ocular surface: pterygium and pinguecula. Pterygium and pinguecula specimens were collected, along with adjacent healthy conjunctiva specimens. RNA was extracted and sequenced. Pairwise comparisons were made of differentially expressed genes (DEGs). Computational methods were used for analysis. Transcripts from 18,630 genes were identified. Comparison of two subgroups of pterygium specimens uncovered evidence of genomic instability associated with inflammation and the immune response; these changes were also observed in pinguecula, but to a lesser extent. Among the top DEGs were four genes encoding tumor suppressors that were downregulated in pterygium: C10orf90, RARRES1, DMBT1 and SCGB3A1; C10orf90 and RARRES1 were also downregulated in pinguecula. Ingenuity Pathway Analysis overwhelmingly linked DEGs to cancer for both lesions; however, both lesions are clearly still benign, as evidenced by the expression of other genes indicating their well-differentiated and non-invasive character. Pathways for epithelial cell proliferation were identified that distinguish the two lesions, as well as genes encoding specific pathway components. Upregulated DEGs common to both lesions, including KRT9 and TRPV3, provide a further insight into pathophysiology. Our findings suggest that pterygium and pinguecula, while benign lesions, are both on the pathological pathway towards neoplastic transformation.

MUC1: Structure, Function, and Clinic Application in Epithelial Cancers

The transmembrane glycoprotein mucin 1 (MUC1) is a mucin family member that has different functions in normal and cancer cells. Owing to its structural and biochemical properties, MUC1 can act as a lubricant, moisturizer, and physical barrier in normal cells. However, in cancer cells, MUC1 often undergoes aberrant glycosylation and overexpression. It is involved in cancer invasion, metastasis, angiogenesis, and apoptosis by virtue of its participation in intracellular signaling processes and the regulation of related biomolecules. This review introduces the biological structure and different roles of MUC1 in normal and cancer cells and the regulatory mechanisms governing these roles. It also evaluates current research progress and the clinical applications of MUC1 in cancer therapy based on its characteristics.