Glyco-Modification of Mucin Hydrogels to Investigate Their Immune Activity

Emergence of Snail Mucus as a Multifunctional Biogenic Material for Biomedical Applications

Snails are mollusks or shelled gastropods found everywhere on Earth. Biologically, snail mucus can be described as a multifunctional natural polymeric gel with adhesive and antimicrobial properties, rendering it a promising ingredient in pharmaceutics and biomedical applications. These properties have been exploited in cosmetics and dermatology applications over the last few years. However, the exploration of snail mucus for other biomedical applications, e.g., wound healing and drug delivery, remains new and very promising. Against this backdrop, this review explores the potential of snail mucus for a wide spectrum of biomedical applications, ranging from wound healing to cancer treatment to regenerative engineering. It will be emphasized how its application in wound healing has gained traction owing to its antimicrobial and anti-inflammatory properties. Beyond wound care, snail mucus has been investigated as a drug delivery vehicle in treating diabetes and targeted cancer therapies. While further extensive research and clinical trials are needed to solidify the efficacy of snail mucus as a biomaterial, this review will shed light on the prospect of using snail mucus alone and in combination with other natural or synthetic biopolymers as soft materials for widespread biomedical applications. STATEMENT OF SIGNIFICANCE: Exploring snail mucus as a biomaterial across various fields, including oncology, drug delivery, cosmetics, antibacterial properties, and wound healing, presents a fascinating avenue for zootherapy research. This review provides an in-depth account of the recent developments in snail mucus' potential for a broad spectrum of biomedical applications, from wound healing to cancer treatment and regenerative engineering. It highlights the growing interest in mucus' use in wound healing, attributed to its antimicrobial and anti-inflammatory properties. It has also been investigated as a drug delivery vehicle for diabetes treatment and targeted cancer therapies. The impact of such research is significant, as it could lead to the creation of innovative biomaterials for a wide range of applications, revolutionizing the field of biomaterials.

Structural determinants of mucins in influenza virus inhibition: The role of sialylated glycans and molecular size

Mucins are heavily glycosylated proteins that play a crucial role in protecting mucosal surfaces against pathogens, including influenza viruses. This study investigates the antiviral properties of bovine submaxillary mucins (BSM) as a model for oral mucins against the influenza virus (A/H3N2 subtype), focusing on glycan composition and mucin size. BSM was purified, and characterized by proteomic and glycomic analysis and its antiviral efficacy was assessed after selective removal of sialic acids, N-glycans, or all glycans via enzymatic and chemical treatments. We employed virus binding and inhibition assays, including microscale thermophoresis (MST) and hemagglutination inhibition (HAI), to characterize processed mucins for structure activity correlations. Removal of sialic acids reduced BSM's antiviral activity by over 10-fold, while complete glycan removal abolished it entirely, highlighting sialylated O-glycans as critical for viral inhibition. N-glycan removal had minimal impact on antiviral efficacy. A size-dependent antiviral effect was observed: smaller mucin fragments (∼50 and 330 kDa), which retained comparable O-glycosylation patterns, showed significantly reduced inhibition and viral binding affinity several orders of magnitude below intact BSM. These findings underscore the importance of mucin size and sialylated O-glycans in antiviral defense mechanisms against influenza.

Galacto-oligosaccharides regulate intestinal mucosal sialylation to counteract antibiotic-induced mucin dysbiosis

Intestinal mucin offers a physical barrier to maintain host-commensal homeostasis. Glycosylation is essential for the appropriate functioning of mucin. Galacto-oligosaccharides (GOS) have been used as a prebiotic with proven intestinal benefits, while their regulatory mechanism on mucin remains unclear. This study employed an antibiotic-treated rat model to mimic gut dysbiosis and attempted to restore gut dysbiosis using GOS. The gut microbiome and intestinal mucus O-glycosylations (O-glycans) in the small intestine were profiled by high-throughput sequencing and glycomics. The sialic acid phenotype at the end of O-glycans was further validated with lectin staining. Expressions of key enzymes in sialic acid metabolism and epithelial morphology were determined as well. Antibiotics significantly increased the relative abundance of Escherichia/Shigella and decreased the relative abundance of Lactobacillus. This was accompanied by decreased microbial sialidase activity and increased sialic acid in the digesta, as well as an increase in epithelial sialidase activity. Analysis of key sialylation enzymes showed the upregulation of α 2,6 sialylation (e.g. ST6GALNACs) and downregulation of α 2,3 sialylation (e.g. ST3GALs) after antibiotic treatment. The glycomics results revealed that antibiotics increased core 4 and α 2,6 sialylated O-glycans and decreased core 1, core 3 and α 2,3 sialylated O-glycans in the intestinal mucus of rats, which was further confirmed by lectin staining. Intestinal histology results demonstrated that antibiotic treatment led to the dysbiosis of intestinal mucus homeostasis. To further test the role of microbiota in regulating intestinal mucus sialylation, we supplemented GOS with antibiotics. The results showed that GOS reversed the effects of antibiotics on the gut microbiota and intestinal mucus O-glycans (especially sialylated O-glycans), characterized by an increase of Lactobacillus and α 2,3 sialylated O-glycans and a decrease of Escherichia/Shigella and α 2,6 sialylated O-glycans. What's more, GOS reduced the stimulation of the intestinal mucosa by lipopolysaccharide (LPS) by increasing α 2,3 sialylated intestinal alkaline phosphatase (IAP) to enhance IAP activity, thereby restoring intestinal mucus homeostasis. Overall, GOS counteracts antibiotic-induced mucin deficiency by remedying the gut ecology and changing the mucin sialylation pattern, as reflected by the increase of α 2,3 sialylated O-glycans and the decrease of α 2,6 sialylated O-glycans.

Preserving the Immune-Privileged Niche of the Nucleus Pulposus: Safeguarding Intervertebral Discs from Degeneration after Discectomy with Synthetic Mucin Hydrogel Injection

Intervertebral disc (IVD) herniation is a prevalent spinal disorder, often necessitating surgical intervention such as microdiscectomy for symptomatic relief and nerve decompression. IVDs comprise a gel-like nucleus pulposus (NP) encased by an annulus fibrosus (AF), and their avascular nature renders them immune-privileged. Microdiscectomy exposes the residual NP to the immune system, precipitating an immune cell infiltration and attack that exacerbates IVD degeneration. While many efforts in the tissue engineering field are directed toward IVD regeneration, the inherently limited regenerative capacity due to the avascular and low-cellularity nature of the disc and the challenging mechanical environment of the spine often impedes success. This study, aiming to prevent IVD degeneration post-microdiscectomy, utilizes mucin-derived gels (Muc-gels) that form a gel at the surgical site, inspired by the natural mucin coating on living organisms to evade immune reorganization. It is shown that type I macrophages are present in severely degenerated human discs. Encapsulating IVDs within Muc-gels prevents fibrous encapsulation and macrophage infiltration in a mouse subcutaneous model. The injection of Muc-gels prevents IVD degeneration in a rat tail IVD degeneration model up to 24 weeks post-operation. Mechanistic investigations indicate that Muc-gels attenuate immune cell infiltration into NPs, offering durable protection against immune attack post-microdiscectomy.

Modifying Naturally Occurring, Nonmammalian-Sourced Biopolymers for Biomedical Applications

Natural biopolymers have a rich history, with many uses across the fields of healthcare and medicine, including formulations for wound dressings, surgical implants, tissue culture substrates, and drug delivery vehicles. Yet, synthetic-based materials have been more successful in translation due to precise control and regulation achievable during manufacturing. However, there is a renewed interest in natural biopolymers, which offer a diverse landscape of architecture, sustainable sourcing, functional groups, and properties that synthetic counterparts cannot fully replicate as processing and sourcing of these materials has improved. Proteins and polysaccharides derived from various sources (crustaceans, plants, insects, etc.) are highlighted in this review. We discuss the common types of polysaccharide and protein biopolymers used in healthcare and medicine, highlighting methods and strategies to alter structures and intra- and interchain interactions to engineer specific functions, products, or materials. We focus on biopolymers obtained from natural, nonmammalian sources, including silk fibroins, alginates, chitosans, chitins, mucins, keratins, and resilins, while discussing strategies to improve upon their innate properties and sourcing standardization to expand their clinical uses and relevance. Emphasis will be placed on methods that preserve the structural integrity and native biological functions of the biopolymers and their makers. We will conclude by discussing the untapped potential of new technologies to manipulate native biopolymers while controlling their secondary and tertiary structures, offering a perspective on advancing biopolymer utility in novel applications within biomedical engineering, advanced manufacturing, and tissue engineering.

Hydrogel-based immunoregulation of macrophages for tissue repair and regeneration

The rational design of hydrogel materials to modulate the immune microenvironment has emerged as a pivotal approach in expediting tissue repair and regeneration. Within the immune microenvironment, an array of immune cells exists, with macrophages gaining prominence in the field of tissue repair and regeneration due to their roles in cytokine regulation to promote regeneration, maintain tissue homeostasis, and facilitate repair. Macrophages can be categorized into two types: classically activated M1 (pro-inflammatory) and alternatively activated M2 (anti-inflammatory and pro-repair). By regulating the physical and chemical properties of hydrogels, the phenotypic transformation and cell behavior of macrophages can be effectively controlled, thereby promoting tissue regeneration and repair. A full understanding of the interaction between hydrogels and macrophages can provide new ideas and methods for future tissue engineering and clinical treatment. Therefore, this paper reviews the effects of hydrogel components, hardness, pore size, and surface morphology on cell behaviors such as macrophage proliferation, migration, and phenotypic polarization, and explores the application of hydrogels based on macrophage immune regulation in skin, bone, cartilage, and nerve tissue repair. Finally, the challenges and future prospects of macrophage-based immunomodulatory hydrogels are discussed.

Covalently grafted human serum albumin coating mitigates the foreign body response against silicone implants in mice

Implantable biomaterials and biosensors are integral components of modern medical systems but often encounter hindrances due to the foreign body response (FBR). Herein, we report an albumin coating strategy aimed at addressing this challenge. Using a facile and scalable silane coupling strategy, human serum albumin (HSA) is covalently grafted to the surface of polydimethylsiloxane (PDMS) implants. This covalently grafted albumin coating remains stable and resistant to displacement by other proteins. Notably, the PDMS with covalently grafted HSA strongly resists the fibrotic capsule formation following a 180-day subcutaneous implantation in C57BL/6 mice. Furthermore, the albumin coating led to reduced recruitment of macrophages and triggered a mild immune activation pattern. Exploration of albumin coatings sourced from various mammalian species has shown that only HSA exhibited a promising anti-FBR effect. The albumin coating method reported here holds the potential to improve and extend the function of silicone-based implants by mitigating the host responses to subcutaneously implanted biomaterials.

DNA Crosslinked Mucin Hydrogels Allow for On-Demand Gel Disintegration and Triggered Particle Release

Whereas hydrogels created from synthetic polymers offer a high level of control over their stability and mechanical properties, their biomedical activity is typically limited. In contrast, biopolymers have evolved over billions of years to integrate a broad range of functionalities into a single design. Thus, biopolymeric hydrogels can show remarkable capabilities such as regulatory behavior, selective barrier properties, or antimicrobial effects. Still, despite their widespread use in numerous biomedical applications, achieving a meticulous control over the physical properties of macroscopic biopolymeric networks remains a challenge. Here, a macroscopic, DNA-crosslinked mucin hydrogel with tunable viscoelastic properties that responds to two types of triggers: temperature alterations and DNA displacement strands, is presented. As confirmed with bulk rheology and single particle tracking, the hybridized base pairs governing the stability of the hydrogel can be opened, thus allowing for a precise control over the hydrogel stiffness and even enabling a full gel-to-sol transition. As those DNA-crosslinked mucin hydrogels possess tunable mechanical properties and can be disintegrated on demand, they can not only be considered for controlled cargo release but may also serve as a role model for the development of smart biomedical materials in applications such as tissue engineering and wound healing.

Glycoprotein Injectable Hydrogels Promote Accelerated Bone Regeneration through Angiogenesis and Innervation

Glycoproteins are gaining prominence as multifunctional biomaterials. The study reports development of glycoprotein mucin as biomaterial promoting bone regeneration. Mucin 1 deletion has resulted in stiffer femoral bones with scarce presence of osteoblasts in trabecular linings and its role has been established in determining bone mass and mineralization. Limited information about its structure limits its processability, exploration as biomaterial, which is discussed in this study. The role of mucin in ECM (extracellular cellular matrix) formation validated by RNA sequencing analysis of human bone marrow derived mesenchymal stem cells is reported. The structure and stability of mucins is dependent on the presence of glycans in its structure. A thermosensitive hydrogel acquired from thermosensitive Poly (N-isopropyl acrylamide)-(PNIPAM) modified mucin and collagen is developed. The hydrogel demonstrates porous structure and mechanical strength. Newly formed bone tissue is observed at 8 weeks post-implantation in the hydrogel treated groups. The formation of blood vessels, nerves, and bone is observed with upregulation of angiopoietin (ANG), neurofilament heavy chain (NF-H), and osteoadherin (OSAD) or osteocalcin (OCN) respectively in rat calvarial defects. The outcome demonstrates that the thermosensitive injectable hydrogel accelerates repair and healing in calvarial bone defects making it a promising biodegradable biomaterial capable of regenerating bone by promoting angiogenesis and innervation.

A Mucin-Based Bio-Ink for 3D Printing of Objects with Anti-Biofouling Properties

With its potential to revolutionize the field of personalized medicine by producing customized medical devices and constructs for tissue engineering at low costs, 3D printing has emerged as a highly promising technology. Recent advancements have sparked increasing interest in the printing of biopolymeric hydrogels. However, owing to the limited printability of those soft materials, the lack of variability in available bio-inks remains a major challenge. In this study, a novel bio-ink is developed based on functionalized mucin-a glycoprotein that exhibits a multitude of biomedically interesting properties such as immunomodulating activity and strong anti-biofouling behavior. To achieve sufficient printability of the mucin-based ink, its rheological properties are tuned by incorporating Laponite XLG as a stabilizing agent. It is shown that cured objects generated from this novel bio-ink exhibit mechanical properties partially similar to that of soft tissue, show strong anti-biofouling properties, good biocompatibility, tunable cell adhesion, and immunomodulating behavior. The presented findings suggest that this 3D printable bio-ink has a great potential for a wide range of biomedical applications, including tissue engineering, wound healing, and soft robotics.

Glycoproteins as a Platform for Making Proton-Conductive Free-Standing Biopolymers

Biopolymers are an attractive environmentally friendly alternative to common synthetic polymers, whereas primarily proteins and polysaccharides are the biomacromolecules that are used for making the biopolymer. Due to the breadth of side chains of such biomacromolecules capable of participating in hydrogen bonding, proteins and polysaccharide biopolymers were also used for the making of proton-conductive biopolymers. Here, we introduce a new platform for combining the merits of both proteins and polysaccharides while using a glycosylated protein for making the biopolymer. We use mucin as our starting point, whereas being a waste of the food industry, it is a highly available and low-cost glycoprotein. We show how we can use different chemical strategies to target either the glycan part or specific amino acids for both crosslinking between the different glycoproteins, thus making a free-standing biopolymer, as well as for introducing superior proton conductivity properties to the formed biopolymer. The resultant proton-conductive soft biopolymer is an appealing candidate for any soft bioelectronic application.

Development of Tofacitinib Loaded pH-Responsive Chitosan/Mucin Based Hydrogel Microparticles: In-Vitro Characterization and Toxicological Screening

Tofacitinib is an antirheumatic drug characterized by a short half-life and poor permeability, which necessitates the development of sustained release formulation with enhanced permeability potential. To achieve this goal, the free radical polymerization technique was employed to develop mucin/chitosan copolymer methacrylic acid (MU-CHI-Co-Poly (MAA))-based hydrogel microparticles. The developed hydrogel microparticles were characterized for EDX, FTIR, DSC, TGA, X-ray diffraction, SEM, drug loading; equilibrium swelling (%), in vitro drug release, sol–gel (%) studies, size and zeta potential, permeation, anti-arthritic activities, and acute oral toxicity studies. FTIR studies revealed the incorporation of the ingredients into the polymeric network, while EDX studies depicted the successful loading of tofacitinib into the network. The thermal analysis confirmed the heat stability of the system. SEM analysis displayed the porous structure of the hydrogels. Gel fraction showed an increasing tendency (74–98%) upon increasing the concentrations of the formulation ingredients. Formulations coated with Eudragit (2% w/w) and sodium lauryl sulfate (1% w/v) showed increased permeability. The formulations equilibrium swelling (%) increased (78–93%) at pH 7.4. Maximum drug loading and release (%) of (55.62–80.52%) and (78.02–90.56%), respectively, were noticed at pH 7.4, where the developed microparticles followed zero-order kinetics with case II transport. Anti-inflammatory studies revealed a significant dose-dependent decrease in paw edema in the rats. Oral toxicity studies confirmed the biocompatibility and non-toxicity of the formulated network. Thus, the developed pH-responsive hydrogel microparticles seem to have the potential to enhance permeability and control the delivery of tofacitinib for the management of rheumatoid arthritis.

Early osteoimmunomodulation by mucin hydrogels augments the healing and revascularization of rat critical-size calvarial bone defects

The design principle of osteogenic bone grafts has shifted from immunological inertness to limiting foreign body response to combined osteoimmunomodulatory activity to promote high-quality endogenous bone regeneration. Recently developed immunomodulatory mucin hydrogels have been shown to elicit very low complement activation and suppress macrophage release and activation after implantation in vivo. However, their immunoregulatory activity has not yet been studied in the context of tissue repair. Herein, we synthesized mucin-monetite composite materials and investigated their early osteoimmunomodulation using a critical-size rat bone defect model. We demonstrated that the composites can polarize macrophages towards the M2 phenotype at weeks 1 and 2. The early osteoimmunomodulation enhanced early osteogenesis and angiogenesis and ultimately promoted fracture healing and engraftment (revascularization of the host vasculature) at weeks 6 and 12. Overall, we demonstrated the applicability of mucin-based immunomodulatory biomaterials to enhance tissue repair in tissue engineering and regenerative medicine.

Recombinant mucin biotechnology and engineering

Mucins represent a largely untapped class of polymeric building block for biomaterials, therapeutics, and other biotechnology. Because the mucin polymer backbone is genetically encoded, sequence-specific mucins with defined physical and biochemical properties can be fabricated using recombinant technologies. The pendent O-glycans of mucins are increasingly implicated in immunomodulation, suppression of pathogen virulence, and other biochemical activities. Recent advances in engineered cell production systems are enabling the scalable synthesis of recombinant mucins with precisely tuned glycan side chains, offering exciting possibilities to tune the biological functionality of mucin-based products. New metabolic and chemoenzymatic strategies enable further tuning and functionalization of mucin O-glycans, opening new possibilities to expand the chemical diversity and functionality of mucin building blocks. In this review, we discuss these advances, and the opportunities for engineered mucins in biomedical applications ranging from in vitro models to therapeutics.

The Pathology of Asthma: What Is Obstructing Our View?

Despite the advent of sophisticated and efficient new biologics to treat inflammation in asthma, the disease persists. Even following treatment, many patients still experience the well-known symptoms of wheezing, shortness of breath, and coughing. What are we missing? Here we examine the evidence that mucus plugs contribute to a substantial portion of disease, not only by physically obstructing the airways but also by perpetuating inflammation. In this way, mucus plugs may act as an immunogenic stimulus even in the absence of allergen or with the use of current therapeutics. The alterations of several parameters of mucus biology, driven by type 2 inflammation, result in sticky and tenacious sputum, which represents a potent threat, first due to the difficulties in expectoration and second by acting as a platform for viral, bacterial, or fungal colonization that allows exacerbations. Therefore, in this way, mucus plugs are an overlooked but critical feature of asthmatic airway disease.

Portable Quartz Crystal Resonator Sensor for Characterising the Gelation Kinetics and Viscoelastic Properties of Hydrogels

Hydrogel biomaterials have found use in various biomedical applications partly due to their biocompatibility and tuneable viscoelastic properties. The ideal rheological properties of hydrogels depend highly on the application and should be considered early in the design process. Rheometry is the most common method to study the viscoelastic properties of hydrogels. However, rheometers occupy much space and are costly instruments. On the other hand, quartz crystal resonators (QCRs) are devices that can be used as low-cost, small, and accurate sensors to measure the viscoelastic properties of fluids. For this reason, we explore the capabilities of a low-cost and compact QCR sensor to sense and characterise the gelation process of hydrogels while using a low sample amount and by sensing two different crosslink reactions: covalent bonds and divalent ions. The gelation of covalently crosslinked mucin hydrogels and physically crosslinked alginate hydrogels could be monitored using the sensor, clearly distinguishing the effect of several parameters affecting the viscoelastic properties of hydrogels, including crosslinking chemistry, polymer concentrations, and crosslinker concentrations. QCR sensors offer an economical and portable alternative method to characterise changes in a hydrogel material's viscous properties to contribute to this type of material design, thus providing a novel approach.

Synthetic Mucin Gels with Self-Healing Properties Augment Lubricity and Inhibit HIV-1 and HSV-2 Transmission

Mucus is a self-healing gel that lubricates the moist epithelium and provides protection against viruses by binding to viruses smaller than the gel's mesh size and removing them from the mucosal surface by active mucus turnover. As the primary nonaqueous components of mucus (≈0.2%-5%, wt/v), mucins are critical to this function because the dense arrangement of mucin glycans allows multivalence of binding. Following nature's example, bovine submaxillary mucins (BSMs) are assembled into "mucus-like" gels (5%, wt/v) by dynamic covalent crosslinking reactions. The gels exhibit transient liquefaction under high shear strain and immediate self-healing behavior. This study shows that these material properties are essential to provide lubricity. The gels efficiently reduce human immunodeficiency virus type 1 (HIV-1) and genital herpes virus type 2 (HSV-2) infectivity for various types of cells. In contrast, simple mucin solutions, which lack the structural makeup, inhibit HIV-1 significantly less and do not inhibit HSV-2. Mechanistically, the prophylaxis of HIV-1 infection by BSM gels is found to be that the gels trap HIV-1 by binding to the envelope glycoprotein gp120 and suppress cytokine production during viral exposure. Therefore, the authors believe the gels are promising for further development as personal lubricants that can limit viral transmission.

Engineering Surfaces with Immune Modulating Properties of Mucin Hydrogels

Hydrogels of cross-linked mucin glycoproteins (Muc-gel) have shown strong immune-modulating properties toward macrophages in vitro, which are translated in vivo by the dampening of the foreign body response to implantation in mice. Beyond mucin hydrogels, other biomaterials such as sensors, electrodes, and other long-term implants would also benefit from such immune-modulating properties. In this work, we aimed to transfer the bioactivity observed for three-dimensional Muc-gels to the surface of two model materials by immobilizing mucin into thin films (Muc-film) using covalent layer-by-layer assembly. We tested how the surface immobilization of mucins affects macrophage responses compared to Muc-gels. We showed that Muc-films on soft polyacrylamide gels mimic Muc-gel in their modulation of macrophage responses with activated gene expression of inflammatory cytokines on day 1 and then dampening them on day 3. Also, the markers of polarized macrophages, M1 and M2, were expressed at the same level for macrophages on Muc-film-coated soft polyacrylamide gels and Muc-gel. In contrast, Muc-film-coated hard polystyrene led to a different macrophage response compared to Muc-gel, having no activated expression of inflammatory cytokines and a different M1 marker expression. This suggested that the substrate mechanical properties and mucin molecular configuration determined by substrate-mucin interactions affect mucin immune-modulating properties. We conclude that mucin immune-modulating properties can be transferred to materials by mucin surface immobilization but will be dependent on the substrate chemical and mechanical properties.

Covalently Crosslinked Pig Gastric Mucin Hydrogels Prepared by Radical-based Chain-Growth and Thiol-ene Mechanisms

Mucin, a high molecular mass hydrophilic glycoprotein, is the main component of mucus that coats every wet epithelium in animals. It is thus intrinsically biocompatible, and with its protein backbone and the o-glycosidic bound oligosaccharides, it contains a plethora of functional groups which can be used for further chemical modifications. In this study we introduce and compare chain-growth and step-growth (thiol-ene) free-radical crosslinked hydrogels prepared from commercially available pig gastric mucin (PGM) as cost-efficient and easily accessible alternative to the more broadly applied bovine submaxillary gland mucin (BSM). For this, PGM was functionalized with photoreactive acrylate groups or allylether-moieties, respectively. Whereas homopolymerization of acrylate functionalized polymers was performed, for thiol-ene crosslinking, the allylether functionalized PGM was cross-linked with thiol-functionalized hyaluronic acid (HA). Morphology, mechanical properties, and cell compatibility of both kinds of PGM hydrogels are characterized and compared. Furthermore, the biocompatibility of these hydrogels could be evaluated in cell culture experiments. This article is protected by copyright. All rights reserved.

Advancing Discovery of Snail Mucins Function and Application

Mucins are a highly glycosylated protein family that are secreted by animals for adhesion, hydration, lubrication, and other functions. Despite their ubiquity, animal mucins are largely uncharacterized. Snails produce mucin proteins in their mucous for a wide array of biological functions, including microbial protection, adhesion and lubrication. Recently, snail mucins have also become a lucrative source of innovation with wide ranging applications across chemistry, biology, biotechnology, and biomedicine. Specifically, snail mucuses have been applied as skin care products, wound healing agents, surgical glues, and to combat gastric ulcers. Recent advances in integrated omics (genomic, transcriptomic, proteomic, glycomic) technologies have improved the characterization of gastropod mucins, increasing the generation of novel biomaterials. This perspective describes the current research on secreted snail mucus, highlighting the potential of this biopolymer, and also outlines a research strategy to fulfill the unmet need of examining the hierarchical structures that lead to the enormous biological and chemical diversity of snail mucus genes.

Modeling Airway Dysfunction in Asthma Using Synthetic Mucus Biomaterials

As asthma worsens, occlusion of airways with mucus significantly contributes to airflow obstruction and reduced lung function. Recent evidence from clinical studies has shown mucus obtained from adults and children with asthma possesses altered mucin composition. However, how these changes alter the functional properties of the mucus gel is not yet fully understood. To study this, we have engineered a synthetic mucus biomaterial to closely mimic the properties of native mucus in health and disease. We demonstrate that this model possesses comparable biophysical and transport properties to native mucus ex vivo collected from human subjects and in vitro isolated from human airway epithelial (HAE) tissue cultures. We found by systematically varying mucin composition that mucus gel viscoelasticity is enhanced when predominantly composed of mucin 5AC (MUC5AC), as is observed in asthma. As a result, asthma-like synthetic mucus gels are more slowly transported on the surface of HAE tissue cultures and at a similar rate to native mucus produced by HAE cultures stimulated with type 2 cytokine IL-13, known to contribute to airway inflammation and MUC5AC hypersecretion in asthma. We also discovered that the barrier function of asthma-like synthetic mucus toward influenza A virus was impaired as evidenced by the increased frequency of infection in MUC5AC-rich hydrogel-coated HAE cultures. Together, this work establishes a biomaterial-based approach to understand airway dysfunction in asthma and related muco-obstructive lung diseases.

Loading of Beclomethasone in Liposomes and Hyalurosomes Improved with Mucin as Effective Approach to Counteract the Oxidative Stress Generated by Cigarette Smoke Extract

In this work beclomethasone dipropionate was loaded into liposomes and hyalurosomes modified with mucin to improve the ability of the payload to counteract the oxidative stress and involved damages caused by cigarette smoke in the airway. The vesicles were prepared by dispersing all components in the appropriate vehicle and sonicating them, thus avoiding the use of organic solvents. Unilamellar and bilamellar vesicles small in size (~117 nm), homogeneously dispersed (polydispersity index lower than 0.22) and negatively charged (~−11 mV), were obtained. Moreover, these vesicle dispersions were stable for five months at room temperature (~25 °C). In vitro studies performed using the Next Generation Impactor confirmed the suitability of the formulations to be nebulized as they were capable of reaching the last stages of the impactor that mimic the deeper airways, thus improving the deposition of beclomethasone in the target site. Further, biocompatibility studies performed by using 16HBE bronchial epithelial cells confirmed the high biocompatibility and safety of all the vesicles. Among the tested formulations, only mucin-hyalurosomes were capable of effectively counteracting the production of reactive oxygen species (ROS) induced by cigarette smoke extract, suggesting that this formulation may represent a promising tool to reduce the damaging effects of cigarette smoke in the lung tissues, thus reducing the pathogenesis of cigarette smoke-associated diseases such as chronic obstructive pulmonary disease, emphysema, and cancer.

N-Glycan Modifications with Negative Charge in a Natural Polymer Mucin from Bovine Submaxillary Glands, and Their Structural Role

Bovine submaxillary mucin (BSM) is a natural polymer used in biomaterial applications for its viscoelasticity, lubricity, biocompatibility, and biodegradability. N-glycans are important for mucin stability and function, but their structures have not been fully characterized, unlike that of O-glycans. In this study, BSM N-glycans were investigated using liquid chromatography-tandem mass spectrometry. The microheterogeneous structures of 32 N-glycans were identified, and the quantities (%) of each N-glycan relative to total N-glycans (100%) were obtained. The terminal N-acetylgalactosamines in 12 N-glycans (sum of relative quantities; 27.9%) were modified with mono- (10 glycans) and disulfations (2 glycans). Total concentration of all sulfated N-glycans was 6.1 pmol in BSM (20 µg), corresponding to 25.3% of all negatively charged glycans (sum of present N-glycans and reported O-glycans). No N-glycans with sialylated or phosphorylated forms were identified, and sulfate modification ions were the only negative charges in BSM N-glycans. Mucin structures, including sulfated N-glycans located in the hydrophobic terminal regions, were indicated. This is the first study to identify the structures and quantities of 12 sulfated N-glycans in natural mucins. These sulfations play important structural roles in hydration, viscoelasticity control, protection from bacterial sialidases, and polymer stabilization to support the functionality of BSM via electrostatic interactions.

Leveraging 3D Model Systems to Understand Viral Interactions with the Respiratory Mucosa

Respiratory viruses remain a significant cause of morbidity and mortality in the human population, underscoring the importance of ongoing basic research into virus-host interactions. However, many critical aspects of infection are difficult, if not impossible, to probe using standard cell lines, 2D culture formats, or even animal models. In vitro systems such as airway epithelial cultures at air-liquid interface, organoids, or 'on-chip' technologies allow interrogation in human cells and recapitulate emergent properties of the airway epithelium-the primary target for respiratory virus infection. While some of these models have been used for over thirty years, ongoing advancements in both culture techniques and analytical tools continue to provide new opportunities to investigate airway epithelial biology and viral infection phenotypes in both normal and diseased host backgrounds. Here we review these models and their application to studying respiratory viruses. Furthermore, given the ability of these systems to recapitulate the extracellular microenvironment, we evaluate their potential to serve as a platform for studies specifically addressing viral interactions at the mucosal surface and detail techniques that can be employed to expand our understanding.