Mucins and Their Role in Shaping the Functions of Mucus Barriers

Normalization of Muc5b ameliorates airway mucus plugging during persistent Pseudomonas aeruginosa infection in the CFTR-/- rat

In cystic fibrosis, the airway gel-forming mucin MUC5B accumulates in the airways, preventing clearance of pathogens like Pseudomonas aeruginosa (PA). The cystic fibrosis transmembrane conductance regulator (CFTR)-/- (KO) rat model exhibits a similar accumulation of Muc5b. Our lab has shown that increased Muc5b precipitates the development of chronic PA infection. We hypothesized that reducing Muc5b in the KO rat airway would prevent occlusive mucus plugs and development of persistent PA infection. Six-month-old KO rats received Muc5b or scramble siRNA via intratracheal instillation. Rats were then inoculated with 106 colony-forming units of mucoid P. aeruginosa isolate PAM57-15 and euthanized at 3- or 14-days post infection (dpi) to assess acute and persistent infection. At 14 dpi, Muc5b siRNA-treated KO rats had increased weight, decreased neutrophilic inflammation, and reduced mucus plugging in the small airways compared with scramble-treated KO and WT rats. These results indicate that pharmacological intervention of Muc5b reduces mucus plugging during persistent PA infection.NEW & NOTEWORTHY Although highly effective modulator therapies for cystic fibrosis (CF) have improved mucus-related outcomes of disease for people with CF, eradication of Pseudomonas aeruginosa (PA) infection has not been achieved in this population. In addition, current therapies for CF do not target mucin hypersecretion directly. Here, we show that a novel approach of normalizing airway Muc5b hypersecretion ameliorates infection-induced mucus plugging and neutrophilic inflammation during persistent PA infection in CFTR-/- rats.

Mutual adhesion of Lactobacillus spp. to intestinal cells: A review of perspectives on surface layer proteins and cell surface receptors

The bacterial ability to adhere and colonize in the gut is a key prerequisite to become a probiotic. Lactobacillus spp. surface layer proteins (SLPs) play an important role for such functions in the human body. Interestingly, all SLPs in spite of their structural variation promote adhesion and colonization. A clear understanding about the binding sites of SLPs with the host and their binding modes would help to precisely reveal the process of Lactobacillus spp.-host interaction. Therefore, in this paper, we have sorted out the Lactobacillus spp. SLPs and their adhesion sites in human intestinal cells. Such SLPs included surface layer protein, motif proteins, binding proteins and moonlighting proteins, while enterocyte adhesion receptors included transmembrane glycoproteins and extracellular matrix proteins. We also summarized the tools to assess the adhesion by Lactobacillus spp. Finally, we recommended that three-dimensional cell models and intestinal microarrays could be major tools for assessing adhesion in the future.

Breaking Down the Bottlebrush: Atomically Detailed Structural Dynamics of Mucins

Mucins, the biomolecular components of mucus, are glycoproteins that form a thick physical barrier at all tissue-air interfaces, forming a first line of defense against pathogens. Structural features of mucins and their interactions with other biomolecules remain largely unexplored due to the challenges associated with their high-resolution characterization. Combining limited mass spectrometry glycomics and protein sequencing data, we present all-atom, explicitly solvated molecular dynamics simulations of a major respiratory mucin, MUC5B. We detail key forces and degrees of freedom imposed by the extensive O-glycosylation, which imbue the canonically observed bottlebrush-like structures to these otherwise intrinsically disordered protein backbones. We compare our simulation results to static structures observed in recent scanning tunneling microscopy experiments as well as other published experimental efforts. Our work represents the demonstration of a workflow applied to a mucin example, which we hope will be employed by other groups to investigate the dynamics and interactions of other mucins, which can inform on structural details currently inaccessible to experimental techniques.

Mucoadhesion across scales: Towards the design of protein-based adhesives

Mucoadhesion is a special case of bioadhesion in which a material adheres to soft mucosal tissues. This review elucidates our current understanding of mucoadhesion across length, time, and energy scales by focusing on relevant structural features of mucus. We highlight the importance of both covalent and non-covalent interactions that can be tailored to maximize mucoadhesive interactions, particularly concerning proteinaceous mucoadhesives, which have been explored only to a limited extent so far in the literature. In particular, we highlight the importance of thiol groups, hydrophobic moieties, and charged species inherent to proteins as key levers to fine tune mucoadhesive performance. Some aspects of protein surface modification by grafting specific functional groups or coupling with polysaccharides to influence mucoadhesive performance are examined. Insights from this review offer a physicochemical roadmap to inform the development of biocompatible, protein-based mucoadhesive systems that can fulfil dual roles for both adhesion and delivery of actives, enabling the fabrication of advanced biomedical, nutritional and allied soft material technologies.

Pseudomonas aeruginosa faces a fitness trade-off between mucosal colonization and antibiotic tolerance during airway infection

Pseudomonas aeruginosa frequently causes antibiotic-recalcitrant pneumonia, but the mechanisms driving its adaptation during human infections remain unclear. To reveal the selective pressures and adaptation strategies at the mucosal surface, here we investigated P. aeruginosa growth and antibiotic tolerance in tissue-engineered airways by transposon insertion sequencing (Tn-seq). Metabolic modelling based on Tn-seq data revealed the nutritional requirements for P. aeruginosa growth, highlighting reliance on glucose and lactate and varying requirements for amino acid biosynthesis. Tn-seq also revealed selection against biofilm formation during mucosal growth in the absence of antibiotics. Live imaging in engineered organoids showed that biofilm-dwelling cells remained sessile while colonizing the mucosal surface, limiting nutrient foraging and reduced growth. Conversely, biofilm formation increased antibiotic tolerance at the mucosal surface. Moreover, mutants with exacerbated biofilm phenotypes protected less tolerant but more cytotoxic strains, contributing to phenotypic heterogeneity. P. aeruginosa must therefore navigate conflicting physical and biological selective pressures to establish chronic infections.

The Intersection of the Oral Microbiome and Salivary Metabolites in Head and Neck Cancer: From Diagnosis to Treatment

Head and neck cancers (HNCs) are the seventh most common cancer worldwide, accounting for 4-5% of all malignancies. Salivary metabolites, which serve as key metabolic intermediates and cell-signalling molecules, are emerging as potential diagnostic biomarkers for HNC. While current research has largely concentrated on these metabolites as biomarkers, a critical gap remains in understanding their fluctuations before and after treatment, as well as their involvement in oral side effects. Recent studies emphasise the role of the oral microbiome and its metabolic activity in cancer progression and treatment efficacy by bacterial metabolites and virulence factors. Oral bacteria, such as P. gingivalis and F. nucleatum, contribute to a pro-inflammatory environment that promotes tumour growth. Additionally, F. nucleatum enhances its virulence through flagellar assembly and iron transport mechanisms, facilitating tumour invasion and survival. Moreover, alterations in the oral microbiome can influence chemotherapy efficacy and toxicity through the microbiota-host irinotecan axis, highlighting the complex interplay between microbial communities and therapeutic outcomes. Salivary metabolite profiles are influenced by factors such as gender, methods, and patient habits like smoking-a major risk factor for HNC. Radiotherapy (RT), a key treatment for HNC, often causes side effects such as xerostomia, oral mucositis, and swallowing difficulties which impact survivors' quality of life. Intensity-modulated radiotherapy (IMRT) aims to improve treatment outcomes and minimise side effects but can still lead to significant salivary gland dysfunction and associated complications. This review underscores the microbial and host interactions affecting salivary metabolites and their implications for cancer treatment and patient outcomes.

Modeling Cystic Fibrosis Chronic Infection Using Engineered Mucus-like Hydrogels

The airway mucus of patients with cystic fibrosis has altered properties, which create a microenvironment primed for chronic infections that are difficult to treat. These complex polymicrobial airway infections and corresponding mammalian-microbe interactions are challenging to model in vitro. Here, we report the development of mucus-like hydrogels with varied compositions and viscoelastic properties reflecting differences between healthy and cystic fibrosis airway mucus. Models of cystic fibrosis and healthy airway microenvironments were created by combining the hydrogels with relevant pathogens, human bronchial epithelial cells, and an antibiotic. Notably, pathogen antibiotic resistance was not solely dependent on the altered properties of the mucus-like hydrogels but was also influenced by culture conditions including microbe species, monomicrobial or polymicrobial culture, and the presence of epithelial cells. Additionally, the cystic fibrosis airway model showed the ability to mimic features characteristic of chronic cystic fibrosis airway infections including sustained polymicrobial growth and increased antibiotic tolerance.

Scalable Extraction of Airway Mucins from Porcine Trachea

Mucins are a major component of the innate defense system in the airways and their biological functions are important to consider in pulmonary disease research. However, the available mucus models for basic research relevant to the lung can be difficult to acquire in sufficient quantity to conduct such studies. Here, we present a new strategy to isolate airway mucins from pig trachea at the milligram to gram scale for use in pulmonary disease research. Using this protocol, we were able to isolate mucins with minimal DNA contamination consisting of ~70% by weight protein. Compared to porcine gastric mucins extracted with the same procedure, the porcine tracheal extract possessed significantly greater O-linked glycoprotein (mucin) content. Particle tracking microrheology was used to evaluate the biophysical properties of porcine trachea mucins. We found porcine tracheal mucins formed a much tighter mesh network and possessed a significantly greater microviscosity compared to lab extracted porcine gastric mucins. In comparison to mucus harvested from human airway tissue cultures, we found porcine tracheal mucins also possessed a greater microviscosity suggesting these mucins can form into a gel-like material at physiological total solids concentrations. These studies establish an accessible means to isolate airway mucins from porcine trachea at large scale for use in pulmonary disease research.

Lateral Assessment of Mucomimetic Hydrogels to Evaluate Correlation between Microscopic and Macroscopic Properties

A major limitation in the development of mucosal drug delivery systems is the design of in vitro models that accurately reflect in vivo conditions. Traditionally, models seek to mimic characteristics of physiological mucus, often focusing on property-specific trial metrics such as rheological behavior or diffusion of a nanoparticle of interest. Despite the success of these models, translation from in vitro results to in vivo trials is limited. As a result, several authors have called for work to develop standardized testing methodologies and characterize the influence of model properties on drug delivery performance. To this end, a series of trials is performed on 12 mucomimetic hydrogels reproduced from literature. Experiments show that there is no consistent correlation between barrier performance and rheological or microstructural properties of the tested mucomimetic hydrogels. In addition, the permeability of both mucopenetrating and mucoadhesive nanoparticles is assessed, revealing non-obvious variations in barrier properties such as the relative contributions of electrostatic and hydrophobic interactions in different models. These results demonstrate the limitations of predicting mucomimetic behavior with common characterization techniques and highlight the importance of testing barrier performance with multiple nanoparticle formulations.

A Strategic Blend of Stabilizing Polymers to Control Particle Surface Charge for Enhanced Mucus Transport and Cell Binding

Mucus layers, viscoelastic gels abundant in anionic mucin glycoproteins, obstruct therapeutic delivery across all mucosal surfaces. We found that strongly positively charged nanoparticles (NPs) rapidly adsorb a mucin protein corona in mucus, impeding cell binding and uptake. To overcome this, we developed mucus-evading, cell-adhesive (MECS) NPs with variable surface charge using Flash NanoPrecipitation, by blending a neutral poly(ethylene glycol) (PEG) corona for mucus transport with a small amount, 5 wt%, of polycationic dimethylaminoethyl methacrylate (PDMAEMA) for increased cell targeting. In vitro experiments confirmed rapid mucus penetration and binding to epithelial cells by MECS NPs, suggesting a breakthrough in mucosal drug delivery.

Phosphatidylcholine Surface Hydration-Dependent Adsorption to Mucin Enhances Intestinal Mucus Barrier Function

The crucial role of zwitterionic phosphatidylcholines (PC) within mucus gel is essential for maintaining intestinal homeostasis, while the underlying mechanism remains incompletely understood. Herein, we compared the dynamic interfacial adsorption behavior of saturated dipalmitoylphosphatidylcholine (DPPC) and unsaturated dioleoylphosphatidylcholine (DOPC) to intestinal mucin and their impact on the intestinal mucus barrier function. Results of quartz crystal microbalance with dissipation showed that the highly surface-hydrated DPPC vesicles exhibited significantly faster and more extensive adsorption to purified intestinal mucin than the slightly surface-hydrated DOPC vesicles. Utilizing an intestinal Caco-2/HT29-MTX coculture model, we observed that DPPC vesicles adsorbed much more to the mucus gel compared to DOPC vesicles. Additionally, DPPC vesicle adsorption displayed increased wetting, and converse for DOPC vesicles. Interestingly, both of them exhibited nearly the same protective effects against cell injury induced by peptic-tryptic digests of gliadin (PTG). The partial mechanism involved the binding of PTG to DPPC and DOPC within the mucus gel, thereby restricting PTG contact with the underlying epithelial cells. These findings shed light on the intricate interfacial dynamics of PC adsorption to mucin and their implications for maintaining the integrity of the intestinal mucus barrier.

Glycomacromolecules to Tailor Crowded and Heteromultivalent Glycocalyx Mimetics

The glycocalyx, a complex carbohydrate layer on cell surfaces, plays a crucial role in various biological processes. Understanding native glycocalyces' complexity is challenging due to their intricate and dynamic nature. Simplified mimics of native glycocalyces offer insights into glycocalyx functions but often lack molecular precision and fail to replicate key features of the natural analogues like molecular crowding and heteromultivalency. We introduce membrane-anchoring precision glycomacromolecules synthesized via solid-phase polymer synthesis (SPPoS) and thiol-induced, light-activated controlled radical polymerization (TIRP), enabling the construction of crowded and heteromultivalent glycocalyx mimetics with varying molecular weights and densities in giant unilamellar vesicles (GUVs). The incorporation and dynamics of glycomacromolecules in the GUVs are examined via microscopy and fluorescence correlation spectroscopy (FCS) and studies on lectin-carbohydrate-mediated adhesion of GUVs reveal inhibitory and promotional adhesion effects corresponding to different glycocalyx mimetic compositions, bridging the gap between synthetic models and native analogues.

A model organism pipeline provides insight into the clinical heterogeneity of TARS1 loss-of-function variants

Aminoacyl-tRNA synthetases (ARSs) are ubiquitously expressed, essential enzymes that complete the first step of protein translation: ligation of amino acids to cognate tRNAs. Genes encoding ARSs have been implicated in myriad dominant and recessive phenotypes, the latter often affecting multiple tissues but with frequent involvement of the central and peripheral nervous systems, liver, and lungs. Threonyl-tRNA synthetase (TARS1) encodes the enzyme that ligates threonine to tRNATHR in the cytoplasm. To date, TARS1 variants have been implicated in a recessive brittle hair phenotype. To better understand TARS1-related recessive phenotypes, we engineered three TARS1 missense variants at conserved residues and studied these variants in Saccharomyces cerevisiae and Caenorhabditis elegans models. This revealed two loss-of-function variants, including one hypomorphic allele (R433H). We next used R433H to study the effects of partial loss of TARS1 function in a compound heterozygous mouse model (R432H/null). This model presents with phenotypes reminiscent of patients with TARS1 variants and with distinct lung and skin defects. This study expands the potential clinical heterogeneity of TARS1-related recessive disease, which should guide future clinical and genetic evaluations of patient populations.

Mucus-Mimicking Mucin-Based Hydrogels by Tandem Chemical and Physical Crosslinking

Mucosal tissues represent a major interface between the body and the external environment and are covered by a highly hydrated mucins gel called mucus. Mucus lubricates, protects and modulates the moisture levels of the tissue and is capitalized in transmucosal drug delivery. Pharmaceutical researchers often use freshly excised animal mucosal membranes to assess mucoadhesion and muco-penetration of pharmaceutical formulations which may struggle with limited accessibility, reproducibility, and ethical questions. Aiming to develop a platform for the rationale study of the interaction of drugs and delivery systems with mucosal tissues, in this work mucus-mimicking mucin-based hydrogels are synthesized by the tandem chemical and physical crosslinking of mucin aqueous solutions. Chemical crosslinking is achieved with glutaraldehyde (0.3% and 0.75% w/v), while physical crosslinking by one or two freeze-thawing cycles. Hydrogels after one freeze-thawing cycle show water content of 97.6-98.1%, density of 0.0529-0.0648 g cm⁻3, and storage and loss moduli of ≈40-60 and ≈3-5 Pa, respectively, that resemble the properties of native gastrointestinal mucus. The mechanical stability of the hydrogels increases over the number of freeze-thawing cycles. Overall results highlight the potential of this simple, reproducible, and scalable method to produce artificial mucus-mimicking hydrogels for different applications in pharmaceutical research.

Clostridioides difficile-mucus interactions encompass shifts in gene expression, metabolism, and biofilm formation

In a healthy colon, the stratified mucus layer serves as a crucial innate immune barrier to protect the epithelium from microbes. Mucins are complex glycoproteins that serve as a nutrient source for resident microflora and can be exploited by pathogens. We aimed to understand how the intestinal pathogen, Clostridioides difficile, independently uses or manipulates mucus to its benefit, without contributions from members of the microbiota. Using a 2-D primary human intestinal epithelial cell model to generate physiologic mucus, we assessed C. difficile-mucus interactions through growth assays, RNA-Seq, biophysical characterization of mucus, and contextualized metabolic modeling. We found that host-derived mucus promotes C. difficile growth both in vitro and in an infection model. RNA-Seq revealed significant upregulation of genes related to central metabolism in response to mucus, including genes involved in sugar uptake, the Wood-Ljungdahl pathway, and the glycine cleavage system. In addition, we identified differential expression of genes related to sensing and transcriptional control. Analysis of mutants with deletions in highly upregulated genes reflected the complexity of C. difficile-mucus interactions, with potential interplay between sensing and growth. Mucus also stimulated biofilm formation in vitro, which may in turn alter the viscoelastic properties of mucus. Context-specific metabolic modeling confirmed differential metabolism and the predicted importance of enzymes related to serine and glycine catabolism with mucus. Subsequent growth experiments supported these findings, indicating mucus is an important source of serine. Our results better define responses of C. difficile to human gastrointestinal mucus and highlight flexibility in metabolism that may influence pathogenesis.

IMPORTANCE

Clostridioides difficile results in upward of 250,000 infections and 12,000 deaths annually in the United States. Community-acquired infections continue to rise, and recurrent disease is common, emphasizing a vital need to understand C. difficile pathogenesis. C. difficile undoubtedly interacts with colonic mucus, but the extent to which the pathogen can independently respond to and take advantage of this niche has not been explored extensively. Moreover, the metabolic complexity of C. difficile remains poorly understood but likely impacts its capacity to grow and persist in the host. Here, we demonstrate that C. difficile uses native colonic mucus for growth, indicating C. difficile possesses mechanisms to exploit the mucosal niche. Furthermore, mucus induces metabolic shifts and biofilm formation in C. difficile, which has potential ramifications for intestinal colonization. Overall, our work is crucial to better understand the dynamics of C. difficile-mucus interactions in the context of the human gut.

The effect of dietary zinc and zinc physiological status on the composition of the gut microbiome in vivo

Zinc serves critical catalytic, regulatory, and structural roles. Hosts and their resident gut microbiota both require zinc, leading to competition, where a balance must be maintained. This systematic review examined evidence on dietary zinc and physiological status (zinc deficiency or high zinc/zinc overload) effects on gut microbiota. This review was conducted according to PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) guidelines and registered in PROSPERO (CRD42021250566). PubMed, Web of Science, and Scopus databases were searched for in vivo (animal) studies, resulting in eight selected studies. Study quality limitations were evaluated using the SYRCLE risk of bias tool and according to ARRIVE guidelines. The results demonstrated that zinc deficiency led to inconsistent changes in α-diversity and short-chain fatty acid production but led to alterations in bacterial taxa with functions in carbohydrate metabolism, glycan metabolism, and intestinal mucin degradation. High dietary zinc/zinc overload generally resulted in either unchanged or decreased α-diversity, decreased short-chain fatty acid production, and increased bacterial metal resistance and antibiotic resistance genes. Additional studies in human and animal models are needed to further understand zinc physiological status effects on the intestinal microbiome and clarify the applicability of utilizing the gut microbiome as a potential zinc status biomarker.

Collagen/gelatin and polysaccharide complexes enhance gastric retention and mucoadhesive properties

This article has focused on collagen-gelatin, the gelation process, as well as blend interaction between collagen/gelatin with various polysaccharides to boost mucoadhesion and gastric retention. The interaction between mucoadhesive materials and mucin layers is of significant interest in the development of drug delivery systems and biomedical applications for effective targeting and prolonged time in the gastrointestinal tract. This paper reviews the current advancement and mucoadhesive properties of collagen/gelatin and different polysaccharide complexes concerning the mucin layer and interactions are briefly highlighted. Collagen/gelatin and polysaccharide blends biocompatible and biodegradable, the complex biomolecules have shown encouraging mucoadhesive properties due to their cationic nature and ability to form hydrogen bonds with mucin glycoproteins. The mucoadhesion mechanism was attributed to the electrostatic interactions between the positively charged amino (NH2) groups of blend biopolymers and the negatively charged sialic acid residues present in mucin glycoprotein. At the end of this article, the encouraging prospect of collagen/polysaccharide complex and mucin glycoprotein is highlighted.

Cerclage prevents ascending intrauterine infection in pregnant mice

BACKGROUND

The treatment for cervical insufficiency is cerclage surgery. Although cerclage is a common therapy for prevention of preterm birth, there is no consensus about its mechanism of efficacy. Previous investigators have hypothesized that cerclage prevents preterm birth by improving the cervical barrier to ascending infection. However, this hypothesis is difficult to study in human pregnancy.

OBJECTIVE

In a mouse model of ascending infection, we hypothesized that a cerclage improves the cervical barrier leading to decreased ascending intrauterine infection and inflammation. An abdominal cerclage was studied because a vaginal cerclage is not feasible in mice.

STUDY DESIGN

To perform an abdominal cerclage, laparotomy was performed on timed, pregnant C57BL/6 mice on gestational day 10 (E10). A 6-0 silk suture was placed around the cervix just below the junction of the 2 uterine horns. Sham controls received the same surgery, but no cerclage was placed. To track ascending infection nonpathogenic E coli K12 was genetically modified to express bioluminescence. On E15, bioluminescent E coli K12 (20 μL of 1×109 bacteria) was inoculated into the vagina. Whole-body bioluminescence imaging was performed 0.5 hours and 24 hours after inoculation. To assess intrauterine inflammation, pathogenic E coli K1 was used. On E15, bacterial inoculums of E coli K1 (20 μL of 1×104 bacteria) were vaginally administered. Samples of uterus, placenta, and fetal membranes were collected 24 hours after inoculation. Gene expression of inflammation-related proteins was compared between 3 groups: (1) sham control surgery + inoculation of phosphate-buffered saline (PBS), (2) sham control surgery + inoculation of E coli K1, and (3) cerclage surgery + inoculation of E coli K1.

RESULTS

Abdominal cerclage was well tolerated. No cases of preterm birth were seen following abdominal cerclage. Whole-body bioluminescent imaging performed 0.5 hours post inoculation showed a strong luminescence signal in the vaginal region of mice in both control and experimental groups indicating successful bacteria inoculation. Twenty-four hours after inoculation, bioluminescent signal was seen ascending into the uterine horns in all control mice. However, in mice with abdominal cerclages, no bioluminescent signal was seen after 24 hours. When the reproductive tissues were imaged separately in control mice, strong bioluminescence signal was detected in the placenta, fetal membranes, and uterus. Gene expression studies showed that cerclage significantly decreased the expression of inflammatory proteins induced by E coli K1 in the uterus, placenta, and fetal membranes.

CONCLUSION

In this mouse model of ascending intrauterine infection, abdominal cerclage prevented ascending infection of E coli. In addition, abdominal cerclage prevented expression of inflammatory cytokines in the uterus, placenta, and membranes of mice. The study provides evidence for a potential mechanism of cerclage success in human pregnancy.

Scale-Dependent Rheology of Synovial Fluid Lubricating Macromolecules

Synovial fluid (SF) is the complex biofluid that facilitates the exceptional lubrication of articular cartilage in joints. Its primary lubricating macromolecules, the linear polysaccharide hyaluronic acid (HA) and the mucin-like glycoprotein proteoglycan 4 (PRG4 or lubricin), interact synergistically to reduce boundary friction. However, the precise manner in which these molecules influence the rheological properties of SF remains unclear. This study aimed to elucidate this by employing confocal microscopy and multiscale rheometry to examine the microstructure and rheology of solutions containing recombinant human PRG4 (rhPRG4) and HA. Contrary to previous assumptions of an extensive HA-rhPRG4 network, it is discovered that rhPRG4 primarily forms stiff, gel-like aggregates. The properties of these aggregates, including their size and stiffness, are found to be influenced by the viscoelastic characteristics of the surrounding HA matrix. Consequently, the rheology of this system is not governed by a single length scale, but instead responds as a disordered, hierarchical network with solid-like rhPRG4 aggregates distributed throughout the continuous HA phase. These findings provide new insights into the biomechanical function of PRG4 in cartilage lubrication and may have implications in the development of HA-based therapies for joint diseases like osteoarthritis.

How Does Airway Surface Liquid Composition Vary in Different Pulmonary Diseases, and How Can We Use This Knowledge to Model Microbial Infections?

Growth environment greatly alters many facets of pathogen physiology, including pathogenesis and antimicrobial tolerance. The importance of host-mimicking environments for attaining an accurate picture of pathogen behaviour is widely recognised. Whilst this recognition has translated into the extensive development of artificial cystic fibrosis (CF) sputum medium, attempts to mimic the growth environment in other respiratory disease states have been completely neglected. The composition of the airway surface liquid (ASL) in different pulmonary diseases is far less well characterised than CF sputum, making it very difficult for researchers to model these infection environments. In this review, we discuss the components of human ASL, how different lung pathologies affect ASL composition, and how different pathogens interact with these components. This will provide researchers interested in mimicking different respiratory environments with the information necessary to design a host-mimicking medium, allowing for better understanding of how to treat pathogens causing infection in these environments.

Nanomedicines for intranasal delivery: understanding the nano-bio interactions at the nasal mucus-mucosal barrier

INTRODUCTION

Intranasal administration is an effective drug delivery routes in modern pharmaceutics. However, unlike other in vivo biological barriers, the nasal mucosal barrier is characterized by high turnover and selective permeability, hindering the diffusion of both particulate drug delivery systems and drug molecules. The in vivo fate of administrated nanomedicines is often significantly affected by nano-biointeractions.

AREAS COVERED

The biological barriers that nanomedicines encounter when administered intranasally are introduced, with a discussion on the factors influencing the interaction between nanomedicines and the mucus layer/mucosal barriers. General design strategies for nanomedicines administered via the nasal route are further proposed. Furthermore, the most common methods to investigate the characteristics and the interactions of nanomedicines when in presence of the mucus layer/mucosal barrier are briefly summarized.

EXPERT OPINION

Detailed investigation of nanomedicine-mucus/mucosal interactions and exploration of their mechanisms provide solutions for designing better intranasal nanomedicines. Designing and applying nanomedicines with mucus interaction properties or non-mucosal interactions should be customized according to the therapeutic need, considering the target of the drug, i.e. brain, lung or nose. Then how to improve the precise targeting efficiency of nanomedicines becomes a difficult task for further research.

Predictive modeling provides insight into the clinical heterogeneity associated with TARS1 loss-of-function mutations

Aminoacyl-tRNA synthetases (ARSs) are ubiquitously expressed, essential enzymes that complete the first step of protein translation: ligation of amino acids to cognate tRNAs. Genes encoding ARSs have been implicated in myriad dominant and recessive phenotypes, the latter often affecting multiple tissues but with frequent involvement of the central and peripheral nervous system, liver, and lungs. Threonyl-tRNA synthetase (TARS1) encodes the enzyme that ligates threonine to tRNATHR in the cytoplasm. To date, TARS1 variants have been implicated in a recessive brittle hair phenotype. To better understand TARS1-related recessive phenotypes, we engineered three TARS1 missense mutations predicted to cause a loss-of-function effect and studied these variants in yeast and worm models. This revealed two loss-of-function mutations, including one hypomorphic allele (R433H). We next used R433H to study the effects of partial loss of TARS1 function in a compound heterozygous mouse model (R433H/null). This model presents with phenotypes reminiscent of patients with TARS1 variants and with distinct lung and skin defects. This study expands the potential clinical heterogeneity of TARS1-related recessive disease, which should guide future clinical and genetic evaluations of patient populations.

In vitro model of human mammary gland microbial colonization (MAGIC) demonstrates distinctive cytokine response to imbalanced human milk microbiota

Despite the established concept of the human mammary gland (MG) as a habitat with its own microbiota, the exact mechanism of MG colonization is still elusive and a well-characterized in vitro model would reinforce studies of the MG microbiota development. We aimed to establish and characterize an in vitro cell model for studying MAmmary Gland mIcrobial Colonization (MAGIC) model. We used the immortalized cell line MCF10A, which expresses the strong polarized phenotype similar to MG ductal epithelium when cultured on a permeable support (Transwell). We analyzed the surface properties of the MAGIC model by gene expression analysis of E-cadherin, tight junction proteins, and mucins and by scanning electron microscopy. To demonstrate the applicability of the model, we tested the adhesion capability of the whole human milk (HM) microbial community and the cellular response of the model when challenged directly with raw HM samples. MCF10A on permeable supports differentiated and formed a tight barrier, by upregulation of CLDN8, MUC1, MUC4, and MUC20 genes. The surface of the model was covered with mucins and morphologically diverse with at least two cell types and two types of microvilli. Cells in the MAGIC model withstood the challenge with heat-treated HM samples and responded differently to the imbalanced HM microbiota by distinctive cytokine response. The microbial profile of the bacteria adhered on the MAGIC model reflected the microbiological profile of the input HM samples. The well-studied MAGIC model could be useful for studies of bacterial attachment to the MG and for in vitro studies of biofilm formation and microbiota development.IMPORTANCEThe MAGIC model may be particularly useful for studies of bacterial attachment to the surface of the mammary ducts and for in vitro studies of biofilm formation and the development of the human mammary gland (MG) microbiota. The model is also useful for immunological studies of the interaction between bacteria and MG cells. We obtained pioneering information on which of the bacteria present in the raw human milk (HM) were able to attach to the epithelium treated directly with raw HM, as well as on the effects of bacteria on the MG epithelial cells. The MAGIC cell model also offers new opportunities for research in other areas of MG physiology, such as the effects of bioactive milk components on microbial colonization of the MG, mastitis prevention, and studies of probiotic development. Since resident MG bacteria may be an important factor in breast cancer development, the MAGIC in vitro tool also offers new opportunities for cancer research.

Development of a canine artificial colonic mucus model for drug diffusion studies

Colonic mucus is a key factor in the colonic environment because it may affect drug absorption. Due to the similarity of human and canine gastrointestinal physiology, dogs are an established preclinical species for the assessment of controlled release formulations. Here we report the development of an artificial colonic mucus model to mimic the native canine one. In vitro models of the canine colonic environment can provide insights for early stages of drug development and contribute to the implementation of the 3Rs (refinement, reduction, and replacement) of animal usage in the drug development process. Our artificial colonic mucus could predict diffusion trends observed in native mucus and was successfully implemented in microscopic and macroscopic assays to study macromolecular permeation through the mucus. The traditional Transwell set up was optimized with the addition of a nylon filter to ensure homogenous representation of the mucus barrier in vitro. In conclusion, the canine artificial colonic mucus can be used to study drug permeation across the mucus and its flexibility allows its use in various set ups depending on the nature of the compound under investigation and equipment availability.

Clostridioides difficile-mucus interactions encompass shifts in gene expression, metabolism, and biofilm formation

In a healthy colon, the stratified mucus layer serves as a crucial innate immune barrier to protect the epithelium from microbes. Mucins are complex glycoproteins that serve as a nutrient source for resident microflora and can be exploited by pathogens. We aimed to understand how the intestinal pathogen, Clostridioides diffiicile, independently uses or manipulates mucus to its benefit, without contributions from members of the microbiota. Using a 2-D primary human intestinal epithelial cell model to generate physiologic mucus, we assessed C. difficile-mucus interactions through growth assays, RNA-Seq, biophysical characterization of mucus, and contextualized metabolic modeling. We found that host-derived mucus promotes C. difficile growth both in vitro and in an infection model. RNA-Seq revealed significant upregulation of genes related to central metabolism in response to mucus, including genes involved in sugar uptake, the Wood-Ljungdahl pathway, and the glycine cleavage system. In addition, we identified differential expression of genes related to sensing and transcriptional control. Analysis of mutants with deletions in highly upregulated genes reflected the complexity of C. difficile-mucus interactions, with potential interplay between sensing and growth. Mucus also stimulated biofilm formation in vitro, which may in turn alter viscoelastic properties of mucus. Context-specific metabolic modeling confirmed differential metabolism and predicted importance of enzymes related to serine and glycine catabolism with mucus. Subsequent growth experiments supported these findings, indicating mucus is an important source of serine. Our results better define responses of C. difficile to human gastrointestinal mucus and highlight a flexibility in metabolism that may influence pathogenesis.

Rapid building block-economic synthesis of long, multi-O-GalNAcylated MUC5AC tandem repeat peptides

The study of mucin function requires access to highly O-glycosylated peptides with multiple tandem repeats. Solid-phase synthesis would be a suitable method, however, the central problem in the synthesis of mucin glycopeptides is the need to use precious and potentially vulnerable glycoamino acid building blocks in excess. In this article, we report the development of a method based on SPPS and native chemical ligation/desulfurization chemistry that allows the rapid, reliable, and glyco-economical synthesis of long multi-O-GalNAcylated peptides. To facilitate access to the glycosyl donor required for the preparation of Fmoc-Ser/Thr(αAc3GalNAc)-OH we used an easily scalable azidophenylselenylation of galactal instead of azidonitration. The problem of low yield when coupling glycoamino acids in small excess was solved by carrying out the reactions in 2-MeTHF instead of DMF and using DIC/Oxyma. Remarkably, quantitative coupling was achieved within 10 minutes using only 1.5 equivalents of glycoamino acid. The method does not require (microwave) heating, thus avoiding side reactions such as acetyl transfer to the N-terminal amino acid. This method also improved the difficult coupling of glycoamino acid to the hydrazine-resin and furnished peptides carrying 10 GalNAc units in high purities (>95%) of crude products. Combined with a one-pot method involving native chemical ligation at a glycoamino acid junction and superfast desulfurization, the method yielded highly pure MUC5AC glycopeptides comprising 10 octapeptide tandem repeats with 20 α-O-linked GalNAc residues within a week.

Dietary supplementation of benzoic acid and essential oils combination enhances intestinal resilience against LPS stimulation in weaned piglets

BACKGROUND

The benefits of combining benzoic acid and essential oils (BAO) to mitigate intestinal impairment during the weaning process have been well established, while the detailed underlying mechanism has not been fully elucidated. Previous research has primarily focused on the reparative effects of BAO on intestinal injury, while neglecting its potential in enhancing intestinal stress resistance.

METHODS

In this study, we investigated the pre-protective effect of BAO against LPS-induced stress using a modified experimental procedure. Piglets were pre-supplemented with BAO for 14 d, followed by a challenge with LPS or saline to collect blood and intestinal samples.

RESULTS

Our findings demonstrated that BAO supplementation led to significant improvements in piglets' final weight, average daily gain, and feed intake/body gain ratio. Additionally, BAO supplementation positively influenced the composition of intestinal microbiota, increasing beneficial Actinobacteriota and Alloprevotella while reducing harmful Desulfobacterota, Prevotella and Oscillospira. Furthermore, BAO supplementation effectively mitigated oxidative disturbances and inflammatory responses induced by acute LPS challenge. This was evidenced by elevated levels of T-AOC, SOD, and GSH, as well as decreased levels of MDA, TNF-α, and IL-6 in the plasma. Moreover, piglets subjected to LPS challenge and pre-supplemented with BAO exhibited significant improvements in intestinal morphological structure and enhanced integrity, as indicated by restored expression levels of Occludin and Claudin-1 compared to the non-supplemented counterparts. Further analysis revealed that BAO supplementation enhanced the jejunal antioxidative capacity by increasing GSH-Px levels and decreasing MDA levels under the LPS challenge and stimulated the activation of the Nrf2 signaling pathway. Additionally, the reduction of TLR4/NF-κB/MAPK signaling pathways activation and proinflammatory factor were also observed in the jejunal of those piglets fed with BAO.

CONCLUSIONS

In summary, our study demonstrates that pre-supplementation of BAO enhances the anti-stress capacity of weaned piglets by improving intestinal microbiota composition, reinforcing the intestinal barrier, and enhancing antioxidative and anti-inflammatory capabilities. These effects are closely associated with the activation of Nrf2 and TLR4/NF-κB/MAPK signaling pathways.

Gastropod Slime-Based Gel as an Adjustable Synthetic Model for Human Airway Mucus

Airway mucus works as a protective barrier in the human body, as it entraps pathogens that will be later cleared from the airways by ciliary transport or by coughing, thus featuring the rheological properties of a highly stretchable gel. Nonetheless, the study of these physical barrier as well as transport properties remains limited due to the restricted and invasive access to lungs and bronchi to retrieve mucus and to the poor repeatability inherent to native mucus samples. To overcome these limits, we report on a biobased synthetic mucus prepared from snail slime and multibranched thiol cross-linker, which are able to establish disulfide bonds, in analogy with the disulfide bonding of mucins, and therefore build viscoelastoplastic hydrogels. The gel macroscopic properties are tuned by modifying the cross-linker and slime concentrations and can quantitatively match those of native sputum from donors with cystic fibrosis (CF) or non-cystic fibrosis bronchiectasis (NCFB) both in the small- and large-deformation regimes. Heterogeneous regimes were locally found in the mucus model by passive microrheology, in which both diffusive and non-diffusive motion are present, similar to what is observed in sputa. The biobased synthetic approach proposed in the present study thus allows to produce, with commercially available components, a promising model to native respiratory mucus regarding both mechanical and, to a lesser extent, physicochemical aspects.

Mechanical Characterization of Mucus on Intestinal Tissues by Atomic Force Microscopy

Mucus is part of the innate immune system that defends the mucosa against microbiota and other infectious threats. The mechanical characteristics of mucus, such as viscosity, elasticity, and lubricity, are critically involved in its barrier function. However, assessing the mechanical properties of mucus remains challenging because of technical limitations. Thus, a new approach that characterizes the mechanical properties of mucus on colonic tissues needs to be developed. Here, we describe a novel strategy to characterize the ex vivo mechanical properties of mucus on colonic tissues using atomic force microscopy. This description includes the preparation of the mouse colon sample, AFM calibration, and determining the elasticity (Young's modulus, E [kPa]) of the mucus layer in the colon.

Biophysical basis of filamentous phage tactoid-mediated antibiotic tolerance in P. aeruginosa

Inoviruses are filamentous phages infecting numerous prokaryotic phyla. Inoviruses can self-assemble into mesoscale structures with liquid-crystalline order, termed tactoids, which protect bacterial cells in Pseudomonas aeruginosa biofilms from antibiotics. Here, we investigate the structural, biophysical, and protective properties of tactoids formed by the P. aeruginosa phage Pf4 and Escherichia coli phage fd. A cryo-EM structure of the capsid from fd revealed distinct biochemical properties compared to Pf4. Fd and Pf4 formed tactoids with different morphologies that arise from differing phage geometries and packing densities, which in turn gave rise to different tactoid emergent properties. Finally, we showed that tactoids formed by either phage protect rod-shaped bacteria from antibiotic treatment, and that direct association with a tactoid is required for protection, demonstrating the formation of a diffusion barrier by the tactoid. This study provides insights into how filamentous molecules protect bacteria from extraneous substances in biofilms and in host-associated infections.

Statistical Methods for Microrheology of Airway Mucus with Extreme Heterogeneity

The mucus lining of the human airway epithelium contains two gel-forming mucins, MUC5B and MUC5AC. During progression of cystic fibrosis (CF), mucus hyper-concentrates as its mucin ratio changes, coinciding with formation of insoluble, dense mucus flakes. We explore rheological heterogeneity of this pathology with reconstituted mucus matching three stages of CF progression and particle-tracking of 200 nm and 1 micron diameter beads. We introduce statistical data analysis methods specific to low signal-to-noise data within flakes. Each bead time series is decomposed into: (i) a fractional Brownian motion (fBm) classifier of the pure time-series signal; (ii) high-frequency static and dynamic noise; and (iii) low-frequency deterministic drift. Subsequent analysis focuses on the denoised fBm classifier ensemble from each mucus sample and bead diameter. Every ensemble fails a homogeneity test, compelling clustering methods to assess levels of heterogeneity. The first binary level detects beads within vs. outside flakes. A second binary level detects within-flake bead signals that can vs. cannot be disentangled from the experimental noise floor. We show all denoised ensembles, within- and outside-flakes, fail a homogeneity test, compelling additional clustering; next, all clusters with sufficient data fail a homogeneity test. These levels of heterogeneity are consistent with outcomes from a stochastic phase-separation process, and dictate applying the generalized Stokes-Einstein relation to each bead per cluster per sample, then frequency-domain averaging to assess rheological heterogeneity. Flakes exhibit a spectrum of gel-like and sol-like domains, outside-flake solutions a spectrum of sol-like domains, painting a rheological signature of the phase-separation process underlying flake-burdened mucus.

The power of weak, transient interactions across biology: A paradigm of emergent behavior

A growing list of diverse biological systems and their equally diverse functionalities provides realizations of a paradigm of emergent behavior. In each of these biological systems, pervasive ensembles of weak, short-lived, spatially local interactions act autonomously to convey functionalities at larger spatial and temporal scales. In this article, a range of diverse systems and functionalities are presented in a cursory manner with literature citations for further details. Then two systems and their properties are discussed in more detail: yeast chromosome biology and human respiratory mucus.

Repetitive and zonal expression profiles of absorption-related genes in the gastrointestinal tract of ascidian Ciona intestinalis type A

Intestinal absorption is essential for heterotrophic bilaterians with a tubular gut. Although the fundamental features of the digestive system were shared among chordates with evolution, the gut morphologies of vertebrates diverged and adapted to different food habitats. The ascidian Ciona intestinalis type A, a genome-wide research model of basal chordates, is used to examine the functional morphology of the intestines because of its transparent juvenile body. In the present study, the characteristic gene expression patterns (GEP) of Ciona absorptive proteins, e.g., brush border membrane enzymes for terminal digestion (lactase, maltase, APA, and APN) and transporters (SGLT1, GLUT5, PEPT1, and B0AT1), were investigated in juveniles and young adults, with a special reference to the absorption of other nutrients by pinocytosis- and phagocytosis-related proteins (megalin, cubilin, amnionless, Dab2, Rab7, LAMP, cathepsins, and MRC1). Whole-mount in situ hybridization revealed that these GEP showed multi-regional and repetitive features along the Ciona gastrointestinal tract, mainly in the stomach and several regions of the intestines. In young adults, many absorption-related genes, including pinocytosis-/phagocytosis-related genes, were also expressed between the stomach and mid-intestine. In the gastrointestinal epithelium, absorption-related genes showed zonal GEP along the epithelial structure. Comparisons of GEP, including other intestinal functions, such as nutrient digestion and intestinal protection, indicated the repetitive assignment of a well-coordinated set of intestinal GEP in the Ciona gastrointestinal tract.

Traceless Protein-Selective Glycan Labeling and Chemical Modification

Executing glycan editing at a molecular level not only is pivotal for the elucidation of complicated mechanisms involved in glycan-relevant biological processes but also provides a promising solution to potentiate disease therapy. However, the precision control of glycan modification or glyco-editing on a selected glycoprotein is by far a grand challenge. Of note is to preserve the intact cellular glycan landscape, which is preserved after editing events are completed. We report herein a versatile, traceless glycan modification methodology for customizing the glycoforms of targeted proteins (subtypes), by orchestrating chemical- and photoregulation in a protein-selective glycoenzymatic system. This method relies on a three-module, ligand-photocleavable linker-glycoenzyme (L-P-G) conjugate. We demonstrated that RGD- or synthetic carbohydrate ligand-containing conjugates (RPG and SPG) would not activate until after the ligand-receptor interaction is accomplished (chemical regulation). RPG and SPG can both release the glycoenzyme upon photoillumination (photoregulation). The adjustable glycoenzyme activity, combined with ligand recognition selectivity, minimizes unnecessary glycan editing perturbation, and photolytic cleavage enables precise temporal control of editing events. An altered target protein turnover and dimerization were observed in our system, emphasizing the significance of preserving the native physiological niche of a particular protein when precise modification on the carbohydrate epitope occurs.

Nanoparticle-Mediated Strategies for Enhanced Drug Penetration and Retention in the Airway Mucosa

Airway mucus is a complex viscoelastic gel composed mainly of water, glycoproteins, lipids, enzymes, minerals, etc. Among them, glycoproteins are the main factors determining mucus's gel-like rheology. Airway mucus forms a protective barrier by secreting mucin, which represents a barrier for absorption, especially for more lipophilic drugs. It rapidly removes drugs from the airway through the physiological mucus clearance mechanism so drugs cannot remain in the lungs or reach the airway epithelial tissue for a long time. Significant progress has been made in enhancing drug lung deposition recently, but strategies are still needed to help drugs break through the lung mucosal barrier. Based on the physiopathological mechanisms of airway mucus, this paper reviews and summarizes strategies to enhance drug penetration and retention in the airway mucosa mediated by nano-delivery systems, including mucosal permeation systems, mucosal adhesion systems, and enzyme-modified delivery systems. On this basis, the potential and challenges of nano-delivery systems for improving airway mucus clearance are revealed. New ideas and approaches are provided for designing novel nano-delivery systems that effectively improve drug retention and penetration in the airway mucus layer.

Mucosa-Mimetic Materials for the Study of Intestinal Homeostasis and Disease

Mucus is a viscoelastic hydrogel that lines and protects the epithelial surfaces of the body that houses commensal microbiota and functions in host defense against pathogen invasion. As a first-line physical and biochemical barrier, intestinal mucus is involved in immune surveillance and spatial organization of the microbiome, while dysfunction of the gut mucus barrier is implicated in several diseases. Mucus can be collected from a variety of mammalian sources for study, however, established methods are challenging in terms of scale and efficiency, as well as with regard to rheological similarity to native human mucus. Therefore, there is a need for mucus-mimetic hydrogels that more accurately reflect the physical and chemical profile of the in vivo human epithelial environment to enable the investigation of the role of mucus in human disease and interactions with the intestinal microbiome. This review will evaluate the material properties of synthetic mucus mimics to date designed to address the above need, with a focus toward an improved understanding of the biochemical and immunological functions of these biopolymers related to utility for research and therapeutic applications.

SARS-CoV-2 induced changes in the glycosylation pattern in the respiratory tract of Golden Syrian hamsters

Even after more than two years of intensive research, not all of the pathophysiological processes of Coronavirus Disease 2019 (COVID-19), induced by severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) infection, have been fully elucidated. The initial virus-host interaction at the respiratory epithelium plays a crucial role in the course and progression of the infection, and is highly dependent on the glycosylation pattern of the host cell and of the secreted mucins. Glycans are polysaccharides that can be attached to proteins and thereby add to their stability and functionality. Lectins are glycan-binding proteins that recognize specific glycan motifs, and lectin histochemistry is a suitable tool to visualize and examine glycosylation pattern changes in tissues. In this study we used lectins with different glycan-specificities for the visualization of glycosylation pattern changes in the respiratory tract of SARS-CoV-2 infected Golden Syrian hamsters. While some lectins (LEL, STL) enable the visualization of the damage to alveolar type 1 pneumocytes, other lectins, e.g., GSLI, visualized the loss and subsequent hyperplasia of type 2 pneumocytes. UEAI staining was co-localized with KI67, a proliferation marker. Double staining of lectins LEL, STL and WGA with specific immune cell markers (Iba1, CD68) showed co-localization and the dominant infiltration of monocyte-derived macrophages into infected alveolar tissue. The elucidation of the glycosylation pattern of the respiratory tract cells in uninfected and infected Golden Syrian hamsters revealed physiological and pathological aspects of the disease that may open new possibilities for therapeutic development.

mRNA nanodelivery systems: targeting strategies and administration routes

With the great success of coronavirus disease (COVID-19) messenger ribonucleic acid (mRNA) vaccines, mRNA therapeutics have gained significant momentum for the prevention and treatment of various refractory diseases. To function efficiently in vivo and overcome clinical limitations, mRNA demands safe and stable vectors and a reasonable administration route, bypassing multiple biological barriers and achieving organ-specific targeted delivery of mRNA. Nanoparticle (NP)-based delivery systems representing leading vector approaches ensure the successful intracellular delivery of mRNA to the target organ. In this review, chemical modifications of mRNA and various types of advanced mRNA NPs, including lipid NPs and polymers are summarized. The importance of passive targeting, especially endogenous targeting, and active targeting in mRNA nano-delivery is emphasized, and different cellular endocytic mechanisms are discussed. Most importantly, based on the above content and the physiological structure characteristics of various organs in vivo, the design strategies of mRNA NPs targeting different organs and cells are classified and discussed. Furthermore, the influence of administration routes on targeting design is highlighted. Finally, an outlook on the remaining challenges and future development toward mRNA targeted therapies and precision medicine is provided.

Designing Superlubricious Hydrogels from Spontaneous Peroxidation Gradients

Hydrogels are hydrated three-dimensional networks of hydrophilic polymers that are commonly used in the biomedical industry due to their mechanical and structural tunability, biocompatibility, and similar water content to biological tissues. The surface structure of hydrogels polymerized through free-radical polymerization can be modified by controlling environmental oxygen concentrations, leading to the formation of a polymer concentration gradient. In this work, 17.5 wt % polyacrylamide hydrogels are polymerized in low (0.01 mol % O2) and high (20 mol % O2) oxygen environments, and their mechanical and tribological properties are characterized through microindentation, nanoindentation, and tribological sliding experiments. Without significantly reducing the elastic modulus of the hydrogel (E* ≈ 200 kPa), we demonstrate an order of magnitude reduction in friction coefficient (from μ = 0.021 ± 0.006 to μ = 0.002 ± 0.001) by adjusting polymerization conditions (e.g., oxygen concentration). A quantitative analytical model based on polyacrylamide chemistry and kinetics was developed to estimate the thickness and structure of the monomer conversion gradient, termed the "surface gel layer". We find that polymerizing hydrogels at high oxygen concentrations leads to the formation of a preswollen surface gel layer that is approximately five times thicker (t ≈ 50 μm) and four times less concentrated (≈ 6% monomer conversion) at the surface prior to swelling compared to low oxygen environments (t ≈ 10 μm, ≈ 20% monomer conversion). Our model could be readily modified to predict the preswollen concentration profile of the polyacrylamide gel surface layer for any reaction conditions─monomer and initiator concentration, oxygen concentration, reaction time, and reaction media depth─or used to select conditions that correspond to a certain desired surface gel layer profile.

The role of mucosal barriers in disease progression and transmission

Mucus is a biological hydrogel that coats and protects all non-keratinized wet epithelial surfaces. Mucins, the primary structural components of mucus, are critical components of the gel layer that protect against invading pathogens. For communicable diseases, pathogen-mucin interactions contribute to the pathogen's fate and the potential for disease progression in-host, as well as the potential for onward transmission. We begin by reviewing in-host mucus filtering mechanisms, including size filtering and interaction filtering, which regulate the permeability of mucus barriers to all molecules including pathogens. Next, we discuss the role of mucins in communicable diseases at the point of transmission (i.e. how the encapsulation of pathogens in emitted mucosal droplets externally to hosts may modulate pathogen infectivity and viability). Overall, mucosal barriers modulate both host susceptibility as well as the dynamics of population-level disease transmission. The study of mucins and their use in models and experimental systems are therefore crucial for understanding the mechanistic biophysical principles underlying disease transmission and the early stages of host infection.

Hypoxia controls expression of kidney-pathogenic MUC1 variants

The interplay between genetic and environmental factors influences the course of chronic kidney disease (CKD). In this context, genetic alterations in the kidney disease gene MUC1 (Mucin1) predispose to the development of CKD. These variations comprise the polymorphism rs4072037, which alters splicing of MUC1 mRNA, the length of a region with variable number of tandem repeats (VNTR), and rare autosomal-dominant inherited dominant-negative mutations in or 5' to the VNTR that causes autosomal dominant tubulointerstitial kidney disease (ADTKD-MUC1). As hypoxia plays a pivotal role in states of acute and chronic kidney injury, we explored the effects of hypoxia-inducible transcription factors (HIF) on the expression of MUC1 and its pathogenic variants in isolated primary human renal tubular cells. We defined a HIF-binding DNA regulatory element in the promoter-proximal region of MUC1 from which hypoxia or treatment with HIF stabilizers, which were recently approved for an anti-anemic therapy in CKD patients, increased levels of wild-type MUC1 and the disease-associated variants. Thus, application of these compounds might exert unfavorable effects in patients carrying MUC1 risk variants.

MUC5AC Genetic Variation Is Associated With Tuberculous Meningitis Cerebral Spinal Fluid Cytokine Responses and Mortality

BACKGROUND

The purpose of this study was to assess if single nucleotide polymorphisms (SNPs) in lung mucins MUC5B and MUC5AC are associated with Mycobacterium tuberculosis outcomes.

METHODS

Independent SNPs in MUC5B and MUC5AC (genotyped by Illumina HumanOmniExpress array) were assessed for associations with tumor necrosis factor (TNF) concentrations (measured by immunoassay) in cerebral spinal fluid (CSF) from tuberculous meningitis (TBM) patients. SNPs associated with CSF TNF concentrations were carried forward for analyses of pulmonary and meningeal tuberculosis susceptibility and TBM mortality.

RESULTS

MUC5AC SNP rs28737416 T allele was associated with lower CSF concentrations of TNF (P = 1.8 × 10-8) and IFN-γ (P = 2.3 × 10-6). In an additive genetic model, rs28737416 T/T genotype was associated with higher susceptibility to TBM (odds ratio [OR], 1.24; 95% confidence interval [CI], 1.03-1.49; P = .02), but not pulmonary tuberculosis (OR, 1.11, 95% CI, .98-1.25; P = .10). TBM mortality was higher among participants with the rs28737416 T/T and T/C genotypes (35/119, 30.4%) versus the C/C genotype (11/89, 12.4%; log-rank P = .005) in a Vietnam discovery cohort (n = 210), an independent Vietnam validation cohort (n = 87; 9/87, 19.1% vs 1/20, 2.5%; log-rank P = .02), and an Indonesia validation cohort (n = 468, 127/287, 44.3% vs 65/181, 35.9%; log-rank P = .06).

CONCLUSIONS

MUC5AC variants may contribute to immune changes that influence TBM outcomes.

Autophagy/Mitophagy in Airway Diseases: Impact of Oxidative Stress on Epithelial Cells

Autophagy is the key process by which the cell degrades parts of itself within the lysosomes. It maintains cell survival and homeostasis by removing molecules (particularly proteins), subcellular organelles, damaged cytoplasmic macromolecules, and by recycling the degradation products. The selective removal or degradation of mitochondria is a particular type of autophagy called mitophagy. Various forms of cellular stress (oxidative stress (OS), hypoxia, pathogen infections) affect autophagy by inducing free radicals and reactive oxygen species (ROS) formation to promote the antioxidant response. Dysfunctional mechanisms of autophagy have been found in different respiratory diseases such as chronic obstructive lung disease (COPD) and asthma, involving epithelial cells. Several existing clinically approved drugs may modulate autophagy to varying extents. However, these drugs are nonspecific and not currently utilized to manipulate autophagy in airway diseases. In this review, we provide an overview of different autophagic pathways with particular attention on the dysfunctional mechanisms of autophagy in the epithelial cells during asthma and COPD. Our aim is to further deepen and disclose the research in this direction to stimulate the develop of new and selective drugs to regulate autophagy for asthma and COPD treatment.

Mirror Image Mucins and Thio Mucins with Tunable Biodegradation

Mucin glycoproteins are the major component of mucus and are integral to the cellular glycocalyx. Mucins play diverse roles in health and disease, are an important element in epithelial tissue models, and have broad therapeutic potential. All mucin applications are currently challenged by their inherent structural heterogeneity and degradation by proteases. In this study, we describe the synthesis and study of chemically defined mucin analogues bearing native glycans. We utilized combinations of enantiomer amino acids and glycan thioether linkages to achieve tunable proteolysis while maintaining cytocompatibility and binding activity. Structural characterization revealed a previously unknown mirror-image helix and sheds light on the molecular drivers of glycoprotein conformation. This work represents an important step toward the development of artificial mucins for biomedical applications.

Pseudomonas aeruginosa type IV pili actively induce mucus contraction to form biofilms in tissue-engineered human airways

The opportunistic pathogen Pseudomonas aeruginosa causes antibiotic-recalcitrant pneumonia by forming biofilms in the respiratory tract. Despite extensive in vitro experimentation, how P. aeruginosa forms biofilms at the airway mucosa is unresolved. To investigate the process of biofilm formation in realistic conditions, we developed AirGels: 3D, optically accessible tissue-engineered human lung models that emulate the airway mucosal environment. AirGels recapitulate important factors that mediate host-pathogen interactions including mucus secretion, flow and air-liquid interface (ALI), while accommodating high-resolution live microscopy. With AirGels, we investigated the contributions of mucus to P. aeruginosa biofilm biogenesis in in vivo-like conditions. We found that P. aeruginosa forms mucus-associated biofilms within hours by contracting luminal mucus early during colonization. Mucus contractions facilitate aggregation, thereby nucleating biofilms. We show that P. aeruginosa actively contracts mucus using retractile filaments called type IV pili. Our results therefore suggest that, while protecting epithelia, mucus constitutes a breeding ground for biofilms.

Mucus Hypersecretion in Chronic Obstructive Pulmonary Disease and Its Treatment

Most patients diagnosed with chronic obstructive pulmonary disease (COPD) present with hallmark features of airway mucus hypersecretion, including cough and expectoration. Airway mucus function as a native immune system of the lung that severs to trap particulate matter and pathogens and allows them to clear from the lung via cough and ciliary transport. Chronic mucus hypersecretion (CMH) is the main factor contributing to the increased risk of morbidity and mortality in specific subsets of COPD patients. It is, therefore, primarily important to develop medications that suppress mucus hypersecretions in these patients. Although there have been some advances in COPD treatment, more work remains to be done to better understand the mechanism underlying airway mucus hypersecretion and seek more effective treatments. This review article discusses the structure and significance of mucus in the lungs focusing on gel-forming mucins and the impacts of CMH in the lungs. Furthermore, we summarize the article with pharmacological and nonpharmacological treatments as well as novel and interventional procedures to control CMH in COPD patients.

Defining the Relationship of Gut Microbiota, Immunity, and Cognition in Early Life-A Narrative Review

Recently, the immune system has been identified as one of the possible main bridges which connect the gut-brain axis. This review aims to examine available evidence on the microbiota-immunity-cognitive relationship and its possible effects on human health early in life. This review was assembled by compiling and analyzing various literature and publications that document the gut microbiota-immune system-cognition interaction and its implications in the pediatric population. This review shows that the gut microbiota is a pivotal component of gut physiology, with its development being influenced by a variety of factors and, in return, supports the development of overall health. Findings from current research focus on the complex relationship between the central nervous system, gut (along with gut microbiota), and immune cells, highlighting the importance of maintaining a balanced interaction among these systems for preserving homeostasis, and demonstrating the influence of gut microbes on neurogenesis, myelin formation, the potential for dysbiosis, and alterations in immune and cognitive functions. While limited, evidence shows how gut microbiota affects innate and adaptive immunity as well as cognition (through HPA axis, metabolites, vagal nerve, neurotransmitter, and myelination).

IL-4 and IL-13: Regulators and Effectors of Wound Repair

Type 2 immunity mediates protective responses to helminths and pathological responses to allergens, but it also has broad roles in the maintenance of tissue integrity, including wound repair. Type 2 cytokines are known to promote fibrosis, an overzealous repair response, but their contribution to healthy wound repair is less well understood. This review discusses the evidence that the canonical type 2 cytokines, IL-4 and IL-13, are integral to the tissue repair process through two main pathways. First, essential for the progression of effective tissue repair, IL-4 and IL-13 suppress the initial inflammatory response to injury. Second, these cytokines regulate how the extracellular matrix is modified, broken down, and rebuilt for effective repair. IL-4 and/or IL-13 amplifies multiple aspects of the tissue repair response, but many of these pathways are highly redundant and can be induced by other signals. Therefore, the exact contribution of IL-4Rα signaling remains difficult to unravel.