Cystic fibrosis: an inherited disease affecting mucin-producing organs

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.

The Tmem16a chloride channel is required for mucin maturation after secretion from goblet-like cells in the Xenopus tropicalis tadpole skin

The TMEM16A chloride channel is proposed as a therapeutic target in cystic fibrosis, where activation of this ion channel might restore airway surface hydration and mitigate respiratory symptoms. While TMEM16A is associated with increased mucin production under stimulated or pro-inflammatory conditions, its role in baseline mucin production, secretion and/or maturation is less well understood. Here, we use the Xenopus tadpole skin mucociliary surface as a model of human upper airway epithelium to study Tmem16a function in mucus production. We found that Xenopus tropicalis Tmem16a is present at the apical membrane surface of tadpole skin small secretory cells that express canonical markers of mammalian "goblet cells" such as Foxa1 and spdef. X. tropicalis Tmem16a functions as a voltage-gated, calcium-activated chloride channel when transfected into mammalian cells in culture. Depletion of Tmem16a from the tadpole skin results in dysregulated mucin maturation post-secretion, with secreted mucins having a disrupted molecular size distribution and altered morphology assessed by sucrose gradient centrifugation and electron microscopy, respectively. Our results show that in the Xenopus tadpole skin, Tmem16a is necessary for normal mucus barrier formation and demonstrate the utility of this model system to discover new biology relevant to human mucosal biology in health and disease.

Using Zebrafish to Study Multiciliated Cell Development and Disease States

Multiciliated cells (MCCs) serve many important functions, including fluid propulsion and chemo- and mechanosensing. Diseases ranging from rare conditions to the recent COVID-19 global health pandemic have been linked to MCC defects. In recent years, the zebrafish has emerged as a model to investigate the biology of MCCs. Here, we review the major events in MCC formation including centriole biogenesis and basal body docking. Then, we discuss studies on the role of MCCs in diseases of the brain, respiratory, kidney and reproductive systems, as well as recent findings about the link between MCCs and SARS-CoV-2. Next, we explore why the zebrafish is a useful model to study MCCs and provide a comprehensive overview of previous studies of genetic components essential for MCC development and motility across three major tissues in the zebrafish: the pronephros, brain ependymal cells and nasal placode. Taken together, here we provide a cohesive summary of MCC research using the zebrafish and its future potential for expanding our understanding of MCC-related disease states.

TRPV4 Channel Modulators as Potential Drug Candidates for Cystic Fibrosis

Cystic fibrosis (CF) is a genetic disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, resulting in defective chloride ion channels. This leads to thick, dehydrated mucus that severely disrupts mucociliary clearance in the respiratory system and triggers infection that eventually is the cause of death of CF patients. Current therapeutic strategies primarily focus on restoring CFTR function, blocking epithelial sodium channels to prevent mucus dehydration, or directly targeting mucus to reduce its viscosity. Among the ion channels expressed in ciliated bronchial epithelial cells, the transient receptor potential vanilloid 4 (TRPV4) channel emerges as a significant channel in CF pathogenesis. Activation of TRPV4 channels affects the regulation of airway surface liquid by modulating sodium absorption and intracellular calcium levels, which indirectly influences CFTR activity. TRPV4 is also involved in the regulatory volume decrease (RVD) process and enhances inflammatory responses in CF patients. Here, we combine current findings on TRPV4 channel modulation as a promising therapeutic approach for CF. Although limited studies have directly explored TRPV4 in CF, emerging evidence indicates that TRPV4 activation can significantly impact key pathological processes in the disease. Further investigation into TRPV4 modulators could lead to innovative treatments that alleviate severe respiratory complications and improve outcomes for CF patients.

Vitamin D for glycemic control following an acute pulmonary exacerbation: A secondary analysis of a multicenter, double-blind, randomized, placebo-controlled trial in adults with cystic fibrosis

Individuals with cystic fibrosis (CF) often incur damage to pancreatic tissue due to a dysfunctional cystic fibrosis transmembrane conductance regulator (CFTR) protein, leading to altered chloride transport on epithelial surfaces and subsequent development of cystic fibrosis-related diabetes (CFRD). Vitamin D deficiency has been associated with the development of CFRD. This was a secondary analysis of a multicenter, double-blind, randomized, placebo-controlled study in adults with CF hospitalized for an acute pulmonary exacerbation (APE), known as the Vitamin D for the Immune System in Cystic Fibrosis (DISC) trial (NCT01426256). This was a pre-planned secondary analysis to examine if a high-dose bolus of cholecalciferol (vitamin D3) can mitigate declined glucose tolerance commonly associated with an acute pulmonary exacerbation (APE). Glycemic control was assessed by hemoglobin A1c (HbA1c) and fasting blood glucose levels before and 12 months after the study intervention. Within 72 hours of hospital admission, participants were randomly assigned to a single dose of oral vitamin D3 (250,000 IU) or placebo, and subsequently, received 50,000 IU of vitamin D3 or placebo every other week, beginning at month 3 and ending on month 12. Forty-nine of the 91 participants in the parent study were eligible for the secondary analysis. There were no differences in 12-month changes in HbA1c or fasting blood glucose in participants randomized to vitamin D or placebo. A high-dose bolus of vitamin D3 followed by maintenance vitamin D3 supplementation did not improve glycemic control in patients with CF after an APE.

Fecal dysbiosis and inflammation in intestinal-specific Cftr knockout mice on regimens preventing intestinal obstruction

Chronic intestinal inflammation is a poorly understood manifestation of cystic fibrosis (CF), which may be refractory to ion channel CF transmembrane conductance regulator (CFTR) modulator therapy. People with CF exhibit intestinal dysbiosis, which has the potential for stimulating intestinal and systemic inflammation. CFTR is expressed in organ epithelia, leukocytes, and other tissues. Here, we investigate the contribution of intestinal epithelium-specific loss of Cftr [iCftr knockout (KO)] to dysbiosis and inflammation in mice treated with either of two antiobstructive dietary regimens necessary to maintain CF mouse models [polyethylene glycol (PEG) laxative or a liquid diet (LiqD)]. Feces collected from iCftr KO mice and their wild-type (WT) sex-matched littermates were used to measure fecal calprotectin to evaluate inflammation and to perform 16S rRNA sequencing to characterize the gut microbiome. Fecal calprotectin was elevated in iCftr KO relative to WT mice that consumed either PEG or LiqD. PEG iCftr KO mice did not show a change in α diversity versus WT mice but demonstrated a significant difference in microbial composition (β diversity) with included increases in the phylum Proteobacteria, the family Peptostreptococcaceae, four genera of Clostridia including C. innocuum, and the mucolytic genus Akkermansia. Fecal microbiome analysis of LiqD-fed iCftr KO mice showed both decreased α diversity and differences in microbial composition with increases in the Proteobacteria family Enterobacteriaceae, Firmicutes families Clostridiaceae and Peptostreptococcaceae, and enrichment of Clostridium perfringens, C. innocuum, C. difficile, mucolytic Ruminococcus gnavus, and reduction of Akkermansia. It was concluded that epithelium-specific loss of Cftr is a major driver of CF intestinal dysbiosis and inflammation with significant similarities to previous studies of pan Cftr KO mice.NEW & NOTEWORTHY Chronic intestinal inflammation is a manifestation of cystic fibrosis (CF), a disease caused by loss of the anion channel CF transmembrane conductance regulator (CFTR) that is expressed in many tissues. This study shows that intestinal epithelial cell-specific loss of CFTR [inducible Cftr knockout (KO)] in mice is sufficient to induce intestinal dysbiosis and inflammation. Experiments were performed on mice consuming two dietary regimens routinely used to prevent obstruction in CF mice.

Measuring Biophysical Properties of Cilia Motility from Mammalian Tissues via Quantitative Video Analysis Methods

Ciliated epithelia are common in various human organs, indeed across many species, and their physiological functions are vital. A number of diseases, of genetic, degenerative, or infectious nature, compromise motile cilia function and lead to severe downstream consequences. Culture of ciliated tissues is a common research approach. We focus here on the video microscopy and analysis pipelines developed over the last few years to phenotype ciliary beating in lung cells, specifically to extract: cilia coverage; ciliary beat frequency distributions; the scale for ciliary dynamical coordination; and cilia beat waveform.

Development of the Pancreatic Ducts and Their Contribution to Organogenesis

The pancreas is a dual-function organ, with exocrine cells that aid in digestion and endocrine cells that regulate glucose homeostasis. These cell types share common progenitors and arise from the embryonic ducts. Early signaling events in the embryonic ducts shape the neonatal, adolescent, and adult exocrine and endocrine pancreas. This chapter discusses recent advances in the tools used to study the ducts and our current understanding of how ductal development contributes to pancreatic organogenesis.

Pharmacodynamic Model of the Dynamic Response of Pseudomonas aeruginosa Biofilms to Antibacterial Treatments

Accurate pharmacokinetic-pharmacodynamic (PK-PD) models of biofilm treatment could be used to guide formulation and administration strategies to better control bacterial lung infections. To this end, we developed a detailed pharmacodynamic model of P. aeruginosa treatment with the front-line antibiotics, tobramycin and colistin, and validated it on a detailed dataset of killing dynamics. A compartmental model structure was developed in which the key features are the diffusion of the drug through a boundary layer to the bacteria, concentration-dependent interactions with bacteria, and the passage of the bacteria through successive transit states before death. The number of transit states employed was greater for tobramycin, which is a ribosomal inhibitor, than for colistin, which disrupts bacterial membranes. For both drugs, the experimentally observed delay in the killing of bacteria following drug exposure was consistent with the sum of the diffusion time and the time for passage through the transit states. For each drug, the PD model with a single set of parameters described data across a ten-fold range of concentrations and for both continuous and transient exposure protocols, as well as for combined drug treatments. The ability to predict drug response over a range of administration protocols allows this PD model to be integrated with PK descriptions to describe in vivo antibiotic response dynamics and to predict drug delivery strategies for the improved control of bacterial lung infections.

Fecal Dysbiosis and Inflammation in Intestinal-Specific Cftr Knockout Mice on Regimens Preventing Intestinal Obstruction

Chronic intestinal inflammation is a poorly understood manifestation of Cystic Fibrosis (CF), which may be refractory to ion channel CFTR modulator therapy. People with CF exhibit intestinal dysbiosis which has potential for stimulating intestinal and systemic inflammation. CFTR is expressed in organ epithelia and in the leukocyte population. Here, we investigate the contribution of intestinal epithelial-specific loss of Cftr (iCftr KO) to dysbiosis and inflammation in mice treated with either of two anti-obstructive dietary regimens necessary to maintain CF mouse models (PEG laxative or a liquid diet, LiqD). Feces collected from iCftr KO mice and their wildtype (WT) sex-matched littermates were used to measure fecal calprotectin and to perform 16S rRNA sequencing to characterize the gut microbiome. Fecal calprotectin was elevated in iCftr KO relative to WT samples of mice consuming either PEG or LiqD. PEG iCftr KO mice did not show a change in α-diversity versus WT but demonstrated a significant difference in microbial composition (β-diversity) with increases in phylum Proteobacteria , family Peptostreptococcaceae , four genera of Clostridia including C. innocuum , and mucolytic genus Akkermansia . Fecal microbiome analysis of LiqD iCftr KO mice showed both decreased α-diversity and differences in microbial composition with increases in Proteobacteria family Enterobacteriaceae , Firmicutes families Clostridiaceae and Peptostreptococcaceae , and enrichment of Clostridium perfringens , C. innocuum , C. difficile , mucolytic Ruminococcus gnavus , and reduction of Akkermansia . It was concluded that epithelial-specific loss of Cftr is a major driver of CF intestinal dysbiosis and inflammation with significant similarities to previous studies of global Cftr KO mice.

New and noteworthy

Chronic intestinal inflammation is a manifestation of cystic fibrosis (CF), a disease caused by loss of the anion channel CFTR that is expressed in many tissues. This study shows that intestinal epithelial cell-specific loss of CFTR (iCftr KO) in mice is sufficient to induce intestinal dysbiosis and inflammation. Studies were performed on mice consuming either dietary regimen (PEG laxative or liquid diet) routinely used to prevent obstruction in CF mice.

Pathogenesis of nontypeable Haemophilus influenzae infections in chronic suppurative lung disease

The respiratory tract antimicrobial defense system is a multilayered defense mechanism that relies upon mucociliary clearance and components of both the innate and adaptive immune systems to protect the lungs from inhaled or aspirated microorganisms. One of these potential pathogens, nontypeable Haemophilus influenzae (NTHi), adopts several, multifaceted redundant strategies to successfully colonize the lower airways and establish a persistent infection. NTHi can impair mucociliary clearance, express multiple multifunctional adhesins for various cell types within the respiratory tract and evade host defenses by surviving within and between cells, forming biofilms, increasing antigenic drift, secreting proteases and antioxidants, and by host-pathogen cross-talk, impair macrophage and neutrophil function. NTHi is recognized as an important pathogen in several chronic lower respiratory disorders, such as protracted bacterial bronchitis, bronchiectasis, cystic fibrosis, and primary ciliary dyskinesia. The persistence of NTHi in human airways, including its capacity to form biofilms, results in chronic infection and inflammation, which can ultimately injure airway wall structures. The complex nature of the molecular pathogenetic mechanisms employed by NTHi is incompletely understood but improved understanding of its pathobiology will be important for developing effective therapies and vaccines, especially given the marked genetic heterogeneity of NTHi and its possession of phase-variable genes. Currently, no vaccine candidates are ready for large phase III clinical trials.

Mucus aberrant properties in CF: Insights from cells and animal models

Cystic fibrosis (CF), an autosomal genetic disorder caused by the dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) protein, is characterized by mucus accumulation in the lungs, the intestinal tract, and the pancreatic ducts. Mucins are high-molecular-weight glycoproteins that govern the biochemical and biophysical properties of mucus. In the CF lung, increased mucus viscoelasticity is associated with decreased mucociliary clearance and defects in host defense mechanisms. The link between defective ion channel and abnormal mucus properties has been investigated in studies involving cell and animal models. In this review article, we discuss recent progress toward understanding the different regions and cells that express CFTR in the airways and how mucus is produced and cleared from the lungs. In addition, we reflect on animal models that provided insights into the organization and the role of the mucin network and how mucus and antimicrobial activities act in concert to protect the lungs from invading pathogens.

PLGA-Based Micro/Nanoparticles: An Overview of Their Applications in Respiratory Diseases

Respiratory diseases, such as asthma and chronic obstructive pulmonary disease (COPD), are critical areas of medical research, as millions of people are affected worldwide. In fact, more than 9 million deaths worldwide were associated with respiratory diseases in 2016, equivalent to 15% of global deaths, and the prevalence is increasing every year as the population ages. Due to inadequate treatment options, the treatments for many respiratory diseases are limited to relieving symptoms rather than curing the disease. Therefore, new therapeutic strategies for respiratory diseases are urgently needed. Poly (lactic-co-glycolic acid) micro/nanoparticles (PLGA M/NPs) have good biocompatibility, biodegradability and unique physical and chemical properties, making them one of the most popular and effective drug delivery polymers. In this review, we summarized the synthesis and modification methods of PLGA M/NPs and their applications in the treatment of respiratory diseases (asthma, COPD, cystic fibrosis (CF), etc.) and also discussed the research progress and current research status of PLGA M/NPs in respiratory diseases. It was concluded that PLGA M/NPs are the promising drug delivery vehicles for the treatment of respiratory diseases due to their advantages of low toxicity, high bioavailability, high drug loading capacity, plasticity and modifiability. And at the end, we presented an outlook on future research directions, aiming to provide some new ideas for future research directions and hopefully to promote their widespread application in clinical treatment.

CDK8 and CDK19 act redundantly to control the CFTR pathway in the intestinal epithelium

CDK8 and CDK19 form a conserved cyclin-dependent kinase subfamily that interacts with the essential transcription complex, Mediator, and also phosphorylates the C-terminal domain of RNA polymerase II. Cells lacking either CDK8 or CDK19 are viable and have limited transcriptional alterations, but whether the two kinases redundantly control cell proliferation and differentiation is unknown. Here, we find in mice that CDK8 is dispensable for regulation of gene expression, normal intestinal homeostasis, and efficient tumourigenesis, and is largely redundant with CDK19 in the control of gene expression. Their combined deletion in intestinal organoids reduces long-term proliferative capacity but is not lethal and allows differentiation. However, double-mutant organoids show mucus accumulation and increased secretion by goblet cells, as well as downregulation of expression of the cystic fibrosis transmembrane conductance regulator (CFTR) and functionality of the CFTR pathway. Pharmacological inhibition of CDK8/19 kinase activity in organoids and in mice recapitulates several of these phenotypes. Thus, the Mediator kinases are not essential for cell proliferation and differentiation in an adult tissue, but they cooperate to regulate specific transcriptional programmes.

High-throughput functional assay in cystic fibrosis patient-derived organoids allows drug repurposing

Background

Cystic fibrosis (CF) is a rare hereditary disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Recent therapies enable effective restoration of CFTR function of the most common F508del CFTR mutation. This shifts the unmet clinical need towards people with rare CFTR mutations such as nonsense mutations, of which G542X and W1282X are most prevalent. CFTR function measurements in patient-derived cell-based assays played a critical role in preclinical drug development for CF and may play an important role to identify new drugs for people with rare CFTR mutations.

Methods

Here, we miniaturised the previously described forskolin-induced swelling (FIS) assay in intestinal organoids from a 96-well to a 384-well plate screening format. Using this novel assay, we tested CFTR increasing potential of a 1400-compound Food and Drug Administration (FDA)-approved drug library in organoids from donors with W1282X/W1282X CFTR nonsense mutations.

Results

The 384-well FIS assay demonstrated uniformity and robustness based on coefficient of variation and Z'-factor calculations. In the primary screen, CFTR induction was limited overall, yet interestingly, the top five compound combinations that increased CFTR function all contained at least one statin. In the secondary screen, we indeed verified that four out of the five statins (mevastatin, lovastatin, simvastatin and fluvastatin) increased CFTR function when combined with CFTR modulators. Statin-induced CFTR rescue was concentration-dependent and W1282X-specific.

Conclusions

Future studies should focus on elucidating genotype specificity and mode-of-action of statins in more detail. This study exemplifies proof of principle of large-scale compound screening in a functional assay using patient-derived organoids.

Mucins and CFTR: Their Close Relationship

Mucociliary clearance is a critical defense mechanism for the lungs governed by regionally coordinated epithelial cellular activities, including mucin secretion, cilia beating, and transepithelial ion transport. Cystic fibrosis (CF), an autosomal genetic disorder caused by the dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) channel, is characterized by failed mucociliary clearance due to abnormal mucus biophysical properties. In recent years, with the development of highly effective modulator therapies, the quality of life of a significant number of people living with CF has greatly improved; however, further understanding the cellular biology relevant to CFTR and airway mucus biochemical interactions are necessary to develop novel therapies aimed at restoring CFTR gene expression in the lungs. In this article, we discuss recent advances of transcriptome analysis at single-cell levels that revealed a heretofore unanticipated close relationship between secretory MUC5AC and MUC5B mucins and CFTR in the lungs. In addition, we review recent findings on airway mucus biochemical and biophysical properties, focusing on how mucin secretion and CFTR-mediated ion transport are integrated to maintain airway mucus homeostasis in health and how CFTR dysfunction and restoration of function affect mucus properties.

An optimized protocol for assessment of sputum macrorheology in health and muco-obstructive lung disease

Background: Airway mucus provides important protective functions in health and abnormal viscoelasticity is a hallmark of muco-obstructive lung diseases such as cystic fibrosis (CF). However, previous studies of sputum macrorheology from healthy individuals and patients with CF using different experimental protocols yielded in part discrepant results and data on a systematic assessment across measurement settings and conditions remain limited.

Objectives: The aim of this study was to develop an optimized and reliable protocol for standardized macrorheological measurements of airway mucus model systems and native human sputum from healthy individuals and patients with muco-obstructive lung disease.

Methods: Oscillatory rheological shear measurements were performed using bovine submaxillary mucin (BSM) at different concentrations (2% and 10% solids) and sputum samples from healthy controls (n = 10) and patients with CF (n = 10). Viscoelastic properties were determined by amplitude and frequency sweeps at 25°C and 37°C with or without solvent trap using a cone-plate geometry.

Results: Under saturated atmosphere, we did not observe any temperature-dependent differences in 2% and 10% BSM macrorheology, whereas in the absence of evaporation control 10% BSM demonstrated a significantly higher viscoelasticity at 37°C. Similarly, during the measurements without evaporation control at 37°C we observed a substantial increase in the storage modulus G′ and the loss modulus G″ of the highly viscoelastic CF sputum but not in the healthy sputum.

Conclusion: Our data show systematically higher viscoelasticity of CF compared to healthy sputum at 25°C and 37°C. For measurements at the higher temperature using a solvent trap to prevent evaporation is essential for macrorheological analysis of mucus model systems and native human sputum. Another interesting finding is that the viscoelastic properties are not much sensitive to the applied experimental deformation and yield robust results despite their delicate consistency. The optimized protocol resulting from this work will facilitate standardized quantitative assessment of abnormalities in viscoelastic properties of airway mucus and response to muco-active therapies in patients with CF and other muco-obstructive lung diseases.

Mucus-targeting therapies of defective mucus clearance for cystic fibrosis: A short review

In the lungs, defective CFTR associated with cystic fibrosis (CF) represents the nidus for abnormal mucus clearance in the airways and consequently a progressive lung disease. Defective CFTR-mediated Cl^- secretion results in altered mucus properties, including concentration, viscoelasticity, and the ratio of the two mucins, MUC5B and MUC5AC. In the past decades, therapies targeting the CF mucus defect, directly or indirectly, have been developed; nevertheless, better treatments to prevent the disease progression are still needed. This review summarizes the existing knowledge on the defective mucus in CF disease and highlights it as a barrier to the development of future inhaled genetic therapies. The use of new mucus-targeting treatments is also discussed, focusing on their potential role to halt the progress of CF lung disease.

Rapid Viscoelastic Characterization of Airway Mucus Using a Benchtop Rheometer

In muco-obstructive lung diseases (e.g., asthma, chronic obstructive pulmonary disease, cystic fibrosis) and other respiratory conditions (e.g., viral/bacterial infections), mucus biophysical properties are altered by goblet cell hypersecretion, airway dehydration, oxidative stress, and the presence of extracellular DNA. Previous studies showed that sputum viscoelasticity correlated with pulmonary function and that treatments affecting sputum rheology (e.g., mucolytics) can result in remarkable clinical benefits. In general, rheological measurements of non-Newtonian fluids employ elaborate, time-consuming approaches (e.g., parallel/cone-plate rheometers and/or microbead particle tracking) that require extensive training to perform the assay and interpret the data. This study tested the reliability, reproducibility, and sensitivity of Rheomuco, a user-friendly benchtop device that is designed to perform rapid measurements using dynamic oscillation with a shear-strain sweep to provide linear viscoelastic moduli (G', G", G*, and tan δ) and gel point characteristics (γc and σc) for clinical samples within 5 min. Device performance was validated using different concentrations of a mucus simulant, 8 MDa polyethylene oxide (PEO), and against traditional bulk rheology measurements. A clinical isolate harvested from an intubated patient with status asthmaticus (SA) was then assessed in triplicate measurements and the coefficient of variation between measurements is <10%. Ex vivo use of a potent mucus reducing agent, TCEP, on SA mucus resulted in a five-fold decrease in elastic modulus and a change toward a more "liquid-like" behavior overall (e.g., higher tan δ). Together, these results demonstrate that the tested benchtop rheometer can make reliable measures of mucus viscoelasticity in clinical and research settings. In summary, the described protocol could be used to explore the effects of mucoactive drugs (e.g., rhDNase, N-acetyl cysteine) onsite to adapt treatment on a case-by-case basis, or in preclinical studies of novel compounds.

Diesel exhaust exposure in mice induces pulmonary fibrosis by TGF-β/Smad3 signaling pathway

BACKGROUND

Epidemiological studies suggest increased risk of lung cancer associated with diesel exhaust (DE) exposure. However, DE-induced lung fibrosis may lead to cancer and needs investigation.

OBJECTIVES

To study the mechanism involved in the initiation of DE- induced lung fibrosis.

METHODS

C57BL/6 mice were exposed to DE for 30 min/day for 5 days/weeks for 8 weeks. Pulmonary function test was performed to measure lung function. Mice were euthanized to collect BALF, blood, and lung tissue. BALF was used for cell count and cytokine analysis. Lung tissue slides were stained to examine structural integrity. RNA from lung tissue was used for RT-PCR. Immunoblots were performed to study fibrosis and EMT pathway.

RESULTS

Mice exposed to DE increase lung resistance and tissue elastance with decrease in inspiratory capacity (p < 0.05) suggesting lung function impairment. BALF showed significantly increased macrophages, neutrophils and monocytes (p < 0.01). Additionally, there was an increase in inflammation and alveolar wall thickening in lungs (p < 0.01) correlates with cellular infiltration. Macrophages had black soot deposition in lung tissue of DE exposed mice. Lung section staining revealed increase in mucus producing goblet cells for clearance of soot in lung. DE exposed lung showed increased collagen deposition and hydroxyproline residue (p < 0.01). Repetitive exposure of DE in mice lead to tissue remodeling in lung, demonstrated by fibrotic foci and smooth muscles. A significant increase in α-SMA and fibronectin (p < 0.05) in lung indicate progression of pulmonary fibrosis. TGF-β/Smad3 signaling was activated with increase in P-smad3 expression in DE exposed mice. Decreased expression of E-cadherin and increased vimentin (p < 0.05) in lungs of DE exposed mice indicate epithelial to mesenchymal transition.

CONCLUSION

DE exposure to mice induced lung injury and pulmonary fibrosis thereby remodeling tissue. The study demonstrates TGF-β/SMAD3 pathway involvement with an activation of EMT in DE exposed mice.

Treatment of cystic fibrosis airway cells with CFTR modulators reverses aberrant mucus properties via hydration

QUESTION

Cystic fibrosis (CF) is characterised by the accumulation of viscous adherent mucus in the lungs. While several hypotheses invoke a direct relationship with cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction (i.e. acidic airway surface liquid (ASL) pH, low bicarbonate (HCO₃ ^-) concentration, airway dehydration), the dominant biochemical alteration of CF mucus remains unknown.

MATERIALS/METHODS

We characterised a novel cell line (CFTR-KO Calu3 cells) and the responses of human bronchial epithelial (HBE) cells from subjects with G551D or F508del mutations to ivacaftor and elexacaftor-tezacaftor-ivacaftor. A spectrum of assays such as short-circuit currents, quantitative PCR, ASL pH, Western blotting, light scattering/refractometry (size-exclusion chromatography with inline multi-angle light scattering), scanning electron microscopy, percentage solids and particle tracking were performed to determine the impact of CFTR function on mucus properties.

RESULTS

Loss of CFTR function in Calu3 cells resulted in ASL pH acidification and mucus hyperconcentration (dehydration). Modulation of CFTR in CF HBE cells did not affect ASL pH or mucin mRNA expression, but decreased mucus concentration, relaxed mucus network ultrastructure and improved mucus transport. In contrast with modulator-treated cells, a large fraction of airway mucins remained attached to naïve CF cells following short apical washes, as revealed by the use of reducing agents to remove residual mucus from the cell surfaces. Extended hydration, but not buffers alkalised with sodium hydroxide or HCO₃ ^-, normalised mucus recovery to modulator-treated cell levels.

CONCLUSION

These results indicate that airway dehydration, not acidic pH and/or low [HCO₃ ^-], is responsible for abnormal mucus properties in CF airways and CFTR modulation predominantly restores normal mucin entanglement.

Human ocular mucins: The endowed guardians of sight

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

The cystic fibrosis lung microenvironment alters antibiotic activity: causes and effects

Chronic airway colonisation by Pseudomonas aeruginosa, a hallmark of cystic fibrosis (CF) lung disease, is associated with increased morbidity and mortality and despite aggressive antibiotic treatment, P. aeruginosa is able to persist in CF airways. In vitro antibiotic susceptibility assays are poor predictors of antibiotic efficacy to treat respiratory tract infections in the CF patient population and the selection of the antibiotic(s) is often made on an empirical base. In the current review, we discuss the factors that are responsible for the discrepancies between antibiotic activity in vitro and clinical efficacy in vivo We describe how the CF lung microenvironment, shaped by host factors (such as iron, mucus, immune mediators and oxygen availability) and the microbiota, influences antibiotic activity and varies widely between patients. A better understanding of the CF microenvironment and population diversity may thus help improve in vitro antibiotic susceptibility testing and clinical decision making, in turn increasing the success rate of antibiotic treatment.

The Gut-Lung Axis in Cystic Fibrosis

Cystic fibrosis (CF) is a heritable, multiorgan disease that impacts all tissues that normally express cystic fibrosis transmembrane conductance regulator (CFTR) protein. While the importance of the airway microbiota has long been recognized, the intestinal microbiota has only recently been recognized as an important player in both intestinal and lung health outcomes for persons with CF (pwCF). Here, we summarize current literature related to the gut-lung axis in CF, with a particular focus on three key ideas: (i) mechanisms through which microbes influence the gut-lung axis, (ii) drivers of microbiota alterations, and (iii) the potential for intestinal microbiota remediation.

The Spectrum of Fungal Colonization and Their Attributable Effects on Cystic Fibrosis Patients with Rare CFTR Genetic Mutations

Chronic airway colonization by bacteria and fungi is very common in CF patients, causing irreversible lung damage. It is known that rates of fungal infections are much lower than those of bacterial infections, however they can worsen the medical condition of CF patients. In this study, we identify the most common fungal species isolated from 31 adult CF patients in Qatar and analyze their correlation with lung function, pulmonary exacerbations, bronchial asthma, and pancreatic insufficiency. Mycological evaluation, as well as medical records, were reviewed for the patients regularly under the adult CF service at Hamad General Hospital in the period between 2017–2019. All CF patients included in this study carry rare CFTR mutations. The majority of those patients (n = 25) carried the c.3700A>G; I1234V mutation, whereas three patients carried the heterozygous mutation (c.1657C>T and c.1115A>T) and the remaining three carried the homozygous mutation (c.920G>A). Twenty-two of the adult CF participants (70.9%) were colonized with fungal species regardless of the type of the CFTR mutation. Candida and Aspergillus species were the most common, colonizing 81% and 45% of the patients, respectively. For Candida colonized patients, Candida dubliniensis was the most frequently reported species (55.6%), whereas Aspergillus fumigatus colonization was the most common (50.0%) among Aspergillus colonized patients. These identified fungal pathogens were associated with poor lung function, pancreatic insufficiency, and asthma in this cohort. Such colonization could possibly aggravate the most known CF complications, notably pulmonary exacerbations, asthma, and pancreatic insufficiency.

Mucociliary Respiratory Epithelium Integrity in Molecular Defense and Susceptibility to Pulmonary Viral Infections

Mucociliary defense, mediated by the ciliated and goblet cells, is fundamental to respiratory fitness. The concerted action of ciliary movement on the respiratory epithelial surface and the pathogen entrapment function of mucus help to maintain healthy airways. Consequently, genetic or acquired defects in lung defense elicit respiratory diseases and secondary microbial infections that inflict damage on pulmonary function and may even be fatal. Individuals living with chronic and acute respiratory diseases are more susceptible to develop severe coronavirus disease-19 (COVID-19) illness and hence should be proficiently managed. In light of the prevailing pandemic, we review the current understanding of the respiratory system and its molecular components with a major focus on the pathophysiology arising due to collapsed respiratory epithelium integrity such as abnormal ciliary movement, cilia loss and dysfunction, ciliated cell destruction, and changes in mucus rheology. The review includes protein interaction networks of coronavirus infection-manifested implications on the molecular machinery that regulates mucociliary clearance. We also provide an insight into the alteration of the transcriptional networks of genes in the nasopharynx associated with the mucociliary clearance apparatus in humans upon infection by severe acute respiratory syndrome coronavirus-2.

Evaluation of Naringenin as a Promising Treatment Option for COPD Based on Literature Review and Network Pharmacology

Chronic obstructive pulmonary disease (COPD) is a chronic respiratory disease characterized by incompletely reversible airflow limitation and seriously threatens the health of humans due to its high morbidity and mortality. Naringenin, as a natural flavanone, has shown various potential pharmacological activities against multiple pathological stages of COPD, but available studies are scattered and unsystematic. Thus, we combined literature review with network pharmacology analysis to evaluate the potential therapeutic effects of naringenin on COPD and predict its underlying mechanisms, expecting to provide a promising tactic for clinical treatment of COPD.

A SYK/SHC1 pathway regulates the amount of CFTR in the plasma membrane

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause the recessive genetic disease cystic fibrosis, where the chloride transport across the apical membrane of epithelial cells mediated by the CFTR protein is impaired. CFTR protein trafficking to the plasma membrane (PM) is the result of a complex interplay between the secretory and membrane recycling pathways that control the number of channels present at the membrane. In addition, the ion transport activity of CFTR at the PM is modulated through post-translational protein modifications. Previously we described that spleen tyrosine kinase (SYK) phosphorylates a specific tyrosine residue in the nucleotide-binding domain 1 domain and this modification can regulate the PM abundance of CFTR. Here we identified the underlying biochemical mechanism using peptide pull-down assays followed by mass spectrometry. We identified in bronchial epithelial cells that the adaptor protein SHC1 recognizes tyrosine-phosphorylated CFTR through its phosphotyrosine-binding domain and that the formation of a complex between SHC1 and CFTR is induced at the PM in the presence of activated SYK. The depletion of endogenous SHC1 expression was sufficient to promote an increase in CFTR at the PM of these cells. The results identify a SYK/SHC1 pathway that regulates the PM levels of CFTR channels, contributing to a better understanding of how CFTR-mediated chloride secretion is regulated.

Observations of, and Insights into, Cystic Fibrosis Mucus Heterogeneity in the Pre-Modulator Era: Sputum Characteristics, DNA and Glycoprotein Content, and Solubilization Time

Airway obstruction with chronic inflammation and infection are major contributors to the lung damage and mortality of cystic fibrosis (CF). A better understanding of the congested milieu of CF airways will aid in improving therapeutic strategies. This article retrospectively reports our observations, and discusses insights gained in the handling and analysis of CF sputa. CF and non-CF mucus samples were surveyed for morphological features by electron microscopy and analyzed for the macromolecular dry weight (MDW), total protein, lipid, carbohydrate, and DNA. Mucus character was investigated with chemical solubilization time as a comparative tool. CF mucus appeared distinctly thick, viscous, and heterogeneous, with neutrophils as the dominant immune cell. CF sputum DNA content varied markedly for and between individuals (~1–10% MDW), as did solubilization times (~1–20 h). CF Sputum DNA up to 7.1% MDW correlated positively with solubilization time, whereas DNA >7.1% MDW correlated negatively. 3D analysis of CF sputa DNA, GP, and solubilization times revealed a dynamic and predictive relationship. Reflecting on the heterogeneous content and character of CF mucus, and the possible interplay in space and time in the respiratory tract of polymeric DNA and mucous glycoproteins, we highlight it’s potential to affect infection-related airway pathologies and the success of therapeutic interventions.

Mucin Secretion in Cystic Fibrosis: A Systematic Review

BACKGROUND

Mucus protects the epithelium against invaders and toxic materials. Sticky and thick mucus is characteristic of CF.

OBJECTIVE

The aim of this systematic review is to characterize the specific mucins secreted in the lung and intestinal tract of CF patients.

METHODS

A systematic literature search was conducted up to December 31, 2019. The following terms were used: "cystic fibrosis" AND "mucin." Case-control studies comparing mucin expression in CF patients to healthy controls were included.

RESULTS

We found 741 eligible studies, 694 studies were rejected because they were performed in animals and not in full text, and 32 studies were excluded being editorials, duplications, review articles, meta-analysis, or not in English. Fifteen studies were eligible for our study, including 150 CF patients compared to 82 healthy controls, all fulfilled the inclusion criteria. The main mucin types expressed in the sinus submucosal glands, sputum, tracheobronchial surface epithelium, and lung submucosal glands were MUC5AC and MUC5B. Increase in the number of sinusoidal submucosal glands and expression of MUC5B was found in CF patients, but no such difference from healthy controls was found for the number of goblet cells in the surface epithelium nor in the expression of -MUC5AC. The opposite was found in the tracheobronchial surface epithelium and in the lungs.

CONCLUSIONS

Increased expression of MUC5AC in the surface epithelium and of MUC5B in the subepithelial glands may be the result of higher secretion rate of mucin into the lumen of the respiratory tract, causing mucus plaque, infection, and inflammation.

First contact: the role of respiratory cilia in host-pathogen interactions in the airways

Respiratory cilia are the driving force of the mucociliary escalator, working in conjunction with secreted airway mucus to clear inhaled debris and pathogens from the conducting airways. Respiratory cilia are also one of the first contact points between host and inhaled pathogens. Impaired ciliary function is a common pathological feature in patients with chronic airway diseases, increasing susceptibility to respiratory infections. Common respiratory pathogens, including viruses, bacteria, and fungi, have been shown to target cilia and/or ciliated airway epithelial cells, resulting in a disruption of mucociliary clearance that may facilitate host infection. Despite being an integral component of airway innate immunity, the role of respiratory cilia and their clinical significance during airway infections are still poorly understood. This review examines the expression, structure, and function of respiratory cilia during pathogenic infection of the airways. This review also discusses specific known points of interaction of bacteria, fungi, and viruses with respiratory cilia function. The emerging biological functions of motile cilia relating to intracellular signaling and their potential immunoregulatory roles during infection will also be discussed.

Stem cells and lung regeneration

The ability to replace defective cells in an airway with cells that can engraft, integrate, and restore a functional epithelium could potentially cure a number of lung diseases. Progress toward the development of strategies to regenerate the adult lung by either in vivo or ex vivo targeting of endogenous stem cells or pluripotent stem cell derivatives is limited by our fundamental lack of understanding of the mechanisms controlling human lung development, the precise identity and function of human lung stem and progenitor cell types, and the genetic and epigenetic control of human lung fate. In this review, we intend to discuss the known stem/progenitor cell populations, their relative differences between rodents and humans, their roles in chronic lung disease, and their therapeutic prospects. Additionally, we highlight the recent breakthroughs that have increased our understanding of these cell types. These advancements include novel lineage-traced animal models and single-cell RNA sequencing of human airway cells, which have provided critical information on the stem cell subtypes, transition states, identifying cell markers, and intricate pathways that commit a stem cell to differentiate or to maintain plasticity. As our capacity to model the human lung evolves, so will our understanding of lung regeneration and our ability to target endogenous stem cells as a therapeutic approach for lung disease.

Advances in Ca2+ modulation of gastrointestinal anion secretion and its dysregulation in digestive disorders (Review)

Intracellular calcium (Ca²⁺) is a critical cell signaling component in gastrointestinal (GI) physiology. Cytosolic calcium ([Ca²⁺]_cyt), as a secondary messenger, controls GI epithelial fluid and ion transport, mucus and neuropeptide secretion, as well as synaptic transmission and motility. The key roles of Ca²⁺ signaling in other types of secretory cell (including those in the airways and salivary glands) are well known. However, its action in GI epithelial secretion and the underlying molecular mechanisms have remained to be fully elucidated. The present review focused on the role of [Ca²⁺]_cyt in GI epithelial anion secretion. Ca²⁺ signaling regulates the activities of ion channels and transporters involved in GI epithelial ion and fluid transport, including Cl^- channels, Ca²⁺-activated K⁺ channels, cystic fibrosis (CF) transmembrane conductance regulator and anion/HCO₃^- exchangers. Previous studies by the current researchers have focused on this field over several years, providing solid evidence that Ca²⁺ signaling has an important role in the regulation of GI epithelial anion secretion and uncovering underlying molecular mechanisms. The present review is largely based on previous studies by the current researchers and provides an overview of the currently known molecular mechanisms of GI epithelial anion secretion with an emphasis on Ca²⁺-mediated ion secretion and its dysregulation in GI disorders. In addition, previous studies by the current researchers demonstrated that different regulatory mechanisms are in place for GI epithelial HCO₃^- and Cl^- secretion. An increased understanding of the roles of Ca²⁺ signaling and its targets in GI anion secretion may lead to the development of novel strategies to inhibit GI diseases, including the enhancement of fluid secretion in CF and protection of the GI mucosa in ulcer diseases.

Novel Anti-Inflammatory Approaches for Cystic Fibrosis Lung Disease: Identification of Molecular Targets and Design of Innovative Therapies

Cystic fibrosis (CF) is the most common genetic disorder among Caucasians, estimated to affect more than 70,000 people in the world. Severe and persistent bronchial inflammation and chronic bacterial infection, along with airway mucus obstruction, are hallmarks of CF lung disease and participate in its progression. Anti-inflammatory therapies are, therefore, of particular interest for CF lung disease. Furthermore, a better understanding of the molecular mechanisms involved in airway infection and inflammation in CF has led to the development of new therapeutic approaches that are currently under evaluation by clinical trials. These new strategies dedicated to CF inflammation are designed to treat different dysregulated aspects such as oxidative stress, cytokine secretion, and the targeting of dysregulated pathways. In this review, we summarize the current understanding of the cellular and molecular mechanisms that contribute to abnormal lung inflammation in CF, as well as the new anti-inflammatory strategies proposed to CF patients by exploring novel molecular targets and novel drug approaches.

In Vitro Reconstitution of an Intestinal Mucus Layer Shows That Cations and pH Control the Pore Structure That Regulates Its Permeability and Barrier Function

Dysfunction of the intestinal mucus barrier causes disorders such as ulcerative colitis and Crohn's disease. The function of this essential barrier may be affected by the periodically changing luminal environment. We hypothesized that the pH and ion concentration in mucus control its porosity, molecular permeability, and the penetration of microbes. To test this hypothesis, we developed a scalable method to extract porcine small intestinal mucus (PSIM). The aggregation and porosity of PSIM were determined using rheometry, spectrophotometry, and microscopy. Aggregation of PSIM at low pH increased both the elastic (G') and viscous (G″) moduli, and it slowed the transmigration of pathogenic Salmonella. Molecular transport was dependent on ion concentration. At moderate concentrations, many microscopic aggregates (2-5 μm in diameter) impeded diffusion. At higher concentrations, PSIM formed aggregate islands, increasing both porosity and diffusion. This in vitro model could lead to a better understanding of mucus barrier functions and improve the treatment of intestinal diseases.

Mucus accumulation in the lungs precedes structural changes and infection in children with cystic fibrosis

Although destructive airway disease is evident in young children with cystic fibrosis (CF), little is known about the nature of the early CF lung environment triggering the disease. To elucidate early CF pulmonary pathophysiology, we performed mucus, inflammation, metabolomic, and microbiome analyses on bronchoalveolar lavage fluid (BALF) from 46 preschool children with CF enrolled in the Australian Respiratory Early Surveillance Team for Cystic Fibrosis (AREST CF) program and 16 non-CF disease controls. Total airway mucins were elevated in CF compared to non-CF BALF irrespective of infection, and higher densities of mucus flakes containing mucin 5B and mucin 5AC were observed in samples from CF patients. Total mucins and mucus flakes correlated with inflammation, hypoxia, and oxidative stress. Many CF BALFs appeared sterile by culture and molecular analyses, whereas other samples exhibiting bacterial taxa associated with the oral cavity. Children without computed tomography-defined structural lung disease exhibited elevated BALF mucus flakes and neutrophils, but little/no bacterial infection. Although CF mucus flakes appeared "permanent" because they did not dissolve in dilute BALF matrix, they could be solubilized by a previously unidentified reducing agent (P2062), but not N-acetylcysteine or deoxyribonuclease. These findings indicate that early CF lung disease is characterized by an increased mucus burden and inflammatory markers without infection or structural lung disease and suggest that mucolytic and anti-inflammatory agents should be explored as preventive therapy.

Novel therapeutic approaches for the management of cystic fibrosis

Cystic fibrosis (CF) is a genetic condition characterised by the build-up of thick, sticky mucus that can damage many of the body's organs. It is a life-long disease that results in a shortened life expectancy, often due to the progression of advanced lung disease. Treatment has previously targeted the downstream symptoms such as diminished mucus clearance and recurrent infection. More recently, significant advances have been made in treating the cause of the disease by targeting the faulty gene responsible. Hope for the development of potential therapies lies with ongoing research into new pharmacological agents and gene therapy. This review gives an overview of CF, and summarises the current evidence regarding the disease management and upcoming strategies aimed at treating or potentially curing this condition.

Intracellular survival and innate immune evasion of Burkholderia cepacia: Improved understanding of quorum sensing-controlled virulence factors, biofilm, and inhibitors

Burkholderia cepacia complex (Bcc) are opportunistic pathogens implicated with nosocomial infections, and high rates of morbidity and mortality, especially in individuals with cystic fibrosis (CF). B. cepacia are naturally resistant to different classes of antibiotics, and can subvert the host innate immune responses by producing quorum sensing (QS) controlled virulence factors and biofilms. It still remains a conundrum as to how exactly the bacterium survives the intracellular environment within the host cells of CF patients and immunocompromised individuals although the bacterium can invade human lung epithelial cells, neutrophils, and murine macrophages. The mechanisms associated with intracellular survival in the airway epithelial cells and the role of QS and virulence factors in B. cepacia infections in cystic fibrosis remain largely unclear. The current review focuses on understanding the role of QS-controlled virulence factors and biofilms, and provides additional impetus to understanding the potentials of QS-inhibitory strategies against B. cepacia.

Exercise and Cystic Fibrosis

Cystic fibrosis (CF) is an autosomal recessive, inherited congenital disease caused by the mutation of the family autosomal CF gene, with cumulative exocrine secretion characterized by inflammation, tracheal remodeling, and mucus accumulation. With the development of modern medical technology, CF patients are living longer lives and receiving more and more treatments, including traditional drugs, physical therapy, and gene therapy. Exercise is widely used to prevent and treat metabolic diseases such as cardiovascular diseases, obesity, diabetes, and metabolic syndrome. Regular exercise is beneficial to aerobic capacity and lung health. Exercise therapy has been of great interest since people realized that CF can be affected by exercise. Exercise alone can be used as an ACT (airway clearance technique), which promotes the removal of mucosal cilia. Exercise therapy is more easily accepted by any society, which helps to normalize the lives of CF patients, rather than placing a psychological burden on them. In this chapter, we will review the latest research progress about exercise in CF.

TMEM16A chloride channel does not drive mucus production

Despite being essential for airway hydration, TMEM16A is not required for mucus (MUC5AC) production. Cell proliferation is the main driver for TMEM16A up-regulation during inflammation.

Airway mucus obstruction is the main cause of morbidity in cystic fibrosis, a disease caused by mutations in the CFTR Cl⁻ channel. Activation of non-CFTR Cl⁻ channels such as TMEM16A can likely compensate for defective CFTR. However, TMEM16A was recently described as a key driver in mucus production/secretion. Here, we have examined whether indeed there is a causal relationship between TMEM16A and MUC5AC production, the main component of respiratory mucus. Our data show that TMEM16A and MUC5AC are inversely correlated during differentiation of human airway cells. Furthermore, we show for the first time that the IL-4–induced TMEM16A up-regulation is proliferation-dependent, which is supported by the correlation found between TMEM16A and Ki-67 proliferation marker during wound healing. Consistently, the notch signaling activator DLL4 increases MUC5AC levels without inducing changes neither in TMEM16A nor in Ki-67 expression. Moreover, TMEM16A inhibition decreased airway surface liquid height. Altogether, our findings demonstrate that up-regulation of TMEM16A and MUC5AC is only circumstantial under cell proliferation, but with no causal relationship between them. Thus, although essential for airway hydration, TMEM16A is not required for MUC5AC production.

Mucus, mucins, and cystic fibrosis

Cystic fibrosis (CF) is both the most common and most lethal genetic disease in the Caucasian population. CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene and is characterized by the accumulation of thick, adherent mucus plaques in multiple organs, of which the lungs, gastrointestinal tract and pancreatic ducts are the most commonly affected. A similar pathogenesis cascade is observed in all of these organs: loss of CFTR function leads to altered ion transport, consisting of decreased chloride and bicarbonate secretion via the CFTR channel and increased sodium absorption via epithelial sodium channel upregulation. Mucosa exposed to changes in ionic concentrations sustain severe pathophysiological consequences. Altered mucus biophysical properties and weakened innate defense mechanisms ensue, furthering the progression of the disease. Mucins, the high-molecular-weight glycoproteins responsible for the viscoelastic properties of the mucus, play a key role in the disease but the actual mechanism of mucus accumulation is still undetermined. Multiple hypotheses regarding the impact of CFTR malfunction on mucus have been proposed and are reviewed here. (a) Dehydration increases mucin monomer entanglement, (b) defective Ca²⁺ chelation compromises mucin expansion, (c) ionic changes alter mucin interactions, and (d) reactive oxygen species increase mucin crosslinking. Although one biochemical change may dominate, it is likely that all of these mechanisms play some role in the progression of CF disease. This article discusses recent findings on the initial cause(s) of aberrant mucus properties in CF and examines therapeutic approaches aimed at correcting mucus properties.

Adapting to the Airways: Metabolic Requirements of Pseudomonas aeruginosa during the Infection of Cystic Fibrosis Patients

Pseudomonas aeruginosa is one of the major causes of morbidity and mortality of cystic fibrosis patients. During the infection, the bacteria colonize the nutritional rich lung mucus, which is present in the airway secretions in the patients, and they adapt their phenotype accordingly to the lung environment. In the airways, P. aeruginosa undergoes a broad metabolic rewiring as a consequence of the nutritional and stressful complexity of the lungs. However, the role of such metabolic rewiring on the infection outcome is poorly understood. Here, we review the metabolic evolution of clinical strains of P. aeruginosa during a cystic fibrosis lung infection and the metabolic functions operating in vivo under patho-physiological conditions. Finally, we discuss the perspective of modeling the cystic fibrosis environment using genome scale metabolic models of P. aeruginosa. Understanding the physiological changes occurring during the infection may pave the way to a more effective treatment for P. aeruginosa lung infections.

Current Practices and Potential Nanotechnology Perspectives for Pain Related to Cystic Fibrosis

Pain is a complex, multidimensional process that negatively affects physical and mental functioning, clinical outcomes, quality of life, and productivity for cystic fibrosis (CF) patients. CF is an inherited multi-system disease that requires a complete approach in order to evaluate, monitor and treat patients. The landscape in CF care has changed significantly, with currently more adult patients than children worldwide. Despite the great advances in supportive care and in our understanding regarding its pathophysiology, there are still numerous aspects of CF pain that are not fully explained. This review aims to provide a critical overview of CF pain research that focuses on pain assessment, prevalence, characteristics, clinical association and the impact of pain in children and adults, along with innovative nanotechnology perspectives for CF management. Specifically, the paper evaluates the pain symptoms associated with CF and examines the relationship between pain symptoms and disease severity. The particularities of gastrointestinal, abdominal, musculoskeletal, pulmonary and chest pain, as well as pain associated with medical procedures are investigated in patients with CF. Disease-related pain is common for patients with CF, suggesting that pain assessment should be a routine part of their clinical care. A summary of the use of nanotechnology in CF and CF-related pain is also given. Further research is clearly needed to better understand the sources of pain and how to improve patients’ quality of life.

The Pros and Cons of Cystic Fibrosis (CF) Patient Use of Herbal Supplements Containing Pulmonaria officinalis L. Extract: the Evidence from an In Vitro Study on Staphylococcus aureus CF Clinical Isolates

The justification for the use of herbal supplements with Pulmonaria officinalis L. extract (POE) in the case of staphylococcal lung colonization/infections characteristic for cystic fibrosis (CF), was examined in vitro. The impact of POE phenolic-rich fraction on the virulence attributes of CF-associated Staphylococcus aureus (S. aureus) clinical strains has been assessed, including pathogen adhesion, biofilm formation on native and protein-conditioned surfaces (mucin, elastin), mature biofilm eradication, staphylococcal protein A expression, α-toxin release, and S. a. adhesion to A549 cells. Cytotoxicity of the extract to lung epithelial cells was also investigated. It was found that POE has bacteriostatic effects at MIC 1⁻2 mg/mL, recognized as of limited efficacy, but at MIC/subMICs it targeted virulence not viability. It usually decreased S. aureus adhesion and less frequently inhibited biofilm formation on native and protein-conditioned surfaces. Observed effect seems to be related to significant reduction by POE of sortase A activity. However, in some cases POE favored the creation of biofilm by staphylococci and S. aureus adhesion to the lung epithelium was not limited. On the other side POE caused significant decrease of S. a. α-toxin synthesis and slightly weakened the expression of SpA. When used at supraMICs POE eradicated mature biofilm, but in some cases with unsatisfying outcomes. Promisingly, POE has been recognized as a safe product, with no cytotoxicity up to 4 mg/mL. These results reflect the positive, negative or neutral anti-staphylococcal properties of POE. It seems that POE may be beneficial as a prophylactic, but not as a therapeutic or supportive agent in the area of CF-integrative medicine. However, introduction the official recommendations needs further in vivo studies.

Case report: Cholecystoduodenostomy for cholestatic liver disease in a premature infant with cystic fibrosis and short gut syndrome

Background

Cholecystoduodenostomy is a surgical procedure that bypasses the extrahepatic biliary tree and connects the gallbladder directly to the duodenum. This case describes the successful use of this procedure in a novel situation.

Case presentation

A premature (34 weeks gestation) female infant with cystic fibrosis required a laparotomy on day 1 of life due to an intrauterine small bowel perforation. Resection of small bowel and ileostomy formation resulted in short gut syndrome, with 82 cm residual small bowel and intact ileocaecal valve. Post-ileostomy reversal at 2 months old, she developed conjugated hyperbilirubinaemia. Despite conservative management including increased enteral feeding, ursodeoxycholic acid, cholecystostomy drain insertion and flushes, her cholestatic jaundice persisted. A liver biopsy revealed an “obstructive/cholestatic” picture with fibrosis. To avoid further shortening her gut with an hepatoportoenterostomy, cholecystoduodenostomy was performed at 3 months of age with subsequent post-operative improvement and eventual normalisation of her clinical jaundice and liver biochemistry.

Conclusions

This is the first reported case of a cholecystoduodenostomy being used successfully to treat an infant with persistent conjugated hyperbilirubinemia, cystic fibrosis and short gut syndrome. Cholecystoduodenostomy is a treatment option that with further study, may be considered for obstruction of the common bile duct in patients with short gut and/or where a shorter operating time with minimal intervention is preferred.