CFTR inhibition mimics the cystic fibrosis inflammatory profile

Autoimmunity in people with cystic fibrosis

Cystic fibrosis (CF) clinicians may see patients who have difficult-to-manage symptoms that do not have a clear CF-related etiology, such as unusual gastrointestinal (GI) complaints, vasculitis, or arthritis. Alterations in immunity, inflammation and intraluminal dysbiosis create a milieu that may lead to autoimmunity, and the CF transmembrane regulator protein may have a direct role as well. While autoantibodies and other autoimmune markers may develop, these may or may not lead to organ involvement, therefore they are helpful but not sufficient to establish an autoimmune diagnosis. Autoimmune involvement of the GI tract is the best-established association. Next steps to understand autoimmunity in CF should include a more in-depth assessment of the community perspective on its impact. In addition, bringing together specialists in various fields including, but not limited to, pulmonology, gastroenterology, immunology, and rheumatology, would lead to cross-dissemination and help define the path forward in basic science and clinical practice.

Influenza A-induced cystic fibrosis transmembrane conductance regulator dysfunction increases susceptibility to Streptococcus pneumoniae

Influenza A virus (IAV) infection is commonly complicated by secondary bacterial infections that lead to increased morbidity and mortality. Our recent work demonstrates that IAV disrupts airway homeostasis, leading to airway pathophysiology resembling cystic fibrosis disease through diminished cystic fibrosis transmembrane conductance regulator (CFTR) function. Here, we use human airway organotypic cultures to investigate how IAV alters the airway microenvironment to increase susceptibility to secondary infection with Streptococcus pneumoniae (Spn). We observed that IAV-induced CFTR dysfunction and airway surface liquid acidification is central to increasing susceptibility to Spn. Additionally, we observed that IAV induced profound transcriptional changes in the airway epithelium and proteomic changes in the airway surface liquid in both CFTR-dependent and -independent manners. These changes correspond to multiple diminished host defense pathways and altered airway epithelial function. Collectively, these findings highlight both the importance of CFTR function during infectious challenge and demonstrate a central role for the lung epithelium in secondary bacterial infections following IAV.

Proteome of airway surface liquid and mucus in newborn wildtype and cystic fibrosis piglets

BACKGROUND

The respiratory tract is protected from inhaled particles and microbes by mucociliary clearance, mediated by the mucus and the cilia creating a flow to move the mucus cephalad. Submucosal glands secrete linear MUC5B mucin polymers and because they pass through the gland duct before reaching the airway surface, bundled strands of 1000-5000 parallel molecules exit the glands. In contrast, the surface goblet cells secrete both MUC5AC and MUC5B.

METHODS

We used mass-spectrometry based proteomic analysis of unstimulated and carbachol stimulated newborn wild-type (WT) and cystic fibrosis transmembrane conductance regulator (CFTR) null (CF) piglet airways to study proteins in the airway surface liquid and mucus, to investigate if levels of MUC5AC and MUC5B were affected by carbachol stimulation and whether the proteins clustered according to function.

RESULTS

Proteins in the first four extracted fractions clustered together and the fifth fraction contained the mucus cluster, mucins and other proteins known to associate with mucins, whereas the traditional airway surface liquid proteins clustered to fraction 1-4 and were absent from the mucus fraction. Carbachol stimulation resulted in increased MUC5AC and MUC5B.

CONCLUSIONS

These results indicate a distinct separation between proteins in the washable surface liquid and the mucus fraction. In fractions 1-4 from newborn CF piglets an additional cluster containing acute phase proteins was observed, suggesting an early inflammatory response in CF piglets. Alternatively, increased levels of these proteins could indicate altered lung development in the CF piglets. This observation suggests that CF airway disease is present at birth and thus, treatment should commence directly after diagnosis.

The Impact of Highly Effective Modulator Therapy on Cystic Fibrosis Microbiology and Inflammation

Highly effective cystic fibrosis (CF) transmembrane conductance regulator (CFTR) modulator therapy (HEMT) corrects the underlying molecular defect causing CF disease. HEMT decreases symptom burden and improves clinical metrics and quality of life for most people with CF (PwCF) and eligible cftr mutations. Improvements in measures of pulmonary health suggest that restoration of function of defective CFTR anion channels by HEMT not only enhances airway mucociliary clearance, but also reduces chronic pulmonary infection and inflammation. This article reviews the evidence for how HEMT influences the dynamic and interdependent processes of infection and inflammation in the CF airway, and what questions remain unanswered.

Bioelectric regulation of intestinal stem cells

Proper regulation of ion balance across the intestinal epithelium is essential for physiological functions, while ion imbalance causes intestinal disorders with dire health consequences. Ion channels, pumps, and exchangers are vital for regulating ion movements (i.e., bioelectric currents) that control epithelial absorption and secretion. Recent in vivo studies used the Drosophila gut to identify conserved pathways that link regulators of Ca²⁺, Na⁺ and Cl^- with intestinal stem cell (ISC) proliferation. These studies laid a foundation for using the Drosophila gut to identify conserved proliferative responses triggered by bioelectric regulators. Here, we review these studies, discuss their significance, as well as the advantages of using Drosophila to unravel conserved bioelectrically induced molecular pathways in the intestinal epithelium under physiological, pathophysiological, and regenerative conditions.

Current evidence on the effect of highly effective CFTR modulation on interleukin-8 in cystic fibrosis

INTRODUCTION

Cystic fibrosis (CF) is a genetically inherited disease, with mortality and morbidity associated with respiratory disease. The inflammatory response in CF is characterized by excessive neutrophil influx to the airways, mainly due to the increased local production and retention of interleukin-8 (IL-8), a potent neutrophil chemoattractant.

AREAS COVERED

We discuss how the chemokine IL-8 dominates the inflammatory profile of the airways in CF lung disease. Cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies are designed to correct the malfunctioning protein resulting from specific CFTR mutations. This review covers current evidence on the impact of CFTR impairment on levels of IL-8 and outlines the influence of effective CFTR modulation on inflammation in CF with a focus on cytokine production. Review of the literature was carried out using the PUBMED database, Google Scholar, and The Cochrane Library databases, using several appropriate generic terms.

EXPERT OPINION

Therapeutic interventions specifically targeting the defective CFTR protein have improved the outlook for CF. Accumulating studies on the effect of highly effective CFTR modulation on inflammation indicate an impact on IL-8 levels. Further studies are required to increase our knowledge of early onset innate inflammatory dysregulation and on anti-inflammatory mechanisms of CFTR modulators.

Transcriptomic analysis of CFTR-impaired endothelial cells reveals a pro-inflammatory phenotype

Cystic fibrosis (CF) is a life-threatening disorder characterised by decreased pulmonary mucociliary and pathogen clearance, and an exaggerated inflammatory response leading to progressive lung damage. CF is caused by bi-allelic pathogenic variants of the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes a chloride channel. CFTR is expressed in endothelial cells (ECs) and EC dysfunction has been reported in CF patients, but a role for this ion channel in ECs regarding CF disease progression is poorly described.We used an unbiased RNA sequencing approach in complementary models of CFTR silencing and blockade (by the CFTR inhibitor CFTRinh-172) in human ECs to characterise the changes upon CFTR impairment. Key findings were further validated in vitro and in vivo in CFTR-knockout mice and ex vivo in CF patient-derived ECs.Both models of CFTR impairment revealed that EC proliferation, migration and autophagy were downregulated. Remarkably though, defective CFTR function led to EC activation and a persisting pro-inflammatory state of the endothelium with increased leukocyte adhesion. Further validation in CFTR-knockout mice revealed enhanced leukocyte extravasation in lung and liver parenchyma associated with increased levels of EC activation markers. In addition, CF patient-derived ECs displayed increased EC activation markers and leukocyte adhesion, which was partially rescued by the CFTR modulators VX-770 and VX-809.Our integrated analysis thus suggests that ECs are no innocent bystanders in CF pathology, but rather may contribute to the exaggerated inflammatory phenotype, raising the question of whether normalisation of vascular inflammation might be a novel therapeutic strategy to ameliorate the disease severity of CF.

Copper-Associated Oxidative Stress Contributes to Cellular Inflammatory Responses in Cystic Fibrosis

Cystic fibrosis (CF) is caused by mutations in the gene encoding the CF Transmembrane Conductance Regulator (CFTR), an apical chloride channel. An early inflammation (EI) in the lung of CF patients occurring in the absence of any bacterial infection has been reported. This EI has been proposed to be associated with oxidative stress (OX-S), generated by deregulations of the oxidant/antioxidant status. Recently, we demonstrated that copper (Cu), an essential trace element, mediates OX-S in bronchial cells. However, the role of this element in the development of CF-EI, in association with OX-S, has never been investigated. Using healthy (16HBE14o-; HBE), CF (CFBE14o-; CFBE), and corrected-wild type CFTR CF (CFBE-wt) bronchial cells, we characterized the inflammation and OX-S profiles in relation to the copper status and CFTR expression and function. We demonstrated that CFBE cells exhibited a CFTR-independent intrinsic inflammation. These cells also exhibited an alteration in mitochondria, UPR (Unfolded Protein Response), catalase, Cu/Zn- and Mn-SOD activities, and an increase in the intracellular content of iron, zinc, and Cu. The increase in Cu concentration was associated with OX-S and inflammatory responses. These data identify cellular Cu as a key factor in the generation of CF-associated OX-S and opens new areas of investigation to better understand CF-associated EI.

Strategies for cystic fibrosis transmembrane conductance regulator inhibition: from molecular mechanisms to treatment for secretory diarrhoeas

Cystic fibrosis transmembrane conductance regulator (CFTR) is an unusual ABC transporter. It acts as an anion‐selective channel that drives osmotic fluid transport across many epithelia. In the gut, CFTR is crucial for maintaining fluid and acid‐base homeostasis, and its activity is tightly controlled by multiple neuro‐endocrine factors. However, microbial toxins can disrupt this intricate control mechanism and trigger protracted activation of CFTR. This results in the massive faecal water loss, metabolic acidosis and dehydration that characterize secretory diarrhoeas, a major cause of malnutrition and death of children under 5 years of age. Compounds that inhibit CFTR could improve emergency treatment of diarrhoeal disease. Drawing on recent structural and functional insight, we discuss how existing CFTR inhibitors function at the molecular and cellular level. We compare their mechanisms of action to those of inhibitors of related ABC transporters, revealing some unexpected features of drug action on CFTR. Although challenges remain, especially relating to the practical effectiveness of currently available CFTR inhibitors, we discuss how recent technological advances might help develop therapies to better address this important global health need.

The Phosphodiesterase Inhibitor Ensifentrine Reduces Production of Proinflammatory Mediators in Well Differentiated Bronchial Epithelial Cells by Inhibiting PDE4

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel that impair airway salt and fluid secretion. Excessive release of proinflammatory cytokines and chemokines by CF bronchial epithelium during airway infection leads to chronic inflammation and a slow decline in lung function; thus, there is much interest in finding safe and effective treatments that reduce inflammation in CF. We showed previously that the cyclic nucleotide phosphodiesterase (PDE) inhibitor ensifentrine (RPL554; Verona Pharma) stimulates the channel function of CFTR mutants with abnormal gating and also those with defective trafficking that are partially rescued using a clinically approved corrector drug. PDE inhibitors also have known anti-inflammatory effects; therefore, we examined whether ensifentrine alters the production of proinflammatory cytokines in CF bronchial epithelial cells. Ensifentrine reduced the production of monocyte chemoattractant protein-1 and granulocyte monocyte colony-stimulating factor (GM-CSF) during challenge with interleukin-1β Comparing the effect of ensifentrine with milrinone and roflumilast, selective PDE3 and PDE4 inhibitors, respectively, demonstrated that the anti-inflammatory effect of ensifentrine was mainly due to inhibition of PDE4. Beneficial modulation of GM-CSF was further enhanced when ensifentrine was combined with low concentrations of the β ₂-adrenergic agonist isoproterenol or the corticosteroid dexamethasone. The results indicate that ensifentrine may have beneficial anti-inflammatory effects in CF airways particularly when used in combination with β ₂-adrenergic agonists or corticosteroids. SIGNIFICANCE STATEMENT: Airway inflammation that is disproportionate to the burden of chronic airway infection causes much of the pathology in the cystic fibrosis (CF) lung. We show here that ensifentrine beneficially modulates the release of proinflammatory factors in well differentiated CF bronchial epithelial cells that is further enhanced when combined with β₂-adrenergic agonists or low-concentration corticosteroids. The results encourage further clinical testing of ensifentrine, alone and in combination with β₂-adrenergic agonists or low-concentration corticosteroids, as a novel anti-inflammatory therapy for CF.

Liposomes Loaded With Phosphatidylinositol 5-Phosphate Improve the Antimicrobial Response to Pseudomonas aeruginosa in Impaired Macrophages From Cystic Fibrosis Patients and Limit Airway Inflammatory Response

Despite intensive antimicrobial and anti-inflammatory therapies, cystic fibrosis (CF) patients are subjected to chronic infections due to opportunistic pathogens, including multidrug resistant (MDR) Pseudomonas aeruginosa. Macrophages from CF patients show many evidences of reduced phagocytosis in terms of internalization capability, phagosome maturation, and intracellular bacterial killing. In this study, we investigated if apoptotic body-like liposomes (ABLs) loaded with phosphatidylinositol 5-phosphate (PI5P), known to regulate actin dynamics and vesicular trafficking, could restore phagocytic machinery while limiting inflammatory response in in vitro and in vivo models of MDR P. aeruginosa infection. Our results show that the in vitro treatment with ABL carrying PI5P (ABL/PI5P) enhances bacterial uptake, ROS production, phagosome acidification, and intracellular bacterial killing in human monocyte-derived macrophages (MDMs) with pharmacologically inhibited cystic fibrosis transmembrane conductance regulator channel (CFTR), and improve uptake and intracellular killing of MDR P. aeruginosa in CF macrophages with impaired bactericidal activity. Moreover, ABL/PI5P stimulation of CFTR-inhibited MDM infected with MDR P. aeruginosa significantly reduces NF-κB activation and the production of TNF-α, IL-1β, and IL-6, while increasing IL-10 and TGF-β levels. The therapeutic efficacy of ABL/PI5P given by pulmonary administration was evaluated in a murine model of chronic infection with MDR P. aeruginosa. The treatment with ABL/PI5P significantly reduces pulmonary neutrophil infiltrate and the levels of KC and MCP-2 cytokines in the lungs, without affecting pulmonary bacterial load. Altogether, these results show that the ABL/PI5P treatment may represent a promising host-directed therapeutic approach to improve the impaired phagocytosis and to limit the potentially tissue-damaging inflammatory response in CF.

Airway Inflammation and Host Responses in the Era of CFTR Modulators

The arrival of cystic fibrosis transmembrane conductance regulator (CFTR) modulators as a new class of treatment for cystic fibrosis (CF) in 2012 represented a pivotal advance in disease management, as these small molecules directly target the upstream underlying protein defect. Further advancements in the development and scope of these genotype-specific therapies have been transformative for an increasing number of people with CF (PWCF). Despite clear improvements in CFTR function and clinical endpoints such as lung function, body mass index (BMI), and frequency of pulmonary exacerbations, current evidence suggests that CFTR modulators do not prevent continued decline in lung function, halt disease progression, or ameliorate pathogenic organisms in those with established lung disease. Furthermore, it remains unknown whether their restorative effects extend to dysfunctional CFTR expressed in phagocytes and other immune cells, which could modulate airway inflammation. In this review, we explore the effects of CFTR modulators on airway inflammation, infection, and their influence on the impaired pulmonary host defences associated with CF lung disease. We also consider the role of inflammation-directed therapies in light of the widespread clinical use of CFTR modulators and identify key areas for future research.

Abnormal n-6 fatty acid metabolism in cystic fibrosis contributes to pulmonary symptoms

Cystic fibrosis (CF) is a recessively inherited fatal disease that is the subject of extensive research and ongoing development of therapeutics targeting the defective protein, cystic fibrosis transmembrane conductance regulator (CFTR). Despite progress, the link between CFTR and clinical symptoms is incomplete. The severe CF phenotypes are associated with a deficiency of linoleic acid, which is the precursor of arachidonic acid. The release of arachidonic acid from membranes via phospholipase A₂ is the rate-limiting step for eicosanoid synthesis and is increased in CF, which contributes to the observed inflammation. A potential deficiency of docosahexaenoic acid may lead to decreased levels of specialized pro-resolving mediators. This pathophysiology may contribute to an early and sterile inflammation, mucus production, and to bacterial colonization, which further increases inflammation and potentiates the clinical symptoms. Advances in lipid technology will assist in elucidating the role of lipid metabolism in CF, and stimulate therapeutic modulations of inflammation.

Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) in Human Lung Microvascular Endothelial Cells Controls Oxidative Stress, Reactive Oxygen-Mediated Cell Signaling and Inflammatory Responses

Background

Perturbation of endothelial function in people with cystic fibrosis (CF) has been reported, which may be associated with endothelial cell expression of the cystic fibrosis transmembrane conductance regulator (CFTR). Previous reports indicate that CFTR activity upregulates endothelial barrier function, endothelial nitric oxide synthase (eNOS) expression and NO release, while limiting interleukin-8 (IL-8) release, in human umbilical vein endothelial cells (HUVECs) in cell culture. In view of reported microvascular dysfunction in people with CF we investigated the role of CFTR expression and activity in the regulation of oxidative stress, cell signaling and inflammation in human lung microvascular endothelial cells (HLMVECs) in cell culture.

Methods

HLMVECs were cultured in the absence and presence of the CFTR inhibitor GlyH-101 and CFTR siRNA. CFTR expression was analyzed using qRT-PCR, immunocytochemistry (IHC) and western blot, and function by membrane potential assay. IL-8 expression was analyzed using qRT-PCR and ELISA. Nrf2 expression, and NF-κB and AP-1 activation were determined using IHC and western blot. The role of the epidermal growth factor receptor (EGFR) in CFTR signaling was investigated using the EGFR tyrosine kinase inhibitor AG1478. Oxidative stress was measured as intracellular ROS and hydrogen peroxide (H₂O₂) concentration. VEGF and SOD-2 were measured in culture supernatants by ELISA.

Results

HLMVECs express low levels of CFTR that increase following inhibition of CFTR activity. Inhibition of CFTR, significantly increased intracellular ROS and H₂O₂ levels over 30 min and significantly decreased Nrf2 expression by 70% while increasing SOD-2 expression over 24 h. CFTR siRNA significantly increased constitutive expression of IL-8 by HLMVECs. CFTR inhibition activated the AP-1 pathway and increased IL-8 expression, without effect on NF-κB activity. Conversely, TNF-α activated the NF-κB pathway and increased IL-8 expression. The effects of TNF-α and GlyH-101 on IL-8 expression were additive and inhibited by AG1478. Inhibition of both CFTR and EGFR in HLMVECs significantly increased VEGF expression. The antioxidant N-acetyl cysteine significantly reduced ROS production and the increase in IL-8 and VEGF expression following CFTR inhibition.

Conclusion

Functional endothelial CFTR limits oxidative stress and contributes to the normal anti-inflammatory state of HLMVECs. Therapeutic strategies to restore endothelial CFTR function in CF are warranted.

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.

Macrophage dysfunction in cystic fibrosis: Nature or nurture?

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) affect the homeostasis of chloride flux by epithelial cells. This has deleterious consequences, especially in respiratory epithelia, where the defect results in mucus accumulation distinctive of cystic fibrosis. CFTR is, however, also expressed in phagocytic cells, like macrophages. Immune cells are highly sensitive to conditioning by their environment; thus, CFTR dysfunction in epithelia influences macrophages by affecting the lung milieu, but the mutations also appear to be directly consequential for intrinsic macrophage functions. Particular mutations can alter CFTR's folding, traffic of the protein to the membrane and function. As such, understanding the intrinsic effects of CFTR mutation requires distinguishing the secondary effects of misfolded CFTR on cell stress pathways from the primary defect of CFTR dysfunction/absence. Investigations into CFTR's role in macrophages have exploited various models, each with their own advantages and limitations. This review summarizes these methodologic approaches, discussing their physiological correspondence and highlighting key findings. The controversy surrounding CFTR-dependent acidification is used as a case study to highlight difficulties in commensurability across model systems. Recent work in macrophage biology, including polarization and host-pathogen interaction studies, brought into the context of CFTR research, offers potential explanations for observed discrepancies between studies. Moreover, the rapid advancement of novel gene editing technologies and new macrophage model systems makes this assessment of the field's models and methodologies timely.

Targeting the Heme Oxygenase 1/Carbon Monoxide Pathway to Resolve Lung Hyper-Inflammation and Restore a Regulated Immune Response in Cystic Fibrosis

In individuals with cystic fibrosis (CF), lung hyper-inflammation starts early in life and is perpetuated by mucus obstruction and persistent bacterial infections. The continuous tissue damage and scarring caused by non-resolving inflammation leads to bronchiectasis and, ultimately, respiratory failure. Macrophages (MΦs) are key regulators of immune response and host defense. We and others have shown that, in CF, MΦs are hyper-inflammatory and exhibit reduced bactericidal activity. Thus, MΦs contribute to the inability of CF lung tissues to control the inflammatory response or restore tissue homeostasis. The non-resolving hyper-inflammation in CF lungs is attributed to an impairment of several signaling pathways associated with resolution of the inflammatory response, including the heme oxygenase-1/carbon monoxide (HO-1/CO) pathway. HO-1 is an enzyme that degrades heme groups, leading to the production of potent antioxidant, anti-inflammatory, and bactericidal mediators, such as biliverdin, bilirubin, and CO. This pathway is fundamental to re-establishing cellular homeostasis in response to various insults, such as oxidative stress and infection. Monocytes/MΦs rely on abundant induction of the HO-1/CO pathway for a controlled immune response and for potent bactericidal activity. Here, we discuss studies showing that blunted HO-1 activation in CF-affected cells contributes to hyper-inflammation and defective host defense against bacteria. We dissect potential cellular mechanisms that may lead to decreased HO-1 induction in CF cells. We review literature suggesting that induction of HO-1 may be beneficial for the treatment of CF lung disease. Finally, we discuss recent studies highlighting how endogenous HO-1 can be induced by administration of controlled doses of CO to reduce lung hyper-inflammation, oxidative stress, bacterial infection, and dysfunctional ion transport, which are all hallmarks of CF lung disease.

Synthesis and Therapeutic Applications of Iminosugars in Cystic Fibrosis

Iminosugars are sugar analogues endowed with a high pharmacological potential. The wide range of biological activities exhibited by these glycomimetics associated with their excellent drug profile make them attractive therapeutic candidates for several medical interventions. The ability of iminosugars to act as inhibitors or enhancers of carbohydrate-processing enzymes suggests their potential use as therapeutics for the treatment of cystic fibrosis (CF). Herein we review the most relevant advances in the field, paying attention to both the chemical synthesis of the iminosugars and their biological evaluations, resulting from in vitro and in vivo assays. Starting from the example of the marketed drug NBDNJ (N-butyl deoxynojirimycin), a variety of iminosugars have exhibited the capacity to rescue the trafficking of F508del-CFTR (deletion of F508 residue in the CF transmembrane conductance regulator), either alone or in combination with other correctors. Interesting results have also been obtained when iminosugars were considered as anti-inflammatory agents in CF lung disease. The data herein reported demonstrate that iminosugars hold considerable potential to be applied for both therapeutic purposes.

Resolvin D1 Reduces Lung Infection and Inflammation Activating Resolution in Cystic Fibrosis

Non-resolving lung inflammation and Pseudomonas aeruginosa infections are the underlying cause of morbidity and mortality in cystic fibrosis (CF). The endogenous lipid mediator resolvin (Rv) D1 is a potent regulator of resolution, and its roles, actions, and therapeutic potential in CF are of interest. Here, we investigated actions and efficacy of RvD1 in preclinical models of cystic fibrosis. Cftr knockout mice with chronic P. aeruginosa lung infection were treated with RvD1 to assess differences in lung bacterial load, inflammation, and tissue damage. Cells from volunteers with CF were treated with RvD1 during ex vivo infection with P. aeruginosa, and effects on phagocytosis and inflammatory signaling were determined. In CF mice, RvD1 reduced bacterial burden, neutrophil infiltration, and histological signs of lung pathology, improving clinical scores of diseases. Mechanistically, RvD1 increased macrophage-mediated bacterial and leukocyte clearance in vivo. The clinical significance of these findings is supported by actions in primary leukocytes and epithelial cells from volunteers with CF where RvD1 enhanced P. aeruginosa phagocytosis and reduced genes and proteins associated to NF-κB activation and leukocyte infiltration. Concentration of RvD1 in sputum from patients with CF was also inversely correlated to those of cytokines and chemokines involved in CF lung pathology. These findings demonstrate efficacy of RvD1 in enhancing resolution of lung inflammation and infections and provide proof of concept for its potential as a prototypic novel pro-resolutive therapeutic approach for CF.

Roles, Actions, and Therapeutic Potential of Specialized Pro-resolving Lipid Mediators for the Treatment of Inflammation in Cystic Fibrosis

Non-resolving inflammation is the main mechanism of morbidity and mortality among patients suffering from cystic fibrosis (CF), the most common life-threatening human genetic disease. Resolution of inflammation is an active process timely controlled by endogenous specialized pro-resolving lipid mediators (SPMs) produced locally in inflammatory loci to restrain this innate response, prevent further damages to the host, and permit return to homeostasis. Lipoxins, resolvins, protectins, and maresins are SPM derived from polyunsaturated fatty acids that limit excessive leukocyte infiltration and pro-inflammatory signals, stimulate innate microbial killing, and enhance resolution. Their unique chemical structures, receptors, and bioactions are being elucidated. Accruing data indicate that SPMs carry protective functions against unrelenting inflammation and infections in preclinical models and human CF systems. Here, we reviewed their roles and actions in controlling resolution of inflammation, evidence for their impairment in CF, and proofs of principle for their exploitation as innovative, non-immunosuppressive drugs to address inflammation and infections in CF.

Increased intracellular Cl- concentration promotes ongoing inflammation in airway epithelium

Airway epithelial cells harbor the capacity of active Cl^- transepithelial transport and play critical roles in modulating innate immunity. However, whether intracellular Cl^- accumulation contributes to relentless airway inflammation remains largely unclear. This study showed that, in airway epithelial cells, intracellular Cl^- concentration ([Cl^-]_i) was increased after Pseudomonas aeruginosa lipopolysaccharide (LPS) stimulation via nuclear factor-κB (NF-κB)-phosphodiesterase 4D (PDE4D)-cAMP signaling pathways. Clamping [Cl^-]_i at high levels or prolonged treatment with LPS augmented serum- and glucocorticoid-inducible protein kinase 1 (SGK1) phosphorylation and subsequently triggered NF-κB activation in airway epithelial cells, whereas inhibition of SGK1 abrogated airway inflammation in vitro and in vivo. Furthermore, Cl^--SGK1 signaling pathway was pronouncedly activated in patients with bronchiectasis, a chronic airway inflammatory disease. Conversely, hydrogen sulfide (H₂S), a sulfhydryl-containing gasotransmitter, confers anti-inflammatory effects through decreasing [Cl^-]_i via activation of cystic fibrosis transmembrane conductance regulator (CFTR). Our study confirms that intracellular Cl^- is a crucial mediator of sustained airway inflammation. Medications that abrogate excessively increased intracellular Cl^- may offer novel targets for the management of airway inflammatory diseases.

Newborn Cystic Fibrosis Pigs Have a Blunted Early Response to an Inflammatory Stimulus

RATIONALE

Studies suggest that inappropriate responses to proinflammatory stimuli might contribute to inflammation in cystic fibrosis (CF) lungs. However, technical challenges have made it difficult to distinguish whether altered responses in CF airways are an intrinsic defect or a secondary effect of chronic disease in their tissue of origin. The CF pig model provides an opportunity to study the inflammatory responses of CF airways at birth, before the onset of infection and inflammation.

OBJECTIVES

To test the hypothesis that acute inflammatory responses are perturbed in porcine CF airways.

METHODS

We investigated the inflammatory responses of newborn CF and non-CF pig airways following a 4-hour exposure to heat-killed Staphylococcus aureus, in vivo and in vitro.

MEASUREMENTS AND MAIN RESULTS

Following an in vivo S. aureus challenge, markers of inflammation were similar between CF and littermate control animals through evaluation of bronchoalveolar lavage and tissues. However, transcriptome analysis revealed genotype-dependent differences as CF pigs showed a diminished host defense response compared with their non-CF counterparts. Furthermore, CF pig airways exhibited an increase in apoptotic pathways and a suppression of ciliary and flagellar biosynthetic pathways. Similar differences were observed in cultured airway epithelia from CF and non-CF pigs exposed to the stimulus.

CONCLUSIONS

Transcriptome profiling suggests that acute inflammatory responses are dysregulated in the airways of newborn CF pigs.

CFTR rescue with VX-809 and VX-770 favors the repair of primary airway epithelial cell cultures from patients with class II mutations in the presence of Pseudomonas aeruginosa exoproducts

BACKGROUND

Progressive airway damage due to bacterial infections, especially with Pseudomonas aeruginosa remains the first cause of morbidity and mortality in CF patients. Our previous work revealed a repair delay in CF airway epithelia compared to non-CF. This delay was partially prevented after CFTR correction (with VRT-325) in the absence of infection. Our goals were now to evaluate the effect of the Orkambi combination (CFTR VX-809 corrector + VX-770 potentiator) on the repair of CF primary airway epithelia, in infectious conditions.

METHODS

Primary airway epithelial cell cultures from patients with class II mutations were mechanically injured and wound healing rates and transepithelial resistances were monitored after CFTR rescue, in the absence and presence of P. aeruginosa exoproducts.

RESULTS

Our data revealed that combined treatment with VX-809 and VX-770 elicited a greater beneficial impact on airway epithelial repair than VX-809 alone, in the absence of infection. The treatment with Orkambi was effective not only in airway epithelial cell cultures from patients homozygous for the F508del mutation but also from heterozygous patients carrying F508del and another class II mutation (N1303 K, I507del). The stimulatory effect of the Orkambi treatment was prevented by CFTR inhibition with GlyH101. Finally, Orkambi combination elicited a slight but significant improvement in airway epithelial repair and transepithelial resistance, despite the presence of P. aeruginosa exoproducts.

CONCLUSIONS

Our findings indicate that Orkambi may favor airway epithelial integrity in CF patients with class II mutations. Complementary approaches would however be needed to further improve CFTR rescue and airway epithelial repair.

Phagocytosis depends on TRPV2-mediated calcium influx and requires TRPV2 in lipids rafts: alteration in macrophages from patients with cystic fibrosis

Whereas many phagocytosis steps involve ionic fluxes, the underlying ion channels remain poorly defined. As reported in mice, the calcium conducting TRPV2 channel impacts the phagocytic process. Macrophage phagocytosis is critical for defense against pathogens. In cystic fibrosis (CF), macrophages have lost their capacity to act as suppressor cells and thus play a significant role in the initiating stages leading to chronic inflammation/infection. In a previous study, we demonstrated that impaired function of CF macrophages is due to a deficient phagocytosis. The aim of the present study was to investigate TRPV2 role in the phagocytosis capacity of healthy primary human macrophage by studying its activity, its membrane localization and its recruitment in lipid rafts. In primary human macrophages, we showed that P. aeruginosa recruits TRPV2 channels at the cell surface and induced a calcium influx required for bacterial phagocytosis. We presently demonstrate that to be functional and play a role in phagocytosis, TRPV2 might require a preferential localization in lipid rafts. Furthermore, CF macrophage displays a perturbed calcium homeostasis due to a defect in TRPV2. In this context, deregulated TRPV2-signaling in CF macrophages could explain their defective phagocytosis capacity that contribute to the maintenance of chronic infection.

Iron Acquisition Mechanisms and Their Role in the Virulence of Burkholderia Species

Burkholderia is a genus within the β-Proteobacteriaceae that contains at least 90 validly named species which can be found in a diverse range of environments. A number of pathogenic species occur within the genus. These include Burkholderia cenocepacia and Burkholderia multivorans, opportunistic pathogens that can infect the lungs of patients with cystic fibrosis, and are members of the Burkholderia cepacia complex (Bcc). Burkholderia pseudomallei is also an opportunistic pathogen, but in contrast to Bcc species it causes the tropical human disease melioidosis, while its close relative Burkholderia mallei is the causative agent of glanders in horses. For these pathogens to survive within a host and cause disease they must be able to acquire iron. This chemical element is essential for nearly all living organisms due to its important role in many enzymes and metabolic processes. In the mammalian host, the amount of accessible free iron is negligible due to the low solubility of the metal ion in its higher oxidation state and the tight binding of this element by host proteins such as ferritin and lactoferrin. As with other pathogenic bacteria, Burkholderia species have evolved an array of iron acquisition mechanisms with which to capture iron from the host environment. These mechanisms include the production and utilization of siderophores and the possession of a haem uptake system. Here, we summarize the known mechanisms of iron acquisition in pathogenic Burkholderia species and discuss the evidence for their importance in the context of virulence and the establishment of infection in the host. We have also carried out an extensive bioinformatic analysis to identify which siderophores are produced by each Burkholderia species that is pathogenic to humans.

Dysregulated Chemokine Signaling in Cystic Fibrosis Lung Disease: A Potential Therapeutic Target

CF lung disease is characterized by a chronic and non-resolving activation of the innate immune system with excessive release of chemokines/cytokines including IL-8 and persistent infiltration of immune cells, mainly neutrophils, into the airways. Chronic infection and impaired immune response eventually lead to pulmonary damage characterized by bronchiectasis, emphysema, and lung fibrosis. As a complete knowledge of the pathways responsible for the exaggerated inflammatory response in CF lung disease is lacking, understanding these pathways could reveal new therapeutic targets, and lead to novel treatments. Therefore, there is a strong rationale for the identification of mechanisms and pathways underlying the exaggerated inflammatory response in CF lung disease. This article reviews the role of inflammation in the pathogenesis of CF lung disease, with a focus on the dysregulated signaling involved in the overexpression of chemokine IL-8 and excessive recruitment of neutrophils in CF airways. The findings suggest that targeting the exaggerated IL-8/IL-8 receptor (mainly CXCR2) signaling pathway in immune cells (especially neutrophils) may represent a potential therapeutic strategy for CF lung disease.

Proteomic profile of cystic fibrosis sputum cells in adults chronically infected with Pseudomonas aeruginosa

Lung disease is the main cause of morbidity and mortality in cystic fibrosis (CF), and involves chronic infection and perturbed immune responses. Tissue damage is mediated mostly by extracellular proteases, but other cellular proteins may also contribute to damage through their effect on cell activities and/or release into sputum fluid by means of active secretion or cell death.

We employed MudPIT (multidimensional protein identification technology) to identify sputum cellular proteins with consistently altered abundance in adults with CF, chronically infected with Pseudomonas aeruginosa, compared with healthy controls. Ingenuity Pathway Analysis, Gene Ontology, protein abundance and correlation with lung function were used to infer their potential clinical significance.

Differentially abundant proteins relate to Rho family small GTPase activity, immune cell movement/activation, generation of reactive oxygen species, and dysregulation of cell death and proliferation. Compositional breakdown identified high abundance of proteins previously associated with neutrophil extracellular traps. Furthermore, negative correlations with lung function were detected for 17 proteins, many of which have previously been associated with lung injury.

These findings expand our current understanding of the mechanisms driving CF lung disease and identify sputum cellular proteins with potential for use as indicators of disease status/prognosis, stratification determinants for treatment prescription or therapeutic targets.

Role of IRE1α/XBP-1 in Cystic Fibrosis Airway Inflammation

Cystic fibrosis (CF) pulmonary disease is characterized by chronic airway infection and inflammation. The infectious and inflamed CF airway environment impacts on the innate defense of airway epithelia and airway macrophages. The CF airway milieu induces an adaptation in these cells characterized by increased basal inflammation and a robust inflammatory response to inflammatory mediators. Recent studies have indicated that these responses depend on activation of the unfolded protein response (UPR). This review discusses the contribution of airway epithelia and airway macrophages to CF airway inflammatory responses and specifically highlights the functional importance of the UPR pathway mediated by IRE1/XBP-1 in these processes. These findings suggest that targeting the IRE1/XBP-1 UPR pathway may be a therapeutic strategy for CF airway disease.

CFTR Controls the Activity of NF-κB by Enhancing the Degradation of TRADD

BACKGROUND/AIMS

Chronic lung infection in cystic fibrosis leads to an inflammatory response that persists because of the chronic presence of bacteria and ultimately leads to a catastrophic failure of lung function.

METHODS

We use a combination of biochemistry, cell and molecular biology to study the interaction of TRADD, a key adaptor molecule in TNFα signaling, with CFTR in the regulation of NFκB.

RESULTS

We show that Wt CFTR binds to and colocalizes with TRADD. TRADD is a key signaling intermediate connecting TNFα with activation of NFκB. By contrast, ΔF508 CFTR does not bind to TRADD. NF-κB activation is higher in CFBE expressing ΔF508 CFTR than in cells expressing Wt CFTR. However, this differential effect is abolished when TRADD levels are knocked down. Transfecting Wt CFTR into CFBE cells reduces NF-κB activity. However the reduction is abolished by the CFTR chloride transport inhibitor-172. Consistently, transfecting in the correctly trafficked CFTR conduction mutants G551D or S341A also fail to reduce NFκB activity. Thus CFTR must be functional if it is to regulate NF-κB activity. We also found that TNFα produced a greater increase in NF-κB activity in CFBE cells than in the same cell when Wt CFTR-corrected. Consistently, the effect is also abolished when TRADD is knocked down by shRNA. Thus, Wt CFTR control of TRADD modulates the physiological activation of NF-κB by TNFα. Based on studies with proteosomal and lysosomal inhibitors, the mechanism by which Wt CFTR, but not ΔF508 CFTR, suppresses TRADD is by lysosomal degradation.

CONCLUSION

We have uncovered a novel mechanism whereby Wt CFTR regulates TNFα signaling by enhancing TRADD degradation. Thus by reducing the levels of TRADD, Wt CFTR suppresses downstream proinflammatory NFκB signaling. By contrast, suppression of NF-κB activation fails in CF cells expressing ΔF508 CFTR.

Defective CFTR- β-catenin interaction promotes NF-κB nuclear translocation and intestinal inflammation in cystic fibrosis

While inflammation with aberrant activation of NF-κB pathway is a hallmark of cystic fibrosis (CF), the molecular mechanisms underlying the link between CFTR defect and activation of NF-κB-mediated pro-inflammatory response remain elusive. Here, we investigated the link between CFTR defect and NF-κB activation in ΔF508cftr-/- mouse intestine and human intestinal epithelial cell lines. Our results show that the NF-κB/COX-2/PGE2 pathway is activated whereas the β-catenin pathway is suppressed in CF mouse intestine and CFTR-knockdown cells. Activation of β-catenin pathway by GSK3 inhibitors suppresses CFTR mutation/knockdown-induced NF-κB/COX-2/PGE2 pathway in ΔF508 mouse intestine and CFTR-knockdown cells. In contrast, suppression of β-catenin signaling induces the nuclear translocation of NF-κB. In addition, CFTR co-localizes and interacts with β-catenin while CFTR mutation disrupts the interaction between NF-κB and β-catenin in mouse intestine. Treatment with proteasome inhibitor MG132 completely reverses the reduced expression of β-catenin in Caco-2 cells. Collectively, these results indicate that CFTR stabilizes β-catenin and prevents its degradation, defect of which results in the activation of NF-κB-mediated inflammatory cascade. The present study has demonstrated a previously unsuspected interaction between CFTR and β-catenin that regulates NF-κB nuclear translocation in mouse intestine. Therefore, our study provides novel insights into the physiological function of CFTR and pathogenesis of CF-related diseases in addition to the NF-κB-mediated intestinal inflammation seen in CF.

Epithelial Anion Transport as Modulator of Chemokine Signaling

The pivotal role of epithelial cells is to secrete and absorb ions and water in order to allow the formation of a luminal fluid compartment that is fundamental for the epithelial function as a barrier against environmental factors. Importantly, epithelial cells also take part in the innate immune system. As a first line of defense they detect pathogens and react by secreting and responding to chemokines and cytokines, thus aggravating immune responses or resolving inflammatory states. Loss of epithelial anion transport is well documented in a variety of diseases including cystic fibrosis, chronic obstructive pulmonary disease, asthma, pancreatitis, and cholestatic liver disease. Here we review the effect of aberrant anion secretion with focus on the release of inflammatory mediators by epithelial cells and discuss putative mechanisms linking these transport defects to the augmented epithelial release of chemokines and cytokines. These mechanisms may contribute to the excessive and persistent inflammation in many respiratory and gastrointestinal diseases.

New use for an old drug: COX-independent anti-inflammatory effects of sulindac in models of cystic fibrosis

Background and Purpose

Pulmonary disease is the main cause of morbidity and mortality in cystic fibrosis (CF) patients due to exacerbated inflammation. To date, the only anti‐inflammatory drug available to CF patients is high‐dose ibuprofen, which can slow pulmonary disease progression, but whose cyclooxygenase‐dependent digestive adverse effects limit its clinical use. Here we have tested sulindac, another non‐steroidal anti‐inflammatory drug with an undefined anti‐inflammatory effect in CF airway epithelial cells.

Experimental Approach

Using in vitro and in vivo models, we NF‐κB activity and IL‐8 secretion. In HeLa‐F508del cells, we performed luciferase reporter gene assays in order to measure i) IL‐8 promoter activity, and ii) the activity of synthetic promoter containing NF‐κB responsive elements. We quantified IL‐8 secretion in airway epithelial CFBE cells cultured at an air‐liquid interface and in a mouse model of CF.

Key Results

Sulindac inhibited the transcriptional activity of NF‐κB and decreased IL‐8 transcription and secretion in TNF‐α stimulated CF cells via a cyclooxygenase‐independent mechanism. This effect was confirmed in vivo in a mouse model of CF induced by intra‐tracheal instillation of LPS, with a significant decrease of the induction of mRNA for MIP‐2, following treatment with sulindac.

Conclusion and Implications

Overall, sulindac decrease lung inflammation by a mechanism independent of cycolooxygenase. This drug could be beneficially employed in CF.

Innate and Adaptive Immunity in Cystic Fibrosis

Cystic fibrosis (CF) lung disease is characterized by persistent and unresolved inflammation, with elevated proinflammatory and decreased anti-inflammatory cytokines, and greater numbers of immune cells. Hyperinflammation is recognized as a leading cause of lung tissue destruction in CF. Hyper-inflammation is not solely observed in the lungs of CF patients, since it may contribute to destruction of exocrine pancreas and, likely, to defects in gastrointestinal tract tissue integrity. Paradoxically, despite the robust inflammatory response, and elevated number of immune cells (such as neutrophils and macrophages), CF lungs fail to clear bacteria and are more susceptible to infections. Here, we have summarized the current understanding of immune dysregulation in CF, which may drive hyperinflammation and impaired host defense.

Bronchial epithelial cell lines and primary nasal epithelial cells from cystic fibrosis respond differently to cigarette smoke exposure

The effects of cigarette smoke extract (CSE) on airway epithelial cells (AECs) from cystic fibrosis (CF) and non-cystic fibrosis (non-CF) individuals are not fully understood. It has been suggested that CSE modulates inflammatory cytokine release from AECs by modulating the epidermal growth factor receptor (EGFR) pathway; these pathways could reveal novel therapeutic targets. We compared the effect of CSE pre-incubation on IL-8 release from CF and non-CF bronchial epithelial cell lines, and separately, with primary nasal epithelial cells (NECs) retrieved from CF and non-CF individuals. We also determined if the EGFR pathway regulates IL-8 release by LPS or cytomix in non-CF and CF AECs at baseline and following CSE exposure. CF and non-CF cell lines, NECs derived from both CF patients (R117H heterozygous and F508del homozygous), and from healthy subjects, were cultured in the presence or absence of CSE, and subsequently exposed to inflammatory stimuli. In cell lines CSE significantly reduced IL-8 release following inflammatory challenge. Conversely, CSE pre-treatment was pro-inflammatory in primary NECs. In NECs from control subjects, CSE increased cytomix and LPS induced IL-8 release, and for the R117H heterozygous NEC cultures, CSE enhanced basal IL-8 release. Cytomix and LPS induced IL-8 release from F508del homozygous NEC cultures was further heightened following CSE pre-treatment. EGFR inhibition mitigated IL-8 release from immortalised and primary non-CF and CF AECs, suggesting that constitutive and CSE elicited IL-8 release from AECs is partly regulated via the EGFR pathway. This study demonstrates the importance of the EGFR cascade in the regulation of constitutive and CSE induced inflammatory mediator release from immortalised and primary AECs. Moreover, it clearly highlights the significance of using primary cells to confirm results obtained from immortalised cell studies, as these model systems may respond very differently to the stimuli under investigation.

CFTR Knockdown induces proinflammatory changes in intestinal epithelial cells

Background

Hyperinflammation is a hallmark feature of cystic fibrosis (CF) airways. However, inflammation has also been documented systemically and, more recently, in extrapulmonary CF-affected tissues such as the pancreas and intestine. The pathogenesis of CF-related inflammation and more specifically the role of the cystic fibrosis transmembrane conductance regulator (CFTR) in that respect are not entirely understood. We have tested the hypothesis that genetic depletion of CFTR will affect the inflammatory status of human intestinal epithelial cell lines.

Methods

CFTR expression was genetically depleted from Caco-2/15 and HT-29 cells using short hairpin RNA interference (shRNAi). Inflammatory conditions were induced by the addition of human recombinant tumor necrosis factor (TNF) or Interleukin-1β (IL-1β) for various periods of time. Gene expression, mRNA stability and secreted levels of interleukin (IL)-6, −8 and 10 were assessed. Analysis of pro- and anti-inflammatory signaling pathways including mitogen-activated protein kinases (p38, ERK 1/2 and JNK), nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor alpha (IκBα), and nuclear factor-kappa B (NF-κB) was also performed. Eosinophils were counted in the jejunal mucosa of Cftr−/− and Cftr+/+ mice.

Results

CFTR gene and protein knockdown caused a significant increase in basal secretion of IL-8 as well as in IL-1β-induced secretion of IL-6 and −8. Release of the anti-inflammatory cytokine, IL-10, remained unaffected by CFTR depletion. The enhanced secretion of IL-8 stems in part from increased IL8 mRNA levels and greater activation of ERK1/2 MAPK, IκBα and NF-κB in the CFTR knockdown cells. By contrast, phosphorylation levels of p38 and JNK MAPK did not differ between control and knockdown cells. We also found a higher number of infiltrating eosinophils in the jejunal mucosa of Cftr −/− females, but not males, compared to Cftr +/+ mice, thus providing in vivo support to our in vitro findings.

Conclusion

Collectively, these data underscore the role played by CFTR in regulating the intestinal inflammatory responses. Such findings lend support to the theory that CFTR exerts functions that may go beyond its role as a chloride channel whereby its disruption may prevent cells to optimally respond to exogenous or endogenous challenges. These observations are of particular interest to CF patients who were found to display alterations in their intestinal microbiota, thus predisposing them to pathogens that may elicit exaggerated inflammatory responses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-015-0107-y) contains supplementary material, which is available to authorized users.

Stimulation of nuclear receptor peroxisome proliferator-activated receptor-γ limits NF-κB-dependent inflammation in mouse cystic fibrosis biliary epithelium

Cystic fibrosis-associated liver disease is a chronic cholangiopathy that negatively affects the quality of life of cystic fibrosis patients. In addition to reducing biliary chloride and bicarbonate secretion, up-regulation of toll-like receptor 4/nuclear factor kappa light-chain-enhancer of activated B cells (NF-κB)-dependent immune mechanisms plays a major role in the pathogenesis of cystic fibrosis-associated liver disease and may represent a therapeutic target. Nuclear receptors are transcription factors that regulate several intracellular functions. Some nuclear receptors, including peroxisome proliferator-activated receptor-γ (PPAR-γ), may counterregulate inflammation in a tissue-specific manner. In this study, we explored the anti-inflammatory effect of PPAR-γ stimulation in vivo in cystic fibrosis transmembrane conductance regulator (Cftr) knockout mice exposed to dextran sodium sulfate and in vitro in primary cholangiocytes isolated from wild-type and from Cftr-knockout mice exposed to lipopolysaccharide. We found that in CFTR-defective biliary epithelium expression of PPAR-γ is increased but that this does not result in increased receptor activity because the availability of bioactive ligands is reduced. Exogenous administration of synthetic agonists of PPAR-γ (pioglitazone and rosiglitazone) up-regulates PPAR-γ-dependent genes, while inhibiting the activation of NF-κB and the secretion of proinflammatory cytokines (lipopolysaccharide-induced CXC chemokine, monocyte chemotactic protein-1, macrophage inflammatory protein-2, granulocyte colony-stimulating factor, keratinocyte chemoattractant) in response to lipopolysaccharide. PPAR-γ agonists modulate NF-κB-dependent inflammation by up-regulating nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor alpha, a negative regulator of NF-κB. Stimulation of PPAR-γ in vivo (rosiglitazone) significantly attenuates biliary damage and inflammation in Cftr-knockout mice exposed to a dextran sodium sulfate-induced portal endotoxemia.

CONCLUSION

These studies unravel a novel function of PPAR-γ in controlling biliary epithelium inflammation and suggest that impaired activation of PPAR-γ contributes to the chronic inflammatory state of CFTR-defective cholangiocytes.

CFTR-regulated MAPK/NF-κB signaling in pulmonary inflammation in thermal inhalation injury

The mechanism underlying pulmonary inflammation in thermal inhalation injury remains elusive. Cystic fibrosis, also hallmarked with pulmonary inflammation, is caused by mutations in CFTR, the expression of which is temperature-sensitive. We investigated whether CFTR is involved in heat-induced pulmonary inflammation. We applied heat-treatment in 16HBE14o- cells with CFTR knockdown or overexpression and heat-inhalation in rats in vivo. Heat-treatment caused significant reduction in CFTR and, reciprocally, increase in COX-2 at early stages both in vitro and in vivo. Activation of ERK/JNK, NF-κB and COX-2/PGE2 were detected in heat-treated cells, which were mimicked by knockdown, and reversed by overexpression of CFTR or VX-809, a reported CFTR mutation corrector. JNK/ERK inhibition reversed heat-/CFTR-knockdown-induced NF-κB activation, whereas NF-κB inhibitor showed no effect on JNK/ERK. IL-8 was augmented by heat-treatment or CFTR-knockdown, which was abolished by inhibition of NF-κB, JNK/ERK or COX-2. Moreover, in vitro or in vivo treatment with curcumin, a natural phenolic compound, significantly enhanced CFTR expression and reversed the heat-induced increases in COX-2/PGE2/IL-8, neutrophil infiltration and tissue damage in the airway. These results have revealed a CFTR-regulated MAPK/NF-κB pathway leading to COX-2/PGE2/IL-8 activation in thermal inhalation injury, and demonstrated therapeutic potential of curcumin for alleviating heat-induced pulmonary inflammation.

Inflammation and its genesis in cystic fibrosis

The host inflammatory response in cystic fibrosis (CF) lung disease has long been recognized as a central pathological feature and an important therapeutic target. Indeed, many believe that bronchiectasis results largely from the oxidative and proteolytic damage comprised within an exuberant airway inflammatory response that is dominated by neutrophils. In this review, we address the longstanding argument of whether or not the inflammatory response is directly attributable to impairment of the cystic fibrosis transmembrane conductance regulator or only secondary to airway obstruction and chronic bacterial infection and challenge the importance of this distinction in the context of therapy. We also review the centrality of neutrophils in CF lung pathophysiology and highlight more recent data that suggest the importance of other cell types and signaling beyond NF-κB activation. We discuss how protease and redox imbalance are critical factors in CF airway inflammation and end by reviewing some of the more promising therapeutic approaches now under development.

Potential application of miRNAs as diagnostic and therapeutic tools in chronic pancreatitis

Chronic pancreatitis (CP) is a progressive inflammatory disease typified by end-stage fibrosis. This disease can also increase the risk of pancreatic cancer. The associated diagnosis, pain and other complications further add to the burden of disease management. In recent years, significant progress has been achieved in identifying miRNAs and their physiological functions, including mRNA repression and protein expression control. Given the extensive effort made on miRNA research, a close correlation has been discovered between certain types of miRNAs and disease progression, particularly for tissue fibrosis. Designing miRNA-related tools for disease diagnosis and therapeutic treatments presents a novel and potential research frontier. In the current review, we discuss various miRNAs closely interacting with CP, as well as the possible development of targeted miRNA therapies in managing this disease.

Endoplasmic reticulum stress in immunity

Immune responses occur in the midst of a variety of cellular stresses that can severely perturb endoplasmic reticulum (ER) function. The unfolded protein response is a three-pronged signaling axis dedicated to preserving ER homeostasis. In this review, we highlight many important and emerging functional roles for ER stress in immunity, focusing on how the bidirectional cross talk between immunological processes and basic cell biology leads to pleiotropic signaling outcomes and enhanced sensitivity to inflammatory stimuli. We also discuss how dysregulated ER stress responses can provoke many diseases, including autoimmunity, firmly positioning the unfolded protein response as a major therapeutic target in human disease.

FOXO1 content is reduced in cystic fibrosis and increases with IGF-I treatment

Cystic fibrosis-related diabetes is to date the most frequent complication in cystic fibrosis (CF). The mechanisms underlying this condition are not well understood, and a possible role of insulin resistance is debated. We investigated insulin signal transduction in CF. Total insulin receptor, IRS1, p85 PI3K, and AKT contents were substantially normal in CF cells (CFBE41o-), whereas winged helix forkhead (FOX)O1 contents were reduced both in baseline conditions and after insulin stimulation. In addition, CF cells showed increased ERK1/2, and reduced β2 arrestin contents. No significant change in SOCS2 was observed. By using a CFTR inhibitor and siRNA, changes in FOXO1 were related to CFTR loss of function. In a CF-affected mouse model, FOXO1 content was reduced in the muscle while no significant difference was observed in liver and adipose tissue compared with wild-type. Insulin-like growth factor 1 (IGF-I) increased FOXO1 content in vitro and in vivo in muscle and adipose tissue. In conclusion; we present the first description of reduced FOXO1 content in CF, which is compatible with reduced gluconeogenesis and increased adipogenesis, both features of insulin insensitivity. IGF-I treatment was effective in increasing FOXO1, thereby suggesting that it could be considered as a potential treatment in CF patients possibly to prevent and treat cystic fibrosis-related diabetes.

Differentiation between human ClC-2 and CFTR Cl− channels with pharmacological agents

It has been difficult to separate/identify the roles of ClC-2 and CFTR in Cl− transport studies. Using pharmacological agents, we aimed to differentiate functionally between ClC-2 and CFTR Cl− channel currents. Effects of CFTR inhibitor 172 (CFTRinh172), N-(4-methylphenylsulfonyl)- N′-(4-trifluoromethylphenyl)urea (DASU-02), and methadone were examined by whole cell patch clamp on Cl− currents in recombinant human ClC-2/human embryonic kidney 293 (ClC-2/HEK293) cells stably transformed with Epstein-Barr nuclear antigen 1 (hClC-2/293EBNA) and human CFTR/HEK293 (hCFTR/HEK293) cells and by short-circuit current ( Isc) measurements in T84 cells. Lubiprostone and forskolin-IBMX were used as activators. CFTRinh172 inhibited forskolin-IBMX-stimulated recombinant human CFTR (hCFTR) and lubiprostone-stimulated recombinant human ClC-2 (hClC-2) Cl− currents in a concentration-dependent manner equipotently. DASU-02 inhibited forskolin-IBMX-stimulated Cl− currents in hCFTR/HEK293 cells, but not lubiprostone-stimulated Cl− currents in hClC-2/293EBNA cells. In T84 cells with basolateral nystatin or 1-ethyl-2-benzimidazolinone (1-EBIO), lubiprostone-stimulated and forskolin-IBMX-cyclosporin A (FICA)-stimulated Isc components were observed. CFTRinh172 inhibited major portions of both components. DASU-02 had no effect on lubiprostone-stimulated Isc but partially inhibited FICA-stimulated Isc. T84 cells in which ClC-2 or CFTR was knocked down using siRNAs were constructed. T84 ClC-2 knockdown cells did not respond to lubiprostone but did respond to forskolin-IBMX in a methadone-insensitive, DASU-02-sensitive manner, indicating CFTR function. T84 CFTR knockdown cells responded separately to lubiprostone and forskolin-IBMX in a methadone-sensitive and DASU-02-insensitive manner, indicating ClC-2 function. Low lubiprostone concentrations activated ClC-2, but not CFTR, and both channels were activated by forskolin-IBMX but have different inhibitor sensitivities. Methadone, but not DASU-02, inhibited ClC-2. DASU-02, but not methadone, inhibited CFTR. In T84 cells, both ClC-2 and CFTR are present and likely play roles in Cl− secretion.

A neutrophil intrinsic impairment affecting Rab27a and degranulation in cystic fibrosis is corrected by CFTR potentiator therapy

Studies have endeavored to reconcile whether dysfunction of neutrophils in people with cystic fibrosis (CF) is a result of the genetic defect or is secondary due to infection and inflammation. In this study, we illustrate that disrupted function of the CF transmembrane conductance regulator (CFTR), such as that which occurs in patients with ∆F508 and/or G551D mutations, correlates with impaired degranulation of antimicrobial proteins. We demonstrate that CF blood neutrophils release less secondary and tertiary granule components compared with control cells and that activation of the low-molecular-mass GTP-binding protein Rab27a, involved in the regulation of granule trafficking, is defective. The mechanism leading to impaired degranulation involves altered ion homeostasis caused by defective CFTR function with increased cytosolic levels of chloride and sodium, yet decreased magnesium measured in CF neutrophils. Decreased magnesium concentration in vivo and in vitro resulted in significantly decreased levels of GTP-bound Rab27a. Treatment of G551D patients with the ion channel potentiator ivacaftor resulted in normalized neutrophil cytosolic ion levels and activation of Rab27a, thereby leading to increased degranulation and bacterial killing. Our results confirm that intrinsic alterations of circulating neutrophils from patients with CF are corrected by ivacaftor, thus illustrating additional clinical benefits for CFTR modulator therapy.

The buffer capacity of airway epithelial secretions

The pH of airway epithelial secretions influences bacterial killing and mucus properties and is reduced by acidic pollutants, gastric reflux, and respiratory diseases such as cystic fibrosis (CF). The effect of acute acid loads depends on buffer capacity, however the buffering of airway secretions has not been well characterized. In this work we develop a method for titrating micro-scale (30 μl) volumes and use it to study fluid secreted by the human airway epithelial cell line Calu-3, a widely used model for submucosal gland serous cells. Microtitration curves revealed that HCO⁻₃ is the major buffer. Peak buffer capacity (β) increased from 17 to 28 mM/pH during forskolin stimulation, and was reduced by >50% in fluid secreted by cystic fibrosis transmembrane conductance regulator (CFTR)-deficient Calu-3 monolayers, confirming an important role of CFTR in HCO⁻₃ secretion. Back-titration with NaOH revealed non-volatile buffer capacity due to proteins synthesized and released by the epithelial cells. Lysozyme and mucin concentrations were too low to buffer Calu-3 fluid significantly, however model titrations of porcine gastric mucins at concentrations near the sol-gel transition suggest that mucins may contribute to the buffer capacity of ASL in vivo. We conclude that CFTR-dependent HCO⁻₃ secretion and epithelially-derived proteins are the predominant buffers in Calu-3 secretions.

Lipoxin A4 and platelet activating factor are involved in E. coli or LPS-induced lung inflammation in CFTR-deficient mice

CFTR (cystic fibrosis transmembrane conductance regulator) is expressed by both neutrophils and platelets. Lack of functional CFTR could lead to severe lung infection and inflammation. Here, we found that mutation of CFTR (F508del) or inhibition of CFTR in mice led to more severe thrombocytopenia, alveolar neutrocytosis and bacteriosis, and lower lipoxin A4/MIP-2 (macrophage inhibitory protein-2) or lipoxin A4/neutrophil ratios in the BAL (bronchoalveolar lavage) during acute E. coli pneumonia. In vitro, inhibition of CFTR promotes MIP-2 production in LPS-stimulated neutrophils; however, lipoxin A4 could dose-dependently suppress this effect. In LPS-induced acute lung inflammation, blockade of PSGL-1 (P-selectin glycoprotein ligand-1) or P-selectin, antagonism of PAF by WEB2086, or correction of mutated CFTR trafficking by KM11060 could significantly increase plasma lipoxin A4 levels in F508del relevant to wildtype mice. Concurrently, F508del mice had higher plasma platelet activating factor (PAF) levels and PAF-AH activity compared to wildtype under LPS challenge. Inhibiting hydrolysis of PAF by a specific PAF-AH (PAF-acetylhydrolase) inhibitor, MAFP, could worsen LPS-induced lung inflammation in F508del mice compared to vehicle treated F508del group. Particularly, depletion of platelets in F508del mice could significantly decrease plasma lipoxin A4 and PAF-AH activity and deteriorate LPS-induced lung inflammation compared to control F508del mice. Taken together, lipoxin A4 and PAF are involved in E. coli or LPS-induced lung inflammation in CFTR-deficient mice, suggesting that lipoxin A4 and PAF might be therapeutic targets for ameliorating CFTR-deficiency deteriorated lung inflammation.

A novel method for pulmonary research: assessment of bioenergetic function at the air-liquid interface

Air–liquid interface cell culture is an organotypic model for study of differentiated functional airway epithelium in vitro. Dysregulation of cellular energy metabolism and mitochondrial function have been suggested to contribute to airway diseases. However, there is currently no established method to determine oxygen consumption and glycolysis in airway epithelium in air–liquid interface. In order to study metabolism in differentiated airway epithelial cells, we engineered an insert for the Seahorse XF24 Analyzer that enabled the measure of respiration by oxygen consumption rate (OCR) and glycolysis by extracellular acidification rate (ECAR). Oxidative metabolism and glycolysis in airway epithelial cells cultured on the inserts were successfully measured. The inserts did not affect the measures of OCR or ECAR. Cells under media with apical and basolateral feeding had less oxidative metabolism as compared to cells on the inserts at air-interface with basolateral feeding. The design of inserts that can be used in the measure of bioenergetics in small numbers of cells in an organotypic state may be useful for evaluation of new drugs and metabolic mechanisms that underlie airway diseases.

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Endothelial cells generate hydrogen peroxide through several enzymatic systems and the mitochondrial electron transport chain

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Redox-sensitive thiols within specific families of proteins such as kinases are key targets for hydrogen peroxide in endothelial cells

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Hydrogen peroxide regulates fundamental processes in endothelial cells including cell growth, proliferation, angiogenesis and vascular tone