Function Of Cystic Fibrosis Transmembrane Conductance Regulator Protein Research Articles

Two novel and correlated CF-causing insertions in the (TG)mTn tract of the CFTR gene.

Two novel and related pathogenic variants of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene were structurally and functionally characterized. These alterations have not been previously described in literature. Two patients with diagnosis of Cystic Fibrosis (CF) based on the presence of one mutated allele, p.Phe508del, pathological sweat test and clinical symptoms were studied. To complete the genotypes of both patients, an extensive genetic and functional analysis of the CFTR gene was performed. Extensive genetic characterization confirmed the presence of p.Phe508del pathogenic variant and revealed, in both patients, the presence of an insertion of part of intron 10 in intron 9 of the CFTR gene, within the (TG)m repeat, with a variable poly-T stretch. The molecular lesions resulted to be very similar in both patients, with only a difference in the number of T in the poly-T stretch. The functional characterization at RNA level revealed a complete anomalous splicing, without exon 10, from the allele with the insertion of both patients. Consequently, the alleles with the insertions are expected not to contribute to the formation of a functional CFTR protein. Molecular and functional features of these alterations are compatible with the definition of novel CF-causing variants of the CFTR gene. This also allowed the completion of the genetic characterization of both patients.

Challenges Facing Airway Epithelial Cell-Based Therapy for Cystic Fibrosis.

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause the life-limiting hereditary disease, cystic fibrosis (CF). Decreased or absent functional CFTR protein in airway epithelial cells leads to abnormally viscous mucus and impaired mucociliary transport, resulting in bacterial infections and inflammation causing progressive lung damage. There are more than 2000 known variants in the CFTR gene. A subset of CF individuals with specific CFTR mutations qualify for pharmacotherapies of variable efficacy. These drugs, termed CFTR modulators, address key defects in protein folding, trafficking, abundance, and function at the apical cell membrane resulting from specific CFTR mutations. However, some CFTR mutations result in little or no CFTR mRNA or protein expression for which a pharmaceutical strategy is more challenging and remote. One approach to rescue CFTR function in the airway epithelium is to replace cells that carry a mutant CFTR sequence with cells that express a normal copy of the gene. Cell-based therapy theoretically has the potential to serve as a one-time cure for CF lung disease regardless of the causative CFTR mutation. In this review, we explore major challenges and recent progress toward this ambitious goal. The ideal therapeutic cell would: (1) be autologous to avoid the complications of rejection and immune-suppression; (2) be safely modified to express functional CFTR; (3) be expandable ex vivo to generate sufficient cell quantities to restore CFTR function; and (4) have the capacity to engraft, proliferate and persist long-term in recipient airways without complications. Herein, we explore human bronchial epithelial cells (HBECs) and induced pluripotent stem cells (iPSCs) as candidate cell therapies for CF and explore the challenges facing their delivery to the human airway.

Triplet CFTR modulators: future prospects for treatment of cystic fibrosis.

Cystic fibrosis (CF) is an autosomal recessive genetic disease characterized by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR). CFTR is a chloride channel responsible for ion flow across epithelial surfaces of lung, sinuses, pancreas, intestine, and liver. Researchers have grouped CFTR genetic mutations into various protein defects: reduced protein synthesis (class 1 mutations), abnormal protein folding and maturation (class 2 mutation), and abnormal gating (class 3 mutation). These mutations usually present as severe forms of CF due to complete absence of CFTR at cell surfaces. Milder forms (eg, protein maturation and conductance defects, classes 4–6) present as less severe forms of CF related to the presence of CFTR at the cell surface. Differences in severity are directly due to CFTR function which is based on the severity of CFTR mutation. This knowledge has proven useful for designing therapy for individual mutations and mutation classes. The discovery and US Food and Drug Administration approval of Kalydeco® (ivacaftor) in early 2011 marked the beginning of a new era of therapies that are focused on improving defective CFTR protein function. However, due to its specificity for the G551D mutation, ivacaftor only benefitŝ5% of CF patients. Approximately 50% of CF patients have two copies of the F508Del mutation, while other CF patients carry only one copy of this gene. More recently, Orkambi®, a two compound medication composed of lumacaftor and ivacaftor, has provided the foundation necessary to further build on molecular concepts of: correction of trafficking, potentiation, and amplification of defective CFTR. These new concepts will form the basis of future CF therapies and extend CFTR treatment to almost 50% of CF patients. Evolving knowledge of the molecular mechanisms responsible for defective CFTR has prompted new research focused on “repair” of each phase of CFTR expression and function, thus creating a new class of combination “CFTR correctors” referred to as “triplet CFTR compounds.” This article will review how patients can be selected and treated with these newer agents that are based on specific mutations. In the future, many CF practitioners have expectations that initiation of treatment for CF patients will occur simply by use of biomarkers of CFTR expression (eg, sweat chloride, nasal potential difference, rectal organoids) rather than testing for specific mutations. As continued research identifies biomarkers with greater specificity and which predict clinical response, therapies can potentially be tailored to individual responses.

VX-659–Tezacaftor–Ivacaftor in Patients with Cystic Fibrosis and One or Two Phe508del Alleles

BackgroundThe next-generation cystic fibrosis transmembrane conductance regulator (CFTR) corrector VX-659, in triple combination with tezacaftor and ivacaftor (VX-659–tezacaftor–ivacaftor), was developed to restore the function of Phe508del CFTR protein in patients with cystic fibrosis.MethodsWe evaluated the effects of VX-659–tezacaftor–ivacaftor on the processing, trafficking, and function of Phe508del CFTR protein using human bronchial epithelial cells. A range of oral VX-659–tezacaftor–ivacaftor doses in triple combination were then evaluated in randomized, controlled, double-blind, multicenter trials involving patients with cystic fibrosis who were heterozygous for the Phe508del CFTR mutation and a minimal-function CFTR mutation (Phe508del–MF genotypes) or homozygous for the Phe508del CFTR mutation (Phe508del–Phe508del genotype). The primary end points were safety and the absolute change from baseline in the percentage of predicted forced expiratory volume in 1 second (FEV1).ResultsVX-659–tezacaftor–ivacaftor significantly improved the processing and trafficking of Phe508del CFTR protein as well as chloride transport in vitro. In patients, VX-659–tezacaftor–ivacaftor had an acceptable safety and side-effect profile. Most adverse events were mild or moderate. VX-659–tezacaftor–ivacaftor resulted in significant mean increases in the percentage of predicted FEV1 through day 29 (P<0.001) of up to 13.3 points in patients with Phe508del–MF genotypes; in patients with the Phe508del–Phe508del genotype already receiving tezacaftor–ivacaftor, adding VX-659 resulted in a further 9.7-point increase in the percentage of predicted FEV1. The sweat chloride concentrations and scores on the respiratory domain of the Cystic Fibrosis Questionnaire–Revised improved in both patient populations.ConclusionsRobust in vitro activity of VX-659–tezacaftor–ivacaftor targeting Phe508del CFTR protein translated into improvements for patients with Phe508del–MF or Phe508del–Phe508del genotypes. VX-659 triple-combination regimens have the potential to treat the underlying cause of disease in approximately 90% of patients with cystic fibrosis. (Funded by Vertex Pharmaceuticals; VX16-659-101 and VX16-659-001 ClinicalTrials.gov numbers, NCT03224351 and NCT03029455.)

VX-445–Tezacaftor–Ivacaftor in Patients with Cystic Fibrosis and One or Two Phe508del Alleles

BackgroundVX-445 is a next-generation cystic fibrosis transmembrane conductance regulator (CFTR) corrector designed to restore Phe508del CFTR protein function in patients with cystic fibrosis when administered with tezacaftor and ivacaftor (VX-445–tezacaftor–ivacaftor).MethodsWe evaluated the effects of VX-445–tezacaftor–ivacaftor on Phe508del CFTR protein processing, trafficking, and chloride transport in human bronchial epithelial cells. On the basis of in vitro activity, a randomized, placebo-controlled, double-blind, dose-ranging, phase 2 trial was conducted to evaluate oral VX-445–tezacaftor–ivacaftor in patients heterozygous for the Phe508del CFTR mutation and a minimal-function mutation (Phe508del–MF) and in patients homozygous for the Phe508del CFTR mutation (Phe508del–Phe508del) after tezacaftor–ivacaftor run-in. Primary end points were safety and absolute change in percentage of predicted forced expiratory volume in 1 second (FEV1) from baseline.ResultsIn vitro, VX-445–tezacaftor–ivacaftor significantly improved Phe508del CFTR protein processing, trafficking, and chloride transport to a greater extent than any two of these agents in dual combination. In patients with cystic fibrosis, VX-445–tezacaftor–ivacaftor had an acceptable safety and side-effect profile. Most adverse events were mild or moderate. The treatment also resulted in an increased percentage of predicted FEV1 of up to 13.8 points in the Phe508del–MF group (P<0.001). In patients in the Phe508del–Phe508del group, who were already receiving tezacaftor–ivacaftor, the addition of VX-445 resulted in an 11.0-point increase in the percentage of predicted FEV1 (P<0.001). In both groups, there was a decrease in sweat chloride concentrations and improvement in the respiratory domain score on the Cystic Fibrosis Questionnaire–Revised.ConclusionsThe use of VX-445–tezacaftor–ivacaftor to target Phe508del CFTR protein resulted in increased CFTR function in vitro and translated to improvements in patients with cystic fibrosis with one or two Phe508del alleles. This approach has the potential to treat the underlying cause of cystic fibrosis in approximately 90% of patients. (Funded by Vertex Pharmaceuticals; VX16-445-001 ClinicalTrials.gov number, NCT03227471; and EudraCT number, 2017-000797-11.)

S737F is a new CFTR mutation typical of patients originally from the Tuscany region in Italy

BackgroundAn increasing number of patients have been described as having a number of Cystic Fibrosis Transmembrane conductance Regulator (CFTR) variants for which it lacks a clear genotype–phenotype correlation. We assesses the clinical features of patients bearing the S737F (p.Ser737Phe) CFTR missense variant and evaluated the residual function of CFTR protein on nasal epithelial cells (NEC).MethodsA retrospective database was performed from individuals homozygous or compound heterozygous for the S737F variant followed in the Cystic Fibrosis (CF) Centre of Florence. We performed a nasal brushing in cooperating patients and compared the results with those of patients followed in the pediatric CF Centre of Naples.Results9/295 (3%) subjects carrying at least S737F CFTR variant on one allele were identified. Patients were diagnosed in 7/9 cases by newborn screening and in two cases for dehydration with hypochloremic metabolic alkalosis; at diagnosis sweat chloride levels (SCL) were in the pathological range in only one case. After a mean follow up of 8,6 years (range 0,5–15,8), SCL were in the pathological range in 8/9 cases (mean age at CF diagnosis: 1,5 years), all patients were pancreatic sufficiency and respiratory function was normal. The gating activity on NEC was 15.6% and 12.7% in two patients compound heterozygous for W1282X and DelE22_24, while it was ranged between 6,2% and 9,8% in CF patients.ConclusionsS737F is a CFTR mutation associated to hypochloremic alkalosis in childhood, mild CF phenotype in teenage years and a residual function of CFTR protein.

MicroRNA-145 Antagonism Reverses TGF-β Inhibition of F508del CFTR Correction in Airway Epithelia.

MicroRNAs (miRNAs) destabilize mRNA transcripts and inhibit protein translation. miR-145 is of particular interest in cystic fibrosis (CF) as it has a direct binding site in the 3'-untranslated region of CFTR (cystic fibrosis transmembrane conductance regulator) and is upregulated by the CF genetic modifier TGF (transforming growth factor)-β. To demonstrate that miR-145 mediates TGF-β inhibition of CFTR synthesis and function in airway epithelia. Primary human CF (F508del homozygous) and non-CF airway epithelial cells were grown to terminal differentiation at the air-liquid interface on permeable supports. TGF-β (5 ng/ml), a miR-145 mimic (20 nM), and a miR-145 antagonist (20 nM) were used to manipulate CFTR function. In CF cells, lumacaftor (3 μM) and ivacaftor (10 μM) corrected mutant F508del CFTR. Quantification of CFTR mRNA, protein, and function was done by standard techniques. miR-145 is increased fourfold in CF BAL fluid compared with non-CF (P < 0.01) and increased 10-fold in CF primary airway epithelial cells (P < 0.01). Exogenous TGF-β doubles miR-145 expression (P < 0.05), halves wild-type CFTR mRNA and protein levels (P < 0.01), and nullifies lumacaftor/ivacaftor F508del CFTR correction. miR-145 overexpression similarly decreases wild-type CFTR protein synthesis (P < 0.01) and function (P < 0.05), and eliminates F508del corrector benefit. miR-145 antagonism blocks TGF-β suppression of CFTR and enhances lumacaftor correction of F508del CFTR. miR-145 mediates TGF-β inhibition of CFTR synthesis and function in airway epithelia. Specific antagonists to miR-145 interrupt TGF-β signaling to restore F508del CFTR modulation. miR-145 antagonism may offer a novel therapeutic opportunity to enhance therapeutic benefit of F508del CFTR correction in CF epithelia.

New treatments targeting the basic defects in cystic fibrosis

Cystic fibrosis (CF) is a monogenic autosomal recessive disorder affecting around 75,000 individuals worldwide. It is a multi-system disease but the main morbidity and mortality is caused by chronic lung disease. Due to newborn screening, a multidisciplinary approach to care and intensive symptomatic treatment, the prognosis has dramatically improved over the last decades and there are currently more adults than children in many countries. However, CF is still a very severe disease with a current median age of life expectancy in the fourth decade of life. The disease is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene which encodes the CFTR protein, a protein kinase A-activated ATP-gated anion channel that regulates the transport of electrolytes such as chloride and bicarbonate. More than 2000 mutations have been reported, although not all of these have functional consequences. An enormous research effort and progress has been made in understanding the consequences of these mutations on the CFTR protein structure and function, and this has led to the approval of two new drug therapies that are able to bind to defective CFTR proteins and partially restore their function. They are mutation-specific therapies and available at present for specific mutations only. They are the first personalized medicine for CF with a possible disease-modifying effect. A pipeline of other compounds is under development with different mechanisms of action. It is foreseeable that new combinations of compounds will further improve the correction of CFTR function. Other strategies including premature stop codon read-through drugs, antisense oligonucleotides that correct the basic defect at the mRNA level or gene editing to restore the defective gene as well as gene therapy approaches are all in the pipeline. All these strategies are needed to develop disease-modifying therapies for all patients with CF.

PharmGKB summary: ivacaftor pathway, pharmacokinetics/pharmacodynamics.

Ivacaftor [VX-770; N-(2,4-Di-tert-butyl-5-hydroxyphenyl)-4-oxo-1,4-dihydroquinoline-3-carboxamide] is one of the first drugs developed to treat an underlying cause of cystic fibrosis (CF) rather than the symptoms. It is a selective small molecule potentiator of the Cystic Fibrosis Transmembrane Conductance Regulator protein (CFTR). Potentiators are a new drug class of CFTR modulators designed to restore CFTR function [1]. The Food and Drug Administration (FDA) has granted ivacaftor orphan drug status because it is indicated in a subset of patients with particular CFTR variants, specifically class III variants. Approximately 30,000 people have CF in the United States, which is below the 200,000 patient threshold for orphan drugs in the United States [1]. CF is an autosomal recessive disorder characterized by sweat chloride concentration above 60 mmol/L, leading to progressive obstructive lung disease and premature mortality, as well as problems in the liver, pancreas, vas deferens, and intestine [2]. CF affects approximately 70,000 people worldwide [3], including approximately 1 of every 3500 infants born in the United States [4], and is caused by inheriting two detrimental copies of the CFTR gene. The CFTR protein is a chloride channel, which maintains ion and water balance intra- and extra-cellularly [5]. The channel opens and closes through ATP binding, hydrolysis, and phosphorylation, which changes the protein conformation to allow chloride ions to flow through the ion gradient between the intracellular and extracellular regions [2]. Defective CFTR function prevents the flow of chloride ions across epithelial cells, which leads to the mucus buildup, infection, inflammation, and progressively decreasing lung function that is characteristic of cystic fibrosis [5].

New Therapeutic Approaches to Modulate and Correct Cystic Fibrosis Transmembrane Conductance Regulator.

Cystic fibrosis transmembrane conductance regulator (CFTR) modulators are clinically available personalized medicines approved for some individuals with cystic fibrosis (CF) to target the underlying defect of disease. This review summarizes strategies used to develop CFTR modulators as therapies that improve function and availability of CFTR protein. Lessons learned from dissemination of ivacaftor across the CF population responsive to this therapy and future approaches to predict and monitor treatment response of CFTR modulators are discussed. The goal remains to expand patient-centered and personalized therapy to all patients with CF, ultimately improving life expectancy and quality of life for this disease.

VX-809 corrects folding defects in cystic fibrosis transmembrane conductance regulator protein through action on membrane-spanning domain 1

Cystic fibrosis (CF) is a fatal genetic disorder associated with defective hydration of lung airways due to the loss of chloride transport through the CF transmembrane conductance regulator protein (CFTR). CFTR contains two membrane-spanning domains (MSDs), two nucleotide-binding domains (NBDs), and a regulatory domain, and its channel assembly requires multiple interdomain contacts. The most common CF-causing mutation, F508del, occurs in NBD1 and results in misfolding and premature degradation of F508del-CFTR. VX-809 is an investigational CFTR corrector that partially restores CFTR function in people who are homozygous for F508del-CFTR. To identify the folding defect(s) in F508del-CFTR that must be repaired to treat CF, we explored the mechanism of VX-809 action. VX-809 stabilized an N-terminal domain in CFTR that contains only MSD1 and efficaciously restored function to CFTR forms that have missense mutations in MSD1. The action of VX-809 on MSD1 appears to suppress folding defects in F508del-CFTR by enhancing interactions among the NBD1, MSD1, and MSD2 domains. The ability of VX-809 to correct F508del-CFTR is enhanced when combined with mutations that improve F508del-NBD1 interaction with MSD2. These data suggest that the use of VX-809 in combination with an additional CFTR corrector that suppresses folding defects downstream of MSD1 may further enhance CFTR function in people with F508del-CFTR.

Disease-relevant proteostasis regulation of cystic fibrosis transmembrane conductance regulator

Mismanaged protein trafficking by the proteostasis network contributes to several conformational diseases, including cystic fibrosis, the most frequent lethal inherited disease in Caucasians. Proteostasis regulators, as cystamine, enable the beneficial action of cystic fibrosis transmembrane conductance regulator (CFTR) potentiators in ΔF508-CFTR airways beyond drug washout. Here we tested the hypothesis that functional CFTR protein can sustain its own plasma membrane (PM) stability. Depletion or inhibition of wild-type CFTR present in bronchial epithelial cells reduced the availability of the small GTPase Rab5 by causing Rab5 sequestration within the detergent-insoluble protein fraction together with its accumulation in aggresomes. CFTR depletion decreased the recruitment of the Rab5 effector early endosome antigen 1 to endosomes, thus reducing the local generation of phosphatidylinositol-3-phosphate. This diverts recycling of surface proteins, including transferrin receptor and CFTR itself. Inhibiting CFTR function also resulted in its ubiquitination and interaction with SQSTM1/p62 at the PM, favoring its disposal. Addition of cystamine prevented the recycling defect of CFTR by enhancing BECN1 expression and reducing SQSTM1 accumulation. Our results unravel an unexpected link between CFTR protein and function, the latter regulating the levels of CFTR surface expression in a positive feed-forward loop, and highlight CFTR as a pivot of proteostasis in bronchial epithelial cells.

Genotype-specific small-molecule therapy for cystic fibrosis

Educational aims Summary The prognosis for patients with cystic fibrosis (CF) has improved greatly over the past 30 years but the median age of survival is still only to the patients late 30s. New treatments are required to decrease morbidity and improve mortality. The basic defect in CF lies in the cystic fibrosis transmembrane conductance regulator ( CFTR ) gene, mutations of which lead to a dysfunctional CFTR protein. The way in which the protein is defective differs between the six so-called mutation classes. An understanding of these classes has led to the development of mutation-specific small-molecule treatments. Class I mutations are caused by the presence of a premature termination codon. Ataluren is a systemic agent that allows read-through of the mutated mRNA and translation of full-length protein. A phase III clinical trial has recently been completed. In class II mutations, the most common of which is Phe508del (previously termed ΔF508), the resulting CFTR protein is misfolded and is not trafficked through the cytoplasm to the cell membrane. CFTR-corrector drugs seek to facilitate such trafficking; recently increased understanding of the complex nature of the misfolding events may explain why this approach is, to date, rather difficult. Improvements in CFTR protein function have been achieved in vivo and clinical trial data are beginning to emerge. It may be necessary to use correctors with potentiators and combination trials of two correctors, VX-809 and VX-661, with or without the CFTR potentiator ivacaftor are underway. The latter was initially developed and tested in patients with the class III mutation Gly551Asp (previously termed G551D). In cells with this mutation, CFTR protein reaches the cell surface but fails to respond to cellular signals to open and conduct chloride. Ivacaftor increases the probability that the channel is open and has led to significant clinical benefit in patients with the Gly551Asp mutation; it is now being investigated in other class III and some class IV mutations. Ivacaftor is the first genotype-specific treatment to demonstrate clinical efficacy and to be approved for licence. Other compounds are currently in development and the field is optimistic that drugs for other genotypes will not be far behind.

Directed differentiation of human pluripotent stem cells into mature airway epithelia expressing functional CFTR protein

Cystic fibrosis (CF) is a fatal genetic disease caused by mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) gene that regulates chloride and water transport across all epithelia and affects multiple organs including the lungs. Here we report an in vitro directed differentiation protocol for generating functional CFTR-expressing airway epithelia from human embryonic stem cells. Carefully timed treatment by exogenous growth factors that mimic endoderm developmental pathways in vivo followed by air-liquid interface culture results in maturation of patches of tight junction-coupled differentiated airway epithelial cells that demonstrate active CFTR transport function. As a proof-of-concept, treatment of CF patient induced pluripotent stem cells (iPSC)-derived epithelial cells with a novel small molecule compound to correct for the common CF-processing mutation resulted in enhanced plasma membrane localization of mature CFTR protein. Our study provides a method for generating patient-specific airway epithelial cells for disease modeling and in vitro drug testing.

Antidiarrheal efficacy of a quinazolin CFTR inhibitor on human intestinal epithelial cell and in mouse model of cholera

Objective:This study aimed to evaluate the antidiarrheal efficacy and pharmacological properties of ethyl 2-(4-oxo-3-o-tolyl-3,4-dihydroquinazolin-2-ylthio)acetate (DQA) as an inhibitor of cystic fibrosis transmembrane conductance regulator protein (CFTR) both in vitro and in vivo.Materials and Methods:The effects of DQA on CFTR function and cell viability were investigated in Fisher rat thyroid (FRT) cells expressing human CFTR and human intestinal epithelial T84 cells by short-circuit current measurements and MTT assays, respectively. In vivo antidiarrheal efficacy of DQA was evaluated in a closed loop model of cholera in mice.Results:In permeabilized FRT cells, apical chloride current induced by CFTR agonists (10 μM forskolin, 100 μM CPT-cAMP, and 20 μM apigenin) was inhibited by DQA with IC50 ~ 20 μM and complete inhibition at 200 μM. The inhibitory effect was reversible and not associated with cytotoxicity to FRT cells (5–500 μM DQA for 24 h). Likewise, DQA effectively inhibited both forskolin and cholera toxin-induced transepithelial chloride secretion in T84 cells. In mice, intraluminal injection of 100 μM DQA reduced cholera toxin (1 μg/closed loop)-induced intestinal fluid secretion by 85% without affecting intestinal fluid absorption.Conclusions:DQA represents a new class of small molecule CFTR inhibitor with potential application in treatment of cholera.

Personalized medicine for cystic fibrosis: the next generation.

The field of personalized medicine, based on genetic information, represents a tremendous but largely unfulfilled opportunity for a future generation of therapies [1]. While better clinical outcomes have been realized using predictive biomarkers in some forms of cancer [2], the influence of genetic information on the treatment of most other human diseases has been limited. However, in the case of the inherited genetic disease cystic fibrosis (CF), pre-emptive possibilities have recently been uncovered. In particular, an investigational drug known as VX-770, has demonstrated great promise in clinical trials in patients with a specific cystic fibrosis transmembrane conductance regulator (CFTR) allele selected for clinical investigation based on data from in vitro studies [3,4]. This article highlights some of the opportunities and challenges associated with developing novel genotype-directed therapies for CF.

Unimpaired Lysosomal Acidification in Respiratory Epithelial Cells in Cystic Fibrosis

The mechanisms remain uncertain by which mutations in CFTR cause lung disease in cystic fibrosis (CF). Teichgräber et al. recently reported increased ceramide in CF lungs, which was proposed to result from defective lysosomal acidification in airway epithelial cells and consequent impairment of pH-dependent ceramide-metabolizing enzymes (Teichgräber, V., Ulrich, M., Endlich, N., Reithmüller, J., Wilker, B., Conceição Ce Olivereira-Munding, C., van Heeckeren, A. M., Barr, M. L., von Kürthy, G., Schmid, K. W., Weller, M., Tümmler, B., Lang, F., Grassme, H., Döring, G., and Gulbins, E. (2008) Nat. Med. 14, 382-391). Here, we measured lysosomal pH in several CFTR-expressing and -deficient cell lines, freshly isolated airway epithelial cells from non-CF and CF mice and humans, and well-differentiated primary cultures of human non-CF and CF airway epithelial cells. Lysosomal pH was measured by ratio imaging using a fluorescent pH indicator consisting of 40-kDa dextran conjugated to Oregon Green 488 and tetramethylrhodamine. In all cell types, lysosomal pH was approximately 4.5, unaffected by the thiazolidinone CFTR inhibitor CFTR(inh)-172, and increased to approximately 6.5 following bafilomycin inhibition of the vacuolar proton pump. Lysosomal pH did not differ significantly in airway epithelial cells from non-CF versus CF humans or mice. Our results provide direct evidence against the conclusions of Teichgräber et al. that lysosomal acidification is CFTR-dependent, impaired in CF, or responsible for ceramide accumulation. As such, alternative mechanisms are needed to explain increased ceramide in CF airways. Non-CFTR mechanisms, such as ClC-type chloride channels, are likely involved in maintaining electroneutrality during organellar acidification.

Genetic Investigations of CFTR Mutations in Congenital Absence of Vas Deferens, Uterus, and Vagina as a Cause of Infertility

A qualitative diagnosis of infertility requires attention to male and female physical abnormalities including endocrine anomalies and genetic conditions that interfere with reproduction. Many genes are likely to be involved in the complex process of reproduction. Congenital bilateral absence of the vas deferens (CBAVD) is a genital form of cystic fibrosis (CF) that is responsible for 2%-6% of male infertility. The incidence of CF varies in different populations; therefore, the incidence of CBAVD will also vary in different populations. The spectrum and distribution of cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations differ between CBAVD and CF patients and are comparable to control individuals. Combinations of particular alleles at several polymorphic loci yield insufficient functional CFTR protein. CFTR mutations are also associated with congenital absence of the uterus and vagina (CAUV). Females with CF are found to be less fertile than normal healthy women. Because of techniques such as intracytoplasmic sperm injection (ICSI), CBAVD patients are now able to father children. Such couples, however, have an increased risk of having a child with cystic fibrosis, and therefore genetic testing and counseling should be provided. Around 10% of obstructive azoospermia is congenital and due to mutations in the CF gene. This review highlights the relationship of mutations in the CFTR gene with CBAVD and CAUV.

TheCFTRM470V Gene Variant as a Potential Modifier of COPD Severity: Study of Serbian Population

Chronic obstructive pulmonary disease (COPD) is a complex disease influenced by genetic and environmental factors. Cystic fibrosis transmembrane conductance regulator (CFTR) protein is an important component of the lung tissue homeostasis, involved in the regulation of the rate of mucociliary clearance. As it is known that certain CFTR variants have consequences on the function of CFTR protein, the aim of this study was to examine the possible role of F508del, M470V, Tn locus, and R75Q variants in COPD development and modulation. Total number of 86 COPD patients and 102 control subjects were included in the study. Possible association between COPD susceptibility, severity, and onset of the disease and allele or genotype of four analyzed CFTR variants was examined. No associations were detected between COPD development, onset of the disease and tested CFTR alleles and genotypes. However, VV470 genotype was associated with mild/moderate COPD stages in comparison to severe/very severe ones (OR = 0.29, 95%CI = 0.11-0.80, p = 0.016). Our study showed that patients with VV470 genotype had a 3.4-fold decreased risk for the appearance of severe/very severe COPD symptoms, and the obtained results indicate that this genotype may have a protective role. These results also suggest the importance of studying CFTR gene as a modifier of this disease.

Epithelial Sodium Channel Inhibition in Primary Human Bronchial Epithelia by Transfected siRNA

Na(+) absorption and Cl(-) secretion are in equilibrium to maintain an appropriate airway surface fluid volume and ensure appropriate mucociliary clearance. In cystic fibrosis, this equilibrium is disrupted by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene resulting in the absence of functional CFTR protein, which in turn results in deficient cAMP-dependent Cl(-) secretion and predominant Na(+) absorption. It has been suggested that down-regulation of the epithelial sodium channel, ENaC, might help to restore airway hydration and reverse the airway phenotype in patients with cystic fibrosis. We used an siRNA approach to analyze the possibility of down-regulating ENaC function in bronchial epithelia and examine the resulting effects on fluid transport. siRNA sequences complementary to each of the three ENaC subunits have been used to establish whether single subunit down-regulation is enough to reduce Na(+) absorption. Transfection was performed by exposure to siRNA for 24 hours at the time of cell seeding on permeable support. By using primary human bronchial epithelial cells we demonstrate that (1) siRNA sequences complementary to ENaC subunits are able to reduce ENaC transcripts and Na(+) channel activity by 50 to 70%, (2) transepithelial fluid absorption decreases, and (3) these functional effects last at least 8 days. A decrease in ENaC mRNA results in a significant reduction of ENaC protein function and fluid absorption through the bronchial epithelium, indicating that an RNA interference approach may improve the airway hydration status in patients with cystic fibrosis.