Regulation of plasma membrane recycling by CFTR

Amelioration of airway and GI disease in G551D-CF ferrets by AAV1 and AAV6

Gene therapy for CF has concentrated on targeting the lung. Here we took a different approach by injecting into the cephalic vein and spraying into the trachea of G551D, CF ferrets either AAV1 or 6 containing Δ27-264-CFTR, a truncated version of CFTR. Treatment with the potentiator VX-770 was halted for 7 days before instillation to induce a disease phenotype. Indeed, all ferrets were pancreas-insufficient when they entered the study. Four ferrets (three receiving AAV1 and one AAV6) were necropsied 48 days after vector delivery, and four (three receiving AAV6, one AAV1) were euthanized or died prior to the planned necropsy. AAV1 or AAV6 vector genomes, mRNA expression, and CFTR protein were detected in all tracheal and lung samples and in the liver, pancreas, and ileum of the treated ferrets. Surface and basal airway cells, pancreatic and bile ducts, and ileal crypts and villi were successfully transduced. Obstruction of the airways accompanied by pulmonary hemorrhaging, plugged pancreatic and bile ducts as well as mucous plugs in the ileum were noticed in untreated but absent from transduced ferrets necropsied at 48 days. Transduction of G551D ferrets suggests that a combination of systemic and airway application may be the preferred route of delivery for CF.

Apical dehydration impairs the cystic fibrosis airway epithelium barrier via a β1-integrin/YAP1 pathway

Defective hydration of airway surface mucosa is associated with lung infection in cystic fibrosis (CF), partly caused by disruption of the epithelial barrier integrity. Although rehydration of the CF airway surface liquid (ASL) alleviates epithelium vulnerability to infection by junctional protein expression, the mechanisms linking ASL to barrier integrity are unknown. We show here the strong degradation of YAP1 and TAZ proteins in well-polarized CF human airway epithelial cells (HAECs), a process that was prevented by ASL rehydration. Conditional silencing of YAP1 in rehydrated CF HAECs indicated that YAP1 expression was necessary for the maintenance of junctional complexes. A higher plasma membrane tension in CF HAECs reduced endocytosis, concurrent with the maintenance of active β1-integrin ectopically located at the apical membrane. Pharmacological inhibition of β1-integrin accumulation restored YAP1 expression in CF HAECs. These results indicate that dehydration of the CF ASL affects epithelial plasma membrane tension, resulting in ectopic activation of a β1-integrin/YAP1 signaling pathway associated with degradation of junctional proteins.

Low-intensity ultrasound activates transmembrane chloride flow through CFTR

Ultrasound has been demonstrated to activate mechanosensitive channels, which is considered the main mechanism of ultrasound neuromodulation. Currently, all channels that have been shown to be sensitive to ultrasound are cation channels. In addition to cation channels, anion channels also play indispensable roles in neural function. However, there have been no research on ultrasound regulation of anion channels until now. If anion channels can be activated by ultrasound as well, they will inevitably lead to more versatility in ultrasound neuromodulation. Cystic fibrosis transmembrane transduction regulator (CFTR) has been demonstrated to be a mechanically sensitive channel, mediating anionic transmembrane flow. To identify that CFTR is sensitive to ultrasound, CFTR was exogenously expressed in HEK293T cells and was stimulated by low intensity ultrasound. Outward currents in CFTR-expressed HEK293T cells were observed by using whole-cell patch clamp when ultrasound (0.8 MHz, 0.20 MPa) was delivered to these cells. These currents were abolished when the CFTR inhibitor (GlyH101) was applied to the solution or chloride ions was cleared from the solution. Meanwhile, the amplitude of these currents increased when the CFTR agonist (Forskolin) was applied. These results suggest that ultrasound stimuli can activate the CFTR to mediate transmembrane flowing of chloride ions at the single cell level. These findings may expand the application of ultrasound in the neuromodulation field.

Polarized transport of membrane and secreted proteins during lumen morphogenesis

A ubiquitous feature of animal development is the formation of fluid-filled cavities or lumina, which transport gases and fluids across tissues and organs. Among different species, lumina vary drastically in size, scale, and complexity. However, all lumen formation processes share key morphogenetic principles that underly their development. Fundamentally, a lumen simply consists of epithelial cells that encapsulate a continuous internal space, and a common way of building a lumen is via opening and enlarging by filling it with fluid and/or macromolecules. Here, we discuss how polarized targeting of membrane and secreted proteins regulates lumen formation, mainly focusing on ion transporters in vertebrate model systems. We also discuss mechanistic differences observed among invertebrates and vertebrates and describe how the unique properties of the Na+/K+-ATPase and junctional proteins can promote polarization of immature epithelia to build lumina de novo in developing organs.

Tryptophan mutations in G3BP1 tune the stability of a cellular signaling hub by weakening transient interactions with Caprin1 and USP10

Intrinsically disordered proteins (IDPs) often coordinate transient interactions with multiple proteins to mediate complex signals within large protein networks. Among these, the IDP hub protein G3BP1 can form complexes with cytoplasmic phosphoprotein Caprin1 and ubiquitin peptidase USP10; the resulting control of USP10 activity contributes to a pathogenic virulence system that targets endocytic recycling of the ion channel CFTR. However, while the identities of protein interactors are known for many IDP hub proteins, the relationship between pairwise affinities and the extent of protein recruitment and activity is not well understood. Here, we describe in vitro analysis of these G3BP1 affinities and show tryptophan substitutions of specific G3BP1 residues reduce its affinity for both USP10 and Caprin1. We show that these same mutations reduce the stability of complexes between the full-length proteins, suggesting that copurification can serve as a surrogate measure of interaction strength. The crystal structure of G3BP1 TripleW (F15W/F33W/F124W) mutant reveals a clear reorientation of the side chain of W33, creating a steric clash with USP10 and Caprin1. Furthermore, an amino-acid scan of USP10 and Caprin1 peptides reveals similarities and differences in the ability to substitute residues in the core motifs as well as specific substitutions with the potential to create higher affinity peptides. Taken together, these data show that small changes in component binding affinities can have significant effects on the composition of cellular interaction hubs. These specific protein mutations can be harnessed to manipulate complex protein networks, informing future investigations into roles of these networks in cellular processes.

Reduced Expression of TMEM16A Impairs Nitric Oxide-Dependent Cl− Transport in Retinal Amacrine Cells

Postsynaptic cytosolic Cl⁻ concentration determines whether GABAergic and glycinergic synapses are inhibitory or excitatory. We have shown that nitric oxide (NO) initiates the release of Cl⁻ from acidic internal stores into the cytosol of retinal amacrine cells (ACs) thereby elevating cytosolic Cl⁻. In addition, we found that cystic fibrosis transmembrane conductance regulator (CFTR) expression and Ca²⁺ elevations are necessary for the transient effects of NO on cytosolic Cl⁻ levels, but the mechanism remains to be elucidated. Here, we investigated the involvement of TMEM16A as a possible link between Ca²⁺ elevations and cytosolic Cl⁻ release. TMEM16A is a Ca²⁺-activated Cl⁻ channel that is functionally coupled with CFTR in epithelia. Both proteins are also expressed in neurons. Based on this and its Ca²⁺ dependence, we test the hypothesis that TMEM16A participates in the NO-dependent elevation in cytosolic Cl⁻ in ACs. Chick retina ACs express TMEM16A as shown by Western blot analysis, single-cell PCR, and immunocytochemistry. Electrophysiology experiments demonstrate that TMEM16A functions in amacrine cells. Pharmacological inhibition of TMEM16A with T16inh-AO1 reduces the NO-dependent Cl⁻ release as indicated by the diminished shift in the reversal potential of GABA_A receptor-mediated currents. We confirmed the involvement of TMEM16A in the NO-dependent Cl⁻ release using CRISPR/Cas9 knockdown of TMEM16A. Two different modalities targeting the gene for TMEM16A (ANO1) were tested in retinal amacrine cells: an all-in-one plasmid vector and crRNA/tracrRNA/Cas9 ribonucleoprotein. The all-in-one CRISPR/Cas9 modality did not change the expression of TMEM16A protein and produced no change in the response to NO. However, TMEM16A-specific crRNA/tracrRNA/Cas9 ribonucleoprotein effectively reduces both TMEM16A protein levels and the NO-dependent shift in the reversal potential of GABA-gated currents. These results show that TMEM16A plays a role in the NO-dependent Cl⁻ release from retinal ACs.

Assessment of hepatic involvement by two-dimensional shear wave elastography in paediatric patients with cystic fibrosis

AIM

This study aimed to investigate parenchymal changes in the liver in paediatric patients with cystic fibrosis (CF) and to analyse diagnostic performance of two-dimensional shear wave elastography (2D-SWE) for the detection of hepatic involvement.

METHODS

Patients with CF treated and followed at our centre were evaluated prospectively. All patients underwent liver tissue stiffness (TS) measurements by 2D-SWE, in addition to routine clinical assessments, laboratory work-up and abdominal ultrasound imaging. Data from patients with CF were compared with healthy control subjects.

RESULTS

This study included 39 patients with CF and 37 healthy controls. Patients had a mean body weight of 29.9 (16.6-55) kg, mean age of 9 (5-17) years, mean height of 130 (107-172) cm and a mean body mass index of 16.1 (12.8-21.4) kg/m² . Average SWE values of the liver were 1.02 (0.70-1.60) m/s in patients with CF (n = 39) and 0.89 (0.60-1.35) m/s in healthy controls (n = 37). Cystic fibrosis patients had significantly increased tissue stifness by liver elastography compared to controls (P = 0.005).

CONCLUSION

Parenchymal liver changes may occur early in cystic fibrosis, which cannot be detected by conventional ultrasonography but may be demonstrated by 2D-SWE. Based on this cross-sectional study, 2D-SWE may be a promising, simple and non-invasive modality for objective monitoring of patients with cystic fibrosis who require lifelong follow-up, by providing numerical data for tissue stiffness early in the disease.

Targeting chloride transport in autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most frequent inherited kidney disease. Transepithelial fluid secretion is one of the key factors of cystogenesis in ADPKD. Multiple studies have suggested that fluid secretion across ADPKD cyst-lining cells is driven by the secretion of chloride, essentially mediated by the CFTR channel and stimulated by increased intracellular levels of 3',5'-cyclic adenosine monophosphate. This review focuses on the pathophysiology of fluid secretion in ADPKD based on the pioneering studies of Jared Grantham and colleagues, and on the follow-up investigations from the molecular level to the potential applications in ADPKD patients. Altogether, the studies of fluid and chloride transport in ADPKD paved the way for innovative therapeutic targets to prevent cyst volume expansion and thus, kidney disease progression.

Chloride channels regulate differentiation and barrier functions of the mammalian airway

The conducting airway forms a protective mucosal barrier and is the primary target of airway disorders. The molecular events required for the formation and function of the airway mucosal barrier, as well as the mechanisms by which barrier dysfunction leads to early onset airway diseases, remain unclear. In this study, we systematically characterized the developmental landscape of the mouse airway using single-cell RNA sequencing and identified remarkably conserved cellular programs operating during human fetal development. We demonstrated that in mouse, genetic inactivation of chloride channel Ano1/Tmem16a compromises airway barrier function, results in early signs of inflammation, and alters the airway cellular landscape by depleting epithelial progenitors. Mouse Ano1-/-mutants exhibited mucus obstruction and abnormal mucociliary clearance that resemble the airway defects associated with cystic fibrosis. The data reveal critical and non-redundant roles for Ano1 in organogenesis, and show that chloride channels are essential for mammalian airway formation and function.

Increases in cytosolic Ca2+ induce dynamin- and calcineurin-dependent internalisation of CFTR

The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-regulated, apical anion channel that regulates ion and fluid transport in many epithelia including the airways. We have previously shown that cigarette smoke (CS) exposure to airway epithelia causes a reduction in plasma membrane CFTR expression which correlated with a decrease in airway surface hydration. The effect of CS on CFTR was dependent on an increase in cytosolic Ca2+. However, the underlying mechanism for this Ca2+-dependent, internalisation of CFTR is unknown. To gain a better understanding of the effect of Ca2+ on CFTR, we performed whole cell current recordings to study the temporal effect of raising cytosolic Ca2+ on CFTR function. We show that an increase in cytosolic Ca2+ induced a time-dependent reduction in whole cell CFTR conductance, which was paralleled by a loss of cell surface CFTR expression, as measured by confocal and widefield fluorescence microscopy. The decrease in CFTR conductance and cell surface expression were both dynamin-dependent. Single channel reconstitution studies showed that raising cytosolic Ca2+ per se had no direct effect on CFTR. In fact, the loss of CFTR plasma membrane activity correlated with activation of calcineurin, a Ca2+-dependent phosphatase, suggesting that dephosphorylation of CFTR was linked to the loss of surface expression. In support of this, the calcineurin inhibitor, cyclosporin A, prevented the Ca2+-induced decrease in cell surface CFTR. These results provide a hitherto unrecognised role for cytosolic Ca2+ in modulating the residency of CFTR at the plasma membrane through a dynamin- and calcineurin-dependent mechanism.

Resveratrol and ivacaftor are additive G551D CFTR-channel potentiators: therapeutic implications for cystic fibrosis sinus disease

BACKGROUND

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene result in defective Cl^- transport and cause chronic bacterial infections in the upper and lower airways of cystic fibrosis (CF) patients. Ivacaftor is a CFTR potentiator that improves Cl^- transport in CF patients with at least 1 copy of the G551D mutation. Resveratrol is also a potent CFTR potentiator that increases determinants of mucociliary transport. The objective of this study is to determine whether resveratrol and ivacaftor improve Cl^- secretion in G551D CFTR over either agent alone.

METHODS

Fisher rat thyroid cells (FRT) transfected with G551D CFTR and human sinonasal epithelial cells (HSNE) containing the CFTR G551D mutation were subjected to pharmacologic manipulation of transepithelial ion transport in Ussing chambers. Activity was further evaluated using whole-cell patch clamp methods in G551D FRT cells.

RESULTS

In G551D FRT cells, resveratrol (100 μM) and ivacaftor (10 μM) significantly increased Cl^- transport (change in short-circuit current, δI_SC = μA/cm² ) compared with single-agent and dimethylsulfoxide vehicle controls (resveratrol + ivacaftor 4.97 ± 0.57 vs ivacaftor 0.74 ± 0.12 vs resveratrol 2.96 ± 0.52 vs control 0.74 ± 0.12; p < 0.001). Maximal Cl^- secretion (20 μM forskolin) was also significantly enhanced (p < 0.0001). Activity was confirmed in G551D HSNE (resveratrol + ivacaftor 4.48 ± 0.39 vs ivacaftor 1.05 ± 0.11 vs. resveratrol 0.84 ± 0.3 vs control, 0.0 ± 0.02; p < 0.001), and whole-cell patch clamp analysis in G551D FRT cells (resveratrol + ivacaftor -2535 ± 179.3 pA vs ivacaftor -1408.9 ± 101.3 pA vs resveratrol; -766.2 ± 71.2 pA; p < 0.0001).

CONCLUSION

Additive improvement in G551D CFTR-mediated Cl^- secretion suggests that resveratrol could enhance ivacaftor therapy in these patients and improve CF-related rhinosinusitis.

Surgical necrotizing enterocolitis in extremely premature neonates is associated with genetic variations in an intergenic region of chromosome 8

BackgroundTwin studies suggest that genetic factors may account for up to 50% increased risk for necrotizing enterocolitis (NEC), but genome-wide association studies for NEC are lacking.MethodsGenotyping was done on Illumina BeadChip, followed by analysis using PLINK with logistic regression under an additive model.ResultsAmong 751 extremely-low-birth-weight (<1,000 g, >401 g) neonates, 30 had surgical NEC. Two hundred and sixty-one single-nucleotide polymorphisms (SNPs) showed association with NEC at P<0.05, of which 35 were significant at P<10-7. Minor allele(s) in a cluster of SNPs spanning a 43-kb region of chromosome 8 (8q23.3) conferred an odds ratio of 4.72 (95% confidence interval (CI): 2.51-8.88) for elevated risk of NEC. Two smaller clusters on chromosome 14 and chromosome 11 exhibited P values of 10-7-10-8. The chromosome 8 cluster is in an intergenic region between CUB and Sushi multiple domains 3 (-1.43 Mb) and trichorhinophalangeal syndrome I (+542 kb). RNA sequencing in this region identified a potential novel open-reading frame corresponding to a long interspersed element-1 retrotransposable element.ConclusionGenetic variation in an intergenic region of chromosome 8 is associated with increased risk for NEC with a mechanism that is yet to be identified.

Cftr Modulates Wnt/β-Catenin Signaling and Stem Cell Proliferation in Murine Intestine

BACKGROUND & AIMS

Cystic fibrosis (CF) patients and CF mouse models have increased risk for gastrointestinal tumors. CF mice show augmented intestinal proliferation of unknown etiology and an altered intestinal environment. We examined the role of the cystic fibrosis transmembrane conductance regulator (Cftr) in Wnt/β-catenin signaling, stem cell proliferation, and its functional expression in the active intestinal stem cell (ISC) population. Dysregulation of intracellular pH (pH_i) in CF ISCs was investigated for facilitation of Wnt/β-catenin signaling.

METHODS

Crypt epithelia from wild-type (WT) and CF mice were compared ex vivo and in intestinal organoids (enteroids) for proliferation and Wnt/β-catenin signaling by standard assays. Cftr in ISCs was assessed by immunoblot of sorted Sox9 ^{enhanced green fluorescent protein(EGFP)} intestinal epithelia and pH_i regulation by confocal microfluorimetry of leucine-rich G-protein-coupled receptor 5 ISCs. Plasma membrane association of the Wnt transducer Dishevelled 2 (Dvl2) was assessed by fluorescence imaging of live enteroids from WT and CF mice crossed with Dvl2-EGFP/ACTB-tdTomato,-EGFP)Luo/J (Rosa^mT/mG) mice.

RESULTS

Relative to WT, CF intestinal crypts showed an ∼30% increase in epithelial and Lgr5+ ISC proliferation and increased Wnt/β-catenin signaling. Cftr was expressed in Sox9^EGFPLo ISCs and loss of Cftr induced an alkaline pH_i in ISCs. CF crypt-base columnar cells showed a generalized increase in plasma membrane Dvl2-EGFP association as compared with WT. Dvl2-EGFP membrane association was charge- and pH-dependent and increased in WT crypt-base columnar cells by Cftr inhibition.

CONCLUSIONS

CF intestine shows increased ISC proliferation and Wnt/β-catenin signaling. Loss of Cftr increases pH_i in ISCs, which stabilizes the plasma membrane association of the Wnt transducer Dvl, likely facilitating Wnt/β-catenin signaling. Absence of Cftr-dependent suppression of ISC proliferation in the CF intestine may contribute to increased risk for intestinal tumors.

Thromboelastogram as a Tool to Predict Hypercoagulability in Children With Cystic Fibrosis

Increased thrombophilic tendency in patients with cystic fibrosis (CF) has recently been reported. The determinants of thrombosis in children with CF remain largely unknown. Our aim in this study was to evaluate the thromboelastography (TEG) profile of children with CF through ROTEM (whole blood rotation thromboelastometry). Nineteen patients with CF and 20 controls were included in the study. Whole blood count, prothrombin time, activated prothrombin time, fibrinogen, d-dimer levels, and ROTEM assays (INTEM, EXTEM) were performed. Clotting time, clot formation time (CFT), and maximum clot firmness (MCF) were determined by INTEM and EXTEM analysis. In INTEM assay, MCF ( P = .001) value was significantly increased and CFT ( P = .031) value was decreased in patients with CF compared with those of the control group. In the EXTEM assay, there was a similar significant increase in MCF ( P = .023) value in patients with CF compared with that of the control group. There was a significant positive correlation between fibrinogen levels and MCF in EXTEM ( r = .72) and INTEM ( r = .76) assays, whereas there was a negative correlation with CFT in EXTEM ( r = -.61) and INTEM ( r = -.67). The results of our study indicated that TEG profiles in patients with CF were more hypercoagulable compared with those of the control group.

Role of Interaction and Nucleoside Diphosphate Kinase B in Regulation of the Cystic Fibrosis Transmembrane Conductance Regulator Function by cAMP-Dependent Protein Kinase A

Cystic fibrosis results from mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-dependent protein kinase A (PKA) and ATP-regulated chloride channel. Here, we demonstrate that nucleoside diphosphate kinase B (NDPK-B, NM23-H2) forms a functional complex with CFTR. In airway epithelia forskolin/IBMX significantly increases NDPK-B co-localisation with CFTR whereas PKA inhibitors attenuate complex formation. Furthermore, an NDPK-B derived peptide (but not its NDPK-A equivalent) disrupts the NDPK-B/CFTR complex in vitro (19-mers comprising amino acids 36–54 from NDPK-B or NDPK-A). Overlay (Far-Western) and Surface Plasmon Resonance (SPR) analysis both demonstrate that NDPK-B binds CFTR within its first nucleotide binding domain (NBD1, CFTR amino acids 351–727). Analysis of chloride currents reflective of CFTR or outwardly rectifying chloride channels (ORCC, DIDS-sensitive) showed that the 19-mer NDPK-B peptide (but not its NDPK-A equivalent) reduced both chloride conductances. Additionally, the NDPK-B (but not NDPK-A) peptide also attenuated acetylcholine-induced intestinal short circuit currents. In silico analysis of the NBD1/NDPK-B complex reveals an extended interaction surface between the two proteins. This binding zone is also target of the 19-mer NDPK-B peptide, thus confirming its capability to disrupt NDPK-B/CFTR complex. We propose that NDPK-B forms part of the complex that controls chloride currents in epithelia.

Targeted CFTR gene disruption with zinc-finger nucleases in human intestinal epithelial cells induces oxidative stress and inflammation

Cystic fibrosis (CF) is a multisystemic pathology caused by mutations of the CF transmembrane conductance regulator (CFTR) gene.

OBJECTIVES

As the intestine harbors the greatest number of CFTR transcripts after birth and since CFTR plays a role in glutathione transport, we hypothesized that CFTR deletion might produce oxidative stress (OxS) and inflammation in CF intestinal epithelial cell.

METHODS

CFTR gene was abrogated in Caco-2/15 enterocytes through the zinc-finger nuclease system. Their oxidative and inflammatory characteristics were appreciated under basal conditions and after the treatment with the pro-oxidant iron-ascorbate (Fe/Asc) complex and pro-inflammatory lipopolysaccharide (LPS).

RESULTS

Intestinal epithelial cells with CFTR knockout spontaneously exhibited an increased lipid peroxidation level, reflected by malondialdehyde overproduction and reduced antioxidant defense characterized by low enzymatic activities of glutathione peroxidase and catalase. CFTR silencing also resulted in elevated protein expression of pro-inflammatory tumor necrosis Factor-α, interleukin-6, cyclooxygenase-2, and the transcription factor nuclear factor-κB. Moreover, exaggerated OxS and inflammation processes occurred in CFTR(-/-) cells in response to the addition of Fe/Asc and LPS, respectively.

CONCLUSIONS

Intestinal Caco-2/15 cells with CFTR deletion, display innate oxidative and inflammatory features while being more sensitive to pro-oxidant and pro-inflammatory stimuli. These two pathophysiological processes could be implicated in CF-related intestinal disorders.

Alterations in blood leukocytes of G551D-bearing cystic fibrosis patients undergoing treatment with ivacaftor

BACKGROUND

Ivacaftor improves clinical outcome by potentiation of mutant G551D CFTR. Due to the presence of CFTR in monocytes and polymorphonuclear neutrophils (PMNs), we hypothesized that ivacaftor may impact leukocyte activation.

METHODS

We examined blood leukocytes from G551D CF subjects prior to and at one and six months after receiving ivacaftor. Blood leukocytes from ivacaftor-naïve G551D, F508del, and healthy controls were also treated with ivacaftor ex vivo to assess mutation-specific effects.

RESULTS

Compared to healthy controls, G551D CF subjects had significantly higher expression of active CD11b on PMNs and of CD63 on monocytes, which were normalized by in vivo ivacaftor treatment. Ex vivo exposure to ivacaftor of blood cells from G551D, but not F508del and healthy subjects, resulted in changes in CXCR2 and CD16 expression on PMNs.

CONCLUSIONS

In vivo and ex vivo exposure of G551D CF leukocytes to ivacaftor resulted in an altered activation profile, suggesting mutation-specific leukocyte modulation.

Resveratrol ameliorates abnormalities of fluid and electrolyte secretion in a hypoxia-Induced model of acquired CFTR deficiency

OBJECTIVE/HYPOTHESIS

Ineffective mucociliary clearance (MCC) is a common pathophysiologic process that underlies airway inflammation and infection. A dominant fluid and electrolyte secretory pathway in the nasal airways is governed by the cystic fibrosis transmembrane conductance regulator (CFTR). Decreased transepithelial Cl(-) transport secondary to an acquired CFTR deficiency may exacerbate respiratory epithelial dysfunction by diminishing MCC and increasing mucus viscosity. The objectives of the present study are to 1) develop a model of acquired CFTR deficiency in sinonasal epithelium using hypoxia, 2) investigate whether the polyphenol resveratrol promotes CFTR-mediated anion transport, 3) explore resveratrol mechanism of action and determine therapeutic suitability for overcoming acquired CFTR defects, and 4) test the drug in the hypoxic model of acquired CFTR deficiency in preparation for a clinical trial in human sinus disease. We hypothesize that hypoxia will induce depletion of airway surface liquid (ASL) secondary to acquired CFTR deficiency and that resveratrol will restore transepithelial Cl(-) secretion and recover ASL hydration.

STUDY DESIGN

Basic science.

METHODS

Murine nasal septal (MNSE) and human sinonasal epithelial (HSNE) cultures were incubated under hypoxic conditions (1% O2 , 5% CO2 ) and transepithelial ion transport (change in short-circuit current = ΔISC ) evaluated in Ussing chambers. Resveratrol was tested using primary cells and HEK293 cells expressing human CFTR by Ussing chamber and patch clamp techniques under both phosphorylating and nonphosphorylating conditions. CFTR activation was evaluated in human explants and by murine in vivo (nasal potential difference) assessment. Cellular cyclic adenosine monophosphate (cAMP) (ELISA) and subsequent CFTR regulatory domain (R-D) phosphorylation (gel-shift assay) were also evaluated. Effects of hypoxia and resveratrol on ASL were tested using confocal laser scanning microscopy (CLSM) and micro-optical coherence tomography (µOCT).

RESULTS

Hypoxia significantly decreased ΔISC (in µA/cm(2) ) attributable to CFTR at 12 and 24 hours of exposure in both MNSE (13.55 ± 0.46 [12 hours]; 12.75 ± 0.07 [24 hours] vs. 19.23 ± 0.18 [control]; P < 0.05) and HSNE (19.55 ± 0.56 [12 hours]; 17.67 ± 1.13 [24 hours] vs. 25.49 ± 1.48 [control]; P < 0.05). We have shown that resveratrol (100 μM) enhanced CFTR-dependent Cl(-) secretion in HSNE to an extent comparable to the recently Food and Drug Administration-approved CFTR potentiator, ivacaftor. Cl(-) transport across human sinonasal explants (78.42 ± 1.75 vs. 1.75 ± 1.5 [control]; P < 0.05) and in vivo murine nasal epithelium (-4 ± 1.8 vs. -0.8 ± 1.7 mV [control]; P < 0.05) were also significantly increased by the drug. No increase in cAMP or CFTR R-D phosphorylation was detected. Inside-out patches showed increased CFTR open probability (NPo/N (N = channel number]) compared to controls in both MNSE (0.329 ± 0.116 vs. 0.119 ± 0.059 [control]; P < 0.05) and HEK293 cells (0.22 ± 0.048 vs. 0.125 ± 0.07 [control]; P < 0.05). ASL thickness was decreased under hypoxic conditions when measured by CLSM (4.19 ± 0.44 vs. 6.88 ± 0.67 [control]; P < 0.05). A 30-minute apical application of resveratrol increased ASL depth in normal epithelium (8.08 ± 1.68 vs. 6.11 ± 0.47 [control]; P < 0.05). Furthermore, hypoxia-induced abnormalities of fluid and electrolyte secretion in sinonasal epithelium were restored with resveratrol treatment (5.55 ± 0.74 vs. 3.13 ± 0.17 [control]; P < 0.05).

CONCLUSIONS

CFTR activation with a leading edge Cl(-) secretagogue such as resveratrol represents an innovative approach to overcoming acquired CFTR defects in sinus and nasal airway disease. This exciting new strategy bears further testing in non-CF individuals with chronic rhinosinusitis.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 125:S1-S13, 2015.

Cystic fibrosis transmembrane conductance regulator-mRNA delivery: a novel alternative for cystic fibrosis gene therapy

BACKGROUND

Cystic fibrosis (CF) is the most frequent lethal genetic disease in the Caucasian population. CF is caused by a defective gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP- and ATP-dependent Cl(-) channel and central regulatory protein in epithelia. CFTR influences the fluid composition of the mucus in the respiratory tract. The most common mutation inducing CF, ΔF508, impairs CFTR processing within the cell and thus prevents functional CFTR expression in the apical membrane. The present study aimed to investigate the functional restoration of CFTR in human CF airway epithelia after transfection with optimized wild-type (wt)CFTR-mRNA.

METHODS

We used primary cultured human nasal epithelial (HNE) cells and the human bronchial epithelial cell line CFBE41o(-) that stably expresses ΔF508-CFTR and carried out transepithelial Ussing chamber measurements after transfection with optimized wtCFTR-mRNA. We confirmed the data obtained using immunofluorescence and protein biochemical approaches.

RESULTS

Transfection of the CFBE41o(-) cells with wtCFTR-mRNA restored cAMP-induced CFTR currents similar to the values seen in control cells (16HBE14o(-)). Using immunofluorescence approaches, we demonstrated that a considerable amount of CFTR is located at the apical surface in the CF cells after transfection. Western blot analyses of wtCFTR-mRNA transfected CFBE41o(-) cells confirmed these findings. Furthermore, we demonstrated physiological relevance by using primary cultured HNE cells and showed an almost two-fold increase in the cAMP-stimulated CFTR current after transfection.

CONCLUSIONS

From these data, we conclude that CFTR-mRNA transfection could comprise a novel alternative for gene therapy to restore impaired CFTR function.

Cystic fibrosis transmembrane conductance regulator dysfunction in VIP knockout mice

Vasoactive intestinal peptide (VIP), a neuropeptide, controls multiple functions in exocrine tissues, including inflammation, and relaxation of airway and vascular smooth muscles, and regulates CFTR-dependent secretion, which contributes to mucus hydration and local innate defense of the lung. We had previously reported that VIP stimulates the VPAC1 receptor, PKCϵ signaling cascade, and increases CFTR stability and function at the apical membrane of airway epithelial cells by reducing its internalization rate. Moreover, prolonged VIP stimulation corrects the molecular defects associated with F508del, the most common CFTR mutation responsible for the genetic disease cystic fibrosis. In the present study, we have examined the impact of the absence of VIP on CFTR maturation, cellular localization, and function in vivo using VIP knockout mice. We have conducted pathological assessments and detected signs of lung and intestinal disease. Immunodetection methods have shown that the absence of VIP results in CFTR intracellular retention despite normal expression and maturation levels. A subsequent loss of CFTR-dependent chloride current was measured in functional assays with Ussing chamber analysis of the small intestine ex vivo, creating a cystic fibrosis-like condition. Interestingly, intraperitoneal administration of VIP corrected tissue abnormalities, close to the wild-type phenotype, as well as associated defects in the vital CFTR protein. The results show in vivo a primary role for VIP chronic exposure in CFTR membrane stability and function and confirm in vitro data.

Cystic fibrosis transmembrane conductance regulator activation by roflumilast contributes to therapeutic benefit in chronic bronchitis

Cigarette smoking causes acquired cystic fibrosis transmembrane conductance regulator (CFTR) dysfunction and is associated with delayed mucociliary clearance and chronic bronchitis. Roflumilast is a clinically approved phosphodiesterase 4 inhibitor that improves lung function in patients with chronic bronchitis. We hypothesized that its therapeutic benefit was related in part to activation of CFTR. Primary human bronchial epithelial (HBE) cells, Calu-3, and T84 monolayers were exposed to whole cigarette smoke (WCS) or air with or without roflumilast treatment. CFTR-dependent ion transport was measured in modified Ussing chambers. Airway surface liquid (ASL) was determined by confocal microscopy. Intestinal fluid secretion of ligated murine intestine was monitored ex vivo. Roflumilast activated CFTR-dependent anion transport in normal HBE cells with a half maximal effective concentration of 2.9 nM. Roflumilast partially restored CFTR activity in WCS-exposed HBE cells (5.3 ± 1.1 μA/cm(2) vs. 1.2 ± 0.2 μA/cm(2) [control]; P < 0.05) and was additive with ivacaftor, a specific CFTR potentiator approved for the treatment of CF. Roflumilast improved the depleted ASL depth of HBE monolayers exposed to WCS (9.0 ± 3.1 μm vs. 5.6 ± 2.0 μm [control]; P < 0.05), achieving 79% of that observed in air controls. CFTR activation by roflumilast also induced CFTR-dependent fluid secretion in murine intestine, increasing the wet:dry ratio and the diameter of ligated murine segments. Roflumilast activates CFTR-mediated anion transport in airway and intestinal epithelia via a cyclic adenosine monophosphate-dependent pathway and partially reverses the deleterious effects of WCS, resulting in augmented ASL depth. Roflumilast may benefit patients with chronic obstructive pulmonary disease with chronic bronchitis by activating CFTR, which may also underlie noninfectious diarrhea caused by roflumilast.

Glucocorticoid dexamethasone regulates the differentiation of mouse conducting airway epithelial progenitor cells

Inhaled glucocorticoid dexamethasone is the most effective treatment of asthma currently available. Epithelial damage and shedding represents a clear manifestation of asthmatic pathologies. However it remains unknown if dexamethasone regulates functions of airway progenitor cells that are responsible for epithelial repair. In present study Secretoglobin1a1 (Scgb1a1) lineage tracing mice were injected intraperitoneally with tamoxifen to induce the expression of green fluorescence protein (GFP) in Scgb1a1-expressing conducting airway progenitor cells. Scgb1a1-expressing progenitor cells were isolated from lungs of Scgb1a1 lineage tracing mice via flow activated cell sorting. In vitro three-dimensional matrigel culture of these progenitor cells revealed that dexamethasone has little effect on the colony forming ability of airway epithelial progenitor cells, but exhibits significant effects on the differentiation of the progenitor cells. Compared to the untreated group, dexamethasone treatment inhibited the expression of forkhead box J1 (FoxJ1) and mucin subtype A & C (Muc5Ac), but promoted the expression of calcium activated chloride channel 3 (Clca3) and cystic fibrosis transmembrane conductance regulator (Cftr). Dexamethasone-induced effects on the expression of FoxJ1, Muc5Ac and Clca3 were abolished or even reversed in the presence of RU486, an antagonist of glucocorticoid receptor, indicating that glucocorticoid receptor plays a role in the regulation of airway epithelial progenitor cells by dexamethasone. These data suggested that, though effective to reduce airway inflammation, dexamethasone treatment alone fails to fully restore the mucociliary clearance function in the treatment of asthma patients.

Regulated recycling of mutant CFTR is partially restored by pharmacological treatment

Efficient trafficking of the cystic fibrosis transmembrane conductance regulator (CFTR) to and from the cell surface is essential for maintaining channel density at the plasma membrane (PM) and ensuring proper physiological activity. The most common mutation, F508del, exhibits reduced surface expression and impaired function despite treatment with currently available pharmacological small molecules, called correctors. To gain more detailed insight into whether CFTR enters compartments that allow corrector stabilization in the cell periphery, we investigated the peripheral trafficking itineraries and kinetics of wild type (WT) and F508del in living cells using high-speed fluorescence microscopy together with fluorogen activating protein detection. We directly visualized internalization and accumulation of CFTR WT from the PM to a perinuclear compartment that colocalized with the endosomal recycling compartment (ERC) markers Rab11 and EHD1, reaching steady-state distribution by 25 minutes. Stimulation by protein kinase A (PKA) depleted this intracellular pool and redistributed CFTR channels to the cell surface, elicited by reduced endocytosis and active translocation to the PM. Corrector or temperature rescue of F508del also resulted in targeting to the ERC and exhibited subsequent PKA-stimulated trafficking to the PM. Corrector treatment (24 hours) led to persistent residence of F508del in the ERC, while thermally destabilized F508del was targeted to lysosomal compartments by 3 hours. Acute addition of individual correctors, C4 or C18, acted on peripheral trafficking steps to partially block lysosomal targeting of thermally destabilized F508del. Taken together, corrector treatment redirects F508del trafficking from a degradative pathway to a regulated recycling route, and proteins that mediate this process become potential targets for improving the efficacy of current and future correctors.

Insulin-like growth factor 1 (IGF-1) enhances the protein expression of CFTR

Low levels of insulin-like growth factor 1 (IGF-1) have been observed in the serum of cystic fibrosis (CF) patients. However, the effects of low serum IGF-1 on the cystic fibrosis transmembrane conductance regulator (CFTR), whose defective function is the primary cause of cystic fibrosis, have not been studied. Here, we show in human cells that IGF-1 increases the steady-state levels of mature wildtype CFTR in a CFTR-associated ligand (CAL)- and TC10-dependent manner; moreover, IGF-1 increases CFTR-mediated chloride transport. Using an acceptor photobleaching fluorescence resonance energy transfer (FRET) assay, we have confirmed the binding of CAL and CFTR in the Golgi. We also show that CAL overexpression inhibits forskolin-induced increases in the cell-surface expression of CFTR. We found that IGF-1 activates TC10, and active TC10 alters the functional association between CAL and CFTR. Furthermore, IGF-1 and active TC10 can reverse the CAL-mediated reduction in the cell-surface expression of CFTR. IGF-1 does not increase the expression of ΔF508 CFTR, whose processing is arrested in the ER. This finding is consistent with our observation that IGF-1 alters the functional interaction of CAL and CFTR in the Golgi. However, when ΔF508 CFTR is rescued with low temperature or the corrector VRT-325 and proceeds to the Golgi, IGF-1 can increase the expression of the rescued ΔF508 CFTR. Our data support a model indicating that CAL-CFTR binding in the Golgi inhibits CFTR trafficking to the cell surface, leading CFTR to the degradation pathway instead. IGF-1-activated TC10 changes the interaction of CFTR and CAL, allowing CFTR to progress to the plasma membrane. These findings offer a potential strategy using a combinational treatment of IGF-1 and correctors to increase the post-Golgi expression of CFTR in cystic fibrosis patients bearing the ΔF508 mutation.

The epithelial sodium channel (ENaC) establishes a trafficking vesicle pool responsible for its regulation

The epithelial sodium channel (ENaC) is the rate-limiting step for sodium reabsorption across tight epithelia. Cyclic-AMP (cAMP) stimulation promotes ENaC trafficking to the apical surface to increase channel number and transcellular Na(+) transport. Removal of corticosteroid supplementation in a cultured cortical collecting duct cell line reduced ENaC expression. Concurrently, the number of vesicles trafficked in response to cAMP stimulation, as measured by a change in membrane capacitance, also decreased. Stimulation with aldosterone restored both the basal and cAMP-stimulated ENaC activity and increased the number of exocytosed vesicles. Knocking down ENaC directly decreased both the cAMP-stimulated short-circuit current and capacitance response in the presence of aldosterone. However, constitutive apical recycling of the Immunoglobulin A receptor was unaffected by alterations in ENaC expression or trafficking. Fischer Rat Thyroid cells, transfected with α,β,γ-mENaC had a significantly greater membrane capacitance response to cAMP stimulation compared to non-ENaC controls. Finally, immunofluorescent labeling and quantitation revealed a smaller number of vesicles in cells where ENaC expression was reduced. These findings indicate that ENaC is not a passive passenger in regulated epithelial vesicle trafficking, but plays a role in establishing and maintaining the pool of vesicles that respond to cAMP stimulation.

CFTR-mediated Cl(-) transport in the acinar and duct cells of rabbit lacrimal gland

PURPOSE

We investigated the role that the cystic fibrosis transmembrane conductance regulator (CFTR) may play in Cl(-) transport in the acinar and ductal epithelial cells of rabbit lacrimal gland (LG).

METHODS

Primary cultured LG acinar cells were processed for whole-cell patch-clamp electrophysiological recording of Cl(-) currents by using perfusion media with high and low [Cl(-)], 10 µM forskolin and 100 µM 3-isobutyl-1-methylxanthine (IBMX), the non-specific Cl(-) channel blocker 4,4'-disothiocyanostilbene-2, 2' sulphonic acid (DIDS; 100 µM) and CFTRinh-172 (10 µM), a specific blocker for CFTR. Ex vivo live cell imaging of [Cl(-)] changes in duct cells was performed on freshly dissected LG duct with a multiphoton confocal laser scanning microscope using a Cl(-) sensitive fluorescence dye, N-[ethoxycarbonylmethyl]-6-methoxy-quinolinium bromide.

RESULTS

Whole-cell patch-clamp studies demonstrated the presence of Cl(-) current in isolated acinar cells and revealed that this Cl(-) current was mediated by CFTR channel. Live cell imaging also showed the presence of CFTR-mediated Cl(-) transport across the plasma membrane of duct cells.

CONCLUSIONS

Our previous data showed the presence of CFTR in all acinar and duct cells within the rabbit LG, with expression most prominent in the apical membranes of duct cells. The present study demonstrates that CFTR is actively involved in Cl(-) transport in both acinar cells and epithelial cells from duct segments, suggesting that CFTR may play a significant role in LG secretion.

Activation of CFTR trafficking and gating by vasoactive intestinal peptide in human bronchial epithelial cells

Cystic fibrosis transmembrane conductance regulator (CFTR) is an apical membrane chloride channel critical to the regulation of fluid, chloride, and bicarbonate transport in epithelia and other cell types. The most common cause of cystic fibrosis (CF) is the abnormal trafficking of CFTR mutants. Therefore, understanding the cellular machineries that transit CFTR from the endoplasmic reticulum to the cell surface is important. Vasoactive intestinal polypeptide (VIP) plays an important role in CFTR-dependent chloride transport. The present study was designed to observe the affection of VIP on the trafficking of CFTR, and channel gating in human bronchial epithelium cells (HBEC). Confocal microscopy revealed CFTR immunofluorescence extending from the apical membrane deeply into the cell cytoplasm. After VIP treatment, apical extension of CFTR immunofluorescence into the cell was reduced and the peak intensity of CFTR fluorescence shifted towards the apical membrane. Western blot showed VIP increased cell surface and total CFTR. Compared with the augmented level of total CFTR, the surface CFTR increased more markedly. Immunoprecipitation founded that the mature form of CFTR had a marked increase in HBEC treated with VIP. VIP led to a threefold increase in Cl(-) efflux in HBEC. Glibenclamide-sensitive and DIDS-insensitive CFTR Cl(-) currents were consistently observed after stimulation with VIP (10(-8) mol/L). The augmentation of CFTR Cl(-) currents enhanced by VIP (10(-8) mol/L) was reversed, at least in part, by the protein kinase A (PKA) inhibitor, H-89 and the protein kinase C (PKC) inhibitor, H-7, suggesting PKA and PKC participate in the VIP-promoted CFTR Cl(-) currents.

Defective adenosine-stimulated cAMP production in cystic fibrosis airway epithelia: a novel role for CFTR in cell signaling

Adenosine (ADO) is an extracellular signaling molecule that is an important regulator of innate lung defense. On binding ADO, the A2B receptor (A2BR) stimulates cAMP production to activate the CFTR Cl(-) channel, increase ciliary beating, and initiate cytokine secretion. We tested the hypothesis that CFTR served as a positive regulator of the A2BRs. We found that A2BR and CFTR coimmunoprecipitated. They also underwent ADO-dependent Förster resonance energy transfer (FRET), which increased from 5% in the absence of agonist to 18% with 100 μM ADO (EC₅₀ 1.7 μM), suggesting that they dynamically associate in the plasma membrane. In contrast, despite colocalization, no FRET was observed between CFTR and GAP43. The interaction between A2BR and CFTR had some specificity: A2BR-stimulated but not forskolin-stimulated cAMP production was ~50% greater in the presence of CFTR, due to a CFTR-dependent increase in plasma membrane A2BR levels. These CFTR-dependent increases in A2BR levels and cAMP production resulted in significantly enhanced ciliary beating and increased cytokine secretion in normal compared to cystic fibrosis airway epithelia. Thus, we hypothesize that CFTR regulates A2BR levels in the plasma membrane to modulate cell signaling and to enhance selective components of the innate lung defense system.

Segmental and subcellular distribution of CFTR in the kidney

Besides its location at the plasma membrane, CFTR is present in intracellular vesicles along both the exocytic and the endocytic pathways. Immunostaining and subcellular fractionation studies of mouse kidney demonstrate that CFTR is located in endosomes of the cells lining the terminal part of the proximal tubule (PT). The PT cells efficiently reabsorb the ultrafiltered low molecular weight (LMW) proteins by apical endocytosis involving the multiligand receptors megalin and cubilin. The progression from early endosomes to lysosomes depends on the integrity of the cytoskeleton, as well as on vesicular acidification. The latter is mediated by the vacuolar H+-ATPase (V-ATPase) and requires an anionic conductance to dissipate the transmembrane potential gradient. CFTR might ensure such chloride conductance, thereby participating to endosomal acidification and protein uptake by PT cells. Immunostaining with well-characterized antibodies shows that CFTR is located in the terminal segment of PT, where it co-distributes with megalin and cubilin. Subcellular fractionation of total mouse kidneys through Percoll gradients demonstrates the co-localization of CFTR with the V-ATPase and early endosome markers including the Cl-/H+ exchanger, ClC-5, and the small GTPase, Rab5a. Deglycosylation studies and immunoblotting show a distinct glycosylation pattern for CFTR in mouse kidney and lung. The segmental and subcellular distribution of CFTR in mouse kidney supports a role for CFTR in PT receptor-mediated endocytosis of ultrafiltered LMW proteins.

CFTR expression regulation by the unfolded protein response

The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel and key regulator of epithelial functions. Mutations in the CFTR gene lead to reduced or dysfunctional CFTR protein and cause cystic fibrosis (CF), a generalized exocrinopathy affecting multiple organs. In the airways, loss of CFTR function leads to thickened mucus, reduced mucociliary clearance, chronic infections, and respiratory failure. Common airway disorders such as bronchitis and chronic obstructive pulmonary disease (COPD) also present CF-like symptoms such as mucus congestion and chronic inflammation without mutations in CFTR. The primary risk factors for COPD and chronic bronchitis include environmental stress insults such as pollutants and infections that often result in hypoxic conditions. Furthermore, environmental factors such as cigarette smoke and reactive oxygen species have been implicated in reduced CFTR function. Activation of cellular stress responses by these factors promotes differential, stress-associated gene expression regulation. During our investigations on the mechanisms of CFTR expression regulation, we have shown that the ER stress response, the unfolded protein response (UPR), decreases CFTR expression at the transcriptional, translational, and maturational levels. Here, we provide a detailed description of the methods we employ to study CFTR expression regulation by the UPR. Similar approaches are applicable in studies on other genes and how they are affected by the UPR.

Excess fluoride interferes with chloride-channel-dependent endocytosis in ameloblasts

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause cystic fibrosis (CF). Both CF and dental fluorosis result in protein retention in mature enamel. We hypothesized that excess fluoride might cause protein retention by interfering with CFTR function, resulting in abnormal expression of proteases and pathological endocytosis. Millimolar concentrations of fluoride reduced uptake of Emdogain, an enamel matrix derivative, in ameloblast-like PABSo-E cells, while stimulating an acidic intracellular environment at the same time. When CFTR function was inhibited by either an siRNA or a chloride channel inhibitor, CFTRinh-172, fluoride's effect on Emdogain uptake was partially blocked. Treatment of cells with CFTR siRNA down-regulated expression of proteases MMP20 and KLK4 and increased intracellular pH. We conclude that excess fluoride inhibits endocytic activity of ameloblasts through the CFTR chloride channel or other chloride channels. The intracellular pH might be the key mechanism by which abnormal proteolytic activity and defective endocytosis cause the residual protein observed in enamel of patients with CF and dental fluorosis.

Toxin mediated diarrhea in the 21 century: the pathophysiology of intestinal ion transport in the course of ETEC, V. cholerae and rotavirus infection

An estimated 4 billion episodes of diarrhea occur each year. As a result, 2–3 million children and 0.5–1 million adults succumb to the consequences of this major healthcare concern. The majority of these deaths can be attributed to toxin mediated diarrhea by infectious agents, such as E. coli, V. cholerae or Rotavirus. Our understanding of the pathophysiological processes underlying these infectious diseases has notably improved over the last years. This review will focus on the cellular mechanism of action of the most common enterotoxins and the latest specific therapeutic approaches that have been developed to contain their lethal effects.

Expression of cystic fibrosis transmembrane conductance regulator in paracervical ganglia

The cystic fibrosis transmembrane conductance regulator (CFTR) is an important protein that acts as a chloride channel and regulates many physiological functions, including salt transport and fluid flow. Mutations in the gene encoding the CFTR protein cause cystic fibrosis. CFTR is expressed in the epithelial cells of the lungs, pancreas, intestines, and other organs. In the peripheral and central nervous system, CFTR expression has been detected in the neurons of rat brains, ganglion cells of rat hearts, human hypothalamus, human spinal cord, and human spinal and sympathetic ganglia. However, CFTR has not been identified in other parts of the nervous system. In this study, we used immunohistochemistry, in situ hybridization, and laser-assisted microdissection (LMD) followed by reverse transcriptase (RT) PCR to identify CFTR proteins and messenger RNA in human and rat paracervical ganglion cells. CFTR and its gene expression were both detected in paracervical ganglion cells, a finding that might link this important protein to the neuronal regulation of female urogenital function. These findings could provide new insights into the symptoms related to the reproductive system frequently observed in female cystic fibrosis patients.

Expression and distribution of cystic fibrosis transmembrane conductance regulator in neurons of the spinal cord

To verify the hypothesis that cystic fibrosis transmembrane conductance regulator (CFTR) is expressed in neurons of the human spinal cord, we investigated the presence and distribution of CFTR protein and mRNA in different segments of the human spinal cord obtained from autopsies. The techniques employed included reverse transcriptase‐polymerase chain reaction (RT‐PCR) to detect CFTR gene expression, in situ hybridization to detect mRNA distribution, and immunohistochemistry to detect protein distribution. The specificity of these experiments was established with extensive controls. We found widespread and abundant expression of CFTR in neurons of the human spinal cord. CFTR protein and mRNA are localized to the cytoplasm of neurons in all segments of the spinal cord but not to glial fibrillary acidic protein (GFAP)‐positive cells. CFTR is a very important molecule, acting as a chloride channel and regulating many physiological functions, including salt transport, fluid flow, and intracellular ion concentrations. Its mutation causes cystic fibrosis. Our finding of abundant CFTR in the spinal cord suggests that this molecule may be significant in the normal function and pathology of the spinal cord. © 2009 Wiley‐Liss, Inc.

Cigarette smoke condensate inhibits transepithelial chloride transport and ciliary beat frequency

OBJECTIVES/HYPOTHESIS

Although the pathophysiology leading to rhinosinusitis is complex, evidence indicates that decreased mucociliary clearance (MCC) is a major contributing feature. Normal respiratory epithelial MCC is an important host defense mechanism that is dependent on proper ciliary beating and the biological properties of the airway surface liquid (ASL). The role that tobacco smoke exposure plays as an inhibitor of MCC has yet to be elucidated. The present study investigates the consequences of cigarette smoke exposure on ciliary function and transepithelial chloride (Cl(-)) secretion, a major determinant of ASL.

STUDY DESIGN

In vitro investigation.

METHODS

Well-characterized primary murine nasal septal epithelial (MNSE) and human sinonasal epithelial (HSNE) cultures were exposed to cigarette smoke condensate (CSC) and compared to control cultures. Effects on ciliary beat frequency (CBF) and Cl(-) secretion were investigated using pharmacologic manipulation.

RESULTS

Change in forskolin-stimulated current (DeltaI(SC)), representing transepithelial Cl(-) secretion, was significantly decreased in CSC exposed MNSE (14.97 +/- 1.2 microA/cm(2) vs. control, 19.1 +/- 1.56 microA/cm(2) [P = .04]) and HSNE (2.68 +/- 0.79 muA/cm(2) vs. control, 10.8 +/- 1.73 microA/cm(2)) cultures (P = .001). Forskolin-stimulated CBF was also significantly reduced when acutely exposed to CSC (5.64 +/- 0.06 Hz vs. control 7.15 +/- 0.18 Hz).

CONCLUSIONS

The present study provides direct evidence that tobacco smoke diminishes two major components of MCC. This links tobacco smoke as a potential contributing and/or exacerbating factor in exposed individuals with chronic rhinosinusitis.

Persistence of essential fatty acid deficiency in cystic fibrosis despite nutritional therapy

To study the evolution of plasma fatty acid composition of patients with cystic fibrosis (CF) in relation to nutritional status, pancreatic function, and development of CF-related liver disease (CFRLD) and diabetes mellitus, 24 CF pediatric patients with stable pulmonary disease were studied before and after an approximate period of 8 y. Nutritional status, pulmonary function, pancreatic function, and presence of CFRLD or diabetes mellitus were recorded. Results were compared with data obtained in 83 healthy children. Patients with CF have significantly lower linoleic acid (LA), docosahexaenoic acid (DHA), lignoceric acid, and LA x DHA product and higher oleic acid, mead acid, dihomo-gamma-linoleic acid, and docosapentaenoic acid (DPA). Comparison of samples taken at first and second studies revealed a significant decrease in LA levels and lignoceric acid associated with a significant increase in dihomo-gamma-linoleic acid levels. Patients with CFRLD showed significantly higher mead acid/arachidonic acid ratio and lower total omega6 polyunsaturated fatty acids content. There was no relation of plasma fatty acids composition with pancreatic function, pulmonary function, or diabetes mellitus. Follow-up of patients with CF shows that essential fatty acids deficiency, particularly in LA and DHA content, persisted unmodified along time despite an adequate nutritional therapy. Future studies after supplementation with omega3 polyunsaturated fatty acids should be undertaken.

Expression and distribution of cystic fibrosis transmembrane conductance regulator in neurons of the human brain

The importance of the molecule cystic fibrosis transmembrane conductance regulator (CFTR) is reflected in the many physiological functions it regulates. It is known to be present in epithelial cells of the lungs, pancreas, sweat glands, gut, and other tissues, and gene mutations of CFTR cause cystic fibrosis (CF). We studied the expression and distribution of CFTR in the human brain with reverse transcriptase polymerase chain reaction, in situ hybridization, and immunohistochemistry. This study demonstrates widespread and abundant expression of CFTR in neurons of the human brain. Techniques of double labeling and evaluation of consecutive tissue sections localized CFTR protein and mRNA signals to the cytoplasm of neurons in all regions of the brain studied, but not to glial cells. The presence of CFTR in central neurons not only provides a possible explanation for the neural symptoms observed in CF patients, but also may lead to a better understanding of the functions of CFTR in the human brain.

Cystic fibrosis transmembrane conductance regulator expression in human spinal and sympathetic ganglia

Cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel protein, and mutations of its gene cause cystic fibrosis. CFTR is known to be expressed in epithelial cells of the respiratory, digestive and reproductive tracts. It is also present in rat neurons and heart ganglion cells. In humans, it is expressed in the hypothalamus, but has not been identified in other parts of the human nervous system. In this study, immunohistochemistry, double-staining immunofluorescence, in situ hybridization, nested reverse transcription-PCR and relative quantification of real-time PCR analysis were performed on spinal and sympathetic ganglia from seven human autopsies with no known nervous system disease. CFTR protein was expressed in most ganglion cells with no obvious difference in the amounts of mRNA transcript in ganglia of different sites. We conclude that CFTR protein and its mRNA were extensively expressed at relatively constant levels in human spinal and sympathetic ganglion cells, and may be important in physiological and pathological conditions. Moreover, CFTR in ganglia may be associated with pathophysiological changes seen in cystic fibrosis.

Lipid metabolism in cystic fibrosis

PURPOSE OF REVIEW

Expression of defective cystic fibrosis transmembrane conductance regulator (CFTR), the cause for cystic fibrosis, affects fatty acid, cholesterol and sphingolipid metabolism. This review summarizes recent observations and evaluates current understanding of mechanisms.

RECENT FINDINGS

Recent observations implicate CFTR, in addition to known effects on fatty acid and cholesterol metabolism, in the regulation of sphingolipid metabolism and suggest that this pathway is relevant to inflammation and infection. A common mechanism on how CFTR affects such a wide spectrum of lipid classes is currently not known. One mechanism for low linoleic acid, amenable to inhibition by docosahexaenoic acid, is increased metabolism in the n-6 fatty acid pathway. Accumulation of free cholesterol in distinct perinuclear compartments, reversible by overexpression of rab9, suggests that cystic fibrosis and the lysosomal storage disease Niemann-Pick-C could share similar cell signaling defects, in addition to increased cAMP signaling and sterol-regulatory element binding protein (SREBP) expression that affect cholesterol metabolism. Novel is the recognition that CFTR modulates ceramide mass and uptake of sphingosine-1- phosphate. Experiments in different cystic fibrosis-mouse models, although not able to establish whether ceramide mass is increased or decreased, suggest that normalization of ceramide decreases infection and selected parameters of inflammation, of relevance to the complex phenotype that characterizes cystic fibrosis.

SUMMARY

Expression of defective CFTR has profound effects on fatty acid, cholesterol and sphingolipid metabolism, for which mechanisms are currently poorly understood. Recent studies in different cystic fibrosis models suggest a causal relationship between altered ceramide mass and increased inflammation and susceptibility to infection. Studies in cystic fibrosis knockout mouse models suggest that normalization of ceramide decreases infection and inflammation. Studies that evaluate the diagnostic and clinical relevance of sphingolipids in patients with cystic fibrosis are needed.

Cystic fibrosis transmembrane conductance regulator gene polymorphisms in patients with primary sclerosing cholangitis

BACKGROUND/AIMS

Primary sclerosing cholangitis (PSC) is a progressive cholestatic disease commonly associated with inflammatory bowel disease (IBD) and characterized by fibrosing inflammatory destruction of bile ducts. The histological features in the liver of PSC patients are similar to those observed in cystic fibrosis (CF). Our aim was to study whether variants in the CFTR gene are associated with the occurrence and/or evolution of PSC.

METHODS

PSC patients (n=140) were genotyped for F508del, the TGmTn variants, and four additional polymorphic loci (1001+11 C>T, M470V, T854T and Q1463Q), and compared to 136 matched healthy controls.

RESULTS

The 1540G-allele, encoding V470, was less frequent in PSC (52%) than in controls (64%, p=0.003), and was associated with protection against PSC in individuals without IBD (OR 0.25, 95% CI 0.12-0.52, p=0.0002). Also TG11-T7 was less frequent in PSC (53%) than in controls (61%, p=0.04), this haplotype was associated with reduced risk for PSC (OR 0.34, 95% CI 0.17-0.70, p=0.003) in individuals without IBD.

CONCLUSIONS

In this cohort of PSC patients, several CFTR-variants affecting the functional properties of the CFTR protein seem to offer protection against the development of PSC, confirming our hypothesis that CFTR might be implicated in the pathogenesis of PSC.

CFTR and defective endocytosis: new insights in the renal phenotype of cystic fibrosis

Inactivation of the chloride channel cystic fibrosis transmembrane conductance regulator (CFTR) causes cystic fibrosis (CF). Although CFTR is expressed in the kidney, no overwhelming renal phenotype is associated with CF. Recent studies have shown that the level of CFTR mRNA in mouse kidney approaches that found in lung. CFTR is particularly abundant in the apical area of proximal tubule cells, where it co-distributes with the Cl(-)/H(+) exchanger ClC-5 and Rab5a in endosomes. The biological relevance of CFTR in proximal tubule endocytosis has been tested in CF mouse models and CF patients. Mice lacking CFTR show a defective receptor-mediated endocytosis, as evidenced by impaired uptake of (125)I-beta(2)-microglobulin, a decreased expression of the cubilin receptor in the kidney, and a significant excretion of cubilin and its low-molecular-weight ligands into the urine. Low-molecular-weight proteinuria (and particularly transferrinuria) is similarly detected in CF patients in comparison with normal controls or patients with chronic lung inflammation. These studies suggest that the functional loss of CFTR impairs the handling of low-molecular-weight proteins by the kidney, supporting a role of CFTR in receptor-mediated endocytosis in proximal tubule cells. The selective proteinuria should be integrated in the pathophysiology of multi-systemic complications increasingly observed in CF patients.

Role of the cystic fibrosis transmembrane conductance channel in human airway smooth muscle

Patients with cystic fibrosis (CF) suffer from asthma-like symptoms and gastrointestinal cramps, attributed to a mutation in the CF transmembrane conductance regulator (CFTR) gene present in a variety of cells. Pulmonary manifestations of the disease include the production of thickened mucus and symptoms of asthma, such as cough and wheezing. A possible alteration in airway smooth muscle (ASM) cell function of patients with CF has not been investigated. The aim of this study was to determine whether the (CFTR) channel is present and affects function of human ASM cells. Cell cultures were obtained from the main or lobar bronchi of patients with and without CF, and the presence of the CFTR channel detected by immunofluorescence. Cytosolic Ca(2+) was measured using Fura-2 and dual-wavelength microfluorimetry. The results show that CFTR is expressed in airway bronchial tissue and in cultured ASM cells. Peak Ca(2+) release in response to histamine was significantly decreased in CF cells compared with non-CF ASM cells (357 +/- 53 nM versus 558 +/- 20 nM; P < 0.001). The CFTR pharmacological blockers, glibenclamide and N-phenyl anthranilic acid, significantly reduced histamine-induced Ca(2+) release in non-CF cells, and similar results were obtained when CFTR expression was varied using antisense oligonucleotides. In conclusion, these data show that the CFTR channel is present in ASM cells, and that it modulates the release of Ca(2+) in response to contractile agents. In patients with CF, a dysfunctional CFTR channel could contribute to the asthma diathesis and gastrointestinal problems experienced by these patients.

Regulation of CFTR trafficking by its R domain

Phosphorylation of the R domain is required for cystic fibrosis transmembrane conductance regulator (CFTR) channel gating, and cAMP/protein kinase A (PKA) simulation can also elicit insertion of CFTR into the plasma membrane from intracellular compartments (Bertrand, C. A., and Frizzell, R. A. (2003) Am. J. Physiol. 285, C1-C18). We evaluated the structural basis of regulated CFTR trafficking by determining agonist-evoked increases in plasma membrane capacitance (Cm) of Xenopus oocytes expressing CFTR deletion mutants. Expression of CFTR as a split construct that omitted the R domain (Deltaamino acids 635-834) produced a channel with elevated basal current (Im) and no DeltaIm or trafficking response (DeltaCm) upon cAMP/PKA stimulation, indicating that the structure(s) required for regulated CFTR trafficking are contained within the R domain. Additional deletions showed that removal of amino acids 817-838, a 22-amino acid conserved helical region having a net charge of -9, termed NEG2 (Xie, J., Adams, L. M., Zhao, J., Gerken, T. A., Davis, P. B., and Ma, J. (2002) J. Biol. Chem. 277, 23019-23027), produced a channel with regulated gating that lacked the agonist-induced increase in CFTR trafficking. Injection of NEG2 peptides into oocytes expressing split DeltaNEG2 CFTR prior to stimulation restored the agonist-evoked DeltaCm, consistent with the concept that this sequence mediates the regulated trafficking event. In support of this idea, DeltaNEG2 CFTR escaped from the inhibition of wild type CFTR trafficking produced by overexpression of syntaxin 1A. These observations suggest that the NEG2 region at the C terminus of the R domain allows stabilization of CFTR in a regulated intracellular compartment from which it traffics to the plasma membrane in response to cAMP/PKA stimulation.

Cholesterol Depletion and Genistein as Tools to Promote F508delCFTR Retention at the Plasma Membrane

BACKGROUND/AIMS

F508delCFTR-, but not wtCFTR-, expressing fibroblasts resemble Niemann Pick type C cells in the massive intracellular accumulation of free cholesterol. The recruitment and activation of F508delCFTR by cholesterol depletion was studied.

METHODS

Filipin staining, forskolin-stimulated anion efflux and FITC-dextran uptake were studied in control cells and fibroblasts treated with 2-hydroxypropyl beta-cyclodextrin phosphatidylcholine large unilamellar vesicles to deplete cellular free cholesterol.

RESULTS

Treatment of F508delCFTR-, but not wtCFTR-, expressing fibroblasts with 2-hydroxypropyl beta-cyclodextrin resulted in a reduction in cellular cholesterol and a potentiation of the forskolin-induced anion efflux. In addition, forskolin also promoted a massive increase in the rate of endocytosis in F508delCFTR fibroblasts, which was absent in genistein- or cyclodextrin-treated cultures.

CONCLUSION

The results not only suggest that reducing cellular cholesterol may serve as pharmacotherapeutic tool in the treatment of cystic fibrosis but also reveal a novel mechanism for genistein regulation of F508delCFTR, i.e. retention by inhibition of endocytosis.

Enhanced cell-surface stability of rescued DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) by pharmacological chaperones

Misfolded proteins destined for the cell surface are recognized and degraded by the ERAD [ER (endoplasmic reticulum) associated degradation] pathway. TS (temperature-sensitive) mutants at the permissive temperature escape ERAD and reach the cell surface. In this present paper, we examined a TS mutant of the CFTR [CF (cystic fibrosis) transmembrane conductance regulator], CFTR DeltaF508, and analysed its cell-surface trafficking after rescue [rDeltaF508 (rescued DeltaF508) CFTR]. We show that rDeltaF508 CFTR endocytosis is 6-fold more rapid (approximately 30% per 2.5 min) than WT (wild-type, approximately 5% per 2.5 min) CFTR at 37 degrees C in polarized airway epithelial cells (CFBE41o-). We also investigated rDeltaF508 CFTR endocytosis under two further conditions: in culture at the permissive temperature (27 degrees C) and following treatment with pharmacological chaperones. At low temperature, rDeltaF508 CFTR endocytosis slowed to WT rates (20% per 10 min), indicating that the cell-surface trafficking defect of rDeltaF508 CFTR is TS. Furthermore, rDeltaF508 CFTR is stabilized at the lower temperature; its half-life increases from <2 h at 37 degrees C to >8 h at 27 degrees C. Pharmacological chaperone treatment at 37 degrees C corrected the rDeltaF508 CFTR internalization defect, slowing endocytosis from approximately 30% per 2.5 min to approximately 5% per 2.5 min, and doubled DeltaF508 surface half-life from 2 to 4 h. These effects are DeltaF508 CFTR-specific, as pharmacological chaperones did not affect WT CFTR or transferrin receptor internalization rates. The results indicate that small molecular correctors may reproduce the effect of incubation at the permissive temperature, not only by rescuing DeltaF508 CFTR from ERAD, but also by enhancing its cell-surface stability.