Specialized proresolving mediator resolvin E1 corrects the altered cystic fibrosis nasal epithelium cilia beating dynamics.

In cystic fibrosis (CF), impaired mucociliary clearance leads to chronic infection and inflammation. However, cilia beating features in a CF altered environment, consisting of dehydrated airway surface liquid layer and abnormal mucus, have not been fully characterized. Furthermore, acute inflammation is normally followed by an active resolution phase requiring specialized proresolving lipid mediators (SPMs) and allowing return to homeostasis. However, altered SPMs biosynthesis has been reported in CF. Here, we explored cilia beating dynamics in CF airways primary cultures and its response to the SPMs, resolvin E1 (RvE1) and lipoxin B4 (LXB4). Human nasal epithelial cells (hNECs) from CF and non-CF donors were grown at air-liquid interface. The ciliary beat frequency, synchronization, orientation, and density were analyzed from high-speed video microscopy using a multiscale Differential Dynamic Microscopy algorithm and an in-house developed method. Mucins and ASL layer height were studied by qRT-PCR and confocal microscopy. Principal component analysis showed that CF and non-CF hNEC had distinct cilia beating phenotypes, which was mostly explained by differences in cilia beat organization rather than frequency. Exposure to RvE1 (10 nM) and to LXB4 (10 nM) restored a non-CF-like cilia beating phenotype. Furthermore, RvE1 increased the airway surface liquid (ASL) layer height and reduced the mucin MUC5AC thickness. The calcium-activated chloride channel, TMEM16A, was involved in the RvE1 effect on cilia beating, hydration, and mucus. Altogether, our results provide evidence for defective cilia beating in CF airway epithelium and a role of RvE1 and LXB4 to restore the main epithelial functions involved in the mucociliary clearance.

Methylprednisolone pulse treatment improves ProSP-C trafficking in twins with SFTPC mutation: An isoform story?

Mutations in the gene encoding surfactant protein C (SP-C) cause interstitial lung disease (ILD), and glucocorticosteroid (GC) treatment is the most recognized therapy in children. We aimed to decipher the mechanisms behind successful GC treatment in twins carrying a BRICHOS c.566G > A (p.Cys189Tyr) mutation in the SP-C gene (SFTPC). METHODS: The twins underwent bronchoscopy before and after GC treatment and immunoblotting analysis of SP-C proprotein (proSP-C) and SP-C mature in bronchoalveolar fluid (BALF). Total RNA was extracted and analysed using quantitative real-time PCR assays. In A549 cells, the processing of mutated protein C189Y was studied by immunofluorescence and immunoblotting after heterologous expression of eukaryotic vectors containing wild type or C189Y mutant cDNA. RESULTS: Before treatment, BALF analysis identified an alteration of the proSP-C maturation process. Functional study of C189Y mutation in alveolar A549 cells showed that pro-SP-CC189Y was retained within the endoplasmic reticulum together with ABCA3. After 5 months of GC treatment with clinical benefit, the BALF analysis showed an improvement of proSP-C processing. SFTPC mRNA analysis in twins revealed a decrease in the expression of total SFTPC mRNA and a change in its splicing, leading to the expression of a second shorter proSP-C isoform. In A549 cells, the processing and the stability of this shorter wild-type proSP-C isoform was similar to that of the longer isoform, but the half-life of the mutated shorter isoform was decreased. These results suggest a direct effect of GC on proSP-C metabolism through reducing the SFTPC mRNA level and favouring the expression of a less stable protein isoform.

Targeting p16INK4a Promotes Lipofibroblasts and Alveolar Regeneration after Early-Life Injury.

Rationale: Promoting endogenous pulmonary regeneration is crucial after damage to restore normal lungs and prevent the onset of chronic adult lung diseases.Objectives: To investigate whether the cell-cycle inhibitor p16INK4a limits lung regeneration after newborn bronchopulmonary dysplasia (BPD), a condition characterized by the arrest of alveolar development, leading to adult sequelae.Methods: We exposed p16INK4a-/- and p16INK4aATTAC (apoptosis through targeted activation of caspase 8) transgenic mice to postnatal hyperoxia, followed by pneumonectomy of the p16INK4a-/- mice. We measured p16INK4a in blood mononuclear cells of preterm newborns, 7- to 15-year-old survivors of BPD, and the lungs of patients with BPD.Measurements and Main Results: p16INK4a concentrations increased in lung fibroblasts after hyperoxia-induced BPD in mice and persisted into adulthood. p16INK4a deficiency did not protect against hyperoxic lesions in newborn pups but promoted restoration of the lung architecture by adulthood. Curative clearance of p16INK4a-positive cells once hyperoxic lung lesions were established restored normal lungs by adulthood. p16INK4a deficiency increased neutral lipid synthesis and promoted lipofibroblast and alveolar type 2 (AT2) cell development within the stem-cell niche. Besides, lipofibroblasts support self-renewal of AT2 cells into alveolospheres. Induction with a PPARγ (peroxisome proliferator-activated receptor γ) agonist after hyperoxia also increased lipofibroblast and AT2 cell numbers and restored alveolar architecture in hyperoxia-exposed mice. After pneumonectomy, p16INK4a deficiency again led to an increase in lipofibroblast and AT2 cell numbers in the contralateral lung. Finally, we observed p16INK4a mRNA overexpression in the blood and lungs of preterm newborns, which persisted in the blood of older survivors of BPD.Conclusions: These data demonstrate the potential of targeting p16INK4a and promoting lipofibroblast development to stimulate alveolar regeneration from childhood to adulthood.

Small Hsps as Therapeutic Targets of Cystic Fibrosis Transmembrane Conductance Regulator Protein.

Human small heat shock proteins are molecular chaperones that regulate fundamental cellular processes in normal and pathological cells. Here, we have reviewed the role played by HspB1, HspB4 and HspB5 in the context of Cystic Fibrosis (CF), a severe monogenic autosomal recessive disease linked to mutations in Cystic Fibrosis Transmembrane conductance Regulator protein (CFTR) some of which trigger its misfolding and rapid degradation, particularly the most frequent one, F508del-CFTR. While HspB1 and HspB4 favor the degradation of CFTR mutants, HspB5 and particularly one of its phosphorylated forms positively enhance the transport at the plasma membrane, stability and function of the CFTR mutant. Moreover, HspB5 molecules stimulate the cellular efficiency of currently used CF therapeutic molecules. Different strategies are suggested to modulate the level of expression or the activity of these small heat shock proteins in view of potential in vivo therapeutic approaches. We then conclude with other small heat shock proteins that should be tested or further studied to improve our knowledge of CFTR processing.

Phosphorylation of the Chaperone-Like HspB5 Rescues Trafficking and Function of F508del-CFTR.

Cystic Fibrosis is a lethal monogenic autosomal recessive disease linked to mutations in Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein. The most frequent mutation is the deletion of phenylalanine at position 508 of the protein. This F508del-CFTR mutation leads to misfolded protein that is detected by the quality control machinery within the endoplasmic reticulum and targeted for destruction by the proteasome. Modulating quality control proteins as molecular chaperones is a promising strategy for attenuating the degradation and stabilizing the mutant CFTR at the plasma membrane. Among the molecular chaperones, the small heat shock protein HspB1 and HspB4 were shown to promote degradation of F508del-CFTR. Here, we investigated the impact of HspB5 expression and phosphorylation on transport to the plasma membrane, function and stability of F508del-CFTR. We show that a phosphomimetic form of HspB5 increases the transport to the plasma membrane, function and stability of F508del-CFTR. These activities are further enhanced in presence of therapeutic drugs currently used for the treatment of cystic fibrosis (VX-770/Ivacaftor, VX-770+VX-809/Orkambi). Overall, this study highlights the beneficial effects of a phosphorylated form of HspB5 on F508del-CFTR rescue and its therapeutic potential in cystic fibrosis.

Identification of a novel 5' alternative CFTR mRNA isoform in a patient with nasal polyposis and CFTR mutations.

Cystic fibrosis may be revealed by nasal polyposis (NP) starting early in life. We performed cystic fibrosis transmembrane conductance regulator (CFTR) DNA and mRNA analyses in the family of a 12-year-old boy presenting with NP and a normal sweat test. Routine DNA analysis only showed the heterozygous c.2551C>T (p.Arg851*) mutation in the child and the father. mRNA analysis showed partial exon skipping due to c.2551C>T and a significant increase in total CFTR mRNA in the patient and the mother, which was attributable to the heterozygous c. -2954G>A variant in the distant promoter region, as demonstrated by in vitro luciferase assays. The 5' rapid amplification of cDNA ends analysis showed the presence of a novel transcript, where the canonical exon 1 was replaced by an alternative exon called 1a-Long. This case report could represent the first description of a CFTR-related disorder associated with the presence of a 5' alternative, probably nonfunctional transcript, similar to those of fetal origin.

Combined computational-experimental analyses of CFTR exon strength uncover predictability of exon-skipping level.

With the increased number of identified nucleotide sequence variations in genes, the current challenge is to classify them as disease causing or neutral. These variants of unknown clinical significance can alter multiple processes, from gene transcription to RNA splicing or protein function. Using an approach combining several in silico tools, we identified some exons presenting weaker splicing motifs than other exons in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. These exons exhibit higher rates of basal skipping than exons harboring no identifiable weak splicing signals using minigene assays. We then screened 19 described mutations in three different exons, and identified exon-skipping substitutions. These substitutions induced higher skipping levels in exons having one or more weak splicing motifs. Indeed, this level remained under 2% for exons with strong splicing motifs and could reach 40% for exons having at least one weak motif. Further analysis revealed a functional exon splicing enhancer within exon 3 that was associated with the SR protein SF2/ASF and whose disruption induced exon skipping. Exon skipping was confirmed in vivo in two nasal epithelial cell brushing samples. Our approach, which point out exons with some splicing signals weaknesses, will help spot splicing mutations of clinical relevance.

Alternative splicing of in-frame exon associated with premature termination codons: implications for readthrough therapies.

The correction of premature termination codons (PTCs) by agents that promote readthrough represents a promising emerging tool for the treatment of many genetic diseases. The efficiency of the treatment, however, varies depending on the stop codon itself and the amount of correctible transcripts related to the efficiency of nonsense-mediated decay. In the current study, a screen by in vitro minigene assay of all six PTCs described in exon 15 of the CFTR gene demonstrated alternative splicing to differing degrees for five of them. Of the five, PTC mutations c.2537G>A (p.Trp846*(UAG) ) and c.2551C>T (p.Arg851*) cause the greatest proportion of transcripts lacking exon 15; both mutations altering exonic splicing regulatory elements. In order to increase the amount of full-length transcripts, different pharmacological treatments were performed showing both negative and positive effects on exon inclusion for the same mutation. Therefore, the total amount of transcripts together with the splicing profile should be assessed to anticipate and improve efficacy of readthrough therapy.

Alternative splicing at a NAGNAG acceptor site as a novel phenotype modifier.

Approximately 30% of alleles causing genetic disorders generate premature termination codons (PTCs), which are usually associated with severe phenotypes. However, bypassing the deleterious stop codon can lead to a mild disease outcome. Splicing at NAGNAG tandem splice sites has been reported to result in insertion or deletion (indel) of three nucleotides. We identified such a mechanism as the origin of the mild to asymptomatic phenotype observed in cystic fibrosis patients homozygous for the E831X mutation (2623G>T) in the CFTR gene. Analyses performed on nasal epithelial cell mRNA detected three distinct isoforms, a considerably more complex situation than expected for a single nucleotide substitution. Structure-function studies and in silico analyses provided the first experimental evidence of an indel of a stop codon by alternative splicing at a NAGNAG acceptor site. In addition to contributing to proteome plasticity, alternative splicing at a NAGNAG tandem site can thus remove a disease-causing UAG stop codon. This molecular study reveals a naturally occurring mechanism where the effect of either modifier genes or epigenetic factors could be suspected. This finding is of importance for genetic counseling as well as for deciding appropriate therapeutic strategies.

Deciphering an isolated lung phenotype of NKX2-1 frameshift pathogenic variant.

Background: to perform a functional analysis of a new NK2 homeobox 1 (NKX2-1) variant (c.85_86del denominated NKX2-1DEL) identified in a family presenting with isolated respiratory disease, in comparison to another frameshift variant (c.254dup denominated NKX2-1DUP) identified in a subject with classical brain-lung-thyroid syndrome. Methods: pathogenic variants were introduced into the pcDNA3-1(+)-wt-TTF1 plasmid. The proteins obtained were analyzed by western blot assay. Subcellular localization was assessed by confocal microscopy in A549 and Nthy cells. Transactivation of SFTPA, SFTPB, SFTPC, and ABCA3 promoters was assessed in A549 cells. Thyroglobulin promoter activity was measured with the paired box gene 8 (PAX8) cofactor in Nthy cells. Results: The two sequence variants were predicted to produce aberrant proteins identical from the 86th amino acid, with deletion of their functional homeodomain, including the nuclear localization signal. However, 3D conformation prediction of the conformation prediction of the mutant protein assumed the presence of a nuclear localization signal, a bipartite sequence, confirmed by confocal microscopy showing both mutant proteins localized in the nucleus and cytoplasm. Transcriptional activity with SFTPA, SFTPB, SFTPC, ABCA3 and thyroglobulin promoters was significantly decreased with both variants. However, with NKX2-1DEL, thyroglobulin transcriptional activity was maintained with the addition of PAX8. Conclusion: These results provide novel insights into understanding the molecular mechanism of phenotypes associated with NKX2-1 pathogenic variants.

Prenatal Ultrasound Suspicion of Cystic Fibrosis in a Multiethnic Population: Is Extensive CFTR Genotyping Needed?

In families without a Cystic Fibrosis (CF) history, fetal ultrasound bowel abnormalities can unexpectedly reveal the disease. Isolated or in association, the signs can be fetal bowel hyperechogenicity, intestinal loop dilatation and non-visualization of fetal gallbladder. In these cases, search for CF transmembrane conductance regulator (CFTR) gene mutations is part of the recommended diagnostic practices, with a search for frequent mutations according to ethnicity, and, in case of the triad of signs, with an exhaustive study of the gene. However, the molecular diagnosis remains a challenge in populations without well-known frequent pathogenic variants. We present a multiethnic cohort of 108 pregnancies with fetal bowel abnormalities in which the parents benefited from an exhaustive study of the CFTR gene. We describe the new homozygous p.Cys1410* mutation in a fetus of African origin. We did not observe the most frequent p.Phe508del mutation in our cohort but evidenced variants undetected by our frequent mutations kit. Thanks to the progress of sequencing techniques and despite the difficulties of interpretation occasionally encountered, we discuss the need to carry out a comprehensive CFTR study in all patients in case of fetal bowel abnormalities.

Unsolved severe chronic rhinosinusitis elucidated by extensive CFTR genotyping.

Severe chronic rhinosinusitis in children should alert clinicians and extensive CFTR genotyping should be performed. We propose that thorough clinical and functional assessment in severe chronic rhinosinusitis is valuable to discover rare mutations which could be treated by CFTR correctors to postpone pulmonary infection.

Deciphering the mechanism of Q145H SFTPC mutation unmasks a splicing defect and explains the severity of the phenotype.

Mutations in the gene encoding surfactant protein C (SFTPC) have led to a broad range of phenotypes from neonatal respiratory distress syndrome to adult interstitial lung disease. We previously identified the c.435G>C variant in the SFTPC gene associated with fatal neonatal respiratory distress syndrome in an infant girl. Although this variation is predicted to change glutamine (Q) at position 145 to histidine (H), its position at the last base of exon 4 and the severity of the phenotype suggested that it might also induce a splicing defect. To test this hypothesis, we used hybrid minigene, biochemical and immunofluorescence tools to decipher the molecular mechanism of the mutation. Immunoblotting and confocal imaging showed similar maturation and localization of wild-type and Q145H proteins, but hybrid minigene analysis showed complete exon 4 skipping. Since the exon 4 is in frame, a putative truncated protein of 160 amino acids would be produced. We have shown that this truncated protein had an altered intracellular trafficking and maturation. The c.435G>C mutation is deleterious not because of its amino acid substitution but because of its subsequent splicing defect and should be referred to as r.325_435del and p.Leu109_Gln145del. The absence of residual full-length transcripts fully explained the severity of the phenotype we observed in the infant.

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

BACKGROUND AND PURPOSE: Pulmonary disease is the main cause of morbidity and mortality in cystic fibrosis (CF) patients due to exacerbated inflammation. To date, the only anti-inflammatory drug available to CF patients is high-dose ibuprofen, which can slow pulmonary disease progression, but whose cyclooxygenase-dependent digestive adverse effects limit its clinical use. Here we have tested sulindac, another non-steroidal anti-inflammatory drug with an undefined anti-inflammatory effect in CF airway epithelial cells. EXPERIMENTAL APPROACH: Using in vitro and in vivo models, we NF-κB activity and IL-8 secretion. In HeLa-F508del cells, we performed luciferase reporter gene assays in order to measure i) IL-8 promoter activity, and ii) the activity of synthetic promoter containing NF-κB responsive elements. We quantified IL-8 secretion in airway epithelial CFBE cells cultured at an air-liquid interface and in a mouse model of CF. KEY RESULTS: Sulindac inhibited the transcriptional activity of NF-κB and decreased IL-8 transcription and secretion in TNF-α stimulated CF cells via a cyclooxygenase-independent mechanism. This effect was confirmed in vivo in a mouse model of CF induced by intra-tracheal instillation of LPS, with a significant decrease of the induction of mRNA for MIP-2, following treatment with sulindac. CONCLUSION AND IMPLICATIONS: Overall, sulindac decrease lung inflammation by a mechanism independent of cycolooxygenase. This drug could be beneficially employed in CF.

COMMD1 modulates noxious inflammation in cystic fibrosis.

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which encodes an epithelial anion channel. Morbidity is mainly due to lung disease, which is characterized by chronic neutrophilic inflammation. Deregulation of inflammatory pathways is observed in the airways of CF patients, as evidenced by exaggerated NF-κB activity, causing an increase in the local release of pro-inflammatory cytokines such as IL-8. COMMD1, a pleiotropic protein, was recently shown to interact with CFTR and to promote CFTR cell surface expression. The effect of COMMD1 on the NF-κB pathway was assessed in CF and non-CF bronchial epithelial cells by knockdown and overexpression experiments. Results showed that (i) COMMD1 knockdown induced NF-κB-dependent transcription, (ii) COMMD1 overexpression inhibited NF-κB activity and was associated with a decrease in IL-8 transcript level and protein secretion. These data demonstrate the anti-inflammatory properties of COMMD1 in bronchial epithelial cells and open new therapeutic avenues in CF.

COMMD1-mediated ubiquitination regulates CFTR trafficking.

The CFTR (cystic fibrosis transmembrane conductance regulator) protein is a large polytopic protein whose biogenesis is inefficient. To better understand the regulation of CFTR processing and trafficking, we conducted a genetic screen that identified COMMD1 as a new CFTR partner. COMMD1 is a protein associated with multiple cellular pathways, including the regulation of hepatic copper excretion, sodium uptake through interaction with ENaC (epithelial sodium channel) and NF-kappaB signaling. In this study, we show that COMMD1 interacts with CFTR in cells expressing both proteins endogenously. This interaction promotes CFTR cell surface expression as assessed by biotinylation experiments in heterologously expressing cells through regulation of CFTR ubiquitination. In summary, our data demonstrate that CFTR is protected from ubiquitination by COMMD1, which sustains CFTR expression at the plasma membrane. Thus, increasing COMMD1 expression may provide an approach to simultaneously inhibit ENaC absorption and enhance CFTR trafficking, two major issues in cystic fibrosis.

Resveratrol rescues cAMP-dependent anionic transport in the cystic fibrosis pancreatic cell line CFPAC1.

BACKGROUND AND PURPOSE: The cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP-dependent chloride channel in the plasma membrane of epithelia whose mutation is the cause of the genetic disease cystic fibrosis (CF). The most frequent CFTR mutation is deletion of Phe(508) and this mutant protein (delF508CFTR) does not readily translocate to the plasma membrane and is rapidly degraded within the cell. We hypothesized that treating epithelial cells with resveratrol, a natural polyphenolic, phyto-ooestrogenic compound from grapes, could modulate both the expression and localization of CFTR. EXPERIMENTAL APPROACH: Cells endogenously expressing CFTR (MDCK1 and CAPAN1 cells) or delF508CFTR (CFPAC1 and airway epithelial cells, deriving from human bronchial biopsies) were treated with resveratrol for 2 or 18 h. The effect of this treatment on CFTR and delF508CFTR expression and localization was evaluated using RT-PCR, Western blot and immunocytochemistry. Halide efflux was measured with a fluorescent dye and with halide-sensitive electrodes. Production of interleukin-8 by these cells was assayed by ELISA. KEY RESULTS: Resveratrol treatment increased CFTR expression or maturation in immunoblotting experiments in MDCK1 cells or in CFPAC1 cells. Indirect immunofluorescence experiments showed a shift of delF508CFTR localization towards the (peri)-membrane area in CFPAC1 cells and in human airway epithelial cells. A cAMP-dependent increase in membrane permeability to halide was detected in resveratrol-treated CFPAC1 cells, and was inhibited by a selective inhibitor of CFTR. CONCLUSION AND IMPLICATIONS: These results show that resveratrol modulated CFTR expression and localization and could rescue cAMP-dependent chloride transport in delF508CFTR cells.

A recurrent deep-intronic splicing CF mutation emphasizes the importance of mRNA studies in clinical practice.

BACKGROUND: The identification by CFTR mRNA studies of a new deep-intronic splicing mutation, c.870-1113_1110delGAAT, in one patient of our series with mild CF symptoms and in three CF patients of an Italian study, led us to evaluate the mutation frequency and phenotype/genotype correlations. METHODS: 266 patients with CF and related disorders and having at least one undetected mutation, were tested at the gDNA level in three French reference laboratories. RESULTS: In total, the mutation was found in 13 unrelated patients (5% of those already carrying a mutation) plus 4 siblings, including one homozygote and 12 heterozygotes having a severe CF mutation. The sweat test was positive in 10/14 documented cases, the diagnosis was delayed after 20 years in 9/15 and pancreatic insufficiency was present in 5/16. CONCLUSION: c.870-1113_1110delGAAT should be considered as CF-causing with phenotype variability and overall delayed diagnosis. Its frequency highlights the potential of mRNA studies.