Vav3 Mediates Pseudomonas aeruginosa Adhesion to the Cystic Fibrosis Airway Epithelium

Pseudomonas aeruginosa (Pa) represents the leading cause of airway infection in cystic fibrosis (CF). Early airways colonization can be explained by enhanced adhesion of Pa to the respiratory epithelium. RNA sequencing (RNA-seq) on fully differentiated primary cultures of airway epithelial cells from CF and non-CF donors predict that VAV3, β1 INTEGRIN, and FIBRONECTIN genes are significantly enriched in CF. Indeed, Vav3 is apically overexpressed in CF, associates with active β1 integrin luminally exposed, and increases fibronectin deposition. These luminal microdomains, rich in fibronectin and β1 integrin and regulated by Vav3, mediate the increased Pa adhesion to the CF epithelium. Interestingly, Vav3 inhibition normalizes the CF-dependent fibronectin and β1-integrin ectopic expression, improves the CF epithelial integrity, and prevents the enhanced Pa trapping to the CF epithelium. Through its capacity to promote a luminal complex with active β1 integrin and fibronectin that favors bacteria trapping, Vav3 may represent a new target in CF.

Combined Bacteriophage and Antibiotic Treatment Prevents Pseudomonas aeruginosa Infection of Wild Type and cftr- Epithelial Cells

With the increase of infections due to multidrug resistant bacterial pathogens and the shortage of antimicrobial molecules with novel targets, interest in bacteriophages as a therapeutic option has regained much attraction. Before the launch of future clinical trials, in vitro studies are required to better evaluate the efficacies and potential pitfalls of such therapies. Here we studied in an ex vivo human airway epithelial cell line model the efficacy of phage and ciprofloxacin alone and in combination to treat infection by Pseudomonas aeruginosa. The Calu-3 cell line and the isogenic CFTR knock down cell line (cftr-) infected apically with P. aeruginosa strain PAO1 showed a progressive reduction in transepithelial resistance during 24 h. Administration at 6 h p.i. of single phage, phage cocktails or ciprofloxacin alone prevented epithelial layer destruction at 24 h p.i. Bacterial regrowth, due to phage resistant mutants harboring mutations in LPS synthesis genes, occurred thereafter both in vitro and ex vivo. However, co-administration of two phages combined with ciprofloxacin efficiently prevented PAO1 regrowth and maintained epithelial cell integrity at 72 p.i. The phage/ciprofloxacin treatment did not induce an inflammatory response in the tested cell lines as determined by nanoString® gene expression analysis. We conclude that combination of phage and ciprofloxacin efficiently protects wild type and cftr- epithelial cells from infection by P. aeruginosa and emergence of phage resistant mutants without inducing an inflammatory response. Hence, phage-antibiotic combination should be a safe and promising anti-Pseudomonas therapy for future clinical trials potentially including cystic fibrosis patients.

Characterization of two rat models of cystic fibrosis-KO and F508del CFTR-Generated by Crispr-Cas9

BACKGROUND

Genetically engineered animals are essential for gaining a proper understanding of the disease mechanisms of cystic fibrosis (CF). The rat is a relevant laboratory model for CF because of its zootechnical capacity, size, and airway characteristics, including the presence of submucosal glands.

METHODS

We describe the generation of a CF rat model (F508del) homozygous for the p.Phe508del mutation in the transmembrane conductance regulator (Cftr) gene. This model was compared to new Cftr -/- rats (CFTR KO). Target organs in CF were examined by histological staining of tissue sections and tooth enamel was quantified by micro-computed tomography. The activity of CFTR was evaluated by nasal potential difference (NPD) and short-circuit current measurements. The effect of VX-809 and VX-770 was analyzed on nasal epithelial primary cell cultures from F508del rats.

RESULTS

Both newborn F508del and Knock out (KO) animals developed intestinal obstruction that could be partly compensated by special diet combined with an osmotic laxative. The two rat models exhibited CF phenotypic anomalies such as vas deferens agenesis and tooth enamel defects. Histology of the intestine, pancreas, liver, and lungs was normal. Absence of CFTR function in KO rats was confirmed ex vivo by short-circuit current measurements on colon mucosae and in vivo by NPD, whereas residual CFTR activity was observed in F508del rats. Exposure of F508del CFTR nasal primary cultures to a combination of VX-809 and VX-770 improved CFTR-mediated Cl- transport.

CONCLUSIONS

The F508del rats reproduce the phenotypes observed in CFTR KO animals and represent a novel resource to advance the development of CF therapeutics.

Cis variants identified in F508del complex alleles modulate CFTR channel rescue by small molecules

Molecules correcting the trafficking (correctors) and gating defects (potentiators) of the cystic fibrosis causing mutation c.1521_1523delCTT (p.Phe508del) begin to be a useful treatment for CF patients bearing p.Phe508del. This mutation has been identified in different genetic contexts, alone or in combination with variants in cis. Until now, 21 exonic variants in cis of p.Phe508del have been identified, albeit at a low frequency. The aim of this study was to evaluate their impact on the efficacy of CFTR-directed corrector/potentiator therapy (Orkambi). The analysis by minigene showed that two out of 15 cis variants tested increased exon skipping (c.609C > T and c.2770G > A). Four cis variants were studied functionally in the absence of p.Phe508del, one of which was found to be deleterious for protein maturation c.1399C > T (p.Leu467Phe). In the presence of p.Phe508del, this variant was the only to prevent the response to Orkambi treatment. This study showed that some patients carrying p.Phe508del complex alleles are predicted to poorly respond to corrector/potentiator treatments. Our results underline the importance to validate treatment efficacy in the context of complex alleles.

Correction of CFTR function in nasal epithelial cells from cystic fibrosis patients predicts improvement of respiratory function by CFTR modulators

Clinical studies with modulators of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) protein have demonstrated that functional restoration of the mutated CFTR can lead to substantial clinical benefit. However, studies have shown highly variable patient responses. The objective of this study was to determine a biomarker predictive of the clinical response. CFTR function was assessed in vivo via nasal potential difference (NPD) and in human nasal epithelial (HNE) cultures by the response to Forskolin/IBMX and the CFTR potentiator VX-770 in short-circuit-current (∆IscF/I+V) experiments. CFTR expression was evaluated by apical membrane fluorescence semi-quantification. Isc measurements discriminated CFTR function between controls, healthy heterozygotes, patients homozygous for the severe F508del mutation and patients with genotypes leading to absent or residual function. ∆IscF/I+V correlated with CFTR cellular apical expression and NPD measurements. The CFTR correctors lumacaftor and tezacaftor significantly increased the ∆IscF/I+V response to about 25% (SEM = 4.4) of the WT-CFTR level and the CFTR apical expression to about 22% (SEM = 4.6) of the WT-CFTR level in F508del/F508del HNE cells. The level of CFTR correction in HNE cultures significantly correlated with the FEV1 change at 6 months in 8 patients treated with CFTR modulators. We provide the first evidence that correction of CFTR function in HNE cell cultures can predict respiratory improvement by CFTR modulators.

Analysis of nasal potential in murine cystic fibrosis models

The nasal epithelium of the mouse closely mimics the bioelectrical phenotype of the human airways. Ion transport across the nasal epithelium induces a nasal transepithelial potential difference. Its measurement by a relatively non-invasive method adapted from humans allows in vivo longitudinal measurements of CFTR-dependent ionic transport in the murine nasal mucosa. This test offers a useful tool to assess CFTR function in preclinical studies for novel therapeutics modulating CFTR activity. Here we extensively review work done to assess transepithelial transport in the murine respiratory epithelium in the basal state and after administration of CFTR modulators. Factors of variability and discriminative threshold between the CF and the WT mice for different readouts are discussed.

Kondo quantum dots and the novel Kondo-doublet interaction

We analyze the interactions between two Kondo quantum dots connected to a Rashba-active quantum wire. We find that the Kondo-doublet interaction, at an interdot distance of the order of the wire Fermi length, is over an order of magnitude greater than the RKKY interaction. The effects induced on the Kondo-doublet interaction by the wire spin-orbit coupling can be used to control the quantum dots spin-spin correlation. These results imply that the widely used assumption that the RKKY is the dominant interaction between Anderson impurities must be revised.