The effect of NO-donors on chloride efflux, intracellular Ca(2+) concentration and mRNA expression of CFTR and ENaC in cystic fibrosis airway epithelial cells

Trikafta Rescues CFTR and Lowers Monocyte P2X7R-Induced Inflammasome Activation in Cystic Fibrosis

RATIONALE

Cystic Fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene and is characterized by sustained inflammation. Adenosine-5'-Triphosphate (ATP) triggers interleukin (IL)-1β secretion via the P2X7 receptor (P2X7R) and activation of the NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) inflammasome.

OBJECTIVES

To explore the effect of the CFTR modulator Trikafta (Elexacaftor/Tezacaftor/Ivacaftor) on CFTR expression and the ATP/P2X7R signaling axis in monocytes and on circulating pro-inflammatory markers.

METHODS

Inflammatory mediators were detected in blood from 42 patients with CF (PWCF) before and after 3 months of Trikafta therapy. Markers of inflammasome activation and IL-1β secretion were measured in monocytes, and following stimulation with ATP and lipopolysaccharides (LPS) in the presence or absence of the P2X7R inhibitor, A438079.

MEASUREMENTS AND MAIN RESULTS

P2X7R is overexpressed in CF monocytes and receptor inhibition decreased NLRP3 expression, caspase-1 activation, and IL-1β secretion. In vitro and in vivo, P2X7R expression is regulated by CFTR function and intracellular chloride (Cl^-) levels. Trikafta therapy restored CFTR expression yet decreased P2X7R in CF monocytes, resulting in normalized Cl^- and potassium efflux, and reduced intracellular calcium levels. CFTR modulator therapy decreased circulating levels of ATP and LPS and reduced inflammasome activation and IL-1β secretion.

CONCLUSIONS

P2X7R expression is regulated by intracellular Cl^- levels, and in CF monocytes promotes inflammasome activation. Trikafta therapy significantly increased CFTR protein expression and reduced ATP/P2X7R -induced inflammasome activation. P2X7R may therefore be a promising target to reduce inflammation in PWCF non-eligible for Trikafta or other CFTR modulator therapy.

Nitric Oxide System and Bronchial Epithelium: More Than a Barrier

Airway epithelium forms a physical barrier that protects the lung from the entrance of inhaled allergens, irritants, or microorganisms. This epithelial structure is maintained by tight junctions, adherens junctions and desmosomes that prevent the diffusion of soluble mediators or proteins between apical and basolateral cell surfaces. This apical junctional complex also participates in several signaling pathways involved in gene expression, cell proliferation and cell differentiation. In addition, the airway epithelium can produce chemokines and cytokines that trigger the activation of the immune response. Disruption of this complex by some inflammatory, profibrotic, and carcinogens agents can provoke epithelial barrier dysfunction that not only contributes to an increase of viral and bacterial infection, but also alters the normal function of epithelial cells provoking several lung diseases such as asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis (CF) or lung cancer, among others. While nitric oxide (NO) molecular pathway has been linked with endothelial function, less is known about the role of the NO system on the bronchial epithelium and airway epithelial cells function in physiological and different pathologic scenarios. Several data indicate that the fraction of exhaled nitric oxide (FENO) is altered in lung diseases such as asthma, COPD, lung fibrosis, and cancer among others, and that reactive oxygen species mediate uncoupling NO to promote the increase of peroxynitrite levels, thus inducing bronchial epithelial barrier dysfunction. Furthermore, iNOS and the intracellular pathway sGC-cGMP-PKG are dysregulated in bronchial epithelial cells from patients with lung inflammation, fibrosis, and malignancies which represents an attractive drug molecular target. In this review we describe in detail current knowledge of the effect of NOS-NO-GC-cGMP-PKG pathway activation and disruption in bronchial epithelial cells barrier integrity and its contribution in different lung diseases, focusing on bronchial epithelial cell permeability, inflammation, transformation, migration, apoptosis/necrosis, and proliferation, as well as the specific NO molecular pathways involved.

Targeting the phosphoinositide-3-kinase/protein kinase B pathway in airway innate immunity

The airway innate immune system maintains the first line of defense against respiratory infections. The airway epithelium and associated immune cells protect the respiratory system from inhaled foreign organisms. These cells sense pathogens via activation of receptors like toll-like receptors and taste family 2 receptors (T2Rs) and respond by producing antimicrobials, inflammatory cytokines, and chemokines. Coordinated regulation of fluid secretion and ciliary beating facilitates clearance of pathogens via mucociliary transport. Airway cells also secrete antimicrobial peptides and radicals to directly kill microorganisms and inactivate viruses. The phosphoinositide-3-kinase/protein kinase B (Akt) kinase pathway regulates multiple cellular targets that modulate cell survival and proliferation. Akt also regulates proteins involved in innate immune pathways. Akt phosphorylates endothelial nitric oxide synthase (eNOS) enzymes expressed in airway epithelial cells. Activation of eNOS can have anti-inflammatory, anti-bacterial, and anti-viral roles. Moreover, Akt can increase the activity of the transcription factor nuclear factor erythroid 2 related factor-2 that protects cells from oxidative stress and may limit inflammation. In this review, we summarize the recent findings of non-cancerous functions of Akt signaling in airway innate host defense mechanisms, including an overview of several known downstream targets of Akt involved in innate immunity.

SLC6A14, an amino acid transporter, modifies the primary CF defect in fluid secretion

The severity of intestinal disease associated with Cystic Fibrosis (CF) is variable in the patient population and this variability is partially conferred by the influence of modifier genes. Genome-wide association studies have identified SLC6A14, an electrogenic amino acid transporter, as a genetic modifier of CF-associated meconium ileus. The purpose of the current work was to determine the biological role of Slc6a14, by disrupting its expression in CF mice bearing the major mutation, F508del. We found that disruption of Slc6a14 worsened the intestinal fluid secretion defect, characteristic of these mice. In vitro studies of mouse intestinal organoids revealed that exacerbation of the primary defect was associated with reduced arginine uptake across the apical membrane, with aberrant nitric oxide and cyclic GMP-mediated regulation of the major CF-causing mutant protein. Together, these studies highlight the role of this apical transporter in modifying cellular nitric oxide levels, residual function of the major CF mutant and potentially, its promise as a therapeutic target.