Impact of KLF4 on Cell Proliferation and Epithelial Differentiation in the Context of Cystic Fibrosis

Intercellular Communication in Airway Epithelial Cell Regeneration: Potential Roles of Connexins and Pannexins

Connexins and pannexins are transmembrane proteins that can form direct (gap junctions) or indirect (connexons, pannexons) intercellular communication channels. By propagating ions, metabolites, sugars, nucleotides, miRNAs, and/or second messengers, they participate in a variety of physiological functions, such as tissue homeostasis and host defense. There is solid evidence supporting a role for intercellular signaling in various pulmonary inflammatory diseases where alteration of connexin/pannexin channel functional expression occurs, thus leading to abnormal intercellular communication pathways and contributing to pathophysiological aspects, such as innate immune defense and remodeling. The integrity of the airway epithelium, which is the first line of defense against invading microbes, is established and maintained by a repair mechanism that involves processes such as proliferation, migration, and differentiation. Here, we briefly summarize current knowledge on the contribution of connexins and pannexins to necessary processes of tissue repair and speculate on their possible involvement in the shaping of the airway epithelium integrity.

Epithelial-Mesenchymal Transition Mechanisms in Chronic Airway Diseases: A Common Process to Target?

Epithelial-to-mesenchymal transition (EMT) is a reversible process, in which epithelial cells lose their epithelial traits and acquire a mesenchymal phenotype. This transformation has been described in different lung diseases, such as lung cancer, interstitial lung diseases, asthma, chronic obstructive pulmonary disease and other muco-obstructive lung diseases, such as cystic fibrosis and non-cystic fibrosis bronchiectasis. The exaggerated chronic inflammation typical of these pulmonary diseases can induce molecular reprogramming with subsequent self-sustaining aberrant and excessive profibrotic tissue repair. Over time this process leads to structural changes with progressive organ dysfunction and lung function impairment. Although having common signalling pathways, specific triggers and regulation mechanisms might be present in each disease. This review aims to describe the various mechanisms associated with fibrotic changes and airway remodelling involved in chronic airway diseases. Having better knowledge of the mechanisms underlying the EMT process may help us to identify specific targets and thus lead to the development of novel therapeutic strategies to prevent or limit the onset of irreversible structural changes.

Elexacaftor/Tezacaftor/Ivacaftor Accelerates Wound Repair in Cystic Fibrosis Airway Epithelium

Background: Cystic fibrosis (CF) airway epithelium shows alterations in repair following damage. In vitro studies showed that lumacaftor/ivacaftor (Orkambi) may favor airway epithelial integrity in CF patients. Our aim was to evaluate the effect of the novel triple combination elexacaftor/tezacaftor/ivacaftor (ETI) on wound repair in CF airway epithelial cells. Methods: A tip-based scratch assay was employed to study wound repair in monolayers of CFBE14o- cells overexpressing the F508del mutation. ETI was added during wound repair. Results: ETI efficiently rescued CFTR F508del maturation and activity, accelerated wound closure and increased wound healing rates of the injured CF cell monolayers. Conclusions: The triple corrector/potentiator combination ETI shows promise in ameliorating wound healing of the airway epithelium in F508del patients.

Human Amniotic Mesenchymal Stem Cells and Fibroblasts Accelerate Wound Repair of Cystic Fibrosis Epithelium

Cystic fibrosis (CF) airways are affected by a deranged repair of the damaged epithelium resulting in altered regeneration and differentiation. Previously, we showed that human amniotic mesenchymal stem cells (hAMSCs) corrected base defects of CF airway epithelial cells via connexin (CX)43-intercellular gap junction formation. In this scenario, it is unknown whether hAMSCs, or fibroblasts sharing some common characteristics with MSCs, can operate a faster repair of a damaged airway epithelium. A tip-based scratch assay was employed to study wound repair in monolayers of CFBE14o- cells (CFBE, homozygous for the F508del mutation). hAMSCs were either co-cultured with CFBE cells before the wound or added to the wounded monolayers. NIH-3T3 fibroblasts (CX43+) were added to wounded cells. HeLa cells (CX43-) were used as controls. γ-irradiation was optimized to block CFBE cell proliferation. A specific siRNA was employed to downregulate CX43 expression in CFBE cells. CFBE cells showed a delayed repair as compared with wt-CFTR cells (16HBE41o-). hAMSCs enhanced the wound repair rate of wounded CFBE cell monolayers, especially when added post wounding. hAMSCs and NIH-3T3 fibroblasts, but not HeLa cells, increased wound closure of irradiated CFBE monolayers. CX43 downregulation accelerated CFBE wound repair rate without affecting cell proliferation. We conclude that hAMSCs and fibroblasts enhance the repair of a wounded CF airway epithelium, likely through a CX43-mediated mechanism mainly involving cell migration.

Krüppel-Like Factor 5 Regulates CFTR Expression Through Repression by Maintaining Chromatin Architecture Coupled with Direct Enhancer Activation

Single cell RNA-sequencing has accurately identified cell types within the human airway that express the Cystic Fibrosis Transmembrane Conductance regulator (CFTR) gene. Low abundance CFTR transcripts are seen in many secretory cells, while high levels are restricted to rare pulmonary ionocytes. Here we focus on the mechanisms coordinating basal CFTR expression in the secretory compartment. Cell-selective regulation of CFTR is achieved within its invariant topologically associating domain by the recruitment of cis-regulatory elements (CREs). CRE activity is coordinated by cell-type-selective transcription factors. One such factor, Krüppel-Like Factor 5 (KLF5), profoundly represses CFTR transcript and protein in primary human airway epithelial cells and airway cell lines. Here we reveal the mechanism of action of KLF5 upon the CFTR gene. We find that depletion or ablation of KLF5 from airway epithelial cells changes higher order chromatin structure at the CFTR locus. Critical looping interactions that are required for normal gene expression are altered, the H3K27ac active chromatin mark is redistributed, and CTCF occupancy is modified. However, mutation of a single KLF5 binding site within a pivotal airway cell CRE abolishes CFTR expression. Hence, KLF5 has both direct activating and indirect repressive effects, which together coordinate CFTR expression in the airway.

Adipose-derived mesenchymal stem cells may reduce intestinal epithelial damage in ulcerative colitis by communicating with macrophages and blocking inflammatory pathways: an analysis in silico

Ulcerative colitis is a chronic, non-specific inflammatory disease that affects mainly the colonic mucosa and submucosa. The pathogenesis of ulcerative colitis is unclear, which limits the development of effective treatments. In this study, single-cell sequencing data from 18 ulcerative colitis samples and 12 healthy controls were downloaded from the Single Cell Portal database, cell types were defined through cluster analysis, and genes in each cluster that were differentially expressed in ulcerative colitis were identified. These genes were enriched in functional pathways related to apoptosis, immunity and inflammation. Analysis using iTALK software suggested extensive communication among immune cells. Single-cell sequencing data from adipose-derived mesenchymal stem cells from three healthy female donors were obtained from the Sequence Read Archive database. The SingleR package was used to identify different cell types, for each of which a stemness score was calculated. Pseudotime analysis was performed to infer the trajectory of cells. SCENIC software was used to identify the gene regulatory network in adipose-derived mesenchymal stem cells, and iTALK software was performed to explore the relationship among macrophages, adipose-derived mesenchymal stem cells and enterocytes. Molecular docking confirmed the possibility of cell-cell interactions via binding between surface receptors and their ligands. The bulk data were downloaded and analyzed to validate the expression of genes. Our bioinformatics analyses suggest that ulcerative colitis involves communication between macrophages and enterocytes via ligand-receptor pairs. Our results further suggest that adipose-derived mesenchymal stem cells may alleviate ulcerative colitis by communicating with macrophages to block inflammation.

CFTR, Cell Junctions and the Cytoskeleton

The multi-organ disease cystic fibrosis (CF) is caused by mutations in the gene encoding the CF transmembrane conductance regulator (CFTR) protein, a cAMP regulated chloride (Cl⁻) and bicarbonate (HCO₃⁻) ion channel expressed at the apical plasma membrane (PM) of epithelial cells. Reduced CFTR protein results in decreased Cl⁻ secretion and excessive sodium reabsorption in epithelial cells, which consequently leads to epithelial dehydration and the accumulation of thick mucus within the affected organs, such as the lungs, pancreas, gastrointestinal (GI) tract, reproductive system and sweat glands. However, CFTR has been implicated in other functions besides transporting ions across epithelia. The rising number of references concerning its association to actin cytoskeleton organization, epithelial cell junctions and extracellular matrix (ECM) proteins suggests a role in the formation and maintenance of epithelial apical basolateral polarity. This review will focus on recent literature (the last 10 years) substantiating the role of CFTR in cell junction formation and actin cytoskeleton organization with its connection to the ECM.

Comparative meta-analysis of cystic fibrosis cell models suggests partial endothelial-to-mesenchymal transition

The mesenchymal conversion of epithelial cells (EMT) has been suggested as a potential contributor in cystic fibrosis (CF) disease progression. Endothelial cells (EndCs), the cells lining blood vessels, express functional CFTR and CFTR impairment promotes endothelial activation and dysfunction. However, if the mesenchymal switch also exists in CF EndCs remains uncharacterized. To understand whether the endothelial-to-mesenchymal transition (EndMT) could occur in CF, we have conducted a transcriptomic meta-analysis of primary CFTR-impaired and patient-derived EndCs, and further compared our results to data from CF epithelial cells (EpCs) where EMT has been demonstrated. As compared to EpCs, we show that CFTR-impaired EndCs display a limited signature of EndMT, and that expression of the mesenchymal inducer Twist1 remained unchanged. Nonetheless, the use of CFTR modulators reduced the expression of mesenchymal markers from CF patient-derived EndCs, suggesting an additional therapeutic added-value next to the known effect on CFTR ion transport.

Pathophysiology of Lung Disease and Wound Repair in Cystic Fibrosis

Cystic fibrosis (CF) is an autosomal recessive, life-threatening condition affecting many organs and tissues, the lung disease being the chief cause of morbidity and mortality. Mutations affecting the CF Transmembrane Conductance Regulator (CFTR) gene determine the expression of a dysfunctional protein that, in turn, triggers a pathophysiological cascade, leading to airway epithelium injury and remodeling. In vitro and in vivo studies point to a dysregulated regeneration and wound repair in CF airways, to be traced back to epithelial CFTR lack/dysfunction. Subsequent altered ion/fluid fluxes and/or signaling result in reduced cell migration and proliferation. Furthermore, the epithelial-mesenchymal transition appears to be partially triggered in CF, contributing to wound closure alteration. Finally, we pose our attention to diverse approaches to tackle this defect, discussing the therapeutic role of protease inhibitors, CFTR modulators and mesenchymal stem cells. Although the pathophysiology of wound repair in CF has been disclosed in some mechanisms, further studies are warranted to understand the cellular and molecular events in more details and to better address therapeutic interventions.