Airway mucus obstruction is the main cause of morbidity in cystic fibrosis, a disease caused by mutations in the CFTR Cl⁻ channel. Activation of non-CFTR Cl⁻ channels such as TMEM16A can likely compensate for defective CFTR. However, TMEM16A was recently described as a key driver in mucus production/secretion. Here, we have examined whether indeed there is a causal relationship between TMEM16A and MUC5AC production, the main component of respiratory mucus. Our data show that TMEM16A and MUC5AC are inversely correlated during differentiation of human airway cells. Furthermore, we show for the first time that the IL-4–induced TMEM16A up-regulation is proliferation-dependent, which is supported by the correlation found between TMEM16A and Ki-67 proliferation marker during wound healing. Consistently, the notch signaling activator DLL4 increases MUC5AC levels without inducing changes neither in TMEM16A nor in Ki-67 expression. Moreover, TMEM16A inhibition decreased airway surface liquid height. Altogether, our findings demonstrate that up-regulation of TMEM16A and MUC5AC is only circumstantial under cell proliferation, but with no causal relationship between them. Thus, although essential for airway hydration, TMEM16A is not required for MUC5AC production.

Airway inflammation, mucus hyperproduction and epithelial remodelling are hallmarks of many chronic airway diseases, including asthma, COPD and cystic fibrosis. While several cytokines are dysregulated in these diseases, most studies focus on the response of airways to interleukin (IL)-4 and IL-13, which have been shown to induce mucus hyperproduction and shift the airway epithelium towards a hypersecretory phenotype.We hypothesised that other cytokines might induce the expression of chloride (Cl⁻) channels/transporters, and regulate epithelial differentiation and mucus production. To this end, fully differentiated human airway basal cells (BCi-NS1.1) were treated with cytokines identified as dysregulated in those diseases, namely IL-8, IL-1β, IL-4, IL-17A, IL-10 and IL-22, and tumour necrosis factor-α.Our results show that the cystic fibrosis transmembrane conductance regulator (CFTR) is the main Cl⁻channel modulated by inflammation, in contrast to transmembrane protein 16A (TMEM16A), whose levels only changed with IL-4. Furthermore, we identified novel roles for IL-10 and IL-22 by influencing epithelial differentiation towards ciliated cells and away from pulmonary ionocytes. In contrast, IL-1β and IL-4 reduced the number of ciliated cells while increasing club cells. Interestingly, while IL-1β, IL-4 and IL-10 upregulated CFTR expression, IL-4 was the only cytokine that increased both its function and the number of CFTR-expressing club cells, suggesting that this cell type may be the main contributor for CFTR function. Additionally, all cytokines assessed increased mucus production through a differential upregulation of MUC5AC and MUC5B transcript levels.This study reveals a novel insight into differentiation resulting from the cross-talk of inflammatory mediators and airway epithelial cells, which is particularly relevant for chronic airway diseases.

Cystic fibrosis (CF) cells display a more cancer-like phenotype vs. non-CF cells. KLF4 overexpression has been described in CF and this transcriptional factor acts as a negative regulator of wt-CFTR. KLF4 is described as exerting its effects in a cell-context-dependent fashion, but it is generally considered a major regulator of proliferation, differentiation, and wound healing, all the processes that are also altered in CF. Therefore, it is relevant to characterize the differential role of KLF4 in these processes in CF vs. non-CF cells. To this end, we used wt- and F508del-CFTR CFBE cells and their respective KLF4 knockout (KO) counterparts to evaluate processes like cell proliferation, polarization, and wound healing, as well as to compare the expression of several epithelial differentiation markers. Our data indicate no major impact of KLF4 KO in proliferation and a differential impact of KLF4 KO in transepithelial electrical resistance (TEER) acquisition and wound healing in wt- vs. F508del-CFTR cells. In parallel, we also observed a differential impact on the levels of some differentiation markers and epithelial-mesencymal transition (EMT)-associated transcription factors. In conclusion, KLF4 impacts TEER acquisition, wound healing, and the expression of differentiation markers in a way that is partially dependent on the CFTR-status of the cell.

Background Idiopathic pulmonary fibrosis (IPF) is characterised by damage to the epithelial layer, closely associated with the alveolar basement membrane (BM). We aimed to investigate how type IV collagen (COL4) in the BM changes with the progression of IPF. Methods COL4 synthesis (PRO-C4) was detected in blood by the nordicPRO-C4 biomarker in patients with IPF from the two prospective, multicentre, observational, longitudinal cohorts, pulmonary fibrosis biomarker (PFBIO) and prospective observation of fibrosis in the lung clinical endpoints (PROFILE). PRO-C4 trajectories over 12 months were compared between progressors and non-progressors by linear mixed effects regression models. Rate of change in PRO-C4 and lung function were compared by Bayesian bivariate longitudinal models. Cox proportional hazards models analysed baseline PRO-C4 and 3 years mortality. COL4 staining in IPF and non-IPF lungs was evaluated by immunohistochemistry. Results In PFBIO and PROFILE, 51/220 (23.2%) and 221/459 (48.1%) patients, respectively, had progressive disease at 12 months. Longitudinal PRO-C4 levels were higher in progressors versus non-progressors (average differences: PFBIO 21.5% (95% CI 3.4% to 42.9%, p=0.0184); PROFILE 10.9% (95% CI 0.8% to 22.1%; p=0.0340). Monthly rate of change in PRO-C4 was steeper in non-survivors versus survivors (mean difference up to 3.12% (95% CI 0.35% to 5.91%)) and was inversely correlated with the change in lung function. High baseline PRO-C4 was associated with increased mortality risk in PFBIO (HR 2.55 (95% CI 1.27 to 5.12), p=0.0083). COL4 staining was higher in IPF versus non-IPF lung but was less obvious in end-stage tissue. Conclusions High and increasing serological PRO-C4 levels were prognostic for progression in two independent IPF cohorts. This study suggests that COL4 synthesis assessed by PRO-C4 is a pathologically relevant biomarker of alveolar BM repair in IPF.

In this study, we revealed that idiopathic pulmonary fibrosis (IPF) lungs are characterized by increased type VI collagen (COL6) gene expression but lower COL6 protein and turnover proportions around airways and blood vessels compared with controls. COL6 and a fragment associated with its production (PRO-C6) increased lung fibroblast viability. These findings highlight that pulmonary fibrotic tissue is characterized by disrupted extracellular matrix and altered tissue remodeling and suggest that COL6 may contribute to fibroblast persistence and fibrosis progression.

Metabolism provides the foundation for all cellular functions. During persistent infections, in adapted pathogenic bacteria metabolism functions radically differently compared with more naïve strains. Whether this is simply a necessary accommodation to the persistence phenotype or if metabolism plays a direct role in achieving persistence in the host is still unclear. Here, we characterize a convergent shift in metabolic function(s) linked with the persistence phenotype during Pseudomonas aeruginosa colonization in the airways of people with cystic fibrosis. We show that clinically-relevant mutations in the key metabolic enzyme, pyruvate dehydrogenase, lead to a host-specialized metabolism together with a lower virulence and immune response recruitment. These changes in infection phenotype are mediated by impaired type III secretion system activity and by secretion of the antioxidant metabolite, pyruvate, respectively. Our results show how metabolic adaptations directly impinge on persistence and pathogenicity in this organism.