Airway surface liquid acidification initiates host defense abnormalities in Cystic Fibrosis

Abstract

Cystic fibrosis (CF) is caused by defective Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein. Morbidity is mainly due to early airway infection. We hypothesized that S. aureus clearance during the first hours of infection was impaired in CF human Airway Surface Liquid (ASL) because of a lowered pH. The ASL pH of human bronchial epithelial cell lines and primary respiratory cells from healthy controls (WT) and patients with CF was measured with a pH microelectrode. The antimicrobial capacity of airway cells was studied after S. aureus apical infection by counting surviving bacteria. ASL was significantly more acidic in CF than in WT respiratory cells. This was consistent with a defect in bicarbonate secretion involving CFTR and SLC26A4 (pendrin) and a persistent proton secretion by ATP12A. ASL demonstrated a defect in S. aureus clearance which was improved by pH normalization. Pendrin inhibition in WT airways recapitulated the CF airway defect and increased S. aureus proliferation. ATP12A inhibition by ouabain decreased bacterial proliferation. Antimicrobial peptides LL-37 and hBD1 demonstrated a pH-dependent activity. Normalizing ASL pH might improve innate airway defense in newborns with CF during onset of S. aureus infection. Pendrin activation and ATP12A inhibition could represent novel therapeutic strategies to normalize pH in CF airways.

LocusFocus: A web-based colocalization tool for the annotation and functional follow-up of GWAS

“…Investigating colocalization of the GWAS p-values with HNE eQTLs for other genes at the locus indicates no significant eQTLs (ANKRD20A10P, ATP12A, RNF17), or a lack of expression in HNE (RNY1P7, RPL26P34, IRX1P1) (Figure 2a, c). Taken together, while biological studies suggest a role for ATP12A in the lung [17][18][19] and have advocated for ATP12A as an alternative CF therapeutic target [23], our studies in the CF population do not support that common variation in expression of this gene affects lung function outcomes.…”

“…Results support strong colocalization for ATP12A in the pancreas as reported [11]. Interestingly, ATP12A has been proposed as a modifier of lung disease severity via its role in pH regulation, which in turn may influence immune response to infections in the CF lung [17][18][19]. Our GWAS on lung disease severity in CF, however, revealed no association at this locus [20].…”

“…The web server computes the LD matrix with the 1000 Genomes on demand using PLINK v1.90b6.9 [15]. Lines shown on the plot represent a summary of GTEx (v7) and primary human nasal epithelial cells' (HNEs) eQTL p-values for ATP12A, a gene proposed as a modifier for CF [17][18][19] (with corresponding y-axis on the right), with each line representing a tissue (eQTLs for other genes within the region can be selected and the plot re-drawn within the same session). Line traces for some tissues do not appear due to no eQTL data for ATP12A for that tissue (likely due to little or no expression).…”

Recombinant Acid Ceramidase Reduces Inflammation and Infection in Cystic Fibrosis

“…One possible explanation for reduced activity is that acid sphingomyelinase function is known to be pH dependent (activity increases as pH lowers to an optimum of around 5) (33,34). The pH of the airway surface liquid in CF remains keenly debated; however, there is some evidence to suggest that homeostasis is disordered and that the pH is lowered (3,4,(35)(36)(37)(38). Another potential explanation is that acid ceramidase and acid sphingomyelinase are known to exist in a complex with interconnected functions (19).…”

The Role of Specialized Pro-Resolving Mediators in Cystic Fibrosis Airways Disease

“…Indeed, an acidified environment is beneficial for bacteria survival. In vivo studies on CF newborn pigs and in vitro data obtained on human airway epithelial cells have demonstrated that bacterial killing is impaired in CF due to more acidic ASL pH ( Pezzulo et al, 2012 ; Simonin et al, 2019 ).…”