Ionocytes and CFTR Chloride Channel Expression in Normal and Cystic Fibrosis Nasal and Bronchial Epithelial Cells

Abstract

The airway epithelium contains ionocytes, a rare cell type with high expression of Forkhead Box I1 (FOXI1) transcription factor and Cystic Fibrosis Transmembrane conductance Regulator (CFTR), a chloride channel that is defective in cystic fibrosis (CF). Our aim was to verify if ionocyte development is altered in CF and to investigate the relationship between ionocytes and CFTR-dependent chloride secretion. We collected nasal cells by brushing to determine ionocyte abundance. Nasal and bronchial cells were also expanded in vitro and reprogrammed to differentiated epithelia for morphological and functional studies. We found a relatively high (~3%) ionocyte abundance in ex vivo nasal samples, with no difference between CF and control individuals. In bronchi, ionocytes instead appeared very rarely as previously reported, thus suggesting a possible proximal–distal gradient in human airways. The difference between nasal and bronchial epithelial cells was maintained in culture, which suggests an epigenetic control of ionocyte development. In the differentiation phase of the culture procedure, we used two media that resulted in a different pattern of CFTR expression: confined to ionocytes or more broadly expressed. CFTR function was similar in both conditions, thus indicating that chloride secretion equally occurs irrespective of CFTR expression pattern.

Single-cell longitudinal analysis of SARS-CoV-2 infection in human airway epithelium identifies target cells, alterations in gene expression, and cell state changes

“…We used high-resolution community detection and merged clusters based on expression of bronchial epithelium cell-type markers in order to isolate some rare cell types, e.g., tuft cells [66,67]. To annotate the different cell types present in HBECs, we analyzed expressions of a range of marker genes that were reported [67][68][69][70][71][72][73][74][75][76][77] and in a molecular cell atlas from Travaglini colleagues [66]. We focused on 8 cell types: (i) basal cells (KRT5, DAPL1, and TP63); (ii) ciliated cells (FOXJ1, CCDC153, CCDC113, MLF1, and LZTFL1); (iii) club cells (SCGB1A1, KRT15, CYP2F2, LYPD2, and CBR2); (iv) BC/club (KRT4 and KRT13); (v) neuroendocrine cells (CHG1 and ASCL1); (vi) Tuft cells (POU2F3, AVIL, GNAT3, and TRPM5); (vi) ionocytes (FOXI1, CFTR, and ASCL3); and (viii) goblet cells (MUC5AC, MUC5B, GP2, and SPDEF).…”

Topography-dependent gene expression and function of common cell archetypes in large and small porcine airways

“…Ionocytes are a rare airway epithelial cell type with an expression pattern resembling renal intercalated cells (Montoro et al, 2018; Plasschaert et al, 2018; Scudieri et al, 2020; Vidarsson et al, 2009); they likely participate in airway epithelial ion and fluid transport. Airway ionocytes express the transcription factor FOXI1 , very high levels of CFTR , and genes for V-ATPase subunits.…”

“…Ciliated cells contain hair-like structures, called cilia, that extend into the airway lumen and work in concert with the airway surface fluid to clear the airway of foreign particles and pathogens (Brody, 2004; Horani et al, 2018; Nanjundappa et al, 2019; Whitsett, 2018; You et al, 2004). In addition to the three major cell types, airway epithelia also contain rare cell types, including pulmonary neuroendocrine cells (PNECs), tuft or brush cells, and CFTR - rich ionocytes (Bankova et al, 2018; Krasteva et al, 2012; Montoro et al, 2018; Ouadah et al, 2019; Perniss et al, 2020; Perniss et al, 2021; Plasschaert et al, 2018; Scudieri et al, 2020; Sui et al, 2018).…”

Airway Surface Liquid pH Regulation in Airway Epithelium Current Understandings and Gaps in Knowledge

“…The airway bronchial epithelium is composed of a variety of cell types, described in Figure 2 [ 1 , 6 ].…”

“…Basal cells display stem cell-like properties and give rise to secretory and ciliated cells in response to epithelial injury. Ionocytes are a rare cell type, recently identified in the adult murine and human trachea, and in human proximal bronchi; they express cystic fibrosis transmembrane regulator (CFTR) protein at high levels [ 6 , 7 ]. Pulmonary neuroendocrine cells (PNEC) are ubiquitous in human adult airway epithelium, and located between epithelial cells adjacent to the basement membrane.…”