A revised airway epithelial hierarchy includes CFTR-expressing ionocytes

Area of Science:

• Pulmonary biology
• Cellular and molecular biology
• Respiratory medicine

Background:

• Asthma and cystic fibrosis primarily affect the lung airways.
• Understanding the cellular makeup of the airway epithelium is key to addressing these diseases.

Purpose of the Study:

• To comprehensively map the cellular composition and hierarchy of the mouse tracheal epithelium.
• To identify novel cell types and progenitor-cell relationships in the airway.
• To investigate the role of specific cell types in airway physiology and disease, particularly cystic fibrosis.

Main Methods:

• Single-cell RNA sequencing (scRNA-seq) to analyze individual cell gene expression.
• In vivo lineage tracing to track cell development and relationships.
• Development of 'pulse-seq' combining scRNA-seq and lineage tracing for dynamic cell tracking.

Main Results:

• Identification of a rare cell type, the Foxi1+ pulmonary ionocyte.
• Characterization of location-dependent functional variations in club cells.
• Discovery of 'hillocks,' a new cell type in high-turnover squamous epithelial structures.
• Identification of disease-relevant subsets of tuft and goblet cells.
• Demonstration that basal progenitor cells replenish tuft, neuroendocrine, and ionocyte populations.
• Confirmation that ionocytes are the primary source of cystic fibrosis transmembrane conductance regulator (Cftr/CFTR) transcripts.
• Mouse ionocyte Foxi1 knockout led to Cftr loss and disrupted airway fluid/mucus, mimicking cystic fibrosis phenotypes.

Conclusions:

• The study establishes a detailed cellular map of the mouse tracheal epithelium.
• Pulmonary ionocytes are identified as critical players in airway fluid/mucus balance and are directly linked to cystic fibrosis pathogenesis.
• This work provides a new cellular framework for understanding and potentially treating airway diseases like cystic fibrosis and asthma.