Transgenic ferret models define pulmonary ionocyte diversity and function.

Area of Science:

• Respiratory Cell Biology
• Mammalian Genetics
• Disease Modeling

Background:

• Studying rare cell types with divergent functions between species, like human pulmonary ionocytes, is challenging due to limitations in traditional animal models.
• Pulmonary ionocytes, rich in cystic fibrosis transmembrane conductance regulator (CFTR), play a vital role in airway physiology, but their precise functions remain unclear, especially in proximal airways.
• Limited presence and divergent biology of ionocytes in mouse proximal trachea hinder the use of conventional transgenic approaches to study their functions.

Purpose of the Study:

• To develop and utilize conditional genetic ferret models to dissect pulmonary ionocyte biology and function.
• To investigate the role of CFTR-dependent ionocyte transport in airway surface liquid homeostasis and mucociliary clearance.
• To identify rare cell progenitors and subtypes of pulmonary ionocytes during airway development.

Main Methods:

• Creation of conditional genetic ferret models for ionocyte lineage tracing (FOXI1-Cre^ERT2::ROSA-TG), ablation (FOXI1-KO), and CFTR deletion (FOXI1-Cre^ERT2::CFTR^L/L).
• Comparison of these models with established cystic fibrosis ferret models.
• Application of single-cell transcriptomics and in vivo lineage tracing techniques.

Main Results:

• Ionocytes were demonstrated to control airway surface liquid absorption, secretion, pH, and mucus viscosity.
• Cystic fibrosis, FOXI1-KO, and FOXI1-specific CFTR deletion ferrets exhibited reduced airway surface liquid volume and impaired mucociliary clearance.
• Three pulmonary ionocyte subtypes and a common progenitor for ionocytes, tuft cells, and neuroendocrine cells were identified via lineage tracing and transcriptomics.

Conclusions:

• Rare pulmonary ionocytes perform critical CFTR-dependent functions in the proximal airway, directly impacting hallmark features of cystic fibrosis airway disease.
• CFTR-dependent transport of chloride (Cl^-) and bicarbonate (HCO₃^-) by ionocytes is essential for regulating airway surface liquid and mucus properties.
• Conditional genetic ferret models offer a powerful platform for studying gene function, cell biology, and disease processes with greater evolutionary conservation to humans.