Targeting cyclic-AMP/phosphodiesterase signaling to quiet nasal tuft cell calcium responses

Abstract

Background: Airway tuft cells, also called solitary chemosensory cells, are enriched in nasal polyps and are likely the main epithelial source of interleukin-25 (IL-25) in chronic rhinosinusitis with nasal polyps (CRSwNP). Tuft cells are activated through G protein-coupled receptors (GPCRs) that signal through Ca2+. These receptors may also lower cyclic AMP (cAMP), but whether the cAMP pathway can be used to suppress tuft cell responses is unknown. Methods: Ca2+ and cAMP were measured by live cell imaging in isolated Trpm5-GFP mouse nasal tuft cells, and Ca2+ responses were measured in primary human nasal epithelial air-liquid interface (ALI) cultures from patients with CRSwNP. Defensin and IL-25 release were measured by ELISA and ciliary beat frequency (CBF) by high-speed imaging. Phosphodiesterase (PDE) expression was assessed using publicly available single cell RNA sequencing datasets. Results: Agonists of bitter taste receptors (T2Rs), the succinate receptor SUCNR1, and the A1 adenosine receptor increased Ca2+ in GFP-positive mouse nasal tuft cells. T2R and A1 receptor stimulation also lowered cAMP, and these decreases were blocked by pertussis toxin. Glucose, which activates taste family 1 receptors, increased cAMP. Tuft cells were enriched for Pde2a. PDE2A-selective inhibitors (PF-05180999 and BAY 60-7550) increased cAMP and reduced agonist-evoked Ca2+ responses in mouse tuft cells. In human nasal ALIs, both compounds reduced denatonium-evoked Ca2+ responses, defensin release, and IL-25 release without increasing CBF. Conclusions: GPCRs that activate nasal tuft cells also lower cAMP, and by raising cAMP through PDE2A inhibition, tuft cell Ca2+ signaling and IL-25 release were reduced in vitro.