Notch signaling stabilizes lengths of motile cilia in multiciliated cells in the lung.

Airway multiciliated cells (MCs) maintain respiratory health by clearing mucus and trapped particles through coordinated ciliary beating. Although ciliary length progressively decreases along the proximal-distal (P-D) axis of the tracheobronchial tree, the mechanisms that maintain this gradient remain unclear. We show that canonical Notch signaling in MCs stabilizes ciliary length across airway regions. Inhibition of Notch signaling shortens tracheal cilia, lengthens distal airway cilia, abolishes the P-D gradient in ciliary length, and induces region-specific changes in gene expression. To assess how environmental factors influence this regulation, we examined germ-free mice and a model of Mycobacterium tuberculosis (M. tb) infection. Germ-free conditions did not alter ciliary architecture, whereas M. tb infection led to elongation of distal airway cilia accompanied by down-regulation of Notch signaling. These findings identify Notch signaling as a key homeostatic regulator that maintains ciliary length and preserves the P-D gradient in airway multiciliated cells.