Abstract
Hair cells (HCs) within the inner ear cochlea are specialized mechanoreceptors required for hearing. Cochlear HCs are not regenerated in mammals, and their loss is a leading cause of deafness in humans. Cochlear supporting cells (SCs) in newborn mice have the capacity to regenerate HCs, but persistent Notch signaling, presumably activated by SC-specific Notch ligand Jagged1 (JAG1), prevents SCs from converting into HCs. Here, employing an organoid platform, we show that while JAG1 participates in HC-fate repression, JAG1's primary function is to preserve the "progenitor-like characteristics" of cochlear SCs. Transcriptomic and mechanistic studies reveal that JAG1/Notch signaling maintains the expression of progenitor and metabolic genes in cochlear SCs and sustains pro-growth pathways, including PI3K-Akt-mTOR signaling, a function that is mediated by Notch1 and Notch2. Finally, we show that JAG1/Notch signaling stimulation with JAG1-Fc peptide enhances the HC-forming capacity of cochlear SCs undergoing maturation in cochlear explants and in vivo .