Deletion ofNotch1during Cochlear Maturation Leads to Rapid Supporting Cell Death and Profound Deafness

Abstract

The sensory region of the mammalian hearing organ contains two main cell types—hair cells and supporting cells. During development, Notch signaling plays an important role in whether a cell becomes either a hair cell or supporting cell by mediating lateral inhibition. However, once the cell fate decisions have been determined, little is understood about the role Notch plays in cochlear maturation. Here, we report that deletion ofNotch1from the early postnatal mouse cochlea in both male and female animals resulted in profound deafness at 6 weeks of age. Histologic analyses at 6 weeks revealed significant hair cell and supporting cell loss throughout theNotch1-deficient cochlea. Early analyses revealed a reduction in supporting cells in the outer hair cell region between postnatal day (P) 2 and P6, without a comparable increase in outer hair cell number, suggesting a mechanism other than lateral inhibition. Consistent with this, we found apoptotic cells in the outer supporting cell region of the cochlea at P1 and P2, indicating thatNotch1is required for outer supporting cell survival during early cochlear maturation. Interestingly, inner supporting cell types were not lost afterNotch1deletion. Surprisingly, we do not detect outer hair cell loss inNotch1mutants until after the onset of hearing, around P14, suggesting that hair cell loss is caused by loss of the supporting cells. Together, these results demonstrate thatNotch1is required for supporting cell survival during early maturation and that loss of these cells causes later loss of the hair cells and cochlear dysfunction.SIGNIFICANCE STATEMENTDuring development, Notch signaling has been shown to be critical in regulating the cell fate choices between hair cells and supporting cells. However, little is known about how Notch functions after those cell fate choices are made. Here, we examine the role ofNotch1in the maturing cochlea. We demonstrate that deletion ofNotch1results in profound deafness by 6 weeks of age. Histologic analyses revealed rapid supporting cell death shortly afterNotch1deletion, followed by eventual loss of the hair cells. These results reveal an unexpected role for Notch in supporting cell survival during cochlear maturation.