Induction of Proliferation and Robust Hair Cell Regeneration in Adult Mouse Cochlea

By June 7, 2019

Yizhou Quan1; Huang, Mingqian1; Shu, Yilai2; Li, Wenyan2; Chen, Zheng-Yi1
1 Department of Otolaryngology and Program in Neuroscience, Harvard Medical School and Eaton Peabody Laboratory, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts 02114, USA;
2 Department of Otolaryngology–Head and Neck Surgery, Eye and ENT Hospital, Shanghai Medical College, Fudan University, Shanghai, China.

Complete quiescence state of adult mammalian cochlea makes it particularly challenging to induce proliferation and regeneration of diverse cochlear cell types whose functions are essential to hearing. Here, we used reprogramming approach in mature mouse inner ear by activating a master cell cycle gene Myc and a progenitor gene Notch1 to induce renewed proliferation, which could allow reprogrammed supporting cells to respond to the signals to transdifferentiate to new hair cells.

Methods :
Whole adult cochlea explant organ culture and microinjection into adult cochlea were used for the study in vitro and in vivo, respectivelyNotch1 and MYC were activated in adult wildtype mice by virus-mediated delivery, or by doxycycline treatment in adult transgenic mouse rtTA/tet-Myc/tet-NICD. Proliferation was studied by EdU incorporation and lineage tracing was performed using Sox2-promoter-driven Cre in the tdTomato (tdT) reporter mice to identify the origin of proliferating cells. Induction of hair cells was done by Ad-Atoh1virus administration following Myc/Notch1-mediated reprogramming.

We demonstrate that co-activation MYC and Notch1 leads to cell cycle re-entry in adult cochlea in vitro and in vivo. Lineage tracing shows diverse cochlear cell types are capable of renewed proliferation. Mechanistically, reprogramming by MYC/NICD is shown by upregulation of inner ear progenitor genes. We show that reprogramming by Myc/NICD is required for hair cell regeneration mediated by ad-Atoh1 in adult cochleaRegenerated hair cells have the characteristics associated with young hair cells, possess functional transduction channels and are able to recruit neuronal fibers with the adult auditory neurons.

Reprogramming of adult mammalian cochleae results in renewed proliferation in diverse cell types. Functional new cochlear hair cells could be regenerated after reprogramming. Renewed proliferation in fully mature mammalian cochlea provides the possibility of using regeneration to treat sensorineural hearing loss including drugs related hearing loss, noise-induced hearing noise and age-related hearing loss.