Developing New Strategies for Hearing Restoration Based on Transcriptional Reprogramming

Hearing loss is a condition with a high prevalence worldwide, often caused by the loss of sensory hair cells in the cochlea that detect sounds. Since the adult mammalian cochlea completely lacks regenerative response to injury, the loss of hair cells results in permanent hearing loss. Thus, for most types of hearing impairments, a definitive therapy would rest on the ability to restore hair cells. Currently, no technologies exist to stimulate supporting cells to re-enter cell cycle to divide in the mammalian organ of Corti to regenerate mature and functional hair cells, and there is no treatment for military personnel who have experienced noise-induced hearing loss. As identification of gene regulatory networks that drive mature hair cell formation is a prerequisite to finding ways to repair when damaged, we have been studying the molecular mechanisms that induce hair cell fate and regulate subsequent differentiation during inner ear development. We previously demonstrated that the inner ear neurosensory cell-specific transcription factors Eya1/Six1 are the key factors controlling hair cell fate induction by interacting with different cofactors. Misexpression of Eya1/Six1 is able to convert cochlear nonsensory cells to hair cells in cochlear explants. In contrast, when Eya1/Six1 are misexpressed with chromatin remodeling complex, cochlear nonsensory cells are converted to spiral ganglion neurons instead of hair cells. However, direct reprogramming of nonsensory cochlear cells into hair cells or neurons by these factors in vivo remains to be shown.

In this proposal, we will use animal models to test the ability of Six1 alone and both Six1/Eya1 together in promoting hair cell regeneration and restoring hearing in adult cochlea with hair cell death. To translate our mechanistic studies into clinical therapies, we will screen compound libraries for small molecules of Six1/Atoh1/Pou4f3 or Six1/Pou4f3 transcriptional agonists. Once such agonists have been identified, we will characterize them for regeneration of cochlear hair cells in adult mouse models with noise injury. While our animal model-based studies of deafness are unlikely to develop therapies that can be applied to humans in the short term, the proposed studies in animal models are necessary before any human work can be contemplated. Our work builds on almost twenty years of experience that we have accumulated in the function of Six1 and Eya1 in the inner ear. This study represents a major step forward to hair cell regeneration, reprogramming or transdifferentiation in the auditory field.

The result that Six1 or Six1/Eya1 is capable of regenerating hair cells and restoring hearing can be advanced in preclinical studies in other animals. The small molecules identified will be protected in patent applications for their in vivo activities to regenerate hair cells and can then be readily advanced in clinics by local delivery in patients with noise injury. This study has the potential to provide novel therapies that will promote cochlear hair cell regeneration and treat hearing loss in Service men and women as well as civilian population with noise-induced hearing loss.