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In situ regeneration of inner hair cells in the damaged cochlea by temporally regulated coexpression of Atoh1 and Tbx2

ABSTRACT: Cochlear inner hair cells (IHCs) are primary sound receptors, and thus in efforts to develop treatments for hearing impairment. IHC regeneration in vivo has been widely attempted, although not yet in the IHC-damaged cochlea. Moreover, the extent to which new IHCs resemble wild-type IHCs remains unclear, as does whether new IHCs can yield hearing improvement. Here, we developed an in vivo mouse model wherein wild-type IHCs were pre-damaged and nonsensory supporting cells were transformed into IHCs by ectopically expressing Atoh1 transiently and Tbx2 permanently. Notably, the new IHCs expressed the functional marker vGlut3 and presented similar transcriptomic and electrophysiological properties as wild-type IHCs. Furthermore, the formation efficiency and maturity of new IHCs were higher than those previously reported, although marked hearing improvement was not achieved, at least partly due to defective mechanoelectrical transduction (MET) in new IHCs. Thus, we successfully regenerated new IHCs resembling wild-type IHCs in multiple aspects in the damaged cochlea. Our findings suggest that the defective MET is a critical barrier preventing the restoration of hearing capacity and should thus facilitate future IHC regeneration studies.

ORGANISM(S): Mus musculus

PROVIDER: GSE188259 | GEO | 2023/11/05

REPOSITORIES: GEO

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Project description:The mouse auditory organ cochlea contains two types of sound receptors: inner hair cells (IHCs) and outer hair cells (OHCs). Tbx2 is expressed in IHCs but repressed in OHCs, and neonatal OHCs that misexpress Tbx2 transdifferentiate into IHC-like cells. However, the extent of this switch from OHCs to IHC-like cells and the underlying molecular mechanism remain poorly understood. Furthermore, whether Tbx2 can transform fully mature adult OHCs into IHC-like cells is unknown. Here, our single-cell transcriptomic analysis revealed that in neonatal OHCs misexpressing Tbx2, 85.6% of IHC genes, including Slc17a8, are upregulated, but only 38.6% of OHC genes, including Ikzf2 and Slc26a5, are downregulated. This suggests that Tbx2 cannot fully reprogram neonatal OHCs into IHCs. Moreover, Tbx2 also failed to completely reprogram cochlear progenitors into IHCs. Lastly, restoring Ikzf2 expression alleviated the abnormalities detected in Tbx2+ OHCs, which supports the notion that Ikzf2 repression by Tbx2 contributes to the transdifferentiation of OHCs into IHC-like cells. Our study evaluates the effects of ectopic Tbx2 expression on OHC lineage development at distinct stages of either male or female mice and provides molecular insights into how Tbx2 disrupts the gene-expression profile of OHCs. This research also lays the groundwork for future studies on OHC regeneration.Significance Statement Elucidation of the molecular and genetic mechanisms governing the determination and stability of cochlear inner hair cells (IHCs) and outer hair cells (OHCs) should provide valuable insights into the regeneration of damaged IHCs and OHCs. Here, we conditionally overexpress Tbx2 in vivo in cochlear sensory progenitors, neonatal OHCs, or adult OHCs. Our results show that Tbx2 overexpression alone can partially destabilize the OHC fate but cannot fully convert OHCs into IHCs. Specifically, we demonstrate that Ikzf2 repression due to Tbx2 overexpression is one of the key pathways disrupting the OHC fate.

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In situ regeneration of inner hair cells in the damaged cochlea by temporally regulated coexpression of Atoh1 and Tbx2

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