Regeneration of Stereocilia of Hair Cells by Forced Atoh1 Expression in the Adult Mammalian Cochlea

Abstract

The hallmark of mechanosensory hair cells is the stereocilia, where mechanical stimuli are converted into electrical signals. These delicate stereocilia are susceptible to acoustic trauma and ototoxic drugs. While hair cells in lower vertebrates and the mammalian vestibular system can spontaneously regenerate lost stereocilia, mammalian cochlear hair cells no longer retain this capability. We explored the possibility of regenerating stereocilia in the noise-deafened guinea pig cochlea by cochlear inoculation of a viral vector carrying Atoh1, a gene critical for hair cell differentiation. Exposure to simulated gunfire resulted in a 60–70 dB hearing loss and extensive damage and loss of stereocilia bundles of both inner and outer hair cells along the entire cochlear length. However, most injured hair cells remained in the organ of Corti for up to 10 days after the trauma. A viral vector carrying an EGFP-labeled Atoh1 gene was inoculated into the cochlea through the round window on the seventh day after noise exposure. Auditory brainstem response measured one month after inoculation showed that hearing thresholds were substantially improved. Scanning electron microscopy revealed that the damaged/lost stereocilia bundles were repaired or regenerated after Atoh1 treatment, suggesting that Atoh1 was able to induce repair/regeneration of the damaged or lost stereocilia. Therefore, our studies revealed a new role of Atoh1 as a gene critical for promoting repair/regeneration of stereocilia and maintaining injured hair cells in the adult mammal cochlea. Atoh1-based gene therapy, therefore, has the potential to treat noise-induced hearing loss if the treatment is carried out before hair cells die.

Organ of Corti and Stria Vascularis: Is there an Interdependence for Survival?

“…The mouse was anesthetized with a mixture of ketamine/xylazine (ketamine 100 mg/kg; xylazine 15 mg/kg; ip), and supplemented as needed. ABRs were recorded in response to tone bursts of 2, 4, 8, 16, 22, and 32 kHz using standard procedures previously described [25,26]. Tone pipe with 1 ms rise cosine on/off ramps were generated digitally using a clock rate of 125 kHz and 16-bit D/A converters.…”

“…The bulla was perforated allowing for exposure of the stapedial artery, basal turn, and apical turn of the cochlea. A silver electrode was placed on the ridge near the round window for recording CM [25]. The ground electrode was implanted in the dorsal neck muscles.…”

Neurog1 can partially replace Atoh1 to differentiate and maintain hair cells in a disorganized organ of Corti

“…Several mutations that interfere with stereocilia bundle organization and homeostasis are known (Hertzano et al, 2008;Kitajiri et al, 2010;Mogensen et al, 2007;Sekerková et al, 2011) and many of these result not only in aberrant bundle morphology but also in the death of HCs (Kersigo and Fritzsch, 2015;Self et al, 1998;Ueyama et al, 2014). Consistent with a role of Atoh1 in stereocilia differentiation, forced expression of Atoh1 can restore hair bundles (Yang et al, 2012).…”

Characterization of the Transcriptome of Nascent Hair Cells and Identification of Direct Targets of the Atoh1 Transcription Factor

“…Previous studies of Atoh1 mutant mice have revealed multiple functions of Atoh1 in the genesis, survival, maturation, and function of hair cells (Bermingham et al, 1999;Chen et al, 2002;Woods et al, 2004;Pan et al, 2012;Yang et al, 2012b;Cai et al, 2013). Overexpression of Atoh1 in immature rodent inner ears can induce ectopic hair cells in both sensory and nonsensory regions of the cochlea (Zheng and Gao, 2000;Woods et al, 2004), suggesting the sufficiency of Atoh1 for hair-cell formation in parts of the inner ear.…”