These are normal inner and outer hair cells. Credit: Neuron, Mizutari et al.

This image shows cochlea after damage only and after damage and replacement of hair cells. Credit: Neuron, Mizutari et al.

Extremely loud noise can cause irreversible hearing loss by damaging sound sensing cells in the inner ear that are not replaced. But researchers reporting in the January 9 issue of the Cell Press journal Neuron have successfully regenerated these cells in mice with noise-induced deafness, partially reversing their hearing loss. The investigators hope the technique may lead to development of treatments to help individuals who suffer from acute hearing loss.

While birds and fish are capable of regenerating sound sensing hair cells in the inner ear, mammals are not. Scientists and clinicians alike have long wondered how they might reprogram humans' inner ear cells to allow hair cells to regenerate. While many methods have been tried, so far, none have been successful.

A team led by Dr. Albert Edge of Harvard Medical School and Massachusetts Eye and Ear Infirmary speculated that a cellular pathway that controls hair cells' fate might be manipulated to regenerate the cells. Their previous research revealed that inhibition of the pathway, called Notch, increases hair cell differentiation.

In this latest work, the investigators found that new hair cells formed after inner ear stem cells were treated with a drug (called a gamma-secretase inhibitor) that blocks the Notch pathway. The researchers also used the drug to treat the inner ears of mice that had noise-induced deafness. "We show that hair cells can be regenerated from the surrounding cells in the cochlea. These cells, called supporting cells, transdifferentiate into hair cells after inhibition of the Notch signaling pathway, and the new hair cell generation results in a recovery of hearing in the region of the cochlea where the new hair cells appear," says Dr. Edge.

The results suggest that the therapy might be a promising treatment for acute noise-induced deafness in humans. "The significance of this study is that hearing loss is a huge problem affecting 250 million worldwide," says Dr. Edge.

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Cell Press: http://www.cellpress.com