LOS ANGELES, CA (Catholic Online) - Previously, it has not been possible to restore the cells once they have been lost due to external factors. Such factors include prolonged loud noise exposure, infection and toxic drugs.

Often suffered by rock musicians and DJs, this form of deafness is generally assumed to be irreversible.

Scientists have now succeeded in partially restoring hearing to mice that had been deafened by loud noise. While still in the early stages, scientists believe it could lead to effective treatments for acute noise-induced deafness in humans.

The tiny sensory hairs in the cochlea are vital to hearing. Sound vibrations transferred from the eardrum shake the hairs, causing nerve messages to be fired to the brain. Without these hairs, the pathway is blocked and no signals are received by the brain's auditory center.

The new approach involves reprogramming inner ear cells by inhibiting a protein called Notch.

Previous laboratory research had shown that Notch signals help prevent stem cells in the cochlea transforming themselves into new sensory hair cells.

"We show that hair cells can be regenerated from the surrounding cells in the cochlea," Lead researcher Dr Albert Edge, from the Harvard Medical School says.

"These cells, called supporting cells, trans-differentiate 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.

"The significance of this study is that hearing loss is a huge problem affecting 250 million worldwide."

A green fluorescent protein was used to label the newly generated hair cells.

Lost hair cells had been replaced and were working, as attested to by electronic measurements of auditory brainstem responses three months after treatment.

Improvement in hearing was seen over a wide range of frequencies. "The missing hair cells had been replaced by new hair cells after the drug treatment, and analysis of their location allowed us to correlate the improvement in hearing to the areas where the hair cells were replaced," Edge says.

"We're excited about these results because they are a step forward in the biology of regeneration and prove that mammalian hair cells have the capacity to regenerate.

"With more research, we think that regeneration of hair cells opens the door to potential therapeutic applications in deafness."

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