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Gene therapy shows promise to help people regrow auditory nerve cells

A new study
outlines how gene therapy could reverse hearing loss and deafness. This may be music to the ears of the roughly 300,000 patients across the globe that depend on cochlear implants to hear.

Australian researchers published their findings Wednesday in the journal Science Translational Medicine. By stimulating gene cells, which were injected into the ear canal with electrical impulses, chemically deafened guinea pigs were able to regrow auditory nerve cells.

The scientists used guinea pigs as test subjects because of the similarities between the ear canals of humans and guinea pigs. While the researchers noted just how effective cochlear implants have been to date in helping those with profound hearing loss, they also noted their limitations. They hope to overcome those limitations through their research.

“People with cochlear implants do well with understanding speech, but their perception of pitch can be poor, so they often miss out on the joy of music,”
said the study’s senior author Gary Housley
, a professor of neuroscience at the University of South Wales.

The cochlea is a tiny seashell-shaped organ located in the inner ear. It is filled with groups of microscopic hair cells that move in response to vibrations, and then convert those vibrations into electrical impulses that are carried to the brain and interpreted as sound. In some people’s ears, either because of genetics, old age, poisoning or loud noises, those tiny hair cells are damaged or lost and scientists haven’t found a way found to regrow them yet. In certain patients who experience profound hearing loss, a cochlear implant with electrodes can help stimulate whatever nerve cells are left.

With this study, Housley and his colleagues encouraged the production of neurotrophins, small proteins that stimulate the growth and maintenance of the hair-like nerve cells. They injected small rings of DNA, called plasmids, into the inner ear of the guinea pigs. Then, they exposed the animals cochleas to electrical currents that mimicked the electrical impulses provided to human cochleas through cochlear implants. By doing so, the membranes of the guinea pigs’ cells became more permeable to the injected DNA. The result triggered the production of neurotrophins and thus, the regrowth of nerve cells. The researchers are hoping that, in human subjects, they can achieve similar results.

While the researchers were ecstatic over the results, some of their enthusiasm was tempered because in some guinea pigs, results began to taper after three to six weeks. They hope to continue studying the application of gene therapy going forward.

“The development of electrode array gene delivery may not only improve the hearing of cochlear implant recipients but also find broader therapeutic applications,” Housely said. “[Gene therapy] could be used to treat a range of neurological disorders, from Parkinson’s disease to psychiatric disorders.”

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