sounds good. New auditory neurons increased in Guinea pig deaf since DNA for a growth factor ( above ), but not in the untreated ears of the same animal.
Translational Neuroscience Facility UNSW
Many people with profound hearing loss were helped by devices called cochlear implants, but their audience is still far from normal. They often have trouble distinguishing different music sites, for example, or to hear a conversation in a noisy room. Now researchers have found a clever way to use cochlear implants to deliver new genes into the ear therapy which, in guinea pigs, significantly improves hearing.
The most common cause of hearing loss is the loss of tiny hair cells inside the cochlea, a spiral hollow structure in the inner ear that converts sound into nerve impulses. Hearing aids, which simply amplify sounds do not help people who have lost these hair cells. Thus, since the 1970s, more than 320,000 children and adults around the world who are deaf or severely hearing impaired have received cochlear implants. Instead of relying on hair cells, the device converts the sounds into electrical impulses and then uses electrodes to transmit these signals to the auditory nerve to the brain. But because the auditory nerve is buried in the tissue, the implants do not work as well as they could if the electrodes were closer to the nerve.
Some researchers have stimulated new neurons to grow inside the cochlea using a protein known as a growth factor. They injected growth factor in the inner ear, or a virus used to deliver a gene encoding it into cells. But growth factor pumped-in does not work for long, unless it is replenished. And viral gene therapy still not put the gene in the right cells, and has risks, as a reaction of the immune system to the virus.
Graduate student Jeremy Pinyon and colleagues in the laboratory of neurosciences Gary Housley at the University of New South Wales in Sydney, Australia, tested another type of gene therapy to deaf guinea pigs made with a drug that kill the hair cells in the cochlea. The researchers created DNA encoding a gene loops of a neurotrophic factor called brain-derived growth factor (BDNF). Upon insertion of a cochlear implant in animals, the team injected the cochlea with a solution of BDNF DNA and then used electrical impulses from the device to create pores in the cells that line the cochlea and cajole DNA to enter the cells. The loops also included a gene for green fluorescent protein so that the scientists could see whether the inserted DNA was taken up by the cells and translated into protein.
In the coming days, the cells began pumping BDNF, which, in turn, stimulated the growth of neurons long bristled at the electrodes. Two weeks after treatment, the researchers tested the sensitivity of the brain of animals were sounds of different frequencies. The results were closer to those of normal animals and much better than those seen in animals that had only a cochlear implant.
"We closed the neural gap," said Housley. Although it is difficult to accurately measure sound perception in guinea pigs, if applied in humans, "we hope that the tonal colors and the wealth will be improved," says Housley, whose team's report appears today ' hui in Science Translational Medicine .
One caveat is that the improved hearing did not last long cells stopped producing BDNF after about 6 weeks and new nerves began to die. DNA loops must be modified to work longer in the cells, Housley said. another potential problem is he does not know how long the cells that received DNA last before dying and ability of BDNF-how is lost. Housley believes that these problems can be solved, however, and he hopes to start a small clinical trial to test the procedure in people within 2 years.
"idea [of using BDNF] was around. But this study is the first to put this idea in collaboration with cochlear implants, "says neuroscientist Jeffrey Holt Hospital Medical School and Harvard Boston Children. The technique is "smart", says researcher hear Yehoash Raphael of the University of Michigan, Ann Arbor, the group used a virus to insert the gene BDNF in the cochlear cells. Housley hope other implanted devices could also offer gene therapy, such as small electrical appliances sometimes inserted into the brain of patients with Parkinson's disease to relieve their symptoms.
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