Cure for Hearing Loss

Hearing loss is more prominent now more than ever. It is well known that mild to moderate hearing loss can have effects on the auditory cortex that may last a lifetime. At University of Pennsylvania, a group of researchers examined the impact of sounds on various aspects of the human body, including hearing loss and cardiovascular disease, to investigate the effects of noise; they stated that different impacts of noise might affect other aspects in one’s daily life, including community annoyance, sleep, etc. The authors also claim that more people need to learn and understand how exposure to sounds affects their hearing and overall health.

Noise-induced hearing loss is the most common occupational disease in the United States (3). This type of hearing loss first begins when the pathway to the cochlea is disrupted. This disruption can occur due to many causes, as there are thousands of genes in the cochlea that can induce deafness in humans; however, some of these specific genes are still in the process of being found and explored.

Dr. Wei-Ming Yu in his paper, “A Gata3-Mafb transcriptional network directs post-synaptic differentiation in synapses specialized for hearing” examined the knockout of the Mafb gene in adult mice. Mafb is a transcription factor that stimulates the formation of the ribbon synapse in the cochlea. The ribbon synapse transmits sound from the inner hair cells to the spiral ganglion neurons in the cochlea. This disruption of the formation of the synapse results in hearing loss in adult mice. Dr. Yu proved that due to this knockout, these mice were not able to distinguish between high and low pitches of sound. Dr. Yu’s knockout experiment determined that Mafb not only plays a crucial role in the formation of the ribbon synapse, but also the hearing process in the auditory system.

Similarly, in the summer of 2015, scientists at Boston Children’s Hospital conducted an experiment to restore the genes involved in hearing in deaf mice. In the study, three Harvard Medical School senior investigators, Dr. Jeffrey R. Holt, Dr. Konstantina Stankovic, and Dr. Luk H. Vandenberghe, examined the effects of a new synthetic vector, Anc80. When introduced into the cochlea, Anc80 transported genes into the outer hair cells. The new vector proved to be a success as it targeted cells of interest in the inner ear and did indeed assist in restoring the lost genes. This demonstrates that presenting the vector to the cochlea would improve hearing loss.

A second study at the Boston Children’s Hospital, administered by Dr. Gwenaëlle Géléoc, examined mice with mutations in the Ush1c gene, which presents the same as Usher type 1c mutations in humans.  This mutation disrupts sound signals received by the brain, which then results in hearing loss. In the image, A is a normal group of hair cells, which move properly when exposed to a sound; however, when the cells are damaged (B), the inner hair cells do not move properly, instead requiring more sound and energy to move. In the study, newborn mice that were given the new Ush1c gene were able to hear soon after being treated. When the corrected Ush1c gene was admitted into the mice’s hair cells, they began to form normal bundles and responded to sound waves and signaling. The researchers hope to use these genetic bases in mice in order to help children who have trouble with hearing.

Dr Wei-Ming Yu and the scientists at Boston Children’s Hospital examined genes that play a role in the auditory processes in mice. These genes are located in the cochlea and the knockout of specific genes can severely affect the mice’s hearing. Both studies hope to find a genetic conclusion that can one day benefit humans. Studies like these are necessary for medical advances in our society.

Sources:

     1. .Gwenaëlle S Géléoc et al. Gene therapy restores auditory and vestibular function in a mouse model of Usher syndrome type 1c. Nature Biotechnology, February 2017 DOI: 10.1038/nbt.3801

     2. “Hearing Loss.” Michels Hearing Aid Centers, 25 Jan. 2017, michelshearing.com/hearing-loss/. (Image)

     3.  University of Pennsylvania School of Medicine. "Negative consequences of noise on overall health." ScienceDaily. ScienceDaily, 29 October 2013. <www.sciencedaily.com/releases/2013/10/131029220800.htm>.

     4. Yu, Wei-Ming, et al. “A Gata3âMafb Transcriptional Network Directs Post-Synaptic Differentiation in Synapses Specialized for Hearing.” ELife, vol. 2, Oct. 2013, doi:10.7554/elife.01341.