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By 2020, hearing loss among adults is expected to increase to more than 44 million adults in America that are older than 20 years old (1). With hearing loss on the rise as generations get older and face natural decline, it is important to understand what contributes to hearing in order to make interventions for the future. The inner ear and vestibular system is responsible for allowing us to hear, but it is a complex system that still has many questions regarding how it works. Particular interest and research has been focused on understanding the hair cells in the inner ear which allows for conversion of sound waves into nerve signals that the brain can interpret. What we did know was that proteins in the membranes of the hair cells open, which allows for an influx of electrically charged ions, such as calcium and potassium, which serve as the nerve signals to the brain. Many years have been dedicated to answering this research question of what membrane proteins are responsible for the nerve signal generation but due to the hard to access location of the inner ear and fewer cells being present in comparison to other senses, such as the 100 million sensory cells within the human retina versus the 16,000 sensory cells in the human inner ear, the answer remained elusive until recently (2).
After many years of intense research, Harvard released results on August 22 in Neuron indicating the link for this conversion of sound into nerve signals– due to a protein called TCM1. TCM1 was first discovered in 2002 and is found to be conserved across vertebrate species. In 2011, a research team identified the protein as being important for auditory transduction in hair cells, sparking the race for understanding how the protein actually contributes to the auditory experience. Now, Harvard has now identified that TCM1 forms a sound/motion-activated pore that creates a signaling cascade responsible for converting sound and movement into nerve signals to travel to the brain (2). The set of experiments in order to confirm this conclusion were based on understanding how the manipulation of the structure of TCM1 contributed to the overall functioning. Working with mice hair cells, researchers manipulated the 17 amino acids that make up the TCM1 protein. With each manipulation, researchers looked into how the ion channels were affected. Five of the substitutions they performed resulted in 80% decrease in hearing, where one completed blocked off the calcium ion channels (2). Having one substitution where the ion channel was blocked off completely confirmed the vital role of TCM1 in hearing transmission.
Now that the molecular gateway responsible for hearing has been identified, it allows for further research to move into understanding how the specific role may be manipulated in order to help populations with hearing loss. Hearing loss is the most common neurologic disorder as it impacts 460 million people worldwide, showing how these results are in the right direction to address this growing medical issue across the globe (3). TCM1 is the protein that can hold the key to helping those facing hearing loss, which is definitely something to be excited about.
- “US: The Prevalence of Hearing Loss Is Expected to Increase Significantly.” Hear-It.org, www.hear-it.org/us-prevalence-hearing-loss-expected-increase-significantly.
- Pesheva , Ekaterina. “Scientists Discover Protein Responsible for Hearing and Balance.” SciTechDaily, 25 Aug. 2018, scitechdaily.com/scientists-discover-protein-responsible-for-hearing-and-balance/.
- Anderson, James. “TMC1: The Molecular Sensor That Converts Sound Into Brain Signals.” ReliaWire, 23 Aug. 2018, reliawire.com/tmc1-hearing-sensor/.