One of the fascinating traits of auditory research is that audiologists and the public alike never know where another potential discovery could come from next. Uncovering the components to hearing loss is just about as complex and complicated as the sensory act of hearing itself, and scientists are constantly logging hours of research and data to hopefully unlock another secret to help treat auditory damage in the future.
The latest audiological breakthrough comes from researchers in France from the Institut Pasteur in Paris and Collège de France, where the professors have discovered a specific protein located in the inner ear region that could prove essential for the sound converting process within the brain. Absence of this protein, which the researchers have identified as protocadherin-15, within the ear could provide a connection for hearing loss development in humans.
There are three known variations of protocadherin-15 that exist within the auditory sensory cells of the inner ear, but it has never been properly understood which type of the protein was essential in the hearing process. Using laboratory mice, the colleagues were able to pinpoint that the CD2 isoform variation of protocadherin-15 was the specific protein crucial for sound conversion, and that the absence of this type of protocadherin-15 within the mice’s hair cells resulted in profound deafness.
These thousands of tiny hair cells aligned through the middle ear work as sensory antennas for sound waves to travel through and be processed through the brain, and when a mutation in the genetic code of the CD2 isoform of protocadherin-15 occurs, or is completely absent, sound stimulation ceases to progress. What else is interesting to note is that any lack of the other protocadherin-15 isoforms had no impact on the mice’s hearing whatsoever, and missing CD2 isoform of protocadherin-15 proteins only occurred in adult mice.
Christine Petit, a Professor at the Institut Pasteur in Paris and lead author of the study, explained how auditory development without this specific protein impacted the sound conversion process, and that further testing could indicate that an absence or alteration of this protein in humans could spell similar auditory trouble.
“The goal of our study was to identify which isoform of protocadherin-15 forms the tip-links, the essential connections of the auditory mechanotransduction machinery within mature hair cells that are needed to convert sound into electrical signals,” Petit said in a statement. “The demonstration of a requirement for protocadherin-15 CD2 for hearing not only in mice but also in humans constitutes a major step in the objective of deciphering the components of the auditory mechanotransduction machinery.”
What this means for human auditory impairment
While it has long been known that the protein protocadherin-15 has played a part in human auditory development, researchers have had a hard time figuring out its exact role within the progression of hearing, as well as which specific type of protocadherin-15 is responsible for sound conversion. This study can help scientists pinpoint exactly where disruption of sound communication between the middle ear and the brain is occurring, and how to fix it. This study is just another example of the hard work and dedication being put forth toward preserving the hearing of millions of people around the globe.
