Our business is all about what environments sound like. Hearing is an essential part of this; however, hearing loss affects 360 million people worldwide according to the World Health Organization. While we are not medical professionals, there has been an exciting new development in potentially reversing hearing loss that we want to share with you, which involves the regeneration of inner ear hair cells. Read on to learn more about this study, which was published in Cell Reports in February 2017.
To understand this new development, one must first understand the basic principles of how hearing works. Essentially, sound waves are detected by the ear, converted into neural signals, and then sent to the brain. The ear has three divisions: the external ear, the middle ear, 
and the inner ear. The external ear collects sound waves and funnels them down the ear canal, where they vibrate the eardrum. Within the middle ear, the eardrum is connected to the middle ear bones. These are the smallest bones in the body and they mechanically carry the sound waves to the inner ear. The inner ear contains the cochlea; this is the organ that converts sound waves into neural signals, which are passed to the brain via the auditory nerve. Coiling around the inside of the cochlea, the organ of Corti contains the cells responsible for hearing, the hair cells, which bend back and forth creating electrical signals. Auditory nerve fibers rest below the hair cells and pass these signals on to the brain. Each of us is born with about 15,000 hair cells per ear, and once damaged, these cells cannot regrow. Noise exposure, aging, and some antibiotics and chemotherapy drugs can lead to hair cell death. In some animals, those cells naturally regenerate, but not in humans.
Harvard Stem Cell Institute researchers at Brigham and Women’s Hospital (BWH) and Massachusetts Eye and Ear Infirmary and colleagues from MIT have developed an approach to replace damaged sound-sensing hair cells, which eventually may lead to therapies for people who live with disabling hearing loss. In the recent Cell Reports study, the researchers identified a small molecule cocktail that increased the population of cells responsible for generating hair cells in the inner ear.
Birds and amphibians are able to regenerate these cells throughout their lives, which provided the base for the researchers’ inspiration to find similar pathways in mammals. They were able to study a small molecule approach, developed at MIT and BWH, to expand progenitor cells from mouse cochlea. The generation of new hair cells was achieved even in cochlear tissue that had been depleted of hair cells by exposure to an antibiotic. Importantly, hair cells produced from the protocols exhibited the same physical features, gene expression, and functionality as typical cochlear hair cells.
Drawing on research from this study, Frequency Therapeutics was founded to translate this breakthrough work in Progenitor Cell Activation (PCA). “Frequency’s development of a disease modifying therapeutic that can be administered with a simple injection could have a profound effect on chronic noise-induced hearing loss, our lead indication, and we are rapidly advancing this program into human clinical trials within the next 18 months” says Chris Loose, PhD, co-founder and CSO of Frequency Therapeutics. At Metropolitan Acoustics, we are waiting with anticipation and optimism for the results of these trials.