Oscar nominated film “The Sound of Metal” pulls at our heartstrings as we learn of a heavy metal drummer whose tinnitus is revealed to actually be a prelude to substantial hearing loss. The movie has the viewer deeply feeling the pain of hearing loss and reminds how our ability to hear is so inextricably linked with some of the joys of life. Hearing is one of our most cherished senses over the course of our lives that brings the joys of conversation and music and keeps us alert and in tune with the world around us. Our hearing allows us to communicate with one another and cultivate cherished relationships with friends and loved ones. Because of the crucial role hearing plays in communication, individuals with hearing loss report negative impacts on their careers and personal lives. Even small disruptions to our ability to communicate, let alone hearing loss, can make anyone feel alienated and frustrated. Unsurprisingly, the personal impacts and emotions often lead to worsening mental health and increased incidences of anxiety and depression. The restoration of hearing on the other hand can lead to some powerful and emotional moments.
Unfortunately, hearing loss is relatively common. Almost 80% of Canadians aged 60-79 have hearing loss, while 40% of Canadians aged 40 to 59 deal with some form of hearing loss. Hearing loss is reasonably prominent worldwide. When looking at hearing loss on a global scale there are hundreds of millions of people with partial or full hearing loss. Currently, inner ear hearing loss, the most common form of hearing loss, has no cure. Depending on the type of damage however, there are treatments to mitigate hearing loss. Cochlear implants bypass the injured or damaged part of your hearing systems and directly stimulate your auditory nerve. There are also treatments like traditional hearing aids, ear implants, and bone-conduction hearing aids. These are incredible advancements but unfortunately they don’t offer a cure. Many of these treatments still rely on either functional auditory nerves, or partly functioning auditory hair cells to treat hearing loss. In cases where either or both of these are too severely damaged, current treatments may not work.
What causes hearing loss?
The inner ear consists of the cochlea – the part used in hearing, and the vestibular system – the domain used in balance. Both of these parts consist of specialized hair cells connected to auditory nerves. Small movements of these incredibly sensitive hairs trigger signals to our brain that we interpret as hearing and balance. These cells and the hairs in healthy individuals develop early, but they don't harbour sufficient stem cell populations that can lend themselves to renewal like other specialized systems. Hearing loss is often caused by the loss or damage of these specialized hair follicles. This damage can result from exposure to loud noises, certain drugs, some infections, and of course, aging. Symptoms of hearing loss can include tinnitus, muffled sounds, trouble hearing consonants and many more. Sometimes our jobs or hobbies can lead to hearing loss. Occupations from construction workers to nightclub workers put us at risk with exposure to constant loud noises. Hobbies that place someone near loud noises frequently like drumming, or DJing can also be a factor leading to hearing loss. Because there aren’t enough stem cells in the inner ear, the specialized cells and follicles cannot renew or replenish themselves when damaged. Once the hairs are damaged or gone, they're gone for good.
How can stem cells be used to treat hearing loss?
Researchers around the world are using the power of stem cells to explore solutions to formerly incurable diseases. The same is true for hearing loss. Maybe even more so. A recent literature review found that we can direct stem cells into auditory hair cells and auditory neurons very efficiently. A team of researchers from Stanford are utilizing the efficient transformation of stem cells to cells for hearing. The team is using autologous (a person's own) cells to treat hearing loss. Their solution consists of genetically reprogramming a person's skin cells back into stem cells or iPSCs. New stem cells can then be directed to turn into the inner ear's hair cells and transplanted into a patient with hearing loss. The patient theoretically will then have novel, healthy inner ear hair follicles that can sense movement and transmit signals once again. This team is currently working on creating these cells in vitro before moving on to more substantial testing.
Another research team has begun testing in animals and has found incredibly high success rates when turning stem cells into hair cells and auditory neurons and has shown tangible hearing restoration in animal models. Injection of stem cells into the animal model ears showed physical improvements in the neurons and the hair cells, and measurements of hearing thresholds for the animals also notably improved. While cellular therapies to restore complete hearing to individuals may be somewhat far away, some cellular therapies seek to make existing treatments more effective. Some research suggests that implantation of cells in combination with cochlear implants may improve the therapeutic utility of both treatments. Amazing moments like this may become more common and with stronger, longer lasting results.
How can you prevent hearing loss?
Any one of us can prepare for hearing loss today, primarily by limiting our exposure to constant loud noises or sudden, very loud noises. We can recognize symptoms of tinnitus like ringing in the ears as potential first signs of hearing loss. We can also prepare for cellular solutions to hearing loss by banking our young cells today. Research has shown that younger cells are easier to manipulate than older cells. What does that mean? Young cells are more easily converted into iPSCs and differentiated into specialized cell types. Specialized cell types like ear hair cells or auditory nerve cells. By banking your cells today you could be providing yourself with the youngest possible autologous cells for therapies like those for heart disease, Alzheimer’s, or hearing loss. Acorn gives you access to cell banking in a non-invasive and affordable way. Prepare for the future today by saving your best cells for your best self.