Iconic super hero Superman, Christopher Reeve, suffered severe spinal injuries in 1995 from a horse riding accident. He became a well-known advocate for stem cell research and it is thanks to his lobbying that the term “stem cell” entered the public arena.

The most common, and established, stem cell therapy used today is bone marrow transplantation, used to treat leukemia. In the future, medical researchers anticipate that technologies derived from stem cell research may be used to treat diseases including cancer, Parkinson’s disease, arthritis, spinal cord injuries, multiple sclerosis, diabetes, blindness and hearing loss.

Hearing loss is one of the most common sensory conditions. While studies have shown that noise-induced hearing loss is going to become the next big epidemic affecting the younger generation (ScienceDaily, 2007) there are many other causes of hearing loss including genetic (inherited), environmental (infections, premature birth and ototoxic drugs) or the natural aging process.

Hair cells are small hair-like projections that line the cochlea, the sensory organ of the inner ear responsible for hearing. We are born with approximately 30,000 hair cells in each ear. In people with normal hearing, hair cells convert sound into electrical signals, which are then transmitted to the brain and subsequently “heard”. People with sensorineural hearing loss may suffer from missing, damaged or too few hair cells.

Unlike other cells in the body, such as skin cells, the regenerative ability of the cochlea is limited, making restoring hearing a challenge. Interestingly, in nature there are no “deaf” birds or fish as they have the remarkable natural ability to quickly regrow damaged hair cells! In humans some natural recovery of damaged hair cells does occur, leading to partial improvement of a temporary hearing loss. However in most cases where the damage is severe, hearing loss is permanent.

• Part 1: Hearing with your bones: The science of restoring hearing
• Part 2: What is a stem cell?
• Part 3: Other avenues