Scientists have found a way to rapidly generate the inner ear hair cells that endow us with our senses of hearing and balance.
In mammals like us, hair cells are not spontaneously replaced, which is why prolonged exposure to loud noise - which permanently damages hair cells - can lead to deafness.
And although hair cells can be grown in the lab dish, current methods to do this are rather inefficient and slow. Usually fewer than ten per cent of cultured cells ultimately become hair cells, and it frequently takes up to 3 weeks, says researcher Aida Costa from the Intituto de Medicina Molecular in Portugal.
Now, working with colleagues from University College London and the Champalimaud Centre for the Unknown, in Portugal, Costa has found a faster way of developing hair cells by reprogramming them using a handful of "transcription" factors. Adding three key factors causes up to 75% of unspecialised "stem" cells to switch fate and become hair cells in under two weeks.
However, great as this sounds, there are still some hurdles to overcome. The resulting cultured cells display a more immature shape, compared with those found in the body, and the hair bundles they display on their surfaces appear disorganised, which might impair their function.
Moreover, the scientists don't yet know if their in-vitro produced hair cells even work like hair cells. Whilst they do have the prerequisite ion channels, or pores, on their surfaces that are required to convert sound vibrations into electrical signals for the brain, the team have not yet done the all-important tests to see if they are actually functional.
An alternative to dish-grown hair cells might be to use a living host instead. In another experiment, the researchers activated the same combination of transcription factors in the inner ear of a chick and successfully triggered the production of cells that looked very much like the native cells. "Chicks and fish can regenerate their own hair cells," cautions Costa, "but we are not sure if the same process will work in humans."
Nevertheless, the more efficient and speedy process the team have uncovered means that, in future, it will be easier to develop high-throughput drug screens for hair cells, to weed out agents that might be harmful to hearing and, conversely, identify protective chemicals that boost the resilience and survival of hair cells to restore or preserve hearing and balance.