Mammalian ear cells can regenerate

The cells responsible for hearing in mammals are capable of regeneration, a study indicates. The surprising finding could lead to new treatments for hearing loss, say researchers.

In birds and other vertebrates, inner-ear sensory cells called hair cells quickly regrow after they’re damaged or destroyed. The regeneration takes place when cells that support each hair cell divide to produce a new hair cell and a new supporting cell. However, researchers have long considered mammalian hair cells irreplaceable. No study had ever shown that mature supporting cells in mammals could divide, much less differentiate into new hair cells (SN: 5/20/06, p. 311: Available to subscribers at Now Hear This).

Trying a new tactic, Andrew Groves of the House Ear Institute in Los Angeles and his colleagues isolated supporting cells from the inner ears of newborn mice and put them in culture dishes.

Within days, Groves’ team noticed that about half the cells were dividing, and a significant portion of the new cells were growing into hair cells. Genetic tests showed that the dividing cells had switched off a gene known as p27, but the gene remained on in the nondividers.

When the researchers performed the same experiment with cells taken from 2-week-old mice, they found that only about 2 percent of the supporting cells divided. This suggests that p27 becomes more firmly switched on with age, they report in the June 22 Nature. However, when Groves and his colleagues tried the experiment with 2-week-old mice genetically engineered to lack p27, about 10 percent of the cells multiplied.

If researchers could come up with a way to turn off p27 in the ear, they might induce hair cell growth in people who have lost these cells, says Groves.