Stem cell research paves way for deafness cure

STEM cell scientists have created inner ear sensory cells in the laboratory, paving the way to a cure for permanent deafness.

The work holds out the prospect of regenerating the sensitive hair cells that turn sound vibrations into nerve signals.

Humans are born with 30,000 hair cells in each ear. When the cells are lost or damaged – possibly due to excessively loud noise – it can lead to permanent hearing loss or tinnitus (ringing in the ears).

Damage to hair cells may also affect balance, causing symptoms of vertigo and dizziness.

Regenerating the sensory hair cells of the inner ear has been the Holy Grail of deafness research. The new breakthrough is the culmination of 10 years’ work by scientists in California.

A team led by Professor Stefan Heller, from Stanford University School of Medicine, succeeded in programming mouse stem cells to develop into immature hair cells.

Viewed under an electron microscope, they were seen to have bundled structures reminiscent of the hair-like tufts of “stereocilia” that give the cells their name.

“They really looked like they were more or less taken out of the ear,” said Prof Heller.

Most importantly, tests showed that the cells responded to being moved the way hair cells do, by converting mechanical signals into electrical ones.

Experts hope the cells, which could be made in large numbers from multiplying stem cells, will provide an invaluable research tool for studying the molecular basis of hearing and deafness.

Further down the line, they may help scientists coax a patient’s hair cells to renew themselves.

US expert David Corey, professor of neurobiology at Harvard University in Boston, said: “This gives us real hope that there might be some kind of therapy for regenerating hair cells. It could take a decade or more, but it’s a possibility.”

The Stanford research, the first to create functional inner ear cells, is reported in the journal Cell.

Prof Heller’s team used both mouse embryonic stem cells and artificially “induced” stem cells made by reprogramming ordinary skin cells. Embryonic stem cells, removed from early-stage embryos, are “mother” cells with the ability to transform into virtually any kind of tissue in the body.

In both cases, the cells were exposed to special cocktails of chemicals that caused them to go through a range of development phases normally seen in the womb.

“We looked at how the ear develops in an embryo, at the developmental steps, and mimicked these steps in a culture dish,” said Prof Heller.

He said the research “demonstrated that generation of replacement hair cells from pluripotent stem cells is feasible, a finding that justifies the development of stem cell-based treatment strategies for hearing and balance disorders”.