Behind the Headlines

Tuesday December 9 2008

The tiny hair cells in the ear are vital in the process of hearing

Hearing problems could be cured by transplanting brain cells into the ear, The Daily Telegraph has claimed. The newspaper says the transplanted cells can switch functions and potentially reverse the inner ear damage that can cause hearing loss.
The research behind this story investigated certain mouse brain cells and whether they could potentially replace damaged inner ear hair cells. The researchers ran several different tests and learned about the characteristics of the brain cells. Crucially, they found that these brain cells (unlike inner ear hair cells) could reproduce, and potentially grow back in the place of damaged hair cells.

The bulk of this research was carried out on mouse cells and tissue in a lab. While this research is of interest, it is much too early to determine whether these types of cells could be used to treat human hearing problems.

Much more research will be needed in animals, to determine if harvesting and transplanting such cells is even possible, and if it would actually improve hearing in animals with hearing loss. Even if successful in animals, gathering human cells is unlikely to be simple and would require brain cell donors.

Where did the story come from?

This study was conducted by Dr Dongguang Wei and colleagues from the University of California and other research centres in the US and France.

It was funded by the National Institute on Deafness and Other Communication Disorders, the California Institute of Regenerative Medicine, and the National Organization of Hearing Research in the US. The study was published in the peer-reviewed journal, Proceedings of the National Academy of Sciences of the USA.

What kind of scientific study was this?

This was an experimental study looking at whether certain brain cells might be capable of forming new inner ear hair cells, which are used in the process of hearing.

The deterioration and death of inner ear hair cells is a major factor in age-related hearing loss, so researchers would like to identify a source of other cells that could replace them, and therefore potentially restore hearing. In general, the body does not replace dead hair cells in the inner ear or the nerve cells that transmit their signals to the brain (called spiral ganglia neurons or SGNs).

It has been found that stem cells from a certain region in the brain, called the forebrain lateral ventricle (LV), are able to generate new nerve cells. There is also a group of cells within the LV region that have projections on their surface and are similar to hair cells in the ear. These are called LV ependymal cells.

LV stem cells might be able to generate new SGNs, and ependymal cells appeared to be similar to ear hair cells but might be able to regenerate. On this basis the researchers wanted to investigate them further. 

The researchers isolated LV ependymal cells from mouse brains and looked at whether they were able to divide and generate new cells in the laboratory. They also looked at whether there was evidence that these cells were dividing inside mouse brains by examining brain slices.

The researchers looked at whether these LV ependymal cells had hair-like projections on their surface and could produce similar proteins to ear hair cells. The researchers then looked for these characteristics in the LV ependymal cells in slices of human brain.

The researchers then took mouse LV ependymal cells and grew them in the laboratory mixed with SGN nerve cells from the inner ear, and looked at whether the ependymal cells would be able to connect with the SGNs.

They then looked at whether the mouse brain cells could form part of the layer of sensory cells of the inner ear. They did this by dissecting out the sensory cell layer, killing off the hair cells and then incubating the cell layer with the ependymal cells to see if they would incorporate into it.

The researchers also looked at the stem cells from the lateral ventricle to see if they could produce nerve cells like the SGNs. Specifically they looked at whether these SGN-like cells could receive signals from hair cells when the two were grown together in the laboratory.

They also looked at whether these SGN-like cells could incorporate into the appropriate part of mouse inner ears (called the organ of Corti) in the laboratory.

What were the results of the study?

The researchers found that some mouse ependymal LV brain cells are able to divide and generate new cells in the laboratory. They also found there was evidence that these types of cells were also dividing while in the brain.

These mouse brain cells were found to produce some of the same proteins typically produced by inner ear hair cells. These brain cells also had hair-like projections on their surfaces, like inner ear hair cells.

The researchers found cells in the ependymal LV layer of human brain similar to those examined in mouse brains.

It was also found that mouse LV ependymal cells could form attachments to nerve cells from the inner ear, and could incorporate into the sensory layer of cells from the ear when grown in the laboratory.

The stem cells from within the lateral ventricle of the brain were able to develop into SGN-like cells and were capable of receiving signals from hair cells. These SGN-like cells could incorporate into the mouse organ of Corti in the laboratory.

What interpretations did the researchers draw from these results?

The researchers suggested that the types of brain cells investigated and methods used in this study could be used in the treatment of hearing loss.

What does the NHS Knowledge Service make of this study?

This research is at an extremely early stage, exploring the characteristics of specific types of brain cells when they are grown in a laboratory.

It is not yet possible to say whether these findings will lead to a treatment for deafness. A lot more research will be needed in animals, initially, to determine if successfully harvesting and transplanting such cells is even possible, and then whether a transplant can improve hearing.

Even if animal testing proved successful, the practicalities of using these cells in humans will also need to be considered, as harvesting brain cells is likely to be complex, and would require suitable donors.

Sir Muir Gray adds...

While this is encouraging news for mice, any human application is some years away.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

Brain stem cells could be transplanted to cure hearing loss, say scientists. The Daily Telegraph, December 9 2008

Brain cell hope for hearing loss. BBC online, December 9 2008

Links to the science

Wei D Levic S, Nie L, et al. Cells of adult brain germinal zone have properties akin to hair cells and can be used to replace inner ear sensory cells after damage. PNAS 2008; Published online before print, December 8 2008


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