Stem-cell-based 'deafness cure'

A “‘cure’ for deafness has been found”, according to the Daily Express . It said that scientists have used stem cell technology to recreate the sensitive “hair cells” that are vital for hearing. These cells are found in the inner ear and do not grow back if damaged, which can result in permanent hearing loss.

The story is based on laboratory research in which researchers succeeded in manipulating mouse stem cells into cells that resembled sensory hair cells. These cells resembled sensory hair cells in shape and their ability to respond to movement.

This innovative research may have short-term practical use in that its methods can be reproduced to create more hair-cell-like stem cells that can be used to further our understanding of their biology. There is also potential for using them to screen drugs that may affect sensory hair cells. However, a stem-cell-based treatment strategy for hearing and balance disorders is a long way off.

Where did the story come from?

The study was carried out by researchers from Stanford University School of Medicine. The research was funded by the US National Institutes of Health, the California Institute for Regenerative Medicine and the McKnight Endowment Fund for Neuroscience. The study was published in the peer-reviewed scientific journal Cell .

The research was generally well reported, though calling it a “cure for deafness”, as some newspapers have, is overstating its impact, considering its very preliminary nature.

What kind of research was this?

This laboratory study aimed to use mouse stem cells to create hair cells, which are specialised cells in the inner ear that are crucial for hearing and balance. These cells do not grow back if they are damaged, and their destruction can lead to permanent hearing loss or balance disorders.

The researchers took stem cells from a mouse embryo and, by adding various biological chemical growth factors in several stages, induced them to develop the characteristics of the highly specialised hair cells. They then looked at how similar their cells were to sensory hair cells.

This is innovative research, and being able to direct the development of cells in culture to create cells with similar features to sensory hair cells is a major achievement. However, this is a laboratory study, and any implications for treatment of human hearing loss or balance disorders are a long way off.

What did the research involve?

To create the laboratory-grown hair-cell-like stem cells, the researchers used both mouse embryonic stem cells (ESCs) and induced pluripotent stem cells (IPSCs), which are adult cells that have been genetically reprogrammed to resemble embryonic stem cells. Pluripotent stem cells can develop into different types of cells depending on the type of biological chemical (growth factor) that they are exposed to.

Using different growth factors, the researchers manipulated these stem cells through the stages of development that would occur naturally in the womb. The cells passed through states in which they would have developed into tissues and structures, such as skin and nerve cells, ear cells and, finally, into a form that resembled sensory hair cells.

To test whether the cells that they had manipulated were like sensory hair cells, the researchers measured levels of certain proteins that are characteristically present in hair cells. Sensory hair cells also have a very specialised shape and protein structure that allows them to detect movement. The researchers looked at the effect of different combinations of growth factors on the production of a protein called myosin VIIa, which is necessary for hair cell function. They used an electron microscope to look at the shape of the cells.

The cells’ ability to detect movement was then tested using a device that agitated the liquid the cells were grown in. The electrical activity of the cells was then recorded.

What were the basic results?

Different combinations of growth factors were found to have different effects on the cells. The growth factors Dkk1, SIS3 and IGF-1 were needed to cause the cells to develop into sensory hair-like cells that produced the protein myosin VIIa. Furthermore, these cells had structures on their surface that looked similar to the hair bundles found on sensory hair cells.

The test of the cells’ ability to detect movement showed that 24 out of 45 cells responded to movement by changing their electrical activity. The researchers say that the type of activity measured was similar to that from immature sensory hair cells in the ear.

How did the researchers interpret the results?

The researchers say that naturally grown hair cells are difficult to obtain in large numbers and, therefore, largely unexplored. They say the method they have used here can be used as guidance for creating more hair-cell-like cells for further study of the biology of these cells.

They say that their success in creating hair-cell-like cells that resemble and behave similarly to sensory hair cells shows 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”.

Conclusion

This laboratory study developed a way of manipulating mouse embryonic stem cells to develop into cells that were similar to sensory hair cells. The cells appeared to resemble sensory hair cells in shape and their ability to respond to movement.

This innovative research may have short-term practical use in that its methods can be reproduced to create more hair-cell-like stem cells. These can be used to further our understanding of the biology of this specialised cell type. There is also potential for using these cells to screen drugs that may affect sensory hair cells. However, a stem-cell-based treatment strategy for hearing and balance disorders is a long way off.