Stem cells for deafness

“Scientists have announced a ‘major breakthrough’ in attempts to find a cure for deafness,” The Times reported. It said that the researchers had used stem cells from the human ear to make the sensory hair cells and brain cells that are ‘vital for hearing’. The BBC also reported the story and said that the next stage will be to “check if the cells can restore hearing”.

This research has shown that stem cells can be isolated from tissue from part of the human foetal inner ear (the cochlear), and can then be grown in the laboratory so that they develop into cells with hair cell and nerve cell-like characteristics. However, the hair cells were not fully developed, and did not show the typical hair-like projections from their surfaces. As such, further experiments will need to investigate whether these cells can become fully functional cells.

Dr Ralph Holme, director of biomedical research at The Royal National Institute for Deaf People (RNID), said: "Stem cell therapy for hearing loss is still some years away, but this research is incredibly promising and opens up exciting possibilities by bringing us closer to restoring hearing in the future."

Where did the story come from?

The research was carried out by Dr Wei Chen and colleagues from the University of Sheffield. The study was funded by The Royal National Institute for Deaf People (MNR), Deafness Research UK (MNR and WM) and the Wellcome Trust. The study is going to be published in the peer-reviewed medical journal Stem Cells.

What kind of scientific study was this?

This laboratory study tried to identify human stem cells that could potentially be used in treatments for deafness. Most cases of deafness are caused by the loss of hair cells in the ears and the nerve cells that transmit messages from these cells to the brain. As these cells are not repaired or replaced, damage is irreversible. Scientists believe that stem cell transplantation might be able to replace some of these damaged cells and therefore treat hearing loss.

Before carrying out this latest research, the researchers had already found that stem cells are present in the foetal human inner ear, but had not yet developed a technique for extracting these. In this study, the researchers wanted to isolate these cells and look at whether they could be grown in the laboratory and had the potential to develop into functioning hair cells and nerve cells.

The researchers obtained tissue from the cochleas of terminated human foetuses aged 9-11 weeks. Ethical approval and informed consent was obtained to use this tissue. The researchers dissolved samples of the cochlear tissue to release the individual cells and grew these cells in petri dishes with various combinations of chemicals that are used to support the growth of stem cells. The best conditions for cell growth were then selected.

The researchers identified stem cells by examining the genes that were switched on in these cells, and the proteins that were produced by them. The researchers searched for types of stem cell that typically expresses genes called SOX2 and OCT4. Once the researchers confirmed that they had isolated stem cells, they investigated how long they could keep these cells alive in the laboratory, and whether the cells had the ability to develop into the sensory hair cells and nerve cells found in the ear.

The cells that developed were examined to see whether they looked like sensory hair cells or nerve cells, and whether they expressed genes and proteins that were typical of these types of cells.

In order to function correctly, both nerve cells and hair cells need to be able to set up electrical currents across their membranes. These currents indicate that the membrane contains certain proteins that allow passage of different electrically charged atoms. The researchers tested these “electrophysiological properties” of the laboratory hair cells and nerve cells by applying currents across their membranes to see if they behaved similarly to the same types of cell taken from a human cochlea.

What were the results of the study?

The researchers successfully extracted cells from the human foetal cochleas, and identified the nutrients and chemicals that best supported the growth of these cells. They found that the cells they isolated expressed genes typical of stem cells, such as OCT4, and genes typical of ear cell progenitors, such as SOX2. The cells continued to divide in the laboratory for seven toeight months, after which time they could live for another four to five months but did not divide.

The researchers found that they could make the cells develop into what looked like nerve cells by treating them in certain ways and using specific combinations of growth factors. These nerve-like cells also had switched-on genes that are typically expressed in nerve cells.

The cells were grown in different conditions which led to them switching on genes that were typical of hair cells. There was also evidence that the “scaffolding” proteins within the cells had been rearranged in a way that was also typical of developing hair cells. Under these conditions, some cells also began to switch on genes typical of cells that support hair cells, called astroglia.

The nerve cells and hair cells grown in the laboratory had different “electrophysiological properties” to their parent stem cells, meaning that they responded in different ways to electrical currents applied across their membranes. The experiment also showed that the laboratory-grown hair cells behaved in ways similar to what would be expected of normal developing hair cells, and the laboratory-grown nerve cells behaved similarly to what had been seen in nerve cells from rat cochleas.

What interpretations did the researchers draw from these results?

The researchers concluded that the types of stem cells that they identified, and the methods they developed, could be used to study the development of human hair cells and nerve cells of the ear, and possibly also for testing the effects of drugs on these cells. They suggest that their techniques may aid the development of treatments for deafness.

What does the NHS Knowledge Service make of this study?

This study aimed to develop techniques for isolating and growing foetal stem cells from the human ear in the laboratory. The hair cell-like cells grown from the stem cells did not show the typical hair-like projections from their surfaces, so further experiments will be needed to investigate whether these cells can become fully developed hair cells.

As reported, Dr Ralph Holme, director of biomedical research at RNID, said: "Stem cell therapy for hearing loss is still some years away, but this research is incredibly promising and opens up exciting possibilities by bringing us closer to restoring hearing in the future."