Deafness – stem cells may save hearing

The use of stem cells transformed into progenitor cells in laboratories of University in Sheffield has caused a significant improvement of hearing in experimental animals.

The scientists were interested in the treatment of hearing disorders which are caused not only by the damage of neural paths connecting cochlea with brain, but also by hair cells deficit. They are sensory cells which are located in the organ of Corti which is a part of cochlea.

According to scientists, current trials of transplanting adult hair cells and auditory neurons into mice have not brought deserved functional improvement (Reyes H et al. 2008, Corrales, C. E et al. 2006). In turn, neuroprogenitor cells isolated from an adult human cochlea had limited proliferate potential what was described in the work of H. Rask-Andersen et al. (2005). That is why the idea of complete deafness restoration in humans was unlikely to be introduced.

According to the researchers led by doctor Wei Chen it is the supplementation of lacking cells which may be the right therapeutic strategy.

In order to do this a special method of stem cells farming was introduced. The algorithm of procedures, owing to which the researchers had led to the creation of progenitor hair cells and progenitor auditory neurons under the influence of various factors, was described. The cells were transplanted into the internal ear of gerbils with deafness. These rodents, as opposed to mice or rats in natural environment, have similar hearing range to humans. That is why they are suitable for the research.

In gerbils the effect of the therapy was studied by measuring their brainwaves which are a reaction to auditory stimulus. The first signs of the reaction to the therapy occurred in the fourth week after the implementation of cells. After about 10 weeks there was a significant improvement which, in relation to the control group, was statistically significant (p<0,0002). Hearing improved by 45% what corresponds to recovery of hearing ability needed to hear a conversation, while previously it was not possible to hear even passing truck. About 1/3 of the animals poorly responded to the treatment, while in another 30% hearing improved even by 90%. In some animals synaptic connections with transplanted cells occurred. The positive thing is that, despite fears which occurred during the implementation of the cells, in none of research animals cancerous centre was found. The results obtained on animals are very promising and can be shifted to a human model. That is why it is necessary to create a safe method of cells transportation into human’s internal ear. Also, ethical dilemmas concerning stem cells should be considered. Nevertheless, according to the scientists, even if in humans such therapy would not be as successful as in gerbils, its combination with e.g. cochlea implant may improve the quality of life of many people.

Written by: Jerzy Bednarski, Jakub Patryn, Michał Czerwiec, Karolina Gasińska

1.Rask-Andersen, H. et al. Regeneration of human auditory nerve. In vitro/in video demonstration of neural progenitor cells in adult human and guinea pig spiral ganglion.Hear. Res. 203, 180–191 (2005)
2.Reyes, J. H. et al. Glutamatergic neuronal differentiation of mouse embryonic stem cells after transient expression of neurogenin 1 and treatment with BDNF and GDNF: in vitroand in vivo studies. J. Neurosci. 28, 12622–12631 (2008)
3.Corrales, C. E. et al. Engraftment and differentiation of embryonic stem cell-derived neural progenitor cells in the cochlear nerve trunk: growth of processes into the organ of Corti. J. Neurobiol. 66, 1489–1500 (2006)
4.Chen W, et al. Restoration of auditory evoked responses by human ES-cell-derived otic progenitors. Nature. 2012 Oct 11;490(7419):278-82. doi: 10.1038/nature11415. Epub 2012 Sep 12.

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