Stem Cell Therapy for Sensorineural Hearing Loss - How Do Glial Cells Interact With Auditory Stem Cells in the Peripheral Auditory System?

Clinical Background of Research
Hearing problems are an extremely significant public health issue. Almost 10 million people in Britain suffer with hearing impairment and forecasts suggest this will rise to 15 million by the year 2030. 'Sensorineural hearing loss' accounts for almost 90% of all hearing problems and occurs as a result of irreversible damage to the inner ear, especially the cochlea, where sound vibrations are converted into nerve signals. Although electrical devices such as Cochlear Implants have been used successfully to help patients of all ages suffering with severe sensorineural hearing loss, the limitations of such devices are gradually becoming apparent. Regenerative medicine provides some hope of biological therapies which may be able to treat sensorineural hearing loss with greater effect than current treatments with electrical devices. In a recent major breakthrough, our laboratory has demonstrated the ability of stem cells to repair and restore function of damaged hearing nerves in animal models of sensorineural hearing loss. This project will build on our previous work by understanding how stem cells integrate with a damaged hearing system.

Importance of this Research
'Glial Cells' are cells which maintain the health of nerve cells. It is well known that nerve damage results in the activation and multiplication of 'glial cells'. In some parts of the nervous system, this process of glial cell multiplication can help with the repair of damaged nerves, but in other parts, such as the brain and spinal cord, the multiplication of glial cells represents scarring which limits further damage to nerves, but also prevents repair.
It has recently been discovered that damage to the hearing nerve also causes multiplication of glial cells, but it remains unclear if this represents an environment which would either support repair or whether it represents scarring. This would obviously have implications on the ability for stem cells to repair the damaged hearing nerve. Hence, understanding the relationship between the glial cells of the hearing system and stem cells is a key factor in the quest to translate this therapy to patients.

Aims of this Research
The aims of this project are to understand the ways in which stem cells communicate with glial cells, and to illustrate whether the response of glial cells to damage of the hearing nerve represents scarring, or whether it represents a favourable environment for and stem cells to repair the hearing nerve. We will then demonstrate how transplanted auditory stem cells integrate with glial cells in animal models of deafness.

Research Plan
The project will be conducted in two phases. The first phase will consist of culturing stem cells programmed for the auditory system to check if they are capable of producing their own glial-like cells. The stem cells will then be cultured alongside glial cells from the cochlea, which will allow the interaction between the two cell types to be studied.
The second phase will consist of determining whether stem cells are able to repair the damaged hearing nerve despite the multiplication of glial cells. This will involve performing careful analysis of the glial cell types in the damaged hearing nerve and how stem cells interact with them. The information gathered from the previous phase will help in describing this relationship.

Host Institution
This project will be undertaken at the Centre for Stem Cell Biology at the University of Sheffield which has international recognition as a centre of excellence for research into Stem Cells. The centre has pioneered the use of stem cells to the inner ear and has all the necessary facilities to carry out this project.

The ability of sensory hair cells and auditory neurones of the human cochlea to regenerate is lost soon after birth, hence later damage to these structures results in an irreversible sensorineural hearing loss. Otic neural progenitors (ONPs) derived from human embryonic stem cells have the potential to restore function in the damaged auditory nerve. However, the interaction between ONPs and glial cells is yet to be described. Furthermore, with the recent finding that auditory nerve damage results in glial cell prolieferation, it is unclear whether this is conducive or inhibitory for ONPs to differentiate into auditory neurone-like cells.

Objectives
1.To determine whether auditory stem cells have the capability of producing glial-like cells

2.To identify whether auditory stem cells are able to interact with primary glial cell cultures in vitro

3.To define the nature of glial responses to injury of the auditory nerve in vivo

4.To understand if auditory stem cells are able to survive in an environment of 'cochlear gliosis'

Design of study

1.ONPs will be expanded in vitro, and reverse transcriptase PCR and immunolabelling will be used to determine the presence of glia-like cells

2. Co-cultures of glial cells and ONPs in vitro will enable the deduction of the inductive influence of the former on the latter.

3. Auditory neurons will be selectively damaged using Oubain in vivo, and the ensuing glial response will be determined through immunohistology.

4. Following exposure to Oubain, ONPs will be surgically inserted into the cochlea in vivo, and their ability to differentiate in a pathological glial environment will be assessed.

Medical opportunities
Understanding the interaction between cochlear glial cells and ONPs is paramount in demonstrating stem cell therapy as a viable solution to SNHL and it will bring us a step closer to clinically translating potential stem cell therapies for SNHL

This research project ultimately aims to benefit those patients who have either congenital or acquired sensorineural hearing loss. Whilst modern cochlear implants have allowed many of these patients to communicate with wider society, there are still a significant number of patients who do not realise the full potential of cochlear implantation. By demonstrating the potential for using stem cells in a clinical setting, cochlear implant users may be the first to benefit as the combined approach of using stem cells with implants may help to reduce the variability in clinical outcomes by improving the neural electrode interface. This will allow a greater number of patients to experience the benefit of cochlear implantation, thus allowing them to make a positive contribution to society. In addition, the implications for children are particularly significant, as improved implant performance may positively influence their learning and development through the conventional education system. With continued development of stem cell therapies for deafness, the future promises a wholly biological solution based around stem cells for sensorieural hearing loss.

The School of Biomedical Sciences at the University of Sheffield shares a number of strong links with the pharmaceutical industry. The development of a stem cell therapy which could be administered through the cochlea will be of particular interest to members of the industry who have experience in exploiting stem cells for clinical application. In addition, the project supervisor has a working relationship with a number of cochlear implant manufacturers around the world, who have exhibited great interest in the potential clinical application of stem cells in the auditory system, which could be employed alongside cochlear implants to improve patient outcomes. Hence, the industrial links which the department collectively possesses presents a means for any potential clinical applications to be fully exploited.

The National Health Service will also be a beneficiary from this research. The applicant of this fellowship will be trained in a number of complex in vitro and in vivo experimental techniques in addition to acquiring skills in statistical analysis. This will allow the fellow to continue building on the sound platform provided by this fellowship to continue in their training as an academic clinician. The addition of a fully trained academic ENT surgeon to the NHS workforce will allow patients to benefit from novel paradigms of treatment with a sound evidence base, which will add to the reputation of the NHS as a world leader in the provision of healthcare.