3d ultrastructural analysis of the subcellular organisation of inner hair cells and of their innervation during ageing.
Lead Research Organisation:
Birkbeck, University of London
Department Name: Biological Sciences
Abstract
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Technical Summary
Hearing deteriorates progressively with age. Recent work has suggested that a major contributory factor is a slowly progressive, systematic loss, beginning early in life, of the afferent terminals that normally surround each inner hair cell (IHC) in the mammalian cochlea. The main aim of this project is to undertake a comprehensive 3D, ultrastructural analysis of the age-related changes to the intracellular organisation and synaptic machinery of IHC and their relationship to the progressive loss and re-organisation of the afferent and efferent terminals that occurs over the life of the animal.
In our current BBSRC-supported project, we have applied two techniques to explore the 3D structural organisation of IHCs and their innervation. We have been able to define the distribution of afferent terminals in unprecedented detail and have revealed a previously unrecognised organisation of the infranuclear region of the IHC, comprising of a network of intracellular membranes, mitochondria and associated vesicles that appears to be related to the distribution of ribbon synapses and afferent terminals. Preliminary work from our laboratory has suggested that this network may deteriorate with age. We now propose to use these techniques, serial block face scanning electron microscopy (SBF-SEM) and electron tomography to detail the progression of structural changes and re-organisations at the IHC and its innervation that occur with ageing. We shall use two different strains of mouse, one which retains good hearing for at least 2 years, and one that is used as a model of early onset hearing loss. We also propose to develop and apply a further technique for 3D electron microscopy, array tomography, which has the advantage of enabling multiple imaging of the same section series at different magnifications.
The project will provide a detailed understanding of the cellular basis of age-related deterioration of hearing.
In our current BBSRC-supported project, we have applied two techniques to explore the 3D structural organisation of IHCs and their innervation. We have been able to define the distribution of afferent terminals in unprecedented detail and have revealed a previously unrecognised organisation of the infranuclear region of the IHC, comprising of a network of intracellular membranes, mitochondria and associated vesicles that appears to be related to the distribution of ribbon synapses and afferent terminals. Preliminary work from our laboratory has suggested that this network may deteriorate with age. We now propose to use these techniques, serial block face scanning electron microscopy (SBF-SEM) and electron tomography to detail the progression of structural changes and re-organisations at the IHC and its innervation that occur with ageing. We shall use two different strains of mouse, one which retains good hearing for at least 2 years, and one that is used as a model of early onset hearing loss. We also propose to develop and apply a further technique for 3D electron microscopy, array tomography, which has the advantage of enabling multiple imaging of the same section series at different magnifications.
The project will provide a detailed understanding of the cellular basis of age-related deterioration of hearing.
Planned Impact
Who will benefit?
1. People with age-related hearing loss
2. Clinical professionals
3. UK and other companies producing cochlear prostheses
4. The wider public
How will they benefit?
Age-related hearing loss (ARHL) is a major disabling condition, affecting the quality of life of elderly people. More than 70% of people over retirement age have hearing loss sufficient to impair normal communication. By contributing to a detailed understanding of the subtle pathologies of hair cells in the earliest stage of progressive ARHL this project will lay foundations for addressing the fundamental bases of auditory deficits. Thus, in the longer term the project will contribute to determining potential pharmaceutical targets of intervention or other means to alleviate these conditions, thereby improving the quality of life for elderly people, and relieving the economic and social burden that they impose, with benefits to the wider public.
In the shorter term, the results of the project will be beneficial clinically in enabling doctors and health workers to inform their patients better about the nature of their disease. The close association of the Ear Institute with the Royal National Throat Nose and Ear hospital provides a conduit for bringing the results of the scientific research to the attention of the clinical community. Professors Forge and Ashmore have professional relationships with this group and are regular speakers to interested professional and patient groups about their research. Companies producing cochlear implants, devices inserted into a deaf ear that can partially restore hearing, are also interested in the fundamental bases of cochlear pathologies that disturb auditory function. This knowledge enables improvements in auditory signal processing strategies to overcome the deficits and widen the candidature for implantation including to those with ARHL. We are already working with one such company to explore preservation of residual hearing after implantation and have contacts with others. These relationships afford opportunities for direct knowledge transfer.
The project will also have impact more widely in cell and structural biology. 3D ultrastructural analysis techniques have not been widely applied and the methods and procedures developed in this project will provide protocols for more widespread application of the emerging technologies, in particular for array tomography which has the potential for more routine application.
The project will also provide an opportunity to retain a talented young scientist with unique skills, Dr Bullen the researcher co-investigator on this application, in the field of auditory research where there is a shortage of young investigators. It will enable her to begin to establish her independent research career, and to cement mutually beneficial collaborations with other laboratories working in related fields. In addition, the project affords opportunities for training in the use of software for manipulation of large data sets which will be exploited through work experience placement of school students and summer studentships for undergraduates and others in established programmes at the Ear Institute and the department at Birkbeck College.
It is important that the results of the work are communicated to the general public. As President of the Physiological Society Prof Ashmore has a remit in communication of science to the public. Dr Moores has a proven track-record of public communication of science. She was the 2006 winner of the prestigious DeMontfort medal for science communication (SET for Britain). Prof Forge and Prof Ashmore have given interviews about hearing and deafness to BBC radio and are regularly involved in presenting their work at events organised by hearing research charities, to whom they also act as advisers. Similar means of communication, with Dr Bullen involved, will be developed during the course of project.
1. People with age-related hearing loss
2. Clinical professionals
3. UK and other companies producing cochlear prostheses
4. The wider public
How will they benefit?
Age-related hearing loss (ARHL) is a major disabling condition, affecting the quality of life of elderly people. More than 70% of people over retirement age have hearing loss sufficient to impair normal communication. By contributing to a detailed understanding of the subtle pathologies of hair cells in the earliest stage of progressive ARHL this project will lay foundations for addressing the fundamental bases of auditory deficits. Thus, in the longer term the project will contribute to determining potential pharmaceutical targets of intervention or other means to alleviate these conditions, thereby improving the quality of life for elderly people, and relieving the economic and social burden that they impose, with benefits to the wider public.
In the shorter term, the results of the project will be beneficial clinically in enabling doctors and health workers to inform their patients better about the nature of their disease. The close association of the Ear Institute with the Royal National Throat Nose and Ear hospital provides a conduit for bringing the results of the scientific research to the attention of the clinical community. Professors Forge and Ashmore have professional relationships with this group and are regular speakers to interested professional and patient groups about their research. Companies producing cochlear implants, devices inserted into a deaf ear that can partially restore hearing, are also interested in the fundamental bases of cochlear pathologies that disturb auditory function. This knowledge enables improvements in auditory signal processing strategies to overcome the deficits and widen the candidature for implantation including to those with ARHL. We are already working with one such company to explore preservation of residual hearing after implantation and have contacts with others. These relationships afford opportunities for direct knowledge transfer.
The project will also have impact more widely in cell and structural biology. 3D ultrastructural analysis techniques have not been widely applied and the methods and procedures developed in this project will provide protocols for more widespread application of the emerging technologies, in particular for array tomography which has the potential for more routine application.
The project will also provide an opportunity to retain a talented young scientist with unique skills, Dr Bullen the researcher co-investigator on this application, in the field of auditory research where there is a shortage of young investigators. It will enable her to begin to establish her independent research career, and to cement mutually beneficial collaborations with other laboratories working in related fields. In addition, the project affords opportunities for training in the use of software for manipulation of large data sets which will be exploited through work experience placement of school students and summer studentships for undergraduates and others in established programmes at the Ear Institute and the department at Birkbeck College.
It is important that the results of the work are communicated to the general public. As President of the Physiological Society Prof Ashmore has a remit in communication of science to the public. Dr Moores has a proven track-record of public communication of science. She was the 2006 winner of the prestigious DeMontfort medal for science communication (SET for Britain). Prof Forge and Prof Ashmore have given interviews about hearing and deafness to BBC radio and are regularly involved in presenting their work at events organised by hearing research charities, to whom they also act as advisers. Similar means of communication, with Dr Bullen involved, will be developed during the course of project.
People |
ORCID iD |
| Carolyn Moores (Principal Investigator) |
Publications
Bullen A
(2015)
Association of intracellular and synaptic organization in cochlear inner hair cells revealed by 3D electron microscopy.
in Journal of cell science
Taylor R
(2015)
Absence of plastin 1 causes abnormal maintenance of hair cell stereocilia and a moderate form of hearing loss in mice.
in Human molecular genetics
| Description | We have been developing further 3D electron microscopy techniques to examine the cellular architecture of cells in the normal, aged and noise-damaged cochlea. Studies to date have concentrated on two features in different hair cell types: the mitochondrial arrangements of outer hair cells (OHC), and the effects of noise and ageing on inner hair cells (IHC) in a mouse model of 'hidden hearing loss'. Cochleae from normal gerbils and mice, from mice exposed to noise and from aged mice have been examined. The auditory status of the animals whose cochleae have been examined has been assessed by recording of Auditory Brainstem Responses (ABR) to enable evaluation of structure-function relationships. ABRs have been recorded from the animals that have been exposed to noise, before exposure, immediately after and at 4 weeks after when auditory thresholds have returned to normal; and serially in the ageing mice; every 3 months from 3 months, to (to date) 18 months of age, with some mice from the colony taken for examination of the cochleae by electron microscopy every 6 months. Electron Tomography (ET), Serial Block Face Scanning Electron Microscopy (SBF-SEM) or array tomography have been applied to examine the cochleae from these animals. The development of the use of array tomography and SBF-SEM has been performed in collaboration with, and with support from JEOL, the electron microscope manufacturer. This collaboration has resulted in a publication in the industry magazine. Data was analysed by semi-manual reconstruction and stereological methods that have been developed in-house. Analysis of the size, shape and distribution of mitochondria in outer hair cells, which complements our published work on the inner hair cell (IHC) revealed relationships between mitochondrial shape and location and indicated that a connection between spatial arrangements and varying morphologies of mitochondria are present across species. This indicates structural organisations crucial to the normal functioning of OHCs. In IHCs, 3D electron microscopy showed the distribution of damaged and healthy terminals around the baso-lateral membrane of IHCs in the noise-damaged region, as well as synaptic densities and ribbon synapses in the regions of damaged synapses. Changes to the intracellular contents of the IHC were also observed. Comparison of the cytoplasmic regions surrounding healthy and damaged synapses on the same cells indicated changes to cellular structures and organelles in the regions local to the synapses. The results indicate that when synapses are lost after noise damage, concomitant changes occur in the inner hair cells. These changes may occur both at regions close to the synapse and in more distant parts of the cell. The results also suggest that synaptic ribbons and synaptic densities may persist for some time after degradation of the afferent terminal. |
| Exploitation Route | Our findings will assist in defining the pathologies underlying "hidden hearing loss" and contribute to efforts to find the appropriate therapies that might alleviate the condition. |
| Sectors | Digital/Communication/Information Technologies (including Software),Healthcare,Pharmaceuticals and Medical Biotechnology |