Bryony Nayagam in Laboratory
Bryony Nayagam in Laboratory
Dr Bryony Nayagam (nee Coleman)
http://www.findanexpert.unimelb.edu.au/researcher/person18963.html
The cochlear implant is able to electrically stimulate auditory neurons in the absence of sensory hair cells, however the auditory nerve continues to degenerate over time. The efficacy of this neural prosthesis is due, at least in part, to critical numbers of surviving auditory neurons in the deaf cochlea. Therefore, maintenance of the integrity and density of auditory neurons is essential for cochlear implant function and for emerging hair cell regenerative therapies to be advantageous. Stem cells are ideal candidates for cochlear cell based therapy, as they have the potential to provide replacement neurons to the degenerating auditory nerve.
Directed differentiation of stem cells into auditory neurons (and sensory neural progenitors) in vitro.
Transplantation of these differentiated neural progenitors into the deafened mammalian cochlea.
Collaborators
We have developed co-culture models as a means by which to direct the differentiation of stem cells toward an auditory neuron lineage. These models confer the advantage of providing the combination of cues required for differentiation, at biologically relevant concentrations. To date, these studies have demonstrated that the co-culture of stem cells with early postnatal organ of Corti explants, induces the formation of bipolar, neurofilament positive neurons over 11 days in vitro, in comparison to control treatments (Coleman et al., 2007 [1], Figure 1). We are currently examining the molecular similarity of these stem cell-derived neurons to auditory neurons in situ, with a view to their transplantation into the deafened mammalian cochlea, to replace degenerating endogenous neurons.
Figure 1. Stem cells can be differentiated into bipolar neurons in vitro Fluorescent photomicrograph depicts neurofilament (NFL) positive, differentiated stem cells, following co-culture with organ of Corti explants. This co-culture model resulted in the production of significantly higher numbers of NFL positive, bipolar neuron-like cells, in comparison to control treatments (p<0.001, ANOVA).
We previously demonstrated that stem cells pre-differentiated into neural precursors are capable of survival following delivery into the deaf cochlea. However, only small numbers of these transplanted cells could be detected within the target site 4 weeks post-transplantation (Coleman et al., 2006; Figure 2). Our current in vivo studies are directed towards the delivery of differentiated stem cells directly into the target site, using biocompatible matrices to limit their dispersal. The aim of these studies is to test whether exogenous neurons are capable of making functional connections in the deafened cochlear environment, and whether these are sufficient to improve hearing thresholds when combined with electrical stimulation.
Figure 1. Stem cell delivery into the deafened guinea pig cochlea (A) Stem cells were pre-differentiated into neural precursors (neurofilament positive), prior to delivery into the deafened guinea pig cochlea (B). Transverse section from a stem cell treated cochlea, labelled for neurofilament protein, illustrating transplanted stem cells retained neuron-specific protein expression for 4 weeks in vivo (arrowheads). (D) Transverse section from a control cochlea (vehicle alone) labelled for neurofilament protein; note the lack of neurofilament immunoreactivity and cells within the scala tympani.
The results from these studies will contribute important information to cell transplantation studies, by illustrating whether exogenous cells can connect anatomically and functionally with auditory neurons; a critical aspect to the success of cell based therapy for auditory nerve replacement and improved cochlear implant efficacy.
The National Health and Medical Research Council of Australia
The University of Melbourne
The Royal Victorian Eye and Ear Hospital
Please e-mail me to request a copy of these publications;
Coleman, B.,* Hardie, N.A., de Silva, M.G. and Shepherd, R.K. A protocol for cryoembedding the adult guinea pig cochlea for fluorescence immunohistology. J. Neurosci. Meth. 176(2): 144-151 (2009)Backhouse, S.**, Coleman, B.**, and Shepherd, R.K*. Surgical access to the mammalian cochlea for cell-based therapies. Experimental Neurology 214(2): 193-200 (2008)
Coleman, B.,* de Silva, M.G. and Shepherd, R.K. The potential of stem cells for auditory neuron generation and replacement. Stem Cells, 25(11): 2685-94 (2007) [3]Coleman, B*. The potential of stem cells for neuronal replacement in the deaf cochlea [PhD]. Department of Otolaryngology,
Coleman, B.*, Fallon, J., Gillespie, L., de Silva, M., Shepherd, R.K. Auditory hair cell explant co-cultures promote the differentiation of stem cells into bipolar neurons. Journal of Experimental Cell Research. 313:232-243 (2007) [1]
Coleman, B.,* Hardman, J., Coco, A., Epp, S., de Silva, M., Crook, J., Shepherd, R.K. Fate of embryonic stem cells transplanted into the deafened mammalian cochlea. Journal of Cell Transplantation. 15(5):369-380 (2006) Hildebrand, M., de Silva, M., Hardman, J., Coleman. B., Shepherd, R.K., Dahl, H*. Survival of stem cells following xenograft implantation into the adult guinea pig cochlea, JARO 6:341-354, (2006)
*corresponding author
**contributed equally
