|LETTER TO EDITOR
|Year : 2013 | Volume
| Issue : 2 | Page : 92-93
Stem cells in otology: A message 'loud and clear'
Department of Internal Medicine, Princess Durru Shehvar Children's and General Hospital, Hyderabad, Andhra Pradesh, India
|Date of Web Publication||15-Jun-2013|
Department of Internal Medicine, Princess Durru Shehvar Children's and General Hospital, Hyderabad, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Gude D. Stem cells in otology: A message 'loud and clear'. Indian J Otol 2013;19:92-3
Sensory neural hearing loss and vestibular dysfunction affect millions of people depriving off their communication and quality of life. The limited regenerative capacity of the inner ear hair cells cripples our attempts at restoration of sensory neural hearing loss and vestibular dysfunction. Loss of hair cells secondary to injury, disease, or genetic mutation; leads to permanent sensory deficits. Transplantation with stem cells augments the repair of tissues by replacing damaged cells and/or by secreting factors that enhance their survival or repair. Transfer of genes responsible for hair cell genesis is also another important option that is being looked at.
Fibrocyte degeneration is an important determinant of presbycusis. Loss of fibrocytes and breakdown of potassium recycling may lead to other degenerative changes in the cochlea, including hair cell and spiral ganglion cell loss. Transplanting fibrocytes (via the easily accessible cochlea's lateral wall) or reversing their degeneration could prevent the progression of presbycusis in some forms of metabolic hearing loss.  Transplantation of autologous mesenchymal stem cells from bone marrow in to inner ear has been found to accelerate natural repair from ototoxic insults. Multiple delivery routes for stem cell transplantation such as cochlear, intravenous, and vestibular injections have been tried with varying successes.
A set of transcription factors to enhance the generation of inducible pluripotent stem (iPS) cells and a second set to initiate the differentiation of hair cells has been proposed. MicroRNAs may be of great importance in regulating both iPS cell formation and differentiation to reprogram cells into hair cells.  Transcriptional regulation of p27 kipl and specific transcription factors such as basic helix-loop-helix transcription factor Math1, Brn3c and Gfil play significant roles in hair cell maintenance and consequent survival. 
In experimental models, intravenous transfusion of umbilical cord blood mesenchymal stem cells have shown to enhance hearing thresholds, outer hair cells, and increase the number of spiral ganglion neurons; restoring hearing in sensorineural hearing loss (SNHL).  Also in a study, embryonic stem cells transplanted into the scala tympani could migrate in the aminoglycoside-affected-cochlea and partly restore the structure of sensory epithelia of the inner ear.  In a noise-induced ototoxicity animal model, stem cell transplantation resulted in survival and integration of these cells into suprastrial regions of the spiral ligament which significantly ameliorated permanent auditory brainstem response (ABR) threshold shift for click stimuli. 
Co-culture between inner ear stem cell spheres (which have potential to bear hair cell markers) and the neonatal organ of corti, can help evaluate and potentially optimize transplantation of inner ear stem cells into the cochlea for hair cell regeneration. 
Transplantation of adult human olfactory mucosa-derived stem cells have proved to help in preserving the auditory function (significantly improve ABR) during early onset progressive SNHL.  Mesenchymal stem cells show extensive integration after injection directly into cochlear tissues. A population of human fetal auditory stem cells has been recently isolated and may be of great efficacy in tackling the difficulties associated with cochlear stem cell purification, expansion, and maintenance.  The efficacy of cochlear implants can also be augmented by replacing the dying cells with new neurons derived from stem cells (apart from the use of neurotrophins).
Stem cells have a promising future in restoration of hearing impairment of various causes and it is only a matter of short while that the gap between research abodes and practicing clinics is abridged.
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