Loss of hair cells in the inner ear is thought to be the primary mechanism behind the progression of age-related hearing loss, though there is some debate over whether it is in fact loss of cells versus loss of the connections that link hair cells to the brain. For some years, the research community has investigated whether or not it is possible to generate new hair cells in a living animal, bypassing the usual inability to replace losses in this cell population. Various approaches to signaling and cell therapy have been attempted, but despite interesting technology demonstrations, there is as yet little progress towards clinical translation of this research.
Various mechanisms can cause sensorineural hearing loss, among which irreversible damage to inner ear hair cells is the main cause. Although the commonly used hearing aids and cochlear implants in clinical practice improve the hearing of patients, their effect depends on the quantity and quality of residual hair cells and spiral neurons. Therefore, the ideal way to treat sensorineural hearing loss is to regenerate hair cells, through the use of stem cells to repair the structure and function of the cochlea, so as to fundamentally restore hearing.
Stem cell therapy in the auditory field has been a research hotspot in recent years. Although some progress has been made, almost all are results at the animal level, and there is still a long way to go before clinical transformation. The microenvironment of inner ear stem cells and the interaction with neighboring cells are very important for inner ear stem cells or sensory precursor cells to induce differentiation into mature inner ear hair cells. In the reported studies, the efficiency of differentiation of inner ear stem cells or sensory precursor cells into hair cells is still low. An insufficient number of new hair cells, immature new hair cells without the function of mature hair cells, and long-term survival of new hair cells are all key problems and difficulties that need to be solved urgently.
These results indicate that it is more difficult to regulate a single signal pathway to regenerate functional hair cells, and it may require coordinated regulation of multiple genes to effectively promote hair cell regeneration and the functional maturity and survival of new hair cells. Still, inducing the committed differentiation of stem cells into hair cells or nerve cells, the exploration of the methods of stem cell transplantation into the inner ear, and the safety research of stem cell transplantation have collectively laid the foundation for the transplantation of stem cells in vivo.