Cochlear Non-Sensory Cells
The mammalian inner ear contains the auditory organ, which is composed of sensory hair cells, non-sensory supporting epithelial cells, and spiral ganglion neurons. The hair cells are responsible for sensing acoustic stimuli, whereas the non-sensory supporting cells have been considered to play a mainly supporting role for hair cell function. However, recent studies indicate that cochlear non-sensory cells play multiple roles, which are all critical for hearing. They actively participate in cochlear development, cell-cell signaling, regulation of hair cell activity, active cochlear mechanics and endocochlear potential generation.
Moreover, cochlear non-sensory cells are a major target for deafness gene mutations. In particular, mutations of the GJB2 gap junction gene are responsible for >50% of hereditary nonsyndromic hearing loss. In the inner ear, the proteins encoded by GJB2 and other gap junction genes, i.e. the connexins, are expressed in non-sensory cells and spiral ganglion neurons, but not in hair cells.
In addition, cochlear supporting cells also have a potential to differentiate into hair cells and play an important role in the hair cell regeneration. Recent studies also suggest that spiral ganglion neurons and their cochlear synapses are a major target for noise-induced hearing loss. It has been found that short-term noise exposure can cause degeneration of synapses between auditory nerves and hair cells even the hair cells still function normally, thereby inducing “hidden” hearing loss. The same pathological mechanism may also underlie the age-related hearing loss.
Hair Transplantation and Therapy