Hypothetical outcome and obstacles
Is it necessary, in the interest of functional repair of the
damaged cochlea, to create specific hair-cell subtypes? We
suggest that the recovery of function might be possible
without the complete replacement of the cochlear architecture.
Any cell that is capable of efficiently transacting
mechanical stimulation and of relaying the stimulus information
to an afferent neuron could function as a replacement
for the repair of damaged cochleae. The potential
benefits of a limited replacement of hair-cell function
cannot currently be assessed; nevertheless, the success of
cochlear implants is an encouraging result, suggesting
that any generation of an electrical signal in response
to mechanical stimulation might partially restore basic
sound perception [48]. The first-generation cochlear
implants of the late 1970 s and early 1980 s used a single channel
electrode that provided electrical stimulation of
the acoustic nerve. Current devices feed the electrical
stimulation to several channels at different sites, mimicking
the tonotopic organization of sound along the longitudinal
axis of the cochlea. Replacing lost hair cells with
stem-cell-derived hair cells along the tonotopic map of the
cochlea might also suffice to restore basic cochlear functions
even without matching the hair-cell phenotype to its
location. It might not be feasible to recreate the delicate
and complex structure of the organ of Corti. A possible
solution could be to replace the lost organ of Corti with a
continuous sheet of ‘generic’ hair cells, similar to the
organization of the avian basilar papilla (Figure 2). Such
an epithelium of hair cells and supporting cells might be
more similar to the sensory epithelia that are found in the
inner ear of non-mammalian vertebrates. An important
aspect of such a sheet of hair cells would be that the cells
could provide trophic support for auditory neurons, for
example, in the form of secreted neurotrophic factors. The
resulting sustenance of auditory neurons could, in turn,
enhance the performance of co-implanted cochlear implants.