Generation Of Functional Peripheral Neurons From Olfactory Neural Precursor Cells

Hearing impairment is one of the most common disabilities in the modern era, affecting 250 million people worldwide. Hearing depends largely on hair cells(HCs) and their associated spiral ganglion neurons (SGNs), and defects in these cells produce permanent deafness. The cochlear sensory epithelium and its associated neural components do not, in mammals, regenerate or repair naturally following severe injury. As functional recovery by innate regeneration is thus not possible, the development of therapeutic techniques that were able to replace damaged cells and thus to restore inner ear function would represent a considerable advance in the treatment of deafness.Recent studies have revealed the potential of cell transplantation for the treatment of inner ear diseases. When implanted in the inner ear, embryonic tissue, neural stem cells (NSCs) and ESCs can survive, migrate toward afferent neurons, and generate neurite projections. However, although morphological and immunohistochemical analyses show that the implanted cells in these studies resemble neurons, no physiological information has been obtained that would identify these cells as functional neurons. In addition, it is not clear whether the cochlea of adults is able to provide the necessary extracellular microenvironment needed to drive these neuron-like cells through the developmental stages that would be required to generate functional afferent neurons and hair cells. Since the ultimate goal of this group of studies is to restore hearing in patients, it is of key importance to assess the function of implanted cells.Aim: The objective of the present study was to induce the differentiation of NPCs towards functional auditory-neuron-like cells, using an established coculture model in vitro to mimic, as closely as possible, the developing cochlear environment.Methods: We undertook to direct the differentiation of NPCs derived from the olfactory bulb in vitro, using established co-culture models.Result: Differentiated NPCs were immunolabeled for peripheral neuron markers. RT-PCR assays also indicated expression of peripheral neuron marker transcripts. Over a period of four weeks in culture, differentiated neuron-like cells showed a number of electrophysiological properties and gradually developed into mature cells compared with SGNs. After two weeks, the newly differentiated neurons also expressed functional ionotropic glutamate receptors.Conclusion: These results demonstrated that NPCs from the olfactory bulb can differentiate into functional auditory neuron-like cells, and thus may potentially provide a source of replacement neurons for repair of the deafened mammalian cochlea.