Bone marrow mononuclear cells (BMMCs) are known to enhance recovery from ischemic insults by secreting angiogenic factors and inducing the expression of angiogenic factors from host tissues. Therefore, the transplantation of BMMCs is considered a potential approach to promoting the repair of ischemic damaged organs. Here, we investigated the influence of BMMCs on progressive hair cell degeneration after transient cochlear ischemia in gerbils. Transient cochlear ischemia was produced by extracranial occlusion of the bilateral vertebral arteries immediately before their entry into the transverse foramen of the cervical vertebra. An intravenous injection of BMMCs prevented ischemia-induced hair cell degeneration and ameliorated hearing impairment. A tracking study showed that BMMCs injected into the femoral vein were limited in the spiral artery of the cochlea, suggesting that, although transplanted BMMCs were retained within the spiral ganglion area of the cochlea, they were neither transdifferentiated into cochlear cells nor fused with the injured hair cells and supporting cells in the organ of Corti to restore their functions. We also showed that the protein level of neurotrophin-3 and glial cell line-derived neurotrophic factor in the organ of Corti was upregulated after treatment with BMMCs. These results suggested that BMMCs have therapeutic potential possibly through paracrine effects. Thus, we propose the use of BMMCs as a potential new therapeutic strategy for hearing loss.
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