High Doses of Radiation Cause Cochlear Immunological Stress and Sensorineural Hearing Loss

Abstract

Radiotherapy is a crucial treatment for head and neck malignancies, but it usually leads to sensorineural hearing loss (SNHL). Changes in the immune microenvironment and sensorial neuroepithelium of the inner ear after radiation exposure remain poorly understood. This study investigated cochlear morphology and macrophages in the inner ear after high-dose irradiation. The heads of 8-week-old Cx3cr1GFP/+ heterozygous male mice were irradiated with 30Gy X-rays and biological samples were taken on the 1st, 7th, and 10th days after irradiation. Auditory brainstem responses were used to assess auditory function in mice. The changes of basal membrane hair cells, spiral ganglion (SGN), and inner ear macrophages were observed using hematoxylin-eosin (HE) staining and immunofluorescence staining. The expression of inflammatory mediators in the inner ear was detected by reverse transcription-polymerase chain reaction (RT-PCR) in cochlear tissue. As a result, there was no significant hair cell loss after high doses of radiation, but the mice developed full-frequency hearing loss on day 10 when HE staining revealed SGN atrophy and immunofluorescence revealed decreased neurofilament expression. The number of macrophages in the inner ear decreased over time. RT-PCR showed that cochlear inflammatory factors and chemokines were briefly up-regulated on the first day after irradiation and then decreased over time. In summary, high-dose irradiation causes acute SNHL that does not involve hair cell loss and may be associated with SGN changes. Radiation-induced SNHL is accompanied by a reduction in cochlear macrophages and changes in the immune microenvironment, but the relationship between the two has yet to be explored.