Expression of Hypoxia-Inducible Factor in the Inner Ear of Noise-Exposed Mouse

Shin, Jung Eun; Kang, Hun Hee; Chung, Jong Woo

Abstract

BACKGROUND AND OBJECTIVES
Investigations regarding the mechanisms of noise-induced hearing loss have suggested that noise exposure induces tissue ischemia, and damages the inner ear. The hypoxia-inducible factor (HIF), a helix-loop-helix PAS transcription factor, is known to prevent hypoxic cell damage in the brain in cases of ischemic attacks. Like the role it plays in the brain, there is a possibility that HIF could be found in the inner ear playing the similar role. MATERIALS AND METHOD: We used 23 (46 ears) BALB/c mice with normal Preyer's reflex to investigate the effect of the noise-induced hearing loss. Hearing threshold was measured by ABR before and after exposing mice to 120 dB SPL broad band white noise 3 hours daily for 5 consecutive days. And after 1 month, the hearing threshold was rechecked to assure the permanent threshold shift. Cochlea were collected for the histological study and the expression of HIF was observed. RESULTS: Control mice showed hearing level of 27.5+/-1.7 dB (mean+/-SD), which was changed to 80.5+/-2.1 dB immediately after 5-day of exposure to noise, and 79.5+/- 2.5 dB after 1 month of noise exposure. For all noise exposed mice, the damage to the outer hair cell and the Organ of Corti was noticeable. HIF was expressed in the spiral limbus, few supporting cells, stria vascularis and spiral ganglion cells of the noise exposed mouse. CONCLUSION: Noise, a form of acoustic trauma to the inner ear, induced damage to the outer hair cells in mice. At the same time, HIF were expressed in all of the studied animals. The possibility of HIF playing a role of protecting the inner ear from the acoustic trauma as it does in the brain should be investigated further.