Abstract
Recent studies have identified sex-differences in auditory physiology and in the susceptibility to noise-induced hearing loss (NIHL). We hypothesize that 17β-estradiol (E2), a known modulator of auditory physiology, may underpin sex-differences in the response to noise trauma. Here, we gonadectomized B6CBAF1/J mice and used a combination of electrophysiological and histological techniques to study the effects of estrogen replacement on peripheral auditory physiology in the absence of noise exposure and on protection from NIHL. Functional analysis of auditory physiology in gonadectomized female mice revealed that E2-treatment modulated the peripheral response to sound in the absence of changes to the endocochlear potential compared to vehicle-treatment. E2-replacement in gonadectomized female mice protected against hearing loss following permanent threshold shift (PTS)- and temporary threshold shift (TTS)-inducing noise exposures. Histological analysis of the cochlear tissue revealed that E2-replacement mitigated outer hair cell loss and cochlear synaptopathy following noise exposure compared to vehicle-treatment. Lastly, using fluorescent in situ hybridization, we demonstrate co-localization of estrogen receptor-2 with type-1C, high threshold spiral ganglion neurons, suggesting that the observed protection from cochlear synaptopathy may occur through E2-mediated preservation of these neurons. Taken together, these data indicate the estrogen signaling pathways may be harnessed for the prevention and treatment of NIHL.
Highlights
Disabling hearing loss afflicts nearly half a billion people worldwide
We demonstrate that estrogen replacement in gonadectomized female mice reduces auditory threshold shifts following both a permanent threshold shift (PTS)-inducing and temporary threshold shift (TTS)-inducing noise exposure
We show that surgical gonadectomy increases, and estrogen replacement decreases, outer hair cells (OHCs) loss and cochlear synaptopathy
Summary
Disabling hearing loss afflicts nearly half a billion people worldwide. Noise-induced hearing loss (NIHL)—a form of acquired hearing loss—comprises a significant portion of this global burden, and its incidence is expected to increase [1,2]. Estrogen receptor-β (estrogen receptor 2 or ESR2) knockout (KO) mice of both sexes are more susceptible to TTS-inducing noise exposures than their wildtype littermate controls, while female ESR2 KO mice display early onset age-related hearing loss (ARHL) [22,23]. Both findings suggest that this protective effect may be, at least in part, mediated via ESR2-signaling.
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