Exosomes mediate sensory hair cell protection in the inner ear
Andrew M. Breglio, … , Matthew J.A. Wood, Lisa L. Cunningham
Andrew M. Breglio, … , Matthew J.A. Wood, Lisa L. Cunningham
Published February 6, 2020
Citation Information: J Clin Invest. 2020;130(5):2657-2672. https://doi.org/10.1172/JCI128867.
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Exosomes mediate sensory hair cell protection in the inner ear

Abstract

Hair cells, the mechanosensory receptors of the inner ear, are responsible for hearing and balance. Hair cell death and consequent hearing loss are common results of treatment with ototoxic drugs, including the widely used aminoglycoside antibiotics. Induction of heat shock proteins (HSPs) confers protection against aminoglycoside-induced hair cell death via paracrine signaling that requires extracellular heat shock 70-kDa protein (HSP70). We investigated the mechanisms underlying this non–cell-autonomous protective signaling in the inner ear. In response to heat stress, inner ear tissue releases exosomes that carry HSP70 in addition to canonical exosome markers and other proteins. Isolated exosomes from heat-shocked utricles were sufficient to improve survival of hair cells exposed to the aminoglycoside antibiotic neomycin, whereas inhibition or depletion of exosomes from the extracellular environment abolished the protective effect of heat shock. Hair cell–specific expression of the known HSP70 receptor TLR4 was required for the protective effect of exosomes, and exosomal HSP70 interacted with TLR4 on hair cells. Our results indicate that exosomes are a previously undescribed mechanism of intercellular communication in the inner ear that can mediate nonautonomous hair cell survival. Exosomes may hold potential as nanocarriers for delivery of therapeutics against hearing loss.

Authors

Andrew M. Breglio, Lindsey A. May, Melanie Barzik, Nora C. Welsh, Shimon P. Francis, Tucker Q. Costain, Lizhen Wang, D. Eric Anderson, Ronald S. Petralia, Ya-Xian Wang, Thomas B. Friedman, Matthew J.A. Wood, Lisa L. Cunningham

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Figure 4

Isolated exosomes protect against neomycin-induced hair cell death.

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Isolated exosomes protect against neomycin-induced hair cell death. Utri...
Utricles were cultured for 24 hours in neomycin, with or without the addition of exosomes isolated from heat-shocked utricles. (A) Exosomes and the non-exosomal fraction (supernatant) were purified from utricle-conditioned media using differential ultracentrifugation (see Figure 2B) and applied to neomycin-treated utricles. (B) Fixed utricles were labeled with the hair cell marker myosin 7a, and images were acquired using laser scanning confocal microscopy. Representative z sections from surface preparations of utricle whole mounts are shown. Scale bar: 20 μm. (C) Neomycin caused hair cell death. Application of isolated exosomes significantly improved hair cell survival. In contrast, no protective effect was observed when the non-exosomal fraction (i.e., exosome-depleted conditioned media) was added. Each data point represents the average hair cell density of an individual utricle. n = 16–20 utricles per condition from 4 independent experiments. Data indicate the mean ± SEM. ***P < 0.001 and ****P < 0.0001, by Brown-Forsythe and Welsh ANOVA followed by Dunnett’s T3 multiple comparisons test.