Posttranslational modification of histones alters their interaction with DNA and nuclear proteins, influencing gene expression and cell fate. In this study, we investigated the effect of G9a (KMT1C, EHMT2), a major histone lysine methyltransferase encoded by the human EHMT2 gene and responsible for histone H3 lysine 9 dimethylation (H3K9me2) on noise-induced permanent hearing loss (NIHL) in adult CBA/J mice. The conditions of noise exposure used in this study led to losses of cochlear synapses and outer hair cells (OHCs) and permanent auditory threshold shifts. Inhibition of G9a with its specific inhibitor BIX 01294 or with siRNA significantly attenuated these pathological features. Treatment with BIX 01294 also prevented the noise-induced decrease of KCNQ4 immunolabeling in OHCs. Additionally, G9a was increased in cochlear cells, including both outer and inner sensory hair cells, some spiral ganglion neurons (SGNs), and marginal cells, 1 h after the completion of the noise exposure. Also subsequent to noise exposure, immunoreactivity for H3K9me2 appeared in some nuclei of OHCs following a high-to-low frequency gradient with more labeled OHCs in the 45-kHz than the 32-kHz region, as well as in the marginal cells and in some SGNs of the basal turn. These findings suggest that epigenetic modifications of H3K9me2 are involved in NIHL and that pharmacological targeting of G9a may offer a strategy for protection against cochlear synaptopathy and NIHL.
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The research project described was supported by grant R01 DC009222 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health. This work was conducted in the WR Building at MUSC in renovated space supported by grant C06 RR014516. Animals were housed in MUSC CRI animal facilities supported by grant C06 RR015455 from the Extramural Research Facilities Program of the National Center for Research Resources. We thank Dr. Jochen Schacht for his valuable comments on the manuscript. We also thank Dr. Yuan Shao in the MUSC Biorepository & Tissue Analysis Shared Resource for technical assistance with cochlear paraffin sections and Andra Talaska for proofreading of the manuscript.
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All research protocols were approved by the Institutional Animal Care & Use Committee at the Medical University of South Carolina. Animal care was under the supervision of Division of Laboratory Animal Resources at MUSC.
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Xiong, H., Long, H., Pan, S. et al. Inhibition of Histone Methyltransferase G9a Attenuates Noise-Induced Cochlear Synaptopathy and Hearing Loss. JARO 20, 217–232 (2019). https://doi.org/10.1007/s10162-019-00714-6
- noise-induced hair cell loss
- lysine methyltransferase G9a
- epigenetic modification
- cochlear synapses
- protection of noise-induced hearing loss