Abstract
Acoustic trauma, one of the leading causes of sensorineural hearing loss, induces sensory hair cell damage in the cochlea. Identifying the molecular mechanisms involved in regulating sensory hair cell death is critical towards developing effective treatments for preventing hair cell damage. Recently, microRNAs (miRNAs) have been shown to participate in the regulatory mechanisms of inner ear development and homeostasis. However, their involvement in cochlear sensory cell degeneration following acoustic trauma is unknown. Here, we profiled the expression pattern of miRNAs in the cochlear sensory epithelium, defined miRNA responses to acoustic overstimulation, and explored potential mRNA targets of miRNAs that may be responsible for the stress responses of the cochlea. Expression analysis of miRNAs in the cochlear sensory epithelium revealed constitutive expression of 176 miRNAs, many of which have not been previously reported in cochlear tissue. Exposure to intense noise caused significant threshold shift and apoptotic activity in the cochleae. Gene expression analysis of noise-traumatized cochleae revealed time-dependent transcriptional changes in the expression of miRNAs. Target prediction analysis revealed potential target genes of the significantly downregulated miRNAs, many of which had cell death- and apoptosis-related functions. Verification of the predicted targets revealed a significant upregulation of Taok1, a target of miRNA-183. Moreover, inhibition of miR-183 with morpholino antisense oligos in cochlear organotypic cultures revealed a negative correlation between the expression levels of miR-183 and Taok1, suggesting the presence of a miR-183/Taok1 target pair. Together, miRNA profiling as well as the target analysis and validation suggest the involvement of miRNAs in the regulation of the degenerative process of the cochlea following acoustic overstimulation. The miR-183/Taok1 target pair is likely to play a role in this regulatory process.
Highlights
The loss of sensory cells in the cochlea due to acoustic overstimulation is irreversible because these cells are completely differentiated and do not regenerate once they die
We screened the expression of 378 miRNAs using quantitative real time PCR array
The remaining miRNAs had diverse expression levels and their DCT values ranged from 3.2 to 13.3. These results revealed the constitutive expression of miRNAs in the cochlear sensory epithelium
Summary
The loss of sensory cells in the cochlea due to acoustic overstimulation is irreversible because these cells are completely differentiated and do not regenerate once they die. To prevent hair cell loss from occurring, understanding the molecular mechanisms involved in regulating the sensory cell death associated with acoustic trauma is critical for the development of effective treatments. Acoustic overstimulation induces sensory cell degeneration via complex pathways with apoptotic and necrotic phenotypes [6,7,8,9,10,11,12]. Multiple apoptosis-related proteins have been identified during noise-induced sensory cell degeneration [13,14,15,16,17,18,19]. Transcriptional changes in apoptosis-related genes have been found following acoustic trauma [20]. These observations illustrate the complexity of cochlear responses to acoustic trauma. The molecular mechanisms responsible for the changes in the expression of these genes are not clear
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