Endogenous SIRT3 activity is dispensable for normal hearing recovery after noise exposure in young adult mice

Abstract

Occupational noise-induced hearing loss (NIHL) affects millions of people worldwide and presents a large social and personal burden. Some genetic variants in the mitochondrial oxidative stress response correlate strongly with susceptibility to NIHL in both humans and mice. Here we test the hypothesis that SIRT3, a regulator of the mitochondrial oxidative stress response, is required in mice for endogenous recovery of auditory thresholds after a sub-traumatic noise exposure. We expose homozygous Sirt3-KO mice and their wild-type littermates to a noise dose that confers a temporary threshold shift, but is not sufficient to permanently reduce cochlear function, compromise cell survival, or damage synaptic structures. We find no difference in hearing function after recovery from noise exposure between the two genotypes, when measured by either auditory brainstem response (ABR) or distortion product otoacoustic emissions (DPOAE). We show that SIRT3-specific immunoreactivity is present in outer hair cells, around the post-synaptic regions of inner hair cells, and faintly within inner hair cells. Nonetheless, outer hair cells and auditory synapses show no increase in loss after noise exposure in the homozygous Sirt3-KO mouse. These data show that SIRT3-dependent processes are not necessary for endogenous hearing recovery after a single, sub-traumatic noise exposure. They demonstrate the existence of cellular mechanisms of cochlear homeostasis in addition to the mitochondrial oxidative stress response. We also present a novel statistical analysis for identifying differences between peak 1 amplitude progressions in ABR waveforms.