The proposed studies address a significant health issue, the high incidence of acquired deafness from noise overstimulation that can result from recreational and workplace-related activities and from service in the military. Activation of the classic stress response by up-regulation of heat shock proteins (Hsps) has been very effective in protecting the inner ear from noise induced hearing loss in animal models. However, a major roadblock to clinical applicability is the lack of an appropriate method to induce the heat shock response in the inner ear in humans. We propose two parallel approaches to further evaluate the heat shock response as a protective strategy against noise trauma in the cochlea and move closer to an efficient therapeutic method. In one approach, we will exploit the findings of a recent screen for molecules that activate HSF1, the transcription factor that is the master regulator of the heat shock response. This screen identified a compound (HSF1A) that efficiently activates the pre-existing pool of HSF1 and results in up-regulation of target Hsp genes. This HSF1 activation reduces the levels of protein damage and cytotoxicity in cultured cell and fly models of neurodegenerative disease. Our preliminary studies were the first evaluation of the efficacy of HSF1A in vivo in the mammal and showed that application of HSF1A induces up-regulation of Hsps in the cochlea. In a second approach, we will investigate an alternative mode of heat shock activation through generation of transgenic mice that conditionally express an activated form of HSF1 (HsfTgAct) in the cochlea and thereby permit a temporary increase in the overall pool of HsfTgAct and promote a more robust heat shock response. We propose to compare the efficiencies of the small molecule and transgenic methods to activate HSP target genes in the ear and to evaluate their relative abilities to protect auditory function from noise trauma. These studies will take a critical step in moving a stalled therapeutic approach towards clinical application. Evidence of significant protection would provide justification for additional pre-clinical animal trials, a strong incentive for additional SF1 activator screens, and a route to testing efficacy in humans. An efficient method to activate the heat shock response in the inner ear could not only provide protection from noise-induced hearing loss for millions of people but would also have application to protection from ototoxins, affecting millions more.
The proposed studies will investigate new approaches to induce the heat shock response in the mouse cochlea to protect it from damage and subsequent hearing loss due to noise exposure. Small molecule and transgenic approaches to induction of this protective pathway will provide paths for clinical testing in humans to alleviate the significant health problem of noise-induced hearing loss.