Foxo3 Mechanisms in Noise Damage

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Noise induced hearing loss (NIHL) has disabled millions of people world-wide. Individual risk for NIHL varies from person to person under similar exposure conditions, suggesting that genetic factors contribute to susceptibility. We have found that mice lacking a transcription factor called FOXO3 become severely and permanently deafened after a noise exposure that only briefly affects their wild-type littermates. FOXO3 has multiple functions in other cell types, including oxidative stress reduction, autophagy, and directly inducing apoptosis. A recent study linked human genetic variations in FOXO3 to a greater susceptibility to occupational NIHL. However, the FOXO3 alleles associated with NIHL drive increased expression of FOXO3. Thus, there is evidence to indicate that FOXO3 is important for hearing preservation, but there is also evidence that excess FOXO3 drives NIHL. In this grant, we seek to address this knowledge gap by researching the mechanisms of FOXO3 function, using translatome sequencing, cell-specific Foxo3 conditional knockouts (cKO), and CRISPR modifications to generate mouse lines that can be used to investigate the human NIHL-linked FOXO3 allele. In Foxo3-knockout (KO) mice, noise eliminates high-frequency outer hair cells (OHCs). We show that this occurs through a rapid cell death program called parthanatos, which is caspase-independent apoptosis. Parthanatos indicates that in the absence of any noise damage, Foxo3-KO OHCs are primed for death. Bulk RNA-Seq data from control Foxo3-KO and wild-type littermates show no evidence for changes in oxidative stress reducers known to be regulated by FOXO3. Instead, we see changes in actin binding genes expressed in OHCs. In Aim 1, we propose to validate this screen and identify markers of OHC distress in the Foxo3-KO through translatome sequencing. In Aim 2, we propose to make cell-specific Foxo3-cKO to identify the cells in which FOXO3 acts. Wild-type mice express FOXO3 protein in both OHCs and in the surrounding supporting cells (SCs). By using inducible DNA recombinases lines specific to either OHCs or SCs, we can ablate FOXO3 function in either cell type. We will expose such Foxo3-cKO mice to noise and determine their NIHL susceptibility. Finally, in Aim 3, we have used CRISPR genetic modification technology to create two mouse lines, one with control sequences (Foxo3-T-allele mice), as well as one homologous to the human FOXO3 allele that confers NIHL susceptibility (Foxo3-G-allele mice). We will validate that the Foxo3-G-allele mouse line has increased levels of FOXO3 in cochlear cells after noise exposure. We hypothesize that this modification promotes apoptosis from FOXO3 activation, and we will test that hypothesis by exposing Foxo3- G-allele mice to noise, measuring their hearing and analyzing potential cellular losses. In sum, through both loss-of-function and gain-of-function experiments, we will analyze FOXO3's role in hearing loss from noise.