Pou3f4-expressing Otic Mesenchyme Cells: A Novel Influence for Spiral Ganglion Neuron Survival

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PROJECT SUMMARY Hearing function depends on the precise connectivity patterns and proper function of specialized cells in the cochlea including spiral ganglion neurons (SGNs) and their presynaptic partners, hair cells. Deficits in the development, survival or function of these cells underlie hearing impairment and the efficacy of cochlear implants. SGNs in particular form the afferent connection between the peripheral and central auditory systems. SGNs are crucial for proper hearing and are particularly vulnerable to damage. We showed recently that Pou3f4, a transcription factor expressed by otic mesenchyme cells, is normally required for SGN survival during postnatal development. Mutations in Pou3f4 cause human hearing loss, and loss of Pou3f4 in mouse models leads to morphological defects in otic mesenchyme and hearing impairment in addition to decreased neuronal survival. Still, we have a limited understanding of how Pou3f4 regulates these processes because the transcriptional targets of Pou3f4 in the cochlea are not well understood. As described in this proposal, I will first seek to determine the function of Pou3f4 in SGN survival by defining the mechanism of action between otic mesenchyme cells and SGNs. Second, I will investigate the potential for otic mesenchyme cells to promote SGN survival using gene therapy. With respect to the mentored research training aspects of this award, I will receive additional training in virus-mediated gene therapy and auditory brainstem response techniques through co-mentorship by Dr. Ronna Hertzano. We predict that downstream targets of Pou3f4 include trophic or other environmental cues that influence SGN survival. I will take a direct approach to determining these mechanisms using a combination of molecular techniques and live imaging experiments. At the same time, our collaborators will be taking an unbiased, “omics”-based approach to identifying Pou3f4 targets. Additionally, I will reintroduce Pou3f4 and its targets both in vitro and in vivo to determine the extent to which mesenchyme cells promote SGN survival. I will be the one of the first to define how otic mesenchyme cells interact with SGNs to impact neuronal survival in the normally developing cochlea, as well as one of the first to determine the extent to which otic mesenchyme cells could be targeted therapeutically to help promote SGN survival in adults. Thus, this work explores a novel question that will complement ongoing work by others on neurotrophins, gene therapy, cell replacement strategies, and auditory prosthetics. The proposed research, mentoring, and career development aspects of this plan will help prepare me for a successful independent research career.