Molecular markers of Alzheimer’s disease pathology in the human inner ear (NOT-AG-23-032) ABSTRACT Alzheimer’s disease (AD) is the most common cause of dementia in the United States and, in addition to the classical symptoms such as memory loss, people with AD have abnormal perceptual and semantic processing of sound. As hearing loss has recently been identified as one of the top risk factors for the development of dementia, there is an urgent unmet need to identify the etiological link between hearing loss and AD, and to develop early interventions. Specifically, the hallmark AD pathology causing neurodegeneration in the brain— the deposition of amyloid-beta (Aβ) protein and phosphorylated tau (p-tau) tangles in the brain— may similarly cause cellular toxicity at the level of the cochlea, damaging the fragile, non-regenerating sensory cells required for human hearing. We propose to test this hypothesis via the expansion of Aim 2 of our grant, “Human Ear Cellular Atlas,” and conduct a multi-faceted analysis of AD pathology in the human inner ear. In Aim 2i, we will define the proteomic signature of perilymph rapidly collected from patients with AD postmortem, and identify proteins unique to or differentially expressed in AD patient perilymph compared with that from age-matched, cognitively normal controls. In Aim 2ii, we will use the collected temporal bones of AD patients to quantify cochlear hair cells, spiral ganglion neurons (which transmit auditory information to the brain), and synapse density between hair cells and SGNs, to determine if pathological changes occur within the AD cochlea compared with controls. Additionally, we will examine the expression of 100+ proteins (identified from perilymph in Aim 2i and including AD-associated proteins) using a highly multiplex approach along with single-cell imaging. Lastly, in Aim 2iii, we will correlate AD patients’ perilymph proteomic signatures and cochlear pathology from Aims 2i and 2ii, respectively, with their clinical and hearing data contained in electronic medical records. We will analyze AD patients’ (1) level of hearing impairment, including audiometric thresholds, word recognition score, and speech- in-noise score; (2) cortical load of p-tau and Aβ measured by clinical imaging or from brain sections; and (3) results of cerebrospinal fluid testing. The results of these experiments will help elucidate the link between AD and hearing loss by providing the first reports of the perilymph proteome and cochlear pathology in patients with AD. Such evidence will help inform the identification of new therapeutic targets for hearing loss as well as potential biomarkers for risk stratification in this population.