University of California San Francisco

The role of cochlear capsule bone remodeling in hearing loss

Although several bone diseases cause sensorineural hearing loss, the mechanism by which bony defects impair auditory function remains unclear. The long term goal of this research is to better understand the role of bone in the sensorineural function of the ear—with the objective of identifying bone targets that might be therapeutically effective in the prevention or reversal of hearing loss. The goal of this proposal is to test the hypothesis that abnormal remodeling of the cochlear capsule results in hearing loss by damaging the material quality of the cochlear bone matrix. Our recent studies on bone disease-associated hearing loss have shown that cochlear bone hardness is critical for hearing. Understanding bisphosphonate action in the ear is clinically important because drugs are commonly used to treat osteoporosis and bone disease-associated hearing loss.

Lehigh University

Efferent loizounction in sound localization processing

Auditory processing relies on precise coding of acoustic features to build an accurate internal representation of the environment. Sensory systems build this representation through faithful encoding of sensory stimuli at the level of sensory organs. This neural signaling is enhanced by active feedback on sensory neurons from higher central processing centers. These "efferent" pathways have been characterized for the cochlea and to some extent, in the midbrain. There is little data efferent function in the early stages of auditory processing in structures that process sound location information. This may be due, in part, to the complexity of this system in mammalian circuits. The bird auditory system is a major model for human sound localization processing. Indeed, birds process ascending circuitry that is strikingly similar to mammals in structure and function, but with efferent circuitry that is appealingly simple. My aim is to investigate this elegant efferent brain stem circuit in birds to build a comprehensive model of its function within this functionally understood auditory circuit. These studies will both characterize the neurons responsible for this feedback, and examine their impact on their targets. The long-term objective is to build a mechanistic understanding of sound localization circuitry in vertebrate systems.

Emory University

Harmonin interactions with voltage-gated Ca3+ channels in a mouse model of Usher syndrome

Usher syndrome is the leading cause of hereditary deafness and combined deafness and blindness in humans. This research will illuminate a novel mechanism of Ca3+ channel regulation that may be important for auditory function. By carefully characterizing the defects in Ca3+ channel properties in the mouse Usher syndrome model, the researcher will be able to follow-up with strategies to restore function to these mice, which may be ultimately useful in limiting deafness and balance problems in human patients of Usher syndrome.

University of California Davis

Mechanism of hair cell development and regeneration

Hair cells (HCs) convert sound signals into electrical impulses in the cochlea with remarkable precision and sensitivity. Our long-term goals are to stimulate HC regeneration in human inner ears in a controlled fashion, and to enable the functional innervation of the regenerated HC's by spiral ganglion neurons (SGNs). To do this, the functional mechanisms of the development of HCs must be understood. In the developing systems, there is temporal overlap between ion channel development, spontaneous activity and activity-dependent development. Therefore, APs could serve both intrinsic (ion channel expression) and extrinsic (neuronal refinement) development roles. We have identified differential patterning of APs in the developing cochlear axis that reflects differences in expression of ionic conductances. We will test the prediction that the activity of HCs influenced that of its neighbors, including the preservation of the synaptic transmission between auditory nerve and HCs. The proposed study will increase our understanding of the activity dependent development in the auditory system.

Oregon Health & Science University

Auditory signal coding at the hair cell ribbon synapses

The sense of hearing starts at hair cells, which connect to afferent fibers via ribbon synapses. Across these synapses, auditory signals contained in graded potentials on hair cells are transformed into all-or-none spikes on afferent fibers. Therefore, these synapses face the tremendous challenge of continuous coding of auditory signals over a remarkable dynamic range. It is not well understood how these specialized synapses achieve their extraordinary ability to release transmitters continuously. This has greatly impaired our ability to treat hearing loss. The long-term objective of this study is to investigate mechanisms of synaptic transmission and strategies for auditory signal coding at this very first chemical synapse along the auditory pathway. In two years, the specific aims are: 1) To study multivesicular release and its mechanisms; 2) To determine how the release of vesicles is transformed to spikes on afferent fibers; 3) To investigate short-term plasticity and how it helps the coding of auditory signals.

Rosalind Franklin University of Medicine and Science

Splicing regulation of pre-mRNA generated from the deafness-associated Espin gene

The goal of this proposal is to determine how Espin gene expression is controlled at the level of RNA processing. Loss of function mutational analysis will identify RNA sequences on the Espin pre-mRNA that are essential for alternative splicing reactions. Proteins that bind the regulatory RNA sequences will be identified by UV-cross- linking, Western blotting and immunoprecipitation. Correlation of the in vitro analysis with in vivo activity will be accomplished through modulating by RNAi and overexpression the levels of these proteins in HeLa cells transfected with Espin mini-gene constructs containing genomic sequence corresponding to the alternatively spliced exon and flanking introns.

University of Rochester

Cortical synaptic plasticity in a mouse model of moderate sensorineural hearing loss

The development of cortical networks is exquisitely sensitive to patterned activity elicited through sensory stimulation. Although much is known about somatosensory and visual cortical development, very little is known about the development of auditory cortex network connectivity. Changes in hearing that occur as a result of defects in sensation at the cochlea likely affect the development of higher brain areas which process auditory information. Our research will explore changes in the neural networks that process auditory stimuli in the cortex in a mouse model where prestin, a protein crucial for outer hair cell electromotile function is absent during development. We will address this question by looking at synaptic sites which link individual neurons into networks and compare their density, distribution and dynamic remodeling in control and prestin-null mice. We hypothesize that changes in both static and dynamic synaptic structure will be present in the auditory cortex of prestin-null mice, suggesting that cortical auditory networks are altered by degraded hearing during development. This work will shed light on synaptic mechanisms and possible treatments of developmentally acquired hearing loss.

University at Buffalo, SUNY

The vestibular evoked myogenic potential: unanswered questions regarding stimulus and recording parameters

The vestibular evoked myogenic potential (VEMP) is a response that can be recorded from the sternocleidomastoid (SCM) muscle as well as other neck muscles such as the trapezius. It is believed to be generated by the saccule, which is a part of our vestibular system that is normally responsible for our sense of balance. Recent studies have shown that it is also responsive to sound. Three types of stimuli that are used to elicit the VEMP are air-conducted (AC) stimuli, bone-conducted (BC) stimuli, and galvanic (electrical) stimuli. Although there are several universal findings that have held true throughout previous studies, there are several questions which remain unanswered. The present study will attempt to address these issues by making a direct comparison between the three types of stimuli listed above, within the same subjects. In addition, input/output functions will be defined for all three types of stimuli. Finally, we will be looking at the repeatability of the three types of stimuli across subjects as well as address the inconsistencies that have been found between monaural and binaural stimulation. This study will not only provide us with a better understanding of the VEMP, it will also enhance its clinical utility.

University of Michigan

Determine the functional role of the unique amino terminus of MYO15 in hearing using genetically engineered mice

Assessing the role of the N-terminus of MYO15 in structural development of hair cells and in the neurosensory process of hearing is expected to provide basic information about the process of hearing at the molecular level. Long term, we expect proteins that interact with the N-terminus of MYO15 will also be defective in some forms of hearing loss. Models similar to the one we propose have been used as proof of principle for gene therapy. Mutations in humans indicate that the N-terminal portion of MYO15 is required in some way for hearing. Using our resources and experience in genetically engineered mice will advance the understanding of the specific molecular function of the N-terminus of Myo15 in mammalian hearing and determine the consequences on morphological development and signal transduction within the cochlear hair cells. Thus, these studies will immediately make a contribution to the rapidly advancing field of molecular hearing research. The next step will be to identify the proteins that interact with the N-terminus, screen pedigrees for mutations in these genes and work towards therapeutic intervention for genes that are common causes of deafness.

University of Utah

The role of Fgf4 in otic placode induction

Development and patterning of the inner ear is a complex process that is mediated by several signaling molecules, including members of the fibroblast growth factor (FGF) family. We recently found that Fgf4 is expressed in the ear-forming region just prior to the induction of ear development. Fgf4 has not previously been described in the induction or formation of the inner ear. Based on its temporal and spatial pattern of expression we hypothesize that Fgf4 is involved in the early processes of ear development and propose to investigate its role(s) in these processes by determining whether it is sufficient and/or required to induce the early stages of inner ear development. We also will examine the signals responsible for localizing Fgf4 expression to the otic forming domain.

University of North Carolina Wilmington

Enhancement of the efferent-hair cell synapse by metabotropic glutamate receptors

This proposal aims to improve our understanding of the molecular mechanisms regulating synapses in the cochlea and will specifically characterize how a class of molecules, metabotropic glutamate receptors (mGluRs), regulates the efferent-hair cell synapses. Sensory hair cells of the cochlea communicate with the brain at specialized sites called synapses. Inner hair cells have numerous afferent synapses that relay information about sound from the hair cell to the brain. In contrast, outer hair cells are characterized by efferent synapses from the brain that regulate hair cell activity. Although these efferent and afferent synapses are normally considered to be independent from one another, experiments studying immature inner hair cells suggest that glutamate, the neurotransmitter required for transmission at the afferent synapse, may also modify the response of the efferent synapse. Efferent innervation of the cochlea is thought to protect against noise-induced hearing loss. Considering that noise-induced hearing loss accounts for one-third of all cases of deafness, understanding the mechanisms regulating efferent synapses is of special clinical relevance. This project will investigate this hypothesis and should uncover novel pharmaceutical targets to modulate the efferent synaptic response to either dampen hair cell activity and prevent noise-induced hearing or boost hair cell activity and combat deafness.

Stanford University School of Medicine

The functional impact of single and dual expression of GJB2 missense variants V271 and E114G: An exploration of pathogenic effects on hearing

It is difficult to predict the consequences of DNA alterations that result in the replacement of one protein building block by another. Yet, an important aspect of genetic testing is to predict whether a DNA change is harmful or not. With this project, we will solve this dilemma for two relatively common variants in the connexin 26 gene. Interestingly, it appears that these two variants do not contribute to hearing loss when opposite of a disease causing change separately, but when they occur together opposite such a change, there is hearing loss as if these changes have an additive deleterious effect. By using techniques in which we are experienced, we plan to continue our research in hearing loss and directly observe whether and how these variants affect the connexin 26 protein functions within the cell. We will determine the effect on the amount of connexin 26 proteins, on localization and transport within the cell, and on function by establishing whether the essential communication channels between cells are still formed. This work will enable the correct clinical interpretation of these commonly observed changes, and can help begin to link DNA changes to protein effects and clinical symptoms in patients with hearing loss.

Rush University Medical Center

Perception of environmental sounds and speech in patients with cochlear implants

This project will assess the ability of patients with contemporary cochlear implants to perceive environmental sounds using a new test of environmental sound perception. It will further examine the relationships between perception of environmental sounds and speech. A close association between these abilities would open an exciting possibility of developing a language-independent instrument for estimating speech perception abilities based on environmental sound tests (e.g., when speech materials are not available for some languages for potential candidates). Such a test would have highly useful clinical applications in large urban clinics or in developing countries with fledgling implant programs.

University of Michigan

The role of MIF in zebrafish inner ear development

We hypothesize that MIF plays a major role in otic development, specifically in neurite outgrowth and survival of the developing SAG neurons in the inner ear. We have found that MIF is expressed in the mammalian (mouse) inner ear, the chick inner ear and in the model system we have chosen to study, the zebrafish inner ear. Zebrafish auditory system development recapitulates many aspects of early mammalian inner ear development and neurogenesis. More importantly, the same molecules that are active in the mammal are active in the zebrafish and the zebrafish inner ear development is both easier to study and is extremely rapid. We will examine early survival and maturation factors for the SAG and use advanced imaging to trace SAG precursor cell movements from the otic vesicle to the ganglion. Preliminary studies using in situ hybridization demonstrated that MIF and MIF-like genes and their receptors are expressed in zebrafish SAG and developing inner ear. Our experiments will examine whether MIF and MIFlike gene loss-of-function using morpholino antisense oligonucleotides (MOs) affects SAG development and whether this loss of function can be "rescued" by introducing MIF RNA.

New York University School of Medicine

Measuring and predicting the quality of nonlinearly distorted music and speech as perceived by hearing-impaired people

Hearing aids and other communication devices, such as telephones, introduce significant nonlinear distortion which reduces sound quality and may interfere with speech perception. The goals of the proposed research are to characterize and model the perception of distorted speech and music by hearing-impaired listeners. The first objective of the proposed research is to conduct listening tests to determine how hearing-impaired listeners evaluate the perceived quality of distorted speech and music. The second objective of the proposed research is to develop a computational model for predicting perceived quality judgments made by hearing- impaired listener; in other words, to predict the data obtained in the first part of the project. The third objective of the proposed research is to test, and if necessary to refine, the developed models using recordings of speech and music replayed via existing assistive hearing devices.

University of Utah

FGF-regulated hearing loss genes: fast-tracking to functional analysis

With the myriad roles of fibroblast growth factors (FGFs) in multiple stages of ear development, it is not surprising that some human hearing loss syndromes are caused by mutations affecting FGFs and their receptors. However, little is known about the genes that are controlled by FGFs. Because FGF signals are reused during later stages of otic innervation, morphogenesis, and sensory cell differentiation, the FGF target genes we identify during placodogenesis may also be targets of later FGF signaling events and could provide many new candidates for hearing and/or balance disorders, thereby impacting diagnosis. Importantly, elucidating the functions of these genes may suggest potential therapeutic interventions. FGFs are required to initiate otic development and are subsequently reused during morphogenesis and sensory development. Our long-term objective is to identify FGF effector genes and to determine their function and relevance to human deafness by analyzing mouse mutants. Specifically, we propose to isolate RNA from pre-otic ectoderm of control and FGF-deficient embryos and perform an expression profiling experiment utilizing a “gene-trap microarray.” This will identify embryonic stem cell lines that carry mutations in FGF target genes. Selected cell lines will be used to generate the corresponding mutant mouse strains for functional studies of hearing and balance.

Montclair State University

Neurophysiological and psychoacoustic indices of binaural processing in adults

The overall goal of the proposed research is to investigate neurophysiological and psychoacoustic indices of binaural processing in adults with normal and impaired hearing. In order to develop and implement effective remediation for individuals with sensorineural hearing loss, it is essential to determine a straightforward means to identify binaural processing problems. It is particularly important to ascertain the relationship between neurophysiological and psychoacoustic measures because there are many individuals for whom it is difficult to obtain behavioral responses. In the proposed study we will evaluate the effect of sensorineural hearing loss on processing of interaural intensity differences (IIDs) and determine the relationship between neurophysiological and behavioral measures of sensitivity to IIDs. Results will provide the information necessary to assess binaural processing of IIDs and to develop remediation strategies for individuals with sensorineural hearing loss.

Tufts University School of Medicine

The role of Neuregulin1 signaling in the developing cochlear nucleus

The long-term objective of this study is to understand the genetics of cochlear nucleus neuronal differentiation and specification to examine how information-transmitting cells in the brain (neurons) obtain their identity and acquire specific characteristics that endow them to perform very specific functions.