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Wednesday, February 7, 2007
Federally Funded Research on Cochlear Implants, Genetics of Hearing Loss, Hair Cell Generation Featured at ARO Conference in Denver
What: Current research funded by the National Institute on Deafness and Other Communication Disorders (NIDCD), one of the National Institutes of Health, will be featured at the 2007 Midwinter Meeting of the Association for Research in Otolaryngology (ARO).
When: February 10-15, 2007
Where: Hyatt Regency Denver at Colorado Convention Center, Denver, CO
Research conducted by NIDCD scientists include:
- Mutation in Gene for Protein Radixin Causes Hearing Loss in Humans
Radixin is an important protein that makes up the hair-like bundles on top of sensory cells in the inner ear. Mutations of the gene RDX, which encodes radixin, have been found to cause deafness in mice. In this study, NIDCD researchers show evidence that two Pakistani families with mutations in the RDX gene also exhibit hearing loss that is not associated with other symptoms. The findings are published in the Jan. 16, 2007, issue of Human Mutation. Title: Mutations of the RDX Gene Cause Nonsyndromic Hearing Loss at the DFNB24 Locus (poster); Principal investigator: Thomas Friedman, Ph.D., NIDCD.
- Mutation that Causes Muenke Syndrome Severely Disrupts Inner Ear Development in Mice
Muenke syndrome, a rare disorder that includes symptoms such as an abnormally shaped skull, dwarfism, and hearing loss, is caused by a mutation in the gene that encodes the protein Fgfr3. Fgfr3 is a receptor for fibroblast growth factors, a protein family that signals nearby cells and kick-starts activities that play a key role in embryonic development and growth, including the development of hearing structures. In this study, researchers show that mice missing the Fgfr3 gene exhibit a broad range of hearing abnormalities, indicating that Fgfr3 regulates many developmental processes in the inner ear. Title: Disruption of Fgfr3 Signaling Results in Defects in Cellular Differentiation, Neuronal Patterning, and Hearing Impairment (poster); Principal investigator: Matthew Kelley, Ph.D., NIDCD.
- Signaling Proteins Help Ear's Sensory Cells "Know" Where to Grow
The process by which an embryo develops the highly-specialized structures necessary for hearing is still a mystery to scientists. A cascade of reactions, kicked off by "signaling" proteins, is critical in directing the activities of an embryo's ' dividing cells. One such family, the Wnt proteins, is of particular importance in initiating reactions in a developing organism, and a disruption of these reactions — caused by a mutation to one or more Wnt genes — can result in developmental defects, diseases, and cancer. NIDCD researchers describe how activities of three Wnt proteins help determine the precise location and orientation of key sensory cells in the inner ear. Title: Wnt Signaling in the Mammalian Cochlea (symposium session); Principal investigator: Matthew Kelley, Ph.D., NIDCD.
- Form of Cadherin 23 Linked to Deafness in Mouse Model Identified
Cadherin 23 is a large protein that composes sensory structures in both the inner ear and retina. Researchers have yet to understand why some mutations to the gene that encodes it, CDH23, cause only deafness while other mutations cause deafness, blindness, and balance problems, as in Usher syndrome type 1. Cadherin 23 also comes in a variety of forms that may be expressed differently in the retina and inner ear. NIDCD researchers examined cadherin 23's various forms and found only one form to be expressed in the cochlea of a mouse model, suggesting that the loss of function of this form is responsible for the mouse's deafness. Title: Cadherin 23 Alternative Splice Variants: Studying the Molecular Basis of Waltzer (poster); Principal investigator: Thomas Friedman, Ph.D., NIDCD.
- 'Motor'-Protein-Containing Particles Help Rev Up Our Hearing
Scientists are exploring how tiny sensory structures in our inner ears, called hair cells, are sensitive to faint sounds. Although all hair cells help convert sound vibrations to electrical signals, inner hair cells relay those signals to the brain, while outer hair cells are thought to play a role in amplifying those signals. With the aid of an atomic force microscope, NIDCD researchers have found that tiny particles packed inside the cell membrane of the outer hair cell are composed of prestin, a 'motor' protein known for causing a cell to change shape in response to an electrical signal. The findings indicate that the membrane particles play a direct role in the expansion and contraction of outer hair cells in response to electrical signals and, most likely, the strengthening of those signals. Title: Evidence for Prestin in 10 nm Particles in the Lateral Membrane Of Outer Hair Cells: an Atomic Force Microscopic Study (podium session); Principal investigator: Kuni Iwasa, Ph.D., NIDCD.
Research conducted by NIDCD-funded scientists include:
- Are Two Cochlear Implants Better Than One?
More and more often, children with profound hearing loss are being fitted with two cochlear implants — one for each ear — in hopes that the child may better home in on a sound's source and gain a more realistic listening experience. In this NIDCD-supported study, researchers assess the sound-localization abilities of children (ages 5 to 14 years) wearing two cochlear implants in comparison to one. The researchers found that most of the children in the study located the source of a sound more accurately when they were wearing two implants as opposed to one. In addition, the team found that improvement in localization was seen only when the child used two implants, but not when a single implant was used; also, the more experienced the child was with two implants, the more adept he or she became at localizing sound. Litovsky's research team is now investigating the effects of bilateral implants on word learning and language acquisition in young-implanted infants and toddlers. Title: Emergence of Localization Abilities in Children with Sequential Bilateral Cochlear Implants (podium session); Principal investigator: Ruth Litovsky, Ph.D., University of Wisconsin.
- Inner Ear Stem Cells May Help Rewire Hearing
When hair cells are destroyed — by disease, injury, or aging — the attached nerve cells, or neurons, that relay electrical signals to the brain are often destroyed as well. In this NIDCD-funded study, scientists demonstrate that stem cells from the inner ear of a mouse can be grown into new neurons. Moreover, these neurons can form new connections with hair cells and carry electrical signals. The findings may one day be used in combination with other potential technologies for the treatment of hearing loss, such as hair cell regeneration and more advanced cochlear implants.Title: Neurons Derived from Inner Ear Stem Cells Form Synapses with De-Afferented Hair Cells (poster); Principal investigator: Albert Edge, Ph.D., Harvard Medical School.
- Restoring the Sixth Sense
Scientists are currently working to develop an implant for some people who lose their sense of balance. Just as the cochlear implant converts sound to electrical signals that stimulate the auditory nerve, a vestibular implant converts movements of the head into signals that stimulate the vestibular nerve. Although this technology is still in the early stages of development, two NIDCD-funded studies describe recent progress. The first study describes a model that predicts current flow for different electrode designs and a second study describes adjustments that would reduce power consumption of an implant in humans. Titles:1)An Anatomically Precise Finite Element Model Predicts Current Flow in Labyrinths Implanted with a Multi-Channel Vestibular Prosthesis (poster) and 2)Paired Linear Accelerometers Emulate Gyros to Reduce Power Consumption and Size for an Implantable Multi-Channel Vestibular Prosthesis (poster); Principal investigator: Charles C. Della Santina, M.D., Ph.D., Johns Hopkins School of Medicine.
- New Tool Helps Scientists Tinker with the Ear's ‘Motor’
NIDCD-supported researchers have developed a computer model to study how outer hair cells, sensory structures in the inner ear, help us to hear. Hair cells convert sound vibrations into electrical signals that are relayed to the brain. The membrane of the outer hair cell can act as a “motor” that amplifies inner ear vibrations and improves the electrical signal by causing the cell to lengthen and contract. If this membrane motor doesn't function, hearing loss results. The computer model simulates the stretching of a cell membrane, a lab technique researchers use to study a membrane's properties. By observing the membrane in more vivid detail, scientists will better understand the membrane-lodged motor that allows us to hear. Title: Modeling Membrane-Cytoskeleton Interaction in the Cochlear Outer Hair Cell Tether Pulling Experiment (poster); Principal investigator: William Brownell, Ph.D., Baylor College of Medicine.
For more information about the Association for Research in Otolaryngology, visit their Web site at www.aro.org.
NIDCD supports and conducts research and research training on the normal and disordered processes of hearing, balance, smell, taste, voice, speech and language and provides health information, based upon scientific discovery, to the public. For more information about NIDCD programs, see the Web site at www.nidcd.nih.gov.
About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.
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