While number of proteins responsible for structural integrity of the mechanosensory bundle of the inner ear hair cells has been identified, how most of these proteins contribute to mechano-electrical transduction is still unknown. Also unknown is whether the lack or modification of MET contributes to the development of deafness and/or vestibular disorders that result from mutations of hair bundle proteins. The goal of the current project is to determine the role of the myosin XVa-based stereocilia elongation complex in mechanotransduction. In homozygous shaker 2 mice (Myo15sh2/sh2), a recessive point mutation in the motor domain of myosin XVa prevents normal localization of this protein to the tips of stereocilia, resulting in abnormally short stereocilia. According to our preliminary data, cochlear outer hair cells of young postnatal Myo15sh2/sh2 mice possess numerous obliquely oriented "tip links" and apparently normal mechanotransduction. In contrast, Myo15sh2/sh2 inner hair cells have equally short stereocilia without any obliquely oriented tip links, but with numerous "top-to-top" links perpendicular to the core of stereocilia. In spite of their abnormal morphology, Myo15sh2/sh2 inner hair cells have a prominent transduction current with "wild type" nanoampere-scale amplitude but abnormal directional sensitivity and no rapid Ca2+dependent deactivation, known as "fast adaptation". The central hypothesis of the proposal is that the myosin XVa- based stereocilia elongation complex is not required for mechanosensitivity of hair cells but may affect directional sensitivity and adaptation of mechanotransduction. This study will determine: 1) the role of myosin XVa in directional sensitivity of the hair bundle;2) localization of known molecular components of stereocilia links in the myosin XVa-deficient hair bundles;3) the role of myosin XVa and its molecular partner, whirlin in the fast adaptation of the transduction current. This study represents a step toward my long-term goal to understand how the hair cells acquire and maintain mechanosensitivity in normal and pathological conditions. Apart from being important for understanding the basic mechanisms of hair cell mechanotransduction, this study will establish how developmental abnormalities of stereocilia growth may affect the transduction machinery. This project will also be the first to study mechanotransduction during restoration of the hair bundle morphology and/or tip links in mammalian cochlear hair cells. Finally, our study will provide a wealth of data on hair cell function in shaker 2 and whirler mice, the animal models for DFNB3 and DFNB31 hereditary deafness in humans. This research is relevant to public health because it investigates exactly how sensory cells of the inner ear acquire and maintain mechanosensitivity in normal and pathological conditions. Our experimental results will help scientists to better understand, prevent, and develop treatments for developmental abnormalities in the sensory cells of the inner ear, which lead to congenital deafness.

Public Health Relevance

This research is relevant to public health because it investigates exactly how sensory cells of the inner ear acquire and maintain mechanosensitivity in normal and pathological conditions. Our experimental results will help scientists to better understand, prevent, and develop treatments for developmental abnormalities in the sensory cells of the inner ear, which lead to congenital deafness.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC008861-04
Application #
8197185
Study Section
Auditory System Study Section (AUD)
Program Officer
Freeman, Nancy
Project Start
2008-12-01
Project End
2013-11-30
Budget Start
2011-12-01
Budget End
2013-11-30
Support Year
4
Fiscal Year
2012
Total Cost
$315,886
Indirect Cost
$100,264
Name
University of Kentucky
Department
Physiology
Type
Schools of Medicine
DUNS #
939017877
City
Lexington
State
KY
Country
United States
Zip Code
40506
Indzhykulian, Artur A; Stepanyan, Ruben; Nelina, Anastasiia et al. (2013) Molecular remodeling of tip links underlies mechanosensory regeneration in auditory hair cells. PLoS Biol 11:e1001583
Ahmed, Zubair M; Frolenkov, Gregory I; Riazuddin, Saima (2013) Usher proteins in inner ear structure and function. Physiol Genomics 45:987-9
Kitajiri, Shin-ichiro; Sakamoto, Takeshi; Belyantseva, Inna A et al. (2010) Actin-bundling protein TRIOBP forms resilient rootlets of hair cell stereocilia essential for hearing. Cell 141:786-98
Novak, Pavel; Li, Chao; Shevchuk, Andrew I et al. (2009) Nanoscale live-cell imaging using hopping probe ion conductance microscopy. Nat Methods 6:279-81
Stepanyan, Ruben; Frolenkov, Gregory I (2009) Fast adaptation and Ca2+ sensitivity of the mechanotransducer require myosin-XVa in inner but not outer cochlear hair cells. J Neurosci 29:4023-34