Hearing impairment is prevalent and has significant implications for quality of life. There are currently no available clinical cures for hereditary inner ear disease or reliable means of preventing age related hearing loss. The mouse serves as an ideal mammalian model for understanding genetic risk factors for hearing impairment and for developing therapeutic measures. Mouse models have facilitated the discovery of genes that underlie hereditary disease in humans, have made it possible to study the role of these genes in inner ear development and function, and hold great promise as models for developing treatments for hereditary inner ear disease. This grant application builds on our observations that congenital secondary hypothyroidism causes profound deafness in Pit1dw mice and thyroid supplementation during pregnancy and early neonatal life is sufficient to protect against hearing impairment. In addition, we observed that Pit1dw hypothyroid mice have delayed and/or abnormal neurogenesis and synaptogenesis. Finally, Pit1dw mutants exhibit changes in cochlear expression of genes likely to be involved in axonal guidance and synapse formation. Based on these preliminary data, we hypothesize that thyroid hormone deficiency in the neonatal period permanently impairs neurogenesis and synapse formation with inner and outer hair cells resulting in deafness that cannot be rescued by later treatment with thyroid hormone. Moreover, we suggest that adult hypothyroidism contributes to age related hearing loss. We propose to: 1) Determine whether inner hair cell function is compromised in Pit1dw mice with congenital, secondary hypothyroidism using physiological tests of exocytosis and measurement of both calcium and potassium currents, 2) Identify a novel set of thyroid hormone regulated genes that affect axonal guidance and synaptogenesis in the cochlea using candidates previously identified by gene expression profiling of Pit1dw and normal cochlea and test the functional activity of the proteins encoded by subset of these genes on cochlear neurogenesis and function. 3) Identify the time sensitive process(es) that are responsive to thyroid hormone replacement in the neonatal period but are not rescued by later thyroid hormone treatment using physiological tests, and assessment of morphological maturation and gene expression. Our investigative team has a track record for accomplishments resulting from cross-disciplinary collaboration, which has brought expertise in auditory physiology and morphology together with expertise in molecular and developmental genetics. This interdisciplinary approach focuses on defining the fundamental process of thyroid hormone stimulation of cochlear development by uncovering the target genes of thyroid hormone action in axonal guidance and synapse formation. Basic information about the molecular genetics and hormonal regulation of cochlear innervation will emerge from these studies, potentially informing efforts at improving innervation of regenerating hair cells.

Public Health Relevance

Understanding thyroid hormone regulation of neurogenesis in the cochlea Lay Narrative Deafness is a common birth defect, affecting about 1 birth in 2000. About half of these children are affected because of genetic reasons, and there is no known cure or prevention. Thyroid hormone is critical for developing normal hearing in humans and mice. In this grant proposal we seek to understand how thyroid hormone influences the growth of neurons and their attachment to the sensory cells in the inner ear. In the long term we are interested in translating the lessons learned in mice to improve diagnosis and treatment of human deafness.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC009590-06
Application #
8494422
Study Section
Auditory System Study Section (AUD)
Program Officer
Freeman, Nancy
Project Start
2009-07-01
Project End
2014-06-30
Budget Start
2013-07-01
Budget End
2014-06-30
Support Year
6
Fiscal Year
2013
Total Cost
$337,291
Indirect Cost
$132,450
Name
Stanford University
Department
Otolaryngology
Type
Schools of Medicine
DUNS #
009214214
City
Stanford
State
CA
Country
United States
Zip Code
94305
Sundaresan, Srividya; Kong, Jee-Hyun; Fang, Qing et al. (2016) Thyroid hormone is required for pruning, functioning and long-term maintenance of afferent inner hair cell synapses. Eur J Neurosci 43:148-61
Sundaresan, S; Balasubbu, S; Mustapha, M (2016) Thyroid hormone is required for the pruning of afferent type II spiral ganglion neurons in the mouse cochlea. Neuroscience 312:165-78
Mendus, D; Rankin-Gee, E K; Mustapha, M et al. (2015) Increased sensitivity to kindling in mice lacking TSP1. Neuroscience 305:302-8
Calton, Melissa A; Lee, Dasom; Sundaresan, Srividya et al. (2014) A lack of immune system genes causes loss in high frequency hearing but does not disrupt cochlear synapse maturation in mice. PLoS One 9:e94549
Mendus, Diana; Sundaresan, Srividya; Grillet, Nicolas et al. (2014) Thrombospondins 1 and 2 are important for afferent synapse formation and function in the inner ear. Eur J Neurosci 39:1256-67
Fang, Qing; Giordimaina, Alicia M; Dolan, David F et al. (2012) Genetic background of Prop1(df) mutants provides remarkable protection against hypothyroidism-induced hearing impairment. J Assoc Res Otolaryngol 13:173-184