Sensorineural hearing loss affects 30 million Americans. Aging, noise-overexposure, infection and ototoxic antibiotics all lead to sensory hair cell degeneration and permanent hearing loss. Recently, hair cell regeneration and partial function restoration were induced in the mature mammalian inner ear. However, little is known about molecular mechanisms that direct functional synapse assembly in either normal developing or regenerated hair cells. Our planned studies will define these mechanisms in vivo and identify molecules required for synapse assembly and hearing restoration in the deafened inner ear. This multi-investigator collaborative project draws on the complementary expertise of Michele Jacob (molecular mechanisms of neuronal synapse assembly), Yehoash Raphael (sensory hair cell regeneration), and Keith Duncan (ion channel function in sensory hair cells). We will focus on efferent olivocochlear (OC) cholinergic inputs from the brain onto sensory hair cells. OC cholinergic activity regulates the sensitivity and frequency selectivity of hearing. ?9/10-containing nicotinic acetylcholine receptors (nAChRs) mediate synaptic transmission in hair cells. Further, normal activity requires the functional coupling and close positioning of ?9/10-nAChRs to small conductance calcium activated potassium channels (SK2). Early SK2 expression is also required for inner hair cell functional maturation and normal exocytotic activity at the afferent presynaptic inputs onto primary auditory neurons that signal sound reception to the brain. Mechanisms that direct the synaptic localization of ?9/10- nAChRs and SK2 channels are undefined. We predict the molecular organization of the OC synapse based on our identification of key components at neuronal ?3-nAChR synapses and preliminary findings of shared components at hair cell ?9/10-nAChR synapses.
In Aim1, we will define the core postsynaptic complex of scaffold and cytoskeletal regulatory proteins at avian OC synapses.
Aim2 will define the specific adapter proteins that link ?9/10-nAChRs and SK2 channels to postsynaptic complex components.
Aim3 will test the in vivo roles of the adapter proteins in directing ?9/10-nAChR and SK2 synaptic localization and functional coupling that are essential for normal hearing. We will test the model in avian developing and regenerated hair cells. We will use loss-of-function and gain-of-function strategies and exploit the spontaneous regeneration and reverse genetic, molecular, morphological, biochemical and functional advantages of chick sensory hair cells. Our findings will provide new insights into the molecular organization of nicotinic synapses in both developing and regenerated hair cells. We will identify novel binding partners for ?9/10-nAChRs and SK2 channels. Further, the studies will provide the first identification of molecular interactions, in vivo, that are essential for synapse assembly and hearing recovery in the deafened inner ear.

Public Health Relevance

Short Narrative: Millions of people suffer permanent hearing loss because aging, noise-overexposure and infection all lead to sensory hair cell degeneration. Our planned studies will provide the first identification of molecular interactions, in vivo, that are required for synapse assembly and hearing restoration in the deafened inner ear.

Agency
National Institute of Health (NIH)
Institute
National Institute on Deafness and Other Communication Disorders (NIDCD)
Type
Research Project (R01)
Project #
5R01DC008802-05
Application #
8519408
Study Section
Special Emphasis Panel (ZRG1-IFCN-M (02))
Program Officer
Freeman, Nancy
Project Start
2009-09-19
Project End
2014-08-31
Budget Start
2013-09-01
Budget End
2014-08-31
Support Year
5
Fiscal Year
2013
Total Cost
$425,721
Indirect Cost
$132,120
Name
Tufts University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
039318308
City
Boston
State
MA
Country
United States
Zip Code
02111
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