The long-term goal of my laboratory is to understand the role of cochlear outer hair cells in hearing and hearing loss both at the molecular and at the systems level. Specifically, we are interested in agents that block or enhance the action of receptors on outer hair cells of the cochlea, which enhance hearing and decrease hearing loss. To design and discover agents that block or enhance receptor action on cochlear outer hair cells, we are cloning neurotransmitter receptors expressed in the hair cells, and modulating expression of these receptors by viral-mediated gene transfer into the cochlea.

Using the guinea pig as an experimental animal model, we have isolated clones for neuronal nicotinic acetylcholine receptors (nAChRs) present on cochlear outer hair cells. We have made antibodies to the α9 and α10 subunits of the nAChR, and utilized these antibodies in Western blot and immunohistochemistry on vestibular and cochlear tissues. We have discovered that the α9 nAChR is located on outer and inner hair cells of the cochlea and found on calyces of type I vestibular hair cells and at the base of type II hair cells of the vestibular endorgans, which are the sites of efferent contact in the auditory and vestibular systems. The efferent system is believed to be responsible for (1) protecting the cochlea from acoustic overstimulation and (2) enhancing sound recognition in the presence of background noise.

We have also developed a method to assess the strength of an animal's efferent system across a multi-frequency extent based on measuring distortion product otoacoustic emissions (DPOAE). We determined that the efferent strength of an animal correlated with the amount of α9 nAChR present in that animal's cochlea, and strong efferent strength correlated with decreased hearing loss associated with exposure to intense noise (Luebke & Foster, J. Neurosci.). In collaboration with Drs. Maison, Liberman, and Zuo, J. Neurosci,) we have also determined that mice over-expressing the α9 nAChR subunit are less susceptible to moderate and intense noise exposures. These studies suggest that acetylcholine is an important neurotransmitter in regulating hearing function, and that the cochlear nAChR is a candidate for therapeutic intervention to prevent hearing damage.

One drawback to studies based on the loss or overexpression of a gene in transgenic mouse models is that it is difficult to separate the acute effects from developmental effects of gain or loss of a gene of interest. To overcome this drawback, we have used virally-mediated gene transfer to deliver mRNAs to the ipsilateral cochleas of adult guinea pigs in vivo. We determined that a modified adenovirus [E1-,E3-, E2b-] could infect cochlear hair cells both in culture and in vivo with no loss of either transduction currents or cochlear function (Luebke et al,Gene Therapy). Furthermore, we determined that the hCMV promoter could drive expression of either lacZ or GFP in infected hair cells, indicating that we have developed a delivery system to express transgenes in cochlear hair cells without causing damage to the infected cells. We are also interested in whether cochlear stem cells can be generated and selected such to be an enriched source of cochlear hair cell progenitors which could be used to restore and and replace lost hair cells and restore auditory function.