Ion Channel Function in Auditory & Vestibular Hair Cells

DESCRIPTION (provided by applicant): The studies proposed here focus on several distinct, yet equally significant lines of inner ear research. The overall goal is to identify the genes and proteins in sensory hair cells that are responsible for the generation and propagation of sensory information in the ear. Each family of genes that will be investigated is associated with inherited human disease and members of each family are expressed in inner ear hair cells. Some of the genes we will investigate are known to cause deafness and/or balance disorders when mutated. Others are candidate deafness genes because they are expressed in hair cells and because known mutations in those genes cause dysfunction in other body tissues. As such, mutations in the candidate genes may cause previously unrecognized forms of genetic auditory and vestibular dysfunction. Broadly, we aim to understand three critical hair cell functions and identify the genes and proteins that underlie those functions. 1) We will examine ion channel genes that determine the hair cell resting potential. Because these proteins are active at rest, i.e., in the absence of stimulation, they have a major impact on how hair cells respond to stimulation. We want to identify exactly which ion channel genes contribute to this function and have selected three families for investigation: the KCNQ family, the HCN family and the Kir2 family. Mutations in KCNQ genes cause deafness and epilepsy, while mutations in HCN and Kir2 genes cause cardiac problems. Members of each of these families are expressed in hair cells, but their precise contributions to hair cell conductances and hair cell function have not been determined. 2) We are also interested to identify the genes that mediate sensory adaptation in hair cells. In response to sustained hair bundle deflections, hair cells adapt which results in a decline in their response. Molecular motors, probably myosin molecules, have been hypothesized to play a role in this function. Furthermore, mutations in several members of the myosin family cause deafness. We will focus on one myosin in particular, Myosin 1c, and use a chemical-genetic strategy to inhibit its function. We will deflect hair bundles and measure their response to determine the contribution of Myosin 1c to adaptation in auditory hair cells. 3) Lastly, we are interested to identify the molecules that contribute to the development and regeneration of sensory transduction in hair cells. We hypothesize that the myosin and cadherin families may contribute to this function. Mutations in members of both families cause Usher's syndrome, characterized by deafness and blindness. We will use chronic inhibition of myosin and cadherin function to investigate the specific contributions of members of these families to development and regeneration of the transduction complex in sensory hair cells. Through these three lines of research we aim to identify several molecules that contribute to normal function of hair cells. Because deficiencies with these critical functions cause deafness and balance disorders, the information gained through these studies will facilitate design of rational strategies to treat genetic inner ear disorders. This project will study some of the genetic causes of inherited deafness and balance disorders. We will investigate a handful of genes, of the approximately 26,000 identified through the human genome project, that we suspect are critical for normal hearing and balance. We expect that this project will produce information that will form the basis for development of future strategies to treat deafness and balance problems in some of the ~28 million Americans who suffer from inner ear disorders.

DESCRIPTION (provided by applicant): The studies proposed here focus on several distinct, yet equally significant lines of inner ear research. The overall goal is to identify the genes and proteins in sensory hair cells that are responsible for the generation and propagation of sensory information in the ear. Each family of genes that will be investigated is associated with inherited human disease and members of each family are expressed in inner ear hair cells. Some of the genes we will investigate are known to cause deafness and/or balance disorders when mutated. Others are candidate deafness genes because they are expressed in hair cells and because known mutations in those genes cause dysfunction in other body tissues. As such, mutations in the candidate genes may cause previously unrecognized forms of genetic auditory and vestibular dysfunction. Broadly, we aim to understand three critical hair cell functions and identify the genes and proteins that underlie those functions. 1) We will examine ion channel genes that determine the hair cell resting potential. Because these proteins are active at rest, i.e., in the absence of stimulation, they have a major impact on how hair cells respond to stimulation. We want to identify exactly which ion channel genes contribute to this function and have selected three families for investigation: the KCNQ family, the HCN family and the Kir2 family. Mutations in KCNQ genes cause deafness and epilepsy, while mutations in HCN and Kir2 genes cause cardiac problems. Members of each of these families are expressed in hair cells, but their precise contributions to hair cell conductances and hair cell function have not been determined. 2) We are also interested to identify the genes that mediate sensory adaptation in hair cells. In response to sustained hair bundle deflections, hair cells adapt which results in a decline in their response. Molecular motors, probably myosin molecules, have been hypothesized to play a role in this function. Furthermore, mutations in several members of the myosin family cause deafness. We will focus on one myosin in particular, Myosin 1c, and use a chemical-genetic strategy to inhibit its function. We will deflect hair bundles and measure their response to determine the contribution of Myosin 1c to adaptation in auditory hair cells. 3) Lastly, we are interested to identify the molecules that contribute to the development and regeneration of sensory transduction in hair cells. We hypothesize that the myosin and cadherin families may contribute to this function. Mutations in members of both families cause Usher's syndrome, characterized by deafness and blindness. We will use chronic inhibition of myosin and cadherin function to investigate the specific contributions of members of these families to development and regeneration of the transduction complex in sensory hair cells. Through these three lines of research we aim to identify several molecules that contribute to normal function of hair cells. Because deficiencies with these critical functions cause deafness and balance disorders, the information gained through these studies will facilitate design of rational strategies to treat genetic inner ear disorders. This project will study some of the genetic causes of inherited deafness and balance disorders. We will investigate a handful of genes, of the approximately 26,000 identified through the human genome project, that we suspect are critical for normal hearing and balance. We expect that this project will produce information that will form the basis for development of future strategies to treat deafness and balance problems in some of the ~28 million Americans who suffer from inner ear disorders.