2010 |
Hailey, Dale Warren |
F32Activity Code Description: To provide postdoctoral research training to individuals to broaden their scientific background and extend their potential for research in specified health-related areas. |
Determining How Aminoglycoside-Induced Hair Cell Death Is Blocked @ University of Washington
DESCRIPTION (provided by applicant): Hair cells in the inner ear are responsible for sensing sounds, and conditions that kill hair cells because hearing loss. Age-related and noise-induced hearing loss is largely attributable to death of hair cells. Similarly, drugs that damage hearing-ototoxic drugs--often do so by killing hair cells. Despite our awareness that many drugs can damage hearing, a number of ototoxic drugs is still used. These include the aminoglycoside antibiotics. Aminoglycosides are used in this country to treat chronic life threatening conditions, and in underdeveloped countries often for non-life threatening infections. Our lab is identifying ways to block hair cell death during aminoglycoside treatment. Because it is very challenging to study aminoglycoside ototoxicity in the human ear, we use zebrafish. In addition to inner ear hair cells, zebrafish have hair cells on their surface in a sensory system called the lateral line. These lateral line hair cells inform the fish about movements in the surrounding water, and are similar to mammalian inner ear hair cells in many respects. Unlike hair cells of the inner ear however, they are on the surface of the fish, they readily take up drugs and dyes from the surrounding water, and they are easy to observe. Particularly notable to us--they are also sensitive to aminoglycoside exposure. We made a collection of fish that carry mutations, and identified mutant fish in which lateral line hair cells are not damaged by aminoglycosides. These rare fish may reveal targets we can use for therapies to prevent aminoglycoside toxicity in humans. I propose to study one such fish-persephone. The persephone mutant is notable because it is indistinguishable from normal fish, except that its hair cells do not die when exposed to aminoglycosides. We identified the gene that is altered in persephone, and established that it moves chloride and bicarbonate ions across cell membranes. Altering the normal movement of these ions somehow dramatically protects hair cells in persephone. I want to understand why this happens. The work proposed here should reveal whether the hair cells in the persephone mutant are themselves different from wild type fish. It should also reveal events leading to death of hair cells in wild type fish that do not occur in persephone. These studies should provide new insights into ways to block hair cell death during aminoglycoside treatment. Drugs exist that specifically affect the ion movement that is altered in persephone, and understanding why persephone hair cells do not die when exposed to aminoglycosides has promise for future therapies to protect human hair cells. PUBLIC HEALTH RELEVANCE: Death of hair cells of the inner ear is a prevalent cause of hearing damage and loss in the general population. A number of conditions cause hair cell death, including exposure to aminoglycoside antibiotics. This proposal is aimed at understanding what happens to hair cells when they are exposed to these antibiotics, and to identify ways to protect hair cells during treatment with these antibiotics.
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0.958 |
2012 — 2014 |
Hailey, Dale Warren |
R03Activity Code Description: To provide research support specifically limited in time and amount for studies in categorical program areas. Small grants provide flexibility for initiating studies which are generally for preliminary short-term projects and are non-renewable. |
Intercellular Trafficking of Labeled Aminoglycosides in Living Hair Cells @ University of Washington
DESCRIPTION (provided by applicant): The vast majority of hearing loss occurs due to the death of mechanosensory hair cells of the inner ear. Many environmental and genetic factors contribute to hair cell death in the human population, including noise, age, and ototoxic drug exposure. This project focuses on hair cell death caused by exposure to a family of ototoxic antibiotics-the aminoglycosides. Aminoglycosides specifically kill hair cells and cells of the proximal tubule of the kidney, in addition to their desired pathogenic targets. While kidney damage is often temporary, loss of inner ear hair cells results in permanent hearing loss. Because the aminoglycosides are effective antibiotics, blocking their ototoxicity has been a longstanding goal of the hearing research community (Forge and Schacht, 2000). Reducing hair cell death caused by aminoglycoside antibiotics would allow us to better treat tuberculosis, meningitis, cystic fibrosis, and a range of systemic infections (Cheng et al., 2009; Lima et al., 2006; Yeat et al., 1997). Why hair cells are uniquely sensitive to aminoglycoside exposure remains unclear. Activity of the mechanotransduction (MET) channel-the channel that opens in response to sound stimuli-- facilitates entry of aminoglycosides into hair cells. Genetic mutations and small molecules that perturb MET channel activity inhibit entry of aminoglycosides and protect hair cells. However, while entry of aminoglycosides is critical for their toxicity, other intracellular events mediate aminoglycoside-induced hair cell death. In a genetic screen, we identified the sentinel mutant which shows striking protection from aminoglycosides, while having no effect on the entry of aminoglycosides into hair cells. Because this mutant affects intracellular trafficking events in other contexts, it suggests that altered intracellular traffickng of aminoglycosides may underlie protection in sentinel. Additionally, we observe that the dynamin inhibitor dynasore-which perturbs many intracellular trafficking events--also protects hair cells from aminoglycoside- induced toxicity. Both of these findings suggest that perturbing the intracellular trafficking of aminoglycosides can reduce their toxicity. To study how aminoglycosides are trafficked within hair cells, I propose to follow the trafficking of the labele aminoglycoside neomycin-TexasRed in hair cells. I will use zebrafish lateral line hair cells because we can easily image these cells in their native context while exposing them to Neomycin- TexasRed, vital dyes, and bioactive molecules. In preliminary pulse label studies, we have monitored movement of labeled neomycin from the stereocilia into intracellular structures, and see alterations in those structures during neomycin exposure. I propose to characterize the intracellular compartments transited by labeled neomycin, and developing tools to perturb intracellular trafficking pathways to identify key trafficking events that underlie aminoglycoside toxicity. PUBLIC HEALTH RELEVANCE: Aminoglycosides are very effective antibiotics used to treat a variety of systemic infections. Unfortunately, treatment with these antibiotics frequently causes permanent hearing loss by killing cells of the inner ear that convert sound into nerve impulses. I propose to investigate ways we can reduce aminoglycosides toxicity by determining where aminoglycosides accumulate and whether we can decrease their toxicity by altering delivery to those intracellular sites.
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0.958 |