Abstracts Category : Other

Characterization of a fourth Schistosoma mansoni glutamate-gated chloride channel subunit

by Hilary Byrne

Schistosomiasis, a neglected tropical disease caused by parasitic trematodes of the genus Schistosoma, affects hundreds of millions of people in developing areas of the world. Chronic schistosome infections impede growth and development, particularly in young children. The threat of resistance development to the only drug currently used to treat schistosomiasis, praziquantel (PZQ), has intensified the need for development of new schistosomicidal compounds. Targeting the nervous system of schistosomes for drug development is promising, as it coordinates many vital parasite functions. Glutamate-gated chloride channels of Schistosoma mansoni (SmGluCls) have been characterized recently and are of particular interest as they have been successfully targeted in other parasites. Four S. mansoni SmGluCl subunits were cloned and three of these were electrophysiologically characterized in Xenopus laevis oocytes and immunolocalized in parasites. The research in this thesis focuses on characterizing the fourth subunit, SmGluCl-4. Research also includes development of a mammalian cell-based fluorescence assay to enable screening of chemical libraries for channel agonists and antagonists. Two-electrode voltage clamp experiments showed that SmGluCl-4 does not form a functional homomeric receptor in oocytes; however, the subunit was localized to the surface of injected oocytes, indicating that unresponsiveness to glutamate was not due to lack of protein expression. Further experiments showed that SmGluCl-4 does not form a heteromeric receptor with other subunits. Although SmGluCl-4 does not form a functional receptor, confocal immunolocalization studies have shown that the subunit is found in both the central and peripheral nervous systems, with distribution patterns similar to the other SmGluCls, indicating that SmGluCl-4 may have a functional role within the parasite that can not be elucidated with our current methods. A yellow-fluorescence protein (YFP) assay to detect SmGluCl channel activity was developed by co-transfecting mammalian cells with plasmids encoding YFP and SmGluCl-2 (a subunit previously shown to form a functional glutamate receptor). Application of glutamate lead to a decrease of fluorescence, indicating functional channel activity. Future work would involve scaling this assay for use in high-throughput screening. La schistosomiase est une maladie tropicale nglige cause par des parasites du genre Schistosoma qui affecte des centaines de millions de personnes dans les pays en voie de dveloppement. La schistosomiase chronique entrave la croissance et le dveloppement, particulirement chez les enfants en bas ge. La menace de dveloppement de rsistance au seul mdicament disponible pour le traitement de la schistosomiase, le PZQ, rend indispensable le dveloppement de nouveaux agents schistosomicides. Le systme nerveux des schistosomes, tant responsable de beaucoup the fonctions vitales du parasite, est une excellente cible pour le dveloppement de nouveaux mdicaments. Les rcepteurs sensitifs auAdvisors/Committee Members: Timothy Geary (Internal/Supervisor).