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    Elucidating the Role of Ferritin in the Iron Metabolic Pathway of Aedes aegypti

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    Author
    Geiser, Dawn Lynn
    Issue Date
    2005
    Keywords
    Aedes aegypti
    ferritin
    iron metabolism
    mosquito
    iron
    secretion
    Committee Chair
    Winzerling, Joy J.
    
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    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    Female mosquitoes of the species, Aedes aegypti (yellow fever mosquito, Diptera), blood feed for oogenesis. Therefore, mosquitoes are exposed to high iron loads and possibly blood-borne pathogens. We are interested in studying iron metabolism in A. aegypti to find methods for controlling mosquito populations, and thereby reduce human exposure to these pathogens. First, we found that the expression of the Aedes ferritin light chain homologue (LCH) is up-regulated by blood feeding. Ferritin LCH and heavy chain homologue (HCH) genes are closely clustered together and both mRNA transcripts increase with iron and oxidative stress (H2O2 and hemin). Second, we show A. aegypti larval cells synthesize and secrete ferritin in response to iron. Cytoplasmic ferritin is maximal at low levels of iron, consists of a specific subunit composition and reflects cytoplasmic iron levels. Secreted ferritin increases in linear relationship to increasing iron dose and is composed of different subunits than cytoplasmic ferritin. HCH and LCH transcripts increase with increasing cytoplasmic iron suggesting transcriptional control of ferritin synthesis. We previously reported that the mosquito HCH mRNA has an iron responsive element (IRE), but LCH mRNA does not have a canonical IRE. We show that iron regulatory protein 1 (IRP1)/IRE binding activity declines in response to increasing cytoplasmic iron levels. These data would indicate that HCH synthesis is controlled at transcription and translation. Third, we report that A. aegypti larval cell cytoplasmic iron concentration does not change temporally with iron treatment. However, membrane iron levels increase with iron over time. Iron temporally up-regulates both HCH and LCH mRNA. Ferritin secretion increases with time in response to iron and reflects that most of the intracellular ferritin is found in the membrane fraction. Membrane ferritin has the same subunit composition as cytoplasmic ferritin. Finally, membrane ferritin is found in both non-iron and iron-treated cells. This suggests a mechanism to store iron from a blood meal in membrane ferritin. These results indicate Aedes ferritin could act as an antioxidant and holoferritin secretion is likely the mechanism whereby mosquito cells protect against iron overload and, thus reduce the intracellular potential for iron-mediated oxidative stress during blood feeding.
    Type
    text
    Electronic Dissertation
    Degree Name
    PhD
    Degree Level
    doctoral
    Degree Program
    Nutritional Sciences
    Graduate College
    Degree Grantor
    University of Arizona
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