The dimorphic fungus Histoplasma capsulatum (Hc) is a facultative intracellular pathogen of macrophages that causes respiratory and systemic disease. The essential nutrient iron lies at the competitive interface between the mammalian host and nearly all microbial pathogens, including Hc. The host displays both constitutive and inducible iron sequestration mechanisms. Iron limitation acts as an important host defense mechanism against Hc in human and mouse macrophage cell culture infection models. As a successful pathogen, Hc expresses iron acquisition mechanisms to obtain this nutrient in the competitive host environment in which it resides during infection. Several Hc iron acquisition mechanisms have been demonstrated or proposed. Hc produces extracellular hydroxamate siderophores during iron-limited growth in vitro. Siderophores may compete with host iron-binding compounds such as transferrin (Tf) to acquire iron for the fungus. Hc also practices ferric reduction via at least three moieties - an extracellular ferric reductase enzyme, extracellular ferric reductant(s), and cell-surface ferric reducing agent(s). Reduction of ferric to ferrous iron causes removal from both host (e.g., Tf) and fungal (siderophore) iron-binding compounds. Finally, Tf releases iron at sufficiently acidic pH, to which Hc may be exposed in its macrophage intracellular compartment. Our hypothesis is that since iron acquisition is essential to Hc's pathogenesis, one or more or a combination of the mechanisms for accomplishing this process may provide effective new antifungal vaccine components and/or antibiotic targets. We propose to examine and determine pathogenic relevance of iron acquisition components and mechanisms for this fungus in the following three Specific Aims. 1) Identify and characterize physiologically relevant iron sources and processes for iron utilization in vitro and during intracellular infection using biochemical approaches. 2) Purify the Hc extracellular ferric reductase, clone the encoding gene, and examine its expression under pathogenically relevant conditions. 3) Identify other Hc structural, biosynthetic, and regulatory genes involved in iron acquisition by molecular genetic approaches and determine their importance in Hc intracellular infection.

Agency
National Institute of Health (NIH)
Institute
National Institute of Allergy and Infectious Diseases (NIAID)
Type
Research Project (R01)
Project #
5R01AI052303-03
Application #
6746893
Study Section
Bacteriology and Mycology Subcommittee 2 (BM)
Program Officer
Duncan, Rory A
Project Start
2002-09-30
Project End
2007-02-28
Budget Start
2004-03-01
Budget End
2005-02-28
Support Year
3
Fiscal Year
2004
Total Cost
$322,548
Indirect Cost
Name
University of Wisconsin Madison
Department
Microbiology/Immun/Virology
Type
Schools of Medicine
DUNS #
161202122
City
Madison
State
WI
Country
United States
Zip Code
53715
Cooper, Kendal G; Woods, Jon P (2009) Secreted dipeptidyl peptidase IV activity in the dimorphic fungal pathogen Histoplasma capsulatum. Infect Immun 77:2447-54
Cooper, Kendal G; Zarnowski, Robert; Woods, Jon P (2009) Histoplasma capsulatum encodes a dipeptidyl peptidase active against the mammalian immunoregulatory peptide, substance P. PLoS One 4:e5281
Zarnowski, Robert; Dobrzyn, Agnieszka; Ntambi, James M et al. (2008) Ferrous, but not ferric, iron maintains homeostasis in Histoplasma capsulatum triacylglycerides. Curr Microbiol 57:153-7
Zarnowski, Robert; Dobrzyn, Agnieszka; Ntambi, James M et al. (2008) Neutral storage lipids of Histoplasma capsulatum: effect of culture age. Curr Microbiol 56:110-4
Aravalli, Rajagopal N; Hu, Shuxian; Woods, Jon P et al. (2008) Histoplasma capsulatum yeast phase-specific protein Yps3p induces Toll-like receptor 2 signaling. J Neuroinflammation 5:30
Zarnowski, Robert; Cooper, Kendal G; Brunold, Laura Schmitt et al. (2008) Histoplasma capsulatum secreted gamma-glutamyltransferase reduces iron by generating an efficient ferric reductant. Mol Microbiol 70:352-68
Bohse, Megan L; Woods, Jon P (2007) Expression and interstrain variability of the YPS3 gene of Histoplasma capsulatum. Eukaryot Cell 6:609-15
Bohse, Megan L; Woods, Jon P (2007) RNA interference-mediated silencing of the YPS3 gene of Histoplasma capsulatum reveals virulence defects. Infect Immun 75:2811-7
Zarnowski, Robert; Connolly, Patricia A; Wheat, L Joseph et al. (2007) Production of extracellular proteolytic activity by Histoplasma capsulatum grown in Histoplasma-macrophage medium is limited to restriction fragment length polymorphism class 1 isolates. Diagn Microbiol Infect Dis 59:39-47
Zarnowski, Robert; Miyazaki, Makoto; Dobrzyn, Agnieszka et al. (2007) Typing of Histoplasma capsulatum strains by fatty acid profile analysis. J Med Microbiol 56:788-97

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