1337. Extracellular Galactosaminogalactan Production Is Required for Aspergillus fumigatus Adherence, Host Cell Interactions and Virulence
Session: Oral Abstract Session: Fungal Pathogenesis, Virulence, and Anti-fungal Therapy
Saturday, October 22, 2011: 2:30 PM
Room: 151AB
Background: Aspergillus fumigatus is the most common mold pathogen of humans, yet few virulence factors have been identified. Although adherence of A. fumigatus to host constituents is a key step in the development of colonization and invasive disease, the molecular mechanisms underlying this process are unknown.   Our aim was to identify the fungal factors required for the adherence of A. fumigatus to host epithelial cells and other biologic substrates.

Methods: We conducted a disruption screen of A. fumigatus transcription factors in order to identify regulatory pathways governing fungal adherence.  Mutants were screened using adherence assays, electronic microscopy observations, cell wall carbohydrate analysis, host cell interaction assays and virulence assays.  Mutants exhibiting a reduction in adherence were then analysed using whole genome transcriptional profiling to identify candidate effector genes governing adherence.  Candidate genes were then studied using gene deletion and phenotypic assays as above.

Results: Mutants deficient in two transcription factors, medA and stuA, exhibited marked reduction in adherence to host cells, abnormally thickened cell walls, and a near complete absence of the cell wall and extracellular glycan galactosaminogalactan (GAG). This defect in adherence could be rescued by the addition of exogenous GAG. A transcriptome comparison of ΔmedA and ΔstuA identified a novel cluster of 5 genes, including a putative glucose epimerase encoding gene, uge3.  Deletion of uge3 completely blocked GAG synthesis, resulting in a strain that was non-adherent to host constituents, and unable to induce host cell damage and epithelial cell cytokine responses.  Blocking GAG synthesis by deleting uge3 also significantly attenuated virulence in a murine model of invasive aspergillosis.

Conclusion: These studies suggest that the A. fumigatus glycan GAG mediates adherence to host constituents and plays an important role in virulence.  Further, we have identified a putative biosynthetic gene cluster that governs GAG synthesis.  Since GAG is absent from higher eukaryotes, this pathway may represent an important target for novel antifungal strategies.


Subject Category: M. Mycology including clinical and basic studies of fungal infections

Fabrice Gravelat, PhD, Microbiology and Immunology, McGill University, Montreal, QC, Canada

Disclosures:

F. Gravelat, None

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