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Aspergillus fumigatus MedA governs adherence, host cell interactions and virulence.

ABSTRACT: In medically important fungi, regulatory elements that control development and asexual reproduction often govern the expression of virulence traits. We therefore cloned the Aspergillus fumigatus developmental modifier MedA and characterized its role in conidiation, host cell interactions and virulence. As in the model organism Aspergillus nidulans, disruption of medA in A. fumigatus dramatically reduced conidiation. However, the conidiophore morphology was markedly different between the two species. Further, gene expression analysis suggested that MedA governs conidiation through different pathways in A. fumigatus compared with A. nidulans. The A. fumigatusDeltamedA strain was impaired in biofilm production and adherence to plastic, as well as adherence to pulmonary epithelial cells, endothelial cells and fibronectin in vitro. The DeltamedA strain also had reduced capacity to damage pulmonary epithelial cells, and stimulate pro-inflammatory cytokine mRNA and protein expression. Consistent with these results, the A. fumigatusDeltamedA strain also exhibited reduced virulence in both an invertebrate and a mammalian model of invasive aspergillosis. Collectively, these results suggest that the downstream targets of A. fumigatus MedA mediate virulence, and may provide novel therapeutic targets for invasive aspergillosis.

SUBMITTER: Gravelat FN

PROVIDER: S-EPMC3370655 | biostudies-literature | 2010 Apr

REPOSITORIES: biostudies-literature

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Aspergillus fumigatus MedA governs adherence, host cell interactions and virulence.

Gravelat Fabrice N FN Ejzykowicz Daniele E DE Chiang Lisa Y LY Chabot Josée C JC Urb Mirjam M Macdonald K Denyese KD al-Bader Nadia N Filler Scott G SG Sheppard Donald C DC

Cellular microbiology 20091104 4

In medically important fungi, regulatory elements that control development and asexual reproduction often govern the expression of virulence traits. We therefore cloned the Aspergillus fumigatus developmental modifier MedA and characterized its role in conidiation, host cell interactions and virulence. As in the model organism Aspergillus nidulans, disruption of medA in A. fumigatus dramatically reduced conidiation. However, the conidiophore morphology was markedly different between the two spec ...[more]

PMID: 19889083

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Project description:The APSES transcription factor (TF) in Aspergillus species is known to govern diverse cellular processes, including growth, development, and secondary metabolism. Here, we investigated functions of the rgdA gene (Afu3g13920) encoding a putative APSES TF in the opportunistic human-pathogenic fungus Aspergillus fumigatus The rgdA deletion resulted in significantly decreased hyphal growth and asexual sporulation. Consistently, transcript levels of the key asexual developmental regulators abaA, brlA, and wetA were decreased in the ?rgdA mutant compared to those in the wild type (WT). Moreover, ?rgdA resulted in reduced spore germination rates and elevated transcript levels of genes associated with conidium dormancy. The conidial cell wall hydrophobicity and architecture were changed, and levels of the RodA protein were decreased in the ?rgdA mutant. Comparative transcriptomic analyses revealed that the ?rgdA mutant showed higher mRNA levels of gliotoxin (GT)-biosynthetic genes and GT production. While the ?rgdA mutant exhibited elevated production of GT, ?rgdA strains showed reduced virulence in the mouse model. In addition, mRNA levels of genes associated with the cyclic AMP (cAMP)-protein kinase A (PKA) signaling pathway and the SakA mitogen-activated protein (MAP) kinase pathway were increased in the ?rgdA mutant. In summary, RgdA plays multiple roles in governing growth, development, GT production, and virulence which may involve attenuation of PKA and SakA signaling.IMPORTANCE Immunocompromised patients are susceptible to infections with the opportunistic human-pathogenic fungus Aspergillus fumigatus This fungus causes systemic infections such as invasive aspergillosis (IA), which is one of the most life-threatening fungal diseases. To control this serious disease, it is critical to identify new antifungal drug targets. In fungi, the transcriptional regulatory proteins of the APSES family play crucial roles in controlling various biological processes, including mating, asexual sporulation and dimorphic growth, and virulence traits. This study found that a putative APSES transcription factor, RgdA, regulates normal growth, asexual development, conidium germination, spore wall architecture and hydrophobicity, toxin production, and virulence in A. fumigatus Better understanding the molecular mechanisms of RgdA in human-pathogenic fungi may reveal a novel antifungal target for future drug development.

Project description:Invasive aspergillosis is initiated when Aspergillus fumigatus adheres to and invades the pulmonary epithelial cells that line the airways and alveoli. To gain deeper insight into how pulmonary epithelial cells respond to A. fumigatus invasion, we used transcriptome sequencing (RNA-seq) to determine the transcriptional response of the A549 type II alveolar epithelial cell line to infection with strains CEA10 and Af293, two clinical isolates of A. fumigatus. Upstream regulator analysis of the data indicated that while both strains activated virtually identical host cell signaling pathways after 16 h of infection, only strain CEA10 activated these pathways after 6 h of infection. Many of the pathways that were predicted to be activated by A. fumigatus, including the tumor necrosis factor (TNF), interleukin-1α (IL-1α), IL-1β, IL-17A, Toll-like receptor 2 (TLR2), and TLR4 pathways, are known to be critical for the host defense against this fungus. We also found that the platelet-derived growth factor BB (PDGF BB) and progesterone receptor (PGR) pathways were activated by A. fumigatus. Using pharmacologic inhibitors, we determined that blocking the PDGF receptor or PGR inhibited the endocytosis of both strains of A. fumigatus in an additive manner. Both the PDGF BB and PGR pathways are also predicted to be activated by infection of A549 cells with other molds, such as Rhizopus delemar and Rhizopus oryzae. Thus, these pathways may represent a common response of pulmonary epithelial cells to mold infection. IMPORTANCE Invasive aspergillosis is a deadly invasive fungal infection that initiates when Aspergillus fumigatus spores are inhaled and come into contact with the epithelial cells that line the airways and alveoli. Understanding this fungus-host interaction is important for the development of novel therapeutics. To gain a deeper understanding of how these airway epithelial cells respond to A. fumigatus during infection, we used RNA-seq to determine the transcriptional response of alveolar epithelial cells to infection with two different clinical isolates of A. fumigatus. Our analysis identified new host response pathways that have not previously been tied to infection with A. fumigatus. Pharmacological inhibition of two of these pathways inhibited the ability of A. fumigatus to invade airway epithelial cells. These two pathways are also predicted to be activated by infection with other filamentous fungi. Thus, these pathways may represent a common response of alveolar epithelial cells to mold infection.

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Project description:Aspergillus fumigatus is an opportunistic fungal pathogen that can cause life-threatening invasive lung infections in immunodeficient patients. The cellular and molecular processes of infection during onset, establishment, and progression of A. fumigatus infections are highly complex and depend on both fungal attributes and the immune status of the host. Therefore, preclinical animal models are of paramount importance to investigate and gain better insight into the infection process. Yet, despite their extensive use, commonly employed murine models of invasive pulmonary aspergillosis are not well understood due to analytical limitations. Here, we present quantitative light sheet fluorescence microscopy (LSFM) to describe fungal growth and the local immune response in whole lungs at cellular resolution within its anatomical context. We analyzed three very common murine models of pulmonary aspergillosis based on immunosuppression with corticosteroids, chemotherapy-induced leukopenia, or myeloablative irradiation. LSFM uncovered distinct architectures of fungal growth and degrees of tissue invasion in each model. Furthermore, LSFM revealed the spatial distribution, interaction, and activation of two key immune cell populations in antifungal defense: alveolar macrophages and polymorphonuclear neutrophils. Interestingly, the patterns of fungal growth correlated with the detected effects of the immunosuppressive regimens on the local immune cell populations. Moreover, LSFM demonstrates that the commonly used intranasal route of spore administration did not result in complete intra-alveolar deposition, as about 80% of fungal growth occurred outside the alveolar space. Hence, characterization by LSFM is more rigorous than by previously used methods employing murine models of invasive pulmonary aspergillosis and pinpoints their strengths and limitations.IMPORTANCE The use of animal models of infection is essential to advance our understanding of the complex host-pathogen interactions that take place during Aspergillus fumigatus lung infections. As in the case of humans, mice need to suffer an immune imbalance in order to become susceptible to invasive pulmonary aspergillosis (IPA), the most serious infection caused by A. fumigatus There are several immunosuppressive regimens that are routinely used to investigate fungal growth and/or immune responses in murine models of invasive pulmonary aspergillosis. However, the precise consequences of the use of each immunosuppressive model for the local immune populations and for fungal growth are not completely understood. Here, to pin down the scenarios involving commonly used IPA models, we employed light sheet fluorescence microscopy (LSFM) to analyze whole lungs at cellular resolution. Our results will be valuable to optimize and refine animal models to maximize their use in future research.

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Aspergillus fumigatus MedA governs adherence, host cell interactions and virulence.

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Aspergillus fumigatus MedA governs adherence, host cell interactions and virulence.

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