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Determining Aspergillus fumigatus transcription factor expression and function during invasion of the mammalian lung.

ABSTRACT: To gain a better understanding of the transcriptional response of Aspergillus fumigatus during invasive pulmonary infection, we used a NanoString nCounter to assess the transcript levels of 467 A. fumigatus genes during growth in the lungs of immunosuppressed mice. These genes included ones known to respond to diverse environmental conditions and those encoding most transcription factors in the A. fumigatus genome. We found that invasive growth in vivo induces a unique transcriptional profile as the organism responds to nutrient limitation and attack by host phagocytes. This in vivo transcriptional response is largely mimicked by in vitro growth in Aspergillus minimal medium that is deficient in nitrogen, iron, and/or zinc. From the transcriptional profiling data, we selected 9 transcription factor genes that were either highly expressed or strongly up-regulated during in vivo growth. Deletion mutants were constructed for each of these genes and assessed for virulence in mice. Two transcription factor genes were found to be required for maximal virulence. One was rlmA, which is required for the organism to achieve maximal fungal burden in the lung. The other was sltA, which regulates of the expression of multiple secondary metabolite gene clusters and mycotoxin genes independently of laeA. Using deletion and overexpression mutants, we determined that the attenuated virulence of the ΔsltA mutant is due in part to decreased expression aspf1, which specifies a ribotoxin, but is not mediated by reduced expression of the fumigaclavine gene cluster or the fumagillin-pseruotin supercluster. Thus, in vivo transcriptional profiling focused on transcription factors genes provides a facile approach to identifying novel virulence regulators.

SUBMITTER: Liu H

PROVIDER: S-EPMC8031882 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Destruction of the pulmonary epithelium is a major feature of lung diseases caused by the mould pathogen Aspergillus fumigatus. Although it is widely postulated that tissue invasion is governed by fungal proteases, A. fumigatus mutants lacking individual or multiple enzymes remain fully invasive, suggesting a concomitant requirement for other pathogenic activities during host invasion. In this study we discovered, and exploited, a novel, tissue non-invasive, phenotype in A. fumigatus mutants lacking the pH-responsive transcription factor PacC. Our study revealed a novel mode of epithelial entry, occurring in a cell wall-dependent manner prior to protease production, and via the Dectin-1 β-glucan receptor. ΔpacC mutants are defective in both contact-mediated epithelial entry and protease expression, and significantly attenuated for pathogenicity in leukopenic mice. We combined murine infection modelling, in vivo transcriptomics, and in vitro infections of human alveolar epithelia, to delineate two major, and sequentially acting, PacC-dependent processes impacting epithelial integrity in vitro and tissue invasion in the whole animal. We demonstrate that A. fumigatus spores and germlings are internalised by epithelial cells in a contact-, actin-, cell wall- and Dectin-1 dependent manner and ΔpacC mutants, which aberrantly remodel the cell wall during germinative growth, are unable to gain entry into epithelial cells, both in vitro and in vivo. We further show that PacC acts as a global transcriptional regulator of secreted molecules during growth in the leukopenic mammalian lung, and profile the full cohort of secreted gene products expressed during invasive infection. Our study reveals a combinatorial mode of tissue entry dependent upon sequential, and mechanistically distinct, perturbations of the pulmonary epithelium and demonstrates, for the first time a protective role for Dectin-1 blockade in epithelial defences. Infecting ΔpacC mutants are hypersensitive to cell wall-active antifungal agents highlighting the value of PacC signalling as a target for antifungal therapy.

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:Inhibition of fungal growth by Congo Red (CR) has been known for a long time and claimed to be associated to a specific binding to fibrillar chains of β-1,3-glucans which blocks cell wall polysaccharide synthesis. It has also been suggested that the effect of CR could be pleiotropic, especially because of its oxido-reductive properties. One way to elucidate the mechanism of action of CR is to identify transcription factors (TF) which regulate the response to CR and interrogate their regulon. The analysis of TF mutants with differential sensitivity to CR would be also a way to identify new regulatory pathways involved in cell wall biosynthesis. During the investigation of the sensitivity to CR of a TF mutant library, several mutants either sensitive or resistant to CR were analysed . The morphology of the conidial germination was affected differently by CR in the parental strain and TF mutants. Abnormal distorted swollen conidia called Quasimodo cells were seen in presence of the CR. The size of the Quasimodo cells in the resistant mutants are bigger and adsorb more CR than the germinating conidia of the sensitive or parental strain. This is associated to a difference in permeability of the mutants. The clearing of the drug from the medium by the resistant strain was mainly responsible for the survival and later growth of some of resting conidia of these mutants which did not adsorb intracellularly the drug whereas in the sensitive mutants all conidia adsorbed the drug and were consequently killed. Although there are some modifications of the composition of the cell wall, a transcriptomic analysis of the mutant showed that CR affected many different pathways, including iron and calcium metabolism. Accordingly, the susceptibility to other cell wall drugs of the sensitive and the resistant TF mutants varied with the mutants and not always in connexion with their sensitivity to CR. Interestingly, a new paradoxical effect of the CR was discovered in the resistant mutant since the growth of one of them could be stimulated after recovering from the CR stress.

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Determining Aspergillus fumigatus transcription factor expression and function during invasion of the mammalian lung.

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