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.

Aspergillus fumigatus Acetate Utilization Impacts Virulence Traits and Pathogenicity

“…In Aspergillus spp., high- and low-affinity carbon source transporters are expressed depending on the concentration of the extracellular carbon source ( 39 ). A similar scenario can be envisaged for transcription factors (TFs), especially as they respond to external stimuli, with some TFs being highly induced under nutrient-limiting conditions and repressed in nutrient-sufficient conditions ( 20 ). Alternatively, Aspergillus transcriptions factors are not always regulated at the transcriptional level as previously shown ( 40 ).…”

“…Our understanding of the utilization of potential food sources during infection mainly relies on in vitro transcriptional studies ( 14 – 16 ). Despite several studies having investigated A. fumigatus gene expression during in vivo infection of chemotherapeutic mouse models of invasive aspergillosis, none of these studies have characterized the modulation of genes encoding components required for carbon source utilization ( 17 – 20 ). The genome of A. fumigatus encodes the acetyl coenzyme A (acetyl-CoA) synthetases (ACS) FacA (Afu4g11080) and PcsA (Afu2g07780), with facA shown to be upregulated in conidia exposed to neutrophils, and the corresponding protein induced by heat shock and repressed during hypoxic conditions ( 14 , 21 , 22 ).…”

Aspergillus fumigatus Fumagillin Contributes to Host Cell Damage

“…Regarding in vivo assays, Liu and coworkers evaluated the virulence ability of the mutant A. fumigatus non-fumagillin producer strain ∆fumR [24]. For that, they used a corticosteroid immunosuppressed mice model, and they did not describe any virulence difference between the mutant and the Wt strain.…”

“…The mycotoxin is produced by a series of enzymes encoded in a biosynthetic cluster located on chromosome 8 of A. fumigatus [22]. The members of the biosynthetic cluster are overexpressed in the lungs of intranasally infected mice [23] and include the fumagillin pathway-specific transcription factor [24]. In fact, a non-fumagillin producer mutant strain caused significantly less cellular damage than the wild type in vitro, demonstrating a potential relevance of this toxin in virulence [23].…”

State-of-the-Art Dermatophyte Infections: Epidemiology Aspects, Pathophysiology, and Resistance Mechanisms

“…Indeed, understanding the functionality of fungal transcription factors and their physiological and mechanistic roles has garnered special attention [ 89 ]. Transcription factors comprise the last link between signal perception and activation of targeted genes.…”