Interference of Aspergillus fumigatus with the immune response.

Aspergillus fumigatus is a saprotrophic filamentous fungus and also the most prevalent airborne fungal pathogen of humans. Depending on the host's immune status, the variety of diseases caused by A. fumigatus ranges from allergies in immunocompetent hosts to life-threatening invasive infections in patients with impaired immunity. In contrast to the majority of other Aspergillus species, which are in most cases nonpathogenic, A. fumigatus features an armory of virulence determinants to establish an infection. For example, A. fumigatus is able to evade the human complement system by binding or degrading complement regulators. Furthermore, the fungus interferes with lung epithelial cells, alveolar macrophages, and neutrophil granulocytes to prevent killing by these immune cells. This chapter summarizes the different strategies of A. fumigatus to manipulate the immune response. We also discuss the potential impact of recent advances in immunoproteomics to improve diagnosis and therapy of an A. fumigatus infection.

Identification of hypoxia-inducible target genes of Aspergillus fumigatus by transcriptome analysis reveals cellular respiration as an important contributor to hypoxic survival.

Aspergillus fumigatus is an opportunistic, airborne pathogen that causes invasive aspergillosis in immunocompromised patients. During the infection process, A. fumigatus is challenged by hypoxic microenvironments occurring in inflammatory, necrotic tissue. To gain further insights into the adaptation mechanism, A. fumigatus was cultivated in an oxygen-controlled chemostat under hypoxic and normoxic conditions. Transcriptome analysis revealed a significant increase in transcripts associated with cell wall polysaccharide metabolism, amino acid and metal ion transport, nitrogen metabolism, and glycolysis. A concomitant reduction in transcript levels was observed with cellular trafficking and G-protein-coupled signaling. To learn more about the functional roles of hypoxia-induced transcripts, we deleted A. fumigatus genes putatively involved in reactive nitrogen species detoxification (fhpA), NAD(+) regeneration (frdA and osmA), nitrogen metabolism (niaD and niiA), and respiration (rcfB). We show that the nitric oxygen (NO)-detoxifying flavohemoprotein gene fhpA is strongly induced by hypoxia independent of the nitrogen source but is dispensable for hypoxic survival. By deleting the nitrate reductase gene niaD, the nitrite reductase gene niiA, and the two fumarate reductase genes frdA and osmA, we found that alternative electron acceptors, such as nitrate and fumarate, do not have a significant impact on growth of A. fumigatus during hypoxia, but functional mitochondrial respiratory chain complexes are essential under these conditions. Inhibition studies indicated that primarily complexes III and IV play a crucial role in the hypoxic growth of A. fumigatus.

Elucidating the fungal stress response by proteomics.

Fungal species need to cope with stress, both in the natural environment and during interaction of human- or plant pathogenic fungi with their host. Many regulatory circuits governing the fungal stress response have already been discovered. However, there are still large gaps in the knowledge concerning the changes of the proteome during adaptation to environmental stress conditions. With the application of proteomic methods, particularly 2D-gel and gel-free, LC/MS-based methods, first insights into the composition and dynamic changes of the fungal stress proteome could be obtained. Here, we review the recent proteome data generated for filamentous fungi and yeasts. This article is part of a Special Issue entitled: Trends in Microbial Proteomics.

Investigation of Aspergillus fumigatus biofilm formation by various "omics" approaches.

In the lung, Aspergillus fumigatus usually forms a dense colony of filaments embedded in a polymeric extracellular matrix called biofilm (BF). This extracellular matrix embeds and glues hyphae together and protects the fungus from an outside hostile environment. This extracellular matrix is absent in fungal colonies grown under classical liquid shake conditions (PL), which were historically used to understand A. fumigatus pathobiology. Recent works have shown that the fungus in this aerial grown BF-like state exhibits reduced susceptibility to antifungal drugs and undergoes major metabolic changes that are thought to be associated to virulence. These differences in pathological and physiological characteristics between BF and liquid shake conditions suggest that the PL condition is a poor in vitro disease model. In the laboratory, A. fumigatus mycelium embedded by the extracellular matrix can be produced in vitro in aerial condition using an agar-based medium. To provide a global and accurate understanding of A. fumigatus in vitro BF growth, we utilized microarray, RNA-sequencing, and proteomic analysis to compare the global gene and protein expression profiles of A. fumigatus grown under BF and PL conditions. In this review, we will present the different signatures obtained with these three "omics" methods. We will discuss the advantages and limitations of each method and their complementarity.