Interactions of an Emerging Fungal Pathogen Scedosporium aurantiacum with Human Lung Epithelial Cells

Abstract

Scedosporium fungi are found in various natural and host-associated environments, including the lungs of cystic fibrosis patients. However, their role in infection development remains underexplored. Here the attachment of conidia of a virulent S. aurantiacum strain WM 06.482 onto the human lung epithelial A549 cells in vitro was visualized using microscopy to examine the initial steps of infection. We showed that 75–80% of fungal conidia were bound to the A549 cells within four hours of co-incubation, and started to produce germ tubes. The germinating conidia seemed to invade the cells through the intercellular space, no intracellular uptake of fungal conidia by the airway epithelial cells after conidial attachment. Transcriptomic analysis of the A549 cells revealed that the up-regulated genes were mainly associated with cell repair and inflammatory processes indicating a protective response against S. aurantiacum infection. Network analysis of the differentially expressed genes showed activation of the innate immune system (NF-kB pathway) leading to the release of pro-inflammatory cytokines. We believe this is the first report showing the transcriptomic response of human alveolar epithelial cells exposed to S. aurantiacum conidia paving a way for better understanding of the mechanism of the infection process.

Insights into the interaction of Scedosporium apiospermum, Scedosporium aurantiacum, Scedosporium minutisporum, and Lomentospora prolificans with lung epithelial cells

“…In this sense, the whole genome transcriptional profiling of A549 cells after 8 h of interaction with S. aurantiacum and A. fumigatus showed several genes that are differentially expressed in comparison with non-infected cells. This highlights the increase in levels of transcripts from genes associated with wound healing, cell repair, and protective response, like genes that encode the chemokines IL-6, IL-8, IL-11, TNF-α, and MUC5, a gene involved in mucin production that indicates the initiation of mucociliary clearance [19,20,26]. In addition, a fibrous-like network secreted by A549 cells surrounding S. apiospermum conidia was previously observed through scanning electron microscopy [7].…”

“…The PRMs also mediate the in vitro adhesion between L. prolificans conidia and mouse peritoneal macrophages [16]. The conidial adhesion followed by its germination was also observed during the in vitro interaction events of S. apiospermum, S. boydii, and S. aurantiacum with lung epithelial cells (A549), lung fibroblasts (MRC-5), and mouse macrophages (RAW 264.7 line) [7,14,19,20]. Interesting studies were also conducted with peritoneal macrophages and polymorphonuclear cells in an effort to investigate the immune responses against Scedosporium/Lomentospora species [10,12,15].…”

The Host Immune Response to Scedosporium/Lomentospora

“…Conidia of Scedosporium / Lomentospora are able to adhere, differentiate into hyphae and form biofilms on human lung epithelial A549 cells, which implies, in a similar way as mentioned above for human larynx epithelial cells, an active participation of the fungus in this interaction [ 61 , 67 , 68 ]. Specifically, S. aurantiacum germinating conidia were able to invade epithelial cells through the intercellular space without intracellular uptake of fungal conidia.…”

Fun(gi)omics: Advanced and Diverse Technologies to Explore Emerging Fungal Pathogens and Define Mechanisms of Antifungal Resistance

“…The molecular feedback triggered by the host cell upon infection offers vital information into the pathogenesis, invasion, and virulence of the pathogenic fungi. For instance, the response of alveolar epithelial cells to Scedosporium aurantiacum infection was studied using RNA-Seq Illumina with paired-end sequence reads to reveal 3,950 differentially expressed genes ( 60 ). Infected host alveolar cells exhibited 2,008 upregulated genes with trends in cell death, inflammation, wound healing, and cell repair.…”