Abstract
The ubiquitous mold Aspergillus fumigatus threatens immunosuppressed patients as inducer of lethal invasive aspergillosis. A. fumigatus conidia are airborne and reach the alveoli, where they encounter alveolar epithelial cells (AEC). Previous studies reported the importance of the surfactant-producing AEC II during A. fumigatus infection via in vitro experiments using cell lines. We established a negative isolation protocol yielding untouched primary murine AEC II with a purity >90%, allowing ex vivo analyses of the cells, which encountered the mold in vivo By label-free proteome analysis of AEC II isolated from mice 24h after A. fumigatus or mock infection we quantified 2256 proteins and found 154 proteins to be significantly differentially abundant between both groups (ANOVA p value ≤ 0.01, ratio of means ≥1.5 or ≤0.67, quantified with ≥2 peptides). Most of these proteins were higher abundant in the infected condition and reflected a comprehensive activation of AEC II on interaction with A. fumigatus This was especially represented by proteins related to oxidative phosphorylation, hence energy production. However, the most strongly induced protein was the l-amino acid oxidase (LAAO) Interleukin 4 induced 1 (IL4I1) with a 42.9 fold higher abundance (ANOVA p value 2.91-10). IL4I1 has previously been found in B cells, macrophages, dendritic cells and rare neurons. Increased IL4I1 abundance in AEC II was confirmed by qPCR, Western blot and immunohistology. Furthermore, A. fumigatus infected lungs showed high levels of IL4I1 metabolic products. Importantly, higher IL4I1 abundance was also confirmed in lung tissue from human aspergilloma. Because LAAO are key enzymes for bactericidal product generation, AEC II might actively participate in pathogen defense. We provide insights into proteome changes of primary AEC II thereby opening new avenues to analyze the molecular changes of this central lung cell on infectious threats. Data are available via ProteomeXchange with identifier PXD005834.
Highlights
The most strongly induced protein was the L-amino acid oxidase (LAAO) Interleukin 4 induced 1 (IL4I1) with a 42.9 fold higher abundance (ANOVA p value 2.91؊10)
A. fumigatus conidia Interact with alveolar epithelial cells (AEC) II—It has been shown that AEC II play significant roles in association with A. fumigatus infection, albeit mostly using in vitro studies with cell lines (29 –33)
A. fumigatus infection is a life-threatening condition for immunosuppressed patients around the globe, because it can develop into invasive aspergillosis, which eventually can lead to death
Summary
The most strongly induced protein was the L-amino acid oxidase (LAAO) Interleukin 4 induced 1 (IL4I1) with a 42.9 fold higher abundance (ANOVA p value 2.91؊10). Aspergillus fumigatus is an ubiquitous saprophytic fungus [1] that grows on decaying organic matter Due to their small size and high surface charge, conidia, the spores of A. fumigatus, are airborne and hundreds are inhaled by humans daily together with the breathing air [2]. N are extremely effective in phagocytosing conidia [8, 9], which is the reason why especially lack or dysfunction of N is associated with a highly increased risk for IA development (10 –12) These phagocytotic members of the lung-associated immune system are all well studied, it is obvious, that alveolar epithelial cells (AEC), that make up the entire more than 100 m2 large respiratory surface of the lung [12] have a much higher likelihood of physically engaging freshly inhaled conidia before any other cell of the immune system [13].
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