Nitrogen, Iron, and Zinc Acquisition: Key Nutrients to Aspergillus fumigatus Virulence

Aspergillus fumigatus is a ubiquitous soil decomposer and an opportunistic pathogen that is characterized by its large metabolic machinery for acquiring nutrients from media. Lately, an ever-increasing number of genes involved in fungal nutrition has been associated with its virulence. Of these, nitrogen, iron, and zinc metabolism-related genes are particularly noteworthy, since 78% of them have a direct implication in virulence. In this review, we describe the sensing, uptake and regulation process of the acquisition of these nutrients, the connections between pathways and the virulence-implicated genes. Nevertheless, only 40% of the genes mentioned in this review have been assayed for roles in virulence, leaving a wide field of knowledge that remains uncertain and might offer new therapeutic and diagnostic targets.This research was funded by the Basque Government: grant number IT1362-19. U.P.-C. and S.C.-S. received a predoctoral fellowship from the University of the Basque Country and Basque Government, respectively

Study of the carbohydrate/protein composition in different strains and morphologies.

<p>(A) Carbohydrate/protein ratio in the crude extracts of the different strains of <i>Candida albicans</i>: Blastoconidia (□) and germ tubes (▪). The results shown correspond to the mean ± SD of three independent experiments. Statistically significant differences between different morphologies are indicated by two asterisks (**) (p<0.05). (B). Regression line for the B16 melanoma (B16M) cell adhesion to hepatic sinusoidal endothelial (HSE) cells induced by the strains and morphologies of <i>C. albicans</i> that lead a significant effect <i>versus</i> their carbohydrate/protein ratio.</p

Results obtained from the killing treatments.

<p>(A–D) Effect of heat and metaperiodate treatments on <i>Candida albicans</i> cell surface studied by incubation with Con A-FITC followed by flow cytometry: cell complexity (side scatter, SSC), cell size (Forward Scatter, FSC), and fluorescence (FL1). R1: live cells. R2: cells killed with heat. R3: cells killed with a 20 mM metaperiodate. R4: cells killed with 50 mM metaperiodate. (E) Effect of heat- and sodium metaperiodate (50 mM)-treated <i>C. albicans</i> blastoconidia on the increase of B16 melanoma (B16M) cell adhesion to HSE. The results shown correspond to the mean ± SD of three independent experiments. Statistically significant differences with respect to the control or between cell conditions are indicated by one and two asterisks (**) (p<0.05), respectively.</p

Effect of the mannose receptor (MR) inhibition.

<p>Effect of the anti-mannose receptor antibodies (anti-MR) on the inhibition of the synthesis of IL-18 (A) and tumor cell adhesion to hepatic sinusoidal endothelial (HSE) cells (B) induced by <i>Candida albicans</i> UPV1413 and its mannoprotein-enriched fraction (MPF): basal medium (□), 30 µg/ml anti-MR (▪). The results shown correspond to the mean ± SD of three independent experiments. Statistically significant differences with respect to the controls or to the cells without antibodies are indicated by one (*) and two asterisks (**) (p<0.05), respectively.</p

Effect of morphology of the different strains of <i>Candida albicans</i> on the increase in B16 melanoma (B16M) cell adhesion to hepatic sinusoidal endothelial (HSE) cells.

<p>Blastoconidia (□) and germ tubes (▪). The results shown correspond to the mean ± SD of three independent experiments. Statistically significant differences with respect to the control or between different morphologies are indicated by one (*) and two asterisks (**) (p<0.05), respectively.</p

A possible role for fumagillin in cellular damage during host infection by Aspergillus fumigatus.

Virulence mechanisms of the pathogenic fungus Aspergillus fumigatus are multifactorial and depend on the immune state of the host, but little is known about the fungal mechanism that develops during the process of lung invasion. In this study, microarray technology was combined with a histopathology evaluation of infected lungs so that the invasion strategy followed by the fungus could be described. To achieve this, an intranasal mice infection was performed to extract daily fungal samples from the infected lungs over four days post-infection. The pathological study revealed a heavy fungal progression throughout the lung, reaching the blood vessels on the third day after exposure and causing tissue necrosis. One percent of the fungal genome followed a differential expression pattern during this process. Strikingly, most of the genes of the intertwined fumagillin/pseurotin biosynthetic gene cluster were upregulated as were genes encoding lytic enzymes such as lipases, proteases (DppIV, DppV, Asp f 1 or Asp f 5) and chitinase (chiB1) as well as three genes related with pyomelanin biosynthesis process. Furthermore, we demonstrate that fumagillin is produced in an in vitro pneumocyte cell line infection model and that loss of fumagillin synthesis reduces epithelial cell damage. These results suggest that fumagillin contributes to tissue damage during invasive aspergillosis. Therefore, it is probable that A. fumigatus progresses through the lungs via the production of the mycotoxin fumagillin combined with the secretion of lytic enzymes that allow fungal growth, angioinvasion and the disruption of the lung parenchymal structure

A possible role for fumagillin in cellular damage during host infection by Aspergillus fumigatus.

Virulence mechanisms of the pathogenic fungus Aspergillus fumigatus are multifactorial and depend on the immune state of the host, but little is known about the fungal mechanism that develops during the process of lung invasion. In this study, microarray technology was combined with a histopathology evaluation of infected lungs so that the invasion strategy followed by the fungus could be described. To achieve this, an intranasal mice infection was performed to extract daily fungal samples from the infected lungs over four days post-infection. The pathological study revealed a heavy fungal progression throughout the lung, reaching the blood vessels on the third day after exposure and causing tissue necrosis. One percent of the fungal genome followed a differential expression pattern during this process. Strikingly, most of the genes of the intertwined fumagillin/pseurotin biosynthetic gene cluster were upregulated as were genes encoding lytic enzymes such as lipases, proteases (DppIV, DppV, Asp f 1 or Asp f 5) and chitinase (chiB1) as well as three genes related with pyomelanin biosynthesis process. Furthermore, we demonstrate that fumagillin is produced in an in vitro pneumocyte cell line infection model and that loss of fumagillin synthesis reduces epithelial cell damage. These results suggest that fumagillin contributes to tissue damage during invasive aspergillosis. Therefore, it is probable that A. fumigatus progresses through the lungs via the production of the mycotoxin fumagillin combined with the secretion of lytic enzymes that allow fungal growth, angioinvasion and the disruption of the lung parenchymal structure

Candida albicans Increases Tumor Cell Adhesion to Endothelial Cells In Vitro: Intraspecific Differences and Importance of the Mannose Receptor

The dimorphic fungus Candida albicans is able to trigger a cytokine-mediated pro-inflammatory response that increases tumor cell adhesion to hepatic endothelium and metastasis. To check the intraspecific differences in this effect, we used an in vitro murine model of hepatic response against C. albicans, which made clear that tumor cells adhered more to endothelium incubated with blastoconidia, both live and killed, than germ tubes. This finding was related to the higher carbohydrate/protein ratio found in blastoconidia. In fact, destruction of mannose ligand residues on the cell surface by metaperiodate treatment significantly reduced tumor cell adhesion induced. Moreover, we also noticed that the effect of clinical strains was greater than that of the reference one. This finding could not be explained by the carbohydrate/protein data, but to explain these differences between strains, we analyzed the expression level of ten genes (ADH1, APE3, IDH2, ENO1, FBA1, ILV5, PDI1, PGK1, QCR2 and TUF1) that code for the proteins identified previously in a mannoprotein-enriched pro-metastatic fraction of C. albicans. The results corroborated that their expression was higher in clinical strains than the reference one. To confirm the importance of the mannoprotein fraction, we also demonstrate that blocking the mannose receptor decreases the effect of C. albicans and its mannoproteins, inhibiting IL-18 synthesis and tumor cell adhesion increase by around 60%. These findings could be the first step towards a new treatment for solid organ cancers based on the role of the mannose receptor in C. albicans-induced tumor progression and metastasis