Ability to grow on lipids accounts for the fully virulent phenotype in neutropenic mice of Aspergillus fumigatus null mutants in the key glyoxylate cycle enzymes

Departamento de Microbiología y Parasitología, Universidad de Alcalá, Carretera Madrid-Barcelona Km 33, Alcalá de Henares, ES-28871 Madrid, Spain.
Fungal Genetics and Biology (Impact Factor: 2.59). 02/2008; 45(1):45-60. DOI: 10.1016/j.fgb.2007.05.002
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Incidence and mortality rates of invasive aspergillosis clearly indicate the need of novel antifungals to treat patients suffering from this disease. Fungal proteins playing a crucial role in pathogenesis and with no orthologue in human cells are considered as primary therapeutic targets for the development of new antifungals with a high therapeutic index, one of the major drawbacks of the standard antifungal therapy, so far. In this work, we have analyzed the role in pathogenesis of the key enzymes of the Aspergillus fumigatus glyxoxylate cycle, isocitrate lyase and malate synthase, two possible candidates to primary therapeutic targets in this fungus. Deletion strains lacking isocitrate lyase (DeltaacuD strains) or malate synthase (DeltaacuE mutants) were constructed in this work. The Neurospora crassa pyr-4 gene was used as the replacing marker in gene deletion experiments. The pathogenicities of DeltaacuD and DeltaacuE mutants were tested in neutropenic mice and compared with those of two reference wild-type isolates A. fumigatus 237 and A. fumigatus 293. Interestingly, virulence and cytological studies clearly indicated the dispensability of the A. fumigatus glyoxylate cycle for pathogenicity. In addition, these results suggested the suitability of the pyr-4 gene as a valuable replacing marker for virulence studies in this fungus, a fact that was further confirmed by gene expression analyses. Finally, growth tests were performed to investigate the germination and growth of the DeltaacuD and DeltaacuE strains in nutrient deprivation environments, resembling the conditions that A. fumigatus conidia face after phagocytosis. Results obtained in this work strongly suggest that the ability to grow on lipids (triglycerides) of A. fumigatus isocitrate lyase and malate synthase deletion strains accounts for their fully virulent phenotype.

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Available from: Maria Cândida Monteiro, Oct 06, 2015
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    • "In A. fumigatus, the isocitrate lyase Icl1, which is part of the glyoxylate cycle, is not required for full virulence (Schobel et al. 2007; Olivas et al. 2008), although this enzyme is constitutively expressed in conidia during germination within macrophages and not in resting conidia (Ebel et al. 2006). C. neoformans also up-regulates Icl1 after phagocytosis by macrophages , although the ICL1 gene is not necessary for full virulence or growth within macrophages (Rude et al. 2002). "
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    ABSTRACT: Fungal pathogens must assimilate local nutrients to establish an infection in their mammalian host. We focus on carbon, nitrogen, and micronutrient assimilation mechanisms, discussing how these influence host-fungus interactions during infection. We highlight several emerging trends based on the available data. First, the perturbation of carbon, nitrogen, or micronutrient assimilation attenuates fungal pathogenicity. Second, the contrasting evolutionary pressures exerted on facultative versus obligatory pathogens have led to contemporary pathogenic fungal species that display differing degrees of metabolic flexibility. The evolutionarily ancient metabolic pathways are conserved in most fungal pathogen, but interesting gaps exist in some species (e.g., Candida glabrata). Third, metabolic flexibility is generally essential for fungal pathogenicity, and in particular, for the adaptation to contrasting host microenvironments such as the gastrointestinal tract, mucosal surfaces, bloodstream, and internal organs. Fourth, this metabolic flexibility relies on complex regulatory networks, some of which are conserved across lineages, whereas others have undergone significant evolutionary rewiring. Fifth, metabolic adaptation affects fungal susceptibility to antifungal drugs, and also presents exciting opportunities for the development of novel therapies.
    Cold Spring Harbor Perspectives in Medicine 09/2014; DOI:10.1101/cshperspect.a019695 · 9.47 Impact Factor
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    • "This phenotype disappears when glucose is added to the germination medium (Berteaux-Lecellier et al., 1995). Similarly, glucose addition suppresses the germination defect of Aspergillus fumigatus asexual spores defective for isocitrate lyase or malate synthase (Olivas et al., 2008). This suggests that when external resources are limiting, growth of germinative mycelia in these fungi can be sustained by spore reserve compounds, whose mobilization requires peroxisome activity. "
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    ABSTRACT: Peroxisomes are versatile and dynamic organelles that are essential for the development of most eukaryotic organisms. In fungi, many developmental processes, such as sexual development, require the activity of peroxisomes. Sexual reproduction in fungi involves the formation of meiotic-derived sexual spores, often takes place inside multicellular fruiting bodies and requires precise coordination between the differentiation of multiple cell types and the progression of karyogamy and meiosis. Different peroxisomal functions contribute to the orchestration of this complex developmental process. Peroxisomes are required to sustain the formation of fruiting bodies and the maturation and germination of sexual spores. They facilitate the mobilization of reserve compounds via fatty acid β-oxidation and the glyoxylate cycle, allowing the generation of energy and biosynthetic precursors. Additionally, peroxisomes are implicated in the progression of meiotic development. During meiotic development in Podospora anserina, there is a precise modulation of peroxisome assembly and dynamics. This modulation includes changes in peroxisome size, number and localization, and involves a differential activity of the protein-machinery that drives the import of proteins into peroxisomes. Furthermore, karyogamy, entry into meiosis and sorting of meiotic-derived nuclei into sexual spores all require the activity of peroxisomes. These processes rely on different peroxisomal functions and likely depend on different pathways for peroxisome assembly. Indeed, emerging studies support the existence of distinct import channels for peroxisomal proteins that contribute to different developmental stages.
    Frontiers in Physiology 09/2013; 4:244. DOI:10.3389/fphys.2013.00244 · 3.53 Impact Factor
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    • "Firstly, the differential roles of glyoxylate cycle enzymes in virulence, which has been studied in multiple mammalian fungal pathogens, could not have been predicted from our comparative transcriptomic analysis. Glyoxylate cycle gene products are required for full virulence in C. albicans (Lorenz & Fink, 2001; Wang et al., 2003; Barelle et al., 2006) and M. grisea (Wang et al., 2003), but not in A. fumigatus (Schobel et al., 2007; Olivas et al., 2008) or C. neoformans (Rude et al., 2002). Indeed, based on our analysis, one might have predicted the necessity of glyoxylate pathway functionality in C. neoformans and A. fumigatus and nonrequirement in M. grisea (Table 2). "
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    ABSTRACT: The capture of pathogen gene expression signatures directly from the host niche promises to fuel our understanding of the highly complex nature of microbial virulence. However, obtaining and interpreting biological information from infected tissues presents multiple experimental and intellectual challenges, from difficulties in extracting pathogen RNA and appropriate choice of experimental design, to interpretation of the resulting infection transcriptome, itself a product of responses to multiple host-derived cues. The recent publication of several host-infecting fungal transcriptomes offers new opportunities to study the commonalities of animal and plant pathogeneses, which in turn might direct the rational design of new and broader spectrum antifungal agents. Here, we examine the transcriptional basis of modelled Aspergillus fumigatus, Candida albicans, Cryptococcus neoformans, Ustilago maydis and Magneporthe infections, placing our analysis of the published findings within the context of the various modelling procedures used, and the relevant pathogen lifestyles, to facilitate the first cross-species comparison of fungal transcription during infectious growth. Significant concordance was identified among infecting transcriptomes of the inhaled fungal pathogens C. neoformans and A. fumigatus. The significance of gene clustering and subtelomeric gene repertoires is also discussed.
    FEMS Microbiology Letters 06/2010; 307(1):1-11. DOI:10.1111/j.1574-6968.2010.01961.x · 2.12 Impact Factor
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