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Abstract
Aspergillus fumigatus is a saprotrophic fungus; its primary habitat is the soil. In its ecological niche, the fungus has learned how to adapt and proliferate in hostile environments. This capacity has helped the fungus to resist and survive against human host defenses and, further, to be responsible for one of the most devastating lung infections in terms of morbidity and mortality. In this review, we will provide (i) a description of the biological cycle of A. fumigatus; (ii) a historical perspective of the spectrum of aspergillus disease and the current epidemiological status of these infections; (iii) an analysis of the modes of immune response against Aspergillus in immunocompetent and immunocompromised patients; (iv) an understanding of the pathways responsible for fungal virulence and their host molecular targets, with a specific focus on the cell wall; (v) the current status of the diagnosis of different clinical syndromes; and (vi) an overview of the available antifungal armamentarium and the therapeutic strategies in the clinical context. In addition, the emergence of new concepts, such as nutritional immunity and the integration and rewiring of multiple fungal metabolic activities occurring during lung invasion, has helped us to redefine the opportunistic pathogenesis of A. fumigatus.
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Affiliation(s)
- Jean-Paul Latgé
- School of Medicine, University of Crete, Heraklion, Crete, Greece
| | - Georgios Chamilos
- School of Medicine, University of Crete, Heraklion, Crete, Greece
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology, Heraklion, Crete, Greece
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Loss O, Bertuzzi M, Yan Y, Fedorova N, McCann BL, Armstrong-James D, Espeso EA, Read ND, Nierman WC, Bignell EM. Mutual independence of alkaline- and calcium-mediated signalling in Aspergillus fumigatus refutes the existence of a conserved druggable signalling nexus. Mol Microbiol 2017; 106:861-875. [PMID: 28922497 PMCID: PMC5725717 DOI: 10.1111/mmi.13840] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/13/2017] [Indexed: 01/03/2023]
Abstract
Functional coupling of calcium‐ and alkaline responsive signalling occurs in multiple fungi to afford efficient cation homeostasis. Host microenvironments exert alkaline stress and potentially toxic concentrations of Ca2+, such that highly conserved regulators of both calcium‐ (Crz) and pH‐ (PacC/Rim101) responsive signalling are crucial for fungal pathogenicity. Drugs targeting calcineurin are potent antifungal agents but also perturb human immunity thereby negating their use as anti‐infectives, abrogation of alkaline signalling has, therefore, been postulated as an adjunctive antifungal strategy. We examined the interdependency of pH‐ and calcium‐mediated signalling in Aspergillus fumigatus and found that calcium chelation severely impedes hyphal growth indicating a critical requirement for this ion independently of ambient pH. Transcriptomic responses to alkaline pH or calcium excess exhibited minimal similarity. Mutants lacking calcineurin, or its client CrzA, displayed normal alkaline tolerance and nuclear translocation of CrzA was unaffected by ambient pH. Expression of a highly conserved, alkaline‐regulated, sodium ATPase was tolerant of genetic or chemical perturbations of calcium‐mediated signalling, but abolished in null mutants of the pH‐responsive transcription factor PacC, and PacC proteolytic processing occurred normally during calcium excess. Taken together our data demonstrate that in A. fumigatus the regulatory hierarchy governing alkaline tolerance circumvents calcineurin signalling.
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Affiliation(s)
- Omar Loss
- Microbiology Section, Centre for Molecular Microbiology and Infection, Imperial College London, London SW7 2AZ, UK
| | - Margherita Bertuzzi
- Manchester Fungal Infection Group, Division of Infection, Immunity and Respiratory Medicine, University of Manchester, Manchester M13 9NT, UK
| | - Yu Yan
- The J. Craig Venter Institute, Infectious Diseases Program, Rockville, MD, USA
| | - Natalie Fedorova
- The J. Craig Venter Institute, Infectious Diseases Program, Rockville, MD, USA
| | - Bethany L McCann
- Manchester Fungal Infection Group, Division of Infection, Immunity and Respiratory Medicine, University of Manchester, Manchester M13 9NT, UK
| | - Darius Armstrong-James
- Fungal Pathogens Laboratory, National Heart and Lung Institute, Imperial College London SW7 2AY, UK
| | - Eduardo A Espeso
- Department of Molecular and Cellular Biology, Centro de Investigaciones Biologicas (C.S.I.C.), Madrid, Spain
| | - Nick D Read
- Manchester Fungal Infection Group, Division of Infection, Immunity and Respiratory Medicine, University of Manchester, Manchester M13 9NT, UK
| | - William C Nierman
- The J. Craig Venter Institute, Infectious Diseases Program, Rockville, MD, USA
| | - Elaine M Bignell
- Manchester Fungal Infection Group, Division of Infection, Immunity and Respiratory Medicine, University of Manchester, Manchester M13 9NT, UK
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Abstract
Morphogenesis in fungi is often induced by extracellular factors and executed by fungal genetic factors. Cell surface changes and alterations of the microenvironment often accompany morphogenetic changes in fungi. In this review, we will first discuss the general traits of yeast and hyphal morphotypes and how morphogenesis affects development and adaptation by fungi to their native niches, including host niches. Then we will focus on the molecular machinery responsible for the two most fundamental growth forms, yeast and hyphae. Last, we will describe how fungi incorporate exogenous environmental and host signals together with genetic factors to determine their morphotype and how morphogenesis, in turn, shapes the fungal microenvironment.
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Affiliation(s)
- Xiaorong Lin
- Department of Biology, Texas A&M University, College Station, Texas 77843-3258
| | - J Andrew Alspaugh
- Department of Medicine, Division of Infectious Diseases, Duke University Medical Center, Durham, North Carolina 27710
| | - Haoping Liu
- Department of Biological Chemistry, University of California, Irvine, California 92697
| | - Steven Harris
- Center for Plant Science Innovation, University of Nebraska-Lincoln, Lincoln, Nebraska 68588
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pH signaling in human fungal pathogens: a new target for antifungal strategies. EUKARYOTIC CELL 2014; 13:342-52. [PMID: 24442891 DOI: 10.1128/ec.00313-13] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Fungi are exposed to broadly fluctuating environmental conditions, to which adaptation is crucial for their survival. An ability to respond to a wide pH range, in particular, allows them to cope with rapid changes in their extracellular settings. PacC/Rim signaling elicits the primary pH response in both model and pathogenic fungi and has been studied in multiple fungal species. In the predominant human pathogenic fungi, namely, Candida albicans, Aspergillus fumigatus, and Cryptococcus neoformans, this pathway is required for many functions associated with pathogenesis and virulence. Aspects of this pathway are fungus specific and do not exist in mammalian cells. In this review, we highlight recent advances in our understanding of PacC/Rim-mediated functions and discuss the growing interest in this cascade and its factors as potential drug targets for antifungal strategies. We focus on both conserved and distinctive features in model and pathogenic fungi, highlighting the specificities of PacC/Rim signaling in C. albicans, A. fumigatus, and C. neoformans. We consider the role of this pathway in fungal virulence, including modulation of the host immune response. Finally, as now recognized for other signaling cascades, we highlight the role of pH in adaptation to antifungal drug pressure. By acting on the PacC/Rim pathway, it may therefore be possible (i) to ensure fungal specificity and to limit the side effects of drugs, (ii) to ensure broad-spectrum efficacy, (iii) to attenuate fungal virulence, (iv) to obtain additive or synergistic effects with existing antifungal drugs through tolerance inhibition, and (v) to slow the emergence of resistant mutants.
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Grice CM, Bertuzzi M, Bignell EM. Receptor-mediated signaling in Aspergillus fumigatus. Front Microbiol 2013; 4:26. [PMID: 23430083 PMCID: PMC3576715 DOI: 10.3389/fmicb.2013.00026] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2012] [Accepted: 02/01/2013] [Indexed: 11/15/2022] Open
Abstract
Aspergillus fumigatus is the most pathogenic species among the Aspergilli, and the major fungal agent of human pulmonary infection. To prosper in diverse ecological niches, Aspergilli have evolved numerous mechanisms for adaptive gene regulation, some of which are also crucial for mammalian infection. Among the molecules which govern such responses, integral membrane receptors are thought to be the most amenable to therapeutic modulation. This is due to the localization of these molecular sensors at the periphery of the fungal cell, and to the prevalence of small molecules and licensed drugs which target receptor-mediated signaling in higher eukaryotic cells. In this review we highlight the progress made in characterizing receptor-mediated environmental adaptation in A. fumigatus and its relevance for pathogenicity in mammals. By presenting a first genomic survey of integral membrane proteins in this organism, we highlight an abundance of putative seven transmembrane domain (7TMD) receptors, the majority of which remain uncharacterized. Given the dependency of A. fumigatus upon stress adaptation for colonization and infection of mammalian hosts, and the merits of targeting receptor-mediated signaling as an antifungal strategy, a closer scrutiny of sensory perception and signal transduction in this organism is warranted.
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Affiliation(s)
- C M Grice
- South Kensington Campus, Imperial College London London, UK
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