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Pool A, Lowder L, Wu Y, Forrester K, Rumbaugh J. Neurovirulence of Cryptococcus neoformans determined by time course of capsule accumulation and total volume of capsule in the brain. J Neurovirol 2013; 19:228-38. [PMID: 23733307 DOI: 10.1007/s13365-013-0169-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2013] [Accepted: 04/29/2013] [Indexed: 10/26/2022]
Abstract
Cryptococcal meningitis remains a significant opportunistic infection in HIV-infected individuals worldwide, despite availability of antiretroviral therapies in developed nations. Current therapy with amphotericin B is difficult to administer and only partially effective. Mechanisms of cryptococcal neuropathogenesis are still not clearly defined. In the present study, we used a C57Bl/6 mouse model with intravenous inoculation of three isogenic strains of Cryptococcus neoformans: H99, Cap59, and Pkr1-33. These strains differ in their capsule production and are normocapsular, hypocapsular, and hypercapsular, respectively. We studied the role of capsule in the morbidity and mortality of our host animal. Surprisingly, we found that the hypercapsular strain was least virulent while the strains that produced less capsule were more virulent and had higher concentrations of organism in the brain. These results suggest that neurovirulence is related to total capsule volume and rate of capsule accumulation in the brain, rather than the amount of capsule produced per organism. Therapies which decrease central nervous system dissemination and inhibit replication rates in the brain may be more effective than therapies which target capsule production.
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Affiliation(s)
- A Pool
- Department of Neurology, Emory University School of Medicine, Atlanta, GA, USA
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52
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Arvanitis M, Glavis-Bloom J, Mylonakis E. Invertebrate models of fungal infection. Biochim Biophys Acta Mol Basis Dis 2013; 1832:1378-83. [PMID: 23517918 DOI: 10.1016/j.bbadis.2013.03.008] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Revised: 03/07/2013] [Accepted: 03/11/2013] [Indexed: 10/27/2022]
Abstract
The morbidity, mortality and economic burden associated with fungal infections, together with the emergence of fungal strains resistant to current antimicrobial agents, necessitate broadening our understanding of fungal pathogenesis and discovering new agents to treat these infections. Using invertebrate hosts, especially the nematode Caenorhabditis elegans and the model insects Drosophila melanogaster and Galleria mellonella, could help achieve these goals. The evolutionary conservation of several aspects of the innate immune response between invertebrates and mammals makes the use of these simple hosts an effective and fast screening method for identifying fungal virulence factors and testing potential antifungal compounds. The purpose of this review is to compare several model hosts that have been used in experimental mycology to-date and to describe their different characteristics and contribution to the study of fungal virulence and the detection of compounds with antifungal properties. This article is part of a Special Issue entitled: Animal Models of Disease.
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Affiliation(s)
- Marios Arvanitis
- Department of Medicine, Warren Alpert Medical School of Brown University, Providence, RI 02903, USA
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53
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Le PT, Ramulu HG, Guijarro L, Paganini J, Gouret P, Chabrol O, Raoult D, Pontarotti P. An automated approach for the identification of horizontal gene transfers from complete genomes reveals the rhizome of Rickettsiales. BMC Evol Biol 2012; 12:243. [PMID: 23234643 PMCID: PMC3575314 DOI: 10.1186/1471-2148-12-243] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2012] [Accepted: 11/22/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Horizontal gene transfer (HGT) is considered to be a major force driving the evolutionary history of prokaryotes. HGT is widespread in prokaryotes, contributing to the genomic repertoire of prokaryotic organisms, and is particularly apparent in Rickettsiales genomes. Gene gains from both distantly and closely related organisms play crucial roles in the evolution of bacterial genomes. In this work, we focus on genes transferred from distantly related species into Rickettsiales species. RESULTS We developed an automated approach for the detection of HGT from other organisms (excluding alphaproteobacteria) into Rickettsiales genomes. Our systematic approach consisted of several specialized features including the application of a parsimony method for inferring phyletic patterns followed by blast filter, automated phylogenetic reconstruction and the application of patterns for HGT detection. We identified 42 instances of HGT in 31 complete Rickettsiales genomes, of which 38 were previously unidentified instances of HGT from Anaplasma, Wolbachia, Candidatus Pelagibacter ubique and Rickettsia genomes. Additionally, putative cases with no phylogenetic support were assigned gene ontology terms. Overall, these transfers could be characterized as "rhizome-like". CONCLUSIONS Our analysis provides a comprehensive, systematic approach for the automated detection of HGTs from several complete proteome sequences that can be applied to detect instances of HGT within other genomes of interest.
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Affiliation(s)
- Phuong Thi Le
- Evolutionary biology and modeling, LATP UMR-CNRS 7353, Aix-Marseille University, 13331, Marseille, France
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Magditch DA, Liu TB, Xue C, Idnurm A. DNA mutations mediate microevolution between host-adapted forms of the pathogenic fungus Cryptococcus neoformans. PLoS Pathog 2012; 8:e1002936. [PMID: 23055925 PMCID: PMC3464208 DOI: 10.1371/journal.ppat.1002936] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2012] [Accepted: 08/15/2012] [Indexed: 11/30/2022] Open
Abstract
The disease cryptococcosis, caused by the fungus Cryptococcus neoformans, is acquired directly from environmental exposure rather than transmitted person-to-person. One explanation for the pathogenicity of this species is that interactions with environmental predators select for virulence. However, co-incubation of C. neoformans with amoeba can cause a “switch” from the normal yeast morphology to a pseudohyphal form, enabling fungi to survive exposure to amoeba, yet conversely reducing virulence in mammalian models of cryptococcosis. Like other human pathogenic fungi, C. neoformans is capable of microevolutionary changes that influence the biology of the organism and outcome of the host-pathogen interaction. A yeast-pseudohyphal phenotypic switch also happens under in vitro conditions. Here, we demonstrate that this morphological switch, rather than being under epigenetic control, is controlled by DNA mutation since all pseudohyphal strains bear mutations within genes encoding components of the RAM pathway. High rates of isolation of pseudohyphal strains can be explained by the physical size of RAM pathway genes and a hypermutator phenotype of the strain used in phenotypic switching studies. Reversion to wild type yeast morphology in vitro or within a mammalian host can occur through different mechanisms, with one being counter-acting mutations. Infection of mice with RAM mutants reveals several outcomes: clearance of the infection, asymptomatic maintenance of the strains, or reversion to wild type forms and progression of disease. These findings demonstrate a key role of mutation events in microevolution to modulate the ability of a fungal pathogen to cause disease. Many diseases are contracted from the environment, rather than from sick people. It is unclear why those species are able to cause disease, since the selective pressures in the environment are presumed to be very different from those found within the host. Cryptococcus neoformans is a fungus that causes life-threatening lung and central nervous system disease in approximately one million people each year. The fungus is inhaled from environmental sources. One hypothesis to account for C. neoformans virulence is that amoeba are predators for this fungus, and surviving strains are pre-selected to be virulent in the human host. On the other hand, experiments have found that amoeba eat C. neoformans. A pseudohyphal cell type can survive, and while protecting against amoeba these cells are unable to cause disease in mouse models. We predicted that the pseudohyphal morphology reflected a change in function of a pathway of genes, and found that all pseudohyphal isolates contain mutations within genes for this pathway. The pseudohyphal trait is unstable, with reversion to normal yeast growth by counter-acting mutations. These mutations can occur during the course of mammalian infection. Our results show that mutation events account for a microevolution system currently described as phenotypic switching, and that mutations, at least under experimental conditions, can regulate pathogen adaptation and influence its host range.
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Affiliation(s)
- Denise A. Magditch
- Division of Cell Biology and Biophysics, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, Missouri, United States of America
| | - Tong-Bao Liu
- Public Health Research Institute Center, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, United States of America
| | - Chaoyang Xue
- Public Health Research Institute Center, University of Medicine and Dentistry of New Jersey, Newark, New Jersey, United States of America
| | - Alexander Idnurm
- Division of Cell Biology and Biophysics, School of Biological Sciences, University of Missouri-Kansas City, Kansas City, Missouri, United States of America
- * E-mail:
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Peroxisomal and mitochondrial β-oxidation pathways influence the virulence of the pathogenic fungus Cryptococcus neoformans. EUKARYOTIC CELL 2012; 11:1042-54. [PMID: 22707485 DOI: 10.1128/ec.00128-12] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
An understanding of the connections between metabolism and elaboration of virulence factors during host colonization by the human-pathogenic fungus Cryptococcus neoformans is important for developing antifungal therapies. Lipids are abundant in host tissues, and fungal pathogens in the phylum basidiomycota possess both peroxisomal and mitochondrial β-oxidation pathways to utilize this potential carbon source. In addition, lipids are important signaling molecules in both fungi and mammals. In this report, we demonstrate that defects in the peroxisomal and mitochondrial β-oxidation pathways influence the growth of C. neoformans on fatty acids as well as the virulence of the fungus in a mouse inhalation model of cryptococcosis. Disease attenuation may be due to the cumulative influence of altered carbon source acquisition or processing, interference with secretion, changes in cell wall integrity, and an observed defect in capsule production for the peroxisomal mutant. Altered capsule elaboration in the context of a β-oxidation defect was unexpected but is particularly important because this trait is a major virulence factor for C. neoformans. Additionally, analysis of mutants in the peroxisomal pathway revealed a growth-promoting activity for C. neoformans, and subsequent work identified oleic acid and biotin as candidates for such factors. Overall, this study reveals that β-oxidation influences virulence in C. neoformans by multiple mechanisms that likely include contributions to carbon source acquisition and virulence factor elaboration.
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56
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Lamrabet O, Merhej V, Pontarotti P, Raoult D, Drancourt M. The genealogic tree of mycobacteria reveals a long-standing sympatric life into free-living protozoa. PLoS One 2012; 7:e34754. [PMID: 22511965 PMCID: PMC3325273 DOI: 10.1371/journal.pone.0034754] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2011] [Accepted: 03/08/2012] [Indexed: 02/07/2023] Open
Abstract
Free-living protozoa allow horizontal gene transfer with and between the microorganisms that they host. They host mycobacteria for which the sources of transferred genes remain unknown. Using BLASTp, we searched within the genomes of 15 mycobacteria for homologous genes with 34 amoeba-resistant bacteria and the free-living protozoa Dictyostelium discoideum. Subsequent phylogenetic analysis of these sequences revealed that eight mycobacterial open-reading frames (ORFs) were probably acquired via horizontal transfer from beta- and gamma-Proteobacteria and from Firmicutes, but the transfer histories could not be reliably established in details. One further ORF encoding a pyridine nucleotide disulfide oxidoreductase (pyr-redox) placed non-tuberculous mycobacteria in a clade with Legionella spp., Francisella spp., Coxiella burnetii, the ciliate Tetrahymena thermophila and D. discoideum with a high reliability. Co-culturing Mycobacterium avium and Legionella pneumophila with the amoeba Acanthamoeba polyphaga demonstrated that these two bacteria could live together in amoebae for five days, indicating the biological relevance of intra-amoebal transfer of the pyr-redox gene. In conclusion, the results of this study support the hypothesis that protists can serve as a source and a place for gene transfer in mycobacteria.
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Affiliation(s)
- Otmane Lamrabet
- URMITE CNRS-IRD UMR 6236, IFR48, Méditerranée Infection, Aix-Marseille Université, Marseille, France
| | - Vicky Merhej
- URMITE CNRS-IRD UMR 6236, IFR48, Méditerranée Infection, Aix-Marseille Université, Marseille, France
| | - Pierre Pontarotti
- Equipe Evolution Biologique et Modélisation UMR 6632, IRF48, Aix-Marseille Université/CNRS, Marseille, France
| | - Didier Raoult
- URMITE CNRS-IRD UMR 6236, IFR48, Méditerranée Infection, Aix-Marseille Université, Marseille, France
| | - Michel Drancourt
- URMITE CNRS-IRD UMR 6236, IFR48, Méditerranée Infection, Aix-Marseille Université, Marseille, France
- * E-mail:
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57
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Vecchiarelli A, Monari C. Capsular Material of Cryptococcus neoformans: Virulence and Much More. Mycopathologia 2012; 173:375-386. [PMID: 22314939 DOI: 10.1007/s11046-011-9513-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Accepted: 11/28/2011] [Indexed: 01/08/2023]
Abstract
The capsule is generally considered one of the more powerful virulence factors of microorganisms, driving research in the field of microbial pathogenesis and in the development of vaccines. Cryptococcus neoformans is unique among the most common human fungal pathogens in that it possesses a complex polysaccharide capsule. This review focuses on the Cryptococcus neoformans capsule from the viewpoint of fungal pathogenesis, and the effective immune response target of the capsule's main component, glucuronoxylomannan.
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Affiliation(s)
- A Vecchiarelli
- Department of Experimental Medicine and Biochemical Sciences, Microbiology Section, University of Perugia, Via del Giochetto, 06126, Perugia, Italy,
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58
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Araujo GDS, Fonseca FL, Pontes B, Torres A, Cordero RJB, Zancopé-Oliveira RM, Casadevall A, Viana NB, Nimrichter L, Rodrigues ML, Garcia ES, de Souza W, Frases S. Capsules from pathogenic and non-pathogenic Cryptococcus spp. manifest significant differences in structure and ability to protect against phagocytic cells. PLoS One 2012; 7:e29561. [PMID: 22253734 PMCID: PMC3257238 DOI: 10.1371/journal.pone.0029561] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2011] [Accepted: 11/30/2011] [Indexed: 01/10/2023] Open
Abstract
Capsule production is common among bacterial species, but relatively rare in eukaryotic microorganisms. Members of the fungal Cryptococcus genus are known to produce capsules, which are major determinants of virulence in the highly pathogenic species Cryptococcus neoformans and Cryptococcus gattii. Although the lack of virulence of many species of the Cryptococcus genus can be explained solely by the lack of mammalian thermotolerance, it is uncertain whether the capsules from these organisms are comparable to those of the pathogenic cryptococci. In this study, we compared the characteristic of the capsule from the non-pathogenic environmental yeast Cryptococcus liquefaciens with that of C. neoformans. Microscopic observations revealed that C. liquefaciens has a capsule visible in India ink preparations that was also efficiently labeled by three antibodies generated to specific C. neoformans capsular antigens. Capsular polysaccharides of C. liquefaciens were incorporated onto the cell surface of acapsular C. neoformans mutant cells. Polysaccharide composition determinations in combination with confocal microscopy revealed that C. liquefaciens capsule consisted of mannose, xylose, glucose, glucuronic acid, galactose and N-acetylglucosamine. Physical chemical analysis of the C. liquefaciens polysaccharides in comparison with C. neoformans samples revealed significant differences in viscosity, elastic properties and macromolecular structure parameters of polysaccharide solutions such as rigidity, effective diameter, zeta potential and molecular mass, which nevertheless appeared to be characteristics of linear polysaccharides that also comprise capsular polysaccharide of C. neoformans. The environmental yeast, however, showed enhanced susceptibility to the antimicrobial activity of the environmental phagocytes, suggesting that the C. liquefaciens capsular components are insufficient in protecting yeast cells against killing by amoeba. These results suggest that capsular structures in pathogenic Cryptococcus species and environmental species share similar features, but also manifest significant difference that could influence their potential to virulence.
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Affiliation(s)
- Glauber de S. Araujo
- Laboratório de Biotecnologia, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial, Rio de Janeiro, Brazil
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Fernanda L. Fonseca
- Laboratório de Estudos integrados em Bioquímica Microbiana, Instituto de Microbiologia Professor Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Bruno Pontes
- LPO-COPEA, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Brazil
| | - Andre Torres
- Instituto de Pesquisa Clínica Evandro Chagas, The Oswaldo Cruz Foundation, Rio de Janeiro, Brazil
| | - Radames J. B. Cordero
- Department of Microbiology and Immunology. Albert Einstein College of Medicine, Bronx, New York, United States of America
| | | | - Arturo Casadevall
- Department of Microbiology and Immunology. Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Nathan B. Viana
- LPO-COPEA, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Brazil
- Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa, Brazil
| | - Leonardo Nimrichter
- Laboratório de Estudos integrados em Bioquímica Microbiana, Instituto de Microbiologia Professor Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Marcio L. Rodrigues
- Laboratório de Estudos integrados em Bioquímica Microbiana, Instituto de Microbiologia Professor Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Eloi S. Garcia
- Laboratório de Biotecnologia, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial, Rio de Janeiro, Brazil
- Instituto Oswaldo Cruz, Rio de Janeiro, Brazil
| | - Wanderley de Souza
- Laboratório de Biotecnologia, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial, Rio de Janeiro, Brazil
- Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Bioimagens, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Susana Frases
- Laboratório de Biotecnologia, Instituto Nacional de Metrologia, Normalização e Qualidade Industrial, Rio de Janeiro, Brazil
- Laboratório de Ultraestrutura Celular Hertha Meyer, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
- * E-mail:
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59
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Amoeba Provide Insight into the Origin of Virulence in Pathogenic Fungi. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 710:1-10. [DOI: 10.1007/978-1-4419-5638-5_1] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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60
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Wozniak KL, Hardison S, Olszewski M, Wormley FL. Induction of protective immunity against cryptococcosis. Mycopathologia 2011; 173:387-94. [PMID: 22143898 DOI: 10.1007/s11046-011-9505-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2011] [Accepted: 10/22/2011] [Indexed: 02/08/2023]
Abstract
Cryptococcus neoformans, the predominant etiological agent of cryptococcosis, is an encapsulated fungal pathogen that can cause life-threatening infections of the central nervous system in immune compromised individuals resulting in high morbidity and mortality. Consequently, several studies have endeavored to understand those mechanisms that mediate resistance and susceptibility to Cryptococcus infection. In this review, we will examine the contributions of various components of the innate and adaptive immune response toward protection against cryptococcosis. We will focus our discussion on studies presented at the 8th International Conference on Cryptococcus and Cryptococcosis (ICCC). Remarkable progress has been made toward our understanding of host immunity and susceptibility to cryptococcal infection and the potential for vaccine development.
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Affiliation(s)
- Karen L Wozniak
- Department of Biology, The University of Texas, San Antonio, TX 78249-0062, USA
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61
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Dynamics of Cryptococcus neoformans-macrophage interactions reveal that fungal background influences outcome during cryptococcal meningoencephalitis in humans. mBio 2011; 2:mBio.00158-11. [PMID: 21828220 PMCID: PMC3149853 DOI: 10.1128/mbio.00158-11] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Cryptococcosis is a multifaceted fungal infection with variable clinical presentation and outcome. As in many infectious diseases, this variability is commonly assigned to host factors. To investigate whether the diversity of Cryptococcus neoformans clinical (ClinCn) isolates influences the interaction with host cells and the clinical outcome, we developed and validated new quantitative assays using flow cytometry and J774 macrophages. The phenotype of ClinCn-macrophage interactions was determined for 54 ClinCn isolates recovered from cerebrospinal fluids (CSF) from 54 unrelated patients, based on phagocytic index (PI) and 2-h and 48-h intracellular proliferation indexes (IPH2 and IPH48, respectively). Their phenotypes were highly variable. Isolates harboring low PI/low IPH2 and high PI/high IPH2 values were associated with nonsterilization of CSF at week 2 and death at month 3, respectively. A subset of 9 ClinCn isolates with different phenotypes exhibited variable virulence in mice and displayed intramacrophagic expression levels of the LAC1, APP1, VAD1, IPC1, PLB1, and COX1 genes that were highly variable among the isolates and correlated with IPH48. Variation in the expression of virulence factors is thus shown here to depend on not only experimental conditions but also fungal background. These results suggest that, in addition to host factors, the patient’s outcome can be related to fungal determinants. Deciphering the molecular events involved in C. neoformans fate inside host cells is crucial for our understanding of cryptococcosis pathogenesis. Cryptococcus neoformans is a life-threatening human fungal pathogen that is responsible for an estimated 1 million cases of meningitis/year, predominantly in HIV-infected patients. The diversity of infecting isolates is well established, as is the importance of the host factors. Interaction with macrophages is a major step in cryptococcosis pathogenesis. How the diversity of clinical isolates influences macrophages’ interactions and impacts cryptococcosis outcome in humans remains to be elucidated. Using new assays, we uncovered how yeast-macrophage interactions were highly variable among clinical isolates and found an association between specific behaviors and cryptococcosis outcome. In addition, gene expression of some virulence factors and intracellular proliferation were correlated. While many studies have established that virulence factors can be differentially expressed as a function of experimental conditions, our study demonstrates that, under the same experimental conditions, clinical isolates behaved differently, a diversity that could participate in the variable outcome of infection in humans.
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62
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Nicola AM, Robertson EJ, Albuquerque P, Derengowski LDS, Casadevall A. Nonlytic exocytosis of Cryptococcus neoformans from macrophages occurs in vivo and is influenced by phagosomal pH. mBio 2011; 2:e00167-11. [PMID: 21828219 PMCID: PMC3150755 DOI: 10.1128/mbio.00167-11] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2011] [Accepted: 07/22/2011] [Indexed: 01/24/2023] Open
Abstract
UNLABELLED A unique aspect of the interaction of the fungus Cryptococcus neoformans with macrophages is the phenomenon of nonlytic exocytosis, also referred to as "vomocytosis" or phagosome extrusion/expulsion, which involves the escape of fungal cells from the phagocyte with the survival of both cell types. This phenomenon has been observed only in vitro using subjective and time-consuming microscopic techniques. In spite of recent advances in our knowledge about its mechanisms, a major question still remaining is whether this phenomenon also occurs in vivo. In this study, we describe a novel flow cytometric method that resulted in a substantial gain in throughput for studying phagocytosis and nonlytic exocytosis in vitro and used it to explore the occurrence of this phenomenon in a mouse model of infection. Furthermore, we tested the hypothesis that host cell phagosomal pH affected nonlytic exocytosis. The addition of the weak bases ammonium chloride and chloroquine resulted in a significant increase of nonlytic exocytosis events, whereas the vacuolar ATPase inhibitor bafilomycin A1 had the opposite effect. Although all three agents are known to neutralize phagosomal acidity, their disparate effects suggest that phagosomal pH is an important and complex variable in this process. Our experiments established that nonlytic exocytosis occurred in vivo with a frequency that is possibly much higher than that observed in vitro. These results in turn suggest that nonlytic exocytosis has a potential role in the pathogenesis of cryptococcosis. IMPORTANCE Cryptococcus neoformans causes disease in people with immune deficiencies such as AIDS. Upon infection, C. neoformans cells are ingested by macrophage immune cells, which provide a niche for survival and replication. After ingestion, macrophages can expel the fungi without causing harm to either cell type, a process named nonlytic exocytosis. To dissect this phenomenon, we evaluated its dependence on the pH inside the macrophage and addressed its occurrence during infection of mice. We developed new techniques using flow cytometry to measure C. neoformans internalization by and nonlytic exocytosis from macrophages. Neutralizing the phagosome acidity changed the rate of nonlytic exocytosis: activity increased with the weak bases chloroquine and ammonium chloride, whereas the vacuolar ATPase inhibitor bafilomycin A1 caused it to decrease. Experiments in mice suggested that nonlytic exocytosis occurred during infection with C. neoformans. These results shed new light on the interaction between C. neoformans and host macrophages.
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Affiliation(s)
- André Moraes Nicola
- Department of Microbiology and Immunology, Albert Einstein College of Medicine of the Yeshiva University, Bronx, New York, USA
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63
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Chrisman CJ, Albuquerque P, Guimaraes AJ, Nieves E, Casadevall A. Phospholipids trigger Cryptococcus neoformans capsular enlargement during interactions with amoebae and macrophages. PLoS Pathog 2011; 7:e1002047. [PMID: 21637814 PMCID: PMC3102711 DOI: 10.1371/journal.ppat.1002047] [Citation(s) in RCA: 95] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2010] [Accepted: 03/11/2011] [Indexed: 11/18/2022] Open
Abstract
A remarkable aspect of the interaction of Cryptococcus
neoformans with mammalian hosts is a consistent increase in capsule
volume. Given that many aspects of the interaction of C.
neoformans with macrophages are also observed with amoebae, we
hypothesized that the capsule enlargement phenomenon also had a protozoan
parallel. Incubation of C. neoformans with Acanthamoeba
castellanii resulted in C. neoformans capsular
enlargement. The phenomenon required contact between fungal and protozoan cells
but did not require amoeba viability. Analysis of amoebae extracts showed that
the likely stimuli for capsule enlargement were protozoan polar lipids. Extracts
from macrophages and mammalian serum also triggered cryptococcal capsular
enlargement. C. neoformans capsule enlargement required
expression of fungal phospholipase B, but not phospholipase C. Purified
phospholipids, in particular, phosphatidylcholine, and derived molecules
triggered capsular enlargement with the subsequent formation of giant cells.
These results implicate phospholipids as a trigger for both C.
neoformans capsule enlargement in vivo and
exopolysaccharide production. The observation that the incubation of C.
neoformans with phospholipids led to the formation of giant cells
provides the means to generate these enigmatic cells in vitro.
Protozoan- or mammalian-derived polar lipids could represent a danger signal for
C. neoformans that triggers capsular enlargement as a
non-specific defense mechanism against potential predatory cells. Hence,
phospholipids are the first host-derived molecules identified to trigger
capsular enlargement. The parallels apparent in the capsular response of
C. neoformans to both amoebae and macrophages provide
additional support for the notion that certain aspects of cryptococcal virulence
emerged as a consequence of environmental interactions with other microorganisms
such as protists. A key event in C. neoformans pathogenesis is capsule enlargement
in mammalian hosts. Historically, this phenomenon was attributed to high
CO2 and iron deprivation but the magnitude of capsular
enlargement observed in vivo cannot be consistently replicated
in vitro. This paper reports that C.
neoformans responds to polar lipid extracts with massive capsule
enlargement, with some cells having dimensions comparable to the giant cells
observed in vivo. Phospholipids are identified in this paper as
the inducers of capsule enlargement. Our work is important because this is the
first host-derived molecule that has been identified as a stimulus of massive
capsule enlargement thus providing a potential mechanism for the capsular
enlargement observed in vivo. Furthermore, the fact that the
signal is common to both macrophages and amoebae suggests that the capsule
enlargement response to phospholipids is a mechanism for fungal sensing of
phagocytic cell predators. This provides another example of a correspondence
between a possible environmental signal and a mechanism of virulence.
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Affiliation(s)
- Cara J. Chrisman
- Department of Microbiology and Immunology,
Albert Einstein College of Medicine, Bronx, New York, United States of
America
| | - Patricia Albuquerque
- Department of Microbiology and Immunology,
Albert Einstein College of Medicine, Bronx, New York, United States of
America
| | - Allan J. Guimaraes
- Department of Microbiology and Immunology,
Albert Einstein College of Medicine, Bronx, New York, United States of
America
| | - Edward Nieves
- Department of Developmental and Molecular
Biology, Albert Einstein College of Medicine, Bronx, New York, United States of
America
- Department of Biochemistry, Albert Einstein
College of Medicine, Bronx, New York, United States of America
| | - Arturo Casadevall
- Department of Microbiology and Immunology,
Albert Einstein College of Medicine, Bronx, New York, United States of
America
- Department of Medicine, Albert Einstein
College of Medicine, Bronx, New York, United States of America
- * E-mail:
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