Project description:Systemic infection with Cryptococcus neoformans, a dangerous and contagious pathogen found throughout the world, frequently results in lethal cryptococcal pneumonia and meningoencephalitis, and no effective treatments of cryptococcosis are available. Here, we describe Prm1, a novel regulator of virulence in C. neoformans. C. neoformans prm1 cells exhibit extreme sensitivity to various environmental stress conditions. Furthermore, prm1 cells show deficiencies in the biosynthesis of chitin, chitosan, and mannoprotein, which in turn result in impairment of cell wall integrity. Treatment of mice with heat-killed prm1 cells was found to facilitate the host immunological defence against infection with wild-type C. neoformans. Further investigation demonstrated that prm1 cells strongly promote pulmonary production of interferon- and Th1 responses, leading to activation of macrophage M1 differentiation and inhibition of M2 polarization. Therefore, our findings suggest that C. neoformans Prm1 may be a viable target for the development of anti-cryptococcosis medications and, cells lacking Prm1 represent a promising candidate for a vaccine.
Project description:Rho-GDP dissociation inhibitors (RDI) are repressors of Rho-type monomeric GTPases that allow for precise control of their target processes, e.g. cytoskeletal arrangement, vesicle trafficking, and polarized growth. In the human pathogenic yeast Cryptococcus neoformans, maintenance of normal cell morphology is vital for pathogenicity. We identified and deleted the gene encoding an RDI homolog in the human fungal pathogen Cryptococcus neoformans and investigated its impact on pathogenicity in animal models of cryptococcosis. Rdi1 deletion resulted in altered vacuole size in tissue culture medium, with corresponding alterations in expression of vesicle trafficking related genes. The rdi1∆ mutant strain showed reduced intracellular survival in macrophages, and severe attenuation of virulence in murine models of cryptococcosis. This reduction in virulence of the rdi1 mutant occurs in the absence of major defects in growth, morphology, or classical virulence-associated phenotypes. Keywords: mutant response, macrophage co-culture
Project description:Cryptococcus neoformans causes meningoencephalitis and is an increasing human health threat. C. neoformans is neurotropic, and persists in the cerebrospinal fluid (CSF) of the mammalian host during infection. In order to survive in the host, pathogenic fungi must procure nutrients such as carbon and nitrogen. To enhance our understanding of nutrient acquisition during infection by Cryptococcus species, we examined utilization of nitrogen sources available in CSF. We screened for growth and capsule production of 817 global environmental and clinical isolates on various sources of nitrogen. Capsule production was assessed using ammonium and urea in the presence or absence of benomyl to determine the relationship of urea exposure to capsule production. Since urea is metabolized to ammonia and CO2 (a known signal for capsule induction), we examined urea metabolism mutants for their response to urea regarding capsule production. Non-preferred nitrogen sources were found to greatly affect capsule production in pathogenic species of Cryptococcus. Urea induced the greatest magnitude of capsule production. Capsule induction by urea was greater in Cryptococcus gattii strains than in C. neoformans strains. In addition, both environmental and clinical strains grew robustly on uric acid, casamino acids, creatinine, and asparagine as sole nitrogen sources. While substantial growth on nitrate was not apparent at day 3, growth was apparent by day 6 for all serotypes. In this study, transcription profiles of urea pathway mutants (ure1 and amt1/2) and WT Cryptococcus neoformans strains were compared in a dye-swap experiment following 1hr exposure to proline or proline + urea (.25g/L).
Project description:An array analysis of C. gattii (C. bacillosporus), intended to identify loci associated with the hypervirulence of the Vancouver Island Outbreak (VIO). 23 C. gattii isolates, representing both VIO strains and control strains, were grown for 24 hours in mammalian macrophages. RNA was isolated and gene expression for each strain quantified relative to pooled RNA from all 23 samples. Linear regression was used to identify loci showing positive or negative correlation with "intracellular proliferation rate", a proxy measure for virulence. Data from this analysis is included in Ma et al, 2009, PNAS 106(31) 12980-12985. The abstract is included below. In 1999, the population of Vancouver Island, Canada, began to experience an outbreak of a fatal fungal disease caused by a highly virulent lineage of Cryptococcus gattii. This organism has recently spread to the Canadian mainland and Pacific Northwest, but the molecular cause of the outbreak remains unknown. Here we show that the Vancouver Island outbreak (VIO) isolates have dramatically increased their ability to replicate within macrophages of the mammalian immune system in comparison with other C. gattii strains. We further demonstrate that such enhanced intracellular parasitism is directly linked to virulence in a murine model of cryptococcosis, suggesting that this phenotype may be the cause of the outbreak. Finally, microarray studies on 24 C. gattii strains reveals that the hypervirulence of the VIO isolates is characterized by the up-regulation of a large group of genes, many of which are encoded by mitochondrial genome or associated with mitochondrial activities. This expression profile correlates with an unusual mitochondrial morphology exhibited by the VIO strains after phagocytosis. Our data thus demonstrate that the intracellular parasitism of macrophages is a key driver of a human disease outbreak, a finding that has significant implications for a wide range of other human pathogens. Dual-colour hybridization (each sample was hybridized against pooled RNA), one array per isolate, 23 biological samples, no technical replicates.
Project description:We compared the interaction between Cryptococcus gattii species complex strain R265 and Cryptococcus neoformans species complex strain H99, molecular type VNI, with murine macrophages to ascertain similarities and differences in their intracellular pathogenic strategy. Parameters analyzed include non-lytic exocytosis using time-lapse microscopy, phagolysosomal pH by dual fluorescent microscopy, intracellular capsular growth, phagolysosomal membrane permeabilization by flow cytometry, and the macrophage transcriptional response by gene expression microarray analysis. Using microarrays, we compared the transcriptional response of Bone Marrow-derived macrophages (BMDM) infected with C. gattii species complex strain R265 or C. neoformans species complex strain H99, relative to uninfected BMDM collected from the same time intervals, 2hr and 24 hr post-infection. For analysis following normalization and summarization steps, a 2-way Analysis of Variance (ANOVA) with linear contrasts for treatment (infection/strain) and time (2 h or 24 h) vs. Control (uninfected) was performed with outputs of P value, Fold Change, and Mean Ratio. A linear contrast of uninfected controls (24 h uninfected vs 2 h uninfected) was also performed to generate a ‘time only’ gene list. Cutoff criteria for filtering gene lists was significant P values (p<0.01) with fold changes greater that 2 or less than –2. Ten genes from the filtered gene lists were selected for validation by qPCR, with four housekeeping genes for normalization and comparison.
Project description:Cryptococcus neoformans causes meningoencephalitis and is an increasing human health threat. C. neoformans is neurotropic, and persists in the cerebrospinal fluid (CSF) of the mammalian host during infection. In order to survive in the host, pathogenic fungi must procure nutrients such as carbon and nitrogen. To enhance our understanding of nutrient acquisition during infection by Cryptococcus species, we examined utilization of nitrogen sources available in CSF. We screened for growth and capsule production of 817 global environmental and clinical isolates on various sources of nitrogen. Capsule production was assessed using ammonium and urea in the presence or absence of benomyl to determine the relationship of urea exposure to capsule production. Since urea is metabolized to ammonia and CO2 (a known signal for capsule induction), we examined urea metabolism mutants for their response to urea regarding capsule production. Non-preferred nitrogen sources were found to greatly affect capsule production in pathogenic species of Cryptococcus. Urea induced the greatest magnitude of capsule production. Capsule induction by urea was greater in Cryptococcus gattii strains than in C. neoformans strains. In addition, both environmental and clinical strains grew robustly on uric acid, casamino acids, creatinine, and asparagine as sole nitrogen sources. While substantial growth on nitrate was not apparent at day 3, growth was apparent by day 6 for all serotypes.