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Survival defects of Cryptococcus neoformans mutants exposed to human cerebrospinal fluid result in attenuated virulence in an experimental model of meningitis.

ABSTRACT: Cryptococcus neoformans is a fungal pathogen that encounters various microenvironments during growth in the mammalian host, including intracellular vacuoles, blood, and cerebrospinal fluid (CSF). Because the CSF is isolated by the blood-brain barrier, we hypothesize that CSF presents unique stresses that C. neoformans must overcome to establish an infection. We assayed 1,201 mutants for survival defects in growth media, saline, and human CSF. We assessed CSF-specific mutants for (i) mutant survival in both human bronchoalveolar lavage (BAL) fluid and fetal bovine serum (FBS), (ii) survival in macrophages, and (iii) virulence using both Caenorhabditis elegans and rabbit models of cryptococcosis. Thirteen mutants exhibited significant survival defects unique to CSF. The mutations of three of these mutants were recreated in the clinical serotype A strain H99: deletions of the genes for a cation ATPase transporter (ena1?), a putative NEDD8 ubiquitin-like protein (rub1?), and a phosphatidylinositol 4-kinase (pik1?). Mutant survival rates in yeast media, saline, and BAL fluid were similar to those of the wild type; however, survival in FBS was reduced but not to the levels in CSF. These mutant strains also exhibited decreased intracellular survival in macrophages, various degrees of virulence in nematodes, and severe attenuation of survival in a rabbit meningitis model. We analyzed the CSF by mass spectrometry for candidate compounds responsible for the survival defect. Our findings indicate that the genes required for C. neoformans survival in CSF ex vivo are necessary for survival and infection in this unique host environment.

SUBMITTER: Lee A

PROVIDER: S-EPMC2950369 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature

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Survival defects of Cryptococcus neoformans mutants exposed to human cerebrospinal fluid result in attenuated virulence in an experimental model of meningitis.

Lee Anthony A Toffaletti Dena L DL Tenor Jennifer J Soderblom Erik J EJ Thompson J Will JW Moseley M Arthur MA Price Michael M Perfect John R JR

Infection and immunity 20100809 10

Cryptococcus neoformans is a fungal pathogen that encounters various microenvironments during growth in the mammalian host, including intracellular vacuoles, blood, and cerebrospinal fluid (CSF). Because the CSF is isolated by the blood-brain barrier, we hypothesize that CSF presents unique stresses that C. neoformans must overcome to establish an infection. We assayed 1,201 mutants for survival defects in growth media, saline, and human CSF. We assessed CSF-specific mutants for (i) mutant survi ...[more]

PMID: 20696827

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Project description:UNLABELLED:Cryptococcus neoformans is the leading cause of fungal meningitis worldwide. Previous studies have characterized the cryptococcal transcriptome under various stress conditions, but a comprehensive profile of the C. neoformans transcriptome in the human host has not been attempted. Here, we extracted RNA from yeast cells taken directly from the cerebrospinal fluid (CSF) of two AIDS patients with cryptococcal meningitis prior to antifungal therapy. The patients were infected with strains of C. neoformans var. grubii of molecular type VNI and VNII. Using RNA-seq, we compared the transcriptional profiles of these strains under three environmental conditions (in vivo CSF, ex vivo CSF, and yeast extract-peptone-dextrose [YPD]). Although we identified a number of differentially expressed genes, single nucleotide variants, and novel genes that were unique to each strain, the overall expression patterns of the two strains were similar under the same environmental conditions. Specifically, yeast cells obtained directly from each patient's CSF were more metabolically active than cells that were incubated ex vivo in CSF. Compared with growth in YPD, some genes were identified as significantly upregulated in both in vivo and ex vivo CSF, and they were associated with genes previously recognized for contributing to pathogenicity. For example, genes with known stress response functions, such as RIM101, ENA1, and CFO1, were regulated similarly in the two clinical strains. Conversely, many genes that were differentially regulated between the two strains appeared to be transporters. These findings establish a platform for further studies of how this yeast survives and produces disease. IMPORTANCE:Cryptococcus neoformans, an environmental, opportunistic yeast, is annually responsible for an estimated million cases of meningitis and over 600,000 deaths, mostly among HIV-infected patients in sub-Saharan Africa and Asia. Using RNA-seq, we analyzed the gene expression of two strains of C. neoformans obtained from the cerebrospinal fluid (CSF) of infected patients, thus creating a comprehensive snapshot of the yeasts' genetic responses within the human body. By comparing the gene expression of each clinical strain under three conditions (in vivo CSF, ex vivo CSF, and laboratory culture), we identified genes and pathways that were uniquely regulated by exposure to CSF and likely crucial for the survival of C. neoformans in the central nervous system. Further analyses revealed genetic diversity between the strains, providing evidence for cryptococcal evolution and strain specificity. This ability to characterize transcription in vivo enables the elucidation of specific genetic responses that promote disease production and progression.

Project description:Background: In Africa, tuberculosis is generally regarded as persisting as one of the most devastating infectious diseases. The pediatric population is particularly vulnerable, with infection of the brain in the form of tuberculous meningitis (TBM) being the most severe manifestation. TBM is often difficult to diagnose in its early stages because of its non-specific clinical presentation. Of particular concern is that late diagnosis, and subsequent delayed treatment, leads to high risk of long-term neurological sequelae, and even death. Using advanced technology and scientific expertise, we are intent on further describing the biochemistry behind this devastating neuroinflammatory disease, with the goal of improving upon its early diagnosis. Method: We used the highly sensitive analytical platform of gas chromatography-mass spectrometry (GC-MS) to analyze amino acid profiles of cerebrospinal fluid (CSF) collected from a cohort of 33 South African pediatric TBM cases, compared to 34 controls. Results: Through the use of a stringent quality assurance procedure and various statistical techniques, we were able to confidently identify five amino acids as being significantly elevated in TBM cases, namely, alanine, asparagine, glycine, lysine, and proline. We found also in an earlier untargeted metabolomics investigation that alanine can be attributed to increased CSF lactate levels, and lysine as a marker of lipid peroxidation. Alanine, like glycine, is an inhibitory neurotransmitter in the brain. Asparagine, as with proline, is linked to the glutamate-glutamine cycle. Asparagine is associated with the removal of increased nitrites in the brain, whereas elevated proline coincides with the classic biochemical marker of increased CSF protein in TBM. All five discriminatory amino acids are linked to ammonia due to increased nitrites in TBM. Conclusion: A large amount of untapped biochemical information is present in CSF of TBM cases, of which amino acid profiling through GC-MS has potential in aiding in earlier diagnosis, and hence crucial earlier treatment.

Dataset Information

Survival defects of Cryptococcus neoformans mutants exposed to human cerebrospinal fluid result in attenuated virulence in an experimental model of meningitis.

Publications

Survival defects of Cryptococcus neoformans mutants exposed to human cerebrospinal fluid result in attenuated virulence in an experimental model of meningitis.

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