inhibition of respiration by nitric oxide induces a mycobacterium tuberculosis dormancy program...
TRANSCRIPT
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Inhibition of respiration by nitric oxide induces a Mycobacterium tuberculosis dormancy program
Voskuil, M.I., Schappinger, D., Visconti, K.C., Harrell, M.I., Dolganov, G.M., Sherman, D.R., and Schoolnik, G.K. (2003). J. Exp. Med. 198(5), 705-
713. doi:10.1084/jem.20030205.
Journal Club PresentationIsabel Gonzaga
BIOL 398: Bioinformatics LaboratoryNovember 12, 2014
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Outline• Tuberculosis latency period is crucial for disease control• Nitric Oxide may be an immune factor crucial for
dormancy• Low concentrations of NO signal induction • Dormancy regulon determined by NO, dormancy and
hypoxia response• NO binding promotes the signal transduction program
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Tuberculosis infection has three developmental stages• TB is a pulmonary infection caused by Mycobacterium
tuberculosis• 3 stage pathogenic sequence
• Inhalation of infection aerosol• Latency: Cell-mediated immunity in granulamatous lesions• Unimpeded bacterial replication (onset of disease)
• 1/3 of the world is latently infected and the most aggressive TB cases exist in latent form• Factors improving latency need to be investigated
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O2 depletion improves M. tuberculosis latent period
• Gradual O2 depletion leads to nonreplicating, persistant state; leads to structural, metabolic and chromosomal changes to the bacteria
• Reduced O2 tensions lead to resistance to antimicrobials
• Introduction of O2 allows for easy conversion to an active form of the bactria
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Nitric Oxide (NO) is an immune factor in certain concentrations• High doses of NO is toxic for bacteria• NO inhibits aerobic respiration in mitochondria and
bacteria• Important signaling agent for eukaryotes• Present study: investigates role of NO in inducing latent
period program
• Hypothesis: NO controls M. tuberculosis growth by inhibiting aerobic respiration
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NO induces gene expression for 48 genes
• A• DETA/NO generated NO
and rapidly induced 48 genes
• B• Response not desensitized
to subsequent doses• NO dissipation returned
induction to basal levels
• C• qRT-PCR measured
induction magnitude of five sentinel NO induced genes
• mRNA levels up to 140x increase
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Dormancy regulon determined by coinduction by NO, low O2 and adaptation to an in vitro dormant state
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Dormancy regulon determined by coinduction by NO, low O2 and adaptation to an in vitro dormant state
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Dormancy regulon increases overall M. tuberculosis fitness in vitro
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Cyanide blocks expression of dormany regulon genes by NO and low O2
• Heme binds to NO and O2; compeitivie inhibitor
• Cyanide: heme-protein inhibitor• Found to block dormancy regulon gene expression without
affecting overall transcription levels• Indicates that a heme-containing protein is likely to be a
component of the NO/low O2 signal transductio system
CN-+HYPHYP
CN-+NO
CN-
NO
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O2 inhibits NO mediated regulon induction
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Cytochrome Oxidase proposed for the NO/Low O2
• CcO is shown to be reversibly inhibited by low concentrations of NO• This proposal must be supported by further functional studies comparing purified
wild type and CcO mutant• Decreasing respiration initiates transcriptional response, and the pathogen is
transformed to stabilize the virus. This lets the pathogen endure longer latency periods
• NO thus serves as an environmental signal for activation of the bacteria by the immune system
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• Low NO concentrations induce 48 gene regulon using the DosR regulator. This inhibits aerobic respiration and slows replication
• Regulon is used to increase fitness in latency• Predicted roles of genes within the dormancy regulon are
supported by previous research of the physiological properties in the dormant state• See: Crowe et al (1992), Yuan et al. (1996), Garbe et al. (1995)
and Narberhaus (2002)
• Literature has yet to prove in vivo functioning's of M. tuberculosis in humans
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CitationsVoskuil, M.I., Schappinger, D., Visconti, K.C., Harrell, M.I., Dolganov, G.M., Sherman, D.R., and Schoolnik, G.K. (2003). Inhibition of respiration by nitric oxide induces a Mycobacterium tuberculosis dormancy program. J. Exp. Med. 198(5), 705-713. doi:10.1084/jem.20030205.
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Acknowledgements• Loyola Marymount University• Kam Dahlquist, Ph. D• TA: Stephen Louie