Transcript Inhibition of respiration by Nitric Oxide induces a

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), 705713. doi:10.1084/jem.20030205.
Journal Club Presentation
Isabel Gonzaga
BIOL 398: Bioinformatics Laboratory
November 12, 2014
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
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
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
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
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
Dormancy regulon determined by
coinduction by NO, low O2 and adaptation
to an in vitro dormant state
Dormancy regulon determined by
coinduction by NO, low O2 and adaptation
to an in vitro dormant state
Dormancy regulon increases overall M.
tuberculosis fitness in vitro
Cyanide blocks expression of dormany
regulon genes by NO and low O2
CN-+HYP
HYP
CN-+NO
CNNO
• 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
O2 inhibits NO mediated regulon induction
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
• 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
Citations
Voskuil, 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.
Acknowledgements
• Loyola Marymount University
• Kam Dahlquist, Ph. D
• TA: Stephen Louie