Transcript Tuberculosis – metabolism and respiration in the absence

Tuberculosis – metabolism and
respiration in the absence of
growth
-- prepared by Shenghua Liang
Table of contents
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Introduction
Animal models of latency
In vitro models of latency and persistence
The signal for persistence
Redox balance during beta-oxidation
Does M. tuberculosis ferment?
The role of F420 in persistence
Conclusions
Tuberculosis
• Caused by aerobic bacteria
mycobacterium tuberculosis
• Top infectious killing diseases. Each year,
– HIV/AIDS 3 million
– Tuberculosis kills 2 million
– Malaria kills 1 million
• Widely spreaded world-wide
– 1/3 carriers, among which 10% dev. disease
• No effective vaccine
Tuberculosis
Tuberculosis
• 1st infection - pulmonary macrophages
• 2nd infection - lymph nodes, kidneys, brain,
and even bone.
• Granuloma
– T/B cell, macrophages
– Necrosis/cell death
– Bacteria go dormant
• Tissue destruction
• Caseation, scars…
Animal models - murine
• Low cost, genetically well-studied, extensive
literature on mouse immu., and availability of
reagents.
• Similar immune control including T-helper 1
response
• Similar granuloma formation, but not progress to
caseation and liquefaction. Becomes chronic.
• Main immune containment depends on nitric
oxide and other reactive nitrogen intermediates.
Animal models – guinea pig and
rabbit
• Very similar disease progression
– Granuloma and caseation
• Rabbit
– Liquefaction, and cavity formation
• Guinea pig
– Before immune onset, bacteria kills
– BCG vaccine helps
Animal models - primates
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The most suitable, but expensive
Infection by bronchial instillation
Granuloma, with caseation
Probably similar immune response
In vitro models of latency and
persistence
• Upon oxygen depletion, M. tuberculosis
becomes dormant in two steps
• NRP-1 – non-replicating persistence stage
1, oxygen lower than 1%
– Cell division stops
• NRP-2 – non-replicating persistence stage
2, oxygen lower than 0.06%
– Shutdown of metabolism
In vitro models of latency and
persistence
• Up-regulates bd-type menaquinol oxidase,
which has higher oxygen affinity.
• NADH dehydrogenase
– Type I, proton pumping, down-regulated
– Type II, non-proton pumping, up-regulated
• ATP synthase units are down-regulated
• ? An energized membrane is maintained
– Survive without external terminal electron
acceptors
In vitro models of latency and
persistence
• Certain nutrients, but not all, are limited in
intraphagosomal environment
• Ribonucleotide reductase is upregulated
• Triacylglycerol synthases are upregulated
• Isocitrate lyase and glycine
dehydrogenase are upregulated
• Stringent response and polyphosphate
metabolism might be crucial for the
adaptation
The signal for persistence
• Nitric oxide inhibit mycobacterial growth
• In mice, DosR, the dormancy regulon regulatory, is upregulated under microaerobic condition
• Nitric oxide and oxygen deprivation have similar
poisoning effect on cytochrome
• DosR is required for dormancy regulon activation and is
essential for anaerobic survival of M. bovis and M.
tuberculosis in vitro.
• dosR mutant is not attenuated for growth and survival in
mouse tissues. – chronic murine granulomas are not
anoxic.
• dosR is required for virulence in guinea pigs. – oxygen is
limited in the caseous lesions in this animal model.
The signal for persistence
• Acellular caseous material that characterize some
human lesions is produced due to reduced survival of
cells in the increasingly anaerobic interior of such
granulomas or due to immune-mediated tissue
destruction is unknown.
• The availability of nutrients might be limited for M.
tuberculosis that are located in hypoxic granuloma.
• Carbon might be obtained from intracellular triglyceride
stores, or from lipids in the surrounding host tissues.
• Stringent response, regulated by RelA, might have a role
during the onset of dormancy.
– Produce ppGpp, which in turn affects ~60 genes
The signal for persistence
• In mice, the primary trigger for chronic TB
is nitric oxide; and in human, anaerobiasis
might be the primary trigger.
• The metabolic state that is induced by
nitric oxide might have important
differences from that induced by hypoxic
conditions.
The role of beta-oxidation and
gluconeogenesis
• Carbon utilization by M. tuberculosis
during infection depend on the activation
state of macrophages.
• Activated macrosome is glucose-deficient
but replete in fatty acids. During
macrosomal survival, enzymes involved in
beta-oxidation, the glyoxylate shunt and
gluconeogensis are induced.
Redox balance during betaoxidation
• Beta-oxidation – the process by which fats are broken
into Acetyl-CoA.
• Beta-oxidation is limited by the availability of terminal
electron acceptors.
• In resting and activated macrophages, genes in
alternative electron-transport pathways are up-regulated.
– Fumarate reductase
– Non-proton pumping type II NADH dehydrogenase
– Nitrate (NO3-) reductase
• Nitrate reductase might simply be required for restoring
redox balance during growth on fatty acids.
Does M. tuberculosis ferment?
• Fermentation – the energy-yielding
anaerobic metabolic breakdown of a
nutrient molecule without net oxidation;
yields lactate, acetic acid, ethanol, etc.