Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Tuberculosis – metabolism and respiration in the absence of growth -- prepared by Shenghua Liang Table of contents • • • • • • • • 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 • • • • 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.