Persistence of Mycobacterium tuberculosis in macrophages and mice requires the glyoxylate shunt enzyme isocitrate lyase

Abstract

Mycobacterium tuberculosis claims more human lives each year than any other bacterial pathogen. Infection is maintained in spite of acquired immunity and resists eradication by antimicrobials. Despite an urgent need for new therapies targeting persistent bacteria, our knowledge of bacterial metabolism throughout the course of infection remains rudimentary. Here we report that persistence of M. tuberculosis in mice is facilitated by isocitrate lyase (ICL), an enzyme essential for the metabolism of fatty acids. Disruption of the icl gene attenuated bacterial persistence and virulence in immune-competent mice without affecting bacterial growth during the acute phase of infection. A link between the requirement for ICL and the immune status of the host was established by the restored virulence of delta icl bacteria in interferon-gamma knockout mice. This link was apparent at the level of the infected macrophage: Activation of infected macrophages increased expression of ICL, and the delta icl mutant was markedly attenuated for survival in activated but not resting macrophages. These data suggest that the metabolism of M. tuberculosis in vivo is profoundly influenced by the host response to infection, an observation with important implications for the treatment of chronic tuberculosis.

The use of microarray analysis to determine the gene expression profiles of Mycobacterium tuberculosis in response to anti-bacterial compounds

“…Genes associated with DNA repair such as end (coding for a probable endonuclease) and recA (encoding recombinase A 26 ) were up-regulated; together with Rv3049c (a probable monoxygenase) and aphC (alkyl hydroperoxide reductase) expressed in response to oxidative stress 27 . Also over-expressed after drug treatment (>3 drugs) were gltA1 (a probable citrate synthase) and icl (isocitrate lyase) similar to changes in metabolism seen under stress conditions 28 . RNA polymerase sigma factors A and B were also induced, together with serine/threonine protein kinases B and G. sigB has been implicated in the M. tuberculosis response to a number of stress conditions 29 .…”

Succinate: a metabolic signal in inflammation

“…Supporting this, it has been shown that survival of Mycobacterium tuberculosis in hypoxic conditions is reduced when pathogen-derived succinate production is inhibited [38], suggesting that this metabolite is required for cell viability. Furthermore, compared to levels in resting macrophages, ICL activity was increased in M. tuberculosis-infected macrophages following activation with LPS [39], suggesting that LPS stimulation may increase the activity of this enzyme and therefore the production of succinate. Interestingly, whereas particular TCA cycle intermediates including succinate are elevated in macrophages following LPS stimulation, isocitrate and IDH are significantly decreased.…”

New insights into the function of granulomas in human tuberculosis

“…This has enabled dissection of the enzymatic apparatus in response to altered environmental conditions. Altered genes include sigma factors [39,40] and PGRS-encoding genes [41], as well as activation of alternative pathways in the citrate cycle to allow metabolism of the abundant lipids in the necrotic centre of granulomas [42,43] and general adaptation to low oxygen tension [44]. More recently, in vitro studies identified a regulon consisting of two sensor kinases, DosS and DosT, under the control of the transcription factor DosR, which sense and control the host response to hypoxia and nitric oxide stress [45][46][47], thus enabling M. tuberculosis to adapt to local conditions during latency [48] (Figure 5).…”