Mycobacterium tuberculosis controls host innate immune activation through cyclopropane modification of a glycolipid effector molecule

Division of Infectious Diseases, Sloan Kettering Institute, Memorial Sloan Kettering Cancer Center, New York, NY 10021, USA.
Journal of Experimental Medicine (Impact Factor: 12.52). 03/2005; 201(4):535-43. DOI: 10.1084/jem.20041668
Source: PubMed

ABSTRACT Mycobacterium tuberculosis (Mtb) infection remains a global health crisis. Recent genetic evidence implicates specific cell envelope lipids in Mtb pathogenesis, but it is unclear whether these cell envelope compounds affect pathogenesis through a structural role in the cell wall or as pathogenesis effectors that interact directly with host cells. Here we show that cyclopropane modification of the Mtb cell envelope glycolipid trehalose dimycolate (TDM) is critical for Mtb growth during the first week of infection in mice. In addition, TDM modification by the cyclopropane synthase pcaA was both necessary and sufficient for proinflammatory activation of macrophages during early infection. Purified TDM isolated from a cyclopropane-deficient pcaA mutant was hypoinflammatory for macrophages and induced less severe granulomatous inflammation in mice, demonstrating that the fine structure of this glycolipid was critical to its proinflammatory activity. These results established the fine structure of lipids contained in the Mtb cell envelope as direct effectors of pathogenesis and identified temporal control of host immune activation through cyclopropane modification of TDM as a critical pathogenic strategy of Mtb.

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Available from: Vivek Rao, Sep 29, 2015
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    • "MTBC strain-specific lipid profiles, notably in the Beijing strain family, have been associated with increased transmission and drug resistance (Reed et al. 2007; Ford et al. 2013). Moreover, a number of in vitro and in vivo studies have reported evidence of variable inflammatory capacities among MTBC strains (Aguilar et al. 2010; Wang et al. 2010) and that both glycolipid biosynthesis and subtle chemical modifications carried by different MA subspecies can substantially affect macrophage cytokine responses and virulence in mice infection models (Reed et al. 2004; Rao et al. 2005; Barkan et al. 2012). Vander Beken et al. (2011) demonstrated the role of these functional group modifications mediated by MAs in eliciting unique inflammatory patterns. "
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    ABSTRACT: Mycolic acids (MAs) are α-alkyl, β-hydroxy long-chain fatty acids found in abundance in the cell envelope of the Mycobacterium tuberculosis complex (MTBC). MAs form an efficient permeability barrier, modulate host innate immune responses, and are the targets of several anti-tuberculosis drugs. Using mass spectrometry, we measured the relative abundance of 80 MA species across 36 clinical isolates of MTBC covering four major phylogenetic lineages. We found significant variations in the MA patterns between different MTBC strains and lineages. MA patterns of "ancient" lineages contrasted those from "modern" lineages, with a lower representation of alpha-mycolates among Lineage 6 strains and an inversion of the methoxy: keto-mycolates ratio in Lineage 1 strains. By interrogating the whole genome sequences of these MTBC strains, we identified relevant single-nucleotide polymorphisms that may sustain the lineage-specific MA patterns. Our results show that the strain genetic background influences MA metabolism and suggests that strain diversity should be considered in the development of new anti-tuberculosis drugs that target MA synthesis.
    MicrobiologyOpen 12/2014; 3(6). DOI:10.1002/mbo3.193 · 2.21 Impact Factor
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    • "Erdman vs. H37Rv is responsible for the stronger immunogenicity of MGM1991. On the other hand, HMA mutant still has the distal and proximal cyclopropanation of the α-mycolic acid and -as already mentioned- we and others have previously shown that cyclopropanation may have suppressive effects on inflammatory responses and the induction of IL-12p40 and TNF-α [8,29,30]. It must be emphasized that too strong inflammatory responses may have undesirable side effects and a correct balance between pro- and anti-inflammatory signals may be needed for optimal vaccine immunogenicity. "
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    ABSTRACT: The existing vaccine against tuberculosis (M. bovis BCG) exerts some protection against the extrapulmonary forms of the disease, particularly in young children, but is not very effective against the pulmonary form of TB, which often results from the reactivation of a latent M. tuberculosis (M.tb)infection. Among the new approaches in TB vaccine development, live attenuated M.tb mutants are a promising new avenue. Here we report on the vaccine potential of two highly attenuated M.tb mutants, MGM1991 and M.tbhma::hyg (HMA), lacking all oxygenated mycolates in their cell wall. In C57BL/6 mice, stronger Th1 (IFN-γ, IL-2 and TNF-α) and IL-17 responses could be induced following subcutaneous vaccination with either of the two mutants, than following vaccination with M. bovis BCG. Significantly more mycobacteria specific IFN-γ producing CD4(+) and particularly CD8(+) T cells could be detected by intracellular cytokine staining in mice vaccinated with the M.tb mutants. Finally, vaccination with either of the two mutants conferred stronger protection against intratracheal M.tb challenge than vaccination with BCG, as indicated by reduced bacterial replication in lungs at 4 to 12 weeks after challenge. Protection against M. tb dissemination, as indicated by reduced bacterial numbers in spleen, was comparable for both mutants to protection conferred by BCG.
    PLoS ONE 10/2013; 8(10):e76442. DOI:10.1371/journal.pone.0076442 · 3.23 Impact Factor
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    • "Our previous work demonstrated that in M. bovis BCG, M. chelonae and M. marinum, TAC inhibits the methyltransferases that introduce cyclopropane rings into mycolates [20]. Members of this methyltransferase family of enzymes include PcaA, CmaA2 and MmaA2, which are all important in the pathophysiology of mycobacteria [13], [21], [22]. However, inhibition of these enzymes is unlikely to explain the antitubercular activity of TAC. "
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    ABSTRACT: Defining the pharmacological target(s) of currently used drugs and developing new analogues with greater potency are both important aspects of the search for agents that are effective against drug-sensitive and drug-resistant Mycobacterium tuberculosis. Thiacetazone (TAC) is an anti-tubercular drug that was formerly used in conjunction with isoniazid, but removed from the antitubercular chemotherapeutic arsenal due to toxic side effects. However, several recent studies have linked the mechanisms of action of TAC to mycolic acid metabolism and TAC-derived analogues have shown increased potency against M. tuberculosis. To obtain new insights into the molecular mechanisms of TAC resistance, we isolated and analyzed 10 mutants of M. tuberculosis that were highly resistant to TAC. One strain was found to be mutated in the methyltransferase MmaA4 at Gly101, consistent with its lack of oxygenated mycolic acids. All remaining strains harbored missense mutations in either HadA (at Cys61) or HadC (at Val85, Lys157 or Thr123), which are components of the β-hydroxyacyl-ACP dehydratase complex that participates in the mycolic acid elongation step. Separately, a library of 31 new TAC analogues was synthesized and evaluated against M. tuberculosis. Two of these compounds, 15 and 16, exhibited minimal inhibitory concentrations 10-fold lower than the parental molecule, and inhibited mycolic acid biosynthesis in a dose-dependent manner. Moreover, overexpression of HadAB HadBC or HadABC in M. tuberculosis led to high level resistance to these compounds, demonstrating that their mode of action is similar to that of TAC. In summary, this study uncovered new mutations associated with TAC resistance and also demonstrated that simple structural optimization of the TAC scaffold was possible and may lead to a new generation of TAC-derived drug candidates for the potential treatment of tuberculosis as mycolic acid inhibitors.
    PLoS ONE 01/2013; 8(1):e53162. DOI:10.1371/journal.pone.0053162 · 3.23 Impact Factor
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