title: Trans-cyclopropanation of mycolic acids on trehalose dimycolate suppresses Mycobacterium tuberculosis -induced inflammation and virulence.
abstract: Recent studies have shown that fine structural modifications of Mycobacterium tuberculosis cell envelope lipids mediate host cell immune activation during infection. One such alteration in lipid structure is cis-cyclopropane modification of the mycolic acids on trehalose dimycolate (TDM) mediated by proximal cyclopropane synthase of alpha mycolates (pcaA), a proinflammatory lipid modification during early infection. Here we examine the pathogenetic role and immunomodulatory function of mycolic acid cyclopropane stereochemistry by characterizing an M. tuberculosis cyclopropane-mycolic acid synthase 2 (cmaA2) null mutant (Delta cmaA2) that lacks trans-cyclopropanation of mycolic acids. Although titers of WT and Delta cmaA2 organisms were identical during mouse infection, Delta cmaA2 bacteria were hypervirulent while inducing larger granulomas than WT M. tuberculosis. The hypervirulence of the Delta cmaA2 strain depended on host TNF-alpha and IFN-gamma. Loss of trans-cyclopropanation enhanced M. tuberculosis-induced macrophage inflammatory responses, a phenotype that was transferable with petroleum ether extractable lipids. Finally, purified TDM lacking trans-cyclopropane rings was 5-fold more potent in stimulating macrophages. These results establish cmaA2-dependent trans-cyclopropanation of TDM as a suppressor of M. tuberculosis-induced inflammation and virulence. In addition, cyclopropane stereochemistries on mycolic acids interact directly with host cells to both positively and negatively influence host innate immune activation.
authors.affiliation: Immunology Program, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
authors.forename: Vivek
authors.initials: V
authors.lastname: Rao
authors.forename: Feng
authors.initials: F
authors.lastname: Gao
authors.forename: Bing
authors.initials: B
authors.lastname: Chen
authors.forename: William R
authors.initials: WR
authors.lastname: Jacobs
authors.forename: Michael S
authors.initials: MS
authors.lastname: Glickman
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D003311:Cord Factors / Q000737:chemistry / Q000276:immunology; D003521:Cyclopropanes / Q000737:chemistry* / Q000378:metabolism; D007249:Inflammation / Q000382:microbiology*; D007371:Interferon-gamma / Q000276:immunology; D008168:Lung / Q000382:microbiology / Q000473:pathology; D008264:Macrophages / Q000166:cytology / Q000276:immunology; D008563:Membrane Lipids / Q000737:chemistry; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D016513:Mice, SCID; D009169:Mycobacterium tuberculosis / Q000737:chemistry / Q000166:cytology / Q000276:immunology* / Q000472:pathogenicity*; D009171:Mycolic Acids / Q000737:chemistry / Q000276:immunology; D015996:Survival Rate; D014376:Tuberculosis; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology
chemical_list: D001426:Bacterial Proteins; C423316:CmaA2 protein, Mycobacterium tuberculosis; D003311:Cord Factors; D003521:Cyclopropanes; D008563:Membrane Lipids; D009171:Mycolic Acids; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; C030797:cyclopropane; D008780:Methyltransferases