Mycobacterium tuberculosis (M.tb), the etiologic agent of tuberculosis, continues to be a highly prevalent deadly worldwide disease that poses a serious public health risk. M.tb is distinctively adapted for long-term survival within human macrophages and is believed in part to mediate its intracellular destiny through the preferential interaction of its cell wall components with host cell phagocytic receptors. The M.tb cell envelope contains molecules decorated in terminal mannose; the most abundant of these are the phosphatidylinositol mannosides, lipomannan, and mannose capped lipoarabinomannan (ManLAM). These mannosylated cell wall molecules engage macrophage C-type lectins that serve as pattern recognition receptors such as the mannose receptor and DC-SIGN. ManLAM plays a central role in tuberculosis pathogenesis by manipulating several macrophage processes that impact the protective immune response such as regulating signaling, microbicidal activity, cytokine production, Ag-processing, trafficking and presentation to T cells. Although the importance of ManLAM in the bacillus-host interface has been intensely studied, virtually nothing is known about the production of ManLAM and the nature of its metabolic processing within macrophages. Knowledge of these events is critical to our understanding of how ManLAM regulates the macrophage processes noted above from its intracellular locale. For other dominant cell wall lipoglycans such as LPS from gram-negative bacteria and lipophosphoglycan from Leishmania spp, intracellular processing can dramatically alter their bioactivity. The goals of this proposal are to 1) define the features of ManLAM intracellular metabolic processing using biochemical methods; and 2) determine the type(s) of ManLAM produced during intracellular growth of virulent M.tb in human macrophages and whether one variant is dominant. We will use metabolic radiolabeled ManLAM in combination with classical biochemical approaches followed by state-of- the-art MS techniques to purify and characterize ManLAM-derived products within human macrophages. We believe that the intracellular metabolites of ManLAM play a critical role in directing specific immunomodulatory responses by the macrophage that enhances M.tb intracellular survival. Characterization of intracellular ManLAM metabolism using biochemical means would represent a significant advance for the field in terms of identifying new molecular targets for diagnostics, therapies and vaccines. ? ? ? ?
| Keiser, Tracy L; Azad, Abul K; Guirado, Evelina et al. (2011) Comparative transcriptional study of the putative mannose donor biosynthesis genes in virulent Mycobacterium tuberculosis and attenuated Mycobacterium bovis BCG strains. Infect Immun 79:4668-73 |
| Torrelles, Jordi B; Schlesinger, Larry S (2010) Diversity in Mycobacterium tuberculosis mannosylated cell wall determinants impacts adaptation to the host. Tuberculosis (Edinb) 90:84-93 |
