Mycobacterial Trehalose Dimycolate Reprograms Macrophage Global Gene Expression and Activates Matrix Metalloproteinases

Abstract

g Trehalose 6,6=-dimycolate (TDM) is a cell wall glycolipid and an important virulence factor of mycobacteria. In order to study the role of TDM in the innate immune response to Mycobacterium tuberculosis, microarray analysis was used to examine gene regulation in murine bone marrow-derived macrophages in response to 90-m-diameter polystyrene microspheres coated with TDM. A large number of genes, particularly those involved in the immune response and macrophage function, were up-or downregulated in response to these TDM-coated beads compared to control beads. Genes involved in the immune response were specifically upregulated in a myeloid differentiation primary response gene 88 (MyD88)-dependent manner. The complexity of the transcriptional response also increased greatly between 2 and 24 h. Matrix metalloproteinases (MMPs) were significantly upregulated at both time points, and this was confirmed by quantitative real-time reverse transcription-PCR (RT-PCR). Using an in vivo Matrigel granuloma model, the presence and activity of MMP-9 were examined by immunohistochemistry and in situ zymography (ISZ), respectively. We found that TDM-coated beads induced MMP-9 expression and activity in Matrigel granulomas. Macrophages were primarily responsible for MMP-9 expression, as granulomas from neutrophil-depleted mice showed staining patterns similar to that for wild-type mice. The relevance of these observations to human disease is supported by the similar induction of MMP-9 in human caseous tuberculosis (TB) granulomas. Given that MMPs likely play an important role in both the construction and breakdown of tuberculous granulomas, our results suggest that TDM may drive MMP expression during TB pathogenesis. Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), infects approximately one-third of the human population and is the leading bacterial cause of human mortality worldwide, killing 1.45 million individuals per year (1). In the majority of cases, however, the bacteria are sequestered within a well-organized granuloma, where they can remain in a poorly characterized, "latent" state for decades. The granuloma structure is typically composed of centrally located, infected macrophages in various stages of degeneration and necrosis, surrounded by epithelioid macrophages, foamy macrophages, and occasional multinucleated giant cells, all bordered by a mixed population of lymphocytes and a fibrous capsule. This capsule consists of a wall of collagen that is laid down by fibroblasts and must be broken down in order for transmission to occur. Infected individuals who are immunocompetent and/or treated can resolve granulomas, with disaggregation of the accumulated leukocytes, dissolution of the extracellular matrix, and either scar formation or a return to the normal pulmonary architecture. In progressively infected individuals, on the other hand, the granuloma liquefies, the capsule wall cavitates and ruptures into an adjacent airway, and the bacilli multiply and are released (2). While some causes of tubercu...

Bacterial immunostat: Mycobacterium tuberculosis lipids and their role in the host immune response

“…As part of this initial response, pattern recognition receptors Toll-like receptor (TLR)-2 and TLR-4 on alveolar macrophages and dendritic cells (and probably also on pneumocytes) engage in recognizing TDM (6,6'-dimycoloyl-α-d-trehalose) and mannosylated lipoarabinomannan of M. tuberculosis 13,14 .…”

“…An alternative model for macrophage activation involves a myeloid differentiation factor 88 (MyD88)-dependent response to TDM 14,24,25 . Bone marrow-derived macrophages (BMMs) from MyD88-knocked out were not able to produce proinflammatory cytokines in response to TDM-coated polystyrene microspheres 24 .…”

“…Free mycolic acid (FM), a major compound involved in biofilm formation 20,21 , is released from TDM at some point in late infection; the latter is recognized for its ability to activate the innate immune response 14,23 . At that infection stage, (1) the capacity of M. tuberculosis to induce pro-inflammatory response is diminished; (2) the bacterium becomes drug tolerant 22 ; and (3) nutrient uptake increases as the host imposes bacterial starvation 22 .…”

The synthesis and biological evaluation of mycobacterial p-hydroxybenzoic acid derivatives (p-HBADs)

“…[1][2][3][4] Many of the lipids and glycolipids that make up the Mtb cell wall are believed to be virulence factors that play a key role in host-pathogen interactions and disease pathogenesis. [5][6][7][8][9][10] Glycosyl processing enzymes are essential for bacterial cell wall biosynthesis and many of the key components of the cell wall display complex carbohydrates. 11,12 The critical and diverse biological functions of these glycans in the life-cycle of the mycobacterium are only beginning to be understood.…”

Interplay of human macrophages and Mycobacterium tuberculosis phenotypes

“…Cording has been observed in both pathogenic and non-pathogenic mycobacteria [339] and depends on the presence of the cord-factor TDM, a cell wall glycolipid with potent immunogenic properties. TDM contributes to the inhibition of phagolysosomal fusion [340], drives granuloma formation [107,341] and activates tissue-damaging matrix metalloproteinases [342], suggesting a role as a virulence factor. Furthermore, cording mycobacteria were observed in vivo in the zebra fish model, and were phagocytosed to a lower degree [343].…”