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Infection and Immunity, October 2005, p. 7064-7068, Vol. 73, No. 10
0019-9567/05/$08.00+0 doi:10.1128/IAI.73.10.7064-7068.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Unité de Glycobiologie Structurale et Fonctionnelle, Unité Mixte de Recherche no. 8576 du Centre National de la Recherche Scientifique, Institut Fédératif de Recherche 118, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq cedex,1 Laboratoire de Dynamique Moléculaire des Interactions Membranaires, UMR CNRS no. 5539, Université des Sciences et Techniques du Languedoc (Montpellier II), 34095 Montpellier Cedex 5, France2
Received 3 November 2004/ Returned for modification 13 December 2004/ Accepted 22 June 2005
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Lipomannan (LM) and lipoarabinomannan (LAM) are major complex lipoglycans ubiquitously found in the mycobacterial cell wall. LM, considered as a direct biosynthetic precursor of LAM, is composed of a phosphatidyl-myo-inositol anchor linked to a D-mannan core. In LAM, the mannan domain is followed of a D-arabinan domain which can be capped by mannosyl or phosphoinositol residues (2, 16, 24). LM and LAM exhibit a wide array of biological activities which enhance antimycobacterial immune defenses or facilitate mycobacterial survival through inhibition of the immune response. The interaction of these lipoglycans with Toll-like receptor 2 (TLR2), CD14, mannose receptor or dendritic cell-specific intracellular adhesion molecule 3 is dependent on structural features of LM and LAM (4, 10, 19, 21-23, 29, 31, 35, 39). LAM from M. tuberculosis was reported to up-regulate MMP-9 expression in the monocytic THP-1 cell line and in macrophages through binding to the mannose receptor (3, 30, 31). However, although recent studies have emphasized the role of LM as a strong immunomodulator (2), no information is available regarding to its potential contribution in MMP-9 secretion.
In this study, we investigated the ability of LM from various mycobacteria, including pathogenic species, to stimulate MMP-9 gene expression and MMP-9 secretion from human macrophage-like THP-1 cells and human primary macrophages. We also addressed the possible involvement of TLR1, TLR2, and CD14 in MMP-9 production in response to LM stimulation.
Induction of MMP-9 from human macrophages in response to mycobacterial LM. Mycobacterium kansasii and Mycobacterium chelonae are two opportunistic pathogens that are particularly virulent in immunocompromised patients and are frequently associated with skin lesions and serious pulmonary diseases (14, 15, 18, 26). The capacities of various LM isolated from M. kansasii (LMMk), M. chelonae (LMMc), and Mycobacterium bovis BCG (LMBCG; sharing the same structure of LM from M. tuberculosis [24]) for triggering the MMP-9 gene expression was first investigated by reverse transcription (RT)-PCR analysis on differentiated THP-1 cells in serum-free medium. LM from M. chelonae (ATCC 19538), M. kansasii (PHR1 901, a clinical isolate), and M. bovis BCG (Pasteur strain 1173P2) were purified as described previously (12, 13). The endotoxin content of each preparation was <20 pg lipopolysaccharide (LPS)/10 µg as determined by the chromogenic Limulus lysate assay (QCL1000; BioWhittaker, Walkersville, MD). Human promonocytic leukemia THP-1 cells (European Collection of Cell Cultures no. 88081201) were differentiated with 50 nM 1,25-dihydroxy-vitamin D3 (Calbiochem, Darmstadt, Germany) for 72 h (34). To determine the effects of LM on the expression levels of the MMP-9 and TIMP-1 genes, 5 x 106 differentiated THP-1 cells were incubated in 12-well plates in RPMI-glutamine serum-free medium with either increasing LM concentrations or 100 ng/ml of LPS from Escherichia coli 055B5 (Sigma) used as a positive control of MMP-9 induction. Following 24-h incubation at 37°C, total RNA was purified from activated cells by using the Nucleospin RNA II kit (Macherey-Nagel, Düren, Germany), according to the manufacturer's instructions. Reverse transcription was performed with 5 µg of total RNA, in presence of M1MLVRT reverse transcriptase (Promega, Madison, WI), oligo(dT) primers, deoxynucleotide triphosphate, and RNasin. PCR amplification was performed by using primer pairs (Eurogentec) designed for the specific detection of human MMP-9, TIMP-1, and GAPDH genes, according to the method of Devy et al. (6). The first-strand sequence amplification was performed with GoTaq polymerase (Promega). Each amplification reaction consisted of an initial denaturation at 94°C and multiple cycles (23, 23, and 17 cycles at 68°C, 65°C, and 69°C for MMP-9, TIMP-1, and GAPDH genes, respectively) and a primer extension step at 72°C. PCR products (208, 627, and 256 bp for MMP-9, TIMP-1, and GAPDH genes, respectively) were separated by electrophoresis on a 2% agarose gel, visualized by ethidium bromide staining, and then analyzed with the Bio-Rad GelDoc analysis system (Bio-Rad, Italy).
As illustrated in Fig. 1A, each LM type was found to up-regulate MMP-9 mRNA synthesis in a dose-dependent manner, whereas in unstimulated cells, no specific product was detected. The induction of MMP-9 mRNA was maximal with 10 µg/ml of LM. LMMk, LMMc, and LMBCG displayed similar MMP-9-inducing activities. Expression levels of GAPDH mRNA, a housekeeping gene product included as an internal control, remained unchanged, regardless of the concentration of LM used.
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FIG. 1. (A) MMP-9 gene (MMP-9) expression in differentiated THP-1 cells in response to LM. Differentiated human promonocytic THP-1 cells were incubated for 24 h with 0.1 to 20 µg/ml of LM purified from M. kansasii (KanLM), M. chelonae (CheLM), or M. bovis BCG (BCGLM) in RPMI-glutamine serum-free medium. LPS from E. coli 055B5 (100 ng/ml) was included as a positive control. Levels of expression of MMP-9 and GAPDH mRNA were determined by RT-PCR as described in the text. GAPDH was used as a constitutively expressed marker. The ratio of fluorescence intensities of MMP-9 and GAPDH (GAPDH) gene PCR products are plotted in the bar graphs. Results are representative of at least three independent experiments. Bar charts are expressed as mean values ± standard errors of the means (SEM). The levels of statistical significance of differences in comparison with unstimulated cells were calculated by using the Student t test (one asterisk indicates a P value of <0.01). (B) Effect of anti-TNF- neutralizing antibodies on MMP-9 mRNA expression in differentiated THP-1 cells stimulated with LM. Differentiated THP-1 cells were stimulated for 24 h with LMMk and LMMc in the absence or presence of 5 µg/ml anti-TNF- neutralizing antibodies (Abs). Levels of expression of MMP-9 and GAPDH mRNA were determined by RT-PCR and expressed as described above. Results are representative of three independent experiments. The statistical significance of differences in comparison with untreated cells by neutralizing Abs was calculated by using the Student t test (two asterisks, P < 0.05; ns, nonsignificant value). (C) MMP-9 gene expression in human primary macrophagic cells in response to LM. Human macrophages derived from blood monocytic cells in the presence of macrophagic colony stimulating factor were incubated for 24 h in RPMI-glutamine serum-free medium and stimulated with either 10 µg/ml of each LM subtype or 100 ng/ml of E. coli 055B5 lipopolysaccharide (LPS). Levels of expression of MMP-9 and GAPDH mRNA were determined by RT-PCR and expressed as described above. Data are representative of one experiment. Similar results were obtained from at least three independent experiments performed with different blood donors. The statistical significance of differences in comparison with unstimulated cells was calculated by using the Student t test (two asterisks, P < 0.05).
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) was previously shown to stimulate secretion of MMP-9 in monocytes/macrophages (20). Although LM is a poor TNF-
-inducing factor in the absence of serum (35), we examined the contribution of low levels of TNF-
released in culture supernatants to induced MMP-9 induction. Hence, differentiated THP-1 cells were stimulated for 24 h at 37°C with 1 or 10 µg/ml of LMMc and LMMk, in fetal calf serum-free RPMI medium, and in the absence or presence of 5 µg/ml of TNF-
-neutralizing goat polyclonal antibodies (R&D Systems, Minneapolis, MN). Neutralization of TNF-
reduced only weakly the secretion of MMP-9 with at most 22% inhibition (Fig. 1B). These results suggest that the vast majority of MMP-9 induced by LM in absence of serum is secreted through a TNF-
-independent mechanism. The MMP-9-inducing capacity of LM was next examined on human blood monocyte-derived macrophages. Human peripheral blood mononuclear cells were isolated by density gradient centrifugation on Lymphoprep separation medium (Nycomed, Oslo, Norway), and adherent monocytes were collected after lymphocyte depletion. Purity of the population was evaluated by flow cytometry analysis (FACScalibur cytometer; Becton Dickinson). Macrophages were derived from monocytes in the presence of 100 ng/ml macrophagic colony-stimulating factor for 48 h in RPMI-glutamine supplemented with 10% heat-inactivated fetal calf serum. Macrophages were then stimulated with 10 µg/ml of LM for 24 h and processed for RT-PCR analysis, as described above. Figure 1C shows that all LM subtypes were potent MMP-9-inducing factors in primary human macrophages. Although LMBCG, LMMc, and LMMk display subtle structural differences pertaining mainly to the nature of fatty acids bound to anchor and the linkage and the degree of substitution in the mannopyranosyl side chains of the mannan core (2, 24), they behave similarly in up-regulating MMP-9 synthesis, suggesting that the MMP-9-inducing activity is a common feature to all mycobacterial LMs.
The amount of MMP-9 protein released in culture supernatants of differentiated THP-1 cells (2 x 105 cells/well) was next quantified by enzyme-linked immunosorbent assay, after 48 h of cell incubation with either LMMk or LMMc in serum-free RPMI medium. Microtiter plates were coated overnight at 4°C with aliquots of cell supernatants, blocked with phosphate-buffered saline (PBS)-0.05% Tween 20-1% bovine serum albumin, and then incubated with biotin-conjugated anti-MMP-9 antibodies (1/500 dilution; Santa Cruz Biotechnology, CA), prior to the addition of extravidin-conjugated peroxidase (1/1,000 dilution) for 30 min. Detection was performed with o-phenylenediamine-dihydrochloride and by reading the absorbance at 490 nm. MMP-9 concentrations in culture supernatants were quantified according to a standard curve generated with human recombinant pro-MMP-9 (R&D Systems, Minneapolis, MN) at concentrations ranging from 2 to 30 ng/ml. LM induced the secretion of MMP-9 in a dose-dependent manner, and the levels of MMP-9 secreted from cells stimulated with LMMk and LMMc were approximately six and five times higher, respectively, than that from unstimulated cells (Fig. 2A).
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FIG. 2. Secretion of MMP-9 in the culture supernatant of differentiated THP-1 cells stimulated with LM. LMMk, KanLM; LMMc, CheLM. (A) Differentiated THP-1 cells were stimulated with increasing concentrations of LMMk or LMMc in RPMI-glutamine medium. Culture supernatants were collected after 48 h and assayed by enzyme-linked immunosorbent assay for MMP-9 secretion. Data presented are from one representative experiment out of three independent experiments with similar results. Results are expressed as mean values ± standard deviations of triplicate wells. The P value for the comparison between untreated and stimulated cells was <0.01. (B) Release of the MMP-9 protein form was investigated by detecting the gelatinase activity by zymography analysis. Differentiated THP-1 cells were incubated with 10 µg/ml of LMMk and LMMc, for 48 h. Control cells () were left unstimulated. (C) Western blot analysis using specific anti-human MMP-9 antibodies. Data are representative of four independent experiments for zymography and two experiments for Western blot analysis.
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Induction of MMP-9 gene by LM is mediated through a TLR1/TLR2- and CD14-dependent pathway.
In an attempt to identify receptors present on the surface of differentiated THP-1 cells that recognize LM and transmit a positive signal for MMP-9 expression, we evaluated the effects of various neutralizing antireceptor antibodies, known to inhibit biological activities of microbial products (21, 29, 31, 35), on MMP-9 synthesis. Differentiated cells were pretreated for 30 min at 37°C with 5 µg/ml of neutralizing antibodies (purchased from BD Biosciences, BD Pharmingen, San Diego, CA, or HBT, Uden, The Netherlands), and then 1 µg/ml of LMMk was added to the cells for 24 h to allow MMP-9 gene expression. The corresponding isotype controls were used as negative controls. As illustrated in Fig. 3, pretreatment with anti-TLR2 (mouse IgG2a clone TL2-1), anti-TLR1 (mouse IgG1
clone GD2.F4), and anti-CD14 (mouse IgG1 clone MEM-18) antibodies inhibited MMP-9 gene expression by 48%, 37%, and 66%, respectively. Surprisingly, the anti-mannose receptor antibody (mouse IgG1
clone 19), previously shown to interfere with MMP-9 gene expression elicited by mannose lipoarabinomannan of M. tuberculosis (31), displayed only a residual inhibitory effect (8%). Antibodies raised against TLR4 (mouse IgG2a
clone HTA 125), a potent LPS-responsive receptor, failed to inhibit MMP-9 gene expression. Incubation with the corresponding control isotype antibodies did not alter MMP-9 mRNA synthesis (data not shown). Altogether, these results suggest the participation of several pattern recognition receptors, in particular, TLR1/TLR2 and CD14, in the signaling pathway leading to MMP-9 induction. These results are consistent with previous studies demonstrating that macrophage activation by LMMk or LMMc is mediated by TLR2 and CD14 but is independent of TLR6 and TLR4 (2, 29, 35). Interestingly, the TLR1/TLR2 heterodimer triggers, through the adaptor protein MyD88, the activation of several signal transduction molecules, leading to the activation of NF-
B and mitogen-activated protein kinases in macrophages (33). Rivera-Marrero et al. (31) demonstrated that induction of MMP-9 by mannose lipoarabinomannan from M. tuberculosis required the transcriptional activation of AP-1 through mitogen-activated protein kinases. According to these authors, the addition of PD-98059, a MEK1 inhibitor, resulted in a total inhibition of MMP-9 induction (31). In preliminary experiments, we have tested the effect of PD-98059 and observed that, at 50 µM, this molecule strongly inhibited LM-induced MMP-9 expression in differentiated THP-1 cells (not shown), suggesting that MEK1 may participate in this transduction signal.
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FIG. 3. Inhibition of the MMP-9 expression by blocking pattern recognition receptors. Differentiated THP-1 cells were pretreated with 5 µg/ml of anti-CD14, anti-TLR1, anti-TLR2, anti-mannose receptor, or control isotype antibodies for 30 min at 37°C, prior to the addition of LMMk (1 µg/ml). After 24 h of incubation, expression levels of MMP-9 and GAPDH mRNA were determined by RT-PCR analysis as described above. Results are expressed as percentages of the MMP-9/GAPDH mRNA expression ratio obtained with LMMk. The ratio values obtained in the absence of antibodies were arbitrarily placed at 100%. Data presented represent the mean values ± SEM of three independent experiments. Statistical analyses were performed by using Student's t test to compare antireceptor Ab-treated cells with nontreated cells (two asterisks, P < 0.05; ns, nonsignificant).
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FIG. 4. TIMP-1 mRNA expression in differentiated THP-1 cells in response to LM. Differentiated THP-1 cells were incubated for 24 h with 10 µg/ml of either LMMk (KanLM) or LMMc (CheLM) in RPMI-glutamine serum-free medium. Expression levels of TIMP-1 and GAPDH mRNA were determined by RT-PCR analysis. The ratios of the fluorescence intensities of TIMP-1 and GAPDH PCR products are plotted in the bar graph. Results are representative of at least three independent experiments. Bar charts are expressed as mean values ± SEM (statistical analyses were performed by using Student's t test [two asterisks, P < 0.05]).
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