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Signaling by toll-like receptor 2 and 4 agonists results in differential gene expression in murine macrophages
M Hirschfeld1, J J Weis, V Toshchakov
1Department of Pathology, University of Utah School of Medicine, Salt Lake City, Utah, USA.
Abstract:
Lipopolysaccharide (LPS) derived from the periodontal pathogen Porphyromonas gingivalis has been reported to differ structurally and functionally from enterobacterial LPS. These studies demonstrate that in contrast to protein-free enterobacterial LPS, a similarly purified preparation of P. gingivalis LPS exhibited potent Toll-like receptor 2 (TLR2), rather than TLR4, agonist activity to elicit gene expression and cytokine secretion in murine macrophages and transfectants. More importantly, TLR2 stimulation by this P. gingivalis LPS preparation resulted in differential expression of a panel of genes that are normally induced in murine macrophages by Escherichia coli LPS. These data suggest that (i) P. gingivalis LPS does not signal through TLR4 and (ii) signaling through TLR2 and through TLR4 differs quantitatively and qualitatively. Our data support the hypothesis that the shared signaling pathways elicited by TLR2 and by TLR4 agonists must diverge in order to account for the distinct patterns of inflammatory gene expression.
Insights
Lipopolysaccharide (LPS) from Porphyromonas gingivalis activates Toll-like receptor 2 (TLR2), not TLR4, in immune cells. This TLR2 activation leads to distinct gene expression patterns compared to other LPS, suggesting unique inflammatory signaling pathways.
Area of Science:
- Immunology
- Microbiology
- Molecular Biology
Background:
- Lipopolysaccharide (LPS) is a major component of Gram-negative bacteria, known to trigger immune responses.
- LPS from different bacterial species can exhibit distinct structural and functional properties.
- Porphyromonas gingivalis is a key pathogen in periodontitis, and its LPS may have unique immune-modulating activities.
Purpose of the Study:
- To investigate the immune-activating properties of LPS from Porphyromonas gingivalis.
- To determine which Toll-like receptors (TLRs) are activated by P. gingivalis LPS.
- To compare the downstream signaling pathways and gene expression profiles induced by P. gingivalis LPS versus enterobacterial LPS.
Main Methods:
- Purification of LPS from P. gingivalis and enterobacteria.
- Stimulation of murine macrophages and transfectants with purified LPS preparations.
- Analysis of gene expression and cytokine secretion using molecular and cellular assays.
- Assessment of TLR2 and TLR4 activation using specific agonists and antagonists.
Main Results:
- P. gingivalis LPS demonstrated potent agonist activity for Toll-like receptor 2 (TLR2), unlike enterobacterial LPS which primarily signals through TLR4.
- TLR2 stimulation by P. gingivalis LPS elicited differential gene expression in murine macrophages compared to TLR4 stimulation by Escherichia coli LPS.
- P. gingivalis LPS did not appear to signal through TLR4.
Conclusions:
- P. gingivalis LPS functions as a TLR2 agonist, mediating distinct immune responses.
- Signaling through TLR2 and TLR4 diverges quantitatively and qualitatively, leading to different inflammatory gene expression patterns.
- These findings support a model where shared TLR signaling pathways diverge to account for distinct inflammatory outcomes.