Identification of Signaling Pathways in Macrophage Exposed to Porphyromonas gingivalis or to Its Purified Cell Wall Components

Abstract

Porphyromonas gingivalis (P. gingivalis) can trigger an inflammatory condition leading to the destruction of periodontal tissues. However P. gingivalis LPS and its fimbriae (FimA) play different roles compared with the live bacteria in the context of intracellular molecule induction and cytokine secretion. To elucidate whether this difference results from different signaling pathways in host immune response to P. gingivalis, its LPS, or its FimA, we examined gene expression profile of human macrophages exposed to P. gingivalis, its LPS, or its FimA. A comparison of gene expression resulted in the identification of three distinct groups of expressed genes. Furthermore, computer-assisted promoter analysis of a subset of each group of differentially regulated genes revealed four putative transcriptional regulation models that associate with transcription factors NFκB, IRF7, and KLF4. Using gene knockout mice and siRNA to silence mouse genes, we showed that both TLR2 and TLR7 are essential for the induction of NFκB-containing genes and NFκB-IFN-sensitive response element (ISRE) cocontaining genes by either P. gingivalis or its purified components. The gene induction via either TLR2 or TLR7 is dependent on both MyD88 and p38 MAPK. However, the unique induction of IFN-β by P. gingivalis LPS requires TLR7 and IFNαβR cosignaling, and the induction of ISRE-containing gene is dependent on the activation of IFN-β autocrine loop. Taken together, these data demonstrate that P. gingivalis and its components induce NFκB-containing genes through either TLR2- or TLR7-MyD88-p38 MAPK pathway, while P. gingivalis LPS uniquely induces ISRE-containing genes, which requires IFNαβR signaling involving IRF7, KLF4, and pY701 STAT1.

The NLR Adaptor ASC/PYCARD Regulates DUSP10, Mitogen-activated Protein Kinase (MAPK), and Chemokine Induction Independent of the Inflammasome

“…The finding that Pg activates NF-B-and TNF-related signaling is consistent with other microarray studies of Pg infection (28,34). Our further assessment of ASC-modulated genes revealed several chemokines that are ASC-dependent.…”

TLR2-Dependent Inflammatory Response to Porphyromonas gingivalis Is MyD88 Independent, whereas MyD88 Is Required To Clear Infection

“…Thus, the nature of the ligand seems to determine whether TLR2 signaling involves MyD88-independent pathways. We next found, as other investigators have described (2), that isolated macrophages respond to live P. gingivalis in a MyD88-dependent manner (data not shown). Therefore, TLR2-dependent, MyD88-independent proinflammatory cytokine production depends on the nature of the ligand and the in vivo context of exposure.…”

Rapid Myeloid Cell Transcriptional and Proteomic Responses to Periodontopathogenic Porphyromonas gingivalis

“…Because ligand interactions with TLR4, but not TLR2 trigger parallel, but separable pathways to influence both NF-B and IFN-linked signal transduction, we examined the P. gingivalis LPS-induced transcriptional profile for potential TRIF adaptor-dependent gene induction, in addition to the evident NF-B pathways. Some IFN-inducible genes were concurrently upregulated by P. gingivalis LPS, along with IFN-␤1, which may contribute to an autocrine loop impacting on IFNinducible genes as reported in other studies, 15 including guanylate binding protein 1, IFN-inducible (GBP1), GBP2, and IFN-induced protein with tetratricopeptide repeats 2 (IFIT2) (Supplemental Table S2 available at http://ajp.amjpathol.org). Moreover, these data suggest that TLR4 signaling pathways were engaged by P. gingivalis LPS.…”

“…Among these targeted populations are innate immune cells of myeloid origin, including recruited peripheral blood monocytes, immature and mature DCs, and differentiated macrophages, yet little is known of their differential responses to inflammatory stimuli, such as P. gingivalis. Prior studies have examined P. gingivalis stimulation of primary human monocyte or macrophage populations, 15 but this has not been examined in these populations relative to one another, nor linked with the central innate immune population of myeloid DCs. Given the common lineage of these myeloid populations and their seminal, but discrete roles in innate and adaptive immunity, we explored their shared and/or differential responses to P. gingivalis LPS as a means to understand their respective contributions in systemic and locally mediated diseases and in guiding T-helper cell recruitment and lineage bias.…”