Faculty of Dentistry, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China.
PLoS One. 2013;8(3):e58496. doi: 10.1371/journal.pone.0058496. Epub 2013 Mar 12.
Porphyromonas gingivalis is a major pathogen of periodontal disease that affects a majority of adults worldwide. Increasing evidence shows that periodontal disease is linked to various systemic diseases like diabetes and cardiovascular disease, by contributing to increased systemic levels of inflammation. Lipopolysaccharides (LPS), as a key virulent attribute of P. gingivalis, possesses significant amount of lipid A heterogeneity containing tetra- (LPS1435/1449) and penta-acylated (LPS1690) structures. Hitherto, the exact molecular mechanism of P. gingivalis LPS involved in periodontal pathogenesis remains unclear, due to limited understanding of the specific receptors and signaling pathways involved in LPS-host cell interactions.
METHODOLOGY/PRINCIPAL FINDINGS: This study systematically investigated the effects of P. gingivalis LPS1435/1449 and LPS1690 on the expression of TLR2 and TLR4 signal transduction and the activation of pro-inflammatory cytokines IL-6 and IL-8 in human gingival fibroblasts (HGFs). We found that LPS1435/1449 and LPS1690 differentially modulated TLR2 and TLR4 expression. NF-κB pathway was significantly activated by LPS1690 but not by LPS1435/1449. In addition, LPS1690 induced significant expression of NF-κB and p38 MPAK pathways-related genes, such as NFKBIA, NFKB1, IKBKB, MAP2K4 and MAPK8. Notably, the pro-inflammatory genes including GM-CSF, CXCL10, G-CSF, IL-6, IL-8 and CCL2 were significantly upregulated by LPS1690 while down-regulated by LPS1435/1449. Blocking assays confirmed that TLR4-mediated NF-κB signaling was vital in LPS1690-induced expression of IL-6 and IL-8 in HGFs.
CONCLUSIONS/SIGNIFICANCE: The present study suggests that the tetra- and penta-acylated lipid A structures of P. gingivalis LPS differentially activate TLR4-mediated NF-κB signaling pathway, and significantly modulate the expression of IL-6 and IL-8 in HGFs. The ability to alter the lipid A structure of LPS could be one of the strategies carried-out by P. gingivalis to evade innate host defense in gingival tissues, thereby contributing to periodontal pathogenesis.
牙龈卟啉单胞菌是一种主要的牙周病病原体，影响着全球大多数成年人。越来越多的证据表明，牙周病与糖尿病和心血管疾病等各种系统性疾病有关，因为它会导致全身炎症水平升高。脂多糖（LPS）作为牙龈卟啉单胞菌的关键毒力属性，具有大量的脂质 A 异质性，包含四酰化（LPS1435/1449）和五酰化（LPS1690）结构。迄今为止，由于对 LPS 与宿主细胞相互作用中涉及的特定受体和信号通路了解有限，牙龈卟啉单胞菌 LPS 参与牙周病发病机制的确切分子机制仍不清楚。
方法/主要发现：本研究系统研究了牙龈卟啉单胞菌 LPS1435/1449 和 LPS1690 对人牙龈成纤维细胞（HGFs）中 TLR2 和 TLR4 信号转导的表达和促炎细胞因子 IL-6 和 IL-8 的激活作用。我们发现 LPS1435/1449 和 LPS1690 可差异调节 TLR2 和 TLR4 的表达。NF-κB 途径被 LPS1690 显著激活，但不受 LPS1435/1449 影响。此外，LPS1690 诱导 NF-κB 和 p38 MAPK 途径相关基因，如 NFKBIA、NFKB1、IKBKB、MAP2K4 和 MAPK8 的显著表达。值得注意的是，GM-CSF、CXCL10、G-CSF、IL-6、IL-8 和 CCL2 等促炎基因被 LPS1690 显著上调，而被 LPS1435/1449 下调。阻断实验证实，TLR4 介导的 NF-κB 信号在 LPS1690 诱导的 HGFs 中 IL-6 和 IL-8 的表达中至关重要。
结论/意义：本研究表明，牙龈卟啉单胞菌 LPS 的四酰化和五酰化脂质 A 结构可差异激活 TLR4 介导的 NF-κB 信号通路，并显著调节 HGFs 中 IL-6 和 IL-8 的表达。改变 LPS 脂质 A 结构的能力可能是牙龈卟啉单胞菌逃避牙龈组织固有宿主防御的策略之一，从而导致牙周病发病机制。
