Glycine Lipids of Porphyromonas gingivalis Are Agonists for Toll-Like Receptor 2

Abstract

The serine-glycine dipeptide lipid classes, including lipid 430 and lipid 654, are produced by the periodontal pathogen Porphyromonas gingivalis and can be detected in lipid extracts of diseased periodontal tissues and teeth of humans. Both serine-glycine lipid classes were previously shown to engage human and mouse Toll-like receptor 2 (TLR2) and to inhibit mouse osteoblast differentiation and function through engagement of TLR2. It is not clear if other lipids related to serine-glycine lipids are also produced by P. gingivalis. The goal of this investigation was to determine whether P. gingivalis produces additional lipid classes similar to the serine-glycine lipids that possess biological properties. P. gingivalis (ATCC 33277) was grown in broth culture, and lipids were extracted and fractionated by high-performance liquid chromatography (HPLC). Lipids were separated using semipreparative HPLC, and specific lipid classes were identified using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and liquid chromatography-multiple reaction monitoring (LC-MRM) mass spectrometric approaches. Two glycine lipid classes were identified, termed lipid 567 and lipid 342, and these lipid classes are structurally related to the serine-glycine dipeptide lipids. Both glycine lipid classes were shown to promote TLR2-dependent tumor necrosis factor alpha (TNF-α) release from bone marrow macrophages, and both were shown to activate human embryonic kidney (HEK) cells through TLR2 and TLR6 but not TLR1. These results demonstrate that P. gingivalis synthesizes glycine lipids and that these lipids engage TLR2 similarly to the previously reported serine-glycine dipeptide lipids.

A novel phosphoglycerol serine-glycine lipodipeptide of Porphyromonas gingivalis is a TLR2 ligand

“…gingivalis (14,15). This comparison revealed that Lipid 1256 is between 10 and 100 times more potent than either Lipid 654 or Lipid 567 in activating human TLR2 or TLR2/TLR6 ( Figure 5B).…”

“…In prior work, fractions were typically collected only for approximately 60 minutes and late-eluting minor lipid constituents were discarded. While the serine-glycine lipodipeptide lipids and the glycine aminolipids were interspersed with phospholipids and complex lipids as they emerged during the first hour (14,15), two late eluting lipid peaks were identified when the fractionation was extended to 2 hours. For the present study, the larger peak emerging at 94-95 min was evaluated.…”

“…Another report has identified a lipoprotein lipase-sensitive TLR2 ligand that is a contaminant of LPS recovered from P. gingivalis and though the product was not chemically characterized, it likely accounts for the TLR2 engagement previously attributed to LPS (13). Serine-glycine lipodipeptides of P. gingivalis, including Lipid 654 and Lipid 430 (14), and glycine aminolipids of P. gingivalis, including Lipid 567 and Lipid 342 (15), are TLR2 ligands but these lipids are not as potent on a mass basis as the common lipopeptide TLR2 ligands, Pam2Cys and Pam3Cys (15). These serine/glycine lipids represent approximately 5% of the total lipids recovered from P. gingivalis (14,15) and could account for at least a portion of the TLR2 engagement observed with the total by guest, on November 4, 2020 www.jlr.org…”

Role for Lipids Secreted by Irradiated Peripheral Blood Mononuclear Cells in Inflammatory Resolution in Vitro

“…If oral pathogens control the production of lipids other than prostanoids by cells of the oral cavity has not been identified but for example, macrophages can release sphingolipids [51]. However, it is the oral pathogens including P. gingivalis producing lipids such as sphingolipids [52], serine-glycine dipeptide lipid [53] and short-chain fatty acids [54] that can in turn manipulate the host inflammatory response in periodontitis and other inflammatory diseases.…”

Evidence for Proline Utilization by Oral Bacterial Biofilms Grown in Saliva

“…Several studies have shown that glycine has an anti-inflammatory role, not just in the oral gingiva (Schaumann et al, 2013 ), but also in sepsis (Spittler et al, 1999 ) by reducing tumor necrosis factor alpha (TNF-α). In contrast to these results, others have shown that glycine contributes to inflammation by promoting toll-like receptor 2 to release increased levels of TNF-α (Nichols et al, 2020 ), and upregulating bone resorption stimulators prostaglandin E2 and cyclooxygenases in periodontitis (Rausch-Fan et al, 2005 ). Further work to investigate the role of proline in immune modulation due to glycine utilization is necessary.…”