Intracellular Adhesion Molecule-1 Is Regulated by Porphyromonas gingivalis Through Nucleotide Binding Oligomerization Domain-Containing Proteins 1 and 2 Molecules in Periodontal Fibroblasts

• Localización: Journal of periodontology, ISSN 0022-3492, Nº. 2, 2014, págs. 358-368
• Idioma: inglés
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• Resumen

  • Background: The mechanism by which Porphyromonas gingivalis regulates intracellular adhesion molecule 1 (ICAM-1) expression in human periodontal ligament cells (hPDLCs) and human gingival fibroblasts (hGFs) is unknown. The aim of this study is to investigate whether nucleotide binding oligomerization domain-containing protein (NOD) 1 and NOD2 are involved in this process and the clinical significance of ICAM-1 in periodontitis.

    Methods: hPDLCs and hGFs were treated with P. gingivalis, l-Ala-?-d-glutamyl-mesodiaminopimelic acid (an agonist for NOD1), and muramyl dipeptide (an agonist for NOD2). Alternatively, cells transfected with small interfering RNA targeting NOD1and NOD2 were treated with P. gingivalis. ICAM-1, NOD1, and NOD2 were detected at mRNA and protein levels. In addition, clinical examinations were performed in 30 healthy controls and 40 patients with chronic periodontitis (CP) before and after treatment, and serum-soluble ICAM-1 (sICAM-1) levels in these individuals were detected by enzyme-linked immunosorbent assay.

    Results: This study shows that P. gingivalis caused an increase in ICAM-1, NOD1, and NOD2 expression in periodontal fibroblasts. There was a linear correlation between ICAM-1 and NOD1 and NOD2 levels. Activation of NOD1 and NOD2 by the specific agonist led to the upregulation of ICAM-1, whereas knocking down NOD1 and NOD2 caused a reduction in P. gingivalis�induced ICAM-1 production. Furthermore, sICAM-1 levels were higher in patients with CP than in healthy controls and were positively related to the clinical periodontal parameters. After periodontal treatment, sICAM-1 levels decreased significantly.

    Conclusions: The present results indicate that sICAM-1 levels are correlated to the severity of periodontitis. NOD1 and NOD2 mediate P. gingivalis�induced ICAM-1 production in periodontal fibroblasts. NOD1 and NOD2 could be considered potential targets for periodontal therapy.

    Inflammation is an immune reaction against infection, injury, or antigenic stimulation. Leukocytes are recruited to the inflammatory site, adhere to and interact with host cells, and release inflammatory cytokines and immune proteins, leading to the inflammatory response. Intracellular adhesion molecule-1 (ICAM-1, CD54) is a transmembrane molecule and a member of circulating cell adhesion molecules and plays a central role in inflammation.1 It binds to lymphocyte function-associated antigen (LFA)-1 and monocyte adhesion molecule-1 on neutrophils, T-cells, and macrophages and acts as a stimulatory receptor for the selective recruitment of leukocytes under different pathologic situations. ICAM-1 is detected as either a transmembrane protein or a soluble form (sICAM-1) in body fluid. Both of the types have the similar function in adhesive activity.2 Porphyromonas gingivalis is identified as one of the major pathogens associated with chronic periodontitis (CP).3 It can be detected in the pathologic gingiva in patients with periodontitis,4,5 which suggests that it reacts with periodontal cells in vivo. In vitro studies have shown that P. gingivalis increases the expression level of ICAM-1 in human epithelial cells,6 as well as human gingival fibroblasts (hGFs).7,8 It has also been reported that P. gingivalis lipopolysaccharide (LPS) upregulates ICAM-1 expression through Toll-like receptors (TLRs).9 TLRs are a group of transmembrane proteins belonging to pattern recognition receptors (PRRs). PRRs are a big family that detects conserved microbial components, including LPS, called pathogen-associated molecular patterns (PAMPs). However, in addition to LPS, P. gingivalis contains other PAMPs, such as peptidoglycan (PGN), which was also reported to induce the production of adhesion molecules.10 Therefore, when intact P. gingivalis organisms stimulate the periodontal cells, other PRRs are thought to take part in the regulation of ICAM-1 expression.

    Nod-like receptors (NLRs) are included among PRRs, in addition to TLRs. NLRs consist of an N-terminal effector domain, an intermediate characteristic structure, NACHT, and a C-terminal leucine-rich repeat domain.11 Nucleotide binding oligomerization domain-containing protein 1 (NOD1) and NOD2 are the first identified sensors among NLRs, whose N-intermediate structure is the caspase activation and recruitment domain. NOD1 and NOD2 recognize the PGN derivatives mesodiaminopimelic acid and muramyl dipeptide (MDP) from Gram-negative bacteria.11 Recent studies have demonstrated that both of the NODs are found in periodontal fibroblasts12,13 and are expressed at a greater level than TLRs in healthy gingival tissues,14 indicating the pivotal roles of NOD1 and NOD2 in triggering an immune response. However, whether they play a role in ICAM-1 expression is unknown.

    A previous study showed that ICAM-1 is highly expressed in pathologic gingiva samples in which a large number of leukocytes have infiltrated.15 High levels of sICAM-1 were found in the gingival crevicular fluid (GCF) in patients with periodontitis before treatment, which decreased after periodontal therapy.16 However, Pischon et al.17 reported that the serum sICAM-1 level is unaffected by therapeutic intervention in aggressive periodontitis. Therefore, the role of sICAM-1 and its clinical significance in periodontitis need to be elucidated.

    The purposes of this study are to investigate the following: 1) the expression levels of ICAM-1 and NOD1 and NOD2 in hGFs and human periodontal ligament cells (hPDLCs) challenged with P. gingivalis; 2) the roles of NODs in the expression of ICAM-1 in both cells; and 3) the change of serum sICAM-1 levels before and after initial periodontal therapy, to potentially explain the clinical significance of sICAM-1.