title: Resistance of MMP9 and TIMP1 to endotoxin tolerance.
abstract: Inflammatory cytokines activate tissue collagenases such as matrix metalloproteinases (MMPs). MMPs are antagonized by tissue inhibitors of metalloproteinases (TIMPs) that attempt to regulate excessive collagenase activity during inflammatory conditions. During chronic inflammatory conditions, induction of endotoxin tolerance negatively regulates the cytokine response in an attempt to curtail excessive host tissue damage. However, little is known about how downregulation of inflammatory cytokines during endotoxin tolerance regulates MMP activities. In this study, human monocyte-derived macrophages were either sensitized or further challenged to induce tolerance with lipopolysaccharide (LPS) from Porphyromonas gingivalis (PgLPS) or Escherichia coli (EcLPS). Inflammatory cytokines, such as TNF-α and IL-1β, and levels of MMP9 and TIMP1 were analyzed by a combination of cytometric bead array, western blot/gelatin zymography and real-time RT-PCR. Functional blocking with anti-TLR4 but not with anti-TLR2 significantly downregulated TNF-α and IL-1β. However, MMP9 levels were not inhibited by toll-like receptor (TLR) blocking. Interestingly, endotoxin tolerance significantly upregulated TIMP1 relative to MMP9 and downmodulated MMP9 secretion and its enzymatic activity. These results suggest that regulatory mechanisms such as induction of endotoxin tolerance could inhibit MMP activities and could facilitate restoring host tissue homeostasis.
authors.affiliation: Department of periodontics, School of Dentistry, West Virginia University, One Medical Center Drive, PO Box 9448, Morgantown, WV 26506, USA mamuthukuru@hsc.wvu.edu.
authors.forename: Manoj
authors.initials: M
authors.lastname: Muthukuru
authors.affiliation: Department of periodontics, College of Dental Medicine, Georgia Health Sciences University, 1120 15th Street, Augusta, GA 30912, USA.
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Cutler
mesh_terms: D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D004731:Endotoxins / Q000302:isolation & purification / Q000633:toxicity*; D004926:Escherichia coli / Q000737:chemistry; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006801:Humans; D008070:Lipopolysaccharides / Q000302:isolation & purification / Q000633:toxicity*; D008264:Macrophages / Q000276:immunology*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D016966:Porphyromonas gingivalis / Q000737:chemistry; D019715:Tissue Inhibitor of Metalloproteinase-1 / Q000378:metabolism*
chemical_list: D016207:Cytokines; D004731:Endotoxins; D008070:Lipopolysaccharides; C560822:TIMP1 protein, human; D019715:Tissue Inhibitor of Metalloproteinase-1; C579270:MMP9 protein, human; D020780:Matrix Metalloproteinase 9
keywords: Endotoxin tolerance; Lipopolysaccharide; MMP; Macrophages; TIMP; Toll like receptors