title: EP4 receptor regulates collagen type-I, MMP-1, and MMP-3 gene expression in human tendon fibroblasts in response to IL-1 beta treatment.
abstract: Tendinopathy is accompanied by inflammation, tendon matrix degradation, or both. Inflammatory cytokine IL-1beta, which is a potent inflammatory mediator, is likely present within the tendon. The purpose of this study was to determine the biological impact of IL-1beta on tendon fibroblasts by assessing the expression of cPLA(2), COX-2, PGE(2) and its receptors (EPs), collagen type-I, and MMPs. We also studied the role of the p38 MAPK pathway in IL-1beta-induced catabolic effects. We found that IL-1beta increased the expression levels of cPLA(2) and COX-2, and also increased the secretion of PGE(2). Induction of MMPs, such as MMP-1 and MMP-3 at the mRNA level, was also observed after stimulation with IL-1beta. Furthermore, the presence of IL-1beta significantly decreased the level of collagen type-I mRNA in tendon fibroblasts. These effects were found to be mediated by selective upregulation of EP(4) receptor, which is a member of G-protein-coupled receptor that transduces the PGE(2) signal. Blocking EP(4) receptor by a specific chemical inhibitor abolished IL-1beta-induced catabolic effects. These results suggest that IL-1beta-induced catabolic action on tendon fibroblasts occurs via the upregulation of two key inflammatory mediators, cPLA(2) and COX-2, which are responsible for the synthesis of PGE(2). IL-1beta further stimulates the expression of EP(4) receptor, suggesting positive feedback regulation which may lead to accelerated catabolic processes in tendon fibroblasts. Studies using pathway-specific chemical inhibitors suggest that the p38 MAPK pathway is the key signaling cascade transducing IL-1beta-mediated catabolic effects. Collectively, our findings suggest that the EP(4) receptor mediates the IL-1beta-induced catabolic metabolism via the p38 MAPK pathway in human tendon fibroblasts and may play a major role in the tendon's degenerative changes often seen in the later stages of tendinopathy.
authors.affiliation: MechanoBiology Laboratory, Departments of Orthopaedic Surgery and Bioengineering, University of Pittsburgh, E1640 Biomedical Science Tower, 210 Lothrop Street, Pittsburgh, PA 15213, USA.
authors.forename: Bhavani P
authors.initials: BP
authors.lastname: Thampatty
authors.forename: Hongxia
authors.initials: H
authors.lastname: Li
authors.forename: Hee-Jeong
authors.initials: HJ
authors.lastname: Im
authors.forename: James H-C
authors.initials: JH
authors.lastname: Wang
mesh_terms: D002478:Cells, Cultured; D024042:Collagen Type I / Q000096:biosynthesis / Q000235:genetics*; D051546:Cyclooxygenase 2 / Q000096:biosynthesis / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D053583:Interleukin-1beta / Q000502:physiology*; D020935:MAP Kinase Signaling System / Q000502:physiology; D008297:Male; D020781:Matrix Metalloproteinase 1 / Q000096:biosynthesis / Q000235:genetics*; D019278:Matrix Metalloproteinase 3 / Q000096:biosynthesis / Q000235:genetics*; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D010741:Phospholipases A / Q000096:biosynthesis / Q000235:genetics; D018078:Receptors, Prostaglandin E / Q000502:physiology*; D058309:Receptors, Prostaglandin E, EP4 Subtype; D013710:Tendons / Q000166:cytology / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology
chemical_list: D024042:Collagen Type I; D053583:Interleukin-1beta; D008565:Membrane Proteins; C545650:PTGER4 protein, human; D018078:Receptors, Prostaglandin E; D058309:Receptors, Prostaglandin E, EP4 Subtype; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D048051:p38 Mitogen-Activated Protein Kinases; D010741:Phospholipases A; D019278:Matrix Metalloproteinase 3; D020781:Matrix Metalloproteinase 1