title: ERK1/2 activation induced by inflammatory cytokines compromises effective host tissue integration of engineered cartilage.
abstract: OBJECTIVE
  Proinflammatory cytokines are known to provoke degradative signaling cascades that promote extracellular matrix disintegration in articular cartilage. Because integration of the repair tissue into the surrounding native cartilage to produce a mechanically stable interface has a profound impact on the viability and functionality of the restored joint surface, this study examined the effects of proinflammatory cytokines on the properties of tissue-engineered cartilage in the context of integration.
  
  
  METHODS
  Using an established in vitro cartilage defect model, we examined the integration of chondrocyte-laden agarose constructs into native articular cartilage and the biochemical and biomechanical alterations of these implants upon treatment with interleukin 1-beta (IL1-beta) and tumor necrosis factor-alpha (TNF-alpha). Additionally, we probed extracellular regulated kinase (ERK) signaling involvement in response to proinflammatory cytokines.
  
  
  RESULTS
  The time-dependent accumulation of extracellular matrix and concomitant increase in Young's modulus observed in the absence of cytokines was significantly decreased upon IL1-beta and TNF-alpha treatment. Push-out test showed the highest interface strength in hybrid cultures maintained without cytokines, which was significantly lowered with IL1-beta and TNF-alpha treatment. Histological characteristics of the interface region are consistent with the biochemical findings. Treatment with an inhibitor of ERK pathway antagonized the deleterious effects caused by both cytokines.
  
  
  CONCLUSIONS
  This study is the first to show the functional catastrophic effects of IL1-beta and TNF-alpha on the biochemical, structural, and integrative properties of tissue-engineered cartilage and their significant counteraction by the blockade of ERK signaling pathway. With the discovery of new potential chemical entities, ERK inhibitor may emerge as a new therapeutic approach for functional integration and mechanical integrity of an engineered cartilage to the host tissue and, therefore, enhance long-term viability and functionality of the restored joint surface.
authors.affiliation: Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis, and Musculoskeletal and Skin Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892-8022, USA.
authors.forename: Farida
authors.initials: F
authors.lastname: Djouad
authors.forename: Lars
authors.initials: L
authors.lastname: Rackwitz
authors.forename: Yingjie
authors.initials: Y
authors.lastname: Song
authors.forename: Sasa
authors.initials: S
authors.lastname: Janjanin
authors.forename: Rocky S
authors.initials: RS
authors.lastname: Tuan
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000187:drug effects*; D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D002356:Cartilage / Q000166:cytology / Q000378:metabolism*; D002417:Cattle; D007150:Immunohistochemistry; D053583:Interleukin-1beta / Q000378:metabolism*; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D023822:Tissue Engineering / Q000379:methods*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
chemical_list: D002070:Butadienes; D053583:Interleukin-1beta; D009570:Nitriles; D014409:Tumor Necrosis Factor-alpha; C113580:U 0126; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9