title: Biochemical composition and turnover of the extracellular matrix of the normal and degenerate intervertebral disc.
abstract: BACKGROUND
  The intervertebral disc (IVD) is a complex cartilaginous structure which functions to resist biomechanical loads during spinal movement. It consists of the highly viscous cartilaginous nucleus pulposus, which is surrounded laterally by a thick outer ring of fibrous cartilage-the annulus fibrosus-and sandwiched inferiorly and superiorly by the cartilage end-plates. The main extracellular matrix molecules of the disc are collagens, proteoglycans, glycoproteins and elastin. The disc also contains appreciable amounts of water, matrix-degrading protease enzymes and their inhibitors, soluble signalling molecules and various metabolic breakdown products.
  
  
  METHODS
  This review provides a comprehensive description of the biochemical composition of the extracellular matrix of the IVD and, specifically, the proteases involved in its molecular turnover. Quantitation of the turnover rates using racemization of aspartic acid as a molecular clock is also discussed.
  
  
  CONCLUSIONS
  Molecular turnover rates of the major constituent matrix macromolecules of the IVD are found to be particularly slow, especially in the case of collagen. Over a normal human life span, this slow turnover may compromise the structural integrity of the IVD extracellular matrix essential for normal physiological functioning.
authors.affiliation: Department of Biomedical Engineering, Technion, Israel Institute of Technology, 32000, Haifa, Israel, sivan.sarit@gmail.com.
authors.forename: Sarit Sara
authors.initials: SS
authors.lastname: Sivan
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Hayes
authors.forename: Ellen
authors.initials: E
authors.lastname: Wachtel
authors.forename: Bruce
authors.initials: B
authors.lastname: Caterson
authors.forename: Yulia
authors.initials: Y
authors.lastname: Merkher
authors.forename: Alice
authors.initials: A
authors.lastname: Maroudas
authors.forename: Sharon
authors.initials: S
authors.lastname: Brown
authors.forename: Sally
authors.initials: S
authors.lastname: Roberts
mesh_terms: D002356:Cartilage / Q000378:metabolism; D003094:Collagen / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D006801:Humans; D007403:Intervertebral Disc / Q000378:metabolism*; D055959:Intervertebral Disc Degeneration / Q000378:metabolism* / Q000473:pathology; D020782:Matrix Metalloproteinases / Q000378:metabolism; D011509:Proteoglycans / Q000378:metabolism
chemical_list: D016326:Extracellular Matrix Proteins; D011509:Proteoglycans; D003094:Collagen; D020782:Matrix Metalloproteinases