title: Aging is associated with increased activities of matrix metalloproteinase-2 and -9 in tenocytes.
abstract: BACKGROUND
  Most tendon pathology is associated with degeneration, which is thought to involve cyclic loading and cumulative age-related changes in tissue architecture. However, the association between aging and degeneration of the extracellular matrix (ECM) in tendons has not been investigated extensively.
  
  
  METHODS
  We examined tenocytes from Achilles tendons taken from rats of three different ages (2, 12, and 24 months). Tenocyte viability was assessed using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. Quantitative real-time polymerase chain reaction (PCR) was used to determine the levels of mRNAs that encode type-I collagen, matrix metalloproteinase (MMP)-2 and -9, tissue inhibitor of metalloproteinase (TIMP)-1 and -2 and transforming growth factor (TGF)-β1. Gelatin zymography was used to evaluate the enzymatic activities of MMP-2 and -9. Furthermore, the concentration of TGF-β1 in conditioned medium was evaluated using enzyme-linked immunosorbent assay (ELISA).
  
  
  RESULTS
  The results of the MTT assay showed that the number of viable tenocytes decreased with age. No differences were observed in the levels of mRNAs that encode type-I collagen and TGF-β1 among the three age groups, and the TGF-β1 concentration did not change with age. However, mRNAs that encode MMP-2 and -9 were significantly more abundant in tenocytes from the aging group, and gelatin zymography revealed that the enzymatic activities of MMP-2 and -9 also increased significantly with age. Furthermore, as compared with young group, mRNAs that encode TIMP-1 and -2 were significantly decreased in tenocytes from the aging group.
  
  
  CONCLUSIONS
  Activities of MMP-2 and MMP-9 in tenocytes increase with age. This might provide a mechanistic explanation of how aging contributes to tendinopathy or tendon rupture with age.
authors.affiliation: Departement of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital, Linkou, Taiwan.
authors.forename: Tung-Yang
authors.initials: TY
authors.lastname: Yu
authors.forename: Jong-Hwei S
authors.initials: JH
authors.lastname: Pang
authors.forename: Katie Pei-Hsuan
authors.initials: KP
authors.lastname: Wu
authors.forename: Max J-L
authors.initials: MJ
authors.lastname: Chen
authors.forename: Chien-Hung
authors.initials: CH
authors.lastname: Chen
authors.forename: Wen-Chung
authors.initials: WC
authors.lastname: Tsai
mesh_terms: D000125:Achilles Tendon / Q000166:cytology* / Q000201:enzymology*; D000367:Age Factors; D000375:Aging / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000502:physiology; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism*; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D020778:Matrix Metalloproteinase 2; C522363:Mmp2 protein, rat; D020780:Matrix Metalloproteinase 9; C572337:Mmp9 protein, rat