title: Tissue-engineered vascular graft remodeling in a growing lamb model: expression of matrix metalloproteinases.
abstract: OBJECTIVE
  We have previously demonstrated the functionality and growth of autologous, living, tissue-engineered vascular grafts (TEVGs) in long-term animal studies. These grafts showed substantial in vivo tissue remodeling and approximation to native arterial wall characteristics. Based on this, in vitro and in vivo matrix metalloproteinase (MMP) activity of TEVGs is investigated as a key marker of matrix remodeling.
  
  
  METHODS
  TEVGs fabricated from biodegradable scaffolds (polyglycolic-acid/poly-4-hydroxybutyrate, PGA/P4HB) seeded with autologous vascular cells were cultured in static and dynamic in vitro conditions. Thereafter, TEVGs were implanted as pulmonary artery replacements in lambs and followed up for 2 years. Gelatin gel zymography to detect MMP-2 and -9 was performed and collagen content quantified (n=5). Latent (pro) and active MMP-2 and -9 were detected.
  
  
  RESULTS
  Comparable levels of active MMP-9 and pro-MMP-2 were detected in static and dynamic culture. Higher levels of active MMP-2 were detected in dynamic cultures. Expression of MMP-2 and -9 was minimal in native grafts but was increased in implanted TEVG. Pro-MMP-9 was expressed 20 weeks post implantation and persisted up to 80 weeks post implantation. Collagen content in vitro was increased in dynamically conditioned TEVG as compared with static constructs and was increased in vivo compared with the corresponding native pulmonary artery.
  
  
  CONCLUSIONS
  MMPs are up-regulated in vitro by dynamic culture conditions and could contribute to increased matrix remodeling, native analogous tissue formation and functional growth of TEVGs in vivo. Monitoring of MMP activity, for example, by molecular imaging techniques, may enable the non-invasive assessment of functional tissue quality in future clinical tissue-engineering applications.
authors.affiliation: Swiss Center for Regenerative Medicine, University Hospital and Department of Surgical Research, University Zurich, Zurich, Switzerland.
authors.forename: Ian
authors.initials: I
authors.lastname: Cummings
authors.forename: Sarah
authors.initials: S
authors.lastname: George
authors.forename: Jens
authors.initials: J
authors.lastname: Kelm
authors.forename: Doerthe
authors.initials: D
authors.lastname: Schmidt
authors.forename: Maximilian Y
authors.initials: MY
authors.lastname: Emmert
authors.forename: Benedikt
authors.initials: B
authors.lastname: Weber
authors.forename: Gregor
authors.initials: G
authors.lastname: Zünd
authors.forename: Simon P
authors.initials: SP
authors.lastname: Hoerstrup
mesh_terms: D020341:Absorbable Implants; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D001807:Blood Vessel Prosthesis; D019917:Blood Vessel Prosthesis Implantation; D003094:Collagen / Q000378:metabolism; D004195:Disease Models, Animal; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D020782:Matrix Metalloproteinases / Q000378:metabolism*; D011651:Pulmonary Artery / Q000201:enzymology / Q000473:pathology / Q000601:surgery; D012756:Sheep; D046509:Tissue Culture Techniques; D023822:Tissue Engineering / Q000379:methods*; D054457:Tissue Scaffolds
chemical_list: D015415:Biomarkers; D003094:Collagen; D020782:Matrix Metalloproteinases; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9