title: Evolution of cell phenotype and extracellular matrix in tissue-engineered heart valves during in-vitro maturation and in-vivo remodeling.
abstract: OBJECTIVE
  Contemporary tissue valves are non-viable, and unable to grow, repair or remodel. It was postulated that tissue-engineered heart valves (TEHV) fabricated from autologous cells and a biodegradable scaffold could yield a dynamic progression of cell phenotype and extracellular matrix (ECM), in vitro and in vivo, and ultimately recapitulate native valve microscopic architecture.
  
  
  METHODS
  Trileaflet valve constructs were fabricated from poly-4-hydroxybutyrate-coated polyglycolic acid seeded with ovine endothelial and carotid artery medial cells, cultured in vitro for 4-14 days in a pulse duplicator, implanted as pulmonary valves in five lambs, and explanted at 4-20 weeks. ECM composition and collagen architecture were examined by histology (including Movat pentachrome stain and picrosirius red under polarized light), and cell phenotype by immunohistochemistry.
  
  
  RESULTS
  Cells from in-vitro constructs (14 days) were activated myofibroblasts, with strong expression of alpha-actin (microfilaments), vimentin (intermediate filaments) and SMemb (non-muscle myosin produced by activated mesenchymal cells). Cells from in-vivo explants at 16-20 weeks were fibroblast-like, with predominant vimentin expression and undetectable levels of alpha-actin (similar to native valve). Collagen elaboration and cellular expression of MMP-13 (collagenase 3) were evident in vitro at 14 days. In-vivo explants had increased collagen accumulation and strong MMP-13 expression at 4-8 weeks, but less activation (decreased expression of SMemb) and patchy endothelial cells at 16-20 weeks. Moreover, the ECM architecture of 16- to 20-week explanted TEHV resembled that of native valves.
  
  
  CONCLUSIONS
  Cell phenotype and ECM in TEHV prepared in vitro and implanted in vivo are dynamic, and reflect the ability of a vital tissue to remodel and, potentially, to grow.
authors.affiliation: Department of Pathology, Brigham and Women's Hospital, Boston, MA 02115, USA.
authors.forename: Elena
authors.initials: E
authors.lastname: Rabkin
authors.forename: Simon P
authors.initials: SP
authors.lastname: Hoerstrup
authors.forename: Masanori
authors.initials: M
authors.lastname: Aikawa
authors.forename: John E
authors.initials: JE
authors.lastname: Mayer
authors.forename: Frederick J
authors.initials: FJ
authors.lastname: Schoen
mesh_terms: D000199:Actins / Q000096:biosynthesis; D000818:Animals; D001688:Biological Products / Q000502:physiology / Q000627:therapeutic use; D001705:Bioprosthesis; D003094:Collagen / Q000096:biosynthesis; D017364:Collagenases / Q000096:biosynthesis; D004195:Disease Models, Animal; D005109:Extracellular Matrix / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D006349:Heart Valve Diseases / Q000628:therapy; D006350:Heart Valve Prosthesis; D006351:Heart Valves / Q000166:cytology* / Q000502:physiology* / Q000637:transplantation; D053509:Matrix Metalloproteinase 13; D010641:Phenotype; D011474:Prosthesis Design; D011664:Pulmonary Valve / Q000166:cytology / Q000502:physiology; D012756:Sheep; D023822:Tissue Engineering; D014746:Vimentin / Q000096:biosynthesis
chemical_list: D000199:Actins; D001688:Biological Products; D014746:Vimentin; D003094:Collagen; D017364:Collagenases; D053509:Matrix Metalloproteinase 13