title: Matrix turnover in human cartilage repair tissue in autologous chondrocyte implantation.
abstract: OBJECTIVE
  Autologous chondrocyte implantation (ACI) is a form of tissue engineering that is being used increasingly to treat damaged articular cartilage. What happens at the graft site subsequent to the transplantation of chondrocytes beneath a periosteal flap has largely remained a matter of conjecture. We examined biopsy samples from the graft site using a panel of specific antibodies to investigate the cellular mechanisms involved and to determine whether remodeling of the matrix occurs.
  
  
  METHODS
  Ten full-depth core biopsy samples were obtained from patients who had undergone ACI 9-30 months previously (ages 28-53 years), in addition to 6 "control" biopsy samples. Cryosections were evaluated by standard histologic examination using polarized light and immunohistochemistry. Antibodies specific for type II collagen (CIIC1) were used, as well as antibodies against the C-propeptide of type II collagen (R160) and its denaturation product (Col2-3/4m), as indicators of anabolism or catabolism. In addition, antibodies to the matrix proteinase-generated neoepitopes of the aggrecan core protein were used to demonstrate either aggrecanase (BC-3 and BC-13) or matrix metalloproteinase (MMP) (BC-4 and BC-14) activity.
  
  
  RESULTS
  All biopsy samples stained for type II collagen, even in areas of fibrocartilaginous morphology. There was evidence of newly synthesized type II collagen in addition to denatured collagen. MMP and aggrecanase activity on the proteoglycan population was evident, with aggrecanase being more active in fibrocartilaginous areas.
  
  
  CONCLUSIONS
  The findings of this study indicate that ACI is capable of not only cartilage repair but, in some cases, regeneration. This may be achieved by the turnover and remodeling of an initial fibrocartilaginous matrix via enzymatic degradation and synthesis of newly formed type II collagen.
authors.affiliation: Centre for Spinal Studies, Robert Jones and Agnes Hunt Orthopaedic Hospital, National Health Service Trust, Oswestry, Shropshire, UK. s.roberts@keele.ac.uk
authors.forename: S
authors.initials: S
authors.lastname: Roberts
authors.forename: A P
authors.initials: AP
authors.lastname: Hollander
authors.forename: B
authors.initials: B
authors.lastname: Caterson
authors.forename: J
authors.initials: J
authors.lastname: Menage
authors.forename: J B
authors.initials: JB
authors.lastname: Richardson
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D002135:Calcium-Binding Proteins / Q000032:analysis / Q000378:metabolism; D002358:Cartilage, Articular / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology; D002648:Child; D019902:Chondrocytes / Q000637:transplantation*; D003094:Collagen / Q000032:analysis / Q000378:metabolism; D024043:Collagen Type II / Q000032:analysis / Q000378:metabolism; D010450:Endopeptidases / Q000032:analysis / Q000378:metabolism; D005109:Extracellular Matrix / Q000737:chemistry / Q000378:metabolism* / Q000473:pathology; D005260:Female; D006025:Glycosaminoglycans / Q000032:analysis / Q000378:metabolism; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D020782:Matrix Metalloproteinases / Q000032:analysis / Q000378:metabolism; D008875:Middle Aged; D014182:Transplantation, Autologous
chemical_list: D002135:Calcium-Binding Proteins; D024043:Collagen Type II; D006025:Glycosaminoglycans; C040072:chondrocalcin; D003094:Collagen; D010450:Endopeptidases; D020782:Matrix Metalloproteinases; C083641:aggrecanase