title: Promoting Endochondral Bone Repair Using Human Osteoarthritic Articular Chondrocytes.
abstract: BACKGROUND
  Current tissue engineering strategies to heal critical-size bone defects through direct bone formation are limited by incomplete integration of grafts with host bone and incomplete graft vascularization. An alternative strategy for bone regeneration is the use of cartilage grafts that form bone through endochondral ossification. Endochondral cartilages stimulate angiogenesis and are remodeled into bone, but are found in very small quantities in growth plates and healing fractures. We sought to develop engineered endochondral cartilage grafts using osteoarthritic (OA) articular chondrocytes as a cell source. Such chondrocytes often undergo hypertrophy, which is a characteristic of endochondral cartilages.
  
  
  METHODS
  We compared the ability of unmodified human OA (hOA) cartilage and cartilage grafts formed in vitro from hOA chondrocytes to undergo endochondral ossification in mice. Scaffold-free engineered chondrocyte grafts were generated by pelleting chondrocytes, followed by culture with transforming growth factor-β1 (TGF-β1) and bone morphogenetic protein 4. Samples derived from either primary or passaged chondrocytes were implanted subcutaneously into immunocompromised mice. Grafts derived from passaged chondrocytes from three patients were implanted into critical-size tibial defects in mice. Bone formation was assessed with histology after 4 weeks of implantation. The composition of tibial repair tissue was quantified with histomorphometry.
  
  
  RESULTS
  Engineered cartilage grafts generated from passaged OA chondrocytes underwent endochondral ossification after implantation either subcutaneously or in bone. Cartilage grafts integrated with host bone at 15 out of 16 junctions. Grafts variably remodeled into woven bone, with the proportion of bony repair tissue in tibial defects ranging from 22% to 85% (average 48%). Bony repair tissue bridged the tibial defects in half of the animals. In contrast, unmodified OA cartilage and engineered grafts formed from primary chondrocytes did not undergo endochondral ossification in vivo.
  
  
  CONCLUSIONS
  hOA chondrocytes can adopt an endochondral phenotype after passaging and TGF-β superfamily treatment. Engineered endochondral cartilage grafts can integrate with host bone, undergo ossification, and heal critical-size long-bone defects in a mouse model. However, additional methods to further enhance ossification of these grafts are required before the clinical translation of this approach.
authors.affiliation: 1 The Orthopaedic Trauma Institute, San Francisco General Hospital, University of California , San Francisco, San Francisco, California.
authors.forename: Chelsea S
authors.initials: CS
authors.lastname: Bahney
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Linsey
authors.initials: L
authors.lastname: Jacobs
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Robert
authors.initials: R
authors.lastname: Tamai
authors.affiliation: 1 The Orthopaedic Trauma Institute, San Francisco General Hospital, University of California , San Francisco, San Francisco, California.
authors.forename: Diane
authors.initials: D
authors.lastname: Hu
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Tammy F
authors.initials: TF
authors.lastname: Luan
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Miqi
authors.initials: M
authors.lastname: Wang
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Reddy
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Michelle
authors.initials: M
authors.lastname: Park
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Sonja
authors.initials: S
authors.lastname: Limburg
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Hubert T
authors.initials: HT
authors.lastname: Kim
authors.affiliation: 1 The Orthopaedic Trauma Institute, San Francisco General Hospital, University of California , San Francisco, San Francisco, California.
authors.forename: Ralph
authors.initials: R
authors.lastname: Marcucio
authors.affiliation: 2 San Francisco Veterans Affairs Medical Center, University of California , San Francisco, San Francisco, California.
authors.forename: Alfred C
authors.initials: AC
authors.lastname: Kuo
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000187:drug effects / Q000473:pathology*; D002358:Cartilage, Articular / Q000473:pathology*; D019902:Chondrocytes / Q000187:drug effects / Q000637:transplantation*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000494:pharmacology; D051379:Mice; D010003:Osteoarthritis / Q000473:pathology*; D015675:Osteocalcin / Q000378:metabolism; D010641:Phenotype; D013977:Tibia / Q000187:drug effects / Q000473:pathology; D023822:Tissue Engineering; D014945:Wound Healing / Q000187:drug effects
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D015675:Osteocalcin
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