title: Premature induction of hypertrophy during in vitro chondrogenesis of human mesenchymal stem cells correlates with calcification and vascular invasion after ectopic transplantation in SCID mice.
abstract: OBJECTIVE
  Functional suitability and phenotypic stability of ectopic transplants are crucial factors in the clinical application of mesenchymal stem cells (MSCs) for articular cartilage repair, and might require a stringent control of chondrogenic differentiation. This study evaluated whether human bone marrow-derived MSCs adopt natural differentiation stages during induction of chondrogenesis in vitro, and whether they can form ectopic stable cartilage that is resistant to vascular invasion and calcification in vivo.
  
  
  METHODS
  During in vitro chondrogenesis of MSCs, the expression of 44 cartilage-, stem cell-, and bone-related genes and the deposition of aggrecan and types II and X collagen were determined. Similarly treated, expanded articular chondrocytes served as controls. MSC pellets were allowed to differentiate in chondrogenic medium for 3-7 weeks, after which the chondrocytes were implanted subcutaneously into SCID mice; after 4 weeks in vivo, samples were evaluated by histology.
  
  
  RESULTS
  The 3-stage chondrogenic differentiation cascade initiated in MSCs was primarily characterized by sequential up-regulation of common cartilage genes. Premature induction of hypertrophy-related molecules (type X collagen and matrix metalloproteinase 13) occurred before production of type II collagen and was followed by up-regulation of alkaline phosphatase activity. In contrast, hypertrophy-associated genes were not induced in chondrocyte controls. Whereas control chondrocyte pellets resisted calcification and vascular invasion in vivo, most MSC pellets mineralized, in spite of persisting proteoglycan and type II collagen content.
  
  
  CONCLUSIONS
  An unnatural pathway of differentiation to chondrocyte-like cells was induced in MSCs by common in vitro protocols. MSC pellets transplanted to ectopic sites in SCID mice underwent alterations related to endochondral ossification rather than adopting a stable chondrogenic phenotype. Further studies are needed to evaluate whether a more stringent control of MSC differentiation to chondrocytes can be achieved during cartilage repair in a natural joint environment.
authors.affiliation: Orthopaedic University Hospital of Heidelberg, Heidelberg, Germany.
authors.forename: Karoliina
authors.initials: K
authors.lastname: Pelttari
authors.forename: Anja
authors.initials: A
authors.lastname: Winter
authors.forename: Eric
authors.initials: E
authors.lastname: Steck
authors.forename: Katrin
authors.initials: K
authors.lastname: Goetzke
authors.forename: Thea
authors.initials: T
authors.lastname: Hennig
authors.forename: Bjoern Gunnar
authors.initials: BG
authors.lastname: Ochs
authors.forename: Thomas
authors.initials: T
authors.lastname: Aigner
authors.forename: Wiltrud
authors.initials: W
authors.lastname: Richter
mesh_terms: D000328:Adult; D000368:Aged; D053674:Aggrecans / Q000235:genetics / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002114:Calcinosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002358:Cartilage, Articular / Q000098:blood supply* / Q000378:metabolism / Q000473:pathology*; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000378:metabolism / Q000473:pathology* / Q000637:transplantation; D002828:Choristoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D024043:Collagen Type II / Q000235:genetics / Q000378:metabolism; D024121:Collagen Type X / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D006984:Hypertrophy / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D008297:Male; D053509:Matrix Metalloproteinase 13 / Q000235:genetics / Q000378:metabolism; D045164:Mesenchymal Stem Cell Transplantation / Q000009:adverse effects* / Q000379:methods; D059630:Mesenchymal Stem Cells / Q000378:metabolism / Q000473:pathology*; D051379:Mice; D016513:Mice, SCID; D008875:Middle Aged; D009389:Neovascularization, Pathologic / Q000235:genetics / Q000378:metabolism
chemical_list: D053674:Aggrecans; D024043:Collagen Type II; D024121:Collagen Type X; D000469:Alkaline Phosphatase; D053509:Matrix Metalloproteinase 13