title: Differential expression of collagen types I, II, III, and X in human osteophytes.
abstract: BACKGROUND
  Osteophytes are neoplastic cartilaginous and osseous protrusions growing at the margins of osteoarthritic joints. Their formation involves complex patterns of cellular proliferation, differentiation, as well as matrix synthesis and turnover that are poorly understood.
  
  
  METHODS
  Here we report on an experimental approach using in situ hybridization and immunohistology to elucidate pathways of chrondrocyte differentiation in human osteophytes. Ab and cDNA probes for collagen types were used as specific parameters for chondrocyte phenotypes.
  
  
  RESULTS
  In early precartilaginous mesenchymal tissue, cytoplasmic mRNA for alpha 1(I) and alpha 1(III) collagen genes (Col1A1 and Col3A1) were found by in situ hybridization, correlating with the distribution of type I and III collagen as revealed by Ab staining. Strong expression of type II collagen both at mRNA and protein levels was the hallmark of chondrogenic differentiation in the cartilaginous zone of osteophytes. Type II collagen expression increased in all cartilaginous and fibrocartilaginous areas with growth and maturation of osteophytes. The signal intensity obtained after in situ hybridization with a COL2A1 probe was high and corresponded to that obtained in fetal cartilage, whereas normal adult articular cartilage usually did not show measurable type II collagen expression. In fibrocartilaginous areas, the most abundant, but heterogeneous tissue type seen in osteophytes, type II and III collagen mRNA expression overlapped considerably. Type III collagen was scattered, both pericellularly and interterritorially, over the whole osteophyte, excluding bone and chondrocytic cells of the deep zone. The strongest type I collagen expression was seen in bone and in the superficial fibrous layer. In areas of endochondral ossification, large chondrocytes were found expressing type X collagen, a specific marker for hypertrophic chondrocytes.
  
  
  CONCLUSIONS
  These results show that discrete stages of cartilage differentiation can be precisely followed in osteophytes using collagen type-specific cDNA probes and Ab as markers. In addition, a fibrocartilaginous chondrocyte phenotype was identified that expresses type II and III, but not type I collagen.
authors.affiliation: Max-Planck-Society, Clinical Research Units for Rheumatology, University of Erlangen-Nürnberg, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Aigner
authors.forename: U
authors.initials: U
authors.lastname: Dietz
authors.forename: H
authors.initials: H
authors.lastname: Stöss
authors.forename: K
authors.initials: K
authors.lastname: von der Mark
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000378:metabolism; D002358:Cartilage, Articular / Q000166:cytology* / Q000378:metabolism; D003094:Collagen / Q000096:biosynthesis* / Q000235:genetics; D005096:Exostoses / Q000378:metabolism*; D006801:Humans; D017403:In Situ Hybridization; D008875:Middle Aged; D009369:Neoplasms / Q000473:pathology; D010003:Osteoarthritis / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis
chemical_list: D012333:RNA, Messenger; D003094:Collagen