title: Inactivation of one allele of the type II collagen gene alters the collagen network in murine articular cartilage and makes cartilage softer.
abstract: OBJECTIVE
  To evaluate the influence of inactivation of one allele ("heterozygous knockout" or "heterozygous inactivation") of the type II procollagen gene (Col2a1) on the biomechanical properties and structure of the articular cartilage and subchondral bone in 15 month old mice.
  
  
  METHODS
  Indentation stiffness of the humerus head articular cartilage was measured by a microindentation method. Cartilage and subchondral bone were prepared for digital densitometry of proteoglycans (PGs), polarised light microscopy (PLM) of collagen, and osteoarthrosis (OA) grading.
  
  
  RESULTS
  Heterozygous inactivation of the Col2a1 gene softened articular cartilage (p=0.002) as measured by indentation stiffness ((mean (SEM) 0.50 (0.07) MPa v 0.94 (0.13) MPa in controls). Fibrillar collagen network exhibited lower birefringence in the intermediate (p=0.04) and deep zones (p=0.01) of cartilage by PLM, indicating either decreased collagen content or a lower degree of fibril parallelism in the knockout mice. The total and zonal thicknesses of articular cartilage were unchanged. Zonal PG contents did not differ significantly. In knockout mice, the prevalence of superficial fibrillation-that is, a sign of OA, was higher than in controls (73% v 21%, p=0.002). The collagen induced birefringence of the superficial zone was not reduced. The subchondral bone volume fraction was lower in knockout mice than in controls, 31% v 43% (p=0.01), and optical retardation values in PLM of bone collagen were slightly but significantly lower (p=0.01).
  
  
  CONCLUSIONS
  Heterozygous inactivation of the Col2a1 gene made articular cartilage softer, altered the collagenous network, reduced subchondral bone volume, and altered its microstructure. Changes in the cartilage collagen network probably contributed to increased susceptibility to OA.
authors.affiliation: Department of Anatomy, University of Kuopio, Finland.
authors.forename: M M
authors.initials: MM
authors.lastname: Hyttinen
authors.forename: J
authors.initials: J
authors.lastname: Töyräs
authors.forename: T
authors.initials: T
authors.lastname: Lapveteläinen
authors.forename: J
authors.initials: J
authors.lastname: Lindblom
authors.forename: D J
authors.initials: DJ
authors.lastname: Prockop
authors.forename: S W
authors.initials: SW
authors.lastname: Li
authors.forename: M
authors.initials: M
authors.lastname: Arita
authors.forename: J S
authors.initials: JS
authors.lastname: Jurvelin
authors.forename: H J
authors.initials: HJ
authors.lastname: Helminen
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001718:Birefringence; D002358:Cartilage, Articular / Q000737:chemistry / Q000502:physiology*; D003094:Collagen / Q000235:genetics* / Q000648:ultrastructure; D003720:Densitometry; D019656:Loss of Heterozygosity; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008859:Microscopy, Polarization; D011509:Proteoglycans / Q000032:analysis; D018709:Statistics, Nonparametric
chemical_list: D011509:Proteoglycans; D003094:Collagen