title: Type II collagen levels correlate with mineralization by articular cartilage vesicles.
abstract: OBJECTIVE
  Pathologic mineralization is common in osteoarthritic (OA) cartilage and may be mediated by extracellular organelles known as articular cartilage vesicles (ACVs). Paradoxically, ACVs isolated from OA human cartilage mineralize poorly in vitro compared with those isolated from normal porcine cartilage. We recently showed that collagens regulate ACV mineralization. We sought to determine differences between collagens and collagen receptors on human and porcine ACVs as a potential explanation of their different mineralization behaviors.
  
  
  METHODS
  ACVs were enzymatically released from old and young human and porcine hyaline articular cartilage. Western blotting was used to determine the presence of types I, II, VI, and X collagen and various collagen receptors on ACVs. Type II collagen was quantified by enzyme-linked immunosorbent assay. Biomineralization was assessed by measuring the uptake of (45)Ca by isolated ACVs in agarose gels and by ACVs in situ in freeze-thawed cartilage.
  
  
  RESULTS
  As previously shown, isolated human ACVs mineralized poorly in response to ATP compared with porcine ACVs, but human and porcine ACVs mineralized similarly in situ in freeze-thawed cartilage. Type II collagen levels were 100-fold higher in isolated human ACVs than in porcine ACVs. Type II collagen in human ACVs was of high molecular weight. Transglutaminase-crosslinked type II collagen showed increased resistance to collagenase, suggesting a possible explanation for residual collagen on human ACVs. Expression of other collagens and collagen receptors was similar on human and porcine ACVs.
  
  
  CONCLUSIONS
  Higher levels of type II collagen in human ACV preparations, perhaps mediated by increased transglutaminase crosslinking, may contribute to the decreased mineralization observed in isolated human ACVs in vitro.
authors.affiliation: Rheumatology Section, Medical College of Wisconsin and Zablocki VA Medical Center, 5000 West National Avenue, Milwaukee, WI 53295, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Jubeck
authors.forename: Emily
authors.initials: E
authors.lastname: Muth
authors.forename: Claudia M
authors.initials: CM
authors.lastname: Gohr
authors.forename: Ann K
authors.initials: AK
authors.lastname: Rosenthal
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002130:Calcium Phosphates / Q000378:metabolism*; D002131:Calcium Pyrophosphate / Q000378:metabolism*; D002358:Cartilage, Articular / Q000378:metabolism* / Q000473:pathology; D024043:Collagen Type II / Q000378:metabolism*; D006801:Humans; D015388:Organelles / Q000378:metabolism* / Q000473:pathology; D010003:Osteoarthritis / Q000378:metabolism / Q000473:pathology; D038981:Receptors, Collagen / Q000378:metabolism; D013552:Swine; D011503:Transglutaminases / Q000378:metabolism; D055815:Young Adult
chemical_list: D002130:Calcium Phosphates; D024043:Collagen Type II; D038981:Receptors, Collagen; C020243:calcium phosphate; D011503:Transglutaminases; D002131:Calcium Pyrophosphate