Open AccessAltered mineralization of human osteoarthritic osteoblasts is attributable to abnormal type I collagen production
Author(s) -
Couchourel Denis,
Aubry Isabelle,
Delalandre Aline,
Lavigne Martin,
MartelPelletier Johanne,
Pelletier JeanPierre,
Lajeunesse Daniel
Publication year - 2009
Publication title -
arthritis & rheumatism
Language(s) - English
Resource type - Journals
eISSN - 1529-0131
pISSN - 0004-3591
DOI - 10.1002/art.24489
Subject(s) - osteopontin , osteocalcin , alkaline phosphatase , chemistry , osteoblast , osteoid , endocrinology , medicine , type i collagen , procollagen peptidase , runx2 , in vitro , biology , biochemistry , enzyme
Objective Bone tissue in osteoarthritis (OA) is composed of abundant undermineralized osteoid matrix. The aim of this study was to investigate the mechanisms responsible for this abnormal matrix, using in vitro OA subchondral osteoblasts. Methods Primary normal and OA osteoblasts were prepared from tibial plateaus. Phenotype was determined by alkaline phosphatase activity, and osteocalcin, osteopontin, prostaglandin E 2 (PGE 2 ), and transforming growth factor β1 (TGFβ1) were assessed by enzyme‐linked immunosorbent assay. Expression of COL1A1 and COL1A2 was determined by real‐time polymerase chain reaction. The production of type I collagen was determined by the release of its C‐terminal propeptide and Western blot analysis. In vitro mineralization was evaluated by alizarin red staining. Inhibition of TGFβ1 expression was performed using a small interfering RNA technique. Results Mineralization of OA osteoblasts was reduced compared with mineralization of normal osteoblasts, even in the presence of bone morphogenetic protein 2 (BMP‐2). Alkaline phosphatase and osteocalcin levels were elevated in OA osteoblasts compared with normal osteoblasts, whereas osteopontin levels were similar. The COL1A1 ‐to‐ COL1A2 messenger RNA ratio was 3‐fold higher in OA osteoblasts compared with normal osteoblasts, and the production of collagen by OA osteoblasts was increased. Because TGFβ1 inhibits BMP‐2–dependent mineralization, and because TGFβ1 levels are ∼4‐fold higher in OA osteoblasts than in normal osteoblasts, inhibiting TGFβ1 levels in OA osteoblasts corrected the abnormal COL1A1 ‐to‐ COL1A2 ratio and increased alizarin red staining. Conclusion Elevated TGFβ1 levels in OA osteoblasts are responsible, in part, for the abnormal ratio of COL1A1 to COL1A2 and for the abnormal production of mature type I collagen. This abnormal COL1A1 ‐to‐ COL1A2 ratio generates a matrix that blunts mineralization in OA osteoblasts.