Altered mineralization of human osteoarthritic osteoblasts is attributable to abnormal type I collagen production

Abstract

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 ␤1 (TGF␤1) 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 TGF␤1 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 TGF␤1 inhibits BMP-2-dependent mineralization, and because TGF␤1 levels are ϳ4-fold higher in OA osteoblasts than in normal osteoblasts, inhibiting TGF␤1 levels in OA osteoblasts corrected the abnormal COL1A1-to-COL1A2 ratio and increased alizarin red staining.Conclusion. Elevated TGF␤1 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.

Temporal Changes in Bone Composition, Architecture, and Strength Following Estrogen Deficiency in Osteoporosis

“…Twelve months post-ovariectomy, this ratio had increased significantly to 610 and thirty-one months following ovariectomy this ratio had almost doubled to 1100. Previously it has been demonstrated using osteoblast-like cells that COL1α2 expression did not vary when cells were exposed to a mineralising media, whereas COL1α1 expression, which was initially high, progressively declined, leading to a decrease in the COL1α1:COL1α2 ratio concomitant with an increase in mineralisation [34]. The current study found that an increase in the COL1α1:COL1α2 ratio is associated with a reduction in mineralisation in the metacarpal bone.…”

Biphasic effects of TGFβ1 on BMP9-induced osteogenic differentiation of mesenchymal stem cells

“…COL1 plays an important functional role during osteogenesis as it augments the cell adhesion and lays a foundation for OPN, OCN and bone matrix mineralization (21,22). OPN and OCN have high affinity of hydroxyapatite and can specifically integrate with the adhesion and connection of cells and tissues (23).…”

Low molecular weight silk fibroin increases alkaline phosphatase and type I collagen expression in MG63 cells

“…2). Osteoarthritis (OA) is a leading cause of morbidity in aging populations and is characterized by degradation and loss of cartilage, inflammation of the synovium, formation of osteophytes, and bone sclerosis (21). Type I collagen levels are elevated in the trabecular bone within the femoral heads of patients with OA, which can lead to an increase in mineralization (22).…”