Abstract
Previous studies have shown a generalised increase in bone mass in patients with osteoarthritis (OA). Using molecular histomorphometry, this study examined the in vivo expression of mRNA encoding bone anabolic factors and collagen type I genes (COL1A1, COL1A2) in human OA and non-OA bone. Bone samples were obtained from the intertrochanteric (IT) region of the proximal femur, a skeletal site distal to the active site of disease, from individuals with hip OA at joint replacement surgery and from autopsy controls. Semi-quantitative reverse transcription-polymerase chain reaction analysis revealed elevated mRNA expression levels of alkaline phosphatase (p < 0.002), osteocalcin (OCN) (p < 0.0001), osteopontin (p < 0.05), COL1A1 (p < 0.0001), and COL1A2 (p < 0.002) in OA bone compared to control, suggesting possible increases in osteoblastic biosynthetic activity and/or bone turnover at the IT region in OA. Interestingly, the ratio of COL1A1/COL1A2 mRNA was almost twofold greater in OA bone compared to control (p < 0.001), suggesting the potential presence of collagen type I homotrimer at the distal site. Insulin-like growth factor (IGF)-I, IGF-II, and transforming growth factor-β1 mRNA levels were similar between OA and control bone. Bone histomorphometric analysis indicated that OA IT bone had increased surface density of bone (p < 0.0003), increased trabecular number (Tb.N) (p < 0.0003), and decreased trabecular separation (Tb.Sp) (p < 0.0001) compared to control bone. When the molecular and histomorphometric data were plotted, positive associations were observed in the controls for OCN/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) versus bone tissue volume (r = 0.82, p < 0.0007) and OCN/GAPDH versus Tb.N (r = 0.56, p < 0.05) and a negative association was observed for OCN/GAPDH versus Tb.Sp (r = -0.64, p < 0.02). These relationships were not evident in trabecular bone from patients with OA, suggesting that bone regulatory processes leading to particular trabecular structures may be altered in this disease. The finding of differential gene expression, as well as architectural changes and differences in molecular histomorphometric associations between OA and controls, at a skeletal site distal to the active site of joint degeneration supports the concept of generalised involvement of bone in the pathogenesis of OA.
Highlights
Osteoarthritis (OA) is an age-related degenerative musculoskeletal disease affecting both males and females and causing significant morbidity and immobility
This study examined the in vivo expression of mRNA encoding bone anabolic factors and collagen type I genes (COL1A1, COL1A2) in human OA and non-OA bone
The ratio of COL1A1/COL1A2 mRNA was almost twofold greater in OA bone compared to control (p < 0.001), suggesting the potential presence of collagen type I homotrimer at the distal site
Summary
Osteoarthritis (OA) is an age-related degenerative musculoskeletal disease affecting both males and females and causing significant morbidity and immobility. The OA bone changes observed at the subchondral region are present at skeletal sites distal to the active joint articular cartilage degeneration, such as the intertrochanteric (IT) and medial principal compressive regions of the proximal femur and iliac crest Studies investigating these distal skeletal sites have found evidence of increased bone volume and trabecular thickness (Tb.Th) and decreased trabecular separation (Tb.Sp) in OA compared to non-OA individuals [9,10,11,12]. The OA OB-like cells in culture are more biosynthetically active, producing increased protein levels of ALP, OCN, and insulin-like growth factor (IGF)-I [15] These OB-cell phenotypic and functional differences may play an important role in the regulation of bone remodelling in OA individuals
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