Sclerostin is expressed in articular cartilage but loss or inhibition does not affect cartilage remodeling during aging or following mechanical injury

Dept Comparative Biology &Safety Sciences, 1201 Amgen Court West, Seattle WA 98119.
Arthritis & Rheumatology (Impact Factor: 7.76). 03/2013; 65(3). DOI: 10.1002/art.37802
Source: PubMed


Sclerostin plays a major role in regulating skeletal bone mass, but its effects in articular cartilage are not known. The purpose of this study was to determine whether genetic loss or pharmacologic inhibition of sclerostin has an impact on knee joint articular cartilage.
Expression of sclerostin was determined in articular cartilage and bone tissue obtained from mice, rats, and human subjects, including patients with knee osteoarthritis (OA). Mice with genetic knockout (KO) of sclerostin and pharmacologic inhibition of sclerostin with a sclerostin-neutralizing monoclonal antibody (Scl-Ab) in aged male rats and ovariectomized (OVX) female rats were used to study the effects of sclerostin on pathologic processes in the knee joint. The rat medial meniscus tear (MMT) model of OA was used to investigate the pharmacologic efficacy of systemic Scl-Ab or intraarticular (IA) delivery of a sclerostin antibody–Fab (Scl-Fab) fragment.
Sclerostin expression was detected in rodent and human articular chondrocytes. No difference was observed in the magnitude or distribution of sclerostin expression between normal and OA cartilage or bone. Sclerostin-KO mice showed no difference in histopathologic features of the knee joint compared to age-matched wild-type mice. Pharmacologic treatment of intact aged male rats or OVX female rats with Scl-Ab had no effect on morphologic characteristics of the articular cartilage. In the rat MMT model, pharmacologic treatment of animals with either systemic Scl-Ab or IA injection of Scl-Fab had no effect on lesion development or severity.
Genetic absence of sclerostin does not alter the normal development of age-dependent OA in mice, and pharmacologic inhibition of sclerostin with Scl-Ab has no impact on articular cartilage remodeling in rats with posttraumatic OA.

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Available from: Qing-Tian Niu, Feb 16, 2015
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    • "A recent study has illustrated that sclerostin expression was enhanced in the chondrocyte clusters of damaged OA articular cartilage but markedly decreased in the subchondral bone osteocytes of post-traumatic OA [15]. Roudier and colleagues also showed sclerostin expression in human articular chondrocytes, including human OA cartilage [31]. "
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    ABSTRACT: The purpose of this study was to analyze sclerostin in plasma and synovial fluid of knee osteoarthritis (OA) patients and to investigate the association between sclerostin levels and the radiographic severity. A total of 190 subjects (95 knee OA patients and 95 healthy controls) were recruited in the present study. Sclerostin levels in plasma and synovial fluid were assessed using an enzyme-linked immunosorbent assay. OA grading was performed using the Kellgren-Lawrence classification. Plasma sclerostin levels were significantly lower in OA patients than in healthy controls (P=0.004). Additionally, sclerostin levels in plasma were significantly higher with respect to paired synovial fluid (P<0.001). Moreover, sclerostin levels in plasma and synovial fluid demonstrated significant inverse correlation with the radiographic severity of knee OA (r=-0.464, P<0.001 and r=-0.592, P<0.001, respectively). Subsequent analysis revealed that there was a positive correlation between plasma and synovial sclerostin levels (r=0.657, P<0.001). Sclerostin was significantly lower in OA plasma samples when compared with healthy controls. Plasma and synovial fluid sclerostin levels were inversely associated with the radiographic severity of knee OA. Therefore, sclerostin may be utilized as a biochemical marker for reflecting disease severity in primary knee OA.
    Full-text · Article · Mar 2014 · Clinical biochemistry
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    • "Indeed, Chan et al. reported that SOST expression was increased significantly in OA cartilage compared to normal [24]. However, a recent study by Roudier et al. [25] failed to demonstrate such an increase of SOST in human OA cartilage and bone samples whereas Jaiprakash et al. indicated that SOST levels were actually decreased in human OA samples [26]. Hence, the regulation of SOST expression in OA bone tissue and cells remains controversial. "
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    ABSTRACT: Wnt/β-catenin (cWnt) signaling plays a key role in osteogenesis by promoting the differentiation and mineralization of osteoblasts, activities altered in human osteoarthritic subchondral osteoblast (OA Ob). Sclerostin (SOST) has been shown to alter cWnt signaling. Sirtuin 1 (SIRT1) acts as a novel bone regulator and represses SOST levels in Ob. However the role of SIRT1 and SOST in OA Ob remains unknown. Herein, we explored the role played by SIRT1 and SOST on the abnormal mineralization and cWnt signaling in OA Ob. Primary human normal and OA Ob were prepared from tibial plateaus. SOST levels were evaluated by immunohistochemistry, the expression and production of genes by qRT-PCR and WB analysis. Their inhibitions were performed using siRNA. cWnt signaling was measured by the TOPflash TCF/lef luciferase reporter assay. Mineralization was determined by alizarin red staining. SOST levels were significantly increased in OA Ob compared to normal and were linked with elevated TGF-β1 levels in these cells. SIRT1 expression was significantly reduced in OA Ob compared to normal yet not modified by TGF-β1. Specific inhibition of SIRT1 increased TGF-β1 and SOST expressions in OA Ob, while stimulating SIRT1 activity with β-Nicotinamide mononucleotide reduced the expression of TGF-β1 and SOST, and increased mineralization in OA Ob. Resveratrol also reduced SOST expression in OA Ob. Reduced cWnt signalling, β-catenin levels, and mineralization in OA Ob were all corrected via reducing SOST expression. These data indicate that high level of SOST is responsible, in part, for the reduced cWnt and mineralization of human OA Ob, which in turn is linked with abnormal SIRT1 levels in these pathological cells.
    Full-text · Article · Oct 2013 · Bone
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    • "Indeed by subdividing the sensitised mice into diseased and non-diseased (Figure 2G), we have shown that systemic bone loss depends on the onset of the local inflammation in the appendicular joints. Several studies have shown that strategies aimed at reducing inflammation (such as TNF-alpha blockade) are effective in reducing bone loss but not in rebuilding lost bone [24]. Treatment with Scl-AbI not only preserved whole body BMD in diseased animals but also increased it to levels above that in healthy control mice (Figure 2G). "
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    ABSTRACT: Patients with chronic inflammatory diseases have increased bone loss and bone fragility and are at increased risk of fracture. Although anti-resorptive drugs are effective in blocking inflammation-induced bone loss, they are less effective at rebuilding bone. We have previously shown that treatment with sclerostin antibody (Scl-AbI) builds bone and can prevent or restore bone loss in a murine model of inflammatory bowel disease. In this study, we tested the effect of Scl-AbI in a murine model of rheumatoid arthritis (the collagen-induced arthritis model, CIA). We hypothesised that sclerostin blockade can protect and restore bone both locally and systemically without affecting progression of inflammation. CIA was induced in male DBA/1 mice, which were treated with either PBS or Scl-AbI (10 mg/kg, weekly) prophylactically for 55 days or therapeutically for 21 days (starting 14 days post onset of arthritis). Systemic inflammation was assessed by measuring the serum concentration of anti-CII IgG1, IgG2a and IgG2b by ELISA. Changes in bone mass and structure, either at sites remote from the joints or at periarticular sites, were measured using DEXA and microCT. Bone focal erosion was assessed in microCT scans of ankle and knee joints. Circulating anti-CII immunoglobulins were significantly elevated in mice with CIA and there were no significant differences in the levels of anti-CII immunoglobulins in mice treated with PBS or Scl-ABI. Prophylactic Scl-AbI treatment prevented the decrease in whole body bone mineral density (BMD) and in the bone volume fraction at axial (vertebral body) and appendicular (tibial proximal metaphysis trabecular and mid-diaphysis cortical bone) sites seen in PBS-treated CIA mice, but did not prevent the formation of focal bone erosions on the periarticular bone in the knee and ankle joints. In the therapeutic study, Scl-AbI restored BMD and bone volume fraction at all assessed sites but was unable to repair focal erosions. Sclerostin blockade prevented or reversed the decrease in axial and appendicular bone mass in the murine model of rheumatoid arthritis, but did not affect systemic inflammation and was unable to prevent or repair local focal erosion.
    Full-text · Article · Sep 2013 · Arthritis research & therapy
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