Targeted Deletion of the Sclerostin Gene in Mice Results in Increased Bone Formation and Bone Strength

Introduction: Sclerosteosis is a rare high bone mass genetic disorder in humans caused by inactivating mutations in SOST, the gene encoding sclerostin. Based on these data, sclerostin has emerged as a key negative regulator of bone mass. We generated SOST knockout (KO) mice to gain a more detailed understanding of the effects of sclerostin deficiency on bone. Materials and Methods: Gene targeting was used to inactivate SOST and generate a line of SOST KO mice. Radiography, densitometry, μCT, histomorphometry, and mechanical testing were used to characterize the impact of sclerostin deficiency on bone in male and female mice. Comparisons were made between same sex KO and wildtype (WT) mice. Results: The results for male and female SOST KO mice were similar, with differences only in the magnitude of some effects. SOST KO mice had increased radiodensity throughout the skeleton, with general skeletal morphology being normal in appearance. DXA analysis of lumbar vertebrae and whole leg showed that there was a significant increase in BMD (>50%) at both sites. μCT analysis of femur showed that bone volume was significantly increased in both the trabecular and cortical compartments. Histomorphometry of trabecular bone revealed a significant increase in osteoblast surface and no significant change in osteoclast surface in SOST KO mice. The bone formation rate in SOST KO mice was significantly increased for trabecular bone (>9‐fold) at the distal femur, as well as for the endocortical and periosteal surfaces of the femur midshaft. Mechanical testing of lumbar vertebrae and femur showed that bone strength was significantly increased at both sites in SOST KO mice. Conclusions: SOST KO mice have a high bone mass phenotype characterized by marked increases in BMD, bone volume, bone formation, and bone strength. These results show that sclerostin is a key negative regulator of a powerful, evolutionarily conserved bone formation pathway that acts on both trabecular and cortical bone.     

New molecular targets for the treatment of osteoarthritis

Osteoarthritis (OA) is a chronic degenerative joint disorder characterized by destruction of the articular cartilage, subchondral bone alterations and synovitis. Current treatments are focused on symptomatic relief but they lack efficacy to control the progression of this disease which is a leading cause of disability. Therefore, the development of effective disease-modifying drugs is urgently needed. Different initiatives are in progress to define the molecular mechanisms involved in the initiation and progression of OA. These studies support the therapeutic potential of pathways relevant in joint metabolism such as Wnt/β-catenin, discoidin domain receptor 2 or proteinase-activated receptor 2. The dysregulation in cartilage catabolism and subchondral bone remodeling could be improved by selective inhibitors of matrix metalloproteinases, aggrecanases and other proteases. Another approach would favor the activity of anabolic processes by using growth factors or regulatory molecules. Recent studies have also revealed the role of oxidative stress and synovitis in the progression of this disease, supporting the development of a number of inhibitory strategies. Novel targets in OA are represented by genes involved in OA pathophysiology discovered using gene network, epigenetic and microRNA approaches. Further insights into the molecular mechanisms involved in OA initiation and progression may lead to the development of new therapies able to control joint destruction and repair.     

A 52‐kb deletion in the SOST‐MEOX1 intergenic region on 17q12‐q21 is associated with van Buchem disease in the Dutch population

Van Buchem disease is an autosomal recessive sclerosing bone dysplasia characterized by skeletal hyperostosis, overgrowth of the mandible, and a liability to entrapment of the seventh and eighth cranial nerves. The genetic determinant maps to chromosome 17q12‐q21. We refined the critical interval to the < 1‐Mb region between D17S2250 and D17S2253 in 15 affected individuals, all of whom shared a common disease haplotype. Furthermore, we report here the identification of a 52‐kb deletion located within the interval and encompassing D17S1789 that is 100% concordant with the disorder. Although the deletion itself does not appear to disrupt the coding region of any known or novel gene(s), the closest flanking genes are MEOX1 on the proximal side, and SOST on the distal side of the deletion. MEOX1 is known to be important for the development of the axial skeleton, whereas the SOST gene is the determinant of sclerosteosis, a disorder that shares many features with van Buchem disease, thus raising the possibility that van Buchem disease results from dysregulation of the expression of one or both of these genes. © 2002 Wiley‐Liss, Inc.     

染氟大鼠血清中硬骨素表达水平及其在Wnt通路调控Runx2表达中作用的实验研究

目的观察染氟大鼠血清中硬骨素(SOST)、核心结合因子(Runx2)表达水平的变化,探讨SOST在经典Wnt通路调控Runx2表达中的作用。方法选取64只大鼠随机分为低剂量组(1.6mg/kgNaF)、中剂量组(16mg/kg NaF)、高剂量组(32mg/kg NaF)和对照组(0mg/kg NaF),每组16只,雌雄各半;采用微电极法进行尿氟、血氟测定;全自动生化分析仪测定血清中碱性磷酸酶(ALP)活力;ELISA试剂盒测定血清中SOST和Runx2。结果高剂量组在第35天时,SOST血清中浓度为(11.55±1.02)μg/L,表达开始下降;Runx2血清中浓度为(120.42±12.40)μg/L,表达开始升高;与对照组比较,差异有统计学意义(P<0.05)。第90天时,高、中剂量组SOST表达明显下降,Runx2表达明显升高,与对照组比较,差异均有统计学意义(P<0.01)。第90天时,大鼠体内SOST与Runx2表达水平呈负相关(r=-0.444,P<0.01)。结论高剂量的氟暴露可致大鼠体内SOST表达水平降低,Runx2表达水平升高;氟致骨损伤的发生可能与SOST的表达降低而对经典Wnt通路进行负调控,进而促进Runx2表达有关。     

脆性骨折及骨关节炎松质骨中经典Wnt通路相关基因表达差异的研究

目的 比较经典Wnt通路相关基因在股骨颈脆性骨折和髋关节骨关节炎病例中的表达差异,探讨相关基因对骨强度的影响。方法 入选病例分为脆性骨折（fragility fracture,FF）组及骨关节炎（osteoarthritis,OA）组,其中,FF组共14例,女性占71.4%,患者平均年龄74.64±6.98岁;OA组共13例,其中女性占76.9%,患者平均年龄66.9±6.98岁;所有标本均来自单侧髋关节置换术患者自愿捐献的新鲜股骨头;咬取股骨头与股骨颈交界中点并远离骨折线处的松质骨,提取总RNA并反转录成cDNA,使用实时荧光定量（quantitative real-time PCR,qRT-PCR）分别检测SOST、DKK-1、Ctnnb1、LRP5、FZD1等基因mRNA的表达水平。结果 脆性骨折组与骨关节炎组比较,SOST基因mRNA水平较高,而Ctnnb1较低,P均<0.05;DKK-1、LRP5、FZD1等基因的mRNA水平差异无统计学意义（P>0.05）。结论 骨强度的降低可能与SOST基因表达增强以及Ctnnb1基因表达的减弱有关。