Welsh School of Pharmacy, Redwood Building, Cardiff University, King Edward VII Avenue, Cardiff, CF10 3NB, UK.
Arthritis Res Ther. 2011;13(6):R203. doi: 10.1186/ar3536. Epub 2011 Dec 9.
Articular cartilage functions in withstanding mechanical loads and provides a lubricating surface for frictionless movement of joints. Osteoarthritis, characterised by cartilage degeneration, develops due to the progressive erosion of structural integrity and eventual loss of functional performance. Osteoarthritis is a multi-factorial disorder; two important risk factors are abnormal mechanical load and genetic predisposition. A single nucleotide polymorphism analysis demonstrated an association of hip osteoarthritis with an Arg324Gly substitution mutation in FrzB, a Wnt antagonist. The purpose of this study was two-fold: to assess whether mechanical stimulation modulates β-catenin signalling and catabolic gene expression in articular chondrocytes, and further to investigate whether there is an interplay of mechanical load and Wnt signalling in mediating a catabolic response.
Chondrocytes were pre-stimulated with recombinant Wnt3A for 24 hours prior to the application of tensile strain (7.5%, 1 Hz) for 30 minutes. Activation of Wnt signalling, via β-catenin nuclear translocation and downstream effects including the transcriptional activation of c-jun, c-fos and Lef1, markers of chondrocyte phenotype (type II collagen (col2a1), aggrecan (acan), SOX9) and catabolic genes (MMP3, MMP13, ADAMTS-4, ADAMTS-5) were assessed.
Physiological tensile strain induced col2a1, acan and SOX9 transcription. Load-induced acan and SOX9 expression were repressed in the presence of Wnt3A. Load induced partial β-catenin nuclear translocation; there was an additive effect of load and Wnt3A on β-catenin distribution, with both extensive localisation in the nucleus and cytoplasm. Immediate early response (c-jun) and catabolic genes (MMP3, ADAMTS-4) were up-regulated in Wnt3A stimulated chondrocytes. With load and Wnt3A there was an additive up-regulation of c-fos, MMP3 and ADAMTS-4 transcription, whereas there was a synergistic interplay on c-jun, Lef1 and ADAMTS-5 transcription.
Our data suggest that load and Wnt, in combination, can repress transcription of chondrocyte matrix genes, whilst enhancing expression of catabolic mediators. Future studies will investigate the respective roles of abnormal loading and genetic predisposition in mediating cartilage degeneration.
关节软骨的功能是承受机械负荷，并为关节的无摩擦运动提供润滑表面。骨关节炎的特征是软骨退化，由于结构完整性的渐进性侵蚀和最终功能丧失而发展。骨关节炎是一种多因素疾病；两个重要的危险因素是异常机械负荷和遗传易感性。单核苷酸多态性分析表明，FrzB 中的 Arg324Gly 取代突变与髋骨关节炎有关，FrzB 是 Wnt 拮抗剂。本研究的目的有两个：评估机械刺激是否调节关节软骨细胞中的β-连环蛋白信号和分解代谢基因表达，以及进一步研究机械负荷和 Wnt 信号在介导分解代谢反应中的相互作用。
软骨细胞在用重组 Wnt3A 预刺激 24 小时后，应用 7.5%、1Hz 的张力应变（拉伸应变）30 分钟。通过β-连环蛋白核易位及其下游效应（包括 c-jun、c-fos 和 Lef1 的转录激活）评估 Wnt 信号的激活，这些下游效应是软骨细胞表型（II 型胶原（col2a1）、聚集蛋白聚糖（acan）、SOX9）和分解代谢基因（MMP3、MMP13、ADAMTS-4、ADAMTS-5）的标志物。
生理拉伸应变诱导 col2a1、acan 和 SOX9 转录。在存在 Wnt3A 的情况下，负载诱导的 acan 和 SOX9 表达受到抑制。负载诱导部分β-连环蛋白核易位；负载和 Wnt3A 对β-连环蛋白分布有相加作用，β-连环蛋白在核和细胞质中均有广泛的定位。即刻早期反应（c-jun）和分解代谢基因（MMP3、ADAMTS-4）在 Wnt3A 刺激的软骨细胞中上调。在负载和 Wnt3A 存在的情况下，c-fos、MMP3 和 ADAMTS-4 的转录呈相加上调，而 c-jun、Lef1 和 ADAMTS-5 的转录呈协同作用。
我们的数据表明，负载和 Wnt 联合作用可以抑制软骨细胞基质基因的转录，同时增强分解代谢介质的表达。未来的研究将研究异常负荷和遗传易感性在介导软骨退变中的各自作用。
