关节软骨和软骨下骨在跑步运动过程中的相互作用及内在机制

There is increasing concern as to how running affects joint health. Numerous studies demonstrate that such effect is closely associated with running intensity, however, the underlying mechanism is not fully understood. Our previous animal studies suggested that the effects of running are intensity-dependent on both articular cartilage and subchondral bone, and, for each intensity, alterations in one tissue relate to the other. Although mechanisms regulating the maintenance of these two tissues are different, compelling evidence indicates that the signal pathways crosstalk. Our previous study also indicated that the Wnt/β-catenin signaling pathway may be involved in the running-induced regulation in osteogenesis and adipogenesis of bone marrow stromal cells. Based on these studies, we hypothesize that biomechanical signals generated by running with different intensities may modulate cartilage metabolism and subchondral bone remodeling through Wnt pathway, and such signaling pathway may also be involved in the interaction of two tissues. To prove our hypothesis, in vivo and in vitro experiments will be performed to examine the changes of articular and subchondral bone, and the interactions between osteoblast and chondrocyte in response to different mechanical loadings, as well as the roles of Wnt pathway in these processes. The data from this proposal will shed light on a novel mechanism for the intensity-dependent effect of running on cartilage and subchondral bone as well as their interactions, and therefore provides evidence for modalities to prevent and manage the running-related osteoarthritis.

跑步对负重关节健康的影响是个令人关注的课题。大量研究显示这种影响与跑步强度密切相关，但相关机理并不清楚。我们以往动物实验结果显示跑步对软骨以及软骨下骨的影响均具有强度依赖性，且同一强度跑步所致的软骨与软骨下骨变化相关联。尽管维持这二种组织健康的调节机制并不相同，但证据显示信号通路能在二者之间相互响应。我们前期的研究证实Wnt/β-catenin信号通路参与调控不同强度跑步对大鼠骨髓间充质细胞成骨分化。基于此，我们设想此信号通路参与调控不同载荷刺激下软骨和软骨下骨的变化以及二者间相互相应。本研究将从体外和体内二个方面探讨不同强度跑台运动对软骨及软骨下骨的影响，阐述不同大小机械负荷作用下软骨细胞和软骨细胞之间的相互作用，明确Wnt/β-catenin信号通路在其间发挥的作用。本研究成果将能更好理解不同强度跑步对软骨和软骨下骨影响的细胞和分子机理，为防治跑步所致骨关节炎提供理论指导和科学依据。

本项目从体外和体内二个方面探讨不同强度跑台运动对软骨及软骨下骨的影响，阐述不同大小机械负荷作用下软骨细胞和软骨细胞之间的相互作用，明确Wnt/β-catenin信号通路在其间发挥的作用。体内研究发现：跑台运动对大鼠关节软骨和软骨下骨的影响与运动强度和时间相关；高强度跑步引起软骨下骨结构和成分的改变，进而影响其力学特性，“脆和硬”的下骨反过来对其上覆盖的软骨产生不利的影响，最终导致软骨的退行性改变；此外，不同强度跑台运动在不同时间点软骨和软骨下骨WNT通路的激活情况不同，8周时间点WNT通路的激活明显降低，而软骨和软骨下骨的激活情况几乎一致；关节腔注射WNT通路特异性抑制剂DKK1在短期内对低强度跑步运动组软骨有保护作用，但这种保护作用随时间的延长而减弱；DKK1关节内注射对中强度组和高强度组无明显作用。体外研究发现：周期性拉伸应力对软骨细胞、成骨细胞和BMSCs的影响与载荷大小相关：适量的拉伸应力有利于软骨细胞的合成代谢，增加BMSCs和祖细胞（针对成骨细胞谱系）的数量，导致BMSCs的成骨分化上调和成脂分化下调；过度的机械牵伸促进了软骨细胞的分解代谢和凋亡，抑制了成骨细胞的成骨分化；此外，细胞共培养发现过度机械牵伸的成骨细胞通过Wnt/β-catenin信号通路诱导软骨细胞分解和凋亡，Wnt抑制剂DKK1可部分抑制这种作用。本项目结果表明：跑台运动对关节软骨和软骨下骨的影响具有时间和强度依赖性，“合适的”机械刺激有益于软骨、软骨下骨健康，为临床“治疗性载荷策略”提供了理论基础；关节软骨和软骨下骨的相互作用与WNT通路有关，DKK1可部分抑制过度机械刺激后的成骨细胞对软骨细胞分解代谢的作用，临床上有可能作为一种软骨保护剂延缓软骨的退变，但目前证据表明其保护作用和时间可能有限，在临床应用前尚需更多的研究。