基于RANKL/JNK/AP-1信号轴探讨芝麻素防治绝经后骨质疏松的作用及分子机制

Over-activated osteoclasts resulted by the condition of estrogen deficiency is the key inducement of postmenopausal osteoporosis, and specifically inhibiting osteoclast differentiation and bone resorption is the major therapeutic way. As the critical role of RANKL/JNK/AP-1 cascade plays in osteoclastogenesis, it is reliable to protect bone loss and osteoporosis via suppressing this signaling pathway. Previously, we have already demonstrated that the agents, praeruptorin C and sesamin could target to RANKL/JNK/AP-1 cascade, according to the drug-selective system established on AP-1 gene luciferase and computer molecular docking techniques. And in deep research, we showed that praeruptorin C potently inhibits osteoclast formation and presenting bone-protecting effects by impairing this signaling pathway. Interestedly, praeruptorin C and sesamin are belonged to phenylpropanoids, and has similar molecular structure. For this, we hypothesized that sesamin would also inhibit osteoclast formation via impairing RANKL/JNK/AP-1 cascade. Focusing on this cascade, the effect and potential mechanisms of sesamin on regulating osteoclast differentiation and bone resorption, as well as bone-protecting effect in vivo will be deeply investigated from three different levels, cell, molecule and animal model, with the aim to providing a novel horizon on new drug development in anti-osteoporosis.

雌激素缺乏造成破骨细胞过度活跃是绝经后骨质疏松发生的重要原因，特异性抑制破骨细胞介导的骨吸收是抗骨质疏松治疗的主要手段。RANKL/JNK/AP-1信号轴在破骨细胞分化过程中扮演重要角色，阻断该信号轴是减少骨丢失的理想方案。我们在前期研究中通过AP-1荧光素酶报告基因和计算机模拟技术构建的药物筛选体系，发现白花前胡丙素和芝麻素可作用于RANKL/JNK/AP-1信号轴。进一步的研究显示，白花前胡丙素可有效抑制破骨细胞形成并介导骨保护效应。更有趣的是，芝麻素与白花前胡丙素同属苯丙素类，具有相似的分子结构。据此，我们推测芝麻素同样可以阻断RANKL/JNK/AP-1信号轴并抑制破骨细胞形成。为此，本研究将以RANKL/JNK/AP-1信号轴为重点，从细胞、分子和模式动物三个层面探讨芝麻素调控破骨细胞分化和骨吸收的功效及其在体内的骨保护效应并阐明其分子机制，以期为抗骨质疏松药物的研发提供新思路。

骨质疏松症是骨科临床亟待解决的问题。特异性抑制破骨细胞介导的骨吸收是抗骨质疏松治疗的主要手段。RANKL/JNK/AP-1信号轴在破骨细胞分化过程中扮演重要角色，阻断该信号轴是减少骨丢失的理想方案。我们在前期研究中通过AP-1荧光素酶报告基因和计算机模拟技术构建的药物筛选体系，发现白花前胡丙素和芝麻素可作用于RANKL/JNK/AP-1信号轴。进一步的研究显示，白花前胡丙素可有效抑制破骨细胞形成并介导骨保护效应。更有趣的是，芝麻素与白花前胡丙素同属苯丙素类，具有相似的分子结构。据此，我们推测芝麻素同样可以阻断RANKL/JNK/AP-1信号轴并抑制破骨细胞形成。首先，本研究利用破骨细胞体外培养技术分别从细胞和基因层面证实：芝麻素在无细胞毒性的浓度下通过减少TRAP阳性多核破骨细胞的数量和面积大小来抑制RANKL诱导的破骨细胞的形成，并通过减少F-actin环的数量和骨吸收坑区域来抑制骨吸收功能。同时发现，芝麻素抑制破骨细胞形成过程中是通过抑制RANKL/JNK/AP-1信号轴和抑制ERK信号通路来实现的。此外，芝麻素降低了破骨细胞特异性基因的表达。股骨标本的Micro-CT分析显示，芝麻素治疗后骨损失减少，小梁骨密度增大，这表明芝麻素通过抑制去卵巢骨质疏松小鼠体内的骨质丢失发挥了保护作用。综上所述，考虑到芝麻素对骨质疏松小鼠骨骼的保护作用与其抑制破骨细胞形成和骨吸收有关，这表明芝麻素在治疗破骨细胞相关疾病如骨质疏松症方面具有潜在价值，为抗骨质疏松药物的研发提供了新的理论依据和治疗靶点。