Sema 4D在骨质疏松颌骨改建中的分子机制及应用研究

With the increase of aging population, restoration for missing teeth in osteoporotic patients is an urgent task. Osteoporosis has long been regarded as a contraindication for dental implant surgery due to the difficult operation handling and high risk of failed ossointegration, as a result of the serious reduction in alveolar bone quantity and progressive deterioration in microstructure. Bone resorption and formation do not occur randomly along the bone surface. Rather, they occur at specific anatomical sites and follow a well-defined sequence of events known as the bone remodeling cycle. Current therapies for osteoporosis target adult bone loss and are centered on restoring the balance between bone formation and resorption, which interfere with natural bone remodeling. Thus, noval pathways based on the understanding of osteoblast regulation and function has revealed new opportunities for developing drugs to stimulate bone formation. Sema 4D is a membrane-bound class 4 protein that widely expressed to control cell migration, regulate the immune response, and mediate tissue development and angiogenesis. Recent studies have suggested that Sema 4D are involved in bone remodeling, triggered by the binding of Sema4D derived from osteoclasts in the regulation of bone formation through its receptor Plexin-B1, which is expressed by osteoblasts. Here we use transgenic mice model to evaluate the role of RhoA in mediating Sema 4D-Plexin-B1 signaling in alveolar bone formation and the involved mechanism in controlling alveolar-derived osteoblast differentiation, proliferation and migration spatiotemporally through Sema 4D-Plexin-B1-RhoA signal axis, thus to provide genetic evidence for Sema 4D as a therapeutic target to activate alveolar bone formation. Furthermore, we will use our previously developed mesoporous bioglass (MBG) scaffold to encapsulate anti-Sema 4D siRNA as a novel controllable drug releasing system, followed by the in vitro assessment on osteoporotic alveolar bone cells and the in vivo study on implantation into alveolar defects in osteoporotic model. We expect that this tissue engineering-based therapy will provide great potential for implant replacement in osteoporotic patients, and the identification of new molecular target will give a remarkable significance in its translation from bench to bedsides.

骨质疏松患者因其牙槽骨萎缩及骨密度降低而加大种植手术难度和风险。传统药物治疗易引发不可逆的临床副作用，使得研究重心转向针对靶向位点、激活成骨潜能，维持骨改建的动态平衡。目前发现分化中的破骨细胞可显著分泌Sema 4D，与成骨细胞表面受体Plexin-B1发生特异性结合，其表达异常与成-破骨细胞偶联的骨改建循环密切相关。本项目以转基因小鼠为模式动物模型，探讨RhoA介导的颌骨来源成骨细胞表面Plexin-B1识别破骨细胞分泌蛋白Sema 4D对颌骨形成的影响，阐明Sema 4D-Plexin-B1-RhoA信号轴在颌骨成骨细胞分化和迁移中的调控，从mRNA、蛋白、细胞及组织层面证明Sema 4D为活化颌骨改建的关键靶点。同时制备针对Sema 4D位点的特异性抗体，与前期开发的MBG复合支架缓释体系结合，应用于骨质疏松牙槽骨缺损模型，为骨质疏松颌骨缺损患者的靶向分子治疗提供新思路。

骨质疏松患者因其牙槽骨萎缩及骨密度降低而加大种植手术难度和风险。传统药物治疗易引发不可逆的临床副作用，使得研究重心转向针对靶向位点、激活成骨潜能，维持骨改建的动态平衡。目前发现分化中的破骨细胞可显著分泌Sema 4D，与成骨细胞表面受体Plexin-B1发生特异性结合，其表达异常与成-破骨细胞偶联的骨改建循环密切相关。本项目通过小干扰RNA降低Sema 4D的表达，探讨RhoA介导的颌骨来源成骨细胞表面Plexin-B1识别破骨细胞分泌蛋白Sema 4D对颌骨形成的影响，从mRNA、蛋白、细胞及组织层面证明Sema 4D为活化颌骨改建的关键靶点。同时制备针对Sema 4D位点的小干扰RNA，并开发骨靶向给药系统D-ASP8-(STR-R8)，用于骨质疏松的靶向预防和治疗，减少毒副作用。并开发出纳米支架材料PLLA，用于与骨靶向给药系统包裹的Sema 4D siRNA结合，形成复合支架缓释体系，应用于骨质疏松股骨和牙槽骨缺损模型，为骨质疏松骨缺损患者的靶向分子治疗提供新思路。