Aβ蛋白促骨质疏松作用及其介导的破骨细胞-成骨细胞失平衡的机制研究

Osteoporosis is a devastating disease having enormous health impacts, particularly considering the global shift towards an aging population. However,the pathogenesis underlying osteoporosis is still elusive. Many studies have proved that amyloid beta peptide (Aβ) was associated with multiple degenerative disorders, such as Alzheimer's disease. However, the relationship between Aβ and osteoporosis has not been well-established yet. Our published paper (BONE，2014) showed that Aβ was elevated remarkably in the osteoporotic bone tissues both from human and ovariectomized rats when compared with the age-/sex-matched controls. Moreover, the expression levels had a negative correlation with corresponding bone mineral density in patients. In addition, Aβ enhanced osteoclast function potently, leading to osteolysis. Furthermore, our preliminary study indicated that the activation effect of Aβ on osteoclast might be related to the MAPK/NF-κB/calcium signal pathways. In addition, Aβ could suppress osteoblast formation and proliferation, indicating that the promoting effect of Aβ on osteoporosis might associate with osteoclast-osteoblast imbalance. In this study, firstly, we will further collect more patient osteoporotic bone specimens from multiple parts of human bodies prone to suffering osteoporosis and examine the relationship between Aβ expression levels and bone mineral density. Moreover, we will examine the Aβ expression levels in different age groups of rats and observe whether Aβ can accelerate osteoporosis after intravenously injecting into OVX rat models and pre-sinile SD rats. Finally, we try to elucidate the underlying molecular mechanism associated with osteoclast activation for MAPK/NF-κB/calcium signal pathways, and with osteoblast differentiation and apoptosis after Aβ treatment. We hope our study will uncover some unknown causes about osteoporosis and thus leading to better prevention and treatment.

骨质疏松症严重危害老年健康，但发病机制仍不明确。研究证实Aβ蛋白(Aβ)与阿尔茨海默病等多种老年退行性疾病密切相关,但其与骨质疏松(OP)关系未明。申请人前期研究发现Aβ在OP患者及动物模型骨组织中高表达,其量与骨密度呈负相关,且Aβ在体外可显著激活破骨细胞导致骨溶解,提示Aβ与OP存在重要联系(BONE,2014)。预实验提示Aβ可能通过MAPK/NF-κB/钙离子通路激活破骨细胞,且可明显抑制成骨细胞生成及增殖。因此,Aβ可能在分子水平通过影响破骨-成骨细胞失平衡而导致OP。本项目拟首先增大临床样本量,进一步明确人体其他OP常见部位骨组织中Aβ表达量与骨密度的联系;并通过静脉给药，考察Aβ促进动物OP的发生情况;最后,体外深入研究Aβ对人破骨细胞激活以及对人成骨细胞分化、凋亡作用的分子机制,从而阐明Aβ通过影响破骨-成骨细胞失平衡导致OP的发病机制，也为开发潜在的抗OP药物提供新靶点。

骨质疏松症已经成为我国老龄化社会面临的严峻公共卫生问题和社会问题，但发病机制仍不明确。研究证实，Aβ蛋白(Aβ)与多种老年退行性疾病密切相关，但其与骨质疏松关系未明。本项目首先通过诱导小鼠骨髓单核细胞分化为破骨细胞，加入Aβ42共培养不影响RANKL诱导的破骨细胞形成，但能够显著增强破骨细胞骨吸收功能。进一步研究发现Aβ42能够增强RANKL诱导的NF-κB活性及增加IκB-α降解，促进ERK磷酸化，增强破骨细胞分化过程中的钙离子震荡，并且增强破骨细胞分化过程中NFAT活性及NFATc1蛋白表达。从而证实Aβ对破骨细胞的激活是通过联合激活NF-κB, MAPK及钙离子信号通路，最终导致转录因子NFATc1活化及入核而实现的。其次，我们通过诱导人骨髓间充质干细胞（hMSCs）分化为成骨细胞，Aβ42共培养能够促进hMSCs成骨分化，深入探讨发现此作用是通过上调hMSCs 的LRP5/6表达及下调β-TrCP酶活性，使β-catenin集聚及入核增多，最终激活Wnt/β-catenin信号通路下游靶基因的表达而介导的。鉴于上述研究结果显示Aβ能够同时促进骨吸收及骨形成，对骨质疏松的作用不一致，我们进一步构建破骨细胞-成骨细胞共培养体系，发现Aβ能够抑制破骨细胞功能及促进成骨细胞分化，提示Aβ对骨质疏松具有双向调节功能。最后，我们通过建立小鼠去势骨质疏松模型，通过腹腔注射Aβ后行MicroCT骨微结构检测及骨组织成分分析，发现Aβ在活体水平促进骨形成。综上所述，Aβ通过破骨细胞-成骨细胞失平衡调控骨质疏松发生发展的生物学功能及其分子机制已基本阐明。我们拟进一步通过构建Aβ基因全敲除及条件性敲除鼠，更加精确及深入探讨Aβ在骨代谢中的作用。