Molecular Mechanisms in Bone Resorption

描述(由申请人提供)：骨质疏松症是一个公共健康问题，在美国大约有2500万人受到影响。无论病因如何，骨质疏松症都以骨重建失衡为特征，破骨细胞性骨吸收超过成骨细胞性骨形成，导致骨量减少或骨量减少。有关骨吸收和破骨细胞形成机制的新信息可能有助于开发减少骨吸收的新策略，并可能导致治疗骨质疏松症的新方法。我们使用了以下颌骨和上颌骨巨细胞骨吸收瘤为特征的一种罕见疾病--大骨节症的模型，以探索调节破骨细胞发育和功能的新途径。切尔鲁贝氏症是由Src Homology 3结合蛋白2(SH3BP2)基因的6个氨基酸区域(415-420)的杂合性错义突变引起的，SH3BP2基因编码一种广泛表达的接头蛋白。这种特殊的时机和局部表达表明，它是人类破骨细胞发生、骨吸收和骨量减少的一种独特而新颖的模型。此外，这些病变的离散位置可能对了解颌骨坏死的病理生理学有重要意义。我们评估了17个大猩猩先证者，发现SH3BP2突变激活了激活的T细胞核因子(NFAT)。NFATc1(又称NFAT2)是破骨细胞生成的主开关。所有这些SH3BP2突变还诱导了破骨细胞标志物酒石酸抗性酸性磷酸酶(TRAP)在RAW 264.7破骨前细胞系中的表达。我们最近的研究表明，SH3BP2刺激一种形式的磷脂酰肌醇特异性磷脂酶C(PI-PLC)，而肌醇磷酸3(IP3)的产生导致内质网释放钙(Ca~(2+))。细胞内钙的增加可以激活钙调神经磷酸酶，使NFAT去磷酸化，促进其移位到细胞核。假说：SH3BP2在破骨细胞生成中起作用，在大脑症患者中，SH3BP2突变改变了SH3BP2的物理性质(翻译后修饰和/或与其他蛋白质结合)，至少一个结果是NFATc1活性增强和随后的破骨细胞生成。目的1.研究野生型和突变型SH3BP2的翻译后修饰。目的2.研究SH3BP2蛋白与蛋白质之间的相互作用。目的3.比较野生型和突变型SH3BP2的成骨机制。公共健康相关性骨质疏松症是一个公共健康问题，在美国大约有2500万人受到影响。无论病因如何，骨质疏松症都以骨重建失衡为特征，破骨细胞性骨吸收超过成骨细胞性骨形成，导致骨量减少或骨量减少。有关骨吸收机制的新信息可能有助于开发减少骨吸收的新策略，并可能导致治疗骨质疏松症的新方法。

Description (provided by applicant): Osteoporosis is a public health problem that affects approximately 25 million people in the United States. Regardless of the etiology, osteoporosis is characterized by an imbalance in bone remodeling, such that osteoclastic bone resorption exceeds osteoblastic bone formation, which leads to low bone mass or osteopenia. New information about mechanisms of bone resorption and osteoclastogenesis may facilitate the development of novel strategies to decrease bone resorption and may lead to new treatments for osteoporosis. We have used the model of cherubism, a rare disorder characterized by giant-cell bone resorptive tumors of the mandible and maxilla, to explore novel pathways that regulate osteoclast development and function. Cherubism is caused by heterozygous missense mutations within a six-amino-acid region (415-420) of the Src homology 3 binding protein 2 (SH3BP2) gene, which encodes a widely expressed adaptor protein. The specific timing and localized expression of cherubism indicates that it is a unique and novel model of human osteoclastogenesis, bone resorption and osteopenia. Moreover the discrete location of these lesions may have important implications for understanding the pathophysiology of osteonecrosis of the jaw. We have assessed 17 cherubism probands and have found that the SH3BP2 mutations activate nuclear factor of activated T cells (NFAT). NFATc1 (also termed NFAT2) is the master switch of osteoclastogenesis. All of these SH3BP2 mutations also induce expression of the osteoclast marker tartrate resistant acid phosphatase (TRAP) in the RAW 264.7 pre-osteoclastic cell line. Our recent studies suggest that SH3BP2 stimulates a form of phosphatidylinositol-specific phospholipase C (PI-PLC), and the production of inositol phosphate 3 (IP3) leads to release of calcium (Ca2+) from the endoplasmic reticulum. The increase in intracellular calcium can activate calcineurin, which dephosphorylates NFAT and promotes its translocation to the nucleus. Hypothesis: SH3BP2 has a role in osteoclastogenesis and SH3BP2 mutations in cherubism patients alter the physical properties (post-translational modifications and/or binding to other proteins) of SH3BP2, with at least one result being enhanced NFATc1 activity and consequent osteoclastogenesis. Aim 1. To examine post-translational modifications in wild-type and mutant SH3BP2. Aim 2. To characterize SH3BP2 Protein-Protein Interactions. Aim 3. To distinguish the osteoclastogenic mechanism for wild-type and mutant SH3BP2. PUBLIC HEALTH RELEVANCE Osteoporosis is a public health problem that affects approximately 25 million people in the United States. Regardless of the etiology, osteoporosis is characterized by an imbalance in bone remodeling, such that osteoclastic bone resorption exceeds osteoblastic bone formation, which leads to low bone mass or osteopenia. New information about mechanisms of bone resorption may facilitate the development of novel strategies to decrease bone resorption and may lead to new treatments for osteoporosis.