Molecular Mechanisms in Bone Resorption

描述（由申请人提供）：骨质疏松症是影响美国约2500万人的公共卫生问题。无论病因如何，骨质疏松症的特点是骨重塑失衡，破骨细胞骨吸收超过成骨细胞骨形成，导致骨量低或骨质减少。关于骨吸收和破骨细胞发生机制的新信息可能促进减少骨吸收的新策略的发展，并可能导致骨质疏松症的新治疗方法。我们利用小天使病（一种罕见的以下颌骨巨细胞骨吸收肿瘤为特征的疾病）模型来探索调节破骨细胞发育和功能的新途径。小天使症是由Src同源3结合蛋白2 （SH3BP2）基因6个氨基酸区（415-420）的杂合错义突变引起的，该基因编码一种广泛表达的适应蛋白。小天使的特异表达时间和局部表达表明它是人类破骨细胞发生、骨吸收和骨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理解颌骨骨坏死的病理生理学具有重要意义。我们评估了17个小天使先显子，发现SH3BP2突变激活了活化T细胞（NFAT）的核因子。NFATc1（也称为NFAT2）是破骨细胞发生的主开关。所有这些SH3BP2突变也诱导破骨细胞标志物酒石酸抗性酸性磷酸酶（TRAP）在RAW 264.7前破骨细胞系中的表达。我们最近的研究表明，SH3BP2刺激一种磷脂酰肌醇特异性磷脂酶C (PI-PLC)，肌醇磷酸3 （IP3）的产生导致钙（Ca2+）从内质网释放。细胞内钙的增加可以激活钙调神经磷酸酶，它使NFAT去磷酸化并促进其向细胞核的易位。假设：SH3BP2在破骨细胞生成中起作用，小天使患者的SH3BP2突变改变了SH3BP2的物理特性（翻译后修饰和/或与其他蛋白质结合），至少有一个结果是NFATc1活性增强，从而导致破骨细胞生成。目的1。目的：检测野生型和突变型SH3BP2的翻译后修饰。目标2。表征SH3BP2蛋白-蛋白相互作用。目标3。目的：区分野生型和突变型SH3BP2的破骨机制。骨质疏松症是一个影响美国大约2500万人的公共卫生问题。无论病因如何，骨质疏松症的特点是骨重塑失衡，破骨细胞骨吸收超过成骨细胞骨形成，导致骨量低或骨质减少。关于骨吸收机制的新信息可能有助于减少骨吸收的新策略的发展，并可能导致骨质疏松症的新治疗方法。

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.