Molecular Mechanisms in Bone Resorption

描述（由申请人提供）：骨质疏松症是一种公共卫生问题，影响美国约2500万人。无论病因如何，骨质疏松症的特征在于骨重建的不平衡，使得成骨细胞骨吸收超过成骨细胞骨形成，这导致低骨量或骨质减少。关于骨吸收和破骨细胞生成机制的新信息可能有助于开发新的策略来减少骨吸收，并可能导致骨质疏松症的新治疗方法。我们已经使用了巨像症的模型，一种罕见的疾病，其特征是下颌骨和上颌骨的巨细胞骨吸收肿瘤，以探索调节破骨细胞发育和功能的新途径。巨像症是由Src同源性3结合蛋白2（SH 3BP 2）基因的6个氨基酸区域（415-420）内的杂合错义突变引起的，该基因编码广泛表达的衔接蛋白。巨颌症的特异性时间和局部表达表明它是一种独特的、新的人类破骨细胞生成、骨吸收和骨质减少的模型。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有重要意义。我们评估了17个先天性巨像症先证者，发现SH 3BP 2突变激活活化T细胞核因子（NFAT）。NFATc 1（也称为NFAT 2）是破骨细胞生成的主开关。所有这些SH 3BP 2突变还诱导破骨细胞标志物酒石酸盐抗性酸性磷酸酶（TRAP）在RAW 264.7前骨细胞系中的表达。我们最近的研究表明，SH 3BP 2刺激一种形式的磷脂酰肌醇特异性磷脂酶C（PI-PLC），磷酸肌醇3（IP 3）的产生导致钙（Ca 2+）从内质网释放。细胞内钙的增加可以激活钙调磷酸酶，其使NFAT去磷酸化并促进其易位到细胞核。假设：SH 3BP 2在破骨细胞生成中具有作用，并且巨掌症患者中的SH 3BP 2突变改变了SH 3BP 2的物理性质（翻译后修饰和/或与其他蛋白质的结合），至少一个结果是NFATc 1活性增强和随后的破骨细胞生成。目标1.研究野生型和突变型SH 3BP 2的翻译后修饰。目标2.表征SH 3BP 2蛋白-蛋白相互作用。目标3。区分野生型和突变型SH 3BP 2的破骨细胞发生机制。骨质疏松症是一种公共卫生问题，影响美国约2500万人。无论病因如何，骨质疏松症的特征在于骨重建的不平衡，使得成骨细胞骨吸收超过成骨细胞骨形成，这导致低骨量或骨质减少。关于骨吸收机制的新信息可能有助于开发新的策略来减少骨吸收，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.