The Role Of Osteoclast PODXL, A Mediator Of Cell Adhesion, In Bone Metabolism

描述（由申请人提供）：我们的长期目标是描述破骨细胞促进骨代谢的分子机制，期望该知识将指导更有效的治疗以促进骨骼健康。理想情况下，新的治疗目标，以减少破骨细胞介导的骨丢失将阻止破骨细胞，同时也保留骨形成。这可能是具有挑战性的，因为越来越多的证据表明，破骨细胞，无论它们是否能够吸收骨，都是成骨细胞正常骨形成所必需的。我们已经检查了在造血/破骨细胞谱系细胞中CD 34家族成员PODXL缺失的小鼠（hem谱系-PODXLdel小鼠）的椎骨。骨密度和成骨细胞数量均升高。出乎意料的是，破骨细胞的数量和大小也明显更高。因此，早期破骨细胞谱系细胞中PODXL的丢失减少了骨吸收，同时保持了成骨细胞的募集和骨形成。我们的体外研究支持破骨细胞谱系细胞中的PODXL表达减少破骨细胞分化。然而，破骨细胞肌动蛋白环的形成和骨吸收需要相对低水平的PODXL表达。我们的研究和PODXL的已知功能导致了我们的中心假设，即必须降低包括CXCR 4和NHERF 1的PODXL膜复合物的早期祖细胞膜表达水平以允许前体融合，并且破骨细胞的活化需要较低水平的该复合物，使其能够再吸收骨。以下具体目标旨在检验这一假设1。确定破骨细胞系PODXL表达变化在骨骼获得和骨维持中的作用。我们将全面表型hem谱系-PODXLdel小鼠，建立卵巢切除术对hem谱系-PODXLdel小鼠骨代谢的影响，确定在合成代谢PTH治疗期间早期破骨细胞谱系细胞中PODXL缺失的影响，并将晚期破骨细胞谱系细胞中PODXL缺失的小鼠与hem谱系-PODXLdel小鼠进行比较。2.探讨PODXL、CXCR 4和NHERF-1复合物影响破骨细胞谱系细胞的分子机制。我们将确定PODXL和NHERF 1的结构域参与复合物的形成，膜的表达，分化，并在分化过程中的内化，解决PODXL，CXCR 4，和NHERF 1基因表达下调的M-CSF的机制，并确定PODXL和结合伙伴的整合素相互作用，肌动蛋白环的形成和破骨细胞功能的影响。 公共卫生相关性：与衰老和绝经后骨质疏松症相关的骨丢失是由于过量的破骨细胞介导的骨吸收。过量的骨质流失会导致使人衰弱的骨折风险。据估计，4400万美国人有患骨质疏松症的风险。在美国，估计有1000万人已经患有这种疾病，另有3400万人被怀疑患有低骨量，并有患这种疾病的风险。美国每年有150万例骨质疏松性骨折，治疗这些骨折的费用估计为120亿至180亿美元。患者和护理人员生产力损失的间接成本增加了数十亿美元。因此，靶向骨吸收破骨细胞同时保持骨形成的疗法有可能对患者产生显著影响。

DESCRIPTION (provided by applicant): Our long term goal is to delineate the molecular mechanisms by which osteoclasts contribute to bone metabolism with the expectation that this knowledge will guide more effective therapies to promote skeletal health. Ideally, new therapy targets to reduce osteoclast-mediated bone loss will block osteoclasts while also preserving bone formation. This may be challenging since evidence is mounting that osteoclasts, whether or not they are capable of resorbing bone, are needed for normal bone formation by osteoblasts. We have examined the vertebrae of mice in which the CD34 family member PODXL is deleted in hematopoietic/osteoclast lineage cells (hem lineage-PODXLdel mice). Bone density and osteoblast numbers were both elevated. Unexpectedly, the number and size of osteoclasts were also significantly higher. Thus, loss of PODXL in early osteoclast lineage cells reduces bone resorption while preserving osteoblast recruitment and bone formation. Our in vitro studies support that PODXL expression in osteoclast lineage cells reduces osteoclast differentiation. However, a relatively low level of PODXL expression is required for osteoclast actin ring formation and bone resorption. Our studies and the known functions of PODXL lead to our central hypothesis that early progenitor membrane expression levels of a PODXL membrane complex including CXCR4 and NHERF1 must be reduced to allow for precursor fusion and lower levels of this complex are required for activation of osteoclasts, enabling them to resorb bone. The following Specific Aims are designed to test this hypothesis 1. Determine the role of osteoclast lineage PODXL expression changes in skeletal acquisition and bone maintenance. We will comprehensively phenotype the hem lineage-PODXLdel mice, establish the effects of ovariectomy on bone metabolism in hem lineage-PODXLdel mice, define the impact of loss of PODXL in early osteoclast lineage cells during anabolic PTH treatment, and compare mice with PODXL deleted in late osteoclast lineage cells to the hem lineage-PODXLdel mice. 2. Interrogate the molecular mechanisms by which the PODXL, CXCR4, and NHERF-1 complex influences osteoclast lineage cells. We will identify structural domains of PODXL and NHERF1 involved in complex formation, membrane expression, differentiation, and internalization during differentiation, resolve the mechanism of down regulation of PODXL, CXCR4, and NHERF1 gene expression by M-CSF, and ascertain the influences of PODXL and binding partners on integrin interactions, actin ring formation, and osteoclast function. PUBLIC HEALTH RELEVANCE: Bone loss associated with aging and postmenopausal osteoporosis is due to excess osteoclast-mediated bone resorption. Excess bone loss leads to risks of debilitating fractures. An estimated 44 million Americans are at risk of osteoporosis. Within the U.S., 10 million people are estimated to already have this disease and an additional 34 million are suspected of having low bone mass and at risk of developing the disease. There are 1.5 million osteoporotic fractures in the U.S. each year and the cost of caring for these fractures is estimated at $12 billion to $18 billion. Indirect costs in lost productivity of patients and care givers add billions to this cost. Thus, therapies that target bone resorbing osteoclasts while preserving bone formation have the potential to have a significant impact on patients.