NOVEL REGULATORY MECHANISMS CONTROLLING BONE REPAIR AND OSTEOPOROSIS

描述（由申请人提供）：骨质疏松症是一种以低骨量为特征的疾病，其导致骨骼的隐性退化，使其变得脆弱并易于骨折。骨质疏松症是由于多种遗传、激素、营养和物理因素单独或共同作用而降低骨骼完整性。雌激素替代通过阻断破骨细胞介导的骨脱矿作用来减缓骨丢失。在这种情况下，甲状旁腺激素（PTH）能够介导骨生长。我们最近进行了一系列的观察，提示雌激素缺乏可能导致骨质疏松症的另一个潜在的重要机制。具体而言，我们发现，氨基末端截短的PTH片段，被认为是无活性的促进快速内化的PTH受体（PTH1R）在骨细胞特异性的方式。这些在其他方面没有生物活性的PTH片段减少了细胞表面上PTH1R的丰度，而没有首先激活受体。这种PTH1R激活和失活的解偶联是由于胞质衔接蛋白的存在，称为EBP 50（ezrin结合蛋白，50 kDa）。EBP 50含有雌激素反应元件。缺乏EBP 50的实验动物具有骨质减少并发展成骨质疏松症。我们假设雌激素增加EBP 50的表达，从而保护成骨细胞PTH1R免受PTH片段的失活作用。本研究的具体目的是：（1）研究性激素对EBP 50的调节作用，（2）确定雌激素诱导EBP 50表达是否有助于恢复PTH对骨的合成代谢作用。将在人和大鼠成骨细胞系中测定性腺激素对EBP 50表达的影响。第二组实验由两部分组成。首先，将从EBP 50缺失小鼠的骨髓制备的异位小骨用作模型系统，以分析PTH和雌激素对骨的影响，与全身效应或供体动物无关。第二部分将研究雌二醇单独或与PTH联合给药对卵巢切除EBP 50缺失小鼠骨恢复的影响。拟议的研究将有助于更好地了解影响骨骼健康的激素事件，并对骨负荷的反应产生重要影响。新的预测措施的脆弱性和潜在的治疗干预的途径可能会开发。这些新研究的目标是描述女性激素对骨骼的影响如何受到某种衔接蛋白的调节。长期目标是确定可用于治疗绝经后骨质疏松症的新型化合物。

DESCRIPTION (provided by applicant): Osteoporosis is a disease that is characterized by low bone mass that results in insidious deterioration of the skeleton leaving it fragile and vulnerable to fracture. Osteoporosis is due to multiple genetic, hormonal, nutritional, and physical factors that act alone or together to diminish skeletal integrity. Estrogen replacement blunts the loss of bone by blocking osteoclast-mediated bone demineralization. In this setting, parathyroid hormone (PTH) is able to mediate bone growth. We recently made a series of observations that suggest another potentially important mechanism by which estrogen deficiency may contribute to osteoporosis. Specifically, we found that amino-terminally truncated PTH fragments that are thought to be inactive promoted rapid internalization of the PTH receptor (PTH1R) in a cell-specific manner in bone. These otherwise biologically inactive PTH fragments reduced the abundance of PTH1R on the cell surface without first activating the receptor. This uncoupling of PTH1R activation and inactivation is due to the presence of a cytoplasmic adaptor protein, termed EBP50 (ezrin-binding protein, 50 kDa). EBP50 contains an estrogen response element. Experimental animals lacking EBP50 have osteopenia and develop osteoporosis. We hypothesize that estrogens increase EBP50 expression, thereby protecting the osteoblast PTH1R against the inactivating effects of PTH fragments. The Specific Aims of this project are: (1) To examine gonadal hormone regulation of EBP50, and (2) to determine if estrogen induction of EBP50 expression contributes to restoring the anabolic action of PTH on bone. The effects of gonadal hormones on EBP50 expression will be determined in osteoblastic human and rat cell lines. The second group of experiments consists of two parts. In the first, ectopic ossicles prepared from bone marrow of EBP50-null mice will be used as a model system to analyze the effects of PTH and estrogens on bone, independent of systemic effects or the donor animal. The second part will examine the effects of estradiol administration alone or in combination with PTH on restoring bone in ovariectomized EBP50-null mice. The proposed studies will lead to a better understanding of the hormonal events that impact bone health and importantly influence the response to bone loading. Novel predictive measures of fragility and potential avenues for therapeutic intervention may be developed. The goal of these new studies is to characterize how the effect of female hormones on bone may be regulated by a certain adapter protein. The long-term objective is to identify novel compounds that can be used to treat post-menopausal osteoporosis.