Sclerostin Antagonism and the Osteocytes Role Prevention of Bone Loss after SCI

产品说明： 目前，对于SCI患者，还没有预防骨丢失或促进骨重建的实用治疗方法。通过Wnt抑制剂（例如，主要由骨细胞产生的硬化素）在骨质疏松症的发病机制中至关重要，尤其是由于废用引起的骨质疏松症。在最近的I期和II期临床试验中，抗硬化素抗体（Scl-Ab）增加绝经后妇女的骨矿物质密度（BMD）。在一项初步研究中，我们发现，当在SCI后7天开始并给药7周时，Scl-Ab几乎完全阻止了SCI诱导的BMD降低，并部分保留了小梁微结构。Scl-Ab还增加离体培养的骨髓祖细胞的成骨细胞生成和减少破骨细胞生成。因此，我们提出了以下问题：1）当SCI后立即开始施用Scl-Ab时，Scl-Ab是否能够完全防止骨丢失; 2）当SCI后28天开始施用Scl-Ab时，当已经发生显著的骨丢失时，Scl-Ab是否能够增加骨量和强度。在这些概念验证研究中，Scl-Ab将以25 mg/kg/周的剂量给药，与我们的初步工作相同。此外，还提出了一项初步研究，以探索给予更低、更临床相关剂量的Scl-Ab对减少SCI相关骨丢失的影响。 一般而言，尤其是SCI后，对机械卸载引起的骨丢失的潜在机制仍知之甚少。骨细胞占所有骨细胞的90%至95%，并且它们被认为是通过将机械信号转换成化学信号来调节破骨细胞和成骨细胞活性的骨重建的协调者。重要的是，我们发现在卵巢切除（OVX）大鼠的骨细胞形态异常，和治疗OVX与Scl-Ab大大改善骨细胞形态。因此，我们假设骨细胞的病理变化可能是SCI动物骨丢失的主要原因，并且Scl-Ab恢复骨细胞结构和功能将挽救SCI相关的骨丢失。为了解决这些问题和假设，提出了三个具体目标：目标1。进行概念验证研究，以评价Scl-Ab在SCI后保持骨完整性的能力。目的1a）测试在SCI时启动Scl-Ab是否完全防止由于SCI引起的骨丢失。25 mg/kg/周的Scl-Ab将在SCI后1小时内开始，并持续2个月。待确定的关键终点将是骨量、微结构、强度、骨形成和吸收的血液和组织形态学标志物以及骨髓祖细胞的成骨细胞生成和破骨细胞生成。目的1b）评估SCI后1个月开始使用Scl-Ab逆转骨丢失的能力。Scl-Ab将在SCI后28天开始，并持续1、4或8周。 目标二。进行一项初步研究，以测试较低剂量的Scl-Ab减少SCI相关骨丢失的能力。类似的 除了Scl-Ab将以两个较低剂量（3或9 mg/kg/月）给药外，将采用达到拟定目标1a的方法。这项工作将提供初步的见解，以最低的成本为临床护理的最低有效剂量的Scl-Ab能够维持治疗效果。 目标3。测试骨细胞功能受损是否是SCI导致骨丢失的机制之一，以及正常骨细胞功能的恢复是否是Scl-Ab挽救这种骨丢失的机制。目的1研究中动物骨细胞的功能特性将通过以下分析进行表征：i）骨细胞形态; ii）骨细胞数量和凋亡; iii）骨细胞基因和蛋白表达;以及iv）骨机械传导途径中涉及的关键因子。 上述研究将是第一项系统评价Scl-Ab预防或逆转SCI后骨丢失的疗效，并探索Scl-Ab如何调节骨细胞功能的研究。如果结果如预期的那样，Scl-Ab可能为改善SCI患者骨骼健康的新型强效药物提供第一个希望。

DESCRIPTION: At present, there is no practical treatment to prevent bone loss, or promote rebuilding of bone, in individuals with SCI. Regulation of Wnt signaling in bone by Wnt inhibitors (e.g., sclerostin, which is mainly produced by osteocytes) is crucial in the pathogenesis of osteoporosis, especially that due to disuse. In a recent phase I and II clinical trial, anti-sclerostin antibodie (Scl-Ab) increased bone mineral density (BMD) in postmenopausal women. In a pilot study we found that, when begun at 7 days after SCI and administered for 7 weeks, Scl-Ab almost completely prevented the SCI-induced reduction of BMD and partially preserved trabecular microarchitecture. Scl-Ab also increased osteoblastogenesis and decreased osteoclastogenesis of ex vivo cultured bone marrow progenitor cells. Thus, we have asked the following questions: 1) Whether Scl-Ab will completely prevent bone loss when its administration is begun immediately after SCI; 2) whether Scl-Ab is able to increase bone mass and strength when its administration is begun 28 days after SCI, when significant bone loss has already developed. In these proof of concept studies, Scl-Ab will be administered at 25 mg/kg/week, as was done in our preliminary work. In addition, a pilot study is proposed to explore the effect of the administration of a lower, more clinically relevant dose of Scl-Ab to reduce SCI-related bone loss. The mechanisms underlying bone loss in response to mechanical unloading in general, and after SCI in particular, remain poorly understood. Osteocytes compose 90% to 95% of all bone cells, and they have been considered as an orchestrator of bone remodeling through regulation of osteoclast and osteoblast activity by transducing mechanical signals into chemical signals. Importantly, we showed abnormalities of osteocyte morphology in ovarectomized (OVX) rats, and treatment of OVX with Scl-Ab greatly improved osteocyte morphology. Thus, we hypothesize that pathological changes in osteocytes are likely a central cause for bone loss in SCI animals, and that restoration of osteocyte structure and function by Scl-Ab will rescue SCI related- bone loss. To address these questions and hypotheses three specific aims are proposed: Aim 1. To perform proof of concept studies to evaluate the ability of Scl-Ab to preserve bone integrity after SCI. Aim 1a) To test whether initiating Scl-Ab at the time of SCI protects completely against bone loss due to SCI. Scl-Ab at 25 mg/kg/week will begin within one hour after SCI and be continued for 2 months. The key endpoints to be determined will be bone mass, microarchitecture, strength, blood and histomorphometric markers for bone formation and resorption, and osteoblastogenesis and osteoclastogenesis of bone marrow progenitors. Aim 1b) To evaluate the ability of Scl-Ab to reverse bone loss when initiated 1 month after SCI. Scl-Ab will be initiated 28 days after SCI and continued for 1, 4 or 8 weeks. Aim 2. To conduct a pilot study to test the ability of lower doses of Scl-Ab to reduce SCI-related bone loss. A similar approach to that proposed Aim 1a will be employed, except that Scl-Ab will be administered at two lower doses (3 or 9 mg/kg/month). This work will provide initial insight as to the minimum effective dose of Scl-Ab capable of maintaining therapeutic efficacy at the lowest cost for clinica care. Aim 3. To test whether impairment of osteocyte function is one mechanism by which SCI causes bone loss, and whether restoration of normal osteocyte function is a mechanism by which Scl-Ab rescues such bone loss. The functional properties of osteocytes in animals from Aim 1 study will be characterized by analysis of: i) osteocyte morphology; ii) osteocyte number and apoptosis; iii) osteocytic gene and protein expression; and iv) key factors involved in bone mechanotransduction pathway. The above studies will be the first study to systematically evaluate the efficacy of Scl-Ab to prevent or reverse bone loss after SCI and to explore how Scl-Ab regulates osteocyte function. If the results are as expected, Scl-Ab might offer the first hope of a novel potent agent to improve bone health in SCI patients.