An ounce of prevention: stopping menopausal bone loss before it starts

总结 “一盎司的预防胜过一磅的治疗”这句格言非常适用于绝经后 骨质疏松绝经后不久，骨质流失率可高达每年3-4%。目前， 没有可接受的方法来防止这种情况。一个好的预防策略将消除骨丢失的增加 而不会过度抑制骨转换，也不会产生脱靶效应。雌激素替代疗法有效 预防绝经期骨质流失，但妇女健康倡议暴露了ERT的风险， 作为一种预防性战略被放弃。像ERT这样的SERM会增加DVT的风险。长期使用 二膦酸盐会增加非典型骨折的风险。为了解决这一治疗差距，我们提出了一个大胆的新方案， 策略，基于集落刺激因子1的生物学。 集落刺激因子1（CSF 1）是成骨细胞释放的主要集落刺激因子， 除RANKL外，是破骨细胞形成所必需的。CSF 1有两种主要亚型， 膜结合同种型（mCSF 1）和可溶性或循环同种型（sCSF 1）。sCSF 1亚型具有 独特的羧基末端延伸。雌激素的退出选择性地上调成骨细胞中的sCSF 1， mCSF 1未发生变化。重要的是，针对CSF 1的同种型不加选择性中和抗体完全阻止了 卵巢切除术（OVX）诱导的小鼠骨丢失。然而，阻断CSF 1的两种亚型不是可行的方法。 雌激素缺乏性骨丢失的预防策略，因为正常的破骨细胞生成需要CSF 1。 我们发现，选择性地删除sCSF 1在体内不会引起表型，不会改变骨的基础率， 转换，但保护小鼠免受OVX诱导的骨丢失。这些数据表明sCSF 1是一种新的治疗药物， 预防雌激素缺乏性骨质流失。这个R21将检验选择性抑制 CSF 1的可溶性同种型防止雌激素缺乏性骨丢失而不影响正常 骨重建或骨质量。在特异性目标1中，将采用噬菌体展示抗体选择以 快速开发一种抗体，通过靶向sCSF 1独特的73个氨基酸的C-末端， 那个异形体在特定目标2中，完全不影响免疫应答的中和抗体给药的剂量和时间 将首先使用连续的体内DXA骨密度来确定OVX野生型小鼠中预防骨丢失的剂量 在OVX野生型小鼠中的测量。用雌激素处理的OVX动物和OVX-sCSF 1-/-小鼠将用作 对照使用防止BMD相对于基线变化的方案，OVX和假手术-OVX野生型动物 将用中和抗体或同种型匹配的对照抗体治疗4周。综合BMD 和身体成分测量，以及离体microCT，生物化学，生物力学和 将进行组织形态学分析。为了确保足够的严谨性，这些研究将在 两种不同品系的老鼠如果成功，这些研究将为一种全新的预防方法提供证据。 绝经后骨质流失

Summary The aphorism “an ounce of prevention is worth a pound of cure” very much applies to postmenopausal osteoporosis. Immediately following menopause, bone loss rates can reach as high as 3-4% per year. At present, there is no acceptable way to prevent this. A good prevention strategy would abrogate the increase in bone loss without over-suppressing bone turnover and without off-target effects. Estrogen replacement therapy effectively prevents menopausal bone loss, but the Women’s Health Initiative exposed the risks of ERT and it has largely been abandoned as a preventive strategy. SERMs like ERT increase the risk of DVT. The long-term use of bisphosphonates increases the risk of atypical fracture. To address this treatment gap, we propose a bold new strategy, based on the biology of Colony Stimulating Factor 1. Colony Stimulating Factor 1 (CSF1) is the principal colony stimulating factor released by osteoblasts and, in addition to RANKL, is absolutely required for osteoclast formation. There are two major isoforms of CSF1, a membrane-bound isoform (mCSF1) and a soluble, or circulating, isoform (sCSF1). The sCSF1 isoform has a unique carboxy-terminus extension. Withdrawal of estrogen selectively up-regulates sCSF1 in osteoblasts, while mCSF1 is unchanged. Importantly, an isoform-indiscriminate neutralizing antibody to CSF1 completely prevents ovariectomy (OVX)-induced bone loss in mice. However, blocking both isoforms of CSF1 is not a viable preventive strategy for estrogen-deficiency bone loss, because CSF1 is required for normal osteoclastogenesis. We found that selectively deleting sCSF1 in vivo causes no phenotype, does not change the basal rate of bone turnover, but protects mice against OVX-induced bone loss. These data point to sCSF1 as a novel therapeutic target to prevent estrogen-deficiency bone loss. This R21 will test the hypothesis that selective inhibition of the soluble isoform of CSF1 protects against estrogen-deficiency bone loss without affecting normal bone remodeling or bone quality. In Specific Aim 1, phage display antibody selection will be employed to rapidly develop an antibody that selectively inhibits sCSF1 by targeting the unique 73 amino acid c-terminus of that isoform. In Specific Aim 2, the dose and timing of neutralizing antibody administration that completely prevents bone loss in OVX wild type mice will first be determined using serial in vivo DXA bone density measurements in OVX wild type mice. OVX animals treated with estrogen and OVX-sCSF1-/- mice will serve as controls. Using the protocol that prevents a change in BMD from baseline, OVX and Sham-OVX wild type animals will be treated with neutralizing antibody or isotype matched control antibody for 4 weeks. Comprehensive BMD and body composition measurements, as well as ex vivo microCT, biochemical, biomechanical and histomorphometric analyses will be undertaken. To ensure adequate rigor, these studies will be performed in two different strains of mice. If successful, these studies will provide evidence for an entirely new way to prevent postmenopausal bone loss before it begins.