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

摘要 “一盎司预防胜过一磅治疗”这句格言非常适用于绝经后。 骨质疏松。绝经后立即发生的骨质流失每年可高达3-4%。目前， 没有可以接受的方法来防止这种情况发生。一个好的预防策略将消除骨丢失的增加。 不会过度抑制骨骼转换，也不会产生偏离目标的效果。有效的雌激素替代疗法 预防绝经期骨质流失，但妇女健康倡议暴露了ERT的风险，它在很大程度上 作为一种预防性战略已被放弃。像ERT这样的SERM会增加DVT的风险。长期使用 双膦酸盐会增加不典型骨折的风险。为了解决这一治疗缺口，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(CSF1)是成骨细胞释放的主要集落刺激因子，在 除了RANKL，对于破骨细胞的形成是绝对必要的。CSF1有两种主要的亚型，a 膜结合亚型(MCSF1)和可溶性或循环亚型(SCSF1)。SCSF1亚型有一个 独特的羧基末端延伸。停用雌激素选择性上调成骨细胞sCSF1，而 MCSF1没有变化。重要的是，针对CSF1的不分青红皂白的中和抗体完全防止 卵巢摘除(OVX)所致的小鼠骨丢失。然而，阻断CSF1的两种异构体并不可行 雌激素缺乏性骨丢失的预防策略，因为CSF1是正常破骨细胞形成所必需的。 我们发现，在体内选择性删除sCSF1不会导致表型改变，也不会改变骨的基础比率 但能保护小鼠免受OVX引起的骨丢失。这些数据表明sCSF1是一种新的治疗方法。 目标是防止雌激素缺乏性骨丢失。这个R21将检验这样的假设：选择性抑制 CSF1的可溶性异构体对雌激素缺乏性骨丢失的保护作用而不影响正常 骨重塑或骨质量。在特定目标1中，噬菌体展示抗体选择将用于 快速研制一种通过靶向独有的73个氨基酸残基c-末端选择性抑制sCSF1的抗体 这是一种异构体。在特定目标2中，完全中和抗体的剂量和时间 将首先使用体内系列DXA骨密度测定OVX野生型小鼠防止骨丢失 OVX野生型小鼠的测量。用雌激素治疗的OVX动物和OVX-sCSF1-/-小鼠将作为 控制。使用防止基线、OVX和Sham-OVX野生型动物骨密度变化的方案 用中和抗体或同型匹配对照抗体治疗4周。综合BMD 和身体成分测量，以及体外显微CT，生化，生物力学和 将进行组织形态计量学分析。为了确保足够的严谨性，这些研究将在 两种不同品系的小鼠。如果成功，这些研究将为一种全新的预防方法提供证据。 绝经后骨质流失在绝经开始前。

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.