R-Spondin3 as a target for anabolic bone therapy

描述（由申请人提供）：使用抗吸收药治疗骨质疏松症具有局限性，部分原因是其无法维持骨形成和骨转换1。据信，周转抑制是显着的副作用，如颌骨骨坏死和非典型骨折的股骨。在这种情况下，寻找新的 增加骨质量和防止脆性骨折的方法已经变得极其重要。PTH是市场上唯一批准的合成代谢药物，有效地增加骨形成，但也增加骨吸收，并在动物研究中与骨肉瘤相关，限制了其长期使用2。在人类和小鼠中激活典型Wnt（C-Wnt）信号突变导致强烈的合成代谢反应并增加骨量和强度的发现为解决这一未满足的医疗需求带来了巨大的希望3，4。尽管目前有几种激活Wnt信号传导的化合物正在进行临床试验，例如sclerostin或Dkk 1的抗体，但最近的临床研究结果显示了时间有限的骨形成作用，提出了关于其治疗用途的多个问题，并说明了我们对骨中Wnt信号传导的理解仍然有限的事实。我们建议在小鼠中测试的假设，抑制Rspo 3在成人骨骼可能是一种新的合成代谢方法骨质疏松症。本提案中的研究将阐明删除Rspo 3在出生后骨稳态中的作用、拮抗Rspo 3在成人骨骼和骨质疏松症模型中的作用以及骨量增加的机制。我们的具体目标是：具体目标1：进一步分析Rspo 3缺失对体内骨稳态和体外骨细胞的影响，并评估Rspo 3的可诱导OB靶向缺失（Col 1a 1-CreERT 2/Rspo 3f/f）在成人骨骼中的作用。具体目标二：在体外和体内探索Rspo 3缺失增加b-连环蛋白稳定性从而增加Wnt信号传导的分子机制。具体目标3：同时，建立一个治疗性干预的模式， 通过产生可诱导的整体Rspo 3敲除（R26 ERCre/Rspo 3f/f）来检测Rspo 3减少/缺失在成人骨骼中和卵巢切除术后的作用，从而检测骨质疏松症。本申请中提出的研究是创新性的，因为我们的数据揭示了RSpondins在骨稳态中的新的和意想不到的作用，并且是重要的，因为它们证明RSpondins水平的降低可以在啮齿动物中诱导强烈的合成代谢反应，出乎意料地使该可溶性Wnt调节剂家族成为治疗干预的潜在靶标。它们也是直接翻译的，因为测试成年骨骼中和OVX后RSPO 3表达减少的效果可能对骨质疏松症和其他骨脆性疾病的治疗具有显著影响。

DESCRIPTION (provided by applicant): The use of anti-resorptives to treat osteoporosis has limitations due in part to their inability to maintain bone formation and bone turnover 1. It is believed that turnover suppression is contributing significantly to side effects such as osteonecrosis of the jaw and atypical fractures of the femur. In this context, the search for novel means to increase bone mass and prevent fragility fractures has become of the utmost importance. PTH, the only approved anabolic drug on the market, increases efficiently bone formation but also increases bone resorption and has been associated with osteosarcoma in animal studies, limiting its long-term use 2. The discovery that activating canonical Wnt (C-Wnt) signaling mutations in humans and mice lead to strong anabolic responses and increase bone mass and strength raised significant hope to resolve this unmet medical need 3, 4. Although several compounds that activate Wnt signaling are currently in clinical trials, such as antibodies to sclerostin or Dkk1, recent clinical findings have shown a time-limited bone formation effect, raising multiple questions about their therapeutic use and illustrating the fact that our understanding of Wnt signaling in bone remains limited 4. We propose here to test in mice the hypothesis that inhibiting Rspo3 in the adult skeleton may be a novel anabolic approach to osteoporosis. The investigations in this proposal will elucidate the effects of deleting Rspo3 in postnatal bone homeostasis, the effects of antagonizing Rspo3 in the adult skeleton and in a model of osteoporosis and the mechanism(s) by which bone mass is increased. Our specific aims are: Specific Aim 1: Further analyze the effects of Rspo3 deletion on bone homeostasis in vivo and on bone cells in vitro and evaluate the effect of inducible OB-targeted deletion (Col1a1-CreERT2 /Rspo3f/f) of Rspo3 in the adult skeleton. Specific Aim 2: Explore in vitro and in vivo the molecular mechanisms by which deletion of Rspo3 increases b-catenin stabilization and thereby Wnt signaling. Specific Aim3: In parallel, establish a model of therapeutic intervention in osteoporosis by generating an inducible global Rspo3 knockout (R26ERCre/Rspo3f/f) to test the effects of Rspo3 reduction/deletion in the adult skeleton and after ovariectomy. The studies proposed in this application are innovative since our data reveal a novel and unexpected role of RSpondins in bone homeostasis, and significant because they demonstrate that reduction in the levels of RSpondins can induce a strong anabolic response in rodents, unexpectedly making this family of soluble Wnt regulators a potential target for therapeutic intervention. They also ar directly translational since testing the effects of reduction of RSPO3 expression in an adult skeleton and after OVX may have a significant impact on the treatment of osteoporosis, and other diseases of bone fragility.