R-Spondin3 as a target for anabolic bone therapy

说明(申请人提供)：使用抗吸收药治疗骨质疏松症有一定的局限性，部分原因是它们不能维持骨形成和骨周转1。据信，周转抑制是导致颌骨坏死和股骨不典型骨折等副作用的重要原因。在这种背景下，对小说的寻找 增加骨量和防止脆性骨折的手段已经变得至关重要。PTH是市场上唯一被批准的合成代谢药物，它有效地促进骨形成，但也增加骨吸收，并且在动物研究中与骨肉瘤有关，限制了它的长期使用2。在人类和小鼠中激活规范的Wnt(C-Wnt)信号突变会导致强烈的合成代谢反应，并增加骨量和强度，这一发现为解决这一未得到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信号的化合物正在进行临床试验，如skerostin或Dkk1的抗体，但最近的临床发现显示出有限的成骨效应。提出了关于它们的治疗用途的多个问题，并说明了我们对骨骼中Wnt信号的理解仍然有限的事实4。在这里，我们建议在小鼠身上测试这样的假设，即在成人骨骼中抑制Rspo3可能是治疗骨质疏松症的一种新的合成代谢方法。这项研究将阐明缺失Rsp3对出生后骨骼稳态的影响，拮抗Rsp3在成年骨骼和骨质疏松模型中的作用，以及骨量增加的机制(S)。我们的具体目标是：特定目的1：进一步分析Rspo3缺失对体内骨稳态和体外骨细胞的影响，并评价成年骨骼中可诱导的OB靶向缺失(Col1a1-CreERT2/Rspo3f/f)的效果。特定目的2：在体外和体内探索Rspo3缺失增加b-catenin稳定性从而增强Wnt信号的分子机制。特异目的3：同时，建立治疗干预模型 通过产生可诱导的整体Rspo3敲除(R26ERCre/Rspo3f/f)来测试Rspo3在成人骨骼和卵巢切除后的减少/缺失的影响，从而导致骨质疏松症。本申请中提出的研究是创新的，因为我们的数据揭示了RSpondins在骨骼动态平衡中的一个新的和意想不到的作用，而且意义重大，因为他们证明RSpondins水平的降低可以在啮齿类动物中诱导强烈的合成代谢反应，出人意料地使这一家族的可溶性Wnt调节器成为治疗干预的潜在靶点。它们也是直接翻译的，因为测试RSP03在成人骨骼中的表达减少的效果和OVX后可能对治疗骨质疏松症和其他骨脆性疾病有重大影响。

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.