Sclerostin and Gsalpha signaling in osteoblasts

描述(由申请人提供)：骨质疏松症是一种退行性疾病，由骨形成相对于骨吸收的失衡引起，估计将有50%的美国人在50岁以上。尽管骨折让人想起童年时打着石膏的四肢，在短暂的康复期间寻求签名和同情，但老年人的脆性骨折要危险得多。50岁以上的髋部骨折患者的一年死亡率高达惊人的24%，而且只有三分之一的人恢复了骨折前的独立功能。随着寿命的延长和人口老龄化，骨质疏松性骨折的成本--每年已经超过180亿美元--肯定会上升。目前治疗骨质疏松症的方法大多是抗吸收的，因此不能治愈。随着最近重组人甲状旁腺激素(Teriparatide，PTH[1-34])的批准，一种对骨形成有强大刺激作用的合成代谢剂现已问世。然而，由于非肠道给药的局限性以及对成骨恶性肿瘤的潜在担忧，所有这些都表明了对骨质疏松症额外治疗的持久需求。规范的Wnt信号通路在骨形成中也起着关键作用，因此靶向Wnt信号通路是治疗骨质疏松症的一个有吸引力的选择。最近的研究强调了硬化素的重要作用，它是一种Wnt信号的抑制剂，有证据表明甲状旁腺素抑制了硬化素的表达，表明这两条通路之间存在着有意义的相互作用。异三聚体G蛋白GS1是甲状旁腺素信号的主要下游介体，通过甲状旁腺激素/甲状旁腺激素相关的多肽受体。我发现，去除小鼠(GS1KO小鼠)成骨细胞系中的GS1会导致严重的骨质疏松症；在这些小鼠中，硬化素的表达显著增加，结果是典型的Wnt信号减少。由于PTH和Wnt通路在骨形成方面可能既有重叠又有不同的作用，在这项应用中，我建议确定硬化素对Wnt信号的抑制如何有助于GS1 KO小鼠骨量的显著减少。我建议将GS1KO小鼠与缺乏skerostin的小鼠(Sost KO小鼠)杂交。在目标1中，我将研究硬化素在GS1KO小鼠胚胎骨骼发育中的作用。在目标2中，我将把骨祖细胞中GS1的消融推迟到出生时，以特别关注硬化素在出生后骨骼动态平衡中的作用。在目标3中，我将采集单个和双个KO小鼠的骨髓基质细胞和颅骨成骨细胞，以建立PTH和Wnt信号通路如何相互作用来调节间充质干细胞的定向和成骨分化。了解甲状旁腺激素和Wnt信号的合成代谢作用的分子机制可能最终为骨质疏松的治疗提供额外的靶点。 公共卫生相关性：骨质疏松症是一种常见的老年退行性疾病，目前尚缺乏治愈这种衰弱疾病的治疗方法。甲状旁腺激素和Wnt信号通路都控制骨形成。这项建议试图了解这两条途径是如何在分子水平上相互作用的，因为更深入地了解骨量增加的过程最终可能会导致治疗骨质疏松症的新疗法。

DESCRIPTION (provided by applicant): Project Summary Osteoporosis, a degenerative disease resulting from an imbalance of bone formation relative to bone resorption, will strike an estimated 50% of Americans over the age of 50. Although fractures call forth images from childhood of a limb in a cast, soliciting autographs and sympathy during a brief period of recovery, fragility fractures in the elderly are far more sinister. The one-year mortality rate for patients over the age of 50 with a hip fracture is an astounding 24%, and only one in three regain their pre-fracture ability to function independently. As lifespans lengthen and the population ages, the costs of osteoporotic fractures - already over $18 billion annually - will surely rise. Current therapies for osteoporosis are mostly anti-resorptive, and therefore not curative. With the recent approval of recombinant human parathyroid hormone (teriparatide, PTH[1-34]), an anabolic agent with potent stimulatory effects on bone formation is now available. However, limitations due to parenteral administration and a potential concern for osteogenic malignancies all point to an enduring need for additional therapies for osteoporosis. The canonical Wnt signaling pathway also has a critical role in bone formation, thus targeting the Wnt pathway is an attractive option for treating osteoporosis. Recent studies have highlighted an important role for sclerostin, an inhibitor of Wnt signaling, and evidence that PTH suppresses sclerostin expression suggests that meaningful cross-talk exists between these two pathways. The heterotrimeric G protein Gs1 is a major downstream mediator of PTH signaling via the PTH/PTH-related peptide receptor. I have found that ablation of Gs1 in the osteoblast lineage in mice (Gs1 KO mice) leads to profound osteoporosis; in these mice sclerostin expression is markedly increased, with a resultant decrease in canonical Wnt signaling. Since the PTH and Wnt pathways likely have both overlapping and distinct actions on bone formation, in this application I propose to determine how inhibition of Wnt signaling by sclerostin contributes to the dramatic reduction of bone mass in Gs1 KO mice. I propose to cross Gs1 KO mice with mice lacking sclerostin (SOST KO mice). In Aim 1 I will examine the role of sclerostin in embryonic skeletal development of Gs1 KO mice. In Aim 2 I will delay ablation of Gs1 in osteoprogenitors until birth, to specifically focus on the function of sclerostin in postnatal skeletal homeostasis. In Aim 3 I will harvest bone marrow stromal cells and calvarial osteoblasts from single and double KO mice to establish how PTH and Wnt signaling pathways interact to regulate mesenchymal lineage commitment and osteogenic differentiation. Understanding the molecular mechanisms underlying the anabolic effects of PTH and Wnt signaling may eventually provide additional targets for the treatment of osteoporosis. PUBLIC HEALTH RELEVANCE: Project Narrative Osteoporosis is a common degenerative disease of aging, and treatments available to cure this debilitating disease are lacking. Parathyroid hormone and the Wnt signaling pathway both act to control bone formation. This proposal seeks to understand how these two pathways interact at the molecular level, as greater insights into the processes by which bone mass is increased may ultimately result in novel therapies for osteoporosis.