Sclerostin and Gsalpha signaling in osteoblasts

描述（由申请人提供）：项目摘要骨质疏松症，一种退行性疾病，由骨形成相对于骨吸收的不平衡引起，估计50%的50岁以上的美国人将受到影响。虽然骨折会让人想起童年时四肢打着石膏的情景，在短暂的恢复期内征求签名和同情，但老年人的脆弱性骨折要危险得多。年龄超过50岁的髋部骨折患者的一年死亡率是惊人的24%，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的老龄化，每年已经超过180亿美元的骨质疏松性骨折的成本肯定会上升。目前骨质疏松症的治疗大多是抗再吸收的，因此不能治愈。随着重组人甲状旁腺激素（特立帕肽，PTH[1-34]）的最近批准，现在可获得一种对骨形成具有强效刺激作用的合成代谢剂。然而，由于胃肠外给药的局限性和对成骨恶性肿瘤的潜在担忧，都表明对骨质疏松症额外治疗的持久需求。经典Wnt信号通路在骨形成中也具有关键作用，因此靶向Wnt通路是治疗骨质疏松症的有吸引力的选择。最近的研究强调了sclerostin的重要作用，它是Wnt信号传导的抑制剂，PTH抑制sclerostin表达的证据表明这两种途径之间存在有意义的串扰。异源三聚体G蛋白Gs1是通过PTH/PTH相关肽受体的PTH信号传导的主要下游介质。我已经发现，在小鼠（Gs1 KO小鼠）成骨细胞谱系中Gs1的消融导致严重的骨质疏松症;在这些小鼠中，sclerostin表达显著增加，从而导致经典Wnt信号转导的减少。由于PTH和Wnt通路可能对骨形成具有重叠和不同的作用，因此在本申请中，我建议确定sclerostin抑制Wnt信号传导如何有助于Gs1 KO小鼠骨量的急剧减少。我建议将Gs1 KO小鼠与缺乏sclerostin的小鼠（SOST KO小鼠）杂交。在目标1中，我将研究硬化蛋白在Gs1基因敲除小鼠胚胎骨骼发育中的作用。在目标2中，我将延迟骨祖细胞中Gs1的消融直到出生，以特别关注出生后骨骼稳态中硬化素的功能。在目标3中，我将收获骨髓基质细胞和颅骨成骨细胞从单和双KO小鼠，以建立PTH和Wnt信号通路如何相互作用，以调节间充质谱系的承诺和成骨分化。了解PTH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症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，缺乏治疗这种使人衰弱的疾病的治疗方法。甲状旁腺激素和Wnt信号通路都起着控制骨形成的作用。该提案旨在了解这两种途径如何在分子水平上相互作用，因为对骨量增加过程的更深入了解最终可能会带来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.