Control of Bone Mass by Progranulin

成人健康骨骼的维持需要协调的骨转换，其中骨形成是 与骨吸收密切相关，允许在维持骨量的情况下进行骨更新。解耦 骨形成和骨吸收的减少是各种情况下骨量丢失的基础 包括衰老、绝经和各种炎性疾病如类风湿性关节炎（RA）。 这些疾病通常与骨吸收增强相关，伴随着骨吸收速率的增加。 形成不足以达到再吸收水平。抗吸收疗法一直是传统的 在这些情况下，治疗低骨量患者的方法，但越来越多的人认识到， 增强骨形成的合成代谢疗法构成了重要的替代策略。先前 研究已经确定成骨细胞谱系细胞中的抑制性G蛋白（Gi）信号传导抑制骨形成， 形成，是女性年龄相关性骨质流失的重要驱动因素，但上游因素 这种信号通路的机制是未知的。成骨细胞系中经典Wnt信号转导的抑制 也与骨形成减少有关。本研究将使用各种小鼠模型来测试 假设由巨噬细胞产生的炎症相关因子颗粒蛋白前体（PGRN） 与年龄相关的骨质流失有关，是炎症细胞因子产生的关键上游调节因子 PGN介导的细胞因子产生通过激活Gi信号传导促进骨丢失， 成骨细胞谱系细胞中典型Wnt信号传导的抑制。这一假设将在三个 具体目标。在具体目标1中，PGRN在骨髓巨噬细胞（BMM）调节的骨中的作用是： 将探索形成。为了做到这一点，我们将确定是否在人口的变化， BEGFR 2促进了PGRN的骨吸收; PGRN的表达是否减少了骨吸收的促进作用？ 骨形成活性;以及从PGRN缺陷小鼠移植骨形成是否能保护 或逆转成年雌性小鼠的骨质流失。具体目标2将解决抑制合成代谢的作用， PGRN对骨形成的负面影响的信号通路。规范Wnt的作用 将在靶向缺失Ctnnb 1（编码b-连环蛋白的基因）的小鼠中体内研究Ctnnb 1通路， 并将在缺乏PGRN表达的成骨细胞谱系细胞中进行体外研究。PGRN的能力 将在体外培养的骨细胞中评估其抑制Gs/环AMP信号传导的能力，并在体内评估其抑制Gs/环AMP信号传导的能力。 限制合成代谢对间歇性PTH给药的反应。具体目标3是一个翻译目标，其中 我们将探讨PGRN在两种与炎症相关的疾病中介导骨丢失的作用- 类风湿性关节炎（RA）和雌激素缺乏引起的骨质疏松症。我们将决定PGRN是否 保护缺陷小鼠免于卵巢切除术（OVX）后的骨丢失和全身性骨丢失， 局部关节侵蚀的K/BxN血清转移模型的RA。PGRN缺失对细胞凋亡的影响 还将评估响应于血清转移和OVX的BBM的炎性表型。骨 将进行骨髓移植研究，以确定PGRN缺陷的BBM是否可以挽救 与OVX和RA相关的骨骼病理学。成功完成本提案中的研究 将阐明骨疾病的发病机制与炎症性疾病，如RA和 绝经后骨质疏松症确定这种关系的细节将导致确定新的 用于预防或逆转这些病症中的骨丢失的治疗靶点。

The maintenance of healthy bones in adults requires coordinated bone turnover where bone formation is closely coupled to bone resorption, allowing bone renewal with the maintenance of bone mass. Uncoupling of bone formation and bone resorption underlies the loss of bone mass seen in a variety of conditions including aging, the menopause, and various inflammatory disorders such as rheumatoid arthritis (RA). These disorders are generally associated with enhanced bone resorption accompanied by rates of bone formation that are inadequate for the level of resorption. Anti-resorptive therapies have been the traditional approach for treating patients with low bone mass in these conditions, but it is increasingly recognized that anabolic therapies that enhance bone formation constitute an important alternative strategy. Previous studies have identified that inhibitory G protein (Gi) signaling in osteoblast lineage cells suppresses bone formation and is an important driver of age-related bone loss in females, but the factors that are upstream of this signaling pathway are unknown. Suppression of canonical Wnt signaling in osteoblast lineage cells is also linked to reduced bone formation. The present study will use a variety of mouse models to test the hypothesis that progranulin (PGRN), an inflammation-associated factor produced by macrophages and implicated in age-related bone loss, is a critical upstream regulator of inflammatory cytokine production and that PGRN-mediated cytokine production promotes bone loss through activation of Gi signaling and suppression of canonical Wnt signaling in osteoblast lineage cells. This hypothesis will be tested in three specific aims. In Specific Aim 1, the role of PGRN in bone marrow macrophage (BMM)-regulated bone formation will be explored. To accomplish this, we will determine whether alternations in the population of BMMs accounts for promotion of bone resorption by PGRN; whether expression of PGRN reduces the pro- osteogenic activity of BMMs; and whether transplantation of BMMs from PGRN-deficient mice can protect or reverse bone loss in adult female mice. Specific Aim 2 will address the role of suppression of anabolic signaling pathways in the negative effects of PGRN on bone formation. The role of the canonical Wnt pathway will be investigated in vivo in mice with targeted deletion of Ctnnb1, the gene encoding b-catenin, and will be investigated in vitro in osteoblast lineage cells lacking expression of PGRN. The ability of PGRN to inhibit Gs/cyclic AMP signaling will be assessed in vitro in cultured osteocytes and in vivo in its ability to limit the anabolic response to intermittent PTH administration. Specific Aim 3 is a translational aim in which we will explore the role of PGRN in mediating bone loss in two disorders associated with inflammation- rheumatoid arthritis (RA) and estrogen deficiency-induced osteoporosis. We will determine whether PGRN deficient mice are protected from bone loss after ovariectomy (OVX) and from systemic bone loss and local joint erosion in the K/BxN serum transfer model of RA. The effect of PGRN deletion on the inflammatory phenotype of BBMs in response to serum transfer and OVX will also be assessed. Bone marrow transplantation studies will be carried out to determine whether PGRN-deficient BBMs can rescue the skeletal pathology associated with OVX and RA. Successful completion of the studies in this proposal will illuminate the pathogenesis of bone disease associated with inflammatory disorders such as RA and postmenopausal osteoporosis. Defining the details of this relationship will lead to the identification of new therapeutic targets for preventing or reversing bone loss in these conditions.