Canonical and Noncanonical Wnt Signaling in Osteoclast Functions

 描述（由申请人提供）：破骨细胞活性过度会导致骨质流失，是一个严重的健康问题，因为它会导致骨质疏松症、肿瘤相关性骨病和其他以骨量和强度降低为特征的疾病。Lrp 5/6拮抗剂sclerostin的抗体是一种有前途的新合成代谢疗法，因为它能增强骨形成。啮齿动物和人类研究表明，这种疗法也减少破骨细胞介导的吸收。Wnt活性增强抑制骨吸收的机制尚不清楚。我们的研究表明，破骨细胞前体（pOC）中Lrp 5/6的靶向缺失减少了成骨细胞的数量和骨形成率，支持Wnt/Lrp在成骨细胞谱系细胞的pOC募集中的作用。在pOC中靶向缺失β-连环蛋白时未观察到这种反应，表明Wnt/Lrp信号传导对破骨细胞谱系细胞的β-连环蛋白非依赖性影响.本课题的重点是研究Wnt/Lrp对pOC分化和成骨细胞募集的影响机制。Wnt 3a在与Lrp 5/6结合时抑制pOC分化。然而，当Lrp 5/6受体不存在时，Wnt 3a增强pOC分化。我们的初步数据显示，在这些情况下，Wnt 3a的行为更像Wnt 5a，并通过Ror 2激活非经典Wnt信号通路。在pOC中缺乏Ror 2的小鼠具有骨硬化症，破骨细胞数量减少。令人惊讶的是，破骨细胞谱系细胞的这种严重减少对成骨细胞数量没有影响，表明Ror 2信号转导抑制成骨细胞募集。我们的初步数据显示，Wnt 3a处理pOC抑制Rank表达并刺激SPHK 1酶的表达，增加其产物趋化因子S1 P的产生。相反，Wnt 5a刺激Rank表达并抑制SPHK 1/S1 P产生。这个建议的中心假设是，有两个竞争的Wnt途径控制破骨细胞分化。典型臂由Wnt 3a激活，Wnt 3a通过Lrp 5/6发出信号，抑制分化并促进S1 P产生。在正常条件下，非典型臂由Wnt 5a和Ror 2激活以刺激破骨细胞分化并抑制S1 P水平，但当Lrp 5/6水平低时，Ror 2也由Wnt 3a参与。我们检验假设的具体目的是：（1）确定Lrp和Ror 2调节SPHK 1和Rank的机制，（2）检查Ror 2和SPHK 1/S1 P在鼠和人破骨细胞谱系细胞中的表达，以及（3）评价鼠和人衰老模型中的成骨细胞谱系细胞募集。这些研究将显著增强我们对Wnt控制骨代谢的机制的理解，并提供重要的新途径来增强Wnt信号对骨合成代谢的影响，同时抑制分解代谢的影响。这些新的治疗方向将改善预防和治疗骨质疏松症和病理性骨丢失的策略，如关节炎和肿瘤引起的骨质溶解。

 DESCRIPTION (provided by applicant): Excessive osteoclast activity causes bone loss and is a significant health issue because it can lead to osteoporosis, tumor-associated bone disease, and other conditions characterized by reduced bone mass and strength. An antibody to the Lrp5/6 antagonist sclerostin is a promising new anabolic therapy because it enhances bone formation. Rodent and human studies indicate that this therapy also reduces osteoclast- mediated resorption. The mechanism(s) by which enhanced Wnt activity suppresses bone resorption is unknown. Our studies reveal that targeted deletion of Lrp5/6 in osteoclast precursors (pOC) reduces osteoblast numbers and bone formation rates, supporting a role for Wnt/Lrp in pOC recruitment of osteoblast lineage cells. This response is not seen with targeted deletion of -catenin in pOCs, indicating -catenin- independent impacts of Wnt/Lrp signaling on osteoclast lineage cells. The focus of this project is to investigate the mechanisms by which Wnt/Lrp influence pOC differentiation and recruitment of osteoblast lineage cells. Wnt3a suppresses pOC differentiation when it binds to Lrp5/6. However, when Lrp5/6 receptors are not present, Wnt3a enhances pOC differentiation. Our preliminary data reveal that in these instances, Wnt3a acts more like Wnt5a and signals through Ror2 to activate noncanonical Wnt signaling pathways. Mice lacking Ror2 in pOCs have osteopetrosis, with reduced osteoclast numbers. Surprisingly, this severe reduction in osteoclast lineage cells had no impact on osteoblast numbers, suggesting that Ror2 signaling suppresses osteoblast recruitment. Our preliminary data reveal that Wnt3a treatment of pOCs represses Rank expression and stimulates expression of the enzyme SPHK1, increasing production of its product, the chemokine S1P. In contrast, Wnt5a stimulates Rank expression and suppresses SPHK1/S1P production. The central hypothesis of this proposal is that there are two competing Wnt pathways that control osteoclast differentiation. The canonical arm is activated by Wnt3a, which signals through Lrp5/6, suppresses differentiation and promotes S1P production. The noncanonical arm is activated by Wnt5a and Ror2 to stimulate osteoclast differentiation and suppress S1P levels under normal conditions, but Ror2 is also engaged by Wnt 3a when Lrp5/6 levels are low. Our Specific Aims to test our hypothesis are to: (1) Determine the mechanisms of Lrp and Ror2 regulation of SPHK1 and Rank, (2) Examine Ror2 and SPHK1/S1P expression in murine and human osteoclast lineage cells, and (3) Evaluate osteoblast lineage cell recruitment in murine and human models of aging. These studies will significantly enhance our understanding of the mechanisms by which Wnts control bone metabolism and provide important new avenues to enhance bone anabolic influences of Wnt signaling while suppressing catabolic influences. These new therapy directions will improve strategies to prevent and treat osteoporosis and pathological bone loss in conditions such as arthritis and tumor-induced osteolysis.