Inhibition of osteoblast function in bone erosion in rheumatoid arthritis

描述（由申请人提供）：类风湿性关节炎（RA）是一种使人衰弱的慢性疾病，可导致炎症关节中的局灶性骨丢失。破骨细胞介导的骨吸收是关节骨丢失的一种机制。然而，我们实验室的数据表明，关节骨丢失（侵蚀）部位的成骨细胞（OB）成熟存在缺陷，同时炎症部位的矿化骨形成受到抑制。成骨细胞的分化和功能依赖于通过骨形态发生蛋白（BMP）和无翅型（Wnt）信号通路的阳性信号。我们已经确定了在小鼠血清转移关节炎（STA）模型中骨侵蚀部位OB分化和功能抑制剂的表达。BMP 3（促成骨BMP 2信号传导的抑制剂）和两种Wnt信号传导途径抑制剂Dickkopf 1（DKK 1）和分泌型卷曲相关蛋白1（sFRP 1）的表达在侵蚀部位被诱导，表明这些因子在RA中抑制OB成熟和功能。在这项资助中，我们将通过测试RA滑膜炎症导致BMP和Wnt信号通路发生改变从而抑制OB功能，从而加速局灶性关节骨丢失的假设，评估两个交叉通路的贡献。在目的1中，我们将测试的假设，BMP 3在抑制OB功能的侵蚀网站，并通过Wnt信号的调制行为发挥独特的作用。将通过组织学定量、microCT定量关节骨和动态组织形态计量学，在BMP 3缺陷型和对照同窝STA小鼠中评价骨侵蚀过程。将在体外聚焦SuperArray测定中确定BMP 3对Wnt信号传导的调节。目的2将测试的假设，增强Wnt信号是保护局灶性骨侵蚀在RA由于增加OB介导的骨形成。这将通过在两种关节炎动物模型中通过抑制GSK-3（A部分）或通过特异性阻断DKK 1活性（B部分）促进Wnt信号传导来实现。TNFa是RA发病机制中的关键细胞因子，是体外OB分化和功能的抑制剂，并在滑膜成纤维细胞中诱导DKK 1。在目的3中，将在体外确定TNF α对关节炎病变内发现的细胞类型中BMP 3和Wnt拮抗剂表达的影响，并且还将确定这些细胞类型中BMP和Wnt信号传导途径之间的潜在相互作用。这些因子的细胞来源将在体内动物模型中鉴定。这些研究旨在确定RA骨形成增强的新靶点。 公共卫生相关性：类风湿性关节炎（RA）是一种慢性自身免疫性疾病，会局部破坏受影响关节内的骨骼，导致患者发病和长期残疾。尽管骨的去除是导致关节中骨丢失的一种机制，但本授权申请中提供的证据表明，由于抑制骨形成成骨细胞的成熟和功能，受影响关节中的骨形成受到抑制。提出的实验旨在确定新的目标，以增加骨形成在关节炎的关节骨丢失的网站。

DESCRIPTION (provided by applicant): Rheumatoid arthritis (RA) is a debilitating chronic disease that leads to focal loss of bone in inflamed joints. Osteoclast-mediated resorption is one mechanism for loss of articular bone. However, data from our laboratory demonstrate a defect in the maturation of bone-forming osteoblasts (OBs) at sites of articular bone loss (erosions), with an accompanying inhibition in the formation of mineralized bone at sites of inflammation. OB differentiation and function is dependant upon positive signaling through the Bone Morphogenic Protein (BMP) and Wingless-type (Wnt) signaling pathways. We have identified expression of inhibitors of OB differentiation and function at sites of bone erosion in the murine serum transfer arthritis (STA) model. Expression of BMP3, an inhibitor of pro-osteogenic BMP2 signaling, and of two Wnt signaling pathway inhibitors, Dickkopf1 (DKK1) and secreted Frizzled related-protein1 (sFRP1), is induced at sites of erosion, implicating these factors in the inhibition of OB maturation and function in RA. In this grant we will evaluate the contribution of two intersecting pathways by testing the hypothesis that inflammation in RA synovium leads to modifications in the BMP and Wnt signaling pathways that inhibit OB function, and thereby accelerates focal articular bone loss. In Aim 1, we will test the hypothesis that BMP3 plays a unique role in the inhibition of OB function at sites of erosion, and acts through modulation of Wnt signaling. The process of bone erosion will be evaluated in BMP3 deficient and control littermate mice with STA by histologic quantitation, quantitation of articular bone by microCT, and dynamic histomorphometry. The regulation of Wnt signaling by BMP3 will be determined in focused SuperArray assays in vitro. Aim 2 will test the hypothesis that enhanced Wnt signaling is protective in focal bone erosion in RA due to augmentation of OB-mediated bone formation. This will be achieved by promoting Wnt signaling in two animal models of arthritis by inhibiting GSK-3 (Part A) or by specifically blocking DKK1 activity (Part B). TNFa, a critical cytokine in RA pathogenesis, is an inhibitor of OB differentiation and function in vitro, and induces DKK1 in synovial fibroblasts. In Aim 3, the effects of TNFa on expression of BMP3 and Wnt antagonists in cell types found within arthritic lesions will be determined in vitro, and potential interactions between the BMP and Wnt signaling pathways in these cell types will also be determined. Cellular sources of these factors will be identified in animal models in vivo. These studies are designed to identify novel targets for the augmentation of bone formation in RA. PUBLIC HEALTH RELEVANCE: Rheumatoid arthritis (RA) is a chronic autoimmune disease that destroys bone locally within affected joints, leading to patient morbidity and long-term disability. Although removal of bone is one mechanism leading to bone loss in joints, evidence presented in this grant application demonstrates that there is a suppression of bone formation in affected joints because of inhibition of the maturation and function of bone forming osteoblast cells. The experiments proposed are designed to identify new targets for the augmentation of bone formation at sites of joint-based bone loss in arthritis.