Analysis of the roles of the Wnt-ligands Wnt9a and Wnt4 in adult bone and joint homeostasis

骨质疏松症（OP）和骨关节炎（OA）是退行性肌肉骨骼疾病，具有非常高的患病率。它主要发生在老年人身上。骨质疏松症的特征是：骨矿物质密度降低，骨丢失和骨脆性增加。OA也与骨改变有关。在这里，主要是在疾病过程中发生变化的软骨下骨。在早期OA中，软骨下骨的骨转换增加，而软骨下骨增厚是晚期OA的特征。因此，通常用于治疗OP的药物，如抗催化作用的双膦酸盐和合成代谢活性的特立帕肽，已经在OA动物模型中测试了潜在的有益作用。这些研究表明，这些药物可以改变疾病的进展。Wnt-配体，其中包括Wnt 9a和Wnt 4，以及Wnt信号传导途径的成员已经被暗示在OP和OA中发挥作用。在这里提出的项目中，我们将使用不同的条件性敲除方法来研究Wnt 9a和Wnt 4在小鼠成年骨和关节稳态中的作用。肢体间充质中Wnt 9a的缺失导致老年小鼠关节中自发性OA样变化的发展。在肢体间充质中Wnt 4的额外损失后，这些变化的发生加速。除了关节改变，我们还观察到骨的改变，并不局限于软骨下区域。在拟议的项目中，我们希望完成Wnt 9a缺失以及肢体间充质中Wnt 9a和Wnt 4的联合缺失后肌肉骨骼改变的表型表征。两种Wnt配体都是由关节中的细胞以及成骨细胞产生的。因此，为了在表型上区分不同细胞/组织对所观察到的骨骼改变的贡献，我们想要使用Prg 4-Cre系在浅表软骨细胞中和使用Osx-Cre系在成骨细胞前体中检查出生后Wnt 9a或Wnt 4缺失后的表型变化。使用体内和体外的方法，我们希望回答的问题，这两个Wnt-配体在成骨细胞，关节软骨细胞和滑膜细胞中使用的信号通路，以及这些Wnt-配体或不同的细胞类型之间是否有所不同。此外，我们希望产生在浅表关节软骨细胞中表达增加水平的转基因小鼠，以观察这是否对手术诱导的OA模型中的OA进展具有有益作用。

Osteoporosis (OP) and osteoarthritis (OA) are degenerative musculoskeletal diseases with a very high prevalence. They occur primarily in elderly people. The hallmarks of osteoporosis are: decreased bone mineral density, loss of bone and increased bone fragility. OA is also associated with bone alterations. Here, it is primarily the subchondral bone that changes during the course of the disease. In early OA, bone turnover is increased in the subchondral bone, while subchondral bone thickening is a characteristic feature of late OA. As such, drugs, such as the anti catalytically acting bisphosphonates and the anabolically active Teriparatide, which are normally used to treat OP, have been tested in OA animal models for potential beneficial effects. These studies showed that these drugs can alter disease progression. Wnt-ligands, amongst them Wnt9a and Wnt4, and members of Wnt signaling pathways have been implicated to play roles in OP and OA. In the project proposed here, we will examine the roles of Wnt9a and Wnt4 in adult bone and joint-homeostasis of the mouse using different conditional knockout approaches. The loss of Wnt9a in the limb mesenchyme results in the development of spontaneous OA-like changes in the joints of aged mice. The onset of these changes is accelerated upon additional loss of Wnt4 in the limb mesenchyme. In addition to the joint alterations, we observed alterations in the bone, which are not restricted to the subchondral region. In the proposed project we want to complete the phenotypic characterization of the musculoskeletal alterations upon loss of Wnt9a and the combined loss of Wnt9a and Wnt4 in the limb mesenchyme. Both Wnt-ligands are produced by cells in the joint as well as by osteoblasts. Hence, in order to phenotypically distinguish between the contribution of the different cells / tissues to the observed skeletal alterations we want to examine the phenotypic changes after postnatal deletion of Wnt9a or Wnt4 in superficial chondrocytes using the Prg4-Cre line and in osteoblast precursors using the Osx-Cre line. Using in vivo and in vitro approaches, we expect to answer the questions which signaling pathways are used by the two Wnt-ligands in osteoblasts, articular chondrocytes, and synoviocytes and whether these differ between the Wnt-ligands or the different cell types. In addition, we want to generate transgenic mice expressing increased levels in superficial articular chondrocytes to see whether this has a beneficial effect on OA-progression in a surgically induced model of OA.