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）是发病率很高的退行性肌肉骨骼疾病。它们主要发生在老年人身上。骨质疏松症的特征是：骨密度降低，骨质流失，骨骼脆性增加。骨性关节炎也与骨改变有关。这里，主要是软骨下骨在疾病过程中发生变化。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的抗催化双膦酸盐和具有合成代谢活性的特立帕肽等药物已在OA动物模型中进行了潜在有益效果的测试。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Wnt9a和Wnt4，以及Wnt信号通路的成员在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敲除方法来研究Wnt9a和Wnt4在小鼠成年骨和关节稳态中的作用。肢体间质中Wnt9a的缺失导致老年小鼠关节发生自发的oa样变化。肢体间质中Wnt4的额外丢失会加速这些变化的发生。除了关节改变外，我们还观察到骨的改变，这些改变并不局限于软骨下区域。在本项目中，我们希望完成Wnt9a缺失以及肢体间质中Wnt9a和Wnt4联合缺失后肌肉骨骼改变的表型表征。这两种wnt配体都由关节细胞和成骨细胞产生。因此，为了从表型上区分不同细胞/组织对观察到的骨骼改变的贡献，我们希望使用Prg4-Cre系和Osx-Cre系来检查出生后表面层软骨细胞中Wnt9a或Wnt4缺失后的表型变化。通过体内和体外方法，我们希望回答以下问题：两种wnt配体在成骨细胞、关节软骨细胞和滑膜细胞中使用哪些信号通路，以及这些信号通路在wnt配体或不同细胞类型之间是否存在差异。此外，我们希望产生表达浅薄关节软骨细胞水平增加的转基因小鼠，以观察这是否对手术诱导的OA模型中的OA进展有有益影响。

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.