The protective function of the Wnt inhibitor sclerostin in inflammatory bone destruction.

在过去的资助期间，我们可以证明，在肿瘤坏死因子α依赖型关节炎小鼠模型(HTNFtg)中，硬化素的遗传缺陷或药物抑制导致疾病严重程度的恶化。缺乏硬化素或接受硬化素抗体治疗的hTNFtg小鼠表现出关节炎症、软骨丢失和骨质侵蚀。从机制上讲，skerostin有效地阻断了肿瘤坏死因子诱导的信号通路，例如p38、NFkappaB的激活，这是关节炎发展的关键步骤。BLOCKADE似乎涉及LRP6，但不依赖于典型的Wnt信号通路。应用另外的小鼠模型，如G6PI和K/BxN血清转移性关节炎明显表明，硬化素抑制的促病作用依赖于肿瘤坏死因子参与关节炎发展的程度。我们在前一个资助期间获得的全部结果有力地表明，硬化素在慢性炎症和炎症性骨丢失中具有迄今未知的保护作用。这些观察结果具有关键意义，因为硬化素的抑制剂已经被开发用于治疗退行性骨骼疾病，而抗体介导的抑制硬化素目前被用于治疗人类绝经后骨质疏松症的临床评估。因此，更详细地研究硬化素在炎症性骨丢失中的作用是至关重要的。本项目的主要目的是验证硬化素对局部骨侵蚀的肿瘤坏死因子依赖性发展的一般保护作用。为此，我们将比较不同的依赖肿瘤坏死因子的小鼠模型(硬化素基因敲除/抗体治疗和硬化素治疗)。为了评估缺乏成纤维细胞特异性LRP6是否是骨破坏的关键，成纤维细胞特异性条件性基因敲除将与相应的关节炎wt和Sost Ko以及抗体治疗的小鼠进行比较。该项目还将包括对滑膜成纤维细胞和成骨细胞中硬化素抑制的细胞因子通路的鉴定和功能分析。此外，硬化素/LRP6与TNFR或其他细胞因子受体相互作用以抑制信号转导的机制将是我们项目的主要方面之一。最后，我们将研究skerostin是否调节细胞因子对滑膜成纤维细胞的增殖、迁移、凋亡和侵袭能力以及对成骨细胞活性和凋亡的影响。

In the past funding period, we could demonstrate that genetic deficiency or pharmacological inhibition of sclerostin led to a deterioration of disease severity in the TNFalpha-dependent arthritis mouse model (hTNFtg). hTNFtg mice that lack sclerostin or that were treated with sclerostin antibodies displayed enhanced joint inflammation, cartilage loss and bone erosion. Mechanistically, sclerostin effectively blocked TNF-induced signalling pathways, e.g. activation of p38, NFkappaB, key steps in arthritis development. Blockade appeared to involve LRP6 but was independent of the canonical Wnt-signalling pathway. Application of additional mouse models, such as the G6PI and the K/BxN serum transfer arthritis obviously revealed that the disease-promoting effect of sclerostin inhibition is dependent on the magnitide of how TNF participates in arthritis development. Our entire results obtained in the previous funding period, strongly indicates that sclerostin has a so far unknown protective role in chronic inflammation and inflammatory bone loss.These observations are of pivotal importance since inhibitors of sclerostin have been developed for the treatment of degenerative bone diseases and antibody-mediated inhibition of sclerostin is currently evaluated clinically for the treatment of postmenopausal osteoporosis in humans. Thus, it is of critical importance to investigate in more detail the role of sclerostin in inflammatory bone loss.The main objective of this project is the verification of a general protective effect of sclerostin on the TNF-dependent development of local bone erosions. For this purpose, we will compare various TNF-dependent mouse models (sclerostin knockout/antibody-treated and sclerostin-treated). For the assessment whether the lack of fibroblast-specific LRP6 is crucial for bone destruction, fibroblast-specific conditional knockouts will be compared with corresponding arthritic wt and Sost ko as well as with antibody-treated mice. The project will also include the identification and functional analyses of cytokine pathways inhibited by sclerostin in synovial fibroblasts and osteoblasts. Furthermore, the mechanism by which sclerostin/LRP6 interacts with TNFR or other cytokine receptors to inhibit signal transduction will be one of the main aspects of our project. Finally, we will investigate whether sclerostin modulates cytokine-mediated effects on proliferation, migration, apoptosis and invasive capacity of synovial fibroblasts as well as on osteoblast activity and apoptosis.