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

在过去的资助期内，我们可以证明遗传缺陷或药理抑制硬化蛋白导致tnfalpha依赖性关节炎小鼠模型（hTNFtg）疾病严重程度的恶化。缺乏硬化蛋白的hTNFtg小鼠或接受硬化蛋白抗体治疗的hTNFtg小鼠表现出关节炎症加剧、软骨丢失和骨质侵蚀。从机制上讲，硬化蛋白有效地阻断了tnf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。阻断似乎涉及LRP6，但独立于典型的wnt信号通路。其他小鼠模型，如G6PI和K/BxN血清转移性关节炎的应用明显表明，硬化蛋白抑制的促病作用依赖于TNF参与关节炎发展的程度。我们在之前的资助期内获得的全部结果强烈表明，硬化蛋白在慢性炎症和炎症性骨质流失中具有迄今未知的保护作用。这些观察结果是至关重要的，因为硬化蛋白抑制剂已被开发用于治疗退行性骨病，抗体介导的硬化蛋白抑制目前正在临床评估用于治疗人类绝经后骨质疏松症。因此，更详细地研究硬化蛋白在炎症性骨质流失中的作用至关重要。该项目的主要目的是验证硬化蛋白对局部骨侵蚀的tnf依赖性发展的一般保护作用。为此，我们将比较各种依赖tnf的小鼠模型（敲除硬化蛋白/抗体处理和硬化蛋白处理）。为了评估缺乏成纤维细胞特异性LRP6是否对骨破坏至关重要，将成纤维细胞特异性条件敲除与相应的关节炎wt和Sost ko以及抗体处理的小鼠进行比较。该项目还将包括鉴定和功能分析滑膜成纤维细胞和成骨细胞中被硬化蛋白抑制的细胞因子通路。此外，sclerostin/LRP6与TNFR或其他细胞因子受体相互作用抑制信号转导的机制将是我们项目的主要方面之一。最后，我们将研究硬化蛋白是否调节细胞因子介导的滑膜成纤维细胞的增殖、迁移、凋亡和侵袭能力，以及成骨细胞的活性和凋亡。

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.