Efficacy of simultaneous blockade of myostatin and activin on the inhibition of joint destruction in experimental arthritis

类风湿关节炎（RA）是一种炎症性关节炎的原型，其特征是慢性炎症、滑膜增生、进行性软骨破坏和骨侵蚀。在最近发表的一篇文章中，我们描述了慢性炎症导致关节炎滑膜组织中肌肉生长抑制素的上调，肌肉生长抑制素的缺乏或药物抑制可极大地改善疾病的严重程度，特别是关节炎小鼠的骨侵蚀和肿块形成。此外，我们最近发现，与肌生长抑制素一样，TGF-ß家族的另一成员激活素A刺激rankl诱导的破骨细胞分化并抑制成骨细胞分化。此外，缺乏激活素A会减少炎症和骨骼破坏。总之，肌肉生长抑制素和激活素似乎都是关节炎发展和相关关节破坏的关键因素。因此，同时抑制肌生长抑制素和激活素A，既阻断破骨细胞发育、巨噬细胞活化和成纤维细胞（FLS）增殖，又促进骨形成，可能是治疗RA关节破坏的有力工具。在这种情况下，一种能够结合和拮抗肌生长抑制素和激活素的蛋白质是天然存在的拮抗剂卵泡listatin (FST)，事实上，重组修饰的FST （FSTΔHBS-mFc）已被证明具有有效阻断肌生长抑制素和激活素信号传导的能力。此外，除了直接阻断肌生长抑制素和激活素外，还可以通过靶向相应的受体从而抑制受体与配体的结合来实现抑制。与此一致，针对Acvr2a/ Acvr2b的双特异性抗体已被证明可以促进完全阻断肌生长抑制素-或激活素a信号反应。考虑到FSTΔHBS-mFc和抗acvr2a /2b抗体的抑制特性，我们想在各种RA小鼠模型中测试这些因素对改善炎症性关节破坏的功效。在本项目中，我们拟研究和比较FSTΔHBS和双特异性抗acvr2a /b抗体在慢性（hTNFtg）和急性（K/BxN血清转移）关节炎模型中对软骨和骨侵蚀、pannus形成、细胞因子和趋化因子产生和免疫细胞浸润的影响。此外，研究这两种抑制剂以及FLS表达的FST对破骨细胞和成骨细胞分化以及FLS攻击行为本身的影响是我们体外研究的重点。在这方面，对关节炎FLS、成骨细胞和bmm的条件培养基实验将提供关于旁分泌肌生成抑制素/激活素对破骨细胞和成骨细胞发育的影响的见解。通过对FLS粘附、增殖、迁移和侵袭的功能分析，可以详细了解激活FLS同时抑制肠膜形成和软骨降解的有效性。

Rheumatoid arthritis (RA) is the prototype of an inflammatory arthritis that is characterized by chronic inflammation, synovial hyperplasia, progressive cartilage destruction and bone erosion. In a recently published work, we described that chronic inflammation leads to an upregulation of myostatin in arthritic synovial tissues and that deficiency or pharmacological inhibition of myostatin highly ameliorates disease severity and in particular bone erosion and pannus formation in arthritic mice. Additionally, we could recently show that like myostatin, another member of the TGF-ß family namely activin A stimulates RANKL-induced osteoclast differentiation and inhibits osteoblast differentiation. Moreover, deficiency of activin A leads to decreased inflammation and bone destruction. Altogether, both myostatin and activin appear to be key players in arthritis development and associated joint destruction.Therefore, inhibiting myostatin and activin A simultaneously, thereby blocking not only osteoclast development, macrophage activation and fibroblast (FLS) proliferation but also promoting bone formation, may provide a powerful tool for the treatment of joint destruction in RA.In this context, a protein which is able to bind and antagonize myostatin as well as activin is the natural occuring antagonist follistatin (FST) and indeed a recombinant modified FST (FSTΔHBS-mFc) has been shown to have the capability to effectively block myostatin as well as activin signaling. Moreover, besides blocking myostatin and activin directly, inhibition could also be achieved by targeting the corresponding receptors thereby inhibiting receptor-ligand binding. In line with this, a dual-specific antibody against Acvr2a/ Acvr2b has been shown to facilitate a complete blockade of the myostatin- or activin A signaling response.Taking the inhibitory properties of FSTΔHBS-mFc and anti-Acvr2a/2b antibody into account, we want to test the efficacy of these factors to ameliorate inflammatory joint destruction in various mouse models of RA. In the present project, we proposed to study and compare the effects of FSTΔHBS and the dual-specific anti-Acvr2a/b antibody on cartilage and bone erosion, pannus formation, cytokine and chemokine production and immune cell infiltration in a chronic (hTNFtg) as well as an acute (K/BxN serum transfer) arthritis model.Moreover, investigating the impact of both inhibitors as well as FLS-expressed FST on osteoclast and osteoblast differentiation and on FLS aggressive behavior itself is focus of our in vitro studies. In this regard, conditioned media experiments with arthritic FLS, osteoblasts and BMMs will provide insights into the impact of paracrine myostatin/ activin on osteoclast and osteoblast development. Functional assays on FLS adhesion, proliferation, migration and invasion should provide detailed information about the effectiveness of simultaneous inhibition on pannus formation and cartilage degradation by activated FLS.