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

类风湿关节炎(RA)是一种以慢性炎症、滑膜增生、进行性软骨破坏和骨侵蚀为特征的炎性关节炎的原型。在最近发表的一项研究中，我们描述了慢性炎症导致关节炎滑膜组织中Myostatin的上调，并且myostatin的缺乏或药物抑制显著改善了关节炎小鼠的疾病严重程度，特别是骨侵蚀和血管疙瘩的形成。此外，我们最近发现，与肌肉抑制素一样，转化生长因子家族的另一个成员，即激活素A，也能刺激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会导致炎症和骨质破坏减少。因此，同时抑制肌肉生长抑素和激活素A，不仅可以阻断破骨细胞的发育、巨噬细胞的激活和成纤维细胞的增殖，还可以促进骨形成，从而为RA关节破坏的治疗提供了一种强有力的工具。在这种情况下，一种既能结合又能拮抗肌肉生长抑素和激活素的蛋白质是天然存在的拮抗剂卵泡抑素，实际上是一种重组修饰的卵泡抑素(FstΔHBs-MFC)，已被证明具有有效阻断肌肉生长抑素和激活素信号的能力。此外，除了直接阻断肌肉生长抑素和激活素外，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。与此相一致的是，一种针对Acvr2a/Acvr2b的双特异性抗体被证明有助于完全阻断肌肉生长抑素或激活素A的信号反应。考虑到FstΔHBs-MFC和抗Acvr2a/2b抗体的抑制特性，我们希望在不同的RA小鼠模型中测试这些因素对减轻炎性关节破坏的有效性。在本项目中，我们建议研究和比较FSTAcvr2a/b双特异性抗体对慢性(HTNFtg)和急性(K/BxN血清转移)关节炎模型的软骨和骨侵蚀、血管疙瘩形成、细胞因子和趋化因子的产生以及免疫细胞的渗透的影响。此外，研究这两种抑制物和表达的Δ对破骨细胞和成骨细胞分化的影响以及对FLS侵袭行为本身的影响是我们体外研究的重点。在这方面，关节炎FLS、成骨细胞和骨髓基质细胞的条件培养实验将为了解旁分泌肌肉抑制素/激活素对破骨细胞和成骨细胞发育的影响提供深入的认识。对FLS的黏附、增殖、迁移和侵袭的功能分析应该提供详细的信息，说明激活的FLS同时抑制血管疙瘩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.