Role of the terminal complement complex in intervertebral disc degeneration

慢性腰痛是人类最常见的健康问题之一，经常与椎间盘（IVD）的退行性变化有关。除了年龄、机械负荷和遗传易感性等危险因素外，椎间盘或邻近终板的损伤也可能引发退行性变。到目前为止，很少有人知道补体系统可能参与IVD变性。针对该主题的唯一一项研究报告了退行性IVD中的末端补体复合物（TCC，C5 b-9）沉积，但正常IVD中没有。补体系统的激活由各种触发物引发，已知其中几种（免疫复合物、特异性基质组分/片段、晶体沉积、组织蛋白酶D）与椎间盘退变相关。我们可以证实TCC在人类退变的IVD中的沉积，特别是在髓核的细胞簇中。因此，该项目的中心假设，即补体系统，特别是TCC，在IVD变性的发展和/或进展中起相关作用是有充分依据的。通过使用先前在体外测定中建立的临床组织样品和不能形成TCC的C6缺陷兔模型，应解决以下中心问题：1）TCC是否在椎间盘退变中起中心作用，2）何种机制导致IVD中的补体激活，以及3）IVD细胞中TCC形成诱导了何种细胞生物学后果。在转化方法中，将确定IVD组织中补体组分、活化产物和调节剂的存在，并将其与不同的临床情况相关联。将阐明IVD细胞中补体成分或调节剂的表达是否受到退行性椎间盘中存在的促炎环境的影响。将使用用于TCC形成的基于IVD细胞的ELISA来研究致病因子对TCC活化的贡献。此外，将在体外表征由IVD细胞中TCC形成诱导的分子过程以及TCC形成的药理学抑制的治疗效果。C6缺陷兔代表了一个独特的模型，以测试TCC形成和创伤诱导的IVD变性的因果关系。这将通过一项动物研究来实现，该研究包括在具有相同遗传背景的C6充足和C6缺陷兔中进行IVD穿刺和终板钻孔。总的来说，该项目的结果将导致更好地了解IVD变性的发病机制，并可能为新的治疗策略定义分子基础。

Chronic low back pain is one of the most common human health problems and frequently associated with degenerative changes of the intervertebral disc (IVD). Besides the risk factors age, mechanical loading and genetic predisposition injuries of the IVD or adjacent endplates can initiate the degenerative process. So far, little is known about a possible involvement of the complement system in IVD degeneration. The only study addressing this topic reported a deposition of the terminal complement complex (TCC, C5b-9) in degenerated but not in normal IVDs. Activation of the complement system is initiated by various triggers, several of which (immune complexes, specific matrix components/fragments, crystal depositions, cathepsin D) are known to be associated with disc degeneration. We could confirm the deposition of TCC in human degenerated IVDs especially in cell clusters of the nucleus pulposus. Thus, the central hypothesis of the project, that the complement system, especially the TCC, plays a relevant role in the development and/or progression of IVD-degeneration is well founded. By the use of clinical tissue samples, previously established in vitro-assays and a C6-deficient rabbit model which cannot form the TCC the central questions 1) whether the TCC plays a central role in disc degeneration, 2) which mechanisms lead to complement activation in the IVD and 3) which cell-biologic consequences are induced by TCC-formation in IVD-cells shall be addressed. In a translational approach, the presence of complement components, activation products and regulators in IVD tissue will be determined and correlated to different clinical situations. It will be clarified if the expression of complement components or regulators in IVD-cells is influenced by a pro-inflammatory milieu present in degenerated discs. An IVD-cell-based ELISA for TCC-formation will be used to study the contribution of pathogenic factors to the activation of TCC. Furthermore, the molecular processes induced by TCC-formation in IVD-cells as well as therapeutic effects of pharmacological inhibition of TCC-formation will be characterized in vitro. The C6-deficient rabbit represents a unique model to test for a causal relationship of TCC-formation and trauma-induced IVD-degeneration. This will be achieved by an animal study comprising IVD-puncture and endplate drilling in C6-sufficient and -deficient rabbits of identical genetic background. Overall, the results of the project will lead to a better understanding of the pathogenesis of IVD-degeneration and might define the molecular basis for new therapeutic strategies.