Role of the terminal complement complex in intervertebral disc degeneration

慢性下腰痛是最常见的人类健康问题之一，常与椎间盘退行性变(IVD)相关。除了年龄、机械负荷和遗传易感性损伤等危险因素外，IVD或邻近终板的遗传易感性损伤也可启动退变过程。到目前为止，对于补体系统在IVD退变中的可能参与还知之甚少。唯一一项针对这一主题的研究报告了变性的IVD中有末端补体复合体(TCC，C5b-9)的沉积，但在正常的IVD中没有。补体系统的激活是由各种触发因素启动的，其中几种(免疫复合物、特定的基质成分/片段、晶体沉积、组织蛋白酶D)已知与椎间盘退变有关。我们可以证实TCC在退行性IVD中的沉积，特别是在髓核的细胞团中。因此，该项目的中心假设，即补体系统，特别是TCC，在IVD退行性变的发生和/或进展中发挥着相关的作用是有根据的。通过使用临床组织标本，先前建立的体外分析和不能形成TCC的C6缺乏的兔模型，中心问题1)TCC是否在椎间盘退变中起中心作用，2)在IVD中导致补体激活的机制，以及3)IVD细胞中TCC的形成导致了哪些细胞生物学后果。在翻译方法中，将确定IVD组织中补体成分、激活产物和调节因子的存在，并将其与不同的临床情况相关联。IVD细胞中补体成分或调节因子的表达是否受到退变椎间盘中存在的促炎环境的影响将得到澄清。以IVD细胞为基础的TCC形成的ELISA法将被用来研究致病因素对TCC激活的贡献。此外，还将在体外研究IVD细胞中TCC形成的分子过程以及药物抑制TCC形成的治疗效果。C6缺乏的兔代表了一种独特的模型来测试TCC形成和创伤诱导的IVD变性之间的因果关系。这将通过一项动物研究来实现，该研究包括对遗传背景相同的C6充足和缺乏的兔子进行IVD穿刺术和终板钻孔。总体而言，该项目的结果将有助于更好地了解IVD变性的发病机制，并可能为新的治疗策略确定分子基础。

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.