Role of purinergic signalling in the immunopathogenesis of pneumococcal meningitis

肺炎球菌脑膜炎是成人中最常见和最严重的细菌性脑膜炎。即使在最好的医疗条件下，15%至20%的患者死于这种疾病，多达三分之一的幸存者仍有神经缺陷。这些神经后遗症反映了不同大脑结构的结构性损伤。这种脑损伤被认为主要是由大规模的中性粒细胞炎症反应引起的，即使在几个小时内完成脑脊液的完全消毒，抗生素治疗几天后也只会很少地改善这种反应。我们假设，炎症消退的延迟--至少部分是--是一个恶性循环的结果，在这个恶性循环中，炎症诱导的细胞损伤导致内源性警报的释放，从而驱动炎症反应，造成进一步的损害。虽然现在有一个快速增长的警报列表在文献中，细胞外ATP(EATP)属于该分子家族中特征最好的成员。在最近的初步实验中，我们的团队已经获得证据表明，[i]不同类型的细胞在暴露于肺炎球菌时将ATP释放到细胞外空间，[ii]eATP有助于肺炎球菌刺激的巨噬细胞产生IL-1β，这是肺炎球菌脑膜炎的重要免疫调节因子。此外，对小鼠大脑的Pilot基因表达分析表明，在肺炎球菌脑膜炎的过程中，嘌呤受体的表达发生了深刻的变化。本研究的重点是研究eATP和嘌呤能信号在肺炎球菌脑膜炎发病机制中的作用。大多数实验将使用我们成熟的小鼠模型进行，该模型非常接近于人类肺炎球菌脑膜炎的临床、免疫学和神经病理学特征。更详细地说，我们计划在小鼠模型和细胞培养系统中确定ATP的细胞来源和释放机制。接下来，将在小鼠模型中研究嘌呤受体的蛋白质表达模式。最后，我们计划通过使用选择性拮抗剂以及缺乏特定嘌呤受体的小鼠来评估eATP和ATP相关信号在宿主防御、免疫调节和颅内并发症(脑损伤)的发展中的功能意义和作用模式。我们认为，这一研究项目将显著提高我们对中枢神经系统免疫调节机制的认识，从而为肺炎球菌脑膜炎的辅助治疗揭示新的靶点。

Pneumococcal meningitis is the most common and most serious form of bacterial meningitis in adults. Even under best medical care, 15 - 20 per cent of patients die of the disease and up to one third of survivors retain neurologic deficits. These neurologic sequelae reflect structural injury to diverse brain structures. This brain injury is thought to be largely caused by the massive neutrophilic inflammatory reaction which is only little modified by antibiotic therapy over days even though complete CSF sterilization occurs within hours. We hypothesized that the delay in resolution of inflammation is - at least partly - the consequence of a vicious cycle in which inflammation-induced cell injury leads to the release of endogenous alarmins that drive the inflammatory response, causing further damage. While there is now a rapidly growing list of alarmins in the literature, extracellular ATP (eATP) belongs to the best characterized members of this molecule family. In recent pilot experiments, our group has obtained evidence that [i] diverse cell types release ATP into the extracellular space upon exposure to pneumococci, and [ii] eATP contributes to the production of interleukin-1beta, an important immune regulator in pneumococcal meningitis, by pneumococci-stimulated macrophages. Moreover, a pilot gene expression analysis of mouse brains has suggested that profound alterations in purinoceptor expression occur during the course of pneumococcal meningitis. The focus of this research proposal is to characterize the function of eATP and purinergic signalling in the pathogenesis of pneumococcal meningitis. Most experiments will be done using our well-established mouse model which closely mimics the clinical, immunological, and neuropathological features of human pneumococcal meningitis. More in detail, we plan to identify the cellular sources and release mechanisms of ATP in the mouse model as well as in cell culture systems. Next, the protein expression pattern of purinoceptors shall be investigated in the mouse model. Finally, we plan to assess the functional significance and the modes of action of eATP and ATP-related signalling in the host defense, immune regulation, and the development of intracranial complications (brain injury) by using selective antagonists as well as mice lacking specific purinoceptors. In our opinion, this research project will markedly improve our knowledge about the mechanisms of the immunoregulation within the central nervous system, thereby revealing new targets for adjuvant therapy of pneumococcal meningitis.