Inhibition of damage-mediated interleukin-1β and interleukin-18 secretion by short chain fatty acids (SCFAs)

细胞外三磷酸腺苷是细胞损伤的危险信号，可诱导单核细胞、巨噬细胞和上皮细胞分泌促炎细胞因子白介素1β(IL-1β)和IL-18。这些细胞因子在宿主对病原体的防御中起着至关重要的作用。然而，细胞因子释放的增加和失控是全身炎症的发病机制之一，全身炎症是严重创伤、大手术或缺血/再灌注损伤后常见的威胁生命的并发症。由于目前没有有效的治疗方法，患者的死亡率仍然高得令人无法接受。因此，开发一种治疗方法来控制损伤介导的细胞因子的释放，同时避免对感染的防御，是非常有临床意义的。本项目旨在研究一种由短链脂肪酸(SCFA)激活、抑制三磷酸腺苷介导的IL-1β和IL-18释放的抗炎机制。单链脂肪酸是由某些肠道细菌在碳水化合物发酵过程中产生和分泌的。在未发表的先导实验中，SCFA和合成的SCFA受体激动剂有效地抑制了三磷酸腺苷诱导的单核细胞、巨噬细胞和结肠上皮细胞释放IL-1β和IL-18，但不能阻止细菌毒素对三磷酸腺苷非依赖性细胞因子的释放。令人惊讶的是，这种抗炎作用似乎是由SCFA受体和烟碱型乙酰胆碱受体(NAChRs)共同介导的。从传统观点来看，nAChRs的功能是配体门控离子通道，允许神经传递。然而，在以前的研究中，我能够证明，单核细胞中nAChRs的激活诱导了一条代谢性、抗炎的信号转导途径。我假设这也适用于SCFA。这为损伤介导的无菌炎症提供了一种全新的治疗方法。本项目的目的是阐明：1.单链脂肪酸是否抑制原代培养的人单核细胞、巨噬细胞和结肠上皮细胞的炎性小体激活和细胞因子的释放；2.将单链脂肪酸的存在转化为nAChRs的代谢性信号以抑制ATP诱导的细胞因子释放的信号转导途径；3.该机制是否在体内活跃，从而有可能进入临床预防无菌炎症的领域。该项目将描述一种新的SCFA诱导的抗炎机制，并将在体内测试其有效性。该项目取得的成果将为无菌全身炎症开辟新的开创性治疗方案。此外，该项目旨在为临床导向的后续项目创造基础。

Extracellular ATP serves as a ”danger signal” indicating cell damage and induces the secretion of the pro-inflammatory cytokines interleukin-1β (IL-1β) and IL-18 by monocytes, macrophages and epithelial cells. These cytokines play a crucial role in host defense against pathogens. An increased and uncontrolled cytokine release, however, contributes to the pathogenesis of systemic inflammation, a frequent and life-threatening complication after severe trauma, major surgery, or ischemia/reperfusion injury. Because no effective therapies are currently available, the mortality in patients is still unacceptably high. Therefore, it is of high clinical interest to develop therapeutic approaches that control the damage-mediated cytokine-release while sparing defense against infections. This project aims to characterize an anti-inflammatory mechanism activated by short chain fatty acids (SCFAs) that inhibits the ATP-mediated release of IL-1β and IL-18. SCFAs are produced and secreted by certain gut bacteria during fermentation of carbohydrates. In unpublished pilot experiments, SCFAs and synthetic agonists of the SCFA receptors efficiently inhibited the ATP-induced IL-1β and IL-18 release by monocytes, macrophages and colon epithelial cells but did not prevent ATP-independent cytokine release in response to a bacterial toxin. Surprisingly, this anti-inflammatory effect seems to be mediated by both, SCFA receptors and nicotinic acetylcholine receptors (nAChRs). From the traditional view, nAChRs function as ligand-gated ion channels allowing neurotransmission. In previous studies, however, I was able to show, that activation of nAChRs in monocytes induces a metabotropic, anti-inflammatory signal transduction pathway. I assume that this also applies to SCFAs. This results in a completely new therapeutic approach for damage-mediated sterile inflammation. The aims of this project are to elucidate: 1. if SCFAs inhibit the ATP-induced inflammasome activation and cytokine release in primary human monocytes, macrophages, and colonic epithelial cells; 2. the signal transduction pathways translating the presence of SCFAs into a metabotropic signal at nAChRs to inhibit ATP-induced cytokine-release; 3. if this mechanism is active in vivo and, thus, has the potential to enter the clinical arena for the prevention of sterile inflammation. This project will characterize a novel SCFA-induced anti-inflammatory mechanism and will test its effectiveness in vivo. The results obtained within this project will open new pioneering therapeutic options for sterile, systemic inflammation. Moreover, this project is intended to create the basis for a clinically oriented follow-up project.