Control of macrophage repolarization and regulation of liver inflammation by HIF-1alpha and STAT3

肝脏拥有约80%的全身巨噬细胞，同时也有髓样细胞（如血液单核细胞）巡逻，它们不断地感知病原体相关的分子模式并最终渗透到肝脏。为了避免在健康稳定状态下免疫反应的不良发作，肝脏可以耐受来自完整微生物群的生理内毒素水平。然而，为了使宿主有效防御细菌感染，需要在炎症和免疫耐受之间进行严格的调节。巨噬细胞的激活在这里是一个中心步骤，因为这种细胞类型能够调节免疫耐受和宿主防御之间的转变。我们假设肝脏巨噬细胞在感染期间平衡促炎和抗炎反应以及适当适应炎症反应是由IL-10和肝巨噬细胞中HIF1alpha和STAT3的转录调控控制的。我们提出，即使存在病原体相关模式，循环单核细胞释放的IL-10也能够触发肝巨噬细胞从促炎到抗炎的极化转变。在由此产生的巨噬细胞中间极化表型中，转录调节因子HIF-1alpha和STAT3被认为通过在氧化呼吸和糖酵解之间切换来控制炎症反应，以促进适当的宿主防御，避免过度炎症和相关的肝组织损伤。我们正计划在最近建立的人类肝类器官模型中研究提出的机制。该模型被证明可以模拟炎症相关的肝功能障碍以及巨噬细胞相关的组织修复，能够在炎症期间恢复肝脏类器官功能。我们将通过小分子抑制剂和siRNA敲低HIF1alpha和STAT3特异性靶向所提出的信号通路的定义事件，并在类器官模型中表征LPS刺激后的细胞因子释放和细菌吞噬能力。在骨髓特异性敲除hif -1 α和STAT3的脓毒症小鼠模型中，我们随后将使用金黄色葡萄球菌和多微生物腹膜污染和感染（PCI）的两种更复杂的感染模型验证我们的体外研究结果。识别控制巨噬细胞相关炎症的关键调节蛋白将提高我们对炎症相关肝功能障碍的理解，并为感染性肝病治疗的新靶向策略铺平道路。

The liver harbours ~80% of all body macrophages and is also patrolled by myeloid cells such as blood monocytes, that continuously sense for pathogen-associated molecular patterns and eventually infiltrate into the liver. To avoid the adverse onset of immune responses under healthy steady state conditions physiological endotoxins levels derived from an intact microbiota are tolerated by the liver. However, to enable an efficient host defence to bacterial infection a tight regulation between inflammation and immunotolerance is needed. Activation of macrophage is herein a central step as this cell type is able to modulate the transitions between immunotolerance and host defence. We hypothesize that balancing pro- and anti-inflammatory responses of liver resident macrophages and an appropriate adaption of the inflammatory response during infection is controlled by IL-10 and transcriptional regulation by HIF1alpha and STAT3 in liver resident macrophages. We propose that IL-10 released by circulating monocytes is able to trigger a polarization shift of liver resident macrophages from a pro-inflammatory to an anti-inflammatory stage even in presence of pathogen associated patterns. In the resulting intermediate macrophage polarization phenotype the transcriptional regulators HIF-1alpha and STAT3 are proposed to control the inflammatory response by switching between oxidative respiration and glycolysis in order to facilitate an appropriate host defence and to avoid exaggerated inflammation and related liver tissue damage. We are planning to study the proposed mechanisms in a recently established human liver organoid model. This model was shown to mimic inflammation-related liver dysfunction as well as macrophage-related tissue repair that is able to restore liver organoid functionality during inflammation. We will specifically target defined events of the proposed signalling pathways by small molecule inhibitors and siRNA knock down of HIF1alpha and STAT3 and characterize cytokine release and bacterial phagocytosis ability after LPS stimulation in the organoid model. In mouse models of sepsis with a myeloid-specific knock-down of HIF-1alpha and STAT3 we will then subsequently verify our in vitro findings using the two more complex infection models with Staphylococcus aureus and polymicrobial peritoneal contamination and infection (PCI).The identification of key regulator proteins that control macrophage-associated inflammation will improve our understanding of inflammation-related liver dysfunction and could pave the way for new targeted strategies for the treatment of infectious liver disease.