The Role of Heme Oxygenase 1 and Carbon Monoxide in Erythrophagocytosis

血红素加氧酶 1 和一氧化碳在红细胞吞噬作用中的作用

• 批准号: 285440904
• 负责人: Professor Dr. Nils Schallner
• 金额: --
• 依托单位: Klinik für Anästhesiologie und Intensivmedizin
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2018-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/285440904?language=en
• 关键词: Role; Heme; Oxygenase; Carbon; Monoxide

Subarachnoid hemorrhage (SAH) leads to neuronal injury and cognitive impairment following heme-induced cerebral inflammation resulting from the accumulation of heme-containing blood components. Elimination of heme occurs through the heme oxygenase (HO) enzymes that degrade heme into biliverdin, iron, and carbon monoxide (CO). Induction of the inducible HO-1 isoform exerts strong cytoprotective effects in numerous disease models including the brain. Exogenous application of low doses of CO can recapitulate the cytoprotective effects of HO-1 induction, but only a few reports have examined the protective effects of CO on neuronal cells in vitro and in vivo. In fact, the majority of reports contend that CO is potently neurotoxic. In direct contrast to this dogma, we have recently identified a novel role for the HO-1 isoform in microglia in response to SAH. Our experimental study in mice, isolated primary microglia and human cerebrospinal fluid (CSF) demonstrated that microglial expression of HO-1 is essential in the response to SAH by mediating clearance of blood and eliminating the pro-oxidant heme burden, but also via the generation of the gas CO that in turn regulates erythrophagocytosis. Absence of HO-1 specifically in microglia resulted in increased neuronal injury and worsened functional outcome. Primary microglia lacking HO-1 demonstrated impaired erythrophagocytosis, which in turn increased neuronal cell death in co-culture experiments. In human SAH patients cisternal hematoma volume was associated with elevations in HO-1 expression and activity. The exact mechanisms as to how the HO-1-CO axis modulates erythrophagocytosis by microglia remains to be elucidated. Red cells and the cellular components are recognized by a series of cognate receptors including CD163, CD36 and TLR4. Whether one or more of these receptors is involved in phagocytosis and blood clearance has not been evaluated. AMP-activated protein kinase (AMPK) is involved in phagocytosis. Since we have previously shown that macrophages increase the generation of reactive oxygen species (ROS) in response to CO and ROS-signaling is known to be linked to AMPK-activity, we posit that the ability of endogenous or exogenous CO to enhance RBC-phagocytosis is in part due to a ROS-dependent activation of AMPK. Microglial expression of the scavenger receptor CD36 has been linked to microglial phagocytosis in intracerebral hemorrhage and Alzheimer's disease. We found that CO rapidly increases CD36 expression in microglia and that microglia deficient in HO-1 show low CD36 expression. These preliminary data suggest that HO-1 and CO regulate erythrophagocytosis partly though a CD36 and ROS-dependent AMPK-signaling axis. We would like to further explore this possible link between intracellular ROS-AMPK signaling and CD36 surface expression and determine its role in HO-1/CO-mediated erythrophagocytosis and neuronal outcome after SAH.

蛛网膜下腔出血（SAH）在血红素诱导的脑炎症后导致神经元损伤和认知障碍，这是由含血红素的血液成分积累引起的。血红素的消除是通过血红素加氧酶（HO）将血红素降解为胆绿素、铁和一氧化碳（CO）来实现的。诱导的HO-1异构体在包括脑在内的许多疾病模型中具有很强的细胞保护作用。外源应用低剂量的CO可以概括HO-1诱导的细胞保护作用，但只有少数报道研究了CO对体外和体内神经元细胞的保护作用。事实上，大多数的报告都认为一氧化碳具有强烈的神经毒性。与此相反，我们最近发现了HO-1亚型在小胶质细胞对SAH的反应中的新作用。我们在小鼠、分离的初级小胶质细胞和人脑脊液（CSF）中进行的实验研究表明，HO-1的小胶质表达在SAH反应中是必不可少的，它通过介导血液清除和消除促氧化血红素负担，同时也通过产生气体CO来调节红细胞吞噬。小胶质细胞中特异性HO-1缺失导致神经元损伤加重和功能预后恶化。在共培养实验中，缺乏HO-1的初级小胶质细胞表现出红细胞吞噬功能受损，这反过来增加了神经元细胞的死亡。在人类SAH患者中，池血肿体积与HO-1表达和活性升高有关。HO-1-CO轴如何调节小胶质细胞的红细胞吞噬作用的确切机制仍有待阐明。红细胞及其细胞成分可被一系列同源受体识别，包括CD163、CD36和TLR4。这些受体中的一种或多种是否参与吞噬和血液清除尚未得到评估。amp活化蛋白激酶（AMPK）参与吞噬作用。由于我们之前已经证明巨噬细胞在响应CO时增加活性氧（ROS）的产生，并且已知ROS信号与AMPK活性有关，因此我们假设内源性或外源性CO增强红细胞吞噬的能力部分是由于ROS依赖的AMPK激活。清道夫受体CD36的小胶质表达与脑出血和阿尔茨海默病的小胶质吞噬有关。我们发现CO在小胶质细胞中迅速增加CD36的表达，而HO-1缺失的小胶质细胞CD36的表达较低。这些初步数据表明，HO-1和CO通过CD36和ros依赖的ampk信号轴部分调节红细胞吞噬。我们希望进一步探索细胞内ROS-AMPK信号与CD36表面表达之间的可能联系，并确定其在HO-1/ co介导的红细胞吞噬和SAH后神经元结局中的作用。