BACKGROUND Sepsis-associated acute brain inflammation, if unresolved, may cause chronic neuroinflammation and resultant neurodegenerative diseases. However, little is known how the transition from acute to chronic neuroinflammation, which is critical for the following progressive neurodegeneration, occurs in sepsis. The goal of this study was to investigate potential immune factors regulating the transition process using a widely used endotoxemia LPS mouse model. This model shows distinct acute and chronic phases of neuroinflammation and recapitulates many cardinal features of Parkinson's disease, thus, providing a unique opportunity for studying phase transition of neuroinflammation. METHODS C57BL/6 J, NLRP3-/-, and IL-1R1-/- mice were employed. Mild and severe endotoxemia were produced by LPS ip injection at 1 or 5 mg/kg. Neuroinflammation in vitro and in vivo was assessed with proinflammatory cytokine expression by qPCR or ELISA and microglial activation by immunohistochemical analysis. Neurodegeneration was measured by manual and stereological counts of nigral dopaminergic neurons and immunohistochemical analysis of protein nitrosylation and α-synuclein phosphorylation. RESULTS LPS-elicited initial increases in mouse brain mRNA levels of TNFα, IL-6, IL-1β, and MCP-1, and nigral microglial activation were not dose-related. By contrast, the delayed increase in brain mature IL-1β levels was dependent on LPS doses and protracted nigral microglial activation was only observed in high dose of LPS-treated mice. LPS-elicited increase in brain mature IL-1β but not IL-1α level was NLRP3-dependent. After high dose LPS treatment, deficiency of NLRP3 or IL-1R1 did not prevent the initiation of acute neuroinflammation but abolished chronic neuroinflammation. Genetic or pharmacological inhibition of the NLRP3-IL-1β axis repressed LPS-stimulated upregulation of chronic neuroinflammatory mediators including MHC-II, NOX2, and Mac1, and protected dopaminergic neurons. Ten months after LPS-elicited severe endotoxemia, nigral persisted microglial activation, elevated nitrosylated proteins and phosphorylated α-synuclein, and significant neuronal degeneration developed in wild-type mice but not in NLRP3-/- or IL-1R1-/- mice. CONCLUSIONS This study uncovers a novel role of the NLRP3-IL-1β signaling pathway in gauging the severity of sepsis-associated inflammation and determining whether acute neuroinflammation will resolve or transition to low grade chronic neuroinflammation. These findings also provide novel targets for developing therapy for severe systemic infection-related neurodegeneration.

中文翻译：

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NLRP3 生成的 IL-1β 在外周脂多糖引起的神经炎症的急性-慢性转变中的新作用：对脓毒症相关神经变性的影响。


背景技术脓毒症相关的急性脑部炎症如果得不到解决，可能会导致慢性神经炎症和由此产生的神经退行性疾病。然而，很少有人知道脓毒症中从急性到慢性神经炎症的转变是如何发生的，这对于随后的进行性神经变性至关重要。本研究的目的是使用广泛使用的内毒素血症 LPS 小鼠模型来研究调节转变过程的潜在免疫因素。该模型显示了神经炎症的不同急性和慢性阶段，并概括了帕金森病的许多主要特征，因此为研究神经炎症的相变提供了独特的机会。方法使用C57BL/6 J、NLRP3-/-和IL-1R1-/-小鼠。腹膜内注射 1 或 5 mg/kg LPS 可产生轻度和重度内毒素血症。通过 qPCR 或 ELISA 评估促炎细胞因子的表达，并通过免疫组织化学分析评估小胶质细胞的活化，从而评估体外和体内的神经炎症。通过黑质多巴胺能神经元的手动和体视计数以及蛋白质亚硝基化和α-突触核蛋白磷酸化的免疫组织化学分析来测量神经变性。结果 LPS 引起小鼠脑中 TNFα、IL-6、IL-1β 和 MCP-1 mRNA 水平的初始增加，并且黑质小胶质细胞激活与剂量无关。相比之下，大脑成熟IL-1β水平的延迟增加取决于LPS剂量，并且仅在高剂量LPS​​处理的小鼠中观察到延长的黑质小胶质细胞激活。 LPS 引起大脑成熟 IL-1β 水平的增加，但不增加 IL-1α 水平，这是 NLRP3 依赖性的。高剂量LPS​​治疗后，NLRP3或IL-1R1的缺乏并不能阻止急性神经炎症的发生，但可以消除慢性神经炎症。 NLRP3-IL-1β轴的遗传或药理学抑制可抑制LPS刺激的慢性神经炎症介质（包括MHC-II、NOX2和Mac1）的上调，并保护多巴胺能神经元。 LPS引发严重内毒素血症十个月后，野生型小鼠中黑质持续小胶质细胞激活，亚硝基化蛋白和磷酸化α-突触核蛋白升高，并出现显着的神经元变性，但NLRP3-/-或IL-1R1-/-小鼠中则没有。结论 这项研究揭示了 NLRP3-IL-1β 信号通路在衡量脓毒症相关炎症的严重程度以及确定急性神经炎症是否会消退或转变为低度慢性神经炎症方面的新作用。这些发现还为开发严重全身感染相关神经变性的治疗方法提供了新的靶点。