Acute neuroinflammation induces AIS structural plasticity in a NOX2-dependent manner.
Acute neuroinflammation induces AIS structural plasticity in a NOX2-dependent manner.
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DOI：
10.1186/s12974-017-0889-3
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发表时间：
2017-06-08
影响因子：
9.3
通讯作者：
Dupree JL
中科院分区：
文献类型：
--
作者：
Benusa SD;George NM;Sword BA;DeVries GH;Dupree JL
慢性小胶质细胞介导的炎症和氧化应激是神经退行性疾病中特征明确的潜在因素，其中反应性炎症小胶质细胞会增强活性氧（ROS）的产生并影响神经元的完整性。最近有研究表明，在慢性炎症期间，神经元完整性会因轴突起始段（AIS）受到靶向破坏而受损，轴突起始段是对动作电位起始至关重要的轴突区域。轴突起始段的破坏与包裹它的反应性炎症小胶质细胞的接触有关，这与疾病进展的关联性增加。虽然很明显慢性小胶质细胞炎症和活性氧产生增加会影响神经元完整性，但对于急性小胶质细胞炎症如何影响轴突起始段的稳定性却知之甚少。在此，我们证明急性神经炎症以活性氧介导和钙蛋白酶依赖的方式诱导轴突起始段的结构可塑性。
给C57BL/6J和NOX2 - / - 小鼠单次注射脂多糖（LPS；5mg/kg）或溶媒（0.9%生理盐水，10mL/kg），并在注射后6小时 - 2周进行分析。在LPS注射24小时后开始给予抗炎药物地多昔（Didox；250mg/kg）或溶媒（0.9%生理盐水，10mL/kg），持续5天；在注射后1周对动物进行分析。使用免疫组织化学（IHC）和实时定量聚合酶链反应（RT - qPCR）评估小胶质细胞炎症，并使用锚蛋白G免疫标记对轴突起始段完整性进行定量分析。通过单因素或双因素方差分析对数据进行统计学比较，当均值差异显著时，采用图基（Tukey）事后检验进行评估。
LPS诱导的神经炎症，其特征是小胶质细胞炎症增强以及产生活性氧的酶表达增加，改变了轴突起始段的蛋白质聚集。重要的是，在小胶质细胞炎症消退后，炎症诱导的轴突起始段变化会逆转。即使在轴突起始段发生显著破坏后，使用抗炎药物地多昔调节炎症反应也会提高轴突起始段的恢复速率。实时定量聚合酶链反应和免疫组织化学分析显示，小胶质细胞中产生活性氧的酶NOX2的表达显著增加，这与轴突起始段的破坏相关。此外，NOX2的缺失阻止了炎症诱导的轴突起始段可塑性，这表明活性氧驱动轴突起始段的结构可塑性。
在存在急性小胶质细胞炎症的情况下，轴突起始段会发生一种能够自发恢复的适应性变化。此外，这种恢复可以通过治疗手段加速。总之，这些发现强调了该区域在病理损伤情况下的动态能力，并提供证据表明轴突起始段是一个可行的治疗靶点。
Chronic microglia-mediated inflammation and oxidative stress are well-characterized underlying factors in neurodegenerative disease, whereby reactive inflammatory microglia enhance ROS production and impact neuronal integrity. Recently, it has been shown that during chronic inflammation, neuronal integrity is compromised through targeted disruption of the axon initial segment (AIS), the axonal domain critical for action potential initiation. AIS disruption was associated with contact by reactive inflammatory microglia which wrap around the AIS, increasing association with disease progression. While it is clear that chronic microglial inflammation and enhanced ROS production impact neuronal integrity, little is known about how acute microglial inflammation influences AIS stability. Here, we demonstrate that acute neuroinflammation induces AIS structural plasticity in a ROS-mediated and calpain-dependent manner. C57BL/6J and NOX2−/− mice were given a single injection of lipopolysaccharide (LPS; 5 mg/kg) or vehicle (0.9% saline, 10 mL/kg) and analyzed at 6 h–2 weeks post-injection. Anti-inflammatory Didox (250 mg/kg) or vehicle (0.9% saline, 10 mL/kg) was administered beginning 24 h post-LPS injection and continued for 5 days; animals were analyzed 1 week post-injection. Microglial inflammation was assessed using immunohistochemistry (IHC) and RT-qPCR, and AIS integrity was quantitatively analyzed using ankyrinG immunolabeling. Data were statistically compared by one-way or two-way ANOVA where mean differences were significant as assessed using Tukey’s post hoc analysis. LPS-induced neuroinflammation, characterized by enhanced microglial inflammation and increased expression of ROS-producing enzymes, altered AIS protein clustering. Importantly, inflammation-induced AIS changes were reversed following resolution of microglial inflammation. Modulation of the inflammatory response using anti-inflammatory Didox, even after significant AIS disruption occurred, increased the rate of AIS recovery. qPCR and IHC analysis revealed that expression of microglial NOX2, a ROS-producing enzyme, was significantly increased correlating with AIS disruption. Furthermore, ablation of NOX2 prevented inflammation-induced AIS plasticity, suggesting that ROS drive AIS structural plasticity. In the presence of acute microglial inflammation, the AIS undergoes an adaptive change that is capable of spontaneous recovery. Moreover, recovery can be therapeutically accelerated. Together, these findings underscore the dynamic capabilities of this domain in the presence of a pathological insult and provide evidence that the AIS is a viable therapeutic target.