Laboratory of Neurobiology, Centro de Investigacion Príncipe Felipe, Eduardo Primo Yufera 3, 46012, Valencia, Spain.
J Neuroinflammation. 2018 Feb 8;15(1):36. doi: 10.1186/s12974-018-1082-z.
Hyperammonemic rats reproduce the cognitive alterations of patients with hepatic encephalopathy, including altered spatial memory, attributed to altered membrane expression of AMPA receptor subunits in hippocampus. Neuroinflammation mediates these cognitive alterations. We hypothesized that hyperammonemia-induced increase in IL-1β in hippocampus would be responsible for the altered GluA1 and GluA2 membrane expression. The aims of this work were to (1) assess if increased IL-1β levels and activation of its receptor are responsible for the changes in GluA1 and/or GluA2 membrane expression in hyperammonemia and (2) identify the mechanisms by which activation of IL-1 receptor leads to altered membrane expression of GluA1 and GluA2.
We analyzed in hippocampal slices from control and hyperammonemic rat membrane expression of AMPA receptors using the BS3 cross-linker and phosphorylation of the GluA1 and GluA2 subunits using phosphor-specific antibodies. The IL-1 receptor was blocked with IL-Ra, and the signal transduction pathways involved in modulation of membrane expression of GluA1 and GluA2 were analyzed using inhibitors of key steps.
Hyperammonemia reduces GluA1 and increases GluA2 membrane expression and reduces phosphorylation of GluA1 at Ser831 and of GluA2 at Ser880. Hyperammonemia increases IL-1β, enhancing activation of IL-1 receptor. This leads to activation of Src. The changes in membrane expression of GluA1 and GluA2 are reversed by blocking the IL-1 receptor with IL-1Ra or by inhibiting Src with PP2. After Src activation, the pathways for GluA2 and GluA1 diverge. Src increases phosphorylation of GluN2B at Tyr14721 and membrane expression of GluN2B in hyperammonemic rats, leading to activation of MAP kinase p38, which binds to and reduces phosphorylation at Thr560 and activity of PKCζ, resulting in reduced phosphorylation at Ser880 and enhanced membrane expression of GluA2. Increased Src activity in hyperammonemic rats also activates PKCδ which enhances phosphorylation of GluN2B at Ser1303, reducing membrane expression of CaMKII and phosphorylation at Ser831 and membrane expression of GluA1.
This work identifies two pathways by which neuroinflammation alters glutamatergic neurotransmission in hippocampus. The steps of the pathways identified could be targets to normalize neurotransmission in hyperammonemia and other pathologies associated with increased IL-1β by acting, for example, on p38 or PKCδ. IL-1β alters membrane expression of GluA1 and GluA2 AMPA receptor subunits by two difrerent mechanisms in the hippocampus of hyperammonemic rats.
高氨血症大鼠再现了肝性脑病患者的认知改变，包括空间记忆改变，这归因于海马 AMPA 受体亚基膜表达的改变。神经炎症介导了这些认知改变。我们假设，海马中 IL-1β的增加会导致 GluA1 和 GluA2 膜表达的改变。本研究的目的是：（1）评估增加的 IL-1β水平和其受体的激活是否是高氨血症时 GluA1 和/或 GluA2 膜表达改变的原因；（2）确定激活 IL-1 受体导致 GluA1 和 GluA2 膜表达改变的机制。
我们使用 BS3 交联剂分析了来自对照和高氨血症大鼠海马切片中 AMPA 受体的膜表达，使用磷酸化特异性抗体分析了 GluA1 和 GluA2 亚基的磷酸化。用 IL-Ra 阻断 IL-1 受体，并用关键步骤的抑制剂分析调节 GluA1 和 GluA2 膜表达的信号转导途径。
高氨血症降低了 GluA1 并增加了 GluA2 的膜表达，同时降低了 GluA1 在 Ser831 和 GluA2 在 Ser880 的磷酸化。高氨血症增加了 IL-1β，增强了 IL-1 受体的激活。这导致 Src 的激活。用 IL-1Ra 阻断 IL-1 受体或用 PP2 抑制 Src 可逆转 GluA1 和 GluA2 的膜表达改变。Src 激活后，GluA2 和 GluA1 的途径分开。Src 增加了高氨血症大鼠中 GluN2B 在 Tyr14721 的磷酸化和 GluN2B 的膜表达，导致 MAP 激酶 p38 的激活，p38 与 Thr560 结合并降低其磷酸化，PKCζ 的活性降低，导致 GluA2 的 Ser880 磷酸化增加和膜表达增强。高氨血症大鼠中增加的 Src 活性还激活了 PKCδ，增加了 GluN2B 在 Ser1303 的磷酸化，降低了 CaMKII 的膜表达和 Ser831 的磷酸化以及 GluA1 的膜表达。
本研究确定了神经炎症改变海马中谷氨酸能神经传递的两种途径。所鉴定的途径中的步骤可以通过作用于 p38 或 PKCδ 等，成为在高氨血症和其他与 IL-1β 增加相关的病理情况下使神经传递正常化的靶点。IL-1β 通过两种不同的机制在高氨血症大鼠的海马中改变 GluA1 和 GluA2 AMPA 受体亚基的膜表达。
Zotero 插件
