During inflammatory demyelination, TNF receptor 1 (TNFR1) mediates detrimental proinflammatory effects of soluble TNF (solTNF), whereas TNFR2 mediates beneficial effects of transmembrane TNF (tmTNF) through oligodendroglia, microglia, and possibly other cell types. This model supports the use of selective inhibitors of solTNF/TNFR1 as anti-inflammatory drugs for central nervous system (CNS) diseases. A potential obstacle is the neuroprotective effect of solTNF pretreatment described in cultured neurons, but the relevance in vivo is unknown. To address this question, we generated mice with neuron-specific depletion of TNFR1, TNFR2, or inhibitor of NF-κB kinase subunit β (IKKβ), a main downstream mediator of TNFR signaling, and applied experimental models of inflammatory demyelination and acute and preconditioning glutamate excitotoxicity. We also investigated the molecular and cellular requirements of solTNF neuroprotection by generating astrocyte-neuron co-cultures with different combinations of wild-type (WT) and TNF and TNFR knockout cells and measuring N-methyl-d-aspartate (NMDA) excitotoxicity in vitro. Neither neuronal TNFR1 nor TNFR2 protected mice during inflammatory demyelination. In fact, both neuronal TNFR1 and neuronal IKKβ promoted microglial responses and tissue injury, and TNFR1 was further required for oligodendrocyte loss and axonal damage in cuprizone-induced demyelination. In contrast, neuronal TNFR2 increased preconditioning protection in a kainic acid (KA) excitotoxicity model in mice and limited hippocampal neuron death. The protective effects of neuronal TNFR2 observed in vivo were further investigated in vitro. As previously described, pretreatment of astrocyte-neuron co-cultures with solTNF (and therefore TNFR1) protected them against NMDA excitotoxicity. However, protection was dependent on astrocyte, not neuronal TNFR1, on astrocyte tmTNF-neuronal TNFR2 interactions, and was reproduced by a TNFR2 agonist. These results demonstrate that neuronal TNF receptors perform fundamentally different roles in CNS pathology in vivo, with neuronal TNFR1 and IKKβ promoting microglial inflammation and neurotoxicity in demyelination, and neuronal TNFR2 mediating neuroprotection in excitotoxicity. They also reveal that previously described neuroprotective effects of solTNF against glutamate excitotoxicity in vitro are indirect and mediated via astrocyte tmTNF-neuron TNFR2 interactions. These results consolidate the concept that selective inhibition of solTNF/TNFR1 with maintenance of TNFR2 function would have combined anti-inflammatory and neuroprotective properties required for safe treatment of CNS diseases.

中文翻译：

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神经元 TNF 受体在 CNS 病理学中的根本不同作用：TNFR1 和 IKKβ 促进脱髓鞘中的小胶质细胞反应和组织损伤，而 TNFR2 保护小鼠免受兴奋性毒性

在炎症性脱髓鞘过程中，TNF 受体 1 (TNFR1) 介导可溶性 TNF (solTNF) 的有害促炎作用，而 TNFR2 通过少突胶质细胞、小胶质细胞和可能的其他细胞类型介导跨膜 TNF (tmTNF) 的有益作用。该模型支持使用 solTNF/TNFR1 的选择性抑制剂作为中枢神经系统 (CNS) 疾病的抗炎药。一个潜在的障碍是在培养的神经元中描述的 solTNF 预处理的神经保护作用，但在体内的相关性尚不清楚。为了解决这个问题，我们生成了神经元特异性缺失 TNFR1、TNFR2 或 NF-κB 激酶亚基 β (IKKβ) 抑制剂（TNFR 信号传导的主要下游介质）的小鼠，并应用了炎症脱髓鞘和急性和预处理的实验模型谷氨酸兴奋性毒性。我们还通过与野生型 (WT) 和 TNF 和 TNFR 敲除细胞的不同组合生成星形胶质细胞-神经元共培养物并在体外测量 N-甲基-d-天冬氨酸 (NMDA) 兴奋性毒性来研究 solTNF 神经保护的分子和细胞需求. 在炎症性脱髓鞘过程中，神经元 TNFR1 和 TNFR2 都不能保护小鼠。事实上，神经元 TNFR1 和神经元 IKKβ 都促进了小胶质细胞反应和组织损伤，并且在铜酮诱导的脱髓鞘中，少突胶质细胞丢失和轴突损伤进一步需要 TNFR1。相比之下，神经元 TNFR2 在小鼠红藻氨酸 (KA) 兴奋性毒性模型中增加了预处理保护，并限制了海马神经元死亡。在体外进一步研究了体内观察到的神经元 TNFR2 的保护作用。如前所述，用 solTNF（以及因此 TNFR1）对星形胶质细胞-神经元共培养物进行预处理可以保护它们免受 NMDA 兴奋性毒性的影响。然而，保护依赖于星形胶质细胞，而不是神经元 TNFR1，取决于星形胶质细胞 tmTNF-神经元 TNFR2 的相互作用，并由 TNFR2 激动剂复制。这些结果表明，神经元 TNF 受体在体内 CNS 病理学中发挥着根本不同的作用，神经元 TNFR1 和 IKKβ 在脱髓鞘中促进小胶质细胞炎症和神经毒性，而神经元 TNFR2 在兴奋性毒性中介导神经保护。他们还揭示了之前描述的 solTNF 在体外对谷氨酸兴奋性毒性的神经保护作用是间接的，并通过星形胶质细胞 tmTNF-神经元 TNFR2 相互作用介导。