Does microglial TNFR2 contribute to the protective role of membrane TNF in EAE?

描述（由申请人提供）：肿瘤坏死因子（TNF）是一种多效性细胞因子，参与调节许多生理和病理过程，如炎症、癌症、自身免疫和感染。TNF还与多种神经系统疾病的发展有关，包括多发性硬化症（MS）。TNF以跨膜（tmTNF）和可溶性（solTNF）两种生物活性形式存在，其功能由TNF受体1 （TNFR1）和TNF受体2 （TNFR2）介导。由于它们的结合亲和力不同，solTNF是TNFR1的主要信号伙伴，而tmTNF优先通过TNFR2发出信号。两种受体激活的细胞过程通常是相反的：TNFR1介导细胞凋亡和慢性炎症，TNFR2介导细胞存活、炎症消退、免疫和髓鞘形成。大量研究强调了区分solTNF和tmTNF功能的重要性，并将MS及其动物模型实验性自身免疫性脑脊髓炎（EAE）与solTNF和TNFR1的有害作用联系起来。在我们自己的研究中，我们不仅证明了solTNF是有害的，而且证明了tmTNF对EAE的修复和髓鞘再生具有保护作用和重要作用。我们发现，用生物制剂XPro1595（一种显性阴性TNF，选择性阻断solTNF而不影响tmTNF）治疗的小鼠，从eae诱导的瘫痪中恢复过来。这与神经保护、髓磷脂完整性改善和髓鞘再生增加有关。这是怎么发生的？我们的假设是，选择性抑制solTNF会导致TNF受体向TNFR2激活的平衡发生变化。这导致tnfr2依赖性级联的下游激活，该级联在EAE中执行tmTNF的保护功能。由于在中枢神经系统中，TNFR2在少突胶质细胞、少突胶质细胞前体、星形胶质细胞和小胶质细胞中表达，所有这些细胞群都可能是tmTNF有益作用的效应者。在这个建议中，我们将专门关注小胶质细胞。我们发现TNFR2在小鼠EAE和ms的小胶质细胞中表达，小胶质细胞中TNFR2的激活已被证明可以诱导抗炎和神经保护介质的产生。在此基础上，我们假设tmTNF激活小胶质细胞中的TNFR2会引发保护性信号级联反应，从而促进tmTNF的有益作用。我们研究的目的是确定小胶质细胞TNFR2是否是EAE中tmTNF保护功能的介质。我们将用一种创新的遗传方法来解决这个问题，该方法由我们实验室生成的一种新的小鼠模型组成，其中TNFR2从骨髓群体（LysMcreTNFR2fl/fl小鼠）中切除，以获得骨髓嵌合体，这将允许对小胶质细胞TNFR2进行特异性研究。这些实验将揭示体内小胶质细胞中的tmTNF-TNFR2信号，这是一个迄今为止尚未解决的问题。我们相信我们的研究将显著推进目前对tmTNF和TNFR2在EAE中的作用的认识，为可能开发选择性solTNF抑制剂作为MS的新疗法提供基础。

DESCRIPTION (provided by applicant): Tumor necrosis factor (TNF) is a pleiotropic cytokine involved in the regulation of numerous physiological and pathological processes such as inflammation, cancer, autoimmunity and infection. TNF is also linked to the development of various neurological disorders, including multiple sclerosis (MS). TNF exists in two biologically active forms, transmembrane (tmTNF) and soluble (solTNF), whose functions are mediated by TNF receptor 1 (TNFR1) and TNF receptor 2 (TNFR2). By virtue of their different binding affinities, solTNF is the primary signaling partner of TNFR1, while tmTNF preferentially signals through TNFR2. The cellular processes activated by the two receptors are often opposite: TNFR1 mediates apoptosis and chronic inflammation, TNFR2 mediates cell survival, resolution of inflammation, immunity and myelination. Numerous studies have underscored the importance of distinguishing between the functions of solTNF and tmTNF, and have associated MS and its animal model experimental autoimmune encephalomyelitis (EAE) to the detrimental effects of solTNF and TNFR1. In our own studies we have demonstrated not only that solTNF is detrimental, but that tmTNF is protective and important for repair and remyelination in EAE. We showed that mice treated with the biologic XPro1595, a dominant negative TNF that selectively blocks solTNF without affecting tmTNF, recover from EAE-induced paralysis. This is associated with neuroprotection, improved myelin integrity and increased remyelination. How does this occur? Our HYPOTHESIS is that selective inhibition of solTNF causes a shift in the balance of TNF receptor activation towards TNFR2. This leads to the downstream activation of TNFR2-dependent cascades which carry out the protective functions of tmTNF in EAE. Since in the CNS TNFR2 is expressed in oligodendrocytes, oligodendrocyte precursors, astrocytes and microglia, all these cell populations could potentially be the effectors of tmTNF beneficial effect. In this proposal we will focus exclusively on microglia. We have found that TNFR2 is expressed in microglia, both in mouse EAE and in MS. Activation of TNFR2 in microglia has been shown to induce the production of anti-inflammatory and neuroprotective mediators. On this basis, we hypothesize that activation of TNFR2 in microglia by tmTNF sets off protective signaling cascades that contribute to tmTNF beneficial effects. The OBJECTIVE of our studies is to determine whether microglial TNFR2 is a mediator of tmTNF protective function in EAE. We will address this question with an innovative genetic approach consisting of a new mouse model generated in our laboratory where TNFR2 is ablated from the myeloid population (LysMcreTNFR2fl/fl mice) to obtain bone-marrow chimeras that will allow for specific investigation of microglial TNFR2. These experiments will shed light on tmTNF-TNFR2 signaling in microglia in vivo, a question that has not been addressed to date. We believe our studies will significantly advance the current knowledge on the role of tmTNF and TNFR2 in EAE, providing the basis for the possible development of a selective solTNF inhibitor as a new therapy for MS.