The Immunoinhibitory Role of CD200-CD200R1 Signaling in Experimental Stroke

描述（由申请人提供）：新出现的数据表明，中风引起的炎症对神经元损伤和临床结果有显著影响。脑缺血后的局部炎症反应强调了先天免疫系统在脑损伤反应中的关键作用，包括小胶质细胞和巨噬细胞的激活。小胶质细胞和其他髓源性细胞上的细胞表面受体（如CD200R1）直接与特定的内源性配体（如CD200R1）相互作用。CD200)在神经元上表达，并通过维持小胶质细胞处于“静息状态”来抑制促炎信号。通常需要这些抑制机制来保持大脑的免疫特权。然而，当这些相互作用被破坏时，小胶质细胞可以被解除抑制并进入强直性激活状态，从而加剧损伤并恶化预后。因此，损伤后小胶质细胞的调节是至关重要的。最近关于神经退行性疾病模型中CD200-CD200R1信号失衡的研究支持了这种相互作用也可能在中风后被破坏的假设。我们实验室的初步数据表明，实验性中风后早期缺血半球的CD200蛋白表达水平下降，表明对小胶质细胞的抑制“刹车”被移除。有趣的是，我们发现卒中后CD200R1蛋白水平同时增加，这与激活的小胶质细胞和外周白细胞募集数量的增加相吻合。在本提案中，我们打算阐明CD200-CD200R1抑制信号在卒中中的作用。在Aim 1中，我们将使用条件神经元CD200敲除和CD200R1（全局）敲除小鼠来探索这些神经元-神经胶质相互作用的功能后果。目的2将继续我们CD200R1介导的抑制机制研究，通过使用CD200R1-/-骨髓嵌合体检查局部（小胶质细胞）和外周（白细胞）对中风的贡献。最后，Aim 3将使用一种小分子CD200R1激动剂（CD200-Fc）来证明治疗中风的治疗策略的原理。本研究的总体目标是研究脑损伤中小胶质细胞激活的免疫调节机制，并确定暂时抑制小胶质细胞/髓细胞激活以促进卒中后更好的预后和增强恢复的有效性。

DESCRIPTION (provided by applicant): Emerging data suggests that stroke-induced inflammation significantly contributes to neuronal injury and clinical outcome. Local inflammatory responses following cerebral ischemia have highlighted a pivotal role for the innate immune system in the brain's response to injury, including the activation of microglia and macrophages. Cell-surface receptors (e.g., CD200R1) on microglia and other myeloid-derived cells directly interact with specific endogenous ligands (e.g ., CD200) expressed on neurons and act to suppress pro- inflammatory signaling by maintaining microglia in a "resting state". Normally these inhibitory mechanisms are required to keep the brain an immune-privileged site. When these interactions are broken, however, microglia can become disinhibited and enter a state of tonic activation, thereby exacerbating injury and worsening outcome. Thus, regulation of microglia after injury is crucial. Recent studies investigating the imbalance of CD200-CD200R1 signaling in models of neurodegenerative disease support the hypothesis that this interaction may also be disrupted following stroke. Preliminary data from our lab suggests that CD200 protein expression levels are decreased in the ischemic hemisphere early after experimental stroke, indicating that the inhibitory 'brake' on microglia is removed. Interestingly, we show a concurrent increase in CD200R1 protein levels after stroke, which coincided with an increased number of activated microglia and peripheral leukocyte recruitment. In this proposal we intend to elucidate the role of CD200-CD200R1 inhibitory signaling in stroke. In Aim 1 we will explore the functional consequences of these neuronal-glial interactions using conditional neuronal CD200 knockout and CD200R1 (global) knockout mice. Aim 2 will continue our mechanistic study of CD200R1- mediated inhibition by examining the local (microglia) and peripheral (leukocyte) contributions to stroke using CD200R1-/- bone marrow chimeras. Finally, Aim 3 will employ a small molecule CD200R1 agonist (CD200-Fc) for proof-of-principle of a therapeutic strategy to treat stroke. The overall goal of this proposal is to investigate the immunoregulatory mechanisms underlying microglia activation in brain injury and determine the efficacy of temporally suppressing microglia/myeloid activation to promote better outcomes and enhance recovery after stroke.