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突出了先天免疫系统在脑损伤反应中的关键作用，包括激活小胶质细胞和巨噬细胞。小胶质细胞和其他髓系来源细胞上的细胞表面受体(如CD200R1)直接与神经元上表达的特定内源性配体(如CD200)相互作用，并通过维持小胶质细胞处于静息状态来抑制促炎信号。正常情况下，这些抑制机制是使大脑保持免疫特权所必需的。然而，当这些相互作用被打破时，小胶质细胞可能会变得不受抑制，进入紧张性激活状态，从而加剧损伤并恶化结局。因此，损伤后小胶质细胞的调节至关重要。最近在神经退行性疾病模型中研究CD200-CD200R1信号失衡的研究支持这样的假设，即这种相互作用在中风后也可能被破坏。我们实验室的初步数据表明，实验性中风后早期，缺血半球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蛋白水平同时升高，这与激活的小胶质细胞和外周血白细胞募集的数量增加相一致。在这项建议中，我们打算阐明CD200-CD200R1抑制信号在卒中中的作用。在目标1中，我们将使用条件性神经元CD200基因敲除和CD200R1(全局)基因敲除小鼠来探索这些神经元-神经胶质细胞相互作用的功能后果。目的2将通过使用CD200R1-/-骨髓嵌合体检测局部(小胶质细胞)和外周(白细胞)在卒中中的作用，继续我们对CD200R1介导的抑制的机制研究。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则。该提案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/髓系激活以促进更好的预后和促进卒中后恢复的有效性。

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.