The Immunoinhibitory Role of CD200-CD200R1 Signaling in Experimental Stroke

描述（由申请方提供）：新的数据表明，卒中诱导的炎症显著促进神经元损伤和临床结局。脑缺血后的局部炎症反应突出了先天免疫系统在脑对损伤的反应中的关键作用，包括小胶质细胞和巨噬细胞的活化。细胞表面受体（例如，CD 200 R1）直接与特异性内源性配体（例如，CD 200）在神经元上表达，并通过将小胶质细胞维持在“静息状态”来抑制促炎信号传导。正常情况下，这些抑制机制是保持大脑作为免疫特权部位所必需的。然而，当这些相互作用被打破时，小胶质细胞可以变得不受抑制并进入紧张性激活状态，从而加剧损伤和恶化结果。因此，损伤后小胶质细胞的调节至关重要。最近研究神经退行性疾病模型中CD 200-CD 200 R1信号传导失衡的研究支持了这种相互作用也可能在卒中后被破坏的假设。来自我们实验室的初步数据表明，在实验性中风后早期，缺血半球的CD 200蛋白表达水平降低，表明对小胶质细胞的抑制性“刹车”被移除。有趣的是，我们发现中风后CD 200 R1蛋白水平同时增加，这与激活的小胶质细胞和外周血白细胞募集数量增加相一致。本研究旨在阐明CD 200-CD 200 R1抑制性信号在脑卒中中的作用。在目标1中，我们将探索这些神经元-胶质细胞相互作用的功能后果，使用条件性神经元CD 200基因敲除和CD 200 R1（全局）基因敲除小鼠。目的2将继续我们的机制研究CD 200 R1介导的抑制，通过检查局部（小胶质细胞）和外周血（白细胞）的贡献中风使用CD 200 R1-/-骨髓嵌合体。最后，目标3将采用小分子CD 200 R1激动剂（CD 200-Fc），用于治疗中风的治疗策略的原理验证。该提案的总体目标是研究脑损伤中小胶质细胞活化的免疫调节机制，并确定暂时抑制小胶质细胞/骨髓活化以促进更好的结局和增强卒中后恢复的疗效。

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.