Contribution of infiltrating macrophages on synaptic function after TBI

描述(申请人提供)：创伤性脑损伤(TBI)是包括阿尔茨海默病(AD)在内的多种神经退行性疾病发展的主要危险因素，最近的许多报告记录了脑损伤后痴呆的发展。在最初的机械伤害之后，TBI激活了一系列分子信号事件，从而导致 神经退行性后遗症，即认知功能障碍。颅脑损伤后最显著的反应之一是诱导了与神经炎症相关的多种信号介质，这一直被归因于天然免疫系统的激活。炎症是一种重要的宿主对损伤的反应，然而，过度和不加控制的炎症传播可能对主要未受影响的组织有害。最近在人类和各种动物模型中的研究表明，小胶质细胞是大脑的常驻免疫细胞，在最初的侮辱后可以保持激活状态数年。尽管一致的发现暗示了脑内长期激活的小胶质细胞的有害影响，但对脑损伤后外周先天免疫反应的作用及其与中枢神经系统组织的相互作用知之甚少。最近的研究表明，Ly6C和CCR2的细胞表面表达是骨髓来源的血液循环单核细胞的炎性亚群的特征。然而，关于Ly6ChiCCR2+单核细胞在颅脑损伤后的病理过程中的作用和功能，目前的认识还存在空白。这一建议的最终目的是阐明该细胞亚群在脑损伤诱导的功能上的贡献 神经炎症，以及突触和认知功能障碍。目的1.研究CCR2信号在遗传和药物上的缺失是否能改善脑损伤所致的突触和认知功能障碍。在野生型和CCR2RFP/RFP小鼠上，将使用受控的皮质撞击来诱导TBI。我们将在损伤后28天检测海马区依赖的认知功能以及稳态突触功能。初步研究表明，与WT小鼠相比，CCR2缺失可消除脑损伤所致的海马区认知功能障碍。目的2.将测定脑损伤后Ly6ChiCCR2+单核/巨噬细胞进入脑实质的时间动力学和炎症分布。除CX3CR1+/GFPCCR2+/RFP小鼠外，其他动物均可诱导出与目标1相同的脑损伤模型。受伤后的多个时间点将被检查，包括急性、亚急性和慢性期。初步数据显示，伤后48小时，经脑外伤治疗的小鼠巨噬细胞浸润显著增加，并且其中的特定亚群类似驻留的小胶质细胞。我们的研究将提供关于外周巨噬细胞聚集在脑损伤所致神经炎的致病作用方面的关键和新的信息，并有可能为其治疗提供一个新的治疗靶点和最佳时间点。

DESCRIPTION (provided by applicant): Traumatic brain injury (TBI) is a major risk factor for the development of multiple neurodegenerative diseases, including Alzheimer's disease (AD) and numerous recent reports document the development of dementia after TBI. Following the initial mechanical insult, TBI activates a cascade of molecular signaling events that can result in neurodegenerative sequelae, namely cognitive dysfunction. One of the most pronounced responses following TBI is the induction of multiple signaling mediators associated with neuroinflammation, consistently attributed to the activation of the innate immune system. Inflammation is a vital host response to injury, however excessive and unchecked propagation of inflammation can be deleterious to primarily unaffected tissues. Recent work in both humans and various animal models has shown that microglia, the brain's resident immune cells, can remain in an activated state for years after the initial insult. Despite consistent findings implicating the deleterious effects of chronically activated microglia in the brain, little is know about the role of the peripheral innate immune response and its interface with CNS tissues following TBI. Recent work has shown that cell surface expression of Ly6C and CCR2 is characteristic of an inflammatory subpopulation of bone marrow derived blood circulating monocytes. However, there is still a gap in the current knowledge as to the role and function of Ly6ChiCCR2+ monocytes in the propagation of TBI- induced pathology. The ultimate goal of this proposal is to elucidate the functional contribution of this cell subpopulation on TBI-induced neuroinflammation, as well as synaptic and cognitive dysfunction. Aim 1. Will examine if genetic and pharmacological deletion of CCR2 signaling ameliorates TBI-induced synaptic and cognitive dysfunction. TBI will be induced using controlled cortical impact on both wild type and CCR2RFP/RFP mice. We will examine hippocampal-dependent cognitive function as well as homeostatic synaptic function, 28 days after injury. Preliminary studies indicate that CCR2 deletion abrogates TBI-induced hippocampal cognitive dysfunction compared to WT mice. Aim 2. Will determine the temporal kinetics and inflammatory profile of TBI-induced Ly6ChiCCR2+ monocytes/macrophages into the brain parenchyma. TBI will be induced as in Aim 1 except using CX3CR1+/GFPCCR2+/RFP mice. Multiple time points following injury will be examined to include acute, subacute, and chronic phases. Preliminary data shows that 48 hours after injury, TBI-treated mice had a significant increase in macrophage infiltration and that a specific subset of those resembled resident microglia. Our studies will provide critical and novel information in regard to the contribution of peripheral macrophage accumulation in the pathogenicity of TBI-induced neuroinflammation and potentially a novel therapeutic target and optimal time point for its treatment.