Chronic and Evolving Inflammation after Traumatic Brain Injury: Microglial Priming and Neuropsychiatric Complications

项目总结/摘要： 创伤性脑损伤（TBI）可导致严重的神经精神问题和神经退行性病变 随着时间的推移而发展。这些问题可能通过神经炎症过程传播， 在初次受伤后继续保持良好状态。Pt.3我们已经报道了小鼠弥漫性TBI导致“小胶质细胞启动” 在皮质和海马区域内，其中小胶质细胞保持在致敏状态，并且高度 在损伤后30天（30 dpi）免疫激发后，炎症性。在这个应用程序中，我们显示了一个独特的 从急性（8-24小时）到亚急性（7天），然后到慢性（30天）皮质炎症/小胶质细胞的阶段转变 TBI后启动。急性TBI后出现炎症反应，并演变为亚急性期7 dpi，其由I型干扰素（IFN）信号传导主导。IFN应答被细胞窘迫激活， 损伤促进免疫反应，可以启动先天免疫细胞，包括小胶质细胞。我们提供 在7 dpi时皮质神经元损伤的证据，具有相应的小胶质细胞活化。Pts.3&6单细胞RNA 皮质7 dpi的seq（scRNAseq）显示了创伤相关的小胶质细胞的独特簇，其受到影响。 的IFNs。这些小胶质细胞参与树突重塑和神经元稳态的抑制。月30日 dpi时，有认知障碍（与HPC和CTX相关），网络连接减少， 致敏小胶质细胞的免疫反应性。小胶质细胞在这些过程中是至关重要的，因为小胶质细胞的消除 （CSF 1 R拮抗剂）预防TBI诱导的神经炎症和IFN信号传导，减弱树突萎缩， 并改善网络连接性。因此，我们假设，干扰素信号的增加是关键， 促进小胶质细胞引发和慢性神经炎症、树突重塑和认知衰退。到 为了解决这个问题，提出了三个目标，即在小鼠中使用中线液压冲击损伤。在Aim-1中，我们将消除 小胶质细胞，以确定小胶质细胞对皮质和海马中其他CNS细胞的影响，急性，亚急性 急性和慢性TBI后。ScRNAseq将用于确定小胶质细胞的转录组特征 随着时间的推移，并与星形胶质细胞，少突胶质细胞和神经元在TBI后的这些关键时间平行。的 重点将是确定哪些细胞表达IFN和IFN受体，以及它们如何对IFN增加作出反应 TBI信号。在Aim-2中，我们将确定IFN信号传导是否在慢性神经炎症、病理学 认知能力下降和TBI后小胶质细胞启动。在此，我们将在IFN-α/B水平上减弱IFN信号传导 受体激活（IFNαRKO，Mgl-IFNαRKO）和IFN产生（STINGKO），以确定 这些干预改善了神经炎症、病理学和小胶质细胞引发。在Aim-3中，我们将确定 如果TBI诱导的小胶质细胞启动、慢性神经炎症和认知能力下降30 dpi被强制逆转， 小胶质细胞周转。我们将在IFN应答最高的7 dpi时去除小胶质细胞（CSF 1 R拮抗剂）， 允许小胶质细胞再增殖至30 dpi。这些目标的完成将为IFN途径提供新的见解 这似乎在TBI后由小胶质细胞介导的急性炎症向慢性炎症的转变中至关重要。

PROJECT SUMMARY/ABSTRACT: Traumatic brain injury (TBI) can lead to significant neuropsychiatric problems and neurodegenerative pathologies that develop with time after injury. These issues may be propagated by neuroinflammatory processes that continue well after the initial injury. Pt.3 We have reported that diffuse TBI in mice leads to “microglial priming” within cortical and hippocampal regions, in which the microglia remain in a sensitized state and are highly inflammatory following an immune challenge 30 days post injury (30 dpi). In this application, we show a distinct phase transition from acute (8-24 h) to sub-acute (7 d) and then to chronic (30 d) cortical-inflammation/microglia priming after TBI. Acutely, there was an inflammatory response after TBI that evolved into a subacute phase 7 dpi that was dominated by interferon (IFN) type I signaling. IFN responses are activated by cell distress and damage to promote an immune response that can prime innate immune cells, including microglia. We provide evidence of cortical neuronal damage 7 dpi with corresponding microglial activation. Pts.3&6 Single cell RNA seq (scRNAseq) of the cortex 7 dpi shows unique clusters of microglia, trauma-associated, that are influenced by IFNs. These microglia are involved in dendritic remodeling and suppression of neuronal homeostasis. At 30 dpi, there was cognitive impairment (associated with HPC & CTX), reduced network connectivity, and increased immune reactivity of primed microglia. Microglia are critical in these processes because microglial elimination (CSF1R antagonist) prevented TBI-induced neuroinflammation and IFN signaling, attenuated dendritic atrophy, and improved network connectivity. Thus, we hypothesize that increased interferon signaling is critical in promoting microglial priming and chronic neuroinflammation, dendritic remodeling, and cognitive decline. To address this, three aims are proposed using a midline fluid percussion injury in mice. In Aim-1, we will eliminate microglia to determine the influence of microglia on other CNS cells in the cortex and hippocampus acutely, sub- acutely, and chronically after TBI. ScRNAseq will be used to determine the transcriptome signature of microglia over time and in parallel with astrocytes, oligodendrocytes, and neurons at 3 these critical times after TBI. The focus will be determining which cells express IFNs and IFN receptors, and how they respond to increased IFN signaling with TBI. In Aim-2, we will determine if IFN signaling is critical in chronic neuroinflammation, pathology, cognitive decline, and microglial priming after TBI. Here, we will attenuate IFN signaling at the levels of IFN-a/b receptor activation (IFNαRKO, Mgl-IFNαRKO) and IFN production (STINGKO) to determine the extent to which these interventions ameliorate neuroinflammation, pathology, and microglial priming. In Aim-3, we will determine if TBI-induced microglial priming, chronic neuroinflammation, and cognitive decline 30 dpi are reversed by forced microglia turnover. We will remove microglia (CSF1R antagonist) when IFN responses are highest 7 dpi, and allow for microglial repopulation to 30 dpi. Completion of these aims will provide new insight on the IFN pathway that appears to be critical in the transition from acute to chronic inflammation mediated by microglia after TBI.