Traumatic brain injury (TBI) can lead to significant neuropsychiatric problems and neurodegenerative pathologies, which develop and persist years after injury. Neuroinflammatory processes evolve over this same period. Therefore, we aimed to determine the contribution of microglia to neuropathology at acute [1 d postinjury (dpi)], subacute (7 dpi), and chronic (30 dpi) time points. Microglia were depleted with PLX5622, a CSF1R antagonist, before midline fluid percussion injury (FPI) in male mice and cortical neuropathology/inflammation was assessed using a neuropathology mRNA panel. Gene expression associated with inflammation and neuropathology were robustly increased acutely after injury (1 dpi) and the majority of this expression was microglia independent. At 7 and 30 dpi, however, microglial depletion reversed TBI-related expression of genes associated with inflammation, interferon signaling, and neuropathology. Myriad suppressed genes at subacute and chronic endpoints were attributed to neurons. To understand the relationship between microglia, neurons, and other glia, single-cell RNA sequencing was completed 7 dpi, a critical time point in the evolution from acute to chronic pathogenesis. Cortical microglia exhibited distinct TBI-associated clustering with increased type-1 interferon and neurodegenerative/damage-related genes. In cortical neurons, genes associated with dopamine signaling, long-term potentiation, calcium signaling, and synaptogenesis were suppressed. Microglial depletion reversed the majority of these neuronal alterations. Furthermore, there was reduced cortical dendritic complexity 7 dpi, reduced neuronal connectively 30 dpi, and cognitive impairment 30 dpi. All of these TBI-associated functional and behavioral impairments were prevented by microglial depletion. Collectively, these studies indicate that microglia promote persistent neuropathology and long-term functional impairments in neuronal homeostasis after TBI.

SIGNIFICANCE STATEMENT Millions of traumatic brain injuries (TBIs) occur in the United States alone each year. Survivors face elevated rates of cognitive and psychiatric complications long after the inciting injury. Recent studies of human brain injury link chronic neuroinflammation to adverse neurologic outcomes, suggesting that evolving inflammatory processes may be an opportunity for intervention. Here, we eliminate microglia to compare the effects of diffuse TBI on neurons in the presence and absence of microglia and microglia-mediated inflammation. In the absence of microglia, neurons do not undergo TBI-induced changes in gene transcription or structure. Microglial elimination prevented TBI-induced cognitive changes 30 d postinjury (dpi). Therefore, microglia have a critical role in disrupting neuronal homeostasis after TBI, particularly at subacute and chronic timepoints.

外伤性脑损伤 (TBI) 可导致严重的神经精神问题和神经退行性疾病，这些问题在受伤后发展并持续数年。神经炎症过程在同一时期发展。因此，我们旨在确定小胶质细胞在急性 [伤后 1 天 (dpi)]、亚急性 (7 dpi) 和慢性 (30 dpi) 时间点对神经病理学的贡献。在雄性小鼠中线液体敲击损伤 (FPI) 之前，小胶质细胞被 CSF1R 拮抗剂 PLX5622 耗尽，并使用神经病理学 mRNA 面板评估皮质神经病理学/炎症。与炎症和神经病理学相关的基因表达在受伤后 (1 dpi) 急剧增加，并且大部分表达与小胶质细胞无关。但是，在 7 dpi 和 30 dpi 时，小胶质细胞耗竭逆转了与 TBI 相关的炎症、干扰素信号传导和神经病理学相关基因的表达。无数亚急性和慢性终点的抑制基因归因于神经元。为了了解小胶质细胞、神经元和其他神经胶质细胞之间的关系，单细胞 RNA 测序在 7 dpi 完成，这是从急性到慢性发病机制演变的关键时间点。皮质小胶质细胞表现出明显的 TBI 相关聚类，1 型干扰素和神经退行性/损伤相关基因增加。在皮质神经元中，与多巴胺信号、长时程增强、钙信号和突触发生相关的基因被抑制。小胶质细胞耗竭逆转了大多数这些神经元改变。此外，皮层树突复杂性降低 7 dpi，神经元结缔组织减少 30 dpi，认知障碍减少 30 dpi。所有这些与 TBI 相关的功能和行为障碍都可以通过小胶质细胞耗竭来预防。总的来说，这些研究表明小胶质细胞促进 TBI 后神经元稳态的持续性神经病理学和长期功能障碍。

意义声明仅在美国，每年就会发生数以百万计的脑外伤 (TBI)。幸存者在刺激性损伤后很长一段时间内都面临着认知和精神并发症的高发率。最近关于人类脑损伤的研究将慢性神经炎症与不良神经系统结果联系起来，表明不断发展的炎症过程可能是干预的机会。在这里，我们消除了小胶质细胞，以比较在存在和不存在小胶质细胞和小胶质细胞介导的炎症的情况下弥漫性 TBI 对神经元的影响。在没有小胶质细胞的情况下，神经元不会经历 TBI 诱导的基因转录或结构变化。小胶质细胞消除在伤后 30 天 (dpi) 阻止了 TBI 引起的认知变化。因此，小胶质细胞在破坏 TBI 后的神经元稳态方面起着关键作用，