Reprogramming Microglial Epigenetic Pathways to Promote Cognitive Recovery after Brain Trauma.

项目概述：创伤性脑损伤触发延迟性分子继发性损伤级联反应，包括 慢性神经炎，导致进行性组织丢失和神经功能障碍，包括 痴呆症。我们已经证明，小胶质细胞在实验后的几个月到几年内被慢性激活。 在小鼠的脑损伤中，促进了与认知能力下降相关的进行性神经退化。小胶质细胞也 在神经退行性变过程中，他们的激活特征发生变化，这可能导致认知能力下降 疾病，包括阿尔茨海默病(AD)和非AD类型的痴呆。其中的一个重要组成部分 病理状态是小胶质细胞从神经修复/神经保护状态转变为适应不良状态 表型转变为持续的、功能失调的神经毒性激活状态。我们的新研究表明，分离的小胶质细胞 慢性损伤的脑部表现出吞噬功能缺陷，同时促炎因子升高 细胞因子和衰老标志物，表明慢性功能障碍/神经毒性激活状态。 此外，我们确定了特异性的组蛋白乙酰化(H3K9ac)和甲基化(H3K27me3)的变化 神经毒性小胶质细胞，这意味着内在的表观遗传机制作为这种慢性表型的驱动因素。 重要的是，新的试点数据表明，通过短期内将小胶质细胞从慢性损伤的大脑中移除 在损伤后1个月开始使用CSF1R抑制剂(PLX5622)可导致 损伤的脑内有抗炎表型的小胶质细胞。这一重置小胶质细胞激活的过程 脑外伤后抑制慢性神经炎性环境，改善长期运动和认知功能 功能恢复。因此，我们的数据表明，通过移除创伤后的免疫记忆， 小胶质细胞表观遗传编程为神经毒性激活状态，促进神经保护性小胶质细胞 激活反应，并改善长期神经恢复。因此，我们假设温和的- 严重颅脑损伤诱导小胶质细胞特定的表观遗传机制，促进慢性神经毒性激活 状态，导致进行性神经变性和认知缺陷。此外，我们预测， 消除这种小胶质细胞表型和/或对促炎表观遗传机制的靶向抑制，甚至 在颅脑损伤后高度延迟的时间点，可以显著改善长期认知恢复。在这里，我们将使用 神经行为、免疫学和分子方法来测试我们的新假设，如下所述 具体目的：1)阐明脑损伤后导致慢性小胶质细胞功能障碍的内在表观遗传学改变。 并向促炎、神经毒性表型转变。2)为了证明小胶质细胞重新填充 延迟给予CSF1R抑制剂后受损的大脑被重新编程为神经恢复剂 以及改善认知功能的神经保护表型。3)确定延迟干预是否 靶向特定表观遗传机制促进神经修复/神经保护小胶质细胞表型 改善颅脑损伤后远期功能恢复。

Project Summary: Traumatic brain injury (TBI) triggers delayed molecular secondary injury cascades, including chronic neuroinflammation, that contribute to progressive tissue loss and neurological deficits, including dementia. We have shown that microglia are chronically activated for months-to-years following experimental TBI in mice, contributing to progressive neurodegeneration associated with cognitive decline. Microglia also undergo changes in their activation profile that may contribute to cognitive decline during neurodegenerative diseases, including Alzheimer’s disease (AD) and dementias of non-AD type. An important component of these pathological states is the maladaptive transformation of microglia from a neurorestorative/neuroprotective phenotype to a persistent, dysfunctional neurotoxic activation state. Our new studies show that microglia isolated from chronically injured brain display deficits in phagocytosis in parallel with elevations of pro-inflammatory cytokines and senescence markers, indicative of a chronic dysfunctional/neurotoxic activation state. Furthermore, we identify specific histone acetylation (H3K9ac) and methylation (H3K27me3) changes in neurotoxic microglia, which implicate intrinsic epigenetic mechanisms as drivers of this chronic phenotype. Importantly, new pilot data show that global removal of microglia from the chronically injured brain by short-term administration of a CSF1R inhibitor (PLX5622) starting at 1-month post-injury results in the repopulation of the injured brain with microglia with an anti-inflammatory phenotype. This process of resetting microglial activation after TBI dampens the chronic neuroinflammatory environment and improves long-term motor and cognitive function recovery. Thus, our data indicates that erasing posttraumatic immunological memory, by removing microglia epigenetically programmed toward a neurotoxic activation state, promotes neuroprotective microglial activation responses and improves long-term neurological recovery. Therefore, we hypothesize that moderate- severe TBI induces specific epigenetic mechanisms in microglia that promote a chronic neurotoxic activation state, causing progressive neurodegeneration and cognitive deficits. Moreover, we predict that strategies that eliminate this microglial phenotype and/or targeted inhibition of pro-inflammatory epigenetic mechanisms, even at highly delayed time points after TBI, can substantially improve long-term cognitive recovery. Here, we will use neurobehavioral, immunological, and molecular approaches to test our novel hypotheses as outlined in following specific aims: 1) To elucidate TBI-induced intrinsic epigenetic changes that lead to chronic microglial dysfunction, with a shift toward a pro-inflammatory, neurotoxic phenotype. 2) To demonstrate that microglia that repopulate the injured brain following delayed administration of CSF1R inhibitor are reprogramed toward a neurorestorative and neuroprotective phenotype that improves cognitive function. 3) To determine whether delayed interventions that target specific epigenetic mechanisms promote the neurorestorative/neuroprotective microglial phenotype and improve long-term functional recovery after TBI.