Novel role and mechanisms of histone deacetylases in traumatic brain injury

新出现的证据表明脑部炎症在脑外伤的病理生理学中发挥着关键作用 创伤（TBI）。TBI后，小胶质细胞/巨噬细胞可能呈现不同的促炎或炎症反应- 分辨表型，分别增强脑损伤或促进脑修复。细胞内 TBI后决定小胶质细胞/巨噬细胞功能表型的分子开关 明白识别这种分子机制可能会揭示新的目标，以调整小胶质细胞/巨噬细胞 向修复性炎症消退表型发展，并改善TBI的长期结局。 组蛋白脱乙酰基酶（HDAC）催化乙酰基从组蛋白和非组蛋白蛋白去除， 从而不仅调节基因转录，而且通过翻译后调节各种蛋白质的活性， 修改.我们和其他人先前的研究表明，I类HDAC（HDAC 1，2， 3，8）减轻脑炎症和改善TBI后的神经功能。然而，当务之急是 阐明不同HDAC亚型的作用，以专注于特定的治疗靶点， 破坏一些HDAC在损伤后脑修复中的有益功能。迄今为止，HDAC亚型 负责预防TBI的人不详。也不知道细胞/分子机制是否 HDAC介导的潜在保护涉及小胶质细胞/巨噬细胞表型的改变。 我们的初步研究首次表明：1）HDAC3的小胶质细胞/巨噬细胞特异性敲除（mKO），但 而不是HDAC1或HDAC2，改善TBI后的神经行为结果。2)HDAC3 mKO改善灰度， 白色物质的完整性，并减轻TBI后的神经炎症。4)HDAC3抑制改善促- 在体外TBI模型神经元牵张损伤（NSI）后炎性小胶质细胞介导的神经毒性。第五章） HDAC3抑制减少了信号转导和转录激活因子1（STAT1）的激活，这是一个关键的信号转导和转录激活因子。 介导小胶质细胞/巨噬细胞中促炎反应的分子。6)皮下递送 RGFP966是一种脑渗透性、强效和特异性HDAC3抑制剂，可改善炎症和感觉运动 TBI后的赤字鉴于这些观察结果，我们提出了三个具体目标来检验新的假设， HDAC3的遗传或药理学消融提供神经保护并改善脑修复， TBI后的长期结果，通过促进炎症解决小胶质细胞/巨噬细胞反应。 目的1：测试HDAC 3 mKO是否改善了脑缺血后灰质和白色物质的完整性和长期神经功能。 创伤性脑损伤将在两种性别的小鼠中用他莫昔芬诱导的HDAC 3诱导受控皮质撞击（CCI）。 敲除小胶质细胞/巨噬细胞。目的2：测试HDAC3-STAT1信号通路的基因敲除 使小胶质细胞/巨噬细胞在TBI后向有益的和炎症消退的表型转变。目标3： 测试特异性HDAC3抑制剂RGFP966在缓解炎症和 在两种性别的年轻成年和老年小鼠中改善长期TBI结果。

Emerging evidence implicates a pivotal role of cerebral inflammation in the pathophysiology of traumatic brain injury (TBI). Following TBI, microglia/macrophages may assume distinct pro-inflammatory or inflammation- resolving phenotypes, which potentiate brain injury or facilitate brain repair, respectively. The intracellular molecular switches that determine microglial/macrophage functional phenotypes after TBI are poorly understood. Identifying such molecular mechanisms may reveal novel targets to tune microglia/macrophages toward the reparative inflammation-resolving phenotype and improve long-term TBI outcomes. Histone deacetylases (HDACs) catalyze the removal of acetyl groups from histone and non-histone proteins, thereby regulating not only gene transcription but also the activity of various proteins through post-translational modifications. Previous studies by us and others demonstrate that pan-inhibitors of Class I HDACs (HDAC1, 2, 3, 8) mitigate brain inflammation and improve neurological functions after TBI. However, it is imperative to elucidate the role of different HDAC subtypes, in order to focus on specific therapeutic targets without disrupting the beneficial functions of some HDACs in post-injury brain repair. To date, the HDAC subtype responsible for protection against TBI is unknown. It is also not known if the cellular/molecular mechanisms underlying HDAC inhibitor-afforded protection involve the alteration of microglial/macrophage phenotype. Our pilot studies show for the first time that: 1) Microglia/macrophage-specific knockout (mKO) of HDAC3, but not HDAC1 or HDAC2, improves neurobehavioral outcomes after TBI. 2) HDAC3 mKO improves gray and white matter integrity, and mitigates neuroinflammation after TBI. 4) HDAC3 inhibition ameliorates pro- inflammatory microglia-mediated neurotoxicity after neuronal stretch injury (NSI), an in vitro TBI model. 5) HDAC3 inhibition reduces the activation of signal transducer and activator of transcription 1 (STAT1), a key molecule that mediates pro-inflammatory responses in microglia/macrophages. 6) Subcutaneous delivery of RGFP966, a brain-penetrant, potent, and specific HDAC3 inhibitor, ameliorates inflammation and sensorimotor deficits after TBI. Given these observations, we propose three specific aims to test the novel hypothesis that genetic or pharmacological ablation of HDAC3 provides neuroprotection and improves brain repair and long-term outcomes after TBI by promoting inflammation-resolving microglial/macrophage responses. Aim 1: Test if HDAC3 mKO improves gray and white matter integrity and long-term neurological functions after TBI. Controlled cortical impact (CCI) will be induced in mice of both sexes with tamoxifen-inducible HDAC3 knockout in microglia/macrophages. Aim 2: Test if genetic knockout of the HDAC3-STAT1 signaling pathway shifts microglia/macrophages toward the beneficial and inflammation-resolving phenotype after TBI. Aim 3: Test the therapeutic potential of the specific HDAC3 inhibitor RGFP966 in resolution of inflammation and improvement of long-term TBI outcomes in young adult and aged mice of both genders.