Novel role and mechanisms of histone deacetylases in traumatic brain injury

新的证据表明，脑部炎症在创伤性脑损伤的病理生理学中起着关键作用 损伤(TBI)。脑外伤后，小胶质细胞/巨噬细胞可能表现出明显的促炎或炎症- 分解表型，它们分别加强脑损伤或促进脑修复。细胞内 决定脑外伤后小胶质/巨噬细胞功能表型的分子开关很差 明白了。识别这种分子机制可能会揭示调节小胶质细胞/巨噬细胞的新靶点 向修复性炎症消退表型转变，改善脑外伤的长期预后。 组蛋白脱乙酰酶(HDAC)催化从组蛋白和非组蛋白蛋白中去除乙酰基， 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。我们和其他人之前的研究表明，I类HDAC的PAN抑制剂(HDAC1，2， 3、8)减轻脑损伤后的脑炎症反应，改善神经功能。然而，必须要 阐明不同的HDAC亚型的作用，以便专注于特定的治疗靶点，而不是 扰乱了一些HDAC在损伤后脑修复中的有益功能。到目前为止，HDAC子类型 负责预防TBI的人还不得而知。目前也不知道细胞/分子机制是否 HDAC抑制剂提供的潜在保护涉及小胶质/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，可改善脑外伤后的神经行为结果。2)HDAC3 MKO改善了灰色和 白质完整性，并减轻脑外伤后的神经炎症。4)HDAC3抑制可改善- 神经细胞牵张损伤(NSI)后炎性小胶质细胞介导的神经毒性--体外脑损伤模型。5) HDAC3抑制减少信号转导和转录激活因子1(STAT1)的激活，STAT1是信号转导和转录激活的关键 在小胶质细胞/巨噬细胞中介导促炎反应的分子。6)皮下注射 RGFP966是一种脑穿透、有效和特异的HDAC3抑制剂，可改善炎症和感觉运动 创伤性脑损伤后的赤字。鉴于这些观察，我们提出了三个具体的目标来测试新的假设 基因或药物消融HDAC3可提供神经保护并改善大脑修复和 通过促进炎症消解小胶质细胞/巨噬细胞反应来评估脑外伤后的长期预后。 目的1：测试HDAC3 MKO是否改善术后灰质和白质的完整性和长期神经功能 TBI。用他莫昔芬诱导的HDAC3将在两性小鼠中诱导控制性皮质撞击(CCI) 小胶质细胞/巨噬细胞中的基因敲除。目的2：检测HDAC3-STAT1信号通路是否存在基因敲除 脑外伤后小胶质细胞/巨噬细胞向有益的和消炎的表型转变。目标3： 测试特异性HDAC3抑制剂RGFP966在消炎和治疗方面的潜力 改善青壮年和老年小鼠的长期脑损伤结果。

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.