Novel molecular strategies to promote functional recovery after traumatic brain injury

创伤性脑损伤（TBI）和TBI后神经系统后遗症是美国军方的主要医疗问题 老兵目前还没有有效的治疗方法来对抗创伤性脑损伤后灾难性的神经功能障碍，部分原因是 因为大多数针对TBI的神经保护疗法针对灰质，但忽视了白色的重要性， 脑实质（WM）损伤，其程度决定了长期神经功能缺损的严重程度。持久 脑外伤后的促炎微环境被认为是加重WM的潜在机制之一 损伤并阻碍WM修复。小胶质细胞和巨噬细胞（Mi/MΦ）是TBI后免疫反应的重要介质 和炎症反应，并可以采取不同的功能状态，以响应特定的 微环境信号越来越多的证据表明，Mi/MΦ的不同功能表型 对损伤WM的炎症状态的调节起重要作用，并最终影响WM的完整性。 具体而言，Mi/MΦ的炎症消退和保护/修复表型对于减轻炎症反应是必不可少的。 由于它们解决了局部炎症，清除了破裂的髓鞘， 细胞碎片，并为脑重塑提供营养因子。关键的分子开关和网络， 确定TBI后Mi/MΦ的总体功能状态的方法知之甚少。 为了填补这一关键的科学空白，我们建议研究盐诱导激酶（SIKs）作为新的调节剂 实验性TBI后Mi/MΦ功能的变化。SIKs通过直接作用于几个基因， 特异性转录调节因子。因此，SIK激活位于决策树的顶点，用于在 M1/MΦ中多态性的、经常相反的免疫应答。参与的科学前提 作为TBI的候选生物靶点的SIK是其滴定免疫平衡朝向炎症消退的能力。 和保护性/修复性表型，同时避免不加选择地抑制免疫功能。 我们的新的初步发现也加强了这一建议的科学前提：1）TBI 在Mi/MΦ中升高SIK 1的表达和活性（磷酸化），但在小鼠的其他脑细胞中不升高; 2） 他莫昔芬诱导的Mi/MΦ（mKO）中SIK 1的选择性敲除改善长期感觉运动功能， TBI后的空间记忆，证实Mi/MΦ SIK 1在TBI神经学结果中的关键作用; 3） 在机制上，SIK 1 mKO驱动Mi/MΦ朝向炎症消退和保护/修复表型 TBI后，从而限制轴突损伤并促进WM修复; 4）腹膜内递送YKL-05-099（YKL）， 一种新的选择性的SIK抑制剂，减轻TBI后的神经炎症和神经功能缺损。因此 拟议中的研究将测试核心假设，即基因缺失或药物抑制SIK 1 通过双重机制改善白色物质恢复和长期TBI结果：1）保护 通过促进炎症消退Mi/MΦ反应对抗早期轴突损伤;和2）增强 慢性期白色物质恢复通过促进修复性Mi/MΦ表型。 如果获得资助，我们将及时有效地实现三个具体目标。目的1：测试是否给药 选择性的SIK抑制剂可以改善TBI的长期预后长达20周。我们将评估治疗效果 在控制皮质撞击（CCI）后，向成年C57 BL/6小鼠腹腔内递送的SIK抑制剂YKL的作用， 性别目的2：测试YKL是否通过抑制SIK 1依赖性神经元凋亡来减轻急性/亚急性期的轴突损伤。 神经毒性Mi/MΦ反应。这一机制的目的将研究Mi/MΦ SIK 1的作用，使用他莫昔芬诱导的 两种性别的Mi/MΦ特异性SIK 1敲除（SIK 1 mKO）和野生型对照小鼠。目标3：测试YKL或SIK 1 mKO通过培养神经营养因子促进脑外伤后长达20周的WM恢复和长期恢复。 促修复Mi/MΦ表型。 YKL的一个严格证实的有益作用将促进其临床转化为一种新的潜力 治疗TBI，以加强脑康复和改善生活质量的退伍军人遭受TBI。

Traumatic brain injury (TBI) and post-TBI neurological sequelae are a major medical concern for US military veterans. There is no effective therapy to battle the catastrophic neurological disabilities after TBI, in part because most neuroprotective therapies against TBI target gray matter but neglect the importance of white matter (WM) injury, the degree of which dictates the severity of long-term neurological deficits. A persistent proinflammatory microenvironment after TBI is considered one underlying mechanism that exacerbates WM injury and hinders WM repair. Microglia and macrophages (Mi/MΦ) are important mediators of post-TBI immune and inflammatory responses and can assume diverse functional states in response to specific microenvironmental signals. Accumulating evidence suggests that the different functional phenotypes of Mi/MΦ contribute considerably to the regulation of inflammatory status of injured WM and ultimately impact WM integrity. Specifically, an inflammation-resolving and protective/reparative phenotype of Mi/MΦ is essential for mitigating WM injury and facilitating WM repair because they resolve local inflammation, clear broken myelin sheath or cellular debris, and supply trophic factors for brain remodeling. The key molecular switches and networks that determine the overall functional state of Mi/MΦ after TBI are poorly understood. To fill this critical scientific gap, we propose to investigate salt-inducible kinases (SIKs) as novel regulators of Mi/MΦ functions after experimental TBI. SIKs potently control gene expression by directly acting on several specific transcriptional regulators. Thus, SIK activation lies at the apex of a decision tree for arbitrating between polymorphic, often-opposing immune responses in Mi/MΦ. The scientific premise underlying the engagement of SIK as a candidate biological target for TBI is its ability to titrate immune balance toward inflammation-resolving and protective/reparative phenotypes, while avoiding indiscriminate suppression of immune function. The scientific premise of this proposal is also strengthened by our new preliminary discoveries: 1) TBI elevates SIK1 expression and activity (phosphorylation) in Mi/MΦ but not in other brain cells in mice; 2) Tamoxifen-induced selective knockout of SIK1 in Mi/MΦ (mKO) improves long-term sensorimotor functions and spatial memory after TBI, confirming a crucial role of Mi/MΦ SIK1 in TBI neurological outcomes; 3) Mechanistically, SIK1 mKO drives Mi/MΦ toward an inflammation-resolving and protective/reparative phenotype after TBI, thus restricting axonal injury and promoting WM repair; 4) Intraperitoneal delivery of YKL-05-099 (YKL), a novel selective SIK inhibitor, attenuates neuroinflammation and neurological deficits after TBI. Accordingly, the proposed studies will test the core hypothesis that genetic deletion or pharmacological inhibition of SIK1 improves white matter restoration and long-term TBI outcomes by dual mechanisms: 1) protecting against early axonal injury by promoting inflammation-resolving Mi/MΦ responses; and 2) enhancing chronic-stage white matter restoration by promoting a reparative Mi/MΦ phenotype. If funded, we will tackle three Specific Aims in a timely and efficient manner. Aim 1: Test if administration of a selective SIK inhibitor improves long-term TBI outcomes for up to 20 weeks. We will assess the therapeutic effects of the SIK inhibitor YKL, delivered i.p. after controlled cortical impact (CCI) to adult C57BL/6 mice of both sexes. Aim 2: Test if YKL attenuates axonal injury at acute/subacute stages via inhibition of SIK1-dependent neurotoxic Mi/MΦ responses. This mechanistic aim will study the role of Mi/MΦ SIK1 using tamoxifen-induced Mi/MΦ-specific SIK1 knockout (SIK1 mKO) and wild-type control mice of both sexes. Aim 3: Test if YKL or SIK1 mKO promotes WM restoration and long-term recovery after TBI for up to 20 weeks by fostering a neurotrophic/ pro-repair Mi/MΦ phenotype. A rigorously confirmed beneficial effect of YKL would facilitate its clinical translation into a novel potential therapeutic for TBI to enhance brain rehabilitation and improve the quality of life for veterans suffering TBI.