Novel molecular strategies to promote functional recovery after traumatic brain injury

创伤性脑损伤(TBI)和脑损伤后的神经后遗症是美国军方关注的一个主要医学问题 退伍军人。目前还没有有效的治疗方法来对抗脑外伤后的灾难性神经残疾，部分原因是 因为大多数针对脑外伤的神经保护疗法针对的是灰质，而忽视了白质的重要性 物质(WM)损伤，其程度决定了长期神经损伤的严重程度。一种执着的 颅脑损伤后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)是脑创伤后免疫的重要介质 和炎症反应，并可以呈现不同的功能状态，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 有助于调节受损西医的炎症状态，并最终影响西医的完整性。 具体地说，Mi/MΦ的炎症消退和保护/修复表型对于缓解 WM损伤和促进WM修复，因为它们解决了局部炎症，清除了破碎的髓鞘或 细胞碎片，并为大脑重塑提供营养因子。关键的分子开关和网络 确定颅脑损伤后Mi/MΦ的整体功能状态。 为了填补这一关键的科学空白，我们建议将盐诱导蛋白激酶(Siks)作为新的调节因子进行研究。 实验性颅脑损伤后Mi/MΦ函数的变化。SIKS通过直接作用于几个 特定的转录调控因子。因此，SIK激活位于决策树的顶端，用于在 在Mi/MΦ中，多态的、通常相反的免疫反应。参与的科学前提是 SIK作为脑损伤的候选生物靶点是其滴定免疫平衡以消炎的能力 和保护/修复表型，同时避免不分青红皂白地抑制免疫功能。 我们的新初步发现也加强了这一提议的科学前提：1)TBI 上调小鼠Mi/MΦ中SIK1的表达和活性(磷酸化)，但在其他脑细胞中不表达；2) 他莫昔芬诱导的选择性敲除Mi/MΦ中的SIK1改善长期感觉运动功能和 脑损伤后的空间记忆，证实了Mi/MΦSIK1在脑损伤后神经预后中的关键作用；3) 从机制上讲，SIK1MKO驱动Mi/MΦ向炎症消解和保护/修复表型转变 4)腹腔注射YKL-05-099(YKL)， 一种新的选择性SIK抑制剂，可减轻脑外伤后的神经炎症和神经功能障碍。因此， 拟议的研究将检验核心假设，即SIK1的基因缺失或药物抑制 通过双重机制改善脑白质恢复和长期脑损伤预后：1)保护 通过促进炎症分解Mi/MΦ反应对抗早期轴突损伤；2)增强 通过促进修复的Mi/MΦ表型进行慢性期白质恢复。 如果获得资金，我们将及时有效地实现三个具体目标。目标1：测试是否给药 一种选择性的SIK抑制剂可改善长达20周的长期脑损伤结果。我们将评估治疗效果 SIK抑制剂YKL的作用。成年C57BL/6小鼠受控皮质撞击(CCI)后 性别。目的2：检测YKL是否通过抑制SIK1依赖减轻急性/亚急性期轴索损伤 神经毒性Mi/MΦ反应。这一机制目标将研究使用他莫昔芬诱导的Mi/MΦsik 1的作用 MI/MΦ特异性SIK1基因敲除小鼠(SIK1MKO)和野生型对照小鼠。目标3：测试YKL或SIK1 MKO通过培养神经营养因子促进颅脑损伤后20周的WM恢复和长期恢复 修复前期Mi/MΦ表型。 严格证实的YKL的有益作用将促进其临床转化为一种新的潜力 治疗颅脑损伤，促进脑康复，提高退伍军人脑损伤患者的生活质量。

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.