Regulation of microglial priming with age and the impact on neural plasticity

 描述（由申请人提供）：退行性疾病发展的最大风险因素是衰老。随着世界上平均年龄的持续增长，老年痴呆症和帕金森氏症等退行性疾病的患病率也在沿着上升。大脑老化的标志包括干细胞磨损、蛋白质稳态丧失、线粒体功能下降和炎症。这些相互关联的表型创造了退行性疾病表现和进展的环境。这些变化的原因和它们出现的顺序仍然不确定，但它们对认知功能和疾病进展的影响是明确的。神经炎症描述了一种促炎细胞因子表达增加的环境;最近，这种炎症状态的原因已被归因于一种称为引发的现象。小胶质细胞是中枢神经系统的主要免疫细胞，具有多种功能，如在海马神经发生中的调节作用。随着小胶质细胞老化，它们表现出对促炎M1极化的偏好和对诱导抗炎/组织修复M2 a/B表型的因子的抗性，这种年龄依赖性变化被称为引发。已显示受损的小胶质细胞功能对神经发生和长时程增强具有有害影响，这表明在正常认知下降以及退行性疾病中发生的认知障碍的快速进展中引发的作用。我的论文利用质谱等技术来研究神经原性小生境中细胞类型发生的与年龄相关的变化。我们最近进行了蛋白质组学分析的年轻和年老的小胶质细胞，揭示了年龄依赖性的改变代谢途径和肌动蛋白/细胞骨架组织。上游调节剂的分析预测RICTOR和皮质酮的抑制。RICTOR是mTORC 2复合物中的核心组分，是哺乳动物雷帕霉素或mTOR信号传导通路的靶点之一，该通路负责感测营养物质丰度。皮质酮是一种哺乳动物糖皮质激素，具有很强的抗炎活性。我们发现，小胶质细胞的RICTOR已被抑制siRNA模仿引发的表型和减弱对糖皮质激素的反应。这些发现得到了文献的支持，表明mTORC 2抑制在巨噬细胞中产生对LPS的增强的炎症反应。因此，我推测mTORC 2活性的年龄依赖性变化有助于小胶质细胞的启动，并且mTORC 2信号传导是糖皮质激素活性的上游调节剂。本申请的具体目的：（i）确定mTORC 2活性是否和如何随年龄改变，以及这种改变如何有助于小胶质细胞的引发（ii）确定糖皮质激素受体活性在引发表现中的作用和mTORC 2调节这种作用的机制（iii）研究小胶质细胞启动是否通过选择性降低幼年小鼠海马中的RICTOR表达来驱动神经发生和神经可塑性的降低。

 DESCRIPTION (provided by applicant): The greatest risk factor for the development of degenerative disease is aging. As the median age in the world continues to rise along with it does the prevalence of degenerative diseases like Alzheimer's and Parkinson's. The hallmarks of the aged brain include stem cell attrition, loss of proteostasis, decreased mitochondrial function, and inflammation. These interconnected phenotypes create the environment in which degenerative diseases manifest and progress. The causes of these changes and the order in which they appear are still uncertain however their impact on cognitive function and disease progression is clear. Neuroinflammation describes an environment with an increased expression of pro-inflammatory cytokines; recently the cause of this inflammatory status has been attributed to a phenomenon known as priming. Microglia are the primary immune cell of the CNS and have diverse responsibilities such as a regulatory role in neurogenesis of the hippocampus. As microglia age they exhibit preference for the pro-inflammatory M1 polarization and a resistance to factors that induce an anti-inflammatory/tissue repair M2a/b phenotype this age dependent change is known as priming. Impaired microglial function has been shown to have deleterious effects on neurogenesis and long-term potentiation suggesting a role for priming in normal cognitive decline as well as the rapid progress of cognitive impairments that occur in degenerative diseases. My dissertation utilizes techniques such as mass spectrometry to study the age related changes that occur in cell types within the neurogenic niche. We recently performed a proteomic analysis of young and old microglia which revealed age-dependent alterations in metabolic pathways and actin/cytoskeletal organization. Analysis of upstream regulators predicted an inhibition of RICTOR and corticosterone. RICTOR is a central component in the mTORC2 complex one half of the mammalian target of rapamycin or mTOR signaling pathway, a pathway responsible for sensing nutrient abundance. Corticosterone is a mammalian glucocorticoid with powerful anti- inflammatory activity. We found that microglia where RICTOR had been inhibited with siRNA mimicked a primed phenotype and attenuated the response to glucocorticoids. These findings are supported by literature showing that mTORC2 inhibition produces an enhanced inflammatory response in macrophages to LPS. Therefore I hypothesize that age-dependent changes in mTORC2 activity contribute to the priming of microglia and that the mTORC2 signaling is an upstream regulator of glucocorticoid activity. The specific aims of this application: (i) to determine if and how mTORC2 activity is altered with age and how this alteration contributes to the priming of microglia (ii) to determine the role of glucocorticoid receptor activity in the manifestation of priming and the mechanism by which mTORC2 regulates this action (iii) to examine if microglial priming drives the reduction in neurogenesis and neural plasticity by selectively reducing RICTOR expression in the hippocampus of young mice.