SIRT1 Limits Microglial Toxicity in Alzheimer's Disease

描述（由申请人提供）：长期以来一直认为小胶质细胞活化有助于阿尔茨海默病（AD）的发病机制。除了对神经元和突触功能造成直接毒性作用外，淀粉样蛋白β（A？）和/或tau蛋白的积累刺激小胶质细胞活化和炎性细胞因子的表达，这可诱导进一步的神经元损伤。阻断小胶质细胞活化中的毒性通路可以有效地防止神经退行性变。然而，调节小胶质细胞环的分子机制仍然难以捉摸。我们以前的研究表明，在原代皮层文化NF-？小胶质细胞中的B活化在小胶质细胞介导的A毒性中起关键作用。抑制NF-？B通过SIRT 1，组蛋白脱乙酰酶的sirtuin家族的成员，在A？处理的原代培养物中保护小胶质细胞免受毒性。在AD大脑中，SIRT 1水平显著降低。培养的小胶质细胞中的SIRT 1表达被A？处理显著减少。基于这些发现，我们假设SIRT 1减少是导致AD小胶质细胞毒性的关键事件，并且小胶质细胞SIRT 1通过抑制NF-κ B抑制A？介导的神经元缺陷。B激活。为了验证这一假设，我们提出了三个具体目标。在目标1中，我们将在表达人淀粉样前体蛋白（hAPP）的小鼠的小胶质细胞中检测SIRT 1，并系统地研究小胶质细胞SIRT 1失活如何影响炎症反应和A？相关的神经元/行为缺陷。在目的2，以确定是否小胶质细胞SIRT 1发挥神经保护作用，通过抑制NF-？B激活，我们将确定是否组成性激活的经典NF-？hAPP小鼠小胶质细胞中的B信号以类似于SIRT 1缺失的方式加剧缺陷。在补充实验中，我们将确定是否抑制NF-？B信号将通过注入有效的NF-？B抑制剂或注射抑制NF-？小胶质细胞中的B。在目的3，以确定小胶质细胞SIRT 1抑制NF-？B，我们将系统地检查SIRT 1是否抑制NF-？B通过脱乙酰化RelA和/或通过减少骨髓细胞中RelA磷酸化。使用染色质免疫沉淀（ChIP）分析，我们将确定是否SIRT 1诱导抑制NF-？B活化涉及髓样细胞中组蛋白（H3 K56 Ac）的脱乙酰化。这些研究的完成将为神经退行性变中调节小胶质细胞环的分子机制提供新的见解。这些研究也将为我们开发SIRT 1增强策略作为AD新治疗方法的长期目标奠定基础。

DESCRIPTION (provided by applicant): Microglial activation has long been proposed to contribute to the pathogenesis of Alzheimer's disease (AD). Besides causing direct toxic effects on neuronal and synaptic functions, accumulation of amyloid beta (A¿) and/or tau stimulates microglial activation and expression of inflammatory cytokines, which can induce further neuronal damage. Blocking the toxic pathway in microglial activation could effectively protect against neurodegeneration. However, the molecular mechanisms modulating the microglial loop remain elusive. Our previous studies in primary cortical cultures suggest that NF-?B activation in microglia plays a critical role in microglial-mediated A¿ toxicity. Inhibition of NF-?B by SIRT1, a member of the sirtuin family of histone deacetylases, protected against microglia toxicity in A¿-treated primary cultures. In AD brains, SIRT1 levels were markedly reduced. SIRT1 expression in cultured microglia was significantly diminished by A¿ treatment. Based on these findings, we hypothesize that SIRT1 reduction is a key event leading to microglial toxicity in AD and that microglial SIRT1 limits A¿-mediated neuronal deficits by suppressing NF-?B activation. To test this hypothesis, we propose three Specific Aims. In Aim 1, we will inactivate SIRT1 in microglia of mice expressing human amyloid precursor protein (hAPP) and systematically examine how microglial SIRT1 inactivation affects inflammatory responses and A¿-related neuronal/behavioral deficits. In Aim 2, to determine if microglial SIRT1 exerts neuroprotection by suppressing NF-?B activation, we will determine if constitutive activation of canonical NF-?B signaling in microglia of hAPP mice exacerbates the deficits in a manner similar to SIRT1 deletion. In complementary experiments, we will determine if inhibiting NF-?B signaling will ameliorate A¿-associated neuronal deficits by infusing a potent NF-?B inhibitor in the brain or injection of a viral vector that inhibits NF-?B in microglia. In Aim 3, to determine the mechanism by which microglial SIRT1 inhibits NF-?B, we will systematically examine if SIRT1 inhibits NF-?B by deacetylating RelA and/or by reducing RelA phosphorylation in myeloid cells. Using chromatin immunoprecipitation (ChIP) analyses, we will then determine if SIRT1- induced suppression of NF-?B activation involves deacetylation of histones (H3K56Ac) in myeloid cells. Completion of the proposed studies will provide new insight into the molecular mechanisms modulating the microglial loop in neurodegeneration. These studies will also lay the foundation for our long-term goal of developing SIRT1-enhancing strategies as a new therapeutic approach for AD.