Metabolic Regulation by Glial Inflammatory Signaling

项目摘要 肥胖症是一个重要的全球性公共卫生问题， 限制了有效治疗的发展。营养过剩引发外周血免疫细胞活化 组织和大脑，这表明针对炎症反应的策略在理论上是可行的。 治疗潜力然而，这些方法在很大程度上仍未得到检验。我们最近证明， 脑胶质细胞（星形胶质细胞和小胶质细胞）中缺乏IKKβ的小鼠显示对饮食诱导的肥胖的易感性降低 (DIO)和食欲过盛，但动力学不同。小胶质细胞活化发生较早，是DIO所必需的 从HFD喂养开始，星形胶质细胞对DIO的敏感性降低，而星形胶质细胞对DIO的保护仅发生在HFD喂养数周后。 HFD暴露。与小胶质细胞在CNS炎症中诱导反应性星形胶质细胞增多的已知作用一致， 这些数据表明，炎症激活的级联反应始于小胶质细胞，随后 触发星形胶质细胞促进DIO 小鼠模型之间的另一个明显区别是， 瘦型小胶质细胞IKKβ基因敲除，提示能量平衡调节与葡萄糖之间的分离 通过小胶质细胞的体内平衡。然而，负责这种表型的分子介质仍然未知。 我们现在已经开发了一个不依赖于饮食的诱导型小胶质细胞激活模型， 设计药物激活受体（DREADD）。表达Gq偶联DREADD的小胶质细胞 受体hM 3D被CNO处理迅速激活，TNF α表达显著上调。 然而，CNO治疗引起葡萄糖耐量的立即改善，即使在HFD喂养的 小鼠出乎意料的是，这种作用可以通过icv预处理来阻断， 拮抗剂或黑皮质素3/4受体拮抗剂。虽然TNF信号可以破坏瘦素的敏感性， 它还增加POMC神经元放电，促进突触可塑性并激活下丘脑神经元， 黑皮质素途径因此，我们假设HFD喂养通过小胶质细胞TLR 4起作用， 触发DIO易感性，但通过黑皮质素途径改善葡萄糖耐量。到 进一步研究这些前提，在目标1中，我们将确定星形胶质细胞的激活是否依赖于 小胶质细胞炎性信号传导和所需的小胶质细胞诱导的DIO。AIM 2将确定是否 小胶质细胞TNF和黑皮质素信号传导是改善葡萄糖耐量所必需的， 小胶质细胞激活。最后，目的3研究了改善葡萄糖耐量的外周机制， 包括转录组学筛选葡萄糖稳态调节的其它小胶质细胞介质。 总之，这些研究将有助于确定小胶质细胞激活的细胞和分子成分， 介导其对肥胖和糖尿病发病机制的影响。

Project Summary Obesity is a significant public health concern worldwide, and the incomplete understanding of its pathogenesis has limited the development of effective treatments. Overnutrition triggers immune cell activation in peripheral tissues and the brain, suggesting that strategies to target the inflammatory response have theoretical therapeutic potential. However, these approaches remain largely untested. We recently demonstrated that mice lacking IKKβ in brain glia (astrocytes and microglia) show reduced susceptibility to diet-induced obesity (DIO) and hyperphagia, but with different kinetics. Microglial activation occurs earlier and is required for DIO susceptibility from the onset of HFD feeding whereas astrocyte protection from DIO only occurs after weeks of HFD exposure. Consistent with the known role of microglia to induce reactive astrocytosis in CNS inflammatory diseases, these data suggest a cascade of inflammatory activation beginning with microglia that subsequently triggers astrocytes to promote DIO. Another stark difference between the mouse models is a paradoxical impairment of glucose tolerance in the lean microglial IKKβ knockout, suggesting dissociation between the regulation of energy balance and glucose homeostasis by microglia. However, the molecular mediators responsible for this phenotype remain unknown. We have now developed a diet-independent inducible model of microglial activation using the Designer Receptor Activated by Designer Drugs (DREADD) approach. Microglia expressing the Gq-coupled DREADD receptor hM3D are rapidly activated by CNO treatment with marked upregulation of TNFa expression. Nevertheless, the CNO treatment causes an immediate improvement in glucose tolerance even in HFD-fed mice. Unexpectedly, this effect can be blocked using icv pretreatment with either a specific TNF receptor antagonist or a melanocortin 3/4 receptor antagonist. While TNF signaling can disrupt leptin sensitivity in hypothalamic neurons, it also increases POMC neuron firing, promotes synaptic plasticity and activates the melanocortin pathway. Therefore, we hypothesize that HFD feeding acts through microglial TLR4 to triggers DIO susceptibility but improve glucose tolerance through the melanocortin pathway. To investigate these premises further, in Aim 1 we will determine whether astrocyte activation is dependent on microglial inflammatory signaling and required for microglia-induced DIO. Aim2 will determine whether microglial TNF and melanocortin signaling are required for the improved glucose tolerance induced by microglial activation. Finally, Aim 3 investigates the peripheral mechanisms of improved glucose tolerance and includes a transcriptomic screen for additional microglial mediators of glucose homeostasis regulation. Together, these studies will help identify the cellular and molecular components of microglial activation that mediate its impact on obesity and diabetes pathogenesis.