Intracellular mechanisms of microglia activation in diet-induced obesity

小胶质细胞是脑和脊髓的卵黄囊来源的单核细胞，在免疫调节中起着至关重要的作用。 反应，包括炎症。最近的工作扩大了小胶质细胞在中枢神经系统中的作用， 中枢神经系统（CNS），包括轴突末梢和树突棘的吞噬作用，因此指向一个活跃的 小胶质细胞在神经元回路发育和可塑性中的作用（Tremblay等，2011年）。饮食诱导的肥胖 (DIO)早在高脂饮食（HFD）后3天就诱导小胶质细胞活化和下丘脑炎症 暴露，在体重发生变化之前（Thaler等人，2012年）。我们 在 控制 也表明激活的小胶质细胞 下丘脑充当参与下丘脑神经回路的突触可塑性的导体， 摄食行为和葡萄糖代谢的影响（Jin等人，2016).小胶质细胞活性的变化， 功能是需要能量需求动态变化的过程。在炎症期间， 线粒体代谢被认为有助于小胶质细胞活化（Voloboueva等人，二〇一三年; Gimeno-Bayon等人，2014; Orihuela等人，2016）。我们的初步数据显示，HFD诱导的 下丘脑炎症和小胶质细胞活化通过增加线粒体解偶联蛋白来抑制 2（UCP 2）表达和快速（3天内）和短暂（第7天逆转）线粒体 小胶质细胞的分裂事件。我们以前已经表明，UCP 2传播线粒体分裂， （Coppola等人，2007; Andrews等人，2008;户田等人，2016）通过激活动态相关肽1 （DRP 1），线粒体分裂使能因子（户田等人，2016）。与此相对应，当我们删除UCP 2时， 选择性地从成年小鼠的小胶质细胞中分离，HFD暴露未能触发下丘脑中线粒体的分裂， 小胶质细胞，并且还减少了HFD诱导的小鼠体重增加和代谢损伤。 综合这些观察，推动了这一提议的中心假设，即DRP 1 在HFD喂养的早期而不是晚期，通过DRP 1激活介导的线粒体分裂是 对于小胶质细胞活化、神经炎症、下丘脑回路适应是不可或缺的，以促进 肥胖为了检验这些假设，我们提出了3个目标：具体目标1将检验UCP 2- 在HFD的早期阶段（到第3天）由DRP 1激活介导的诱导线粒体分裂 进食对于下丘脑小胶质细胞活化、炎症和肥胖易感性至关重要。 具体目标2将检验HFD诱导的小胶质细胞活化需要DRP 1用于HFD诱导的小胶质细胞活化的假设。 HFD早期而非晚期小胶质细胞中快速和短暂的线粒体分裂事件 喂养以促进肥胖。特异性目标3将确定HFD喂养的DIO中活化的小胶质细胞是否 小鼠是弓形POMC和AgRP神经元突触适应的上游控制者。 这些研究的执行将为全身葡萄糖的中枢调节提供新的见解 通过靶向脑线粒体动力学，提供了对抗糖尿病的新途径。

Microglia, the yolk sack-derived monocytes of the brain and spinal cord, plays a crucial role in immune responses, including inflammation. Recent work has expanded the role of microglia in the central nervous system (CNS), which includes phagocytosis of axon terminals and dendritic spines, thus pointing to an active role of microglia in neuronal circuit development and plasticity (Tremblay et al., 2011). Diet-induced obesity (DIO) induces microglia activation and hypothalamic inflammation as early as 3 days after high fat diet (HFD) exposure, before changes in body weight occur (Thaler et al., 2012). We in control also showed that activated microglia the hypothalamus act as a conductor of synaptic plasticity of the hypothalamic neurocircuitry involved in the of feeding behavior and glucose metabolism (Jin et al., 2016).Changes in microglial activity and function are processes that require dynamic changes in energy demand. During inflammation, changes in mitochondrial metabolism were suggested to contribute to microglia activation (Voloboueva et al., 2013; Gimeno-Bayon et al., 2014; Orihuela et al., 2016). Our preliminary data revealed that HFD-induced hypothalamic inflammation and microglia activation is paralleled by increased mitochondrial uncoupling protein 2 (UCP2) expression and a rapid (within 3 days) and transient (by day 7 days it is reversed) mitochondria fission event in microglia cells. We have previously shown that UCP2 propagates mitochondrial fission (Coppola et al., 2007; Andrews et al., 2008; Toda et al., 2016) via activation of dynamic-related peptide 1 (DRP1), a mitochondrial fission enabler (Toda et al., 2016). Corresponding with this, when we deleted UCP2 selectively from microglia in adult mice, HFD-exposure failed to trigger fission of mitochondria in hypothalamic microglia cells, and, it also diminished HFD-induced body weight gain and metabolic impairments of mice. Taken together these observations gave impetus to the central hypothesis of this proposal which is that DRP1 mediated mitochondrial fission via DRP1 activation in the early but not late phase of HFD feeding is indispensible for microglia activation, neuroinflammation, hypothalamic circuit adaptation to promote obesity. To test these hypotheses, we propose 3 Aims: Specific Aim 1 will test the hypothesis that UCP2- induced mitochondrial fission mediated by DRP1 activation in the early phase (by day 3) of HFD feeding is critical for hypothalamic microglia activation, inflammation and obesity susceptibility. Specific Aim 2 will test the hypothesis that HFD-induced microglia activation requires DRP1 for the rapid and transient mitochondria fission event in microglia cells in early but not late phase of HFD feeding to promote obesity. Specific Aim 3 will determine whether activated microglia in HFD-fed DIO mice are upstream controllers of synaptic adaptations of arcuate POMC and AgRP neurons. The execution of these studies will deliver novel insights into central regulation of whole body glucose metabolism and offer novel avenues to combat diabetes by targeting brain mitochondrial dynamics.