Bellesi Michele, de Vivo Luisa, Chini Mattia, Gilli Francesca, Tononi Giulio, Cirelli Chiara
Department of Psychiatry, University of Wisconsin-Madison, Madison, Wisconsin 53719.
Department of Experimental and Clinical Medicine, Section of Neuroscience and Cell Biology, Università Politecnica delle Marche, Ancona, 60026, Italy, and.
J Neurosci. 2017 May 24;37(21):5263-5273. doi: 10.1523/JNEUROSCI.3981-16.2017.
We previously found that and its ligand , astrocytic genes involved in phagocytosis, are upregulated after acute sleep deprivation. These results suggested that astrocytes may engage in phagocytic activity during extended wake, but direct evidence was lacking. Studies in humans and rodents also found that sleep loss increases peripheral markers of inflammation, but whether these changes are associated with neuroinflammation and/or activation of microglia, the brain's resident innate immune cells, was unknown. Here we used serial block-face scanning electron microscopy to obtain 3D volume measurements of synapses and surrounding astrocytic processes in mouse frontal cortex after 6-8 h of sleep, spontaneous wake, or sleep deprivation (SD) and after chronic (∼5 d) sleep restriction (CSR). Astrocytic phagocytosis, mainly of presynaptic components of large synapses, increased after both acute and chronic sleep loss relative to sleep and wake. MERTK expression and lipid peroxidation in synaptoneurosomes also increased to a similar extent after short and long sleep loss, suggesting that astrocytic phagocytosis may represent the brain's response to the increase in synaptic activity associated with prolonged wake, clearing worn components of heavily used synapses. Using confocal microscopy, we then found that CSR but not SD mice show morphological signs of microglial activation and enhanced microglial phagocytosis of synaptic elements, without obvious signs of neuroinflammation in the CSF. Because low-level sustained microglia activation can lead to abnormal responses to a secondary insult, these results suggest that chronic sleep loss, through microglia priming, may predispose the brain to further damage. We find that astrocytic phagocytosis of synaptic elements, mostly of presynaptic origin and in large synapses, is upregulated already after a few hours of sleep deprivation and shows a further significant increase after prolonged and severe sleep loss, suggesting that it may promote the housekeeping of heavily used and strong synapses in response to the increased neuronal activity of extended wake. By contrast, chronic sleep restriction but not acute sleep loss activates microglia, promotes their phagocytic activity, and does so in the absence of overt signs of neuroinflammation, suggesting that like many other stressors, extended sleep disruption may lead to a state of sustained microglia activation, perhaps increasing the brain's susceptibility to other forms of damage.
我们之前发现，参与吞噬作用的星形胶质细胞基因及其配体在急性睡眠剥夺后会上调。这些结果表明，星形胶质细胞可能在长时间清醒期间参与吞噬活动，但缺乏直接证据。对人类和啮齿动物的研究还发现，睡眠不足会增加外周炎症标志物，但这些变化是否与神经炎症和/或小胶质细胞（大脑中固有的先天免疫细胞）的激活有关尚不清楚。在这里，我们使用连续块面扫描电子显微镜对小鼠额叶皮质在睡眠6 - 8小时、自发清醒或睡眠剥夺（SD）后以及慢性（约5天）睡眠限制（CSR）后的突触和周围星形胶质细胞突起进行三维体积测量。相对于睡眠和清醒状态，急性和慢性睡眠剥夺后星形胶质细胞的吞噬作用（主要针对大型突触的突触前成分）均增加。突触体中MERTK表达和脂质过氧化在短期和长期睡眠剥夺后也有类似程度的增加，这表明星形胶质细胞的吞噬作用可能代表大脑对与长时间清醒相关的突触活动增加的反应，清除频繁使用的突触中磨损的成分。然后，我们使用共聚焦显微镜发现，CSR小鼠而非SD小鼠表现出小胶质细胞激活的形态学迹象以及增强的对突触元件的小胶质细胞吞噬作用，且脑脊液中无明显神经炎症迹象。由于低水平的持续性小胶质细胞激活可导致对二次损伤的异常反应，这些结果表明，慢性睡眠剥夺通过小胶质细胞致敏，可能使大脑更容易受到进一步损伤。我们发现，突触元件的星形胶质细胞吞噬作用，大多起源于突触前且针对大型突触，在睡眠剥夺几小时后就已上调，在长期严重睡眠剥夺后进一步显著增加，这表明它可能促进频繁使用且强大的突触的清理，以应对长时间清醒时增加的神经元活动。相比之下，慢性睡眠限制而非急性睡眠剥夺会激活小胶质细胞，促进其吞噬活动，且在无明显神经炎症迹象的情况下发生，这表明与许多其他应激源一样，长期睡眠中断可能导致持续性小胶质细胞激活状态，可能增加大脑对其他形式损伤的易感性。
