不同年龄小鼠脱髓鞘动物模型中脑内星形胶质细胞激活情况的观察

目的 观察星形胶质细胞在不同年龄(青壮年及中老年)cuprizone(CPZ)脱髓鞘小鼠模型中的激活特点,探讨星形胶质细胞激活与髓鞘脱失可能存在的内在联系.方法 选取6周龄(青壮年)及9月龄(中老年)雄性C57 BL/6小鼠建立CPZ导致的急性脱髓鞘动物模型,经0.2％ CPZ处理6周后,通过体质量测量及卢卡斯快蓝(luxol fast blue,LFB)染色观察模型建立是否成功,利用免疫组织化学染色检测实验组(CPZ)和对照组(CTL)小鼠胼胝体(corpus callosum,CC)及皮层( cortex,CTX)区胶质纤维酸性蛋白(glial fibrillary acidic protein,GFAP)和髓鞘碱性蛋白(myelin basic protein,MBP)表达变化,并通过Western blot方法进一步检测GFAP及MBP蛋白表达差异.结果 0.2％ CPZ处理6周后,青壮年CPZ小鼠于胼胝体及皮层区GFAP阳性细胞数显著增多(P＜0.01),同时伴有显著的MBP表达下降(P＜0.01);中老年小鼠于胼胝体区GFAP阳性细胞数增多较明显(P＜0.05),并伴有MBP表达明显下降(P＜0.05);GFAP阳性细胞数的增多和MBP表达下降均表现为青壮年组更加明显(P＜0.01).结论 星形胶质细胞的激活于青壮年小鼠更加明显,并与髓鞘损伤呈现出一定的正相关性,星形胶质细胞激活可能是参与髓鞘损伤的重要原因.     

Spinal Cord Contusion

Spinal cord injury is a major cause of disability with devastating neurological outcomes and lim-ited therapeutic opportunities, even though there are thousands of publications on spinal cord injury annually. There are two major types of spinal cord injury, transaction of the spinal cord and spinal cord contusion. Both can theoretically be treated, but there is no well documented treatment in human being. As for spinal cord contusion, we have developed an operation with fabulous result.     

Store-operated calcium entry in neuroglia

Neuroglial cells are homeostatic neural cells. Generally, they are electrically non-excitable and their activation is associated with the generation of complex intracellular Ca²⁺ signals that define the “Ca²⁺ excitability” of glia. In mammalian glial cells the major source of Ca²⁺ for this excitability is the lumen of the endoplasmic reticulum (ER), which is ultimately (re)filled from the extracellular space. This occurs via store-operated Ca²⁺ entry (SOCE) which is supported by a specific signaling system connecting the ER with plasmalemmal Ca²⁺ entry. Here, emptying of the ER Ca²⁺ store is necessary and sufficient for the activation of SOCE, and without Ca²⁺ influx via SOCE the ER store cannot be refilled. The molecular arrangements underlying SOCE are relatively complex and include plasmalemmal channels, ER Ca²⁺ sensors, such as stromal interaction molecule, and possibly ER Ca²⁺ pumps (of the SERCA type). There are at least two sets of plasmalemmal channels mediating SOCE, the Ca²⁺-release activated channels, Orai, and transient receptor potential (TRP) channels. The molecular identity of neuroglial SOCE has not been yet identified unequivocally. However, it seems that Orai is predominantly expressed in microglia, whereas astrocytes and oligodendrocytes rely more on TRP channels to produce SOCE. In physiological conditions the SOCE pathway is instrumental for the sustained phase of the Ca²⁺ signal observed following stimulation of metabotropic receptors on glial cells.     

Lipocalin-2 deficiency attenuates neuroinflammation and brain injury after transient middle cerebral artery occlusion in mice

Lipocalin-2 (LCN2) is a secreted protein of the lipocalin family, but little is known about the expression or the role of LCN2 in the central nervous system. Here, we investigated the role of LCN2 in ischemic stroke using a rodent model of transient cerebral ischemia. Lipocalin-2 expression was highly induced in the ischemic brain and peaked at 24 hours after reperfusion. After transient middle cerebral artery occlusion, LCN2 was predominantly expressed in astrocytes and endothelial cells, whereas its receptor (24p3R) was mainly detected in neurons, astrocytes, and endothelial cells. Brain infarct volumes, neurologic scores, blood–brain barrier (BBB) permeabilities, glial activation, and inflammatory mediator expression were significantly lower in LCN2-deficient mice than in wild-type animals. Lipocalin-2 deficiency also attenuated glial neurotoxicity in astrocyte/neuron cocultures after oxygen-glucose deprivation. Our results indicate LCN2 has a critical role in brain injury after ischemia/reperfusion, and that LCN2 may contribute to neuronal cell death in the ischemic brain by promoting neurotoxic glial activation, neuroinflammation, and BBB disruption.     

Impaired brain energy metabolism in the BACHD mouse model of Huntington's disease: critical role of astrocyte–neuron interactions

Huntington''s disease (HD) is caused by cytosine-adenine-guanine (CAG) repeat expansions in the huntingtin (Htt) gene. Although early energy metabolic alterations in HD are likely to contribute to later neurodegenerative processes, the cellular and molecular mechanisms responsible for these metabolic alterations are not well characterized. Using the BACHD mice that express the full-length mutant huntingtin (mHtt) protein with 97 glutamine repeats, we first demonstrated localized in vivo changes in brain glucose use reminiscent of what is observed in premanifest HD carriers. Using biochemical, molecular, and functional analyses on different primary cell culture models from BACHD mice, we observed that mHtt does not directly affect metabolic activity in a cell autonomous manner. However, coculture of neurons with astrocytes from wild-type or BACHD mice identified mutant astrocytes as a source of adverse non-cell autonomous effects on neuron energy metabolism possibly by increasing oxidative stress. These results suggest that astrocyte-to-neuron signaling is involved in early energy metabolic alterations in HD.     

Regulation of activity of P2X7 receptor by its splice variants in cultured mouse astrocytes

Of purinergic receptors, P2X7 receptor (P2X7R, defined as a full‐length receptor) has unique characteristics, and its activation leads to ion channel activity and pore formation, causing cell death. Previously, we demonstrated that P2X7R expressed by nonstimulated astrocyte cultures obtained from SJL‐strain mice exhibits constitutive activation, implying its role in maintenance of cellular homeostasis. To obtain novel insights into its physiological roles, we examined whether constitutive activation of P2X7R is regulated by expression of its splice variants in such resting astrocytes, and whether their distinct expression profiles in different mouse strains affect activation levels of astrocytic P2X7Rs. In SJL‐ and ddY‐mouse astrocytes, spontaneous YO‐PRO‐1 uptake, an indicator of pore activity of P2X7R, was detected, but the uptake by the formers was significantly greater than that by the latter. Between the two mouse strains, there was a difference in their sensitivity of YO‐PRO‐1 uptake to antagonists, but not in the expression levels and sequences of P2X7R and pannexin‐1. Regarding expression of splice variants of P2X7R, expression of P2X7R variant‐3 (P2X7R‐v3) and ‐4 (P2X7R‐v4), but not variant‐2 and ‐k, was lower in SJL‐mouse astrocytes than in ddY‐mouse ones. On transfection of P2X7R‐v3 and ‐v4 into SJL‐mouse astrocytes, the pore activity was attenuated as in the case of the HEK293T cell‐expression system. These findings demonstrate that basal activity of P2X7R expressed by resting astrocytes is negatively regulated by P2X7R‐v3 and ‐v4, and that their distinct expression profiles result in the different activation levels of astrocytic P2X7Rs in different mouse strains. GLIA 2014;62:440–451     

Astrocyte glycogenolysis is triggered by store‐operated calcium entry and provides metabolic energy for cellular calcium homeostasis

Astrocytic glycogen, the only storage form of glucose in the brain, has been shown to play a fundamental role in supporting learning and memory, an effect achieved by providing metabolic support for neurons. We have examined the interplay between glycogenolysis and the bioenergetics of astrocytic Ca²⁺ homeostasis, by analyzing interdependency of glycogen and store‐operated Ca²⁺ entry (SOCE), a mechanism in cellular signaling that maintains high endoplasmatic reticulum (ER) Ca²⁺ concentration and thus provides the basis for store‐dependent Ca²⁺ signaling. We stimulated SOCE in primary cultures of murine cerebellar and cortical astrocytes, and determined glycogen content to investigate the effects of SOCE on glycogen metabolism. By blocking glycogenolysis, we tested energetic dependency of SOCE‐related Ca²⁺ dynamics on glycogenolytic ATP. Our results show that SOCE triggers astrocytic glycogenolysis. Upon inhibition of adenylate cyclase with 2',5'‐dideoxyadenosine, glycogen content was no longer significantly different from that in unstimulated control cells, indicating that SOCE triggers astrocytic glycogenolysis in a cAMP‐dependent manner. When glycogenolysis was inhibited in cortical astrocytes by 1,4‐dideoxy‐1,4‐imino‐D‐arabinitol, the amount of Ca²⁺ loaded into ER via sarco/endoplasmic reticulum Ca²‐ATPase (SERCA) was reduced, which suggests that SERCA pumps preferentially metabolize glycogenolytic ATP. Our study demonstrates SOCE as a novel pathway in stimulating astrocytic glycogenolysis. We also provide first evidence for a new functional role of brain glycogen, in providing local ATP to SERCA, thus establishing the bioenergetic basis for astrocytic Ca²⁺ signaling. This mechanism could offer a novel explanation for the impact of glycogen on learning and memory. GLIA 2014;62:526–534     

Astrocytic activation in the anterior cingulate cortex is critical for sleep disorder under neuropathic pain

Insomnia, depression, and anxiety disorder are common problems for people with neuropathic pain. In this study, mild noxious heat stimuli increased the duration and number of spontaneous pain‐like behaviors in sciatic nerve‐ligated mice. We used functional magnetic resonance imaging to visualize the increased blood oxygenation level‐dependent signal intensity in the anterior cingulate cortex (ACC) of mice with sciatic nerve ligation under mild noxious stimuli. Such stimuli significantly increased the release of glutamate in the ACC of nerve‐ligated mice. In addition, sciatic nerve ligation and mild noxious stimuli changed the morphology of astrocytes in the ACC. Treatment of cortical astrocytes with glutamate caused astrocytic activation, as detected by a stellate morphology. Furthermore, glutamate induced the translocation of GAT‐3 to astrocyte cell membranes using primary cultured glial cells from the mouse cortex. Moreover, the GABA level at the synaptic cleft in the ACC of nerve‐ligated mice was significantly decreased exposure to mild noxious stimuli. Finally, we investigated whether astrocytic activation in the ACC could directly mediate sleep disorder. With the optogenetic tool channel rhodopsin‐2 (ChR2), we demonstrated that selective photostimulation of these astrocytes in vivo triggered sleep disturbance. Taken together, these results suggest that neuropathic pain‐like stimuli activated astrocytes in the ACC and decreased the extracellular concentration of GABA via an increase in the release of glutamate. Furthermore, these findings provide novel evidence that astrocytic activation in the ACC can mimic sleep disturbance in mice. Synapse 68:235–247, 2014 . © 2014 Wiley Periodicals, Inc.