Induction of atypical EAE mediated by transgenic production of IL‐6 in astrocytes in the absence of systemic IL‐6

Interleukin (IL)‐6 is crucial for the induction of many murine models of autoimmunity including experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. While IL‐6‐deficient mice (IL‐6 KO) are resistant to EAE, we showed previously that in transgenic mice with astrocyte‐targeted production of IL‐6‐restricted to the cerebellum (GFAP‐IL6), EAE induced with MOG_35–55 was redirected away from the spinal cord to the cerebellum. To further establish the importance of IL‐6 produced in the central nervous system, we have generated mice producing IL‐6 essentially only in the brain by crossing the GFAP‐IL6 mice with IL‐6 KO mice. Interestingly, GFAP‐IL6‐IL‐6 KO mice showed a milder but almost identical phenotype as the GFAP‐IL6 mice, which correlated with a lower load of inflammatory cells and decreased microglial reactivity. These results indicate that not only is cerebellar IL‐6 production and eventual leakage into the peripheral compartment the dominating factor controlling this type of EAE but that it can also facilitate induction of autoimmunity in the absence of normal systemic IL‐6 production. © 2013 Wiley Periodicals, Inc.     

Brain‐derived neurotrophic factor/TrkB signaling regulates daily astroglial plasticity in the suprachiasmatic nucleus: Electron‐microscopic evidence in mouse

Synchronization of circadian rhythms to the 24‐h light/dark (L/D) cycle is associated with daily rearrangements of the neuronal‐glial network of the suprachiasmatic nucleus of the hypothalamus (SCN), the central master clock orchestrating biological functions in mammals. These anatomical plastic events involve neurons synthesizing vasoactive intestinal peptide (VIP), known as major integrators of photic signals in the retinorecipient region of the SCN. Using an analog‐sensitive kinase allele murine model (TrkB^F616A), we presently show that the pharmacological blockade of the tropomyosin‐related kinase receptor type B (TrkB), the high‐affinity receptor of brain‐derived neurotrophic factor (BDNF), abolished day/night changes in the dendrite enwrapping of VIP neurons by astrocytic processes (glial coverage), used as an index of SCN plasticity on electron‐microscopic sections. Therefore, the BDNF/TrkB signaling pathway exerts a permissive role on the ultrastructural rearrangements that occur in SCN under L/D alternance, an action that could be a critical determinant of the well‐established role played by BDNF in the photic regulation of the SCN. In contrast, the extent of glial coverage of non‐VIP neighboring dendrites was not different at daytime and nighttime in TrkB^F616A mice submitted to TrkB inactivation or not receiving any pharmacological treatment. These data not only show that BDNF regulates SCN structural plasticity across the 24‐h cycle but also reinforce the view that the daily changes in SCN architecture subserve the light synchronization process.     

Differential glial activation during the degeneration of Purkinje cells and mitral cells in the PCD mutant mice

Purkinje Cell Degeneration (PCD) mice harbor a nna1 gene mutation which leads to an early and rapid degeneration of Purkinje cells (PC) between the third and fourth week of age. This mutation also underlies the death of mitral cells (MC) in the olfactory bulb (OB), but this process is slower and longer than in PC. No clear interpretations supporting the marked differences in these neurodegenerative processes exist. Growing evidence suggests that either beneficial or detrimental effects of gliosis in damaged regions would underlie these divergences. Here, we examined the gliosis occurring during PC and MC death in the PCD mouse. Our results demonstrated different glial reactions in both affected regions. PC disappearance stimulated a severe gliosis characterized by strong morphological changes, enhanced glial proliferation, as well as the release of pro‐inflammatory mediators. By contrast, MC degeneration seems to promote a more attenuated glial response in the PCD OB compared with that of the cerebellum. Strikingly, cerebellar oligodendrocytes died by apoptosis in the PCD, whereas bulbar ones were not affected. Interestingly, the level of nna1 mRNA under normal conditions was higher in the cerebellum than in the OB, probably related to a faster neurodegeneration and stronger glial reaction in its absence. The glial responses may thus influence the neurodegenerative course in the cerebellum and OB of the mutant mouse brain, providing harmful and beneficial microenvironments, respectively. © 2012 Wiley Periodicals, Inc.     

Ischemic preconditioning via epsilon protein kinase C activation requires cyclooxygenase-2 activation in vitro

The signaling pathway of cyclooxygenase-2 (COX-2) induction following ischemic preconditioning (IPC) in brain remains undefined. To determine role of COX-2 in ischemic preconditioning, we used two in vitro models: mixed cortical neuron/astrocyte cell cultures and organotypic hippocampal slice cultures. We simulated IPC by exposing cell or slice cultures to 1 h or 15 min of oxygen/glucose deprivation (OGD), respectively, 48 h prior to ischemia. To mimic ischemia in vitro, we exposed cell or slice cultures to OGD of 4 h or 40 min, respectively. In cell cultures, these experiments revealed that COX-2 induction peaked at 24 h following IPC in cell culture. Inhibition of COX-2 activation with 50 microM NS-398 (a COX-2 selective inhibitor) abolished IPC-mediated neuroprotection in both in vitro models. Next, we tested whether epsilon protein kinase C (epsilonPKC) and extracellular signal regulated kinase 1/2 (ERK1/2) activation was involved in IPC-mediated neuroprotection and COX-2 expression in cell culture. Cell cultures were treated with an epsilonPKC-specific activating peptide (psiepsilonRACK, 100 nM) for 1 h, and 48 h later were exposed to OGD. epsilonPKC activation increased ERK1/2 phosphorylation and COX-2 induction and conferred neuroprotection similar to IPC. Additionally, inhibition of either epsilonPKC or ERK1/2 activation abolished COX-2 expression and neuroprotection due to ischemic preconditioning. These results demonstrate a crucial role for the epsilonPKC-->ERK1/2-->COX-2 pathway in the induction of neuroprotection via ischemic preconditioning.     

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.     

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.     

In the presence of danger：the extracellular matrix defensive response to central nervous system injury

Glial cells in the central nervous system （CNS） contribute to formation of the extracellular matrix, which provides adhesive sites, signaling molecules, and a diffusion barrier to enhance efficient on and axon potential propagation. In the normal adult CNS, the extracellular matrix （ECM） is relatively stable except in selected regions characterized by dynamic remodeling. However, after trauma such as a spinal cord injury or cortical contusion, the lesion epicenter becomes a focus of acute neuroinflammation. The activation of the surrounding glial cells leads to a dramatic change in the composition of the ECM at the edges of the lesion, creating a perilesion environment dominated by growth inhibitory molecules and restoration of the peripheral/ central nervous system border. An advantage of this response is to limit the invasion of damaging cells and diffusion of toxic molecules into the spared tissue regions, but this occurs at the cost of inhibiting migration of endogenous repair cells and preventing axonal regrowth. The following review was prepared by reading and discussing over 200 research articles in the field published in PubMed and selecting those with significant impact and/or controversial points. This article highlights structural and functional features of the normal adult CNS ECM and then focuses on the reactions of glial cells and changes in the perilesion border that occur following spinal cord or contusive brain injury. Current research strategies directed at modifying the inhibitory perilesion microenvironment without eliminating the protective functions of glial cell activation are discussed.     

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.