Central nervous system-infiltrated immune cells induce calcium increase in astrocytes via astroglial purinergic signaling

Interaction between autoreactive immune cells and astroglia is an important part of the pathologic processes that fuel neurodegeneration in multiple sclerosis. In this inflammatory disease, immune cells enter into the central nervous system (CNS) and they spread through CNS parenchyma, but the impact of these autoreactive immune cells on the activity pattern of astrocytes has not been defined. By exploiting naïve astrocytes in culture and CNS-infiltrated immune cells (CNS IICs) isolated from rat with experimental autoimmune encephalomyelitis (EAE), here we demonstrate previously unrecognized properties of immune cell–astrocyte interaction. We show that CNS IICs but not the peripheral immune cell application, evokes a rapid and vigorous intracellular Ca²⁺ increase in astrocytes by promoting glial release of ATP. ATP propagated Ca²⁺ elevation through glial purinergic P2X7 receptor activation by the hemichannel-dependent nucleotide release mechanism. Astrocyte Ca²⁺ increase is specifically triggered by the autoreactive CD4⁺ T-cell application and these two cell types exhibit close spatial interaction in EAE. Therefore, Ca²⁺ signals may mediate a rapid astroglial response to the autoreactive immune cells in their local environment. This property of immune cell–astrocyte interaction may be important to consider in studies interrogating CNS autoimmune disease.     

Glutamate transporter 1-expressing glia in the rat substantia nigra—Morphometric analysis and relationships to synapses

Glial cells have a major role in protecting neurons against various forms of stress. Especially, astrocytes mediate the bulk of glutamate clearance in the brain via specific membrane transporters (GLAST and GLT1), thereby preventing the occurrence of excitotoxic events. Although glutamate-mediated mechanisms are thought to contribute to nigral dopaminergic neuron degeneration in Parkinson's disease, detailed information on the organization of glia in the substantia nigra is still lacking. The present study was performed to provide quantitative information on the organization of astroglia and on the relationships between astrocytes and excitatory synapses in the rat substantia nigra. Using immunolabeling of GLT1 and confocal imaging, we found that the substantia nigra was filled with a dense meshwork of immunoreactive astrocyte processes. Stereological analysis performed on electron microscope images revealed that the density of immunoreactive astrocyte plasma membranes was substantial, close to 1 μm²/μm³, in the substantia nigra neuropil, both in the pars compacta and the pars reticulata. Excitatory synapses had on average two thirds of their perimeters free from glia, a disposition that may favor transmitter spillover. The density of glutamatergic synapses, as quantified on confocal images by the simultaneous detection of bassoon and of vesicular glutamate transporter 1 or 2, was very low (0.01 and 0.025 per μm³ in the reticulata and compacta subdivisions, respectively). Thus the ratio of GLT1-expressing glial membrane surface to glutamatergic synapses was very high (40–100 μm²), suggesting an efficient regulation of extracellular glutamate concentrations.     

Schwann cells: Rescuers of central demyelination

The presence of peripheral myelinating cells in the central nervous system (CNS) has gained the neurobiologist attention over the years. Despite the confirmed presence of Schwann cells in the CNS in pathological conditions, and the long list of their beneficial effects on central remyelination, the cues that impede or allow Schwann cells to successfully conquer and remyelinate central axons remain partially undiscovered. A better knowledge of these factors stands out as crucial to foresee a rational therapeutic approach for the use of Schwann cells in CNS repair. Here, we review the diverse origins of Schwann cells into the CNS, both peripheral and central, as well as the CNS components that inhibit Schwann survival and migration into the central parenchyma. Namely, we analyze the astrocyte- and the myelin-derived components that restrict Schwann cells into the CNS. Finally, we highlight the unveiled mode of invasion of these peripheral cells through the central environment, using blood vessels as scaffolds to pave their ways toward demyelinated lesions. In short, this review presents the so far uncovered knowledge of this complex CNS-peripheral nervous system (PNS) relationship.     

NF-E2-related factor 2 activation boosts antioxidant defenses and ameliorates inflammatory and amyloid properties in human Presenilin-1 mutated Alzheimer's disease astrocytes

Alzheimer's disease (AD) is a common dementia affecting a vast number of individuals and significantly impairing quality of life. Despite extensive research in animal models and numerous promising treatment trials, there is still no curative treatment for AD. Astrocytes, the most common cell type of the central nervous system, have been shown to play a role in the major AD pathologies, including accumulation of amyloid plaques, neuroinflammation, and oxidative stress. Here, we show that inflammatory stimulation leads to metabolic activation of human astrocytes and reduces amyloid secretion. On the other hand, the activation of oxidative metabolism leads to increased reactive oxygen species production especially in AD astrocytes. While healthy astrocytes increase glutathione (GSH) release to protect the cells, Presenilin-1-mutated AD patient astrocytes do not. Thus, chronic inflammation is likely to induce oxidative damage in AD astrocytes. Activation of NRF2, the major regulator of cellular antioxidant defenses, encoded by the NFE2L2 gene, poses several beneficial effects on AD astrocytes. We report here that the activation of NRF2 pathway reduces amyloid secretion, normalizes cytokine release, and increases GSH secretion in AD astrocytes. NRF2 induction also activates the metabolism of astrocytes and increases the utilization of glycolysis. Taken together, targeting NRF2 in astrocytes could be a potent therapeutic strategy in AD.     

Astrocytes enhance glioblastoma growth

Glioblastoma (GBM) is a deadly disease with a need for deeper understanding and new therapeutic approaches. The microenvironment of glioblastoma has previously been shown to guide glioblastoma progression. In this study, astrocytes were investigated with regard to their effect on glioblastoma proliferation through correlative analyses of clinical samples and experimental in vitro and in vivo studies. Co-culture techniques were used to investigate the GBM growth enhancing potential of astrocytes. Cell sorting and RNA sequencing were used to generate a GBM-associated astrocyte signature and to investigate astrocyte-induced GBM genes. A NOD scid GBM mouse model was used for in vivo studies. A gene signature reflecting GBM-activated astrocytes was associated with poor prognosis in the TCGA GBM dataset. Two genes, periostin and serglycin, induced in GBM cells upon exposure to astrocytes were expressed at higher levels in cases with high “astrocyte signature score”. Astrocytes were shown to enhance glioblastoma cell growth in cell lines and in a patient-derived culture, in a manner dependent on cell–cell contact and involving increased cell proliferation. Furthermore, co-injection of astrocytes with glioblastoma cells reduced survival in an orthotopic GBM model in NOD scid mice. In conclusion, this study suggests that astrocytes contribute to glioblastoma growth and implies this crosstalk as a candidate target for novel therapies.     

Pathology of inflammatory diseases of the nervous system: Human disease versus animal models

Numerous recent studies have been performed to elucidate the function of microglia, macrophages, and astrocytes in inflammatory diseases of the central nervous system. Regarding myeloid cells a core pattern of activation has been identified, starting with the activation of resident homeostatic microglia followed by recruitment of blood borne myeloid cells. An initial state of proinflammatory activation is at later stages followed by a shift toward an-anti-inflammatory and repair promoting phenotype. Although this core pattern is similar between experimental models and inflammatory conditions in the human brain, there are important differences. Even in the normal human brain a preactivated microglia phenotype is evident, and there are disease specific and lesion stage specific differences in the contribution between resident and recruited myeloid cells and their lesion state specific activation profiles. Reasons for these findings reside in species related differences and in differential exposure to different environmental cues. Most importantly, however, experimental rodent studies on brain inflammation are mainly focused on autoimmune encephalomyelitis, while there is a very broad spectrum of human inflammatory diseases of the central nervous system, triggered and propagated by a variety of different immune mechanisms.     

New insights into Wnt signaling alterations in amyotrophic lateral sclerosis: a potential therapeutic target?

Amyotrophic lateral sclerosis is a fatal neurodegenerative disorder characterized by upper and lower motor neuron degeneration, which leads to progressive paralysis of skeletal muscles and, ultimately, respiratory failure between 2–5 years after symptom onset. Unfortunately, currently accepted treatments for amyotrophic lateral sclerosis are extremely scarce and only provide modest benefit. As a consequence, a great effort is being done by the scientific community in order to achieve a better understanding of the different molecular and cellular processes that influence the progression and/or outcome of this neuropathological condition and, therefore, unravel new potential targets for therapeutic intervention. Interestingly, a growing number of experimental evidences have recently shown that, besides its well-known physiological roles in the developing and adult central nervous system, the Wnt family of proteins is involved in different neuropathologica conditions, including amyotrophic lateral sclerosis. These proteins are able to modulate, at least, three different signaling pathways, usually known as canonical(β-catenin dependent) and non-canonical(β-catenin independent) signaling pathways. In the present review, we aim to provide a general overview of the current knowledge that supports the relationship between the Wnt family of proteins and its associated signaling pathways and amyotrophic lateral sclerosis pathology, as well as their possible mechanisms of action. Altogether, the currently available knowledge suggests that Wnt signaling modulation might be a promising therapeutic approach to ameliorate the histopathological and functional deficits associated to amyotrophic lateral sclerosis, and thus improve the progression and outcome of this neuropathology.     

骨髓间充质干细胞通过调节LPS-TLR4通路抑制肝星形细胞活化的作用机制

目的研究人骨髓间充质干细胞（BMSC）是否可通过干预LPS-TLR4通路,调控肝星状细胞（HSC）LX2活化,阐明BMSC在肝纤维化形成中的作用。方法体外共培养BMSC、LX2,分为BMSC＋LX2（LPS刺激）组、TLR4阻断剂＋LX2（LPS刺激）组、LX2（LPS刺激）组、BMSC（LPS刺激）组、LX2（无LPS刺激）组,培养6、12、36、48 h;收集上清,ELISA检测IL-8及TGFβ表达,RT-PCR检测LX2的TLR4、Myd88及NF-κB的表达,Western Blot检测TGFβ、SMA、ColⅠ、MyD88、TLR4表达。免疫荧光检测NF-κB细胞内表达情况。结果 LPS可以刺激LX2活化,活化的LX2分泌IL-8及TGFβ增多,TGFβ、SMA、ColⅠ、MyD88、TLR4表达增加,NF-κB p65主要为核内表达。与BMSC共培养后,LPS导致的LX2活化减弱,LX2的TGF-β、SMA、ColⅠ、MyD88、TLR4的表达下降,NF-κB p65胞浆表达为主。结论 BMSC可以通过干预LPS-TLR4通路抑制LX2的活化。     

黄芪甲苷对氧糖剥夺复氧后星形胶质细胞上TNF-α与AQP-4表达的影响

目的:探索黄芪甲苷(astragaloside IV,ASIV)对氧糖剥夺复氧(oxygen glucose deprivation/reperfusion,OGD/R)后星形胶质细胞上肿瘤坏死因子-α(tumor necrosis facror-alpha,TNF-α)与水通道蛋-4(aquaporin-4,AQP-4)表达的影响。方法:选用第二代第1 d的星形胶质细胞。将星形胶质细胞放入缺氧培养箱(1%O_2、94%N2、5%CO_2),分别干预1、2、3、4 h,复氧24 h后用RT-PCR和Western Blot检测AQP-4和TNF-α的表达情况。将星形胶质细胞分为对照组、OGD/R组、OGD/R+0.001μmol/ml ASIV组、OGD/R+0.01μmol/ml ASIV组,用RT-PCR和免疫荧光检测AQP-4和TNF-α的表达情况。结果:RT-PCR和Western Blot结果显示:氧糖剥夺复氧后AQP-4和TNF-α的表达均增加,且AQP-4在OGD3 h时表达达到高峰,TNF-α在OGD1 h时表达达到高峰(P0.05);OGD3h+0.001μmol/ml ASIV组和OGD3 h+0.01μmol/ml ASIV组的AQP-4基因表达水平较OGD3 h组相比均明显降低(P0.05);与OGD3 h组相比,OGD3 h+0.001μmol/ml ASIV组的AQP-4蛋白表达水平明显降低(P0.05);OGD1 h+0.001μmol/ml ASIV组和OGD1 h+0.01μmol/ml ASIV组的TNF-α基因表达水平与OGD1 h组相比均明显降低(P0.05);与OGD1 h组相比,OGD1 h+0.001μmol/ml ASIV组的TNF-α蛋白表达水平明显降低(P0.05)。结论:氧糖剥夺复氧模型可以诱导星形胶质细胞上TNF-α和AQP-4的表达,且TNF-α的表达先于AQP-4;黄芪甲苷可能是通过下调TNF-α的表达来影响AQP-4的表达,进而影响细胞水肿。     

大鼠局灶性脑缺血后Cdh1 mRNA水平及Cdh1蛋白分布的改变

目的:探讨大鼠局灶性脑缺血损伤后Cdh1 mRNA水平的变化及其在不同类型神经细胞中的分布变化。方法:雄性成年SD大鼠30只,线栓法建立右侧大脑中动脉缺血模型,分别于缺血前和缺血再灌注后1、3、7d采用实时荧光定量PCR技术检测缺血侧和非缺血侧脑组织中Cdh1 mRNA的水平;缺血再灌注后7d免疫荧光双标法检测Cdh1在神经元和星形胶质细胞中的分布情况。结果:脑缺血前,两侧脑组织中Cdh1 mRNA的水平差异无统计学意义。缺血再灌注后1、3、7d,缺血侧脑组织Cdh1 mRNA水平均低于非缺血侧脑组织(P0.05);缺血再灌注后7d,与非缺血侧相比,缺血侧神经元明显减少,星形胶质细胞增多;在非缺血侧Cdh1主要表达于神经元,星形胶质细胞中表达较少,在缺血侧Cdh1在神经元及激活的星形胶质细胞中均有表达。结论:大鼠局灶性脑缺血损伤后,缺血侧Cdh1 mRNA的水平较非缺血侧降低,且Cdh1在神经元和星形胶质细胞中分布情况发生变化。