Gi/o protein-coupled receptors inhibit neurons but activate astrocytes and stimulate gliotransmission

G protein-coupled receptors (GPCRs) play key roles in intercellular signaling in the brain. Their effects on cellular function have been largely studied in neurons, but their functional consequences on astrocytes are less known. Using both endogenous and chemogenetic approaches with DREADDs, we have investigated the effects of G_q and G_i/o GPCR activation on astroglial Ca²⁺-based activity, gliotransmitter release, and the functional consequences on neuronal electrical activity. We found that while G_qGPCR activation led to cellular activation in both neurons and astrocytes, G_i/oGPCR activation led to cellular inhibition in neurons and cellular activation in astrocytes. Astroglial activation by either G_q or G_i/o protein-mediated signaling stimulated gliotransmitter release, which increased neuronal excitability. Additionally, activation of G_q and G_i/o DREADDs in vivo increased astrocyte Ca²⁺ activity and modified neuronal network electrical activity. Present results reveal additional complexity of the signaling consequences of excitatory and inhibitory neurotransmitters in astroglia-neuron network operation and brain function.     

Glial mechanisms underlying substance use disorders

Addiction is a devastating disorder that produces persistent maladaptive changes to the central nervous system, including glial cells. Although there is an extensive body of literature examining the neuronal mechanisms of substance use disorders, effective therapies remain elusive. Glia, particularly microglia and astrocytes, have an emerging and meaningful role in a variety of processes beyond inflammation and immune surveillance, and may represent a promising therapeutic target. Indeed, glia actively modulate neurotransmission, synaptic connectivity and neural circuit function, and are critically poised to contribute to addictive‐like brain states and behaviors. In this review, we argue that glia influence the cellular, molecular, and synaptic changes that occur in neurons following drug exposure, and that this cellular relationship is critically modified following drug exposure. We discuss direct actions of abused drugs on glial function through immune receptors, such as Toll‐like receptor 4, as well as other mechanisms. We highlight how drugs of abuse affect glia‐neural communication, and the profound effects that glial‐derived factors have on neuronal excitability, structure, and function. Recent research demonstrates that glia have brain region‐specific functions, and glia in different brain regions have distinct contributions to drug‐associated behaviors. We will also evaluate the evidence demonstrating that glial activation is essential for drug reward and drug‐induced dopamine release, and highlight clinical evidence showing that glial mechanisms contribute to drug abuse liability. In this review, we synthesize the extensive evidence that glia have a unique, pivotal, and underappreciated role in the development and maintenance of addiction.     

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.     

补阳还五汤对大鼠化疗相关外周神经痛的预防作用及其机制

目的观察补阳还五汤对紫杉醇诱导的大鼠外周神经痛的预防作用,并以脊髓大麻素受体为主要靶点,探讨其作用机制。方法将50只SD大鼠随机分为对照组、模型组、预防组、AM630组、AM251组,每组10只。除对照组外,其余各组于实验第1,3,5,7天分别腹腔注射紫杉醇2 mg/kg;预防组在建模的同时每天予补阳还五汤2.5 g/(kg·d)灌胃干预14 d;AM630组在预防组的基础上于每天灌胃前予3 mg/kg大麻素Ⅱ型受体(CBR2)阻滞剂AM630腹腔注射;AM251组在预防组的基础上于每天灌胃前予1.5 mg/kg大麻素Ⅰ型受体(CBR1)阻滞剂AM251腹腔注射。每7 d记录1次各组大鼠体质量,并使用von fery纤维丝测试各组大鼠机械缩足阈值(MWT),共观察28 d;实验观察28 d后使用RT-PCR检测各组大鼠脊髓组织中CBR1、CBR2、胶质纤维酸性蛋白(GFAP)、白细胞介素-1β(IL-1β)、肿瘤坏死因子-α(TNF-α)的mRNA表达水平。结果实验第7,14,21,28天,各组大鼠体质量增量比较差异均无统计学意义(P均>0.05)。模型组实验第7,14,21,28天的MWT均显著低于同期对照组(P均<0.05);预防组、AM251组实验第14,21,28天的MWT均显著高于同期模型组(P均<0.05),但AM630组与模型组比较、预防组与AM251组比较差异均无统计学意义(P均>0.05)。模型组CBR2、CBR1、GFAP mRNA表达水平与对照组比较差异均无统计学意义(P均>0.05),IL-1β、TNF-αmRNA表达水平明显高于对照组(P均<0.05);预防组和AM251组CBR2 mRNA表达水平明显高于模型组(P均<0.05),IL-1β、TNF-αmRNA表达水平均明显低于模型组(P均<0.05);AM630组与模型组比较、预防组与AM251组比较各相关蛋白mRNA表达水平差异均无统计学意义(P均>0.05)。结论补阳还五汤可以预防紫杉醇诱导的外周神经痛,机制可能与其激活脊髓CBR2,并进一步抑制脊髓IL-1β、TNF-α等炎症细胞因子的表达有关。     

大鼠骨癌痛模型中脊髓背角神经元与星型胶质细胞相互联系的研究

目的:研究大鼠骨癌痛模型中脊髓背角神经元与星型胶质细胞相互联系。方法:利用Walker256乳腺癌细胞建立大鼠骨癌痛模型后，分别鞘内注射药物阻断神经元的活化（c-Fos反义寡核苷酸探针，c-Fos ASO）和星形胶质细胞的活化（L-α-aminoadipate，L-α-AA），然后分别检测大鼠痛行为学改变；利用免疫荧光染色法和Western blot实验检测大鼠脊髓背角神经元活化标记物c-Fos和星形胶质细胞标记物GFAP的表达变化。结果:骨癌痛大鼠出现了显著的痛行为学改变并激活了脊髓背角神经元和星形胶质细胞，表现为早期c-Fos和晚期GFAP的表达增加。鞘内注射c-Fos ASO或L-α-AA均有明显镇痛效果。免疫荧光染色提示c-Fos ASO不仅能显著抑制骨癌痛大鼠神经元的活化，而且对星形胶质细胞的活化也有抑制作用。与此同时，Western blot显示L-α-AA不但抑制了星形胶质细胞的活化，也缩短了神经元的活化时间。结论:神经元和星形胶质细胞相互联系伴随着骨癌痛的发生发展。因此，研究新的镇痛策略，应综合考虑两者的协调关系。     

Defined astrocytic expression of human amyloid precursor protein in Tg2576 mouse brain

Transgenic Tg2576 mice expressing human amyloid precursor protein (hAPP) with the Swedish mutation are among the most frequently used animal models to study the amyloid pathology related to Alzheimer's disease (AD). The transgene expression in this model is considered to be neuron-specific. Using a novel hAPP-specific antibody in combination with cell type-specific markers for double immunofluorescent labelings and laser scanning microscopy, we here report that—in addition to neurons throughout the brain—astrocytes in the corpus callosum and to a lesser extent in neocortex express hAPP. This astrocytic hAPP expression is already detectable in young Tg2576 mice before the onset of amyloid pathology and still present in aged Tg2576 mice with robust amyloid pathology in neocortex, hippocampus, and corpus callosum. Surprisingly, hAPP immunoreactivity in cortex is restricted to resting astrocytes distant from amyloid plaques but absent from reactive astrocytes in close proximity to amyloid plaques. In contrast, neither microglial cells nor oligodendrocytes of young or aged Tg2576 mice display hAPP labeling. The astrocytic expression of hAPP is substantiated by the analyses of hAPP mRNA and protein expression in primary cultures derived from Tg2576 offspring. We conclude that astrocytes, in particular in corpus callosum, may contribute to amyloid pathology in Tg2576 mice and thus mimic this aspect of AD pathology.     

Mitotic activity,modulation of DNA processing,and purinergic signalling in the adult rat auditory brainstem following sensory deafferentation

A complex scenario of cellular network reorganization is caused by unilateral sensory deafferentation (USD) in the adult rat central auditory system. We asked whether this plasticity response involves mitosis. Immunohistochemistry was applied to brainstem sections for the detection and localization of mitotic markers Ki67 and PCNA, the growth‐associated protein Gap43 and purine receptor P2X4. Fluorescent double staining was done for Ki67:PCNA and for both of them with HuC/HuD (neurons), S100 (astrocytes), Iba1 (microglia) and P2X4. Inquiring 1–7 days after USD, we found Ki67 expression to be changed in cellular profiles of cochlear nucleus (CN) with a significant increase in number by 1–3 days, followed by reset to control level within 1 week. USD‐induced mitosis exclusively occurred in microglia and was absent elsewhere in the auditory brainstem. PCNA staining of small cellular profiles increased similarly but remained elevated. PCNA staining intensity also changed in CN, superior olive and inferior colliculus in neuronal nuclei, suggesting shifts in DNA processing. No apoptotic cell death was detected in any region of the adult auditory brainstem after USD. A comparison of anterograde and retrograde effects of nerve damage revealed proliferating microglia expressing P2X4 receptors in CN upon USD, but not in the facial nucleus after facial nerve transection. In conclusion, the deafferentation model studied here permits insight into the capacity of the adult mammalian brain to invoke mitosis among glia cells, adjustment of gene processing in neurons and purinergic signalling between them, jointly accounting for a multilayered neuro‐ and glioplastic response.     

Astrocytes,the rising stars of the glioblastoma microenvironment

Glioblastoma (GBM) is an aggressive primary tumor, causing thousands of deaths worldwide every year. The mean survival of patients with GBM remains below 20 months despite current available therapies. GBM cells' interactions with their stromal counterparts are crucial for tumor development. Astrocytes are glial cells that comprise ~50% of all brain cells and are therefore likely to establish direct contact with GBM cells. As other tumor cell types can hijack fibroblasts or immune cells to facilitate tumor growth, GBM cells can actually activate astrocytes, namely, the tumor associated astrocytes (TAAs), to promote GBM invasion in the healthy tissue. TAAs have thus been shown to be involved in GBM cells growth and limited response to radiation or chemotherapy (i.e., Temozolomide). Nevertheless, even though the interest in the cancer research community is increasing, the role of TAAs during GBM development is still overlooked. Yet, obtaining an in-depth understanding of the mechanisms by which TAAs influence GBM progression might lead to the development of new therapeutic strategies. This article therefore reports the different levels of GBM progression at which TAAs have been recently described to be involved in, including tumor cells' proliferation/invasion and resistance to therapies, especially through the activity of extracellular vesicles.     

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.