Astrocyte regulation of CNS inflammation and remyelination

TRPM7 Mediates Neuropathic Pain by Activating mTOR Signaling in Astrocytes after Spinal Cord Injury in Rats

In this study, we investigated whether transient receptor melastatin 7 (TRPM7), known as a non-selective cation channel, inhibits neuropathic pain after spinal cord injury (SCI) and how TRPM7 regulates neuropathic pain. Neuropathic pain was developed 4 weeks after moderate contusive SCI and TRPM7 was markedly upregulated in astrocytes in the lamina I and II of L4-L5 dorsal horn. In addition, both mechanical allodynia and thermal hyperalgesia were significantly alleviated by a TRPM7 inhibitor, carvacrol. In particular, carvacrol treatment inhibited mechanistic target of rapamycin (mTOR) signaling, which was activated in astrocytes. When rats were treated with rapamycin, an inhibitor of mTOR signaling, neuropathic pain was significantly inhibited. Furthermore, blocking TRPM7 and mTOR signaling by carvacrol and rapamycin inhibited astrocyte activation in lamina I and II of dorsal spinal cord and reduced the level of p-JNK and p-c-Jun, which are known to be activated in astrocytes. Finally, inhibiting TRPM7/mTOR signaling also downregulated the production of pain-related factors such as tumor necrosis factor-α, interleukin-6, interleukin-1β, chemokine (C-C motif) ligand (CCL) 2, CCL-3, CCL-4, CCL-20, chemokine C-X-C motif ligand 1, and matrix metalloproteinase 9 which are known to be involved in the induction and/or maintenance of neuropathic pain after SCI. These results suggest an important role of TRPM7-mediated mTOR signaling in astrocyte activation and thereby induction and/or maintenance of neuropathic pain after SCI.

Citrullinated isomer of myelin basic protein can induce inflammatory responses in astrocytes

Purpose

During the course of demyelinating inflammatory diseases, myelin-derived proteins, including myelin basic protein(MBP), are secreted into extracellular space. MBP shows extensive post-translational modifications, including deimination/citrullination. Deiminated MBP is structurally less ordered, susceptible to proteolytic attack, and more immunogenic than unmodified MBP. This study investigated the effect of the deiminated/citrullinated isomer of MBP(C8) and the unmodified isomer of MBP(C1) on cultured primary astrocytes.

Methods

MBP charge isomers were isolated/purified from bovine brain. Primary astrocyte cultures were prepared from the 2-day-old Wistar rats. For evaluation of glutamate release/uptake a Fluorimetric glutamate assay was used. Expression of peroxisome proliferator-activated receptor-gamma(PPAR-γ), excitatory amino acid transporter 2(EAAT2), the inhibitor of the nuclear factor kappa-B(ikB) and high mobility group-B1(HMGB1) protein were assayed by Western blot analysis. IL-17A expression was determined in cell medium by ELISA.

Results

We found that MBP(C8) and MBP(C1) acted differently on the uptake/release of glutamate in astrocytes: C1 increased glutamate uptake and did not change its release, whereas C8 decreased glutamate release but did not change its uptake. Both isomers increased the expression of PPAR-γ and EAAT2 to the same degree. Western blots of cell lysates revealed decreased expression of ikB and increased expression of HMGB1 proteins after treatment of astrocytes by C8. Moreover, C8-treated cells released more nitric oxide and proinflammatory IL-17A than C1-treated cells.

Conclusions

These data suggest that the most immunogenic deiminated isomer C8, in parallel to the decreases in glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B(NF-kB).

Summary statement

The most modified-citrullinated myelin basic protein charge isomer decreases glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B in astrocytes.

Tonabersat Significantly Reduces Disease Progression in an Experimental Mouse Model of Multiple Sclerosis

Multiple sclerosis (MS) is a neurodegenerative disease marked by chronic neuroinflammation thought to be mediated by the inflammasome pathway. Connexin 43 (Cx43) hemichannels contribute to the activation of the inflammasome through the release of adenosine triphosphate (ATP) inflammasome activation signals. The objective of the study was to evaluate if the Cx43 hemichannel blocker, tonabersat, is effective in modulating the inflammatory response and reducing disability in the myelin oligodendrocyte glycoprotein 35-55-induced experimental autoimmune encephalomyelitis (MOG35-55 EAE) model of MS. Here, we show that the Cx43 hemichannel blocking drug, tonabersat, significantly reduced expression of neuroinflammatory markers for microglial activation (ionized calcium-binding adapter molecule 1 (Iba1)) and astrogliosis (glial fibrillary acidic protein (GFAP)) while preserving myelin basic protein (MBP) expression levels in the corpus callosum, motor cortex, and striatum regions of the brain in MOG35-55 EAE mice. Reduced NOD-like receptor protein 3 (NLRP3) inflammasome complex assembly and Caspase-1 activation confirmed the drug's mode of action. MOG35-55 EAE mice showed clinical signs of MS, but MOG35-55 EAE mice treated with tonabersat retained behavior closer to normal. These data suggest that clinical trial phase IIb-ready tonabersat may merit further investigation as a promising candidate for MS treatment.

Elucidating the Therapeutic Utility of Olaparib in Sulfatide-Induced Human Astrocyte Toxicity and Neuroinflammation

Metachromatic leukodystrophy (MLD) is a severe demyelinating, autosomal recessive genetic leukodystrophy, with no curative treatment. The disease is underpinned by mutations in the arylsulfatase A gene (ARSA), resulting in deficient activity of this lysosomal enzyme, and consequential accumulation of galactosylceramide-3-O-sulfate (sulfatide) in the brain. Most of the effects in the brain have been attributed to the accumulation of sulfatides in oligodendrocytes and their cell damage. In contrast, less is known regarding sulfatide toxicity in astrocytes. Poly (ADP-ribose) polymerase (PARP) inhibitors are anti-cancer therapeutics that have proven efficacy in preclinical models of many neurodegenerative and inflammatory diseases, but have never been tested for MLD. Here, we examined the toxic effect of sulfatides on human astrocytes and restoration of this cell damage by the marketed PARP-1 inhibitor, Olaparib. Cultured human astrocytes were treated with increasing concentrations of sulfatides (5-100 μM) with or without Olaparib (100 nM). Cell viability assays were used to ascertain whether sulfatide-induced toxicity was rescued by Olaparib. Immunofluorescence, calcium (Ca2+) imaging, ROS, and mitochondrial damage assays were also used to explore the effects of sulfatides and Olaparib. ELISAs were performed and chemotaxis of peripheral blood immune cells was measured to examine the effects of Olaparib on sulfatide-induced inflammation in human astrocytes. Here, we established a concentration-dependent (EC50∼20 μM at 24 h) model of sulfatide-induced astrocyte toxicity. Our data demonstrate that sulfatide-induced astrocyte toxicity involves (i) PARP-1 activation, (ii) pro-inflammatory cytokine release, and (iii) enhanced chemoattraction of peripheral blood immune cells. Moreover, these sulfatide-induced effects were attenuated by Olaparib (IC50∼100 nM). In addition, sulfatide caused impairments of ROS production, mitochondrial stress, and Ca2+ signaling in human astrocytes, that were indicative of metabolic alterations and that were also alleviated by Olaparib (100 nM) treatment. Our data support the hypothesis that sulfatides can drive astrocyte cell death and demonstrate that Olaparib can dampen many facets of sulfatide-induced toxicity, including, mitochondrial stress, inflammatory responses, and communication between human astrocytes and peripheral blood immune cells. These data are suggestive of potential therapeutic utility of PARP inhibitors in the sphere of rare demyelinating diseases, and in particular MLD. Graphical abstract. Proposed mechanism of action of Olaparib in sulfatide-treated astrocytes. Human astrocytes treated for 24 h with sulfatides increase PARP-1 expression and die. PARP-1 overexpression is modulated by Ca2+ release from the endoplasmic reticulum, thus enhancing intracellular Ca2+ concentration. PARP-1 inhibition with Olaparib reduces Ca2+ influx and cell death. Olaparib also decreases IL-6, IL-8, IL-17, and CX3CL1 release from sulfatide-stimulated astrocytes, suggesting that PARP-1 plays a role in dampening neuroinflammation in MLD. This is confirmed by the reduction of immune cell migration such as lymphocytes, NK cells, and T cells towards sulfatide-treated astrocytes. Moreover, mitochondrial stress and ROS production induced by sulfatides are rescued by PARP-1 inhibition. Future studies will focus on the signaling cascades triggered by PARP-1-mediated currents in reactive astrocytes and Olaparib as a potential therapeutic target for MLD.

The Effects of Antipsychotics in Experimental Models of Krabbe Disease

The role of altered myelin in the onset and development of schizophrenia and changes in myelin due to antipsychotics remains unclear. Antipsychotics are D₂ receptor antagonists, yet D₂ receptor agonists increase oligodendrocyte progenitor numbers and limit oligodendrocyte injury. Conflicting studies suggest these drugs promote the differentiation of neural progenitors to oligodendrocyte lineage, while others report antipsychotics inhibit the proliferation and differentiation of oligodendrocyte precursors. Here, we utilised in-vitro (human astrocytes), ex-vivo (organotypic slice cultures) and in-vivo (twitcher mouse model) experimental study designs of psychosine-induced demyelination, a toxin that accumulates in Krabbe disease (KD), to investigate direct effects of antipsychotics on glial cell dysfunction and demyelination. Typical and atypical antipsychotics, and selective D₂ and 5HT_2A receptor antagonists, attenuated psychosine-induced cell viability, toxicity, and morphological aberrations in human astrocyte cultures. Haloperidol and clozapine reduced psychosine-induced demyelination in mouse organotypic cerebellar slices. These drugs also attenuated the effects of psychosine on astrocytes and microglia and restored non-phosphorylated neurofilament levels, indicating neuroprotective effects. In the demyelinating twitcher mouse model of KD, haloperidol improved mobility and significantly increased the survival of these animals. Overall, this study suggests that antipsychotics directly regulate glial cell dysfunction and exert a protective effect on myelin loss. This work also points toward the potential use of these pharmacological agents in KD.

The Adverse Outcome Pathway Framework Applied to Neurological Symptoms of COVID-19

Several reports have shown that the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has the potential to also be neurotropic. However, the mechanisms by which SARS-CoV-2 induces neurologic injury, including neurological and/or psychological symptoms, remain unclear. In this review, the available knowledge on the neurobiological mechanisms underlying COVID-19 was organized using the AOP framework. Four AOPs leading to neurological adverse outcomes (AO), anosmia, encephalitis, stroke, and seizure, were developed. Biological key events (KEs) identified to induce these AOs included binding to ACE2, blood–brain barrier (BBB) disruption, hypoxia, neuroinflammation, and oxidative stress. The modularity of AOPs allows the construction of AOP networks to visualize core pathways and recognize neuroinflammation and BBB disruption as shared mechanisms. Furthermore, the impact on the neurological AOPs of COVID-19 by modulating and multiscale factors such as age, psychological stress, nutrition, poverty, and food insecurity was discussed. Organizing the existing knowledge along an AOP framework can represent a valuable tool to understand disease mechanisms and identify data gaps and potentially contribute to treatment, and prevention. This AOP-aligned approach also facilitates synergy between experts from different backgrounds, while the fast-evolving and disruptive nature of COVID-19 emphasizes the need for interdisciplinarity and cross-community research.

Can the administration of platelet lysates to the brain help treat neurological disorders?

Neurodegenerative disorders of the central nervous system (CNS) and brain traumatic insults are characterized by complex overlapping pathophysiological alterations encompassing neuroinflammation, alterations of synaptic functions, oxidative stress, and progressive neurodegeneration that eventually lead to irreversible motor and cognitive dysfunctions. A single pharmacological approach is unlikely to provide a complementary set of molecular therapeutic actions suitable to resolve these complex pathologies. Recent preclinical data are providing evidence-based scientific rationales to support biotherapies based on administering neurotrophic factors and extracellular vesicles present in the lysates of human platelets collected from healthy donors to the brain. Here, we present the most recent findings on the composition of the platelet proteome that can activate complementary signaling pathways in vivo to trigger neuroprotection, synapse protection, anti-inflammation, antioxidation, and neurorestoration. We also report experimental data where the administration of human platelet lysates (HPL) was safe and resulted in beneficial neuroprotective effects in established rodent models of neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, traumatic brain injury, and stroke. Platelet-based biotherapies, prepared from collected platelet concentrates (PC), are emerging as a novel pragmatic and accessible translational therapeutic strategy for treating neurological diseases. Based on this assumption, we further elaborated on various clinical, manufacturing, and regulatory issues that need to be addressed to ensure the ethical supply, quality, and safety of HPL preparations for treating neurodegenerative and traumatic pathologies of the CNS. HPL made from PC may become a unique approach for scientifically based treatments of neurological disorders readily accessible in low-, middle-, and high-income countries.

Cellular inhibitor of apoptosis 2 (cIAP2) restricts neuroinflammation during experimental autoimmune encephalomyelitis

Background

Immune activation, neuroinflammation, and cell death are the hallmarks of multiple sclerosis (MS), which is an autoimmune demyelinating disease of the central nervous system (CNS). It is well-documented that the cellular inhibitor of apoptosis 2 (cIAP2) is induced by inflammatory stimuli and regulates adaptive and innate immune responses, cell death, and the production of inflammatory mediators. However, the impact of cIAP2 on neuroinflammation associated with MS and disease severity remains unknown.

Methods

We used experimental autoimmune encephalomyelitis (EAE), a widely used mouse model of MS, to assess the effect of cIAP2 deletion on disease outcomes. We performed a detailed analysis on the histological, cellular, and molecular levels. We generated and examined bone-marrow chimeras to identify the cIAP2-deficient cells that are critical to the disease outcomes.

Results

cIAP2^−/− mice exhibited increased EAE severity, increased CD4⁺ T cell infiltration, enhanced proinflammatory cytokine/chemokine expression, and augmented demyelination. This phenotype was driven by cIAP2-deficient non-hematopoietic cells. cIAP2 protected oligodendrocytes from cell death during EAE by limiting proliferation and activation of brain microglia. This protective role was likely exerted by cIAP2-mediated inhibition of the non-canonical NLRP3/caspase-8-dependent myeloid cell activation during EAE.

Conclusions

Our findings suggest that cIAP2 is needed to modulate neuroinflammation, cell death, and survival during EAE. Significantly, our data demonstrate the critical role of cIAP2 in limiting the activation of microglia during EAE, which could be explored for developing MS therapeutics in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02527-6.

Tissue inhibitor of metalloproteinases 1 is involved in ROS-mediated inflammation via regulating matrix metalloproteinase 1 expression in the sea cucumber Apostichopus japonicus

Tissue inhibitors of metalloproteinases (TIMPs) serve as matrix metalloproteinase (MMP) inhibitors in the pathogenesis of inflammatory diseases in vertebrates. We cloned and characterised the TIMP1 gene from Apostichopus japonicus using RACE approaches (designated as AjTIMP1). For Vibrio splendidus-challenged sea cucumbers, the peak expression of AjTIMP1 mRNAs in coelomocytes was detected at 24 h (23.44-fold) and remained at high levels (4.01-fold) until 72 h. Similarly, AjTIMP1 expression was upregulated in primary coelomocytes exposed to 10 μg mL^-1 LPS. AjTIMP1 was expressed in all tissues, and the highest expression was observed in the body wall. Functional investigation revealed an imbalance in the ratio of AjMMP1/AjTIMP1 in the skin ulceration syndrome (SUS) diseased group; it was sharply up-regulated to 3.97:1 compared with the healthy group. Furthermore, when AjTIMP1 was knocked down using small interfering RNA (siRNA-KD) to 0.4-fold, AjMMP1 and AjMMP19 were upregulated to 1.99- and 1.85-fold, respectively. AjTIMP1 siRNA-KD can promote ROS production by 26.2%, whereas AjMMP1 siRNA-KD can eliminate the increase in ROS. In inflamed tissues, collagen I and III levels were decreased by 33.1% and 33.6%, respectively, in the AjTIMP1 siRNA group at 24 h AjTIMP1 was involved in the inflammatory response by mediating ROS formation and collagen degradation.

Modeling and Targeting Neuroglial Interactions with Human Pluripotent Stem Cell Models

Generation of relevant and robust models for neurological disorders is of main importance for both target identification and drug discovery. The non-cell autonomous effects of glial cells on neurons have been described in a broad range of neurodegenerative and neurodevelopmental disorders, pointing to neuroglial interactions as novel alternative targets for therapeutics development. Interestingly, the recent breakthrough discovery of human induced pluripotent stem cells (hiPSCs) has opened a new road for studying neurological and neurodevelopmental disorders “in a dish”. Here, we provide an overview of the generation and modeling of both neuronal and glial cells from human iPSCs and a brief synthesis of recent work investigating neuroglial interactions using hiPSCs in a pathophysiological context.

Prolonged ethanol exposure alters glutamate uptake leading to astrogliosis and neuroinflammation in adult zebrafish brain

High ethanol (EtOH) consumption is a serious condition that induces tremors, alcoholic psychosis, and delirium, being considered a public health problem worldwide. Prolonged EtOH exposure promotes neurodegeneration, affecting several neurotransmitter systems and transduction signaling pathways. Glutamate is the major excitatory amino acid in the central nervous system (CNS) and the extracellular glutamatergic tonus is controlled by glutamate transporters mostly located in astrocytes. Here, we explore the effects of prolonged EtOH exposure on the glutamatergic uptake system and its relationship with astroglial markers (GFAP and S100B), neuroinflammation (IL-1β and TNF-α), and brain derived neurotrophic factor (BDNF) levels in the CNS of adult zebrafish. Animals were exposed to 0.5% EtOH for 7, 14, and 28 days continuously. Glutamate uptake was significantly decreased after 7 and 14 days of EtOH exposure, returning to baseline levels after 28 days of exposure. No alterations were observed in crucial enzymatic activities linked to glutamate uptake, like Na,K-ATPase or glutamine synthetase. Prolonged EtOH exposure increased GFAP, S100B, and TNF-α levels after 14 days. Additionally, increased BDNF mRNA levels were observed after 14 and 28 days of EtOH exposure, while BDNF protein levels increased only after 28 days. Collectively, our data show markedly brain astroglial, neuroinflammatory and neurotrofic responses after an initial impairment of glutamate uptake following prolonged EtOH exposure. This neuroplasticity event could play a key role in the modulatory effect of EtOH on glutamate uptake after 28 days of continuous exposure.

Hybrid Nanoparticles as a Novel Tool for Regulating Psychosine-Induced Neuroinflammation and Demyelination In Vitro and Ex vivo

Polymeric nanoparticles are being extensively investigated as an approach for brain delivery of drugs, especially for their controlled release and targeting capacity. Nose-to-brain administration of nanoparticles, bypassing the blood brain barrier, offers a promising strategy to deliver drugs to the central nervous system. Here, we investigated the potential of hybrid nanoparticles as a therapeutic approach for demyelinating diseases, more specifically for Krabbe's disease. This rare leukodystrophy is characterized by the lack of enzyme galactosylceramidase, leading to the accumulation of toxic psychosine in glial cells causing neuroinflammation, extensive demyelination and death. We present evidence that lecithin/chitosan nanoparticles prevent damage associated with psychosine by sequestering the neurotoxic sphingolipid via physicochemical hydrophobic interactions. We showed how nanoparticles prevented the cytotoxicity caused by psychosine in cultured human astrocytes in vitro, and how the nanoparticle size and PDI augmented while the electrostatic charges of the surface decreased, suggesting a direct interaction between psychosine and the nanoparticles. Moreover, we studied the effects of nanoparticles ex vivo using mouse cerebellar organotypic cultures, observing that nanoparticles prevented the demyelination and axonal damage caused by psychosine, as well as a moderate prevention of the astrocytic death. Taken together, these results suggest that lecithin-chitosan nanoparticles are a potential novel delivery system for drugs for certain demyelinating conditions such as Krabbe's disease, due to their dual effect: not only are they an efficient platform for drug delivery, but they exert a protective effect themselves in tampering the levels of psychosine accumulation.

Role of astroglial toll-like receptors (TLRs) in central nervous system infections, injury and neurodegenerative diseases

Central nervous system (CNS) innate immunity plays essential roles in infections, neurodegenerative diseases, and brain or spinal cord injuries. Astrocytes and microglia are the principal cells that mediate innate immunity in the CNS. Pattern recognition receptors (PRRs), expressed by astrocytes and microglia, sense pathogen-derived or endogenous ligands released by damaged cells and initiate the innate immune response. Toll-like receptors (TLRs) are a well-characterized family of PRRs. The contribution of microglial TLR signaling to CNS pathology has been extensively investigated. Even though astrocytes assume a wide variety of key functions, information about the role of astroglial TLRs in CNS disease and injuries is limited. Because astrocytes display heterogeneity and exhibit phenotypic plasticity depending on the effectors present in the local milieu, they can exert both detrimental and beneficial effects. TLRs are modulators of these paradoxical astroglial properties. The goal of the current review is to highlight the essential roles played by astroglial TLRs in CNS infections, injuries and diseases. We discuss the contribution of astroglial TLRs to host defense as well as the dissemination of viral and bacterial infections in the CNS. We examine the link between astroglial TLRs and the pathogenesis of neurodegenerative diseases and present evidence showing the pivotal influence of astroglial TLR signaling on sterile inflammation in CNS injury. Finally, we define the research questions and areas that warrant further investigations in the context of astrocytes, TLRs, and CNS dysfunction.

Beneficial contribution of induced pluripotent stem cell-progeny to Connexin 47 dynamics during demyelination-remyelination

Oligodendrocytes are extensively coupled to astrocytes, a phenomenon ensuring glial homeostasis and maintenance of central nervous system myelin. Molecular disruption of this communication occurs in demyelinating diseases such as multiple sclerosis. Less is known about the vulnerability and reconstruction of the panglial network during adult demyelination‐remyelination. Here, we took advantage of lysolcithin‐induced demyelination to investigate the expression dynamics of the oligodendrocyte specific connexin 47 (Cx47) and to some extent that of astrocyte Cx43, and whether this dynamic could be modulated by grafted induced pluripotent stem cell (iPSC)‐neural progeny. Our data show that disruption of Cx43‐Cx47 mediated hetero‐cellular gap‐junction intercellular communication following demyelination is larger in size than demyelination. Loss of Cx47 expression is timely rescued during remyelination and accelerated by the grafted neural precursors. Moreover, mouse and human iPSC‐derived oligodendrocytes express Cx47, which co‐labels with astrocyte Cx43, indicating their integration into the panglial network. These data suggest that in rodents, full lesion repair following transplantation occurs by panglial reconstruction in addition to remyelination. Targeting panglial elements by cell therapy or pharmacological compounds may help accelerating or stabilizing re/myelination in myelin disorders.

Neuronal Ablation of Alpha/Beta Interferon (IFN-α/β) Signaling Exacerbates Central Nervous System Viral Dissemination and Impairs IFN-γ Responsiveness in Microglia/Macrophages

Alpha/beta interferon (IFN-α/β) signaling through the IFN-α/β receptor (IFNAR) is essential to limit virus dissemination throughout the central nervous system (CNS) following many neurotropic virus infections. However, the distinct expression patterns of factors associated with the IFN-α/β pathway in different CNS resident cell populations implicate complex cooperative pathways in IFN-α/β induction and responsiveness. Here we show that mice devoid of IFNAR1 signaling in calcium/calmodulin-dependent protein kinase II alpha (CaMKIIα) expressing neurons (CaMKIIcre:IFNAR^fl/fl mice) infected with a mildly pathogenic neurotropic coronavirus (mouse hepatitis virus A59 strain [MHV-A59]) developed severe encephalomyelitis with hind-limb paralysis and succumbed within 7 days. Increased virus spread in CaMKIIcre:IFNAR^fl/fl mice compared to IFNAR^fl/fl mice affected neurons not only in the forebrain but also in the mid-hind brain and spinal cords but excluded the cerebellum. Infection was also increased in glia. The lack of viral control in CaMKIIcre:IFNAR^fl/fl relative to control mice coincided with sustained Cxcl1 and Ccl2 mRNAs but a decrease in mRNA levels of IFNα/β pathway genes as well as Il6, Tnf, and Il1β between days 4 and 6 postinfection (p.i.). T cell accumulation and IFN-γ production, an essential component of virus control, were not altered. However, IFN-γ responsiveness was impaired in microglia/macrophages irrespective of similar pSTAT1 nuclear translocation as in infected controls. The results reveal how perturbation of IFN-α/β signaling in neurons can worsen disease course and disrupt complex interactions between the IFN-α/β and IFN-γ pathways in achieving optimal antiviral responses.IMPORTANCE IFN-α/β induction limits CNS viral spread by establishing an antiviral state, but also promotes blood brain barrier integrity, adaptive immunity, and activation of microglia/macrophages. However, the extent to which glial or neuronal signaling contributes to these diverse IFN-α/β functions is poorly understood. Using a neurotropic mouse hepatitis virus encephalomyelitis model, this study demonstrated an essential role of IFN-α/β receptor 1 (IFNAR1) specifically in neurons to control virus spread, regulate IFN-γ signaling, and prevent acute mortality. The results support the notion that effective neuronal IFNAR1 signaling compensates for their low basal expression of genes in the IFN-α/β pathway compared to glia. The data further highlight the importance of tightly regulated communication between the IFN-α/β and IFN-γ signaling pathways to optimize antiviral IFN-γ activity.

Brain Structural and Functional Alterations in Mice Prenatally Exposed to LPS Are Only Partially Rescued by Anti-Inflammatory Treatment

Aberrant immune activity during neurodevelopment could participate in the generation of neurological dysfunctions characteristic of several neurodevelopmental disorders (NDDs). Numerous epidemiological studies have shown a link between maternal infections and NDDs risk; animal models of maternal immune activation (MIA) have confirmed this association. Activation of maternal immune system during pregnancy induces behavioral and functional alterations in offspring but the biological mechanisms at the basis of these effects are still poorly understood. In this study, we investigated the effects of prenatal lipopolysaccharide (LPS) exposure in peripheral and central inflammation, cortical cytoarchitecture and behavior of offspring (LPS-mice). LPS-mice reported a significant increase in interleukin-1β (IL-1β) serum level, glial fibrillary acidic protein (GFAP)- and ionized calcium-binding adapter molecule 1 (Iba1)-positive cells in the cortex. Furthermore, cytoarchitecture analysis in specific brain areas, showed aberrant alterations in minicolumns’ organization in LPS-mice adult brain. In addition, we demonstrated that LPS-mice presented behavioral alterations throughout life. In order to better understand biological mechanisms whereby LPS induced these alterations, dams were treated with meloxicam. We demonstrated for the first time that exposure to LPS throughout pregnancy induces structural permanent alterations in offspring brain. LPS-mice also present severe behavioral impairments. Preventive treatment with meloxicam reduced inflammation in offspring but did not rescue them from structural and behavioral alterations.

The emerging role of galectins in (re)myelination and its potential for developing new approaches to treat multiple sclerosis

Multiple sclerosis (MS) is an inflammatory, demyelinating and neurodegenerative disease of the central nervous system with unknown etiology. Currently approved disease-modifying treatment modalities are immunomodulatory or immunosuppressive. While the applied drugs reduce the frequency and severity of the attacks, their efficacy to regenerate myelin membranes and to halt disease progression is limited. To achieve such therapeutic aims, understanding biological mechanisms of remyelination and identifying factors that interfere with remyelination in MS can give respective directions. Such a perspective is given by the emerging functional profile of galectins. They form a family of tissue lectins, which are potent effectors in processes as diverse as adhesion, apoptosis, immune mediator release or migration. This review focuses on endogenous and exogenous roles of galectins in glial cells such as oligodendrocytes, astrocytes and microglia in the context of de- and (re)myelination and its dysregulation in MS. Evidence is arising for a cooperation among family members so that timed expression and/or secretion of galectins-1, -3 and -4 result in modifying developmental myelination, (neuro)inflammatory processes, de- and remyelination. Dissecting the mechanisms that underlie the distinct activities of galectins and identifying galectins as target or tool to modulate remyelination have the potential to contribute to the development of novel therapeutic strategies for MS.

Dose-dependent effect of cannabinoid WIN-55,212-2 on myelin repair following a demyelinating insult

Dysfunctions in the endocannabinoid system have been associated with experimental animal models and multiple sclerosis patients. Interestingly, the endocannabinoid system has been reported to confer neuroprotection against demyelination. The present study aims to assess the effects of the cannabinoid agonist WIN-55,212-2 in cuprizone fed animals on myelin repair capacity. Animals exposed to cuprizone were simultaneously treated withWIN-55,212-2, behaviorally tested and finally the corpus callosum was exhaustively studied by Western blotting, qRT-PCR and a myelin staining procedure. We report that the long-term administration of WIN-55,212-2 reduced the global amount of CB₁ protein. Histological analysis revealed clear demyelination after being fed cuprizone for three weeks. However, cuprizone-fed mice subjected to 0.5 mg/Kg of WIN-55,212-2 displayed no differences when compared to controls during demyelination, although there was a robust increase in the myelinated axons during the remyelination phase. These animals displayed better performance on contextual fear conditioning which was in turn non-attributable to an antinociceptive effect. In contrast, a 1 mg/Kg dosage caused a remarkable demyelination accompanied by limited potential for myelin repair. Upon drug administration while mice ongoing demyeliniation, the expression of Aif1 (microglia) and Gfap (astrocytes) followed a dose-dependent manner whereas the expression of both markers was apparently attenuated during remyelination. Treatment with vehicle or 0.5 mg/Kg of the drug during demyelination increased the expression of Pdgfra (oligodendrocyte precursor cells) but this did not occur when 1 mg/Kg was administered. In conclusion, the drug at 0.5 mg/Kg did not alter myelin architecture while 1 mg/Kg had a deleterious effect in this model.

Evidence of hippocampal astrogliosis and antioxidant imbalance after L-tyrosine chronic administration in rats

Tyrosinemia type II is a genetic disorder characterized by elevated blood levels of the amino acid tyrosine caused by the deficiency of tyrosine aminotransferase enzyme, resulting in neurologic and developmental difficulties in the patients. Although neurological sequelae are common in Tyrosinemia type II patients, the mechanisms involved are still poorly understood. The oxidative stress appears to be, at least in part, responsible for neurological complication in this inborn error metabolism. We observed that an acute injection of tyrosine in rats caused a massive oxidative stress in different brain structures. The glutathione system and superoxide dismutase enzyme are relevant antioxidant strategies of the cells and tissues, including in the brain. Other important point is the strong relation between oxidative damage and inflammatory events. Herein, we investigated the effects of chronic administration of tyrosine in the hippocampus of young rats, with emphasis in the activity of GSH related enzymes and superoxide dismutase enzyme, and the astrocytosis. We observed that rats exposed to high levels of tyrosine presented an increased content of tyrosine, which was associated with an increment in the activity of glutathione peroxidase and glutathione reductase as well as with a diminished activity of superoxide dismutase. This antioxidant imbalance was accompanied by enhanced glial fibrillary acidic protein immunoreactivity, a marker of astrocytes, in the brain area studied. In conclusion, hippocampus astrogliosis is also a characteristic of brain alteration in Tyrosinemia. In addition, the chronic exposition to high levels of tyrosine is associated with an alteration in the activity of fundamental antioxidant enzymes.

Astrocytes in myelination and remyelination

Astrocytes are known to play critical roles in central nervous system development, homeostasis, and response to injury. In addition to well-defined functions in synaptic signalling and blood-brain barrier control, astrocytes are now emerging as important contributors to white matter health. Here, we review the roles of astrocytes in myelin formation and regeneration (remyelination), focusing on both direct interactions with oligodendrocyte lineage cells, and indirect influences via crosstalk with central nervous system resident macrophages, microglia.

TIMP-1 Attenuates the Development of Inflammatory Pain Through MMP-Dependent and Receptor-Mediated Cell Signaling Mechanisms

Unresolved inflammation is a significant predictor for developing chronic pain, and targeting the mechanisms underlying inflammation offers opportunities for therapeutic intervention. During inflammation, matrix metalloproteinase (MMP) activity contributes to tissue remodeling and inflammatory signaling, and is regulated by tissue inhibitors of metalloproteinases (TIMPs). TIMP-1 and -2 have known roles in pain, but only in the context of MMP inhibition. However, TIMP-1 also has receptor-mediated cell signaling functions that are not well understood. Here, we examined how TIMP-1-dependent cell signaling impacts inflammatory hypersensitivity and ongoing pain. We found that hindpaw injection of complete Freund's adjuvant (CFA) increased cutaneous TIMP-1 expression that peaked prior to development of mechanical hypersensitivity, suggesting that TIMP-1 inhibits the development of inflammatory hypersensitivity. To examine this possibility, we injected TIMP-1 knockout (T1KO) mice with CFA and found that T1KO mice exhibited rapid onset thermal and mechanical hypersensitivity at the site of inflammation that was absent or attenuated in WT controls. We also found that T1KO mice exhibited hypersensitivity in adjacent tissues innervated by different sets of afferents, as well as skin contralateral to the site of inflammation. Replacement of recombinant murine (rm)TIMP-1 alleviated hypersensitivity when administered at the site and time of inflammation. Administration of either the MMP inhibiting N-terminal or the cell signaling C-terminal domains recapitulated the antinociceptive effect of full-length rmTIMP-1, suggesting that rmTIMP-1inhibits hypersensitivity through MMP inhibition and receptor-mediated cell signaling. We also found that hypersensitivity was not due to genotype-specific differences in MMP-9 activity or expression, nor to differences in cytokine expression. Administration of rmTIMP-1 prevented mechanical hypersensitivity and ongoing pain in WT mice, collectively suggesting a novel role for TIMP-1 in the attenuation of inflammatory pain.

Astroglia in Leukodystrophies

Leukodystrophies are genetically determined disorders affecting the white matter of the central nervous system. The combination of MRI pattern recognition and next-generation sequencing for the definition of novel disease entities has recently demonstrated that many leukodystrophies are due to the primary involvement and/or mutations in genes selectively expressed by cell types other than the oligodendrocytes, the myelin-forming cells in the brain. This has led to a new definition of leukodystrophies as genetic white matter disorders resulting from the involvement of any white matter structural component. As a result, the research has shifted its main focus from oligodendrocytes to other types of neuroglia. Astrocytes are the housekeeping cells of the nervous system, responsible for maintaining homeostasis and normal brain physiology and to orchestrate repair upon injury. Several lines of evidence show that astrocytic interactions with the other white matter cellular constituents play a primary pathophysiologic role in many leukodystrophies. These are thus now classified as astrocytopathies. This chapter addresses how the crosstalk between astrocytes, other glial cells, axons and non-neural cells are essential for the integrity and maintenance of the white matter in health. It also addresses the current knowledge of the cellular pathomechanisms of astrocytic leukodystrophies, and specifically Alexander disease, vanishing white matter, megalencephalic leukoencephalopathy with subcortical cysts and Aicardi-Goutière Syndrome.

TIMP-1 Attenuates the Development of Inflammatory Pain Through MMP-Dependent and Receptor-Mediated Cell Signaling Mechanisms

Unresolved inflammation is a significant predictor for developing chronic pain, and targeting the mechanisms underlying inflammation offers opportunities for therapeutic intervention. During inflammation, matrix metalloproteinase (MMP) activity contributes to tissue remodeling and inflammatory signaling, and is regulated by tissue inhibitors of metalloproteinases (TIMPs). TIMP-1 and -2 have known roles in pain, but only in the context of MMP inhibition. However, TIMP-1 also has receptor-mediated cell signaling functions that are not well understood. Here, we examined how TIMP-1-dependent cell signaling impacts inflammatory hypersensitivity and ongoing pain. We found that hindpaw injection of complete Freund’s adjuvant (CFA) increased cutaneous TIMP-1 expression that peaked prior to development of mechanical hypersensitivity, suggesting that TIMP-1 inhibits the development of inflammatory hypersensitivity. To examine this possibility, we injected TIMP-1 knockout (T1KO) mice with CFA and found that T1KO mice exhibited rapid onset thermal and mechanical hypersensitivity at the site of inflammation that was absent or attenuated in WT controls. We also found that T1KO mice exhibited hypersensitivity in adjacent tissues innervated by different sets of afferents, as well as skin contralateral to the site of inflammation. Replacement of recombinant murine (rm)TIMP-1 alleviated hypersensitivity when administered at the site and time of inflammation. Administration of either the MMP inhibiting N-terminal or the cell signaling C-terminal domains recapitulated the antinociceptive effect of full-length rmTIMP-1, suggesting that rmTIMP-1inhibits hypersensitivity through MMP inhibition and receptor-mediated cell signaling. We also found that hypersensitivity was not due to genotype-specific differences in MMP-9 activity or expression, nor to differences in cytokine expression. Administration of rmTIMP-1 prevented mechanical hypersensitivity and ongoing pain in WT mice, collectively suggesting a novel role for TIMP-1 in the attenuation of inflammatory pain.

Synaptic alterations and immune response are sexually dimorphic in a non-pertussis toxin model of experimental autoimmune encephalomyelitis

Multiple sclerosis is an autoimmune disorder of the central nervous system (CNS) characterized by locomotor impairments, cognitive deficits, affective disorders, and chronic pain. Females are predominately affected by MS compared to males and develop motor symptoms earlier. However, key symptoms affect all patients regardless of sex. Previous studies have shown that demyelination and axonal damage play key roles in symptom development, but it is unclear why sex differences exist in MS onset, and effective symptom treatment is still lacking. We here used a non-pertussis toxin (nPTX) experimental autoimmune encephalomyelitis (EAE) model in C57BL/6 mice, to explore chronic symptoms and sex differences in CNS autoimmunity. We observed that, like in humans, female mice developed motor disease earlier than males. Further, changes in pre- and post-synaptic protein expression levels were observed in a sexually dimorphic manner with an overall shift towards excitatory signaling. Our data suggest that this shift towards excitatory signaling is achieved through different mechanisms in males and females. Altogether, our study helps to better understand sex-specific disease mechanisms to ultimately develop better diagnostic and treatment tools.

A detrimental role of RelB in mature oligodendrocytes during experimental acute encephalomyelitis

Background

Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system (CNS). It is firmly established that overactivation of the p65 (RelA) nuclear factor kappa B (NF-κB) transcription factor upregulates expression of inflammatory mediators in both immune and non-immune resident CNS cells and promotes inflammation during MS. In contrast to p65, NF-κB family member RelB regulates immune cell development and can limit inflammation. Although RelB expression is induced during inflammation in the CNS, its role in MS remains unknown.

Methods

To examine the role of RelB in non-immune CNS cells, we generated mice with RelB specifically deleted in astrocytes (RelB^ΔAST), oligodendrocytes (RelB^ΔOLIGO), or neural progenitor-derived cells (RelB^ΔNP). We used experimental autoimmune encephalomyelitis (EAE), an accepted mouse model of MS, to assess the effect of RelB deletion on disease outcomes and performed analysis on the histological, cellular, and molecular level.

Results

Despite being a negative regulator of inflammation, conditional knockout of RelB in non-immune resident CNS cells surprisingly decreased the severity of EAE. This protective effect was recapitulated by conditional deletion of RelB in oligodendrocytes but not astrocytes. Deletion of RelB in oligodendrocytes reduced disease severity, promoted survival of mature oligodendrocytes, and correlated with increased activation of p65 NF-κB.

Conclusions

These findings suggest that RelB fine tunes inflammation and cell death/survival during EAE. Importantly, our data points out the detrimental role RelB plays in controlling survival of mature oligodendrocytes, which could be explored as a viable option to treat MS in the future.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1548-7) contains supplementary material, which is available to authorized users.

Neuregulin-1/ErbB network: An emerging modulator of nervous system injury and repair

Neuregulin-1 (Nrg-1) is a member of the Neuregulin family of growth factors with essential roles in the developing and adult nervous system. Six different types of Nrg-1 (Nrg-1 type I-VI) and over 30 isoforms have been discovered; however, their specific roles are not fully determined. Nrg-1 signals through a complex network of protein-tyrosine kinase receptors, ErbB2, ErbB3, ErbB4 and multiple intracellular pathways. Genetic and pharmacological studies of Nrg-1 and ErbB receptors have identified a critical role for Nrg-1/ErbB network in neurodevelopment including neuronal migration, neural differentiation, myelination as well as formation of synapses and neuromuscular junctions. Nrg-1 signaling is best known for its characterized role in development and repair of the peripheral nervous system (PNS) due to its essential role in Schwann cell development, survival and myelination. However, our knowledge of the impact of Nrg-1/ErbB on the central nervous system (CNS) has emerged in recent years. Ongoing efforts have uncovered a multi-faceted role for Nrg-1 in regulating CNS injury and repair processes. In this review, we provide a timely overview of the most recent updates on Nrg-1 signaling and its role in nervous system injury and diseases. We will specifically highlight the emerging role of Nrg-1 in modulating the glial and immune responses and its capacity to foster neuroprotection and remyelination in CNS injury. Nrg-1/ErbB network is a key regulatory pathway in the developing nervous system; therefore, unraveling its role in neuropathology and repair can aid in development of new therapeutic approaches for nervous system injuries and associated disorders.

Aquaporin 4: A key player in Parkinson's disease

Parkinson's disease (PD) is one of the most prevalent neurodegenerative diseases which occur in aged people worldwide. Given that a sequence of cellular and molecular mechanisms, including oxidative stresses, apoptosis, inflammatory pathways, microglia, astrocyte activation, and aquaporin 4 (AQP4) are associated with initiation and the progression of PD. AQP4 may affect various pathways (i.e., α-synuclein, inflammatory pathways, and microglia and astrocyte activation). Few reports have evaluated the relationship between AQP4 and PD-related cellular and molecular pathways. Here, for the first time, we highlighted the relationship between AQP4 and molecular mechanisms involved in PD pathogenesis.

Impaired Remyelination in a Mouse Model of Huntington Disease

White matter (WM) abnormalities are a well-established feature of Huntington disease (HD), although their nature is not fully understood. Here, we asked whether remyelination as a measure of WM plasticity is impaired in a model of HD. Using the cuprizone assay, we examined demyelination and remyelination responses in YAC128 HD mice. Treatment with 0.2% cuprizone (CPZ) for 6 weeks resulted in significant reduction in mature (GSTπ-positive) oligodendrocyte counts and FluoroMyelin staining in the corpus callosum, leading to similar demyelination states in YAC128 and wild-type (WT) mice. Six weeks following cessation of CPZ, we observed robust remyelination in WT mice as indicated by an increase in mature oligodendrocyte counts and FluoroMyelin staining. In contrast, YAC128 mice exhibited an impaired remyelination response. The increase in mature oligodendrocyte counts in YAC128 HD mice following CPZ cessation was lower than that of WT. Furthermore, there was no increase in FluoroMyelin staining compared to the demyelinated state in YAC128 mice. We confirmed these findings using electron microscopy where the CPZ-induced reduction in myelinated axons was reversed following CPZ cessation in WT but not YAC128 mice. Our findings demonstrate that remyelination is impaired in YAC128 mice and suggest that WM plasticity may be compromised in HD.

Activation of microglia and astrocytes: a roadway to neuroinflammation and Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that is of high importance to the neuroscience world, yet the complex pathogenicity is not fully understood. Inflammation is usually observed in AD and could implicate both beneficial or detrimental effects depending on the severity of the disease. During initial AD pathology, microglia and astrocyte activation is beneficial since they are involved in amyloid-beta clearance. However, with the progression of the disease, activated microglia elicit detrimental effects by the overexpression of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) bringing forth neurodegeneration in the surrounding brain regions. This results in decline in Aβ clearance by microglia; Aβ accumulation thus increases in the brain resulting in neuroinflammation. Thus, Aβ accumulation is the effect of increased release of pro-inflammatory molecules. Reactive astrocytes acquire gain of toxic function and exhibits neurotoxic effects with loss of neurotrophic functions. Astrocyte dysfunctioning results in increased release of cytokines and inflammatory mediators, neurodegeneration, decreased glutamate uptake, loss of neuronal synapses, and ultimately cognitive deficits in AD. We discuss the role of intracellular signaling pathways in the inflammatory responses produced by astrocytes and microglial activation, including the glycogen synthase kinase-3β, nuclear factor kappa B cascade, mitogen-activated protein kinase pathways and c-Jun N-terminal kinase. In this review, we describe the role of neuroinflammation in the chronicity of AD pathogenesis and an overview of the recent research towards the development of new therapies to treat this disorder.

Intercellular Communication Is Key for Protective IFNα/β Signaling During Viral Central Nervous System Infection

A variety of viruses can induce central nervous system (CNS) infections and neurological diseases, although the incidence is rare. Similar to peripheral infections, IFNα/β induction and signaling constitutes a first line of defense to limit virus dissemination. However, CNS-resident cells differ widely in their repertoire and magnitude of both basal and inducible components in the IFNα/β pathway. While microglia as resident myeloid cells have been implicated as prominent sentinels of CNS invading pathogens or insults, astrocytes are emerging as key responders to many neurotropic RNA virus infections. Focusing on RNA viruses, this review discusses the role of astrocytes as IFNα/β inducers and responders and touches on the role of IFNα/β receptor signaling in regulating myeloid cell activation and IFNγ responsiveness. A summary picture emerges implicating IFNα/β not only as key in establishing the classical "antiviral" state, but also orchestrating cell mobility and IFNγ-mediated effector functions.

Reactive Astrocytes as Drug Target in Alzheimer's Disease

Alzheimer's disease is a neurodegenerative disease characterized by deposition of extracellular amyloid-β, intracellular neurofibrillary tangles, and loss of cortical neurons. However, the mechanism underlying neurodegeneration in Alzheimer's disease (AD) remains to be explored. Many of the researches on AD have been primarily focused on neuronal changes. Current research, however, broadens to give emphasis on the importance of nonneuronal cells, such as astrocytes. Astrocytes play fundamental roles in several cerebral functions and their dysfunctions promote neurodegeneration and, eventually, retraction of neuronal synapses, which leads to cognitive deficits found in AD. Astrocytes become reactive as a result of deposition of Aβ, which in turn have detrimental consequences, including decreased glutamate uptake due to reduced expression of uptake transporters, altered energy metabolism, altered ion homeostasis (K⁺ and Ca⁺), increased tonic inhibition, and increased release of cytokines and inflammatory mediators. In this review, recent insights on the involvement of, tonic inhibition, astrocytic glutamate transporters and aquaporin in the pathogenesis of Alzheimer's disease are provided. Compounds which increase expression of GLT1 have showed efficacy for AD in preclinical studies. Tonic inhibition mediated by GABA could also be a promising target and drugs that block the GABA synthesizing enzyme, MAO-B, have shown efficacy. However, there are contradictory evidences on the role of AQP4 in AD.

HFE Genotype Restricts the Response to Paraquat in a Mouse Model of Neurotoxicity

Parkinson's disease is marked clinically by motor dysfunction and pathologically by dopaminergic cell loss in the substantia nigra and iron accumulation in the substantia nigra. The driver underlying iron accumulation remains unknown and could be genetic or environmental. The HFE protein is critical for the regulation of cellular iron uptake. Mutations within this protein are associated with increased iron accumulation including in the brain. We have focused on the commonly occurring H63D variant of the HFE gene as a disease modifier in a number of neurodegenerative diseases. To investigate the role of H63D HFE genotype, we generated a mouse model in which the wild-type (WT) HFE gene is replaced by the H67D gene variant (mouse homolog of the human H63D gene variant). Using paraquat toxicity as the model for Parkinson's disease, we found that WT mice responded as expected with significantly greater motor function, loss of tyrosine hydroxylase staining and increase microglial staining in the substantia nigra, and an increase in R2 relaxation rate within the substantia nigra of the paraquat-treated mice compared to their saline-treated counterparts. In contrast, the H67D mice showed a remarkable resistance to paraquat treatment; specifically differing from the WT mice with no changes in motor function or changes in R2 relaxation rates following paraquat exposure. At baseline, there were differences between the H67D HFE mice and WT mice in gut microbiome profile and increased L-ferritin staining in the substantia nigra that could account for the resistance to paraquat. Of particular note, the H67D HFE mice regardless of whether or not they were treated with paraquat had significantly less tyrosine hydroxylase immunostaining than WT. Our results clearly demonstrate that the HFE genotype impacts the expression of tyrosine hydroxylase in the substantia nigra, the gut microbiome and the response to paraquat providing additional support that the HFE genotype is a disease modifier for Parkinson's disease. Moreover, the finding that the HFE mutant mice are resistant to paraquat may provide a model in which to study resistant mechanisms to neurotoxicants.

Alpha/Beta Interferon (IFN-α/β) Signaling in Astrocytes Mediates Protection against Viral Encephalomyelitis and Regulates IFN-γ-Dependent Responses

The contribution of distinct central nervous system (CNS) resident cells to protective alpha/beta interferon (IFN-α/β) function following viral infections is poorly understood. Based on numerous immune regulatory functions of astrocytes, we evaluated the contribution of astrocyte IFN-α/β signaling toward protection against the nonlethal glia- and neuronotropic mouse hepatitis virus (MHV) strain A59. Analysis of gene expression associated with IFN-α/β function, e.g., pattern recognition receptors (PRRs) and interferon-stimulated genes (ISGs), revealed lower basal mRNA levels in brain-derived astrocytes than in microglia. Although astrocytes poorly induced Ifnβ mRNA following infection, they upregulated various mRNAs in the IFN-α/β pathway to a higher extent than microglia, supporting effective IFN-α/β responsiveness. Ablation of the IFN-α/β receptor (IFNAR) in astrocytes using mGFAPcre IFNAR^fl/fl mice resulted in severe encephalomyelitis and mortality, coincident with uncontrolled virus replication. Further, virus spread was not restricted to astrocytes but also affected microglia and neurons, despite increased and sustained Ifnα/β and ISG mRNA levels within the CNS. IFN-γ, a crucial mediator for MHV control, was not impaired in infected mGFAPcre IFNAR^fl/fl mice despite reduced T cell CNS infiltration. Unexpectedly however, poor induction of IFN-γ-dependent major histocompatibility complex (MHC) class II expression on microglia supported that defective IFN-γ signaling contributes to uncontrolled virus replication. A link between sustained elevated IFN-α/β and impaired responsiveness to IFN-γ supports the novel concept that temporally limited early IFN-α/β responses are critical for effective antiviral IFN-γ function. Overall, our results imply that IFN-α/β signaling in astrocytes is not only critical in limiting early CNS viral spread but also promotes protective antiviral IFN-γ function.IMPORTANCE An antiviral state established by IFN-α/β contains initial viral spread as adaptive immunity develops. While it is apparent that the CNS lacks professional IFN-α/β producers and that resident cells have distinct abilities to elicit innate IFN-α/β responses, protective interactions between inducer and responder cells require further investigation. Infection with a glia- and neuronotropic coronavirus demonstrates that astrocytes mount a delayed but more robust response to infection than microglia, despite their lower basal mRNA levels of IFN-α/β-inducing components. Lethal, uncontrolled viral dissemination following ablation of astrocyte IFN-α/β signaling revealed the importance of IFN-α/β responses in a single cell type for protection. Sustained global IFN-α/β expression associated with uncontrolled virus did not suffice to protect neurons and further impaired responsiveness to protective IFN-γ. The results support astrocytes as critical contributors to innate immunity and the concept that limited IFN-α/β responses are critical for effective subsequent antiviral IFN-γ function.

An adverse outcome pathway for parkinsonian motor deficits associated with mitochondrial complex I inhibition

Epidemiological studies have observed an association between pesticide exposure and the development of Parkinson's disease, but have not established causality. The concept of an adverse outcome pathway (AOP) has been developed as a framework for the organization of available information linking the modulation of a molecular target [molecular initiating event (MIE)], via a sequence of essential biological key events (KEs), with an adverse outcome (AO). Here, we present an AOP covering the toxicological pathways that link the binding of an inhibitor to mitochondrial complex I (i.e., the MIE) with the onset of parkinsonian motor deficits (i.e., the AO). This AOP was developed according to the Organisation for Economic Co-operation and Development guidelines and uploaded to the AOP database. The KEs linking complex I inhibition to parkinsonian motor deficits are mitochondrial dysfunction, impaired proteostasis, neuroinflammation, and the degeneration of dopaminergic neurons of the substantia nigra. These KEs, by convention, were linearly organized. However, there was also evidence of additional feed-forward connections and shortcuts between the KEs, possibly depending on the intensity of the insult and the model system applied. The present AOP demonstrates mechanistic plausibility for epidemiological observations on a relationship between pesticide exposure and an elevated risk for Parkinson's disease development.

Krabbe's leukodystrophy: Approaches and models in vitro

This Review describes some in vitro approaches used to investigate the mechanisms involved in Krabbe's disease, with particular regard to the cellular systems employed to study processes of inflammation, apoptosis, and angiogenesis. The aim was to update the knowledge on the results obtained from in vitro models of this neurodegenerative disorder and provide stimuli for future research. For a long time, the nonavailability of established neural cells has limited the understanding of neuropathogenic mechanisms in Krabbe's leukodystrophy. More recently, the development of new Krabbe's disease cell models has allowed the identification of neurologically relevant pathogenic cascades, including the major role of elevated psychosine levels. Thus, direct and/or indirect roles of psychosine in the release of cytokines, reactive oxygen species, and nitric oxide and in the activation of kinases, caspases, and angiogenic factors results should be clearer. In parallel, it is now understood that the presence of globoid cells precedes oligodendrocyte apoptosis and demyelination. The information described here will help to continue the research on Krabbe's leukodystrophy and on potential new therapeutic approaches for this disease that even today, despite numerous attempts, is without cure. © 2016 Wiley Periodicals, Inc.

The Physiological Basis of Cervical Facet-Mediated Persistent Pain: Basic Science and Clinical Challenges

Synopsis Chronic neck pain is a common condition and a primary clinical symptom of whiplash and other spinal injuries. Loading-induced neck injuries produce abnormal kinematics between the vertebrae, with the potential to injure facet joints and the afferent fibers that innervate the specific joint tissues, including the capsular ligament. Mechanoreceptive and nociceptive afferents that innervate the facet have their peripheral terminals in the capsule, cell bodies in the dorsal root ganglia, and terminal processes in the spinal cord. As such, biomechanical loading of these afferents can initiate nociceptive signaling in the peripheral and central nervous systems. Their activation depends on the local mechanical environment of the joint and encodes the neural processes that initiate pain and lead to its persistence. This commentary reviews the complex anatomical, biomechanical, and physiological consequences of facet-mediated whiplash injury and pain. The clinical presentation of facet-mediated pain is complex in its sensory and emotional components. Yet, human studies are limited in their ability to elucidate the physiological mechanisms by which abnormal facet loading leads to pain. Over the past decade, however, in vivo models of cervical facet injury that reproduce clinical pain symptoms have been developed and used to define the complicated and multifaceted electrophysiological, inflammatory, and nociceptive signaling cascades that are involved in the pathophysiology of whiplash facet pain. Integrating the whiplash-like mechanics in vivo and in vitro allows transmission of pathophysiological mechanisms across scales, with the hope of informing clinical management. Yet, despite these advances, many challenges remain. This commentary further describes and highlights such challenges. J Orthop Sports Phys Ther 2017;47(7):450-461. Epub 16 Jun 2017. doi:10.2519/jospt.2017.7255.

CXCL10 and CXCL13 chemokines in patients with relapsing remitting and primary progressive multiple sclerosis

OBJECTIVES

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system characterized by a variable clinical course. Different pathogenic mechanisms responsible for relapsing remitting (RRMS) and primary progressive multiple sclerosis (PPMS) are modulated by immunological process with important role of chemokine network. CXCL10 and CXCL13 chemokines act as chemoattractants and modulators of proinflammatory reactions promoting process of demyelination. In the present study, we investigated the concentrations of CXCL10 and CXCL13 in serum and cerebrospinal fluid (CSF) of patients with RRMS and PPMS.

MATERIALS AND METHODS

The study groups comprised 25 RRMS patients (39,5±12years), 24 PPMS patients (49,9±10,5years), 31 healthy individuals (36±10,4years) with tension headache without symptoms of inflammatory diseases. A quantitive test kit based on ELISA has been used for chemokines measurement. Correlations analysis between the levels of CXCL10, CXCL13 and patient age, duration of MS, EDSS and IgG index were done.

RESULTS

The mean concentration of CXCL10 in the CSF was statistically significantly higher in RRMS in comparison with the control group. The mean concentration of CXCL13 in the CSF was significantly higher in RRMS and PPMS than in the control group. The results have shown that in the stable phase of MS without relapse, mean concentration of CXCL10 and CXCL13 in CSF did not differ significantly between RRMS and PPMS. In PPMS a positive correlation between IgG index and CSF CXCL10 level or CSF CXCL13 level was observed. In RRMS a positive correlation between IgG index and CSF CXCL13 level was observed.

CONCLUSIONS

These data indicate involvement of CXCL10 and CXCL13 chemokines in immunopathogenetic mechanisms in MS. There was no significant difference between mean CXCL10 or CXCL13 concentrations in the CSF in both RRMS and PPMS patients. No significant correlations were found between patient age and chemokines levels in theCSF in all groups. It suggest that these chemokines play similar role in inflammatory process despite more pronounced neurodegenerative process in PPMS.

Crosstalk between sphingolipids and vitamin D3: potential role in the nervous system

Sphingolipids are both structural and bioactive compounds. In particular, ceramide and sphingosine 1-phosphate regulate cell fate, inflammation and excitability. 1-α,25-dihydroxyvitamin D3 (1,25(OH)2 D3 ) is known to play an important physiological role in growth and differentiation in a variety of cell types, including neural cells, through genomic actions mediated by its specific receptor, and non-genomic effects that result in the activation of specific signalling pathways. 1,25(OH)2 D3 and sphingolipids, in particular sphingosine 1-phosphate, share many common effectors, including calcium regulation, growth factors and inflammatory cytokines, but it is still not known whether they can act synergistically. Alterations in the signalling and concentrations of sphingolipids and 1,25(OH)2 D3 have been found in neurodegenerative diseases and fingolimod, a structural analogue of sphingosine, has been approved for the treatment of multiple sclerosis. This review, after a brief description of the role of sphingolipids and 1,25(OH)2 D3 , will focus on the potential crosstalk between sphingolipids and 1,25(OH)2 D3 in neural cells.

Investigation into experimental toxicological properties of plant protection products having a potential link to Parkinson's disease and childhood leukaemia

In 2013, EFSA published a literature review on epidemiological studies linking exposure to pesticides and human health outcome. As a follow up, the EFSA Panel on Plant Protection Products and their residues (PPR Panel) was requested to investigate the plausible involvement of pesticide exposure as a risk factor for Parkinson's disease (PD) and childhood leukaemia (CHL). A systematic literature review on PD and CHL and mode of actions for pesticides was published by EFSA in 2016 and used as background documentation. The Panel used the Adverse Outcome Pathway (AOP) conceptual framework to define the biological plausibility in relation to epidemiological studies by means of identification of specific symptoms of the diseases as AO. The AOP combines multiple information and provides knowledge of biological pathways, highlights species differences and similarities, identifies research needs and supports regulatory decisions. In this context, the AOP approach could help in organising the available experimental knowledge to assess biological plausibility by describing the link between a molecular initiating event (MIE) and the AO through a series of biologically plausible and essential key events (KEs). As the AOP is chemically agnostic, tool chemical compounds were selected to empirically support the response and temporal concordance of the key event relationships (KERs). Three qualitative and one putative AOP were developed by the Panel using the results obtained. The Panel supports the use of the AOP framework to scientifically and transparently explore the biological plausibility of the association between pesticide exposure and human health outcomes, identify data gaps, define a tailored testing strategy and suggests an AOP's informed Integrated Approach for Testing and Assessment (IATA).

Astrocytic Orosomucoid-2 Modulates Microglial Activation and Neuroinflammation

Orosomucoid (ORM) is an acute-phase protein that belongs to the immunocalin subfamily, a group of small-molecule-binding proteins with immunomodulatory functions. Little is known about the role of ORM proteins in the CNS. The aim of the present study was to investigate the brain expression of ORM and its role in neuroinflammation. Expression of Orm2, but not Orm1 or Orm3, was highly induced in the mouse brain after systemic injection of lipopolysaccharide (LPS). Plasma levels of ORM2 were also significantly higher in patients with cognitive impairment than in normal subjects. RT-PCR, Western blot, and immunofluorescence analyses revealed that astrocytes are the major cellular sources of ORM2 in the inflamed mouse brain. Recombinant ORM2 protein treatment decreased microglial production of proinflammatory mediators and reduced microglia-mediated neurotoxicity in vitro LPS-induced microglial activation, proinflammatory cytokines in hippocampus, and neuroinflammation-associated cognitive deficits also decreased as a result of intracerebroventricular injection of recombinant ORM2 protein in vivo Moreover, lentiviral shRNA-mediated Orm2 knockdown enhanced LPS-induced proinflammatory cytokine gene expression and microglial activation in the hippocampus. Mechanistically, ORM2 inhibited C-C chemokine ligand 4 (CCL4)-induced microglial migration and activation by blocking the interaction of CCL4 with C-C chemokine receptor type 5. Together, the results from our cultured glial cells, mouse neuroinflammation model, and patient studies suggest that ORM2 is a novel mediator of astrocyte-microglial interaction. We also report that ORM2 exerts anti-inflammatory effects by modulating microglial activation and migration during brain inflammation. ORM2 can be exploited therapeutically for the treatment of neuroinflammatory diseases.SIGNIFICANCE STATEMENT Neural cell interactions are important for brain physiology and pathology. Particularly, the interaction between non-neuronal cells plays a central role in regulating brain inflammation, which is closely linked to many brain disorders. Here, we newly identified orosomucoid-2 (ORM2) as an endogenous protein that mediates such non-neuronal glial cell interactions. Based on the critical role of astrocyte-derived ORM2 in modulating microglia-mediated neuroinflammation, ORM2 can be exploited for the diagnosis, prevention, or treatment of devastating brain disorders that have a strong neuroinflammatory component, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis.

Glia-neuron interactions in neurological diseases: Testing non-cell autonomy in a dish

For the past century, research on neurological disorders has largely focused on the most prominently affected cell types - the neurons. However, with increasing knowledge of the diverse physiological functions of glial cells, their impact on these diseases has become more evident. Thus, many conditions appear to have more complex origins than initially thought. Since neurological pathologies are often sporadic with unknown etiology, animal models are difficult to create and might only reflect a small portion of patients in which a mutation in a gene has been identified. Therefore, reliable in vitro systems to studying these disorders are urgently needed. They might be a pre-requisite for improving our understanding of the disease mechanisms as well as for the development of potential new therapies. In this review, we will briefly summarize the function of different glial cell types in the healthy central nervous system (CNS) and outline their implication in the development or progression of neurological conditions. We will then describe different types of culture systems to model non-cell autonomous interactions in vitro and evaluate advantages and disadvantages. This article is part of a Special Issue entitled SI: Exploiting human neurons.

Sinomenine activates astrocytic dopamine D2 receptors and alleviates neuroinflammatory injury via the CRYAB/STAT3 pathway after ischemic stroke in mice

Background

Astrocyte-mediated neuroinflammation plays a critical role in ischemic stroke-induced secondary cerebral injury. Previous studies have suggested that the dopamine D2 receptor (DRD2) acts as a key target in regulating the neuroinflammatory response. However, the underlying molecular mechanisms are still unknown, and effective DRD2 agonists are lacking. In the present study, we examined the anti-inflammatory and neuroprotective effects of sinomenine (Sino), a monomeric compound with potential immunoregulatory properties in nervous system.

Methods

TTC staining, apoptosis assay, evaluation of brain edema, and neurological assessment were performed in the middle cerebral artery occlusion (MCAO) mouse model. Primary astrocytes exposed to oxygen glucose deprivation (OGD) were used in the in vitro experiments. Quantitative PCR was applied to assess the levels of inflammatory cytokines. Multi-labeling immunofluorescence, Western blot, co-immunoprecipitation, and electrophoretic mobility shift assay (EMSA) were also used to investigate the molecular mechanisms underlying the Sino-mediated anti-inflammatory effects in vivo and in vitro.

Results

Sino remarkably attenuated the cerebral infarction and neuronal apoptosis, reduced the levels of inflammatory cytokines, and alleviated neurological deficiency in MCAO mice. Sino significantly inhibited astrocytic activation and STAT3 phosphorylation as well as increased DRD2 and αB-crystallin (CRYAB) expression after MCAO. In vitro, Sino blocked OGD-induced activation of STAT3 and generation of pro-inflammatory cytokines in primary astrocytes, and these effects were significantly abolished by either DRD2 or CRYAB knockdown. Additionally, Sino induced up-regulation and nuclear translocation of CRYAB in astrocytes and enhanced the interaction between CRYAB and STAT3, which further inhibited the activation and DNA-binding activity of STAT3.

Conclusions

Our study demonstrates that Sino activates astrocytic DRD2 and thereby suppresses neuroinflammation via the CRYAB/STAT3 pathway, which sheds some light on a promising therapeutic strategy for ischemic stroke.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0739-8) contains supplementary material, which is available to authorized users.

Precision Medicine in Multiple Sclerosis: Future of PET Imaging of Inflammation and Reactive Astrocytes

Non-invasive molecular imaging techniques can enhance diagnosis to achieve successful treatment, as well as reveal underlying pathogenic mechanisms in disorders such as multiple sclerosis (MS). The cooperation of advanced multimodal imaging techniques and increased knowledge of the MS disease mechanism allows both monitoring of neuronal network and therapeutic outcome as well as the tools to discover novel therapeutic targets. Diverse imaging modalities provide reliable diagnostic and prognostic platforms to better achieve precision medicine. Traditionally, magnetic resonance imaging (MRI) has been considered the golden standard in MS research and diagnosis. However, positron emission tomography (PET) imaging can provide functional information of molecular biology in detail even prior to anatomic changes, allowing close follow up of disease progression and treatment response. The recent findings support three major neuroinflammation components in MS: astrogliosis, cytokine elevation, and significant changes in specific proteins, which offer a great variety of specific targets for imaging purposes. Regardless of the fact that imaging of astrocyte function is still a young field and in need for development of suitable imaging ligands, recent studies have shown that inflammation and astrocyte activation are related to progression of MS. MS is a complex disease, which requires understanding of disease mechanisms for successful treatment. PET is a precise non-invasive imaging method for biochemical functions and has potential to enhance early and accurate diagnosis for precision therapy of MS. In this review we focus on modulation of different receptor systems and inflammatory aspect of MS, especially on activation of glial cells, and summarize the recent findings of PET imaging in MS and present the most potent targets for new biomarkers with the main focus on experimental MS research.

A distinct brain pathway links viral RNA exposure to sickness behavior

Sickness behaviors and metabolic responses to invading pathogens are common to nearly all types of infection. These responses evolved to provide short-term benefit to the host to ward off infection, but impact on quality of life, and when prolonged lead to neurodegeneration, depression, and cachexia. Among the major infectious agents, viruses most frequently enter the brain, resulting in profound neuroinflammation. We sought to define the unique features of the inflammatory response in the brain to these infections. We demonstrate that the molecular pathway defining the central response to dsRNA is distinct from that found in the periphery. The behavioral and physical response to the dsRNA mimetic poly I:C is dependent on signaling via MyD88 when it is delivered centrally, whereas this response is mediated via the TRIF pathway when delivered peripherally. We also define the likely cellular candidates for this MyD88-dependent step. These findings suggest that symptom management is possible without ameliorating protective antiviral immune responses.

Lipopolysaccharide-Induced Apoptosis of Astrocytes: Therapeutic Intervention by Minocycline

Astrocytes are most abundant glial cell type in the brain and play a main defensive role in central nervous system against glutamate-induced toxicity by virtue of numerous transporters residing in their membranes and an astrocyte-specific enzyme glutamine synthetase (GS). In view of that, a dysregulation in the astrocytic activity following an insult may result in glutamate-mediated toxicity accompanied with astrocyte and microglial activation. The present study suggests that the lipopolysaccharide (LPS)-induced inflammation results in significant astrocytic apoptosis compared to other cell types in hippocampus and minocycline could not efficiently restrict the glutamate-mediated toxicity and apoptosis of astrocytes. Upon LPS exposure 76 % astrocytes undergo degeneration followed by 44 % oligodendrocytes, 26 % neurons and 10 % microglia. The pronounced astrocytic apoptosis resulted from the LPS-induced glutamate excitotoxicity leading to their hyperactivation as evident from their hypertrophied morphology, glutamate transporter 1 upregulation and downregulation of GS. Therapeutic minocycline treatment to LPS-infused rats efficiently restricted the inflammatory response and degeneration of other cell types but could not significantly combat with the apoptosis of astrocytes. Our study demonstrates a novel finding on cellular degeneration in the hippocampus revealing more of astrocytic death and suggests a more careful consideration on the protective efficacy of minocycline.

Restraining reactive oxygen species in Listeria monocytogenes promotes the apoptosis of glial cells

OBJECTIVES

Listeria monocytogenes is a facultative anaerobic foodborne pathogen that can traverse the blood-brain barrier and cause brain infection. L. monocytogenes infection induces host cell apoptosis in several cell types. In this study, we investigated the apoptosis of human glioma cell line U251 invaded by L. monocytogenes and evaluated the function of bacterial reactive oxygen species (ROS) during infection.

METHODS

Bacterial ROS level was reduced by carrying out treatment with N-acetyl cysteine (NAC) and diphenyleneiodonium chloride (DPI). After infection, the apoptosis of U251 cells was examined by flow cytometry assay and propidium iodide staining.

RESULTS

DPI and NAC efficiently decreased ROS level in L. monocytogenes without affecting bacterial growth. Moreover, the apoptosis of glial cells was enhanced upon invasion of DPI- and NAC-pretreated L. monocytogenes.

DISCUSSION

Results indicate that the apoptosis of glial cells can be induced by L. monocytogenes, and that the inhibition of bacterial ROS increases the apoptosis of host cells.

Anti-SPAG16 antibodies in primary progressive multiple sclerosis are associated with an elevated progression index

BACKGROUND AND PURPOSE

Sperm-associated antigen 16 (SPAG16), a sperm protein which is upregulated in reactive astrocytes in multiple sclerosis (MS) lesions, has recently been identified as a novel autoantibody target in MS. The aim of this study was to investigate whether anti-SPAG16 antibody levels differ between MS subtypes (relapsing-remitting, RR; primary or secondary progressive, PP, SP) and whether antibody positivity is associated with clinical characteristics.

METHODS

Plasma anti-SPAG16 antibody levels were determined by recombinant protein enzyme-linked immunosorbent assay (ELISA) in 374 MS patients (274 RRMS, 39 SPMS and 61 PPMS) and 106 healthy controls.

RESULTS

Significantly elevated anti-SPAG16 antibodies were found in 22% of MS patients with 93% specificity. Anti-SPAG16 seropositivity was associated with an increased Expanded Disability Status Scale (EDSS) in overall MS. A higher proportion of PPMS patients showed anti-SPAG16 antibody reactivity (34%) compared to RRMS (19%) and SPMS (26%), and presented with higher anti-SPAG16 antibody levels. Seropositive PPMS patients had a significantly increased progression index compared to seronegative patients.

CONCLUSIONS

Anti-SPAG16 antibodies are associated with an increased EDSS in overall MS, indicating that they are linked to a worse MS disease outcome. Moreover, the presence of anti-SPAG16 antibodies may be a biomarker for a more severe disease in PPMS patients, as indicated by an increased progression index.

A New Outlook on Mental Illnesses: Glial Involvement Beyond the Glue

Mental illnesses have long been perceived as the exclusive consequence of abnormalities in neuronal functioning. Until recently, the role of glial cells in the pathophysiology of mental diseases has largely been overlooked. However recently, multiple lines of evidence suggest more diverse and significant functions of glia with behavior-altering effects. The newly ascribed roles of astrocytes, oligodendrocytes and microglia have led to their examination in brain pathology and mental illnesses. Indeed, abnormalities in glial function, structure and density have been observed in postmortem brain studies of subjects diagnosed with mental illnesses. In this review, we discuss the newly identified functions of glia and highlight the findings of glial abnormalities in psychiatric disorders. We discuss these preclinical and clinical findings implicating the involvement of glial cells in mental illnesses with the perspective that these cells may represent a new target for treatment.