IFN-γ-induced increase in the mobility of MHC class II compartments in astrocytes depends on intermediate filaments

NLRP3 inflammasome mediates astroglial dysregulation of innate and adaptive immune responses in schizophrenia

Mounting evidence indicates the involvement of neuroinflammation in the development of schizophrenia (SCZ), but the potential role of astroglia in this phenomenon remains poorly understood. We assessed the molecular and functional consequences of inflammasome activation using induced pluripotent stem cell (iPSC)-derived astrocytes generated from SCZ patients and healthy controls (CTRL). Screening protein levels in astrocytes at baseline identified lower expression of the NLRP3-ASC complex in SCZ, but increased Caspase-1 activity upon specific NLRP3 stimulation compared to CTRL. Using transcriptional profiling, we found corresponding downregulations of NLRP3 and ASC/PYCARD in both iPSC-derived astrocytes, and in a large (n = 429) brain postmortem case-control sample. Functional analyses following NLRP3 activation revealed an inflammatory phenotype characterized by elevated production of IL-1β/IL-18 and skewed priming of helper T lymphocytes (Th1/Th17) by SCZ astrocytes. This phenotype was rescued by specific inhibition of NLRP3 activation, demonstrating its dependence on the NLRP3 inflammasome. Taken together, SCZ iPSC-astrocytes display unique, NLRP3-dependent inflammatory characteristics that are manifested via various cellular functions, as well as via dysregulated innate and adaptive immune responses.

The Type III Intermediate Filament Protein Peripherin Regulates Lysosomal Degradation Activity and Autophagy

Peripherin belongs to heterogeneous class III of intermediate filaments, and it is the only intermediate filament protein selectively expressed in the neurons of the peripheral nervous system. It has been previously discovered that peripherin interacts with proteins important for the endo-lysosomal system and for the transport to late endosomes and lysosomes, such as RAB7A and AP-3, although little is known about its role in the endocytic pathway. Here, we show that peripherin silencing affects lysosomal abundance but also positioning, causing the redistribution of lysosomes from the perinuclear area to the cell periphery. Moreover, peripherin silencing affects lysosomal activity, inhibiting EGFR degradation and the degradation of a fluorogenic substrate for proteases. Furthermore, we demonstrate that peripherin silencing affects lysosomal biogenesis by reducing the TFEB and TFE3 contents. Finally, in peripherin-depleted cells, the autophagic flux is strongly inhibited. Therefore, these data indicate that peripherin has an important role in regulating lysosomal biogenesis, and positioning and functions of lysosomes, affecting both the endocytic and autophagic pathways. Considering that peripherin is the most abundant intermediate filament protein of peripheral neurons, its dysregulation, affecting its functions, could be involved in the onset of several neurodegenerative diseases of the peripheral nervous system characterized by alterations in the endocytic and/or autophagic pathways.

HLA-transgenic mouse models to study autoimmune central nervous system diseases

It is known that certain human leukocyte antigen (HLA) genes are associated with autoimmune central nervous system (CNS) diseases, such as multiple sclerosis (MS), but their exact role in disease susceptibility and etiopathogenesis remains unclear. The best studied HLA-associated autoimmune CNS disease is MS, and thus will be the primary focus of this review. Other HLA-associated autoimmune CNS diseases, such as autoimmune encephalitis and neuromyelitis optica will be discussed. The lack of animal models to accurately capture the complex human autoimmune response remains a major challenge. HLA transgenic (tg) mice provide researchers with powerful tools to investigate the underlying mechanisms promoting susceptibility and progression of HLA-associated autoimmune CNS diseases, as well as for elucidating the myelin epitopes potentially targeted by T cells in autoimmune disease patients. We will discuss the potential role(s) of autoimmune disease-associated HLA alleles in autoimmune CNS diseases and highlight information provided by studies using HLA tg mice to investigate the underlying pathological mechanisms and opportunities to use these models for development of novel therapies.

Neuroprotective efficacy of the glucocorticoid receptor modulator PT150 in the rotenone mouse model of Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder worldwide. Current treatments for PD largely center around dopamine replacement therapies and fail to prevent the progression of pathology, underscoring the need for neuroprotective interventions. Approaches that target neuroinflammation, which occurs prior to dopaminergic neuron (DAn) loss in the substantia nigra (SN), represent a promising therapeutic strategy. The glucocorticoid receptor (GR) has been implicated in the neuropathology of PD and modulates numerous neuroinflammatory signaling pathways in the brain. Therefore, we investigated the neuroprotective effects of the novel GR modulator, PT150, in the rotenone mouse model of PD, postulating that inhibition of glial inflammation would protect DAn and reduce accumulation of neurotoxic misfolded ⍺-synuclein protein. C57Bl/6 mice were exposed to 2.5 mg/kg/day rotenone by intraperitoneal injection for 14 days. Upon completion of rotenone dosing, mice were orally treated at day 15 with 30 mg/kg/day or 100 mg/kg/day PT150 in the 14-day post-lesioning incubation period, during which the majority of DAn loss and α-synuclein (α-syn) accumulation occurs. Our results indicate that treatment with PT150 reduced both loss of DAn and microgliosis in the nigrostriatal pathway. Although morphologic features of astrogliosis were not attenuated, PT150 treatment promoted potentially neuroprotective activity in these cells, including increased phagocytosis of hyperphosphorylated α-syn. Ultimately, PT150 treatment reduced the loss of DAn cell bodies in the SN, but not the striatum, and prohibited intra-neuronal accumulation of α-syn. Together, these data indicate that PT150 effectively reduced SN pathology in the rotenone mouse model of PD.

Neuroprotective Efficacy of the Glucocorticoid Receptor Modulator PT150 in the Rotenone Mouse Model of Parkinson's Disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder worldwide. Current treatments for PD largely center around dopamine replacement therapies and fail to prevent the progression of pathology, underscoring the need for neuroprotective interventions. Approaches that target neuroinflammation, which occurs prior to dopaminergic neuron (DAn) loss in the substantia nigra (SN), represent a promising therapeutic strategy. The glucocorticoid receptor (GR) has been implicated in the neuropathology of PD and modulates numerous neuroinflammatory signaling pathways in the brain. Therefore, we investigated the neuroprotective effects of the novel GR modulator, PT150, in the rotenone mouse model of PD, postulating that inhibition of glial inflammation would protect DAn and reduce accumulation of neurotoxic misfolded ⍺-synuclein protein. C57Bl/6 mice were exposed to 2.5 mg/kg/day rotenone by intraperitoneal injection for 14 days, immediately followed by oral treatment with 30 mg/kg/day or 100 mg/kg/day PT150 in the 14-day post-lesioning incubation period, during which the majority of DAn loss and α-synuclein (α-syn) accumulation occurs. Our results indicate that treatment with PT150 reduced both loss of DAn and microgliosis in the nigrostriatal pathway. Although morphologic features of astrogliosis were not attenuated, PT150 treatment promoted potentially neuroprotective activity in these cells, including increased phagocytosis of hyperphosphorylated α-syn. Ultimately, PT150 treatment reduced the loss of DAn cell bodies in the SN, but not the striatum, and prohibited intra-neuronal accumulation of α-syn. Together, these data indicate that PT150 effectively reduced SN pathology in the rotenone mouse model of PD.

Astrocyte Reactivity and Neurodegeneration in the Female Rat Brain Following Alcohol Dependence

Recent evidence suggests that alcohol use disorder (AUD) may manifest itself differently in women compared to men. Women experience AUDs on an accelerated timeline and may have certain regional vulnerabilities. In male rats, neuronal cell death and astrocyte reactivity are noted following induction of alcohol dependence in an animal model of an AUD. However, the regional and temporal patterns of neurodegeneration and astrocyte reactivity have yet to be fully examined in females using this model. Therefore, adult female rats were exposed to a 4-day binge model of alcohol dependence followed by different periods of abstinence. Histological markers for FluoroJade B, a label of degenerating neurons, and vimentin, a marker for reactive astrocytes, were utilized. The expression of these markers in cortical and limbic regions was quantified immediately after their last dose (e.g., T0), or 2, 7, and 14 days later. Significant neuronal cell death was noted in the entorhinal cortex and the hippocampus, similar to previous reports in males, but also in several cortical regions not previously observed. Vimentin immunoreactivity was noted in the same regions as previously reported, in addition to three novel regions. Vimentin immunoreactivity also occurred at earlier and later time points in some cortical and hippocampal regions. These data suggest that both neuronal cell death and astrocyte reactivity could be more widespread in females compared to males. Therefore, this study provides a framework for specific regions and time points which should be examined in future studies of alcohol-induced damage that include female rats.

HIV Infection: Shaping the Complex, Dynamic, and Interconnected Network of the Cytoskeleton

HIV-1 has evolved a plethora of strategies to overcome the cytoskeletal barrier (i.e., actin and intermediate filaments (AFs and IFs) and microtubules (MTs)) to achieve the viral cycle. HIV-1 modifies cytoskeletal organization and dynamics by acting on associated adaptors and molecular motors to productively fuse, enter, and infect cells and then traffic to the cell surface, where virions assemble and are released to spread infection. The HIV-1 envelope (Env) initiates the cycle by binding to and signaling through its main cell surface receptors (CD4/CCR5/CXCR4) to shape the cytoskeleton for fusion pore formation, which permits viral core entry. Then, the HIV-1 capsid is transported to the nucleus associated with cytoskeleton tracks under the control of specific adaptors/molecular motors, as well as HIV-1 accessory proteins. Furthermore, HIV-1 drives the late stages of the viral cycle by regulating cytoskeleton dynamics to assure viral Pr55Gag expression and transport to the cell surface, where it assembles and buds to mature infectious virions. In this review, we therefore analyze how HIV-1 generates a cell-permissive state to infection by regulating the cytoskeleton and associated factors. Likewise, we discuss the relevance of this knowledge to understand HIV-1 infection and pathogenesis in patients and to develop therapeutic strategies to battle HIV-1.

Biological agents and the aging brain: glial inflammation and neurotoxic signaling

Neuroinflammation is a universal characteristic of brain aging and neurological disorders, irrespective of the disease state. Glial inflammation mediates this signaling, through astrocyte and microglial polarization from neuroprotective to neurotoxic phenotypes. Glial reactivity results in the loss of homeostasis, as these cells no longer provide support to neurons, in addition to the production of chronically toxic pro-inflammatory mediators. These glial changes initiate an inflammatory brain state that injures the central nervous system (CNS) over time. As the brain ages, glia are altered, including increased glial cell numbers, morphological changes, and either a pre-disposition or inability to become reactive. These alterations induce age-related neuropathologies, ultimately leading to neuronal degradation and irreversible damage associated with disorders of the aged brain, including Alzheimer's Disease (AD) and other related diseases. While the complex interactions of these glial cells and the brain are well studied, the role additional stressors, such as infectious agents, play on age-related neuropathology has not been fully elucidated. Both biological agents in the periphery, such as bacterial infections, or in the CNS, including viral infections like SARS-CoV-2, push glia into neuroinflammatory phenotypes that can exacerbate pathology within the aging brain. These biological agents release pattern associated molecular patterns (PAMPs) that bind to pattern recognition receptors (PRRs) on glial cells, beginning an inflammatory cascade. In this review, we will summarize the evidence that biological agents induce reactive glia, which worsens age-related neuropathology.

Epigenetic orchestration of host immune defences by Mycobacterium tuberculosis

Being among the top 10 causes of adult deaths, tuberculosis (TB) disease is considered a major global public health concern to address. The human tuberculosis pathogen, Mycobacterium tuberculosis (Mtb), is an extremely competent and well-versed pathogen that promotes pathogenesis by evading the host immune systems through numerous tactics. Investigations revealed that Mtb could evade the host defense mechanisms by reconfiguring the host gene transcription and causing epigenetic changes. Although results indicate the link between epigenetics and disease manifestation in other bacterial infections, little is known regarding the kinetics of the epigenetic alterations in mycobacterial infection. This literature review discusses the studies in Mtb-induced epigenetic alterations inside the host and its contribution in the host immune evasion strategies. It also discusses how the Mtb-induced alterations could be used as 'epibiomarkers' to diagnose TB. Additionally, this review also discusses therapeutic interventions to be enhanced through remodification by 'epidrugs'.

Are cytoskeleton changes observed in astrocytes functionally linked to aging?

Astrocytes are active participants in the performance of the Central Nervous System (CNS) in both health and disease. During aging, astrocytes are susceptible to reactive astrogliosis, a molecular state characterized by functional changes in response to pathological situations, and cellular senescence, characterized by loss of cell division, apoptosis resistance, and gain of proinflammatory functions. This results in two different states of astrocytes, which can produce proinflammatory phenotypes with harmful consequences in chronic conditions. Reactive astrocytes and senescent astrocytes share morpho-functional features that are dependent on the organization of the cytoskeleton. However, such changes in the cytoskeleton have yet to receive the necessary attention to explain their role in the alterations of astrocytes that are associated with aging and pathologies. In this review, we summarize all the available findings that connect changes in the cytoskeleton of the astrocytes with aging. In addition, we discuss future avenues that we believe will guide such a novel topic.

Immune Functions of Astrocytes in Viral Neuroinfections

Neuroinfections of the central nervous system (CNS) can be triggered by various pathogens. Viruses are the most widespread and have the potential to induce long-term neurologic symptoms with potentially lethal outcomes. In addition to directly affecting their host cells and inducing immediate changes in a plethora of cellular processes, viral infections of the CNS also trigger an intense immune response. Regulation of the innate immune response in the CNS depends not only on microglia, which are fundamental immune cells of the CNS, but also on astrocytes. These cells align blood vessels and ventricle cavities, and consequently, they are one of the first cell types to become infected after the virus breaches the CNS. Moreover, astrocytes are increasingly recognized as a potential viral reservoir in the CNS; therefore, the immune response initiated by the presence of intracellular virus particles may have a profound effect on cellular and tissue physiology and morphology. These changes should be addressed in terms of persisting infections because they may contribute to recurring neurologic sequelae. To date, infections of astrocytes with different viruses originating from genetically distinct families, including Flaviviridae, Coronaviridae, Retroviridae, Togaviridae, Paramyxoviridae, Picomaviridae, Rhabdoviridae, and Herpesviridae, have been confirmed. Astrocytes express a plethora of receptors that detect viral particles and trigger signaling cascades, leading to an innate immune response. In this review, we summarize the current knowledge on virus receptors that initiate the release of inflammatory cytokines from astrocytes and depict the involvement of astrocytes in immune functions of the CNS.

Advantages of Rho-associated kinases and their inhibitor fasudil for the treatment of neurodegenerative diseases

Ras homolog (Rho)-associated kinases (ROCKs) belong to the serine-threonine kinase family, which plays a pivotal role in regulating the damage, survival, axon guidance, and regeneration of neurons. ROCKs are also involved in the biological effects of immune cells and glial cells, as well as the development of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Previous studies by us and others confirmed that ROCKs inhibitors attenuated the symptoms and progression of experimental models of the abovementioned neurodegenerative diseases by inhibiting neuroinflammation, regulating immune imbalance, repairing the blood-brain barrier, and promoting nerve repair and myelin regeneration. Fasudil, the first ROCKs inhibitor to be used clinically, has a good therapeutic effect on neurodegenerative diseases. Fasudil increases the activity of neural stem cells and mesenchymal stem cells, thus optimizing cell therapy. This review will systematically describe, for the first time, the effects of abnormal activation of ROCKs on T cells, B cells, microglia, astrocytes, oligodendrocytes, and pericytes in neurodegenerative diseases of the central nervous system, summarize the therapeutic potential of fasudil in several experimental models of neurodegenerative diseases, and clarify the possible cellular and molecular mechanisms of ROCKs inhibition. This review also proposes that fasudil is a novel potential treatment, especially in combination with cell-based therapy. Findings from this review add support for further investigation of ROCKs and its inhibitor fasudil for the treatment of neurodegenerative diseases.

Independent actions by HIV-1 Tat and morphine to increase recruitment of monocyte-derived macrophages into the brain in a region-specific manner

Despite advances in the treatment of human immunodeficiency virus (HIV), approximately one-half of people infected with HIV (PWH) experience neurocognitive impairment. Opioid use disorder (OUD) can exacerbate the cognitive and pathological changes seen in PWH. HIV increases inflammation and immune cell trafficking into the brain; however, less is known about how opioid use disorder affects the recruitment of immune cells. Accordingly, we examined the temporal consequences of HIV-1 Tat and/or morphine on the recruitment of endocytic cells (predominantly perivascular macrophages and microglia) in the dorsal striatum and hippocampus by infusing multi-colored, fluorescently labeled dextrans before and after exposure. To address this question, transgenic mice that conditionally expressed HIV-1 Tat (Tat+), or their control counterparts (Tat-), received three sequential intracerebroventricular (i.c.v.) infusions of Cascade Blue-, Alexa Fluor 488-, and Alexa Fluor 594-labeled dextrans, respectively infused 1 day before, 1-day after, or 13-days after morphine and/or Tat exposure. At the end of the study, the number of cells labeled with each fluorescent dextran were counted. The data demonstrated a significantly higher influx of newly-labeled cells into the perivascular space than into the parenchyma. In the striatum, Tat or morphine exposure increased the number of endocytic cells in the perivascular space, while only morphine increased the recruitment of endocytic cells into the parenchyma. In the hippocampus, morphine (but not Tat) increased the influx of dextran-labeled cells into the perivascular space, but there were too few labeled cells within the hippocampal parenchyma to analyze. Collectively, these data suggest that HIV-1 Tat and morphine act independently to increase the recruitment of endocytic cells into the brain in a region-specific manner.

Distinct and Dynamic Transcriptome Adaptations of iPSC-Generated Astrocytes after Cytokine Stimulation

Astrocytes (ACs) do not only play a role in normal neurogenesis and brain homeostasis, but also in inflammatory and neurodevelopmental disorders. We studied here the different patterns of inflammatory activation triggered by cytokines in human induced pluripotent stem cell (iPSC)-derived ACs. An optimized differentiation protocol provided non-inflamed ACs. These cells reacted to TNFα with a rapid translocation of NFκB, while AC precursors showed little response. Transcriptome changes were quantified at seven time points (2–72 h) after stimulation with TNFα, IFNγ or TNFα plus IFNγ. TNFα triggered a strong response within 2 h. It peaked from 12–24 h and reverted towards the ground state after 72 h. Activation by IFNγ was also rapid, but the response pattern differed from that of TNFα. For instance, several chemokines up-regulated by TNFα were not affected by IFNγ. Instead, MHC-II-related antigen presentation was drastically enhanced. The combination of the two cytokines led to a stronger and more persistent response. For instance, TRIB3 up-regulation by the combination of TNFα plus IFNγ may have slowed NFκB inactivation. Additionally, highly synergistic regulation was observed for inflammation modifiers, such as CASP4, and for STAT1-controlled genes. The combination of the cytokines also increased oxidative stress markers (e.g., CHAC1), led to phenotypic changes in ACs and triggered markers related to cell death. In summary, these data demonstrate that there is a large bandwidth of pro-inflammatory AC states, and that single markers are not suitable to describe AC activation or their modulation in disease, development and therapy.

Neuroinflammation and galectins: a key relationship in neurodegenerative diseases

Neurodegeneration is a pathological condition that is associated with the loss of neuronal function and structure. In neurodegenerative diseases, mounting evidence indicates that neuroinflammation is a common factor that contributes to neuronal damage and neurodegeneration. Neuroinflammation is characterized by the activation of microglia, the neuroimmune cells of the central nervous system (CNS), which have been implicated as active contributors to neuronal damage. Glycan structure modification is defining the outcome of neuroinflammation and neuronal regeneration; moreover, the expression of galectins, a group of lectins that specifically recognize β-galactosides, has been proposed as a key factor in neuronal regeneration and modulation of the inflammatory response. Of the different galectins identified, galectin-1 stimulates the secretion of neurotrophic factors in astrocytes and promotes neuronal regeneration, whereas galectin-3 induces the proliferation of microglial cells and modulates cell apoptosis. Galectin-8 emerged as a neuroprotective factor, which, in addition to its immunosuppressive function, could generate a neuroprotective environment in the brain. This review describes the role of galectins in the activation and modulation of astrocytes and microglia and their anti- and proinflammatory functions within the context of neuroinflammation. Furthermore, it discusses the potential use of galectins as a therapeutic target for the inflammatory response and remodeling in damaged tissues in the central nervous system.

Roles of vimentin in health and disease

More than 27 yr ago, the vimentin knockout (Vim-/- ) mouse was reported to develop and reproduce without an obvious phenotype, implying that this major cytoskeletal protein was nonessential. Subsequently, comprehensive and careful analyses have revealed numerous phenotypes in Vim-/- mice and their organs, tissues, and cells, frequently reflecting altered responses in the recovery of tissues following various insults or injuries. These findings have been supported by cell-based experiments demonstrating that vimentin intermediate filaments (IFs) play a critical role in regulating cell mechanics and are required to coordinate mechanosensing, transduction, signaling pathways, motility, and inflammatory responses. This review highlights the essential functions of vimentin IFs revealed from studies of Vim-/- mice and cells derived from them.

Differential Cytokine-Induced Responses of Polarized Microglia

The role of select pro- and anti-inflammatory mediators in driving microglial cell polarization into classically (M1), or alternatively, (M2) activated states, as well as the subsequent differential responses of these induced phenotypes, was examined. Expression of PD-L1, MHC-II, MHC-I, arginase 1 (Arg-1), and inducible nitric oxide synthase (iNOS) was assessed using multi-color flow cytometry. We observed that both pro- and anti-inflammatory mediators induced PD-L1 expression on non-polarized microglia. Moreover, IFN-γ stimulated significant MHC class I and II expression on these cells. Interestingly, we observed that only IL-4 treatment induced Arg-1 expression, indicating M2 polarization. These M2 cells were refractory to subsequent depolarization and maintained their alternatively activated state. Furthermore, PD-L1 expression was significantly induced on these M2-polarized microglia after treatment with pro-inflammatory mediators, but not anti-inflammatory cytokines. In addition, we observed that only LPS induced iNOS expression in microglial cells, indicating M1 polarization. Furthermore, IFN-γ significantly increased the percentage of M1-polarized microglia expressing iNOS. Surprisingly, when these M1-polarized microglia were treated with either IL-6 or other anti-inflammatory cytokines, they returned to their non-polarized state, as demonstrated by significantly reduced expression of iNOS. Taken together, these results demonstrate differential responses of microglial cells to mediators present in dissimilar microenvironments.

Exocytosis in Astrocytes

Until recently, astrocytes were thought to be a part of a simple "brain glue" providing only a supporting role for neurons. However, the discoveries of the last two decades have proven astrocytes to be dynamic partners participating in brain metabolism and actively influencing communication between neurons. The means of astrocyte-neuron communication are diverse, although regulated exocytosis has received the most attention but also caused the most debate. Similar to most of eukaryotic cells, astrocytes have a complex range of vesicular organelles which can undergo exocytosis as well as intricate molecular mechanisms that regulate this process. In this review, we focus on the components needed for regulated exocytosis to occur and summarise the knowledge about experimental evidence showing its presence in astrocytes.

Plectin in the Central Nervous System and a Putative Role in Brain Astrocytes

Plectin, a high-molecular-mass cytolinker, is abundantly expressed in the central nervous system (CNS). Currently, a limited amount of data about plectin in the CNS prevents us from seeing the complete picture of how plectin affects the functioning of the CNS as a whole. Yet, by analogy to its role in other tissues, it is anticipated that, in the CNS, plectin also functions as the key cytoskeleton interlinking molecule. Thus, it is likely involved in signalling processes, thereby affecting numerous fundamental functions in the brain and spinal cord. Versatile direct and indirect interactions of plectin with cytoskeletal filaments and enzymes in the cells of the CNS in normal physiological and in pathologic conditions remain to be fully addressed. Several pathologies of the CNS related to plectin have been discovered in patients with plectinopathies. However, in view of plectin as an integrator of a cohesive mesh of cellular proteins, it is important that the role of plectin is also considered in other CNS pathologies. This review summarizes the current knowledge of plectin in the CNS, focusing on plectin isoforms that have been detected in the CNS, along with its expression profile and distribution alongside diverse cytoskeleton filaments in CNS cell types. Considering that the bidirectional communication between neurons and glial cells, especially astrocytes, is crucial for proper functioning of the CNS, we place particular emphasis on the known roles of plectin in neurons, and we propose possible roles of plectin in astrocytes.

TNF-α and α-synuclein fibrils differently regulate human astrocyte immune reactivity and impair mitochondrial respiration

Here, we examine the cellular changes triggered by tumor necrosis factor alpha (TNF-α) and different alpha-synuclein (αSYN) species in astrocytes derived from induced pluripotent stem cells. Human astrocytes treated with TNF-α display a strong reactive pro-inflammatory phenotype with upregulation of pro-inflammatory gene networks, activation of the nuclear factor κB (NF-κB) pathway, and release of pro-inflammatory cytokines, whereas those treated with high-molecular-weight αSYN fibrils acquire a reactive antigen (cross)-presenting phenotype with upregulation of major histocompatibility complex (MHC) genes and increased human leukocyte antigen (HLA) molecules at the cell surface. Surprisingly, the cell surface location of MHC proteins is abrogated by larger F110 fibrillar polymorphs, despite the upregulation of MHC genes. Interestingly, TNF-α and αSYN fibrils compete to drive the astrocyte immune reactive response. The astrocyte immune responses are accompanied by an impaired mitochondrial respiration, which is exacerbated in Parkinson's disease (PD) astrocytes. Our data provide evidence for astrocytic involvement in PD pathogenesis and reveal their complex immune reactive responses to exogenous stressors.

Methods for Monitoring Endocytosis in Astrocytes

Endocytosis is a vesicle-based mechanism by which eukaryotic cells internalize extracellular material. There are several types of this universal mechanism linked to different types of endocytosed cargo, including pathogens; therefore, several approaches can be applied. Here, we describe techniques that are applicable to study the internalization of flaviviruses; dextrans; transporters, such as, glutamate transporter vGlut1; and peptidergic signaling molecules, including atrial natriuretic peptide into astrocytes, the most heterogeneous neuroglial cells, which play a key homeostatic role in the central nervous system.

Widespread Decrease of Cerebral Vimentin-Immunoreactive Astrocytes in Depressed Suicides

Post-mortem investigations have implicated cerebral astrocytes immunoreactive (-IR) for glial fibrillary acidic protein (GFAP) in the etiopathology of depression and suicide. However, it remains unclear whether astrocytic subpopulations IR for other astrocytic markers are similarly affected. Astrocytes IR to vimentin (VIM) display different regional densities than GFAP-IR astrocytes in the healthy brain, and so may be differently altered in depression and suicide. To investigate this, we compared the densities of GFAP-IR astrocytes and VIM-IR astrocytes in post-mortem brain samples from depressed suicides and matched non-psychiatric controls in three brain regions (dorsomedial prefrontal cortex, dorsal caudate nucleus and mediodorsal thalamus). A quantitative comparison of the fine morphology of VIM-IR astrocytes was also performed in the same regions and subjects. Finally, given the close association between astrocytes and blood vessels, we also assessed densities of CD31-IR blood vessels. Like for GFAP-IR astrocytes, VIM-IR astrocyte densities were found to be globally reduced in depressed suicides relative to controls. By contrast, CD31-IR blood vessel density and VIM-IR astrocyte morphometric features in these regions were similar between groups, except in prefrontal white matter, in which vascularization was increased and astrocytes displayed fewer primary processes. By revealing a widespread reduction of cerebral VIM-IR astrocytes in cases vs. controls, these findings further implicate astrocytic dysfunctions in depression and suicide.

Mobilisation and redistribution of multivesicular bodies to the endfeet of reactive astrocytes in acute endogenous toxic encephalopathies

Endogenous toxicity caused by systemic inflammation as well as by acute liver failure triggers a wide range of dysfunctional disorders in the brain ranging from delirium and acute psychosis to coma. Astrocytes, the main homeostatic cells of the central nervous system (CNS), play a key role in pathophysiology of neurotoxic insults. We examined the cecal ligation and puncture (CLP) and acetaminophen-induced liver failure (AILF) of Wistar rats, and analysed ultrastructure of astrocytes in the brain cortex and subcortical white matter of sensorimotor zone with transmission electron microscopy. Both models showed significant similarities in reactive changes of astroglial endosomal machinery. In survived animals (with relative prevalence in the CLP-model), at 24 h after intervention we found an increase in number of multivesicular bodies (MVBs) in astroglial perikarya and astroglial processes. In particular, the number of MVBs substantially (3 times of control values) increased in the perivascular astroglial endfeet. Increased number of MVBs in astrocytes was associated with the lesser degree of intracellular oedema and with signs of compensated oedematous tissue changes. In deceased animals, up to 24 h after intervention, single MVBs were localised mainly in astroglial perikarya, and their number was not significantly changed compared to control. Activation of astroglial endosomal-exosomal machinery in both models reflects the uniform pattern of reactive changes of astroglia in these two systemic conditions and may represent activation of astroglial defence in sepsis-associated encephalopathy (SAE) and acute hepatic encephalopathy (AHE). Our data highlight the special role of astroglial adaptive activity in the counterbalancing of an impaired brain homeostasis under action of endogenous toxins. Accumulation of MVBs in astrocytic processes indicates the activation of their intercellular and gliovascular interactions through endo- and exocytosis in SAE and AHE.

Exocytosis of large-diameter lysosomes mediates interferon γ-induced relocation of MHC class II molecules toward the surface of astrocytes

Astrocytes are the key homeostatic cells in the central nervous system; initiation of reactive astrogliosis contributes to neuroinflammation. Pro-inflammatory cytokine interferon γ (IFNγ) induces the expression of the major histocompatibility complex class II (MHCII) molecules, involved in antigen presentation in reactive astrocytes. The pathway for MHCII delivery to the astrocyte plasma membrane, where MHCII present antigens, is unknown. Rat astrocytes in culture and in organotypic slices were exposed to IFNγ to induce reactive astrogliosis. Astrocytes were probed with optophysiologic tools to investigate subcellular localization of immunolabeled MHCII, and with electrophysiology to characterize interactions of single vesicles with the plasmalemma. In culture and in organotypic slices, IFNγ augmented the astrocytic expression of MHCII, which prominently co-localized with lysosomal marker LAMP1-EGFP, modestly co-localized with Rab7, and did not co-localize with endosomal markers Rab4A, EEA1, and TPC1. MHCII lysosomal localization was corroborated by treatment with the lysosomolytic agent glycyl-L-phenylalanine-β-naphthylamide, which reduced the number of MHCII-positive vesicles. The surface presence of MHCII was revealed by immunolabeling of live non-permeabilized cells. In IFNγ-treated astrocytes, an increased fraction of large-diameter exocytotic vesicles (lysosome-like vesicles) with prolonged fusion pore dwell time and larger pore conductance was recorded, whereas the rate of endocytosis was decreased. Stimulation with ATP, which triggers cytosolic calcium signaling, increased the frequency of exocytotic events, whereas the frequency of full endocytosis was further reduced. In IFNγ-treated astrocytes, MHCII-linked antigen surface presentation is mediated by increased lysosomal exocytosis, whereas surface retention of antigens is prolonged by concomitant inhibition of endocytosis.

Characterization of Vimentin-Immunoreactive Astrocytes in the Human Brain

Astrocytes are commonly identified by their expression of the intermediate filament protein glial fibrillary acidic protein (GFAP). GFAP-immunoreactive (GFAP-IR) astrocytes exhibit regional heterogeneity in density and morphology in the mouse brain as well as morphological diversity in the human cortex. However, regional variations in astrocyte distribution and morphology remain to be assessed comprehensively. This was the overarching objective of this postmortem study, which mainly exploited the immunolabeling of vimentin (VIM), an intermediate filament protein expressed by astrocytes and endothelial cells which presents the advantage of more extensively labeling cell structures. We compared the densities of vimentin-immunoreactive (VIM-IR) and GFAP-IR astrocytes in various brain regions (prefrontal and primary visual cortex, caudate nucleus, mediodorsal thalamus) from male individuals having died suddenly in the absence of neurological or psychiatric conditions. The morphometric properties of VIM-IR in these brain regions were also assessed. We found that VIM-IR astrocytes generally express the canonical astrocytic markers Aldh1L1 and GFAP but that VIM-IR astrocytes are less abundant than GFAP-IR astrocytes in all human brain regions, particularly in the thalamus, where VIM-IR cells were nearly absent. About 20% of all VIM-IR astrocytes presented a twin cell morphology, a phenomenon rarely observed for GFAP-IR astrocytes. Furthermore VIM-IR astrocytes in the striatum were often seen to extend numerous parallel processes which seemed to give rise to large VIM-IR fiber bundles projecting over long distances. Moreover, morphometric analyses revealed that VIM-IR astrocytes were more complex than their mouse counterparts in functionally homologous brain regions, as has been previously reported for GFAP-IR astrocytes. Lastly, the density of GFAP-IR astrocytes in gray and white matter were inversely correlated with vascular density, but for VIM-IR astrocytes this was only the case in gray matter, suggesting that gliovascular interactions may especially influence the regional heterogeneity of GFAP-IR astrocytes. Taken together, these findings reveal special features displayed uniquely by human VIM-IR astrocytes and illustrate that astrocytes display important region- and marker-specific differences in the healthy human brain.

Endosomal-Lysosomal Processing of Neurodegeneration-Associated Proteins in Astrocytes

Most common neurodegenerative diseases (NDs) are characterized by deposition of protein aggregates that are resulted from misfolding, dysregulated trafficking, and compromised proteolytic degradation. These proteins exert cellular toxicity to a broad range of brain cells and are found in both neurons and glia. Extracellular monomeric and oligomeric ND-associated proteins are taken up by astrocytes, the most abundant glial cell in the brain. Internalization, intracellular trafficking, processing, and disposal of these proteins are executed by the endosomal-lysosomal system of astrocytes. Endosomal-lysosomal organelles thus mediate the cellular impact and metabolic fate of these toxic protein species. Given the indispensable role of astrocytes in brain metabolic homeostasis, the endosomal-lysosomal processing of these proteins plays a fundamental role in altering the trajectory of neurodegeneration. This review aims at summarizing the mounting evidence that has established the essential role of astrocytic endosomal-lysosomal organelles in the processing of amyloid precursor proteins, Apolipoprotein E (ApoE), tau, alpha synuclein, and huntingtin, which are associated with NDs such as Alzheimer’s, Parkinson’s, and Huntington diseases.

The Diversity of Intermediate Filaments in Astrocytes

Despite the remarkable complexity of the individual neuron and of neuronal circuits, it has been clear for quite a while that, in order to understand the functioning of the brain, the contribution of other cell types in the brain have to be accounted for. Among glial cells, astrocytes have multiple roles in orchestrating neuronal functions. Their communication with neurons by exchanging signaling molecules and removing molecules from extracellular space takes place at several levels and is governed by different cellular processes, supported by multiple cellular structures, including the cytoskeleton. Intermediate filaments in astrocytes are emerging as important integrators of cellular processes. Astrocytes express five types of intermediate filaments: glial fibrillary acidic protein (GFAP); vimentin; nestin; synemin; lamins. Variability, interactions with different cellular structures and the particular roles of individual intermediate filaments in astrocytes have been studied extensively in the case of GFAP and vimentin, but far less attention has been given to nestin, synemin and lamins. Similarly, the interplay between different types of cytoskeleton and the interaction between the cytoskeleton and membranous structures, which is mediated by cytolinker proteins, are understudied in astrocytes. The present review summarizes the basic properties of astrocytic intermediate filaments and of other cytoskeletal macromolecules, such as cytolinker proteins, and describes the current knowledge of their roles in normal physiological and pathological conditions.

RACK7 recognizes H3.3G34R mutation to suppress expression of MHC class II complex components and their delivery pathway in pediatric glioblastoma

Histone H3 point mutations have been identified in incurable pediatric brain cancers, but the mechanisms through which these mutations drive tumorigenesis are incompletely understood. Here, we provide evidence that RACK7 (ZMYND8) recognizes the histone H3.3 patient mutation (H3.3G34R) in vitro and in vivo. We show that RACK7 binding to H3.3G34R suppresses transcription of CIITA, which is the master regulator of MHC (major histocompatibility complex) class II molecules and genes involved in vesicular transport of MHC class II molecules to the cell surface, resulting in suppression of MHC class II molecule expression and transport. CRISPR-based knock-in correction of the H3.3G34R mutation in human pediatric glioblastoma (pGBM) cells significantly reduces overall RACK7 chromatin binding and derepresses the same set of genes as does knocking out RACK7 in the H3.3G34R pGBM cells. By demonstrating that H3.3G34R and RACK7 work together, our findings suggest a potential molecular mechanism by which H3.3G34R promotes cancer.

Nestin affects fusion pore dynamics in mouse astrocytes

AIM

Astrocytes play a homeostatic role in the central nervous system and influence numerous aspects of neurophysiology via intracellular trafficking of vesicles. Intermediate filaments (IFs), also known as nanofilaments, regulate a number of cellular processes including organelle trafficking and adult hippocampal neurogenesis. We have recently demonstrated that the IF protein nestin, a marker of neural stem cells and immature and reactive astrocytes, is also expressed in some astrocytes in the unchallenged hippocampus and regulates neurogenesis through Notch signalling from astrocytes to neural stem cells, possibly via altered trafficking of vesicles containing the Notch ligand Jagged-1.

METHODS

We thus investigated whether nestin affects vesicle dynamics in astrocytes by examining single vesicle interactions with the plasmalemma and vesicle trafficking with high-resolution cell-attached membrane capacitance measurements and confocal microscopy. We used cell cultures of astrocytes from nestin-deficient (Nes^-/- ) and wild-type (wt) mice, and fluorescent dextran and Fluo-2 to examine vesicle mobility and intracellular Ca²⁺ concentration respectively.

RESULTS

Nes^-/- astrocytes exhibited altered sizes of vesicles undergoing full fission and transient fusion, altered vesicle fusion pore geometry and kinetics, decreased spontaneous vesicle mobility and altered ATP-evoked mobility. Purinergic stimulation evoked Ca²⁺ signalling that was slightly attenuated in Nes^-/- astrocytes, which exhibited more oscillatory Ca²⁺ responses than wt astrocytes.

CONCLUSION

These results demonstrate at the single vesicle level that nestin regulates vesicle interactions with the plasmalemma and vesicle trafficking, indicating its potential role in astrocyte vesicle-based communication.

Gliocrine System: Astroglia as Secretory Cells of the CNS

Astrocytes are secretory cells, actively participating in cell-to-cell communication in the central nervous system (CNS). They sense signaling molecules in the extracellular space, around the nearby synapses and also those released at much farther locations in the CNS, by their cell surface receptors, get excited to then release their own signaling molecules. This contributes to the brain information processing, based on diffusion within the extracellular space around the synapses and on convection when locales relatively far away from the release sites are involved. These functions resemble secretion from endocrine cells, therefore astrocytes were termed to be a part of the gliocrine system in 2015. An important mechanism, by which astrocytes release signaling molecules is the merger of the vesicle membrane with the plasmalemma, i.e., exocytosis. Signaling molecules stored in astroglial secretory vesicles can be discharged into the extracellular space after the vesicle membrane fuses with the plasma membrane. This leads to a fusion pore formation, a channel that must widen to allow the exit of the Vesiclal cargo. Upon complete vesicle membrane fusion, this process also integrates other proteins, such as receptors, transporters and channels into the plasma membrane, determining astroglial surface signaling landscape. Vesiclal cargo, together with the whole vesicle can also exit astrocytes by the fusion of multivesicular bodies with the plasma membrane (exosomes) or by budding of vesicles (ectosomes) from the plasma membrane into the extracellular space. These astroglia-derived extracellular vesicles can later interact with various target cells. Here, the characteristics of four types of astroglial secretory vesicles: synaptic-like microvesicles, dense-core vesicles, secretory lysosomes, and extracellular vesicles, are discussed. Then machinery for vesicle-based exocytosis, second messenger regulation and the kinetics of exocytotic vesicle content discharge or release of extracellular vesicles are considered. In comparison to rapidly responsive, electrically excitable neurons, the receptor-mediated cytosolic excitability-mediated astroglial exocytotic vesicle-based transmitter release is a relatively slow process.

Nestin Null Mice Show Improved Reversal Place Learning

The intermediate filament protein nestin is expressed by neural stem cells, but also by some astrocytes in the neurogenic niche of the hippocampus in the adult rodent brain. We recently reported that nestin-deficient (Nes^−/−) mice showed increased adult hippocampal neurogenesis, reduced Notch signaling from Nes^−/− astrocytes to the neural stem cells, and impaired long-term memory. Here we assessed learning and memory of Nes^−/− mice in a home cage set up using the IntelliCage system, in which the mice learn in which cage corner a nose poke earns access to drinking water. Nes^−/− and wildtype mice showed comparable place learning assessed as the incorrect corner visit ratio and the incorrect nose poke ratio. However, during reversal place learning, a more challenging task, Nes^−/− mice, compared to wildtype mice, showed improved learning over time demonstrated by the incorrect visit ratio and improved memory extinction over time assessed as nose pokes per visit to the previous drinking corner. In addition, Nes^−/− mice showed increased explorative activity as judged by the increased total numbers of corner visits and nose pokes. We conclude that Nes^−/− mice exhibit improved reversal place learning and memory extinction, a finding which together with the previous results supports the concept of the dual role of hippocampal neurogenesis in cognitive functions.

Study of the immunogenicity of outer membrane protein A (ompA) gene from Acinetobacter baumannii as DNA vaccine candidate in vivo

OBJECTIVES

Acinetobacter baumannii is one the most dangerous opportunistic pathogens in hospitalized infections. This bacterium is resistant to 90% of commercial antibiotics. Therefore, developing new strategies to cure A. baumannii-infections is urgent. The DNA vaccines new approach in which the immunogen can be directly expressed inside the target cells through cloning of immunogen into an expression vector. The outer membrane protein A(OmpA) is one the critical factors in pathogenicity of A. baumannii which has been repeatedly described as a powerful immunogen to trigger the immune responses. As the pure form of the OmpA is insoluble, vaccine delivery is very hard.

MATERIALS AND METHODS

We previously cloned the ompA gene from A. baumannii into the eukaryotic expression vector pBudCE4.1 and observed that the OmpA protein has been considerably expressed in eukaryotic cell model. In current study, the immunogenic potential of pBudCE4.1-ompA has been evaluated in mice model of experimental. The serum levels of IgM, IgG, IL-2, IL-4, IL-12 and INF-γ were measured by enzyme-linked immunosorbent assay (ELISA) after immunization with ompA-vaccine. The protective efficiency of the designed-DNA vaccine was evaluated following intranasal administration of mice with toxic dose of A. baumannii.

RESULTS

Obtained data showed the elevated levels of IgM, IgG, IL-2, IL-4, IL-12 and INF-γ in serum following the vaccine administration and mice who immunized with recombinant vector were survived more than control group.

CONCLUSION

These findings indicate ompA-DNA vaccine is potent to trigger humoral and cellular immunity responses although further experiments are needed.

ZIKV Strains Differentially Affect Survival of Human Fetal Astrocytes versus Neurons and Traffic of ZIKV-Laden Endocytotic Compartments

Malformations of the fetal CNS, known as microcephaly, have been linked to Zika virus (ZIKV) infection. Here, the responses of mammalian and mosquito cell lines, in addition to primary human fetal astrocytes and neurons were studied following infection by ZIKV strains Brazil 2016 (ZIKV-BR), French Polynesia 2013 (ZIKV-FP), and Uganda #976 1947 (ZIKV-UG). Viral production, cell viability, infectivity rate, and mobility of endocytotic ZIKV-laden vesicles were compared. All cell types (SK-N-SH, Vero E6, C6/36, human fetal astrocytes and human fetal neurons) released productive virus. Among primary cells, astrocytes were more susceptible to ZIKV infection than neurons, released more progeny virus and tolerated higher virus loads than neurons. In general, the infection rate of ZIKV-UG strain was the highest. All ZIKV strains elicited differences in trafficking of ZIKV-laden endocytotic vesicles in the majority of cell types, including astrocytes and neurons, except in mosquito cells, where ZIKV infection failed to induce cell death. These results represent a thorough screening of cell viability, infection and production of three ZIKV strains in five different cell types and demonstrate that ZIKV affects vesicle mobility in all but mosquito cells.

Glial Cell Expression of PD-L1

The programmed death (PD)-1/PD-L1 pathway is a well-recognized negative immune checkpoint that results in functional inhibition of T-cells. Microglia, the brain-resident immune cells are vital for pathogen detection and initiation of neuroimmune responses. Moreover, microglial cells and astrocytes govern the activity of brain-infiltrating antiviral T-cells through upregulation of PD-L1 expression. While T-cell suppressive responses within brain are undoubtedly beneficial to the host, preventing cytotoxic damage to this vital organ, establishment of a prolonged anti-inflammatory milieu may simultaneously lead to deficiencies in viral clearance. An immune checkpoint blockade targeting the PD-1: PD-L1 (B7-H1; CD274) axis has revolutionized contemporary treatment for a variety of cancers. However, the therapeutic potential of PD1: PD-L1 blockade therapies targeting viral brain reservoirs remains to be determined. For these reasons, it is key to understand both the detrimental and protective functions of this signaling pathway within the brain. This review highlights how glial cells use PD-L1 expression to modulate T-cell effector function and limit detrimental bystander damage, while still retaining an effective defense of the brain.

Syk and Hrs Regulate TLR3-Mediated Antiviral Response in Murine Astrocytes

Toll-like receptors (TLRs) sense the presence of pathogen-associated molecular patterns. Nevertheless, the mechanisms modulating TLR-triggered innate immune responses are not yet fully understood. Complex regulatory systems exist to appropriately direct immune responses against foreign or self-nucleic acids, and a critical role of hepatocyte growth factor-regulated tyrosine kinase substrate (HRS), endosomal sorting complex required for transportation-0 (ESCRT-0) subunit, has recently been implicated in the endolysosomal transportation of TLR7 and TLR9. We investigated the involvement of Syk, Hrs, and STAM in the regulation of the TLR3 signaling pathway in a murine astrocyte cell line C8-D1A following cell stimulation with a viral dsRNA mimetic. Our data uncover a relationship between TLR3 and ESCRT-0, point out Syk as dsRNA-activated kinase, and suggest the role for Syk in mediating TLR3 signaling in murine astrocytes. We show molecular events that occur shortly after dsRNA stimulation of astrocytes and result in Syk Tyr-342 phosphorylation. Further, TLR3 undergoes proteolytic processing; the resulting TLR3 N-terminal form interacts with Hrs. The knockdown of Syk and Hrs enhances TLR3-mediated antiviral response in the form of IFN-β, IL-6, and CXCL8 secretion. Understanding the role of Syk and Hrs in TLR3 immune responses is of high importance since activation and precise execution of the TLR3 signaling pathway in the brain seem to be particularly significant in mounting an effective antiviral defense. Infection of the brain with herpes simplex type 1 virus may increase the secretion of amyloid-β by neurons and astrocytes and be a causal factor in degenerative diseases such as Alzheimer's disease. Errors in TLR3 signaling, especially related to the precise regulation of the receptor transportation and degradation, need careful observation as they may disclose foundations to identify novel or sustain known therapeutic targets.

Astroglia in Sepsis Associated Encephalopathy

Cellular pathophysiology of sepsis associated encephalopathy (SAE) remains poorly characterised. Brain pathology in SAE, which is manifested by impaired perception, consciousness and cognition, results from multifactorial events, including high levels of systemic cytokines, microbial components and endotoxins, which all damage the brain barriers, instigate neuroinflammation and cause homeostatic failure. Astrocytes, being the principal homeostatic cells of the central nervous system contribute to the brain defence against infection. Forming multifunctional anatomical barriers, astroglial cells maintain brain-systemic interfaces and restrict the damage to the nervous tissue. Astrocytes detect, produce and integrate inflammatory signals between immune cells and cells of brain parenchyma, thus regulating brain immune response. In SAE astrocytes are present in both reactive and astrogliopathic states; balance between these states define evolution of pathology and neurological outcomes. In humans pathophysiology of SAE is complicated by frequent presence of comorbidities, as well as age-related remodelling of the brain tissue with senescence of astroglia; these confounding factors further impact upon SAE progression and neurological deficits.

Fingolimod Suppresses the Proinflammatory Status of Interferon-γ-Activated Cultured Rat Astrocytes

Astroglia, the primary homeostatic cells of the central nervous system, play an important role in neuroinflammation. They act as facultative immunocompetent antigen-presenting cells (APCs), expressing major histocompatibility complex (MHC) class II antigens upon activation with interferon (IFN)-γ and possibly other proinflammatory cytokines that are upregulated in disease states, including multiple sclerosis (MS). We characterized the anti-inflammatory effects of fingolimod (FTY720), an established drug for MS, and its phosphorylated metabolite (FTY720-P) in IFN-γ-activated cultured rat astrocytes. The expression of MHC class II compartments, β₂ adrenergic receptor (ADR-β₂), and nuclear factor kappa-light-chain enhancer of activated B cells subunit p65 (NF-κB p65) was quantified in immunofluorescence images acquired by laser scanning confocal microscopy. In addition, MHC class II-enriched endocytotic vesicles were labeled by fluorescent dextran and their mobility analyzed in astrocytes subjected to different treatments. FTY720 and FTY720-P treatment significantly reduced the number of IFN-γ-induced MHC class II compartments and substantially increased ADR-β₂ expression, which is otherwise small or absent in astrocytes in MS. These effects could be partially attributed to the observed decrease in NF-κB p65 expression, because the NF-κB signaling cascade is activated in inflammatory processes. We also found attenuated trafficking and secretion from dextran-labeled endo-/lysosomes that may hinder efficient delivery of MHC class II molecules to the plasma membrane. Our data suggest that FTY720 and FTY720-P at submicromolar concentrations mediate anti-inflammatory effects on astrocytes by suppressing their action as APCs, which may further downregulate the inflammatory process in the brain, constituting the therapeutic effect of fingolimod in MS.

Hypoxia-induced 26S proteasome dysfunction increases immunogenicity of mesenchymal stem cells

Bone marrow-derived allogeneic (donor derived) mesenchymal stem cells (MSCs) are immunoprivileged and are considered to be prominent candidates for regenerative therapy for numerous degenerative diseases. Even though the outcome of initial allogeneic MSCs based clinical trials was encouraging, the overall enthusiasm, of late, has dimmed down. This is due to failure of long-term survival of transplanted cells in the recipient. In fact, recent analyses of allogeneic MSC-based studies demonstrated that cells after transplantation turned immunogenic and were subsequently rejected by host immune system. The current study reveals a novel mechanism of immune switch in MSCs. We demonstrate that hypoxia, a common denominator of ischemic tissues, induces an immune shift in MSCs from immunoprivileged to immunogenic state. The immunoprivilege of MSCs is preserved by downregulation or the absence of major histocompatibility complex class II (MHC-II) molecules. We found that 26S proteasome-mediated intracellular degradation of MHC-II helps maintain the absence of MHC-II expression on cell surface in normoxic MSCs and preserves their immunoprivilege. The exposure to hypoxia leads to dissociation of 19S and 20S subunits, and inactivation of 26S proteasome. This prevented the degradation of MHC-II and, as a result, the MSCs became immunogenic. Furthermore, we found that hypoxia-induced decrease in the levels of a chaperon protein HSP90α is responsible for inactivation of 26S proteasome. Maintaining HSP90α levels in hypoxic MSCs preserved the immunoprivilege of MSCs. Therefore, hypoxia-induced inactivation of 26S proteasome assembly instigates loss of immunoprivilege of allogeneic mesenchymal stem cells. Maintaining 26S proteasome activity in mesenchymal stem cells preserves their immunoprivilege.

Nestin Regulates Neurogenesis in Mice Through Notch Signaling From Astrocytes to Neural Stem Cells

The intermediate filament (nanofilament) protein nestin is a marker of neural stem cells, but its role in neurogenesis, including adult neurogenesis, remains unclear. Here, we investigated the role of nestin in neurogenesis in adult nestin-deficient (Nes–/–) mice. We found that the proliferation of Nes–/– neural stem cells was not altered, but neurogenesis in the hippocampal dentate gyrus of Nes–/– mice was increased. Surprisingly, the proneurogenic effect of nestin deficiency was mediated by its function in the astrocyte niche. Through its role in Notch signaling from astrocytes to neural stem cells, nestin negatively regulates neuronal differentiation and survival; however, its expression in neural stem cells is not required for normal neurogenesis. In behavioral studies, nestin deficiency in mice did not affect associative learning but was associated with impaired long-term memory.

Astroglia in Alzheimer's Disease

Alzheimer's disease is the most common cause of dementia. Cellular changes in the brains of the patients suffering from Alzheimer's disease occur well in advance of the clinical symptoms. At the cellular level, the most dramatic is a demise of neurones. As astroglial cells carry out homeostatic functions of the brain, it is certain that these cells are at least in part a cause of Alzheimer's disease. Historically, Alois Alzheimer himself has recognised this at the dawn of the disease description. However, the role of astroglia in this disease has been understudied. In this chapter, we summarise the various aspects of glial contribution to this disease and outline the potential of using these cells in prevention (exercise and environmental enrichment) and intervention of this devastating disease.

Cytoplasmic Intermediate Filaments in Cell Biology

Intermediate filaments (IFs) are one of the three major elements of the cytoskeleton. Their stability, intrinsic mechanical properties, and cell type-specific expression patterns distinguish them from actin and microtubules. By providing mechanical support, IFs protect cells from external forces and participate in cell adhesion and tissue integrity. IFs form an extensive and elaborate network that connects the cell cortex to intracellular organelles. They act as a molecular scaffold that controls intracellular organization. However, IFs have been revealed as much more than just rigid structures. Their dynamics is regulated by multiple signaling cascades and appears to contribute to signaling events in response to cell stress and to dynamic cellular functions such as mitosis, apoptosis, and migration.

Astrocyte activation and reactive gliosis-A new target in stroke?

Stroke is an acute insult to the central nervous system (CNS) that triggers a sequence of responses in the acute, subacute as well as later stages, with prominent involvement of astrocytes. Astrocyte activation and reactive gliosis in the acute stage of stroke limit the tissue damage and contribute to the restoration of homeostasis. Astrocytes also control many aspects of neural plasticity that is the basis for functional recovery. Here, we discuss the concept of intermediate filaments (nanofilaments) and the complement system as two handles on the astrocyte responses to injury that both present attractive opportunities for novel treatment strategies modulating astrocyte functions and reactive gliosis.

Effect of Chronic Oxidative Stress on Neuroinflammatory Response Mediated by CD4+T Cells in Neurodegenerative Diseases

In a state of oxidative stress, there is an increase of reactive species, which induce an altered intracellular signaling, leading to dysregulation of the inflammatory response. The inability of the antioxidant defense systems to modulate the proinflammatory response is key to the onset and progression of neurodegenerative diseases. The aim of this work is to review the effect of the state of oxidative stress on the loss of regulation of the inflammatory response on the microglia and astrocytes, the induction of different CD4⁺T cell populations in neuroinflammation, as well as its role in some neurodegenerative diseases. For this purpose, an intentional search of original articles, short communications, and reviews, was carried out in the following databases: PubMed, Scopus, and Google Scholar. The articles reviewed included the period from 1997 to 2017. With the evidence obtained, we conclude that the loss of redox balance induces alterations in the differentiation and number of CD4⁺T cell subpopulations, leading to an increase in Th1 and Th17 response. This contributes to the development of neuroinflammation as well as loss of the regulation of the inflammatory response in neurodegenerative diseases such as Alzheimer's (AD), Parkinson's (PD), and Multiple Sclerosis (MS). In contrast, regulatory T cells (Tregs) and Th2 modulate the inflammatory response of effect of T cells, microglia, and astrocytes. In this respect, it has been found that the mobilization of T cells with anti-inflammatory characteristics toward damaged regions of the CNS can provide neuroprotection and become a therapeutic strategy to control inflammatory processes in neurodegeneration.

Effects of triptolide on the expression of MHC II in microglia in kainic acid‑induced epilepsy

The purpose of the present study was to determine whether triptolide (T10) had any effect on major histocompatibility complex class II (MHC II) expression in kainic acid (KA)‑activated microglia, and to investigate the underlying molecular mechanism. BV‑2 microglia were pretreated with T10 prior to activation with KA. The expression level of MHC II and class II transactivator (CIITA) mRNA was determined via reverse transcription‑polymerase chain reaction. The expression of MHC II, CIITA and the phosphorylation level of c‑Jun and proto‑oncogene c‑Fos (c‑Fos) was determined by western blotting. The protein expression level of MHC II was determined by immunocytochemistry. It was observed that the mRNA and protein levels of MHC II and CIITA were increased in KA‑activated BV‑2 microglia, and that this increase was almost completely eliminated by T10. AP‑1 is a family of homodimers or heterodimers, composed of Jun family and Fos family proteins. Sequence analysis revealed an AP‑1 DNA binding site in the promoter of CIITA. The phosphorylation of c‑Jun and c‑Fos was increased in KA‑activated microglia, while T10 was able to suppress the phosphorylation of c‑Jun and c‑Fos in KA‑activated microglia. These data suggested that T10 may exert suppressive effects on MHC II expression in KA‑activated microglia, and that the mechanism may involve the regulation of AP‑1 activity.

PKH26 labeling of extracellular vesicles: Characterization and cellular internalization of contaminating PKH26 nanoparticles

PKH lipophilic dyes are highly fluorescent and stain membranes by intercalating their aliphatic portion into the exposed lipid bilayer. They have established use in labeling and tracking of cells in vivo and in vitro. Despite wide use of PKH-labeled extracellular vesicles (EVs) in cell targeting and functional studies, nonEV-associated fluorescent structures have never been examined systematically, nor was their internalization by cells. Here, we have characterized PKH26-positive particles in lymphoblastoid B exosome samples and exosome-free controls stained by ultracentrifugation, filtration, and sucrose-cushion-based and sucrose-gradient-based procedures, using confocal imaging and asymmetric-flow field-flow fractionation coupled to multi-angle light-scattering detector analysis. We show for the first time that numerous PKH26 nanoparticles (nine out of ten PKH26-positive particles) are formed during ultracentrifugation-based exosome staining, which are almost indistinguishable from PKH26-labeled exosomes in terms of size, surface area, and fluorescence intensity. When PKH26-labeled exosomes were purified through sucrose, PKH26 nanoparticles were differentiated from PKH26-labeled exosomes based on their reduced size. However, PKH26 nanoparticles were only physically removed from PKH26-labeled exosomes when separated on a sucrose gradient, and at the expense of low PKH26-labeled exosome recovery. Overall, low PKH26-positive particle recovery is characteristic of filtration-based exosome staining. Importantly, PKH26 nanoparticles are internalized by primary astrocytes into similar subcellular compartments as PKH26-labeled exosomes. Altogether, PKH26 nanoparticles can result in false-positive signals for stained EVs that can compromise the interpretation of EV internalization. Thus, for use in EV uptake and functional studies, sucrose-gradient-based isolation should be the method of choice to obtain PKH26-labeled exosomes devoid of PKH26 nanoparticles.

Ångstrom-size exocytotic fusion pore: Implications for pituitary hormone secretion

In the past, vesicle content release was thought to occur immediately and completely after triggering of exocytosis. However, vesicles may merge with the plasma membrane to form an Ångstrom diameter fusion pore that prevents the exit of secretions from the vesicle lumen. The advantage of such a narrow pore is to minimize the delay between the trigger and the release. Instead of stimulating a sequence of processes, leading to vesicle merger with the plasma membrane and a formation of a fusion pore, the stimulus only widens the pre-established fusion pore. The fusion pore may be stable and may exhibit repetitive opening of the vesicle lumen to the cell exterior accompanied by a content discharge. Such release of vesicle content is partial (subquantal), and depends on fusion pore open time, diameter and the diffusibility of the cargo. Such transient mode of fusion pore opening was not confirmed until the development of the membrane capacitance patch-clamp technique, which enables high-resolution measurement of changes in membrane surface area. It allows millisecond dwell-time measurements of fusion pores with subnanometer diameters. Currently, the soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) proteins are considered to be key entities in end-stage exocytosis, and the SNARE complex assembly/disassembly may regulate the fusion pore. Moreover, lipids or other membrane constituents with anisotropic (non-axisymmetric) geometry may also favour the establishment of stable narrow fusion pores, if positioned in the neck of the fusion pore.

Astroglial vesicular network: evolutionary trends, physiology and pathophysiology

Intracellular organelles, including secretory vesicles, emerged when eukaryotic cells evolved some 3 billion years ago. The primordial organelles that evolved in Archaea were similar to endolysosomes, which developed, arguably, for specific metabolic tasks, including uptake, metabolic processing, storage and disposal of molecules. In comparison with prokaryotes, cell volume of eukaryotes increased by several orders of magnitude and vesicle traffic emerged to allow for communication between distant intracellular locations. Lysosomes, first described in 1955, a prominent intermediate of endo- and exocytotic pathways, operate virtually in all eukaryotic cells including astroglia, the most heterogeneous type of homeostatic glia in the central nervous system. Astrocytes support neuronal network activity in particular through elaborated secretion, based on a complex intracellular vesicle network dynamics. Deranged homeostasis underlies disease and astroglial vesicle traffic contributes to the pathophysiology of neurodegenerative (Alzheimer's disease, Huntington's disease), neurodevelopmental diseases (intellectual deficiency, Rett's disease) and neuroinfectious (Zika virus) disorders. This review addresses astroglial cell-autonomous vesicular traffic network, as well as its into primary and secondary vesicular network defects in diseases, and considers this network as a target for developing new therapies for neurological conditions.