Astrocytes negatively regulate neurogenesis through the Jagged1-mediated Notch pathway

Optogenetics in Alzheimer's Disease: Focus on Astrocytes

Alzheimer's disease (AD) is the most common form of dementia, resulting in disability and mortality. The global incidence of AD is consistently surging. Although numerous therapeutic agents with promising potential have been developed, none have successfully treated AD to date. Consequently, the pursuit of novel methodologies to address neurodegenerative processes in AD remains a paramount endeavor. A particularly promising avenue in this search is optogenetics, enabling the manipulation of neuronal activity. In recent years, research attention has pivoted from neurons to glial cells. This review aims to consider the potential of the optogenetic correction of astrocyte metabolism as a promising strategy for correcting AD-related disorders. The initial segment of the review centers on the role of astrocytes in the genesis of neurodegeneration. Astrocytes have been implicated in several pathological processes associated with AD, encompassing the clearance of β-amyloid, neuroinflammation, excitotoxicity, oxidative stress, and lipid metabolism (along with a critical role in apolipoprotein E function). The effect of astrocyte-neuronal interactions will also be scrutinized. Furthermore, the review delves into a number of studies indicating that changes in cellular calcium (Ca2+) signaling are one of the causes of neurodegeneration. The review's latter section presents insights into the application of various optogenetic tools to manipulate astrocytic function as a means to counteract neurodegenerative changes.

From Youthful Vigor to Aging Decline: Unravelling the Intrinsic and Extrinsic Determinants of Hippocampal Neural Stem Cell Aging

Since Joseph Altman published his pioneering work demonstrating neurogenesis in the hippocampus of adult rats, the number of publications in this field increased exponentially. Today, we know that the adult hippocampus harbors a pool of adult neural stem cells (NSCs) that are the source of life-long neurogenesis and plasticity. The functions of these NSCs are regulated by extrinsic cues arising from neighboring cells and the systemic environment. However, this tight regulation is subject to imbalance with age, resulting in a decline in adult NSCs and neurogenesis, which contributes to the progressive deterioration of hippocampus-related cognitive functions. Despite extensive investigation, the mechanisms underlying this age-related decline in neurogenesis are only incompletely understood, but appear to include an increase in NSC quiescence, changes in differentiation patterns, and NSC exhaustion. In this review, we summarize recent work that has improved our knowledge of hippocampal NSC aging, focusing on NSC-intrinsic mechanisms as well as cellular and molecular changes in the niche and systemic environment that might be involved in the age-related decline in NSC functions. Additionally, we identify future directions that may advance our understanding of NSC aging and the concomitant loss of hippocampal neurogenesis and plasticity.

Effects of High-Fat and High-Fat High-Sugar Diets in the Anxiety, Learning and Memory, and in the Hippocampus Neurogenesis and Neuroinflammation of Aged Rats

High-caloric diets induce several deleterious alterations in the human body, including the brain. However, information on the effects of these diets on the elderly brain is scarce. Therefore, we studied the effects of 2 months of treatment with high-fat (HF) and high-fat-high-sugar (HFHS) diets on aged male Wistar rats at 18 months. Anxiety levels were analyzed using the open-field and plus-maze tests, while learning and memory processes were analyzed using the Morris water maze test. We also analyzed neurogenesis using doublecortin (DCX) and neuroinflammation using glial fibrillary acidic protein (GFAP). In aged rats, the HFHS diet impaired spatial learning, memory, and working memory and increased anxiety levels, associated with a reduction in the number of DCX cells and an increase in GFAP cells in the hippocampus. In contrast, the effects of the HF diet were lighter, impairing spatial memory and working memory, and associated with a reduction in DCX cells in the hippocampus. Thus, our results suggest that aged rats are highly susceptible to high-caloric diets, even if they only started in the elderly, with an impact on cognition and emotions. Furthermore, diets rich in saturated fats and sugar are more detrimental to aged rats than high-fat diets are.

Adult hippocampal neurogenesis in Alzheimer's disease: A roadmap to clinical relevance

Adult hippocampal neurogenesis (AHN) drops sharply during early stages of Alzheimer's disease (AD), via unknown mechanisms, and correlates with cognitive status in AD patients. Understanding AHN regulation in AD could provide a framework for innovative pharmacological interventions. We here combine molecular, behavioral, and clinical data and critically discuss the multicellular complexity of the AHN niche in relation to AD pathophysiology. We further present a roadmap toward a better understanding of the role of AHN in AD by probing the promises and caveats of the latest technological advancements in the field and addressing the conceptual and methodological challenges ahead.

Pathogenomic Signature and Aberrant Neurogenic Events in Experimental Cerebral Ischemic Stroke: A Neurotranscriptomic-Based Implication for Dementia

BACKGROUND

Cerebral ischemic stroke is caused due to neurovascular damage or thrombosis, leading to neuronal dysfunction, neuroinflammation, neurodegeneration, and regenerative failure responsible for neurological deficits and dementia. The valid therapeutic targets against cerebral stroke remain obscure. Thus, insight into neuropathomechanisms resulting from the aberrant expression of genes appears to be crucial.

OBJECTIVE

In this study, we have elucidated how neurogenesis-related genes are altered in experimental stroke brains from the available transcriptome profiles in correlation with transcriptome profiles of human postmortem stroke brain tissues.

METHODS

The transcriptome datasets available on the middle cerebral artery occlusion (MCAo) rat brains were obtained from the Gene Expression Omnibus, National Center for Biotechnology Information. Of the available datasets, 97 samples were subjected to the meta-analysis using the network analyst tool followed by Cytoscape-based enrichment mapping analysis. The key differentially expressed genes (DEGs) were validated and compared with transcriptome profiling of human stroke brains.

RESULTS

Results revealed 939 genes are differently expressed in the brains of the MCAo rat model of stroke, in which 30 genes are key markers of neural stem cells, and regulators of neurogenic processes. Its convergence with DEGs from human stroke brains has revealed common targets.

CONCLUSION

This study has established a panel of highly important DEGs to signify the potential therapeutic targets for neuroregenerative strategy against pathogenic events associated with cerebral stroke. The outcome of the findings can be translated to mitigate neuroregeneration failure seen in various neurological and metabolic disease manifestations with neurocognitive impairments.

Gut brain interaction theory reveals gut microbiota mediated neurogenesis and traditional Chinese medicine research strategies

Adult neurogenesis is the process of differentiation of neural stem cells (NSCs) into neurons and glial cells in certain areas of the adult brain. Defects in neurogenesis can lead to neurodegenerative diseases, mental disorders, and other maladies. This process is directionally regulated by transcription factors, the Wnt and Notch pathway, the extracellular matrix, and various growth factors. External factors like stress, physical exercise, diet, medications, etc., affect neurogenesis and the gut microbiota. The gut microbiota may affect NSCs through vagal, immune and chemical pathways, and other pathways. Traditional Chinese medicine (TCM) has been proven to affect NSCs proliferation and differentiation and can regulate the abundance and metabolites produced by intestinal microorganisms. However, the underlying mechanisms by which these factors regulate neurogenesis through the gut microbiota are not fully understood. In this review, we describe the recent evidence on the role of the gut microbiota in neurogenesis. Moreover, we hypothesize on the characteristics of the microbiota-gut-brain axis based on bacterial phyla, including microbiota's metabolites, and neuronal and immune pathways while providing an outlook on TCM's potential effects on adult neurogenesis by regulating gut microbiota.

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.

Reproducibility of developmental neuroplasticity in in vitro brain tissue models

The current prevalence of neurodevelopmental, neurodegenerative diseases, stroke and brain injury stimulates studies aimed to identify new molecular targets, to select the drug candidates, to complete the whole set of preclinical and clinical trials, and to implement new drugs into routine neurological practice. Establishment of protocols based on microfluidics, blood-brain barrier- or neurovascular unit-on-chip, and microphysiological systems allowed improving the barrier characteristics and analyzing the regulation of local microcirculation, angiogenesis, and neurogenesis. Reconstruction of key mechanisms of brain development and even some aspects of experience-driven brain plasticity would be helpful in the establishment of brain in vitro models with the highest degree of reliability. Activity, metabolic status and expression pattern of cells within the models can be effectively assessed with the protocols of system biology, cell imaging, and functional cell analysis. The next generation of in vitro models should demonstrate high scalability, 3D or 4D complexity, possibility to be combined with other tissues or cell types within the microphysiological systems, compatibility with bio-inks or extracellular matrix-like materials, achievement of adequate vascularization, patient-specific characteristics, and opportunity to provide high-content screening. In this review, we will focus on currently available and prospective brain tissue in vitro models suitable for experimental and preclinical studies with the special focus on models enabling 4D reconstruction of brain tissue for the assessment of brain development, brain plasticity, and drug kinetics.

New Insights Into the Role of Aberrant Hippocampal Neurogenesis in Epilepsy

Data accumulated over the past four decades have confirmed that adult hippocampal neurogenesis (HN) plays a key role in the wide spectrum of hippocampal pathology. Epilepsy is a disorder of the central nervous system characterized by spontaneous recurrent seizures. Although neurogenesis in persistent germinative zones is altered in the adult rodent models of epilepsy, the effects of seizure-induced neurogenesis in the epileptic brain, in terms of either a pathological or reparative role, are only beginning to be explored. In this review, we described the most recent advances in neurogenesis in epilepsy and outlooked future directions for neural stem cells (NSCs) and epilepsy-in-a-dish models. We proposed that it may help in refining the underlying molecular mechanisms of epilepsy and improving the therapies and precision medicine for patients with epilepsy.

Reactive Astrocytes Prevent Maladaptive Plasticity after Ischemic Stroke

Restoration of functional connectivity is a major contributor to functional recovery after stroke. We investigated the role of reactive astrocytes in functional connectivity and recovery after photothrombotic stroke in mice with attenuated reactive gliosis (GFAP^-/-Vim^-/-). Infarct volume and longitudinal functional connectivity changes were determined by in vivo T2-weighted magnetic resonance imaging (MRI) and resting-state functional MRI. Sensorimotor function was assessed with behavioral tests, and glial and neural plasticity responses were quantified in the peri-infarct region. Four weeks after stroke, GFAP^-/-Vim^-/- mice showed impaired recovery of sensorimotor function and aberrant restoration of global neuronal connectivity. These mice also exhibited maladaptive plasticity responses, shown by higher number of lost and newly formed functional connections between primary and secondary targets of cortical stroke regions and increased peri-infarct expression of the axonal plasticity marker Gap43. We conclude that reactive astrocytes modulate recovery-promoting plasticity responses after ischemic stroke.

Astrocyte Reactivity in Alzheimer's Disease: Therapeutic Opportunities to Promote Repair

Astrocytes are fast climbing the ladder of importance in neurodegenerative disorders, particularly in Alzheimer's disease (AD), with the prominent presence of reactive astrocytes sur- rounding amyloid β- plaques, together with activated microglia. Reactive astrogliosis, implying morphological and molecular transformations in astrocytes, seems to precede neurodegeneration, suggesting a role in the development of the disease. Single-cell transcriptomics has recently demon- strated that astrocytes from AD brains are different from "normal" healthy astrocytes, showing dys- regulations in areas such as neurotransmitter recycling, including glutamate and GABA, and im- paired homeostatic functions. However, recent data suggest that the ablation of astrocytes in mouse models of amyloidosis results in an increase in amyloid pathology as well as in the inflammatory profile and reduced synaptic density, indicating that astrocytes mediate neuroprotective effects. The idea that interventions targeting astrocytes may have great potential for AD has therefore emerged, supported by a range of drugs and stem cell transplantation studies that have successfully shown a therapeutic effect in mouse models of AD. In this article, we review the latest reports on the role and profile of astrocytes in AD brains and how manipulation of astrocytes in animal mod- els has paved the way for the use of treatments enhancing astrocytic function as future therapeutic avenues for AD.

The neurogenic niche in Alzheimer's disease

Adult hippocampal neurogenesis is the process of generation and functional incorporation of new neurons, formed by adult neural stem cells in the dentate gyrus. Adult hippocampal neurogenesis is highly dependent upon the integration of dynamic external stimuli and is instrumental in the formation of new spatial memories. Adult hippocampal neurogenesis is therefore uniquely sensitive to the summation of neuronal circuit and neuroimmune environments that comprise the neurogenic niche, and has powerful implications in diseases of aging and neurological disorders. This sensitivity underlies the neurogenic niche alterations commonly observed in Alzheimer's disease, the most common form of dementia. This review summarizes Alzheimer's disease associated changes in neuronal network activity, neuroinflammatory processes, and adult neural stem cell fate choice that ultimately result in neurogenic niche dysfunction and impaired adult hippocampal neurogenesis. A more comprehensive understanding of the complex changes mediating neurogenic niche disturbances in Alzheimer's disease will aid development of future therapies targeting adult neurogenesis.

Adult brain cytogenesis in the context of mood disorders: From neurogenesis to the emergent role of gliogenesis

Psychiatric disorders severely impact patients' lives. Motivational, cognitive and emotional deficits are the most common symptoms observed in these patients and no effective treatment is still available, either due to the adverse side effects or the low rate of efficacy of currently available drugs. Neurogenesis recovery has been one important focus in the treatment of psychiatric disorders, which undeniably contributes to the therapeutic action of antidepressants. However, glial plasticity is emerging as a new strategy to explore the deficits observed in mood disorders and the efficacy of therapeutic interventions. Thus, it is crucial to understand the mechanisms behind glio- and neurogenesis to better define treatments and preventive therapies, once adult cytogenesis is of pivotal importance to cognitive and emotional components of behavior, both in healthy and pathological contexts, including in psychiatric disorders. Here, we review the concepts and history of neuro- and gliogenesis, providing as well a reflection on the functional importance of cytogenesis in the context of disease.

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.

Novel Approaches Used to Examine and Control Neurogenesis in Parkinson's Disease

Neurogenesis is a key mechanism of brain development and plasticity, which is impaired in chronic neurodegeneration, including Parkinson’s disease. The accumulation of aberrant α-synuclein is one of the features of PD. Being secreted, this protein produces a prominent neurotoxic effect, alters synaptic plasticity, deregulates intercellular communication, and supports the development of neuroinflammation, thereby providing propagation of pathological events leading to the establishment of a PD-specific phenotype. Multidirectional and ambiguous effects of α-synuclein on adult neurogenesis suggest that impaired neurogenesis should be considered as a target for the prevention of cell loss and restoration of neurological functions. Thus, stimulation of endogenous neurogenesis or cell-replacement therapy with stem cell-derived differentiated neurons raises new hopes for the development of effective and safe technologies for treating PD neurodegeneration. Given the rapid development of optogenetics, it is not surprising that this method has already been repeatedly tested in manipulating neurogenesis in vivo and in vitro via targeting stem or progenitor cells. However, niche astrocytes could also serve as promising candidates for controlling neuronal differentiation and improving the functional integration of newly formed neurons within the brain tissue. In this review, we mainly focus on current approaches to assess neurogenesis and prospects in the application of optogenetic protocols to restore the neurogenesis in Parkinson’s disease.

Modulation of Glial Function in Health, Aging, and Neurodegenerative Disease

In the central nervous system (CNS), glial cells, such as microglia and astrocytes, are normally associated with support roles including contributions to energy metabolism, synaptic plasticity, and ion homeostasis. In addition to providing support for neurons, microglia and astrocytes function as the resident immune cells in the brain. The glial function is impacted by multiple aspects including aging and local CNS changes caused by neurodegeneration. During aging, microglia and astrocytes display alterations in their homeostatic functions. For example, aged microglia and astrocytes exhibit impairments in the lysosome and mitochondrial function as well as in their regulation of synaptic plasticity. Recent evidence suggests that glia can also alter the pathology associated with many neurodegenerative disorders including Alzheimer's disease (AD) and Parkinson's disease (PD). Shifts in the microbiome can impact glial function as well. Disruptions in the microbiome can lead to aberrant microglial and astrocytic reactivity, which can contribute to an exacerbation of disease and neuronal dysfunction. In this review, we will discuss the normal physiological functions of microglia and astrocytes, summarize novel findings highlighting the role of glia in aging and neurodegenerative diseases, and examine the contribution of microglia and astrocytes to disease progression.

Synergic Neuroprotection Between Ligusticum Chuanxiong Hort and Borneol Against Ischemic Stroke by Neurogenesis via Modulating Reactive Astrogliosis and Maintaining the Blood-Brain Barrier

Background:Ligusticum chuanxiong Hort (LCH) is a famous ethnomedicine in Asia known for its excellent output on stroke treatment, and borneol usually acts as an assistant for its reducing permeability of the blood–brain barrier (BBB) after stroke. Although their synergy against brain ischemia was verified in previous studies, the potential mechanism is still unknown.

Methods: The research aimed to explore the exact synergic mechanisms between LCH and borneol on neurogenesis within the areas of the dentate gyrus and subventricular zone. After treating middle cerebral artery occlusion rats with LCH (0.1 g/kg) and/or borneol (0.08 g/kg), the neurological severity score, brain infarct ratio, Nissl staining, Evans blue permeability, BBB ultrastructure, and expressions of von Willebrand factor and tight junction–associated proteins were measured. Co-localizations of Nestin⁺/BrdU⁺ and doublecortin⁺/BrdU⁺, and expressions of neuronal nuclei (NeuN) and glial fibrillary acidic protein (GFAP) were observed under a fluorescence microscope. Moreover, astrocyte polarization markers of complement component 3 and pentraxin 3, and relevant neurotrophins were also detected by immunoblotting.

Results: Basically, LCH and borneol had different focuses, although both of them decreased infarct areas, and increased quantity of Nissl bodies and expression of brain-derived neurotrophic factor. LCH increased the neurological severity score, NeuN⁺ cells, and the ratios of Nestin⁺/BrdU⁺ and doublecortin⁺/BrdU⁺, and decreased GFAP⁺ cells and ciliary neurotrophic factor expression. Additionally, it regulated the expressions of complement component 3 and pentraxin 3 to transform astrocyte phenotypes. Borneol improved BBB ultrastructure and increased the expressions of von Willebrand factor, tight junction–associated proteins, vascular endothelial growth factor, and vascular endothelial growth factor receptor 2. Unexpectedly, their combined therapy showed more obvious regulations on the Nissl score, Evans blue permeability, doublecortin⁺/BrdU⁺, NeuN⁺ cells, brain-derived neurotrophic factor, and vascular endothelial growth factor than both of their monotherapies.

Conclusions: The results indicated that LCH and borneol were complementary to each other in attenuating brain ischemia by and large. LCH mainly promoted neural stem cell proliferation, neurogenesis, and mature neuron preservation, which was probably related to the transformation of reactive astrocytes from A1 subtype to A2, while borneol preferred to maintain the integrity of the BBB, which provided neurogenesis with a homeostatic environment.

Photothermal Response Induced by Nanocage-Coated Artificial Extracellular Matrix Promotes Neural Stem Cell Differentiation

Strategies to increase the proportion of neural stem cells that differentiate into neurons are vital for therapy of neurodegenerative disorders. In vitro, the extracellular matrix composition and topography have been found to be important factors in stem cell differentiation. We have developed a novel artificial extracellular matrix (aECM) formed by attaching gold nanocages (AuNCs) to glass coverslips. After culturing rat neural stem cells (rNSCs) on these gold nanocage-coated surfaces (AuNC-aECMs), we observed that 44.6% of rNSCs differentiated into neurons compared to only 27.9% for cells grown on laminin-coated glass coverslips. We applied laser irradiation to the AuNC-aECMs to introduce precise amounts of photothermally induced heat shock in cells. Our results showed that laser-induced thermal stimulation of AuNC-aECMs further enhanced neuronal differentiation (56%) depending on the laser intensity used. Response to these photothermal effects increased the expression of heat shock protein 27, 70, and 90α in rNSCs. Analysis of dendritic complexity showed that this thermal stimulation promoted neuronal maturation by increasing dendrite length as thermal dose was increased. In addition, we found that cells growing on AuNC-aECMs post laser irradiation exhibited action potentials and increased the expression of voltage-gated Na+ channels compared to laminin-coated glass coverslips. These results indicate that the photothermal response induced in cells growing on AuNC-aECMs can be used to produce large quantities of functional neurons, with improved electrochemical properties, that can potentially be transplanted into a damaged central nervous system to provide replacement neurons and restore lost function.

Interleukin-17A promotes the differentiation of bone marrow mesenchymal stem cells into neuronal cells

Ischemia or hemorrhagic stroke is one of the leading causes of death and permanent disability in the worldwide population. As a consequence of the potential increasing in stroke, stem cell therapy is currently an area of intense focus. However, there are less data available regarding the promotion of healing efficacy after stroke. The present study aimed to investigate whether the cytokine interleukin-17A (IL-17A) could have a role in promoting the neuronal differentiation of mesenchymal stem cells (MSCs) and to investigate the associated molecular mechanism. Firstly, different concentration of IL-17A at range from 5-40 ng/mL was applied to stimulate bone marrow MSCs (BMSCs) during the course of neurogenic differentiation. Then reverse transcription-PCR, histological analyses and immunofluorescence assays were used to determine the optimum concentration of IL-17A in promoting the neuronal differentiation of BMSCs, which was 20 ng/mL. Mechanistically, Wnt signaling pathway was activated and Notch signaling pathway was suppressed. In addition, there were antergic effect of these two signaling pathways modulating the neurogenic differentiation of BMSCs induced by IL-17A. The present study demonstrated the potential role of IL-17A-based BMSCs strategy for promoting neuronal differentiation in vitro. However, the treatment efficacy could be considerably confirmed in animals with ischemia stroke. Therefore, a more sophisticated strategy that addresses the complicated treatment associated with stroke is needed.

Intermittent Fasting Alleviates Cognitive Impairments and Hippocampal Neuronal Loss but Enhances Astrocytosis in Mice with Subcortical Vascular Dementia

BACKGROUND

Intermittent fasting (IF) is found to exhibit neuroprotection against various insults, including ischemia; however, IF has been mainly applied before disease onset. It remains unknown whether IF implementation alleviates the long-term detrimental effects of a disease after its establishment.

OBJECTIVES

To investigate the IF effects on cognitive impairments and cerebrovascular pathologies in a subcortical vascular dementia (SVaD) mouse model.

METHODS

The SVaD model was developed by inducing hypoperfusion and hyperlipidemia in apoE-deficient (apoE-/-) mice. We subjected 10-week-old apoE-/- mice to bilateral common carotid artery stenosis using micro-coils after they were fed a high-fat diet (HFD; 45% energy) for 6 weeks to induce hyperlipidemia. Age-matched wild-type C57BL/6J mice received sham surgery after undergoing an identical HFD treatment. Both the SVaD model and wild-type mice either started a 1-month IF regimen (time-restricted feeding for 6 hours per day) or continued the standard diet ad libitum (6.2% fat energy) at 8 weeks post-surgery. We assessed mice weight, food intake, and outcomes in a behavioral test battery before, during, and after the IF regimen, prior to histopathological analyses (microvessel density, neuronal density, white matter damage, astrocytosis) of their brains.

RESULTS

SVaD model mice on the IF regimen (SVaD-IF) exhibited higher mean recognition and spatial working memory performance compared to SVaD mice fed ad libitum (SVaD-AL; P < 0.01). Additionally, SVaD-IF mice had ∼5% higher hippocampal neuronal density in the dentate gyrus (DG) and cornu ammonis 1 regions than SVaD-AL mice (P < 0.001), which paralleled their post-IF cognitive enhancements. However, SVaD-IF mice showed an ∼50% increase in hippocampal DG astrocytosis compared to SVaD-AL mice (P < 0.05), with no significant differences in microvessel densities among the 2 groups.

CONCLUSIONS

The improvements in SVaD-IF mice suggest that IF could be a potential nonpharmacological remedy for SVaD. This finding could stimulate future investigations on IF's neuroprotective potential across many neurovascular diseases.

Astrogliosis and episodic memory in late life: higher GFAP is related to worse memory and white matter microstructure in healthy aging and Alzheimer's disease

Astrocytes play a formative role in memory consolidation during physiological conditions; when dysregulated, astrocytes release glial fibrillary acidic protein (GFAP), which has been linked with negative memory outcomes in animal studies. We examined the association between blood GFAP, memory, and white matter (WM) integrity, accounting for blood markers of AD pathology (i.e., Aβ42) and neurodegeneration (i.e., total tau; neurofilament light chain) in 114 older adults (asymptomatic, n = 69; MCI/AD dementia, n = 45). Higher levels of GFAP were associated with lower memory scores (p < 0.0001), such that for 1 SD increase in mean GFAP values, the memory composite score decreased on average by 0.49 (Standard error = 0.071). These results remained significant after controlling for diagnostic status and AD-related blood biomarkers. Higher GFAP was also related to lower WM integrity in regions vulnerable to AD pathology; however, WM integrity did not account for the association between GFAP and memory. Study findings suggest that higher blood levels of a marker of astrogliosis may reflect impoverished memory functions and white matter health, independent of markers of amyloid or neurodegeneration.

Cypermethrin Impairs Hippocampal Neurogenesis and Cognitive Functions by Altering Neural Fate Decisions in the Rat Brain

Neurogenesis is a developmental process that involves fine-tuned coordination between self-renewal, proliferation, and differentiation of neural stem cells (NSCs) into neurons. However, early-life assault with environmental toxicants interferes with the regular function of genes, proteins, and other molecules that build brain architecture resulting in attenuated neurogenesis. Cypermethrin is a class II synthetic pyrethroid pesticide extensively used in agriculture, veterinary, and residential applications due to its low mammalian toxicity, high bio-efficacy, and enhanced stability. Despite reports on cypermethrin-mediated behavioral and biochemical alterations, till now, no study implicates whether cypermethrin exposure has any effect on neurogenesis. Therefore, the present study was undertaken to comprehend the effects of cypermethrin treatment on embryonic and adult neurogenesis. We found that cypermethrin exposure led to a considerable decrease in the BrdU/Sox-2+, BrdU/Dcx+, and BrdU/NeuN+ co-labeled cells indicating that cypermethrin treatment decreases NSC proliferation and generation of mature and functional neurons. On the contrary, the generation of BrdU/S100β+ glial cells was increased resulting in neurogliogenesis imbalance in the hippocampus. Further, cypermethrin treatment also led to an increased number of BrdU/cleaved caspase-3+ and Fluoro-Jade B+ cells suggesting an induction of apoptosis in NSCs and increased degeneration of neurons in the hippocampus. Overall, these results explicate that cypermethrin exposure not only reduces the NSC pool but also disturbs the neuron-astrocyte ratio and potentiates neurodegeneration in the hippocampus, leading to cognitive dysfunctions in rats.

Astroglial cells as neuroendocrine targets in forebrain development: Implications for sex differences in psychiatric disease

Astroglial cells are the most abundant cell type in the mammalian brain. They are implicated in almost every aspect of brain physiology, including maintaining homeostasis, building and maintaining the blood brain barrier, and the development and maturation of neuronal networks. Critically, astroglia also express receptors for gonadal sex hormones, respond rapidly to gonadal hormones, and are able to synthesize hormones. Thus, they are positioned to guide and mediate sexual differentiation of the brain, particularly neuronal networks in typical and pathological conditions. In this review, we describe astroglial involvement in the organization and development of the brain, and consider known sex differences in astroglial responses to understand how astroglial cell-mediated organization may play a role in forebrain sexual dimorphisms in human populations. Finally, we consider how sexually dimorphic astroglial responses and functions in development may lead to sex differences in vulnerability for neuropsychiatric disorders.

Vimentin's side gig: Regulating cellular proteostasis in mammalian systems

Intermediate filaments (IFs) perform a diverse set of well-known functions including providing structural support for the cell and resistance to mechanical stress, yet recent evidence has revealed unexpected roles for IFs as stress response proteins. Previously, it was shown that the type III IF protein vimentin forms cage-like structures around centrosome-associated proteins destined for degradation, structures referred to as aggresomes, suggesting a role for vimentin in protein turnover. However, vimentin's function at the aggresome has remained largely understudied. In a recent report, vimentin was shown to be dispensable for aggresome formation, but played a critical role in protein turnover at the aggresome through localizing proteostasis-related machineries, such as proteasomes, to the aggresome. Here, we review evidence for vimentin's function in proteostasis and highlight the organismal implications of these findings.

Extracellular Vesicles, Influential Players of Intercellular Communication within Adult Neurogenic Niches

Adult neurogenesis, involving the generation of functional neurons from adult neural stem cells (NSCs), occurs constitutively in discrete brain regions such as hippocampus, sub-ventricular zone (SVZ) and hypothalamus. The intrinsic structural plasticity of the neurogenic process allows the adult brain to face the continuously changing external and internal environment and requires coordinated interplay between all cell types within the specialized microenvironment of the neurogenic niche. NSC-, neuronal- and glia-derived factors, originating locally, regulate the balance between quiescence and self-renewal of NSC, their differentiation programs and the survival and integration of newborn cells. Extracellular Vesicles (EVs) are emerging as important mediators of cell-to-cell communication, representing an efficient way to transfer the biologically active cargos (nucleic acids, proteins, lipids) by which they modulate the function of the recipient cells. Current knowledge of the physiological role of EVs within adult neurogenic niches is rather limited. In this review, we will summarize and discuss EV-based cross-talk within adult neurogenic niches and postulate how EVs might play a critical role in the regulation of the neurogenic process.

From structural resilience to cell specification - Intermediate filaments as regulators of cell fate

During the last decades intermediate filaments (IFs) have emerged as important regulators of cellular signaling events, ascribing IFs with functions beyond the structural support they provide. The organ and developmental stage‐specific expression of IFs regulate cell differentiation within developing or remodeling tissues. Lack of IFs causes perturbed stem cell differentiation in vasculature, intestine, nervous system, and mammary gland, in transgenic mouse models. The aberrant cell fate decisions are caused by deregulation of different stem cell signaling pathways, such as Notch, Wnt, YAP/TAZ, and TGFβ. Mutations in genes coding for IFs cause an array of different diseases, many related to stem cell dysfunction, but the molecular mechanisms remain unresolved. Here, we provide a comprehensive overview of how IFs interact with and regulate the activity, localization and function of different signaling proteins in stem cells, and how the assembly state and PTM profile of IFs may affect these processes. Identifying when, where and how IFs and cell signaling congregate, will expand our understanding of IF‐linked stem cell dysfunction during development and disease.

Intracerebroventricular Delivery of Human Umbilical Cord Mesenchymal Stem Cells as a Promising Therapy for Repairing the Spinal Cord Injury Induced by Kainic Acid

Spinal cord injury (SCI) is a common pathological condition that leads to permanent or temporal loss of motor and autonomic functions. Kainic acid (KA), an agonist of kainate receptors, a type of ionotropic glutamate receptor, is widely used to induce experimental neurodegeneration models of CNS. Mesenchymal Stem Cells (MSC) therapy applied at the injured nervous tissue have emerged as a promising therapeutic treatment. Here we used a validated SCI experimental model in which an intraparenchymal injection of KA into the C5 segment of rat spinal cord induced an excitotoxic lesion. Three days later, experimental animals were treated with an intracerebroventricular injection of human umbilical cord (hUC) MSC whereas control group only received saline solution. Sensory and motor skills as well as neuronal and glial reaction of both groups were recorded. Differences in motor behavior, neuronal counting and glial responses were observed between hUC-MSC-treated and untreated rats. According to the obtained results, we suggest that hUC-MSC therapy delivered into the fourth ventricle using the intracerebroventricular via can exert a neuroprotective or neurorestorative effect on KA-injected animals.

Deciphering New Players in the Neurogenic Adult Hippocampal Niche

In the mammalian adult hippocampus, new neurons are continuously generated throughout life in the subgranular zone of the dentate gyrus. Increasing evidence point out the contribution of adult-born hippocampal granule cells (GCs) to cognitive processes such as learning and memory, indicating the relevance of understanding the molecular mechanisms that control the development of these new neurons in the preexisting hippocampal circuits. Cell proliferation and functional integration of adult-born GCs is a process highly regulated by different intrinsic and extrinsic factors. In this review, we discuss recent advances related with cellular components and extrinsic signals of the hippocampal neurogenic niche that support and modulate neurogenesis under physiological conditions.

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.

Neurogenesis From Embryo to Adult - Lessons From Flies and Mice

The human brain is composed of billions of cells, including neurons and glia, with an undetermined number of subtypes. During the embryonic and early postnatal stages, the vast majority of these cells are generated from neural progenitors and stem cells located in all regions of the neural tube. A smaller number of neurons will continue to be generated throughout our lives, in localized neurogenic zones, mainly confined at least in rodents to the subependymal zone of the lateral ventricles and the subgranular zone of the hippocampal dentate gyrus. During neurogenesis, a combination of extrinsic cues interacting with temporal and regional intrinsic programs are thought to be critical for increasing neuronal diversity, but their underlying mechanisms need further elucidation. In this review, we discuss the recent findings in Drosophila and mammals on the types of cell division and cell interactions used by neural progenitors and stem cells to sustain neurogenesis, and how they are influenced by glia.

Cholinergic and inflammatory phenotypes in transgenic tau mouse models of Alzheimer's disease and frontotemporal lobar degeneration

An early and sizeable loss of basal forebrain cholinergic neurons is a well-characterized feature associated with measurable deficits in spatial learning and cognitive impairment in patients with Alzheimer’s disease. In addition, pro-inflammatory glial cells such as astrocytes and microglia may play a key role in the neurodegenerative cascade of Alzheimer’s disease and tauopathies. We recently presented two mouse models: Line 1, expressing the truncated tau fragment identified as the core of the Alzheimer’s paired helical filament, and Line 66, expressing full-length human tau carrying a double mutation (P301S and G335D). Line 1 mice have a pathology that is akin to Alzheimer’s, whilst Line 66 resembles frontotemporal lobar degeneration. However, their cholinergic and inflammatory phenotypes remain elusive. We performed histological evaluation of choline acetyltransferase, acetylcholinesterase, p75 neurotrophin receptor, microglial ionized calcium binding adaptor molecule 1 and astrocytic glial fibrillary acidic protein in the basal forebrain, hippocampus and cortex of these models. A significant lowering of choline acetyltransferase-positive neurons and p75-positive neurons in the basal forebrain of Line 1 at 3, 6 and 9 months was observed in two independent studies, alongside a significant decrease in acetylcholinesterase staining in the cortex and hippocampus. The reductions in choline acetyltransferase positivity varied between 30% and 50% at an age when Line 1 mice show spatial learning impairments. Furthermore, an increase in microglial ionized calcium binding adaptor molecule 1 staining was observed in the basal forebrain, hippocampus and entorhinal cortex of Line 1 at 6 months. Line 66 mice displayed an intact cholinergic basal forebrain, and no difference in p75-positive neurons at 3 or 9 months. In addition, Line 66 exhibited significant microglial ionized calcium binding adaptor molecule 1 increase in the basal forebrain and hippocampus, suggesting a prominent neuroinflammatory profile. Increased concentrations of microglial interleukin-1β and astrocytic complement 3 were also seen in the hippocampus of both Line 1 and Line 66. The cholinergic deficit in Line 1 mice confirms the Alzheimer’s disease-like phenotype in Line 1 mice, whilst Line 66 revealed no measurable change in total cholinergic expression, a phenotypic trait of frontotemporal lobar degeneration. These two transgenic lines are therefore suitable for discriminating mechanistic underpinnings between the Alzheimer’s and frontotemporal lobar degeneration-like phenotypes of these mice.

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.

The role of GFAP and vimentin in learning and memory

Intermediate filaments (also termed nanofilaments) are involved in many cellular functions and play important roles in cellular responses to stress. The upregulation of glial fibrillary acidic protein (GFAP) and vimentin (Vim), intermediate filament proteins of astrocytes, is the hallmark of astrocyte activation and reactive gliosis in response to injury, ischemia or neurodegeneration. Reactive gliosis is essential for the protective role of astrocytes at acute stages of neurotrauma or ischemic stroke. However, GFAP and Vim were also linked to neural plasticity and regenerative responses in healthy and injured brain. Mice deficient for GFAP and vimentin (GFAP-/-Vim-/-) exhibit increased post-traumatic synaptic plasticity and increased basal and post-traumatic hippocampal neurogenesis. Here we assessed the locomotor and exploratory behavior of GFAP-/-Vim-/- mice, their learning, memory and memory extinction, by using the open field, object recognition and Morris water maze tests, trace fear conditioning, and by recording reversal learning in IntelliCages. While the locomotion, exploratory behavior and learning of GFAP-/-Vim-/- mice, as assessed by object recognition, the Morris water maze, and trace fear conditioning tests, were comparable to wildtype mice, GFAP-/-Vim-/- mice showed more pronounced memory extinction when tested in IntelliCages, a finding compatible with the scenario of an increased rate of reorganization of the hippocampal circuitry.

Vimentin is required for normal accumulation of body fat

Intermediate filaments (nanofilaments) have many functions, especially in response to cellular stress. Mice lacking vimentin (Vim-/-) display phenotypes reflecting reduced levels of cell activation and ability to counteract stress, for example, decreased reactivity of astrocytes after neurotrauma, decreased migration of astrocytes and fibroblasts, attenuated inflammation and fibrosis in lung injury, delayed wound healing, impaired vascular adaptation to nephrectomy, impaired transendothelial migration of lymphocytes and attenuated atherosclerosis. To address the role of vimentin in fat accumulation, we assessed the body weight and fat by dual-energy X-ray absorptiometry (DEXA) in Vim-/- and matched wildtype (WT) mice. While the weight of 1.5-month-old Vim-/- and WT mice was comparable, Vim-/- mice showed decreased body weight at 3.5, 5.5 and 8.5 months (males by 19-22%, females by 18-29%). At 8.5 months, Vim-/- males and females had less body fat compared to WT mice (a decrease by 24%, p < 0.05, and 33%, p < 0.0001, respectively). The body mass index in 8.5 months old Vim-/- mice was lower in males (6.8 vs. 7.8, p < 0.005) and females (6.0 vs. 7.7, p < 0.0001) despite the slightly lower body length of Vim-/- mice. Increased mortality was observed in adult Vim-/- males. We conclude that vimentin is required for the normal accumulation of body fat.

Intranasal Administration of PACAP Is an Efficient Delivery Route to Reduce Infarct Volume and Promote Functional Recovery After Transient and Permanent Middle Cerebral Artery Occlusion

Intranasal (IN) administration appears to be a suitable route for clinical use as it allows direct delivery of bioactive molecules to the central nervous system, reducing systemic exposure and sides effects. Nevertheless, only some molecules can be transported to the brain from the nasal cavity. This led us to compare the efficiency of an IN, intravenous (IV), and intraperitoneal (IP) administration of pituitary adenylate cyclase-activating polypeptide (PACAP) after transient or permanent middle cerebral artery occlusion (MCAO) in C57BL/6 mice. The results show that the neuroprotective effect of PACAP is much more efficient after IN administration than IV injection while IP injection had no effect. IN administration of PACAP reduced the infarct volume when injected within 6 h after the reperfusion and improved functional recovery up to at least 1 week after the ischemia.

Endogenous neural precursor cells in health and disease

Neurogenesis persists in the adult brain of mammals in the subventricular zone (SVZ) of the lateral ventricles and in the subgranular zone (SGZ) of the dentate gyrus (DG). The complex interactions between intrinsic and extrinsic signals provided by cells in the niche but also from distant sources regulate the fate of neural stem/progenitor cells (NPCs) in these sites. This fine regulation is perturbed in aging and in pathological conditions leading to a different NPC behavior, tailored to the specific physio-pathological features. Indeed, NPCs exert in physiological and pathological conditions important neurogenic and non-neurogenic regulatory functions and participate in maintaining and protecting brain tissue homeostasis. In this review, we discuss intrinsic and extrinsic signals that regulate NPC activation and NPC functional role in various homeostatic and non-homeostatic conditions.

[Astroglia-mediated regulation of cell development in the model of neurogenic niche in vitro treated with Aβ1-42]

Neurogenesis is a complex process which governs embryonic brain development and is importants for brain plasticity throughout the whole life. Postnatal neurogenesis occurs in neurogenic niches that regulate the processes of proliferation and differentiation of stem and progenitor cells under the action of stimuli that trigger the mechanisms of neuroplasticity. Cells of glial and endothelial origin are the key regulators of neurogenesis. It is known that physiological neurogeneses is crucial for memory formation, whereas reparative neurogenesis provides partial repair of altered brain structure and compensation of neurological deficits caused by brain injury. Dysregulation of neurogenesis is a characteristics of various neurodevelopmental and neurodegenerative diseases, particularly, Alzheimer's disease which is very important medical and social problem. In the in vitro model of the neurogenic niche using hippocampal neurospheres as a source of stem/progenitor cells and astrocytes, we studied effects of astrocyte activation on the expression of markers of different stages of cell proliferation and differentiation. We found that aberrant mechanisms of development of stem and progenitor cells, caused by the beta-amyloid (Aβ1-42), can be partially restored by targeted activation of GFAP-expressing cells in the neurogenic niche.

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.

Vimentin Phosphorylation Is Required for Normal Cell Division of Immature Astrocytes

Vimentin (VIM) is an intermediate filament (nanofilament) protein expressed in multiple cell types, including astrocytes. Mice with VIM mutations of serine sites phosphorylated during mitosis (VIM^SA/SA) show cytokinetic failure in fibroblasts and lens epithelial cells, chromosomal instability, facilitated cell senescence, and increased neuronal differentiation of neural progenitor cells. Here we report that in vitro immature VIM^SA/SA astrocytes exhibit cytokinetic failure and contain vimentin accumulations that co-localize with mitochondria. This phenotype is transient and disappears with VIM^SA/SA astrocyte maturation and expression of glial fibrillary acidic protein (GFAP); it is also alleviated by the inhibition of cell proliferation. To test the hypothesis that GFAP compensates for the effect of VIM^SA/SA in astrocytes, we crossed the VIM^SA/SA and GFAP^−/− mice. Surprisingly, the fraction of VIM^SA/SA immature astrocytes with abundant vimentin accumulations was reduced when on GFAP^−/− background. This indicates that the disappearance of vimentin accumulations and cytokinetic failure in mature astrocyte cultures are independent of GFAP expression. Both VIM^SA/SA and VIM^SA/SAGFAP^−/− astrocytes showed normal mitochondrial membrane potential and vulnerability to H₂O₂, oxygen/glucose deprivation, and chemical ischemia. Thus, mutation of mitotic phosphorylation sites in vimentin triggers formation of vimentin accumulations and cytokinetic failure in immature astrocytes without altering their vulnerability to oxidative stress.

Vimentin regulates Notch signaling strength and arterial remodeling in response to hemodynamic stress

The intermediate filament (IF) cytoskeleton has been proposed to regulate morphogenic processes by integrating the cell fate signaling machinery with mechanical cues. Signaling between endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) through the Notch pathway regulates arterial remodeling in response to changes in blood flow. Here we show that the IF-protein vimentin regulates Notch signaling strength and arterial remodeling in response to hemodynamic forces. Vimentin is important for Notch transactivation by ECs and vimentin knockout mice (VimKO) display disrupted VSMC differentiation and adverse remodeling in aortic explants and in vivo. Shear stress increases Jagged1 levels and Notch activation in a vimentin-dependent manner. Shear stress induces phosphorylation of vimentin at serine 38 and phosphorylated vimentin interacts with Jagged1 and increases Notch activation potential. Reduced Jagged1-Notch transactivation strength disrupts lateral signal induction through the arterial wall leading to adverse remodeling. Taken together we demonstrate that vimentin forms a central part of a mechanochemical transduction pathway that regulates multilayer communication and structural homeostasis of the arterial wall.

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.

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.

Role of Astrocytes in the Neurogenic Niches

In the mammalian brain, highly specialized astrocytes serve as neural stem cells (NSCs) that divide and give rise to new neurons, in a process called neurogenesis. During embryonic development NSCs generate almost all neurons of the brain. Soon after birth the neurogenic potential of NSCs is highly reduced, and neurogenesis occurs only in two specialized brain regions called the neurogenic niches. Niche cells are essential to stem cells as they provide structural and nutritional support, and control fundamental stem cell decisions. Astrocytes, major components of the adult neurogenic niches, are evolving as important regulators of neurogenesis, by controlling NSC proliferation, fate choice, and differentiation of the progeny. Therefore, astrocytes contribute to neurogenesis in two ways: as NSCs and as niche cells. This review highlights the role of astrocyte-like NSCs during development and adulthood, and summarizes how niche astrocytes control the process of adult neurogenesis.

Astrocytes' Contribution to Adult Neurogenesis in Physiology and Alzheimer's Disease

Adult neurogenesis is one of the most drastic forms of brain plasticity in adulthood and there is a growing body of evidence showing that, in the hippocampus, this process contributes to mechanisms of memory as well as depression. Interestingly, adult neurogenesis is tightly regulated by the neurogenic niche, which provides a structural and molecular scaffold for stem cell proliferation and the differentiation and functional integration of new neurons. In this review, we highlight the role of astrocytes in the regulation of adult neurogenesis in the context of cognitive function. We also discuss how the changes in astrocytes function may dysregulate adult neurogenesis and contribute to cognitive impairment in the context of Alzheimer's disease.

Knockdown of Butyrylcholinesterase but Not Inhibition by Chlorpyrifos Alters Early Differentiation Mechanisms in Human Neural Stem Cells

Butyrylcholinesterase (BChE) is the evolutionary counterpart to acetylcholinesterase (AChE). Both are expressed early in nervous system development prior to cholinergic synapse formation. The organophosphate pesticide chlorpyrifos (CPF) primarily exerts toxicity through the inhibition of AChE, which results in excess cholinergic stimulation at the synapse. We hypothesized that the inhibition of AChE and BChE by CPF may impair early neurogenesis in neural stem cells (NSCs). To model neurodevelopment in vitro, we used human NSCs derived from induced pluripotent stem cells (iPSCs) with a focus on the initial differentiation mechanisms. Over the six days of NSC differentiation, the BChE activity and mRNA expression significantly increased, while the AChE activity and expression remained unchanged. The CPF treatment (10 μM) caused 82% and 92% inhibition of AChE and BChE, respectively. The CPF exposure had no effect on the cell viability or the expression of the differentiation markers HES5, DCX, or MAP2. However, the shRNA-knockdown of the BChE expression resulted in the decreased or delayed expression of the transcription factors HES5 and HES3. BChE may have a role in the differentiation of NSCs independent of, or in addition to, its enzymatic activity.

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.

Neural stem cell therapies and hypoxic-ischemic brain injury

Hypoxic-ischemic brain injury is a significant cause of morbidity and mortality in the adult as well as in the neonate. Extensive pre-clinical studies have shown promising therapeutic effects of neural stem cell-based treatments for hypoxic-ischemic brain injury. There are two major strategies of neural stem cell-based therapies: transplanting exogenous neural stem cells and boosting self-repair of endogenous neural stem cells. Neural stem cell transplantation has been proved to improve functional recovery after brain injury through multiple by-stander mechanisms (e.g., neuroprotection, immunomodulation), rather than simple cell-replacement. Endogenous neural stem cells reside in certain neurogenic niches of the brain and response to brain injury. Many molecules (e.g., neurotrophic factors) can stimulate or enhance proliferation and differentiation of endogenous neural stem cells after injury. In this review, we first present an overview of neural stem cells during normal brain development and the effect of hypoxic-ischemic injury on the activation and function of endogenous neural stem cells in the brain. We then summarize and discuss the current knowledge of strategies and mechanisms for neural stem cell-based therapies on brain hypoxic-ischemic injury, including neonatal hypoxic-ischemic brain injury and adult ischemic stroke.

Injury Leads to the Appearance of Cells with Characteristics of Both Microglia and Astrocytes in Mouse and Human Brain

Microglia and astrocytes have been considered until now as cells with very distinct identities. Here, we assessed the heterogeneity within microglia/monocyte cell population in mouse hippocampus and determined their response to injury, by using single-cell gene expression profiling of cells isolated from uninjured and deafferented hippocampus. We found that in individual cells, microglial markers Cx3cr1, Aif1, Itgam, and Cd68 were co-expressed. Interestingly, injury led to the co-expression of the astrocyte marker Gfap in a subpopulation of Cx3cr1-expressing cells from both the injured and contralesional hippocampus. Cells co-expressing astrocyte and microglia markers were also detected in the in vitro LPS activation/injury model and in sections from human brain affected by stroke, Alzheimer's disease, and Lewy body dementia. Our findings indicate that injury and chronic neurodegeneration lead to the appearance of cells that share molecular characteristics of both microglia and astrocytes, 2 cell types with distinct embryologic origin and function.

Attenuation of reactive gliosis in stroke-injured mouse brain does not affect neurogenesis from grafted human iPSC-derived neural progenitors

Induced pluripotent stem cells (iPSCs) or their progeny, derived from human somatic cells, can give rise to functional improvements after intracerebral transplantation in animal models of stroke. Previous studies have indicated that reactive gliosis, which is associated with stroke, inhibits neurogenesis from both endogenous and grafted neural stem/progenitor cells (NSPCs) of rodent origin. Here we have assessed whether reactive astrocytes affect the fate of human iPSC-derived NSPCs transplanted into stroke-injured brain. Mice with genetically attenuated reactive gliosis (deficient for GFAP and vimentin) were subjected to cortical stroke and cells were implanted adjacent to the ischemic lesion one week later. At 8 weeks after transplantation, immunohistochemical analysis showed that attenuated reactive gliosis did not affect neurogenesis or commitment towards glial lineage of the grafted NSPCs. Our findings, obtained in a human-to-mouse xenograft experiment, provide evidence that the reactive gliosis in stroke-injured brain does not affect the formation of new neurons from intracortically grafted human iPSC-derived NSPCs. However, for a potential clinical translation of these cells in stroke, it will be important to clarify whether the lack of effect of reactive gliosis on neurogenesis is observed also in a human-to-human experimental setting.