Interactions Between Neural Progenitor Cells and Microglia in the Subventricular Zone: Physiological Implications in the Neurogenic Niche and After Implantation in the Injured Brain

Glioblastoma Therapy: Past, Present and Future

Glioblastoma (GB) stands out as the most prevalent and lethal form of brain cancer. Although great efforts have been made by clinicians and researchers, no significant improvement in survival has been achieved since the Stupp protocol became the standard of care (SOC) in 2005. Despite multimodality treatments, recurrence is almost universal with survival rates under 2 years after diagnosis. Here, we discuss the recent progress in our understanding of GB pathophysiology, in particular, the importance of glioma stem cells (GSCs), the tumor microenvironment conditions, and epigenetic mechanisms involved in GB growth, aggressiveness and recurrence. The discussion on therapeutic strategies first covers the SOC treatment and targeted therapies that have been shown to interfere with different signaling pathways (pRB/CDK4/RB1/P16ink4, TP53/MDM2/P14arf, PI3k/Akt-PTEN, RAS/RAF/MEK, PARP) involved in GB tumorigenesis, pathophysiology, and treatment resistance acquisition. Below, we analyze several immunotherapeutic approaches (i.e., checkpoint inhibitors, vaccines, CAR-modified NK or T cells, oncolytic virotherapy) that have been used in an attempt to enhance the immune response against GB, and thereby avoid recidivism or increase survival of GB patients. Finally, we present treatment attempts made using nanotherapies (nanometric structures having active anti-GB agents such as antibodies, chemotherapeutic/anti-angiogenic drugs or sensitizers, radionuclides, and molecules that target GB cellular receptors or open the blood-brain barrier) and non-ionizing energies (laser interstitial thermal therapy, high/low intensity focused ultrasounds, photodynamic/sonodynamic therapies and electroporation). The aim of this review is to discuss the advances and limitations of the current therapies and to present novel approaches that are under development or following clinical trials.

Functional Analysis of a Novel Immortalized Murine Microglia Cell Line in 3D Spheroid Model

Microglia are the residential immune cells of central nervous system and they are crucial for brain development and homeostasis, as well as the progression of inflammatory brain diseases. To study microglia's physiological and pathological functions, one of the most widely used models is primary microglia culture from neonatal rodents. However, primary microglia culture is time consuming and needs a great number of animals. In our microglia culture, we found a strain of spontaneously immortalized microglia that continued to divide without any known genetic intervention. We confirmed the immortalization of these cells for uninterrupted thirty passages and we named them as immortalized microglia like-1 cells (iMG-1). The iMG-1 cells kept their microglia morphology, and they expressed macrophage/microglia-specific proteins of CD11b, CD68, P2RY12, and IBA1 in vitro. iMG-1 cells were responsive to inflammatory stimulations with lipopolysaccharide (LPS) and Polyinosinic:polycytidylic acid (pIpC), triggering increased mRNA/protein levels of IL1-β, IL-6, TNF-α, and interferons. LPS and pIpC treated iMG-1 cells also significantly increased their accumulation of lipid droplets (LDs). We also generated a 3D spheroid model using immortalized neural progenitor cells and iMG-1 cells with defined percentages to study neuroinflammation. The iMG-1 cells distributed evenly in spheroids, and they regulated the basal mRNA levels of cytokines of neural progenitors in 3D spheroid. iMG-1 cells were responsive to LPS by increased expression of IL-6 and IL1-β in spheroids. Together, this study indicated the reliability of iMG-1 which could be readily available to study the physiological and pathological functions of microglia.

Extracellular vesicles in the glioblastoma microenvironment: A diagnostic and therapeutic perspective

Glioblastoma (GBM), is the most malignant form of gliomas and the most common and lethal primary brain tumor in adults. Conventional cancer treatments have limited to no efficacy on GBM. GBM cells respond and adapt to the surrounding brain parenchyma known as tumor microenvironment (TME) to promote tumor preservation. Among specific TME, there are 3 of particular interest for GBM biology: the perivascular niche, the subventricular zone neurogenic niche, and the immune microenvironment. GBM cells and TME cells present a reciprocal feedback which results in tumor maintenance. One way that these cells can communicate is through extracellular vesicles. These vesicles include exosomes and microvesicles that have the ability to carry both cancerous and non-cancerous cargo, such as miRNA, RNA, proteins, lipids, and DNA. In this review we will discuss the booming topic that is extracellular vesicles, and how they have the novelty to be a diagnostic and targetable vehicle for GBM.

Chronic exposure to aflatoxin B1 increases hippocampal microglial pyroptosis and vulnerability to stress in mice

BACKGROUND

Chronic aflatoxin B1 (AFB1) exposure may increase the risk of multiple neuropsychiatric disorders. Stress is considered one of the main contributors to major depressive disorder. Whether and how chronic AFB1 exposure affects vulnerability to stress is unclear.

METHODS

Mice were exposed for three weeks to AFB1 (100 µg/kg/d) and/or chronic mild stress (CMS). The vulnerability behaviors in response to stress were assessed in the forced swimming test (FST), sucrose preference test (SPT), and tail suspension test (TST). Microglial pyroptosis was investigated using immunofluorescence, enzyme-linked immunosorbent assays, and western blot assay in the hippocampus of mice. Hippocampal neurogenesis and the effects of AFB1-treated microglia on proliferation and differentiation of neural stem/precursor cells (NSPCs) were assessed via immunofluorescence in the hippocampus of mice.

RESULTS

Mice exposed to CMS in the presence of AFB1 exhibited markedly greater vulnerability to stress than mice treated with CMS or AFB1 alone, as indicated by reduced sucrose preference and longer immobility time in the forced swimming test. Chronic aflatoxin B1 exposure resulted in changes in the microglial morphology and increase in TUNEL⁺ microglia and GSDMD⁺ microglia in the hippocampal dentate gyrus. When mice were exposed to both CMS and AFB1, pyroptosis-related molecules (such as NLRP3, caspase-1, GSDMD-N, and interleukin-1β) were significantly upregulated in the hippocampus. These molecules were also significantly enhanced by AFB1 in primary microglial cultures. AFB1-treated mice showed decrease in the numbers of BrdU⁺, BrdU-DCX⁺, and BrdU-NeuN⁺ cells in the hippocampal dentate gyrus, as well as the percentages of BrdU⁺ cells that were NeuN⁺ in the presence or absence of CMS when compared with vehicle-treated mice. The combination of AFB1 and CMS exacerbated these effects to an even greater extent. The number of DCX⁺ cells correlated negatively with the percentage of ameboid microglia, TUNEL⁺ microglia and GSDMD⁺ microglia in the hippocampal dentate gyrus. AFB1-treated microglia suppressed the proliferation and neuronal differentiation of NSPCs in vitro.

CONCLUSION

Chronic AFB1 exposure induces microglial pyroptosis, promoting an adverse neurogenic microenvironment that impairs hippocampal neurogenesis, which may render mice more vulnerable to stress.

primiReference: a reference for analysis of primary-microRNA expression in single-nucleus sequencing data

Single-nucleus RNA-sequencing technology has revolutionized understanding of nuanced changes in gene expression between cell types within tissues. Unfortunately, our understanding of regulatory RNAs, such as microRNAs (miRNAs), is limited through both single-cell and single-nucleus techniques due to the short length of miRNAs in the cytoplasm and the incomplete reference of longer primary miRNA (pri-miRNA) transcripts in the nucleus. We build a custom reference to align and count pri-miRNA sequences in single-nucleus data. Using young and aged subventricular zone (SVZ) nuclei, we show differential expression of pri-miRNAs targeting genes involved in neural stem cells (NSC) differentiation in the aged SVZ. Furthermore, using wild-type and 5XFAD mouse model cortex nuclei, to validate the use of primiReference, we find cell-type-specific expression of pri-miRNAs known to be involved in Alzheimer's disease (AD). pri-miRNAs likely contribute to NSC dysregulation with age and AD pathology. primiReference is paramount in capturing a global profile of gene expression and regulation in single-nucleus data and can provide key insights into cell-type-specific expression of pri-miRNAs, paving the way for future studies of regulation and pathway dysregulation. By looking at pri-miRNA abundance and transcriptional differences, regulation of gene expression by miRNAs in disease and aging can be further explored.

Modulation of the Microglial Nogo-A/NgR Signaling Pathway as a Therapeutic Target for Multiple Sclerosis

Current therapeutics targeting chronic phases of multiple sclerosis (MS) are considerably limited in reversing the neural damage resulting from repeated inflammation and demyelination insults in the multi-focal lesions. This inflammation is propagated by the activation of microglia, the endogenous immune cell aiding in the central nervous system homeostasis. Activated microglia may transition into polarized phenotypes; namely, the classically activated proinflammatory phenotype (previously categorized as M1) and the alternatively activated anti-inflammatory phenotype (previously, M2). These transitional microglial phenotypes are dynamic states, existing as a continuum. Shifting microglial polarization to an anti-inflammatory status may be a potential therapeutic strategy that can be harnessed to limit neuroinflammation and further neurodegeneration in MS. Our research has observed that the obstruction of signaling by inhibitory myelin proteins such as myelin-associated inhibitory factor, Nogo-A, with its receptor (NgR), can regulate microglial cell function and activity in pre-clinical animal studies. Our review explores the microglial role and polarization in MS pathology. Additionally, the potential therapeutics of targeting Nogo-A/NgR cellular mechanisms on microglia migration, polarization and phagocytosis for neurorepair in MS and other demyelination diseases will be discussed.

Drugs and Endogenous Factors as Protagonists in Neurogenic Stimulation

Neurogenesis is a biological process characterized by new neurons formation from stem cells. For decades, it was believed that neurons only multiplied during development and in the postnatal period but the discovery of neural stem cells (NSCs) in mature brain promoted a revolution in neuroscience field. In mammals, neurogenesis consists of migration, differentiation, maturation, as well as functional integration of newborn cells into the pre-existing neuronal circuit. Actually, NSC density drops significantly after the first stages of development, however in specific places in the brain, called neurogenic niches, some of these cells retain their ability to generate new neurons and glial cells in adulthood. The subgranular (SGZ), and the subventricular zones (SVZ) are examples of regions where the neurogenesis process occurs in the mature brain. There, the potential of NSCs to produce new neurons has been explored by new advanced methodologies and in neuroscience for the treatment of brain damage and/or degeneration. Based on that, this review highlights endogenous factors and drugs capable of stimulating neurogenesis, as well as the perspectives for the use of NSCs for neurological and neurodegenerative diseases.

Facet-Dependent Activity of CeO2 Nanozymes Regulate the Fate of Human Neural Progenitor Cell via Redox Homeostasis

Neural progenitor cells (NPCs) therapy, a promising therapeutic strategy for neurodegenerative diseases, has a huge challenge to ensure high survival rate and neuronal differentiation rate. Cerium oxide (CeO₂) nanoparticles exhibit multienzyme mimetic activities and have shown the capability of regulating reactive oxygen species (ROS), which is a pivotal mediator for intracellular redox homeostasis in NPCs, regulating biological processes including differentiation, proliferation, and apoptosis. In the present study, the role of facet-dependent CeO₂-mediated redox homeostasis in regulating self-renewal and differentiation of NPCs is reported for the first time. The cube-, rod-, and octahedron-shaped CeO₂ nanozymes with different facets are prepared. Among the mentioned nanozymes, the cube enclosed by the (100) facet exhibits the highest CAT-like activity, causing it to provide superior protection to NPCs from oxidative stress induced by H₂O₂; meanwhile, the octahedron enclosed by the (111) facet with the lowest CAT-like activity induces the most ROS production in ReNcell CX cells, which promotes neuronal differentiation by activated AKT/GSK-3β/β-catenin pathways. A further mechanistic study indicated that the electron density of the surface Ce atoms changed continuously with different crystal facets, which led to their different CAT-like activity and modulation of redox homeostasis in NPCs. Altogether, the different surface chemistry and atomic architecture of active sites on CeO₂ exert modulation of redox homeostasis and the fate of NPCs.

Reduced microglia activation following metformin administration or microglia ablation is sufficient to prevent functional deficits in a mouse model of neonatal stroke

Background

Neonatal stroke is a devastating insult that can lead to life-long impairments. In response to hypoxic–ischaemic injury, there is loss of neurons and glia as well as a neuroinflammatory response mediated by resident immune cells, including microglia and astrocytes, which can exacerbate damage. Administration of the antidiabetic drug metformin has been shown to improve functional outcomes in preclinical models of brain injury and the cellular basis for metformin-mediated recovery is unknown. Given metformin’s demonstrated anti-inflammatory properties, we investigated its role in regulating the microglia activation and used a microglia ablation strategy to investigate the microglia-mediated outcomes in a mouse model of neonatal stroke.

Methods

Hypoxia-ischaemia (H-I) was performed on post-natal day 8. Metformin was administered for one week, starting one day after injury. Immunohistochemistry was used to examine the spatiotemporal response of microglia and astrocytes after hypoxia-ischaemia, with or without metformin treatment. To evaluate the effects of microglia depletion after hypoxia-ischaemia, we delivered Plexxikon 5622 for 1 or 2 weeks post-injury. The regional pattern of microglia and astrocyte depletion was assessed through immunohistochemistry. Motor behaviour was assessed with the righting reflex, hindlimb suspension, grip strength and cylinder tests.

Results

Herein, we revealed a spatiotemporally regulated response of microglia and astrocytes after hypoxia-ischaemia. Metformin treatment after hypoxia-ischaemia had no effect on microglia number and proliferation, but significantly reduced microglia activation in all regions examined, concomitant with improved behavioural outcomes in injured mice. Plexxikon 5622 treatment successfully ablated microglia, resulting in a > 90% depletion in microglia in the neonatal brain. Microglia rapidly repopulated upon treatment cessation of Plexxikon. Most interesting, microglia ablation was sufficient to reduce functional deficits after hypoxia-ischaemia, mimicking the effects of 1 week of metformin treatment post-injury.

Conclusion

These results highlight the importance of regulating the neuroinflammatory response after neonatal stroke to promote recovery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02487-x.

Microglia and putative macrophages of the subfornical organ: structural and functional features

The subfornical organ is an important regulator of water-salt metabolism and energy balance of the body, involved in the control of the cardiovascular system and immune regulation. The organ comprises several cell populations, among which microglia and macrophages remain uncharacterized. This study aimed at structural, cytochemical, and functional characterization of microglia and macrophages of the subfornical organ in rats. Brain specimens were collected from mature male Wistar rats (n = 8). Microglia and macrophages were revealed by immunostaining with poly- and monoclonal antibodies against calcium-binding protein Iba1 and lysosomal protein CD68; the slides were examined by light and confocal laser microscopy. The study provides a comprehensive morphological characterization of microglial cells and macrophages of the subfornical organ. We demonstrate that the majority of Iba1-expressing cells in this area of the brain are microglial cells, not macrophages. Pre-activated state of the subfornical organ microglia may reflect structural and functional features of this organ and specific functions of local microglia. Subependymal microglial cells, the processes of which penetrate into the third ventricle of the brain, constitute a distinct subpopulation among the Iba1-expressing cells of the subfornical organ. Apart from microglial elements, the subfornical organ contains few tissue macrophages with characteristic strong expression of CD68 accompanied by undetectable or weak expression of Iba1.

Role of Extracellular Vesicles in Glia-Neuron Intercellular Communication

Cross talk between glia and neurons is crucial for a variety of biological functions, ranging from nervous system development, axonal conduction, synaptic transmission, neural circuit maturation, to homeostasis maintenance. Extracellular vesicles (EVs), which were initially described as cellular debris and were devoid of biological function, are now recognized as key components in cell-cell communication and play a critical role in glia-neuron communication. EVs transport the proteins, lipids, and nucleic acid cargo in intercellular communication, which alters target cells structurally and functionally. A better understanding of the roles of EVs in glia-neuron communication, both in physiological and pathological conditions, can aid in the discovery of novel therapeutic targets and the development of new biomarkers. This review aims to demonstrate that different types of glia and neuronal cells secrete various types of EVs, resulting in specific functions in intercellular communications.

The Subventricular Zone in Glioblastoma: Genesis, Maintenance, and Modeling

Glioblastoma (GBM) is a malignant tumor with a median survival rate of 15-16 months with standard care; however, cases of successful treatment offer hope that an enhanced understanding of the pathology will improve the prognosis. The cell of origin in GBM remains controversial. Recent evidence has implicated stem cells as cells of origin in many cancers. Neural stem/precursor cells (NSCs) are being evaluated as potential initiators of GBM tumorigenesis. The NSCs in the subventricular zone (SVZ) have demonstrated similar molecular profiles and share several distinctive characteristics to proliferative glioblastoma stem cells (GSCs) in GBM. Genomic and proteomic studies comparing the SVZ and GBM support the hypothesis that the tumor cells and SVZ cells are related. Animal models corroborate this connection, demonstrating migratory patterns from the SVZ to the tumor. Along with laboratory and animal research, clinical studies have demonstrated improved progression-free survival in patients with GBM after radiation to the ipsilateral SVZ. Additionally, key genetic mutations in GBM for the most part carry regulatory roles in the SVZ as well. An exciting avenue towards SVZ modeling and determining its role in gliomagenesis in the human context is human brain organoids. Here we comprehensively discuss and review the role of the SVZ in GBM genesis, maintenance, and modeling.

Engineering Tissues of the Central Nervous System: Interfacing Conductive Biomaterials with Neural Stem/Progenitor Cells

Conductive biomaterials provide an important control for engineering neural tissues, where electrical stimulation can potentially direct neural stem/progenitor cell (NS/PC) maturation into functional neuronal networks. It is anticipated that stem cell-based therapies to repair damaged central nervous system (CNS) tissues and ex vivo, "tissue chip" models of the CNS and its pathologies will each benefit from the development of biocompatible, biodegradable, and conductive biomaterials. Here, technological advances in conductive biomaterials are reviewed over the past two decades that may facilitate the development of engineered tissues with integrated physiological and electrical functionalities. First, one briefly introduces NS/PCs of the CNS. Then, the significance of incorporating microenvironmental cues, to which NS/PCs are naturally programmed to respond, into biomaterial scaffolds is discussed with a focus on electrical cues. Next, practical design considerations for conductive biomaterials are discussed followed by a review of studies evaluating how conductive biomaterials can be engineered to control NS/PC behavior by mimicking specific functionalities in the CNS microenvironment. Finally, steps researchers can take to move NS/PC-interfacing, conductive materials closer to clinical translation are discussed.

Temporal Characterization of Microglia-Associated Pro- and Anti-Inflammatory Genes in a Neonatal Inflammation-Sensitized Hypoxic-Ischemic Brain Injury Model

Hypoxic-ischemic encephalopathy (HIE) mainly affects preterm and term newborns, leading to a high risk of brain damage. Coexisting infection/inflammation and birth asphyxia are key factors associated with intracerebral increase of proinflammatory cytokines linked to HIE. Microglia are key mediators of inflammation during perinatal brain injury, characterized by their phenotypic plasticity, which may facilitate their participation in both the progression and resolution of injury-induced inflammation. The purpose of this study was to investigate the temporal expression of genes associated with pro- and anti-inflammatory cytokines as well as the nucleotide-binding domain, leucine-rich repeat protein (NLRP-3) inflammasome from microglia cells. For this purpose, we used our established neonatal rat model of inflammation-sensitized hypoxic-ischemic (HI) brain injury in seven-day-old rats. We assessed gene expression profiles of 11 cytokines and for NLRP-3 using real-time PCR from sorted CD11b/c microglia of brain samples at different time points (3.5 h after LPS injection and 0, 5, 24, 48, and 72 hours post HI) following different treatments: vehicle, E. coli lipopolysaccharide (LPS), vehicle/HI, and LPS/HI. Our results showed that microglia are early key mediators of the inflammatory response and exacerbate the inflammatory response following HI, polarizing into a predominant proinflammatory M1 phenotype in the early hours post HI. The brains only exposed to HI showed a delay in the expression of proinflammatory cytokines. We also demonstrated that NLRP-3 plays a role in the inflammatory resolution with a high expression after HI insult. The combination of both, a preinfection/inflammation condition and hypoxia-ischemia, resulted in a higher proinflammatory cytokine storm, highlighting the significant contribution of acute inflammation sensitizing prior to a hypoxic insult on the severity of perinatal brain damage.

The Impact of Maternal Antioxidants on Prenatal Stress Effects on Offspring Neurobiology and Behavior

Prenatal stress is a neuropsychiatric risk factor, and effects may be mediated by prenatal oxidative stress. Cell types in the brain sensitive to oxidative stress-cortical microglia and cortical and hippocampal interneurons-may be altered by oxidative stress generated during prenatal stress and may be neurobiological substrates for altered behavior. Our objective was to determine the critical nature of oxidative stress in prenatal stress effects by manipulating prenatal antioxidants. CD1 mouse dams underwent restraint embryonic day 12 to 18 three times daily or no stress and received intraperitoneal injections before each stress period of vehicle, N-acetylcysteine (200 mg/kg daily), or astaxanthin (30 mg/kg before first daily stress, 10 mg/kg before second/third stresses). Adult male and female offspring behavior, microglia, and interneurons were assessed. Results supported the hypothesis that prenatal stress-induced oxidative stress affects microglia; microglia ramification increased after prenatal stress, and both antioxidants prevented these effects. In addition, N-acetylcysteine or astaxanthin was effective in preventing distinct male and female interneuron changes; decreased female medial frontal cortical parvalbumin interneurons was prevented by either antioxidant; increased male medial frontal cortical parvalbumin interneurons was prevented by N-acetylcysteine and decreased male hippocampal GAD67GFP+ cells prevented by astaxanthin. Prenatal stress-induced increased anxiety-like behavior and decreased sociability were not prevented by prenatal antioxidants. Sensorimotor gating deficits in males was partially prevented by prenatal astaxanthin. This study demonstrates the importance of oxidative stress for persistent impacts on offspring cortical microglia and interneurons, but did not link these changes with anxiety-like, social, and sensorimotor gating behaviors.

Hepatoma Derived Growth Factor Enhances Oligodendrocyte Genesis from Subventricular Zone Precursor Cells

Oligodendrocytes, the myelinating cells of the central nervous system (CNS), perform vital functions in neural protection and communication, as well as cognition. Enhanced production of oligodendrocytes has been identified as a therapeutic approach for neurodegenerative and neurodevelopmental disorders. In the postnatal brain, oligodendrocytes are generated from the neural stem and precursor cells (NPCs) in the subventricular zone (SVZ) and parenchymal oligodendrocyte precursor cells (OPCs). Here, we demonstrate exogenous Hepatoma Derived Growth Factor (HDGF) enhances oligodendrocyte genesis from murine postnatal SVZ NPCs in vitro without affecting neurogenesis or astrogliogenesis. We further show that this is achieved by increasing proliferation of both NPCs and OPCs, as well as OPC differentiation into oligodendrocytes. In vivo results demonstrate that intracerebroventricular infusion of HDGF leads to increased oligodendrocyte genesis from SVZ NPCs, as well as OPC proliferation. Our results demonstrate a novel role for HDGF in regulating SVZ precursor cell proliferation and oligodendrocyte differentiation.

RNA Profiling of Mouse Ependymal Cells after Spinal Cord Injury Identifies the Oncostatin Pathway as a Potential Key Regulator of Spinal Cord Stem Cell Fate

Ependymal cells reside in the adult spinal cord and display stem cell properties in vitro. They proliferate after spinal cord injury and produce neurons in lower vertebrates but predominantly astrocytes in mammals. The mechanisms underlying this glial-biased differentiation remain ill-defined. We addressed this issue by generating a molecular resource through RNA profiling of ependymal cells before and after injury. We found that these cells activate STAT3 and ERK/MAPK signaling post injury and downregulate cilia-associated genes and FOXJ1, a central transcription factor in ciliogenesis. Conversely, they upregulate 510 genes, seven of them more than 20-fold, namely Crym, Ecm1, Ifi202b, Nupr1, Rbp1, Thbs2 and Osmr—the receptor for oncostatin, a microglia-specific cytokine which too is strongly upregulated after injury. We studied the regulation and role of Osmr using neurospheres derived from the adult spinal cord. We found that oncostatin induced strong Osmr and p-STAT3 expression in these cells which is associated with reduction of proliferation and promotion of astrocytic versus oligodendrocytic differentiation. Microglial cells are apposed to ependymal cells in vivo and co-culture experiments showed that these cells upregulate Osmr in neurosphere cultures. Collectively, these results support the notion that microglial cells and Osmr/Oncostatin pathway may regulate the astrocytic fate of ependymal cells in spinal cord injury.

Environmental enrichment ameliorates high-fat diet induced olfactory deficit and decrease of parvalbumin neurons in the olfactory bulb in mice

Overweight induced by high-fat diet (HFD) represents one of the major health concerns in modern societies, which can cause lasting peripheral and central metabolic disorders in all age groups. Specifically, childhood obesity could lead to life-long impact on brain development and functioning. On the other hand, environmental enrichment (EE) has been demonstrated to be beneficial for learning and memory. Here, we explored the impact of high-fat diet on olfaction and organization of olfactory bulb cells in adolescent mice, and the effect of EE intervention thereon. Puberty mice (3-week-old) fed with HFD for 10 weeks exhibited poorer odor sensitivity and olfactory memory relative to controls consuming standard chows. The behavioral deficits were rescued in the HFD group with EE intervention. Neuroanatomically, parvalbumin (PV) interneurons in the olfactory bulb (OB) were reduced in the HFD-fed animals relative to control, while EE intervention also normalized this alteration. In contrast, cells expressing calbindin (CB), doublecortin (DCX) in the OB were not altered. Our findings suggest that PV interneurons may play a crucial role in mediating the HFD-induced olfactory deficit in adolescent mice, and can also serve a protective effect of EE against the functional deficit.

Adult Neural Stem Cells as Promising Targets in Psychiatric Disorders

The development of new therapies for psychiatric disorders is of utmost importance, given the enormous toll these disorders pose to society nowadays. This should be based on the identification of neural substrates and mechanisms that underlie disease etiopathophysiology. Adult neural stem cells (NSCs) have been emerging as a promising platform to counteract brain damage. In this perspective article, we put forth a detailed view of how NSCs operate in the adult brain and influence brain homeostasis, having profound implications at both behavioral and functional levels. We appraise evidence suggesting that adult NSCs play important roles in regulating several forms of brain plasticity, particularly emotional and cognitive flexibility, and that NSC dynamics are altered upon brain pathology. Furthermore, we discuss the potential therapeutic value of utilizing adult endogenous NSCs as vessels for regeneration, highlighting their importance as targets for the treatment of multiple mental illnesses, such as affective disorders, schizophrenia, and addiction. Finally, we speculate on strategies to surpass current challenges in neuropsychiatric disease modeling and brain repair.

Microglia as the Critical Regulators of Neuroprotection and Functional Recovery in Cerebral Ischemia

Microglial activation is considered as the critical pathogenic event in diverse central nervous system disorders including cerebral ischemia. Proinflammatory responses of activated microglia have been well reported in the ischemic brain and neuroinflammatory responses of activated microglia have been believed to be the potential therapeutic strategy. However, despite having proinflammatory roles, microglia can have significant anti-inflammatory roles and they are associated with the production of growth factors which are responsible for neuroprotection and recovery after ischemic injury. Microglia can directly promote neuroprotection by preventing ischemic infarct expansion and promoting functional outcomes. Indirectly, microglia are involved in promoting anti-inflammatory responses, neurogenesis, and angiogenesis in the ischemic brain which are crucial pathophysiological events for ischemic recovery. In fact, anti-inflammatory cytokines and growth factors produced by microglia can promote neuroprotection and attenuate neurobehavioral deficits. In addition, microglia regulate phagocytosis, axonal regeneration, blood-brain barrier protection, white matter integrity, and synaptic remodeling, which are essential for ischemic recovery. Microglia can also regulate crosstalk with neurons and other cell types to promote neuroprotection and ischemic recovery. This review mainly focuses on the roles of microglia in neuroprotection and recovery following ischemic injury. Furthermore, this review also sheds the light on the therapeutic potential of microglia in stroke patients.

Macrophages and Stem Cells-Two to Tango for Tissue Repair?

Macrophages (MCs) are present in all tissues, not only supporting homeostasis, but also playing an important role in organogenesis, post-injury regeneration, and diseases. They are a heterogeneous cell population due to their origin, tissue specificity, and polarization in response to aggression factors, depending on environmental cues. Thus, as pro-inflammatory M1 phagocytic MCs, they contribute to tissue damage and even fibrosis, but the anti-inflammatory M2 phenotype participates in repairing processes and wound healing through a molecular interplay with most cells in adult stem cell niches. In this review, we emphasize MC phenotypic heterogeneity in health and disease, highlighting their systemic and systematic contribution to tissue homeostasis and repair. Unraveling the intervention of both resident and migrated MCs on the behavior of stem cells and the regulation of the stem cell niche is crucial for opening new perspectives for novel therapeutic strategies in different diseases.

Microglia induce neurogenic protein expression in primary cortical cells by stimulating PI3K/AKT intracellular signaling in vitro

Emerging evidence suggests that microglia can support neurogenesis. Little is known about the mechanisms by which microglia regulate the cortical environment and stimulate cortical neurogenesis. We used an in vitro co-culture model system to investigate the hypothesis that microglia respond to soluble signals from cortical cells, particularly following mechanical injury, to alter the cortical environment and promote cortical cell proliferation, differentiation, and survival. Analyses of cortical cell proliferation, cell death, neurogenic protein expression, and intracellular signaling were performed on uninjured and injured cortical cells in co-culture with microglial cell lines. Microglia soluble cues enhanced cortical cell viability and proliferation cortical cells. Co-culture of injured cortical cells with microglia significantly reduced cell death of cortical cells. Microglial co-culture significantly increased Nestin + and α-internexin + cortical cells. Multiplex ELISA and RT-PCR showed decreased pro-inflammatory cytokine production by microglia co-cultured with injured cortical cells. Inhibition of AKT phosphorylation in cortical cells blocked microglial-enhanced cortical cell viability and expression of neurogenic markers in vitro. This in vitro model system allows for assessment of the effect of microglial-derived soluble signals on cortical cell viability, proliferation, and stages of differentiation during homeostasis or following mechanical injury. These data suggest that microglia cells can downregulate inflammatory cytokine production following activation by mechanical injury to enhance proliferation of new cells capable of neurogenesis via activation of AKT intracellular signaling. Increasing our understanding of the mechanisms that drive microglial-enhanced cortical neurogenesis during homeostasis and following injury in vitro will provide useful information for future primary cell and in vivo studies.

Brain Disorders and Chemical Pollutants: A Gap Junction Link?

The incidence of brain pathologies has increased during last decades. Better diagnosis (autism spectrum disorders) and longer life expectancy (Parkinson's disease, Alzheimer's disease) partly explain this increase, while emerging data suggest pollutant exposures as a possible but still underestimated cause of major brain disorders. Taking into account that the brain parenchyma is rich in gap junctions and that most pollutants inhibit their function; brain disorders might be the consequence of gap-junctional alterations due to long-term exposures to pollutants. In this article, this hypothesis is addressed through three complementary aspects: (1) the gap-junctional organization and connexin expression in brain parenchyma and their function; (2) the effect of major pollutants (pesticides, bisphenol A, phthalates, heavy metals, airborne particles, etc.) on gap-junctional and connexin functions; (3) a description of the major brain disorders categorized as neurodevelopmental (autism spectrum disorders, attention deficit hyperactivity disorders, epilepsy), neurobehavioral (migraines, major depressive disorders), neurodegenerative (Parkinson's and Alzheimer's diseases) and cancers (glioma), in which both connexin dysfunction and pollutant involvement have been described. Based on these different aspects, the possible involvement of pollutant-inhibited gap junctions in brain disorders is discussed for prenatal and postnatal exposures.

Leptin enhances adult neurogenesis and reduces pathological features in a transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most common dementia worldwide and is characterized by the presence of senile plaques by amyloid-beta (Aβ) and neurofibrillary tangles of hyperphosphorylated Tau protein. These changes lead to progressive neuronal degeneration and dysfunction, resulting in severe brain atrophy and cognitive deficits. With the discovery that neurogenesis persists in the adult mammalian brain, including brain regions affected by AD, studies of the use of neural stem cells (NSCs) for the treatment of neurodegenerative diseases to repair or prevent neuronal cell loss have increased. Here we demonstrate that leptin administration increases the neurogenic process in the dentate gyrus of the hippocampus as well as in the subventricular zone of lateral ventricles of adult and aged mice. Chronic treatment with leptin increased NSCs proliferation with significant effects on proliferation and differentiation of newborn cells. The expression of the long form of the leptin receptor, LepRb, was detected in the neurogenic niches by reverse qPCR and immunohistochemistry. Moreover, leptin modulated astrogliosis, microglial cell number and the formation of senile plaques. Additionally, leptin led to attenuation of Aβ-induced neurodegeneration and superoxide anion production as revealed by Fluoro-Jade B and dihydroethidium staining. Our study contributes to the understanding of the effects of leptin in the brain that may lead to the development of new therapies to treat Alzheimer's disease.

To Become or Not to Become Tumorigenic: Subventricular Zone Versus Hippocampal Neural Stem Cells

Neural stem cells (NSCs) persist in the adult mammalian brain in two neurogenic regions: the subventricular zone lining the lateral ventricles and the dentate gyrus of the hippocampus. Compelling evidence suggests that NSCs of the subventricular zone could be the cell type of origin of glioblastoma, the most devastating brain tumor. Studies in glioblastoma patients revealed that NSCs of the tumor-free subventricular zone, harbor cancer-driver mutations that were found in the tumor cells but were not present in normal cortical tissue. Endogenous mutagenesis can also take place in hippocampal NSCs. However, to date, no conclusive studies have linked hippocampal mutations with glioblastoma development. In addition, glioblastoma cells often invade or are closely located to the subventricular zone, whereas they do not tend to infiltrate into the hippocampus. In this review we will analyze possible causes by which subventricular zone NSCs might be more susceptible to malignant transformation than their hippocampal counterparts. Cellular and molecular differences between the two neurogenic niches, as well as genotypic and phenotypic characteristics of their respective NSCs will be discussed regarding why the cell type originating glioblastoma brain tumors has been linked mainly to subventricular zone, but not to hippocampal NSCs.

Neural Stem Cell Niche and Adult Neurogenesis

Adult neurogenesis is a process that generates new and functional neurons from neural stem cells (NSCs) in a specialized neurogenic niche throughout life. Misregulated neurogenesis is detrimental to normal brain functions. To ensure proper neurogenesis, the niche cells must respond to extrinsic cues while fulfilling the intrinsic requirements of the neurogenic program and adapting their roles accordingly to influence NSC behavior. Understanding how the neurogenic niche executes its functions may guide strategies to maintain its integrative process and provide a permissive milieu for neurogenesis. In this review, we summarize the recent discoveries of interactive regulation of NSCs and neurogenesis by neurogenic niche and its implications in functional integrity of adult brain and neurological disorders.

Characterization of gene expression changes in human neural stem cells and endothelial cells modeling a neurovascular microenvironment

Angiogenesis-mediated neovascularization correlates with recovery after intracerebral implantation of neural stem cells (NSCs) in stroke. To elucidate NSCs' mechanism of action, it is essential to understand how these interact with the brain's vasculature after implantation. Using an all-human endothelial cell (EC, D3 cell line) and NSC (STROC05 and CTXOE03) co-culture model, fluorescently activated cell sorting (FACS) was used to isolate each cell type for a comparison of gene expression between monocultures of undifferentiated proliferating and differentiated non-proliferating cells. Gene expression for angiogenic factors (vascular endothelial growth factor, platelet derived growth factor, angiopoietin), as well as cell survival (brain derived neurotrophic factor, fibroblast growth factor) and migration (stromal cell-derived factor-1a) were measured and contrasted with the corresponding receptors on each cell type. The cellular source of extracellular matrix defining the basement membrane (vitronectin, fibronectin, laminin, collagen I and IV) and neuropil (hyaluronic acid, aggrecan, neurocan, thrombospondin, nidogen and brain associated link protein-1) was evaluated for NSCs and ECs. Co-culturing dramatically changed the expression profiles of each cell type in comparison to undifferentiated, but also differentiated cells. These results indicate that monocultures provide a poor model to investigate the cellular signaling involved in a tissue repair response. Co-cultures of NSCs and ECs forming vasculature-like structures (VLS) provide a more complex model to investigate NSC-induced neovascularization. These in vitro studies are essential to tease out individual cell signaling in NSCs and ECs to develop a mechanistic understanding of the efficacy of NSCs as a therapeutic for stroke.

Therapeutic Plasticity of Neural Stem Cells

Neural stem cells (NSCs) have garnered significant scientific and commercial interest in the last 15 years. Given their plasticity, defined as the ability to develop into different phenotypes inside and outside of the nervous system, with a capacity of almost unlimited self-renewal, of releasing trophic and immunomodulatory factors, and of exploiting temporal and spatial dynamics, NSCs have been proposed for (i) neurotoxicity testing; (ii) cellular therapies to treat CNS diseases; (iii) neural tissue engineering and repair; (iv) drug target validation and testing; (v) personalized medicine. Moreover, given the growing interest in developing cell-based therapies to target neurodegenerative diseases, recent progress in developing NSCs from human-induced pluripotent stem cells has produced an analog of endogenous NSCs. Herein, we will review the current understanding on emerging conceptual and technological topics in the neural stem cell field, such as deep characterization of the human compartment, single-cell spatial-temporal dynamics, reprogramming from somatic cells, and NSC manipulation and monitoring. Together, these aspects contribute to further disentangling NSC plasticity to better exploit the potential of those cells, which, in the future, might offer new strategies for brain therapies.

Dynamic Modelling of Interactions between Microglia and Endogenous Neural Stem Cells in the Brain during a Stroke

In this paper, we study the interactions between microglia and neural stem cells and the impact of these interactions on the brain cells during a stroke. Microglia cells, neural stem cells, the damage on brain cells from the stroke and the impacts these interactions have on living brain cells are considered in the design of mathematical models. The models consist of ordinary differential equations describing the effects of microglia on brain cells and the interactions between microglia and neural stem cells in the case of a stroke. Variables considered include: resident microglia, classically activated microglia, alternatively activated microglia, neural stem cells, tissue damage on cells in the brain, and the impacts these interactions have on living brain cells. The first model describes what happens in the brain at the stroke onset during the first three days without the generation of any neural stem cells. The second model studies the dynamic effect of microglia and neural stem cells on the brain cells following the generation of neural stem cells and potential recovery after this stage. We look at the stability and the instability of the models which are both studied analytically. The results show that the immune cells can help the brain by cleaning dead cells and stimulating the generation of neural stem cells; however, excessive activation may cause damage and affect the injured region. Microglia have beneficial and harmful functions after ischemic stroke. The microglia stimulate neural stem cells to generate new cells that substitute dead cells during the recovery stage but sometimes the endogenous neural stem cells are highly sensitive to inflammatory in the brain.

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.

Neural Stem Cells of the Subventricular Zone as the Origin of Human Glioblastoma Stem Cells. Therapeutic Implications

Human glioblastoma is the most aggressive type of primary malignant brain tumors. Standard treatment includes surgical resection followed by radiation and chemotherapy but it only provides short-term benefits and the prognosis of these brain tumors is still very poor. Glioblastomas contain a population of glioma stem cells (GSCs), with self-renewal ability, which are partly responsible for the tumor resistance to therapy and for the tumor recurrence after treatment. The human adult subventricular zone contains astrocyte-like neural stem cells (NSCs) that are probably reminiscent of the radial glia present in embryonic brain development. There are numerous molecules involved in the biology of subventricular zone NSCs that are also instrumental in glioblastoma development. These include cytoskeletal proteins, telomerase, tumor suppressor proteins, transcription factors, and growth factors. Interestingly, genes encoding these molecules are frequently mutated in glioblastoma cells. Indeed, it has been recently shown that NSCs in the subventricular zone are a potential cell of origin that contains the driver mutations of human glioblastoma. In this review we will describe common features between GSCs and subventricular zone NSCs, and we will discuss the relevance of this important finding in terms of possible future therapeutic strategies.

Cellular stress mechanisms of prenatal maternal stress: Heat shock factors and oxidative stress

Development of the brain prenatally is affected by maternal experience and exposure. Prenatal maternal psychological stress changes brain development and results in increased risk for neuropsychiatric disorders. In this review, multiple levels of prenatal stress mechanisms (offspring brain, placenta, and maternal physiology) are discussed and their intersection with cellular stress mechanisms explicated. Heat shock factors and oxidative stress are closely related to each other and converge with the inflammation, hormones, and cellular development that have been more deeply explored as the basis of prenatal stress risk. Increasing evidence implicates cellular stress mechanisms in neuropsychiatric disorders associated with prenatal stress including affective disorders, schizophrenia, and child-onset psychiatric disorders. Heat shock factors and oxidative stress also have links with the mechanisms involved in other kinds of prenatal stress including external exposures such as environmental toxicants and internal disruptions such as preeclampsia. Integrative understanding of developmental neurobiology with these cellular and physiological mechanisms is necessary to reduce risks and promote healthy brain development.