The chemokine SDF1 regulates migration of dentate granule cells

Research Progress of CXCR4-Targeting Radioligands for Oncologic Imaging

C-X-C motif chemokine receptor 4 (CXCR4) plays a key role in various physiological functions, such as immune processes and disease development, and can influence angiogenesis, proliferation, and distant metastasis in tumors. Recently, several radioligands, including peptides, small molecules, and nanoclusters, have been developed to target CXCR4 for diagnostic purposes, thereby providing new diagnostic strategies based on CXCR4. Herein, we focus on the recent research progress of CXCR4-targeting radioligands for tumor diagnosis. We discuss their application in the diagnosis of hematological tumors, such as lymphomas, multiple myelomas, chronic lymphocytic leukemias, and myeloproliferative tumors, as well as nonhematological tumors, including tumors of the esophagus, breast, and central nervous system. Additionally, we explored the theranostic applications of CXCR4-targeting radioligands in tumors. Targeting CXCR4 using nuclear medicine shows promise as a method for tumor diagnosis, and further research is warranted to enhance its clinical applicability.

Abnormal chromatin remodeling caused by ARID1A deletion leads to malformation of the dentate gyrus

ARID1A, an SWI/SNF chromatin-remodeling gene, is commonly mutated in cancer and hypothesized to be a tumor suppressor. Recently, loss-of-function of ARID1A gene has been shown to cause intellectual disability. Here we generate Arid1a conditional knockout mice and investigate Arid1a function in the hippocampus. Disruption of Arid1a in mouse forebrain significantly decreases neural stem/progenitor cells (NSPCs) proliferation and differentiation to neurons within the dentate gyrus (DG), increasing perinatal and postnatal apoptosis, leading to reduced hippocampus size. Moreover, we perform single-cell RNA sequencing (scRNA-seq) to investigate cellular heterogeneity and reveal that Arid1a is necessary for the maintenance of the DG progenitor pool and survival of post-mitotic neurons. Transcriptome and ChIP-seq analysis data demonstrate that ARID1A specifically regulates Prox1 by altering the levels of histone modifications. Overexpression of downstream target Prox1 can rescue proliferation and differentiation defects of NSPCs caused by Arid1a deletion. Overall, our results demonstrate a critical role for Arid1a in the development of the hippocampus and may also provide insight into the genetic basis of intellectual disabilities such as Coffin-Siris syndrome, which is caused by germ-line mutations or microduplication of Arid1a.

CXCR4 knockout induces neuropathological changes in the MPTP-lesioned model of Parkinson's disease

C-X-C chemokine receptor type 4 (CXCR4) is highly expressed in Parkinson's disease (PD) mice's brains and is related to astrocyte signaling and microglial activation. This makes CXCR4 related to neuroinflammation and also makes CXCR4 considered to be the PD development mechanism and possible therapeutic targets. Therefore, it is worth studying the effect of CXCR4 on neuropathological changes and its potential therapeutic value for PD. This study aimed to investigate the effect of CXCR4 knockout on neuropathological changes in the mouse model of PD and its mechanism. In this study, CXCR4-WT and CXCR4^+/- C57BL mice were used to make Parkinson's model. Behavioral experiments, dopaminergic neuron markers, neuroinflammation, and blood-brain barrier damage were detected to verify the effect of CXCR4 knockout on neuropathological changes. CXCR4 knockout improved the behavioral results and tyrosine hydroxylase (TH) expression of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned mice. In the substantia nigra (SN) area of the brain of PD mouse model, the number of Iba1-positive (p = 0.0004) and GFAP-positive cells (p = 0.0349) was significantly lower in CXCR4 knockout group than CXCR4-WT group. CXCR4 knockout reduced MPTP-induced infiltration of peripheral immune cells and the expression of pro-inflammatory cytokines. CXCR4 knockout also protected blood-brain barrier (BBB) from MPTP-induced damage. In conclusion, CXCR4 knockout inhibits the degeneration of dopamine neurons, microglial and astrocyte activation, neuroinflammation, and BBB damages in the MPTP-lesioned PD mice.

Neutrophil modulation of behavior and cognition in health and disease: The unexplored role of an innate immune cell

Behavior and cognition are multifaceted processes influenced by genetics, synaptic plasticity, and neuronal connectivity. Recent reports have demonstrated that peripheral inflammation and peripheral immune cells play important roles in the preservation and deterioration of behavior/cognition under various conditions. Indeed, several studies show that the activity of peripheral immune cells can be critical for normal cognitive function. Neutrophils are the most abundant immune cells in the mammalian system. Their activation is critical to the initiation of the inflammatory process and critical for wound healing. Neutrophils are the first cells to be activated and recruited to the central nervous system in both injury and disease. However, our understanding of the role these cells play in behavior and cognition is limited. The present review will summarize what is currently known about the effect the activation of these cells has on various behaviors and cognitive processes.

BKM120 alters the migration of doublecortin-positive cells in the dentate gyrus of mice

BKM120 is an inhibitor of class I phosphoinositide 3-kinases and its anti-cancer effects have been demonstrated in various solid cancer models. BKM120 is highly brain permeable and has been reported to induce mood disturbances in clinical trials. Therefore, we examined whether BKM120 produces anxiety- and depression-like behaviors in mice, as with patients receiving BKM120 in clinical trials. In this study, repeated BKM120 treatment (2.0 or 5.0mg/kg, i.p., five times at 12-h interval) significantly induced anxiety- and depression-like behaviors in mice. Although abnormal changes in hippocampal neurogenesis have been suggested to, at least in part, associated with the pathogenesis of depression and anxiety, BKM120 did not affect the incorporation of 5-bromo-2'-deoxyuridine or the expression of doublecortin (DCX); however, it significantly enhanced the radial migration of DCX-positive cells in the dentate gyrus. BKM120-induced changes in migration were not accompanied by obvious neuronal damage in the hippocampus. Importantly, BKM120-induced anxiety- and depression-like behaviors were positively correlated with the extent of DCX-positive cell migration. Concomitantly, p-Akt expression was significantly decreased in the dentate gyrus. Moreover, the expression of p-c-Jun N-terminal kinase (JNK), p-DCX, and Ras homolog family member A (RhoA)-GTP decreased significantly, particularly in aberrantly migrated DCX-positive cells. Together, the results suggest that repeated BKM120 treatment enhances the radial migration of DCX-positive cells and induces anxiety- and depression-like behaviors by regulating the activity of Akt, JNK, DCX, and RhoA in the dentate gyrus. It also suggests that the altered migration of adult-born neurons in the dentate gyrus plays a role in mood disturbances.

Co-receptor signaling in the pathogenesis of neuroHIV

The HIV co-receptors, CCR5 and CXCR4, are necessary for HIV entry into target cells, interacting with the HIV envelope protein, gp120, to initiate several signaling cascades thought to be important to the entry process. Co-receptor signaling may also promote the development of neuroHIV by contributing to both persistent neuroinflammation and indirect neurotoxicity. But despite the critical importance of CXCR4 and CCR5 signaling to HIV pathogenesis, there is only one therapeutic (the CCR5 inhibitor Maraviroc) that targets these receptors. Moreover, our understanding of co-receptor signaling in the specific context of neuroHIV is relatively poor. Research into co-receptor signaling has largely stalled in the past decade, possibly owing to the complexity of the signaling cascades and functions mediated by these receptors. Examining the many signaling pathways triggered by co-receptor activation has been challenging due to the lack of specific molecular tools targeting many of the proteins involved in these pathways and the wide array of model systems used across these experiments. Studies examining the impact of co-receptor signaling on HIV neuropathogenesis often show activation of multiple overlapping pathways by similar stimuli, leading to contradictory data on the effects of co-receptor activation. To address this, we will broadly review HIV infection and neuropathogenesis, examine different co-receptor mediated signaling pathways and functions, then discuss the HIV mediated signaling and the differences between activation induced by HIV and cognate ligands. We will assess the specific effects of co-receptor activation on neuropathogenesis, focusing on neuroinflammation. We will also explore how the use of substances of abuse, which are highly prevalent in people living with HIV, can exacerbate the neuropathogenic effects of co-receptor signaling. Finally, we will discuss the current state of therapeutics targeting co-receptors, highlighting challenges the field has faced and areas in which research into co-receptor signaling would yield the most therapeutic benefit in the context of HIV infection. This discussion will provide a comprehensive overview of what is known and what remains to be explored in regard to co-receptor signaling and HIV infection, and will emphasize the potential value of HIV co-receptors as a target for future therapeutic development.

Imaging Voltage in Complete Neuronal Networks Within Patterned Microislands Reveals Preferential Wiring of Excitatory Hippocampal Neurons

Voltage imaging with fluorescent dyes affords the opportunity to map neuronal activity in both time and space. One limitation to imaging is the inability to image complete neuronal networks: some fraction of cells remains outside of the observation window. Here, we combine voltage imaging, post hoc immunocytochemistry, and patterned microisland hippocampal culture to provide imaging of complete neuronal ensembles. The patterned microislands completely fill the field of view of our high-speed (500 Hz) camera, enabling reconstruction of the spiking patterns of every single neuron in the network. Cultures raised on microislands are similar to neurons grown on coverslips, with parallel developmental trajectories and composition of inhibitory and excitatory cell types (CA1, CA3, and dentate granule cells, or DGC). We calculate the likelihood that action potential firing in one neuron triggers action potential firing in a downstream neuron in a spontaneously active network to construct a functional connection map of these neuronal ensembles. Importantly, this functional map indicates preferential connectivity between DGC and CA3 neurons and between CA3 and CA1 neurons, mimicking the neuronal circuitry of the intact hippocampus. We envision that patterned microislands, in combination with voltage imaging and methods to classify cell types, will be a powerful method for exploring neuronal function in both healthy and disease states. Additionally, because the entire neuronal network is sampled simultaneously, this strategy has the power to go further, revealing all functional connections between all cell types.

NRSF deficiency leads to abnormal postnatal development of dentate gyrus and impairment of progenitors in subgranular zone of hippocampus

Neuron-restrictive silencing factor (NRSF) is a zinc-finger transcription factor that regulates expression of a diverse set of genes. However, NRSF function in brain development still remains elusive. In the present study, we generated NRSF-conditional knockout (NRSF-cKO) mice by hGFAP-Cre/loxp system to study the effect of NRSF deficiency on brain development. Results showed that NRSF conditional knockout caused a smaller hippocampus and a thinner granule cell layer (GCL) in mice. Moreover, the reduction and disarrangement of GFAP+ cells in subgranular zone (SGZ) of NRSF-cKO mice was accompanied with the decreased number of premature neurons, neural stem cells (NSCs) and neural progenitor cells (NPCs), as well as compromising the majority of mitotically active cells. The analysis of postnatal development of hippocampus indicated the existence of an abnormality at postnatal day (P) 8, rather than at P1, in NRSF-cKO mice, although the densities of Ki67+ cells with mitotic ability in dentate gyrus were relatively unaffected at P1 and P8. Meanwhile, NRSF deficiency led to abnormal organization of SGZ at P8 during postnatal development. RNA-Seq analysis revealed 79 deregulated genes in hippocampus of NRSF-cKO mice at P8, which were involved in p53 signal transduction, neuron migration and negative regulation of cell proliferation, etc. The deregulation of p53 pathway in NRSF-cKO mice at P1 and P8 was evidenced, of which p21/Cdkn1a was accumulated in a portion of NSCs and NPCs in hippocampus during postnatal development. Together, these results, for the first time, revealed that NRSF could significantly influence the postnatal development of hippocampus, especially the formation of SGZ.

Transcriptome profiling of human pluripotent stem cell-derived cerebellar organoids reveals faster commitment under dynamic conditions

Human-induced pluripotent stem cells (iPSCs) have great potential for disease modeling. However, generating iPSC-derived models to study brain diseases remains a challenge. In particular, the ability to recapitulate cerebellar development in vitro is still limited. We presented a reproducible and scalable production of cerebellar organoids by using the novel single-use Vertical-Wheel bioreactors, in which functional cerebellar neurons were obtained. Here, we evaluate the global gene expression profiles by RNA sequencing (RNA-seq) across cerebellar differentiation, demonstrating a faster cerebellar commitment in this novel dynamic differentiation protocol. Furthermore, transcriptomic profiles suggest a significant enrichment of extracellular matrix (ECM) in dynamic-derived cerebellar organoids, which can better mimic the neural microenvironment and support a consistent neuronal network. Thus, an efficient generation of organoids with cerebellar identity was achieved for the first time in a continuous process using a dynamic system without the need of organoids encapsulation in ECM-based hydrogels, allowing the possibility of large-scale production and application in high-throughput processes. The presence of factors that favors angiogenesis onset was also detected in dynamic conditions, which can enhance functional maturation of cerebellar organoids. We anticipate that large-scale production of cerebellar organoids may help developing models for drug screening, toxicological tests, and studying pathological pathways involved in cerebellar degeneration.

An early Sox2-dependent gene expression programme required for hippocampal dentate gyrus development

The hippocampus is a brain area central for cognition. Mutations in the human SOX2 transcription factor cause neurodevelopmental defects, leading to intellectual disability and seizures, together with hippocampal dysplasia. We generated an allelic series of Sox2 conditional mutations in mouse, deleting Sox2 at different developmental stages. Late Sox2 deletion (from E11.5, via Nestin-Cre) affects only postnatal hippocampal development; earlier deletion (from E10.5, Emx1-Cre) significantly reduces the dentate gyrus (DG), and the earliest deletion (from E9.5, FoxG1-Cre) causes drastic abnormalities, with almost complete absence of the DG. We identify a set of functionally interconnected genes (Gli3, Wnt3a, Cxcr4, p73 and Tbr2), known to play essential roles in hippocampal embryogenesis, which are downregulated in early Sox2 mutants, and (Gli3 and Cxcr4) directly controlled by SOX2; their downregulation provides plausible molecular mechanisms contributing to the defect. Electrophysiological studies of the Emx1-Cre mouse model reveal altered excitatory transmission in CA1 and CA3 regions.

Drebrin regulates cytoskeleton dynamics in migrating neurons through interaction with CXCR4

Stromal cell-derived factor-1 (SDF-1) and chemokine receptor type 4 (CXCR4) are regulators of neuronal migration (e.g., GnRH neurons, cortical neurons, and hippocampal granule cells). However, how SDF-1/CXCR4 alters cytoskeletal components remains unclear. Developmentally regulated brain protein (drebrin) stabilizes actin polymerization, interacts with microtubule plus ends, and has been proposed to directly interact with CXCR4 in T cells. The current study examined, in mice, whether CXCR4 under SDF-1 stimulation interacts with drebrin to facilitate neuronal migration. Bioinformatic prediction of protein-protein interaction highlighted binding sites between drebrin and crystallized CXCR4. In migrating GnRH neurons, drebrin, CXCR4, and the microtubule plus-end binding protein EB1 were localized close to the cell membrane. Coimmunoprecipitation (co-IP) confirmed a direct interaction between drebrin and CXCR4 using wild-type E14.5 whole head and a GnRH cell line. Analysis of drebrin knockout (DBN1 KO) mice showed delayed migration of GnRH cells into the brain. A decrease in hippocampal granule cells was also detected, and co-IP confirmed a direct interaction between drebrin and CXCR4 in PN4 hippocampi. Migration assays on primary neurons established that inhibiting drebrin (either pharmacologically or using cells from DBN1 KO mice) prevented the effects of SDF-1 on neuronal movement. Bioinformatic prediction then identified binding sites between drebrin and the microtubule plus end protein, EB1, and super-resolution microscopy revealed decreased EB1 and drebrin coexpression after drebrin inhibition. Together, these data show a mechanism by which a chemokine, via a membrane receptor, communicates with the intracellular cytoskeleton in migrating neurons during central nervous system development.

Relevance of the CXCR4/CXCR7-CXCL12 axis and its effect in pathophysiological conditions

The impact of the C-X-C receptor (CXCR) 7 and its close co-player CXCR4 in different physiological and pathophysiological processes has been extensively investigated within the last decades. Following activation by their shared ligand C-X-C ligand (CXCL) 12, both chemokine receptors can induce various routes of cell signaling and/or scavenge CXCL12 from the extracellular environment. This contributes to organ development and maintenance of homeostasis. Alterations of the CXCR4/CXCR7-CXCL12 axis have been detected in diseases such as cancer, central nervous system and cardiac disorders, and autoimmune diseases. These alterations include changes of the expression pattern, distribution, or downstream effects. The progression of the diseases can be regulated in preclinical models by the use of various modulators suggesting that this axis serves as a promising therapeutic target. It is therefore of great interest to investigate CXCR4/CXCR7/CXCL12 modulators in clinical development, with several CXCR4 and CXCL12 modulators such as plerixafor, ulocuplumab, balixafortide, and olaptesed pegol having already reached this stage. An overview is presented of the most important diseases whose outcomes can be positively or negatively regulated by the CXCR4/CXCR7-CXCL12 axis and summarizes preclinical and clinical data of modulators of that axis. Contrary to CXCR4 and CXCL12 modulators, CXCR7 modulators have, thus far, not been extensively studied. Therefore, more (pre)clinical investigations are needed.

The Role of Immune Factors in Shaping Fetal Neurodevelopment

Fetal neurodevelopment in utero is profoundly shaped by both systemic maternal immunity and local processes at the maternal-fetal interface. Immune pathways are a critical participant in the normal physiology of pregnancy and perturbations of maternal immunity due to infections during this period have been increasingly linked to a diverse array of poor neurological outcomes, including diseases that manifest much later in postnatal life. While experimental models of maternal immune activation (MIA) have provided groundbreaking characterizations of the maternal pathways underlying pathogenesis, less commonly examined are the immune factors that serve pathogen-independent developmental functions in the embryo and fetus. In this review, we explore what is known about the in vivo role of immune factors in fetal neurodevelopment during normal pregnancy and provide an overview of how MIA perturbs the proper orchestration of this sequence of events. Finally, we discuss how the dysregulation of immune factors may contribute to the manifestation of a variety of neurological disorders.

Natural and forced neurogenesis in the adult brain: Mechanisms and their possible application to treat neurological disorders

Neural stem cells (NSCs) in the adult hippocampus generate new neurons via a process referred to as neurogenesis, supporting cognitive functions. Since altered neurogenesis has been reportedly associated with several diseases such as epilepsy, the molecular basis of NSC activity is an important focus in the study of neurogenesis. Furthermore, facilitation of neurogenesis in the injured brain would be an ideal approach to replenish lost neurons for damage recovery. However, natural neurogenesis by endogenous NSCs in the adult brain is insufficient for complete recovery after severe injury. Recent advances in understanding forced neurogenesis from brain-resident non-neuronal cells by direct reprogramming and clearing hurdles to achieve it have improved the ability to replace damaged neurons in the brain. In this review, we describe molecular mechanisms underlying natural and forced neurogenesis, and discuss future directions for treatments of diseases in the central nervous system.

QTY code designed thermostable and water-soluble chimeric chemokine receptors with tunable ligand affinity

Chemokine receptors are of great interest as they play a critical role in many immunological and pathological processes. The ability to study chemokine receptors in aqueous solution without detergent would be significant because natural receptors require detergents to become soluble. We previously reported using the QTY code to design detergent-free chemokine receptors. We here report the design of 2 detergent-free chimeric chemokine receptors that were experimentally unattainable in detergent solution. We designed chimeric receptors by switching the N terminus and 3 extracellular (EC) loops between different receptors. Specifically, we replaced the N terminus and 3 EC loops of CCR5^QTY with the N terminus and 3 EC loops of CXCR4. The ligand for CXCR4; namely CXCL12, binds to the chimeric receptor CCR5^QTY (7TM)-CXCR4 (N terminus+3 EC loops), but with lower affinity compared to CXCR4; the CCL5 ligand of CCR5 binds the chimeric receptor with ∼20× lower affinity. The chimeric design helps to elucidate the mechanism of native receptor-ligand interaction. We also show that all detergent-free QTY-designed chemokine receptors, expressed in Escherichia coli, bind to their respective chemokines with affinities in the nanomolar (nM) range, similar to the affinities of native receptors and SF9-produced QTY variants. These QTY-designed receptors exhibit remarkable thermostability in the presence of arginine and retain ligand-binding activity after heat treatment at 60 °C for 4 h and 24 h, and at 100 °C for 10 min. Our design approach enables affordable scale-up production of detergent-free QTY variant chemokine receptors with tunable functionality for various uses.

An Agonist of the CXCR4 Receptor Strongly Promotes Regeneration of Degenerated Motor Axon Terminals

The activation of the G-protein coupled receptor CXCR4 by its ligand CXCL12α is involved in a large variety of physiological and pathological processes, including the growth of B cells precursors and of motor axons, autoimmune diseases, stem cell migration, inflammation, and several neurodegenerative conditions. Recently, we demonstrated that CXCL12α potently stimulates the functional recovery of damaged neuromuscular junctions via interaction with CXCR4. This result prompted us to test the neuroregeneration activity of small molecules acting as CXCR4 agonists, endowed with better pharmacokinetics with respect to the natural ligand. We focused on NUCC-390, recently shown to activate CXCR4 in a cellular system. We designed a novel and convenient chemical synthesis of NUCC-390, which is reported here. NUCC-390 was tested for its capability to induce the regeneration of motor axon terminals completely degenerated by the presynaptic neurotoxin α-Latrotoxin. NUCC-390 was found to strongly promote the functional recovery of the neuromuscular junction, as assayed by electrophysiology and imaging. This action is CXCR4 dependent, as it is completely prevented by AMD3100, a well-characterized CXCR4 antagonist. These data make NUCC-390 a strong candidate to be tested in human therapy to promote nerve recovery of function after different forms of neurodegeneration.

Chemokines: Key Molecules that Orchestrate Communication among Neurons, Microglia and Astrocytes to Preserve Brain Function

In the CNS, chemokines and chemokine receptors are involved in pleiotropic physiological and pathological activities. Several evidences demonstrated that chemokine signaling in the CNS plays key homeostatic roles and, being expressed on neurons, glia and endothelial cells, chemokines mediate the bidirectional cross-talk among parenchymal cells. An efficient communication between neurons and glia is crucial to establish and maintain a healthy brain environment which ensures normal functionality. Glial cells behave as active sensors of environmental changes induced by neuronal activity or detrimental insults, supporting and exerting neuroprotective activities. In this review we summarize the evidence that chemokines (CXCL12, CX3CL1, CXCL16 and CCL2) modulate neuroprotective processes upon different noxious stimuli and participate to orchestrate neurons-microglia-astrocytes action to preserve and limit brain damage. This article is part of a Special Issue entitled: Honoring Ricardo Miledi - outstanding neuroscientist of XX-XXI centuries.

PlexinA2 Forward Signaling through Rap1 GTPases Regulates Dentate Gyrus Development and Schizophrenia-like Behaviors

Dentate gyrus (DG) development requires specification of granule cell (GC) progenitors in the hippocampal neuroepithelium, as well as their proliferation and migration into the primordial DG. We identify the Plexin family members Plxna2 and Plxna4 as important regulators of DG development. Distribution of immature GCs is regulated by Sema5A signaling through PlxnA2 and requires a functional PlxnA2 GTPase-activating protein (GAP) domain and Rap1 small GTPases. In adult Plxna2^−/− but not Plxna2-GAP-deficient mice, the dentate GC layer is severely malformed, neurogenesis is compromised, and mossy fibers form aberrant synaptic boutons within CA3. Behavioral studies with Plxna2^−/− mice revealed deficits in associative learning, sociability, and sensorimotor gating—traits commonly observed in neuropsychiatric disorder. Remarkably, while morphological defects are minimal in Plxna2-GAP-deficient brains, defects in fear memory and sensorimotor gating persist. Since allelic variants of human PLXNA2 and RAP1 associate with schizophrenia, our studies identify a biochemical pathway important for brain development and mental health.

Experience-Dependent Regulation of Cajal-Retzius Cell Networks in the Developing and Adult Mouse Hippocampus

In contrast to their near-disappearance in the adult neocortex, Cajal-Retzius cells have been suggested to persist longer in the hippocampus. A distinctive feature of the mature hippocampus, not maintained by other cortical areas, is its ability to sustain adult neurogenesis. Here, we have investigated whether environmental manipulations affecting hippocampal postnatal neurogenesis have a parallel impact on Cajal-Retzius cells. We used multiple mouse reporter lines to unequivocally identify Cajal-Retzius cells and quantify their densities during postnatal development. We found that exposure to an enriched environment increased the persistence of Cajal-Retzius cells in the hippocampus, but not in adjacent cortical regions. We did not observe a similar effect for parvalbumin-expressing interneurons, which suggested the occurrence of a cell type-specific process. In addition, we did not detect obvious changes either in Cajal-Retzius cell electrophysiological or morphological features, when compared with what previously reported in animals not exposed to enriched conditions. However, optogenetically triggered synaptic output of Cajal-Retzius cells onto local interneurons was enhanced, consistent with our observation of higher Cajal-Retzius cell densities. In conclusion, our data reveal a novel form of hippocampal, cell type-specific, experience-dependent network plasticity. We propose that this phenomenon may be involved in the regulation of enrichment-dependent enhanced hippocampal postnatal neurogenesis.

Developmental biology of the meninges

The meninges are membranous layers surrounding the central nervous system. In the head, the meninges lie between the brain and the skull, and interact closely with both during development. The cranial meninges originate from a mesenchymal sheath on the surface of the developing brain, called primary meninx, and undergo differentiation into three layers with distinct histological characteristics: the dura mater, the arachnoid mater, and the pia mater. While genetic regulation of meningeal development is still poorly understood, mouse mutants and other models with meningeal defects have demonstrated the importance of the meninges to normal development of the calvaria and the brain. For the calvaria, the interactions with the meninges are necessary for the progression of calvarial osteogenesis during early development. In later stages, the meninges control the patterning of the skull and the fate of the sutures. For the brain, the meninges regulate diverse processes including cell survival, cell migration, generation of neurons from progenitors, and vascularization. Also, the meninges serve as a stem cell niche for the brain in the postnatal life. Given these important roles of the meninges, further investigation into the molecular mechanisms underlying meningeal development can provide novel insights into the coordinated development of the head.

Stem Cells: A New Hope for Hearing Loss Therapy

Permanent hearing loss was considered which cannot be cured since cochlear hair cells and primary afferent neurons cannot be regenerated. In recent years, due to the in-depth study of stem cell and its therapeutic potential, regenerating auditory sensory cells is made possible. By using two strategies of endogenous stem cell activation and exogenous stem cell transplantation, researchers hope to find methods to restore hearing function. However, there are complex factors that need to be considered in the in vivo application of stem cell therapy, such as stem cell-type choice, signaling pathway regulations, transplantation approaches, internal environment of the cochlea, and external stimulation. After years of investigations, some theoretic progress has been made in the treatment of hearing loss using stem cells, but there are also many problems which limited its application that need to be solved. Understanding the future perspective of stem cell therapy in hearing loss, solving the encountered problems, and promoting its development are the common goals of audiological researchers. In this review, we present critical experimental findings of stem cell therapy on treatment of hearing loss and intend to bring hope to researchers and patients.

Adaptive Immunodeficiency in WHIM Syndrome

Cysteine-X-cysteine chemokine receptor 4 (CXCR4) is a broadly expressed and multifunctional G protein-coupled chemokine receptor critical for organogenesis, hematopoiesis, and antimicrobial host defense. In the hematopoietic system, the binding of CXCR4 to its cognate chemokine ligand, CXCL12, mediates leukocyte trafficking, distribution, survival, activation, and proliferation. Warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is a rare, autosomal dominant, combined immunodeficiency disorder caused by mutations in the C-terminus of CXCR4 that prevent receptor downregulation and therefore result in pathologically increased signaling. The “M” in the acronym WHIM refers to myelokathexis, the retention of neutrophils in the bone marrow resulting in neutropenia, which explains in part the increased susceptibility to bacterial infection. However, WHIM patients also present with B and T lymphopenia, which may explain the susceptibility to human papillomavirus (HPV), the cause of warts. The impact of WHIM mutations on lymphocytes and adaptive immunity has received less attention than myelokathexis and is the focus of this review.

Cell-Biological Requirements for the Generation of Dentate Gyrus Granule Neurons

The dentate gyrus (DG) receives highly processed information from the associative cortices functionally integrated in the trisynaptic hippocampal circuit, which contributes to the formation of new episodic memories and the spontaneous exploration of novel environments. Remarkably, the DG is the only brain region currently known to have high rates of neurogenesis in adults (Andersen et al., 1966, 1971). The DG is involved in several neurodegenerative disorders, including clinical dementia, schizophrenia, depression, bipolar disorder and temporal lobe epilepsy. The principal neurons of the DG are the granule cells. DG granule cells generated in culture would be an ideal model to investigate their normal development and the causes of the pathologies in which they are involved and as well as possible therapies. Essential to establish such in vitro models is the precise definition of the most important cell-biological requirements for the differentiation of DG granule cells. This requires a deeper understanding of the precise molecular and functional attributes of the DG granule cells in vivo as well as the DG cells derived in vitro. In this review we outline the neuroanatomical, molecular and cell-biological components of the granule cell differentiation pathway, including some growth- and transcription factors essential for their development. We summarize the functional characteristics of DG granule neurons, including the electrophysiological features of immature and mature granule cells and the axonal pathfinding characteristics of DG neurons. Additionally, we discuss landmark studies on the generation of dorsal telencephalic precursors from pluripotent stem cells (PSCs) as well as DG neuron differentiation in culture. Finally, we provide an outlook and comment critical aspects.

Expression of α-synuclein is regulated in a neuronal cell type-dependent manner

α-Synuclein, the major component of Lewy bodies (LBs) and Lewy neurites (LNs), is expressed in presynapses under physiologically normal conditions and is involved in synaptic function. Abnormal intracellular aggregates of misfolded α-synuclein such as LBs and LNs are pathological hallmarks of synucleinopathies, including Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). According to previous studies using pathological models overexpressing α-synuclein, high expression of this protein in neurons is a critical risk factor for neurodegeneration. Therefore, it is important to know the endogenous expression levels of α-synuclein in each neuronal cell type. We previously reported differential expression profiles of α-synuclein in vitro and in vivo. In the wild-type mouse brain, particularly in vulnerable regions affected during the progression of idiopathic PD, α-synuclein is highly expressed in neuronal cell bodies of some early PD-affected regions, such as the olfactory bulb, the dorsal motor nucleus of the vagus, and the substantia nigra pars compacta. Synaptic expression of α-synuclein is mostly accompanied by expression of vesicular glutamate transporter-1, an excitatory synapse marker protein. In contrast, α-synuclein expression in inhibitory synapses differs among brain regions. Recently accumulated evidence indicates the close relationship between differential expression profiles of α-synuclein and selective vulnerability of certain neuronal populations. Further studies on the regulation of α-synuclein expression will help to understand the mechanism of LB pathology and provide an innovative therapeutic strategy to prevent PD and DLB onset.

Potential use of CXCL12/CXCR4 and sonic hedgehog pathways as therapeutic targets in medulloblastoma

Medulloblastoma (MB) is the most common malignant brain tumor occurring in children, and although high long-term survival rates have been reached with current therapeutic protocols, several neurological injuries are still observed among survivors. It has been shown that the development of MB is highly dependent on the microenvironment surrounding it and that the CXCL12 chemokine and its receptor, CXCR4 and the Sonic Hedgehog (SHH) pathway are crucial for cerebellar development, coordinating proliferation and migration of embryonic cells and malfunctions in these axes can lead to MB development. Indeed, the concomitant overactivation of these axes was suggested to define a new MB molecular subgroup. New molecules are being studied, aiming to inhibit either CXCR4 or the SHH pathways and have been tested in preclinical settings for the treatment of cancers. The use of these molecules could improve MB treatment and save patients from aggressive surgery, chemotherapy and radiotherapy regimens, which are responsible for severe neurological consequences. This review aims to summarize current data about the experimental inhibition of CXCR4 and SHH pathways in MB and its potential implications in treatment of this cancer.

Adult neurogenesis and its role in brain injury and psychiatric diseases

In the adult mammalian brain, neural stem cells (NSCs) reside in two neurogenic regions, the walls of the lateral ventricles, and the subgranular zone of the hippocampus, which generate new neurons for the olfactory bulb and dentate gyrus, respectively. These adult NSCs retain their self-renewal ability and capacity to differentiate into neurons and glia as demonstrated by in vitro studies. However, their contribution to tissue repair in disease and injury is limited, lending credence to the claim by prominent neuropathologist Ramón y Cajal that 'once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably'. However, recent progress toward understanding the fundamental biology of adult NSCs and their role in pathological conditions has provided new insight into the potential therapeutic utility of endogenous NSCs. In this short review, we highlight two topics: the altered behavior of NSCs after brain damage and the dysfunction of NSCs and oligodendrocyte precursor cells, another type of undifferentiated cell in the adult brain, in mood affective disorders.

Design and evaluation of a CXCR4 targeting peptide 4DV3 as an HIV entry inhibitor and a ligand for targeted drug delivery

The feasibility of utilizing the cell surface chemokine receptor CXCR4 for human immunodeficiency virus (HIV) entry inhibition and as an intracellular portal for targeted drug delivery was evaluated. Novel DV3 ligands (1DV3, 2DV3, and 4DV3) were designed, synthesized and conjugated to various probes (fluorescein isothiocyanate (FITC) or biotin) and cargos with sizes ranging from 10 to 50 nm (polyethylene glycol (PEG), streptavidin, and a polymeric nanoparticle). 4DV3 conjugated probes inhibited HIV-1 entry into the CXCR4-expressing reporter cell line TZM-bl (IC₅₀ at 553 nM) whereas 1DV3 and 2DV3 did not. 4DV3 also inhibited binding of anti-CXCR4 antibody 44,708 to TZM-bl cells with nanomolar potency, while the small-molecule CXCR4 antagonist AMD3100 did not. Molecular modeling suggested simultaneous binding of a single 4DV3 molecule to four CXCR4 molecules. Differences in CXCR4-binding sites could explain the discrete inhibitory effects observed for 4DV3, the 44,708 antibody and AMD3100. In the Sup-T1 cell chemotaxis assay, the 4DV3 ligand functioned as a CXCR4 allosteric enhancer. In addition, 4DV3 ligand-conjugated cargos with sizes ranging from 10 to 50 nm were taken up into CXCR4-expressing Sup-T1 and TZM-bl cells, demonstrating that CXCR4 could serve as a drug delivery portal for nanocarriers. The uptake of 4DV3 functionalized nanocarriers combined with the allosteric interaction with CXCR4 suggests enhanced endocytosis occurs when 4DV3 is the targeting ligand. The current results indicate that 4DV3 might serve as a prototype for a new type of dual function ligand, one that acts as a HIV-1 entry inhibitor and a CXCR4 drug delivery targeting ligand.

Differential α-synuclein expression contributes to selective vulnerability of hippocampal neuron subpopulations to fibril-induced toxicity

The accumulation of misfolded α-synuclein (aSyn) and neuron loss define several neurodegenerative disorders including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). However, the precise relationship between pathology and neurotoxicity and why these processes disproportionately affect certain neuron subpopulations are poorly understood. We show here that Math2-expressing neurons in the hippocampal Cornu ammonis (CA), a region significantly affected by aSyn pathology in advanced PD and DLB, are highly susceptible to pathological seeding with pre-formed fibrils (PFFs), in contrast to dentate gyrus neurons, which are relatively spared. Math2⁺ neurons also exhibited more rapid and severe cell loss in both in vitro and in vivo models of synucleinopathy. Toxicity resulting from PFF exposure was dependent on endogenous aSyn and could be attenuated by N-acetyl-cysteine through a glutathione-dependent process. Moreover, aSyn expression levels strongly correlate with relative vulnerability among hippocampal neuron subtypes of which Math2⁺ neurons contained the highest amount. Consistent with this, antisense oligonucleotide (ASO)-mediated knockdown of aSyn reduced the neuronal pathology in a time-dependent manner. However, significant neuroprotection was observed only with early ASO intervention and a substantial reduction of aSyn pathology, indicating toxicity occurs after a critical threshold of pathological burden is exceeded in vulnerable neurons. Together, our findings reveal considerable heterogeneity in endogenous aSyn levels among hippocampal neurons and suggest that this may contribute to the selective vulnerability observed in the context of synucleinopathies.

CXCL12α/SDF-1 from perisynaptic Schwann cells promotes regeneration of injured motor axon terminals

The neuromuscular junction has retained through evolution the capacity to regenerate after damage, but little is known on the inter-cellular signals involved in its functional recovery from trauma, autoimmune attacks, or neurotoxins. We report here that CXCL12α, also abbreviated as stromal-derived factor-1 (SDF-1), is produced specifically by perisynaptic Schwann cells following motor axon terminal degeneration induced by α-latrotoxin. CXCL12α acts via binding to the neuronal CXCR4 receptor. A CXCL12α-neutralizing antibody or a specific CXCR4 inhibitor strongly delays recovery from motor neuron degeneration in vivo Recombinant CXCL12α in vivo accelerates neurotransmission rescue upon damage and very effectively stimulates the axon growth of spinal cord motor neurons in vitro These findings indicate that the CXCL12α-CXCR4 axis plays an important role in the regeneration of the neuromuscular junction after motor axon injury. The present results have important implications in the effort to find therapeutics and protocols to improve recovery of function after different forms of motor axon terminal damage.

Ectopic neurogenesis induced by prenatal antiepileptic drug exposure augments seizure susceptibility in adult mice

Recent clinical studies suggest that environmental insults, such as valproic acid (VPA) exposure, in utero can have adverse effects on brain function of the offspring in later life, although the underlying mechanisms of these impairments remain poorly understood. By focusing on the property of neural stem/progenitor cells (NS/PCs) residing in the adult hippocampus, we identified the mechanism of increased seizure sensitivity in prenatally VPA-exposed adult mice. Furthermore, we found that voluntary exercise can overcome the adverse effects through normalizing VPA-induced transcriptome alterations in NS/PCs. We believe that our study provides insights for further understanding and developing treatment strategies for neurological disorders induced by prenatal environmental insults.

Epilepsy is a neurological disorder often associated with seizure that affects ∼0.7% of pregnant women. During pregnancy, most epileptic patients are prescribed antiepileptic drugs (AEDs) such as valproic acid (VPA) to control seizure activity. Here, we show that prenatal exposure to VPA in mice increases seizure susceptibility in adult offspring through mislocalization of newborn neurons in the hippocampus. We confirmed that neurons newly generated from neural stem/progenitor cells (NS/PCs) are integrated into the granular cell layer in the adult hippocampus; however, prenatal VPA treatment altered the expression in NS/PCs of genes associated with cell migration, including CXC motif chemokine receptor 4 (Cxcr4), consequently increasing the ectopic localization of newborn neurons in the hilus. We also found that voluntary exercise in a running wheel suppressed this ectopic neurogenesis and countered the enhanced seizure susceptibility caused by prenatal VPA exposure, probably by normalizing the VPA-disrupted expression of multiple genes including Cxcr4 in adult NS/PCs. Replenishing Cxcr4 expression alone in NS/PCs was sufficient to overcome the aberrant migration of newborn neurons and increased seizure susceptibility in VPA-exposed mice. Thus, prenatal exposure to an AED, VPA, has a long-term effect on the behavior of NS/PCs in offspring, but this effect can be counteracted by a simple physical activity. Our findings offer a step to developing strategies for managing detrimental effects in offspring exposed to VPA in utero.

CXCL12-mediated feedback from granule neurons regulates generation and positioning of new neurons in the dentate gyrus

Adult hippocampal neurogenesis is implicated in learning and memory processing. It is tightly controlled at several levels including progenitor proliferation as well as migration, differentiation and integration of new neurons. Hippocampal progenitors and immature neurons reside in the subgranular zone (SGZ) and are equipped with the CXCL12-receptor CXCR4 which contributes to defining the SGZ as neurogenic niche. The atypical CXCL12-receptor CXCR7 functions primarily by sequestering extracellular CXCL12 but whether CXCR7 is involved in adult neurogenesis has not been assessed. We report that granule neurons (GN) upregulate CXCL12 and CXCR7 during dentate gyrus maturation in the second postnatal week. To test whether GN-derived CXCL12 regulates neurogenesis and if neuronal CXCR7 receptors influence this process, we conditionally deleted Cxcl12 and Cxcr7 from the granule cell layer. Cxcl12 deletion resulted in lower numbers, increased dispersion and abnormal dendritic growth of immature GN and reduced neurogenesis. Cxcr7 ablation caused an increase in progenitor proliferation and progenitor numbers and reduced dispersion of immature GN. Thus, we provide a new mechanism where CXCL12-signals from GN prevent dispersion and support maturation of newborn GN. CXCR7 receptors of GN modulate the CXCL12-mediated feedback from GN to the neurogenic niche.

The chemokines CXCL12 and CXCL14 differentially regulate connective tissue markers during limb development

Connective tissues (CT) support and connect organs together. Understanding the formation of CT is important, as CT deregulation leads to fibrosis. The identification of CT specific markers has contributed to a better understanding of CT function during development. In developing limbs, Osr1 transcription factor is involved in the differentiation of irregular CT while the transcription factor Scx labels tendon. In this study, we show that the CXCL12 and CXCL14 chemokines display distinct expression pattern in limb CT during chick development. CXCL12 positively regulates the expression of OSR1 and COL3A1, a collagen subtype of irregular CT, while CXCL14 activates the expression of the tendon marker SCX. We provide evidence that the CXCL12 effect on irregular CT involves CXCR4 receptor and vessels. In addition, the expression of CXCL12, CXCL14 and OSR genes is suppressed by the anti-fibrotic BMP signal. Finally, mechanical forces, known to be involved in adult fibrosis, control the expression of chemokines, CT-associated transcription factors and collagens during limb development. Such unexpected roles of CXCL12 and CXCL14 chemokines during CT differentiation can contribute to a better understanding of the fibrosis mechanisms in adult pathological conditions.

Drebrin in Neuronal Migration and Axonal Growth

During development, production of neurons from neural stem cells, migration of neurons from their birthplace to their final location, and extension of neurites, axons, and dendrites are important for the formation of functional neuronal circuits. The actin cytoskeleton has major roles in the morphological development of neurons. In this chapter, we focused on the distribution and function of the actin-binding protein, drebrin, to elucidate the importance of drebrin-bound F-actin in neurons during early developmental stages of neurons in embryonic, postnatal, and adult brains. There are three major isoforms of drebrin in the chicken brain (E1, E2, and A) and two major isoforms in the mammalian brain (E and A). Among these drebrin isoforms, drebrin E1 and E2 in chicken and drebrin E in the mammalian brain are involved in these neuronal stages. In migrating neurons of the developing and adult brain, drebrin is localized at the base of filopodia of leading processes, to regulate neuronal migration. In axonal growth cones, drebrin is localized in the transitional zone to regulate axonal growth by inhibiting actomyosin interactions and mediating the interactions between F-actin and microtubules. For axonal collateral branching, drebrin is localized at axonal actin patches and the base of filopodia, to accelerate the transition from actin patches to filopodia and stabilize the filopodia.

The Secretome of Microglia Regulate Neural Stem Cell Function

Brain injury is associated with neuroinflammation, and microglia are key players in this process. Microglia can acquire pro-inflammatory or anti-inflammatory properties, but how this affects neural stem cells (NSCs) remains controversial. Here, NSCs were grown in conditioned media collected from either non-stimulated microglia, or microglia stimulated with pro- or anti-inflammatory agents. NSC survival, proliferation, migration, and differentiation were investigated thereafter. We found that NSCs kept in conditioned medium from the anti-inflammatory microglial subtype had better survival, increased migration, and lower astrocytic differentiation compared to NSCs grown in conditioned medium collected from the pro-inflammatory subtype. Finally, we found that NSCs differentiated in microglial conditioned media generated cells expressing the pro-inflammatory chemokine CCL2, most pronounced when differentiated in medium from the pro-inflammatory microglia subtype. Our results show that microglial subtypes regulate NSCs differently and induce generation of cells with inflammatory properties.

Functional Implications of miR-19 in the Migration of Newborn Neurons in the Adult Brain

Altered microRNA profiles have been implicated in human brain disorders. However, the functional contribution of individual microRNAs to neuronal development and function is largely unknown. Here, we report biological functions for miR-19 in adult neurogenesis. We determined that miR-19 is enriched in neural progenitor cells (NPCs) and downregulated during neuronal development in the adult hippocampus. By manipulating miR-19 in NPCs for gain- and loss-of-function studies, we discovered that miR-19 regulates cell migration by directly targeting Rapgef2. Concordantly, dysregulation of miR-19 in NPCs alters the positioning of newborn neurons in the adult brain. Furthermore, we found abnormal expression of miR-19 in human NPCs generated from schizophrenic patient-derived induced pluripotent stem cells (iPSCs) that have been described as displaying aberrant migration. Our study demonstrates the significance of posttranscriptional gene regulation by miR-19 in preventing the irregular migration of adult-born neurons that may contribute to the etiology of schizophrenia.

Dynamics and function of CXCR4 in formation of the granule cell layer during hippocampal development

In the developing hippocampus, granule cell progenitors (GCPs) arising in the ventricular zone (VZ) migrate to the subpial region, and form the granule cell layer (GCL) of the dentate gyrus (DG). To understand the mechanism of GCL formation, we investigated the dynamics and function of CXCR4 which is expressed by the GCPs and is a receptor of the CXCL12 chemokine secreted by cells surrounding the DG. In the VZ, CXCR4 was expressed on the plasma membrane of the GCPs. During their migration and in the DG, CXCR4 was internalized and accumulated as puncta close to the centrosomes, Golgi apparatus, and lysosomes. Phosphatase analysis suggested that both phosphorylated and dephosphorylated CXCR4 exist on the plasma membrane, whereas CXCR4 in intracellular puncta was mainly dephosphorylated. Intraventricular administration of the CXCR4 antagonist AMD3100 resulted in the disappearance of CXCR4 expression from the intracellular puncta, and its appearance on the plasma membranes. Furthermore, AMD3100 treatment resulted in precocious differentiation, delayed migration, and ectopic GCPs. Taken together, these results suggest that during the development and migration of GCPs, CXCR4 on the plasma membrane is phosphorylated, internalized, sorted to the centrosomes, Golgi apparatus, and lysosomes, and functionally regulates GCP differentiation, migration and positioning.

COUP-TFI mitotically regulates production and migration of dentate granule cells and modulates hippocampal Cxcr4 expression

Development of the dentate gyrus (DG), the primary gateway for hippocampal inputs, spans embryonic and postnatal stages, and involves complex morphogenetic events. We have previously identified the nuclear receptor COUP-TFI as a novel transcriptional regulator in the postnatal organization and function of the hippocampus. Here, we dissect its role in DG morphogenesis by inactivating it in either granule cell progenitors or granule neurons. Loss of COUP-TFI function in progenitors leads to decreased granule cell proliferative activity, precocious differentiation and increased apoptosis, resulting in a severe DG growth defect in adult mice. COUP-TFI-deficient cells express high levels of the chemokine receptor Cxcr4 and migrate abnormally, forming heterotopic clusters of differentiated granule cells along their paths. Conversely, high COUP-TFI expression levels downregulate Cxcr4 expression, whereas increased Cxcr4 expression in wild-type hippocampal cells affects cell migration. Finally, loss of COUP-TFI in postmitotic cells leads to only minor and transient abnormalities, and to normal Cxcr4 expression. Together, our results indicate that COUP-TFI is required predominantly in DG progenitors for modulating expression of the Cxcr4 receptor during granule cell neurogenesis and migration.

The CD24 surface antigen in neural development and disease

A cell's surface molecular signature enables its reciprocal interactions with the associated microenvironments in development, tissue homeostasis and pathological processes. The CD24 surface antigen (heat-stable antigen, nectadrin; small cell lung cancer antigen cluster-4) represents a prime example of a neural surface molecule that has long been known, but whose diverse molecular functions in intercellular communication we have only begun to unravel. Here, we briefly summarize the molecular fundamentals of CD24 structure and provide a comprehensive review of CD24 expression and functional studies in mammalian neural developmental systems and disease models (rodent, human). Striving for an integrated view of the intracellular signaling processes involved, we discuss the most pertinent routes of CD24-mediated signaling pathways and functional networks in neurobiology (neural migration, neurite extension, neurogenesis) and pathology (tumorigenesis, multiple sclerosis).

Neuropilin 2 Signaling Is Involved in Cell Positioning of Adult-born Neurons through Glycogen Synthase Kinase-3β (GSK3β)

Proper positioning of neurons is fundamental for brain functions. However, little is known on how adult-born neurons generated in the hilar side of hippocampal dentate gyrus migrate into the granular cell layer. Because class 3 Semaphorins (Sema3) are involved in dendritic growth of these newborn neurons, we examined whether they are essential for cell positioning. We disrupted Sema3 signaling by silencing neuropilin 1 (NRP1) or 2 (NRP2), the main receptors for Sema3A and Sema3F, in neural progenitors of adult mouse dentate gyrus. Silencing of NRP2, but not NRP1, affected cell positioning of adult newborn neurons. Glycogen synthase kinase-3β (GSK3β) knockdown phenocopied this NRP2 silencing-mediated cell positioning defect, but did not affect dendritic growth. Furthermore, GSK3β is activated upon stimulation with Sema3F, and GSK3β overexpression rescued the cell positioning phenotypes seen in NRP2-deficient neurons. These results point to a new role for NRP2 in the positioning of neurons during adult hippocampal neurogenesis, acting via the GSK3β signaling pathway.

Enhanced Migration of Neural Stem Cells by Microglia Grown on a Three-Dimensional Graphene Scaffold

One of the key challenges in engineering neural tissues for cell-based therapies is to develop a biocompatible scaffold material to direct neural stem cell (NSC) behaviors. One great advantage for a scaffold would be to induce NSC migration toward pathological sites during regeneration and repair. In particular, the inflammatory responses in the pathological zone, which are mainly mediated by microglia in the central nervous system, affect the repair capacity of NSCs through NSC migration. Recently, graphene was used as a neural interface and scaffold material, but few studies have addressed the relationship between microglia and NSCs in a graphene culture system. In this study, we used a combination of immunofluorescence, Western blotting, enzyme-linked immunosorbent assays, and scanning electron microscopy to investigate how conditioned medium (CM) produced from microglia grown on two-dimensional graphene (2D-G) films or three-dimensional graphene (3D-G) foams govern NSC migration. The results revealed that the CM produced by microglia grown in 3D-G cultures could promote neurosphere formation, facilitate NSC migration from the neurospheres, and increase single cell polarization by activating the stromal cell-derived factor 1 α (SDF-1α)/CXC chemokine receptor 4 (CXCR4) signaling pathway and enhancing cell adhesion on the substrate. By contrast, the 2D-G CM failed to achieve these results. Our study suggests the great potential of 3D-G as a neural scaffold for NSC-based therapy in tissue engineering and regenerative medicine.

SDF-1 and CXCR4 play an important role in adult SVZ lineage cell proliferation and differentiation

Evidence has shown that stromal cell-derived factor (SDF-1/CXCL12) plays an important role in maintaining adult neural progenitor cells (NPCs). SDF-1 is also known to enhance recovery by recruiting NPCs to damaged regions and recent studies have revealed that SDF-1α exhibits pleiotropism, thereby differentially affecting NPC subpopulations. In this study, we investigated the role of SDF-1 in in vitro NPC self-renewal, proliferation and differentiation, following treatment with different concentrations of SDF-1 or a CXCR4 antagonist, AMD3100. We observed that AMD3100 inhibited the formation of primary neurospheres. However, SDF-1 and AMD3100 exhibited no effect on proliferation upon inclusion of growth factors in the media. Following growth factor withdrawal, AMD3100 and SDF-1 treatment resulted in differential effects on NPC proliferation. SDF-1, at a concentration of 500ng/ml, resulted in an increase in the relative proportion of oligodendrocytes following growth factor withdrawal-induced differentiation. Using CXCR4 knockout mice, we observed that SDF-1 affected NPC proliferation in the sub-ventricular zone (SVZ). We also investigated the occurrence of differential CXCR4 expression at different stages during lineage progression. These results clearly indicate that signaling interactions between SDF-1 and CXCR4 play an important role in adult SVZ lineage cell proliferation and differentiation.

Growth factor therapy sequesters inflammation in affording neuroprotection in cerebrovascular diseases

INTRODUCTION

In recent years, accumulating evidence has demonstrated the key role of inflammation in the progression of cerebrovascular diseases. Inflammation can persist over prolonged period of time after the initial insult providing a wider therapeutic window. Despite the acute endogenous upregulation of many growth factors after the injury, it is not sufficient to protect against inflammation and to regenerate the brain. Therapeutic approaches targeting both dampening inflammation and enhancing growth factors are likely to provide beneficial outcomes in cerebrovascular disease.

AREAS COVERED

In this mini review, we discuss major growth factors and their beneficial properties to combat the inflammation in cerebrovascular diseases. Emerging biotechnologies which facilitate the therapeutic effects of growth factors are also presented in an effort to provide insights into the future combination therapies incorporating both central and peripheral abrogation of inflammation. Expert commentary: Many studies discussed in this review have demonstrated the therapeutic effects of growth factors in treating cerebrovascular diseases. It is unlikely that one growth factor can be used to treat these complex diseases. Combination of growth factors and anti-inflammatory modulators may clinically improve outcomes for patients. In particular, transplantation of stem cells may be able to achieve both goals of modulating inflammation and upregulating growth factors. Large preclinical studies and multiple laboratory collaborations are needed to advance these findings from bench to bedside.

Tangential migration of glutamatergic neurons and cortical patterning during development: Lessons from Cajal-Retzius cells

Tangential migration is a mode of cell movement, which in the developing cerebral cortex, is defined by displacement parallel to the ventricular surface and orthogonal to the radial glial fibers. This mode of long-range migration is a strategy by which distinct neuronal classes generated from spatially and molecularly distinct origins can integrate to form appropriate neural circuits within the cortical plate. While it was previously believed that only GABAergic cortical interneurons migrate tangentially from their origins in the subpallial ganglionic eminences to integrate in the cortical plate, it is now known that transient populations of glutamatergic neurons also adopt this mode of migration. These include Cajal-Retzius cells (CRs), subplate neurons (SPs), and cortical plate transient neurons (CPTs), which have crucial roles in orchestrating the radial and tangential development of the embryonic cerebral cortex in a noncell-autonomous manner. While CRs have been extensively studied, it is only in the last decade that the molecular mechanisms governing their tangential migration have begun to be elucidated. To date, the mechanisms of SPs and CPTs tangential migration remain unknown. We therefore review the known signaling pathways, which regulate parameters of CRs migration including their motility, contact-redistribution and adhesion to the pial surface, and discuss this in the context of how CR migration may regulate their signaling activity in a spatial and temporal manner. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 847-881, 2016.

Epithelial cells supply Sonic Hedgehog to the perinatal dentate gyrus via transport by platelets

Dentate neural stem cells produce neurons throughout life in mammals. Sonic hedgehog (Shh) is critical for maintenance of these cells; however, the perinatal source of Shh is enigmatic. In the present study, we examined the role of Shh expressed by hair follicles (HFs) that expand perinatally in temporal concordance with the proliferation of Shh-responding dentate stem cells. Specific inhibition of Shh from HFs or from epithelial sources in general hindered development of Shh-responding dentate stem cells. We also found that the blood–brain barrier (BBB) of the perinatal dentate gyrus (DG) is leaky with stem cells in the dentate exposed to blood-born factors. In attempting to identify how Shh might be transported in blood, we found that platelets contain epithelial Shh, provide Shh to the perinatal DG and that inhibition of platelet generation reduced hedgehog-responsive dentate stem cells.

DOI:http://dx.doi.org/10.7554/eLife.07834.001

Although most of the neurons in the brain have been made by the time we are born, new neurons develop throughout life in part of the brain called the hippocampus. These neurons are thought to help with learning and forming memories. Conditions such as depression and Alzheimer's disease have been linked to not being able to produce enough new neurons.

The neurons develop from a pool of stem cells in part of the hippocampus. A protein called Sonic Hedgehog (Shh) helps to ensure there are enough stem cells and control when they develop into new neurons. The brain cells that produce Shh in adult mice do not appear until a week after birth, by which point the stem cells are already present and generating neurons. This has led scientists to question where these cells get Shh from around the time of birth.

One idea is that cells outside of the brain contribute the Shh such as hair follicles—the structures that hairs grow out of—in the scalp. Hair follicles produce Shh, develop at around the same time as the brain stem cells, and are known to regulate the development of other nearby stem cells. So, Choe et al. conducted a series of experiments in genetically engineered newborn mice and found that the brain stem cells multiply at around the same time that the hair follicles start to produce Shh. Furthermore, reducing the amount of Shh produced by the hair follicles hampered the growth of these stem cells and caused fewer neurons to develop from the stem cell pool.

These results raised the question of how Shh gets from the hair follicles to the stem cell pool in the developing brain. In adult animals, a barrier exists between the brain and the blood supply to protect the brain from infection. However, parts of this barrier are still leaky before birth, which might allow blood cells to carry Shh to the brain. Cloe et al. found that platelets—the blood cells responsible for clotting—are able to carry Shh to the brain stem cell pool. Further experiments showed that preventing platelets from forming caused fewer stem cells to develop.

The suggestion that Shh from the epithelium—the tissue layer that hair follicles are found in—is able to signal to the brain during a specific window of time raises several questions that require further study. Does epithelial Shh also signal to other organs during embryonic or postnatal development? Does injury to the nervous system that increases the permeability of the blood–brain barrier lead to the delivery of Shh to the brain via the circulation in adult animals?

DOI:http://dx.doi.org/10.7554/eLife.07834.002

Are neural crest stem cells the missing link between hematopoietic and neurogenic niches?

Hematopoietic niches are defined as cellular and molecular microenvironments that regulate hematopoietic stem cell (HSC) function together with stem cell autonomous mechanisms. Many different cell types have been characterized as contributors to the formation of HSC niches, such as osteoblasts, endothelial cells, Schwann cells, and mesenchymal progenitors. These mesenchymal progenitors have themselves been classified as CXC chemokine ligand (CXCL) 12-abundant reticular (CAR) cells, stem cell factor expressing cells, or nestin-positive mesenchymal stem cells (MSCs), which have been recently identified as neural crest-derived cells (NCSCs). Together, these cells are spatially associated with HSCs and believed to provide appropriate microenvironments for HSC self-renewal, differentiation, mobilization and hibernation both by cell-cell contact and soluble factors. Interestingly, it appears that regulatory pathways governing the hematopoietic niche homeostasis are operating in the neurogenic niche as well. Therefore, this review paper aims to compare both the regulation of hematopoietic and neurogenic niches, in order to highlight the role of NCSCs and nervous system components in the development and the regulation of the hematopoietic system.

Identification of a sustained neurogenic zone at the dorsal surface of the adult mouse hippocampus and its regulation by the chemokine SDF-1

We identified a previously unknown neurogenic region at the dorsal surface of the hippocampus; (the "subhippocampal zone," SHZ) in the adult brain. Using a reporter mouse in which SHZ cells and their progeny could be traced through the expression of EGFP under the control of the CXCR4 chemokine receptor promoter we observed the presence of a pool of EGFP expressing cells migrating in direction of the dentate gyrus (DG), which is maintained throughout adulthood. This population appeared to originate from the SHZ where cells entered a caudal migratory stream (aCMS) that included the fimbria, the meninges and the DG. Deletion of CXCR4 from neural stem cells (NSCs) or neuroinflammation resulted in the appearance of neurons in the DG, which were the result of migration of NSCs from the SHZ. Some of these neurons were ectopically placed. Our observations indicate that the SHZ is a neurogenic zone in the adult brain through migration of NSCs in the aCMS. Regulation of CXCR4 signaling in these cells may be involved in repair of the DG and may also give rise to ectopic granule cells in the DG in the context of neuropathology.