Stromal cell-derived factor 1 is secreted by meningeal cells and acts as chemotactic factor on neuronal stem cells of the cerebellar external granular layer

CXCL12 promotes the crossing of retinal ganglion cell axons at the optic chiasm

Binocular vision requires the segregation of retinal ganglion cell (RGC) axons extending from the retina into the ipsilateral and contralateral optic tracts. RGC axon segregation occurs at the optic chiasm, which forms at the ventral diencephalon midline. Using expression analyses, retinal explants and genetically modified mice, we demonstrate that CXCL12 (SDF1) is required for axon segregation at the optic chiasm. CXCL12 is expressed by the meninges bordering the optic pathway, and CXCR4 by both ipsilaterally and contralaterally projecting RGCs. CXCL12 or ventral diencephalon meninges potently promoted axon outgrowth from both ipsilaterally and contralaterally projecting RGCs. Further, a higher proportion of axons projected ipsilaterally in mice lacking CXCL12 or its receptor CXCR4 compared with wild-type mice as a result of misrouting of presumptive contralaterally specified RGC axons. Although RGCs also expressed the alternative CXCL12 receptor ACKR3, the optic chiasm developed normally in mice lacking ACKR3. Our data support a model whereby meningeal-derived CXCL12 helps drive axon growth from CXCR4-expressing RGCs towards the diencephalon midline, enabling contralateral axon growth. These findings further our understanding of the molecular and cellular mechanisms controlling optic pathway development.

Human cerebellar organoids with functional Purkinje cells

Research on human cerebellar development and disease has been hampered by the need for a human cell-based system that recapitulates the human cerebellum's cellular diversity and functional features. Here, we report a human organoid model (human cerebellar organoids [hCerOs]) capable of developing the complex cellular diversity of the fetal cerebellum, including a human-specific rhombic lip progenitor population that have never been generated in vitro prior to this study. 2-month-old hCerOs form distinct cytoarchitectural features, including laminar organized layering, and create functional connections between inhibitory and excitatory neurons that display coordinated network activity. Long-term culture of hCerOs allows healthy survival and maturation of Purkinje cells that display molecular and electrophysiological hallmarks of their in vivo counterparts, addressing a long-standing challenge in the field. This study therefore provides a physiologically relevant, all-human model system to elucidate the cell-type-specific mechanisms governing cerebellar development and disease.

Novel model of cortical-meningeal organoid co-culture system improves human cortical brain organoid cytoarchitecture

Human cortical organoids (hCOs), derived from human induced pluripotent stem cells (iPSCs), provide a platform to interrogate mechanisms of human brain development and diseases in complex three- dimensional tissues. However, current hCO development methods lack important non-neural tissues, such as the surrounding meningeal layer, that have been shown to be essential for normal corticogenesis and brain development. Here, we first generated hCOs from a single rosette to create more homogenous organoids with consistent size around 250 µm by day 5. We then took advantage of a 3D co-culture system to encapsulate brain organoids with a thin layer of meningeal cells from the very early stages of cortical development. Immunostaining analysis was performed to display different cortical layer markers during different stages of development. Real-time monitoring of organoid development using IncuCyte displayed enhanced morphology and increased growth rate over time. We found that meningeal-encapsulated organoids illustrated better laminar organization by exhibiting higher expression of REELIN by Cajal-Retzius neurons. Presence of meningeal cells resulted in a greater expansion of TBR2 intermediate progenitor cells (IPCs), the deep cortical layer (CTIP2) and upper cortical layer (BRN2). Finally, meningeal-encapsulated organoids enhanced outer radial glial and astrocyte formation illustrated by stronger expression of HOPX and GFAP markers, respectively. This study presents a novel 3D co-culture platform to more closely mimic the in vivo cortical brain structure and enable us to better investigating mechanisms underlying the neurodevelopmental disorders during embryonic development.

Impact of aging on meningeal gene expression

BACKGROUND

The three-layered meninges cover and protect the central nervous system and form the interface between cerebrospinal fluid and the brain. They are host to a lymphatic system essential for maintaining fluid dynamics inside the cerebrospinal fluid-filled subarachnoid space and across the brain parenchyma via their connection to glymphatic structures. Meningeal fibroblasts lining and traversing the subarachnoid space have direct impact on the composition of the cerebrospinal fluid through endocytotic uptake as well as extensive protein secretion. In addition, the meninges are an active site for immunological processes and act as gatekeeper for immune cells entering the brain. During aging in mice, lymphatic drainage from the brain is less efficient contributing to neurodegenerative processes. Aging also affects the immunological status of the meninges, with increasing numbers of T cells, changing B cell make-up, and altered macrophage complement.

METHODS

We employed RNASeq to measure gene expression and to identify differentially expressed genes in meninges isolated from young and aged mice. Using Ingenuity pathway, GO term, and MeSH analyses, we identified regulatory pathways and cellular functions in meninges affected by aging.

RESULTS

Aging had profound impact on meningeal gene expression. Pathways related to innate as well as adaptive immunity were affected. We found evidence for increasing numbers of T and B lymphocytes and altered activity profiles for macrophages and other myeloid cells. Furthermore, expression of pro-inflammatory cytokine and chemokine genes increased with aging. Similarly, the complement system seemed to be more active in meninges of aged mice. Altered expression of solute carrier genes pointed to age-dependent changes in cerebrospinal fluid composition. In addition, gene expression for secreted proteins showed age-dependent changes, in particular, genes related to extracellular matrix composition and organization were affected.

CONCLUSIONS

Aging has profound effects on meningeal gene expression; thereby affecting the multifaceted functions meninges perform to maintain the homeostasis of the central nervous system. Thus, age-dependent neurodegenerative processes and cognitive decline are potentially in part driven by altered meningeal function.

Parasagittal Fibroblastic Meningioma in Accompaniment with Scalp Basal Cell Carcinoma: Report of a Case

Introduction: Accompaniment of meningioma with other tumors especially cerebral tumors is quite rare. In some institutes, cases of simultaneous meningioma and glioma are seen and reported previously. Case Presentation: We reported a meningioma with the accompaniment of scalp basal cell carcinoma (BCC) with no signs and symptoms of Gorlin syndrome and no history of radiation. Conclusions: Expression of some adjacent cancerous lesions might have a local cancerous induction effect.

Stem Cells and Targeted Gene Therapy in Brain and Spinal Cord Tumors

The CNS tumors, in particular those with malignant characteristics, are prominent burdens around the world with high mortality and low cure rate. Given that, researchers were curious about novel treatments with promising effectiveness which resulted in shifting the dogmatism era of neurogenesis to the current concept of postnatal neurogenesis. Considering all existing stem cells, various strategies are available for treating CNS cancers, including hematopoietic stem cells transplantation, mesenchymal stem cells transplantation, neural stem cells (NSCs) transplantation, and using stem cells as genetic carriers called "suicide gene therapy". Despite some complications, this ongoing therapeutic method has succeeded in decreasing tumor volume, inhibiting tumor progression, and enhancing patients' survival. These approaches could lead to acceptable results, relatively better safety, and tolerable side effects compared to conventional chemo and radiotherapy. Accordingly, this treatment will be applicable to a wide range of CNS tumors in the near future. Furthermore, tumor genomic analysis and understanding of the underlying molecular mechanisms will help researchers determine patient selection criteria for targeted gene therapy.

The Conflicting Role of Caffeine Supplementation on Hyperoxia-Induced Injury on the Cerebellar Granular Cell Neurogenesis of Newborn Rats

Preterm birth disrupts cerebellar development, which may be mediated by systemic oxidative stress that damages neuronal developmental stages. Impaired cerebellar neurogenesis affects several downstream targets important for cognition, emotion, and speech. In this study, we demonstrate that oxidative stress induced with high oxygen (80%) for three or five postnatal days (P3/P5) could significantly damage neurogenesis and proliferative capacity of granular cell precursor and Purkinje cells in rat pups. Reversal of cellular neuronal damage after recovery to room air (P15) was augmented by treatment with caffeine. However, downstream transcripts important for migration and differentiation of postmitotic granular cells were irreversibly reduced by hyperoxia, without rescue by caffeine. Protective effects of caffeine in the cerebellum were limited to neuronal survival but failed to restore important transcript signatures.

CXCR4/CXCL12-mediated entrapment of axons at the injury site compromises optic nerve regeneration

Regenerative failure in the mammalian optic nerve is generally attributed to axotomy-induced retinal ganglion cell (RGC) death, an insufficient intrinsic regenerative capacity, and an extrinsic inhibitory environment. Here, we show that a chemoattractive CXCL12/CXCR4-dependent mechanism prevents the extension of growth-stimulated axons into the distal nerve. The chemokine CXCL12 is chemoattractive toward axonal growth cones in an inhibitory environment, and these effects are entirely abolished by the specific knockout of its receptor, CXCR4 (CXCR4-/-), in cultured regenerating RGCs. Notably, 8% of naïve RGCs express CXCL12 and transport the chemokine along their axons in the nerve. Thus, axotomy causes its release at the injury site. However, most osteopontin-positive α-RGCs, the main neuronal population that survives optic nerve injury, express CXCR4 instead. Thus, CXCL12-mediated attraction prevents growth-stimulated axons from regenerating distally in the nerve, indicated by axons returning to the lesion site. Accordingly, specific depletion of CXCR4 in RGC reduces aberrant axonal growth and enables long-distance regeneration. Likewise, CXCL12 knockout in RGCs fully mimics these CXCR4-/- effects. Thus, active CXCL12/CXCR4-mediated entrapment of regenerating axons to the injury site contributes to regenerative failure in the optic nerve.

Single-Cell Transcriptomic Analyses of the Developing Meninges Reveal Meningeal Fibroblast Diversity and Function

The meninges are a multilayered structure composed of fibroblasts, blood and lymphatic vessels, and immune cells. Meningeal fibroblasts secrete a variety of factors that control CNS development, yet strikingly little is known about their heterogeneity or development. Using single-cell sequencing, we report distinct transcriptional signatures for fibroblasts in the embryonic dura, arachnoid, and pia. We define new markers for meningeal layers and show conservation in human meninges. We find that embryonic meningeal fibroblasts are transcriptionally distinct between brain regions and identify a regionally localized pial subpopulation marked by the expression of μ-crystallin. Developmental analysis reveals a progressive, ventral-to-dorsal maturation of telencephalic meninges. Our studies have generated an unparalleled view of meningeal fibroblasts, providing molecular profiles of embryonic meningeal fibroblasts by layer and yielding insights into the mechanisms of meninges development and function.

Meninges: A Widespread Niche of Neural Progenitors for the Brain

Emerging evidence highlights the several roles that meninges play in relevant brain functions as they are a protective membrane for the brain, produce and release several trophic factors important for neural cell migration and survival, control cerebrospinal fluid dynamics, and embrace numerous immune interactions affecting neural parenchymal functions. Furthermore, different groups have identified subsets of neural progenitors residing in the meninges during development and in the adulthood in different mammalian species, including humans. Interestingly, these immature neural cells are able to migrate from the meninges to the neural parenchyma and differentiate into functional cortical neurons or oligodendrocytes. Immature neural cells residing in the meninges promptly react to brain disease. Injury-induced expansion and migration of meningeal neural progenitors have been observed following experimental demyelination, traumatic spinal cord and brain injury, amygdala lesion, stroke, and progressive ataxia. In this review, we summarize data on the function of meninges as stem cell niche and on the presence of immature neural cells in the meninges, and discuss their roles in brain health and disease. Furthermore, we consider the potential exploitation of meningeal neural progenitors for the regenerative medicine to treat neurological disorders.

A preliminary study on the development of a novel biomatrix by decellularization of bovine spinal meninges for tissue engineering applications

Here, we aim at developing a novel biomatrix from decellularized bovine spinal meninges for tissue engineering and regenerative medicine applications. Within this concept, the bovine spinal meninges were decellularized using 1% Triton X-100 for 48 h, and residual nuclear content was determined with double-strand DNA content analysis and agarose gel electrophoresis. The major matrix components such as sulfated GAGs and collagen before and after the decellularization process were analyzed with DMMB, hydroxyproline assay and SDS-PAGE. Subsequently, the native bovine spinal meninges (nBSM) and decellularized BSM (dBSM) were physiochemically characterized via ATR-FTIR spectroscopy, TGA, DMA and tensile strength test. The dsDNA content in the nBSM was 153.39 ± 53.93 ng/mg dry weight, versus in the dBSM was 39.47 ± 4.93 ng/mg (n = 3) dry weight and DNA fragments of more than 200 bp in length were not detected in the dBSM by agarose gel electrophoresis. The sulfated GAGs contents for nBSM and dBSM were observed to be 10.87 ± 1.2 and 11.42 ± 2.01 μg/mg dry weight, respectively. The maximum strength of dBSM in dry and wet conditions was found to be 19.67 ± 0.21 MPa and 13.97 ± 0.17 MPa, while nBSM (dry) was found to be 26.26 ± 0.28 MPa. MTT, SEM, and histology results exhibited that the cells attached to the surface of dBSM, and proliferated on the dBSM. In conclusion, the in vitro preliminary study has demonstrated that the dBSM might be a proper and new bioscaffold for tissue engineering and regenerative medicine applications.

Axon Guidance and Collective Cell Migration by Substrate-Derived Attractants

Neurons have evolved specialized growth structures to reach and innervate their target cells. These growth cones express specific receptor molecules that sense environmental cues and transform them into steering decisions. Historically, various concepts of axon guidance have been developed to better understand how axons reach and identify their targets. The essence of these efforts seems to be that growth cones require solid substrates and that major guidance decisions are initiated by extracellular cues. These sometimes highly conserved ligands and receptors have been extensively characterized and mediate four major guidance forces: chemoattraction, chemorepulsion, contact attraction and contact repulsion. However, during development, cells, too, do migrate in order to reach molecularly-defined niches at target locations. In fact, axonal growth could be regarded as a special case of cellular migration, where only a highly polarized portion of the cell is elongating. Here, I combine several examples from genetically tractable model organisms, such as Drosophila or zebrafish, in which cells and axons are guided by attractive cues. Regardless, if these cues are secreted into the extracellular space or exposed on cellular surfaces, migrating cells and axons seem to keep close contact with these attractants and seem to detect them right at their source. Migration towards and along such substrate-derived attractants seem to be particularly robust, as genetic deletion induces obvious searching behaviors and permanent guidance errors. In addition, forced expression of these factors in ectopic tissues is highly distractive too, regardless of the pattern of other endogenous cues. Thus, guidance and migration towards and along attractive tissues is a powerful steering mechanism that exploits affinity differences to the surroundings and, in some instances, determines growth trajectories from source to target region.

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.

Integrity of Cajal-Retzius cells in the reeler-mouse hippocampus

Cajal-Retzius (CR) cells are early-born glutamatergic neurons that are primarily known as the early main source of the signal protein Reelin. In the reeler mutant, the absence of Reelin causes severe defects in the radial migration of neurons, resulting in abnormal cortical layering. To date, the exact morphological properties of CR-cells independent of Reelin are unknown. With this in view, we studied the ontogenesis, density, and distribution of CR-cells in reeler mice that were cross-bred with a CXCR4-EGFP reporter mouse line, thus enabling us to clearly identify CR-cells positions in the disorganized hippocampus of the reeler mouse. As evidenced by morphological analysis, differences were found regarding CR-cell distribution and density: generally, we found fewer CR-cells in the developing and adult reeler hippocampus as compared to the hippocampus of wild-type animals (WT); however, in reeler mice, CR-cells were much more closely associated to the hippocampal fissure (HF), resulting in relatively higher local CR-cell densities. This higher local cell density was accompanied by stronger immunoreactivity of the CXCR4 ligand, stroma-derived factor-1 (SDF-1) that is known to regulate CR-cell positioning. Importantly, confocal microscopy indicates an integration of CR-cells into the developing and adult hippocampal network in reeler mice, raising evidence that network integration of CR-cells might be independent of Reelin.

CXCR4-targeting nanobodies differentially inhibit CXCR4 function and HIV entry

The chemokine receptor CXCR4 and its ligand CXCL12 contribute to a variety of human diseases, such as cancer. CXCR4 is also a major co-receptor facilitating HIV entry. Accordingly, CXCR4 is considered as an attractive therapeutic target. Drug side effects and poor pharmacokinetic properties have been major hurdles that have prevented the implementation of CXCR4-directed inhibitors in treatment regimes. We evaluated the activity of a new and promising class of biologics, namely CXCR4-targeting nanobodies, with the purpose of identifying nanobodies that would preferentially inhibit HIV infection, while minimally disturbing other CXCR4-related functions. All CXCR4-interacting nanobodies inhibited CXCL12 binding and receptor-mediated calcium mobilization with comparable relative potencies. Importantly, the anti-HIV-1 activity of the nanobodies did not always correlate with their ability to modulate CXCR4 signaling and function, indicating that the anti-HIV and anti-CXCR4 activity are not entirely overlapping and may be functionally separated. Three nanobodies with divergent activity profiles (VUN400, VUN401 and VUN402) were selected for in depth biological evaluation. While all three nanobodies demonstrated inhibitory activity against a wide range of HIV (X4) strains, VUN402 poorly blocked CXCL12-induced CXCR4 internalization, chemotaxis and changes in cell morphology. Each of these nanobodies recognized distinct, although partially overlapping epitopes on CXCR4, which might underlie their distinct activity profiles. Our results demonstrate the potential of CXCR4-targeting nanobody VUN402 as a novel lead and starting point for the development of a more potent and selective anti-HIV agent.

Encapsulation of young donor age dopaminergic grafts in a GDNF-loaded collagen hydrogel further increases their survival, reinnervation, and functional efficacy after intrastriatal transplantation in hemi-Parkinsonian rats

Biomaterials have been shown to significantly improve the outcome of cellular reparative approaches for Parkinson's disease in experimental studies because of their ability to provide transplanted cells with a supportive microenvironment and shielding from the host immune system. However, given that the margin for improvement in such reparative therapies is considerable, further studies are required to fully investigate and harness the potential of biomaterials in this context. Given that several recent studies have demonstrated improved brain repair in Parkinsonian models when using dopaminergic grafts derived from younger foetal donors, we hypothesized that encapsulating these cells in a supportive biomaterial would further improve their reparative efficacy. Thus, this study aimed to determine the impact of a GDNF-loaded collagen hydrogel on the survival, reinnervation, and functional efficacy of dopaminergic neurons derived from young donors. To do so, hemi-Parkinsonian (6-hydroxydopamine-lesioned) rats received intrastriatal transplants of embryonic day 12 cells extracted from the rat ventral mesencephalon either alone, in a collagen hydrogel, with GDNF, or in a GDNF-loaded collagen hydrogel. Methamphetamine-induced rotational behaviour was assessed at three weekly intervals for a total of 12 weeks, after which rats were sacrificed for postmortem assessment of graft survival. We found that, following intrastriatal transplantation to the lesioned striatum, the GDNF-loaded collagen hydrogel significantly increased the survival (4-fold), reinnervation (5.4-fold), and functional efficacy of the embryonic day 12 dopaminergic neurons. In conclusion, this study further demonstrates the significant potential of biomaterial hydrogel scaffolds for cellular brain repair approaches in neurodegenerative diseases such as Parkinson's disease.

Using biomaterials to modulate chemotactic signaling for central nervous system repair

Chemotaxis enables cellular communication and movement within the body. This review focuses on exploiting chemotaxis as a tool for repair of the central nervous system (CNS) damaged from injury and/or degenerative diseases. Chemokines and factors alone may initiate repair following CNS injury/disease, but exogenous administration may enhance repair and promote regeneration. This review will discuss critical chemotactic molecules and factors that may promote neural regeneration. Additionally, this review highlights how biomaterials can impact the presentation and delivery of chemokines and growth factors to alter the regenerative response.

Multisystem multitasking by CXCL12 and its receptors CXCR4 and ACKR3

Chemokines are named and best known for their chemotactic cytokine activity in the hematopoietic system; however, their importance extends far beyond leukocytes, cell movement and immunoregulation. CXCL12, the most protean of chemokines, regulates development in multiple systems, including the hematopoietic, cardiovascular and nervous systems, and regulates diverse cell functions, including differentiation, distribution, activation, immune synapse formation, effector function, proliferation and survival in the immune system alone. The broad importance of CXCL12 is revealed by the complex lethal developmental phenotypes in mice lacking either Cxcl12 or either one of its two known 7-transmembrane domain receptors Cxcr4 and Ackr3, as well as by gain-of-function mutations in human CXCR4, which cause WHIM syndrome, a multisystem and combined immunodeficiency disease and the only Mendelian condition caused by a chemokine system mutation. In addition, wild type CXCR4 is important in the pathogenesis of HIV/AIDS and cancer. Thus, CXCL12 and its receptors CXCR4 and ACKR3 provide extraordinary examples of multisystem multitasking in the chemokine system in both health and disease.

Embryology

With the growing recognition of the extent and prevalence of human cerebellar disorders, an understanding of developmental programs that build the mature cerebellum is necessary. In this chapter we present an overview of the basic epochs and key molecular regulators of the developmental programs of cerebellar development. These include early patterning of the cerebellar territory, the genesis of cerebellar cells from multiple spatially distinct germinal zones, and the extensive migration and coordinated cellular rearrangements that result in the formation of the exquisitely foliated and laminated mature cerebellum. This knowledge base is founded on extensive analysis of animal models, particularly mice, due in large part to the ease of genetic manipulation of this important model organism. Since cerebellar structure and function are largely conserved across species, mouse cerebellar development is highly relevant to humans and has led to important insights into the developmental pathogenesis of human cerebellar disorders. Human fetal cerebellar development remains largely undescribed; however, several human-specific developmental features are known which are relevant to human disease and underline the importance of ongoing human fetal research.

Immunoregulatory effect of mast cells influenced by microbes in neurodegenerative diseases

When related to central nervous system (CNS) health and disease, brain mast cells (MCs) can be a source of either beneficial or deleterious signals acting on neural cells. We review the current state of knowledge about molecular interactions between MCs and glia in neurodegenerative diseases such as Multiple Sclerosis, Alzheimer's disease, Amyotrophic Lateral Sclerosis, Parkinson's disease, Epilepsy. We also discuss the influence on MC actions evoked by the host microbiota, which has a profound effect on the host immune system, inducing important consequences in neurodegenerative disorders. Gut dysbiosis, reduced intestinal motility and increased intestinal permeability, that allow bacterial products to circulate and pass through the blood-brain barrier, are associated with neurodegenerative disease. There are differences between the microbiota of neurologic patients and healthy controls. Distinguishing between cause and effect is a challenging task, and the molecular mechanisms whereby remote gut microbiota can alter the brain have not been fully elucidated. Nevertheless, modulation of the microbiota and MC activation have been shown to promote neuroprotection. We review this new information contributing to a greater understanding of MC-microbiota-neural cells interactions modulating the brain, behavior and neurodegenerative processes.

Neural Stem Cell Plasticity: Advantages in Therapy for the Injured Central Nervous System

The physiological and pathological properties of the neural germinal stem cell niche have been well-studied in the past 30 years, mainly in animals and within given limits in humans, and knowledge is available for the cyto-architectonic structure, the cellular components, the timing of development and the energetic maintenance of the niche, as well as for the therapeutic potential and the cross talk between neural and immune cells. In recent years we have gained detailed understanding of the potentiality of neural stem cells (NSCs), although we are only beginning to understand their molecular, metabolic, and epigenetic profile in physiopathology and, further, more can be invested to measure quantitatively the activity of those cells, to model in vitro their therapeutic responses or to predict interactions in silico. Information in this direction has been put forward for other organs but is still limited in the complex and very less accessible context of the brain. A comprehensive understanding of the behavior of endogenous NSCs will help to tune or model them toward a desired response in order to treat complex neurodegenerative diseases. NSCs have the ability to modulate multiple cellular functions and exploiting their plasticity might make them into potent and versatile cellular drugs.

Phenotypic outcomes in Mouse and Human Foxc1 dependent Dandy-Walker cerebellar malformation suggest shared mechanisms

FOXC1 loss contributes to Dandy-Walker malformation (DWM), a common human cerebellar malformation. Previously, we found that complete Foxc1 loss leads to aberrations in proliferation, neuronal differentiation and migration in the embryonic mouse cerebellum (Haldipur et al., 2014). We now demonstrate that hypomorphic Foxc1 mutant mice have granule and Purkinje cell abnormalities causing subsequent disruptions in postnatal cerebellar foliation and lamination. Particularly striking is the presence of a partially formed posterior lobule which echoes the posterior vermis DW 'tail sign' observed in human imaging studies. Lineage tracing experiments in Foxc1 mutant mouse cerebella indicate that aberrant migration of granule cell progenitors destined to form the posterior-most lobule causes this unique phenotype. Analyses of rare human del chr 6p25 fetal cerebella demonstrate extensive phenotypic overlap with our Foxc1 mutant mouse models, validating our DWM models and demonstrating that many key mechanisms controlling cerebellar development are likely conserved between mouse and human.

DOI:http://dx.doi.org/10.7554/eLife.20898.001

CXCL12/CXCR4/CXCR7 Chemokine Axis in the Central Nervous System: Therapeutic Targets for Remyelination in Demyelinating Diseases

The chemokine CXCL12 plays a vital role in regulating the development of the central nervous system (CNS) by binding to its receptors CXCR4 and CXCR7. Recent studies reported that the CXCL12/CXCR4/CXCR7 axis regulates both embryonic and adult oligodendrocyte precursor cells (OPCs) in their proliferation, migration, and differentiation. The changes in the expression and distribution of CXCL12 and its receptors are tightly associated with the pathological process of demyelination in multiple sclerosis (MS), suggesting that modulating the CXCL12/CXCR4/CXCR7 axis may benefit myelin repair by enhancing OPC recruitment and differentiation. This review aims to integrate the current findings of the CXCL12/CXCR4/CXCR7 signaling pathway in the CNS and to highlight its role in oligodendrocyte development and demyelinating diseases. Furthermore, this review provides potential therapeutic strategies for myelin repair by analyzing the relevance between the pathological changes and the regulatory roles of CXCL12/CXCR4/CXCR7 during MS.

Anatomy of the Spinal Meninges

BACKGROUND

The spinal meninges have received less attention than the cranial meninges in the literature, although several points remain debatable and poorly understood, like their phylogenesis, their development, and their interactions with the spinal cord. Their constancy among the chordates shows their crucial importance in central nervous system homeostasis and suggests a role far beyond mechanical protection of the neuraxis.

OBJECTIVE

This work provides an extensive study of the spinal meninges, from an overview of their phylogenesis and embryology to a descriptive and topographic anatomy with clinical implications. It examines their involvement in spinal cord development, functioning, and repair.

METHODS

This work is a review of the literature using PubMed as a search engine on Medline.

RESULTS

The stages followed by the meninges along the phylogenesis could not be easily compared with their development in vertebrates for methodological aspects and convergence processes throughout evolution. The distinction between arachnoid and pia mater appeared controversial. Several points of descriptive anatomy remain debatable: the functional organization of the arterial network, and the venous and lymphatic drainages, considered differently by classical anatomic and neuroradiological approaches. Spinal meninges are involved in neurodevelopment and neurorepair producing neural stem cells and morphogens, in cerebrospinal fluid dynamics and neuraxis functioning by the synthesis of active molecules, and the elimination of waste products of central nervous system metabolism.

CONCLUSION

The spinal meninges should be considered as dynamic functional formations evolving over a lifetime, with ultrastructural features and functional interactions with the neuraxis remaining not fully understood.

Asymmetric cell division of granule neuron progenitors in the external granule layer of the mouse cerebellum

The plane of division of granule neuron progenitors (GNPs) was analysed with respect to the pial surface in P0 to P14 cerebellum and the results showed that there was a significant bias towards the plane of cell division being parallel to pial surface across this developmental window. In addition, the distribution of β-Catenin in anaphase cells was analysed, which showed that there was a significant asymmetry in the distribution of β-Catenin in dividing GNPs. Further, inhibition of Sonic Hedgehog (Shh) signalling had an effect on plane of cell division. Asymmetric distribution of β-Catenin was shown to occur towards the source of a localized extracellular cue.

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.

Foxc1 dependent mesenchymal signalling drives embryonic cerebellar growth

Loss of Foxc1 is associated with Dandy-Walker malformation, the most common human cerebellar malformation characterized by cerebellar hypoplasia and an enlarged posterior fossa and fourth ventricle. Although expressed in the mouse posterior fossa mesenchyme, loss of Foxc1 non-autonomously induces a rapid and devastating decrease in embryonic cerebellar ventricular zone radial glial proliferation and concurrent increase in cerebellar neuronal differentiation. Subsequent migration of cerebellar neurons is disrupted, associated with disordered radial glial morphology. In vitro, SDF1α, a direct Foxc1 target also expressed in the head mesenchyme, acts as a cerebellar radial glial mitogen and a chemoattractant for nascent Purkinje cells. Its receptor, Cxcr4, is expressed in cerebellar radial glial cells and conditional Cxcr4 ablation with Nes-Cre mimics the Foxc1-/- cerebellar phenotype. SDF1α also rescues the Foxc1-/- phenotype. Our data emphasizes that the head mesenchyme exerts a considerable influence on early embryonic brain development and its disruption contributes to neurodevelopmental disorders in humans.

Role of CXCL12 and CXCR4 in normal cerebellar development and medulloblastoma

Chemokines and its receptors have significant impact on physiological and pathological processes and studies concerning their association with tumor biology are subject of great interest in scientific community. CXCL12/CXCR4 axis has been widely studied due to its significant role in tumor microenvironment, but it is also important to development and maintenance of tissues and organs, for example, in the brain and cerebellum. Studies have demonstrated that CXCL12 and CXCR4 are required for normal cerebellar development and that dysfunction in this pathway may be involved with medulloblastoma pathogenesis. In this context, a new molecular subgroup has been suggested based on the importance of the association between CXCR4 overexpression and sonic hedgehog subgroup. Treatment using CXCR4 antagonists showed significant results, evidencing the important role and possible therapeutic capacity of CXCR4 in MB. This review summarizes studies on MB cell biology, focusing on a chemokine-receptor axis, CXCL12/CXCR4, that may have implications for treatment strategies once it can improve life expectancy and reduce neurocognitive sequelae of patients with this neoplasia.

Chemokine signaling in development and disease

Chemokines are a group of small, secreted molecules that signal through G protein-coupled receptors to promote cell survival and proliferation and to provide directional guidance to migrating cells. CXCL12 is one of the most evolutionary conserved chemokines and signals through the chemokine receptor CXCR4 to guide cell migration during embryogenesis, immune cell trafficking and cancer metastasis. Here and in the accompanying poster, we provide an overview of chemokine signaling, focusing on CXCL12, and we highlight some of the different chemokine-dependent strategies used to guide migrating cells.

Sema3E/PlexinD1 regulates the migration of hem-derived Cajal-Retzius cells in developing cerebral cortex

During the development of the cerebral cortex, Cajal-Retzius (CR) cells settle in the preplate and coordinate the precise growth of the neocortex. Indeed, CR cells migrate tangentially from specific proliferative regions of the telencephalon (for example, the cortical hem (CH)) to populate the entire cortical surface. This is a very finely tuned process regulated by an emerging number of factors that has been sequentially revealed in recent years. However, the putative participation of one of the major families of axon guidance molecules in this process, the Semaphorins, was not explored. Here we show that Semaphorin-3E (Sema3E) is a natural negative regulator of the migration of PlexinD1-positive CR cells originating in the CH. Our results also indicate that Sema3E/PlexinD1 signalling controls the motogenic potential of CR cells in vitro and in vivo. Indeed, absence of Sema3E/PlexinD1 signalling increased the migratory properties of CR cells. This modulation implies negative effects on CXCL12/CXCR4 signalling and increased ADF/Cofilin activity.

Cxcl12/Cxcr4 signaling controls the migration and process orientation of A9-A10 dopaminergic neurons

CXCL12/CXCR4 signaling has been reported to regulate three essential processes for the establishment of neural networks in different neuronal systems: neuronal migration, cell positioning and axon wiring. However, it is not known whether it regulates the development of A9-A10 tyrosine hydroxylase positive (TH(+)) midbrain dopaminergic (mDA) neurons. We report here that Cxcl12 is expressed in the meninges surrounding the ventral midbrain (VM), whereas CXCR4 is present in NURR1(+) mDA precursors and mDA neurons from E10.5 to E14.5. CXCR4 is activated in NURR1(+) cells as they migrate towards the meninges. Accordingly, VM meninges and CXCL12 promoted migration and neuritogenesis of TH(+) cells in VM explants in a CXCR4-dependent manner. Moreover, in vivo electroporation of Cxcl12 at E12.5 in the basal plate resulted in lateral migration, whereas expression in the midline resulted in retention of TH(+) cells in the IZ close to the midline. Analysis of Cxcr4(-/-) mice revealed the presence of VM TH(+) cells with disoriented processes in the intermediate zone (IZ) at E11.5 and marginal zone (MZ) at E14. Consistently, pharmacological blockade of CXCR4 or genetic deletion of Cxcr4 resulted in an accumulation of TH(+) cells in the lateral aspect of the IZ at E14, indicating that CXCR4 is required for the radial migration of mDA neurons in vivo. Altogether, our findings demonstrate that CXCL12/CXCR4 regulates the migration and orientation of processes in A9-A10 mDA neurons.

Chemokines induce axon outgrowth downstream of Hepatocyte Growth Factor and TCF/β-catenin signaling

Axon morphogenesis is a complex process regulated by a variety of secreted molecules, including morphogens and growth factors, resulting in the establishment of the neuronal circuitry. Our previous work demonstrated that growth factors [Neurotrophins (NT) and Hepatocyte Growth Factor (HGF)] signal through β-catenin during axon morphogenesis. HGF signaling promotes axon outgrowth and branching by inducing β-catenin phosphorylation at Y142 and transcriptional regulation of T-Cell Factor (TCF) target genes. Here, we asked which genes are regulated by HGF signaling during axon morphogenesis. An array screening indicated that HGF signaling elevates the expression of chemokines of the CC and CXC families. In line with this, CCL7, CCL20, and CXCL2 significantly increase axon outgrowth in hippocampal neurons. Experiments using blocking antibodies and chemokine receptor antagonists demonstrate that chemokines act downstream of HGF signaling during axon morphogenesis. In addition, qPCR data demonstrates that CXCL2 and CCL5 expression is stimulated by HGF through Met/b-catenin/TCF pathway. These results identify CC family members and CXCL2 chemokines as novel regulators of axon morphogenesis downstream of HGF signaling.

The CXCL16-CXCR6 chemokine axis in glial tumors

Since chemokines and their receptors play a pivotal role in tumors, we investigated the CXCL16-CXCR6-axis in human astroglial tumors. The transmembrane chemokine CXCL16 is heavily expressed by tumor, microglial and endothelial cells in situ and in vitro. In contrast, the receptor CXCR6 is restricted in glioblastomas to a small subset of proliferating cells positive for the stem-cell markers Musashi, Nanog, Sox2 and Oct4. In particular, the vast majority (about 90%) of Musashi-positive cells stained also for CXCR6. Thus, CXCL16 is highly expressed by glial tumor and stroma cells whereas CXCR6 defines a subset of cells with stem cell character.

Interstitial flow in a 3D microenvironment increases glioma invasion by a CXCR4-dependent mechanism

Brain tumor invasion leads to recurrence and resistance to treatment. Glioma cells invade in distinct patterns, possibly determined by microenvironmental cues including chemokines, structural heterogeneity, and fluid flow. We hypothesized that flow originating from pressure differentials between the brain and tumor is active in glioma invasion. Using in vitro models, we show that interstitial flow promotes cell invasion in multiple glioma cell lines. Flow effects were CXCR4-dependent, because they were abrogated by CXCR4 inhibition. Furthermore, CXCR4 was activated in response to flow, which could be responsible for enhanced cell motility. Flow was seen to enhance cell polarization in the flow direction, and this flow-induced polarization could be blocked by CXCR4 inhibition or CXCL12 oversaturation in the matrix. Furthermore, using live imaging techniques in a three-dimensional flow chamber, there were more cells migrating and more cells migrating in the direction of flow. This study shows that interstitial flow is an active regulator of glioma invasion. The new mechanisms of glioma invasion that we identify here-namely, interstitial flow-enhanced motility, activation of CXCR4, and CXCL12-driven autologous chemotaxis-are significant in therapy to prevent or treat brain cancer invasion. Current treatment strategies can lead to edema and altered flow in the brain, and one popular experimental treatment in clinical trials, convection enhanced delivery, involves enhancement of flow in and around the tumor. A better understanding of how interstitial flow at the tumor margin can alter chemokine distributions, cell motility, and directed invasion offers a better understanding of treatment failure. .

An infernal trio: the chemokine CXCL12 and its receptors CXCR4 and CXCR7 in tumor biology

Chemokines are small peptide mediators that play a role in many physiological and pathological processes. Apart from their initially discovered function in trafficking of leukocytes, they also influence migration, proliferation, survival and gene expression of a variety of cell types in their respective microenvironment. Chemokines can exert these effects via their respective G protein-coupled receptor. Over the recent decade, the involvement of chemokines and their respective receptors in tumor biology has been successively elucidated. This review will focus on the signaling and effects of the widespread chemokine CXCL12 and its long known G protein-coupled receptor CXCR4 and the recently discovered non-G protein-coupled receptor CXCR7 with a detailed reflection on glioma biology.

Proteolytic processing of SDF-1α by matrix metalloproteinase-2 impairs CXCR4 signaling and reduces neural progenitor cell migration

Neural stem cells and neural progenitor cells (NPCs) exist throughout life and are mobilized to replace neurons, astrocytes and oligodendrocytes after injury. Stromal cell-derived factor 1 (SDF-1, now named CXCL12) and its receptor CXCR4, an α-chemokine receptor, are critical for NPC migration into damaged areas of the brain. Our previous studies demonstrated that immune activated and/or HIV-1-infected human monocyte-derived-macrophages (MDMs) induced a substantial increase of SDF-1 production by human astrocytes. However, matrix metalloproteinase (MMP)-2, a protein up-regulated in HIV-1-infected macrophages, is able to cleave four amino acids from the N-terminus of SDF-1, resulting in a truncated SDF-1(5-67). In this study, we investigate the diverse signaling and function induced by SDF-1α and SDF-1(5-67) in human cortical NPCs. SDF-1(5-67) was generated by incubating human recombinant SDF-1α with MMP-2 followed by protein determination via mass spectrometry, Western blotting and ELISA. SDF-1α induced time-dependent phosphorylation of extracellular signal-regulated kinases (ERK) 1/2, Akt-1, and diminished cyclic adenosine monophosphate (cAMP). In contrast, SDF-1(5-67) failed to induce these signaling. SDF-1α activation of CXCR4 induced migration of NPCs, an effect that is dependent on ERK1/2 and Akt-1 pathways; whereas SDF-1(5-67) failed to induce NPC migration. This observation provides evidence that MMP-2 may affect NPC migration through post-translational processing of SDF-1α.

Chemokine CXCL12 and its receptors in the developing central nervous system: emerging themes and future perspectives

Homeostatic chemokine CXCL12 (also known as SDF-1) and its receptor CXCR4 are indispensable for the normal development of the nervous system. This chemokine system plays a plethora of functions in numerous neural developmental processes, from which the underlying molecular and cellular mechanisms are beginning to be unravelled. Recent identification of CXCR7 as a second receptor for CXCL12 provides opportunities to gain deeper insights into how CXCL12 operates in the nervous system. Here, we review the diverse roles of CXCL12 in the developing central nervous system, summarize the recent progress in uncovering CXCR7 functions, and discuss the emerging common themes from these works and future perspectives.

CXCR4-Expressing Glial Precursor Cells Demonstrate Enhanced Migratory Tropism for Glioma

Malignant glioma remains one of the most intractable of human cancers principally due to the highly infiltrative nature of these neoplasms. The use of neural precursor cells (NPC) has received considerable attention based on their ability to selectively migrate towards disseminated areas of tumor in vivo and their described ability to deliver tumor-directed therapies specifically to infiltrating tumor cells. Fundamental to optimizing the use of these cells for potential clinical translation is the development of an understanding regarding the biologic cues that govern their ability to migrate towards infiltrative glioma foci. To this end, in this paper we detail that NPC selected for double-expression of the glial-precursor marker A2B5 and the cell-surface chemokine receptor, CXCR4, demonstrate enhanced in vitro glioma-directed tropism. These findings demonstrate the relevance of these markers for the phenotypic segregation of an optimally tumor-tropic NPC sub-population as a means of enhancing NPC-based therapeutic strategies for the treatment of glioma.

Cellular and subcellular localization of CXCL12 and CXCR4 in rat nociceptive structures: physiological relevance

Initial studies implicated the chemokine CXC motif ligand 12 (CXCL12) and its cognate CXC motif receptor 4 (CXCR4) in pain modulation. However, there has been no description of the distribution, transport and axonal sorting of CXCL12 and CXCR4 in rat nociceptive structures, and their direct participation in nociception modulation has not been demonstrated. Here, we report that acute intrathecal administration of CXCL12 induced mechanical hypersensitivity in naive rats. This effect was prevented by a CXCR4-neutralizing antibody. To determine the morphological basis of this behavioural response, we used light and electron microscopic immunohistochemistry to map CXCL12- and CXCR4-immunoreactive elements in dorsal root ganglia, lumbar spinal cord, sciatic nerve and skin. Light microscopy analysis revealed CXCL12 and CXCR4 immunoreactivity in calcitonin gene related peptide-containing peptidergic primary sensory neurons, which were both conveyed to central and peripheral sensory nerve terminals. Electron microscopy clearly demonstrated CXCL12 and CXCR4 immunoreactivity in primary sensory nerve terminals in the dorsal horn; both were sorted into small clear vesicles and large dense-core vesicles. This suggests that CXCL12 and CXCR4 are trafficked from nerve cell bodies to the dorsal horn. Double immunogold labelling for CXCL12 and calcitonin gene related peptide revealed partial vesicular colocalization in axonal terminals. We report, for the first time, that CXCR4 receptors are mainly located on the neuronal plasma membrane, where they are present at pre-synaptic and post-synaptic sites of central terminals. Receptor inactivation experiments, behavioural studies and morphological analyses provide strong evidence that the CXCL12/CXCR4 system is involved in modulation of nociceptive signalling.

Identification of cancer stem cells from human glioblastomas: growth and differentiation capabilities and CD133/prominin-1 expression

CD133 can be a marker of tumorigenic CSCs (cancer stem cells) in human GBM (glioblastoma multiforme), although tumorigenic CD133-negative CSCs have been also isolated. Additional evidence indicates that CSCs from GBM exhibit different phenotypes, with increasing interest in the potential significance of the different CSCs with respect to diagnosis, prognosis and the development of novel targets for treatment. We have analysed the expression of CD133 in freshly isolated cells from 15 human GBM specimens. Only 4 of them contained cells positive for AC133 by FACS analysis, and all of them yielded distinct CSC lines, whereas only 6 CSC lines were obtained from the other 11 GBMs. Of these 10 CSCs lines, we further characterized 6 CSC lines. Three CSCs grew as fast-growing neurospheres with higher clonogenic ability, whereas the remaining 3 grew as slow-growing semi-adherent spheres of lower clonogenicity. In addition, the former CSC lines displayed better differentiation capabilities than the latter ones. PCR and Western blot analysis showed that all 6 GBM CSC lines expressed CD133/prominin-1, suggesting that cells negative by FACS analysis may actually represent cells expressing low levels of CD133 undetected by FACS. Nevertheless, all the 6 CSC lines were tumorigenic in nude mice. In conclusion, CSCs from human primary GBMs show different phenotypes and variable levels of CD133 expression, but these parameters did not directly correlate with the tumorigenic potential.

Inflammatory regulators of redirected neural migration in the injured brain

Brain injury following stroke or trauma induces the migration of neuroblasts derived from subventricular zone neural precursor cells (NPCs) towards the damaged tissue, where they then have the potential to contribute to repair. Enhancing the recruitment of new cells thus presents an enticing prospect for the development of new therapeutic approaches to treat brain injury; to this end, an understanding of the factors regulating this process is required. During the neuroinflammatory response to ischemic and traumatic brain injuries, a plethora of pro- and anti-inflammatory cytokines, chemokines and growth factors are released in the damaged tissue, and recent work indicates that a variety of these are able to influence injury-induced migration. In this review, we will discuss the contribution of specific chemokines and growth factors towards stimulating NPC migration in the injured brain.