Myelination of rodent hippocampal neurons in culture

Disease phenotypic screening in neuron-glia cocultures identifies blockers of inflammatory neurodegeneration

Neuropathology is often mediated by interactions between neurons and glia that cannot be modeled by monocultures. However, cocultures are difficult to use and analyze for high-content screening. Here, we perform compound screening using primary neuron-glia cultures to model inflammatory neurodegeneration, live-cell stains, and automated classification of neurons, astrocytes or microglia using open-source software. Out of 227 compounds with known bioactivities, 29 protected against lipopolysaccharide-induced neuronal loss, including drugs affecting adrenergic, steroid, inflammatory and MAP kinase signaling. The screen also identified physiological compounds, such as noradrenaline and progesterone, that protected and identified neurotoxic compounds, such as a TLR7 agonist, that induced microglial proliferation. Most compounds used here have not been tested in a neuron-glia coculture neurodegeneration assay previously. Thus, combining a complex cellular disease model with high-content screening of known compounds and automated image analysis allows identification of important biology, as well as potential targets and drugs for treatment.

A computational model to uncover the biophysical underpinnings of neural firing heterogeneity in dissociated hippocampal cultures

Calcium (Ca2+ ) imaging reveals a variety of correlated firing in cultures of dissociated hippocampal neurons, pinpointing the non-synaptic paracrine release of glutamate as a possible mediator for such firing patterns, although the biophysical underpinnings remain unknown. An intriguing possibility is that extracellular glutamate could bind metabotropic receptors linked with inositol trisphosphate (IP3 ) mediated release of Ca2+ from the endoplasmic reticulum of individual neurons, thereby modulating neural activity in combination with sarco/endoplasmic reticulum Ca2+ transport ATPase (SERCA) and voltage-gated Ca2+ channels (VGCC). However, the possibility that such release may occur in different neuronal compartments and can be inherently stochastic poses challenges in the characterization of such interplay between various Ca2+ channels. Here we deploy biophysical modeling in association with Monte Carlo parameter sampling to characterize such interplay and successfully predict experimentally observed Ca2+ patterns. The results show that the neurotransmitter level at the plasma membrane is the extrinsic source of heterogeneity in somatic Ca2+ transients. Our analysis, in particular, identifies the origin of such heterogeneity to an intrinsic differentiation of hippocampal neurons in terms of multiple cellular properties pertaining to intracellular Ca2+ signaling, such as VGCC, IP3 receptor, and SERCA expression. In the future, the biophysical model and parameter estimation approach used in this study can be upgraded to predict the response of a system of interconnected neurons.

The Mechanical Microenvironment Regulates Axon Diameters Visualized by Cryo-Electron Tomography

Axonal varicosities or swellings are enlarged structures along axon shafts and profoundly affect action potential propagation and synaptic transmission. These structures, which are defined by morphology, are highly heterogeneous and often investigated concerning their roles in neuropathology, but why they are present in the normal brain remains unknown. Combining confocal microscopy and cryo-electron tomography (Cryo-ET) with in vivo and in vitro systems, we report that non-uniform mechanical interactions with the microenvironment can lead to 10-fold diameter differences within an axon of the central nervous system (CNS). In the brains of adult Thy1-YFP transgenic mice, individual axons in the cortex displayed significantly higher diameter variation than those in the corpus callosum. When being cultured on lacey carbon film-coated electron microscopy (EM) grids, CNS axons formed varicosities exclusively in holes and without microtubule (MT) breakage, and they contained mitochondria, multivesicular bodies (MVBs), and/or vesicles, similar to the axonal varicosities induced by mild fluid puffing. Moreover, enlarged axon branch points often contain MT free ends leading to the minor branch. When the axons were fasciculated by mimicking in vivo axonal bundles, their varicosity levels reduced. Taken together, our results have revealed the extrinsic regulation of the three-dimensional ultrastructures of central axons by the mechanical microenvironment under physiological conditions.

Inhibition of Connexin 36 attenuates HMGB1-mediated depressive-like behaviors induced by chronic unpredictable mild stress

BACKGROUND

High mobility group box 1 (HMGB1) released by neurons and microglia was demonstrated to be an important mediator in depressive-like behaviors induced by chronic unpredictable mild stress (CUMS), which could lead to the imbalance of two different metabolic approaches in kynurenine pathway (KP), thus enhancing glutamate transmission and exacerbating depressive-like behaviors. Evidence showed that HMGB1 signaling might be regulated by Connexin (Cx) 36 in inflammatory diseases of central nervous system (CNS). Our study aimed to further explore the role of Cx36 in depressive-like behaviors and its relationship with HMGB1.

METHODS

After 4-week chronic stress, behavioral tests were conducted to evaluate depressive-like behaviors, including sucrose preference test (SPT), tail suspension test (TST), forced swimming test (FST), and open field test (OFT). Western blot analysis and immunofluorescence staining were used to observe the expression and location of Cx36. Enzyme-linked immunosorbent assay (ELISA) was adopted to detect the concentrations of inflammatory cytokines. And the excitability and inward currents of hippocampal neurons were recorded by whole-cell patch clamping.

RESULTS

The expression of Cx36 was significantly increased in hippocampal neurons of mice exposed to CUMS, while treatment with glycyrrhizinic acid (GZA) or quinine could both down-regulate Cx36 and alleviate depressive-like behaviors. The proinflammatory cytokines like HMGB1, tumor necrosis factor alpha (TNF-α), and interleukin-1β (IL-1β) were all elevated by CUMS, and application of GZA and quinine could decrease them. In addition, the enhanced excitability and inward currents of hippocampal neurons induced by lipopolysaccharide (LPS) could be reduced by either GZA or quinine.

CONCLUSIONS

Inhibition of Cx36 in hippocampal neurons might attenuates HMGB1-mediated depressive-like behaviors induced by CUMS through down-regulation of the proinflammatory cytokines and reduction of the excitability and intracellular ion overload.

Immediate induction of varicosities by transverse compression but not uniaxial stretch in axon mechanosensation

Uniaxial stretch is believed to drive diffuse axonal injury (DAI) in mild traumatic brain injury (mTBI). Axonal varicosities are enlarged structures along axonal shafts and represent a hallmark feature of DAI. Here we report that axonal varicosities initiate in vivo immediately after head impact and are mainly induced by transverse compression but not uniaxial stretch. Vertical and lateral impacts to the mouse head induced axonal varicosities in distinct brain regions before any changes of microglial markers. Varicosities preferentially formed along axons perpendicular to impact direction. In cultured neurons, whereas 50% uniaxial strain was needed to rapidly induce axonal varicosities in a nanowrinkled stretch assay, physiologically-relevant transverse compression effectively induced axonal varicosities in a fluid puffing assay and can generate large but nonuniform deformation simulated by finite element analysis. Therefore, impact strength and direction may determine the threshold and spatial pattern of axonal varicosity initiation, respectively, partially resulting from intrinsic properties of axon mechanosensation.

Terahertz exposure enhances neuronal synaptic transmission and oligodendrocyte differentiation in vitro

Terahertz (THz) frequency occupies a large portion of the electromagnetic spectrum that is between the infrared and microwave regions. Recent advances in THz application have stimulated interests regarding the biological effects within this frequency range. In the current study, we report that irradiation with a single-frequency THz laser on mice cortical neuron cultures increases excitatory synaptic transmission and neuronal firing activities. Microarray assay reveals gene expression dynamics after THz exposure, which is consistent with morphology and electrophysiology results. Besides, certain schedule of THz irradiation inhibits the proliferation of oligodendrocyte precursor cells (OPCs) and promotes OPC differentiation. Of note, the myelination process is enhanced after THz exposure. In summary, our observations suggest that THz irradiation can modulate the functions of different neuronal cells, with different sensitivity to THz. These results provide important understanding of the mechanisms that govern THz interactions with nervous systems and suggest THz wave as a new strategy for neuromodulation.

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THz irradiation increases excitatory synaptic transmission and neuronal firing

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Microarray assay reveals neuronal gene expression dynamics after THz exposure

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THz irradiation promotes the maturation of oligodendrocytes

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The myelination process in neuron is enhanced after THz exposure

Novel in vitro Experimental Approaches to Study Myelination and Remyelination in the Central Nervous System

Myelin is the lipidic insulating structure enwrapping axons and allowing fast saltatory nerve conduction. In the central nervous system, myelin sheath is the result of the complex packaging of multilamellar extensions of oligodendrocyte (OL) membranes. Before reaching myelinating capabilities, OLs undergo a very precise program of differentiation and maturation that starts from OL precursor cells (OPCs). In the last 20 years, the biology of OPCs and their behavior under pathological conditions have been studied through several experimental models. When co-cultured with neurons, OPCs undergo terminal maturation and produce myelin tracts around axons, allowing to investigate myelination in response to exogenous stimuli in a very simple in vitro system. On the other hand, in vivo models more closely reproducing some of the features of human pathophysiology enabled to assess the consequences of demyelination and the molecular mechanisms of remyelination, and they are often used to validate the effect of pharmacological agents. However, they are very complex, and not suitable for large scale drug discovery screening. Recent advances in cell reprogramming, biophysics and bioengineering have allowed impressive improvements in the methodological approaches to study brain physiology and myelination. Rat and mouse OPCs can be replaced by human OPCs obtained by induced pluripotent stem cells (iPSCs) derived from healthy or diseased individuals, thus offering unprecedented possibilities for personalized disease modeling and treatment. OPCs and neural cells can be also artificially assembled, using 3D-printed culture chambers and biomaterial scaffolds, which allow modeling cell-to-cell interactions in a highly controlled manner. Interestingly, scaffold stiffness can be adopted to reproduce the mechanosensory properties assumed by tissues in physiological or pathological conditions. Moreover, the recent development of iPSC-derived 3D brain cultures, called organoids, has made it possible to study key aspects of embryonic brain development, such as neuronal differentiation, maturation and network formation in temporal dynamics that are inaccessible to traditional in vitro cultures. Despite the huge potential of organoids, their application to myelination studies is still in its infancy. In this review, we shall summarize the novel most relevant experimental approaches and their implications for the identification of remyelinating agents for human diseases such as multiple sclerosis.

Aberrant oligodendroglial LDL receptor orchestrates demyelination in chronic cerebral ischemia

Oligodendrocytes express low-density lipoprotein receptor (LDLR) to endocytose cholesterol for the maintenance of adulthood myelination. However, the potential role of LDLR in chronic cerebral ischemia-related demyelination remains unclear. We used bilateral carotid artery stenosis (BCAS) to induce sustained cerebral ischemia in mice. This hypoxic-ischemic injury caused a remarkable decrease in oligodendroglial LDLR, with impaired oligodendroglial differentiation and survival. Oligodendroglial cholesterol levels, however, remained unchanged. Mouse miR-344e-3p and the human homolog miR-410-3p, 2 miRNAs directly targeting Ldlr, were identified in experimental and clinical leukoaraiosis and were thus implicated in the LDLR reduction. Lentiviral delivery of LDLR ameliorated demyelination following chronic cerebral ischemia. By contrast, Ldlr-/- mice displayed inadequate myelination in the corpus callosum. Ldlr-/- oligodendrocyte progenitor cells (OPCs) exhibited reduced ability to differentiate and myelinate axons in vitro. Transplantation with Ldlr-/- OPCs could not rescue the BCAS-induced demyelination. Such LDLR-dependent myelin restoration might involve a physical interaction of the Asn-Pro-Val-Tyr (NPVY) motif with the phosphotyrosine binding domain of Shc, which subsequently activated the MEK/ERK pathway. Together, our findings demonstrate that the aberrant oligodendroglial LDLR in chronic cerebral ischemia impairs myelination through intracellular signal transduction. Preservation of oligodendroglial LDLR may provide a promising approach to treat ischemic demyelination.

Nonlinearity of the coefficient of thermal expansion in brain tissue

The coefficient of thermal expansion (CTE) in biological tissues is an integral parameter behind the application of electromagnetic energy to biomedical technologies; however, its behavior is far from being fully characterized. In this study, we apply digital image correlation (DIC) to non-invasively measure the microscale thermal expansions of recently excised embryonic E18 rodent brain tissue slices. Although the CTE has been measured previously in soft tissues, the literature surrounding the expansion of brain tissue remains sparse. Previous work in measuring the thermal expansion behavior of soft tissue often simplifies the results into a single measurement of a linear CTE parameter and fails to convey the temperature-dependent nonlinearity that exists. In this work, we demonstrate that: (1) the coefficient of brain tissue is more similar to fat than blood, and (2) there exists a significant nonlinear increase in CTE at physiologically-relevant temperatures. This suggests some limitations with the interpretation of previously reported values of the CTE, which are often measured at room temperature.

Predominant differentiation of rat fetal neural stem cells into functional oligodendrocytes in vitro

Oligodendrocytes form myelin in the CNS. A fast method to produce large quantity of oligodendrocytes that have the capacity of myelinating CNS neurons would be very useful for treating CNS injuries or demyelinating diseases, or for research purposes. We developed a simple standard protocol for predominant differentiation of rat fetal neural stem cells (NSCs) into oligodendrocytes. We adopted a new method to purify the oligodendrocytes and co-cultured the newly differentiated oligodendrocytes with hippocampal neurons to confirm their myelination capability. NSCs from embryonic day 14 (E14) were propagated at the presence of basic fibroblast growth factor and platelet derived growth factor alpha, and then differentiated in the medium containing triiodothyronine. Four extracellular matrix (ECM), poly-d-lysine (PDL), PDL-laminin, fibronectin, and matrigel, were examined for NSC differentiation. About 90 % of NSCs differentiated into oligodendrocytes on matrigel compared to 32 % on PDL or PDL-laminin, and 26 % on fibronectin after 3 weeks of differentiation, demonstrating the significant influence of ECM. Further, newly differentiated oligodendrocytes were co-cultured with hippocampal neurons from E18 rat embryos resulting in robust myelination of neurites at three weeks. In summary, we present a simplified and efficient method to predominantly generate oligodendrocytes from NSCs that is potentially very useful for CNS demyelination diseases.

Region-specific interneuron demyelination and heightened anxiety-like behavior induced by adolescent binge alcohol treatment

Adolescent binge drinking represents a major public health challenge and can lead to persistent neurological and mental conditions, but the underlying pathogenic mechanisms remain poorly understood. Using a mouse model of adolescent binge ethanol treatment (ABET), we found that this treatment induced behavioral changes associated with demyelination in different brain regions. After ABET, adolescent mice exhibited anxiogenic behaviors with no change in locomotion on the elevated plus maze, and impaired spatial memory indicated by a significant reduction in spontaneous alternation in the Y maze test. Both effects persisted into adulthood. Anatomical studies further showed that ABET induced a significant reduction of parvalbumin-positive (PV+) GABAergic interneurons and myelin density in the hippocampus and medial prefrontal cortex (mPFC). While these deficits in PV+ interneurons and myelin persisted into early adulthood in the hippocampus, the myelin density recovered in the mPFC. Moreover, whereas ABET mainly damaged myelin of PV+ axons in the hippocampus, it primarily damaged myelin of PV-negative axons in the mPFC. Thus, our findings reveal that an adolescent binge alcohol treatment regimen disrupts spatial working memory, increases anxiety-like behaviors, and exerts unique temporal and spatial patterns of gray matter demyelination in the hippocampus and mPFC.

Copper chelation and autoimmunity differentially impact myelin in the hippocampal-prefrontal circuit

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. About 50% of MS patients develop deficits in learning, memory and executive function, which are accompanied by demyelinating lesions in the hippocampus and/or prefrontal cortex (PFC). Why demyelination in these regions occurs in some patients but not in others and what is the underlying mechanism remain unclear. Here we report that myelin density in the hippocampus and PFC is markedly reduced in the cuprizone model, but not in the chronic experimental autoimmune encephalomyelitis. These two models can be used for studying different neuropathophysiological aspects of demyelinating diseases.

Function and Mechanism of Myelin Regulation in Alcohol Abuse and Alcoholism

Excessive alcohol use has adverse effects on the central nervous system (CNS) and can lead to alcohol use disorders (AUDs). Recent studies have suggested that myelin reductions may directly contribute to CNS dysfunctions associated with AUDs. Myelin consists of compact lipid membranes wrapped around axons to provide electrical insulation and trophic support. Regulation of myelin is considered as a new form of neural plasticity due to its profound impacts on the computation of neural networks. In this review, the authors first discuss experimental evidence showing how alcohol exposure causes demyelination in different brain regions, often accompanied by deficits in cognition and emotion. Next, they discuss postulated molecular and cellular mechanisms underlying alcohol's impact on myelin. It is clear that more extensive investigations are needed in this important but underexplored research field in order to gain a better understanding of the myelin-behavior relationship and to develop new treatment strategies for AUDs.

Leukocyte expression profiles reveal gene sets with prognostic value for seizure-free outcome following stereotactic laser amygdalohippocampotomy

Among patients with intractable epilepsy, the most commonly performed surgical procedure is craniotomy for amygdalohippocampectomy (AH). Stereotactic laser amygdalohippocampotomy (SLAH) has also been recently employed as a minimally invasive treatment for intractable temporal lobe epilepsy (TLE). Among patients treated with AH and SLAH approximately 65% and 54% of patients become seizure-free, respectively. Therefore, selection criteria for surgical candidates with improved prognostic value for post-operative seizure-free outcome are greatly needed. In this study, we perform RNA sequencing (RNA-Seq) on whole blood leukocyte samples taken from 16 patients with intractable TLE prior to SLAH to test the hypothesis that pre-operative leukocyte RNA expression profiles are prognostic for post-operative seizure outcome. Multidimensional scaling analysis of the RNA expression data indicated separate clustering of patients with seizure free (SF) and non-seizure-free (NSF) outcomes. Differential expression (DE) analysis performed on SF versus NSF groups revealed 24 significantly differentially expressed genes (≥2.0-fold change, p-value < 0.05, FDR <0.05). Network and pathway analyses identified differential activation of pathways involved in lipid metabolism, morphology of oligodendrocytes, inflammatory response, and development of astrocytes. These results suggest that pre-operative leukocyte expression profiles have prognostic value for seizure outcome following SLAH.

A Microbiomechanical System for Studying Varicosity Formation and Recovery in Central Neuron Axons

Axonal varicosities are enlarged structures along the shafts of axons with a high degree of heterogeneity. They are present not only in brains with neurodegenerative diseases or injuries, but also in the normal brain. Here, we describe a newly-established micromechanical system to rapidly, reliably, and reversibly induce axonal varicosities, allowing us to understand the mechanisms governing varicosity formation and heterogeneous protein composition. This system represents a novel means to evaluate the effects of compression and shear stress on different subcellular compartments of neurons, different from other in vitro systems that mainly focus on the effect of stretching. Importantly, owing to the unique features of our system, we recently made a novel discovery showing that the application of pressurized fluid can rapidly and reversibly induce axonal varicosities through the activation of a transient receptor potential channel. Our biomechanical system can be utilized conveniently in combination with drug perfusion, live cell imaging, calcium imaging, and patch clamp recording. Therefore, this method can be adopted for studying mechanosensitive ion channels, axonal transport regulation, axonal cytoskeleton dynamics, calcium signaling, and morphological changes related to traumatic brain injury.

Suppression of Inflammatory Demyelinaton and Axon Degeneration through Inhibiting Kv3 Channels

The development of neuroprotective and repair strategies for treating progressive multiple sclerosis (MS) requires new insights into axonal injury. 4-aminopyridine (4-AP), a blocker of voltage-gated K⁺ (Kv) channels, is used in symptomatic treatment of progressive MS, but the underlying mechanism remains unclear. Here we report that deleting Kv3.1—the channel with the highest 4-AP sensitivity—reduces clinical signs in experimental autoimmune encephalomyelitis (EAE), a mouse model for MS. In Kv3.1 knockout (KO) mice, EAE lesions in sensory and motor tracts of spinal cord were markedly reduced, and radial astroglia were activated with increased expression of brain derived neurotrophic factor (BDNF). Kv3.3/Kv3.1 and activated BDNF receptors were upregulated in demyelinating axons in EAE and MS lesions. In spinal cord myelin coculture, BDNF treatment promoted myelination, and neuronal firing via altering channel expression. Therefore, suppressing Kv3.1 alters neural circuit activity, which may enhance BNDF signaling and hence protect axons from inflammatory insults.

Neurons define non-myelinated axon segments by the regulation of galectin-4-containing axon membrane domains

The mechanism underlying selective myelination of axons versus dendrites or neuronal somata relies on the expression of somatodendritic membrane myelination inhibitors (i.e. JAM2). However, axons still present long unmyelinated segments proposed to contribute to axonal plasticity and higher order brain functions. Why these segments remain unmyelinated is still an unresolved issue. The bifunctional lectin galectin-4 (Gal-4) organizes the transport of axon glycoproteins by binding to N-acetyllactosamine (LacNac) termini of N-glycans. We have shown that Gal-4 is sorted to segmental domains (G4Ds) along the axon surface, reminiscent of these long unmyelinated axon segments in cortical neurons. We report here that oligodendrocytes (OLGs) do not deposit myelin on Gal-4 covered surfaces or myelinate axonal G4Ds. In addition, Gal-4 interacts and co-localizes in G4Ds with contactin-1, a marker of another type of non-myelinated segments, the nodes of Ranvier. Neither Gal-4 expression nor G4D dimensions are affected by myelin extracts or myelinating OLGs, but are reduced with neuron maturation. As in vitro, Gal-4 is consistently segregated from myelinated structures in the brain. Our data shape the novel concept that neurons establish axon membrane domains expressing Gal-4, the first inhibitor of myelination identified in axons, whose regulated boundaries delineate myelination-incompetent axon segments along development.

Pre-culture Sudan Black B treatment suppresses autofluorescence signals emitted from polymer tissue scaffolds

In tissue engineering, autofluorescence of polymer scaffolds often lowers the image contrast, making it difficult to examine cells and subcellular structures. Treating the scaffold materials with Sudan Black B (SBB) after cell fixation can effectively suppress autofluorescence, but this approach is not conducive to live cell imaging. Post-culture SBB treatment also disrupts intracellular structures and leads to reduced fluorescence intensity of the targets of interest. In this study, we introduce pre-culture SBB treatment to suppress autofluorescence, where SBB is applied to polymeric scaffold materials before cell seeding. The results show that the autofluorescence signals emitted from polycaprolactone (PCL) scaffolds in three commonly used fluorescence channels effectively decrease without diminishing the fluorescence signals emitted from the cells. The pre-culture SBB treatment does not significantly affect cell viability. The autofluorescence suppressive effect does not substantially diminish during the culturing period up to 28 days. The results also show that cell migration, proliferation, and myogenic differentiation in pre-culture SBB-treated groups do not exhibit statistical difference from the non-treated groups. As such, this approach greatly improves the fluorescence image quality for examining live cell behaviors and dynamics while the cells are cultured within autofluorescent polymer scaffolds.

Polarity of varicosity initiation in central neuron mechanosensation

Little is known about mechanical regulation of morphological and functional polarity of central neurons. In this study, we report that mechanical stress specifically induces varicosities in the axons but not the dendrites of central neurons by activating TRPV4, a Ca2+/Na+-permeable mechanosensitive channel. This process is unexpectedly rapid and reversible, consistent with the formation of axonal varicosities in vivo induced by mechanical impact in a mouse model of mild traumatic brain injury. In contrast, prolonged stimulation of glutamate receptors induces varicosities in dendrites but not in axons. We further show that axonal varicosities are induced by persistent Ca2+ increase, disassembled microtubules (MTs), and subsequently reversible disruption of axonal transport, and are regulated by stable tubulin-only polypeptide, an MT-associated protein. Finally, axonal varicosity initiation can trigger action potentials to antidromically propagate to the soma in retrograde signaling. Therefore, our study demonstrates a new feature of neuronal polarity: axons and dendrites preferentially respond to physical and chemical stresses, respectively.

Dynamic Meso-Scale Anchorage of GPI-Anchored Receptors in the Plasma Membrane: Prion Protein vs. Thy1

The central mechanism for the transmission of the prion protein misfolding is the structural conversion of the normal cellular prion protein to the pathogenic misfolded prion protein, by the interaction with misfolded prion protein. This process might be enhanced due to the homo-dimerization/oligomerization of normal prion protein. However, the behaviors of normal prion protein in the plasma membrane have remained largely unknown. Here, using single fluorescent-molecule imaging, we found that both prion protein and Thy1, a control glycosylphosphatidylinositol-anchored protein, exhibited very similar intermittent transient immobilizations lasting for a few seconds within an area of 24.2 and 3.5 nm in diameter in CHO-K1 and hippocampal neurons cultured for 1- and 2-weeks, respectively. Prion protein molecules were immobile during 72% of the time, approximately 1.4× more than Thy1, due to prion protein’s higher immobilization frequency. When mobile, prion protein diffused 1.7× slower than Thy1. Prion protein’s slower diffusion might be caused by its transient interaction with other prion protein molecules, whereas its brief immobilization might be due to temporary association with prion protein clusters. Prion protein molecules might be newly recruited to prion protein clusters all the time, and simultaneously, prion protein molecules in the cluster might be departing continuously. Such dynamic interactions of normal prion protein molecules would strongly enhance the spreading of misfolded prion protein.

Prevalent presence of periodic actin-spectrin-based membrane skeleton in a broad range of neuronal cell types and animal species

Actin, spectrin, and associated molecules form a periodic, submembrane cytoskeleton in the axons of neurons. For a better understanding of this membrane-associated periodic skeleton (MPS), it is important to address how prevalent this structure is in different neuronal types, different subcellular compartments, and across different animal species. Here, we investigated the organization of spectrin in a variety of neuronal- and glial-cell types. We observed the presence of MPS in all of the tested neuronal types cultured from mouse central and peripheral nervous systems, including excitatory and inhibitory neurons from several brain regions, as well as sensory and motor neurons. Quantitative analyses show that MPS is preferentially formed in axons in all neuronal types tested here: Spectrin shows a long-range, periodic distribution throughout all axons but appears periodic only in a small fraction of dendrites, typically in the form of isolated patches in subregions of these dendrites. As in dendrites, we also observed patches of periodic spectrin structures in a small fraction of glial-cell processes in four types of glial cells cultured from rodent tissues. Interestingly, despite its strong presence in the axonal shaft, MPS is disrupted in most presynaptic boutons but is present in an appreciable fraction of dendritic spine necks, including some projecting from dendrites where such a periodic structure is not observed in the shaft. Finally, we found that spectrin is capable of adopting a similar periodic organization in neurons of a variety of animal species, including Caenorhabditis elegans, Drosophila, Gallus gallus, Mus musculus, and Homo sapiens.

Human embryonic stem cell-derived oligodendrocyte progenitors remyelinate the brain and rescue behavioral deficits following radiation

Radiation therapy to the brain is a powerful tool in the management of many cancers, but it is associated with significant and irreversible long-term side effects, including cognitive decline and impairment of motor coordination. Depletion of oligodendrocyte progenitors and demyelination are major pathological features that are particularly pronounced in younger individuals and severely limit therapeutic options. Here we tested whether human ESC-derived oligodendrocytes can functionally remyelinate the irradiated brain using a rat model. We demonstrate the efficient derivation and prospective isolation of human oligodendrocyte progenitors, which, upon transplantation, migrate throughout the major white matter tracts resulting in both structural and functional repair. Behavioral testing showed complete recovery of cognitive function while additional recovery from motor deficits required concomitant transplantation into the cerebellum. The ability to repair radiation-induced damage to the brain could dramatically improve the outlook for cancer survivors and enable more effective use of radiation therapies, especially in children.

Optimizing culture medium composition to improve oligodendrocyte progenitor cell yields in vitro from subventricular zone-derived neural progenitor cell neurospheres

Neural Stem and Progenitor Cells (NSC/NPC) are gathering tangible recognition for their uses in cell therapy and cell replacement therapies for human disease, as well as a model system to continue research on overall neural developmental processes in vitro. The Subventricular Zone is one of the largest NSC/NPC niches in the developing mammalian Central Nervous System, and persists through to adulthood. Oligodendrocyte progenitor cell (OPC) enriched cultures are usefull tools for in vitro studies as well as for cell replacement therapies for treating demyelination diseases. We used Subventricular Zone-derived NSC/NPC primary cultures from newborn mice and compared the effects of different growth factor combinations on cell proliferation and OPC yield. The Platelet Derived Growth Factor-AA and BB homodimers had a positive and significant impact on OPC generation. Furthermore, heparin addition to the culture media contributed to further increase overall culture yields. The OPC generated by this protocol were able to mature into Myelin Basic Protein-expressing cells and to interact with neurons in an in vitro co-culture system. As a whole, we describe an optimized in vitro method for increasing OPC.

3D in vitro modeling of the central nervous system

There are currently more than 600 diseases characterized as affecting the central nervous system (CNS) which inflict neural damage. Unfortunately, few of these conditions have effective treatments available. Although significant efforts have been put into developing new therapeutics, drugs which were promising in the developmental phase have high attrition rates in late stage clinical trials. These failures could be circumvented if current 2D in vitro and in vivo models were improved. 3D, tissue-engineered in vitro systems can address this need and enhance clinical translation through two approaches: (1) bottom-up, and (2) top-down (developmental/regenerative) strategies to reproduce the structure and function of human tissues. Critical challenges remain including biomaterials capable of matching the mechanical properties and extracellular matrix (ECM) composition of neural tissues, compartmentalized scaffolds that support heterogeneous tissue architectures reflective of brain organization and structure, and robust functional assays for in vitro tissue validation. The unique design parameters defined by the complex physiology of the CNS for construction and validation of 3D in vitro neural systems are reviewed here.

In vitro models for neurotoxicology research

The nervous system has a highly complex organization, including many cell types with multiple functions, with an intricate anatomy and unique structural and functional characteristics; the study of its (dys)functionality following exposure to xenobiotics, neurotoxicology, constitutes an important issue in neurosciences.

‘Body-on-a-Chip’ Technology and Supporting Microfluidics

In order to effectively streamline current drug development protocols, there is a need to generate high information content preclinical screens capable of generating data with a predictive power in relation to the activity of novel therapeutics in humans. Given the poor predictive power of animal models, and the lack of complexity and interconnectivity of standard in vitro culture methodologies, many investigators are now moving toward the development of physiologically and functionally accurate culture platforms composed of human cells to investigate cellular responses to drug compounds in high-throughput preclinical studies. The generation of complex, multi-organ in vitro platforms, built to recapitulate physiological dimensions, flow rates and shear stresses, is being investigated as the logical extension of this drive. Production and application of a biologically accurate multi-organ platform, or ‘body-on-a-chip’, would facilitate the correct modelling of the dynamic and interconnected state of living systems for high-throughput drug studies as well as basic and applied biomolecular research. This chapter will discuss current technologies aimed at producing ‘body-on-a-chip’ models, as well as highlighting recent advances and important challenges still to be met in the development of biomimetic single-organ systems for drug development purposes.

Concepts for regulation of axon integrity by enwrapping glia

Long axons and their enwrapping glia (EG; Schwann cells (SCs) and oligodendrocytes (OLGs)) form a unique compound structure that serves as conduit for transport of electric and chemical information in the nervous system. The peculiar cytoarchitecture over an enormous length as well as its substantial energetic requirements make this conduit particularly susceptible to detrimental alterations. Degeneration of long axons independent of neuronal cell bodies is observed comparatively early in a range of neurodegenerative conditions as a consequence of abnormalities in SCs and OLGs . This leads to the most relevant disease symptoms and highlights the critical role that these glia have for axon integrity, but the underlying mechanisms remain elusive. The quest to understand why and how axons degenerate is now a crucial frontier in disease-oriented research. This challenge is most likely to lead to significant progress if the inextricable link between axons and their flanking glia in pathological situations is recognized. In this review I compile recent advances in our understanding of the molecular programs governing axon degeneration, and mechanisms of EG’s non-cell autonomous impact on axon-integrity. A particular focus is placed on emerging evidence suggesting that EG nurture long axons by virtue of their intimate association, release of trophic substances, and neurometabolic coupling. The correction of defects in these functions has the potential to stabilize axons in a variety of neuronal diseases in the peripheral nervous system and central nervous system (PNS and CNS).

A rapid and reproducible assay for modeling myelination by oligodendrocytes using engineered nanofibers

Current methods for studying oligodendrocyte myelination using primary neurons are limited by the time, cost and reproducibility of myelination in vitro. Nanofibers with diameters of >0.4 μm fabricated from electrospinning of liquid polystyrene are suitable scaffolds for concentric membrane wrapping by oligodendrocytes. With the advent of aligned electrospinning technology, nanofibers can be rapidly fabricated, standardized, and configured into various densities and patterns as desired. Notably, the minimally permissive culture environment of fibers provides investigators with an opportunity to explore the autonomous oligodendrocyte cellular processes underlying differentiation and myelination. The simplicity of the system is conducive to monitoring oligodendrocyte proliferation, migration, differentiation and membrane wrapping in the absence of neuronal signals. Here we describe protocols for the fabrication and preparation of nanofibers aligned on glass coverslips for the study of membrane wrapping by rodent oligodendrocytes. The entire protocol can be completed within 2 weeks.

Tetramethylpyrazine protects against scopolamine-induced memory impairments in rats by reversing the cAMP/PKA/CREB pathway

Tetramethylpyrazine is used in the treatment of many neurological diseases because of its neuroprotective effect. Here, we demonstrate that administration of tetramethylpyrazine effectively reverses memory deficits induced by scopolamine. Moreover, tetramethylpyrazine preserves postsynaptic protein synthesis and restores cAMP/PKA/CREB pathway signaling deficits. Our study not only explores the actions of tetramethylpyrazine on synapses, but also provides novel evidence for the possible therapeutic use of tetramethylpyrazine in dementia.