Dysregulation of mTOR signaling mediates common neurite and migration defects in both idiopathic and 16p11.2 deletion autism neural precursor cells

Autism spectrum disorder (ASD) is defined by common behavioral characteristics, raising the possibility of shared pathogenic mechanisms. Yet, vast clinical and etiological heterogeneity suggests personalized phenotypes. Surprisingly, our iPSC studies find that six individuals from two distinct ASD subtypes, idiopathic and 16p11.2 deletion, have common reductions in neural precursor cell (NPC) neurite outgrowth and migration even though whole genome sequencing demonstrates no genetic overlap between the datasets. To identify signaling differences that may contribute to these developmental defects, an unbiased phospho-(p)-proteome screen was performed. Surprisingly despite the genetic heterogeneity, hundreds of shared p-peptides were identified between autism subtypes including the mTOR pathway. mTOR signaling alterations were confirmed in all NPCs across both ASD subtypes, and mTOR modulation rescued ASD phenotypes and reproduced autism NPC-associated phenotypes in control NPCs. Thus, our studies demonstrate that genetically distinct ASD subtypes have common defects in neurite outgrowth and migration which are driven by the shared pathogenic mechanism of mTOR signaling dysregulation.

Fraping: A computational tool for detecting slight differences in fluorescence recovery after photobleaching (FRAP) data for actin polymerization analysis

Fluorescence recovery after photobleaching (FRAP) is a laser method of light microscopy to evaluate the rapid movement of fluorescent molecules. To have a more reliable approach to analyze data from FRAP, we designed Fraping, a free access R library to data analysis obtained from FRAP. Unlike other programs, Fraping has a new form of analyzing curves of FRAP using statistical analysis based on the average curve difference. To evaluate our library, we analyzed the differences of actin polymerization in real time between dendrites and secondary neurites of cultured neuron transfected with LifeAct to track F-actin changes of neurites. We found that Fraping provided greater sensitivity than the conventional model using mobile fraction analysis. Likewise, this approach allowed us to normalize the fluorescence to the size area of interest and adjust data curves choosing the best parametric model. In addition, this library was supplemented with data simulation to have a more significant enrichment for the analysis behavior. We concluded that Fraping is a method that reduces bias when analyzing two data groups as compared with the conventional methods. This method also allows the users to choose a more suitable analysis approach according to their requirements. RESEARCH HIGHLIGHTS: Fraping is a new programming tool to analyze FRAP data to normalize fluorescence recovery curves. The conventional method uses one-point analysis, and the new one compares all the points to define the similarity of the fluorescence recovery.

Interactions of Neuronally Induced Stem Cells from Apical Papilla Spheres, Stems Cells from Apical Papilla, and Human Umbilical Vascular Endothelial Cells on Vasculogenesis and Neurogenesis

INTRODUCTION

Stem cell-based dental pulp regeneration has been extensively studied, mainly focusing on exploiting dental stem cells' osteogenic and angiogenic potentials. Dental stem cells' neurogenic role is often overlooked. Stem cells from apical papilla (SCAPs), originating from the neural crest and capable of sphere formation, display potent neurogenic capacity. This study aimed to investigate the interactions of neuronally induced stem cells from apical papilla (iSCAP) spheres, SCAPs, and human umbilical vascular endothelial cells (HUVECs) on vasculogenesis and neurogenesis.

METHODS

SCAPs were isolated and characterized using flow cytometry and multilineage differentiation assays. SCAP monolayer culture and spheres were neuronally induced by a small molecule neural induction medium, and the neural gene expression and neurite formation at days 0, 3, and 7 were evaluated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and using phase-contrast light and fluorescence microscopy. Direct coculture or pulp-on-chip was used to investigate iSCAP sphere interaction with SCAPs and HUVECs. RT-qPCR, fluorescence microscopy, and immunostaining with β-tubulin III, alpha-smooth muscle actin, and CD31 were used to study neural gene expression, neurite formation, and neurovascular cell interactions.

RESULTS

Neural induction medium with small molecules rapidly induced SCAP differentiation toward neural-like cells. Gene expression of Nestin, β-tubulin III, microtubule-associated protein 2, neuron-specific enolase, and NeuN was higher in iSCAP spheres than in iSCAPs. iSCAP spheres formed more and longer neurites compared with iSCAPs. iSCAP sphere, HUVEC, and SCAP direct coculture significantly enhanced vessel formation along with up-regulated VEGF (P < .001) and multiple neural markers, such as Nestin (P < .01), microtubule-associated protein 2 (P < .001), S100 (P < .001), and NG2 (P < .001). iSCAP spheres, SCAPs, and HUVECs cultured in a pulp-on-chip system promoted endothelial and neural cell migration toward each other and alpha-smooth muscle actin-positive and CD31-positive cells assembling for the vascular constitution.

CONCLUSIONS

iSCAP-formed spheres interact with SCAPs and HUVECs, promoting vasculogenesis and neurogenesis.

Probing brain tissue microstructure with MRI: principles, challenges, and the role of multidimensional diffusion-relaxation encoding

Diffusion MRI uses the random displacement of water molecules to sensitize the signal to brain microstructure and to properties such as the density and shape of cells. Microstructure modeling techniques aim to estimate these properties from acquired data by separating the signal between virtual tissue 'compartments' such as the intra-neurite and the extra-cellular space. A key challenge is that the diffusion MRI signal is relatively featureless compared with the complexity of brain tissue. Another challenge is that the tissue microstructure is wildly different within the gray and white matter of the brain. In this review, we use results from multidimensional diffusion encoding techniques to discuss these challenges and their tentative solutions. Multidimensional encoding increases the information content of the data by varying not only the b-value and the encoding direction but also additional experimental parameters such as the shape of the b-tensor and the echo time. Three main insights have emerged from such encoding. First, multidimensional data contradict common model assumptions on diffusion and T2 relaxation, and illustrates how the use of these assumptions cause erroneous interpretations in both healthy brain and pathology. Second, many model assumptions can be dispensed with if data are acquired with multidimensional encoding. The necessary data can be easily acquired in vivo using protocols optimized to minimize Cramér-Rao lower bounds. Third, microscopic diffusion anisotropy reflects the presence of axons but not dendrites. This insight stands in contrast to current 'neurite models' of brain tissue, which assume that axons in white matter and dendrites in gray matter feature highly similar diffusion. Nevertheless, as an axon-based contrast, microscopic anisotropy can differentiate gray and white matter when myelin alterations confound conventional MRI contrasts.

Magnetic activation of TREK1 triggers stress signalling and regulates neuronal branching in SH-SY5Y cells

TWIK-related K⁺ 1 (TREK1) is a potassium channel expressed in the nervous system with multiple functions including neurotransmission and is a prime pharmacological target for neurological disorders. TREK1 gating is controlled by a wide range of external stimuli including mechanical forces. Previous work has demonstrated that TREK1 can be mechano-activated using magnetic nanoparticles (MNP) functionalised with antibodies targeted to TREK1 channels. Once the MNP are bound, external dynamic magnetic fields are used to generate forces on the TREK channel. This approach has been shown to drive cell differentiation in cells from multiple tissues. In this work we investigated the effect of MNP-mediated TREK1 mechano-activation on early stress response pathways along with the differentiation and connectivity of neuronal cells using the model neuronal cell line SH-SY5Y. Results showed that TREK1 is well expressed in SH-SY5Y and that TREK1-MNP initiate c-Myc/NF-κB stress response pathways as well as Nitrite production after magnetic stimulation, indicative of the cellular response to mechanical cues. Results also showed that TREK1 mechano-activation had no overall effect on neuronal morphology or expression of the neuronal marker βIII-Tubulin in Retinoic Acid (RA)/Brain-derived Neurotrophic factor (BDNF) differentiated SH-SY5Y but did increase neurite number. These results suggest that TREK1 is involved in cellular stress response signalling in neuronal cells, which leads to increased neurite production, but is not involved in regulating RA/BDNF mediated neuronal differentiation.

Transepithelial Effect of Probiotics in a Novel Model of Gut Lumen to Nerve Signaling

Recent studies have shown that the gut microbiome changes brain function, behavior, and psychiatric and neurological disorders. The Gut-Brain Axis (GBA) provides a neuronal pathway to explain this. But exactly how do commensal bacteria signal through the epithelial layer of the large intestine to activate GBA nerve afferents? An in vitro model is described. We differentiated two human cell lines: Caco2Bbe1 into mature epithelium on 0.4-micron filters and then SH-SY5Y into mature neurons in 24-well plates. These were co-cultured by placing the epithelium-laden filters 1 mm above the neurons. Twenty-four hours later they were tri-cultured by apical addition of 10⁷Lactobacillus rhamnosus or Lactobacillus fermentum which settled on the epithelium. Alone, the Caco2bbe1 cells stimulated neurite outgrowth in underlying SH-SY5Y. Beyond this, the lactobacilli were well tolerated and stimulated further neurite outgrowth by 24 h post-treatment, though not passing through the filters. The results provide face validity for a first-of-kind model of transepithelial intestinal lumen-to nerve signaling. The model displays the tight junctional barrier characteristics found in the large intestine while at the same time translating stimulatory signals from the bacteria through epithelial cells to attracted neurons. The model is easy to set-up with components widely available.

Formation of Three-Dimensional Spheres Enhances the Neurogenic Potential of Stem Cells from Apical Papilla

Cell-based neural regeneration is challenging due to the difficulty in obtaining sufficient neural stem cells with clinical applicability. Stem cells from apical papilla (SCAPs) originating from embryonic neural crests with high neurogenic potential could be a promising cell source for neural regeneration. This study aimed to investigate whether the formation of 3D spheres can promote SCAPs' neurogenic potential.

MATERIAL AND METHODS

Three-dimensional SCAP spheres were first generated in a 256-well agarose microtissue mold. The spheres and single cells were individually cultured on collagen I-coated μ-slides. Cell morphological changes, neural marker expression, and neurite outgrowth were evaluated by confocal microscope, ELISA, and RT-qPCR.

RESULTS

Pronounced morphological changes were noticed in a time-dependent manner. The migrating cells' morphology changed from fibroblast-like cells to neuron-like cells. Compared to the 2D culture, neurite length, number, and the expression of multiple progenitors, immature and mature neural markers were significantly higher in the 3D spheres. BDNF and NGF-β may play a significant role in the neural differentiation of SCAP spheres.

CONCLUSION

The formation of 3D spheres enhanced the neurogenic potential of SCAPs, suggesting the advantage of using the 3D spheres of SCAPs for treating neural diseases.

A peptide inhibitor that rescues polyglutamine-induced synaptic defects and cell death through suppressing RNA and protein toxicities

Polyglutamine (polyQ) diseases, including spinocerebellar ataxias and Huntington's disease, are progressive neurodegenerative disorders caused by CAG triplet-repeat expansion in the coding regions of disease-associated genes. In this study, we found that neurotoxic small CAG (sCAG) RNA species, microscopic Ataxin-2 CAG RNA foci, and protein aggregates exist as independent entities in cells. Synaptic defects and neurite outgrowth abnormalities were observed in mutant Ataxin-2-expressing mouse primary cortical neurons. We examined the suppression effects of the CAG RNA-binding peptide beta-structured inhibitor for neurodegenerative diseases (BIND) in mutant Ataxin-2-expressing mouse primary cortical neurons and found that both impaired synaptic phenotypes and neurite outgrowth defects were rescued. We further demonstrated that BIND rescued cell death through inhibiting sCAG RNA production, Ataxin-2 CAG RNA foci formation, and mutant Ataxin-2 protein translation. Interestingly, when the expanded CAG repeats in the mutant Ataxin-2 transcript was interrupted with the alternative glutamine codon CAA, BIND's inhibitory effect on mutant protein aggregation was lost. We previously demonstrated that BIND interacts physically and directly with expanded CAG RNA sequences. Our data provide evidence that the BIND peptide associates with transcribed mutant CAG RNA to inhibit the formation of toxic species, including sCAG RNA, RNA foci, and polyQ protein translation and aggregation.

Tissue-engineered in vitro modeling of the impact of Schwann cells in amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disease affecting upper and lower motor neurons (MN). To investigate whether Schwann cells could be involved in the disease pathogenesis, we developed a tissue-engineered 3D in vitro model that combined MNs cocultured with astrocytes and microglia seeded on top of a collagen sponge populated with epineurium fibroblasts to enable 3D axonal migration. C2C12 myoblasts were seeded underneath the sponge in presence or absence of Schwann cells. To reproduce an ALS cellular microenvironment, MNs, astrocytes and microglia were extracted from SOD1^G93A mice recapitulating many aspects of the human disease. This 3D ALS in vitro model was compared with a 3D control made of cells isolated from SOD1^WT mice. We showed that normal Schwann cells strongly enhanced MN axonal migration in the 3D control model but had no effect in the ALS model. However, ALS-derived Schwann cells isolated from SOD1^G93A mice failed to significantly improve axonal migration in both models. These results suggest that a cell therapy using healthy Schwann cells may not be effective in promoting axonal regeneration in ALS. In addition, this 3D ALS model could be used to study the impact of other cell types on ALS by various combinations of normal and diseased cells. This article is protected by copyright. All rights reserved.

Trimethylamine N-Oxide Reduces Neurite Density and Plaque Intensity in a Murine Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most common aging-associated neurodegenerative disease; nevertheless, the etiology and progression of the disease is still incompletely understood. We have previously shown that the microbially-derived metabolite trimethylamine N-oxide (TMAO) is elevated in the cerebrospinal fluid (CSF) of individuals with cognitive impairment due to AD and positively correlates with increases in CSF biomarkers for tangle, plaque, and neuronal pathology.

OBJECTIVE

We assessed the direct impact of TMAO on AD progression.

METHODS

To do so, transgenic 5XFAD mice were supplemented with TMAO for 12 weeks. Neurite density was assessed through quantitative brain microstructure imaging with neurite orientation dispersion and density imaging magnetic resonance imaging (MRI). Label-free, quantitative proteomics was performed on cortex lysates from TMAO-treated and untreated animals. Amyloid-β plaques, astrocytes, and microglia were assessed by fluorescent immunohistochemistry and synaptic protein expression was quantified via western blot.

RESULTS

Oral TMAO administration resulted in significantly reduced neurite density in several regions of the brain. Amyloid-β plaque mean intensity was reduced, while plaque count and size remained unaltered. Proteomics analysis revealed that TMAO treatment impacted the expression of 30 proteins (1.5-fold cut-off) in 5XFAD mice, including proteins known to influence neuronal health and amyloid-β precursor protein processing. TMAO treatment did not alter astrocyte and microglial response nor cortical synaptic protein expression.

CONCLUSION

These data suggest that elevated plasma TMAO impacts AD pathology via reductions in neurite density.

Primary Cilia Structure Is Prolonged in Enteric Neurons of 5xFAD Alzheimer's Disease Model Mice

Neurodegenerative diseases such as Alzheimer’s disease (AD) have long been acknowledged as mere disorders of the central nervous system (CNS). However, in recent years the gut with its autonomous nervous system and the multitude of microbial commensals has come into focus. Changes in gut properties have been described in patients and animal disease models such as altered enzyme secretion or architecture of the enteric nervous system. The underlying cellular mechanisms have so far only been poorly investigated. An important organelle for integrating potentially toxic signals such as the AD characteristic A-beta peptide is the primary cilium. This microtubule-based signaling organelle regulates numerous cellular processes. Even though the role of primary cilia in a variety of developmental and disease processes has recently been recognized, the contribution of defective ciliary signaling to neurodegenerative diseases such as AD, however, has not been investigated in detail so far. The AD mouse model 5xFAD was used to analyze possible changes in gut functionality by organ bath measurement of peristalsis movement. Subsequently, we cultured primary enteric neurons from mutant mice and wild type littermate controls and assessed for cellular pathomechanisms. Neurite mass was quantified within transwell culturing experiments. Using a combination of different markers for the primary cilium, cilia number and length were determined using fluorescence microscopy. 5xFAD mice showed altered gut anatomy, motility, and neurite mass of enteric neurons. Moreover, primary cilia could be demonstrated on the surface of enteric neurons and exhibited an elongated phenotype in 5xFAD mice. In parallel, we observed reduced β-Catenin expression, a key signaling molecule that regulates Wnt signaling, which is regulated in part via ciliary associated mechanisms. Both results could be recapitulated via in vitro treatments of enteric neurons from wild type mice with A-beta. So far, only a few reports on the probable role of primary cilia in AD can be found. Here, we reveal for the first time an architectural altered phenotype of primary cilia in the enteric nervous system of AD model mice, elicited potentially by neurotoxic A-beta. Potential changes on the sub-organelle level—also in CNS-derived neurons—require further investigations.

Corrigendum: Object-Based Analyses in FIJI/ImageJ to Measure Local RNA Translation Sites in Neurites in Response to Aβ1-42 Oligomers

[This corrects the article DOI: 10.3389/fnins.2020.00547.].

Conditioned medium of E17 rat brain cells induced differentiation of primary colony of mice blastocyst into neuron-like cells

Background

Conditioned medium is the medium obtained from certain cultured cells and contained secretome from the cells. The secretome, which can be in the form of growth factors, cytokines, exosomes, or other proteins secreted by the cells, can induce the differentiation of cells that still have pluripotent or multipotent properties.

Objectives

This study examined the effects of conditioned medium derived from E17 rat brain cells on cells with pluripotent properties.

Methods

The conditioned medium used in this study originated from E17 rat brain cells. The CM was used to induce the differentiation of primary colonies of mice blastocysts. Primary colonies were stained with alkaline phosphatase to analyze the pluripotency. The morphological changes in the colonies were examined, and the colonies were stained with GFAP and Neu-N markers on days two and seven after adding the conditioned medium.

Results

The conditioned medium could differentiate the primary colony, beginning with the formation of embryoid-body-like structure; round GFAP positive cells were identified. Finally, neuron-like cells testing positive for Neu-N were observed on the seventh day after adding the conditioned medium.

Conclusions

Conditioned medium from different species, in this case, E17 rat brain cells, induced and promoted the differentiation of the primary colony from mice blastocysts into neuron-like cells. The addition of CM mediated neurite growth in the differentiation process.

SVCT2 Overexpression and Ascorbic Acid Uptake Increase Cortical Neuron Differentiation, Which Is Dependent on Vitamin C Recycling between Neurons and Astrocytes

During brain development, sodium–vitamin C transporter (SVCT2) has been detected primarily in radial glial cells in situ, with low-to-absent expression in cerebral cortex neuroblasts. However, strong SVCT2 expression is observed during the first postnatal days, resulting in increased intracellular concentration of vitamin C. Hippocampal neurons isolated from SVCT2 knockout mice showed shorter neurites and low clustering of glutamate receptors. Other studies have shown that vitamin C-deprived guinea pigs have reduced spatial memory, suggesting that ascorbic acid (AA) and SVCT2 have important roles in postnatal neuronal differentiation and neurite formation. In this study, SVCT2 lentiviral overexpression induced branching and increased synaptic proteins expression in primary cultures of cortical neurons. Analysis in neuroblastoma 2a (Neuro2a) and human subventricular tumor C3 (HSVT-C3) cells showed similar branching results. SVCT2 was mainly observed in the cell membrane and endoplasmic reticulum; however, it was not detected in the mitochondria. Cellular branching in neuronal cells and in a previously standardized neurosphere assay is dependent on the recycling of vitamin C or reduction in dehydroascorbic acid (DHA, produced by neurons) by glial cells. The effect of WZB117, a selective glucose/DHA transporter 1 (GLUT1) inhibitor expressed in glial cells, was also studied. By inhibiting GLUT1 glial cells, a loss of branching is observed in vitro, which is reproduced in the cerebral cortex in situ. We concluded that vitamin C recycling between neurons and astrocyte-like cells is fundamental to maintain neuronal differentiation in vitro and in vivo. The recycling activity begins at the cerebral postnatal cortex when neurons increase SVCT2 expression and concomitantly, GLUT1 is expressed in glial cells.

RNA Localization and Local Translation in Glia in Neurological and Neurodegenerative Diseases: Lessons from Neurons

Cell polarity is crucial for almost every cell in our body to establish distinct structural and functional domains. Polarized cells have an asymmetrical morphology and therefore their proteins need to be asymmetrically distributed to support their function. Subcellular protein distribution is typically achieved by localization peptides within the protein sequence. However, protein delivery to distinct cellular compartments can rely, not only on the transport of the protein itself but also on the transport of the mRNA that is then translated at target sites. This phenomenon is known as local protein synthesis. Local protein synthesis relies on the transport of mRNAs to subcellular domains and their translation to proteins at target sites by the also localized translation machinery. Neurons and glia specially depend upon the accurate subcellular distribution of their proteome to fulfil their polarized functions. In this sense, local protein synthesis has revealed itself as a crucial mechanism that regulates proper protein homeostasis in subcellular compartments. Thus, deregulation of mRNA transport and/or of localized translation can lead to neurological and neurodegenerative diseases. Local translation has been more extensively studied in neurons than in glia. In this review article, we will summarize the state-of-the art research on local protein synthesis in neuronal function and dysfunction, and we will discuss the possibility that local translation in glia and deregulation thereof contributes to neurological and neurodegenerative diseases.

Influence of Acetylcholine Esterase Inhibitors and Memantine, Clinically Approved for Alzheimer's Dementia Treatment, on Intestinal Properties of the Mouse

Four drugs are currently approved for the treatment of Alzheimer’s disease (AD) by the FDA. Three of these drugs—donepezil, rivastigmine, and galantamine—belong to the class of acetylcholine esterase inhibitors. Memantine, a NMDA receptor antagonist, represents the fourth and a combination of donepezil and memantine the fifth treatment option. Recently, the gut and its habitants, its microbiome, came into focus of AD research and added another important factor to therapeutic considerations. While the first data provide evidence that AD patients might carry an altered microbiome, the influence of administered drugs on gut properties and commensals have been largely ignored so far. However, the occurrence of digestive side effects with these drugs and the knowledge that cholinergic transmission is crucial for several gut functions enforces the question if, and how, this medication influences the gastrointestinal system and its microbial stocking. Here, we investigated aspects such as microbial viability, colonic propulsion, and properties of enteric neurons, affected by assumed intestinal concentration of the four drugs using the mouse as a model organism. All ex vivo administered drugs revealed no direct effect on fecal bacteria viability and only a high dosage of memantine resulted in reduced biofilm formation of E. coli. Memantine was additionally the only compound that elevated calcium influx in enteric neurons, while all acetylcholine esterase inhibitors significantly reduced esterase activity in colonic tissue specimen and prolonged propulsion time. Both, acetylcholine esterase inhibitors and memantine, had no effect on general viability and neurite outgrowth of enteric neurons. In sum, our findings indicate that all AD symptomatic drugs have the potential to affect distinct intestinal functions and with this—directly or indirectly—microbial commensals.

Vitamin C Recycling Regulates Neurite Growth in Neurospheres Differentiated In Vitro

The reduced form of vitamin C, ascorbic acid (AA), has been related with gene expression and cell differentiation in the cerebral cortex. In neurons, AA is mainly oxidized to dehydroascorbic acid (DHA); however, DHA cannot accumulate intracellularly because it induces metabolic changes and cell death. In this context, it has been proposed that vitamin C recycling via neuron–astrocyte coupling maintains AA levels and prevents DHA parenchymal accumulation. To date, the role of this mechanism during the outgrowth of neurites is unknown. To stimulate neuronal differentiation, adhered neurospheres treated with AA and retinoic acid (RA) were used. Neuritic growth was analyzed by confocal microscopy, and the effect of vitamin C recycling (bystander effect) in vitro was studied using different cells. AA stimulates neuritic growth more efficiently than RA. However, AA is oxidized to DHA in long incubation periods, generating a loss in the formation of neurites. Surprisingly, neurite growth is maintained over time following co-incubation of neurospheres with cells that efficiently capture DHA. In this sense, astrocytes have high capacity to recycle DHA and stimulate the maintenance of neurites. We demonstrated that vitamin C recycling in vitro regulates the morphology of immature neurons during the differentiation and maturation processes.

Fhod3 Controls the Dendritic Spine Morphology of Specific Subpopulations of Pyramidal Neurons in the Mouse Cerebral Cortex

Changes in the shape and size of the dendritic spines are critical for synaptic transmission. These morphological changes depend on dynamic assembly of the actin cytoskeleton and occur differently in various types of neurons. However, how the actin dynamics are regulated in a neuronal cell type-specific manner remains largely unknown. We show that Fhod3, a member of the formin family proteins that mediate F-actin assembly, controls the dendritic spine morphogenesis of specific subpopulations of cerebrocortical pyramidal neurons. Fhod3 is expressed specifically in excitatory pyramidal neurons within layers II/III and V of restricted areas of the mouse cerebral cortex. Immunohistochemical and biochemical analyses revealed the accumulation of Fhod3 in postsynaptic spines. Although targeted deletion of Fhod3 in the brain did not lead to any defects in the gross or histological appearance of the brain, the dendritic spines in pyramidal neurons within presumptive Fhod3-positive areas were morphologically abnormal. In primary cultures prepared from the Fhod3-depleted cortex, defects in spine morphology were only detected in Fhod3 promoter-active cells, a small population of pyramidal neurons, and not in Fhod3 promoter-negative pyramidal neurons. Thus, Fhod3 plays a crucial role in dendritic spine morphogenesis only in a specific population of pyramidal neurons in a cell type-specific manner.

MMP-9 Processing of Intestinal Smooth Muscle-derived GDNF is Required for Neurotrophic Action on Enteric Neurons

The neurotrophin GDNF guides development of the enteric nervous system (ENS) in embryogenesis and directs survival and axon outgrowth in postnatal myenteric neurons in vitro. GDNF expression in intestinal smooth muscle cells is dynamic, with upregulation by inflammatory cytokines in vitro or intestinal inflammation in vivo, but the role of post-translational proteolytic cleavage is undefined. In a co-culture model of myenteric neurons, smooth muscle and glia, inhibition of serine or cysteine protease activity was ineffective against the >2-fold increase in axon density caused by TNFα. However, inhibitors of metalloproteinases (MMP) identified an essential role of MMP-9, and qPCR and western blotting showed that pro-inflammatory cytokines increased both mRNA and protein expression for MMP-9, in both cellular lysates and conditioned medium (CM). Inhibition of MMP-9 prevented the cytokine-induced increase in mature GDNF in CM or cellular lysates of co-cultures or cell lines of intestinal smooth muscle cells (ISMC) from adult rat colon. Western blotting showed parallel upregulation of mature GDNF and MMP-9 vs control in ISMC isolated on Day 2 of TNBS-induced colitis. Nonetheless, transfection of GDNF plasmid into HEK-293 cells as a carrier system, or directly into the co-culture model, conveyed a strong neurotrophic effect that was MMP-9 dependent. We conclude that MMP-9 activity is required for the neurotrophic effects of GDNF on myenteric neurons in vitro. However, the coordinated upregulation of GDNF and MMP-9 in intestinal smooth muscle by inflammatory cytokines provides a supportive, target cell-derived environment that limits inflammatory damage to the ENS.

Object-Based Analyses in FIJI/ImageJ to Measure Local RNA Translation Sites in Neurites in Response to Aβ1-42 Oligomers

Subcellular protein delivery is especially important in signal transduction and cell behavior, and is typically achieved by localization signals within the protein. However, protein delivery can also rely on localization of mRNAs that are translated at target sites. Although once considered heretical, RNA localization has proven to be highly conserved in eukaryotes. RNA localization and localized translation are especially relevant in polarized cells like neurons where neurites extend dozens to hundreds of centimeters away from the soma. Local translation confers dendrites and axons the capacity to respond to their environment in an acute manner without fully relying on somatic signals. The relevance of local protein synthesis in neuron development, maintenance and disease has not been fully acknowledged until recent years, partly due to the limited amount of locally produced proteins. For instance, in hippocampal neurons levels of newly synthesized somatic proteins can be more than 20–30 times greater than translation levels of neuritic proteins. Thus local translation events can be easily overlooked under the microscope. Here we describe an object-based analysis used to visualize and quantify local RNA translation sites in neurites. Newly synthesized proteins are tagged with puromycin and endogenous RNAs labeled with SYTO. After imaging, signals corresponding to neuritic RNAs and proteins are filtered with a Laplacian operator to enhance the edges. Resulting pixels are converted into objects and selected by automatic masking followed by signal smoothing. Objects corresponding to RNA or protein and colocalized objects (RNA and protein) are quantified along individual neurites. Colocalization between RNA and protein in neurites correspond to newly synthesized proteins arising from localized RNAs and represent localized translation sites. To test the validity of our analyses we have compared control neurons to Aβ_1–42-treated neurons. Aβ is involved in the pathology of Alzheimer’s disease and was previously reported to induce local translation in axons and dendrites which in turn contributes to the disease. We have observed that Aβ increases the synthesis of neuritic proteins as well as the fraction of translating RNAs in distal sites of the neurite, suggesting an induction of local protein synthesis. Our results thus confirm previous reports and validate our quantification method.

Modeling Hypoxia-Induced Neuropathies Using a Fast and Scalable Human Motor Neuron Differentiation System

Human motor neuron (MN) diseases encompass a spectrum of disorders. A critical barrier to dissecting disease mechanisms is the lack of appropriate human MN models. Here, we describe a scalable, suspension-based differentiation system to generate functional human MN diseases in 3 weeks. Using this model, we translated recent findings that mRNA mis-localization plays a role in disease development to the human context by establishing a membrane-based system that allows efficient fractionation of MN cell soma and neurites. In response to hypoxia, used to mimic diabetic neuropathies, MNs upregulated mitochondrial transcripts in neurites; however, mitochondria were decreased. These data suggest that hypoxia may disrupt translation of mitochondrial mRNA, potentially leading to neurite damage and development of neuropathies. We report the development of a novel human MN model system to investigate mechanisms of disease affecting soma and/or neurites that facilitates the rapid generation and testing of patient-specific MN diseases.

Mechanical Response of Neural Cells to Physiologically Relevant Stiffness Gradients

Understanding the influence of the mechanical environment on neurite behavior is crucial in the development of peripheral nerve repair solutions, and could help tissue engineers to direct and guide regeneration. In this study, a new protocol to fabricate physiologically relevant hydrogel substrates with controlled mechanical cues is proposed. These hydrogels allow the analysis of the relative effects of both the absolute stiffness value and the local stiffness gradient on neural cell behavior, particularly for low stiffness values (1-2 kPa). NG108-15 neural cell behavior is studied using well-characterized collagen gradient substrates with stiffness values ranging from 1 to 10 kPa and gradient slopes of either 0.84 or 7.9 kPa mm-1 . It is found that cell orientation is influenced by specific combinations of stiffness value and stiffness gradient. The results highlight the importance of considering the type of hydrogel as well as both the absolute value of the stiffness and the steepness of its gradient, thus introducing a new framework for the development of tissue engineered scaffolds and the study of substrate stiffness.

Acid Ceramidase Depletion Impairs Neuronal Survival and Induces Morphological Defects in Neurites Associated with Altered Gene Transcription and Sphingolipid Content

The ASAH1 gene encodes acid ceramidase (AC), an enzyme that is implicated in the metabolism of ceramide (Cer). Mutations in the ASAH1 gene cause two different disorders, Farber disease (FD), a rare lysosomal storage disorder, and a rare form of spinal muscular atrophy combined with progressive myoclonic epilepsy (SMA-PME). In the absence of human in vitro neuronal disease models and to gain mechanistic insights into pathological effects of ASAH1 deficiency, we established and characterized a stable ASAH1 knockdown (ASAH1KD) SH-SY5Y cell line. ASAH1KD cells displayed reduced proliferation due to elevated apoptosis and G1/S cell cycle arrest. Distribution of LAMP1-positive lysosomes towards the cell periphery and significantly shortened and less branched neurites upon differentiation, implicate AC for lysosome positioning and neuronal development, respectively. Lipidomic analysis revealed changes in the intracellular levels of distinct sphingolipid species, importantly without Cer accumulation, in line with altered gene transcription within the sphingolipid pathway. Additionally, the transcript levels for Rho GTPases (RhoA, Rac1, and Cdc42), which are key regulators of axonal orientation, neurite branching and lysosome positioning were found to be dysregulated. This study shows the critical role of AC in neurons and suggests how AC depletion leads to defects seen in neuropathology of SMA-PME and FD.

SUIKER: Quantification of antigens in cell organelles, neurites and cellular sub-structures by imaging

Quantification of fluorescence colocalization and intensity of strongly overlapping cells, e.g., neuronal cultures, is challenging for programs that use image segmentation to identify cells as individual objects. Moreover, learning to use and apply one of the large imaging packages can be very time- and/or resource-demanding. Therefore, we developed the free and highly interactive image analysis program SUIKER (program for SUperImposing KEy Regions) that quantifies colocalization of different proteins or other features over an entire image field. The software allows definition of cellular subareas by subtraction ("punching out") of structures identified in one channel from structures in a second channel. This allows, e.g., definition of neurites without cell bodies. Moreover, normalization to live or total cell numbers is possible. Providing a detailed manual that contains image analysis examples, we demonstrate how the program uses a combination of colocalization information and fluorescence intensity to quantify carbohydrate-specific stains on neurites. SUIKER can import any multichannel histology or cell culture image, builds on user-guided threshold setting, batch processes large image stacks, and exports all data (including the settings, results and metadata) in flexible formats to be used in Excel.

Advanced diffusion magnetic resonance imaging in patients with Alzheimer's and Parkinson's diseases

The prevalence of neurodegenerative diseases is increasing as human longevity increases. The objective biomarkers that enable the staging and early diagnosis of neurodegenerative diseases are eagerly anticipated. It has recently become possible to determine pathological changes in the brain without autopsy with the advancement of diffusion magnetic resonance imaging techniques. Diffusion magnetic resonance imaging is a robust tool used to evaluate brain microstructural complexity and integrity, axonal order, density, and myelination via the micron-scale displacement of water molecules diffusing in tissues. Diffusion tensor imaging, a type of diffusion magnetic resonance imaging technique is widely utilized in clinical and research settings; however, it has several limitations. To overcome these limitations, cutting-edge diffusion magnetic resonance imaging techniques, such as diffusional kurtosis imaging, neurite orientation dispersion and density imaging, and free water imaging, have been recently proposed and applied to evaluate the pathology of neurodegenerative diseases. This review focused on the main applications, findings, and future directions of advanced diffusion magnetic resonance imaging techniques in patients with Alzheimer’s and Parkinson’s diseases, the first and second most common neurodegenerative diseases, respectively.

Development and Application of Cochlear Implant-Based Electric-Acoustic Stimulation of Spiral Ganglion Neurons

Cochlear implants are currently the most effective treatment for profound sensorineural hearing loss. However, their therapeutic effect is limited by the survival and proper physiological function of spiral ganglion neurons (SGNs), which are targeted by the cochlear implant. It is therefore critical to explore the mechanism behind the effect of electric-acoustic stimulation (EAS) on the targeted SGNs. In this work, a biocompatible cochlear implant/graphene EAS system was created by combining a cochlear implant to provide the electrically transformed sound stimulation with graphene as the conductive neural interface. SGNs were cultured on the graphene and exposed to EAS from the cochlear implant. Neurite extension of SGNs was accelerated with long-term stimulation, which might contribute to the development of growth cones. Our system allows us to study the effects of cochlear implants on SGNs in a low-cost and time-saving way, and this might provide profound insights into the use of cochlear implants and thus be of benefit to the populations suffering from sensorineural hearing loss.

Unconventional Roles of Cytoskeletal Mitotic Machinery in Neurodevelopment

At first look, cell division and neurite formation seem to be two different, essential biological processes. However, both processes require extensive reorganization of the cytoskeleton, and especially microtubules. Remarkably, in recent years, independent work from several groups has shown that multiple cytoskeletal components previously considered specific for the mitotic machinery play important roles in neurite initiation and extension. In this review article, we describe how several cytoplasmic and mitotic microtubule motors, components of mitotic kinetochores, and cortical actin participate in reorganization of the microtubule network required to form and maintain axons and dendrites. The emerging similarities between these two biological processes will certainly generate new insights into the mechanisms generating the unique morphology of neurons.

Ataxia in Patients With Bi-Allelic NFASC Mutations and Absence of Full-Length NF186

The etiology of hereditary ataxia syndromes is heterogeneous, and the mechanisms underlying these disorders are often unknown. Here, we utilized exome sequencing in two siblings with progressive ataxia and muscular weakness and identified a novel homozygous splice mutation (c.3020-1G > A) in neurofascin (NFASC). In RNA extracted from fibroblasts, we showed that the mutation resulted in inframe skipping of exon 26, with a deprived expression of the full-length transcript that corresponds to NFASC isoform NF186. To further investigate the disease mechanisms, we reprogrammed fibroblasts from one affected sibling to induced pluripotent stem cells, directed them to neuroepithelial stem cells and finally differentiated to neurons. In early neurogenesis, differentiating cells with selective depletion of the NF186 isoform showed significantly reduced neurite outgrowth as well as fewer emerging neurites. Furthermore, whole-cell patch-clamp recordings of patient-derived neuronal cells revealed a lower threshold for openings, indicating altered Na⁺ channel kinetics, suggesting a lower threshold for openings as compared to neuronal cells without the NFASC mutation. Taken together, our results suggest that loss of the full-length NFASC isoform NF186 causes perturbed neurogenesis and impaired neuronal biophysical properties resulting in a novel early-onset autosomal recessive ataxia syndrome.

Searching for the neurite density with diffusion MRI: Challenges for biophysical modeling

In vivo mapping of the neurite density with diffusion MRI (dMRI) is a high but challenging aim. First, it is unknown whether all neurites exhibit completely anisotropic ("stick-like") diffusion. Second, the "density" of tissue components may be confounded by non-diffusion properties such as T2 relaxation. Third, the domain of validity for the estimated parameters to serve as indices of neurite density is incompletely explored. We investigated these challenges by acquiring data with "b-tensor encoding" and multiple echo times in brain regions with low orientation coherence and in white matter lesions. Results showed that microscopic anisotropy from b-tensor data is associated with myelinated axons but not with dendrites. Furthermore, b-tensor data together with data acquired for multiple echo times showed that unbiased density estimates in white matter lesions require data-driven estimates of compartment-specific T2 values. Finally, the "stick" fractions of different biophysical models could generally not serve as neurite density indices across the healthy brain and white matter lesions, where outcomes of comparisons depended on the choice of constraints. In particular, constraining compartment-specific T2 values was ambiguous in the healthy brain and had a large impact on estimated values. In summary, estimating neurite density generally requires accounting for different diffusion and/or T2 properties between axons and dendrites. Constrained "index" parameters could be valid within limited domains that should be delineated by future studies.

Long-Term Denervated Rat Schwann Cells Retain Their Capacity to Proliferate and to Myelinate Axons in vitro

Functional recovery is poor after peripheral nerve injury and delayed surgical repair or when nerves must regenerate over long distances to reinnervate distant targets. A reduced capacity of Schwann cells (SCs) in chronically denervated distal nerve stumps to support and interact with regenerating axons may account for the poor outcome. In an in vitro system, we examined the capacity of adult, long-term denervated rat SCs to proliferate and to myelinate neurites in co-cultures with fetal dorsal root ganglion (DRG) neurons. Non-neuronal cells were counted immediately after their isolation from the distal sciatic nerve stumps that were subjected to acute denervation of 7 days or chronic denervation of either 7 weeks or 17 months. Thereafter, equal numbers of the non-neural cells were co-cultured with purified dissociated DRG neurons for 5 days. The co-cultures were then treated with ³H-Thymidine for 24 h to quantitate SC proliferation with S100 immunostaining and autoradiography. After a 24-day period of co-culture, Sudan Black staining was used to visualize and count myelin segments that were elaborated around DRG neurites by the SCs. Isolated non-neural cells from 7-week chronically denervated nerve stumps increased 2.5-fold in number compared to ~2 million in 7 day acutely denervated stumps. There were only <0.2 million cells in the 17-week chronically denervated stumps. Nonetheless, these chronically denervated SCs maintained their proliferative capacity although the capacity was reduced to 30% in the 17-month chronically denervated distal nerve stumps. Moreover, the chronically denervated SCs retained their capacity to myelinate DRG neurites: there was extensive myelination of the neurites by the acutely and chronically denervated SCs after 24 days co-culture. There were no significant differences in the extent of myelination. We conclude that the low numbers of surviving SCs in chronically denervated distal nerve stumps retain their ability to respond to axonal signals to divide and to elaborate myelin. However, their low numbers consequent to their poor survival and their reduced capacity to proliferate account, at least in part, for the poor functional recovery after delayed surgical repair of injured nerve and/or the repair of injured nerves far from their target organs.

Creating Biomimetic Anisotropic Architectures with Co-Aligned Nanofibers and Macrochannels by Manipulating Ice Crystallization

The continuous evolution of tissue engineering scaffolds has been driven by the desire to recapitulate structural features and functions of the natural extracellular matrix (ECM). However, it is still an extreme challenge to create a three-dimensional (3D) scaffold with both aligned nanofibers and aligned interconnected macrochannels to mimic the ECM of anisotropic tissues. Here, we develop a facile strategy to create such a scaffold composed of oriented nanofibers and interconnected macrochannels in the same direction, with various natural polymers typically used for tissue regeneration. The orientation of nanofibers and interconnected macrochannels can be easily tuned by manipulating ice crystallization. The scaffold demonstrates both structural and functional features similar to the natural ECM of anisotropic tissues. Taking silk fibroin as an example, the scaffold with radially oriented nanofibers and interconnected macrochannels is more efficient for capturing cells and promoting the growth of both nonadherent embryonic dorsal root ganglion neurons (DRGs) and adherent human umbilical vein endothelial cells (HUVECs) compared to the widely used scaffold types. Interestingly, DRGs and neurites on the SF scaffold demonstrate a 3D growth mode similar to that of natural nerve tissues. Furthermore, the coaligned nanofibers and macrochannels of the scaffold can direct HUVECs to assemble into blood vessel-like structures and their collagen deposition in their arrangement direction. The strategy could inspire the design and development of multifunctional 3D scaffolds with desirable structural features for engineering different tissues.

Withania somnifera Extract Protects Model Neurons from In Vitro Traumatic Injury

Withania somnifera has been used in traditional medicine for a variety of neural disorders. Recently, chronic neurodegenerative conditions have been shown to benefit from treatment with this extract. To evaluate the action of this extract on traumatically injured neurons, the efficacy of W. somnifera root extract as a neuroprotective agent was examined in cultured model neurons exposed to an in vitro injury system designed to mimic mild traumatic brain injury (TBI). Neuronal health was evaluated by staining with annexin V (an early, apoptotic feature) and monitoring released lactate dehydrogenase activity (a terminal cell loss parameter). Potential mechanisms underlying the observed neuroprotection were examined. Additionally, morphological changes were monitored following injury and treatment. Although no differences were found in the expression of the antioxidant transcription factor nuclear factor erythroid 2-like 2 (Nrf2) or other Nrf2-related downstream components, significant changes were seen in apoptotic signaling. Treatment with the extract resulted in an increased length of neurites projecting from the neuronal cell body after injury. W. somnifera extract treatment also resulted in reduced cell death in the model neuron TBI system. The cell death factor Bax was involved (its expression was reduced 2-fold by the treatment) and injury-induced reduction in neurite lengths and numbers was reversed by the treatment. This all indicates that W. somnifera root extract was neuroprotective and could have therapeutic potential to target factors involved in secondary injury and long-term sequelae of mild TBI.

Transglutaminase 2: Friend or foe? The discordant role in neurons and astrocytes

Members of the transglutaminase family catalyze the formation of isopeptide bonds between a polypeptide-bound glutamine and a low molecular weight amine (e.g., spermidine) or the ɛ-amino group of a polypeptide-bound lysine. Transglutaminase 2 (TG2), a prominent member of this family, is unique because in addition to being a transamidating enzyme, it exhibits numerous other activities. As a result, TG2 plays a role in many physiological processes, and its function is highly cell type specific and relies upon a number of factors, including conformation, cellular compartment location, and local concentrations of Ca²⁺ and guanine nucleotides. TG2 is the most abundant transglutaminase in the central nervous system (CNS) and plays a pivotal role in the CNS injury response. How TG2 affects the cell in response to an insult is strikingly different in astrocytes and neurons. In neurons, TG2 supports survival. Overexpression of TG2 in primary neurons protects against oxygen and glucose deprivation (OGD)-induced cell death and in vivo results in a reduction in infarct volume subsequent to a stroke. Knockdown of TG2 in primary neurons results in a loss of viability. In contrast, deletion of TG2 from astrocytes results in increased survival following OGD and improved ability to protect neurons from injury. Here, a brief overview of TG2 is provided, followed by a discussion of the role of TG2 in transcriptional regulation, cellular dynamics, and cell death. The differing roles TG2 plays in neurons and astrocytes are highlighted and compared to how TG2 functions in other cell types.

Cryopreservation of Primary Mouse Neurons: The Benefit of Neurostore Cryoprotective Medium

Primary neuronal culture from rodents is a well-established model to investigate cellular neurobiology in vitro. However, for this purpose cell cultures need to be generated expressly, requiring extensive animal handling. Furthermore, often the preparation of fresh culture generates an excess of cells that are ultimately wasted. Therefore the ability to successfully cryopreserve primary neural cells would represent an important resource for neuroscience research and would allow to significantly reduce the sacrifice of animals. We describe here a novel freezing medium that allows long-term cryopreservation of primary mouse neurons prepared from E15.5 embryos. Combining imaging, biochemical and electrophysiological analyses, we found that cryopreserved cultures are viable and mature regarding morphology and functionality. These findings suggest that cryopreserved neurons are a valuable alternative to acutely dissociated neural cultures.

A Method to Culture GABAergic Interneurons Derived from the Medial Ganglionic Eminence

Understanding the mechanisms guiding interneuron development is a central aspect of the current research on cortical/hippocampal interneurons, which is highly relevant to brain function and pathology. In this methodological study we have addressed the setup of protocols for the reproducible culture of dissociated cells from murine medial ganglionic eminences (MGEs), to provide a culture system for the analysis of interneurons in vitro. This study includes the detailed protocols for the preparation of the dissociated cells, and for their culture on optimal substrates for cell migration or differentiation. These cultures enriched in interneurons may allow the investigation of the migratory behavior of interneuron precursors and their differentiation in vitro, up to the formation of morphologically identifiable GABAergic synapses. Live imaging of MGE-derived cells plated on proper substrates shows that they are useful to study the migratory behavior of the precursors, as well as the behavior of growth cones during the development of neurites. Most MGE-derived precursors develop into polarized GABAergic interneurons as determined by axonal, dendritic, and GABAergic markers. We present also a comparison of cells from WT and mutant mice as a proof of principle for the use of these cultures for the analysis of the migration and differentiation of GABAergic cells with different genetic backgrounds. The culture enriched in interneurons described here represents a useful experimental system to examine in a relatively easy and fast way the morpho-functional properties of these cells under physiological or pathological conditions, providing a powerful tool to complement the studies in vivo.

Obesity during pregnancy in the mouse alters the Netrin-1 responsiveness of foetal arcuate nucleus neuropeptide Y neurones

When individuals undergo gestation in an obese dam, they are at increased risk for impairments in the ability of the brain to regulate body weight. In rodents, gestation in an obese dam leads to a number of changes to the development of the hypothalamic neurones that regulate body weight, including reduced neuronal connectivity at birth. In the present study, we aimed to clarify how this neural circuitry develops normally, as well as to explore the mechanism underpinning the deficiency in connectivity seen in foetuses developing in obese dams. First, we developed an in vitro model for observing and manipulating the axonal growth of foetal arcuate nucleus (ARN) neuropeptide (NPY) neurones. We then used this model to test 2 hypotheses: (i) ARN NPY neurones respond to Netrin-1, one of a small number of axon growth and guidance factors that regulate neural circuit formation throughout the developing brain; and (ii) Netrin-1 responsiveness would be lost upon exposure to the inflammatory cytokine interleukin (IL)-6, which is elevated in foetuses developing in obese dams. We observed that ARN NPY neurones responded to Netrin-1 with a significant expansion of their growth cones, comprising the terminal apparatus that neurones use to navigate. Unexpectedly, we found further that NPY neurones from obese pregnancies had a reduced responsiveness to Netrin-1, raising the possibility that ARN NPY neurones from foetuses developing in obese dams were phenotypically different from normal NPY neurones. Finally, we observed that IL-6 treatment of normal NPY neurones in vitro led to a reduced growth cone responsiveness to Netrin-1, essentially causing them to behave similarly to NPY neurones from obese pregnancies. These results support the hypothesis that IL-6 can disrupt the normal process of axon growth from NPY neurones, and suggest one possible mechanism for how the body weight regulating circuitry fails to develop properly in the offspring of obese dams.

Ubiquitin C-terminal hydrolase L1 (UCH-L1): structure, distribution and roles in brain function and dysfunction

Ubiquitin C-terminal hydrolase L1 (UCH-L1) is an extremely abundant protein in the brain where, remarkably, it is estimated to make up 1–5% of total neuronal protein. Although it comprises only 223 amino acids it has one of the most complicated 3D knotted structures yet discovered. Beyond its expression in neurons UCH-L1 has only very limited expression in other healthy tissues but it is highly expressed in several forms of cancer. Although UCH-L1 is classed as a deubiquitinating enzyme (DUB) the direct functions of UCH-L1 remain enigmatic and a wide array of alternative functions has been proposed. UCH-L1 is not essential for neuronal development but it is absolutely required for the maintenance of axonal integrity and UCH-L1 dysfunction is implicated in neurodegenerative disease. Here we review the properties of UCH-L1, and how understanding its complex structure can provide new insights into its roles in neuronal function and pathology.

Protocols for assessing mitophagy in neuronal cell lines and primary neurons

Mitochondria are organelles that regulate essential eukaryotic functions including generating energy, sequestering excess calcium, and modulating cell survival. In order for neurons to thrive, mitochondria have to be continuously replenished by maintaining autophagic-lysosomal mediated degradation of mitochondria (mitophagy) and mitochondrial biogenesis. While a plethora of image- and biochemical-based techniques have been developed for measuring autophagy (macroautophagy) in eukaryotic cells, the molecular toolbox for quantifying and assessing mitophagy in neurons continues to evolve. Compared to proliferating cells, quantifying mitophagy in neurons poses a technical challenge given that mitochondria are predominantly present in neurites (axons and dendrites) and are highly dynamic. In this chapter, we provide a brief overview on mitophagy and provide a list of validated fluorescence- and biochemistry-based techniques used for assessing mitophagy in neuronal cells and primary neurons. Secondly, we provide comprehensive guidelines for interpreting steady-state levels of mitophagy and mitophagic flux in neurons using modern fluorescence- and biochemistry-based techniques. Finally, we provide a comprehensive list of common pitfalls to avoid when assessing mitophagy and offer practical solutions to overcome technical issues.

Identification of a Protein Network Driving Neuritogenesis of MGE-Derived GABAergic Interneurons

Interneurons are essential modulators of brain activity and their abnormal maturation may lead to neural and intellectual disabilities. Here we show that cultures derived from murine medial ganglionic eminences (MGEs) produce virtually pure, polarized γ-aminobutyric acid (GABA)-ergic interneurons that can form morphologically identifiable inhibitory synapses. We show that Rac GTPases and a protein complex including the GIT family scaffold proteins are expressed during maturation in vitro, and are required for the normal development of neurites. GIT1 promotes neurite extension in a conformation-dependent manner, while affecting its interaction with specific partners reduces neurite branching. Proteins of the GIT network are concentrated at growth cones, and interaction mutants may affect growth cone behavior. Our findings identify the PIX/GIT1/liprin-α1/ERC1 network as critical for the regulation of interneuron neurite differentiation in vitro, and show that these cultures represent a valuable system to identify the molecular mechanisms driving the maturation of cortical/hippocampal interneurons.

Stereotactic injection of shrna GSK-3β-AAV promotes axonal regeneration after spinal cord injury

Evidence suggested that glycogen synthase kinase-3β (GSK-3β) is involved in Nogo-66 inhibiting axonal regeneration in vitro, but its effect in vivo was poorly understood. We showed that stereotactic injection of shRNA GSK-3β-adeno associated virus (GSK-3β-AAV) diminished syringomyelia and promoted axonal regeneration after spinal cord injury (SCI), using stereotactic injection of shRNA GSK-3β-AAV (tested with Western blotting and RT-PCR) into the sensorimotor cortex of rats with SCI and by the detection of biotin dextran amine (BDA)-labeled axonal regeneration. We also determined the right position to inject into the sensorimotor cortex. Our findings consolidate the hypothesis that downregulation of GSK-3β promotes axonal regeneration after SCI.

Using Cultured Mammalian Neurons to Study Cellular Processes and Neurodegeneration: A Suite of Undergraduate Lab Exercises

Cell culture is a powerful tool for exploring cellular function. Culturing primary neurons has revealed how neurons communicate in learning and memory (Kandel, 2006) and provided insights into the mechanisms of neurodegenerative diseases such as Parkinson's and Alzheimer's disease (Alberio et al., 2012; Trinchese, et al., 2004). Here we describe a series of four modular laboratory exercises to integrate this neuroscience technique in undergraduate teaching laboratories. First, we describe the modular approach. Then we provide educators with simple techniques for culturing rat primary neurons, performing immunohistochemistry to label cellular components, and illustrating neurodegeneration caused by reactive oxygen species. We describe teaching exercises that culminate in student-generated research projects. Finally, we describe potential barriers students may face when integrating modern cell culture experiments into teaching laboratories.

Blockade of transient receptor potential cation channel subfamily V member 1 promotes regeneration after sciatic nerve injury

The transient receptor potential cation channel subfamily V member 1 (TRPV1) provides the sensation of pain (nociception). However, it remains unknown whether TRPV1 is activated after peripheral nerve injury, or whether activation of TRPV1 affects neural regeneration. In the present study, we established rat models of unilateral sciatic nerve crush injury, with or without pretreatment with AMG517 (300 mg/kg), a TRPV1 antagonist, injected subcutaneously into the ipsilateral paw 60 minutes before injury. At 1 and 2 weeks after injury, we performed immunofluorescence staining of the sciatic nerve at the center of injury, at 0.3 cm proximal and distal to the injury site, and in the dorsal root ganglia. Our results showed that Wallerian degeneration occurred distal to the injury site, and neurite outgrowth and Schwann cell regeneration occurred proximal to the injury. The number of regenerating myelinated and unmyelinated nerve clusters was greater in the AMG517-pretreated rats than in the vehicle-treated group, most notably 2 weeks after injury. TRPV1 expression in the injured sciatic nerve and ipsilateral dorsal root ganglia was markedly greater than on the contralateral side. Pretreatment with AMG517 blocked this effect. These data indicate that TRPV1 is activated or overexpressed after sciatic nerve crush injury, and that blockade of TRPV1 may accelerate regeneration of the injured sciatic nerve.

Synapsin knockdown is associated with decreased neurite outgrowth, functional synaptogenesis impairment, and fast high-frequency neurotransmitter release

Synapsins (Syns) are an evolutionarily conserved family of synaptic vesicle-associated proteins related to fine tuning of synaptic transmission. Studies with mammals have partially clarified the different roles of Syns; however, the presence of different genes and isoforms and the development of compensatory mechanisms hinder accurate data interpretation. Here, we use a simple in vitro monosynaptic Helix neuron connection, reproducing an in vivo physiological connection as a reliable experimental model to investigate the effects of Syn knockdown. Cells overexpressing an antisense construct against Helix Syn showed a time-dependent decrease of Syn immunostaining, confirming protein loss. At the morphological level, Syn-silenced cells showed a reduction in neurite linear outgrowth and branching and in the size and number of synaptic varicosities. Functionally, Syn-silenced cells presented a reduced ability to form synaptic connections; however, functional chemical synapses showed similar basal excitatory postsynaptic potentials and similar short-term plasticity paradigms. In addition, Syn-silenced cells presented faster neurotransmitter release and decreased postsynaptic response toward the end of long tetanic presynaptic stimulations, probably related to an impairment of the synaptic vesicle trafficking resulting from a different vesicle handling, with an increased readily releasable pool and a compromised reserve pool.

Effect of Rho-kinase pathway on neurite outgrowth of rat hippocampal neurons under atomic force microscopy

Hippocampal neurons of neonatal rats were cultured in serum-free culture medium for 5 days in vitro, and treated with the Rho-kinase inducer lysophosphatidic acid. Atomic force microscopy revealed that the numbers of level-1, -2 and -3 neurites protruding from rat hippocampal neurons was significantly reduced. After treatment with the Rho kinase inhibitor Y27632, a significant increase in the numbers of these neurites was observed. Our experimental findings indicate that the Rho-kinase pathway is closely associated with the neurites of hippocampal neurons.

Neurotoxic effects of local anesthetics on the mouse neuroblastoma NB2a cell line

Local anesthetics are used clinically for peripheral nerve blocks, epidural anesthesia, spinal anesthesia and pain management; large concentrations, continuous application and long exposure time can cause neurotoxicity. The mechanism of neurotoxicity caused by local anesthetics is unclear. Neurite outgrowth and apoptosis can be used to evaluate neurotoxic effects. Mouse neuroblastoma cells were induced to differentiate and generate neurites in the presence of local anesthetics. The culture medium was removed and replaced with serum-free medium plus 20 μl combinations of epidermal growth factor and fibroblast growth factor containing tetracaine, prilocaine, lidocaine or procaine at concentrations of 1, 10, 25, or 100 μl prior to neurite measurement. Cell viability, iNOS, eNOS and apoptosis were evaluated. Local anesthetics produced toxic effects by neurite inhibition at low concentrations and by apoptosis at high concentrations. There was an inverse relation between local anesthetic concentrations and cell viability. Comparison of different local anesthetics showed toxicity, as assessed by cell viability and apoptotic potency, in the following order: tetracaine > prilocaine > lidocaine > procaine. Procaine was the least neurotoxic local anesthetic and because it is short-acting, may be preferred for pain prevention during short procedures.

Effect of type-2 astrocytes on the viability of dorsal root ganglion neurons and length of neuronal processes

The role of type-2 astrocytes in the repair of central nervous system injury remains poorly understood. In this study, using a relatively simple culture condition in vitro, type-2 astrocytes, differentiated from oligodendrocyte precursor cells by induction with bone morphogenetic protein-4, were co-cultured with dorsal root ganglion neurons. We examined the effects of type-2 astrocytes differentiated from oligodendrocyte precursor cells on the survival and growth of dorsal root ganglion neurons. Results demonstrated that the number of dorsal root ganglion neurons was higher following co-culture of oligodendrocyte precursor cells and type-2 astrocytes than when cultured alone, but lower than that of neurons co-cultured with type-1 astrocytes. The length of the longest process and the length of all processes of a single neuron were shortest in neurons cultured alone, followed by neurons co-cultured with type-2 astrocytes, then neurons co-cultured with oligodendrocyte precursor cells, and longest in neurons co-cultured with type-1 astrocytes. These results indicate that co-culture with type-2 astrocytes can increase neuronal survival rate and process length. However, compared with type-1 astrocytes and oligodendrocyte precursor cells, the promotion effects of type-2 astrocytes on the growth of dorsal root ganglion neurons were weaker.

A rapid and sensitive automated image-based approach for in vitro and in vivo characterization of cell morphology and quantification of cell number and neurite architecture

Stereological methods for tissue cell counting, specifically for neuron quantification, decrease systematic error and sampling bias; however, they are tedious, labor intensive, and time consuming. Approaches for cell (neuron) quantification in vitro are not accurate, sensitive, or subsequently reproducible. Neuronal phenotype is related to alterations in cell morphology and neurite pattern. The techniques currently available for quantification of these features present several limitations. In this unit, we provide validated automated procedures for in vivo and in vitro quantification of cell number, morphological cell changes, and neurite morphometry in a fast, simple, and reliable manner. Our method counts up to 8 times as many neurons in less than 5% to 10% of the time required for stereological analysis (optical fractionator). In summary, this technology offers an unparalleled opportunity to examine features of cells at high resolution in a complex three-dimensional environment. These techniques provide an exceptional in vivo and in vitro system for neurotoxicity studies, disease modeling, and drug discovery.

Endosomal pH in neuronal signaling and synaptic transmission: role of Na(+)/H(+) exchanger NHE5

Neuronal precursor cells extend multiple neurites during development, one of which extends to form an axon whereas others develop into dendrites. Chemical stimulation of N-methyl D-aspartate (NMDA) receptor in fully-differentiated neurons induces projection of dendritic spines, small spikes protruding from dendrites, thereby establishing another layer of polarity within the dendrite. Neuron-enriched Na⁺/H⁺ exchanger NHE5 contributes to both neurite growth and dendritic spine formation. In resting neurons and neuro-endocrine cells, neuron-enriched NHE5 is predominantly associated with recycling endosomes where it colocalizes with nerve growth factor (NGF) receptor TrkA. NHE5 potently acidifies the lumen of TrkA-positive recycling endosomes and regulates cell-surface targeting of TrkA, whereas chemical stimulation of NMDA receptors rapidly recruits NHE5 to dendritic spines, alkalinizes dendrites and down-regulates the dendritic spine formation. Possible roles of NHE5 in neuronal signaling via proton movement in subcellular compartments are discussed.

Automated imaging system for fast quantitation of neurons, cell morphology and neurite morphometry in vivo and in vitro

Quantitation of neurons using stereologic approaches reduces bias and systematic error, but is time-consuming and labor-intensive. Accurate methods for quantifying neurons in vitro are lacking; conventional methodologies are limited in reliability and application. The morphological properties of the soma and neurites are a key aspect of neuronal phenotype and function, but the assays commonly used in such evaluations are beset with several methodological drawbacks. Herein we describe automated techniques to quantify the number and morphology of neurons (or any cell type, e.g., astrocytes) and their processes with high speed and accuracy. Neuronal quantification from brain tissue using a motorized stage system yielded results that were statistically comparable to those generated by stereology. The approach was then adapted for in vitro neuron and neurite outgrowth quantification. To determine the utility of our methods, rotenone was used as a neurotoxicant leading to morphological changes in neurons and cell death, astrocytic activation, and loss of neurites. Importantly, our technique counted about 8 times as many neurons in less than 5-10% of the time taken by manual stereological analysis.

Effect of Y-27632 on the cultured retinal neurocytes of rats

AIM

To investigate the effect of Y-27632 on the survival and neurite outgrowth of the cultured retinal neurocytes.

METHODS

After the postnatal day 2-3, Sprague-Dawley retinal neurocytes were cultured for 48 hours, the culture media was replaced with serum-free media (control group) and serum-free media contained 30µmol/L Y-27632 (Y-27632 group), and the cells were continually cultured another 48 hours. The cultured retinal neurocytes were identified with anti-neuron specific enolase (NSE) immunocytochemistry. The survival state of those cells was estimated by MTT assay, and the neurite outgrowth of those cells was evaluated by the computerized image-analysis system.

RESULTS

Compared with the control group, the absorbance values of cells survival in Y-27632 group increased 12.90% and 33.33% respectively after 72 and 96 hours culture. Y-27632 had no significant effect on the diameter of cultured retinal neurocytes. Compared with the control group, Y-27632 induced a stable improvement of neurite outgrowth of retinal neurocytes after 72 and 96 hours culture (P=0.001).

CONCLUSION

Y-27632 could promote the survival and neurite outgrowth of the early postnatal cultured retinal neurocytes.