MAP2 is localized to the dendrites of hippocampal neurons which develop in culture

The Protective Effect of Docosahexaenoic Acid on Mitochondria in SH-SY5Y Model of Rotenone-Induced Toxicity

Background: Polyunsaturated fatty acids in particular omega-3 fatty acids, such as docosahexaenoic acid (DHA), are essential nutrients and components of the plasma membrane. They are involved in various processes, including synaptic development, functionality, integrity, and plasticity, and are therefore thought to have general neuroprotective properties. Considerable research evidence further supports the beneficial effects of omega-3 fatty acids, specifically on mitochondria, through their antioxidant and anti-apoptotic properties, making them an attractive addition in treatment options for neurodegenerative disorders in which mitochondrial alterations are commonly observed. However, precise information on the underlying protective mechanisms is still lacking. Methods: We utilized the most common neuronal cell line (SH-SY5Y) and induced mitochondrial oxidative stress through the addition of rotenone. To study the potential protective effect of DHA, the cells were additionally pre-treated with DHA prior to rotenone administration. By combining SILAC labeling, mitochondria enrichment, and subsequent proteomic analyses, we aimed to determine the capacity of DHA to alleviate mitochondrial oxidative stress in vitro and further shed light on the molecular mechanisms contributing to the proposed neuroprotective effect. Results: We confirmed a reduced cell viability and an increased abundance of reactive oxygen species upon rotenone treatment, DHA pre-treatment was shown to decrease said species. Additionally proteomic analysis revealed an increased expression of mitochondrial proteins in DHA pre-treated cells. Conclusions: With our study, we were able to define a potential compensatory mechanism by which the inhibition of complex I is overcome by an increased activity of the fatty acid beta oxidation in response to DHA.

Adhesion G protein-coupled receptor ADGRG1 promotes protective microglial response in Alzheimer's disease

Germline genetic architecture of Alzheimer's disease (AD) indicates microglial mechanisms of disease susceptibility and outcomes. However, the mechanisms that enable microglia to mediate protective responses to AD pathology remain elusive. Adgrg1 is specifically expressed in yolk-sac-derived microglia. This study reveals the role of yolk-sac-derived microglia in AD pathology, highlighting the function of ADGRG1 in modulating microglial protective responses to amyloid deposition. Utilizing both constitutive and inducible microglial Adgrg1 knockout 5xFAD models, we demonstrate that Adgrg1 deficiency leads to increased amyloid deposition, exacerbated neuropathology, and accelerated cognitive impairment. Transcriptomic analyses reveal a distinct microglial state characterized by downregulated genes associated with homeostasis, phagocytosis, and lysosomal functions. Functional assays in mouse models and human embryonic stem cells-derived microglia support that microglial ADGRG1 is required for efficient Aβ phagocytosis. Together, these results uncover a GPCR-dependent microglial response to Aβ, pointing towards potential therapeutic strategies to alleviate disease progression by enhancing microglial functional competence.

Concerted transcriptional regulation of the morphogenesis of hypothalamic neurons by ONECUT3

Acquisition of specialized cellular features is controlled by the ordered expression of transcription factors (TFs) along differentiation trajectories. Here, we find a member of the Onecut TF family, ONECUT3, expressed in postmitotic neurons that leave their Ascl1+/Onecut1/2+ proliferative domain in the vertebrate hypothalamus to instruct neuronal differentiation. We combined single-cell RNA-seq and gain-of-function experiments for gene network reconstruction to show that ONECUT3 affects the polarization and morphogenesis of both hypothalamic GABA-derived dopamine and thyrotropin-releasing hormone (TRH)+ glutamate neurons through neuron navigator-2 (NAV2). In vivo, siRNA-mediated knockdown of ONECUT3 in neonatal mice reduced NAV2 mRNA, as well as neurite complexity in Onecut3-containing neurons, while genetic deletion of Onecut3/ceh-48 in C. elegans impaired neurocircuit wiring, and sensory discrimination-based behaviors. Thus, ONECUT3, conserved across neuronal subtypes and many species, underpins the polarization and morphological plasticity of phenotypically distinct neurons that descend from a common pool of Ascl1+ progenitors in the hypothalamus.

Mechanism of Yishen Chuchan decoction intervention of Parkinson's disease based on network pharmacology and experimental verification

The incidence of Parkinson's disease (PD) rises rapidly with the increase of age. With the advent of global aging, the number of patients with PD is rising along with the elderly population, especially in China. Previously, we found that Yishen chuchan decoction (YCD), prescribed based on clinical experience, has the potential of alleviating symptoms, delaying the progression, and controlling the development of PD. Nonetheless, the underlying mechanistic role is yet to be explored.

Aim

This research examined the possible therapeutic effects of YCD in alleviating PD via a systematic approach with network pharmacology and experimental validation, aiming at providing a new understanding of traditional Chinese medicine management regarding PD.

Methods

The chemical structure and properties of YCD were adopted from Traditional Chinese Medicine System Pharmacology Database (TCMSP), SwissADME, PubChem, and PubMed. The potential targets for YCD and PD were identified using Swiss Target Prediction, GeneCard, PubChem, and UniProt. The herbal-component-target network was created via the Cytoscape software. Moreover, by using the STRING database, the protein-protein interaction (PPI) network was screened. Gene function GO and KEGG pathway enrichment analyses were performed via the Metascape database. YCD-medicated Rat Serum from Sprague-Dawley (SD) Rats was prepared, and SH-SY5Y cells were preconditioned with rotenone to develop the PD model. To examine the impact of YCD on these cells and explore the mechanistic role of the p38 mitogen-activated protein kinase (MAPK) pathway, the cells were pretreated with either serum or a p38 MAPK pathway inhibitor. This study employed the Cell Counting Kit (CCK)-8 assay and Hoechst 33,342 staining to evaluate the viability and morphological changes induced by the YCD-medicated rat serum on rotenone-treated SH-SY5Y cells. Apoptosis was assessed by Flow cytometry. Immunofluorescence staining assessed the microtubule-associated protein 2 (MAP2) level. Enzyme-linked immunosorbent assay (ELISA) was employed to quantify the concentrations of inflammatory mediators interleukin-1β (IL-1β), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α). Also, reactive oxygen species (ROS) and superoxide dismutase (SOD) levels were determined. Western Blotting measured the expression of total and phospho-p38 MAPK (p-p38).

Results

This study identified 65 active components in YCD, which were found to target 801 specific genes. By screening, 63 potential core targets were identified from a pool of 172 overlapping targets between PD and YCD. These targets were examined by GO and KEGG analyses revealing their substantial correlation to MAPK, PI3K-Akt signaling pathways, positively controlling protein phosphorylation, and pathways of neurodegenerative diseases. SH-SY5Y cells were treated with 2 μM rotenone for 48 h, which reduced cell viability to 50 %, and reduced MAP2 expression, increased the rate of apoptosis, oxidative stress, inflammation, and p-p38 expressions. YCD-medicated rat serum significantly improved the viability, reduced the apoptosis rate, and increased the MAP2 expression. YCD-medicated serum increased SOD, reduced ROS and suppressed IL-6, IL-1β and TNF-α levels, thus inhibiting oxidative stress and inflammation in rotenone-treated SH-SY5Y cells. Moreover, YCD-medicated serum substantially lowered the p-p38 expression induced by rotenone. SB203580, a specific inhibitor of p38 MAPK, could also inhibit the p-p38 expression, apoptosis, and restore morphological damage of cells, also improve inflammation and oxidative stress.

Conclusion

YCD enhanced cell viability and reduced apoptosis rate, inflammation, and oxidative stress in vitro. These beneficial effects could potentially involve the suppression of p38 pathway and suppressed the phosphorylation of p38 MAPK.

Phase separation on microtubules: from droplet formation to cellular function?

Microtubules are cytoskeletal polymers that play important roles in numerous cellular processes, ranging from the control of cell shape and polarity to cell division and intracellular transport. Many of these roles rely on proteins that bind to microtubule ends and shafts, carry intrinsically disordered regions, and form complex multivalent interaction networks. A flurry of recent studies demonstrated that these properties allow diverse microtubule-binding proteins to undergo liquid-liquid phase separation (LLPS) in vitro. It is proposed that LLPS could potentially affect multiple microtubule-related processes, such as microtubule nucleation, control of microtubule dynamics and organization, and microtubule-based transport. Here, we discuss the evidence in favor and against the occurrence of LLPS and its functional significance for microtubule-based processes in cells.

Characterization of a Human Neuronal Culture System for the Study of Cofilin-Actin Rod Pathology

Cofilactin rod pathology, which can initiate synapse loss, has been extensively studied in rodent neurons, hippocampal slices, and in vivo mouse models of human neurodegenerative diseases such as Alzheimer's disease (AD). In these systems, rod formation induced by disease-associated factors, such as soluble oligomers of Amyloid-β (Aβ) in AD, utilizes a pathway requiring cellular prion protein (PrPC), NADPH oxidase (NOX), and cytokine/chemokine receptors (CCR5 and/or CXCR4). However, rod pathways have not been systematically assessed in a human neuronal model. Here, we characterize glutamatergic neurons differentiated from human-induced pluripotent stem cells (iPSCs) for the formation of rods in response to activators of the PrPC-dependent pathway. Optimization of substratum, cell density, and use of glial-conditioned medium yielded a robust system for studying the development of Aβ-induced rods in the absence of glia, suggesting a cell-autonomous pathway. Rod induction in younger neurons requires ectopic expression of PrPC, but this dependency disappears by Day 55. The quantification of proteins within the rod-inducing pathway suggests that increased PrPC and CXCR4 expression may be factors in the doubling of the rod response to Aβ between Days 35 and 55. FDA-approved antagonists to CXCR4 and CCR5 inhibit the rod response. Rods were predominantly observed in dendrites, although severe cytoskeletal disruptions prevented the assignment of over 40% of the rods to either an axon or dendrite. In the absence of glia, a condition in which rods are more readily observed, neurons mature and fire action potentials but do not form functional synapses. However, PSD95-containing dendritic spines associate with axonal regions of pre-synaptic vesicles containing the glutamate transporter, VGLUT1. Thus, our results identified stem cell-derived neurons as a robust model for studying cofilactin rod formation in a human cellular environment and for developing effective therapeutic strategies for the treatment of dementias arising from multiple proteinopathies with different rod initiators.

Droplet-based transcriptome profiling of individual synapses

Synapses are crucial structures that mediate signal transmission between neurons in complex neural circuits and display considerable morphological and electrophysiological heterogeneity. So far we still lack a high-throughput method to profile the molecular heterogeneity among individual synapses. In the present study, we develop a droplet-based single-cell (sc) total-RNA-sequencing platform, called Multiple-Annealing-and-Tailing-based Quantitative scRNA-seq in Droplets, for transcriptome profiling of individual neurites, primarily composed of synaptosomes. In the synaptosome transcriptome, or 'synaptome', profiling of both mouse and human brain samples, we detect subclusters among synaptosomes that are associated with neuronal subtypes and characterize the landscape of transcript splicing that occurs within synapses. We extend synaptome profiling to synaptopathy in an Alzheimer's disease (AD) mouse model and discover AD-associated synaptic gene expression changes that cannot be detected by single-nucleus transcriptome profiling. Overall, our results show that this platform provides a high-throughput, single-synaptosome transcriptome profiling tool that will facilitate future discoveries in neuroscience.

Organelle mapping in dendrites of human iPSC-derived neurons reveals dynamic functional dendritic Golgi structures

Secretory pathways within dendrites of neurons have been proposed for local transport of newly synthesized proteins. However, little is known about the dynamics of the local secretory system and whether the organelles are transient or stable structures. Here, we quantify the spatial and dynamic behavior of dendritic Golgi and endosomes during differentiation of human neurons generated from induced pluripotent stem cells (iPSCs). In early neuronal development, before and during migration, the entire Golgi apparatus transiently translocates from the soma into dendrites. In mature neurons, dynamic Golgi elements, containing cis and trans cisternae, are transported from the soma along dendrites, in an actin-dependent process. Dendritic Golgi outposts are dynamic and display bidirectional movement. Similar structures were observed in cerebral organoids. Using the retention using selective hooks (RUSH) system, Golgi resident proteins are transported efficiently into Golgi outposts from the endoplasmic reticulum. This study reveals dynamic, functional Golgi structures in dendrites and a spatial map for investigating dendrite trafficking in human neurons.

High-Throughput Screening Assay for Detecting Drug-Induced Changes in Synchronized Neuronal Oscillations and Potential Seizure Risk Based on Ca2+ Fluorescence Measurements in Human Induced Pluripotent Stem Cell (hiPSC)-Derived Neuronal 2D and 3D Cultures

Drug-induced seizure liability is a significant safety issue and the basis for attrition in drug development. Occurrence in late development results in increased costs, human risk, and delayed market availability of novel therapeutics. Therefore, there is an urgent need for biologically relevant, in vitro high-throughput screening assays (HTS) to predict potential risks for drug-induced seizure early in drug discovery. We investigated drug-induced changes in neural Ca²⁺ oscillations, using fluorescent dyes as a potential indicator of seizure risk, in hiPSC-derived neurons co-cultured with human primary astrocytes in both 2D and 3D forms. The dynamics of synchronized neuronal calcium oscillations were measured with an FDSS kinetics reader. Drug responses in synchronized Ca²⁺ oscillations were recorded in both 2D and 3D hiPSC-derived neuron/primary astrocyte co-cultures using positive controls (4-aminopyridine and kainic acid) and negative control (acetaminophen). Subsequently, blinded tests were carried out for 25 drugs with known clinical seizure incidence. Positive predictive value (accuracy) based on significant changes in the peak number of Ca²⁺ oscillations among 25 reference drugs was 91% in 2D vs. 45% in 3D hiPSC-neuron/primary astrocyte co-cultures. These data suggest that drugs that alter neuronal activity and may have potential risk for seizures can be identified with high accuracy using an HTS approach using the measurements of Ca²⁺ oscillations in hiPSC-derived neurons co-cultured with primary astrocytes in 2D.

Far from home: the role of glial mRNA localization in synaptic plasticity

Neurons and glia are highly polarized cells, whose distal cytoplasmic functional subdomains require specific proteins. Neurons have axonal and dendritic cytoplasmic extensions containing synapses whose plasticity is regulated efficiently by mRNA transport and localized translation. The principles behind these mechanisms are equally attractive for explaining rapid local regulation of distal glial cytoplasmic projections, independent of their cell nucleus. However, in contrast to neurons, mRNA localization has received little experimental attention in glia. Nevertheless, there are many functionally diverse glial subtypes containing extensive networks of long cytoplasmic projections with likely localized regulation that influence neurons and their synapses. Moreover, glia have many other neuron-like properties, including electrical activity, secretion of gliotransmitters and calcium signaling, influencing, for example, synaptic transmission, plasticity and axon pruning. Here, we review previous studies concerning glial transcripts with important roles in influencing synaptic plasticity, focusing on a few cases involving localized translation. We discuss a variety of important questions about mRNA transport and localized translation in glia that remain to be addressed, using cutting-edge tools already available for neurons.

Cypin binds to tubulin heterodimers and microtubule protofilaments and regulates microtubule spacing in developing hippocampal neurons

Cytosolic PSD-95 interactor (cypin) is a multifunctional, guanine deaminase that plays a major role in shaping the morphology of the dendritic arbor of hippocampal and cortical neurons. Cypin catalyzes the Zn2+-dependent deamination of guanine to xanthine, which is then metabolized to uric acid by xanthine oxidase. Cypin binds to tubulin heterodimers via its carboxyl terminal region (amino acids (aa) 350-454), which contains a collapsin response mediator protein (CRMP) homology domain (aa 350-403). Moreover, this region alone is not sufficient to facilitate microtubule polymerization; therefore, additional cypin regions must be involved in this process. Here, we asked whether cypin binds to fully formed microtubules and how overexpression of cypin regulates the microtubule cytoskeleton in dendrites of cultured hippocampal neurons. Protein-protein docking strategies confirm that the cypin homodimer binds to tubulin heterodimers via amino acids within aa 350-454. Biochemical pull-down data suggest that aa 1-220 are necessary for cypin binding to soluble tubulin heterodimers and to taxol-stabilized microtubules. Molecular docking of the cypin homodimer to soluble tubulin heterodimers reveals a consistently observed docking pose using aa 47-71, 113-118, 174-178, and 411-418, which is consistent with our biochemical data. Additionally, overexpression of cypin in hippocampal neurons results in decreased spacing between microtubules. Our results suggest that several protein domains facilitate cypin-mediated polymerization of tubulin heterodimers into microtubules, possibly through a mechanism whereby cypin dimers bind to multiple tubulin heterodimers.

Dysfunctional Glymphatic System with Disrupted Aquaporin 4 Expression Pattern on Astrocytes Causes Bacterial Product Accumulation in the CSF during Pneumococcal Meningitis

Pneumococcal meningitis, inflammation of the meninges due to an infection of the Central Nervous System caused by Streptococcus pneumoniae (the pneumococcus), is the most common form of community-acquired bacterial meningitis globally. Aquaporin 4 (AQP4) water channels on astrocytic end feet regulate the solute transport of the glymphatic system, facilitating the exchange of compounds between the brain parenchyma and the cerebrospinal fluid (CSF), which is important for the clearance of waste away from the brain. Wistar rats, subjected to either pneumococcal meningitis or artificial CSF (sham control), received Evans blue-albumin (EBA) intracisternally. Overall, the meningitis group presented a significant impairment of the glymphatic system by retaining the EBA in the CSF compartments compared to the uninfected sham group. Our results clearly showed that during pneumococcal meningitis, the glymphatic system does not function because of a detachment of the astrocytic end feet from the blood-brain barrier (BBB) vascular endothelium, which leads to misplacement of AQP4 with the consequent loss of the AQP4 water channel's functionality. IMPORTANCE The lack of solute drainage due to a dysfunctional glymphatic system leads to an increase of the neurotoxic bacterial material in the CSF compartments of the brain, ultimately leading to brain-wide neuroinflammation and neuronal damage with consequent impairment of neurological functions. The loss of function of the glymphatic system can therefore be a leading cause of the neurological sequelae developing post-bacterial meningitis.

α-Synuclein Impacts on Intrinsic Neuronal Network Activity Through Reduced Levels of Cyclic AMP and Diminished Numbers of Active Presynaptic Terminals

α-synuclein (α-Syn) is intimately linked to synucleinopathies like Parkinson’s disease and dementia with Lewy bodies. However, the pathophysiological mechanisms that are triggered by this protein are still largely enigmatic. α-Syn overabundance may cause neurodegeneration through protein accumulation and mitochondrial deterioration but may also result in pathomechanisms independent from neuronal cell death. One such proposed pathological mechanism is the influence of α-Syn on non-stimulated, intrinsic brain activity. This activity is responsible for more than 90% of the brain’s energyconsumption, and is thus thought to play an eminent role in basic brain functionality. Here we report that α-Syn substantially disrupts intrinsic neuronal network burst activity in a long-term neuronal cell culture model. Mechanistically, the impairment of network activity originates from reduced levels of cyclic AMP and cyclic AMP-mediated signaling as well as from diminished numbers of active presynaptic terminals. The profound reduction of network activity due to α-Syn was mediated only by intracellularly expressed α-Syn, but not by α-Syn that is naturally released by neurons. Conversely, extracellular pre-formed fibrils of α-Syn mimicked the effect of intracellular α-Syn, suggesting that they trigger an off-target mechanism that is not activated by naturally released α-Syn. A simulation-based model of the network activity in our cultures demonstrated that even subtle effect sizes in reducing outbound connectivity, i.e., loss of active synapses, can cause substantial global reductions in non-stimulated network activity. These results suggest that even low-level loss of synaptic output capabilities caused by α-Syn may result in significant functional impairments in terms of intrinsic neuronal network activity. Provided that our model holds true for the human brain, then α-Syn may cause significant functional lesions independent from neurodegeneration.

Vav3-Deficient Astrocytes Enhance the Dendritic Development of Hippocampal Neurons in an Indirect Co-culture System

Vav proteins belong to the class of guanine nucleotide exchange factors (GEFs) that catalyze the exchange of guanosine diphosphate (GDP) by guanosine triphosphate (GTP) on their target proteins. Here, especially the members of the small GTPase family, Ras homolog family member A (RhoA), Ras-related C3 botulinum toxin substrate 1 (Rac1) and cell division control protein 42 homolog (Cdc42) can be brought into an activated state by the catalytic activity of Vav-GEFs. In the central nervous system (CNS) of rodents Vav3 shows the strongest expression pattern in comparison to Vav2 and Vav1, which is restricted to the hematopoietic system. Several studies revealed an important role of Vav3 for the elongation and branching of neurites. However, little is known about the function of Vav3 for other cell types of the CNS, like astrocytes. Therefore, the following study analyzed the effects of a Vav3 knockout on several astrocytic parameters as well as the influence of Vav3-deficient astrocytes on the dendritic development of cultured neurons. For this purpose, an indirect co-culture system of native hippocampal neurons and Vav3-deficient cortical astrocytes was used. Interestingly, neurons cultured in an indirect contact with Vav3-deficient astrocytes showed a significant increase in the dendritic complexity and length after 12 and 17 days in vitro (DIV). Furthermore, Vav3-deficient astrocytes showed an enhanced regeneration in the scratch wound heal assay as well as an altered profile of released cytokines with a complete lack of CXCL11, reduced levels of IL-6 and an increased release of CCL5. Based on these observations, we suppose that Vav3 plays an important role for the development of dendrites by regulating the expression and the release of neurotrophic factors and cytokines in astrocytes.

Muscarinic Acetylcholine Receptor Localization on Distinct Excitatory and Inhibitory Neurons Within the ACC and LPFC of the Rhesus Monkey

Acetylcholine (ACh) can act on pre- and post-synaptic muscarinic receptors (mAChR) in the cortex to influence a myriad of cognitive processes. Two functionally-distinct regions of the prefrontal cortex-the lateral prefrontal cortex (LPFC) and the anterior cingulate cortex (ACC)-are differentially innervated by ascending cholinergic pathways yet, the nature and organization of prefrontal-cholinergic circuitry in primates are not well understood. Using multi-channel immunohistochemical labeling and high-resolution microscopy, we found regional and laminar differences in the subcellular localization and the densities of excitatory and inhibitory subpopulations expressing m1 and m2 muscarinic receptors, the two predominant cortical mAChR subtypes, in the supragranular layers of LPFC and ACC in rhesus monkeys (Macaca mulatta). The subset of m1+/m2+ expressing SMI-32+ pyramidal neurons labeled in layer 3 (L3) was denser in LPFC than in ACC, while m1+/m2+ SMI-32+ neurons co-expressing the calcium-binding protein, calbindin (CB) was greater in ACC. Further, we found between-area differences in laminar m1+ dendritic expression, and m2+ presynaptic localization on cortico-cortical (VGLUT1+) and sub-cortical inputs (VGLUT2+), suggesting differential cholinergic modulation of top-down vs. bottom-up inputs in the two areas. While almost all inhibitory interneurons-identified by their expression of parvalbumin (PV+), CB+, and calretinin (CR+)-expressed m1+, the localization of m2+ differed by subtype and area. The ACC exhibited a greater proportion of m2+ inhibitory neurons compared to the LPFC and had a greater density of presynaptic m2+ localized on inhibitory (VGAT+) inputs targeting proximal somatodendritic compartments and axon initial segments of L3 pyramidal neurons. These data suggest a greater capacity for m2+-mediated cholinergic suppression of inhibition in the ACC compared to the LPFC. The anatomical localization of muscarinic receptors on ACC and LPFC micro-circuits shown here contributes to our understanding of diverse cholinergic neuromodulation of functionally-distinct prefrontal areas involved in goal-directed behavior, and how these interactions maybe disrupted in neuropsychiatric and neurological conditions.

Neurotoxic Potential of Deoxynivalenol in Murine Brain Cell Lines and Primary Hippocampal Cultures

Chronic exposure to the mycotoxin deoxynivalenol (DON) from grain-based food and feed affects human and animal health. Known consequences include entereopathogenic and immunotoxic defects; however, the neurotoxic potential of DON has only come into focus more recently due to the observation of behavioural disorders in exposed farm animals. DON can cross the blood-brain barrier and interfere with the homeostasis/functioning of the nervous system, but the underlying mechanisms of action remain elusive. Here, we have investigated the impact of DON on mouse astrocyte and microglia cell lines, as well as on primary hippocampal cultures by analysing different toxicological endpoints. We found that DON has an impact on the viability of both glial cell types, as shown by a significant decrease of metabolic activity, and a notable cytotoxic effect, which was stronger in the microglia. In astrocytes, DON caused a G1 phase arrest in the cell cycle and a decrease of cyclic-adenosine monophosphate (cAMP) levels. The pro-inflammatory cytokine tumour necrosis factor (TNF)-α was secreted in the microglia in response to DON exposure. Furthermore, the intermediate filaments of the astrocytic cytoskeleton were disturbed in primary hippocampal cultures, and the dendrite lengths of neurons were shortened. The combined results indicated DON's considerable potential to interfere with the brain cell physiology, which helps explain the observed in vivo neurotoxicological effects.

NgCAM and VAMP2 reveal that direct delivery and dendritic degradation maintain axonal polarity

Neurons are polarized cells of extreme scale and compartmentalization. To fulfill their role in electrochemical signaling, axons must maintain a specific complement of membrane proteins. Despite being the subject of considerable attention, the trafficking pathway of axonal membrane proteins is not well understood. Two pathways, direct delivery and transcytosis, have been proposed. Previous studies reached contradictory conclusions about which of these mediates delivery of axonal membrane proteins to their destination, in part because they evaluated long-term distribution changes and not vesicle transport. We developed a novel strategy to selectively label vesicles in different trafficking pathways and determined the trafficking of two canonical axonal membrane proteins, neuron-glia cell adhesion molecule and vesicle-associated membrane protein-2. Results from detailed quantitative analyses of transporting vesicles differed substantially from previous studies and found that axonal membrane proteins overwhelmingly undergo direct delivery. Transcytosis plays only a minor role in axonal delivery of these proteins. In addition, we identified a novel pathway by which wayward axonal proteins that reach the dendritic plasma membrane are targeted to lysosomes. These results redefine how axonal proteins achieve their polarized distribution, a crucial requirement for elucidating the underlying molecular mechanisms.

SIRT5 Represses Neurotrophic Pathways and Aβ Production in Alzheimer's Disease by Targeting Autophagy

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in elderly individuals and characterized by impaired cognition and accumulation of β-amyloid (Aβ). Activating autophagy to clear Aβ is a plausible approach for AD treatment. The levels of Aβ and autophagy signaling factors in APP695/PS1-dE9 transgenic (APP/PS1) mice were detected by immuno histological analysis, real-time PCR, and the western blotting assay. The progression of AD was determined by Aβ levels, activated neurons (MAP2+), and microglia (Iba-1⁺). The learning ability was measured using a Morris water maze. Reactive oxygen species (ROS) production, malondialdehyde (MDA) levels, and mitochondrial superoxide dismutase (SOD) activity were checked to determine oxidative stress. AD mice exhibited impaired autophagy and a decreased level of SIRT5. SIRT5 overexpression promoted autophagy, manifested by elevated Becn1 and ratio of LC3b-II/I, as well as suppressed oxidative stress. The SIRT5-ameliorated neuron damage was correlated with suppressed activation of microglia and astrocytes. Elevated SIRT5 expression decreased the inflammation in AD brains and neurons. Inhibition of autophagy abolished the protective role of SIRT5 in neurons during AD. Our findings suggested that SIRT5 overexpression could ameliorate the progression of AD both in vitro and in vivo through activating autophagy. We presented ectopic expression of SIRT5 as a promising therapeutic approach for AD.

NeuriteNet: A convolutional neural network for assessing morphological parameters of neurite growth

BACKGROUND

During development or regeneration, neurons extend processes (i.e., neurites) via mechanisms that can be readily analyzed in culture. However, defining the impact of a drug or genetic manipulation on such mechanisms can be challenging due to the complex arborization and heterogeneous patterns of neurite growth in vitro. New Method: NeuriteNet is a Convolutional Neural Network (CNN) sorting model that uses a novel adaptation of the XRAI saliency map overlay, which is a region-based attribution method. NeuriteNet compares neuronal populations based on differences in neurite growth patterns, sorts them into respective groups, and overlays a saliency map indicating which areas differentiated the image for the sorting procedure.

RESULTS

In this study, we demonstrate that NeuriteNet effectively sorts images corresponding to dissociated neurons into control and treatment groups according to known morphological differences. Furthermore, the saliency map overlay highlights the distinguishing features of the neuron when sorting the images into treatment groups. NeuriteNet also identifies novel morphological differences in neurons cultured from control and genetically modified mouse strains. Comparison with Existing Methods: Unlike other neurite analysis platforms, NeuriteNet does not require manual manipulations, such as segmentation of neurites prior to analysis, and is more accurate than experienced researchers for categorizing neurons according to their pattern of neurite growth.

CONCLUSIONS

NeuriteNet can be used to effectively screen for morphological differences in a heterogeneous group of neurons and to provide feedback on the key features distinguishing those groups via the saliency map overlay.

Nrg1/ErbB2 regulates differentiation and apoptosis of neural stem cells in the cochlear nucleus through PI3K/Akt pathway

Sensorineural hearing loss (SNHL) is a common causes of disability. Neural stem cells (NSCs) from the cochlear nuclei have been considered to be a potential direction for the treatment of SNHL. Neuregulin 1 (NRG1)/ErbB2 signaling displays an essential role in nervous system development. In this study, we aimed to explore the roles of NRG1/ErbB2 in differentiation and apoptosis of cochlear nuclei NSCs. The data showed that the expression of NGR1 and ErbB2 in cochlear nuclei NSCs isolated from rats were increased with the age of rats. NRG1 treatment reduced the nestin-positive cells number, increased the MAP2-positive and GFAP-positive cells number, decreased the expression of cleaved-caspase-3, and increased the activation of PI3K/AKT. ErbB2 knockdown by lentiviral-mediated ErbB2 shRNA infection reversed the effect of NRG1 on cochlear nuclei NSCs. LY294002 administration further enhanced the effect of ErbB2 silencing on the expression of nestin, MAP2, GFAP and cleaved-caspase-3. Taken together, NRG1/ErbB2 regulates differentiation and apoptosis of cochlear nucleus NSCs through PI3K/Akt pathway.

Inhibition of miR-331-3p and miR-9-5p ameliorates Alzheimer's disease by enhancing autophagy

Alzheimer's disease (AD) is currently ranked as the third leading cause of death for eldly people, just behind heart disease and cancer. Autophagy is declined with aging. Our study determined the biphasic changes of miR-331-3p and miR-9-5p associated with AD progression in APPswe/PS1dE9 mouse model and demonstrated inhibiting miR-331-3p and miR-9-5p treatment prevented AD progression by promoting the autophagic clearance of amyloid beta (Aβ). Methods: The biphasic changes of microRNAs were obtained from RNA-seq data and verified by qRT-PCR in early-stage (6 months) and late-stage (12 months) APPswe/PS1dE9 mice (hereinafter referred to as AD mice). The AD progression was determined by analyzing Aβ levels, neuron numbers (MAP2⁺) and activated microglia (CD68⁺IBA1⁺) in brain tissues using immunohistological and immunofluorescent staining. MRNA and protein levels of autophagic-associated genes (Becn1, Sqstm1, LC3b) were tested to determine the autophagic activity. Morris water maze and object location test were employed to evaluate the memory and learning after antagomirs treatments in AD mice and the Aβ in the brain tissues were determined. Results: MiR-331-3p and miR-9-5p are down-regulated in early-stage of AD mice, whereas up-regulated in late-stage of AD mice. We demonstrated that miR-331-3p and miR-9-5p target autophagy receptors Sequestosome 1 (Sqstm1) and Optineurin (Optn), respectively. Overexpression of miR-331-3p and miR-9-5p in SH-SY5Y cell line impaired autophagic activity and promoted amyloid plaques formation. Moreover, AD mice had enhanced Aβ clearance, improved cognition and mobility when treated with miR-331-3p and miR-9-5p antagomirs at late-stage. Conclusion: Our study suggests that using miR-331-3p and miR-9-5p, along with autophagic activity and amyloid plaques may distinguish early versus late stage of AD for more accurate and timely diagnosis. Additionally, we further provide a possible new therapeutic strategy for AD patients by inhibiting miR-331-3p and miR-9-5p and enhancing autophagy.

Protocol for Evaluating Neuronal Polarity in Murine Models

The establishment of polarity is crucial for the physiology and wiring of neurons. Therefore, monitoring the axo-dendritic specification allows the mechanisms and signals associated with development, growth, and disease to be explored. Here, we describe major and minor steps to study polarity acquisition, using primary cultures of hippocampal neurons isolated from embryonic rat hippocampi, for in vitro monitoring. Furthermore, we use in utero electroporated, GFP-expressing embryonic mouse brains for visualizing cortical neuron migration and polarization in situ. Some underreported after-protocol steps are also included.

For complete details on the use and execution of this protocol, please refer to Wilson et al. (2020).

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Dissection, isolation, and digestion of embryonic (E18.5) rat hippocampi

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Culturing isolated hippocampal neurons and monitoring polarity acquisition in vitro

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In utero electroporation of embryonic (E15.5) mouse brains with GFP plasmids

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Visualization of migration and polarization of E17.5–E18.5 cortical neurons in situ

RNA-binding proteins balance brain function in health and disease

Posttranscriptional gene expression including splicing, RNA transport, translation, and RNA decay provides an important regulatory layer in many if not all molecular pathways. Research in the last decades has positioned RNA-binding proteins (RBPs) right in the center of posttranscriptional gene regulation. Here, we propose interdependent networks of RBPs to regulate complex pathways within the central nervous system (CNS). These are involved in multiple aspects of neuronal development and functioning, including higher cognition. Therefore, it is not sufficient to unravel the individual contribution of a single RBP and its consequences but rather to study and understand the tight interplay between different RBPs. In this review, we summarize recent findings in the field of RBP biology and discuss the complex interplay between different RBPs. Second, we emphasize the underlying dynamics within an RBP network and how this might regulate key processes such as neurogenesis, synaptic transmission, and synaptic plasticity. Importantly, we envision that dysfunction of specific RBPs could lead to perturbation within the RBP network. This would have direct and indirect (compensatory) effects in mRNA binding and translational control leading to global changes in cellular expression programs in general and in synaptic plasticity in particular. Therefore, we focus on RBP dysfunction and how this might cause neuropsychiatric and neurodegenerative disorders. Based on recent findings, we propose that alterations in the entire regulatory RBP network might account for phenotypic dysfunctions observed in complex diseases including neurodegeneration, epilepsy, and autism spectrum disorders.

Poly I:C-induced maternal immune challenge reduces perineuronal net area and raises spontaneous network activity of hippocampal neurons in vitro

Activation of the maternal immune system (MIA) during gestation is linked to neuropsychiatric diseases like schizophrenia. While many studies address behavioural aspects, less is known about underlying cellular mechanisms. In the following study, BALB/c mice received intraperitoneal injections of polyinosinic-polycytidylic acid (Poly I:C) (20 µg/ml) or saline (0.9%) at gestation day (GD) 9.5 before hippocampal neurons were isolated and cultured from embryonic mice for further analysis. Interestingly, strongest effects were observed when the perineuronal net (PNN) wearing subpopulation of neurons was analysed. Here, a significant reduction of aggrecan staining intensity, area and soma size could be detected. Alterations of PNNs are often linked to neuropsychiatric diseases, changes in synaptic plasticity and in electrophysiology. Utilizing multielectrode array analysis (MEA), we observed a remarkable increase of the spontaneous network activity in neuronal networks after 21 days in vitro (DIV) when mother mice suffered a prenatal immune challenge. As PNNs are associated with GABAergic interneurons, our data indicate that this neuronal subtype might be stronger affected by a prenatal MIA. Degradation or damage of this subtype might cause the hyperexcitability observed in the whole network. In addition, embryonic neurons of the Poly I:C condition developed significantly shorter axons after five days in culture, while dendritic parameters and apoptosis rate remained unchanged. Structural analysis of synapse numbers revealed an increase of postsynaptic density 95 (PSD-95) puncta after 14 DIV and an increase of presynaptic vesicular glutamate transporter (vGlut) puncta after 21 DIV, while inhibitory synaptic proteins were not altered.

The HERC1 ubiquitin ligase regulates presynaptic membrane dynamics of central synapses

HERC1 is a ubiquitin ligase protein, which, when mutated, induces several malformations and intellectual disability in humans. The animal model of HERC1 mutation is the mouse tambaleante characterized by: (1) overproduction of the protein; (2) cerebellar Purkinje cells death by autophagy; (3) dysregulation of autophagy in spinal cord motor neurons, and CA3 and neocortical pyramidal neurons; (4) impairment of associative learning, linked to altered spinogenesis and absence of LTP in the lateral amygdala; and, (5) motor impairment due to delayed action potential transmission, decrease synaptic transmission efficiency and altered myelination in the peripheral nervous system. To investigate the putative role of HERC1 in the presynaptic dynamics we have performed a series of experiments in cultured tambaleante hippocampal neurons by using transmission electron microscopy, FM1-43 destaining and immunocytochemistry. Our results show: (1) a decrease in the number of synaptic vesicles; (2) reduced active zones; (3) less clathrin immunoreactivity and less presynaptic endings over the hippocampal main dendritic trees; which contrast with (4) a greater number of endosomes and autophagosomes in the presynaptic endings of the tambaleante neurons relative to control ones. Altogether these results show an important role of HERC1 in the regulation of presynaptic membrane dynamics.

mTOR activation due to APPL1 deficiency exacerbates hyperalgesia via Rab5/Akt and AMPK signaling pathway in streptozocin-induced diabetic rats

Painful diabetic neuropathy is a common complication of diabetes mellitus with obscure underlying mechanisms. The adaptor protein APPL1 is critical in mediating the insulin sensitizing and insulin signaling. In neurons, APPL1 reportedly affects synaptic plasticity, while its role in the pathogenesis of painful diabetic neuropathy is masked. Our Western blotting revealed significantly decreased APPL1 expression in the dorsal horn in streptozocin-induced rats versus the control rats, coupled with concomitant mechanical and thermal hyperalgesia. Afterward, the determination of exact localization of APPL1 in spinal cord by immunofluorescent staining assay revealed highly expressed APPL1 in the lamina of spinal dorsal horn in control rats, with the overexpression in neurons, microglia, and underexpression in astrocytes. The APPL1 expression in laminae I and II was significantly downregulated in painful diabetic neuropathy rats. In addition, APPL1 deficiency or overexpression contributed to the increase or decrease of Map and Bassoon, respectively. The localization and immunoactivity of APPL1 and mammalian target of rapamycin (mTOR) were determined in spinal dorsal horn in painful diabetic neuropathy rats and control rats by immunohistochemistry, suggesting pronounced decrease in APPL1 expression in the superficial layer of the spinal cord in painful diabetic neuropathy rats, with p-mTOR expression markedly augmented. APPL1 knockdown by infection with lentiviral vector facilitated the activation of mTOR and abrogated mechanical withdrawal threshold values in painful diabetic neuropathy rats. Genetically overexpressed APPL1 significantly eliminated the activation of mTOR and resulted in the augmented mechanical withdrawal threshold values and thermal withdrawal latency values. Furthermore, the APPL1 levels affect phosphorylation of adenosine monophosphate-activated protein kinase (AMPK), and Akt, as well as the small GTPase, Rab5 expression in painful diabetic neuropathy rats. Our results uncovered a novel mechanism by which APPL1 deficiency facilitates the mTOR activation and thus exacerbates the hyperalgesia in streptozocin-induced diabetic rats, presumably via the regulation of Rab5/Akt and AMPK signaling pathway.

The Protective Effects of Up-Regulating Prostacyclin Biosynthesis on Neuron Survival in Hippocampus

Cellular arachidonic acid (AA), an unsaturated fatty acid found ubiquitously in plasma membranes, is metabolized to different prostanoids, such as prostacyclin (PGI2) and prostaglandin E2 (PGE2), by the three-step reactions coupling the upstream cyclooxygenase (COX) isoforms (COX-1 and COX-2) with the corresponding individual downstream synthases. While the vascular actions of these prostanoids are well-characterized, their specific roles in the hippocampus, a major brain area for memory, are poorly understood. The major obstacle for its understanding in the brain was to mimic the biosynthesis of each prostanoid. To solve the problem, we utilized Single-Chain Hybrid Enzyme Complexes (SCHECs), which could successfully control cellular AA metabolites to the desired PGI2 or PGE2. Our in vitro studies suggested that neurons with higher PGI2 content and lower PGE2 content exhibited survival protection and resistance to Amyloid-β-induced neurotoxicity. Further extending to an in vivo model, the hybrid of PGI2-producing transgenic mice and Alzheimer's disease (AD) mice showed restored long-term memory. These findings suggested that the vascular prostanoids, PGI2 and PGE2, exerted significant regulatory influences on neuronal protection (by PGI2), or damage (by PGE2) in the hippocampus, and raised a concern that the wide uses of aspirin in cardiovascular diseases may exert negative impacts on neurodegenerative protection. Graphic Abstract Our study intended to understand the crosstalk of prostanoids in the hippocampus, a major brain area impacted in AD, by using hybrid enzymes to redirect the synthesis of prostanoids to PGE2 and PGI2, respectively. Our data indicated that during inflammation, the vascular mediators, PGI2 and PGE2, exerted significant regulatory influences on neuronal protection (by PGI2), or damage (by PGE2) in the hippocampus. These findings also raised a concern that the widely uses of non-steroidal anti-inflammatory drugs in cardiovascular diseases may exert negative impacts on neurodegenerative protection.

Treatment with Mesenchymal-Derived Extracellular Vesicles Reduces Injury-Related Pathology in Pyramidal Neurons of Monkey Perilesional Ventral Premotor Cortex

Functional recovery after cortical injury, such as stroke, is associated with neural circuit reorganization, but the underlying mechanisms and efficacy of therapeutic interventions promoting neural plasticity in primates are not well understood. Bone marrow mesenchymal stem cell-derived extracellular vesicles (MSC-EVs), which mediate cell-to-cell inflammatory and trophic signaling, are thought be viable therapeutic targets. We recently showed, in aged female rhesus monkeys, that systemic administration of MSC-EVs enhances recovery of function after injury of the primary motor cortex, likely through enhancing plasticity in perilesional motor and premotor cortices. Here, using in vitro whole-cell patch-clamp recording and intracellular filling in acute slices of ventral premotor cortex (vPMC) from rhesus monkeys (Macaca mulatta) of either sex, we demonstrate that MSC-EVs reduce injury-related physiological and morphologic changes in perilesional layer 3 pyramidal neurons. At 14-16 weeks after injury, vPMC neurons from both vehicle- and EV-treated lesioned monkeys exhibited significant hyperexcitability and predominance of inhibitory synaptic currents, compared with neurons from nonlesioned control brains. However, compared with vehicle-treated monkeys, neurons from EV-treated monkeys showed lower firing rates, greater spike frequency adaptation, and excitatory:inhibitory ratio. Further, EV treatment was associated with greater apical dendritic branching complexity, spine density, and inhibition, indicative of enhanced dendritic plasticity and filtering of signals integrated at the soma. Importantly, the degree of EV-mediated reduction of injury-related pathology in vPMC was significantly correlated with measures of behavioral recovery. These data show that EV treatment dampens injury-related hyperexcitability and restores excitatory:inhibitory balance in vPMC, thereby normalizing activity within cortical networks for motor function.SIGNIFICANCE STATEMENT Neuronal plasticity can facilitate recovery of function after cortical injury, but the underlying mechanisms and efficacy of therapeutic interventions promoting this plasticity in primates are not well understood. Our recent work has shown that intravenous infusions of mesenchymal-derived extracellular vesicles (EVs) that are involved in cell-to-cell inflammatory and trophic signaling can enhance recovery of motor function after injury in monkey primary motor cortex. This study shows that this EV-mediated enhancement of recovery is associated with amelioration of injury-related hyperexcitability and restoration of excitatory-inhibitory balance in perilesional ventral premotor cortex. These findings demonstrate the efficacy of mesenchymal EVs as a therapeutic to reduce injury-related pathologic changes in the physiology and structure of premotor pyramidal neurons and support recovery of function.

Neuroprotective effect of Convolvulus pluricaulis Choisy in oxidative stress model of cerebral ischemia reperfusion injury and assessment of MAP2 in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Convolvulus pluricaulis Choisy commonly known as Shankhapushpi, is traditionally prescribed for nerve debility, loss of memory, epilepsy and as nervine tonic. Plant also proved to have diverse pharmacological activity but the neuroprotection in ischemic stroke were not found.

AIM OF THE STUDY

To investigate the effect of Convolvulus pluricaulis against bilateral common carotid artery (BCCA) occlusion induced cerebral ischemic reperfusion injury.

MATERIALS AND METHODS

The neuroprotective activity of Convolvulus pluricaulis against bilateral common carotid artery (BCCA) occlusion induced cerebral ischemic reperfusion (I/S) injury. Sprague-Dawley rats of either sex (200-250 g) were divided into nine groups of 8 rats each. Sham and control group, saline treated 10 ml/kg orally. Third group treated with Quercetin 25 mg/kg orally and fourth to ninth groups treated with chloroform and ethanol extract of Convolvulus pluricaulis 100, 200, and 400 mg/kg (p.o.) respectively. Control, Quercetin and extract treated groups underwent 30 min BCCA occlusion and 24 h reperfusion on 10th day but sham underwent same surgery without BCCA occlusion and 24 h reperfusion on 10th day. The antioxidant enzymatic and non-enzymatic levels were estimated by UV spectroscopic method and cerebral infarction area, Blood brain barrier disruption, microtubule-associated protein 2 immunohistochemical and histopathological studies were carried out.

RESULTS

The results of the study indicate that the chloroform and ethanol extract of Convolvulus pluricaulis showed neuroprotective activity by a significant decrease in lipid peroxidation (p < 0.001) and an increase in superoxide dismutase (p < 0.01, p < 0.001), catalase (p < 0.01, p < 0.001), glutathione (p < 0.001), and total thiol (p < 0.001) levels in extract-treated groups as compared to control group. Measurement of cerebral infarction area, blood brain barrier disruption, microtubule-associated protein 2 immunohistochemical and histopathological studies further supported the protective effect of the extract.

CONCLUSIONS

Present study revile that Convolvulus pluricaulis has potent neuroprotection against bilateral common carotid artery (BCCA) occlusion induced cerebral ischemic reperfusion injury.

Identification of Psychoplastogenic N,N-Dimethylaminoisotryptamine (isoDMT) Analogues through Structure-Activity Relationship Studies

Ketamine, N,N-dimethyltryptamine (DMT), and other psychoplastogens possess enormous potential as neurotherapeutics due to their ability to potently promote neuronal growth. Here, we report the first-ever structure-activity relationship study with the explicit goal of identifying novel psychoplastogens. We have discovered several key features of the psychoplastogenic pharmacophore and used this information to develop N,N-dimethylaminoisotryptamine (isoDMT) psychoplastogens that are easier to synthesize, have improved physicochemical properties, and possess reduced hallucinogenic potential as compared to their DMT counterparts.

Deletion of the Nucleotide Exchange Factor Vav3 Enhances Axonal Complexity and Synapse Formation but Tampers Activity of Hippocampal Neuronal Networks In Vitro

Vav proteins activate GTPases of the RhoA subfamily that regulate the cytoskeleton and are involved in adhesion, migration, differentiation, polarity and the cell cycle. While the importance of RhoA GTPases for neuronal morphology is undisputed, their regulation is less well understood. In this perspective, we studied the consequences of the deletion of Vav2, Vav3 and Vav2 and 3 (Vav2^-/-, Vav3^-/-, Vav2^-/-/3^-/-) for the development of embryonic hippocampal neurons in vitro. Using an indirect co-culture system of hippocampal neurons with primary wild-type (WT) cortical astrocytes, we analysed axonal and dendritic parameters, structural synapse numbers and the spontaneous network activity via immunocytochemistry and multielectrode array analysis (MEA). Here, we observed a higher process complexity in Vav3^-/-, but not in Vav2^-/- neurons after three and five days in vitro (DIV). Furthermore, an enhanced synapse formation was observed in Vav3^-/- after 14 days in culture. Remarkably, Vav2^-/-/3^-/- double knockout neurons did not display synergistic effects. Interestingly, these differences were transient and compensated after a cultivation period of 21 days. Network analysis revealed a diminished number of spontaneously occurring action potentials in Vav3^-/- neurons after 21 DIV. Based on these results, it appears that Vav3 participates in key events of neuronal differentiation.

Smart motors and cargo steering drive kinesin-mediated selective transport

Neurons are polarized cells, with dendrites and axons that require different complements of membrane proteins to fulfill their specialized functions. Membrane proteins are synthesized in the somatodendritic domain and delivered to their target membranes via long-range vesicle transport. Most anterograde vesicle transport is mediated by kinesin motors, but it is unclear how kinesins are targeted to axons or dendrites. Two main models have been proposed to explain kinesin selectivity. In the smart motor model, kinesin selectivity is conferred by a preference of the kinesin motor domain for specific subsets of microtubules. In the cargo steering model, kinesin selectivity is modulated by the vesicular cargo to which the motor is bound. We evaluate the evidence for both models and conclude that while the smart motor model may explain axonal selectivity, cargo steering is required for dendritic selectivity. Future work will determine the relative contributions of these models to polarized transport in living neurons.

MicroRNAs are Necessary for BMP-7-induced Dendritic Growth in Cultured Rat Sympathetic Neurons

Neuronal connectivity is dependent on size and shape of the dendritic arbor. However, mechanisms controlling dendritic arborization, especially in the peripheral nervous system, are not completely understood. Previous studies have shown that bone morphogenetic proteins (BMPs) are important initiators of dendritic growth in peripheral neurons. In this study, we examined the hypothesis that post-transcriptional regulation mediated by microRNAs (miRNAs) is necessary for BMP-7-induced dendritic growth in these neurons. To examine the role of miRNAs in BMP-7-induced dendritic growth, microarray analyses was used to profile miRNA expression in cultured sympathetic neurons from the superior cervical ganglia of embryonic day 21 rat pups at 6 and 24 h after treatment with BMP-7 (50 ng/mL). Our data showed that BMP-7 significantly regulated the expression of 43 of the 762 miRNAs. Of the 43 miRNAs, 22 showed robust gene expression; 14 were upregulated by BMP-7 and 8 were downregulated by BMP-7. The expression profile for miR-335, miR-664-1*, miR-21, and miR-23b was confirmed using qPCR analyses. Functional studies using morphometric analyses of dendritic growth in cultured sympathetic neurons transfected with miRNA mimics and inhibitors indicated that miR-664-1*, miR-23b, and miR-21 regulated early stages of BMP-7-induced dendritic growth. In summary, our data provide evidence for miRNA-mediated post-transcriptional regulation as important downstream component of BMP-7 signaling during early stages of dendritic growth in sympathetic neurons.

UBAP1 mutations cause juvenile-onset hereditary spastic paraplegias (SPG80) and impair UBAP1 targeting to endosomes

We aimed to find a new causative gene and elucidate the molecular mechanisms underlying a new type of hereditary spastic paraplegia (HSP). Patients with HSP were recruited from the Japan Spastic Paraplegia Research Consortium (JASPAC). Exome sequencing of genomic DNA from patients in four families was carried out, followed by Sanger sequencing of the UBAP1 gene. A mouse homolog of one UBAP1 frameshift mutation carried by one of the patients was created as a disease model. Functional properties of the UBAP1 wild type and UBAP1-mutant in mouse hippocampus neurons were examined. We identified three novel heterozygous loss of function mutations (c.425_426delAG, c.312delC, and c.535G>T) in the UBAP1 gene as the genetic cause of a new type of HSP (SPG80). All the patients presented identical clinical features of a pure type of juvenile-onset HSP. Functional studies on mouse hippocampal neurons revealed that the C-terminal deletion UBAP1-mutant of our disease model had lost its ability to bind ubiquitin in vitro. Overexpression of the UBAP1 wild type interacts directly with ubiquitin on enlarged endosomes, while the UBAP1-mutant cannot be recruited to endosome membranes. Our study demonstrated that mutations in the UBAP1 gene cause a new type of HSP and elucidated its pathogenesis. The full-length UBAP1 protein is involved in endosomal dynamics in neurons, while loss of UBAP1 function may perturb endosomal fusion and sorting of ubiquitinated cargos. These effects could be more prominent in neurons, thereby giving rise to the phenotype of a neurodegenerative disease such as HSP.

Overexpression of COX6B1 protects against I/R‑induced neuronal injury in rat hippocampal neurons

Cerebrovascular disease (CVD) is one of the leading causes of mortality worldwide. The role of cytochrome c oxidase subunit 6B1 (COX6B1) in the central nervous system remains unclear. The present study aimed to analyze the role of COX6B1 in rat hippocampal neurons extracted from fetal rats. The subcellular localization of the neuron‑specific marker microtubule‑associated protein 2 was detected by immunofluorescence assay. Cell viability was assessed using a cell counting kit, and the levels of apoptosis and cytosolic Ca2+ were analyzed by flow cytometry. The expression levels of the molecular factors downstream to COX6B1 were determined using reverse transcription‑quantitative polymerase chain reaction and western blotting. Reoxygenation following oxygen‑glucose deprivation (OGD) decreased cell viability and the expression levels of COX6B1 in a time‑dependent manner, and 60 min of reoxygenation was identified as the optimal time period for establishing an ischemia/reperfusion (I/R) model. Overexpression of COX6B1 was demonstrated to reverse the viability of hippocampal neurons following I/R treatment. Specifically, COX6B1 overexpression decreased the cytosolic concentration of Ca2+ and suppressed neuronal apoptosis, which were increased following I/R treatment. Furthermore, overexpression of COX6B1 increased the protein expression levels of apoptosis regulator BCL‑2 and mitochondrial cytochrome c (cyt c), and decreased the protein expression levels of apoptosis regulator BCL2‑associated X and cytosolic cyt c in I/R model cells. Collectively, the present study results suggested that COX6B1 overexpression may reverse I/R‑induced neuronal damage by increasing the viability of neurons, by decreasing the cytosolic levels of Ca2+ and by suppressing apoptosis. These results may facilitate the development of novel strategies for the prevention and treatment of CVD.

Reversible association with motor proteins (RAMP): A streptavidin-based method to manipulate organelle positioning

We report the development and characterization of a method, named reversible association with motor proteins (RAMP), for manipulation of organelle positioning within the cytoplasm. RAMP consists of coexpressing in cultured cells (i) an organellar protein fused to the streptavidin-binding peptide (SBP) and (ii) motor, neck, and coiled-coil domains from a plus-end-directed or minus-end-directed kinesin fused to streptavidin. The SBP-streptavidin interaction drives accumulation of organelles at the plus or minus end of microtubules, respectively. Importantly, competition of the streptavidin-SBP interaction by the addition of biotin to the culture medium rapidly dissociates the motor construct from the organelle, allowing restoration of normal patterns of organelle transport and distribution. A distinctive feature of this method is that organelles initially accumulate at either end of the microtubule network in the initial state and are subsequently released from this accumulation, allowing analyses of the movement of a synchronized population of organelles by endogenous motors.

Ketamine destabilizes growth of dendritic spines in developing hippocampal neurons in vitro via a Rho‑dependent mechanism

The safety of anesthetics on the developing brain has caused concern. Ketamine, an N-methyl-D-aspartate receptor antagonist, is widely used as a general pediatric anesthetic. Recent studies suggested that ketamine alters the plasticity of dendritic spines in the developing brain and may be an important contributing factor to learning and cognitive impairment. However, the underlying molecular mechanism remains poorly understood. Therefore, the aim of the present study was to investigate the effect of ketamine on the plasticity of dendritic spines in cultured hippocampal neurons and the potential underlying mechanisms. After 5 days in vitro, rat hippocampal neurons were exposed to different concentrations (100, 300 and 500 µM) of ketamine for 6 h. Ketamine decreased the number and length of dendritic spines in a dose-dependent manner. Ketamine at a concentration of 300 µM caused an upregulation of transforming protein RhoA (RhoA) and Rho-associated kinase (ROCK) protein. These effects were inhibited by the ROCK inhibitor Y27632. These results suggested that ketamine induces loss and shortening of dendritic spines in hippocampal neurons via activation of the RhoA/ROCK signaling pathway.

Effect of sevoflurane on the ATPase activity of hippocampal neurons in a rat model of cerebral ischemia-reperfusion injury via the cAMP-PKA signaling pathway

We aim to investigate the effects of sevoflurane on the ATPase activity of the hippocampal neurons in rats with cerebral ischemia-reperfusion injury (IRI) via the cyclic adenosine monophosphate (cAMP) and protein kinase A (PKA) signaling pathway. Sixty rats were assigned into the normal, model and sevoflurane groups (n = 20, the latter two groups were established as focal cerebral IRI models). The ATPase activity was detected using an ultramicro Na (+)-K (+)-ATP enzyme kit. Immunohistochemical staining was used to detect the positive protein expression of cAMP and PKA. The hippocampal neurons were assigned to the normal, IRI, IRI + sevoflurane, IRI + forskolin, IRI + H89 and IRI + sevoflurane + H89 groups. qRT-PCR and Western blotting were performed for the expressions of cAMP, PKA, cAMP-responsive element-binding protein (CREB) and brain derived neurotrophic factor (BDNF). The normal and sevoflurane groups exhibited a greater positive protein expression of cAMP and PKA than the model group. Compared with the normal group, the expressions of cAMP, PKA, CREB and BDNF all reduced in the IRI, model and IRI + H89 groups. The sevoflurane group showed higher cAMP, PKA, CREB and BDNF expressions than the model group. Compared with the IRI group, ATPase activity and expressions of cAMP, PKA, CREB and BDNF all increased in the normal, IRI + sevoflurane and IRI + forskolin groups but decreased in the IRI + H89 group. It suggests that sevoflurane could enhance ATPase activity in hippocampal neurons of cerebral IRI rats through activating cAMP-PKA signaling pathway.

Neuronal LRP4 regulates synapse formation in the developing CNS

The low-density lipoprotein receptor-related protein 4 (LRP4) is essential in muscle fibers for the establishment of the neuromuscular junction. Here, we show that LRP4 is also expressed by embryonic cortical and hippocampal neurons, and that downregulation of LRP4 in these neurons causes a reduction in density of synapses and number of primary dendrites. Accordingly, overexpression of LRP4 in cultured neurons had the opposite effect inducing more but shorter primary dendrites with an increased number of spines. Transsynaptic tracing mediated by rabies virus revealed a reduced number of neurons presynaptic to the cortical neurons in which LRP4 was knocked down. Moreover, neuron-specific knockdown of LRP4 by in utero electroporation of LRP4 miRNA in vivo also resulted in neurons with fewer primary dendrites and a lower density of spines in the developing cortex and hippocampus. Collectively, our results demonstrate an essential and novel role of neuronal LRP4 in dendritic development and synaptogenesis in the CNS.

Map2 Expression in the Developing Human Fetal Spinal Cord and following Xenotransplantation

Human fetal spinal cord (FSC) tissue was obtained from elective abortions at 6-14 wk gestational age (GA). The specimens were then either immediately processed for immunohistochemical analysis or xenotransplantation. In the latter case, donor tissue was prepared as a dissociated cell suspension and then introduced either sub-pially or intraspinally into contusion lesions of the adult rat midthoracic spinal cord. The xenografts were subsequently examined by conventional histological and immunohistochemical methods at 2-3 mo postgrafting. Immunostaining showed that MAP2 was expressed heavily in cells residing in the mantle layer of the human fetal spinal cord in situ as early as 6 wk GA. Subpial and intraparenchymal xenografts also were intensely immunoreactive for MAP2, but no staining of surrounding host neural tissue was detected. We conclude that the differential expression of MAP2 can be used to distinguish human graft tissue from the surrounding rat spinal cord in this xenograft paradigm. Under appropriate staining conditions, MAP2 can thus serve to facilitate analyses of host-graft integration, donor cell migration, and neuritic outgrowth.

High frequency stimulation induces sonic hedgehog release from hippocampal neurons

Sonic hedgehog (SHH) as a secreted protein is important for neuronal development in the central nervous system (CNS). However, the mechanism about SHH release remains largely unknown. Here, we showed that SHH was expressed mainly in the synaptic vesicles of hippocampus in both young postnatal and adult rats. High, but not low, frequency stimulation, induces SHH release from the neurons. Moreover, removal of extracellular Ca²⁺, application of tetrodotoxin (TTX), an inhibitor of voltage-dependent sodium channels, or downregulation of soluble n-ethylmaleimide-sensitive fusion protein attachment protein receptors (SNAREs) proteins, all blocked SHH release from the neurons in response to HFS. Our findings suggest a novel mechanism to control SHH release from the hippocampal neurons.

Endoplasmic reticulum-mediated signalling in cellular microdomains

The endoplasmic reticulum (ER) is a prime mediator of cellular signalling due to its functions as an internal cellular store for calcium, as well as a site for synthesis of proteins and lipids. Its peripheral network of sheets and tubules facilitates calcium and lipid signalling, especially in areas of the cell that are more distant to the main cytoplasmic network. Specific membrane proteins shape the peripheral ER architecture and influence the network stability to project into restricted spaces. The signalling microdomains are anatomically separate from the cytoplasm as a whole and exhibit localized protein, ion channel and cytoskeletal element expression. Signalling can also occur between the ER and other organelles, such as the Golgi or mitochondria. Lipids made in the ER membrane can be sent to the Golgi via specialized transfer proteins and specific phospholipid synthases are enriched at ER-mitochondria junctions to more efficiently expedite phospholipid transfer. As a hub for protein and lipid synthesis, a store for intracellular calcium [Ca²⁺ ]_i and a mediator of cellular stress, the ER is an important cellular organelle. Its ability to organize into tubules and project into restricted spaces allows for discrete and temporal signalling, which is important for cellular physiology and organism homoeostasis.

Rab5 and its effector FHF contribute to neuronal polarity through dynein-dependent retrieval of somatodendritic proteins from the axon

An open question in cell biology is how the general intracellular transport machinery is adapted to perform specialized functions in polarized cells such as neurons. Here we illustrate this adaptation by elucidating a role for the ubiquitous small GTPase Ras-related protein in brain 5 (Rab5) in neuronal polarity. We show that inactivation or depletion of Rab5 in rat hippocampal neurons abrogates the somatodendritic polarity of the transferrin receptor and several glutamate receptor types, resulting in their appearance in the axon. This loss of polarity is not caused primarily by increased transport from the soma to the axon but rather by decreased retrieval from the axon to the soma. Retrieval is also dependent on the Rab5 effector Fused Toes (FTS)-Hook-FTS and Hook-interacting protein (FHIP) (FHF) complex, which interacts with the minus-end-directed microtubule motor dynein and its activator dynactin to drive a population of axonal retrograde carriers containing somatodendritic proteins toward the soma. These findings emphasize the importance of both biosynthetic sorting and axonal retrieval for the polarized distribution of somatodendritic receptors at steady state.

Immunohistochemical and Ultrastructural Studies of Oligodendrogliomas Revealed Features of Neuronal Differentiation

In an attempt to characterize differentiation in oligodendrogliomas, 39 cases were examined immunohistochemically with 5 neuronal markers, synaptophysin, neuron- specific enolase, neurofilament proteins, protein gene product (PGP) 9.5, and micro tubule-associated protein 2 (MAP2), in addition to glial fibrillary acidic protein (GFAP). Positive immunolabeling was obtained for neuron-specific enolose in 29 cases (74%), synaptophysin in 21 cases (54%), PGP 9.5 in 33 cases (85%), and MAP2 in 23 cases (59%). All cases were negative for neurofilament, and 90% stained for GFAP. Eight cases were further studied ultrastructurally, and in five cases features of neuronal differentiation were identified in some of the typical neoplastic oligodendro cytes—small neuritic cellular processes with microtubules and focal synapse-like junc tions, as well as sparse neurosecretory granules. It was concluded that, both immuno histochemically and ultrastructurally, oligodendrogliomas may exhibit features of neuronal differentiation. These previously unreported features of oligodendrogliomas call into question conventional immunohistochemical and electron microscopic crite ria used in distinguishing oligodendrogliomas from tumors showing similar histologic appearance, especially central neurocytomas and dysembryoplastic neuroepithelial tu mors. Int J Surg Pathol 2(1):47-56 1994

Axon Initial Segment Cytoskeleton: Architecture, Development, and Role in Neuron Polarity

The axon initial segment (AIS) is a specialized structure in neurons that resides in between axonal and somatodendritic domains. The localization of the AIS in neurons is ideal for its two major functions: it serves as the site of action potential firing and helps to maintain neuron polarity. It has become increasingly clear that the AIS cytoskeleton is fundamental to AIS functions. In this review, we discuss current understanding of the AIS cytoskeleton with particular interest in its unique architecture and role in maintenance of neuron polarity. The AIS cytoskeleton is divided into two parts, submembrane and cytoplasmic, based on localization, function, and molecular composition. Recent studies using electron and subdiffraction fluorescence microscopy indicate that submembrane cytoskeletal components (ankyrin G, βIV-spectrin, and actin filaments) form a sophisticated network in the AIS that is conceptually similar to the polygonal/triangular network of erythrocytes, with some important differences. Components of the AIS cytoplasmic cytoskeleton (microtubules, actin filaments, and neurofilaments) reside deeper within the AIS shaft and display structural features distinct from other neuronal domains. We discuss how the AIS submembrane and cytoplasmic cytoskeletons contribute to different aspects of AIS polarity function and highlight recent advances in understanding their AIS cytoskeletal assembly and stability.

Building Blocks of Functioning Brain: Cytoskeletal Dynamics in Neuronal Development

Neural connectivity requires proper polarization of neurons, guidance to appropriate target locations, and establishment of synaptic connections. From when neurons are born to when they finally reach their synaptic partners, neurons undergo constant rearrangment of the cytoskeleton to achieve appropriate shape and polarity. Of particular importance to neuronal guidance to target locations is the growth cone at the tip of the axon. Growth-cone steering is also dictated by the underlying cytoskeleton. All these changes require spatiotemporal control of the cytoskeletal machinery. This review summarizes the proteins that are involved in modulating the actin and microtubule cytoskeleton during the various stages of neuronal development.

Hippocampal Synaptic Expansion Induced by Spatial Experience in Rats Correlates with Improved Information Processing in the Hippocampus

Spatial water maze (WM) overtraining induces hippocampal mossy fiber (MF) expansion, and it has been suggested that spatial pattern separation depends on the MF pathway. We hypothesized that WM experience inducing MF expansion in rats would improve spatial pattern separation in the hippocampal network. We first tested this by using the the delayed non-matching to place task (DNMP), in animals that had been previously trained on the water maze (WM) and found that these animals, as well as animals treated as swim controls (SC), performed better than home cage control animals the DNMP task. The "catFISH" imaging method provided neurophysiological evidence that hippocampal pattern separation improved in animals treated as SC, and this improvement was even clearer in animals that experienced the WM training. Moreover, these behavioral treatments also enhance network reliability and improve partial pattern separation in CA1 and pattern completion in CA3. By measuring the area occupied by synaptophysin staining in both the stratum oriens and the stratun lucidum of the distal CA3, we found evidence of structural synaptic plasticity that likely includes MF expansion. Finally, the measures of hippocampal network coding obtained with catFISH correlate significantly with the increased density of synaptophysin staining, strongly suggesting that structural synaptic plasticity in the hippocampus induced by the WM and SC experience is related to the improvement of spatial information processing in the hippocampus.