Axonally synthesized β-actin and GAP-43 proteins support distinct modes of axonal growth

Unraveling Axonal Transcriptional Landscapes: Insights from iPSC-Derived Cortical Neurons and Implications for Motor Neuron Degeneration

Neuronal function and pathology are deeply influenced by the distinct molecular profiles of the axon and soma. Traditional studies have often overlooked these differences due to the technical challenges of compartment specific analysis. In this study, we employ a robust RNA-sequencing (RNA-seq) approach, using microfluidic devices, to generate high-quality axonal transcriptomes from iPSC-derived cortical neurons (CNs). We achieve high specificity of axonal fractions, ensuring sample purity without contamination. Comparative analysis revealed a unique and specific transcriptional landscape in axonal compartments, characterized by diverse transcript types, including protein-coding mRNAs, RNAs encoding ribosomal proteins (RPs), mitochondrial-encoded RNAs, and long non-coding RNAs (lncRNAs). Previous works have reported the existence of transcription factors (TFs) in the axon. Here, we detect a set of TFs specific to the axon and indicative of their active participation in transcriptional regulation. To investigate transcripts and pathways essential for central motor neuron (MN) degeneration and maintenance we analyzed KIF1C-knockout (KO) CNs, modeling hereditary spastic paraplegia (HSP), a disorder associated with prominent length-dependent degeneration of central MN axons. We found that several key factors crucial for survival and health were absent in KIF1C-KO axons, highlighting a possible role of these also in other neurodegenerative diseases. Taken together, this study underscores the utility of microfluidic devices in studying compartment-specific transcriptomics in human neuronal models and reveals complex molecular dynamics of axonal biology. The impact of KIF1C on the axonal transcriptome not only deepens our understanding of MN diseases but also presents a promising avenue for exploration of compartment specific disease mechanisms.

The Axonal Actin Filament Cytoskeleton: Structure, Function, and Relevance to Injury and Degeneration

Early investigations of the neuronal actin filament cytoskeleton gave rise to the notion that, although growth cones exhibit high levels of actin filaments, the axon shaft exhibits low levels of actin filaments. With the development of new tools and imaging techniques, the axonal actin filament cytoskeleton has undergone a renaissance and is now an active field of research. This article reviews the current state of knowledge about the actin cytoskeleton of the axon shaft. The best understood forms of actin filament organization along axons are axonal actin patches and a submembranous system of rings that endow the axon with protrusive competency and structural integrity, respectively. Additional forms of actin filament organization along the axon have also been described and their roles are being elucidated. Extracellular signals regulate the axonal actin filament cytoskeleton and our understanding of the signaling mechanisms involved is being elaborated. Finally, recent years have seen advances in our perspective on how the axonal actin cytoskeleton is impacted by, and contributes to, axon injury and degeneration. The work to date has opened new venues and future research will undoubtedly continue to provide a richer understanding of the axonal actin filament cytoskeleton.

RNA-binding proteins in pain

RNAs are meticulously controlled by proteins. Through direct and indirect associations, every facet in the brief life of an mRNA is subject to regulation. RNA-binding proteins (RBPs) permeate biology. Here, we focus on their roles in pain. Chronic pain is among the largest challenges facing medicine and requires new strategies. Mounting pharmacologic and genetic evidence obtained in pre-clinical models suggests fundamental roles for a broad array of RBPs. We describe their diverse roles that span RNA modification, splicing, stability, translation, and decay. Finally, we highlight opportunities to expand our understanding of regulatory interactions that contribute to pain signaling. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications Translation > Regulation RNA in Disease and Development > RNA in Disease.

P53-induced GAP-43 Upregulation in Primary Cortical Neurons of Rats

OBJECTIVES

In this study, we employed an in vitro culturing technique to investigate the impact of p53 on the modulation of growth-associated protein-43 (GAP-43) within the primary cortical neurons of rat specimens.

METHODS

(1) Within the first 24 hours after birth, the bilateral cortex was extracted from newborn Wistar rats and primary cortical neurons were cultured and identified. (2) The changes in the mRNA and protein expressions of GAP-43 induced by p53 in rat primary cortical neurons cultured in vitro were identified utilizing real-time polymerase chain reaction and western blot techniques.

RESULTS

(1) Lentiviral transfection of p53 within primary cortical neurons of rats elicited elevated levels of both mRNA and protein expressions of GAP-43, consequently culminating in a noteworthy augmentation of p53 expression. (2) The introduction of a p53 inhibitor in rat primary cortical neurons resulted in a reduction in both mRNA and protein expressions of GAP-43.

CONCLUSION

Within primary rat cortical neurons, p53 has the potential to prompt an augmentation in both the transcriptional and protein expression levels of the GAP-43 protein.

Hallmarks of peripheral nerve injury and regeneration

Peripheral nerves are functional networks in the body. Disruption of these networks induces varied functional consequences depending on the types of nerves and organs affected. Despite the advances in microsurgical repair and understanding of nerve regeneration biology, restoring full functions after severe traumatic nerve injuries is still far from achieved. While a blunted growth response from axons and errors in axon guidance due to physical barriers may surface as the major hurdles in repairing nerves, critical additional cellular and molecular aspects challenge the orderly healing of injured nerves. Understanding the systematic reprogramming of injured nerves at the cellular and molecular levels, referred to here as "hallmarks of nerve injury regeneration," will offer better ideas. This chapter discusses the hallmarks of nerve injury and regeneration and critical points of failures in the natural healing process. Potential pharmacological and nonpharmacological intervention points for repairing nerves are also discussed.

Control of Selective mRNA Translation in Neuronal Subcellular Compartments in Health and Disease

In multiple cell types, mRNAs are transported to subcellular compartments, where local translation enables rapid, spatially localized, and specific responses to external stimuli. Mounting evidence has uncovered important roles played by local translation in vivo in axon survival, axon regeneration, and neural wiring, as well as strong links between dysregulation of local translation and neurologic disorders. Omic studies have revealed that >1000 mRNAs are present and can be selectively locally translated in the presynaptic and postsynaptic compartments from development to adulthood in vivo A large proportion of the locally translated mRNAs is specifically upregulated or downregulated in response to distinct extracellular signals. Given that the local translatome is large, selectively translated, and cue-specifically remodeled, a fundamental question concerns how selective translation is achieved locally. Here, we review the emerging regulatory mechanisms of local selective translation in neuronal subcellular compartments, their mRNA targets, and their orchestration. We discuss mechanisms of local selective translation that remain unexplored. Finally, we describe clinical implications and potential therapeutic strategies in light of the latest advances in gene therapy.

Spinal cord injury regulates circular RNA expression in axons

Introduction

Neurons transport mRNA and translational machinery to axons for local translation. After spinal cord injury (SCI), de novo translation is assumed to enable neurorepair. Knowledge of the identity of axonal mRNAs that participate in neurorepair after SCI is limited. We sought to identify and understand how axonal RNAs play a role in axonal regeneration.

Methods

We obtained preparations enriched in axonal mRNAs from control and SCI rats by digesting spinal cord tissue with cold-active protease (CAP). The digested samples were then centrifuged to obtain a supernatant that was used to identify mRNA expression. We identified differentially expressed genes (DEGS) after SCI and mapped them to various biological processes. We validated the DEGs by RT-qPCR and RNA-scope.

Results

The supernatant fraction was highly enriched for mRNA from axons. Using Gene Ontology, the second most significant pathway for all DEGs was axonogenesis. Among the DEGs was Rims2, which is predominately a circular RNA (circRNA) in the CNS. We show that Rims2 RNA within spinal cord axons is circular. We found an additional 200 putative circRNAs in the axonal-enriched fraction. Knockdown in primary rat cortical neurons of the RNA editing enzyme ADAR1, which inhibits formation of circRNAs, significantly increased axonal outgrowth and increased the expression of circRims2. Using Rims2 as a prototype we used Circular RNA Interactome to predict miRNAs that bind to circRims2 also bind to the 3'UTR of GAP-43, PTEN or CREB1, all known regulators of axonal outgrowth. Axonally-translated GAP-43 supports axonal elongation and we detect GAP-43 mRNA in the rat axons by RNAscope.

Discussion

By enriching for axonal RNA, we detect SCI induced DEGs, including circRNA such as Rims2. Ablation of ADAR1, the enzyme that regulates circRNA formation, promotes axonal outgrowth of cortical neurons. We developed a pathway model using Circular RNA Interactome that indicates that Rims2 through miRNAs can regulate the axonal translation GAP-43 to regulate axonal regeneration. We conclude that axonal regulatory pathways will play a role in neurorepair.

Advances in Understanding the Molecular Mechanisms of Neuronal Polarity

The establishment and maintenance of neuronal polarity are important for neural development and function. Abnormal neuronal polarity establishment commonly leads to a variety of neurodevelopmental disorders. Over the past three decades, with the continuous development and improvement of biological research methods and techniques, we have made tremendous progress in the understanding of the molecular mechanisms of neuronal polarity establishment. The activity of positive and negative feedback signals and actin waves are both essential in this process. They drive the directional transport and aggregation of key molecules of neuronal polarity, promote the spatiotemporal regulation of ordered and coordinated interactions of actin filaments and microtubules, stimulate the specialization and growth of axons, and inhibit the formation of multiple axons. In this review, we focus on recent advances in these areas, in particular the important findings about neuronal polarity in two classical models, in vitro primary hippocampal/cortical neurons and in vivo cortical pyramidal neurons, and discuss our current understanding of neuronal polarity.​.

Axonal mRNA binding of hnRNP A/B is crucial for axon targeting and maturation of olfactory sensory neurons

Spatiotemporal control of gene expression is important for neural development and function. Here, we show that heterogeneous nuclear ribonucleoprotein (hnRNP) A/B is highly expressed in developing olfactory sensory neurons (OSNs), and its knockout results in reduction in mature OSNs and aberrant targeting of OSN axons to the olfactory bulb. RNA immunoprecipitation analysis reveals that hnRNP A/B binds to a group of mRNAs that are highly related to axon projections and synapse assembly. Approximately 11% of the identified hnRNP A/B targets, including Pcdha and Ncam2, encode cell adhesion molecules. In Hnrnpab knockout mice, PCDHA and NCAM2 levels are significantly reduced at the axon terminals of OSNs. Furthermore, deletion of the hnRNP A/B-recognition motif in the 3' UTR of Pcdha leads to impaired PCDHA expression at the OSN axon terminals. Therefore, we propose that hnRNP A/B facilitates OSN maturation and axon projection by regulating the local expression of its target genes at axon terminals.

MiR-29c Inhibits TNF-α-Induced ROS Production and Apoptosis in Mouse Hippocampal HT22 Cell Line

Recent reports have suggested that abnormal miR-29c expression in hippocampus have been implicated in the pathophysiology of some neurodegenerative and neuropsychiatric diseases. However, the underlying effect of miR-29c in regulating hippocampal neuronal function is not clear. In this study, HT22 cells were infected with lentivirus containing miR-29c or miR-29c sponge. Cell counting kit-8 (CCK8) and lactate dehydrogenase (LDH) assay kit were applied to evaluate cell viability and toxicity before and after TNF-α administration. Reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Hoechst 33258 staining and TUNEL assay were used to evaluate cell apoptosis. The expression of key mRNA/proteins (TNFR1, Bcl-2, Bax, TRADD, FADD, caspase-3, -8 and -9) in the apoptosis pathway was detected by PCR or WB. In addition, the protein expression of microtubule-associated protein-2 (MAP-2), nerve growth-associated protein 43 (GAP-43) and synapsin-1 (SYN-1) was detected by WB. As a result, we found that miR-29c overexpression could improve cell viability, attenuate LDH release, reduce ROS production and inhibit MMP depolarization in TNF-α-treated HT22 cells. Furthermore, miR-29c overexpression was found to decrease apoptotic rate, along with decreased expression of Bax, cleaved caspase-3, cleaved caspase-9, and increased expression of Bcl-2 in TNF-α-treated HT22 cells. However, miR-29c sponge exhibited an opposite effects. In addition, in TNF-α-treated HT22 cells, miR-29c overexpression could decrease the expressions of TNFR1, TRADD, FADD and cleaved caspase-8. However, in HT22 cells transfected with miR-29c sponge, TNF-α-induced the expressions of TNFR1, TRADD, FADD and cleaved caspase-8 was significantly exacerbated. At last, TNF-α-induced the decreased expression of MAP-2, GAP-43 and SYN-1 was reversed by miR-29c but exacerbated by miR-29c sponge. Overall, our study demonstrated that miR-29c protects against TNF-α-induced HT22 cells injury through alleviating ROS production and reduce neuronal apoptosis. Therefore, miR-29c might be a potential therapeutic agent for TNF-α accumulation and toxicity-related brain diseases.

Microfluidic Manipulation for Biomedical Applications in the Central and Peripheral Nervous Systems

Physical injuries and neurodegenerative diseases often lead to irreversible damage to the organizational structure of the central nervous system (CNS) and peripheral nervous system (PNS), culminating in physiological malfunctions. Investigating these complex and diverse biological processes at the macro and micro levels will help to identify the cellular and molecular mechanisms associated with nerve degeneration and regeneration, thereby providing new options for the development of new therapeutic strategies for the functional recovery of the nervous system. Due to their distinct advantages, modern microfluidic platforms have significant potential for high-throughput cell and organoid cultures in vitro, the synthesis of a variety of tissue engineering scaffolds and drug carriers, and observing the delivery of drugs at the desired speed to the desired location in real time. In this review, we first introduce the types of nerve damage and the repair mechanisms of the CNS and PNS; then, we summarize the development of microfluidic platforms and their application in drug carriers. We also describe a variety of damage models, tissue engineering scaffolds, and drug carriers for nerve injury repair based on the application of microfluidic platforms. Finally, we discuss remaining challenges and future perspectives with regard to the promotion of nerve injury repair based on engineered microfluidic platform technology.

Local translation in primary afferents and its contribution to pain

ABSTRACT

Chronic pain remains a significant problem due to its prevalence, impact, and limited therapeutic options. Progress in addressing chronic pain is dependent on a better understanding of underlying mechanisms. Although the available evidence suggests that changes within the central nervous system contribute to the initiation and maintenance of chronic pain, it also suggests that the primary afferent plays a critical role in all phases of the manifestation of chronic pain in most of those who suffer. Most notable among the changes in primary afferents is an increase in excitability or sensitization. A number of mechanisms have been identified that contribute to primary afferent sensitization with evidence for both increases in pronociceptive signaling molecules, such as voltage-gated sodium channels, and decreases in antinociceptive signaling molecules, such as voltage-dependent or calcium-dependent potassium channels. Furthermore, these changes in signaling molecules seem to reflect changes in gene expression as well as posttranslational processing. A mechanism of sensitization that has received far less attention, however, is the local or axonal translation of these signaling molecules. A growing body of evidence indicates that this process not only is dynamically regulated but also contributes to the initiation and maintenance of chronic pain. Here, we review the biology of local translation in primary afferents and its relevance to pain pathobiology.

RNA-Binding Proteins as Epigenetic Regulators of Brain Functions and Their Involvement in Neurodegeneration

A central aspect of nervous system development and function is the post-transcriptional regulation of mRNA fate, which implies time- and site-dependent translation, in response to cues originating from cell-to-cell crosstalk. Such events are fundamental for the establishment of brain cell asymmetry, as well as of long-lasting modifications of synapses (long-term potentiation: LTP), responsible for learning, memory, and higher cognitive functions. Post-transcriptional regulation is in turn dependent on RNA-binding proteins that, by recognizing and binding brief RNA sequences, base modifications, or secondary/tertiary structures, are able to control maturation, localization, stability, and translation of the transcripts. Notably, most RBPs contain intrinsically disordered regions (IDRs) that are thought to be involved in the formation of membrane-less structures, probably due to liquid-liquid phase separation (LLPS). Such structures are evidenced as a variety of granules that contain proteins and different classes of RNAs. The other side of the peculiar properties of IDRs is, however, that, under altered cellular conditions, they are also prone to form aggregates, as observed in neurodegeneration. Interestingly, RBPs, as part of both normal and aggregated complexes, are also able to enter extracellular vesicles (EVs), and in doing so, they can also reach cells other than those that produced them.

The timing point of exercise intervention regulates neuropathic pain-related molecules in the ipsilateral dorsal root ganglion neurons after sciatic nerve injury

The purpose of this study was to determine whether the timing of tread-mill exercise application can control expression levels of neuropathic pain- and regeneration-related proteins in the ipsilateral lumbar 4 (L4) to 6 (L6) dorsal root ganglion cells (DRG) after sciatic nerve injury (SNI). The experimental rats were randomly divided into five groups: the normal control, SNI+sedentary (IS), exercise+SNI (EI), SNI+exercise (IE), exercise+SNI+exercise (EIE) groups. The rats in exercise groups per-formed treadmill exercise at a speed of 8 m/min for 30 min once a day during 14 days before and/or after SNI. For investigating the expression of specific neuropathic pain and regeneration-related proteins in DRG, we prepared L4 to L6 DRG in the ipsilateral side. In the quantitative analysis, growth associated protein 43 (GAP-43) and brain-derived neurotrophic factor levels were further increased in the ipsilateral DRG at all treadmill exercise groups than those in IS group. In the histological findings, GAP-43 was qualitatively increased IE and EIE groups than IS group at DRG. Wnt3a and β-catenin were dramatically downregulated in EIE and IE groups than IS groups. In addition, nuclear factor kappa-light-chain-enhancer of activated B cells and tumor necrosis factor-α were significantly decreased in IE and EIE groups than IS group in the ipsilateral DRG. Our findings suggested novel information that regular low-intensity exercise before and/or after SNI might be a therapeutic and preventive approaches for relieving neuropathic pain and improving axonal elongation after peripheral nerve injury.

Distinct Mechanisms of Endomembrane Reorganization Determine Dissimilar Transport Pathways in Plant RNA Viruses

Plant viruses exploit the endomembrane system of infected cells for their replication and cell-to-cell transport. The replication of viral RNA genomes occurs in the cytoplasm in association with reorganized endomembrane compartments induced by virus-encoded proteins and is coupled with the virus intercellular transport via plasmodesmata that connect neighboring cells in plant tissues. The transport of virus genomes to and through plasmodesmata requires virus-encoded movement proteins (MPs). Distantly related plant viruses encode different MP sets, or virus transport systems, which vary in the number of MPs and their properties, suggesting their functional differences. Here, we discuss two distinct virus transport pathways based on either the modification of the endoplasmic reticulum tubules or the formation of motile vesicles detached from the endoplasmic reticulum and targeted to endosomes. The viruses with the movement proteins encoded by the triple gene block exemplify the first, and the potyviral system is the example of the second type. These transport systems use unrelated mechanisms of endomembrane reorganization. We emphasize that the mode of virus interaction with cell endomembranes determines the mechanism of plant virus cell-to-cell transport.

Identification of cortical interneuron cell markers in mouse embryos based on machine learning analysis of single-cell transcriptomics

Mammalian cortical interneurons (CINs) could be classified into more than two dozen cell types that possess diverse electrophysiological and molecular characteristics, and participate in various essential biological processes in the human neural system. However, the mechanism to generate diversity in CINs remains controversial. This study aims to predict CIN diversity in mouse embryo by using single-cell transcriptomics and the machine learning methods. Data of 2,669 single-cell transcriptome sequencing results are employed. The 2,669 cells are classified into three categories, caudal ganglionic eminence (CGE) cells, dorsal medial ganglionic eminence (dMGE) cells, and ventral medial ganglionic eminence (vMGE) cells, corresponding to the three regions in the mouse subpallium where the cells are collected. Such transcriptomic profiles were first analyzed by the minimum redundancy and maximum relevance method. A feature list was obtained, which was further fed into the incremental feature selection, incorporating two classification algorithms (random forest and repeated incremental pruning to produce error reduction), to extract key genes and construct powerful classifiers and classification rules. The optimal classifier could achieve an MCC of 0.725, and category-specified prediction accuracies of 0.958, 0.760, and 0.737 for the CGE, dMGE, and vMGE cells, respectively. The related genes and rules may provide helpful information for deepening the understanding of CIN diversity.

Formononetin: A Pathway to Protect Neurons

Formononetin (FMN) is a phytoestrogen member of the flavonoid family, which has the pharmacological effects of antioxidative, antihypertensive, antitumor, and anti-infective. FMN demonstrates potential in the prevention and treatment of diseases, specifically neurological diseases, such as traumatic brain injury (TBI), spinal cord injury (SCI), ischemic stroke, cerebral ischemia-reperfusion, Alzheimer’s disease, and nerve tumor. Herein, a literature search is conducted to provide information on the signaling pathways of neuroprotection of formononetin based on the neuroprotective study. The significant neuroprotective function of FMN makes it a novel candidate for the development of drugs targeting the central nervous system.

RNA and neuronal function: the importance of post-transcriptional regulation

The brain represents an organ with a particularly high diversity of genes that undergo post-transcriptional gene regulation through multiple mechanisms that affect RNA metabolism and, consequently, brain function. This vast regulatory process in the brain allows for a tight spatiotemporal control over protein expression, a necessary factor due to the unique morphologies of neurons. The numerous mechanisms of post-transcriptional regulation or translational control of gene expression in the brain include alternative splicing, RNA editing, mRNA stability and transport. A large number of trans-elements such as RNA-binding proteins and micro RNAs bind to specific cis-elements on transcripts to dictate the fate of mRNAs including its stability, localization, activation and degradation. Several trans-elements are exemplary regulators of translation, employing multiple cofactors and regulatory machinery so as to influence mRNA fate. Networks of regulatory trans-elements exert control over key neuronal processes such as neurogenesis, synaptic transmission and plasticity. Perturbations in these networks may directly or indirectly cause neuropsychiatric and neurodegenerative disorders. We will be reviewing multiple mechanisms of gene regulation by trans-elements occurring specifically in neurons.

KHSRP loss increases neuronal growth and synaptic transmission and alters memory consolidation through RNA stabilization

The KH-type splicing regulatory protein (KHSRP) is an RNA-binding protein linked to decay of mRNAs with AU-rich elements. KHSRP was previously shown to destabilize Gap43 mRNA and decrease neurite growth in cultured embryonic neurons. Here, we have tested functions of KHSRP in vivo. We find upregulation of 1460 mRNAs in neocortex of adult Khsrp-/- mice, of which 527 bind to KHSRP with high specificity. These KHSRP targets are involved in pathways for neuronal morphology, axon guidance, neurotransmission and long-term memory. Khsrp-/- mice show increased axon growth and dendritic spine density in vivo. Neuronal cultures from Khsrp-/- mice show increased axon and dendrite growth and elevated KHSRP-target mRNAs, including subcellularly localized mRNAs. Furthermore, neuron-specific knockout of Khsrp confirms these are from neuron-intrinsic roles of KHSRP. Consistent with this, neurons in the hippocampus and infralimbic cortex of Khsrp-/- mice show elevations in frequency of miniature excitatory postsynaptic currents. The Khsrp-/- mice have deficits in trace conditioning and attention set-shifting tasks compared Khsrp+/+ mice, indicating impaired prefrontal- and hippocampal-dependent memory consolidation with loss of KHSRP. Overall, these results indicate that deletion of KHSRP impairs neuronal development resulting in alterations in neuronal morphology and function by changing post-transcriptional control of neuronal gene expression.

Intra-axonal translation of Khsrp mRNA slows axon regeneration by destabilizing localized mRNAs

Axonally synthesized proteins support nerve regeneration through retrograde signaling and local growth mechanisms. RNA binding proteins (RBP) are needed for this and other aspects of post-transcriptional regulation of neuronal mRNAs, but only a limited number of axonal RBPs are known. We used targeted proteomics to profile RBPs in peripheral nerve axons. We detected 76 proteins with reported RNA binding activity in axoplasm, and levels of several change with axon injury and regeneration. RBPs with altered levels include KHSRP that decreases neurite outgrowth in developing CNS neurons. Axonal KHSRP levels rapidly increase after injury remaining elevated up to 28 days post axotomy. Khsrp mRNA localizes into axons and the rapid increase in axonal KHSRP is through local translation of Khsrp mRNA in axons. KHSRP can bind to mRNAs with 3'UTR AU-rich elements and targets those transcripts to the cytoplasmic exosome for degradation. KHSRP knockout mice show increased axonal levels of KHSRP target mRNAs, Gap43, Snap25, and Fubp1, following sciatic nerve injury and these mice show accelerated nerve regeneration in vivo. Together, our data indicate that axonal translation of the RNA binding protein Khsrp mRNA following nerve injury serves to promote decay of other axonal mRNAs and slow axon regeneration.

Electrical Stimulation Increases Axonal Growth from Dorsal Root Ganglia Co-Cultured with Schwann Cells in Highly Aligned PLA-PPy-Au Microfiber Substrates

Nerve regeneration is a slow process that needs to be guided for distances greater than 5 mm. For this reason, different strategies are being studied to guide axonal growth and accelerate the axonal growth rate. In this study, we employ an electroconductive fibrillar substrate that is able to topographically guide axonal growth while accelerating the axonal growth rate when subjected to an exogenous electric field. Dorsal root ganglia were seeded in co-culture with Schwann cells on a substrate of polylactic acid microfibers coated with the electroconductive polymer polypyrrole, adding gold microfibers to increase its electrical conductivity. The substrate is capable of guiding axonal growth in a highly aligned manner and, when subjected to an electrical stimulation, an improvement in axonal growth is observed. As a result, an increase in the maximum length of the axons of 19.2% and an increase in the area occupied by the axons of 40% were obtained. In addition, an upregulation of the genes related to axon guidance, axogenesis, Schwann cells, proliferation and neurotrophins was observed for the electrically stimulated group. Therefore, our device is a good candidate for nerve regeneration therapies.

RSK1 promotes mammalian axon regeneration by inducing the synthesis of regeneration-related proteins

In contrast to the adult mammalian central nervous system (CNS), the neurons in the peripheral nervous system (PNS) can regenerate their axons. However, the underlying mechanism dictating the regeneration program after PNS injuries remains poorly understood. Combining chemical inhibitor screening with gain- and loss-of-function analyses, we identified p90 ribosomal S6 kinase 1 (RSK1) as a crucial regulator of axon regeneration in dorsal root ganglion (DRG) neurons after sciatic nerve injury (SNI). Mechanistically, RSK1 was found to preferentially regulate the synthesis of regeneration-related proteins using ribosomal profiling. Interestingly, RSK1 expression was up-regulated in injured DRG neurons, but not retinal ganglion cells (RGCs). Additionally, RSK1 overexpression enhanced phosphatase and tensin homolog (PTEN) deletion-induced axon regeneration in RGCs in the adult CNS. Our findings reveal a critical mechanism in inducing protein synthesis that promotes axon regeneration and further suggest RSK1 as a possible therapeutic target for neuronal injury repair.

This study shows that p90 ribosomal S6 kinase 1 (RSK1) responds differentially to nerve injury in the peripheral and central nervous systems, and identifies it as a crucial regulator of axonal regeneration; mechanistically, RSK1 preferentially induces the synthesis of regeneration-related proteins via the RSK1-eEF2K-eEF2 axis.

In situ cryo-electron tomography reveals local cellular machineries for axon branch development

Neurons are highly polarized cells forming an intricate network of dendrites and axons. They are shaped by the dynamic reorganization of cytoskeleton components and cellular organelles. Axon branching allows the formation of new paths and increases circuit complexity. However, our understanding of branch formation is sparse due to the lack of direct in-depth observations. Using in situ cellular cryo-electron tomography on primary mouse neurons, we directly visualized the remodeling of organelles and cytoskeleton structures at axon branches. Strikingly, branched areas functioned as hotspots concentrating organelles to support dynamic activities. Unaligned actin filaments assembled at the base of premature branches accompanied by filopodia-like protrusions. Microtubules and ER comigrated into preformed branches to support outgrowth together with accumulating compact, ∼500-nm mitochondria and locally clustered ribosomes. We obtained a roadmap of events supporting the hypothesis of local protein synthesis selectively taking place at axon branches, allowing them to serve as unique control hubs for axon development and downstream neural network formation.

The Fine Art of Writing a Message: RNA Metabolism in the Shaping and Remodeling of the Nervous System

Neuronal morphogenesis, integration into circuits, and remodeling of synaptic connections occur in temporally and spatially defined steps. Accordingly, the expression of proteins and specific protein isoforms that contribute to these processes must be controlled quantitatively in time and space. A wide variety of post-transcriptional regulatory mechanisms, which act on pre-mRNA and mRNA molecules contribute to this control. They are thereby critically involved in physiological and pathophysiological nervous system development, function, and maintenance. Here, we review recent findings on how mRNA metabolism contributes to neuronal development, from neural stem cell maintenance to synapse specification, with a particular focus on axon growth, guidance, branching, and synapse formation. We emphasize the role of RNA-binding proteins, and highlight their emerging roles in the poorly understood molecular processes of RNA editing, alternative polyadenylation, and temporal control of splicing, while also discussing alternative splicing, RNA localization, and local translation. We illustrate with the example of the evolutionary conserved Musashi protein family how individual RNA-binding proteins are, on the one hand, acting in different processes of RNA metabolism, and, on the other hand, impacting multiple steps in neuronal development and circuit formation. Finally, we provide links to diseases that have been associated with the malfunction of RNA-binding proteins and disrupted post-transcriptional regulation.

Axonal mRNA localization and translation: local events with broad roles

Messenger RNA (mRNA) can be transported and targeted to different subcellular compartments and locally translated. Local translation is an evolutionally conserved mechanism that in mammals, provides an important tool to exquisitely regulate the subcellular proteome in different cell types, including neurons. Local translation in axons is involved in processes such as neuronal development, function, plasticity, and diseases. Here, we summarize the current progress on axonal mRNA transport and translation. We focus on the regulatory mechanisms governing how mRNAs are transported to axons and how they are locally translated in axons. We discuss the roles of axonally synthesized proteins, which either function locally in axons, or are retrogradely trafficked back to soma to achieve neuron-wide gene regulation. We also examine local translation in neurological diseases. Finally, we give a critical perspective on the remaining questions that could be answered to uncover the fundamental rules governing local translation, and discuss how this could lead to new therapeutic targets for neurological diseases.

Epitranscriptomic signatures in stem cell differentiation to the neuronal lineage

Considered to be a field that is continuously growing, epitranscriptomics analyzes the modifications that occur in RNA transcripts and their downstream effects. As epigenetic modifications found in DNA and histones exhibit specific roles on various biological processes, also epitranscriptomic marks control gene expression patterns that are crucial for proper cell proliferation, differentiation and tissue development. Thus, various epitranscriptomic signatures have been identified to play specific roles during stem cell differentiation towards the neuronal and glial lineages, axonal guidance, synaptic plasticity, thus leading to the development of the mature brain tissue. Here we describe in-depth molecular mechanism underlying the most important RNA modifications with emerging roles in the nervous system.

Growth Hormone (GH) Enhances Endogenous Mechanisms of Neuroprotection and Neuroplasticity after Oxygen and Glucose Deprivation Injury (OGD) and Reoxygenation (OGD/R) in Chicken Hippocampal Cell Cultures

As a classical growth promoter and metabolic regulator, growth hormone (GH) is involved in development of the central nervous system (CNS). This hormone might also act as a neurotrophin, since GH is able to induce neuroprotection, neurite growth, and synaptogenesis during the repair process that occurs in response to neural injury. After an ischemic insult, the neural tissue activates endogenous neuroprotective mechanisms regulated by local neurotrophins that promote tissue recovery. In this work, we investigated the neuroprotective effects of GH in cultured hippocampal neurons exposed to hypoxia-ischemia injury and further reoxygenation. Hippocampal cell cultures obtained from chick embryos were incubated under oxygen-glucose deprivation (OGD, <5% O₂, 1 g/L glucose) conditions for 24 h and simultaneously treated with GH. Then, cells were either collected for analysis or submitted to reoxygenation and normal glucose incubation conditions (OGD/R) for another 24 h, in the presence of GH. Results showed that OGD injury significantly reduced cell survival, the number of cells, dendritic length, and number of neurites, whereas OGD/R stage restored most of those adverse effects. Also, OGD/R increased the mRNA expression of several synaptogenic markers (i.e., NRXN1, NRXN3, NLG1, and GAP43), as well as the growth hormone receptor (GHR). The expression of BDNF, IGF-1, and BMP4 mRNAs was augmented in response to OGD injury, and exposure to OGD/R returned it to normoxic control levels, while the expression of NT-3 increased in both conditions. The addition of GH (10 nM) to hippocampal cultures during OGD reduced apoptosis and induced a significant increase in cell survival, number of cells, and doublecortin immunoreactivity (DCX-IR), above that observed in the OGD/R stage. GH treatment also protected dendrites and neurites during OGD, inducing plastic changes reflected in an increase and complexity of their outgrowths during OGD/R. Furthermore, GH increased the expression of NRXN1, NRXN3, NLG1, and GAP43 after OGD injury. GH also increased the BDNF expression after OGD, but reduced it after OGD/R. Conversely, BMP4 was upregulated by GH after OGD/R. Overall, these results indicate that GH protective actions in the neural tissue may be explained by a synergic combination between its own effect and that of other local neurotrophins regulated by autocrine/paracrine mechanisms, which together accelerate the recovery of tissue damaged by hypoxia-ischemia.

HuD Regulates mRNA-circRNA-miRNA Networks in the Mouse Striatum Linked to Neuronal Development and Drug Addiction

Simple Summary

Gene expression controls all aspects of life, including that of humans. Genes are expressed by copying the information stored in the DNA into RNA molecules, and this process is regulated in part by multiple RNA-binding proteins (RBPs). One such protein, HuD, plays a critical role in the development of neurons and has been implicated in childhood brain tumors, neurodegenerative disorders (Parkinson’s, Alzheimer’s, and ALS), and drug abuse. In addition, HuD participates in neuronal remodeling mechanisms in the mature brain and promotes regeneration of peripheral nerves. HuD primarily binds to transcribed messenger RNAs, which are then stabilized for translation into proteins. However, recent studies demonstrate that HuD also regulates the expression of non-coding RNAs, such as circular RNAs (circRNAs) and microRNAs (miRNAs). In this study, we examined the role of HuD in the control of non-coding RNA expression in the mouse striatum, a brain region associated both with normal behaviors and pathological conditions such as drug abuse. Our results show that HuD regulates mRNA-circRNA-miRNA networks involved in the expression of genes associated with brain development and remodeling of neuronal connections. These findings suggest the possibility of new mechanisms controlling brain development, neurodegenerative diseases, and substance use disorders.

Abstract

The RNA-binding protein HuD (a.k.a., ELAVL4) is involved in neuronal development and synaptic plasticity mechanisms, including addiction-related processes such as cocaine conditioned-place preference (CPP) and food reward. The most studied function of this protein is mRNA stabilization; however, we have recently shown that HuD also regulates the levels of circular RNAs (circRNAs) in neurons. To examine the role of HuD in the control of coding and non-coding RNA networks associated with substance use, we identified sets of differentially expressed mRNAs, circRNAs and miRNAs in the striatum of HuD knockout (KO) mice. Our findings indicate that significantly downregulated mRNAs are enriched in biological pathways related to cell morphology and behavior. Furthermore, deletion of HuD altered the levels of 15 miRNAs associated with drug seeking. Using these sets of data, we predicted that a large number of upregulated miRNAs form competing endogenous RNA (ceRNA) networks with circRNAs and mRNAs associated with the neuronal development and synaptic plasticity proteins LSAMP and MARK3. Additionally, several downregulated miRNAs form ceRNA networks with mRNAs and circRNAs from MEF2D, PIK3R3, PTRPM and other neuronal proteins. Together, our results indicate that HuD regulates ceRNA networks controlling the levels of mRNAs associated with neuronal differentiation and synaptic physiology.

The effect of Rho Kinase inhibition on corneal nerve regeneration in vitro and in vivo

PURPOSE

Impairment of corneal nerves can lead to neurotrophic keratopathy accompanied with severe ocular surface damage, which due to limited treatment options, can result in severe visual deterioration. This study evaluates a possible new treatment by enhancing the corneal nerve regeneration using a Rho Kinase inhibitor (Y27632). ROCK is known to play an important role in regulating cell morphology, adhesion and motility but little is known about its role in corneal nerve regeneration.

METHODS

Effects of ROCK inhibition on murine peripheral nerves was assessed in single cell- and wound healing assays as well as a 3D in vitro model. Furthermore, Sholl analysis evaluating neuronal branching and life-death assays evaluating toxicity of the inhibitor were performed. An in vivo mouse model was established, with monitoring weekly corneal nerve regrowth using confocal microscopy. Additionally, corneal nerve fiber length was evaluated by immunofluorescence staining. Underlying pathways were examined by qrtPCR.

RESULTS

ROCK inhibition leads to a significant enhancement of fiber growth in vitro. Sholl analysis revealed a higher degree of branching of treated fibers. Cytotoxicity assay showed no influence of Y27632 on cellular survival. In vivo measurement revealed significant enhanced regeneration after injury in the treated group. QrtPCR of trigeminal ganglia confirmed ROCK knock-down as well as altered pathways.

CONCLUSION

The inhibition of ROCK after corneal nerve injury resulted in an enhanced regrowth of fibers in vitro and in vivo. This might be a step towards a new therapeutic concept for the treatment of impaired corneal nerves in diseases such as neurotrophic keratopathy.

Local Translation Across Neural Development: A Focus on Radial Glial Cells, Axons, and Synaptogenesis

In the past two decades, significant progress has been made in our understanding of mRNA localization and translation at distal sites in axons and dendrites. The existing literature shows that local translation is regulated in a temporally and spatially restricted manner and is critical throughout embryonic and post-embryonic life. Here, recent key findings about mRNA localization and local translation across the various stages of neural development, including neurogenesis, axon development, and synaptogenesis, are reviewed. In the early stages of development, mRNAs are localized and locally translated in the endfeet of radial glial cells, but much is still unexplored about their functional significance. Recent in vitro and in vivo studies have provided new information about the specific mechanisms regulating local translation during axon development, including growth cone guidance and axon branching. Later in development, localization and translation of mRNAs help mediate the major structural and functional changes that occur in the axon during synaptogenesis. Clinically, changes in local translation across all stages of neural development have important implications for understanding the etiology of several neurological disorders. Herein, local translation and mechanisms regulating this process across developmental stages are compared and discussed in the context of function and dysfunction.

Elucidating the Pivotal Neuroimmunomodulation of Stem Cells in Spinal Cord Injury Repair

Spinal cord injury (SCI) is a distressing incident with abrupt onset of the motor as well as sensory dysfunction, and most often, the injury occurs as result of high-energy or velocity accidents as well as contact sports and falls in the elderly. The key challenges associated with nerve repair are the lack of self-repair as well as neurotrophic factors and primary and secondary neuronal apoptosis, as well as factors that prevent the regeneration of axons locally. Neurons that survive the initial traumatic damage may be lost due to pathogenic activities like neuroinflammation and apoptosis. Implanted stem cells are capable of differentiating into neural cells that replace injured cells as well as offer local neurotrophic factors that aid neuroprotection, immunomodulation, axonal sprouting, axonal regeneration, and remyelination. At the microenvironment of SCI, stem cells are capable of producing growth factors like brain-derived neurotrophic factor and nerve growth factor which triggers neuronal survival as well as axonal regrowth. Although stem cells have proven to be of therapeutic value in SCI, the major disadvantage of some of the cell types is the risk for tumorigenicity due to the contamination of undifferentiated cells prior to transplantation. Local administration of stem cells via either direct cellular injection into the spinal cord parenchyma or intrathecal administration into the subarachnoid space is currently the best transplantation modality for stem cells during SCI.

CNTs-CaP/chitosan-coated AZ91D magnesium alloy extract promoted rat dorsal root ganglia neuron growth via activating ERK signalling pathway

Increasing attention has been paid on the application of biodegradable materials such as magnesium and its alloys in neuron repair. AZ91D magnesium alloy coated with carbon nanotubes (CNTs) and/or calcium phosphate (CaP)/chitosan (CS) was fabricated in this study. To evaluate the bioactivity of these AZ91D-based composites, the extracts were prepared by immersing samples in modified simulated body fluid (m-SBF) for 0, 2, 8, 16, 24, 34, 44, 60, or 90 days. Immunofluorescence staining for neuronal class III β-tubulin (TUJ1) revealed that both CNTs-CaP/CS-AZ91D and CaP/CS-AZ91D extracts promoted axon outgrowth of dorsal root ganglia (DRG) neurons, accompanied with increased expression of phosphorylated focal adhesion kinase (p-FAK) and growth associated protein-43 (GAP-43). Besides, the extracts increased the expression and the release of neurotrophic factors including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). ERK signalling was activated in DRG neurons after treating with either CNTs-CaP/CS-AZ91D or CaP/CS-AZ91D extracts, and its inhibition with U0126 counteracted the beneficial effects of these extracts on DRG neuron. Overall, the extracts from these AZ91D-based composites might promote DRG neuron growth via activating ERK signalling pathway. Notably, CNTs-CaP/CS-AZ91D extracts showed a better promoting effect on neuron growth than CaP/CS-AZ91D. Assessment of ion elements showed that the addition of CNTs coating enhanced magnesium corrosion resistance and reduced the deposition of calcium and phosphorus on the surface of CaP/CS-AZ91D alloy. These findings demonstrate that CNTs-CaP/CS-AZ91D likely provide a more suitable environment for neuron growth, which suggests a potential implantable biomaterial for the treatment of nerve injury. SIGNIFICANCE: AZ91D magnesium alloy coated with carbon nanotubes (CNTs) and/or calcium phosphate (CaP)/chitosan (CS) was fabricated and their immersion extracts were prepared using modified simulated body fluid in this study. Both extracts from CNTs-CaP/CS and CaP/CS-coated AZ91D magnesium alloy promotes rat dorsal root ganglia (DRG) neuron growth via activating ERK signalling pathway. Notably, the addition of CNTs improves the performance of CaP/CS-AZ91D. For the first time, our research demonstrates that CNTs-CaP/CS-AZ91D likely provide a suitable environment for neuron growth, suggesting these AZ91D-based composites as potential implantable biomaterials for the treatment of nerve injury.

Epitranscriptomic Analysis of m6A Methylome After Peripheral Nerve Injury

N6-methyladenosine (m6A) is one of the most plentiful internal RNA modifications, especially in eukaryotic messenger RNA (mRNA), which plays pivotal roles in the regulation of mRNA life cycle and nerve development. However, the mRNA m6A methylation pattern in peripheral nervous injury (PNI) has not been investigated. In this study, sciatic nerve samples were collected from 7 days after sciatic nerve injury (SNI) and control rats. Quantitative real-time PCR demonstrated that m6A-related methyltransferase/demethylase genes were remarkably upregulated in SNI group compared with control group. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) was performed to reveal the m6A methylation landscape. The results showed that 4,014 m6A peaks were significantly altered, including 2,144 upregulated and 1,870 downregulated m6A peaks, which were corresponded to 1,858 genes. Moreover, 919 differentially expressed genes were identified by the conjoint analysis of MeRIP-seq and RNA-seq. GO and KEGG pathway analyses were performed to determine the biological functions and signaling pathways of the m6A-modified genes. Notably, these genes were mainly related to the immune system process, cell activation, and nervous system development in GO analysis. KEGG pathway analysis revealed that these genes were involved in the cell cycle, B cell receptor signaling pathway, axon guidance pathway, and calcium signaling pathway. Furthermore, the m6A methylation and protein expression levels of autophagy-related gene (Atg7) were increased, together with the activation of autophagy. These findings shed some light on the epigenetic regulation of gene expression, which may provide a new opinion to promote functional recovery after PNI.

Axonal Transport and Local Translation of mRNA in Neurodegenerative Diseases

Since neurons have long neurites including axons, it is crucial for the axons to transport many intracellular substances such as proteins and mitochondria in order to maintain their morphology and function. In addition, mRNAs have also been shown to be transported within axons. RNA-binding proteins form complexes with mRNAs, and regulate transport of the mRNAs to axons, as well as locally translate them into proteins. Local translation of mRNAs actively occurs during the development and damage of neurons, and plays an important role in axon elongation, regeneration, and synapse formation. In recent years, it has been reported that impaired axonal transport and local translation of mRNAs may be involved in the pathogenesis of some neurodegenerative diseases. In this review, we discuss the significance of mRNA axonal transport and their local translation in amyotrophic lateral sclerosis/frontotemporal dementia, spinal muscular atrophy, Alzheimer’s disease, and fragile X syndrome.

Axon-enriched lincRNA ALAE is required for axon elongation via regulation of local mRNA translation

Long intergenic noncoding RNAs (lincRNAs) are critical regulators involved in diverse biological processes. However, the roles and related mechanisms of lincRNAs in axon development are largely unknown. Here we report an axon-enriched lincRNA regulating axon elongation, referred to as ALAE. Profiling of highly expressed lincRNAs detected abundant and enriched ALAE in the axons of dorsal root ganglion (DRG) neurons, where it locally promoted axon elongation. Mechanically, ALAE directly interacted with the KH3-4 domains of KH-type splicing regulatory protein (KHSRP) and impeded its association with growth-associated protein 43 (Gap43) mRNA. Knockdown of ALAE reduced the protein but not the mRNA level of GAP43 in the axons of DRG neurons. Furthermore, local disruption of the interaction between ALAE and KHSRP in the axon significantly inhibited Gap43 mRNA translation, impairing axon elongation. This study implies crucial roles of axon-enriched lincRNAs in spatiotemporal regulation of local translation during axon development.

Presynaptic protein synthesis and brain plasticity: From physiology to neuropathology

To form and maintain extremely intricate and functional neural circuitry, mammalian neurons are typically endowed with highly arborized dendrites and a long axon. The synapses that link neurons to neurons or to other cells are numerous and often too remote for the cell body to make and deliver new proteins to the right place in time. Moreover, synapses undergo continuous activity-dependent changes in their number and strength, establishing the basis of neural plasticity. The innate dilemma is then how a highly complex neuron provides new proteins for its cytoplasmic periphery and individual synapses to support synaptic plasticity. Here, we review a growing body of evidence that local protein synthesis in discrete sites of the axon and presynaptic terminals plays crucial roles in synaptic plasticity, and that deregulation of this local translation system is implicated in various pathologies of the nervous system.

Rat Sciatic Nerve Axoplasm Proteome Is Enriched with Ribosomal Proteins during Regeneration Processes

Axons are complex subcellular compartments that are extremely long in relation to cell bodies, especially in peripheral nerves. Many processes are required and regulated during axon injury, including anterograde and retrograde transport, glia-to-axon macromolecular transfer, and local axonal protein synthesis. Many in vitro omics approaches have been used to gain insight into these processes, but few have been applied in vivo. Here we adapted the osmotic ex vivo axoplasm isolation method and analyzed the adult rat sciatic-nerve-extruded axoplasm by label-free quantitative proteomics before and after injury. 2087 proteins groups were detected in the axoplasm, revealing translation machinery and microtubule-associated proteins as the most overrepresented biological processes. Ribosomal proteins (73) were detected in the uninjured axoplasm and increased their levels after injury but not within whole sciatic nerves. Meta-analysis showed that detected ribosomal proteins were present in in vitro axonal proteomes. Because local protein synthesis is important for protein localization, we were interested in detecting the most abundant newly synthesized axonal proteins in vivo. With an MS/MS-BONCAT approach, we detected 42 newly synthesized protein groups. Overall, our work indicates that proteomics profiling is useful for local axonal interrogation and suggests that ribosomal proteins may play an important role, especially during injury.

Autocrine insulin pathway signaling regulates actin dynamics in cell wound repair

Cells are exposed to frequent mechanical and/or chemical stressors that can compromise the integrity of the plasma membrane and underlying cortical cytoskeleton. The molecular mechanisms driving the immediate repair response launched to restore the cell cortex and circumvent cell death are largely unknown. Using microarrays and drug-inhibition studies to assess gene expression, we find that initiation of cell wound repair in the Drosophila model is dependent on translation, whereas transcription is required for subsequent steps. We identified 253 genes whose expression is up-regulated (80) or down-regulated (173) in response to laser wounding. A subset of these genes were validated using RNAi knockdowns and exhibit aberrant actomyosin ring assembly and/or actin remodeling defects. Strikingly, we find that the canonical insulin signaling pathway controls actin dynamics through the actin regulators Girdin and Chickadee (profilin), and its disruption leads to abnormal wound repair. Our results provide new insight for understanding how cell wound repair proceeds in healthy individuals and those with diseases involving wound healing deficiencies.

Effect of Vitamin B Complex Treatment on Macrophages to Schwann Cells Association during Neuroinflammation after Peripheral Nerve Injury

Peripheral nerve injury (PNI) triggers a complex multi-cellular response involving the injured neurons, Schwann cells (SCs), and immune cells, often resulting in poor functional recovery. The aim of this study was to investigate the effects of the treatment with vitamin B (B1, B2, B3, B5, B6, and B12) complex on the interaction between macrophages and SCs during the recovery period after PNI. Transection of the motor branch of the femoral nerve followed by reconstruction by termino-terminal anastomosis was used as an experimental model. Isolated nerves from the sham (S), operated (O), and operated groups treated with the B vitamins (OT group) were used for immunofluorescence analysis. The obtained data indicated that PNI modulates interactions between macrophages and SCs in a time-dependent manner. The treatment with B vitamins complex promoted the M1-to M2-macrophage polarization and accelerated the transition from the non-myelin to myelin-forming SCs, an indicative of SCs maturation. The effect of B vitamins complex on both cell types was accompanied with an increase in macrophage/SC interactions, all of which correlated with the regeneration of the injured nerve. Clearly, the capacity of B vitamins to modulate macrophages-SCs interaction may be promising for the treatment of PNI.

Axonal mRNA translation in neurological disorders

It is increasingly recognized that local protein synthesis (LPS) contributes to fundamental aspects of axon biology, in both developing and mature neurons. Mutations in RNA-binding proteins (RBPs), as central players in LPS, and other proteins affecting RNA localization and translation are associated with a range of neurological disorders, suggesting disruption of LPS may be of pathological significance. In this review, we substantiate this hypothesis by examining the link between LPS and key axonal processes, and the implicated pathophysiological consequences of dysregulated LPS. First, we describe how the length and autonomy of axons result in an exceptional reliance on LPS. We next discuss the roles of LPS in maintaining axonal structural and functional polarity and axonal trafficking. We then consider how LPS facilitates the establishment of neuronal connectivity through regulation of axonal branching and pruning, how it mediates axonal survival into adulthood and its involvement in neuronal stress responses.

Splenic sympathetic signaling contributes to acute neutrophil infiltration of the injured spinal cord

Background

Alterations in the immune system are a complication of spinal cord injury (SCI) and have been linked to an excessive sympathetic outflow to lymphoid organs. Still unknown is whether these peripheral immune changes also contribute for the deleterious inflammatory response mounted at the injured spinal cord.

Methods

We analyzed different molecular outputs of the splenic sympathetic signaling for the first 24 h after a thoracic compression SCI. We also analyzed the effect of ablating the splenic sympathetic signaling to the innate immune and inflammatory response at the spleen and spinal cord 24 h after injury.

Results

We found that norepinephrine (NE) levels were already raised at this time-point. Low doses of NE stimulation of splenocytes in vitro mainly affected the neutrophils’ population promoting an increase in both frequency and numbers. Interestingly, the interruption of the sympathetic communication to the spleen, by ablating the splenic nerve, resulted in reduced frequencies and numbers of neutrophils both at the spleen and spinal cord 1 day post-injury.

Conclusion

Collectively, our data demonstrates that the splenic sympathetic signaling is involved in the infiltration of neutrophils after spinal cord injury. Our findings give new mechanistic insights into the dysfunctional regulation of the inflammatory response mounted at the injured spinal cord.

CB1-receptor-mediated inhibitory LTD triggers presynaptic remodeling via protein synthesis and ubiquitination

Long-lasting forms of postsynaptic plasticity commonly involve protein synthesis-dependent structural changes of dendritic spines. However, the relationship between protein synthesis and presynaptic structural plasticity remains unclear. Here, we investigated structural changes in cannabinoid-receptor 1 (CB₁)-mediated long-term depression of inhibitory transmission (iLTD), a form of presynaptic plasticity that involves a protein-synthesis-dependent long-lasting reduction in GABA release. We found that CB₁-iLTD in acute rat hippocampal slices was associated with protein synthesis-dependent presynaptic structural changes. Using proteomics, we determined that CB₁ activation in hippocampal neurons resulted in increased ribosomal proteins and initiation factors, but decreased levels of proteins involved in regulation of the actin cytoskeleton, such as ARPC2 and WASF1/WAVE1, and presynaptic release. Moreover, while CB₁-iLTD increased ubiquitin/proteasome activity, ubiquitination but not proteasomal degradation was critical for structural and functional presynaptic CB₁-iLTD. Thus, CB₁-iLTD relies on both protein synthesis and ubiquitination to elicit structural changes that underlie long-term reduction of GABA release.

Studying ALS: Current Approaches, Effect on Potential Treatment Strategy

Amyotrophic lateral sclerosis (ALS) is one of the most common neurodegenerative diseases, characterized by inevitable progressive paralysis. To date, only two disease modifying therapeutic options are available for the patients with ALS, although they show very modest effect on disease course. The main reason of failure in the field of pharmacological correction of ALS is inability to untangle complex relationships taking place during ALS initiation and progression. Traditional methods of research, based on morphology or transgenic animal models studying provided lots of information about ALS throughout the years. However, translation of these results to humans was unsuccessful due to incomplete recapitulation of molecular pathology and overall inadequacy of the models used in the research.In this review we summarize current knowledge regarding ALS molecular pathology with depiction of novel methods applied recently for the studies. Furthermore we describe present and potential treatment strategies that are based on the recent findings in ALS disease mechanisms.

Formononetin recovered injured nerve functions by enhancing synaptic plasticity in ischemic stroke rats

BACKGROUND AND OBJECTIVES

Formononetin has protective effect against ischemic stroke. It's unclear whether it can restore the nerve functions after stroke.

METHODS

SD rats were subjected with middle cerebral artery occlusion (MCAO), and divided into sham, model and formononetin (30 mg/kg) groups. Neurobehavioral tests (modified Neurological Severity Score [mNSS] and rotarod) were performed before and at 1, 3, 7 and 14 days after MCAO. Then, the rats were sacrificed and the brain sections were processed for neuronal differentiation and synaptic plasticity.

RESULTS

Compared with the sham group, the scores of mNSS were significantly increased, and the residence time on the rotating drum was significantly decreased in the MCAO rats. Compared with the model group, the scores of mNSS were significantly decreased, and the residence time on the rotating drum was increased in the formononetin (30 mg/kg) group. Formononetin significantly increased the number of neuronal dendritic spines and the expression of β III-tubulin, GAP-43, NGF, BDNF, p-Trk A, p-Trk B, p-AKT and p-ERK 1/2.

CONCLUSIONS

Formononetin recovered injured nerve functions after ischemic stroke. PI3K/AKT/ERK pathway might involve in the beneficial effect of formononetin on the neuronal differentiation and synaptic plasticity.

The Puzzling Role of Neuron-Specific PMCA Isoforms in the Aging Process

The aging process is a physiological phenomenon associated with progressive changes in metabolism, genes expression, and cellular resistance to stress. In neurons, one of the hallmarks of senescence is a disturbance of calcium homeostasis that may have far-reaching detrimental consequences on neuronal physiology and function. Among several proteins involved in calcium handling, plasma membrane Ca²⁺-ATPase (PMCA) is the most sensitive calcium detector controlling calcium homeostasis. PMCA exists in four main isoforms and PMCA2 and PMCA3 are highly expressed in the brain. The overall effects of impaired calcium extrusion due to age-dependent decline of PMCA function seem to accumulate with age, increasing the susceptibility to neurotoxic insults. To analyze the PMCA role in neuronal cells, we have developed stable transfected differentiated PC12 lines with down-regulated PMCA2 or PMCA3 isoforms to mimic age-related changes. The resting Ca²⁺ increased in both PMCA-deficient lines affecting the expression of several Ca²⁺-associated proteins, i.e., sarco/endoplasmic Ca²⁺-ATPase (SERCA), calmodulin, calcineurin, GAP43, CCR5, IP₃Rs, and certain types of voltage-gated Ca²⁺ channels (VGCCs). Functional studies also demonstrated profound changes in intracellular pH regulation and mitochondrial metabolism. Moreover, modification of PMCAs membrane composition triggered some adaptive processes to counterbalance calcium overload, but the reduction of PMCA2 appeared to be more detrimental to the cells than PMCA3.

The m6A epitranscriptome: transcriptome plasticity in brain development and function

The field of epitranscriptomics examines the recently deciphered form of gene expression regulation that is mediated by type- and site-specific RNA modifications. Similarly to the role played by epigenetic mechanisms - which operate via DNA and histone modifications - epitranscriptomic modifications are involved in the control of the delicate gene expression patterns that are needed for the development and activity of the nervous system and are essential for basic and higher brain functions. Here we describe the mechanisms that are involved in the writing, erasing and reading of N⁶-methyladenosine, the most prevalent internal mRNA modification, and the emerging roles played by N⁶-methyladenosine in the nervous system.

Neurotrophins induce fission of mitochondria along embryonic sensory axons

Neurotrophins are growth factors that have a multitude of roles in the nervous system. We report that neurotrophins induce the fission of mitochondria along embryonic chick sensory axons driven by combined PI3K and Mek-Erk signaling. Following an initial burst of fission, a new steady state of neurotrophin-dependent mitochondria length is established. Mek-Erk controls the activity of the fission mediator Drp1 GTPase, while PI3K may contribute to the actin-dependent aspect of fission. Drp1-mediated fission is required for nerve growth factor (NGF)-induced collateral branching in vitro and expression of dominant negative Drp1 impairs the branching of axons in the developing spinal cord in vivo. Fission is also required for NGF-induced mitochondria-dependent intra-axonal translation of the actin regulatory protein cortactin, a previously determined component of NGF-induced branching. Collectively, these observations unveil a novel biological function of neurotrophins; the regulation of mitochondrial fission and steady state mitochondrial length and density in axons.

PKCγ promotes axonal remodeling in the cortico-spinal tract via GSK3β/β-catenin signaling after traumatic brain injury

Traumatic brain injury (TBI) is a common cause of death and disability. Enhancing the midline-crossing of the contralateral corticospinal tract (CST) to the denervated side of spinal cord facilitates functional recovery after TBI. Activation of the gamma isoform of PKC (PKCγ) in contralateral CST implicates its roles in promoting CST remodeling after TBI. In this study, we deployed loss and gain of function strategies in N2a cells and primary cortical neurons in vitro, and demonstrated that PKCγ is not only important but necessary for neuronal differentiation, neurite outgrowth and axonal branching but not for axonal extension. Mechanically, through the phosphorylation of GSK3β, PKCγ stabilizes the expression of cytosolic β-catenin and increase GAP43 expression, thus promoting axonal outgrowth. Further, rAAV2/9-mediated delivery of constitutive PKCγ in the corticospinal tract after unilateral TBI in vivo additionally showed that specifically delivery of active PKCγ mutant to cortical neuron promotes midline crossing of corticospinal fibers from the uninjured side to the denervated cervical spinal cord. This PKCγ-mediated injury response promoted sensorimotor functional recovery. In conclusion, PKCγ mediates stability of β-catenin through the phosphorylation of GSK3β to facilitate neuronal differentiation, neurite outgrowth and axonal branching, and PKCγ maybe a novel therapeutic target for physiological and functional recovery after TBI.