The role of axon guidance molecules in the pathogenesis of epilepsy

Current treatments for epilepsy can only manage the symptoms of the condition but cannot alter the initial onset or halt the progression of the disease. Consequently, it is crucial to identify drugs that can target novel cellular and molecular mechanisms and mechanisms of action. Increasing evidence suggests that axon guidance molecules play a role in the structural and functional modifications of neural networks and that the dysregulation of these molecules is associated with epilepsy susceptibility. In this review, we discuss the essential role of axon guidance molecules in neuronal activity in patients with epilepsy as well as the impact of these molecules on synaptic plasticity and brain tissue remodeling. Furthermore, we examine the relationship between axon guidance molecules and neuroinflammation, as well as the structural changes in specific brain regions that contribute to the development of epilepsy. Ample evidence indicates that axon guidance molecules, including semaphorins and ephrins, play a fundamental role in guiding axon growth and the establishment of synaptic connections. Deviations in their expression or function can disrupt neuronal connections, ultimately leading to epileptic seizures. The remodeling of neural networks is a significant characteristic of epilepsy, with axon guidance molecules playing a role in the dynamic reorganization of neural circuits. This, in turn, affects synapse formation and elimination. Dysregulation of these molecules can upset the delicate balance between excitation and inhibition within a neural network, thereby increasing the risk of overexcitation and the development of epilepsy. Inflammatory signals can regulate the expression and function of axon guidance molecules, thus influencing axonal growth, axon orientation, and synaptic plasticity. The dysregulation of neuroinflammation can intensify neuronal dysfunction and contribute to the occurrence of epilepsy. This review delves into the mechanisms associated with the pathogenicity of axon guidance molecules in epilepsy, offering a valuable reference for the exploration of therapeutic targets and presenting a fresh perspective on treatment strategies for this condition.

Transcriptomic and bioinformatics analysis of the mechanism by which erythropoietin promotes recovery from traumatic brain injury in mice

Recent studies have found that erythropoietin promotes the recovery of neurological function after traumatic brain injury.However,the precise mechanism of action remains unclea r.In this study,we induced moderate traumatic brain injury in mice by intrape ritoneal injection of erythro poietin for 3 consecutive days.RNA sequencing detected a total of 4065 differentially expressed RNAs,including 1059 mRNAs,92 microRNAs,799 long non-coding RNAs,and 2115circular RNAs.Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analyses revealed that the coding and non-coding RNAs that were differentially expressed after traumatic brain injury and treatment with erythropoietin play roles in the axon guidance pathway,Wnt pathway,and MAPK pathway.Constructing competing endogenous RNA networks showed that regulatory relationship between the differentially expressed non-coding RNAs and mRNAs.Because the axon guidance pathway was repeatedly enriched,the expression of Wnt5a and Ephb6,key factors in the axonal guidance pathway,was assessed.Ephb6 expression decreased and Wnt5a expression increased after traumatic brain injury,and these effects were reversed by treatment with erythro poietin.These findings suggest that erythro poietin can promote recove ry of nerve function after traumatic brain injury through the axon guidance pathway.

Netrin-1 signaling pathway mechanisms in neurodegenerative diseases

Netrin-1 and its receptors play crucial roles in inducing axonal growth and neuronal migration during neuronal development.Their profound impacts then extend into adulthood to encompass the maintenance of neuronal survival and synaptic function.Increasing amounts of evidence highlight several key points:(1)Diminished Netrin-1 levels exacerbate pathological progression in animal models of Alzheimer’s disease and Parkinson’s disease,and potentially,similar alterations occur in humans.(2)Genetic mutations of Netrin-1 receptors increase an individuals’susceptibility to neurodegenerative disorders.(3)Therapeutic approaches targeting Netrin-1 and its receptors offer the benefits of enhancing memory and motor function.(4)Netrin-1 and its receptors show genetic and epigenetic alterations in a variety of cancers.These findings provide compelling evidence that Netrin-1 and its receptors are crucial targets in neurodegenerative diseases.Through a comprehensive review of Netrin-1 signaling pathways,our objective is to uncover potential therapeutic avenues for neurodegenerative disorders.

Lysophospholipids in retinal axon guidance: roles and cell signaling

Nerve regeneration in the central nervous system（CNS）has become a holy grail of biomedical research.To understand nerve growth that would be required for efficient regeneration,many scientists have turned to developing systems where nerve growth is abundant and normal neural connections are established.One aspect of this neural development,which would also be important in nerve regeneration,

Understanding axon guidance: attraction, repulsion, and statistical physics

Understanding axon guidance is important for developing therapies to restore neuronal connections damaged by injury or disease. Axons migrate in response to extraceUular guidance molecules that induce or inhibit axon outgrowth activity within the axon. The direction of guidance is determined by the attractive and repulsive responses that the axon has to the guidance cues. In a deterministic model of guidance, the direction of guidance can be precisely determined if the attractive and repulsive effect that each cue has on the axon is known. But what if there are numerous attractive and repulsive responses induced by multiple guidance cues, and the direction of the attractive and repulsive events fluctuates？ If the effect that each attractive and repulsive event has on guidance becomes too complex to measure then understand- ing how each molecular cue influences the guidance decision becomes impossible.

What we know about axons in Parkinson’s disease

Tremendous research efforts have been made regarding the pathogenesis of Parkinson’s disease(PD).However,there are still no effective strategies to restore midbrain dopaminergic(mDA)innervation and prevent disease progression.One possibility is that we may have been neglecting the role of axons in mDA neuronal degeneration.This review first summarizes mDA axon development during the early stage of PD and discusses how axon guidance defects contribute to PD vulnerability.Furthermore,we review axonal transport dysregulation in the numerous PD-related genetic mutations,including Parkin,PINK1,DJ1,LRRK2 and SNCA.The evidence suggests that proper axonal transport is crucial for neuronal function and survival.Finally,advanced tools for axonal studies were evaluated,including light-sheet and super-resolution microscopy.These adapted microscopes have been used to help solve questions unanswered before.Overall,the role of axon terminals in the initiation of the degeneration cascade remains undeciphered,and more research in the related area may be conducted further to restore dopamine levels in the striatum to alleviate the motor complications of PD.

RACK1 regulates neural development

Receptor for activated C kinase 1（RACK1）is an evolutionarily conserved scaffolding protein within the tryptophan-aspartate（WD）repeat family of proteins.RACK1 can bind multiple signaling molecules concurrently,as well as stabilize and anchor proteins.RACK1 also plays an important role at focal adhesions,where it acts to regulate cell migration.In addition,RACK1 is a ribosomal binding protein and thus,regulates translation.Despite these numerous functions,little is known about how RACK1 regulates nervous system development.Here,we review three studies that examine the role of RACK1 in neural development.In brief,these papers demonstrate that（1）RACK-1,the C.elegans homolog of mammalian RACK1,is required for axon guidance;（2）RACK1 is required for neurite extension of neuronally differentiated rat PC12cells;and（3）RACK1 is required for axon outgrowth of primary mouse cortical neurons.Thus,it is evident that RACK1 is critical for appropriate neural development in a wide range of species,and future discoveries could reveal whether RACK1 and its signaling partners are potential targets for treatment of neurodevelopmental disorders or a therapeutic approach for axonal regeneration.

Validation of a novel animal model for sciatic nerve repair with an adipose-derived stem cell loaded fibrin conduit

Despite the regenerative capabilities of peripheral nerves, severe injuries or neuronal trauma of critical size impose immense hurdles for proper restoration of neuro-muscular circuitry. Autologous nerve grafts improve re-establishment of connectivity, but also comprise substantial donor site morbidity. We developed a rat model which allows the testing of different cell applications, i.e., mesenchymal stem cells, to improve nerve regeneration in vivo. To mimic inaccurate alignment of autologous nerve grafts with the injured nerve, a 20 mm portion of the sciatic nerve was excised, and sutured back in place in reversed direction. To validate the feasibility of our novel model, a fibrin gel conduit containing autologous undifferentiated adipose-derived stem cells was applied around the coaptation sites and compared to autologous nerve grafts. After evaluating sciatic nerve function for 16 weeks postoperatively, animals were sacrificed, and gastrocnemius muscle weight was determined along with morphological parameters（g-ratio, axon density ＆ diameter） of regenerating axons. Interestingly, the addition of undifferentiated adipose-derived stem cells resulted in a significantly improved re-myelination, axon ingrowth and functional outcome, when compared to animals without a cell seeded conduit. The presented model thus displays several intriguing features： it imitates a certain mismatch in size, distribution and orientation of axons within the nerve coaptation site. The fibrin conduit itself allows for an easy application of cells and, as a true critical-size defect model, any observed improvement relates directly to the performed intervention. Since fibrin and adipose-derived stem cells have been approved for human applications, the technique can theoretically be performed on humans. Thus, we suggest that the model is a powerful tool to investigate cell mediated assistance of peripheral nerve regeneration.

Expression of the tyrosine kinase receptor EphA5 and its ligand ephrin-A5 during mouse spinal cord development

Objectives To study the expression patterns of two Eph family molecules, the receptor EphA5, and the ligand ephrin-A5, during spinal cord development. Methods The receptor expression was analyzed using beta-galactosidase knockin mice, and affinity ligand probe binding. The ligand expression was assessed using two different affinity probes, and knockout mouse tissues as controls. Results EphA5 was expressed in the ventral spinal cord, while ephrin-A5 was located in the dorsolateral regions of the spinal cord throughout development. Conclusions These results show that EphA5 and ephrin-A5 are expressed over broad developmental stages and may play important roles in establishing the dorsoventral organization of the spinal cord.

Neuronal guidance genes in health and diseases

Neurons migrate from their birthplaces to the destinations,and extending axons navigate to their synaptic targets by sensing various extracellular cues in spatiotemporally controlled manners.These evolutionally conserved guidance cues and their receptors regulate multiple aspects of neural development to establish the highly complex nervous system by mediating both short-and long-range cell-cell communications.Neuronal guidance genes(encoding cues,receptors,or downstream signal transducers)are critical not only for development of the nervous system but also for synaptic maintenance,remodeling,and function in the adult brain.One emerging theme is the combinatorial and complementary functions of relatively limited classes of neuronal guidance genes in multiple processes,including neuronal migration,axonal guidance,synaptogenesis,and circuit formation.Importantly,neuronal guidance genes also regulate cell migration and cell-cell communications outside the nervous system.We are just beginning to understand how cells integrate multiple guidance and adhesion signaling inputs to determine overall cellular/subcellular behavior and how aberrant guidance signaling in various cell types contributes to diverse human diseases,ranging from developmental,neuropsychiatric,and neurodegenerative disorders to cancer metastasis.We review classic studies and recent advances in understanding signaling mechanisms of the guidance genes as well as their roles in human diseases.Furthermore,we discuss the remaining chalienges and therapeutic potentials of modulating neuronal guidance pathways in neural repair.

Effect of Ephrin-A1/EphA2 on Invasion of Trophoblastic Cells

The effect of axon guidance factors ephrin-A1/EphA2 on the invasion of trophoblastic cells and the possible mechanism were investigated in this study. The expression of EphA2 in vascular endothelial cells was detected by immunohistochemistry. The proliferation and invasion of TEV-1 cells （an extravillous trophoblastic cell line） in first trimester were determined by cell counting kit-8 （CCK-8） and Transwell invasion assay. Real-time PCR was used to detect the expression ofephrin-A1 in TEV-I cells treated with EphA2 at different concentrations （10, 50, 100, 500, 1000 and 5000 μg/L）. The results showed： （1） EphA2 was expressed in the vascular endothelial cells; （2） EphA2 could promote the proliferation of TEV-1 cells. The proliferative capacity reached a peak in TEV-1 cells treated with 100 μg/L EphA2 （P〈0.05）; （3） EphA2 could increase the invasion of TEV-1 cells. The invasive ability was the greatest in TEV-1 cells treated with 500 pg/L EphA2 （P〈0.05）; （4） in the presence of EphA2 （0-500 μg/L）, the expression of ephrin-A1 was increased concentration-dependently （P〈0.05）, but when the concentration of EphA2 was over 500 μg/L, the expression of ephrin-A 1 ceased to increase （P〉0.05）. It was concluded that EphA2 can promote the invasion and proliferation of the human extravillous trophoblastic cells probably by regulating the ephrin-A1 ligand.

The astrocyte scar – not so inhibitory after all?

Damaged adult central nervous system axons have very limited regenerative capacity,if any.Other than an intrinsic deficiency（Liu et al.,2011）in axonal extension and guidance compared to embryonic neurons or peripheral neurons,the injury site is also generally viewed to be non-permissive for axonal regrowth.In particular,

The Yin and Yang of Wnt/Ryk axon guidance in development and regeneration

In the developing embryo,nascent axons navigate towards their specific targets to establish the intricate network of axonal connections linking neurons within the mature nervous system.Molecular navigational systems comprising repulsive and attractive guidance cues form chemotactic gradients along the pathway of the exploring growth cone.Axon-bound receptors detect these gradients and determine the trajectory of the migrating growth cone.In contrast to their benevolent role in the developing nervous system,repulsive guidance receptors are detrimental to the axon’s ability to regenerate after injury in the adult.In this review we explore the essential and beneficial role played by the chemorepulsive Wnt receptor,Ryk/Derailed in axon navigation in the embryonic nervous system(the Yin function).Specifically,we focus on the role of Wnt5a/Rykmediated guidance in the establishment of two major axon tracts in the mammalian central nervous system,the corticospinal tract and the corpus callosum.Recent studies have also identified Ryk as a major suppressor of axonal regeneration after spinal cord injury.Thus,we also discuss this opposing aspect of Ryk function in axonal regeneration where its activity is a major impediment to axon regrowth(the Yang function).

Microtubule dynamics in axon guidance

Precise modulation of the cytoskeleton is involved in a variety of cellular processes including cell division, migration, polarity, and adhesion. In developing post-mitotic neurons, extracellular guidance cues not only trigger signaling cascades that act at a distance to indirectly regulate microtubule distribution, and assembly and disassembly in the growth cone, but also directly modulate microtubule stability and dynamics through coupling of guidance receptors with microtubules to control growth-cone turning. Microtubule-associated proteins including classical microtubule-associated proteins and microtubule plus-end tracking proteins are required for modulating microtubule dynamics to influence growth-cone steering. Multiple key signaling components, such as calcium, small GTPases, glycogen synthase kinase-313, and c-Jun N-terminal kinase, link upstream signal cascades to microtubule stability and dynamics in the growth cone to control axon outgrowth and projection. Understanding the functions and regulation of microtubule dynamics in the growth cone provides new insights into the molecular mechanisms of axon guidance.

Large-scale microfluidic gradient arrays reveal axon guidance behaviors in hippocampal neurons

High-throughput quantitative approaches to study axon growth behaviors have remained a challenge.We have developed a 1024-chamber microfluidic gradient generator array that enables large-scale investigations of axon guidance and growth dynamics from individual primary mammalian neurons,which are exposed to gradients of diffusible molecules.Our microfluidic method(a)generates statistically rich data sets,(b)produces a stable,reproducible gradient with negligible shear stresses on the culture surface,(c)is amenable to the long-term culture of primary neurons without any unconventional protocol,and(d)eliminates the confounding influence of cell-secreted factors.Using this platform,we demonstrate that hippocampal axon guidance in response to a netrin-1 gradient is concentration-dependent—attractive at higher concentrations and repulsive at lower concentrations.We also show that the turning of the growth cone depends on the angle of incidence of the gradient.Our study highlights the potential of microfluidic devices in producing large amounts of data from morphogen and chemokine gradients that play essential roles not only in axonal navigation but also in stem cell differentiation,cell migration,and immune response.

TRIM-9 functions in the UNC-6/UNC-40 pathway to regulate ventral guidance

TRIpartite Motif （TRIM） family proteins are ring finger domain-containing, multi-domain proteins implicated in many biological processes. Members of the TRIM-9/C-I subfamily of TRIM proteins, including TRIM-9, MIDI and MID2, have neuronal functions and are associated with neurological diseases. To explore whether the functions of C-I TRIM proteins are conserved in invertebrates, we analyzed Caenorhabditis elegans and Drosophila trim-9 mutants. C. elegans trim-9 mutants exhibit defects in the ventral guidance of hermaphrodite specific neuron （HSN） and the touch neuron AVM. Further genetic analyses indicate that TRIM-9 participates in the UNC-6-UNC-40 attraction pathway. Asymmetric distribution of UNC-40 during HSN development is normal in trim-9 mutants. However, the asymmetric localization of MIG-10, a downstream effector of UNC-40, is abolished in trim-9 mutants. These results suggest that TRIM-9 functions upstream of MIG- 10 in the UNC- 40 pathway. Moreover, we showed that TRIM-9 exhibits E3 ubiquitin ligase activity in vitro and this activity is important for TRIM-9 function in vivo. Additionally, we found that Drosophila trim-9 is required for the midline attraction of a group of sensory neuron axons. Over-expression of the Netrin/UNC-6 receptor Frazzled suppresses the guidance defects in trim-9 mutants. Our study reveals an evolutionarily conserved function of TRIM-9 in the UNC-40/Frazzled-mediated UNC-6/Netrin attraction pathway.

Neurotrophin treatment to promote regeneration after traumatic CNS injury

Neurotrophins are a family of growth factors that have been found to be central for the development and functional maintenance of the nervous system, participating in neurogenesis, neuronal survival, axonal growth, synaptogenesis and activity-dependent forms of synaptic plasticity. Trauma in the adult nervous system can disrupt the functional circuitry of neurons and result in severe functional deficits. The limitation of intrinsic growth capacity of adult nervous system and the presence of an inhospitable environment are the major hurdles for axonal regeneration of lesioned adult neurons. Neurotrophic factors have been shown to be excellent candidates in mediating neuronal repair and establishing functional circuitry via activating several growth signaling mechanisms including neuron-intrinsic regenerative programs. Here, we will review the effects of various neurotrophins in mediating recovery after injury to the adult spinal cord.

The function of DNA topoisomerase IIβ in neuronal development

Type II DNA topoisomerases（Tops）are ATP-dependent enzymes that catalyze topological transformations of genomic DNA by the transport of one DNA double helix through another.In mammals,there are 2 isoforms of DNA Top II, termed Top IIβ and Top IIβ.The IIβ isoform is abundantly expressed in cells that have undergone the final cell division and are committed to differentiation into neuronal cells.In recent years,there have been accumulating studies showing the significant role of Top IIβ in neuronal development through regulating expression of certain genes in cells committed to the neuronal fate after the final division.These genes are involved in the processes of neuronal differentiation,migration,axon guidance and so on.The present review mainly focused on the research progress on the role of Top IIβ in neuronal development over the recent decades.