Axonal Growth Research Articles

Enhanced axon outgrowth of spinal motor neurons in co-culturing with dorsal root ganglions antagonizes the growth inhibitory environment

IntroductionForming a bridge made of functional axons to span the lesion is essential to reconstruct the motor circuitry following spinal cord injury (SCI). Dorsal root ganglion (DRG) axons are robust in axon growth and have been proved to facilitate the growth of cortical neurons in a process of axon-facilitated axon regeneration. However, whether DRG transplantation affects the axon outgrowth of spinal motor neurons (SMNs) that play crucial roles in motor circuitry remains unclear. MethodsWe investigated the axonal growth patterns of co-cultured DRGs and SMN aggregates (SMNAs) taking advantage of a well-designed 3D-printed in vitro system. Chondroitin sulphate proteoglycans (CSPG) induced inhibitory matrix was introduced to imitate the inhibitory environment following SCI. Axonal lengths of DRG, SMNA or DRG & SMNA cultured on the permissive or CSPG induced inhibitory matrix were measured and compared. ResultsOur results indicated that under the guidance of full axonal connection generated from two opposing populations of DRGs, SMNA axons were growth-enhanced and elongated along the DRG axon bridge to distances that they could not otherwise reach. Quantitatively, the co-culture increased the SMNA axonal length by 32.1 %. Moreover, the CSPG matrix reduced the axonal length of DRGs and SMNAs by 46.2 % and 17.7 %, respectively. This inhibitory effect was antagonized by the co-culture of DRGs and SMNAs. Especially for SMNAs, they extended the axons across the CSPG-coating matrix, reached the lengths close to those of SMNAs cultured on the permissive matrix alone. ConclusionsThis study deepens our understanding of axon-facilitated reconstruction of the motor circuitry. Moreover, the results support SCI treatment utilizing the enhanced outgrowth of axons to restore functional connectivity in SCI patients.

Progress in methods for evaluating Schwann cell myelination and axonal growth in peripheral nerve regeneration via scaffolds.

Peripheral nerve injury (PNI) is a neurological disorder caused by trauma that is frequently induced by accidents, war, and surgical complications, which is of global significance. The severity of the injury determines the potential for lifelong disability in patients. Artificial nerve scaffolds have been investigated as a powerful tool for promoting optimal regeneration of nerve defects. Over the past few decades, bionic scaffolds have been successfully developed to provide guidance and biological cues to facilitate Schwann cell myelination and orientated axonal growth. Numerous assessment techniques have been employed to investigate the therapeutic efficacy of nerve scaffolds in promoting the growth of Schwann cells and axons upon the bioactivities of distinct scaffolds, which have encouraged a greater understanding of the biological mechanisms involved in peripheral nerve development and regeneration. However, it is still difficult to compare the results from different labs due to the diversity of protocols and the availability of innovative technologies when evaluating the effectiveness of novel artificial scaffolds. Meanwhile, due to the complicated process of peripheral nerve regeneration, several evaluation methods are usually combined in studies on peripheral nerve repair. Herein, we have provided an overview of the evaluation methods used to study the outcomes of scaffold-based therapies for PNI in experimental animal models and especially focus on Schwann cell functions and axonal growth within the regenerated nerve.

Chronic Adaptations in the Dorsal Horn Following a Cervical Spinal Cord Injury in Primates.

Spinal cord injury (SCI) is devastating, with limited treatment options and variable outcomes. Most in vivo SCI research has focused on the acute and early post-injury periods, and the promotion of axonal growth, so little is understood about the clinically stable chronic state, axonal growth over time, and what plasticity endures. Here, we followed animals into the chronic phase following SCI, to address this gap. Male macaques received targeted deafferentation, affecting three digits of one hand, and were divided into short (4-6 months) or long-term (11-12 months) groups, based on post-injury survival times. Monkeys were assessed behaviorally, where possible, and all exhibited an initial post-injury deficit in manual dexterity, with gradual functional recovery over 2 months. We previously reported extensive sprouting of somatosensory corticospinal (S1 CST) fibers in the dorsal horn in the first five post-injury months. Here, we show that by 1 year, the S1 CST sprouting is pruned, with the terminal territory resembling control animals. This was reflected in the number of putatively "functional" synapses observed, which increased over the first 4-5 months, and then returned to baseline by 1 year. Microglia density also increased in the affected dorsal horn at 4-6 months and then decreased, but did not return to baseline by 1 year, suggesting refinement continues beyond this time. Overall, there is a long period of reorganization and consolidation of adaptive circuitry in the dorsal horn, extending well beyond the initial behavioral recovery. This provides a potential window to target therapeutic opportunities during the chronic phase.

A Novel Superparamagnetic Multifunctional Nerve Scaffold: A Remote Actuation Strategy to Boost In Situ Extracellular Vesicles Production for Enhanced Peripheral Nerve Repair.

Extracellular vesicles (EVs) have inherent advantages over cell-based therapies in regenerative medicine because of their cargos of abundant bioactive cues. Several strategies are proposed to tune EVs production in vitro. However, it remains a challenge for manipulation of EVs production in vivo, which poses significant difficulties for EVs-based therapies that aim to promote tissue regeneration, particularly for long-term treatment of diseases like peripheral neuropathy. Herein, a superparamagnetic nanocomposite scaffold capable of controlling EVs production on-demand is constructed by incorporating polyethyleneglycol/polyethyleneimine modified superparamagnetic nanoparticles into a polyacrylamide/hyaluronic acid double-network hydrogel (Mag-gel). The Mag-gel is highly sensitive to a rotating magnetic field (RMF), and can act as mechano-stimulative platform to exert micro/nanoscale forces on encapsulated Schwann cells (SCs), an essential glial cell in supporting nerve regeneration. By switching the ON/OFF state of the RMF, the Mag-gel can scale up local production of SCs-derived EVs (SCs-EVs) both in vitro and in vivo. Further transcriptome sequencing indicates an enrichment of transcripts favorable in axon growth, angiogenesis, and inflammatory regulation of SCs-EVs in the Mag-gel with RMF, which ultimately results in optimized nerve repair in vivo. Overall, this research provides a noninvasive and remotely time-scheduled method for fine-tuning EVs-based therapies to accelerate tissue regeneration, including that of peripheral nerves.

Are There Lipid Membrane-Domain Subtypes in Neurons with Different Roles in Calcium Signaling?

Lipid membrane nanodomains or lipid rafts are 10–200 nm diameter size cholesterol- and sphingolipid-enriched domains of the plasma membrane, gathering many proteins with different roles. Isolation and characterization of plasma membrane proteins by differential centrifugation and proteomic studies have revealed a remarkable diversity of proteins in these domains. The limited size of the lipid membrane nanodomain challenges the simple possibility that all of them can coexist within the same lipid membrane domain. As caveolin-1, flotillin isoforms and gangliosides are currently used as neuronal lipid membrane nanodomain markers, we first analyzed the structural features of these components forming nanodomains at the plasma membrane since they are relevant for building supramolecular complexes constituted by these molecular signatures. Among the proteins associated with neuronal lipid membrane nanodomains, there are a large number of proteins that play major roles in calcium signaling, such as ionotropic and metabotropic receptors for neurotransmitters, calcium channels, and calcium pumps. This review highlights a large variation between the calcium signaling proteins that have been reported to be associated with isolated caveolin-1 and flotillin-lipid membrane nanodomains. Since these calcium signaling proteins are scattered in different locations of the neuronal plasma membrane, i.e., in presynapses, postsynapses, axonal or dendritic trees, or in the neuronal soma, our analysis suggests that different lipid membrane-domain subtypes should exist in neurons. Furthermore, we conclude that classification of lipid membrane domains by their content in calcium signaling proteins sheds light on the roles of these domains for neuronal activities that are dependent upon the intracellular calcium concentration. Some examples described in this review include the synaptic and metabolic activity, secretion of neurotransmitters and neuromodulators, neuronal excitability (long-term potentiation and long-term depression), axonal and dendritic growth but also neuronal cell survival and death.

FERMT2 cleavage impacts APP metabolism in a Src‐dependent manner

AbstractBackground FERMT2 has been identified as a genetic risk factor for AD. We have reported that the FERMT2 protein is a partner of APP and a loss of FERMT2 (kindlin‐2) function altered both axonal growth and long‐term potentiation in an APP‐dependent manner. In this study, we aimed to identify the molecular mechanisms leading to loss of FERMT2 function.MethodWe aimed to identify proteases and other factors that regulate the cleavage of FERMT2 protein, which appears to be a mechanism that modulates its functions. The impact on FERMT2 cleavage and molecular interactions were analyzed by Co‐IP and WB. Consequences of these molecular interactions between FERMT2 and its partners on APP metabolism were then investigated using HEK‐APP cell lines.ResultWe identified a caspase‐dependent cleavage of FERMT2 that could be a molecular mechanism involved in the regulation of cell adhesion processes by inhibiting the ability of FERMT2 to interact with its partners. Furthermore, these results suggest that c‐Src activity, already known to regulate FERMT2 pathway, may have an impact on APP metabolism through regulation of FERMT2 cleavage.ConclusionAltogether, our data provide new mechanisms for understanding the involvement of the genetic risk factor FERMT2 in the pathophysiological processes of AD.

Rewiring the future: drugs abused in adolescence may predispose to mental illness in adult life by altering dopamine axon growth.

Adolescence is a period of increased exploration and novelty-seeking, which includes new social behaviors, as well as drug experimentation, often spurred on by peer pressure. This is unfortunate, as the immature state of the adolescent brain makes it particularly susceptible to the negative developmental impact of drug use. During adolescence, dopamine terminals, which have migrated from the ventral tegmental area, pause in the nucleus accumbens, before segregating by either forming local connections or growing towards the prefrontal cortex (PFC). This developmentally late and lengthy process renders adolescent dopamine axon pathfinding vulnerable to disruption by substance use. Indeed, exposure to stimulant drugs in adolescent male mice, but not females, triggers dopamine axons to mistarget the nucleus accumbens and to grow ectopically to the PFC. Some evidence suggests that at this novel site, the functional organization of the ectopic dopamine axons mirrors that of the intended target. The structural rewiring dysregulates local synaptic connectivity, leading to poor impulse control ability, deficits of which are a core symptom of substance-use disorders. In the present commentary, we argue that different substances of abuse induce dopamine mistargeting events with the off-target trajectory prescribed by the type of drug, leading to psychiatric outcomes later in life.

Quantitative Biofabrication Platform for Collagen-Based Peripheral Nerve Grafts with Structural and Chemical Guidance.

Owing to its crucial role in the human body, collagen has immense potential as a material for the biofabrication of tissues and organs. However, highly refined fabrication using collagen remains difficult, primarily because of its notably soft properties. A quantitative biofabrication platform to construct collagen-based peripheral nerve grafts, incorporating bionic structural and chemical guidance cues, is introduced. A viscoelastic model for collagen, which facilitates simulating material relaxation and fabricating collagen-based neural grafts, achieving a maximum channel density similar to that of the native nerve structure of longitudinal microchannel arrays, is established. For axonal regeneration over considerable distances, a gradient printing control model and quantitative method are developed to realize the high-precision gradient distribution of nerve growth factor required to obtain nerve grafts through one-step bioprinting. Experiments verify that the bioprinted graft effectively guides linear axonal growth in vitro and in vivo. This study should advance biofabrication methods for a variety of human tissue-engineering applications requiring tailored cues.

<i>In silico</i> prediction of the transcription factor-enhancer interaction as a first stage of axonal growth regulation

The development of neurodegenerative diseases is associated with proper neuronal circuit formation, axonal guidance. The DCC receptor (deleted in colorectal cancer / colorectal cancer suppressor) and SHH (sonic hedgehog protein) are among the key regulators of axonal guidance.Aim. Interaction prediction of specific enhancer regions of DCC and SHH genes with respectively annotated transcription factors.Materials and methods. An in silico study was performed. The iEnhancer-2L and ES-ARCNN algorithms were selected to estimate enhancer sequence strength. The interaction between transcription factor and enhancer sequence was assessed using the molecular docking method. The enhancer sequence of DCC and SHH protein genes were taken from the NCBI open-source database in FASTA format. Ensembl database was used for enhancer mapping, GeneCards was used for screening and selection of potentially appropriate enhancers and transcription factors associated with these enhancers. The structures of transcription factors as well as their DNA-binding domains were taken from the UniProtKB/Swiss-prot database. An HDOCK scoring function was used as a metric for assessing the possibility of interaction of the target gene transcription factor with associated enhancer sequence.Results. The results showed that the interactions of transcription factor NANOG with the DCC gene enhancer sequence and the interaction of transcription factor CEBPA with the SHH gene enhancer sequence predicted by molecular docking method are potentially possible. The iEnhancer-2L and ES-ARCNN algorithms predicted the enhancer sequence of the SHH gene as strong one. The enhancer sequence of the DCC gene was estimated as strong in the iEnhancer-2L algorithm and as weak in ES-ARCNN. Binding of the DCC gene enhancer sequence to the transcription factor NANOG at 1–206 bp and 686–885 bp sites is the most probable, binding of the SHH gene enhancer sequence to the transcription factor CEBPA at 1–500 bp (HDOCK limitation of 500 bp) is possible.Conclusion. In silico techniques applied in this study demonstrated satisfactory results of predicting the interaction of the transcription factor with the enhancer sequence. Limitations of the current techniques is the lack of consideration of specific transcription factor binding sites. This drawback can be eliminated by implementing an ab initio molecular dynamics simulations into the present pipeline.

Human Adipose Tissue Lysate-Based Hydrogel for Lasting Immunomodulation to Effectively Improve Spinal Cord Injury Repair.

The long-term inflammatory microenvironment is one of the main obstacles to inhibit acute spinal cord injury (SCI) repair. The natural adipose tissue-derived extracellular matrix hydrogel shows effective anti-inflammatory regulation because of its unique protein components. However, the rapid degradation rate and removal of functional proteins during the decellularization process impair the lasting anti-inflammation function of the adipose tissue-derived hydrogel. To address this problem, adipose tissue lysate provides an effective way for SCI repair due to its abundance of anti-inflammatory and nerve regeneration-related proteins. Thereby, human adipose tissue lysate-based hydrogel (HATLH) with an appropriate degradation rate is developed, which aims to in situ long-term recruit and induce anti-inflammatory M2 macrophages through sustainedly released proteins. HATLH can recruit and polarize M2 macrophages while inhibiting pro-inflammatory M1 macrophages regardless of human or mouse-originated. The axonal growth of neuronal cells also can be effectively improved by HATLH and HATLH-induced M2 macrophages. In vivo experiments reveal that HATLH promotes endogenous M2 macrophages infiltration in large numbers (3.5 × 105/100µL hydrogel) and maintains a long duration for over a month. In a mouse SCI model, HATLH significantly inhibits local inflammatory response, improves neuron and oligodendrocyte differentiation, enhances axonal growth and remyelination, as well as accelerates neurological function restoration.

Congenital Zika Virus Infection Impairs Corpus Callosum Development.

Congenital Zika syndrome (CZS) is a set of birth defects caused by Zika virus (ZIKV) infection during pregnancy. Microcephaly is its main feature, but other brain abnormalities are found in CZS patients, such as ventriculomegaly, brain calcifications, and dysgenesis of the corpus callosum. Many studies have focused on microcephaly, but it remains unknown how ZIKV infection leads to callosal malformation. To tackle this issue, we infected mouse embryos in utero with a Brazilian ZIKV isolate and found that they were born with a reduction in callosal area and density of callosal neurons. ZIKV infection also causes a density reduction in PH3+ cells, intermediate progenitor cells, and SATB2+ neurons. Moreover, axonal tracing revealed that callosal axons are reduced and misrouted. Also, ZIKV-infected cultures show a reduction in callosal axon length. GFAP labeling showed that an in utero infection compromises glial cells responsible for midline axon guidance. In sum, we showed that ZIKV infection impairs critical steps of corpus callosum formation by disrupting not only neurogenesis, but also axon guidance and growth across the midline.

Kamikihito reduces β-amyloid25-35-induced axon damage via neurotrophic factors.

The Japanese herbal medicine kamikihito (KKT) is widely used for insomnia, anorexia, anemia, and depression. Recently, the efficacy of KKT against Alzheimer's disease (AD) has been demonstrated in clinical and non-clinical studies. To address the mechanism underlying the effect of KKT on AD, we examined the effects of KKT in β-amyloid (Aβ)25-35-exposed primary cultured neurons. The effects of KKT on Aβ25-35-induced neurotoxicity were assessed by immunocytochemical assays and Sholl analysis of neurites, and the influence of KKT on neurotrophic factor (NF) gene expression was examined using RT-PCR analysis. As a result, Aβ25-35 exposure attenuated the arborization of neurites of single cultured hippocampal neurons, and KKT treatment for 3days ameliorated the Aβ25-35-induced impairment of tau-positive axon outgrowth. This ameliorative effect of KKT was largely abolished by the Trk inhibitor K252a, and expression of NFs, nerve growth factor (Ngf), brain-derived neurotrophic factor (Bdnf), neurotrophin-3 (NT-3) was significantly increased by KKT. These results indicate that KKT ameliorates axonal atrophy via NFs signaling, providing a mechanistic basis for treatment of AD with KKT.

Piezoelectrically induced augmented functionality of primary cultured hippocampal neurons on electrospun PVDF-(Na, K) NbO3 composite fibers

Owing to the risk of permanent disability of the associated tissue/organ, peripheral nerve injuries present one of the major concerns. As growth and regeneration of axons are sensitive towards electrical activity of substrate, polyvinylidene difluoride (PVDF)−10 vol% sodium potassium niobate (NKN) piezoelectric composite fibers were electrospun and corona poled at 17 kV. Electrospun PVDF-NKN fibrous scaffolds show remarkable increase in the average number of dendrites per neuron and mean soma area of primary cultured hippocampal neurons of embryonic mice which further increases after polarization (∼ 1.3 and 1.6 times of unpoled PVDF, respectively). The developed composite can be suggested as a potential candidate for peripheral nerve regeneration.

Biomimicking 3D soft scaffold combined with electrical stimulation to manipulate neural stem cell differentiation for guidance spinal cord injury repair

Spinal cord injury repair has remained a challenging issue in the medical field, and in recent years neural stem cell-based therapies have shown great potential. However, the survival and controlled differentiation of neural stem cells (NSCs) remain a problem, since the majority of materials can’t provide a suitable microenvironment for NSCs. In this work, we design and develop a conductive hydrogel mimicking spinal cord tissue as a biomimetic 3D biomaterial soft scaffold to improve the survival microenvironment and regulate the differentiation direction of NSCs. Significantly, the designed hydrogel matches the spinal cord tissue in aspects of mechanical properties, electrical conductivity, and pore structure. Moreover, the hydrogel possesses injectability, self-healing and haemostatic properties. Combining hydrogel with electrical stimulation (ES) induces loaded NSCs to be more inclined toward neuronal differentiation, axonal growth, and myelin regeneration, while reducing astrocyte development. This treatment strategy will ultimately achieve spinal cord injury repair and motor function restoration while avoiding glial scar deposition. This mimicking spinal cord 3D soft scaffolds combined with ES provide a promising therapeutic strategy for spinal cord injury repair.

Evaluating the toxic mechanism of 1,2-diacetylbenzene in neural cells/tissues: The favorable impact of silibinin

1,2-diacetylbenzene (1,2-DAB) is a neurotoxic component of aromatic solvents commonly used in industrial applications that induces neuropathological changes in animals. This study unraveled the toxic impact of 1,2-DAB in nerve tissues, explant cultures, and neuron-glial cultures, and explored whether herbal products can mitigate its toxicity. The effects of DAB on axonal transport were studied in retinal explant cultures grown in a micro-patterned dish. The mitochondrial movement in the axons was captured using time-lapse video recordings. The results showed that 1,2-DAB, but not 1,3-DAB inhibited axonal outgrowth and mitochondrial movement in a dose-dependent manner. The toxicity of 1,2-DAB was further studied in spinal cord tissues and cultures. 1,2-DAB selectively induced modifications of microtubules and neurofilaments in spinal cord tissues. 1,2-DAB also potently induced cell damage in both neuronal and glial cultures. Further, 1,2-DAB-induced cellular ATP depletion precedes cell damage in glial cells. Interestingly, treatment with the herbal products silibinin or silymarin effectively mitigated 1,2-DAB-induced toxicity in spinal cord tissues and neuronal/glial cultures. Collectively, the molecular toxicity of 1,2-DAB in neural tissues involves protein modification, ATP depletion, and axonal transport defects, leading to cell death. Silibinin and silymarin show promising neuroprotective effects against 2-DAB-induced toxicity.

A scaffold containing zinc oxide for Schwann cell-mediated axon growth

Objective. Schwann cells (SCs) transplanted in damaged nervous tissue promote axon growth, which may support the recovery of function lost after injury. However, SC transplant-mediated axon growth is often limited and lacks direction. Approach. We have developed a zinc oxide (ZnO) containing fibrous scaffold consisting of aligned fibers of polycaprolactone (PCL) with embedded ZnO nanoparticles as a biodegradable, bifunctional scaffold for promoting and guiding axon growth. This scaffold has bifunctional properties wherein zinc is released providing bioactivity and ZnO has well-known piezoelectric properties where piezoelectric materials generate electrical activity in response to minute deformations. In this study, SC growth, SC-mediated axon extension, and the presence of myelin basic protein (MBP), as an indicator of myelination, were evaluated on the scaffolds containing varying concentrations of ZnO in vitro. SCs and dorsal root ganglion (DRG) neurons were cultured, either alone or in co-culture, on the scaffolds. Main results. Findings demonstrated that scaffolds with 1 wt.% ZnO promoted the greatest SC growth and SC-mediated axon extension. The presence of brain-derived neurotrophic factor (BDNF) was also determined. BDNF increased in co-cultures for all scaffolds as compared to SCs or DRGs cultured alone on all scaffolds. For co-cultures, cells on scaffolds with low levels of ZnO (0.5 wt.% ZnO) had the highest amount of BDNF as compared to cells on higher ZnO-containing scaffolds (1 and 2 wt.%). MBP immunostaining was only detected in co-cultures on PCL control scaffolds (without ZnO). Significance. The results of this study demonstrate the potential of the ZnO-containing scaffolds for SC-mediated axon growth and its potential for use in nervous tissue repair.

Co-overexpression of OPN, IGF-1 and CNTF augment the therapeutic effect of DPSC on spinal cord injury

Background aimsSpinal cord injury (SCI) is one of the most complex and destructive diseases of the nervous system, which can lead to permanent loss of tactile perception. But existing treatment methods have limited effects. To establish a novel method that may be therapeutic in repairing the injured spinal cord, gene-modified dental pulp stem cells (DPSCs) were injected in situ. MethodsAdenovirus carrying osteopontin (OPN), Insulin-like growth factor 1 (IGF-1) and cailiary-derived neurotrophic factor (CNTF) (Ad-OIC) was constructed. After modified with Ad-OIC, supernatant of DPSC were co-cultured with HT-22 cells and the effect of DPSC-OIC on the HT-22 cells were evaluated via Cell Counting Kit-8 (CCK-8) assay, Real-Time polymerase chain reaction (PCR) analysis, laser confocal microscopy and fluorescence activating cell sorter (FACS). DPSC-OIC were injected in the lesion area of injured spinal cord and the survival time of transplanted cells were measured by bioluminescence imaging system. The recovery of the injured spinal cord was evaluated by behavioral score, radiological evaluation and immunopathological analysis. ResultsDPSC-OIC could enhance the proliferation and axon growth of HT-22 cells, and protect HT-22 cells from H2O2 induced apoptosis. The transplanted DPSC-Null or DPSC-OIC could survive for more than two weeks in local injection site. DPSC-OIC treatment could increase Basso-Mouse Scale (BMS) scores, improve Magnetic Resonance Imaging (MRI) manifestation and promote bladder function recovery. Less apoptotic neurons and more proliferative cells were found in the lesion area of DPSC-OIC treated spinal cord. Nestin+ cells and neural stem cell marker (Sox2) were both up-regulated after DPSC-OIC treatment. Additionally, inhibitory extracellular matrix proteoglycan Neural/Glial Antigen 2 (NG2) was down-regulated and axon growth promotive factor fibronectin was up-regulated after both DPSC-Null (DPSCs infected with Ad-Null) and DPSC-OIC treatments. ConclusionsDPSC-OIC could be a novel effective method for treating SCI.

Axons of cortical basket cells originating from dendrites develop higher local complexity than axons emerging from basket cell somata.

Neuronal differentiation is regulated by neuronal activity. Here, we analyzed dendritic and axonal growth of Basket cells (BCs) and non-Basket cells (non-BCs) using sparse transfection of channelrhodopsin-YFP and repetitive optogenetic stimulation in slice cultures of rat visual cortex. Neocortical interneurons often display axon-carrying dendrites (AcDs). We found that the AcDs of BCs and non-BCs were, on average, the most complex dendrites. Further, the AcD configuration had an influence on BC axonal development. Axons originating from an AcD formed denser arborizations with more terminal endings within the dendritic field of the parent cell. Intriguingly, this occurred already in unstimulated BCs, and complexity was not increased further by optogenetic stimulation. However, optogenetic stimulation exerted a growth-promoting effect on axons emerging from BC somata. The axons of non-BCs neither responded to the AcD configuration nor to the optogenetic stimulation. The results suggest that the formation of locally dense BC plexuses is regulated by spontaneous activity. Moreover, in the AcD configuration, the AcD and the axon it carries mutually support each other's growth.

Hybrid Electrically Conductive Hydrogels with Local Nerve Growth Factor Release Facilitate Peripheral Nerve Regeneration.

It is challenging to treat peripheral nerve injury (PNI) clinically. As the gold standard for peripheral nerve repair, autologous nerve grafting remains a critical limitation, including tissue availability, donor-site morbidity, immune rejection, etc. Recently, conductive hydrogels (CHs) have shown potential applications in neural bioengineering due to their good conductivity, biocompatibility, and low immunogenicity. Herein, a hybrid electrically conductive hydrogel composed of acrylic acid derivatives, gelatin, and heparin with sustained nerve growth factor (NGF) release property was developed. The rat sciatic nerve injury (SNI) model (10 mm long segment defect) was used to investigate the efficacy of these hydrogel conduits in facilitating peripheral nerve repair. The results showed that the hydrogel conduits had excellent conductivity, mechanical properties, and biocompatibility. In addition, NGF immobilized in the hydrogel conduits had good sustained release characteristics. Finally, functional recovery and electrophysiological evaluations, together with histological analysis, indicated that the hydrogel conduits immobilizing NGF had superior effects on motor recovery, axon growth, and remyelination, thereby significantly accelerating the repairing of the sciatic nerve. This study demonstrated that hybrid electrically conductive hydrogels with local NGF release could be effectively used for PNI repair.

Electroconductive and Immunomodulatory Natural Polymer‐Based Hydrogel Bandages Designed for Peripheral Nerve Regeneration

AbstractSuccessful regeneration of the peripheral nerve relies on the collaborative efforts of neural cells and immune cells. Conductive hydrogels have yielded promising results in supporting axonal growth; however, their inability to regulate the immune response and their poor biological integration with tissues hinder the repair of injured peripheral nerves. Herein, an adhesive conductive immunomodulatory nerve hydrogel bandage is developed for nerve regeneration. The nerve bandage hydrogel is prepared from the bioactive material extracellular matrix (ECM), oxidized polysaccharides, and poly(3,4‐ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) by self‐assembly and dynamic Schiff base cross‐linking. The drug indole‐3‐propionic acid (IPA) is loaded into nerve bandages and contributes to the rapid chemotaxis of neutrophils in the dorsal root ganglia and modulation of the immune system. In addition, the conductive hydrogel bandage exhibits close conformal contact with the injured nerve, forming a stable and tightly coupled electrical bridge with the electroresponsive neural tissue. In summary, the nerve bandage effectively promote nerve regeneration and enable both anatomical and functional recovery of neural tissue while preventing muscle atrophy. This work provides a new strategy for peripheral nerve regeneration and may have critical clinical applications in the future.