Electrical stimulation induces calcium-dependent release of NGF from cultured Schwann cells

Electrical Stimulation: How It Works and How to Apply It

Electrical stimulation is emerging as a perioperative strategy to improve peripheral nerve regeneration and enhance functional recovery. Despite decades of research, new insights into the complex multifaceted mechanisms of electrical stimulation continue to emerge, providing greater understanding of the neurophysiology of nerve regeneration. In this study, we summarize what is known about how electrical stimulation modulates the molecular cascades and cellular responses innate to nerve injury and repair, and the consequential effects on axonal growth and plasticity. Further, we discuss how electrical stimulation is delivered in preclinical and clinical studies and identify knowledge gaps that may provide opportunities for optimization.

Types of Short-Duration Electrical Stimulation-Induced Efficiency in the Axonal Regeneration and Recovery: Comparative in Vivo Study in Rat Model of Repaired Sciatic Nerve and its Tibial Branch after Transection Injury

The restoration of adequate function and sensation in nerves following an injury is often insufficient. Electrical stimulation (ES) applied during nerve repair can promote axon regeneration, which may enhance the likelihood of successful functional recovery. However, increasing operation time and complexity are associated with limited clinical use of ES. This study aims to better assess whether short-duration ES types (voltage mode vs. current mode) are able to produce enhanced regenerative activity following peripheral nerve repair in rat models. Wistar rats were randomly divided into 3 groups: no ES (control), 30-minute ES with a current pulse, and 30-minute ES with a voltage pulse. All groups underwent sciatic nerve transection and repair using a silicone tube to bridge the 6-mm gap between the stumps. In the 2 groups other than the control, ES was applied after the surgical repair. Outcomes were evaluated using electrophysiology, histology, and serial walking track analysis. Biweekly walking tracks test over 12 weeks revealed that subjects that underwent ES experienced more rapid functional improvement than subjects that underwent repair alone. Electrophysiological analysis of the newly intratubular sciatic nerve at week 12 revealed strong motor function recovery in rats that underwent 30-minute ES. Histologic analysis of the sciatic nerve and its tibial branch at 12 weeks demonstrated robust axon regrowth in all groups. Both types of short-duration ES applied during nerve repair can promote axon regrowth and enhance the chances of successful functional recovery.

Postoperatively Noninvasive Optogenetic Stimulation via Upconversion Nanoparticles Enhancing Sciatic Nerve Repair

The efficacy of electrical stimulation facilitating peripheral nerve regeneration is evidenced extensively, while the associated secondary damage resulting from repeated electrode invasion and indiscriminate stimulation is inevitable. Here, we present an optogenetics strategy that utilizes upconversion nanoparticles (UCNPs) to convert deeply penetrating near-infrared excitation into blue emission, which activates an adeno-associated virus-encoding ChR2 photoresponsive ion channel on cell membranes. The induced Ca2+ flux, similar to the ion flux in the electrical stimulation approach, efficiently regulates viability and proliferation, secretion of nerve growth factor, and neural function of RSC96 cells. Furthermore, deep near-infrared excitation is harnessed to stimulate autologous Schwann cells in situ via a UCNP-composited scaffold, which enhances nerve sprouting and myelination, consequently promoting functional recovery, electrophysiological restoration, and reinnervation of damaged nerves. This developed postoperatively noninvasive optogenetics strategy presents a novel, minimally traumatic, and enduring therapeutic stimulus to effectively promote peripheral nerve repair.

Perspectives on the Novel Multifunctional Nerve Guidance Conduits: From Specific Regenerative Procedures to Motor Function Rebuilding

Peripheral nerve injury potentially destroys the quality of life by inducing functional movement disorders and sensory capacity loss, which results in severe disability and substantial psychological, social, and financial burdens. Autologous nerve grafting has been commonly used as treatment in the clinic; however, its rare donor availability limits its application. A series of artificial nerve guidance conduits (NGCs) with advanced architectures are also proposed to promote injured peripheral nerve regeneration, which is a complicated process from axon sprouting to targeted muscle reinnervation. Therefore, exploring the interactions between sophisticated NGC complexes and versatile cells during each process including axon sprouting, Schwann cell dedifferentiation, nerve myelination, and muscle reinnervation is necessary. This review highlights the contribution of functional NGCs and the influence of microscale biomaterial architecture on biological processes of nerve repair. Progressive NGCs with chemical molecule induction, heterogenous topographical morphology, electroactive, anisotropic assembly microstructure, and self-powered electroactive and magnetic-sensitive NGCs are also collected, and they are expected to be pioneering features in future multifunctional and effective NGCs.

Mapping the hotspots and future trends of electrical stimulation for peripheral nerve injury: A bibliometric analysis from 2002 to 2023

Peripheral nerve injuries often result in severe personal and social burden, and even with surgical treatment, patients continue to have poor clinical outcomes. Over the past two decades, electrical stimulation has been shown to promote axonal regeneration and alleviate refractory neuropathic pain. The aim of this study was to analyse this field using a bibliometric approach. Literature was searched through Web of Science Core Collection (WOSCC) for the years 2002-2023. Literature analysis included: (1) Describing publication trends in the field. (2) Exploring collaborative network relationships. (3) Finding research advances and research hotspots in the field. (4) Summarizing research trends in the field. With the number of studies in this field still increasing, a total of 693 publications were included in the analysis. This field of research is interdisciplinary in nature. Research hotspots include peripheral nerve regeneration, the treatment of neuropathic pain, materials for nerve injury repair, and the restoration of sensory function in patients with peripheral nerve injury. Correspondingly, the development of nerve conduits and systems for peripheral nerve electrical stimulation, clinical trials of peripheral nerve electrical stimulation, and tactile recovery and movement for amputees have shown significant promise as future research trends in this field.

Oriented Graphene Oxide Scaffold Promotes Nerve Regeneration in vitro and in vivo

Background

Treating peripheral nerve injuries (PNI) with defects remains challenging in clinical practice. The commercial conduits have shown suboptimal nerve regeneration and functional recovery due to their basic tubular design without electroactive and oriented topographical cues.

Purpose

To develop a new scaffold with oriented microstructure and electroactive Graphene oxide (GO) and investigate its' therapeutic effect on nerve regeneration in vitro and in vivo.

Methods

This study employed a straightforward approach to co-spin PCL and GO, yielding an oriented hybrid nanofibrous scaffold known as the O-GO/PCL scaffold. The physical and chemical properties of nanofibrous scaffold were tested by scanning electron microscopy (SEM), transmission electron microscope (TEM), tensile test and so on. Primary Schwann cells (SCs) and dorsal root ganglia (DRG) were used to investigate the impact of the newly developed scaffolds on the biological behavior of neural cells in vitro. Transcriptome sequencing (mRNA-seq) was employed to probe the underlying mechanisms of the synergistic effect of electroactive GO and longitudinal topographic guidance on nerve regeneration. Furthermore, the developed O-GO/PCL scaffold was utilized to bridge a 10-mm sciatic nerve defect in rat, aiming to investigate its therapeutic potential for peripheral nerve regeneration in vivo.

Results and discussion

The SEM and TEM revealed that the newly developed O-GO/PCL scaffold showed longitudinally oriented microstructure and GO particles were homogenously and uniformly distributed inside the nanofibers. Primary SCs were utilized to assess the biocompatibility of the GO-based scaffold, revealing that negligible cytotoxicity when GO concentration does not exceed 0.5%. In vitro analysis of nerve regeneration demonstrated that axons in the O-GO/PCL group exhibited an average length of 1054.88 ± 161.32 µm, significant longer than those in the other groups (P < 0.05). Moreover, mRNA sequencing results suggested that the O-GO/PCL scaffold could enhance nerve regeneration by upregulating genes associated with neural regeneration, encompassing ion transport, axon guidance and cell-cell interactions. Most importantly, we employed the O-GO/PCL scaffold to repair a 10-mm sciatic nerve defect in rat, resulting in augmented nerve regeneration, myelination, and functional recovery.

Conclusion

The O-GO/PCL scaffold with oriented microstructure and electroactive GO represents a promising heral nerve reconstruction.

Advancements in autologous peripheral nerve transplantation care: a review of strategies and practices to facilitate recovery

Autologous peripheral nerve transplantation, a pioneering technique in nerve injury treatment, has demonstrated remarkable progress. We examine recent nursing strategies and methodologies tailored to various anatomical sites, highlighting their role in postoperative recovery enhancement. Encompassing brachial plexus, upper limb, and lower limb nerve transplantation care, this discussion underscores the importance of personalized rehabilitation plans, interdisciplinary collaboration, and innovative approaches like nerve electrical stimulation and nerve growth factor therapy. Moreover, the exploration extends to effective complication management and prevention strategies, encompassing infection control and pain management. Ultimately, the review concludes by emphasizing the advances achieved in autologous peripheral nerve transplantation care, showcasing the potential to optimize postoperative recovery through tailored and advanced practices.

A Perspective on Electrical Stimulation and Sympathetic Regeneration in Peripheral Nerve Injuries

Peripheral nerve injuries (PNIs) are common and devastating. The current standard of care relies on the slow and inefficient process of nerve regeneration after surgical intervention. Electrical stimulation (ES) has been shown to both experimentally and clinically result in improved regeneration and functional recovery after PNI for motor and sensory neurons; however, its effects on sympathetic regeneration have never been studied. Sympathetic neurons are responsible for a myriad of homeostatic processes that include, but are not limited to, blood pressure, immune response, sweating, and the structural integrity of the neuromuscular junction. Almost one quarter of the axons in the sciatic nerve are from sympathetic neurons, and their importance in bodily homeostasis and the pathogenesis of neuropathic pain should not be underestimated. Therefore, as ES continues to make its way into patient care, it is not only important to understand its impact on all neuron subtypes, but also to ensure that potential adverse effects are minimized. This piece gives an overview of the effects of ES in animals models and in humans while offering a perspective on the potential effects of ES on sympathetic axon regeneration.

Review of Piezoelectrical Materials Potentially Useful for Peripheral Nerve Repair

It has increasingly been recognized that electrical currents play a pivotal role in cell migration and tissue repair, in a process named "galvanotaxis". In this review, we summarize the current evidence supporting the potential benefits of electric stimulation (ES) in the physiology of peripheral nerve repair (PNR). Moreover, we discuss the potential of piezoelectric materials in this context. The use of these materials has deserved great attention, as the movement of the body or of the external environment can be used to power internally the electrical properties of devices used for providing ES or acting as sensory receptors in artificial skin (e-skin). The fact that organic materials sustain spontaneous degradation inside the body means their piezoelectric effect is limited in duration. In the case of PNR, this is not necessarily problematic, as ES is only required during the regeneration period. Arguably, piezoelectric materials have the potential to revolutionize PNR with new biomedical devices that range from scaffolds and nerve-guiding conduits to sensory or efferent components of e-skin. However, much remains to be learned regarding piezoelectric materials, their use in manufacturing of biomedical devices, and their sterilization process, to fine-tune their safe, effective, and predictable in vivo application.

Application of optogenetic glial cells to neuron-glial communication

Optogenetic techniques combine optics and genetics to enable cell-specific targeting and precise spatiotemporal control of excitable cells, and they are increasingly being employed. One of the most significant advantages of the optogenetic approach is that it allows for the modulation of nearby cells or circuits with millisecond precision, enabling researchers to gain a better understanding of the complex nervous system. Furthermore, optogenetic neuron activation permits the regulation of information processing in the brain, including synaptic activity and transmission, and also promotes nerve structure development. However, the optimal conditions remain unclear, and further research is required to identify the types of cells that can most effectively and precisely control nerve function. Recent studies have described optogenetic glial manipulation for coordinating the reciprocal communication between neurons and glia. Optogenetically stimulated glial cells can modulate information processing in the central nervous system and provide structural support for nerve fibers in the peripheral nervous system. These advances promote the effective use of optogenetics, although further experiments are needed. This review describes the critical role of glial cells in the nervous system and reviews the optogenetic applications of several types of glial cells, as well as their significance in neuron-glia interactions. Together, it briefly discusses the therapeutic potential and feasibility of optogenetics.

Clinical applications of electrical stimulation for peripheral nerve injury: a systematic review

Introduction

Peripheral nerve injuries are common neurologic injuries that are challenging to treat with current therapies. Electrical stimulation has been shown to accelerate reinnervation and enhance functional recovery. This study aims to review the literature on clinical application of electrical stimulation for peripheral nerve injury.

Methods

PubMed and Embase were sourced from 1995 to August 2022. Selection was based on predetermined inclusion/exclusion criteria. Eight hundred and thirty-five articles were screened with seven being included in this review.

Results

Two hundred and twenty-nine patients with peripheral nerve injuries were represented. Six of the studies were randomized controlled trials. A variety of nerve injuries were represented with all being in the upper extremity and supraclavicular region. Electrical stimulation protocols and evaluation varied. Electrodes were implanted in four studies with one also implanting the stimulator. Length of stimulation per session was either 20 mins or 1 h. Median stimulation frequency was 20 Hz. Stimulation intensity varied from 3 to 30V; pulse width ranged from 0.1 to 1.007 ms. Three protocols were conducted immediately after surgery. Patients were followed for an average of 13.5 months and were evaluated using electrophysiology and combinations of motor, sensory, and functional criteria.

Discussion

Patients who received electrical stimulation consistently demonstrated better recovery compared to their respective controls. Electrical stimulation for peripheral nerve injury is a novel treatment that has not been well-studied in humans. Our review illustrates the potential benefit in implementing this approach into everyday practice. Future research should aim to optimize protocol for clinical use.

Electrical stimulation accelerates Wallerian degeneration and promotes nerve regeneration after sciatic nerve injury

Following peripheral nerve injury (PNI), Wallerian degeneration (WD) in the distal stump can generate a microenvironment favorable for nerve regeneration. Brief low-frequency electrical stimulation (ES) is an effective treatment for PNI, but the mechanism underlying its effect on WD remains unclear. Therefore, we hypothesized that ES could enhance nerve regeneration by accelerating WD. To verify this hypothesis, we used a rat model of sciatic nerve transection and provided ES at the distal stump of the injured nerve. The injured nerve was then evaluated after 1, 4, 7, 14 and 21 days post injury (dpi). The results showed that ES significantly promoted the degeneration and clearance of axons and myelin, and the dedifferentiation of Schwann cells. It upregulated the expression of BDNF and NGF and increased the number of monocytes and macrophages. Through transcriptome sequencing, we systematically investigated the effect of ES on the molecular processes involved in WD at 4 dpi. Evaluation of nerves bridged using silicone tubing after transection showed that ES accelerated early axonal and vascular regeneration while delaying gastrocnemius atrophy. These results demonstrate that ES promotes nerve regeneration by accelerating WD and upregulating the expression of neurotrophic factors.

Basic mechanisms of peripheral nerve injury and treatment via electrical stimulation

Previous studies on the mechanisms of peripheral nerve injury (PNI) have mainly focused on the pathophysiological changes within a single injury site. However, recent studies have indicated that within the central nervous system, PNI can lead to changes in both injury sites and target organs at the cellular and molecular levels. Therefore, the basic mechanisms of PNI have not been comprehensively understood. Although electrical stimulation was found to promote axonal regeneration and functional rehabilitation after PNI, as well as to alleviate neuropathic pain, the specific mechanisms of successful PNI treatment are unclear. We summarize and discuss the basic mechanisms of PNI and of treatment via electrical stimulation. After PNI, activity in the central nervous system (spinal cord) is altered, which can limit regeneration of the damaged nerve. For example, cell apoptosis and synaptic stripping in the anterior horn of the spinal cord can reduce the speed of nerve regeneration. The pathological changes in the posterior horn of the spinal cord can modulate sensory abnormalities after PNI. This can be observed in cases of ectopic discharge of the dorsal root ganglion leading to increased pain signal transmission. The injured site of the peripheral nerve is also an important factor affecting post-PNI repair. After PNI, the proximal end of the injured site sends out axial buds to innervate both the skin and muscle at the injury site. A slow speed of axon regeneration leads to low nerve regeneration. Therefore, it can take a long time for the proximal nerve to reinnervate the skin and muscle at the injured site. From the perspective of target organs, long-term denervation can cause atrophy of the corresponding skeletal muscle, which leads to abnormal sensory perception and hyperalgesia, and finally, the loss of target organ function. The mechanisms underlying the use of electrical stimulation to treat PNI include the inhibition of synaptic stripping, addressing the excessive excitability of the dorsal root ganglion, alleviating neuropathic pain, improving neurological function, and accelerating nerve regeneration. Electrical stimulation of target organs can reduce the atrophy of denervated skeletal muscle and promote the recovery of sensory function. Findings from the included studies confirm that after PNI, a series of physiological and pathological changes occur in the spinal cord, injury site, and target organs, leading to dysfunction. Electrical stimulation may address the pathophysiological changes mentioned above, thus promoting nerve regeneration and ameliorating dysfunction.

Neuronal activity-dependent ATP enhances the pro-growth effect of repair Schwann cell extracellular vesicles by increasing their miRNA-21 loading

Functional recovery after peripheral nerve injuries is critically dependent on axonal regeneration. Several autonomous and non-cell autonomous processes regulate axonal regeneration, including the activation of a growth-associated transcriptional program in neurons and the reprogramming of differentiated Schwann cells (dSCs) into repair SCs (rSCs), triggering the secretion of neurotrophic factors and the activation of an inflammatory response. Repair Schwann cells also release pro-regenerative extracellular vesicles (EVs), but is still unknown whether EV secretion is regulated non-cell autonomously by the regenerating neuron. Interestingly, it has been described that nerve activity enhances axonal regeneration by increasing the secretion of neurotrophic factors by rSC, but whether this activity modulates pro-regenerative EV secretion by rSC has not yet been explored. Here, we demonstrate that neuronal activity enhances the release of rSC-derived EVs and their transfer to neurons. This effect is mediated by activation of P2Y receptors in SCs after activity-dependent ATP release from sensory neurons. Importantly, activation of P2Y in rSCs also increases the amount of miRNA-21 present in rSC-EVs. Taken together, our results demonstrate that neuron to glia communication by ATP-P2Y signaling regulates the content of SC-derived EVs and their transfer to axons, modulating axonal elongation in a non-cell autonomous manner.

Non-Pharmacological Therapeutic Options for the Treatment of Alzheimer’s Disease

Alzheimer’s disease is a growing global crisis in need of urgent diagnostic and therapeutic strategies. The current treatment strategy mostly involves immunotherapeutic medications that have had little success in halting disease progress. Hypotheses for pathogenesis and development of AD have been expanded to implicate both organ systems as well as cellular reactions. Non-pharmacologic interventions ranging from minimally to deeply invasive have attempted to address these diverse contributors to AD. In this review, we aim to delineate mechanisms underlying such interventions while attempting to provide explanatory links between the observed differences in disease states and postulated metabolic or structural mechanisms of change. The techniques discussed are not an exhaustive list of non-pharmacological interventions against AD but provide a foundation to facilitate a deeper understanding of the area of study.

Electroceuticals for peripheral nerve regeneration

Electroceuticals provide promising opportunities for peripheral nerve regeneration, in terms of modulating the extensive endogenous tissue repair mechanisms between neural cell body, axons and target muscles. However, great challenges remain to deliver effective and controllable electroceuticals via bioelectronic implantable device. In this review, the modern fabrication methods of bioelectronic conduit for bridging critical nerve gaps after nerve injury are summarized, with regard to conductive materials and core manufacturing process. In addition, to deliver versatile electrical stimulation, the integration of implantable bioelectronic device is discussed, including wireless energy harvesters, actuators and sensors. Moreover, a comprehensive insight of beneficial mechanisms is presented, including up-to-date in vitro, in vivo and clinical evidence. By integrating conductive biomaterials, 3D engineering manufacturing process and bioelectronic platform to deliver versatile electroceuticals, the modern biofabrication enables comprehensive biomimetic therapies for neural tissue engineering and regeneration in the new era.

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.

Conductive polypyrrole-coated electrospun chitosan nanoparticles/poly(D,L-lactide) fibrous mat: influence of drug delivery and Schwann cells proliferation

For nerve tissue engineering (NTE), scaffolds with the ability to release drugs under control and support the rapid proliferation of cells are very important for the repair of nerve defects. This study aimed to fabricate a conductive drug-loaded fiber mat by electrospinning and assess its potential as a scaffold for Schwann cells proliferation. The conductive polypyrrole (PPy) was coated on an electrospun poly (D, L-lactide) (PLA) fibrous mat, which was simultaneously embedded with protein-loaded chitosan nanoparticles and ibuprofen as a model small molecule drug. The fibrous mat shows suitable conductivity, mechanical properties, and hydrophilicity for NTE. For drug release and degradation studies, the fibrous mat can achieve sustained release of bovine serum albumin (BSA) and ibuprofen, and the PPy coating can increase the surface wettability and conductivity while slowing down the degradation of the fibrous mat. The application of electrical stimulation (ES) to the fibrous mat can accelerate the release of ibuprofen, but there was no significant effect on the release rate of the protein. The fibrous mat showed no cytotoxicityin vitro, and Schwann cells (SCs) can adhere, grow, and proliferate well on mats. At the 120th hour of culturein vitro, the relative growth rate of SCs on the conductive drug-loaded fibrous mat reached 198.22 ± 2.34%, which was an increase of 37.93% compared to the SCs on the drug-loaded fibrous mat with ES. The density and elongation of SCs on the conductive drug-loaded fibrous mat were greater than those on the PLA fibrous mat, indicating that the conductive polypyrrole-coated electrospun chitosan nanoparticles/PLA fibrous mat has good potential for application in nerve regeneration.

New Insights and Emerging Therapeutic Approaches in Prostate Cancer

Prostate cancer is the second most frequently diagnosed cancer in men and several therapeutic approaches are currently available for patient's care. Although the androgen receptor status represents a good predictor of response to androgen deprivation therapy, prostate cancer frequently becomes resistant to this approach and spreads. The molecular mechanisms that contribute to progression and drug-resistance of this cancer remain still debated. However, few therapeutic options are available for patient's management, at this stage. Recent years have seen a great expansion of the studies concerning the role of stromal-epithelial interactions and tumor microenvironment in prostate cancer progression. The findings so far collected have provided new insights into diagnostic and clinical management of prostate cancer patients. Further, new fascinating aspects concerning the intersection of the androgen receptor with survival factors as well as calcium channels have been reported in cultured prostate cancer cells and mouse models. The results of these researches have opened the way for a better understanding of the basic mechanisms involved in prostate cancer invasion and drug-resistance. They have also significantly expanded the list of new biomarkers and druggable targets in prostate cancer. The primary aim of this manuscript is to provide an update of these issues, together with their translational aspects. Exploiting the power of novel promising therapeutics would increase the success rate in the diagnostic path and clinical management of patients with advanced disease.

An electroceutical approach enhances myelination via upregulation of lipid biosynthesis in the dorsal root ganglion

As the myelin sheath is crucial for neuronal saltatory conduction, loss of myelin in the peripheral nervous system (PNS) leads to demyelinating neuropathies causing muscular atrophy, numbness, foot deformities and paralysis. Unfortunately, few interventions are available for such neuropathies, because previous pharmaceuticals have shown severe side effects and failed in clinical trials. Therefore, exploring new strategies to enhance PNS myelination is critical to provide solution for such intractable diseases. This study aimed to investigate the effectiveness of electrical stimulation (ES) to enhance myelination in the mouse dorsal root ganglion (DRG) - an ex vivo model of the PNS. Mouse embryonic DRGs were extracted at E13 and seeded onto Matrigel-coated surfaces. After sufficient growth and differentiation, screening was carried out by applying ES in the 1-100 Hz range at the beginning of the myelination process. DRG myelination was evaluated via immunostaining at the intermediate (19 DIV) and mature (30 DIV) stages. Further biochemical analyses were carried out by utilizing RNA sequencing, qPCR and biochemical assays at both intermediate and mature myelination stages. Imaging of DRG myelin lipids was carried out via time-of-flight secondary ion mass spectrometry (ToF-SIMS). With screening ES conditions, optimal condition was identified at 20 Hz, which enhanced the percentage of myelinated neurons and average myelin length not only at intermediate (129% and 61%) but also at mature (72% and 17%) myelination stages. Further biochemical analyses elucidated that ES promoted lipid biosynthesis in the DRG. ToF-SIMS imaging showed higher abundance of the structural lipids, cholesterol and sphingomyelin, in the myelin membrane. Therefore, promotion of lipid biosynthesis and higher abundance of myelin lipids led to ES-mediated myelination enhancement. Given that myelin lipid deficiency is culpable for most demyelinating PNS neuropathies, the results might pave a new way to treat such diseases via electroceuticals.

Electrotherapy for urethral modulation: Are extracellular matrix molecules and growth factors potential targets?

AIMS

To evaluate the expression of genes and proteins involved in the urethral components: vessels, nerves, and extracellular matrix, in female rats after trauma by vaginal distension (VD) and after electrical stimulation therapy (electrotherapy).

METHODS

We analyzed the urethras of three groups of 18 female rats 30 days posttrauma by VD: control (no interventions); trauma (animals that had VD); and electrotherapy group (those that had VD and were treated with electrical stimulation). We compared the expression of vascular endothelial growth factor (VEGF), nerve growth factor (NGF), collagen types I and III (COL1a1 and COL3a1), and lysyl-oxidase like 1 (LOXL1) among the groups. Real-time reverse transcription-polymerase chain reaction, Western blot, and immunohistochemistry were used for molecule quantification. We used the Kruskal-Wallis test and analysis of variance for statistical analyses with p < 0.05 for significance.

RESULTS

The COL1a1 gene expression was higher in the electrotherapy group than the trauma group (p = 0.036). COL3a1, VEGF, NGF, LOXL1 messenger RNA (mRNA) expression did not differ among the groups (p ≥ 0.05). COL1a1, COL3a1, VEGF, NGF, LOXL1 protein levels did not significantly differ among the groups (p ≥ 0.05) in Western blot analysis or immunohistochemistry assays.

CONCLUSIONS

Electrotherapy caused a long-term increase in the COL1a1 mRNA level but did not change COL1a1 protein expression or VEGF, NGF, COL3a1, and LOXL1 genes and proteins in the urethras of rats after trauma by VD.

Comparison of the Efficacy of Optogenetic Stimulation of Glia versus Neurons in Myelination

Increasing evidence demonstrates that optogenetics contributes to the regulation of brain behavior, cognition, and physiology, particularly during myelination, potentially allowing for the bidirectional modulation of specific cell lines with spatiotemporal accuracy. However, the type of cell to be targeted, namely, glia vs neurons, and the degree to which optogenetically induced cell activity can regulate myelination during the development of the peripheral nervous system (PNS) are still underexplored. Herein, we report the comparison of optogenetic stimulation (OS) of Schwann cells (SCs) and motor neurons (MNs) for activation of myelination in the PNS. Capitalizing on these optogenetic tools, we confirmed that the formation of the myelin sheath was initially promoted more by OS of calcium translocating channelrhodopsin (CatCh)-transfected SCs than by OS of transfected MNs at 7 days in vitro (DIV). Additionally, the level of myelination was substantially enhanced even until 14 DIV. Surprisingly, after OS of SCs, > 91.1% ± 5.9% of cells expressed myelin basic protein, while that of MNs was 67.8% ± 6.1%. The potent effect of OS of SCs was revealed by the increased thickness of the myelin sheath at 14 DIV. Thus, the OS of SCs could highly accelerate myelination, while the OS of MNs only somewhat promoted myelination, indicating a clear direction for the optogenetic application of unique cell types for initiating and promoting myelination. Together, our findings support the importance of precise cell type selection for use in optogenetics, which in turn can be broadly applied to overcome the limitations of optogenetics after injury.

Effect of Intraoperative Electrical Stimulation on Recovery after Rat Sciatic Nerve Isograft Repair

Peripheral nerve injuries, associated with significant morbidity, can benefit from electrical stimulation (ES), as demonstrated in animal studies through improved axonal growth. This study combined the clinical gold standard of isograft repair in a rat model of sciatic nerve injury to evaluate the effects of intraoperative ES on functional tests and histology. Forty rats underwent a surgically induced gap injury to the right sciatic nerve and subsequent repair with an isograft. Half of these rats were randomly selected to receive 10 min of intraoperative ES. Functional testing, including response time to a heat stimulus and motor functional tests, were conducted. Histology of the sciatic nerves and gastrocnemius muscles were analyzed after 6 and 12 weeks of recovery. Rats that underwent ES treatment showed incremental improvements in motor function between weeks 2 and 12, with a significantly higher push-off response than the no-ES controls after 6 weeks. Although no differences were detected between groups in the sensory testing, significant improvements over time were noted in the ES group. Histology parameters, sciatic nerve measures, and gastrocnemius muscle weights demonstrated nerve recovery over time for both the ES and no-ES control groups. Although ES promoted improvements in motor function comparable to that in previous studies, the benefits of intraoperative ES were not detectable in other metrics of this rat model of peripheral nerve injury. Future work is needed to optimize sensory testing in the rodent injury model and compare electrical activity of collagen scaffolds to native tissue to detect differences.

Schwann Cell Role in Selectivity of Nerve Regeneration

Peripheral nerve injuries result in the loss of the motor, sensory and autonomic functions of the denervated segments of the body. Neurons can regenerate after peripheral axotomy, but inaccuracy in reinnervation causes a permanent loss of function that impairs complete recovery. Thus, understanding how regenerating axons respond to their environment and direct their growth is essential to improve the functional outcome of patients with nerve lesions. Schwann cells (SCs) play a crucial role in the regeneration process, but little is known about their contribution to specific reinnervation. Here, we review the mechanisms by which SCs can differentially influence the regeneration of motor and sensory axons. Mature SCs express modality-specific phenotypes that have been associated with the promotion of selective regeneration. These include molecular markers, such as L2/HNK-1 carbohydrate, which is differentially expressed in motor and sensory SCs, or the neurotrophic profile after denervation, which differs remarkably between SC modalities. Other important factors include several molecules implicated in axon-SC interaction. This cell–cell communication through adhesion (e.g., polysialic acid) and inhibitory molecules (e.g., MAG) contributes to guiding growing axons to their targets. As many of these factors can be modulated, further research will allow the design of new strategies to improve functional recovery after peripheral nerve injuries.

CNT/Sericin Conductive Nerve Guidance Conduit Promotes Functional Recovery of Transected Peripheral Nerve Injury in a Rat Model

Peripheral nerve injury usually leads to poor outcomes such as painful neuropathies and disabilities. Autogenous nerve grafting is the current gold standard; however, the limited source of a donor nerve remains a problem. Numerous tissue engineering nerve guidance conduits have been developed as substitutes for autografts. However, a few conduits can achieve the reparative effect equivalent to autografts. Here, we report for the development and application of a carbon nanotube (CNT)/sericin nerve conduit with electrical conductivity and suitable mechanical properties for nerve repair. This CNT/sericin conduit possesses favorable properties including biocompatibility, biodegradability, porous microarchitecture, and suitable swelling property. We thus applied this conduit for bridging a 10 mm gap defect of a transected sciatic nerve combined with electrical stimulation (ES) in a rat injury model. By the end of 12 weeks, we observed that the CNT/sericin conduit combined with electrical stimulation could effectively promote both structural repair and functional recovery comparable to those of the autografts, evidenced by the morphological and histological analyses, electrophysiological responses, functional studies, and target muscle reinnervation evaluations. These findings suggest that this electric conductive CNT/sericin conduit combined with electrical stimulation may have the potential to serve as a new alternative for the repair of transected peripheral nerves.

Migrating Schwann cells direct axon regeneration within the peripheral nerve bridge

Schwann cells within the peripheral nervous system possess a remarkable regenerative potential. Current research shows that peripheral nerve-associated Schwann cells possess the capacity to promote repair of multiple tissues including peripheral nerve gap bridging, skin wound healing, digit tip repair as well as tooth regeneration. One of the key features of the specialized repair Schwann cells is that they become highly motile. They not only migrate into the area of damaged tissue and become a key component of regenerating tissue but also secrete signaling molecules to attract macrophages, support neuronal survival, promote axonal regrowth, activate local mesenchymal stem cells, and interact with other cell types. Currently, the importance of migratory Schwann cells in tissue regeneration is most evident in the case of a peripheral nerve transection injury. Following nerve transection, Schwann cells from both proximal and distal nerve stumps migrate into the nerve bridge and form Schwann cell cords to guide axon regeneration. The formation of Schwann cell cords in the nerve bridge is key to successful peripheral nerve repair following transection injury. In this review, we first examine nerve bridge formation and the behavior of Schwann cell migration in the nerve bridge, and then discuss how migrating Schwann cells direct regenerating axons into the distal nerve. We also review the current understanding of signals that could activate Schwann cell migration and signals that Schwann cells utilize to direct axon regeneration. Understanding the molecular mechanism of Schwann cell migration could potentially offer new therapeutic strategies for peripheral nerve repair.

Hormesis and Ginseng: Ginseng Mixtures and Individual Constituents Commonly Display Hormesis Dose Responses, Especially for Neuroprotective Effects

This paper demonstrates that ginseng mixtures and individual ginseng chemical constituents commonly induce hormetic dose responses in numerous biological models for endpoints of biomedical and clinical relevance, typically providing a mechanistic framework. The principal focus of ginseng hormesis-related research has been directed toward enhancing neuroprotection against conditions such as Alzheimer's and Parkinson's Diseases, stroke damage, as well as enhancing spinal cord and peripheral neuronal damage repair and reducing pain. Ginseng was also shown to reduce symptoms of diabetes, prevent cardiovascular system damage, protect the kidney from toxicities due to immune suppressant drugs, and prevent corneal damage, amongst other examples. These findings complement similar hormetic-based chemoprotective reports for other widely used dietary-type supplements such as curcumin, ginkgo biloba, and green tea. These findings, which provide further support for the generality of the hormetic dose response in the biomedical literature, have potentially important public health and clinical implications.

Fabrication of a Highly Conductive Silk Knitted Composite Scaffold by Two-Step Electrostatic Self-Assembly for Potential Peripheral Nerve Regeneration

Peripheral nerve injury is a common serious disease, and the electrical conductivity of nerve scaffolds is of special significance for nerve regeneration. Here, a highly conductive silk knitted composite scaffold was prepared by utilizing hydrogen bonding and electrostatic adsorption between silk amino, graphene (RGO), and polyaniline (PANI). Compared to traditional in situ polymerization of aniline (ANI), the surface of the RGO/PANI/silk conductive knitted scaffold prepared by two-step electrostatic self-assembly had more uniform PANI particles and lower resistance; when GO was 1 g/L and ANI was 0.4, 0.6, or 0.8 mol/L, the RGO/PANI/silk scaffold had better electrical properties when the conductivity was between 0.62 × 10^-3 and 1.72 × 10^-3 S/cm. The scaffolds had good conductive stability under different physical stresses and good mechanical properties, wherein ultimately the strength, elongation at break, and Young's modulus ranges were 28.07-34.97 MPa, 105.91-109.85%, and 10.2-12.48 MPa, respectively, and so they provided good support. Conductive scaffolds had ordered loops, fiber structure, and large pore sizes between 40 and 70 μm. In summary, RGO/PANI/silk scaffold with good conductivity, pore size distribution, mechanical properties, thermal properties had potential applications in the field of peripheral nerve regeneration.

Bionanotube/Poly(3,4-ethylenedioxythiophene) Nanohybrid as an Electrode for the Neural Interface and Dopamine Sensor

Poly(3,4-ethylene dioxythiophene) (PEDOT) is a promising conductive material widely used for interfacing with tissues in biomedical fields because of its unique properties. However, obtaining high charge injection capability and high stability remains challenging. In this study, pristine carbon nanotubes (CNTs) modified by dopamine (DA) self-polymerization on the surface polydopamine (PDA@CNTs) were utilized as dopants of PEDOT to prepare hybrid films through electrochemical deposition on the indium tin oxide (ITO) electrode. The PDA@CNTs-PEDOT film of the nanotube network topography exhibited excellent stability and strong adhesion to the ITO substrate compared with PEDOT and PEDOT/ p-toulene sulfonate. The PDA@CNTs-PEDOT-coated ITO electrodes demonstrated lower impedance and enhanced charge storage capacity than the bare ITO. When applying exogenous electrical stimulation (ES), robust long neurites sprouted from the dorsal root ganglion (DRG) neurons cultured on the PDA@CNTs-PEDOT film. Moreover, ES promoted Schwann cell migration out from the DRG spheres and enhanced myelination. The PDA@CNTs-PEDOT film served as an excellent electrochemical sensor for the detection of DA in the presence of biomolecule interferences. Results would shed light into the advancement of conducting nanohybrids for applications in the multifunctional bioelectrode in neuroscience.

Enhanced Neurite Outgrowth on a Multiblock Conductive Nerve Scaffold with Self-Powered Electrical Stimulation

Electrical stimulation (ES) is widely applied to promote nerve regeneration. Currently, metal needles are used to exert external ES, which may cause pain and risk of infection. In this work, a multiblock conductive nerve scaffold with self-powered ES by the consumption of glucose and oxygen is prepared. The conductive substrate is prepared by in situ polymerization of polypyrrole (PPy) on the nanofibers of bacterial cellulose (BC). Platinum nanoparticles are electrodeposited on the anode side for glucose oxidation, while nitrogen-doped carbon nanotubes (N-CNTs) are loaded on the cathode side for oxygen reduction. The scaffold shows good mechanical property, flexibility and conductivity. The scaffold can form a potential difference of above 300 mV between the anode and the cathode in PBS with 5 × 10^-3 m glucose. Dorsal root ganglions cultured on the Pt-BC/PPy-N-CNTs scaffold are 55% longer in mean neurite length than those cultured on BC/PPy. In addition, in vivo study indicates that the Pt-BC/PPy-N-CNTs scaffold promotes nerve regeneration compared with the BC/PPy group. This paper presents a novel design of a nerve scaffold with self-powered ES. In the future, it can be combined with other features to promote nerve regeneration.

Beyond Trophic Factors: Exploiting the Intrinsic Regenerative Properties of Adult Neurons

Injuries and diseases of the peripheral nervous system (PNS) are common but frequently irreversible. It is often but mistakenly assumed that peripheral neuron regeneration is robust without a need to be improved or supported. However, axonal lesions, especially those involving proximal nerves rarely recover fully and injuries generally are complicated by slow and incomplete regeneration. Strategies to enhance the intrinsic growth properties of reluctant adult neurons offer an alternative approach to consider during regeneration. Since axons rarely regrow without an intimately partnered Schwann cell (SC), approaches to enhance SC plasticity carry along benefits to their axon partners. Direct targeting of molecules that inhibit growth cone plasticity can inform important regenerative strategies. A newer approach, a focus of our laboratory, exploits tumor suppressor molecules that normally dampen unconstrained growth. However several are also prominently expressed in stable adult neurons. During regeneration their ongoing expression “brakes” growth, whereas their inhibition and knockdown may enhance regrowth. Examples have included phosphatase and tensin homolog deleted on chromosome ten (PTEN), a tumor suppressor that inhibits PI3K/pAkt signaling, Rb1, the protein involved in retinoblastoma development, and adenomatous polyposis coli (APC), a tumor suppressor that inhibits β-Catenin transcriptional signaling and its translocation to the nucleus. The identification of several new targets to manipulate the plasticity of regenerating adult peripheral neurons is exciting. How they fit with canonical regeneration strategies and their feasibility require additional work. Newer forms of nonviral siRNA delivery may be approaches for molecular manipulation to improve regeneration.

Electrical stimulation enhances neuronal cell activity mediated by Schwann cell derived exosomes

Electrical stimulation (ES) therapy has good effects in patients with nervous system injury-related diseases. ES promotes nerve cell regeneration and stimulates Schwann cells to express neurotrophic factors. The incidence of stress urinary incontinence (SUI) among elderly people is increasing. Some studies suggest that damage to the pudendal nerve is closely related to the pathogenesis of SUI. It has also been found that pelvic ES can reduce SUI symptoms in a rat model of SUI caused by pudendal nerve injury. Clinically, pelvic floor electrical stimulation is effective in patients with mild to moderate SUI. These studies indicate that ES may ameliorate damage to the pudendal nerve and thus achieve the goal of SUI treatment, although the mechanism of action of this treatment remains unclear. Therefore, the purpose of the present study was to clarify the relationships among ES, neural cells and Schwann cells at the cellular level. We applied ES to nerve cells at 100 mV/mm or 200 mV/mm for 0, 0.5, 1, or 2 h to investigate changes in nerve cell activity. We then co-cultured the nerve cells with Schwann cells to explore the influence of single-culture and co-culture conditions on the nerve cells. Compared to non-ES, ES of the nerve cells increased their activity. Compared to those in single culture, co-cultured nerve cells exhibited an additional increase in activity. We also found that Schwann cell derived exosomes could promote the activity of nerve cells, with glutamate and calcium ions playing a potential role in this process. These results suggest that the mutual regulation of neural cells and Schwann cells plays an important role in the process by which ES ameliorates neurological function, which may provide a basis for subsequent studies.

Lycium barbarum polysaccharide encapsulated Poly lactic-co-glycolic acid Nanofibers: cost effective herbal medicine for potential application in peripheral nerve tissue engineering

Nerve regeneration is a serious clinical challenge following peripheral nerve injury. Lycium barbarum polysaccharide (LBP) is the major component of wolfberry extract, which has been shown to be neuroprotective and promising in nerve recovery in many studies. Electrospun nanofibers, especially core-shell structured nanofibers being capable of serving as both drug delivery system and tissue engineering scaffolds, are well known to be suitable scaffolds for regeneration of peripheral nerve applications. In this study, LBP was incorporated into core-shell structured nanofibrous scaffolds via coaxial electrospinning. Alamar blue assays were performed to investigate the proliferation of both PC12 and Schwann cells cultured on the scaffolds. The neuronal differentiation of PC12 cells was evaluated by NF200 expression with immunostaining and morphology changes observed by SEM. The results indicated that the released LBP dramatically enhanced both proliferation and neuronal differentiation of PC12 cells induced by NGF. Additionally, the promotion of Schwann cells myelination and neurite outgrowth of DRG neurons were also observed on LBP loaded scaffolds by LSCM with immunostaining. In summary, LBP, as a drug with neuroprotection, encapsulated into electrospun nanofibers could be a potential candidate as tissue engineered scaffold for peripheral nerve regeneration.

Tetramethylpyrazine Protects Neurons from Oxygen-Glucose Deprivation-Induced Death

Background

To explore the theoretical basis for protecting the brain from ischemic stroke with tetramethylpyrazine, we studied whether and how tetramethylpyrazine could protect neurons against the oxygen-glucose deprivation (OGD)-induced death and whether transient receptor potential cation channel, subfamily C, member 6 (TRPC6) was involved.

Material/Methods

Primary rat cortical neurons were cultured and an OGD model was established in the presence or absence of tetramethylpyrazine. Neuronal death was assessed by measuring the uptake of membrane-impermeable PI. Western blot analysis was used to determine the protein expressions of TRPC6 and caspase-3. The involvement of TRPC6 was tested via RNAi against TRPC6.

Results

OGD-induced neuronal death was decreased by tetramethylpyrazine in a concentration-dependent manner. The expression of TRPC6 protein was decreased by OGD. Furthermore, downregulating TRPC6 by RNA interfering mimicked the effect of OGD in neuronal death. Tetramethylpyrazine attenuated OGD-induced TRPC6 downregulation in a tetramethylpyrazine concentration-dependent manner. However, these effects of tetramethylpyrazine on attenuating OGD-induced neuronal death were abolished by TRPC6 RNAi.

Conclusions

Tetramethylpyrazine can protect neurons from oxygen-glucose deprivation-induced death, possibly via TRPC6.

Ultrasound-mediated piezoelectric differentiation of neuron-like PC12 cells on PVDF membranes

Electrical and/or electromechanical stimulation has been shown to play a significant role in regenerating various functionalities in soft tissues, such as tendons, muscles, and nerves. In this work, we investigate the piezoelectric polymer polyvinylidene fluoride (PVDF) as a potential substrate for wireless neuronal differentiation. Piezoelectric PVDF enables generation of electrical charges on its surface upon acoustic stimulation, inducing neuritogenesis of PC12 cells. We demonstrate that the effect of pure piezoelectric stimulation on neurite generation in PC12 cells is comparable to the ones induced by neuronal growth factor (NGF). In inhibitor experiments, our results indicate that dynamic stimulation of PVDF by ultrasonic (US) waves activates calcium channels, thus inducing the generation of neurites via a cyclic adenosine monophosphate (cAMP)-dependent pathway. This mechanism is independent from the well-studied NGF induced mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK) pathway. The use of US, in combination with piezoelectric polymers, is advantageous since focused power transmission can occur deep into biological tissues, which holds great promise for the development of non-invasive neuroregenerative devices.

Validation of electrical stimulation models: intracellular calcium measurement in three-dimensional scaffolds

Peripheral nerve injury can be disabling. Regeneration is limited by the rate of axonal extension, and proximal injury to peripheral nerves can take over a year to reach target organs. Electrical stimulation (ES) has been shown to increase the rate of neurite growth, though the mechanism is not yet well understood. In our prior manuscript, we developed a computational model that demonstrates how ES can functionally elevate intracellular calcium concentration ([Ca²⁺]_i) based on ES intensity and duration. In this article, we validate the computation model for the [Ca²⁺]_i changes in neuron soma. Embryonic chicken dorsal root ganglion cells were suspended in 3-dimensional collagen scaffolds. Fura-2 was used to measure [Ca²⁺]_i in response to biphasic ES pulses ranging from 70 to 60,000 V/m in intensity and from 10 µs to 100 ms in duration. The computational model most closely matched the experimental data of the neurons with the highest [Ca²⁺]_i elevation for ES pulses 100 µs or greater in duration. Nickel (200 µM) and cadmium (200 µM) blocked 98-99% of the [Ca²⁺]_i rise, indicating that the rise in [Ca²⁺]_i in response to ES is via voltage-dependent calcium channels. The average [Ca²⁺]_i rise in response to ES was about one-tenth of the peak rise. Therefore, the computational model is validated for elevating [Ca²⁺]_i of neurons and can be used as a tool for designing efficacious ES protocols for improving neuronal regeneration.NEW & NOTEWORTHY Electrical stimulation is used to enhance neuron growth, and the role of neuronal intracellular calcium concentration ([Ca²⁺]_i) is an area of research interest. Widely varying stimulation parameters in the literature make it difficult to compare stimulation protocols. The results in this manuscript are the first to show neuronal [Ca²⁺]_i in response to a broad and defined range of electrical pulse durations and intensities. These results validate our previously published novel computational model of [Ca²⁺]_i.

Electrical Differentiation of Mesenchymal Stem Cells into Schwann-Cell-Like Phenotypes Using Inkjet-Printed Graphene Circuits

Graphene-based materials (GBMs) have displayed tremendous promise for use as neurointerfacial substrates as they enable favorable adhesion, growth, proliferation, spreading, and migration of immobilized cells. This study reports the first case of the differentiation of mesenchymal stem cells (MSCs) into Schwann cell (SC)-like phenotypes through the application of electrical stimuli from a graphene-based electrode. Electrical differentiation of MSCs into SC-like phenotypes is carried out on a flexible, inkjet-printed graphene interdigitated electrode (IDE) circuit that is made highly conductive (sheet resistance < 1 kΩ/sq) via a postprint pulse-laser annealing process. MSCs immobilized on the graphene printed IDEs and electrically stimulated/treated (etMSCs) display significant enhanced cellular differentiation and paracrine activity above conventional chemical treatment strategies [≈85% of the etMSCs differentiated into SC-like phenotypes with ≈80 ng mL^-1 of nerve growth factor (NGF) secretion vs. 75% and ≈55 ng mL^-1 for chemically treated MSCs (ctMSCs)]. These results help pave the way for in vivo peripheral nerve regeneration where the flexible graphene electrodes could conform to the injury site and provide intimate electrical simulation for nerve cell regrowth.

Electrical stimulation drives chondrogenesis of mesenchymal stem cells in the absence of exogenous growth factors

Electrical stimulation (ES) is known to guide the development and regeneration of many tissues. However, although preclinical and clinical studies have demonstrated superior effects of ES on cartilage repair, the effects of ES on chondrogenesis remain elusive. Since mesenchyme stem cells (MSCs) have high therapeutic potential for cartilage regeneration, we investigated the actions of ES during chondrogenesis of MSCs. Herein, we demonstrate for the first time that ES enhances expression levels of chondrogenic markers, such as type II collagen, aggrecan, and Sox9, and decreases type I collagen levels, thereby inducing differentiation of MSCs into hyaline chondrogenic cells without the addition of exogenous growth factors. ES also induced MSC condensation and subsequent chondrogenesis by driving Ca2+/ATP oscillations, which are known to be essential for prechondrogenic condensation. In subsequent experiments, the effects of ES on ATP oscillations and chondrogenesis were dependent on extracellular ATP signaling via P2X4 receptors, and ES induced significant increases in TGF-β1 and BMP2 expression. However, the inhibition of TGF-β signaling blocked ES-driven condensation, whereas the inhibition of BMP signaling did not, indicating that TGF-β signaling but not BMP signaling mediates ES-driven condensation. These findings may contribute to the development of electrotherapeutic strategies for cartilage repair using MSCs.

Low-level laser irradiation modulates brain-derived neurotrophic factor mRNA transcription through calcium-dependent activation of the ERK/CREB pathway

Low-level laser (LLL) irradiation has been reported to promote neuronal differentiation, but the mechanism remains unclear. Brain-derived neurotrophic factor (BDNF) has been confirmed to be one of the most important neurotrophic factors because it is critical for the differentiation and survival of neurons during development. Thus, this study aimed to investigate the effects of LLL irradiation on Bdnf messenger RNA (mRNA) transcription and the molecular pathway involved in LLL-induced Bdnf mRNA transcription in cultured dorsal root ganglion neurons (DRGNs) using Ca²⁺ imaging, pharmacological detections, RNA interference, immunocytochemistry assay, Western blot, and qPCR analysis. We show here that LLL induced increases in the [Ca²⁺] _i level, Bdnf mRNA transcription, cAMP-response element-binding protein (CREB) phosphorylation, and extracellular signal-regulated kinase (ERK) phosphorylation, mediated by Ca²⁺ release via inositol triphosphate receptor (IP3R)-sensitive calcium (Ca²⁺) stores. Blockade of Ca²⁺ increase suppressed Bdnf mRNA transcription, CREB phosphorylation, and ERK phosphorylation. Downregulation of phosphorylated (p)-CREB reduced Bdnf mRNA transcription triggered by LLL. Furthermore, blockade of ERK using PD98059 inhibitor reduced p-CREB and Bdnf mRNA transcription induced by LLL. Taken together, these findings establish the Ca²⁺-ERK-CREB cascade as a potential signaling pathway involved in LLL-induced Bdnf mRNA transcription. To our knowledge, this is the first report of the mechanisms of Ca²⁺-dependent Bdnf mRNA transcription triggered by LLL. These findings may help further explore the complex molecular signaling networks in LLL-triggered nerve regeneration in vivo and may also provide experimental evidence for the development of LLL for clinical applications.

CaMKII-Mediated CREB Phosphorylation Is Involved in Ca2+-Induced BDNF mRNA Transcription and Neurite Outgrowth Promoted by Electrical Stimulation

Electrical stimulation (ES)-triggered up-regulation of brain-derived neurotrophic factor (BDNF) and neurite outgrowth in cultured rat postnatal dorsal root ganglion neurons (DRGNs) is calcium (Ca²⁺)-dependent. The effects of increased Ca²⁺ on BDNF up-regulation and neurite outgrowth remain unclear. We showed here that ES increased phosphorylation of the cAMP-response element binding protein (CREB). Blockade of Ca²⁺ suppressed CREB phosphorylation and neurite outgrowth. Down-regulation of phosphorylated (p)-CREB reduced BDNF transcription and neurite outgrowth triggered by ES. Furthermore, blockade of calmodulin-dependent protein kinase II (CaMKII) using the inhibitors KN93 or KN62 reduced p-CREB, and specific knockdown of the CaMKIIα or CaMKIIβ subunit was sufficient to suppress p-CREB. Recombinant BDNF or hyperforin reversed the effects of Ca²⁺ blockade and CaMKII knockdown. Taken together, these data establish a potential signaling pathway of Ca²⁺-CaMKII-CREB in neuronal activation. To our knowledge, this is the first report of the mechanisms of Ca²⁺-dependent BDNF transcription and neurite outgrowth triggered by ES. These findings might help further investigation of complex molecular signaling networks in ES-triggered nerve regeneration in vivo.

Robust neurite extension following exogenous electrical stimulation within single walled carbon nanotube-composite hydrogels

The use of exogenous electrical stimulation to promote nerve regeneration has achieved only limited success. Conditions impeding optimized outgrowth may arise from inadequate stimulus presentation due to differences in injury geometry or signal attenuation. Implantation of an electrically-conductive biomaterial may mitigate this attenuation and provide a more reproducible signal. In this study, a conductive nanofiller (single-walled carbon nanotubes [SWCNT]) was selected as one possible material to manipulate the bulk electrical properties of a collagen type I-10% Matrigel™ composite hydrogel. Neurite outgrowth within hydrogels (SWCNT or nanofiller-free controls) was characterized to determine if: (1) nanofillers influence neurite extension and (2) electrical stimulation of the nanofiller composite hydrogel enhances neurite outgrowth. Increased SWCNT loading (10-100-μg/mL) resulted in greater bulk conductivity (up to 1.7-fold) with no significant changes to elastic modulus. Neurite outgrowth increased 3.3-fold in 20-μg/mL SWCNT loaded biomaterials relative to the nanofiller-free control. Electrical stimulation promoted greater outgrowth (2.9-fold) within SWCNT-free control. The concurrent presentation of electrical stimulation and SWCNT-loaded biomaterials resulted in a 7.0-fold increase in outgrowth relative to the unstimulated, nanofiller-free controls. Local glia residing within the DRG likely contribute, in part, to the observed increases in outgrowth; but it is unknown which specific nanofiller properties influence neurite extension. Characterization of neuronal behavior in model systems, such as those described here, will aid the rational development of biomaterials as well as the appropriate delivery of electrical stimuli to support nerve repair.

STATEMENT OF SIGNIFICANCE

Novel biomedical devices delivering electrical stimulation are being developed to mitigate symptoms of Parkinson's, treat drug-resistant depression, control movement or enhance verve regeneration. Carbon nanotubes and other novel materials are being explored for novel nano-neuro devices based on their unique properties. Neuronal growth on carbon nanotubes has been studied in 2D since the early 2000s demonstrating increased outgrowth, synapse formation and network activity. In this work, single-walled carbon nanotubes were selected as one possible electrically-conductive material, dispersed within a 3D hydrogel containing primary neurons; extending previous 2D work to 3D to evaluate outgrowth within nanomaterial composites with electrical stimulation. This is the first study to our knowledge that stimulates neurons in 3D composite nanomaterial-laden hydrogels. Examination of electrically conductive biomaterials may serve to promote regrowth following injury or in long term stimulation.

Strategies to promote peripheral nerve regeneration: electrical stimulation and/or exercise

Enhancing the regeneration of axons is often considered to be a therapeutic target for improving functional recovery after peripheral nerve injury. In this review, the evidence for the efficacy of electrical stimulation (ES), daily exercise and their combination in promoting nerve regeneration after peripheral nerve injuries in both animal models and in human patients is explored. The rationale, effectiveness and molecular basis of ES and exercise in accelerating axon outgrowth are reviewed. In comparing the effects of ES and exercise in enhancing axon regeneration, increased neural activity, neurotrophins and androgens are considered to be common requirements. Similarly, there are sex-specific requirements for exercise to enhance axon regeneration in the periphery and for sustaining synaptic inputs onto injured motoneurons. ES promotes nerve regeneration after delayed nerve repair in humans and rats. The effectiveness of exercise is less clear. Although ES, but not exercise, results in a significant misdirection of regenerating motor axons to reinnervate different muscle targets, the loss of neuromuscular specificity encountered has only a very small impact on resulting functional recovery. Both ES and exercise are promising experimental treatments for peripheral nerve injury that seem to be ready to be translated to clinical use.

Biological conduit small gap sleeve bridging method for peripheral nerve injury: regeneration law of nerve fibers in the conduit

The clinical effects of 2-mm small gap sleeve bridging of the biological conduit to repair peripheral nerve injury are better than in the traditional epineurium suture, so it is possible to replace the epineurium suture in the treatment of peripheral nerve injury. This study sought to identify the regeneration law of nerve fibers in the biological conduit. A nerve regeneration chamber was constructed in models of sciatic nerve injury using 2-mm small gap sleeve bridging of a biodegradable biological conduit. The results showed that the biological conduit had good histocompatibility. Tissue and cell apoptosis in the conduit apparently lessened, and regenerating nerve fibers were common. The degeneration regeneration law of Schwann cells and axons in the conduit was quite different from that in traditional epineurium suture. During the prime period for nerve fiber regeneration (2-8 weeks), the number of Schwann cells and nerve fibers was higher in both proximal and distal ends, and the effects of the small gap sleeve bridging method were better than those of the traditional epineurium suture. The above results provide an objective and reliable theoretical basis for the clinical application of the biological conduit small gap sleeve bridging method to repair peripheral nerve injury.

Electroactive Tissue Scaffolds with Aligned Pores as Instructive Platforms for Biomimetic Tissue Engineering

Tissues in the body are hierarchically structured composite materials with tissue-specific chemical and topographical properties. Here we report the preparation of tissue scaffolds with macroscopic pores generated via the dissolution of a sacrificial supramolecular polymer-based crystal template (urea) from a biodegradable polymer-based scaffold (polycaprolactone, PCL). Furthermore, we report a method of aligning the supramolecular polymer-based crystals within the PCL, and that the dissolution of the sacrificial urea yields scaffolds with macroscopic pores that are aligned over long, clinically-relevant distances (i.e., centimeter scale). The pores act as topographical cues to which rat Schwann cells respond by aligning with the long axis of the pores. Generation of an interpenetrating network of polypyrrole (PPy) and poly(styrene sulfonate) (PSS) in the scaffolds yields electroactive tissue scaffolds that allow the electrical stimulation of Schwann cells cultured on the scaffolds which increases the production of nerve growth factor (NGF).

Peripheral Nerve Regeneration Strategies: Electrically Stimulating Polymer Based Nerve Growth Conduits

Treatment of large peripheral nerve damages ranges from the use of an autologous nerve graft to a synthetic nerve growth conduit. Biological grafts, in spite of many merits, show several limitations in terms of availability and donor site morbidity, and outcomes are suboptimal due to fascicle mismatch, scarring, and fibrosis. Tissue engineered nerve graft substitutes utilize polymeric conduits in conjunction with cues both chemical and physical, cells alone and or in combination. The chemical and physical cues delivered through polymeric conduits play an important role and drive tissue regeneration. Electrical stimulation (ES) has been applied toward the repair and regeneration of various tissues such as muscle, tendon, nerve, and articular tissue both in laboratory and clinical settings. The underlying mechanisms that regulate cellular activities such as cell adhesion, proliferation, cell migration, protein production, and tissue regeneration following ES is not fully understood. Polymeric constructs that can carry the electrical stimulation along the length of the scaffold have been developed and characterized for possible nerve regeneration applications. We discuss the use of electrically conductive polymers and associated cell interaction, biocompatibility, tissue regeneration, and recent basic research for nerve regeneration. In conclusion, a multifunctional combinatorial device comprised of biomaterial, structural, functional, cellular, and molecular aspects may be the best way forward for effective peripheral nerve regeneration.

Activated astrocytes enhance the dopaminergic differentiation of stem cells and promote brain repair through bFGF

Astrocytes provide neuroprotective effects against degeneration of dopaminergic (DA) neurons and play a fundamental role in DA differentiation of neural stem cells. Here we show that light illumination of astrocytes expressing engineered channelrhodopsin variant (ChETA) can remarkably enhance the release of basic fibroblast growth factor (bFGF) and significantly promote the DA differentiation of human embryonic stem cells (hESCs) in vitro. Light activation of transplanted astrocytes in the substantia nigra (SN) also upregulates bFGF levels in vivo and promotes the regenerative effects of co-transplanted stem cells. Importantly, upregulation of bFGF levels, by specific light activation of endogenous astrocytes in the SN, enhances the DA differentiation of transplanted stem cells and promotes brain repair in a mouse model of Parkinson's disease (PD). Our study indicates that astrocyte-derived bFGF is required for regulation of DA differentiation of the stem cells and may provide a strategy targeting astrocytes for treatment of PD.

Bridging peripheral nerves using a deacetyl chitin conduit combined with short-term electrical stimulation

Previous studies have demonstrated that deacetyl chitin conduit nerve bridging or electrical stimulation can effectively promote the regeneration of the injured peripheral nerve. We hypothesized that the combination of these two approaches could result in enhanced regeneration. Rats with right sciatic nerve injury were subjected to deacetyl chitin conduit bridging combined with electrical stimulation (0.1 ms, 3 V, 20 Hz, for 1 hour). At 6 and 12 weeks after treatment, nerve conduction velocity, myelinated axon number, fiber diameter, axon diameter and the thickness of the myelin sheath in the stimulation group were better than in the non-stimulation group. The results indicate that deacetyl chitin conduit bridging combined with temporary electrical stimulation can promote peripheral nerve repair.

The parameters of transcutaneous electrical nerve stimulation are critical to its regenerative effects when applied just after a sciatic crush lesion in mice

We investigated the effect of two frequencies of transcutaneous electrical nerve stimulation (TENS) applied immediately after lesion on peripheral nerve regeneration after a mouse sciatic crush injury. The animals were anesthetized and subjected to crushing of the right sciatic nerve and then separated into three groups: nontreated, Low-TENS (4 Hz), and High-TENS (100 Hz). The animals of Low- and High-TENS groups were stimulated for 2 h immediately after the surgical procedure, while the nontreated group was only positioned for the same period. After five weeks the animals were euthanized, and the nerves dissected bilaterally for histological and histomorphometric analysis. Histological assessment by light and electron microscopy showed that High-TENS and nontreated nerves had a similar profile, with extensive signs of degeneration. Conversely, Low-TENS led to increased regeneration, displaying histological aspects similar to control nerves. High-TENS also led to decreased density of fibers in the range of 6-12 μm diameter and decreased fiber diameter and myelin area in the range of 0-2 μm diameter. These findings suggest that High-TENS applied just after a peripheral nerve crush may be deleterious for regeneration, whereas Low-TENS may increase nerve regeneration capacity.