Endogenous electric currents might guide rostral migration of neuroblasts

Regulation of neural stem cells by innervating neurons

The adult central nervous system (CNS) hosts several niches, in which the neural stem and precursor cells (NPCs) reside. The subventricular zone (SVZ) lines the lateral brain ventricles and the subgranular zone (SGZ) is located in the dentate gyrus of the hippocampus. SVZ and SGZ NPCs replace neurons and glia in the homeostatic as well as diseased or injured states. Recently, NPCs have been found to express neurotransmitter receptors, respond to electrical stimulation and interact with neurons, suggesting that neuron-NPC communication is an emerging critical regulator of NPC biology. In this review, we discuss reports that demonstrate neuronal innervation and control of the neurogenic niches. We discuss the role of innervating neurons in regulating NPC fates, such as activation, proliferation, and differentiation. Our review focuses primarily on the innervation of the SVZ niche by the following neuronal types: glutamatergic, GABAergic projection and interneurons, cholinergic, dopaminergic, serotonergic, neuropeptidergic, nitrergic, and noradrenergic. We also discuss the origins of SVZ niche innervating neurons, such as striatum, cortex, basal ganglia, raphe nuclei, substantia nigra and ventral tegmental area, hypothalamus, and locus coeruleus. Our review highlights the various roles of innervating neurons in SVZ NPC fates in a spatiotemporal manner and emphasizes a need for future investigation into the impact of neuronal innervation on NPC gliogenesis.

Nanomedicine in Neuroprotection, Neuroregeneration, and Blood-Brain Barrier Modulation: A Narrative Review

Nanomedicine is a newer, promising approach to promote neuroprotection, neuroregeneration, and modulation of the blood-brain barrier. This review includes the integration of various nanomaterials in neurological disorders. In addition, gelatin-based hydrogels, which have huge potential due to biocompatibility, maintenance of porosity, and enhanced neural process outgrowth, are reviewed. Chemical modification of these hydrogels, especially with guanidine moieties, has shown improved neuron viability and underscores tailored biomaterial design in neural applications. This review further discusses strategies to modulate the blood-brain barrier-a factor critically associated with the effective delivery of drugs to the central nervous system. These advances bring supportive solutions to the solving of neurological conditions and innovative therapies for their treatment. Nanomedicine, as applied to neuroscience, presents a significant leap forward in new therapeutic strategies that might help raise the treatment and management of neurological disorders to much better levels. Our aim was to summarize the current state-of-knowledge in this field.

Subthalamic nucleus but not entopeduncular nucleus deep brain stimulation enhances neurogenesis in the SVZ-olfactory bulb system of Parkinsonian rats

Introduction

Deep brain stimulation (DBS) is a highly effective treatment option in Parkinson's disease. However, the underlying mechanisms of action, particularly effects on neuronal plasticity, remain enigmatic. Adult neurogenesis in the subventricular zone-olfactory bulb (SVZ-OB) axis and in the dentate gyrus (DG) has been linked to various non-motor symptoms in PD, e.g., memory deficits and olfactory dysfunction. Since DBS affects several of these non-motor symptoms, we analyzed the effects of DBS in the subthalamic nucleus (STN) and the entopeduncular nucleus (EPN) on neurogenesis in 6-hydroxydopamine (6-OHDA)-lesioned hemiparkinsonian rats.

Methods

In our study, we applied five weeks of continuous bilateral STN-DBS or EPN-DBS in 6-OHDA-lesioned rats with stable dopaminergic deficits compared to 6-OHDA-lesioned rats with corresponding sham stimulation. We injected two thymidine analogs to quantify newborn neurons early after DBS onset and three weeks later. Immunohistochemistry identified newborn cells co-labeled with NeuN, TH and GABA within the OB and DG. As a putative mechanism, we simulated the electric field distribution depending on the stimulation site to analyze direct electric effects on neural stem cell proliferation.

Results

STN-DBS persistently increased the number of newborn dopaminergic and GABAergic neurons in the OB but not in the DG, while EPN-DBS does not impact neurogenesis. These effects do not seem to be mediated via direct electric stimulation of neural stem/progenitor cells within the neurogenic niches.

Discussion

Our data support target-specific effects of STN-DBS on adult neurogenesis, a putative modulator of non-motor symptoms in Parkinson's disease.

Conductive gradient hydrogels allow spatial control of adult stem cell fate

Electrical gradients are fundamental to physiological processes including cell migration, tissue formation, organ development, and response to injury and regeneration. Current electrical modulation of cells is primarily studied under a uniform electrical field. Here we demonstrate the fabrication of conductive gradient hydrogels (CGGs) that display mechanical properties and varying local electrical gradients mimicking physiological conditions. The electrically-stimulated CGGs enhanced human mesenchymal stem cell (hMSC) viability and attachment. Cells on CGGs under electrical stimulation showed a high expression of neural progenitor markers such as Nestin, GFAP, and Sox2. More importantly, CGGs showed cell differentiation toward oligodendrocyte lineage (Oligo2) in the center of the scaffold where the electric field was uniform with a greater intensity, while cells preferred neuronal lineage (NeuN) on the edge of the scaffold on a varying electric field at lower magnitude. Our data suggest that CGGs can serve as a useful platform to study the effects of electrical gradients on stem cells and potentially provide insights on developing new neural engineering applications.

State of the Art and Current Challenges on Electroactive Biomaterials and Strategies for Neural Tissue Regeneration

The loss or failure of an organ/tissue stands as one of the healthcare system's most prevalent, devastating, and costly challenges. Strategies for neural tissue repair and regeneration have received significant attention due to their particularly strong impact on patients' well-being. Many research efforts are dedicated not only to control the disease symptoms but also to find solutions to repair the damaged tissues. Neural tissue engineering (TE) plays a key role in addressing this problem and significant efforts are being carried out to develop strategies for neural repair treatment. In the last years, active materials allowing to tune cell-materials interaction are being increasingly used, representing a recent paradigm in TE applications. Among the most important stimuli influencing cell behavior are the electrical and mechanical ones. In this way, materials with the ability to provide this kind of stimuli to the neural cells seem to be appropriate to support neural TE. In this scope, this review summarizes the different biomaterials types used for neural TE, highlighting the relevance of using active biomaterials and electrical stimulation. Furthermore, this review provides not only a compilation of the most relevant studies and results but also strategies for novel and more biomimetic approaches for neural TE.

Investigating the reliability of the evoked response in human iPSCs-derived neuronal networks coupled to micro-electrode arrays

In vitro models of neuronal networks have emerged as a potent instrument for gaining deeper insights into the intricate mechanisms governing the human brain. Notably, the integration of human-induced pluripotent stem cells (hiPSCs) with micro-electrode arrays offers a means to replicate and dissect both the structural and functional elements of the human brain within a controlled in vitro environment. Given that neuronal communication relies on the emission of electrical (and chemical) stimuli, the employment of electrical stimulation stands as a mean to comprehensively interrogate neuronal assemblies, to better understand their inherent electrophysiological dynamics. However, the establishment of standardized stimulation protocols for cultures derived from hiPSCs is still lacking, thereby hindering the precise delineation of efficacious parameters to elicit responses. To fill this gap, the primary objective of this study resides in delineating effective parameters for the electrical stimulation of hiPSCs-derived neuronal networks, encompassing the determination of voltage amplitude and stimulation frequency able to evoke reliable and stable responses. This study represents a stepping-stone in the exploration of efficacious stimulation parameters, thus broadening the electrophysiological activity profiling of neural networks sourced from human-induced pluripotent stem cells.

A Bioresorbable and Conductive Scaffold Integrating Silicon Membranes for Peripheral Nerve Regeneration

Peripheral nerve injury represents one of the most common types of traumatic damage, severely impairing motor and sensory functions, and posttraumatic nerve regeneration remains a major challenge. Electrical cues are critical bioactive factors that promote nerve regrowth, and bioartificial scaffolds incorporating conductive materials to enhance the endogenous electrical field have been demonstrated to be effective. The utilization of fully biodegradable scaffolds can eliminate material residues, and circumvent the need for secondary retrieval procedures. Here, a fully bioresorbable and conductive nerve scaffold integrating N-type silicon (Si) membranes is proposed, which can deliver both structural guidance and electrical cues for the repair of nerve defects. The entire scaffold is fully biodegradable, and the introduction of N-type Si can significantly promote the proliferation and production of neurotrophic factors of Schwann cells and enhance the calcium activity of dorsal root ganglion (DRG) neurons. The conductive scaffolds enable accelerated nerve regeneration and motor functional recovery in rodents with sciatic nerve transection injuries. This work sheds light on the advancement of bioresorbable and electrically active materials to achieve desirable neural interfaces and improved therapeutic outcomes, offering essential strategies for regenerative medicine.

Bioelectronic medicine potentiates endogenous NSCs for neurodegenerative diseases

Neurodegenerative diseases (NDs) are commonly observed and while no therapy is universally applicable, cell-based therapies are promising. Stem cell transplantation has been investigated, but endogenous neural stem cells (eNSCs), despite their potential, especially with the development of bioelectronic medicine and biomaterials, remain understudied. Here, we compare stem cell transplantation therapy with eNSC-based therapy and summarize the combined use of eNSCs and developing technologies. The rapid development of implantable biomaterials has resulted in electronic stimulation becoming increasingly effective and decreasingly invasive. Thus, the combination of bioelectronic medicine and eNSCs has substantial potential for the treatment of NDs.

Stimulation strategies for electrical and magnetic modulation of cells and tissues

Electrical phenomena play an important role in numerous biological processes including cellular signaling, early embryogenesis, tissue repair and remodeling, and growth of organisms. Electrical and magnetic effects have been studied on a variety of stimulation strategies and cell types regarding cellular functions and disease treatments. In this review, we discuss recent advances in using three different stimulation strategies, namely electrical stimulation via conductive and piezoelectric materials as well as magnetic stimulation via magnetic materials, to modulate cell and tissue properties. These three strategies offer distinct stimulation routes given specific material characteristics. This review will evaluate material properties and biological response for these stimulation strategies with respect to their potential applications in neural and musculoskeletal research.

A novel ex vivo assay to define charge-balanced electrical stimulation parameters for neural precursor cell activation in vivo

Endogenous neural stem cells and their progeny (together termed neural precursor cells (NPCs)) are promising candidates to facilitate neuroregeneration. Charge-balanced biphasic monopolar stimulation (BPMP) is a clinically relevant approach that can activate NPCs both in vitro and in vivo. Herein, we established a novel ex vivo stimulation system to optimize the efficacy of BPMP electric field (EF) application in activating endogenous NPCs. Using the ex vivo system, we discerned that cathodal amplitude of 200 μA resulted in the greatest NPC pool expansion and enhanced cathodal migration. Application of the same stimulation parameters in vivo resulted in the same NPC activation in the mouse brain. The design and implementation of the novel ex vivo model bridges the gap between in vitro and in vivo systems, enabling a moderate throughput stimulation system to explore and optimize EF parameters that can be applied to clinically relevant brain injury/disease models.

Effects of the radio electric asymmetric conveyer (REAC) on motor disorders: An integrative review

Introduction

The radio electric asymmetric conveyer (REAC) is a technology that has the purpose of restoring the cellular polarity triggering the rebalancing of the endogenous bioelectric field, which considering the neurological dysfunctions, affects the neural communication mechanisms. The studies published so far show that the REAC neuromodulation technology has positive effects in treating these dysfunctions, with the principles of endogenous bioelectricity as a basis to achieve these effects.

Objectives

This study aims to review the literature that explored the effects of REAC protocols on motor control and to identify which mechanisms would be involved.

Materials and methods

This integrative review considered studies that used REAC as a therapeutic intervention directed at human motor control and experimental research with animals that applied REAC to obtain effects related to motor behavior.

Results

Ten articles were included, eight clinical and two experimental studies. The clinical studies used the neuro postural optimization (NPO) protocol in 473 patients, of which 53 were healthy subjects, 91 were Alzheimer's disease patients, 128 were patients with atypical swallowing, 12 subjects with neurological diseases, and 189 were without the specification of disease. The experimental studies used the antalgic neuromodulation and neurodegeneration protocols in animal models.

Conclusion

The information integrated in this review made it possible to consider REAC technology a promising resource for treating motor control dysfunctions. It is possible to infer that the technology promotes functional optimization of neuronal circuits that may be related to more efficient strategies to perform motor tasks.

Screening Biophysical Sensors and Neurite Outgrowth Actuators in Human Induced-Pluripotent-Stem-Cell-Derived Neurons

All living cells maintain a charge distribution across their cell membrane (membrane potential) by carefully controlled ion fluxes. These bioelectric signals regulate cell behavior (such as migration, proliferation, differentiation) as well as higher-level tissue and organ patterning. Thus, voltage gradients represent an important parameter for diagnostics as well as a promising target for therapeutic interventions in birth defects, injury, and cancer. However, despite much progress in cell and molecular biology, little is known about bioelectric states in human stem cells. Here, we present simple methods to simultaneously track ion dynamics, membrane voltage, cell morphology, and cell activity (pH and ROS), using fluorescent reporter dyes in living human neurons derived from induced neural stem cells (hiNSC). We developed and tested functional protocols for manipulating ion fluxes, membrane potential, and cell activity, and tracking neural responses to injury and reinnervation in vitro. Finally, using morphology sensor, we tested and quantified the ability of physiological actuators (neurotransmitters and pH) to manipulate nerve repair and reinnervation. These methods are not specific to a particular cell type and should be broadly applicable to the study of bioelectrical controls across a wide range of combinations of models and endpoints.

Bioelectric Potential in Next-Generation Organoids: Electrical Stimulation to Enhance 3D Structures of the Central Nervous System

Pluripotent stem cell-derived organoid models of the central nervous system represent one of the most exciting areas in in vitro tissue engineering. Classically, organoids of the brain, retina and spinal cord have been generated via recapitulation of in vivo developmental cues, including biochemical and biomechanical. However, a lesser studied cue, bioelectricity, has been shown to regulate central nervous system development and function. In particular, electrical stimulation of neural cells has generated some important phenotypes relating to development and differentiation. Emerging techniques in bioengineering and biomaterials utilise electrical stimulation using conductive polymers. However, state-of-the-art pluripotent stem cell technology has not yet merged with this exciting area of bioelectricity. Here, we discuss recent findings in the field of bioelectricity relating to the central nervous system, possible mechanisms, and how electrical stimulation may be utilised as a novel technique to engineer “next-generation” organoids.

Galvanotactic Migration of Glioblastoma and Brain Metastases Cells

Galvanotaxis, the migration along direct current electrical fields, may contribute to the invasion of brain cancer cells in the tumor-surrounding tissue. We hypothesized that pharmacological perturbation of the epidermal growth factor (EGF) receptor and downstream phosphatidylinositol 3-kinase (PI3K)/AKT pathway prevent galvanotactic migration. In our study, patient-derived glioblastoma and brain metastases cells were exposed to direct current electrical field conditions. Velocity and direction of migration were estimated. To determine the effects of EGF receptor antagonist afatinib and AKT inhibitor capivasertib, assays of cell proliferation, apoptosis and immunoblot analyses were performed. Both inhibitors attenuated cell proliferation in a dose-dependent manner and induced apoptosis. We found that most of the glioblastoma cells migrated preferentially in an anodal direction, while brain metastases cells were unaffected by direct current stimulations. Afatinib presented only a mild attenuation of galvanotaxis. In contrast, capivasertib abolished the migration of glioblastoma cells without genetic alterations in the PI3K/AKT pathway, but not in cells harboring PTEN mutation. In these cells, an increase in the activation of ERK1/2 may in part substitute the inhibition of the AKT pathway. Overall, our data demonstrate that glioblastoma cells migrate in the electrical field and the PI3K/AKT pathway was found to be highly involved in galvanotaxis.

Physiological Electric Field: A Potential Construction Regulator of Human Brain Organoids

Brain organoids can reproduce the regional three-dimensional (3D) tissue structure of human brains, following the in vivo developmental trajectory at the cellular level; therefore, they are considered to present one of the best brain simulation model systems. By briefly summarizing the latest research concerning brain organoid construction methods, the basic principles, and challenges, this review intends to identify the potential role of the physiological electric field (EF) in the construction of brain organoids because of its important regulatory function in neurogenesis. EFs could initiate neural tissue formation, inducing the neuronal differentiation of NSCs, both of which capabilities make it an important element of the in vitro construction of brain organoids. More importantly, by adjusting the stimulation protocol and special/temporal distributions of EFs, neural organoids might be created following a predesigned 3D framework, particularly a specific neural network, because this promotes the orderly growth of neural processes, coordinate neuronal migration and maturation, and stimulate synapse and myelin sheath formation. Thus, the application of EF for constructing brain organoids in a3D matrix could be a promising future direction in neural tissue engineering.

Transmembrane H+ fluxes and the regulation of neural induction in Xenopus laevis

It has previously been reported that in ex vivo planar explants prepared from Xenopus laevis embryos, the intracellular pH (pHi) increases in cells of the dorsal ectoderm from stage 10.5 to 11.5 (i.e. 11-12.5 hpf). It was proposed that such increases (potentially due to H+ being extruded, sequestered, or buffered in some manner), play a role in regulating neural induction. Here, we used an extracellular ion-selective electrode to non-invasively measure H+ fluxes at eight locations around the equatorial circumference of intact X. laevis embryos between stages 9-12 (˜7-13.25 hpf). We showed that at stages 9-11, there was a small H+ efflux recorded from all the measuring positions. At stage 12 there was a small, but significant, increase in the efflux of H+ from most locations, but the efflux from the dorsal side of the embryo was significantly greater than from the other positions. Embryos were also treated from stages 9-12 with bafilomycin A1, to block the activity of the ATP-driven H+ pump. By stage 22 (24 hpf), these embryos displayed retarded development, arresting before the end of gastrulation and therefore did not display the usual anterior and neural structures, which were observed in the solvent-control embryos. In addition, expression of the early neural gene, Zic3, was absent in treated embryos compared with the solvent controls. Together, our new in vivo data corroborated and extended the earlier explant-derived report describing changes in pHi that were suggested to play a role during neural induction in X. laevis embryos.

P2Y2 deficiency impacts adult neurogenesis and related forebrain functions

Adult neurogenesis occurs particularly in the subgranular zone (SGZ) of the hippocampus and the subventricular zone (SVZ) of the lateral ventricle. This continuous addition of neurons to pre-existing neuronal networks is essential for intact cognitive and olfactory functions, respectively. Purinergic signaling modulates adult neurogenesis, however, the role of individual purinergic receptor subtypes in this dynamic process and related cognitive performance is poorly understood. In this study, we analyzed the role of P2Y₂ receptor in the neurogenic niches and in related forebrain functions such as spatial working memory and olfaction using mice with a targeted deletion of the P2Y₂ receptor (P2Y2^-/- ). Proliferation, migration, differentiation, and survival of neuronal precursor cells (NPCs) were analyzed by BrdU assay and immunohistochemistry; signal transduction pathway components were analyzed by immunoblot. In P2Y2^-/- mice, proliferation of NPCs in the SGZ and the SVZ was reduced. However, migration, neuronal fate decision, and survival were not affected. Moreover, p-Akt expression was decreased in P2Y2^-/- mice. P2Y2^-/- mice showed an impaired performance in the Y-maze and a higher latency in the hidden food test. These data indicate that the P2Y₂ receptor plays an important role in NPC proliferation as well as in hippocampus-dependent working memory and olfactory function.

Glioblastoma cell migration is directed by electrical signals

Electric field (EF) directed cell migration (electrotaxis) is known to occur in glioblastoma multiforme (GBM) and neural stem cells, with key signalling pathways frequently dysregulated in GBM. One such pathway is EGFR/PI3K/Akt, which is down-regulated by peroxisome proliferator activated receptor gamma (PPARγ) agonists. We investigated the effect of electric fields on primary differentiated and glioma stem cell (GSCs) migration, finding opposing preferences for anodal and cathodal migration, respectively. We next sought to determine whether chemically disrupting Akt through PTEN upregulation with the PPARγ agonist, pioglitazone, would modulate electrotaxis of these cells. We found that directed cell migration was significantly inhibited with the addition of pioglitazone in both differentiated GBM and GSCs subtypes. Western blot analysis did not demonstrate any change in PPARγ expression with and without exposure to EF. In summary we demonstrate opposing EF responses in primary GBM differentiated cells and GSCs can be inhibited chemically by pioglitazone, implicating GBM EF modulation as a potential target in preventing tumour recurrence.

Construction of Bio-Piezoelectric Platforms: From Structures and Synthesis to Applications

Piezoelectric materials, with their unique ability for mechanical-electrical energy conversion, have been widely applied in important fields such as sensing, energy harvesting, wastewater treatment, and catalysis. In recent years, advances in material synthesis and engineering have provided new opportunities for the development of bio-piezoelectric materials with excellent biocompatibility and piezoelectric performance. Bio-piezoelectric materials have attracted interdisciplinary research interest due to recent insights on the impact of piezoelectricity on biological systems and their versatile biomedical applications. This review therefore introduces the development of bio-piezoelectric platforms from a broad perspective and highlights their design and engineering strategies. State-of-the-art biomedical applications in both biosensing and disease treatment will be systematically outlined. The relationships between the properties, structure, and biomedical performance of the bio-piezoelectric materials are examined to provide a deep understanding of the working mechanisms in a physiological environment. Finally, the development trends and challenges are discussed, with the aim to provide new insights for the design and construction of future bio-piezoelectric materials.

Neuromodulation-Based Stem Cell Therapy in Brain Repair: Recent Advances and Future Perspectives

Stem cell transplantation holds a promising future for central nervous system repair. Current challenges, however, include spatially and temporally defined cell differentiation and maturation, plus the integration of transplanted neural cells into host circuits. Here we discuss the potential advantages of neuromodulation-based stem cell therapy, which can improve the viability and proliferation of stem cells, guide migration to the repair site, orchestrate the differentiation process, and promote the integration of neural circuitry for functional rehabilitation. All these advantages of neuromodulation make it one potentially valuable tool for further improving the efficiency of stem cell transplantation.

Endogenous Electric Signaling as a Blueprint for Conductive Materials in Tissue Engineering

Bioelectricity plays an important role in cell behavior and tissue modulation, but is understudied in tissue engineering research. Endogenous electrical signaling arises from the transmembrane potential inherent to all cells and contributes to many cell behaviors, including migration, adhesion, proliferation, and differentiation. Electrical signals are also involved in tissue development and repair. Synthetic and natural conductive materials are under investigation for leveraging endogenous electrical signaling cues in tissue engineering applications due to their ability to direct cell differentiation, aid in maturing electroactive cell types, and promote tissue functionality. In this review, we provide a brief overview of bioelectricity and its impact on cell behavior, report recent literature using conductive materials for tissue engineering, and discuss opportunities within the field to improve experimental design when using conductive substrates.

Intrinsic Mechanisms Regulating Neuronal Migration in the Postnatal Brain

Neuronal migration is a fundamental brain development process that allows cells to move from their birthplaces to their sites of integration. Although neuronal migration largely ceases during embryonic and early postnatal development, neuroblasts continue to be produced and to migrate to a few regions of the adult brain such as the dentate gyrus and the subventricular zone (SVZ). In the SVZ, a large number of neuroblasts migrate into the olfactory bulb (OB) along the rostral migratory stream (RMS). Neuroblasts migrate in chains in a tightly organized micro-environment composed of astrocytes that ensheath the chains of neuroblasts and regulate their migration; the blood vessels that are used by neuroblasts as a physical scaffold and a source of molecular factors; and axons that modulate neuronal migration. In addition to diverse sets of extrinsic micro-environmental cues, long-distance neuronal migration involves a number of intrinsic mechanisms, including membrane and cytoskeleton remodeling, Ca²⁺ signaling, mitochondria dynamics, energy consumption, and autophagy. All these mechanisms are required to cope with the different micro-environment signals and maintain cellular homeostasis in order to sustain the proper dynamics of migrating neuroblasts and their faithful arrival in the target regions. Neuroblasts in the postnatal brain not only migrate into the OB but may also deviate from their normal path to migrate to a site of injury induced by a stroke or by certain neurodegenerative disorders. In this review, we will focus on the intrinsic mechanisms that regulate long-distance neuroblast migration in the adult brain and on how these pathways may be modulated to control the recruitment of neuroblasts to damaged/diseased brain areas.

Electric field stimulation for tissue engineering applications

Electric fields are involved in numerous physiological processes, including directional embryonic development and wound healing following injury. To study these processes in vitro and/or to harness electric field stimulation as a biophysical environmental cue for organised tissue engineering strategies various electric field stimulation systems have been developed. These systems are overall similar in design and have been shown to influence morphology, orientation, migration and phenotype of several different cell types. This review discusses different electric field stimulation setups and their effect on cell response.

Novel Electrode Designs for Neurostimulation in Regenerative Medicine: Activation of Stem Cells

Neural stem and progenitor cells (i.e., neural precursors) are found within specific regions in the central nervous system and have great regenerative capacity. These cells are electrosensitive and their behavior can be regulated by the presence of electric fields (EFs). Electrical stimulation is currently used to treat neurological disorders in a clinical setting. Herein we propose that electrical stimulation can be used to enhance neural repair by regulating neural precursor cell (NPC) kinetics and promoting their migration to sites of injury or disease. We discuss how intrinsic and extrinsic factors can affect NPC migration in the presence of an EF and how this impacts electrode design with the goal of enhancing tissue regeneration. We conclude with an outlook on future clinical applications of electrical stimulation and highlight technological advances that would greatly support these applications.

How Do Electric Fields Coordinate Neuronal Migration and Maturation in the Developing Cortex?

During development the vast majority of cells that will later compose the mature cerebral cortex undergo extensive migration to reach their final position. In addition to intrinsically distinct migratory behaviors, cells encounter and respond to vastly different microenvironments. These range from axonal tracts to cell-dense matrices, electrically active regions and extracellular matrix components, which may all change overtime. Furthermore, migrating neurons themselves not only adapt to their microenvironment but also modify the local niche through cell-cell contacts, secreted factors and ions. In the radial dimension, the developing cortex is roughly divided into dense progenitor and cortical plate territories, and a less crowded intermediate zone. The cortical plate is bordered by the subplate and the marginal zone, which are populated by neurons with high electrical activity and characterized by sophisticated neuritic ramifications. Neuronal migration is influenced by these boundaries resulting in dramatic changes in migratory behaviors as well as morphology and electrical activity. Modifications in the levels of any of these parameters can lead to alterations and even arrest of migration. Recent work indicates that morphology and electrical activity of migrating neuron are interconnected and the aim of this review is to explore the extent of this connection. We will discuss on one hand how the response of migrating neurons is altered upon modification of their intrinsic electrical properties and whether, on the other hand, the electrical properties of the cellular environment can modify the morphology and electrical activity of migrating cortical neurons.

Integrating Bioelectrical Currents and Ca2+ Signaling with Biochemical Signaling in Development and Pathogenesis

Roles of bioelectrical signals are increasingly recognized in excitable and nonexcitable non-neural tissues. Diverse ion-selective channels, pumps, and gap junctions participate in bioelectrical signaling, including those transporting calcium ions (Ca2+). Ca2+ is the most versatile transported ion, because it serves as an electrical charge carrier and a biochemical regulator for multiple molecular binding, enzyme, and transcription activities. We aspire to learn how bioelectrical signals crosstalk to biochemical/biomechanical signals. In this study, we review four recent studies showing how bioelectrical currents and Ca2+ signaling affect collective dermal cell migration during feather bud elongation, affect chondrogenic differentiation in limb development, couple with mechanical tension in aligning gut smooth muscle, and affect mitochondrial function and skeletal muscle atrophy. We observe bioelectrical signals involved in several developmental and pathological conditions in chickens and mice at multiple spatial scales: cellular, cellular collective, and subcellular. These examples inspire novel concept and approaches for future basic and translational studies.

Voltage-gated ion channels mediate the electrotaxis of glioblastoma cells in a hybrid PMMA/PDMS microdevice

Transformed astrocytes in the most aggressive form cause glioblastoma, the most common cancer in the central nervous system with high mortality. The physiological electric field by neuronal local field potentials and tissue polarity may guide the infiltration of glioblastoma cells through the electrotaxis process. However, microenvironments with multiplex gradients are difficult to create. In this work, we have developed a hybrid microfluidic platform to study glioblastoma electrotaxis in controlled microenvironments with high throughput quantitative analysis by machine learning-powered single cell tracking software. By equalizing the hydrostatic pressure difference between inlets and outlets of the microchannel, uniform single cells can be seeded reliably inside the microdevice. The electrotaxis of two glioblastoma models, T98G and U-251MG, requires an optimal laminin-containing extracellular matrix and exhibits opposite directional and electro-alignment tendencies. Calcium signaling is a key contributor in glioblastoma pathophysiology but its role in glioblastoma electrotaxis is still an open question. Anodal T98G electrotaxis and cathodal U-251MG electrotaxis require the presence of extracellular calcium cations. U-251MG electrotaxis is dependent on the P/Q-type voltage-gated calcium channel (VGCC) and T98G is dependent on the R-type VGCC. U-251MG electrotaxis and T98G electrotaxis are also mediated by A-type (rapidly inactivating) voltage-gated potassium channels and acid-sensing sodium channels. The involvement of multiple ion channels suggests that the glioblastoma electrotaxis is complex and patient-specific ion channel expression can be critical to develop personalized therapeutics to fight against cancer metastasis. The hybrid microfluidic design and machine learning-powered single cell analysis provide a simple and flexible platform for quantitative investigation of complicated biological systems.

Electric Field Application In Vivo Regulates Neural Precursor Cell Behavior in the Adult Mammalian Forebrain

Deep brain stimulation (DBS), which uses electrical stimulation, is a well-established neurosurgical technique used to treat neurologic disorders. Despite its broad therapeutic use, the effects of electrical stimulation on brain cells is not fully understood. Here, we examine the effects of electrical stimulation on neural stem and progenitor cells (collectively neural precursor cells; NPCs) from the subventricular zone in the adult forebrain of C57BL/6J mice. Previous work has demonstrated that adult-derived NPCs are electro sensitive and undergo rapid and directed migration in response to application of clinically relevant electric fields (EFs). We examine NPC proliferation kinetics and their differentiation profile following EF application using in vitro and in vivo assays. In vitro direct current electrical stimulation of 250 mV/mm is sufficient to elicit a 2-fold increase in the neural stem cell pool and increases neurogenesis and oligogenesis. In vivo, asymmetric biphasic electrical stimulation similarly increases the size of the NPC pool and alters neurogenesis. These findings provide insight into the effects of electrical stimulation on NPCs and suggest its potential use as a regenerative approach to neural repair.

Postnatal neuronal migration in health and disease

Postnatal neuronal migration modulates neuronal circuit formation and function throughout life and is conserved among species. Pathological conditions activate the generation of neuroblasts in the ventricular-subventricular zone (V-SVZ) and promote their migration towards a lesion. However, the neuroblasts generally terminate their migration before reaching the lesion site unless their intrinsic capacity is modified or the environment is improved. It is important to understand which factors impede neuronal migration for functional recovery of the brain. We highlight similarities and differences in the mechanisms of neuroblast migration under physiological and pathological conditions to provide novel insights into endogenous neuronal regeneration.

Charge-Balanced Electrical Stimulation Can Modulate Neural Precursor Cell Migration in the Presence of Endogenous Electric Fields in Mouse Brains

Electric fields (EFs) can direct cell migration and are crucial during development and tissue repair. We previously reported neural precursor cells (NPCs) are electrosensitive cells that can undergo rapid and directed migration towards the cathode using charge-balanced electrical stimulation in vitro. Here, we investigate the ability of electrical stimulation to direct neural precursor migration in mouse brains in vivo. To visualize migration, fluorescent adult murine neural precursors were transplanted onto the corpus callosum of adult male mice and intracortical platinum wire electrodes were implanted medial (cathode) and lateral (anode) to the injection site. We applied a charge-balanced biphasic monopolar stimulation waveform for three sessions per day, for 3 or 6 d. Irrespective of stimulation, the transplanted neural precursors had a propensity to migrate laterally along the corpus callosum, and applied stimulation affected that migration. Further investigation revealed an endogenous EF along the corpus callosum that correlated with the lateral migration, suggesting that the applied EF would need to overcome endogenous cues. There was no difference in transplanted cell differentiation and proliferation, or inflammatory cell numbers near the electrode leads and injection site comparing stimulated and implanted non-stimulated brains. Our results support that endogenous and applied EFs are important considerations for designing cell therapies for tissue repair in vivo.

Physiologic Electrical Fields Direct Retinal Ganglion Cell Axon Growth In Vitro

Purpose

The purpose of this study was to characterize the ability of applied electrical fields (EFs) to direct retinal ganglion cell (RGC) axon growth as well as to assess whether Rho GTPases play a role in translating electrical cues to directional cues.

Methods

Full-thickness, early postnatal mouse retina was cultured in electrotaxis chambers and exposed to EFs of varying strengths (50–200 mV/mm). The direction of RGC axon growth was quantified from time-lapsed videos. The rate of axon growth and responsiveness to changes in EF polarity were also assessed. The effect of toxin B, a broad-spectrum inhibitor of Rho GTPase signaling, and Z62954982, a selective inhibitor of Rac1, on EF-directed growth was determined.

Results

In the absence of an EF, RGC axons demonstrated indiscriminate directional growth from the explant edge. Retinal cultures exposed to an EF of 100 and 200 mV/mm showed markedly asymmetric growth, with 74.2% and 81.2% of axons oriented toward the cathode, respectively (P < 0.001). RGC axons responded to acute changes in EF polarity by redirecting their growth toward the “new” cathode. This galvanotropic effect was partially neutralized by toxin B and Rac1 inhibitor Z62954982.

Conclusions

RGC axons exhibit cathode-directed growth in the presence of an EF. This effect is mediated in part by the Rho GTPase signaling cascade.

Controlling properties of human neural progenitor cells using 2D and 3D conductive polymer scaffolds

Human induced pluripotent stem cell-derived neural progenitor cells (hNPCs) are a promising cell source for stem cell transplantation to treat neurological diseases such as stroke and peripheral nerve injuries. However, there have been limited studies investigating how the dimensionality of the physical and electrical microenvironment affects hNPC function. In this study, we report the fabrication of two- and three-dimensional (2D and 3D respectively) constructs composed of a conductive polymer to compare the effect of electrical stimulation of hydrogel-immobilized hNPCs. The physical dimension (2D vs 3D) of stimulating platforms alone changed the hNPCs gene expression related to cell proliferation and metabolic pathways. The addition of electrical stimulation was critical in upregulating gene expression of neurotrophic factors that are important in regulating cell survival, synaptic remodeling, and nerve regeneration. This study demonstrates that the applied electrical field controls hNPC properties depending on the physical nature of stimulating platforms and cellular metabolic states. The ability to control hNPC functions can be beneficial in understanding mechanistic changes related to electrical modulation and devising novel treatment methods for neurological diseases.

Static Magnetic Field Induced Neural Stem/Progenitor Cell Early Differentiation and Promotes Maturation

The potential impacts of magnetic field exposures on brain development have raised public concern. In the present study, we aimed to investigate the biophysical effects of moderate-intensity (0.5 T, Tesla) static magnetic field (SMF) on mice neural progenitor cells (mNPCs). Our results showed that the SMF exposure increased the number of neurosphere formation and enhanced proliferative activity in mNPCs. In addition, our flow cytometry data demonstrated that the proportions of S phase and G2/M phase mNPCs were remarkably increased following 5 days of SMF exposure. Moreover, the level of a mitotic regulatory protein, cyclin B, was upregulated after SMF exposure. Furthermore, the mNPCs exposed to SMF exhibited a significant increase in Sox2 expression. When mNPCs were induced to differentiation, our immunofluorescence assay revealed that the percentage of neurons (Tuj-1-positive cells) but not astrocyte (s100β-positive cells) was significantly higher and displayed morphological complexity in the SMF group. Finally, our electrophysiological results demonstrated the mNPC-derived neurons from the SMF group showing a significantly increased in input resistance, which indicated more functional maturation. Based on these findings, it appears reasonable to suggest that SMF exposure could affect normal neurogenesis and promote neural lineage differentiation as well as neuronal maturation.

Electrical stimulation of cell growth and neurogenesis using conductive and nonconductive microfibrous scaffolds

The effect of exogenous electrical stimulation on cell viability, attachment, growth, and neurogenesis was examined using PC12 cells in microfibrous viscose-rayon scaffolds immersed in culture medium. The scaffolds were applied either in their nonconductive state or after coating the fibres with 200 nm of gold to give a scaffold sheet resistivity of (13 ± 1.3) Ω square−1. The cells were treated for 12 days using direct current electrical stimulation of 2 h per day. No cytotoxic effects were observed when up to 500 mV (8.3 mV mm−1) was applied to the scaffolds without gold, or when up to 100 mV (1.7 mV mm−1) was applied to the scaffolds with gold. Compared with unstimulated cells, whereas electrical stimulation significantly enhanced cell growth and attachment in the nonconductive scaffolds without gold, similar effects were not found for the conductive scaffolds with gold. Neural differentiation in the presence of nerve growth factor was improved by electrical stimulation in both scaffolds; however, neurite development and the expression of key differentiation markers were greater in the nonconductive scaffolds without gold than in the scaffolds with gold. Application of the same current to scaffolds with and without gold led to much higher levels of neurogenesis in the scaffolds without gold. This work demonstrates that substantial benefits in terms of cell growth and neural differentiation can be obtained using electric fields exerted across nonconductive microfibrous scaffolds, and that this approach to electrical stimulation can be more effective than when the stimulus is applied to cells on conductive scaffolds.

Neural responses to electrical stimulation in 2D and 3D in vitro environments

Electrical stimulation (ES) to manipulate the central (CNS) and peripheral nervous system (PNS) has been explored for decades, recently gaining momentum as bioelectronic medicine advances. The application of ES in vitro to modulate a variety of cellular functions, including regenerative potential, migration, and stem cell fate, are being explored to aid neural degeneration, dysfunction, and injury. This review describes the materials and approaches for the application of ES to the PNS and CNS microenvironments, towards an improved understanding of how ES can be harnessed for beneficial clinical applications. Emphasized are some recent advances in ES, including conductive polymers, methods of charge transfer, impact on neural cells, and a brief overview of alternative methodologies for cellular targeting including magneto, ultrasonic, and optogenetic stimulation. This review will examine how heterogenous cell populations, including neurons, glia, and neural stem cells respond to a wide range of conductive 2D and 3D substrates, stimulation regimes, known mechanisms of response, and how cellular sources impact the response to ES.

Primary Cilia-An Underexplored Topic in Major Mental Illness

Though much progress has been made in recent years towards understanding the function and physiology of primary cilia, they remain a somewhat elusive organelle. Some studies have explored the role of primary cilia in the developing nervous system, and their dysfunction has been linked with several neurosensory deficits. Yet, very little has been written on their potential role in psychiatric disorders. This article provides an overview of some of the functions of primary cilia in signalling pathways, and demonstrates that they are a worthy candidate in psychiatric research. The links between primary cilia and major mental illness have been demonstrated to exist at several levels, spanning genetics, signalling pathways, and pharmacology as well as cell division and migration. The primary focus of this review is on the sensory role of the primary cilium and the neurodevelopmental hypothesis of psychiatric disease. As such, the primary cilium is demonstrated to be a key link between the cellular environment and cell behaviour, and hence of key importance in the considerations of the nature and nurture debate in psychiatric research.

EDEn-Electroceutical Design Environment: Ion Channel Tissue Expression Database with Small Molecule Modulators

The emerging field of bioelectricity has revealed numerous new roles for ion channels beyond the nervous system, which can be exploited for applications in regenerative medicine. Developing such biomedical interventions for birth defects, cancer, traumatic injury, and bioengineering first requires knowledge of ion channel targets expressed in tissues of interest. This information can then be used to select combinations of small molecule inhibitors and/or activators that manipulate the bioelectric state. Here, we provide an overview of electroceutical design environment (EDEn), the first bioinformatic platform that facilitates the design of such therapeutic strategies. This database includes information on ion channels and ion pumps, linked to known chemical modulators and their properties. The database also provides information about the expression levels of the ion channels in over 100 tissue types. The graphical interface allows the user to readily identify chemical entities that can alter the electrical properties of target cells and tissues.

Mechanisms of invasion and motility of high-grade gliomas in the brain

High-grade gliomas are especially difficult tumors to treat due to their invasive behavior. This has led to extensive research focusing on arresting glioma cell migration. Cell migration involves the sensing of a migratory cue, followed by polarization in the direction of the cue, and reorganization of the actin cytoskeleton to allow for a protrusive leading edge and a contractile trailing edge. Transmission of these forces to produce motility also requires adhesive interactions of the cell with the extracellular microenvironment. In glioma cells, transmembrane receptors such as CD44 and integrins bind the cell to the surrounding extracellular matrix that provides a substrate on which the cell can exert the requisite forces for cell motility. These various essential parts of the migratory machinery are potential targets to halt glioma cell invasion. In this review, we discuss the mechanisms of glioma cell migration and how they may be targeted in anti-invasion therapies.

Nucleus Basalis of Meynert Stimulation for Dementia: Theoretical and Technical Considerations

Deep brain stimulation (DBS) of nucleus basalis of Meynert (NBM) is currently being evaluated as a potential therapy to improve memory and overall cognitive function in dementia. Although, the animal literature has demonstrated robust improvement in cognitive functions, phase 1 trial results in humans have not been as clear-cut. We hypothesize that this may reflect differences in electrode location within the NBM, type and timing of stimulation, and the lack of a biomarker for determining the stimulation's effectiveness in real time. In this article, we propose a methodology to address these issues in an effort to effectively interface with this powerful cognitive nucleus for the treatment of dementia. Specifically, we propose the use of diffusion tensor imaging to identify the nucleus and its tracts, quantitative electroencephalography (QEEG) to identify the physiologic response to stimulation during programming, and investigation of stimulation parameters that incorporate the phase locking and cross frequency coupling of gamma and slower oscillations characteristic of the NBM's innate physiology. We propose that modulating the baseline gamma burst stimulation frequency, specifically with a slower rhythm such as theta or delta will pose more effective coupling between NBM and different cortical regions involved in many learning processes.

Skin-derived precursor cells undergo substrate-dependent galvanotaxis that can be modified by neighbouring cells

Many cell types respond to electric fields (EFs) through cell migration, a process termed galvanotaxis. The galvanotactic response is critical for development and wound healing. Here we investigate whether skin-derived precursor cells (SKPs), which have the potential to differentiate into mesodermal and peripheral neural cell types, undergo directed migration in the presence of an EF. We found that EF application promotes SKP migration towards the anode. The migratory response is substrate-dependent as SKPs undergo directed migration on laminin and Matrigel, but not collagen. The majority of SKPs express the undifferentiated cell markers nestin, fibronectin and Sox2, after both EF application and in sister cultures with no EF application, suggesting that EFs do not promote cell differentiation. Co-cultures of SKPs and brain-derived neural precursor cells (NPCs), a population of cells that undergo rapid, cathode-directed migration, reveal that in the presence of NPCs an increased percentage of SKPs undergo galvanotaxis, providing evidence that cells can provide cues to modify the galvanotactic response. We propose that a better understanding of SKP migration in the presence of EFs may provide insight into improved strategies for wound repair.

Neural stem cell heterogeneity in the mammalian forebrain

The brain was long considered an organ that underwent very little change after development. It is now well established that the mammalian central nervous system contains neural stem cells that generate progeny that are capable of making new neurons, astrocytes, and oligodendrocytes throughout life. The field has advanced rapidly as it strives to understand the basic biology of these precursor cells, and explore their potential to promote brain repair. The purpose of this review is to present current knowledge about the diversity of neural stem cells in vitro and in vivo, and highlight distinctions between neural stem cell populations, throughout development, and within the niche. A comprehensive understanding of neural stem cell heterogeneity will provide insights into the cellular and molecular regulation of neural development and lifelong neurogenesis, and will guide the development of novel strategies to promote regeneration and neural repair.

The bioelectric code: An ancient computational medium for dynamic control of growth and form

What determines large-scale anatomy? DNA does not directly specify geometrical arrangements of tissues and organs, and a process of encoding and decoding for morphogenesis is required. Moreover, many species can regenerate and remodel their structure despite drastic injury. The ability to obtain the correct target morphology from a diversity of initial conditions reveals that the morphogenetic code implements a rich system of pattern-homeostatic processes. Here, we describe an important mechanism by which cellular networks implement pattern regulation and plasticity: bioelectricity. All cells, not only nerves and muscles, produce and sense electrical signals; in vivo, these processes form bioelectric circuits that harness individual cell behaviors toward specific anatomical endpoints. We review emerging progress in reading and re-writing anatomical information encoded in bioelectrical states, and discuss the approaches to this problem from the perspectives of information theory, dynamical systems, and computational neuroscience. Cracking the bioelectric code will enable much-improved control over biological patterning, advancing basic evolutionary developmental biology as well as enabling numerous applications in regenerative medicine and synthetic bioengineering.

Bioelectric signaling in regeneration: Mechanisms of ionic controls of growth and form

The ability to control pattern formation is critical for the both the embryonic development of complex structures as well as for the regeneration/repair of damaged or missing tissues and organs. In addition to chemical gradients and gene regulatory networks, endogenous ion flows are key regulators of cell behavior. Not only do bioelectric cues provide information needed for the initial development of structures, they also enable the robust restoration of normal pattern after injury. In order to expand our basic understanding of morphogenetic processes responsible for the repair of complex anatomy, we need to identify the roles of endogenous voltage gradients, ion flows, and electric fields. In complement to the current focus on molecular genetics, decoding the information transduced by bioelectric cues enhances our knowledge of the dynamic control of growth and pattern formation. Recent advances in science and technology place us in an exciting time to elucidate the interplay between molecular-genetic inputs and important biophysical cues that direct the creation of tissues and organs. Moving forward, these new insights enable additional approaches to direct cell behavior and may result in profound advances in augmentation of regenerative capacity.

The Role of Direct Current Electric Field-Guided Stem Cell Migration in Neural Regeneration

Effective directional axonal growth and neural cell migration are crucial in the neural regeneration of the central nervous system (CNS). Endogenous currents have been detected in many developing nervous systems. Experiments have demonstrated that applied direct current (DC) electric fields (EFs) can guide axonal growth in vitro, and attempts have been made to enhance the regrowth of damaged spinal cord axons using DC EFs in in vivo experiments. Recent work has revealed that the migration of stem cells and stem cell-derived neural cells can be guided by DC EFs. These studies have raised the possibility that endogenous and applied DC EFs can be used to direct neural tissue regeneration. Although the mechanism of EF-directed axonal growth and cell migration has not been fully understood, studies have shown that the polarization of cell membrane proteins and the activation of intracellular signaling molecules are involved in the process. The application of EFs is a promising biotechnology for regeneration of the CNS.

Electrical Guidance of Human Stem Cells in the Rat Brain

Limited migration of neural stem cells in adult brain is a roadblock for the use of stem cell therapies to treat brain diseases and injuries. Here, we report a strategy that mobilizes and guides migration of stem cells in the brain in vivo. We developed a safe stimulation paradigm to deliver directional currents in the brain. Tracking cells expressing GFP demonstrated electrical mobilization and guidance of migration of human neural stem cells, even against co-existing intrinsic cues in the rostral migration stream. Transplanted cells were observed at 3 weeks and 4 months after stimulation in areas guided by the stimulation currents, and with indications of differentiation. Electrical stimulation thus may provide a potential approach to facilitate brain stem cell therapies.

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Developed a technology and device delivering electric current to the brain in vivo

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Achieved stable delivery of currents to brain with monitoring and safety concerns

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Exhibited effective guidance of migration of transplanted human NSCs in live brain

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Demonstrated enhanced motility, survival, and differentiation of the guided hNSCs

Endogenous Bioelectric Signaling Networks: Exploiting Voltage Gradients for Control of Growth and Form

Living systems exhibit remarkable abilities to self-assemble, regenerate, and remodel complex shapes. How cellular networks construct and repair specific anatomical outcomes is an open question at the heart of the next-generation science of bioengineering. Developmental bioelectricity is an exciting emerging discipline that exploits endogenous bioelectric signaling among many cell types to regulate pattern formation. We provide a brief overview of this field, review recent data in which bioelectricity is used to control patterning in a range of model systems, and describe the molecular tools being used to probe the role of bioelectrics in the dynamic control of complex anatomy. We suggest that quantitative strategies recently developed to infer semantic content and information processing from ionic activity in the brain might provide important clues to cracking the bioelectric code. Gaining control of the mechanisms by which large-scale shape is regulated in vivo will drive transformative advances in bioengineering, regenerative medicine, and synthetic morphology, and could be used to therapeutically address birth defects, traumatic injury, and cancer.

Electrophoresis of cell membrane heparan sulfate regulates galvanotaxis in glial cells

Endogenous electric fields modulate many physiological processes by promoting directional migration, a process known as galvanotaxis. Despite the importance of galvanotaxis in development and disease, the mechanism by which cells sense and migrate directionally in an electric field remains unknown. Here, we show that electrophoresis of cell surface heparan sulfate (HS) critically regulates this process. HS was found to be localized at the anode-facing side in fetal neural progenitor cells (fNPCs), fNPC-derived astrocytes and brain tumor-initiating cells (BTICs), regardless of their direction of galvanotaxis. Enzymatic removal of HS and other sulfated glycosaminoglycans significantly abolished or reversed the cathodic response seen in fNPCs and BTICs. Furthermore, Slit2, a chemorepulsive ligand, was identified to be colocalized with HS in forming a ligand gradient across cellular membranes. Using both imaging and genetic modification, we propose a novel mechanism for galvanotaxis in which electrophoretic localization of HS establishes cell polarity by functioning as a co-receptor and provides repulsive guidance through Slit-Robo signaling.

Environmental Factors That Influence Stem Cell Migration: An "Electric Field"

Environmental Stimulus of Electric Fields on Stem Cell Migration. The movement of cells in response to electric potential gradients is called galvanotaxis. In vivo galvanotaxis, powered by endogenous electric fields (EFs), plays a critical role during development and wound healing. This review aims to provide a perspective on how stem cells transduce EFs into directed migration and an understanding of the current literature relating to the mechanisms by which cells sense and transduce EFs. We will comment on potential EF-based regenerative medicine therapeutics.