PI3K mediated electrotaxis of embryonic and adult neural progenitor cells in the presence of growth factors

The role of TGF-β in the electrotactic reaction of mouse 3T3 fibroblasts in vitro

Endogenous electric fields (EFs) serve as a crucial signal to guide cell movement in processes such as wound healing, embryonic development, and cancer metastasis. However, the mechanism underlying cell electrotaxis remains poorly understood. A plausible hypothesis suggests that electrophoretic or electroosmotic forces may rearrange charged components of the cell membrane, including receptors for chemoattractants which induce asymmetric signaling and directional motility. This study aimed to explore the role of Transforming Growth Factor Beta (TGFβ) signaling in the electrotactic reaction of 3T3 fibroblasts. Our findings indicate that inhibiting canonical and several non-canonical signaling pathways originating from the activated TGF-β receptor does not hinder the directed migration of 3T3 cells to the cathode. Furthermore, suppression of TGF-β receptor expression does not eliminate the directional migration effect of 3T3 cells in the electric field. Additionally, there is no observed redistribution of the TGF-β receptor in the electric field. However, our studies affirm the significant involvement of Phosphoinositide 3-Kinase (PI3K) in electrotaxis, suggesting that in our model, its activation is likely associated with factors independent of TGFβ action.

Advances in Material-Assisted Electromagnetic Neural Stimulation

Bioelectricity plays a crucial role in organisms, being closely connected to neural activity and physiological processes. Disruptions in the nervous system can lead to chaotic ionic currents at the injured site, causing disturbances in the local cellular microenvironment, impairing biological pathways, and resulting in a loss of neural functions. Electromagnetic stimulation has the ability to generate internal currents, which can be utilized to counter tissue damage and aid in the restoration of movement in paralyzed limbs. By incorporating implanted materials, electromagnetic stimulation can be targeted more accurately, thereby significantly improving the effectiveness and safety of such interventions. Currently, there have been significant advancements in the development of numerous promising electromagnetic stimulation strategies with diverse materials. This review provides a comprehensive summary of the fundamental theories, neural stimulation modulating materials, material application strategies, and pre-clinical therapeutic effects associated with electromagnetic stimulation for neural repair. It offers a thorough analysis of current techniques that employ materials to enhance electromagnetic stimulation, as well as potential therapeutic strategies for future applications.

Electrical stimulation induced pre-vascularization of engineered dental pulp tissue

Vascularization is a key step to achieve pulp tissue regeneration and in vitro pre-vascularized dental pulp tissue could be applied as a graft substitute for dental pulp tissue repair. In this study, human dental pulp stem cells (DPSCs) and human umbilical vein endothelial cells (hUVECs) were co-cultured in 3D Matrigel and 150 mV/mm electric fields (EFs) were used to promote the construction of pre-vascularized dental pulp tissue. After optimizing co-cultured ratio of two cell types, immunofluorescence staining, and live/dead detection were used to investigate the effect of EFs on cell survival, differentiation and vessel formation in 3D engineered dental pulp tissue. RNA sequencing was used to investigate the potential molecular mechanisms by which EF regulates vessel formation in 3D engineered dental pulp tissue. Here we identified that EF-induced pre-vascularized engineered dental pulp tissue not only had odontoblasts, but also had a rich vascular network, and smooth muscle-like cells appeared around the blood vessels. The GO enrichment analysis showed that these genes were significantly enriched in regulation of angiogenesis, cell migration and motility. The most significant term of the KEGG pathway analysis were NOTCH signaling pathway and Calcium signaling pathway etc. The PPI network revealed that NOTCH1 and IL-6 were central hub genes. Our study indicated that EFs significantly promoted the maturation and stable of blood vessel in 3D engineered pulp tissue and provided an experimental basis for the application of EF in dental pulp angiogenesis and regeneration.

bHLH transcription factors Hes1, Ascl1 and Oligo2 exhibit different expression patterns in the process of physiological electric fields-induced neuronal differentiation

BACKGROUND

Recent studies have shown that the expression of bHLH transcription factors Hes1, Ascl1, and Oligo2 has an oscillating balance in neural stem cells (NSCs) to maintain their self-proliferation and multi-directional differentiation potential. This balance can be disrupted by exogenous stimulation. Our previous work has identified that electrical stimulation could induce neuronal differentiation of mouse NSCs.

METHODS

To further evaluate if physiological electric fields (EFs)-induced neuronal differentiation is related to the expression patterns of bHLH transcription factors Hes1, Ascl1, and Oligo2, mouse embryonic brain NSCs were used to investigate the expression changes of Ascl1, Hes1 and Oligo2 in mRNA and protein levels during EF-induced neuronal differentiation.

RESULTS

Our results showed that NSCs expressed high level of Hes1, while expression of Ascl1 and Oligo2 stayed at very low levels. When NSCs exited proliferation, the expression of Hes1 in differentiated cells began to decrease and oscillated at the low expression level. Oligo2 showed irregular changes in low expression level. EF-stimulation significantly increased the expression of Ascl1 at mRNA and protein levels accompanied by an increased percentage of neuronal differentiation. What's more, over-expression of Hes1 inhibited the neuronal differentiation induced by EFs.

CONCLUSION

EF-stimulation directed neuronal differentiation of NSCs by promoting the continuous accumulation of Ascl1 expression and decreasing the expression of Hes1.

Electrical stimulation affects the differentiation of transplanted regionally specific human spinal neural progenitor cells (sNPCs) after chronic spinal cord injury

BACKGROUND

There are currently no effective clinical therapies to ameliorate the loss of function that occurs after spinal cord injury. Electrical stimulation of the rat spinal cord through the rat tail has previously been described by our laboratory. We propose combinatorial treatment with human induced pluripotent stem cell-derived spinal neural progenitor cells (sNPCs) along with tail nerve electrical stimulation (TANES). The purpose of this study was to examine the influence of TANES on the differentiation of sNPCs with the hypothesis that the addition of TANES would affect incorporation of sNPCs into the injured spinal cord, which is our ultimate goal.

METHODS

Chronically injured athymic nude rats were allocated to one of three treatment groups: injury only, sNPC only, or sNPC + TANES. Rats were sacrificed at 16 weeks post-transplantation, and tissue was processed and analyzed utilizing standard histological and tissue clearing techniques. Functional testing was performed. All quantitative data were presented as mean ± standard error of the mean. Statistics were conducted using GraphPad Prism.

RESULTS

We found that sNPCs were multi-potent and retained the ability to differentiate into mainly neurons or oligodendrocytes after this transplantation paradigm. The addition of TANES resulted in more transplanted cells differentiating into oligodendrocytes compared with no TANES treatment, and more myelin was found. TANES not only promoted significantly higher numbers of sNPCs migrating away from the site of injection but also influenced long-distance axonal/dendritic projections especially in the rostral direction. Further, we observed localization of synaptophysin on SC121-positive cells, suggesting integration with host or surrounding neurons, and this finding was enhanced when TANES was applied. Also, rats that were transplanted with sNPCs in combination with TANES resulted in an increase in serotonergic fibers in the lumbar region. This suggests that TANES contributes to integration of sNPCs, as well as activity-dependent oligodendrocyte and myelin remodeling of the chronically injured spinal cord.

CONCLUSIONS

Together, the data suggest that the added electrical stimulation promoted cellular integration and influenced the fate of human induced pluripotent stem cell-derived sNPCs transplanted into the injured spinal cord.

Direct-Current Electrical Field Stimulation of Patient-Derived Colorectal Cancer Cells

Several cues for a directional migration of colorectal cancer cells were identified as being crucial in tumor progression. However, galvanotaxis, the directional migration in direct-current electrical fields, has not been investigated so far. Therefore, we asked whether direct-current electrical fields could be used to mobilize colorectal cancer cells along field vectors. For this purpose, five patient-derived low-passage cell lines were exposed to field strengths of 150-250 V/m in vitro, and migration along the field vectors was investigated. To further study the role of voltage-gated calcium channels on galvanotaxis and intracellular signaling pathways that are associated with migration of colorectal cancer cells, the cultures were exposed to selective inhibitors. In three out of five colorectal cancer cell lines, we found a preferred cathodal migration. The cellular integrity of the cells was not impaired by exposure of the cells to the selected field strengths. Galvanotaxis was sensitive to inhibition of voltage-gated calcium channels. Furthermore, signaling pathways such as AKT and MEK, but not STAT3, were also found to contribute to galvanotaxis in our in vitro model system. Overall, we identify electrical fields as an important contributor to the directional migration of colorectal cancer cells.

Micro-Current Stimulation Can Modulate the Adipogenesis Process by Regulating the Insulin Signaling Pathway in 3T3-L1 Cells and ob/ob Mice

Obesity is a disease in which fat is abnormally or excessively accumulated in the body, and many studies have been conducted to overcome it with various techniques. In this study, we evaluated whether micro-current stimulation (MCS) can be applied to prevent obesity by regulating the adipogenesis through 3T3-L1 cells and ob/ob mice. To specify the intensity of MCS, Oil Red O staining was conducted with various intensities of MCS. Based on these, subsequent experiments used 200 and 400 μA for the intensity of MCS. The expressions of insulin signaling pathway-related proteins, including phosphorylation of IGF-1 and IR, were decreased in all MCS groups, and in turn, downstream signals such as Akt and ERK were decreased. In addition, MCS reduced the nucleus translocation of PPAR-γ and decreased the protein expression of C/EBP-α. In the ob/ob mouse model, MCS reduced body weight gain and abdominal adipose tissue volume. In particular, the concentration of triglycerides in serum was also decreased. Taken together, our findings showed that MCS inhibited lipid accumulation by regulating insulin signaling in 3T3-L1, and it was effective at reducing body weight and adipose tissue volume in ob/ob mice. These suggest that MCS may be a useful treatment approach for obesity.

Electric field stimulation boosts neuronal differentiation of neural stem cells for spinal cord injury treatment via PI3K/Akt/GSK-3β/β-catenin activation

BACKGROUND

Neural stem cells (NSCs) are considered as candidates for cell replacement therapy in many neurological disorders. However, the propensity for their differentiation to proceed more glial rather than neuronal phenotypes in pathological conditions limits positive outcomes of reparative transplantation. Exogenous physical stimulation to favor the neuronal differentiation of NSCs without extra chemical side effect could alleviate the problem, providing a safe and highly efficient cell therapy to accelerate neurological recovery following neuronal injuries.

RESULTS

With 7-day physiological electric field (EF) stimulation at 100 mV/mm, we recorded the boosted neuronal differentiation of NSCs, comparing to the non-EF treated cells with 2.3-fold higher MAP2 positive cell ratio, 1.6-fold longer neuronal process and 2.4-fold higher cells ratio with neuronal spontaneous action potential. While with the classical medium induction, the neuronal spontaneous potential may only achieve after 21-day induction. Deficiency of either PI3Kγ or β-catenin abolished the above improvement, demonstrating the requirement of the PI3K/Akt/GSK-3β/β-catenin cascade activation in the physiological EF stimulation boosted neuronal differentiation of NSCs. When transplanted into the spinal cord injury (SCI) modelled mice, these EF pre-stimulated NSCs were recorded to develop twofold higher proportion of neurons, comparing to the non-EF treated NSCs. Along with the boosted neuronal differentiation following transplantation, we also recorded the improved neurogenesis in the impacted spinal cord and the significantly benefitted hind limp motor function repair of the SCI mice.

CONCLUSIONS

In conclusion, we demonstrated physiological EF stimulation as an efficient method to boost the neuronal differentiation of NSCs via the PI3K/Akt/GSK-3β/β-catenin activation. Pre-treatment with the EF stimulation induction before NSCs transplantation would notably improve the therapeutic outcome for neurogenesis and neurofunction recovery of SCI.

Coupling cell shape and velocity leads to oscillation and circling in keratocyte galvanotaxis

During wound healing, fish keratocyte cells undergo galvanotaxis where they follow a wound-induced electric field. In addition to their stereotypical persistent motion, keratocytes can develop circular motion without a field or oscillate while crawling in the field direction. We developed a coarse-grained phenomenological model that captures these keratocyte behaviors. We fit this model to experimental data on keratocyte response to an electric field being turned on. A critical element of our model is a tendency for cells to turn toward their long axis, arising from a coupling between cell shape and velocity, which gives rise to oscillatory and circular motion. Galvanotaxis is influenced not only by the field-dependent responses, but also cell speed and cell shape relaxation rate. When the cell reacts to an electric field being turned on, our model predicts that stiff, slow cells react slowly but follow the signal reliably. Cells that polarize and align to the field at a faster rate react more quickly and follow the signal more reliably. When cells are exposed to a field that switches direction rapidly, cells follow the average of field directions, while if the field is switched more slowly, cells follow a "staircase" pattern. Our study indicated that a simple phenomenological model coupling cell speed and shape is sufficient to reproduce a broad variety of different keratocyte behaviors, ranging from circling to oscillation to galvanotactic response, by only varying a few parameters.

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.

Engineering Tissues of the Central Nervous System: Interfacing Conductive Biomaterials with Neural Stem/Progenitor Cells

Conductive biomaterials provide an important control for engineering neural tissues, where electrical stimulation can potentially direct neural stem/progenitor cell (NS/PC) maturation into functional neuronal networks. It is anticipated that stem cell-based therapies to repair damaged central nervous system (CNS) tissues and ex vivo, "tissue chip" models of the CNS and its pathologies will each benefit from the development of biocompatible, biodegradable, and conductive biomaterials. Here, technological advances in conductive biomaterials are reviewed over the past two decades that may facilitate the development of engineered tissues with integrated physiological and electrical functionalities. First, one briefly introduces NS/PCs of the CNS. Then, the significance of incorporating microenvironmental cues, to which NS/PCs are naturally programmed to respond, into biomaterial scaffolds is discussed with a focus on electrical cues. Next, practical design considerations for conductive biomaterials are discussed followed by a review of studies evaluating how conductive biomaterials can be engineered to control NS/PC behavior by mimicking specific functionalities in the CNS microenvironment. Finally, steps researchers can take to move NS/PC-interfacing, conductive materials closer to clinical translation are discussed.

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.

Effects of Electroactive materials on nerve cell behaviors and applications in peripheral nerve repair

Peripheral nerve damage can lead to loss of function or even complete disability, which bring about a huge burden on both the patient and society. Regulating nerve cell behavior and...

Antioxidative and Conductive Nanoparticles-Embedded Cell Niche for Neural Differentiation and Spinal Cord Injury Repair

Following spinal cord injury (SCI), the transmission of electrical signals is interrupted, and an oxidative microenvironment is generated, hindering nerve regeneration and functional recovery. The strategies of regulating oxidative pathological microenvironment while restoring endogenous electrical signal transmission hold promise for SCI treatment. However, challenges are still faced in simply fabricating bioactive scaffolds with both antioxidation and conductivity. Herein, aiming to construct an antioxidative and conductive microenvironment for nerve regeneration, the difunctional polypyrrole (PPy) nanoparticles were developed and incorporated into bioactive collagen/hyaluronan hydrogel. Owing to the embedded PPy in hydrogel, the encapsulated bone marrow mesenchymal stem cells (BMSCs) can be protected from oxidative damage, and their neuronal differentiation was promoted by the synergy between conductivity and electrical stimulation, which is proved to be related to PI3K/Akt and the mitogen-activated protein kinase (MAPK) pathway. In SCI rats, the BMSC-laden difunctional hydrogel restored the transmission of bioelectric signals and inhibited secondary damage, thereby facilitating neurogenesis, resulting in prominent nerve regeneration and functional recovery. Overall, taking advantage of a difunctional nanomaterial to meet two essential requirements in SCI repair, this work provides intriguing insights into the design of biomaterials for nerve regeneration and tissue engineering.

Migration of Human Renal Tubular Epithelial Cells in Response to Physiological Electric Signals

Restoration of proximal tubular cell integrity and function after ischemic injury involves cell migration and proliferation. Endogenous fields are present during embryonic development and wound healing. Electric field (EF)-induced effects on cell migration have been observed in many cell types. This study investigated the effect of physiological direct current EF (dc EF) on the motility of renal epithelial cells. Human renal tubular epithelial (HK-2) and human-derived renal epithelial (HEK-293) cells were exposed to dc EF at physiological magnitude. Cell images were recorded and analyzed using an image analyzer. Cell lysates were used to detect protein expression by western blot. Scratch wounds were created in monolayers of HK-2 cells, and wound areas of cells were measured in response to EF exposure. Cells migrated significantly faster in the presence of an EF and toward the cathode. Application of an EF led to activation of the Erk1/2, p38 MAPK, and Akt signaling pathways. Pharmacological inhibition of Erk1/2, p38 MAPK, and Akt impaired EF-induced migratory responses, such as motility rate and directedness. In addition, exposure of the monolayers to EF enhanced EF-induced HK-2 wound healing. Our results suggest that EFs augment the rate of single renal epithelium migration and induce cell cathodal migration through activation of Erk1/2, p38 MAPK, and Akt signaling. Moreover, exposure of the renal epithelium to EF facilitated closure of in vitro small wounds by enhancing cell migration.

Self-Assembling Hydrogel Structures for Neural Tissue Repair

Hydrogel materials have been employed as biological scaffolds for tissue regeneration across a wide range of applications. Their versatility and biomimetic properties make them an optimal choice for treating the complex and delicate milieu of neural tissue damage. Aside from finely tailored hydrogel properties, which aim to mimic healthy physiological tissue, a minimally invasive delivery method is essential to prevent off-target and surgery-related complications. The specific class of injectable hydrogels termed self-assembling peptides (SAPs), provide an ideal combination of in situ polymerization combined with versatility for biofunctionlization, tunable physicochemical properties, and high cytocompatibility. This review identifies design criteria for neural scaffolds based upon key cellular interactions with the neural extracellular matrix (ECM), with emphasis on aspects that are reproducible in a biomaterial environment. Examples of the most recent SAPs and modification methods are presented, with a focus on biological, mechanical, and topographical cues. Furthermore, SAP electrical properties and methods to provide appropriate electrical and electrochemical cues are widely discussed, in light of the endogenous electrical activity of neural tissue as well as the clinical effectiveness of stimulation treatments. Recent applications of SAP materials in neural repair and electrical stimulation therapies are highlighted, identifying research gaps in the field of hydrogels for neural regeneration.

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.

Electric signals counterbalanced posterior vs anterior PTEN signaling in directed migration of Dictyostelium

Background

Cells show directed migration response to electric signals, namely electrotaxis or galvanotaxis. PI3K and PTEN jointly play counterbalancing roles in this event via a bilateral regulation of PIP3 signaling. PI3K has been proved essential in anterior signaling of electrotaxing cells, whilst the role of PTEN remains elusive.

Methods

Dictyostelium cells with different genetic backgrounds were treated with direct current electric signals to investigate the genetic regulation of electrotaxis.

Results

We demonstrated that electric signals promoted PTEN phosphatase activity and asymmetrical translocation to the posterior plasma membrane of the electrotaxing cells. Electric stimulation produced a similar but delayed rear redistribution of myosin II, immediately before electrotaxis started. Actin polymerization is required for the asymmetric membrane translocation of PTEN and myosin. PTEN signaling is also responsible for the asymmetric anterior redistribution of PIP3/F-actin, and a biased redistribution of pseudopod protrusion in the forwarding direction of electrotaxing cells.

Conclusions

PTEN controls electrotaxis by coordinately regulating asymmetric redistribution of myosin to the posterior, and PIP3/F-actin to the anterior region of the directed migration cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00580-x.

Electrical Stimulation Promotes Stem Cell Neural Differentiation in Tissue Engineering

Nerve injuries and neurodegenerative disorders remain serious challenges, owing to the poor treatment outcomes of in situ neural stem cell regeneration. The most promising treatment for such injuries and disorders is stem cell-based therapies, but there remain obstacles in controlling the differentiation of stem cells into fully functional neuronal cells. Various biochemical and physical approaches have been explored to improve stem cell-based neural tissue engineering, among which electrical stimulation has been validated as a promising one both in vitro and in vivo. Here, we summarize the most basic waveforms of electrical stimulation and the conductive materials used for the fabrication of electroactive substrates or scaffolds in neural tissue engineering. Various intensities and patterns of electrical current result in different biological effects, such as enhancing the proliferation, migration, and differentiation of stem cells into neural cells. Moreover, conductive materials can be used in delivering electrical stimulation to manipulate the migration and differentiation of stem cells and the outgrowth of neurites on two- and three-dimensional scaffolds. Finally, we also discuss the possible mechanisms in enhancing stem cell neural differentiation using electrical stimulation. We believe that stem cell-based therapies using biocompatible conductive scaffolds under electrical stimulation and biochemical induction are promising for neural regeneration.

Bioelectric signaling: Reprogrammable circuits underlying embryogenesis, regeneration, and cancer

How are individual cell behaviors coordinated toward invariant large-scale anatomical outcomes in development and regeneration despite unpredictable perturbations? Endogenous distributions of membrane potentials, produced by ion channels and gap junctions, are present across all tissues. These bioelectrical networks process morphogenetic information that controls gene expression, enabling cell collectives to make decisions about large-scale growth and form. Recent progress in the analysis and computational modeling of developmental bioelectric circuits and channelopathies reveals how cellular collectives cooperate toward organ-level structural order. These advances suggest a roadmap for exploiting bioelectric signaling for interventions addressing developmental disorders, regenerative medicine, cancer reprogramming, and synthetic bioengineering.

Direct Current Electric Stimulation Alters the Frequency and the Distribution of Mitotic Cells in Planarians

Background: The use of direct current electric stimulation (DCS) is an effective strategy to treat disease and enhance body functionality. Thus, treatment with DCS is an attractive biomedical alternative, but the molecular underpinnings remain mostly unknown. The lack of experimental models to dissect the effects of DCS from molecular to organismal levels is an important caveat. Here, we introduce the planarian flatworm Schmidtea mediterranea as a tractable organism for in vivo studies of DCS. We developed an experimental method that facilitates the application of direct current electrical stimulation to the whole planarian body (pDCS). Materials and Methods: Planarian immobilization was achieved by combining treatment with anesthesia, agar embedding, and low temperature via a dedicated thermoelectric cooling unit. Electric currents for pDCS were delivered using pulled glass microelectrodes. The electric potential was supplied through a constant voltage power supply. pDCS was administered up to six hours, and behavioral and molecular effects were measured by using video recordings, immunohistochemistry, and gene expression analysis. Results: The behavioral immobilization effects are reversible, and pDCS resulted in a redistribution of mitotic cells along the mediolateral axis of the planarian body. The pDCS effects were dependent on the polarity of the electric field, which led to either increase in reductions in mitotic densities associated with the time of pDCS. The changes in mitotic cells were consistent with apparent redistribution in gene expression of the stem cell marker smedwi-1. Conclusion: The immobilization technique presented in this work facilitates studies aimed at dissecting the effects of exogenous electric stimulation in the adult body. Treatment with DCS can be administered for varying times, and the consequences evaluated at different levels, including animal behavior, cellular and transcriptional changes. Indeed, treatment with pDCS can alter cellular and transcriptional parameters depending on the polarity of the electric field and duration of the exposure.

Analysis of the Differential Gene and Protein Expression Profiles of Corneal Epithelial Cells Stimulated with Alternating Current Electric Fields

In cells, intrinsic endogenous direct current (DC) electric fields (EFs) serve as morphogenetic cues and are necessary for several important cellular responses including activation of multiple signaling pathways, cell migration, tissue regeneration and wound healing. Endogenous DC EFs, generated spontaneously following injury in physiological conditions, directly correlate with wound healing rate, and different cell types respond to these EFs via directional orientation and migration. Application of external DC EFs results in electrode polarity and is known to activate intracellular signaling events in specific direction. In contrast, alternating current (AC) EFs are known to induce continuous bidirectional flow of charged particles without electrode polarity and also minimize electrode corrosion. In this context, the present study is designed to study effects of AC EFs on corneal epithelial cell gene and protein expression profiles in vitro. We performed gene and antibody arrays, analyzed the data to study specific influence of AC EFs, and report that AC EFs has no deleterious effect on epithelial cell function. Gene Ontology results, following gene and protein array data analysis, showed that AC EFs influence similar biological processes that are predominantly responsive to organic substance, chemical, or external stimuli. Both arrays activate cytokine–cytokine receptor interaction, MAPK and IL-17 signaling pathways. Further, in comparison to the gene array data, the protein array data show enrichment of diverse activated signaling pathways through several interconnecting networks.

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.

Polarization of ADAM17-driven EGFR signalling in electric field-guided collective migration of epidermal sheets

Endogenous electric field is considered to play an important role in promoting collective migration of epidermis to the wound centre. However, most studies are focused on the effect of bioelectric field on the movement and migration of single epithelial cell; the molecular mechanisms about collective migration of epidermal monolayers remain unclear. Here, we found that EFs dramatically promoted the collective migration of HaCaT cells towards the anode, activated the sheddase activity of ADAM17 and increased the phosphorylation level of EGFR. Moreover, EGFR phosphorylation and HB-EGF shedding level were significantly decreased by the ADAM17 inhibitor TAPI-2 or siADAM17 under EFs, which subsequently attenuated the directed migration of HaCaT sheets. Notably, the inhibition of EF-regulated collective migration by siADAM17 was rescued by addition of recombinant HB-EGF. Furthermore, we observed that F-actin was dynamically polarized along the leading edge of the migrated sheets under EFs and that this polarization was regulated by ADAM17/HB-EGF/EGFR signalling. In conclusion, our study indicated that ADAM17 contributed to the collective directional movement of the epidermal monolayer by driving HB-EGF release and activating EGFR under EFs, and this pathway also mediated the polarization of F-actin in migrating sheets, which is essential in directional migration.

Applied electric fields suppress osimertinib-induced cytotoxicity via inhibiting FOXO3a nuclear translocation through AKT activation

Osimertinib is a third-generation epidermal growth factor receptor tyrosine kinase inhibitor against T790M-mutant non-small cell lung cancer (NSCLC). Acquired resistance to osimertinib is a growing clinical challenge that is not fully understood. Endogenous electric fields (EFs), components of the tumor microenvironment, are associated with cancer cell migration and proliferation. However, the impact of EFs on drug efficiency has not been studied. In this study, we observed that EFs counteracted the effects of osimertinib. EFs of 100 mV/mm suppressed osimertinib-induced cell death and promoted cell proliferation. Transcriptional analysis revealed that the expression pattern induced by osimertinib was altered by EFs stimulation. KEGG analysis showed that differential expression genes were mostly enriched in PI3K-AKT pathway. Then, we found that osimertinib inhibited AKT phosphorylation, while EFs stimulation resulted in significant activation of AKT, which could override the effects generated by osimertinib. Importantly, pharmacological inhibition of PI3K/AKT by LY294002 diminished EF-induced activation of AKT and restored the cytotoxicity of osimertinib suppressed by EFs, which proved that AKT activation was essential for EFs to attenuate the efficacy of osimertinib. Furthermore, activation of AKT by EFs led to phosphorylation of forkhead box O3a (FOXO3a), and reduction in nuclear translocation of FOXO3a induced by osimertinib, resulting in decreased expression of Bim and attenuated cytotoxicity of osimertinib. Taken together, we demonstrated that EFs suppressed the antitumor activity of osimertinib through AKT/FOXO3a/Bim pathway, and combination of PI3K/AKT inhibitor with osimertinib counteracted the effects of EFs. Our findings provided preliminary data for therapeutic strategies to enhance osimertinib efficacy in NSCLC patients.

Substrate-Dependent Galvanotaxis of Directly Reprogrammed Human Neural Precursor Cells

Background: Neural precursor cells (NPCs) hold great promise for neural repair. Endogenous NPCs, found in the subventricular zone of the adult brain, proliferate and migrate toward lesion sites; however, it is not sufficient for neural repair. NPCs are electrosensitive cells that undergo directed migration in an electric field (EF). Here, we examined the EF-induced migration of a clinically relevant human NPC population. Materials & Methods: We examined the effects of different substrates and microenvironments on human NPC galvanotaxis. Results: Human NPCs increased their migration speed in the presence of an EF, and the direction of migration (anodal vs. cathodal) varied between substrates. The secretome and extracellular pH were not significant factors in EF-induced migration; however, our results are consistent with substrate stiffness playing a role in the direction of cell migration. Conclusion: These findings provide insight into the importance of the microenvironment on modulating human NPC migration and highlight substrate-dependent considerations for neurorepair.

A Semi-automated and Scalable 3D Spheroid Assay to Study Neuroblast Migration

The subventricular zone of the mammalian brain is the major source of adult born neurons. These neuroblasts normally migrate long distances to the olfactory bulbs but can be re-routed to locations of injury and promote neuroregeneration. Mechanistic understanding and pharmacological targets regulating neuroblast migration is sparse. Furthermore, lack of migration assays limits development of pharmaceutical interventions targeting neuroblast recruitment. We therefore developed a physiologically relevant 3D neuroblast spheroid migration assay that permits the investigation of large numbers of interventions. To verify the assay, 1,012 kinase inhibitors were screened for their effects on migration. Several induced significant increases or decreases in migration. MuSK and PIK3CB were selected as putative targets and their knockdown validated increased neuroblast migration. Thus, compounds identified through this assay system could be explored for their potential in augmenting neuroblast recruitment to sites of injury for neuroregeneration, or for decreasing malignant invasion.

The excitable signal transduction networks: movers and shapers of eukaryotic cell migration

In response to a variety of external cues, eukaryotic cells display varied migratory modes to perform their physiological functions during development and in the adult. Aberrations in cell migration result in embryonic defects and cancer metastasis. The molecular components involved in cell migration are remarkably conserved between the social amoeba Dictyostelium and mammalian cells. This makes the amoeba an excellent model system for studies of eukaryotic cell migration. These migration-associated components can be grouped into three networks: input, signal transduction and cytoskeletal. In migrating cells, signal transduction events such as Ras or PI3K activity occur at the protrusion tips, referred to as 'front', whereas events such as dissociation of PTEN from these regions are referred to as 'back'. Asymmetric distribution of such front and back events is crucial for establishing polarity and guiding cell migration. The triggering of these signaling events displays properties of biochemical excitability including all-or-nothing responsiveness to suprathreshold stimuli, refractoriness, and wave propagation. These signal transduction waves originate from a point and propagate towards the edge of the cell, thereby driving cytoskeletal activity and cellular protrusions. Any change in the threshold for network activation alters the range of the propagating waves and the size of cellular protrusions which gives rise to various migratory modes in cells. Thus, this review highlights excitable signal transduction networks as key players for coordinating cytoskeletal activities to drive cell migration in all eukaryotes.

SCHEEPDOG: Programming Electric Cues to Dynamically Herd Large-Scale Cell Migration

Directed cell migration is critical across biological processes spanning healing to cancer invasion, yet no existing tools allow real-time interactive guidance over such migration. We present a new bioreactor that harnesses electrotaxis-directed cell migration along electric field gradients-by integrating four independent electrodes under computer control to dynamically program electric field patterns, and hence steer cell migration. Using this platform, we programmed and characterized multiple precise, two-dimensional collective migration maneuvers in renal epithelia and primary skin keratinocyte ensembles. First, we demonstrated on-demand, 90-degree collective turning. Next, we developed a universal electrical stimulation scheme capable of programming arbitrary 2D migration maneuvers such as precise angular turns and migration in a complete circle. Our stimulation scheme proves that cells effectively time-average electric field cues, helping to elucidate the transduction timescales in electrotaxis. Together, this work represents an enabling platform for controlling cell migration with broad utility across many cell types.

Electrical stimulation as a novel tool for regulating cell behavior in tissue engineering

Recently, electrical stimulation as a physical stimulus draws lots of attention. It shows great potential in disease treatment, wound healing, and mechanism study because of significant experimental performance. Electrical stimulation can activate many intracellular signaling pathways, and influence intracellular microenvironment, as a result, affect cell migration, cell proliferation, and cell differentiation. Electrical stimulation is using in tissue engineering as a novel type of tool in regeneration medicine. Besides, with the advantages of biocompatible conductive materials coming into view, the combination of electrical stimulation with suitable tissue engineered scaffolds can well combine the benefits of both and is ideal for the field of regenerative medicine. In this review, we summarize the various materials and latest technologies to deliver electrical stimulation. The influences of electrical stimulation on cell alignment, migration and its underlying mechanisms are discussed. Then the effect of electrical stimulation on cell proliferation and differentiation are also discussed.

Overlapping migratory mechanisms between neural progenitor cells and brain tumor stem cells

Neural stem cells present in the subventricular zone (SVZ), the largest neurogenic niche of the mammalian brain, are able to self-renew as well as generate neural progenitor cells (NPCs). NPCs are highly migratory and traverse the rostral migratory stream (RMS) to the olfactory bulb, where they terminally differentiate into mature interneurons. NPCs from the SVZ are some of the few cells in the CNS that migrate long distances during adulthood. The migratory process of NPCs is highly regulated by intracellular pathway activation and signaling from the surrounding microenvironment. It involves modulation of cell volume, cytoskeletal rearrangement, and isolation from compact extracellular matrix. In malignant brain tumors including high-grade gliomas, there are cells called brain tumor stem cells (BTSCs) with similar stem cell characteristics to NPCs but with uncontrolled cell proliferation and contribute to tumor initiation capacity, tumor progression, invasion, and tumor maintenance. These BTSCs are resistant to chemotherapy and radiotherapy, and their presence is believed to lead to tumor recurrence at distal sites from the original tumor location, principally due to their high migratory capacity. BTSCs are able to invade the brain parenchyma by utilizing many of the migratory mechanisms used by NPCs. However, they have an increased ability to infiltrate the tight brain parenchyma and utilize brain structures such as myelin tracts and blood vessels as migratory paths. In this article, we summarize recent findings on the mechanisms of cellular migration that overlap between NPCs and BTSCs. A better understanding of the intersection between NPCs and BTSCs will to provide a better comprehension of the BTSCs' invasive capacity and the molecular mechanisms that govern their migration and eventually lead to the development of new therapies to improve the prognosis of patients with malignant gliomas.

Electromagnetic fields alter the motility of metastatic breast cancer cells

Interactions between cells and their environment influence key physiologic processes such as their propensity to migrate. However, directed migration controlled by extrinsically applied electrical signals is poorly understood. Using a novel microfluidic platform, we found that metastatic breast cancer cells sense and respond to the net direction of weak (∼100 µV cm-1), asymmetric, non-contact induced Electric Fields (iEFs). iEFs inhibited EGFR (Epidermal Growth Factor Receptor) activation, prevented formation of actin-rich filopodia, and hindered the motility of EGF-treated breast cancer cells. The directional effects of iEFs were nullified by inhibition of Akt phosphorylation. Moreover, iEFs in combination with Akt inhibitor reduced EGF-promoted motility below the level of untreated controls. These results represent a step towards isolating the coupling mechanism between cell motility and iEFs, provide valuable insights into how iEFs target multiple diverging cancer cell signaling mechanisms, and demonstrate that electrical signals are a fundamental regulator of cancer cell migration.

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.

Electrical stimulation affects neural stem cell fate and function in vitro

Electrical stimulation (ES) has been applied in cell culture system to enhance neural stem cell (NSC) proliferation, neuronal differentiation, migration, and integration. According to the mechanism of its function, ES can be classified into induced electrical (EFs) and electromagnetic fields (EMFs). EFs guide axonal growth and induce directional cell migration, whereas EMFs promote neurogenesis and facilitates NSCs to differentiate into functional neurons. Conductive nanomaterials have been used as functional scaffolds to provide mechanical support and biophysical cues in guiding neural cell growth and differentiation and building complex neural tissue patterns. Nanomaterials may have a combined effect of topographical and electrical cues on NSC migration and differentiation. Electrical cues may promote NSC neurogenesis via specific ion channel activation, such as SCN1α and CACNA1C. To accelerate the future application of ES in preclinical research, we summarized the specific setting, such as current frequency, intensity, and stimulation duration used in various ES devices, as well as the nanomaterials involved, in this review with the possible mechanisms elucidated. This review can be used as a checklist for ES work in stem cell research to enhance the translational process of NSCs in clinical application.

Electrotaxis of Glioblastoma and Medulloblastoma Spheroidal Aggregates

Treatment of neuroepithelial cancers remains a daunting clinical challenge, particularly due to an inability to address rampant invasion deep into eloquent regions of the brain. Given the lack of access, and the dispersed nature of brain tumor cells, we explore the possibility of electric fields inducing directed tumor cell migration. In this study we investigate the properties of populations of brain cancer undergoing electrotaxis, a phenomenon whereby cells are directed to migrate under control of an electrical field. We investigate two cell lines for glioblastoma and medulloblastoma (U87mg & DAOY, respectively), plated as spheroidal aggregates in Matrigel-filled electrotaxis channels, and report opposing electrotactic responses. To further understand electrotactic migration of tumor cells, we performed RNA-sequencing for pathway discovery to identify signaling that is differentially affected by the exposure of direct-current electrical fields. Further, using selective pharmacological inhibition assays, focused on the PI3K/mTOR/AKT signaling axis, we validate whether there is a causal relationship to electrotaxis and these mechanisms of action. We find that U87 mg electrotaxis is abolished under pharmacological inhibition of PI3Kγ, mTOR, AKT and ErbB2 signaling, whereas DAOY cell electrotaxis was not attenuated by these or other pathways evaluated.

Ascl1 Regulates Electric Field-Induced Neuronal Differentiation Through PI3K/Akt Pathway

Directing differentiation of neural stem/progenitor cells (NSCs/NPCs) to produce functional neurons is one of the greatest challenges in regenerative medicine. Our previous paper has confirmed that electrical stimulation has a high efficiency of triggering neuronal differentiation by using isolated filum terminale (FT)-derived NPCs. To further clarify the intrinsic molecular mechanisms, protein-protein interaction (PPI) network analysis was applied to pinpoints novel hubs in electric field (EF)-induced neuronal differentiation. In this study, siRNA transfection of Achaete-scute homolog 1 (Ascl1) in NPCs or NPCs was followed by direct current stimulation at 150 mV/mm. Neuronal differentiation rate and protein expression level were analyzed after 7 or 14 days of electrical stimulation. The data showed that the expression level of Ascl1 was enhanced by electrical stimulation and positively correlated to EF strength. Moreover, we identified that the expression of Ascl1 positively regulated neuronal differentiation of NPCs and can be up-regulated by EF-stimulation through the activation of phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway. Therefore, this study provides new insights into the role of Ascl1 and its relevant PI3K/Akt pathway in regulating of EF-induced neuronal differentiation and pointed out that continuous expression of Ascl1 in NPCs is required for EF-induced neuronal differentiation.

Steered migration and changed morphology of human astrocytes by an applied electric field

Direct current electric field (DC EF) plays a role in influencing the biological behaviors and functions of cells. We hypothesize that human astrocytes (HAs) could also be influenced in EF. Astrocytes, an important type of nerve cells with a high proportion quantitatively, are generally activated and largely decide the brain repair results after brain injury. So far, no electrotaxis study on HAs has been performed. We here obtained HAs derived from brain trauma patients. After purification and identification, HAs were seeded in the EF chamber and recorded in a time-lapse image system. LY294002 and U0126 were then used to probe the role of PI3K or ERK signaling pathway on cellular behaviors. The results showed that HAs could be guided to migrate to the anode in DC EFs, in a voltage-dependent manner. The HAs displayed elongated cell bodies and reoriented perpendicularly to the EF in morphology. When treated with LY294002 or U0126, alternation of parameters such as cellular verticality, track speed, displacement speed, long axis, vertical length and circularity were inhibited partly as expected, while the EF-induced directedness was not terminated even at a high drug dosage which was not consistent with previous electrotaxis studies. In conclusion, applied EFs steered the patient-derived HAs directional migration and changed morphology, in which PI3K and ERK pathways at least partially participate. The characteristics of HAs to EF stimulation may be involved in wound healing and neural regeneration, which could be utilized as a novel treatment strategy in brain injury.

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.

Potential Application of Electrical Stimulation in Stem Cell-Based Treatment against Hearing Loss

Deafness is a common human disease, which is mainly caused by irreversible damage to hair cells and spiral ganglion neurons (SGNs) in the mammalian cochlea. At present, replacement of damaged or missing hair cells and SGNs by stem cell transplantation therapy is an effective treatment. However, the survival rate of stem cell transplantation is low, with uncontrollable differentiation hindering its application. Most researchers have focused on biochemical factors to regulate the growth and differentiation of stem cells, whereas little study has been performed using physical factors. This review intends to illustrate the current problems in stem cell-based treatment against deafness and to introduce electric field stimulation as a physical factor to regulate stem cell behavior and facilitate stem cell therapy to treat hearing loss in the future.

Calcium influx differentially regulates migration velocity and directedness in response to electric field application

Neural precursor cells (NPCs) respond to externally applied direct current electrical fields (DCEFs) by undergoing rapid and directed migration toward the cathode in a process known as galvanotaxis. It is unknown if the underlying mechanisms of galvanotactic migration is common to non-electrosensitive cells and if so, how NPCs and other galvanotactic cells sense and transduce electrical fields into cellular motility. In this study, we show that distinct aspects of NPC galvanotactic migration: motility (quantified through |velocity|) and directedness, are differentially regulated by calcium. We use low-Ca²⁺ culture conditions; an intracellular Ca²⁺ chelator; and voltage gated calcium channel (VGCC) inhibitors to specific channels expressed on NPCs, to demonstrate the role of Ca²⁺ influx in DCEF-induced NPC migration. Consistent with existing literature, we show Ca²⁺ is involved in F-actin polymerization that lengthens NPC membrane protrusions necessary for cellular motility. However, inhibiting Ca²⁺ results in reduced velocity but has no effect on DCEF-induced directedness. This dissociation between velocity and directedness reveal that these migration parameters can be independently regulated, thus suggesting a parallel process of sensing DCEFs by NPCs.

Effect of pharmacological modulation of actin and myosin on collective cell electrotaxis

Electrotaxis-the directional migration of cells in response to an electric field-is most evident in multicellular collectives and plays an important role in physiological contexts. While most cell types respond to applied electric fields of the order of a Volt per centimeter, our knowledge of the factors influencing this response is limited. This is especially true for collective cell electrotaxis, in which the subcellular migration response within a cell has to be coordinated with coupled neighboring cells. Here, we investigated the effect of the level of actin cytoskeleton polymerization and myosin activity on collective cell electrotaxis of Madin-Darby Canine Kidney (MDCK) cells in response to a weak electric field of physiologically relevant magnitude. We modulated the polymerization state of the actin cytoskeleton using the depolymerizing agent cytochalasin D or the polymerizing agent jasplakinolide. We also modulated the contractility of the cell using the myosin motor inhibitor blebbistatin or the phosphatase inhibitor calyculin A. While all the above pharmacological treatments altered cell speed to various extents, we found that only increasing the contractility and a high level of increase/stabilization of polymerized actin had a strong inhibitory effect specifically on the directedness of collective cell electrotaxis. On the other hand, even as the effect of the actin modulators on collective cell migration was varied, most conditions of actin and myosin pharmacological modulation-except for high level of actin polymerization/stabilization-resulted in cell speeds that were similar in the absence or presence of the electric field. Our results led us to speculate that the applied electric field may largely impact the cellular apparatus specifying the polarity of collective cell migration, rather than the functioning of the migratory apparatus. Bioelectromagnetics. 39:289-298, 2018. © 2018 Wiley Periodicals, Inc.

Electrotaxis: Cell Directional Movement in Electric Fields

Electrotaxis plays an important role during embryogenesis, inflammation, wound healing, and tumour metastasis. However, the mechanisms at play during electrotaxis are still poorly understood. Therefore intensive studies on signaling pathways involved in this phenomenon should be carried out. In this chapter, we described an experimental system for studying electrotaxis of Amoeba proteus, mouse embryonic fibroblasts (MEF), Walker carcinosarcoma cells WC256, and bone marrow adherent cells (BMAC).

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.

Requirement of Pax6 for the integration of guidance cues in cell migration

The intricate patterns of cell migration that are found throughout development are generated through a vast array of guidance cues. Responding integratively to distinct, often conflicting, migratory signals is probably crucial for cells to reach their correct destination. Pax6 is a master transcription factor with key roles in neural development that include the control of cell migration. In this study, we have investigated the ability of cells derived from cortical neurospheres from wild-type (WT) and Pax6^-/- mouse embryos to integrate diverging guidance cues. We used two different cues, either separately or in combination: substratum nanogrooves to induce contact guidance, and electric fields (EFs) to induce electrotaxis. In the absence of an EF, both WT and Pax6^-/- cells aligned and migrated parallel to grooves, and on a flat substrate both showed marked electrotaxis towards the cathode. When an EF was applied in a perpendicular orientation to grooves, WT cells responded significantly to both cues, migrating in highly oblique trajectories in the general direction of the cathode. However, Pax6^-/- cells had an impaired response to both cues simultaneously. Our results demonstrate that these neurosphere derived cells have the capacity to integrate diverging guidance cues, which requires Pax6 function.

Requirement of Pax6 for the integration of guidance cues in cell migration

The intricate patterns of cell migration that are found throughout development are generated through a vast array of guidance cues. Responding integratively to distinct, often conflicting, migratory signals is probably crucial for cells to reach their correct destination. Pax6 is a master transcription factor with key roles in neural development that include the control of cell migration. In this study, we have investigated the ability of cells derived from cortical neurospheres from wild-type (WT) and Pax6^-/- mouse embryos to integrate diverging guidance cues. We used two different cues, either separately or in combination: substratum nanogrooves to induce contact guidance, and electric fields (EFs) to induce electrotaxis. In the absence of an EF, both WT and Pax6^-/- cells aligned and migrated parallel to grooves, and on a flat substrate both showed marked electrotaxis towards the cathode. When an EF was applied in a perpendicular orientation to grooves, WT cells responded significantly to both cues, migrating in highly oblique trajectories in the general direction of the cathode. However, Pax6^-/- cells had an impaired response to both cues simultaneously. Our results demonstrate that these neurosphere derived cells have the capacity to integrate diverging guidance cues, which requires Pax6 function.

Excitable Signal Transduction Networks in Directed Cell Migration

Although directed migration of eukaryotic cells may have evolved to escape nutrient depletion, it has been adopted for an extensive range of physiological events during development and in the adult organism. The subversion of these movements results in disease, such as cancer. Mechanisms of propulsion and sensing are extremely diverse, but most eukaryotic cells move by extending actin-filled protrusions termed macropinosomes, pseudopodia, or lamellipodia or by extension of blebs. In addition to motility, directed migration involves polarity and directional sensing. The hundreds of gene products involved in these processes are organized into networks of parallel and interconnected pathways. Many of these components are activated or inhibited coordinately with stimulation and on each spontaneously extended protrusion. Moreover, these networks display hallmarks of excitability, including all-or-nothing responsiveness and wave propagation. Cellular protrusions result from signal transduction waves that propagate outwardly from an origin and drive cytoskeletal activity. The range of the propagating waves and hence the size of the protrusions can be altered by lowering or raising the threshold for network activation, with larger and wider protrusions favoring gliding or oscillatory behavior over amoeboid migration. Here, we evaluate the variety of models of excitable networks controlling directed migration and outline critical tests. We also discuss the utility of this emerging view in producing cell migration and in integrating the various extrinsic cues that direct migration.

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