Functional electrical stimulation-facilitated proliferation and regeneration of neural precursor cells in the brains of rats with cerebral infarction

Targeting Neurogenesis in Seeking Novel Treatments for Ischemic Stroke

The interruption of cerebral blood flow leads to ischemic cell death and results in ischemic stroke. Although ischemic stroke is one of the most important causes of long-term disability and mortality, limited treatments are available for functional recovery. Therefore, extensive research has been conducted to identify novel treatments. Neurogenesis is regarded as a fundamental mechanism of neural plasticity. Therefore, therapeutic strategies targeting neurogenesis are thought to be promising. Basic research has found that therapeutic intervention including cell therapy, rehabilitation, and pharmacotherapy increased neurogenesis and was accompanied by functional recovery after ischemic stroke. In this review, we consolidated the current knowledge of the relationship between neurogenesis and treatment for ischemic stroke. It revealed that many treatments for ischemic stroke, including clinical and preclinical ones, have enhanced brain repair and functional recovery post-stroke along with neurogenesis. However, the intricate mechanisms of neurogenesis and its impact on stroke recovery remain areas of extensive research, with numerous factors and pathways involved. Understanding neurogenesis will lead to more effective stroke treatments, benefiting not only stroke patients but also those with other neurological disorders. Further research is essential to bridge the gap between preclinical discoveries and clinical implementation.

Guhong injection promotes post-stroke functional recovery via attenuating cortical inflammation and apoptosis in subacute stage of ischemic stroke

BACKGROUND

As a leading cause of death and disability, alternative therapies for stroke are still limited by its complicated pathophysiological manifestations. Guhong injection (GHI), consisting of safflower aqueous extract and aceglutamide, has been widely applied for the clinical treatment of cerebrovascular diseases, especially ischemic stroke and post-stroke recovery, in China. Recently, a series of studies have reported the positive effect of GHI against cerebral ischemia/reperfusion injury via targeting various molecular mechanisms. However, questions remain on whether treatment with GHI contributes to better functional recovery after stroke and if so, the potential mechanisms and active substances.

PURPOSE

The aim of this work was to explore the potential therapeutic possibilities of GHI for the neurological and behavioral recovery after stroke and to investigate the underlying molecular mechanisms as well as active substances.

METHODS

The neural and motor deficits as well as cortical lesions after GHI treatment were investigated in a mouse model of transient ischemic stroke. Based on the substance identification of GHI, network pharmacology combined with an experimental verification method was used to systematically decipher the biological processes and signaling pathways closely related to GHI intervention in response to post-stroke functional outcomes. Subsequently, ingenuity pathway analysis (IPA) analysis was performed to determine the anti-stroke active substances targeting to the hub targets involved in the significant molecular pathways regulated by GHI treatment.

RESULTS

Therapeutically, administration of GHI observably ameliorated the post-stroke recovery of neural and locomotor function as well as reduced infarct volume and histopathological damage to the cerebral cortex in subacute stroke mice. According to 26 identified or tentatively characterized substances in GHI, the compound-target-pathway network was built. Bioinformatics analysis suggested that inflammatory and apoptotic pathways were tightly associated with the anti-stroke effect of GHI. Based on protein-protein interaction network analysis, the hub targets (such as NF-κB p65, TNF-α, IL-6, IL-1β, Bax, Bcl-2, and Caspase-3) involved in inflammation and apoptosis were selected. On the one hand, immunofluorescence and ELISA results showed that GHI (10 ml/kg) treatment obviously reduced NF-κB p65 nuclear translocation as well as decreased the abnormally elevated concentrations of proinflammatory cytokines (TNF-α, IL-6, and IL-1β) in damaged cortex tissues. On the other hand, GHI (10 ml/kg) treatment significantly downregulated the number of TUNEL-positive apoptotic cells in ischemic cortex and effectively restored the abnormal expression of Bax, Bcl-2, and Caspase-3. Based on the results of IPA, hydroxysafflor yellow A, baicalin, scutellarin, gallic acid, syringin, chlorogenic acid, kaempferol, kaempferol-3-O-β-rutinoside, and rutin acted synergistically on core targets, which could be considered as the active substances of GHI.

CONCLUSION

Overall, the current findings showed that the beneficial action of GHI on improving post-stroke functional recovery of subacute stroke mice partly via the modulation of cortical inflammation and apoptosis. These findings not only provide a reliable reference for the clinical application of GHI, but also shed light on a promising alternative therapeutic strategy for ischemic stroke patients.

Different paradigms of transcranial electrical stimulation improve motor function impairment and striatum tissue injuries in the collagenase-induced intracerebral hemorrhage rat model

Background

In the horizon of therapeutic restrictions in intracerebral hemorrhage (ICH), recently, non-invasive transcranial electrical stimulation (tES) has achieved considerable prosperities. Translational studies have postulated that transcranial direct current stimulation (tDCS) and the other types of tES remain potentially a novel therapeutic option to reverse or stabilize cognitive and motor impairments.

Objective

The aim of this study was to comparatively evaluate the effects of the four main paradigms of tES, including tDCS, transcranial alternating (tACS), pulsed (tPCS), and random noise (tRNS) stimulations on collagenase-induced sensorimotor impairments and striatum tissue damage in male rats.

Methods

To induce ICH, 0.5 μl of collagenase was injected into the right striatum of male Sprague Dawley rats. One day after surgery, tES, was applied to the animals for seven consecutive days. Motor functions were appraised by neurological deficit score, rotarod, and wire hanging tests on the day before surgery and postoperative days 3, 7, and 14. After behavioral tests, brain tissue was prepared appropriately to perform the stereological evaluations.

Results

The results indicated that the application of the four tES paradigms (tDCS, tACS, tRNS, and tPCS) significantly reversed motor disorders in collagenase-induced ICH groups. Further, the motor function improvement of tACS and tRNS receiving rats in wire-hanging and rotarod tests were higher than the other two tES receiving groups. Structural changes and stereological assessments also confirmed the results of behavioral functions.

Conclusion

Our findings suggest that in addition to tDCS application in the treatment of ICH, other tES paradigms, especially tACS and tRNS may be considered as add-on therapeutic strategies in stroke.

Electrical stimulation of human neural stem cells via conductive polymer nerve guides enhances peripheral nerve recovery

Severe peripheral nerve injuries often result in permanent loss of function of the affected limb. Current treatments are limited by their efficacy in supporting nerve regeneration and behavioral recovery. Here we demonstrate that electrical stimulation through conductive nerve guides (CNGs) enhances the efficacy of human neural progenitor cells (hNPCs) in treating a sciatic nerve transection in rats. Electrical stimulation strengthened the therapeutic potential of NPCs by upregulating gene expression of neurotrophic factors which are critical in augmenting synaptic remodeling, nerve regeneration, and myelination. Electrically-stimulated hNPC-containing CNGs are significantly more effective in improving sensory and motor functions starting at 1-2 weeks after treatment than either treatment alone. Electrophysiology and muscle assessment demonstrated successful re-innervation of the affected target muscles in this group. Furthermore, histological analysis highlighted an increased number of regenerated nerve fibers with thicker myelination in electrically-stimulated hNPC-containing CNGs. The elevated expression of tyrosine kinase receptors (Trk) receptors, known to bind to neurotrophic factors, indicated the long-lasting effect from electrical stimulation on nerve regeneration and distal nerve re-innervation. These data suggest that electrically-enhanced stem cell-based therapy provides a regenerative rehabilitative approach to promote peripheral nerve regeneration and functional recovery.

Enriching neural stem cell and anti-inflammatory glial phenotypes with electrical stimulation after traumatic brain injury in male rats

Traumatic brain injury (TBI) by an external physical impact results in compromised brain function via undesired neuronal death. Following the injury, resident and peripheral immune cells, astrocytes, and neural stem cells (NSCs) cooperatively contribute to the recovery of the neuronal function after TBI. However, excessive pro‐inflammatory responses of immune cells, and the disappearance of endogenous NSCs at the injury site during the acute phase of TBI, can exacerbate TBI progression leading to incomplete healing. Therefore, positive outcomes may depend on early interventions to control the injury‐associated cellular milieu in the early phase of injury. Here, we explore electrical stimulation (ES) of the injury site in a rodent model (male Sprague–Dawley rats) to investigate its overall effect on the constituent brain cell phenotype and composition during the acute phase of TBI. Our data showed that a brief ES for 1 hr on day 2 of TBI promoted anti‐inflammatory phenotypes of microglia as assessed by CD206 expression and increased the population of NSCs and Nestin⁺ astrocytes at 7 days post‐TBI. Also, ES effectively increased the number of viable neurons when compared to the unstimulated control group. Given the salience of microglia and neural stem cells for healing after TBI, our results strongly support the potential benefit of the therapeutic use of ES during the acute phase of TBI to regulate neuroinflammation and to enhance neuroregeneration.

Mesenchymal stem cell therapy alleviates the neuroinflammation associated with acquired brain injury

Ischemic stroke and traumatic brain injury (TBI) comprise two particularly prevalent and costly examples of acquired brain injury (ABI). Following stroke or TBI, primary cell death and secondary cell death closely model disease progression and worsen outcomes. Mounting evidence indicates that long‐term neuroinflammation extensively exacerbates the secondary deterioration of brain structure and function. Due to their immunomodulatory and regenerative properties, mesenchymal stem cell transplants have emerged as a promising approach to treating this facet of stroke and TBI pathology. In this review, we summarize the classification of cell death in ABI and discuss the prominent role of inflammation. We then consider the efficacy of bone marrow–derived mesenchymal stem/stromal cell (BM‐MSC) transplantation as a therapy for these injuries. Finally, we examine recent laboratory and clinical studies utilizing transplanted BM‐MSCs as antiinflammatory and neurorestorative treatments for stroke and TBI. Clinical trials of BM‐MSC transplants for stroke and TBI support their promising protective and regenerative properties. Future research is needed to allow for better comparison among trials and to elaborate on the emerging area of cell‐based combination treatments.

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.

Conductive polymers to modulate the post-stroke neural environment

Despite the prevalence of stroke, therapies to augment recovery remain limited. Here we focus on the use of conductive polymers for cell delivery, drug release, and electrical stimulation to optimize the post-stroke environment for neural recovery. Conductive polymers and their interactions with in vitro and in vivo neural systems are explored. The ability to continuously modify the neural environment utilizing conductive polymers provides applications in directing stem cell differentiation and increasing neural repair. This exciting class of polymers offers new approaches to optimizing the post-stroke brain to improve functional recovery.

NGF/FAK signal pathway is implicated in angiogenesis after acute cerebral ischemia in rats

Neurogenesis in the cerebral infarction after an ischemic event is important to the rehabilitation of patients. However, the mechanism of angiogenesis around cerebral ischemia is not clear. Our study designed to test whether the nerve growth factor (NGF)-P-focal adhesion kinase (FAK) signaling pathway for associations with angiogenesis plays a key role in post-acute cerebral ischemia of rats. Firstly, we implanted the Matrigel, a carrier of basement membrane matrix, into the abdominal skin of rats to identify the relevant components of the NGF-P-FAK signaling pathway related to angiogenesis. Secondly, we used a model established by ligation of the middle cerebral artery (MCA) to observe the effect of the same signal pathway on angiogenesis in the subventricular and subgranular zones of the dentate gyrus(SVG and SGZ). The results showed that the tissue scores was significantly increased by NGF. However, the tissue scores was signifcaintly decreased by FAK inhibitor TAE226. Furthermore, CD31 and α-SMA were significantly increased by NGF and were decreased by anti-NGF and TAE226 in Matrigel. The P-FAK protein expression in Matrigel was markedly increased by NGF and decreased by TAE226. In the SVZ and SVG of cerebral ischemia, the numbers of BrdU-positive cells were significantly increased by NGF and decreased by TAE226, respectively. Our findings suggest that the therapy targeting the NGF-P-FAK signaling pathway may be an option for patients suffering from cerebral ischemia.

Basic Fibroblast Growth Factor Protects Astrocytes Against Ischemia/Reperfusion Injury by Upregulating the Caveolin-1/VEGF Signaling Pathway

A previous in vivo study demonstrated that intracerebroventricular injection of basic fibroblast growth factor (bFGF) in middle cerebral artery occlusion rats increased the expression of caveolin-1 (cav-1) and vascular endothelial growth factor (VEGF) in cerebral ischemia penumbra. Because astrocytes are the largest population in the brain, the aim of this in vitro study was to investigate the influence of bFGF on cav-1 and VEGF expression in rat astrocytes following oxygen glucose deprivation/reoxygenation (OGD/R). For this, an ischemic model in vitro of oxygen glucose deprivation lasting for 6 h, followed by 24 h of reoxygenation was used. Primary astrocytes from newborn rats were pre-treated with siRNA targeting bFGF before OGD/R. Cell viability was measured by a CCK-8 assay. The protein and mRNA expressions of bFGF, cav-1, and VEGF were evaluated by western blotting, immunofluorescence staining, and reverse transcription-quantitative polymerase chain reaction. The results showed that OGD/R reduced cell viability, which was decreased further following bFGF knockdown; however, restoring bFGF improved cell survival. A cav-1 inhibitor abrogated the effect of bFGF on cell viability. The expression levels of bFGF mRNA, bFGF protein, cav-1 mRNA, cav-1 protein, and VEGF protein were higher in OGD/R astrocytes. bFGF knockdown markedly decreased the expression levels of cav-1 mRNA, cav-1 protein, and VEGF protein, which were effectively reversed by exogenous bFGF treatment. Moreover, exogenous bFGF treatment significantly increased the expression levels of cav-1 mRNA, cav-1 protein, and VEGF protein in OGD/R astrocytes; however, a cav-1 inhibitor abolished the effect of bFGF on VEGF protein expression. These results suggested that bFGF may protect astrocytes against ischemia/reperfusion injury by upregulating caveolin-1/VEGF signaling pathway.

Unraveling the mechanistic effects of electric field stimulation towards directing stem cell fate and function: A tissue engineering perspective

Electric field (EF) stimulation can play a vital role in eliciting appropriate stem cell response. Such an approach is recently being established to guide stem cell differentiation through osteogenesis/neurogenesis/cardiomyogenesis. Despite significant recent efforts, the biophysical mechanisms by which stem cells sense, interpret and transform electrical cues into biochemical and biological signals still remain unclear. The present review critically analyses the variety of EF stimulation approaches that can be employed to evoke appropriate stem cell response and also makes an attempt to summarize the underlying concepts of this notion, placing special emphasis on stem cell based tissue engineering and regenerative medicine. This review also discusses the major signaling pathways and cellular responses that are elicited by electric stimulation, including the participation of reactive oxygen species and heat shock proteins, modulation of intracellular calcium ion concentration, ATP production and numerous other events involving the clustering or reassembling of cell surface receptors, cytoskeletal remodeling and so on. The specific advantages of using external electric stimulation in different modalities to regulate stem cell fate processes are highlighted with explicit examples, in vitro and in vivo.

Effects of Human ES-Derived Neural Stem Cell Transplantation and Kindling in a Rat Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the leading causes of death and disability in the population worldwide, with a broad spectrum of symptoms and disabilities. Posttraumatic hyperexcitability is one of the most common neurological disorders that affect people after a head injury. A reliable animal model of posttraumatic hyperexcitability induced by TBI which allows one to test effective treatment strategies is yet to be developed. To address these issues, in the present study, we tested human embryonic stem cell-derived neural stem cell (NSC) transplantation in an animal model of posttraumatic hyperexcitability in which the brain injury was produced in one hemisphere of immunodeficient athymic nude rats by controlled cortical impact, and spontaneous seizures were produced by repeated electrical stimulation (kindling) in the contralateral hemisphere. At 14 wk posttransplantation, we report human NSC (hNSC) survival and differentiation into all 3 neural lineages in both sham and injured animals. We observed twice as many surviving hNSCs in the injured versus sham brain, and worse survival on the kindled side in both groups, indicating that kindling/seizures are detrimental to survival or proliferation of hNSCs. We also replicated our previous finding that hNSCs can ameliorate deficits on the novel place recognition task,33 but such improvements are abolished following kindling. We found no significant differences pre- or post-kindling on the elevated plus maze. No significant correlations were observed between hNSC survival and cognitive performance on either task. Together these findings suggest that Shef6-derived hNSCs may be beneficial as a therapy for TBI, but not in animals or patients with posttraumatic hyperexcitability.

State of the Art: Novel Applications for Cortical Stimulation

OBJECTIVE

Electrical stimulation via implanted electrodes that overlie the cortex of the brain is an upcoming neurosurgical technique that was hindered for a long time by insufficient knowledge of how the brain functions in a dynamic, physiological, and pathological way, as well as by technological limitations of the implantable stimulation devices.

METHODS

This paper provides an overview of cortex stimulation via implantable devices and introduces future possibilities to improve cortex stimulation.

RESULTS

Cortex stimulation was initially used preoperatively as a technique to localize functions in the brain and only later evolved into a treatment technique. It was first used for pain, but more recently a multitude of pathologies are being targeted by cortex stimulation. These disorders are being treated by stimulating different cortical areas of the brain. Risks and complications are essentially similar to those related to deep brain stimulation and predominantly include haemorrhage, seizures, infection, and hardware failures. For cortex stimulation to fully mature, further technological development is required to predict its outcomes and improve stimulation designs. This includes the development of network science-based functional connectivity approaches, genetic analyses, development of navigated high definition transcranial alternating current stimulation, and development of pseudorandom stimulation designs for preventing habituation.

CONCLUSION

In conclusion, cortex stimulation is a nascent but very promising approach to treating a variety of diseases, but requires further technological development for predicting outcomes, such as network science based functional connectivity approaches, genetic analyses, development of navigated transcranial electrical stimulation, and development of pseudorandom stimulation designs for preventing habituation.

The Role of bFGF in the Excessive Activation of Astrocytes Is Related to the Inhibition of TLR4/NFκB Signals

Astrocytes have critical roles in immune defense, homeostasis, metabolism, and synaptic remodeling and function in the central nervous system (CNS); however, excessive activation of astrocytes with increased intermediate filaments following neuronal trauma, infection, ischemia, stroke, and neurodegenerative diseases results in a pro-inflammatory environment and promotes neuronal death. As an important neurotrophic factor, the secretion of endogenous basic fibroblast growth factor (bFGF) contributes to the protective effect of neuronal cells, but the mechanism of bFGF in reactive astrogliosis is still unclear. In this study, we demonstrated that exogenous bFGF attenuated astrocyte activation by reducing the expression of glial fibrillary acidic protein (GFAP) and other markers, including neurocan and vimentin, but not nestin and decreased the levels of pro-inflammatory cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), via the regulation of the upstream toll-like receptor 4/nuclear factor κB (TLR4/NFκB) signaling pathway. Our study suggests that the function of bFGF is not only related to the neuroprotective and neurotrophic effect but also involved in the inhibition of excessive astrogliosis and glial scarring after neuronal injury.

Electrical Stimulation Elicits Neural Stem Cells Activation: New Perspectives in CNS Repair

Researchers are enthusiastically concerned about neural stem cell (NSC) therapy in a wide array of diseases, including stroke, neurodegenerative disease, spinal cord injury, and depression. Although enormous evidences have demonstrated that neurobehavioral improvement may benefit from NSC-supporting regeneration in animal models, approaches to endogenous and transplanted NSCs are blocked by hurdles of migration, proliferation, maturation, and integration of NSCs. Electrical stimulation (ES) may be a selective non-drug approach for mobilizing NSCs in the central nervous system. This technique is suitable for clinical application, because it is well established and its potential complications are manageable. Here, we provide a comprehensive review of the emerging positive role of different electrical cues in regulating NSC biology in vitro and in vivo, as well as biomaterial-based and chemical stimulation of NSCs. In the future, ES combined with stem cell therapy or other cues probably becomes an approach for promoting brain repair.

Involuntary, Forced and Voluntary Exercises Equally Attenuate Neurocognitive Deficits in Vascular Dementia by the BDNF-pCREB Mediated Pathway

A rat model of vascular dementia was used to compare the effects of involuntary exercise induced by functional electrical stimulation (FES), forced exercise and voluntary exercise on the recovery of cognitive function recovery and its underlying mechanisms. In an involuntary exercise (I-EX) group, FES was used to induce involuntary gait-like running on ladder at 12 m/min. A forced exercise group (F-EX) and a voluntary exercise group (V-EX) exercised by wheel running. The Barnes maze was used for behavioral assessment. Brain-derived neurotrophic factor (BDNF), phosphorylated extracellular signal-regulated kinase 1 and 2 (ERK1/2) and cAMP response element binding protein (CREB) positive cells in hippocampal CA1, CA2/3 and dentate gyrus (DG) regions were evaluated using immunohistochemical methods. Western blotting was used to assess the levels of BDNF, phosphorylated protein kinase B (Akt), tropomyosin receptor kinase B (TrkB), mitogen-activated protein kinase 1 and 2 (MEK1/2), ERK1/2 and CREB in BDNF-pCREB signaling in the hippocampus and prefrontal cortex. Involuntary, forced and voluntary exercises were all found to reverse the cognitive deficits of vascular dementia with about equal effectiveness. The number of BDNF, pCREB and pERK1/2 immunopositive cells was significantly increased in the hippocampal CA1, CA2/3 and DG regions in all three exercise groups. In addition, involuntary exercise activated BDNF and the phosphorylation of Akt, TrkB, MEK1/2, ERK1/2 and CREB in the hippocampus and prefrontal cortex equally as well as voluntary or forced exercise. These results suggest that involuntary exercise induced by FES may be as beneficial for alleviating cognitive deficits after cerebral ischemia.