Transdifferentiation of brain-derived neurotrophic factor (BDNF)-secreting mesenchymal stem cells significantly enhance BDNF secretion and Schwann cell marker proteins

Potential role of Schwann cells in neuropathic pain

Neuropathic pain (NPP) is a common syndrome associated with most forms of disease, which poses a serious threat to human health. NPP may persist even after the nociceptive stimulation is eliminated, and treatment is extremely challenging in such cases. Schwann cells (SCs) form the myelin sheaths around neuronal axons and play a crucial role in neural information transmission. SCs can secrete trophic factors to nourish and protect axons, and can further secrete pain-related factors to induce pain. SCs may be activated by peripheral nerve injury, triggering the transformation of myelinated and non-myelinated SCs into cell phenotypes that specifically promote repair. These differentiated SCs provide necessary signals and spatial clues for survival, axonal regeneration, and nerve regeneration of damaged neurons. They can further change the microenvironment around the regions of nerve injury, and relieve the pain by repairing the injured nerve. Herein, we provide a comprehensive overview of the biological characteristics of SCs, discuss the relationship between SCs and nerve injury, and explore the potential mechanism of SCs and the occurrence of NPP. Moreover, we summarize the feasible strategies of SCs in the treatment of NPP, and attempt to elucidate the deficiencies and defects of SCs in the treatment of NPP.

Therapeutic Potential of Mesenchymal Stem Cells in the Treatment of Epilepsy and Their Interaction with Antiseizure Medications

Epilepsy is a life-threatening neurological disease that affects approximately 70 million people worldwide. Although the vast majority of patients may be successfully managed with currently used antiseizure medication (ASM), the search for alternative therapies is still necessary due to pharmacoresistance in about 30% of patients with epilepsy. Here, we review the effects of ASMs on stem cell treatment when they could be, as expected, co-administered. Indeed, it has been reported that ASMs produce significant effects on the differentiation and determination of stem cell fate. In addition, we discuss more recent findings on mesenchymal stem cells (MSCs) in pre-clinical and clinical investigations. In this regard, their ability to differentiate into various cell types, reach damaged tissues and produce and release biologically active molecules with immunomodulatory/anti-inflammatory and regenerative properties make them a high-potential therapeutic tool to address neuroinflammation in different neurological disorders, including epilepsy. Overall, the characteristics of MSCs to be genetically engineered, in order to replace dysfunctional elements with the aim of restoring normal tissue functioning, suggested that these cells could be good candidates for the treatment of epilepsy refractory to ASMs. Further research is required to understand the potential of stem cell treatment in epileptic patients and its interaction with ASMs.

Development and In Vitro Differentiation of Schwann Cells

Schwann cells are glial cells of the peripheral nervous system. They exist in several subtypes and perform a variety of functions in nerves. Their derivation and culture in vitro are interesting for applications ranging from disease modeling to tissue engineering. Since primary human Schwann cells are challenging to obtain in large quantities, in vitro differentiation from other cell types presents an alternative. Here, we first review the current knowledge on the developmental signaling mechanisms that determine neural crest and Schwann cell differentiation in vivo. Next, an overview of studies on the in vitro differentiation of Schwann cells from multipotent stem cell sources is provided. The molecules frequently used in those protocols and their involvement in the relevant signaling pathways are put into context and discussed. Focusing on hiPSC- and hESC-based studies, different protocols are described and compared, regarding cell sources, differentiation methods, characterization of cells, and protocol efficiency. A brief insight into developments regarding the culture and differentiation of Schwann cells in 3D is given. In summary, this contribution provides an overview of the current resources and methods for the differentiation of Schwann cells, it supports the comparison and refinement of protocols and aids the choice of suitable methods for specific applications.

Stem Cell- and Cell-Based Therapies for Ischemic Stroke

Stroke is the second cause of disability worldwide as it is expected to increase its incidence and prevalence. Despite efforts to increase the number of patients eligible for recanalization therapies, a significant proportion of stroke survivors remain permanently disabled. This outcome boosted the search for efficient neurorestorative methods. Stem cells act through multiple pathways: cell replacement, the secretion of growth factors, promoting endogenous reparative pathways, angiogenesis, and the modulation of neuroinflammation. Although neural stem cells are difficult to obtain, pose a series of ethical issues, and require intracerebral delivery, mesenchymal stem cells are less immunogenic, are easy to obtain, and can be transplanted via intravenous, intra-arterial, or intranasal routes. Extracellular vesicles and exosomes have similar actions and are easier to obtain, also allowing for engineering to deliver specific molecules or RNAs and to promote the desired effects. Appropriate timing, dosing, and delivery protocols must be established, and the possibility of tumorigenesis must be settled. Nonetheless, stem cell- and cell-based therapies for stroke have already entered clinical trials. Although safe, the evidence for efficacy is less impressive so far. Hopefully, the STEP guidelines and the SPAN program will improve the success rate. As such, stem cell- and cell-based therapy for ischemic stroke holds great promise.

Exosomes derived from differentiated human ADMSC with the Schwann cell phenotype modulate peripheral nerve-related cellular functions

Peripheral nerve regeneration remains a significant clinical challenge due to the unsatisfactory functional recovery and public health burden. Exosomes, especially those derived from mesenchymal stem cells (MSCs), are promising as potential cell-free therapeutics and gene therapy vehicles for promoting neural regeneration. In this study, we reported the differentiation of human adipose derived MSCs (hADMSCs) towards the Schwann cell (SC) phenotype (hADMSC-SCs) and then isolated exosomes from hADMSCs with and without differentiation (i.e., dExo vs uExo). We assessed and compared the effects of uExo and dExo on antioxidative, angiogenic, anti-inflammatory, and axon growth promoting properties by using various peripheral nerve-related cells. Our results demonstrated that hADMSC-SCs secreted more neurotrophic factors and other growth factors, compared to hADMSCs without differentiation. The dExo isolated from hADMSC-SCs protected rat SCs from oxidative stress and enhanced HUVEC migration and angiogenesis. Compared to uExo, dExo also had improved performances in downregulating pro-inflammatory gene expressions and cytokine secretions and promoting axonal growth of sensory neurons differentiated from human induced pluripotent stem cells. Furthermore, microRNA (miRNA) sequencing analysis revealed that exosomes and their parent cells shared some similarities in their miRNA profiles and exosomes displayed a distinct miRNA signature. Many more miRNAs were identified in dExo than in uExo. Several upregulated miRNAs, like miRNA-132-3p and miRNA-199b-5p, were highly related to neuroprotection, anti-inflammation, and angiogenesis. The dExo can effectively modulate various peripheral nerve-related cellular functions and is promising for cell-free biological therapeutics to enhance neural regeneration.

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Exosomes were isolated from hADMSCs with and without differentiation towards SC phenotype (i.e., dExo vs uExo).

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hADMSC-SCs secreted more growth factors compared to hADMSCs without differentiation.

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The dExo protected rat SCs from oxidative stress and enhanced endothelial cell migration and angiogenesis.

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dExo promoted axonal growth of sensory neurons differentiated from hiPSCs.

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miRNA sequencing analysis unveiled and compared the exosomal and cellular miRNA profiles.

Gastrodin modified polyurethane conduit promotes nerve repair via optimizing Schwann cells function

Peripheral nerve regeneration and functional recovery remain a major clinical challenge. Nerve guidance conduit (NGC) that can regulate biological behavior of Schwann cells (SCs) and facilitate axonal regeneration through microenvironmental remodeling is beneficial for nerve regeneration and functional recovery. Gastrodin, a main constituent of a Chinese traditional herbal medicine, has been known to display several biological and pharmacological properties, especially antioxidative, anti‐inflammatory and nerve regeneration. Herein, polyurethane (PU) NGCs modified by different weight ratio of Gastrodin (0, 1 and 5 wt%) were designed for sequential and sustainable drug release, that created a favorable microenvironment for nerve regeneration. The scaffold showed suitable pore structure and biocompatibility in vitro, and evidently promoted morphological and functional recovery of regenerated sciatic nerves in vivo. Compared to the PU and 1%Gastrodin/PU scaffolds, the 5%Gastrodin/PU significantly enhanced the proliferation, migration and myelination of SCs and up-regulated expression of neurotrophic factors, as well as induction of the differentiation of PC12 cells. Interestingly, the obvious anti-inflammatory response was observed in 5%Gastrodin/PU by reduced expression of TNF-α and iNOS, which also evidenced by the few fibrous capsule formation in the subcutaneous implantation. Such a construct presented a similarity to autograft in vivo repairing a 10 mm sciatic nerve defects. It was able to not only boost the regenerated area of nerve and microvascular network, but also facilitate functional axons growth and remyelination, leading to highly improved functional restoration. These findings demonstrate that the 5%Gastrodin/PU NGC efficiently promotes nerve regeneration, indicating their potential for use in peripheral nerve regeneration applications.

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NGC with a sustained release of Gastrodin creates a favorable microenvironment. .

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Gastrodin/PU has superior anti-inflammatory effects.

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SCs-mediated tissue engineering strategies effectively drive myelination.

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5Gastrodin/PU boosts nerve regeneration and functional restoration in vivo.

Bone Marrow Mesenchymal Stem Cell Condition Medium Loaded on PCL Nanofibrous Scaffold Promoted Nerve Regeneration After Sciatic Nerve Transection in Male Rats

Nowadays, researchers pay a vast deal of attention to neural tissue regeneration due to its tremendous effect on the patient's life. There are many strategies, from using conventional autologous nerve grafts to the newly developed methods for reconstructing damaged nerves. Among the various therapeutic methods, incorporating highly potent biomolecules and growth factors, the damaged nerve site would promote nerve regeneration. The aim was to examine the efficiency of a mesenchymal stem cell condition medium (MSC-CM) loaded on a 3D-polycaprolactone (PCL) scaffold as a nerve conduit in an axotomy rat model. Twenty-four mature male rats were classified into four groups: controls (the animals of this group were intact), axotomy (10 mm piece of the nerve was removed), axotomy (10-mm piece of the nerve was removed) + scaffold, and axotomy (10-mm piece of the nerve was removed) + MSC-CM-loaded scaffold. We followed up nerve motor function using a sciatic function index and electromyography activity of the gastrocnemius muscle. At 12 weeks post axotomy, sciatic nerve and dorsal root ganglion specimens and L4 and L5 spinal cord segments were separated from the rats and were analyzed by stereological, immunohistochemistry, and RT-PCR procedures. The rats of the axotomy group presented the expected gross locomotor deficit. Stereological parameters, immunohistochemistry of GFAP, and gene expression of S100, NGF, and BDNF were significantly enhanced in the CM-loaded scaffold group compared with the axotomy group. The most observed similarity was noted between the results of the control group and the CM-loaded scaffold group. Our results support the potential applicability of MSC-CM-loaded PCL nanofibrous scaffold to treat peripheral nerve injury (PNI).

Biomaterial-supported MSC transplantation enhances cell-cell communication for spinal cord injury

The spinal cord is part of the central nervous system (CNS) and serves to connect the brain to the peripheral nervous system and peripheral tissues. The cell types that primarily comprise the spinal cord are neurons and several categories of glia, including astrocytes, oligodendrocytes, and microglia. Ependymal cells and small populations of endogenous stem cells, such as oligodendrocyte progenitor cells, also reside in the spinal cord. Neurons are interconnected in circuits; those that process cutaneous sensory input are mainly located in the dorsal spinal cord, while those involved in proprioception and motor control are predominately located in the ventral spinal cord. Due to the importance of the spinal cord, neurodegenerative disorders and traumatic injuries affecting the spinal cord will lead to motor deficits and loss of sensory inputs.

Spinal cord injury (SCI), resulting in paraplegia and tetraplegia as a result of deleterious interconnected mechanisms encompassed by the primary and secondary injury, represents a heterogeneously behavioral and cognitive deficit that remains incurable. Following SCI, various barriers containing the neuroinflammation, neural tissue defect (neurons, microglia, astrocytes, and oligodendrocytes), cavity formation, loss of neuronal circuitry, and function must be overcame. Notably, the pro-inflammatory and anti-inflammatory effects of cell–cell communication networks play critical roles in homeostatic, driving the pathophysiologic and consequent cognitive outcomes. In the spinal cord, astrocytes, oligodendrocytes, and microglia are involved in not only development but also pathology. Glial cells play dual roles (negative vs. positive effects) in these processes. After SCI, detrimental effects usually dominate and significantly retard functional recovery, and curbing these effects is critical for promoting neurological improvement. Indeed, residential innate immune cells (microglia and astrocytes) and infiltrating leukocytes (macrophages and neutrophils), activated by SCI, give rise to full-blown inflammatory cascades. These inflammatory cells release neurotoxins (proinflammatory cytokines and chemokines, free radicals, excitotoxic amino acids, nitric oxide (NO)), all of which partake in axonal and neuronal deficit.

Given the various multifaceted obstacles in SCI treatment, a combinatorial therapy of cell transplantation and biomaterial implantation may be addressed in detail here. For the sake of preserving damaged tissue integrity and providing physical support and trophic supply for axon regeneration, MSC transplantation has come to the front stage in therapy for SCI with the constant progress of stem cell engineering. MSC transplantation promotes scaffold integration and regenerative growth potential. Integrating into the implanted scaffold, MSCs influence implant integration by improving the healing process. Conversely, biomaterial scaffolds offer MSCs with a sheltered microenvironment from the surrounding pathological changes, in addition to bridging connection spinal cord stump and offering physical and directional support for axonal regeneration. Besides, Biomaterial scaffolds mimic the extracellular matrix to suppress immune responses.

Here, we review the advances in combinatorial biomaterial scaffolds and MSC transplantation approach that targets certain aspects of various intercellular communications in the pathologic process following SCI. Finally, the challenges of biomaterial-supported MSC transplantation and its future direction for neuronal regeneration will be presented.

Neuroregeneration and functional recovery after stroke: advancing neural stem cell therapy toward clinical application

Stroke is a main cause of death and disability worldwide. The ability of the brain to self-repair in the acute and chronic phases after stroke is minimal; however, promising stem cell-based interventions are emerging that may give substantial and possibly complete recovery of brain function after stroke. Many animal models and clinical trials have demonstrated that neural stem cells (NSCs) in the central nervous system can orchestrate neurological repair through nerve regeneration, neuron polarization, axon pruning, neurite outgrowth, repair of myelin, and remodeling of the microenvironment and brain networks. Compared with other types of stem cells, NSCs have unique advantages in cell replacement, paracrine action, inflammatory regulation and neuroprotection. Our review summarizes NSC origins, characteristics, therapeutic mechanisms and repair processes, then highlights current research findings and clinical evidence for NSC therapy. These results may be helpful to inform the direction of future stroke research and to guide clinical decision-making.

Interferon-Gamma and Interleukin-1Beta Enhance the Secretion of Brain-Derived Neurotrophic Factor and Promotes the Survival of Cortical Neurons in Brain Injury

Neuro-inflammation is associated with the production of cytokines, which influence neuronal and glial functions. Although the proinflammatory cytokines interferon-γ (IFN-γ) and interleukin-1Beta (IL-1β) are thought to be the major mediators of neuro-inflammation, their role in brain injury remains ill-defined. The objective of this study was to examine the effect of IFN-γ and IL-1β on survival of cortical neurons in stab wound injury in mice. A stab wound injury was made in the cortex of male BALB/c mice. Injured mice (I) were divide into IFN-γ and IL-1β treatment experiments. Mice in I + IFN-γ group were treated with IFN-γ (ip, 10 µg/kg/day) for 1, 3 and 7 days and mice in I + IL-1β group were treated with 5 IP injection of IL-1β (0.5 µg /12 h). Appropriate control mice were maintained for comparison. Immunostaining of frozen brain sections for astrocytes (GFAP), microglia (Iba-1) and Fluoro-Jade B staining for degenerating neurons were used. Western blotting and ELISA for brain-derived neurotrophic factor (BDNF) were done on the tissues isolated from the injured sites. Results showed a significant increase in the number of both astrocytes and microglia in I + IFN-γ and I + IL-1β groups. There were no significant changes in the number of astrocytes or microglia in noninjury groups (NI) treated with IFN-γ or IL-1β. The number of degenerating neurons significantly decreased in I + IFN-γ and I + IL-1β groups. GFAP and BDNF levels were significantly increased in I + IFN-γ and I + IL-1β groups. Interferon-γ and IL-1β induce astrogliosis, microgliosis, enhance the secretion of BDNF, one of the many neurotrophic factors after brain injury, and promote the survival of cortical neurons in stab wound brain injury.

Self-assembling peptide hydrogels functionalized with LN- and BDNF- mimicking epitopes synergistically enhance peripheral nerve regeneration

The regenerative capacity of the peripheral nervous system is closely related to the role that Schwann cells (SCs) play in construction of the basement membrane containing multiple extracellular matrix proteins and secretion of neurotrophic factors, including laminin (LN) and brain-derived neurotrophic factor (BDNF). Here, we developed a self-assembling peptide (SAP) nanofiber hydrogel based on self-assembling backbone Ac-(RADA)4-NH2 (RAD) dual-functionalized with laminin-derived motif IKVAV (IKV) and a BDNF-mimetic peptide epitope RGIDKRHWNSQ (RGI) for peripheral nerve regeneration, with the hydrogel providing a three-dimensional (3D) microenvironment for SCs and neurites. Methods: Circular dichroism (CD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the secondary structures, microscopic structures, and morphologies of self-assembling nanofiber hydrogels. Then the SC adhesion, myelination and neurotrophin secretion were evaluated on the hydrogels. Finally, the SAP hydrogels were injected into hollow chitosan tubes to bridge a 10-mm-long sciatic nerve defect in rats, and in vivo gene expression at 1 week, axonal regeneration, target muscular re-innervation, and functional recovery at 12 weeks were assessed. Results: The bioactive peptide motifs were covalently linked to the C-terminal of the self-assembling peptide and the functionalized peptides could form well-defined nanofibrous hydrogels capable of providing a 3D microenvironment similar to native extracellular matrix. SCs displayed improved cell adhesion on hydrogels with both IKV and RGI, accompanied by increased cell spreading and elongation relative to other groups. RSCs cultured on hydrogels with IKV and RGI showed enhanced gene expression of NGF, BDNF, CNTF, PMP22 and NRP2, and decreased gene expression of NCAM compared with those cultured on other three groups after a 7-day incubation. Additionally, the secretion of NGF, BDNF, and CNTF of RSCs was significantly improved on dual-functionalized peptide hydrogels after 3 days. At 1 week after implantation, the expressions of neurotrophin and myelin-related genes in the nerve grafts in SAP and Autograft groups were higher than that in Hollow group, and the expression of S100 in groups containing both IKV and RGI was significantly higher than that in groups containing either IKV or RGI hydrogels, suggesting enhanced SC proliferation. The morphometric parameters of the regenerated nerves, their electrophysiological performance, the innervated muscle weight and remodeling of muscle fibers, and motor function showed that RAD/IKV/RGI and RAD/IKV-GG-RGI hydrogels could markedly improve axonal regeneration with enhanced re-myelination and motor functional recovery through the synergetic effect of IKV and RGI functional motifs. Conclusions: We found that the dual-functionalized SAP hydrogels promoted RSC adhesion, myelination, and neurotrophin secretion in vitro and successfully bridged a 10-mm gap representing a sciatic nerve defect in rats in vivo. The results demonstrated the synergistic effect of IKVAV and RGI on axonal regrowth and function recovery after peripheral nerve injury.

Construction of Biofunctionalized Anisotropic Hydrogel Micropatterns and Their Effect on Schwann Cell Behavior in Peripheral Nerve Regeneration

Hydrogels have promising application in tissue regeneration due to their excellent physicochemical and biocompatible properties, whereas anisotropic micropatterns are been proven to directionally induce cell alignment and accelerate cell migration. However, an effect of biofunctionalized anisotropic hydrogel micropatterns on nerve regeneration has rarely been reported. In this study, the anisotropic polyacrylamide (PAM) hydrogel micropatterns with aligned ridge/groove structures were first prepared via in situ free radical polymerization and micromolding, and then biofunctionalized using YIGSR peptide for better promoting cell growth. The morphology, swelling ratio, wettability, mechanical properties, and stability of the prepared hydrogel were characterized. The successful immobilization of YIGSR peptide on the PAM hydrogel was monitored using FTIR, immunofluorescence staining, and ELISA. The effects on adhesion, directional growth, and biological function of Schwann cells were evaluated. The results displayed that the anisotropic PAM hydrogel micropatterns with inner porous structure possessed good stability, swelling, and mechanical properties. The YIGSR peptide could be well immobilized on hydrogel micropatterns with a percentage of 62.6%. The biofunctionalized anisotropic hydrogel micropatterns could effectively regulate the orientation growth of Schwann cells, and obviously up-regulate BDNF (40%) and β-actin (50%) expression compared with single hydrogel micropatterns, without negatively affecting the normal secretion of neurotropic factors by Schwann cells. To the best of our knowledge, this is the first time to study the construction and effect of biofunctionalized anisotropic hydrogel micropatterns on nerve regeneration, which may provide an experimental and theoretical basis for the design and development of artificial implants for nerve regeneration application.

Effects of GDNF-Transfected Marrow Stromal Cells on Rats with Intracerebral Hemorrhage

OBJECTIVE

The present study aimed to investigate the effects of Mesenchymal stem cells/glial cell line derived neurotrophic factor (MSCs/GDNF) transplantation on nerve reconstruction in rats with intracerebral hemorrhage.

METHODS

GDNF transduction to MSCs was using adenovirus vector pAdEasy-1-pAdTrack-CMV prepared. Intracerebral hemorrhage (ICH) was induced by injection of collagenase and heparin into the caudate putamen. At the third day after a collagenase-induced ICH, adult male SD rats were randomly divided into saline group, MSCs group and MSCs/GDNF group. Immunofluorescence and RT-PCR were performed to detect the differentiation of MSCs or MSCs with an adenovirus vector encoding GDNF gene in vivo and in vitro.

RESULT

After 6 hours of induction, both MSCs and MSCs/GDNF expressed neuro or glial specific markers and synaptic-associated proteins (SYN, GAP-43, PSD-95); additionally, they secreted bioactive compounds (BDNF, NGF-β). MSCs/GDNF transplantation, compared to MSCs and saline solution injection, significantly improved neurological functions after ICH. The grafted MSCs or MSCs/GDNF survived in the striatum after 2 weeks of transplantation and expressed the neural cell-specific biomarkers NSE, MAP2, and GFAP.

CONCLUSION

These findings demonstrate that MSCs/GDNF transplantation contributes to improved neurological function in experimental ICH rats. The mechanisms are possibly due to neuronal replacement and enhanced neurotrophic factor secretion.

Human bone marrow-derived MSCs spontaneously express specific Schwann cell markers

In peripheral nerve injuries, Schwann cells (SC) play pivotal roles in regenerating damaged nerve. However, the use of SC in clinical cell-based therapy is hampered due to its limited availability. In this study, we aim to evaluate the effectiveness of using an established induction protocol for human bone marrow derived-MSC (hBM-MSCs) transdifferentiation into a SC lineage. A relatively homogenous culture of hBM-MSCs was first established after serial passaging (P3), with profiles conforming to the minimal criteria set by International Society for Cellular Therapy (ISCT). The cultures (n = 3) were then subjected to a series of induction media containing β-mercaptoethanol, retinoic acid, and growth factors. Quantitative RT-PCR, flow cytometry, and immunocytochemistry analyses were performed to quantify the expression of specific SC markers, that is, S100, GFAP, MPZ and p75 NGFR, in both undifferentiated and transdifferentiated hBM-MSCs. Based on these analyses, all markers were expressed in undifferentiated hBM-MSCs and MPZ expression (mRNA transcripts) was consistently detected before and after transdifferentiation across all samples. There was upregulation at the transcript level of more than twofolds for NGF, MPB, GDNF, p75 NGFR post-transdifferentiation. This study highlights the existence of spontaneous expression of specific SC markers in cultured hBM-MSCs, inter-donor variability and that MSC transdifferentiation is a heterogenous process. These findings strongly oppose the use of a single marker to indicate SC fate. The heterogenous nature of MSC may influence the efficiency of SC transdifferentiation protocols. Therefore, there is an urgent need to re-define the MSC subpopulations and revise the minimal criteria for MSC identification.

Progress in research into spinal cord injury repair: Tissue engineering scaffolds and cell transdifferentiation

As with all tissues of the central nervous system, the low regeneration ability of spinal cord tissue after injury decreases the potential for repair and recovery. Initially, in spinal cord injuries (SCI), often the surgeon can only limit further damage by early surgical decompression. However, with the development of basic science, especially the development of genetic engineering, molecular biology, tissue engineering, and materials science, some promising progress has been made in promoting the repair of central nervous system injuries. For example, transplantation of neural stem cells (NSCs), olfactory ensheathing cells (OECs), and gene- mediated transdifferentiation to repair central nervous system injury. This paper summarizes the progress and prospects of SCI repair with tissue engineering scaffold and cell transdifferentiation from an extensive literatures.

A novel primary culture method for high-purity satellite glial cells derived from rat dorsal root ganglion

Satellite glial cells surround neurons within dorsal root ganglia. Previous studies have focused on single-cell suspensions of cultured neurons derived from rat dorsal root ganglia. At present, the primary culture method for satellite glial cells derived from rat dorsal root ganglia requires no digestion skill. Hence, the aim of the present study was to establish a novel primary culture method for satellite glial cells derived from dorsal root ganglia. Neonatal rat spine was collected and an incision made to expose the transverse protrusion and remove dorsal root ganglia. Dorsal root ganglia were freed from nerve fibers, connective tissue, and capsule membranes, then rinsed and transferred to 6-well plates, and cultured in a humidified 5% CO₂ incubator at 37°C. After 3 days in culture, some cells had migrated from dorsal root ganglia. After subculture, cells were identified by immunofluorescence labeling for three satellite glial cell-specific markers: glutamine synthetase, glial fibrillary acidic protein, and S100β. Cultured cells expressed glutamine synthetase, glial fibrillary acidic protein, and S100β, suggesting they are satellite glial cells with a purity of > 95%. Thus, we have successfully established a novel primary culture method for obtaining high-purity satellite glial cells from rat dorsal root ganglia without digestion.

Genetic Manipulation and Selection of Mouse Mesenchymal Stem Cells for Delivery of Therapeutic Factors In Vivo

Bone marrow-derived mesenchymal stem cells (MSCs) hold great potential as an ex vivo cellular system for delivery of therapeutic proteins to the diseased or damaged central nervous system (CNS). This adult stem cell population has considerable translational potential for autologous transplantation due to lack of ethical concerns, accessibility, multipotent nature, and plasticity. Here we describe a methodology and outline a strategy using lentiviral vectors for producing lines of MSCs hypersecreting neurotrophic growth factors (e.g., brain-derived neurotrophic factor (BDNF) and/or glial cell line-derived neurotrophic factor (GDNF)) together with a reporter protein such as green fluorescent protein (GFP) that may be used for in vitro and in vivo neuroprotection bioassays. This approach provides exciting opportunities for basic research and proof-of-concept studies.

Stem cell-based approaches to enhance nerve regeneration and improve functional outcomes in vascularized composite allotransplantation

PURPOSE OF REVIEW

The current review will discuss the current understanding of nerve regeneration in vascularized composite allotransplantation (VCA). The success of proximal arm and leg transplants has been hampered by the limitations of nerve regrowth across long distances resulting in poor regeneration and functional recovery. Relevant research in stem-cell therapies to overcome these issues will be reviewed.

RECENT FINDINGS

The effect of rejection on nerve regeneration in the VCA may be unpredictable and may be quite different for the nerve allograft. The issues that limit functional outcome are likely common to both VCA and proximal nerve injuries or replantation. Stem-cell therapies have focused on augmenting Schwann cell function and appear promising.

SUMMARY

A better understanding of the effects of transplant rejection on nerve regeneration and function, as well as the factors that affect regeneration over long distances may inform further therapeutic approaches for improvement.

Advances in Controlling Differentiation of Adult Stem Cells for Peripheral Nerve Regeneration

Adult stems cells, possessing the ability to grow, migrate, proliferate, and transdifferentiate into various specific phenotypes, constitute a great asset for peripheral nerve regeneration. Adult stem cells' ability to undergo transdifferentiation is sensitive to various cell-to-cell interactions and external stimuli involving interactions with physical, mechanical, and chemical cues within their microenvironment. Various studies have employed different techniques for transdifferentiating adult stem cells from distinct sources into specific lineages (e.g., glial cells and neurons). These techniques include chemical and/or electrical induction as well as cell-to-cell interactions via co-culture along with the use of various 3D conduit/scaffold designs. Such scaffolds consist of unique materials that possess controllable physical/mechanical properties mimicking cells' natural extracellular matrix. However, current limitations regarding non-scalable transdifferentiation protocols, fate commitment of transdifferentiated stem cells, and conduit/scaffold design have required new strategies for effective stem cells transdifferentiation and implantation. In this progress report, a comprehensive review of recent advances in the transdifferentiation of adult stem cells via different approaches along with multifunctional conduit/scaffolds designs is presented for peripheral nerve regeneration. Potential cellular mechanisms and signaling pathways associated with differentiation are also included. The discussion with current challenges in the field and an outlook toward future research directions is concluded.

Bioactivity-Guided Isolation of Neuritogenic Factor from the Seeds of the Gac Plant (Momordica cochinchinensis)

Nerve growth factor (NGF) is an endogenously produced protein with the capacity to induce central nervous system (CNS) neuronal differentiation and repair. NGF signaling involves its binding to tropomyosin-related kinase (Trk) receptors, internalization, and initiation of phosphorylation cascades which cause microtubule reorganization and neuronal outgrowth. Because NGF cannot cross the blood-brain barrier, its therapeutic use is limited. Synthetic peptides that can act as NGF receptor agonists (NGF mimetics) are known to attenuate neurodegenerative pathologies in experimental models of Alzheimer's disease and Parkinson's disease; however, the existence of plant-based NGF mimetics is uncertain. For this reason, we recently completed a high throughput screening of over 1100 nutraceuticals (vitamins, herbal plant parts, polyphenolics, teas, fruits, and vegetables) to identify neuritogenic factor using a PC-12 cell model. Remarkably we found only one, commonly known as the seed of Gac plant (Momordica cochinchinensis) (MCS). In the current study, we further investigated this seed for its neuritogenic effect using bioactivity-guided chemical separations. The data show no biological neuritogenic activity in any chemical solvent fraction, where activity was exclusive to the crude protein. MSC crude proteins were then separated by 1D electrophoresis, where the active neuritogenic activity was confirmed to have a molecular mass of approximately 17 kDa. Subsequently, the 17kDa band was excised, digested, and run on a UPLC-MS/MS with a Q Exactive Hybrid Quadrupole-Orbitrap Mass Spectrometer with data evaluated diverse tools such as X! Tandem, OMS, and K-score algorithms. Proteomic evaluation of the 17kDa band confirmed evidence for 11S globulin subunit beta, napin, oleosin, Momordica trypsin inhibitors (TI) MCoTI-I /II, and many isoforms of Two Inhibitor Peptide Topologies (TIPTOPs). While all peptides identified correspond to the genus/species, Momordica cochinchinensis and Cucumis Sativus, a significant limitation of the analysis is the nonexistence of full annotation for the Momordica cochinchinensis proteome. In conclusion, these findings demonstrate that there is a stable protein within MCS having a mass of 17kDa with the capacity to induce neurite outgrowth. Future work will be required to establish the therapeutic value of the MCS for the treatment of neurodegenerative diseases.

Adult Stem Cell-Based Strategies for Peripheral Nerve Regeneration

Peripheral nerve injuries (PNI) occur as the result of sudden trauma and can lead to life-long disability, reduced quality of life, and heavy economic and social burdens. Although the peripheral nervous system (PNS) has the intrinsic capacity to regenerate and regrow axons to a certain extent, current treatments frequently show incomplete recovery with poor functional outcomes, particularly for large PNI. Many surgical procedures are available to halt the propagation of nerve damage, and the choice of a procedure depends on the extent of the injury. In particular, recovery from large PNI gaps is difficult to achieve without any therapeutic intervention or some form of tissue/cell-based therapy. Autologous nerve grafting, considered the "gold standard" is often implemented for treatment of gap formation type PNI. Although these surgical procedures provide many benefits, there are still considerable limitations associated with such procedures as donor site morbidity, neuroma formation, fascicle mismatch, and scarring. To overcome such restrictions, researchers have explored various avenues to improve post-surgical outcomes. The most commonly studied methods include: cell transplantation, growth factor delivery to stimulate regenerating axons and implanting nerve guidance conduits containing replacement cells at the site of injury. Replacement cells which offer maximum benefits for the treatment of PNI, are Schwann cells (SCs), which are the peripheral glial cells and in part responsible for clearing out debris from the site of injury. Additionally, they release growth factors to stimulate myelination and axonal regeneration. Both primary SCs and genetically modified SCs enhance nerve regeneration in animal models; however, there is no good source for extracting SCs and the only method to obtain SCs is by sacrificing a healthy nerve. To overcome such challenges, various cell types have been investigated and reported to enhance nerve regeneration.In this review, we have focused on cell-based strategies aimed to enhance peripheral nerve regeneration, in particular the use of mesenchymal stem cells (MSCs). Mesenchymal stem cells are preferred due to benefits such as autologous transplantation, routine isolation procedures, and paracrine and immunomodulatory properties. Mesenchymal stem cells have been transplanted at the site of injury either directly in their native form (undifferentiated) or in a SC-like form (transdifferentiated) and have been shown to significantly enhance nerve regeneration. In addition to transdifferentiated MSCs, some studies have also transplanted ex-vivo genetically modified MSCs that hypersecrete growth factors to improve neuroregeneration.