Mesenchymal Stem Cells Enhance Nerve Regeneration in a Rat Sciatic Nerve Repair and Hindlimb Transplant Model

Mesenchymal stem cell therapy for Alzheimer's disease: A novel therapeutic approach for neurodegenerative diseases

Alzheimer's disease (AD) is one of the most progressive and prevalent types of neurodegenerative diseases in the aging population (aged >65 years) and is considered a major factor for dementia, affecting 55 million people worldwide. In the current scenario, drug-based therapies have been employed for the treatment of Alzheimer's disease but are only able to provide symptomatic relief to patients rather than a permanent solution from Alzheimer's. Recent advancements in stem cell research unlock new horizons for developing effective and highly potential therapeutic approaches due to their self-renewal, self-replicating, regenerative, and high differentiation capabilities. Stem cells come in multiple lineages such as embryonic, neural, and induced pluripotent, among others. Among different kinds of stem cells, mesenchymal stem cells are the most investigated for Alzheimer's treatment due to their multipotent nature, low immunogenicity, ability to penetrate the blood-brain barrier, and low risk of tumorigenesis, immune & inflammatory modulation, etc. They have been seen to substantially promote neurogenesis, synaptogenesis by secreting neurotrophic growth factors, as well as in ameliorating the Aβ and tau-mediated toxicity. This review covers the pathophysiology of AD, new medications, and therapies. Further, it will focus on the advancements and benefits of Mesenchymal Stem Cell therapies, their administration methods, clinical trials concerning AD progression, along with their future prospective.

Dynamic Seeding versus Microinjection of Adipose-Derived Mesenchymal Stem Cells to Acellular Nerve Allograft Reconstructions

BACKGROUND

Functional recovery after acellular nerve allograft (ANA) reconstruction remains inferior to that after autologous nerve grafting, but improved outcomes have been demonstrated with the addition of adipose-derived mesenchymal stem cells (MSCs). Controversy exists regarding the optimal cell-delivery method to enhance ANA reconstructions. The authors investigated the functional recovery of ANAs after dynamic seeding versus microinjection of MSCs.

METHODS

Forty Lewis rats underwent reconstruction of a 10-mm sciatic nerve defect. Animals were divided into 4 groups: reversed autograft, ANA alone, dynamically seeded ANA, or ANA injected with MSCs. During the survival period, ultrasound measurements of the tibialis anterior muscle cross-sectional area were performed. At 12 weeks, functional recovery was evaluated using measurements of ankle contracture, compound muscle action potential, maximum isometric tetanic force, muscle mass, histomorphometry, and immunofluorescence.

RESULTS

The dynamic seeding and microinjection groups demonstrated higher cross-sectional tibialis anterior muscle area recovery than autografts and ANAs alone at week 8 and weeks 4 and 8, respectively. The ankle contracture and compound muscle action potential amplitude recovery were superior in autografts and both seeding methods compared with ANAs alone. The microinjection group demonstrated significantly higher isometric tetanic force, muscle mass, and number of axons compared with ANAs alone. Both seeding methods showed higher CD34 densities compared with ANAs alone. No significant differences between dynamic seeding and microinjection were observed in functional or histologic outcomes.

CONCLUSIONS

The addition of MSCs to ANAs demonstrated earlier motor regeneration compared with autografts and ANAs alone. Both seeding methods improved functional outcomes in the rat sciatic nerve defect model.

Administration of Human-Derived Mesenchymal Stem Cells Activates Locally Stimulated Endogenous Neural Progenitors and Reduces Neurological Dysfunction in Mice after Ischemic Stroke

Increasing evidence shows that the administration of mesenchymal stem cells (MSCs) is a promising option for various brain diseases, including ischemic stroke. Studies have demonstrated that MSC transplantation after ischemic stroke provides beneficial effects, such as neural regeneration, partially by activating endogenous neural stem/progenitor cells (NSPCs) in conventional neurogenic zones, such as the subventricular and subgranular zones. However, whether MSC transplantation regulates the fate of injury-induced NSPCs (iNSPCs) regionally activated at injured regions after ischemic stroke remains unclear. Therefore, mice were subjected to ischemic stroke, and mCherry-labeled human MSCs (h-MSCs) were transplanted around the injured sites of nestin-GFP transgenic mice. Immunohistochemistry of brain sections revealed that many GFP+ cells were observed around the grafted sites rather than in the regions in the subventricular zone, suggesting that transplanted mCherry+ h-MSCs stimulated GFP+ locally activated endogenous iNSPCs. In support of these findings, coculture studies have shown that h-MSCs promoted the proliferation and neural differentiation of iNSPCs extracted from ischemic areas. Furthermore, pathway analysis and gene ontology analysis using microarray data showed that the expression patterns of various genes related to self-renewal, neural differentiation, and synapse formation were changed in iNSPCs cocultured with h-MSCs. We also transplanted h-MSCs (5.0 × 104 cells/µL) transcranially into post-stroke mouse brains 6 weeks after middle cerebral artery occlusion. Compared with phosphate-buffered saline-injected controls, h-MSC transplantation displayed significantly improved neurological functions. These results suggest that h-MSC transplantation improves neurological function after ischemic stroke in part by regulating the fate of iNSPCs.

The role of orthobiologics in chronic wound healing

Chronic wounds, characterized by prolonged healing processes, pose a significant medical challenge with multifaceted aetiologies, including local and systemic factors. Here, it explores the complex pathogenesis of chronic wounds, emphasizing the disruption in the normal phases of wound healing, particularly the inflammatory phase, leading to an imbalance in extracellular matrix (ECM) dynamics and persistent inflammation. Senescent cell populations further contribute to impaired wound healing in chronic lesions. Traditional medical management focuses on addressing underlying causes, but many chronic wounds resist to conventional treatments, necessitating innovative approaches. Recent attention has turned to autologous orthobiologics, such as platelet-rich plasma (PRP), platelet-rich fibrin (PRF) and mesenchymal stem cells (MSCs), as potential regenerative interventions. These biologically derived materials, including bone marrow aspirate/concentrate (BMA/BMAC) and adipose tissue-derived stem cells (ADSCs), exhibit promising cytokine content and regenerative potential. MSCs, in particular, have emerged as key players in wound healing, influencing inflammation and promoting tissue regeneration. This paper reviews relevant scientific literature regarding basic science and brings real-world evidence regarding the use of orthobiologics in the treatment of chronic wounds, irrespective of aetiology. The discussion highlights the regenerative properties of PRP, PRF, BMA, BMAC and SVF, showcasing their potential to enhance wound healing. Despite advancements, further research is essential to elucidate the specific roles of each orthobiologic and determine optimal applications for different wound types. The conclusion underscores the evolving landscape in chronic wound management, with a call for more comprehensive studies to refine treatment strategies and maximize the benefits of regenerative medicine.

Prospect of Mesenchymal Stem Cells in Enhancing Nerve Regeneration in Brachial Plexus Injury in Animals: A Systematic Review

Objectives

Brachial plexus injuries (BPI), although rare, often results in significant morbidity. Stem cell was thought to be one of BPI treatment modalities because of their nerve-forming regeneration potential. Although there is a possibility for the use of mesenchymal stem cells as one of BPI treatment, it is still limited on animal studies. Therefore, this systematic review aimed to analyze the role of mesenchymal stem cells in nerve regeneration in animal models of brachial plexus injury.

Method

This study is a systematic review with PROSPERO registration number CRD4202128321. Literature searching was conducted using keywords experimental, animal, brachial plexus injury, mesenchymal stem cell implantation, clinical outcomes, electrophysiological outcomes, and histologic outcomes. Searches were performed in the PubMed, Scopus, and ScienceDirect databases. The risk of bias was assessed using SYRCLE's risk of bias tool for animal studies. The data obtained were described and in-depth analysis was performed.

Result

Four studies were included in this study involving 183 animals from different species those are rats and rabbits. There was an increase in muscle weight and shortened initial onset time of muscle contraction in the group treated with stem cells. Electrophysiological results showed that mesenchymal stem cells exhibited higher (Compound muscle action potential) CMAP amplitude and shorter CMAP latency than control but not better than autograft. Histological outcomes showed an increase in axon density, axon number, and the formation of connections between nerve cells and target muscles.

Conclusion

Mesenchymal stem cell implantation to animals with brachial plexus injury showed its ability to regenerate nerve cells as evidenced by clinical, electrophysiological, and histopathological results. However, this systematic study involved experimental animals from various species so that the results cannot be uniformed, and conclusion should be drawn cautiously.

Enhancement of nerve regeneration through schwann cell-mediated healing in a 3D printed polyacrylonitrile conduit incorporating hydrogel and graphene quantum dots: a study on rat sciatic nerve injury model

Despite recent technological advancements, effective healing from sciatic nerve damage remains inadequate. Cell-based therapies offer a promising alternative to autograft restoration for peripheral nerve injuries, and 3D printing techniques can be used to manufacture conduits with controlled diameter and size. In this study, we investigated the potential of Wharton's jelly-derived mesenchymal stem cells (WJMSCs) differentiated into schwann cells, using a polyacrylonitrile (PAN) conduit filled with fibrin hydrogel and graphene quantum dots (GQDs) to promote nerve regeneration in a rat sciatic nerve injury model. We investigated the potential of WJMSCs, extracted from the umbilical cord, to differentiate into schwann cells and promote nerve regeneration in a rat sciatic nerve injury model. WJMSCs were 3D cultured and differentiated into schwann cells within fibrin gel for two weeks. A 3 mm defect was created in the sciatic nerve of the rat model, which was then regenerated using a conduit/fibrin, conduit covered with schwann cells in fibrin/GQDs, GQDs in fibrin, and a control group without any treatment (n= 6/group). At 10 weeks after transplantation, motor and sensory functions and histological improvement were assessed. The WJMSCs were extracted, identified, and differentiated. The differentiated cells expressed typical schwann cell markers, S100 and P75.In vivoinvestigations established the durability and efficacy of the conduit to resist the pressures over two months of implantation. Histological measurements showed conduit efficiency, schwann cell infiltration, and association within the fibrin gel and lumen. Rats treated with the composite hydrogel-filled PAN conduit with GQDs showed significantly higher sensorial recovery than the other groups. Histological results showed that this group had significantly more axon numbers and remyelination than others. Our findings suggest that the conduit/schwann approach has the potential to improve nerve regeneration in peripheral nerve injuries, with future therapeutic implications.

Treatment of Alzheimer's Disease: Beyond Symptomatic Therapies

In an ever-increasing aged world, Alzheimer's disease (AD) represents the first cause of dementia and one of the first chronic diseases in elderly people. With 55 million people affected, the WHO considers AD to be a disease with public priority. Unfortunately, there are no final cures for this pathology. Treatment strategies are aimed to mitigate symptoms, i.e., acetylcholinesterase inhibitors (AChEI) and the N-Methyl-D-aspartate (NMDA) antagonist Memantine. At present, the best approaches for managing the disease seem to combine pharmacological and non-pharmacological therapies to stimulate cognitive reserve. Over the last twenty years, a number of drugs have been discovered acting on the well-established biological hallmarks of AD, deposition of β-amyloid aggregates and accumulation of hyperphosphorylated tau protein in cells. Although previous efforts disappointed expectations, a new era in treating AD has been working its way recently. The Food and Drug Administration (FDA) gave conditional approval of the first disease-modifying therapy (DMT) for the treatment of AD, aducanumab, a monoclonal antibody (mAb) designed against Aβ plaques and oligomers in 2021, and in January 2023, the FDA granted accelerated approval for a second monoclonal antibody, Lecanemab. This review describes ongoing clinical trials with DMTs and non-pharmacological therapies. We will also present a future scenario based on new biomarkers that can detect AD in preclinical or prodromal stages, identify people at risk of developing AD, and allow an early and curative treatment.

Stem cells in the treatment of Alzheimer's disease - Promises and pitfalls

Alzheimer's disease (AD) is the most widespread form of neurodegenerative disorder that causes memory loss and multiple cognitive issues. The underlying mechanisms of AD include the build-up of amyloid-β and phosphorylated tau, synaptic damage, elevated levels of microglia and astrocytes, abnormal microRNAs, mitochondrial dysfunction, hormonal imbalance, and age-related neuronal loss. However, the etiology of AD is complex and involves a multitude of environmental and genetic factors. Currently, available AD medications only alleviate symptoms and do not provide a permanent cure. Therefore, there is a need for therapies that can prevent or reverse cognitive decline, brain tissue loss, and neural instability. Stem cell therapy is a promising treatment for AD because stem cells possess the unique ability to differentiate into any type of cell and maintain their self-renewal. This article provides an overview of the pathophysiology of AD and existing pharmacological treatments. This review article focuses on the role of various types of stem cells in neuroregeneration, the potential challenges, and the future of stem cell-based therapies for AD, including nano delivery and gaps in stem cell technology.

Hypoxic culture of umbilical cord mesenchymal stem cell-derived sEVs prompts peripheral nerve injury repair

Introduction

Repair and regeneration of the peripheral nerve are important for the treatment of peripheral nerve injury (PNI) caused by mechanical tears, external compression injuries and traction injuries. Pharmacological treatment can promote the proliferation of fibroblasts and Schwann cells (SCs), which longitudinally fill the endoneurial canal and form Bungner’s band, helping the repair of peripheral nerves. Therefore, the development of new drugs for the treatment of PNI has become a top priority in recent years.

Methods

Here, we report that small extracellular vesicles (sEVs) produced from umbilical cord mesenchymal stem cells (MSC-sEVs) cultured under hypoxia promote repair and regeneration of the peripheral nerve in PNI and may be a new therapeutic drug candidate.

Results

The results showed that the amount of secreted sEVs was significantly increased in UC-MSCs compared with control cells after 48 h of culture at 3% oxygen partial pressure in a serum-free culture system. The identified MSC-sEVs could be taken up by SCs in vitro, promoting the growth and migration of SCs. In a spared nerve injury (SNI) mouse model, MSC-sEVs accelerated the recruitment of SCs at the site of PNI and promoted peripheral nerve repair and regeneration. Notably, repair and regeneration in the SNI mouse model were enhanced by treatment with hypoxic cultured UC-MSC-derived sEVs.

Discussion

Therefore, we conclude that hypoxic cultured UC-MSC-derived sEVs may be a promising candidate drug for repair and regeneration in PNI.

MiRNA-206 Affects the Recovery of Sciatic Function by Stimulating BDNF Activity through the Down-regulation of Notch3 Expression

OBJECTIVE

To investigate the effects and mechanisms of microRNA 206 (miRNA-206) on neurological recovery through Notch receptor 3 (Notch3).

METHODS

The sciatic functional index (SFI), nerve conduction velocity (NCV), tricipital muscle wet weight (TWW) and cross-sectional area of the muscular fiber, and grip strength of posterior limbs were detected by establishing a model of the sciatic nerve to evaluate the effect of sciatic nerve injury model. miRNA-206 expression in the model was detected by real-time quantitative polymerase chain reaction (qRT-PCR), to regulate the effects of miRNA-206 on the proliferation of gastrocnemius myocytes by Cell Counting Kit-8 (CCK-8).

RESULTS

SFI of the model established by immediate epineurium suture after sciatic nerve resection was in the range of -150% to -100% and TWW, the average area of gastrocnemius myocytes, the NCV, and the grasping power of the hind limbs in the model were all lower than those in the normal group. And in the model, TWW, the average area of gastrocnemius myocytes, NCV, and grip strength of posterior limbs were lower in the normal group, which verified the successful establishment of the model.

CONCLUSION

Over-expression of miRNA-206 can down-regulate Notch3 expression, and then stimulate brain-derived neurotrophic factor (BDNF) activity to promote the repair and functional recovery of sciatic nerve injury.

Human dental pulp stem cell monolayer and spheroid therapy after spinal motor root avulsion in adult rats

Spinal cord injuries result in severe neurological deficits and neuronal loss, with poor functional recovery. Mesenchymal stem cells have shown promising results; therefore the present objective of this work was to compare motor recovery after treatment with human dental pulp stem cells (hDPSC) cultivated in monolayer (2D) or as spheroids (3D), following avulsion and reimplantation of spinal motor roots in adult rats. Thus, 72 adult female Lewis rats were divided into 4 groups: avulsion (AV); avulsion followed by reimplantation (AR); avulsion associated with reimplant and 2D cell therapy (AR + 2D), and avulsion associated with reimplant and 3D cell therapy (AR + 3D). The application of the cells in 2D and 3D was performed by microsurgery, with subsequent functional assessment using a walking track test (Catwalk system), immunohistochemistry, neuronal survival, and qRT-PCR in 1-, 4-, and 12-weeks post-injury. The animals in the AR + 2D and AR + 3D groups showed the highest neuronal survival rates, and immunofluorescence revealed downregulation of GFAP, and Iba-1, with preservation of synaptophysin, indicating a reduction in glial reactivity, combined with the maintenance of pre-synaptic inputs. There was an increase in anti-inflammatory (IL-4, TGFβ) and a reduction of pro-inflammatory factors (IL-6, TNFα) in animals treated with reimplantation and hDPSC. As for the functional recovery, in all analyzed parameters, the AR + 2D group performed better and was superior to the avulsion alone. Overall, our results indicate that the 2D and 3D cell therapy approaches provide successful immunomodulation and motor recovery, consistent with advanced therapies after spinal cord injury.

Comprehensive dynamic and kinematic analysis of the rodent hindlimb during over ground walking

The rat hindlimb is a frequently utilized pre-clinical model system to evaluate injuries and pathologies impacting the hindlimbs. These studies have demonstrated the translational potential of this model but have typically focused on the force generating capacity of target muscles as the primary evaluative outcome. Historically, human studies investigating extremity injuries and pathologies have utilized biomechanical analysis to better understand the impact of injury and extent of recovery. In this study, we expand that full biomechanical workup to a rat model in order to characterize the spatiotemporal parameters, ground reaction forces, 3-D joint kinematics, 3-D joint kinetics, and energetics of gait in healthy rats. We report data on each of these metrics that meets or exceeds the standards set by the current literature and are the first to report on all these metrics in a single set of animals. The methodology and findings presented in this study have significant implications for the development and clinical application of the improved regenerative therapeutics and rehabilitative therapies required for durable and complete functional recovery from extremity traumas, as well as other musculoskeletal pathologies.

The success of biomaterial-based tissue engineering strategies for peripheral nerve regeneration

Peripheral nerve injury is a clinically common injury that causes sensory dysfunction and locomotor system degeneration, which seriously affects the quality of the patients' daily life. Long gapped defects in large nerve are difficult to repair via surgery and limited donor source of autologous nerve greatly challenges the successful nerve repair by transplantation. Significantly, remarkable progress has been made in repairing the peripheral nerve injury using artificial nerve grafts and a variety of products for peripheral nerve repair have emerged been approved globally in recent years. The raw materials of these commercial products includes natural/synthetic polymers, extracellular matrix. Despite a lot of effort, the desirable functional recovery still remains great challenges in long gapped nerve defects. Thus this review discusses the recent development of tissue engineering products for peripheral nerve repair and the design of bionic grafts improving the local microenvironment for accelerating nerve regeneration against locomotor disorder, which may provide potential strategies for the repair of long gaps or thick nerve defects by multifunctional biomaterials.

A Shock to the (Nervous) System: Bioelectricity Within Peripheral Nerve Tissue Engineering

The peripheral nervous system has the remarkable ability to regenerate in response to injury. However, this is only successful over shorter nerve gaps and often provides poor outcomes for patients. Currently, the gold standard of treatment is the surgical intervention of an autograft, whereby patient tissue is harvested and transplanted to bridge the nerve gap. Despite being the gold standard, more than half of patients have dissatisfactory functional recovery after an autograft. Peripheral nerve tissue engineering aims to create biomaterials that can therapeutically surpass the autograft. Current tissue-engineered constructs are designed to deliver a combination of therapeutic benefits to the regenerating nerve, such as supportive cells, alignment, extracellular matrix, soluble factors, immunosuppressants, and other therapies. An emerging therapeutic opportunity in nerve tissue engineering is the use of electrical stimulation (ES) to modify and enhance cell function. ES has been shown to positively affect four key cell types, such as neurons, endothelial cells, macrophages, and Schwann cells, involved in peripheral nerve repair. Changes elicited include faster neurite extension, cellular alignment, and changes in cell phenotype associated with improved regeneration and functional recovery. This review considers the relevant modes of administration and cellular responses that could underpin incorporation of ES into nerve tissue engineering strategies. Impact Statement Tissue engineering is becoming increasingly complex, with multiple therapeutic modalities often included within the final tissue-engineered construct. Electrical stimulation (ES) is emerging as a viable therapeutic intervention to be included within peripheral nerve tissue engineering strategies; however, to date, there have been no review articles that collate the information regarding the effects of ES on key cell within peripheral nerve injury. This review article aims to inform the field on the different therapeutic effects that may be achieved by using ES and how they may become incorporated into existing strategies.

Application of extracorporeal shock wave therapy in nervous system diseases: A review

Neurological disorders are one of the leading causes of morbidity and mortality worldwide, and their therapeutic options remain limited. Recent animal and clinical studies have shown the potential of extracorporeal shock wave therapy (ESWT) as an innovative, safe, and cost-effective option to treat neurological disorders. Moreover, the cellular and molecular mechanism of ESWT has been proposed to better understand the regeneration and repairment of neurological disorders by ESWT. In this review, we discuss the principles of ESWT, the animal and clinical studies involving the use of ESWT to treat central and peripheral nervous system diseases, and the proposed cellular and molecular mechanism of ESWT. We also discuss the challenges encountered when applying ESWT to the human brain and spinal cord and the new potential applications of ESWT in treating neurological disorders.

Periodontal ligament stem cells as a promising therapeutic target for neural damage

BACKGROUND

The damaged neuronal cells of adult mammalian lack the regenerative ability to replace the neuronal connections. Periodontal ligament stem cells (PDLSCs) are the promising source for neuroregenerative applications that can improve the injured microenvironment of the damaged neural system. They provide neuronal progenitors and neurotrophic, anti-apoptotic and anti-inflammatory factors. In this study, we aimed to comprehensively explore the various neuronal differentiation potentials of PDLSCs for application in neural regeneration therapy.

MAIN TEXT

PDLSCs have superior potential to differentiate into various neural-like cells through a dedifferentiation stage followed by differentiation process without need for cell division. Diverse combination of nutritional factors can be used to induce the PDLSCs toward neural lineage. PDLSCs when coupled with biomaterials could have significant implications for neural tissue repair. PDLSCs can be a new clinical research target for Alzheimer's disease treatment, multiple sclerosis and cerebral ischemia. Moreover, PDLSCs have beneficial effects on retinal ganglion cell regeneration and photoreceptor survival. PDLSCs can be a great source for the repair of injured peripheral nerve through the expression of several neural growth factors and differentiation into Schwann cells.

CONCLUSION

In conclusion, these cells are an appealing source for utilizing in clinical treatment of the neuropathological disorders. Although significant in vitro and in vivo investigations were carried out in order for neural differentiation evaluation of these cells into diverse types of neurons, more preclinical and clinical studies are needed to elucidate their therapeutic potential for neural diseases.

Hypoxia pretreatment enhances the therapeutic potential of mesenchymal stem cells (BMSCs) on ozone-induced lung injury in rats

Ozone (O₃) gas is a double-sided weapon. It provides a shield that protects life on earth from the harmful ultraviolet (UV) rays, but ground-level O₃ is considered an urban air pollutant. So, a rat model of chronic O₃ inhalation was established to assess the biochemical and morphological alterations in the lung tissue and to investigate the ameliorative effects of bone marrow-derived mesenchymal stem cells (BMSCs) with or without hypoxia pre-treatment. Forty-two adult male albino rats were divided into four groups: control, ozone-exposed, normoxic BMSC-treated, and hypoxic BMSC-treated groups. Lung tissue sections were processed for light and electron microscope examination, immunohistochemical staining for caspase 3, and iNOS. Quantitative real-time PCR for IL-1α, IL-17, TNF-α, and Nrf2 mRNA gene expression were also performed. Chronic O₃ exposure caused elevated inflammatory cytokines and decreased antioxidant Nrf2 mRNA expression. Marked morphological alterations with increased collagen deposition and elevated apoptotic markers and iNOS were evident. BMSC treatment showed immunomodulatory (decreased inflammatory cytokine gene expression), antioxidant (increased Nrf2 expression and decreased iNOS), and anti-apoptotic (decreased caspase3 expression) effects. Consequently, ameliorated lung morphology with diminished collagen deposition was observed. Hypoxia pretreatment enhanced BMSC survival by MTT assay. It also augmented the previously mentioned effects of BMSCs on the lung tissue as proved by statistical analysis. Lung morphology was similar to that of control group. In conclusion, hypoxia pretreatment represents a valuable intervention to enhance the effects of MSCs on chronic lung injury.

Implantable Biomaterials for Peripheral Nerve Regeneration-Technology Trends and Translational Tribulations

The use of autografted nerve in surgical repair of peripheral nerve injuries (PNI) is severely limited due to donor site morbidity and restricted tissue availability. As an alternative, synthetic nerve guidance channels (NGCs) are available on the market for surgical nerve repair, but they fail to promote nerve regeneration across larger critical gap nerve injuries. Therefore, such injuries remain unaddressed, result in poor healing outcomes and are a limiting factor in limb reconstruction and transplantation. On the other hand, a myriad of advanced biomaterial strategies to address critical nerve injuries are proposed in preclinical literature but only few of those have found their way into clinical practice. The design of synthetic nerve grafts should follow rational criteria and make use of a combination of bioinstructive cues to actively promote nerve regeneration. To identify the most promising NGC designs for translation into applicable products, thorough mode of action studies, standardized readouts and validation in large animals are needed. We identify design criteria for NGC fabrication according to the current state of research, give a broad overview of bioactive and functionalized biomaterials and highlight emerging composite implant strategies using therapeutic cells, soluble factors, structural features and intrinsically conductive substrates. Finally, we discuss translational progress in bioartificial conduits for nerve repair from the surgeon's perspective and give an outlook toward future challenges in the field.

Dynamic seeding versus microinjection of mesenchymal stem cells for acellular nerve allograft: an in vitro comparison

BACKGROUND

Mesenchymal stem cell (MSC)-supplemented acellular nerve allografts (ANA) are a potential strategy to improve the treatment of segmental nerve defects. Prior to clinical translation, optimal cell delivery methods must be defined. While two techniques, dynamic seeding and microinjection, have been described, the seeding efficiency, cell viability, and distribution of MSCs in ANAs are yet to be compared.

METHODS

Sciatic nerve segments of Sprague-Dawley rats were decellularized, and MSCs were harvested from the adipose tissue of Lewis rats. Cell viability was evaluated after injection of MSCs through a 27-gauge needle at different flow rates (10, 5, and 1 µL/min). MSCs were dynamically seeded or longitudinally injected into ANAs. Cell viability, seeding efficiency, and distribution were evaluated using LIVE/DEAD and MTS assays, scanning electron microscopy, and Hoechst staining.

RESULTS

No statistically significant difference in cell viability after injection at different flow rates was seen. After cell delivery, 84.1 ± 3.7% and 87.8 ± 2.8% of MSCs remained viable in the dynamic seeding and microinjection group, respectively (p = 0.41). The seeding efficiency of microinjection (100.4%±5.6) was significantly higher than dynamic seeding (48.1%±8.6) on day 1 (p = 0.001). Dynamic seeding demonstrated a significantly more uniform cell distribution over the course of the ANA compared to microinjection (p = 0.02).

CONCLUSION

MSCs remain viable after both dynamic seeding and microinjection in ANAs. Higher seeding efficiency was observed with microinjection, but dynamic seeding resulted in a more uniform distribution. In vivo studies are required to assess the effect on gene expression profiles and functional motor outcomes.

Mesenchymal Stem/Stromal Cells and Their Paracrine Activity-Immunomodulation Mechanisms and How to Influence the Therapeutic Potential

With high clinical interest to be applied in regenerative medicine, Mesenchymal Stem/Stromal Cells have been widely studied due to their multipotency, wide distribution, and relative ease of isolation and expansion in vitro. Their remarkable biological characteristics and high immunomodulatory influence have opened doors to the application of MSCs in many clinical settings. The therapeutic influence of these cells and the interaction with the immune system seems to occur both directly and through a paracrine route, with the production and secretion of soluble factors and extracellular vesicles. The complex mechanisms through which this influence takes place is not fully understood, but several functional manipulation techniques, such as cell engineering, priming, and preconditioning, have been developed. In this review, the knowledge about the immunoregulatory and immunomodulatory capacity of MSCs and their secretion products is revisited, with a special focus on the phenomena of migration and homing, direct cell action and paracrine activity. The techniques for homing improvement, cell modulation and conditioning prior to the application of paracrine factors were also explored. Finally, multiple assays where different approaches were applied with varying success were used as examples to justify their exploration.

Three-dimensional-printed polycaprolactone/polypyrrole conducting scaffolds for differentiation of human olfactory ecto-mesenchymal stem cells into Schwann cell-like phenotypes and promotion of neurite outgrowth

Implantation of a suitable nerve guide conduit (NGC) seeded with sufficient Schwann cells (SCs) is required to improve peripheral nerve regeneration efficiently. Given the limitations of isolating and culturing SCs, using various sources of stem cells, including mesenchymal stem cells (MSCs) obtained from nasal olfactory mucosa, can be desirable. Olfactory ecto-MSCs (OE-MSCs) are a new population of neural crest-derived stem cells that can proliferate and differentiate into SCs and can be considered a promising autologous alternative to produce SCs. Regardless, a biomimetic physicochemical microenvironment in NGC such as electroconductive substrate can affect the fate of transplanted stem cells, including differentiation toward SCs and nerve regeneration. Therefore, in this study, the effect of 3D printed polycaprolactone (PCL)/polypyrrole (PPy) conductive scaffolds on differentiation of human OE-MSCS into functional SC-like phenotypes was investigated. Biological evaluation of 3D printed scaffolds was examined by in vitro culturing the OE-MSCs on samples surfaces, and conductivity showed no effect on increased cell attachment, proliferation rate, viability, and distribution. In contrast, immunocytochemical staining and real-time polymerase chain reaction analysis indicated that 3D structures coated with PPy could provide a favorable microenvironment for OE-MSCs differentiation. In addition, it was found that differentiated OE-MSCs within PCL/PPy could secrete the highest amounts of nerve growth factor and brain-derived neurotrophic factor neurotrophic factors compared to pure PCL and 2D culture. After co-culturing with PC12 cells, a significant increase in neurite outgrowth on PCL/PPy conductive scaffold seeded with differentiated OE-MSCs. These findings indicated that 3D printed PCL/PPy conductive scaffold could support differentiation of OE-MSCs into SC-like phenotypes to promote neurite outgrowth, suggesting their potential for neural tissue engineering applications.

Tissue Engineering and Its Potential to Reduce Prostate Cancer Treatment Sequelae-Narrative Review

Tissue engineering offers the possibility to overcome limitations of current management for postprostatectomy incontinence and ED. Developed in recent years biotechnological feasibility of mesenchymal stem cell isolation, in vitro cultivation and implantation became the basis for new cell-based therapies oriented to induce regeneration of adult tissue. The perspective to offer patients suffering from post-prostatectomy incontinence or erectile dysfunction minimal invasive one-time procedure utilizing autologous stem cell transplantation is desired management.

Mesenchymal stem cells and local tacrolimus delivery synergistically enhance neurite extension

BACKGROUND

The aim of this study was to investigate the combined effect of mesenchymal stem cells (MSC) and local delivery of tacrolimus (FK506) on nerve regeneration when applied to nerve autografts and decellularized allografts.

METHODS

A three-dimensional in vitro compartmented cell culture system consisting of a neonatal dorsal root ganglion adjacent to a nerve graft was used to evaluate the regenerating neurites into the peripheral nerve scaffold. Nerve autografts and allografts were treated with (i) undifferentiated MSCs, (ii) FK506 (100 ng/mL) or (iii) both (N = 9/group). After 48 hours, neurite extension was measured to quantify nerve regeneration and stem cell viability was evaluated.

RESULTS

Stem cell viability was confirmed in all MSC-treated grafts. Neurite extension was superior in autografts treated with FK506, and MSCs and FK506 combined (p < 0.001 and p = 0.0001, respectively), and autografts treated with MSCs (p = 0.12) were comparable to untreated autografts. In allografts, FK506 treatment and combined treatment were superior to controls (p < 0.001 and p = 0.0001, respectively), and treatment with MSCs (p = 0.09) was comparable to controls. All autograft groups were superior compared to their respective allograft treatment group (p < 0.05) in neurite extension.

CONCLUSIONS

Alone, either MSC or FK506 treatment improved neurite outgrowth, and combined they further enhanced neurite extension in both autografts and allografts.

Peripheral nerve regeneration: A comparative study of the effects of autologous bone marrow-derived mesenchymal stem cells, platelet-rich plasma, and lateral saphenous vein graft as a conduit in a dog model

BACKGROUND

The quality of healing of peripheral nerve injuries remains a common challenge causing pain and poor quality of life for millions of people and animals annually.

AIMS

The objectives of this study were to evaluate the healing quality of facial nerve injury in a dog model following local treatment using an autologous injection of platelet-rich plasma (PRP) or bone marrow-derived mesenchymal stem cells (BM-MSCs) at the injury site in combination with the application of an autologous saphenous vein graft as a conduit.

METHODS

20 apparently healthy adult Mongrel dogs were randomly divided into 4 equal groups. Dogs in groups 1, 2, and 3 were subjected to facial nerve neurectomy and saphenous vein conduit graft implantation at the site of facial nerve injury. Dogs in groups 2 and 3 received 1 ml of autologous PRP and BM-MSCs, respectively. Injections were administered directly in the vein conduit immediately after nerve injury. Dogs in group 1 (grafted but not treated; control) received only an autologous vein graft, and those in group 4 (normal control) received no graft and no PRP or BM-MSCs treatment. The dogs were monitored daily for 8 weeks after surgery. Clinical evaluation of the facial nerve, including lower eyelid, ear drooping, upper lip, and tongue functions, was carried out once per week using a numerical scoring system of 0-3. At the end of the study period (week 8), the facial nerve injury site was evaluated grossly for the presence of adhesions using a numerical scoring system of 0-3. The facial nerve injury site was histopathologically assessed for the existence of perivascular mononuclear cell infiltration, fibrous tissue deposition, and axonal injury using H&E-stained tissue sections.

RESULTS

Clinically, BM-MSCs treated dogs experienced significant (p < 0.05) improvement in the lower eyelid, ear, lip, and tongue functions 4 weeks postoperatively compared to other groups. Grossly, the facial nerve graft site in the BM-MSCs treated group showed significantly (p < 0.05) lesser adhesion scores than the other groups. Histopathologically, there was significantly (p < 0.05) less perivascular mononuclear cell infiltration, less collagen deposition, and more normal axons at the facial nerve injury site in the BM-MSCs treated group compared to the other groups.

CONCLUSION

This study showed clinically significant enhancement of nerve regeneration by applying autologous BM-MSCs and autologous vein grafting at the site of facial nerve injury. However, further clinical trials are warranted before this application can be recommended to treat traumatic nerve injuries in the field.

Peripheral Nerve Regeneration Using Different Germ Layer-Derived Adult Stem Cells in the Past Decade

Peripheral nerve injuries (PNIs) are some of the most common types of traumatic lesions affecting the nervous system. Although the peripheral nervous system has a higher regenerative ability than the central nervous system, delayed treatment is associated with disturbances in both distal sensory and functional abilities. Over the past decades, adult stem cell-based therapies for peripheral nerve injuries have drawn attention from researchers. This is because various stem cells can promote regeneration after peripheral nerve injuries by differentiating into neural-line cells, secreting various neurotrophic factors, and regulating the activity of in situ Schwann cells (SCs). This article reviewed research from the past 10 years on the role of stem cells in the repair of PNIs. We concluded that adult stem cell-based therapies promote the regeneration of PNI in various ways.

Mesenchymal Stem Cell Therapy for Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease responsible for 60-70% of the 50 million cases of dementia worldwide. It is characterized by neuronal cell death, shrinkage of brain tissue, and progressive cognitive, motor, and behavioral impairment, which often leads to death. Although current treatment has helped improve the patient's quality of life, it has not been able to alter the underlying disease pathology of AD. Studies have shown that mesenchymal stem cells (MSCs)—a group of multipotent stem cells—have the ability to stimulate neuroregeneration and inhibit disease progression. More recently, extracellular vesicles (EVs) from cytokine-preconditioned MSCs have also shown to induce immunomodulatory and neuroprotective effects in AD models. This review will aim to compile pertinent preclinical AD research on transgenic mice as well as clinical trials on MSC-based therapy from diverse sources.

Evidence-Based Approach to Nerve Gap Repair in the Upper Extremity: A Review of the Literature and Current Algorithm for Surgical Management

The upper extremity is the most common site for nerve injuries. In most cases, direct repair can be performed, but when a critical gap occurs, special techniques must be used to enhance nerve regeneration and allow recovery of sensory and motor functions. These techniques include the use of autografts, processed nerve allografts, and conduits. However, surprisingly few studies have compared outcomes from the different methods of nerve gap repair in a rigorous fashion. There is a lack of evidence-based guidelines for the management of digital and motor and mixed nerve injuries with a nerve gap. The purpose of this study is to perform a comprehensive literature review and propose a rational algorithm for management of nerve injuries with a critical gap.

Combined local delivery of tacrolimus and stem cells in hydrogel for enhancing peripheral nerve regeneration

The application of scaffold-based stem cell transplantation to enhance peripheral nerve regeneration has great potential. Recently, the neuroregenerative potential of tacrolimus (a U.S. Food and Drug Administration-approved immunosuppressant) has been explored. In this study, a fibrin gel-based drug delivery system for sustained and localized tacrolimus release was combined with rat adipose-derived mesenchymal stem cells (MSC) to investigate cell viability in vitro. Tacrolimus was encapsulated in poly(lactic-co-glycolic) acid (PLGA) microspheres and suspended in fibrin hydrogel, using concentrations of 0.01 and 100 ng/ml. Drug release over time was measured. MSCs were cultured in drug-released media collected at various days to mimic systemic exposure. MSCs were combined with (i) hydrogel only, (ii) empty PLGA microspheres in the hydrogel, (iii) 0.01, and (iv) 100 ng/ml of tacrolimus PLGA microspheres in the hydrogel. Stem cell presence and viability were evaluated. A sustained release of 100 ng/ml tacrolimus microspheres was observed for up to 35 days. Stem cell presence was confirmed and cell viability was observed up to 7 days, with no significant differences between groups. This study suggests that combined delivery of 100 ng/ml tacrolimus and MSCs in fibrin hydrogel does not result in cytotoxic effects and could be used to enhance peripheral nerve regeneration.

Schwann-like cell conditioned medium promotes angiogenesis and nerve regeneration

Vascular network reconstruction plays a pivotal role in the axonal regeneration and nerve function recovery after peripheral nerve injury. Increasing evidence indicates that Schwann cells (SCs) can promote nerve function repair, and the beneficial effects attributed to SCs therapy may exert their therapeutic effects through paracrine mechanisms. Recently, the previous research of our group demonstrated the promising neuroregenerative capacity of Schwann-like cells (SCLCs) derived from differentiated human embryonic stem cell-derived neural stem cells (hESC-NSCs) in vitro. Herein, the effects of SC-like cell conditioned medium (SCLC-CM) on angiogenesis and nerve regeneration were further explored. The assays were performed to show the pro-angiogenic effects of SCLC-CM, such as promoted endothelial cell proliferation, migration and tube formation in vitro. In addition, Sprague-Dawley rats were treated with SCLC-CM after sciatic nerve crush injury, SCLC-CM was conducive for the recovery of sciatic nerve function, which was mainly manifested in the SFI increase, the wet weight ratio of gastrocnemius muscle, as well as the number and thickness of myelin. The SCLC-CM treatment reduced the Evans blue leakage and increased the expression of CD34 microvessels. Furthermore, SCLC-CM upregulated the expressions of p-Akt and p-mTOR in endothelial cells. In conclusion, SCLC-CM promotes angiogenesis and nerve regeneration, it is expected to become a new treatment strategy for peripheral nerve injury.

Applications of Mesenchymal Stem Cells in Skin Regeneration and Rejuvenation

Mesenchymal stem cells (MSCs) are multipotent stem cells derived from adult stem cells. Primary MSCs can be obtained from diverse sources, including bone marrow, adipose tissue, and umbilical cord blood. Recently, MSCs have been recognized as therapeutic agents for skin regeneration and rejuvenation. The skin can be damaged by wounds, caused by cutting or breaking of the tissue, and burns. Moreover, skin aging is a process that occurs naturally but can be worsened by environmental pollution, exposure to ultraviolet radiation, alcohol consumption, tobacco use, and undernourishment. MSCs have healing capacities that can be applied in damaged and aged skin. In skin regeneration, MSCs increase cell proliferation and neovascularization, and decrease inflammation in skin injury lesions. In skin rejuvenation, MSCs lead to production of collagen and elastic fibers, inhibition of metalloproteinase activation, and promote protection from ultraviolet radiation-induced senescence. In this review, we focus on how MSCs and MSC-derived molecules improve diseased and aged skin. Additionally, we emphasize that induced pluripotent stem cell (iPSC)-derived MSCs are potentially advanced MSCs, which are suitable for cell therapy.

Gold Nanoparticles Combined Human β-Defensin 3 Gene-Modified Human Periodontal Ligament Cells Alleviate Periodontal Destruction via the p38 MAPK Pathway

Periodontitis is a chronic inflammatory disease with plaques as the initiating factor, which will induce the destruction of periodontal tissues. Numerous studies focused on how to obtain periodontal tissue regeneration in inflammatory environments. Previous studies have reported adenovirus-mediated human β-defensin 3 (hBD3) gene transfer could potentially enhance the osteogenic differentiation of human periodontal ligament cells (hPDLCs) and bone repair in periodontitis. Gold nanoparticles (AuNPs), the ideal inorganic nanomaterials in biomedicine applications, were proved to have synergetic effects with gene transfection. To further observe the potential promoting effects, AuNPs were added to the transfected cells. The results showed the positive effects of osteogenic differentiation while applying AuNPs into hPDLCs transfected by adenovirus encoding hBD3 gene. In vivo, after rat periodontal ligament cell (rPDLC) transplantation into SD rats with periodontitis, AuNPs combined hBD3 gene modification could also promote periodontal regeneration. The p38 mitogen-activated protein kinase (MAPK) pathway was demonstrated to potentially regulate both the in vitro and in vivo processes. In conclusion, AuNPs can promote the osteogenic differentiation of hBD3 gene-modified hPDLCs and periodontal regeneration via the p38 MAPK pathway.

Mesenchymal Stem Cells Derived from Wharton's Jelly Can Differentiate into Schwann Cell-Like Cells and Promote Peripheral Nerve Regeneration in Acellular Nerve Grafts

BACKGROUND

Schwann cells (SCs) secrete neurotrophic factors and provide structural support and guidance during axonal regeneration. However, nearby nerves may be damaged to obtain primary SCs, and there is a lack of nervous tissue donors. We investigated the potential of Wharton's Jelly-derived mesenchymal stem cells (WJ-MSCs) in differentiating into Schwann cell-like cells (WJ-SCLCs) as an alternative to SCs. We also examined whether implantation of WJ-SCLCs-laden acellular nerve grafts (ANGs) are effective in inducing functional recovery and nerve regeneration in an animal model of peripheral nerve injury.

METHODS

The differentiation of WJ-MSCs into WJ-SCLCs was determined by analyzing SC-specific markers. The secretion of neurotrophic factors was assessed by the Neuro Discovery antibody array. Neurite outgrowth and myelination of axons were found in a co-culture system involving motor neuron cell lines. The effects of ANGs on repairing sciatic nerves were evaluated using video gait angle test, isometric tetanic force analysis, and toluidine blue staining.

RESULTS

Compared with undifferentiated WJ-MSCs, WJ-SCLCs showed higher expression levels of SC-specific markers such as S100β, GFAP, KROX20, and NGFR. WJ-SCLCs also showed higher secreted amounts of brain-derived neurotrophic factor, glial cell-derived neurotrophic factor, and granulocyte-colony stimulating factor than did WJ-MSCs. WJ-SCLCs effectively promoted the outgrowth and myelination of neurites in motor neuron cells, and WJ-SCLCs laden ANGs significantly facilitated peripheral nerve regeneration in an animal model of sciatic nerve injury.

CONCLUSION

WJ-MSCs were readily differentiated into WJ-SCLCs, which effectively promoted the regeneration of peripheral nerves. Transplantation of WJ-SCLCs with ANGs might be useful for assisting peripheral nerve regeneration.

Mesenchymal stem cell treatment for peripheral nerve injury: a narrative review

Peripheral nerve injuries occur as the result of sudden trauma and lead to reduced quality of life. The peripheral nervous system has an inherent capability to regenerate axons. However, peripheral nerve regeneration following injury is generally slow and incomplete that results in poor functional outcomes such as muscle atrophy. Although conventional surgical procedures for peripheral nerve injuries present many benefits, there are still several limitations including scarring, difficult accessibility to donor nerve, neuroma formation and a need to sacrifice the autologous nerve. For many years, other therapeutic approaches for peripheral nerve injuries have been explored, the most notable being the replacement of Schwann cells, the glial cells responsible for clearing out debris from the site of injury. Introducing cultured Schwann cells to the injured sites showed great benefits in promoting axonal regeneration and functional recovery. However, there are limited sources of Schwann cells for extraction and difficulties in culturing Schwann cells in vitro. Therefore, novel therapeutic avenues that offer maximum benefits for the treatment of peripheral nerve injuries should be investigated. This review focused on strategies using mesenchymal stem cells to promote peripheral nerve regeneration including exosomes of mesenchymal stem cells, nerve engineering using the nerve guidance conduits containing mesenchymal stem cells, and genetically engineered mesenchymal stem cells. We present the current progress of mesenchymal stem cell treatment of peripheral nerve injuries.

Neural Regenerative Potential of Stem Cells Derived from the Tooth Apical Papilla

The regenerative effects of stem cells derived from dental tissues have been previously investigated. This study assessed the potential of human tooth stem cells from apical papilla (SCAP) on nerve regeneration. The SCAP collected from nine individuals were characterized and polarized by exposure to interferon-γ (IFN-γ). IFN-γ increased kynurenine and interleukin-6 (IL-6) production by SCAP, without affecting the cell viability. IFN-γ-primed SCAP exhibited a decrease of brain-derived neurotrophic factor (BDNF) mRNA levels, followed by an upregulation of glial cell-derived neurotrophic factor mRNA. Ex vivo, the co-culture of SCAP with neurons isolated from the rat dorsal root ganglion induced neurite outgrowth, accompanied by increased BDNF secretion, irrespective of IFN-γ priming. In vivo, the local application of SCAP reduced the mechanical and thermal hypersensitivity in Wistar rats that had been submitted to sciatic chronic constriction injury. The SCAP also reduced the pain scores, according to the evaluation of the Grimace scale, partially restoring the myelin damage and BDNF immunopositivity secondary to nerve lesion. Altogether, our results provide novel evidence about the regenerative effects of human SCAP, indicating their potential to handle nerve injury-related complications.

Highly elastic, electroconductive, immunomodulatory graphene crosslinked collagen cryogel for spinal cord regeneration

Novel amino-functionalized graphene crosslinked collagen based nerve conduit having appropriate electric (3.8 ± 0.2 mSiemens/cm) and mechanical cues (having young modulus value of 100-347 kPa) for stem cell transplantation and neural tissue regeneration was fabricated using cryogelation. The developed conduit has shown sufficiently high porosity with interconnectivity between the pores. Raman spectroscopy analysis revealed the increase in orderliness and crosslinking of collagen molecules in the developed cryogel due to the incorporation of amino-functionalized graphene. BM-MSCs grown on graphene collagen cryogels have shown enhanced expression of CD90 and CD73 gene upon electric stimulation (100 mV/mm) contributing towards maintaining their stemness. Furthermore, an increased secretion of ATP from BM-MSCs grown on graphene collagen cryogel was also observed upon electric stimulation that may help in regeneration of neurons and immuno-modulation. Neuronal differentiation of BM-MSCs on graphene collagen cryogel in the presence of electric stimulus showed an enhanced expression of MAP-2 kinase and β-tubulin III. Immunohistochemistry studies have also demonstrated the improved neuronal differentiation of BM-MSCs. BM-MSCs grown on electro-conductive collagen cryogels under inflammatory microenvironment in vitro showed high indoleamine 2,3 dioxygenase activity. Moreover, macrophages cells grown on graphene collagen cryogels have shown high CD206 (M2 polarization marker) and CD163 (M2 polarization marker) and low CD86 (M1 polarization marker) gene expression demonstrating M2 polarization of macrophages, which may aid in tissue repair. In an organotypic culture, the developed cryogel conduit has supported cellular growth and migration from adult rat spinal cord. Thus, this novel electro-conductive graphene collagen cryogels have potential for suppressing the neuro-inflammation and promoting the neuronal cellular migration and proliferation, which is a major barrier during the spinal cord regeneration.

Applied Bioengineering in Tissue Reconstruction, Replacement, and Regeneration

IMPACT STATEMENT

The use of autologous tissue in the reconstruction of tissue defects has been the gold standard. However, current standards still face many limitations and complications. Improving patient outcomes and quality of life by addressing these barriers remain imperative. This article provides historical perspective, covers the major limitations of current standards of care, and reviews recent advances and future prospects in applied bioengineering in the context of tissue reconstruction, replacement, and regeneration.

[Experimental study on autologous injectable platelets rich fibrin combined with bone mesenchymal stem cells in treating sciatic nerve injury in rats]

OBJECTIVE

To investigate the effectiveness of autologous injectable platelet rich fibrin (i-PRF) combined with bone marrow mesenchymal stem cells (BMSCs) for sciatic nerve injury in rats.

METHODS

BMSCs were isolated and cultured from tibial bone marrow of Sprague Dawley (SD) neonatal rats aged 10-15 days and passaged to the 4th generation. i-PRF was prepared from posterior orbital venous blood of adult SD rats by improved low-speed centrifugation. Twenty-four adult SD rats were selected and randomly divided into 4 groups with 6 rats in each group after the sciatic nerve Ⅲ degree injury model was established by modified crush injury method. Groups A, B, C, and D were injected with BMSCs suspension+autologous i-PRF, autologous i-PRF, BMSCs suspension, and normal saline, respectively. The Basso-Beattie-Bresnahan (BBB) score was used to evaluate the recovery of neurological function of the affected limb of rats every week from 1 to 8 weeks after operation. At 2 months after operation, the rats were sacrificed and the histological changes of sciatic nerve were observed by HE staining. The microstructural changes of nerve fibers, myelin sheath, and nucleus were observed by transmission electron microscope. The expressions of N-cadherin, Nestin, and glial fibrillary acidic protein (GFAP) were detected by Western blot.

RESULTS

No immune rejection or death occurred in the rats after operation. There was no significant difference in BBB scores between groups at 1 week after operation ( P>0.05); at 2-8 weeks after operation, BBB scores in group A were significantly higher than those in groups B, C, and D, and in groups B, C than in group D ( P<0.05), there was no significant difference between groups B and C ( P>0.05). HE staining showed that the nerve fibers in group A arranged in order, without defect or demyelination; the nerve fibers in group B were not clear and slightly swollen; some of the nerve fibers in group C were disordered and demyelinated; the nerve fibers in group D were not continuous, obviously demyelinated, and some of the nerve adventitia damaged. Transmission electron microscope showed that the structure of nerve fibers in group A was clear, myelin sheath was complete, and nucleus was dense; group B was slightly less than group A; group C had fuzzy structure, demyelination, and hollowing out; group D had disorder structure, demyelination, and hollowing out, and the middle part of nerve adventitia continuity. Western blot detection results showed that there was no significant difference in the relative expression of Nestin between groups ( P>0.05). The relative expression of N-cadherin was significantly lower in groups B, C, and D than in group A, in groups C and D than in group B, and in group D than in group C ( P<0.05). The relative expression of GFAP was significantly lower in groups B, C, and D than in group A, in group D than in groups B and C ( P<0.05); there was no significant difference between groups B and C ( P>0.05).

CONCLUSION

Autologous i-PRF combined with BMSCs can effectively treat sciatic nerve tissue injury in rats.

Human umbilical cord derived mesenchymal stem cells in peripheral nerve regeneration

BACKGROUND

Peripheral nerve injury can occur as a result of trauma or disease and carries significant morbidity including sensory and motor loss. The body has limited ability for nerve regeneration and functional recovery. Left untreated, nerve lesions can cause lifelong disability. Traditional treatment options such as neurorrhaphy and neurolysis have high failure rates. Surgical reconstruction with autograft carries donor site morbidity and often provide suboptimal results. Mesenchymal stem cells (MSCs) are known to have promising regenerative potential and have gained attention as a treatment option for nerve lesions. It is however, unclear whether it can be effectively used for nerve regeneration.

AIM

To evaluate the evidence for the use of human umbilical cord derived MSCs (UCMSCs) in peripheral nerve regeneration.

METHODS

We carried out a systematic literature review in accordance with the PRISMA protocol. A literature search was performed from conception to September 2019 using PubMed, EMBASE and Web of Science. The results of eligible studies were appraised. A risk of bias analysis was carried out using Cochrane’s RoB 2.0 tool.

RESULTS

Fourteen studies were included in this review. A total of 279 subjects, including both human and animal were treated with UCMSCs. Four studies obtained UCMSCs from a third-party source and the remainder were harvested by the investigators. Out of the 14 studies, thirteen conducted xenogenic transplantation into nerve injury models. All studies reported significant improvement in nerve regeneration in the UCMSC treated groups compared with the various different controls and untreated groups.

CONCLUSION

The evidence summarised in this PRISMA systematic review of in vivo studies supports the notion that human UCMSC transplantation is an effective treatment option for peripheral nerve injury.

Strategies for Peripheral Nerve Repair

PURPOSE OF REVIEW

This review focuses on biomechanical and cellular considerations required for development of biomaterials and engineered tissues suitable for implantation following PNI, as well as translational requirements relating to outcome measurements for testing success in patients.

RECENT FINDINGS

Therapies that incorporate multiple aspects of the regenerative environment are likely to be key to improving therapies for nerve regeneration. This represents a complex challenge when considering the diversity of biological, chemical and mechanical factors involved. In addition, clinical outcome measures following peripheral nerve repair which are sensitive and responsive to changes in the tissue microenvironment following neural injury and regeneration are required.

SUMMARY

Effective new therapies for the treatment of PNI are likely to include engineered tissues and biomaterials able to evoke a tissue microenvironment that incorporates both biochemical and mechanical features supportive to regeneration. Translational development of these technologies towards clinical use in humans drives a concomitant need for improved clinical measures to quantify nerve regeneration.

Mesenchymal Stem Cell-Laden Hydrogel Microfibers for Promoting Nerve Fiber Regeneration in Long-Distance Spinal Cord Transection Injury

Mesenchymal stem cell (MSC)-based regenerative medicine is widely considered as a promising approach for repairing tissue and re-establishing function in spinal cord injury (SCI). However, low survival rate, uncontrollable migration, and differentiation of stem cells after implantation represent major challenges toward the clinical deployment of this approach. In this study, we fabricated three-dimensional MSC-laden microfibers via electrospinning in a rotating cell culture to mimic nerve tissue, control stem cell behavior, and promote integration with the host tissue. The hierarchically aligned fibrin hydrogel was used as the MSC carrier though a rotating method and the aligned fiber structure induced the MSC-aligned adhesion on the surface of the hydrogel to form microscale cell fibers. The MSC-laden microfiber implantation enhanced the donor MSC neural differentiation, encouraged the migration of host neurons into the injury gap and significantly promoted nerve fiber regeneration across the injury site. Abundant GAP-43- and NF-positive nerve fibers were observed to regenerate in the caudal, rostral, and middle sites of the injury position 8 weeks after the surgery. The NF fiber density reached to 29 ± 6 per 0.25 mm² at the middle site, 82 ± 13 per 0.25 mm² at the adjacent caudal site, and 70 ± 23 at the adjacent rostral site. Similarly, motor axons labeled with 5-hydroxytryptamine were significantly regenerated in the injury gap, which was 122 ± 22 at the middle injury site that was beneficial for motor function recovery. Most remarkably, the transplantation of MSC-laden microfibers significantly improved electrophysiological expression and re-established limb motor function. These findings highlight the combination of MSCs with microhydrogel fibers, the use of which may become a promising method for MSC implantation and SCI repair.

Repair strategies for injured peripheral nerve: Review

Compromised functional regains in about half of the patients following surgical nerve repair pose a serious socioeconomic burden to the society. Although surgical strategies such as end-to-end neurorrhaphy, nerve grafting and nerve transfer are widely applied in distal injuries leading to optimal recovery; however in proximal nerve defects functional outcomes remain unsatisfactory. Biomedical engineering approaches unite the efforts of the surgeons, engineers and biologists to develop regeneration facilitating structures such as extracellular matrix based supportive polymers and tubular nerve guidance channels. Such polymeric structures provide neurotrophic support from injured nerve stumps, retard the fibrous tissue infiltration and guide regenerating axons to appropriate targets. The development and application of nerve guidance conduits (NGCs) to treat nerve gap injuries offer clinically relevant and feasible solutions. Enhanced understanding of the nerve regeneration processes and advances in NGCs design, polymers and fabrication strategies have led to developing modern NGCs with superior regeneration-conducive capacities. Current review focuses on the advances in surgical and engineering approaches to treat peripheral nerve injuries. We suggest the incorporation of endothelial cell growth promoting cues and factors into the NGC interior for its possible enhancement effects on the axonal regeneration process that may result in substantial functional outcomes.

Experimental Protocol of MSC Differentiation into Neural Lineage for Nerve Tissue Regeneration Using Polymeric Scaffolds

The treatment of neurodegenerative diseases is still a challenging grindstone in reconstructive surgeries and regenerative medicine. The retention of mesenchymal stem cells (MSCs) to retain remarkable properties of differentiating into motor neuron-like cells and Schwann cells can prove to be effective in repairing disorders. Moreover, the ultrafine electrospun nanofibers provide a favorable and conducive platform for proliferation and differentiation of MSCs. The development of new 3D culture methods with electrospun scaffolds that closely mimic the physiological niche of cells will help us to understand the functional benefits of MSCs in regeneration process. This article highlights the protocols for isolation of MSCs from rat bone marrow and their subsequent culture on nanofiber scaffolds. Furthermore, this chapter summarizes the various procedures including isolation of the MSCs, their seeding on electrospun nanofibrous scaffolds, and their proliferation and differentiation into neural lineage upon appropriate induction. The materials and preparation of various reagents used at different steps of the protocol are also summarized in detail.

Evaluation of dual release of stromal cell-derived factor-1 and basic fibroblast growth factor with nerve conduit for peripheral nerve regeneration: An experimental study in mice

BACKGROUND

The development of drug delivery systems has enabled the release of multiple bioactive molecules. The efficacy of nerve conduits coated with dual controlled release of stromal cell-derived factor-1 (SDF-1) and basic fibroblast growth factor (bFGF) for peripheral nerve regeneration was investigated.

MATERIALS AND METHODS

Sixty-two C57BL6 mice were used for peripheral nerve regeneration with a nerve conduit (inner diameter, 1 mm, and length, 7 mm) and an autograft. The mice were randomized into five groups based on the different repairs of nerve defects. In the group of repair with conduits alone (n = 9), a 5-mm sciatic nerve defect was repaired by the nerve conduit. In the group of repair with conduits coated with bFGF (n = 10), SDF-1 (n = 10), and SDF-1/bFGF (n = 10), it was repaired by the nerve conduit with bFGF gelatin, SDF-1 gelatin, and SDF-1/bFGF gelatin, respectively. In the group of repair with autografts (n = 10), it was repaired by the resected nerve itself. The functional recovery, nerve regeneration, angiogenesis, and TGF-β1 gene expression were assessed.

RESULTS

In the conduits coated with SDF-1/bFGF group, the mean sciatic functional index value (-88.68 ± 10.64, p = .034) and the axon number (218.8 ± 111.1, p = .049) were significantly higher than the conduit alone group, followed by the autograft group; in addition, numerous CD34-positive cells and micro vessels were observed. TGF-β1 gene expression relative values in the conduits with SDF-1/bFGF group at 3 days (7.99 ± 5.14, p = .049) significantly increased more than the conduits alone group.

CONCLUSION

Nerve conduits coated with dual controlled release of SDF-1 and bFGF promoted peripheral nerve regeneration.

Reactive oxygen species-responsive drug delivery systems for the treatment of neurodegenerative diseases

Neurodegenerative diseases and disorders seriously impact memory and cognition and can become life-threatening. Current medical techniques attempt to combat these detrimental effects mainly through the administration of neuromedicine. However, drug efficacy is limited by rapid dispersal of the drugs to off-target sites while the site of administration is prone to overdose. Many neuropathological conditions are accompanied by excessive reactive oxygen species (ROS) due to the inflammatory response. Accordingly, ROS-responsive drug delivery systems have emerged as a promising solution. To guide intelligent and comprehensive design of ROS-responsive drug delivery systems, this review article discusses the two following topics: (1) the biology of ROS in both healthy and diseased nervous systems and (2) recent developments in ROS-responsive, drug delivery system design. Overall, this review article would assist efforts to make better decisions about designing ROS-responsive, neural drug delivery systems, including the selection of ROS-responsive functional groups.

Neurons-derived extracellular vesicles promote neural differentiation of ADSCs: a model to prevent peripheral nerve degeneration

Potential mechanisms involved in neural differentiation of adipocyte derived stem cells (ADSCs) are still unclear. In the present study, extracellular vesicles (EVs) were tested as a potential mechanism involved in the neuronal differentiation of stem cells. In order to address this, ADSCs and neurons (BRC) were established in primary culture and co-culture at three timepoints. Furthermore, we evaluated protein and transcript levels of differentiated ADSCs from the same timepoints, to confirm phenotype change to neuronal linage. Importantly, neuron-derived EVs cargo and EVs originated from co-culture were analyzed and tested in terms of function, such as gene expression and microRNA levels related to the adult neurogenesis process. Ideal neuron-like cells were identified and, therefore, we speculated the in vivo function of these cells in acute sciatic nerve injury. Overall, our data demonstrated that ADSCs in indirect contact with neurons differentiated into neuron-like cells. Neuron-derived EVs appear to play an important role in this process carrying SNAP25, miR-132 and miR-9. Additionally, in vivo neuron-like cells helped in microenvironment modulation probably preventing peripheral nerve injury degeneration. Consequently, our findings provide new insight of future methods of ADSC induction into neuronal linage to be applied in peripheral nerve (PN) injury.

Mesenchymal stem cell therapy assisted by nanotechnology: a possible combinational treatment for brain tumor and central nerve regeneration

Mesenchymal stem cells (MSCs) intrinsically possess unique features that not only help in their migration towards the tumor-rich environment but they also secrete versatile types of secretomes to induce nerve regeneration and analgesic effects at inflammatory sites. As a matter of course, engineering MSCs to enhance their intrinsic abilities is growing in interest in the oncology and regenerative field. However, the concern of possible tumorigenesis of genetically modified MSCs prompted the development of non-viral transfected MSCs armed with nanotechnology for more effective cancer and regenerative treatment. Despite the fact that a large number of successful studies have expanded our current knowledge in tumor-specific targeting, targeting damaged brain site remains enigmatic due to the presence of a blood–brain barrier (BBB). A BBB is a barrier that separates blood from brain, but MSCs with intrinsic features of transmigration across the BBB can efficiently deliver desired drugs to target sites. Importantly, MSCs, when mediated by nanoparticles, can further enhance tumor tropism and can regenerate the damaged neurons in the central nervous system through the promotion of axon growth. This review highlights the homing and nerve regenerative abilities of MSCs in order to provide a better understanding of potential cell therapeutic applications of non-genetically engineered MSCs with the aid of nanotechnology.

Adipose-Derived Mesenchymal Stem Cells Applied in Fibrin Glue Stimulate Peripheral Nerve Regeneration

Mesenchymal stem cells (MSCs) hold a great promise for cell therapy. To date, they represent one of the best choices for the treatment of post-traumatic injuries of the peripheral nervous system. Although autologous can be easily transplanted in the injured area, clinical advances in this filed have been impaired by lack of preservation of graft cells into the injury area after transplantation. Indeed, cell viability is not retained after injection into the blood stream, and cells injected directly into the area of injury either are washed off or inhibit regeneration through scar formation and neuroma development. This study proposes a new way of MSCs delivery to the area of traumatic injury by using fibrin glue, which not only fixes cells at the site of application but also provides extracellular matrix support. Using a sciatic nerve injury model, MSC derived from adipose tissue embedded in fibrin glue were able to enter the nerve and migrate mainly retrogradely after transplantation. They also demonstrated a neuroprotective effect on DRG L5 sensory neurons and stimulated axon growth and myelination. Post-traumatic changes of the sensory neuron phenotype were also improved. Importantly, MSCs stimulated nerve angiogenesis and motor function recovery. Therefore, our data suggest that MSC therapy using fibrin glue is a safe and efficient method of cell transplantation in cases of sciatic nerve injury, and that this method of delivery of regeneration stimulants could be beneficial for the successful treatment of other central and peripheral nervous system conditions.

Advances in stem cell treatment for sciatic nerve injury

INTRODUCTION

The sciatic nerve is one of the peripheral nerves that is most prone to injuries. After injury, the connection between the nervous system and the distal organs is disrupted, and delayed treatment results in distal organ atrophy and total disability. Regardless of great advances in the fields of neurosurgery, biological sciences, and regenerative medicine, total functional recovery is yet to be achieved.

AREAS COVERED

Cell-based therapy for the treatment of peripheral nerve injuries (PNIs) has brought a new perspective to the field of regenerative medicine. Having the ability to differentiate into neural and glial cells, stem cells enhance neural regeneration after PNIs. Augmenting axonal regeneration, remyelination, and muscle mass preservation are the main mechanisms underlying stem cells' beneficial effects on neural regeneration.

EXPERT OPINION

Despite the usefulness of employing stem cells for the treatment of PNIs in pre-clinical settings, further assessments are still needed in order to translate this approach into clinical settings. Mesenchymal stem cells, especially adipose-derived stem cells, with the ability of autologous transplantation, as well as easy harvesting procedures, are speculated to be the most promising source to be used in the treatment of PNIs.