Schwann-like cells seeded in acellular nerve grafts improve nerve regeneration

Evaluation of combined effects of brief electrical stimulation and Schwann-like cells on sciatic nerve injury model

Severe nerve injuries can be treated with electrical stimulation and stem cell therapies, but little is known about the potential benefits of combining these two treatments. In an effort to investigate this combination, we conducted a study to evaluate the effectiveness of electrical stimulation and Schwann-like cell transplantation in female Wistar albino rats. Our study consisted of five groups of rats: a sham group, an injury group, an electrical stimulation group, a Schwann-like cell group, and a combination group. The experimental groups received electrical stimulation, Schwann-like cell transplantation, or both. The animals sciatic function index was evaluated during a 6-week recovery period, and nerve conduction velocity, wet muscle mass, and nerve tissues were also analyzed. The results of the study showed that all experimental groups had a faster functional recovery compared to the injury group, although the difference between groups was not statistically significant. Both the combination group and the Schwann-like cell transplantation group had a higher nerve conduction velocity compared to the other experimental groups. However, there was no significant difference between the combination and Schwann-like cell transplantation groups. Nonetheless, histological analysis showed a better axonal reorganization in the combination group. The study provides preliminary evidence of the potential benefits of combining electrical stimulation and Schwann-like cell transplantation in treating severe nerve injuries. However, further studies with larger sample sizes are needed to confirm these findings and optimize the treatment parameters.

Clinical evaluation of the perception of post-trauma paresthesia in the mandible, using a biomimetic material: A preliminary study in humans

There is a great effort from numerous research groups in the development of materials and therapeutic strategies for the functional recovery of patients who have suffered peripheral nerve injuries (PNI). In an article in vivo, the formation of a nerve bridge was observed, reconnecting the distal and proximal stumps, in the sciatic nerve of rats, indicating the effective participation of the biomaterial in the recovery of peripheral nerve injuries. For the current pilot study, 15 cases of multiple fractures of the mandible, with involvement of the inferior alveolar nerve (IAN) were selected and studied: JC (control cases) n = 6 with conventional treatment, and JT (treated cases) n = 9, with the use of biomimetic biomaterial. The evaluation of the return to sensitivity was measured through a self-assessment, where the patients assigned scores from 0 to 10, where zero (0) represented the complete absence of sensitivity and ten (10) the normality of the perception of local sensitivity. Patients were evaluated from the preoperative period to the 360th day. The statistical results obtained by the t-Student, Shapiro-Wilk normality and non-parametric One-Way ANOVA tests indicated statistically significant differences (p < 0.005; 0.005 e 0.5 respectively), between the two treatments, which were reflected in the clinical results observed, we also calculate the size of the effect represented by ϵ², calculated by Cohen's d. The results indicate a great difference between the treatments performed,ϵ² = 1.00. In the 6 cases followed up in the JC group, four remained with a significant deficit until the end of the evaluations and two indicated the remission of the lack of sensitivity in this period. In the JT group, in 28 days, all cases indicated complete remission of the lack of sensitivity with healing concentration. In one of the cases where there was a complete rupture of the mental nerve, the (score-10) was observed in 60 days. The observed results indicate the existence of a statistical significance between the groups and an important relationship when using the biomimetic biomaterial during the recovery of the perception of sensitivity in polytraumatized patients, compatible with the results observed in laboratory animals, which may indicate its clinical feasibility in the reduction of sequelae in PNI.

Engineered hydrogels for peripheral nerve repair

Peripheral nerve injury (PNI) is a complex disease that often appears in young adults. It is characterized by a high incidence, limited treatment options, and poor clinical outcomes. This disease not only causes dysfunction and psychological disorders in patients but also brings a heavy burden to the society. Currently, autologous nerve grafting is the gold standard in clinical treatment, but complications, such as the limited source of donor tissue and scar tissue formation, often further limit the therapeutic effect. Recently, a growing number of studies have used tissue-engineered materials to create a natural microenvironment similar to the nervous system and thus promote the regeneration of neural tissue and the recovery of impaired neural function with promising results. Hydrogels are often used as materials for the culture and differentiation of neurogenic cells due to their unique physical and chemical properties. Hydrogels can provide three-dimensional hydration networks that can be integrated into a variety of sizes and shapes to suit the morphology of neural tissues. In this review, we discuss the recent advances of engineered hydrogels for peripheral nerve repair and analyze the role of several different therapeutic strategies of hydrogels in PNI through the application characteristics of hydrogels in nerve tissue engineering (NTE). Furthermore, the prospects and challenges of the application of hydrogels in the treatment of PNI are also discussed.

Peripheral Nerve Regeneration: Opportunities and Challenges

Peripheral nerve injury has detrimental effects on the quality of life for patients and is a worldwide issue with high rates of morbidity. Research on the molecular mechanisms of nerve injury, microsurgical techniques, and advances in stem cell research have led to substantial progress in the field of translational neurophysiology. Current research on peripheral nerve regeneration aims to accelerate peripheral nerve development through pluripotent stem cells and potential use of smart exosomes, pharmacological agents, and bioengineering of nerve conduits. In this article critically reviewed and summarized various methods used for peripheral nerve regeneration and highlight the opportunities and challenges that come along with these strategies.

Role of adipose tissue grafting and adipose-derived stem cells in peripheral nerve surgery

The application of autologous fat grafting in reconstructive surgery is commonly used to improve functional form. This review aims to provide an overview of the scientific evidence on the biology of adipose tissue, the role of adipose-derived stem cells, and the indications of adipose tissue grafting in peripheral nerve surgery. Adipose tissue is easily accessible through the lower abdomen and inner thighs. Non-vascularized adipose tissue grafting does not support oxidative and ischemic stress, resulting in variable survival of adipocytes within the first 24 hours. Enrichment of adipose tissue with a stromal vascular fraction is purported to increase the number of adipose-derived stem cells and is postulated to augment the long-term stability of adipose tissue grafts. Basic science nerve research suggests an increase in nerve regeneration and nerve revascularization, and a decrease in nerve fibrosis after the addition of adipose-derived stem cells or adipose tissue. In clinical studies, the use of autologous lipofilling is mostly applied to secondary carpal tunnel release revisions with promising results. Since the use of adipose-derived stem cells in peripheral nerve reconstruction is relatively new, more studies are needed to explore safety and long-term effects on peripheral nerve regeneration. The Food and Drug Administration stipulates that adipose-derived stem cell transplantation should be minimally manipulated, enzyme-free, and used in the same surgical procedure, e.g. adipose tissue grafts that contain native adipose-derived stem cells or stromal vascular fraction. Future research may be shifted towards the use of tissue-engineered adipose tissue to create a supportive microenvironment for autologous graft survival. Shelf-ready alternatives could be enhanced with adipose-derived stem cells or growth factors and eliminate the need for adipose tissue harvest.

Effect of acellular nerve scaffold containing human umbilical cord-derived mesenchymal stem cells on nerve repair and regeneration in rats with sciatic nerve defect

Background

The aim of the present study was to investigate the effect of acellular nerve scaffold (ANS) containing human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) on nerve repair and regeneration in rats with sciatic nerve defect.

Methods

Sciatic nerve trunks were removed from 6 female Sprague-Dawley (SD) rats, and ANS was prepared by lyophilization + enzymatic method and divided into A, B, C, D and E groups according to different treatment times. hUC-MSCs were isolated from the collected umbilical cords and cultured, and then ANS-hUC-MSCs complexes were made. The other 24 adult female SD rats were randomly divided into the control, autograft, ANS, and ANS-hUC-MSCs groups, and a rat model of sciatic nerve defect was established. Hematoxylin-eosin (HE) staining, Luxol fast blue (LFB) staining, Masson staining, and scanning electron microscopy were used to observe the morphology and tissue structure of ANS. The performance of ANS was evaluated by mechanical detection, and hydroxyproline (HYP) content was evaluated using a biochemical kit. Flow cytometry was adopted to detect the levels of hUC-MSCs surface antigens CD29, CD44, and CD34, as well as electrophysiological detection and muscle wet weight recovery rate for measuring rat muscle performance.

Results

ANS was prepared according to group A method and had good mechanical properties, with less residues of cells and myelin, and higher HYP content, indicating that this scaffold had the best performance. ANS-hUC-MSCs significantly reduced myelin injury in the sciatic nerve, and increased axonal regeneration, effectively improving sciatic nerve injury in rats. In addition, ANS-hUC-MSCs significantly increased compound muscle action potential (CMAP), nerve conduction velocity (NCV), and muscle wet weight, and reduced muscle atrophy.

Conclusions

ANS containing hUC-MSCs can promote nerve repair and regeneration in rats with sciatic nerve defects.

Acellular nerve graft enriched with mesenchymal stem cells in the transfer of the phrenic nerve to the musculocutaneous nerve in a C5-C6 brachial plexus avulsion in a rat model

INTRODUCTION

Phrenic nerve transfer has been shown to achieve good nerve regeneration in brachial plexus avulsion. Acellular nerve allografts (ANAs) showed inferior results to autografts, which is why its use with mesenchymal stem cells (MSCs) is currently being studied. The aim is to study the effect of BM-MSCs associated with ANAs in a rat model of phrenic nerve transfer to the musculocutaneous nerve in a C5-C6 avulsion.

MATERIAL AND METHODS

42 Wistar-Lewis rats underwent a C5-C6 lesion in the right forelimb by excising a 3 mm segment from both roots, followed by a phrenic nerve transfer to the musculocutaneous nerve associated with the interposition of a three types of nerve graft (randomly distributed): control (autograft) group (n = 12), ANAs group (n = 12), and ANAs + BM-MSCs group (n = 18) After 12 weeks, amplitude and latency of the NAP and the compound motor action potential (CMAP) were measured. Biceps muscles were studied by histological analysis and nerve grafts by electron microscopy and fluorescence analysis.

RESULTS

Statistically significant reductions were found in latency of the CMAP between groups control (2.48 ± 0.47 ms) and experimental (ANAs: 4.38 ± 0.78 ms, ANAs + BM-MSCs: 4.08 ± 0.85 ms) and increases in the amplitude of the CMAP between groups control (0.04388 ± 0.02 V) and ANAs + BM-MSCs (0.02275 ± 0.02 V), as well as in the thickness of the myelin sheath between groups control (0.81 ± 0.07 μm) and experimental (ANAs: 0.72 ± 0.08 μm, ANAs + BM-MSCs: 0.72 ± 0.07 μm) and in the area of the myelin sheath between groups control (13.09 ± 2.67 μm² ) and ANAs (10.01 ± 2.97 μm² ) (p < .05). No statistically significant differences have been found between groups ANAs and ANAs + BM-MSCs.

CONCLUSIONS

This study presents a model for the study of lesions of the upper trunk and validates the autologous graft as the gold standard.

Comparison of mesenchymal stem cell attachment efficiency in acellular neural graft for peripheral nerve regeneration

Decellularized nerve allograft is an alternative to autologous nerve graft for nerve defects but has shown inferior clinical outcomes. Mesenchymal stem cells can play a key role in improving nerve regeneration of decellularized nerve allografts. The purpose of this study was to compare different mesenchymal stem cell seeding methods and to find the most efficient way to attach cells to nerve grafts for peripheral nerve regeneration. Wharton's jelly mesenchymal stem cells were collected from human umbilical cords and were seeded in the acellular nerve graft in five different ways as follows: PBS injection, fibrin glue drop, Matrigel drop, bioreactor, and Matrigel injection. A 6-mm sciatic nerve defect of Sprague-Dawley rats was bridged using mesenchymal stem cells-laden acellular nerve grafts according to the five seeding methods. Two days after implantation, the nerve tissue was biopsied and analyzed by the immunofluorescence staining of nuclei. The number of Wharton's jelly mesenchymal stem cells (+ h Nuclei) was counted in the inside, outside, and the total area of the graft sections under 200X magnification. The highest efficiency of mesenchymal stem cell attachment inside the graft and the highest total number of attached mesenchymal stem cells was observed in the group using Matrigel injection (p < 0.0001). This study showed mesenchymal stem cells can be more effectively attached to decellularized nerve graft using the injection method with Matrigel than other static or dynamic seeding methods in vivo.

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.

Proposed Mechanisms of Targeting COVID-19 by Delivering Mesenchymal Stem Cells and Their Exosomes to Damaged Organs

With the outbreak of coronavirus disease (COVID-19) caused by novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the world has been facing an unprecedented challenge. Considering the lack of appropriate therapy for COVID-19, it is crucial to develop effective treatments instead of supportive approaches. Mesenchymal stem cells (MSCs) as multipotent stromal cells have been shown to possess treating potency through inhibiting or modulating the pathological events in COVID-19. MSCs and their exosomes participate in immunomodulation by controlling cell-mediated immunity and cytokine release. Furthermore, they repair the renin-angiotensin-aldosterone system (RAAS) malfunction, increase alveolar fluid clearance, and reduce the chance of hypercoagulation. Besides the lung, which is the primary target of SARS-CoV-2, the heart, kidney, nervous system, and gastrointestinal tract are also affected by COVID-19. Thus, the efficacy of targeting these organs via different delivery routes of MSCs and their exosomes should be evaluated to ensure safe and effective MSCs administration in COVID-19. This review focuses on the proposed therapeutic mechanisms and delivery routes of MSCs and their exosomes to the damaged organs. It also discusses the possible application of primed and genetically modified MSCs as a promising drug delivery system in COVID-19. Moreover, the recent advances in the clinical trials of MSCs and MSCs-derived exosomes as one of the promising therapeutic approaches in COVID-19 have been reviewed.

The interaction of stem cells and vascularity in peripheral nerve regeneration

The degree of nerve regeneration after peripheral nerve injury can be altered by the microenvironment at the site of injury. Stem cells and vascularity are postulated to be a part of a complex pathway that enhances peripheral nerve regeneration; however, their interaction remains unexplored. This review aims to summarize current knowledge on this interaction, including various mechanisms through which trophic factors are promoted by stem cells and angiogenesis. Angiogenesis after nerve injury is stimulated by hypoxia, mediated by vascular endothelial growth factor, resulting in the growth of pre-existing vessels into new areas. Modulation of distinct signaling pathways in stem cells can promote angiogenesis by the secretion of various angiogenic factors. Simultaneously, the importance of stem cells in peripheral nerve regeneration relies on their ability to promote myelin formation and their capacity to be influenced by the microenvironment to differentiate into Schwann-like cells. Stem cells can be acquired through various sources that correlate to their differentiation potential, including embryonic stem cells, neural stem cells, and mesenchymal stem cells. Each source of stem cells serves its particular differentiation potential and properties associated with the promotion of revascularization and nerve regeneration. Exosomes are a subtype of extracellular vesicles released from cell types and play an important role in cell-to-cell communication. Exosomes hold promise for future transplantation applications, as these vesicles contain fewer membrane-bound proteins, resulting in lower immunogenicity. This review presents pre-clinical and clinical studies that focus on selecting the ideal type of stem cell and optimizing stem cell delivery methods for potential translation to clinical practice. Future studies integrating stem cell-based therapies with the promotion of angiogenesis may elucidate the synergistic pathways and ultimately enhance nerve regeneration.

Application of stem cells in peripheral nerve regeneration

Traumatic peripheral nerve injury is a worldwide clinical issue with high morbidity. The severity of peripheral nerve injury can be classified as neurapraxia, axonotmesis or neurotmesis, according to Seddon's classification, or five different degrees according to Sunderland's classification. Patients with neurotmesis suffer from a complete transection of peripheral nerve stumps and are often in need of surgical repair of nerve defects. The applications of autologous nerve grafts as the golden standard for peripheral nerve transplantation meet some difficulties, including donor nerve sacrifice and nerve mismatch. Attempts have been made to construct tissue-engineered nerve grafts as supplements or even substitutes for autologous nerve grafts to bridge peripheral nerve defects. The incorporation of stem cells as seed cells into the biomaterial-based scaffolds increases the effectiveness of tissue-engineered nerve grafts and largely boosts the regenerative process. Numerous stem cells, including embryonic stem cells, neural stem cells, bone marrow mesenchymal stem cells, adipose stem cells, skin-derived precursor stem cells and induced pluripotent stem cells, have been used in neural tissue engineering. In the current review, recent trials of stem cell-based tissue-engineered nerve grafts have been summarized; potential concerns and perspectives of stem cell therapeutics have also been contemplated.

Gene expression and growth factor analysis in early nerve regeneration following segmental nerve defect reconstruction with a mesenchymal stromal cell-enhanced decellularized nerve allograft

The purpose of this study was to evaluate the molecular mechanisms underlying nerve repair by a decellularized nerve allograft seeded with adipose-derived mesenchymal stromal cells (MSCs) and compare it to the unseeded allograft and autograft nerve.

METHODS

Undifferentiated MSCs were seeded onto decellularized nerve allografts and used to reconstruct a 10 mm gap in a rat sciatic nerve model. Gene expression profiles of genes essential for nerve regeneration and immunohistochemical staining (IHC) for PGP9.5, NGF, RECA-1, and S100 were obtained 2 weeks postoperatively.

RESULTS

Semi-quantitative RT-PCR analysis showed that the angiogenic molecule VEGFA was significantly increased in seeded allografts, and transcription factor SOX2 was downregulated in seeded allografts. Seeded grafts showed a significant increase in immunohistochemical markers NGF and RECA-1, when compared with unseeded allografts.

CONCLUSIONS

MSCs contributed to the secretion of trophic factors. A beneficial effect of the MSCs on angiogenesis was found when compared with the unseeded nerve allograft, but implanted MSCs did not show evidence of differentiation into Schwann cell-like cells.

Skeletal muscle-derived cells repair peripheral nerve defects in mice

Skeletal muscle-derived cells have strong secretory function, while skeletal muscle-derived stem cells, which are included in muscle-derived cells, can differentiate into Schwann cell-like cells and other cell types. However, the effect of muscle-derived cells on peripheral nerve defects has not been reported. In this study, 5-mm-long nerve defects were created in the right sciatic nerves of mice to construct a peripheral nerve defect model. Adult female C57BL/6 mice were randomly divided into four groups. For the muscle-derived cell group, muscle-derived cells were injected into the catheter after the cut nerve ends were bridged with a polyurethane catheter. For external oblique muscle-fabricated nerve conduit and polyurethane groups, an external oblique muscle-fabricated nerve conduit or polyurethane catheter was used to bridge the cut nerve ends, respectively. For the sham group, the sciatic nerves on the right side were separated but not excised. At 8 and 12 weeks post-surgery, distributions of axons and myelin sheaths were observed, and the nerve diameter was calculated using immunofluorescence staining. The number, diameter, and thickness of myelinated nerve fibers were detected by toluidine blue staining and transmission electron microscopy. Muscle fiber area ratios were calculated by Masson’s trichrome staining of gastrocnemius muscle sections. Sciatic functional index was recorded using walking footprint analysis at 4, 8, and 12 weeks after operation. The results showed that, at 8 and 12 weeks after surgery, myelin sheaths and axons of regenerating nerves were evenly distributed in the muscle-derived cell group. The number, diameter, and myelin sheath thickness of myelinated nerve fibers, as well as gastrocnemius muscle wet weight and muscle area ratio, were significantly higher in the muscle-derived cell group compared with the polyurethane group. At 4, 8, and 12 weeks post-surgery, sciatic functional index was notably increased in the muscle-derived cell group compared with the polyurethane group. These criteria of the muscle-derived cell group were not significantly different from the external oblique muscle-fabricated nerve conduit group. Collectively, these data suggest that muscle-derived cells effectively accelerated peripheral nerve regeneration. This study was approved by the Animal Ethics Committee of Plastic Surgery Hospital, Chinese Academy of Medical Sciences (approval No. 040) on September 28, 2016.

Current Status of Therapeutic Approaches against Peripheral Nerve Injuries: A Detailed Story from Injury to Recovery

Peripheral nerve injury is a complex condition with a variety of signs and symptoms such as numbness, tingling, jabbing, throbbing, burning or sharp pain. Peripheral nerves are fragile in nature and can easily get damaged due to acute compression or trauma which may lead to the sensory and motor functions deficits and even lifelong disability. After lesion, the neuronal cell body becomes disconnected from the axon's distal portion to the injury site leading to the axonal degeneration and dismantlement of neuromuscular junctions of targeted muscles. In spite of extensive research on this aspect, complete functional recovery still remains a challenge to be resolved. This review highlights detailed pathophysiological events after an injury to a peripheral nerve and the associated factors that can either hinder or promote the regenerative machinery. In addition, it throws light on the available therapeutic strategies including supporting therapies, surgical and non-surgical interventions to ameliorate the axonal regeneration, neuronal survival, and reinnervation of peripheral targets. Despite the availability of various treatment options, we are still lacking the optimal treatments for a perfect and complete functional regain. The need for the present age is to discover or design such potent compounds that would be able to execute the complete functional retrieval. In this regard, plant-derived compounds are getting more attention and several recent reports validate their remedial effects. A plethora of plants and plant-derived phytochemicals have been suggested with curative effects against a number of diseases in general and neuronal injury in particular. They can be a ray of hope for the suffering individuals.

Mesenchymal Stem Cells for Regenerative Medicine

In recent decades, the biomedical applications of mesenchymal stem cells (MSCs) have attracted increasing attention. MSCs are easily extracted from the bone marrow, fat, and synovium, and differentiate into various cell lineages according to the requirements of specific biomedical applications. As MSCs do not express significant histocompatibility complexes and immune stimulating molecules, they are not detected by immune surveillance and do not lead to graft rejection after transplantation. These properties make them competent biomedical candidates, especially in tissue engineering. We present a brief overview of MSC extraction methods and subsequent potential for differentiation, and a comprehensive overview of their preclinical and clinical applications in regenerative medicine, and discuss future challenges.

Seeding decellularized nerve allografts with adipose-derived mesenchymal stromal cells: An in vitro analysis of the gene expression and growth factors produced

Mesenchymal stromal cells (MSCs) secrete many soluble growth factors and have previously been shown to stimulate nerve regeneration. MSC-seeded processed nerve allografts could potentially be a promising method for large segmental motor nerve injuries. Further progress in our understanding of how the functions of MSCs can be leveraged for peripheral nerve repair is required before making clinical translation. The present study, therefore, investigated whether interactions of adipose-derived MSCs with decellularized nerve allografts can improve gene and protein expression of growth factors that may support nerve regeneration. Human nerve allografts (n = 30) were decellularized and seeded with undifferentiated human adipose-derived MSCs. Subsequently, the MSCs and MSC-seeded grafts were isolated on days 3, 7, 14, and 21 in culture for RNA expression analysis by qRT-PCR. Evaluated genes included NGF, BDNF, PTN, GAP43, MBP, PMP22, VEGF, and CD31. Growth factor production was evaluated and quantified using enzyme-linked immunosorbent assay (ELISA). On day 21, semi-quantitative RT-PCR analysis showed that adherence of MSCs to nerve allografts significantly enhances mRNA expression of neurotrophic, angiogenic, endothelial, and myelination markers (e.g., BDNF, VEGF, CD31, and MBP). ELISA results revealed an upregulation of BDNF and reduction of both VEGF and NGF protein levels. This study demonstrates that seeding of undifferentiated adipose-derived MSCs onto processed nerve allografts permits the secretion of neurotrophic and angiogenic factors that can stimulate nerve regeneration. These favorable molecular changes suggest that MSC supplementation of nerve allografts may have potential in improving nerve regeneration.

Sericin Nerve Guidance Conduit Delivering Therapeutically Repurposed Clobetasol for Functional and Structural Regeneration of Transected Peripheral Nerves

Peripheral nerve injury often causes significant function loss. Autologous nerve grafting as a gold-standard repair strategy for treating such an injury is limited by donor nerve supply. Tissue-engineered nerve guidance conduits (TENGCs) as a promising alternative for autografting are challenged by large nerve gaps. Herein, we fabricate a glutaraldehyde-cross-linked sericin nerve guidance conduit (GSC) incorporated with clobetasol, a glucocorticoid receptor agonist, for repairing a 10 mm long sciatic nerve gap in a rat model. The GSC exhibits biocompatibility and regeneration-favorable physicochemical properties. GSC's degradation products promote the secretion of neurotrophic factors in Schwann cells. By repurposing clobetasol for peripheral nerve regeneration, our work uncovers clobetasol's previously unknown functions in promoting Schwann cell proliferation and upregulating the expression of myelin-related genes. Importantly, the implantation of this clobetasol-loaded GSC in vivo leads to successful regeneration of the transected sciatic nerve. Strikingly, the regeneration outcome is functionally comparable to that of autologous nerve grafting (evidenced by three parameters). Specifically, the static sciatic index (SSI), relative reaction time (RRT) and nerve conduction velocity (NCV) in Clobetasol/GSC group are -74.55, 1.30, and 46.4 mm/s at Week 12, respectively, while these parameters are -64.53, 1.23, and 49.8 mm/s in Autograft group. Thus, this work represents the first report unveiling clobetasol's potential in peripheral nerve regeneration, reveals the feasibility of applying a sericin conduit for repairing a large nerve defect, and demonstrates the effectiveness of the clobetasol-loaded-GSC based strategy in transected nerves' regeneration.

Contralateral C7 transfer combined with acellular nerve allografts seeded with differentiated adipose stem cells for repairing upper brachial plexus injury in rats

Nerve grafting has always been necessary when the contralateral C7 nerve root is transferred to treat brachial plexus injury. Acellular nerve allograft is a promising alternative for the treatment of nerve defects, and results were improved by grafts laden with differentiated adipose stem cells. However, use of these tissue-engineered nerve grafts has not been reported for the treatment of brachial plexus injury. The aim of the present study was to evaluate the outcome of acellular nerve allografts seeded with differentiated adipose stem cells to improve nerve regeneration in a rat model in which the contralateral C7 nerve was transferred to repair an upper brachial plexus injury. Differentiated adipose stem cells were obtained from Sprague-Dawley rats and transdifferentiated into a Schwann cell-like phenotype. Acellular nerve allografts were prepared from 15-mm bilateral sections of rat sciatic nerves. Rats were randomly divided into three groups: acellular nerve allograft, acellular nerve allograft + differentiated adipose stem cells, and autograft. The upper brachial plexus injury model was established by traction applied away from the intervertebral foramen with micro-hemostat forceps. Acellular nerve allografts with or without seeded cells were used to bridge the gap between the contralateral C7 nerve root and C5–6 nerve. Histological staining, electrophysiology, and neurological function tests were used to evaluate the effect of nerve repair 16 weeks after surgery. Results showed that the onset of discernible functional recovery occurred earlier in the autograft group first, followed by the acellular nerve allograft + differentiated adipose stem cells group, and then the acellular nerve allograft group; moreover, there was a significant difference between autograft and acellular nerve allograft groups. Compared with the acellular nerve allograft group, compound muscle action potential, motor conduction velocity, positivity for neurofilament and S100, diameter of regenerating axons, myelin sheath thickness, and density of myelinated fibers were remarkably increased in autograft and acellular nerve allograft + differentiated adipose stem cells groups. These findings confirm that acellular nerve allografts seeded with differentiated adipose stem cells effectively promoted nerve repair after brachial plexus injuries, and the effect was better than that of acellular nerve repair alone. This study was approved by the Animal Ethics Committee of the First Affiliated Hospital of Sun Yat-sen University of China (approval No. 2016-150) in June 2016.

The effect of co-transplantation of nerve fibroblasts and Schwann cells on peripheral nerve repair

Combinations of fibroblasts (Fbs) and corresponding epithelial cells have been widely used in many tissues, such as the skin and breast tissues, to augment tissue repair and remodeling. Recently, a large amount of new data has indicated that nerve Fbs play critical roles in Schwann cells (SCs) and axons in vitro. However, little is known regarding the effects of co-transplanting nerve Fbs and SCs on peripheral nerve repair in vivo. The aim of this study was to investigate the effect of co-transplanting sciatic nerve Fbs (SN-Fbs) and sciatic nerve SCs (SN-SCs) on nerve regeneration. We developed a 5 mm nerve-defect model in mice using a polyurethane (PUR) catheter and then injected one of four different mixtures of cells into the catheters to form the following four groups: pure Matrigel (Control group), SN-Fbs alone (SN-Fb group), SN-Fbs combined with SN-SCs at a ratio of 1:2 (Fb&SC group) and SN-SCs alone (SN-SC group). Histological and functional analyses were performed 3 months later. The results indicated that in vitro, the expression levels of NGF, BDNF and GDNF were significantly higher, and in vivo, a more moderate amount of extracellular matrix was produced in the Fb&SC group than in the SN-SC group. Compared to the other groups, co-transplanting SN-Fbs with SCs at a 1:2 ratio had significantly positive effects on nerve regeneration and functional recovery.

Stem cell therapy for nerve injury

Peripheral nerve injury has remained a substantial clinical complication with no satisfactory treatment options. Despite the great development in the field of microsurgery, some severe types of neural injuries cannot be treated without causing tension to the injured nerve. Thus, current studies have focused on the new approaches for the treatment of peripheral nerve injuries. Stem cells with the ability to differentiate into a variety of cell types have brought a new perspective to this matter. In this review, we will discuss the use of three main sources of mesenchymal stem cells in the treatment of peripheral nerve injuries.

Sciatic nerve regeneration by transplantation of in vitro differentiated nucleus pulposus progenitor cells

Aim: To assess the applicability of mouse intervertebral disc-derived nucleus pulposus (NP) progenitor cells as a cell source for sciatic nerve regeneration. Materials & methods: P0-Cre/Floxed-EGFP-transgenic mouse-derived NP progenitor cells were differentiated to Schwann-like cells in conventional induction medium. Schwann-like cells were subsequently transplanted into a mouse model of sciatic nerve transection, and nerve regeneration assessed by immunohistochemistry, electron microscopy and functional walking track analysis and heat stimulus reflex. Results & conclusion: NP progenitor cells differentiated into Schwann-like cells. Transplantation of these cells promoted myelinated axon formation, morphology restoration and nerve function improvement. NP progenitor cells have the capacity to differentiate into neuronal cells and are candidates for peripheral nerve regeneration therapy.

Biomaterials and cells for neural tissue engineering: Current choices

The treatment of nerve injuries has taken a new dimension with the development of tissue engineering techniques. Prior to tissue engineering, suturing and surgery were the only options for effective treatment. With the advent of tissue engineering, it is now possible to design a scaffold that matches the exact biological and mechanical properties of the tissue. This has led to substantial reduction in the complications posed by surgeries and suturing to the patients. New synthetic and natural polymers are being applied to test their efficiency in generating an ideal scaffold. Along with these, cells and growth factors are also being incorporated to increase the efficiency of a scaffold. Efforts are being made to devise a scaffold that is biodegradable, biocompatible, conducting and immunologically inert. The ultimate goal is to exactly mimic the extracellular matrix in our body, and to elicit a combination of biochemical, topographical and electrical cues via various polymers, cells and growth factors, using which nerve regeneration can efficiently occur.

Advances and Future Applications of Augmented Peripheral Nerve Regeneration

Peripheral nerve injuries remain a significant source of long lasting morbidity, disability, and economic costs. Much research continues to be performed in areas related to improving the surgical outcomes of peripheral nerve repair. In this review, the physiology of peripheral nerve regeneration and the multitude of efforts to improve surgical outcomes are discussed. Improvements in tissue engineering that have allowed for the use of synthetic conduits seeded with neurotrophic factors are highlighted. Selected pre-clinical and available clinical data using cell based methods such as Schwann cell, undifferentiated, and differentiated stem cell transplantation to guide and enhance peripheral nerve regeneration are presented. The limitations that still exist in the utility of neurotrophic factors and cell-based therapies are outlined. Strategies that are most promising for translation into the clinical arena are suggested.

Decellular Nerve Allografts

Multiple treatment options are available for patients who have peripheral nerve injuries with a gap. Decellular nerve allografts are one option and provide an extracellular scaffold for neuronal cells to migrate for axonal regrowth. Immunosuppression is not needed because improved nerve processing technologies have rendered decellular nerve allografts nonimmunogenic. These allografts have also shown promising results in both animal and human studies as an alternative repair option.

Nerve defect repair by differentiated adipose-derived stem cells and chondroitinase ABC-treated acellular nerves

OBJECTIVE

To evaluate the effects of differentiated adipose-derived stem cells (dADSC) and chondroitinase ABC (ChABC)-treated acellular nerves (ACN) in building artificial nerves and repairing nerve defects.

METHODS

ADSC were isolated from the adipose tissue of Wistar rats, induced to differentiate into Schwann-like cells, and implanted into ChABC-treated ACN to repair a 15-mm sciatic nerve defect in Sprague-Dawley rats (the experimental group, group D). The control groups were an autologous nerve transplantation group (group E); ACN (group A), ChABC-treated ACN graft group (group B), and dADSC + ACN (group C). Twelve weeks after surgery, electromyography recordings, tricep surae muscle wet weight recovery rate, and axon counts were measured to evaluate the repair of peripheral nerve defects.

RESULTS

The nerve conduction velocity, compound muscle action potentials, tricep surae muscle wet weight recovery rate, and myelinated axon counts in the ChABC-ACN/dADSC group were significantly higher than in the other groups (P < 0.05), which were all lower than the autologous group (P < 0.05).

CONCLUSIONS

The combination of ChABC-treated ACN and dADSC exhibited a synergistic effect in promoting nerve regeneration, and could be an alternative for effective tissue-engineered nerves.