Transplantation of induced pluripotent stem cell-derived neurospheres for peripheral nerve repair

Fabrication of Artificial Nerve Conduits Used in a Long Nerve Gap: Current Reviews and Future Studies

There are many commercially available artificial nerve conduits, used mostly to repair short gaps in sensory nerves. The stages of nerve regeneration in a nerve conduit are fibrin matrix formation between the nerve stumps joined to the conduit, capillary extension and Schwann cell migration from both nerve stumps, and, finally, axon extension from the proximal nerve stump. Artificial nerves connecting transected nerve stumps with a long interstump gap should be biodegradable, soft and pliable; have the ability to maintain an intrachamber fibrin matrix structure that allows capillary invasion of the tubular lumen, inhibition of scar tissue invasion and leakage of intratubular neurochemical factors from the chamber; and be able to accommodate cells that produce neurochemical factors that promote nerve regeneration. Here, we describe current progress in the development of artificial nerve conduits and the future studies needed to create nerve conduits, the nerve regeneration of which is compatible with that of an autologous nerve graft transplanted over a long nerve gap.

Peripheral nerve regeneration by bioabsorbable nerve conduits filled with platelet-rich fibrin

PURPOSE

To repair peripheral nerve defects and seek alternatives for autografts, nerve conduits with various growth factors and cells have been invented. Few pieces of literature report the effect of nerve conduits plus platelet-rich fibrin (PRF). This study aimed to investigate the effectiveness of nerve conduits filled with PRF.

METHODS

The model of a 10 mm sciatic nerve gap in a rat was used to evaluate peripheral nerve regeneration. The thirty rats were randomly divided into one of the following three groups (n = 10 per group). Autogenous nerve grafts (autograft group), conduits filled with phosphate-buffered saline (PBS) (PBS group), or conduits filled with PRF group (PRF group). We assessed motor and sensory functions for the three groups at 4, 8, and 12 weeks postoperatively. In addition, axon numbers were measured 12 weeks after repair of the peripheral nerve gaps.

RESULTS

Significant differences in motor function were observed between the autograft group and the other two groups at 12 weeks postoperatively. In the test to evaluate the recovery of sensory function, there were significant differences between the PBS group and the other two groups at all time points. The most axon number was found in the autograft group. The axon number of the PRF group was significantly more extensive than that of the PBS group.

CONCLUSIONS

The nerve conduit filled with PRF promoted the axon regeneration of the sciatic nerve and improved sensory function.

Artificial Nerve Containing Stem Cells, Vascularity and Scaffold; Review of Our Studies

To promote nerve regeneration within a conduit (tubulation), we have performed studies using a tube model based on four important concepts for tissue engineering: vascularity, growth factors, cells, and scaffolds. A nerve conduit containing a blood vascular pedicle (vessel-containing tube) accelerated axon regeneration and increased the axon regeneration distance; however, it did not increase the number or diameter of the axons that regenerated within the tube. A vessel-containing tube with bone-marrow-derived mesenchymal stem cell (BMSC) transplantation led to the increase in the number and diameter of regenerated axons. Intratubularly transplanted decellularized allogenic nerve basal lamellae (DABLs) worked as a frame to maintain the fibrin matrix structure containing neurochemical factors and to anchor the transplanted stem cells within the tube. For the clinical application of nerve conduits, they should exhibit capillary permeability, biodegradability, and flexibility. Nerbridge® (Toyobo Co. Ltd., Osaka, Japan) is a commercially available artificial nerve conduit. The outer cylinder is a polyglycolic acid (PGA) fiber mesh and possesses capillary permeability. We used the outer cylinder of Nerbridge as a nerve conduit. A 20-mm sciatic nerve deficit was bridged by the PGA mesh tube containing DABLs and BMSCs, and the resulting nerve regeneration was compared with that obtained through a 20-mm autologous nerve graft. A neve-regeneration rate of about 70%-80% was obtained in 20-mm-long autologous nerve autografts using the new conduits.

Development and In Vitro Differentiation of Schwann Cells

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

Fate and contribution of induced pluripotent stem cell-derived neurospheres transplanted with nerve conduits to promote peripheral nerve regeneration in mice

BACKGROUND

We previously demonstrated that a bioabsorbable nerve conduit coated with mouse induced pluripotent stem cell (iPSC)-derived neurospheres accelerated peripheral nerve regeneration in mice.

OBJECTIVE

We examined the fate and utility of iPSC-derived neurospheres transplanted with nerve conduits for the treatment of sciatic nerve gaps in mice.

METHODS

Complete 5-mm defects were created in sciatic nerves and reconstructed using nerve conduits that were either uncoated or coated with mouse iPSC-derived neurospheres. The survival of the neurospheres on the nerve conduits was tracked using an in vivo imaging. The localization of the transplanted cells and regenerating axons was examined histologically. The gene expression levels in the nerve conduits were evaluated.

RESULTS

The neurospheres survived for at least 14 days, peaking at 4--7 days after implantation. The grafted neurospheres remained as Schwann-like cells within the nerve conduits and migrated into the regenerated axons. The expression levels of ATF3, BDNF, and GDNF in the nerve conduit coated with neurospheres were upregulated.

CONCLUSIONS

Mouse iPSC-derived neurospheres transplanted with nerve conduits for the treatment of sciatic nerve defects in mice migrated into regenerating axons, survived as Schwann-like cells, and promoted axonal growth with an elevation in the expression of nerve regeneration-associated trophic factors.

Brain Organoids: Filling the Need for a Human Model of Neurological Disorder

Neurological disorders are among the leading causes of death worldwide, accounting for almost all onsets of dementia in the elderly, and are known to negatively affect motor ability, mental and cognitive performance, as well as overall wellbeing and happiness. Currently, most neurological disorders go untreated due to a lack of viable treatment options. The reason for this lack of options is s poor understanding of the disorders, primarily due to research models that do not translate well into the human in vivo system. Current models for researching neurological disorders, neurodevelopment, and drug interactions in the central nervous system include in vitro monolayer cell cultures, and in vivo animal models. These models have shortcomings when it comes to translating research about disorder pathology, development, and treatment to humans. Brain organoids are three-dimensional (3D) cultures of stem cell-derived neural cells that mimic the development of the in vivo human brain with high degrees of accuracy. Researchers have started developing these miniature brains to model neurodevelopment, and neuropathology. Brain organoids have been used to model a wide range of neurological disorders, including the complex and poorly understood neurodevelopmental and neurodegenerative disorders. In this review, we discuss the brain organoid technology, placing special focus on the different brain organoid models that have been developed, discussing their strengths, weaknesses, and uses in neurological disease modeling.

Experimental study on the efficacy of a hybrid artificial nerve: The hot dog method

INTRODUCTION

We hypothesized that hybrid artificial nerves might overcome the limitations of a nerve conduit by isolating nerve fascicles from autologous nerves. Nerve sacrifice during harvest, a drawback of conventional autologous nerve transplantation, may be reduced by the hot dog method. The hot dog method (based on the morphology of hybrid artificial nerves) adds nerve conduits to autologous nerve fascicles.

METHODS

Forty-eight rats with a 10-mm sciatic nerve defect were divided into six groups (n = 8 per group) according to the neural reconstruction method: autologous nerve transplantation, the hot dog method, nerve conduit, nerve fascicle transplantation, sham control, and nerve fascicle isolation were classified as Groups I, II, III, IV, V, and VI, respectively. The sciatic nerve function was assessed in these groups, a histological evaluation was performed, and statistical analyses were conducted based on these data.

RESULTS

Group III (nerve conduit) and Group IV (nerve fascicle transplantation) showed the lowest functional and axonal regenerative effects, followed by Group II (hot dog method) and Group I (autologous nerve transplantation). Group VI (nerve fascicle isolation) tended to achieve better recovery in motor function and axonal regeneration than Group I (autologous nerve transplantation).

CONCLUSIONS

The hot dog method is simple, safe, and easy to execute. This method can serve as a new neural reconstruction method that uses artificial nerves.

Long-term survival of transplanted induced pluripotent stem cell-derived neurospheres with nerve conduit into sciatic nerve defects in immunosuppressed mice

Since the advent of induced pluripotent stem cells (iPSCs), clinical trials using iPSC-based cell transplantation therapy have been performed in various fields of regenerative medicine. We previously demonstrated that the transplantation of mouse iPSC-derived neurospheres containing neural stem/progenitor cells with bioabsorbable nerve conduits promoted nerve regeneration in the long term in murine sciatic nerve defect models. However, it remains unclear how long the grafted iPSC-derived neurospheres survived and worked after implantation. In this study, the long-term survival of the transplanted mouse iPSC-derived neurospheres with nerve conduits was evaluated in high-immunosuppressed or non-immunosuppressed mice using in vivo imaging for the development of iPSC-based cell therapy for peripheral nerve injury. Complete 5-mm long defects were created in the sciatic nerves of immunosuppressed and non-immunosuppressed mice and reconstructed using nerve conduits coated with iPSC-derived neurospheres labeled with ffLuc. The survival of mouse iPSC-derived neurospheres on nerve conduits was monitored using in vivo imaging. The transplanted iPSC-derived neurospheres with nerve conduits survived for 365 days after transplantation in the immunosuppressed allograft models, but only survived for at least 14 days in non-immunosuppressed allograft models. This is the first study to find the longest survival rate of stem cells with nerve conduits transplanted into the peripheral nerve defects using in vivo imaging and demonstrates the differences in graft survival rate between the immunosuppressed allograft model and immune responsive allograft model. In the future, if iPSC-derived neurospheres are successfully transplanted into peripheral nerve defects with nerve conduits using iPSC stock cells without eliciting an immune response, axonal regeneration will be induced due to the longstanding supportive effect of grafted cells on direct remyelination and/or secretion of trophic factors.

Bioabsorbable nerve conduits three-dimensionally coated with human induced pluripotent stem cell-derived neural stem/progenitor cells promote peripheral nerve regeneration in rats

Peripheral nerve regeneration using nerve conduits has been less effective than autogenous nerve grafts. To overcome this hurdle, we developed a tissue-engineered nerve conduit coated with mouse induced pluripotent stem cell (iPSC)-derived neurospheres, for the first time, which accelerated nerve regeneration in mice. We previously demonstrated the long-term efficacy and safety outcomes of this hybrid nerve conduit for mouse peripheral nerve regeneration. In this study, we investigated the therapeutic potential of nerve conduits coated with human iPSC (hiPSC)-derived neurospheres in rat sciatic nerve defects, as a translational preclinical study. The hiPSC-derived quaternary neurospheres containing neural stem/progenitor cells were three-dimensionally cultured within the nerve conduit (poly l-lactide and polycaprolactone copolymer) for 14 days. Complete 5-mm defects were created as a small size peripheral nerve defect in sciatic nerves of athymic nude rats and reconstructed with nerve conduit alone (control group), nerve conduits coated with hiPSC-derived neurospheres (iPS group), and autogenous nerve grafts (autograft group) (n = 8 per group). The survival of the iPSC-derived neurospheres was continuously tracked using in vivo imaging. At 12 weeks postoperatively, motor and sensory function and histological nerve regeneration were evaluated. Before implantation, the hiPSC-derived quaternary neurospheres that three-dimensional coated the nerve conduit were differentiated into Schwann-like cells. The transplanted hiPSC-derived neurospheres survived for at least 56 days after implantation. The iPS group showed non-significance higher sensory regeneration than the autograft group. Although there was no actual motor functional nerve regeneration in the three groups: control, iPS, and autograft groups, the motor function in the iPS group recovered significantly better than that in the control group, but it did not recover to the same level as that in the autograft group. Histologically, the iPS group demonstrated significantly higher axon numbers and areas, and lower G-ratio values than the control group, whereas the autograft group demonstrated the highest axon numbers and areas and the lowest G-ratio values. Nerve conduit three-dimensionally coated with hiPSC-derived neurospheres promoted axonal regeneration and functional recovery in repairing rat sciatic nerve small size defects. Transplantation of hiPSC-derived neurospheres with nerve conduits is a promising clinical iPSC-based cell therapy for the treatment of peripheral nerve defects.

Advances and clinical challenges for translating nerve conduit technology from bench to bed side for peripheral nerve repair

Injuries to the peripheral nervous system remain a large-scale clinical problem. These injuries often lead to loss of motor and/or sensory function that significantly affects patients' quality of life. The current neurosurgical approach for peripheral nerve repair involves autologous nerve transplantation, which often leads to clinical complications. The most pressing need is to increase the regenerative capacity of existing tubular constructs in the repair of large nerve gaps through development of tissue-engineered approaches that can surpass the performance of autografts. To fully realize the clinical potential of nerve conduit technology, there is a need to reconsider design strategies, biomaterial selection, fabrication techniques and the various potential modifications to optimize a conduit microenvironment that can best mimic the natural process of regeneration. In recent years, a significant progress has been made in the designing and functionality of bioengineered nerve conduits to bridge long peripheral nerve gaps in various animal models. However, translation of this work from lab to commercial scale has not been achieve. The current review summarizes recent advances in the development of tissue engineered nerve guidance conduits (NGCs) with regard to choice of material, novel fabrication methods, surface modifications and regenerative cues such as stem cells and growth factors to improve regeneration performance. Also, the current clinical potential and future perspectives to achieve therapeutic benefits of NGCs will be discussed in context of peripheral nerve regeneration.

Perspectives on 3D Bioprinting of Peripheral Nerve Conduits

The peripheral nervous system controls the functions of sensation, movement and motor coordination of the body. Peripheral nerves can get damaged easily by trauma or neurodegenerative diseases. The injury can cause a devastating effect on the affected individual and his aides. Treatment modalities include anti-inflammatory medications, physiotherapy, surgery, nerve grafting and rehabilitation. 3D bioprinted peripheral nerve conduits serve as nerve grafts to fill the gaps of severed nerve bodies. The application of induced pluripotent stem cells, its derivatives and bioprinting are important techniques that come in handy while making living peripheral nerve conduits. The design of nerve conduits and bioprinting require comprehensive information on neural architecture, type of injury, neural supporting cells, scaffold materials to use, neural growth factors to add and to streamline the mechanical properties of the conduit. This paper gives a perspective on the factors to consider while bioprinting the peripheral nerve conduits.

Biomedical applications of muscle-derived stem cells: from bench to bedside

INTRODUCTION

Skeletal muscle-derived stem cells (Sk-MDSCs) are considered promising sources of adult stem cell therapy. Skeletal muscle comprises approximately 40-50% of the total body mass with marked potential for postnatal adaptive response, such as muscle hypertrophy, hyperplasia, atrophy, and regenerative capacity. This strongly suggests that skeletal muscle contains various stem/progenitor cells related to muscle-nerve-vascular tissues, which would support the above postnatal events even in adulthood.

AREA COVERED

The focus of this review is the therapeutic potential of the Sk-MDSCs as an adult stem cell autograft. For this purpose, the validity of cell isolation and purification, tissue reconstitution capacity in vivo after transplantation, comparison of the results of basic mouse and preclinical human studies, potential problematic and beneficial aspects, and effective usage have been discussed following the history of clinical applications.

EXPERT OPINION

Although the clinical application of Sk-MDSCs began as a therapy for the systemic disease of Duchenne muscular dystrophy, here, through the unique local injection method, therapy for severely damaged peripheral nerves, particularly the long-gap nerve transection, has been introduced. The beneficial aspects of the use of Sk-MDSCs as the source of local tissue transplantation therapy have also been discussed.

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.

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.

The Use and Delivery of Stem Cells in Nerve Regeneration: Preclinical Evidence and Regulatory Considerations

Outcomes following peripheral nerve injury remain poor despite the regenerative capacity displayed by the peripheral nervous system. Current therapies are limited and do not provide satisfactory functional recovery in a multitude of cases. Biomaterials have decreased the need for nerve autograft across small nerve gaps in small-caliber nerves, but the lack of a cellular substrate presents a limiting factor to the effectiveness of this therapy. Schwann cells are the supportive cells in the peripheral nervous system and play an integral role in the physiological response and regeneration following nerve injury. Limitations to autologous Schwann cells include donor site morbidity during harvesting, limited expansion capability, and finite source. Stem cells are multipotent or pluripotent cells with self-renewing capabilities that show promise to improve functional recovery following nerve injury. Differentiation of stem cells into supportive Schwann cells could provide additional trophic support without the disadvantages of autologous Schwann cells, providing an avenue to improve existing therapies. A variety of stem cells have been evaluated in animal models for this clinical application; the current options, along with their clinical feasibility, are summarized in this article.

Nerve capping with a nerve conduit for the treatment of painful neuroma in the rat sciatic nerve

OBJECTIVE

Treatment of painful neuroma remains difficult, despite the availability of numerous surgical procedures. Recently, nerve capping treatment for painful neuroma using artificial nerve conduits has been introduced in clinical and basic research. However, the appropriate length of the nerve conduit and the pain relief mechanism have not been determined. In this study the authors aimed to investigate nerve capping treatment with a bioabsorbable nerve conduit using the rat sciatic nerve amputation model. Using histological analysis, the authors focused on the nerve conduit length and pain relief mechanism.

METHODS

Sixteen Sprague Dawley rats were evaluated for neuropathic pain using an autotomy (self-amputation) score and gross and histological changes of the nerve stump 2, 4, 8, and 12 weeks after sciatic nerve neurectomy without capping. Forty-five rats were divided into 3 experimental groups, no capping (control; n = 15), capping with a 3-mm nerve conduit (n = 15), and capping with a 6-mm nerve conduit (n = 15). All rats were evaluated using an autotomy score and nerve stump histology 12 weeks after neurectomy. The nerve conduit was approximately 0.5 mm larger than the 1.5-mm diameter of the rat sciatic nerves to prevent nerve constriction.

RESULTS

The autotomy scores gradually exacerbated with time. Without capping, a typical bulbous neuroma was formed due to random axonal regeneration 2 weeks after neurectomy. Subsequently, the adhesion surrounding the neuroma expanded over time for 12 weeks, and at the 12-week time point, the highest average autotomy scores were observed in the no-capping (control) group, followed by the 3- and the 6-mm nerve conduit groups. Histologically, the distal axonal fibers became thinner and terminated within the 6-mm nerve conduit, whereas they were elongated and protruded across the 3-mm nerve conduit. Minimal perineural scar formation was present around the terminated axonal fibers in the 6-mm nerve conduit group. Expressions of anti-α smooth muscle actin and anti-sigma-1 receptor antibodies in the nerve stump significantly decreased in the 6-mm nerve conduit group.

CONCLUSIONS

In the rat sciatic nerve amputation model, nerve capping treatment with a bioabsorbable nerve conduit provided relief from neuroma-induced neuropathic pain and prevented perineural scar formation and neuroinflammation around the nerve stump. The appropriate nerve conduit length was determined to be more than 4 times the diameter of the original nerve.

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

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

In vitro enhancement and functional characterization of neurite outgrowth by undifferentiated adipose-derived stem cells

Adipose‑derived stem cells (ASCs) can easily be obtained and expanded in vitro for use in autologous cell therapy. Via their production of cytokines and neurotrophic factors, transplanted ASCs provide neuroprotection, neovascularization and induction of axonal sprouting. However, the influencing mechanism of undifferentiated ASCs on nerve regeneration is currently only partially understood. In the present study, undifferentiated ASCs and cutaneous primary afferent dorsal root ganglion (DRG) neurons were co‑cultured in order to investigate their interaction. ASCs were isolated from adult rat fat tissue. The presence of characteristic stem cell markers was determined by flow cytometry in three subsequent passages. Adipogenic, osteogenic, chondrogenic and glial differentiation was performed in order to evaluate their differentiation capacity. A direct co‑culture system with DRG cells was established to determine the effect of undifferentiated pluripotent ASCs on neurite elongation. Neurite outgrowth, length and number was examined in the co‑culture and compared with single‑culture cells and cells stimulated with nerve growth factor (NGF). In ASC cultures, NGF expression was assessed by ELISA. The present results demonstrated that the specific mesenchymal stem cell surface markers CD44, CD73 and CD90 were detected in all three subsequent passages of the isolated ASCs. In accordance, ASC differentiation into adipogenic, osteogenic, chondrogenic and Schwann cell phenotype was conducted successfully. Neurite outgrowth of DRG neurons was enhanced following co‑culture with ASCs, resulting in increased neurite length after 24 h of cultivation. Furthermore, neurite outgrowth of DRG neurons was directed towards the undifferentiated ASC and direct cell‑to‑cell contact was observed. In summary, the results of the present study revealed an interaction between the two cell types with guidance of neurite growth towards the undifferentiated ASC. These findings suggest that the use of undifferentiated ASC optimizing tissue‑engineered constructs may be promising for peripheral nerve repair.

Adipose-derived stem cells and the stromal vascular fraction in polyglycolic acid-collagen nerve conduits promote rat facial nerve regeneration

Adipose-derived stem cells (ADSCs) and the stromal vascular fraction (SVF) promote nerve regeneration. Biodegradable nerve conduits are used to treat peripheral nerve injuries, but their efficiencies are lower than those of autologous nerve grafts. This study developed biodegradable nerve conduits containing ADSCs and SVF and evaluated their facial nerve regenerating abilities in a rat model with a 7-mm nerve defect. SVF and ADSCs were individually poured into nerve conduits with polyglycolic acid-type I collagen as a scaffold (ADSCs and SVF groups). The conduits were grafted on to the nerve defects. As the control, the defect was bridged with polyglycolic acid-collagen nerve conduits without cells. At 13 weeks, after transplantation, the regenerated nerves were evaluated physiologically and histologically. The compound muscle action potential of the SVF group was significantly higher in amplitude than that of the control group. Electron microscopy showed that the axon diameter of the SVF group was the largest, followed by the ADSC group and control group with significant differences among them. The SVF group had the largest fiber diameter, followed by the ADSC group and control group with significant differences among them. The ADSC group had the highest myelin thickness, followed by the SVF group and control group with significant differences among them. Identical excellent promoting effects on nerve regeneration were observed in both the ADSC and SVF groups. Using SVF in conduits was more practical than using ADSCs because only the enzymatic process was required to prepare SVF, indicating that SVF could be more suitable to induce nerve regeneration.

Matrices, scaffolds & carriers for cell delivery in nerve regeneration

Nerve injuries can be life-long debilitating traumas that severely impact patients' quality of life. While many acellular neural scaffolds have been developed to aid the process of nerve regeneration, complete functional recovery is still very difficult to achieve, especially for long-gap peripheral nerve injury and most cases of spinal cord injury. Cell-based therapies have shown many promising results for improving nerve regeneration. With recent advances in neural tissue engineering, the integration of biomaterial scaffolds and cell transplantation are emerging as a more promising approach to enhance nerve regeneration. This review provides an overview of important considerations for designing cell-carrier biomaterial scaffolds. It also discusses current biomaterials used for scaffolds that provide permissive and instructive microenvironments for improved cell transplantation.

Transcutaneous carbon dioxide application with hydrogel prevents muscle atrophy in a rat sciatic nerve crush model

The acceleration of nerve regeneration remains a clinical challenge. We previously demonstrated that transcutaneous CO₂ application using a novel hydrogel increases the oxygen concentration in local tissue via an "artificial Bohr effect" with the potential to prevent muscle atrophy. In this study, we investigated the effect of transcutaneous CO₂ administration on limb function after peripheral nerve injury in a rat sciatic nerve injury model. In total, 73 Sprague-Dawley rats were divided into a sham group, a control group (crush injury to sciatic nerve and no treatment) or a CO₂ group (crush injury with transcutaneous CO₂ application). CO₂ was administered percutaneously for 20 min five times per week. Scores for the sciatic function index and pinprick test were significantly higher in the CO₂ group than control group. The muscle wet weight ratios of the tibialis anterior and soleus muscles were higher in the CO₂ group than control group. Electrophysiological examination showed that the CO₂ group had higher compound motor action potential amplitudes and shorter distal motor latency than the control group. Histological examination of the soleus muscle sections at postoperative week 2 showed shorter fiber diameter in the control group than in the CO₂ group. The mRNA expression of Atrogin-1 and MuRF-1 was lower, mRNA expression of VEGF and myogenin and MyoD was higher in CO₂ group at postoperative week 2 compared to the control group.

CLINICAL SIGNIFICANCE

Transcutaneous CO₂ application has the therapeutic potential to accelerate the recovery of muscle atrophy in peripheral nerve injury. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1653-1658, 2018.

Prospective applications of induced pluripotent stem cells in military medicine

Soldiers involved in combat operations worldwide may be subjected to a wide array of tissue-specific injuries of varying degrees, thereby undergoing complicated medical treatments and prolonged rehabilitations. In many cases involving inadequate recovery, soldiers are further mentally traumatized as they can no longer serve their beloved country. In addition, many severe injuries can lead to soldiers being incapacitated for life and unable to perform even the most basic day-to-day activities. Present therapy for combat injuries is majorly aimed at alleviating pain and limiting further tissue damage from secondary infections. Cell-based therapy using stem cells is a promising tissue regenerative source, which will help our soldiers to recuperate from the severe injuries, and in some cases, even continue their service for the country after complete recovery. In this context, we would like to discuss the yet fully untapped potential of induced pluripotent stem cells (iPSCs) in regenerative medicine on the battlefield. In this review, we shall try to explore the rationale behind the use of these cells for military medicine, as well as the conventional and novel approaches to produce them for therapeutic applications. We shall also attempt to elucidate the evolving trends of battlefield injuries throughout history and the ongoing research on regeneration of tissues of specific interest using iPSCs and their potential role in combat medicine in the future. Additionally, we shall also discuss the concept of stem cell bio-banking for military personnel as a personalized safeguard against crippling and traumatic combat injuries.

Protective effect of biodegradable nerve conduit against peripheral nerve adhesion after neurolysis

OBJECTIVE Peripheral nerve adhesion caused by extraneural and intraneural scar formation after neurolysis leads to nerve dysfunction. The authors previously developed a novel very flexible biodegradable nerve conduit composed of poly(L-lactide) and poly(ε-caprolactone) for use in peripheral nerve regeneration. In the present study, they investigated the effect of protective nerve wrapping on preventing adhesion in a rat sciatic nerve adhesion model. METHODS Rat sciatic nerves were randomly assigned to one of the following four groups: a no-adhesion group, which involved neurolysis alone without an adhesion procedure; an adhesion group, in which the adhesion procedure was performed after neurolysis, but no treatment was subsequently administered; a nerve wrap group, in which the adhesion procedure was performed after neurolysis and protective nerve wrapping was then performed with the nerve conduit; and a hyaluronic acid (HA) group, in which the adhesion procedure was performed after neurolysis and nerve wrapping was then performed with a 1% sodium HA viscous solution. Six weeks postoperatively, the authors evaluated the extent of scar formation using adhesion scores and biomechanical and histological examinations and assessed nerve function with electrophysiological examination and gastrocnemius muscle weight measurement. RESULTS In the adhesion group, prominent scar tissue surrounded the nerve and strongly adhered to the nerve biomechanically and histologically. The motor nerve conduction velocity and gastrocnemius muscle weight were the lowest in this group. Conversely, the adhesion scores were significantly lower, motor nerve conduction velocity was significantly higher, and gastrocnemius muscle weight was significantly higher in the nerve wrap group than in the adhesion group. Additionally, the biomechanical breaking strength was significantly lower in the nerve wrap group than in the adhesion group and HA group. The morphological properties of axons in the nerve wrap group were preserved. Intraneural macrophage invasion, as assessed by the number of CD68- and CCR7-positive cells, was less severe in the nerve wrap group than in the adhesion group. CONCLUSIONS The nerve conduit prevented post-neurolysis peripheral nerves from developing adhesion and allowed them to maintain their nerve function because it effectively blocked scarring and prevented adhesion-related damage in the peripheral nerves.

Bioabsorbable nerve conduits coated with induced pluripotent stem cell-derived neurospheres enhance axonal regeneration in sciatic nerve defects in aged mice

Aging influences peripheral nerve regeneration. Nevertheless, most basic research of bioabsorbable nerve conduits including commercial products have been performed in very young animals. Results from these studies may not provide information about axonal regeneration in aged tissue, because young nerve tissue holds sufficient endogenous potential for axonal regeneration. The clinical target age for nerve conduit application is most likely going to increase with a rapidly growing elderly population. In the present study, we examined axonal regeneration after sciatic nerve defects in aged and young mice. 5-mm sciatic nerve defects in young (6 weeks old) and aged (92 weeks old) mice were reconstructed using nerve conduits (composed of a poly lactide and caprolactone) or autografts. In addition, in aged mice, sciatic nerve defects were reconstructed using nerve conduits coated with mouse induced pluripotent stem cell (iPSc)-derived neurospheres. Using electrophysiological and histological techniques, we demonstrated axonal regeneration was significantly less effective in aged than in young mice both for nerve conduits and for nerve autografts. However, despite the low regenerative capacity of the peripheral nerve in aged mice, axonal regeneration significantly increased when nerve conduits coated with iPSc-derived neurospheres, rather than nerve conduits alone, were used. The present study shows that aging negatively affects peripheral nerve regeneration based on nerve conduits in mice. However, axonal regeneration using nerve conduits was improved when supportive iPSc-derived neurospheres were added in the aged mice. We propose that tissue-engineered bioabsorbable nerve conduits in combination with iPSc-derived neurospheres hold therapeutic potential both in young and elderly patients. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1752-1758, 2018.

Human embryonic stem cell dispersion in electrospun PCL fiber scaffolds by coating with laminin-521 and E-cadherin-Fc

Advances in human pluripotent cell cultivation and differentiation protocols have led to production of stem cell-derived progenitors as a promising cell source for replacement therapy. Three-dimensional (3-D) culture is a better mimic of the natural niche for stem cells and is widely used for disease modeling. Here, we describe a nonaggregate culture system of human embryonic stem cells inside electrospun polycaprolactone (PCL) fiber scaffolds combined with defined extracellular proteins naturally occurring in the stem cell niche. PCL fiber scaffolds coated with recombinant human laminin-521 readily supported initial stem cell attachment and growth from a single-cell suspension. The combination of recombinant E-cadherin-Fc and laminin-521 further improved cell dispersion rendering a uniform cell population. Finally, we showed that the cells cultured in E-cadherin-Fc- and laminin-521-coated PCL scaffolds could differentiate into all three germ layers. Importantly, we provided a chemically defined 3-D system in which pluripotent stem cells grown and differentiated avoiding the formation of cell aggregates. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1226-1236, 2018.

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.

Advances in Nerve Guidance Conduit-Based Therapeutics for Peripheral Nerve Repair

Peripheral nerve injuries have high incidence rates, limited treatment options and poor clinical outcomes, rendering a significant socioeconomic burden. For effective peripheral nerve repair, the gap or site of injury must be structurally bridged to promote correct reinnervation and functional regeneration. However, effective repair becomes progressively more difficult with larger gaps. Autologous nerve grafting remains the best clinical option for the repair of large gaps (20-80 mm) despite being associated with numerous limitations including permanent donor site morbidity, a lack of available tissue and the formation of neuromas. To meet the clinical demand of large gap repair and overcome these limitations, tissue engineering has led to the development of nerve guidance conduit-based therapeutics. This review focuses on the advances of nerve guidance conduit-based therapeutics in terms of their structural properties including biomimetic composition, permeability, architecture, and surface modifications. Associated biochemical properties, pertaining to the incorporation of cells and neurotrophic factors, are also reviewed. After reviewing the progress in the field, we conclude by presenting an outlook on their clinical translatability and the next generation of therapeutics.

A Long-Gap Peripheral Nerve Injury Therapy Using Human Skeletal Muscle-Derived Stem Cells (Sk-SCs): An Achievement of Significant Morphological, Numerical and Functional Recovery

Losses in vital functions of the somatic motor and sensory nervous system are induced by severe long-gap peripheral nerve transection injury. In such cases, autologous nerve grafts are the gold standard treatment, despite the unavoidable sacrifice of other healthy functions, whereas the prognosis is not always favorable. Here, we use human skeletal muscle-derived stem cells (Sk-SCs) to reconstitute the function after long nerve-gap injury. Muscles samples were obtained from the amputated legs from 9 patients following unforeseen accidents. The Sk-SCs were isolated using conditioned collagenase solution, and sorted as CD34⁺/45^- (Sk-34) and CD34^-/45^-/29⁺ (Sk-DN/29⁺) cells. Cells were separately cultured/expanded under optimal conditions for 2 weeks, then injected into the athymic nude mice sciatic nerve long-gap model (7-mm) bridging an acellular conduit. After 8–12 weeks, active cell engraftment was observed only in the Sk-34 cell transplanted group, showing preferential differentiation into Schwann cells and perineurial/endoneurial cells, as well as formation of the myelin sheath and perineurium/endoneurium surrounding regenerated axons, resulted in 87% of numerical recovery. Differentiation into vascular cell lineage (pericyte and endothelial cells) were also observed. A significant tetanic tension recovery (over 90%) of downstream muscles following electrical stimulation of the sciatic nerve (at upper portion of the gap) was also achieved. In contrast, Sk-DN/29⁺ cells were completely eliminated during the first 4 weeks, but relatively higher numerical (83% vs. 41% in axon) and functional (80% vs. 60% in tetanus) recovery than control were observed. Noteworthy, significant increase in the formation of vascular networks in the conduit during the early stage (first 2 weeks) of recovery was observed in both groups with the expression of key factors (mRNA and protein levels), suggesting the paracrine effects to angiogenesis. These results suggested that the human Sk-SCs may be a practical source for autologous stem cell therapy following severe peripheral nerve injury.

Episomal Induced Pluripotent Stem Cells Promote Functional Recovery of Transected Murine Peripheral Nerve

Traumatic peripheral nerve neurotmesis occurs frequently and functional recovery is often slow and impaired. Induced pluripotent stem cells (iPSCs) have shown much promise in recent years due to its regenerative properties similar to that of embryonic stem cells. However, the potential of iPSCs in promoting the functional recovery of a transected peripheral nerve is largely unknown. This study is the first to investigate in vivo effects of episomal iPSCs (EiPSCs) on peripheral nerve regeneration in a murine sciatic nerve transection model. Episomal iPSCs refer to iPSCs that are generated via Oct3/4-Klf4-Sox2 plasmid reprogramming instead of the conventional viral insertion techniques. It represents a relatively safer form of iPSC production without permanent transgene integration which may raise questions regarding risks of genomic mutation. A minimal number of EiPSCs were added directly to the transected nerve. Functional recovery of the EiPSC group was significantly improved compared to the negative control group when assessed via serial five-toe spread measurement and gait analysis of ankle angles. EiPSC promotion of nerve regeneration was also evident on stereographic analysis of axon density, myelin thickness, and axonal cross-sectional surface area. Most importantly, the results observed in EiPSCs are similar to that of the embryonic stem cell group. A roughly ten-fold increase in neurotrophin-3 levels was seen in EiPSCs which could have contributed to peripheral nerve regeneration and recovery. No abnormal masses or adverse effects were noted with EiPSC administration after one year of follow-up. We have hence shown that functional recovery of the transected peripheral nerve can be improved with the use of EiPSC therapy, which holds promise for the future of nerve regeneration.

Use of electrospinning to construct biomaterials for peripheral nerve regeneration

A number of limitations associated with the use of hollow nerve guidance conduits (NGCs) require further discussion. Most importantly, the functional recovery outcomes after the placement of hollow NGCs are poor even after the successful bridging of peripheral nerve injuries. However, nerve regeneration scaffolds built using electric spinning have several advantages that may improve functional recovery. Thus, the present study summarizes recent developments in this area, including the key cells that are combined with the scaffold and associated with nerve regeneration, the structure and configuration of the electrospinning design (which determines the performance of the electrospinning scaffold), the materials the electrospinning fibers are composed of, and the methods used to control the morphology of a single fiber. Additionally, this study also discusses the processes underlying peripheral nerve regeneration. The primary goals of the present review were to evaluate and consolidate the findings of studies that used scaffolding biomaterials built by electrospinning used for peripheral nerve regeneration support. It is amazing that the field of peripheral nerve regeneration continues to consistently produce such a wide variety of innovative techniques and novel types of equipment, because the introduction of every new process creates an opportunity for advances in materials for nerve repair.

Stem cell regenerative potential for plastic and reconstructive surgery

Stem cells represent heterogeneous population of undifferentiated cells with unique characteristics of long term self renewal and plasticity. Moreover, they are capable of active migration to diseased tissues, secretion of different bioactive molecules, and they have immunosuppressive potential as well. They occur in all tissues through life and are involved in process of embryogenesis and regeneration. During last decades stem cells attracted significant attention in each field of medicine, including plastic and reconstructive surgery. The main goal of the present review article is to present and discuss the potential of stem cells and to provide information about their safe utilization in chronic wounds and fistulae healing, scar management, breast reconstruction, as well as in bone, tendon and peripheral nerve regeneration.

Pluripotent stem cells for Schwann cell engineering

Tissue engineering of Schwann cells (SCs) can serve a number of purposes, such as in vitro SC-related disease modeling, treatment of peripheral nerve diseases or peripheral nerve injury, and, potentially, treatment of CNS diseases. SCs can be generated from autologous stem cells in vitro by recapitulating the various stages of in vivo neural crest formation and SC differentiation. In this review, we survey the cellular and molecular mechanisms underlying these in vivo processes. We then focus on the current in vitro strategies for generating SCs from two sources of pluripotent stem cells, namely embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Different methods for SC engineering from ESCs and iPSCs are reviewed and suggestions are proposed for optimizing the existing protocols. Potential safety issues regarding the clinical application of iPSC-derived SCs are discussed as well. Lastly, we will address future aspects of SC engineering.

Construction of Tissue-Engineered Nerve Conduits Seeded with Neurons Derived from Hair-Follicle Neural Crest Stem Cells

Tissue-engineered nerve conduits are widely used for the study of peripheral nerve injury repair. With regard to repairing long nerve defects, stem-cell-derived neurons are recommended as seed cells. As hair-follicle neural crest stem cells (hfNCSCs) are easily to be harvested from patients and have the potential to differentiate into neuronal cells, hfNCSCs-derived neurons are an ideal candidate choice. Acellular nerve grafts, a type of biological material scaffold, with intact collagen structure, with biocompatibility and less toxicity are obtained through removing live cells with 1 % lysolecithin, are also an ideal choice. In the present report, we describe a tissue-engineered nerve conduit seeded with rat hfNCSCs-derived neurons into the beagle acellular sciatic nerve scaffold. Our goal is to provide a novel engineered therapeutic for repairing peripheral nerve injury with long distance defects.

Modification of surface/neuron interfaces for neural cell-type specific responses: a review

Surface/neuron interfaces have played an important role in neural repair including neural prostheses and tissue engineered scaffolds. This comprehensive literature review covers recent studies on the modification of surface/neuron interfaces. These interfaces are identified in cases both where the surfaces of substrates or scaffolds were in direct contact with cells and where the surfaces were modified to facilitate cell adhesion and controlling cell-type specific responses. Different sources of cells for neural repair are described, such as pheochromocytoma neuronal-like cell, neural stem cell (NSC), embryonic stem cell (ESC), mesenchymal stem cell (MSC) and induced pluripotent stem cell (iPS). Commonly modified methods are discussed including patterned surfaces at micro- or nano-scale, surface modification with conducting coatings, and functionalized surfaces with immobilized bioactive molecules. These approaches to control cell-type specific responses have enormous potential implications in neural repair.

Does glioblastoma cyst fluid promote sciatic nerve regeneration?

Glioblastoma cyst fluid contains growth factors and extracellular matrix proteins which are known as neurotrophic and neurite-promoting agents. Therefore, we hypothesized that glioblastoma cyst fluid can promote the regeneration of injured peripheral nerves. To validate this hypothesis, we transected rat sciatic nerve, performed epineural anastomosis, and wrapped the injured sciatic nerve with glioblastoma cyst fluid- or saline-soaked gelatin sponges. Neurological function and histomorphological examinations showed that compared with the rats receiving local saline treatment, those receiving local glioblastoma cyst fluid treatment had better sciatic nerve function, fewer scars, greater axon area, counts and diameter as well as fiber diameter. These findings suggest that glioblastoma cyst fluid can promote the regeneration of injured sciatic nerve and has the potential for future clinical application in patients with peripheral nerve injury.

Dual Inhibition of Activin/Nodal/TGF-β and BMP Signaling Pathways by SB431542 and Dorsomorphin Induces Neuronal Differentiation of Human Adipose Derived Stem Cells

Damage to the nervous system can cause devastating diseases or musculoskeletal dysfunctions and transplantation of progenitor stem cells can be an excellent treatment option in this regard. Preclinical studies demonstrate that untreated stem cells, unlike stem cells activated to differentiate into neuronal lineage, do not survive in the neuronal tissues. Conventional methods of inducing neuronal differentiation of stem cells are complex and expensive. We therefore sought to determine if a simple, one-step, and cost effective method, previously reported to induce neuronal differentiation of embryonic stem cells and induced-pluripotent stem cells, can be applied to adult stem cells. Indeed, dual inhibition of activin/nodal/TGF-β and BMP pathways using SB431542 and dorsomorphin, respectively, induced neuronal differentiation of human adipose derived stem cells (hADSCs) as evidenced by formation of neurite extensions, protein expression of neuron-specific gamma enolase, and mRNA expression of neuron-specific transcription factors Sox1 and Pax6 and matured neuronal marker NF200. This process correlated with enhanced phosphorylation of p38, Erk1/2, PI3K, and Akt1/3. Additionally, in vitro subcutaneous implants of SB431542 and dorsomorphin treated hADSCs displayed significantly higher expression of active-axonal-growth-specific marker GAP43. Our data offers novel insights into cell-based therapies for the nervous system repair.

Zonisamide Enhances Neurite Elongation of Primary Motor Neurons and Facilitates Peripheral Nerve Regeneration In Vitro and in a Mouse Model

No clinically applicable drug is currently available to enhance neurite elongation after nerve injury. To identify a clinically applicable drug, we screened pre-approved drugs for neurite elongation in the motor neuron-like NSC34 cells. We found that zonisamide, an anti-epileptic and anti-Parkinson’s disease drug, promoted neurite elongation in cultured primary motor neurons and NSC34 cells in a concentration-dependent manner. The neurite-scratch assay revealed that zonisamide enhanced neurite regeneration. Zonisamide was also protective against oxidative stress-induced cell death of primary motor neurons. Zonisamide induced mRNA expression of nerve growth factors (BDNF, NGF, and neurotrophin-4/5), and their receptors (tropomyosin receptor kinase A and B). In a mouse model of sciatic nerve autograft, intragastric administration of zonisamide for 1 week increased the size of axons distal to the transected site 3.9-fold. Zonisamide also improved the sciatic function index, a marker for motor function of hindlimbs after sciatic nerve autograft, from 6 weeks after surgery. At 8 weeks after surgery, zonisamide was protective against denervation-induced muscle degeneration in tibialis anterior, and increased gene expression of Chrne, Colq, and Rapsn, which are specifically expressed at the neuromuscular junction. We propose that zonisamide is a potential therapeutic agent for peripheral nerve injuries as well as for neuropathies due to other etiologies.

Chitosan tubes can restore the function of resected phrenic nerves

OBJECTIVES

We previously reported that the phrenic nerve could be morphologically repaired by implantation of a chitosan nanofibre tube (C-tube). In the current study, we investigated whether implantation of C-tubes could improve the function of an injured phrenic nerve using a beagle dog model.

METHODS

Seven beagle dogs underwent right thoracotomy under general anaesthesia. An approximately 5 mm length of the right phrenic nerve was resected. Five dogs had a C-tube implantation (C-tube group) and other two dogs did not have the C-tube implantation (control group). Diaphragm movements were longitudinally measured by X-ray fluoroscopy before surgery, immediately after the surgery, and 3, 6 and 12 months after the surgery. The diaphragm movement was determined by diaphragm levels at inspiration and expiration phases, and the excursion difference between them was calculated. At 12 months after the surgery, rethoracotomy was performed to examine electrical phrenic nerve conduction. The C-tube and phrenic nerve were then excised for histological assessment of nerve regeneration.

RESULTS

Three of the five animals of the C-tube group showed improvement of diaphragm movement with time. In these three animals, slow phrenic nerve conduction was observed. Histological assessment showed that the injured nerve was connected by newly regenerating nerve fibres surrounded by granulation tissue within the C-tube. On the other hand, the animals in the control group and two animals of the C-tube group showed neither improved diaphragm movement, nor electrical conduction to the diaphragm. No nerve fibre regeneration was found by histology.

CONCLUSIONS

Our results suggest that, in addition to morphological improvement, C-tube implantation can functionally improve the injured phrenic nerve by promoting phrenic nerve regeneration.

Recent advances in stem cell-mediated peripheral nerve repair

A major advance in the field of peripheral nerve repair has been the advent of stem and progenitor cell use to supplement the regenerative environment in animal models of nerve injury. As Schwann cell replacements, stem cells may be even better suited to promoting regeneration in these scenarios. We review the recent literature detailing the search for the definitive Schwann cell replacement cell, including a look at genetic modification of transplanted cells for nerve injury repair.

Augmenting peripheral nerve regeneration using stem cells: A review of current opinion

Outcomes following peripheral nerve injury remain frustratingly poor. The reasons for this are multifactorial, although maintaining a growth permissive environment in the distal nerve stump following repair is arguably the most important. The optimal environment for axonal regeneration relies on the synthesis and release of many biochemical mediators that are temporally and spatially regulated with a high level of incompletely understood complexity. The Schwann cell (SC) has emerged as a key player in this process. Prolonged periods of distal nerve stump denervation, characteristic of large gaps and proximal injuries, have been associated with a reduction in SC number and ability to support regenerating axons. Cell based therapy offers a potential therapy for the improvement of outcomes following peripheral nerve reconstruction. Stem cells have the potential to increase the number of SCs and prolong their ability to support regeneration. They may also have the ability to rescue and replenish populations of chromatolytic and apoptotic neurons following axotomy. Finally, they can be used in non-physiologic ways to preserve injured tissues such as denervated muscle while neuronal ingrowth has not yet occurred. Aside from stem cell type, careful consideration must be given to differentiation status, how stem cells are supported following transplantation and how they will be delivered to the site of injury. It is the aim of this article to review current opinions on the strategies of stem cell based therapy for the augmentation of peripheral nerve regeneration.

Sweat gland regeneration after burn injury: is stem cell therapy a new hope?

Stem cells are the seeds of tissue repair and regeneration and a promising source for novel therapies. The skin of patients with an extensive deep burn injury is repaired by a hypertrophic scar without regeneration of sweat glands and therefore loses the function of perspiration. Stem cell therapy provides the possibility of sweat gland regeneration. In particular, recent studies have reported the reprogramming of mesenchymal stromal cells into sweat gland-like (SGL) cells. We present an overview of recent researches into sweat gland regeneration with stem cells. Difficulties of sweat gland regeneration after deep burns have been elaborated. The advantage and disadvantage of several stem cell types in sweat gland regeneration have been discussed. Additionally, the possible mechanisms for reprogramming stem cells to SGL cells are summarized. A brief discussion on clinical application of stem cell-derived SGL cells is also presented. This review may possibly provide some implications for sweat gland regeneration.

Undifferentiated and differentiated adipose-derived stem cells improve nerve regeneration in a rat model of facial nerve defect

Autologous nerve grafting is the current procedure used for repairing facial nerve gaps. As an alternative to this method, tissue engineering cell-based therapy using induced pluripotent stem cells, Schwann cells and bone marrow-derived mesenchymal stem cells has been proposed. However, these cells have major problems, including tumorigenesis in induced pluripotent stem cells and invasiveness and limited tissue associated with harvesting for the other cells. Here, we investigated the therapeutic potential of adipose-derived stem cells (ASCs), which can be harvested easily and repeatedly by a minimally invasive liposuction procedure. The ASCs had characteristics of mesenchymal tissue lineages and could differentiate into Schwann-like cells that were relatively simple to isolate and expand in culture. In an in vivo study, a silicone conduit containing undifferentiated ASCs, differentiated ASCs or Schwann cells were transplanted, embedded in a collagen gel and the efficacy of repair of a 7 mm-gap in the rat facial nerve examined. Morphometric quantification analysis of regenerated facial nerves after a regeneration period of 13 weeks showed that undifferentiated ASCs, differentiated ASCs, and Schwann cells had similar potential for nerve regeneration. Furthermore, the functional recovery of facial nerve regeneration using a rat facial palsy scoring system in the three groups was close to that in autologous nerve graft positive controls. These findings suggest that undifferentiated and differentiated ASCs may both have therapeutic potential in facial nerve regeneration as a source of Schwann cells in cell-based therapy performed as an alternative to autologous nerve grafts. Copyright © 2014 John Wiley & Sons, Ltd.

Neural tissue engineering options for peripheral nerve regeneration

Tissue engineered nerve grafts (TENGs) have emerged as a potential alternative to autologous nerve grafts, the gold standard for peripheral nerve repair. Typically, TENGs are composed of a biomaterial-based template that incorporates biochemical cues. A number of TENGs have been used experimentally to bridge long peripheral nerve gaps in various animal models, where the desired outcome is nerve tissue regeneration and functional recovery. So far, the translation of TENGs to the clinic for use in humans has met with a certain degree of success. In order to optimize the TENG design and further approach the matching of TENGs with autologous nerve grafts, many new cues, beyond the traditional ones, will have to be integrated into TENGs. Furthermore, there is a strong requirement for monitoring the real-time dynamic information related to the construction of TENGs. The aim of this opinion paper is to specifically and critically describe the latest advances in the field of neural tissue engineering for peripheral nerve regeneration. Here we delineate new attempts in the design of template (or scaffold) materials, especially in the context of biocompatibility, the choice and handling of support cells, and growth factor release systems. We further discuss the significance of RNAi for peripheral nerve regeneration, anticipate the potential application of RNAi reagents for TENGs, and speculate on the possible contributions of additional elements, including angiogenesis, electrical stimulation, molecular inflammatory mediators, bioactive peptides, antioxidant reagents, and cultured biological constructs, to TENGs. Finally, we consider that a diverse array of physicochemical and biological cues must be orchestrated within a TENG to create a self-consistent coordinated system with a close proximity to the regenerative microenvironment of the peripheral nervous system.

Recent advances in nerve tissue engineering

Nerve injury secondary to trauma, neurological disease or tumor excision presents a challenge for surgical reconstruction. Current practice for nerve repair involves autologous nerve transplantation, which is associated with significant donor-site morbidity and other complications. Previously artificial nerve conduits made from polycaprolactone, polyglycolic acid and collagen were approved by the FDA (USA) for nerve repair. More recently, there have been significant advances in nerve conduit design that better address the requirements of nerve regrowth. Innovations in materials science, nanotechnology, and biology open the way for the synthesis of new generation nerve repair conduits that address issues currently faced in nerve repair and regeneration. This review discusses recent innovations in this area, including the use of nanotechnology to improve the design of nerve conduits and to enhance nerve regeneration.

Preferential and comprehensive reconstitution of severely damaged sciatic nerve using murine skeletal muscle-derived multipotent stem cells

Loss of vital functions in the somatic motor and sensory nervous systems can be induced by severe peripheral nerve transection with a long gap following trauma. In such cases, autologous nerve grafts have been used as the gold standard, with the expectation of activation and proliferation of graft-concomitant Schwann cells associated with their paracrine effects. However, there are a limited number of suitable sites available for harvesting of nerve autografts due to the unavoidable sacrifice of other healthy functions. To overcome this problem, the potential of skeletal muscle-derived multipotent stem cells (Sk-MSCs) was examined as a novel alternative cell source for peripheral nerve regeneration. Cultured/expanded Sk-MSCs were injected into severely crushed sciatic nerve corresponding to serious neurotmesis. After 4 weeks, engrafted Sk-MSCs preferentially differentiated into not only Schwann cells, but also perineurial/endoneurial cells, and formed myelin sheath and perineurium/endoneurium, encircling the regenerated axons. Increased vascular formation was also observed, leading to a favorable blood supply and waste product excretion. In addition, engrafted cells expressed key neurotrophic and nerve/vascular growth factor mRNAs; thus, endocrine/paracrine effects for the donor/recipient cells were also expected. Interestingly, skeletal myogenic capacity of expanded Sk-MSCs was clearly diminished in peripheral nerve niche. The same differentiation and tissue reconstitution capacity of Sk-MSCs was sufficiently exerted in the long nerve gap bridging the acellular conduit, which facilitated nerve regeneration/reconnection. These effects represent favorable functional recovery in Sk-MSC-treated mice, as demonstrated by good corduroy walking. We also demonstrated that these differentiation characteristics of the Sk-MSCs were comparable to native peripheral nerve-derived cells, whereas the therapeutic capacities were largely superior in Sk-MSCs. Therefore, Sk-MSCs can be a novel/suitable alternative cell source for healthy nerve autografts.

Acceleration of peripheral nerve regeneration using nerve conduits in combination with induced pluripotent stem cell technology and a basic fibroblast growth factor drug delivery system

Various modifications including addition of Schwann cells or incorporation of growth factors with bioabsorbable nerve conduits have been explored as options for peripheral nerve repair. However, no reports of nerve conduits containing both supportive cells and growth factors have been published as a regenerative therapy for peripheral nerves. In the present study, sciatic nerve gaps in mice were reconstructed in the following groups: nerve conduit alone (control group), nerve conduit coated with induced pluripotent stem cell (iPSc)-derived neurospheres (iPSc group), nerve conduit coated with iPSc-derived neurospheres and basic fibroblast growth factor (bFGF)-incorporated gelatin microspheres (iPSc + bFGF group), and autograft. The fastest functional recovery and the greatest axon regeneration occurred in the autograft group, followed in order by the iPSc + bFGF group, iPSc group, and control group until 12 weeks after reconstruction. Thus, peripheral nerve regeneration using nerve conduits and functional recovery in mice was accelerated by a combination of iPSc-derived neurospheres and a bFGF drug delivery system. The combination of all three fundamental methodologies, iPSc technology for supportive cells, bioabsorbable nerve conduits for scaffolds, and a bFGF drug delivery system for growth factors, was essential for peripheral nerve regenerative therapy.