Clinical translation of stem cell based interventions for spinal cord injury - Are we there yet?

Olig2-enriched exosomes: A novel therapeutic approach for cuprizone-induced demyelination

The research aims to study the therapeutic impact of HEK293-XPack-Olig2 cell-derived exosomes on remyelination of the corpus callosum in a cuprizone-induced demyelinating disease model. A lentiviral vector expressing Olig2 was constructed using XPack technology. The highly abundant Olig2 exosomes (ExoOs) were isolated by centrifugation for subsequent experiments. Western blot, nanoparticle tracking analysis (NTA), and electron microscopy showed no significant difference in particle size and morphology between Exos and ExoOs, and a high level of Olig2 expression could be detected in ExoOs, indicating that exosome modification by XPack technology was successful. The Black Gold/Fluromyelin staining analysis showed that the ExoOs group significantly reduced the demyelination area in the corpus callosum compared to the PBS and Exos groups. Additionally, the PDGFRα/APC staining of the demyelinating region revealed an increase in APC+ oligodendrocytes and a decrease in PDGFRα+ oligodendrocyte progenitor cells (OPCs) in the ExoOs group. Furthermore, there was evident myelin regeneration in the demyelinated areas after ExoOs treatment, with better g-ratio and a higher number of intact myelin compared to the other treatment groups. The level of Sox10 expression in the brain tissue of the ExoOs group were higher compared to those of the PBS and Exos groups. The demyelination process can be significantly slowed down by the XPack-modified exosomes, the differentiation of OPCs promoted, and myelin regeneration accelerated under pathological conditions. This process is presumed to be achieved by changing the expression level of intracellular differentiation-related genes after exosomes transport Olig2 enriched into oligodendrocyte progenitors.

Wearable and implantable biosensors: mechanisms and applications in closed-loop therapeutic systems

This review article examines the current state of wearable and implantable biosensors, offering an overview of their biosensing mechanisms and applications. We also delve into integrating these biosensors with therapeutic systems, discussing their operational principles and incorporation into closed-loop devices. Biosensing strategies are broadly categorized into chemical sensing for biomarker detection, physical sensing for monitoring physiological conditions such as pressure and temperature, and electrophysiological sensing for capturing bioelectrical activities. The discussion extends to recent developments in drug delivery and electrical stimulation devices to highlight their significant role in closed-loop therapy. By integrating with therapeutic devices, biosensors enable the modulation of treatment regimens based on real-time physiological data. This capability enhances the patient-specificity of medical interventions, an essential aspect of personalized healthcare. Recent innovations in integrating biosensors and therapeutic devices have led to the introduction of closed-loop wearable and implantable systems capable of achieving previously unattainable therapeutic outcomes. These technologies represent a significant leap towards dynamic, adaptive therapies that respond in real-time to patients' physiological states, offering a level of accuracy and effectiveness that is particularly beneficial for managing chronic conditions. This review also addresses the challenges associated with biosensor technologies. We also explore the prospects of these technologies to address their potential to transform disease management with more targeted and personalized treatment solutions.

Current status and future perspectives on stem cell transplantation for spinal cord injury

BACKGROUND

Previous assessments of stem cell therapy for spinal cord injuries (SCI) have encountered challenges and constraints. Current research primarily emphasizes safety in early-phase clinical trials, while systematic reviews prioritize effectiveness, often overlooking safety and translational feasibility. This situation prompts inquiries regarding the readiness for clinical adoption.

AIM

To offer an up-to-date systematic literature review of clinical trial results con cerning stem cell therapy for SCI.

METHODS

A systematic search was conducted across major medical databases [PubMed, Embase, Reference Citation Analysis (RCA), and Cochrane Library] up to October 14, 2023. The search strategy utilized relevant Medical Subject Heading (MeSH) terms and keywords related to "spinal cord", "injury", "clinical trials", "stem cells", "functional outcomes", and "adverse events". Studies included in this review consisted of randomized controlled trials and non-randomized controlled trials reporting on the use of stem cell therapies for the treatment of SCI.

RESULTS

In a comprehensive review of 66 studies on stem cell therapies for SCI, 496 papers were initially identified, with 237 chosen for full-text analysis. Among them, 236 were deemed eligible after excluding 170 for various reasons. These studies encompassed 1086 patients with varying SCI levels, with cervical injuries being the most common (42.2%). Bone marrow stem cells were the predominant stem cell type used (71.1%), with various administration methods. Follow-up durations averaged around 84.4 months. The 32.7% of patients showed functional impro vement from American spinal injury association Impairment Scale (AIS) A to B, 40.8% from AIS A to C, 5.3% from AIS A to D, and 2.1% from AIS B to C. Sensory improvements were observed in 30.9% of patients. A relatively small number of adverse events were recorded, including fever (15.1%), headaches (4.3%), muscle tension (3.1%), and dizziness (2.6%), highlighting the potential for SCI recovery with stem cell therapy.

CONCLUSION

In the realm of SCI treatment, stem cell-based therapies show promise, but clinical trials reveal potential adverse events and limitations, underscoring the need for meticulous optimization of transplantation conditions and parameters, caution against swift clinical implementation, a deeper understanding of SCI pathophysiology, and addressing ethical, tumorigenicity, immunogenicity, and immunotoxicity concerns before gradual and careful adoption in clinical practice.

Transplantation of Wnt3a-modified neural stem cells promotes neural regeneration and functional recovery after spinal cord injury via Wnt-Gli2 pathway

Neural stem cell (NSCs) transplantation has great potential in the treatment of spinal cord injury (SCI). Previous studies have indicated that the Wnt pathway could regulate the expression of basic helix-loop-helix (bHLH) family factor Hes5 and Mash1 in NSCs, but not through the notch intracellular domain. This suggests that there are other signals involved in this process. The aim of this study was to investigate the role of Wnt-Gli2 pathway in the treatment of SCI by transplanting neural stem cells. NSCs were isolated from the striata of embryonic day 14 mice. Activation of the Wnt pathway was achieved using Wnt3a protein, while Gli2 was inhibited using Gli2-siRNA. Expression levels of Gli2 and bHLH factors were assessed using western blotting. NSCs proliferation was evaluated using CCK-8 assay, and neural differentiation was determined by immunofluorescence staining. Finally, the modified NSCs were transplanted into mice with SCI, and their effects were assessed using behavioral and histological tests. Our results demonstrated that Wnt3a promoted the expression of Mash1 through Gli2. Moreover, the expression of Ngn1 and Hes1 was up-regulated, while Hes5 was down-regulated. Wnt3a also promoted NSCs proliferation and neural differentiation through this signaling pathway. In vivo experiments showed that NSCs transplantation mediated by Wnt3a-Gli2 signaling increased the number of neurons and resulted in improved Basso Mouse Scale scores. In conclusion, our findings suggest that Gli2 plays a role in mediating the regulation of Wnt3a signaling on promoting NSCs proliferation and neural differentiation. This pathway is therefore important in NSCs-mediated SCI recovery.

Artificially reprogrammed stem cells deliver transcytosable nanocomplexes for improved spinal cord repair

Stem cell transplantation holds great promise for restoring function after spinal cord injury (SCI), but its therapeutic efficacy heavily depends on the innate capabilities of the cells and the microenvironment at the lesion site. Herein, a potent cell therapeutic (NCs@SCs) is engineered by artificially reprogramming bone marrow mesenchymal stem cells (BMSCs) with oxidation-responsive transcytosable gene-delivery nanocomplexes (NCs), which endows cells with robust oxidative stress resistance and improved cytokine secretion. NCs@SCs can accumulate in the injured spinal cord after intravenous administration via chemotaxis and boost successive transcytosis to deliver NCs to neurons, augmenting ciliary neurotrophic factor (CNTF) production in both BMSCs and neurons in response to elevated ROS levels. Furthermore, NCs@SCs can actively sense and eliminate ROS and re-educate recruited M1-like macrophages into the anti-inflammatory M2 phenotype via a paracrine pathway, ultimately reshaping the inflammatory microenvironment. Synergistically, NCs@SCs exhibit durable survival and provide neuroprotection against secondary damage, enabling significant locomotor function recovery in SCI rats. Transcriptome analysis reveals that regulation of the ROS/MAPK signaling pathway is involved in SCI therapy by NCs@SCs. This study presents a nanomaterial-mediated cell-reprogramming approach for developing live cell therapeutics, showing significant potential in the treatment of SCI and other neuro-injury disorders.

Nanozyme-Integrated Thermoresponsive In Situ Forming Hydrogel Enhances Mesenchymal Stem Cell Viability and Paracrine Effect for Efficient Spinal Cord Repair

Mesenchymal stem cell (MSC)-based therapy has emerged as a promising strategy for the treatment of spinal cord injury (SCI). However, the hostile microenvironment of SCI, which can adversely affect the survival and paracrine effect of the implanted MSCs, severely limits the therapeutic efficacy of this approach. Here, we report on a ceria nanozyme-integrated thermoresponsive in situ forming hydrogel (CeNZ-gel) that can enable dual enhancement of MSC viability and paracrine effect, leading to highly efficient spinal cord repair. The sol-gel transition property of the CeNZ-gel at body temperature ensures uniform coverage of the hydrogel in injured spinal cord tissues. Our results demonstrate that the CeNZ-gel significantly increases the viability of transplanted MSCs in the microenvironment by attenuating oxidative stress and, more importantly, promotes the secretion of angiogenic factors from MSCs by inducing autophagy of MSCs. The synergy between the oxidative stress-relieving effect of CeNZs and the paracrine effect of MSCs accelerates angiogenesis, nerve repair, and motor function recovery after SCI, providing an efficient strategy for MSC-based SCI therapy.

Porous microneedle patch with sustained delivery of extracellular vesicles mitigates severe spinal cord injury

The transplantation of mesenchymal stem cells-derived secretome, particularly extracellular vesicles is a promising therapy to suppress spinal cord injury-triggered neuroinflammation. However, efficient delivery of extracellular vesicles to the injured spinal cord, with minimal damage, remains a challenge. Here we present a device for the delivery of extracellular vesicles to treat spinal cord injury. We show that the device incorporating mesenchymal stem cells and porous microneedles enables the delivery of extracellular vesicles. We demonstrate that topical application to the spinal cord lesion beneath the spinal dura, does not damage the lesion. We evaluate the efficacy of our device in a contusive spinal cord injury model and find that it reduces the cavity and scar tissue formation, promotes angiogenesis, and improves survival of nearby tissues and axons. Importantly, the sustained delivery of extracellular vesicles for at least 7 days results in significant functional recovery. Thus, our device provides an efficient and sustained extracellular vesicles delivery platform for spinal cord injury treatment.

Cell transplantation therapies for spinal cord injury focusing on bone marrow mesenchymal stem cells: Advances and challenges

Spinal cord injury (SCI) is a devastating condition with complex pathological mechanisms that lead to sensory, motor, and autonomic dysfunction below the site of injury. To date, no effective therapy is available for the treatment of SCI. Recently, bone marrow-derived mesenchymal stem cells (BMMSCs) have been considered to be the most promising source for cellular therapies following SCI. The objective of the present review is to summarize the most recent insights into the cellular and molecular mechanism using BMMSC therapy to treat SCI. In this work, we review the specific mechanism of BMMSCs in SCI repair mainly from the following aspects: Neuroprotection, axon sprouting and/or regeneration, myelin regeneration, inhibitory microenvironments, glial scar formation, immunomodulation, and angiogenesis. Additionally, we summarize the latest evidence on the application of BMMSCs in clinical trials and further discuss the challenges and future directions for stem cell therapy in SCI models.

Engineered extracellular vesicles for delivery of siRNA promoting targeted repair of traumatic spinal cord injury

Spinal cord injury (SCI) is a severe disease of the nervous system that causes irreparable damage and loss of function, for which no effective treatments are available to date. Engineered extracellular vesicles (EVs) carrying therapeutic molecules hold promise as an alternative SCI therapy depending on the specific functionalized EVs and the appropriate engineering strategy. In this study, we demonstrated the design of a drug delivery system of peptide CAQK-modified, siRNA-loaded EVs (C-EVs-siRNA) for SCI-targeted therapy. The peptide CAQK was anchored through a chemical modification to the membranes of EVs isolated from induced neural stem cells (iNSCs). CCL2-siRNA was then loaded into the EVs through electroporation. The modified EVs still maintained the basic properties of EVs and showed favorable targeting and therapeutic effects in vitro and in vivo. C-EVs-siRNA specifically delivered siRNA to the SCI region and was taken up by target cells. C-EVs-siRNA used the inherent anti-inflammatory and neuroreparative functions of iNSCs-derived EVs in synergy with the loaded siRNA, thus enhancing the therapeutic effect against SCI. The combination of targeted modified EVs and siRNA effectively regulated the microenvironmental disturbance after SCI, promoted the transformation of microglia/macrophages from M1 to M2 and limited the negative effects of the inflammatory response and neuronal injury on functional recovery in mice after SCI. Thus, engineered EVs are a potentially feasible and efficacious treatment for SCI, and may also be used to develop targeted treatments for other diseases.

Clinical translation of stem cell therapy for spinal cord injury still premature: results from a single-arm meta-analysis based on 62 clinical trials

BACKGROUND

How much scientific evidence is there to show that stem cell therapy is sufficient in preclinical and clinical studies of spinal cord injury before it is translated into clinical practice? This is a complicated problem. A single, small-sample clinical trial is difficult to answer, and accurate insights into this question can only be given by systematically evaluating all the existing evidence.

METHODS

The PubMed, Ovid-Embase, Web of Science, and Cochrane databases were searched from inception to February 10, 2022. Two independent reviewers performed the literature search, identified and screened the studies, and performed a quality assessment and data extraction.

RESULTS

In total, 62 studies involving 2439 patients were included in the analysis. Of these, 42 were single-arm studies, and 20 were controlled studies. The meta-analysis showed that stem cells improved the ASIA impairment scale score by at least one grade in 48.9% [40.8%, 56.9%] of patients with spinal cord injury. Moreover, the rate of improvement in urinary and gastrointestinal system function was 42.1% [27.6%, 57.2%] and 52.0% [23.6%, 79.8%], respectively. However, 28 types of adverse effects were observed to occur due to stem cells and transplantation procedures. Of these, neuropathic pain, abnormal feeling, muscle spasms, vomiting, and urinary tract infection were the most common, with an incidence of > 20%. While no serious adverse effects such as tumorigenesis were reported, this could be due to the insufficient follow-up period.

CONCLUSIONS

Overall, the results demonstrated that although the efficacy of stem cell therapy is encouraging, the subsequent adverse effects remain concerning. In addition, the clinical trials had problems such as small sample sizes, poor design, and lack of prospective registration, control, and blinding. Therefore, the current evidence is not sufficiently strong to support the clinical translation of stem cell therapy for spinal cord injury, and several problems remain. Additional well-designed animal experiments and high-quality clinical studies are warranted to address these issues.

Enhanced effect of combining bone marrow mesenchymal stem cells (BMMSCs) and pulsed electromagnetic fields (PEMF) to promote recovery after spinal cord injury in mice

Spinal cord injury (SCI) is a destructive traumatic disease of the central nervous system without satisfying therapy efficiency. Bone marrow mesenchymal stem cells (BMMSCs) therapy promotes the neurotrophic factors’ secretion and axonal regeneration, thereby promoting recovery of SCI. Pulsed electromagnetic fields (PEMF) therapy has been proven to promote neural growth and regeneration. Both BMMSCs and PEMF have shown curative effects for SCI; PEMF can further promote stem cell differentiation. Thus, we explored the combined effects of BMMSCs and PEMF and the potential interaction between these two therapies in SCI. Compared with the SCI control, BMMSCs, and PEMF groups, the combinational therapy displayed the best therapeutic effect. Combinational therapy increased the expression levels of nutritional factors including brain‐derived neurotrophic factor (BDNF), nerve growth factors (NGF) and vascular endothelial growth factor (VEGF), enhanced neuron preservation (NeuN and NF‐200), and increased axonal growth (MBP and myelin sheath). Additionally, PEMF promoted the expression levels of BDNF and VEGF in BMMSCs via Wnt/β‐catenin signaling pathway. In summary, the combined therapy of BMMSCs and PEMF displayed a more satisfactory effect than BMMSCs and PEMF therapy alone, indicating a promising application of combined therapy for the therapy of SCI.

The Time Sequence of Gene Expression Changes after Spinal Cord Injury

Gene expression changes following spinal cord injury (SCI) are time-dependent, and an accurate understanding of these changes can be crucial in determining time-based treatment options in a clinical setting. We performed RNA sequencing of the contused spinal cord of rats at five different time points from the very acute to chronic stages (1 hour, 1 day, 1 week, 1 month, and 3 months) following SCI. We identified differentially expressed genes (DEGs) and Gene Ontology (GO) terms at each time point, and 14,257 genes were commonly expressed at all time points. The biological process of the inflammatory response was increased at 1 hour and 1 day, and the cellular component of the integral component of the synaptic membrane was increased at 1 day. DEGs associated with cell activation and the innate immune response were highly enriched at 1 week and 1 month, respectively. A total of 2841 DEGs were differentially expressed at any of the five time points, and 18 genes (17 upregulated and 1 downregulated) showed common expression differences at all time points. We found that interleukin signaling, neutrophil degranulation, eukaryotic translation, collagen degradation, LGI–ADAM interactions, GABA receptor, and L1CAM-ankyrin interactions were prominent after SCI depending on the time post injury. We also performed gene–drug network analysis and found several potential antagonists and agonists which can be used to treat SCI. We expect to discover effective treatments in the clinical field through further studies revealing the efficacy and safety of potential drugs.

Human Adipose-Derived Stem Cells Combined with Nano-Hydrogel Promote Functional Recovery after Spinal Cord Injury in Rats

Simple Summary

Nerve regeneration and functional recovery after spinal cord injury (SCI) are worldwide problems. Scientists have achieved encouraging results in the repair of spinal cord injuries using natural or synthetic materials. In this paper, we report that nano-hydrogel combined with human adipose-derived stem cells regulate the inflammatory microenvironment, protect neurons and axons, and promote motor function recovery. In addition, three proteins related to neuronal and axonal growth were screened by Liquid chromatography-mass spectrometry. These results provide evidence for clinical treatment of spinal cord injury.

Abstract

The treatment of spinal cord injury aims to reconstruct the fiber connection and restore the interrupted neural pathways. Adipose mesenchymal stem cells (ADSCs) can promote the recovery of motor functions in spinal cord injury. However, poor survival of ADSCs and leakage outside of the injury site after local transplantation reduce the number of cells, which seriously attenuates the cumulative effect. We performed heterotopic transplantation on rats with severe spinal cord injury using human ADSCs loaded within self-assembly hydrogel RADA16-RGD (R: arginine; A: alanine; D: aspartic acid; G: glycine). Our results indicate that the combined transplantation of human ADSCs with RADA16-RGD improved the survival of ADSCs at the injured site. The inflammatory reaction was inhibited, with improved survival of the neurons and increased residual area of nerve fibers and myelin protein. The functional behaviors were promoted, as determined by the Basso, Beattie, and Bresnahan (BBB) locomotor rating scale score and electrophysiological measurements. ADSCs can promote the repair of spinal cord injury. This study provides new ideas for the treatment of spinal cord injury.

What Is the Optimal Timing of Transplantation of Neural Stem Cells in Spinal Cord Injury? A Systematic Review and Network Meta-Analysis Based on Animal Studies

Objective

The optimal transplantation timing of neural stem cells in spinal cord injury is fully explored in animal studies to reduce the risk of transformation to clinical practice and to provide valuable reference for future animal studies and clinical research.

Method

Seven electronic databases, namely, PubMed, Web of Science, Embase, Wanfang, Chinese Scientific Journal Database (CSJD-VIP), China Biomedical Literature Database (CBM), and China National Knowledge Infrastructure (CNKI), were searched. The studies were retrieved from inception to November 2021. Two researchers independently screened the literature, extracted data, and evaluated the methodological quality based on the inclusion criteria.

Results and Discussion

Thirty-nine studies were incorporated into the final analyses. Based on the subgroup of animal models and transplantation dose, the results of network meta-analysis showed that the effect of transplantation in the subacute phase might be the best. However, the results of traditional meta-analysis were inconsistent. In the moderate-dose group of moderate spinal cord injury model and the low-dose group of severe spinal cord injury model, transplantation in the subacute phase did not significantly improve motor function. Given the lack of evidence for direct comparison between different transplantation phases, the indirectness of our network meta-analysis, and the low quality of evidence in current animal studies, our confidence in recommending cell transplantation in the subacute phase is limited. In the future, more high-quality, direct comparative studies are needed to explore this issue in depth.

Spinal Cord Injury: A Systematic Review and Network Meta-Analysis of Therapeutic Strategies Based on 15 Types of Stem Cells in Animal Models

Objective: The optimal therapeutic strategies of stem cells for spinal cord injury (SCI) are fully explored in animal studies to promote the translation of preclinical findings to clinical practice, also to provide guidance for future animal experiments and clinical studies.

Methods: PubMed, Web of Science, Embase, CNKI, Wangfang, VIP, and CBM were searched from inception to September 2021. Screening of search results, data extraction, and references quality evaluation were undertaken independently by two reviewers.

Results and Discussion: A total of 188 studies were included for data analysis. Results of traditional meta-analysis showed that all 15 diverse types of stem cells could significantly improve locomotor function of animals with SCI, and results of further network meta-analysis showed that adipose-derived mesenchymal stem cells had the greatest therapeutic potential for SCI. Moreover, a higher dose (≥1 × 106) of stem cell transplantation had better therapeutic effect, transplantation in the subacute phase (3–14 days, excluding 3 days) was the optimal timing, and intralesional transplantation was the optimal route. However, the evidence of current animal studies is of limited quality, and more high-quality research is needed to further explore the optimal therapeutic strategies of stem cells, while the design and implementation of experiments, as well as measurement and reporting of results for animal studies, need to be further improved and standardized to reduce the risk when the results of animal studies are translated to the clinic.

Systematic Review Registration: [website], identifier [registration number].

Hypoxia-stimulated mesenchymal stem cell-derived exosomes loaded by adhesive hydrogel for effective angiogenic treatment of spinal cord injury

Due to the limited efficacy of current clinical treatment strategies, functional recovery after traumatic spinal cord injury (SCI) remains a knotty problem to be solved. Apart from anti-inflammation and cell replenishing treatments, accumulating evidence implies that promoting angiogenesis would also potentially benefit tissue regeneration after SCI. In this research, inspired by the role of exosomes in cell-cell communication and exosomal alteration resulting from cells under stress, exosomes were engineered through hypoxia stimulation to mesenchymal stem cells and were proposed as an alternative for promoting angiogenesis in SCI therapy. Hypoxia-stimulated exosomes (hypo-Exo) were transplanted into the injured spinal cord via encapsulation in a peptide-modified adhesive hydrogel for pro-angiogenic therapy of SCI. The adhesive peptide PPFLMLLKGSTR-modified hyaluronic acid hydrogel replenished the spinal cavity caused by SCI and achieved the local delivery of exosomes. The hypoxia-inducible factor 1-alpha content in hypo-Exo was significantly increased, resulting in the overexpression of vascular endothelial growth factor in the endothelial cells surrounding the transplant system. Ultimately, prominent angiogenesis and functional recovery after injury were demonstrated both in vitro and in vivo, indicating the immense potential of hydrogel-encapsulated hypo-Exo in treating central nervous system trauma and other ischemia diseases.

Regenerative rehabilitation with conductive biomaterials for spinal cord injury

The individual approaches of regenerative medicine efforts alone and rehabilitation efforts alone have not yet fully restored function after severe spinal cord injury (SCI). Regenerative rehabilitation may be leveraged to promote regeneration of the spinal cord tissue, and promote reorganization of the regenerated neural pathways and intact spinal circuits for better functional recovery for SCI. Conductive biomaterials may be a linchpin that empowers the synergy between regenerative medicine and rehabilitation approaches, as electrical stimulation applied to the spinal cord could facilitate neural reorganization. In this review, we discuss current regenerative medicine approaches in clinical trials and the rehabilitation, or neuromodulation, approaches for SCI, along with their respective translational limitations. Furthermore, we review the translational potential, in a surgical context, of conductive biomaterials (e.g., conductive polymers, carbon-based materials, metallic nanoparticle-based materials) as they pertain to SCI. While pre-formed scaffolds may be difficult to translate to human contusion SCIs, injectable composites that contain blended conductive components and can form within the injury may be more translational. However, given that there are currently no in vivo SCI studies that evaluated conductive materials combined with rehabilitation approaches, we discuss several limitations of conductive biomaterials, including demonstrating safety and efficacy, that will need to be addressed in the future for conductive biomaterials to become SCI therapeutics. Even so, the use of conductive biomaterials creates a synergistic opportunity to merge the fields of regenerative medicine and rehabilitation and redefine what regenerative rehabilitation means for the spinal cord. STATEMENT OF SIGNIFICANCE: For spinal cord injury (SCI), the individual approaches of regenerative medicine and rehabilitation are insufficient to fully restore functional recovery; however, the goal of regenerative rehabilitation is to combine these two disparate fields to maximize the functional outcomes. Concepts similar to regenerative rehabilitation for SCI have been discussed in several reviews, but for the first time, this review considers how conductive biomaterials may synergize the two approaches. We cover current regenerative medicine and rehabilitation approaches for SCI, and the translational advantages and disadvantages, in a surgical context, of conductive biomaterials used in biomedical applications that may be additionally applied to SCI. Furthermore, we identify the current limitations and translational challenges for conductive biomaterials before they may become therapeutics for SCI.

Exosomes derived from olfactory ensheathing cells provided neuroprotection for spinal cord injury by switching the phenotype of macrophages/microglia

Transplantation of olfactory ensheathing cells (OECs) has been demonstrated to be beneficial for spinal cord injury (SCI) by modulating neuroinflammation, supporting neuronal survival and promoting angiogenesis. Besides OECs, the conditioned medium (CM) from OECs has also been proved to have therapeutic effects for SCI, indicating that the bioactive substances secreted by OECs are essential for its protective effects. Nevertheless, there is still little information regarding the underlying mechanisms. Considering that exosomes are crucial for intercellular communication and could be secreted by different types of cells, we speculated that the therapeutic potential of OECs for SCI might be partially based on their exosomes. To examine whether OECs could secret exosomes, we isolated exosomes by polyethylene glycol‐based method, and identified them by electron microscopy study, nanoparticle tracking analysis (NTA) and western blotting. In view of phagocytic ability of microglia and its distinct roles in microenvironment regulation after SCI, we then focused the effects of OECs‐derived exosomes (OECs‐Exo) on microglial phenotypic regulation. We found that the extracted OECs‐Exo could be engulfed by microglia and partially reverse the LPS‐induced pro‐inflammatory polarization through inhibiting NF‐κB and c‐Jun signaling pathways in vitro. Furthermore, OECs‐Exo were found to inhibit the polarization of pro‐inflammatory macrophages/microglia while increased the numbers of anti‐inflammatory cells after SCI. Considering that the neuronal injury is closely related to the activation state of macrophages/microglia, co‐culture of microglia and neurons were performed. Neuronal death induced by LPS‐treated microglia could be significantly alleviated when microglia treated by LPS plus OECs‐Exo in vitro. After SCI, NeuN‐immunostaining and axonal tract‐tracing were performed to assess neuronal survival and axon preservation. Our data showed that the OECs‐Exo promoted the neuronal survival and axon preservation, and facilitated functional recovery after SCI. Our findings provide a promising therapeutic strategy for SCI based on exosome‐immunomodulation.

Evaluation of the Clinical Efficacy of Stem Cell Transplantation in the Treatment of Spinal Cord Injury: A Systematic Review and Meta-analysis

Stem cell transplantation has been applied to treat spinal cord injury (SCI) in clinical trials for many years. However, the clinical efficacies of stem cell transplantation in SCI have been quite diverse. The purpose of our study was to systematically investigate the efficacy of stem cell transplantation in patients with SCI. The PubMed, Web of Science, Ovid-Medline, Cochrane Library, China National Knowledge Infrastructure, VIP, Wanfang, and SinoMed databases were searched until October 27, 2020. Quantitative and qualitative data were analyzed by Review Manager 5.3 and R. Nine studies (n = 328) were included, and the overall risk of bias was moderate. The ASIA Impairment Scale (AIS) grading improvement rate was analyzed in favor of stem cell transplantation group [odds ratio (OR) = 6.06, 95% confidence interval (CI): 3.16–11.62, P < 0.00001]. Urodynamic indices also showed improvement in bladder function. In subgroup analyses, the results indicated that in patients with complete (AIS A) SCI, with the application of cell numbers between n*(10⁷–10⁸), two cell types (i.e., bone marrow–derived mesenchymal stem cells and bone marrow mononuclears), and treatment time of more than 6 months, stem cell transplantation was more beneficial for sensorimotor function (P < 0.05 for all groups). The risk of fever incidence in the stem cell transplantation group was 4.22 (95% CI: 1.7–10.22, P = 0.001), and principal component analysis (PCA) suggested it was more related to transplanted cell numbers. Thus, stem cell transplantation can promote functional recovery in SCI patients. Moreover, the type and quantity of transplanted stem cells and treatment time are important factors affecting the therapeutic effect of stem cell transplantation in SCI. Further studies are needed to evaluate the effects and elucidate the mechanisms of these factors on stem cell therapy in SCI.

Rapid and effective treatment of traumatic spinal cord injury using stem cell derived exosomes

Traumatic spinal cord injury is a fatal acute event without effective clinical therapies. Following the trauma, immediate neural protection and microenvironment mitigation are vitally important for nerve tissue repair, where stem cell-based therapies could be eclipsed by the deficiency of cells due to the hostile microenvironment as well as the transport and preservation processes. Effective emergency strategies are required to be convenient, biocompatible, and stable. Herein, we assess an emergency cell-free treatment using mesenchymal stem cell-derived exosomes, which have proven capable of comprehensive mitigation of the inhibitory lesion microenvironment. The clinically validated fibrin glue is utilized to encapsulate the exosomes and in-situ gelates in transected rat spinal cords to provide a substrate for exosome delivery as well as nerve tissue growth. The emergency treatment alleviates the inflammatory and oxidative microenvironment, inducing effective nerve tissue repair and functional recovery. The therapy presents a promising strategy for effective emergency treatment of central nervous system trauma.

Nerve growth factor (NGF) with hypoxia response elements loaded by adeno-associated virus (AAV) combined with neural stem cells improve the spinal cord injury recovery

The ischemia and hypoxia microenvironment after spinal cord injury (SCI) makes SCI repair a challenging problem. With various stimulus, chances for neural stem cells (NSCs) to differentiate into neurons, astrocytes, oligodendrocytes are great and is considered as a potential source of the stem cell therapy to SCI. Our research used adeno-associated virus (AAV) to carry the target gene to transfect neural stem cells. Transfected NSCs can express nerve growth factor (NGF) navigated by five hypoxia-responsive elements (5HRE). Therefore, the 5HRE-NGF-NSCs could express NGF specifically in hypoxia sites to promote the tissue repair and function recovery. Based on the regeneration of neurocytes and promotion of the recovery found in SCI models, via locomotor assessment, histochemical staining and molecular examinations, our results demonstrated that 5HRE-NGF-NSCs could improve the motor function, neurons survival and molecules expression of SCI rats. Meanwhile, the downregulated expression of autophagy-related proteins indicated the inhibitive effect of 5HRE-NGF-NSCs on autophagy. Our research showed that 5HRE-NGF-NSCs contribute to SCI repair which might via inhibiting autophagy and improving the survival rate of neuronal cells. The new therapy also hampered the hyperplasia of neural glial scars and induced axon regeneration. These positive functions of 5HRE-NGF-NSCs all indicate a promising SCI treatment.

Transplantation Strategies for Spinal Cord Injury Based on Microenvironment Modulation

Spinal cord injury (SCI) is different from peripheral nerve injury; it results in devastating and permanent damage to the spine, leading to severe motor, sensory and autonomic dysfunction. SCI produces a complex microenvironment that can result in hemorrhage, inflammation and scar formation. Not only does it significantly limit regeneration, but it also challenges a multitude of transplantation strategies. In order to promote regeneration, researchers have recently begun to focus their attention on strategies that manipulate the complicated microenvironment produced by SCI. And some have achieved great therapeutic effects. Hence, reconstructing an appropriate microenvironment after transplantation could be a potential therapeutic solution for SCI. In this review, first, we aim to summarize the influential compositions of the microenvironment and their different effects on regeneration. Second, we highlight recent research that used various transplantation strategies to modulate different microenvironments produced by SCI in order to improve regeneration. Finally, we discuss future transplantation strategies regarding SCI.

Hypoxia Response Element-Directed Expression of aFGF in Neural Stem Cells Promotes the Recovery of Spinal Cord Injury and Attenuates SCI-Induced Apoptosis

Reducing neuronal death after spinal cord injury (SCI) is considered to be an important strategy for the renovation of SCI. Studies have shown that, as an important regulator of the development and maintenance of neural structure, acidic fibroblast growth factor (aFGF) has the role of tissue protection and is considered to be an effective drug for the treatment of SCI. Neural stem cells (NSCs) are rendered with the remarkable characteristics to self-replace and differentiate into a variety of cells, so it is promising to be used in cell transplantation therapy. Based on the facts above, our main aim of this research is to explore the role of NSCs expressing aFGF meditated by five hypoxia-responsive elements (5HRE) in the treatment of SCI by constructing AAV–5HRE–aFGF–NSCs and transplanting it into the area of SCI. Our research results showed that AAV–5HRE–aFGF–NSCs can effectively restore the motor function of rats with SCI. This was accomplished by inhibiting the expression of caspase 12/caspase 3 pathway, EIF2α–CHOP pathway, and GRP78 protein to inhibit apoptosis.

Biomaterials reinforced MSCs transplantation for spinal cord injury repair

Due to the complex pathophysiological mechanism, spinal cord injury (SCI) has become one of the most intractable central nervous system (CNS) diseases to therapy. Stem cell transplantation, mesenchymal stem cells (MSCs) particularly, appeals to more and more attention along with the encouraging therapeutic results for the functional regeneration of SCI. However, traditional cell transplantation strategies have some limitations, including the unsatisfying survival rate of MSCs and their random diffusion from the injection site to ambient tissues. The application of biomaterials in tissue engineering provides a new horizon. Biomaterials can not only confine MSCs in the injured lesions with higher cell viability, but also promote their therapeutic efficacy. This review summarizes the strategies and advantages of biomaterials reinforced MSCs transplantation to treat SCI in recent years, which are clarified in the light of various therapeutic effects in pathophysiological aspects of SCI.

Cellular therapy for treatment of spinal cord injury in Zebrafish model

Spinal cord injury is a serious problem with a high rate of morbidity and mortality for all persons, especially young people (15-25 years old). Due to the large burden and the costs incurred on the government, finding the best therapeutic approach is necessary. In this respect, treatment strategies based on the disease mechanism can be effective. After the first trauma of spinal cord cascades, cellular events happen one after the other known as secondary trauma. The mechanism of secondary events of spinal cord injury could be helpful for target therapy as trying to stop the secondary trauma. Herein, some medical and surgical therapy has been introduced and cell therapy strategy was considered as a recent method. Actually, cell therapy is defined as the application of different cells including mesenchymal stem cells, embryonic stem cells, induced pluripotent stem cells, and some others to replace or reconstruct the damaged tissues and restore their functions. However, as a newly emerged therapeutic method, cell therapy should be used through various subclinical studies in animal models to assess the efficacy of the treatment under controlled conditions. In this review, the role of Zebrafish as a recommended model has been discussed and combinatory approach as the probably most useful treatment has been suggested.

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

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

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

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

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

[Human umbilical cord mesenchymal stem cells differentiate into neuron-like cells after induction with B27-supplemented serum-free medium]

OBJECTIVE

To evaluate the capacity and efficiency of human umbilical cord mesenchymal stem cells (HUCMSCs) to differentiate into neuron- like cells after induction with B27- supplemented serum- free medium.

METHODS

HUCMSCs at passage 4 were cultured for 14 days with serum-containing medium (SCM) (group A), SCM supplemented with 20 ng/mL nerve growth factor (NGF) and 10 ng/mL basic fibroblast growth factor (bFGF) (group B), serum-free medium (SFM) (group C), or SFM supplemented with 20 ng/mL NGF and 10 ng/mL bFGF. The culture medium were changed every 3 days and the growth of the neurospheres was observed using an inverted microscope. The cell markers were analyzed with flow cytometry and the expressions of nestin, neuron- specific enolase (NSE), neurofilament heavy polypeptide (NEFH), and glial fibrillary acidic protein (GFAP) were quantified by quantitative real-time PCR (qRT-PCR) and Western blotting.

RESULTS

Before induction, HUCMSCs expressed abundant mesenchymal stem cell surface markers including CD29 (99.5%), CD44 (49.6%) and CD105 (77.7%). Neuron-like cells were observed in the cultures on days 7, 10, and 14, and the cell differentiation was the best in group D, followed by groups C, B and A. In all the 4 groups, the cellular expressions of nestin and GFAP gradually lowered while those of NEFH and NSE increased progressively. The expressions of GFAP, NEFH, nestin and NSE were significantly different between group A and the other 3 groups (P < 0.001 or 0.05).

CONCLUSIONS

B27-supplemented SFM effectively induces the differentiation of HUCMSCs into neuron- like cells, and the supplementation with cytokines (NGF and bFGF) strongly promotes the cell differentiation.

A Guide to Extract Spinal Cord for Translational Stem Cell Biology Research: Comparative Analysis of Adult Human, Porcine, and Rodent Spinal Cord Stem Cells

Improving the clinical translation of animal-based neural stem/progenitor cell (NSPC) therapies to humans requires an understanding of intrinsic human and animal cell characteristics. We report a novel in vitro method to assess spinal cord NSPCs from a small (rodent) and large (porcine) animal model in comparison to human NSPCs. To extract live adult human, porcine, and rodent spinal cord tissue, we illustrate a strategy using an anterior or posterior approach that was simulated in a porcine model. The initial expansion of primary NSPCs is carried out using the neurosphere assay followed by a pharmacological treatment phase during which NSPCs derived from humans, porcines, and rodents are assessed in parallel using the same defined parameters. Using this model, NSPCs from all species demonstrated multi-lineage differentiation and self-renewal. Importantly, these methods provide conditions to enable the direct comparison of species-dependent cell behavior in response to specific exogenous signals.

Transplantation of Human Mesenchymal Stem-Cell-Derived Exosomes Immobilized in an Adhesive Hydrogel for Effective Treatment of Spinal Cord Injury

Spinal cord injury is among the most fatal diseases. The complicated inhibitory microenvironment requires comprehensive mitigation. Exosomes derived from mesenchymal stem cells (MSCs) are natural biocarriers of cell paracrine secretions that bear the functions of microenvironment regulation. However, the effective retention, release, and integration of exosomes into the injured spinal cord tissue are poorly defined. Herein, an innovative implantation strategy is established using human MSC-derived exosomes immobilized in a peptide-modified adhesive hydrogel (Exo-pGel). Unlike systemic admistration of exosomes, topical transplantation of the Exo-pGel provides an exosome-encapsulated extracellular matrix to the injured nerve tissue, thereby inducing effecient comprehensive mitigation of the SCI microenvironment. The implanted exosomes exhibit efficient retention and sustained release in the host nerve tissues. The Exo-pGel elicits significant nerve recovery and urinary tissue preservation by effectively mitigating inflammation and oxidation. The Exo-pGel therapy presents a promising strategy for effective treatment of central nervous system diseases based on exosome implantation.

Scar Tissue-Targeting Polymer Micelle for Spinal Cord Injury Treatment

Spinal cord injury (SCI) is a devastating disorder, leading to permanent motor and sensory deficit. Despite recent advances in neurosciences, the treatment efficacy on SCI patients remains unsatisfactory, mainly due to the poor accumulation, short retention, and lack of controlled release of therapeutics in lesion tissue. Herein, an injured spinal cord targeting prodrug polymer micelle is built. An esterase-responsive bond is used to link apocynin (APO) monomer, because of the enhanced esterase activity found in microglia cells after activation, which ensures a controlled degradation of APO prodrug (Allyloxypolyethyleneglycol-b-poly [2-(((4-acetyl-2-methoxyphenoxy)carbonyl)oxy)ethyl methacrylate], APEG-PAPO or PAPO) by activated microglia cells. A scar tissue-homing peptide (cysteine-alanine-glutamine-lysine, CAQK) is introduced to the PAPO to endow the polymer micelle the lesion tissue-targeting ability. As a result, this CAQK-modified prodrug micelle (cPAM) exhibits an improved accumulation and prolonged retention in lesion tissue compared to the control micelle. The cPAM also leads to superior tissue protection and sustained motor function recovery than the control groups in a mouse model of SCI. In conclusion, the cPAM induces an effective treatment of SCI by the lesion tissue specific delivery of the prodrug polymer via its robust scar binding effect, making the scar tissue a drug releasing platform for sustained treatment of SCI.

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

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

Tubular scaffold with microchannels and an H-shaped lumen loaded with bone marrow stromal cells promotes neuroregeneration and inhibits apoptosis after spinal cord injury

As a result of its complex histological structure, regeneration patterns of grey and white matter are quite different in the spinal cord. Therefore, tissue engineering scaffolds for repairing spinal cord injury must be able to adapt to varying neural regeneration patterns. The aim of the present study was to improve a previously reported spinal cord‐mimicking partition‐type scaffold by adding microchannels on a single tubular wall along its longitudinal axis, thus integrating the two architectures of a single H‐shaped central tube and many microchannels. Next, the integrated scaffold was loaded with bone marrow stromal cells (BMSCs) and transplanted to bridge the 5‐mm defect of a complete transverse lesion in the thoracic spinal cord of rats. Subsequently, effects on nerve regeneration, locomotion function recovery, and early neuroprotection were observed. After 1 year of repair, the integrated scaffold could guide the regeneration of axons appearing in the debris of degraded microchannels, especially serotonin receptor 1A receptor‐positive axonal tracts, which were relatively orderly arranged. Moreover, a network of nerve fibres was present, and a few BMSCs expressed neuronal markers in tubular lumens. Functionally, electrophysiological and locomotor functions of rats were partially recovered. In addition, we found that BMSCs could protect neurons and oligodendrocytes from apoptosis during the early stage of implantation. Taken together, our results demonstrate the potential of this novel integrated scaffold loaded with BMSCs to promote spinal cord regeneration through mechanical guidance and neuroprotective mechanisms.

Regenerative Therapies for Spinal Cord Injury

Spinal cord injury (SCI) is a serious problem that primarily affects younger and middle-aged adults at its onset. To date, no effective regenerative treatment has been developed. Over the last decade, researchers have made significant advances in stem cell technology, biomaterials, nanotechnology, and immune engineering, which may be applied as regenerative therapies for the spinal cord. Although the results of clinical trials using specific cell-based therapies have proven safe, their efficacy has not yet been demonstrated. The pathophysiology of SCI is multifaceted, complex and yet to be fully understood. Thus, combinatorial therapies that simultaneously leverage multiple approaches will likely be required to achieve satisfactory outcomes. Although combinations of biomaterials with pharmacologic agents or cells have been explored, few studies have combined these modalities in a systematic way. For most strategies, clinical translation will be facilitated by the use of minimally invasive therapies, which are the focus of this review. In addition, this review discusses previously explored therapies designed to promote neuroregeneration and neuroprotection after SCI, while highlighting present challenges and future directions. Impact Statement To date there are no effective treatments that can regenerate the spinal cord after injury. Although there have been significant preclinical advances in bioengineering and regenerative medicine over the last decade, these have not translated into effective clinical therapies for spinal cord injury. This review focuses on minimally invasive therapies, providing extensive background as well as updates on recent technological developments and current clinical trials. This review is a comprehensive resource for researchers working towards regenerative therapies for spinal cord injury that will help guide future innovation.

The Emerging Role of lncRNAs in Spinal Cord Injury

Spinal cord injury (SCI) is a highly debilitating disease and is increasingly being recognized as an important global health priority. However, the mechanisms underlying SCI have not yet been fully elucidated, and effective therapies for SCI are lacking. Long noncoding RNAs (lncRNAs), which form a major class of noncoding RNAs, have emerged as novel targets for regulating several physiological functions and mediating numerous neurological diseases. Notably, gene expression profile analyses have demonstrated aberrant changes in lncRNA expression in rats or mice after traumatic or nontraumatic SCI. LncRNAs have been shown to be associated with multiple pathophysiological processes following SCI including inflammation, neural apoptosis, and oxidative stress. They also play a crucial role in the complications associated with SCI, such as neuropathic pain. At the same time, some lncRNAs have been found to be therapeutic targets for neural stem cell transplantation and hydrogen sulfide treatment aimed at alleviating SCI. Therefore, lncRNAs could be promising biomarkers for the diagnosis, treatment, and prognosis of SCI. However, further researches are required to clarify the therapeutic effects of lncRNAs on SCI and the mechanisms underlying these effects. In this study, we reviewed the current progress of the studies on the involvement of lncRNAs in SCI, with the aim of drawing attention towards their roles in this debilitating condition.

Stem cell/cellular interventions in human spinal cord injury: Is it time to move from guidelines to regulations and legislations? Literature review and Spinal Cord Society position statement

PURPOSE

In preclinical studies, many stem cell/cellular interventions demonstrated robust regeneration and/or repair in case of SCI and were considered a promising therapeutic candidate. However, data from clinical studies are not robust. Despite lack of substantial evidence for the efficacy of these interventions in spinal cord injury (SCI), many clinics around the world offer them as "therapy." These "clinics" claim efficacy through patient testimonials and self-advertisement without any scientific evidence to validate their claims. Thus, SCS established a panel of experts to review published preclinical studies, clinical studies and current global guidelines/regulations on usage of cellular transplants and make recommendations for their clinical use.

METHODS

The literature review and draft position statement was compiled and circulated among the panel and relevant suggestions incorporated to reach consensus. This was discussed and finalized in an open forum during the SCS Annual Meeting, ISSICON.

RESULTS

Preclinical evidence suggests safety and clinical potency of cellular interventions after SCI. However, evidence from clinical studies consisted of mostly case reports or uncontrolled case series/studies. Data from animal studies cannot be generalized to human SCI with regard to toxicity prediction after auto/allograft transplantation.

CONCLUSIONS

Currently, cellular/stem cell transplantation for human SCI is experimental and needs to be tested through a valid clinical trial program. It is not ethical to provide unproven transplantation as therapy with commercial implications. To stop the malpractice of marketing such "unproven therapies" to a vulnerable population, it is crucial that all countries unite to form common, well-defined regulations/legislation on their use in SCI. These slides can be retrieved from Electronic Supplementary Material.

Bridging the gap: Spinal cord fusion as a treatment of chronic spinal cord injury

Despite decades of animal experimentation, human translation with cell grafts, conduits, and other strategies has failed to cure patients with chronic spinal cord injury (SCI). Recent data show that motor deficits due to spinal cord transection in animal models can be reversed by local application of fusogens, such as Polyethylene glycol (PEG). Results proved superior at short term over all other treatments deployed in animal studies, opening the way to human trials. In particular, removal of the injured spinal cord segment followed by PEG fusion of the two ends along with vertebral osteotomy to shorten the spine holds the promise for a cure in many cases.

Polysialic-Acid-Based Micelles Promote Neural Regeneration in Spinal Cord Injury Therapy

Spinal cord injury (SCI) routinely causes the immediate loss and disruption of neurons followed by complicated secondary injuries, including inflammation, oxidative stress, and dense glial scar formation. Inhibitory factors in the lesion scar and poor intrinsic neural regeneration capacity restrict functional recovery after injury. Minocycline, which has neuroprotective activity, can alleviate secondary injury, but the long-term administration of this drug may cause toxicity. Polysialic acid (PSA) is a large cell-surface carbohydrate that is critical for central nervous system development and is capable of promoting precursor cell migration, axon path finding, and synaptic remodeling; thus, PSA plays a vital role in tissue repair and regeneration. Here, we developed a PSA-based minocycline-loaded nanodrug delivery system (PSM) for the synergistic therapy of spinal cord injury. The prepared PSM exerted marked anti-inflammatory and neuroprotective activities both in vitro and in vivo. The administration of PSM could significantly protect neurons and myelin sheaths from damage, reduce the formation of glial scar, recruit endogenous neural stem cells to the lesion site, and promote the regeneration of neurons and the extension of long axons throughout the glial scar, thereby largely improving the locomotor function of SCI rats and exerting a superior therapeutic effect. The findings might provide a novel strategy for SCI synergistic therapy and the utilization of PSA in other central nervous system diseases.

Minimally Invasive and Regenerative Therapeutics

Advances in biomaterial synthesis and fabrication, stem cell biology, bioimaging, microsurgery procedures, and microscale technologies have made minimally invasive therapeutics a viable tool in regenerative medicine. Therapeutics, herein defined as cells, biomaterials, biomolecules, and their combinations, can be delivered in a minimally invasive way to regenerate different tissues in the body, such as bone, cartilage, pancreas, cardiac, skeletal muscle, liver, skin, and neural tissues. Sophisticated methods of tracking, sensing, and stimulation of therapeutics in vivo using nano-biomaterials and soft bioelectronic devices provide great opportunities to further develop minimally invasive and regenerative therapeutics (MIRET). In general, minimally invasive delivery methods offer high yield with low risk of complications and reduced costs compared to conventional delivery methods. Here, minimally invasive approaches for delivering regenerative therapeutics into the body are reviewed. The use of MIRET to treat different tissues and organs is described. Although some clinical trials have been performed using MIRET, it is hoped that such therapeutics find wider applications to treat patients. Finally, some future perspective and challenges for this emerging field are highlighted.