Graft of the gelatin sponge scaffold containing genetically-modified neural stem cells promotes cell differentiation, axon regeneration, and functional recovery in rat with spinal cord transection

Stem cell-derived exosomes for traumatic spinal cord injury: a systematic review and network meta-analysis based on a rat model

BACKGROUND AIMS

Exosome therapy for traumatic spinal cord injury (TSCI) is a current research hotspot, but its therapeutic effect and the best source of stem cells for exosomes are unclear.

METHODS

The Web of Science, PubMed, Embase, Cochrane, and Scopus databases were searched from inception to March 28, 2023. Literature screening, data extraction and risk of bias assessment were performed independently by two investigators.

RESULTS

A total of 40 studies were included for data analysis. The findings of our traditional meta-analysis indicate that exosomes derived from stem cells significantly improve the motor function of TSCI at various time points (1 week: weighted mean difference [WMD] = 1.58, 95% confidence interval [CI] 0.87-2.30] 2 weeks: WMD = 3.12, 95% CI 2.64-3.61; 3 weeks: WMD = 4.44, 95% CI 3.27-5.60; 4 weeks: WMD = 4.54, 95% CI 3.42-5.66). Four kinds of stem cell-derived exosomes have been studied: bone marrow mesenchymal stem cells, adipose mesenchymal stem cells, umbilical cord mesenchymal stem cells and neural stem cells. The results of the network meta-analysis showed that there was no significant statistical difference in the therapeutic effect among the exosomes derived from four kinds of stem cells at different treatment time points. Although exosomes derived from bone marrow mesenchymal stem cells are the current research focus, exosomes derived from neural stem cells have the most therapeutic potential and should become the focus of future attention.

CONCLUSIONS

The exosomes derived from stem cells can significantly improve the motor function of TSCI rats, and the exosomes derived from neural stem cells have the most therapeutic potential. However, the lower evidence quality of animal studies limits the reliability of experimental results, emphasizing the need for more high-quality, direct comparative studies to explore the therapeutic efficacy of exosomes and the best source of stem cells.

The potential of gene therapies for spinal cord injury repair: a systematic review and meta-analysis of pre-clinical studies

Currently, there is no cure for traumatic spinal cord injury but one therapeutic approach showing promise is gene therapy. In this systematic review and meta-analysis, we aim to assess the efficacy of gene therapies in pre-clinical models of spinal cord injury and the risk of bias. In this meta-analysis, registered at PROSPERO (Registration ID: CRD42020185008), we identified relevant controlled in vivo studies published in English by searching the PubMed, Web of Science, and Embase databases. No restrictions of the year of publication were applied and the last literature search was conducted on August 3, 2020. We then conducted a random-effects meta-analysis using the restricted maximum likelihood estimator. A total of 71 studies met our inclusion criteria and were included in the systematic review. Our results showed that overall, gene therapies were associated with improvements in locomotor score (standardized mean difference [SMD]: 2.07, 95% confidence interval [CI]:1.68–2.47, Tau² = 2.13, I² = 83.6%) and axonal regrowth (SMD: 2.78, 95%CI: 1.92–3.65, Tau² = 4.13, I² = 85.5%). There was significant asymmetry in the funnel plots of both outcome measures indicating the presence of publication bias. We used a modified CAMARADES (Collaborative Approach to Meta-Analysis and Review of Animal Data in Experimental Studies) checklist to assess the risk of bias, finding that the median score was 4 (IQR:3–5). In particular, reports of allocation concealment and sample size calculations were lacking. In conclusion, gene therapies are showing promise as therapies for spinal cord injury repair, but there is no consensus on which gene or genes should be targeted.

Development of Gelatin-Coated Hydrogel Microspheres for Novel Bioink Design: A Crosslinker Study

The development of vascularized tissue is a substantial challenge within the field of tissue engineering and regenerative medicine. Studies have shown that positively-charged microspheres exhibit dual-functions: (1) facilitation of vascularization and (2) controlled release of bioactive compounds. In this study, gelatin-coated microspheres were produced and processed with either EDC or transglutaminase, two crosslinkers. The results indicated that the processing stages did not significantly impact the size of the microspheres. EDC and transglutaminase had different effects on surface morphology and microsphere stability in a simulated colonic environment. Incorporation of EGM and TGM into bioink did not negatively impact bioprintability (as indicated by density and kinematic viscosity), and the microspheres had a uniform distribution within the scaffold. These microspheres show great potential for tissue engineering applications.

Electroactive Scaffolds to Improve Neural Stem Cell Therapy for Spinal Cord Injury

Spinal cord injury (SCI) is a serious condition caused by damage to the spinal cord through trauma or disease, often with permanent debilitating effects. Globally, the prevalence of SCI is estimated between 40 to 80 cases per million people per year. Patients with SCI can experience devastating health and socioeconomic consequences from paralysis, which is a loss of motor, sensory and autonomic nerve function below the level of the injury that often accompanies SCI. SCI carries a high mortality and increased risk of premature death due to secondary complications. The health, social and economic consequences of SCI are significant, and therefore elucidation of the complex molecular processes that occur in SCI and development of novel effective treatments is critical. Despite advances in medicine for the SCI patient such as surgery and anaesthesiology, imaging, rehabilitation and drug discovery, there have been no definitive findings toward complete functional neurologic recovery. However, the advent of neural stem cell therapy and the engineering of functionalized biomaterials to facilitate cell transplantation and promote regeneration of damaged spinal cord tissue presents a potential avenue to advance SCI research. This review will explore this emerging field and identify new lines of research.

Novel nanofibrous membrane-supporting stem cell sheets for plasmid delivery and cell activation to accelerate wound healing

The integration of biomaterials with cells for high overall performances is vitally important in tissue engineering, as scaffold-free cell sheet lacks enough mechanical performance and cell viability while cell-free scaffold possesses limited biological functions. In this study, we propose a new strategy to strengthen cell sheets and enhance cell activity for accelerating wound healing based on a novel sandwich structure of cell sheet-plasmid@membrane-cell sheet (CpMC). Specifically, the CpMC contains two adipose-derived stem cell (ADSC) sheets on outer surfaces and an electrospun gelatin/chitosan nanofibrous membrane (NFM) encapsulating vascular endothelial growth factor (VEGF) plasmids in between. The physicochemical properties of NFM including swelling, stiffness, strength, elasticity, and biodegradation can be tailored by simply adjusting the ratio between gelatin and chitosan to be 7:3 which is optimal for most effectively supporting ADSCs adhesion and proliferation. The swelling/biodegradation of NFM mediates the sustained release of encapsulated VEGF plasmids into adjacent ADSCs, and NFM assists VEGF plasmids to promote the differentiation of ADSCs into endothelial, epidermal, and fibroblast cells, in support of the neoangiogenesis and regeneration of cutaneous tissues within 2 weeks. The proposed membrane-supporting cell sheet strategy provides a new route to tissue engineering, and the developed CpMC demonstrates a high potential for clinical translation.

Developing a mechanically matched decellularized spinal cord scaffold for the in situ matrix-based neural repair of spinal cord injury

Tissue engineering is a promising strategy to repair spinal cord injury (SCI). However, a bioscaffold with mechanical properties that match those of the pathological spinal cord tissue and a pro-regenerative matrix that allows robust neurogenesis for overcoming post-SCI scar formation has yet to be developed. Here, we report that a mechanically enhanced decellularized spinal cord (DSC) scaffold with a thin poly (lactic-co-glycolic acid) (PLGA) outer shell may fulfill the requirements for effective in situ neuroengineering after SCI. Using chemical extraction and electrospinning methods, we successfully constructed PLGA thin shell-ensheathed DSC scaffolds (PLGA-DSC scaffolds) in a way that removed major inhibitory components while preserving the permissive matrix. The DSCs exhibited good cytocompatibility with neural stem cells (NSCs) and significantly enhanced their differentiation toward neurons in vitro. Due to the mechanical reinforcement, the implanted PLGA-DSC scaffolds showed markedly increased resilience to infiltration by myofibroblasts and the deposition of dense collagen matrix, thereby creating a neurogenic niche favorable for the targeted migration, residence and neuronal differentiation of endogenous NSCs after SCI. Furthermore, PLGA-DSC presented a mild immunogenic property but prominent ability to polarize macrophages from the M1 phenotype to the M2 phenotype, leading to significant tissue regeneration and functional restoration after SCI. Taken together, the results demonstrate that the mechanically matched PLGA-DSC scaffolds show promise for effective tissue repair after SCI.

Mash-1 modified neural stem cells transplantation promotes neural stem cells differentiation into neurons to further improve locomotor functional recovery in spinal cord injury rats

BACKGROUND

Spinal cord injury (SCI) leads to severe motor and sensory dysfunctions. Neural stem cells (NSCs) transplantation therapy plays a positive role in functional recovery after SCI, but the effectiveness of this therapy is limited by inadequate differentiation ability of transplanted NSCs. Mammalian achaete-scute homologue-1 (Mash-1) has been reported to improve differentiation of NSCs. Thus, this study modified NSCs with Mash-1 to repair SCI.

METHODS

NSCs isolated from rat embryo hippocampus were cultured and identified in vitro and further transfected with the lentiviral vectors (Lv-Mash-1). After establishing a SCI rat model, the rats were transplanted with Mash-1 modified NSCs, the histopathological changes of rat spinal cord were detected by hematoxylin-eosin (HE) staining, and the locomotor activity of rats was evaluated with the Basso, Beattie and Bresnahan (BBB) scale. The NSCs cultured in vitro or extracted from SCI rat spinal cord were identified by immunofluorescence (IF). Mash-1, β3-Tubulin, and NeuN expressions in those cells were determined by Western blotting and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR).

RESULTS

NSCs isolated from rat embryo hippocampus were Nestin- and NeuN-positive. NSC transplantation modified by Mash-1 increased BBB score of SCI rats and promoted recovery in lesion site of SCI rats. Mash-1 overexpression also promoted β3-Tubulin and NeuN expressions in NSCs cultured in vitro or extracted from spinal cord of SCI rats.

CONCLUSION

Mash-1 overexpression promoted NSC differentiation into neurons, and further improved locomotor functional recovery of SCI rats.

Signatures of altered DNA methylation gene expression after central and peripheral nerve injury

Nerve damage can lead to movement and sensory dysfunction, with high morbidity and disability rates causing severe burdens on patients, families, and society. DNA methylation is a kind of epigenetics, and a great number of previous studies have demonstrated that DNA methylation plays an important role in the process of nerve regeneration and remodeling. However, compared with the central nervous system, the peripheral nervous system shows stronger recovery after injury, which is related to the complex microenvironment and epigenetic changes occurring at the site of injury. Therefore, what common epigenetic changes between the central and peripheral nervous systems remain to be elucidated. We first screened differential methylation genes after spinal cord injury and sciatic nerve injury using whole-genome bisulfite sequencing and methylated DNA immunoprecipitation sequencing, respectively. Subsequently, a total of 16 genes had the same epigenetic changes after spinal cord injury and sciatic nerve injury. The Gene Ontology analysis and Kyoto Encyclopedia of Genes and Genomes enrichment analysis were performed to identify the critical biological processes and pathways. Furthermore, a protein-protein interaction network analysis indicated that Dnm3, Ntrk3, Smurf1, Dpysl2, Kalrn, Shank1, Dlg2, Arsb, Reln, Bmp5, Numbl, Prickle2, Map6, and Htr7 were the core genes. These outcomes may provide novel insights into the molecular mechanism of the subacute phase of nerve injury. These verified genes can offer potential diagnostic and therapeutic targets for nerve injury.

Neural Stem Cell Transplantation Improves Locomotor Function in Spinal Cord Transection Rats Associated with Nerve Regeneration and IGF-1 R Expression

Transplantation of neural stem cells (NSCs) is a potential strategy for the treatment of spinal cord transection (SCT). Here we investigated whether transplanted NSCs would improve motor function of rats with SCT and explored the underlying mechanism. First, the rats were divided into sham, SCT, and NSC groups. Rats in the SCT and NSC groups were all subjected to SCT in T10, and were administered with media and NSC transplantation into the lesion site, respectively. Immunohistochemistry was used to label Nestin-, TUNEL-, and NeuN-positive cells and reveal the expression and location of type I insulin-like growth factor receptor (IGF-1 R). Locomotor function of hind limbs was assessed by Basso, Beattie, Bresnahan (BBB) score and inclined plane test. The conduction velocity and amplitude of spinal nerve fibers were measured by electrophysiology and the anatomical changes were measured using magnetic resonance imaging. Moreover, expression of IGF-1 R was determined by real-time polymerase chain reaction and Western blotting. The results showed that NSCs could survive and differentiate into neurons in vitro and in vivo. SCT-induced deficits were reduced by NSC transplantation, including increase in NeuN-positive cells and decrease in apoptotic cells. Moreover, neurophysiological profiles indicated that the latent period was decreased and the peak-to-peak amplitude of spinal nerve fibers conduction was increased in transplanted rats, while morphological measures indicated that fractional anisotropy and the number of nerve fibers in the site of spinal cord injury were increased after NSC transplantation. In addition, mRNA and protein level of IGF-1 R were increased in the rostral segment in the NSC group, especially in neurons. Therefore, we concluded that NSC transplantation promotes motor function improvement of SCT, which might be associated with activated IGF-1 R, especially in the rostral site. All of the above suggests that this approach has potential for clinical treatment of spinal cord injury.

Biomaterials and Gene Manipulation in Stem Cell-Based Therapies for Spinal Cord Injury

Spinal cord injury (SCI), a prominent health issue, represents a substantial portion of the global health care burden. Stem cell-based therapies provide novel solutions for SCI treatment, yet obstacles remain in the form of low survival rate, uncontrolled differentiation, and functional recovery. The application of engineered biomaterials in stem cell therapy provides a physicochemical microenvironment that mimics the stem cell niche, facilitating self-renewal, stem cell differentiation, and tissue reorganization. Nonetheless, external microenvironment support is inadequate, and some obstacles persist, for example, limited sources, gradual aging, and immunogenicity of stem cells. Targeted stem cell gene manipulation could eliminate many of these drawbacks, allowing safer, more effective use under regulation of intrinsic mechanisms. Additionally, through genetic labeling of stem cells, their role in tissue engineering may be elucidated. Therefore, combining stem cell therapy, materials science, and genetic modification technologies may shed light on SCI treatment. Herein, recent advances and advantages of biomaterials and gene manipulation, especially with respect to stem cell-based therapies, are highlighted, and their joint performance in SCI is evaluated. Current technological limitations and perspectives on future directions are then discussed. Although this combination is still in the early stages of development, it is highly likely to substantially contribute to stem cell-based therapies in the foreseeable future.

Abnormal DNA Methylation in Thoracic Spinal Cord Tissue Following Transection Injury

Background

Spinal cord injury (SCI) is a serious disease with high disability and mortality rates, with no effective therapeutic strategies available. In SCI, abnormal DNA methylation is considered to be associated with axonal regeneration and cell proliferation. However, the roles of key genes in potential molecular mechanisms of SCI are not clear.

Material/Methods

Subacute spinal cord injury models were established in Wistar rats. Histological observations and motor function assessments were performed separately. Whole-genome bisulfite sequencing (WGBS) was used to detect the methylation of genes. Gene ontology (GO) term enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were performed using the DAVID database. Protein–protein interaction (PPI) networks were analyzed by Cytoscape software.

Results

After SCI, many cavities, areas of necrotic tissue, and many inflammatory cells were observed, and motor function scores were low. After the whole-genome bisulfite sequencing, approximately 96 DMGs were screened, of which 50 were hypermethylated genes and 46 were hypomethylated genes. KEGG pathway analysis highlighted the Axon Guidance pathway, Endocytosis pathway, T cell receptor signaling pathway, and Hippo signaling pathway. Expression patterns of hypermethylated genes and hypomethylated genes detected by qRT-PCR were the opposite of WGBS data, and the difference was significant.

Conclusions

Abnormal methylated genes and key signaling pathways involved in spinal cord injury were identified through histological observation, behavioral assessment, and bioinformatics analysis. This research can serve as a source of additional information to expand understanding of spinal cord-induced epigenetic changes.

Stem cell transplantation and functional recovery after spinal cord injury: a systematic review and meta-analysis

Spinal cord injury is a significant cause of motor dysfunctions. There is no definite cure for it, and most of the therapeutic modalities are only symptomatic treatment. In this systematic review and meta-analysis, the effectiveness of stem cell therapy in the treatment of the spinal cord injuries in animal models was studied and evaluated. A systematic search through medical databases by using appropriate keywords was conducted. The relevant reports were reviewed in order to find out cases in which inclusion and exclusion criteria had been fulfilled. Finally, 89 articles have been considered, from which 28 had sufficient data for performing statistical analyses. The findings showed a significant improvement in motor functions after cell therapy. The outcome was strongly related to the number of transplanted cells, site of injury, chronicity of the injury, type of the damage, and the induction of immune-suppression. According to our data, improvements in functional recovery after stem cell therapy in the treatment of spinal cord injury in animal models was noticeable, but its outcome is strongly related to the site of injury, number of transplanted cells, and type of transplanted cells.

Biomaterial Scaffolds in Regenerative Therapy of the Central Nervous System

The central nervous system (CNS) is the most important section of the nervous system as it regulates the function of various organs. Injury to the CNS causes impairment of neurological functions in corresponding sites and further leads to long-term patient disability. CNS regeneration is difficult because of its poor response to treatment and, to date, no effective therapies have been found to rectify CNS injuries. Biomaterial scaffolds have been applied with promising results in regeneration medicine. They also show great potential in CNS regeneration for tissue repair and functional recovery. Biomaterial scaffolds are applied in CNS regeneration predominantly as hydrogels and biodegradable scaffolds. They can act as cellular supportive scaffolds to facilitate cell infiltration and proliferation. They can also be combined with cell therapy to repair CNS injury. This review discusses the categories and progression of the biomaterial scaffolds that are applied in CNS regeneration.

Assessment of the characteristics and biocompatibility of gelatin sponge scaffolds prepared by various crosslinking methods

This comparative study aims to identify a biocompatible and effective crosslinker for preparing gelatin sponges. Glutaraldehyde (GTA), genipin (GP), 1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide (EDC), and microbial transglutaminase (mTG) were used as crosslinking agents. The physical properties of the prepared samples were characterized, and material degradation was studied in vitro with various proteases and in vivo through subcutaneous implantation of the sponges in rats. Adipose-derived stromal stem cells (ADSCs) were cultured and inoculated onto the scaffolds to compare the cellular biocompatibility of the sponges. Cellular seeding efficiency and digestion time of the sponges were also evaluated. Cellular viability and proliferation in scaffolds were analyzed by fluorescence staining and MTT assay. All the samples exhibited high porosity, good swelling ratio, and hydrolysis properties; however, material strength, hydrolysis, and enzymolytic properties varied among the samples. GTA–sponge and GP–sponge possessed high compressive moduli, and EDC–sponge exhibited fast degradation performance. GTA and GP sponge implants exerted strong in vivo rejections, and the former showed poor cell growth. mTG–sponge exhibited the optimal comprehensive performance, with good porosity, compressive modulus, anti-degradation ability, and good biocompatibility. Hence, mTG–sponge can be used as a scaffold material for tissue engineering applications.

3D scaffolds for brain tissue regeneration: architectural challenges

Critical analysis of experimental studies on 3D scaffolds for brain tissue engineering.

Therapeutic Effect of Curcumin and Methylprednisolone in the Rat Spinal Cord Injury

In addition to imperiling an individual's daily life, spinal cord injury (SCI), a catastrophic medical damage, can permanently impair an individual's body function. Methylprednisolone (MP), a medically accepted therapeutic drug for SCI, is highly controversial for the lack of consensus on its true therapeutic effect. In recent years, curcumin has served as a potential and novel therapeutic drug in SCI. Our study was intended to investigate the precise effect of MP and curcumin in SCI. We examined the function of MP and curcumin in a SCI model rat, both in vivo and in vitro, and found that there was a momentous improvement in Basso-Beattie-Bresnahan scores in the MP-treated group when compared with Cur-treated group within 14 days. Results obtained from the histological, immunohistochemistry and ultrastructural examinations evidenced the curative effect of MP was better than curcumin before Day 14. Nonetheless, there was a significant variation in the treatment effect between the MP-treated and Cur-treated groups after 14 days. The curcumin's effectiveness was more obvious than MP after 14 days following SCI. As such, we surmise that curcumin has a better therapeutic potential than MP with a prolong treatment time in the wake of SCI. Anat Rec, 301:686-696, 2018. © 2017 Wiley Periodicals, Inc.

Current progress in the derivation and therapeutic application of neural stem cells

Neural stem cells (NSCs) have a unique role in neural regeneration. Cell therapy based on NSC transplantation is a promising tool for the treatment of nervous system diseases. However, there are still many issues and controversies associated with the derivation and therapeutic application of these cells. In this review, we summarize the different sources of NSCs and their derivation methods, including direct isolation from primary tissues, differentiation from pluripotent stem cells and transdifferentiation from somatic cells. We also review the current progress in NSC implantation for the treatment of various neural defects and injuries in animal models and clinical trials. Finally, we discuss potential optimization strategies for NSC derivation and propose urgent challenges to the clinical translation of NSC-based therapies in the near future.

Human placenta-derived mesenchymal stem cells loaded on linear ordered collagen scaffold improves functional recovery after completely transected spinal cord injury in canine

Traumatic spinal cord injury (SCI) is a major challenge in the clinic. In this study, we sought to examine the synergistic effects of linear ordered collagen scaffold (LOCS) and human placenta-derived mesenchymal stem cells (hPMSCs) when transplanted into completely transected beagle dogs. After 36 weeks observation, we found that LOCS+hPMSCs implants promoted better hindlimb locomotor recovery than was observed in the non-treatment (control) group and LOCS group. Histological analysis showed that the regenerated tissue after treatment was well integrated with the host tissue, and dramatically reduced the volume of cystic and chondroitin sulfate proteoglycans (CSPGs) expression. Furthermore, the LOCS+hPMSCs group also showed more neuron-specific βIII-tubulin (Tuj-1)- and NeuN-positive neurons in the lesion area, as well as axonal regeneration, remyelination and synapse formation in the lesion site. Additionally, dogs in the LOCS+hPMSCs group experienced enhanced sprouting of both ascending (CGRP-positive) sensory fibers and descending (5-HT- and TH-positive) motor fibers at the lesion area. All these data together suggested that the combined treatment had beneficial effects on neuronal regeneration and functional improvement in a canine complete transection model. Therefore, LOCS+hPMSCs implantation holds a great promise for bridging the nerve defect and may be clinically useful in the near future.

Biocompatibility of reduced graphene oxide nanoscaffolds following acute spinal cord injury in rats

Background:

Graphene has unique electrical, physical, and chemical properties that may have great potential as a bioscaffold for neuronal regeneration after spinal cord injury. These nanoscaffolds have previously been shown to be biocompatible in vitro; in the present study, we wished to evaluate its biocompatibility in an in vivo spinal cord injury model.

Methods:

Graphene nanoscaffolds were prepared by the mild chemical reduction of graphene oxide. Twenty Wistar rats (19 male and 1 female) underwent hemispinal cord transection at approximately the T2 level. To bridge the lesion, graphene nanoscaffolds with a hydrogel were implanted immediately after spinal cord transection. Control animals were treated with hydrogel matrix alone. Histologic evaluation was performed 3 months after the spinal cord transection to assess in vivo biocompatibility of graphene and to measure the ingrowth of tissue elements adjacent to the graphene nanoscaffold.

Results:

The graphene nanoscaffolds adhered well to the spinal cord tissue. There was no area of pseudocyst around the scaffolds suggestive of cytotoxicity. Instead, histological evaluation showed an ingrowth of connective tissue elements, blood vessels, neurofilaments, and Schwann cells around the graphene nanoscaffolds.

Conclusions:

Graphene is a nanomaterial that is biocompatible with neurons and may have significant biomedical application. It may provide a scaffold for the ingrowth of regenerating axons after spinal cord injury.

Increased Understanding of Stem Cell Behavior in Neurodegenerative and Neuromuscular Disorders by Use of Noninvasive Cell Imaging

Numerous neurodegenerative and neuromuscular disorders are associated with cell-specific depletion in the human body. This imbalance in tissue homeostasis is in healthy individuals repaired by the presence of endogenous stem cells that can replace the lost cell type. However, in most disorders, a genetic origin or limited presence or exhaustion of stem cells impairs correct cell replacement. During the last 30 years, methods to readily isolate and expand stem cells have been developed and this resulted in a major change in the regenerative medicine field as it generates sufficient amount of cells for human transplantation applications. Furthermore, stem cells have been shown to release cytokines with beneficial effects for several diseases. At present however, clinical stem cell transplantations studies are struggling to demonstrate clinical efficacy despite promising preclinical results. Therefore, to allow stem cell therapy to achieve its full potential, more insight in their in vivo behavior has to be achieved. Different methods to noninvasively monitor these cells have been developed and are discussed. In some cases, stem cell monitoring even reached the clinical setting. We anticipate that by further exploring these imaging possibilities and unraveling their in vivo behavior further improvement in stem cell transplantations will be achieved.

Intrinsic and extrinsic determinants of central nervous system axon outgrowth into alginate-based anisotropic hydrogels

Appropriate target reinnervation and functional recovery after spinal cord injury depend on longitudinally directed regrowth of injured axons. Anisotropic alginate-based capillary hydrogels (ACH) support peripheral nervous system derived axon growth, which is accompanied by glial supporting cell migration into the ACH. The aim of the present study was to analyze central nervous system (CNS) derived (entorhinal cortex, spinal cord slice cultures) axon regrowth into ACH containing linearly aligned capillaries of defined capillary sizes without and with gelatin constituent. Anisotropic ACH were prepared by ionotropic gel formation using Ba(2+), Cu(2+), Sr(2+), or Zn(2+) ions resulting in gels with average capillary diameters of 11, 13, 29, and 89μm, respectively. Postnatal rat entorhinal cortex or spinal cord slice cultures were placed on top of 500μm thick ACH. Seven days later axon growth and astroglial migration into the ACH were determined. Axon density within capillaries correlated positively with increasing capillary diameters, whereas longitudinally oriented axon outgrowth diminished with increasing capillary diameter. Axons growing into the hydrogels were always accompanied by astrocytes strongly suggesting that respective cells are required to mediate CNS axon elongation into ACH. Overall, midsize capillary diameter ACH appeared to be the best compromise between axon density and orientation. Taken together, ACH promote CNS axon ingrowth, which is determined by the capillary diameter and migration of slice culture derived astroglia into the hydrogel.

STATEMENT OF SIGNIFICANCE

Biomaterials are investigated as therapeutic tools to bridge irreversible lesions following traumatic spinal cord injury. The goal is to develop biomaterials, which promote longitudinally oriented regeneration of as many injured axons as possible as prerequisite for substantial functional recovery. Optimal parameters of the biomaterial have yet to be defined. In the present study we show that increasing capillary diameters within such hydrogels enhanced central nervous system axon regeneration at the expense of longitudinal orientation. Axon ingrowth into the hydrogels was only observed in the presence of glial supporting cells, namely astrocytes. This suggests that alginate-based hydrogels need to be colonized with respective cells in order to facilitate axon ingrowth.

Cell Therapy Augments Functional Recovery Subsequent to Spinal Cord Injury under Experimental Conditions

The spinal cord injury leads to enervation of normal tissue homeostasis ultimately leading to paralysis. Until now there is no proper cure for the treatment of spinal cord injury. Recently, cell therapy in animal spinal cord injury models has shown some progress of recovery. At present, clinical trials are under progress to evaluate the efficacy of cell transplantation for the treatment of spinal cord injury. Different types of cells such as pluripotent stem cells derived neural cells, mesenchymal stromal cells, neural stem cells, glial cells are being tested in various spinal cord injury models. In this review we highlight both the advances and lacuna in the field of spinal cord injury by discussing epidemiology, pathophysiology, molecular mechanism, and various cell therapy strategies employed in preclinical and clinical injury models and finally we discuss the limitations and ethical issues involved in cell therapy approach for treating spinal cord injury.

Mild hypothermia combined with a scaffold of NgR-silenced neural stem cells/Schwann cells to treat spinal cord injury

Because the inhibition of Nogo proteins can promote neurite growth and nerve cell differentiation, a cell-scaffold complex seeded with Nogo receptor (NgR)-silenced neural stem cells and Schwann cells may be able to improve the microenvironment for spinal cord injury repair. Previous studies have found that mild hypothermia helps to attenuate secondary damage in the spinal cord and exerts a neuroprotective effect. Here, we constructed a cell-scaffold complex consisting of a poly(D,L-lactide-co-glycolic acid) (PLGA) scaffold seeded with NgR-silenced neural stem cells and Schwann cells, and determined the effects of mild hypothermia combined with the cell-scaffold complexes on the spinal cord hemi-transection injury in the T₉ segment in rats. Compared with the PLGA group and the NgR-silencing cells + PLGA group, hindlimb motor function and nerve electrophysiological function were clearly improved, pathological changes in the injured spinal cord were attenuated, and the number of surviving cells and nerve fibers were increased in the group treated with the NgR-silenced cell scaffold + mild hypothermia at 34°C for 6 hours. Furthermore, fewer pathological changes to the injured spinal cord and more surviving cells and nerve fibers were found after mild hypothermia therapy than in injuries not treated with mild hypothermia. These experimental results indicate that mild hypothermia combined with NgR gene-silenced cells in a PLGA scaffold may be an effective therapy for treating spinal cord injury.