Transduced Schwann cells promote axon growth and myelination after spinal cord injury

Schwann Cell-Derived Exosomal Vesicles: A Promising Therapy for the Injured Spinal Cord

Exosomes are nanoscale-sized membrane vesicles released by cells into their extracellular milieu. Within these nanovesicles reside a multitude of bioactive molecules, which orchestrate essential biological processes, including cell differentiation, proliferation, and survival, in the recipient cells. These bioactive properties of exosomes render them a promising choice for therapeutic use in the realm of tissue regeneration and repair. Exosomes possess notable positive attributes, including a high bioavailability, inherent safety, and stability, as well as the capacity to be functionalized so that drugs or biological agents can be encapsulated within them or to have their surface modified with ligands and receptors to imbue them with selective cell or tissue targeting. Remarkably, their small size and capacity for receptor-mediated transcytosis enable exosomes to cross the blood-brain barrier (BBB) and access the central nervous system (CNS). Unlike cell-based therapies, exosomes present fewer ethical constraints in their collection and direct use as a therapeutic approach in the human body. These advantageous qualities underscore the vast potential of exosomes as a treatment option for neurological injuries and diseases, setting them apart from other cell-based biological agents. Considering the therapeutic potential of exosomes, the current review seeks to specifically examine an area of investigation that encompasses the development of Schwann cell (SC)-derived exosomal vesicles (SCEVs) as an approach to spinal cord injury (SCI) protection and repair. SCs, the myelinating glia of the peripheral nervous system, have a long history of demonstrated benefit in repair of the injured spinal cord and peripheral nerves when transplanted, including their recent advancement to clinical investigations for feasibility and safety in humans. This review delves into the potential of utilizing SCEVs as a therapy for SCI, explores promising engineering strategies to customize SCEVs for specific actions, and examines how SCEVs may offer unique clinical advantages over SC transplantation for repair of the injured spinal cord.

Temporary induction of hypoxic adaptations by preconditioning fails to enhance Schwann cell transplant survival after spinal cord injury

Hypoxic preconditioning is protective in multiple models of injury and disease, but whether it is beneficial for cells transplanted into sites of spinal cord injury (SCI) is largely unexplored. In this study, we analyzed whether hypoxia-related preconditioning protected Schwann cells (SCs) transplanted into the contused thoracic rat spinal cord. Hypoxic preconditioning was induced in SCs prior to transplantation by exposure to either low oxygen (1% O₂ ) or pharmacological agents (deferoxamine or adaptaquin). All preconditioning approaches induced hypoxic adaptations, including increased expression of HIF-1α and its target genes. These adaptations, however, were transient and resolved within 24 h of transplantation. Pharmacological preconditioning attenuated spinal cord oxidative stress and enhanced transplant vascularization, but it did not improve either transplanted cell survival or recovery of sensory or motor function. Together, these experiments show that hypoxia-related preconditioning is ineffective at augmenting either cell survival or the functional outcomes of SC-SCI transplants. They also reveal that the benefits of hypoxia-related adaptations induced by preconditioning for cell transplant therapies are not universal.

Recombinant Adenoviruses for Delivery of Therapeutics Following Spinal Cord Injury

The regeneration of nerve tissue after spinal cord injury is a complex and poorly understood process. Medication and surgery are not very effective treatments for patients with spinal cord injuries. Gene therapy is a popular approach for the treatment of such patients. The delivery of therapeutic genes is carried out in a variety of ways, such as direct injection of therapeutic vectors at the site of injury, retrograde delivery of vectors, and ex vivo therapy using various cells. Recombinant adenoviruses are often used as vectors for gene transfer. This review discusses the advantages, limitations and prospects of adenovectors in spinal cord injury therapy.

Elucidating the Pivotal Neuroimmunomodulation of Stem Cells in Spinal Cord Injury Repair

Spinal cord injury (SCI) is a distressing incident with abrupt onset of the motor as well as sensory dysfunction, and most often, the injury occurs as result of high-energy or velocity accidents as well as contact sports and falls in the elderly. The key challenges associated with nerve repair are the lack of self-repair as well as neurotrophic factors and primary and secondary neuronal apoptosis, as well as factors that prevent the regeneration of axons locally. Neurons that survive the initial traumatic damage may be lost due to pathogenic activities like neuroinflammation and apoptosis. Implanted stem cells are capable of differentiating into neural cells that replace injured cells as well as offer local neurotrophic factors that aid neuroprotection, immunomodulation, axonal sprouting, axonal regeneration, and remyelination. At the microenvironment of SCI, stem cells are capable of producing growth factors like brain-derived neurotrophic factor and nerve growth factor which triggers neuronal survival as well as axonal regrowth. Although stem cells have proven to be of therapeutic value in SCI, the major disadvantage of some of the cell types is the risk for tumorigenicity due to the contamination of undifferentiated cells prior to transplantation. Local administration of stem cells via either direct cellular injection into the spinal cord parenchyma or intrathecal administration into the subarachnoid space is currently the best transplantation modality for stem cells during SCI.

Ghrelin peptide improves glial conditioned medium effects on neuronal differentiation of human adipose mesenchymal stem cells

The influences of ghrelin on neural differentiation of adipose-derived mesenchymal stem cells (ASCs) were investigated in this study. The expression of typical neuronal markers, such as protein gene product 9.5 (PGP9.5) and Microtubule Associated Protein 2 (MAP2), as well as glial Fibrillary Acid Protein (GFAP) as a glial marker was evaluated in ASCs in different conditions. In particular, 2 µM ghrelin was added to control ASCs and to ASCs undergoing neural differentiation. For this purpose, ASCs were cultured in Conditioned Media obtained from Olfactory Ensheathing cells (OEC-CM) or from Schwann cells (SC-CM). Data on marker expression were gathered after 1 and 7 days of culture by fluorescence immunocytochemistry and flow cytometry. Results show that only weak effects were induced by the addition of only ghrelin. Instead, dynamic ghrelin-induced modifications were detected on the increased marker expression elicited by glial conditioned media. In fact, the combination of ghrelin and conditioned media consistently induced a further increase of PGP9.5 and MAP2 expression, especially after 7 days of treatment. The combination of ghrelin with SC-CM produced the most evident effects. Weak or no modifications were found on conditioned medium-induced GFAP increases. Observations on the ghrelin receptor indicate that its expression in control ASCs, virtually unchanged by the addition of only ghrelin, was considerably increased by CM treatment. These increases were enhanced by combining ghrelin and CM treatment, especially at 7 days. Overall, it can be assumed that ghrelin favors a neuronal rather than a glial ASC differentiation.

Schwann cell remyelination of the central nervous system: why does it happen and what are the benefits?

Myelin sheaths, by supporting axonal integrity and allowing rapid saltatory impulse conduction, are of fundamental importance for neuronal function. In response to demyelinating injuries in the central nervous system (CNS), oligodendrocyte progenitor cells (OPCs) migrate to the lesion area, proliferate and differentiate into new oligodendrocytes that make new myelin sheaths. This process is termed remyelination. Under specific conditions, demyelinated axons in the CNS can also be remyelinated by Schwann cells (SCs), the myelinating cell of the peripheral nervous system. OPCs can be a major source of these CNS-resident SCs-a surprising finding given the distinct embryonic origins, and physiological compartmentalization of the peripheral and central nervous system. Although the mechanisms and cues governing OPC-to-SC differentiation remain largely undiscovered, it might nevertheless be an attractive target for promoting endogenous remyelination. This article will (i) review current knowledge on the origins of SCs in the CNS, with a particular focus on OPC to SC differentiation, (ii) discuss the necessary criteria for SC myelination in the CNS and (iii) highlight the potential of using SCs for myelin regeneration in the CNS.

Schwann Cell-Like Cells: Origin and Usability for Repair and Regeneration of the Peripheral and Central Nervous System

Functional recovery after neurotmesis, a complete transection of the nerve fiber, is often poor and requires a surgical procedure. Especially for longer gaps (>3 mm), end-to-end suturing of the proximal to the distal part is not possible, thus requiring nerve graft implantation. Artificial nerve grafts, i.e., hollow fibers, hydrogels, chitosan, collagen conduits, and decellularized scaffolds hold promise provided that these structures are populated with Schwann cells (SC) that are widely accepted to promote peripheral and spinal cord regeneration. However, these cells must be collected from the healthy peripheral nerves, resulting in significant time delay for treatment and undesired morbidities for the donors. Therefore, there is a clear need to explore the viable source of cells with a regenerative potential similar to SC. For this, we analyzed the literature for the generation of Schwann cell-like cells (SCLC) from stem cells of different origins (i.e., mesenchymal stem cells, pluripotent stem cells, and genetically programmed somatic cells) and compared their biological performance to promote axonal regeneration. Thus, the present review accounts for current developments in the field of SCLC differentiation, their applications in peripheral and central nervous system injury, and provides insights for future strategies.

Secretion of a mammalian chondroitinase ABC aids glial integration at PNS/CNS boundaries

Schwann cell grafts support axonal growth following spinal cord injury, but a boundary forms between the implanted cells and host astrocytes. Axons are reluctant to exit the graft tissue in large part due to the surrounding inhibitory environment containing chondroitin sulphate proteoglycans (CSPGs). We use a lentiviral chondroitinase ABC, capable of being secreted from mammalian cells (mChABC), to examine the repercussions of CSPG digestion upon Schwann cell behaviour in vitro. We show that mChABC transduced Schwann cells robustly secrete substantial quantities of the enzyme causing large-scale CSPG digestion, facilitating the migration and adhesion of Schwann cells on inhibitory aggrecan and astrocytic substrates. Importantly, we show that secretion of the engineered enzyme can aid the intermingling of cells at the Schwann cell-astrocyte boundary, enabling growth of neurites over the putative graft/host interface. These data were echoed in vivo. This study demonstrates the profound effect of the enzyme on cellular motility, growth and migration. This provides a cellular mechanism for mChABC induced functional and behavioural recovery shown in in vivo studies. Importantly, we provide in vitro evidence that mChABC gene therapy is equally or more effective at producing these effects as a one-time application of commercially available ChABC.

Hypoxia-Inducible Factor 1α (HIF-1α) Counteracts the Acute Death of Cells Transplanted into the Injured Spinal Cord

Cellular transplantation is in clinical testing for a number of central nervous system disorders, including spinal cord injury (SCI). One challenge is acute transplanted cell death. To prevent this death, there is a need to both establish when the death occurs and develop approaches to mitigate its effects. Here, using luciferase (luc) and green fluorescent protein (GFP) expressing Schwann cell (SC) transplants in the contused thoracic rat spinal cord 7 d postinjury, we establish via in vivo bioluminescent (IVIS) imaging and stereology that cell death occurs prior to 2–3 d postimplantation. We then test an alternative approach to the current paradigm of enhancing transplant survival by including multiple factors along with the cells. To stimulate multiple cellular adaptive pathways concurrently, we activate the hypoxia-inducible factor 1α (HIF-1α) transcriptional pathway. Retroviral expression of VP16-HIF-1α in SCs increased HIF-α by 5.9-fold and its target genes implicated in oxygen transport and delivery (VEGF, 2.2-fold) and cellular metabolism (enolase, 1.7-fold). In cell death assays in vitro, HIF-1α protected cells from H₂O₂-induced oxidative damage. It also provided some protection against camptothecin-induced DNA damage, but not thapsigargin-induced endoplasmic reticulum stress or tunicamycin-induced unfolded protein response. Following transplantation, VP16-HIF-1α increased SC survival by 34.3%. The increase in cell survival was detectable by stereology, but not by in vivo luciferase or ex vivo GFP IVIS imaging. The results support the hypothesis that activating adaptive cellular pathways enhances transplant survival and identifies an alternative pro-survival approach that, with optimization, could be amenable to clinical translation.

Regeneration of Spinal Cord Connectivity Through Stem Cell Transplantation and Biomaterial Scaffolds

Significant progress has been made in the treatment of spinal cord injury (SCI). Advances in post-trauma management and intensive rehabilitation have significantly improved the prognosis of SCI and converted what was once an “ailment not to be treated” into a survivable injury, but the cold hard fact is that we still do not have a validated method to improve the paralysis of SCI. The irreversible functional impairment of the injured spinal cord is caused by the disruption of neuronal transduction across the injury lesion, which is brought about by demyelination, axonal degeneration, and loss of synapses. Furthermore, refractory substrates generated in the injured spinal cord inhibit spontaneous recovery. The discovery of the regenerative capability of central nervous system neurons in the proper environment and the verification of neural stem cells in the spinal cord once incited hope that a cure for SCI was on the horizon. That hope was gradually replaced with mounting frustration when neuroprotective drugs, cell transplantation, and strategies to enhance remyelination, axonal regeneration, and neuronal plasticity demonstrated significant improvement in animal models of SCI but did not translate into a cure in human patients. However, recent advances in SCI research have greatly increased our understanding of the fundamental processes underlying SCI and fostered increasing optimism that these multiple treatment strategies are finally coming together to bring about a new era in which we will be able to propose encouraging therapies that will lead to appreciable improvements in SCI patients. In this review, we outline the pathophysiology of SCI that makes the spinal cord refractory to regeneration and discuss the research that has been done with cell replacement and biomaterial implantation strategies, both by itself and as a combined treatment. We will focus on the capacity of these strategies to facilitate the regeneration of neural connectivity necessary to achieve meaningful functional recovery after SCI.

Spinal cord injury: pathophysiology, treatment strategies, associated challenges, and future implications

Axonal regeneration and formation of tripartite (axo-glial) junctions at damaged sites is a prerequisite for early repair of injured spinal cord. Transplantation of stem cells at such sites of damage which can generate both neuronal and glial population has gained impact in terms of recuperation upon infliction with spinal cord injury. In spite of the fact that a copious number of pre-clinical studies using different stem/progenitor cells have shown promising results at acute and subacute stages, at the chronic stages of injury their recovery rates have shown a drastic decline. Therefore, developing novel therapeutic strategies are the need of the hour in order to assuage secondary morbidity and effectuate improvement of the spinal cord injury (SCI)-afflicted patients' quality of life. The present review aims at providing an overview of the current treatment strategies and also gives an insight into the potential cell-based therapies for the treatment of SCI.

Decellularized peripheral nerve supports Schwann cell transplants and axon growth following spinal cord injury

Schwann cell (SC) transplantation has been comprehensively studied as a strategy for spinal cord injury (SCI) repair. SCs are neuroprotective and promote axon regeneration and myelination. Nonetheless, substantial SC death occurs post-implantation, which limits therapeutic efficacy. The use of extracellular matrix (ECM)-derived matrices, such as Matrigel, supports transplanted SC survival and axon growth, resulting in improved motor function. Because appropriate matrices are needed for clinical translation, we test here the use of an acellular injectable peripheral nerve (iPN) matrix. Implantation of SCs in iPN into a contusion lesion did not alter immune cell infiltration compared to injury only controls. iPN implants were larger and contained twice as many SC-myelinated axons as Matrigel grafts. SC/iPN animals performed as well as the SC/Matrigel group in the BBB locomotor test, and made fewer errors on the grid walk at 4 weeks, equalizing at 8 weeks. The fact that this clinically relevant iPN matrix is immunologically tolerated and supports SC survival and axon growth within the graft offers a highly translational possibility for improving efficacy of SC treatment after SCI. To our knowledge, it is the first time that an injectable PN matrix is being evaluated to improve the efficacy of SC transplantation in SCI repair.

Combined effects of rat Schwann cells and 17β-estradiol in a spinal cord injury model

Spinal cord injury (SCI) is a devastating traumatic event which burdens the affected individuals and the health system. Schwann cell (SC) transplantation is a promising repair strategy after SCI. However, a large number of SCs do not survive following transplantation. Previous studies demonstrated that 17β-estradiol (E2) protects different cell types and reduces tissue damage in SCI experimental animal model. In the current study, we evaluated the protective potential of E2 on SCs in vitro and investigated whether the combination of hormonal and SC therapeutic strategy has a better effect on the outcome after SCI. Primary SC cultures were incubated with E2 for 72 h. In a subsequent experiment, thoracic contusion SCI was induced in male rats followed by sustained administration of E2 or vehicle. Eight days after SCI, DiI-labeled SCs were transplanted into the injury epicenter in vehicle and E2-treated animals. The combinatory regimen decreased neurological and behavioral deficits and protected neurons and oligodendrocytes in comparison to vehicle rats. Moreover, E2 and SC significantly decreased the number of Iba-1+ (microglia) and GFAP⁺ cells (astrocyte) in the SCI group. In addition, we found a significant reduction of mitochondrial fission-markers (Fis1) and an increase of fusion-markers (Mfn1 and Mfn2) in the injured spinal cord after E2 and SC treatment. These data demonstrated that E2 protects SCs against hypoxia-induced SCI and improves the survival of transplanted SCs.

Aligned fibrous PVDF-TrFE scaffolds with Schwann cells support neurite extension and myelination in vitro

OBJECTIVE

Polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE), which is a piezoelectric, biocompatible polymer, holds promise as a scaffold in combination with Schwann cells (SCs) for spinal cord repair. Piezoelectric materials can generate electrical activity in response to mechanical deformation, which could potentially stimulate spinal cord axon regeneration. Our goal in this study was to investigate PVDF-TrFE scaffolds consisting of aligned fibers in supporting SC growth and SC-supported neurite extension and myelination in vitro.

APPROACH

Aligned fibers of PVDF-TrFE were fabricated using the electrospinning technique. SCs and dorsal root ganglion (DRG) explants were co-cultured to evaluate SC-supported neurite extension and myelination on PVDF-TrFE scaffolds.

MAIN RESULTS

PVDF-TrFE scaffolds supported SC growth and neurite extension, which was further enhanced by coating the scaffolds with Matrigel. SCs were oriented and neurites extended along the length of the aligned fibers. SCs in co-culture with DRGs on PVDF-TrFE scaffolds promoted longer neurite extension as compared to scaffolds without SCs. In addition to promoting neurite extension, SCs also formed myelin around DRG neurites on PVDF-TrFE scaffolds.

SIGNIFICANCE

This study demonstrated PVDF-TrFE scaffolds containing aligned fibers supported SC-neurite extension and myelination. The combination of SCs and PVDF-TrFE scaffolds may be a promising tissue engineering strategy for spinal cord repair.

Macrophage depletion and Schwann cell transplantation reduce cyst size after rat contusive spinal cord injury

Schwann cell transplantation is a promising therapy for the treatment of spinal cord injury (SCI) and is currently in clinical trials. In our continuing efforts to improve Schwann cell transplantation strategies, we sought to determine the combined effects of Schwann cell transplantation with macrophage depletion. Since macrophages are major inflammatory contributors to the acute spinal cord injury, and are the major phagocytic cells, we hypothesized that transplanting Schwann cells after macrophage depletion will improve cell survival and integration with host tissue after SCI. To test this hypothesis, rat models of contusive SCI at thoracic level 8 were randomly subjected to macrophage depletion or not. In rat subjected to macrophage depletion, liposomes filled with clodronate were intraperitoneally injected at 1, 3, 6, 11, and 18 days post injury. Rats not subjected to macrophage depletion were intraperitoneally injected with liposomes filled with phosphate buffered saline. Schwann cells were transplanted 1 week post injury in all rats. Biotinylated dextran amine (BDA) was injected at thoracic level 5 to evalute axon regeneration. The Basso, Beattie, and Bresnahan locomotor test, Gridwalk test, and sensory test using von Frey filaments were performed to assess functional recovery. Immunohistochemistry was used to detect glial fibrillary acidic protein, neurofilament, and green fluorescent protein (GFP), and also to visulize BDA-labelled axons. The GFP labeled Schwann cell and cyst and lesion volumes were quantified using stained slides. The numbers of BDA-positive axons were also quantified. At 8 weeks after Schwann cell transplantation, there was a significant reduction in cyst and lesion volumes in the combined treatment group compared to Schwann cell transplantation alone. These changes were not associated, however, with improved Schwann cell survival, axon growth, or locomotor recovery. Although combining Schwann cell transplantation with macrophage depletion does improve histopathology of the injury site, the effect on axon growth and behavioral recovery appears no better than what can be achieved with Schwann cell transplants alone.

Adult skin-derived precursor Schwann cell grafts form growths in the injured spinal cord of Fischer rats

In this study, GFP⁺ skin-derived precursor Schwann cells (SKP-SCs) from adult rats were grafted into the injured spinal cord of immunosuppressed rats. Our goal was to improve grafted cell survival in the injured spinal cord, which is typically low. Cells were grafted in hyaluronan-methylcellulose hydrogel (HAMC) or hyaluronan-methylcellulose modified with laminin- and fibronectin-derived peptide sequences (eHAMC). The criteria for selection of hyaluronan was for its shear-thinning properties, making the hydrogel easy to inject, methylcellulose for its inverse thermal gelation, helping to keep grafted cells in situ, and fibronectin and laminin to improve cell attachment and, thus, prevent cell death due to dissociation from substrate molecules (i.e., anoikis). Post-mortem examination revealed large masses of GFP⁺ SKP-SCs in the spinal cords of rats that received cells in HAMC (5 out of n = 8) and eHAMC (6 out of n = 8). Cell transplantation in eHAMC caused significantly greater spinal lesions compared to lesion and eHAMC only control groups. A parallel study showed similar masses in the contused spinal cord of rats after transplantation of adult GFP⁺ SKP-SCs without a hydrogel or immunosuppression. These findings suggest that adult GFP⁺ SKP-SCs, cultured/transplanted under the conditions described here, have a capacity for uncontrolled proliferation. Growth-formation in pre-clinical research has also been documented after transplantation of: human induced pluripotent stem cell-derived neural stem cells (Itakura et al 2015 PLoS One 10 e0116413), embryonic stem cells and embryonic stem cell-derived neurons (Brederlau et al 2006 Stem Cells 24 1433-40; Dressel et al 2008 PLoS One 3 e2622), bone marrow derived mesenchymal stem cells (Jeong et al 2011 Circ. Res. 108 1340-47) and rat nerve-derived SCs following in vitro expansion for >11 passages (Funk et al 2007 Eur. J. Cell Biol. 86 207-19; Langford et al 1988 J. Neurocytology 17 521-9; Morrissey et al 1991 J. Neurosci. 11 2433-42). It is of upmost importance to define the precise culture/transplantation parameters for maintenance of normal cell function and safe and effective use of cell therapy.

Seeding nerve sutures with minced nerve-graft (MINE-G): a simple method to improve nerve regeneration in rats

BACKGROUND

The aim of this study was to assess the effect of seeding the distal nerve suture with nerve fragments in rats.

METHODS

On 20 rats, a 15 mm sciatic nerve defect was reconstructed with a nerve autograft. In the Study Group (10 rats), a minced 1 mm nerve segment was seeded around the nerve suture. In the Control Group (10 rats), a nerve graft alone was used. At 4 and 12 weeks, a walking track analysis with open field test (WTA), hystomorphometry (number of myelinated fibers (n), fiber density (FD) and fiber area (FA) and soleus and gastrocnemius muscle weight ratios (MWR) were evaluated. The Student t-test was used for statistical analysis.

RESULTS

At 4 and 12 weeks the Study Group had a significantly higher n and FD (p = .043 and .033). The SMWR was significantly higher in the Study Group at 12 weeks (p = .0207).

CONCLUSIONS

Seeding the distal nerve suture with nerve fragments increases the number of myelinated fibers, the FD and the SMWR. The technique seems promising and deserves further investigation to clarify the mechanisms involved and its functional effects.

Intraspinal Delivery of Schwann Cells for Spinal Cord Injury

Cell transplant-mediated tissue repair of the damaged spinal cord is being tested in several clinical trials. The current candidates are neural stem cells, stromal cells, and autologous Schwann cells (aSC). Due to their peripheral origin and limited penetration of astrocytic regions, aSC are transplanted intralesionally as compared to neural stem cells that are transplanted into intact spinal cord. Injections into either location can cause iatrogenic injury, and thus technical precision is important in the therapeutic risk-benefit equation. In this chapter, we discuss how we bridged from transplant studies in large animals to human application for two Phase 1 aSC transplant studies, one subacute and one chronic. Preclinical SC transplant studies conducted at the University of Miami in 2009-2012 in rodents, minipigs, and primates supported a successful Investigational New Drug (IND) submission for a Phase 1 trial in subacute complete spinal cord injury (SCI). Our studies optimized the safety and efficiency of intralesional cell delivery for subacute human SCI and led to the development of new simpler techniques for cell delivery into subjects with chronic SCI. Key parameters of delivery methodology include precision localization of the injury site, stereotaxic devices to control needle trajectory, method of entry into the spinal cord, spinal cord motion reduction, the volume and density of the cell suspension, rate of delivery, and control of shear stresses on cells.

Regulated viral BDNF delivery in combination with Schwann cells promotes axonal regeneration through capillary alginate hydrogels after spinal cord injury

Grafting of cell-seeded alginate capillary hydrogels into a spinal cord lesion site provides an axonal bridge while physically directing regenerating axonal growth in a linear pattern. However, without an additional growth stimulus, bridging axons fail to extend into the distal host spinal cord. Here we examined whether a combinatory strategy would support regeneration of descending axons across a cervical (C5) lateral hemisection lesion in the rat spinal cord. Following spinal cord transections, Schwann cell (SC)-seeded alginate hydrogels were grafted to the lesion site and AAV5 expressing brain-derived neurotrophic factor (BDNF) under control of a tetracycline-regulated promoter was injected caudally. In addition, we examined whether SC injection into the caudal spinal parenchyma would further enhance regeneration of descending axons to re-enter the host spinal cord. Our data show that both serotonergic and descending axons traced by biotinylated dextran amine (BDA) extend throughout the scaffolds. The number of regenerating axons is significantly increased when caudal BDNF expression is activated and transient BDNF delivery is able to sustain axons after gene expression is switched off. Descending axons are confined to the caudal graft/host interface even with continuous BDNF expression for 8weeks. Only with a caudal injection of SCs, a pathway facilitating axonal regeneration through the host/graft interface is generated allowing axons to successfully re-enter the caudal spinal cord.

STATEMENT OF SIGNIFICANCE

Recovery from spinal cord injury is poor due to the limited regeneration observed in the adult mammalian central nervous system. Biomaterials, cell transplantation and growth factors that can guide axons across a lesion site, provide a cellular substrate, stimulate axon growth and have shown some promise in increasing the growth distance of regenerating axons. In the present study, we combined an alginate biomaterial with linear channels with transplantation of Schwann cells within and beyond the lesion site and injection of a regulatable vector for the transient expression of brain-derived neurotrophic factor (BDNF). Our data show that only with the full combination axons extend across the lesion site and that expression of BDNF beyond 4weeks does not further increase the number of regenerating axons.

Engrafted peripheral blood-derived mesenchymal stem cells promote locomotive recovery in adult rats after spinal cord injury

Spinal cord injury (SCI) is a severe trauma of central nervous system (CNS). Numerous stem cells have been applied for SCI therapy. Peripheral blood-derived mesenchymal stem cells (PBMSCs) have captured researchers' attention by virtue of pluripotency and effectiveness. However, little work has been performed on whether PBMSCs play roles and what role, if any, in the lesion microenvironment. Through the investigation of the differentiation, neuroprotection and immunoloregulation of engrafted PBMSCs, we found that the expression of glial fibrillary acidic protein (GFAP) was inhibited. Meanwhile, myelin basic protein (MBP), neurofilament protein-200 (NF-200) and microtubule associated protein-2 (MAP-2) were promoted after PBMSC transplantation (PBMSCT) by immunohistochemistry. Though engrafted PKH26+PBMSCs could survive in vivo for at least 8 w, they could not respectively express GFAP, MBP and neuronal specific neucleoprotein (NeuN) by immunofluorescence. Additionally, Flow cytometry demonstrated that the number of CD4+IL17+Th17 cells decreased while CD4+CD25+Foxp3+Treg ones increased after PBMSCT (P < 0.01). Immunohistochemistry and Elisa both showed a lower expression of IL-6 and IL-17a while a higher expression of TGF-β after PBMSCT (P < 0.05). RT-PCR indicated that Th17-relevant genes including RORγT, IL-6 and IL-21 were inhibited and resulted in the decrease of IL-23a and IL-22 secretion (P < 0.05); Treg-relevant genes including FoxP3 and TGF-β and the secretion of IL-10 were improved (P < 0.05). Accordingly, we concluded that the PBMSCT-relevant therapy took effect not through the differentiation of PBMSCs into CNS cells, but through regulating Th17/Treg-relevant gene expression, inhibiting Th17-relevant gene expression and meanwhile promoting Treg-relevant gene expression, and eventually resulted in promotion of the functional recovery of SCI rats.

Cyclosporine-immunosuppression does not affect survival of transplanted skin-derived precursor Schwann cells in the injured rat spinal cord

A major goal of Schwann cell (SC) transplantation for spinal cord injury (SCI) is to fill the injury site to create a bridge for regenerating axons. However, transplantation of peripheral nerve SCs requires an invasive biopsy, which may result in nerve damage and donor site morbidity. SCs derived from multipotent stem cells found in skin dermis (SKP-SCs) are a promising alternative. Regardless of source, loss of grafted SCs post-grafting is an issue in studies of regeneration, with survival rates ranging from ∼1 to 20% after ≥6 weeks in rodent models of SCI. Immune rejection has been implicated in these low survival rates. Therefore, our aim was to explore the role of the immune response on grafted SKP-SC survival in Fischer rats with a spinal hemisection injury. We compared SKP-SC survival 6 weeks post-transplantation in: (I) cyclosporine-immunosuppressed rats (n=8), (II) immunocompetent rats (n=9), and (III) rats of a different sub-strain than the SKP-SC donor rats (n=7). SKP-SC survival was similar in all groups, suggesting immune rejection was not a main factor in SKP-SC loss observed in this study. SKP-SCs were consistently found on laminin expressed at the injury site, indicating detachment-mediated apoptosis (i.e., anoikis) might play a major role in grafted cell loss.

Schwann Cell Precursors from Human Pluripotent Stem Cells as a Potential Therapeutic Target for Myelin Repair

Schwann cells play a crucial role in successful nerve repair and regeneration by supporting both axonal growth and myelination. However, the sources of human Schwann cells are limited both for studies of Schwann cell development and biology and for the development of treatments for Schwann cell-associated diseases. Here, we provide a rapid and scalable method to produce self-renewing Schwann cell precursors (SCPs) from human pluripotent stem cells (hPSCs), using combined sequential treatment with inhibitors of the TGF-β and GSK-3 signaling pathways, and with neuregulin-1 for 18 days under chemically defined conditions. Within 1 week, hPSC-derived SCPs could be differentiated into immature Schwann cells that were functionally confirmed by their secretion of neurotrophic factors and their myelination capacity in vitro and in vivo. We propose that hPSC-derived SCPs are a promising, unlimited source of functional Schwann cells for treating demyelination disorders and injuries to the peripheral nervous system.

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hPSC-SCPs are highly expandable under chemically defined medium condition

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hPSC-SCPs can rapidly and efficiently differentiate into functional Schwann cells

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SCP-SCs myelinate axon and secrete various neurotrophic factors

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SCP-SCs promote axonal regeneration in sciatic nerve-damaged mice

From transplanting Schwann cells in experimental rat spinal cord injury to their transplantation into human injured spinal cord in clinical trials

Among the potential therapies designed to repair the injured spinal cord is cell transplantation, notably the use of autologous adult human Schwann cells (SCs). Here, we detail some of the critical research accomplished over the last four decades to establish a foundation that enables these cells to be tested in clinical trials. New culture systems allowed novel information to be gained about SCs, including discovering ways to stimulate their proliferation to acquire adequately large numbers for transplantation into the injured human spinal cord. Transplantation of rat SCs into rat models of spinal cord injury has demonstrated that SCs promote repair of injured spinal cord. Additional work required to gain approval from the Food and Drug Administration for the first SC trial in the Miami Project is disclosed. This trial and a second one now underway are described.

Concomitant differentiation of a population of mouse embryonic stem cells into neuron-like cells and schwann cell-like cells in a slow-flow microfluidic device

BACKGROUND

To send meaningful information to the brain, an inner ear cochlear implant (CI) must become closely coupled to as large and healthy a population of remaining spiral ganglion neurons (SGN) as possible. Inner ear gangliogenesis depends on macrophage migration inhibitory factor (MIF), a directionally attractant neurotrophic cytokine made by both Schwann and supporting cells (Bank et al., 2012). MIF-induced mouse embryonic stem cell (mESC)-derived "neurons" could potentially substitute for lost or damaged SGN. mESC-derived "Schwann cells" produce MIF, as do all Schwann cells (Huang et al., a; Roth et al., 2007; Roth et al., 2008) and could attract SGN to a "cell-coated" implant.

RESULTS

Neuron- and Schwann cell-like cells were produced from a common population of mESCs in an ultra-slow-flow microfluidic device. As the populations interacted, "neurons" grew over the "Schwann cell" lawn, and early events in myelination were documented. Blocking MIF on the Schwann cell side greatly reduced directional neurite outgrowth. MIF-expressing "Schwann cells" were used to coat a CI: Mouse SGN and MIF-induced "neurons" grew directionally to the CI and to a wild-type but not MIF-knockout organ of Corti explant.

CONCLUSIONS

Two novel stem cell-based approaches for treating the problem of sensorineural hearing loss are described. Developmental Dynamics 246:7-27, 2017. © 2016 Wiley Periodicals, Inc.

Neurotrophic Factors Used to Treat Spinal Cord Injury

The application of neurotrophic factors as a therapy to improve morphological and behavioral outcomes after experimental spinal cord injury (SCI) has been the focus of many studies. These studies vary markedly in the type of neurotrophic factor that is delivered, the mode of administration, and the location, timing, and duration of the treatment. Generally, the majority of studies have had significant success if neurotrophic factors are applied in or close to the lesion site during the acute or the subacute phase after SCI. Comparatively fewer studies have administered neurotrophic factors in order to directly target the somata of injured neurons. The mode of delivery varies between acute injection of recombinant proteins, subacute or chronic delivery using a variety of strategies including osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells, or precursor/stem cells. In this brief review, we summarize the state of play of many of the therapies using these factors, most of which have been undertaken in rodent models of SCI.

The efficacy of Schwann cell transplantation on motor function recovery after spinal cord injuries in animal models: A systematic review and meta-analysis

AIM

This article aimed to assess the efficacy of Schwann cell transplantation on motor function recovery in animal model of spinal cord injuries via meta-analysis.

METHODS

An extended search was carried out in the electronic databases of Medline (via PubMed), EMBASE (via OvidSP), CENTRAL, SCOPUS, Web of Science (BIOSIS), and ProQuest. Finally, 41 eligible studies conducted on 1046 animals including 517 control animals and 529 transplanted animals were included in the meta-analysis. Pooled standardized mean difference (SMD) and odds ratio (OR) with 95% confidence interval (95% CI) were reported.

RESULTS

The findings showed that treatment with Schwann cells leads to a modest motor function recovery after spinal cord injury (SMD=0.85; 95% CI: 0.63-1.07; p<0.001). Transplantation of these cells in acute phase of the injury (immediately after the injury) (OR=4.30; 95% CI: 1.53-12.05; p=0.007), application of mesenchymal/skin-derived precursors (OR=2.34; 95% CI: 1.28-4.29; p=0.008), and cells with human sources are associated with an increase in efficacy of Schwann cells (OR=10.96; 95% CI: 1.49-80.77; p=0.02). Finally, it seems that the efficacy of Schwann cells in mice is significantly lower than rats (OR=0.03; 95% CI: 0.003-0.41; p=0.009).

CONCLUSION

Transplantation of Schwann cells can moderately improve motor function recovery. It seems that inter-species differences might exist regarding the efficacy of this cells. Therefore, this should be taken into account when using Schwann cells in clinical trials regarding spinal cord injuries.

Isolation and Characterization of Rat Mesenchymal Stem Cells Derived from Granulocyte Colony-Stimulating Factor-Mobilized Peripheral Blood

Mesenchymal stem cells (MSCs) have been isolated from many tissues and organs. However, there is much dispute as to whether MSCs exist in peripheral blood. This may be due to the limited identification methods of MSCs, especially the lack of detection markers for phenotypic characteristics. In this study, as many as 10 surface markers of MSCs derived from rat peripheral blood (rPBMSCs) were analyzed after granulocyte colony-stimulating factor mobilization. Our results suggest that mobilized rPBMSCs overexpress mesenchymal markers, including CD90, CD44, CD29, CD73 and CD105, but do not express CD45, CD11b, CD79a, CD34 or HLA-DR. This is in conformity with the standard definition of MSCs by the International Society for Cellular Therapy. In addition, the colony-forming efficiency of the mobilized rat peripheral blood was 15.83 ± 1.61/106, significantly outnumbering that of the nonmobilized group, which was 0.28 ± 0.1/106 (p < 0.01). Combining the growth characteristics with the differential capacities of mobilized rPBMSCs towards forming osteocytes, chondrocytes and adipocytes, we further confirmed the existence of rPBMSCs. Additionally, this treatment could improve locomotive function after spinal cord injury (SCI) in rats. Due to their convenient collection, fewer complications, cost effectiveness and suitability for autograft, PBMSCs might be a substitute for MSCs derived from bone marrow and provide promising prospects for the cell-based therapy of SCI.

Efficacy of Schwann cell transplantation for spinal cord repair is improved with combinatorial strategies

When cells (including Schwann cells; SCs) of the peripheral nervous system (PNS) could be purified and expanded in number in tissue culture, Richard Bunge in 1975 envisioned that the SCs could be introduced to repair the central nervous system (CNS), as SCs enable axons to regenerate after PNS injury. Importantly, autologous human SCs could be transplanted into injured human spinal cord. Availability of the new culture systems to study interactions between sensory neurons, SCs and fibroblasts increased our knowledge of SC biology in the 1970s and '80s. Joining the Miami Project to Cure Paralysis in 1989 brought the opportunity to use this knowledge to initiate spinal cord repair studies. Development of a rat complete spinal cord transection/SC bridge model allowed the demonstration that axons regenerate into the SC bridge. Together with study of contused rat spinal cord, it was concluded that implanted SCs reduce cavitation, protect tissue around the lesion, support axon regeneration and form myelin. SC transplantation efficacy was improved when combined with neurotrophins, elevation of cyclic AMP levels, olfactory ensheathing cells, a steroid or chondroitinase. Increased efficacy meant higher numbers of axons, particularly from the brainstem, and more SC-myelinated axons in the implants and improvement in hindlimb movements. Human SCs support axon regeneration as do rat SCs. Astrocytes at the SC bridge-host spinal cord interfaces play a key role in determining whether axons enter the SC milieu. The SC work described here contributed to gaining approval from the FDA for an initial autologous human SC clinical trial (at the Miami Project) that has been completed and found to be safe.

Does the preclinical evidence for functional remyelination following myelinating cell engraftment into the injured spinal cord support progression to clinical trials?

This article reviews all historical literature in which rodent-derived myelinating cells have been engrafted into the contused adult rodent spinal cord. From 2500 initial PubMed citations identified, human cells grafts, bone mesenchymal stem cells, olfactory ensheathing cells, non-myelinating cell grafts, and rodent grafts into hemisection or transection models were excluded, resulting in the 67 studies encompassed in this review. Forty five of those involved central nervous system (CNS)-derived cells, including neural stem progenitor cells (NSPCs), neural restricted precursor cells (NRPs) or oligodendrocyte precursor cells (OPCs), and 22 studies involved Schwann cells (SC). Of the NSPC/NPC/OPC grafts, there was no consistency with respect to the types of cells grafted and/or the additional growth factors or cells co-grafted. Enhanced functional recovery was reported in 31/45 studies, but only 20 of those had appropriate controls making conclusive interpretation of the remaining studies impossible. Of those 20, 19 were properly powered and utilized appropriate statistical analyses. Ten of those 19 studies reported the presence of graft-derived myelin, 3 reported evidence of endogenous remyelination or myelin sparing, and 2 reported both. For the SC grafts, 16/21 reported functional improvement, with 11 having appropriate cellular controls and 9/11 using proper statistical analyses. Of those 9, increased myelin was reported in 6 studies. The lack of consistency and replication among these preclinical studies are discussed with respect to the progression of myelinating cell transplantation therapies into the clinic.

Taking a bite out of spinal cord injury: do dental stem cells have the teeth for it?

Dental stem cells are an emerging star on a stage that is already quite populated. Recently, there has been a lot of hype concerning these cells in dental therapies, especially in regenerative endodontics. It is fitting that most research is concentrated on dental regeneration, although other uses for these cells need to be explored in more detail. Being a true mesenchymal stem cell, their capacities could also prove beneficial in areas outside their natural environment. One such field is the central nervous system, and in particular, repairing the injured spinal cord. One of the most formidable challenges in regenerative medicine is to restore function to the injured spinal cord, and as yet, a cure for paralysis remains to be discovered. A variety of approaches have already been tested, with graft-based strategies utilising cells harbouring appropriate properties for neural regeneration showing encouraging results. Here we present a review focusing on properties of dental stem cells that endorse their use in regenerative medicine, with particular emphasis on repairing the damaged spinal cord.

Predegenerated Schwann cells--a novel prospect for cell therapy for glaucoma: neuroprotection, neuroregeneration and neuroplasticity

Glaucoma is an optic neuropathy that leads to irreversible blindness. Because the current therapies are not sufficient to protect against glaucoma-induced visual impairment, new treatment approaches are necessary to prevent disease progression. Cell transplantation techniques are currently considered to be among the most promising opportunities for nervous system damage treatment. The beneficial effects of undifferentiated cells have been investigated in experimental models of glaucoma, however experiments were accompanied by various barriers, which would make putative treatment difficult or even impossible to apply in a clinical setting. The novel therapy proposed in our study creates conditions to eliminate some of the identified barriers described for precursor cells transplantation and allows us to observe direct neuroprotective and pro-regenerative effects in ongoing optic neuropathy without additional modifications to the transplanted cells. We demonstrated that the proposed novel Schwann cell therapy might be promising, effective and easy to apply, and is safer than the alternative cell therapies for the treatment of glaucoma.

Low-frequency electrical stimulation induces the proliferation and differentiation of peripheral blood stem cells into Schwann cells

BACKGROUND

Functional recovery after peripheral nerve injury remains a tough problem at present. Specifically, a type of glial cell exists in peripheral nerves that promotes axonal growth and myelin formation and secretes various active substances, such as neurotrophic factors, extracellular matrix and adherence factors. These substances have important significance for the survival, growth and regeneration of nerve fibers. Numerous recent studies have shown that electrical stimulation can increase the number of myelinated nerve fibers. However, whether electrical stimulation acts on neurons or Schwann cells has not been verified in vivo. This study investigates low-frequency electrical stimulation-induced proliferation and differentiation of peripheral blood stem cells into Schwann cells and explores possible mechanisms.

METHODS

Peripheral blood stem cells from Sprague-Dawley rats were primarily cultured. Cells in passage 3 were divided into 4 groups: a low-frequency electrical stimulation group (20 Hz, 100 μs, 3 V), a low-frequency electrical stimulation+PD98059 (blocking the extracellular signal-regulated kinase [ERK] signaling pathway) group, a PD98059 group and a control group (no treatment). After induction, the cells were characterized. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazoliumbromide assay was employed to measure the absorbance values at 570 nm in the 4 groups. A Western blot assay was used to detect the expression of cyclin D1 and cyclin-dependent kinase 4 (CDK4) in each group.

RESULTS

No significant difference in cell viability was detected before induction. Peripheral blood stem cells from the 4 groups differentiated into Schwann cells. Phosphorylated ERK 1/2, cyclin D1 and CDK4 protein levels were highest in the low-frequency electrical stimulation group and lowest in the ERK blockage group. Phosphorylated ERK 1/2, cyclin D1 and CDK4 protein levels in the low-frequency electrical stimulation+ERK blockage group were lower than those in the low-frequency electrical stimulation group but higher than those in the ERK blockage group.

CONCLUSIONS

Low-frequency electrical stimulation contributed to the proliferation of peripheral blood stem cells cultured in vitro and induced differentiation into Schwann cells. The ERK signaling pathway underlies cell proliferation and differentiation.

The role of the serotonergic system in locomotor recovery after spinal cord injury

Serotonin (5-HT), a monoamine neurotransmitter synthesized in various populations of brainstem neurons, plays an important role in modulating the activity of spinal networks involved in vertebrate locomotion. Following spinal cord injury (SCI) there is a disruption of descending serotonergic projections to spinal motor areas, which results in a subsequent depletion in 5-HT, the dysregulation of 5-HT transporters as well as the elevated expression, super-sensitivity and/or constitutive auto-activation of specific 5-HT receptors. These changes in the serotonergic system can produce varying degrees of locomotor dysfunction through to paralysis. To date, various approaches targeting the different components of the serotonergic system have been employed to restore limb coordination and improve locomotor function in experimental models of SCI. These strategies have included pharmacological modulation of serotonergic receptors, through the administration of specific 5-HT receptor agonists, or by elevating the 5-HT precursor 5-hydroxytryptophan, which produces a global activation of all classes of 5-HT receptors. Stimulation of these receptors leads to the activation of the locomotor central pattern generator (CPG) below the site of injury to facilitate or improve the quality and frequency of movements, particularly when used in concert with the activation of other monoaminergic systems or coupled with electrical stimulation. Another approach has been to employ cell therapeutics to replace the loss of descending serotonergic input to the CPG, either through transplanted fetal brainstem 5-HT neurons at the site of injury that can supply 5-HT to below the level of the lesion or by other cell types to provide a substrate at the injury site for encouraging serotonergic axon regrowth across the lesion to the caudal spinal cord for restoring locomotion.

Spinal cord regeneration

Three theories of regeneration dominate neuroscience today, all purporting to explain why the adult central nervous system (CNS) cannot regenerate. One theory proposes that Nogo, a molecule expressed by myelin, prevents axonal growth. The second theory emphasizes the role of glial scars. The third theory proposes that chondroitin sulfate proteoglycans (CSPGs) prevent axon growth. Blockade of Nogo, CSPG, and their receptors indeed can stop axon growth in vitro and improve functional recovery in animal spinal cord injury (SCI) models. These therapies also increase sprouting of surviving axons and plasticity. However, many investigators have reported regenerating spinal tracts without eliminating Nogo, glial scar, or CSPG. For example, many motor and sensory axons grow spontaneously in contused spinal cords, crossing gliotic tissue and white matter surrounding the injury site. Sensory axons grow long distances in injured dorsal columns after peripheral nerve lesions. Cell transplants and treatments that increase cAMP and neurotrophins stimulate motor and sensory axons to cross glial scars and to grow long distances in white matter. Genetic studies deleting all members of the Nogo family and even the Nogo receptor do not always improve regeneration in mice. A recent study reported that suppressing the phosphatase and tensin homolog (PTEN) gene promotes prolific corticospinal tract regeneration. These findings cannot be explained by the current theories proposing that Nogo and glial scars prevent regeneration. Spinal axons clearly can and will grow through glial scars and Nogo-expressing tissue under some circumstances. The observation that deleting PTEN allows corticospinal tract regeneration indicates that the PTEN/AKT/mTOR pathway regulates axonal growth. Finally, many other factors stimulate spinal axonal growth, including conditioning lesions, cAMP, glycogen synthetase kinase inhibition, and neurotrophins. To explain these disparate regenerative phenomena, I propose that the spinal cord has evolved regenerative mechanisms that are normally suppressed by multiple extrinsic and intrinsic factors but can be activated by injury, mediated by the PTEN/AKT/mTOR, cAMP, and GSK3b pathways, to stimulate neural growth and proliferation.

Biphasic bisperoxovanadium administration and Schwann cell transplantation for repair after cervical contusive spinal cord injury

Schwann cells (SCs) hold promise for spinal cord injury (SCI) repair; however, there are limitations for its use as a lone treatment. We showed that acute inhibition of the phosphatase and tensin homolog deleted on chromosome ten (PTEN) by bisperoxovanadium (bpV) was neuroprotective and enhanced function following cervical hemicontusion SCI. We hypothesized that combining acute bpV therapy and delayed SC engraftment would further improve neuroprotection and recovery after cervical SCI. Adult female Sprague-Dawley (SD) rats were randomly sorted into 5 groups: sham, vehicle, bpV, SC transplantation, and bpV+SC transplantation. SCs were isolated from adult green fluorescent protein (GFP)-expressing SD rats (GFP-SCs). 200 μg/kg bpV(pic) was administered intraperitoneally (IP) twice daily for 7 days post-SCI in bpV-treated groups. GFP-SCs (1×10(6) in 5 μl medium) were transplanted into the lesion epicenter at the 8th day post-SCI. Forelimb function was tested for 10 weeks and histology was assessed. bpV alone significantly reduced lesion (by 40%, p<0.05) and cavitation (by 65%, p<0.05) and improved functional recovery (p<0.05) compared to injury alone. The combination promoted similar neuroprotection (p<0.01 vs. injury); however, GFP-SCs alone did not. Both SC-transplanted groups exhibited remarkable long-term SC survival, SMI-31(+) axon ingrowth and RECA-1(+) vasculature presence in the SC graft; however, bpV+SCs promoted an 89% greater axon-to-lesion ratio than SCs only. We concluded that bpV likely contributed largely to the neuroprotective and functional benefits while SCs facilitated considerable host-tissue interaction and modification. The combination of the two shows promise as an attractive strategy to enhance recovery after SCI.

Neurotrophic factors for spinal cord repair: Which, where, how and when to apply, and for what period of time?

A variety of neurotrophic factors have been used in attempts to improve morphological and behavioural outcomes after experimental spinal cord injury (SCI). Here we review many of these factors, their cellular targets, and their therapeutic impact on spinal cord repair in different, primarily rodent, models of SCI. A majority of studies report favourable outcomes but results are by no means consistent, thus a major aim of this review is to consider how best to apply neurotrophic factors after SCI to optimize their therapeutic potential. In addition to which factors are chosen, many variables need be considered when delivering trophic support, including where and when to apply a given factor or factors, how such factors are administered, at what dose, and for how long. Overall, the majority of studies have applied neurotrophic support in or close to the spinal cord lesion site, in the acute or sub-acute phase (0-14 days post-injury). Far fewer chronic SCI studies have been undertaken. In addition, comparatively fewer studies have administered neurotrophic factors directly to the cell bodies of injured neurons; yet in other instructive rodent models of CNS injury, for example optic nerve crush or transection, therapies are targeted directly at the injured neurons themselves, the retinal ganglion cells. The mode of delivery of neurotrophic factors is also an important variable, whether delivered by acute injection of recombinant proteins, sub-acute or chronic delivery using osmotic minipumps, cell-mediated delivery, delivery using polymer release vehicles or supporting bridges of some sort, or the use of gene therapy to modify neurons, glial cells or precursor/stem cells. Neurotrophic factors are often used in combination with cell or tissue grafts and/or other pharmacotherapeutic agents. Finally, the dose and time-course of delivery of trophic support should ideally be tailored to suit specific biological requirements, whether they relate to neuronal survival, axonal sparing/sprouting, or the long-distance regeneration of axons ending in a different mode of growth associated with terminal arborization and renewed synaptogenesis. This article is part of a Special Issue entitled SI: Spinal cord injury.

A role for neuropilins in the interaction between Schwann cells and meningeal cells

In their natural habitat, the peripheral nerve, Schwann cells (SCs) form nicely aligned pathways (also known as the bands of Büngner) that guide regenerating axons to their targets. Schwann cells that are implanted in the lesioned spinal cord fail to align in pathways that could support axon growth but form cellular clusters that exhibit only limited intermingling with the astrocytes and meningeal cells (MCs) that are present in the neural scar. The formation of cell clusters can be studied in co-cultures of SCs and MCs. In these co-cultures SCs form cluster-like non-overlapping cell aggregates with well-defined boundaries. There are several indications that neuropilins (NRPs) play an important role in MC-induced SC aggregation. Both SCs and MCs express NRP1 and NRP2 and SCs express the NRP ligands Sema3B, C and E while MCs express Sema3A, C, E and F. We now demonstrate that in SC-MC co-cultures, siRNA mediated knockdown of NRP2 in SCs decreased the formation of SC clusters while these SCs maintained their capacity to align in bands of Büngner-like columnar arrays. Unexpectedly, knockdown of NRP1 expression resulted in a significant increase in SC aggregation. These results suggest that a reduction in NRP2 expression may enhance the capacity of implanted SCs to interact with MCs that invade a neural scar formed after a lesion of the spinal cord.

Gene therapy strategies for the treatment of spinal cord injury

Spinal cord injury is a complex pathology often resulting in functional impairment and paralysis. Gene therapy has emerged as a possible solution to the problems of limited neural tissue regeneration through the administration of factors promoting axonal growth, while also offering long-term local delivery of therapeutic molecules at the injury site. Of note, gene therapy is our response to the requirements of neural and glial cells following spinal cord injury, providing, in a time-dependent manner, growth substances for axonal regeneration and eliminating axonal growth inhibitors. Herein, we explore different gene therapy strategies, including targeting gene expression to modulate the presence of neurotrophic growth or survival factors and increase neural tissue plasticity. Special attention is given to describing advances in viral and non-viral gene delivery systems, as well as the available routes of gene delivery. Finally, we discuss the future of combinatorial gene therapies and give consideration to the implementation of gene therapy in humans.

Combination of engineered Schwann cell grafts to secrete neurotrophin and chondroitinase promotes axonal regeneration and locomotion after spinal cord injury

Transplantation of Schwann cells (SCs) is a promising therapeutic strategy for spinal cord repair. SCs introduced into lesions support axon regeneration, but because these axons do not exit the transplant, additional approaches with SCs are needed. Here, we transplanted SCs genetically modified to secrete a bifunctional neurotrophin (D15A) and chondroitinase ABC (ChABC) into a subacute contusion injury in rats. We examined the effects of these modifications on graft volume, SC number, degradation of chondroitin sulfate proteoglycans (CSPGs), astrogliosis, SC myelination of axons, propriospinal and supraspinal axon numbers, locomotor outcome (BBB scoring, CatWalk gait analysis), and mechanical and thermal sensitivity on the hind paws. D15A secreted from transplanted SCs increased graft volume and SC number and myelinated axon number. SCs secreting ChABC significantly decreased CSPGs, led to some egress of SCs from the graft, and increased propriospinal and 5-HT-positive axons in the graft. SCs secreting both D15A and ChABC yielded the best responses: (1) the largest number of SC myelinated axons, (2) more propriospinal axons in the graft and host tissue around and caudal to it, (3) more corticospinal axons closer to the graft and around and caudal to it, (4) more brainstem neurons projecting caudal to the transplant, (5) increased 5-HT-positive axons in the graft and caudal to it, (6) significant improvement in aspects of locomotion, and (7) improvement in mechanical and thermal allodynia. This is the first evidence that the combination of SC transplants engineered to secrete neurotrophin and chondroitinase further improves axonal regeneration and locomotor and sensory function.

Combining Neurotrophin-Transduced Schwann Cells and Rolipram to Promote Functional Recovery from Subacute Spinal Cord Injury

Following spinal cord injury (SCI), both an inhibitory environment and lack of intrinsic growth capacity impede axonal regeneration. In a previous study, prevention of cyclic adenosine monophosphate (AMP) hydrolysis by the phosphodiesterase-4 inhibitor rolipram, in combination with Schwann cell (SC) grafts, promoted significant supraspinal and proprioceptive fiber growth and/or sparing and improved locomotion. In another study, transplanted SCs transduced to generate a bifunctional neurotrophin (D15A) led to significant increases in graft SCs and axons, including supraspinal and myelinated axons. Here we studied the growth and myelination of local and supraspinal axons and functional outcome following the combination of rolipram administration and neurotrophin-transduced SC implantation after SCI. Rolipram was administered subcutaneously for 4 weeks immediately after contusion at vertebral T8 (25.0-mm weight drop, MASCIS impactor). GFP or GFP-D15A-transduced SCs were injected into the injury epicenter 1 week after SCI. GFP-D15A SC grafts and GFP SC grafts with rolipram contained significantly more serotonergic fibers compared to GFP SCs. SC myelinated axons were increased significantly in GFP SC with rolipram-treated animals compared to animals receiving SCI alone. Rolipram administered with either GFP or GFP-D15A SCs significantly increased numbers of brain stem-derived axons below the lesion/implant area and improved hindlimb function. Compared to the single treatments, the combination led to the largest SC grafts, the highest numbers of serotonergic fibers in the grafts, and increased numbers of axons from the reticular formation below the lesion/implant area and provided the greatest improvement in hindlimb function. These findings demonstrate the therapeutic potential for a combination therapy involving the maintenance of cyclic AMP levels and neurotrophin-transduced SCs to repair the subacutely injured spinal cord.

Preliminary report of multiple cell therapy for patients with multiple system atrophy

The aim of this study is to explore the safety and therapeutic effect of multiple cell transplantations on patients with multiple system atrophy. Ten patients suffering from multiple system atrophy were treated by multiple cell transplantations from August 2005 to March 2011. They were six males and four females, with an average age of 51.90 ± 12.92 years (23-66 years). Multiple cell types were transplanted by intravenous, intrathecal, and intracranial routes; for example, 0.4-0.5 × 10(6)/kg umbilical cord mesenchymal cells by intravenous drip, intrathecal implantation of 2.0 × 10(6) Schwann cells and 2.0-5.0 × 10(6) neural progenitor cells through cerebellar cistern puncture, or 2 × 10(6) olfactory ensheathing cells and 4 × 10(6) neural progenitor cells injected into key points for neural network restoration (KPNNR). The neurological function was assessed before and after treatment with the International Cooperative Ataxia Rating Scale (ICARS) by the World Federation of Neurology and the Unified Multiple System Atrophy Rating Scale (UMSARS). The patients achieved neurological function amelioration after treatment, which included improvements in walking ability, gaits, standing, speech, and muscular tension; the ICARS score decreased from a preoperative 46.30 ± 14.50 points to postoperative 41.90 ± 18.40 points (p = 0.049). The UMSARS score decreased from preoperative 50.00 ± 20.65 points to postoperative 46.56 ± 23.05 points (p = 0.037). Among them, two patients remained stable and underwent a second treatment 0.5-1 year after the first therapy. After treatment, five patients were followed up for more than 6 months. Balance and walking ability improved further in four patients, while one patient remained stable for over 6 months. In conclusion, a strategy of comprehensive cell-based neurorestorative therapy for patients with multiple system atrophy is safe and appears to be beneficial. This manuscript is published as part of the International Association of Neurorestoratology (IANR) supplement issue of Cell Transplantation.

Genetically modified mesenchymal stem cells (MSCs) promote axonal regeneration and prevent hypersensitivity after spinal cord injury

Neurotrophins and the transplantation of bone marrow-derived stromal cells (MSCs) are both candidate therapies targeting spinal cord injury (SCI). While some studies have suggested the ability of MSCs to transdifferentiate into neural cells, other SCI studies have proposed anti-inflammatory and other mechanisms underlying established beneficial effects. We grafted rat MSCs genetically modified to express MNTS1, a multineurotrophin that binds TrkA, TrkB and TrkC, and p75(NTR) receptors or MSC-MNTS1/p75(-) that binds mainly to the Trk receptors. Seven days after contusive SCI, PBS-only, GFP-MSC, MSC-MNTS1/GFP or MSC-MNTS1/p75(-)/GFP were delivered into the injury epicenter. All transplanted groups showed reduced inflammation and cystic cavity size compared to control SCI rats. Interestingly, transplantation of the MSC-MNTS1 and MSC-MNTS1/p75(-), but not the naïve MSCs, enhanced axonal growth and significantly prevented cutaneous hypersensitivity after SCI. Moreover, transplantation of MSC-MNTS1/p75(-) promoted angiogenesis and modified glial scar formation. These findings suggest that MSCs transduced with a multineurotrophin are effective in promoting cell growth and improving sensory function after SCI. These novel data also provide insight into the neurotrophin-receptor dependent mechanisms through which cellular transplantation leads to functional improvement after experimental SCI.