Oligodendrocytes and radial glia derived from adult rat spinal cord progenitors: morphological and immunocytochemical characterization

Neutrophil Recruitment and Leukocyte Response Following Focused Ultrasound and Microbubble Mediated Blood-Brain Barrier Treatments

(Appeared originally in Theranostics 2021; 11:1655-1671) Reprinted under Creative Commons Attribution License.

Isolate and Culture Neural Stem Cells from the Mouse Adult Spinal Cord

Whereas neural stem cells and their niches have been extensively studied in the brain, little is known on these cells, their environment, and their function in the adult spinal cord. Adult spinal cord neural stem cells are located in a complex niche surrounding the central canal, and these cells expressed genes which are specifically expressed in the caudal central nervous system (CNS). In-depth characterization of these cells in vivo and in vitro will provide interesting clues on the possibility to utilize this endogenous cell pool to treat spinal cord damages. We describe here a procedure to derive and culture neural spinal cord stem cells from adult mice using the neurosphere method.

Regionally Specific Human Pre-Oligodendrocyte Progenitor Cells Produce Both Oligodendrocytes and Neurons after Transplantation in a Chronically Injured Spinal Cord Rat Model after Glial Scar Ablation

Chronic spinal cord injury (SCI) is a devastating medical condition. In the acute phase after injury, there is cell loss resulting in chronic axonal damage and loss of sensory and motor function including loss of oligodendrocytes that results in demyelination of axons and further dysfunction. In the chronic phase, the inhibitory environment within the lesion including the glial scar can arrest axonal growth and regeneration and can also potentially affect transplanted cells. We hypothesized that glial scar ablation (GSA) along with cell transplantation may be required as a combinatorial therapy to achieve functional recovery, and therefore we proposed to examine the survival and fate of human induced pluripotent stem cell (iPSC) derived pre-oligodendrocyte progenitor cells (pre-OPCs) transplanted in a model of chronic SCI, whether this was affected by GSA, and whether this combination of treatments would result in functional recovery. In this study, chronically injured athymic nude (ATN) rats were allocated to one of three treatment groups: GSA only, pre-OPCs only, or GSA+pre-OPCs. We found that human iPSC derived pre-OPCs were multi-potent and retained the ability to differentiate into mainly oligodendrocytes or neurons when transplanted into the chronically injured spinal cords of rats. Twelve weeks after cell transplantation, we observed that more of the transplanted cells differentiated into oligodendrocytes when the glial scar was ablated compared with no GSA. Further, we also observed that a higher percentage of transplanted cells differentiated into V2a interneurons and motor neurons in the pre-OPCs only group when compared with GSA+pre-OPCs. This suggests that the local environment created by ablation of the glial scar may have a significant effect on the fate of cells transplanted into the injury site.

Neutrophil recruitment and leukocyte response following focused ultrasound and microbubble mediated blood-brain barrier treatments

Rationale: Delivery of therapeutic agents to the brain is limited by the presence of the blood-brain barrier (BBB). An emerging strategy to temporarily and locally increase the permeability of the BBB is the use of transcranial focused ultrasound (FUS) and systematically injected microbubbles (MBs). FUS+MB BBB treatments cause an acute inflammatory response, marked by a transient upregulation of pro-inflammatory genes; however, the cellular immune response remains unknown.

Methods: FUS+MB BBB treatments were monitored in real-time using two-photon fluorescence microscopy and transgenic EGFP Wistar rats, which harbour several fluorescent cell types. Leukocyte identification and counts were confirmed using magnetic resonance imaging-guided FUS+MB BBB treatments. Participation of leukocytes in reducing β-amyloid pathology following repeated FUS+MB BBB treatments was investigated in the TgCRND8 mouse model of Alzheimer's disease.

Results: Intravascular leukocyte activity indicative of acute inflammation were identified, including transendothelial migration, formation of cell aggregates, and cell masses capable of perturbing blood flow. Leukocyte responses were only observed after the onset of sonication. Neutrophils were identified to be a key participating leukocyte. Significantly more neutrophils were detected in the sonicated hemisphere compared to the contralateral hemisphere, and to untreated controls. Three to five biweekly FUS+MB BBB treatments did not induce significantly more neutrophil recruitment, nor neutrophil phagocytosis of β-amyloid plaques, in TgCRND8 mice compared to untreated controls.

Conclusions: This study provides evidence that the cellular aspect of the peripheral immune response triggered by FUS+MB BBB treatments begins immediately after sonication, and emphasizes the importance for further investigations to be conducted to understand leukocyte dynamics and cerebral blood flow responses to FUS+MB BBB treatments.

The leading edge: Emerging neuroprotective and neuroregenerative cell-based therapies for spinal cord injury

Spinal cord injuries (SCIs) are associated with tremendous physical, social, and financial costs for millions of individuals and families worldwide. Rapid delivery of specialized medical and surgical care has reduced mortality; however, long-term functional recovery remains limited. Cell-based therapies represent an exciting neuroprotective and neuroregenerative strategy for SCI. This article summarizes the most promising preclinical and clinical cell approaches to date including transplantation of mesenchymal stem cells, neural stem cells, oligodendrocyte progenitor cells, Schwann cells, and olfactory ensheathing cells, as well as strategies to activate endogenous multipotent cell pools. Throughout, we emphasize the fundamental biology of cell-based therapies, critical features in the pathophysiology of spinal cord injury, and the strengths and limitations of each approach. We also highlight salient completed and ongoing clinical trials worldwide and the bidirectional translation of their findings. We then provide an overview of key adjunct strategies such as trophic factor support to optimize graft survival and differentiation, engineered biomaterials to provide a support scaffold, electrical fields to stimulate migration, and novel approaches to degrade the glial scar. We also discuss important considerations when initiating a clinical trial for a cell therapy such as the logistics of clinical-grade cell line scale-up, cell storage and transportation, and the delivery of cells into humans. We conclude with an outlook on the future of cell-based treatments for SCI and opportunities for interdisciplinary collaboration in the field.

Advances in ex vivo models and lab-on-a-chip devices for neural tissue engineering

The technologies related to ex vivo models and lab-on-a-chip devices for studying the regeneration of brain, spinal cord, and peripheral nerve tissues are essential tools for neural tissue engineering and regenerative medicine research. The need for ex vivo systems, lab-on-a-chip technologies and disease models for neural tissue engineering applications are emerging to overcome the shortages and drawbacks of traditional in vitro systems and animal models. Ex vivo models have evolved from traditional 2D cell culture models to 3D tissue-engineered scaffold systems, bioreactors, and recently organoid test beds. In addition to ex vivo model systems, we discuss lab-on-a-chip devices and technologies specifically for neural tissue engineering applications. Finally, we review current commercial products that mimic diseased and normal neural tissues, and discuss the future directions in this field.

Rapid Serum-Free Isolation of Oligodendrocyte Progenitor Cells from Adult Rat Spinal Cord

Oligodendrocyte progenitor cells (OPCs) play a pivotal role in both health and disease within the central nervous system, with oligodendrocytes, arising from resident OPCs, being the main myelinating cell type. Disruption in OPC numbers can lead to various deleterious health defects. Numerous studies have described techniques for isolating OPCs to obtain a better understanding of this cell type and to open doors for potential treatments of injury and disease. However, the techniques used in the majority of these studies involve several steps and are time consuming, with current culture protocols using serum and embryonic or postnatal cortical tissue as a source of isolation. We present a primary culture method for the direct isolation of functional adult rat OPCs, identified by neuron-glial antigen 2 (NG2) and platelet derived growth factor receptor alpha (PDGFrα) expression, which can be obtained from the adult spinal cord. Our method uses a simple serum-free cocktail of 3 growth factors - FGF₂, PDGF_AA, and IGF-I, to expand adult rat OPCs in vitro to 96% purity. Cultured cells can be expanded for at least 10 passages with very little manipulation and without losing their phenotypic progenitor cell properties, as shown by immunocytochemistry and RT-PCR. Cultured adult rat OPCs also maintain their ability to differentiate into GalC positive cells when incubated with factors known to stimulate their differentiation. This new isolation method provides a new source of easily accessible adult stem cells and a powerful tool for their expansion in vitro for studies aimed at central nervous system repair.

Remyelination improvement after neurotrophic factors secreting cells transplantation in rat spinal cord injury

OBJECTIVES

Neurotrophic factors secreting cells (NTS-SCs) may be a superior cell source for cell-based therapy in neurodegenerative diseases. NTS-SCs are able to secrete some neurotrophic Such as nerve growth factor and glia-derived neurotrophic factor. Our primary aim was to assess transplantation of neurotrophic factor secreting cells derived from human adipose-derived stem cells (hADSCs) into the damaged spinal cord rats and determine the potential of these cells in remyelination.

MATERIALS AND METHODS

To this end, 40 adult male Wistar rats were categorized into four groups including; control, lysolecithin (Lysophosphatidylcholines or LPC), vehicle, and NTS-SCs transplan-tation. Local demyelination was induced using LPC injection into the lateral column of spinal cord. Seven days after the lysolecithin lesion, the cells transplantation was performed. The ultrastructure of myelinated fibers was examined with a transmission electron microscope to determine the extent of myelin destruction and remyelinization 4 weeks post cell transplantation. Moreover, the presence of oligodendrocyte in the lesion of spinal cord was assessed by immunohistochemistry procedure.

RESULTS

The results of current study indicated that in NTF-SCs transplantation group, the remyelination process and the mean of myelin sheath thickness as well as axonal diameters were significantly higher than other groups (P<0.001). Furthermore, immunohistochemistry analysis revealed that in NTF-SCs transplantation group more than 10 percent of transplanted cells were positive for specific markers of oligodendrocyte cells.

CONCLUSION

NTF-SCs transplantation represents a valuable option for cell-based therapy in the nervous tissue damages.

Exercise Training Promotes Functional Recovery after Spinal Cord Injury

The exercise training is an effective therapy for spinal cord injury which has been applied to clinic. Traditionally, the exercise training has been considered to improve spinal cord function only through enhancement, compensation, and replacement of the remaining function of nerve and muscle. Recently, accumulating evidences indicated that exercise training can improve the function in different levels from end-effector organ such as skeletal muscle to cerebral cortex through reshaping skeletal muscle structure and muscle fiber type, regulating physiological and metabolic function of motor neurons in the spinal cord and remodeling function of the cerebral cortex. We compiled published data collected in different animal models and clinical studies into a succinct review of the current state of knowledge.

Cellular Therapies in Trauma and Critical Care Medicine: Forging New Frontiers

Trauma is a leading cause of death in both military and civilian populations worldwide. Although medical advances have improved the overall morbidity and mortality often associated with trauma, additional research and innovative advancements in therapeutic interventions are needed to optimize patient outcomes. Cell-based therapies present a novel opportunity to improve trauma and critical care at both the acute and chronic phases that often follow injury. Although this field is still in its infancy, animal and human studies suggest that stem cells may hold great promise for the treatment of brain and spinal cord injuries, organ injuries, and extremity injuries such as those caused by orthopedic trauma, burns, and critical limb ischemia. However, barriers in the translation of cell therapies that include regulatory obstacles, challenges in manufacturing and clinical trial design, and a lack of funding are critical areas in need of development. In 2015, the Department of Defense Combat Casualty Care Research Program held a joint military–civilian meeting as part of its effort to inform the research community about this field and allow for effective planning and programmatic decisions regarding research and development. The objective of this article is to provide a “state of the science” review regarding cellular therapies in trauma and critical care, and to provide a foundation from which the potential of this emerging field can be harnessed to mitigate outcomes in critically ill trauma patients.

Rodent Hypoxia-Ischemia Models for Cerebral Palsy Research: A Systematic Review

Cerebral palsy (CP) is a complex multifactorial disorder, affecting approximately 2.5-3/1000 live term births, and up to 22/1000 prematurely born babies. CP results from injury to the developing brain incurred before, during, or after birth. The most common form of this condition, spastic CP, is primarily associated with injury to the cerebral cortex and subcortical white matter as well as the deep gray matter. The major etiological factors of spastic CP are hypoxia/ischemia (HI), occurring during the last third of pregnancy and around birth age. In addition, inflammation has been found to be an important factor contributing to brain injury, especially in term infants. Other factors, including genetics, are gaining importance. The classic Rice-Vannucci HI model (in which 7-day-old rat pups undergo unilateral ligation of the common carotid artery followed by exposure to 8% oxygen hypoxic air) is a model of neonatal stroke that has greatly contributed to CP research. In this model, brain damage resembles that observed in severe CP cases. This model, and its numerous adaptations, allows one to finely tune the injury parameters to mimic, and therefore study, many of the pathophysiological processes and conditions observed in human patients. Investigators can recreate the HI and inflammation, which cause brain damage and subsequent motor and cognitive deficits. This model further enables the examination of potential approaches to achieve neural repair and regeneration. In the present review, we compare and discuss the advantages, limitations, and the translational value for CP research of HI models of perinatal brain injury.

Isolation of Neural Stem/Progenitor Cells from the Periventricular Region of the Adult Rat and Human Spinal Cord

Adult rat and human spinal cord neural stem/progenitor cells (NSPCs) cultured in growth factor-enriched medium allows for the proliferation of multipotent, self-renewing, and expandable neural stem cells. In serum conditions, these multipotent NSPCs will differentiate, generating neurons, astrocytes, and oligodendrocytes. The harvested tissue is enzymatically dissociated in a papain-EDTA solution and then mechanically dissociated and separated through a discontinuous density gradient to yield a single cell suspension which is plated in neurobasal medium supplemented with epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), and heparin. Adult rat spinal cord NSPCs are cultured as free-floating neurospheres and adult human spinal cord NSPCs are grown as adherent cultures. Under these conditions, adult spinal cord NSPCs proliferate, express markers of precursor cells, and can be continuously expanded upon passage. These cells can be studied in vitro in response to various stimuli, and exogenous factors may be used to promote lineage restriction to examine neural stem cell differentiation. Multipotent NSPCs or their progeny can also be transplanted into various animal models to assess regenerative repair.

Optimizing culture medium composition to improve oligodendrocyte progenitor cell yields in vitro from subventricular zone-derived neural progenitor cell neurospheres

Neural Stem and Progenitor Cells (NSC/NPC) are gathering tangible recognition for their uses in cell therapy and cell replacement therapies for human disease, as well as a model system to continue research on overall neural developmental processes in vitro. The Subventricular Zone is one of the largest NSC/NPC niches in the developing mammalian Central Nervous System, and persists through to adulthood. Oligodendrocyte progenitor cell (OPC) enriched cultures are usefull tools for in vitro studies as well as for cell replacement therapies for treating demyelination diseases. We used Subventricular Zone-derived NSC/NPC primary cultures from newborn mice and compared the effects of different growth factor combinations on cell proliferation and OPC yield. The Platelet Derived Growth Factor-AA and BB homodimers had a positive and significant impact on OPC generation. Furthermore, heparin addition to the culture media contributed to further increase overall culture yields. The OPC generated by this protocol were able to mature into Myelin Basic Protein-expressing cells and to interact with neurons in an in vitro co-culture system. As a whole, we describe an optimized in vitro method for increasing OPC.

Impact of chemokines on the properties of spinal cord-derived neural progenitor cells in a rat spinal cord lesion model

The existence of endogenous neural progenitor cells (NPCs) in the adult spinal cord (sc) provides the potential for tailored repair therapies after spinal cord injury (SCI). This study investigates the impact of inflammatory mediators on properties of NPC cultures derived from adult rats after SCI. The Infinite Horizon impactor was used to apply 200-kdyn thoracic sc lesions in adult rats. Control groups received laminectomies to equivalent sc regions. Thoracic sc segments were taken for neurosphere cell cultures. Cell proliferation was found to be significantly higher in lesion groups. Neurosphere-derived cells differentiated into neurons, oligodendroglia, and astroglia. Lesion cultures exhibited significantly higher amounts of glial fibrillary acidic protein (GFAP) mRNA (P < 0.0005) and β-III-tubulin mRNA (P < 0.05) compared with sham animals. Neurospheres from different treatment groups exhibited the same amounts of tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 mRNA. C-C chemokine receptor (CCR) expression on neurospheres was examined by real-time RT-PCR. CCR1 was expressed most consistently in mRNA levels in neurospheres from both treatment groups. After cell differentiation, CCR1 mRNA amounts decreased. CCR1 was detectable by immunohistochemistry in neurospheres and differentiated cells of both groups. Application of CCL3 during differentiation cycles led to significantly higher GFAP mRNA amounts in sham animals compared with CCL3-free cultures; in contrast, CCL3 had no impact on cell differentiation in the lesion group. In conclusion, impact SCI alters differentiation tendencies and proliferation rates of adult-derived sc NPCs. Thereby, CCR1/CCL3 promotes specifically astroglial differentiation of NPCs, which provides a potential target for future neurorestorative approaches.

Transplantation of human adipose-derived stem cells enhances remyelination in lysolecithin-induced focal demyelination of rat spinal cord

Adipose-derived stem cells (ADSCs) are a desirable stem cell source in neurodegenerative diseases treatment due to their ability to differentiate into different cell lineages. In this study, we transplanted human ADSCs (hADSCs) into a lysophosphatidylcholine (lysolecithin) model of multiple sclerosis (MS) and determined the efficiency of these cells in remyelination process. Forty adult rats were randomly divided into control, lysolecithin, vehicle, and transplantation groups, and focal demyelination was induced by lysolecithin injection into spinal cord. To assess motor performance, all rats were examined weekly with a standard EAE scoring scale. Four weeks after cell transplantation, to assess the extent of demyelination and remyelination, Luxol Fast Blue staining was used. In addition, immunohistochemistry technique was used for assessment of the presence of oligodendrocyte phenotype cells in damaged spinal cord. Our results indicated that hADSCs had ability to differentiate into oligodendrocyte phenotype cells and improved remyelination process. Moreover, the evaluation of rat motor functions showed that animals which were treated with hADSC compared to other groups had significant improvement (P < 0.001). Our finding showed that hADSCs transplantation for cell-based therapies may play a proper cell source in the treatment of neurodegenerative diseases such as MS.

Change of fate commitment in adult neural progenitor cells subjected to chronic inflammation

Neural progenitor cells (NPCs) have regenerative capabilities that are activated during inflammation. We aimed at elucidating how NPCs, with special focus on the spinal cord-derived NPCs (SC-NPCs), are affected by chronic inflammation modeled by experimental autoimmune encephalomyelitis (EAE). NPCs derived from the subventricular zone (SVZ-NPCs) were also included in the study as a reference from a distant inflammatory site. We also investigated the transcriptional and functional difference between the SC-NPCs and SVZ-NPCs during homeostatic conditions. NPCs were isolated and propagated from the SVZ and cervical, thoracic, and caudal regions of the SC from naive rats and rats subjected to EAE. Using Affymetrix microarray analyses, the global transcriptome was measured in the different NPC populations. These analyses were paralleled by NPC differentiation studies. Assessment of basal transcriptional and functional differences between NPC populations in naive rat revealed a higher neurogenic potential in SVZ-NPCs compared with SC-NPCs. Conversely, during EAE, the neurogenicity of the SC-NPCs was increased while their gliogenicity was decreased. We detected an overall increase of inflammation and neurodegeneration-related genes while the developmentally related profile was decreased. Among the decreased functions, we isolated a gliogenic signature that was confirmed by differentiation assays where the SC-NPCs from EAE generated fewer oligodendrocytes and astrocytes but more neurons than control cultures. In summary, NPCs displayed differences in fate-regulating genes and differentiation potential depending on their rostrocaudal origin. Inflammatory conditions downregulated gliogenicity in SC-NPCs, promoting neurogenicity. These findings give important insight into neuroinflammatory diseases and the mechanisms influencing NPC plasticity during these conditions.

Development and characterization of a new inbred transgenic rat strain expressing DsRed monomeric fluorescent protein

The inbred rat is a suitable model for studying human disease and because of its larger size is more amenable to complex surgical manipulation than the mouse. While the rodent fulfills many of the criteria for transplantation research, an important requirement is the ability to mark and track donors cells and assess organ viability. However, tracking ability is limited by the availability of transgenic (Tg) rats that express suitable luminescent or fluorescent proteins. Red fluorescent protein cloned from Discosoma coral (DsRed) has several advantages over other fluorescent proteins, including in vivo detection in the whole animal and ex vivo visualization in organs as there is no interference with autofluorescence. We generated and characterized a novel inbred Tg Lewis rat strain expressing DsRed monomeric (DsRed mono) fluorescent protein under the control of a ubiquitously expressed ROSA26 promoter. DsRed mono Tg rats ubiquitously expressed the marker gene as detected by RT-PCR but the protein was expressed at varying levels in different organs. Conventional skin grafting experiments showed acceptance of DsRed monomeric Tg rat skin on wild-type rats for more than 30 days. Cardiac transplantation of DsRed monomeric Tg rat hearts into wild-type recipients further showed graft acceptance and long-term organ viability (>6 months). The DsRed monomeric Tg rat provides marked cells and/or organs that can be followed for long periods without immune rejection and therefore is a suitable model to investigate cell tracking and organ transplantation.

Evidence that the central canal lining of the spinal cord contributes to oligodendrogenesis during postnatal development and adulthood in intact rats

Two waves of oligodendrogenesis in the ventricular zone of the spinal cord (SC-VZ) during rat development, which take place between embryonic days 14 and 18 (E14-E18) and E20-E21, have been described. In the VZ of the brain, unlike the SC-VZ, a third wave of oligodendrogenesis occurs during the first weeks of postnatal development. Using immunofluorescence staining of intact rat SC tissue, we noticed the presence of small numbers of Olig2(+) /Sox-10(+) cells inside the lining of the central canal (CC) during postnatal development and adulthood. Olig2(+) /Sox-10(+) cells appeared inside the lining of the CC shortly after birth, and their number reached a maximum of approximately 0.65 ± 0.14 cell/40-μm section during the second postnatal week. After the latter development, the number of Olig2(+) /Sox-10(+) cells decreased to 0.21 ± 0.07 (P36) and 0.18 ± 0.1 cell/section (P120). At P21, Olig2(+) /Sox-10(+) cells inside the CC lining started to express other oligodendroglial markers such as CNPase, RIP, and APC. Olig2(+) /Sox-10(+) cells usually did not proliferate inside the CC lining and were only rarely found to be immunoreactive against oligodendrocyte progenitor markers such as NG2 or PDGFRα. Using 5-bromo-2-deoxyuridine administration at P2, P11, P22, or P120-P125, we revealed that these cells arose in the CC lining during postnatal development and adulthood. Our findings confirmed that the CC lining is the source of a small number of cells with an oligodendroglial phenotype during postnatal development and adulthood in the SC of intact rats.

Molecular imaging in stem cell therapy for spinal cord injury

Spinal cord injury (SCI) is a serious disease of the center nervous system (CNS). It is a devastating injury with sudden loss of motor, sensory, and autonomic function distal to the level of trauma and produces great personal and societal costs. Currently, there are no remarkable effective therapies for the treatment of SCI. Compared to traditional treatment methods, stem cell transplantation therapy holds potential for repair and functional plasticity after SCI. However, the mechanism of stem cell therapy for SCI remains largely unknown and obscure partly due to the lack of efficient stem cell trafficking methods. Molecular imaging technology including positron emission tomography (PET), magnetic resonance imaging (MRI), optical imaging (i.e., bioluminescence imaging (BLI)) gives the hope to complete the knowledge concerning basic stem cell biology survival, migration, differentiation, and integration in real time when transplanted into damaged spinal cord. In this paper, we mainly review the molecular imaging technology in stem cell therapy for SCI.

Bioimaging of Transgenic Rats Established at Jichi Medical University: Applications in Transplantation Research

Research in the life sciences has been greatly advanced by the ability to directly visualize cells, tissues, and organs. Preclinical studies often involve many small and large animal experiments and, frequently, cell and organ transplantations. The rat is an excellent animal model for the development of transplantation and surgical techniques because of its small size and ability to breed in small spaces. Ten years ago, we established color-imaging transgenic rats and methods for the direct visualization of their tissues. Since then, our transgenic rats have been used throughout the various fields that are concerned with cell transplantation therapy. In this minireview, we summarize results from some of the groups that have used our transgenic rats at the bench level and in cell transplantation research.

Host induction by transplanted neural stem cells in the spinal cord: further evidence for an adult spinal cord neurogenic niche

AIM

To explore the hypothesis that grafts of exogenous stem cells in the spinal cord of athymic rats or rats with transgenic motor neuron disease can induce endogenous stem cells and initiate intrinsic repair mechanisms that can be exploited in amyotrophic lateral sclerosis therapeutics.

MATERIALS & METHODS

Human neural stem cells (NSCs) were transplanted into the lower lumbar spinal cord of healthy rats or rats with transgenic motor neuron disease to explore whether signals related to stem cells can initiate intrinsic repair mechanisms in normal and amyotrophic lateral sclerosis subjects. Patterns of migration and differentiation of NSCs in the gray and white matter, with emphasis on the central canal region and ependymal cell-driven neurogenesis, were analyzed.

RESULTS

Findings suggest that there is extensive cross-signaling between transplanted NSCs and a putative neurogenic niche in the ependyma of the lower lumbar cord. The formation of a neuronal cord from NSC-derived cells next to ependyma suggests that this structure may serve a mediating or auxiliary role for ependymal induction.

CONCLUSION

These findings raise the possibility that NSCs may stimulate endogenous neurogenesis and initiate intrinsic repair mechanisms in the lower spinal cord.

SPARC-like 1 (SC1) is a diversely expressed and developmentally regulated matricellular protein that does not compensate for the absence of SPARC in the CNS

SPARC-like 1 (SC1) is a member of the SPARC family of matricellular proteins that has been implicated in the regulation of processes such as cell migration, proliferation, and differentiation. Here we show that SC1 exhibits remarkably diverse and dynamic expression in the developing and adult nervous system. During development, SC1 localizes to radial glia and pial-derived structures, including the vasculature, choroid plexus, and pial membranes. SC1 is not downregulated in postnatal development, but its expression shifts to distinct time windows in subtypes of glia and neurons, including astrocytes, large projection neurons, Bergmann glia, Schwann cells, and ganglionic satellite cells. In addition, SC1 expression levels and patterns are not altered in the SPARC null mouse, suggesting that SC1 does not compensate for the absence of SPARC. We conclude that SC1 and SPARC may share significant homology, but are likely to have distinct but complementary roles in nervous system development.

The multifaceted effects of agmatine on functional recovery after spinal cord injury through Modulations of BMP-2/4/7 expressions in neurons and glial cells

Presently, few treatments for spinal cord injury (SCI) are available and none have facilitated neural regeneration and/or significant functional improvement. Agmatine (Agm), a guanidinium compound formed from decarboxylation of L-arginine by arginine decarboxylase, is a neurotransmitter/neuromodulator and been reported to exert neuroprotective effects in central nervous system injury models including SCI. The purpose of this study was to demonstrate the multifaceted effects of Agm on functional recovery and remyelinating events following SCI. Compression SCI in mice was produced by placing a 15 g/mm² weight for 1 min at thoracic vertebra (Th) 9 segment. Mice that received an intraperitoneal (i.p.) injection of Agm (100 mg/kg/day) within 1 hour after SCI until 35 days showed improvement in locomotor recovery and bladder function. Emphasis was made on the analysis of remyelination events, neuronal cell preservation and ablation of glial scar area following SCI. Agm treatment significantly inhibited the demyelination events, neuronal loss and glial scar around the lesion site. In light of recent findings that expressions of bone morphogenetic proteins (BMPs) are modulated in the neuronal and glial cell population after SCI, we hypothesized whether Agm could modulate BMP- 2/4/7 expressions in neurons, astrocytes, oligodendrocytes and play key role in promoting the neuronal and glial cell survival in the injured spinal cord. The results from computer assisted stereological toolbox analysis (CAST) demonstrate that Agm treatment dramatically increased BMP- 2/7 expressions in neurons and oligodendrocytes. On the other hand, BMP- 4 expressions were significantly decreased in astrocytes and oligodendrocytes around the lesion site. Together, our results reveal that Agm treatment improved neurological and histological outcomes, induced oligodendrogenesis, protected neurons, and decreased glial scar formation through modulating the BMP- 2/4/7 expressions following SCI.

Isolate and culture neural stem cells from the mouse adult spinal cord

Whereas neural stem cells and their niches have been extensively studied in the brain, little is known on these cells, their environment and their function in the adult spinal cord. Adult spinal cord neural stem cells are located in a complex niche surrounding the central canal and these cells expressed genes which are specifically expressed in the caudal central nervous system (CNS). In depth characterization of these cells in vivo and in vitro will provide interesting clues on the possibility to utilize this endogenous cell pool to treat spinal cord damages. We describe here a procedure to derive and culture neural spinal cord stem cells from adult mice using the neurosphere method.

Advances in stem cell therapy for spinal cord injury

Spinal cord injury (SCI) is a devastating condition producing great personal and societal costs and for which there is no effective treatment. Stem cell transplantation is a promising therapeutic strategy, though much preclinical and clinical research work remains. Here, we briefly describe SCI epidemiology, pathophysiology, and experimental and clinical stem cell strategies. Research in stem cell biology and cell reprogramming is rapidly advancing, with the hope of moving stem cell therapy closer to helping people with SCI. We examine issues important for clinical translation and provide a commentary on recent developments, including termination of the first human embryonic stem cell transplantation trial in human SCI.

Ephrin-B3 decreases the survival of adult rat spinal cord-derived neural stem/progenitor cells in vitro and after transplantation into the injured rat spinal cord

Although transplantation of neural stem/progenitor cells (NSPC) encourages regeneration and repair after spinal cord injury (SCI), the survival of transplanted NSPC is limited. Ephrin-B3 has been shown to reduce the death of endogenous NSPC in the subventricular zone of the mouse brain without inducing uncontrolled proliferation. Due to similarities in the environment of the brain and spinal cord, we hypothesized that ephrin-B3 might reduce the death of both transplanted and endogenous spinal cord-derived NSPC. Both normal and injured (26 g clip compression) spinal cords were examined. Ephrin-B3-Fc was tested, and Fc fragments and phosphate-buffered saline (PBS) were used as controls. We found that EphA4 receptors were expressed by spinal cord-derived NSPC and expressed in the normal and injured rat spinal cord (higher expression in the latter). In vitro, ephrin-B3-Fc did not significantly reduce the survival of NSPC except at 1 μg/mL (P<0.05), but Fc fragments alone reduced NSPC survival at all doses in a dose-dependent fashion. In vivo, intrathecal infusion of ephrin-B3-Fc increased the proliferation of endogenous ependymal cells and the proportion of proliferating cells that expressed the glial fibrillary acidic protein astrocytic marker in the injured spinal cord compared with the infusion of PBS (P<0.05). However, in the injured spinal cord, the infusion of either ephrin-B3-Fc or Fc fragments alone caused a 20-fold reduction in the survival of transplanted NSPC (P<0.001). Thus, after SCI, ephrin-B3-Fc and Fc fragments are toxic to transplanted NSPC.

Non-viral gene therapy for spinal cord regeneration

Spinal cord injury (SCI) normally results in life-long disabilities and a broad range of secondary complications. Advances in therapeutic delivery during the past few decades offer hope for such victims. However, the limited functional improvement shown in in vivo studies hinders effective therapeutic application in clinical practice. Recent studies showed that gene vectors can transfect cells present in the lesion of an injured spinal cord (endogenous cells) and thereby produce therapeutic molecules with long-lasting biological effects that promote neural tissue regeneration. In this article we review recent advances in non-viral gene delivery into neural cells and their use for gene therapy in SCI.

In Vivo Bioimaging Rats for Translational Research in Cell and Tissue Transplantation

The rat is an excellent cell transplantation model. In accordance with the innovative development of in vivo bioimaging technology, over the last decade we have been developing an engineered rat system based on transgenic technology and have been demonstrating the usefulness of the system with genetically encoded imaging probes such as fluorescent and luminescent proteins. In cooperation with the Japan Society for Organ Preservation and Medical Biology (President: Professor T. Asano), we have also been using luciferase-Tg rats for research into organ preservation and cell transplantation. In this minireview, we introduce the results obtained recently by using these powerful experimental tools during international collaboration in cell transplantation research.

Stem cell aging and plasticity in the Drosophila nervous system

The majority of neural stem cells (NSCs) are considered as very plastic precursors that, in vitro, can divide indefinitely or differentiate into neurons or glia under specific conditions. However, in vivo, these cells actively proliferate during development, and later enter quiescence or apoptosis. This raises the issue as to whether stem cells keep their plastic behavior throughout their life, which may impact their therapeutic potential in regenerative medicine. Using the Gcm/Glide (for Glial cell missing/Glial cell deficient) transcription factor, which is able to trigger a complete and stable fate conversion into glia when ectopically expressed, we recently reported that the plasticity of Drosophila NSCs, commonly called neuroblasts (NBs), is age-dependent. When challenged with Gcm/Glide, newborn NBs are more easily converted into glia than old ones. Furthermore, the few old NBs that can be converted frequently generate cells with a stable (NB/glia) intermediate identity, a phenotype characteristic of cancer cells. We here discuss the concept of aging in NSC fate conversion and speculate on how our findings impact the ongoing debate concerning NSC plasticity.

Cyp26b1 mediates differential neurogenicity in axial-specific populations of adult spinal cord progenitor cells

Utilization of endogenous adult spinal cord progenitor cells (SCPCs) for neuronal regeneration is a promising strategy for spinal cord repair. To mobilize endogenous SCPCs for injury repair, it is necessary to understand their intrinsic properties and to identify signaling factors that can stimulate their neurogenic potential. In this study, we demonstrate that adult mouse SCPCs express distinct combinatorial Hox genes and exhibit axial-specific stem cell properties. Lumbar-derived neurospheres displayed higher primary sphere formation and greater neurogenicity compared with cervical- and thoracic-derived neurospheres. To further understand the mechanisms governing neuronal differentiation of SCPCs from specific axial regions, we examined the neurogenic responses of adult SCPCs to retinoic acid (RA), an essential factor for adult neurogenesis. Although RA is a potent inducer of neuronal differentiation, we found that RA enhanced the generation of neurons specifically in cervical- but not lumbar-derived cells. We further demonstrate that the differential RA response was mediated by the RA-degrading enzyme cytochrome P450 oxidase b1 Cyp26b1. Lumbar cells express high levels of Cyp26b1 and low levels of the RA-synthesizing enzyme retinaldehyde dehydrogenase Raldh2, resulting in limited activation of the RA signaling pathway in these cells. In contrast, low Cyp26b1 expression in cervical spinal cord progenitor cells allows RA signaling to be readily activated upon RA treatment. The intrinsic heterogeneity and signaling factor regulation among adult SCPCs suggest that different niche factor regimens are required for site-specific mobilization of endogenous SCPCs from distinct spatial regions of the spinal cord for injury repair.

Neural stem/progenitor cells from the adult human spinal cord are multipotent and self-renewing and differentiate after transplantation

Neural stem/progenitor cell (NSPC) transplantation is a promising therapy for spinal cord injury (SCI). However, little is known about NSPC from the adult human spinal cord as a donor source. We demonstrate for the first time that multipotent and self-renewing NSPC can be cultured, passaged and transplanted from the adult human spinal cord of organ transplant donors. Adult human spinal cord NSPC require an adherent substrate for selection and expansion in EGF (epidermal growth factor) and FGF2 (fibroblast growth factor) enriched medium. NSPC as an adherent monolayer can be passaged for at least 9 months and form neurospheres when plated in suspension culture. In EGF/FGF2 culture, NSPC proliferate and primarily express nestin and Sox2, and low levels of markers for differentiating cells. Leukemia inhibitory factor (LIF) promotes NSPC proliferation and significantly enhances GFAP expression in hypoxia. In differentiating conditions in the presence of serum, these NSPC show multipotentiality, expressing markers of neurons, astrocytes, and oligodendrocytes. Dibutyryl cyclic AMP (dbcAMP) significantly enhances neuronal differentiation. We transplanted the multipotent NSPC into SCI rats and show that the xenografts survive, are post-mitotic, and retain the capacity to differentiate into neurons and glia.

Together, these findings reveal that multipotent self-renewing NSPC cultured and passaged from adult human spinal cords of organ transplant donors, respond to exogenous factors that promote selective differentiation, and survive and differentiate after transplantation into the injured spinal cord.

Adult spinal cord radial glia display a unique progenitor phenotype

Radial glia (RG) are primarily embryonic neuroglial progenitors that express Brain Lipid Binding Protein (Blbp a.k.a. Fabp7) and Glial Fibrillary Acidic Protein (Gfap). We used these transcripts to demarcate the distribution of spinal cord radial glia (SCRG) and screen for SCRG gene expression in the Allen Spinal Cord Atlas (ASCA). We reveal that neonatal and adult SCRG are anchored in a non-ventricular niche at the spinal cord (SC) pial boundary, and express a “signature” subset of 122 genes, many of which are shared with “classic” neural stem cells (NSCs) of the subventricular zone (SVZ) and SC central canal (CC). A core expressed gene set shared between SCRG and progenitors of the SVZ and CC is particularly enriched in genes associated with human disease. Visualizing SCRG in a Fabp7-EGFP reporter mouse reveals an extensive population of SCRG that extend processes around the SC boundary and inwardly (through) the SC white matter (WM), whose abundance increases in a gradient from cervical to lumbar SC. Confocal analysis of multiple NSC-enriched proteins reveals that postnatal SCRG are a discrete and heterogeneous potential progenitor population that become activated by multiple SC lesions, and that CC progenitors are also more heterogeneous than previously appreciated. Gene ontology analysis highlights potentially unique regulatory pathways that may be further manipulated in SCRG to enhance repair in the context of injury and SC disease.

Radial glia: progenitor, pathway, and partner

Radial glia (RG) are a glial cell type that can be found from the earliest stages of CNS development. They are clearly identifiable by their unique morphology, having a periventricular cell soma and a long process extending all the way to the opposite pial surface. Due to this striking morphology, RG have long been thought of as a transient substrate for neuron migration in the developing brain. In fact, RG cells, far from exclusively serving as a passive scaffold for cell migration, have a remarkably diverse range of critical functions in CNS development and function. These include serving as progenitors of neurons and glia both during development as well as in response to injury, helping to direct axonal and dendritic process outgrowth, and regulating synaptic development and function. RG also engage in extensive bidirectional signaling both with neurons and one another. This review describes the diversity of RG cell types in the CNS and discusses their many important activities.

Spinal cord injury: From inflammation to glial scar

BACKGROUND

Glial scar (GS) is the most important inhibitor factor to neuroregeneration after spinal cord injury (SCI) and behaves as a tertiary lesion. The present review of the literature searched for representative studies concerning GS and therapeutic strategies to neuroregeneration.

METHODS

The author used the PubMed database and Google scholar to search articles published in the last 20 years. Key words used were SCI, spinal cord (SC) inflammation, GS, and SCI treatment.

RESULTS

Both inflammation and GS are considered important events after SCI. Despite the fact that firstly they seem to cause benefit, in the end they cause more harm than good to neuroregeneration. Each stage has its own aspects under the influence of the immune system causing inflammation, from the primary to secondary lesion and from those to GS (tertiary lesion).

CONCLUSION

Future studies should stress the key points where and when GS presents itself as an inhibitory factor to neuroregeneration. Considering GS as an important event after SCI, the author defends GS as being a tertiary lesion. Current strategies are presented with emphasis on stem cells and drug therapy. A better understanding will permit the development of a therapeutic basis in the treatment of the SCI patients considering each stage of the lesion, with emphasis on GS and neuroregeneration.

Intrathecal transplantation of stem cells by lumbar puncture for thoracic spinal cord injury in the rat

STUDY DESIGN

Experimental investigation of intrathecal transplantation of stem cells by lumbar puncture (LP) in a rat model that simulates human thoracic spinal cord injury (SCI).

OBJECTIVES

To examine the distribution and phenotype of spinal cord-derived neural stem/progenitor cells (NSPCs) and bone marrow-derived mesenchymal stromal cells (BMSCs) following LP transplantation in SCI rats.

SETTING

Toronto Western Research Institute, Toronto, Ontario, Canada.

METHODS

NSPCs or BMSCs were transplanted via LP at level L3-5 1 week after compression SCI at T8. Rats were killed at 3, 17 and 27 days after LP transplantation and the relative distribution of cells at C4, T8 and L3-5 was quantitated. The phenotype of the NSPC and BMSC was assessed with immunocytochemistry in vitro and following LP transplantation.

RESULTS

By 4 weeks, more NSPC migrated to the lesion site relative to BMSC and uninjured animals. However, there was no preferential homing of either of these types of cells into the parenchyma of the injury site, and most of the transplanted cells remained in the intrathecal space. In vitro, spinal cord-derived NSPC proliferated and expressed nestin, but after LP transplantation, NSPC became post-mitotic and primarily expressed oligodendrocyte markers. In contrast, BMSC did not express any neural antigens in vivo.

CONCLUSION

LP is a minimally invasive method of cell transplantation that produces wide dissemination of cells in the subarachnoid space of the spinal cord. This is the first study to report and quantify the phenotype and spatial distribution of LP transplanted NSPC and BMSC in the intact and injured spinal cord.

Reaction of oligoglia to spinal cord injury in rats and transplantation of human olfactory ensheathing cells

In experiments on rats with lateral TVIII hemisection of the spinal cord and transplantation of ensheating olfactory cells, we studied structural changes at the lesion site and adjacent rostral and dorsal regions of the spinal cord. The state of oligodendrocytes and myelin fibers and motor function in experimental animal were analyzed. Open field testing (BBB test) showed that motor functions steadily increased (by 13% on average) within the interval from day 21 to day 53 after transplantation. Histological examination showed that groups of transplanted cells carrying human nuclear marker (HNu(+)cells) were still present at the lesion site 30 days after surgery. Some of these cells migrated in the rostral and caudal directions from the injection site to a distance up to 6 mm. At the initial period after hemisection, the number of oligodendrocytes (O4(+)-cells) in the immediate vicinity to the lesion site decreased 2-fold, but no significant changes in the number of neurons were found in the rostral and dorsal fragments of the spinal cord compared to the corresponding parameter in controls. Sixty days after transplantation, the cross-section area in the rostral part of the spinal cord at a distance of 3 mm from damage site increased by 15.3% compared to the control. The number of O4(+)-cells at the lesion site and in adjacent rostral and caudal parts of the spinal cord by 22.8% surpassed that in the control group. The number of remyelinated axons also increased. These findings suggest that the absence of pronounced structural changes in the rostral and caudal parts of the spinal cord compared to lesion site at early stages after damage and cell transplantation. At the same time, pronounced activation of oligodendrocytes in this region suggests their involvement together with Schwann cells into remyelination of regenerating axons, which can serve as a factor of partial restoration of motor functions after spinal cord injury.

A comparative study of the structural organization of spheres derived from the adult human subventricular zone and glioblastoma biopsies

Sphere forming assays have been useful to enrich for stem like cells in a range of tumors. The robustness of this system contrasts the difficulties in defining a stem cell population based on cell surface markers. We have undertaken a study to describe the cellular and organizational composition of tumorspheres, directly comparing these to neurospheres derived from the adult human subventricular zone (SVZ). Primary cell cultures from brain tumors were found to contain variable fractions of cells positive for tumor stem cell markers (CD133 (2-93%)/SSEA1 (3-15%)/CXCR4 (1-72%)). All cultures produced tumors upon xenografting. Tumorspheres contained a heterogeneous population of cells, but were structurally organized with stem cell markers present at the core of spheres, with markers of more mature glial progenitors and astrocytes at more peripheral location. Ultrastructural studies showed that tumorspheres contained a higher fraction of electron dense cells in the core than the periphery (36% and 19%, respectively). Neurospheres also contained a heterogeneous cell population, but did not have an organization similar to tumorspheres. Although tumorspheres clearly display irregular and neoplastic cells, they establish an organized structure with an outward gradient of differentiation. We suggest that this organization is central in maintaining the tumor stem cell pool.

Voluntary exercise increases oligodendrogenesis in spinal cord

Exercise has been shown to increase hippocampal neurogenesis, but the effects of exercise on oligodendrocyte generation have not yet been reported. In this study, we evaluated the hypothesis that voluntary exercise may affect neurogenesis, and more in particular, oligodendrogenesis in the thoracic segment of the intact spinal cord of adult nestin-GFP transgenic mice. Voluntary exercise for 7 and 14 days increased nestin-GFP expression around the ependymal area. In addition, voluntary exercise for 7 days significantly increased nestin-GFP expression in both the white and gray matter of the thoracic segment of the intact spinal cord, whereas, 14-day exercise decreased nestin-GFP expression. Markers for immature oligodendrocytes (transferrin and CNPase) were significantly increased after 7 days of voluntary exercise. These results suggest that voluntary exercise positively influences oligodendrogenesis in the intact spinal cord, emphasizing the beneficial effects of voluntary exercise as a possible co-treatment for spinal cord injury.

Isolation of human multipotent neural progenitors from adult filum terminale

Stem cells have been isolated from several CNS regions, including the spinal cord. However, the terminal end of the spinal cord, filum terminale, has been referred to as a fibrovascular tag without neurogenic potential and of no clinical significance. Recently, we were fortunate to acquire some samples of this tissue. We show for the first time that progenitor cells exhibiting the hallmarks of stem cells can be isolated from adult human filum terminale (FTNPs). More specifically, FTNPs self-renew and proliferate to form neurospheres, and exhibit tripotent differentiation into neurons, astrocytes, and oligodendrocytes. Equally important, FTNPs develop the electrophysiological profile of neurons and glia. Whole-cell patch-clamp recordings show beta-III-tubulin(+) neurons exhibiting overshooting action potentials, displaying both the fast inactivating TTX-sensitive sodium current as well as 4-AP and TEA sensitive potassium currents. To assess potency in vivo, FTNPs were transplanted into the posterior periventricular region of control or ischemic rat brains. Despite a vigorous immune response against the xenograft, FTNPs survived and were found not only in the graft area but had also migrated to the lesioned CA1 region. Notwithstanding the immune response, FTNPs differentiated into astrocytes, but no neuronal differentiation was observed in the transplant milieu tested. However, neuronal differentiation in vivo cannot be ruled out and assessment of the conditions necessary to promote neurogenesis in vivo requires more research. Significantly, no tumor formation or aberrant cell morphology was seen in or adjacent to the graft area. Thus, filum terminale provides a novel source of adult human neural progenitor cells that develop into functional neurons with possible clinical applications.

Region-specific differentiation potential of adult rat spinal cord neural stem/precursors and their plasticity in response to in vitro manipulation

This study characterized the differentiation of neural stem/precursor cells (NSPCs) isolated from different levels of the spinal cord (cervical vs lumbar cord) and different regions along the neuraxis (brain vs cervical spinal cord) of adult male Wistar enhanced green fluorescent protein rats. The differentiation of cervical spinal cord NSPCs was further examined after variation of time in culture, addition of growth factors, and changes in cell matrix and serum concentration. Brain NSPCs did not differ from cervical cord NSPCs in the percentages of neurons, astrocytes, or oligodendrocytes but produced 26.9% less radial glia. Lumbar cord NSPCs produced 30.8% fewer radial glia and 6.9% more neurons compared with cervical cord NSPCs. Spinal cord NSPC differentiation was amenable to manipulation by growth factors and changes in in vitro conditions. This is the first study to directly compare the effect of growth factors, culturing time, serum concentration, and cell matrix on rat spinal cord NSPCs isolated, propagated, and differentiated under identical conditions.

Adult spinal cord stem/progenitor cells transplanted as neurospheres preferentially differentiate into oligodendrocytes in the adult rat spinal cord

Neural stem/progenitor cells (NSPCs) capable of generating new neurons and glia reside in the adult mammalian spinal cord. Transplantation of NSPCs has therapeutic potential for spinal cord injury, although there is limited information on the ability of these cells to survive and differentiate in vivo. Neurospheres cultured from the periventricular region of the adult spinal cord contain NSPCs that are self-renewing and multipotent. We examined the survival, proliferation, migration, and differentiation of adult spinal cord NSPCs generated from green fluorescent protein (GFP) transgenic rats and transplanted into the intact spinal cord. The grafted GFP-expressing cells survived for at least 6 weeks in vivo and migrated from the injection site along the rostro-caudal axis of the spinal cord. Transplanted cells transiently proliferated following transplantation and approximately 17% of the GFP-positive cells were apoptotic at 1 day. Also, better survival was seen with NSPCs transplanted as neurospheres in comparison to NSPCs transplanted as dissociated cells. By 1 week posttransplantation, grafted cells primarily expressed an oligodendrocytic phenotype and only 2% differentiated into astrocytes. Approximately 75% versus 38% of the grafted cells differentiated into oligodendrocytes after transplantation into spinal white versus gray matter, respectively. This is the first report to examine the time course of cell survival, proliferation, apoptosis, and phenotypic differentiation of transplanted NSPSs in the spinal cord. This is also the first report to examine the differences between transplanted NSPCs grafted as neurospheres or dissociated cells, and to compare the differentiation potential after transplantation into spinal cord white versus gray matter.