Influence of local environment on the differentiation of neural stem cells engrafted onto the injured spinal cord

The aOECs Facilitate the Neuronal Differentiation of Neural Stem Cells in the Inflammatory Microenvironment Through Up-Regulation of Bioactive Factors and Activation of Wnt3/β-Catenin Pathway

The therapeutic application of neural stem cells (NSCs) in the central nerve system (CNS) injury is a promising strategy for combating irreversible neuronal loss. However, a variety of obvious inflammatory responses following nerve injury rapidly create an unfavorable microenvironment for survival and neuronal differentiation of NSCs in lesion area, limiting the efficacy of NSC-based therapy for CNS injury. It remained unknown how to effectively increase the neuronal differentiation efficiency of NSCs through transplantation. Here, we demonstrated that curcumin (CCM)-activated olfactory ensheathing cells (aOECs) effectively promoted neuronal differentiation of NSCs in the activated microglial inflammatory condition, and co-transplantation of aOECs and NSCs improved neurological recovery of rats after spinal cord injury (SCI), as evidenced by higher expression levels of neuronal markers and lower expression levels of glial markers in the differentiated cells, greater number of Tuj-1-positive cells as well as higher Basso, Beattie, and Bresnahan (BBB) locomotor scale, compared to the corresponding controls. Pathologically, hematoxylin and eosin (HE) staining and immunostaining also showed that aOECs remarkably enhanced the in vivo neuronal differentiation of NSCs and migration, and nerve repair. Further analysis revealed that the underlying mechanisms of aOECs potentiating the neuronal conversion of NSCs under inflammatory environment were tightly associated with up-regulation of anti-inflammatory cytokines and neurotrophic factors in OECs, and importantly, the activation of Wnt3/β-catenin pathway was likely involved in the mechanisms underlying the observed cellular events. Therefore, this study provides a promising strategy for SCI repair by co-transplantation of aOECs and NSCs.

Biomaterial-Based bFGF Delivery for Nerve Repair

Diseases in the nervous system are common in the human body. People have to suffer a great burden due to huge economic costs and poor prognosis of the diseases. Many treatment modalities are now available that can make recovery better. Managing nutritional factors is also helpful for such diseases. The basic fibroblast growth factor (bFGF) is one of the major nutritional factors, which plays a crucial role in organogenesis and tissue homeostasis. It plays a role in cell proliferation, migration, and differentiation, thereby regulating angiogenesis and wound healing and repair of the muscle, bone, and nerve. The study on how to improve the stability of bFGF to increase the treatment effect for different diseases has garnered tremendous attention. Biomaterials are the popular methods to improve the stability of bFGF because they are safe for the living body as they are biocompatible. Biomaterials can be loaded with bFGF and delivered locally to achieve the goal of sustained bFGF release. In the present review, we report different types of biomaterials that are used for bFGF delivery for nerve repair and briefly report how the introduced bFGF can function in the nervous system. We aim to provide summative guidance for future studies about nerve injury using bFGF.

Inhibition of phosphodiesterase-4 in the spinal dorsal horn ameliorates neuropathic pain via cAMP-cytokine-Cx43 signaling in mice

Background

The spinal phosphodiesterase‐4 (PDE4) plays an important role in chronic pain. Inhibition of PDE4, an enzyme catalyzing the hydrolysis of cyclic adenosine monophosphate AMP (cAMP), produces potent antinociceptive activity. However, the antinociceptive mechanism remains largely unknown. Connexin43 (Cx43), a gap junction protein, has been shown to be involved in controlling pain transduction at the spinal level; restoration of Cx43 expression in spinal astrocytes to the normal levels reduces nerve injury‐induced pain. Here, we evaluate the novel mechanisms involving spinal cAMP‐Cx43 signaling by which PDE4 inhibitors produce antinociceptive activity.

Methods

First, we determined the effect of PDE4 inhibitors rolipram and roflumilast on partial sciatic nerve ligation (PSNL)‐induced mechanical hypersensitivity. Next, we observed the role of cAMP‐Cx43 signaling in the effect of PDE4 inhibitors on PSNL‐induced mechanical hypersensitivity.

Results

Single or repeated, intraperitoneal or intrathecal administration of rolipram or roflumilast significantly reduced mechanical hypersensitivity in mice following PSNL. In addition, repeated intrathecal treatment with either of PDE4 inhibitors reduced PSNL‐induced downregulation of cAMP and Cx43, and upregulation of proinflammatory cytokines tumor necrosis factor‐α (TNF‐α) and interleukin‐1β. Furthermore, the antinociceptive effects of PDE4 inhibitors were attenuated by the protein kinase A (PKA) inhibitor H89, TNF‐α, or Cx43 antagonist carbenoxolone. Finally, PSNL‐induced upregulation of PDE4B and PDE4D, especially the PDE4B subtype, was reduced by treatment with either of the PDE4 inhibitors.

Conclusions

The results suggest that the antinociceptive effect of PDE4 inhibitors is contributed by increasing Cx43 expression via cAMP‐PKA‐cytokine signaling in the spinal dorsal horn.

Three Growth Factors Induce Proliferation and Differentiation of Neural Precursor Cells In Vitro and Support Cell-Transplantation after Spinal Cord Injury In Vivo

Stem cell therapy with neural precursor cells (NPCs) has the potential to improve neuroregeneration after spinal cord injury (SCI). Unfortunately, survival and differentiation of transplanted NPCs in the injured spinal cord remains low. Growth factors have been successfully used to improve NPC transplantation in animal models, but their extensive application is associated with a relevant financial burden and might hinder translation of findings into the clinical practice. In our current study, we assessed the potential of a reduced number of growth factors in different combinations and concentrations to increase proliferation and differentiation of NPCs in vitro. After identifying a “cocktail” (EGF, bFGF, and PDGF-AA) that directed cell fate towards the oligodendroglial and neuronal lineage while reducing astrocytic differentiation, we translated our findings into an in vivo model of cervical clip contusion/compression SCI at the C6 level in immunosuppressed Wistar rats, combining NPC transplantation and intrathecal administration of the growth factors 10 days after injury. Eight weeks after SCI, we could observe surviving NPCs in the injured animals that had mostly differentiated into oligodendrocytes and oligodendrocytic precursors. Moreover, “Stride length” and “Average Speed” in the CatWalk gait analysis were significantly improved 8 weeks after SCI, representing beneficial effects on the functional recovery with NPC transplantation and the administration of the three growth factors. Nevertheless, no effects on the BBB scores could be observed over the course of the experiment and regeneration of descending tracts as well as posttraumatic myelination remained unchanged. However, reactive astrogliosis, as well as posttraumatic inflammation and apoptosis was significantly reduced after NPC transplantation and GF administration. Our data suggest that NPC transplantation is feasible with the use of only EGF, bFGF, and PDGF-AA as supporting growth factors.

In vivo monitoring of remnant undifferentiated neural cells following human induced pluripotent stem cell-derived neural stem/progenitor cells transplantation

Transplantation of human-induced pluripotent stem cell-derived neural stem/progenitor cells (hiPSC-NS/PCs) is a promising treatment for a variety of neuropathological conditions. Although previous reports have indicated the effectiveness of hiPSC-NS/PCs transplantation into the injured spinal cord of rodents and nonhuman primates, long-term observation of hiPSC-NS/PCs post-transplantation suggested some "unsafe" differentiation-resistant properties, resulting in disordered overgrowth. These findings suggest that, even if "safe" NS/PCs are transplanted into the human central nervous system (CNS), the dynamics of cellular differentiation of stem cells should be noninvasively tracked to ensure safety. Positron emission tomography (PET) provides molecular-functional information and helps to detect specific disease conditions. The current study was conducted to visualize Nestin (an NS/PC marker)-positive undifferentiated neural cells in the CNS of immune-deficient (nonobese diabetic-severe combined immune-deficient) mice after hiPSC-NS/PCs transplantation with PET, using 18 kDa translocator protein (TSPO) ligands as labels. TSPO was recently found to be expressed in rodent NS/PCs, and its expression decreased with the progression of neuronal differentiation. We hypothesized that TSPO would also be present in hiPSC-NS/PCs and expressed strongly in residual immature neural cells after transplantation. The results showed high levels of TSPO expression in immature hiPSC-NS/PCs-derived cells, and decreased TSPO expression as neural differentiation progressed in vitro. Furthermore, PET with [18 F] FEDAC (a TSPO radioligand) was able to visualize the remnant undifferentiated hiPSC-NS/PCs-derived cells consisting of TSPO and Nestin+ cells in vivo. These findings suggest that PET with [18 F] FEDAC could play a key role in the safe clinical application of CNS repair in regenerative medicine.

Adult Neural Progenitor Cells Transplanted into Spinal Cord Injury Differentiate into Oligodendrocytes, Enhance Myelination, and Contribute to Recovery

Long-term survival and integration of neural progenitor cells (NPCs) transplanted following spinal cord injury (SCI) have been observed. However, questions concerning the differentiation choice, the mechanism of action, and the contribution of NPCs to functional recovery remains unanswered. Therefore, we investigated the differentiation of NPCs, global transcriptomal changes in transplanted NPCs, the effect of NPCs on neuroinflammation, and the causality between NPC transplantation and functional recovery. We found that NPCs transplanted following SCI differentiate mainly into oligodendrocytes and enhance myelination, upregulate genes related to synaptic signaling and mitochondrial activity, and downregulate genes related to cytokine production and immune system response. NPCs suppress the expression of pro-inflammatory cytokines/chemokines; moreover, NPC ablation confirm that NPCs were responsible for enhanced recovery in hindlimb locomotor function. Understanding the reaction of transplanted NPCs is important for exploiting their full potential. Existence of causality implies that NPCs are useful in the treatment of SCI.

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NPCs differentiate mainly into oligodendrocytes and enhance myelination

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NPCs suppress expression of pro-inflammatory cytokines/chemokines

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Causality exists between transplantation of NPCs and functional recovery

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NPCs upregulate genes related to synaptic signaling, oligodendrocytes/myelination

Lymphotoxin β receptor-mediated NFκB signaling promotes glial lineage differentiation and inhibits neuronal lineage differentiation in mouse brain neural stem/progenitor cells

BACKGROUND

Lymphotoxin (LT) is a lymphokine mainly expressed in lymphocytes. LTα binds one or two membrane-associated LTβ to form LTα2β1 or LTα1β2 heterotrimers. The predominant LTα1β2 binds to LTβ receptor (LTβR) primarily expressed in epithelial and stromal cells. Most studies on LTβR signaling have focused on the organization, development, and maintenance of lymphoid tissues. However, the roles of LTβR signaling in the nervous system, particularly in neurogenesis, remain unknown. Here, we investigated the role of LTβR-mediated NFκB signaling in regulating neural lineage differentiation.

METHODS

The C57BL/6J wild-type and GFAP-dnIκBα transgenic mice were used. Serum-free embryoid bodies were cultured from mouse embryonic stem cells and further induced into neural stem/progenitor cells (NSCs/NPCs). Primary neurospheres were cultured from embryonic and adult mouse brains followed by monolayer culture for amplification/passage. NFκB activation was determined by adenovirus-mediated NFκB-firefly-luciferase reporter assay and p65/RelB/p52 nuclear translocation assay. LTβR mRNA expression was evaluated by quantitative RT-PCR and LTβR protein expression was determined by immunohistochemistry and Western blot analysis. Multilabeled immunocytochemistry or immunohistochemistry followed by fluorescent confocal microscopy and quantitative analysis of neural lineage differentiation were performed. Graphing and statistical analysis were performed with GraphPad Prism software.

RESULTS

In cultured NSCs/NPCs, LTα1β2 stimulation induced an activation of classical and non-classical NFκB signaling. The expression of LTβR-like immunoreactivity in GFAP+/Sox2+ NSCs was identified in well-established neurogenic zones of adult mouse brain. Quantitative RT-PCR and Western blot analysis validated the expression of LTβR in cultured NSCs/NPCs and brain neurogenic regions. LTβR expression was significantly increased during neural induction. LTα1β2 stimulation in cultured NSCs/NPCs promoted astroglial and oligodendrocytic lineage differentiation, but inhibited neuronal lineage differentiation. Astroglial NFκB inactivation in GFAP-dnIκBα transgenic mice rescued LTβR-mediated abnormal phenotypes of cultured NSCs/NPCs.

CONCLUSION

This study provides the first evidence for the expression and function of LTβR signaling in NSCs/NPCs. Activation of LTβR signaling promotes glial lineage differentiation. Our results suggest that neurogenesis is regulated by the adaptive immunity and inflammatory responses.

Neural stem cell therapy aiming at better functional recovery after spinal cord injury

Injury to the spinal cord causes transection of axon fibers and neural cell death, resulting in disruption of the neural network and severe functional loss. Reconstruction of the damaged neural circuits was once considered to be hopeless as the adult mammalian central nervous system has very poor ability to regenerate. For this reason, there is currently no effective therapeutic treatment for spinal cord injury (SCI). However, with recent developments in stem cell research and cell culture technology, regenerative therapy using neural stem cell (NSC) transplantation has rapidly been developed, and this therapeutic strategy makes it possible to rebuild the destroyed neural circuits. In this review, we discuss the recent breakthroughs in NSC transplantation therapy for SCI. Developmental Dynamics 247:75-84, 2018. © 2017 Wiley Periodicals, Inc.

Neutrophils Induce Astroglial Differentiation and Migration of Human Neural Stem Cells via C1q and C3a Synthesis

Inflammatory processes play a key role in pathophysiology of many neurologic diseases/trauma, but the effect of immune cells and factors on neurotransplantation strategies remains unclear. We hypothesized that cellular and humoral components of innate immunity alter fate and migration of human neural stem cells (hNSC). In these experiments, conditioned media collected from polymorphonuclear leukocytes (PMN) selectively increased hNSC astrogliogenesis and promoted cell migration in vitro. PMN were shown to generate C1q and C3a; exposure of hNSC to PMN-synthesized concentrations of these complement proteins promoted astrogliogenesis and cell migration. Furthermore, in vitro, Abs directed against C1q and C3a reversed the fate and migration effects observed. In a proof-of-concept in vivo experiment, blockade of C1q and C3a transiently altered hNSC migration and reversed astroglial fate after spinal cord injury. Collectively, these data suggest that modulation of the innate/humoral inflammatory microenvironment may impact the potential of cell-based therapies for recovery and repair following CNS pathology.

Stem cell transplantation for spinal cord injury repair

Stem cells, especially neural stem cells (NSCs), are a very attractive cell source for potential reconstruction of injured spinal cord though either neuroprotection, neural regeneration, remyelination, replacement of lost neural cells, or reconnection of disrupted axons. The later have great potential since recent studies demonstrate long-distance growth and connectivity of axons derived from transplanted NSCs after spinal cord injury (SCI). In addition, transplanted NSCs constitute a permissive environment for host axonal regeneration and serve as new targets for host axonal connection. This reciprocal connection between grafted neurons and host neurons constitutes a neuronal relay formation that could restore functional connectivity after SCI.

Engineering Stem Cells for Biomedical Applications

Stem cells are characterized by a number of useful properties, including their ability to migrate, differentiate, and secrete a variety of therapeutic molecules such as immunomodulatory factors. As such, numerous pre-clinical and clinical studies have utilized stem cell-based therapies and demonstrated their tremendous potential for the treatment of various human diseases and disorders. Recently, efforts have focused on engineering stem cells in order to further enhance their innate abilities as well as to confer them with new functionalities, which can then be used in various biomedical applications. These engineered stem cells can take on a number of forms. For instance, engineered stem cells encompass the genetic modification of stem cells as well as the use of stem cells for gene delivery, nanoparticle loading and delivery, and even small molecule drug delivery. The present Review gives an in-depth account of the current status of engineered stem cells, including potential cell sources, the most common methods used to engineer stem cells, and the utilization of engineered stem cells in various biomedical applications, with a particular focus on tissue regeneration, the treatment of immunodeficiency diseases, and cancer.

Proinflammatory cytokines downregulate connexin 43-gap junctions via the ubiquitin-proteasome system in rat spinal astrocytes

Astrocytic gap junctions formed by connexin 43 (Cx43) are crucial for intercellular communication between spinal cord astrocytes. Various neurological disorders are associated with dysfunctional Cx43-gap junctions. However, the mechanism modulating Cx43-gap junctions in spinal astrocytes under pathological conditions is not entirely clear. A previous study showed that treatment of spinal astrocytes in culture with pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) decreased both Cx43 expression and gap junction intercellular communication (GJIC) via a c-jun N-terminal kinase (JNK)-dependent pathway. The current study further elaborates the intracellular mechanism that decreases Cx43 under an inflammatory condition. Cycloheximide chase analysis revealed that TNF-α (10 ng/ml) alone or in combination with IFN-γ (5 ng/ml) accelerated the degradation of Cx43 protein in cultured spinal astrocytes. The reduction of both Cx43 expression and GJIC induced by a mixture of TNF-α and IFN-γ were blocked by pretreatment with proteasome inhibitors MG132 (0.5 μM) and epoxomicin (25 nM), a mixture of TNF-α and IFN-γ significantly increased proteasome activity and Cx43 ubiquitination. In addition, TNF-α and IFN-γ-induced activation of ubiquitin-proteasome systems was prevented by SP600125, a JNK inhibitor. Together, these results indicate that a JNK-dependent ubiquitin-proteasome system is induced under an inflammatory condition that disrupts astrocytic gap junction expression and function, leading to astrocytic dysfunction and the maintenance of the neuroinflammatory state.

Polarized Macrophages Have Distinct Roles in the Differentiation and Migration of Embryonic Spinal-cord-derived Neural Stem Cells After Grafting to Injured Sites of Spinal Cord

Spinal cord injury (SCI) frequently provokes serious detrimental outcomes because neuronal regeneration is limited in the central nervous system (CNS). Thus, the creation of a permissive environment for transplantation therapy with neural stem/progenitor cells (NS/PCs) is a promising strategy to replace lost neuronal cells, promote repair, and stimulate functional plasticity after SCI. Macrophages are important SCI-associated inflammatory cells and a major source of secreted factors that modify the lesion milieu. Here, we used conditional medium (CM) from bone marrow-derived M1 or M2 polarized macrophages to culture murine NS/PCs. The NS/PCs showed enhanced astrocytic versus neuronal/oligodendrocytic differentiation in the presence of M1- versus M2-CM. Similarly, cotransplantation of NS/PCs with M1 and M2 macrophages into intact or injured murine spinal cord increased the number of engrafted NS/PC-derived astrocytes and neurons/oligodendrocytes, respectively. Furthermore, when cotransplantated with M2 macrophages, the NS/PC-derived neurons integrated into the local circuitry and enhanced locomotor recovery following SCI. Interesting, engrafted M1 macrophages promoted long-distance rostral migration of NS/PC-derived cells in a chemokine (C-X-C motif) receptor 4 (CXCR4)-dependent manner, while engrafted M2 macrophages resulted in limited cell migration of NS/PC-derived cells. Altogether, these findings suggest that the cotransplantation of NS/PCs together with polarized macrophages could constitute a promising therapeutic approach for SCI repair.

Activated CD8+ T lymphocytes inhibit neural stem/progenitor cell proliferation: role of interferon-gamma

The ability of neural stem/progenitor cells (NSCs) to self-renew, migrate to damaged sites, and differentiate into neurons has renewed interest in using them in therapies for neurodegenerative disorders. Neurological diseases, including viral infections of the brain, are often accompanied by chronic inflammation, whose impact on NSC function remains unexplored. We have previously shown that chronic neuroinflammation, a hallmark of experimental herpes simplex encephalitis (HSE) in mice, is dominated by brain-infiltrating activated CD8 T-cells. In the present study, activated CD8 lymphocytes were found to suppress NSC proliferation profoundly. Luciferase positive (luc⁺) NSCs co-cultured with activated, MHC-matched, CD8⁺ lymphocytes (luc⁻) showed two- to five-fold lower luminescence than co-cultures with un-stimulated lymphocytes. On the other hand, similarly activated CD4⁺ lymphocytes did not suppress NSC growth. This differential lymphocyte effect on proliferation was confirmed by decreased BrdU uptake by NSC cultured with activated CD8 T-cells. Interestingly, neutralizing antibodies to interferon-gamma (IFN-γ) reversed the impact of CD8 lymphocytes on NSCs. Antibodies specific to the IFN-γ receptor-1 subunit complex abrogated the inhibitory effects of both CD8 lymphocytes and IFN-γ, indicating that the inhibitory effect of these cells was mediated by IFN-γ in a receptor-specific manner. In addition, activated CD8 lymphocytes decreased levels of nestin and Sox2 expression in NSCs while increasing GFAP expression, suggesting possible induction of an altered differentiation state. Furthermore, NSCs obtained from IFN-γ receptor-1 knock-out embryos were refractory to the inhibitory effects of activated CD8⁺ T lymphocytes on cell proliferation and Sox2 expression. Taken together, the studies presented here demonstrate a role for activated CD8 T-cells in regulating NSC function mediated through the production of IFN-γ. This cytokine may influence neuro-restorative processes and ultimately contribute to the long-term sequelae commonly seen following herpes encephalitis.

NFκB signaling regulates embryonic and adult neurogenesis

Both embryonic and adult neurogenesis involves the self-renewal/proliferation, survival, migration and lineage differentiation of neural stem/progenitor cells. Such dynamic process is tightly regulated by intrinsic and extrinsic factors and complex signaling pathways. Misregulated neurogenesis contributes much to a large range of neurodevelopmental defects and neurodegenerative diseases. The signaling of NFκB regulates many genes important in inflammation, immunity, cell survival and neural plasticity. During neurogenesis, NFκB signaling mediates the effect of numerous niche factors such as cytokines, chemokines, growth factors, extracellular matrix molecules, but also crosstalks with other signaling pathways such as Notch, Shh, Wnt/β-catenin. This review summarizes current progress on the NFκB signaling in all aspects of neurogenesis, focusing on the novel role of NFκB signaling in initiating early neural differentiation of neural stem cells and embryonic stem cells.

Implantation of a collagen scaffold seeded with adult rat hippocampal progenitors in a rat model of penetrating brain injury

Penetrating brain injury (PBI) is a complex central nervous system injury in which mechanical damage to brain parenchyma results in hemorrhage, ischemia, broad areas of necrosis, and eventually cavitation. The permanent loss of brain tissue affords the possibility of treatment using a biomaterial scaffold to fill the lesion site and potentially deliver pharmacological or cellular therapeutic agents. The administration of cellular therapy may be of benefit in both mitigating the secondary injury process and promoting regeneration through replacement of certain cell populations. This study investigated the survival and differentiation of adult rat hippocampal neural progenitor cells delivered by a collagen scaffold in a rat model of PBI. The cell-scaffold construct was implanted 1 week after injury and was observed to remain intact with open pores upon analysis 4 weeks later. Implanted neural progenitors were found to have survived within the scaffold, and also to have migrated into the surrounding brain. Differentiated phenotypes included astrocytes, oligodendrocytes, vascular endothelial cells, and possibly macrophages. The demonstrated multipotency of this cell population in vivo in the context of traumatic brain injury has implications for regenerative therapies, but additional stimulation appears necessary to promote neuronal differentiation outside normally neurogenic regions.

Effects of Olig2-overexpressing neural stem cells and myelin basic protein-activated T cells on recovery from spinal cord injury

Neural stem cell (NSC) transplantation is a major focus of current research for treatment of spinal cord injury (SCI). However, it is very important to promote the survival and differentiation of NSCs into myelinating oligodendrocytes (OLs). In this study, myelin basic protein-activated T (MBP-T) cells were passively immunized to improve the SCI microenvironment. Olig2-overexpressing NSCs were infected with a lentivirus carrying the enhanced green fluorescent protein (GFP) reporter gene to generate Olig2-GFP-NSCs that were transplanted into the injured site to differentiate into OLs. Transferred MBP-T cells infiltrated the injured spinal cord, produced neurotrophic factors, and induced the differentiation of resident microglia and/or infiltrating blood monocytes into an "alternatively activated" anti-inflammatory macrophage phenotype by producing interleukin-13. As a result, the survival of transplanted NSCs increased fivefold in MBP-T cell-transferred rats compared with that of the vehicle-treated control. In addition, the differentiation of MBP-positive OLs increased 12-fold in Olig2-GFP-NSC-transplanted rats compared with that of GFP-NSC-transplanted controls. In the MBP-T cell and Olig2-GFP-NSC combined group, the number of OL-remyelinated axons significantly increased compared with those of all other groups. However, a significant decrease in spinal cord lesion volume and an increase in spared myelin and behavioral recovery were observed in Olig2-NSC- and NSC-transplanted MBP-T cell groups. Collectively, these results suggest that MBP-T cell adoptive immunotherapy combined with NSC transplantation has a synergistic effect on histological and behavioral improvement after traumatic SCI. Although Olig2 overexpression enhances OL differentiation and myelination, the effect on functional recovery may be surpassed by MBP-T cells.

Roles of activated astrocyte in neural stem cell proliferation and differentiation

Recent studies demonstrated that the molecules secreted from astrocytes play important roles in the cell fate determination of neural stem cells (NSCs). However, the exact molecules involved and its possible mechanisms in the process remain largely unknown. In this study, astrocyte-conditioned medium (ACM) obtained from astrocytes unstimulated or stimulated by lipopolysaccharide was prepared to treat NSCs. The results showed that both the proliferation and differentiation of NSCs treated with stimulated ACMs were significantly increased compared with those treated with unstimulated ACM. Interleukin-6 (IL-6) antibody neutralization of the ACMs decreased NSC proliferation and astrogliogenesis, while NSC neurogenesis was increased. In contrast, recombinant IL-6 cytokine increased NSC proliferation and astrogliogenesis, but decreased neurogenesis. Furthermore, the expression of phosphorylated signal transducer and activator of transcription 3 (p-stat3) protein as well as serial of basic helix-loop-helix transcription factors (bHLH) mRNA in NSCs exposed to stimulated ACMs significantly increased, respectively. The expression levels of p-stat3 protein and bHLH mRNA of NSCs were significantly altered after adding anti-IL-6 antibody or recombinant IL-6, respectively. The data suggest that IL-6 secreted from activated astrocytes participates in ACM-induced proliferation and differentiation of NSCs via the phosphorylation of stat3 signals and the expression of bHLH transcription factors.

Cellular and paracellular transplants for spinal cord injury: a review of the literature

BACKGROUND

Experimental approaches to limit the spinal cord injury and to promote neurite outgrowth and improved function from a spinal cord injury have exploded in recent decades. Due to the cavitation resulting after a spinal cord injury, newer important treatment strategies have consisted of implanting scaffolds with or without cellular transplants. There are various scaffolds, as well as various different cellular transplants including stem cells at different levels of differentiation, Schwann cells and peripheral nerve implants, that have been reviewed. Also, attention has been given to different re-implantation techniques in avulsion injuries.

METHODS

Using standard search engines, this literature is reviewed.

CONCLUSION

Cellular and paracellular transplantation for application to spinal cord injury offers promising results for those patients with spinal cord pathology.

Cyclosporin A increases recovery after spinal cord injury but does not improve myelination by oligodendrocyte progenitor cell transplantation

BACKGROUND

Transplantation of oligodendrocyte precursor cells (OPCs) is an attractive therapy for demyelinating diseases. Cyclosporin A (CsA) is one of the foremost immunosuppressive agents and has widespread use in tissue and cell transplantation. However, whether CsA affects survival and differentiation of engrafted OPCs in vivo is unknown. In this study, the effect of CsA on morphological, functional and immunological aspects, as well as survival and differentiation of engrafted OPCs in injured spinal cord was explored.

RESULTS

We transplanted green fluorescent protein (GFP) expressed OPCs (GFP-OPCs) into injured spinal cords of rats treated with or without CsA (10 mg/kg). Two weeks after cell transplantation, more GFP-positive cells were found in CsA-treated rats than that in vehicle-treated ones. However, the engrafted cells mostly differentiated into astrocytes, but not oligodendrocytes in both groups. In the CsA-treated group, a significant decrease in spinal cord lesion volume along with increase in spared myelin and neurons were found compared to the control group. Such histological improvement correlated well with an increase in behavioral recovery. Further study suggested that CsA treatment could inhibit infiltration of T cells and activation of resident microglia and/or macrophages derived from infiltrating monocytes in injured spinal cords, which contributes to the survival of engrafted OPCs and repair of spinal cord injury (SCI).

CONCLUSIONS

These results collectively indicate that CsA can promote the survival of engrafted OPCs in injured spinal cords, but has no effect on their differentiation. The engrafted cells mostly differentiated into astrocytes, but not oligodendrocytes. The beneficial effect of CsA on SCI and the survival of engrafted cells may be attributed to its neuroprotective effect.

Differentiation of neural precursor cell-derived oligodendrocyte progenitor cells following transplantation into normal and injured spinal cords

Demyelination contributes to the functional deficits after spinal cord injury (SCI). Therefore, remyelination may be an important strategy to facilitate repair after SCI. Oligodendrocyte precursor cells (OPCs) are immature oligodendrocytes and can differentiate into myelin-forming cells of central nervous system under certain conditions. OPC transplantation is an attractive approach for the treatment of demyelinating diseases. In this study, we transplanted OPCs expressing green fluorescent protein (GFP-OPCs) into normal and injured rat spinal cords to evaluate the differentiation of transplanted OPCs in vivo. Unfortunately, the grafted GFP-OPCs, in spinal cord whether normal or injured, were all differentiated into astrocytes, but not oligodendrocytes. Our further study indicated that inflammatory environment might not be the key factor influencing the differentiation of OPCs. Some spinal cord components, such as bone morphogenetic proteins (BMPs), were the major factors that induced OPCs to differentiate into astrocytes. The three types of BMP receptor (BMPRIA, IB and II) could all be detected in OPCs, and the astroglial differentiation of OPCs induced by spinal cord homogenate extract (SCHE) in vitro could be blocked partly by noggin, an antagonist of BMP. These results suggested that the BMPR signal transduction pathway might be one of the key factors which determine the differentiation direction of engrafted OPCs in spinal cord.

Activated spinal cord ependymal stem cells rescue neurological function

Spinal cord injury (SCI) is a major cause of paralysis. Currently, there are no effective therapies to reverse this disabling condition. The presence of ependymal stem/progenitor cells (epSPCs) in the adult spinal cord suggests that endogenous stem cell-associated mechanisms might be exploited to repair spinal cord lesions. epSPC cells that proliferate after SCI are recruited by the injured zone, and can be modulated by innate and adaptive immune responses. Here we demonstrate that when epSPCs are cultured from rats with a SCI (ependymal stem/progenitor cells injury [epSPCi]), these cells proliferate 10 times faster in vitro than epSPC derived from control animals and display enhanced self renewal. Genetic profile analysis revealed an important influence of inflammation on signaling pathways in epSPCi after injury, including the upregulation of Jak/Stat and mitogen activated protein kinase pathways. Although neurospheres derived from either epSPCs or epSPCi differentiated efficiently to oligodendrocites and functional spinal motoneurons, a better yield of differentiated cells was consistently obtained from epSPCi cultures. Acute transplantation of undifferentiated epSPCi or the resulting oligodendrocyte precursor cells into a rat model of severe spinal cord contusion produced a significant recovery of motor activity 1 week after injury. These transplanted cells migrated long distances from the rostral and caudal regions of the transplant to the neurofilament-labeled axons in and around the lesion zone. Our findings demonstrate that modulation of endogenous epSPCs represents a viable cell-based strategy for restoring neuronal dysfunction in patients with spinal cord damage.

Analysis of host-mediated repair mechanisms after human CNS-stem cell transplantation for spinal cord injury: correlation of engraftment with recovery

BACKGROUND

Human central nervous system-stem cells grown as neurospheres (hCNS-SCns) self-renew, are multipotent, and have potential therapeutic applications following trauma to the spinal cord. We have previously shown locomotor recovery in immunodeficient mice that received a moderate contusion spinal cord injury (SCI) and hCNS-SCns transplantation 9 days post-injury (dpi). Engrafted hCNS-SCns exhibited terminal differentiation to myelinating oligodendrocytes and synapse-forming neurons. Further, selective ablation of human cells using Diphtheria toxin (DT) abolished locomotor recovery in this paradigm, suggesting integration of human cells within the mouse host as a possible mechanism for the locomotor improvement. However, the hypothesis that hCNS-SCns could alter the host microenvironment as an additional or alternative mechanism of recovery remained unexplored; we tested that hypothesis in the present study.

METHODS AND FINDINGS

Stereological quantification of human cells using a human-specific cytoplasmic marker demonstrated successful cell engraftment, survival, migration and limited proliferation in all hCNS-SCns transplanted animals. DT administration at 16 weeks post-transplant ablated 80.5% of hCNS-SCns. Stereological quantification for lesion volume, tissue sparing, descending serotonergic host fiber sprouting, chondroitin sulfate proteoglycan deposition, glial scarring, and angiogenesis demonstrated no evidence of host modification within the mouse spinal cord as a result of hCNS-SCns transplantation. Biochemical analyses supplemented stereological data supporting the absence of neural stem-cell mediated host repair. However, linear regression analysis of the number of engrafted hCNS-SCns vs. the number of errors on a horizontal ladder beam task revealed a strong correlation between these variables (r = -0.78, p<0.05), suggesting that survival and engraftment were directly related to a quantitative measure of recovery.

CONCLUSIONS

Altogether, the data suggest that the locomotor improvements associated with hCNS-SCns transplantation were not due to modifications within the host microenvironment, supporting the hypothesis that human cell integration within the host circuitry mediates functional recovery following a 9 day delayed transplant.

Cytomegalovirus infection and interferon-gamma modulate major histocompatibility complex class I expression on neural stem cells

Cytomegalovirus (CMV) is the leading transmittable cause of congenital brain abnormalities in children and infection results in fatal ventriculoencephalitis in advanced acquired immunodeficiency syndrome (AIDS) patients. Pathology associated with CMV brain infection is seen predominantly in the periventricular region, an area known to harbor neural stem cells (NSCs). In the present study, using an adult model of murine CMV brain infection, the authors demonstrated that nestin-positive NSCs in the subventricular zone are susceptible to murine CMV infection. Furthermore, primary NSC cultures supported productive murine CMV replication with a 1000-fold increase in viral titers by 5 days post infection (d.p.i). Previous studies from the authors' laboratory demonstrated that CD8 lymphocytes were essential in protecting the brain against murine CMV infection. In the present study, the authors found that interferon (IFN)-gamma treatment increased the expression of major histocompatibility complex (MHC) class I on NSCs. Viral infection, on the other hand, inhibited this IFN-gamma-induced MHC up-regulation. In addition to increasing MHC class I expression, IFN-gamma (but not tumor necrosis factor [TNF]-alpha, interleukin [IL]-1 beta, or IL-10) also suppressed NSC proliferation in vitro. This decrease in proliferation was not accompanied by apoptosis or extracellular release of cellular lactate dehydrogenase (LDH), suggesting that the effects were not due to direct cytotoxicity. These studies demonstrate that NSCs are susceptible to murine CMV infection and inflammatory mediators, such as IFN-gamma, alter cellular characteristics which may have an impact on their reparative functions.

The interaction of Nogo-66 receptor with Nogo-p4 inhibits the neuronal differentiation of neural stem cells

The Nogo-66 receptor (NgR) has been found throughout axons in the adult and maturing CNS. An interaction of Nogo on the oligodendrocyte surface with NgR on axons has been suggested to play an important role in limiting axonal growth. In our study, we found that neural stem cells (NSCs) derived from the spinal cords of rats expressed NgR significantly. After normal NSCs differentiation, the average neuronal neurite length was 97.80+/-6.97 microm and the percentage of differentiated neurons was 34.73+/-5.21% 3 days after the differentiation was initiated in vitro. If NSCs were allowed to differentiate in the presence of Nogo-p4 (the active segment of Nogo-66), the average neurite length and the percentage of differentiated neurons were decreased, respectively, to 60.31+/-6.58 microm and 10.26+/-1.22%. An siRNA-mediated knockdown of NgR on NSCs could reverse the inhibitory effect of Nogo-p4 and restore the average neuronal neurite length as well as the percentage of differentiated neurons to 94.01+/-8.37 microm and 31.84+/-4.03%. These results deepen our knowledge about the distribution of NgR and provide a possible strategy of treating NSCs to ameliorate neuronal differentiation after transplantation.

Interleukin-1beta mediates proliferation and differentiation of multipotent neural precursor cells through the activation of SAPK/JNK pathway

Neural precursor cells (NPCs) have been experimentally used to repair the damaged nervous system either by exogenous transplantation or by endogenous activation. In post-injury inflammation, an array of cytokines including interleukin-1beta (IL-1beta) are released by host as well as invading immune cells and increased markedly. In the present study, we investigated the effects of IL-1beta on the survival, proliferation, differentiation and migration of NPCs as well as underlying intracellular signaling pathways. NPCs derived from the E16 rat brain were expanded in neurospheres that were found to express IL-1beta, IL-1RI and IL-1RII, but not IL-1alpha and IL-1ra. IL-1beta inhibited the proliferation of NPCs in a dose-dependent manner, an effect that can be reversed by IL-1ra, an antagonist for IL-1 receptor. This inhibitory effect of IL-1beta on NPCs proliferation resulted in part from its effect on increased apoptosis of NPCs. Moreover, IL-1ra did not affect NPCs lineage fate but rather inhibited GFAP expression in differentiated astrocytes. We also found that IL-1ra had no effect on the transmigration of NPCs in vitro. Finally, we showed that the effect of IL-1beta on NPCs proliferation and differentiation appeared to be mediated by SAPK/JNK, but not ERK, P38MAPK nor NF-kappaB pathways. These findings collectively suggest that the inflammatory environment following CNS injuries may influence the ability of NPCs to repair the damage.

Cyclosporine affects the proliferation and differentiation of neural stem cells in culture

Cyclosporine is one of the foremost immunosuppressive agents for cell, tissue, and organ transplantation. Cyclosporine is, however, associated with significant side effects in the host, and may also affect the fate of the donor cells. This study was performed to test whether cyclosporine may change the fate of neural stem cells, as neural stem cell transplant has become a potential treatment for neurological disorders and damage. Results of this study showed that cyclosporine inhibited the proliferation significantly in a dosage-dependent manner. Cyclosporine also affected the differentiation of neural stem cells, which mainly increased astrocyte genesis and decreased neuron differentiation.

Most C6 Cells Are Cancer Stem Cells: Evidence from Clonal and Population Analyses

Cancer stem cells have been isolated from human gliomas and many other parenchymal tumors. It was previously assumed that many established malignant cell lines also contain a rare subpopulation of stem cells. This study was designed to investigate the fraction of cancer stem cells in the C6 glioma cell line using clonal and population analyses, rather than isolating methods, which are based on specific markers. Interestingly, in the serum-containing medium, each of the 67 single C6 cells plated per miniwell was able to generate a clone and subclones, which subsequently gave rise to a xenograft glioma in the BALB/C-nude mouse. The CD133- C6 cells also possessed clonogenic, self-renewal, and tumorigenic capacities. Moreover, our findings indicated that brief exposure to Hoechst 33342 was harmful to the clonogenicity and proliferation of individual C6 cells. Therefore, the non-side-population cells may be deprived of their stem cell features in the process of Hoechst 33342 staining as a step in isolating a Hoechst-negative side population with flow cytometry. Thus, we concluded that the C6 line was mainly composed of cancer stem cells, although many of them were neither CD133+ nor side population.

Embryonic stem cells produce neurotrophins in response to cerebral tissue extract: Cell line-dependent differences

In the present study, we compare the capacity of two different embryonic stem (ES) cell lines to secrete neurotrophins in response to cerebral tissue extract derived from healthy or injured rat brains. The intrinsic capacity of the embryonic cell lines BAC7 (feeder cell-dependent cultivation) to release brain-derived neurotrophic factor (BDNF) or neurotrophin-3 (NT-3) exceeded the release of these factors by CGR8 cells (feeder cell-free growth) by factors of 10 and 4, respectively. Nerve growth factor (NGF) was secreted only by BAC7 cells. Conditioning of cell lines with cerebral tissue extract derived from healthy or fluid percussion-injured rat brains resulted in a significant time-dependent increase in BDNF release in both cell lines. The increase in BDNF release by BAC7 cells was more pronounced when cells were incubated with brain extract derived from injured brain. However, differences in neurotrophin release associated with the origin of brain extract were at no time statistically significant. Neutrophin-3 and NGF release was inhibited when cell lines were exposed to cerebral tissue extract. The magnitude of the response to cerebral tissue extract was dependent on the intrinsic capacity of the cell lines to release neurotrophins. Our results clearly demonstrate significant variations in the intrinsic capability of different stem cell lines to produce neurotrophic factors. Furthermore, a significant modulation of neurotrophic factor release was observed following conditioning of cell lines with tissue extract derived from rat brains. A significant modulation of neurotrophin release dependent on the source of cerebral tissue extract used was not observed.