Neural stem/progenitor cells as a promising candidate for regenerative therapy of the central nervous system

NSPCs-ES: mechanisms and functional impact on central nervous system diseases

Patients with central neuronal damage may suffer severe consequences, but effective therapies remain unclear. Previous research has established the transplantation of neural stem cells that generate new neurons to replace damaged ones. In a new field of scientific research, the extracellular secretion of NPSCs (NSPCs-ES) has been identified as an alternative to current chemical drugs. Many preclinical studies have shown that NSPCs-ES are effective in models of various central nervous system diseases (CNS) injuries, from maintaining functional structures at the cellular level to providing anti-inflammatory functions at the molecular level, as well as improving memory and motor functions, reducing apoptosis in neurons, and mediating multiple signaling pathways. The NSPC-ES can travel to the damaged tissue and exert a broad range of therapeutic effects by supporting and nourishing damaged neurons. However, gene editing and cell engineering techniques have recently improved therapeutic efficacy by modifying NSPCs-ES. Consequently, future research and application of NSPCs-ES may provide a novel strategy for the treatment of CNS diseases in the future. In this review, we summarize the current progress on these aspects.

The role of small extracellular vesicles and microRNA as their cargo in the spinal cord injury pathophysiology and therapy

Spinal cord injury (SCI) is a devastating condition with a complex pathology that affects a significant portion of the population and causes long-term consequences. After primary injury, an inflammatory cascade of secondary injury occurs, followed by neuronal cell death and glial scar formation. Together with the limited regenerative capacity of the central nervous system, these are the main reasons for the poor prognosis after SCI. Despite recent advances, there is still no effective treatment. Promising therapeutic approaches include stem cells transplantation, which has demonstrated neuroprotective and immunomodulatory effects in SCI. This positive effect is thought to be mediated by small extracellular vesicles (sEVs); membrane-bound nanovesicles involved in intercellular communication through transport of functional proteins and RNA molecules. In this review, we summarize the current knowledge about sEVs and microRNA as their cargo as one of the most promising therapeutic approaches for the treatment of SCI. We provide a comprehensive overview of their role in SCI pathophysiology, neuroprotective potential and therapeutic effect.

Maintenance of Hypoimmunogenic Features via Regulation of Endogenous Antigen Processing and Presentation Machinery

Universally acceptable donor cells have been developed to address the unmet need for immunotypically matched materials for regenerative medicine. Since forced expression of hypoimmunogenic genes represses the immune response, we established universal pluripotent stem cells (PSCs) by replacing endogenous β2-microglobulin (β2m) with β2m directly conjugated to human leukocyte antigen (HLA)-G, thereby simultaneously suppressing HLA-I expression and the natural killer (NK) cell-mediated immune response. These modified human PSCs retained their pluripotency and differentiation capacity; however, surface presentation of HLA-G was absent from subsequently differentiated cells, particularly cells of neural lineages, due to the downregulation of antigen processing and presentation machinery (APM) genes. Induction of APM genes by overexpression of NLR-family CARD domain-containing 5 (NLRC5) or activator subunit of nuclear factor kappa B (NF-κB) heterodimer (RelA) recovered the surface expression of HLA-G and the hypoimmunogenicity of neural cells. Our findings enhance the utility of hypoimmunogenic cells as universal donors and will contribute to the development of off-the-shelf stem-cell therapeutics.

Lipocalin-2 mediates the rejection of neural transplants

Lipocalin-2 (LCN2) has been implicated in promoting apoptosis and neuroinflammation in neurological disorders; however, its role in neural transplantation remains unknown. In this study, we cultured and differentiated Lund human mesencephalic (LUHMES) cells into human dopaminergic-like neurons and found that LCN2 mRNA was progressively induced in mouse brain after the intrastriatal transplantation of human dopaminergic-like neurons. The induction of LCN2 protein was detected in a subset of astrocytes and neutrophils infiltrating the core of the engrafted sites, but not in neurons and microglia. LCN2-immunoreactive astrocytes within the engrafted sites expressed lower levels of A1 and A2 astrocytic markers. Recruitment of microglia, neutrophils, and monocytes after transplantation was attenuated in LCN2 deficiency mice. The expression of M2 microglial markers was significantly elevated and survival of engrafted neurons was markedly improved after transplantation in LCN2 deficiency mice. Brain type organic cation transporter (BOCT), the cell surface receptor for LCN2, was induced in dopaminergic-like neurons after differentiation, and treatment with recombinant LCN2 protein directly induced apoptosis in dopaminergic-like neurons in a dose-dependent manner. Our results, therefore, suggested that LCN2 is a neurotoxic factor for the engrafted neurons and a modulator of neuroinflammation. LCN2 inhibition may be useful in reducing rejection after neural transplantation.

Biomaterial Strategies to Bolster Neural Stem Cell-Mediated Repair of the Central Nervous System

Stem cell therapies have the potential to not only repair, but to regenerate tissue of the central nervous system (CNS). Recent studies demonstrate that transplanted stem cells can differentiate into neurons and integrate with the intact circuitry after traumatic injury. Unfortunately, the positive findings described in rodent models have not been replicated in clinical trials, where the burden to maintain the cell viability necessary for tissue repair becomes more challenging. Low transplant survival remains the greatest barrier to stem cell-mediated repair of the CNS, often with fewer than 1-2% of the transplanted cells remaining after 1 week. Strategic transplantation parameters, such as injection location, cell concentration, and transplant timing achieve only modest improvements in stem cell transplant survival and appear inconsistent across studies. Biomaterials provide researchers with a means to significantly improve stem cell transplant survival through two mechanisms: (1) a vehicle to deliver and protect the stem cells and (2) a substrate to control the cytotoxic injury environment. These biomaterial strategies can alleviate cell death associated with delivery to the injury and can be used to limit cell death after transplantation by limiting cell exposure to cytotoxic signals. Moreover, it is likely that control of the injury environment with biomaterials will lead to a more reliable support for transplanted cell populations. This review will highlight the challenges associated with cell delivery in the CNS and the advances in biomaterial development and deployment for stem cell therapies necessary to bolster stem cell-mediated repair.

Advances in immunotherapy for the treatment of spinal cord injury

Spinal cord injury (SCI) is a leading cause of morbidity and disability in the world. Over the past few decades, the exact molecular mechanisms describing secondary, persistent injuries, as well as primary and transient injuries, have attracted massive attention to the clinicians and researchers. Recent investigations have distinctly shown the critical roles of innate and adaptive immune responses in regulating sterile neuroinflammation and functional outcomes after SCI. In past years, some promising advances in immunotherapeutic options have efficaciously been identified for the treatment of SCI. In our narrative review, we have mainly focused on the new therapeutic strategies such as the maturation and apoptosis of immune cells by several agents, mesenchymal stem cells (MSCs) as well as multi-factor combination therapy, which have recently provided novel ideas and prospects for the future treatment of SCI. This article also illustrates the latest progress in clarifying the potential roles of innate and adaptive immune responses in SCI, the progression and specification of prospective immunotherapy and outstanding issues in the area.

Injecting Immunosuppressive M2 Macrophages Alleviates the Symptoms of Periodontitis in Mice

Periodontitis is the second most common oral disease affecting tooth-supporting structures. The tissue damage is mainly initiated by the excessive secretion of proinflammatory cytokines by immune cells. Macrophages are a type of antigen-presenting cells that influence the adaptive immunity function. We used a unique set of cytokines, i.e., a combination of IL-4, IL-13, and IL-10, to stimulate macrophages into a subset of M2 polarization cells that express much higher levels of ARG-1, CD206, and PDL-2 genes. The cells’ anti-inflammatory potential was tested with mixed-lymphocyte reaction assay, which showed that this subset of macrophages could increase IL-2 secretion and suppress IL-17, IL-6, and TNF-α secretion by splenocytes. The gram-negative bacterial species Porphyromonas gingivalis was used to initiate an inflammatory process in murine periodontal tissues. In the meantime, cell injection therapy was used to dampen the excessive immune reaction and suppress osteoclast differentiation during periodontitis. Maxilla was collected and analyzed for osteoclast formation. The results indicated that mice in the cell injection group exhibited less osteoclast activity within the periodontal ligament region than in the periodontitis group. Moreover, the injection of M2 macrophages sustained the regulatory population ratio. Therefore, the M2 macrophages induced under the stimulation of IL-4, IL-13, and IL-10 combined had tremendous immune modulation ability. Injecting these cells into local periodontal tissue could effectively alleviate the symptom of periodontitis.

Current status and future prospects of stem cell therapy in Alzheimer's disease

Alzheimer's disease is a common progressive neurodegenerative disorder, pathologically characterized by the presence of β-amyloid plaques and neurofibrillary tangles. Current treatment approaches using drugs only alleviate the symptoms without curing the disease, which is a serious issue and influences the quality of life of the patients and their caregivers. In recent years, stem cell technology has provided new insights into the treatment of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Currently, the main sources of stem cells include neural stem cells, embryonic stem cells, mesenchymal stem cells, and induced pluripotent stem cells. In this review, we discuss the pathophysiology and general treatment of Alzheimer's disease, and the current state of stem cell transplantation in the treatment of Alzheimer's disease. We also assess future challenges in the clinical application and drug development of stem cell transplantation as a treatment for Alzheimer's disease.

Comparative study of xeno-free induction protocols for neural differentiation of human dental pulp stem cells in vitro

OBJECTIVE

To compare three different xeno-free protocols for neural differentiation of human dental pulp stem cells (DPSC).

METHODS

DPSC were treated with three different media to induce neural differentiation namely N1 (DMEM for 5 days), N2 (PSC neural induction media for 7 days) and N3 (neural media with B27 supplement, 40 ng/ml bFGF and 20 ng/ml EGF for 21 days). Cell proliferation (MTS assay), morphology, gene (qPCR for NESTIN, VIMENTIN, TUB-3, ENO2, NF-M and NF-H) and protein expression (flow cytometry) of neurogenic markers were assessed at different time points and compared to untreated cells (DMEM supplemented with 10% FBS). Statistical analysis was performed with global significance level of 5%.

RESULTS

N1 and N2 formulations increased the genetic expression of two out of six genes TUB-3, NF-M and TUB-3, NF-H, respectively, whereas N3 elevated the expression of all genes by the late stage. N3 also stimulated protein expression for NESTIN, TUB-3 and NF-H. Cells treated with both N2 and N3 presented neuron-like morphology, decreased proliferation and expression of stemness genes at protocol end point.

CONCLUSION

N3 was the most effective formulation in promoting a neurogenic shift in gene and protein expression. Cells provided with the N3 formulation exhibited neuron-like morphology, elaborating axonal-like projections concomitant with cell cycle withdrawal and reduced expression of stemness genes indicating greater commitment to a neurogenic lineage.

Spinal Progenitor-Laden Bridges Support Earlier Axon Regeneration Following Spinal Cord Injury

IMPACT STATEMENT

Spinal cord injury (SCI) results in loss of tissue innervation below the injury. Spinal progenitors have a greater ability to repair the damage and can be injected into the injury, but their regenerative potential is hampered by their poor survival after transplantation. Biomaterials can create a cell delivery platform and generate a more hospitable microenvironment for the progenitors within the injury. In this work, polymeric bridges are used to deliver embryonic spinal progenitors to the injury, resulting in increased progenitor survival and subsequent regeneration and functional recovery, thus demonstrating the importance of combined therapeutic approaches for SCI.

Treatment of multiple system atrophy - the past, present and future

Multiple system atrophy is a sporadic progressive degenerative disease which is characterized by multiple central nervous systems involved. So far, there is no effective medicine to cure MSA. The main research direction of treatment includes immunization transplantation and cytotherapy. Human umbilical cord blood is the residue of blood in the placenta and umbilical cord after fetal delivery. It is the most abundant cell bank and its usage is not limited to treat hematological diseases. The researches about hUCB-MNC treatment on MSA are increasing gradually. The potential of other MSC is also discussed. Lateral atlanto-occipital space puncture is an ingenious way created by Professor Dianrong Gong. More than 30 cases of MSA have been treated by this method with fine clinical effect and without serious complications. It indicates that stem cells treatment is a valid method for refractory nerve system diseases.

Secretome of Undifferentiated Neural Progenitor Cells Induces Histological and Motor Improvements in a Rat Model of Parkinson's Disease

Parkinson's disease (PD) is a progressive neurodegenerative movement disorder that results from the death of dopamine (DA) neurons. Over recent years, differentiated or undifferentiated neural stem cells (NSCs) transplantation has been widely used as a means of cell replacement therapy. However, compelling evidence has brought attention to the array of bioactive molecules produced by stem cells, defined as secretome. As described in the literature, other cell populations have a high‐neurotrophic activity, but little is known about NSCs. Moreover, the exploration of the stem cell secretome is only in its initial stages, particularly as applied to neurodegenerative diseases. Thus, we have characterized the secretome of human neural progenitor cells (hNPCs) through proteomic analysis and investigated its effects in a 6‐hydroxidopamine (6‐OHDA) rat model of PD in comparison with undifferentiated hNPCs transplantation. Results revealed that the injection of hNPCs secretome potentiated the histological recovery of DA neurons when compared to the untreated group 6‐OHDA and those transplanted with cells (hNPCs), thereby supporting the functional motor amelioration of 6‐OHDA PD animals. Additionally, hNPCs secretome proteomic characterization has revealed that these cells have the capacity to secrete a wide range of important molecules with neuroregulatory actions, which are most likely support the effects observed. Overall, we have concluded that the use of hNPCs secretome partially modulate DA neurons cell survival and ameliorate PD animals’ motor deficits, disclosing improved results when compared to cell transplantation approaches, indicating that the secretome itself could represent a route for new therapeutic options for PD regenerative medicine. stem cells translational medicine2018;7:829–838

Huwe1 is a novel mediator of protection of neural progenitor L2.3 cells against oxygen‑glucose deprivation injury

Hypoxic‑ischemic encephalopathy is one of the most notable causes of brain injury in newborns. Cerebral ischemia and reperfusion lead to neuronal damage and neurological disability. In vitro and in vivo analyses have indicated that E3 ubiquitin protein ligase (Huwe1) is important for the process of neurogenesis during brain development; however, the exact biological function and the underlying mechanism of Huwe1 remain controversial. In the present study, neural progenitor cells, L2.3, of which we previously generated from rat E14.5 cortex, were used to investigate the role of Huwe1 and its effects on the downstream N‑Myc‑Delta‑like 3‑Notch1 signaling pathway during oxygen‑glucose deprivation (OGD). To evaluate the role of Huwe1 in L2.3 cells, transduction, cell viability, lactate dehydrogenase, 5‑bromo‑2'deoxyurine incorporation, western blotting and immunocytochemical assays were performed. The results of the present study indicated that Huwe1 rescued L2.3 cells from OGD‑induced insults by inhibiting proliferation and inducing neuronal differentiation. In addition, Huwe1 was suggested to mediate the survival of L2.3 cells by inhibiting the activation of the N‑Myc‑Notch1 signaling pathway. Of note, the effects of Huwe1 on Notch1 signaling were completely abolished by knockdown of N‑Myc, indicating that Huwe1 may require N‑Myc to suppress the activation of the Notch1 signaling in L2.3 cells. The determination of the neuroprotective function of the Huwe1‑N‑Myc‑Notch1 axis may provide insight into novel potential therapeutic targets for the treatment of ischemic stroke.

Novel biomaterials to study neural stem cell mechanobiology and improve cell-replacement therapies

Neural stem cells (NSCs) are a valuable cell source for tissue engineering, regenerative medicine, disease modeling, and drug screening applications. Analogous to other stem cells, NSCs are tightly regulated by their microenvironmental niche, and prior work utilizing NSCs as a model system with engineered biomaterials has offered valuable insights into how biophysical inputs can regulate stem cell proliferation, differentiation, and maturation. In this review, we highlight recent exciting studies with innovative material platforms that enable narrow stiffness gradients, mechanical stretching, temporal stiffness switching, and three-dimensional culture to study NSCs. These studies have significantly advanced our knowledge of how stem cells respond to an array of different biophysical inputs and the underlying mechanosensitive mechanisms. In addition, we discuss efforts to utilize engineered material scaffolds to improve NSC-based translational efforts and the importance of mechanobiology in tissue engineering applications.

Brain-Derived Neurotrophic Factor Increases Synaptic Protein Levels via the MAPK/Erk Signaling Pathway and Nrf2/Trx Axis Following the Transplantation of Neural Stem Cells in a Rat Model of Traumatic Brain Injury

Brain-derived neurotrophic factor (BDNF) plays an important role in promoting the growth, differentiation, survival and synaptic stability of neurons. Presently, the transplantation of neural stem cells (NSCs) is known to induce neural repair to some extent after injury or disease. In this study, to investigate whether NSCs genetically modified to encode the BDNF gene (BDNF/NSCs) would further enhance synaptogenesis, BDNF/NSCs or naive NSCs were directly engrafted into lesions in a rat model of traumatic brain injury (TBI). Immunohistochemistry, western blotting and RT-PCR were performed to detect synaptic proteins, BDNF-TrkB and its downstream signaling pathways, at 1, 2, 3 or 4 weeks after transplantation. Our results showed that BDNF significantly increased the expression levels of the TrkB receptor gene and the phosphorylation of the TrkB protein in the lesions. The expression levels of Ras, phosphorylated Erk1/2 and postsynaptic density protein-95 were elevated in the BDNF/NSCs-transplanted groups compared with those in the NSCs-transplanted groups throughout the experimental period. Moreover, the nuclear factor (erythroid-derived 2)-like 2/Thioredoxin (Nrf2/Trx) axis, which is a specific therapeutic target for the treatment of injury or cell death, was upregulated by BDNF overexpression. Therefore, we determined that the increased synaptic proteins level implicated in synaptogenesis might be associated with the activation of the MAPK/Erk1/2 signaling pathway and the upregulation of the antioxidant agent Trx modified by BDNF-TrkB following the BDNF/NSCs transplantation after TBI.

Gene Editing, Gene Therapy, and Cell Xenotransplantation: Cell Transplantation Across Species

PURPOSE OF REVIEW

Cell xenotransplantation has the potential to provide a safe, ethically acceptable, unlimited source for cell replacement therapies. This review focuses on genetic modification strategies aimed to overcome remaining hurdles standing in the way of clinical porcine islet transplantation and to develop neural cell xenotransplantation.

RECENT FINDINGS

In addition to previously described genetic modifications aimed to mitigate hyperacute rejection, instant blood-mediated inflammatory reaction, and cell-mediated rejection, new data showing the possibility of increasing porcine islet insulin secretion by transgenesis is an interesting addition to the array of genetically modified pigs available for xenotransplantation. Moreover, combining multiple modifications is possible today thanks to new, improved genomic editing tools.

SUMMARY

Genetic modification of large animals, pigs in particular, has come a long way during the last decade. These modifications can help minimize immunological and physiological incompatibilities between porcine and human cells, thus allowing for better tolerance and function of xenocells.

Old and new challenges in Parkinson's disease therapeutics

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the degeneration of dopaminergic neurons and/or loss od neuronal projections, in several dopaminergic networks. Current treatments for idiopathic PD rely mainly on the use of pharmacologic agents to improve motor symptomatology of PD patients. Nevertheless, so far PD remains an incurable disease. Therefore, it is of utmost importance to establish new therapeutic strategies for PD treatment. Over the last 20 years, several molecular, gene and cell/stem-cell therapeutic approaches have been developed with the aim of counteracting or retarding PD progression. The scope of this review is to provide an overview of PD related therapies and major breakthroughs achieved within this field. In order to do so, this review will start by focusing on PD characterization and current treatment options covering thereafter molecular, gene and cell/stem cell-based therapies that are currently being studied in animal models of PD or have recently been tested in clinical trials. Among stem cell-based therapies, those using MSCs as possible disease modifying agents for PD therapy and, specifically, the MSCs secretome contribution to meet the clinical challenge of counteracting or retarding PD progression, will be more deeply explored.

Evaluating the toxicity of silicon dioxide nanoparticles on neural stem cells using RNA-Seq

Neural stem cells are characterized by self-renewal and multipotency, and a capacity to regenerate in response to brain injury or neurodegenerative disease.

LXR agonists promote the proliferation of neural progenitor cells through MEK-ERK pathway

The liver X receptors (LXRs) are transcriptional regulators of lipid homeostasis and may be critical for neurodegeneration and neurogenesis in vivo. However, it remains largely unknown about the role of LXRs and its agonists in the in vitro proliferation of neural progenitor cells (NPCs). Here we revealed for the first time that LXRs were markedly expressed in mouse NPCs and were critical for the in vitro proliferation. LXR agonists GW3965 and LXR623 promoted the proliferation of wildtype NPCs, but not NPCs from LXR double-knockout mice. Mechanistically, phosphorylation of MEK1/2 and ERK1/2 in NPCs was enhanced upon LXR agonist treatment, while abrogation of MEK/ERK phosphorylation by the inhibitors PD98059 and U0126 impaired the proliferation of wildtype NPCs in the presence or absence of LXR agonists. Collectively, our findings suggest that LXR agonists GW3965 and LXR623 can stimulate the NPC proliferation in LXR- and MEK/ERK-dependent manner.

Tissue Engineering Approaches to Modulate the Inflammatory Milieu following Spinal Cord Injury

Tissue engineering strategies have shown promise in promoting healing and regeneration after spinal cord injury (SCI); however, these strategies are limited by inflammation and the immune response. Infiltration of cells of the innate and adaptive immune responses and the inflammation that follows cause secondary damage adjacent to the injury, increased scarring, and a potently inhibitory environment for the regeneration of damaged neurons. While the inflammation that ensues is typically associated with limited regeneration, the immune response is a crucial element in the closing of the blood-brain barrier, minimizing the spread of injury, and initiating healing. This review summarizes the strategies that have been developed to modulate the immune response towards an anti-inflammatory environment that is permissive to the regeneration of neurons, glia, and parenchyma. We focus on the use of biomaterials, biologically active molecules, gene therapy, nanoparticles, and stem cells to modulate the immune response, and illustrate concepts for future therapies. Current clinical treatments for SCI are limited to systemic hypothermia or methylprednisolone, which both act by systemically mitigating the effects of immune response but have marginal efficacy. Herein, we discuss emerging research strategies to further enhance these clinical treatments by directly targeting specific aspects of the immune response.

Effects of neural progenitor cells on post-stroke neurological impairment-a detailed and comprehensive analysis of behavioral tests

Systemic transplantation of neural progenitor cells (NPCs) in rodents reduces functional impairment after cerebral ischemia. In light of upcoming stroke trials regarding safety and feasibility of NPC transplantation, experimental studies have to successfully analyze the extent of NPC-induced neurorestoration on the functional level. However, appropriate behavioral tests for analysis of post-stroke motor coordination deficits and cognitive impairment after NPC grafting are not fully established. We therefore exposed male C57BL6 mice to either 45 min (mild) or 90 min (severe) of cerebral ischemia, using the thread occlusion model followed by intravenous injection of PBS or NPCs 6 h post-stroke with an observation period of three months. Post-stroke motor coordination was assessed by means of the rota rod, tight rope, corner turn, inclined plane, grip strength, foot fault, adhesive removal, pole test and balance beam test, whereas cognitive impairment was analyzed using the water maze, the open field and the passive avoidance test. Significant motor coordination differences after both mild and severe cerebral ischemia in favor of NPC-treated mice were observed for each motor coordination test except for the inclined plane and the grip strength test, which only showed significant differences after severe cerebral ischemia. Cognitive impairment after mild cerebral ischemia was successfully assessed using the water maze test, the open field and the passive avoidance test. On the contrary, the water maze test was not suitable in the severe cerebral ischemia paradigm, as it too much depends on motor coordination capabilities of test mice. In terms of both reliability and cost-effectiveness considerations, we thus recommend the corner turn, foot fault, balance beam, and open field test, which do not depend on durations of cerebral ischemia.

Effects of acute versus post-acute systemic delivery of neural progenitor cells on neurological recovery and brain remodeling after focal cerebral ischemia in mice

Intravenous transplantation of neural progenitor cells (NPCs) induces functional recovery after stroke, albeit grafted cells are not integrated into residing neural networks. However, a systematic analysis of intravenous NPC delivery at acute and post-acute time points and their long-term consequences does not exist. Male C57BL6 mice were exposed to cerebral ischemia, and NPCs were intravenously grafted on day 0, on day 1 or on day 28. Animals were allowed to survive for up to 84 days. Mice and tissues were used for immunohistochemical analysis, flow cytometry, ELISA and behavioral tests. Density of grafted NPCs within the ischemic hemisphere was increased when cells were transplanted on day 28 as compared with transplantation on days 0 or 1. Likewise, transplantation on day 28 yielded enhanced neuronal differentiation rates of grafted cells. Post-ischemic brain injury, however, was only reduced when NPCs were grafted at acute time points. On the contrary, reduced post-ischemic functional deficits due to NPC delivery were independent of transplantation paradigms. NPC-induced neuroprotection after acute cell delivery was due to stabilization of the blood–brain barrier (BBB), reduction in microglial activation and modulation of both peripheral and central immune responses. On the other hand, post-acute NPC transplantation stimulated post-ischemic regeneration via enhanced angioneurogenesis and increased axonal plasticity. Acute NPC delivery yields long-term neuroprotection via enhanced BBB integrity and modulation of post-ischemic immune responses, whereas post-acute NPC delivery increases post-ischemic angioneurogenesis and axonal plasticity. Post-ischemic functional recovery, however, is independent of NPC delivery timing, which offers a broad therapeutic time window for stroke treatment.

Neural stem cell protects aged rat brain from ischemia-reperfusion injury through neurogenesis and angiogenesis

Neural stem cells (NSCs) show therapeutic potential for ischemia in young-adult animals. However, the effect of aging on NSC therapy is largely unknown. In this work, NSCs were transplanted into aged (24-month-old) and young-adult (3-month-old) rats at 1 day after stroke. Infarct volume and neurobehavioral outcomes were examined. The number of differentiated NSCs was compared in aged and young-adult ischemic rats and angiogenesis and neurogenesis were also determined. We found that aged rats developed larger infarcts than young-adult rats after ischemia (P<0.05). The neurobehavioral outcome was also worse for aged rats comparing with young-adult rats. Brain infarction and neurologic deficits were attenuated after NSC transplantation in both aged and young-adult rats. The number of survived NSCs in aged rats was similar to that of the young-adult rats (P>0.05) and most of them were differentiated into glial fibrillary acidic protein(+) (GFAP(+)) cells. More importantly, angiogenesis and neurogenesis were greatly enhanced in both aged and young-adult rats after transplantation compared with phosphate-buffered saline (PBS) control (P<0.05), accompanied by increased expression of vascular endothelial growth factor (VEGF). Our results showed that NSC therapy reduced ischemic brain injury, along with increased angiogenesis and neurogenesis in aged rats, suggesting that aging-related microenvironment does not preclude a beneficial response to NSCs transplantation during cerebral ischemia.

Human induced pluripotent stem cells are a novel source of neural progenitor cells (iNPCs) that migrate and integrate in the rodent spinal cord

Transplantation of human neural progenitor cells (NPCs) into the brain or spinal cord to replace lost cells, modulate the injury environment, or create a permissive milieu to protect and regenerate host neurons is a promising therapeutic strategy for neurological diseases. Deriving NPCs from human fetal tissue is feasible, although problematic issues include limited sources and ethical concerns. Here we describe a new and abundant source of NPCs derived from human induced pluripotent stem cells (iPSCs). A novel chopping technique was used to transform adherent iPSCs into free-floating spheres that were easy to maintain and were expandable (EZ spheres) (Ebert et al. [2013] Stem Cell Res 10:417-427). These EZ spheres could be differentiated towards NPC spheres with a spinal cord phenotype using a combination of all-trans retinoic acid (RA) and epidermal growth factor (EGF) and fibroblast growth factor-2 (FGF-2) mitogens. Suspension cultures of NPCs derived from human iPSCs or fetal tissue have similar characteristics, although they were not similar when grown as adherent cells. In addition, iPSC-derived NPCs (iNPCs) survived grafting into the spinal cord of athymic nude rats with no signs of overgrowth and with a very similar profile to human fetal-derived NPCs (fNPCs). These results suggest that human iNPCs behave like fNPCs and could thus be a valuable alternative for cellular regenerative therapies of neurological diseases.

Canonical BMP-Smad signalling promotes neurite growth in rat midbrain dopaminergic neurons

Ventral midbrain (VM) dopaminergic (DA) neurons project to the dorsal striatum via the nigrostriatal pathway to regulate voluntary movements, and their loss leads to the motor dysfunction seen in Parkinson's disease (PD). Despite recent progress in the understanding of VM DA neurogenesis, the factors regulating nigrostriatal pathway development remain largely unknown. The bone morphogenetic protein (BMP) family regulates neurite growth in the developing nervous system and may contribute to nigrostriatal pathway development. Two related members of this family, BMP2 and growth differentiation factor (GDF)5, have neurotrophic effects, including promotion of neurite growth, on cultured VM DA neurons. However, the molecular mechanisms regulating their effects on DA neurons are unknown. By characterising the temporal expression profiles of endogenous BMP receptors (BMPRs) in the developing and adult rat VM and striatum, this study identified BMP2 and GDF5 as potential regulators of nigrostriatal pathway development. Furthermore, through the use of noggin, dorsomorphin and BMPR/Smad plasmids, this study demonstrated that GDF5- and BMP2-induced neurite outgrowth from cultured VM DA neurons is dependent on BMP type I receptor activation of the Smad 1/5/8 signalling pathway.

Ventral midbrain neural stem cells have delayed neurogenic potential in vitro

Neural stem cells (NSCs) have been the focus of an intensive effort to direct their differentiation in vitro towards desired neuronal phenotypes for cell replacement therapies. It is thought that NSCs derived from older embryos have limited neurogenic capacity and are restricted towards an astroglial fate. This idea is largely based on studies that typically analysed NSC-derived progeny following one week of in vitro differentiation. In this report, the neurogenic capacity of older ventral midbrain (VM) NSCs was assessed. When the older NSCs were differentiated for three weeks, there were significant increases in the numbers of newly born neurons at 14 and 21 days, as assessed by 5-bromo-2'-deoxyuridine (BrdU) incorporation. Therefore this study demonstrates that older NSCs retain significantly more neurogenic potential than was previously thought. These data have implications for NSC preparatory protocols and the choice of donor age for cell transplantation studies, and contributes to the understanding of NSC behaviour in vitro.

BMP2 and GDF5 induce neuronal differentiation through a Smad dependant pathway in a model of human midbrain dopaminergic neurons

Parkinson's disease is the second most common neurodegenerative disease, and is characterised by the progressive degeneration of the nigrostriatal dopaminergic (DA) system. Current treatments are symptomatic, and do not protect against the DA neuronal loss. One of the most promising treatment approaches is the application of neurotrophic factors to rescue the remaining population of nigrostriatal DA neurons. Therefore, the identification of new neurotrophic factors for midbrain DA neurons, and the subsequent elucidation of the molecular bases of their effects, are important. Two related members of the bone morphogenetic protein (BMP) family, BMP2 and growth differentiation factor 5 (GDF5), have been shown to have neurotrophic effects on midbrain DA neurons both in vitro and in vivo. However, the molecular (signalling pathway(s)) and cellular (direct neuronal or indirect via glial cells) mechanisms of their effects remain to be elucidated. Using the SH-SH5Y human neuronal cell line, as a model of human midbrain DA neurons, we have shown that GDF5 and BMP2 induce neurite outgrowth via a direct mechanism. Furthermore, we demonstrate that these effects are dependent on BMP type I receptor activation of canonical Smad 1/5/8 signalling.

Human induced pluripotent stem cell-derived neural stem cells survive, migrate, differentiate, and improve neurologic function in a rat model of middle cerebral artery occlusion

Introduction

Stroke is a major cause of permanent neurologic damage, with few effective treatments available to restore lost function. Induced pluripotent stem cells (iPSCs) have the potential to generate all cell types in vitro and can be generated from a stroke patient. Therefore, iPSCs are attractive donor sources of genetically identical “patient-specific” cells to hold promise in therapy for stroke. In the present study, we established a four-stage culture system by using serum-free medium and retinoic acid (RA) to differentiate iPSCs into neural stem cells (NSCs) effectively and stably. Our hypothesis was that iPSC-derived NSCs would survive, migrate, and differentiate in vivo, and improve neurologic function after transplantation into the brains of rats with ischemic stroke.

Methods

Human iPSCs (iPS-S-01) and human ESCs (HuES17) were used to differentiate into NSCs by using our four-stage culture system. iPSCs and differentiated NSCs were characterized by immunocytochemistry staining and reverse transcription-polymerase chain reaction (RT-PCR) analysis. After establishment of focal cerebral ischemia with occlusion of the middle cerebral artery (MCA) and cell transplantation, animals were killed at 1 week and 2 weeks to analyze survival, migration, and differentiation of implanted cells in brain tissue. Animal behavior was evaluated via rope grabbing, beam walking, and Morris water maze tests.

Results

iPSCs were efficiently induced into NSCs by using a newly established four-stage induction system in vitro. iPSCs expressed pluripotency-associated genes Oct4, Sox2, and Nanog before NSC differentiation. The iPSC-derived NSCs spontaneously differentiated into neurons and astrocytes, which highly express β-tubulin and glial fibrillary acidic protein (GFAP), respectively. On transplantation into the striatum, CM-DiI labeled iPSC-derived NSCs were found to migrate into the ischemia area at 1 week and 2 weeks, and animal-function recovery was significantly improved in comparison with control groups at 3 weeks.

Conclusions

The four-stage induction system is stable and effective to culture, differentiate, and induce iPSCs to NSCs by using serum-free medium combined with retinoic acid (RA). Implanted iPSC-derived NSCs were able to survive, migrate into the ischemic brain area to differentiate into mature neural cells, and seem to have potential to restore lost neurologic function from damage due to stroke in a rat model.

Cell-based therapy for ischemic stroke

INTRODUCTION

Stroke is a major cause of mortality and disability in adults worldwide. Unfortunately, current therapy which targets vessel recanalization has a narrow treatment window, and at this time neuroprotective approaches are not effective for stroke treatment. However, after stroke the parenchymal and endothelial cells in the central nervous system (CNS) respond in concert to ischemic stressors and create a microenvironment in which successful recovery may ensue. Neurogenesis, synaptogenesis, axonal sprouting, glial cell activation, angiogenesis and vascular remodeling within the brain and the spinal cord are stimulated post stroke. Cell based-therapy amplifies these endogenous restorative effects within the CNS to promote functional outcome.

AREAS COVERED

This article reviews current knowledge of cell-based therapy in the adult brain after stroke, including transplanted cell type, benefits and risks, with an emphasis on mechanisms of action.

EXPERT OPINION

Experimental studies and clinical trials with cell-based therapy in stroke appear promising. Cell-based therapy is not intended for the replacement of damaged cells, but for the remodeling of the CNS by promoting neuroplasticity, angiogenesis and immunomodulation. However, there are risks associated with the use of cell-based therapy, and adequate evaluation of these potential risks is a prerequisite before clinical application for stroke patients.

Systematic Review of Induced Pluripotent Stem Cell Technology as a Potential Clinical Therapy for Spinal Cord Injury

Transplantation therapies aimed at repairing neurodegenerative and neuropathological conditions of the central nervous system (CNS) have utilized and tested a variety of cell candidates, each with its own unique set of advantages and disadvantages. The use and popularity of each cell type is guided by a number of factors including the nature of the experimental model, neuroprotection capacity, the ability to promote plasticity and guided axonal growth, and the cells' myelination capability. The promise of stem cells, with their reported ability to give rise to neuronal lineages to replace lost endogenous cells and myelin, integrate into host tissue, restore functional connectivity, and provide trophic support to enhance and direct intrinsic regenerative ability, has been seen as a most encouraging step forward. The advent of the induced pluripotent stem cell (iPSC), which represents the ability to “reprogram” somatic cells into a pluripotent state, hails the arrival of a new cell transplantation candidate for potential clinical application in therapies designed to promote repair and/or regeneration of the CNS. Since the initial development of iPSC technology, these cells have been extensively characterized in vitro and in a number of pathological conditions and were originally reported to be equivalent to embryonic stem cells (ESCs). This review highlights emerging evidence that suggests iPSCs are not necessarily indistinguishable from ESCs and may occupy a different “state” of pluripotency with differences in gene expression, methylation patterns, and genomic aberrations, which may reflect incomplete reprogramming and may therefore impact on the regenerative potential of these donor cells in therapies. It also highlights the limitations of current technologies used to generate these cells. Moreover, we provide a systematic review of the state of play with regard to the use of iPSCs in the treatment of neurodegenerative and neuropathological conditions. The importance of balancing the promise of this transplantation candidate in the light of these emerging properties is crucial as the potential application in the clinical setting approaches. The first of three sections in this review discusses (A) the pathophysiology of spinal cord injury (SCI) and how stem cell therapies can positively alter the pathology in experimental SCI. Part B summarizes (i) the available technologies to deliver transgenes to generate iPSCs and (ii) recent data comparing iPSCs to ESCs in terms of characteristics and molecular composition. Lastly, in (C) we evaluate iPSC-based therapies as a candidate to treat SCI on the basis of their neurite induction capability compared to embryonic stem cells and provide a summary of available in vivo data of iPSCs used in SCI and other disease models.

Expression of heme oxygenase-1 in neural stem/progenitor cells as a potential mechanism to evade host immune response

Besides their therapeutic benefit as cell source, neural stem/progenitor cells (NSPCs) exhibit immunosuppressive properties of great interest for modulating immune response in the central nervous system. To decipher the mechanisms of NSPC-mediated immunosuppression, activated T cells were exposed to NSPCs isolated from fetal rat brains. Analyses revealed that NSPCs inhibited T-cell proliferation and interferon-gamma production in a dose-dependent manner. A higher proportion of helper T cells (CD4+ T cells) was found in the presence of NSPCs, but analyses of FoxP3 population indicated that T-cell suppression was not secondary to an induction of suppressive regulatory T cells (FoxP3+ CD4+ CD25+). Conversely, induction of the high affinity interleukin-2 (IL-2) receptor (CD25) and the inability of IL-2 to rescue T-cell proliferation suggest that NSPCs display immunosuppressive activity without affecting T-cell activation. Cultures in Transwell chambers or addition of NSPC-conditioned medium to activated T cells indicated that part of the suppressive activity was not contact dependent. We therefore searched for soluble factors that mediate NSPC immunosuppression. We found that NSPCs express several immunosuppressive molecules, but the ability of these cells to inhibit T-cell proliferation was only counteracted by heme oxygenase (HO) inhibitors in association or not with nitric oxide synthase inhibitors. Taken together, our findings highlight a dynamic crosstalk between NSPCs and T lymphocytes and provide the first evidence of an implication of HO-1 in mediating the immunosuppressive effects of the NSPCs.

Intranasal Delivery of Neural Stem Cells: A CNS-specific, Non-invasive Cell-based Therapy for Experimental Autoimmune Encephalomyelitis

The therapeutic potential of adult neural stem cells (aNSCs) has been shown in EAE, an animal model of MS, administered by either i.c.v. or i.v. injection. However, i.c.v. is an invasive approach, while the i.v. route of aNSCs is associated with a non-specific immune suppression in the periphery. Here we demonstrate that intranasal (i.n.) delivery of fluorescently labeled aNSCs resulted in their appearance in the olfactory bulb, cortex, hippocampus, striatum, brainstem, and spinal cord. These cells induce functional recovery from ongoing EAE similar to that achieved with i.v. injected aNSCs, with comparable anti-inflammatory and remeylination effects in CNS inflammatory foci. Importantly, unlike the peripheral immune suppression brought about by i.v. NSCs, intranasal delivery did not influence peripheral immune responses. We conclude that aNSCs can be reliably delivered to the CNS via the nasal route to induce functional recovery and confer immunomodulation and remyelination in EAE. Intranasal administration of NSCs provides a highly promising, noninvasive and CNS-specific alternative to current cell-based approaches in treating EAE.

Characterization of embryonic cortical neuron death in prolonged cell suspension

Cell transplantation may be an effective therapeutic strategy for many neurodegenerative diseases. However, difficulty in obtaining a sufficient amount of donor cells and low graft survival are two major limiting factors. Dissociation of cells from tissues or culture is an inevitable step for cell transplantation, and cell viability in suspension may influence the outcome of the cell therapy. To this end, we asked whether the suspension time of freshly dissociated neurons in vitro affects their viability. Following 4-24h cell suspension, primary cortical neurons underwent cell death. Interestingly, the neurons exhibited only marginal caspase-3 immunoreactivity with very few sub-G1 apoptotic cell proportions in flow cytometry. In addition, the suppression of caspase-3 or Bax action failed to prevent cell death of primary cortical neurons, indicating minimal apoptotic cell death. On the other hand, there was a marked increase in the TdT-mediated dUTP nick end labeling-positive and propidium iodide-labeled necrotic cells (∼50%) with enhanced poly [ADP-ribose] polymerase-1 activity. Therefore, prevention against necrosis rather than apoptosis may be required for optimal benefits in cell transplantation.

Ethical implications in the use of embryonic and adult neural stem cells

The advent and growth of technological advances have led to new routes of knowledge. Thereby, we currently face new challenges. We have just started to get a glimpse of the structural and functional role of neural stem cells in differentiation and migration processes, the origin of synaptic networks, and subsequent readjustments in specific circuits. A whole range of treatment possibilities originates from this knowledge that potentially can be used for different neurological diseases in humans. Although this is an encouraging scenario, it implies that the human brain is the object of such study, as well as its potential manipulation and transplantation. It is, therefore, pertinent that ethical principles should be followed in such research to have proper balance between what can be done and what should be done, according to every specific context. Hence, it is wise to consider ethical implications in every research project, along with potential clinical applications, under the principle of causing no harm, following risk and benefit rules in decision making and with respect of the human condition as a priority.