Long-term survival of human neural stem cells in the ischemic rat brain upon transient immunosuppression

Isolation and Culture of Neural Stem/Progenitor Cells from the Postnatal Periventricular Region

Due to the complexity of the neural stem cell (NSC) niche organization, the lack of specific NSC markers, and the difficulty of long-term tracking these cells and their progeny in vivo, the functional properties of the endogenous NSCs remain largely unexplored. These limitations have led to the development of methodologies to efficiently isolate, expand, and differentiate NSCs ex vivo. We describe here the peculiarities of the neurosphere assay (NSA) as a methodology that allows to efficiently isolate, expand, and differentiate somatic NSCs derived from the postnatal and adult forebrain periventricular region while preserving proliferation, self-renewal, and multipotency, the main attributes that provide their functional identification.

Hypoproliferative human neural progenitor cell xenografts survived extendedly in the brain of immunocompetent rats

Background

There is a huge controversy about whether xenograft or allograft in the “immune-privileged” brain needs immunosuppression. In animal studies, the prevailing sophisticated use of immunosuppression or immunodeficient animal is detrimental for the recipients, which results in a short lifespan of animals, confounds functional behavioral readout of the graft benefits, and discourages long-term follow-up.

Methods

Neuron-restricted neural progenitor cells (NPCs) were derived from human embryonic stem cells (ESCs, including H1, its gene-modified cell lines for better visualization, and HN4), propagated for different passages, and then transplanted into the brain of immunocompetent rats without immunosuppressants. The graft survivals, their cell fates, and HLA expression levels were examined over time (up to 4 months after transplantation). We compared the survival capability of NPCs from different passages and in different transplantation sites (intra-parenchyma vs. para- and intra-cerebroventricle). The host responses to the grafts were also investigated.

Results

Our results show that human ESC-derived neuron-restricted NPCs survive extendedly in adult rat brain parenchyma with no need of immunosuppression whereas a late-onset graft rejection seems inevitable. Both donor HLA antigens and host MHC-II expression level remain relatively low with little change over time and cannot predict the late-onset rejection. The intra-/para-cerebroventricular human grafts are more vulnerable to the immune attack than the intrastriatal counterparts. Prevention of graft hyperplasia by using hypoproliferative late passaged human NPCs further significantly extends the graft survival time. Our new data also shows that a subpopulation of host microglia upregulate MHC-II expression in response to the human graft, but fail to present the human antigen to the host immune system, suggestive of the immune-isolation role of the blood–brain barrier (BBB).

Conclusions

The present study confirms the “immune privilege” of the brain parenchyma and, more importantly, unveils that choosing hypoproliferative NPCs for transplantation can benefit graft outcome in terms of both lower tumor-genic risk and the prolonged survival time without immunosuppression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02427-1.

Mesenchymal stem cells from human umbilical cord regulate the expression of major histocompatibility complex in human neural stem cells and their lineages

hNSCs (human neural stem cells) derived from embryonic tissue and aborted fetal brains are considered to be the most promising candidates for neurodegenerative and other CNS(central nervous system) diseases. However, the most common problem, which limited successful use of these allogeneic hNSC therapy, is immune rejection. Mesenchymal stem cells (MSCs) from human umbilical cord (hUC-MSCs) are receiving increasing attention for their immune-modulatory properties. In the current studies, we firstly investigated the immunogenecity of hNSCs as well as their lineages in cultures with the presence or absence of interferon gamma (IFNγ), a pro-inflammatory factors. Our data revealed that the majority of hNSCs and astrocytes expressed MHCI (major histocompatibility complex class I) while neurons hardly expressed MHCI (<5%) in the absence of IFNγ. In addition, neither hNSCs nor neurons expressed MHCII while a subpopulation (about 18 %) of astrocytes expressed MHCII without IFNγ stimulation. However, the addition of IFNγ in cultures significantly increased the expressions of MHCII on hNSCs and astrocytes. However, IFNγ did not affect the expression of MHCI on hNSCs and astrocytes. We then investigated whether hUC-MSCs had the capacity of regulating the immunogenecity of hNSCs as well as their lineages in a co-culture system. We found that hUC-MSCs did not affect the expression of MHCI on hNSCs and their lineages, however, these cells were able to significantly inhibit the IFNγ-induced up-regulation of MHCII on hNSCs and astrocytes (p < 0.001). Thus, our results suggest that hUC-MSCs may serve as potentially useful modulators to reduce the immunogenicity of allogeneic hNSCs in clinical application.

Intracerebral transplantation of HLA-homozygous human iPSC-derived neural precursors ameliorates the behavioural and pathological deficits in a rodent model of ischaemic stroke

OBJECTIVES

Human-induced pluripotent stem cells (hiPSCs) are a promising cell source for treating ischaemic stroke. Although autologous hiPSCs provide the advantage of avoiding immune rejection, their practical limitations, such as substantial amount of time and costs to generate individual iPSC lines, have hampered their widespread application in clinical settings. In this study, we investigated the therapeutic potential of neural precursor cells derived from human HLA-homozygous induced pluripotent stem cells (hiPSC-NPCs) following intracerebral transplantation into a rodent model of middle cerebral artery occlusion (MCAo).

MATERIALS AND METHODS

We differentiated a GMP-grade HLA-homozygous hiPSC line (CMC-hiPSC-004) into neural precursor cells for transplantation into rats at the subacute stage of ischaemic stroke (ie at 7 days after the induction of MCAo). To investigate functional recovery, the transplanted animals were subjected to five behavioural tests, namely the rotarod, stepping, mNSS, staircase and apomorphine-induced rotation tests, for up to 12 weeks, followed by histological analyses.

RESULTS

We observed that the hiPSC-NPC transplantation produced significant behavioural improvements. At 12 weeks post-transplantation, a high proportion of transplanted cells survived and had differentiated into MAP2⁺ mature neurons, GABAergic neurons and DARPP32⁺ medium spiny neurons. The transplanted cells formed neuronal connections with striatal neurons in the host brain. In addition, hiPSC-NPC transplantation gave rise to enhanced endogenous repair processes, including decreases of post-stroke neuroinflammation and glial scar formation and an increase of proliferating endogenous neural stem cells in the subventricular zone as well as the perilesional capillary networks.

CONCLUSIONS

These results strongly suggest that HLA-homozygous hiPSC-NPCs may be useful for treating ischaemic stroke patients.

Intracerebral Transplantation of BDNF-overexpressing Human Neural Stem Cells (HB1.F3.BDNF) Promotes Migration, Differentiation and Functional Recovery in a Rodent Model of Huntington's Disease

Huntington's disease (HD) is a dominantly inherited neurodegenerative disorder caused by abnormally expanded CAG repeats in the huntingtin gene. The huntingtin gene mutation leads to the progressive degeneration of striatal GABAergic medium spiny neurons (MSN) and reduces the level of brain-derived neurotrophic factor (BDNF) in HD patient's brain. BDNF is an essential neurotrophic factor for the cortico-striatal synaptic activity and the survival of GABAergic neurons. In this study, we transplanted BDNF-overexpressing human neural stem cells (HB1.F3.BDNF) into the contra-lateral side of unilateral quinolinic acid (QA)-lesioned striatum of HD rat model. The results of in vivo transplantation were monitored using various behavioral tests, 4.7 T animal magnetic resonance imaging (MRI) and immunohistochemical staining. We observed that the QA-lesioned rats receiving HB1.F3.BDNF cells exhibited significant behavioral improvements in the stepping, rotarod and apomorphine-induced rotation tests. Interestingly, contralaterally transplanted cells were migrated to the QA-lesioned striatum and the size of lateral ventricle was reduced. Histological analyses further revealed that the transplanted cells, which had migrated to the QA lesion site, were differentiated into the cells of GABAergic, MSN-type neurons expressing DARPP-32, and neural networks were established between the transplanted cells and the host brain, as revealed by retrograde tracing. Finally, there was a significant reduction of inflammatory response in HB1.F3.BDNF-transplanted HD animal model, compared with vehicle-transplanted group. Taken together, these results suggest that HB1.F3.BDNF can be an effective therapeutic strategy to treat HD patients in the future.

Results from Phase I Clinical Trial with Intraspinal Injection of Neural Stem Cells in Amyotrophic Lateral Sclerosis: A Long-Term Outcome

The main objective of this phase I trial was to assess the feasibility and safety of microtransplanting human neural stem cell (hNSC) lines into the spinal cord of patients with amyotrophic lateral sclerosis (ALS). Eighteen patients with a definite diagnosis of ALS received microinjections of hNSCs into the gray matter tracts of the lumbar or cervical spinal cord. Patients were monitored before and after transplantation by clinical, psychological, neuroradiological, and neurophysiological assessment. For up to 60 months after surgery, none of the patients manifested severe adverse effects or increased disease progression because of the treatment. Eleven patients died, and two underwent tracheotomy as a result of the natural history of the disease. We detected a transitory decrease in progression of ALS Functional Rating Scale Revised, starting within the first month after surgery and up to 4 months after transplantation. Our results show that transplantation of hNSC is a safe procedure that causes no major deleterious effects over the short or long term. This study is the first example of medical transplantation of a highly standardized cell drug product, which can be reproducibly and stably expanded ex vivo, comprising hNSC that are not immortalized, and are derived from the forebrain of the same two donors throughout this entire study as well as across future trials. Our experimental design provides benefits in terms of enhancing both intra‐ and interstudy reproducibility and homogeneity. Given the potential therapeutic effects of the hNSCs, our observations support undertaking future phase II clinical studies in which increased cell dosages are studied in larger cohorts of patients. stem cells translational medicine2019;8:887&897

Transplantation of clinical-grade human neural stem cells reduces neuroinflammation, prolongs survival and delays disease progression in the SOD1 rats

Stem cells are emerging as a therapeutic option for incurable diseases, such as Amyotrophic Lateral Sclerosis (ALS). However, critical issues are related to their origin as well as to the need to deepen our knowledge of the therapeutic actions exerted by these cells. Here, we investigate the therapeutic potential of clinical-grade human neural stem cells (hNSCs) that have been successfully used in a recently concluded phase I clinical trial for ALS patients (NCT01640067). The hNSCs were transplanted bilaterally into the anterior horns of the lumbar spinal cord (four grafts each, segments L3–L4) of superoxide dismutase 1 G93A transgenic rats (SOD1 rats) at the symptomatic stage. Controls included untreated SOD1 rats (CTRL) and those treated with HBSS (HBSS). Motor symptoms and histological hallmarks of the disease were evaluated at three progressive time points: 15 and 40 days after transplant (DAT), and end stage. Animals were treated by transient immunosuppression (for 15 days, starting at time of transplantation). Under these conditions, hNSCs integrated extensively within the cord, differentiated into neural phenotypes and migrated rostro-caudally, up to 3.77 ± 0.63 cm from the injection site. The transplanted cells delayed decreases in body weight and deterioration of motor performance in the SOD1 rats. At 40DAT, the anterior horns at L3–L4 revealed a higher density of motoneurons and fewer activated astroglial and microglial cells. Accordingly, the overall survival of transplanted rats was significantly enhanced with no rejection of hNSCs observed. We demonstrated that the beneficial effects observed after stem cell transplantation arises from multiple events that counteract several aspects of the disease, a crucial feature for multifactorial diseases, such as ALS. The combination of therapeutic approaches that target different pathogenic mechanisms of the disorder, including pharmacology, molecular therapy and cell transplantation, will increase the chances of a clinically successful therapy for ALS.

Advances in stem cell therapy for amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic Lateral Sclerosis (ALS) is a progressive, incurable neurodegenerative disease that targets motoneurons. Cell-based therapies have generated widespread interest as a potential therapeutic approach but no conclusive results have yet been reported either from pre-clinical or clinical studies.

AREAS COVERED

This is an integrated review of pre-clinical and clinical studies focused on the development of cell-based therapies for ALS. We analyze the biology of stem cell treatments and results obtained from pre-clinical models of ALS and examine the methods and the results obtained to date from clinical trials. We discuss scientific, clinical, and ethical issues and propose some directions for future studies.

EXPERT OPINION

While data from individual studies are encouraging, stem-cell-based therapies do not yet represent a satisfactory, reliable clinical option. The field will critically benefit from the introduction of well-designed, randomized and reproducible, powered clinical trials. Comparative studies addressing key issues such as the nature, properties, and number of donor cells, the delivery mode and the selection of proper patient populations that may benefit the most from cell-based therapies are now of the essence. Multidisciplinary networks of experts should be established to empower effective translation of research into the clinic.

Anticonvulsant effects after grafting of rat, porcine, and human mesencephalic neural progenitor cells into the rat subthalamic nucleus

Cell transplantation based therapy is a promising strategy for treating intractable epilepsies. Inhibition of the subthalamic nucleus (STN) or substantia nigra pars reticulata (SNr) is a powerful experimental approach for remote control of different partial seizure types, when targeting the seizure focus is not amenable. Here, we tested the hypothesis that grafting of embryonic/fetal neural precursor cells (NPCs) from various species (rat, human, pig) into STN or SNr of adult rats induces anticonvulsant effects. To rationally refine this approach, we included NPCs derived from the medial ganglionic eminence (MGE) and ventral mesencephalon (VM), both of which are able to develop a GABAergic phenotype. All VM- and MGE-derived cells showed intense migration behavior after grafting into adult rats, developed characteristics of inhibitory interneurons, and survived at least up to 4 months after transplantation. By using the intravenous pentylenetetrazole (PTZ) seizure threshold test in adult rats, transient anticonvulsant effects were observed after bilateral grafting of NPCs derived from human and porcine VM into STN, but not after SNr injection (site-specificity). In contrast, MGE-derived NPCs did not cause anticonvulsant effects after grafting into STN or SNr (cell-specificity). Neither induction of status epilepticus by lithium-pilocarpine to induce neuronal damage prior to the PTZ test nor pretreatment of MGE cells with retinoic acid and potassium chloride to increase differentiation into GABAergic neurons could enhance anticonvulsant effectiveness of MGE cells. This is the first proof-of-principle study showing anticonvulsant effects by bilateral xenotransplantation of NPCs into the STN. Our study highlights the value of VM-derived NPCs for interneuron-based cell grafting targeting the STN.

Detection of neuroinflammation before selective neuronal loss appearance after mild focal ischemia using [18F]DPA-714 imaging

Background

Translocator protein (TSPO) imaging can be used to detect neuroinflammation (including microglial activation) after acute cerebral infarction. However, longitudinal changes of TSPO binding after mild ischemia that induces selective neuronal loss (SNL) without acute infarction are not well understood. Here, we performed TSPO imaging with [¹⁸F]DPA-714 to determine the time course of neuroinflammation and SNL after mild focal ischemia.

Results

Mild focal ischemia was induced by middle cerebral artery occlusion (MCAO) for 20 min. In MCAO rats without acute infarction investigated by 2, 3, 5-triphenyltetrazolium chloride (TTC) staining, in vitro ARG revealed a significant increase of [¹⁸F]DPA-714 binding in the ipsilateral striatum compared with that in the contralateral side at 1, 2, 3, and 7 days after MCAO. Increased [¹⁸F]DPA-714 binding was observed in the cerebral cortex penumbra, reaching maximal values at 7 days after MCAO. Activation of striatal microglia and astrocytes was observed with immunohistochemistry of ionized calcium binding adaptor molecule 1 (Iba1) and glial fibrillary acidic protein (GFAP) at 2, 3, and 7 days after MCAO. SNL was investigated with Nissl staining and neuronal nuclei (NeuN) immunostaining and observed in the ischemic core region of the striatum on days 3 and 7 after MCAO. We confirmed that total distribution volume of [¹⁸F]DPA-714 in the ipsilateral striatum was significantly increased at 2 and 7 days after MCAO using positron emission tomography (PET).

Conclusions

[¹⁸F]DPA-714 binding measured with in vitro ARG was increased before SNL appeared, and this change was detected by in vivo PET. These findings suggest that TSPO PET imaging might be useful for detection of neuroinflammation leading to SNL after focal ischemia.

Brain and spinal cord injury repair by implantation of human neural progenitor cells seeded onto polymer scaffolds

Hypoxic-ischemic (HI) brain injury and spinal cord injury (SCI) lead to extensive tissue loss and axonal degeneration. The combined application of the polymer scaffold and neural progenitor cells (NPCs) has been reported to enhance neural repair, protection and regeneration through multiple modes of action following neural injury. This study investigated the reparative ability and therapeutic potentials of biological bridges composed of human fetal brain-derived NPCs seeded upon poly(glycolic acid)-based scaffold implanted into the infarction cavity of a neonatal HI brain injury or the hemisection cavity in an adult SCI. Implantation of human NPC (hNPC)–scaffold complex reduced the lesion volume, induced survival, engraftment, and differentiation of grafted cells, increased neovascularization, inhibited glial scar formation, altered the microglial/macrophage response, promoted neurite outgrowth and axonal extension within the lesion site, and facilitated the connection of damaged neural circuits. Tract tracing demonstrated that hNPC–scaffold grafts appear to reform the connections between neurons and their targets in both cerebral hemispheres in HI brain injury and protect some injured corticospinal fibers in SCI. Finally, the hNPC–scaffold complex grafts significantly improved motosensory function and attenuated neuropathic pain over that of the controls. These findings suggest that, with further investigation, this optimized multidisciplinary approach of combining hNPCs with biomaterial scaffolds provides a more versatile treatment for brain injury and SCI.

Biodegradable scaffolds seeded with human fetal brain cells can help repair neurological injuries in rodents. A team led by Kook In Park and Il-Shin Lee from the Yonsei University College of Medicine in Seoul, South Korea, created a mesh of plastic fibers that they bathed in neural progenitor cells. Over the course of several days, these cells differentiated into different types of brain cells, including neurons and glia. The researchers implanted these cell-scaffold complexes into the sites of injury in two rodent models: newborn mice with oxygen deprivation to the brain, and adult rats with severed spinal cords. In both cases, the treatment helped the injured tissues heal and improved the neurological or motor function of the animals. The authors suggest these tissue-engineered structures could also help people with brain or spine injuries.

Stem cell therapy for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the loss of motor neurons. Currently, no effective therapy is available to treat ALS, except for Riluzole, which has only limited clinical benefits. Stem-cell-based therapy has been intensively and extensively studied as a potential novel treatment strategy for ALS and has been shown to be effective, at least to some extent. In this article, we will review the current state of research on the use of stem cell therapy in the treatment of ALS and discuss the most promising stem cells for the treatment of ALS.

The immune response of stem cells in subretinal transplantation

Stem cell transplantation is a potential curative treatment for degenerative diseases of the retina. Among cell injection sites, the subretinal space (SRS) is particularly advantageous as it is maintained as an immune privileged site by the retinal pigment epithelium (RPE) layer. Thus, the success of subretinal transplantation depends on maintenance of RPE integrity. Moreover, both embryonic stem cells (ESCs) and mesenchymal stem cells (MSCs) have negligible immunogenicity and in fact are immunosuppressive. Indeed, many studies have demonstrated that immunosuppressive drugs are not necessary for subretinal transplantation of stem cells if the blood-retinal barrier is not breached during surgery. The immunogenicity of induced pluripotent stem cells (iPSCs) appears more complex, and requires careful study before clinical application. Despite low rates of graft rejection in animal models, survival rates for ESCs, MSCs, and iPSCs in retina are generally poor, possibly due to resident microglia activated by cell transplantation. To improve graft survival in SRS transplantation, damage to the blood-retinal barrier must be minimized using appropriate surgical techniques. In addition, agents that inhibit microglial activation may be required. Finally, immunosuppressants may be required, at least temporarily, until the blood-retinal barrier heals. We review surgical methods and drug regimens to enhance the likelihood of graft survival after SRS transplantation.

Human neural stem cells alleviate Alzheimer-like pathology in a mouse model

Background

Alzheimer’s disease (AD) is an inexorable neurodegenerative disease that commonly occurs in the elderly. The cognitive impairment caused by AD is associated with abnormal accumulation of amyloid-β (Aβ) and hyperphosphorylated tau, which are accompanied by inflammation. Neural stem cells (NSCs) are self-renewing, multipotential cells that differentiate into distinct neural cells. When transplanted into a diseased brain, NSCs repair and replace injured tissues after migration toward and engraftment within lesions. We investigated the therapeutic effects in an AD mouse model of human NSCs (hNSCs) that derived from an aborted human fetal telencephalon at 13 weeks of gestation. Cells were transplanted into the cerebral lateral ventricles of neuron-specific enolase promoter-controlled APPsw-expressing (NSE/APPsw) transgenic mice at 13 months of age.

Results

Implanted cells extensively migrated and engrafted, and some differentiated into neuronal and glial cells, although most hNSCs remained immature. The hNSC transplantation improved spatial memory in these mice, which also showed decreased tau phosphorylation and Aβ42 levels and attenuated microgliosis and astrogliosis. The hNSC transplantation reduced tau phosphorylation via Trk-dependent Akt/GSK3β signaling, down-regulated Aβ production through an Akt/GSK3β signaling-mediated decrease in BACE1, and decreased expression of inflammatory mediators through deactivation of microglia that was mediated by cell-to-cell contact, secretion of anti-inflammatory factors generated from hNSCs, or both. The hNSC transplantation also facilitated synaptic plasticity and anti-apoptotic function via trophic supplies. Furthermore, the safety and feasibility of hNSC transplantation are supported.

Conclusions

These findings demonstrate the hNSC transplantation modulates diverse AD pathologies and rescue impaired memory via multiple mechanisms in an AD model. Thus, our data provide tangible preclinical evidence that human NSC transplantation could be a safe and versatile approach for treating AD patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-015-0035-6) contains supplementary material, which is available to authorized users.

Human neural stem cell transplantation in ALS: initial results from a phase I trial

Background

We report the initial results from a phase I clinical trial for ALS. We transplanted GMP-grade, fetal human neural stem cells from natural in utero death (hNSCs) into the anterior horns of the spinal cord to test for the safety of both cells and neurosurgical procedures in these patients. The trial was approved by the Istituto Superiore di Sanità and the competent Ethics Committees and was monitored by an external Safety Board.

Methods

Six non-ambulatory patients were treated. Three of them received 3 unilateral hNSCs microinjections into the lumbar cord tract, while the remaining ones received bilateral (n = 3 + 3) microinjections. None manifested severe adverse events related to the treatment, even though nearly 5 times more cells were injected in the patients receiving bilateral implants and a much milder immune-suppression regimen was used as compared to previous trials.

Results

No increase of disease progression due to the treatment was observed for up to18 months after surgery. Rather, two patients showed a transitory improvement of the subscore ambulation on the ALS-FRS-R scale (from 1 to 2). A third patient showed improvement of the MRC score for tibialis anterior, which persisted for as long as 7 months. The latter and two additional patients refused PEG and invasive ventilation and died 8 months after surgery due to the progression of respiratory failure. The autopsies confirmed that this was related to the evolution of the disease.

Conclusions

We describe a safe cell therapy approach that will allow for the treatment of larger pools of patients for later-phase ALS clinical trials, while warranting good reproducibility. These can now be carried out under more standardized conditions, based on a more homogenous repertoire of clinical grade hNSCs. The use of brain tissue from natural miscarriages eliminates the ethical concerns that may arise from the use of fetal material.

Trial registration

EudraCT:2009-014484-39.

Adult stem cell as new advanced therapy for experimental neuropathic pain treatment

Neuropathic pain (NP) is a highly invalidating disease resulting as consequence of a lesion or disease affecting the somatosensory system. All the pharmacological treatments today in use give a long lasting pain relief only in a limited percentage of patients before pain reappears making NP an incurable disease. New approaches are therefore needed and research is testing stem cell usage. Several papers have been written on experimental neuropathic pain treatment using stem cells of different origin and species to treat experimental NP. The original idea was based on the capacity of stem cell to offer a totipotent cellular source for replacing injured neural cells and for delivering trophic factors to lesion site; soon the researchers agreed that the capacity of stem cells to contrast NP was not dependent upon their regenerative effect but was mostly linked to a bidirectional interaction between the stem cell and damaged microenvironment resident cells. In this paper we review the preclinical studies produced in the last years assessing the effects induced by several stem cells in different models of neuropathic pain. The overall positive results obtained on pain remission by using stem cells that are safe, of easy isolation, and which may allow an autologous transplant in patients may be encouraging for moving from bench to bedside, although there are several issues that still need to be solved.

Proteomic analysis of immature rat pups brain in response to hypoxia and ischemia challenge

Hypoxia and ischemia significantly affects perinatal brain development, even worse in preterm infants. However, the details of the mechanism leading to permanent brain damage after hypoxia-ischemia attack have not been fully elucidated. Proteomics could provide insight into the potential mechanism and help to promote the clinical treatment. In this study, quantitative analysis was performed 24 hours after hypoxia-ischemia using liquid-chromatography mass spectrometry coupled to label-free analysis. Compared to control, 193 proteins were present only in hypoxic-ischemic group. In addition, 34 proteins were more than 2 folds up-regulated and 14 proteins were more than 2 folds down-regulated in hypoxia-ischemia group. Gene Ontology database showed that the majority of differentially expressed proteins comprised mitochondrial proteins et al. Molecular function analysis revealed that the majority of proteins were involved in ion binding et al. Biological process analysis showed that the majority of proteins were involved in response to organic substance et al. STRING 9.0 software analysis were used to explore the complex interactions existed among the proteins. Western blot were used to verify the fold changes of some proteins-microtubule-associated protein 2 and microtubule-associated protein tau. This novel study performed a full-scale screening of the proteomics research in hypoxic-ischemic brain damage of immature rat.

A multi-modality platform to image stem cell graft survival in the naïve and stroke-damaged mouse brain

Neural stem cell implantations have been extensively investigated for treatment of brain diseases such as stroke. In order to follow the localization and functional status of cells after implantation noninvasive imaging is essential. Therefore, we developed a comprehensive multi-modality platform for in vivo imaging of graft localization, density, and survival using 19F magnetic resonance imaging in combination with bioluminescence imaging. We quantitatively analyzed cell graft survival over the first 4 weeks after transplantation in both healthy and stroke-damaged mouse brain and correlated our findings of graft vitality with the host innate immune response. The multi-modality imaging platform will help to improve cell therapy also in context other than stroke and to gain indispensable information for clinical translation.

The influence of immunosuppressive drugs on neural stem/progenitor cell fate in vitro

In allogenic and xenogenic transplantation, adequate immunosuppression plays a major role in graft survival, especially over the long term. The effect of immunosuppressive drugs on neural stem/progenitor cell fate has not been sufficiently explored. The focus of this study is to systematically investigate the effects of the following four different immunotherapeutic strategies on human neural progenitor cell survival/death, proliferation, metabolic activity, differentiation and migration in vitro: (1) cyclosporine A (CsA), a calcineurin inhibitor; (2) everolimus (RAD001), an mTOR-inhibitor; (3) mycophenolic acid (MPA, mycophenolate), an inhibitor of inosine monophosphate dehydrogenase and (4) prednisolone, a steroid. At the minimum effective concentration (MEC), we found a prominent decrease in hNPCs' proliferative capacity (BrdU incorporation), especially for CsA and MPA, and an alteration of the NAD(P)H-dependent metabolic activity. Cell death rate, neurogenesis, gliogenesis and cell migration remained mostly unaffected under these conditions for all four immunosuppressants, except for apoptotic cell death, which was significantly increased by MPA treatment.

Minocycline treatment and bone marrow mononuclear cell transplantation after endothelin-1 induced striatal ischemia

We explored whether the modulation of microglia activation with minocycline is beneficial to the therapeutic actions of bone marrow mononuclear cells (BMMCs) transplanted after experimental stroke. Male Wistar adult rats were divided in four experimental groups: ischemic control saline treated (G1, N = 6), ischemic minocycline treated (G2, N = 5), ischemic BMMC treated (G3, N = 5), and ischemic minocycline/BMMC treated (G4, N = 6). There was a significant reduction in the number of ED1+ cells in G3 animals (51.31 ± 2.41, P < 0.05), but this effect was more prominent following concomitant treatment with minocycline (G4 = 29.78 ± 1.56). There was conspicuous neuronal preservation in the brains of G4 animals (87.97 ± 4.27) compared with control group (G1 = 47.61 ± 2.25, P < 0.05). The behavioral tests showed better functional recovery in animals of G2, G3, and G4, compared with G1 and baseline (P < 0.05). The results suggest that a proper modulation of microglia activity may contribute to a more permissive ischemic environment contributing to increased neuroprotection and functional recovery following striatal ischemia.

Amelioration of motor/sensory dysfunction and spasticity in a rat model of acute lumbar spinal cord injury by human neural stem cell transplantation

Introduction

Intraspinal grafting of human neural stem cells represents a promising approach to promote recovery of function after spinal trauma. Such a treatment may serve to: I) provide trophic support to improve survival of host neurons; II) improve the structural integrity of the spinal parenchyma by reducing syringomyelia and scarring in trauma-injured regions; and III) provide neuronal populations to potentially form relays with host axons, segmental interneurons, and/or α-motoneurons. Here we characterized the effect of intraspinal grafting of clinical grade human fetal spinal cord-derived neural stem cells (HSSC) on the recovery of neurological function in a rat model of acute lumbar (L3) compression injury.

Methods

Three-month-old female Sprague–Dawley rats received L3 spinal compression injury. Three days post-injury, animals were randomized and received intraspinal injections of either HSSC, media-only, or no injections. All animals were immunosuppressed with tacrolimus, mycophenolate mofetil, and methylprednisolone acetate from the day of cell grafting and survived for eight weeks. Motor and sensory dysfunction were periodically assessed using open field locomotion scoring, thermal/tactile pain/escape thresholds and myogenic motor evoked potentials. The presence of spasticity was measured by gastrocnemius muscle resistance and electromyography response during computer-controlled ankle rotation. At the end-point, gait (CatWalk), ladder climbing, and single frame analyses were also assessed. Syrinx size, spinal cord dimensions, and extent of scarring were measured by magnetic resonance imaging. Differentiation and integration of grafted cells in the host tissue were validated with immunofluorescence staining using human-specific antibodies.

Results

Intraspinal grafting of HSSC led to a progressive and significant improvement in lower extremity paw placement, amelioration of spasticity, and normalization in thermal and tactile pain/escape thresholds at eight weeks post-grafting. No significant differences were detected in other CatWalk parameters, motor evoked potentials, open field locomotor (Basso, Beattie, and Bresnahan locomotion score (BBB)) score or ladder climbing test. Magnetic resonance imaging volume reconstruction and immunofluorescence analysis of grafted cell survival showed near complete injury-cavity-filling by grafted cells and development of putative GABA-ergic synapses between grafted and host neurons.

Conclusions

Peri-acute intraspinal grafting of HSSC can represent an effective therapy which ameliorates motor and sensory deficits after traumatic spinal cord injury.

ATM-deficient human neural stem cells as an in vitro model system to study neurodegeneration

Loss of ATM kinase, a transducer of the DNA damage response and redox sensor, causes the neurodegenerative disorder ataxia-telangiectasia (A-T). While a great deal of progress has been made in elucidating the ATM-dependent DNA damage response (DDR) network, a key challenge remains in understanding the selective susceptibility of the nervous system to faulty DDR. Several factors appear implicated in the neurodegenerative phenotype in A-T, but which of them plays a crucial role remains unclear, especially since mouse models of A-T do not fully mirror the respective human syndrome. Therefore, a number of human neural stem cell (hNSC) systems have been developed to get an insight into the molecular mechanisms of neurodegeneration as consequence of ATM inactivation. Here we review the hNSC systems developed by us an others to model A-T.

Effects of atelocollagen on neural stem cell function and its migrating capacity into brain in psychiatric disease model

Stem cell therapy is well proposed as a potential method for the improvement of neurodegenerative damage in the brain. Among several different procedures to reach the cells into the injured lesion, the intravenous (IV) injection has benefit as a minimally invasive approach. However, for the brain disease, prompt development of the effective treatment way of cellular biodistribution of stem cells into the brain after IV injection is needed. Atelocollagen has been used as an adjunctive material in a gene, drug and cell delivery system because of its extremely low antigenicity and bioabsorbability to protect these transplants from intrabody environment. However, there is little work about the direct effect of atelocollagen on stem cells, we examined the functional change of survival, proliferation, migration and differentiation of cultured neural stem cells (NSCs) induced by atelocollagen in vitro. By 72-h treatment 0.01-0.05% atelocollagen showed no significant effects on survival, proliferation and migration of NSCs, while 0.03-0.05% atelocollagen induced significant reduction of neuronal differentiation and increase of astrocytic differentiation. Furthermore, IV treated NSCs complexed with atelocollagen (0.02%) could effectively migrate into the brain rather than NSC treated alone using chronic alcohol binge model rat. These experiments suggested that high dose of atelocollagen exerts direct influence on NSC function but under 0.03% of atelocollagen induces beneficial effect on regenerative approach of IV administration of NSCs for CNS disease.

Increasing doublecortin expression promotes migration of human embryonic stem cell-derived neurons

Human embryonic stem cell-derived neuronal progenitors (hNPs) provide a potential source for cellular replacement following neurodegenerative diseases. One of the greatest challenges for future neuron replacement therapies will be to control extensive cell proliferation and stimulate cell migration of transplanted cells. The doublecortin (DCX) gene encodes the protein DCX, a microtubule-associated protein essential for the migration of neurons in the human brain. In this study, we tested whether increasing the expression of DCX in hNPs would favorably alter their proliferation and migration. Migration and proliferation of hNPs was compared between hNPs expressing a bicistronic DCX/IRES-GFP transgene and those expressing a green fluorescent protein (GFP) transgene introduced by piggyBac-mediated transposition. The DCX-transfected hNPs showed a significant decrease in their proliferation and migrated significantly further on two different substrates, Matrigel and brain slices. Additionally, a dense network of nestin-positive (+) and vimentin+ fibers were found to extend from neurospheres transplanted onto brain slices, and this fiber growth was increased from neurospheres containing DCX-transfected hNPs. In summary, our results show that increased DCX expression inhibits proliferation and promotes migration of hNPs.

Rescuing the neonatal brain from hypoxic injury with autologous cord blood

Brain injury resulting from perinatal hypoxic-ischemic encephalopathy (HIE) is a major cause of acute mortality in infants and chronic neurologic disability in surviving children. Recent multicenter clinical trials demonstrated the effectiveness of hypothermia initiated within the first 6 postnatal hours to reduce the risk of death or major neurological disabilities among neonates with HIE. However, in these trials, approximately 40% of cooled infants died or survived with significant impairments. Therefore, adjunct therapies are required to improve the outcome in neonates with HIE. Cord blood (CB) is a rich source of stem cells. Administration of human CB cells in animal models of HIE has generally resulted in improved outcomes and multiple mechanisms have been suggested including anti-inflammation, release of neurotrophic factors and stimulation of endogenous neurogenesis. Investigators at Duke are conducting studies of autologous CB infusion in neonates with HIE and in children with cerebral palsy. These pilot studies indicate no added risk from the regimens used, but results of ongoing placebo-controlled trials are needed to assess efficacy. Meanwhile, further investigations are warranted to determine the best strategies, that is, timing, dosing, route of delivery, choice of stem cells and ex vivo modulations, to attain long-term benefits of CB stem cell therapy.

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

Neural transplantation is a promising therapeutic strategy for neurodegenerative diseases and other disorders of the central nervous system (CNS) such as Parkinson and Huntington diseases, multiple sclerosis or stroke. Although cell replacement therapy already went through clinical trials for some of these diseases using fetal human neuroblasts, several significant limitations led to the search for alternative cell sources that would be more suitable for intracerebral transplantation.Taking into account logistical and ethical issues linked to the use of tissue derived from human fetuses, and the immunologically special status of the CNS allowing the occurrence of deleterious immune reactions, neural stem/progenitor cells (NSPCs) appear to be an interesting cell source candidate. In addition to their ability for replacing cell populations lost during the pathological events, NSPCs also display surprising therapeutic effects of neuroprotection and immunomodulation. A better knowledge of the mechanisms involved in these specific characteristics will hopefully lead in the future to a successful use of NSPCs in regenerative medicine for CNS disorders.

Concise review: self-renewal in the central nervous system: neural stem cells from embryo to adult

The recent discovery of neural stem cells (NSCs) in the adult mammalian brain has fostered a plethora of translational and preclinical studies to investigate future therapeutic approaches for the cure of neurodegenerative diseases. These studies are finally at the clinical stage, and some of them are already under way. The definition of a bona fide stem cell has long been the object of much debate focused on the establishment of standard and univocal criteria to distinguish between stem and progenitor cells. It is commonly accepted that NSCs have to fulfill two basic requirements, the capacity for long-term self-renewal and the potential for differentiation, which account for their physiological role, namely central nervous system tissue homeostasis. Strategies such as immortalization or reprogramming of somatic cells to the embryonic-like stage of pluripotency indicate the relevance of extensive self-renewal ability of NSCs either in vitro or in vivo. Moreover, the discovery of stem-like tumor cells in brain tumors, such as gliomas, accompanied by the isolation of these cells through the same paradigm used for related healthy cells, has provided further evidence of the key role that self-renewal plays in the development and progression of neurodegenerative diseases and cancer. In this review we provide an overview of the current understanding of the self-renewal capacity of nontransformed human NSCs, with or without immortalization or reprogramming, and of stem-like tumor cells, referring to both research and therapeutic studies.

Noninvasive monitoring of immunosuppressive drug efficacy to prevent rejection of intracerebral glial precursor allografts

The development of cell-based therapies opens up new avenues for treating a myriad of diseases of the central nervous system (CNS). While significant effort is being directed toward development of patient-specific, autologous transplantable cells, at present, the majority of cell transplantation studies performed clinically utilize allografts. In this context, the issue of graft rejection and immunoprotection is of key importance. In this study, we transplanted mouse glial-restricted progenitors into immunodeficient, immunocompetent, and immunosuppressed mice and monitored their survival noninvasively using bioluminescence imaging (BLI). With the use of serial BLI, we evaluated both the prevalence and dynamics of cell rejection. We demonstrate that allografts in immunocompetent mice were rejected at a rate of 69.2% (n = 13) indicating that graft tolerance is possible even without immunosuppression. Immunosuppression using a combination of rapamycin and FK506 or cyclosporin failed to fully protect the grafts. FK506 and rapamycin treatment resulted in a slight improvement of immunoprotection (22.2% rejected, n = 9) compared to cyclosporin A (55.6% rejected, n = 9); however, the difference was not significant. Notably, immunohistochemistry revealed leukocytes infiltrating the graft area in both rejecting and nonrejecting immunocompetent animals, but not in immunodeficient animals. The induction of an inflammatory process, even in surviving allografts, has implications for their long-term survival and functionality.

Cell type-associated differences in migration, survival, and immunogenicity following grafting in CNS tissue

Cell transplantation has been suggested to display several neuroprotective and/or neuroregenerative effects in animal models of central nervous system (CNS) trauma. However, while most studies report on clinical observations, currently little is known regarding the actual fate of the cell populations grafted and whether or how the brain's innate immune system, mainly directed by activated microglia and astrocytes, interacts with autologous cellular implants. In this study, we grafted well-characterized neural stem cell, mouse embryonic fibroblast, dendritic cell, bone marrow mononuclear cell, and splenocyte populations, all isolated or cultured from C57BL/6-eGFP transgenic mice, below the capsula externa (CE) of healthy C57BL/6 mice and below the inflamed/demyelinated CE of cuprizone-treated C57BL/6 mice. Two weeks postgrafting, an extensive quantitative multicolor histological analysis was performed in order (i) to quantify cell graft localization, migration, survival, and toxicity and (ii) to characterize endogenous CNS immune responses against the different cell grafts. Obtained results indicate dependence on the cell type grafted: (i) a different degree of cell graft migration, survival, and toxicity and (ii) a different organization of the endogenous immune response. Based on these observations, we warrant that further research should be undertaken to understand-and eventually control-cell graft-induced tissue damage and activation of the brain's innate immune system. The latter will be inevitable before cell grafting in the CNS can be performed safely and successfully in clinical settings.

Differential pathotropism of non-immortalized and immortalized human neural stem cell lines in a focal demyelination model

Cell therapy is reaching the stage of phase I clinical trials for post-traumatic, post-ischemic, or neurodegenerative disorders, and the selection of the appropriate cell source is essential. In order to assess the capacity of different human neural stem cell lines (hNSC) to contribute to neural tissue regeneration and to reduce the local inflammation after an acute injury, we transplanted GMP-grade non-immortalized hNSCs and v-myc (v-IhNSC), c-myc T58A (T-IhNSC) immortalized cells into the corpus callosum of adult rats after 5 days from focal demyelination induced by lysophosphatidylcholine. At 15 days from transplantation, hNSC and T-IhNSC migrated to the lesioned area where they promoted endogenous remyelination and differentiated into mature oligodendrocytes, while the all three cell lines were able to integrate in the SVZ. Moreover, where demyelination was accompanied by an inflammatory reaction, a significant reduction of microglial cells' activation was observed. This effect correlated with a differential migratory pattern of transplanted hNSC and IhNSC, significantly enhanced in the former, thus suggesting a specific NSC-mediated immunomodulatory effect on the local inflammation. We provide evidence that, in the subacute phase of a demyelination injury, different human immortalized and non-immortalized NSC lines, all sharing homing to the stem niche, display a differential pathotropism, both through cell-autonomous and non-cell autonomous effects. Overall, these findings promote IhNSC as an inexhaustible cell source for large-scale preclinical studies and non-immortalized GMP grade hNSC lines as an efficacious, safe, and reliable therapeutic tool for future clinical applications.

Endogenous neural precursors influence grafted neural stem cells and contribute to neuroprotection in the parkinsonian rat

Neuroprotective and neurorescue effects after neural stem/precursor cell (NPC) transplantation have been reported, but the mechanisms underlying such phenomena are not well understood. Our recent findings in a rat Parkinson's disease (PD) model indicate that transplantation of NPCs before a 6-hydroxydopamine (6-OHDA) insult can result in nigrostriatal protection which is associated with endogenous NPC proliferation, migration and neurogenesis. Here, we sought to determine whether the observed endogenous NPC response (i) contributes to transplanted NPC-mediated neuroprotection; and/or (ii) affects graft phenotype and function. Host Fischer 344 rats were administered the antimitotic agent cytosine-β-d-arabinofuranoside (Ara-C) to eliminate actively proliferating endogenous neural precursors before being transplanted with NPCs and treated with 6-OHDA to induce nigrostriatal degeneration. Behavioral and histological analyses demonstrate that the neuroprotective response observed in NPC transplanted animals which had not received Ara-C was significantly attenuated in animals which did receive pre-transplant Ara-C. Also, while grafts in Ara-C-treated animals showed no decrease in cell number, they exhibited significantly reduced expression of the neural stem cell regulators nestin and sonic hedgehog. In addition, inhibition of the endogenous NPC response resulted in an exaggerated host glial reaction. Overall, the study establishes for the first time that endogenous NPCs contribute to transplanted NPC-mediated therapeutic effects by affecting both grafted and mature host cells in unique ways. Thus, both endogenous and transplanted NPCs are important in creating an environment suitable for neural protection and rescue, and harnessing their synergistic interaction may lead to the optimization of cell-based therapies for PD.

Intravenous neural stem cells abolish nociceptive hypersensitivity and trigger nerve regeneration in experimental neuropathy

A nonphysiological repair of the lesioned nerve leading to the formation of neurinomas, altered nerve conduction, and spontaneous firing is considered the main cause of the events underlying neuropathic pain. It was investigated whether neural stem cell (NSCs) administration could lead to a physiological nerve repair, thus to a reduction of neuropathic pain symptoms such as hyperalgesia and allodynia in a well-established model of this pain (sciatic nerve chronic constriction injury [CCI]). Moreover, since we and others showed that the peripheral nerve lesion starts a cascade of neuroinflammation-related events that may maintain and worsen the original lesion, the effect of NSCs on sciatic nerve pro- and antiinflammatory cytokines in CCI mice was investigated. NSCs injected intravenously, when the pathology was already established, induced a significant reduction in allodynia and hyperalgesia already 3 days after administration, demonstrating a therapeutic effect that lasted for at least 28 days. Responses changed with the number of administered NSCs, and the effect on hyperalgesia could be boosted by a new NSC administration. Treatment significantly decreased proinflammatory, activated antiinflammatory cytokines in the sciatic nerve, and reduced spinal cord Fos expression in laminae I-VI. Moreover, in NSC-treated animals, a reparative process and an improvement of nerve morphology is present at a later time. Since NSC effect on pain symptoms preceded nerve repair and was maintained after cells had disappeared from the lesion site, we suggest that regenerative, behavioral, and immune NSC effects are largely due to microenvironmental changes they might induce at the lesion site.

Transplanted neural stem/precursor cells instruct phagocytes and reduce secondary tissue damage in the injured spinal cord

Transplanted neural stem/precursor cells possess peculiar therapeutic plasticity and can simultaneously instruct several therapeutic mechanisms in addition to cell replacement. Here, we interrogated the therapeutic plasticity of neural stem/precursor cells after their focal implantation in the severely contused spinal cord. We injected syngeneic neural stem/precursor cells at the proximal and distal ends of the contused mouse spinal cord and analysed locomotor functions and relevant secondary pathological events in the mice, cell fate of transplanted neural stem/precursor cells, and gene expression and inflammatory cell infiltration at the injured site. We used two different doses of neural stem/precursor cells and two treatment schedules, either subacute (7 days) or early chronic (21 days) neural stem/precursor cell transplantation after the induction of experimental thoracic severe spinal cord injury. Only the subacute transplant of neural stem/precursor cells enhanced the recovery of locomotor functions of mice with spinal cord injury. Transplanted neural stem/precursor cells survived undifferentiated at the level of the peri-lesion environment and established contacts with endogenous phagocytes via cellular-junctional coupling. This was associated with significant modulation of the expression levels of important inflammatory cell transcripts in vivo. Transplanted neural stem/precursor cells skewed the inflammatory cell infiltrate at the injured site by reducing the proportion of 'classically-activated' (M1-like) macrophages, while promoting the healing of the injured cord. We here identify a precise window of opportunity for the treatment of complex spinal cord injuries with therapeutically plastic somatic stem cells, and suggest that neural stem/precursor cells have the ability to re-programme the local inflammatory cell microenvironment from a 'hostile' to an 'instructive' role, thus facilitating the healing or regeneration past the lesion.

Neural stem cell gene therapy ameliorates pathology and function in a mouse model of globoid cell leukodystrophy

Murine neural stem cells (mNSCs), either naive or genetically modified to express supranormal levels of β-galactocerebrosidase (GALC), were transplanted into the brain of Twitcher mice, a murine model of globoid cell leukodystrophy, a severe sphingolipidosis. Cells engrafted long-term into the host cytoarchitecture, producing functional GALC. Levels of enzyme activity in brain and spinal cord tissues were enhanced when GALC-overexpressing NSC were used. Enzymatic correction correlated with reduced tissue storage, decreased activation of astroglia and microglia, delayed onset of symptoms, and longer lifespan. Mechanisms underlying the therapeutic effect of mNSC included widespread enzyme distribution, cross-correction of host cells, anti-inflammatory activity, and neuroprotection. Similar cell engraftment and metabolic correction were reproduced using human NSC. Thus, NSC gene therapy rapidly reconstitutes sustained and long-lasting enzyme activity in central nervous system tissues. Combining this approach with treatments targeting the systemic disease associated with leukodystrophies may provide significant therapeutic benefit. Stem Cells 2011;29:1559–1571

Injected Versus Oral Cyclosporine for Human Neural Progenitor Grafting in Rats

BACKGROUND

Neural cell transplantation is a promising therapy for stroke, but rejection of human cells in animal models is an obstacle to furthering this research. Many antirejection strategies have been reported, but few comparison data are available. We asked if human neural cell grafts would have different survival or differentiation with injected or oral cyclosporine regimens.

METHODS

Rats received intracerebral grafts of human embryonic stem cell-derived neural progenitors, and 6 rats each were randomized to 4 cyclosporine regimens: 1) daily injections, 2) initial injections followed by oral drug in the drinking water, 3) oral drug only, or 4) no cyclosporine. Histology was performed 14 days after grafting for quantification of markers of human cells, neural cell types, and immune cells.

RESULTS

More rats in the injection (6/6) and injection+oral (5/6) groups had surviving graft cells than in the oral (1/6) and control (3/6) groups (p<0.05), with a trend toward a greater number of surviving graft cells as well. All rats with surviving graft cells also had these cells co-label for a neural progenitor marker, and a minority of graft cells co-labeled for a cell division marker and a neuronal marker. Rats with areas of dead graft cell debris were seen in all of the groups. In these areas, cells that labeled for microglial markers also contained the human nuclear marker in their cytoplasm, suggesting phagocytosis of the graft cells.

CONCLUSIONS

Human neural cell survival in rat brain tissue differed between cyclosporine regimens, but microglial phagocytosis of graft cells occurred in all the groups. Frequent injection of laboratory animals is undesirable, and a compromise strategy of peritransplant injections followed by drug in the drinking water showed good results in preventing graft cell rejection. Further research is needed to optimize the antirejection approach for this application.

Hypoxia in the regulation of neural stem cells

In aerobic organisms, oxygen is a critical factor in tissue and organ morphogenesis from embryonic development throughout post-natal life, as it regulates various intracellular pathways involved in cellular metabolism, proliferation, survival and fate. In the mammalian central nervous system, oxygen plays a critical role in regulating the growth and differentiation state of neural stem cells (NSCs), multipotent neuronal precursor cells that reside in a particular microenvironment called the neural stem cell niche and that, under certain physiological and pathological conditions, differentiate into fully functional mature neurons, even in adults. In both experimental and clinical settings, oxygen is one of the main factors influencing NSCs. In particular, the physiological condition of mild hypoxia (2.5-5.0% O(2)) typical of neural tissues promotes NSC self-renewal; it also favors the success of engraftment when in vitro-expanded NSCs are transplanted into brain of experimental animals. In this review, we analyze how O(2) and specifically hypoxia impact on NSC self-renewal, differentiation, maturation, and homing in various in vitro and in vivo settings, including cerebral ischemia, so as to define the O(2) conditions for successful cell replacement therapy in the treatment of brain injury and neurodegenerative diseases.

Creating permissive microenvironments for stem cell transplantation into the central nervous system

Traumatic injury to the central nervous system (CNS) is highly debilitating, with the clinical need for regenerative therapies apparent. Neural stem/progenitor cells (NSPCs) are promising because they can repopulate lost or damaged cells and tissues. However, the adult CNS does not provide an optimal milieu for exogenous NSPCs to survive, engraft, differentiate, and integrate with host tissues. This review provides an overview of tissue engineering strategies to improve stem cell therapies by providing a defined microenvironment during transplantation. The use of biomaterials for physical support, growth factor delivery, and cellular co-transplantation are discussed. Providing the proper environment for stem cell survival and host tissue integration is crucial in realizing the full potential of these cells in CNS repair strategies.

Gene therapy for lysosomal storage disorders

INTRODUCTION

Lysosomal storage disorders (LSDs) encompass more than 50 distinct diseases, caused by defects in various aspects of lysosomal function. Neurodegeneration and/or dysmyelination are the hallmark of roughly 70% of LSDs. Gene therapy represents a promising approach for the treatment of CNS manifestations in LSDs, as it has the potential to provide a permanent source of the deficient enzyme, either by direct injection of vectors or by transplantation of gene-corrected cells. In this latter approach, the biology of neural stem/progenitor cells and hematopoietic cells might be exploited.

AREAS COVERED

Based on an extensive literature search up until March 2011, the author reviews and discusses the progress, the crucial aspects and the major challenges towards the development of novel gene therapy strategies aimed to target the CNS, with particular attention to direct intracerebral gene delivery and transplantation of neural stem/progenitor cells.

EXPERT OPINION

The implementation of viral vector delivery systems with specific tropism, regulated transgene expression, low immunogenicity and low genotoxic risk and the improvement in isolation and manipulation of relevant cell types to be transplanted, are fundamental challenges to the field. Also, combinatorial strategies might be required to achieve full correction in LSDs with neurological involvement.