Primate embryonic stem cell-derived neuronal progenitors transplanted into ischemic brain

Systemic transplantation of embryonic stem cells accelerates brain lesion decrease and angiogenesis

As stem cells can regenerate damaged tissue, their therapeutic potential on brain damage has been investigated. In this study, the effects of embryonic stem cell transplantation on brain damage were investigated by using a photochemically induced thrombotic brain damage model. Mice with systemic transplantation of embryonic stem cells expressing enhanced green fluorescence protein on day 1 showed a smaller brain lesion size on day 8 than the control mice. The smaller lesion was accompanied by the increase in the number of microvessels at the border of the damaged area. Inside and around the damaged lesion, no EGFP-positive cells were observed. These findings suggested that embryonic stem cell transplantation reduced the brain lesion through the acceleration of angiogenesis by endogenous endothelial cells.

Tridermal tumorigenesis of induced pluripotent stem cells transplanted in ischemic brain

Stroke is a major neurologic disorder. Induced pluripotent stem (iPS) cells can be produced from basically any part of patients, with high reproduction ability and pluripotency to differentiate into various types of cells, suggesting that iPS cells can provide a hopeful therapy for cell transplantation. However, transplantation of iPS cells into ischemic brain has not been reported. In this study, we showed that the iPS cells fate in a mouse model of transient middle cerebral artery occlusion (MCAO). Undifferentiated iPS cells (5 x 10(5)) were transplanted into ipsilateral striatum and cortex at 24 h after 30 mins of transient MCAO. Behavioral and histologic analyses were performed at 28 day after the cell transplantation. To our surprise, the transplanted iPS cells expanded and formed much larger tumors in mice postischemic brain than in sham-operated brain. The clinical recovery of the MCAO+iPS group was delayed as compared with the MCAO+PBS (phosphate-buffered saline) group. iPS cells formed tridermal teratoma, but could supply a great number of Dcx-positive neuroblasts and a few mature neurons in the ischemic lesion. iPS cells have a promising potential to provide neural cells after ischemic brain injury, if tumorigenesis is properly controlled.

Hematopoietic stem cell transplantation protects mice from lethal stroke

Stroke is a major cause of mortality and morbidity in the United States. The ideal therapeutic approach would minimize cell death and regenerate brain tissue. In order to investigate some questions that are related to such an approach, we have generated a mouse model in which we induce a stroke using the middle cerebral artery occlusion method. After 2h occlusion followed by reperfusion, 99% of mice died within 8 days of stroke. Total bone marrow cell transplantation by intravenous injection revealed an optimal timing of cell transfer in two doses on days 1 (same day of surgery) and 2 after surgery. Moreover, intravenous injection of Sca1+ bone marrow cells (enriched in hematopoietic stem cells) showed a dose-response effect on survival. Surviving mice also had no signs of apparent paralysis or weakness. Tracking analysis using donor stem cells expressing LacZ revealed only few donor cells in the brain. We conclude that hematopoietic stem cell-rich Sca1+ bone marrow cell transplantation after stroke protects the brain of a sizeable portion of mice subjected to stroke and alleviate remarkably the resulting neurological morbidity in surviving mice.

Activated T-cells inhibit neurogenesis by releasing granzyme B: rescue by Kv1.3 blockers

There is a great need for pharmacological approaches to enhance neural progenitor cell (NPC) function particularly in neuroinflammatory diseases with failed neuroregeneration. In diseases such as multiple sclerosis and stroke, T-cell infiltration occurs in periventricular zones where NPCs are located and is associated with irreversible neuronal loss. We studied the effect of T-cell activation on NPC functions. NPC proliferation and neuronal differentiation were impaired by granzyme B (GrB) released by the T-cells. GrB mediated its effects by the activation of a Gi-protein-coupled receptor leading to decreased intracellular levels of cAMP and subsequent expression of the voltage-dependent potassium channel, Kv1.3. Importantly, blocking channel activity with margatoxin or blocking its expression reversed the inhibitory effects of GrB on NPCs. We have thus identified a novel pathway in neurogenesis. The increased expression of Kv1.3 in pathological conditions makes it a novel target for promoting neurorestoration.

Murine neural stem/progenitor cells protect neurons against ischemia by HIF-1alpha-regulated VEGF signaling

Focal cerebral ischemia following middle cerebral artery occlusion (MCAO) stimulates a robust cytogenic response from the adult subventricular zone (SVZ) that includes massive proliferation of neural stem/progenitor cells (NSPCs) and cellular migration into the injury area. To begin to explore beneficial roles of NSPCs in this response, we investigated the ability of embryonic and postnatal NSPCs to promote neuronal survival under conditions of in vivo and in vitro ischemia. Intracerebral transplantation of NSPCs attenuated neuronal apoptosis in response to focal ischemia induced by transient MCAO, and prevented neuronal cell death of cortical neurons in response to oxygen-glucose deprivation (OGD) in culture. NSPC-mediated neuroprotection was blocked by the pharmacological inhibitors of vascular endothelial growth factor (VEGF), SU1498 and Flt-1Fc. Embryonic and postnatal NSPCs were both intrinsically resistant to brief OGD exposure, and constitutively expressed both hypoxia-inducible factor 1α (HIF-1α) transcription factor and its downstream target, VEGF. Genomic deletion of HIF-1α by Cre-mediated excision of exon 2 in NSPC cultures resulted in >50% reduction of VEGF production and ablation of NSPC-mediated neuroprotection. These findings indicate that NSPCs promote neuronal survival under ischemic conditions via HIF-1α-VEGF signaling pathways and support a role for NSPCs in promotion of neuronal survival following stroke.

Transplantation of human neural precursor cells in Matrigel scaffolding improves outcome from focal cerebral ischemia after delayed postischemic treatment in rats

Transplantation of neural cells is a potential approach for stroke treatment, but disruption of tissue architecture may limit transplant efficacy. One strategy for enhancing the ability of transplants to restore brain structure and function is to administer cells together with biomaterial scaffolding. We electrocoagulated the distal middle cerebral artery in adult rats and, 3 weeks later, injected one of the following into the infarct cavity: artificial cerebrospinal fluid, Matrigel scaffolding, human embryonic stem cell-derived neuronal precursor cells, scaffolding plus cells, or cells cultured in and administered together with scaffolding. Five weeks after transplantation, the latter two groups showed approximately 50% and approximately 60% reductions, respectively, in infarct cavity volume. Rats given cells cultured in and administered together with scaffolding also showed (1) survival and neuronal differentiation of transplanted cells shown by immunostaining for neuronal marker proteins and cleaved caspase-3, and by patch-clamp recording, 8 weeks after transplantation and (2) improved outcome on tests of sensorimotor and cognitive functions, 4 to 9 weeks after transplantation. These results indicate that transplantation of human neural cells together with biomaterial scaffolding has the potential to improve the outcome from stroke, even when treatment is delayed for several weeks after the ischemic event.

Intracarotid administration of human bone marrow mononuclear cells in rat photothrombotic ischemia

Background

Increasing evidence suggests that cell therapy improves functional recovery in experimental models of stroke and myocardial infarction. So far only small pilot trials tested the effects of cell therapy in stroke patients, whereas large clinical trials were conducted in patients with ischemic heart disease. To investigate the therapeutic benefit of cell therapy to improve the recovery after stroke, we determined the efficacy of bone marrow derived mononuclear cells, which were shown to improve the recovery in experimental and clinical acute myocardial infarction studies, in a rat stroke model.

Methods

Adult male Wistar rats were randomly assigned to receive either five million human bone marrow mononuclear cells (hBMC) or placebo intraarterially 3 days after photothrombotic ischemia. For immunosuppression the animals received daily injections of cyclosporine throughout the experiment, commencing 24 hours before the cell transplantation. A battery of behavioral tests was performed before and up to 4 weeks after ischemia.

Results

Body temperature and body weight revealed no difference between groups. Neurological deficits measured by the Rotarod test, the adhesive-removal test and the cylinder test were not improved by hBMC transplantation compared to placebo.

Conclusions

This study demonstrates that hBMC do not improve functional recovery when transplanted intraaterially 3 days after the onset of focal cerebral ischemia. A possible reason for the failed neurological improvement after cell therapy might be the delayed treatment initiation compared to other experimental stroke studies that showed efficacy of bone marrow mononuclear cells.

Stem cells in the treatment of stroke

Stroke is an often devastating insult resulting in neurological deficit lasting greater than 24 hours. In the United States, stroke is the third leading cause of death. In those who do not succumb, any outcome from total recovery over a period of weeks to months to persistent profound neurological deficits is possible. Present treatment centers on the decision to administer tissue plasminogen activator, subsequent medical stabilization and early intervention with rehabilitation and risk factor management. The advent of stem cell therapy presents an exciting new frontier for research in stroke treatment, with the potential to cause a paradigm shift from symptomatic control and secondary prevention to reconstitution of neural networks and prevention of neuronal cell death after neurologic injury.

Endothelial cells support survival, proliferation, and neuronal differentiation of transplanted adult ischemia-induced neural stem/progenitor cells after cerebral infarction

Transplantation of neural stem cells (NSCs) has been proposed as a therapy for a range of neurological disorders. To realize the potential of this approach, it is essential to control survival, proliferation, migration, and differentiation of NSCs after transplantation. NSCs are regulated in vivo, at least in part, by their specialized microenvironment or "niche." In the adult central nervous system, neurogenic regions, such as the subventricular and subgranular zones, include NSCs residing in a vascular niche with endothelial cells. Although there is accumulating evidence that endothelial cells promote proliferation of NSCs in vitro, there is no description of their impact on transplanted NSCs. In this study, we grafted cortex-derived stroke-induced neural stem/progenitor cells, obtained from adult mice, onto poststroke cortex in the presence or absence of endothelial cells, and compared survival, proliferation, and neuronal differentiation of the neural precursors in vivo. Cotransplantation of endothelial cells and neural stem/progenitor cells increased survival and proliferation of ischemia-induced neural stem/progenitor cells and also accelerated neuronal differentiation compared with transplantation of neural precursors alone. These data indicate that reconstitution of elements in the vascular niche enhances transplantation of adult neural progenitor cells.

The angiotensin II type 2 receptor in the brain

Recent clinical studies indicate that blockade of the renin-angiotensin system is important to prevent stroke, and accumulating results of basic research also indicate the possible involvement of the central renin-angiotensin system in ischaemic brain damage and cognition. When the angiotensin II type 1 receptor is blocked by an angiotensin type 1 receptor blocker, unbound angiotensin II acts preferentially on the angiotensin II type 2 (AT(2)) receptor. These results suggest the pathophysiological importance of the AT(2) receptor in the clinical use of angiotensin type 1 receptor blockers, which are widely used in patients with hypertension with the expectation of a decrease in the onset of cardiovascular and cerebrovascular disease. We review here the possible roles of AT(2) receptor activation in the brain, focusing on ischaemic stroke, cognitive function and neurogenesis, and potential effects of specific AT(2) receptor agonists.

Optimizing the success of cell transplantation therapy for stroke

Stem cell transplantation has evolved as a promising experimental treatment approach for stroke. In this review, we address the major hurdles for successful translation from basic research into clinical applications and discuss possible strategies to overcome these issues. We summarize the results from present pre-clinical and clinical studies and focus on specific areas of current controversy and research: (i) the therapeutic time window for cell transplantation; (ii) the selection of patients likely to benefit from such a therapy; (iii) the optimal route of cell delivery to the ischemic brain; (iv) the most suitable cell types and sources; (v) the potential mechanisms of functional recovery after cell transplantation; and (vi) the development of imaging techniques to monitor cell therapy.

Neurotrophism of bone marrow stromal cells to embryonic stem cells: noncontact induction and transplantation to a mouse ischemic stroke model

Embryonic stem (ES) cell-derived cell products may serve as a source of cells for regenerative medicine. Currently available technologies for the induction of ES cells into neural lineage cells require extended culturing in vitro and complex procedural manipulations, with variable yields of heterogeneous cells, which have hindered the prospective use of cell derivatives for treatment of ischemic stroke. We established a simple and efficient method to derive mouse ES cells into neural lineage cells using an 8-day coculture with the bone marrow stromal cells MS5, followed by a 6-day propagation culture and a 4-day selection culture. The protocol generated a relatively high yield of neural lineage cells without any mesodermal and endodermal lineage commitment. In in vivo study, these derived cells could improve the cognitive function of ischemic stroke mice. Three weeks after transplantation, migration of implanted cells to lesioned areas was noted. It was also evident of a normalization of pyramidal neuron density and morphology in hippocampal CA1 region. One (1/17) episode of teratoma development was noted. Data suggested that MS5 cells may exert a neurotrophic effect to enhance neural differentiation of ES cells and MS5-induced ES cell-derived cells appeared to be applicable to cell therapy for ischemic stroke.

Gene and Stem Cell Therapy in Ischemic Stroke

Possible strategies for treating ischemic stroke include neuroprotection (preventing injured neurons from undergoing apoptosis in the acute phase of cerebral ischemia) and stem cell therapy (the repair of disrupted neuronal networks with newly born neurons in the chronic phase of cerebral ischemia). First, we estimated the neuroprotective effect of glial cell line-derived neurotrophic factor (GDNF) by administration of GFNF protein. GDNF protein showed a direct protective effect against ischemic brain damage. Pretreatment of animals with adenoviral vector containing GDNF gene (Ad-GDNF) 24 h before the subsequent transient middle cerebral artery occlusion (MCAO) effectively reduced infarcted volume. Secondly, we studied the neuroprotective effect of a calcium channel blocker, azelnidipine, or a by-product of heme degradation, biliverdin. Both azelnidipine and biliverdin had a neuroprotective effect in the ischemic brain through their antioxidative property. Lastly, we developed a restorative stroke therapy with a bioaffinitive scaffold, which is able to provide an appropriate platform for newly born neurons. In the future, we will combine these strategies to develop more effective therapies for treatment of strokes.

Committed neural progenitor cells derived from genetically modified bone marrow stromal cells ameliorate deficits in a rat model of stroke

Bone marrow stromal cells (MSCs) are an excellent source of cells for treating a variety of central nervous system diseases. In this study, we report the efficient induction of committed neural progenitor cells from rat and human MSCs (NS-MSCs) by introduction of cells with the intracellular domain of Notch-1 followed by growth in the free-floating culture system. NS-MSCs successfully formed spheres, in which cells highly expressed the neural precursor cell markers. The commitment of spheres to neural lineage cells was confirmed by their successful differentiation into neuronal cells when exposed to a differentiation medium. To determine the therapeutic potential of NS-MSCs, cells were transplanted into the cortex and striatum in a rat model of focal cerebral ischemia. The survival, distribution, and integration of NS-MSCs in the host brain were very high, and at day 100, grafted NS-MSCs were positive for dopaminergic, glutamatergic, and gamma-amino butyric acid(GABA)ergic neuronal markers. They extended long neurites for nearly 6.3 mm and many of these expressed synaptophysin. Significant behavioral recovery was also observed in limb-placing and water-maze tests. These suggest a high potential for this MSC approach in the replenishment of neural cells for stroke and for a wide range of neurodegenerative conditions that require various types of neural cells.

Stem cells for ischemic brain injury: a critical review

No effective therapy is currently available to promote recovery following ischemic stroke. Stem cells have been proposed as a potential source of new cells to replace those lost due to central nervous system injury, as well as a source of trophic molecules to minimize damage and promote recovery. We undertook a detailed review of data from recent basic science and preclinical studies to investigate the potential application of endogenous and exogenous stem cell therapies for treatment of cerebral ischemia. To date, spontaneous endogenous neurogenesis has been observed in response to ischemic injury, and can be enhanced via infusion of appropriate cytokines. Exogenous stem cells from multiple sources can generate neural cells that survive and form synaptic connections after transplantation in the stroke-injured brain. Stem cells from multiple sources cells also exhibit neuroprotective properties that may ameliorate stroke deficits. In many cases, functional benefits observed are likely independent of neural differentiation, although the exact mechanisms remain poorly understood. Future studies of neuroregeneration will require the demonstration of function in endogenously born neurons following focal ischemia. Further, methods are currently lacking to demonstrate definitively the therapeutic effect of newly introduced neural cells. Increased plasticity following stroke may facilitate the functional integration of new neurons, but the loss of appropriate guidance cues and supporting architecture in the infarct cavity will likely impede the restoration of lost circuitry. Thus careful investigation of the mechanisms underlying trophic benefits will be essential. Evidence to date suggests that continued development of stem cell therapies may ultimately lead to viable treatment options for ischemic brain injury.

Erythropoietin increases the motility of human bone marrow-multipotent stromal cells (hBM-MSCs) and enhances the production of neurotrophic factors from hBM-MSCs

Cell therapy has been extensively studied as an approach to repair damage in nervous system diseases. Multipotent stromal cells [MSCs] are well known to have neuroprotective effects and neural differentiation potential. The ability to induce migration of MSCs near nervous system damage via direct transplantation or via intravenous injections and increase the secretion of neurotrophic factors from MSCs might improve our ability to repair damage to the nervous system through cell therapy. In the present study, we investigated whether recombinant human erythropoietin [rhEPO], known to have a hematopoietic effect, could increase the motility of human bone marrow [hBM]-MSCs and enhance production of neurotrophic factors from hBM-MSCs. Based on the results of our MTT assay, trypan blue staining, and bromodeoxyuridine ELISA, rhEPO treatment increases the viability of MSCs but not their proliferation. With a migration assay kit, we demonstrated that the motility of hBM-MSCs was enhanced in rhEPO-treated cells. Immunoblotting assays revealed increased expression of phospho-Akt, phospho-GSK-3beta, phospho-extracellular signal-regulated kinase (ERK), beta PAK-interacting exchange factor (PIX), CXCR4, phospho tyrosine kinase B (TrkB), and vascular endothelial growth factor receptor-2 [VEGFR-2] in rhEPO-treated cells. Reverse transcription-polymerase chain reaction and gelatin zymography demonstrated that rhEPO treatment induces MMP-2 mRNA level and activity. In the studies using ELISAs, we found that rhEPO could increase levels of stromal cell-derived factor-1alpha, VEGF, and brain-derived neurotrophic factors. These findings suggest that rhEPO can increase the viability and motility of hBM-MSCs by affecting various intracellular signals including Akt, ERK, beta-PIX, CXCR4, TrkB, VEGFR-2, and MMP-2 and can enhance the production of neurotrophic factors from hBM-MSCs.

Inflammation, plasticity and real-time imaging after cerebral ischemia

With an incidence of approximately 350 in 100,000, stroke is the third leading cause of death and a major cause of disability in industrialized countries. At present, although progress has been made in understanding the molecular pathways that lead to ischemic cell death, the current clinical treatments remain poorly effective. There is mounting evidence that inflammation plays an important role in cerebral ischemia. Experimentally and clinically, brain response to ischemic injury is associated with an acute and prolonged inflammatory process characterized by the activation of resident glial cells, production of inflammatory cytokines as well as leukocyte and monocyte infiltration in the brain, events that may contribute to ischemic brain injury and affect brain recovery and plasticity. However, whether the post-ischemic inflammatory response is deleterious or beneficial to brain recovery is presently a matter of debate and controversies. Here, we summarize the current knowledge on the molecular mechanisms underlying post-ischemic neuronal plasticity and the potential role of inflammation in regenerative processes and functional recovery after stroke. Furthermore, because of the dynamic nature of the brain inflammatory response, we highlight the importance of the development of novel experimental approaches such as real-time imaging. Finally, we discuss the novel transgenic reporter mice models that have allowed us to visualize and to analyze the processes such as neuroinflammation and neuronal repair from the ischemic brains of live animals.

The potential of neural stem cells to repair stroke-induced brain damage

Acute injuries to CNS such as stroke induce neural progenitor proliferation in adult brain which might be an endogenous attempt to self-repair. This process is known to be altered by several exogenous and endogenous modulators including growth factors that could help to reinforce the post-stroke neurogenesis. Increasing the neurogenesis may be a future therapeutic option to decrease the cognitive and behavioral deficits following stroke. In addition, transplantation of various types of stem cells into the injured brain is currently thought to be an exciting option to replace the neurons lost in the post-ischemic brain. These include immortalized stem cell lines, neural progenitors prepared from embryonic and adult animals and mesenchymal stem cells. Using exogenous stem cells in addition to modulating endogenous neurogenesis, we may be able to repair the injured brain after a devastating stroke. This article reviewed the current literature of these two issues.

Transplantation of human embryonic stem cell-derived neural precursor cells and enriched environment after cortical stroke in rats: cell survival and functional recovery

Cortical stem cell transplantation may help replace lost brain cells after stroke and improve the functional outcome. In this study, we transplanted human embryonic stem cell (hESC)-derived neural precursor cells (hNPCs) or vehicle into the cortex of rats after permanent distal middle cerebral artery occlusion (dMCAO) or sham-operation, and followed functional recovery in the cylinder and staircase tests. The hNPCs were examined prior to transplantation, and they expressed neuroectodermal markers but not markers for undifferentiated hESCs or non-neural cells. The rats were housed in either enriched environment or standard cages to examine the effects of additive rehabilitative therapy. In the behavioral tests dMCAO groups showed significant impairments compared with sham group before transplantation. Vehicle groups remained significantly impaired in the cylinder test 1 and 2 months after vehicle injection, whereas hNPC transplanted groups did not differ from the sham group. Rehabilitation or hNPC transplantation had no effect on reaching ability measured in the staircase test, and no differences were found in the cortical infarct volumes. After 2 months we measured cell survival and differentiation in vivo using stereology and confocal microscopy. Housing had no effect on cell survival or differentiation. The majority of the transplanted hNPCs were positive for the neural precursor marker nestin. A portion of transplanted cells expressed neuronal markers 2 months after transplantation, whereas only a few cells co-localized with astroglial or oligodendrocyte markers. In conclusion, hESC-derived neural precursor transplants provided some improvement in sensorimotor function after dMCAO, but did not restore more complicated sensorimotor functions.

Transplanted human embryonic neural stem cells survive, migrate, differentiate and increase endogenous nestin expression in adult rat cortical peri-infarction zone

Transplantation of stem cells is a potential therapeutic strategy for stroke damage. The survival, migration, and differentiation of transplanted human embryonic neural stem cells in the acute post-ischemic environment were characterized and endogenous nestin expression after transplantation was investigated. Human embryonic neural stem cells obtained from the temporal lobe cortex were cultured and labeled with fluorescent 1,1'-dioctadecy-6,6'-di (4-sulfopheyl)-3,3,3',3'-tetramethylindocarbocyanin (DiI) in vitro. Labeled cells were transplanted into cortical peri-infarction zones of adult rats 24 h after permanent middle cerebral artery occlusion. Survival, migration, and differentiation of grafted cells were quantified in immunofluorescence-stained sections from rats sacrificed at 7, 14, and 28 days after transplantation. Endogenous nestin-positive cells in the cortical peri-infarction zone were counted at serial time points. The cells transplanted into the cortical peri-infarction zone displayed the morphology of living cells and became widely located around the ischemic area. Moreover, some of the transplanted cells expressed nestin, GFAP, or NeuN in the peri-infarction zone. Furthermore, compared with the control group, endogenous nestin-positive cells in the peri-infarction zone had increased significantly 7 days after cell transplantation. These results confirm the survival, migration, and differentiation of transplanted cells in the acute post-ischemic environment and enhanced endogenous nestin expression within a brief time window. These findings indicate that transplantation of neural stem cells into the peri-infarction zone may be performed as early as 24 h after ischemia.

Preclinical assessment of stem cell therapies for neurological diseases

Stem cells, as subjects of study for use in treating neurological diseases, are envisioned as a replacement for lost neurons and glia, a means of trophic support, a therapeutic vehicle, and, more recently, a tool for in vitro modeling to understand disease and to screen and personalize treatments. In this review we analyze the requirements of stem cell-based therapy for clinical translation, advances in stem cell research toward clinical application for neurological disorders, and different animal models used for analysis of these potential therapies. We focus on Parkinson's disease (typically defined by the progressive loss of dopaminergic nigral neurons), stroke (neurodegeneration associated with decreased blood perfusion in the brain), and multiple sclerosis (an autoimmune disorder that generates demyelination, axonal damage, astrocytic scarring, and neurodegeneration in the brain and spinal cord). We chose these disorders for their diversity and the number of people affected by them. An additional important consideration was the availability of multiple animal models in which to test stem cell applications for these diseases. We also discuss the relationship between the limited number of systematic stem cell studies performed in animals, in particular nonhuman primates and the delayed progress in advancing stem cell therapies to clinical success.

Mesenchymal stem cells promote proliferation of endogenous neural stem cells and survival of newborn cells in a rat stroke model

Mesenchymal stem cells (MSCs) secrete bioactive factors that exert diverse responses in vivo. In the present study, we explored mechanism how MSCs may lead to higher functional recovery in the animal stroke model. Bone marrow-derived MSCs were transplanted into the brain parenchyma 3 days after induction of stroke by occluding middle cerebral artery for 2 h. Stoke induced proliferation of resident neural stem cells in subventricular zone. However, most of new born cells underwent cell death and had a limited impact on functional recovery after stroke. Transplantation of MSCs enhanced proliferation of endogenous neural stem cells while suppressing the cell death of newly generated cells. Thereby, newborn cells migrated toward ischemic territory and differentiated in ischemic boundaries into doublecortin+ neuroblasts at higher rates in animals with MSCs compared to control group. The present study indicates that therapeutic effects of MSCs are at least partly ascribed to dual functions of MSCs by enhancing endogenous neurogenesis and protecting newborn cells from deleterious environment. The results reinforce the prospects of clinical application using MSCs in the treatment of neurological disorders.

Therapeutic strategy for ischemic stroke

Possible strategies for treating ischemic stroke include: (1) Neuroprotection: preventing damaged neurons from undergoing apoptosis in the acute phase of cerebral ischemia; (2) Stem cell therapy: the repair of broken neuronal networks with newly born neurons in the chronic phase of cerebral ischemia. Firstly, we studied the neuroprotective effect of a calcium channel blocker, azelnidipine, or a by-product of heme degradation, biliverdin, in the ischemic brain. These results revealed both azelnidipine and biliverdin had a neuroprotective effect in the ischemic brain through their anti-oxidative property. Secondly, we investigated the role of granulocyte colony-stimulating factor (G-CSF) by administering G-CSF to rats after cerebral ischemia and found G-CSF plays a critical role in neuroprotection. Lastly, we developed a restorative stroke therapy with a bio-affinitive scaffold, which is able to provide an appropriate environment for newly born neurons. In the future, we will combine these strategies to develop more effective therapies for treatment of strokes.

Functional integration of newly generated neurons into striatum after cerebral ischemia in the adult rat brain

BACKGROUND AND PURPOSE

Ischemic injury can induce neurogenesis in the striatum. Those newborn neurons can express glutamic acid decarboxylase and choline acetyltransferase, markers of GABAergic and cholinergic neurons, respectively. The present study investigated whether these GABAergic and cholinergic new neurons could differentiate into functional cells.

METHODS

Retrovirus containing the EGFP gene was used to label dividing cells in striatal slices prepared from adult rat brains after middle cerebral artery occlusion. EGFP-targeted immunostaining and immunoelectron microscopy were performed to detect whether newborn neurons could anatomically form neuronal polarity and synapses with pre-existent neurons. Patch clamp recording on acute striatal slices of brains at 6 to 8 weeks after middle cerebral artery occlusion was used to determine whether the newborn neurons could display functional electrophysiological properties.

RESULTS

EGFP-expressing (EGFP(+)) signals could be detected mainly in the cell body in the first 2 weeks. From the fourth to thirteenth weeks after their birth, EGFP(+) neurons gradually formed neuronal polarity and showed a time-dependent increase in dendrite length and branch formation. EGFP(+) cells were copositive for NeuN and glutamic acid decarboxylase (EGFP(+)-NeuN(+)-GAD(67)(+)), MAP-2, and choline acetyltransferase (EGFP(+)-MAP-2(+)-ChAT(+)). They also expressed phosphorylated synapsin I (EGFP(+)-p-SYN(+)) and showed typical synaptic structures comprising dendrites and spines. Both GABAergic and cholinergic newborn neurons could fire action potentials and received excitatory and inhibitory synaptic inputs because they displayed spontaneous postsynaptic currents in picrotoxin- and CNQX-inhibited manners.

CONCLUSIONS

Ischemia-induced newly formed striatal GABAergic and cholinergic neurons could become functionally integrated into neural networks in the brain of adult rats after stroke.

Tenascin-R promotes neuronal differentiation of embryonic stem cells and recruitment of host-derived neural precursor cells after excitotoxic lesion of the mouse striatum

Loss of GABAergic projection neurons under excitotoxic conditions in the striatum is associated with a disturbance of motor and cognitive functions as seen, for instance, in Huntington's disease. Since current treatments cannot replace degenerated neurons, research on alternative therapeutic approaches needs to be pursued. In this context, the transplantation of genetically modified stem cells into lesioned brain areas of patients is a possible alternative. In this study, green fluorescent protein-labeled murine embryonic stem cells (ESCs) were stably transfected to overexpress the extracellular matrix molecule tenascin-R (TNR), which is expressed by striatal GABAergic neurons. TNR-overexpressing ESCs were analyzed in comparison with their parental cells regarding neural differentiation and migration in vitro, and after transplantation into the striatum of quinolinic acid-treated mice, which serve as a model for Huntington's disease. In comparison with sham-transfected control cells, TNR-overexpressing ESCs showed enhanced differentiation into neurons in vitro, reduced migration in vitro and in vivo, and increased generation of GABAergic neurons and decreased numbers of astrocytes 1 month and 2 months after transplantation, but without significant effects on locomotor functions. Interestingly, TNR-overexpressing ESCs transplanted into the striatum attracted host-derived neuroblasts from the rostral migratory stream and promoted stem cell-mediated recruitment of host-derived newborn neurons within the grafted area. Thus, we show for the first time that overexpression of an extracellular matrix molecule by in vitro predifferentiated ESCs exerts beneficial effects on tissue regeneration in a mouse model of neurodegenerative disease. Disclosure of potential conflicts of interest is found at the end of this article.

Neural stem cells in the mammalian brain

New fundamental results on stem cell biology have been obtained in the past 15 years. These results allow us to reinterpret the functioning of the cerebral tissue in health and disease. Proliferating stem cells have been found in the adult brain, which can be involved in postinjury repair and can replace dead cells under specific conditions. Numerous genomic mechanisms controlling stem cell proliferation and differentiation have been identified. The involvement of stem cells in the genesis of malignant tumors has been demonstrated. Neural stem cell tropism toward tumors has been shown. These findings suggest new lines of research on brain functioning and development. Stem cells can be used to develop radically new treatments of neurodegenerative and cancer diseases of the brain.

Derivation and cloning of a novel rhesus embryonic stem cell line stably expressing tau-green fluorescent protein

Embryonic stem cells (ESC) have the ability of indefinite self-renewal and multilineage differentiation, and they carry great potential in cell-based therapies. The rhesus macaque is the most relevant preclinical model for assessing the benefit, safety, and efficacy of ESC-based transplantations in the treatment of neurodegenerative diseases. In the case of neural cell grafting, tracing both the neurons and their axonal projections in vivo is essential for studying the integration of the grafted cells in the host brain. Tau-Green fluorescent protein (tau-GFP) is a powerful viable lineage tracer, allowing visualization of cell bodies, dendrites, and axons in exquisite detail. Here, we report the first rhesus monkey ESC line that ubiquitously and stably expresses tau-GFP. First, we derived a new line of rhesus monkey ESC (LYON-ES1) that show marker expression and cell cycle characteristics typical of primate ESCs. LYON-ES1 cells are pluripotent, giving rise to derivatives of the three germ layers in vitro and in vivo through teratoma formation. They retain all their undifferentiated characteristics and a normal karyotype after prolonged culture. Using lentiviral infection, we then generated a monkey ESC line stably expressing tau-GFP that retains all the characteristics of the parental wild-type line and is clonogenic. We show that neural precursors derived from the tau-GFP ESC line are multipotent and that their fate can be precisely mapped in vivo after grafting in the adult rat brain. Disclosure of potential conflicts of interest is found at the end of this article.

Adherent self-renewable human embryonic stem cell-derived neural stem cell line: functional engraftment in experimental stroke model

Background

Human embryonic stem cells (hESCs) offer a virtually unlimited source of neural cells for structural repair in neurological disorders, such as stroke. Neural cells can be derived from hESCs either by direct enrichment, or by isolating specific growth factor-responsive and expandable populations of human neural stem cells (hNSCs). Studies have indicated that the direct enrichment method generates a heterogeneous population of cells that may contain residual undifferentiated stem cells that could lead to tumor formation in vivo.

Methods/Principal Findings

We isolated an expandable and homogenous population of hNSCs (named SD56) from hESCs using a defined media supplemented with epidermal growth factor (EGF), basic fibroblast growth factor (bFGF) and leukemia inhibitory growth factor (LIF). These hNSCs grew as an adherent monolayer culture. They were fully neuralized and uniformly expressed molecular features of NSCs, including nestin, vimentin and radial glial markers. These hNSCs did not express the pluripotency markers Oct4 or Nanog, nor did they express markers for the mesoderm or endoderm lineages. The self-renewal property of the hNSCs was characterized by a predominant symmetrical mode of cell division. The SD56 hNSCs differentiated into neurons, astrocytes and oligodendrocytes throughout multiple passages in vitro, as well as after transplantation. Together, these criteria confirm the definitive NSC identity of the SD56 cell line. Importantly, they exhibited no chromosome abnormalities and did not form tumors after implantation into rat ischemic brains and into naïve nude rat brains and flanks. Furthermore, hNSCs isolated under these conditions migrated toward the ischemia-injured adult brain parenchyma and improved the independent use of the stroke-impaired forelimb two months post-transplantation.

Conclusions/Significance

The SD56 human neural stem cells derived under the reported conditions are stable, do not form tumors in vivo and enable functional recovery after stroke. These properties indicate that this hNSC line may offer a renewable, homogenous source of neural cells that will be valuable for basic and translational research.

Derive and conquer: sourcing and differentiating stem cells for therapeutic applications

Although great progress has been made in the isolation and culture of stem cells, the future of stem-cell-based therapies and their productive use in drug discovery and regenerative medicine depends on two key factors: finding reliable sources of multipotent and pluripotent cells and the ability to control their differentiation to generate desired derivatives. It is essential for clinical applications to establish reliable sources of pathogen-free human embryonic stem cells (ESCs) and develop suitable differentiation techniques. Here, we address some of the problems associated with the sourcing of human ESCs and discuss the current status of stem-cell differentiation technology.

Human neural stem cells migrate along the nigrostriatal pathway in a primate model of Parkinson's disease

Although evidence of damage-directed neural stem cell (NSC) migration has been well-documented in the rodent, to our knowledge it has never been confirmed or quantified using human NSC (hNSC) in an adult non-human primate modeling a human neurodegenerative disease state. In this report, we attempt to provide that confirmation, potentially advancing basic stem cell concepts toward clinical relevance. hNSCs were implanted into the caudate nucleus (bilaterally) and substantia nigra (unilaterally) of 7, adult St. Kitts African green monkeys (Chlorocebus sabaeus) with previous exposure to systemic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a neurotoxin that disrupts the dopaminergic nigrostriatal pathway. A detailed quantitative analysis of hNSC migration patterns at two time points (4 and 7 months) following transplantation was performed. Density contour mapping of hNSCs along the dorsal-ventral and medial-lateral axes of the brain suggested that >80% of hNSCs migrated from the point of implantation to and along the impaired nigrostriatal pathway. Although 2/3 of hNSCs were transplanted within the caudate, <1% of 3x10(6) total injected donor cells were identified at this site. The migrating hNSC did not appear to be pursuing a neuronal lineage. In the striatum and nigrostriatal pathway, but not in the substantia nigra, some hNSCs were found to have taken a glial lineage. The property of neural stem cells to align themselves along a neural pathway rendered dysfunctional by a given disease is potentially a valuable clinical tool.

Neuroplasticity and cellular therapy in cerebral infarction

Stroke is the second to third most common cause of death in adults, and more than a third of people who survive a stroke will have severe disability. Therapeutic options currently centre on fibrinolytic treatment, but its limitations restrict use to a small proportion of patients. Although a wide range of neuroprotective substances has been effective in experimental models, they have repeatedly failed in clinical trials because of toxicity or loss of effectiveness. Recent strategies based on neuroplasticity and cellular therapy have shown significant efficacy in improving functional recovery in experimental models, although further study is still necessary to clarify how the brain responds to ischaemic damage and is able to reorganize itself in the long term. Although steps must still be taken to ensure the safety and feasibility of treatments based on neuroplasticity and cellular therapy, neurorepair strategies provide promising future therapeutic options for stroke.

Neural stem/precursor cells for the treatment of ischemic stroke

In ischemic stroke, the third most frequent cause of mortality in industrialized countries, therapeutic options have until now been limited to the first hours after disease onset. Cell transplantation has emerged in various neurological disorders, including experimental stroke, as a successful recovery-promoting approach also in the post-acute stroke phase. However, before envisaging any translation into humans of such promising cell-based approaches we still need to clarify: (i) the ideal cell source for transplantation, (ii) the most appropriate route of cell administration, and, last but not least, (iii) the best approach to achieve an appropriate and functional integration of transplanted cells into the host tissue. Here we discuss, with special emphasis on neural stem/precursor cells, potential mechanisms that may be involved in the action of cell-based therapies in stroke.

Cell therapy in models for temporal lobe epilepsy

For patients with refractory epilepsy it is important to search for alternative treatments. One of these potential treatments could be introducing new cells or modulating endogenous neurogenesis to reconstruct damaged epileptic circuits or to bring neurotransmitter function back into balance. In this review the scientific basis of these cell therapy strategies is discussed and the results are critically evaluated. Research on cell transplantation strategies has mainly been performed in animal models for temporal lobe epilepsy, in which seizure foci or seizure propagation pathways are targeted. Promising results have been obtained, although there remains a lot of debate about the relevance of the animal models, the appropriate target for transplantation, the suitable cell source and the proper time point for transplantation. From the presented studies it should be evident that transplanted cells can survive and sometimes even integrate in an epileptic brain and in a brain that is subjected to epileptogenic interventions. There is evidence that transplanted cells can partially restore damaged structures and/or release substances that modulate existent or induced hyperexcitability. Even though several studies show encouraging results, more studies need to be done in animal models with spontaneous seizures in order to have a better comparison to the human situation.

Cell transplantation therapy for stroke

No treatment currently exists to restore lost neurological function after stroke. A growing number of studies highlight the potential of stem cell transplantation as a novel therapeutic approach for stroke. In this review we summarize these studies, discuss potential mechanisms of action of the transplanted cells, and emphasize the need to determine parameters that are critical for transplantation success.

Neuroprotection and neurosupplementation in ischaemic brain

Possible strategies for treating ischaemic stroke include: (i) neuroprotection (preventing damaged neurons from undergoing apoptosis in the acute phase of cerebral ischaemia), and (ii) neurosupplementation (the repair of broken neuronal networks with newly born neurons in the chronic phase of cerebral ischaemia). In this paper, we review our recent progress in development of these distinct new strategies for treatment of damaged brain following a stroke. Firstly, we investigated the role of endogenous IL-6 (interleukin-6), which is one of the cytokines drastically induced by ischaemic stimuli, by administering IL-6RA (anti-IL-6 receptor monoclonal antibody) to mice. We found that endogenous IL-6 plays a critical role in neuroprotection and that its role may be mediated by STAT3 (signal transducer and activator of transcription-3) activation. Secondly, we studied the endogenous sources of the newly born neurons in the ischaemic striatum by region- and cell-type-specific cell labelling techniques. The results revealed that the SVZ (subventricular zone) is the principal source of the neuronal progenitors that migrate laterally towards the infarcted regions, and differentiate into newly born neurons. Finally, we developed a restorative stroke therapy with a bio-affinitive scaffold, which is an appropriate poly-porous structure releasing bioactive substances such as neurotrophic factor. This bio-affinitive scaffold is able to give an appropriate environment for newly born neurons. In future, we will combine these strategies to develop more effective therapies for treatment of strokes.

Administration of Ex Vivo-expanded Bone Marrow-derived Endothelial Progenitor Cells Attenuates Focal Cerebral Ischemia-reperfusion Injury in Rats

OBJECTIVE

This study aimed to examine early effects of ex vivo-expanded bone marrow-derived endothelial progenitor cells (EPCs) on focal cerebral ischemia-reperfusion injury.

METHODS

EPCs were obtained from mononuclear cells of autologous bone marrow of a rat. After culture on fibronectin-coated dishes for 10 to 14 days, 2.5 x 10 cells of EPCs were administered transarterially after 90 minute occlusion of the middle cerebral artery.

RESULTS

Administration of EPCs significantly reduced both the infarct volume and the scores of neurological deficits at 24 and 48 hours. EPCs administered 2 hours after insult did not reduce infarct volume, but attenuated neurological deficits at 24 hours. Administration of EPCs significantly reduced the number of myeloperoxidase-immunoreactive cells in the ischemic lesion at 24 hours and increased regional cortical blood flow at 48 hours. EPCs were observed in the ischemic hemisphere and around the endothelial layer of the pial arteries. Most of them expressed endothelial nitric oxide synthase.

CONCLUSION

Administration of ex vivo-expanded bone marrow-derived EPCs reduced infarct volume and neurological deficits in acute focal brain ischemia-reperfusion injury caused, at least in part, by attenuation of endothelial dysfunction.

Stem cells for the treatment of neurological disorders

Many common neurological disorders, such as Parkinson's disease, stroke and multiple sclerosis, are caused by a loss of neurons and glial cells. In recent years, neurons and glia have been generated successfully from stem cells in culture, fueling efforts to develop stem-cell-based transplantation therapies for human patients. More recently, efforts have been extended to stimulating the formation and preventing the death of neurons and glial cells produced by endogenous stem cells within the adult central nervous system. The next step is to translate these exciting advances from the laboratory into clinically useful therapies.

The therapeutic potential of neural stem cells

Recent evidence shows that transplantation of neural stem/precursor cells may protect the central nervous system from inflammatory damage through a 'bystander' mechanism that is alternative to cell replacement. This novel mechanism, which might improve the success of transplantation procedures, is exerted by undifferentiated neural stem cells, the functional characteristics of which are regulated by important stem cell regulators released by CNS-resident and blood-borne inflammatory cells. Here, we discuss this alternative bystander mechanism in the context of the atypical ectopic perivascular niche. We propose that it is the most challenging example of reciprocal therapeutic crosstalk between the inflamed CNS and systemically transplanted neural stem cells.

Mechanisms of neural plasticity following brain injury

Brain insults cause rapid cell death, and a disruption of functional circuits, in the affected regions. As the injured tissue recovers from events associated with cell death, regenerative processes are activated that over months lead to a certain degree of functional recovery. Factors produced by new neurons and glia, axonal sprouting of surviving neurons, and new synapse formation help to re-establish some of the lost functions. The timing and location of such events is crucial in the success of the regenerative process. Comprehensive gene expression profiling and proteomic analyses have enabled a deeper molecular and cellular mechanistic understanding of post-injury brain regeneration. These new mechanistic insights are aiding the design of novel therapeutic modalities that enhance regeneration.