Differentiation of engrafted neuronal-restricted precursor cells is inhibited in the traumatically injured spinal cord

Differentiation of pluripotent neural stem cells engrafted into the adult normal and injured spinal cord is restricted to the glial lineage, suggesting that in vitro induction toward a neuronal lineage prior to transplantation and/or modification of the host environment may be necessary to initiate and increase the differentiation of neurons. In the present study, we investigated the differentiation of neuronal-restricted precursors (NRPs) grafted into the normal and contused adult rat spinal cord. NRPs proliferated through multiple passages in the presence of FGF2 and NT3 and differentiated into only neurons in vitro in the presence of retinoic acid and the absence of FGF2. Differentiated NRPs expressed GABA, glycine, glutamate, and ChAT. Two weeks to 2 months after engraftment of undifferentiated NRPs into adult normal spinal cord, large numbers of surviving cells were seen in all of the animals. The majority differentiated into betaIII-tubulin-positive neurons. Some transplanted NRPs expressed GABA and small numbers were glutamate- and ChAT-positive. NRPs were also transplanted into the epicenter of the contused adult rat spinal cord. Two weeks to 2 months after transplantation, some engrafted NRPs remained undifferentiated nestin-positive cells. Small numbers were MAP2- or betaIII-tubulin-positive neurons. However, the expression of GABA, glutamate, or ChAT was not observed. These results show that NRPs can differentiate into different types of neurons in the normal adult rat spinal cord, but that such differentiation is inhibited in the injured spinal cord. Manipulation of the microenvironment in the injured spinal cord will likely be necessary to facilitate neuronal replacement.     

Transplantation of fetal spinal cord tissue into the chronically injured adult rat spinal cord

Transplants of fetal central nervous system (CNS) tissue into the acutely injured rat spinal cord have been demonstrated to differentiate and partially integrate with the adjacent host neuropil. In the present study, we examined the potential for applying a transplantation approach to chronic spinal cord lesions. In particular, we were interested in learning whether host-graft fusion would be adversely affected by an advanced histopathology characterized in part by glial scar formation. Hemisection cavities were prepared at lumbar levels of the adult rat spinal cord 2-7 weeks prior to the transplantation of spinal cord tissue obtained from 14-day rat fetuses. Graft survival, differentiation, and integration with the host spinal cord were subsequently evaluated by light microscopic techniques at post-transplantation intervals of 1-6 months. Immunocytochemistry was also employed to examine the extent of astrocytic scar formation at the host-graft interface and serotoninergic innervation of the grafts. In some other cases, anterograde and retrograde transport of wheat germ agglutinin-conjugated horseradish peroxidase was used to determine whether axonal projections were formed between the host spinal cords and grafts. By 2 weeks after injury the initial lesion cavities were surrounded by a continuous astrocytic scar which remained intact for at least 7 weeks after injury in nongrafted control animals. In other animals, transplantation into these advanced lesions resulted in well-differentiated grafts with a 90% long-term survival rate. Although dense gliosis was still present along the lesion surfaces of the recipient spinal cord, foci of confluent host-graft neuropil were observed where interruptions in the scar had occurred. Donor tissue integrated most often with the host spinal cord at interfaces with host gray matter; however, some implants also exhibited sites of fusion with damaged host white matter. Thus, some regions of confluent graft and host neuropil could be routinely identified, despite the presence of a dense glial scar along the walls of the chronic lesion site at the time of transplantation. Anterograde and retrograde tract-tracing results suggested that some axonal projections into these grafts had originated from host neurons located immediately adjacent to the donor-recipient interface. In addition, immunocytochemistry revealed some host serotoninergic axons (presumably of supraspinal origin) traversing nongliotic interfaces. The results of this study raise the possibility that grafted fetal CNS tissue has a capacity for stimulating partial regression of an established glial scar.(ABSTRACT TRUNCATED AT 400 WORDS)     

Differentiation of endogenous neural precursors following spinal cord injury in adult rats☆

BACKGROUND： Studies have shown that cell death can activate proliferation of endogenous neural stem cells and promote newly generated cells to migrate to a lesion site.
OBJECTIVE： To observe regeneration and differentiation of neural cells following spinal cord injury in adult rats and to quantitatively analyze the newly differentiated cells.
DESIGN, TIME AND SETTING： A cell biology experiment was performed at the Institute of Orthopedics and Medical Experimental Center, Lanzhou University, between August 2005 and October 2007.
MATERIALS： Fifty adult, Wistar rats of both sexes; 5-bromodeoxyuridine （BrdU, Sigma, USA）; antibodies against neuron-specific enolase, glial fibrillary acidic protein, and myelin basic protein （Chemicon, USA）.
METHODS： Twenty-five rats were assigned to the spinal cord injury group and received a spinal cord contusion injury. Materials were obtained at day 1, 3, 7, 15, and 29 after injury, with 5 rats for each time point. Twenty-five rats were sham-treated by removing the lamina of the vertebral arch without performing a contusion.
MAIN OUTCOME MEASURES： The phenotype of BrdU-labeled cells, i.e., expression and distribution of surface markers for neurons （neuron-specific enolase）, astrocytes （glial fibrillary acidic protein）, and oligodendrocytes （myelin basic protein）, were identified with immunofluorescence double-labeling. Confocal microscopy was used to detect double-labeled cells by immunofluorescence. Quantitative analysis of newly generated cells was performed with stereological counting methods.
RESULTS： There was significant cell production and differentiation after adult rat spinal cord injury. The quantity of newly-generated BrdU-labeled cells in the spinal cord lesion was 75-fold greater than in the corresponding area of control animals. Endogenous neural precursor cells differentiated into astrocytes and oligodendrocytes, however spontaneous neuronal differentiation was not detected. Between 7 and 29 d after spinal cord injury, newl     

Differentiation of endogenous neural precursors following spinal cord injury in adult rats

BACKGROUND:Studies have shown that cell death can activate proliferation of endogenous neural stem cells and promote newly generated cells to migrate to a lesion site.OBJECTIVE:To observe regeneration and differentiation of neural cells following spinal cord injury in adult rats and to quantitatively analyze the newly differentiated cells.DESIGN,TIME AND SETTING:A cell biology experiment was performed at the Institute of Orthopedics and Medical Experimental Center,Lanzhou University.between August 2005 and October 2007.MATERIALS:Fifty adult,Wistar rats of both sexes;5-bromodeoxyuridine(BrdU,Sigma,USA);antibodies against neuron-specific enolase,glial fibrillary acidic protein,and myelin basic protein(Chemicon,USA).METHODS:Twenty-five rats were assigned to the spinal cord injury group and received a spinal cord contusion injury.Materials were obtained at day 1,3,7,15,and 29 after injury,with 5 rats for each time point.Twenty-five rats were sham-treated by removing the lamina of the vertebral arch without performing a contusion.MAIN OUTCOME MEASURES:The phenotype of BrdU-labeled cells,i.e.,expression and distribution of surface markers for neurons(neuron-specific enolase),astrocytes(glial fibrillary acidic protein),and oligodendrocytes(myelin basic protein),were identified with immunofluorescence double-labeling.Confocal microscopy was used to detect double-labeled cells by immunofluorescence.Quantitative analysis of newly generated cells was performed with stereological counting methods.RESULTS:There was significant cell production and differentiation after adult rat spinal cord injury.The quantity of newly-generated BrdU-labeled cells in the spinal cord lesion was 75-fold greater than in the corresponding area of control animals.Endogenous neural precursor cells differentiated into astrocytes and oligodendrocytes,however spontaneous neuronal difierentiation was not detected.Between 7 and 29 d after spinal cord injury,newly generated cells expressed increasingly more mature oligodendrocyte and astrocyte markers.CONCLUSION:Spinal cord injury is a direct inducer of regeneration and differentiation of neural cells.Endogenous neural precursor cells Can difierentiate into astrocytes and oligodendrocytes following adult rat spinal cord injury.     

Human glial-restricted progenitors survive, proliferate, and preserve electrophysiological function in rats with focal inflammatory spinal cord demyelination

Transplantation of glial progenitor cells results in transplant-derived myelination and improved function in rodents with genetic dysmyelination or chemical demyelination. However, glial cell transplantation in adult CNS inflammatory demyelinating models has not been well studied. Here we transplanted human glial-restricted progenitor (hGRP) cells into the spinal cord of adult rats with inflammatory demyelination, and monitored cell fate in chemically immunosuppressed animals. We found that hGRPs migrate extensively, expand within inflammatory spinal cord lesions, do not form tumors, and adopt a mature glial phenotype, albeit at a low rate. Human GRP-transplanted rats, but not controls, exhibited preserved electrophysiological conduction across the spinal cord, though no differences in behavioral improvement were noted between the two groups. Although these hGRPs myelinated extensively after implantation into neonatal shiverer mouse brain, only marginal remyelination was observed in the inflammatory spinal cord demyelination model. The low rate of transplant-derived myelination in adult rat spinal cord may reflect host age, species, transplant environment/location, and/or immune suppression regime differences. We conclude that hGRPs have the capacity to myelinate dysmyelinated neonatal rodent brain and preserve conduction in the inflammatory demyelinated adult rodent spinal cord. The latter benefit is likely dependent on trophic support and suggests further exploration of potential of glial progenitors in animal models of chronic inflammatory demyelination.     

脊髓损伤的移植治疗进展

脊髓损伤的治疗是神经科学领域的难点热点问题之一。本以神经干细胞移植为重点综述了脊髓损伤的多种移植治疗方案及其治疗效果。并对比不同治疗方案的优缺点阐述了应用于临床治疗的可能性。     

Lineage-restricted neural precursors survive, migrate, and differentiate following transplantation into the injured adult spinal cord

Fetal spinal cord from embryonic day 14 (E14/FSC) has been used for numerous transplantation studies of injured spinal cord. E14/FSC consists primarily of neuronal (NRP)- and glial (GRP)-restricted precursors. Therefore, we reasoned that comparing the fate of E14/FSC with defined populations of lineage-restricted precursors will test the in vivo properties of these precursors in CNS and allow us to define the sequence of events following their grafting into the injured spinal cord. Using tissue derived from transgenic rats expressing the alkaline phosphatase (AP) marker, we found that E14/FSC exhibited early cell loss at 4 days following acute transplantation into a partial hemisection injury, but the surviving cells expanded to fill the entire injury cavity by 3 weeks. E14/FSC grafts integrated into host tissue, differentiated into neurons, astrocytes, and oligodendrocytes, and demonstrated variability in process extension and migration out of the transplant site. Under similar grafting conditions, defined NRP/GRP cells showed excellent survival, consistent migration out of the injury site and robust differentiation into mature CNS phenotypes, including many neurons. Few immature cells remained at 3 weeks in either grafts. These results suggest that by combining neuronal and glial restricted precursors, it is possible to generate a microenvironmental niche where emerging glial cells, derived from GRPs, support survival and neuronal differentiation of NRPs within the non-neurogenic and non-permissive injured adult spinal cord, even when grafted into acute injury. Furthermore, the NRP/GRP grafts have practical advantages over fetal transplants, making them attractive candidates for neural cell replacement.     

MR imaging of lineage-restricted neural precursors following transplantation into the adult spinal cord

Neural precursor cell (NPC) transplantation is a promising strategy for treatment of CNS injuries and neurodegenerative disorders because of potential for cell replacement. An important element of future clinical applications is development of a non-invasive procedure to follow NPC fate. We show that neuronal-restricted precursors (NRPs) and glial-restricted precursors (GRPs), NPCs with lineage restrictions for neurons and glia, respectively, can be labeled in vitro with the superparamagnetic iron oxide contrast agent Feridex. Following engraftment into intact adult spinal cord, labeled cells robustly survived in white and gray matter and migrated selectively along white matter tracts up to 5 mm. Localization of cells was reliably established using ex vivo magnetic resonance imaging of spinal cords. Imaging coincided with histological detection of iron and the human alkaline phosphatase transgene in most grafting sites, including the stream of migrating cells. Following transplantation, magnetically labeled cells exhibited mature morphologies and differentiated into neurons, astrocytes, and oligodendrocytes, similar to grafts of unlabeled NRPs and GRPs. Interestingly, Feridex-labeled cells, but not unlabeled cells, induced influx of ED1-positive macrophages/microglia. Small numbers of these phagocytic cells took up iron from grafted cells, while the majority of Feridex label was found in transplanted cells. We conclude that Feridex labeling does not inhibit NPC differentiation and can be used to reliably localize NPCs by MRI following engraftment into adult CNS, with the possible exception of areas of rapidly proliferating cells. The present results are relevant for MR-guided clinical application of transplantation strategies in treatment of spinal cord injury and other CNS pathologies.     

Rat hair follicle stem cells differentiate and promote recovery following spinal cord injury

Emerging studies of treating spinal cord injury （SCI） with adult stem cells led us to evaluate the effects of transplantation of hair follicle stem cells in rats with a compression-induced spinal cord lesion. Here, we proposed a hypothesis that rat hair follicle stem cell transplantation can promote the recovery of injured spinal cord. Compression-induced spinal cord injury was induced in Wistar rats in this study. The bulge area of the rat vibdssa follicles was isolated, cultivated and characterized with nestin as a stem cell marker. 5-Bromo-2＇-deoxyuridine （BrdU） labeled bulge stem cells were transplanted into rats with spinal cord injury. Immunohistochemical staining results showed that some of the grafted cells could survive and differentiate into oligodendrocytes （receptor-interacting protein positive cells） and neuronal-like cells （~lll-tubulin positive cells） at 3 weeks after transplantation. In addition, recovery of hind limb locomotor function in spinal cord injury rats at 8 weeks following cell transplantation was assessed using the Basso, Beattie and Bresnahan （BBB） locomotor rating scale. The results demon- strate that the grafted hair follicle stem cells can survive for a long time period in vivo and differentiate into neuronal- and glial-like cells. These results suggest that hair follicle stem cells can promote the recovery of spinal cord injury.     

Adult human spinal cord harbors neural precursor cells that generate neurons and glial cells in vitro

Adult human and rodent brains contain neural stem and progenitor cells, and the presence of neural stem cells in the adult rodent spinal cord has also been described. Here, using electron microscopy, expression of neural precursor cell markers, and cell culture, we investigated whether neural precursor cells are also present in adult human spinal cord. In well-preserved nonpathological post-mortem human adult spinal cord, nestin, Sox2, GFAP, CD15, Nkx6.1, and PSA-NCAM were found to be expressed heterogeneously by cells located around the central canal. Ultrastructural analysis revealed the existence of immature cells close to the ependymal cells, which display characteristics of type B and C cells found in the adult rodent brain subventricular region, which are considered to be stem and progenitor cells, respectively. Completely dissociated spinal cord cells reproducibly formed Sox2(+) nestin(+) neurospheres containing proliferative precursor cells. On differentiation, these generate glial cells and gamma-aminobutyric acid (GABA)-ergic neurons. These results provide the first evidence for the existence in the adult human spinal cord of neural precursors with the potential to differentiate into neurons and glia. They represent a major interest for endogenous regeneration of spinal cord after trauma and in degenerative diseases.     

Leukemia inhibitory factor promotes the neuronal development of spinal cord precursors from the neural tube.

Recent evidence from our laboratory has shown that leukemia inhibitory factor (LIF) can act early in peripheral nervous system development. We have investigated a potential role of LIF in the developing spinal cord. In explants and dissociated cultures of spinal cord primordium, LIF stimulated a profuse neurite outgrowth. To determine if these effects were related to neuronal differentiation, cells were plated at low cell density and stained for neurofilament. LIF stimulated an increase in the number of newly differentiated neurons, without inducing proliferation of the precursors. Given that LIF has previously reported effects as a cholinergic switching factor for sympathetic neurons, we investigated whether LIF had similar effects in these spinal cord cultures. LIF increased the number of cholinergic neurons in proportion to its overall effect on the stimulation of all neurofilament positive neurons in the culture. These data show that LIF stimulates the generation of spinal cord neurons from their precursors and further implicates a role for LIF in nervous system development.     

Regrowth of axons into the distal spinal cord through a Schwann-cell-seeded mini-channel implanted into hemisected adult rat spinal cord

Schwann cells (SCs) have been shown to be a key element in promoting axonal regeneration after being grafted into the central nervous system (CNS). In the present study, SC-supported axonal regrowth was tested in an adult rat spinal cord implantation model. This model is characterized by a right spinal cord hemisection at the eighth thoracic segment, implantation of a SC-containing mini-channel and restoration of cerebrospinal fluid circulation by suturing the dura. We demonstrate that a tissue cable containing grafted SCs formed an effective bridge between the two stumps of the hemicord 1 month after transplantation. Approximately 10 000 myelinated and unmyelinated axons (1 : 9) per cable were found at its midpoint. In addition to propriospinal axons and axons of peripheral nervous system (PNS) origin, axons from as many as 19 brainstem regions also grew into the graft without additional treatments. Most significantly, some regenerating axons in the SC grafts were able to penetrate through the distal graft-host interface to re-enter the host environment, as demonstrated by anterograde axonal labelling. These axons coursed toward, and then entered the grey matter where terminal bouton-like structures were observed. In channels containing no SCs, limited axonal growth was seen within the graft and no axons penetrated the distal interface. These findings further support the notion that SCs are strong promotors of axonal regeneration and that the mini-channel model may be appropriate for further investigation of axonal re-entry, synaptic reconnection and functional recovery following spinal cord injury.     

Implantation of dendritic cells in injured adult spinal cord results in activation of endogenous neural stem/progenitor cells leading to de novo neurogenesis and functional recovery

We report a treatment for spinal cord injury involving implantation of dendritic cells (DCs), which act as antigen-presenting cells in the immune system. The novel mechanisms underlying this treatment produce functional recovery. Among the immune cells tested, DCs showed the strongest activity inducing proliferation and survival of neural stem/progenitor cells (NSPCs) in vitro. Furthermore, in DC-implanted adult mice, endogenous NSPCs in the injured spinal cord were activated for mitotic de novo neurogenesis. These DCs produced neurotrophin-3 and activated endogenous microglia in the injured spinal cord. Behavioral analysis revealed the locomotor functions of DC-implanted mice to have recovered significantly as compared to those of control mice. Our results suggest that DC-implantation exerts trophic effects, including activation of endogenous NSPCs, leading to repair of the injured adult spinal cord.     

Human embryonic stem cells differentiate into oligodendrocytes in high purity and myelinate after spinal cord transplantation

Human embryonic stem cells (hESCs) demonstrate remarkable proliferative and developmental capacity. Clinical interest arises from their ability to provide an apparently unlimited cell supply for transplantation, and from the hope that they can be directed to desirable phenotypes in high purity. Here we present for the first time a method for obtaining oligodendrocytes and their progenitors in high yield from hESCs. We expanded hESCs, promoted their differentiation into oligodendroglial progenitors, amplified those progenitors, and then promoted oligodendroglial differentiation using positive selection and mechanical enrichment. Transplantation into the shiverer model of dysmyelination resulted in integration, differentiation into oligodendrocytes, and compact myelin formation, demonstrating that these cells display a functional phenotype. This differentiation protocol provides a means of generating human oligodendroglial lineage cells in high purity, for use in studies of lineage development, screening assays of oligodendroglial-specific compounds, and treating neurodegenerative diseases and traumatic injuries to the adult CNS.     

Neurogenesis in the adult spinal cord in an experimental model of multiple sclerosis

Multiple sclerosis is an inflammatory disease of the central nervous system characterized by inflammation, demyelination, axonal degeneration and accumulation of neurological disability. Previously, we demonstrated that stem cells constitute a possible endogenous source for remyelination. We now addressed the question of whether neurogenesis can occur in neuroinflammatory lesions. We demonstrated that, in experimental autoimmune encephalomyelitis, induced in rats 1,1'-dioctadecyl-6,6'-di(4sulphopentyl)-3,3,3',3'tetramethylindocarbocyanin(DiI)-labelled ependymal cells not only proliferated but descendants migrated to the area of neuroinflammation and differentiated into cells expressing the neuronal markers beta-III-tubulin and NeuN. Furthermore, these cells were immunoreactive for bromodeoxyuridine and PCNA, markers for cells undergoing cell proliferation. Using the whole-cell patch-clamp technique on freshly isolated 1, DiI-labelled cells from spinal cord lesions we demonstrated the ability of these cells to fire overshooting action potentials similar to those of immature neurones. We thus provide the first evidence for the initiation of neurogenesis in neuroinflammatory lesions in the adult spinal cord.     

Current states of endogenous stem cells in adult spinal cord

New neurons are continuously generated throughout life in the subgranular zone in the dentate gyrus of the mammalian hippocampus and in the subventricular zone of the lateral ventricles. With the aid of new methodologies, significant progress has been made in the characterization of endogenous stem cells (ependymal cells) and their development in the adult spinal cord. Recent studies have shed light on essential extrinsic and intrinsic molecular mechanisms that govern sequential steps of neurogenesis in the adult spinal cord. This review discusses the occurrence, origin, and specific makers of ependymal cells; the factors regulating neurogenesis of multipotent ependymal cells; and the implications of ependymal cells in the repair of spinal cord injuries. © 2014 Wiley Periodicals, Inc.     

移植人脐带间充质干细胞修复大鼠脊髓损伤

背景：已知人脐带间充质干细胞对脊髓损伤存在着潜在的治疗价值,然而,当前对移植人脐带间充质干细胞治疗脊髓损伤及机制方面研究很少。 目的：观察人脐带间充质干细胞对脊髓损伤大鼠的治疗效果。 方法：40只Wistar大鼠建立脊髓损伤模型,38只造模成功后随机摸球法分为3组：空白对照组：只接受单纯损伤,不做任何移植;DMEM移植组：损伤后1周予以5 μL DMEM局部移植;细胞移植组：损伤后1周予以5 μL准备好的人脐带间充质干细胞局部移植(细胞数1×106)。移植后对实验动物通过BBB评分、体感诱发电位与运动诱发电位观察后肢功能恢复情况。分别于损伤后2,4,6,8,10周随机于细胞移植组抽取大鼠2只,免疫组织化学染色观察人脐带间充质干细胞存活、迁移、分化,通过胶质纤维酸性蛋白阳性细胞染色比较各组损伤局部胶质瘢痕形成面积。 结果与结论：BBB评分损伤后4周细胞移植组高于其他两组(P < 0.05),损伤后12周细胞移植组与其他两组相比SEP、MEP潜伏期缩短、波幅值增高(P < 0.05)。免疫组织化学染色示人脐带间充质干细胞可向神经元、星形胶质细胞和少突胶质细胞分化,分化的少突胶质细胞并包绕轴突形成髓鞘。细胞移植组损伤局部胶质瘢痕面积均小于其他两组(P < 0.05),空白对照组、DMEM移植组间差异无显著性(P > 0.05)。提示未经体外诱导的人脐带间充质干细胞可于损伤大鼠脊髓体内向神经元、星形胶质细胞、少突胶质细胞分化,减小胶质瘢痕,并促进脊髓损伤大鼠神经功能的恢复。     

Doublecortin expression levels in adult brain reflect neurogenesis

Progress in the field of neurogenesis is currently limited by the lack of tools enabling fast and quantitative analysis of neurogenesis in the adult brain. Doublecortin (DCX) has recently been used as a marker for neurogenesis. However, it was not clear whether DCX could be used to assess modulations occurring in the rate of neurogenesis in the adult mammalian central nervous system following lesioning or stimulatory factors. Using two paradigms increasing neurogenesis levels (physical activity and epileptic seizures), we demonstrate that quantification of DCX-expressing cells allows for an accurate measurement of modulations in the rate of adult neurogenesis. Importantly, we excluded induction of DCX expression during physiological or reactive gliogenesis and excluded also DCX re-expression during regenerative axonal growth. Our data validate DCX as a reliable and specific marker that reflects levels of adult neurogenesis and its modulation. We demonstrate that DCX is a valuable alternative to techniques currently used to measure the levels of neurogenesis. Importantly, in contrast to conventional techniques, analysis of neurogenesis through the detection of DCX does not require in vivo labelling of proliferating cells, thereby opening new avenues for the study of human neurogenesis under normal and pathological conditions.     

Integration of genetically modified adult astrocytes into the lesioned rat spinal cord

Combination of ex vivo gene transfer and cell transplantation is now considered as a potentially useful strategy for the treatment of spinal cord injury. In a perspective of clinical application, autologous transplantation could be an option of choice. We analyzed the fate of adult rat cortical astrocytes genetically engineered with a lentiviral vector transplanted into a lesioned rat spinal cord. Cultures of adult rat cortical astrocytes were infected with an HIV-1-derived vector (TRIP-CMV-GFP) and labeled with the fluorescent dye Hoechst. Transfected and labeled astrocyte suspension was injected at T11 in rats in which spinal cord transection at T7-T8 levels had been carried out 1 week earlier. Six weeks after grafting, the animals were sacrificed and transplants were retrieved either by Hoechst fluorescence or by immunohistochemistry for detection of glial fibrillary acidic protein (GFAP) and vimentin. Grafted astrocytes expressing green fluorescent protein (GFP) were found both at the injection and transection sites. Genetically modified astrocytes thus survived, integrated, and migrated within the host parenchyma when grafted into the completely transected rat spinal cord. In addition, they retained some ability to express the GFP transgene for at least 6 weeks after transplantation. Adult astrocytes infected with lentiviral vectors can therefore be a valuable tool for the delivery of therapeutic factors into the lesioned spinal cord.     

Human embryonic stem cell-derived neural precursors develop into neurons and integrate into the host brain

Whether and how in-vitro-produced human neural precursors mature and integrate into the brain are crucial to the utility of human embryonic stem (hES) cells in treating neurological disorders. After transplantation into the ventricles of neonatal immune-deficient mice, hES-cell-derived neural precursors stopped expressing the cell division marker Ki67, except in neurogenic areas, and differentiated into neurons and then glia in a temporal course intrinsic to that of human cells regardless of location. The human cells located in the gray matter became neurons in the olfactory bulb and striatum, whereas those in the white matter produced exclusively glia. Importantly, the grafted human cells formed synapses. Thus, the in-vitro-produced human neural precursors follow their intrinsic temporal program to produce neurons and glia and, in response to environmental signals, generate cells appropriate to their target regions and integrate into the brain.