Neurotrophin-3 gene transduction of mouse neural stem cells promotes proliferation and neuronal differentiation in organotypic hippocampal slice cultures

Emerging Pro-neurogenic Therapeutic Strategies for Neurodegenerative Diseases: A Review of Pre-clinical and Clinical Research

The neuroscience community has largely accepted the notion that functional neurons can be generated from neural stem cells in the adult brain, especially in two brain regions: the subventricular zone of the lateral ventricles and the subgranular zone in the dentate gyrus of the hippocampus. However, impaired neurogenesis has been observed in some neurodegenerative diseases, particularly in Alzheimer's, Parkinson's, and Huntington's diseases, and also in Lewy Body dementia. Therefore, restoration of neurogenic function in neurodegenerative diseases emerges as a potential therapeutic strategy to counteract, or at least delay, disease progression. Considering this, the present study summarizes the different neuronal niches, provides a collection of the therapeutic potential of different pro-neurogenic strategies in pre-clinical and clinical research, providing details about their possible modes of action, to guide future research and clinical practice.

Neural stem cells promote neuroplasticity: a promising therapeutic strategy for the treatment of Alzheimer's disease

Recent studies have demonstrated that neuroplasticity, such as synaptic plasticity and neurogenesis, exists throughout the normal lifespan but declines with age and is significantly impaired in individuals with Alzheimer's disease. Hence, promoting neuroplasticity may represent an effective strategy with which Alzheimer's disease can be alleviated. Due to their significant ability to self-renew, differentiate, and migrate, neural stem cells play an essential role in reversing synaptic and neuronal damage, reducing the pathology of Alzheimer's disease, including amyloid-β, tau protein, and neuroinflammation, and secreting neurotrophic factors and growth factors that are related to plasticity. These events can promote synaptic plasticity and neurogenesis to repair the microenvironment of the mammalian brain. Consequently, neural stem cells are considered to represent a potential regenerative therapy with which to improve Alzheimer's disease and other neurodegenerative diseases. In this review, we discuss how neural stem cells regulate neuroplasticity and optimize their effects to enhance their potential for treating Alzheimer's disease in the clinic.

Overexpression of NT-3 in the hippocampus suppresses the early phase of the adult neurogenic process

The dentate gyrus (DG) of the hippocampus regulates stress-related emotional behaviors and ensures neurogenesis throughout life. Neurotrophin-3 (NT-3) is a neurotrophic factor that regulates neuronal differentiation, survival, and synaptic formation in both the peripheral and central nervous systems. NT-3 is expressed in the adult DG of the hippocampus; several chronic stress conditions enhance NT-3 expression in rodents. However, functional modulation of the adult DG by NT-3 signaling remains unclear. To directly investigate the impact of NT-3 on DG function, NT-3 was overexpressed in the hippocampal ventral DG by an adeno-associated virus carrying NT-3 (AAV-NT-3). Four weeks following the AAV-NT-3 injection, high NT-3 expression was observed in the ventral DG. We examined the influence of NT-3 overexpression on the neuronal responses and neurogenic processes in the ventral DG. NT-3 overexpression significantly increased the expression of the mature DG neuronal marker calbindin and immediate early genes, such as Fos and Fosb, thereby suggesting DG neuronal activation. During neurogenesis, the number of proliferating cells and immature neurons in the subgranular zone of the DG significantly decreased in the AAV-NT-3 group. Among the neurogenesis-related factors, Vegfd, Lgr6, Bmp7, and Drd1 expression significantly decreased. These results demonstrated that high NT-3 levels in the hippocampus regulate the activation of mature DG neurons and suppress the early phase of neurogenic processes, suggesting a possible role of NT-3 in the regulation of adult hippocampal function under stress conditions.

rAAV2-Mediated Restoration of GALC in Neural Stem Cells from Krabbe Patient-Derived iPSCs

Krabbe disease is a rare neurodegenerative fatal disease. It is caused by deficiency of the lysosomal enzyme galactocerebrosidase (GALC), which results in progressive accumulation of galactolipid substrates in myelin-forming cells. However, there is still a lack of appropriate neural models and effective approaches for Krabbe disease. We generated induced pluripotent stem cells (iPSCs) from a Krabbe patient previously. Here, Krabbe patient-derived neural stem cells (K-NSCs) were induced from these iPSCs. By using nine kinds of recombinant adeno-associated virus (rAAV) vectors to infect K-NSCs, we found that the rAAV2 vector has high transduction efficiency for K-NSCs. Most importantly, rAAV2-GALC rescued GALC enzymatic activity in K-NSCs. Our findings not only establish a novel patient NSC model for Krabbe disease, but also firstly indicate the potential of rAAV2-mediated gene therapy for this devastating disease.

Overexpression of NT3P75-2 gene modified bone marrow mesenchymal stem cells supernatant promotes neurological function recovery in ICH rats

Intracerebral hemorrhage (ICH) is an acute cerebrovascular disease with high mortality and long-term disability rates. Stem cell transplantation and neurotrophic factor therapy have shown great potential in ICH. It has been established that mutated NT3 (NT3P75 - 2) can enhance the positive biological functions of NT3 by decreasing its affinity to the P75-2 receptor. The present study aimed to explore whether NT3P75-2 could further improve neurological recovery after ICH. First, we constructed three stable BMSC cell lines (GFP, GFP-NT3 overexpressed and GFP-NT3P75 - 2 overexpressed) by lentivirus infection. Next, rats were injected with fresh supernatants of these three cell lines on days 1 (24 h) and 3 (72 h) post-ICH induction. Behavioral evaluations were conducted to assess the neurological recovery of ICH rats. We further evaluated changes in microglia activation, neuron survival and proliferation of neural stem cells. Compared with the GFP group and the GFP-NT3 group, animals in the GFP-NT3P75 - 2 group exhibited better motor function improvements and milder neuroinflammation response. Meanwhile, overexpression of NT3P75 - 2 significantly decreased neuronal apoptosis and increased number of SOX2 - positive cells. Taken together, our study demonstrated that early administration of NT3P75 - 2 enriched BMMSC supernatants significantly enhanced neuro-functional recovery after ICH by regulating neuroinflammation response, neuronal survival and increasing neural stem cell number, providing a new therapeutic strategy and direction for early treatment of ICH.

Quantitative proteomics reveals potential anti-inflammatory protein targets of radial extracorporeal shock wave therapy in TNF-α-induced model of acute inflammation in primary human tenocytes

Tendinopathy refers to a type of tendon disease with a multifactorial spectrum. Recent research has begun to reveal the effects of inflammation on the tendinopathic process, especially in the first stage of tendinopathy. Radial extracorporeal shock wave therapy (rESWT) has been successfully used to treat orthopedic diseases. However, the molecular mechanisms underlying the anti-inflammatory effects of rESWT on tumor necrosis factor-α treated tenocytes have not been fully elucidated. In this study, we applied total protein tandem mass tag-labeled quantitative proteomics with liquid chromatography-mass spectrometer/mass spectrometer technology to identify differentially expressed proteins (DEPs) among inflammatory tenocytes, rESWT inflammatory tenocytes, and controls using three biological replicates. Human tenocytes were used and they were cultured in vitro. In total, 1028 and 40 DEPs were detected for control versus inflammatory tenocytes and for inflammatory tenocytes versus rESWT inflammatory tenocytes, respectively. Further, we identified integrin α2, selenoprotein S, and NLR family CARD domain-containing protein 4 as pivotal molecular targets of the anti-inflammatory effects of rESWT. This is the first study to provide a reference proteomic map for inflammatory tenocytes and rESWT inflammatory tenocytes. Our findings provide crucial insight into the molecular mechanisms underscoring the anti-inflammatory effects of rESWT in tendinopathy.

The Beneficial Potential of Genetically Modified Stem Cells in the Treatment of Stroke: a Review

The last two decades have witnessed a surge in investigations proposing stem cells as a promising strategy to treat stroke. Since growth factor release is considered as one of the most important aspects of cell-based therapy, stem cells over-expressing growth factors are hypothesized to yield higher levels of therapeutic efficiency. In pre-clinical studies of the last 15 years that were investigating the efficiency of stem cell therapy for stroke, a variety of stem cell types were genetically modified to over-express various factors. In this review we summarize the current knowledge on the therapeutic efficiency of stem cell-derived growth factors, encompassing techniques employed and time points to evaluate. In addition, we discuss several types of stem cells, including the recently developed model of epidermal neural crest stem cells, and genetically modified stem cells over-expressing specific factors, which could elevate the restorative potential of naive stem cells. The restorative potential is based on enhanced survival/differentiation potential of transplanted cells, apoptosis inhibition, infarct volume reduction, neovascularization or functional improvement. Since the majority of studies have focused on the short-term curative effects of genetically engineered stem cells, we emphasize the need to address their long-term impact.

Ghrelin promotes midbrain neural stem cells differentiation to dopaminergic neurons through Wnt/β-catenin pathway

Ghrelin plays a neuroprotective role in the process of dopaminergic (DAergic) neurons degeneration in Parkinson's disease (PD). However, it still largely unknown whether ghrelin could affect the midbrain neural stem cells (mbNSCs) from which DAergic neurons are originated. In the present study, we observed that ghrelin enhanced mbNSCs proliferation, and promoted neuronal differentiation especially DAergic neuron differentiation both in vitro and ex vivo. The messenger RNA levels of Wnt1, Wnt3a, and glial cell line-derived neurotrophic factor were increased in response to the ghrelin treatment. Results showed that Wnt/β-catenin pathway was relevant to this DAergic neuron differentiation induced by ghrelin. Our finding gave a new evidence that ghrelin may enable clinical therapies for PD by its neurogenesis role.

Therapeutic Plasticity of Neural Stem Cells

Neural stem cells (NSCs) have garnered significant scientific and commercial interest in the last 15 years. Given their plasticity, defined as the ability to develop into different phenotypes inside and outside of the nervous system, with a capacity of almost unlimited self-renewal, of releasing trophic and immunomodulatory factors, and of exploiting temporal and spatial dynamics, NSCs have been proposed for (i) neurotoxicity testing; (ii) cellular therapies to treat CNS diseases; (iii) neural tissue engineering and repair; (iv) drug target validation and testing; (v) personalized medicine. Moreover, given the growing interest in developing cell-based therapies to target neurodegenerative diseases, recent progress in developing NSCs from human-induced pluripotent stem cells has produced an analog of endogenous NSCs. Herein, we will review the current understanding on emerging conceptual and technological topics in the neural stem cell field, such as deep characterization of the human compartment, single-cell spatial-temporal dynamics, reprogramming from somatic cells, and NSC manipulation and monitoring. Together, these aspects contribute to further disentangling NSC plasticity to better exploit the potential of those cells, which, in the future, might offer new strategies for brain therapies.

Aspects of excitatory/inhibitory synapses in multiple brain regions are correlated with levels of brain-derived neurotrophic factor/neurotrophin-3

Appropriate synapse formation during development is necessary for normal brain function, and synapse impairment is often associated with brain dysfunction. Brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) are key factors in regulating synaptic development. We previously reported that BDNF/NT-3 secretion was enhanced by calcium-dependent activator protein for secretion 2 (CADPS2). Although BDNF/NT-3 and CADPS2 are co-expressed in various brain regions, the effect of Cadps2-deficiency on brain region-specific BDNF/NT-3 levels and synaptic development remains elusive. Here, we show developmental changes of BDNF/NT-3 levels and we assess disruption of excitatory/inhibitory synapses in multiple brain regions (cerebellum, hypothalamus, striatum, hippocampus, parietal cortex and prefrontal cortex) of Cadps2 knockout (KO) mice compared with wild-type (WT) mice. Compared with WT, BDNF levels in KO mice were reduced in young/adult hippocampus, but increased in young hypothalamus, while NT-3 levels were reduced in adult cerebellum and young hippocampus, but increased in adult parietal cortex. Immunofluorescence of vGluT1, an excitatory synapse marker, and vGAT, an inhibitory synapse marker, in adult KO showed that vGluT1 was higher in the cerebellum and parietal cortex but lower in the hippocampus, whereas vGAT was lower in the hippocampus and parietal cortex compared with WT. Immunolabeling for both vGluT1 and vGAT was increased in the parietal cortex but vGAT was decreased in the cerebellum in adult KO compared with WT. These data suggest that CADPS2-mediated secretion of BDNF/NT-3 may be involved in development and maturation of synapses and in the balance between inhibitory and excitatory synapses.

[Experimental study of lentivirus-mediated Nogo extracellular peptide residues 1-40 gene and neurotrophin 3 gene co-transduction in neural stem cells]

Objective

To explore the feasibility of co-transduction and co-expression of Nogo extracellular peptide residues 1-40 (NEP1-40) gene and neurotrophin 3 (NT-3) gene into neural stem cells (NSCs).

Methods

NSCs were derived from the cortex tissue of Sprague Dawley rat embryo. The experiment included 5 groups: no-load lentiviral vector transducted NSCs (group A), NEP1-40 transducted NSCs (group B), NT-3 transducted NSCs (group C), NEP1-40 and NT-3 corporately transducted NSCs (group D), and blank control (group E). Target genes were transducted into NSCs by lentiviral vectors of different multiplicity of infection (MOI; 5, 10, 15) for different time (24, 48, 72 hours). Fluorescent microscope was used to observe the expression of fluorescence protein and acquire the optimum MOI and optimum collection time. Real-time fluorescence quantitative PCR and Western blot tests were utilized to evaluate the gene expressions of NEP1-40 and NT-3 in NSCs and protein expressions of NEP1-40 and NT-3 in NSCs and in culture medium.

Results

The optimum MOI for both target gene was 10 and the optimum collection time was 48 hours. The real-time fluorescence quantitative PCR and Western blot results showed that the mRNA and protein relative expressions of NEP1-40 in groups B and D were significantly higher than those in groups A and C ( P<0.05), but no significant difference was found between groups B and D, and between groups A and C ( P>0.05). The mRNA and protein relative expressions of NT-3 in groups C and D were significantly higher than those in groups A and B ( P<0.05), but no significant difference was found between groups A and B, and between groups C and D ( P>0.05).

Conclusion

NEP1-40 and NT-3 gene can be successfully co-transducted into NSCs by the mediation of lentiviral vector. The expressions of the two target genes are stable and have no auxo-action or antagonism between each other.

Cell-Cell Connection Enhances Proliferation and Neuronal Differentiation of Rat Embryonic Neural Stem/Progenitor Cells

Cell-cell interaction as one of the niche signals plays an important role in the balance of stem cell quiescence and proliferation or differentiation. In order to address the effect and the possible mechanisms of cell-cell connection on neural stem/progenitor cells (NSCs/NPCs) proliferation and differentiation, upon passaging, NSCs/NPCs were either dissociated into single cell as usual (named Group I) or mechanically triturated into a mixture of single cell and small cell clusters containing direct cell-cell connections (named Group II). Then the biological behaviors including proliferation and differentiation of NSCs/NPCs were observed. Moreover, the expression of gap junction channel, neurotrophic factors and the phosphorylation status of MAPK signals were compared to investigate the possible mechanisms. Our results showed that, in comparison to the counterparts in Group I, NSCs/NPCs in Group II survived well with preferable neuronal differentiation. In coincidence with this, the expression of connexin 45 (Cx45), as well as brain derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3) in Group II were significantly higher than those in Group I. Phosphorylation of ERK1/2 and JNK2 were significantly upregulated in Group II too, while no change was found about p38. Furthermore, the differences of NSCs/NPCs biological behaviors between Group I and II completely disappeared when ERK and JNK phosphorylation were inhibited. These results indicated that cell-cell connection in Group II enhanced NSCs/NPCs survival, proliferation and neuronal differentiation through upregulating the expression of gap junction and neurotrophic factors. MAPK signals- ERK and JNK might contribute to the enhancement. Efforts for maintaining the direct cell-cell connection are worth making to provide more favorable niches for NSCs/NPCs survival, proliferation and neuronal differentiation.

The Effects of Different Factors on the Behavior of Neural Stem Cells

The repair of central nervous system (CNS) injury has been a worldwide problem in the biomedical field. How to reduce the damage to the CNS and promote the reconstruction of the damaged nervous system structure and function recovery has always been the concern of nerve tissue engineering. Multiple differentiation potentials of neural stem cell (NSC) determine the application value for the repair of the CNS injury. Thus, how to regulate the behavior of NSCs becomes the key to treating the CNS injury. So far, a large number of researchers have devoted themselves to searching for a better way to regulate the behavior of NSCs. This paper summarizes the effects of different factors on the behavior of NSCs in the past 10 years, especially on the proliferation and differentiation of NSCs. The final purpose of this review is to provide a more detailed theoretical basis for the clinical repair of the CNS injury by nerve tissue engineering.

Neurotrophin Signaling and Stem Cells-Implications for Neurodegenerative Diseases and Stem Cell Therapy

Neurotrophins (NTs) are members of a neuronal growth factor protein family whose action is mediated by the tropomyosin receptor kinase (TRK) receptor family receptors and the p75 NT receptor (p75NTR), a member of the tumor necrosis factor (TNF) receptor family. Although NTs were first discovered in neurons, recent studies have suggested that NTs and their receptors are expressed in various types of stem cells mediating pivotal signaling events in stem cell biology. The concept of stem cell therapy has already attracted much attention as a potential strategy for the treatment of neurodegenerative diseases (NDs). Strikingly, NTs, proNTs, and their receptors are gaining interest as key regulators of stem cells differentiation, survival, self-renewal, plasticity, and migration. In this review, we elaborate the recent progress in understanding of NTs and their action on various stem cells. First, we provide current knowledge of NTs, proNTs, and their receptor isoforms and signaling pathways. Subsequently, we describe recent advances in the understanding of NT activities in various stem cells and their role in NDs, particularly Alzheimer's disease (AD) and Parkinson's disease (PD). Finally, we compile the implications of NTs and stem cells from a clinical perspective and discuss the challenges with regard to transplantation therapy for treatment of AD and PD.

Dynamic expression of srGAP2 in cell nuclei and cytoplasm during the differentiation of rat neural stem cells in vitro

Different SLIT-ROBO Rho GTPase-activating proteins (srGAPs) have different levels of expression and diverse functions during neural development. Although srGAP2 is expressed in developmental brain tissue, little is known about its influence on cellular development of the nervous system. In the current study, dynamic expression of endogenous srGAP2 during neural stem cell/progenitor cell (NSC/NPC) differentiation in vitro was investigated in order to elucidate the association between the dynamic expression of srGAP2 and neural development. srGAP2 was expressed in undifferentiated NSCs/NPCs, and differentiated neurons and astrocytes with distinct expression patterns. In conjunction with the differentiation of NSCs/NPCs in vitro, the number of srGAP2+ cells markedly reduced. The percentage of srGAP2+ cells in the population of nestin+ and β‑tubulin III+ cells was significantly downregulated while in the population of glial fibrillary acidic protein‑positive cells, almost all cells were srGAP2+. srGAP2 was predominantly expressed in the cell nucleus in all cell types. srGAP2 was also weakly expressed in the cytoplasm of nestin+ and β‑tubulin III+ cells at 3 and 7 days in vitro. However levels were gradually downregulated during the process of differentiation and almost disappeared in β‑tubulin III+ cells at 14 days. The results from the present study suggest that srGAP2 is involved in regulating NSC/NPC differentiation during neural development. The translocation of srGAP2 in the cytoplasm and cell nucleus in different cell types may function as a director in decisions regarding cell fate.

Scutellarin promotes microglia-mediated astrogliosis coupled with improved behavioral function in cerebral ischemia

Scutellarin, an anti-inflammatory agent, has been reported to suppress microglia activation. It promotes astrocytic reaction but through activated microglia. Here we sought to determine more specifically the outcomes of scutellarin treatment in reactive astrocytes in rats subjected to middle cerebral artery occlusion (MCAO). GFAP, MAP-2 and PSD-95 expression was assessed in reactive astrocytes in scutellarin injected MCAO rats. Expression of BDNF, NT-3 and IGF-1, and cell cycle markers cyclin-D1/B1 was also evaluated. In vitro, the above-mentioned proteins were also investigated in TNC 1 and primary astrocytes, treated respectively with conditioned medium from BV-2 microglia with or without pretreatment of scutellarin and lipopolysaccharide. Behavioral study was conducted to ascertain if scutellarin would improve the neurological functions of MCAO rats. In MCAO, reactive astrocytes in the penumbral areas were hypertrophic bearing long extending processes; expression of all the above-mentioned markers was markedly augmented. When compared to the controls, TNC1/primary astrocytes responded vigorously to conditioned medium derived from BV-2 microglia treated with scutellarin + lipopolysaccharide as shown by enhanced expression of all the above markers by Western and immunofluorescence analysis. By electron microscopy, hypertrophic TNC1 astrocytes in this group showed abundant microfilaments admixed with microtubules. In MCAO rats given scutellarin treatment, neurological scores were significantly improved coupled with a marked decrease in infarct size when compared with the matching controls. It is concluded that scutellarin is neuroprotective and that it can amplify astrogliosis but through activated microglia. Scutellarin facilitates tissue remodeling in MCAO that maybe linked to improvement of neurological functions.

Neurotrophic Factors and Their Potential Applications in Tissue Regeneration

Neurotrophic factors are growth factors that can nourish neurons and promote neuron survival and regeneration. They have been studied as potential drug candidates for treating neurodegenerative diseases. Since their identification, there are more and more evidences to indicate that neurotrophic factors are also expressed in non-neuronal tissues and regulate the survival, anti-inflammation, proliferation and differentiation in these tissues. This mini review summarizes the characteristics of the neurotrophic factors and their potential clinical applications in the regeneration of neuronal and non-neuronal tissues.

The effects of controlled release of neurotrophin-3 from PCLA scaffolds on the survival and neuronal differentiation of transplanted neural stem cells in a rat spinal cord injury model

Neural stem cells (NSCs) have emerged as a potential source for cell replacement therapy following spinal cord injury (SCI). However, poor survival and low neuronal differentiation remain major obstacles to the use of NSCs. Biomaterials with neurotrophic factors are promising strategies for promoting the proliferation and differentiation of NSCs. Silk fibroin (SF) matrices were demonstrated to successfully deliver growth factors and preserve their potency. In this study, by incorporating NT-3 into a SF coating, we successfully developed NT-3-immobilized scaffolds (membranes and conduits). Sustained release of bioactive NT-3 from the conduits for up to 8 weeks was achieved. Cell viability was confirmed using live/dead staining after 14 days in culture. The efficacy of the immobilized NT-3 was confirmed by assessing NSC neuronal differentiation in vitro. NSC neuronal differentiation was 55.2 ± 4.1% on the NT-3-immobilized membranes, which was significantly higher than that on the NT-3 free membrane. Furthermore, 8 weeks after the NSCs were seeded into conduits and implanted in rats with a transected SCI, the conduit+NT-3+NSCs group achieved higher NSC survival (75.8 ± 15.1%) and neuronal differentiation (21.5 ± 5.2%) compared with the conduit+NSCs group. The animals that received the conduit+NT-3+NSCs treatment also showed improved functional outcomes, as well as increased axonal regeneration. These results indicate the feasibility of fabricating NT-3-immobilized scaffolds using the adsorption of NT-3/SF coating method, as well as the potential of these scaffolds to induce SCI repair by promoting survival and neuronal differentiation of transplanted NSCs.

Nanoparticles carrying neurotrophin-3-modified Schwann cells promote repair of sciatic nerve defects

Schwann cells and neurotrophin-3 play an important role in neural regeneration, but the secretion of neurotrophin-3 from Schwann cells is limited, and exogenous neurotrophin-3 is inactived easily in vivo. In this study, we have transfected neurotrophin-3 into Schwann cells cultured in vitro using nanoparticle liposomes. Results showed that neurotrophin-3 was successfully transfected into Schwann cells, where it was expressed effectively and steadily. A composite of Schwann cells transfected with neurotrophin-3 and poly(lactic-co-glycolic acid) biodegradable conduits was transplanted into rats to repair 10-mm sciatic nerve defects. Transplantation of the composite scaffold could restore the myoelectricity and wave amplitude of the sciatic nerve by electrophysiological examination, promote nerve axonal and myelin regeneration, and delay apoptosis of spinal motor neurons. Experimental findings indicate that neurotrophin-3 transfected Schwann cells combined with bridge grafting can promote neural regeneration and functional recovery after nerve injury.

Adult neurogenesis and glial oncogenesis: when the process fails

Malignant brain tumors, including glioblastoma multiforme (GBM), are known for their high degree of invasiveness, aggressiveness, and lethality. These tumors are made up of heterogeneous cell populations and only a small part of these cells (known as cancer stem cells) is responsible for the initiation and recurrence of the tumor. The biology of cancer stem cells and their role in brain tumor growth and therapeutic resistance has been extensively investigated. Recent work suggests that glial tumors arise from neural stem cells that undergo a defective process of differentiation. The understanding of this process might permit the development of novel treatment strategies targeting cancer stem cells. In the present review, we address the mechanisms underlying glial tumor formation, paying special attention to cancer stem cells and the role of the microenvironment in preserving them and promoting tumor growth. Recent advancements in cancer stem cell biology, especially regarding tumor initiation and resistance to chemo- or radiotherapy, have led to the development of novel treatment strategies that focus on the niche of the stem cells that make up the tumor. Encouraging results from preclinical studies predict that these findings will be translated into the clinical field in the near future.

Spatial relationship between NSCs/NPCs and microvessels in rat brain along prenatal and postnatal development

Neurogenesis and angiogenesis are two parallel processes that occur in brain development and repair, and so share some molecular signals. In order to better understand the interaction between the genesis of neural cells and vessels during brain development, the density of microvessels and the number of nestin positive neural stem/neural progenitor cells (NSCs/NPCs) around microvasculature in various brain regions was quantified. Results showed that the density of microvessels remained at a relative low level during embryonic development and dramatically increased after postnatal day 3 (P3), especially in subventricular zone. The number of nestin positive NSCs/NPCs per microvessel in neurogenic brain regions continually increased with fetal brain development and then gradually dropped down during postnatal development. The highest density of NSCs/NPCs appeared at postnatal day 1 (P1) and dramatically decreased after P3. Similar pattern was observed in striatum. In the olfactory bulb, the cerebral cortex and cerebellum, the dramatic decrease of NSCs/NPCs density appeared after P7, especially in the cerebral cortex. Our results demonstrated that anatomically, the spatial relationship between NSCs/NPCs and microvessels changed during brain development. The alteration patterns in neurogenic brain regions differed from non-neurogenic brain regions.

The mental retardation-associated protein srGAP3 regulates survival, proliferation, and differentiation of rat embryonic neural stem/progenitor cells

The mental retardation-associated protein, srGAP3 is highly expressed in neurogenic sites. It is thought to regulate the key aspects of neuronal development and functions. Little is known about the interaction between srGAP3 and immature neural stem cells/neural progenitor cells (NSCs/NPCs). In the current study, the expression of srGAP3 in NSCs/NPCs was detected. Then, survival, proliferation, differentiation, and morphological alteration of NSCs/NPCs were assessed after a lentivirus-mediated knockdown of srGAP3. The results showed that srGAP3 is highly expressed in NSCs/NPCs both in vitro and in vivo. After knockdown of srGAP3 (LV3-srGAP3 infection), viability and proliferation of NSCs/NPCs dramatically decreased, approximately 85% displayed a similar morphology with type I cells that have no or only few indistinguishable processes. After 7 days culture in a differentiation medium, 62.5%±8.3% of cells in the srGAP3 knockdown group were nestin-positive and 24.8%±5.8% of them were β-tubulin III-positive, which are significantly higher (30.2%±9.9% and 14.6%±2.7%) than in the control group (LV3-NC infection). In addition, cells in the knockdown group had significantly fewer, but longer processes. Our results demonstrate that srGAP3 knockdown negatively regulates NSCs/NPCs survival, proliferation, differentiation, and morphological alteration, particularly, process formation. Taken together, our results provide strong evidence that srGAP3 is involved in the regulation of biological behavior and the morphological features in rat NSCs/NPCs in vitro.

Functions of neurotrophins and growth factors in neurogenesis and brain repair

The identification and isolation of multipotent neural stem and progenitor cells in the brain, giving rise to neurons, astrocytes, and oligodendrocytes initiated many studies in order to understand basic mechanisms of endogenous neurogenesis and repair mechanisms of the nervous system and to develop novel therapeutic strategies for cellular regeneration therapies in brain disease. A previous review (Trujillo et al., Cytometry A 2009;75:38-53) focused on the importance of extrinsic factors, especially neurotransmitters, for directing migration and neurogenesis in the developing and adult brain. Here, we extend our review discussing the effects of the principal growth and neurotrophic factors as well as their intracellular signal transduction on neurogenesis, fate determination and neuroprotective mechanisms. Many of these mechanisms have been elucidated by in vitro studies for which neural stem cells were isolated, grown as neurospheres, induced to neural differentiation under desired experimental conditions, and analyzed for embryonic, progenitor, and neural marker expression by flow and imaging cytometry techniques. The better understanding of neural stem cells proliferation and differentiation is crucial for any therapeutic intervention aiming at neural stem cell transplantation and recruitment of endogenous repair mechanisms.

Neuroprotection of neurotrophin-3 against focal cerebral ischemia/reperfusion injury is regulated by hypoxia-responsive element in rats

Exogenous delivery of the neurotrophin-3 (NT-3) gene may provide a potential therapeutic strategy for ischemic stroke. To investigate the neuroprotective effects of NT-3 expression controlled by 5HRE after focal cerebral ischemia, we constructed a recombinant retrovirus vector (RV) with five copies of hypoxia-responsive elements (5HRE or 5H) and NT-3 and delivered it to the rat brain. Three groups of rats received RV-5H-NT3, RV-5H-EGFP or saline injection. Three days after gene transfer, the rats underwent 90min of transient middle cerebral artery occlusion (tMCAO), followed by 1-28days of reperfusion. Three days after tMCAO, brain NT-3 expression was significantly increased in the RV-5H-NT3-transduced animals compared with the RV-5H-EGFP or saline group, and brain infarct volume was smaller in the RV-5H-NT3-transduced group than the RV-5H-EGFP or saline group. The percentage of TUNEL-positive cells was reduced in RV-5H-NT3-transduced brains compared with the RV-5H-EGFP or saline group 3 and 7days after tMCAO. Furthermore, the neurological status of RV-5H-NT3-transduced rats was better than that of RV-5H-EGFP- or saline-transduced animals from 1day to 4weeks after tMCAO. Our results demonstrated that 5HRE could modulate NT-3 expression in the ischemic brain environment and that the up-regulated NT-3 could effectively improve neurological status following tMCAO due to decreased initial damage. To avoid unexpected side effects, 5HRE-controlled gene expression might be a useful tool for gene therapy of ischemic disorders in the central nervous system.