VEGF-induced neuroprotection, neurogenesis, and angiogenesis after focal cerebral ischemia

Perlecan domain V is neuroprotective and proangiogenic following ischemic stroke in rodents

Stroke is the leading cause of long-term disability and the third leading cause of death in the United States. While most research thus far has focused on acute stroke treatment and neuroprotection, the exploitation of endogenous brain self-repair mechanisms may also yield therapeutic strategies. Here, we describe a distinct type of stroke treatment, the naturally occurring extracellular matrix fragment of perlecan, domain V, which we found had neuroprotective properties and enhanced post-stroke angiogenesis, a key component of brain repair, in rodent models of stroke. In both rat and mouse models, Western blot analysis revealed elevated levels of perlecan domain V. When systemically administered 24 hours after stroke, domain V was well tolerated, reached infarct and peri-infarct brain vasculature, and restored stroke-affected motor function to baseline pre-stroke levels in these multiple stroke models in both mice and rats. Post-stroke domain V administration increased VEGF levels via a mechanism involving brain endothelial cell α5β1 integrin, and the subsequent neuroprotective and angiogenic actions of domain V were in turn mediated via VEGFR. These results suggest that perlecan domain V represents a promising approach for stroke treatment.

Effects of transplantation with bone marrow-derived mesenchymal stem cells modified by Survivin on experimental stroke in rats

BACKGROUND

This study was performed to determine whether injury induced by cerebral ischemia could be further improved by transplantation with bone marrow-derived mesenchymal stem cells (MSCs) modified by Survivin (SVV).

METHODS

MSCs derived from bone marrow of male Sprague-Dawley rats were infected by the self-inactive lentiviral vector GCFU carrying green fluorescent protein (GFP) gene and SVV recombinant vector (GCFU-SVV). In vitro, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) were detected in infected MSCs supernatants under hypoxic conditions by ELSIA. In vivo, experiments consisted of three groups, one receiving intravenous injection of 500 μl of phosphate-buffered saline (PBS) without cells (control group) and two groups administered the same volume solution with either three million GFP-MSCs (group GFP) or SVV/GFP-MSCs (group SVV). All animals were submitted to 2-hour middle cerebral artery occlusion (MCAO) and then reperfusion. Differentiation and survival of the transplanted MSCs were determined by confocal microscope. Western blot was used to detect the expression of VEGF and bFGF in ischemic tissue. A 2,3,5-triphenyltetrazolium chloride (TTC) staining was used to assess the infarct volume. Evaluation of neurological function was performed using a modified Neurological Severity Score (mNSS).

RESULTS

In vitro, modification with SVV further increased secretion of VEGF and bFGF under hypoxic condition. In vivo, only very few transplantated cells co-expressed GFP and NeuN. The survival transplanted cells in the group SVV was 1.3-fold at 4 days after transplantation and 3.4-fold higher at 14 days after transplantation, respectively, when compared with group GFP. Expression of VEGF and bFGF in the ischemic tissue were further up-regulated by modification with SVV. Moreover, modification with SVV further reduced the cerebral infarct volume by 5.2% at 4 days after stroke and improved post-stroke neurological function at 14 days after transplantation.

CONCLUSION

Modification with SVV could further enhance the therapeutic effects of MSCs possibly through improving the MSCs survival capacity and up-regulating the expression of protective cytokines in the ischemic tissue.

Cerebral blood flow alteration in neuroprotection following cerebral ischaemia

The best neuroprotectant for acute ischaemic stroke would always be the rapid return of oxygen and glucose to physiological levels. This is currently provided by thrombolysis which restores blood flow to the ischaemic region. The attempt to confer neuroprotection by targeting the brain parenchyma has shown promise in experimental stroke models, but has unequivocally failed to translate to the clinic. Neuroprotective therapy primarily targets the biochemical cascade that produces cell death following cerebral ischaemia. However, these agents may also alter signal transduction that controls cerebral blood flow, for example glutamate, which may affect the outcome after ischaemia. In these cases, neuroprotection may potentially be due to the improved access to oxygen and glucose rather than biochemical prevention of cell death. Improvement in cerebral blood flow is an important but often overlooked effect of neuroprotective therapy, analogous to the protective effects of drug-induced hypothermia. This short review will discuss cerebral blood flow alteration and protection of the brain in the context of ischaemic preconditioning, oxygen sensing and thrombolysis. Future neuroprotection studies in cerebral ischaemia require stringent monitoring of cerebral blood flow, plus other physiological parameters. This will increase the chances that any protection observed may be able to translate to human therapy.

Inhibition of VEGF signaling pathway attenuates hemorrhage after tPA treatment

An angiogenic factor, vascular endothelial growth factor (VEGF), might be associated with the blood-brain barrier (BBB) disruption after focal cerebral ischemia; however, it remains unknown whether hemorrhagic transformation (HT) after tissue plasminogen activator (tPA) treatment is related to the activation of VEGF signaling pathway in BBB. Here, we hypothesized that inhibition of VEGF signaling pathway can attenuate HT after tPA treatment. Rats subjected to thromboembolic focal cerebral ischemia were assigned to a permanent ischemia group and groups treated with tPA at 1 or 4 hours after ischemia. Anti-VEGF neutralizing antibody or control antibody was administered simultaneously with tPA. At 24 hours after ischemia, we evaluated the effects of the antibody on the VEGF expression, matrix metalloproteinase-9 (MMP-9) activation, degradation of BBB components, and HT. Delayed tPA treatment at 4 hours after ischemia promoted expression of VEGF in BBB, MMP-9 activation, degradation of BBB components, and HT. Compared with tPA and control antibody, combination treatment with tPA and the anti-VEGF neutralizing antibody significantly attenuated VEGF expression in BBB, MMP-9 activation, degradation of BBB components, and HT. It also improved motor outcome and mortality. Inhibition of VEGF signaling pathway may be a promising therapeutic strategy for attenuating HT after tPA treatment.

Cellular and molecular determinants of stroke-induced changes in subventricular zone cell migration

A remarkable aspect of adult neurogenesis is that the tight regulation of subventricular zone (SVZ) neuroblast migration is altered after ischemic stroke and newborn neurons emigrate towards the injury. This phenomenon is an essential component of endogenous repair and also serves to illuminate normal mechanisms and rules that govern SVZ migration. Stroke causes inflammation that leads to cytokine and chemokine release, and SVZ neuroblasts that express their receptors are recruited. Metalloproteinases create pathways and new blood vessels provide a scaffold to facilitate neuroblast migration between the SVZ and the infarct. Most experiments have studied the peri-lesion parenchyma and relatively little is known about SVZ remodeling after stroke. Migration in the SVZ is tightly regulated by cellular interactions and molecular signaling; how are these altered after stroke to allow emigration? Do ependymal cells contribute to this process, given their reported neurogenic potential? How does stroke affect ependymal cell regulation of cerebrospinal fluid flow? Given the heterogeneity of SVZ progenitors, do all types of neuroblasts migrate out, or is this confined to specific subtypes of cells? We discuss these and other questions in our review and propose experiments to address them.

Acute hepatocyte growth factor treatment induces long-term neuroprotection and stroke recovery via mechanisms involving neural precursor cell proliferation and differentiation

Hepatocyte growth factor (HGF) is an interesting candidate for acute stroke treatment as shown by continuous infusion or gene delivery protocols. However, little is known about HGF-mediated long-term effects. The present study therefore analyzed long-term effects of an acute intrastriatal HGF treatment (5 μg) after a 45-minute stroke, with regard to brain injury and neurologic recovery. Hepatocyte growth factor induced long-term neuroprotection as assessed by infarct volume and neuronal cell death analysis for as long as 4 weeks after stroke, which was associated with sustained neurologic recovery as evidenced by corner-turn and tight-rope tests. Analyzing underlying mechanisms of HGF-induced sustained neuroprotection, enhanced cell proliferation followed by increased neuronal differentiation of neural precursor cells (NPCs) was observed in the ischemic striatum of HGF-treated mice, which persisted for up to 4 weeks. In line with this, HGF promoted neurosphere formation as well as proliferation of NPC and decreased caspase-3-dependent hypoxic injury in vitro. Preservation of blood-brain barrier integrity 24  hours after stroke was furthermore noticed in animals receiving HGF, which was associated with the inhibition of matrix metalloproteases (MMP)-2 and MMP-9 at 4 and 24  hours, respectively. We suggest that sustained recruitment of proliferating cells together with improved neurovascular remodeling provides an explanation for HGF-induced long-term neuroprotection.

Emerging roles for the BAI1 protein family in the regulation of phagocytosis, synaptogenesis, neurovasculature, and tumor development

While G-protein-coupled receptors (GPCRs) have received considerable attention for their biological activity in a diversity of physiological functions and have become targets for therapeutic intervention in many diseases, the function of the cell adhesion subfamily of GPCRs remains poorly understood. Within this group, the family of brain angiogenesis inhibitor molecules (BAI1-3) has become increasingly appreciated for their diverse roles in biology and disease. In particular, recent findings suggest emerging roles for BAI1 in the regulation of phenomena including phagocytosis, synaptogenesis, and the inhibition of tumor growth and angiogenesis via the processing of its extracellular domain into secreted vasculostatins. Here we summarize the known biological features of the BAI proteins, including their structure, proteolysis events, and interacting partners, and their recently identified ability to regulate certain signaling pathways. Finally, we discuss the potential of the BAIs as therapeutics or targets for diseases as varied as cancer, stroke, and schizophrenia.

Vascular endothelial growth factor and substrate mechanics regulate in vitro tubulogenesis of endothelial progenitor cells

Endothelial progenitor cells (EPCs) in the circulatory system have been suggested to maintain vascular homeostasis and contribute to adult vascular regeneration and repair. These processes require that EPCs break down the extracellular matrix (ECM), migrate, differentiate and undergo tube morphogenesis. Evidently, the ECM plays a critical role by providing biochemical and biophysical cues that regulate cellular behaviour. Using a chemically and mechanically tunable hydrogel to study tube morphogenesis in vitro, we show that vascular endothelial growth factor (VEGF) and substrate mechanics co-regulate tubulogenesis of EPCs. High levels of VEGF are required to initiate tube morphogenesis and activate matrix metalloproteinases (MMPs), which enable EPC migration. Under these conditions, the elasticity of the substrate affects the progression of tube morphogenesis. With decreases in substrate stiffness, we observe decreased MMP expression while increased cellular elongation, with intracellular vacuole extension and coalescence to open lumen compartments. RNAi studies demonstrate that membrane type 1-MMP (MT1-MMP) is required to enable the movement of EPCs on the matrix and that EPCs sense matrix stiffness through signalling cascades leading to the activation of the RhoGTPase Cdc42. Collectively, these results suggest that coupled responses for VEGF stimulation and modulation of substrate stiffness are required to regulate tube morphogenesis of EPCs.

Bone marrow mononuclear cells protect neurons and modulate microglia in cell culture models of ischemic stroke

Although several studies have provided evidence for the therapeutic potential of bone marrow-derived mononuclear cells (MNCs) in animal models of stroke, the mechanisms underlying their benefits remain largely unknown. We have determined the neuroprotective potential of MNCs in primary neuronal cultures exposed to various injuries in vitro. Cortical neurons in culture were exposed to oxygen-glucose deprivation, hypoxia, or hydrogen peroxide, and cell death was assayed by MTT, caspase-3 activation or TUNEL labelling at 24 hrs. Cultures were randomized to cotreatment with MNC-derived supernatants or media before injury exposure. In separate experiments, macrophage or microglial cultures were exposed to lipopolypolysacharide (LPS) in the presence and absence of MNC-derived supernatants. Neuronal cultures were then exposed to conditioned media derived from activated macrophages or microglia. Cytokines from the supernantants of MNC cultures exposed to normoxia or hypoxia were also estimated by enzyme-linked immunosorbant assay (ELISA). MNC-derived supernatants attenuated neuronal death induced by OGD, hypoxia, hydrogen peroxide, and conditioned macrophage/microglial media and contain a number of trophic factors, including interleukin-10, insulin-like growth factor-1, vascular endothelial growth factor, and stromal cell-derived factor-1. MNCs provide broad neuroprotection against a variety of injuries relevant to stroke.

Natural compounds from traditional medicinal herbs in the treatment of cerebral ischemia/reperfusion injury

More and more attention in the field of drug discovery has been focused on the neuroprotection of natural compounds from traditional medicinal herbs. Cerebral ischemia is a complex pathological process involving a series of mechanisms, and a framework for the development of neuroprotectants from traditional herb medicine is a promising treatment for cerebral ischemia. Natural compounds with the effects of anti-oxidation, anti-inflammation, calcium antagonization, anti-apoptosis, and neurofunctional regulation exhibit preventive or therapeutic effects on experimental ischemic brain injury. According to the pharmacological mechanisms underlying neuroprotection, we evaluated natural products from traditional medicinal herbs that exhibit protective effects on ischemic brain injury and characterized the promising targets.

Angiogenesis in old-aged subjects after ischemic stroke: a cautionary note for investigators

Angiogenesis represents a form of neovascularisation of exceptional importance in numerous pathological conditions including stroke. In this context it is directly related to neuroregeneration which is seen in close proximity. However, numerous experimental data have been drawn from studies that have ignored the age criterion. This is extremely important as angiogenesis is different in young versus old subjects. Extrapolating data obtained from studies performed in young subjects or "in vitro" to old-age patients could lead to inexact conclusions since the dynamics of angiogenesis is age-dependent.

The current review covers the key features of brain senescence including morphological and functional changes related to the brain parenchyma, its vascular network and blood flow which could possibly influence the process of angiogenesis. This is followed by a description of post-stroke angiogenesis and its relationship to neuroregeneration and its modulation by vascular endothelial growth factor (VEGF) and insulin-like growth factor 1 (IGF 1), the most important factors active in old brain after ischemic injury.

The treatment of TBI with human marrow stromal cells impregnated into collagen scaffold: functional outcome and gene expression profile

We have previously demonstrated that human marrow stromal cells (hMSCs) embedded in collagen I scaffolds significantly enhance the restorative therapeutic effect of hMSCs after traumatic brain injury (TBI). In this study, we test the hypothesis that the collagen scaffold alters gene expression in hMSCs and that hMSCs impregnated into scaffolds increase the astrocytic expression of vascular endothelial growth factor (VEGF) in the injured brain. Following TBI induced by controlled cortical impact injury, scaffold with hMSCs (3.0×10(6)), hMSCs-only and saline were implanted into the lesion cavity one week after brain injury (n=8/each group). Morris water maze and modified neurological severity scores were performed to evaluate the spatial learning and sensorimotor functions, respectively. Lesion volume and expression of VEGF were measured one week after different treatments. In vitro, total RNA from hMSCs was extracted one week after culture with or without collagen I scaffold for evaluation of gene microarrays. Furthermore, an RT-PCR study on a select subgroup of genes was performed to identify the changes of expression between the culturing hMSCs with collagen scaffolds and hMSCs only. The treatment of TBI with collagen scaffold impregnated with hMSCs significantly decreases the functional deficits from TBI within 7days after treatment, and significantly enhances the VEGF expression of astrocytes in the injured brain compared to the hMSCs-only group. In vitro data indicate that collagen scaffolds stimulate hMSCs to express multiple factors which may contribute to hMSC survival, tissue repair and functional recovery after TBI.

Sustained expression of vascular endothelial growth factor and angiopoietin-1 improves blood-spinal cord barrier integrity and functional recovery after spinal cord injury

Spinal cord injury (SCI) results in immediate disruption of the spinal vascular network, triggering an ischemic environment and initiating secondary degeneration. Promoting angiogenesis and vascular stability through the induction of vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1), respectively, provides a possible therapeutic approach in treating SCI. We examined whether supplementing the injured environment with these two factors, which are significantly reduced following injury, has an effect on lesion size and functional outcome. Sustained delivery of both VEGF(165) and Ang-1 was realized using viral vectors based on the adeno-associated virus (AAV), which were injected directly into the lesion epicenter immediately after injury. Our results indicate that the combined treatment with VEGF and Ang-1 resulted in both reduced hyperintense lesion volume and vascular stabilization, as determined by magnetic resonance imaging (MRI). Western blot analysis indicated that the viral vector expression was maintained into the chronic phase of injury, and that the use of the AAV vectors did not exacerbate infiltration of microglia into the lesion epicenter. The combined treatment with AAV-VEGF and AAV-Ang-1 improved locomotor recovery in the chronic phase of injury. These results indicate that combining angiogenesis with vascular stabilization may have potential therapeutic applications following SCI.

Mitochondrial protection attenuates inflammation-induced impairment of neurogenesis in vitro and in vivo

The impairment of hippocampal neurogenesis has been linked to the pathogenesis of neurological disorders from chronic neurodegenerative disease to the progressive cognitive impairment of children who receive brain irradiation. Numerous studies provide evidence that inflammation downregulates neurogenesis, with multiple factors contributing to this impairment. Although mitochondria are one of the primary targets of inflammatory injury, the role of mitochondrial function in the modulation of neurogenesis remains relatively unstudied. In this study, we used neurosphere-derived cells to show that immature doublecortin (Dcx)-positive neurons are uniquely sensitive to mitochondrial inhibition, demonstrating rapid loss of mitochondrial potential and cell viability compared with glial cells and more mature neurons. Mitochondrial inhibition for 24 h produced no significant changes in astrocyte or oligodendrocyte viability, but reduced viability of mature neurons by 30%, and reduced survival of Dcx(+) cells by 60%. We demonstrate that protection of mitochondrial function with mitochondrial metabolites or the mitochondrial chaperone mtHsp75/mortalin partially reverses the inflammation-associated impairment of neurogenesis in vitro and in irradiated mice in vivo. Our findings highlight mitochondrial mechanisms involved in neurogenesis and indicate mitochondria as a potential target for protective strategies to prevent the impairment of neurogenesis by inflammation.

Biphasic actions of HMGB1 signaling in inflammation and recovery after stroke

Stroke induces a complex web of pathophysiology that may evolve over hours to days and weeks after onset. It is now recognized that inflammation is an important phenomenon that can dramatically influence outcomes after stroke. In this minireview, we explore the hypothesis that inflammatory signals after stroke are biphasic in nature. The high-mobility group box 1 (HMGB1) protein is discussed as an example of this idea. HMGB1 is normally present in the nucleus. Under ischemic conditions, it is released extracellularly from many types of cells. During the acute phase poststroke, HMGB1 promotes necrosis and influx of damaging inflammatory cells. However, during the delayed phase poststroke, HMGB1 can mediate beneficial plasticity and recovery in many cells of the neurovascular unit. These emerging findings support the hypothesis that inflammation after stroke can be both detrimental and beneficial, depending on the cellular situations involved.

Human microglia transplanted in rat focal ischemia brain induce neuroprotection and behavioral improvement

Background and Purpose

Microglia are resident immunocompenent and phagocytic cells of central nervous system (CNS), which produce various cytokines and growth factors in response to injury and thereby regulate disease pathology. The purpose of this study is to investigate the effects of microglial transplantation on focal cerebral ischemia model in rat.

Methods

Transient middle cerebral artery occlusion (MCAO) in rats was induced by the intraluminal filament technique. HMO6 cells, human microglial cell line, were transplanted intravenously at 48 hours after MCAO. Functional tests were performed and the infarct volume was measured at 7 and 14 days after MCAO. Migration and cell survival of transplanted microglial cells and host glial reaction in the brain were studied by immunohistochemistry. Gene expression of neurotrophic factors, cytokines and chemokines in transplanted cells and host rat glial cells was determined by laser capture microdissection (LCM) and quantitative real time-PCR.

Results

HMO6 human microglial cells transplantion group demonstrated significant functional recovery compared with control group. At 7 and 14 days after MCAO, infarct volume was significantly reduced in the HMO group. In the HMO6 group, number of apoptotic cells was time-dependently reduced in the infarct core and penumbra. In addition, number of host rat microglia/macrophages and reactive astrocytes was significantly decreased at 7 and 14 days after MCAO in the penumbra. Gene expression of various neurotrophic factors (GDNF, BDNF, VEGF and BMP7) and anti-inflammatory cytokines (IL4 and IL5) was up-regulated in transplanted HMO6 cells of brain tissue compared with those in culture. The expression of GDNF and VEGF in astrocytes in penumbra was significantly up-regulated in the HMO6 group.

Conclusions

Our results indicate that transplantation of HMO6 human microglial cells reduces ischemic deficits and apoptotic events in stroke animals. The results were mediated by modulation of gliosis and neuroinflammation, and neuroprotection provided by neurotrophic factors of endogenous and transplanted cells-origin.

Therapeutic Potential of Non-Psychotropic Cannabidiol in Ischemic Stroke

Cannabis contains the psychoactive component delta⁹-tetrahydrocannabinol (delta⁹-THC), and the non-psychoactive components cannabidiol (CBD), cannabinol, and cannabigerol. It is well-known that delta⁹-THC and other cannabinoid CB₁ receptor agonists are neuroprotective during global and focal ischemic injury. Additionally, delta⁹-THC also mediates psychological effects through the activation of the CB₁ receptor in the central nervous system. In addition to the CB₁ receptor agonists, cannabis also contains therapeutically active components which are CB₁ receptor independent. Of the CB₁ receptor-independent cannabis, the most important is CBD. In the past five years, an increasing number of publications have focused on the discovery of the anti-inflammatory, anti-oxidant, and neuroprotective effects of CBD. In particular, CBD exerts positive pharmacological effects in ischemic stroke and other chronic diseases, including Parkinson’s disease, Alzheimer’s disease, and rheumatoid arthritis. The cerebroprotective action of CBD is CB₁ receptor-independent, long-lasting, and has potent anti-oxidant activity. Importantly, CBD use does not lead to tolerance. In this review, we will discuss the therapeutic possibility of CBD as a cerebroprotective agent, highlighting recent pharmacological advances, novel mechanisms, and therapeutic time window of CBD in ischemic stroke.

Niaspan treatment induces neuroprotection after stroke

INTRODUCTION

Niaspan, an extended-release formulation of Niacin (vitamin B3), has been widely used to increase high density lipoprotein (HDL) cholesterol and to prevent cardiovascular diseases and stroke. In this study, we tested whether Niaspan administered acutely after stroke is neuroprotective.

METHODS

Adult male rats (n=8/group) were subjected to 2h of middle cerebral artery occlusion (MCAo) and treated with or without different doses of Niaspan (20, 40 or 80 mg/kg) at 2 and 24h after MCAo. A battery of functional outcome tests was performed, and serum HDL and triglycerides were measured. Rats were sacrificed at 7 days after MCAo and lesion volumes were measured. The optimal dose of Niaspan treatment of stroke was chosen for immunostaining: deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL), cleaved caspase-3, tumor necrosis factor alpha (TNF-alpha), vascular endothelial growth factor (VEGF) and phosphorylated phosphatidylinositol 3-kinase (p-PI3K). Another set of rats (n=4/group) were killed at 7 days after MCAo for Western blot assay.

RESULTS

Niaspan dose-dependently reduced infarct volume and improved functional outcome after stroke. No significant difference in HDL and triglyceride levels was detected between Niaspan treatments and MCAo control groups. Niaspan treatment significantly decreased the number of TUNEL-positive cells (105+/-17) and cleaved caspase-3 expression (381+/-33) in the ischemic brain compared to MCAo control (165+/-18; 650+/-61, respectively; p<or=0.05). Niaspan treatment significantly reduced the expression of TNF-alpha (9.7+/-1.1% vs. 16+/-2.2%; p<or=0.05) and negative correlations were observed between the functional tests and the expression of TNF-alpha (r=-0.71, p<or=0.05). Niaspan treatment also significantly increased the expression of VEGF (5.2+/-0.9%) and PI3K/Akt (0.381+/-0.04%) in the ischemic brain compared with non-treated MCAo control (2.6+/-0.4%; 0.24+/-0.03, respectively; p<or=0.05). The functional outcome was positively correlated with p-PI3K (r=0.7, p<or=0.05).

CONCLUSIONS

Treatment of stroke with Niaspan at 2h after MCAo reduces infarct volume and improves neurological outcome and provides neuroprotection. The neuroprotective effects of Niaspan were associated with reduction of apoptosis and attenuation of TNF-alpha expression. VEGF and the PI3K/Akt pathway may contribute to the Niaspan-induced neuroprotection after stroke.

Vascular endothelial growth factor increases neurogenesis after traumatic brain injury

Activation of endogenous stem cells has been proposed as a novel form of therapy in a variety of neurologic disorders including traumatic brain injury (TBI). Vascular endothelial growth factor (VEGF) is expressed in the brain after TBI and serves as a potent activator of angiogenesis and neurogenesis. In this study, we infused exogenous VEGF into the lateral ventricles of mice for 7 days after TBI using mini-osmotic pumps to evaluate the effects on recovery and functional outcome. The results of our study show that VEGF significantly increases the number of proliferating cells in the subventricular zone and in the perilesion cortex. Fate analysis showed that most newborn cells differentiated into astrocytes and oligodendroglia and only a few cells differentiated into neurons. Functional outcome was significantly better in mice treated with VEGF compared with vehicle-treated animals after TBI. Injury size was significantly smaller at 90 days after TBI in VEGF-treated animals, suggesting additional neuroprotective effects of VEGF. In conclusion, VEGF significantly augments neurogenesis and angiogenesis and reduces lesion volumes after TBI. These changes are associated with significant improvement in recovery rates and functional outcome.

Transgenic ablation of doublecortin-expressing cells suppresses adult neurogenesis and worsens stroke outcome in mice

Injury stimulates neurogenesis in the adult brain, but the role of injury-induced neurogenesis in brain repair and recovery is uncertain. One strategy for investigating this issue is to ablate neuronal precursors and thereby prevent neurogenesis, but this is difficult to achieve in a specific fashion. We produced transgenic mice that express herpes simplex virus thymidine kinase (TK) under control of the promoter for doublecortin (Dcx), a microtubule-associated protein expressed in newborn and migrating neurons. Treatment for 14 days with the antiviral drug ganciclovir (GCV) depleted Dcx-expressing and BrdU-labeled cells from the rostral subventricular zone and dentate gyrus, and abolished neurogenesis and associated neuromigration induced by focal cerebral ischemia. GCV treatment of Dcx-TK transgenic, but not WT, mice also increased infarct size and exacerbated postischemic sensorimotor behavioral deficits measured by rotarod, limb placing, and elevated body swing tests. These findings provide evidence that injury-induced neurogenesis contributes to stroke outcome and might therefore be a target for stroke therapy.

Inhibition of reactive astrocytes with fluorocitrate retards neurovascular remodeling and recovery after focal cerebral ischemia in mice

Glial scarring is traditionally thought to be detrimental after stroke. But emerging studies now suggest that reactive astrocytes may also contribute to neurovascular remodeling. Here, we assessed the effects and mechanisms of metabolic inhibition of reactive astrocytes in a mouse model of stroke recovery. Five days after stroke onset, astrocytes were metabolically inhibited with fluorocitrate (FC, 1 nmol). Markers of reactive astrocytes (glial fibrillary acidic protein (GFAP), HMGB1), markers of neurovascular remodeling (CD31, synaptophysin, PSD95), and behavioral outcomes (neuroscore, rotarod latency) were quantified from 1 to 14 days. As expected, focal cerebral ischemia induced significant neurological deficits in mice. But over the course of 14 days after stroke onset, a steady improvement in neuroscore and rotarod latencies were observed as the mice spontaneously recovered. Reactive astrocytes coexpressing GFAP and HMGB1 increased in peri-infarct cortex from 1 to 14 days after cerebral ischemia in parallel with an increase in the neurovascular remodeling markers CD31, synaptophysin, and PSD95. Compared with stroke-only controls, FC-treated mice demonstrated a significant decrease in HMGB1-positive reactive astrocytes and neurovascular remodeling, as well as a corresponding worsening of behavioral recovery. Our results suggest that reactive astrocytes in peri-infarct cortex may promote neurovascular remodeling, and these glial responses may aid functional recovery after stroke.

VEGF in the nervous system

Vascular endothelial growth factor (VEGF, VEGFA) is critical for blood vessel growth in the developing and adult nervous system of vertebrates. Several recent studies demonstrate that VEGF also promotes neurogenesis, neuronal patterning, neuroprotection and glial growth. For example, VEGF treatment of cultured neurons enhances survival and neurite growth independently of blood vessels. Moreover, evidence is emerging that VEGF guides neuronal migration in the embryonic brain and supports axonal and arterial co-patterning in the developing skin. Even though further work is needed to understand the various roles of VEGF in the nervous system and to distinguish direct neuronal effects from indirect, vessel-mediated effects, VEGF can be considered a promising tool to promote neuronal health and nerve repair.

Menstrual blood cells display stem cell-like phenotypic markers and exert neuroprotection following transplantation in experimental stroke

Cell therapy remains an experimental treatment for neurological disorders. A major obstacle in pursuing the clinical application of this therapy is finding the optimal cell type that will allow benefit to a large patient population with minimal complications. A cell type that is a complete match of the transplant recipient appears as an optimal scenario. Here, we report that menstrual blood may be an important source of autologous stem cells. Immunocytochemical assays of cultured menstrual blood reveal that they express embryonic-like stem cell phenotypic markers (Oct4, SSEA, Nanog), and when grown in appropriate conditioned media, express neuronal phenotypic markers (Nestin, MAP2). In order to test the therapeutic potential of these cells, we used the in vitro stroke model of oxygen glucose deprivation (OGD) and found that OGD-exposed primary rat neurons that were co-cultured with menstrual blood-derived stem cells or exposed to the media collected from cultured menstrual blood exhibited significantly reduced cell death. Trophic factors, such as VEGF, BDNF, and NT-3, were up-regulated in the media of OGD-exposed cultured menstrual blood-derived stem cells. Transplantation of menstrual blood-derived stem cells, either intracerebrally or intravenously and without immunosuppression, after experimentally induced ischemic stroke in adult rats also significantly reduced behavioral and histological impairments compared to vehicle-infused rats. Menstrual blood-derived cells exemplify a source of "individually tailored" donor cells that completely match the transplant recipient, at least in women. The present neurostructural and behavioral benefits afforded by transplanted menstrual blood-derived cells support their use as a stem cell source for cell therapy in stroke.

Deafferentation enhances neurogenesis in the young and middle aged hippocampus but not in the aged hippocampus

Increased neurogenesis in the dentate gyrus (DG) after brain insults such as excitotoxic lesions, seizures, or stroke is a well known phenomenon in the young hippocampus. This plasticity reflects an innate compensatory response of neural stem cells (NSCs) in the young hippocampus to preserve function or minimize damage after injury. However, injuries to the middle-aged and aged hippocampi elicit either no or dampened neurogenesis response, which could be due to an altered plasticity of NSCs and/or the hippocampus with age. We examined whether the plasticity of NSCs to increase neurogenesis in response to a milder injury such as partial deafferentation is preserved during aging. We quantified DG neurogenesis in the hippocampus of young, middle-aged, and aged F344 rats after partial deafferentation. A partial deafferentation of the left hippocampus without any apparent cell loss was induced via administration of Kainic acid (0.5 μg in 1.0 μl) into the right lateral ventricle of the brain. In this model, degeneration of CA3 pyramidal neurons and dentate hilar neurons in the right hippocampus results in loss of commissural axons which leads to partial deafferentation of the dendrites of dentate granule cells and CA1-CA3 pyramidal neurons in the left hippocampus. Quantification of newly born cells that are added to the dentate granule cell layer at postdeafferentation days 4-15 using 5'-bromodeoxyuridine (BrdU) labeling revealed greatly increased addition of newly born cells (∼three fold increase) in the deafferented young and middle-aged hippocampi but not in the deafferented aged hippocampus. Measurement of newly born neurons using doublecortin (DCX) immunostaining also revealed similar findings. Analyses using BrdU-DCX dual immunofluorescence demonstrated no changes in neuronal fate-choice decision of newly born cells after deafferentation, in comparison to the age-matched naive hippocampus in all age groups. Thus, the plasticity of hippocampal NSCs to increase DG neurogenesis in response to a milder injury such as partial hippocampal deafferentation is preserved until middle age but lost at old age.

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.

Variants of the Matrix Metalloproteinase-2 but not the Matrix Metalloproteinase-9 genes significantly influence functional outcome after stroke

Background

Multiple lines of evidence suggest that genetic factors contribute to stroke recovery. The matrix metalloproteinases -2 (MMP-2) and -9 (MMP-9) are modulators of extracellular matrix components, with important regulatory functions in the Central Nervous System (CNS). Shortly after stroke, MMP-2 and MMP-9 have mainly damaging effects for brain tissue. However, MMPs also have a beneficial activity in angiogenesis and neurovascular remodelling during the delayed neuroinflammatory response phase, thus possibly contributing to stroke functional recovery.

Methods

In the present study, the role of MMP-2 and MMP-9 genetic variants in stroke recovery was investigated in 546 stroke patients. Functional outcome was assessed three months after a stroke episode using the modified Rankin Scale (mRS), and patients were classified in two groups: good recovery (mRS ≤ 1) or poor recovery (mRS>1). Haplotype tagging single nucleotide polymorphisms (SNPs) in the MMP-2 (N = 21) and MMP-9 (N = 4) genes were genotyped and tested for association with stroke outcome, adjusting for significant non-genetic clinical variables.

Results

Six SNPs in the MMP-2 gene were significantly associated with stroke outcome (0.0018<P < 0.0415), two of which survived the Bonferroni correction for multiple testing. In the subset of ischemic stroke patients, association of five of these SNPs remained positive (0.0042<P < 0.0306). No significant associations were found for the MMP-9 gene.

Conclusions

The results presented strongly indicate that MMP-2 genetic variants are an important mediator of functional outcome after stroke.

Neuroprotective effect of combined hypoxia-induced VEGF and bone marrow-derived mesenchymal stem cell treatment

PURPOSES

To avoid unwanted adverse effects of higher doses of single treatment of stem cells and gene therapy and increase the therapeutic efficacies, we hypothesized the combined therapy with stem cells and gene therapy. This study assessed the neuroprotective effects of combined gene therapy and stem cell treatment under ischemic hypoxia conditions using hypoxia-inducible vascular endothelial growth factor (VEGF) and bone marrow-derived mesenchymal stem cells (BMSC).

METHODS

Experimental groups included the control which was N2A cells transfected with empty vectors, the transfection only group which was N2A cells treated with pEpo-SV-VEGF alone, the BMSC only group which was N2A cells transfected with empty vectors and cocultured with BMSCs, and the combined treatment group which was N2A cells treated with pEpo-SV-VEGF and cocultured with BMSCs. Each group was transfected for 4 h and cultured at 37 degrees C and 5% CO2 for 24 h. Each group was then cultivated under hypoxic conditions (1% O2) for 12 h. Neuroprotective effects were assessed by reverse transcription polymerase chain reaction, annexin V, and cytotoxicity assay.

RESULTS

Neurons exposed to hypoxic conditions exhibited neuronal apoptosis. Compared to single treatments, the combined hypoxia-inducible VEGF and BMSC treatment demonstrated a significant increase in VEGF expression and decreased neuronal apoptosis.

CONCLUSIONS

These results suggest that combined pEpo-SV-VEGF and BMSC treatment is effective in protecting neurons against hypoxic ischemic injury.

Vascular endothelial growth factor receptor-2 inhibition promotes cell death and limits endothelial cell proliferation in a neonatal rodent model of stroke

BACKGROUND AND PURPOSE

Recent studies in neonatal rodent stroke models suggest that recovery is due in part to upregulation of hypoxia-inducible factor-1-a and its downstream target, vascular endothelial growth factor. Vascular endothelial growth factor is upregulated after a hypoxic insult and is involved in neuronal survival, angiogenesis, and neurogenesis during the recovery process.

METHODS

We performed a 1.5-hour transient middle cerebral artery occlusion in 10-day-old rats with injury verified by diffusion-weighted MRI during occlusion to determine the effects of vascular endothelial growth factor receptor-2 (VEGFR2) inhibition on injury, apoptosis, and angiogenesis. Two days after reperfusion, the pups received either the VEGFR inhibitor, SU5416 (10 mg/kg per dose) or vehicle (1% dimethyl sulfoxide) for 3 days.

RESULTS

VEGFR2 inhibition worsened injury 7 days after injury when compared with the vehicle-treated and injury-alone groups (P<0.01). Furthermore, receptor inhibition was associated with increased VEGFR2 expression 5 days after injury (P<0.05) and increased spectrin cleavage with a shift in favor of the calpain-mediated, caspase-3-independent cleavage (P<0.01). Increased areas of cleaved caspase-3 staining were seen in treated rats at 7 days (P<0.01) There were no differences in gliosis or macrophage recruitment as measured by glial fibrillary acidic protein and Iba-1 expression at this time point. Lastly, VEGFR2 inhibition did not affect the overall vessel surface area but reduced endothelial cell proliferation in injured caudate.

CONCLUSIONS

Inhibition of VEGFR2 signaling worsens injury, affects cell death, and reduces endothelial cell proliferation after neonatal stroke. Injury exacerbation may be in part due to a shift of cell fate from apoptosis to necrosis on the continuum spectrum of cell death as well as effects on angiogenesis in the injured brain.

Growth factors improve neurogenesis and outcome after focal cerebral ischemia

Stem cells have been proposed as a new form of cell-based therapy in a variety of disorders, including acute and degenerative brain diseases. Endogenous neural stem cells (eNSC) reside in the subventricular zone and in the subgranular zone of the hippocampus. eNSC are capable of self-renewal and differentiation into functional glia and neurons. Unfortunately, spontaneous brain regeneration is inefficient for clinically significant improvement following brain injury. However, eNSC responses may be augmented considerably by perturbing the pathways governing cell proliferation, migration and differentiation by application of exogenous growth factors. Importantly, current evidence suggests that such perturbations may lead to better functional outcome after stroke. This article summarizes the progress made in this field.

Neuronal I kappa B kinase beta protects mice from autoimmune encephalomyelitis by mediating neuroprotective and immunosuppressive effects in the central nervous system

Some aspects of CNS-directed autoimmunity in multiple sclerosis are modeled in mice by immunization with myelin Ags where tissue damage is driven by myelin-reactive Th1 and Th17 effector lymphocytes. Whether the CNS plays an active role in controlling such autoimmune diseases is unknown. We used mice in which IkappaB kinase beta was deleted from Ca(2+)/calmodulin-dependent kinase IIalpha-expressing neurons (nIKKbetaKO) to investigate the contribution of neuronal NF-kappaB to the development of myelin oligodendrocyte glycoprotein 35-55-induced experimental autoimmune encephalomyelitis. We show that nIKKbetaKO mice developed a severe, nonresolving disease with increased axon loss compared with controls and this was associated with significantly reduced CNS production of neuroprotective factors (vascular endothelial growth factor, CSF1-R, and FLIP) and increased production of proinflammatory cytokines (IL-6, TNF, IL-12, IL-17, and CD30L) and chemokines. The isolation of CNS-infiltrating monocytes revealed greater numbers of CD4(+) T cells, reduced numbers of NK1.1(+) cells, and a selective accumulation of Th1 cells in nIKKbetaKO CNS from early in the disease. Our results show that neurons play an important role in determining the quality and outcome of CNS immune responses, specifically that neuronal IkappaB kinase beta is required for neuroprotection, suppression of inflammation, limitation of Th1 lymphocyte accumulation, and enhancement of NK cell recruitment in experimental autoimmune encephalomyelitis-affected CNS and stress the importance of neuroprotective strategies for the treatment of multiple sclerosis.

Impaired expression of neuroprotective molecules in the HIF-1alpha pathway following traumatic brain injury in aged mice

Elderly traumatic brain injury (TBI) patients have higher rates of mortality and worse functional outcome than non-elderly TBI patients. The mechanisms involved in poor outcomes in the elderly are not well understood. Hypoxia-inducible factor-1 alpha (HIF-1alpha) is a basic helix-loop-helix transcription factor that modulates expression of key genes involved in neuroprotection. In this study, we studied the expression of HIF-1alpha and its target survival genes, heme oxygenase-1 (HO-1), vascular endothelial growth factor (VEGF), and erythropoietin (EPO) in the brains of adult versus aged mice following controlled cortical impact (CCI) injury. Adult (5-6 months) and aged (23-24 months) C57Bl/6 mice were injured using a CCI device. At 72 h post-injury, mice were sacrificed and the injured cortex was used for mRNA and protein analysis using real-time reverse transcription--polymerase chain reaction (RT-PCR) and Western blotting protocols. Following injury, HIF-1alpha, HO-1, and VEGF showed upregulation in both the young and aged mice, but in the aged animals the increase in HIF-1alpha and VEGF in response to injury was much lower than in the adult injured animals. EPO was upregulated in the adult injured brain, but not in the aged injured brain. These results support the hypothesis that reduced expression of genes in the HIF-1alpha neuroprotective pathway in aging may contribute to poor prognosis in the elderly following TBI.

Forebrain neurogenesis after focal Ischemic and traumatic brain injury

Neural stem cells persist in the adult mammalian forebrain and are a potential source of neurons for repair after brain injury. The two main areas of persistent neurogenesis, the subventricular zone (SVZ)-olfactory bulb pathway and hippocampal dentate gyrus, are stimulated by brain insults such as stroke or trauma. Here we focus on the effects of focal cerebral ischemia on SVZ neural progenitor cells in experimental stroke, and the influence of mechanical injury on adult hippocampal neurogenesis in models of traumatic brain injury (TBI). Stroke potently stimulates forebrain SVZ cell proliferation and neurogenesis. SVZ neuroblasts are induced to migrate to the injured striatum, and to a lesser extent to the peri-infarct cortex. Controversy exists as to the types of neurons that are generated in the injured striatum, and whether adult-born neurons contribute to functional restoration remains uncertain. Advances in understanding the regulation of SVZ neurogenesis in general, and stroke-induced neurogenesis in particular, may lead to improved integration and survival of adult-born neurons at sites of injury. Dentate gyrus cell proliferation and neurogenesis similarly increase after experimental TBI. However, pre-existing neuroblasts in the dentate gyrus are vulnerable to traumatic insults, which appear to stimulate neural stem cells in the SGZ to proliferate and replace them, leading to increased numbers of new granule cells. Interventions that stimulate hippocampal neurogenesis appear to improve cognitive recovery after experimental TBI. Transgenic methods to conditionally label or ablate neural stem cells are beginning to further address critical questions regarding underlying mechanisms and functional significance of neurogenesis after stroke or TBI. Future therapies should be aimed at directing appropriate neuronal replacement after ischemic or traumatic injury while suppressing aberrant integration that may contribute to co-morbidities such as epilepsy or cognitive impairment.

Neuroprotection using gene therapy to induce vascular endothelial growth factor-A expression

Engineered zinc-finger protein (ZFP) transcription factors induce the expression of endogenous genes and can be remotely delivered using adenoviral vectors. One such factor, Ad-32Ep65-Flag (Ad-p65), targets and induces expression of vascular endothelial growth factor (VEGF; also called VEGF-A) splice variants in their normal biological stoichiometry. We show that Ad-p65 transfection of primary motor neurons results in VEGF variant expression and a significant increase in axon outgrowth in these cells. Given the neuroprotective effects of VEGF and its ability to increase neurite outgrowth, we examined the efficacy of Ad-p65 to enhance motor neuron regeneration in vivo using rats that have undergone recurrent laryngeal nerve (RLN)-crush injury. Injection of Ad-p65 after RLN crush accelerated the return of vocal fold mobility and the percentage of nerve-endplate contacts in the thyroarytenoid muscle. Overall, adenoviral delivery of an engineered ZFP transcription factor inducing VEGF-A splice variant expression enhances nerve regeneration. ZFP transcription factor gene therapy to increase expression of the full complement of VEGF-A splice variants is a promising avenue for the treatment of nerve injury and neurodegeneration.

Vascular endothelial growth factor prevents G93A-SOD1-induced motor neuron degeneration

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disorder characterized by selective loss of motor neurons (MNs). Twenty percent of familial ALS cases are associated with mutations in Cu(2+)/Zn(2+) superoxide dismutase (SOD1). To specifically understand the cellular mechanisms underlying mutant SOD1 toxicity, we have established an in vitro model of ALS using rat primary MN cultures transfected with an adenoviral vector encoding a mutant SOD1, G93A-SOD1. Transfected cells undergo axonal degeneration and alterations in biochemical responses characteristic of cell death such as activation of caspase-3. Vascular endothelial growth factor (VEGF) is an angiogenic and neuroprotective growth factor that can increase axonal outgrowth, block neuronal apoptosis, and promote neurogenesis. Decreased VEGF gene expression in mice results in a phenotype similar to that seen in patients with ALS, thus linking loss of VEGF to the pathogenesis of MN degeneration. Decreased neurotrophic signals prior to and during disease progression may increase MN susceptibility to mutant SOD1-induced toxicity. In this study, we demonstrate a decrease in VEGF and VEGFR2 levels in the spinal cord of G93A-SOD1 ALS mice. Furthermore, in isolated MN cultures, VEGF alleviates the effects of G93A-SOD1 toxicity and neuroprotection involves phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling. Overall, these studies validate the usefulness of VEGF as a potential therapeutic factor for the treatment of ALS and give valuable insight into the responsible signaling pathways and mechanisms involved.

Intact and injured endothelial cells differentially modulate postnatal murine forebrain neural stem cells

Neural stem cells (NSCs) persist in the forebrain subventricular zone (SVZ) within a niche containing endothelial cells. Evidence suggests that endothelial cells stimulate NSC expansion and neurogenesis. Experimental stroke increases neurogenesis and angiogenesis, but how endothelial cells influence stroke-induced neurogenesis is unknown. We hypothesized intact or oxygen-glucose deprived (OGD) endothelial cells secrete factors that enhance neurogenesis. We co-cultured mouse SVZ neurospheres (NS) with endothelial cells, or differentiated NS in endothelial cell-conditioned medium (ECCM). NS also were expanded in ECCM from OGD-exposed (OGD-ECCM) endothelial cells to assess injury effects. ECCM significantly increased NS production. NS co-cultured with endothelial cells or ECCM generated more immature-appearing neurons and oligodendrocytes, and astrocytes with radial glial-like/reactive morphology than controls. OGD-ECCM stimulated neuroblast migration and yielded neurons with longer processes and more branching. These data indicate that intact and injured endothelial cells exert differing effects on NSCs, and suggest targets for stimulating regeneration after brain insults.

Attenuation of brain response to vascular endothelial growth factor-mediated angiogenesis and neurogenesis in aged mice

BACKGROUND AND PURPOSE

Alterations of neuroangiogenic response play important roles in the development of aging-related neurodisorders and affect gene-based therapies. We tested brain response to vascular endothelial growth factor (VEGF) in aged mice.

METHODS

Adeno-associated viral vector (AAV)-VEGF, an adeno-associated viral vector expressing VEGF, was injected into the brain of 3-, 12-, and 24-month-old mice. AAV-LacZ-injected mice were used as controls (n=6). Before euthanasia at 6 weeks after vector injection, the mice were intraperitoneally injected with 5-bromodeoxyuridine for 3 consecutive days. The vascular density and the number of neuroprogenitors were analyzed.

RESULTS

Injection of AAV-VEGF increased the vascular density in the brain of 3-, 12-, and 24-month-old mice by 22%+/-7% (AAV-VEGF: 320+/-15 per 10x field versus AAV-LacZ: 263+/-8, P<0.05), 20%+/-8 (AAV-VEGF: 300+/-9 versus AAV-LacZ: 250+/-11, P<0.05), and 7%+/-16% (AAV-VEGF: 257+/-27 versus AAV-LacZ: 236+/-13, P=0.283), respectively. There were more VEGF receptor-positive neuroprogenitors in the subventricular zone of AAV-VEGF-injected 3- (22+/-2) and 12-month-old mice (21+/-5) than that of 24-month-old mice (7+/-1). More 5-bromodeoxyuridine-positive endothelial cells and neuroprogenitors were detected around the injection site and subventricular zone of 3- (13+/-4) and 12-month-old mice (14+/-5) than that of 24-month-old mice (1+/-1). VEGF receptor 2 was upregulated in AAV-VEGF-injected brains of 3- and 12-month-old mice, but not in 24-month-old mice.

CONCLUSIONS

The angiogenic and neurogenic response to VEGF stimulation is attenuated in the aged mouse brain, which may be due to reduced VEGF receptor activity.

Postischemic IGF-1 gene transfer promotes neurovascular regeneration after experimental stroke

Promoting neural regeneration after cerebral infarction has emerged as a potential approach for the treatment of stroke. Insulin-like growth factor 1 (IGF-1) possesses both neurotrophic and angiogenic properties. The aim of this study was to determine whether postischemic gene transfer of IGF-1 enhances neurovascular regeneration in a mouse model of permanent focal cerebral ischemia. Long-term cerebral IGF-1 overexpression was achieved with adeno-associated viral vector (AAV) by stereotaxic injection at 24 h after a stroke. Adeno-associated viral vector-green fluorescent protein (GFP) or saline was injected as a control. The success of postischemic gene transduction was confirmed by a strong GFP signal and by increased IGF-1 protein expression in the peri-infarct region. Postischemic gene transfer of IGF-1 significantly enhanced vascular density at 8 weeks after a stroke in the peri-infarct and injection needle tract area compared with AAV-GFP or saline treatment, as shown by immunohistochemical staining with the vascular marker lectin. Furthermore, increased vascular density was associated with improved local vascular perfusion. Immunohistochemical staining with the neuronal progenitor marker, DCX (doublecortin), and the cell proliferation marker, BrdU (5-bromo-2-deoxyuridine-5-monophosphate), indicated that AAV-IGF-1 treatment potently increased neurogenesis compared with AAV-GFP injection. These data show that postischemic treatment of IGF-1 effectively promoted neural and vascular regeneration in the chronic stage of cerebral infarction.

Activation of mammalian Tolloid-like 1 expression by hypoxia in human neuroblastoma SH-SY5Y cells

Mammalian Tolloid-like 1 (mTll-1) is an astacin metalloprotease that is a member of the Tolloid family of proteins. mTll-1 cleaves chordin, an inhibitor of bone morphogenetic proteins (BMPs) and potentiates activity of the BMPs. Prenatal stress and glucocorticoids decrease mTll-1 expression whereas voluntary exercise increase mTll-1 gene expression in the mouse hippocampus. Here, we studied the underlying molecular mechanisms by which hypoxia regulates human mTll-1 gene expression. When cells were subjected to hypoxia, the expression of endogenous mTll-1 was upregulated in SH-SY5Y human neuroblastoma cells. Dual-luciferase assay and site-directed mutagenesis showed the presence of hypoxia responsive elements (HREs) at position 625 that was essential for activation of mTll-1 expression under hypoxic conditions. The binding of hypoxia-inducible factor (HIF-1) protein to the HREs was confirmed by gel shift assay. These results indicate that the HRE motif is directly involved in the activation of the mTll-1 transcription under hypoxic conditions.

Brain angiogenesis in developmental and pathological processes: neurovascular injury and angiogenic recovery after stroke

Pathophysiologic responses in brain after stroke are highly complex. Thus far, a singular focus on saving neurons alone has not revealed any clinically effective neuroprotectants. To address this limitation, the concept of a neurovascular unit was developed. Within this conceptual framework, brain function and dysfunction are manifested at the level of cell-cell signaling between neuronal, glial and vascular elements. For stroke, coordinated responses at the neurovascular interface will mediate acute as well as chronic events in ischemic and hemorrhagic brain tissue. In this minireview, we briefly survey two representative examples of neurovascular responses in stroke. During the early acute phase of neurovascular injury, blood-brain barrier perturbations should predominate with key roles for various matrix proteases. During the delayed phase, brain angiogenesis may provide the critical neurovascular substrates for neuronal remodeling. In this minireview, we propose the hypothesis that the biphasic nature of neurovascular responses represents an endogenous attempt by damaged parenchyma to trigger brain angiogenesis and repair. This phenomenon may allow acute deleterious signals to transition into beneficial effects during stroke recovery. Understanding how neurovascular signals and substrates make the transition from initial injury to angiogenic recovery will be important if we are to find new therapeutic approaches for stroke.

Induction of neuronal vascular endothelial growth factor expression by cAMP in the dentate gyrus of the hippocampus is required for antidepressant-like behaviors

The cAMP cascade and vascular endothelial growth factor (VEGF) are critical modulators of depression. Here we have tested whether the antidepressive effect of the cAMP cascade is mediated by VEGF in the adult hippocampus. We used a conditional genetic system in which the Aplysia octopamine receptor (Ap oa(1)), a G(s)-coupled receptor, is transgenically expressed in the forebrain neurons of mice. Chronic activation of the heterologous Ap oa(1) by its natural ligand evoked antidepressant-like behaviors, accompanied by enhanced phosphorylation of cAMP response element-binding protein and transcription of VEGF in hippocampal dentate gyrus (DG) neurons. Selective knockdown of VEGF in these cells during the period of cAMP elevation inhibited the antidepressant-like behaviors. These findings reveal a molecular interaction between the cAMP cascade and VEGF expression, and the pronounced behavioral consequences of this interaction shed light on the mechanism underlying neuronal VEGF functions in antidepression.

Angiopoietin 2 mediates the differentiation and migration of neural progenitor cells in the subventricular zone after stroke

Ischemic stroke stimulates neurogenesis in the adult rodent brain. The molecules underlying stroke-induced neurogenesis have not been fully investigated. Using real-time reverse transcription-PCR, we found that stroke substantially up-regulated angiopoietin 2 (ANG2), a proangiogenic gene, expression in subventricular zone neural progenitor cells. Incubation of neural progenitor cells with recombinant human ANG2 significantly increased the number of beta-III tubulin-positive cells, a marker of immature neurons, but did not alter the number of glial fibrillary acidic protein (GFAP)-positive cells, a marker of astrocytes, suggesting that ANG2 promotes neuronal differentiation. Blockage of the ANG2 receptor, Tie2, with small interference RNA (siRNA)-Tie2 attenuated recombinant human ANG2 (rhANG2)-increased beta-III tubulin mRNA levels compared with levels in the progenitor cells transfected with control siRNA. Chromatin immunoprecipitation analysis revealed that CCAAT/enhancer-binding protein (C/EBP beta) up-regulated by rhANG2 bound to beta-III tubulin, which is consistent with published data that there are several C/EBP beta binding sites in the promoter of beta-III tubulin gene. In addition, rhANG2 enhanced migration of neural progenitor cells measured by single neurosphere assay. Blockage of Tie2 with siRNA-Tie2 and a Tie2-neutralizing antibody did not suppress ANG2-enhanced migration. However, inhibition of matrix metalloproteinases with GM6001 blocked ANG2-enhanced migration. Collectively, our data suggest that interaction of ANG2, a proangiogenic factor, with its receptor Tie2 promotes neural progenitor cell differentiation into neuronal lineage cells, whereas ANG2 regulates neural progenitor cell migration through matrix metalloproteinases, which do not require its receptor Tie2.

Preconditioning and tolerance against cerebral ischaemia: from experimental strategies to clinical use

Neuroprotection and brain repair in patients after acute brain damage are still major unfulfilled medical needs. Pharmacological treatments are either ineffective or confounded by adverse effects. Consequently, endogenous mechanisms by which the brain protects itself against noxious stimuli and recovers from damage are being studied. Research on preconditioning, also known as induced tolerance, over the past decade has resulted in various promising strategies for the treatment of patients with acute brain injury. Several of these strategies are being tested in randomised clinical trials. Additionally, research into preconditioning has led to the idea of prophylactically inducing protection in patients such as those undergoing brain surgery and those with transient ischaemic attack or subarachnoid haemorrhage who are at high risk of brain injury in the near future. In this Review, we focus on the clinical issues relating to preconditioning and tolerance in the brain; specifically, we discuss the clinical situations that might benefit from such procedures. We also discuss whether preconditioning and tolerance occur naturally in the brain and assess the most promising candidate strategies that are being investigated.

Mechanisms and targets for angiogenic therapy after stroke

Stroke remains a major health problem worldwide, and is the leading cause of serious long-term disability. Recent findings now suggest that strategies to enhance angiogenesis after focal cerebral ischemia may provide unique opportunities to improve clinical outcomes during stroke recovery. In this mini-review, we survey emerging mechanisms and potential targets for angiogenic therapies in brain after stroke. Multiple elements may be involved, including growth factors, adhesion molecules and progenitor cells. Furthermore, cross talk between angiogenesis and neurogenesis may also provide additional substrates for plasticity and remodeling in the recovering brain. A better understanding of the molecular interplay between all these complex pathways may lead to novel therapeutic avenues for tackling this difficult disease.

Enhanced neurogenesis and cell migration following focal ischemia and peripheral stimulation in mice

Peripheral stimulation and physical therapy can promote neurovascular plasticity and functional recovery after CNS disorders such as ischemic stroke. Using a rodent model of whisker-barrel cortex stroke, we have previously demonstrated that whisker activity promotes angiogenesis in the penumbra of the ischemic barrel cortex. This study explored the potential of increased peripheral activity to promote neurogenesis and neural progenitor migration toward the ischemic barrel cortex. Three days after focal barrel cortex ischemia in adult mice, whiskers were manually stimulated (15 min x 3 times/day) to enhance afferent signals to the ischemic barrel cortex. 5-Bromo-2'-deoxyuridine (BrdU, i.p.) was administered once daily to label newborn cells. At 14 days after stroke, whisker stimulation significantly increased vascular endothelial growth factor and stromal-derived factor-1 expression in the penumbra. The whisker stimulation animals showed increased doublecortin (DCX) positive and DCX/BrdU-positive cells in the ipsilateral corpus of the white matter but no increase in BrdU-positive cells in the subventricular zone, suggesting a selective effect on neuroblast migration. Neurogenesis indicated by neuronal nuclear protein and BrdU double staining was also enhanced by whisker stimulation in the penumbra at 30 days after stroke. Local cerebral blood flow was better recovered in mice that received whisker stimulation. It is suggested that the enriched microenvironment created by specific peripheral stimulation increases regenerative responses in the postischemic brain and may benefit long-term functional recovery from ischemic stroke.

Nitric oxide donor up-regulation of SDF1/CXCR4 and Ang1/Tie2 promotes neuroblast cell migration after stroke

We tested the hypothesis that a nitric oxide donor, DETA-NONOate, up-regulates stromal cell-derived factor-1 (SDF1) and angiopoietin 1 (Ang1) in the ischemic brain and their respective receptors chemokine CXC motif receptor 4 (CXCR4) and Tie2 in the subventricular zone (SVZ) and thereby promote SVZ neuroblast cell migration after stroke. C57BL/6J mice were subjected to middle cerebral artery occlusion (MCAo), and 24 hr later DETA-NONOate (0.4 mg/kg) or phosphate-buffered solution was intravenously administered. Mice were sacrificed at 14 days for histological assessment or sacrificed at 3 days for analysis by real-time polymerase chain reaction and migration after MCAo. To elucidate whether SDF1/CXCR4 and Ang1/Tie2 pathways mediate DETA-NONOate-induced SVZ migration after stroke, SDF1alpha, Ang1 peptide, a specific antagonist of CXCR4 (AMD3100), and a neutralizing antibody of Tie2 (anti-Tie2) were used in vitro. DETA-NONOate significantly increased the percentage area of doublecortin (DCX, a marker of migrating neuroblasts)-immunoreactive cells in the SVZ and ischemic boundary zone. DETA-NONOate significantly increased the expression of SDF1 and Ang1 in the ischemic border and up-regulated CXCR4 and Tie2 in the SVZ compared with MCAo control. DCX-positive cell migration from SVZ explants was significantly increased in the DETA-NONOate treatment group compared with MCAo-alone animals. In vitro, SDF1alpha and Ang1 significantly increased SVZ explants cell migration. In addition, inhibition of CXCR4 or Tie2 significantly attenuated DETA-NONOate-induced SVZ cell migration. Our data indicate that treatment of stroke with a nitric oxide donor up-regulates SDF1/CXCR4 and Ang1/Tie2 pathways and thereby likely increases SVZ neuroblast cell migration.

VEGF-A/VEGFR-2 signaling leading to cAMP response element-binding protein phosphorylation is a shared pathway underlying the protective effect of preconditioning on neurons and endothelial cells

Preconditioning protects endothelial cells as well as neurons from ischemic injury. In 7-d-old rat pups, ligating the carotid artery 1 h before hypoxia damaged the ipsilateral cerebral hemisphere; in contrast, ligating the artery 24 h before hypoxia provided complete neuroprotection. The protective effect of the 24 h artery ligation preconditioning model requires the activation of cAMP response element-binding protein (CREB). We tested the hypothesis that vascular endothelial growth factor (VEGF)-A/VEGF receptor-2 (VEGFR-2) signaling that leads to CREB activation is the shared pathway underlying the protective effect of preconditioning in neurons and endothelial cells. VEGF-A, VEGFR-1, or VEGFR-2 was inhibited by antisense oligodeoxynucleotides (ODNs) in vivo and by a VEGF-A neutralizing antibody or VEGFR-2 inhibitor in vitro. CREB phosphorylation (pCREB) and VEGF-A and VEGFR-2 expression were increased and colocalized in vascular endothelial cells and neurons in the ipsilateral cerebral cortex 24 h after ligation. The antisense ODN blockades of VEGF-A and VEGFR-2 decreased pCREB and reduced the protection of 24 h ligation preconditioning. Furthermore, oxygen-glucose deprivation (OGD) preconditioning upregulated VEGF-A, VEGFR-2, and pCREB levels and protected immortalized H19-7 neuronal cells and b.End3 vascular endothelial cells against 24 h OGD cell death. Blocking VEGF-A or VEGFR-2 reduced CREB activation and the effects of OGD preconditioning in neuronal cells and endothelial cells. Transfecting a serine-133 phosphorylation mutant CREB also inhibited the protective effect of OGD preconditioning. We conclude that VEGF-A/VEGFR-2 signaling leading to CREB phosphorylation is the shared pathway underlying the preconditioning-induced protective effect in neurons and vascular endothelial cells in the developing brain.

Ex vivo VEGF delivery by neural stem cells enhances proliferation of glial progenitors, angiogenesis, and tissue sparing after spinal cord injury

The present study was undertaken to examine multifaceted therapeutic effects of vascular endothelial growth factor (VEGF) in a rat spinal cord injury (SCI) model, focusing on its capability to stimulate proliferation of endogenous glial progenitor cells. Neural stem cells (NSCs) can be genetically modified to efficiently transfer therapeutic genes to diseased CNS. We adopted an ex vivo approach using immortalized human NSC line (F3 cells) to achieve stable and robust expression of VEGF in the injured spinal cord. Transplantation of NSCs retrovirally transduced to overexpress VEGF (F3.VEGF cells) at 7 days after contusive SCI markedly elevated the amount of VEGF in the injured spinal cord tissue compared to injection of PBS or F3 cells without VEGF. Concomitantly, phosphorylation of VEGF receptor flk-1 increased in F3.VEGF group. Stereological counting of BrdU+ cells revealed that transplantation of F3.VEGF significantly enhanced cellular proliferation at 2 weeks after SCI. The number of proliferating NG2+ glial progenitor cells (NG2+/BrdU+) was also increased by F3.VEGF. Furthermore, transplantation of F3.VEGF increased the number of early proliferating cells that differentiated into mature oligodendrocytes, but not astrocytes, at 6 weeks after SCI. F3.VEGF treatment also increased the density of blood vessels in the injured spinal cord and enhanced tissue sparing. These anatomical results were accompanied by improved BBB locomotor scores. The multifaceted effects of VEGF on endogenous gliogenesis, angiogenesis, and tissue sparing could be utilized to improve functional outcomes following SCI.

Neural differentiation potential of human bone marrow-derived mesenchymal stromal cells: misleading marker gene expression

BACKGROUND

In contrast to pluripotent embryonic stem cells, adult stem cells have been considered to be multipotent, being somewhat more restricted in their differentiation capacity and only giving rise to cell types related to their tissue of origin. Several studies, however, have reported that bone marrow-derived mesenchymal stromal cells (MSCs) are capable of transdifferentiating to neural cell types, effectively crossing normal lineage restriction boundaries. Such reports have been based on the detection of neural-related proteins by the differentiated MSCs. In order to assess the potential of human adult MSCs to undergo true differentiation to a neural lineage and to determine the degree of homogeneity between donor samples, we have used RT-PCR and immunocytochemistry to investigate the basal expression of a range of neural related mRNAs and proteins in populations of non-differentiated MSCs obtained from 4 donors.

RESULTS

The expression analysis revealed that several of the commonly used marker genes from other studies like nestin, Enolase2 and microtubule associated protein 1b (MAP1b) are already expressed by undifferentiated human MSCs. Furthermore, mRNA for some of the neural-related transcription factors, e.g. Engrailed-1 and Nurr1 were also strongly expressed. However, several other neural-related mRNAs (e.g. DRD2, enolase2, NFL and MBP) could be identified, but not in all donor samples. Similarly, synaptic vesicle-related mRNA, STX1A could only be detected in 2 of the 4 undifferentiated donor hMSC samples. More significantly, each donor sample revealed a unique expression pattern, demonstrating a significant variation of marker expression.

CONCLUSION

The present study highlights the existence of an inter-donor variability of expression of neural-related markers in human MSC samples that has not previously been described. This donor-related heterogeneity might influence the reproducibility of transdifferentiation protocols as well as contributing to the ongoing controversy about differentiation capacities of MSCs. Therefore, further studies need to consider the differences between donor samples prior to any treatment as well as the possibility of harvesting donor cells that may be inappropriate for transplantation strategies.

Cell migration in the normal and pathological postnatal mammalian brain

In the developing brain, cell migration is a crucial process for structural organization, and is therefore highly regulated to allow the correct formation of complex networks, wiring neurons, and glia. In the early postnatal brain, late developmental processes such as the production and migration of astrocyte and oligodendrocyte progenitors still occur. Although the brain is completely formed and structured few weeks after birth, it maintains a degree of plasticity throughout life, including axonal remodeling, synaptogenesis, but also neural cell birth, migration and integration. The subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus are the two main neurogenic niches in the adult brain. Neural stem cells reside in these structures and produce progenitors that migrate toward their ultimate location: the olfactory bulb and granular cell layer of the DG respectively. The aim of this review is to synthesize the increasing information concerning the organization, regulation and function of cell migration in a mature brain. In a normal brain, proteins involved in cell-cell or cell-matrix interactions together with secreted proteins acting as chemoattractant or chemorepellant play key roles in the regulation of neural progenitor cell migration. In addition, recent data suggest that gliomas arise from the transformation of neural stem cells or progenitor cells and that glioma cell infiltration recapitulates key aspects of glial progenitor migration. Thus, we will consider glioma migration in the context of progenitor migration. Finally, many observations show that brain lesions and neurological diseases trigger neural stem/progenitor cell activation and migration toward altered structures. The factors involved in such cell migration/recruitment are just beginning to be understood. Inflammation which has long been considered as thoroughly disastrous for brain repair is now known to produce some positive effects on stem/progenitor cell recruitment via the regulation of growth factor signaling and the secretion of a number of chemoattractant cytokines. This knowledge is crucial for the development of new therapeutic strategies. One of these strategies could consist in increasing the mobilization of endogenous progenitor cells that could replace lost cells and improve functional recovery.

Status epilepticus during old age is not associated with enhanced hippocampal neurogenesis

Increased production of new neurons in the adult dentate gyrus (DG) by neural stem/progenitor cells (NSCs) following acute seizures or status epilepticus (SE) is a well known phenomenon. However, it is unknown whether NSCs in the aged DG have similar ability to upregulate neurogenesis in response to SE. We examined DG neurogenesis after the induction of continuous stages III-V seizures (SE) for over 4 h in both young adult (5-months old) and aged (24-months old) F344 rats. The seizures were induced through 2-4 graded intraperitoneal injections of the excitotoxin kainic acid (KA). Newly born cells in the DG were labeled via daily intraperitoneal injections of the 5'-bromodeoxyuridine (BrdU) for 12 days, which commenced shortly after the induction of SE in KA-treated rats. New cells and neurons in the subgranular zone (SGZ) and the granule cell layer (GCL) were analyzed at 24 h after the last BrdU injection using BrdU and doublecortin (DCX) immunostaining, BrdU-DCX and BrdU-NeuN dual immunofluorescence and confocal microscopy, and stereological cell counting. Status epilepticus enhanced the numbers of newly born cells (BrdU(+) cells) and neurons (DCX(+) neurons) in young adult rats. In contrast, similar seizures in aged rats, though greatly increased the number of newly born cells in the SGZ/GCL, failed to increase neurogenesis due to a greatly declined neuronal fate-choice decision of newly born cells. Only 9% of newly born cells in the SGZ/GCL differentiated into neurons in aged rats that underwent SE, in comparison to the 76% neuronal differentiation observed in age-matched control rats. Moreover, the number of newly born cells that migrate abnormally into the dentate hilus (i.e., ectopic granule cells) after SE in the aged hippocampus is 92% less than that observed in the young adult hippocampus after similar SE. Thus, SE fails to increase the addition of new granule cells to the GCL in the aged DG, despite a considerable upregulation in the production of new cells, and SE during old age leads to much fewer ectopic granule cells. These results have clinical relevance because earlier studies have implied that both increased and abnormal neurogenesis occurring after SE in young animals contributes to chronic epilepsy development.