VEGF-C is a trophic factor for neural progenitors in the vertebrate embryonic brain

Vascular endothelial growth factor receptor 3 directly regulates murine neurogenesis

Neural stem cells (NSCs) are slowly dividing astrocytes that are intimately associated with capillary endothelial cells in the subventricular zone (SVZ) of the brain. Functionally, members of the vascular endothelial growth factor (VEGF) family can stimulate neurogenesis as well as angiogenesis, but it has been unclear whether they act directly via VEGF receptors (VEGFRs) expressed by neural cells, or indirectly via the release of growth factors from angiogenic capillaries. Here, we show that VEGFR-3, a receptor required for lymphangiogenesis, is expressed by NSCs and is directly required for neurogenesis. Vegfr3:YFP reporter mice show VEGFR-3 expression in multipotent NSCs, which are capable of self-renewal and are activated by the VEGFR-3 ligand VEGF-C in vitro. Overexpression of VEGF-C stimulates VEGFR-3-expressing NSCs and neurogenesis in the SVZ without affecting angiogenesis. Conversely, conditional deletion of Vegfr3 in neural cells, inducible deletion in subventricular astrocytes, and blocking of VEGFR-3 signaling with antibodies reduce SVZ neurogenesis. Therefore, VEGF-C/VEGFR-3 signaling acts directly on NSCs and regulates adult neurogenesis, opening potential approaches for treatment of neurodegenerative diseases.

Vascular endothelial growth factors and receptors: anti-angiogenic therapy in the treatment of cancer

Vascular endothelial growth factors (VEGFs) are critical regulators of vascular and lymphatic function during development, in health and in disease. There are five mammalian VEGF ligands and three VEGF receptor tyrosine kinases. In addition, several VEGF co-receptors that lack intrinsic catalytic activity, but that indirectly modulate the responsiveness to VEGF contribute to the final biological effect. This review describes the molecular features of VEGFs, VEGFRs and co-receptors with focus on their role in the treatment of cancer.

Evolution of the VEGF-regulated vascular network from a neural guidance system

The vascular network is closely linked to the neural system, and an interdependence is displayed in healthy and in pathophysiological responses. How has close apposition of two such functionally different systems occurred? Here, we present a hypothesis for the evolution of the vascular network from an ancestral neural guidance system. Biological cornerstones of this hypothesis are the vascular endothelial growth factor (VEGF) protein family and cognate receptors. The primary sequences of such proteins are conserved from invertebrates, such as worms and flies that lack discernible vascular systems compared to mammals, but all these systems have sophisticated neuronal wiring involving such molecules. Ancestral VEGFs and receptors (VEGFRs) could have been used to develop and maintain the nervous system in primitive eukaryotes. During evolution, the demands of increased morphological complexity required systems for transporting molecules and cells, i.e., biological conductive tubes. We propose that the VEGF-VEGFR axis was subverted by evolution to mediate the formation of biological tubes necessary for transport of fluids, e.g., blood. Increasingly, there is evidence that aberrant VEGF-mediated responses are also linked to neuronal dysfunctions ranging from motor neuron disease, stroke, Parkinson's disease, Alzheimer's disease, ischemic brain disease, epilepsy, multiple sclerosis, and neuronal repair after injury, as well as common vascular diseases (e.g., retinal disease). Manipulation and correction of the VEGF response in different neural tissues could be an effective strategy to treat different neurological diseases.

Expression of vascular endothelial growth factor receptor-3 mRNA in the developing rat cerebellum

Vascular endothelial growth factor receptor (VEGFR)-3, a receptor for VEGF-C and VEGF-D, has recently been suggested to play an important role during neuronal development. To characterize its potential role in CNS ontogenesis, we investigated the spatiotemporal and cellular expression of VEGFR-3 in developing and mature rat cerebellum using in situ hybridization. VEGFR-3 expression appeared as early as E15, and was restricted to the ventricular zone of the cerebellar primordium, the germinative neuroepithelium, but was absent by E20. Instead, the expression area of VEGFR-3 in the cerebellum grew in parallel with cerebellar development. From E20 on, two populations of VEGFR-3-expressing cells can be clearly distinguished in the developing cerebellum: a population of differentiating and postmitotic neurons and the Bergmann glia. VEGFR-3 expression in neurons occurred during the period of neuronal differentiation, and increased with maturation. In particular, the expression of VEGFR-3 mRNA revealed different temporal patterns in different neuronal populations. Neurons generated early, Purkinje cells, and deep nuclear neurons expressed VEGFR-3 mRNA during late embryonic stages, whereas VEGFR-3 transcription in local interneurons appeared by P14 with weaker expression. In addition, Bergmann glia expressed VEGFR-3 throughout cerebellar maturation into adulthood. However, receptor expression was absent in the progenitors in the external granular layer and during further migration. The results of this study suggest that VEGFR-3 has even broader functions than previously thought, regulating both developmental processes and adult neuronal function in the cerebellum.

New insights into the development of lymphoid tissues

Secondary lymphoid organs are important locations for the initiation of adaptive immune responses. They develop before birth, and their formation requires interaction between lymphotoxin-α₁ß₂-expressing lymphoid-tissue inducer cells and lymphotoxin-ß receptor-expressing stromal organizer cells. Here, we discuss new insights into the earliest phases of peripheral lymph node and Peyer's patch formation that occur before lymphotoxin-ß receptor signalling and suggest a role for the developing nervous system. In addition, we discuss the differing requirements for the postnatal formation of mucosa-associated lymphoid tissues and tertiary lymphoid structures that develop at sites of chronic inflammation.

Maternal dietary choline deficiency alters angiogenesis in fetal mouse hippocampus

We examined whether maternal dietary choline modulates angiogenesis in fetal brain. Pregnant C57BL/6 mice were fed either a choline-deficient (CD), control (CT), or choline-supplemented diet (CS) from days 12 to 17 (E12-17) of pregnancy and then fetal brains were studied. In CD fetal hippocampus, proliferation of endothelial cells (EC) was decreased by 32% (p < 0.01 vs. CT or CS) while differentiated EC clusters (expressing factor VIII related antigen (RA)) increased by 25% (p < 0.01 vs. CT or CS). These changes were associated with > 25% decrease in the number of blood vessels in CD fetal hippocampus (p < 0.01 vs. CT and CS), with no change in total cross-sectional area of these blood vessels. Expression of genes for the angiogenic signals derived from both endothelial and neuronal progenitor cells (NPC) was increased in CD fetal hippocampus VEGF C (Vegfc), 2.0-fold, p < 0.01 vs. CT and angiopoietin 2 (Angpt2), 2.1-fold, (p < 0.01 vs. CT)). Similar increased expression was observed in NPC isolated from E14 fetal mouse brains and exposed to low (5 microM), CT (70 microM), or high choline (280 microM) media for 72 h (low choline caused a 9.7-fold increase in relative gene expression of Vegfc (p < 0.001 vs. CT and high) and a 3.4-fold increase in expression of Angpt2, (p < 0.05 vs. CT and high). ANGPT2 protein was increased 42.2% (p < 0.01). Cytosine-phosphate-guanine dinucleotide islands in the proximity of the promoter areas of Vegfc and Angpt2 were hypomethylated in low choline NPC compared to CT NPC (p < 0.01). We conclude that maternal dietary choline intake alters angiogenesis in the developing fetal hippocampus.

Characterization of novel VEGF (vascular endothelial growth factor)-C splicing isoforms from mouse

VEGF (vascular endothelial growth factor)-C is a major growth factor implicated in various physiological processes, such as angiogenesis and lymphangiogenesis. In the present paper, we report the identification of three short VEGF-C splicing isoforms (VEGF-C62, VEGF-C129 and VEGF-C184) from immortalized mouse kidney PTECs (proximal tubular epithelial cells). Semi-quantitative RT (reverse transcription)-PCR analysis showed these isoforms were universally expressed to varying degrees in different tissues with high expression levels in the kidney. In immortalized PTECs and podocytes, VEGF-C62 can activate phosphorylation of FAK (focal adhesion kinase) and promote cell adhesion to substratum. Cell survival was also increased by VEGF-C62 treatment in the absence of serum. VEGF-C62 can also reduce cell proliferation in PTECs and podocytes. Nucleolin was one of the proteins that associated with VEGF-C62 in pull-down assays using GST (glutathione transferase) fusion proteins as bait, indicating different protein binding requirements for VEGF-C62 compared with VEGF-C. In conclusion, these newly identified VEGF-C isoforms represent a new class of proteins, which are potentially involved in epithelial cell adhesion and proliferation through novel receptor pathways.

VEGFR2 (KDR/Flk1) signaling mediates axon growth in response to semaphorin 3E in the developing brain

Common factors are thought to control vascular and neuronal patterning. Here we report an in vivo requirement for the vascular endothelial growth factor receptor type 2 (VEGFR2) in axon tract formation in the mouse brain. We show that VEGFR2 is expressed by neurons of the subiculum and mediates axonal elongation in response to the semaphorin (Sema) family molecule, Sema3E. We further show that VEGFR2 associates with the PlexinD1/Neuropilin-1 (Nrp1) receptor complex for Sema3E and becomes tyrosine-phosphorylated upon Sema3E stimulation. In subicular neurons, Sema3E triggers VEGFR2-dependent activation of the phosphatidylinositol-3 kinase (PI3K)/Akt pathway that is required for the increase in axonal growth. These results implicate VEGFR2 in axonal wiring through a mechanism dependent on Sema3E and independent of vascular endothelial growth factor (VEGF) ligands. This mechanism provides an explanation as to how a semaphorin can activate an axon growth promoting response in developing neurons.

Expression of vascular endothelial growth factor receptor-3 mRNA in the rat developing forebrain and retina

Vascular endothelial growth factor receptor (VEGFR)-3, a receptor for VEGF-C and VEGF-D, is expressed in neural progenitor cells, but there has been no comprehensive study of its distribution in the developing brain. Here, the temporal and cell-specific expression of VEGFR-3 mRNA was studied in the developing rat forebrain and eye. Expression appeared along the ventricular and subventricular zones of the lateral and third ventricles showing ongoing neurogenesis as early as embryonic day 13 but was progressively down-regulated during development and remained in the subventricular zone and rostral migratory stream of the adult forebrain. VEGFR-3 expression was also detectable in some differentiating and postmitotic neurons in the developing cerebral cortex, including Cajal-Retzius cells, cortical plate neurons, and subplate neurons. Expression in the subplate increased significantly during the early postnatal period but was absent by postnatal day 14. It was also highly expressed in nonneural tissues of the eye during development, including the retinal pigment epithelium, the retinal ciliary margin, and the lens, but persisted in a subset of cells in the pigmented ciliary epithelium of the adult eye. In contrast, there was weak or undetectable expression in the early neural retina, but a subset of retinal neurons in the postnatal and mature retina showed intense signals. These unique spatiotemporal mRNA expression patterns suggest that VEGFR-3 might mediate the regulation of both neurogenesis and adult neuronal function in the rat forebrain and eye.

Vascular endothelial growth factor and its high-affinity receptor (VEGFR-2) are highly expressed in the human forebrain and cerebellum during development

Vascular endothelial growth factor (VEGF) is an angiogenic and neurotrophic factor in both adult and neonatal animals, but its expression and role have been incompletely studied in the developing human brain. We analyzed the distribution of VEGF and its high-affinity receptor VEGFR-2 in the human forebrain and cerebellum at developmental stages from 14 weeks' gestation (WG) to the13th postnatal month. Tissue samples free of detectable neuropathologic abnormalities were assessed by immunohistochemistry and confocal microscopy using anti-human VEGF and VEGFR-2 antibodies. The VEGFR-2 was first expressed in the whole cerebral mantle and in migrating cells in the intermediate zone, whereas VEGFwas found in superficial layers of the cortical plate, in radial glia, and in the cerebellar external germinal cell layer. From 23 WG, temporospatial VEGFR-2 expression was superimposable on that ofVEGF in the cortical plate, intermediate zone, basal ganglia, limbicstructures, and external germinal cell layer. The VEGF/VEGFR-2-positive astrocytes were observed during their generation and migration from 23 WG to the first postnatal month. The VEGF-positive mature oligodendrocytes were observed in myelinating structures in the forebrain from birth and in the cerebellum from 24WG. These data suggest that VEGF and VEGFR-2 are likely involved in several aspects of human brain development.

Human neural stem cells: a model system for the study of Lesch-Nyhan disease neurological aspects

The study of Lesch-Nyhan-diseased (LND) human brain is crucial for understanding how mutant hypoxanthine-phosphoribosyltransferase (HPRT) might lead to neuronal dysfunction. Since LND is a rare, inherited disorder caused by a deficiency of the enzyme HPRT, human neural stem cells (hNSCs) that carry this mutation are a precious source for delineating the consequences of HPRT deficiency and for developing new treatments. In our study we have examined the effect of HPRT deficiency on the differentiation of neurons in hNSCs isolated from human LND fetal brain. We have examined the expression of a number of transcription factors essential for neuronal differentiation and marker genes involved in dopamine (DA) biosynthetic pathway. LND hNSCs demonstrate aberrant expression of several transcription factors and DA markers. HPRT-deficient dopaminergic neurons also demonstrate a striking deficit in neurite outgrowth. These results represent direct experimental evidence for aberrant neurogenesis in LND hNSCs and suggest developmental roles for other housekeeping genes in neurodevelopmental disease. Moreover, exposure of the LND hNSCs to retinoic acid medium elicited the generation of dopaminergic neurons. The lack of precise understanding of the neurological dysfunction in LND has precluded development of useful therapies. These results evidence aberrant neurogenesis in LND hNSCs and suggest a role for HPRT gene in neurodevelopment. These cells combine the peculiarity of a neurodevelopmental model and a human, neural origin to provide an important tool to investigate the pathophysiology of HPRT deficiency and more broadly demonstrate the utility of human neural stem cells for studying the disease and identifying potential therapeutics.

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

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

The neurovascular link in health and disease: an update

Although the nervous and vascular systems are functionally different, they show a high degree of anatomic parallelism and cross-talk. They also share similar mechanisms and molecular cues that regulate their development and maintenance. Malfunctioning of this cross-talk can cause or influence several vascular and neuronal disorders. In this review, we first provide a brief overview of the molecular and cellular mechanisms that govern the neurovascular link. Second, we focus on two neurodegenerative diseases, Alzheimer's disease and amyotrophic lateral sclerosis, to illustrate how a defective neurovascular link might contribute to their pathogenesis. Finally, we briefly discuss some therapeutic implications of the neurovascular link for designing strategies to treat these diseases.

Blocked inhibitory serine-phosphorylation of glycogen synthase kinase-3alpha/beta impairs in vivo neural precursor cell proliferation

BACKGROUND

Adult neurogenesis augments neuronal plasticity, and deficient neurogenesis might contribute to mood disorders and schizophrenia and impede treatment responses. Because these diseases might be associated with inadequately controlled glycogen synthase kinase-3 (GSK3), we tested whether blocked inhibitory serine-phosphorylation of GSK3 impairs neurogenesis.

METHODS

Neural precursor cell (NPC) proliferation was measured by dentate gyrus bromodeoxyuridine (BrdU) labeling in GSK3alpha/beta(21A/21A/9A/9A) knockin mice with serine-to-alanine mutations to block inhibitory serine-phosphorylation of GSK3 while it remains within the physiological range, because GSK3 is not overexpressed.

RESULTS

There was a drastic 40% impairment in neurogenesis in vivo in GSK3 knockin mice compared with wild-type mice. Impaired neurogenesis could be due to effects of GSK3 in NPCs or in surrounding cells that modulate NPCs. In vitro proliferation was equivalent for NPCs from GSK3 knockin and wild-type mice, suggesting an in vivo deficiency in GSK3 knockin mice of external support for NPC proliferation. Measurements of two neurotrophins that promote neurogenesis demonstrated less hippocampal vascular endothelial growth factor but not brain-derived growth factor in GSK3 knockin mice than wild-type mice, reinforcing the possibility that insufficient environmental support in GSK3 knockin mice might contribute to impaired neurogenesis. In vivo chronic co-administration of lithium and fluoxetine, which each increase inhibitory serine-phosphorylation of wild-type GSK3, increased NPC proliferation in wild-type but not GSK3 knockin mice.

CONCLUSIONS

Blocked inhibitory control of GSK3 impaired neurogenesis and the capacity of therapeutic drugs to stimulate neurogenesis, likely through deficient environmental factors that support neurogenesis, which might contribute to psychiatric diseases and responses to therapeutic drugs.

Vascular endothelial growth factor-C protects prostate cancer cells from oxidative stress by the activation of mammalian target of rapamycin complex-2 and AKT-1

Recurrence and subsequent metastatic transformation of cancer develops from a subset of malignant cells, which show the ability to resist stress and to adopt to a changing microenvironment. These tumor cells have distinctly different growth factor pathways and antiapoptotic responses compared with the vast majority of cancer cells. Long-term therapeutic success can only be achieved by identifying and targeting factors and signaling cascades that help these cells survive during stress. Both microarray and immunohistochemical analysis on human prostate cancer tissue samples have shown an increased expression of vascular endothelial growth factor-C (VEGF-C) in metastatic prostate cancer. We have discovered that VEGF-C acts directly on prostate cancer cells to protect them against oxidative stress. VEGF-C increased the survival of prostate cancer cells during hydrogen peroxide stress by the activation of AKT-1/protein kinase Balpha. This activation was mediated by mammalian target of rapamycin complex-2 and was not observed in the absence of oxidative stress. Finally, the transmembrane nontyrosine kinase receptor neuropilin-2 was found to be essential for the VEGF-C-mediated AKT-1 activation. Indeed, our findings suggest a novel and distinct function of VEGF-C in protecting cancer cells from stress-induced cell death, thereby facilitating cancer recurrence and metastasis. This is distinctly different from the known function of VEGF-C in inducing lymphangiogenesis.

VEGFR-3/Flt-4 mediates proliferation and chemotaxis in glial precursor cells

Neuronal and vascular cells share common chemical signals. Vascular endothelial growth factor (VEGF)-C and -D and their receptor VEGFR-3/Flt-4 mediate lymphangiogenesis, but they occur also in the brain. Quantitative RT-PCR of mouse brain tissues and cultivated cells showed that the VEGFR-3 gene is highest transcribed in postnatal brain and in glial precursor cells whereas VEGF-C and -D are variably produced by different neuronal and glial cells. In neurospheres (neural stem cells) VEGFR-3 was induced by differentiation with platelet-derived growth factor (PDGF). In functional studies with an A2B5- and nestin-positive, O4-negative murine glial precursor cell line, VEGF-C and -D stimulated phosphorylation of the kinases Erk1/2; this signal transduction was inhibited by UO126. Both peptides induced the proliferation of glial precursor cells which could be inhibited by UO126. Furthermore, VEGF-D considerably enhanced their migration into an open space in a wound-healing assay. These results show that VEGF-C/-D together with its receptor VEGFR-3 provides an auto-/paracrine growth and chemotactic system for glial precursors in the developing brain.

A stem cell niche for intermediate progenitor cells of the embryonic cortex

The excitatory neurons of the mammalian cerebral cortex arise from asymmetric divisions of radial glial cells in the ventricular zone and symmetric division of intermediate progenitor cells (IPCs) in the subventricular zone (SVZ) of the embryonic cortex. Little is known about the microenvironment in which IPCs divide or whether a stem cell niche exists in the SVZ of the embryonic cortex. Recent evidence suggests that vasculature may provide a niche for adult stem cells but its role in development is less clear. We have investigated the vasculature in the embryonic cortex during neurogenesis and find that IPCs are spatially and temporally associated with blood vessels during cortical development. Intermediate progenitors mimic the pattern of capillaries suggesting patterns of angiogenesis and neurogenesis are coordinated during development. More importantly, we find that IPCs divide near blood vessel branch points suggesting that cerebral vasculature establishes a stem cell niche for intermediate progenitors in the SVZ. These data provide novel evidence for the presence of a neurogenic niche for intermediate progenitors in the embryonic SVZ and suggest blood vessels are important for proper patterning of neurogenesis.

Role and therapeutic potential of VEGF in the nervous system

The development of the nervous and vascular systems constitutes primary events in the evolution of the animal kingdom; the former provides electrical stimuli and coordination, while the latter supplies oxygen and nutrients. Both systems have more in common than originally anticipated. Perhaps the most striking observation is that angiogenic factors, when deregulated, contribute to various neurological disorders, such as neurodegeneration, and might be useful for the treatment of some of these pathologies. The prototypic example of this cross-talk between nerves and vessels is the vascular endothelial growth factor or VEGF. Although originally described as a key angiogenic factor, it is now well established that VEGF also plays a crucial role in the nervous system. We describe the molecular properties of VEGF and its receptors and review the current knowledge of its different functions and therapeutic potential in the nervous system during development, health, disease and in medicine.

A novel role for anosmin-1 in the adhesion and migration of oligodendrocyte precursors

At embryonic stages of development, oligodendrocyte precursors (OPCs) generated in the preoptic area colonize the entire optic nerve (ON). Different factors controlling migration of ON OPCs have been identified, including secreted growth factors, morphogens and guidance cues, as well as cell adhesion molecules. We have shown previously that the soluble form of the extracellular matrix (ECM) protein anosmin-1, impairs OPC migration induced by FGF-2. In the present work, we show that anosmin-1 is expressed by both migrating OPCs and axons of the retinal ganglion cells in the embryonic ON. In vitro, we observe that OPC migration is strongly impaired by contact with anosmin-1 when used as a substrate and, in contrast to previous results, this effect is independent of FGF-2/FGFR1 signaling. We also show that OPCs preferentially adhere to anosmin-1 when compared with other ECM molecules used as substrates, and that when the endogenous anosmin-1 expressed by OPCs is blocked, OPC adhesion to all the different substrates (including anosmin-1), is significantly reduced. This novel effect of anosmin-1 on cell adhesion is also independent of FGF-2/FGFR1. We finally demonstrate that the blockade of the endogenous anosmin-1 expressed by OPCs impairs their migration. Our data suggest that the endogenous anosmin-1 expressed by OPCs is necessary for the correct adhesion of these cells to the different components of the ECM (including anosmin-1 itself), contributing to the migration of these cells.

Guidance of vascular development: lessons from the nervous system

The vascular system of vertebrates consists of an organized, branched network of arteries, veins, and capillaries that penetrates all the tissues of the body. One of the most striking features of the vascular system is that its branching pattern is highly stereotyped, with major and secondary branches forming at specific sites and developing highly conserved organ-specific vascular patterns. The factors controlling vascular patterning are not yet completely understood. Recent studies have highlighted the anatomic and structural similarities between blood vessels and nerves. The 2 networks are often aligned, with nerve fibers and blood vessels following parallel routes. Furthermore, both systems require precise control over their guidance and growth. Several molecules with attractive and repulsive properties have been found to modulate the proper guidance of both nerves and blood vessels. These include the Semaphorins, the Slits, and the Netrins and their receptors. In this review, we describe the molecular mechanisms by which blood vessels and axons achieve proper path finding and the molecular cues that are involved in their guidance.

Expression profile of differentiating serotonin neurons derived from rhesus embryonic stem cells and comparison to adult serotonin neurons

The rhesus monkey embryonic stem cell line 366.4 differentiates into serotonin neurons. We examined the genetic cascade during differentiation and compared ESC-derived serotonin neurons to adult monkey serotonin neurons. RNA was extracted from ESC colonies, embryoid bodies (EBs), neurospheres in selection (N1) and proliferation stages (N2), differentiated serotonin neurons (N3) and from laser captured (LC) serotonin neurons of spayed female macaques treated with placebo, estrogen (E), progesterone (P) or E+P. The RNA was labeled and hybridized to Rhesus Monkey Affymetrix Gene Chips (n=1 per stage and 2 per animal treatment). Gene expression was examined with GeneSifter software. 545 genes that were related to developmental processes showed a threefold or greater change between stages. TGFb, Wnt, VEGF and Hedgehog signaling pathways showed the highest percent of probe set changes during differentiation. Genes in the categories (a) homeobox binding and transcription factors, (b) growth factors and receptors, (c) brain and neural specific factors and (d) serotonin specific factors are reported. Pivotal genes were confirmed with quantitative RT-PCR. In the serotonin developmental cascade, FGFR2 was robustly expressed at each stage. GATA3 was robustly expressed in EBs. Sonic hedgehog (Shh), PTCH (Shh-R) and Fev1 transcription factor expression coincided with the induction of serotonin specific marker genes during N1-selection. A majority of the examined genes were expressed in adult serotonin neurons. However, in the ESC-derived neurons, there was significant over-representation of probe sets related to cell cycle, axon guidance & dorso-ventral axis formation. This analysis suggests that the 366.4 cell line possesses cues for serotonin differentiation at early stages of differentiation, but that ESC-derived serotonin neurons are still immature.

Differential regulation of vascular endothelial growth factor-C and its receptor in the rat hippocampus following transient forebrain ischemia

We investigated the changes in the expression of vascular endothelial growth factor-C (VEGF-C) and its receptor, VEGFR-3, in the rat hippocampus following transient forebrain ischemia. The expression profiles of VEGF-C and VEGFR-3 were very similar in the control hippocampi, where both genes were constitutively expressed in neurons in the pyramidal cell and granule cell layers. The spatiotemporal expression pattern of VEGF-C was similar to that of VEGFR-3 in the ischemic hippocampus, and in the CA1 and dentate hilar regions both VEGF-C and VEGFR-3 were strongly expressed in activated glial cells rather than in neurons. Most of the activated glial cells expressing both genes were reactive astrocytes, although some were a subpopulation of brain macrophages. In the dentate gyrus, however, VEGFR-3 expression was transiently increased in the innermost layer of granule cells on days 7-10 after reperfusion, coinciding with an increase in polysialylated neural cell adhesion molecule staining--a marker for immature neurons. These data suggest that VEGF-C may be involved in glial reaction via paracrine or autocrine mechanisms in the ischemic brain and may carry out specific roles in adult hippocampal neurogenesis during ischemic insults.

Role of platelet-derived growth factors in physiology and medicine

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) have served as prototypes for growth factor and receptor tyrosine kinase function for more than 25 years. Studies of PDGFs and PDGFRs in animal development have revealed roles for PDGFR-alpha signaling in gastrulation and in the development of the cranial and cardiac neural crest, gonads, lung, intestine, skin, CNS, and skeleton. Similarly, roles for PDGFR-beta signaling have been established in blood vessel formation and early hematopoiesis. PDGF signaling is implicated in a range of diseases. Autocrine activation of PDGF signaling pathways is involved in certain gliomas, sarcomas, and leukemias. Paracrine PDGF signaling is commonly observed in epithelial cancers, where it triggers stromal recruitment and may be involved in epithelial-mesenchymal transition, thereby affecting tumor growth, angiogenesis, invasion, and metastasis. PDGFs drive pathological mesenchymal responses in vascular disorders such as atherosclerosis, restenosis, pulmonary hypertension, and retinal diseases, as well as in fibrotic diseases, including pulmonary fibrosis, liver cirrhosis, scleroderma, glomerulosclerosis, and cardiac fibrosis. We review basic aspects of the PDGF ligands and receptors, their developmental and pathological functions, principles of their pharmacological inhibition, and results using PDGF pathway-inhibitory or stimulatory drugs in preclinical and clinical contexts.

Control of glial precursor cell development in the mouse optic nerve by sonic hedgehog from retinal ganglion cells

The development of glial precursor cells in the mammalian optic nerve depends on retinal ganglion cell (RGC) axons, but the signals that mediate this neuron-to-glia interaction have not been fully characterized. Sonic hedgehog (Shh) is expressed by RGCs, and we showed previously that it is required for the specification of astrocyte lineage cells at the optic disc. To study the role of RGC-derived Shh on astrocyte development at later developmental stages, we generated mice with a conditional ablation of Shh in the peripheral retina and analyzed gene expression and glial cell development in the optic nerve. Astrocyte development was initiated in the optic nerves of these mutant mice; however, the expression of Hedgehog (Hh) target genes, Gli1 and Ptch1 and cell cycle genes, Ccnd1 and Cdc25b in the optic nerves were downregulated. Astrocyte proliferation was markedly reduced. Oligodendrocyte precursor cells were fewer in the optic nerves of mutant mice, possibly as a consequence of reduced secretion of growth factors by astrocytes. At a later developmental stage, optic nerve axons displayed signs of Wallerian degeneration, including reduction of astrocyte processes, degenerating glial cells and formation of distended axons. We also demonstrate that the Hh pathway can be activated in optic nerve-derived astrocytes in vitro, but fails to induce cell cycle gene expression and proliferation. RGC-derived Shh signalling isthus necessary in vivo for maintenance of astrocyte proliferation, affecting both axo-glial and normal glial cell development in the optic nerve.

The postoperative brain tumour stem cell (BTSC) niche and cancer recurrence

Currently, surgical resection is one of only a few options for treating brain cancer. Unfortunately, postoperative tumour recurrence remains almost inevitable despite additional radiation or chemotherapy treatment following resection. Clinical observations and a growing body of experimental evidence have led to speculation that there is a population of persistent brain tumour stem cells (BTSCs)--or brain tumour initiating cells--that are difficult to completely remove surgically. Furthermore, residual BTSCs following surgery may actually be more resistant to subsequent radiation and/or chemotherapies. It remains to be determined if brain surgeries render the postoperative tissue microenvironment more favourable for the survival and growth of BTSCs, and therefore the recurrence of brain tumours.We hypothesise that BTSC-based tumour recurrence may develop within a specific niche of the aberrant tumour microenvironment. Even when the gross appearance of the primary tumour seems confined, BTSCs (albeit accounting only for a small population of tumour cells) may microscopically enter the stroma, hampering curative surgeries. This article discusses the theory that surgical resection of brain tumours generates niches recruiting BTSCs to the surgical wounds, stimulating the proliferation and invasiveness of BTSCs, and leading to tumour recurrence. Postoperative brains are marked with active wound repair in peritumoural margins, which is likely to be accompanied by increased inflammatory paracrine production, angiogenesis and reactive astrogliosis. The postoperative BTSC niche concept is consistent with the observation that brain tumour recurrence usually occurs in tissues that are proximal to the resection margin. In this article, we intend to reflect recent advances that may lead to novel strategies to eliminate postoperative brain tumour recurrence.

TNF receptor I sensitizes neurons to erythropoietin- and VEGF-mediated neuroprotection after ischemic and excitotoxic injury

CNS neurons use robust cytoprotective mechanisms to ensure survival and functioning under conditions of injury. These involve pathways induced by endogenous neuroprotective cytokines such as erythropoietin (EPO). Recently, in contrast to its well known deleterious roles, TNF has also been shown to exhibit neuroprotective properties. In the present study, we investigated the molecular mechanisms by which TNF receptor (TNFR)I mediates neuroprotection by comparing the gene expression profiles of lesioned cortex from WT and TNFRI KO mice after permanent middle cerebral artery occlusion. Several known neuroprotective molecules were identified as TNFRI targets, notably members of the Bcl-2 family, DNA repair machinery and cell cycle, developmental, and differentiation factors, neurotransmitters and growth factors, as well as their receptors, including EPO receptor (EPOR), VEGF, colony-stimulating factor receptor 1, insulin-like growth factor (IGF), and nerve growth factor (NGF). Further analysis showed that induction of EPOR and VEGF expression in primary cortical neurons after glucose deprivation (GD) largely depended on TNFRI and was further up-regulated by TNF. Also, EPO- and VEGF-induced neuroprotection against GD, oxygen-glucose deprivation, and NMDA excitotoxicity depended significantly on TNFRI presence. Finally, EPO prevented neuronal damage induced by kainic acid in WT but not TNFRI KO mice. Our results identify cross-talk between tissue protective cytokines, specifically that TNFRI is necessary for constitutive and GD-induced expression of EPOR and VEGF and for EPO-mediated neuroprotection.

Molecular and cell biology of brain tumor stem cells: lessons from neural progenitor/stem cells

✓ The results of studies conducted in the past several years have suggested that malignant brain tumors may harbor a small fraction of tumor-initiating cells that are likely to cause tumor recurrence. These cells are known as brain tumor stem cells (BTSCs) because of their multilineage potential and their ability to self-renew in vitro and to recapitulate original tumors in vivo. The understanding of BTSCs has been greatly advanced by knowledge of neural progenitor/stem cells (NPSCs), which are multipotent and self-renewing precursor cells for neurons and glia. In this article, the authors summarize evidence that genetic mutations that deregulate asymmetric cell division by affecting cell polarity, spindle orientation, or cell fate determinants may result in the conversion of NPSCs to BTSCs. In addition, they review evidence that BTSCs and normal NPSCs may reside in similar vascularized microenvironments, where similar evolutionarily conserved signaling pathways control their proliferation. Finally, they discuss preliminary evidence that mechanisms of BTSC-associated infiltrativeness may be similar to those underlying the migration of NPSCs and neurons.

Secreted factors from olfactory mucosa cells expanded as free-floating spheres increase neurogenesis in olfactory bulb neurosphere cultures

BACKGROUND

The olfactory epithelium is a neurogenic tissue comprising a population of olfactory receptor neurons that are renewed throughout adulthood by a population of stem and progenitor cells. Because of their relative accessibility compared to intra-cranially located neural stem/progenitor cells, olfactory epithelium stem and progenitor cells make attractive candidates for autologous cell-based therapy. However, olfactory stem and progenitor cells expand very slowly when grown as free-floating spheres (olfactory-spheres) under growth factor stimulation in a neurosphere assay.

RESULTS

In order to address whether olfactory mucosa cells extrinsically regulate proliferation and/or differentiation of immature neural cells, we cultured neural progenitor cells derived from mouse neonatal olfactory bulb or subventricular zone (SVZ) in the presence of medium conditioned by olfactory mucosa-derived spheres (olfactory-spheres). Our data demonstrated that olfactory mucosa cells produced soluble factors that affect bulbar neural progenitor cell differentiation but not their proliferation when compared to control media. In addition, olfactory mucosa derived soluble factors increased neurogenesis, especially favouring the generation of non-GABAergic neurons. Olfactory mucosa conditioned medium also contained several factors with neurotrophic/neuroprotective properties. Olfactory-sphere conditioned medium did not affect proliferation or differentiation of SVZ-derived neural progenitors.

CONCLUSION

These data suggest that the olfactory mucosa does not contain factors that are inhibitory to neural stem/progenitor cell proliferation but does contain factors that steer differentiation toward neuronal phenotypes. Moreover, they suggest that the poor expansion of olfactory-spheres may be in part due to intrinsic properties of the olfactory epithelial stem/progenitor cell population.

Making a tumour's bed: glioblastoma stem cells and the vascular niche

Parallel to the role that normal stem cells play in organogenesis, cancer stem cells are thought to be crucial for tumorigenesis. Understanding normal development might therefore lead to better treatments of cancer. We review recent data that stem cells of glioblastoma, a highly malignant brain tumour, seem to be dependent on cues from aberrant vascular niches that mimic the normal neural stem cell niche. These data have direct implications for cancer, highlighting the similarity between normal and malignant stem cells and identifying the tumour microenvironment as a target for new therapies.

Sonic hedgehog promotes the migration and proliferation of optic nerve oligodendrocyte precursors

Optic nerve (ON) oligodendrocyte precursors (OPCs) are generated under the influence of the Sonic hedgehog (Shh) in the preoptic area from where they migrate to colonise the entire nerve. The molecular events that control this migration are still poorly understood. Recent studies suggested that Shh is often used by the same cell population to control different processes, including cell proliferation and migration, raising the possibility that Shh could contribute to these aspects of OPC development. In support of this idea, we show here that Shh induces the proliferation of OPCs derived from embryonic mouse ON explants and acts as a chemoattractant for their migration. In ovo injections of hybridomas secreting Shh-specific blocking antibody decreases the number of OPCs present in chick ONs, particularly in the retinal portion of the nerve. Altogether these data indicate that Shh contributes to OPC proliferation and distribution along the ON, in addition to their specification.

Molecular regulation of angiogenesis and lymphangiogenesis

Blood vessels and lymphatic vessels form extensive networks that are essential for the transport of fluids, gases, macromolecules and cells within the large and complex bodies of vertebrates. Both of these vascular structures are lined with endothelial cells that integrate functionally into different organs, acquire tissue-specific specialization and retain plasticity; thereby, they permit growth during tissue repair or in disease settings. The angiogenic growth of blood vessels and lymphatic vessels coordinates several biological processes such as cell proliferation, guided migration, differentiation and cell-cell communication.

Expression of stem cell markers in human astrocytomas of different WHO grades

According to new hypotheses astrocytomas/gliomas either arise from or attract neural stem cells. Biological markers, particularly antigenic markers, have played a significant role for the characterization of these tumour stem cells (TSCc). Because these studies have been performed with single experimental samples mostly from gliomas, we investigated the expression of the stem cell markers CD133/Prominin, Nestin, Sox-2, Musashi-1, CXCR4, Flt-4/VEGFR-3 and CD105/Endoglin in 72 astrocytomas of different WHO-grades and compared it to normal adult human brain. Expression of their mRNA was quantified by quantitative RT-PCR, of their protein by counting immunopositive cells. In contrast to normal brain, tumour samples showed a high variability for the expression of all markers. However, their mean expression was significantly increased in astrocytomas, but this depended on the WHO grade only for CD133, Nestin, Sox-2 and Musashi-1. Confocal microscopy revealed that these markers mostly could be co-stained with glial fibrillary acidic protein, a marker for astoglial cells, but less frequently with the proliferation marker Ki-67/MIB-1. These markers sometimes, but not necessarily could be co-stained with each other in complex patterns. Our results show that most astrocytomas contain considerable portions of cells expressing stem cell markers. It appears that some of these cells originate from tumour genesis (supporting the stem cell hypothesis) while others are attracted by the tumours. Further functional markers are required to differentiate these TSC-types.

Potential roles of bone marrow stem cells in stroke therapy

There is a need for improved therapies, in terms of utility and effectiveness, for stroke patients; however, over the years, numerous clinical trials of potential drugs have failed to demonstrate positive results. The emerging field of stem cell research has raised several hopes of a therapy for neurological diseases, including stroke. This review discusses the recent clinical trials and pilot studies using stem cells in stroke patients and highlights key issues that must be addressed to improve the chances of successfully developing a new strategy for stroke patients using adult stem cells.

Different networks, common growth factors: shared growth factors and receptors of the vascular and the nervous system

Growth factors and their respective receptors are key regulators during development and for homeostasis of the nervous system. In addition, changes in growth factor function, availability or downstream signaling is involved in many neuropathological disorders like Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, stroke and brain tumours. Research of the recent years revealed that some growth factors, initially discovered as neural growth factors are also affecting blood vessels [e.g. nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF)]. Likewise, vascular growth factors, such as vascular endothelial growth factor (VEGF), which was previously described as an endothelial cell specific mitogen, also affect neural cells. The discovery of shared growth factors affecting the vascular and the nervous system is of relevance for potential therapies of vascular and neurological diseases. This review aims to give an overview about the growing field of common growth factors and receptors within the two different networks.

IL-1beta regulates blood-brain barrier permeability via reactivation of the hypoxia-angiogenesis program

Loss of blood-brain barrier (BBB) integrity is believed to be an early and significant event in lesion pathogenesis in the inflammatory demyelinating disease multiple sclerosis (MS), and understanding mechanisms involved may lead to novel therapeutic avenues for this disorder. Well-differentiated endothelium forms the basis of the BBB, while astrocytes control the balance between barrier stability and permeability via production of factors that restrict or promote vessel plasticity. In this study, we report that the proinflammatory cytokine IL-1beta, which is prominently expressed in active MS lesions, causes a shift in the expression of these factors to favor plasticity and permeability. The transcription factor, hypoxia inducible factor-1 (HIF-1), plays a significant role in this switch. Using a microarray-based approach, we found that in human astrocytes, IL-1beta induced the expression of genes favoring vessel plasticity, including HIF-1alpha and its target, vascular endothelial growth factor-A (VEGF-A). Demonstrating relevance to MS, we showed that HIF-1alpha and VEGF-A were expressed by reactive astrocytes in active MS lesions, while the VEGF receptor VEGFR2/flk-1 localized to endothelium and IL-1 to microglia/macrophages. Suggesting functional significance, we found that expression of IL-1beta in the brain induced astrocytic expression of HIF-1alpha, VEGF-A, and BBB permeability. In addition, we confirmed VEGF-A to be a potent inducer of BBB permeability and angiogenesis, and demonstrated the importance of IL-1beta-induced HIF-1alpha in its regulation. These results suggest that IL-1beta contributes to BBB permeability in MS via reactivation of the HIF-VEGF axis. This pathway may represent a potential therapeutic target to restrict lesion formation.

Localisation of lymphatic vessels and vascular endothelial growth factors-C and -D in human and mouse skeletal muscle with immunohistochemistry

The present study was aimed to localise lymphatic vessels and their growth factors in human and mouse skeletal muscle with immunohistochemistry and specific antibodies (VEGFR-3, LYVE-1, VEGF-C and VEGF-D). The largest lymphatic vessels were found in perimysial connective tissue next to the arteries and veins, as has been shown earlier with electron microscopy. As a new finding, we also found small LYVE-1 positive vessels in the capillary bed between muscle fibres. These vessels were located next to CD31 positive blood capillaries and were of the same size, but fewer in number. In addition, we described the localisation of the two main lymphangiogenic growth factor proteins, vascular endothelial growth factor-C and -D. Both proteins were expressed in skeletal muscle at mRNA and protein levels. VEGF-D was located under the sarcolemma in some of the muscle fibres, in the endothelia of larger blood vessels and in fibroblasts. VEGF-C protein was localised to the nerves and muscle spindles, to fibroblasts and surrounding connective tissue, but was not found in muscle fibres or endothelial cells. Our results are the first to suggest the presence of lymphatic capillaries throughout the skeletal muscle, and to present the localisation of VEGF-C and -D in the muscles.

Anosmin-1 modulates the FGF-2-dependent migration of oligodendrocyte precursors in the developing optic nerve

Oligodendrocyte precursors (OPCs) originate at specific domains within the neural tube before migrating to colonize the entire CNS. Once in their target areas, these cells differentiate into oligodendrocytes, the myelin-forming cells in the CNS. Using the embryonic mouse optic nerve as an experimental model, we have analyzed the influence of FGF-2 on OPC development. FGF-2 exerts a dose-dependent motogenic effect on the migration of plp-dm20+ and it also acts as a chemoattractant on these cells. These effects produced by FGF-2 are principally mediated by the FGFR1 receptor, which is expressed by OPCs. Anosmin-1 is the protein that is defective in the X-linked form of human Kallmann syndrome. This protein is expressed by retinal axons and it also interacts with FGFR1, thereby impairing the migration of OPCs. Because both Anosmin-1 and FGF-2 are present in the optic nerve in vivo, we propose a model whereby the relative concentration of these two proteins modulates the migration of OPCs during development through their interaction with FGFR1. This FGF-2/FGFR1/Anosmin-1 system may be relevant in the context of demyelinating diseases.

VEGF activates divergent intracellular signaling components to regulate retinal progenitor cell proliferation and neuronal differentiation

During vertebrate neurogenesis, multiple extracellular signals influence progenitor cell fate choices. The process by which uncommitted progenitor cells interpret and integrate signals is not well understood. We demonstrate here that in the avascular chicken retina, vascular endothelial growth factor (VEGF) secreted by postmitotic neurons acts through the FLK1 receptor present on progenitor cells to influence cell proliferation and commitment. Augmenting VEGF signals increases progenitor cell proliferation and decreases retinal ganglion cell genesis. Conversely, absorbing endogenous VEGF ligand or disrupting FLK1 activity attenuates cell proliferation and enhances retinal ganglion cell production. In addition, we provide evidence that VEGF signals transmitted by the FLK1 receptor activate divergent intracellular signaling components, which regulate different responses of progenitor cells. VEGF-induced proliferation is influenced by the MEK-ERK pathway, as well as by the basic helix-loop-helix factor HES1. By contrast, VEGF-dependent ganglion cell suppression does not require MEK-ERK activation, but instead relies on VEGF-stimulated HES1 activity, which is independent of NOTCH signaling. Moreover, elevated HES1 expression promotes progenitor cell proliferation and prevents overproduction of retinal ganglion cells owing to the loss of VEGF or sonic hedgehog (SHH), another signal that suppresses ganglion cell development. Based on previous and current findings, we propose that HES1 serves as a convergent signaling node within early retinal progenitor cells to integrate various cell-extrinsic cues, including VEGF and SHH, in order to control cell proliferation and neuronal specification.