semaxinib and Brain-Injuries

Stimulating the endogenous repair process after traumatic brain injury (TBI) can be an important approach in neuroregenerative medicine. Vascular endothelial growth factor (VEGF) is one of the molecules that can increase de novo hippocampal neurogenesis. Here, we tested whether VEGF signaling through Flk1 (VEGF receptor 2) is involved in the neurogenic process after experimental TBI. We found that Flk1 is expressed both by neuroblasts in the subgranular layer (SGL) and by maturing granule neurons in the adult dentate gyrus (DG) of the hippocampus. After lateral fluid percussion TBI (LFP-TBI) in the rat, we detected elevated VEGF levels and also increased numbers of de novo neurons in the ipsilateral DG. To test the involvement of VEGF and Flk1 in the neurogenic process directly, we delivered recombinant VEGF or SU5416, an inhibitor to Flk1, into the ipsilateral cerebral ventricle of injured animals. We found that VEGF infusion significantly increased the number of BrdU+/Prox1+ new neurons, decreased the number of TUNEL+ cells, but did not change the number of BrdU+ newborn cells per se. Infusion with SU5416 caused no significant changes. Our results suggest that (a) VEGF is a part of the molecular signaling network that mediates de novo hippocampal neurogenesis after TBI; (b) VEGF predominantly mediates survival of de novo granule neurons rather than proliferation of neuroblasts in the injured brain; and (c) additional VEGF receptor(s) and/or other molecular mechanism(s) are also involved in mediating increased neurogenesis following injury.

Topics: Animals; Biomarkers; Brain Injuries; Bromodeoxyuridine; Cell Death; Cell Proliferation; Disease Models, Animal; Doublecortin Domain Proteins; Hippocampus; In Situ Nick-End Labeling; Indoles; Infusion Pumps, Implantable; Male; Microtubule-Associated Proteins; Nerve Regeneration; Neurogenesis; Neuropeptides; Protein Kinase Inhibitors; Pyrroles; Rats; Rats, Sprague-Dawley; Recovery of Function; Stem Cells; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factor Receptor-2

Hypoxic ischemia (HI) in neonates causes significant neurodevelopmental sequelae. Pharmacological agents designed to target specific transcription factors expressed in neurons and vasculature may provide powerful therapy against HI. Vascular endothelial growth factor-A (VEGF-A) and cAMP response element-binding protein (CREB) both underlie learning and memory, and survival of the nervous system. We examined whether CREB activation is a shared pathway underlying VEGF-A's protection in neurons and cerebral vascular endothelial cells. VEGF-A was used in a HI model of rat pups and in oxygen-glucose-deprivation (OGD) models of immortalized H19-7 neurons and b.End3 cerebral vascular endothelial cells. We found that VEGF-A activated VEGF receptor-2 (VEGFR-2), phosphorylated CREB in neurons and endothelial cells, and protected against HI, and inhibiting VEGFR-2 before VEGF-A reduced the protective effect of VEGF-A in rat pups. VEGF-A also up-regulated VEGFR-2 and phosphorylated CREB, and protected H19-7 neurons and b.End3 endothelial cells against OGD. Inhibiting VEGFR-2 and extracellular signal-regulated kinase (ERK), respectively, reduced VEGF-A-induced CREB phosphorylation and protection of H19-7 and b.End3 cells against OGD. Transfecting H19-7 and b.End3 cells with a serine-133 phosphorylation mutant CREB also inhibited VEGF-A's protection of both types of cells. We conclude that CREB phosphorylation through VEGFR-2/ERK signaling is the shared pathway that underlies VEGF-A's protection of neurons and vascular endothelial cells.

Topics: Animals; Animals, Newborn; Brain Injuries; Cell Survival; Cells, Cultured; Chromones; CREB-Binding Protein; Disease Models, Animal; Dose-Response Relationship, Drug; Endothelial Cells; Enzyme Inhibitors; Extracellular Signal-Regulated MAP Kinases; Glial Fibrillary Acidic Protein; Glucose; Hypoxia; Hypoxia-Ischemia, Brain; Indoles; Injections, Intraventricular; Male; Morpholines; Neurons; Phosphorylation; Placenta Growth Factor; Platelet Endothelial Cell Adhesion Molecule-1; Pregnancy Proteins; Pyrroles; Rats; Rats, Sprague-Dawley; Serine; Signal Transduction; Time Factors; Transfection; Up-Regulation; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factor Receptor-2

Post-traumatic epilepsy, partly due to the loss of hilar neurons of the hippocampus, is a frequent long-term consequence of traumatic brain injury (TBI). We and others found that the levels of vascular endothelial growth factor (VEGF) that can act as a neuroprotectant increase after TBI. Here we tested whether VEGF and its receptor VEGFR2 are involved in mediating the death or survival of hilar neurons after injury. We demonstrated that VEGFR2 is expressed by most, if not all, hilar neurons and that these neurons are dying in large numbers as indicated by Fluoro-Jade B histology after fluid percussion TBI. To directly test the involvement of VEGFR2 and VEGF in the injury-induced apoptotic death of hilar neurons, we delivered SU5416, an inhibitor to VEGFR2, or recombinant VEGF into the ipsilateral cerebral ventricle of injured animals. We found that blocking VEGFR2 by SU5416 significantly increased the number of apoptotic (TUNEL-positive) cells in the hilus. Infusion of VEGF, however, failed to reduce the number of TUNEL-positive cells. Our results suggest that VEGFR2 is involved in mediating death or survival of hilar neurons after injury but delivering additional exogenous VEGF does not provide further protection from TBI-induced death of hilar neurons.

Topics: Animals; Brain Injuries; Cell Death; Dentate Gyrus; Fluoresceins; Fluorescent Dyes; Immunohistochemistry; In Situ Nick-End Labeling; Indoles; Injections, Intraventricular; Male; Neurons; Neuroprotective Agents; Organic Chemicals; Protein Kinase Inhibitors; Pyrroles; Rats; Rats, Sprague-Dawley; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factor Receptor-2

Angiogenesis following traumatic brain injuries (TBIs) may be of importance for post-traumatic reparative processes and the development of secondary injuries. We have previously shown expression of vascular endothelial growth factor (VEGF), a major regulator of endothelial cell proliferation, angiogenesis and vascular permeability, and VEGF receptors (VEGFR1 and 2) after TBI in rat. In the present work we tried to further elucidate the role of VEGF after TBI by performing specific VEGFR2 activity inhibition. In rats subjected to VEGFR2 blockage we report an increased haemorrhagic area (P < 0.05), early increase in serum levels of neural injury marker neuron-specific enolase (P < 0.05) and glial injury marker S100beta (P < 0.05), and increased numbers of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labelling- (TUNEL-) and FluoroJade B- (P < 0.05) positive cells, all increases preceding the known VEGF/VEGFR vascular response in brain trauma. An increase in lesion area, as measured by decreased microtubuli-associated protein 2 expression (P < 0.05) and increased glial fibrillary acidic protein reactivity (P < 0.05), could also be demonstrated. In addition, vascular density, as measured by von Willebrandt factor-positive cells, was decreased (P < 0.05). No differences in post-traumatic inflammatory response, as measured by stainings for macrophages, granulocytes and intracellular adhesion molecules, were shown between the groups. Taken together, our findings point towards VEGF/VEGFR2 up-regulation after TBI as being an important endogenous cytoprotective mechanism in TBI. The possible importance of VEGF on the vascular, neuronal and glial compartments of the neurovascular unit after TBI is discussed.

Topics: Angiogenesis Inhibitors; Animals; Brain Injuries; Cell Count; Cell Death; Disease Models, Animal; Female; Fluoresceins; Glial Fibrillary Acidic Protein; Immunosorbent Techniques; In Situ Hybridization; In Situ Nick-End Labeling; Indoles; Microtubule-Associated Proteins; Myelin-Associated Glycoprotein; Nerve Degeneration; Nerve Growth Factors; Neuroglia; Organic Chemicals; Pyrroles; Rats; Rats, Sprague-Dawley; S100 Calcium Binding Protein beta Subunit; S100 Proteins; Time Factors; Vascular Endothelial Growth Factor Receptor-2