VEGF enhances angiogenesis and promotes blood-brain barrier leakage in the ischemic brain

Mechanisms of hyperbaric oxygen-induced neuroprotection in a rat model of subarachnoid hemorrhage

Acute cerebral ischemia occurs after subarachnoid hemorrhage (SAH) because of increased intracranial pressure (ICP) and decreased cerebral perfusion pressure (CPP). The effect of hyperbaric oxygen (HBO) on physiological and clinical outcomes after SAH, as well as the expressions of hypoxia-inducible factor-1alpha (HIF-1alpha) and its target genes, such as BNIP3 and VEGF was evaluated. Eighty-five male SD rats (300 to 350 g) were randomly assigned to sham, SAH, and SAH+HBO groups. Subarachnoid hemorrhage was induced by endovascular perforation. Cortical cerebral blood flow (CBF), ICP, brain water content, brain swelling, neurologic function, and mortality were assessed. HBO (100% O2, 2.8 ATA for 2 h) was initiated at 1 h after SAH. Rats were sacrificed at 24 h to harvest tissues for Western blot or for histology. Apoptotic morphology accompanied by strong immunostaining of HIF-1alpha, VEGF, and BNIP3 were observed in the hippocampus and the cortex after SAH. Increased expressions of HIF-1alpha, VEGF, and BNIP3 were quantified by Western blot. HBO reduced the expressions of HIF-1alpha, VEGF, and BNIP3, diminished neuronal damage and improved CBF and neurologic function. HBO reduced early brain injury after SAH, probably by inhibition of HIF-1alpha and its target genes, which led to the decrease of apoptosis and preservation of the blood-brain barrier function.

Vascular endothelial growth factor gene expression in middle cerebral artery occlusion in the rat

BACKGROUND

Focal cerebral ischemia induces up-regulation of angiogenic growth factors such as vascular endothelial growth factor (VEGF), which may have both beneficial and harmful effects to the ischemic brain. Vascular endothelial growth factor is up-regulated in models of brain ischemia, but the underlying mechanisms in vivo remain unclear. In the present report we have investigated the concomitant changes in VEGF and glyceraldehyde dehydrogenase (GAPDH) mRNA expression in a model of permanent and transient cerebral ischemia.

METHODS

Male Sprague-Dawley rats were exposed to permanent or transient (2 h) middle cerebral artery occlusion (PMCAO, TMCAO). Brain samples were collected at survival times ranging from 6 h to 1 week, and the levels of VEGF164 and GAPDH mRNA were determined using reverse-transcriptase real-time polymerase chain reaction (RT-PCR).

RESULTS

The VEGF mRNA levels decreased gradually over the observation period in a similar manner in both PMCAO and TMCAO. Maximum levels, seen at early observation time points, did not significantly deviate from sham controls. No statistically significant changes in GAPDH mRNA levels were observed, but there was a tendency towards a postischemic decrease with subsequent return to control levels over time. The VEGF/GAPDH ratio followed a pattern of decrease similar to VEGF mRNA alone.

CONCLUSION

The VEGF mRNA levels at 6 h after MCAO remain near baseline and thereafter decline, regardless of whether the occlusion is permanent or transient (2 h). The findings raise the question of other than transcriptional regulation of VEGF in cerebral ischemia.

Molecular and cellular mechanisms of neuroprotection by vascular endothelial growth factor

The present view of the neuroprotective functions and mechanisms of action of vascular endothelial growth factor (VEGF) is based on studies of neuronal ischemic/hypoxic models in vivo and in vitro. Endogenous neuronal VEGF increases in the ischemic brain and plays a neuroprotective role in the pathophysiologic processes that follow stroke. Exogenous VEGF, directly administered or overexpressed by gene delivery into rat brains, reduces ischemic brain infarct and decreases hypoxic neuronal death. The main neuroprotective mechanisms of VEGF include: (1) modulation of the phosphatidylinositol 3'-kinase (PI3K)/Akt/nuclear factor-kappaB signaling pathway, inhibition of caspase-3 activity, and reduction of ischemic neuronal apoptosis; (2) inhibition of outward delayed rectifier potassium channel currents and increase of ischemia-induced tyrosine phosphorylation of Kv1.2 potassium channel proteins via activation of the PI3K pathway; and (3) enhancement of proliferation and migration of neural progenitors in the subventricular zone and improvement of striatal neurogenesis and maturation of newborn neurons in adult rat brains after stroke.

Functional recovery in aged and young rats after embolic stroke: treatment with a phosphodiesterase type 5 inhibitor

BACKGROUND AND PURPOSE

Advanced age is associated with a decrease in brain plasticity compared with the young adult. Sildenafil, a phosphodiesterase type 5 (PDE5) inhibitor promotes brain plasticity and improves functional outcome after stroke in the young animal. Here, we test the hypothesis that sildenafil provides restorative therapeutic benefit to the aged animal.

METHODS

Male Wistar rats (aged, 18-month old; young, 3-month old) were subjected to embolic stroke. Saline or sildenafil was administered daily at a dose of 2 mg/kg orally or 10 mg/kg subcutaneously for 7 consecutive days starting 24 hour after stroke onset.

RESULTS

Aged rats exhibited significant impairment of functional recovery and reductions of vascular density, and endothelial cell proliferation compared with young rats. Aged rats treated with sildenafil at a dose of 10 mg/kg but not 2 mg/kg, showed significant improvements of functional recovery and concomitant increases in cortical cyclic guanosine 3',5'-cyclic monophosphate (cGMP) level, vascular density, endothelial cell proliferation, and synaptogenesis compared with aged rats treated with saline. In young rats, treatment with sildenafil at a dose of 2 or 10 mg/kg significantly enhanced functional recovery and amplified brain plasticity compared with young rats treated with saline.

CONCLUSIONS

Age is associated with reduction of angiogenesis, and poor neurological functional recovery after stroke. However, treatment of aged stroke rats with sildenafil improves functional recovery that is likely fostered by enhancement of angiogenesis and synaptogenesis.

Treatments for stroke

Stroke is the third leading cause of death and the leading cause of disability in developed countries, yet remains a poorly treated condition. Treatments for stroke can be aimed at acutely improving blood flow or protecting brain tissue against ischaemia, enhancing stroke recovery or reducing the risk of stroke recurrence. This paper reviews each of these approaches, particularly focusing on mechanisms for which there are agents in clinical trials. There are a number of appealing neuroprotective agents in Phase II and III clinical trials. However, the majority of acute treatments are likely to suffer from a narrow therapeutic time window and hence limited patient access. Combinations of acute approaches are likely to offer the greatest benefit, but present challenges in development. Promotion of recovery following stroke offers enormous potential for successful therapeutic intervention. Excitingly, new developments in preclinical research have identified possible ways in which this may be achieved.

The differences between high and low-dose administration of VEGF to dopaminergic neurons of in vitro and in vivo Parkinson's disease model

Vascular endothelial growth factor (VEGF) has previously been shown to display neuroprotective effects on dopaminergic (DA) neurons. In this study, we investigated whether the effects of VEGF were dose-dependent or not. First, VEGF was shown to be neuroprotective on 6-hydroxydopamine (6-OHDA)-treated murine DA neurons in vitro, although the 1 ng/ml of VEGF displayed more neuroprotective effects than 100 ng/ml. Furthermore, using 2 sizes of capsules (small/large) with different secreting quantities, 6-OHDA-treated rats receiving the small capsule filled with VEGF-secreting cells (BHK-VEGF) into the striatum showed a significant decrease in amphetamine-induced rotational behavior in number and a significant preservation of TH-positive fibers compared to those receiving the large BHK-VEGF capsule as well as those receiving BHK-Control capsule. Rats receiving the large BHK-VEGF capsule showed much more glial proliferation, angiogenesis, and brain edema around the capsule than those with the small one. High-dose administration of VEGF might cause poor circulation related to brain edema, although low-dose administration of VEGF displays neuroprotective effects on DA neurons. Our results demonstrate the importance of administration dose of VEGF, suggesting that low-dose administration of VEGF might be desirable for Parkinson's disease.

Estradiol regulates angiopoietin-1 mRNA expression through estrogen receptor-alpha in a rodent experimental stroke model

BACKGROUND AND PURPOSE

Female, compared with male, animals are protected from cerebral ischemic injury. Physiological concentrations of 17beta-estradiol (E2) reduce damage in experimental stroke. E2 augments angiogenesis in reproductive organs and noncerebral vascular beds. We hypothesized that E2 protects brain in stroke through modulation of angiogenesis. We quantified molecular markers of angiogenesis and capillary density before and after unilateral middle cerebral artery occlusion (MCAO).

METHODS

Female animals were ovariectomized, treated with 25 microg E2 or placebo implants, and subjected to 2-hour MCAO and 22 hours of reperfusion. Brain angiopoietin-1 (Ang-1), Ang-2, Tie-1, Tie-2, vascular endothelial growth factor (VEGF), VEGF R1, and VEGF R2 mRNA levels were determined by RNAse protection assays, and CD31-positive vessels were counted.

RESULTS

E2, but not ischemia, upregulated cerebral Ang-1 mRNA by 49%. Capillary density was higher in the brains of E2-treated animals. In estrogen receptor-alpha knockout (ERKO) mice, E2-mediated induction of Ang-1 mRNA was absent relative to wild-type littermates.

CONCLUSIONS

These results suggest that E2 increases Ang-1 and enhances capillary density in brain under basal conditions, priming the MCA territory for survival after experimental focal ischemia.

Hepatocyte growth factor suppresses vascular endothelial growth factor-induced expression of endothelial ICAM-1 and VCAM-1 by inhibiting the nuclear factor-kappaB pathway

Vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) are potent angiogenic factors that have been used clinically to induce angiogenesis. However, concerns have been raised about VEGF because of its proinflammatory actions, which include enhancing the adhesion of leukocytes to endothelial cells. We have examined the possible antiinflammatory effects of HGF on the vasculature. HGF, unlike VEGF, did not alter leukocyte adhesion to endothelial cells. Instead it inhibited VEGF-induced leukocyte-endothelial cell interactions and the endothelial expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1). In a skin inflammation model, VEGF-treated mice showed a significant increase of leukocytes infiltrated or adherent to the luminal surface of blood vessels, as compared with vehicle- or HGF-treated mice. The VEGF effect was markedly suppressed by coadministration of HGF. RT-PCR and promoter analysis revealed that HGF downregulated VEGF-mediated expression of ICAM-1 and VCAM-1 at the transcriptional level. Furthermore, these inhibitory effects coincided with suppression of IkappaB kinase activity, and this in turn prevented the activation of the inflammatory transcription factor NF-kappaB. Taken together, our results demonstrate that HGF suppresses VEGF-induced inflammation presumably by inhibiting the endothelial NF-kappaB pathway. This suggests that combined treatment with HGF and VEGF could be superior to treatment with either factor alone for enhancing therapeutic angiogenesis while avoiding inflammation.

Analysis of combined treatment of embolic stroke in rat with r-tPA and a GPIIb/IIIa inhibitor

Suppression of platelet activation improves the efficacy of thrombolytic therapy for stroke. Thus, combination treatment with recombinant tissue plasminogen activator (r-tPA) and 7E3 F(ab')2, a GPIIb/IIIa inhibitor that binds the platelet to fibrin, may improve the efficacy of thrombolytic therapy in embolic stroke. Magnetic resonance imaging (MRI) was used to monitor treatment response in rats subjected to embolic middle cerebral artery (MCA) occlusion (MCAo). Animals were randomized into treated (n=12) and control (n=10) groups and received intravenous combination therapy or saline, respectively, 4 hours after MCAo. Magnetic resonance imaging (MRI) measurements performed 1 hour after MCAo showed no difference between groups. However, an increased incidence (50%) of MCA recanalization was found in the treated group at 24 hours compared with 20% in the control group. The area of low cerebral blood flow at 24 and 48 hours was significantly smaller in the combination treatment group, and the lesion size, as indicated from the T2 and T1 maps, differed significantly between groups. Fluorescence microscopy measurements of cerebral microvessels perfused with fluorescein isothiocyanate-dextran and measurements of infarct volume revealed that the combination treatment significantly increased microvascular patency and reduced infarct volume, respectively, compared with the control rats. The efficacy of combination treatment 4 hours after ischemia is reflected by MRI indices of tissue perfusion, MCA recanalization, and reduction of lesion volume. The treatment also reduced secondary microvascular perfusion deficits.

Adrenomedullin Gene Delivery Protects Against Cerebral Ischemic Injury by Promoting Astrocyte Migration and Survival

Adrenomedullin (AM) has been shown to protect against ischemia/reperfusion-induced myocardial infarction and apoptosis. In the present study, we examined the potential neuroprotective action of delayed AM gene transfer in cerebral ischemia. Three days after a 1-hr occlusion of the middle cerebral artery (MCAO), rats were injected intravenously with adenovirus harboring human AM cDNA. The experiment was terminated 7 days after MCAO. AM gene transfer significantly reduced cerebral infarct size compared with that of rats before virus injection and compared with that of rats injected with control virus. The expression of recombinant human AM was identified in ischemic brain by immunostaining. Morphological analyses showed that AM gene transfer enhanced the survival and migration of astrocytes into the ischemic core. Cerebral ischemia markedly increased astrocyte apoptosis, and AM gene delivery significantly reduced apoptosis to near normal levels as seen in sham control rats. Similarly, in primary cultured astrocytes, AM stimulated cell migration and inhibited hypoxia/reoxygenation-induced apoptosis. The effects of AM on both migration and apoptosis were abolished by calcitonin gene-related peptide [CGRP(8-37)], an AM receptor antagonist. Enhanced cell survival after AM gene transfer was accompanied by markedly increased cerebral nitric oxide and Bcl-2 levels, as well as Akt and GSK-3beta phosphorylation, but reduced NADPH oxidase activity and superoxide production. Inactivation of GSK-3beta by phosphorylation led to reduced GSK-3beta activity and caspase- 3 activation. These results indicate that exogenous AM provides neuroprotection against cerebral ischemia injury by enhancing astrocyte survival and migration and inhibiting apoptosis through suppression of oxidative stress-mediated signaling events.

Angiogenesis in symptomatic intracranial atherosclerosis: predominance of the inhibitor endostatin is related to a greater extent and risk of recurrence

BACKGROUND AND PURPOSE

Angiogenesis may be beneficial in chronic myocardial and limb ischemia, but its role in intracranial atherosclerosis remains unknown. We aimed to investigate the relationship between the pro-angiogenic vascular endothelial growth factor (VEGF) and the anti-angiogenic endostatin, and the extent and risk of recurrence of symptomatic intracranial atherosclerosis.

METHODS

Of a total of 94 consecutive patients with symptomatic intracranial stenoses, 40 fulfilled all inclusion criteria. Intracranial stenoses were confirmed by magnetic resonance angiography. Magnetic resonance imaging (MRI) including diffusion-weighted sequences was conducted. Plasmatic VEGF and endostatin were determined from blood samples obtained 3 months after stroke onset, and patients were followed-up thereafter.

RESULTS

A total of 144 intracranial stenoses were confirmed (median number per patient=3). Endostatin/VEGF ratio gradually augmented with the increasing number of intracranial stenoses (r=0.35, P=0.02). Diabetes mellitus (OR, 6.04; CI, 1.1 to 32.2; P=0.03) and a higher endostatin/VEGF ratio (OR, 15.7; CI, 2.2 to 112.3; P=0.006) were independently associated with a greater extent of intracranial atherosclerosis. During a median follow-up of 13 months, 8 patients (20%) experienced a new cerebral ischemic event. A higher baseline endostatin concentration was an independent predictor of new events (hazard ratio, 7.24; CI, 1.6 to 33.8; P=0.011) in a Cox regression model after adjustment for age, sex, number of stenotic vessels, and risk factors. Patients with a higher endostatin level had a lower survival free of new events (P=0.01, log-rank test).

CONCLUSIONS

A predominance of the inhibitor endostatin within the endogenous angiogenic response is associated with a greater extent and risk of recurrence of symptomatic intracranial atherosclerosis, suggesting that angiogenesis may be beneficial in this condition.

Retroviral delivery of homeobox D3 gene induces cerebral angiogenesis in mice

Angiogenesis is regulated by concerted actions of angiogenic and angiostatic factors. Homeobox D3 gene (HOXD3) is a potent proangiogenic transcription factor that promotes angiogenesis by modulating the expression of matrix-degrading proteinases, integrins, and extracellular matrix components. Application of HOXD3 can promote angiogenesis in the skin, but its role in other vascular beds has not been examined. The authors examined HOXD3 expression in human brain vessels by in situ hybridization. Although little or no HOXD3 mRNA was detected in normal brain vessels, increased levels of HOXD3 and its target gene, alpha V beta 3, were found in angiogenic vessels in human brain arteriovenous malformations. The authors further investigated whether HOXD3 plays a role in cerebral angiogenesis in a murine model. Expression of HOXD3 in mouse brain was achieved through retroviral vector-mediated HOXD3 gene transfer. HOXD3 expression lead to a significant induction of cerebral angiogenesis as shown by quantitative microvessel counting (HOXD3: 241 +/- 19 vessels/mm2 vs. saline: 150 +/- 14 vessels/mm2, P < 0.05). The data also showed that focal cerebral blood flow was increased in the angiogenic region with less vascular leakage. Moreover, expression of HOXD3 led to an increase in the expression of a direct downstream target gene alpha V beta 3 integrin. The data suggest that HOXD3 may play an important role in regulating cerebral angiogenesis, and that gene transfer of HOXD3 may provide a novel and potent means to stimulate angiogenesis.

Increased severity of cerebral ischemic injury in vascular endothelial growth factor-B-deficient mice

Vascular endothelial growth factor-B (VegfB) is an angiogenic protein related to VegfA, although it acts on a different set of tyrosine kinase receptors. Like VegfA, VegfB is expressed in the brain and is induced at sites of brain injury. VegfA has neuroprotective and angiogenic effects, but VegfA-knockout mice die in utero, so the effect of endogenous VegfA signaling in neuropathologic states, such as cerebral ischemia, cannot be tested directly. In contrast, VegfB-knockout mice survive to adulthood with little abnormality in the absence of pathologic stresses. To determine if VegfB regulates the severity of cerebral ischemia, the middle cerebral artery was occluded in VegfB-knockout, heterozygous, and wild-type mice, and the volume of the resulting cerebral infarcts and associated impairment of neurologic function were measured. Infarct volume was increased by approximately 40% and neurologic impairment was more severe in VegfB-knockout mice, implying that endogenous VegfB acts to protect the brain from ischemic injury. VegfB also protected cultured cerebral cortical neurons from hypoxic injury, suggesting that its protective action is mediated at least in part through a direct effect on neurons.

In vivo magnetic resonance imaging tracks adult neural progenitor cell targeting of brain tumor

Using magnetic resonance imaging (MRI), we described a method for noninvasively tracking grafted neural progenitor cells and bone marrow stromal cells (MSCs) in brain tumor of the rat. Neural progenitor cells and MSCs were labeled with lipophilic dye-coated superparamagnetic particles. The labeled neural progenitor cells and MSCs were transplanted to rats via the cisterna magna and a tail vein, respectively, 1 week after 9L-gliosarcoma cell implantation. Three-dimensional (3D) gradient echo and contrast agent images revealed dynamic migration of adult neural progenitor cells and MSCs detected by loss of MRI signals towards tumor mass and infiltrated tumor cells. Prussian blue staining and fluorescent microscope analysis showed that grafted cells targeted tumor cells and areas with grafted cells corresponded to areas with loss of MRI signals. These results demonstrate that the MRI technique provides a sensitive method for in vivo assessment of grafted cells targeting tumor mass and infiltrated tumor cells and that adult neural progenitor cells and MSCs can target tumor aggregates in the brain.

Src family kinase-inhibitor PP2 reduces focal ischemic brain injury

OBJECTIVES

To investigate the neuroprotective potential of the Src family kinase (SFK) inhibitor 4-amino-5-(4-chlorophenyl)-7-(t-butyl) pyrazolo(3,4-d)pyrimidine (PP2) in transient focal cerebral ischemia in the rat.

MATERIAL AND METHODS

Sprague-Dawley rats were exposed to transient (90 min) middle cerebral artery occlusion (MCAO) and evaluated after 1 day of survival. PP2 (1.5 mg/kg i.p.) or vehicle was given 30 min after MCAO. The lesions were examined with magnetic resonance imaging (MRI), tri-phenyl tetrazolium chloride (TTC) staining and the functional outcome was determined using neurological scoring according to Bederson et al.

RESULTS

PP2-treated rats showed approximately 50% reduction of infarct size on T2-weighted MRI and in TTC staining compared with controls (P < 0.05). Moreover, the neurological score was better in the PP2 group than controls (P < 0.05).

CONCLUSION

PP2 is a potential neuroprotective agent in cerebral ischemia-reperfusion. The interference of PP2 with SFKs and/or other pathways remains to be elucidated.

Vascular endothelial growth factor and the nervous system

Vascular endothelial growth factor (VEGF) is an angiogenic factor essential for the formation of new blood vessels during embryogenesis and in many pathological conditions. A new role for VEGF as a neurotrophic factor has recently emerged. In the developing nervous system, VEGF plays a pivotal role not only in vascularization, but also in neuronal proliferation, and the growth of coordinated vascular and neuronal networks. After injury to the nervous system, activation of VEGF and its receptors may restore blood supply and promote neuronal survival and repair. There is a growing body of evidence that VEGF is essential for motor neurone survival, and that aberrant regulation of VEGF may play a role in the degeneration of neurones in diseases such as amyotrophic lateral sclerosis.

Vascular endothelial growth factor is increased in cerebrospinal fluid after traumatic brain injury in infants and children

OBJECTIVE

Vascular endothelial growth factor (VEGF) is an important regulator of angiogenesis, the formation of which is triggered by hypoxia, cytokines, and growth factors and is also induced by activation of the adenosine 2B receptor. VEGF is neuroprotective in several models of experimental brain injury and is increased in brain after traumatic brain injury (TBI) in humans and experimental animals. Adenosine is a neuroprotective purine metabolite that increases in cerebrospinal fluid (CSF) after clinical TBI in children. We hypothesized that VEGF levels would 1). be increased in CSF after TBI in infants and children, and 2). be preceded by increases in CSF adenosine. To test this hypothesis, we designed a case-control study to compare the CSF of infants and children after severe TBI with that of uninjured children.

METHODS

Using an Institutional Review Board-approved protocol, we compared CSF concentrations of VEGF (by enzyme-linked immunosorbent assay) and adenosine (by high-performance liquid chromatography) in 73 samples from 14 infants and children with severe TBI (Glasgow Coma Scale score <or=8) with those in CSF from 5 noninjured control subjects. Patients received standard neurointensive care.

RESULTS

Mean VEGF levels were increased after TBI versus control (39.8 +/- 6.2 versus 14.9 +/- 1.5 ng/dl, mean +/- standard error of the mean, P = 0.0002) and peaked at 91.6 +/- 26.4 ng/dl, approximately 6 times control (P = 0.001). Peak VEGF occurred at 22.4 hours after injury. There was a trend toward increased adenosine concentration after TBI versus control (18.3 +/- 3.5 versus 11.5 +/- 2.3 nmol/L), but this did not reach statistical significance. A multivariate regression model showed an independent, significant association between the concentrations of VEGF and adenosine.

CONCLUSION

VEGF is increased in CSF after pediatric TBI, and this increase is associated with an increase in CSF adenosine. These results may imply that a component of the vascular regenerative response of the brain is initiated rapidly after TBI and continues for several days after injury. Further investigation is warranted to determine 1). whether this association is causative, 2). the role of adenosine in triggering the increase in CSF VEGF concentration, and 3). the exact role VEGF that plays after injury.

Induction of HIF1alpha but not HIF2alpha in motoneurons after ventral funiculus axotomy-implication in neuronal survival strategies

Spinal cord injury is frequently associated with local tissue hypoxia. As neuronal cells are susceptible to damage caused by low oxygen levels, hypoxia-induced activation of tissue-protective factors could represent an endogenous mechanism for neuron survival following injury. We studied in vivo, in a rat model of intraspinal axotomy of motoneurons, the cell- and time-dependent regulation of the hypoxia-inducible transcription factors (HIFs), HIF1alpha and HIF2alpha, as well as one of their target genes, vascular endothelial growth factor (VEGF). VEGF is a potent hypoxia-regulated angiogenic growth factor with recently discovered neuroprotective and neurotrophic activities. While neither HIF1alpha, HIF2alpha, nor VEGF mRNA were detected in noninjured motoneurons, we found a strong induction of HIF1alpha, but not HIF2alpha mRNA in axotomized motoneurons. HIF1alpha expression peaked at about 7 days after injury. Moreover, we found increased VEGF mRNA and protein expression around and within the scar but also within motoneurons, peaking around 3 days after axotomy. In addition, increased survival of cultured motoneurons after treatment with VEGF could also be shown. We conclude that axotomized motoneurons in this model respond to injury by specific induction of HIF1alpha and VEGF expression that may provide an endogenous mechanism with the potential to promote motoneuron survival after injury.

VEGF disrupts the neonatal blood-brain barrier and increases life span after non-ablative BMT in a murine model of congenital neurodegeneration caused by a lysosomal enzyme deficiency

The course of certain congenital neurodegenerative diseases like lysosomal storage diseases (LSDs) begins shortly after birth and can progress quickly. Ideally, therapeutic interventions for LSDs, which include bone marrow transplantation (BMT), recombinant enzyme replacement, or systemic viral-mediated gene therapy, should be initiated at birth. However, the blood-brain barrier (BBB) remains an obstacle to effective therapy even when these strategies are initiated at birth. We studied whether VEGF, an endothelial cell mitogen and permeability factor, can open the BBB in newborn mice for therapeutic purposes. Intravenous (IV) administration of VEGF at birth increased BBB permeability within 2 h. The increased permeability persisted for at least 24 h, became undetectable 48 h after injection, and was restricted to newborns. Systemic VEGF treatment before BMT or administration of recombinant lentivirus resulted in increased numbers of both donor cells and virus-transduced cells, respectively, in the recipient brain. Administration of VEGF before BMT in newborn mice with a neurodegenerative LSD, globoid-cell leukodystrophy, resulted in a significant increase in life span compared to affected animals that were injected with saline before BMT.

Signaling pathways for early brain injury after subarachnoid hemorrhage

Few studies have examined the signaling pathways that contribute to early brain injury after subarachnoid hemorrhage (SAH). Using a rat SAH model, the authors explored the role of vascular endothelial growth factor (VEGF) and mitogen-activation protein kinase (MAPK) in early brain injury. Male Sprague-Dawley rats (n = 172) weighing 300 to 350 g were used for the experimental SAH model, which was induced by puncturing the bifurcation of the left anterior cerebral and middle cerebral arteries. The blood-brain barrier (BBB), brain edema, intracranial pressure, and mortality were evaluated at 24 hours after SAH. The phosphorylation of VEGF and different MAPK subgroups (ERK1/2, p38, and JNK) were examined in both the cortex and the major cerebral arteries. Experimental SAH increased intracranial pressure, BBB permeability, and brain edema and produced high mortality. SAH induced phosphorylation of VEGF and MAPKs in the cerebral arteries and, to a lesser degree, in the cortex. PP1, an Src-family kinase inhibitor, reduced BBB permeability, brain edema, and mortality and decreased the phosphorylation of VEGF and MAPKs. The authors conclude that VEGF contributes to early brain injury after SAH by enhancing the activation of the MAPK pathways, and that the inhibition of these pathways might offer new treatment strategies for SAH.

Co-accumulation of vascular endothelial growth factor with beta-amyloid in the brain of patients with Alzheimer's disease

Alzheimer's disease (AD) is accompanied by the progressive deposition of beta-amyloid (Abeta) in both senile plaques and cerebral blood vessels, loss of central neurons, and vessel damage. Cerebral hypoperfusion is one of the major clinical features in AD and likely plays a critical role in its pathogenesis. In addition to its major roles in angiogenesis, vascular endothelial growth factor (VEGF) has neurotrophic and neuroprotective effects. VEGF is an ischemia-inducible factor and increased expression of VEGF often occurs in AD. Although the presence of VEGF immunoreactivity in the AD brain has been described previously, the direct interaction of VEGF with Abeta has not been established. Here, we show that VEGF is co-localized with Abeta plaques in the brains of patients with AD. In vitro experiments show that VEGF binds to Abeta with high affinity (K(D) approximate to 50 pM). VEGF is co-aggregated with Abeta without any apparent effect on the rate of aggregation, strongly binds to pre-aggregated Abeta, and is very slowly released from the co-aggregated complex. Continuous deposition of VEGF in the amyloid plaques most likely results in deficiency of available VEGF under hypoperfusion and, thus, may contribute to neurodegeneration and vascular dysfunction in the progression of AD.

Neuroprotection of ischemic brain by vascular endothelial growth factor is critically dependent on proper dosage and may be compromised by angiogenesis

Vascular endothelial growth factor (VEGF) is currently considered a potential pharmacologic agent for stroke therapy because of its strong neuroprotective and angiogenic capacities. Nonetheless, it is unclear how neuroprotection and angiogenesis by exogenous VEGF are related and whether they are concurrent events. In this study, the authors evaluated by stereology the effect of VEGF on neuronal and vascular volume densities of normal and ischemic brain cortices of adult male Sprague-Dawley rats. Ischemia was induced by a 4-hour occlusion of the middle cerebral artery. Low, intermediate, and high doses of VEGF165 were infused through the internal carotid artery for 7 days by an indwelling osmotic pump. The low and intermediate doses, which did not induce angiogenesis, significantly promoted neuroprotection of ischemic brains and did not damage neurons of normal brains. In contrast, the high dose that induced angiogenesis showed no neuroprotection of ischemic brains and damaged neurons of normal brains. These findings suggest that in vivo neuroprotection of ischemic brains by exogenous VEGF does not necessarily occur simultaneously with angiogenesis. Instead, neuroprotection may be greatly compromised by doses of VEGF capable of inducing angiogenesis. Stroke intervention efforts attempting to induce neuroprotection and angiogenesis concurrently through VEGF monotherapy should be approached with caution.

VEGF: necessary to prevent motoneuron degeneration, sufficient to treat ALS?

Since Charcot recognized the devastating disorder amyotrophic lateral sclerosis (ALS) in 1874, many theories have been proposed to explain its pathogenesis, but it remains as deadly and incurable as ever. Three years ago it was reported that reduced levels of vascular endothelial growth factor (VEGF) caused ALS-like motoneuron degeneration in mice. Recent evidence indicates that insufficient VEGF is also a risk factor for ALS in humans. Although VEGF was once considered to be only a specific angiogenic factor, emerging evidence indicates that it also displays important neuroprotective activity. These insights have primed widespread interest in developing VEGF-based therapies for (moto)neuron degenerative disorders, raising new hope for the treatment of ALS and other neurodegenerative diseases.

Circulating Tissue Kallikrein Levels Correlate With Severity of Carotid Atherosclerosis

Background— Vascular growth factors are upregulated in stroke patients, but it remains unknown if they correlate with carotid atherosclerosis.

Methods and Results— A case-control study was conducted to determine: (1) possible association between biomarkers of angiogenesis or inflammation and carotid stenosis; and (2) the impact of revascularization on the same biomarkers. Circulating vascular endothelial growth factor (VEGF), basic fibroblast GF (bFGF), tissue kallikrein (tK), and high-sensitivity C-reactive protein (hs-CRP) were measured in 89 patients with carotid obstruction and 45 age-matched controls. Patients were stratified as <50% carotid stenosis (CAS; n=16); 50% to 69% CAS (n=12); 70% to 99% CAS (n=43); and carotid occlusion (CAO; n=18). No association was found between VEGF, bFGF, or hs-CRP and obstruction grading. TK augmented from 360±30 in <50% CAS ( P =NS versus controls) to 509±72 in moderate CAS ( P <0.05), 1159±178 in high-grade CAS ( P <0.02), and 1616±403 pg/mL in CAO ( P <0.01). A threshold of 508 pg/mL provided the maximized predictive value of high-grade obstruction. After revascularization, tK decreased from 1410±352 to 782±86 pg/mL ( P <0.01), whereas no change was detected in nonoperated cases. Hs-CRP was unaffected by revascularization.

Conclusions— Angiogenic factors are heterogeneously expressed in patients with carotid atherosclerosis. The tK measurement may be useful for the diagnosis and monitoring of atherosclerotic disease.

Combination therapy of stroke in rats with a nitric oxide donor and human bone marrow stromal cells enhances angiogenesis and neurogenesis

We tested the hypothesis that intravenous infusion of human marrow stromal cells (hMSC) with a nitric oxide donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) aminio] diazen-1-ium-1,2-diolate (DETA/NONOate), enhances angiogenesis, neurogenesis and neurological functional recovery after stroke in rats compared to individual therapy. Experimental groups consist of rats subjected to 2 h of middle cerebral artery occlusion (MCAo) and at 24 h after MCAo intravenous injection of (n=10/group): Group 1: phosphate buffered saline (PBS 1 ml) for control. Group 2: NONOate alone (0.4 mg/kg). Group 3: hMSCs (1 x 10(6)) alone. Group 4: hMSCs (1 x 10(6)) with NONOate (0.4 mg/kg). Functional tests and immunohistochemical staining were performed. Marginal functional recovery after treatment of stroke was found with 1 x 10(6) hMSCs alone (p=0.06) and no benefit was detected with NONOate alone (0.4 mg/kg, p=0.64). However, NONOate+hMSCs in combination significantly induced functional recovery (p<0.05). Treatment using hMSC in combination with NONOate significantly increased vessel perimeter and endothelial cell proliferation compared with hMSC or NONOate alone treatment (p<0.05). Cell proliferation and neurogenesis were assessed with bromodeoxyuridine (BrdU) labeling and immunostaining for cell type-specific markers. Combination treatment promoted increased, BrdU positive cell number in the subventricular zone (SVZ), migrating neuronal doublecortin immunoreactive cells and VEGF and bFGF expression in the ischemic boundary area compared to individual treatment. The functional therapeutic enhancement of combination treatment may be attributed to increased plasticity induced by the combination of a nitric oxide donor and hMSC therapy. These data suggest that pharmacological and cellular therapy may provide an additive therapeutic benefit after stroke.

Vascular endothelial cadherin and beta-catenin in human fetoplacental vessels of pregnancies complicated by Type 1 diabetes: associations with angiogenesis and perturbed barrier function

AIMS/HYPOTHESIS

Increased angiogenesis of fetoplacental vessels is a feature of pregnancies complicated by Type 1 diabetes mellitus, but the underlying molecular mechanisms are unknown. This investigation tests whether the diabetic maternal environment alters the phenotypic expression of placental vascular endothelial cadherin and beta-catenin, which have been implicated as key molecules in barrier formation and angiogenesis in the endothelium.

METHODS

Term placental microvessels from normal pregnancies (n=8) and from those complicated by Type 1 diabetes (n=8) were perfused with 76-Mr dextran tracers (1 mg/ml) and subjected to immunocytochemistry, immunoblotting and microscopy. Junctional integrity, localisation and phosphorylation were investigated along with total protein levels of vascular endothelial cadherin, beta-catenin and vascular endothelial growth factor. Stereological sampling and estimation tools were used to quantify aspects of angiogenesis and endothelial proliferation.

RESULTS

In the Type 1 diabetic placentae, junctional localisations of vascular endothelial cadherin and beta-catenin altered significantly, with more than 50% of microvessels showing complete loss of immunoreactivity and with no overall loss of total protein. Tracer leakage was associated with these vessels. There was a two- to three-fold increase in vessels showing junctional phospho-tyrosine immunoreactivity and hyperphosphorylated beta-catenin. Vascular endothelial growth factor levels were higher in these placentae. A four-fold increase in endothelial proliferation was observed, along with an increase in total length of capillaries without any change in luminal diameter.

CONCLUSIONS/INTERPRETATION

Molecular perturbations of vascular endothelial cadherin and beta-catenin occur in fetoplacental vessels of pregnancies complicated by Type 1 diabetes. Phosphorylation and loss of these molecules from the adherens junctional domains may be influenced in part by the elevated levels of vascular endothelial growth factor in the placenta. Perturbations of the junctional proteins may explain the observed breach in barrier integrity and may contribute to the mechanisms that drive proliferation and increases in capillary length.

Post-ischemic administration of heparin-binding epidermal growth factor-like growth factor (HB-EGF) reduces infarct size and modifies neurogenesis after focal cerebral ischemia in the rat

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a hypoxia-inducible, neuroprotective protein that also stimulates proliferation of neuronal precursor cells. Accordingly, HB-EGF may contribute to recovery from cerebral injury through direct neuroprotective effects, by enhancing neurogenesis, or both. When administered by the intracerebroventricular route 1-3 days after focal cerebral ischemia in adult rats, HB-EGF decreased the volume of the resulting infarcts and reduced post-ischemic neurological deficits. HB-EGF also increased the incorporation of bromodeoxyuridine into cells expressing the immature neuronal marker protein TUC-4 in the dentate subgranular and rostral subventricular zones, consistent with increased proliferation of neuronal precursors. However, HB-EGF decreased the number of newborn neurons that migrated into the ischemic striatum, perhaps partly because reduction of infarct size by HB-EGF also reduced the stimulus to migration. To determine if HB-EGF might also directly inhibit migration of neuronal precursors, we co-cultured subventricular zone (SVZ) explants treated with HB-EGF or vehicle together with hypoxic cerebral cortical explants, and measured cell migration from the former toward the latter. HB-EGF reduced directed migration of SVZ cells toward the cortical explants, possibly due to a local chemoattractant effect on neuronal precursor cells, which may be mediated through the HB-EGF-specific receptor, N-arginine dibasic convertase. The delayed neuroprotective effect of HB-EGF may have implications for efforts to prolong the therapeutic window for intervention in stroke.

VEGF: a critical player in neurodegeneration

VEGF is a prototype angiogenic factor, but recent evidence indicates that this growth factor also has direct effects on neural cells. Abnormal regulation of VEGF expression has now been implicated in several neurodegenerative disorders, including motoneuron degeneration. This has stimulated an increasing interest in assessing the therapeutic potential of VEGF as a neuroprotective agent for such neurodegenerative disorders.

Vascular endothelial growth factor induces abnormal microvasculature in the endoglin heterozygous mouse brain

Hereditary hemorrhagic telangiectasia (HHT), associated with brain arteriovenous malformations, is caused by a loss of function mutation in either the endoglin (HHT1) or activin receptor-like kinase 1 gene (ALK-1, HHT2). Endoglin heterozygous (Eng+/-)mice have been proposed as a disease model. To better understand the role of endoglin in vascular malformation development, we examined the effect of vascular endothelial growth factor (VEGF) hyperstimulation on microvessels in adult endoglin heterozygous (Eng+/-) mice using an adenoviral vector to deliver recombinant human VEGF165 cDNA (AdhVEGF) into basal ganglia. VEGF expression was increased in AdhVEGF mice compared with the AdlacZ and saline group (P < 0.05) and localized to multiple cell types (neurons, astrocytes, endothelial cells, and smooth muscle cells) by double-labeled immunostaining. VEGF overexpression increased microvessel count for up to 4 weeks in both the Eng+/+ and Eng+/- groups (Eng+/+ 185 +/- 14 vs. Eng+/- 201 +/- 10 microvessels/mm2). Confocal microscopic examination revealed grossly abnormal microvessels in eight of nine Eng+/- mouse brains compared with zero of nine in Eng+/+ mice (P < 0.05). Abnormal microvessels featured enlargement, clustering, twist, or spirals. VEGF receptor Flk-1 and TGF-beta receptor 1 (T beta R1) expression were reduced in the Eng+/- mouse brain compared with control. Excessive VEGF stimulation may play a pivotal role in the initiation and development of brain vessel malformations in states of relative endoglin insufficiency in adulthood. These observations are relevant to our general understanding of the maintenance of vascular integrity.

Effects of vascular endothelial growth factor on isolated fetal alveolar type II cells

Previous investigations gained from in vivo or lung explant studies suggested that VEGF is an autocrine proliferation and maturation factor for developing alveolar type II cells. The objective of this work was to determine whether VEGF exerted its growth and maturation effects directly on isolated type II cells. These were isolated from 19-day fetal rat lung and cultured in defined medium. The presence of VEGF receptor-2 was assessed in cultured cells at the pre- and posttranslational levels. Recombinant VEGF(165), formerly found to be active on lung explants, failed to enhance type II cell proliferation estimated by thymidine and 5-bromo-2'-deoxy-uridine incorporation. It increased choline incorporation in saturated phosphatidylcholine by 27% but did not increase phospholipid surfactant pool size. VEGF (100 ng/ml) left unchanged the transcript level of surfactant proteins (SP)-A, SP-C, and SP-D but increased SP-B transcripts to four times the control steady-state level. VEGF slightly retarded, but did not prevent, the in vitro transdifferentiation of type II into type I cells, as assessed by immunolabeling of the type I cell marker T1alpha. We conclude that, with the exception of SP-B expression, which appears to be controlled directly, the previously observed effects of this VEGF isoform on type II cells are likely to be exerted indirectly through reciprocal paracrine interactions involving other lung cell types.

VEGF165 therapy exacerbates secondary damage following spinal cord injury

Vascular endothelial growth factor (VEGF) demonstrates potent and well-characterized effects on endothelial cytoprotection and angiogenesis. In an attempt to preserve spinal microvasculature and prolong the endogenous neovascular response observed transiently following experimental spinal cord injury (SCI), exogenous recombinant human VEGF (rhVEGF165) was injected into the injured rat spinal cord. Adult female Fischer 344 rats were subjected to moderate SCI (12.5 g-cm) using the NYU impactor. At 72 h after injury, animals were randomly assigned to three experimental groups receiving no microinjection or injection of saline or saline containing 2 microg of rhVEGF165. Acutely, VEGF injection resulted in significant microvascular permeability and infiltration of leukocytes into spinal cord parenchyma. 6 weeks postinjection, no significant differences were observed in most measures of microvascular architecture following VEGF treatment, but analysis of histopathology in spinal cord tissue revealed profound exacerbation of lesion volume. These results support the idea that intraparenchymal application of the proangiogenic factor VEGF may exacerbate SCI, likely through its effect on vessel permeability.

Structural, functional, and molecular MR imaging of the microvasculature

Magnetic resonance imaging (MRI) is widely applied for functional imaging of the microcirculation and for functional and structural studies of the microvasculature. The interest in the capabilities of MRI in noninvasively monitoring changes in vascular structure and function expanded over the past years, with specific efforts directed toward the development of novel imaging methods for quantification of angiogenesis. Molecular imaging approaches hold promise for further expansion of the ability to characterize the microvasculature. Exciting applications for MRI are emerging in the study of the biology of microvessels and in the evaluation of potential pharmaceutical modulators of vascular function and development, and preclinical MRI tools can serve for the design of mechanism-of-action-based noninvasive clinical methods for monitoring response to therapy. The aim of this review is to provide a current snapshot of recent developments in this rapidly evolving field.

Novel therapeutic strategy to treat brain ischemia: overexpression of hepatocyte growth factor gene reduced ischemic injury without cerebral edema in rat model

BACKGROUND

Although cerebral occlusive disease leads to cerebral ischemic events, an effective treatment has not yet been established. An ideal therapeutic approach to treat ischemia might have both aspects of enhancement of collateral formation and prevention of neuronal death. Hepatocyte growth factor (HGF) is a potent angiogenic factor that also acts as a neurotrophic factor. Thus, in this study, we examined the therapeutic effects of HGF on brain injury in a rat permanent middle cerebral artery occlusion model.

METHODS AND RESULTS

Gene transfer into the brain was performed by injection of human HGF gene with hemagglutinating virus of Japan-envelope vector into the cerebrospinal fluid via the cisterna magna. Overexpression of the HGF gene resulted in a significant decrease in the infarcted brain area as assessed by triphenyltetrazolium chloride staining, whereas rats transfected with control vector exhibited a wide area of brain death after 24 hours of ischemia. Consistently, the decrease in neurological deficit was significantly attenuated in rats transfected with the HGF gene at 24 hours after the ischemic event. Stimulation of angiogenesis was also detected in rats transfected with the HGF gene compared with controls. Of importance, no cerebral edema or destruction of the blood-brain barrier was observed in rats transfected with the HGF gene.

CONCLUSIONS

Overall, the present study demonstrated that overexpression of the HGF gene attenuated brain ischemic injury in a rat model, without cerebral edema, through angiogenic and neuroprotective actions. In particular, the reduction of brain injury by HGF may provide a new therapeutic option to treat cerebrovascular disease.

The Potential Role of Vascular Endothelial Growth Factor in the Central Nervous System

During the past decade, vascular endothelial growth factor (VEGF) has been widely investigated, and reported to have pleiotropic functions in the central nervous system (CNS) and its supporting physiological environment. VEGF is involved in not only such well-known functions as angiogenesis, accentuation of vessel permeability, and glial proliferation, but also more recently acknowledged functions such as neuroprotection and even neurogenesis itself. Most recently, the neurogenesis function has attracted much attention, and a number of research groups have taken up the challenge of elucidating this activity. In keeping with this trend, our knowledge of VEGF receptors has increased, and certain suggestions concerning the mechanisms of neuroprotection have come to light in the course of the ongoing work, though at times what the researchers had to work with was only a tiny percent of the signal transduction of VEGF. Together with flt-1 (VEGF receptor 1) and flk-1 (VEGF receptor 2), neuropilin (NP) is frequently described as being involved in the neuroprotective effects of VEGF. In this review, both the direct and indirect neuroprotective effects of VEGF, including various signaling pathways as well as the neurogenesis induced by this factor, are discussed in the context of the newly emerging insights into the biological mechanisms of VEGF and closely related, interacting molecules.

VEGF: once regarded as a specific angiogenic factor, now implicated in neuroprotection

Both blood vessels and nerves are guided to their target. Vascular endothelial growth factor (VEGF)A is a key signal in the induction of vessel growth (a process termed angiogenesis). Though initial studies, now a decade ago, indicated that VEGF is an endothelial cell-specific factor, more recent findings revealed that VEGF also has direct effects on neural cells. Genetic studies showed that mice with reduced VEGF levels develop adult-onset motor neuron degeneration, reminiscent of the human neurodegenerative disorder amyotrophic lateral sclerosis (ALS). Additional genetic studies confirmed that VEGF is a modifier of motor neuron degeneration in humans and in SOD1(G93A) mice--a model of ALS. Reduced VEGF levels may promote motor neuron degeneration by limiting neural tissue perfusion and VEGF-dependent neuroprotection. VEGF also affects neuron death after acute spinal cord or cerebral ischemia, and has also been implicated in other neurological disorders such as diabetic and ischemic neuropathy, nerve regeneration, Parkinson's disease, Alzheimer's disease and multiple sclerosis. These findings have raised growing interest in assessing the therapeutic potential of VEGF for neurodegenerative disorders.

Vascular endothelial growth factor (VEGF) in seizures: a double-edged sword

Vascular endothelial growth factor (VEGF) is a vascular growth factor which induces angiogenesis (the development of new blood vessels), vascular permeability, and inflammation. In brain, receptors for VEGF have been localized to vascular endothelium, neurons, and glia. VEGF is upregulated after hypoxic injury to the brain, which can occur during cerebral ischemia or high-altitude edema, and has been implicated in the blood-brain barrier breakdown associated with these conditions. Given its recently-described role as an inflammatory mediator, VEGF could also contribute to the inflammatory responses observed in cerebral ischemia. After seizures, blood-brain barrier breakdown and inflammation is also observed in brain, albeit on a lower scale than that observed after stroke. Recent evidence has suggested a role for inflammation in seizure disorders. We have described striking increases in VEGF protein in both neurons and glia after pilocarpine-induced status epilepticus in the brain. Increases in VEGF could contribute to the blood-brain barrier breakdown and inflammation observed after seizures. However, VEGF has also been shown to be neuroprotective across several experimental paradigms, and hence could potentially protect vulnerable cells from damage associated with seizures. Therefore, the role of VEGF after seizures could be either protective or destructive. Although only further research will determine the exact nature of VEGF's role after seizures, preliminary data indicate that VEGF plays a protective role after seizures.

VEGF: a critical player in neurodegeneration

VEGF is a prototype angiogenic factor, but recent evidence indicates that this growth factor also has direct effects on neural cells. Abnormal regulation of VEGF expression has now been implicated in several neurodegenerative disorders, including motoneuron degeneration. This has stimulated an increasing interest in assessing the therapeutic potential of VEGF as a neuroprotective agent for such neurodegenerative disorders.

Increased brain injury and vascular leakage after pretreatment with p38-inhibitor SB203580 in transient ischemia

OBJECTIVES

Focal cerebral ischemia activates intracellular signaling pathways including the mitogen-activated protein kinase p38, which may be involved in the process of ischemic brain injury. In this study, the effect of pretreatment with the p38-inhibitor SB203580 on infarct size and blood-brain barrier (BBB) breakdown was investigated with magnetic resonance imaging (MRI).

MATERIALS AND METHODS

Rats were given SB203580 (n = 6) or vehicle (n = 6) in the right lateral ventricle prior to transient (90 min) middle cerebral artery occlusion (MCAO) on the left side. The rats were examined with serial MRI during MCAO, at reperfusion and after 1 and 4 days.

RESULTS

The mean infarct size on T2-weighted images after 1 day was significantly higher in the SB203580-treated group than in controls (300 +/- 95 mm3 vs 126 +/- 75 mm3; P < 0.01). Vascular gadolinium leakage, indicating BBB breakdown, was significantly larger in the SB203580-treated group than in controls after 1 day (median leakage score 18.5; range 15-21 vs 6.5; 4-17; P < 0.05) and 4 days (11; 6-15 vs 3.5; 1-9; P < 0.05), although no significant difference was seen initially.

CONCLUSION

Pretreatment with SB203580 may aggravate ischemic brain injury and cerebral vascular leakage in the present model of transient ischemia.

Vascular Endothelial Growth Factor Expression and Angiogenesis Induced by Chronic Cerebral Hypoperfusion in Rat Brain

OBJECTIVE

In a rat model, we studied the time courses of vascular endothelial growth factor (VEGF) expression and angiogenesis induced by chronic cerebral hypoperfusion in the brain, and we investigated the histological basis of normal-perfusion pressure breakthrough.

METHODS

Twenty-one Sprague-Dawley rats were randomly divided into a control group (n = 3) and a model group assessed at various time points after the creation of a carotid artery-jugular vein fistula (12 h, n = 3; 24 h, n = 3; 72 h, n = 3; 7 d, n = 3; 21 d, n = 3; 90 d, n = 3). The time courses of the expression of VEGF messenger ribonucleic acid (mRNA) and protein in rat brain were analyzed with semiquantitative reverse transcriptase-polymerase chain reaction and Western blot assays, respectively. Immunohistochemical techniques were used to evaluate VEGF protein localization with rabbit polyclonal anti-rat VEGF, VEGF receptor (VEGFR) expression with rabbit polyclonal antibodies to VEGFR-1 and -2, microvascular density with mouse monoclonal anti-rat CD31, and astrocytic reactivity with polyclonal anti-glial fibrillary acidic protein, in cerebral cortical tissue of the right middle cerebral artery territory.

RESULTS

Three alternative splicing forms, i.e., VEGF(188), VEGF(164), and VEGF(120), were observed in cerebral cortical tissue of the right middle cerebral artery territory in semiquantitative reverse transcriptase-polymerase chain reaction analyses. VEGF(164) mRNA was the predominant isoform expressed in rat brain. VEGF(188) mRNA and VEGF(120) mRNA were also detected but at very low levels (not statistically significant). Low levels of VEGF(164) mRNA were observed in the control brains. However, VEGF(164) mRNA levels were significantly increased in the model brains at 24 hours postoperatively, peaked by 7 days, decreased by 21 days, and returned to basal levels by 90 days after fistula formation. VEGF protein expression, as measured in Western blot assays, was also increased in rat brains in the model group from 24 hours to 21 days postoperatively but returned to control levels by 90 days after fistula formation. VEGF immunohistochemical analyses indicated that this increased expression was mostly associated with endothelial cells. Consistent with the VEGF protein expression findings, up-regulation of VEGFR-1 but not VEGFR-2 expression on endothelial cells in the model brains was observed. Microvascular density in the rat brains began to increase significantly 7 days after fistula formation in the model group, as assessed immunohistochemically, and the increase was maintained for 90 days. Although no prominent astrocytic reactivity was observed in the rat brains throughout the experiments, there was an absence of astrocytic foot processes surrounding some cerebral capillaries 90 days after fistula formation in the model group.

CONCLUSION

These results demonstrated that chronic cerebral hypoperfusion could induce sustained up-regulation of VEGF mRNA and protein expression in rat brain, which was correlated with angiogenesis. An absence of corresponding astrocytic reactivity during angiogenesis may be an important factor accounting for structural deficits of the blood-brain barrier and the occurrence of normal-perfusion pressure breakthrough.

Hypoxic induction of endoglin via mitogen-activated protein kinases in mouse brain microvascular endothelial cells

BACKGROUND AND PURPOSE

Endoglin (CD105) is a membrane glycoprotein that is mutated in hereditary hemorrhagic telangiectasia (Osler-Rendu-Weber disease) and shows increased expression in proliferating endothelial cells during angiogenesis.

METHODS

We investigated the effect of hypoxia on endoglin expression in murine cerebral microvascular endothelial (bEND.3) cells in vitro and the possible involvement of mitogen-activated protein kinase (MAPK) pathways.

RESULTS

Hypoxia increased endoglin mRNA and protein expression in bEND.3 cells, which was associated with phosphoactivation of extracellular signal-related kinase (ERK), p38 MAPK, and Jun amino-terminal kinase (JNK). Inhibitors of p38 decreased hypoxic induction of endoglin expression, as did dominant negative MAPK kinase 3 (MKK3), which activates p38. In contrast, constitutively active MKK3 or JNK1 potentiated the hypoxic induction of endoglin.

CONCLUSIONS

These results indicate that hypoxia induces the expression of endoglin at both the mRNA and protein levels and that induction is regulated by the p38 and perhaps also JNK pathways.

Differential temporal expression of matrix metalloproteinases after spinal cord injury: relationship to revascularization and wound healing

OBJECT

Matrix metalloproteinases (MMPs), particularly MMP-9/gelatinase B, promote early inflammation and barrier disruption after spinal cord injury (SCI). Early blockade of MMPs after injury provides neuroprotection and improves motor outcome. There is recent evidence, however, that MMP-9 and MMP-2/gelatinase A participate in later wound healing in the injured cord. The authors therefore examined the activity of these gelatinases during revascularization and glial scar formation in the contused murine spinal cord.

METHODS

Gelatinase activity was evaluated using gelatin zymography 24 hours after a mild, moderate, or severe contusion injury. The active form of MMP-2 was not detected, whereas MMP-9 activity was evident in all SCI groups and rose with increasing injury severity. The temporal expression of gelatinases was then examined using gelatin zymography after a moderate SCI. The active form of MMP-9 was most prominent at 1 day, extended through the early period of revascularization, and returned to control by 14 days. The active form of MMP-2 appeared at 7 days postinjury and remained elevated compared with that documented in sham-treated mice for at least 21 days. Increased MMP-2 activity coincided with both revascularization and glial scar formation. Using in situ zymography, gelatinolytic activity was detected in the meninges, vascular elements, glia, and macrophage-like cells in the injured cord. Results of immunolabeling confirmed the presence of gelatinase in vessels during revascularization and in reactive astrocytes associated with glial scar formation.

CONCLUSIONS

These findings suggest that although MMP-9 and -2 exhibit overlapping expression during revascularization, the former is associated with acute injury responses and the latter with formation of a glial scar.

Survivin-dependent angiogenesis in ischemic brain: molecular mechanisms of hypoxia-induced up-regulation

Approaches to regulating angiogenesis in the brain, which may diminish parenchymal damage after stroke, are lacking. Survivin, the inhibitor of apoptosis protein, is up-regulated in vitro in vascular endothelial cells by angiogenic factors, including vascular endothelial cell growth factor (VEGF). To evaluate the in vivo role of survivin in the brain in response to hypoxia/ischemia, we used a mouse model of stroke and show that 2 days after permanent middle cerebral artery occlusion, survivin is uniquely expressed by microvessels that form in the peri-infarct and infarct regions. The extent of vascularization of the infarct is dependent on expression of survivin, since vessel density is significantly reduced in mice with heterozygous deficiency of the survivin gene (survivin+/- mice), even though infarct sizes were not different. Hypoxia alone induces survivin expression in the brain, by cultured endothelial cells and by embryonic stem cells, but this response is at least partially independent of VEGF, hypoxia inducible factor 1alpha, or placental growth factor. Delineating the spatiotemporal pattern of expression of survivin after stroke, and the molecular mechanisms by which this is regulated, may provide novel approaches to therapeutically optimize angiogenesis in a variety of ischemic disorders.

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

Vascular endothelial growth factor (VEGF) is an angiogenic protein with therapeutic potential in ischemic disorders, including stroke. VEGF confers neuroprotection and promotes neurogenesis and cerebral angiogenesis, but the manner in which these effects may interact in the ischemic brain is poorly understood. We produced focal cerebral ischemia by middle cerebral artery occlusion for 90 minutes in the adult rat brain and measured infarct size, neurological function, BrdU labeling of neuroproliferative zones, and vWF-immunoreactive vascular profiles, without and with intracerebroventricular administration of VEGF on days 1-3 of reperfusion. VEGF reduced infarct size, improved neurological performance, enhanced the delayed survival of newborn neurons in the dentate gyrus and subventricular zone, and stimulated angiogenesis in the striatal ischemic penumbra, but not the dentate gyrus. We conclude that in the ischemic brain VEGF exerts an acute neuroprotective effect, as well as longer latency effects on survival of new neurons and on angiogenesis, and that these effects appear to operate independently. VEGF may, therefore, improve histological and functional outcome from stroke through multiple mechanisms.

Cerebral microvessel responses to focal ischemia

Cerebral microvessels have a unique ultrastructure form, which allows for the close relationship of the endothelium and blood elements to the neurons they serve, via intervening astrocytes. To focal ischemia, the cerebral microvasculature rapidly displays multiple dynamic responses. Immediate events include breakdown of the primary endothelial cell permeability barrier, with transudation of plasma, expression of endothelial cell-leukocyte adhesion receptors, loss of endothelial cell and astrocyte integrin receptors, loss of their matrix ligands, expression of members of several matrix-degrading protease families, and the appearance of receptors associated with angiogenesis and neovascularization. These events occur pari passu with neuron injury. Alterations in the microvessel matrix after the onset of ischemia also suggest links to changes in nonvascular cell viability. Microvascular obstruction within the ischemic territory occurs after occlusion and reperfusion of the feeding arteries ("focal no-reflow" phenomenon). This can result from extrinsic compression and intravascular events, including leukocyte(-platelet) adhesion, platelet-fibrin interactions, and activation of coagulation. All of these events occur in microvessels heterogeneously distributed within the ischemic core. The panorama of acute microvessel responses to focal cerebral ischemia provide opportunities to understand interrelationships between neurons and their microvascular supply and changes that underlie a number of central nervous system neurodegenerative disorders.