Massive inborn angiogenesis in the brain scarcely raises cerebral blood flow

The Preventive Effect of Exercise and Oral Branched-Chain Amino Acid Supplementation on Obesity-Induced Brain Changes in Ldlr−/−.Leiden Mice

Exercise and dietary interventions are promising approaches to tackle obesity and its obesogenic effects on the brain. We investigated the impact of exercise and possible synergistic effects of exercise and branched-chain amino acids (BCAA) supplementation on the brain and behavior in high-fat-diet (HFD)-induced obese Ldlr−/−.Leiden mice. Baseline measurements were performed in chow-fed Ldlr−/−.Leiden mice to assess metabolic risk factors, cognition, and brain structure using magnetic resonance imaging. Thereafter, a subgroup was sacrificed, serving as a healthy reference. The remaining mice were fed an HFD and divided into three groups: (i) no exercise, (ii) exercise, or (iii) exercise and dietary BCAA. Mice were followed for 6 months and aforementioned tests were repeated. We found that exercise alone changed cerebral blood flow, attenuated white matter loss, and reduced neuroinflammation compared to non-exercising HFD-fed mice. Contrarily, no favorable effects of exercise on the brain were found in combination with BCAA, and neuroinflammation was increased. However, cognition was slightly improved in exercising mice on BCAA. Moreover, BCAA and exercise increased the percentage of epididymal white adipose tissue and muscle weight, decreased body weight and fasting insulin levels, improved the circadian rhythm, and transiently improved grip strength. In conclusion, BCAA should be supplemented with caution, although beneficial effects on metabolism, behavior, and cognition were observed.

Microvascular Alterations in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder associated with continual decline in cognition and ability to perform routine functions such as remembering familiar places or understanding speech. For decades, amyloid beta (Aβ) was viewed as the driver of AD, triggering neurodegenerative processes such as inflammation and formation of neurofibrillary tangles (NFTs). This approach has not yielded therapeutics that cure the disease or significant improvements in long-term cognition through removal of plaques and Aβ oligomers. Some researchers propose alternate mechanisms that drive AD or act in conjunction with amyloid to promote neurodegeneration. This review summarizes the status of AD research and examines research directions including and beyond Aβ, such as tau, inflammation, and protein clearance mechanisms. The effect of aging on microvasculature is highlighted, including its contribution to reduced blood flow that impairs cognition. Microvascular alterations observed in AD are outlined, emphasizing imaging studies of capillary malfunction. The review concludes with a discussion of two therapies to protect tissue without directly targeting Aβ for removal: (1) administration of growth factors to promote vascular recovery in AD; (2) inhibiting activity of a calcium-permeable ion channels to reduce microglial activation and restore cerebral vascular function.

Increased putamen hypercapnic vasoreactivity in levodopa-induced dyskinesia

In a rodent model of Parkinson's disease (PD), levodopa-induced involuntary movements have been linked to striatal angiogenesis - a process that is difficult to document in living human subjects. Angiogenesis can be accompanied by localized increases in cerebral blood flow (CBF) responses to hypercapnia. We therefore explored the possibility that, in the absence of levodopa, local hypercapnic CBF responses are abnormally increased in PD patients with levodopa-induced dyskinesias (LID) but not in their nondyskinetic (NLID) counterparts. We used H215O PET to scan 24 unmedicated PD subjects (12 LID and 12 NLID) and 12 matched healthy subjects in the rest state under normocapnic and hypercapnic conditions. Hypercapnic CBF responses were compared to corresponding levodopa responses from the same subjects. Group differences in hypercapnic vasoreactivity were significant only in the posterior putamen, with greater CBF responses in LID subjects compared with the other subjects. Hypercapnic and levodopa-mediated CBF responses measured in this region exhibited distinct associations with disease severity: the former correlated with off-state motor disability ratings but not symptom duration, whereas the latter correlated with symptom duration but not motor disability. These are the first in vivo human findings linking LID to microvascular changes in the basal ganglia.

Motor neurons control blood vessel patterning in the developing spinal cord

Formation of a precise vascular network within the central nervous system is of critical importance to assure delivery of oxygen and nutrients and for accurate functionality of neuronal networks. Vascularization of the spinal cord is a highly stereotypical process. However, the guidance cues controlling blood vessel patterning in this organ remain largely unknown. Here we describe a new neuro-vascular communication mechanism that controls vessel guidance in the developing spinal cord. We show that motor neuron columns remain avascular during a developmental time window, despite expressing high levels of the pro-angiogenic vascular endothelial growth factor (VEGF). We describe that motor neurons express the VEGF trapping receptor sFlt1 via a Neuropilin-1-dependent mechanism. Using a VEGF gain-of-function approach in mice and a motor neuron-specific sFlt1 loss-of-function approach in chicken, we show that motor neurons control blood vessel patterning by an autocrine mechanism that titrates motor neuron-derived VEGF via their own expression of sFlt1.

The guidance cues regulating blood vessel patterning in the central nervous system remain unclear. Here, the authors show in mice and chicken developing spinal cord that motor neurons control blood vessel patterning by an autocrine mechanism titrating VEGF via the expression of its trapping receptor sFlt1.

Effects of voluntary exercise on structure and function of cortical microvasculature

Aerobic activity has been shown highly beneficial to brain health, yet much uncertainty still surrounds the effects of exercise on the functioning of cerebral microvasculature. This study used two-photon fluorescence microscopy to examine cerebral hemodynamic alterations as well as accompanying geometric changes in the cortical microvascular network following five weeks of voluntary exercise in transgenic mice endogenously expressing tdTomato in vascular endothelial cells to allow visualization of microvessels irrespective of their perfusion levels. We found a diminished microvascular response to a hypercapnic challenge (10% FiCO₂) in running mice when compared to that in nonrunning controls despite commensurate increases in transcutaneous CO₂ tension. The flow increase to hypercapnia in runners was 70% lower than that in nonrunners (p = 0.0070) and the runners' arteriolar red blood cell speed changed by only half the amount seen in nonrunners (p = 0.0085). No changes were seen in resting hemodynamics or in the systemic physiological parameters measured. Although a few unperfused new vessels were observed on visual inspection, running did not produce significant morphological differences in the microvascular morphometric parameters, quantified following semiautomated tracking of the microvascular networks. We propose that voluntary running led to increased cortical microvascular efficiency and desensitization to CO₂ elevation.

Nogo-A regulates vascular network architecture in the postnatal brain

Recently, we discovered a new role for the well-known axonal growth inhibitory molecule Nogo-A as a negative regulator of angiogenesis in the developing central nervous system. However, how Nogo-A affected the three-dimensional (3D) central nervous system (CNS) vascular network architecture remained unknown. Here, using vascular corrosion casting, hierarchical, synchrotron radiation μCT-based network imaging and computer-aided network analysis, we found that genetic ablation of Nogo-A significantly increased the three-dimensional vascular volume fraction in the postnatal day 10 (P10) mouse brain. More detailed analysis of the cerebral cortex revealed that this effect was mainly due to an increased number of capillaries and capillary branchpoints. Interestingly, other vascular parameters such as vessel diameter, -length, -tortuosity, and -volume were comparable between both genotypes for non-capillary vessels and capillaries. Taken together, our three-dimensional data showing more vessel segments and branchpoints at unchanged vessel morphology suggest that stimulated angiogenesis upon Nogo-A gene deletion results in the insertion of complete capillary micro-networks and not just single vessels into existing vascular networks. These findings significantly enhance our understanding of how angiogenesis, vascular remodeling, and three-dimensional vessel network architecture are regulated during central nervous system development. Nogo-A may therefore be a potential novel target for angiogenesis-dependent central nervous system pathologies such as brain tumors or stroke.

Flow-metabolism dissociation in the pathogenesis of levodopa-induced dyskinesia

Levodopa-induced dyskinesia (LID) is the most common, disruptive complication of Parkinson's disease (PD) pharmacotherapy, yet despite decades of research, the changes in regional brain function underlying LID remain largely unknown. We previously found that the cerebral vasomotor and metabolic responses to levodopa are dissociated in PD subjects. Nonetheless, it is unclear whether levodopa-mediated dissociation is exaggerated in LID or distinguishes LID from non-LID subjects. To explore this possibility, we used dual-tracer positron emission tomography to quantify regional cerebral blood flow and metabolic activity in 28 PD subjects (14 LID, 14 non-LID), scanned before and during intravenous levodopa infusion. Levodopa-mediated dissociation was most prominent in the posterior putamen (P < 0.0001) and greater in LID than in non-LID and test-retest subjects. Strikingly, LID subjects also showed increased sensorimotor cortex (SMC) activity in the baseline, unmedicated state. Imaging data from an independent PD sample (106 subjects) linked these differences to loss of mesocortical dopamine terminals in advanced patients. In aggregate, the data suggest that LID results from an overactive vasomotor response to levodopa in the putamen on a background of disease-related increases in SMC activity. LID may thus be amenable to treatment that modulates the function of these 2 regions.

Making microvascular networks work: angiogenesis, remodeling, and pruning

The adequate and efficient functioning of the microcirculation requires not only numerous vessels providing a large surface area for transport but also a structure that provides short diffusion distances from capillaries to tissue and efficient distribution of convective blood flow. Theoretical models show how a combination of angiogenesis, remodeling, and pruning in response to hemodynamic and metabolic stimuli, termed "angioadaptation," generates well organized, functional networks.

Quantitative assessment of angiogenesis, perfused blood vessels and endothelial tip cells in the postnatal mouse brain

During development and in various diseases of the CNS, new blood vessel formation starts with endothelial tip cell selection and vascular sprout migration, followed by the establishment of functional, perfused blood vessels. Here we describe a method that allows the assessment of these distinct angiogenic steps together with antibody-based protein detection in the postnatal mouse brain. Intravascular and perivascular markers such as Evans blue (EB), isolectin B4 (IB4) or laminin (LN) are used alongside simultaneous immunofluorescence on the same sections. By using confocal laser-scanning microscopy and stereological methods for analysis, detailed quantification of the 3D postnatal brain vasculature for perfused and nonperfused vessels (e.g., vascular volume fraction, vessel length and number, number of branch points and perfusion status of the newly formed vessels) and characterization of sprouting activity (e.g., endothelial tip cell density, filopodia number) can be obtained. The entire protocol, from mouse perfusion to vessel analysis, takes ∼10 d.

Activation of auditory white matter tracts as revealed by functional magnetic resonance imaging

INTRODUCTION

The ability of functional magnetic resonance imaging (fMRI) to detect activation in brain white matter (WM) is controversial. In particular, studies on the functional activation of WM tracts in the central auditory system are scarce. We utilized fMRI to assess and characterize the entire auditory WM pathway under robust experimental conditions involving the acquisition of a large number of functional volumes, the application of broadband auditory stimuli of high intensity, and the use of sparse temporal sampling to avoid scanner noise effects and increase signal-to-noise ratio.

METHODS

Nineteen healthy volunteers were subjected to broadband white noise in a block paradigm; each run had four sound-on/off alternations and was repeated nine times for each subject. Sparse sampling (TR=8 s) was used.

RESULTS

In addition to traditional gray matter (GM) auditory center activation, WM activation was detected in the isthmus and midbody of the corpus callosum (CC), tapetum, auditory radiation, lateral lemniscus, and decussation of the superior cerebellar peduncles. At the individual level, 13 of 19 subjects (68 %) had CC activation. Callosal WM exhibited a temporal delay of approximately 8 s in response to the stimulation compared with GM.

CONCLUSIONS

These findings suggest that direct evaluation of the entire functional network of the central auditory system may be possible using fMRI, which may aid in understanding the neurophysiological basis of the central auditory system and in developing treatment strategies for various central auditory disorders.

VEGF significantly restores impaired memory behavior in Alzheimer's mice by improvement of vascular survival

The functional impact of amyloid peptides (Aβs) on the vascular system is less understood despite these pathologic peptides are substantially deposited in the brain vasculature of Alzheimer's patients. Here we show substantial accumulation of Aβs 40 and 42 in the brain arterioles of Alzheimer's patients and of transgenic Alzheimer's mice. Purified Aβs 1–40 and 1–42 exhibited vascular regression activity in the in vivo animal models and vessel density was reversely correlated with numbers and sizes of amyloid plaques in human patients. A significant high number of vascular cells underwent cellular apoptosis in the brain vasculature of Alzheimer's patients. VEGF significantly prevented Aβ-induced endothelial apoptosis in vitro. Neuronal expression of VEGF in transgenic mice restored memory behavior of Alzheimer's. These findings provide conceptual implication of improvement of vascular functions as a novel therapeutic approach for the treatment of Alzheimer's disease.

Vascular endothelial growth factor promotes pericyte coverage of brain capillaries, improves cerebral blood flow during subsequent focal cerebral ischemia, and preserves the metabolic penumbra

BACKGROUND AND PURPOSE

Therapeutic angiogenesis aims at improving cerebral blood flow by amplification of vascular sprouting, thus promoting tissue survival under conditions of subsequent ischemia. It remains unknown whether induced angiogenesis leads to the formation of functional vessels that indeed result in hemodynamic improvements. Observations of hemodynamic steal phenomena and disturbed neurovascular integrity after vascular endothelial growth factor delivery questioned the concept of therapeutic angiogenesis.

METHODS

Mice were treated with recombinant human vascular endothelial growth factor (0.02 μg/d; intracerebroventricular) for 3 to 21 days and subsequently exposed to 90-minute middle cerebral artery occlusion. Angiogenesis, histological brain injury, IgG extravasation, cerebral blood flow, protein synthesis and energy state, and pericyte coverage on brain capillaries were evaluated in a multiparametric approach combining histochemical, autoradiographic, and regional bioluminescence techniques.

RESULTS

Vascular endothelial growth factor increased brain capillary density within 10 days and reduced infarct volume and inflammation after subsequent middle cerebral artery occlusion, and, when delivered for prolonged periods of 21 days, enhanced postischemic blood-brain barrier integrity. Increased cerebral blood flow was noted in ischemic brain areas exhibiting enhanced angiogenesis and was associated with preservation of the metabolic penumbra, defined as brain tissue in which protein synthesis has been suppressed but ATP preserved. Vascular endothelial growth factor enhanced pericyte coverage of brain endothelial cells via mechanisms involving increased N-cadherin expression on cerebral microvessels.

CONCLUSIONS

That cerebral blood flow is increased during subsequent ischemic episodes, leading to the stabilization of cerebral energy state, fosters hope that by promoting new vessel formation brain tissue survival may be improved.

Formation of the collateral circulation is regulated by vascular endothelial growth factor-A and a disintegrin and metalloprotease family members 10 and 17

RATIONALE

The density of native (preexisting) collaterals varies widely and is a significant determinant of variation in severity of stroke, myocardial infarction, and peripheral artery disease. However, little is known about mechanisms responsible for formation of the collateral circulation in healthy tissues.

OBJECTIVE

We previously found that variation in vascular endothelial growth factor (VEGF) expression causes differences in collateral density of newborn and adult mice. Herein, we sought to determine mechanisms of collaterogenesis in the embryo and the role of VEGF in this process.

METHODS AND RESULTS

Pial collaterals begin forming between embryonic day 13.5 and 14.5 as sprout-like extensions from arterioles of existing cerebral artery trees. Global VEGF-A overexpressing mice (Vegf(hi/+)) formed more, and Vegf(lo/+) formed fewer, collaterals during embryogenesis, in association with differences in vascular patterning. Conditional global reduction of Vegf or Flk1 only during collaterogenesis significantly reduced collateral formation, but now without affecting vascular patterning, and the effects remained in adulthood. Endothelial-specific Vegf reduction had no effect on collaterogenesis. Endothelial-specific reduction of a disintegrin-and-metalloprotease-domain-10 (Adam10) and inhibition of γ-secretase increased collateral formation, consistent with their roles in VEGF-induced Notch1 activation and suppression of prosprouting signals. Endothelial-specific knockdown of Adam17 reduced collateral formation, consistent with its roles in endothelial cell migration and embryonic vascular stabilization, but not in activation of ligand-bound Notch1. These effects also remained in adulthood.

CONCLUSIONS

Formation of pial collaterals occurs during a narrow developmental window via a sprouting angiogenesis-like mechanism, requires paracrine VEGF stimulation of fetal liver kinase 1-Notch signaling, and adult collateral number is dependent on embryonic collaterogenesis.

Hypoxia-inducible factor 1 activation from adipose protein 2-cre mediated knockout of von Hippel-Lindau gene leads to embryonic lethality

von Hippel-Lindau protein, an E3 ubiquitin ligase from the von Hippel-Lindau (Vhl) gene, inhibits the transcriptional activity of hypoxia-inducible factor 1α in cells. To gain insight into the hypoxia-inducible factor 1α signalling pathway in adipose tissue, a study was conducted to generate fat-specific Vhl knockout mice. Cre-recombinase (Cre)/locus of crossover in P1(loxP) technology was used in the knockout study. The mice carrying floxed-Vhl alleles were crossed with adipose protein 2 (aP2)-Cre mice, in which the Cre gene is driven by the aP2 (fatty acid binding protein 4) gene promoter. The homozygous knockout mice exhibited embryonic lethality at E14.5-E18.5. The homozygous embryos suffered from haemorrhages in the brain and liver. Hypoxia-inducible factor 1α protein and its target gene protein, vascular endothelial growth factor, increased in the brain and liver. Endothelial proliferation and capillary leakage were observed in the tissues. Heterozygous knockout mice appeared normal in development, growth and reproductivity. β-galactosidase reporter mice were used in the analysis of tissue-specificity of Cre in aP2-Cre mice. Strong Cre activity was observed in the dorsal hindbrain region and vertebrae of E12.5 embryos. These results suggest that in the aP2-Cre mice, the recombinase activity is expressed in the central nervous system of the embryos. Central and peripheral haemorrhages are responsible for the embryonic lethality in the homozygous knockout mice.

Inhibitors of Glioma Growth that Reveal the Tumour to the Immune System

Treated glioblastoma patients survive from 6 to 14 months. In the first part of this review, we describe glioma origins, cancer stem cells and the genomic alterations that generate dysregulated cell division, with enhanced proliferation and diverse response to radiation and chemotherapy. We review the pathways that mediate tumour cell proliferation, neo-angiogenesis, tumor cell invasion, as well as necrotic and apoptotic cell death. Then, we examine the ability of gliomas to evade and suppress the host immune system, exhibited at the levels of antigen recognition and immune activation, limiting the effective signaling between glioma and host immune cells.The second part of the review presents current therapies and their drawbacks. This is followed by a summary of the work of our laboratory during the past 20 years, on oligosaccharide and glycosphingolipid inhibitors of astroblast and astrocytoma division. Neurostatins, the O-acetylated forms of gangliosides GD1b and GT1b naturally present in mammalian brain, are cytostatic for normal astroblasts, but cytotoxic for rat C6 glioma cells and human astrocytoma grades III and IV, with ID50 values ranging from 200 to 450 nM. The inhibitors do not affect neurons or fibroblasts up to concentrations of 4 μM or higher.At least four different neurostatin-activated, cell-mediated antitumoral processes, lead to tumor destruction: (i) inhibition of tumor neovascularization; (ii) activation of microglia; (iii) activation of natural killer (NK) cells; (iv) activation of cytotoxic lymphocytes (CTL). The enhanced antigenicity of neurostatin-treated glioma cells, could be related to their increased expression of connexin 43. Because neurostatins and their analogues show specific activity and no toxicity for normal cells, a clinical trial would be the logical next step.

Vascular endothelial growth factor is upregulated by L-dopa in the parkinsonian brain: implications for the development of dyskinesia

Angiogenesis and increased permeability of the blood-brain barrier have been reported to occur in animal models of Parkinson's disease and l-dopa-induced dyskinesia, but the significance of these phenomena has remained unclear. Using a validated rat model of l-dopa-induced dyskinesia, this study demonstrates that chronic treatment with l-dopa dose dependently induces the expression of vascular endothelial growth factor in the basal ganglia nuclei. Vascular endothelial growth factor was abundantly expressed in astrocytes and astrocytic processes in the proximity of blood vessels. When co-administered with l-dopa, a small molecule inhibitor of vascular endothelial growth factor signalling significantly attenuated the development of dyskinesia and completely blocked the angiogenic response and associated increase in blood-brain barrier permeability induced by the treatment. The occurrence of angiogenesis and vascular endothelial growth factor upregulation was verified in post-mortem basal ganglia tissue from patients with Parkinson's disease with a history of dyskinesia, who exhibited increased microvascular density, microvascular nestin expression and an upregulation of vascular endothelial growth factor messenger ribonucleic acid. These congruent findings in the rat model and human patients indicate that vascular endothelial growth factor is implicated in the pathophysiology of l-dopa-induced dyskinesia and emphasize an involvement of the microvascular compartment in the adverse effects of l-dopa pharmacotherapy in Parkinson's disease.

Association of chronic vascular changes with functional outcome after traumatic brain injury in rats

We tested the hypothesis that vascular remodeling in the cortex, hippocampus, and thalamus is associated with long-term functional recovery after traumatic brain injury (TBI). We induced TBI with lateral fluid-percussion (LFP) injury in adult rats. Animals were followed-up for 9 months, during which we tested motor performance using a neuroscore test, spatial learning and memory with a Morris water maze, and seizure susceptibility with a pentylenetetrazol (PTZ) test. At 8 months, they underwent structural MRI, and cerebral blood flow (CBF) was assessed by arterial spin labeling (ASL) MRI. Then, rats were perfused for histology to assess the density of blood vessels. In the perilesional cortex, the CBF decreased by 56% (p < 0.01 compared to controls), and vessel density increased by 28% (p < 0.01). There was a negative correlation between CBF in the perilesional cortex and vessel density (r = -0.75, p < 0.01). However, in the hippocampus, we found a 13% decrease in CBF ipsilaterally (p < 0.05) and 20% contralaterally (p < 0.01), and no change in vessel number. In the ipsilateral thalamus, the increase in CBF (34%, p < 0.01) was associated with a remarkable increase in vessel density (78%, p < 0.01). Animals showed motor impairment that was not associated with vascular changes. Instead, poor performance in the Morris water maze correlated with enhanced thalamic vessel density (r = -0.81, p < 0.01). Finally, enhanced seizure susceptibility was associated with reduced CBF in the ipsilateral hippocampus (r = 0.78, p < 0.05) and increased vascular density in the thalamus (r = 0.69, p < 0.05). There was little interaction between the behavioral measures. The present study demonstrates that each of the investigated brain areas has a unique pattern of vascular abnormalities. Chronic alterations in CBF could not be attributed to changes in vascular density. Association of thalamic hypervascularity to epileptogenesis warrants further studies. Finally, hippocampal hypoperfusion may predict later seizure susceptibility in the LFP injury model of TBI, which could be of value for pre-clinical antiepileptogenesis trials.

Rapid three-dimensional quantification of VEGF-induced scaffold neovascularisation by microcomputed tomography

Microcomputed tomography (micro-CT) is increasingly being used to analyze the three-dimensional structure and architecture of microvascular networks. Therefore we have evaluated a micro-CT analysis of VEGF-induced vessel ingrowth into a porous polyurethane scaffold through comparison with analyses by CD31 immunohistochemistry, vascular perfusion by intravital Lycopersicon esculentum lectin perfusion and vascular corrosion casting. Micro-CT scanning found a similar level of vascularisation within the VEGF treated scaffolds to that determined by the other analytical methods. However, although the relative increase in vascularisation (17 fold above PBS controls p<0.05) induced by VEGF determined by micro-CT was similar to the perfusion based analyses (20.1 and 10.4 fold for lectin perfusion and vascular corrosion respectively p<0.05), it differed substantially from that determined by CD31 immunohistochemistry (3.2 fold p<0.05). This difference was due to a large proportion of unperfused vessels in the PBS control that were not present in the VEGF group. The increase in perfusion probably resulted in part from an increase in average vessel diameter. Though this increase was detected by micro-CT, the actual diameters were overestimated by 60-90% most likely as a consequence of a merging effect for juxtaposed vessels. Thus whilst micro-CT gives an accurate three-dimensional quantification of the VEGF-induced increase in perfused vessels, resolution needs to be maximized for accurate sizing of a microvascular network's components.

A 3D-investigation shows that angiogenesis in primate cerebral cortex mainly occurs at capillary level

This paper describes the use of a new 3D high-resolution imaging technique dedicated to functional vessels for a systematic quantitative study of angiogenesis in the primate cortex. We present a new method which permits, using synchrotron X-ray micro-tomography imaging, the identification of micro-vascular components as well as their automatic numerical digitalization and extraction from very large 3D image analysis and post-treatments. This method is used to analyze various levels of micro-vascular organization and their postnatal modifications. Comparing newborn- and adult marmosets, we found an increase in vascular volume (270%), exchange surface (260%) and vessel length (290%) associated to a decrease in distances between vessel and tissue (32%). The increase in relative vascular volumes between the two ages, examined through the whole cortical depth, has been found to be mainly sustained by events occurring at the capillary level, and only marginally at the perforating vessel level. This work shows that the postnatal cortical maturation classically described in terms of synaptogenesis, gliogenesis and connectivity plasticity is accompanied by an intensive remodeling of micro-vascular patterns.

VEGF overexpression improves mice cognitive abilities after unilateral common carotid artery occlusion

Angiogenesis and neurogenesis are adaptive responses protecting cerebral tissue from hypoxic-ischemic injury. Both processes seem to be governed by hypoxia-induced growth factors, of which vascular endothelial growth factor (VEGF) is a prominent example. The aim of this study was to investigate the influence of VEGF overexpression (V1 mice) on mice cognitive function and cerebral structure under moderate cerebral oligemia. In 33 V1 and wild-type (wt) mice, the left common carotid artery was permanently occluded (CCAO) under acute (48 h) and subchronic (12 days) conditions. Sham operation was performed in 35 mice (controls). Psychometric testing was done using holeboard test and Morris Water Maze system, immunohistochemistry was performed for detection of cerebral apoptosis, nestin and CD31 expression. The results show that under control conditions V1 mice showed better spatial cognitive abilities as compared to their wt littermates. During CCAO, time and distance to reach a hidden platform in Water Maze were shorter in V1 mice as compared to wt animals, indicative of faster learning and better spatial memory processes. While no signs of necrosis or apoptosis were detected, immunohistochemistry showed that VEGF transgenity was related to higher number of nestin-positive precursor cells. Finally, acute CCAO was paralleled by a reduction of CD31 staining in wt but not V1 mice. We conclude that VEGF overexpression led to a protective effect on cognitive function, because V1 mice showed evidence for faster spatial learning and better memory, as well as an increased number of neuronal precursor cells and a prevention of endothelial cell loss after CCAO.

Malignant astrocytic glioma: genetics, biology, and paths to treatment

Malignant astrocytic gliomas such as glioblastoma are the most common and lethal intracranial tumors. These cancers exhibit a relentless malignant progression characterized by widespread invasion throughout the brain, resistance to traditional and newer targeted therapeutic approaches, destruction of normal brain tissue, and certain death. The recent confluence of advances in stem cell biology, cell signaling, genome and computational science and genetic model systems have revolutionized our understanding of the mechanisms underlying the genetics, biology and clinical behavior of glioblastoma. This progress is fueling new opportunities for understanding the fundamental basis for development of this devastating disease and also novel therapies that, for the first time, portend meaningful clinical responses.

Novel three-dimensional analysis tool for vascular trees indicates complete micro-networks, not single capillaries, as the angiogenic endpoint in mice overexpressing human VEGF(165) in the brain

To adequately supply tissues with oxygen and nutrients, the formation of functional vascular networks requires generation of normal, healthy vessels and their arrangement into an effective network architecture. While our knowledge about the development of single vessels significantly increased during the last years, mechanisms responsible for network formation are still poorly understood. This is probably due to the lack of suitable methods for quantification of structural properties of microvascular networks. Previously we showed that cerebral blood flow is not increased in mice exhibiting a 2- to 3-fold higher density of normal and perfused capillaries as a result of transgenic overexpression of the human vascular endothelial growth factor (VEGF(165)). Here we used vascular corrosion casting and hierarchical micro-computed tomography combined with a new network analysis tool to characterize the vascular architecture in gray and white matter of these mice. Our results indicate that VEGF overexpression leads to formation of additional micro-networks connected to higher order vessels rather than insertion of individual capillaries into the existing vessel structure. This implies that the smallest "angiogenic quantum", i.e. the final, stable result of angiogenesis and subsequent remodeling, is not a single microvessel, but a complete micro-network. In conclusion, high-resolution 3D imaging combined with network analysis can substantially improve our understanding of vascular architecture, beneficial for the development of therapeutic angiogenesis as a clinical tool for applications such as wound healing or treatment of ischemic diseases.

Human vascular endothelial growth factor protects axotomized retinal ganglion cells in vivo by activating ERK-1/2 and Akt pathways

Based on its trophic effects on neurons and vascular cells, vascular endothelial growth factor (VEGF) is a promising candidate for the treatment of neurodegenerative diseases. To evaluate the therapeutic potential of VEGF, we here examined effects of this growth factor on the degeneration of axotomized retinal ganglion cells (RGCs), which, as CNS-derived neurons, offer themselves in an excellent way to study neuroprotection in vivo. Making use of a transgenic mouse line that constitutively expresses human VEGF under a neuron-specific enolase promoter, we show that (1) the VEGF-transgenic retina overexpresses human VEGF, (2) RGCs carry the VEGF receptor-2, and (3) vascular networks in normal and axotomized VEGF-transgenic (tg) retinas do not differ from control animals. After axotomy, RGCs of VEGF-tg mice were protected against delayed degeneration, as compared with wild-type littermates. Western blots revealed increased phosphorylated ERK-1/2 and Akt and reduced phosphorylated p38 and activated caspase-3 levels in axotomized VEGF-transgenic retinas. Intravitreous injections of pharmacological ERK-1/2 (PD98059) or Akt (LY294002) inhibitors showed that VEGF exerts neuroprotection by dual activation of ERK-1/2 and Akt pathways. In view that axotomy-induced RGC death occurs slowly and considering that RGCs are CNS-derived neurons, we predict the clinical implementation of VEGF in neurodegenerative diseases of both brain and retina.

Short and long-term effects of hVEGF-A(165) in Cre-activated transgenic mice

We have generated a transgenic mouse where hVEGF-A(165) expression has been silenced with loxP-STOP fragment, and we used this model to study the effects of hVEGF-A(165) over-expression in mice after systemic adenovirus mediated Cre-gene transfer. Unlike previous conventional transgenic models, this model leads to the expression of hVEGF-A(165) in only a low number of cells in the target tissues in adult mice. Levels of hVEGF-A(165) expression were moderate and morphological changes were found mainly in the liver, showing typical signs of active angiogenesis. Most mice were healthy without any major consequences up to 18 months after the activation of hVEGF-A(165) expression. However, one mouse with a high plasma hVEGF-A(165) level died spontaneously because of bleeding into abdominal cavity and having liver hemangioma, haemorrhagic paratubarian cystic lesions and spleen peliosis. Also, two mice developed malignant tumors (hepatocellular carcinoma and lung adenocarcinoma), which were not seen in control mice. We conclude that long-term uncontrolled hVEGF-A(165) expression in only a limited number of target cells in adult mice can be associated with pathological changes, including possible formation of malignant tumors and uncontrolled bleeding in target tissues. These findings have implications for the design of long-term clinical trials using hVEGF-A(165) gene and protein.

The phosphatidylinositol-3 kinase/Akt pathway mediates VEGF's neuroprotective activity and induces blood brain barrier permeability after focal cerebral ischemia

Based on its trophic influence on neurons and vascular cells, vascular endothelial growth factor (VEGF) is a promising candidate for stroke treatment. VEGF's survival-promoting effects are purchased at the expense of an increased blood brain barrier permeability, which potentially compromises tissue survival. The mechanisms via which VEGF protects the brain against ischemia remained unknown. We examined signaling pathways underlying VEGF's neuroprotective activity in our transgenic mouse line, which expresses human VEGF165 under a neuron-specific enolase (NSE) promoter. We show that VEGF receptor-2 (Flk-1) is expressed on ischemic neurons and astrocytes and is activated by VEGF. Following 90-min episodes of middle cerebral artery occlusion, VEGF increased phosphorylated (but not total) Akt and ERK-1/-2 and reduced phosphorylated mitogen activated protein kinase/p38 and c-Jun NH2-terminal kinase (JNK)-1/-2 levels, at the same time decreasing inducible NO synthase expression in ischemic neurons. Inhibition of Akt with Wortmannin reversed VEGF's neuroprotective properties, diminished brain swelling, and restored the vascular permeability induced by VEGF to below levels in WT animals. The aggravation of brain injury by Wortmannin was associated with the restitution of p38, but not of JNK-1/-2, ERK-1/-2, or inducible NOS (iNOS). Our data demonstrate that VEGF mediates both neuroprotection and blood brain barrier permeability via the phosphatidylinositol-3 kinase (PI3K)/Akt pathway. Based on our observation that VEGF neuroprotection and vascular leakage depend on PI3K/Akt, which is putatively regulated by VEGF receptor-2, we predict that it may not easily be possible to make use of VEGF's neuroprotective function without accepting its unfavorable consequence, the increased vascular permeability.

Evolution of apparent diffusion coefficient and transverse relaxation time (T2) in the subchronic stage of global cerebral oligemia in different rat models

Using magnetic resonance imaging techniques, we examined the time course of apparent diffusion coefficient (ADC), T2, and T2* relaxation times in 1-year-old rats after different forms of cerebral oligemia had been induced by (1) transient systemic hypotension, (2) permanent bilateral carotid artery occlusion (BCCAO), and (3) combined hypotension and BCCAO over a time period of 14 days after the oligemic event. These groups were compared with a group of sham-operated adult rats (controls, 4) to rule out a drift of the parameters over time. The animals were examined in a 2.35 T scanner. ADC, T2, and T2* were measured in both hemispheres of rat parietotemporal cerebral cortex, thalamic nuclei, and hippocampus 1 day before as well as on days 1, 3, 7, and 14 after sham operation and in different models of oligemia, respectively. Hypotension alone had no significant effect on MRI parameters in rat brain. After BCCAO, an increase in T2* was observed. If a permanent BCCAO was combined with transient hypotension, however, 84% of 1-year-old animals died within 14 days after surgery. In the surviving animals, significant changes in ADC, T2, and T2* were observed in the hippocampus and parietotemporal cerebral cortex. ADC showed a decrease on day 1 after oligemia, and an increase on days 3, 7, and 14. The T2* and T2 values were markedly increased on days 7 and 14 after surgery. In conclusion, only severe oligemia combining BCCAO and hypotension induces significant changes in tissue integrity (as shown by ADC) and in blood oxygenation levels in the subchronic period, whereas no significant changes were detected if permanent BCCAO or transient hypotension was applied separately.

Cerebral metabolic response to low blood flow: possible role of cytochrome oxidase inhibition

The reactions of cerebral metabolism to imposed changes of cerebral blood flow (CBF) are poorly understood. A common explanation of the mismatched CBF and oxygen consumption (CMR(O(2))) during neuronal excitation holds that blood flow rises more than oxygen consumption to compensate for an absent oxygen reserve in brain mitochondria. The claim conversely implies that oxygen consumption must decline when blood flow declines. As the prevailing rate of reaction of oxygen with cytochrome c oxidase is linked to the tension of oxygen, the claim fails to explain how oxygen consumption is maintained during moderate reductions of CBF imposed by hyperventilation (hypocapnia) or cyclooxygenase (COX) inhibition. To resolve this contradiction, we extended the previously published oxygen delivery model with a term allowing for the adjustment of the affinity of cytochrome c oxidase to a prevailing oxygen tension. The extended model predicted constant oxygen consumption at moderately reduced blood flow. We determined the change of affinity of cytochrome c oxidase in the extended model by measuring CBF in seven, and CMR(O(2)) in five, young healthy volunteers before and during COX inhibition with indomethacin. The average CBF declined 35%, while neither regional nor average CMR(O(2)) changed significantly. The adjustment of cytochrome c oxidase affinity to the declining oxygen delivery could be ascribed to a hypothetical factor with several properties in common with nitric oxide.

Stereological studies of capillary length density in the frontal cortex of schizophrenics

The presence of microvasculature abnormalities in the prefrontal cortex of schizophrenics was proposed in a recent study of molecular signatures of schizophrenia [Prabakaran et al (2004) Mol Psychiat 9:684-697]. To assess this possibility further, we investigated capillary length densities in prefrontal cortex area 9 and anterior cingulate cortex area 24 in postmortem brains from 13 schizophrenics and 13 age- and sex-matched controls. To check that our sample of brains shared cardinal neuropathological features of schizophrenia with previously reported case studies, we also measured cortical gray matter volumes and cortical thickness in areas 9 and 24. The mean cortical gray matter volume was significantly reduced in brains from schizophrenics compared to controls. Mean cortical thickness was significantly reduced in area 24, but not in area 9, in schizophrenics. There were no differences in mean capillary length densities in either area 9 or 24 between the two groups. Thus, alterations in capillary length density in the prefrontal cortex cannot be considered a general feature of schizophrenia. Compromised brain metabolism and occurrence of oxidative stress in the brain of schizophrenics are likely caused by other mechanisms.

Angiogenesis--a self-adapting principle in hypoxia

Normal tissue function depends on adequate supply of oxygen through blood vessels. Reduced oxygen supply (hypoxia) induces a variety of specific adaptation mechanisms in mammals that occur at the cellular, local and systemic level. These mechanisms are in part governed by the activation of the hypoxia-inducible transcription factors HIF-1 and HIF-2. Prolyl and asparaginyl hydroxylases as recently characterized oxygen sensors allow the regulation of HIFs that in turn modulate expression of hypoxically regulated genes such as VEGF. VEGF plays a key role in the formation of a functional and integrated vascular network required during physiological processes such as embryogenesis or female reproductive cycle as well as during a variety of pathological processes such tumor growth, wound healing, retinopathy and ischemic diseases (myocardial infarction, cerebral ischemia). However, other angiogenic factors, such as angiopoietins, PDGF, ephrins and erythropoietin are additionally needed to enable the formation of a functional vascular network. Many of these factors are activated during hypoxia although no HIF binding sites have yet been identified in the regulatory sequences of theses genes. Hypoxia-induced gene products that result in new vessel growth may be part of a self-regulated physiological protection mechanism preventing cell injury, especially under conditions of chronically reduced blood blow (chronic ischemia).