Correlation of VEGF and angiopoietin expression with disruption of blood-brain barrier and angiogenesis after focal cerebral ischemia

Cytokines and innate inflammation in the pathogenesis of human traumatic brain injury

There is an increasing recognition that following traumatic brain injury, a cascade of inflammatory mediators is produced, and contributes to the pathological consequences of central nervous system injury. This review summarises the key literature from pre-clinical models that underlies our understanding of innate inflammation following traumatic brain injury before focussing on the growing evidence from human studies. In addition, the underlying molecular mediators responsible for blood brain barrier dysfunction have been discussed. In particular, we have highlighted the different sampling methodologies available and the difficulties in interpreting human data of this sort. Ultimately, understanding the innate inflammatory response to traumatic brain injury may provide a therapeutic avenue in the treatment of central nervous system disease.

Induction of angiopoietin-2 after spinal cord injury

Angiopoietin-1 (Ang-1) and angiopoietin-2 (Ang-2) have opposing effects on blood vessels, with Ang-2 being mainly induced during the endothelial barrier breakdown. It is known that spinal cord injury (SCI) induces lasting decreases in Ang-1 levels, underlying endothelial barrier disruption, but the expression of Ang-2 in spinal cord injury has not been studied. We characterized Ang-2 after SCI using a clinically relevant rat model of contusion SCI. We found that SCI induces marked and persistent upregulation of Ang-2 (up to 10 weeks after SCI), which does not reflect well-characterized temporal profile of the blood-spinal cord barrier (BSCB) breakdown after SCI, and thus suggests other role(s) for Ang-2 in injured spinal cords. Furthermore, we also found that higher Ang-2 levels were associated with more successful locomotor recovery after SCI, both in SCI rats with markedly better spontaneous motor recovery and in SCI rats receiving a neuroprotective pharmacological intervention (amiloride), suggesting a beneficial role for Ang-2 in injured spinal cords. Immunocytochemical analyses revealed that Ang-2 was not induced in endothelial cells, but in perivascular and non-vascular cells labeled with glial fibrillary acidic protein (GFAP) or with chondroitin sulfate proteoglycan (NG2). Therefore, it is unlikely that induction of Ang-2 contributes to vascular dysfunction underlying functional impairment after SCI, but rather that it contributes to the beneficial pro-angiogenic and/or gliogenic processes underlying recovery processes after SCI.

Growth factors in ischemic stroke

Data from pre-clinical and clinical studies provide evidence that colony-stimulating factors (CSFs) and other growth factors (GFs) can improve stroke outcome by reducing stroke damage through their anti-apoptotic and anti-inflammatory effects, and by promoting angiogenesis and neurogenesis. This review provides a critical and up-to-date literature review on CSF use in stroke. We searched for experimental and clinical studies on haemopoietic GFs such as granulocyte CSF, erythropoietin, granulocyte-macrophage colony-stimulating factor, stem cell factor (SCF), vascular endothelial GF, stromal cell-derived factor-1α and SCF in ischemic stroke. We also considered studies on insulin-like growth factor-1 and neurotrophins. Despite promising results from animal models, the lack of data in human beings hampers efficacy assessments of GFs on stroke outcome. We provide a comprehensive and critical view of the present knowledge about GFs and stroke, and an overview of ongoing and future prospects.

Vessel size imaging reveals pathological changes of microvessel density and size in acute ischemia

The aim of this study was to test the feasibility of vessel size imaging with precise evaluation of apparent diffusion coefficient and cerebral blood volume and to apply this novel technique in acute stroke patients within a pilot group to observe the microvascular responses in acute ischemic tissue. Microvessel density-related quantity Q and mean vessel size index (VSI) were assessed in 9 healthy volunteers and 13 acute stroke patients with vessel occlusion within 6 hours after symptom onset. Our results in healthy volunteers matched with general anatomical observations. Given the limitation of a small patient cohort, the median VSI in the ischemic area was higher than that in the mirrored region in the contralateral hemisphere (P<0.05). Decreased Q was observed in the ischemic region in 2 patients, whereas no obvious changes of Q were found in the remaining 11 patients. In a patient without recanalization, the VSI hyperintensity in the subcortical area matched well with the final infarct. These data reveal that different observations of microvascular response in the acute ischemic tissue seem to emerge and vessel size imaging may provide useful information for the definition of ischemic penumbra and have an impact on future therapeutic approaches.

Hypoxia-ischemia and retinal ganglion cell damage

Retinal hypoxia is the potentially blinding mechanism underlying a number of sight-threatening disorders including central retinal artery occlusion, ischemic central retinal vein thrombosis, complications of diabetic eye disease and some types of glaucoma. Hypoxia is implicated in loss of retinal ganglion cells (RGCs) occurring in such conditions. RGC death occurs by apoptosis or necrosis. Hypoxia-ischemia induces the expression of hypoxia inducible factor-1α and its target genes such as vascular endothelial growth factor (VEGF) and nitric oxide synthase (NOS). Increased production of VEGF results in disruption of the blood retinal barrier leading to retinal edema. Enhanced expression of NOS results in increased production of nitric oxide which may be toxic to the cells resulting in their death. Excess glutamate release in hypoxic-ischemic conditions causes excitotoxic damage to the RGCs through activation of ionotropic and metabotropic glutamate receptors. Activation of glutamate receptors is thought to initiate damage in the retina by a cascade of biochemical effects such as neuronal NOS activation and increase in intracellular Ca²⁺ which has been described as a major contributing factor to RGC loss. Excess production of proinflammatory cytokines also mediates cell damage. Besides the above, free-radicals generated in hypoxic-ischemic conditions result in RGC loss because of an imbalance between antioxidant- and oxidant-generating systems. Although many advances have been made in understanding the mediators and mechanisms of injury, strategies to improve the damage are lacking. Measures to prevent neuronal injury have to be developed.

The immunology of stroke: from mechanisms to translation

Immunity and inflammation are key elements of the pathobiology of stroke, a devastating illness second only to cardiac ischemia as a cause of death worldwide. While the immune system participates in the brain damage produced by ischemia, the damaged brain, in turn, exerts a powerful immunosuppressive effect that promotes fatal intercurrent infections and threatens the survival of stroke patients. Inflammatory signaling is instrumental in all stages of the ischemic cascade, from the early damaging events triggered by arterial occlusion, to the late regenerative processes underlying post-ischemic tissue repair. Recent developments have revealed that stroke, like multiple sclerosis, engages both innate and adaptive immunity. But, unlike multiple sclerosis, adaptive immunity triggered by newly exposed brain antigens does not have an impact on the acute phase of the damage. Nevertheless, modulation of adaptive immunity exerts a remarkable protective effect on the ischemic brain and offers the prospect of new stroke therapies. However, immunomodulation is not devoid of deleterious side effects, and gaining a better understanding of the reciprocal interaction between the immune system and the ischemic brain is essential to harness the full therapeutic potential of the immunology of stroke.

Inhibition of VEGF signaling pathway attenuates hemorrhage after tPA treatment

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

Temporal profile of Src, SSeCKS, and angiogenic factors after focal cerebral ischemia: correlations with angiogenesis and cerebral edema

A better understanding of the underlying mechanisms of angiogenesis and vascular permeability is necessary for the development of therapeutic strategies for ischemic injury. The purpose of this study was to examine the spatial and temporal expression of Src and Src-suppressed C kinase substrate (SSeCKS) in brain after middle cerebral artery occlusion (MCAO) and elucidate the relationships among Src, SSeCKS, and the key angiogenic factors present after stroke. Rats were subjected to either MCAO or sham operation. Reverse transcriptase-polymerase chain reaction and Western blotting results revealed that Src gradually increased starting as early as 2 h after MCAO and remained high for 1 day. In contrast, SSeCKS decreased after MCAO. Src expression correlated positively with that of vascular endothelial growth factor and angiopoietin-2, and negatively with that of SSeCKS, angiopoietin-1, and zonula occludens-1. However, SSeCKS had the reverse correlations. Changes in the expression of these factors correlated with the progress of angiogenesis and cerebral edema. Dynamic temporal changes in Src and SSeCKS expression may modulate angiogenesis and cerebral edema formation after focal cerebral ischemia.

A large screening of angiogenesis biomarkers and their association with neurological outcome after ischemic stroke

BACKGROUND

The induction of angiogenesis after stroke may enhance neurorestorative processes. Our aim was to examine the endogenous angiogenesis balance and their association with long-term clinical outcome in ischemic stroke patients.

METHODS

A total of 109 stroke subjects were included in the study. Firstly, plasma samples were obtained from control subjects (n = 26) and tPA-treated stroke patients (n = 29) at baseline (within 3h of symptoms onset), 1, 2, 12, 24h after tPA treatment, at discharge and 3 months after the ischemic event. Angiogenic promoters (PDGF-AA, PDGF-BB, HGF, FGF, KGF, HB-EGF, TPO, VEGF, VEGFR-1, VEGFR-2 and SDF-1α) and inhibitors (endostatin, angiostatin, thrombospondin-1 and thrombospondin-2) were analyzed by Searchlight(®) technology or ELISA. Additionally, baseline and 24h endostatin plasma level was determined in a new set of stroke patients (n = 80). Clinical parameters (NIHSS, mRS, mortality and hemorrhagic transformation events) were assessed to evaluate outcome.

RESULTS

Baseline PDGF-BB, endostatin and thrombospondin-2 levels were higher in stroke patients than in controls (p < 0.05). A pro-angiogenic balance was associated with lower NIHSS scores and less intracranial hemorrhagic complications. Interestingly, a high baseline endostatin level was associated to long-term functional dependency (mRS > 2; p = 0.004). Finally, a baseline endostatin cut-off point of 184 ng/mL was an independent predictor of functional dependency at three months in the multiple logistic regression with an odds ratio of 8.9 (95% CI: 2.7-28.8; p = 0.0002).

CONCLUSIONS

Our results indicate that an early pro-angiogenic balance is associated with mild short-term neurological deficit, while an acute anti-angiogenesis status determined by high endostatin plasma level predicts a worse long-term functional outcome.

Mean microvessel segment length and radius after embolic stroke: Comparison of magnetic resonance imaging (MRI) and laser scanning confocal microscopy (LSCM)

We offer a new means of noninvasively assessing mean microvessel segment length and radius after ischemic stroke. This method involves measuring changes in T₂ and T₂⁎ after injecting an intravascular superparamagnetic iron oxide contrast agent and result was verified using laser scanning confocal microscopy (LSCM) of both normal brain tissue and the ischemic recovery region. Embolic stroke was induced in 8 male Wistar rats and magnetic resonance imaging (MRI) performed 1 day and 6 weeks later. On MRI taken at 6 weeks, MRI of the recovery region revealed a significant increase in mean vessel size index (VSI) (5.75 ± 0.54 vs 4.81 ± 0.3 9μm; p < 0.001) and decrease in mean segment length (MSL) (16.61 ± 2.33 vs 26.52 ± 3.20 μm; p < 0.001) compared to the normal contralateral hemisphere, comparable with published values. There was also a significant correlation between MSL and VSI measured by MRI vs LSCM in the recovery region and normal contralateral hemisphere (p < 0.001). Our data suggest that a) morphological changes in the microvasculature can be measured noninvasively using MRI, and b) both MRI and LSCM give comparable information about both of these important parameters.

Angiogenesis is present in experimental autoimmune encephalomyelitis and pro-angiogenic factors are increased in multiple sclerosis lesions

Background

Angiogenesis is a common finding in chronic inflammatory diseases; however, its role in multiple sclerosis (MS) is unclear. Central nervous system lesions from both MS and experimental autoimmune encephalomyelitis (EAE), the animal model of MS, contain T cells, macrophages and activated glia, which can produce pro-angiogenic factors. Previous EAE studies have demonstrated an increase in blood vessels, but differences between the different phases of disease have not been reported. Therefore we examined angiogenic promoting factors in MS and EAE lesions to determine if there were changes in blood vessel density at different stages of EAE.

Methods

In this series of experiments we used a combination of vascular casting, VEGF ELISA and immunohistochemistry to examine angiogenesis in experimental autoimmune encephalomyelitis (EAE). Using immunohistochemistry we also examined chronic active MS lesions for angiogenic factors.

Results

Vascular casting and histological examination of the spinal cord and brain of rats with EAE demonstrated that the density of patent blood vessels increased in the lumbar spinal cord during the relapse phase of the disease (p < 0.05). We found an increased expression of VEGF by inflammatory cells and a decrease in the recently described angiogenesis inhibitor meteorin. Examination of chronic active human MS tissues demonstrated glial expression of VEGF and glial and blood vessel expression of the pro-angiogenic receptor VEGFR2. There was a decreased expression of VEGFR1 in the lesions compared to normal white matter.

Conclusions

These findings reveal that angiogenesis is intimately involved in the progression of EAE and may have a role in MS.

Krogh cylinders in retinal development, panretinal hypoperfusion and diabetic retinopathy

The volume of cells that a length of capillary supplies with O(2) is called a Krogh cylinder. This geometric 'tissue unit' was named after the Danish zoophysiologist and Nobel laureate August Krogh who made important discoveries in the fields of external and internal respiration in the first half of the last century. Krogh's ideas concerning tissue O(2) distribution can be extrapolated to retinal oxygenation by larger vessels (including arterioles, arteries and even veins) and by vessel groups within higher-order 'microvascular units' (including the choroid). During retinal development, for example, the difference in pO(2) levels within arteries and capillaries determines Krogh cylinders of different radius and establishes the periarterial capillary-free zone of His. The O(2) supply to the venous end of a tissue unit may be compromised during periods of reduced perfusion, increased O(2) consumption or hypoxaemia, resulting in an 'anoxic corner' of the Krogh cylinder. A funnel of hypometabolic (and therefore hypoxia-tolerant) cells will likely intervene between the necrotic cells and unaffected cells located closer to the O(2) source. Macular perivenular whitening heralds anoxic corners and/or hypoxic funnels owing to hypoperfusion within second-order microvascular units. In eyes with extensive retinal capillary closure from diabetes, Krogh cylinders surround the medium-sized arteries and veins that form arteriovenous shunts while traversing the midperipheral retina. These isolated tissue units incorporate an outer sheath of hypoxic cells within which vascular endothelial growth factor is upregulated. This 'angiogenic sheath' expands following retinal detachment; it corresponds to the hypoxia-tolerant funnel within capillary-based tissue units and to the cerebral penumbra after stroke.

Thymosin beta4 improves functional neurological outcome in a rat model of embolic stroke

Thymosin beta4 (Tbeta4) is a developmentally expressed 43-amino acid peptide that inhibits organization of the actin-cytoskeleton by sequestration of G-actin monomers. Tbeta4 improves cardiac function after myocardial infarction in adult mice and promotes healing properties in both dermal and corneal wounds. We tested the hypothesis that Tbeta4 improves functional neurological outcome in a rat model of embolic stroke.

EXPERIMENTAL PROCEDURES

Male Wistar rats (n=18) were subjected to embolic middle cerebral artery occlusion (MCAo). Tbeta4 (6 mg/kg, IP) was administered 24 h after MCAo and then every 3 days for four additional doses (n=9). Rats treated with saline were used as a control (n=9). The adhesive-removal test (ART) and modified Neurological Severity Score (mNSS) were performed to measure functional outcome. Rats were sacrificed 56 days after MCAo. Immunostaining was performed with antibodies against NG-2 (chondroitin sulfate proteoglycan), CNPase (2", 3"-cyclic nucleotide 3'-phosphodiesterase) to detect immature and mature oligodendrocytes. Neurofilament-H (NF-H) antibodies were used to detect axons while myelinated axons were identified with Bielschowsky/Luxol (B/L) Blue staining. EBA (endothelial barrier antigen) was used for detection of mature vessels.

RESULTS

Ischemic rats treated with Tbeta4 demonstrated a significant overall improvement (P<0.01) in the ART and the mNSS when compared to controls. Significant improvement was observed beginning at 14 and 35 days, respectively. Lesion volumes showed no significant differences between the two groups. Treatment with Tbeta4 increased myelinated axons and increased vessel density in the ischemic boundary (P<0.05) and augmented remyelination which was associated with an increase of oligodendrocyte progenitor cells (OPCs) and myelinating oligodendrocytes (P<0.05).

CONCLUSIONS

The present study suggests that Tbeta4 improves neurological functional outcome after embolic stroke in rats. Axonal remodeling from mobilization of OPCs is proposed as contributing to Tbeta4 induced functional improvement.

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

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

VEGF promotes angiogenesis and functional recovery in stroke rats

We evaluated the effects of intranasal vascular endothelial growth factor VEGF on neurological function and angiogenesis in ischemic boundary following cerebral ischemia. Sprague-Dawley rats were randomized into sham operation group (n = 9), VEGF group (n = 18), and control group (n = 18). The VEGF and control rats were intranasally administered (IN) with VEGF or saline, starting three days after middle cerebral artery occlusion (MCAO) and daily. Neurological scores were obtained at 1, 7, and 14 days after MCAO. Rats were sacrificed at 14 days, the von Willebrand factor (vWF) immunoreactive, BrdU(+)/vWF(+) cells, and microvessels were evaluated respectively. Compared to the control rats, intranasal administration of VEGF improved behavioral recovery, and increased the number of vWF(+), BrdU(+)/vWF(+) cells, and FITC-dextran perfused microvessels in ischemic boundary (p < .01). Our data suggest that intranasal administration of VEGF may induce angiogenesis in ischemic boundary and improve behavioral recovery following cerebral ischemia in rats, which may provide a powerful strategy for stroke.

Catalpol increases brain angiogenesis and up-regulates VEGF and EPO in the rat after permanent middle cerebral artery occlusion

To investigate the role and mechanism of catalpol in brain angiogenesis in a rat model of stroke, the effect of catalpol (5 mg/kg; i.p) or vehicle administered 24 hours after permanent middle cerebral artery occlusion (pMCAO) on behavior, angiogenesis, ultra-structural integrity of brain capillary endothelial cells, and expression of EPO and VEGF were assessed. Repeated treatments with Catalpol reduced neurological deficits and significantly improved angiogenesis, while significantly increasing brain levels of EPO and VEGF without worsening BBB edema. These results suggested that catalpol might contribute to infarcted-brain angiogenesis and ameliorate the edema of brain capillary endothelial cells (BCECs) by upregulating VEGF and EPO coordinately.

Association of growth factors with arterial recanalization and clinical outcome in patients with ischemic stroke treated with tPA

SUMMARY BACKGROUND

Growth factors (GF) such as vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1) and granulocyte-colony stimulating factor (G-CSF) have been associated with greater efficacy of tissue plasminogen activator (tPA) in experimental studies.

OBJECTIVES

To study the association of these GF with arterial recanalization and clinical outcome in patients with acute ischemic stroke treated with tPA.

METHODS

We prospectively studied 79 patients with ischemic stroke attributable to MCA occlusion treated with i.v. tPA within the first 3 h from onset of symptoms. Continuous transcranial color-coded sonography (TCCS) was performed during the first 2 h after tPA bolus to assess early MCA recanalization. Hemorrhagic transformation (HT) was classified according to ECASS II definitions. Good functional outcome was defined as a Rankin scale score of 0-2 at 90 days. GF levels were determined by ELISA.

RESULTS

Mean serum levels of VEGF, G-CSF and Ang-1 at baseline were significantly higher in patients with early MCA recanalization (n = 30) (all P < 0.0001). In the multivariate analysis, serum levels of VEGF (OR, 1.03), G-CSF (OR, 1.02) and Ang-1 (OR, 1.07) were independently associated with early MCA recanalization (all P < 0.0001). On the other hand, patients with parenchymal hematoma (PH) (n = 20) showed higher levels of Ang-1 (P < 0.0001). Ang-1 (OR, 1.12; P < 0.0001) was independently associated with PH, whereas patients with good outcome (n = 38) had higher levels of G-CSF (P < 0.0001). G-CSF was independently associated with good outcome (OR, 1.12; P = 0.036).

CONCLUSIONS

These findings suggest that GF may enhance arterial recanalization in patients with ischemic stroke treated with t-PA, although they might increase the HT.

The role of angiogenesis in damage and recovery from ischemic stroke

Ischemic stroke is burdened with a high morbidity and mortality in our society. However, there are few effective and largely available therapies for this devastating disease. In additon to advancing acute reperfusion therapies, there is a need to develop treatments aimed to promote repair and regeneration of brain tissue damaged by ischemia (neurorecovery). Therapeutic angiogenesis and vasculogenesis represent novel approaches of regenerative medicine that may help in the cure of patients with acute ischemic stroke. Translation of our knowledge about these processes from the bench to bedside is still underway. Although angiogenesis (the sprouting of new blood vessels from pre-existing vascular structures) is likely to contribute to neurorepair, the finality of the angiogenic response in acute ischemic stroke has not been fully elucidated. The first therapeutic approach to angiogenesis after ischemic stroke would be the modulation of the endogenous angiogenic response. In this setting, early instauration of physical activity, statins, and peroxisome proliferator-activated receptor-gamma agonists may enhance angiogenesis and neuroregeneration. Gene therapy with vascular growth factors has been successfully tested in patients affected by chronic myocardial and peripheral ischemia. Regarding brain ischemia, experiments in animal models have shown that the effect of these growth factors is critically affected by the dosage, route of delivery, and time of administration in relation to stroke onset. In addition, the optimal angiogenic substance is unknown. Finally, vectors for gene transfer should be further optimized. Therapeutic vasculogenesis consists of the administration of exogenous endothelial progenitor cells in order to enhance brain repair processes. Endothelial progenitor cells may be recruited in response to cerebral ischemia and participate in reparative vasculogenesis after acute ischemic stroke. Further research is needed to clarify their role and therapeutic applicability in human brain ischemia.

Angiogenesis and Microvascular Remodeling: A Brief History and Future Roadmap

Angiogenesis and vessel remodeling determine the integrative control of the architectural structure and functional behaviors of the microcirculation over the lifetime of an organism. Vascular remodeling is the basis of promising therapeutic strategies, including vascularization of ischemic organs. The history of angiogenesis research is long-more than 250 years-and the Microcirculatory Society has been the birthplace of numerous techniques, assays, and scientific concepts that have stimulated massive research endeavors in the pharmaceutical and medical arena. At present, angiogenesis isa dynamic field in which the molecular genetic and proteomic components of the process are still being identified, while integrative systems approaches are once again being recognized as essential to understand microvascular assembly in vivo across multiple scales from cells to whole vessel networks. A short history of people and ideas in this field is presented, followed by discussion of emerging directions receiving intense attention today and major questions that remain unanswered. The primary conclusion is that the need for scientists trained in the integrative approaches nurtured by the Microcirculatory Society over the past 50 years has never been greater, as it is clear that a complete mechanistic understanding of vessel adaptation (based on genomic and proteomic supporting casts) will now require deeper studies of angiogenesis and microvascular remodeling in the exquisite complexity of the native microenvironment-the microcirculation.

Accumulation of macromolecules in brain parenchyma in acute phase of cerebral infarction/reperfusion

Ischemia-reperfusion injury is induced by recovery of blood flow after ischemia. This phenomenon is a main cause of ischemic brain injury. The integrity of the blood-brain barrier (BBB) fails after cerebral ischemia and reperfusion. Further elucidation of this phenomenon promotes to develop treatment strategies for ischemia-reperfusion injury. In the present study, we attempted to examine the time-dependent change of ischemia-reperfusion injury in relation to BBB disorders at acute phase in a transient middle cerebral artery occlusion (t-MCAO) model rat as a cerebral infarction and reperfusion model. Brain cell damage after the reperfusion was assessed by 2, 3, 5-triphenyltetrazolium chloride (TTC) staining. To clarify a time-dependent change of the integrity of BBB, fluorescein isothiocyanate (FITC)-dextran (150 kDa) was injected intravenously into t-MCAO rats, and time-dependent localization of FITC-dextran was monitored in ex vivo. As a result, obvious brain damage was firstly observed at 3 h after reperfusion following 1 h of MCAO. In contrast, the leakage of FITC-dextran from cerebral vessels was observed immediately after the reperfusion. The present data suggest that the integrity of BBB failed prior to the occurrence of serious brain damage induced by ischemia-reperfusion, and that macromolecules such as water-soluble polymers and proteins which cannot pass through the BBB under normal condition would reach brain parenchyma at early stage after reperfusion. These findings would be useful to establish a novel treatment strategy for reperfusion injury after cerebral infarction.

The role and regulation of hypoxia-inducible factor-1alpha expression in brain development and neonatal hypoxic-ischemic brain injury

During neonatal hypoxic-ischemic brain injury, activation of transcription of a series of genes is induced to stimulate erythropoiesis, anti-apoptosis, apoptosis, necrosis and angiogenesis. A key factor mediating these gene transcriptions is hypoxia-inducible factor-1alpha (HIF-1alpha). During hypoxia, HIF-1alpha protein is stabilized and heterodimerizes with HIF-1beta to form HIF-1, subsequently regulating the expression of target genes. HIF-1alpha participates in early brain development and proliferation of neuronal precursor cells. Under pathological conditions, HIF-1alpha is known to play an important role in neonatal hypoxic-ischemic brain injury: on the one hand, HIF-1alpha has neuroprotective effects whereas it can also have neurotoxic effects. HIF-1alpha regulates the transcription of erythropoietin (EPO), which induces several pathways associated with neuroprotection. HIF-1alpha also promotes the expression of vascular endothelial cell growth factor (VEGF), which is related to neovascularization in hypoxic-ischemic brain areas. In addition, HIF-1alpha has an anti-apoptotic effect by increasing the expression of anti-apoptotic factors such as EPO during mild hypoxia. The neurotoxic effects of HIF-1alpha are represented by its participation in the apoptotic process by increasing the stability of the tumor suppressor protein p53 during severe hypoxia. Moreover, HIF-1alpha plays a role in cell necrosis, by interacting with calcium and calpain. HIF-1alpha can also exacerbate brain edema via increasing the permeability of the blood-brain barrier (BBB). Given these properties, HIF-1alpha has both neuroprotective and neurotoxic effects after hypoxia-ischemia. These events are cell type specific and related to the severity of hypoxia. Unravelling of the complex functions of HIF-1alpha may be important when designing neuroprotective therapies for hypoxic-ischemic brain injury.

Arterio-arterial malformation between a high origin radial artery and brachial artery within the cubital fossa - its clinical and embryological significance: a case report

Introduction

Arterial variations of the upper extremity are commonly seen in the radial and ulnar arteries. Arterial variations can be damaged through iatrogenic means if not properly documented.

Case presentation

A rare arterial anomaly was found in a 61-year-old female cadaver consisting of an arterio-arterial malformation between a high-origin radial artery and the brachial artery within the cubital fossa. The high-origin radial artery arose from the axillary artery, deep to the pectoralis minor muscle. It coursed superficially through the anterior compartment of the arm, converging with the more deeply placed brachial artery in the cubital fossa.

Conclusion

Our finding demonstrates the still vast array of possible arterial varieties and the need for awareness in order to prevent iatrogenic injury. We also provide supportive evidence of intussusceptive angiogenesis’ involvement in the formation of larger vessels.

Blood vessel remodeling in pig ovarian follicles during the periovulatory period: an immunohistochemistry and SEM-corrosion casting study

BACKGROUND

The present research aims to describe the process of vascular readjustment occurring in pig ovary during the periovulatory phase (from LH surge to ovulation) that drives the transformation of the follicle, a limited blood supplied structure, into the corpus luteum, a highly vascularised endocrine gland required to maintain high levels of progesterone in pregnancy. The swine model was chosen because it is characterized by a long periovulatory window (about 40-44 hrs-similar to human) that permits to recover follicles at a precise endocrinological timing.

METHODS

By validated hormonal protocol (eCG+hCG), able to mimic the physiologic gonadotropin stimulation, preovulatory follicles (PreOFs, 60 h-eCG), follicles in the middle (early periovulatory follicles, EPerOFs, 18 h-hCG) or late (LPerOFs, 36 h-hCG) periovulatory phase were isolated from prepubertal gilts. To understand the angiogenic process, morphological/morphometrical analyses were performed by combining immunohistochemistry (IHC) and SEM of vascular corrosion casts (VCC) techniques.

RESULTS

PreOFs showed a vascular plexus with proliferating endothelial cells (EPI). This plexus was characterized by a dense inner capillary network, with angiogenic figures, connected to the outer network by anastomotic vessels (arterioles and venules of the middle network). EPerOFs decreased their EPI, blood vessel extension in the outer network, and evidenced a reduced compactness of blood vessels. In LPerOFs, a rapid neovascularization was associated to an intensive tissue remodeling: the follicle acquired an undulated aspect presenting arterioles/venules near the basal membrane, increased vascular extension by EPI, sprouting and non-sprouting angiogenesis.The analysis of vascular geometric relations and branching angles evidenced similar values at all stages.

CONCLUSION

These data allow us to hypothesize that EPerOFs are in a quiescent status. LPerOFs represent the "metamorphic" follicles that rapidly turn-on angiogenesis to sustain a successful corpus luteum formation. Particularly, it is interesting to underlie that the non-sprouting angiogenesis, typical of structures in rapid neovascularization, occurred only in the LPerOFs. Moreover, vascular geometric relations showed as blood vessel remodeling occurs with the "maximum output and the minimum energetic expense".This knowledge will allow to better understand the mechanisms regulating the reproductive success and to clarify the complex physiological angiogenic process in adult tissues.

Heparin-binding EGF-like growth factor increases intestinal microvascular blood flow in necrotizing enterocolitis

BACKGROUND & AIMS

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in neonates. Although the exact etiology remains unknown, decreased intestinal blood flow is believed to play a critical role. We have shown that heparin-binding epidermal growth factor-like growth factor (HB-EGF) protects the intestines from injury in a rodent model of NEC. Our current goal was to assess the effect of HB-EGF on intestinal microvascular blood flow and intestinal injury in rat pups subjected to experimental NEC.

METHODS

Newborn rat pups were subjected to stress by exposure to hypoxia, hypothermia, hypertonic feedings, and lipopolysaccharide, with some pups receiving HB-EGF (800 microg x kg(-1) x dose(-1)) added to the feeds. Control animals received breast milk. Intestinal injury was graded using a standard histologic injury scoring system. Microvascular blood flow was assessed by fluorescein isothiocyanate/dextran angiography, with fluorescent images subjected to quantification, and by scanning electron microscopy.

RESULTS

Intestinal microvascular blood flow (defined as the extent of vascular filling with fluorescein isothiocyanate/dextran) was significantly decreased in pups subjected to stress compared with breast-fed pups. Stressed pups treated with HB-EGF had significantly increased microvascular blood flow. The changes in villous microvasculature correlated with histologic injury scores, with stressed pups treated with HB-EGF showing decreased histologic injury.

CONCLUSIONS

HB-EGF significantly preserved intestinal microvascular blood flow in pups subjected to experimental NEC, indicating that HB-EGF may play a critical role in the treatment of various diseases manifested by decreased intestinal blood flow, including NEC.

The dose-effectiveness of intranasal VEGF in treatment of experimental stroke

The aim of the present study was to assess the dose-effectiveness of intranasal (IN) vascular endothelial growth factor (VEGF)in the treatment of experimental stroke. Sprague-Dawley rats were randomized into four groups as IN low (100 microg/ml), IN middle (200 microg/ml) and IN high (500 microg/ml) VEGF-treated group, and IN saline-treated group (n=12), given recombinant human VEGF 165 or saline intranasally. Focal cerebral ischemia was induced by transient (90 min) middle cerebral artery occlusion (MCAO) method. Behavioral neurological deficits were assessed 1, 7 and 14 d after the onset of MCAO. Rats were sacrificed at 14 d, the brain sections were stained and an image analysis system was used to calculate the infarct volume. Microvessels were labeled by FITC-dextran and the segment lengths, diameters and number of microvessels were measured by Image Pro-Plus Version 6.0 software. Fourteen days post MCAO, infarct volume significantly reduced (P<0.01) in rats which received the middle dose of IN VEGF when compared to IN saline. And middle dose of VEGF significantly improved behavioral recovery (P<0.01). No significant difference in the behavioral recovery and infarct volume was observed between the saline-treated group and the low or high VEGF-treated groups (P>0.05). Compared to IN saline, middle and high doses of VEGF significantly increased the segment length, diameter and number of microvessels (P<0.01). No significant difference in the segment length, diameter and number of microvessels was observed between the IN saline-treated group and the low VEGF-treated group (P>0.05). The middle dose of IN VEGF was most effective on reducing infarct volume, improving behavioral recovery and enhancing angiogenesis in stroke brain, which can be used in the following treatments to further evaluate the effect of VEGF.

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

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

Inhibition of Src activity decreases tyrosine phosphorylation of occludin in brain capillaries and attenuates increase in permeability of the blood-brain barrier after transient focal cerebral ischemia

Disruption of the blood-brain barrier (BBB) caused by cerebral ischemia can initiate the development and progression of brain injuries, which may lead to irreversible dysfunction of the central nervous system. It is likely that tyrosine phosphorylation of a membrane-associated tight junctional protein, occludin, is important for the interaction of occludin with intracellular proteins, ZO-1 to ZO-3, and it regulates vascular permeability. Little is known about the pathophysiological alterations of tight junctional proteins after transient focal cerebral ischemia. In this study, we examined the tyrosine phosphorylation of occludin in isolated brain capillaries after transient focal cerebral ischemia. We further examined the effects of the Src-family tyrosine kinase inhibitor, PP2, on the tyrosine phosphorylation of occludin and on vascular permeability and infarct volume. Transient focal ischemia increased the tyrosine phosphorylation of occludin in the isolated brain capillaries. The administration of PP2 attenuated this phosphorylation, which was coincident with an inhibition of BBB leakage and a decrease in infarct volume. These results suggest that the increase in the tyrosine phosphorylation of occludin in the brain capillaries may be linked to the disruption of tight junctions, whose disruption can cause dysfunction of the BBB and the consequent increase in infarct volume.

Dual-color fluorescence imaging in a nude mouse orthotopic glioma model

We sought to establish a new orthotopic glioma model of nude mice by transfer of DsRed2, a red fluorescent protein gene, to malignant glioma cells and to perfuse the tissue with fluorescein isothiocyanate (FITC) dextran in vivo, which would permit the concurrent detection of brain tumor invasion and angiogenesis in vivo by florescence microscopy. 9L or U87 malignant glioma cells with DsRed2 expression were intracerebrally injected into the nude mice. FITC-dextran was administered intravenously to the mice bearing DsRed2-9L or DsRed2-U87 cells immediately before they were sacrificed at 10 days or 15 days after the implantation, respectively. Coronal vibratome sections were examined using 2D and 3D fluorescence microscopy and the results were compared with those examined by routine hematoxylin and eosin (H & E) staining. Angiogenesis induced by glioma was confirmed by two-dimensional and three-dimensional imaging analysis. DsRed2 fluorescence clearly demarcated the primary tumor margins and readily allowed for the visualization of local invasion at the single-cell level in the brain adjacent to tumor. We found that a few tumor cells migrated from the tumor mass along the aberrant microvasculature, but did not extend out of the angiogenic areas. However, locally invasive foci were very difficult to detect by H & E staining. We demonstrated, for the first time, that abnormal vascular structure and glioma cells can be visualized concurrently by fluorescence microscopy. This method is superior to H & E staining for the detection and study of physiologically relevant patterns of brain tumor invasion and angiogenesis in vivo.

Neurorestorative therapies for stroke: underlying mechanisms and translation to the clinic

Restorative cell-based and pharmacological therapies for experimental stroke substantially improve functional outcome. These therapies target several types of parenchymal cells (including neural stem cells, cerebral endothelial cells, astrocytes, oligodendrocytes, and neurons), leading to enhancement of endogenous neurogenesis, angiogenesis, axonal sprouting, and synaptogenesis in the ischaemic brain. Interaction between these restorative events probably underpins the improvement in functional outcome. This Review provides examples of cell-based and pharmacological restorative treatments for stroke that stimulate brain plasticity and functional recovery. The molecular pathways activated by these therapies, which induce remodelling of the injured brain via angiogenesis, neurogenesis, and axonal and dendritic plasticity, are discussed. The ease of treating intact brain tissue to stimulate functional benefit in restorative therapy compared with treating injured brain tissue in neuroprotective therapy might more readily help with translation of restorative therapy from the laboratory to the clinic.

Angiogenesis after cerebral ischemia

Though the vascular system of the adult brain is extremely stable under normal baseline conditions, endothelial cells start to proliferate in response to brain ischemia. The induction of angiogenesis, primarily in the ischemic boundary zone, enhances oxygen and nutrient supply to the affected tissue. Additionally, the generation of new blood vessels facilitates highly coupled neurorestorative processes including neurogenesis and synaptogenesis which in turn lead to improved functional recovery. To take advantage of angiogenesis as a therapeutic concept for stroke treatment, the knowledge of the precise molecular mechanisms is mandatory. Especially, since a couple of growth factors involved in post-ischemic angiogenesis may have detrimental adverse effects in the brain by increasing vascular permeability. This article summarizes the knowledge of molecular mechanisms of angiogenesis following cerebral ischemia. Finally, experimental pharmacological and cellular approaches to stimulate and enhance post-ischemic angiogenesis are discussed.

Netrin-4 enhances angiogenesis and neurologic outcome after cerebral ischemia

Functional recovery after cerebral ischemia is mediated by the regeneration of vascular networks and the restoration of synaptic architecture. Netrins have been implicated in neuronal pathfinding and angiogenesis. In this study, we investigated the expression of Netrin-4 and its putative receptors, deleted in colorectal cancer (DCC), Unc5A, and Unc5B after distal middle cerebral artery occlusion in mice. Netrin-4 protein was also administered intracerebroventricularly to examine its effect on angiogenesis and behavioral recovery. Netrin-4 protein was highly upregulated in the ischemic core as soon as 1 day after cerebral ischemia, with subsequent downregulation after 1 week. Its expression was limited to the area of blood-brain barrier damage and was seen on both blood vessels and astrocytic foot processes. Although there was not a significant upregulation of the putative Netrin-4 receptor Unc5A and Unc5B, there was a significant increase in expression of the DCC receptor on neuronal processes in the peri-infarct cortex. Intracerebroventricular administration of Netrin-4 into the ischemic brain increased blood vessel density, endothelial proliferation, and improved behavioral recovery at 1 week after stroke, but did not have an effect on blood-brain barrier permeability or infarct size. These findings suggest that Netrin-4 may improve poststroke functional recovery by enhancing blood vessel proliferation.

Activated protein C promotes neovascularization and neurogenesis in postischemic brain via protease-activated receptor 1

Activated protein C (APC) is a serine protease with anticoagulant and direct cytoprotective activities. Early postischemic APC application activates the cellular protein C pathway in brain endothelium and neurons, which is neuroprotective. Whether late APC administration after a transient ischemic attack is neuroprotective and whether APC influences brain repair is not known. Here, we determined safety and efficacy of late APC and tissue-plasminogen activator (tPA) administrations in a mouse model of transient brain ischemia. tPA given at 6 h after onset of ischemia killed all mice within 2 d, whereas APC given at 6 or 24 h after ischemia onset improved significantly functional outcome and reduced spread of the ischemic lesion. At 7 d postischemia, APC multiple dosing (0.8 mg/kg, i.p.) at 6-72 or 72-144 h enhanced comparably cerebral perfusion in the ischemic border by approximately 40% as shown by in vivo lectin-FITC angiography, blocked blood-brain barrier leakage of serum proteins, and increased the number of endothelial replicating cells by 4.5- to 4.7-fold. APC multidosing at 6-72 h or 72-144 h increased proliferation of neuronal progenitor cells in the subventricular zone (SVZ) by 40-50% and migration of newly formed neuroblasts from the SVZ toward the ischemic border by approximately twofold. The effects of APC on neovascularization and neurogenesis were mediated by protease-activated receptor 1 and were independent of the reduction by APC of infarction volume. Our data show that delayed APC administration is neuroprotective and mediates brain repair (i.e., neovascularization and neurogenesis), suggesting a significant extension of the therapeutic window for APC intervention in postischemic brain.

Cornel iridoid glycoside promotes neurogenesis and angiogenesis and improves neurological function after focal cerebral ischemia in rats

The aim of this study was to investigate the effects of cornel iridoid glycoside (CIG), an ingredient extracted from a traditional Chinese herb Cornus officinalis, on neurological function and neurogenesis after ischemic stroke. CIG was intragastrically administered to rats in doses of 20, 60 and 180 mg/kg/day, starting 3 h after the onset of middle cerebral artery occlusion (MCAO). The behavioral test was performed by using the modified neurological severity score (mNSS). Rats were sacrificed 7, 14, or 28 days after ischemia occurred. Neurogenesis and angiogenesis were detected by using immunofluorescence staining. The messenger ribonucleic acid (mRNA) expression of vascular endothelial growth factor (VEGF) and its receptor Flk-1 was measured by RT-PCR, and the protein expression of VEGF was determined by Western blotting analysis. The treatment with CIG at the doses of 60 and 180 mg/kg/day significantly improved neurological function, and increased the number of bromodeoxyuridine (BrdU)-positive cells and nestin-positive cells in the subventricular zone of rats 7, 14 and 28 days after ischemia. The number of newly mature neurons and blood vessels in striatum, as indicated by BrdU/NeuN and vWF immunoreactivity, respectively, was also increased in CIG-treated rats 28 days after stroke. CIG treatment obviously enhanced the mRNA expression of VEGF and its receptor Flk-1 and the protein expression of VEGF 7 and 28 days after ischemia. The results indicated that CIG promoted neurogenesis and angiogenesis and improved neurological function after ischemia in rats, and the mechanism might be related to CIG's increasing VEGF and Flk-1 in the brain.

Role of endothelial nitric oxide synthetase in arteriogenesis after stroke in mice

Arteriogenesis supports restored perfusion in the ischemic brain and improves long-term functional outcome after stroke. We investigate the role of endothelial nitric oxide synthetase (eNOS) and a nitric oxide (NO) donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl) amino] diazen-1-ium-1, 2-diolate (DETA-NONOate), in promoting arteriogenesis after stroke. Adult wild-type (WT, n=18) and eNOS-knockout (eNOS(-/-), n=36) mice were subjected to transient (2.5 h) right middle cerebral artery occlusion (MCAo) and were treated with or without DETA-NONOate (0.4 mg/kg) 24 h after MCAo. Functional evaluation was performed. Animals were sacrificed 3 days after MCAo for arterial cell culture studies, or 14 days for immunohistochemical analysis. Consistent with previous studies, eNOS(-/-) mice exhibited a higher mortality rate (P<0.05, n=18/group) and more severe neurological functional deficit after MCAo than WT mice (P<0.05, n=12/group). Decreased arteriogenesis, was evident in eNOS(-/-) mice compared with WT mice, as demonstrated by reduced vascular smooth muscle cell (VSMC) proliferation, arterial density and diameter in the ischemic brain. eNOS(-/-) mice treated with DETA-NONOate had a significantly decreased mortality rate and improved functional recovery, and exhibited enhanced arteriogenesis identified by increased VSMC proliferation, and upregulated arterial density and diameter compared to eNOS(-/-) mice after stroke (P<0.05, n=12/group). To elucidate the mechanisms underlying eNOS/NO mediated arteriogenesis, VSMC migration was measured in vitro. Arterial cell migration significantly decreased in the cultured common carotid artery (CCA) derived from eNOS(-/-) mice 3 days after MCAo compared to WT arterial cells. DETA-NONOate-treatment significantly attenuated eNOS(-/-)-induced decrease of arterial cell migration compared to eNOS(-/-) control artery (P<0.05; n=6/group). Using VSMC culture, DETA-NONOate significantly increased VSMC migration, while inhibition of NOS significantly decreased VSMC migration (P<0.05; n=6/group). Our data indicated that eNOS not only promotes vascular dilation but also increases VSMC proliferation and migration, and thereby enhances arteriogenesis after stroke. Therefore, increase eNOS may play an important role in regulating of arteriogenesis after stroke.

Therapeutic benefits of angiogenetic gene-modified human mesenchymal stem cells after cerebral ischemia

Intravenous transplantation of human mesenchymal stem cells (hMSCs) expanded from adult bone marrow ameliorates functional deficits in rat cerebral infarction models. Several hypotheses to account for the therapeutic mechanisms have been suggested, but angiogenesis is thought to be of critical importance. Recently, we have reported the therapeutic benefits of hMSCs which have been transfected with the angiopoietin-1 gene in a rat permanent middle cerebral artery occlusion (MCAO) model. To potentially enhance the therapeutic effects of angiopoietin-1 gene-modified hMSC (Ang-hMSC), we transfected hMSCs with the angiopoietin-1 gene and the VEGF gene, and investigated whether the combination of Ang-1 and VEGF gene-modified hMSCs (Ang-VEGF-hMSC) contribute to functional recovery in a rat MCAO model. We induced MCAO using intraluminal vascular occlusion, and hMSCs, Ang-hMSCs, VEGF-hMSCs or Ang-VEGF-hMSCs were intravenously infused 6 h later. MRI and behavioral analyses revealed that rats receiving Ang-VEGF-hMSCs showed the greatest structural-functional recovery as compared to the other groups. These results suggest that intravenous administration of hMSCs transfected with the angiopoietin-1 and VEGF gene using a fiber-mutant adenovirus vector may represent a new strategy for the treatment of ischemia.

Endogenous matrix metalloproteinase (MMP)-3 and MMP-9 promote the differentiation and migration of adult neural progenitor cells in response to chemokines

Adult neurogenesis is regulated by both intrinsic programs and extrinsic stimuli. The enhanced proliferation of adult neural stem/progenitor cells (aNPCs) in the subventricular zone and the migration of neuroblasts toward the ischemic region in adult brains present a unique challenge as well as an opportunity to understand the molecular mechanisms underlying the extrinsic cue-induced neurogenic responses. Matrix metalloproteinases (MMPs) are a family of proteinases known to play a role in extracellular matrix remodeling and cell migration. However, their presence in aNPCs and their potential function in injury-induced aNPC migration remain largely unexplored. Here we demonstrate that in response to two injury-induced chemokines, stromal cell-derived factor 1 (SDF-1) and vascular endothelial growth factor, aNPCs differentiated into migratory cells that expressed increased levels of MMP-3 and MMP-9. Whereas differentiated neuroblasts and a subpopulation of astrocytes migrated toward the chemokines, undifferentiated progenitors did not migrate. Blocking the expression of MMP-3 or MMP-9 in aNPCs interfered with both the differentiation of aNPCs and chemokine-induced cell migration. Thus, endogenous MMPs expressed by aNPCs are important for mediating their neurogenic response to extrinsic signals.

Contribution of bone marrow-derived cells associated with brain angiogenesis is primarily through leukocytes and macrophages

OBJECTIVE

We investigated the role of bone marrow-derived cells (BMDCs) in an angiogenic focus, induced by VEGF stimulation.

METHODS AND RESULTS

BM from GFP donor mice was isolated and transplanted into lethally irradiated recipients. Four weeks after transplantation, groups of mice received adeno-associated viral vector (AAV)-VEGF or AAV-lacZ gene (control) injection and were euthanized at 1 to 24 weeks. BMDCs were characterized by double-labeled immunostaining. The function of BMDCs was further examined through matrix metalloproteinase (MMP)-2 and -9 activity. We found that capillary density increased after 2 weeks, peaked at 4 weeks (P<0.01), and sustained up to 24 weeks after gene transfer. GFP-positive BMDCs infiltration in the angiogenic focus began at 1 week, peaked at 2 weeks, and decreased thereafter. The GFP-positive BMDCs were colocalized with CD45 (94%), CD68 (71%), 5% Vimentin (5%), CD31/von Willebrand factor (vWF) (1%), and alpha-smooth muscle actin (alpha -SMA, 0.5%). Infiltrated BMDCs expressed MMP-9. MMP-9 KO mice confirmed the dependence of the angiogenic response on MMP-9 availability.

CONCLUSIONS

Nearly all BMDCs in the angiogenic focus showed expression for leukocytes/macrophages, indicating that BMDCs minimally incorporated into the neovasculature. Colocalization of MMPs with GFP suggests that BMDCs play a critical role in VEGF-induced angiogenic response through up-regulation of MMPs.

VEGF increases blood-brain barrier permeability to Evans blue dye and tetanus toxin fragment C but not adeno-associated virus in ALS mice

Entry of most compounds into the CNS is impeded by the blood-brain barrier (BBB). Because vascular endothelial growth factor (VEGF) is important in the formation and maintenance of the BBB and is known to modulate BBB permeability in newborn rodents, we tested the hypothesis that VEGF may enhance BBB permeability in adult mice. We examined the effect of VEGF on the CNS distribution of three different agents: a small molecule (Evans blue dye) that is known to bind plasma proteins, an exogenous protein (tetanus toxin fragment C; TTC), and a viral vector (recombinant adeno-associated virus serotype 2/5 marked with lacZ; rAAV2/5-lacZ). Pretreatment with VEGF (20 mug; i.v.) increased permeability of the BBB to Evans blue dye and TTC as detected by augmented concentrations of these substances in the cerebrum, brainstem, and spinal cord. By contrast, VEGF did not alter BBB permeability to AAV2/5-lacZ, as defined by beta-galactosidase activity assay. These data demonstrate the potential utility of VEGF for pharmacological modulation of the BBB, and indicate that the increase in BBB permeability mediated by VEGF is limited by the size of the delivered substance.

Mesenchymal stem cells transplantation could be beneficial for treatment of experimental ischemic stroke in rats

Cell therapy is prospective, modern attempt to ischemic stroke treatment. It has been being widely worked out recently. We suggest mesenchymal stem cells (MSC) as a cell therapy agent in the therapy of this disease. Experiments were carried out in inbred male Wistar-Kyoto rats. Animals were subjected to middle cerebral artery occlusion (MCAO). MSCs were isolated from rat bone marrow, expanded in culture and labelled with vital fluorescent dye PKH-26. Then 5 x 10(6) cells were injected into the tail vein on the day of MCAO and three days later. Control group animals received PBS injection (negative control). Cognitive function restoration was estimated by Morris Water Maze testing during 6 weeks after MCAO. Animals were sacrificed 1, 2, 3, 5 days and 1, 2, 4 and 6 weeks after operation. Intravenous MSC transplantation decreased post-operation mortality and benefited behavioural and neurological recovery. Experimental groups animals revealed changes in aseptic inflammation processes which were completed faster comparing to control group. That effect correlated with accelerated glial scar formation. Reduction of the infarct volumes and such post-stroke after-effects as border zone gliosis and liquor cysts formation accompanied by increased angiogenesis and subventricular zone cells proliferation were shown after cell therapy. The obtained results referred to both cell therapy groups. Thus, MSC injection benefited post-stroke rehabilitation irrespective of transplantation time. However, further investigation should be carried out in order to find out the mechanism of their action.

Astrocyte responses to injury: VEGF simultaneously modulates cell death and proliferation

Hypoxia is linked to changes in blood-brain barrier (BBB) permeability, and loss of BBB integrity is characteristic of many pathological brain diseases including stroke. In particular, astrocytes play a central role in brain homeostasis and BBB function. We investigated how hypoxia affects astrocyte survival and assessed whether VEGF release through hypoxia-inducible factor-1alpha (HIF-1alpha) induction plays a role in tolerance of these cells to insult. Thus primary astrocytes were subjected to normoxic (21% O(2)), hypoxic (1% O(2)), or near-anoxic (<0.1% O(2)) conditions in the presence or absence of glucose. Cell death was significantly initiated after combined oxygen glucose deprivation, and, surprisingly, astrocyte proliferation increased concomitantly. Near anoxic, but not hypoxic, conditions stabilized HIF-1alpha protein and provoked DNA binding activity, whereas oxygen and glucose deprivation accelerated HIF-1alpha accumulation. Unexpectedly, Hif-1alpha knockdown studies showed that elevated VEGF levels following increased insult was only partially due to HIF-1alpha induction, suggesting alternative mechanisms of VEGF regulation. Notably, endogenous VEGF signaling during insult was essential for cell fate since VEGF inhibition appreciably augmented cell death and reduced proliferation. These data suggest Hif-1 only partially contributes to VEGF-mediated astrocyte responses during chronic injury (as occurs in clinical hypoxic/ischemic insults) that may ultimately be responsible for disrupting BBB integrity.

Ischemic stroke and neurogenesis in the subventricular zone

The subventricular zone (SVZ) of the lateral ventricle contains neural stem and progenitor cells that generate neuroblasts, which migrate to the olfactory bulb where they differentiate into interneurons. Ischemic stroke induces neurogenesis in the SVZ and these cells migrate to the boundary of the ischemic lesion. This article reviews current data on cytokinetics, signaling pathways and vascular niche that are involved in processes of proliferation, differentiation, and migration of neural progenitor cells after stroke.

Vascular actions of estrogens: functional implications

The impact of estrogen exposure in preventing or treating cardiovascular disease is controversial. But it is clear that estrogen has important effects on vascular physiology and pathophysiology, with potential therapeutic implications. Therefore, the goal of this review is to summarize, using an integrated approach, current knowledge of the vascular effects of estrogen, both in humans and in experimental animals. Aspects of estrogen synthesis and receptors, as well as general mechanisms of estrogenic action are reviewed with an emphasis on issues particularly relevant to the vascular system. Recent understanding of the impact of estrogen on mitochondrial function suggests that the longer lifespan of women compared with men may depend in part on the ability of estrogen to decrease production of reactive oxygen species in mitochondria. Mechanisms by which estrogen increases endothelial vasodilator function, promotes angiogenesis, and modulates autonomic function are summarized. Key aspects of the relevant pathophysiology of inflammation, atherosclerosis, stroke, migraine, and thrombosis are reviewed concerning current knowledge of estrogenic effects. A number of emerging concepts are addressed throughout. These include the importance of estrogenic formulation and route of administration and the impact of genetic polymorphisms, either in estrogen receptors or in enzymes responsible for estrogen metabolism, on responsiveness to hormone treatment. The importance of local metabolism of estrogenic precursors and the impact of timing for initiation of treatment and its duration are also considered. Although consensus opinions are emphasized, controversial views are presented to stimulate future research.

Coupling of angiogenesis and neurogenesis in cultured endothelial cells and neural progenitor cells after stroke

Angiogenesis and neurogenesis are coupled processes. Using a coculture system, we tested the hypothesis that cerebral endothelial cells activated by ischemia enhance neural progenitor cell proliferation and differentiation, while neural progenitor cells isolated from the ischemic subventricular zone promote angiogenesis. Coculture of neural progenitor cells isolated from the subventricular zone of the adult normal rat with cerebral endothelial cells isolated from the stroke boundary substantially increased neural progenitor cell proliferation and neuronal differentiation and reduced astrocytic differentiation. Conditioned medium harvested from the stroke neural progenitor cells promoted capillary tube formation of normal cerebral endothelial cells. Blockage of vascular endothelial growth factor receptor 2 suppressed the effect of the endothelial cells activated by stroke on neurogenesis as well as the effect of the supernatant obtained from stroke neural progenitor cells on angiogenesis. These data suggest that angiogenesis couples to neurogenesis after stroke and vascular endothelial growth factor likely mediates this coupling.

Activation of protease-activated receptor1 mediates induction of matrix metalloproteinase-9 by thrombin in rat primary astrocytes

Thrombin plays an important role in diverse neurological processes such as proliferation, cell migration, differentiation and neuroinflammation. In this study, we investigated the effect of thrombin on matrix metalloprotease-9 (MMP-9) expression in rat primary astrocytes. Thrombin (1-10U/ml) induced a significant increase in MMP-9 activity as measured by gelatin zymography. Thrombin also increased MMP-9 mRNA expression. Among three isotypes of thrombin receptor, i.e. protease-activated receptor (PAR)-1, -3 and -4, PAR1 agonist (1-100muM) but not PAR3 and PAR4 agonist induced MMP-9 expression. Inhibition of thrombin-induced MMP-9 production by SCH 79797 (10-50nM), a selective PAR1 receptor antagonist, confirmed that PAR1 is a main receptor for thrombin-induced MMP-9 expression. In astrocytes, thrombin activated Erk1/2, and it was inhibited by PD98059. In this study, thrombin-induced MMP-9 expression was inhibited by PD98059. PAR1 agonist activated Erk1/2 and PD98059 inhibited PAR1 agonist-induced MMP-9 expression. MMP-9 promoter reporter assay confirmed the positive effect of ERK1/2 on MMP-9 expression. These results suggest that the activation of PAR1 mediates thrombin-induced MMP-9 expression through the regulation of Erk1/2.

Themes and strategies for studying the biology of stroke recovery in the poststroke epoch

BACKGROUND AND PURPOSE

This review will focus on the emerging principles of neural repair after stroke, and on the overlap between cellular mechanisms of neural repair in stroke and clinical principles of recovery and rehabilitation.

SUMMARY OF REVIEW

Stroke induces axonal sprouting and neurogenesis. Axonal sprouting occurs in tissue adjacent to the stroke and its connected cortical areas, and from sites that are contralateral to the infarct. Neurogenesis produces newly born immature neurons in peri-infarct striatum and cortex. Stimulation of both axonal sprouting and neurogenesis is associated with improved recovery in animal models of stroke. A unique cellular environment in the poststroke brain supports neural repair: an association of angiogenic and remodeling blood vessels with newly born immature neurons in a neurovasclar niche. Controversies in the field of neural repair after stroke persist, and relate to the locations of axonal sprouting in animal models of stroke and how these correlate to patterns of human remapping and recovery, and to the different models of stroke used in studies of neurogenesis.

CONCLUSIONS

On a cellular level, the phenomenology of neural repair after stroke has been defined and unique regenerative environments in the poststroke brain identified. As the field moves toward specific studies of causal mechanisms in poststroke repair, it will need to maintain a perspective of the animal models suited to the study of neural repair after stroke as they relate to the patterns of recovery in humans in this disease.