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

Novel rat model for neurocysticercosis using Taenia solium

Neurocysticercosis is caused by Taenia solium infecting the central nervous system and is the leading cause of acquired epilepsy and convulsive conditions worldwide. Research into the pathophysiology of the disease and appropriate treatment is hindered by lack of cost-effective and physiologically similar animal models. We generated a novel rat neurocysticercosis model using intracranial infection with activated T. solium oncospheres. Holtzman rats were infected in two separate groups: the first group was inoculated extraparenchymally and the second intraparenchymally, with different doses of activated oncospheres. The groups were evaluated at three different ages. Histologic examination of the tissue surrounding T. solium cysticerci was performed. Results indicate that generally infected rats developed cysticerci in the brain tissue after 4 months, and the cysticerci were observed in the parenchymal, ventricle, or submeningeal brain tissue. The route of infection did not have a statistically significant effect on the proportion of rats that developed cysticerci, and there was no dependence on infection dose. However, rat age was crucial to the success of the infection. Epilepsy was observed in 9% of rats with neurocysticercosis. In histologic examination, a layer of collagen tissue, inflammatory infiltrate cells, perivascular infiltrate, angiogenesis, spongy change, and mass effect were observed in the tissue surrounding the cysts. This study presents a suitable animal model for the study of human neurocysticercosis.

Recent Progress in Endothelial Progenitor Cell Culture Systems: Potential for Stroke Therapy

Endothelial progenitor cells (EPCs) participate in endothelial repair and angiogenesis due to their abilities to differentiate into endothelial cells and to secrete protective cytokines and growth factors. Consequently, there is considerable interest in cell therapy with EPCs isolated from peripheral blood to treat various ischemic injuries. Quality and quantity-controlled culture systems to obtain mononuclear cells enriched in EPCs with well-defined angiogenic and anti-inflammatory phenotypes have recently been developed, and increasing evidence from animal models and clinical trials supports the idea that transplantation of EPCs contributes to the regenerative process in ischemic organs and is effective for the therapy of ischemic cerebral injury. Here, we briefly describe the general characteristics of EPCs, and we review recent developments in culture systems and applications of EPCs and EPC-enriched cell populations to treat ischemic stroke.

Persistent Angiogenesis in the Autism Brain: An Immunocytochemical Study of Postmortem Cortex, Brainstem and Cerebellum

In the current work, we conducted an immunocytochemical search for markers of ongoing neurogenesis (e.g. nestin) in auditory cortex from postmortem sections of autism spectrum disorder (ASD) and age-matched control donors. We found nestin labeling in cells of the vascular system, indicating blood vessels plasticity. Evidence of angiogenesis was seen throughout superior temporal cortex (primary auditory cortex), fusiform cortex (face recognition center), pons/midbrain and cerebellum in postmortem brains from ASD patients but not control brains. We found significant increases in both nestin and CD34, which are markers of angiogenesis localized to pericyte cells and endothelial cells, respectively. This labeling profile is indicative of splitting (intussusceptive), rather than sprouting, angiogenesis indicating the blood vessels are in constant flux rather than continually expanding.

Hydrogen Sulfide Attenuates Tissue Plasminogen Activator-Induced Cerebral Hemorrhage Following Experimental Stroke

Tissue plasminogen activator (tPA), the only approved drug for the treatment of ischemic stroke, increases the risk of cerebral hemorrhage. Here, we investigated whether the newly identified gaso-transmitter hydrogen sulfide (H2S), when used in combination with tPA, reduced the hemorrhagic transformation following stroke. In a mouse model of middle cerebral artery occlusion (MCAO), intravenous injection of tPA enhanced cerebral hemorrhage, which was significantly attenuated by the co-administration of two structurally unrelated H2S donors, ADT-OH and NaHS. By assessing extravasation of Evans blue into the ischemic hemisphere as well as brain edema following MCAO, we further showed that a tPA-exacerbated BBB disruption was significantly ameliorated by the co-administration of ADT-OH. In the mouse MCAO model, tPA upregulated Akt activation, vascular endothelial growth factor (VEGF) expression, and metalloproteinase 9 (MMP9) activity in the ischemic brain, which was remarkably attenuated by ADT-OH. In the in vitro glucose-oxygen deprivation (OGD) model, ADT-OH markedly attenuated tPA-enhanced Akt activation and VEGF expression in brain microvascular endothelial cells. Finally, ADT-OH improved functional outcomes in mice subjected to MCAO and tPA infusion. In conclusion, H2S donors reduced tPA-induced cerebral hemorrhage by possibly inhibiting the Akt-VEGF-MMP9 cascade. Administration of H2S donors has potential as a novel modality to improve the safety of tPA following stroke.

Bone marrow stromal cell transplantation through tail vein injection promotes angiogenesis and vascular endothelial growth factor expression in cerebral infarct area in rats

BACKGROUND AIMS

This study sought to identify correlations between vascular endothelial growth factor (VEGF) expression after tail-vein injection of rat-derived bone marrow stromal cells (BMSCs) and neurogenesis and angiogenesis in cerebral infarct of rats.

METHODS

Rats with intraluminal middle cerebral artery occlusion were injected in a tail vein with Hoechst-labeled BMSCs. Functional recovery from cerebral infarction was observed through the use of a locomotion score. The brains of injected rats were sliced, and Hoechst-labeled BMSCs in the infarct and peri-infarct areas and subventricular zone (SVZ) were detected with the use of fluorescence microscopy. Ki-67 (as a cell proliferation marker) and VEGF expression were determined by means of immunohistochemistry. Neurofibril formation and angiogenesis were examined by means of Bielschowsky staining.

RESULTS

Within 1 to 2 weeks after BMSC injection, rats showed significantly improved locomotion scores compared with rats without BMSC injection (P < 0.01). Viable BMSCs were found in the peri-infarct area. The numbers of Ki-67-positive and VEGF-positive cells in the peri-infarct area and SVZ of injected rats were significantly increased compared with the control group (P < 0.01). Numerous new vessels, neurofibrils and anastomosed vasculatures were present in the infarct area. These neurofibrils mainly surrounded the neovasculatures.

CONCLUSIONS

These results indicate that BMSC-transplantation in rats through tail vein injection can increase neurogenesis, perhaps as the result of VEGF-mediated and/or Ki-67-mediated angiogenesis.

Magnetic resonance imaging and cell-based neurorestorative therapy after brain injury

Restorative cell-based therapies for experimental brain injury, such as stroke and traumatic brain injury, substantially improve functional outcome. We discuss and review state of the art magnetic resonance imaging methodologies and their applications related to cell-based treatment after brain injury. We focus on the potential of magnetic resonance imaging technique and its associated challenges to obtain useful new information related to cell migration, distribution, and quantitation, as well as vascular and neuronal remodeling in response to cell-based therapy after brain injury. The noninvasive nature of imaging might more readily help with translation of cell-based therapy from the laboratory to the clinic.

Dynamic regulation of aquaporin-4 water channels in neurological disorders

Aquaporin-4 water channels play a central role in brain water regulation in neurological disorders. Aquaporin-4 is abundantly expressed at the astroglial endfeet facing the cerebral vasculature and the pial membrane, and both its expression level and subcellular localization significantly influence brain water transport. However, measurements of aquaporin-4 levels in animal models of brain injury often report opposite trends of change at the injury core and the penumbra. Furthermore, aquaporin-4 channels play a beneficial role in brain water clearance in vasogenic edema, but a detrimental role in cytotoxic edema and exacerbate cell swelling. In light of current evidence, we still do not have a complete understanding of the role of aquaporin-4 in brain water transport. In this review, we propose that the regulatory mechanisms of aquaporin-4 at the transcriptional, translational, and post-translational levels jointly regulate water permeability in the short and long time scale after injury. Furthermore, in order to understand why aquaporin-4 channels play opposing roles in cytotoxic and vasogenic edema, we discuss experimental evidence on the dynamically changing osmotic gradients between blood, extracellular space, and the cytosol during the formation of cytotoxic and vasogenic edema. We conclude with an emerging picture of the distinct osmotic environments in cytotoxic and vasogenic edema, and propose that the directions of aquaporin-4-mediated water clearance in these two types of edema are distinct. The difference in water clearance pathways may provide an explanation for the conflicting observations of the roles of aquaporin-4 in edema resolution.

MicroRNA-150 regulates blood-brain barrier permeability via Tie-2 after permanent middle cerebral artery occlusion in rats

The mechanism of blood-brain barrier (BBB) disruption, involved in poststroke edema and hemorrhagic transformation, is important but elusive. We investigated microRNA-150 (miR-150)-mediated mechanism in the disruption of BBB after stroke in rats. We found that up-regulation of miR-150 increased permeability of BBB as detected by MRI after permanent middle cerebral artery occlusion in vivo as well as increased permeability of brain microvascular endothelial cells after oxygen-glucose deprivation in vitro. The expression of claudin-5, a key tight junction protein, was decreased in the ischemic boundary zone after up-regulation of miR-150. We found in brain microvascular endothelial cells that overexpression of miR-150 decreased not only cell survival rate but also the expression levels of claudin-5 after oxygen-glucose deprivation. With dual-luciferase assay, we confirmed that miR-150 could directly regulate the angiopoietin receptor Tie-2. Moreover, silencing Tie-2 with lentivirus-delivered small interfering RNA reversed the effect of miR-150 on endothelial permeability, cell survival, and claudin-5 expression. Furthermore, poststroke treatment with antagomir-150, a specific miR-150 antagonist, contributed to BBB protection, infarct volume reduction, and amelioration of neurologic deficits. Collectively, our findings suggested that miR-150 could regulate claudin-5 expression and endothelial cell survival by targeting Tie-2, thus affecting the permeability of BBB after permanent middle cerebral artery occlusion in rats, and that miR-150 might be a potential alternative target for the treatment of stroke.-Fang, Z., He, Q.-W., Li, Q., Chen, X.-L., Baral, S., Jin, H.-J., Zhu, Y.-Y., Li, M., Xia, Y.-P., Mao, L., Hu, B. MicroRNA-150 regulates blood-brain barrier permeability via Tie-2 after permanent middle cerebral artery occlusion in rats.

Cannabidiol protects an in vitro model of the blood-brain barrier from oxygen-glucose deprivation via PPARγ and 5-HT1A receptors

BACKGROUND AND PURPOSE

In vivo and in vitro studies have demonstrated a protective effect of cannabidiol (CBD) in reducing infarct size in stroke models and against epithelial barrier damage in numerous disease models. We aimed to investigate whether CBD also affects blood-brain barrier (BBB) permeability following ischaemia.

EXPERIMENTAL APPROACH

Human brain microvascular endothelial cell (HBMEC) and human astrocyte co-cultures modelled the BBB. Ischaemia was modelled by oxygen-glucose deprivation (OGD) and permeability was measured by transepithelial electrical resistance.

KEY RESULTS

CBD (10 μM) prevented the increase in permeability caused by 4 h OGD. CBD was most effective when administered before the OGD, but protective effects were observed up to 2 h into reperfusion. This protective effect was inhibited by a PPARγ antagonist and partly reduced by a 5-HT1A receptor antagonist, but was unaffected by antagonists of cannabinoid CB1 or CB2 receptors, TRPV1 channels or adenosine A2A receptors. CBD also reduced cell damage, as measured by LDH release and by markers of cellular adhesion, such as the adhesion molecule VCAM-1. In HBMEC monocultures, CBD decreased VCAM-1 and increased VEGF levels, effects which were inhibited by PPARγ antagonism.

CONCLUSIONS AND IMPLICATIONS

These data suggest that preventing permeability changes at the BBB could represent an as yet unrecognized mechanism of CBD-induced neuroprotection in ischaemic stroke, a mechanism mediated by activation of PPARγ and 5-HT1A receptors.

Chronic cocaine disrupts neurovascular networks and cerebral function: optical imaging studies in rodents

Cocaine abuse can lead to cerebral strokes and hemorrhages secondary to cocaine's cerebrovascular effects, which are poorly understood. We assessed cocaine's effects on cerebrovascular anatomy and function in the somatosensory cortex of the rat's brain. Optical coherence tomography was used for in vivo imaging of three-dimensional cerebral blood flow (CBF) networks and to quantify CBF velocities (CBFv), and multiwavelength laser-speckle-imaging was used to simultaneously measure changes in CBFv, oxygenated (Δ[HbO2] ) and deoxygenated hemoglobin (Δ[HbR] ) concentrations prior to and after an acute cocaine challenge in chronically cocaine exposed rats. Immunofluorescence techniques on brain slices were used to quantify microvasculature density and levels of vascular endothelial growth factor (VEGF). After chronic cocaine (2 and 4 weeks), CBFv in small vessels decreased, whereas vasculature density and VEGF levels increased. Acute cocaine further reduced CBFv and decreased Δ[HbO2] and this decline was larger and longer lasting in 4 weeks than 2 weeks cocaine-exposed rats, which indicates that risk for ischemia is heightened during intoxication and that it increases with chronic exposures. These results provide evidence of cocaine-induced angiogenesis in cortex. The CBF reduction after chronic cocaine exposure, despite the increases in vessel density, indicate that angiogenesis was insufficient to compensate for cocaine-induced disruption of cerebrovascular function.

Promoting recovery from ischemic stroke

Over recent decades, experimental and clinical stroke studies have identified a number of neurorestorative treatments that stimulate neural plasticity and promote functional recovery. In contrast to the acute stroke treatments thrombolysis and endovascular thrombectomy, neurorestorative treatments are still effective when initiated days after stroke onset, which makes them applicable to virtually all stroke patients. In this article, selected physical, pharmacological and cell-based neurorestorative therapies are discussed, with special emphasis on interventions that have already been transferred from the laboratory to the clinical setting. We explain molecular and structural processes that promote neural plasticity, discuss potential limitations of neurorestorative treatments, and offer a speculative viewpoint on how neurorestorative treatments will evolve.

The role of vascular endothelial growth factor in the regulation of development and functioning of the brain: new target molecules for pharmacotherapy

Vascular endothelial growth factors (VEGFs) have been shown to participate in atherosclerosis, arteriogenesis, cerebral edema, neuroprotection, neurogenesis, angiogenesis, postischemic brain and vessel repair. Most of these actions involve VEGF-A and the VEGFR-2 receptor. VEGF signaling pathways represent an important potential for treatment of neurological diseases affecting the brain

Ischemia-induced Angiogenesis is Attenuated in Aged Rats

To study whether focal angiogenesis is induced in aged rodents after permanent distal middle cerebral artery occlusion (MCAO), young adult (3-month-old) and aged (24-month-old) Fisher 344 rats underwent MCAO and sacrificed up to two months after MCAO. Immunohistochemistry and synchrotron radiation microangiography were performed to examine the number of newly formed blood vessels in both young adult and aged rats post-ischemia. We found that the number of capillaries and small arteries in aged brain was the same as young adult brain. In addition, we found that after MCAO, the number of blood vessels in the peri-infarct region of ipsilateral hemisphere in aged ischemic rats was significantly increased compared to the aged sham rats (p<0.05). We also confirmed that ischemia-induced focal angiogenesis occurred in young adult rat brain while the blood vessel density in young adult ischemic brain was significantly higher than that in the aged ischemic brain (p<0.05). Our data suggests that focal angiogenesis in aged rat brain can be induced in response to ischemic brain injury, and that aging impedes brain repairing and remodeling after ischemic stroke, possible due to the limited response of angiogenesis.

Coupling of neurogenesis and angiogenesis after ischemic stroke

Stroke is a leading cause of mortality and severe long-term disability worldwide. Development of effective treatment or new therapeutic strategies for ischemic stroke patients is therefore crucial. Ischemic stroke promotes neurogenesis by several growth factors including FGF-2, IGF-1, BDNF, VEGF and chemokines including SDF-1, MCP-1. Stroke-induced angiogenesis is similarly regulated by many factors most notably, eNOS and CSE, VEGF/VEGFR2, and Ang-1/Tie2. Important findings in the last decade have revealed that neurogenesis is not the stand-alone consideration in the fight for full functional recovery from stroke. Angiogenesis has been also shown to be critical in improving post-stroke neurological functional recovery. More than that, recent evidence has shown a highly possible interplay or dependence between stroke-induced neurogenesis and angiogenesis. Moving forward, elucidating the underlying mechanisms of this coupling between stroke-induced neurogenesis and angiogenesis will be of great importance, which will provide the basis for neurorestorative therapy. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

A TEM protocol for quality assurance of in vitro cellular barrier models and its application to the assessment of nanoparticle transport mechanisms across barriers

We report here a protocol to characterise and monitor the quality of in vitro human cellular barrier models using Transmission Electron Microscopy (TEM), which can be applied for transport assays, mechanistic studies and screening of drug/compound (including nanoparticle) penetration across such biological barriers. Data from two examples of biological barriers are given, namely the hCMEC/D3 endothelial blood-brain barrier model, and the Caco-2 intestinal epithelial barrier model, to show the general applicability of the method. Several aspects of this method are applicable to the quality assurance of in vitro barrier models, e.g., assessment of the multi or mono-layer structure of the endothelial cells; identification of any potential "holes" in the barrier that could confound transport assay results; validation of tight junction expression; and determination of the types and amounts of key cellular organelles present in the barrier to account for any significant changes in phenotype that may occur compared to the in vivo situation. The method described here provides a key advantage in that it prevents loss of the filter membrane during monolayer sectioning, thereby preserving critical details associated with the basal cell membrane. Applicability of the protocol for other in vitro biological barriers, such as the blood-foetus, blood-testes, blood-cerebrospinal fluid (CSF) and lung alveolar-capillary barriers is also discussed. Additionally, we demonstrate the use of the method for assessment of nanoparticle transport across cellular barriers and elucidation of transcytosis mechanisms. Sequential events of cellular endocytosis, localisation and transcytosis can be described in detail by TEM imaging, revealing useful sub-cellular details that provide evidence for the mechanism of nanoparticle transport in the hCMEC/D3 blood-brain barrier model and the Caco-2 intestinal epithelial cell model. Potential artefacts resulting from the nanoparticles interacting with the Transwell membranes can also be assessed.

Morphogens and blood-brain barrier function in health and disease

The microvasculature of the brain forms a protective blood-brain barrier (BBB) that ensures a homeostatic environment for the central nervous system (CNS), which is essential for optimal brain functioning. The barrier properties of the brain endothelial cells are maintained by cells surrounding the capillaries, such as astrocytes and pericytes. Together with the endothelium and a basement membrane, these supporting cells form the neurovascular unit (NVU). Accumulating evidence indicates that the supporting cells of the NVU release a wide variety of soluble factors that induce and control barrier properties in a concentration-dependent manner. The current review provides a comprehensive overview of how such factors, called morphogens, influence BBB integrity and functioning. Since impaired BBB function is apparent in numerous CNS disorders and is often associated with disease severity, we also discuss the potential therapeutic value of these morphogens, as they may represent promising therapies for a wide variety of CNS disorders.

Human umbilical cord blood-derived mesenchymal stem cells improve functional recovery through thrombospondin1, pantraxin3, and vascular endothelial growth factor in the ischemic rat brain

Cell therapy is a potential therapeutic method for cerebral ischemia, which remains a serious problem. In the search for more effective therapeutic methods, many kinds of stem cells from various tissues have been developed and tested as candidate therapeutic agents. Among them, human umbilical cord blood (hUCB)-derived mesenchymal stem cells (MSCs) are widely used for cell therapy because of their genetic flexibility. To confirm that they are effective and understand how they affect ischemic neural cells, hUCB-MSCs were directly administered ipsilaterally into an ischemic zone induced by middle cerebral artery occlusion (MCAO). We found that the neurobehavioral performance of the hUCB-MSC group was significantly improved compared with that of the vehicle-injected control group. The infarct was also remarkably smaller in the hUCB-MSC group. Additionally, hUCB-MSC transplantation resulted in a greater number of newly generated cells and angiogenic and tissue repair factors and a lower number of inflammatory events in the penumbra zone. To determine why these events occurred, hUCB-MSCs were assayed under hypoxic and normoxic conditions in vitro. The results showed that hUCB-MSCs exhibit higher expression levels of thrombospondin1, pantraxin3, and vascular endothelial growth factor under hypoxic conditions than under normoxic conditions. These results were found to be correlated with our in vivo immunofluorescent staining results. On the basis of these findings, we suggest that hUCB-MSCs may have a beneficial effect on cerebral ischemia, especially through angiogenesis, neurogenesis, and anti-inflammatory effects, and thus could be used as a therapeutic agent to treat neurological disorders such as cerebral ischemia.

Intranasal administration of human umbilical cord mesenchymal stem cells-conditioned medium enhances vascular remodeling after stroke

Stem cell-based treatments have been reported to be a potential strategy for stroke. However, tumorigenic potential and low survival rates of transplanted cells could attenuate the efficacy of the stem cell-based treatments. The application of stem cell-condition medium (CM) may be a practicable approach to conquer these limitations. In this study, we investigated whether intranasal administration of human umbilical cord mesenchymal stem cells (hUCMSCs)-CM has the therapeutic effects in rats after stroke. Adult male rats were subjected to middle cerebral artery occlusion (MCAo) and were treated by intranasal routine with or without hUCMSCs-CM (1 ml/kg/d), starting 24h after MCAo and daily for 14 days. Neurological functional tests, blood brain barrier (BBB) leakage, were measured. Angiogenesis and angiogenic factor expression were measured by immunohistochemistry, and Western blot, respectively. hUCMSCs-CM treatment of stroke by intranasal routine starting 24h after MCAo in rats significantly enhances BBB functional integrity and promotes functional outcome but does not decrease lesion volume compared to rats in DMEM/F12 medium control group and saline control group. Treatment of ischemic rats with hUCMSCs-CM by intranasal routine also significantly decreases the levels of Ang2 and increases the levels of both Ang1 and Tie2 in the ischemic brain. To take together, increased expression of Ang1 and Tie2 and decreased expression of Ang2, induced by hUCMSCs-CM treatment, contribute to vascular remodeling in the ischemic brain which plays an important role in functional outcome after stroke.

Vitexin reduces hypoxia-ischemia neonatal brain injury by the inhibition of HIF-1alpha in a rat pup model

Previous studies have demonstrated that the early suppression of HIF-1α after hypoxia-ischemia (HI) injury provides neuroprotection. Vitexin (5, 7, 4-trihydroxyflavone-8-glucoside), an HIF-1α inhibitor, is a c-glycosylated flavone that has been identified in medicinal plants. Therefore, we hypothesized that treatment with vitexin would protect against HI brain injury. Newborn rat pups were subjected to unilateral carotid artery ligation followed by 2.5 h of hypoxia (8% O2 at 37 °C). Vitexin (30, 45 or 60 mg/kg) was administered intraperitoneally at 5 min or 3 h after HI. Vitexin, administered 5 min after HI, was neuroprotective as seen by decreased infarct volume evaluated at 48 h post-HI. This neuroprotection was removed when vitexin was administered 3 h after HI. Neuronal cell death, blood-brain barrier (BBB) integrity, brain edema, HIF-1α and VEGF protein levels were evaluated using a combination of Nissl staining, IgG staining, brain water content, immunohistochemistry and Western blot at 24 and 48 h after HI. The long-term effects of vitexin were evaluated by brain atrophy measurement, Nissl staining and neurobehavioral tests. Vitexin (45 mg/kg) ameliorated brain edema, BBB disruption and neuronal cell death; Upregulation of HIF-1α by dimethyloxalylglycine (DMOG) increased the BBB permeability and brain edema compared to HI alone. Vitexin attenuated the increase in HIF-1α and VEGF. Vitexin also had long-term effects of protecting against the loss of ipsilateral brain and improveing neurobehavioral outcomes. In conclusion, our data indicate early HIF-1α inhibition with vitexin provides both acute and long-term neuroprotection in the developing brain after neonatal HI injury.

Evidence for an enduring ischaemic penumbra following central retinal artery occlusion, with implications for fibrinolytic therapy

The rationale behind hyperacute fibrinolytic therapy for cerebral and retinal arterial occlusion is to rescue ischaemic cells from irreversible damage through timely restitution of tissue perfusion. In cerebral stroke, an anoxic tissue compartment (the "infarct core") is surrounded by a hypoxic compartment (the "ischaemic penumbra"). The latter comprises electrically-silent neurons that undergo delayed apoptotic cell death within 1-6 h unless salvaged by arterial recanalisation. Establishment of an equivalent hypoxic compartment within the inner retina following central retinal artery occlusion (CRAO) isn't widely acknowledged. During experimental CRAO, electroretinography reveals 3 oxygenation-based tissue compartments (anoxic, hypoxic and normoxic) that contribute 32%, 27% and 41% respectively to the pre-occlusion b-wave amplitude. Thus, once the anoxia survival time (≈2 h) expires, the contribution from the infarcted posterior retina is irreversibly extinguished, but electrical activity continues in the normoxic periphery. Inbetween these compartments, an annular hypoxic zone (the "penumbra obscura") endures in a structurally-intact but functionally-impaired state until retinal reperfusion allows rapid recovery from electrical silence. Clinically, residual circulation of sufficient volume flow rate generates the heterogeneous fundus picture of "partial" CRAO. Persistent retinal venous hypoxaemia signifies maximal extraction of oxygen by an enduring "polar penumbra" that permeates or largely replaces the infarct core. On retinal reperfusion some days later, the retinal venous oxygen saturation reverts to normal and vision improves. Thus, penumbral inner retina, marginally oxygenated by the choroid or by residual circulation, isn't at risk of delayed apoptotic infarction (unlike hypoxic cerebral cortex). Emergency fibrinolytic intervention is inappropriate, therefore, once the duration of CRAO exceeds 2 h.

Delayed inhibition of VEGF signaling after stroke attenuates blood-brain barrier breakdown and improves functional recovery in a comorbidity-dependent manner

Diabetes is a common comorbidity in stroke patients and a strong predictor of poor functional outcome. To provide a more mechanistic understanding of this clinically relevant problem, we focused on how diabetes affects blood-brain barrier (BBB) function after stroke. Because the BBB can be compromised for days after stroke and thus further exacerbate ischemic injury, manipulating its function presents a unique opportunity for enhancing stroke recovery long after the window for thrombolytics has passed. Using a mouse model of Type 1 diabetes, we discovered that ischemic stroke leads to an abnormal and persistent increase in vascular endothelial growth factor receptor 2 (VEGF-R2) expression in peri-infarct vascular networks. Correlating with this, BBB permeability was markedly increased in diabetic mice, which could not be prevented with insulin treatment after stroke. Imaging of capillary ultrastructure revealed that BBB permeability was associated with an increase in endothelial transcytosis rather than a loss of tight junctions. Pharmacological inhibition (initiated 2.5 d after stroke) or vascular-specific knockdown of VEGF-R2 after stroke attenuated BBB permeability, loss of synaptic structure in peri-infarct regions, and improved recovery of forepaw function. However, the beneficial effects of VEGF-R2 inhibition on stroke recovery were restricted to diabetic mice and appeared to worsen BBB permeability in nondiabetic mice. Collectively, these results suggest that aberrant VEGF signaling and BBB dysfunction after stroke plays a crucial role in limiting functional recovery in an experimental model of diabetes. Furthermore, our data highlight the need to develop more personalized stroke treatments for a heterogeneous clinical population.

MiR-335 Regulates Hif-1α to Reduce Cell Death in Both Mouse Cell Line and Rat Ischemic Models

Hypoxia inducible factor-1α facilitates cellular adaptation to hypoxic conditions. Hence its tight regulation is crucial in hypoxia related diseases such as cerebral ischemia. Changes in hypoxia inducible factor-1α expression upon cerebral ischemia influence the expression of its downstream genes which eventually determines the extent of cellular damage. MicroRNAs are endogenous regulators of gene expression that have rapidly emerged as promising therapeutic targets in several diseases. In this study, we have identified miR-335 as a direct regulator of hypoxia inducible factor-1α and as a potential therapeutic target in cerebral ischemia. MiR-335 and hypoxia inducible factor-1α mRNA showed an inverse expression profile, both in vivo and in vitro ischemic conditions. Given the biphasic nature of hypoxia inducible factor-1α expression during cerebral ischemia, miR-335 mimic was found to reduce infarct volume in the early time (immediately after middle cerebral artery occlusion) of embolic stroke animal models while the miR-335 inhibitor appears to be beneficial at the late time of stroke (24 hrs after middle cerebral artery occlusion). Modulation of hypoxia inducible factor-1α expression by miR-335 also influenced the expression of crucial genes implicated in neurovascular permeability, cell death and maintenance of the blood brain barrier. These concerted effects, resulting in a reduction in infarct volume bring about a beneficial outcome in ischemic stroke.

Temporal assessment of vascular reactivity and functionality using MRI during postischemic proangiogenenic vascular remodeling

Postischemic angiogenesis is an important recovery mechanism. Both arteries and veins are upregulated during angiogenesis, but eventually there are more angiogenic veins than arteries in terms of number and length. It is critical to understand how the veins are modulated after ischemia and then transitioned into angiogenic vessels during the proangiogenic stage to finally serve as a restorative strength to the injured area. Using a rat model of transient focal cerebral ischemia, the hypercapnic blood oxygen level-dependent (BOLD) response was used to evaluate vascular reactivity, while the hyperoxic BOLD and tissue oxygen level-dependent (TOLD) responses were used to evaluate the vascular functionality at 1, 3, and 7days after ischemia. Vessel-like venous signals appeared on R2* maps on days 3 and 7, but not on day 1. The large hypercapnic BOLD responses on days 3 and 7 indicated that these areas have high vascular reactivity. The temporal correlation between vascular reactivity and the immunoreactivity to desmin and VEGF further indicates that the integrity of vascular reactivity is associated with the pericyte coverage as regulated by the VEGF level. Vascular functionality remained low on days 1, 3, and 7, as reflected by the small hyperoxic BOLD and large hyperoxic TOLD responses, indicating the low oxygen consumption of the ischemic tissues. These functional changes in proangiogenic veins may be critical for angiogenesis.

Growth factors for the treatment of ischemic brain injury (growth factor treatment)

In recent years, growth factor therapy has emerged as a potential treatment for ischemic brain injury. The efficacy of therapies that either directly introduce or stimulate local production of growth factors and their receptors in damaged brain tissue has been tested in a multitude of models for different Central Nervous System (CNS) diseases. These growth factors include erythropoietin (EPO), vascular endothelial growth factor (VEGF), brain-derived neurotrophic factor (BDNF), and insulin-like growth factor (IGF-1), among others. Despite the promise shown in animal models, the particular growth factors that should be used to maximize both brain protection and repair, and the therapeutic critical period, are not well defined. We will review current pre-clinical and clinical evidence for growth factor therapies in treating different causes of brain injury, as well as issues to be addressed prior to application in humans.

Multiple therapeutic effects of progranulin on experimental acute ischaemic stroke

In the central nervous system, progranulin, a glycoprotein growth factor, plays a crucial role in maintaining physiological functions, and progranulin gene mutations cause TAR DNA-binding protein-43-positive frontotemporal lobar degeneration. Although several studies have reported that progranulin plays a protective role against ischaemic brain injury, little is known about temporal changes in the expression level, cellular localization, and glycosylation status of progranulin after acute focal cerebral ischaemia. In addition, the precise mechanisms by which progranulin exerts protective effects on ischaemic brain injury remains unknown. Furthermore, the therapeutic potential of progranulin against acute focal cerebral ischaemia, including combination treatment with tissue plasminogen activator, remains to be elucidated. In the present study, we aimed to determine temporal changes in the expression and localization of progranulin after ischaemia as well as the therapeutic effects of progranulin on ischaemic brain injury using in vitro and in vivo models. First, we demonstrated a dynamic change in progranulin expression in ischaemic Sprague-Dawley rats, including increased levels of progranulin expression in microglia within the ischaemic core, and increased levels of progranulin expression in viable neurons as well as induction of progranulin expression in endothelial cells within the ischaemic penumbra. We also demonstrated that the fully glycosylated mature secretory isoform of progranulin (∼88 kDa) decreased, whereas the glycosylated immature isoform of progranulin (58-68 kDa) markedly increased at 24 h and 72 h after reperfusion. In vitro experiments using primary cells from C57BL/6 mice revealed that the glycosylated immature isoform was secreted only from the microglia. Second, we demonstrated that progranulin could protect against acute focal cerebral ischaemia by a variety of mechanisms including attenuation of blood-brain barrier disruption, neuroinflammation suppression, and neuroprotection. We found that progranulin could regulate vascular permeability via vascular endothelial growth factor, suppress neuroinflammation after ischaemia via anti-inflammatory interleukin 10 in the microglia, and render neuroprotection in part by inhibition of cytoplasmic redistribution of TAR DNA-binding protein-43 as demonstrated in progranulin knockout mice (C57BL/6 background). Finally, we demonstrated the therapeutic potential of progranulin against acute focal cerebral ischaemia using a rat autologous thrombo-embolic model with delayed tissue plasminogen activator treatment. Intravenously administered recombinant progranulin reduced cerebral infarct and oedema, suppressed haemorrhagic transformation, and improved motor outcomes (P = 0.007, 0.038, 0.007 and 0.004, respectively). In conclusion, progranulin may be a novel therapeutic target that provides vascular protection, anti-neuroinflammation, and neuroprotection related in part to vascular endothelial growth factor, interleukin 10, and TAR DNA-binding protein-43, respectively.

Neuroprotective effect of the hairy root extract of Angelica gigas NAKAI on transient focal cerebral ischemia in rats through the regulation of angiogenesis

Background

In this study, we investigated the neuroprotective effect of the hairy root extract of Angelica gigas NAKAI (Angelica Gigantis Radix) on transient focal cerebral ischemia in rats through the regulation of angiogenesis molecules.

Methods

Male Sprague-Dawley rats were induced focal cerebral ischemia by a transient middle cerebral artery occlusion (tMCAO) for 90 min, and then orally administrated with the water extract of A. gigas hairy roots (AG). After 24 h reperfusion, infarction volume and the changes of BBB permeability were measured by TTC and Evans Blue (EB) staining. The neuronal cell damage and the activation of glial cells were assessed by immunohistochemistry in the ischemic brain. The expression of angiogenesis-induced proteins such as angiopoietin-1 (Ang-1), and vascular endothelial growth factor (VEGF), inflammatory protein such as intercellular adhesion molecule-1 (CAM-1), tight junction proteins such as ZO-1, and Occludin and the phosphorylation of phosphatidylinositol 3-kinase (PI3K)/AKT were determined in the ischemic brains by Western blot, respectively.

Results

The treatment of AG extract significantly decreased the volumes of brain infarction, and edema in MACO-induced ischemic rats. AG extract decreased the increase of BBB permeability, and neuronal death and inhibited the activation of astrocytes and microglia in ischemic brains. AG extract also significantly increased the expression of Ang-1, Tie-2, VEGF, ZO-1 and Occludin through activation of the PI3K/Akt pathway. AG extract significantly increased the expression of ICAM-1 in ischemic brains.

Conclusions

Our results indicate that the hairy root of AG has a neuroprotective effect in ischemic stroke.

Vitamin D prevents hypoxia/reoxygenation-induced blood-brain barrier disruption via vitamin D receptor-mediated NF-kB signaling pathways

Maintaining blood-brain barrier integrity and minimizing neuronal injury are critical components of any therapeutic intervention following ischemic stroke. However, a low level of vitamin D hormone is a risk factor for many vascular diseases including stroke. The neuroprotective effects of 1,25(OH)2D3 (vitamin D) after ischemic stroke have been studied, but it is not known whether it prevents ischemic injury to brain endothelial cells, a key component of the neurovascular unit. We analyzed the effect of 1,25(OH)2D3 on brain endothelial cell barrier integrity and tight junction proteins after hypoxia/reoxygenation in a mouse brain endothelial cell culture model that closely mimics many of the features of the blood-brain barrier in vitro. Following hypoxic injury in bEnd.3 cells, 1,25(OH)2D3 treatment prevented the decrease in barrier function as measured by transendothelial electrical resistance and permeability of FITC-dextran (40 kDa), the decrease in the expression of the tight junction proteins zonula occludin-1, claudin-5, and occludin, the activation of NF-kB, and the increase in matrix metalloproteinase-9 expression. These responses were blocked when the interaction of 1,25(OH) )2D3 with the vitamin D receptor (VDR) was inhibited by pyridoxal 5'-phosphate treatment. Our findings show a direct, VDR-mediated, protective effect of 1,25(OH) )2D3 against ischemic injury-induced blood-brain barrier dysfunction in cerebral endothelial cells.

Hydrogen sulfide inhalation decreases early blood-brain barrier permeability and brain edema induced by cardiac arrest and resuscitation

The effects of hydrogen sulfide (H2S) on blood-brain barrier (BBB) and brain edema after cardiac arrest (CA) and cardiopulmonary resuscitation (CPR) remain poorly understood. We investigated the effects of exogenous 80-p.p.m. H2S gas on BBB, brain water content, neurologic outcome, and survival rate after CA and CPR. Cardiopulmonary resuscitation followed CA induced in rats by ventricular fibrillation for 6 minutes. Results show that inhalation of 80-p.p.m. H2S significantly reduced the permeability of the BBB in both in the cortex and hippocampus at 24 hours after resuscitation. Hydrogen sulfide also lessened brain edema in the cortex and hippocampus, ameliorated neurologic outcome as evaluated by neurologic deficit score and tape removal test, and improved the 14-day survival rate. Hydrogen sulfide also attenuated CA and CPR-induced increases of matrix metalloproteinase-9 (MMP-9) activity and vascular endothelial growth factor (VEGF) expression, and increased the expression of angiogenin-1 (Ang-1). These results indicate that inhalation of 80-p.p.m. H2S immediately after CPR attenuated BBB permeability and brain edema, and improved neurologic outcome and 14-day survival of rats after CA. The therapeutic benefits of H2S could be associated with suppression of MMP-9 and VEGF expression and increased expression of Ang-1.

Angiogenesis-regulating microRNAs and Ischemic Stroke

Stroke is a leading cause of death and disability worldwide. Ischemic stroke is the dominant subtype of stroke and results from focal cerebral ischemia due to occlusion of major cerebral arteries. Thus, the restoration or improvement of reduced regional cerebral blood supply in a timely manner is very critical for improving stroke outcomes and poststroke functional recovery. The recovery from ischemic stroke largely relies on appropriate restoration of blood flow via angiogenesis. Newly formed vessels would allow increased cerebral blood flow, thus increasing the amount of oxygen and nutrients delivered to affected brain tissue. Angiogenesis is strictly controlled by many key angiogenic factors in the central nervous system, and these molecules have been well-documented to play an important role in the development of angiogenesis in response to various pathological conditions. Promoting angiogenesis via various approaches that target angiogenic factors appears to be a useful treatment for experimental ischemic stroke. Most recently, microRNAs (miRs) have been identified as negative regulators of gene expression in a post-transcriptional manner. Accumulating studies have demonstrated that miRs are essential determinants of vascular endothelial cell biology/angiogenesis as well as contributors to stroke pathogenesis. In this review, we summarize the knowledge of stroke-associated angiogenic modulators, as well as the role and molecular mechanisms of stroke-associated miRs with a focus on angiogenesis-regulating miRs. Moreover, we further discuss their potential impact on miR-based therapeutics in stroke through targeting and enhancing post-ischemic angiogenesis.

Stroke increases neural stem cells and angiogenesis in the neurogenic niche of the adult mouse

The unique cellular and vascular architecture of the adult ventricular-subventricular zone (V/SVZ) neurogenic niche plays an important role in regulating neural stem cell function. However, the in vivo identification of neural stem cells and their relationship to blood vessels within this niche in response to stroke remain largely unknown. Using whole-mount preparation of the lateral ventricle wall, we examined the architecture of neural stem cells and blood vessels in the V/SVZ of adult mouse over the course of 3 months after onset of focal cerebral ischemia. Stroke substantially increased the number of glial fibrillary acidic protein (GFAP) positive neural stem cells that are in contact with the cerebrospinal fluid (CSF) via their apical processes at the center of pinwheel structures formed by ependymal cells residing in the lateral ventricle. Long basal processes of these cells extended to blood vessels beneath the ependymal layer. Moreover, stroke increased V/SVZ endothelial cell proliferation from 2% in non-ischemic mice to 12 and 15% at 7 and 14 days after stroke, respectively. Vascular volume in the V/SVZ was augmented from 3% of the total volume prior to stroke to 6% at 90 days after stroke. Stroke-increased angiogenesis was closely associated with neuroblasts that expanded to nearly encompass the entire lateral ventricular wall in the V/SVZ. These data indicate that stroke induces long-term alterations of the neural stem cell and vascular architecture of the adult V/SVZ neurogenic niche. These post-stroke structural changes may provide insight into neural stem cell mediation of stroke-induced neurogenesis through the interaction of neural stem cells with proteins in the CSF and their sub-ependymal neurovascular interaction.

Effects of ischemic preconditioning on VEGF and pFlk-1 immunoreactivities in the gerbil ischemic hippocampus after transient cerebral ischemia

Ischemia preconditioning (IPC) displays an important adaptation of the CNS to sub-lethal ischemia. In the present study, we examined the effect of IPC on immunoreactivities of VEGF-, and phospho-Flk-1 (pFlk-1) following transient cerebral ischemia in gerbils. The animals were randomly assigned to four groups (sham-operated-group, ischemia-operated-group, IPC plus (+) sham-operated-group, and IPC+ischemia-operated-group). IPC was induced by subjecting gerbils to 2 min of ischemia followed by 1 day of recovery. In the ischemia-operated-group, a significant loss of neurons was observed in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) alone 5 days after ischemia-reperfusion, however, in all the IPC+ischemia-operated-groups, pyramidal neurons in the SP were well protected. In immunohistochemical study, VEGF immunoreactivity in the ischemia-operated-group was increased in the SP at 1 day post-ischemia and decreased with time. Five days after ischemia-reperfusion, strong VEGF immunoreactivity was found in non-pyramidal cells, which were identified as pericytes, in the stratum oriens (SO) and radiatum (SR). In the IPC+sham-operated- and IPC+ischemia-operated-groups, VEGF immunoreactivity was significantly increased in the SP. pFlk-1 immunoreactivity in the sham-operated- and ischemia-operated-groups was hardly found in the SP, and, from 2 days post-ischemia, pFlk-1 immunoreactivity was strongly increased in non-pyramidal cells, which were identified as pericytes. In the IPC+sham-operated-group, pFlk-1 immunoreactivity was significantly increased in both pyramidal and non-pyramidal cells; in the IPC+ischemia-operated-groups, the similar pattern of VEGF immunoreactivity was found in the ischemic CA1, although the VEGF immunoreactivity was strong in non-pyramidal cells at 5 days post-ischemia. In brief, our findings show that IPC dramatically augmented the induction of VEGF and pFlk-1 immunoreactivity in the pyramidal cells of the CA1 after ischemia-reperfusion, and these findings suggest that the increases of VEGF and Flk-1 expressions may be necessary for neurons to survive from transient ischemic damage.

Inhibition of Src phosphorylation reduces damage to the blood-brain barrier following transient focal cerebral ischemia in rats

The disruption of the blood-brain barrier (BBB) caused by cerebral ischemia determines the extent of injury and patient prognosis. Inhibitors of Src can markedly minimize the infarct size and preserve neurological function. The Src protein tyrosine kinase (PTK) inhibitor, PP2, protects the rat brain against ischemic injury, possibly through the reduction of vascular endothelial growth factor A (VEGFA) expression and the upregulation of claudin-5 expression, which preserves the integrity of the BBB. In this study, the expression levels of phosphorylated (p)-Src, VEGFA and claudin-5 were determined to investigate the changes occurring in the levels of these proteins and to determine the benefits of PP2 treatment following cerebral ischemia/reperfusion (I/R). Our study included a sham-operated group, an I/R group, a vehicle-treated group (V) and a PP2-treated group (PP2). We found that the rats in the PP2 group exhibited greater preservation of neurological function and reduced VEGFA and p-Src protein expression compared with the rats in the I/R and V groups. Moreover, the mRNA and protein levels of claudin-5 were markedly higher in the PP2 group than in the I/R group or the V group after 3 days of reperfusion. Immunofluorescence staining revealed that the co-localized immunostaining of fibrinogen and claudin-5 was reduced in the PP2 group, which suggests that the exudation of fibrinogen in this group was less than that in the I/R and V groups. Furthermore, the reduced co-localization of immunostaining of glial fibrillary acidic protein (GFAP) and claudin-5 indicated that the rats in the PP2 group had only a slight disruption of the BBB. These findings suggested that PP2 treatment attenuated the disruption of the BBB following ischemia and minimized the neurological deficit; these effects were associated with a decreased VEGFA expression and an increased claudin-5 expression. Members of the Src PTK family may be critical targets for the protection of the BBB following cerebral ischemia.

Poxue Huayu and Tianjing Busui Decoction for cerebral hemorrhage (Upregulation of neurotrophic factor expression): Upregulation of neurotrophic factor expression

This study established a rat model of cerebral hemorrhage by injecting autologous anticoagulated blood. Rat models were intragastrically administered 5, 10, 20 g/kg Poxue Huayu and Tianjing Busui Decoction, supplemented with Hirudo, raw rhubarb, raw Pollen Typhae, gadfly, Fructrs Trichosanthis, Radix Notoginseng, Rhizoma Acori Talarinowii, and glue of tortoise plastron, once a day, for 14 consecutive days. Results demonstrated that brain water content significantly reduced in rats with cerebral hemorrhage, and intracerebral hematoma volume markedly reduced after treatment. Immunohistochemical staining revealed that brain-derived neurotrophic factor, tyrosine kinase B and vascular endothelial growth factor expression noticeably increased around the surrounding hematoma. Reverse transcription-PCR revealed that brain-derived neurotrophic factor and tyrosine kinase B mRNA expression significantly increased around the surrounding hematoma. Neurologic impairment obviously reduced. These results indicated that Poxue Huayu and Tianjing Busui Decoction exert therapeutic effects on cerebral hemorrhage by upregulating the expression of brain-derived neurotrophic factor.

Lack of dystrophin results in abnormal cerebral diffusion and perfusion in vivo

Dystrophin, the main component of the dystrophin–glycoprotein complex, plays an important role in maintaining the structural integrity of cells. It is also involved in the formation of the blood–brain barrier (BBB). To elucidate the impact of dystrophin disruption in vivo, we characterized changes in cerebral perfusion and diffusion in dystrophin-deficient mice (mdx) by magnetic resonance imaging (MRI). Arterial spin labeling (ASL) and diffusion-weighted MRI (DWI) studies were performed on 2-month-old and 10-month-old mdx mice and their age-matched wild-type controls (WT). The imaging results were correlated with Evan's blue extravasation and vascular density studies. The results show that dystrophin disruption significantly decreased the mean cerebral diffusivity in both 2-month-old (7.38± 0.30 × 10⁻⁴mm²/s) and 10-month-old (6.93 ± 0.53 × 10⁻⁴ mm²/s) mdx mice as compared to WT (8.49±0.24×10⁻⁴, 8.24±0.25× 10⁻⁴mm²/s, respectively). There was also an 18% decrease in cerebral perfusion in 10-month-old mdx mice as compared to WT, which was associated with enhanced arteriogenesis. The reduction in water diffusivity in mdx mice is likely due to an increase in cerebral edema or the existence of large molecules in the extracellular space from a leaky BBB. The observation of decreased perfusion in the setting of enhanced arteriogenesis may be caused by an increase of intracranial pressure from cerebral edema. This study demonstrates the defects in water handling at the BBB and consequently, abnormal perfusion associated with the absence of dystrophin.

Vascular endothelial growth factor increases during blood-brain barrier-enhanced permeability caused by Phoneutria nigriventer spider venom

Phoneutria nigriventer spider accidental envenomation provokes neurotoxic manifestations, which when critical, results in epileptic-like episodes. In rats, P. nigriventer venom (PNV) causes blood-brain barrier breakdown (BBBb). The PNV-induced excitotoxicity results from disturbances on Na⁺, K⁺ and Ca²⁺ channels and glutamate handling. The vascular endothelial growth factor (VEGF), beyond its angiogenic effect, also, interferes on synaptic physiology by affecting the same ion channels and protects neurons from excitotoxicity. However, it is unknown whether VEGF expression is altered following PNV envenomation. We found that adult and neonates rats injected with PNV showed immediate neurotoxic manifestations which paralleled with endothelial occludin, β-catenin, and laminin downregulation indicative of BBBb. In neonate rats, VEGF, VEGF mRNA, and Flt-1 receptors, glutamate decarboxylase, and calbindin-D28k increased in Purkinje neurons, while, in adult rats, the BBBb paralleled with VEGF mRNA, Flk-1, and calbindin-D28k increases and Flt-1 decreases. Statistically, the variable age had a role in such differences, which might be due to age-related unequal maturation of blood-brain barrier (BBB) and thus differential cross-signaling among components of the glial neurovascular unit. The concurrent increases in the VEGF/Flt-1/Flk-1 system in the cerebellar neuron cells and the BBBb following PNV exposure might imply a cytokine modulation of neuronal excitability consequent to homeostatic perturbations induced by ion channels-acting PNV neuropeptides. Whether such modulation represents neuroprotection needs further investigation.

Endogenous neurogenesis following ischaemic brain injury: insights for therapeutic strategies

Ischaemic stroke is among the most common yet most intractable types of central nervous system (CNS) injury in the adult human population. In the acute stages of disease, neurons in the ischaemic lesion rapidly die and other neuronal populations in the ischaemic penumbra are vulnerable to secondary injury. Multiple parallel approaches are being investigated to develop neuroprotective, reparative and regenerative strategies for the treatment of stroke. Accumulating evidence indicates that cerebral ischaemia initiates an endogenous regenerative response within the adult brain that potentiates adult neurogenesis from populations of neural stem and progenitor cells. A major research focus has been to understand the cellular and molecular mechanisms that underlie the potentiation of adult neurogenesis and to appreciate how interventions designed to modulate these processes could enhance neural regeneration in the post-ischaemic brain. In this review, we highlight recent advances over the last 5 years that help unravel the cellular and molecular mechanisms that potentiate endogenous neurogenesis following cerebral ischaemia and are dissecting the functional importance of this regenerative mechanism following brain injury. This article is part of a Directed Issue entitled: Regenerative Medicine: the challenge of translation.

Low-dose candesartan enhances molecular mediators of neuroplasticity and subsequent functional recovery after ischemic stroke in rats

We have previously reported that angiotensin type 1 receptor (AT1R) blockade with candesartan exerts neurovascular protection after experimental cerebral ischemia. Here, we tested the hypothesis that a low, subhypotensive dose of candesartan enhances neuroplasticity and subsequent functional recovery through enhanced neurotrophic factor expression in rats subjected to ischemia reperfusion injury. Male Wistar rats (290-300 g) underwent 90 min of middle cerebral artery occlusion (MCAO) and received candesartan (0.3 mg/kg) or saline at reperfusion and then once every 24 h for 7 days. Functional deficits were assessed in a blinded manner at 1, 3, 7, and 14 days after MCAO. Animals were sacrificed 14-day post-stroke and the brains perfused for infarct size by cresyl violet. Western blot and immunohistochemistry were used to assess the expression of growth factors and synaptic proteins. Candesartan-treated animals showed a significant reduction in the infarct size [t (13) = -5.5, P = 0.0001] accompanied by functional recovery in Bederson [F (1, 13) = 7.9, P = 0.015], beam walk [F (1, 13) = 6.7, P = 0.023], grip strength [F (1, 13) = 15.2, P = 0.0031], and rotarod performance [F (1, 14) = 29.8, P < 0.0001]. In addition, candesartan-treated animals showed significantly higher expression of active metalloproteinase-3 (MMP-3), laminin, and angiopoietin-1 (Ang-1). The expression of vascular endothelial growth factor (VEGF) and brain-derived neurotrophic factor (BDNF) and its receptor was significantly increased in the animals treated with candesartan. Also, we observed significant increases in neuroplasticity markers, synaptophysin, and PSD-95. These results indicate that low-dose candesartan had a large and enduring effect on measures of plasticity, and this accompanied the functional recovery after ischemic stroke.

Angiogenesis in multiple sclerosis and experimental autoimmune encephalomyelitis

Angiogenesis, the formation of new vessels, is found in Multiple Sclerosis (MS) demyelinating lesions following Vascular Endothelial Growth Factor (VEGF) release and the production of several other angiogenic molecules. The increased energy demand of inflammatory cuffs and damaged neural cells explains the strong angiogenic response in plaques and surrounding white matter. An angiogenic response has also been documented in an experimental model of MS, experimental allergic encephalomyelitis (EAE), where blood–brain barrier disruption and vascular remodelling appeared in a pre-symptomatic disease phase. In both MS and EAE, VEGF acts as a pro-inflammatory factor in the early phase but its reduced responsivity in the late phase can disrupt neuroregenerative attempts, since VEGF naturally enhances neuron resistance to injury and regulates neural progenitor proliferation, migration, differentiation and oligodendrocyte precursor cell (OPC) survival and migration to demyelinated lesions. Angiogenesis, neurogenesis and oligodendroglia maturation are closely intertwined in the neurovascular niches of the subventricular zone, one of the preferential locations of inflammatory lesions in MS, and in all the other temporary vascular niches where the mutual fostering of angiogenesis and OPC maturation occurs. Angiogenesis, induced either by CNS inflammation or by hypoxic stimuli related to neurovascular uncoupling, appears to be ineffective in chronic MS due to a counterbalancing effect of vasoconstrictive mechanisms determined by the reduced axonal activity, astrocyte dysfunction, microglia secretion of free radical species and mitochondrial abnormalities. Thus, angiogenesis, that supplies several trophic factors, should be promoted in therapeutic neuroregeneration efforts to combat the progressive, degenerative phase of MS.

Biphasic mechanisms of neurovascular unit injury and protection in CNS diseases

In the past decade, evidence has emerged that there is a variety of bidirectional cell-cell and/or cell-extracellular matrix interactions within the neurovascular unit (NVU), which is composed of neuronal, glial, and vascular cells along with extracellular matrix. Many central nervous system diseases, which lead to NVU dysfunction, have common features such as glial activation/transformation and vascular/blood-brain-barrier alteration. These phenomena show dual opposite roles, harmful at acute phase and beneficial at chronic phase. This diverse heterogeneity may induce biphasic clinical courses, i.e. degenerative and regenerative processes in the context of dynamically coordinated cellcell/ cell-matrix interactions in the NVU. A deeper understanding of the seemingly contradictory actions in cellular levels is essential for NVU protection or regeneration to suppress the deleterious inflammatory reactions and promote adaptive remodeling after central nervous system injury. This mini-review will present an overview of recent progress in the biphasic roles of the NVU and discuss the clinical relevance of NVU responses associated with central nervous system diseases, such as stroke and other chronic neurodegenerative diseases.

Developmental and pathological angiogenesis in the central nervous system

Angiogenesis, the formation of new blood vessels from pre-existing vessels, in the central nervous system (CNS) is seen both as a normal physiological response as well as a pathological step in disease progression. Formation of the blood-brain barrier (BBB) is an essential step in physiological CNS angiogenesis. The BBB is regulated by a neurovascular unit (NVU) consisting of endothelial and perivascular cells as well as vascular astrocytes. The NVU plays a critical role in preventing entry of neurotoxic substances and regulation of blood flow in the CNS. In recent years, research on numerous acquired and hereditary disorders of the CNS has increasingly emphasized the role of angiogenesis in disease pathophysiology. Here, we discuss molecular mechanisms of CNS angiogenesis during embryogenesis as well as various pathological states including brain tumor formation, ischemic stroke, arteriovenous malformations, and neurodegenerative diseases.

Electroacupuncture improves recovery after hemorrhagic brain injury by inducing the expression of angiopoietin-1 and -2 in rats

Background

Angiopoietin (Ang) is one of the major effectors of angiogenesis, playing a critical role in neurovascular remodeling after stroke. Acupuncture has been widely used for treating stroke in China for a long time. Recently, we have demonstrated that electroacupuncture (EA) can accelerate intracerebral hemorrhage (ICH)-induced angiogenesis in rats. In the present study, we investigated the effect of EA on the expression of Ang-1 and Ang-2 in the brain after ICH.

Methods

ICH was induced by stereotactic injection of collagenase type VII into the right globus pallidus. Adult male Sprague–Dawley rats were randomized into the following four groups: sham-operation (SHAM), stroke-no electroacupuncture (SNE), stroke-EA at the Zusanli acupoint (SEZ), and stroke-EA at a nonacupoint (SEN). EA was applied to the bilateral Zusanli (ST36) acupoint in the SEZ group and a nonacupoint in the SEN group. The expression of Ang-1 and Ang-2 was evaluated by immunohistochemistry and quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR).

Results

Some Ang-1 and Ang-2 immunoreactive microvessels with a dilated outline were detected in the perihematomal tissues after ICH, and the vessels extended into the clot from the surrounding area since day 7. The expression of Ang-1 increased notably as long as 2 weeks after ICH, while Ang-2 immunoreactivity declined at about 7 days following a striking upregulation at 3 days. EA at the Zusanli (ST36) acupoint upregulated the expression of Ang-1 and Ang-2 at both the protein and mRNA levels. However, EA at a nonacupoint had little effect on the expression of Ang-1 and Ang-2.

Conclusions

Our data suggest that EA at the Zusanli (ST36) acupoint exerts neuroprotective effects on hemorrhagic stroke by upregulation of Ang-1 and Ang-2.