Yongting Wang

CXCR4 Antagonist AMD3100 Protects Blood–Brain Barrier Integrity and Reduces Inflammatory Response After Focal Ischemia in Mice

Background and Purpose— Inflammatory response plays a critical role in propagating tissue damage after focal cerebral ischemia. CXCL12 is a key chemokine for leukocyte recruitment. However, the role of CXCL12 and its receptor CXCR4 in ischemia-induced inflammatory response is unclear. Here we use the pharmacological antagonist of CXCR4, AMD3100, to investigate the function of CXCL12/CXCR4 in regulating inflammatory response during acute ischemia. Methods— Adult male CD-1 mice (n=184) underwent permanent suture middle cerebral artery occlusion (MCAO). AMD3100 was injected for 3 days (1 mg/kg/day) after MCAO. Brain water content, infarct volume, neurological score, and myeloperoxidase (MPO) expression and activity were examined at 24, 48, and 72 hours after MCAO. Proinflammatory cytokine RNA and protein levels in brain tissue were measured by RT-PCR and enzyme linked immunosorbent assay. Results— Neurological score was greatly improved in AMD3100-treated mice compared with the control mice 3 days after MCAO (P<0.05). Brain edema–induced change of water content, IgG protein leakage, Evans blue extravasation, occludin, and ZO-1 expression in ipsilateral hemisphere were alleviated by acute treatment of AMD3100. MPO expression and activity revealed that AMD3100 profoundly reduced the number of MPO-positive cells in the ischemic region (P<0.05). It also attenuated proinflammatory cytokines including interleukin 6, tumor necrosis factor &agr;, and interferon &ggr;; their mRNA and protein levels changed accordingly compared with the controls (P<0.05). Conclusions— CXCR4 antagonist AMD3100 significantly suppressed inflammatory response and reduced blood–brain barrier disruption after MCAO. AMD3100 attenuated ischemia-induced acute inflammation by suppressing leukocyte migration and infiltration, in addition to reducing proinflammatory cytokine expression in the ischemic region.

Netrin-1 Hyperexpression in Mouse Brain Promotes Angiogenesis and Long-Term Neurological Recovery After Transient Focal Ischemia

Background and Purpose— Netrin-1 (NT-1) stimulates endothelial cell proliferation and migration in vitro and promotes focal neovascularization in the adult brain in vivo. This in vivo study in mice investigated the effect of NT-1 hyperexpression on focal angiogenesis and long-term functional outcome after transient middle cerebral artery occlusion (tMCAO). Methods— Adeno-associated viral vectors carrying either the NT-1 gene (AAV–NT-1) or GFP (AAV-GFP) were generated and injected into the brains of separate groups of 93 mice. Seven days later, tMCAO followed by 7–28 days of reperfusion were carried out. Histological outcomes and behavioral deficits were quantified 7–28 days after tMCAO. Small cerebral vessel network and angiogenesis were assessed 28 days after tMCAO, using synchrotron radiation microangiography and immunohistochemistry. Results— Western blot and immunohistochemistry showed that on the day of tMCAO, NT-1 hyperexpression had been achieved in both normal and ischemic hemispheres. Immunofluorescence imaging showed that NT-1 expression was primarily in neurons and astrocytes. Ischemia-induced infarction in the NT-1 hyperexpression group was attenuated in comparison to saline or AAV-GFP–treated groups (P<0.01). Similarly, neurological deficits were greatly improved in AAV–NT-1–treated mice compared with mice in saline or AAV-GFP–treated groups (P<0.05). In addition, angiogenesis was increased in AAV–NT-1–treated mice compared with the other 2 groups (P<0.05). In vivo synchrotron radiation microangiography 28 days after tMCAO revealed more branches in AAV–NT-1–treated mice than in other groups. Conclusions— AAV–NT-1 induced NT-1 hyperexpression before tMCAO reduced infarct size, enhanced neovascularization, and improved long-term functional recovery.

Roles of Chemokine CXCL12 and its Receptors in Ischemic Stroke

Chemokine CXC ligand 12 (CXCL12), originally named stromal cell-derived factor-1 (SDF-1), is a member of the CXC chemokine subfamily. CXCL12 is found to be expressed by all cell types that are presented in the central nervous system (CNS). It works in conjunction with the G-protein coupled receptor CXCR4, which is found at the surface of a variety of cells including neurons, astrocytes, microglia, bone marrow-derived cells, as well as other progenitor cells. Recent studies revealed that CXCL12 could also bind and signal through receptor CXCR7. CXCL12 and CXCR4 are constitutively expressed in the brain but are up-regulated in the ischemic penumbra regions following ischemic stroke. CXCL12/CXCR4 play important roles in multiple processes after ischemic stroke, which include inflammatory response, focal angiogenesis, and the recruitment of bone marrow-derived cells (BMCs) and neural progenitor cell (NPC) to injury. In addition to its roles in stroke pathology, CXCL12 is also thought to be a key regulator in stroke repairing. This review will focus on the function of CXCL12/CXCR4 in post-stroke inflammation and neurovascular repairing. The potential application of CXCL12 modulation in clinical stroke treatment is also discussed.

Mesenchymal Stem Cells Maintain Blood‐Brain Barrier Integrity by Inhibiting Aquaporin‐4 Upregulation After Cerebral Ischemia

Rationale: Cerebral ischemia upregulates aquaporin‐4 expression, increases blood‐brain barrier (BBB) permeability, and induces brain edema. Mesenchymal stem cells (MSCs) can repress inflammatory cytokines and show great potential for ischemic stroke therapy. However, the effect of MSCs regarding the protection of ischemia‐induced BBB break down is unknown. Objective: We test whether MSCs therapy protects BBB integrity and explore the molecular mechanisms of aquaporin‐4 on BBB integrity. Methods and Results: Two hundred and twenty‐eight adult CD1 male mice underwent 90 minutes transient middle cerebral artery occlusion and received 2 × 105 MSCs intracranial transplantation. The neurological severity score was improved and both ischemia‐induced brain edema and BBB leakage were reduced in MSC‐treated mice. MSCs therapy reduced astrocyte apoptosis and inhibited ischemia‐induced aquaporin‐4 upregulation. In addition, small‐interfering RNA knockdown of aquaporin‐4 after cerebral ischemia effectively reduced aquaporin‐4 expression, brain edema, BBB leakage, and astrocyte apoptosis. Conditional medium from lipopolysaccharide (LPS)‐activated microglia enhanced aquaporin‐4 expression, p38 and JNK phosphorylation, and apoptosis of cultured astrocytes. MSC treatment reduced the expression of inflammatory cytokines in LPS‐activated microglia, and subsequently reduced aquaporin‐4 expression and apoptosis of astrocytes. Knockdown of aquaporin‐4 in cultured astrocytes also reduced apoptosis. Treatment with p38 and JNK inhibitors showed that p38, but not the JNK signaling pathway, was responsible for the aquaporin‐4 upregulation. Conclusion: MSCs protected BBB integrity by reducing the apoptosis of astrocytes after ischemic attack, which was due to the attenuation of inflammatory response and downregulation of aquaporin‐4 expression via p38 signaling pathway. Stem Cells 2014;32:3150–3162

Neural stem cell protects aged rat brain from ischemia-reperfusion injury through neurogenesis and angiogenesis

Neural stem cells (NSCs) show therapeutic potential for ischemia in young-adult animals. However, the effect of aging on NSC therapy is largely unknown. In this work, NSCs were transplanted into aged (24-month-old) and young-adult (3-month-old) rats at 1 day after stroke. Infarct volume and neurobehavioral outcomes were examined. The number of differentiated NSCs was compared in aged and young-adult ischemic rats and angiogenesis and neurogenesis were also determined. We found that aged rats developed larger infarcts than young-adult rats after ischemia (P<0.05). The neurobehavioral outcome was also worse for aged rats comparing with young-adult rats. Brain infarction and neurologic deficits were attenuated after NSC transplantation in both aged and young-adult rats. The number of survived NSCs in aged rats was similar to that of the young-adult rats (P>0.05) and most of them were differentiated into glial fibrillary acidic protein+ (GFAP+) cells. More importantly, angiogenesis and neurogenesis were greatly enhanced in both aged and young-adult rats after transplantation compared with phosphate-buffered saline (PBS) control (P<0.05), accompanied by increased expression of vascular endothelial growth factor (VEGF). Our results showed that NSC therapy reduced ischemic brain injury, along with increased angiogenesis and neurogenesis in aged rats, suggesting that aging-related microenvironment does not preclude a beneficial response to NSCs transplantation during cerebral ischemia.

Metformin attenuates blood-brain barrier disruption in mice following middle cerebral artery occlusion

BackgroundMetformin, a widely used hypoglycemic drug, reduces stroke incidence and alleviates chronic inflammation in clinical trials. However, the effect of metformin in ischemic stroke is unclear. Here, we investigated the effect of metformin on ischemic stroke in mice and further explored the possible underlying mechanisms.MethodsNinety-eight adult male CD-1 mice underwent 90-minute transient middle cerebral artery occlusion (tMCAO). Metformin (200 mg/kg) was administrated for up to 14 days. Neurobehavioral outcomes, brain infarct volume, inflammatory factors, blood-brain barrier (BBB) permeability and AMPK signaling pathways were evaluated following tMCAO. Oxygen glucose deprivation was performed on bEND.3 cells to explore the mechanisms of metformin in inhibiting inflammatory signaling pathways.ResultsInfarct volume was reduced in metformin-treated mice compared to the control group following tMCAO (P < 0.05). Neurobehavioral outcomes were greatly improved in metformin-treated mice (P < 0.05). MPO+ cells, Gr1+ cells, MPO activity and BBB permeability were decreased after metformin administration (P < 0.05). In addition, metformin activated AMPK phosphorylation, inhibited NF- κB activation, down-regulated cytokine (IL-1 β, IL-6, TNF- α) and ICAM-1 expression following tMCAO (P < 0.05). Furthermore, metformin activated AMPK signaling pathway and alleviated oxygen-glucose deprivation-induced ICAM-1 expression in bEND.3 cells (P < 0.05). Compound C, a selective AMPK inhibitor, eliminated this promotional effect.ConclusionsMetformin down-regulated ICAM-1 in an AMPK-dependent manner, which could effectively prevent ischemia-induced brain injury by alleviating neutrophil infiltration, suggesting that metformin is a promising therapeutic agent in stroke therapy.

Melatonin pretreatment improves the survival and function of transplanted mesenchymal stem cells after focal cerebral ischemia.

Mesenchymal stem cell (MSC) transplantation has been shown to be beneficial in treating cerebral ischemia. However, such benefit is limited by the low survival of transplanted MSCs in an ischemic microenvironment. Previous studies showed that melatonin pretreatment can increase MSC survival in the ischemic kidney. However, whether it will improve MSC survival in cerebral ischemia is unknown. Our study examined the effect of melatonin pretreatment on MSCs under ischemia-related conditions in vitro and after transplantation into ischemic rat brain. Results showed that melatonin pretreatment greatly increased survival of MSCs in vitro and reduced their apoptosis after transplantation into ischemic brain. Melatonin-treated MSCs (MT-MSCs) further reduced brain infarction and improved neurobehavioral outcomes. Angiogenesis, neurogenesis, and the expression of vascular endothelial growth factor (VEGF) were greatly increased in the MT-MSC-treated rats. Melatonin treatment increased the level of p-ERK1/2 in MSCs, which can be blocked by the melatonin receptor antagonist luzindole. ERK phosphorylation inhibitor U0126 completely reversed the protective effects of melatonin, suggesting that melatonin improves MSC survival and function through activating the ERK1/2 signaling pathway. Thus, stem cells pretreated by melatonin may represent a feasible approach for improving the beneficial effects of stem cell therapy for cerebral ischemia.

The biphasic function of microglia in ischemic stroke.

ABSTRACT Microglia are brain resident macrophages originated from primitive progenitor cells in the yolk sac. Microglia can be activated within hours and recruited to the lesion site. Traditionally, microglia activation is considered to play a deleterious role in ischemic stroke, as inhibition of microglia activation attenuates ischemia induced brain injury. However, increasing evidence show that microglia activation is critical for attenuating neuronal apoptosis, enhancing neurogenesis, and promoting functional recovery after cerebral ischemia. Differential polarization of microglia could likely explain the biphasic role of microglia in ischemia. We comprehensively reviewed the mechanisms involved in regulating microglia activation and polarization. The latest discoveries of microRNAs in modulating microglia function are discussed. In addition, the interaction between microglia and other cells including neurons, astrocytes, oligodendrocytes, and stem cells were also reviewed. Future therapies targeting microglia may not exclusively aim at suppressing microglia activation, but also at modulating microglia polarization at different stages of ischemic stroke. More work is needed to elucidate the cellular and molecular mechanisms of microglia polarization under ischemic environment. The roles of microRNAs and transplanted stem cells in mediating microglia activation and polarization during brain ischemia also need to be further studied.

Postacute Stromal Cell–Derived Factor-1α Expression Promotes Neurovascular Recovery in Ischemic Mice

Background and Purpose— Acute interventions of stroke are often challenged by a narrow treatment window. In this study, we explore treatments in the postacute phase of stroke with wider windows of opportunity. We investigated the effects of stromal cell–derived factor (SDF-1&agr;) in neurovascular recovery during the postacute phase and downstream signaling pathways, underlying SDF-1&agr;–mediated neurovascular recovery. Methods— Adult male Institute of Cancer Research (ICR) mice underwent middle cerebral artery occlusion. One week after middle cerebral artery occlusion, the animals received stereotactic injection of adenoassociated virus (AAV) carrying SDF-1&agr; gene as treatment or AAV-green fluorescent protein as control and were monitored for 5 weeks. Neurobehavioral outcomes were evaluated, and brain atrophy was measured. Neurogenesis and angiogenesis were examined. The proliferation and migration of neural progenitor cells were evaluated. Downstream pathways of SDF-1&agr; were investigated. Inflammatory response was monitored. Results— Neurobehavioral outcomes were improved, and brain atrophy was greatly reduced for ⩽5 weeks in AAV-SDF-1&agr; groups when compared with the control. SDF-1 receptor CXCR4 was upregulated and colocalized with neural and endothelial progenitor cells. The number of nestin+ and doublecortin+/bromodeoxyuridine+ cells in the subventricular zone, doublecortin+ and neuron+/bromodeoxyuridine+ cells in the perifocal region, and cluster of differentiation (CD)31+ and bromodeoxyuridine+/CD31+ microvessels are also significantly increased in AAV-SDF-1&agr; groups. Administration of CXCR4 antagonist AMD3100 eliminated the beneficial effects of SDF-1&agr;. SDF-1&agr;/CXCR4 interaction activated AKT, extracellular signal-regulated kinases (ERK), and P38 mitogen-activated protein kinase (MAPK) signaling pathways but not the c-Jun N-terminal kinase (JNK) pathway. Conclusions— SDF-1&agr; promoted neurogenesis and angiogenesis during the postacute phase of ischemia without eliciting an inflammatory response. AAV-SDF-1&agr; expression represents a promising avenue for ischemic stroke therapy with a wider treatment window.

Silica-coated superparamagnetic iron oxide nanoparticles targeting of EPCs in ischemic brain injury

Intravenous transplantation of endothelial progenitor cells (EPCs) reduced ischemic brain injury. However, less cell homing to damaged sites limited its functions. In present study, we labeled EPCs with silica-coated superparamagnetic iron oxide nanoparticles (SiO4@SPIONs) and applied exterior magnetic field to guide SiO4@SPIONs-labeled EPCs (SiO4@SPIONs-EPCs) to the ischemic hemisphere of the brain. We optimized SiO4@SPIONs labeling dose, which did not affect proliferation, migration and tube formation of EPCs in vitro. SiO4@SPIONs-EPCs homing was greatly increased in ischemic hemisphere with magnetic field treatment in mice underwent transient middle cerebral artery occlusion (tMCAO). Injection of SiO4@SPIONs-EPCs and followed by magnetic field treatment showed improved neurobehavioral outcomes, reduced brain atrophic volume, increased microvessel density and VEGF expression in the ischemic perifocal region compared to groups without magnetic field treatment (p < 0.05). Our results demonstrated that exterior magnetic field could guide SiO4@SPIONs-EPCs to ischemic region and enhance therapeutic effect, suggesting that magnetic-guided SiO4@SPIONs-EPCs delivery is a promising approach in cerebral ischemic therapy.