A reproducible model of middle cerebral artery occlusion in mice: hemodynamic, biochemical, and magnetic resonance imaging

Stroke and Translational Research - Review of Experimental Models with a Focus on Awake Ischaemic Induction and Anaesthesia

Animal models are an indispensable tool in the study of ischaemic stroke with hundreds of drugs emerging from the preclinical pipeline. However, all of these drugs have failed to translate into successful treatments in the clinic. This has brought into focus the need to enhance preclinical studies to improve translation. The confounding effects of anaesthesia on preclinical stroke modelling has been raised as an important consideration. Various volatile and injectable anaesthetics are used in preclinical models during stroke induction and for outcome measurements such as imaging or electrophysiology. However, anaesthetics modulate several pathways essential in the pathophysiology of stroke in a dose and drug dependent manner. Most notably, anaesthesia has significant modulatory effects on cerebral blood flow, metabolism, spreading depolarizations, and neurovascular coupling. To minimise anaesthetic complications and improve translational relevance, awake stroke induction has been attempted in limited models. This review outlines anaesthetic strategies employed in preclinical ischaemic rodent models and their reported cerebral effects. Stroke related complications are also addressed with a focus on infarct volume, neurological deficits, and thrombolysis efficacy. We also summarise routinely used focal ischaemic stroke rodent models and discuss the attempts to induce some of these models in awake rodents.

Electroacupuncture Promotes Angiogenesis in Mice with Cerebral Ischemia by Inhibiting miR-7

OBJECTIVE

To observe the angiogenesis effect of electroacupuncture (EA) at Shuigou acupoint (GV 26) in the treatment of cerebral ischemia, and explore the value of miRNA-7 (miR-7) in it.

METHODS

First, 48 mice were randomly divided into sham operation, middle cerebral artery occlusion (MCAO) model, and EA treatment groups. Then 9 mice were divided into carrier control group, miR-7 knockout group and miR-7 overexpression group (n=3 each group). Finally, 20 mice were divided into model and carrier control group, model and miR-7 knockout group, EA treatment and carrier control group and EA treatment and miR-7 overexpression group, with 3-6 mice in each group. The MCAO model was established in the MCAO and EA groups. Neurological deficit score and 2,3,5-triphenyltetrazolium chloride (TTC) staining were used to evaluate the severity of cerebral ischemia. Hematoxylin-eosin staining was used to describe basic pathological changes. Immunohistochemistry was used to quantify cerebral microvessel density. Real-time PCR and Western blot were used to detect the expression of miR-7 and its downstream target genes Krüppel-like factor 4/vascular endothelial growth factor (KLF4/VEGF) and angiopoietin-2 (ANG-2) in the ischemic cerebral cortex.

RESULTS

After EA, neurological deficit scores and infarction volumes decreased, and the density of cerebral microvessels increased. In the MCAO group, miR-7 expression was higher than that in the sham group (P<0.01). After EA at GV 26, miR-7 expression decreased (P<0.01) and the expression of downstream target genes KLF4/VEGF and ANG-2 increased as compared with the MCAO group (P<0.01). After EA combined with overexpression of miR-7, the expression of downstream target genes KLF4/VEGF and ANG-2 decreased compared to the control EA group (P<0.01). After miR-7 knockdown, the expression of KLF4/VEGF and ANG-2 increased (P<0.05 or P<0.01).

CONCLUSIONS

EA could promote angiogenesis in MCAO mice likely by inhibiting the expression of miR-7 and relieving inhibition of downstream target genes KLF4/VEGF and ANG-2.

Annexin A6 mitigates neurological deficit in ischemia/reperfusion injury by promoting synaptic plasticity

AIMS

Alleviating neurological dysfunction caused by acute ischemic stroke (AIS) remains intractable. Given Annexin A6 (ANXA6)'s potential in promoting axon branching and repairing cell membranes, the study aimed to explore ANXA6's potential in alleviating AIS-induced neurological dysfunction.

METHODS

A mouse middle cerebral artery occlusion model was established. Brain and plasma ANXA6 levels were detected at different timepoints post ischemia/reperfusion (I/R). We overexpressed and down-regulated brain ANXA6 and evaluated infarction volume, neurological function, and synaptic plasticity-related proteins post I/R. Plasma ANXA6 levels were measured in patients with AIS and healthy controls, investigating ANXA6 expression's clinical significance.

RESULTS

Brain ANXA6 levels initially decreased, gradually returning to normal post I/R; plasma ANXA6 levels showed an opposite trend. ANXA6 overexpression significantly decreased the modified neurological severity score (p = 0.0109) 1 day post I/R and the infarction area at 1 day (p = 0.0008) and 7 day (p = 0.0013) post I/R, and vice versa. ANXA6 positively influenced synaptic plasticity, upregulating synaptophysin (p = 0.006), myelin basic protein (p = 0.010), neuroligin (p = 0.078), and tropomyosin-related kinase B (p = 0.150). Plasma ANXA6 levels were higher in patients with AIS (1.969 [1.228-3.086]) compared to healthy controls (1.249 [0.757-2.226]) (p < 0.001), that served as an independent risk factor for poor AIS outcomes (2.120 [1.563-3.023], p < 0.001).

CONCLUSIONS

This study is the first to suggest that ANXA6 enhances synaptic plasticity and protects against transient cerebral ischemia.

Alleviated cerebral infarction in male mice lacking all nitric oxide synthase isoforms after middle cerebral artery occlusion

PURPOSE

The role of the nitric oxide synthases (NOSs) system in cerebral infarction has been examined in pharmacological studies with non-selective NOSs inhibitors. However, due to the non-specificity of the non-selective NOSs inhibitors, its role remains to be fully elucidated. We addressed this issue in mice in which neuronal, inducible, and endothelial NOS isoforms were completely disrupted.

METHODS AND RESULTS

We newly generated mice lacking all three NOSs by crossbreeding each single NOS-/- mouse. In the male, cerebral infarct size at 24 h after middle cerebral artery occlusion (MCAO) was significantly smaller in the triple n/i/eNOSs-/- genotype as compared with wild-type genotype. Neurological deficit score and mortality rate were also significantly lower in the triple n/i/eNOSs-/- than in the WT genotype. In contrast, in the female, there was no significant difference in the cerebral infarct size in the two genotypes. In the male triple n/i/eNOSs-/- genotype, orchiectomy significantly increased the cerebral infarct size, and in the orchiectomized male triple n/i/eNOSs-/- genotype, treatment with testosterone significantly reduced it. Cyclopaedic and quantitative comparisons of mRNA expression levels in cerebral infarct lesions between the male wild-type and triple n/i/eNOSs-/- genotypes at 1 h after MCAO revealed significant involvements of decreased oxidative stress and mitigated mitochondrial dysfunction in the alleviated cerebral infarction in the male triple n/i/eNOSs-/- genotype.

CONCLUSIONS

These results provide the first evidence that the NOSs system exerts a deleterious effect against acute ischemic brain injury in the male.

Serum amyloid A-dependent inflammasome activation and acute injury in a mouse model of experimental stroke

Serum amyloid A (SAA) proteins increase dramatically in the blood following inflammation. Recently, SAAs are increased in humans following stroke and in ischemic animal models. However, the impact of SAAs on whether this signal is critical in the ischemic brain remains unknown. Therefore, we investigated the role of SAA and SAA signaling in the ischemic brain. Wildtype and SAA deficient mice were exposed to middle cerebral artery occlusion and reperfusion, examined for the impact of infarct volumes, behavioral changes, inflammatory markers, TUNEL staining, and BBB changes. The underlying mechanisms were investigated using SAA deficient mice, transgenic mice and viral vectors. SAA levels were significantly increase following MCAo and mice deficient in SAAs showed reduced infarct volumes and improved behavioral outcomes. SAA deficient mice showed a reduction in TUNEL staining, inflammation and decreased glial activation. Mice lacking acute phase SAAs demonstrated a reduction in expression of the NLRP3 inflammasome and SAA/NLRP3 KO mice showed improvement. Restoration of SAA expression via SAA tg mice or adenoviral expression reestablished the detrimental effects of SAA. A reduction in BBB permeability was seen in the SAA KO mice and anti-SAA antibody treatment reduced the effects on ischemic injury. SAA signaling plays a critical role in regulating NLRP3-induced inflammation and glial activation in the ischemic brain. Blocking this signal will be a promising approach for treating ischemic stroke.

Mass cytometric analysis of the immune cell landscape after traumatic brain injury elucidates the role of complement and complement receptors in neurologic outcomes

Following traumatic brain injury (TBI), a neuroinflammatory response can persist for years and contribute to the development of chronic neurological manifestations. Complement plays a central role in post-TBI neuroinflammation, and C3 opsonins and the anaphylatoxins (C3a and C5a) have been implicated in promoting secondary injury. We used single cell mass cytometry to characterize the immune cell landscape of the brain at different time points after TBI. To specifically investigate how complement shapes the post-TBI immune cell landscape, we analyzed TBI brains in the context of CR2-Crry treatment, an inhibitor of C3 activation. We analyzed 13 immune cell types, including peripheral and brain resident cells, and assessed expression of various receptors. TBI modulated the expression of phagocytic and complement receptors on both brain resident and infiltrating peripheral immune cells, and distinct functional clusters were identified within same cell populations that emerge at different phases after TBI. In particular, a CD11c+ (CR4) microglia subpopulation continued to expand over 28 days after injury, and was the only receptor to show continuous increase over time. Complement inhibition affected the abundance of brain resident immune cells in the injured hemisphere and impacted the expression of functional receptors on infiltrating cells. A role for C5a has also been indicated in models of brain injury, and we found significant upregulation of C5aR1 on many immune cell types after TBI. However, we demonstrated experimentally that while C5aR1 is involved in the infiltration of peripheral immune cells into the brain after injury, it does not alone affect histological or behavioral outcomes. However, CR2-Crry improved post-TBI outcomes and reduced resident immune cell populations, as well as complement and phagocytic receptor expression, indicating that its neuroprotective effects are mediated upstream of C5a generation, likely via modulating C3 opsonization and complement receptor expression.

MicroRNA152-3p Protects Against Ischemia/Reperfusion-Induced Bbb Destruction Possibly Targeting the MAP3K2/JNK/c-Jun Pathway

In the current study, we reported that overexpression of miR-152-3p effectively ameliorated neurological deficits and protected blood-brain barrier(BBB) integrity in middle cerebral artery occlusion (MCAO) rats. In an in vitro model, the level of miR-152-3p was significantly decreased in bEnd.3 cells after oxygen–glucose deprivation/reperfusion (OGD/R) insult. miR-152-3p overexpressing bEnd.3 cell monolayers were protected from OGD/R-induced microvascular hyperpermeability. The miR-152-3p-mediated protective effect was associated with lower apoptosis of endothelia by negatively modulating the MAP3K2/JNK/c-Jun pathway.

SMAlow/undetectable pericytes differentiate into microglia- and macrophage-like cells in ischemic brain

Pericytes are multipotent perivascular cells that play important roles in CNS injury. However, controversial findings exist on how pericytes change and whether they differentiated into microglia-like cells after ischemic stroke. This discrepancy is mainly due to the lack of pericyte-specific markers: the "pericyte" population identified in previous studies contained vascular smooth muscle cells (vSMCs) and/or fibroblasts. Therefore, it remains unclear which cell type differentiates into microglia-like cells after stroke. In this study, lineage-tracing technique was used to mark α-smooth muscle actin (SMA)low/undetectable pericytes, vSMCs, and fibroblasts, and their fates were analyzed after ischemic stroke. We found that SMAlow/undetectable pericytes and fibroblasts but not vSMCs substantially proliferated at the subacute phase after injury, and that SMAlow/undetectable pericyte but not vSMCs or fibroblasts differentiated into Iba1+ cells after ischemic stroke. Further imaging flow cytometry analysis revealed that SMAlow/undetectable pericytes differentiated into both microglia and macrophages at day 7 after stroke. These results demonstrate that SMAlow/undetectable pericytes rather than vSMCs or fibroblasts differentiate into both microglia-like and macrophage-like cells after stroke, suggesting that these pericytes may be targeted in the treatment of ischemic stroke.

Antioxidant Polyphenols of Antirhea borbonica Medicinal Plant and Caffeic Acid Reduce Cerebrovascular, Inflammatory and Metabolic Disorders Aggravated by High-Fat Diet-Induced Obesity in a Mouse Model of Stroke

Metabolic disorders related to obesity and type 2 diabetes are associated with aggravated cerebrovascular damages during stroke. In particular, hyperglycemia alters redox and inflammatory status, leading to cerebral endothelial cell dysfunction, blood–brain barrier (BBB) disruption and brain homeostasis loss. Polyphenols constitute the most abundant dietary antioxidants and exert anti-inflammatory effects that may improve cerebrovascular complications in stroke. This study evaluated the effects of the characterized polyphenol-rich extract of Antirhea borbonica medicinal plant and its major constituent caffeic acid on a high-fat diet (HFD)-induced obesity mouse model during ischemic stroke, and murine bEnd3 cerebral endothelial cells in high glucose condition. In vivo, polyphenols administered by oral gavage for 12 weeks attenuated insulin resistance, hyperglycemia, hyperinsulinemia and dyslipidemia caused by HFD-induced obesity. Polyphenols limited brain infarct, hemorrhagic transformation and BBB disruption aggravated by obesity during stroke. Polyphenols exhibited anti-inflammatory and antioxidant properties by reducing IL-1β, IL-6, MCP-1, TNF-α and Nrf2 overproduction as well as total SOD activity elevation at the cerebral or peripheral levels in obese mice. In vitro, polyphenols decreased MMP-2 activity that correlated with MCP-1 secretion and ROS intracellular levels in hyperglycemic condition. Protective effects of polyphenols were linked to their bioavailability with evidence for circulating metabolites including caffeic acid, quercetin and hippuric acid. Altogether, these findings show that antioxidant polyphenols reduced cerebrovascular, inflammatory and metabolic disorders aggravated by obesity in a mouse model of stroke. It will be relevant to assess polyphenol-based strategies to improve the clinical consequences of stroke in the context of obesity and diabetes.

Bridging the Transient Intraluminal Stroke Preclinical Model to Clinical Practice: From Improved Surgical Procedures to a Workflow of Functional Tests

Acute ischemic stroke (AIS) remains a leading cause of mortality, despite significant advances in therapy (endovascular thrombectomy). Failure in developing novel effective therapies is associated with unsuccessful translation from preclinical studies to clinical practice, associated to inconsistent and highly variable infarct areas and lack of relevant post-stroke functional evaluation in preclinical research. To outreach these limitations, we optimized the intraluminal transient middle cerebral occlusion, a widely used mouse stroke model, in two key parameters, selection of appropriate occlusion filaments and time of occlusion, which show a significant variation in the literature. We demonstrate that commercially available filaments with short coating length (1–2 mm), together with 45-min occlusion, results in a consistent affected brain region, similar to what is observed in most patients with AIS. Importantly, a dedicated post-stroke care protocol, based on clinical practice applied to patients who had stroke, resulted in lower mortality and improved mice welfare. Finally, a battery of tests covering relevant fine motor skills, sensory functions, and learning/memory behaviors revealed a significant effect of tMCAO brain infarction, which is parallel to patient symptomatology as measured by relevant clinical scales (NIH Stroke Scale, NIHSS and modified Rankin Scale, mRS). Thus, in order to enhance translation to clinical practice, future preclinical stroke research must consider the methodology described in this study, which includes improved reproducible surgical procedure, postoperative care, and the battery of functional tests. This will be a major step s closing the gap from bench to bedside, rendering the development of novel effective therapeutic approaches.

Cerebral ischemia induced iron deposit, ferritin accumulation, nuclear receptor coactivator 4-depletion and ferroptosis

BACKGROUND

The neuronal death upon cerebral ischemia shares not only characteristics of necrosis, apoptosis and autophagy, but exhibits also biochemical and morphological characteristics of ferroptosis. Ferroptosis is a regulated form of cell death which is considered to be an oxidative iron-dependent process. It is now commonly accepted that iron and free radicals are considered to cause lipid peroxidation as well as the oxidation of proteins and nucleic acids, leading to increased membrane and enzymatic dysfunction, and finally contributing to cell death. Although ferroptosis was first described in cancer cells, emerging evidence now links mechanisms of ferroptosis to many different diseases, including cerebral ischemia.

METHODS

The objective of this study was to identify the ferroptosis key players and the underlying biochemical pathways leading to cell death upon focal cerebral ischemia in mice by using immunofluorescence, Western blotting, histochemistry and densitometry.

RESULTS

In this study, we demonstrated that cerebral ischemia induced iron-deposition, down-regulated dramatically the expression of the glutathione peroxidase 4 (GPX4), decreased the expression of the nuclear receptor coactivator 4 (NCOA4) and induced inappropriate accumulation of ferritin in the ischemic brain. This supports the hypothesis that an ischemic insult may induce ferroptosis through inhibition of GPX4.

CONCLUSION

We conclude that iron excess following cerebral ischemia leads to cell death despite activation of compensatory mechanisms for iron homeostasis, as illustrated by the accumulation of ferritins. These data emphasize the presence of a cellular mechanism that allows neuronal cells to handle restriction in iron overload.

Fast Imaging of Mitochondrial Thioredoxin Reductase Using a Styrylpyridinium-Based Two-Photon Ratiometric Fluorescent Probe

Thioredoxin reductase (TrxR) is a pivotal antioxidant enzyme, but there remains a challenge for its fast imaging. This work describes the combination of a hydroxyl styrylpyridinium scaffold as the push-pull fluorophore with a carbonate-bridged 1,2-dithiolane unit as the reaction site to develop a fast mitochondrial TrxR2 probe, DSMP. It manifested a plethora of excellent properties including a rapid specific response (12 min), large Stokes shift (170 nm), ratiometric two-photon imaging, favorable binding with TrxR (K_m = 12.5 ± 0.2 μM), and the ability to cross the blood-brain barrier. With the aid of DSMP, we visualized the increased mitochondrial TrxR2 activity in cancer cells compared to normal cells. This offers the direct imaging evidence of the connection between the increased TrxR2 activity and the development of cancer. Additionally, the probe allowed the visualization of the loss in TrxR2 activity in a cellular Parkinson's disease model and, more importantly, in mouse brain tissues of a middle cerebral artery occlusion model for ischemic stroke.

NgR1 pathway expression in cerebral ischemic Sprague-Dawley rats with cognitive impairment

Objective(s):

This study aimed to determine the effect of ischemic occlusion duration and recovery time course on motor and cognitive function, identify optimal conditions for assessing cognitive function with minimal interference from motor deficits, and elucidate the underlying mechanism of axonal inhibitors.

Materials and Methods:

Sprague-Dawley (SD) rats were randomly allocated to the transient middle cerebral artery occlusion (tMCAO) 60-min (tMCAO60min), tMCAO90min, tMCAO120min, and sham groups. We conducted forelimb grip strength, two-way shuttle avoidance task, and novel object recognition task (NORT)tests at three time points (14, 21, and 28 days). Expression of Nogo receptor-1 (NgR1), the endogenous antagonist lateral olfactory tract usher substance, ras homolog family member A (Rho-A), and RhoA-activated Rho kinase (ROCK) was examined in the ipsilateral thalamus.

Results:

There was no difference in grip strength between sham and tMCAO_90min rats at 28 days. tMCAO_90min and tMCAO_120min rats showed lower discrimination indices in the NORT than sham rats on day 28. Compared with that in sham rats, the active avoidance response rate was lower in tMCAO_90min rats on days 14, 21, and 28 and in tMCAO_120min rats on days 14 and 21. Furthermore, 50-54% of rats in the tMCAO_90min group developed significant cognitive impairment on day 28, and thalamic NgR1, RhoA, and ROCK expression were greater in tMCAO_90min rats than in sham rats.

Conclusion:

Employing 90-min tMCAO in SD rats and assessing cognitive function 28 days post-stroke could minimize motor dysfunction effects in cognitive function assessments. Axonal inhibitor deregulation could be involved in poststroke cognitive impairment.

Activation of astroglial CB1R mediates cerebral ischemic tolerance induced by electroacupuncture

There are no effective treatments for stroke. The activation of endogenous protective mechanisms is a promising therapeutic approach, which evokes the intrinsic ability of the brain to protect itself. Accumulated evidence strongly suggests that electroacupuncture (EA) pretreatment induces rapid tolerance to cerebral ischemia. With regard to mechanisms underlying ischemic tolerance induced by EA, many molecules and signaling pathways are involved, such as the endocannabinoid system, although the exact mechanisms have not been fully elucidated. In the current study, we employed mutant mice, neuropharmacology, microdialysis, and virus transfection techniques in a middle cerebral artery occlusion (MCAO) model to explore the cell-specific and brain region-specific mechanisms of EA-induced neuroprotection. EA pretreatment resulted in increased ambient endocannabinoid (eCB) levels and subsequent activation of ischemic penumbral astroglial cannabinoid type 1 receptors (CB₁R) which led to moderate upregulation of extracellular glutamate that protected neurons from cerebral ischemic injury. These findings provide a novel cellular mechanism of EA and a potential therapeutic target for ischemic stroke.

Animal models of stroke

Stroke is a devastating disease with high morbidity and mortality. Animal models are indispensable tools that can mimic stroke processes and can be used for investigating mechanisms and developing novel therapeutic regimens. As a heterogeneous disease with complex pathophysiology, mimicking all aspects of human stroke in one animal model is impossible. Each model has unique strengths and weaknesses. Models such as transient or permanent intraluminal thread occlusion middle cerebral artery occlusion (MCAo) models and thromboembolic models are the most commonly used in simulating human ischemic stroke. The endovascular filament occlusion model is characterized by easy manipulation and accurately controllable reperfusion and is suitable for studying the pathogenesis of focal ischemic stroke and reperfusion injury. Although the reproducibility of the embolic model is poor, it is more convenient for investigating thrombolysis. Rats are the most frequently used animal model for stroke. This review mainly outlines the stroke models of rats and discusses their strengths and shortcomings in detail.

The Cytoskeletal Elements MAP2 and NF-L Show Substantial Alterations in Different Stroke Models While Elevated Serum Levels Highlight Especially MAP2 as a Sensitive Biomarker in Stroke Patients

In the setting of ischemic stroke, the neurofilament subunit NF-L and the microtubule-associated protein MAP2 have proven to be exceptionally ischemia-sensitive elements of the neuronal cytoskeleton. Since alterations of the cytoskeleton have been linked to the transition from reversible to irreversible tissue damage, the present study investigates underlying time- and region-specific alterations of NF-L and MAP2 in different animal models of focal cerebral ischemia. Although NF-L is increasingly established as a clinical stroke biomarker, MAP2 serum measurements after stroke are still lacking. Therefore, the present study further compares serum levels of MAP2 with NF-L in stroke patients. In the applied animal models, MAP2-related immunofluorescence intensities were decreased in ischemic areas, whereas the abundance of NF-L degradation products accounted for an increase of NF-L-related immunofluorescence intensity. Accordingly, Western blot analyses of ischemic areas revealed decreased protein levels of both MAP2 and NF-L. The cytoskeletal alterations are further reflected at an ultrastructural level as indicated by a significant reduction of detectable neurofilaments in cortical axons of ischemia-affected areas. Moreover, atomic force microscopy measurements confirmed altered mechanical properties as indicated by a decreased elastic strength in ischemia-affected tissue. In addition to the results from the animal models, stroke patients exhibited significantly elevated serum levels of MAP2, which increased with infarct size, whereas serum levels of NF-L did not differ significantly. Thus, MAP2 appears to be a more sensitive stroke biomarker than NF-L, especially for early neuronal damage. This perspective is strengthened by the results from the animal models, showing MAP2-related alterations at earlier time points compared to NF-L. The profound ischemia-induced alterations further qualify both cytoskeletal elements as promising targets for neuroprotective therapies.

PCSK9 (Proprotein Convertase Subtilisin Kexin Type 9) Inhibition in Hyperglycemic Mice Increases the Risk of Hemorrhagic Transformation of Ischemic Stroke

[Figure: see text].

Paeoniflorin improves functional recovery through repressing neuroinflammation and facilitating neurogenesis in rat stroke model

Background

Microglia, neuron, and vascular cells constitute a dynamic functional neurovascular unit, which exerts the crucial role in functional recovery after ischemic stroke. Paeoniflorin, the principal active component of Paeoniae Radix, has been verified to exhibit neuroprotective roles in cerebralischemic injury. However, the mechanisms underlying the regulatory function of Paeoniflorin on neurovascular unit after cerebral ischemia are still unclear.

Methods

In this study, adult male rats were treated with Paeoniflorin following transient middle cerebral artery occlusion (tMCAO), and then the functional behavioral tests (Foot-fault test and modified improved neurological function score, mNSS), microglial activation, neurogenesis and vasculogenesis were assessed.

Results

The current study showed that Paeoniflorin treatment exhibited a sensorimotor functional recovery as suggested via the Foot-fault test and the enhancement of spatial learning as suggested by the mNSS in rat stroke model. Paeoniflorin treatment repressed microglial cell proliferation and thus resulted in a significant decrease in proinflammatory cytokines IL-1β, IL-6 and TNF-α. Compared with control, Paeoniflorin administration facilitated von Willebrand factor (an endothelia cell marker) and doublecortin (a neuroblasts marker) expression, indicating that Paeoniflorin contributed to neurogenesis and vasculogenesis in rat stroke model. Mechanistically, we verified that Paeoniflorin repressed JNK and NF-κB signaling activation.

Conclusions

These results demonstrate that Paeoniflorin represses neuroinflammation and facilitates neurogenesis in rat stroke model and might be a potential drug for the therapy of ischemic stroke.

IL-27 Protects the Brain from Ischemia-Reperfusion Injury via the gp130/STAT3 Signaling Pathway

The occurrence of ischemia-reperfusion (I/R) injury leads to dysfunction as well as high rates of morbidity and mortality in stroke, and new effective therapeutic strategies for I/R are still needed. We investigated the effect of IL-27 on I/R injury-induced neurological function impairment, cerebral infarction volume and variation in levels of inflammatory factors in mice with middle cerebral artery occlusion (MCAO), as well as concentration of LDH and neuronal apoptosis in a neuron oxygen-glucose deprivation and reperfusion (OGD/R) model mediated by gp130/STAT3 signaling in vitro. Our results indicated that IL-27 could bind to its receptor of gp130 to attenuate the I/R injury-induced impairment function and cerebral infarction volume, and decrease inflammatory cytokines TNF-α, IL-1β and MCP-1 but increase anti-inflammatory factors IL-10 and TGF-β in vivo, while inhibiting LDH leakage and neuronal apoptosis through activation of STAT3 to antagonize I/R induction. Our results suggest that IL-27 may protect the brain from I/R injury through the gp130/STAT3 signaling pathway.

A review of experimental models of focal cerebral ischemia focusing on the middle cerebral artery occlusion model

Cerebral ischemic stroke is a leading cause of death and disability, but current pharmacological therapies are limited in their utility and effectiveness. In vitro and in vivo models of ischemic stroke have been developed which allow us to further elucidate the pathophysiological mechanisms of injury and investigate potential drug targets. In vitro models permit mechanistic investigation of the biochemical and molecular mechanisms of injury but are reductionist and do not mimic the complexity of clinical stroke. In vivo models of ischemic stroke directly replicate the reduction in blood flow and the resulting impact on nervous tissue. The most frequently used in vivo model of ischemic stroke is the intraluminal suture middle cerebral artery occlusion (iMCAO) model, which has been fundamental in revealing various aspects of stroke pathology. However, the iMCAO model produces lesion volumes with large standard deviations even though rigid surgical and data collection protocols are followed. There is a need to refine the MCAO model to reduce variability in the standard outcome measure of lesion volume. The typical approach to produce vessel occlusion is to induce an obstruction at the origin of the middle cerebral artery and reperfusion is reliant on the Circle of Willis (CoW). However, in rodents the CoW is anatomically highly variable which could account for variations in lesion volume. Thus, we developed a refined approach whereby reliance on the CoW for reperfusion was removed. This approach improved reperfusion to the ischemic hemisphere, reduced variability in lesion volume by 30%, and reduced group sizes required to determine an effective treatment response by almost 40%. This refinement involves a methodological adaptation of the original surgical approach which we have shared with the scientific community via publication of a visualised methods article and providing hands-on training to other experimental stroke researchers.

Differential Responses of Transplanted Stem Cells to Diseased Environment Unveiled by a Molecular NIR-II Cell Tracker

Stem cell therapy holds high promises in regenerative medicine. The major challenge of clinical translation is to precisely and quantitatively evaluate the in vivo cell distribution, migration, and engraftment, which cannot be easily achieved by current techniques. To address this issue, for the first time, we have developed a molecular cell tracker with a strong fluorescence signal in the second near-infrared (NIR-II) window (1,000-1,700 nm) for real-time monitoring of in vivo cell behaviors in both healthy and diseased animal models. The NIR-II tracker (CelTrac1000) has shown complete cell labeling with low cytotoxicity and profound long-term tracking ability for 30 days in high spatiotemporal resolution for semiquantification of the biodistribution of transplanted stem cells. Taking advantage of the unique merits of CelTrac1000, the responses of transplanted stem cells to different diseased environments have been discriminated and unveiled. Furthermore, we also demonstrate CelTrac1000 as a universal and effective technique for ultrafast real-time tracking of the cellular migration and distribution in a 100 μm single-cell cluster spatial resolution, along with the lung contraction and heart beating. As such, this NIR-II tracker will shift the optical cell tracking into a single-cell cluster and millisecond temporal resolution for better evaluating and understanding stem cell therapy, affording optimal doses and efficacy.

Activation of CB1R-Dependent PGC-1α Is Involved in the Improved Mitochondrial Biogenesis Induced by Electroacupuncture Pretreatment

Electroacupuncture (EA) pretreatment induces cerebral ischemic tolerance; however, the mechanism remains poorly understood. This study aimed to determine the participation of peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α)-mediated mitochondrial biogenesis in the neuroprotection of EA and whether cannabinoid receptor 1 (CB1R) is involved in this mechanism. At 2 hours after EA pretreatment, adult male C57BL/6j mice were subjected to 60-minute right middle cerebral artery occlusion (MCAO). Mitochondrial function, the level of mitochondrial biogenesis-related proteins (nuclear transcription factor 1, NRF1; mitochondrial transcription factor A, TFAM), and mitochondrial DNA (mtDNA) were measured. A small interfering RNA (siRNA) targeting PGC-1α and the CB1R antagonists AM251 and SR141716A were given to the animals before EA pretreatment, and mitochondrial function and biogenesis were examined after MCAO. EA ameliorated the mitochondrial function, upregulated the NRF1 and TFAM expression, and increased the mtDNA levels and the volume and number of mitochondria. EA pretreatment increased the expression of PGC-1α, whereas the PGC-1α siRNA and CB1R antagonists reversed the improved neuroprotection and increased mitochondrial biogenesis induced by EA. Our results indicated that EA pretreatment protects the mitochondria and promotes mitochondrial biogenesis by activating CB1R-dependent PGC-1α, which provides a novel mechanism for EA pretreatment-induced ischemic tolerance.

Protective Effects of Antioxidant Polyphenols against Hyperglycemia-Mediated Alterations in Cerebral Endothelial Cells and a Mouse Stroke Model

SCOPE

Hyperglycemia alters cerebral endothelial cell and blood-brain barrier functions, aggravating cerebrovascular complications such as stroke during diabetes. Redox and inflammatory changes play a causal role. This study evaluates polyphenol protective effects in cerebral endothelial cells and a mouse stroke model during hyperglycemia.

METHODS AND RESULTS

Murine bEnd.3 cerebral endothelial cells and a mouse stroke model are exposed to a characterized, polyphenol-rich extract of Antirhea borbonica or its predominant constituent caffeic acid, during hyperglycemia. Polyphenol effects on redox, inflammatory and vasoactive markers, infarct volume, and hemorrhagic transformation are determined. In vitro, polyphenols improve reactive oxygen species levels, Cu/Zn superoxide dismutase activity, and both NAPDH oxidase 4 and nuclear factor erythroid 2-related factor 2 (Nrf2) gene expression deregulated by high glucose. Polyphenols reduce Nrf2 nuclear translocation and counteract nuclear factor-ĸappa B activation, interleukin-6 secretion, and the altered production of vasoactive markers mediated by high glucose. In vivo, polyphenols reduce cerebral infarct volume and hemorrhagic transformation aggravated by hyperglycemia. Polyphenols attenuate redox changes, increase vascular endothelial-Cadherin production, and decrease neuro-inflammation in the infarcted hemisphere.

CONCLUSION

Polyphenols protect against hyperglycemia-mediated alterations in cerebral endothelial cells and a mouse stroke model. It is relevant to assess polyphenol benefits to improve cerebrovascular damages during diabetes.

Deficiency of platelet adhesion molecule CD226 causes megakaryocyte development and platelet hyperactivity

This study used constitutive CD226 gene knockout (KO) mice as a model to investigate the functions and mechanisms of CD226 in megakaryocyte (MK) maturation and platelet activation. Although CD226 deficiency did not cause MK polyploidization or platelet granule abnormalities, increased MK counts were detected in the femora bone marrow (BM) and spleen of CD226 KO mice. Particularly, CD226 KO mice have a more extensive membrane system in MKs and platelets than wild-type (WT) mice. We also demonstrated that CD226 KO mice displayed increased platelet counts, shortened bleeding time, and enhanced platelet aggregation. CD226 KO platelets had an increased mature platelet ratio compared to the control platelets. In addition, the observed reduction in bleeding time may be due to decreased nitric oxide (NO) production in the platelets. Platelet-specific CD226-deficient mice showed similar increased MK counts, shortened bleeding time, enhanced platelet aggregation, and decreased NO production in platelets. Furthermore, we performed middle cerebral artery occlusion-reperfusion surgery on WT and CD226 KO mice to explore the potential effect of CD226 on acute ischemia-reperfusion injury; the results revealed that CD226 deficiency led to significantly increased infarct area. Thus, CD226 is a promising candidate for the treatment of thrombotic disorders.

Silencing of microRNA-494 inhibits the neurotoxic Th1 shift via regulating HDAC2-STAT4 cascade in ischaemic stroke

BACKGROUND AND PURPOSE

T helper cell 1 (Th1)-skewed neurotoxicity contributes to the poor outcome of stroke in rodents. Here, we have elucidated the mechanism of the Th1/Th2 shift in acute ischaemic stroke (AIS) patients at hyperacute phase and have looked for a miRNA-based therapeutic target.

EXPERIMENTAL APPROACH

MiR-494 levels in blood from AIS patients and controls were measured by real-time PCR. C57BL/6J mice were subjected to transient middle cerebral artery occlusion, and cortical neurons were subjected to oxygen-glucose deprivation. Luciferase reporter system, chromatin immunoprecipitation sequencing (ChIP-Seq), and ChIP-PCR were used to uncover possible mechanisms.

KEY RESULTS

In lymphocytes from AIS patients, there was a Th1/Th2 shift and histone deacetylase 2 (HDAC2) was markedly down-regulated. ChIP-seq showed that HDAC2 binding sites were enriched in regulation of Th1 cytokine production, and ChIP-PCR confirmed that HDAC2 binding was changed at the intron of STAT4 and the promoter of T-box transcription factor 21 (T-bet) in lymphocytes from AIS patients. MiR-494 was the most significantly increased miRNA in lymphocytes from AIS patients, and miR-494-3p directly targeted HDAC2. A strong association existed between miR-494 and Th1 cytokines, and neurological deficit as measured by the National Institute of Health Stroke Scale (NIHSS) in AIS patients. In vitro and in vivo experiments showed that antagomir-494 reduced Th1 shift-mediated neuronal and sensorimotor functional damage in the mouse model of ischaemic stroke, via the HDAC2-STAT4 pathway.

CONCLUSION AND IMPLICATIONS

We demonstrated that miR-494 inhibition prevented Th1-skewed neurotoxicity through regulation of the HDAC2-STAT4 cascade.

Inhibition of histone deacetylase 3 by MiR-494 alleviates neuronal loss and improves neurological recovery in experimental stroke

HDAC3 is an essential negative regulator of neuronal plasticity and memory formation. Although a chemical inhibitor has been invented, little is known about its endogenous modulators. We explored whether miR-494 affects HDAC3-mediated neuronal injury following acute ischemic stroke. A substantial increase in plasma miR-494 was detected in AIS patients and was positively associated with the mRS at one year after symptom onset. The miR-494 levels were transiently increased in the infarcted brain tissue of mice. In contrast, miR-494 levels were reduced in neurons but increased in the medium after OGD. Intracerebroventricular injection of miR-494 agomir reduced neuronal apoptosis and infarct volume at the acute stage of MCAO, promoted axonal plasticity and long-term outcomes at the recovery stage, suppressed neuronal ataxin-3 and HDAC3 expression and increased acetyl-H3K9 levels in the ipsilateral hemisphere. In vitro studies confirmed that miR-494 posttranslationally inhibited HDAC3 in neurons and prevented OGD-induced neuronal axonal injury. The HDAC3 inhibitor increased acetyl-H3K9 levels and reversed miR-494 antagomir-aggravated acute cerebral ischemic injury, as well as brain atrophy and long-term functional recovery. These results suggest that miR-494 may serve as a predictive biomarker of functional outcomes in AIS patients and a potential therapeutic target for the treatment of ischemic stroke.

Inhibition of TIM-4 protects against cerebral ischaemia-reperfusion injury

TIM‐4 plays an important role in ischaemia‐reperfusion injury of liver and kidney; however, the effects of TIM‐4 on cerebral ischaemia‐reperfusion injury (IRI) are unknown. The purpose of the present study was to investigate the potential role of TIM‐4 in experimental brain ischaemia‐reperfusion injury. In this study, cerebral ischaemia reperfusion was induced by transient middle cerebral artery occlusion (MCAO) for 1 hour in C57/BL6 mice. The TIM‐4 expression was detected in vivo or vitro by real‐time quantitative polymerase chain reaction, Western blot and flow cytometric analysis. In vivo, the administration of anti‐TIM‐4 antibodies significantly suppressed apoptosis, inhibited inflammatory cells and enhanced anti‐inflammatory responses. In vitro, activated microglia exhibited reduced cellular proliferation and induced IRI injury when co‐cultured with neurons; these effects were inhibited by anti‐TIM‐4 antibody treatment. Similarly, microglia transfected with TIM‐4 siRNA and stimulated by LPS + IFN‐γ alleviated the TIM‐4‐mediated damage to neurons. Collectively, our data indicate that the inhibition of TIM‐4 can improve the inflammatory response and exerts a protective effect in cerebral ischaemia‐reperfusion injury.

Analysis of skin morphological features and real-time monitoring using snapshot hyperspectral imaging

We propose a snapshot hyperspectral imaging system and methods for skin morphological feature analysis and real-time monitoring of skin activities. The analysis method includes a strategy using weighted subtractions between sub-channel images to extract absorption information due to specific chromophores within skin tissue, for example hemoglobin and melanin. Based on morphological analysis results, we carry out real-time monitoring of the skin features to verify the ability of this method to provide temporal responses of the skin tissue activities, which is experimentally shown to be useful in the measurement of heartrate, monitoring of the tissue recovery after a body exercise, and studying of the tissue response due to a vascular occlusion. Compared to conventional multispectral imaging system, the proposed system improves the device simplicity and is immune to motion artifacts. Coupled with the extraction algorithms, the hyperspectral imaging promises a robust skin assessment tool with abilities for qualitative visualization and potentially quantitative analysis of skin features, useful in the applications of cosmetics and clinical dermatology.

Microcirculatory Changes in Experimental Models of Stroke and CNS-Injury Induced Immunodepression

Stroke is the second-leading cause of death globally and the leading cause of disability in adults. Medical complications after stroke, especially infections such as pneumonia, are the leading cause of death in stroke survivors. Systemic immunodepression is considered to contribute to increased susceptibility to infections after stroke. Different experimental models have contributed significantly to the current knowledge of stroke pathophysiology and its consequences. Each model causes different changes in the cerebral microcirculation and local inflammatory responses after ischemia. The vast majority of studies which focused on the peripheral immune response to stroke employed the middle cerebral artery occlusion method. We review various experimental stroke models with regard to microcirculatory changes and discuss the impact on local and peripheral immune response for studies of CNS-injury (central nervous system injury) induced immunodepression.

JNK-IN-8, a c-Jun N-terminal kinase inhibitor, improves functional recovery through suppressing neuroinflammation in ischemic stroke

C‐Jun N‐terminal kinase (JNK) is a pivotal MAPK (mitogen‐activated protein kinase), which activated by ischemia brain injury and plays a fairly crucial function in cerebral ischemic injury. Emerging studies demonstrated that JNK‐IN‐8 (a JNK inhibitor with high specificity) regulates traumatic brain injury through controlling neuronal apoptosis and inflammation. However, the function of JNK‐IN‐8 in ischemic stroke and the mechanisms underlying of JNK‐IN‐8 about neuroprotection are not well understood. In this work, male rats were treated with JNK‐IN‐8 after transient middle cerebral artery occlusion, and then the modified improved neurological function score (mNSS), the foot‐fault test (FFT), interleukin‐1β (IL‐1β), IL‐6, and tumor necrosis factor‐α (TNF‐α) levels were assessed. We found that JNK‐IN‐8‐treated rats with MCAO exerted an observable melioration in space learning as tested by the improved mNSS, and showed sensorimotor functional recovery as measured by the FFT. JNK‐IN‐8 also played anti‐inflammatory roles as indicated through decreased activation of microglia and decreased IL‐6, IL‐1β, and TNF‐α expression. Furthermore, JNK‐IN‐8 suppressed the activation of JNK and nuclear factor‐κB (NF‐κB) signaling as indicated by the decreased level of phosphorylated‐JNK and p65. All data demonstrate that JNK‐IN‐8 inhibits neuroinflammation and improved neurological function by inhibiting JNK/NF‐κB and is a promising agent for the prevention of ischemic brain injury.

USP18 Overexpression Protects against Focal Cerebral Ischemia Injury in Mice by Suppressing Microglial Activation

The activation of inflammatory cytokines following stroke leads to neuron apoptosis and microglial activation, both of which are involved in ischemic brain damages. The ubiquitin-specific protease 18 (USP18) negatively regulated the expression of inflammatory cytokines and suppresses microglial activation. This study aims to determine whether USP18 expression protects against brain damage in ischemic models of stroke. We investigated USP18 expression, overexpression, and knockout under ischemic conditions in vitro and in vivo. Using BV2 microglial cells under oxygen and glucose deprivation (OGD) and 60 min transient middle cerebral artery occlusion (MCAO) in mice as models of ischemia, we assessed the infarct volume, the extent of neurogenesis, the expression of proinflammatory cytokines and Janus Kinases(JAKs)/Signal Transducer and Activator of Transcription (STAT) pathway members. BV2 cells under OGD for 0, 6, 12, or 24 h exhibited decreased USP18 expression and increased expression of the proinflammatory cytokines including interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor (TNF)-α, and interferon (INF)-γ. Lentiviral overexpression of USP18 in MCAO mice significantly decreased the infarct volume and significantly increased the number of new neurons that coexpressed bromodeoxyuridine (BrdU)/neuronal nuclei (NeuN). Additionally, microglial activation was inhibited, including the suppression of the JAK/STAT pathway and the proinflammatory cytokines expression. In vitro experiments demonstrated that USP18 inhibited BV2 microglial activity and reduced the mRNA and protein levels of NF-κB, JAK1, p-JAK1, STAT1, and p-STAT1 in BV2 microglial cells. USP18 overexpression decreased ischemic brain injury through the suppression of microglial activation by negatively regulating the release of proinflammatory cytokines.

Neuroprotective effect ofPanax ginsengextract against cerebral ischemia–reperfusion-injury-induced oxidative stress in middle cerebral artery occlusion models

The present study investigated the in vivo neuroprotective role of Panax ginseng extract (PGE) pretreatment against transient cerebral ischemia in a middle cerebral artery occlusion (MCAO) model. Rats were randomly divided as follows: group I, control; group II, sham-operated; group III, where animals were subjected to MCAO surgery; and group IV, where animals were orally administered 10 mL PGE per day (200 mg/kg of body weight per day) for 30 d followed by MCAO induction at day 31. Following 24 h of reperfusion, blood and tissue (brain, liver, and kidney) samples were collected for biochemical and histopathological examination. Biochemical testing included lipid profile, liver enzymes, kidney function tests, C-reactive protein (CRP), lactate dehydrogenase (LDH), glucose, and total protein estimation. Tissue antioxidants (catalase, superoxide dismutase, and glutathione) were assessed in brain, liver, and kidney tissues. MCAO-induced histopathological changes were also examined in the tissues. Pretreatment with PGE showed significant improvement in tissue antioxidant status in brain, liver and kidney tissues. PGE treatment maintains plasma lipid profile, liver enzymes, kidney function, and CRP, LDH, and glucose levels. Histologically, monocytes and macrophage infiltration were observed in the tissues of MCAO animals, whereas PGE treatment preserved tissue architecture and minimal monocyte infiltration. PGE supplementation showed a neuroprotective effect against ischemia–reperfusion injury by effectively increasing endogenous antioxidant enzyme activity.

Long-term depression induced by endogenous cannabinoids produces neuroprotection via astroglial CB1R after stroke in rodents

Ischemia not only activates cell death pathways but also triggers endogenous protective mechanisms. However, it is largely unknown what is the essence of the endogenous neuroprotective mechanisms induced by preconditioning. In this study we demonstrated that systemic injection of JZL195, a selective inhibitor of eCB clearance enzymes, induces in vivo long-term depression at CA3-CA1 synapses and at PrL-NAc synapses produces neuroprotection. JZL195-elicited long-term depression is blocked by AM281, the antagonist of cannabinoid 1 receptor (CB₁R) and is abolished in mice lacking cannabinoid CB₁ receptor (CB₁R) in astroglial cells, but is conserved in mice lacking CB₁R in glutamatergic or GABAergic neurons. Blocking the glutamate NMDA receptor and the synaptic trafficking of glutamate AMPA receptor abolishes both long-term depression and neuroprotection induced by JZL195. Mice lacking CB₁R in astroglia show decreased neuronal death following cerebral ischemia. Thus, an acute elevation of extracellular eCB following eCB clearance inhibition results in neuroprotection through long-term depression induction after sequential activation of astroglial CB₁R and postsynaptic glutamate receptors.

Activation of cannabinoid receptor 1 is involved in protection against mitochondrial dysfunction and cerebral ischaemic tolerance induced by isoflurane preconditioning

Background

Isoflurane preconditioning (IPC) induces cerebral ischaemic tolerance, but the mechanism remains poorly understood. The aim of this study was to determine changes in mitochondrial function in the brain after IPC, and whether the cannabinoid receptor 1 (CB1R) could be involved in the mechanism of mitochondrial protection mediated by IPC.

Methods

Adult male Sprague-Dawley rats were pretreated with isoflurane 2% for 1 h day -1 , for 5 days consecutively, and then subjected to 120 min right middle cerebral artery occlusion. Cannabinoid receptor 1 expression in the cellular and mitochondrial membrane was measured. The CB1R agonist HU-210 was administered alone, or the antagonists AM251 and SR141716A were given to the animals before each preconditioning. Neurological scores, infarct volume, apoptosis, and mitochondrial function were examined after middle cerebral artery occlusion.

Results

Expression of CB1R on cellular and mitochondrial membranes was increased 6 h after preconditioning. Both IPC and HU-210 administration before middle cerebral artery occlusion improved neurological outcomes and reduced infarct volume. Isoflurane preconditioning increased the expression of the anti-apoptotic proteins Bcl-2 and Bcl-X L and reduced apoptosis in neurones. Isoflurane preconditioning and HU-210 also markedly preserved the activity of respiratory chain complexes, reduced mitochondrial radical generation, preserved mitochondrial membrane potential, and inhibited mitochondrial permeability transition pore opening. Cannabinoid receptor 1 antagonists abolished the improvement in mitochondrial function and the neuroprotective effects induced by IPC.

Conclusions

Our results indicate that IPC elicits brain ischaemic tolerance and mitochondrial protection by activating the CB1R, which provides a new mechanism for IPC-induced neuroprotection against cerebral ischaemia.

Non-invasive Vagus Nerve Stimulation Protects Against Cerebral Ischemia/Reperfusion Injury and Promotes Microglial M2 Polarization Via Interleukin-17A Inhibition

Microglia play an essential role during cerebral an ischemia/reperfusion (I/R)-related inflammatory process. Because the M2 phenotype of microglia exhibits anti-inflammation activity, it has become a promising target for anti-inflammatory therapy. Vagus nerve stimulation (VNS) reportedly has neuroprotective effects against cerebral I/R injuries via its anti-inflammatory action. The aim of this study was to investigate the ability of non-invasive VNS (nVNS) to alleviate cerebral I/R in mice by promoting microglial M2 polarization. Neurological scoring and cerebral infarct volume assessments were performed 72 h after a middle cerebral artery occlusion (MCAO)-induced stroke. M2 phenotype microglia were identified by immunohistochemistry staining using Arg-1 and Iba-1 antibodies. The protein expressions of Arg-1, IL-17A, IL-10, Bax, and Bcl-2 were detected by Western blot. Apoptotic cells were detected using TUNEL staining. According to our results, nVNS decreased infarct volume, improved neurological outcomes, reduced apoptotic neurons (TUNEL⁺NeuN⁺ cells), and promoted microglial M2 polarization as indicated by elevated Arg-1 protein expression and increased Arg-1⁺ cells after MCAO. Moreover, nVNS attenuated the increased levels of IL-17A protein expression after MCAO. To test the possible involvement of IL-17A in nVNS-induced neuroprotection and microglial M2 polarization, 1-μg recombinant IL-17A (rIL-17A) was intranasally administered once daily for three consecutive days after reperfusion. We found that the intranasal administration of rIL-17A nullified the nVNS-induced promotion of microglial M2 polarization. Furthermore, rIL-17A administration abolished the neuroprotective effect of nVNS. In conclusion, our study identifies microglial M2 polarization as an important mechanism underlying the nVNS-mediated neuroprotection against cerebral I/R. This effect of nVNS could be attributed to the inhibition of IL-17A expression.

Attenuation of stroke damage by angiotensin II type 2 receptor stimulation via peroxisome proliferator-activated receptor-gamma activation

The brain renin-angiotensin system plays a crucial role in ischemic stroke. It is known that stimulation of the angiotensin II type 2 (AT₂) receptor protects against ischemic brain injury. We recently demonstrated that AT₂ receptor stimulation by compound 21 (C21), a direct AT₂ receptor agonist, inhibited vascular intimal proliferation with activation of peroxisome proliferator-activated receptor-gamma (PPAR-γ). However, whether direct AT₂ receptor stimulation protects against ischemic brain injury via PPAR-γ activation is still unknown. 8-week-old male C57BL/6 J mice were subjected to middle cerebral artery (MCA) occlusion. 2 weeks before MCA occlusion, they were administered C21 with or without GW9662, a PPAR-γ antagonist. Neurologic deficit, ischemic size, superoxide anion, superoxide dismutase (SOD) activity, expression of NADPH subunits and blood brain barrier (BBB) stabilization were assessed 24 h after MCA occlusion. Cerebral blood flow (CBF) was measured in the core and periphery of the MCA territory before, immediately after, 1 h and 24 h after MCA occlusion. Treatment with C21 markedly decreased the neurologic deficit and ischemic size with an increase in CBF, SOD activity and BBB stabilization genes compared with the non-treated group. Co-administration of GW9662 partially attenuated this protective effect of C21 on neurologic deficit and ischemic size via an increase in superoxide anion production and a decrease of SOD activity and BBB stabilization genes, while GW9662 treatment alone had no significant effect on neurologic deficit and ischemic size. These results suggest that direct AT₂ receptor stimulation has a preventive effect on stroke-induced brain injury partly due to activation of PPAR-γ.

Hypoxia, hibernation and Neuroprotection: An Experimental Study in Mice

Hibernation is a unique physiological state that evolved to survive periods of food shortages. It is characterized by profound decreases in metabolic rate, body temperature and physiological functions. Studies have shown that animals in hibernation can resist neurological damage. Here, we aimed to study whether hypoxia can induce a hibernation-like state in a traditionally non-hibernating animal and whether it is neuroprotective. All procedures were conducted according to international guidelines on laboratory animal safety. Mice C57BL/6 (19-21g) were placed into a 125 mL jar with fresh air and the jar was sealed with a rubber plug. For each run, the tolerance limit was judged by the animals' appearance for "air hunger". The animal was removed from the jar as soon as its first gasping breath appeared and was moved to another fresh-air-containing jar of similar volume. This procedure was performed in four runs. The hypoxia exposure significantly decreased oxygen (O2) consumption, carbon dioxide (CO2) production, respiratory rate and heart rate. Meanwhile, rectal temperature reached a minimum of 12.7±2.56°C, which is lower than a wide range of ambient temperatures. The mimicked hibernation decreased the infarct size in a focal cerebral ischemia mouse model. Our findings suggest the possibility of inducing suspended animation-like hibernation states for medical applications post injury.

Neuronal expression of the mitochondrial protein prohibitin confers profound neuroprotection in a mouse model of focal cerebral ischemia

The mitochondrial protein prohibitin (PHB) has emerged as an important modulator of neuronal survival in different injury modalities . We previously showed that viral gene transfer of PHB protects CA1 neurons from delayed neurodegeneration following transient forebrain ischemia through mitochondrial mechanisms. However, since PHB is present in all cell types, it is not known if its selective expression in neurons is protective, and if the protection occurs also in acute focal ischemic brain injury, the most common stroke type in humans. Therefore, we generated transgenic mice overexpressing human PHB1 specifically in neurons (PHB1 Tg). PHB1 Tg mice and littermate controls were subjected to transient middle cerebral artery occlusion (MCAo). Infarct volume and sensory-motor impairment were assessed three days later. Under the control of a neuronal promoter (CaMKIIα), PHB1 expression was increased by 50% in the forebrain and hippocampus in PHB1 Tg mice. The brain injury produced by MCAo was reduced by 63 ± 11% in PHB1 Tg mice compared to littermate controls. This reduction was associated with improved sensory-motor performance, suggesting that the salvaged brain remains functional. Approaches to enhance PHB expression may be useful to ameliorate the devastating impact of cerebral ischemia on the brain.

Cerebral Artery Diameter in Inbred Mice Varies as a Function of Strain

Many strains of mice are utilized in mouse models of cerebrovascular diseases. Variations in vascular anatomy between these strains has been documented and may influence the phenotype in stroke models. To address inter-strain variations in the circle of Willis anatomy, the diameters of internal carotid, posterior communicating, anterior cerebral, and middle cerebral arteries in 144 mice from 32 inbred strains were measured. Arterial diameters were analyzed as a function of animal weight, age, and strain. Variations in the structure of the circle of Willis across strains were observed and noted. While right-sided anterior cerebral arteries were significantly greater in diameter than their left-sided counterparts across most strains, variations in arterial diameter are strain specific. Adult mouse weight was not found to be associated with arterial diameter across strains, suggesting that cerebral artery size is associated with strain independently of weight. This study demonstrates strain dependent variations in the murine circle of Willis, which should be taken into consideration when studying mouse models of cerebrovascular diseases.

Focal Ischaemic Infarcts Expand Faster in Cerebellar Cortex than Cerebral Cortex in a Mouse Photothrombotic Stroke Model

It is generally accepted that the cerebellum is particularly vulnerable to ischaemic injury, and this may contribute to the high mortality arising from posterior circulation strokes. However, this has not been systematically examined in an animal model. This study compared the development and resolution of matched photothrombotic microvascular infarcts in the cerebellar and cerebral cortices in adult 129/SvEv mice of both sexes. The photothrombotic lesions were made using tail vein injection of Rose Bengal with a 532 nm laser projected onto a 2 mm diameter aperture over the target region of the brain (with skull thinning). Infarct size was then imaged histologically following 2 h to 30-day survival using serial reconstruction of haematoxylin and eosin stained cryosections. This was complemented with immunohistochemistry for neuron and glial markers. At 2 h post-injury, the cerebellar infarct volume averaged ~ 2.7 times that of the cerebral cortex infarcts. Infarct volume reached maximum in the cerebellum in a quarter of the time (24 h) taken in the cerebral cortex (4 days). Remodelling resolved the infarcts within a month, leaving significantly larger residual injury volume in the cerebellum. The death of neurons in the core lesion at 2 h was confirmed by NeuN and Calbindin immunofluorescence, alongside activation of astrocytes and microglia. The latter persisted in the region within and surrounding the residual infarct at 30 days. This comparison of acute focal ischaemic injuries in cerebellar and cerebral cortices provides direct confirmation of exacerbation of neuropathology and faster kinetics in the cerebellum.

Neuroprotective Effects of Bioactive Compounds and MAPK Pathway Modulation in "Ischemia"-Stressed PC12 Pheochromocytoma Cells

This review surveys the efforts taken to investigate in vitro neuroprotective features of synthetic compounds and cell-released growth factors on PC12 clonal cell line temporarily deprived of oxygen and glucose followed by reoxygenation (OGD/R). These cells have been used previously to mimic some of the properties of in vivo brain ischemia-reperfusion-injury (IRI) and have been instrumental in identifying common mechanisms such as calcium overload, redox potential, lipid peroxidation and MAPKs modulation. In addition, they were useful for establishing the role of certain membrane penetrable cocktails of antioxidants as well as potential growth factors which may act in neuroprotection. Pharmacological mechanisms of neuroprotection addressing modulation of the MAPK cascade and increased redox potential by natural products, drugs and growth factors secreted by stem cells, in either undifferentiated or nerve growth factor-differentiated PC12 cells exposed to ischemic conditions are discussed for future prospects in neuroprotection studies.

Cell-Based Drug Delivery and Use of Nano-and Microcarriers for Cell Functionalization

Cell functionalization with recently developed various nano- and microcarriers for therapeutics has significantly expanded the application of cell therapy and targeted drug delivery for the effective treatment of a number of diseases. The aim of this progress report is to review the most recent advances in cell-based drug vehicles designed as biological transporter platforms for the targeted delivery of different drugs. For the design of cell-based drug vehicles, different pathways of cell functionalization, such as covalent and noncovalent surface modifications, internalization of carriers are considered in greater detail together with approaches for cell visualization in vivo. In addition, several animal models for the study of cell-assisted drug delivery are discussed. Finally, possible future developments and applications of cell-assisted drug vehicles toward targeted transport of drugs to a designated location with no or minimal immune response and toxicity are addressed in light of new pathways in the field of nanomedicine.

Thromboembolic Model of Cerebral Ischemia and Reperfusion in Mice

Ischemic stroke is the fourth leading cause of death in the USA and a prominent cause of death globally. Besides thrombolytic therapy used in a small subset of patients, no alternative therapeutic strategy has been shown to improve the outcome of stroke patients. Preclinical models of ischemic stroke are an essential tool for investigating pathogenic processes that happen after the ischemic insult, as well as to screen for candidate therapeutic interventions. There are several models of rodent ischemic stroke including mechanical occlusion, thromboembolic stroke, and photothrombotic stroke. However, models that permit studying stroke in the context of thrombolytic therapy, such as thromboembolic models, are becoming of increasing interest to the research community. In this chapter, we describe a thromboembolic model of ischemic stroke with and without tissue-plasminogen activator-induced reperfusion. We describe protocols for microemboli preparation, surgical procedure, and post-stroke assessment of animals.

A hemorrhagic transformation model of mechanical stroke therapy with acute hyperglycemia in mice

Clinical benefit for mechanical thrombectomy (MT) in stroke was recently demonstrated in multiple large prospective studies. Acute hyperglycemia (HG) is an important risk factor of poor outcome in stroke patients, including those that underwent MT. The aim of this therapy is to achieve a complete reperfusion in a short time, given that reperfusion damage is dependent on the duration of ischemia. Here, we investigated the effects of acute HG in a mouse model of ischemic stroke induced by middle cerebral artery occlusion (MCAO). Hyperglycemic (intraperitoneal [ip] injection of glucose) and control (ip saline injection) 10-week male C57BL6 mice were subjected to MCAO (30, 90, and 180 min) followed by reperfusion obtained by withdrawal of the monofilament. Infarct volume, hemorrhagic transformation (HT), neutrophil infiltration, and neurological scores were assessed at 24 hr by performing vital staining, ELISA immunofluorescence, and behavioral test, respectively. Glucose injection led to transient HG (blood glucose = 250-390 mg/dL) that significantly increased infarct volume, HT, and worsened neurological outcome. In addition, we report that HG promoted blood-brain barrier disruption as shown by hemoglobin accumulation in the brain parenchyma and tended to increase neutrophil extravasation within the infarcted area. Acute HG increased neurovascular damage for all MCAO durations tested. HTs were observed as early as 90 min after ischemia under hyperglycemic conditions. This model mimics MT ischemia/reperfusion and allows the exploration of brain injury in hyperglycemic conditions.

Prevention of an increase in cortical ligand binding to AMPA receptors may represent a novel mechanism of endogenous brain protection by G-CSF after ischemic stroke

PURPOSE

Using G-CSF deficient mice we recently demonstrated neuroprotective properties of endogenous G-CSF after ischemic stroke. The present follow-up study was designed to check, whether specific alterations in ligand binding densities of excitatory glutamate or inhibitory GABAA receptors may participate in this effect.

METHODS

Three groups of female mice were subjected to 45 minutes of MCAO: wildtype, G-CSF deficient and G-CSF deficient mice substituted with G-CSF. Infarct volumes were determined after 24 hours and quantitative in vitro receptor autoradiography was performed using [3H]MK-801, [3H]AMPA and [3H]muscimol for labeling of NMDA, AMPA and GABAA receptors, respectively. Ligand binding densities were analyzed in regions in the ischemic core, peri-infarct areas and corresponding contralateral regions.

RESULTS

Infarct volumes did not significantly differ between the experimental groups. Ligand binding densities of NMDA and GABAA receptors were widely in the same range. However, AMPA receptor binding densities in G-CSF deficient mice were substantially enhanced compared to wildtype mice. G-CSF substitution in mice lacking G-CSF largely reversed this effect.

CONCLUSIONS

Although infarct volumes did not differ 24 hours after ischemia the increase of AMPA receptor binding densities in G-CSF deficient mice may explain the bigger infarcts previously observed at later time-points with the same stroke model.

Surprising outcomes in cannabinoid CB1/CB2 receptor double knockout mice in two models of ischemia

AIMS

We tested the hypothesis that CB1/CB2 receptor double knockout would produce significant increases in infarct size and volume and significant worsening in clinical score, using two mouse models, one of permanent ischemia and one of ischemia/reperfusion.

MAIN METHODS

Focal cerebral infarcts were created using either photo induced permanent injury or transient middle cerebral artery occlusion. Infarct volume and motor function were evaluated in cannabinoid receptor 1/cannabinoid receptor 2 double knockout mice.

KEY FINDINGS

The results surprisingly revealed that CB1/CB2 double knockout mice showed improved outcomes, with the most improvements in the mouse model of permanent ischemia.

SIGNIFICANCE

Although the number of individuals suffering from stroke in the United States and worldwide will continue to grow, therapeutic intervention for treatment following stroke remains frustratingly limited. Both the cannabinoid 1 receptor (CB1R) and the cannabinoid 2 receptor (CB2R) have been studied in relationship to stroke. Deletion of the CB2R has been shown to worsen outcome, while selective CB2R agonists have been demonstrated to be neuroprotective following stroke. Although initial studies of CB1R knockout mice demonstrated increased injury following stroke, indicating that activation of the CB1R was neuroprotective, later studies of selective antagonists of the CB1R also demonstrated a protective effect. Surprisingly the double knockout animals had improved outcome. Since the phenotype of the double knockout is not dramatically changed, significant changes in the contribution of other homeostatic pathways in compensation for the loss of these two important receptors may explain these apparently contradictory results.