TTC, fluoro-Jade B and NeuN staining confirm evolving phases of infarction induced by middle cerebral artery occlusion

Suppressing nuclear translocation of microglial PKM2 confers neuroprotection via downregulation of neuroinflammation after mouse cerebral ischemia-reperfusion injury

Pyruvate kinase M2 (PKM2) is a key metabolic enzyme. Yet, its role in cerebral ischemia injury remains unclear. In this study we demonstrated that PKM2 expression was increased in the microglia after mouse cerebral ischemia-reperfusion (I/R) injury. We found that microglial polarization-mediated pro-inflammatory effect was mediated by PKM2 after cerebral I/R. Mechanistically, our results revealed that nuclear PKM2 mediated ischemia-induced microglial polarization through association with acetyl-H3K9. Hif-1α mediated the effect of nuclear PKM2/histone H3 on microglial polarization. PKM2-dependent Histone H3/Hif-1α modifications contributed the expression of CCL2 and induced up-regulation of microglial polarization in peri-infarct, resulting in neuroinflammation. Inhibiting nuclear translocation of microglial PKM2 reduced ischemia-induced pro-inflammation and promoted neuronal survival. Together, this study identifies nucleus PKM2 as a crucial mediator for regulating ischemia-induced neuroinflammation, suggesting PKM2 as a potential therapeutic target in ischemic stroke.

Tissue Kallikrein supplementation in ischemic phase protects the neurovascular unit and attenuates reperfusion-induced injury in ischemic stroke

Tissue kallikrein (TK) has emerged as a potential neuroprotective agent in ischemic stroke (IS), yet the optimal timing and mechanisms of TK therapy remain unclear. Here, we established a causal link between lower baseline TK levels and an increased risk of stroke through a retrospective, multicenter cohort study involving 2115 initially non-stroke subjects monitored for 5 years. Sequentially, we observed a notable increase in bradykinin receptor 2 (B2R) levels during the ischemic phase of the IS model, while levels of TK and bradykinin receptor 1 (B1R) remained stable. Intriguingly, both B1R and B2R exhibited a significant elevation 24 h after reperfusion. Further investigations in preclinical models demonstrated that TK supplementation activates the PI3K/AKT signaling pathway via enhanced B2R expression during the ischemic phase, leading to nuclear translocation of Hif-1α. This activation enhances the expression of VEGF and eNOS, thereby fortifying the neurovascular unit. Moreover, it suppresses the activation of the kallikrein-kinin system induced by reperfusion injury, effectively reducing inflammation, ROS production, apoptosis, and endothelial barrier dysfunction. Thus, our findings highlight the significance of TK supplementation during the ischemic phase in attenuating reperfusion-induced injury in IS, providing a mechanistic rationale for determining the optimal timing for TK supplementation therapy.

Escape of Kdm6a from X chromosome is detrimental to ischemic brains via IRF5 signaling

The role of chromatin biology and epigenetics in disease progression is gaining increasing recognition. Genes that escape X chromosome inactivation (XCI) can impact neuroinflammation through epigenetic mechanisms. Our prior research has suggested that the X escapee genes Kdm6a and Kdm5c are involved in microglial activation after stroke in aged mice. However, the underlying mechanisms remain unclear. We hypothesized that Kdm6a/5c demethylate H3K27Me3/H3K4Me3 in microglia respectively, and mediate the transcription of interferon regulatory factor 5 (IRF5) and IRF4, leading to microglial pro-inflammatory responses and exacerbated stroke injury. Aged (17-20 months) Kdm6a/5c microglial conditional knockout (CKO) female mice (one allele of the gene) were subjected to a 60-min middle cerebral artery occlusion (MCAO). Gene floxed females (two alleles) and males (one allele) were included as controls. Infarct volume and behavioral deficits were quantified 3 days after stroke. Immune responses including microglial activation and infiltration of peripheral leukocytes in the ischemic brain were assessed by flow cytometry. Epigenetic modification of IRF5/4 by Kdm6a/5c were analyzed by CUT&RUN assay. The demethylation of H3K27Me3 by kdm6a increased IRF5 transcription; meanwhile Kdm5c demethylated H3K4Me3 to repress IRF5. Both Kdm6a fl/fl and Kdm5c fl/fl mice had worse stroke outcomes compared to fl/y and CKO mice. Gene floxed females showed more robust expression of CD68 in microglia, elevated brain and plasma levels of IL-1β or TNF-α, after stroke. We concluded that IRF5 signaling plays a critical role in mediating the deleterious effect of Kdm6a; whereas Kdm5c's effect is independent of IRF5.

Farrerol Alleviates Cerebral Ischemia-Reperfusion Injury by Promoting Neuronal Survival and Reducing Neuroinflammation

Ischemia-reperfusion (I/R) injury is a key influencing factor in the outcome of stroke. Inflammatory response, oxidative stress, and neuronal apoptosis are among the main factors that affect the progression of I/R injury. Farrerol (FAR) is a natural compound that can effectively inhibit the inflammatory response and oxidative stress. However, the role of FAR in cerebral I/R injury remains unknown. In this study, we found that FAR reduced brain injury and neuronal viability after cerebral I/R injury. Meanwhile, administration of FAR also reduced the inflammatory response of microglia after brain injury. Mechanistically, FAR treatment directly reduced neuronal death after oxygen glucose deprivation/re-oxygenation (OGD/R) through enhancing cAMP-response element binding protein (CREB) activation to increase the expression of downstream neurotrophic factors and anti-apoptotic genes. Moreover, FAR decreased the activation of nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways, inhibited microglia activation, and reduced the production of inflammatory cytokines in microglia after OGD/R treatment or LPS stimulation. The compromised inflammatory response by FAR directly promoted the survival of neurons after OGD/R. In conclusion, FAR exerted a protective effect on cerebral I/R injury by directly decreasing neuronal death through upregulating CREB expression and attenuating neuroinflammation. Therefore, FAR could be a potentially effective drug for the treatment of cerebral I/R injury.

Transcranial direct current stimulation enhances the protective effect of isoflurane preconditioning on cerebral ischemia/reperfusion injury: A new mechanism associated with the nuclear protein Akirin2

AIMS

Ischemic stroke is a major cause of disability and mortality worldwide. Transcranial direct current stimulation (tDCS) and isoflurane (ISO) preconditioning exhibit neuroprotective properties. However, it remains unclear whether tDCS enhances the protective effect of ISO preconditioning on ischemic stroke, and the underlying mechanisms are yet to be clarified.

METHOD

A model of middle cerebral artery occlusion (MCAO), a rat ischemia-reperfusion (I/R) injury model, and an in vitro oxygen-glucose deprivation/re-oxygenation (O/R) model of ischemic injury were developed. ISO preconditioning and tDCS were administered daily for 7 days before MCAO modeling. Triphenyltetrazolium chloride staining, modified neurological severity score, and hanging-wire test were conducted to assess infarct volume and neurological outcomes. Untargeted metabolomic experiments, adeno-associated virus, lentiviral vectors, and small interfering RNA techniques were used to explore the underlying mechanisms.

RESULTS

tDCS/DCS enhanced the protective effects of ISO pretreatment on I/R injury-induced brain damage. This was evidenced by reduced infarct volume and improved neurological outcomes in rats with MCAO, as well as decreased cortical neuronal death after O/R injury. Untargeted metabolomic experiments identified oxidative phosphorylation (OXPHOS) as a critical pathological process for ISO-mediated neuroprotection from I/R injury. The combination of tDCS/DCS with ISO preconditioning significantly inhibited I/R injury-induced OXPHOS. Mechanistically, Akirin2, a small nuclear protein that regulates cell proliferation and differentiation, was found to decrease in the cortex of rats with MCAO and in cortical primary neurons subjected to O/R injury. Akirin2 functions upstream of phosphatase and tensin homolog deleted on chromosome 10 (PTEN). tDCS/DCS was able to further upregulate Akirin2 levels and activate the Akirin2/PTEN signaling pathway in vivo and in vitro, compared with ISO pretreatment alone, thereby contributing to the improvement of cerebral I/R injury.

CONCLUSION

tDCS treatment enhances the neuroprotective effects of ISO preconditioning on ischemic stroke by inhibiting oxidative stress and activating Akirin2-PTEN signaling pathway, highlighting potential of combination therapy in ischemic stroke.

The SWELL1 Channel Promotes Ischemic Brain Damage by Mediating Neuronal Swelling and Glutamate Toxicity

Cytotoxic neuronal swelling and glutamate excitotoxicity are two hallmarks of ischemic stroke. However, the underlying molecular mechanisms are not well understood. Here, it is reported that SWELL1, the essential subunit of the volume-regulated anion channel (VRAC), plays a dual role in ischemic injury by promoting neuronal swelling and glutamate excitotoxicity. SWELL1 expression is upregulated in neurons and astrocytes after experimental stroke in mice. The neuronal SWELL1 channel is activated by intracellular hypertonicity, leading to Cl- influx-dependent cytotoxic neuronal swelling and subsequent cell death. Additionally, the SWELL1 channel in astrocytes mediates pathological glutamate release, indicated by increases in neuronal slow inward current frequency and tonic NMDAR current. Pharmacologically, targeting VRAC with a new inhibitor, an FDA-approved drug Dicumarol, attenuated cytotoxic neuronal swelling and cell death, reduced astrocytic glutamate release, and provided significant neuroprotection in mice when administered either before or after ischemia. Therefore, these findings uncover the pleiotropic effects of the SWELL1 channel in neurons and astrocytes in the pathogenesis of ischemic stroke and provide proof of concept for therapeutically targeting it in this disease.

Phosphorus Dendrimers Co-deliver Fibronectin and Edaravone for Combined Ischemic Stroke Treatment via Cooperative Modulation of Microglia/Neurons and Vascular Regeneration

The development of new multi-target combination treatment strategies to tackle ischemic stroke (IS) remains to be challenging. Herein, a proof-of-concept demonstration of an advanced nanomedicine formulation composed of macrophage membrane (MM)-camouflaged phosphorous dendrimer (termed as AK137)/fibronectin (FN) nanocomplexes (NCs) loaded with antioxidant edaravone (EDV) to modulate both microglia and neurons for effective IS therapy is showcased. The created MM@AK137-FN/EDV (M@A-F/E) NCs with a mean size of 260 nm possess good colloidal stability, sustained EDV release kinetics, and desired cytocompatibility. By virtue of MM decoration, the M@A-F/E NCs can cross blood-brain barrier, act on microglia to exert the anti-inflammatory (AK137 and FN) and antioxidative (FN and EDV) effects in vitro for oxidative stress alleviation, microglia M2 polarization, and reduction of pro-inflammatory cytokine secretion, and act on neuron cells to be anti-apoptotic. In a transient middle cerebral artery occlusion rat model, the developed M@A-F/E NCs can exert enhanced antioxidant/anti-inflammatory/anti-apoptotic therapeutic effects to comprehensively regulate the brain microenvironment and promote vascular regeneration to collaboratively restore the blood flow after ischemia-reperfusion. The designed MM-coated NCs composed of all-active ingredients of phosphorous dendrimers, FN, and EDV that can fully regulate the brain inflammatory microenvironment may expand their application scope in other neurodegenerative diseases.

Central IRF4/5 Signaling Are Critical for Microglial Activation and Impact on Stroke Outcomes

Microglia and monocytes play a critical role in immune responses to cerebral ischemia. Previous studies have demonstrated that interferon regulatory factor 4 (IRF4) and IRF5 direct microglial polarization after stroke and impact outcomes. However, IRF4/5 are expressed by both microglia and monocytes, and it is not clear if it is the microglial (central) or monocytic (peripheral) IRF4-IRF5 regulatory axis that functions in stroke. In this work, young (8-12 weeks) male pep boy (PB), IRF4 or IRF5 flox, and IRF4 or IRF5 conditional knockout (CKO) mice were used to generate 8 types of bone marrow chimeras, to differentiate the role of central (PB-to-IRF CKO) vs. peripheral (IRF CKO-to-PB) phagocytic IRF4-IRF5 axis in stroke. Chimeras generated from PB and flox mice were used as controls. All chimeras were subjected to 60-min middle cerebral artery occlusion (MCAO) model. Three days after the stroke, outcomes and inflammatory responses were analyzed. We found that PB-to-IRF4 CKO chimeras had more robust microglial pro-inflammatory responses than IRF4 CKO-to-PB chimeras, while ameliorated microglial response was seen in PB-to-IRF5 CKO vs. IRF5 CKO-to-PB chimeras. PB-to-IRF4 or IRF5 CKO chimeras had worse or better stroke outcomes respectively than their controls, whereas IRF4 or 5 CKO-to-PB chimeras had similar outcomes compared to controls. We conclude that the central IRF4/5 signaling is responsible for microglial activation and mediates stroke outcomes.

Striatal Blood Flow Changes by Middle Cerebral Artery Occlusion and Its Effect on Neurological Deficits in Mice

OBJECTIVE

We attempted to record the regional cerebral blood flow (CBF) simultaneously at various regions of the cerebral cortex and the striatum during middle cerebral artery (MCA) occlusion and to evaluate neurological deficits and infarct formation.

METHODS

In male C57BL/6J mice, CBF was recorded in three regions including the ipsilateral cerebral cortex and the striatum with laser Doppler flowmeters, and the origin of MCA was occluded with a monofilament suture for 15-90 min. After 48 h, neurological deficits were evaluated, and infarct was examined by triphenyltetrazolium chloride (TTC) staining.

RESULTS

CBF decrease in the striatum was approximately two-thirds of the MCA-dominant region of the cortex during MCA occlusion. The characteristic CBF fluctuation because of spontaneously occurred spreading depolarization observed throughout the cortex was not found in the striatum. Ischemic foci with slight lower staining to TTC were found in the ipsilateral striatum in MCA-occluded mice for longer than 30 min (n = 54). Twenty-nine among 64 MCA-occluded mice exhibited neurological deficits even in the absence of apparent infarct with minimum staining to TTC in the cortex, and the severity of neurological deficits was not correlated with the size of the cortical infarct.

CONCLUSION

Neurological deficits might be associated with the ischemic striatum rather than with cortical infarction.

p39 Affects Myelin Formation in Cerebral Ischemic Injury

Stroke is a significant public health issue, and research has consistently focused on studying the mechanisms of injury and identifying new targets. As a CDK5 activator, p39 plays a crucial role in various diseases. In this article, we will explore the role and mechanism of p39 in cerebral ischemic injury. We measured the level of p39 using western blot and QPCR at various time points following cerebral ischemia-reperfusion (I/R) injury. The results indicated a significant reduction in the level of p39. TTC staining and behavioral results indicate that the knockout of p39 (p39KO) provides neuroprotection in the short-term. Interestingly, the behavioral dysfunction in p39KO mice was exacerbated after the repair phase of I/R. Further study revealed that this deterioration may be due to demyelination induced by elevated p35 levels. In summary, our study offers profound insights into the significance of p39 in both the acute and repair stages of ischemic injury recovery and a theoretical foundation for future therapeutic drug exploration.

Brain Swelling versus Infarct Size: A Problematizing Review

In human stroke, brain swelling is an important predictor of neurological outcome and mortality, yet treatments to reduce or prevent brain swelling are extremely limited, due in part to an inadequate understanding of mechanisms. In preclinical studies on cerebroprotection in animal models of stroke, historically, the focus has been on reducing infarct size, and in most studies, a reduction in infarct size has been associated with a corresponding reduction in brain swelling. Unfortunately, such findings on brain swelling have little translational value for treating brain swelling in patients with stroke. This is because, in humans, brain swelling usually becomes evident, either symptomatically or radiologically, days after the infarct size has stabilized, requiring that the prevention or treatment of brain swelling target mechanism(s) that are independent of a reduction in infarct size. In this problematizing review, we highlight the often-neglected concept that brain edema and brain swelling are not simply secondary, correlative phenomena of stroke but distinct pathological entities with unique molecular and cellular mechanisms that are worthy of direct targeting. We outline the advances in approaches for the study of brain swelling that are independent of a reduction in infarct size. Although straightforward, the approaches reviewed in this study have important translational relevance for identifying novel treatment targets for post-ischemic brain swelling.

The Hydrogen Sulfide Donor AP39 Reduces Glutamate-mediated Excitotoxicity in a Rat Model of Brain Ischemia

The vast majority of stroke cases are classified as ischemic stroke, but effective pharmacotherapy strategies to treat brain infarction are still limited. Glutamate, which is a primary mediator of excitotoxicity, contributes to neuronal damage in numerous pathologies, including ischemia. The aim of this study was to investigate the effect of the hydrogen sulfide donor AP39 on excitotoxicity. AP39 was administered as a single dose of 100 nmol/kg b.w. i.v. 10 min after the restoration of blood flow and 100 min after middle cerebral artery occlusion (MCAO) in male Sprague-Dawley rats. Neurological deficits by Phillips's score, and infarct volume by TTC staining were evaluated (n = 8). LC-MS was used to determine the extracellular glutamate concentration in microdialysates collected intrasurgically and from freely moving animals 24 h and 3 days after reperfusion (n = 6). The expression of proteins involved in the regulation of glutamatergic transmission was investigated 24 h after reperfusion by Western-blot analysis (n = 6). The results were verified by double-immunostaining of brain cryosections (n = 6). The results showed a significant longitudinal decrease in extracellular glutamate concentrations in the motor cortex and hippocampus in MCAO + AP39 rats compared to MCAO rats. Moreover, the administration of AP39 increased the content of the GLT-1 transporter and reduced the content of VGLUT1 in the ischemic core. Upregulation of the GLT-1 transporter responsible for glutamate reuptake from the synaptic cleft, and downregulation of VGLUT1, which regulates glutamate transport to synaptic vesicles, indicate that these are important mechanisms by which AP39 reduces extracellular glutamate concentrations and, consequently, excitotoxicity after ischemia.

Changes in excitatory amino acid transporters in response to remote ischaemic preconditioning and glutamate excitotoxicity

The successful implementation of remote ischaemic conditioning as a clinical neuroprotective strategy requires a thorough understanding of its basic principles, which can be modified for each patient. The mechanisms of glutamate homeostasis appear to be a key component. In the current study, we focused on the brain-to-blood glutamate shift mediated by glutamate transporters (excitatory amino acid transports [EAATs]) and the effect of remote ischaemic preconditioning (RIPC) as a mediator of ischaemic tolerance. We used model mimicking ischaemia-mediated excitotoxicity (intracerebroventricular administration of glutamate) to avoid the indirect effect of ischaemia-triggered mechanisms. We found quantitative changes in EAAT2 and EAAT3 and altered membrane trafficking of EAAT1 on the cells of the choroid plexus. These changes could underlie the beneficial effects of ischaemic tolerance. There was reduced oxidative stress and increased glutathione level after RIPC treatment. Moreover, we determined the stimulus-specific response on EAATs. While glutamate overdose stimulated EAAT2 and EAAT3 overexpression, RIPC induced membrane trafficking of EAAT1 and EAAT2 rather than a change in their expression. Taken together, mechanisms related to glutamate homeostasis, especially EAAT-mediated transport, represents a powerful tool of ischaemic tolerance and allow a certain amount of flexibility based on the stimulus used.

Jasminoidin reduces ischemic stroke injury by regulating microglia polarization via PASK-EEF1A1 axis

Jasminoidin (JAS) can alleviate ischemic stroke (IS) injury, but its molecular mechanism remains undefined. The polarization of microglia affects IS process. This research is powered to probe whether the molecular mechanism of JAS for IS treatment is coupled with microglia polarization. IS modeling in mice was accomplished by middle cerebral artery occlusion (MCAO) and model mice were injected with 25 and 50 mg/mL JAS, followed by determination of infarct volume, brain water content, and histological changes in mouse brains. The microglia modeling was performed by 1-h oxygen-glucose deprivation and 24-h reoxygenation. Oxygen-glucose deprivation/reoxygenation (OGD/R)-induced microglia were treated with JAS and transfected with Per-Arnt-Sim kinase (PASK)-overexpressing plasmid, subsequent to which cell viability and lactate dehydrogenase (LDH) level were determined. The mRNA or protein expressions of examined genes in microglia and brain tissues were detected by quantitative real-time polymerase chain reaction or western blot. MCAO-induced massive infarction, edema, and injury in mouse brain tissues, upregulated interleukin-1 beta (IL-1β), FcγRIIB (CD32), tumor necrosis factor alpha (TNF-α), PASK, p-eukaryotic elongation factor 1A1 (EEF1A1), and p-EEF1A1/EEF1A1 levels, but downregulated mannose receptor 1 (CD206), arginase-1 (Arg-1) and interleukin-10 (IL-10), and EEF1A1 expressions, which was reversed by JAS. OGD/R treatment decreased microglial viability as well as expressions of CD206, Arg-1, IL-10, and EEF1A1, yet increased cytotoxicity and levels of IL-1β, CD32, TNF-α, PASK, p-EEF1A1, and p-EEF1A1/EEF1A1, which was reversed by JAS. PASK overexpression reversed the effects of JAS on microglia. JAS reduces IS injury by regulating microglia polarization via PASK-EEF1A1 axis.

Microglia Exhibit Distinct Heterogeneity Rather than M1/M2 Polarization within the Early Stage of Acute Ischemic Stroke

The classification of microglial M1/M2 polarization in the acute phase of ischemic stroke remains controversial, which has limited further advances in neuroprotective strategy. To thoroughly assess the microglial phenotypes, we made the middle cerebral artery occlusion model in mice to simulate the acute pathological processes of ischemic stroke from normal conditions to acute cerebral ischemia and then to the early reperfusion period. The temporal changes in gene profiles, cell subtypes, and microglial function were comprehensively analyzed using single-cell RNA sequencing. We identified 37,614 microglial cells and divided them into eight distinct subpopulations. Mic_home, Mic_pre1, and Mic_pre2 subpopulations were three clusters mainly composed of cells from the control samples, in which Mic_home was a homeostatic subpopulation characterized by high expression of Hpgd and Tagap, and Mic_pre1 and Mic_pre2 were two clusters with preliminary inflammatory activation characteristics marked by P2ry13 and Wsb1 respectively. Mic_M1L1 and Mic_M1L2 subpopulations exhibited M1-like polarization manifested by the upregulation of inflammatory genes after ischemic stroke, while the intrinsic heterogeneity on the level of inflammatory responses and neurotrophic support properties was observed. Moreover, we identified three unique clusters of cells with low inflammation levels. Mic_np1, Mic_np2, and Mic_np3 were characterized by high expression of Arhgap45, Rgs10, and Pkm respectively. However, these cells did not show significant M2-like characteristics and their classic microglia function was also attenuated. These subpopulations exhibited higher activation of neuropeptide functional pathways. At last, we performed cell-cell communication analysis and identified major couplings contributing to the interaction between microglia and other cell populations. In summary, our study elucidated the temporal heterogeneity of microglia in the acute phase of ischemic stroke, which may facilitate the identification of effective neuroprotective targets to curb ischemic damage at an early stage.

Cathepsin B knockout confers significant brain protection in the mouse model of stroke

BACKGROUND

Significant advances have been made in our understanding of the endolysosomal cycle. Disruption of this cycle leads to cell death. The objective of this study aims to investigate the role of disrupted endolysosomal cycle in brain ischemia-reperfusion injury.

METHODS

A total of 57 mice were randomly assigned into four experimental groups: (i) wildtype (wt) sham control; (ii) wt middle cerebral artery occlusion (MCAO); (iii) cathepsin B (CTSB) knockout (KO) sham control; and (iv) CTSB KO MCAO. Mice were subjected either to 0 min (sham) or 40 min of MCAO, followed by reperfusion for 1 or 7 days. Physical and behavioral examinations were conducted in the 7-day reperfusion group for 7 consecutive days after MCAO. Confocal microscopy was used to assess the levels, redistributions, and co-localizations of key endolysosomal cycle-related proteins. Histopathology was examined by light microscopy.

RESULTS

Confocal microscopy revealed a significant accumulation of CTSB in post-ischemic penumbral neurons relative to those in the sham group. In addition, N-ethylmaleimide sensitive factor ATPase (NSF) was irreversibly depleted in these neurons. Furthermore, CTSB-immunostained structures were enlarged and diffusely distributed in both the cytoplasm and extracellular space, indicating the release of CTSB from post-ischemic neurons. Compared to wt mice, CTSB KO mice showed a significant decrease in hippocampal injury area, a significant increase in the number of survival neurons in the striatal core area, and a significant improvement in physical and functional performance in post-MCAO mice.

CONCLUSION

Brain ischemia leads to a cascade of events leading to inactivation of NSF, disruption of the endolysosomal cycle, endolysosomal structural buildup and damage, and the release of CTSB, eventually resulting in brain ischemia reperfusion injury. CTSB KO in mice protected the brain from ischemia-reperfusion injury.

X, but not Y, Chromosomal Complement Contributes to Stroke Sensitivity in Aged Animals

Post-menopausal women become vulnerable to stroke and have poorer outcomes and higher mortality than age-matched men, and previous studies suggested that sex chromosomes play a vital role in mediating stroke sensitivity in the aged. It is unknown if this is due to effects of the X or Y chromosome. The present study used the XY* mouse model (with four genotypes: XX and XO gonadal females and XY and XXY gonadal males) to compare the effect of the X vs. Y chromosome compliment in stroke. Aged (18-20 months) and gonadectomized young (8-12 weeks) mice were subjected to a 60-min middle cerebral artery occlusion. Infarct volume and behavioral deficits were quantified 3 days after stroke. Microglial activation and infiltration of peripheral leukocytes in the aged ischemic brain were assessed by flow cytometry. Plasma inflammatory cytokine levels by ELISA, and brain expression of two X chromosome-linked genes, KDM6A and KDM5C by immunochemistry, were also examined. Both aged and young XX and XXY mice had worse stroke outcomes compared to XO and XY mice, respectively; however, the difference between XX vs. XXY and XO vs. XY aged mice was minimal. Mice with two copies of the X chromosome showed more robust microglial activation, higher brain-infiltrating leukocytes, elevated plasma cytokine levels, and enhanced co-localization of KDM6A and KDM5C with Iba1+ cells after stroke than mice with one X chromosome. The number of X chromosomes mediates stroke sensitivity in aged mice, which might be processed through the X chromosome-linked genes and the inflammatory responses.

Glycogen synthase kinase-3β mediates toll-like receptors 4/nuclear factor kappa-B-activated cerebral ischemia-reperfusion injury through regulation of fat mass and obesity-associated protein

BACKGROUND

Glycogen synthase kinase-3β (GSK3β), fat mass and obesity-associated protein (FTO), and toll-like receptors 4 (TLR4) take on critical significance in different biological processes, whereas their interactions remain unclear. The objective was the investigation of the interaction effect in cerebral ischemia-reperfusion (I/R) injury.

METHODS

The function of the cerebral cortex in the mouse middle cerebral artery occlusion (MCAO) model (each group n = 6) and P12 cells oxygen-glucose deprivation/reoxygenation (OGD/R) model was analyzed using short hairpin GSK3β lentivirus and overexpression of FTO lentivirus (in vitro), TLR4 inhibitor (TAK242), and LiCl to regulate GSK3β, FTO, TLR4 expression, and GSK3β activity, respectively.

RESULTS

After GSK3β knockdown in the OGD/R model of PC12 cells, the levels of TLR4 and p-p65 were lower than in the control, and the level of FTO was higher than in the control. Knockdown GSK3β reversed the OGD/R-induced nuclear factor kappa-B transfer to the intranuclear nuclei. As indicated by the result, TLR4 expression was down-regulated by overexpressed FTO, and TLR4 expression was up-regulated notably after inhibition of FTO with the use of R-2HG. After the inhibition of the activity of GSK3β in vivo, the reduction of FTO in mice suffering from MCAO was reversed.

CONCLUSIONS

Our research shows that GSK3β/FTO/TLR4 pathway contributes to cerebral I/R injury.

Selenium supplementation provides potent neuroprotection following cerebral ischemia in mice

Despite progress in reperfusion therapy, functional recovery remains suboptimal in many stroke patients, with oxidative stress, inflammation, dysbiosis, and secondary neurodegeneration constituting the major hurdles to recovery. The essential trace element selenium is emerging as a promising therapeutic agent for stroke. However, although several rodent studies have shown that selenium can protect against cell loss following cerebral ischemia, no study has yet examined whether selenium can enhance long-term functional recovery. Moreover, published studies have typically reported a single mechanism of action underlying selenium-mediated stroke recovery. However, we propose that selenium is more likely to have multifaceted actions. Here, we show that selenomethionine confers a potent neuroprotective effect in a canonical filament-induced transient middle cerebral artery occlusion (tMCAO) mouse model. Post-tMCAO selenium treatment significantly reduces the cerebral infarct volume, oxidative stress, and ferroptosis and enhances post-tMCAO motor performance in the acute phase after stroke. Moreover, analysis of the gut microbiota reveals that acute selenium treatment reverses stroke-induced gut dysbiosis. Longer-term selenium supplementation activates intrinsic neuroprotective mechanisms, prevents secondary neurodegeneration, alleviates systemic inflammation, and diminishes gut microbe-derived circulating trimethylamine N-oxide. These findings demonstrate that selenium treatment even after cerebral ischemia has long-term and multifaceted neuroprotective effects, highlighting its clinical potential.

Preclinical models of middle cerebral artery occlusion: new imaging approaches to a classic technique

Stroke remains a major burden on patients, families, and healthcare professionals, despite major advances in prevention, acute treatment, and rehabilitation. Preclinical basic research can help to better define mechanisms contributing to stroke pathology, and identify therapeutic interventions that can decrease ischemic injury and improve outcomes. Animal models play an essential role in this process, and mouse models are particularly well-suited due to their genetic accessibility and relatively low cost. Here, we review the focal cerebral ischemia models with an emphasis on the middle cerebral artery occlusion technique, a "gold standard" in surgical ischemic stroke models. Also, we highlight several histologic, genetic, and in vivo imaging approaches, including mouse stroke MRI techniques, that have the potential to enhance the rigor of preclinical stroke evaluation. Together, these efforts will pave the way for clinical interventions that can mitigate the negative impact of this devastating disease.

The critical role of KLF4 in regulating the activation of A1/A2 reactive astrocytes following ischemic stroke

BACKGROUND

We have previously demonstrated that the expression of kruppel-like transcription factor-4 (KLF-4) is upregulated in astrocytes following acute ischemic stroke (AIS) and found that KLF4 confers vascular protection against cerebral ischemic injury. However, the functional role of KLF4 in astrocyte after AIS is far from clear.

METHODS

The intrinsic relationship between KLF4 and A1/A2 reactive astrocytes and the impact of astrocytic KLF4 on the activation of A1/A2 subtype astrocytes were evaluated in middle cerebral artery occlusion (MCAO) mice and oxygen-glucose deprivation and restoration (OGD/R) astrocytes.

RESULTS

Our results demonstrated that astrocytic KLF4 expression and complement C3-positive A1 and S100 calcium binding protein A10 (S100A10)-positive A2 astrocytes were induced in the ischemic penumbra following focal cerebral ischemia, and the time course of upregulation of astrocytic KLF4 correlated closely with the activation of A2 astrocytes. The dual immunofluorescent studies displayed that in the ischemic hemisphere, where the high levels of KLF4 were expressed, there were relatively low levels of C3 expressed in the reactive astrocytes and vice versa, but KLF4 was always co-stained well with S100A10. Mechanistic analyses revealed that astrocytic KLF4 inhibited the activation of A1 astrocyte but promoted A2 astrocyte polarization after OGD/R by modulating expressions of nuclear factor-kB.

CONCLUSIONS

Astrocyte-derived KLF4 has a critical role in regulating the activation of A1/A2 reactive astrocytes following AIS.

Rodent Stroke Models to Study Functional Recovery and Neural Repair

Rodent ischemic stroke models are essential research tools for studying this highly prevalent disease and represent a critical element in the translational pipeline for development of new therapies. The majority of ischemic stroke models have been developed to study the acute phase of the disease and neuroprotective strategies, but a subset of models is better suited for studying stroke recovery. Each model therefore has characteristics that lend itself to certain types of investigations and outcome measures, and it is important to consider both explicit and implicit details when designing experiments that utilize each model. The following chapter briefly summarizes the known aspects of the main rodent stroke models with emphasis on their clinical relevance and suitability for studying recovery and neural repair following stroke.

Spatiotemporal profile of neutrophil extracellular trap formation in a mouse model of ischemic stroke

Background

Thromboinflammatory processes modulate the complex pathophysiology of cerebral ischemia-reperfusion (I/R) injury in ischemic stroke, but the exact underlying mechanisms remain poorly understood. Emerging evidence indicates that neutrophil extracellular traps (NETs) might play an important role in the thromboinflammatory cascade. In addition, the link between von Willebrand factor (VWF) and neutrophil recruitment in the ischemic brain might promote thromboinflammation, possibly by the formation of NETs.

Objectives

To study NET formation in a murine model of cerebral I/R injury in ischemic stroke.

Methods

The filament-induced transient middle cerebral artery occlusion model was used to induce 60 minutes of focal cerebral ischemia after which reperfusion was allowed. At different time points postischemia, NETs were identified in the ischemic mouse brain using quantitative immunofluorescence microscopy.

Results

NETs could be identified in the ipsilateral brain hemisphere. Interestingly, NETs could already be detected at 6 hours poststroke. Their presence increased at 12 hours, was highest at 24 hours, and decreased again 48 hours postischemia. Remarkably, NETs were predominantly localized within the brain vasculature postischemia, suggesting that NETs play a role in secondary microthrombosis. Strikingly, NET formation was significantly decreased in VWF-deficient mice compared to littermate wild-type mice 24 hours postischemia, indicating a possible role for VWF in promoting NETosis in the ischemic brain.

Conclusion

This study identified the spatiotemporal profile of NET formation in a mouse model of cerebral I/R injury in ischemic stroke. NETs, potentially in combination with VWF, might be attractive targets for the development of novel therapeutic strategies in ischemic stroke treatment.

Optimizing intraluminal monofilament model of ischemic stroke in middle-aged Sprague-Dawley rats

Intraluminal monofilament model of middle cerebral artery occlusion (MCAO) is widely adopted for ischemic stroke; and Sprague-Dawley (SD) rats are commonly used rodents for preclinical research. Due to the paucity of information on the appropriate monofilament size for inducing MCAO in SD rats and the importance of including middle-aged models in ischemic stroke studies, we aimed to: (i). determine an appropriate Doccol^® monofilament size for middle-aged male SD rats which weighed > 500 g following 24-h transient MCAO survival as well as (ii). demonstrate the optimal Doccol^® filament size for middle-aged males (≤ 500 g) and females (273-300 g) while using young adult male SD rats (372-472 g) as control for severity of infarct volume following 7-days post-MCAO. All rats were subjected to 90-min transient MCAO. We show that 0.43 mm Doccol^® monofilament size is more appropriate to induce large infarct lesion and optimal functional deficit when compared to 0.45 mm and 0.47 mm at 24 h post-MCAO. Our data on infarct volumes at 7 days post-MCAO as well as the observed weight loss and functional deficits at post-MCAO days 1, 3 and 7 demonstrate that 0.41 mm, 0.37 mm and 0.39 mm are optimal Doccol^® filament sizes for middle-aged male (477.3 ± 39.61 g) and female (302.6 ± 26.28 g) as well as young-adult male (362.2 ± 28.38 g) SD rats, respectively.

A steroid receptor coactivator small molecule "stimulator" attenuates post-stroke ischemic brain injury

Introduction: Pathologic remodeling of the brain following ischemic stroke results in neuronal loss, increased inflammation, oxidative stress, astrogliosis, and a progressive decrease in brain function. We recently demonstrated that stimulation of steroid receptor coactivator 3 with the small-molecule stimulator MCB-613 improves cardiac function in a mouse model of myocardial ischemia. Since steroid receptor coactivators are ubiquitously expressed in the brain, we reasoned that an MCB-613 derivative (MCB-10-1), could protect the brain following ischemic injury. To test this, we administered MCB-10-1 to rats following middle cerebral artery occlusion and reperfusion. Methods: Neurologic impairment and tissue damage responses were evaluated on day 1 and day 4 following injury in rats treated with control or 10-1. Results: We show that 10-1 attenuates injury post-stroke. 10-1 decreases infarct size and mitigates neurologic impairment. When given within 30 min post middle cerebral artery occlusion and reperfusion, 10-1 induces lasting protection from tissue damage in the ischemic penumbra concomitant with: (1) promotion of reparative microglia; (2) an increase in astrocyte NRF2 and GLT-1 expression; (3) early microglia activation; and (4) attenuation of astrogliosis. Discussion: Steroid receptor coactivator stimulation with MCB-10-1 is a potential therapeutic strategy for reducing inflammation and oxidative damage that cause neurologic impairment following an acute ischemic stroke.

The immunopathology of B lymphocytes during stroke-induced injury and repair

B cells, also known as B lymphocytes or lymphoid lineage cells, are a historically understudied cell population with regard to brain-related injuries and diseases. However, an increasing number of publications have begun to elucidate the different phenotypes and roles B cells can undertake during central nervous system (CNS) pathology, including following ischemic and hemorrhagic stroke. B cell phenotype is intrinsically linked to function following stroke, as they may be beneficial or detrimental depending on the subset, timing, and microenvironment. Factors such as age, sex, and presence of co-morbidity also influence the behavior of post-stroke B cells. The following review will briefly describe B cells from origination to senescence, explore B cell function by integrating decades of stroke research, differentiate between the known B cell subtypes and their respective activity, discuss some of the physiological influences on B cells as well as the influence of B cells on certain physiological functions, and highlight the differences between B cells in healthy and disease states with particular emphasis in the context of ischemic stroke.

Ligustroflavone exerts neuroprotective activity through suppression of NLRP1 inflammasome in ischaemic stroke mice

Inflammation is thought to play an important role in the pathophysiology of ischaemic stroke, which is a main cause of disability and morbidity worldwide. Inhibition of the NOD-like receptor protein 1 (NLRP1) inflammasome has been reported to alleviate the inflammatory response in cell and animal models. Ligustroflavone (LIG) is a compound derived from Ligustrum lucidum, which shows anti-inflammatory activity and may play a beneficial role in a number of neurological diseases. To date, the potential for LIG to act through NLRP1 as a treatment for ischemic stroke has not been studied. The present study established an ischaemic stroke model by middle cerebral artery occlusion (MCAO). Modified neurological severity scoring, open-field and the Rotarod test were used to assess neurological deficits. Staining with Hoechst 33258 and western blotting were used to evaluate neuronal damage. Expression levels of NLRP1 inflammasome complexes and inflammatory cytokines were determined using western blotting, enzyme-linked immunosorbent assay and reverse transcription-quantitative PCR. Treatment with LIG minimized the impairment of neurological function and blocked neuronal damage in MCAO mice. In addition, treatment with LIG attenuated the upregulation of expression levels of the NLRP1 inflammasome complexes and the inflammatory cytokines TNF-α, IL-18, IL-6 and IL-1β. Overall, LIG played an important role in anti-inflammatory and neuroprotective activity in MCAO models of ischaemic stroke.

Aging Is Associated With Lower Neuroactive Steroids and Worsened Outcomes Following Cerebral Ischemia in Male Mice

Ischemic stroke is a leading cause of disability and death, and aging is the main nonmodifiable risk factor. Following ischemia, neuroactive steroids have been shown to play a key role in cerebroprotection. Thus, brain steroid concentrations at the time of injury as well as their regulation after stroke are key factors to consider. Here, we investigated the effects of age and cerebral ischemia on steroid levels, behavioral outcomes, and neuronal degeneration in 3- and 18-month-old C57BL/6JRj male mice. Ischemia was induced by middle cerebral artery occlusion for 1 hour followed by reperfusion (MCAO/R) and analyses were performed at 6 hours after MCAO. Extended steroid profiles established by gas chromatography coupled with tandem mass spectrometry revealed that (1) brain and plasma concentrations of the main 5α-reduced metabolites of progesterone, 11-deoxycorticosterone, and corticosterone were lower in old than in young mice; (2) after MCAO/R, brain concentrations of progesterone, 5α-dihydroprogesterone, and corticosterone increased in young mice; and (3) after MCAO/R, brain concentrations of 5α-reduced metabolites of progesterone, 3α5α-tetrahydrodeoxycorticosterone, and 3β5α-tetrahydrodeoxycorticosterone were lower in old than in young mice. After ischemia, old mice showed increased sensori-motor deficits and more degenerating neurons in the striatum than young mice. Altogether, these findings strongly suggest that the decreased capacity of old mice to metabolize steroids toward the 5α-reduction pathway comparatively to young mice may contribute to the worsening of their stroke outcomes.

Regulation of microglial activation in stroke in aged mice: a translational study

Numerous neurochemical changes occur with aging and stroke mainly affects the elderly. Our previous study has found interferon regulatory factor 5 (IRF5) and 4 (IRF4) regulate neuroinflammation in young stroke mice. However, whether the IRF5-IRF4 regulatory axis has the same effect in aged brains is not known. In this study, aged (18-20-month-old), microglial IRF5 or IRF4 conditional knockout (CKO) mice were subjected to a 60-min middle cerebral artery occlusion (MCAO). Stroke outcomes were quantified at 3d after MCAO. Flow cytometry and ELISA were performed to evaluate microglial activation and immune responses. We found aged microglia express higher levels of IRF5 and lower levels of IRF4 than young microglia after stroke. IRF5 CKO aged mice had improved stroke outcomes; whereas worse outcomes were seen in IRF4 CKO vs. their flox controls. IRF5 CKO aged microglia had significantly lower levels of IL-1β and CD68 than controls; whereas significantly higher levels of IL-1β and TNF-α were seen in IRF4 CKO vs. control microglia. Plasma levels of TNF-α and MIP-1α were decreased in IRF5 CKO vs. flox aged mice, and IL-1β/IL-6 levels were increased in IRF4 CKO vs. controls. The anti-inflammatory cytokines (IL-4/IL-10) levels were higher in IRF5 CKO, and lower in IRF4 CKO aged mice vs. their flox controls. IRF5 and IRF4 signaling drives microglial pro- and anti-inflammatory response respectively; microglial IRF5 is detrimental and IRF4 beneficial for aged mice in stroke. IRF5-IRF4 axis is a promising target for developing new, effective therapeutic strategies for the cerebral ischemia.

Plasma mid-regional pro-adrenomedullin: A biomarker of the ischemic penumbra in hyperacute stroke

Reperfusion therapy has improved the outcomes of ischemic stroke but also emphasized the importance of ischemic penumbra. However, blood biomarkers are currently unavailable for this region. Adrenomedullin (ADM) is a neuroprotective peptide, secreted in a compensatory response to brain ischemia. We thus investigated whether an increase in mid-regional pro-ADM (MR-proADM), a stable peptide fragment of the ADM precursor, could act as a biomarker by predicting the ischemic penumbra in hyperacute ischemic stroke (HAIS). We prospectively enrolled consecutive HAIS patients (n = 119; median age, 77 years; male, 59.7%) admitted to our institutes from July 2017 to March 2019 and evaluated plasma MR-proADM levels within 4.5 h of onset. MR-proADM levels in HAIS were compared to healthy controls (n = 1298; median age, 58 years; male, 33.2%) in the Japan Multi-Institutional Collaborative Cohort Study from 2013 to 2017. Furthermore, we evaluated whether MR-proADM levels were associated with the penumbra estimated by clinical-diffusion mismatch (CDM) (National Institute of Health Stroke Scale [NIHSS] ≥8, diffusion ischemic core volume ≤25 ml), or magnetic resonance angiography-diffusion-weighted imaging mismatch (MDM) (NIHSS ≥5, a proximal vessel occlusion with core volume ≤25 ml, or a proximal vessel stenosis/distal vessel occlusion with core volume ≤15 ml). In a case-control study, multivariate logistic analysis showed a significant association between HAIS and MR-proADM ≥0.54 nmol/L (adjusted odds ratio, 7.92 [95% CI, 4.17-15.02], p < 0.001). Though MR-proADM levels in HAIS did not correlate with the ischemic core volume (r_s  = 0.09, p = 0.348), they were higher in HAIS with CDM (n = 34; 0.81 vs. 0.61 nmol/L, p < 0.001) or MDM (n = 26; 0.83 vs. 0.62 nmol/L, p = 0.002). These differences remained significant after adjusting baseline factors (adjusted odds ratio, 4.06 [95% CI, 1.31-12.55], p = 0.015 and 4.65 [1.35-16.11], p = 0.015, respectively). Plasma MR-proADM is elevated in HAIS, especially in those with a substantial penumbra, suggesting potential as a blood biomarker in this region.

The Ca2+-gated channel TMEM16A amplifies capillary pericyte contraction and reduces cerebral blood flow after ischemia

Pericyte-mediated capillary constriction decreases cerebral blood flow in stroke after an occluded artery is unblocked. The determinants of pericyte tone are poorly understood. We show that a small rise in cytoplasmic Ca2+ concentration ([Ca2+]i) in pericytes activated chloride efflux through the Ca2+-gated anion channel TMEM16A, thus depolarizing the cell and opening voltage-gated calcium channels. This mechanism strongly amplified the pericyte [Ca2+]i rise and capillary constriction evoked by contractile agonists and ischemia. In a rodent stroke model, TMEM16A inhibition slowed the ischemia-evoked pericyte [Ca2+]i rise, capillary constriction, and pericyte death; reduced neutrophil stalling; and improved cerebrovascular reperfusion. Genetic analysis implicated altered TMEM16A expression in poor patient recovery from ischemic stroke. Thus, pericyte TMEM16A is a crucial regulator of cerebral capillary function and a potential therapeutic target for stroke and possibly other disorders of impaired microvascular flow, such as Alzheimer's disease and vascular dementia.

Biophoton imaging identification of delayed functional neural circuit injury after cerebral ischemia-reperfusion

BACKGROUND

The evaluation of structural changes after stroke has made great progress; however, it remains difficult to evaluate functional neural changes.

NEW METHOD

Here, we report a novel imaging technique that could monitor delayed functional neural circuit injury in an animal model of cerebral ischemia-reperfusion. The changes in 50 mM glutamate-induced biophotonic activities in functional neural circuits in rat brain slices after middle cerebral artery occlusion were investigated with an ultraweak biophoton imaging system.

RESULTS

Six hours after ischemia-reperfusion, the rats presented a significant decrease in motion ability together with a large part of the unstained 2,3,5-Triphenyltetrazolium chloride (TTC) area in the ischemia-reperfusion side, whereas the intensity of the biophoton emissions was consistent on both the ischemia-reperfusion and non-ischemic sides of brain slices. Twenty-four hours after reperfusion, the behavior evaluation and TTC staining recovered slightly, and the intensity of the biophoton emissions was weaker on the ischemia-reperfusion side than on the contralateral side. One week after reperfusion, the behavioral test and TTC staining recovered to normal levels; however, the intensity of the biophoton emissions was decreased significantly on both the ischemia-reperfusion and contralateral sides, and such changes were even distinguished in different brain areas, such as the sensory and motor coteries and striatum.

CONCLUSION

These findings suggest that delayed functional neural circuit injury induced by cerebral ischemia-reperfusion could be identified with biophoton imaging techniques, providing a novel functional evaluation method for animal models of cerebral ischemia-reperfusion.

Interruption of endolysosomal trafficking leads to stroke brain injury

BACKGROUND AND PURPOSE

Dysfunction of the endolysosomal system can cause cell death. A key molecule for controlling the endolysosomal trafficking activities is the N-ethylmaleimide-sensitive factor (NSF) ATPase. This study investigates the cascades of NSF ATPase inactivation events, endolysosomal damage, cathepsin release, and neuronal death after focal brain ischemia.

METHODS

A total of 62 rats were used in this study. They were subjected to sham surgery or 2 h of focal brain ischemia followed by 1, 4, and 24 h of reperfusion. Confocal microscopy and Western blot analysis were utilized to analyze the levels, redistribution, and co-localization of key proteins of the Golgi apparatus, late endosomes, endolysosomes, and lysosomes. Light and electron microscopy were used to examine the histopathology, protein aggregation, and endolysosomal ultrastructures.

RESULTS

Two hours of focal brain ischemia in rats led to acute neuronal death at the striatal core in 4 h and a slower type of neuronal death in the neocortical area during 1-24 h reperfusion periods. Confocal microscopy showed that NSF immunoreactivity was irreversibly and selectively depleted from most, if not all, post-ischemic penumbral neurons. Western blot analysis further demonstrated that NSF depletion from brain sections was due to its deposition into dense inactive aggregates that could not be recognized by the NSF antibody. Commitantly, the Golgi apparatus was completely fragmented and cathepsin B (CTSB)-containing endolysosomal structures, as well as p62/SQSTM1- and EEA1-immunopositive structures were massively accumulated in the post-ischemic penumbral neurons. Ultimately, CTSB was released into the cytoplasm and extracellular space, causing stroke brain injury.

CONCLUSION

Stroke Inactivates NSF, resulting in disruption of the reforming of functional endolysosomal compartments, blockade of the endocytic and autophagic pathways, a large scale of CTSB release into the cytoplasm and extracellular space, and stroke brain injury in the rat model.

Effects of Bone Marrow Stromal Cells (BMSCs) on Behavior, Infarct Size and HIF-1α Expression in Stroke Rats

This study aims to assess BMSCs’ effect on the behavior, infarct size and HIF-1α expression in stroke rats. Rats were separated into sham group, CVA group and BMSCs group with 10 rats in each group followed by analysis of neuroethology scores, brain tissue pathology and infarct size, and HIF-1α level in brain tissues. No difference of neurological scores was found between CVA group and BMSCs group after 3 hours (P > 0.05). After BMSCs transplantation, the nerve score was significantly reduced (P < 0.05) and cognitive function was significantly improved compared to CVA group. Compared with sham rats, CAV rats had a larger area of infarction and the infarcted tissue cells showed degeneration or necrosis with reduced cell number and obvious edema, which were all improved in BMSCs group. CVA group showed a larger area of infarct tissue (P < 0.05), which was reduced in BMSCs group (P < 0.05). Compared with sham group, CVA group showed significantly upregulated HIF-1α level (P < 0.05) which was reduced in BMSCs group (P < 0.05). BMSCs has a certain repair effect on the ethology of stroke rats possibly via inhibition of HIF-1α level in cerebral infarction and brain tissue.

Electroacupuncture reactivates estrogen receptors to restore the neuroprotective effect of estrogen against cerebral ischemic stroke in long-term ovariectomized rats

BACKGROUND

Stroke is a sexually dimorphic disease and a leading cause of death and disability. Estrogen replacement therapy (ERT) confers beneficial neuroprotective effects if administered within a widely accepted time window called the "critical period." However, very few studies have explored the idea of modulating the critical period to enable long-term post-menopausal women to regain more benefits from estrogen therapy. Here, motivated by previous findings that electroacupuncture could both alter estrogen metabolism and induce significant tolerance against stroke, it was explored whether EA could restore estrogen's neuroprotection against cerebral ischemia in long-term ovariectomized (OVX) rats.

METHODS

We implemented 1 week(w)-EA pretreatment on OVX-10w or OVX-20w rats, and tested the expression of estrogen receptors, and detected the ERT's neuroprotection against stroke induced by middle cerebral artery occlusion (MCAO).

RESULTS

We found that the expression levels of phospho-ERα-S118 and estrogen receptor β (ERβ) in the striatum of OVX-10w rats were significantly decreased and ERT's neuroprotection was abolished in the OVX-10w rats. However, EA-1w pretreatment could significantly recover the expression levels of phospho-ERα-S118 and ERβ, and also restored the neuroprotective effects of ERT in OVX-10w rats. However, EA-1w pretreatment could not restore the expression of estrogen receptors and ERT's neuroprotection in OVX-20w rats.

CONCLUSION

Taken together, our study indicates that EA may be an easy intervention that can restore the efficacy of estrogen therapy during the "critical period," which has the potential to improve the stroke outcomes of an enormous number of long-term post-menopausal women. However, the time-sensitive influences for how EA and estrogen metabolism interact with each other should be considered.

Propofol Protects against Cerebral Ischemia/Reperfusion Injury by Down-Regulating Long Noncoding RNA SNHG14

Cerebral ischemia-reperfusion (CI/R) injury is a serious central nervous system disease. Propofol (PPF) exerts a neuroprotective effect in CI/R injury; the underlying cause is still unclear. Here, we cultured mouse hippocampal neuron (HT22 cells) in oxygen-glucose deprivation/reoxygenation (OGD/R) conditions to mimic CI/R injury in vitro. PPF treatment promoted cell viability and reduced apoptotic cells in the OGD/R-treated HT22 cells, which was effectively abrogated by SNHG14 overexpression. Moreover, we constructed a CI/R injury mouse model on C57BL/6J mice by middle cerebral artery occlusion/reperfusion (MCAO/R), followed by administration of PPF. PPF reduced neuronal damage and loss, enhanced glial cell hyperplasia, and ameliorated cerebral cortex tissue damage and brain infarct in MCAO/R-induced mice. SNHG14 overexpression aggravated MCAO/R-induced CI/R injury in mice. Furthermore, SNHG14 promoted the expression of Atg5 and Beclin 1 via competitively binding miR-30b-5p, which contributed to activate autophagy and apoptosis in HT22 cells. In addition, the levels of p-p38 and p-SP1 were reduced in the OGD/R-treated HT22 cells in the presence of PPF. SP1 interacted with the promoter of SNHG14 and elevated the expression of SNHG14. PPF treatment inhibited the SP1-mediated up-regulation of SNHG14. In conclusion, this work demonstrates that PPF inhibits SNHG14 expression though the p38 MAPK signaling pathway. SNHG14 promotes Atg5 and Beclin 1 expression by sponging miR-30b-5p and thus activates autophagy and aggravates CI/R injury.

Neuronal CD200 Signaling Is Protective in the Acute Phase of Ischemic Stroke

BACKGROUND AND PURPOSE

CD200 (cluster of differentiation 200), a highly glycosylated protein primarily expressed on neurons in the central nervous system, binds with its receptor CD200R to form an endogenous inhibitory signal against immune responses. However, little is known about the effect of neuronal CD200 signaling in cerebral ischemia. The aim of this study was to investigate how neuronal CD200 signaling impacts poststroke inflammation and the ischemic injury.

METHODS

CD200 tma1^lf/fl:Thy1CreER mice were treated with tamoxifen to induce conditional gene knockout (ICKO) of neuronal CD200. The mice were subjected to a 60-minute transient middle cerebral artery occlusion. Stroke outcomes, apoptotic cell death, immune cell infiltration, microglia activation, and other inflammatory profiles were evaluated at 3 and 7 days after stroke.

RESULTS

Infarct volumes were significantly larger, and behavioral deficits more severe in ICKO versus control mice at 3 days after middle cerebral artery occlusion. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay also revealed a significant increase in apoptotic neuronal death in CD200 ICKO mice. An enhancement in lymphocytic infiltration and microglial proinflammatory responses were revealed by flow cytometry at 3 and 7 days after stroke in ICKO mice, accompanied by an increased microglial phagocytosis activity. Plasma proinflammatory cytokine (TNFα [tumor necrosis factor alpha] and IL [interleukin]-1β) levels significantly increased at 3 days, and IL-1β/IL-6 levels increased at 7 days in ICKO versus control animals. ICKO led to significantly lower baseline level of CD200 both in brain and plasma.

CONCLUSIONS

Neuronal CD200 inhibits proinflammatory responses and is protective against stroke injury.

Expression of miR-200c corresponds with increased reactive oxygen species and hypoxia markers after transient focal ischemia in mice

Embolic stroke results in a necrotic core of cells destined to die, but also a peri-ischemic, watershed penumbral region of potentially salvageable brain tissue. Approaches to effectively differentiate between the ischemic and peri-ischemic zones is critical for novel therapeutic discovery to improve outcomes in survivors of stroke. MicroRNAs are a class of small non-coding RNAs regulating gene translation that have region- and cell-specific expression and responses to ischemia. We have previously reported that global inhibition of cerebral microRNA-200c after experimental stroke in mice is protective, however delineating the post-stroke sub-regional and cell-type specific patterns of post-stroke miR-200c expression are necessary to minimize off-target effects and advance translational application. Here, we detail a novel protocol to visualize regional miR-200c expression after experimental stroke, complexed with visualization of regional ischemia and markers of oxidative stress in an experimental stroke model in mice. In the present study we demonstrate that the fluorescent hypoxia indicator pimonidazole hydrochloride, the reactive-oxygen-species marker 8-hydroxy-deoxyguanosine, neuronal marker MAP2 and NeuN, and the reactive astrocyte marker GFAP can be effectively complexed to determine regional differences in ischemic injury as early as 30 min post-reperfusion after experimental stroke, and can be effectively used to distinguish ischemic core from surrounding penumbral and unaffected regions for targeted therapy. This multi-dimensional post-stroke immunofluorescent imaging protocol enables a greater degree of sub-regional mechanistic investigation, with the ultimate goal of developing more effective post-stroke pharmaceutical therapy.

Neuroprotective effects of four different fluids on cerebral ischaemia/reperfusion injury in rats through stabilization of the blood-brain barrier

Protecting the blood–brain barrier (BBB) is a potential strategy to treat cerebral ischaemic injury. We previously reported that hypertonic sodium chloride hydroxyethyl starch 40 (HSH) treatment alleviates brain injury induced by transient middle cerebral artery occlusion (tMCAO). However, other fluids, including 20% mannitol (MN), 3% hypertonic sodium chloride (HTS) and hydroxyethyl starch 130/0.4 solution (HES), have the same effect as HSH in cerebral ischaemia/reperfusion injury (CI/RI) remains unclear. The present study evaluated the protective effects of these four fluids on the BBB in tMCAO rats. Sprague–Dawley (SD) rats were randomly assigned to six groups. A CI/RI rat model was established by tMCAO for 120 min followed by 24 h of reperfusion. The sham and tMCAO groups were treated with normal saline (NS), whereas the other four groups were treated with the four fluids. After 24 h of reperfusion, neurological function, brain oedema, brain infarction volume, permeability of the BBB, cortical neuron loss and protein and mRNA expression were assessed. The four fluids (especially HSH) alleviated neurological deficits and decreased the infarction volume, brain oedema, BBB permeability and cortical neuron loss induced by tMCAO. The expression levels of GFAP, IL‐1β, TNF‐α, MMP‐9, MMP‐3, AQP4, MMP‐9, PDGFR‐β and RGS5 were decreased, whereas the expression levels of laminin and claudin‐5 were increased. These data suggested that small‐volume reperfusion using HSH, HES, MN and HTS ameliorated CI/RI, probably by attenuating BBB disruption and postischaemic inflammation, with HSH exerting the strongest neuroprotective effect.

Single-Cell Microwell Platform Reveals Circulating Neural Cells as a Clinical Indicator for Patients with Blood-Brain Barrier Breakdown

Central nervous system diseases commonly occur with the destruction of the blood-brain barrier. As a primary cause of morbidity and mortality, stroke remains unpredictable and lacks cellular biomarkers that accurately quantify its occurrence and development. Here, we identify NeuN⁺/CD45⁻/DAPI⁺ phenotype nonblood cells in the peripheral blood of mice subjected to middle cerebral artery occlusion (MCAO) and stroke patients. Since NeuN is a specific marker of neural cells, we term these newly identified cells as circulating neural cells (CNCs). We find that the enumeration of CNCs in the blood is significantly associated with the severity of brain damage in MCAO mice (p < 0.05). Meanwhile, the number of CNCs is significantly higher in stroke patients than in negative subjects (p < 0.0001). These findings suggest that the amount of CNCs in circulation may serve as a clinical indicator for the real-time prognosis and progression monitor of the occurrence and development of ischemic stroke and other nervous system disease.

Modified middle cerebral artery occlusion model provides detailed intraoperative cerebral blood flow registration and improves neurobehavioral evaluation

BACKGROUND

Middle cerebral artery occlusion (MCAO) with 1 -h ischemia followed by reperfusion is a widely used stroke model in rodents that has significant limitations such as high mortality and severe neurological deficit hampering comprehensive neurobehavioral evaluation. The goal of this study was to establish a mouse model of 30-minute MCAO followed by 48 h of reperfusion and compare it with 1 -h MCAO followed by 24 h of reperfusion.

NEW METHOD

Here we propose a modified MCAO model that is favorable for both neurobehavioral and infarct volume evaluation. The model includes shorter ischemic time (30 min) of MCAO followed by 48 h of reperfusion and use of standardized intraoperative partial and total reperfusion, which allows for the detailed evaluation of initial and total reperfusion by means of the monitoring of CBF by LDF.

RESULTS AND COMPARISON WITH EXISTING METHOD

Intraoperative CBF parameters and infarct volume (1-h MCAO at 24 h: 69 ± 9; 30-minute MCAO at 48 h: 65 ± 14 mm3) did not significantly differ between groups. Neurological deficit was less severe in 30-minute MCAO group where mice also had significantly longer ambulatory distance and time, lower resting time, and higher vertical count on the OPF. The latency to fall in the rotarod test was significantly higher in 30-minute MCAO group. The mortality was higher after 1 -h MCAO.

CONCLUSIONS

30-minute MCAO followed by 48 h of reperfusion causes intraoperative ischemia, reperfusion and infarct volume comparable with 1 -h MCAO followed by 24 h of reperfusion but results in lower mortality with milder neurological deficit allowing for more extensive neurobehavioral evaluation.

Role of microglial and endothelial CD36 in post-ischemic inflammasome activation and interleukin-1β-induced endothelial activation

Cerebral ischemia is associated with an acute inflammatory response that contributes to the resulting injury. The innate immunity receptor CD36, expressed in microglia and endothelium, and the pro-inflammatory cytokine interleukin-1β (IL-1β) are involved in the mechanisms of ischemic injury. Since CD36 has been implicated in activation of the inflammasome, the main source of IL-1β, we investigated whether CD36 mediates brain injury through the inflammasome and IL-1β. We found that active caspase-1, a key inflammasome component, is decreased in microglia of CD36-deficient mice subjected to transient middle cerebral artery occlusion, an effect associated with a reduction in brain IL-1β. Conditional deletion of CD36 either in microglia or endothelium reduced ischemic injury in mice, attesting to the pathogenic involvement of CD36 in both cell types. Application of an ischemic brain extract to primary brain endothelial cell cultures from wild type (WT) mice induced IL-1β-dependent endothelial activation, reflected by increases in the cytokine colony stimulating factor-3, a response markedly attenuated in CD36-deficient endothelia. Similarly, the increase in colony stimulating factor-3 induced by recombinant IL-1β was attenuated in CD36-deficient compared to WT endothelia. We conclude that microglial CD36 is a key determinant of post-ischemic IL-1β production by regulating caspase-1 activity, whereas endothelial CD36 is required for the full expression of the endothelial activation induced by IL-1β. The data identify microglial and endothelial CD36 as critical upstream components of the acute inflammatory response to cerebral ischemia and viable putative therapeutic targets.

Sulfide catabolism ameliorates hypoxic brain injury

The mammalian brain is highly vulnerable to oxygen deprivation, yet the mechanism underlying the brain's sensitivity to hypoxia is incompletely understood. Hypoxia induces accumulation of hydrogen sulfide, a gas that inhibits mitochondrial respiration. Here, we show that, in mice, rats, and naturally hypoxia-tolerant ground squirrels, the sensitivity of the brain to hypoxia is inversely related to the levels of sulfide:quinone oxidoreductase (SQOR) and the capacity to catabolize sulfide. Silencing SQOR increased the sensitivity of the brain to hypoxia, whereas neuron-specific SQOR expression prevented hypoxia-induced sulfide accumulation, bioenergetic failure, and ischemic brain injury. Excluding SQOR from mitochondria increased sensitivity to hypoxia not only in the brain but also in heart and liver. Pharmacological scavenging of sulfide maintained mitochondrial respiration in hypoxic neurons and made mice resistant to hypoxia. These results illuminate the critical role of sulfide catabolism in energy homeostasis during hypoxia and identify a therapeutic target for ischemic brain injury.

LncRNA H19 promotes inflammatory response induced by cerebral ischemia-reperfusion injury through regulating the miR-138-5p-p65 axis

Recent studies have shown that long non-coding RNA(LncRNA) H19 is up-regulated in the brain of rats suffering from cerebral ischemia-reperfusion (I/R) injury, inducing severe disability and mortality. Little was known about the molecular mechanisms underlying the involvement of H19 in cerebral I/R injury. In this study, a rat model of I/R was induced by transient middle cerebral artery occlusion (tMCAO). PC-12 cells exposed to oxygen and glucose deprivation/reoxygenation (OGD/R) were used as an in vitro model. Our results show that H19 is up-regulated in both in vivo and in our in vitro model. Further study indicated that knockdown of H19 promotes cell proliferation, decreases the rate of cell apoptosis, and ameliorates inflammation after OGD/R simulation. Our in vivo study shows that H19 knockdown ameliorates inflammation and improves neurological function in our rat model of tMCAO. Remarkably, the results from our luciferase reporter assays suggest that H19 negatively regulates the expression of miR-138-5p, and p65 was identified as a target of miR-138-5p. To sum up, this study demonstrated that H19 promotes an inflammatory response and improves neurological function in a rat model of tMCAO by regulating the expression of miR-138-5p and p65. This study reveals the important role and underlying mechanism of H19 in the progress of cerebral I/R injury, which could serve as a potential target for further treatment.

Preferential Targeting Cerebral Ischemic Lesions with Cancer Cell-Inspired Nanovehicle for Ischemic Stroke Treatment

The poor drug delivery to cerebral ischemic regions is a key challenge of ischemic stroke treatment. Inspired by the intriguing blood-brain barrier (BBB)-penetrating ability of 4T1 cancer cells upon their brain metastasis, we herein designed a promising biomimetic nanoplatform by camouflaging a succinobucol-loaded pH-sensitive polymeric nanovehicle with a 4T1 cell membrane (MPP/SCB), aiming to promote the preferential targeting of cerebral ischemic lesions to attenuate the ischemia/reperfusion injury. In transient middle cerebral artery occlusion (tMCAO) rat models, MPP/SCB could be preferentially delivered to the ischemic hemisphere with a 4.79-fold higher than that in the normal hemisphere. Moreover, MPP/SCB produced notable enhancement of microvascular reperfusion in the ischemic hemisphere, resulting in a 69.9% reduction of infarct volume and showing remarkable neuroprotective effects of tMCAO rats, which was superior to the counterpart uncamouflaged nanovehicles (PP/SCB). Therefore, this design provides a promising nanoplatform to target the cerebral ischemic lesions for ischemic stroke therapy.

Galectin-3 protects against ischemic stroke by promoting neuro-angiogenesis via apoptosis inhibition and Akt/Caspase regulation

Post-stroke neurological deficits and mortality are often associated with vascular disruption and neuronal apoptosis. Galectin-3 (Gal3) is a potent pro-survival and angiogenic factor. However, little is known about its protective role in the cerebral ischemia/reperfusion (I/R) injury. We have previously shown significant up-regulation of Gal3 in the post-stroke rat brain, and that blocking of Gal3 with neutralizing antibody decreases the cerebral blood vessel density. Our current study demonstrates that intracerebral local delivery of the Gal3 into rat brain at the time of reperfusion exerts neuroprotection. Ischemic lesion volume and neuronal cell death were significantly reduced as compared with the vehicle-treated MCAO rat brains. Gal3 increased vessel density and neuronal survival after I/R in rat brains. Importantly, Gal3-treated groups showed significant improvement in motor and sensory functional recovery. Gal3 increased neuronal cell viability under in vitro oxygen-glucose deprivation conditions in association with increased phosphorylated-Akt, decreased phosphorylated-ERK1/2, and reduced caspase-3 activity. Gene expression analysis showed down regulation of pro-apoptotic and inflammatory genes including Fas-ligand, and upregulation of pro-survival and pro-angiogenic genes including Bcl-2, PECAM, and occludin. These results indicate a key role for Gal3 in neuro-vascular protection and functional recovery following ischemic stroke through modulation of angiogenic and apoptotic pathways.

X chromosome escapee genes are involved in ischemic sexual dimorphism through epigenetic modification of inflammatory signals

BACKGROUND

Stroke is a sexually dimorphic disease. Previous studies have found that young females are protected against ischemia compared to males, partially due to the protective effect of ovarian hormones, particularly estrogen (E2). However, there are also genetic and epigenetic effects of X chromosome dosage that contribute to stroke sensitivity and neuroinflammation after injury, especially in the aged. Genes that escape from X chromosome inactivation (XCI) contribute to sex-specific phenotypes in many disorders. Kdm5c and kdm6a are X escapee genes that demethylate H3K4me3 and H3K27me3, respectively. We hypothesized that the two demethylases play critical roles in mediating the stroke sensitivity.

METHODS

To identify the X escapee genes involved in stroke, we performed RNA-seq in flow-sorted microglia from aged male and female wild type (WT) mice subjected to middle cerebral artery occlusion (MCAO). The expression of these genes (kdm5c/kdm6a) were confirmed in four core genotypes (FCG) mice and in post-mortem human stroke brains by immunohistochemistry (IHC), Western blot, and RT-PCR. Chromatin immunoprecipitation (ChIP) assays were conducted to detect DNA levels of inflammatory interferon regulatory factor (IRF) 4/5 precipitated by histone H3K4 and H3K27 antibodies. Manipulation of kdm5c/kdm6a expression with siRNA or lentivirus was performed in microglial culture, to determine downstream pathways and examine the regulatory roles in inflammatory cytokine production.

RESULTS

Kdm5c and kdm6a mRNA levels were significantly higher in aged WT female vs. male microglia, and the sex difference also existed in ischemic brains from FCG mice and human stroke patients. The ChIP assay showed the IRF 4/5 had higher binding levels to demethylated H3K4 or H3K27, respectively, in female vs. male ischemic microglia. Knockdown or over expression of kdm5c/kdm6a with siRNA or lentivirus altered the methylation of H3K4 or H3K27 at the IRF4/5 genes, which in turn, impacted the production of inflammatory cytokines.

CONCLUSIONS

The KDM-Histone-IRF pathways are suggested to mediate sex differences in cerebral ischemia. Epigenetic modification of stroke-related genes constitutes an important mechanism underlying the ischemic sexual dimorphism.

Development of a photochemical thrombosis investigation system to obtain a rabbit ischemic stroke model

Photochemical thrombosis is a method for the induction of ischemic stroke in the cerebral cortex. It can generate localized ischemic infarcts in the desired region; therefore, it has been actively employed in establishing an ischemic stroke animal model and in vivo assays of diagnostic and therapeutic techniques for stroke. To establish a rabbit ischemic stroke model and overcome the shortcoming of previous studies that were difficult to build a standardized photothrombotic rabbit model, we developed a photochemical thrombosis induction system that can produce consistent brain damage on a specific area. To verify the generation of photothrombotic brain damage using the system, longitudinal magnetic resonance imaging, 2,3,5-triphenyltetrazolium chloride staining, and histological staining were applied. These analytical methods have a high correlation for ischemic infarction and are appropriate for analyzing photothrombotic brain damage in the rabbit brain. The results indicated that the photothrombosis induction system has a main advantage of being accurately controlled a targeted region of photothrombosis and can produce cerebral hemisphere lesions on the target region of the rabbit brain. In conjugation with brain atlas, it can induce photochemical ischemic stroke locally in the part of the brain that is responsible for a particular brain function and the system can be used to develop animal models with degraded specific functions. Also, the photochemical thrombosis induction system and a standardized rabbit ischemic stroke model that uses this system have the potential to be used for verifications of biomedical techniques for ischemic stroke at a preclinical stage in parallel with further performance improvements.

Fisetin Attenuates Myocardial Ischemia-Reperfusion Injury by Activating the Reperfusion Injury Salvage Kinase (RISK) Signaling Pathway

Ischemia-reperfusion (I/R) injury is an unavoidable injury that occurs during revascularization procedures. In the previous study, we reported that fisetin is a natural flavonoid that attenuates I/R injury by suppressing mitochondrial oxidative stress and mitochondrial dysfunction. Though fisetin is reported as a GSK3β inhibitor, it remains unclear whether it attenuates myocardial ischemia by activating the phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) pathway, thereby inhibiting the downstream GSK3β, or by directly interacting with GSK3β while rendering its cardioprotection. In this study, the research team investigates the possible mechanism of action of fisetin while rendering its cardioprotective effect against myocardial I/R injury in rats. For this investigation, the team utilized two myocardial I/R models: Ligation of the left anterior descending artery and Langendorff isolated heart perfusion system. The latter has no neurohormonal influences. The PI3K inhibitor (Wortmannin, 0.015 mg/kg), GSK3β inhibitor (SB216763, 0.7 mg/kg), and fisetin (20 mg/kg) were administered intraperitoneally before inducing myocardial I/R. The result of this study reveals that the administration of fisetin decreases the myocardial infarct size, apoptosis, lactate dehydrogenase, and creatine kinase in serum\perfusate of the rat hearts subjected to I/R. However, the inhibition of PI3K with Wortmannin significantly reduced the cardioprotective effect of fisetin both in the ex vivo and vivo models. The administration of GSK3β inhibitor after the administration of fisetin and Wortmannin, re-establishing the cardioprotection, indicates the major role of PI3K in fisetin action. Changes in myocardial oxidative stress (level) and mitochondrial functional preservation of interfibrillar and subsarcolemmal mitochondria support the above findings. Hence, the team here reports that fisetin conferred its cardioprotection against I/R injury by activating the PI3K/Akt/GSK3β signaling pathway in rat hearts.