The neuroprotective effects of isoflurane preconditioning in a murine transient global cerebral ischemia-reperfusion model: the role of the Notch signaling pathway

Research hotspots and frontiers of preconditioning in cerebral ischemia: A bibliometric analysis

Background

Preconditioning is a promising strategy against ischemic brain injury, and numerous studies in vitro and in vivo have demonstrated its neuroprotective effects. However, at present there is no bibliometric analysis of preconditioning in cerebral ischemia. Therefore, a comprehensive overview of the current status, hot spots, and emerging trends in this research field is necessary.

Materials and methods

Studies on preconditioning in cerebral ischemia from January 1999-December 2022 were retrieved from the Web of Science Core Collection (WOSCC) database. CiteSpace was used for data mining and visual analysis.

Results

A total of 1738 papers on preconditioning in cerebral ischemia were included in the study. The annual publications showed an upwards and then downwards trend but currently remain high in terms of annual publications. The US was the leading country, followed by China, the most active country in recent years. Capital Medical University published the largest number of articles. Perez-Pinzon, Miguel A contributed the most publications, while KITAGAWA K was the most cited author. The focus of the study covered three areas: (1) relevant diseases and experimental models, (2) types of preconditioning and stimuli, and (3) mechanisms of ischemic tolerance. Remote ischemic preconditioning, preconditioning of mesenchymal stem cells (MSCs), and inflammation are the frontiers of research in this field.

Conclusion

Our study provides a visual and scientific overview of research on preconditioning in cerebral ischemia, providing valuable information and new directions for researchers.

Obstructive sleep apnea affects cognition: dual effects of intermittent hypoxia on neurons

Obstructive sleep apnea (OSA) is a common respiratory disorder. Multiple organs, especially the central nervous system (CNS), are damaged, and dysfunctional when intermittent hypoxia (IH) occurs during sleep for a long time. The quality of life of individuals with OSA is significantly impacted by cognitive decline, which also escalates the financial strain on their families. Consequently, the development of novel therapies becomes imperative. IH induces oxidative stress, endoplasmic reticulum stress, iron deposition, and neuroinflammation in neurons. Synaptic dysfunction, reactive gliosis, apoptosis, neuroinflammation, and inhibition of neurogenesis can lead to learning and long-term memory impairment. In addition to nerve injury, the role of IH in neuroprotection was also explored. While causing neuron damage, IH activates the neuronal self-repairing mechanism by regulating antioxidant capacity and preventing toxic protein deposition. By stimulating the proliferation and differentiation of neural stem cells (NSCs), IH has the potential to enhance the ratio of neonatal neurons and counteract the decline in neuron numbers. This review emphasizes the perspectives and opportunities for the neuroprotective effects of IH and informs novel insights and therapeutic strategies in OSA.

Ischemia-reperfusion injury: molecular mechanisms and therapeutic targets

Ischemia-reperfusion (I/R) injury paradoxically occurs during reperfusion following ischemia, exacerbating the initial tissue damage. The limited understanding of the intricate mechanisms underlying I/R injury hinders the development of effective therapeutic interventions. The Wnt signaling pathway exhibits extensive crosstalk with various other pathways, forming a network system of signaling pathways involved in I/R injury. This review article elucidates the underlying mechanisms involved in Wnt signaling, as well as the complex interplay between Wnt and other pathways, including Notch, phosphatidylinositol 3-kinase/protein kinase B, transforming growth factor-β, nuclear factor kappa, bone morphogenetic protein, N-methyl-D-aspartic acid receptor-Ca2+-Activin A, Hippo-Yes-associated protein, toll-like receptor 4/toll-interleukine-1 receptor domain-containing adapter-inducing interferon-β, and hepatocyte growth factor/mesenchymal-epithelial transition factor. In particular, we delve into their respective contributions to key pathological processes, including apoptosis, the inflammatory response, oxidative stress, extracellular matrix remodeling, angiogenesis, cell hypertrophy, fibrosis, ferroptosis, neurogenesis, and blood-brain barrier damage during I/R injury. Our comprehensive analysis of the mechanisms involved in Wnt signaling during I/R reveals that activation of the canonical Wnt pathway promotes organ recovery, while activation of the non-canonical Wnt pathways exacerbates injury. Moreover, we explore novel therapeutic approaches based on these mechanistic findings, incorporating evidence from animal experiments, current standards, and clinical trials. The objective of this review is to provide deeper insights into the roles of Wnt and its crosstalk signaling pathways in I/R-mediated processes and organ dysfunction, to facilitate the development of innovative therapeutic agents for I/R injury.

Protective Effect of Ulinastatin on Cognitive Function After Hypoxia

Ulinastatin (UTI) has neuroprotective properties. Neurologic insults, including hypoxia and use of anesthetic agents, cause postoperative cognitive dysfunction and alter gamma-aminobutyric acid (GABA) function. This study aimed to assess whether UTI could preserve learning and memory using a zebrafish hypoxic behavior model and biomarkers. Zebrafish (6-8 months of age and 2.5-3.5 cm long) were divided into eight groups as follows: phosphate-buffered saline (PBS) control, hypoxia + PBS, UTI (10,000, 50,000, and 100,000 units/kg), and hypoxia with UTI (10,000, 50,000, and 100,000 units/kg) groups. The endpoints of the T-maze experiment included total time, distance moved, and frequency in target or opposite compartment. We also measured the degree of brain infarction using 2,3,5‑triphenyltetrazolium chloride staining, assessed SA-β-galactosidase activity, and examined GABA_A receptor expression using real-time polymerase chain reaction. In a dose-dependent manner, UTI affected learning and memory in zebrafish. Despite hypoxia, 100,000 units/kg of UTI preserved preference (time and distance) for the target compartment. More than 50,000 units/kg of UTI also showed reduced hypoxia-induced brain infarction, decreased SA-β-galactosidase levels, and upregulated GABA_A receptors. This study demonstrated that the location of the GABA_A receptor is affected by hypoxia or UTI.

Gli2-induced lncRNA Peg13 alleviates cerebral ischemia-reperfusion injury by suppressing Yy1 transcription in a PRC2 complex-dependent manner

Endothelial cell dysfunction plays an important role in cerebral ischemia-reperfusion (I/R) injury. LncRNA Peg13 is reported to be down-regulated in brain microvascular endothelial cells (BMVECs) induced by glucose-oxygen deprivation (OGD), but the mechanism of its involvement in I/R progression remains to be further explored. Here, mouse BMVECs (bEnd.3 cells) were treated with OGD / reoxygenation (OGD/R) to simulate I/R injury in vitro. Peg13 and Gli2 expression was decreased in OGD/R-treated bEnd.3 cells. And overexpression of Peg13 or Gli2 prevented OGD/R-induced reduction in cell migration and angiogenesis, as well as upregulation in cell apoptosis and oxidative stress levels. Mechanism exploration showed that Gli2 promoted the transcription of Peg13. And Peg13 repressed Yy1 transcription by binding to Ezh2 (a key subunit of PRC2 complex) and inducing the enrichment of H3K27me3 in Yy1 promoter region, thereby suppressing the transcriptional inhibition effect of Yy1 on Notch3 and promoting the expression of Notch3. Consistently, Notch3 overexpression hindered OGD/R-induced endothelium dysfunction. In addition, a brain I/R injury model was established using middle cerebral artery occlusion surgery. And lentivirus-mediated Gli2 and Peg13 overexpression vectors were injected into mice via the lateral ventricle one week before surgery. The results showed that overexpression of Peg13 or Gli2 alleviated I/R-induced neurological deficit, cerebral infarct and cerebral edema. And simultaneous overexpression of Peg13 and Gli2 showed a better protective effect than overexpression of Gli2 or Peg13 alone. In conclusion, Peg13 regulated by Gli2 inhibits Yy1 transcription in a PCR2 complex-dependent manner, and blocks the transcriptional repression of Notch3 by Yy1, thereby exerting neuroprotective effects on cerebral I/R injury.

Molecular mechanisms of developmental pathways in neurological disorders: a pharmacological and therapeutic review

Developmental signalling pathways such as Wnt/β-catenin, Notch and Sonic hedgehog play a central role in nearly all the stages of neuronal development. The term 'embryonic' might appear to be a misnomer to several people because these pathways are functional during the early stages of embryonic development and adulthood, albeit to a certain degree. Therefore, any aberration in these pathways or their associated components may contribute towards a detrimental outcome in the form of neurological disorders such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and stroke. In the last decade, researchers have extensively studied these pathways to decipher disease-related interactions, which can be used as therapeutic targets to improve outcomes in patients with neurological abnormalities. However, a lot remains to be understood in this domain. Nevertheless, there is strong evidence supporting the fact that embryonic signalling is indeed a crucial mechanism as is manifested by its role in driving memory loss, motor impairments and many other processes after brain trauma. In this review, we explore the key roles of three embryonic pathways in modulating a range of homeostatic processes such as maintaining blood-brain barrier integrity, mitochondrial dynamics and neuroinflammation. In addition, we extensively investigated the effect of these pathways in driving the pathophysiology of a range of disorders such as Alzheimer's, Parkinson's and diabetic neuropathy. The concluding section of the review is dedicated to neurotherapeutics, wherein we identify and list a range of biological molecules and compounds that have shown enormous potential in improving prognosis in patients with these disorders.

miR-223 Enhances the Neuroprotection of Estradiol Against Oxidative Stress Injury by Inhibiting the FOXO3/TXNIP Axis

Alzheimer's disease (AD) is an irreversible neurodegenerative disorder characterized by complex pathogenesis, of which oxidative stress has long been regarded as a major mechanism. Previously, the protective effects of estradiol on SH-SY5Y cells against Aβ42-induced injuries were demonstrated. In this study, the protection of SH-SY5Y cells by estradiol from H₂O₂-caused oxidative stress injury and Alzheimer's mice was further confirmed. H₂O₂ downregulated, whereas estradiol upregulated miR-223 expression. miR-223 overexpression promoted cell viability, inhibited cell apoptosis, reduced ROS levels, enhanced Superoxide Dismutase (SOD) activity, and decreased malondialdehyde (MDA) content. However, miR-223 inhibition exerted opposite effects. miR-223 directly targeted forkhead box O3 (FOXO3) and inhibited FOXO3 expression. H₂O₂ increased, whereas estradiol decreased thioredoxin interacting protein (TXNIP) levels; FOXO3 positively regulated TXNIP protein levels. In SH-SY5Y cells, FOXO3 overexpression increased, whereas FOXO3 knockdown reduced the cell apoptosis and ROS levels. FOXO3 bound to TXNIP promoter region and activated TXNIP transcription, whereas the activation could be partially inhibited by estradiol. Collectively, the FOXO3/TXNIP axis is downstream of miR-223. miR-223 enhances the neuroprotection of estradiol against oxidative stress injury through the FOXO3/TXNIP axis.

Celastrol attenuates ischemia/reperfusion-mediated memory dysfunction by downregulating AK005401/MAP3K12

BACKGROUND

Oxidative stress induces mitochondrial dysfunction, causing memory loss. Long noncoding RNAs influence mitochondrial function and suppress oxidative stress by regulating target protein expression and gene transcription. Celastrol, a natural antioxidant extracted from Tripterygium wilfordii Hook F. ("Thunder of God Vine"), effectively alleviates oxidative stress-mediated tissue injury. In the present study, we examined the effects of celastrol on memory dysfunction induced by ischemia/reperfusion (I/R) and elucidated the mechanisms underlying these effects.

METHODS

C57BL/6 mice were used to mimic I/R using the bilateral common carotid clip reperfusion method, and a hippocampal cell line (HT-22) cells were used to establish a model of oxygen-glucose deprivation/reoxygenation (OGD/R). We observed changes in behavior and mitochondrial structure. Cell activity, cell respiration, and antioxidant capacity were measured. MAP3K12, p-JNK, p-c-Jun, p-Akt/Akt, PI3K, Bcl-2, and Bax expression were evaluated.

RESULTS

I/R or OGD/R significantly increased AK005401 and MAP3K12 expression, further attenuating PI3K/Akt activation, promoting reactive oxygen species generation and causing mitochondrial dysfunction and cell apoptosis, thereby resulting in memory dysfunction. Celastrol increased antioxidant capacity, inhibited cell apoptosis, and improved mitochondrial function, effectively improving learning and memory by downregulating AK005401 and MAP3K12 and activating PI3K/Akt.

CONCLUSIONS

The AK005401/MAP3K12 signaling pathway has an important role in I/R-mediated hippocampal injury, and celastrol can potentially reduce or possibly prevent I/R-induced neuronal injury by downregulating AK005401/MAP3K12 signaling.

Review Cerebral Ischemic Tolerance and Preconditioning: Methods, Mechanisms, Clinical Applications, and Challenges

Stroke is one of the leading causes of morbidity and mortality worldwide, and it is increasing in prevalence. The limited therapeutic window and potential severe side effects prevent the widespread clinical application of the venous injection of thrombolytic tissue plasminogen activator and thrombectomy, which are regarded as the only approved treatments for acute ischemic stroke. Triggered by various types of mild stressors or stimuli, ischemic preconditioning (IPreC) induces adaptive endogenous tolerance to ischemia/reperfusion (I/R) injury by activating a multitude cascade of biomolecules, for example, proteins, enzymes, receptors, transcription factors, and others, which eventually lead to transcriptional regulation and epigenetic and genomic reprogramming. During the past 30 years, IPreC has been widely studied to confirm its neuroprotection against subsequent I/R injury, mainly including local ischemic preconditioning (LIPreC), remote ischemic preconditioning (RIPreC), and cross preconditioning. Although LIPreC has a strong neuroprotective effect, the clinical application of IPreC for subsequent cerebral ischemia is difficult. There are two main reasons for the above result: Cerebral ischemia is unpredictable, and LIPreC is also capable of inducing unexpected injury with only minor differences to durations or intensity. RIPreC and pharmacological preconditioning, an easy-to-use and non-invasive therapy, can be performed in a variety of clinical settings and appear to be more suitable for the clinical management of ischemic stroke. Hoping to advance our understanding of IPreC, this review mainly focuses on recent advances in IPreC in stroke management, its challenges, and the potential study directions.

Activation of AK005401 aggravates acute ischemia/reperfusion mediated hippocampal injury by directly targeting YY1/FGF21

Ischemia exerts a negative impact on mitochondrial function, which ultimately results in neuronal damage via alterations in gene transcription and protein expression. Long non- coding RNAs (LncRNAs) play pivotal roles in the regulation of target protein expression and gene transcription. In the present study, we observed the effect of an unclassical LncRNA AK005401on ischemia/reperfusion (I/R) ischemia-mediated hippocampal injury and investigated the regulatory role of fibroblast growth factor 21 (FGF21) and Yin Yang 1 (YY1). C57Black/6 mice were subjected to I/R using the bilateral common carotid clip reperfusion method, and AK005401 siRNA oligos were administered via intracerebroventricular injection. HT22 cells were used to establish a model of oxygen-glucose deprivation/reoxygenation (OGD/R). We observed pathological morphology and mitochondrial structure. Neuronal apoptosis was evident. Cell activity, cell respiration, FGF21, YY1, and antioxidant capacity were evaluated. I/R or OGD/R significantly increased the expressions of AK005401and YY1 and decreased FGF21expression, which further attenuated the activation of PI3K/Akt, promoted reactive oxygen species (ROS) generation, and then caused mitochondria dysfunction and cell apoptosis, which were reversed by AK005401 siRNA oligos and were aggravated by overexpression of AK005401 and YY1. We conclude that AK005401/YY1/FGF21 signaling pathway has an important role in I/R-mediated hippocampal injury.

Expression of Notch and Wnt/β-catenin signaling pathway in acute phase severe brain injury rats and the effect of exogenous thyroxine on those pathways

BACKGROUND

With the rapid development of economy, transportation and industry, the incidence of severe traumatic brain injury (sTBI) is rising rapidly, which is one of the main traumatic diseases threatening human life. It is very difficult for sTBI patients to regenerate and repair the central nervous and recover the brain function. Moreover, no effective neuroprotective drug has been found in the treatment of sTBI patients. Seeking drugs to promote nerve repair has become a hot and difficult problem. It is widely accepted that thyroxine is one of the essential hormones in the human body, which not only promotes the growth and development of the nervous system, but also plays an important role in maintaining adult brain function. There are many reports of modern research on thyroxine, mainly focusing on the changes of thyroid hormone levels and their effects on the prognosis after injury. Besides, most of them are observed in clinical cases. Currently, there are few dynamic experimental studies about observing whether thyroxine can promote the repair of central nervous system at different stages after sTBI. In our previous experiment, we found that Wnt/β-catenin signaling pathway, whose functions are opposite to Notch signaling pathway, can be further activated by exogenous thyroxine in rats with sTBI. As a result, we are interested in the expression of Notch and Wnt/β-catenin signaling pathway in acute phase sTBI rats and the effect of thyroxine on those pathways.

OBJECTIVE

To investigate expression of Notch and Wnt/β-catenin signaling pathway in acute phase severe brain injury rats and the effect of thyroxine on those pathways by observing dynamically Notch and Wnt/β-catenin signaling pathway, NSS, GFAP, S100B, Bcl-2, Bax, etc. METHODS: 108 rats were randomly divided into Group A (normal control group), Group B (normal-thyroxine group), Group C (TBI group), Group D (TBI+ low-dose thyroxine group), Group E (TBI + moderate-dose thyroxine) and Group F (TBI + high-dose thyroxine) with 18 rats in each group. The animal model was established according to Feeney's free-fall method, and administered with thyroxine or physiological saline at 6 h after sTBI. Six rats in each group were randomly killed on the 1st, 3rd and 7th days after intragastric administration. The changes of brain pathology and NSS were observed. The level of Wnt3a, β-catenin, Notch1 and Hes1 mRNA was detected by RT-PCR method, and the level of GFAP and S100B protein in serum was detected by ELISA. The expression of Bcl-2 and Bax was detected by immunohistochemistry.

RESULTS

(1) There was no significant change in brain pathology and NSS in groups A and B, but the changes of brain pathology and NSS in group D, E and F were significantly less than those in group C, especially in groups E and F. (2) RT-PCR showed that there was no change in the expression of Wnt3a mRNA, β-catenin mRNA, Notch1 and Hes1 mRNA in groups A and B. Compared with group C, the expression of Wnt3a mRNA and β-catenin mRNA in group D increased significantly on the 7th day after sTBI, especially in groups E and F; expression of Notch1 and Hes1 mRNA in groups D, E and F increased gradually with time, especially in group F. (3) ELISA showed that Compared with group C, GFAP and S100B in group D did not change significantly at 3 time points, GFAP in groups E and F decreased gradually with time and reached the lowest value on the 7th day, and S100B in groups E and F decreased gradually with time, especially in group F. (4) Compared with group C, the expression of BCL-2 in brain tissue of groups D, E and F increased gradually with time, and peaked on the 7th day, and the increase of E and F was more obvious. The expression of Bax in brain tissue of group D, E and F decreased gradually with time.

CONCLUSION

Exogenous thyroxine has no effect on Notch and Wnt/β-catenin signaling pathway in normal rats. After TBI, exogenous thyroxine can activate Notch and Wnt/β-catenin, and have a synergistic effect on the repair of central nervous system, which may be related to the up-regulation of Notch and Wnt/β-catenin signaling pathway mRNA expression and the increase of BDNF and NGF, and resist apoptosis in the brain of sTBI rats.

Cell Death Pathways in Ischemic Stroke and Targeted Pharmacotherapy

Ischemic stroke is one of the significant causes of morbidity and mortality, affecting millions of people across the globe. Cell injury in the infarct region is an inevitable consequence of focal cerebral ischemia. Subsequent reperfusion exacerbates the harmful effect and increases the infarct volume. These cellular injuries follow either a regulated pathway involving tightly structured signaling cascades and molecularly defined effector mechanisms or a non-regulated pathway, also known as accidental cell death, where the process is biologically uncontrolled. Classical cell death pathways are long established and well reported in several articles that majorly define apoptotic cell death. A recent focus on cell death study also considers investigation on non-classical pathways that are tightly regulated, may or may not involve caspases, but non-apoptotic. Pathological cell death is a cardinal feature of different neurodegenerative diseases. Although ischemia cannot be classified as a neurodegenerative disease, it is a cerebrovascular event where the infarct region exhibits aberrant cell death. Over the past few decades, several therapeutic options have been implicated for ischemic stroke. However, their use has been hampered owing to the number of limitations that they possess. Ischemic penumbral neurons undergo apoptosis and become dysfunctional; however, they are salvageable. Thus, understanding the role of different cell death pathways is crucial to aid in the modern treatment of protecting apoptotic neurons.

The Effects of Electroacupuncture in a Rat Model of Cerebral Ischemia-Reperfusion Injury Following Middle Cerebral Artery Occlusion Involves MicroRNA-223 and the PTEN Signaling Pathway

Background

In China, electroacupuncture (EA) is used to treat the symptoms of ischemic stroke. However, the mechanisms involved in the effects of EA in cerebral ischemia remain to be investigated. This study aimed to investigate the molecular mechanism underlying the effects of EA in a rat model of cerebral ischemia-reperfusion injury (CIRI) induced by middle cerebral artery occlusion (MCAO).

Material/Methods

Seventy-five male Sprague-Dawley rats were divided into five groups: the sham group (with sham surgery), the model group (the MCAO model), the EA group (treated with EA), the EA control group, and the EA+antagomir-223-3p group. Rats in the model of CIRI underwent MCAO for 90 minutes. EA was performed on the second postoperative day and was performed at the Waiguan (TE5) and Zusanli (ST36) acupoints. The rat brains were evaluated for structural and molecular markers.

Results

EA treatment significantly upregulated the expression of microRNA-223 (miR-223), NESTIN, and NOTCH1, and downregulated the expression of PTEN in the subventricular zone (SVZ) and hippocampus. The luciferase reporter assay supported that PTEN was a direct target of miR-223, and antagomiR-223-3p reversed the effects of EA and reduced the increase in NESTIN and inhibition of PTEN expression associated with EA treatment. There was a negative correlation between PTEN expression and the number of neural stem cells (NSCs).

Conclusions

In a rat model of CIRI following MCAO, EA activated the NOTCH pathway, promoted the expression of miR-223, increased the number of NSCs, and reduced the expression of PTEN.

Preactivation of Notch1 in remote ischemic preconditioning reduces cerebral ischemia-reperfusion injury through crosstalk with the NF-κB pathway

Background

Remote ischemic preconditioning (RIPC) initiates endogenous protective pathways in the brain from a distance and represents a new, promising paradigm in neuroprotection against cerebral ischemia-reperfusion (I/R) injury. However, the underlying mechanism of RIPC-mediated cerebral ischemia tolerance is complicated and not well understood. We reported previously that preactivation of Notch1 mediated the neuroprotective effects of cerebral ischemic preconditioning in rats subjected to cerebral I/R injury. The present study seeks to further explore the role of crosstalk between the Notch1 and NF-κB signaling pathways in the process of RIPC-induced neuroprotection.

Methods

Middle cerebral artery occlusion and reperfusion (MCAO/R) in adult male rats and oxygen-glucose deprivation and reoxygenation (OGD/R) in primary hippocampal neurons were used as models of I/R injury in vivo and in vitro, respectively. RIPC was induced by a 3-day procedure with 4 cycles of 5 min of left hind limb ischemia followed by 5 min of reperfusion each day before MCAO/R. Intracerebroventricular DAPT injection and sh-Notch1 lentivirus interference were used to inhibit the Notch1 signaling pathway in vivo and in vitro, respectively. After 24 h of reperfusion, neurological deficit scores, infarct volume, neuronal apoptosis, and cell viability were assessed. The protein expression levels of NICD, Hes1, Phospho-IKKα/β (p-IKK α/β), Phospho-NF-κB p65 (p-NF-κB p65), Bcl-2, and Bax were assessed by Western blotting.

Results

RIPC significantly improved neurological scores and reduced infarct volume and neuronal apoptosis in rats subjected to I/R injury. OGD preconditioning significantly reduced neuronal apoptosis and improved cell viability after I/R injury on days 3 and 7 after OGD/R. However, the neuroprotective effect was reversed by DAPT in vivo and attenuated by Notch1-RNAi in vitro. RIPC significantly upregulated the expression of proteins related to the Notch1 and NF-κB pathways. NF-κB signaling pathway activity was suppressed by a Notch1 signaling pathway inhibitor and Notch1-RNAi.

Conclusions

The neuroprotective effect of RIPC against cerebral I/R injury was associated with preactivation of the Notch1 and NF-κB pathways in neurons. The NF-κB pathway is a downstream target of the Notch1 pathway in RIPC and helps protect focal cerebral I/R injury.

Neuroprotective Effects of Cerebral Ischemic Preconditioning in a Rat Middle Cerebral Artery Occlusion Model: The Role of the Notch Signaling Pathway

Cerebral ischemia-reperfusion (I/R) injury is a major problem worldwide. The Notch signaling pathway plays an important role in neural progenitor cell differentiation and in the inflammatory response after central nervous system injury. This study evaluated whether the neuroprotective effect of cerebral ischemic preconditioning (cIPC) is mediated by the preactivation of the Notch signaling pathway. A rat middle cerebral artery occlusion/reperfusion (MCAO/R) model and glucose deprivation/reoxygenation (OGD/R) cell model were constructed to detect the neuroprotective effects of cIPC. In in vivo experiments, cIPC reduces the neurological functional deficit, cerebral infarction, and cellular apoptosis in the hippocampus induced by middle cerebral artery occlusion/reperfusion (MCAO/R), thus indicating that cIPC can improve neurologic function. Moreover, cIPC can reveal the expression peak of Jagged1, Notch1, NICD, and Hes1 protein, thereby indicating that cIPC can preactivate Notch signaling. However, cIPC-induced improvements in neurologic function are compromised by the γ-secretase inhibitor N-(N-(3,5-difluorophenacetyl)-1-alanyl)-S-phenylglycine t-butyl ester (DAPT). In in vitro experiments, OGD preconditioning (OGDPC) can clearly upregulate Notch1 expression in the OGD/R-treated neuron and neural stem cell. Notch1 pre-overexpression can decrease neuron death and apoptosis under OGD/R treatment. Notch1 pre-overexpression can decrease the percentage of G1 stage cells and increase the percentage of S stage cells in OGD/R-treated neural stem cell. Furthermore, Notch1 pre-knockdown has the opposite effect on cell survival, apoptosis, and cycle in both OGD/R-treated neuron and neural stem cell. In conclusion, our results demonstrate that the neuroprotective effects of cIPC in a rat MCAO/R model are mediated by the preactivation of the Notch signaling pathway.

Salvinorin A preserves cerebral pial artery autoregulation after forebrain ischemia via the PI3K/AKT/cGMP pathway

This study aimed to investigate the protective effect of salvinorin A on the cerebral pial artery after forebrain ischemia and explore related mechanisms. Thirty Sprague-Dawley rats received forebrain ischemia for 10 min. The dilation responses of the cerebral pial artery to hypercapnia and hypotension were assessed in rats before and 1 h after ischemia. The ischemia reperfusion (IR) control group received DMSO (1 µL/kg) immediately after ischemia. Two different doses of salvinorin A (10 and 20 µg/kg) were administered following the onset of reperfusion. The 5th, 6th, and 7th groups received salvinorin A (20 µg/kg) and LY294002 (10 µM), L-NAME (10 μM), or norbinaltorphimine (norBIN, 1 μM) after ischemia. The levels of cGMP in the cerebrospinal fluid (CSF) were also measured. The phosphorylation of AKT (p-AKT) was measured in the cerebral cortex by western blot at 24 h post-ischemia. Cell necrosis and apoptosis were examined by hematoxylin-eosin staining (HE) and TUNEL staining, respectively. The motor function of the rats was evaluated at 1, 2, and 5 days post-ischemia. The dilation responses of the cerebral pial artery were significantly impaired after ischemia and were preserved by salvinorin A treatment. In addition, salvinorin A significantly increased the levels of cGMP and p-AKT, suppressed cell necrosis and apoptosis of the cerebral cortex and improved the motor function of the rats. These effects were abolished by LY294002, L-NAME, and norBIN. Salvinorin A preserved cerebral pial artery autoregulation in response to hypercapnia and hypotension via the PI3K/AKT/cGMP pathway.

MicroRNA-137 regulates hypoxia-induced retinal ganglion cell apoptosis through Notch1

The apoptosis of retinal ganglion cells (RGCs) is a hallmark of several optic neuropathies. MicroRNAs (miRNAs) are recently identified regulators of various biological processes. However, the role of miRNAs in regulating RGC apoptosis remains largely unknown. We herein aimed to demonstrate that miR-137 acts as a hypoxia-responsive gene in RGCs that is downregulated under hypoxic conditions. It was observed that overexpression of miR-137 markedly aggravated hypoxia-induced cell apoptosis, whereas inhibition of miR-137 effectively protected RGCs against hypoxia-induced apoptosis. Hypoxia induced Notch1 expression and signaling activation, while blocking Notch signaling significantly aggravated hypoxia-induced cell apoptosis. Further data revealed that the pro-survival Akt signaling pathway was involved in miR-137-Notch signaling pathway-mediated RGC protection. Knockdown of Notch significantly reversed the effect of anti‑miR-137 on RGC protection and Akt signaling activation. In addition, blocking Akt signaling also significantly abrogated the protective effect of anti-miR-137 on hypoxia-induced cell injury. Overall, the results of the present study demonstrated that miR-137 targets Notch1 expression, revealing a novel link between miR-137 and Notch signaling, and suggesting that a miR-137/Notch1 axis may serve as a potential molecular target for the treatment of hypoxia-induced retinal diseases.

Isoflurane exposure regulates the cell viability and BDNF expression of astrocytes via upregulation of TREK‑1

Neonatal isoflurane exposure in rodents disrupts hippocampal cognitive functions, including learning and memory, and astrocytes may have an important role in this process. However, the molecular mechanisms underlying this disruption are not fully understood. The present study investigated the role of TWIK-related K⁺ channel (TREK-1) in isoflurane-induced cognitive impairment. Lentiviruses were used to overexpress or knockdown TREK-1 in astrocytes exposed to increasing concentrations of isoflurane or O₂ for 2 h. Subsequently, the mRNA and protein expression of brain-derived neurotrophic factor (BDNF), caspase-3, Bcl-2-associated X (Bax) and TREK-1 was measured by reverse transcription-quantitative polymerase chain reaction and western blot analysis, respectively. In addition, cell viability was assessed by a 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium monosodium salt assay. The results demonstrated that, prior to manipulating TREK-1, isoflurane significantly decreased the cell viability and BDNF expression, and increased Bax, caspase-3 and TREK-1 expression was observed. However, TREK-1 overexpression in astrocytes significantly downregulated BDNF expression, and upregulated Bax and caspase-3 expression. Furthermore, lentiviral-mediated short hairpin RNA knockdown of TREK-1 effectively inhibited the isoflurane-induced changes in BDNF, Bax and caspase-3 expression. Taken together, the results of the present study indicate that isoflurane-induced cell damage in astrocytes may be associated with TREK-1-mediated inhibition of BDNF and provide a reference for the safe use of isoflurane anesthesia in infants and children.

Intermittent hypoxia training blunts cerebrocortical presenilin 1 overexpression and amyloid-β accumulation in ethanol-withdrawn rats

Abrupt cessation of chronic alcohol consumption triggers signaling cascades that harm vulnerable brain regions and produce neurobehavioral deficits. We have demonstrated that a program of intermittent, normobaric hypoxia training (IHT) in rats prevents brain damage and neurobehavioral impairment resulting from abrupt ethanol withdrawal (EW). Moreover, EW induced expression of stress-activated protein kinase p38 and presenilin 1 (PS1), the catalytic subunit of γ-secretase that produces the neurotoxic amyloid-β (Aβ) peptides Aβ40 and Aβ42. We tested the hypotheses that 1) IHT limits EW-induced activation of the p38-PS1 axis, thereby attenuating γ-secretase activation and Aβ accumulation, and 2) EW disables heat shock protein 25 (HSP25), a p38 substrate, molecular chaperone, and antioxidant, and provokes protein carbonylation in a manner suppressed by IHT. Adult male rats completed two cycles of a 4-wk ethanol diet (6.5% wt/vol) and a 3-wk EW or an isocaloric, dextrin-based control diet. A 20-day IHT program (5-8 daily cycles of 5-10 min of 9.5-10% fractional inspired O₂ + 4 min of 21% fractional inspired O₂) was administered during the first EW phase. After the second EW phase, the brain was excised and the prefrontal cortex extracted. PS1, phosphorylated p38 (p-p38), and HSP25 were analyzed by immunoblot, PS1 messenger RNA by quantitative polymerase chain reaction, protein carbonyl content by spectrometry, and Aβ40 and Aβ42 contents by enzyme-linked immunosorbent assay. IHT attenuated the EW-associated increases in PS1, p-p38, Aβ40, Aβ42, and protein carbonyl contents, but not that of PS1 messenger RNA, while preserving functionally competent HSP25 dimers in EW rats. Collectively, these findings suggest that IHT may attenuate EW-induced γ-secretase overactivation by suppressing activation of the p38-PS1 axis and by preventing oxidative protein damage.

Aerobic exercise combined with huwentoxin-I mitigates chronic cerebral ischemia injury

Ca²⁺ channel blockers have been shown to protect neurons from ischemia, and aerobic exercise has significant protective effects on a variety of chronic diseases. The present study injected huwentoxin-I (HWTX-I), a spider peptide toxin that blocks Ca²⁺ channels, into the caudal vein of a chronic cerebral ischemia mouse model, once every 2 days, for a total of 15 injections. During this time, a subgroup of mice was subjected to treadmill exercise for 5 weeks. Results showed amelioration of cortical injury and improved neurological function in mice with chronic cerebral ischemia in the HWTX-I + aerobic exercise group. The combined effects of HWTX-I and exercise were superior to HWTX-I or aerobic exercise alone. HWTX-I effectively activated the Notch signal transduction pathway in brain tissue. Aerobic exercise up-regulated synaptophysin mRNA expression. These results demonstrated that aerobic exercise, in combination with HWTX-I, effectively relieved neuronal injury induced by chronic cerebral ischemia via the Notch signaling pathway and promoting synaptic regeneration.

Notch signaling in cerebrovascular diseases (Review)

The Notch signaling pathway is a crucial regulator of numerous fundamental cellular processes. Increasing evidence suggests that Notch signaling is involved in inflammation and oxidative stress, and thus in the progress of cerebrovascular diseases. In addition, Notch signaling in cerebrovascular diseases is associated with apoptosis, angiogenesis and the function of blood-brain barrier. Despite the contradictory results obtained to date as to whether Notch signaling is harmful or beneficial, the regulation of Notch signaling may provide a novel strategy for the treatment of cerebrovascular diseases.

HO-1 Signaling Activation by Pterostilbene Treatment Attenuates Mitochondrial Oxidative Damage Induced by Cerebral Ischemia Reperfusion Injury

Ischemia reperfusion (IR) injury (IRI) is harmful to the cerebral system and causes mitochondrial oxidative stress. The antioxidant response element (ARE)-mediated antioxidant pathway plays an important role in maintaining the redox status of the brain. Heme oxygenase-1 (HO-1), combined with potent AREs in the promoter of HO-1, is a highly effective therapeutic target for protection against cerebral IRI. Pterostilbene (PTE), a natural dimethylated analog of resveratrol from blueberries, is a strong natural antioxidant. PTE has been shown to be beneficial for some nervous system diseases and may regulate HO-1 signaling. This study was designed to investigate the protective effects of PTE on cerebral IRI and to elucidate potential mechanisms underlying those effects. Mouse brains and cultured HT22 neuron cells were subjected to IRI. Prior to this procedure, the brains or cells were exposed to PTE in the absence or presence of the HO-1 inhibitor ZnPP or HO-1 small interfering RNA (siRNA). PTE conferred a cerebral protective effect, as shown by increased neurological scores, viable neurons and decreased brain edema as well as a decreased ion content and apoptotic ratio in vivo. PTE also increased the cell viability and decreased the lactate dehydrogenase (LDH) leakage and apoptotic ratio in vitro. ZnPP and HO-1 siRNA both blocked PTE-mediated cerebral protection by inhibiting HO-1 signaling and further inhibited two HO-1 signaling-related antioxidant molecules:

NAD(P)H

quinone oxidoreductase 1 (NQO1) and glutathione S-transferases (GSTs), which are induced by PTE. PTE also promoted a well-preserved mitochondrial membrane potential (MMP), mitochondria complex I activity, and mitochondria complex IV activity, increased the mitochondrial cytochrome c level, and decreased the cytosolic cytochrome c level. However, this PTE-elevated mitochondrial function was reversed by ZnPP or HO-1 siRNA treatment. In summary, our results demonstrate that PTE treatment attenuates cerebral IRI by reducing IR-induced mitochondrial oxidative damage through the activation of HO-1 signaling.

Electroacupuncture Pretreatment Attenuates Cerebral Ischemic Injury via Notch Pathway-Mediated Up-Regulation of Hypoxia Inducible Factor-1α in Rats

We have reported electroacupuncture (EA) pretreatment induced the tolerance against focal cerebral ischemia through activation of canonical Notch pathway. However, the underlying mechanisms have not been fully understood. Evidences suggest that up-regulation of hypoxia inducible factor-1α (HIF-1α) contributes to neuroprotection against ischemia which could interact with Notch signaling pathway in this process. Therefore, the current study is to test that up-regulation of HIF-1α associated with Notch pathway contributes to the neuroprotection of EA pretreatment. Sprague–Dawley rats were treated with EA at the acupoint “Baihui (GV 20)” 30 min per day for successive 5 days before MCAO. HIF-1α levels were measured before and after reperfusion. Then, HIF-1α antagonist 2ME2 and γ-secretase inhibitor MW167 were used. Neurologic deficit scores, infarction volumes, neuronal apoptosis, and Bcl2/Bax were evaluated. HIF-1α and Notch1 intracellular domain (NICD) were assessed. The results showed EA pretreatment enhanced the neuronal expression of HIF-1α, reduced infarct volume, improved neurological outcome, inhibited neuronal apoptosis, up-regulated expression of Bcl-2, and down-regulated expression of Bax after reperfusion in the penumbra, while the beneficial effects were attenuated by 2ME2. Furthermore, intraventricular injection with MW167 efficiently suppressed both up-regulation of NICD and HIF-1α after reperfusion. However, administration with 2ME2 could only decrease the expression of HIF-1α in the penumbra. In conclusion, EA pretreatment exerts neuroprotection against ischemic injury through Notch pathway-mediated up-regulation of HIF-1α.

The Role of SUMO-Conjugating Enzyme Ubc9 in the Neuroprotection of Isoflurane Preconditioning Against Ischemic Neuronal Injury

Preconditioning with volatile anesthetics can create an ischemia tolerance against cerebral ischemia-reperfusion injury. We investigated whether ubiquitin conjugase 9 (Ubc9), the E2 conjugase for SUMOylation, is associated with neuroprotection induced by isoflurane preconditioning (IsoPC). In vitro, Ubc9 protein expression was evaluated at 4 and 24 h after reoxygenation. The role of Ubc9 in the neuroprotective effect was assessed in the presence or absence of Ubc9 small interfering RNA (siRNA). In vivo, rats were preconditionally exposed for 1 h to 2 % isoflurane for five consecutive days followed by middle cerebral artery occlusion. Neurobehavioral scores and infarction volume were determined at different times after reperfusion. The role of Ubc9 in ischemic tolerance was evaluated by intracerebroventricular microinjection with the Ubc9 siRNA. We showed that isoflurane preconditioning improved the cell viability of the SH-SY5Y cells that were challenged by oxygen-glucose deprivation. It also reduced brain infarct volumes and improved neurologic outcomes in the focal cerebral ischemic rat. The expression of Ubc9 was upregulated by isoflurane preconditioning. Knockdown of Ubc9 significantly attenuated the isoflurane preconditioning-induced neuroprotective effects. Isoflurane preconditioning-induced neuroprotection against ischemic injuries is mediated by Ubc9. These results suggest a novel mechanism for isoflurane preconditioning-induced tolerance to cerebral ischemia.