Glycogen Synthase Kinase 3β Influences Injury Following Cerebral Ischemia/Reperfusion in Rats

Meldonium, as a potential neuroprotective agent, promotes neuronal survival by protecting mitochondria in cerebral ischemia-reperfusion injury

BACKGROUND

Stroke is a globally dangerous disease capable of causing irreversible neuronal damage with limited therapeutic options. Meldonium, an inhibitor of carnitine-dependent metabolism, is considered an anti-ischemic drug. However, the mechanisms through which meldonium improves ischemic injury and its potential to protect neurons remain largely unknown.

METHODS

A rat model with middle cerebral artery occlusion (MCAO) was used to investigate meldonium's neuroprotective efficacy in vivo. Infarct volume, neurological deficit score, histopathology, neuronal apoptosis, motor function, morphological alteration and antioxidant capacity were explored via 2,3,5-Triphenyltetrazolium chloride staining, Longa scoring method, hematoxylin and eosin staining, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling assay, rotarod test, transmission electron microscopy and Oxidative stress index related kit. A primary rat hippocampal neuron model subjected to oxygen-glucose deprivation reperfusion was used to study meldonium's protective ability in vitro. Neuronal viability, mitochondrial membrane potential, mitochondrial morphology, respiratory function, ATP production, and its potential mechanism were assayed by MTT cell proliferation and cytotoxicity assay kit, cell-permeant MitoTracker® probes, mitochondrial stress, real-time ATP rate and western blotting.

RESULTS

Meldonium markedly reduced the infarct size, improved neurological function and motor ability, and inhibited neuronal apoptosis in vivo. Meldonium enhanced the morphology, antioxidant capacity, and ATP production of mitochondria and inhibited the opening of the mitochondrial permeability transition pore in the cerebral cortex and hippocampus during cerebral ischemia-reperfusion injury (CIRI) in rats. Additionally, meldonium improved the damaged fusion process and respiratory function of neuronal mitochondria in vitro. Further investigation revealed that meldonium activated the Akt/GSK-3β signaling pathway to inhibit mitochondria-dependent neuronal apoptosis.

CONCLUSION

Our study demonstrated that meldonium shows a neuroprotective function during CIRI by preserving the mitochondrial function, thus prevented neurons from apoptosis.

Glycogen synthase kinase-3β: A multifaceted player in ischemia-reperfusion injury and its therapeutic prospects

Ischemia-reperfusion injury (IRI) results in irreversible metabolic dysfunction and structural damage to tissues or organs, posing a formidable challenge in the field of organ implantation, cardiothoracic surgery, and general surgery. Glycogen synthase kinase-3β (GSK-3β) a multifunctional serine/threonine kinase, is involved in a variety of biological processes, including cell proliferation, apoptosis, and immune response. Phosphorylation of its tyrosine 216 and serine 9 sites positively and negatively regulates the activation and inactivation of the enzyme. Significantly, inhibition or inactivation of GSK-3β provides protection against IRI, making it a viable target for drug development. Though numerous GSK-3β inhibitors have been identified to date, the development of therapeutic treatments remains a considerable distance away. In light of this, this review summarizes the complicated network of GSK-3β roles in IRI. First, we provide an overview of GSK-3β's basic background. Subsequently, we briefly review the pathological mechanisms of GSK-3β in accelerating IRI, and highlight the latest progress of GSK-3β in multiorgan IRI, encompassing heart, brain, kidney, liver, and intestine. Finally, we discuss the current development of GSK-3β inhibitors in various organ IRI, offering a thorough and insightful reference for GSK-3β as a potential target for future IRI therapy.

Argon neuroprotection in ischemic stroke and its underlying mechanism

Ischemic stroke (IS), primarily caused by cerebrovascular obstruction, results in severe neurological deficits and has emerged as a leading cause of death and disability worldwide. Recently, there has been increasing exploration of the neuroprotective properties of the inert gas argon. Argon has exhibited impressive neuroprotection in many in vivo and ex vivo experiments without signs of adverse effects, coupled with the advantages of being inexpensive and easily available. However, the efficient administration strategy and underlying mechanisms of neuroprotection by argon in IS are still unclear. This review summarizes current research on the neuroprotective effects of argon in IS with the goal to provide effective guidance for argon application and to elucidate the potential mechanisms of argon neuroprotection. Early and appropriate argon administration at as high a concentration as possible offers favorable neuroprotection in IS. Argon inhalation has been shown to provide some long-term protection benefits. Argon provides the anti-oxidative stress, anti-inflammatory and anti-apoptotic cytoprotective effects mainly around Toll-like receptor 2/4 (TLR2/4), mediated by extracellular signal-regulated kinase 1/2 (ERK1/2), nuclear factor (erythroid-derived 2)-like 2 (Nrf2), nuclear factor kappa-B (NF-ĸB) and B-cell leukemia/lymphoma 2 (Bcl-2). Therefore, argon holds significant promise as a novel clinical neuroprotective gas agent for ischemic stroke after further researches to identify the optimal application strategy and elucidate the underlying mechanism.

Neuroprotective Effect of Zishen Huoxue Decoction treatment on Vascular Dementia by activating PINK1/Parkin mediated Mitophagy in the Hippocampal CA1 Region

ETHNOPHARMACOLOGICAL RELEVANCE

Zishen Huoxue Decoction (ZSHXD) is a Traditional Chinese Medicine (TCM) prescription for the treatment of vascular dementia (VD). Although the clinical effects of ZSHXD have been demonstrated, the molecular mechanisms underlying the neuroprotective effects of ZSHXD remain unclear.

AIM OF THE STUDY

To explore whether the neuroprotective effect of Zishen Huoxue Decoction (ZSHXD) treatment is associated with the PINK1/Parkin pathway-mediated mitophagy in hippocampal CA1 region of 2-VO model rats.

MATERIALS AND METHODS

Seventy-two male SD rats were randomly divided into the sham group, model group, Donepezil (0.45 mg/kg) group, ZSHXD low dose group (8.9 g/kg), ZSHXD medium dose group (17.8 g/kg), and ZSHXD high dose group (35.6 g/kg). Two-vessel occlusion (2-VO) rat model is established to evaluate the therapeutic effect of ZSHXD pretreatment. Hematoxylin-eosin (HE) staining is conducted to detect the morphological changes of neurons and the number of normal neurons in the hippocampal CA1 region. Then, the mitochondrial function and structure were reflected by the mitochondrial membrane potential (MMP) levels and transmission electron microscopy (TEM). Meanwhile, the expression of mitophagy related proteins mediated by PINK1/Parkin was detected by western blot (WB). After that, malondialdehyde (MDA) and superoxide dismutase (SOD) levels were measured by Elisa. At last, the apoptosis-related proteins Caspase-3、Bax、Bcl-2 were measured by WB.

RESULTS

The results depict that ZSHXD has dose-dependently improved the cognitive function in 2-VO model rats. It has also been showed that ZSHXD can alleviate neuron damage, rescue the mitochondrial structural injury and dysfunction in hippocampal CA1 region. Besides, ZSHXD has increased the activity of SOD and decreased the activity of MDA. In addition, ZSHXD can inhibit apoptosis with Caspase-3, Bax decreasing and Bcl-2 increasing. Specially, the protection of ZSHXD showed in 2-VO model rats is along with the upregulation of PINK1, Parkin and LC3-Ⅱ/Ⅰ, and downregulation of p62 in the hippocampal CA1 region.

CONCLUSIONS

This study reveals that ZSHXD protects the 2-VO model rats from ischemic injury by activating the PINK1/Parkin-mediated mitophagy in the hippocampal CA1 region.

Exploring the molecular mechanism of Yinao Fujian formula on ischemic stroke based on network pharmacology and experimental verification

Background

Ischemic stroke (IS) is a leading cause of long-term disability and even mortality, threatening people's lives. Yinao Fujian (YNFJ) formula is a Traditional Chinese Medicine formula that has been widely used to treat patients with IS. However, the molecular mechanism of YNFJ for the treatment of IS is still elusive. Our study aimed to explore the potential protective effect and the underlying mechanisms of YNFJ on IS using a network pharmacology approach coupled with experimental validation.

Materials and methods

Effective compounds of YNFJ were collected from BATMAN-TCM and TCMSP databases, while IS targets were obtained from GeneCards, OMIM, TTD and DrugBank databases. The protein-protein interaction (PPI) network was constructed to further screen the hub targets of YNFJ in IS treatment. GO and KEGG enrichment analyses were used to identify the critical biological processes and signaling pathways of YNFJ for IS. Moreover, Nissl staining, HE, TTC staining and Tunel staining were used in the MCAO model to prove the neuroprotective effect of YNFJ. Oxidative damage, inflammatory factor release and related pathways were tested in MCAO rat model and hypoxia-induced BV2 cell model, respectively.

Results

We found that YNFJ treatment significantly alleviated MCAO-induced nerve damage and apoptosis. Then, network pharmacology screening combined with literature research revealed IL6, TNF, PTGS2, NFKBIA and NFE2L2 as the critical targets in a PPI network. Moreover, the top 20 signaling pathways and biological processes associated with the protective effects of YNFJ on IS were enriched through GO and KEGG analyses. Further analysis indicated that NF-κB and Nrf2/HO-1 signaling pathways might be highly involved in the protective effects of YNFJ on IS. Finally, in vitro and in vivo experiments confirmed that YNFJ inhibited the release of inflammatory factors (IL-6 and TNF-α) and MDA content, and increased the activity of SOD. In terms of the mechanism, YNFJ inhibited the release of inflammatory factors by suppressing the NF-κB pathway and decreased the expression of iNOS and COX-2 to protect microglia from inflammation damage. In addition, YNFJ initiated the dissociation of Keap-1 and Nrf2, and activated the downstream protein HO-1, NQO1, thus decreasing oxidative stress.

Conclusion

Taken together, the findings in our research showed that the protective effects of YNFJ on IS were mainly achieved by regulating the NF-κB and Nrf2/HO-1 signaling pathways to inhibit oxidative stress damage and inflammatory damage of microglia.

Genetic and Pharmacological Modulation of P75 Neurotrophin Receptor Attenuate Brain Damage After Ischemic Stroke in Mice

The precursor nerve growth factor (ProNGF) and its receptor p75 neurotrophin receptor (p75NTR) are upregulated in several brain diseases, including ischemic stroke. The activation of p75NTR is associated with neuronal apoptosis and inflammation. Thus, we hypothesized that p75NTR modulation attenuates brain damage and improves functional outcomes after ischemic stroke. Two sets of experiments were performed. (1) Adult wild-type (WT) C57BL/6 J mice were subjected to intraluminal suture-middle cerebral artery occlusion (MCAO) to induce cerebral ischemia. Pharmacological inhibitor of p75NTR, LM11A-31 (50 mg/kg), or normal saline was administered intraperitoneally (IP) 1 h post-MCAO, and animals survived for 24 h. (2) Adult p75NTR heterozygous knockout (p75NTR+/-) and WT were subjected to photothrombotic (pMCAO) to induce ischemic stroke, and the animals survived for 72 h. The sensory-motor function of animals was measured using Catwalk XT. The brain samples were collected to assess infarction volume, edema, hemorrhagic transformation, neuroinflammation, and signaling pathway at 24 and 72 h after the stroke. The findings described that pharmacological inhibition and genetic knocking down of p75NTR reduce infarction size, edema, and hemorrhagic transformation following ischemic stroke. Additionally, p75NTR modulation significantly decreased several anti-apoptosis markers and improved sensory motor function compared to the WT mice following ischemic stroke. Our observations exhibit that the involvement of p75NTR in ischemic stroke and modulation of p75NTR could improve the outcome of ischemic stroke by increasing cell survival and enhancing motor performance. LM11A-31 has the potential to be a promising therapeutic agent for ischemic stroke. However, more evidence is needed to illuminate the efficacy of LM11A-31 in ischemic stroke.

Exploring the Neuroprotective Effects of Lithium in Ischemic Stroke: A literature review

Ischemic stroke ranks among the foremost clinical causes of mortality and disability, instigating neuronal degeneration, fatalities, and various sequelae. While standard treatments, such as intravenous thrombolysis and endovascular thrombectomy, prove effective, they come with limitations. Hence, there is a compelling need to develop neuroprotective agents capable of improving the functional outcomes of the nervous system. Numerous preclinical studies have demonstrated that lithium can act in multiple molecular pathways, including glycogen synthase kinase 3(GSK-3), the Wnt signaling pathway, the mitogen-activated protein kinase (MAPK)/ extracellular signal-regulated kinase (ERK) signaling pathway, brain-derived neurotrophic factor (BDNF), mammalian target of rapamycin (mTOR), and glutamate receptors. Through these pathways, lithium has been shown to affect inflammation, autophagy, apoptosis, ferroptosis, excitotoxicity, and other pathological processes, thereby improving central nervous system (CNS) damage caused by ischemic stroke. Despite these promising preclinical findings, the number of clinical trials exploring lithium's efficacy remains limited. Additional trials are imperative to thoroughly ascertain the effectiveness and safety of lithium in clinical settings. This review delineates the mechanisms underpinning lithium's neuroprotective capabilities in the context of ischemic stroke. It elucidates the intricate interplay between these mechanisms and sheds light on the involvement of mitochondrial dysfunction and inflammatory markers in the pathophysiology of ischemic stroke. Furthermore, the review offers directions for future research, thereby advancing the understanding of the potential therapeutic utility of lithium and establishing a theoretical foundation for its clinical application.

New insights into the role of GSK-3β in the brain: from neurodegenerative disease to tumorigenesis

Glycogen synthase kinase 3 (GSK-3) is a serine/threonine kinase widely expressed in various tissues and organs. Unlike other kinases, GSK-3 is active under resting conditions and is inactivated upon stimulation. In mammals, GSK-3 includes GSK-3 α and GSK-3β isoforms encoded by two homologous genes, namely, GSK3A and GSK3B. GSK-3β is essential for the control of glucose metabolism, signal transduction, and tissue homeostasis. As more than 100 known proteins have been identified as GSK-3β substrates, it is sometimes referred to as a moonlighting kinase. Previous studies have elucidated the regulation modes of GSK-3β. GSK-3β is involved in almost all aspects of brain functions, such as neuronal morphology, synapse formation, neuroinflammation, and neurological disorders. Recently, several comparatively specific small molecules have facilitated the chemical manipulation of this enzyme within cellular systems, leading to the discovery of novel inhibitors for GSK-3β. Despite these advancements, the therapeutic significance of GSK-3β as a drug target is still complicated by uncertainties surrounding the potential of inhibitors to stimulate tumorigenesis. This review provides a comprehensive overview of the intricate mechanisms of this enzyme and evaluates the existing evidence regarding the therapeutic potential of GSK-3β in brain diseases, including Alzheimer's disease, Parkinson's disease, mood disorders, and glioblastoma.

Lyoniresinol attenuates cerebral ischemic stroke injury in MCAO rat based on oxidative stress suppression via regulation of Akt/GSK-3β/Nrf2 signaling

Stroke is one of the predominant causes of death and disability. Currently, besides thrombolytic therapy, neuroprotection is also generally recognized as a promising way for stroke treatment, which would be very important for the functional recovery of stroke patients. However, it's reported that all the current available neuroprotective drugs have failed in clinical investigations of stroke treatments so far. Lyoniresinol (LNO) is a natural lignan with powerful antioxidant and cytoprotective activities. In this study, OGD/R leaded HT22 cell damage models and Middle Cerebral Artery Occlusion (MCAO) rats were used to investigate the effect of LNO on cerebral ischemic stroke injury and related mechanisms. The cell experiments revealed LNO can suppress the oxygen glucose deprivation-reoxygenation (OGD/R) induced apoptosis of HT22 cells. Subsequently, LNO can improve nerve function deficit and brain injury in MCAO rats with a higher neurological function scores and less infarct size. And the further molecular mechanisms studies suggested LNO activated the PI3K/AKT/GSK-3β/NRF2 signaling and improved the oxidative stress in cells to inhibit the OGD/R induced apoptosis in HT22 cells. Collectively, our findings would be useflu for the further drug development of LNO as new drug for stroke and its related diseases.

Qishen Yiqi Dripping Pills for Cardiovascular Diseases: Effects and Mechanisms

Qishen Yiqi Dripping Pills (QSYQ) is a compound of Chinese medicine, which has been used to treat coronary heart disease and cardiac dysfunction. Its natural components include astragaloside IV, flavonoids, danshensu, protocatechualdehyde, salvianolic acid B, salvianolic acid A, ginsenosides Rg1, ginsenosides Rb1, and essential oils, etc. It exerts effects of nourishing qi and promoting blood circulation to relieve pain. In this review, the bioactive components of QSYQ and its effects for treating cardiovascular diseases and possible mechanism were summarized, providing references for further study and clinical application of QSYQ.

Peroxiredoxin-6 Released by Astrocytes Contributes to Neuroapoptosis During Ischemia

Peroxiredoxin-6 (PRDX6), a member of the peroxiredoxin family, has progressively emerged as a possible therapeutic target for a variety of brain diseases, particularly Alzheimer's disease and ischemic stroke. However, the role of PRDX6 in neurons under ischemic conditions has remained elusive. Here, we found that astrocytes could release PRDX6 extracellularly after OGD/R, and that PRDX6 release actually worsened neuroapoptosis under OGD/R. We discovered a unique PRDX6/RAGE/JNK signaling pathway that contributes to the effect of neuroapoptosis. We applied a specific inhibitor of the RAGE signaling pathway in a mouse MCAO model and observed significant alterations in animal behavior. Considered together, our findings show the crucial role of the astrocyte-released PRDX6 in the process of neuroapoptosis caused by OGD/R, and could provide novel insights for investigating the molecular mechanism of protecting brain function from ischemia-reperfusion injury.

GSK-3β RNAi Lentivirus Affects Neuronal Damage and Nuclear Factor E2-Related Factor 2 (Nrf2) Expression in Cerebral Infarction Rats

We investigated the effect of GSK-3β RNAi lentivirus on neuronal damage and Nrf2 level in rats with cerebral infarction. 40 rats were assigned into sham group, CI group, Vector group and GSK-3β RNAi group followed by analysis of cell damage and oxidative stress, neurological scores, cerebral infarction volume, and brain water content as well as brain morphology by H&E staining and Nrf2 protein level by Western blot. Compared with sham group, GSK-3β mRNA in neurons of CI group and Vector group was significantly elevated (P < 0.05) with reduced level in GSK-3β RNAi group (P < 0.05); 3 hours after surgery, there was no change in neuroethology scores of rats in CI group, Vector group and GSK-3β RNAi group (P > 0.05). While 1 and 3 days later, the scores of rats were significantly improved (P < 0.05) and brain water content was reduced in GSK-3β RNAi group (P < 0.05) without difference between CI group and Vector group (P > 0.05). Compared with sham group, infarct size in CI group and Vector group was increased (P < 0.05) and reduced in GSK-3β RNAi group (P < 0.05) without difference between CI group and Vector group (P > 0.05). Meanwhile, CI group and Vector group showed significantly downregulated Nrf2, Srx1 and Trx1 proteins (P < 0.05), which were increased in GSK-3β RNAi group (P < 0.05). In conclusion, GSK-3β RNAi lentivirus can promote the expression of Nrf2 and exert an inhibitory effect on neurons of rats with cerebral infarction, therefore protecting brain tissue.

Sestrin2 in hypoxia and hypoxia-related diseases

Objectives: Sestrin2 is a stress-inducible protein and play an important role in adapting stress states of cells. This article reviewed the role of Sestrin2 in hypoxia and hypoxia-related diseases to provide new perspectives for future research and new therapeutic targets for hypoxia-related diseases.

Methods: A review was conducted through an electronic search of PubMed and Medline databases. Keywords included Sestrin2, ROS, hypoxia, and hypoxia-related disease. Articles from 2008 to 2021 were mostly included and older ones were not excluded.

Results: Sestrin2 is upregulated under various stress conditions, especially hypoxia. Under hypoxic condition, Sestrin2 plays a protective role by reducing the generation of ROS through various pathways, such as adenosine monophosphatea-ctivated protein kinase (AMPK) / mammalian target of rapamycin (mTOR) pathway and nuclear factor-E2-related factor2 (Nrf2) pathway. In addition, Sestrin2 is involved in various hypoxia-related diseases, such as cerebral hypoxic disease, myocardial hypoxic disease, hypoxia-related respiratory disease, and diabetes.

Discussion: Sestrin2 is involved in various hypoxia-related diseases and maybe a therapeutic target. Furthermore, most studies focus on cerebral and myocardial ischemia reperfusion. More researches on hypoxia-related respiratory diseases, kidney injury, and diabetes are needed in future.

Upregulation of Glutaredoxin 2 alleviates oxygen-glucose deprivation/reoxygenation-induced apoptosis and ROS production in neurons by enhancing Nrf2 signaling via modulation of GSK-3β

Glutaredoxin 2 (GRX2) is an antioxidative protein that exerts a key role in various pathological processes. However, whether GRX2 participates in modulating the oxidative stress during cerebral ischemia/reperfusion, injury is undermined. This study aimed to determine the potential role of GRX2 in regulating oxidative stress in cultured neurons induced by oxygen-glucose deprivation/reoxygenation (OGD/R), a cellular model for study of cerebral ischemia/reperfusion injury in vitro. Here, we showed that GRX2 expression was decreased in neurons subjected to OGD/R exposure. The upregulation of GRX2 markedly improved the viability of OGD/R-exposed neurons and caused a marked reduction in OGD/R-induced apoptosis and reactive oxygen species (ROS) production. On the contrary, depletion of GRX2 exacerbated the OGD/R-induced apoptosis and ROS production in cultured neurons. Moreover, GRX2 upregulation increased nuclear expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and enhanced the activation of Nrf2/ARE signaling associated with modulation of glycogen synthase kinase-3β (GSK-3β) inhibition. Notably, inhibition of Nrf2 markedly abrogated GRX2-mediated protection against OGD/R-induced apoptosis and oxidative stress. Overall, these findings elucidate that GRX2 plays an essential role in regulating the protection against OGD/R-induced apoptosis and oxidative stress in neurons associated with its ability to enhance the activation of Nrf2 via modulation of GSK-3β. Our study indicates that GRX2 may play a key role in modulating neuronal apoptosis and oxidative stress induced by cerebral ischemia/reperfusion injury.

Inhibition of glycogen synthase kinase 3β improves cognitive function in aged mice by upregulating claudin presences in cerebral endothelial cells

Glycogen synthase kinase-3β (GSK-3β), a serine/threonine protein kinase, is widely distributed in mammalian brains. Since GSK-3β plays a vital role in the development of neurodegenerative disorders, the present study was designed to investigate the role of GSK-3β in the blood-brain barrier (BBB) permeability in aged mice. Morris water maze test was used to examine mouse cognitive function. BBB permeability was examined by the leakage of fluorescence signals of low-molecular weight dextran. GSK-3β inhibitor, 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8), was administrated in aged mice and in cultured mouse brain microvascular endothelial cells (bEnd.3). Compared with young mice, aged mice had increased leftover signals of dextran in the hippocampus and a lower score in the maze test, suggesting that aged mice have abnormal leakage of BBB and cognitive dysfunction. The protein expression of Toll-like receptor 4 (TLR4) was increased, whereas the protein expressions of junction proteins (claudin1 and claudin5) were reduced in endothelial cells of BBB in aged mice. Phosphorylated level of serine 9, an inhibitory residue in GSK-3β protein, was decreased. TDZD-8 treatment downregulated TLR4 protein expression, upregulated claudin1 and claudin5 protein expressions, and significantly improved cognitive function in aged mice. In bEnd.3 cells, TDZD-8 treatment reduced TLR4 expression and increased claudin5 expression in cells stimulated with lipopolysaccharides. In conclusion, the inhibition of GSK-3β activity downregulates aging-induced TLR4 expression and restores the BBB integrity, resulting in the improvement of cognitive function in aged mice.

Electroacupuncture pretreatment prevents ischemic stroke and inhibits Wnt signaling-mediated autophagy through the regulation of GSK-3β phosphorylation

Electroacupuncture (EA), a traditional Chinese replacement therapy, is widely accepted to treat ischemic stroke. Increasing evidence show that autophagy is involved in the process of cerebral ischemia injury and the Wnt/GSK3β pathway, playing an important role in protecting central nervous system. In this study, rats were treated with EA prior to focal ischemia by middle cerebral artery occlusion (MCAO). Deficit score, infarct volumes and levels of autophagy markers, such as LC3I, LC3II and p62, were assessed with either PI3K inhibitor wortmannin or a GSK-3β inhibitor LiCl. Oxygen-glucose deprivation/re-oxygenation (OGD/R) was made in the primitive neuron in vitro, and was respectively treated with autophagy inhibitors 3-MA, LiCl, GSK3β siRNA, or mTOR inhibitor rapamycin. The results indicated that EA pretreatment increased the levels of autophagy marker LC3-II and reduced the levels of p62. Meanwhile, deficit outcome was improved, and infarct volumes were reduced by EA pretreatment. Furthermore, the beneficial effects of EA pretreatment were reversed by wortmannin. LiCl and GSK3β siRNA can mimic the neuroprotective effects of EA pretreatment by downregulating autophagy, and increasing protein levels of p-mTOR, p-GSK3β and β-catenin in OGD/R neurons. However, the protective effects of GSK3β siRNA were blocked by rapamycin. These results suggest that EA pretreatment induces tolerance to cerebral ischemia by inhibiting autophagy via the Wnt pathway through the inhibition of GSK3β.

The Neuroprotective Mechanism of Spinal Cord Stimulation in Spinal Cord Ischemia/Reperfusion Injury

BACKGROUND

Spinal cord ischemia/reperfusion (I/R) injury following thoracoabdominal aneurysm surgery can lead to severe lower limb neurologic defect. The preliminary result of our study suggested that spinal cord stimulation (SCS) postconditioning effectively protected spinal cord from I/R injury on rabbits. But the mechanism is unknown. In this study, we further investigated the mechanism of SCS postconditioning.

METHOD

New Zealand white rabbits were randomly divided into sham, I/R, I/R + 2 Hz SCS, and I/R + 50 Hz SCS group (n = 24/group). Transient spinal cord ischemia was induced by infrarenal aortic balloon occlusion and performed on all rabbits except rabbits of sham group. Rabbits of I/R group received no further intervention. Rabbits of I/R + 2 Hz SCS and I/R + 50 Hz SCS group received 2 Hz or 50 Hz SCS for 30 min at the onset of reperfusion and then daily. The expression of Akt (serine-threonine kinase)/p-Akt, STAT3 (signal transducer and activator of transcription 3)/p-STAT3 and GSK-3β (glycogen synthase kinase)/p-GSK-3β of spinal cord were measured by Western blot analysis at 8 h, 1 day, 3 day, and 7 day of reperfusion.

RESULT

The Akt expressions of sham, I/R, I/R + 2 Hz SCS, and I/R + 50 Hz SCS group were not significantly different at all prescribed time points, while the p-Akt expression of I/R + 2 Hz SCS group was significantly higher than that of I/R group and sham group at all prescribed time points; The STAT3 and p-STAT3 expression of I/R, I/R + 2 Hz SCS, and I/R + 50 Hz SCS group were not significantly different at all prescribed time points except that at 1day of reperfusion the p-STAT3 expression of I/R + 50 Hz SCS group was significantly lower than I/R group. The GSK-3β and p-GSK-3β expressions of I/R, I/R + 2 Hz SCS and I/R + 50 Hz SCS group were not significantly different at all prescribed time points.

CONCLUSION

The neuroprotective effect of 2 Hz SCS postconditioning in spinal cord I/R injury is related to Akt activation but not regulation of STAT3 and GSK-3β phosphorylation.

Overexpression of lemur tyrosine kinase-2 protects neurons from oxygen-glucose deprivation/reoxygenation-induced injury through reinforcement of Nrf2 signaling by modulating GSK-3β phosphorylation

Lemur tyrosine kinase-2 (LMTK2), a newly identified serine/threonine kinase, is a potential regulator of cell survival and apoptosis. However, little is known about its role in regulating neuronal survival during cerebral ischemia/reperfusion injury. The present study aimed to explore the potential function of LMTK2 in regulating neuronal survival using an in vitro model of oxygen-glucose deprivation/reoxygenation (OGD/R)-induced injury. Herein, we found that LMTK2 expression was markedly decreased in neurons following OGD/R exposure. Gain-of-function experiments demonstrated that LMTK2 overexpression significantly improved the viability and reduced apoptosis of neurons with OGD/R-induced injury. Moreover, LMTK2 overexpression reduced the production of reactive oxygen species (ROS) in OGD/R-exposed neurons. Notably, our results elucidated that LMTK2 overexpression reinforced the activation of nuclear factor erythroid 2-related factor (Nrf2)/antioxidant response element (ARE) antioxidant signaling associated with increased glycogen synthase kinase-3β (GSK-3β) phosphorylation. GSK-3β inhibition by its specific inhibitor significantly reversed LMTK2-inhibition-linked apoptosis and ROS production. Additionally, silencing Nrf2 partially reversed the LMTK2-overexpression-mediated neuroprotective effect in OGD/R-injured neurons. Taken together, our results demonstrated that LMTK2 overexpression alleviated OGD/R-induced neuronal apoptosis and oxidative damage by enhancing Nrf2/ARE antioxidant signaling via modulation of GSK-3β phosphorylation. Our study suggests LMTK2 is a potential target for neuroprotection during cerebral ischemia/reperfusion.

Downregulation of microRNA-302b-3p relieves oxygen-glucose deprivation/re-oxygenation induced injury in murine hippocampal neurons through up-regulating Nrf2 signaling by targeting fibroblast growth factor 15/19

MicroRNAs have emerged as critical mediators of cerebral ischaemia/reperfusion injury. Recent studies have demonstrated that microRNA-302b-3p (miR-302b-3p) plays an important role in regulating apoptosis and oxidative stress in various cells. However, whether miR-302b-3p is involved in regulating cerebral ischaemia/reperfusion injury-induced neuronal apoptosis and oxidative stress remains unknown. In the present study, we explored the potential function and molecular mechanism of miR-302b-3p in oxygen-glucose deprivation/re-oxygenation (OGD/R)-induced neuronal injury, using an in vitro model of cerebral ischaemia/reperfusion injury. We found that miR-302b-3p expression was up-regulated by OGD/R treatment in neurons. The inhibition of miR-302b-3p improved cell viability, and reduced apoptosis and the production of reactive oxygen species, showing a protective effect against OGD/R-induced injury. Interestingly, miR-302b-3p was shown to target and modulate murine fibroblast growth factor 15 (FGF15). Moreover, our results showed that miR-302b-3p down-regulation contributed to the promotion of nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE)-mediated antioxidant signaling associated with the inactivation of glycogen synthase kinase-3β. However, the knockdown of FGF15 significantly reversed the miR-302b-3p inhibition-mediated protective effect in OGD/R-treated neurons. Overall, these results demonstrated that miR-302b-3p inhibition confers a neuroprotective effect in OGD/R-treated neurons by up-regulating Nrf2/ARE antioxidant signaling via targeting FGF15, providing a novel target for neuroprotection in cerebral ischaemia/reperfusion injury.

Sestrin2 overexpression attenuates focal cerebral ischemic injury in rat by increasing Nrf2/HO-1 pathway-mediated angiogenesis

Sestrin2 (Sesn2) is a stress response protein which expresses neuroprotective characteristics in some neurodegenerative disorders. However, the impact of Sesn2 on the clinical outcome of stroke is unclear. The nuclear factor-erythroid 2 related factor 2/heme oxygenase-1 (Nrf2/HO-1) pathway is a key factor in angiogenesis, which aids in attenuating cerebral ischemia damage. In this study the investigators examine the effects of Sesn2 on cerebral ischemia damage by increasing angiogenesis through the Nrf2/HO-1 signaling pathway. Healthy adult Sprague-Dawley (SD) rats were exposed to photochemical cerebral ischemia while AAV injection was used to overexpress Sesn2. At 5 days after photochemical embolization, the investigators observed a reduction in neurological problems, decreased infarct volume, and diminished neuronal injury in the Sesn2 overexpression samples compared to the controls. To further explore these defensive mechanisms, the investigators also silenced Nrf2. While Sesn2, Nrf2, HO-1, and VEGF were significantly increased following cerebral ischemia, overexpression of Sesn2 further increased their expression. After silencing Nrf2, the opposite effect was observed. These results imply that Sestrin2 may activate the Nrf2 / HO-1 pathway, leading to enhanced angiogenesis following photothrombotic cerebral ischemia.

MicroRNA-135b-5p prevents oxygen-glucose deprivation and reoxygenation-induced neuronal injury through regulation of the GSK-3β/Nrf2/ARE signaling pathway

INTRODUCTION

MicroRNAs (miRNAs) are emerging as critical regulators in the pathological process of cerebral ischemia/reperfusion injury. miRNAs play an important role in regulating neuronal survival. miR-135b-5p has been reported as an important miRNA in regulating cell apoptosis. However, the role of miR-135b-5p in regulating neuronal survival remains poorly understood. Here, we aimed to investigate the role of miR-135b-5p in cerebral ischemia/ reperfusion using an in vitro model of oxygen-glucose deprivation and reoxygenation-(OGD/R) induced neuron injury.

MATERIAL AND METHODS

miRNA, mRNA and protein expression was detected by real-time quantitative polymerase chain reaction and Western blot. Cell viability was detected by cell counting kit-8 and lactate dehydrogenase assays. Cell apoptosis was detected by caspase-3 activity assay. Oxidative stress was determined using commercial kits. The target of miR-135b-5p was confirmed by dual-luciferase reporter assay.

RESULTS

We found that miR-135b-5p expression was significantly decreased in hippocampal neurons receiving OGD/R treatment. Overexpression of miR-135b-5p markedly alleviated OGD/R-induced cell injury and oxidative stress, whereas suppression of miR-135b-5p showed the opposite effects. We observed that miR-135b-5p directly targeted the 3'-untranslated region of glycogen synthase kinase-3β (GSK-3β). We found that miR-135b-5p negatively regulates the expression of GSK-3β in hippocampal neurons. Moreover, miR-135b-5p overexpression promotes activation of nuclear factor erythroid 2-related factor 2 (Nrf2)/antioxidant response element (ARE) signaling. However, the restoration of GSK-3β expression significantly reversed the protective effects of miR-135b-5p overexpression.

CONCLUSIONS

Overall, our results suggest that miR-135b-5p protects neurons against OGD/R-induced injury through downregulation of GSK-3β and promotion of the Nrf2/ARE signaling pathway-mediated antioxidant responses.

Nrf2-mediated neuroprotection against oxygen-glucose deprivation/reperfusion injury by emodin via AMPK-dependent inhibition of GSK-3β

Objectives

Our study verified the neuroprotective properties of emodin against oxygen-glucose deprivation/reoxygenation (OGD/R) and demonstrated its mechanism.

Methods

Human neuronal SH-SY5Y cells were investigated by analysing cell viability, lactate dehydrogenase levels, expression of molecules related to apoptotic cell death, and using biochemical techniques, flow cytometry and Western blot assays.

Key findings

Emodin reduced OGD/R-lead to neurotoxicity in SH-SY5Y cells. OGD/R significantly increased levels of cleaved poly ADP ribose polymerase, cleaved caspase-3, cleaved caspase-9, p53, p21 and Bax protein. However, emodin treatment effectively inhibited these OGD/R-induced changes. Emodin treatment also increased HO-1 and NQO1 expression in a concentration- and time-dependent manner and caused antioxidant response element (ARE) transcription activity and nuclear Nrf2 accumulation. Emodin phosphorylated AMPK and GSK3β, and pretreatment of cells with an AMPK inhibitor suppressed emodin-induced nuclear Nrf2 accumulation and HO-1 and NQO1 expression. AMPK inhibitor treatment decreased GSK3β phosphorylation, suggesting that AMPK is upstream of GSK3β, Nrf2, HO-1 and NQO1. Emodin's neuroprotective effect was completely blocked by HO-1, NQO1 and Nrf2 knock-down and an AMPK inhibitor, indicating the action of AMPK/GSK3β/Nrf2/ARE in the neuroprotective effect of emodin subjected to OGD/R.

Conclusions

Emodin treatment protected against OGD/R-lead to neurotoxicity by potentiating Nrf2/ARE-regulated neuroprotection through the AMPK/GSK3β pathway, indicating that emodin may be useful for treating neurodegenerative disorders.

Humanin analogue, S14G-humanin, has neuroprotective effects against oxygen glucose deprivation/reoxygenation by reactivating Jak2/Stat3 signaling through the PI3K/AKT pathway

Stroke, characterized by a disruption of blood supply to the brain, is a major cause of morbidity and mortality worldwide. Although humanin, a 24-amino acid polypeptide, has been identified to have multiple neuroprotective functions, the level of humanin in plasma has been demonstrated to decrease with age, which likely limits the effects against stroke injury. A potent humanin analogue, S14G-humanin (HNG), generated by replacement of Ser14 with glycine, has been demonstrated to have 1,000-fold stronger biological activity than humanin. The present study established an in vitro oxygen glucose deprivation/reoxygenation (OGD/R) model using SH-SY5Y neuroblastoma cells to mimic the in vivo ischemia/reperfusion injury in stroke. Adding HNG (0-10 µg/l) to SH-SY5Y cells to different extents blocked OGD/R-induced reduction of cell viability and antioxidative capacity, as well as decreased the elevated apoptosis rate induced by OGD/R, with the most evident effects at 1 µg/l HNG. Janus kinase 2 (Jak2)/signal transducer and activator of transcription 3 (Stat3) signaling was attenuated in OGD/R processes, yet reactivated with HNG treatment. FLLL32 (5 µM), a specific inhibitor of the signal, abolished effects of HNG on anti-apoptosis and antioxidation in OGD/R processes. Co-treatment with HNG and FLLL32 failed to interrupt upregulation of cytochrome c, B-cell lymphoma 2-associated X protein and cleaved caspase-3 provoked by OGD/R. Similar to FLLL32, Jak2/Stat3 signaling activated by HNG was also repressed by inhibitor of phosphoinositide 3-kinase (PI3K; 10 µM LY294002) or protein kinase B (AKT; 5 µM MK-2206 2HCl). These data collectively indicated that HNG has neuroprotective effects against OGD/R by reactivating Jak2/Stat3 signaling through the PI3K/AKT pathway, suggesting that HNG may be a promising agent in the management of stroke.

Role of glycogen synthase kinase 3 in ischemia-induced blood-brain barrier disruption in aged female rats

Estrogen receptors have protective effects against ischemic brain injury. However, the molecular mechanisms underlying this phenomenon have yet to be well studied. Given that inhibition of glycogen synthase kinase (GSK3) can reduce cerebral ischemia/reperfusion injury, we hypothesized that estrogen receptors-mediated protective effects against ischemia-induced blood-brain barrier (BBB) disruption involve inhibition of GSK3. Thus, we evaluated GSK3 expression in the brain of ovariectomized female rats, and examined the effects of intracerebroventricular pre-treatments of SB216763, GSK3 inhibitor, on BBB permeability following middle cerebral artery occlusion (MCAO). We also examined the role of specific estrogen receptor subtype in regulation of GSK3 expression and BBB permeability after MCAO. We found that ovariectomized female rats exhibited increased mRNA levels of estrogen receptor α (ERα) and estrogen receptor β (ERβ), and increased protein levels of GSK3β but not GSK3α in brain cortical areas. Furthermore, intracerebroventricular pre-treatments of SB216763 dose-dependently attenuated brain infarction volume, brain water contents, neurological deficits, and BBB disruption, and increased tight junction protein ZO-1 and occludin expression at 24 h following MCAO. Finally, activation of ERβ but not ERα dose-dependently decreased GSK3β expression at 24 h following MCAO. This was associated with increased tight junction protein expression and improved neurological scores. Thus, our study suggested that activation of ERβ may protect against brain ischemia-induced BBB disruption by inhibiting GSK3β-mediated signaling.

Phospholipase A2 of Peroxiredoxin 6 Plays a Critical Role in Cerebral Ischemia/Reperfusion Inflammatory Injury

Microglia-mediated inflammation is an important step in the progression of cerebral ischemia/reperfusion injury and the associated production of receptors of immunomoudulation, including Toll-like receptors (TLRs). Peroxiredoxin 6 (Prdx6) has been demonstrated as the endogenous antioxidant protein for its peroxidase properties. However, the role of the independent phospholipase A2 (iPLA2) activity of Prdx6 in stroke has not been well studied. In this study, we evaluated whether blocking the calcium-iPLA2 activity of Prdx6 using siRNA and inhibitors (1-hexadecyl-3-(trifluoroethgl)-sn-glycerol-2 phosphomethanol, MJ33) would have a critical effect on inflammatory brain damage. We conducted oxygen-glucose deprivation (OGD)/recovery (R) in vitro and middle cerebral artery occlusion (MCAO) in vivo in a microglia/neuron co-culture system and in rats. In vitro, we found that Prdx6-iPLA2 activity was associated with the secretion of neurotoxic inflammatory mediators interleukin1β (IL-1β), interleukin-17 (IL-17) and interleukin-23 (IL-23) and elevated expression of Toll-like receptor 2/4 (TLR2/4), leading to the formation of nuclear factor-kappa B (NF-κB), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in microglial cells. In vivo, combined treatment with Prdx6-iPLA2 activity inhibitor MJ33 showed a greater diminution in neurologic deficits, cerebral infarction, brain water content and inflammatory molecules than Prdx6-siRNA treatment alone. Our findings provide new insight into Prdx6-iPLA2 function in the brain. Inhibition of Prdx6-iPLA2 activity by gene therapy and/or pharmacology may constitute a promising new therapeutic approach to the treatment of stroke.

GSK-3β as a target for protection against transient cerebral ischemia

Stroke remains the leading cause of death and disability worldwide. This fact highlights the need to search for potential drug targets that can reduce stroke-related brain damage. We showed recently that a glycogen synthase kinase-3β (GSK-3β) inhibitor attenuates tissue plasminogen activator-induced hemorrhagic transformation after permanent focal cerebral ischemia. Here, we examined whether GSK-3β inhibition mitigates early ischemia-reperfusion stroke injury and investigated its potential mechanism of action. We used the rat middle cerebral artery occlusion (MCAO) model to mimic transient cerebral ischemia. At 3.5 h after MCAO, cerebral blood flow was restored, and rats were administered DMSO (vehicle, 1% in saline) or GSK-3β inhibitor TWS119 (30 mg/kg) by intraperitoneal injection. Animals were sacrificed 24 h after MCAO. TWS119 treatment reduced neurologic deficits, brain edema, infarct volume, and blood-brain barrier permeability compared with those in the vehicle group. TWS119 treatment also increased the protein expression of β-catenin and zonula occludens-1 but decreased β-catenin phosphorylation while suppressing the expression of GSK-3β. These results indicate that GSK-3β inhibition protects the blood-brain barrier and attenuates early ischemia-reperfusion stroke injury. This protection may be related to early activation of the Wnt/β-catenin signaling pathway.

Mitochondrial fission and fusion in secondary brain damage after CNS insults

Mitochondria are dynamically active organelles, regulated through fission and fusion events to continuously redistribute them across axons, dendrites, and synapses of neurons to meet bioenergetics requirements and to control various functions, including cell proliferation, calcium buffering, neurotransmission, oxidative stress, and apoptosis. However, following acute or chronic injury to CNS, altered expression and function of proteins that mediate fission and fusion lead to mitochondrial dynamic imbalance. Particularly, if the fission is abnormally increased through pro-fission mediators such as Drp1, mitochondrial function will be impaired and mitochondria will become susceptible to insertion of proapototic proteins. This leads to the formation of mitochondrial transition pore, which eventually triggers apoptosis. Thus, mitochondrial dysfunction is a major promoter of neuronal death and secondary brain damage after an insult. This review discusses the implications of mitochondrial dynamic imbalance in neuronal death after acute and chronic CNS insults.