Astrocyte GGTI-mediated Rac1 prenylation upregulates NF-κB expression and promotes neuronal apoptosis following hypoxia/ischemia

The Brain at High Altitude: From Molecular Signaling to Cognitive Performance

The brain requires over one-fifth of the total body oxygen demand for normal functioning. At high altitude (HA), the lower atmospheric oxygen pressure inevitably challenges the brain, affecting voluntary spatial attention, cognitive processing, and attention speed after short-term, long-term, or lifespan exposure. Molecular responses to HA are controlled mainly by hypoxia-inducible factors. This review aims to summarize the cellular, metabolic, and functional alterations in the brain at HA with a focus on the role of hypoxia-inducible factors in controlling the hypoxic ventilatory response, neuronal survival, metabolism, neurogenesis, synaptogenesis, and plasticity.

Exosomal Micro-RNA-96 Derived From Bone Marrow Mesenchymal Stem Cells Inhibits Doxorubicin-Induced Myocardial Toxicity by Inhibiting the Rac1/Nuclear Factor-κB Signaling Pathway

Background

Exosomes are small membranous structures released from cells into the blood, regulating various biological processes. However, the role of exosomes in cardiotoxicity remains largely unclear. This study investigated the functional mechanism of exosomal microRNA‐96 (miR‐96) derived from bone marrow mesenchymal stem cells (BMSCs) in myocardial toxicity induced by doxorubicin.

Methods and Results

BMSCs were transfected with miR‐96 mimic, miR‐96 inhibitor, or the negative control before exosome isolation. The functional mechanism of BMSC‐derived exosomal miR‐96 was investigated in doxorubicin‐induced cell and rat models. The cardiac function, histological morphology, and fiber content of myocardium were examined. The expression levels of the following biomarkers were measured for assessment of cardiac injury: creatine kinase isoenzyme MB, cardiac troponin I, brain natriuretic peptide, soluble suppression of tumorigenesis‐2, tumor necrosis factor‐α, interleukin‐1β, interleukin‐6, superoxide dismutase, glutathione peroxidase, and malondialdehyde. Cell Counting Kit‐8 assay was used to measure the survival rate of cardiomyocytes. The expressions of miR‐96, Rac1, p‐IKKα/IKKα, p‐IKKβ/IKKβ, p‐IκBα/IκBα and p‐p65/p65 in myocardium and cardiomyocytes were also assessed. The targeting relationship between miR‐96 and Rac1 was verified by dual‐luciferase reporter assay. miR‐96 was downregulated, Rac1 was upregulated and the nuclear factor‐κB signaling pathway was activated in doxorubicin‐induced cell and animal models. Doxorubicin decreased antioxidative enzymes (superoxide dismutase and glutathione peroxidase) and increased myocardial injury biomarkers (creatine kinase isoenzyme MB, cardiac troponin I, and brain natriuretic peptide), proinflammatory cytokines (tumor necrosis factor‐α, interleukin‐1β, and interleukin‐6), malondialdehyde, and myocardial fibers. Exosomes derived from BMSCs ameliorated doxorubicin‐induced myocardial injuries. Overexpression of miR‐96 in exosomes derived from BMSCs further enhanced the protection of myocardium and cardiomyocytes against doxorubicin‐induced toxicity while miR‐96 knockdown abolished the protective effects of exosomes derived from BMSCs. Rac1 was a target gene of miR‐96. Rac1 inhibition could downregulate the expression of the nuclear factor‐κB signaling and further reverse the promotion of miR‐96 knockdown on doxorubicin‐induced myocardial toxicity.

Conclusions

BMSC‐derived exosomal miR‐96 protects myocardium against doxorubicin‐induced toxicity by inhibiting the Rac/nuclear factor‐κB signaling pathway.

Upregulated Long Non-coding RNA ALMS1-IT1 Promotes Neuroinflammation by Activating NF-κB Signaling in Ischemic Cerebral Injury

BACKGROUND

ALMS1-IT1, a recently identified lncRNA, has been proven to play a crucial role in regulating tumor progression and predicting the survival time of tumor patients. Data analysis from the Human Body Map (HBM) revealed that ALMS1-IT1 is expressed mainly in brain tissues.

METHODS

In this study, the role of ALMS1-IT in regulating neuro-inflammation and functional recovery was investigated after ischemic cerebral damage. To this end, the rat model of transient middle cerebral artery occlusion (tMCAO) was constructed, the cell model of oxygen-glucose deprivation (OGD) was established using BV2 microglial cells, and the aberrant expression of ALMS1-IT1 was assessed in brain tissues. After ALMS1- IT1 knockdown through intrathecal injection of Lv-shALMS1-IT1, neuro-inflammatory response and functional tests including a modified neurological severity score (mNSS) and a foot-fault test were assessed.

RESULTS

The level of ALMS1-IT1 was promptly enhanced at 12 hours (h) following MCAO, peaking at 48 h, and remaining high at day 14 compared to the sham group. Pro-inflammatory cytokines (IL-1β, IL-6, and TNF- α) were increased after MCAO, whereas ALMS1-IT1 inhibition suppressed the expression of IL-1β, IL-6 and TNF-α in MCAO rats. The results from mNSS and foot-fault test showed that ALMS1-IT1 knockdown significantly improved spatial learning and sensorimotor function of MCAO rats. Mechanistically, ALMS1-IT1 knockdown suppressed the activation of NF-κB signaling in vitro and in vivo, as evidenced by decreased p65 expression and p65 nuclear translocation. ALMS1-IT1 overexpression facilitated pro-inflammatory cytokines expression in microglia, whereas the effect was blocked by treatment with JSH-23 (a specific NF-κB inhibitor).

CONCLUSION

These data demonstrated that ALMS1-IT1 inhibition improved neurological function of MCAO rats, at least in part by repressing NF-κB-dependent neuro-inflammation.

Acteoside isolated from Colebrookea oppositifolia attenuates I/R brain injury in Wistar rats via modulation of HIF-1α, NF-κB, and VEGF pathways

AIMS

The objective of this study was to assess the anti-stroke activity of acteoside isolated from methanolic root extract of C. oppositifolia METHODS: Ischemia-reperfusion(I/R) brain injury was induced in Wistar rats to assess the anti-stroke activity of acteoside. Rats were pretreated with acteoside (10, 25 & 50 mg/kg, p.o.) before the induction of I/R injury. Parameters such as neurological, motor-cognitive functions were evaluated along with morphological (brain volume, infarct size), biochemical (SOD, Catalase, GSH, lipid peroxidation, TNF-α, IL-6, IL-10, ICAM-1, HIF-1α, VEGF, and NF-κB), histopathological, and gene expression studies (HIF-1α, VEGF) were performed to study the protective effect of acteoside against I/R induced brain injury.

RESULTS

I/R injury caused significant deterioration of neurological (p < 0.01), motor (p < 0.01) and cognitive (p < 0.01) functions, associated with increase in the brain volume (p < 0.01), and infarct size (p < 0.01); increase in the levels of MDA, TNF-α, IL-6, ICAM-1, HIF-1α, VEGF, and NF-κB along with significant decrease in SOD, catalase, GSH, and IL-10 (p < 0.01 for all parameters) compared to Sham control group. Histology of brain tissue of disease control group exhibited significant vascular changes, neutrophil infiltration, cerebral oedema, and necrosis of the neuronal cells. Further, the gene-expression studies showed significant increase in the HIF-1α (p < 0.01) and VEGF (p < 0.01) mRNA levels in the I/R control compared to Sham control. Interestingly, the acteoside (10, 25 & 50 mg/kg) has prevented the neurological, motor and cognitive dysfunctions, along with inhibiting the morphological, biochemical, histological and gene expression changes induced by I/R-injury (p < 0.05 for 10 mg; p < 0.01 for 25 & 50 mg/kg of acteoside for all the parameters).

CONCLUSION

These findings suggest that acteoside possess potent anti-stroke activity through modulation of HIF-1α, NF-κB, and VEGF pathway along with its potent antioxidant activity.

The p38 MAPK/NF-κB pathway mediates GLT-1 up-regulation during cerebral ischemic preconditioning-induced brain ischemic tolerance in rats

Our previous finding suggests that p38 MAPK contributes to the GLT-1 upregulation during induction of brain ischemic tolerance by cerebral ischemic preconditioning (CIP), however, the underlying mechanism is still unclear. Here, we investigated the molecular mechanisms underlying the CIP-induced GLT-1 upregulation by using Western blotting, Co-immunoprecipitation (Co-IP), electrophoretic mobility shift assay (EMSA) and thionin staining in rat hippocampus CA1 subset. We found that application of BAY11-7082 (an inhibitor of NF-κB), or dihydrokainate (an inhibitor of GLT-1), or SB203580 (an inhibitor of p38 MAPK) could attenuate the CIP-induced neuronal protection in hippocampus CA1 region of rats. Moreover, CIP caused rapid activation of NF-κB, as evidenced by nuclear translocation of NF-κB p50 protein, which led to active p50/p65 dimer formation and increased DNA binding activity. GLT-1 was also increased after CIP. Pretreatment with BAY11-7082 blocked the CIP-induced GLT-1 upregulation. The above results suggest that NF-κB participates in GLT-1 up-regulation during the induction of brain ischemic tolerance by CIP. We also found that pretreatment with SB203580 caused significant reduction of NF-κB p50 protein in nucleus, NF-κB p50/p65 dimer nuclear translocation and DNA binding activity of NF-κB. Together, we conclude that p38 MAPK/NF-κB pathway participates in the mediation of GLT-1 up-regulation during the induction of brain ischemic tolerance induced by CIP.

Glucagon-like peptide-1 cleavage product GLP-1(9-36) reduces neuroinflammation from stroke via the activation of insulin-like growth factor 1 receptor in astrocytes

Glucagon-like peptide-1 (GLP-1) is an endogenous gut hormone and a key regulator in maintaining glucose homeostasis by stimulating insulin secretion. Its natural cleavage product GLP-1 (9-36), which was formerly considered a "bio-inactive" metabolite mainly due to its low affinity for GLP-1 receptor, possesses unique properties such as cardiovascular protection. Little is known about the effects and mechanisms of GLP-1 (9-36) in cerebral ischemia and reperfusion injury. Here, we report that systemic application of GLP-1 (9-36) in adult mice facilitated functional recovery and reduced infarct volume, astrogliosis, and neuronal apoptosis following middle cerebral artery occlusion and reperfusion. Interestingly, these effects were still observed in GLP-1 receptor knockout (Glp-1r^KO) mice but were partially reversed in insulin-like growth factor 1 (IGF-1) receptor knockdown (Igf-1r^KD) mice. Primary astrocytes were cultured and subjected to oxygen-glucose deprivation/reoxygenation (OGD/R), and enzyme-linked immunosorbent assay indicated that GLP-1 (9-36) pretreatment reduces tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 levels. This effect was not diminished in Glp-1r^KO astrocytes but was reversed in Igf-1r^KO astrocytes, emphasizing that the anti-inflammatory effect of GLP-1 (9-36) in astrocytes is independent of GLP-1 receptor signaling and is instead mediated by IGF-1 receptor. Immunoprecipitation experiments showed that GLP-1 (9-36) directly interacts with IGF-1 receptor in astrocytes. Western blot data indicated that GLP-1 (9-36) activates IGF-1 receptor and downstream PI3K-AKT pathway in astrocytes upon OGD/R injury, which was abrogated by preincubation with IGF-1 receptor autophosphorylation inhibitor picropodophyllin. Thus, our findings suggest that GLP-1 (9-36) improved stroke outcome by reducing inflammation in astrocytes via interaction with IGF-1 receptor.

Pleiotropic effects of statins on brain cells

Starting with cholesterol homeostasis, the first part of the review addresses various aspects of cholesterol metabolism in neuronal and glial cells and the mutual crosstalk between the two cell types, particularly the transport of cholesterol from its site of synthesis to its target loci in neuronal cells, discussing the multiple mechanistic aspects and transporter systems involved. Statins are next analyzed from the point of view of their chemical structure and its impingement on their pharmacological properties and permeability through cell membranes and the blood-brain barrier in particular. The following section then discusses the transcriptional effects of statins and the changes they induce in brain cell genes associated with a variety of processes, including cell growth, signaling and trafficking, uptake and synthesis of cholesterol. We review the effects of statins at the cellular level, analyzing their impact on the cholesterol composition of the nerve and glial cell plasmalemma, neurotransmitter receptor mobilization, myelination, dendritic arborization of neurons, synaptic vesicle release, and cell viability. Finally, the role of statins in disease is exemplified by Alzheimer and Parkinson diseases and some forms of epilepsy, both in animal models and in the human form of these pathologies.

Targeting prenylation inhibition through the mevalonate pathway

Protein prenylation is a critical mediator in several diseases including cancer and acquired immunodeficiency syndrome (AIDS). Therapeutic intervention has focused primarily on directly targeting the prenyltransferase enzymes, FTase and GGTase I and II. To date, several drugs have advanced to clinical trials and while promising, they have yet to gain approval in a medical setting due to off-target effects and compensatory mechanisms activated by the body which results in drug resistance. While the development of dual inhibitors has mitigated undesirable side effects, potency remains sub-optimal for clinical development. An alternative approach involves antagonizing the upstream mevalonate pathway enzymes, FPPS and GGPPS, which mediate prenylation as well as cholesterol synthesis. The development of these inhibitors presents novel opportunities for dual inhibition of cancer-driven prenylation as well as cholesterol accumulation. Herein, we highlight progress towards the development of inhibitors against the prenylation machinery.

Protective effect of dexmedetomidine against diabetic hyperglycemia-exacerbated cerebral ischemia/reperfusion injury: An in vivo and in vitro study

AIMS

Dexmedetomidine (Dex) has been noted to have neuroprotective effect against cerebral ischemia-reperfusion (I/R) injury. However, the effect of Dex in diabetic hyperglycemia-exacerbated cerebral I/R injury and its underlying mechanism remain unclear.

MAIN METHODS

The infarct volume and brain edema were evaluated by 2,3,5-triphenyltetrazolium chloride staining and standard wet-dry method. Modified neurological severity score was utilized to assess the neurological deficits. The oxidative stress and inflammation were evaluated by detecting reactive oxygen species (ROS), malondialdehyde (MDA), tumor necrosis factor (TNF)-α and interleukin (IL)-1β. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay and cell count kit-8 were applied to measure cell apoptosis and viability.

KEY FINDINGS

Dex treatment reduced infarct volume, decreased brain water content and improved neurological deficit in middle cerebral artery occlusion/reperfusion (MCAO/R) mice. Dex treatment reduced the levels of ROS, MDA, TNF-α and IL-1β in the entire middle cerebral artery territory of diabetic mice subjected to MCAO/R, as well as in primary culture of mouse hippocampal neurons stimulated with 50 mM glucose and oxygen glucose deprivation/reperfusion. Dex treatment inhibited neuronal apoptosis induced by diabetic hyperglycemia-exacerbated cerebral I/R injury. Dex upregulated nuclear factor of activated T-cells 5 (NFAT5) and Sirtuin 1 (SIRT1) expression, induced NF-E2-related factor 2 (Nrf2) translocation from cytoplasm to nucleus and inhibited the acetylation of Nrf2. However, these changes triggered by Dex treatment were abrogated by NFAT5 knockdown.

SIGNIFICANCE

Dex protects against diabetic hyperglycemia-exacerbated cerebral I/R injury through attenuation of oxidative stress, inflammation and apoptosis. The underlying mechanism is at least the NFAT5/SIRT1/Nrf2 signaling pathway dependent.

TRPV1 mediates astrocyte activation and interleukin-1β release induced by hypoxic ischemia (HI)

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is a serious birth complication with high incidence in both advanced and developing countries. Children surviving from HIE often have severe long-term sequela including cerebral palsy, epilepsy, and cognitive disabilities. The severity of HIE in infants is tightly associated with increased IL-1β expression and astrocyte activation which was regulated by transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel in the TRP family.

METHODS

Neonatal hypoxic ischemia (HI) and oxygen-glucose deprivation (OGD) were used to simulate HIE in vivo and in vitro. Primarily cultured astrocytes were used for investigating the expression of glial fibrillary acidic protein (GFAP), IL-1β, Janus kinase 2 (JAK2), signal transducer and activator of transcription 3 (STAT3), and activation of the nucleotide-binding, oligomerization domain (NOD)-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome by using Western blot, q-PCR, and immunofluorescence. Brain atrophy, infarct size, and neurobehavioral disorders were evaluated by Nissl staining, 2,3,5-triphenyltetrazolium chloride monohydrate (TTC) staining and neurobehavioral tests (geotaxis reflex, cliff aversion reaction, and grip test) individually.

RESULTS

Astrocytes were overactivated after neonatal HI and OGD challenge. The number of activated astrocytes, the expression level of IL-1β, brain atrophy, and shrinking infarct size were all downregulated in TRPV1 KO mice. TRPV1 deficiency in astrocytes attenuated the expression of GFAP and IL-1β by reducing phosphorylation of JAK2 and STAT3. Meanwhile, IL-1β release was significantly reduced in TRPV1 deficiency astrocytes by inhibiting activation of NLRP3 inflammasome. Additionally, neonatal HI-induced neurobehavioral disorders were significantly improved in the TRPV1 KO mice.

CONCLUSIONS

TRPV1 promotes activation of astrocytes and release of astrocyte-derived IL-1β mainly via JAK2-STAT3 signaling and activation of the NLRP3 inflammasome. Our findings provide mechanistic insights into TRPV1-mediated brain damage and neurobehavioral disorders caused by neonatal HI and potentially identify astrocytic TRPV1 as a novel therapeutic target for treating HIE in the subacute stages (24 h).

Thalidomide alleviates bone cancer pain by down-regulating expressions of NF-κB and GFAP in spinal astrocytes in a mouse model

Aim: Thalidomide is one of the first line therapies in cancer pain management. Previous study has shown that thalidomide decreases the expression of tumor necrosis factor alpha in the mouse spinal cord. However, the exact cellular and molecular mechanism underlying the effect of thalidomide remains unclear. Here, we investigated the effect of thalidomide on the expression level of NF-κB as well as glial fibrillary acidic protein (GFAP) in the spinal cord astrocyte in a mice model. Materials and methods: MC57G fibrosarcoma cells were intramedullary injected into the right femurs of C57/BL mice to induce behaviors related to bone cancer pain. Postoperative thalidomide was administered intraperitoneally to the mice at dose of 100 mg/kg/day for 7 days. The effect of thalidomide on pain hypersensitivity was checked by behavioral testing. The expression levels of NF-κB and GFAP in spinal cord were evaluated by using Western blotting and Immunohistochemistry. Results: Compared with the controls, the tumor-bearing mice showed substantial pain-related behaviors. Furthermore, the expression levels of both NF-κB and GFAP increased significantly in the spinal cord astrocytes of the tumor-bearing mice. Treating the tumor-bearing mice with thalidomide results in a dramatic reduction in pain behaviors and a significant decrease of NF-κB and GFAP expressions. Conclusions: Thalidomide alleviates the pain behaviors probably by down-regulating the expression of NF-κB and GFAP.

Acteoside Attenuates Oxidative Stress and Neuronal Apoptosis in Rats with Focal Cerebral Ischemia-Reperfusion Injury

Acteoside (ACT) has been shown to exert antioxidant and neuroprotective effects in neurodegenerative diseases. However, the effect of ACT on cerebral ischemia-reperfusion (I/R) injury is not yet clear. In this study, we found that ACT administration reduced infarct volume and brain edema, and improved neurological deficits, as indicated by the decreased modified neurological severity score. Administration of ACT strikingly reduced oxidative stress, accompanied by decreased levels of reactive oxygen species and malondialdehyde and increased levels of superoxide dismutase and catalase in a rat model of middle cerebral artery occlusion/reperfusion (MCAO/R). Furthermore, ACT administration reduced the number of terminal deoxynucleotidyl transferase uridine 5'-triphosphate (UTP) nick-end labeling-positive cells in the cerebral cortex of ischemic side of MCAO/R rats, accompanied by downregulation of B cell lymphoma 2 (Bcl-2) associated X protein and cleaved caspase-3 proteins and upregulation of Bcl-2 protein. Additionally, ACT treatment inhibited the protein kinase R/eukaryotic initiation factor-2α stress pathway in the brains of MCAO/R rats. Our results demonstrated that ACT attenuates oxidative stress and neuronal apoptosis in MCAO/R rats, suggesting that ACT may serve as a novel therapeutic candidate for the treatment of I/R brain injury.

Dyrk2 involved in regulating LPS-induced neuronal apoptosis

The activation of relevant signaling pathways plays a very important role in LPS-induced neuronal damage. Dual-specificity tyrosine-phosphorylation-regulated kinase 2(Dyrk2), as a phosphokinase that can directly or indirectly phosphorylate signal molecules, was recently reported to down-regulate Type I Interferon(TIF) by promoting ser527 phosphorylation of TBK1. To further investigate the role of Dyrk2 in neuroinflammation, we for the first time focused on its function in LPS-induced neuronal damage. We found LPS stimulation increased the expression of Dyrk2 in the nucleus and cytoplasm of neurons. In addition, overexpression of Dyrk2 not only reduced the level of TNF-α induction, but also obviously inhibited LPS-induced neuronal apoptosis. We further found that Dyrk2 promoted the induction of phospho-Akt, phospho-p65 and phospho-p38MAPK (p38 mitogen-activated protein kinase), but immunoprecipitation showed Dyrk2 interacted with and Akt, p38MAPK and IκBα (IkappaB-alpha), except NF-κB subunit p65. These findings suggest Dyrk2 can inhibit LPS-induced neuronal apoptosis and plays key roles in LPS-indcued signaling pathways by its phosphokinase function. These data provide a novel viewpoint that Dyrks family may have an important role in neuroinflammation, and provide a potential molecular target for improving neuronal apoptosis.

Control of astrocyte morphology by Rho GTPases

Astrocytes modulate and support neuronal and synapse function via numerous mechanisms that often rely on diffusion of signalling molecules, ions or metabolites through extracellular space. As a consequence, the spatial arrangement and the distance between astrocyte processes and neuronal structures are of functional importance. Likewise, changes of astrocyte structure will affect the ability of astrocytes to interact with neurons. In contrast to neurons, where rapid morphology changes are critically involved in many aspects of physiological brain function, a role of astrocyte restructuring in brain physiology is only beginning to emerge. In neurons, small GTPases of the Rho family are powerful initiators and modulators of structural changes. Less is known about the functional significance of these signalling molecules in astrocytes. Here, we review recent experimental evidence for the role of RhoA, Cdc42 and Rac1 in controlling dynamic astrocyte morphology as well as experimental tools and analytical approaches for studying astrocyte morphology changes.

Eupatilin exerts neuroprotective effects in mice with transient focal cerebral ischemia by reducing microglial activation

Microglial activation and its-driven neuroinflammation are characteristic pathogenetic features of neurodiseases, including focal cerebral ischemia. The Artemisia asiatica (Asteraceae) extract and its active component, eupatilin, are well-known to reduce inflammatory responses. But the therapeutic potential of eupatilin against focal cerebral ischemia is not known, along with its anti-inflammatory activities on activated microglia. In this study, we investigated the neuroprotective effect of eupatilin on focal cerebral ischemia through its anti-inflammation, particularly on activated microglia, employing a transient middle cerebral artery occlusion/reperfusion (tMCAO), combined with lipopolysaccharide-stimulated BV2 microglia. Eupatilin exerted anti-inflammatory responses in activated BV2 microglia, in which it reduced secretion of well-known inflammatory markers, including nitrite, IL-6, TNF-α, and PGE₂, in a concentration-dependent manner. These observed in vitro effects of eupatilin led to in vivo neuroprotection against focal cerebral ischemia. Oral administration of eupatilin (10 mg/kg) in a therapeutic paradigm significantly reduced brain infarction and improved neurological functions in tMCAO-challenged mice. The same benefit was also observed when eupatilin was given even within 5 hours after MCAO induction. In addition, the neuroprotective effects of a single administration of eupatilin (10 mg/kg) immediately after tMCAO challenge persisted up to 3 days after tMCAO. Eupatilin administration reduced the number of Iba1-immunopositive cells across ischemic brain and induced their morphological changes from amoeboid into ramified in the ischemic core, which was accompanied with reduced microglial proliferation in ischemic brain. Eupatilin suppressed NF-κB signaling activities in ischemic brain by reducing IKKα/β phosphorylation, IκBα phosphorylation, and IκBα degradation. Overall, these data indicate that eupatilin is a neuroprotective agent against focal cerebral ischemia through the reduction of microglial activation.

Upregulation of neuronal zinc finger protein A20 expression is required for electroacupuncture to attenuate the cerebral inflammatory injury mediated by the nuclear factor-kB signaling pathway in cerebral ischemia/reperfusion rats

Background

Zinc finger protein A20 (tumor necrosis factor alpha-induced protein 3) functions as a potent negative feedback inhibitor of the nuclear factor-kB (NF-kB) signaling. It exerts these effects by interrupting the activation of IkB kinase beta (IKKβ), the most critical kinase in upstream of NF-kB, and thereby controlling inflammatory homeostasis. We reported previously that electroacupuncture (EA) could effectively suppress IKKβ activation. However, the mechanism underlying these effects was unclear. Therefore, the current study further explored the effects of EA on A20 expression in rat brain and investigated the possible mechanism of A20 in anti-neuroinflammation mediated by EA using transient middle cerebral artery occlusion (MCAO) rats.

Methods

Rats were treated with EA at the “Baihui (GV20),” “Hegu (L14),” and “Taichong (Liv3)” acupoints once a day starting 2 h after focal cerebral ischemia. The spatiotemporal expression of A20, neurobehavioral scores, infarction volumes, cytokine levels, glial cell activation, and the NF-kB signaling were assessed at the indicated time points. A20 gene interference (overexpression and silencing) was used to investigate the role of A20 in mediating the neuroprotective effects of EA and in regulating the interaction between neuronal and glial cells by suppressing neuronal NF-kB signaling during cerebral ischemia/reperfusion-induced neuroinflammation.

Results

EA treatment increased A20 expression with an earlier peak and longer lasting upregulation. The upregulated A20 protein was predominantly located in neurons in the cortical zone of the ischemia/reperfusion. Furthermore, neuronal A20 cell counts were positively correlated with neurobehavioral scores but negatively correlated with infarct volume, the accumulation of pro-inflammatory cytokines, and glial cell activation. Moreover, the effects of EA on improving the neurological outcome and suppressing neuroinflammation in the brain were reversed by A20 silencing. Finally, A20 silencing also suppressed the ability of EA to inhibit neuronal NF-kB signaling pathway.

Conclusions

Ischemia/reperfusion cortical neurons in MCAO rats are the main cell types that express A20, and there is a correlation between A20 expression and the suppression of neuroinflammation and the resulting neuroprotective effects. EA upregulated neuronal A20 expression, which played an essential role in the anti-inflammatory effects of EA by suppressing the neuronal NF-kB signaling pathway in the brains of MCAO rats.

Protective mechanisms of microRNA-27a against oxygen-glucose deprivation-induced injuries in hippocampal neurons

Hypoxic injuries during fetal distress have been shown to cause reduced expression of microRNA-27a (miR-27a), which regulates sensitivity of cortical neurons to apoptosis. We hypothesized that miR-27a overexpression attenuates hypoxia- and ischemia-induced neuronal apoptosis by regulating FOXO1, an important transcription factor for regulating the oxidative stress response. miR-27a mimic was transfected into hippocampal neurons to overexpress miR-27a. Results showed increased hippocampal neuronal viability and decreased caspase-3 expression. The luciferase reporter gene system demonstrated that miR-27a directly binded to FOXO1 3'UTR in hippocampal neurons and inhibited FOXO1 expression, suggesting that FOXO1 was the target gene for miR-27a. These findings confirm that miR-27a protects hippocampal neurons against oxygen-glucose deprivation-induced injuries. The mechanism might be mediated by modulation of FOXO1 and apoptosis-related gene caspase-3 expression.

Anti-inflammatory effect of cholera toxin B subunit in experimental stroke

Background

Cholera toxin B subunit (CTB) has multifaceted immunoregulatory functions. Immunity plays an important role in the mechanism of stroke. However, little is known about whether CTB is beneficial for stroke.

Methods

CTB was administered intraperitoneally after ischemia to rats subjected to transient focal ischemia. Infarct volumes, body weight loss, and neurologic deficits were measured. Cytokines, microglia/macrophage activation, and transcriptional factors in the ischemic brain were tested. The mRNA expressions of IL-1β and TNF-α were tested in the microglia/macrophage isolated from the ischemic hemisphere. γδT cells, IL-17-producing γδT cells, Th17 cells, and regulatory T (Treg) cells in the ischemic brain were tested. γδT cells and Treg cells in the peripheral blood were also evaluated.

Results

CTB reduced infarct volumes, neurologic deficits, and body weight loss after ischemia. At 24 h after ischemia, CTB downregulated the levels of IL-1β, TNF-α, NF-kB p65, phosphorylated-ERK1/2, and microglia/macrophage activation and suppressed NF-kB binding activity, but did not affect the level of ERK1/2. The mRNA expressions of IL-1β and TNF-α in the microglia/macrophage isolated from the ischemic hemisphere were suppressed after CTB therapy. In the ischemic hemisphere, CTB treatment reduced the levels of γδT cells, IL-17-producing γδT cells, and IL-17 at both 24 and 72 h after ischemia, while Th17 cells were not affected. After CTB treatment, the levels of Treg cells, TGF-β, and IL-10 remained unchanged at 24 h and upregulated at 72 h after ischemia. Inactivation of Treg cells using anti-CD25 attenuated the increase of TGF-β and IL-10 induced by CTB at 72 h after ischemia. In the peripheral blood, CTB increased Treg cells and suppressed γδT cells at 24 h after ischemia. And then at 72 h after ischemia, it increased Treg cells but did not impact γδT cells. CTB had no effect on cytokines, transcription factors, infiltrating γδT cells, and Treg cells in the brain of shams. In the peripheral blood of shams, CTB increased Treg cells at both 24 and 72 h, while it did not affect γδT cells.

Conclusions

CTB decreased neurologic impairment and tissue injury after cerebral ischemia via its immunomodulatory functions, including inhibiting microglia/macrophage activation, suppressing γδT cells, and inducing production of Treg cells, thus regulating the secretion of related cytokines. Suppression of NF-kB and ERK1/2 pathways is involved in the neuroprotective mechanism of CTB.

Treadmill exercise promotes neuroprotection against cerebral ischemia-reperfusion injury via downregulation of pro-inflammatory mediators

BACKGROUND

Stroke is one of the major causes of morbidity and mortality worldwide, which is associated with serious physical deficits that affect daily living and quality of life and produces immense public health and economic burdens. Both clinical and experimental data suggest that early physical training after ischemic brain injury may reduce the extent of motor dysfunction. However, the exact mechanisms have not been fully elucidated. The aim of this study was to investigate the effects of aerobic exercise on neuroprotection and understand the underlying mechanisms.

MATERIALS AND METHODS

Middle cerebral artery occlusion (MCAO) was conducted to establish a rat model of cerebral ischemia-reperfusion injury to mimic ischemic stroke. Experimental animals were divided into the following three groups: sham (n=34), MCAO (n=39), and MCAO plus treadmill exercise (n=28). The effects of aerobic exercise intervention on ischemic brain injury were evaluated using functional scoring, histological analysis, and Bio-Plex Protein Assays.

RESULTS

Early aerobic exercise intervention was found to improve motor function, prevent death of neuronal cells, and suppress the activation of microglial cells and astrocytes. Furthermore, it was observed that aerobic exercise downregulated the expression of the cytokine interleukin-1β and the chemokine monocyte chemotactic protein-1 after transient MCAO in experimental rats.

CONCLUSION

This study demonstrates that treadmill exercise rehabilitation promotes neuroprotection against cerebral ischemia-reperfusion injury via the downregulation of proinflammatory mediators.