Hypoxic Preconditioning Attenuates Neuronal Cell Death by Preventing MEK/ERK Signaling Pathway Activation after Transient Global Cerebral Ischemia in Adult Rats

Hypoxic Preconditioning Attenuates Neuroinflammation via Inhibiting NF-κB/NLRP3 Axis Mediated by p-MLKL after Transient Global Cerebral Ischemia

Hypoxic preconditioning (HPC) has been reported to alleviate neuronal damage and microglial activation in hippocampal CA1 after transient global cerebral ischemia (tGCI). However, the molecular mechanism is unclear. Recent studies identified that nuclear factor-kappa-B (NF-κB)/oligomerization domain-like receptors protein (NLRP) 3 inflammasome pathway is mainly involved in the activation of microglia and that phosphorylated (p)-mixed lineage kinase domain-like (MLKL) is related to the regulation of NF-κB/NLRP3 axis. Hence, in this study, we set out to investigate whether HPC attenuates neuronal damage and microglial activation through inhibiting NF-κB/NLRP3 axis mediated by p-MLKL after tGCI in CA1 of male rats. We found that HPC decreased NLRP3 inflammasome in microglia and inhibited M1 polarization of microglia in CA1 after tGCI. Mechanistically, HPC inhibited the activation of NF-κB signaling pathway and reduced the mRNA and protein levels of NLRP3 inflammasome after tGCI. Additionally, the knockdown of p-MLKL by short hairpin RNA (shRNA) administration inhibited the activation of the NF-κB signaling pathway and reduced the formation of NLRP3 inflammasome, thus attenuating M1 polarization of microglia and decreasing the release of interleukin 1 beta (IL-1β) and necrosis factor alpha (TNF-α) in CA1 post ischemia. We consider that p-MLKL in microglia may be derived from necroptotic neurons after tGCI. In conclusion, the new finding in this study is that HPC-induced neuroprotection against tGCI through inhibiting NF-κB/NLRP3 pathway mediated by p-MLKL.

DUSP6 Deficiency Attenuates Neurodegeneration after Global Cerebral Ischemia

Transient global cerebral ischemia (tGCI) resulting from cardiac arrest causes selective neurodegeneration in hippocampal CA1 neurons. Although the effect is clear, the underlying mechanisms directing this process remain unclear. Previous studies have shown that phosphorylation of Erk1/2 promotes cell survival in response to tGCI. DUSP6 (also named MKP3) serves as a cytosolic phosphatase that dephosphorylates Erk1/2, but the role of DUSP6 in tGCI has not been characterized. We found that DUSP6 was specifically induced in the cytoplasm of hippocampal CA1 neurons 4 to 24 h after tGCI. DUSP6-deficient mice showed normal spatial memory acquisition and retention in the Barnes maze. Impairment of spatial memory acquisition and retention after tGCI was attenuated in DUSP6-deficient mice. Neurodegeneration after tGCI, revealed by Fluoro-Jade C and H&E staining, was reduced in the hippocampus of DUSP6-deficient mice and DUSP6 deficiency enhanced the phosphorylation and nuclear translocation of Erk1/2 in the hippocampal CA1 region. These data support the role of DUSP6 as a negative regulator of Erk1/2 signaling and indicate the potential of DUSP6 inhibition as a novel therapeutic strategy to treat neurodegeneration after tGCI.

Hypoxic postconditioning promotes neurogenesis by modulating the metabolism of neural stem cells after cerebral ischemia

Ischemic stroke is one of the most lethal and severely disabling diseases that seriously affects human health and quality of life. The maintenance of self-renewal and differentiation of neural stem cells are closely related to metabolism. This study aimed to investigate whether hypoxic postconditioning (HPC) could promote neurogenesis after ischemic stroke, and to investigate the role of neuronal stem cell metabolism in HPC-induced neuroprotection. Male C57BL/6 mice were subjected to transient middle cerebral artery occlusion (MCAO), and HPC was performed for 3 h per day. Immunofluorescence staining was used to assess neurogenesis. The cell line NE-4C was used to elucidate the proliferation of neuronal stem cells in 21% O2 or 8% O2. HPC promoted the recovery of neurological function in mice on day 14. HPC promoted neuronal precursor proliferation in the subventricular zone (SVZ) on day 7 and enhanced neuronal precursor migration in the basal ganglia and cortex on day 14. Fatty acid oxidation (FAO) and glycolysis of neural stem cells in the SVZ changed after MCAO with or without HPC. HPC promoted the proliferation of NE-4C stem cells, decreased FAO and increased glycolysis. All these beneficial effects of HPC were ablated by the application of an FAO activator or a glycolysis inhibitor. In conclusion, cerebral ischemia modulated the FAO and glycolysis of neural stem cells. HPC promoted the proliferation and migration of neural stem cells after MCAO, and these effects may be related to the regulation of metabolism, including FAO and glycolysis.

Repetitive transcranial magnetic stimulation increases neurological function and endogenous neural stem cell migration via the SDF-1α/CXCR4 axis after cerebral infarction in rats

Neural stem cell (NSC) migration is closely associated with brain development and is reportedly involved during recovery from ischaemic stroke. Chemokine signalling mediated by stromal cell-derived factor 1α (SDF-1α) and its receptor CXC chemokine receptor 4 (CXCR4) has been previously documented to guide the migration of NSCs. Although repetitive transcranial magnetic stimulation (rTMS) can increase neurological function in a rat stroke model, its effects on the migration of NSCs and associated underlying mechanism remain unclear. Therefore, the present study investigated the effects of rTMS on ischaemic stroke following middle cerebral artery occlusion (MCAO). All rats underwent rTMS treatment 24 h after MCAO. Neurological function, using modified Neurological Severity Scores and grip strength test and NSC migration, which were measured using immunofluorescence staining, were analysed at 7 and 14 days after MCAO, before the protein expression levels of the SDF-1α/CXCR4 axis was evaluated using western blot analysis. AMD3100, a CXCR4 inhibitor, was used to assess the effects of SDF-1α/CXCR4 signalling. In addition, neuronal survival was investigated using Nissl staining at 14 days after MCAO. It was revealed that rTMS increased the neurological recovery of rats with MCAO, facilitated the migration of NSC, augmented the expression levels of the SDF-1α/CXCR4 axis and decreased neuronal loss. Furthermore, the rTMS-induced positive responses were significantly abolished by AMD3100. Overall, these results indicated that rTMS conferred therapeutic neuroprotective properties, which can restore neurological function after ischaemic stroke, in a manner that may be associated with the activation of the SDF-1α/CXCR4 axis.

Hypoxia and brain aging: Neurodegeneration or neuroprotection?

The absolute reliance of the mammalian brain on oxygen to generate ATP renders it acutely vulnerable to hypoxia, whether at high altitude or in clinical settings of anemia or pulmonary disease. Hypoxia is pivotal to the pathogeneses of myriad neurological disorders, including Alzheimer's, Parkinson's and other age-related neurodegenerative diseases. Conversely, reduced environmental oxygen, e.g. sojourns or residing at high altitudes, may impart favorable effects on aging and mortality. Moreover, controlled hypoxia exposure may represent a treatment strategy for age-related neurological disorders. This review discusses evidence of hypoxia's beneficial vs. detrimental impacts on the aging brain and the molecular mechanisms that mediate these divergent effects. It draws upon an extensive literature search on the effects of hypoxia/altitude on brain aging, and detailed analysis of all identified studies directly comparing brain responses to hypoxia in young vs. aged humans or rodents. Special attention is directed toward the risks vs. benefits of hypoxia exposure to the elderly, and potential therapeutic applications of hypoxia for neurodegenerative diseases. Finally, important questions for future research are discussed.

Data-Driven Computational Modeling Identifies Determinants of Glioblastoma Response to SHP2 Inhibition

Oncogenic protein tyrosine phosphatases have long been viewed as drug targets of interest, and recently developed allosteric inhibitors of SH2 domain-containing phosphatase-2 (SHP2) have entered clinical trials. However, the ability of phosphatases to regulate many targets directly or indirectly and to both promote and antagonize oncogenic signaling may make the efficacy of phosphatase inhibition challenging to predict. Here we explore the consequences of antagonizing SHP2 in glioblastoma, a recalcitrant cancer where SHP2 has been proposed as a useful drug target. Measuring protein phosphorylation and expression in glioblastoma cells across 40 signaling pathway nodes in response to different drugs and for different oxygen tensions revealed that SHP2 antagonism has network-level, context-dependent signaling consequences that affect cell phenotypes (e.g., cell death) in unanticipated ways. To map specific signaling consequences of SHP2 antagonism to phenotypes of interest, a data-driven computational model was constructed based on the paired signaling and phenotype data. Model predictions aided in identifying three signaling processes with implications for treating glioblastoma with SHP2 inhibitors. These included PTEN-dependent DNA damage repair in response to SHP2 inhibition, AKT-mediated bypass resistance in response to chronic SHP2 inhibition, and SHP2 control of hypoxia-inducible factor expression through multiple MAPKs. Model-generated hypotheses were validated in multiple glioblastoma cell lines, in mouse tumor xenografts, and through analysis of The Cancer Genome Atlas data. Collectively, these results suggest that in glioblastoma, SHP2 inhibitors antagonize some signaling processes more effectively than existing kinase inhibitors but can also limit the efficacy of other drugs when used in combination. SIGNIFICANCE: These findings demonstrate that allosteric SHP2 inhibitors have multivariate and context-dependent effects in glioblastoma that may make them useful components of some combination therapies, but not others.

H2S attenuates injury after ischemic stroke by diminishing the assembly of CaMKII with ASK1-MKK3-p38 signaling module

Cerebral ischemia/reperfusion (I/R) injury is a leading cause of learning and memory dysfunction. Hydrogen sulfide (H₂S) has been shown to confer neuroprotection in various neurodegenerative diseases, including cerebral I/R-induced hippocampal CA1 injury. However, the underlying mechanisms have not been completely understood. In the present study, rats were pretreated with SAM/NaHS (SAM, an H₂S agonist, and NaHS, an H₂S donor) only or SAM/NaHS combined with CaM (an activator of CaMKII) prior to cerebral ischemia. The Morris water maze test demonstrated that SAM/NaHS could alleviate learning and memory impairment induced by cerebral I/R injury. Cresyl violet staining was used to show the survival of hippocampal CA1 pyramidal neurons. SAM/NaHS significantly increased the number of surviving cells, whereas CaM weakened the protection induced by SAM/NaHS. The immunohistochemistry results indicated that the number of Iba1-positive microglia significantly increased after cerebral I/R. Compared with the I/R group, the number of Iba1-positive microglia in the SAM/NaHS groups significantly decreased. Co-Immunoprecipitation and immunoblotting were conducted to demonstrate that SAM/NaHS suppressed the assembly of CaMKII with the ASK1-MKK3-p38 signal module after cerebral I/R, which decreased the phosphorylation of p38. In contrast, CaM significantly inhibited the effects of SAM/NaHS. Taken together, the results suggested that SAM/NaHS could suppress cerebral I/R injury by downregulating p38 phosphorylation via decreasing the assembly of CaMKII with the ASK1-MKK3-p38 signal module.

Down-regulation of microRNA-429 alleviates myocardial injury of rats with coronary heart disease

In recent years, the impact of microRNAs (miRNAs) on coronary heart disease (CHD) has been identified. This study was aimed to investigate the regulative role of microRNA (miR-429) in myocardial injury of rats with CHD. Expression of miR-429 in CHD patients and healthy people was detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR). The CHD rat models were injected with normal saline, mimics negative control (NC), miR-429 mimics, inhibitors NC and miR-429 inhibitors twice a week, for 4 weeks. Levels of inflammatory factors, oxidative stress indices as well as apoptosis of cardiomyocytes were determined by a series of assays. Expression of miR-429 was up-regulated in CHD patients. Reduced miR-429 could decline the expression of oxidative stress-related factors and inflammation-related factors, and inhibit the apoptosis of cardiomyocytes in rats with CHD. Moreover, the down-regulation of miR-429 could promote the expression of CrkL and repress activation of the MEK/ERK signaling pathway. This study reveals that restrained miR-429 could exert a protective impact on myocardial injury of rats with CHD by suppressing oxidative stress, inflammation reaction and apoptosis of cardiomyocytes. The function mechanisms may relate to the up-regulation of CrkL and inhibition of the MEK/ERK signaling pathway.

Sodium Hydrosulfide Post-conditioning Protects Hippocampal CA1 Neurons from Neuronal Cell Injury in the Rat Model of Transient Global Cerebral Ischemia Through Activation of Extracellular-regulated Kinases Signaling

INTRODUCTION

The effect of hydrogen sulfide (H2S) on global cerebral ischemia remains partially understood. This study aimed to investigate the neuroprotective effect of sodium hydrosulfide (NaHS, a donor of H2S) post-conditioning and its underlying mechanism in a transient global cerebral ischemia (tGCI) model.

MATERIALS & METHODS

The tGCI rat model was established by the four-vessel occlusion method. Wistar rats were randomly assigned into 6 groups: sham, tGCI, tGCI +NaHS, tGCI+vehicle, tGCI+U0126 and tGCI+U0126+NaHS groups. Neurons survival was assessed by Nissl staining and NeuN immunostaining. Levels of extracellular extracellular-regulated kinases (ERK)1/2 and p-ERK1/2 were determined by western blot and immunohistochemistry (IHC). Intraperitoneal injection of NaHS (24 µmol/kg) at 24 h post-tGCI attenuated tGCI-induced decrease of the survival and NeuN-positive neurons in the hippocampal CA1 subregion.

RESULTS

Compared to the sham group, tGCI significantly up-regulated p-ERK1/2 protein at 26 and 48 h post-tGCI. NaHS post-conditioning further enhanced the phosphorylation of ERK1/2 at 26, 48 and 168 h post-tGCI. Nevertheless, U0126 (an inhibitor of MEK1/2) pre-treatment reduced the p-ERK1/2 level in both the tGCI+ U0126 group and the tGCI+ U0126+ NaHS group. IHC staining revealed that p-ERK1/2-positive cell could be observed in several hippocampal subregions of the rats receiving NaHS post-conditioning. Immunofluorescence staining showed that some neurons were double-stained with p-ERK1/2 and NeuN. Furthermore, U0126 pre-treatment significantly attenuated the protective effect of NaHS post-conditioning on the neurons survival and NeuNpositive neurons in CA1 subregion.

CONCLUSION

These results suggested that NaHS post-conditioning can protect hippocampal CA1 neurons from tGCI-induced injury, at least partially, through activation of ERK1/2 signaling.

Effect of Phosphorylated-Extracellular Regulated Kinase 1/2 Inhibitor on Retina from Light-induced Photoreceptor Degeneration

Background

The demonstrated role of mitogen-activated protein kinase (MAPK) in both cell apoptosis and the inflammation pathway makes it an attractive target for photoreceptor protection. The aim of this study was to investigate the protective effects of MAPK antagonists against photoreceptor degeneration and retinal inflammation in a rat model of light-induced retinal degeneration.

Methods

Sprague Dawley rats were treated with intravitreal injections of MAPK antagonists, inhibitors of p-P38, phosphorylated-extracellular regulated kinase (p-ERK) 1/2, and p-c-Jun N-terminal kinase (JNK) just before they were assigned to dark adaptation. After dark adaptation for 24 h, rats were exposed to blue light (2500 lux) in a light box for 24 h, and then returned to the normal 12-h light/12-h dark cycle. Samples were collected at different time points. MAPK expression during light exposure was examined with immunofluorescence. Photoreceptor death was detected with histopathology and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. The expression of retinal p-ERK1/2, caspase 3, activated caspase 3, tumor necrosis factor (TNF)-α, and interleukin (IL)-1β was examined by Western blotting. Differences between groups were evaluated using unpaired one-way analysis of variance and least significant difference post hoc tests.

Results

MAPKs (P38, ERK1/2, and p-JNK) were phosphorylated and activated in the light injury groups, compared with normal group, and their expressions were mainly elevated in the outer nuclear layer (ONL). Among the selected MAPK antagonists, only the p-ERK1/2 inhibitor attenuated the loss of photoreceptors and the thinning of ONL in light injury groups. Besides, p-ERK1/2 inhibitor refrained light-induced photoreceptor apoptosis, which was presented by TUNEL positive cells. Light injury significantly increased the expression of p-ERK1/2 (1.12 ± 0.06 vs. 0.57 ± 0.08, t = 9.99, P < 0.05; 1.23 ± 0.03 vs. 0.57 ± 0.08, t = 11.90, P < 0.05; and 1.12 ± 0.12 vs. 0.57 ± 0.08, t = 9.86, P < 0.05; F = 49.55, P < 0.001), and induced caspase 3 activating (0.63 ± 0.06 vs. 0.14 ± 0.05, t = 13.67, P < 0.05; 0.74 ± 0.05 vs. 0.14 ± 0.05, t = 16.87, P < 0.05; and 0.80 ± 0.05 vs. 0.14 ± 0.05, t = 18.57, P < 0.05; F = 100.15, P < 0.001), compared with normal group. The p-ERK1/2 inhibitor significantly reduced p-ERK1/2 overexpression (0.61 ± 0.06 vs. 1.12 ± 0.06, t = -9.26, P < 0.05; 0.77 ± 0.06 vs. 1.23 ± 0.03, t = -8.29, P < 0.05; and 0.68 ± 0.03 vs. 1.12 ± 0.12, t = -7.83, P < 0.05; F = 49.55, P < 0.001) and downregulated caspase 3 activating (0.23 ± 0.04 vs. 0.63 ± 0.06, t = -11.24, P < 0.05; 0.43 ± 0.03 vs. 0.74 ± 0.05, t = -8.86, P < 0.05; and 0.58 ± 0.03 vs. 0.80 ± 0.05, t = -6.17, P < 0.05; F = 100.15, P < 0.001), compared with light injury group. No significant change in the total level of caspase 3 was seen in different groups (F = 0.56, P = 0.75). As for inflammation, light injury significantly increased the expression of TNF-α (0.42 ± 0.04 vs. 0.25 ± 0.05, t = 5.99, P < 0.05; 0.65 ± 0.03 vs. 0.25 ± 0.05, t = 14.87, P < 0.05; and 0.86 ± 0.04 vs. 0.25 ± 0.05, t = 22.58, P < 0.05; F = 160.27, P < 0.001) and IL-1β (0.24 ± 0.01 vs. 0.19 ± 0.02, t = 2.33, P < 0.05; 0.35 ± 0.02 vs. 0.19 ± 0.02, t = 7.97, P < 0.05; and 0.48 ± 0.04 vs. 0.19 ± 0.02, t = 14.69, P < 0.05; F = 77.29, P < 0.001), compared with normal group. P-ERK1/2 inhibitor significantly decreased the overexpression of TNF-α (0.22 ± 0.02 vs. 0.42 ± 0.04, t = -7.40, P < 0.05; 0.27 ± 0.02 vs. 0.65 ± 0.03, t = -14.27, P < 0.05; and 0.33 ± 0.03 vs. 0.86 ± 0.04, t = -19.58, P < 0.05; F = 160.27, P < 0.001) and IL-1β (0.13 ± 0.03 vs. 0.24 ± 0.01, t = -5.77, P < 0.05; 0.17 ± 0.01 vs. 0.22 ± 0.02, t = -9.18, P < 0.05; and 0.76 ± 0.05 vs. 0.48 ± 0.04, t = -13.12, P < 0.05; F = 77.29, P < 0.001), compared with light injury group.

Conclusion

The p-ERK1/2 inhibitor might protect the retina from light-induced photoreceptor degeneration and retinal inflammation.

Role of Phosphatidylinositol-3 Kinase Pathway in NMDA Preconditioning: Different Mechanisms for Seizures and Hippocampal Neuronal Degeneration Induced by Quinolinic Acid

N-methyl D-aspartate (NMDA) preconditioning is evoked by the administration of a subtoxic dose of NMDA and is protective against neuronal excitotoxicity. This effect may involve a diversity of targets and cell signaling cascades associated to neuroprotection. Phosphatidylinositol-3 kinase/protein kinase B (PI3K/Akt) and mitogen-activated protein kinases (MAPKs) such as extracellular regulated protein kinase 1/2 (ERK1/2) and p38^MAPK pathways play a major role in neuroprotective mechanisms. However, their involvement in NMDA preconditioning was not yet fully investigated. The present study aimed to evaluate the effect of NMDA preconditioning on PI3K/Akt, ERK1/2, and p38^MAPK pathways in the hippocampus of mice and characterize the involvement of PI3K on NMDA preconditioning-evoked prevention of seizures and hippocampal cell damage induced by quinolinic acid (QA). Thus, mice received wortmannin (a PI3K inhibitor) and 15 min later a subconvulsant dose of NMDA (preconditioning) or saline. After 24 h of this treatment, an intracerebroventricular QA infusion was administered. Phosphorylation levels and total content of Akt, glycogen synthase protein kinase-3β (GSK-3β), ERK1/2, and p38^MAPK were not altered after 24 h of NMDA preconditioning with or without wortmmanin pretreatment. Moreover, after QA administration, behavioral seizures, hippocampal neuronal degeneration, and Akt activation were evaluated. Inhibition of PI3K pathway was effective in abolishing the protective effect of NMDA preconditioning against QA-induced seizures, but did not modify neuronal protection promoted by preconditioning as evaluated by Fluoro-Jade B staining. The study confirms that PI3K participates in the mechanism of protection induced by NMDA preconditioning against QA-induced seizures. Conversely, NMDA preconditioning-evoked protection against neuronal degeneration is not altered by PI3K signaling pathway inhibition. These results point to differential mechanisms regarding protection against a behavioral and cellular manifestation of neural damage.

Brief hypoxic cycles improve uterine contractile function after prolonged hypoxia in term-pregnant but not in nonpregnant rats in vitro

During labour, the uterus itself is vulnerable to hypoxia/ischemia that can occur with each strong contraction and this may ultimately cause dysfunctional labour in some women. Periods of Intermittent re-oxygenations are beneficial to tissues subjected to hypoxia to wash out metabolic by-products that have been accumulated during hypoxic stresses which may affect the tissue viability. We proposed that short intermittent hypoxic episodes may protect the uterus from subsequent sustained long hypoxia. To investigate this, two sets of experiments were performed on term-pregnant and nonpregnant rat uterine tissues. In one set of experiment the uterus was subjected to sustained long hypoxia for 40 min and then allowed to recover in 100% O₂. In the other set of experiment the uterus was subjected to 3 cycles of 2 min hypoxia each separated by 20 min reoxygenation and followed by a sustained long hypoxia for 40 min and then allowed to recover. We found that challenging the uterine tissues with intermittent short hypoxic episodes improved the uterine contractility significantly after the sustained long hypoxia in term-pregnant but not in non-pregnant tissues. These results suggest that a mechanism of uterine tolerance (preconditioning) is confined to uterine tissues very close to labour and it is a protective phenomenon to improve the uterine activity despite the long-lasting paradoxical metabolic challenges that occur during the repeated strong labour contractions.

PD149163 induces hypothermia to protect against brain injury in acute cerebral ischemic rats

Therapeutic hypothermia is a promising strategy for acute cerebral ischemia via physical or pharmacological methods. In this study, we pharmacologically induced hypothermia on Sprague Dawley rats by intraperitoneally injecting PD149163. We found that mild hypothermia was induced by PD149163 treatment without local cerebral blood flow (LCBF) alteration. To evaluate the neuroprotective effects of PD149163, TTC staining, HE staining and Nissl's staining were performed in our study. We found that PD149163 could prevent neuronal damage, and inhibit proliferation and activation of glial cells induced by ischemia. Simultaneously, we observed PD149163 ameliorated apoptosis characterized by down-regulated caspase-3 and Bax, but elevated Bcl-2. Moreover, PD149163 dramatically reduced JNK and AMPK/mTOR signaling pathway activation, and thereby inhibited autophagy by increased P62 expression, decreased the ratio of LC₃-Ⅱ to LC₃-Ⅰ and the expression of Beclin. Taken together, the present findings reveal the therapeutic effects of PD149163-induced hypothermia in brain ischemia, and provide a new strategy for stroke treatment.

Autophagosome maturation mediated by Rab7 contributes to neuroprotection of hypoxic preconditioning against global cerebral ischemia in rats

Autophagy disruption leads to neuronal damage in hypoxic–ischemic brain injury. Rab7, a member of the Rab GTPase superfamily, has a unique role in the regulation of autophagy. Hypoxic preconditioning (HPC) provides neuroprotection against transient global cerebral ischemia (tGCI). However, the underlying mechanisms remain poorly understood. Thus, the current study explored the potential molecular mechanism of the neuroprotective effect of HPC by investigating how Rab7 mediates autophagosome (AP) maturation after tGCI in adult rats. We found that HPC attenuated AP accumulation in the hippocampal CA1 region after tGCI via restoration of autophagic flux. We also confirmed that this HPC-induced neuroprotection was not caused by the increase in lysosomes or the improvement of lysosomal function after tGCI. Electron microscopic analysis then revealed an increase in autolysosomes in CA1 neurons of HPC rats. Moreover, the inhibition of autophagosome-lysosome fusion by chloroquine significantly aggravated neuronal death in CA1, indicating that AP maturation contributes to HPC-induced neuroprotection against neuronal injury after tGCI. Furthermore, the activation of Rab7 was found to be involved in the neuroprotective effect of AP maturation after HPC. At last, the knockdown of ultraviolet radiation resistance-associated gene (UVRAG) in vivo disrupted the interaction between Vps16 and Rab7, attenuated the activation of Rab7, interrupted autophagic flux, and ultimately abrogated the HPC-induced neuroprotection against tGCI. Our results indicated that AP maturation was enhanced by the activation of Rab7 via UVRAG-Vps16 interaction, which further demonstrated the potential neuroprotective role of Rab7 in HPC against tGCI-induced neuronal injury in adult rats.

Upregulation of Cdh1 signaling in the hippocampus attenuates brain damage after transient global cerebral ischemia in rats

Cerebral ischemia is a major cause of brain dysfunction. The E3 ubiquitin ligase anaphase-promoting complex and its coactivator Cdh1 have been reported to be involved in the regulation of neuronal survival, differentiation, axonal growth and synaptic development in the central nervous system. However, its role in the ischemic brain and the underlying mechanisms remain poorly understood. The present study aimed to investigate the effects of Cdh1 overexpression on the ischemic rat brain by direct intra-hippocampal injection of lentivirus-delivered Cdh1 before transient global cerebral ischemia reperfusion. Spatial memory acquisition and retention were assessed using a Morris water maze task. Neuronal damage, glial activation, oxidative stress and the synaptic ultrastructure were also examined. The results indicated that a recombinant Cdh1-encoding lentiviral vector can upregulate the expression of Cdh1 in the rat hippocampus. Cdh1 overexpression increased the survival rates of rats, reversed the abnormal accumulation of cyclin B1, alleviated neuronal death, inhibited glial activation, mitigated oxidative stress, modulated synaptic plasticity and improved neurological deficits caused by ischemia. Our study indicates that targeting the Cdh1 signaling pathway in the hippocampus may provide a promising therapeutic strategy for the clinical treatment of transient global cerebral ischemia.

Preconditioning in neuroprotection: From hypoxia to ischemia

Sublethal hypoxic or ischemic events can improve the tolerance of tissues, organs, and even organisms from subsequent lethal injury caused by hypoxia or ischemia. This phenomenon has been termed hypoxic or ischemic preconditioning (HPC or IPC) and is well established in the heart and the brain. This review aims to discuss HPC and IPC with respect to their historical development and advancements in our understanding of the neurochemical basis for their neuroprotective role. Through decades of collaborative research and studies of HPC and IPC in other organ systems, our understanding of HPC and IPC-induced neuroprotection has expanded to include: early- (phosphorylation targets, transporter regulation, interfering RNA) and late- (regulation of genes like EPO, VEGF, and iNOS) phase changes, regulators of programmed cell death, members of metabolic pathways, receptor modulators, and many other novel targets. The rapid acceleration in our understanding of HPC and IPC will help facilitate transition into the clinical setting.

Role of ERK1/2 activation and nNOS uncoupling on endothelial dysfunction induced by lysophosphatidylcholine

BACKGROUND AND AIMS

Lysophosphatidylcholine (LPC) - a main component of oxidized LDL - is involved in endothelial dysfunction that precedes atherosclerosis, with an increased superoxide anions and a reduced NO production via endothelial NO synthase (eNOS) uncoupling. However, there is no evidence about the mechanisms involved in neuronal NOS (nNOS) uncoupling. Extracellular signal-regulated kinase (ERK) is related to the control of NO production and inflammatory gene transcription activation in atherosclerosis. Our aim was to investigate the role of nNOS/ERK1/2 pathway on endothelial dysfunction induced by LPC, in mouse aorta and human endothelial cells.

METHODS

Thoracic aorta from wild type mice was used to perform vascular reactivity studies in the presence or absence of LPC. Human endothelial cells were used to investigate the effect of LPC on expression of nNOS and his products NO and H₂O₂.

RESULTS

LPC reduced acetylcholine (ACh)-induced vasodilation in mouse aorta (Emax_CT/LPC = ∼95 ± 2/62 ± 3%, p = 0.0004) and increased phenylephrine-induced vasoconstriction (Emax_CT/LPC = ∼4 ± 0,1/6 ± 0,1 mN/mm, p = 0.0002), with a reduction in NO (fluorescence intensity_CT/LPC = 91 ± 3/62±2 × 10³, p = 0.0002) and H₂O₂ (fluorescence intensity_CT/LPC = ∼16 ± 0,8/10 ± 0,7 × 10³, p = 0.0041) production evocated by ACh. An inhibition of nNOS by TRIM (Emax_CT/CT+TRIM = ∼93 ± 1/43 ± 3%, p = 0,0048; Emax_LPC/LPC+TRIM = ∼62 ± 3/65 ± 3%) or H₂O₂ degradation by catalase (Emax_CT/CT+cat = ∼93 ± 1/46 ± 2%, p < 0,001; Emax_LPC/LPC+cat = ∼62,8 ± 3,2/60,5 ± 4,7%) reduced the relaxation in the control but not in LPC group. PD98059, an ERK1/2 inhibitor, abolished the increase in vasoconstriction in LPC-treated vessels (Emax_LPC/LPC+PD = ∼6 ± 0,1/3 ± 0,1 mN/mm, p = 0.0001). LPC also reduced the dimer/monomer proportion and increased nNOS^ser852 phosphorylation.

CONCLUSIONS

LPC induced nNOS uncoupling and nNOS^Ser852 phosphorylation, reduced NO and H₂O₂ production and improved superoxide production by modulating ERK1/2 activity in human and murine endothelial cells.

Rapamycin Reduced Ischemic Brain Damage in Diabetic Animals Is Associated with Suppressions of mTOR and ERK1/2 Signaling

The objectives of the present study are to investigate the activation of mTOR and ERK1/2 signaling after cerebral ischemia in diabetic rats and to examine the neuroprotective effects of rapamycin. Ten minutes transient global cerebral ischemia was induced in straptozotocin-induced diabetic hyperglycemic rats and non-diabetic, euglycemic rats. Brain samples were harvested after 16 h of reperfusion. Rapamycin or vehicle was injected 1 month prior to the induction of ischemia. The results showed that diabetes increased ischemic neuronal cell death and associated with elevations of p-P70S6K and Ras/ERK1/2 and suppression of p-AMPKα. Rapamycin ameliorated diabetes-enhanced ischemic brain damage and suppressed phosphorylation of P70S6K and ERK1/2. It is concluded that diabetes activates mTOR and ERK1/2 signaling pathways in rats subjected to transient cerebral ischemia and inhibition of mTOR by rapamycin reduces ischemic brain damage and suppresses the mTOR and ERK1/2 signaling in diabetic settings.

Resveratrol protects CA1 neurons against focal cerebral ischemic reperfusion-induced damage via the ERK-CREB signaling pathway in rats

Ischemic stroke is a primary cause of mortality and disability in the aged population. Resveratrol (Res), a natural polyphenol enriched in plants, presents diverse biological activities, e.g., antiinflammatory and anti-oxidation effects. Here, we evaluated whether Res pretreatment influenced focal cerebral ischemia-induced cognitive impairment, and we explored the underlying mechanisms in rats. The results showed that a single administration of Res (30mg/kg, i.p.) at 1 or 4h, but not at 24h before focal cerebral ischemia exerted significant neuroprotective effects, including a reduction in hippocampal CA1 neuronal death and spatial cognition deficits caused by ischemia. The neuroprotective effects of Res were suppressed by pretreatment with MK801, an NMDA receptor blocker, or U0126, an extracellular signal regulated kinase 1/2 (ERK1/2) kinase inhibitor. A western blot analysis revealed that Res treatment at 1h before ischemia significantly increased ERK1/2 phosphorylation and cyclic-AMP response element binding protein (CREB) phosphorylation in the CA1 region of the hippocampus, which can be prevented with U0126 pretreatment. The results showed that the NMDA receptor-mediated ERK-CREB signaling pathway might participates in Res-induced neuroprotection in rats with focal cerebral ischemia.

The role of Akt (protein kinase B) and protein kinase C in ischemia-reperfusion injury

Stroke is a leading cause of long-term disability and death in the United States. Currently, tissue plasminogen activator (tPA), is the only Food and Drug Administration-approved treatment for acute ischemic stroke. However, the use of tPA is restricted to a small subset of acute stroke patients due to its limited 3-h therapeutic time window. Given the limited therapeutic options at present and the multi-factorial progression of ischemic stroke, emphasis has been placed on the discovery and use of combination therapies aimed at various molecular targets contributing to ischemic cell death. Protein kinase C (PKC) and Akt (protein kinase B) are serine/threonine kinases that play a critical role in mediating ischemic-reperfusion injury and cellular growth and survival, respectively. The present review will examine the role of PKC and Akt in the cellular response to ischemic-reperfusion injury.

The neuroprotection of hypoxic preconditioning on rat brain against traumatic brain injury by up-regulated transcription factor Nrf2 and HO-1 expression

Hypoxic preconditioning (HPC) increases the inherent tolerance of brain tissue suffering from severe hypoxia or ischemia insult by stimulating the protective ability of the brain. However, little is known concerning the effect of HPC on traumatic brain injury (TBI). We designed this study to investigate the effect of HPC on TBI and explore its underlying mechanisms. We found that HPC significantly alleviates neurological dysfunction, lessens brain edema, reduces cell apoptosis, increases neuronal survival, up-regulates the expressions of Nrf2 and HO-1, and decreases the inducer of protein carbonyls, 4-hydroxy-2-nonenal, and 8-hydroxy-2-deoxyguanosine in the brain tissue of rats 24h after brain injury. However, no influence was observed in normal rats after only 3d of hypoxic training. Results further indicated that HPC protects the brain against traumatic damage. This protective effect may be achieved by up-regulating Nrf2 and HO-1 expression and alleviating oxidative stress damage.

Repetitive ischemic preconditioning attenuates inflammatory reaction and brain damage after focal cerebral ischemia in rats: involvement of PI3K/Akt and ERK1/2 signaling pathway

Ischemic preconditioning (IPC) has been demonstrated to provide a neuroprotection against brain damage produced by focal cerebral ischemia. However, it is elusive whether ischemic preconditioning attenuates ischemic brain damage through modulating phosphatidylinositol 3-kinase/Akt (PI3K/Akt) and extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway. In the present study, we first explored the best scheme of repetitive ischemic preconditioning (RIPC) to protect rat brain against ischemic damage and then further investigated the underlying mechanisms in RIPC's neuroprotection. Adult male Sprague-Dawley rats underwent ischemic preconditioning or (and) middle cerebral artery occlusion (MCAO). LY294002 or (and) PD98059 were injected intracerebroventricularly to selectively inhibit the activation of PI3K/Akt or ERK1/2. Neurological deficit scores, cerebral infarct volume, and morphological characteristic were detected at corresponding time after cerebral ischemia. The enzymatic activity of myeloperoxidase (MPO) was measured 24 h after cerebral ischemia. Expressions of p-Akt, t-Akt, p-ERK1/2, t-ERK1/2, nuclear factor-kappa B (NF-κB) p65, and cyclooxygenase-2 (COX-2) in ischemic brain were determined by Western blot. The release of tumor necrosis factor-α (TNF-α) in blood was examined by ELISA. In the various schemes of RIPC, IPC2 × 5 min causes less neuronal damage in the cortex and subcortex of ischemic brain and provides an obvious alleviation of cerebral infarction and neurological deficit after lethal ischemia. IPC2 × 5 min significantly reduces cerebral infarct volume, neurological deficit scores, and MPO activity; all of which were diminished by LY294002 or (and) PD98059. IPC2 × 5 min significantly upregulates the expressions of p-Akt and p-ERK1/2, which were inhibited by LY294002 or (and) PD98059. IPC2 × 5 min significantly downregulates the expressions of NF-κB p65 and COX-2 and attenuates the release of TNF-α; all of which were abolished by LY294002 or (and) PD98059. IPC2 × 5 min is the best scheme of RIPC to protect rat brain against cerebral ischemia. IPC2 × 5 min attenuates brain damage in rats subjected to lethal ischemia, and this neuroprotection is associated with inhibition of neuroinflammation through modulating PI3K/Akt and ERK1/2 signaling pathway.

A combination of four active compounds alleviates cerebral ischemia-reperfusion injury in correlation with inhibition of autophagy and modulation of AMPK/mTOR and JNK pathways

SMXZF is a combination of Rb1, Rg1, schizandrin, and DT-13 (6:9:5:4) derived from Sheng-mai San, a widely used Chinese traditional medicine for the treatment of cardiovascular and cerebral diseases. The present study explores the inhibitory effects and signaling pathways of SMXZF on autophagy induced by cerebral ischemia-reperfusion injury. Male C57BL/6 mice were subjected to ischemia-reperfusion insult by right middle cerebral artery occlusion (MCAO) for 1 hr with subsequent 24 hr reperfusion. Three doses of SMXZF (4.5, 9, and 18 mg/kg) were administered intraperitoneally (i.p.) after ischemia for 1 hr. An autophagic inhibitor, 3-methyladenine (3-MA; 300 μg/kg), was administered i.p. 20 min before ischemia as a positive drug. We found that SMXZF significantly increased cerebral blood flow and reduced the infarct volume, brain water content, and the neurological deficits in a dose-dependent manner. Similar to the positive control, SMXZF at 18 mg/kg also significantly inhibited autophagosome formation. Immunofluorescence staining and Western blotting demonstrated that SMXZF could significantly decrease the expression levels of beclin1 and microtubule-associated protein 1 light chain 3. SMXZF also remarkably inhibited the phosphorylation of adenosine monophosphate-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) as well as the expression of c-Jun N-terminal kinase (JNK) and its phosphorylation induced by 24 hr reperfusion. Finally, we demonstrated that the optimal administration time of SMXZF was at the early period of reperfusion. This study reveals that SMXZF displays neuroprotective effect against focal ischemia-reperfusion injury, possibly associated with autophagy inactivation through AMPK/mTOR and JNK pathways.

Early MEK1/2 inhibition after global cerebral ischemia in rats reduces brain damage and improves outcome by preventing delayed vasoconstrictor receptor upregulation

Background

Global cerebral ischemia following cardiac arrest is associated with increased cerebral vasoconstriction and decreased cerebral blood flow, contributing to delayed neuronal cell death and neurological detriments in affected patients. We hypothesize that upregulation of contractile ET_B and 5-HT_1B receptors, previously demonstrated in cerebral arteries after experimental global ischemia, are a key mechanism behind insufficient perfusion of the post-ischemic brain, proposing blockade of this receptor upregulation as a novel target for prevention of cerebral hypoperfusion and delayed neuronal cell death after global cerebral ischemia. The aim was to characterize the time-course of receptor upregulation and associated neuronal damage after global ischemia and investigate whether treatment with the MEK1/2 inhibitor U0126 can prevent cerebrovascular receptor upregulation and thereby improve functional outcome after global cerebral ischemia. Incomplete global cerebral ischemia was induced in Wistar rats and the time-course of enhanced contractile responses and the effect of U0126 in cerebral arteries were studied by wire myography and the neuronal cell death by TUNEL. The expression of ET_B and 5-HT_1B receptors was determined by immunofluorescence.

Results

Enhanced vasoconstriction peaked in fore- and midbrain arteries 3 days after ischemia. Neuronal cell death appeared initially in the hippocampus 3 days after ischemia and gradually increased until 7 days post-ischemia. Treatment with U0126 normalised cerebrovascular ET_B and 5-HT_1B receptor expression and contractile function, reduced hippocampal cell death and improved survival rate compared to vehicle treated animals.

Conclusions

Excessive cerebrovascular expression of contractile ET_B and 5-HT_1B receptors is a delayed response to global cerebral ischemia peaking 3 days after the insult, which likely contributes to the development of delayed neuronal damage. The enhanced cerebrovascular contractility can be prevented by treatment with the MEK1/2 inhibitor U0126, diminishes neuronal damage and improves survival rate, suggesting MEK1/2 inhibition as a novel strategy for early treatment of neurological consequences following global cerebral ischemia.

The roles of p38 MAPK/MSK1 signaling pathway in the neuroprotection of hypoxic postconditioning against transient global cerebral ischemia in adult rats

Postconditioning has regenerated interest as a mechanical intervention against cerebral ischemia/reperfusion injury, but its molecular mechanisms remain unknown. We previously reported that hypoxic postconditioning (HPC) ameliorated neuronal death induced by transient global cerebral ischemia (tGCI) in hippocampal CA1 subregion of adult rats. This study tested the hypothesis that p38-mitogen-activated protein kinase (p38 MAPK)/mitogen- and stress-response kinase 1 (MSK1) signaling pathway plays a role in the HPC-induced neuroprotection. Male Wistar rats were subjected to 10 min ischemia induced by applying the four-vessel occlusion method. HPC with 120 min was applied at 24 h after reperfusion. Immunohistochemistry and Western blot were used to detect the expression of phosphorylation of p38 MAPK and MSK1, as well as cleaved caspase-3. We found that HPC induced a significant increase of phosphorylated p38 MAPK and MSK1 in neurons of hippocampal CA1 region and a significant decrease in glial cells after tGCI as well. Furthermore, HPC attenuated caspase-3 cleavation triggered by tGCI in CA1 region. Moreover, p38 MAPK inhibition by SB203580 significantly decreased the phosphorylation of MSK1, increased cleaved caspase-3 expression, and abolished the neuroprotection of HPC. These findings suggested that p38 MAPK/MSK1 signaling axis contributed to HPC-mediated neuroprotection against tGCI, at least in part, by regulating the activation of caspase-3.