Ischemic Tolerance Research Articles

Ventricular depolarisation vectors in exercise induced myocardial ischaemia

Ischaemia reduces membrane excitability and conduction of myocardial depolarisation. This would alter the synergy of electromotive forces that contribute to a resultant force at any instant. Changes in magnitude and direction of resultant forces are reflected in electrocardiographic signals. Here we show a method for obtaining the coordinates of resultant electrical forces during exercise derived from a bipolar orthogonal lead system for calculation of electrical vectors in three planes. In a trial, analysis of changes in vectors indicated that the extent of reduction in magnitude with exercise was significantly greater in groups of patients categorized by impaired effort tolerance and signs of ischaemia. Measurement of changes in the spectrum of depolarisation vectors during exercise has the potential for non-invasive assessment of myocardial ischaemia. This could be the basis of a portable, low-cost tool for investigation of patients with symptoms suggestive of coronary artery disease.

Sleep, Preconditioning and Stroke.

Sleep is a complex physiological and behavioral state, which is needed for homeostasis at a cellular (neurons), organ (brain), and individual level, known to be fundamental for survival. Despite its importance, it is estimated that one third of the adult population is sleep deprived1 or complains about sleep disturbances.2 Sleep disorders, classified into 6 major categories according to the recent International Classification of Sleep Disorders,3 determine sleep fragmentation, which in turn induces autonomic nervous system dysfunction, increases inflammation, alters coagulation, and induces oxidative stress responses.4,5 Sleep deprivation (SD)/fragmentation has been linked to several pathological conditions, including stroke (in the present review, the term stroke always refers to ischemic stroke).6,7 In the first part of this review, we address the role of sleep modulation in the pathophysiology of brain ischemia (Figure 1),8–12 and we briefly discuss the current epidemiological evidence linking sleep disorders to stroke risk. In the second part, we review the concept of ischemic preconditioning (IP), and we discuss the role of sleep as a potential preconditioning factor able to induce ischemic tolerance and neuroprotection.13 Figure 1. The vicious and virtuous circles of sleep and stroke interaction. Sleep disruption after experimental stroke is detrimental, whereas promoting sleep after an ischemic event facilitates neuroplasticity and recovery in turn determining a better stroke outcome. REM indicates rapid eye movement; and SWS, slow-wave sleep. ### Animal Studies Sleep may be artificially manipulated by inducing either SD or sleep enhancement before or after experimental stroke. Animal models have shown that increasing the length and repetition of SD after stroke is linked to detrimental effects affecting both stroke evolution and functional recovery.9,11,14 Additionally, it has been shown that the number of apoptotic …

Ischemic Preconditioning Protects Astrocytes against Oxygen Glucose Deprivation Via the Nuclear Erythroid 2-Related Factor 2 Pathway.

Induction of ischemic preconditioning (IPC) represents a potential therapy against cerebral ischemia by activation of adaptive pathways and modulation of mitochondria to induce ischemic tolerance to various cells and tissues. Mitochondrial dysfunction has been ascribed to contribute to numerous neurodegenerative conditions and cerebral ischemia. Nuclear erythroid 2-related factor 2 (Nrf2) is a transcription factor that has traditionally been involved in upregulating cellular antioxidant systems to combat oxidative stress in the brain; however, the association of Nrf2 with mitochondria in the brain remains unclear. In the present study, we investigated the effects of Nrf2 on (i) IPC-induced protection of astrocytes; (ii) OXPHOS protein expression; and (iii) mitochondrial supercomplex formation.Oxygen-glucose deprivation (OGD) was used as an in vitro model of cerebral ischemia and IPC in cultured rodent astrocytes derived from WT C57Bl/6J and Nrf2-/- mice. OXPHOS proteins were probed via western blotting, and supercomplexes were determined by blue native gel electrophoresis.IPC-induced cytoprotection in wild-type, but not Nrf2-/- mouse astrocyte cultures following a lethal duration of OGD. In addition, our results suggest that Nrf2 localizes to the outer membrane in non-synaptic brain mitochondria, and that a lack of Nrf2 in vivo produces altered supercomplex formation in mitochondria.Our findings support a role of Nrf2 in mediating IPC-induced protection in astrocytes, which can profoundly impact the ischemic tolerance of neurons. In addition, we provide novel evidence for the association of Nrf2 to brain mitochondria and supercomplex formation. These studies offer new targets and pathways of Nrf2, which may be heavily implicated following cerebral ischemia.

Loss of caveolin-1 alters cardiac mitochondrial function and increases susceptibility to stress

Introduction: Cardiovascular disease (CVD) is the leading cause of morbidity and mortality in the United States. Caveolae, membrane micro-domains enriched in cholesterol, glycosphingolipids, sphingomyelin and the protein caveolin, are critical to ischemic tolerance. We have previously described a specific role for caveolin-3 (Cav-3) in cardiac protection via regulation of mitochondrial function; however, little is known about the role of caveolin-1 (Cav-1) in cardiac mitochondrial bioenergetics. We hypothesized that Cav-1 is crucial in maintaining healthy cardiac mitochondria. Material and Methods: We performed a series of experiments to assess the role of Cav-1 upon mitochondrial functionality, comparing heart tissues and isolated mitochondria from wildtype (WT) and global Cav-1 knock-out (KO) mice. Percoll-purified WT mitochondria were immunogold labeled and imaged by TEM to localize Cav-1 protein to specific mitochondrial membranes. Furthermore, oxygen consumption was evaluated in isolated papillary muscle fibers by high-resolution respirometry using Oroboros O2k oxygraph. Superoxide free radical production was investigated by electron paramagnetic resonance imaging (EPR) using the spin probe DEPMPO in isolated mitochondria. Results: Immunogold labeling showed Cav-1 localization to outer and inner mitochondrial membranes. In Cav-1 KO mice relative oxygen flux was slightly increased in the presence of complex I substrates and ADP. Furthermore, in Cav-1 KO mice, cytochrome c response (a marker for outer mitochondrial damage) was significantly correlated to total complex I & II respiration (malate, pyruvate, glutamate, ADP, and succinate) with increased respiration at higher cytochrome c responses, indicating potential outer mitochondrial membrane damage. ROS was decreased in Cav-1 KO mice during state IV respiration with complex I & II substrates measured by EPR suggesting overall decreased mitochondrial function. Conclusion: Cav-1 may be a critical regulator of cardiac mitochondrial function. Cav-1 may therefore be a viable therapeutic target to alter cardiac mitochondrial bioenergetics.

Hyperthermia with different temperatures inhibits proliferation and promotes apoptosis through the EGFR/STAT3 pathway in C6 rat glioma cells.

Malignant gliomas are a group of aggressive neoplasms among human cancers. The curative effects of current treatments are finite for improving the prognosis of patients. Hyperthermia (HT) is an effective treatment for cancers; however, the effects of HT with different temperatures in treatment of MG and relevant mechanisms remain unclear. MTT assay and Annexin V-fluorescein isothiocyanate/propidium iodide staining were used for investigating the proliferation and apoptosis of C6 cells, respectively. Western blotting was applied to detect the expression of proteins. Ultrasonography was employed to evaluate the tumor formation rate, growth rate, angiogenesis rate and degree of hardness of tumors in vivo. The authors certified that HT with 42–46°C × 1 h, 1 t could inhibit proliferation, promote apoptosis, reduce tumor formation rate, growth rate, angiogenesis rate, degree of hardness of tumors, ischemic tolerance and anoxic tolerance, and have synergy with temozolomide in C6 cells. Long-term HT (43°C × 1 h, 1 t/5 d, 90 d) did not cut down the sensitivity of C6 cells to HT, and sustainably inhibited the proliferation of C6 cells. Furthermore, the authors proved HT produced these effects primarily through inhibition of the EGFR/STAT3/HIF-1A/VEGF-A pathway.

Neuronal SIRT1 (Silent Information Regulator 2 Homologue 1) Regulates Glycolysis and Mediates Resveratrol-Induced Ischemic Tolerance.

Resveratrol, at least in part via SIRT1 (silent information regulator 2 homologue 1) activation, protects against cerebral ischemia when administered 2 days before injury. However, it remains unclear if SIRT1 activation must occur, and in which brain cell types, for the induction of neuroprotection. We hypothesized that neuronal SIRT1 is essential for resveratrol-induced ischemic tolerance and sought to characterize the metabolic pathways regulated by neuronal Sirt1 at the cellular level in the brain. We assessed infarct size and functional outcome after transient 60 minute middle cerebral artery occlusion in control and inducible, neuronal-specific SIRT1 knockout mice. Nontargeted primary metabolomics analysis identified putative SIRT1-regulated pathways in brain. Glycolytic function was evaluated in acute brain slices from adult mice and primary neuronal-enriched cultures under ischemic penumbra-like conditions. Resveratrol-induced neuroprotection from stroke was lost in neuronal Sirt1 knockout mice. Metabolomics analysis revealed alterations in glucose metabolism on deletion of neuronal Sirt1, accompanied by transcriptional changes in glucose metabolism machinery. Furthermore, glycolytic ATP production was impaired in acute brain slices from neuronal Sirt1 knockout mice. Conversely, resveratrol increased glycolytic rate in a SIRT1-dependent manner and under ischemic penumbra-like conditions in vitro. Our data demonstrate that resveratrol requires neuronal SIRT1 to elicit ischemic tolerance and identify a novel role for SIRT1 in the regulation of glycolytic function in brain. Identification of robust neuroprotective mechanisms that underlie ischemia tolerance and the metabolic adaptations mediated by SIRT1 in brain are crucial for the translation of therapies in cerebral ischemia and other neurological disorders.

The neuroprotective effect of transient ischemic attacks before ischemic stroke; acute phase response as a possible mechanism

Background: TIAs not only indicate the inherent risk of stroke, but also provide tolerance to ischemia through a process called ischemic tolerance (IT). The Acute Phase Reaction (APR) is a candidate mechanism for IT.

The Intervention Effect of Total Flavonoids of Mao Dongqing on Cerebral Ischaemic Tolerance Model in Mice

<h3>Background</h3> The aim of this study was to explore the intervention effect and mechanism of total flavonoids of Mao Dongqing on cerebral ischaemic tolerance using modern technology. <h3>Methods</h3> To establish the mouse cerebral ischaemic tolerance model, we used the method of blocking the blood flow of the bilateral common carotid arteries twice. After the first operation, each group was given the corresponding medicine, once a day for 5 days. After the second operation, the content of TXB₂, 6-keto-PGF1 in plasma and the expression of c-fos, COX-2 in brain tissue and the morphological changes of brain by HE staining were observed over 24 hours. <h3>Results</h3> The mouse cerebral ischaemic tolerance model was a copy success. The total flavonoids of Mao Dongqing significantly reduced the content of plasma B₂ (TXB₂) in the animal model, significantly increased the content of 6-keto-PGF_1α in plasma and reduced the ratio of TXB₂ to 6-keto-PGF1_α, which suggested that platelet function was improved. They decreased the expression of c-fos and COX-2 in brain tissue and significantly reduced the degree of pathological damage of brain tissue. This indicates that they had an anti-cerebral ischaemic effect. <h3>Conclusion</h3> Ischaemic preconditioning can induce cerebral ischaemic tolerance. The total flavonoids of Mao Dongqing and ischaemic preconditioning have a synergistic effect by inhibition of the overexpression of immediate early gene c-fos, COX-2 and improved platelet function. It can reduce brain injury and promote the formation of cerebral ischaemic tolerance.

Integrity of Cerebellar Fastigial Nucleus Intrinsic Neurons Is Critical for the Global Ischemic Preconditioning.

Excitation of intrinsic neurons of cerebellar fastigial nucleus (FN) renders brain tolerant to local and global ischemia. This effect reaches a maximum 72 h after the stimulation and lasts over 10 days. Comparable neuroprotection is observed following sublethal global brain ischemia, a phenomenon known as preconditioning. We hypothesized that FN may participate in the mechanisms of ischemic preconditioning as a part of the intrinsic neuroprotective mechanism. To explore potential significance of FN neurons in brain ischemic tolerance we lesioned intrinsic FN neurons with excitotoxin ibotenic acid five days before exposure to 20 min four-vessel occlusion (4-VO) global ischemia while analyzing neuronal damage in Cornu Ammoni area 1 (CA1) hippocampal area one week later. In FN-lesioned animals, loss of CA1 cells was higher by 22% compared to control (phosphate buffered saline (PBS)-injected) animals. Moreover, lesion of FN neurons increased morbidity following global ischemia by 50%. Ablation of FN neurons also reversed salvaging effects of five-minute ischemic preconditioning on CA1 neurons and morbidity, while ablation of cerebellar dentate nucleus neurons did not change effect of ischemic preconditioning. We conclude that FN is an important part of intrinsic neuroprotective system, which participates in ischemic preconditioning and may participate in naturally occurring neuroprotection, such as “diving response”.

The role of stump pressure and cerebral oximetry in predicting ischaemic brain damage during carotid endarterectomy

ABSTRACTObjective is to compare the predictive value of stump pressure (SP) and cerebral oximetry (rSO2) levels in the evaluation of ischaemic injury of the cerebrum during clamping of the carotid artery (CCA) without temporary shunt (TS). Methods We included 84 patients with an asymptomatic stenosis (>70%) of the internal carotid artery (ICA) who underwent carotid endarterectomy (CEA) under GA. Cerebral ischaemic tolerance (CIT) was determined on the basis of SP, rSO2 and ∆rSO2 (↓rSO2 from baseline) during CCA. The levels of S100 protein (S100) and neuron-specific enolase (NSE) were measured on each stage of the study. MRI was performed for all patients. Results There were no perioperative strokes and myocardial infarctions during the study. Temporary shutdown of blood flow in CAs during CEA is accompanied by a significant elevation of S100, NSE concentration with their subsequent restoration (three days after surgery). ROC analysis showed that none of the methods for CIT assessment (SP, rSO2 and ∆rSO2) was a valuable predictor of cerebral damage during CEA. Conclusion SP with a threshold value of ≤40 mmHg has an average quality of prediction (AUC = 63).∆rSO2 of ≥20% and a threshold value of rSO2 ≤ 40% have an unsatisfactory quality of prediction (AUC < 60).

Gender-specific impairment of in vitro sinoatrial node chronotropic responses and of myocardial ischemia tolerance in rats exposed prenatally to betamethasone

Excessive fetal glucocorticoid exposure has been linked to increased susceptibility to hypertension and cardiac diseases in the adult life, a process called fetal programming. The cardiac contribution to the hypertensive phenotype of glucocorticoid-programmed progeny is less known, therefore, we investigated in vitro cardiac functional parameters from rats exposed in utero to betamethasone.Pregnant Wistar rats received vehicle (VEH) or betamethasone (BET, 0.1mg/kg, i.m.) at gestational days 12, 13, 18 and 19. Male and female offspring were killed at post-natal day 30 and the right atrium (RA) was isolated to in vitro evaluation of drug-induced chronotropic responses. Additionally, whole hearts were retrograde-perfused in a Langendorff apparatus and infarct size in response to in vitro ischemia/reperfusion (I/R) protocol was evaluated.Male and female progeny from BET-exposed pregnant rats had reduced birth weight, a hallmark of fetal programming. Male BET-progeny had increased basal RA rate, impaired chronotropic responses to noradrenaline and adenosine, and increased myocardial damage to I/R. Though a 12-fold reduction in the negative chronotropic responses to adenosine, the effects of non-metabolisable adenosine receptor agonists 5′-(N-ethylcarboxamido)adenosine or 2-Chloro-adenosine were not different between VEH- and BET-exposed male rats. BET-exposed female offspring presented no cardiac dysfunction.Prenatal BET exposure engenders male-specific impairment of sinoatrial node function and on myocardial ischemia tolerance resulting, at least in part, from an increased adenosine metabolism in the heart. In light of the importance of adenosine in the cardiac physiology our results suggest a link between reduced adenosinergic signaling and the cardiac dysfunctions observed in glucocorticoid-induced fetal programming.

Sestrin2 prevents age-related intolerance to ischemia and reperfusion injury by modulating substrate metabolism.

A novel stress-inducible protein, Sestrin2 (Sesn2), declines in the heart with aging. AMPK has emerged as a pertinent stress-activated kinase that has been shown to have cardioprotective capabilities against myocardial ischemic injury. We identified the interaction between Sesn2 and AMPK in the ischemic heart. To determine whether ischemic AMPK activation-modulated by the Sesn2-AMPK complex in the heart-is impaired in aging that sensitizes the heart to ischemic insults, young C57BL/6 mice (age 3-4 mo), middle-aged mice (age 10-12 mo), and aged mice (age 24-26 mo) were subjected to left anterior descending coronary artery occlusion for in vivo regional ischemia. The ex vivo working heart system was used for measuring substrate metabolism. The protein level of Sesn2 in hearts was gradually decreased with aging. Of interest, ischemic AMPK activation was blunted in aged hearts compared with young hearts (P < 0.05); the AMPK downstream glucose uptake and the rate of glucose oxidation were significantly impaired in aged hearts during ischemia and reperfusion (P < 0.05 vs. young hearts). Myocardial infarction size was larger in aged hearts (P < 0.05 vs. young hearts). Immunoprecipitation with Sesn2 Ab revealed that cardiac Sesn2 forms a complex with AMPK and upstream liver kinase B1 (LKB1) during ischemia. Of interest, the binding affinity between Sesn2 and AMPK upstream LKB1 is impaired in aged hearts during ischemia (P < 0.05 vs. young hearts). Furthermore, Sesn2-knockout hearts demonstrate a cardiac phenotype and response to ischemic stress that is similar to wild-type aged hearts (i.e., impaired ischemic AMPK activation and higher sensitivity to ischemia- and reperfusion- induced injury). Adeno-associated virus-Sesn2 was delivered to aged hearts via a coronary delivery approach and significantly rescued the protein level of Sesn2 and the ischemic tolerance of aged hearts; therefore, Sesn2 is a scaffold protein that mediates AMPK activation in the ischemic myocardium via an interaction with AMPK upstream LKB1. Decreased Sesn2 levels in aging lead to a blunted ischemic AMPK activation, alterations in substrate metabolism, and an increased sensitivity to ischemic insults-Quan, N., Sun, W., Wang, L., Chen, X., Bogan, J. S., Zhou, X., Cates, C., Liu, Q., Zheng, Y., Li J. Sestrin2 prevents age-related intolerance to ischemia and reperfusion injury by modulating substrate metabolism.

Effect of Anesthetics on Efficiency of Remote Ischemic Preconditioning.

Remote ischemic preconditioning of hind limbs (RIPC) is an effective method for preventing brain injury resulting from ischemia. However, in numerous studies RIPC has been used on the background of administered anesthetics, which also could exhibit neuroprotective properties. Therefore, investigation of the signaling pathways triggered by RIPC and the effect of anesthetics is important. In this study, we explored the effect of anesthetics (chloral hydrate and Zoletil) on the ability of RIPC to protect the brain from injury caused by ischemia and reperfusion. We found that RIPC without anesthesia resulted in statistically significant decrease in neurological deficit 24h after ischemia, but did not affect the volume of brain injury. Administration of chloral hydrate or Zoletil one day prior to brain ischemia produced a preconditioning effect by their own, decreasing the degree of neurological deficit and lowering the volume of infarct with the use of Zoletil. The protective effects observed after RIPC with chloral hydrate or Zoletil were similar to those observed when only the respective anesthetic was used. RIPC was accompanied by significant increase in the level of brain proteins associated with the induction of ischemic tolerance such as pGSK-3β, BDNF, and HSP70. However, Zoletil did not affect the level of these proteins 24h after injection, and chloral hydrate caused increase of only pGSK-3β. We conclude that RIPC, chloral hydrate, and Zoletil produce a significant neuroprotective effect, but the simultaneous use of anesthetics with RIPC does not enhance the degree of neuroprotection.

The Focal-Focal Preconditioning Effect of Photothrombotic Impact on the Signaling Protein Profile in the Penumbra Surrounding the Ischemic Core Induced by Another Photothrombotic Impact.

Ischemic tolerance is the establishment of brain resistance to severe ischemic damage by a mild preconditioning stimulus, insufficient to irreversible tissue damage, but capable of initiating a defense response. We developed the model of focal-focal ischemic tolerance, in which the first local photothrombotic infarct (PTI) in the rat brain cortex reduced the infarct caused by second PTI applied to the contralateral cortex of the same rat 7days later. Using antibody microarrays, we compared protein profiles in the penumbra surrounding the PTI core after single and double PTI. We observed up- or downregulation of several dozens of proteins that are aimed at neurodegeneration or neuroprotection. Both single and double PTI induced damaging processes in the rat cerebral cortex that included over-expression of various pro-apoptotic and signaling proteins and downregulation of other signaling proteins and regulators of proliferation, some components of actin, intermediate fiber and microtubular cytoskeletons, and proteins involved in vesicle transport and synaptic transmission. The simultaneous protective processes included the upregulation of different signaling and anti-apoptotic proteins, stimulators of proliferation, and proteins involved in remodeling of actin cytoskeleton. The elevated expression of some signaling proteins, such as calcium-dependent PLCγ1, PKVα1, CaMKIIα, calnexin, and calreticulin was preserved after double PTI. Less pro-survival proteins were downregulated in the penumbra after double than single impact.

Tolerance of isolated rabbit hearts to short ischemic periods is affected by increased LV mass fraction.

Hypertrophied hearts are known for increased risk of arrhythmias and are linked with reduced ischemic tolerance. However, still little is known about state characterized only by increased left ventricle (LV) mass fraction. Seventeen isolated rabbit hearts with various LV mass were divided into two groups according to LV weight/heart weight ratio (LVW/HW ratio), namely group H and L (with higher and lower LVW/HW ratio, respectively) and underwent three short cycles of global ischemia and reperfusion. The differences in electrogram (heart rate, QRS(max), mean number, onset and dominant form of ventricular premature beats) and in biochemical markers of myocardial injury (creatine kinase, lactate dehydrogenase - LDH) and lipid peroxidation (4-hydroxy-2-nonenal - 4-HNE) were studied. As compared to group L, hearts in group H exhibited lower tolerance to ischemia expressed as higher incidence and severity of arrhythmias in the first ischemic period as well as increase of LDH and 4-HNE after the first reperfusion. In the third cycle of ischemia-reperfusion, the preconditioning effect was observed in both electrophysiological parameters and LDH release in group H. Our results showed consistent trends when comparing changes in electrograms and biochemical markers. Moreover, 4-HNE seems to be good potential parameter of moderate membrane alteration following ischemia-reperfusion injury.

Opposing effects on cardiac function by calorie restriction in different-aged mice.

SummaryCalorie restriction (CR) increases average and maximum lifespan and exhibits an apparent beneficial impact on age‐related diseases. Several studies have shown that CR initiated either in middle or old age could improve ischemic tolerance and rejuvenate the aging heart; however, the data are not uniform when initiated in young. The accurate time to initiate CR providing maximum benefits for cardiac remodeling and function during aging remains unclear. Thus, whether a similar degree of CR initiated in mice of different ages could exert a similar effect on myocardial protection was investigated in this study. C57BL/6 mice were subjected to a calorically restricted diet (40% less than the ad libitum diet) for 3 months initiated in 3, 12, and 19 months. It was found that CR significantly reversed the aging phenotypes of middle‐aged and old mice including cardiac remodeling (cardiomyocyte hypertrophy and cardiac fibrosis), inflammation, mitochondrial damage, telomere shortening, as well as senescence‐associated markers but accelerated in young mice. Furthermore, whole‐genome microarray demonstrated that the AMP‐activated protein kinase (AMPK)–Forkhead box subgroup ‘O’ (FOXO) pathway might be a major contributor to contrasting regulation by CR initiated in different ages; thus, increased autophagy was seen in middle‐aged and old mice but decreased in young mice. Together, the findings demonstrated promising myocardial protection by 40% CR should be initiated in middle or old age that may have vital implications for the practical nutritional regimen.

Stimulated CB1 Cannabinoid Receptor Inducing Ischemic Tolerance and Protecting Neuron from Cerebral Ischemia.

It is reported that endogenous cannabinoids can cause vasodilation and bradycardia. They have anti-inflammatory effect and protect endothelial cells from injury, therefore they have potential application prospect in the prevention of cardio-cerebrovascular diseases. However, the mechanisms of the neuroprotection mediated by cannabinoid 1 receptors (CB1Rs) have not been uncovered in detail. Nearly one hundred of new publications relevant to the theme are almost selected from Pubmed. The advanced details associated with the involvement of CB1R in cerebral ischemia as well as cerebral ischemic tolerance are reviewed. Anandamide system is mainly made up of cannabinoid receptors, their endogenous ligands and some related enzymes. The activation of the system mediates various molecular events so that plays a crucial role in the neuroprotection of cerebral ischemia. Increasing evidences suggest that CB1R is one of key molecules that mediate cerebral ischemia and cerebral ischemia tolerance. It is likely to provide an appropriate antioxidant balance by increasing endogenous free radical scavengers and helpful to exert the neuroprotective effects. Moreover, MAPKs, including ERK1/2, c-Jun Nterminal kinase (JNK) and p38MAPK can be recruited and stimulated through a complex signaling networks mediated by CB1R. Considerable evidences have indicated that CB1R was a crucial regulator for ERK1/2 signaling pathway. It is known that PI3K/Akt is a classical signaling pathway and its activation exerts neuroprotective effect via significant promoting cell survival. Glycogen synthase kinase-3β (GSK-3β) is an important downstream target of p-Akt. The PI3K/Akt/GSK-3β signaling pathway mediated by CB1Rs takes an important part in cerebral ischemic injury. PKC and CB1R are found to be abundantly co-expressed in presynaptic nerve endings of brain. There are considerable reports that different PKC isozymes played vital roles respectively in cerebral ischemic injury and preconditioning. The CB1R -mediated activation of PKCε can effectively stimulate ischemic tolerance. CB1R played an important part via several signaling pathways in the protection from ischemic stroke and in ischemic tolerance. The involved molecular signaling pathways include ERK1/2, PI3K/Akt/GSK-3β and the translocation and activation of PKCε. With the intimate association between CB1R and neuron injuries, to target the receptor will exert neuroprotective effects on cerebral ischemia, which provides wide foreground for a novel therapy target.

Sphingosine kinase 2 activates autophagy and protects neurons against ischemic injury through interaction with Bcl-2 via its putative BH3 domain

Our previous findings suggest that sphingosine kinase 2 (SPK2) mediates ischemic tolerance and autophagy in cerebral preconditioning. The aim of this study was to determine by which mechanism SPK2 activates autophagy in neural cells. In both primary murine cortical neurons and HT22 hippocampal neuronal cells, overexpression of SPK2 increased LC3II and enhanced the autophagy flux. SPK2 overexpression protected cortical neurons against oxygen glucose deprivation (OGD) injury, as evidenced by improvement of neuronal morphology, increased cell viability and reduced lactate dehydrogenase release. The inhibition of autophagy effectively suppressed the neuroprotective effect of SPK2. SPK2 overexpression reduced the co-immunoprecipitation of Beclin-1 and Bcl-2, while Beclin-1 knockdown inhibited SPK2-induced autophagy. Both co-immunoprecipitation and GST pull-down analysis suggest that SPK2 directly interacts with Bcl-2. SPK2 might interact to Bcl-2 in the cytoplasm. Notably, an SPK2 mutant with L219A substitution in its putative BH3 domain was not able to activate autophagy. A Tat peptide fused to an 18-amino acid peptide encompassing the native, but not the L219A mutated BH3 domain of SPK2 activated autophagy in neural cells. The Tat-SPK2 peptide also protected neurons against OGD injury through autophagy activation. These results suggest that SPK2 interacts with Bcl-2 via its BH3 domain, thereby dissociating it from Beclin-1 and activating autophagy. The observation that Tat-SPK2 peptide designed from the BH3 domain of SPK2 activates autophagy and protects neural cells against OGD injury suggest that this structure may provide the basis for a novel class of therapeutic agents against ischemic stroke.

MicroRNA Changes in Preconditioning-Induced Neuroprotection.

Preconditioning is a paradigm in which sublethal stress-prior to a more injurious insult-induces protection against injury. In the central nervous system (CNS), preconditioning against ischemic stroke is induced by short durations of ischemia, brief seizures, exposure to anesthetics, and other stresses. Increasing evidence supports the contribution of microRNAs (miRNAs) to the pathogenesis of cerebral ischemia and ischemic tolerance induced by preconditioning. Studies investigating miRNA changes induced by preconditioning have to date identified 562 miRNAs that change expression levels after preconditioning, and 15% of these changes were reproduced in at least one additional study. Of miRNAs assessed as changed by preconditioning in more than one study, about 40% changed in the same direction in more than one study. Most of the studies to assess the role of specific miRNAs in the neuroprotective mechanism of preconditioning were performed in vitro, with fewer studies manipulating individual miRNAs in vivo. Thus, while many miRNAs change in response to preconditioning stimuli, the mechanisms underlying their effects are not well understood. The data does suggest that miRNAs may play significant roles in preconditioning-induced neuroprotection. This review focuses on the current state of knowledge of the possible role of miRNAs in preconditioning-induced cerebral protection.

Learning To Suffer

PURPOSE: To compare the effect of volume-matched high-intensity interval training (HIIT) and moderate-intensity continuous training (CONT) on ischaemic muscle pain tolerance and high-intensity exercise tolerance. METHODS: Twenty healthy adults were randomly assigned to either 6 weeks of HIIT (6-8 x 5 min at halfway between lactate threshold and maximal oxygen uptake [50%Δ]) or volume-matched CONT (~60–80 min at 90% lactate threshold) on a cycle ergometer. Immediately pre- and post-training, participants completed a tourniquet test to examine ischaemic muscle pain tolerance and two time to exhaustion (TTE) trials at 50%Δ to examine exercise tolerance; the post-training TTE trials were completed at the pre-training 50%Δ (same absolute intensity) and the post-training 50%Δ (same relative intensity). RESULTS: HIIT and CONT resulted in similar improvements in all markers of aerobic fitness (P>0.05). Compared with pre-training, HIIT increased TTE at the same absolute and relative intensity as pre-training (148% and 43%, respectively) to a greater extent than CONT (38% and -4%, respectively) (P<0.05). HIIT increased pain tolerance (41%, P<0.001), which demonstrated moderate non-significant associations with the increase in TTE at the same relative intensity as pre-training (r=0.50, P=0.07), however pain tolerance was unaffected by CONT (-3%, P>0.05). CONCLUSION: The repeated exposure to a high-intensity noxious exercise training stimuli increases ischemic muscle pain tolerance, which is independent of the improvements in aerobic fitness induced by endurance training. This increase in ischemic muscle pain tolerance may be an important contributor to the increase in high-intensity exercise tolerance following HIIT. Key words: Central nervous system; endurance; exercise tolerance; high-intensity interval training; muscle fatigue; muscle pain.