Role of mitogen- and stress-activated kinases in ischemic injury

Neuroprotection of paclitaxel against cerebral ischemia/reperfusion-induced brain injury through JNK3 signaling pathway

In this study, we investigated the neuroprotective effects of paclitaxel in transient cerebral ischemia and possible regulatory mechanism of these neuroprotection. Our data showed that paclitaxel can down-regulate the increased MLK3, JNK3, c-Jun, Bcl-2, and caspase-3 phosphorylation induced by ischemia injury. Cresyl violet staining and immunohistochemistry results demonstrated that paclitaxel had neuroprotective effect against ischemia/reperfusion-induced neuronal cell death. These results indicated that paclitaxel has neuroprotection in ischemic injury through JNK3 signaling pathway and provided a novel possible drug in therapeutics of brain ischemia.

Downregulation of mitogen-activated protein kinase 1 of Leishmania donovani field isolates is associated with antimony resistance

Emergence of resistance to pentavalent antimonials has become a severe obstacle in the treatment of visceral leishmaniasis (VL) on the Indian subcontinent. The mechanisms operating in laboratory-generated strains are somewhat known, but the determinants of clinical antimony resistance are not well understood. By utilizing a DNA microarray expression profiling approach, we identified a gene encoding mitogen-activated protein kinase 1 (MAPK1) for the kinetoplast protozoan Leishmania donovani (LdMAPK1) that was consistently downregulated in antimony-resistant field isolates. The expression level of the gene was validated by real-time PCR. Furthermore, decreased expression of LdMAPK1 was also confirmed at the protein level in resistant isolates. Primary structure analysis of LdMAPK1 revealed the presence of all of the characteristic features of MAPK1. When expressed in Escherichia coli, the recombinant enzyme showed kinase activity with myelin basic protein as the substrate and was inhibited by staurosporine. Interestingly, overexpression of this gene in a drug-sensitive laboratory strain and a resistant field isolate resulted in increased the sensitivity of the transfectants to potassium antimony tartrate, suggesting that it has a role in antimony resistance. Our results demonstrate that downregulation of LdMAPK1 may be in part correlated with antimony drug resistance in Indian VL isolates.

Late cerebral ischaemia after subarachnoid haemorrhage: is cerebrovascular receptor upregulation the mechanism behind?

Late cerebral ischaemia after subarachnoid haemorrhage (SAH) carries high morbidity and mortality because of reduced cerebral blood flow (CBF) and subsequent cerebral ischaemia. This is associated with upregulation of contractile receptors in cerebral artery smooth muscles via the activation of intracellular signalling. In addition, delayed cerebral ischaemia after SAH is associated with inflammation and disruption of the blood-brain barrier (BBB). This article reviews recent evidence concerning the roles of vasoconstrictor receptor upregulation, inflammation and BBB breakdown in delayed cerebral ischaemia after SAH. In addition, recent studies investigating the role of various intracellular signalling pathways in these processes and the possibilities of targeting signalling components in SAH treatment are discussed. Studies using a rat SAH model have demonstrated that cerebral arteries increase their sensitivity to endogenous agonists such as ET-1 and 5-HT by increasing their smooth muscle expression of receptors for these after SAH. This is associated with reduced CBF and neurological deficits. A number of signal transduction components mediating this receptor upregulation have been identified, including the MEK-ERK1/2 pathway. Inhibition of MEK-ERK1/2 signalling has been shown to prevent cerebrovascular receptor upregulation and normalize CBF and neurological function after SAH in rats. At the same time, in rat SAH, certain cytokines and BBB-regulating proteins are upregulated in cerebral artery smooth muscles and treatment with MEK-ERK1/2 inhibitors prevents the induction of these proteins. Thus, inhibitors of MEK-ERK1/2 signalling exert multimodal beneficial effects in SAH.

T33, a novel peroxisome proliferator-activated receptor γ/α agonist, exerts neuroprotective action via its anti-inflammatory activities

AIM

To examine the neuroprotective effects of T33, a peroxisome proliferator-activated receptor gamma/alpha (PPARγ/α) agonist, in acute ischemic models in vitro and in vivo.

METHODS

Primary astrocytes subjected to oxygen-glucose deprivation/reperfusion (O/R) and BV-2 cells subjected to hypoxia were used as a model simulating the ischemic core and penumbra, respectively. The mRNA levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) were measured using qPCR. The levels of TNF-α secreted by BV-2 cells were measured using ELISA. Protein levels of cyclooxygenase-2 (COX-2), p65, phosphorylated I-κBα/I-κBα, phosphorylated I-κB kinase (pIKK), phosphorylated eukaryote initiation factor 2α (p-eIF-2α)/eIF-2α and p-p38/p38 were detected using Western blot. PPARγ activity was measured using EMSA. The neuroprotection in vivo was examined in rat middle cerebral artery occlusion (MCAO) model with neurological scoring and TTC staining.

RESULTS

Addition of T33 (0.5 μmol/L) increased the level of I-κBα protein in primary astrocytes subjected to O/R, which was due to promoting protein synthesis without affecting degradation. In primary astrocytes subjected to O/R, addition of T33 amplified I-κBα gene transcription and mRNA translation, thus suppressing the nuclear factor-kappa B (NF-κB) pathway and reducing inflammatory mediators (TNF-α, IL-1β, and COX-2). In BV-2 cells subjected to hypoxia, T33 (0.5 μmol/L) reduced TNF-α, COX-2, and p-P38 production, which was antagonized by pre-administration of the specific PPARγ antagonist GW9662 (30 μmol/L). T33 (2 mg/kg, ip) attenuated MCAO-induced inflammatory responses and brain infarction, which was antagonized by pre-administered GW9662 (4 mg/kg, ip).

CONCLUSION

T33 exerted anti-inflammatory effects in the ischemic core and penumbra via PPARγ activation, which contributed to its neuroprotective action.

Acclimation to decompression: stress and cytokine gene expression in rat lungs

Previous studies demonstrated that animals exposed to repeated compression-decompression stress acclimated (i.e., developed reduced susceptibility) to rapid decompression. This study endeavored to characterize inflammatory and stress-related gene expression and signal transduction associated with acclimation to rapid decompression. Rats were divided into four groups: 1) control-sham: pressure naïve rats; 2) acclimation-sham: nine acclimation dives [70 feet seawater (fsw), 30 min]; 3) control-dive: test dive only (175 fsw, 60 min); and 4) acclimation-dive: nine acclimation dives and a test dive. After the test dive, rats were observed for decompression sickness (DCS). Expression of 13 inflammatory and stress-related genes and Akt (or PKB, a serine/threonine protein kinase) and MAPK phosphorylation of lung tissue were examined. The expression of immediate early gene/transcription factor early growth response gene 1 (Egr-1) was observed in both control and acclimation animals with DCS but not in animals without DCS. Increased Egr-1 in control-dive animals with DCS was significantly greater than in acclimation-dive animals with DCS. TNF-α, IL-1β, IL-6, and IL-10 were significantly elevated in control-DCS animals. Acclimation-DCS animals had increased TNF-α, but there was no change in IL-1β, IL-6, and IL-10. High levels of Akt phosphorylation were observed in lungs of acclimation-sham, acclimation-dive, and control-dive animals; phosphorylated ERK1/2 was only observed in animals with DCS. This study suggests that activation of ERK1/2 and upregulation of Egr-1 and its target cytokine genes by rapid decompression may play a role in the initiation and progression of DCS. It may be that the downregulated expression of these genes in animals with DCS is associated with previous exposure to repeated compression-decompression cycles. This study represents an initial step toward understanding the molecular mechanisms associated with acclimation to decompression.

Heat-shock protein 90 alpha (HSP90α) modulates signaling pathways towards tolerance of oxidative stress and enhanced survival of hepatocytes of Mugil cephalus

Oxidative stress causes damage at the cellular level and activates a number of signaling pathways. Earlier, we have demonstrated that pollutant-related oxidative stress upregulates heat-shock protein 90 alpha (HSP90α) against stress insult in hepatocytes of Mugil cephalus living in a polluted estuary. However, the impact of pollution-induced HSP90α upregulation on stress tolerance is not clear. Here we propose that the effect of stress resistance depends on the ability of HSP90α to modulate the signaling pathways involving proteins such as apoptosis signal-regulating kinase 1, c-Jun NH(2)-terminal protein kinase 1/2, signal transducers and activators of transcription, extracellular signal-regulated kinase 1/2, protein kinase B, nuclear factor-kappa binding, Ets-like protein 1, and B cell lymphoma-2. In order to investigate this, the activation of HSP90α-associated signaling molecules was examined by Western blotting and immunohistochemistry. The relationship between the protein expression patterns was identified by Spearman's rank correlation analysis. The signaling proteins exhibited differential modulation as revealed from their expression patterns in pollutant-exposed fish hepatocytes, in comparison with the control fish hepatocytes. The results suggested that in spite of the prevalence of oxidative stress in pollutant-exposed fish hepatocytes, the stress-mediated induction of HSP90α enabled the hepatocytes to become stress tolerant and to survive by modulating the actions of key proteins and kinases in the signal transduction pathways.

Zinc: new clues to diverse roles in brain ischemia

Cerebral ischemia is a leading cause of morbidity and mortality, reflecting the extraordinary sensitivity of the brain to a brief loss of blood flow. A significant goal has been to identify pathways of neuronal injury that are selectively activated after stroke and may be amenable to drug therapy. An important advance was made nearly 25 years ago when Ca(2+) overload was implicated as a critical link between glutamate excitotoxicity and ischemic neurodegeneration. However, early hope for effective therapies faded as glutamate-targeted trials repeatedly failed to demonstrate efficacy in humans. In a review in 2000 in this journal, we described new evidence linking a related cation, zinc (Zn(2+)), to neuronal injury, emphasizing sources and mechanisms of Zn(2+) toxicity. The current review highlights progress over the last decade, emphasizing mechanisms through which Zn(2+) ions (from multiple sources) participate together with Ca(2+) in different stages of cascades of ischemic injury.

Signal transducers and activators of transcription: STATs-mediated mitochondrial neuroprotection

Cerebral ischemia is defined as little or no blood flow in cerebral circulation, characterized by low tissue oxygen and glucose levels, which promotes neuronal mitochondria dysfunction leading to cell death. A strategy to counteract cerebral ischemia-induced neuronal cell death is ischemic preconditioning (IPC). IPC results in neuroprotection, which is conferred by a mild ischemic challenge prior to a normally lethal ischemic insult. Although many IPC-induced mechanisms have been described, many cellular and subcellular mechanisms remain undefined. Some reports have suggested key signal transduction pathways of IPC, such as activation of protein kinase C epsilon, mitogen-activated protein kinase, and hypoxia-inducible factors, that are likely involved in IPC-induced mitochondria mediated-neuroprotection. Moreover, recent findings suggest that signal transducers and activators of transcription (STATs), a family of transcription factors involved in many cellular activities, may be intimately involved in IPC-induced ischemic tolerance. In this review, we explore current signal transduction pathways involved in IPC-induced mitochondria mediated-neuroprotection, STAT activation in the mitochondria as it relates to IPC, and functional significance of STATs in cerebral ischemia.

Oxidative stress in ischemic brain damage: mechanisms of cell death and potential molecular targets for neuroprotection

Significant amounts of oxygen free radicals (oxidants) are generated during cerebral ischemia/reperfusion, and oxidative stress plays an important role in brain damage after stroke. In addition to oxidizing macromolecules, leading to cell injury, oxidants are also involved in cell death/survival signal pathways and cause mitochondrial dysfunction. Experimental data from laboratory animals that either overexpress (transgenic) or are deficient in (knock-out) antioxidant proteins, mainly superoxide dismutase, have provided strong evidence of the role of oxidative stress in ischemic brain damage. In addition to mitochondria, recent reports demonstrate that NADPH oxidase (NOX), an important pro-oxidant enzyme, is also involved in the generation of oxidants in the brain after stroke. Inhibition of NOX is neuroprotective against cerebral ischemia. We propose that superoxide dismutase and NOX activity in the brain is a major determinant for ischemic damage/repair and that these major anti- and pro-oxidant enzymes are potential endogenous molecular targets for stroke therapy.

Acute inhibition of TAK1 protects against neuronal death in cerebral ischemia

Neuronal apoptosis contributes to ischemic brain damage and neurodegenerative disorders. Key regulators of neuronal apoptosis are the transcription factor NF-κB and the MAP kinases p38/MAPK and JNK, which share a common upstream activator, the mitogen-activated protein kinase kinase kinase (MAP3K) TGFβ-activated kinase 1 (TAK1). Here we investigate the function of TAK1 in ischemia-induced neuronal apoptosis. In primary cortical neurons, TAK1 was activated by oxygen glucose deprivation (OGD), an in vitro model of cerebral ischemia. We found that short-term inhibition of TAK1 protected against OGD in vitro and reduced the infarct volume after middle cerebral artery occlusion in vivo. Prolonged inhibition or deletion of the TAK1 gene in neurons was, however, not protective. Short-term, but not prolonged inhibition of TAK1 interfered with the activation of p38/MAPK and JNK by OGD, the induction of the pro-oxidative genes Cox-2, Nox-2, and p40(phox), and the formation of superoxide. We found that prolonged TAK1 inhibition upregulated another MAP3K, apoptosis signal-regulating kinase-1, which is able to compensate for TAK1 inhibition. Our study demonstrates that TAK1 is a central target for short-term inhibition of key signaling pathways and neuroprotection in cerebral ischemia.

P2 receptor antagonists prevent synaptic failure and extracellular signal-regulated kinase 1/2 activation induced by oxygen and glucose deprivation in rat CA1 hippocampus in vitro

To investigate the role of purinergic P2 receptors under ischemia, we studied the effect of P2 receptor antagonists on synaptic transmission and mitogen-activated protein kinase (MAPK) activation under oxygen and glucose deprivation (OGD) in rat hippocampal slices. The effect of the P2 antagonists pyridoxalphosphate-6-azophenyl-2',4'-disulfonate (PPADS, unselective, 30 μm), N( 6) -methyl-2'-deoxyadenosine-3',5'-bisphosphate (MRS2179, selective for P2Y(1) receptor, 10 μm), Brilliant Blue G (BBG, selective for P2X(7) receptor, 1 μm), and 5-[[[(3-phenoxyphenyl)methyl][(1S)-1,2,3,4-tetrahydro-1-naphthalenyl]amino]carbonyl]-1,2,4-benzenetricarboxylic acid (A-317491, selective for P2X(3) receptor, 10 μm), and of the newly synthesized P2X(3) receptor antagonists 2-amino-9-(5-iodo-2-isopropyl-4-methoxybenzyl)adenine (PX21, 1 μm) and 2-amino-9-(5-iodo-2-isopropyl-4-methoxybenzyl)-N( 6)-methyladenine (PX24, 1 μm), on the depression of field excitatory postsynaptic potentials (fEPSPs) and anoxic depolarization (AD) elicited by 7 min of OGD were evaluated. All antagonists significantly prevented these effects. The extent of CA1 cell injury was assessed 3 h after the end of 7 min of OGD by propidium iodide staining. Substantial CA1 pyramidal neuronal damage, detected in untreated slices exposed to OGD injury, was significantly prevented by PPADS (30 μm), MRS2179 (10 μm), and BBG (1 μm). Western blot analysis showed that, 10 min after the end of the 7 min of OGD, extracellular signal-regulated kinase (ERK)1/2 MAPK activation was significantly increased. MRS2179, BBG, PPADS and A-317491 significantly counteracted ERK1/2 activation. Hippocampal slices incubated with the ERK1/2 inhibitors 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophenylthio)butadiene (U0126, 10 μm) and α-[amino[(4-aminophenyl)thio]methylene]-2-(trifluoromethyl) benzeneacetonitrile (SL327, 10 μm) showed significant fEPSP recovery after OGD and delayed AD, supporting the involvement of ERK1/2 in neuronal damage induced by OGD. These results indicate that subtypes of hippocampal P2 purinergic receptors have a harmful effect on neurotransmission in the CA1 hippocampus by participating in AD appearance and activation of ERK1/2.

Exercise inhibits neuronal apoptosis and improves cerebral function following rat traumatic brain injury

Exercise is reported to inhibit neuronal apoptotic cell death in the hippocampus and improve learning and memory. However, the effect of exercise on inhibition of neuronal apoptosis surrounding the area of damage after traumatic brain injury (TBI) and the improvement of cerebral dysfunction following TBI are unknown. Here, we investigate the effect of exercise on morphology and cerebral function following TBI in rats. Wistar rats received TBI by a pneumatic controlled injury device were randomly divided into two groups: (1) non-exercise group and (2) exercise group. The exercise group ran on a treadmill for 30 min/day at 22 m/min for seven consecutive days. Immunohistochemical and behavioral studies were performed following TBI. The number of single-stranded DNA (ssDNA)-positive cells around the damaged area early after TBI was significantly reduced in the exercise group compared with the non-exercise group (P < 0.05). Furthermore, most ssDNA-positive cells in the non-exercise group co-localized with neuronal cells. However, in the exercise group, a few ssDNA-positive cells co-localized with neurons. In addition, there was a significant increase in neuronal cell number and improvement in cerebral dysfunction after TBI in the exercise group compared with the non-exercise group (P < 0.05). These results indicate that exercise following TBI inhibits neuronal degeneration and apoptotic cell death around the damaged area, which results in improvement of cerebral dysfunction. In summary, treadmill running improved cerebral dysfunction following TBI, indicating its potential as an effective clinical therapy. Therefore, exercise therapy (rehabilitation) in the early phase following TBI is important for recuperation from cerebral dysfunction.

Protective effect of Ilex latifolia, a major component of "kudingcha", against transient focal ischemia-induced neuronal damage in rats

AIMS OF THE STUDY

Ilex latifolia (Aquifoliaceae), a primary component of "kudingcha", has been used in Chinese folk medicine to treat various kinds of diseases including headaches, inflammatory diseases, and cardiac ischemic injury. The present study investigated the protective effect of the ethanol extract of Ilex latifolia against transient, focal, ischemia-induced neuronal damage.

MATERIALS AND METHODS

Transient focal ischemia was induced by 2 h middle cerebral artery occlusion followed by 24 h reperfusion (MCAO/reperfusion) in rats. After MCAO/reperfusion, brain infarction and neuronal death were measured by triphenyltetrazolium chloride and hematoxylin and eosin staining, respectively. Glutathione concentration and lipid peroxidation rate were measured. The expression levels of phosphorylated mitogen activated proteins kinases (MAPKs), cyclooxygenase 2 (COX-2), and anti-apoptotic and pro-apoptotic proteins were detected by Western blot.

RESULTS

Ilex latifolia (50-200 mg/kg) significantly reduced MCAO/reperfusion-induced infarction and edema formation, neurological deficits, and brain cell death. Depletion of glutathione level and lipid peroxidation induced by MCAO/reperfusion were inhibited by administration of Ilex latifolia. The increase of phosphorylated MAPKs, COX-2, and proapoptotic proteins and the decrease of antiapoptotic protein in MCAO/reperfusion rats were significantly inhibited by treatment with Ilex latifolia.

CONCLUSION

Ilex latifolia ameliorated ischemic injury induced by MCAO/reperfusion in rats, and this neuroprotective effect might be associated with its anti-apoptotic effect, resulting from anti-oxidative and anti-inflammatory actions.

Apoptotic mechanisms for neuronal cells in early brain injury after subarachnoid hemorrhage

OBJECTS

The major causes of death and disability in subarachnoid hemorrhage (SAH) may be early brain injury (EBI) and cerebral vasospasm. Although cerebral vasospasm has been studied and treated by a lot of drugs, the outcome is not improved even if vasospasm is reversed. Based on these data, EBI is considered a primary target for future research, and apoptosis may be involved in EBI after experimental SAH.

METHODS

We reviewed the published literature about the relationship between SAH induced EBI and apoptosis in PubMed.

RESULT

Most available information can be obtained from the endovascular filament perforation animal model. After onset of SAH, intracranial pressure is increased and then cerebral blood flow is reduced. Many factors are involved in the mechanism of apoptotic cell death in EBI after SAH. In the neuronal cells, both intrinsic and extrinsic pathways of apoptosis can occur. Some antiapoptotic drugs were studied and demonstrated a protective effect against EBI after SAH. However, apoptosis in EBI after SAH has been little studied and further studies will provide us more beneficial findings.

CONCLUSIONS

The study of apoptosis in EBI after experimental SAH may give us new therapies for SAH.

Reactive Oxygen Species-Dependent c-Fos/Activator Protein 1 Induction Upregulates Heme Oxygenase-1 Expression by Bradykinin in Brain Astrocytes

Heme oxygenase-1 (HO-1) plays a crucial role in tissue pathological changes such as brain injuries. Our previous studies have demonstrated that bradykinin (BK) induces the expression of several inflammatory proteins, including matrix metalloproteinase-9 and COX-2, via mitogen-activated protein kinases and nuclear factor-κB (NF-κB) in rat brain astrocytes (RBA-1). However, the molecular mechanisms underlying BK-induced HO-1 expression in RBA-1 cells remain poorly defined. Here we demonstrated that BK induced HO-1 expression and enzymatic activity via a B(2) BK receptor-activated reactive oxygen species (ROS)-dependent signaling pathway. NADPH oxidase (Nox)-dependent ROS generation led to activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun-N-terminal kinase (JNK) and then activated the downstream molecules NF-κB and c-Jun, respectively. The c-Fos, an activator protein 1 (AP-1) subunit, was upregulated by activation of NF-κB and c-Jun, which bound to HO-1 promoter and thereby turned on transcription of HO-1 gene. The rat HO-1 promoter containing a putative AP-1 cis-binding site was identified as a crucial domain linking to BK action. Taken together, these results suggested that in RBA-1 cells, activation of ERK/NF-κB and JNK/c-Jun cascades by a Nox/ROS-dependent event enhancing c-Fos/AP-1 activity is essential for HO-1 upregulation and activation induced by BK. Moreover, ROS-dependent NF-E2-related factor 2 activation also contributes to HO-1 induction by BK in astrocytes.

Isolation and identification of anti-inflammatory constituents from Ligusticum chuanxiong and their underlying mechanisms of action on microglia

Stroke is the third most common cause of death worldwide. Recent findings showed that the severity of cerebrovascular diseases including ischemic stroke correlates with inflammation mediated responses in the neural cells. During ischemia, inflammatory mediators including tumor necrosis factor-alpha (TNF-α) and nitric oxide are produced by microglia, which play a central role in the pathogenesis of the disease. Ligusticum chuanxiong (LCX) is a commonly used traditional Chinese medicine (TCM) for empiric treatment of cerebrovascular and cardiovascular diseases for many centuries. By applying a bioactivity-guided fractionation scheme, two compounds with inhibition on neuroinflammation were isolated from LCX. Using chromatographic and spectrometric methods, they were identified to be senkyunolide A and Z-ligustilide. They could inhibit the production of proinflammatory mediators in lipopolysaccharide (LPS)-stimulated murine BV-2 microglial cells and human peripheral blood monocyte derived macrophages. In addition, both compounds protected Neuro-2a cells from neuroinflammatory toxicity induced by the conditioned culture media produced by LPS-stimulated BV-2 cells. The underlying mechanisms of action of senkyunolide A were further delineated. Its inhibitory effects were shown to be independent of the phosphorylation of mitogen-activated protein kinases (MAPK) and translocation of nuclear factor kappa B (NF-κB). However, senkyunolide A could increase the degradation of TNF-α mRNA and reduce its half life by 43%. In conclusion, bioactivity-guided fractionation is an effective way of isolating bioactive compounds from medicinal herbs. In addition, senkyunolide A and Z-ligustilide isolated from LCX may be considered as potential complementary drug candidates for treating inflammatory processes associated with cerebrovascular diseases.

Microglial activation in stroke: therapeutic targets

Microglial activation is an early response to brain ischemia and many other stressors. Microglia continuously monitor and respond to changes in brain homeostasis and to specific signaling molecules expressed or released by neighboring cells. These signaling molecules, including ATP, glutamate, cytokines, prostaglandins, zinc, reactive oxygen species, and HSP60, may induce microglial proliferation and migration to the sites of injury. They also induce a nonspecific innate immune response that may exacerbate acute ischemic injury. This innate immune response includes release of reactive oxygen species, cytokines, and proteases. Microglial activation requires hours to days to fully develop, and thus presents a target for therapeutic intervention with a much longer window of opportunity than acute neuroprotection. Effective agents are now available for blocking both microglial receptor activation and the microglia effector responses that drive the inflammatory response after stroke. Effective agents are also available for targeting the signal transduction mechanisms linking these events. However, the innate immune response can have beneficial as well deleterious effects on outcome after stoke, and a challenge will be to find ways to selectively suppress the deleterious effects of microglial activation after stroke without compromising neurovascular repair and remodeling.

Thrombin-induced neuronal protection: role of the mitogen activated protein kinase/ribosomal protein S6 kinase pathway

Our previous studies have found that intracerebral pretreatment with a low dose of thrombin (thrombin preconditioning, TPC) reduces infarct volume and attenuates brain edema after focal cerebral ischemia. In this study, we examined whether TPC protects against the neuronal death induced by oxygen glucose deprivation (OGD), and whether the protection is through thrombin receptors and the p44/42 mitogen activated protein kinases (MAPK)/ribosomal protein S6 kinases (p70 S6K) pathway. Expression of protease-activated receptors (PARs) mRNA was detected in cultured primary rat neurons and thrombin upregulated PAR-1 and PAR-4 mRNA expression. TPC reduced OGD-induced neuronal death (e.g. dead cells: 52.5 ± 5.4% vs. 72.3 ± 7.2% in the control group, n=6, p<0.01). Agonists of PAR-1 and PAR-4 mimicked the effects of thrombin and reduced OGD-induced neuronal death. Pretreatment with thrombin or PAR agonists induced the upregulation of activated p44/42 MAPK and p70S6K (Thr 421/Ser 424). PD98059, an inhibitor of p44/42 MAPK kinase, blocked thrombin-induced upregulation of activated p44/42 MAPK and p70S6K. It also reduced TPC-induced neuronal protection (e.g. dead cells: 68.2 ± 5.2% vs. 56.9 ± 4.6% in vehicle+TPC group, n=6, p<0.05). These results suggest that TPC-induced ischemic tolerance is through activation of thrombin receptors and the p44/42 MAPK/p70S6K pathway.

Increased expression of glucose transporter 3 in gerbil brains following magnesium sulfate treatment and focal cerebral ischemic injury

Glucose is the primary energy substrate for neurons. Glucose transporter 3 (Glut3) localizes at the neuronal cellular membrane, which transports glucose from the extracelluar space into neurons. Ischemia results in an increased energy demand that is associated with profound changes in brain energy metabolism. Magnesium sulfate (MgSO(4)) ameliorates ischemia-induced neuronal death in the rat and gerbil model. We investigated the effects of MgSO(4) administration on the expression of Glut3 in cortex and hippocampus of gerbils during ischemia. The focal cerebral ischemia was produced by unilateral occlusion of the right common carotid artery and right middle cerebral artery. Following ischemia, Glut3 expression increased significantly versus non-ischemic (contra-lateral) cortex and hippocampus. MgSO(4) treatment significantly increased the level of Glut3 expression in the non-ischemic and ischemic cortex and hippocampus. We found that the MgSO(4)-induced increase in Glut3 expression was not reversed by administration of U0126, a MEK kinase inhibitor. These results suggest that other factors may function to modulate the MgSO(4)-induced Glut3 response. In all, our data showed that MgSO(4) increases the expression of Glut3 in the cortex and hippocampus of gerbil brains both in non-ischemia and ischemia status. However, the MEK signaling pathway might not be involved in MgSO(4)-induced Glut3 expression following focal ischemia.

6-Mercaptopurine exerts an immunomodulatory and neuroprotective effect on permanent focal cerebral occlusion in rats

BACKGROUND

A bursting cascade of inflammation imposes progressive neurological deterioration after experimental stroke has been demonstrated. In our study, 6-mercaptopurine (6-mp) has been successful in alleviating cerebral infarct in a rodent permanent middle cerebral artery occlusion (pMCAO) model. The present study was aimed to examine the effect of 6-mp on cytokine levels in experimental stroke.

METHODS

The rodent pMCAO model was employed. A dose of 2 mg/kg 6-mp or vehicle (0.1 mol/L PBS) was administered intraperitoneally 30 min after the induction of pMCAO. Neurological score, serum, and cerebrospinal fluid (CSF) cytokines such as IL-1beta, IL-6, and TNF-alpha and infarct volume were determined 48 h after pMCAO.

RESULTS

Cerebral infarction volume was significantly decreased in animals treated with 6-mp (74.3%, p < 0.01), and the ratio of tissue edema was also decreased in 6-mp-treated groups (71%). Animals receiving 6-mp thus showed a significant decrease in IL-1 and TNF-alpha (18/43% and 48/64% in CSF/serum, respectively) when compared with the pMCAO groups (p < 0.01).

CONCLUSION

This study demonstrates that 6-mp interposes the production of IL-1 and TNF-alpha in CSF and serum, attenuates ischemic brain injury, and thus alleviates neurological deficits in the pMCAO animals. These findings also offer first evidence that 6-mp may attenuate TNF-alpha-related neuron apoptosis and also support the notion that 6-mp and other anti-inflammatory agents could potentially have therapeutic uses in cases of cerebral infarct.

Huperzine a improves chronic inflammation and cognitive decline in rats with cerebral hypoperfusion

Chronic cerebral hypoperfusion has been suggested to contribute to the progression of dementia. Inflammation and white matter lesion (WML) are involved in the pathologic process. This study investigated whether huperzine A, a natural acetylcholinesterase (AChE) inhibitor, has beneficial effects on long-lasting inflammation as well as cognitive impairment in a rat model of cerebral hypoperfusion and how it plays these roles. Chronic cerebral hypoperfusion was induced by occlusion of bilateral common carotid arteries (two-vessel occlusion; 2VO). Huperzine A was initially given 150 min after 2VO and daily for 3, 7, 14, and 28 days. Learning and memory dysfunction as tested by Morris water maze performance was observed in 2VO-operated rats and was significantly improved by huperzine A treatment. WML and activation staining of immune cells were evaluated by Klüver-Barrera (KB) and immunohistochemistry, respectively. Myelin damage and increased immunostains were found in optic tract at all indicated days. Huperzine A treatment significantly ameliorated all these phenomena. Moreover, huperzine A also suppressed overexpression of the inflammatory factor tumor necrosis factor-alpha (TNF-alpha) and overphosphorylation of JNK and p38 mitogen-activated protein kinases (MAPKs) in a cell model of chronic hypoxia. Preincubation with mecamylamine (MEC), a nicotinic acetylcholine receptor (nAChR) antagonist, for 30 min before hypoxia notably reversed the effects of huperzine A on TNF-alpha production and MAPKs phosphorylation. In conclusion, delayed and chronic administration of huperzine A could protect against 2VO-induced cognitive impairment, which might be related to its beneficial effects on WML, and the nAChR-dependent cholinergic anti-inflammation pathway plays an important role.

Thioredoxin and HSP90 alpha modulate ASK1-JNK1/2 signaling in stressed hepatocytes of Mugil cephalus

Induction of antioxidant proteins like thioredoxin (Trx) and heat shock protein 90 alpha (HSP90 alpha) is a crucial step in the cellular response to oxidative stress. Here, we report the impact of environmental stress on Trx and HSP90 alpha expressions in freshly isolated hepatocytes of Mugil cephalus living in either a contaminated (Test; Ennore) or uncontaminated (Control; Kovalam) estuary. Modulation in the activities of signal transduction molecules like apoptosis signal-regulating kinase 1 (ASK1) and c-Jun NH(2)-terminal kinase 1/2 (JNK1/2) were also investigated to understand their functional role under natural stressed condition. The expression pattern of the proteins was determined by immunoblotting and the relationship between the proteins was identified by regression analysis. Test fish hepatocytes demonstrated significant upregulation (P<0.05) in the levels of Trx and HSP90 alpha and insignificant inductions in the expression pattern of ASK1 and JNK1/2 than control fish hepatocytes. These findings provide direct evidence that Trx and HSP90 alpha induction in fish hepatocytes under stress may aid cell survival by negatively regulating ASK1 expression and thereby functionally antagonizing the apoptotic role of JNK1/2 in natural aquatic systems.

Neuroprotection of ethanol against ischemia/reperfusion-induced brain injury through decreasing c-Jun N-terminal kinase 3 (JNK3) activation by enhancing GABA release

Our latest study indicated that ethanol could attenuate cerebral ischemia/reperfusion-induced brain injury through activating Ionotropic glutamate receptors Kainate Family (Gluk1)-kainate (KA) receptors and gamma-aminobutyric acid (GABA) receptors. However, the possible mechanism of the neuroprotective effects of ethanol remains unclear. In this study we report that ethanol shows neuroprotective effects against ischemic brain injury through enhancing GABA release and then decreasing c-Jun N-terminal kinase 3 (JNK3) activation. Electrophysiologic recording indicated that ethanol enhances GABA release from presynaptic neurons and the released GABA subsequently inhibits the KA receptor-mediated whole-cell currents. Moreover, our data show that ethanol can inhibit the increased assembly of the Gluk2-PSD-95-MLK3 (postsynaptic density protein-95, PSD-95 and mixed-lineage kinase 3, MLK3) module induced by cerebral ischemia and the activation of the MLK3-MKK4/7-JNK (mitogen-activated protein kinase kinase 4/7, MKK4/7) cascade. Pretreatment of the GABA(A) receptor antagonist bicuculline and antagonist of VGCC (a broad-spectrum blocker of the voltage-gated calcium channel [VGCC]) Chromic (CdCl(2)) can demolish the neuroprotective effects of ethanol. The results suggest that during ischemia-reperfusion, ethanol may activate presynaptic Gluk1-KA and facilitate Ca(2+)-dependent GABA release. The released GABA activates postsynaptic GABA(A) receptors, which suppress the ischemic depolarization and decrease the association of signaling module Gluk2-PSD-95-MLK3 induced by the activation of postsynaptic Gluk2-KA receptors. There is a raised possibility that ethanol inhibiting the JNK3 apoptotic pathway (MLK3/MKK4/7/JNK3/c-Jun/Fas-L) performs a neuroprotective function against ischemic brain injury.

Prolonged activation of ERK triggers glutamate-induced apoptosis of astrocytes: neuroprotective effect of FK506

Although, astrocytes are more resistant than neurons to ischemic injury, astrocyte death has been demonstrated in animal models of brain ischemia. Astrocytes death after ischemia/reperfusion may strongly affect neuronal survival because of the absence of their trophic and metabolic support to neurons, and astrocytic glutamate uptake. Early signals involved in astrocytes death are poorly understood. We demonstrated enhanced and mostly cytoplasmic activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) during glutamate-induced apoptosis of cultured astrocytes. Treatment with UO126, inhibitor of MEK1, threo-beta-benzyloxyaspartic acid, glutamate transporter inhibitor, and FK506, a cytoprotective drug prevented ERK activation and glutamate-induced apoptosis. Over-expression of ERK dual specificity phosphatases 5 and 6 reduced apoptosis in transfected astrocytes. Prolonged ERK1/2 activation was observed in ischemic brain: in the nucleus and cytoplasm of astrocytes in the cerebral cortex, and exclusively in the cytoplasm of astrocytes in the striatum. Global gene expression profiling in the cortex revealed that FK506 blocks middle cerebral artery occlusion-induced expression of numerous genes associated with ERK signaling pathway and apoptosis. The results demonstrate a pro-apoptotic role of sustained activation of ERK1/2 signaling in glutamate-induced death of astrocytes and the ability of FK506 to block both ERK activation and astrocytic cell death in vitro and in ischemic brains.

Fibroblasts from long-lived mutant mice show diminished ERK1/2 phosphorylation but exaggerated induction of immediate early genes

Skin-derived fibroblasts from long-lived mutant mice, including the Snell dwarf mice and mice defective in growth hormone receptor (GHRKO mice), are resistant to death induced by oxidative stress or by UV light, but the molecular mechanism for their stress resistance is unknown. This study shows that phosphorylation of the stress-activated protein kinases ERK1/2 induced by peroxide, cadmium, or paraquat is attenuated in cells from these mice. Induction of ERK phosphorylation by UV light was not altered in the Snell dwarf cells, and neither JNK nor p38 kinase showed increased phosphorylation in response to any of the stresses tested. Surprisingly, stress-induced elevation of mRNA for certain immediate early genes (Egr-1 and Fos) was higher in Snell-derived cells than in control cells, despite the evidence of lower ERK phosphorylation. Thus cells from Snell dwarf mice differ from controls in two ways: (a) lower induction of ERK1/2 phosphorylation and (b) increased expression of some ERK-dependent immediate early genes. These alterations in kinase pathways may contribute to the resistance of these cells to lethal injury.

Regulation of matrix metalloproteinase-9 gene expression in MPP+- or 6-OHDA-treated human neuroblastoma SK-N-BE(2)C cells

The aberrant expression of matrix metalloproteinases (MMPs) is known to play an important role in various neurodegenerative diseases, such as Parkinson's disease. In the present study, we found that two well-known dopaminergic neurotoxins, 6-OHDA and MPP(+), induced the expression of MMP-9 in SK-N-BE(2)C human neuroblastoma and Cath.a mouse dopaminergic cell lines. Treatment with MMP-9 inhibitors attenuated the neuronal cell death induced by either 6-OHDA or MPP(+), suggesting that MMP-9 plays an important role in this neurotoxin-mediated cell death. Further mechanistic studies showed that 6-OHDA and MPP(+) increased MMP-9 gene expression by inducing NF-kappaB and AP-1 binding to the MMP-9 promoter. Reactive oxygen species (ROS) appeared to be involved in MMP-9 expression because treatment with the free radical scavenger, N-acetylcysteine (NAC), suppressed both 6-OHDA- and MPP(+)-induced MMP-9 promoter activities. Treatment with several signaling pathway-specific inhibitors revealed that the PI3 kinase inhibitor, LY294002, suppressed 6-OHDA- and MPP(+)-induced MMP-9 promoter activities, whereas the p38 MAPK inhibitor, SB203580, inhibited 6-OHDA-, but not MPP(+)-induced promoter activity. These results collectively suggest that ROS, PI3 kinase, NF-kappaB, and AP-1 are commonly involved in 6-OHDA- and MPP(+)-induced MMP-9 gene expression, and that p38 MAPK is differentially involved. Therefore, controlling MMP-9 expression may have therapeutic potential in Parkinson's disease, which is caused by various neurotoxins, such as 6-OHDA and MPP(+).

ERK and cell death: ERK1/2 in neuronal death

Extracellular signal-regulated kinase (ERK) is a versatile protein kinase that regulates many cellular functions. Growing evidence suggests that ERK1/2 plays a crucial role in promoting cell death in a variety of neuronal systems, including neurodegenerative diseases. It is believed that the magnitude and the duration of ERK1/2 activity determine its cellular function. In this review, we summarize recent evidence for a role of ERK1/2 in neuronal death. Furthermore, we discuss the mechanisms involved in ERK1/2 mediating neuronal death.

Edaravone protects against apoptotic neuronal cell death and improves cerebral function after traumatic brain injury in rats

Edaravone is a novel free radical scavenger used clinically in patients with acute cerebral infarction; however, it has not been assessed in traumatic brain injury (TBI). We investigated the effects of edaravone on cerebral function and morphology following TBI. Rats received TBI with a pneumatic controlled injury device. Edaravone (3 mg/kg) or physiological saline was administered intravenously following TBI. Numbers of 8-OHdG-, 4-HNE-, and ssDNA-positive cells around the damaged area after TBI were significantly decreased in the edaravone group compared with the saline group (P < 0.01). There was a significant increase in neuronal cell number and improvement in cerebral dysfunction after TBI in the edaravone group compared with the saline group (P < 0.01). Edaravone administration following TBI inhibited free radical-induced neuronal degeneration and apoptotic cell death around the damaged area. In summary, edaravone treatment improved cerebral dysfunction following TBI, suggesting its potential as an effective clinical therapy.

Mitogen-activated protein kinase p38alpha and retinal ischemic preconditioning

In previous studies, inhibition of mitogen-activated protein kinase (MAP) p38 significantly improved recovery and attenuated apoptosis after retinal ischemia in rats. Yet, ischemic preconditioning (IPC) attenuated the ischemia-induced increase in p38 expression. We hypothesized that p38 was required for induction of ischemic tolerance by IPC. We examined the mechanisms of involvement of p38 in IPC neuroprotection. IPC or ischemia was induced in rat retina in vivo. Recovery after ischemia performed 24h after IPC was assessed functionally (electroretinography) and histologically at 7d after ischemia in the presence or absence of inhibition of p38. We examined the role of p38alpha in the mimicking of IPC produced by opening mitochondrial KATP channels using diazoxide, or stimulation of p38 activation by anisomycin. The importance of adenosine receptors in p38 activation after IPC was assessed using specific blockers of adenosine A1 and A2a receptors. Interfering RNA (siRNA) or SB203580 was used to block p38alpha. Phosphorylated p38 levels were measured. Phosphorylated p38 protein increased with IPC. Interfering RNA (siRNA) to p38alpha prior to IPC, or inhibiting p38 activation with SB203580, with ischemia following 24h later, significantly attenuated the neuroprotective effect of IPC. Anisomycin administered to increase p38 mimicked IPC, an effect blocked by SB203580. IPC-mimicking with diazoxide, an opener of mitochondrial KATP channels, was diminished with p38alpha siRNA. Adenosine receptor blockade did not decrease the elevated levels of phosphorylated p38 after IPC. Specific inhibition of p38alpha suggests that this MAPK is involved in the protective effects of IPC, and that p38 is downstream of mitochondrial KATP channels, but not adenosine receptors, in this neuroprotection.

The novel free radical scavenger, edaravone, increases neural stem cell number around the area of damage following rat traumatic brain injury

Edaravone is a novel free radical scavenger that is clinically employed in patients with acute cerebral infarction, but has not previously been used to treat traumatic brain injury (TBI). In this study, we investigated the effect of edaravone administration on rat TBI. In particular, we used immunohistochemistry to monitor neural stem cell (NSC) proliferation around the area damaged by TBI. Two separate groups of rats were administered saline or edaravone (3 mg/kg) after TBI and then killed chronologically. We also used ex vivo techniques to isolate NSCs from the damaged region and observed nestin-positive cells at 1, 3, and 7 days following TBI in both saline- and edaravone-treated groups. At 3 days following TBI in both groups, there were many large cells that morphologically resembled astrocytes. At 1 and 7 days following TBI in the saline group, there were a few small nestin-positive cells. However, in the edaravone group, there were many large nestin-positive cells at 7 days following TBI. At 3 and 7 days following TBI, the number of nestin-positive cells in the edaravone group increased significantly compared with the saline group. There were many single-stranded DNA-, 8-hydroxy-2'-deoxyguanosine-, and 4-hydroxy-2-nonenal-positive cells in the saline group following TBI, but only a few such cells in the edaravone group following TBI. Furthermore, almost all ssDNA-positive cells in the saline group co-localized with Hu, nestin, and glial fibrillary acidic protein (GFAP) staining, but not in the edaravone group. In the ex vivo study, spheres could only be isolated from injured brain tissue in the saline group at 3 days following TBI. However, in the edaravone group, spheres could be isolated from injured brain tissue at both 3 and 7 days following TBI. The number of spheres isolated from injured brain tissue in the edaravone group showed a significant increase compared with the saline group. The spheres isolated from both saline and edaravone groups were immunopositive for nestin, but not Tuj1 or vimentin. Moreover, the spheres differentiated into Tuj1-, GFAP-, and O4-positive cells after 4 days in culture without bFGF. This result indicated that the spheres were neurospheres composed of NSCs that could differentiate into neurons and glia. Edaravone administration inhibited production of free radicals known to induce neuronal degeneration and cell death after brain injury, and protected nestin-positive cells, including NSCs, with the potential to differentiate into neurons and glia around the area damaged by TBI.

Effect of p38MAPK on immunofunction of spleen macrophages from heat stressed rats

AIM: To investigate the role of p38MAPK in Bip protein-mediated functional changes of mild heat stressed rat splenic macrophages in vitro.

METHODS: Rat splenic macrophages were pretreated with p38MAPK inhibitor and placed into 41 ℃ incubator for mild heat stress. One hour later, temperature was restored to 37 ℃ in inhibition group. Non stressed rat spleen macrophages were assigned to the control group, and macrophages which was heat stressed at 41 ℃ for 1 h (stress group) were used as controls, too. Three groups were detected for macrophage phagocytosis, cytotoxicity and chemotaxis. At the same time p38MAPK protein and Bip protein expressions were detected.

RESULTS: p38MAPK inhibitor pretreated rat splenic macrophages, when compared with the stress group, their phagocytosis, cytotoxicity and chemotaxis were significantly lowered after mild heat stress (0.17 ± 0.01 vs 0.74 ± 0.03, 33.32 ± 3.55 vs 82.07 ± 5.17, 24.20% ± 2.39% vs 60.80% ± 4.02%, all P < 0.01). In stress group p38MAPK protein expressions were significantly increased; compared with the stress group, p38MAPK protein expressions were significantly inhibited after p38MAPK inhibitor pretreatment in inhibition group (p38/β-actin: 2.863 ± 0.794 vs 4.752 ± 1.386, P < 0.01). p38MAPK inhibitor pretreatment also caused changes in Bip protein expressions (Bip/β-actin) in the stress group from 1.2702 ± 0.5345 dropped to 1.0281 ± 1.0614 in inhibition group (P < 0.05).

CONCLUSION: p38 inhibitors can significantly inhibit mild heat stressed rat splenic macrophage phagocytosis, cytotoxicity and chemotaxis, which inhibit p38MAPK and Bip protein expressions.

Preconditioning neuroprotection in global cerebral ischemia involves NMDA receptor-mediated ERK-JNK3 crosstalk

Previous work has demonstrated that ischemic preconditioning neuroprotection is associated with inhibition of JNK pathway activation. The present study was designed to examine the hypothesis that the suppression of JNK3 activation by preconditioning is mediated by NMDA receptors and crosstalk between ERK1/2 and JNK3. Preconditioning (3 min ischemia) 2 days before global cerebral ischemia (8-min) markedly decreased neuronal degeneration in hippocampus CA1, an effect abolished by pretreatment with the NMDA receptor antagonist, MK-801. Furthermore, preconditioning abolished cerebral ischemia-induced JNK3 activation and enhanced ERK1/2 activation, an effect reversed by MK-801. Due to the inverse relationship between ERK1/2 and JNK3 activation following preconditioning, we hypothesized that ERK1/2 may regulate JNK3 activation following preconditioning. In support of this contention, pretreatment with the MEK inhibitor, PD98059 significantly attenuated preconditioning-induced ERK1/2 phosphorylation, and strongly reversed preconditioning down-regulation of JNK3 phosphorylation. This finding suggests that ERK1/2 signaling is responsible for preconditioning-induced down-regulation of JNK3 activation. Western blot analysis and immunohistochemistry further demonstrated that preconditioning, in an NMDA-dependent manner, enhanced activation of the pro-survival factors, p-CREB and Bcl-2, while attenuating activation of putative pro-death factors, p-c-Jun and Fas-L in the hippocampus CA1. As a whole, the study demonstrates that preconditioning attenuation of pro-death JNK3 in the hippocampus CA1 following global cerebral ischemia is mediated by NMDA receptor-induced crosstalk between ERK1/2 and JNK3. The ERK1/2-mediated reduction of JNK3 activation leads to enhanced pro-survival signaling (P-CREB and Bcl-2 induction) and attenuation of pro-death signaling (p-c-Jun and Fas-L), with subsequent induction of ischemic tolerance.

Neuroprotection of ethanol against cerebral ischemia/reperfusion induced brain injury through GABA receptor activation

In this study we investigated whether ethanol could play neuroprotective effects against ischemic brain injury and the related mechanism. Cresyl violet staining results demonstrated that moderate dose of ethanol administered intracerebroventricularly (i.c.v.) had neuroprotective effect against ischemia-reperfusion induced neuronal cell death. Ethanol also inhibited the phosphorylation of JNK3 induced by cerebral ischemia-reperfusion. Three separate drugs, NS3763 (the selective antagonist of GluR5), GluR5 antisense oligodeoxynucleotides (AS-ODNs) and Bicuculline (an antagonist of GABA receptors), were found to inhibit the neuroprotective effect of ethanol. Moreover, the GABA receptor agonist muscimol could attenuate the JNK3 phosphorylation. Taken together, the results suggest that during ischemia-reperfusion ethanol may activate presynaptic GluR5-KA and postsynaptic GABA receptors continuously, and the activation of GABA receptors inhibits the JNK3 signal pathway. The results show a novel potential mechanism underlying ethanol protective effects.

Neuroprotective strategies targeting apoptotic and necrotic cell death for stroke

It has been a major challenge to develop effective therapeutics for stroke, a leading cause of death and serious debilitation. Intensive research in the past 15 years have implicated many regulators and the related mechanisms by which neuronal cell death is regulated. It is now clear that even a brief ischemic stroke may trigger complex cellular events that lead to both apoptotic and necrotic neuronal cell death in a progressive manner. Although efforts at developing specific chemical inhibitors for validated targets have been successful for in vitro enzymatic assays, the development of some of such inhibitors into human therapy has been often hindered by their in vivo bioavailability profile. Considerations for the ability to chemically target a cellular mechanism in manner compatible with disease targets in vivo might be emphasized early in the development process by putting a priority on identifying key targets that can be effectively targeted chemically. Thorough interrogation of cellular pathways by saturation chemical genetics may provide a novel strategy to identify multiple key molecular entities that can be targeted chemically in order to select a target suitable for the treatment of intended human diseases such as stroke.

Role of Rac1 GTPase in JNK signaling and delayed neuronal cell death following global cerebral ischemia

The overall goal of this study was to determine the role of Rac1 in POSH/MLK/JNK signaling and delayed neuronal cell death following cerebral ischemia. Temporal studies revealed that Rac1 GTPase activation was significantly elevated in hippocampus CA1 at 10 min to 72 h after cerebral ischemia reperfusion, with peak levels 30 min to 6 h after reperfusion. Total Rac1 protein levels were not significantly changed following cerebral ischemia. Rac1 has been shown to interact with POSH (plenty of SH3s), a scaffold protein that binds to and regulates MLK3 and JNK activation. Co-immunoprecipitation (Co-IP) studies revealed that POSH-Rac1-MLK3 complex formation displayed a significant and prolonged elevation after reperfusion, with a correlative increase in phosphorylation/activation of MLK3 as compared to sham controls. Intracerebroventricular administration of Rac1 antisense oligonucleotides (AS-ODNs) significantly attenuated Rac1 levels and Rac1 activation at 30 min after reperfusion, with a correlated significant attenuation of POSH-MLK3-Rac1 complex formation and MLK3 activation in hippocampus CA1. Infusion of Rac1 AS-ODNs also significantly attenuated post-ischemic activation of JNK, downstream of MLK3, and strongly protected the hippocampus CA1 from ischemic damage. Missense oligos had no effect on any of the parameters measured. The Rac1 AS-ODNs results were further confirmed by administration of a Rac1 inhibitor (NSC23766), which markedly attenuated activation of Rac1 and JNK, and significantly attenuated apoptotic delayed neuronal cell death following cerebral ischemia. As a whole, these studies demonstrate an important role for Rac1 in activation of the prodeath MLK3-JNK kinase signaling pathway and delayed neuronal cell death following cerebral ischemia.

NMDA receptor dependent PGC-1alpha up-regulation protects the cortical neuron against oxygen-glucose deprivation/reperfusion injury

The peroxisome proliferator activated receptor coactivator 1 alpha (PGC-1alpha) is a nuclear transcriptional coactivator that is widely expressed in the brain areas. Over-expression of PGC-1alpha can protect neuronal cells from oxidant-induced injury. The purpose of the current study is to investigate the role of PGC-1alpha in the oxygen (anoxia) deprivation (OGD) neurons. The PGC-1alpha mRNA and protein level between control and OGD neurons were examined by real-time PCR and Western blot. More PGC-1alpha expression was found in the OGD neurons compared with the normal group. Over-expression of PGC-1alpha suppressed cell apoptosis while inhibition of the PGC-1alpha expression induced cell apoptosis in OGD neurons. Furthermore, increase of PGC-1alpha resulted in activation of N-methyl-D-aspartate (NMDA) receptor, p38, and ERK mitogen-activated protein kinase (MAPK) pathway. The blocking of the NMDA receptor by its antagonists MK-801 reduced PGC-1alpha mRNA expression in OGD neurons, while NMDA itself can directly induce the expression of PGC-1alpha in neuronal cells. At the same time, PD98059 (ERK MAPK inhibitor) and SB203580 (P38 MAPK inhibitor) also prevented the up-regulation of PGC-1alpha in OGD neurons and MK801 can inhibit the expression of P38 and ERK MAPK. These data suggested that the expression of PGC-1alpha was up-regulated in OGD mice cortical neurons, which protected the neurons against OGD injury. Moreover, this effect was correlated to the NMDA receptor and the ERK and P38 MAPK pathway. The protective effect of PGC-1alpha on OGD cortical neurons may be useful for stroke therapy.

ERK phosphorylation mediates sildenafil-induced myocardial protection against ischemia-reperfusion injury in mice

Sildenafil, a selective inhibitor of phosphodiesterase type 5, induces powerful protection against myocardial ischemia-reperfusion injury through activation of cGMP-dependent protein kinase (PKG). We further hypothesized that PKG-dependent activation of survival kinase ERK may play a causative role in sildenafil-induced cardioprotection via induction of endothelial nitric oxide synthase (eNOS)/inducible nitric oxide synthase (iNOS) and Bcl-2. Our results show that acute intracoronary infusion of sildenafil in Langendorff isolated mouse hearts before global ischemia-reperfusion significantly reduced myocardial infarct size (from 29.4 +/- 2.4% to 15.9 +/- 3.0%; P < 0.05). Cotreatment with ERK inhibitor PD98059 abrogated sildenafil-induced protection (31.8 +/- 4.4%). To further evaluate the role of ERK in delayed cardioprotection, mice were treated with sildenafil (ip) 24 h before global ischemia-reperfusion. PD98059 was administered (ip) 30 min before sildenafil treatment. Infarct size was reduced from 27.6 +/- 3.3% in controls to 7.1 +/- 1.5% in sildenafil-treated mice (P < 0.05). The delayed protective effect of sildenafil was also abolished by PD98059 (22.5 +/- 2.3%). Western blots revealed that sildenafil significantly increased phosphorylation of ERK1/2 and GSK-3beta and induced iNOS, eNOS, Bcl-2, and PKG activity in the heart 24 h after treatment. PD98059 inhibited the enhanced expression of iNOS, eNOS, and Bcl-2 and the phosphorylation of GSK-3beta. PD98059 had no effect on the sildenafil-induced activation of PKG. We conclude that these studies provide first direct evidence that PKG-dependent ERK phosphorylation is indispensable for the induction of eNOS/iNOS and Bcl-2 and the resulting cardioprotection by sildenafil.

Blockade of the translocation and activation of c-Jun N-terminal kinase 3 (JNK3) attenuates dopaminergic neuronal damage in mouse model of Parkinson's disease

Increasing evidence suggests that c-Jun N-terminal kinase (JNK) is an important kinase mediating neuronal death in Parkinson's disease (PD) model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). JNK3, the only neural-specific isoform, may play an important role in mediating the neurotoxic effects of MPTP in dopaminergic neuronal injury. To analyze the variation in JNK3 activation, the levels of phospho-JNK3 were measured at the various time points of occurrence of MPTP-induced lesions. In our study, we observed that during MPTP intoxication, two peaks of JNK3 activation appeared at 8 and 24h. To further define the mechanism of JNK3 activation and translocation, the antioxidant N-acetylcysteine (NAC), the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine, and the alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate (KA) receptor antagonist 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX) were administered to the mice 30 min after each of the four MPTP injections. The results revealed that NAC clearly inhibited JNK3 activation during the early intoxication, whereas ketamine preferably attenuated JNK3 activation during the latter intoxication. DNQX had no significant effects on JNK3 activation during intoxication. Consequently, reactive oxygen species (ROS) and the NMDA receptor were closely associated with JNK3 activation following MPTP intoxication. NAC and ketamine exerted a preventive effect against MPTP-induced loss of tyrosine hydroxylase-positive neurons and suppressed the nuclear translocation of JNK3, suggesting that NAC and ketamine can prevent MPTP-induced dopaminergic neuronal death by suppressing JNK3 activation.

GluR6-containing KA receptor mediates the activation of p38 MAP kinase in rat hippocampal CA1 region during brain ischemia injury

Our previous study showed that kainate (KA) receptor subunit GluR6 played an important role in ischemia-induced MLK3 and JNK activation and neuronal degeneration through the GluR6-PSD95-MLK3 signaling module. However, whether the KA receptors subunit GluR6 is involved in the activation of p38 MAP kinase during the transient brain ischemia/reperfusion (I/R) in the rat hippocampal CA1 subfield is still unknown. In this present study, we first evaluated the time-course of phospho-p38 MAP kinase at various time-points after 15 min of ischemia and then observed the effects of antagonist of KA receptor subunit GluR6, GluR6 antisence oligodeoxynucleotides on the phosphorylation of p38 MAP kinase induced by I/R. Results showed that inhibiting KA receptor GluR6 or suppressing the expression of KA receptor GluR6 could down-regulate the elevation of phospho-p38 MAP kinase induced by I/R. These drugs also reduced the phosphorylation of MLK3, MKK3/MKK6, MKK4, and MAPKAPK2. Additionally, our results indicated administration of three drugs, including p38 MAP kinase inhibitor before brain ischemia significantly decreased the number of TUNEL-positive cells detected at 3 days of reperfusion and increased the number of the surviving CA1 pyramidal cells at 5 days of reperfusion after 15 min of ischemia. Taken together, we suggest that GluR6-contained KA receptors can mediate p38 MAP kinase activation through a kinase cascade, including MLK3, MKK3/MKK6, and MKK4 and then induce increased phosphorylation of MAPKAPK-2 during ischemia injury and ultimately result in neuronal cell death in the rat hippocampal CA1 region.

Isoflurane preconditioning activates HIF-1alpha, iNOS and Erk1/2 and protects against oxygen-glucose deprivation neuronal injury

Preconditioning neurons with isoflurane, a commonly used volatile anesthetic in clinical practice, improves tolerance of subsequent ischemia in both intact animal models and in vitro preparations. To investigate the mechanisms of this protection, we primarily cultured rat hippocampal neurons and simulated ischemia in vitro by oxygen-glucose deprivation (OGD). Neuron viability was measured. Neuron injury was observed by inverted phase contrast microscope and assessed by lactate dehydrogenase (LDH) release. Gene expression was examined by Western blot and reverse transcription-polymerase chain reaction (RT-PCR). Isoflurane exposure for 2 h at 24 h before a 2 h OGD dose-dependently reduced cell injury. Isoflurane accumulated phosphorylation/activation of extracellular signal-related kinases 1 and 2 (Erk1/2) and hypoxia inducible factor (HIF)-1alpha, a transcription factor involved in cell survival. Inhibition of the phospho-Erk1/2 partially abolished the isoflurane preconditioning-induced HIF-1alpha protein content accumulation and neuroprotection. Isoflurane also increased inducible nitric oxide synthase (iNOS) mRNA levels, a downstream gene of HIF-1alpha. Thus, the current results indicate that isoflurane preconditioning activates HIF-1alpha during protection against OGD neuronal injury and the activation might be partly mediated by the Erk1/2 pathway.

Generation of endogenous hydrogen sulfide by cystathionine gamma-lyase limits renal ischemia/reperfusion injury and dysfunction

The generation of endogenous hydrogen sulfide may either limit or contribute to the degree of tissue injury caused by ischemia/reperfusion. A total of 74 male Wistar rats were used to investigate the effects of endogenous and exogenous hydrogen sulfide in renal ischemia/reperfusion. Administration of the irreversible cystathionine gamma-lyase (CSE) inhibitor, dL-propargylglycine, prevented the recovery of renal function after 45 min ischemia and 72 h reperfusion. The hydrogen sulfide donor sodium hydrosulfide attenuated the (renal, tubular, and glomerular) dysfunction and injury caused by 45 min ischemia and 6 h reperfusion. Western blot analysis of kidneys taken at 30 min reperfusion showed that sodium hydrosulfide significantly attenuated phosphorylation of mitogen-activated protein kinases (p-38, c-JUN N-terminal protein kinase 1/2, and extracellular signal-regulated kinase 1/2) and activation of nuclear factor-kappaB. At 6 h reperfusion, sodium hydrosulfide significantly attenuated the histological score for acute tubular necrosis, the activation of caspase-3 and Bid, the decline in the expression of anti-apoptotic Bcl-2, and the expression of nuclear factor-kappaB-dependent proteins (inducible nitric oxide synthase, cyclo-oxygenase-2, and intercellular adhesion molecule-1). These findings suggest that (1) the synthesis of endogenous hydrogen sulfide by CSE is essential to protect the kidney against ischemia/reperfusion injury and dysfunction and aids in the recovery of renal function following ischemia/reperfusion, (2) hydrogen sulfide generated by sodium hydrosulfide reduces ischemia/reperfusion injury and dysfunction, and morphological changes of the kidney, and (3) the observed protective effects of hydrogen sulfide are due to both anti-apoptotic and anti-inflammatory effects.

Role of the p38 mitogen-activated protein kinase/cytosolic phospholipase A2 signaling pathway in blood-brain barrier disruption after focal cerebral ischemia and reperfusion

Cytosolic phospholipase A(2) (cPLA(2)) is a key enzyme that mediates arachidonic acid metabolism, which causes cerebral ischemia-induced oxidative injury, blood-brain barrier (BBB) dysfunction, and edema. Recent reports have shown that p38 mitogen-activated protein kinase (MAPK) is related to phosphorylation and activation of cPLA(2) and release of arachidonic acid. However, involvement of the p38 MAPK pathway in cPLA(2) activation and of reactive oxygen species in expression of p38 MAPK/cPLA(2) after ischemia-reperfusion injury in the brain remains unclear. To address these issues, we used a model of transient focal cerebral ischemia (tFCI) in rats. Western blot analysis showed a significant increase in expression of phospho-p38 MAPK and phospho-cPLA(2) in rat brain cortex after tFCI. Activity assays showed that both p38 MAPK and cPLA(2) activation markedly increased 1 day after reperfusion. Intraventricular administration of SB203580 significantly suppressed activation and phosphorylation of cPLA(2) and attenuated BBB extravasation and subsequent edema. Moreover, overexpression of copper/zinc-superoxide dismutase remarkably diminished activation and phosphorylation of both p38 MAPK and cPLA(2) after reperfusion. These findings suggest that the p38 MAPK/cPLA(2) pathway may promote BBB disruption with secondary vasogenic edema and that superoxide anions can stimulate this pathway after ischemia-reperfusion injury.

Effects of unoprostone on phosphorylated extracellular signal-regulated kinase expression in endothelin-1-induced retinal and optic nerve damage

Endothelin-1 (ET-1), a potent vasoconstrictor peptide, has been implicated in the development of normal- and high-tension glaucoma. We investigated the effects of unoprostone on extracellular signal-regulated kinase (ERK) in ET-1-induced retinal ganglion cell (RGC) death and optic nerve injury. Our morphometric study showed that intravitreal injection of ET-1 led to cell loss in the RGC layer (RGCL) in 28 days. Western blot analysis showed decreased neurofilament (NF) protein in the optic nerve 28 days after ET-1 injection. In this in vivo model, increased phosphorylated ERK (p-ERK) was observed in the retina on 1 day and subsequently in the optic nerve from 7 days after ET-1 injection. Simultaneous injection of M1, as a metabolite of unoprostone, showed further increased p-ERK levels compared with ET-1 injection alone. Our morphometric study of flat-mount preparations stained with cresyl violet or retrograde labeling with a neuro-tracer and Western blot analysis of NF showed that inhibition of ERK phosphorylation led to acceleration of ET-1-induced RGC death and optic nerve damage. In addition, M1 significantly attenuated both RGC loss and the decrease in NF protein induced by ET-1. The protective effects of M1 were significantly inhibited by U0126, an ERK inhibitor. These results suggest that unoprostone has neuroprotective effects against ET-1-induced neuronal injury through ERK phosphorylation.