Tyrosine phosphorylation of microtubule-associated protein kinase after transient ischemia in the gerbil brain

[Comparative analysis of post-translational modifications in plasma proteome of patients with cerebral ischemia based on HPLC-MS/MS method]

The relative differences between post-translational modifications (PTM) of proteins in blood plasma samples of patients with cerebral ischemia (CI) and healthy people were investigated using of the method of label-free comparative proteomic analysis based on the technology of tandem HPLC-MS/MS. For PTM detection we used multiple MS/MS search in the database Mascot for variable PTM and Progenesis LS-MS software. In the CI plasma samples, we observed an increase in the proportion of peptides with such PTM as phosphorylation of serine, threonine, and tyrosine, acetylation of lysine and protein N-term, ubiquitination of lysine and deamidation of glutamine related to clinically significant processes were revealed.

Protective Effects of UCF-101 on Cerebral Ischemia-Reperfusion (CIR) is Depended on the MAPK/p38/ERK Signaling Pathway

This study was aimed to investigate the treatment mechanisms of 5-[5-(2-nitrophenyl) furfuryliodine]-1,3-diphenyl-2-thiobarbituric acid (UCF-101) in cerebral ischemia-reperfusion (CIR) model rats. Total of 54 healthy male Wistar rats were randomly assigned into three groups, namely sham group, vehicle group, and UCF-101 group. The CIR-injured model was established by right middle cerebral artery occlusion and reperfusion. Neurological function was assessed by an investigator according to the Longa neurologic deficit scores. Meanwhile, the cerebral tissue morphology and apoptotic neurons were evaluated by H&E and TUNEL staining, respectively. Additionally, the expressions of caspase 3, p-p38, and p-ERK were detected by immunohistochemistry or/and Western blotting assays. As results, neurologic deficit and pathological damage were obviously enhanced and TUNEL positive neurons were significantly increased in CIR-injured rats, as compared with those in sham group. Furthermore, the expressions of caspase 3, p-p38, and p-ERK were also significantly increased in vehicle group than those in sham group (P < 0.05). However, UCF-101 treatment could markedly weaken the neurologic deficit with lower scores and improve pathological condition. After UCF-101 treatment, TUNEL positive neurons as well as the expression of caspase 3 were significantly decreased than those in vehicle group (P < 0.05). Besides, p-p38 was decreased while p-ERK was increased in UCF-101 group than those in vehicle group (P < 0.05). Therefore, we concluded that the protective effects of UCF-101 might be associated with apoptosis process and MAPK signaling pathway in the CIR-injured model.

Lithium regulates hippocampal neurogenesis by ERK pathway and facilitates recovery of spatial learning and memory in rats after transient global cerebral ischemia

Recent studies have demonstrated that lithium has a neuroprotective effect against brain ischemia. Whether this effect is mediated by hippocampal neurogenesis remains unknown. The ERK (extracellular signal-regulated kinase) pathway plays an essential role in regulating neurogenesis. The present study was undertaken to investigate whether lithium regulates hippocampal neurogenesis by the ERK pathway and improves spatial learning and memory deficits in rats after ischemia. Rats were daily injected with lithium (1 mmol/kg) and 2 weeks later subjected to 15-min ischemia induced by four-vessel occlusion method. 5-bromo-2'-deoxyuridine (Brdu; 50mg/kg) was administrated twice daily at postischemic day 6, or for 3 days from postischemic day 6 to 8. We found that lithium increased the ERK1/2 activation after ischemia by western blotting analysis. There was a significant increase in Brdu-positive cells in the hippocampal dentate gyrus after lithium treatment, compared with ischemia group at postischemic days 7 and 21; furthermore, the survival rate of Brdu-positive cells was elevated by lithium. Inhibition of the ERK1/2 activation by U0126 diminished these effects of lithium. The percentages of Brdu-positive cells that expressed a neuronal marker or an astrocytic marker were not significantly influenced by lithium. Moreover, lithium improved the impaired spatial learning and memory ability in Morris water maze, and U0126 attenuated the behavioral improvement by lithium. These results suggest that lithium up-regulates the generation and survival of new-born cells in the hippocampus by the ERK pathway and improves the behavioral disorder in rats after transient global cerebral ischemia.

Involvement of Raf-1/MEK/ERK1/2 signaling pathway in zinc-induced injury in rat renal cortical slices

Zinc is an essential nutrient that can also be toxic. We have previously reported that zinc-related renal toxicity is due, in part, to free radical generation in the renal epithelial cell line, LLC-PK(1) cells. We have also shown that an MEK1/2 inhibitor, U0126, markedly inhibits zinc-induced renal cell injury. In this study, we investigated the role of an upstream MEK/ERK pathway, Raf-1 kinase pathway, and the transcription factor and ERK substrate Elk-1, in rat renal cortical slices exposed to zinc. Immediately after preparing slices from rat renal cortex, the slices were incubated in medium containing Raf-1 and MEK inhibitors. ERK1/2 and Elk-1 activation were determined by Western blot analysis for phosphorylated ERK (pERK) 1/2 and phosphorylated Elk-1 (pElk-1) in nuclear fractions prepared from slices exposed to zinc. Zinc caused not only increases in 4-hydroxynonenal (4-HNE) modified protein and lipid peroxidation, as an index of oxidant stress, and decreases in PAH accumulation, as that of renal cell injury in the slices. Zinc also induced a rapid increase in ERK/Elk-1 activity accompanied by increased expressions of pERK and pElk-1 in the nuclear fraction. A Raf-1 kinase inhibitor and an MEK1/2 inhibitor U0126 significantly attenuated zinc-induced decreases PAH accumulation in the slices. The Raf-1 kinase inhibitor and U0126 also suppressed ERK1/2 activation in nuclear fractions prepared from slices treated with zinc. The present results suggest that a Raf-1/MEK/ERK1/2 pathway and the ERK substrate Elk-1 are involved in free radical-induced injury in rat renal cortical slices exposed to zinc.

Hyperacute neuropathological findings after proton beam radiosurgery of the rat hippocampus

OBJECTIVE

To study the hyperacute histological and immunohistochemical effects of stereotactic proton beam irradiation of the rat hippocampus.

METHODS

Nine rats underwent proton beam radiosurgery of one hippocampus with nominal doses of cobalt-2, -12, and -60 Gray equivalents (n = 3 each). Control animals (n = 3) were not irradiated. Animals were killed 5 hours after irradiation and brain sections were stained for Nissl, silver degeneration, deoxyribonucleic acid (DNA) fragmentation (DNAF), and the activated form of two mitogen-activated protein kinases (MAPKs), phospho-Erk1/2 (P-Erk1/2) and p38. Stained cells in the hippocampus expressing DNAF and/or P-Erk1/2 were counted. Confocal microscopy with double immunofluorescent staining was used to examine cellular colocalization of DNAF and P-Erk1/2.

RESULTS

Both DNAF and P-Erk1/2 showed quantitative dose-dependent increases in staining in the targeted hippocampus compared with the contralateral side and controls. This finding was restricted to the subgranular proliferative zone of the hippocampus. Both markers also were up-regulated on the contralateral side when compared with controls in a dose-dependent fashion. Simultaneous staining for DNAF and P-Erk1/2 was found in fewer than half of all cells. p38 was unchanged compared with controls. Although Nissl staining appeared normal, silver stain confirmed dose-dependent cellular degeneration.

CONCLUSION

DNAF, a marker of cell death, was present in rat hippocampi within 5 hours of delivery of cobalt-2 Gray equivalents stereotactically focused irradiation, suggesting that even low-dose radiosurgery has hyperacute neurotoxic effects. Activated mitogen-activated protein kinase was incompletely colocalized with DNAF, suggesting that activation of this cascade is neither necessary nor sufficient to initiate acute cell death after irradiation.

Serum thymic factor, FTS, attenuates cisplatin nephrotoxicity by suppressing cisplatin-induced ERK activation

Serum thymic factor (FTS), a thymic peptide hormone, has been reported to attenuate the bleomycin-induced pulmonary injury and also experimental pancreatitis and diabetes. In the present study, we investigated the effect of FTS on cis-diamminedichloroplatinum II (cisplatin)-induced nephrotoxicity. We have already demonstrated that cephaloridine, a nephrotoxic antibiotic, leads to extracellular signal-regulated protein kinase (ERK) activation in the rat kidney, which probably contributes to cephaloridine-induced renal dysfunction. The aim of this study was to examine the effect of cisplatin on ERK activation in the rat kidney and also the effect of FTS on cisplatin-induced nephrotoxicity in rats. In vitro treatment of LLC-PK1 cells with FTS significantly ameliorated cisplatin-induced cell injury. Treatment of rats with intravenous cisplatin for 3 days markedly induced renal dysfunction and increased platinum contents in the kidney cortex. An increase in pERK was detected in the nuclear fraction prepared from the rat kidney cortex from days 1 to 3 after injection of cisplatin. FTS suppressed cisplatin-induced renal dysfunction and ERK activation in the kidney. FTS did not influence any Pt contents in the kidney after cisplatin administration. FTS has been shown to enhance the in vivo expression of heat shock protein (HSP) 70 in the kidney cortex. The beneficial role of FTS against cisplatin nephrotoxicity may be mediated in part by HSP70, as suggested by its up-regulation in the kidney cortex treated with FTS alone. Our results suggest that FTS participates in protection from cisplatin-induced nephrotoxicity by suppressing ERK activation caused by cisplatin.

ERK1/2 are involved in low potassium-induced apoptotic signaling downstream of ASK1-p38 MAPK pathway in cultured cerebellar granule neurons

We have recently reported that the ASK1-p38 MAPK pathway has an important role in the low potassium (LK)-induced apoptosis of cultured cerebellar granule neurons. In the present study, we observed that ERK1/2 were significantly activated 6 h after a change of medium from HK (high potassium) to LK. In addition, U0126, a specific inhibitor of MEKs, remarkably prevented the apoptosis of cultured cerebellar granule neurons. Then, we examined the mechanism underlying the activation of ERK1/2 in the LK-induced apoptotic pathway. The addition of SB203580, an inhibitor of p38 MAPK, suppressed the increase in the phosphorylation of ERK1/2 after the change to LK medium. Furthermore, we found that the expression of a constitutively active mutant of ASK1, an upstream kinase of p38 MAPK, enhanced the phosphorylation of ERK1/2. These results suggest that ERK1/2 play a crucial role in LK-induced apoptosis of cultured cerebellar granule neurons and that the LK-stimulated activation of ERK1/2 is regulated by the ASK1-p38 MAPK pathway.

Protective Effect of Serum Thymic Factor, FTS, on Cephaloridine-Induced Nephrotoxicity in Rats

Serum thymic factor (FTS), a thymic peptide hormone, has been reported to increase superoxide disumutase (SOD) levels in senescence-accelerated mice. In the present study, we examined the effect of FTS on cephaloridine (CER)-induced nephrotoxicity in vivo and in vitro. We previously reported that CER led to extracellular signal-regulated protein kinase (ERK) activation in the rat kidney. So, we also investigated whether FTS has an effect on ERK activation induced by CER. Treatment of male Sprague-Dawley rats with intravenous CER (1.2 g/kg) for 24 h markedly increased BUN and plasma creatinine levels and urinary excretion of glucose and protein, decreased creatinine clearance and also led to marked pathological changes in the proximal tubules, as revealed by electron micrographs. An increase in phosphorylated ERK (pERK) was detected in the nuclear fraction prepared from the rat kidney cortex 24 h after CER injection. Pretreatment of rats with FTS (50 microg/kg, i.v.) attenuated the CER-induced renal dysfunction and pathological damage. FTS also suppressed CER-induced ERK activation in the kidney. In vitro treatment of the established cell line, LLC-PK1 cells, with FTS significantly ameliorated CER-induced cell injury, as measured by lactate dehydrogenase (LDH) leakage. Our results, taken together with our previous report that MEK inhibitors ameliorated CER-induced renal cell injury and ERK activation induced by CER, suggest that FTS participates in protection from CER-induced nephrotoxicity by suppressing ERK activation induced by CER.

Depolarization activates ERK and proline-rich tyrosine kinase 2 (PYK2) independently in different cellular compartments in hippocampal slices

In the hippocampus, extracellular signal-regulated kinase (ERK) and the non-receptor protein proline-rich tyrosine kinase 2 (PYK2) are activated by depolarization and involved in synaptic plasticity. Both are also activated under pathological conditions following ischemia, convulsions, or electroconvulsive shock. Although in non-neuronal cells PYK2 activates ERK through the recruitment of Src-family kinases (SFKs), the link between these pathways in the hippocampus is not known. We addressed this question using K(+)-depolarized rat hippocampal slices. Depolarization increased the phosphorylation of PYK2, SFKs, and ERK. These effects resulted from Ca(2+) influx through voltage-gated Ca(2+) channels and were diminished by GF109203X, a protein kinase C inhibitor. Inhibition of SFKs with PP2 decreased PYK2 tyrosine phosphorylation dramatically, but not its autophosphorylation on Tyr-402. Moreover, PYK2 autophosphorylation and total tyrosine phosphorylation were profoundly altered in fyn-/- mice, revealing an important functional relationship between Fyn and PYK2 in the hippocampus. In contrast, ERK activation was unaltered by PP2, Fyn knock-out, or LY294002, a phosphatidyl-inositol-3-kinase inhibitor. ERK activation was prevented by MEK inhibitors that had no effect on PYK2. Immunofluorescence of hippocampal slices showed that PYK2 and ERK were activated in distinct cellular compartments in somatodendritic regions and nerve terminals, respectively, with virtually no overlap. Activation of ERK was critical for the rephosphorylation of a synaptic vesicle protein, synapsin I, following depolarization, underlining its functional importance in nerve terminals. Thus, in hippocampal slices, in contrast to cell lines, depolarization-induced activation of non-receptor tyrosine kinases and ERK occurs independently in distinct cellular compartments in which they appear to have different functional roles.

4-Aminopyridine-induced epileptogenesis depends on activation of mitogen-activated protein kinase ERK

Extracellular signal-regulated kinases such as ERK1 [p44 mitogen-activated protein kinase (MAPK)] and ERK2 (p42 MAPK) are activated in the CNS under physiological and pathological conditions such as ischemia and epilepsy. Here, we studied the activation state of ERK1/2 in rat hippocampal slices during application of the K(+) channel blocker 4-aminopyridine (4AP, 50 micro m), a procedure that enhances synaptic transmission and leads to the appearance of epileptiform activity. Hippocampal slices superfused with 4AP-containing medium exhibited a marked activation of ERK1/2 phosphorylation that peaked within about 20 min. These effects were not accompanied by changes in the activation state of c-Jun N-terminal kinase (JNK), another member of the MAP kinase superfamily. 4AP-induced ERK1/2 activation was inhibited by the voltage-gated Na(+) channel blocker tetrodotoxin (1 micro m). We also found that application of the ERK pathway inhibitors U0126 (50 micro m) or PD98059 (100 micro m) markedly reduced 4AP-induced epileptiform synchronization, thus abolishing ictal discharges in the CA3 area. The effects induced by U0126 or PD98059 were not associated with changes in the amplitude and latency of the field potentials recorded in the CA3 area following electrical stimuli delivered in the dentate hylus. These data demonstrate that activation of ERK1/2 accompanies the appearance of epileptiform activity induced by 4AP and suggest a cause-effect relationship between the ERK pathway and epileptiform synchronization.

Activation of extracellular signal-regulated kinases (ERK) during reperfusion of ischemic spinal cord

The extracellular signal-regulated kinases (ERK) participate in numerous signaling pathways and are abundantly expressed in the CNS. It has been proposed that ERK activation promotes survival in models of neuronal injury. Inhibition of MEK, the upstream kinase that activates ERK, however, leads to neuroprotection in models of cerebral ischemia and trauma, suggesting that in this context ERK activation contributes to cellular damage. The effect of ischemia and reperfusion on activity and expression of ERK was investigated using a reversible model of rabbit spinal cord ischemia. Active ERK was observed in nai;ve animals, which decreased during 15 to 60 min of ischemia. Upon reperfusion, a robust activation of ERK was observed in animals occluded for 60 min that remained permanently paraplegic. Immunohistochemical analyses revealed increased staining of phosphorylated ERK (pERK) in glial cells and faint nuclear staining in motor neurons of animals occluded for 60 min and reperfused for 18 h. In contrast ERK activity did not increase in animals occluded for 15 min that regained motor function. No evidence of increased pERK immunoreactivity in motor neurons or nuclear translocation was noted in these animals. ERK1 was demonstrated to be identical to a p46 c-Jun/ATF-2 kinase previously shown to be activated by reperfusion after a 60-min occlusion. The results suggest that activation of ERK during reperfusion of ischemic spinal cord participates in the cellular pathways leading to neuronal damage.

Involvement of MEK/ERK pathway in cephaloridine-induced injury in rat renal cortical slices

We have previously reported that free radical-mediated injury induced by cephaloridine (CER) is enhanced by phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, in rat renal cortical slices. We have also shown that PKC activation in mitochondria is involved in CER-induced nephrotoxicity in rats. We investigated the role of a downstream PKC pathway, a MEK/ERK pathway, in free radical-induced injury in rat renal cortical slices exposed to CER. Immediately after preparing slices from rat renal cortex, the slices were incubated in the medium containing MEK inhibitors. ERK1/2 activation was determined by Western blot analysis for phosphorylated ERK (pERK) 1/2 protein in nucleus fraction prepared from the slices exposed to CER. Prominently, CER caused not only increases in lipid peroxidation as an index of free radical generation and in LDH leakage as that of cell injury in the slices, but also marked activation of ERK1/2 in nucleus fraction. PD98059 and U0126, MEK1/2 inhibitors, significantly attenuated CER-induced increases in lipid peroxidation and LDH leakage in the slices. PD98059 also suppressed ERK1/2 activation in nucleus fraction prepared from the slices treated with CER. Inhibition of other MAP kinase pathways, p38 MAP kinase and c-Jun N-terminal kinase (JNK) had no effect on CER-induced increases in lipid peroxidation level and LDH leakage in the slices. The present results suggest that a MEK/ERK pathway down stream of a PKC pathway is probably involved in free radical-induced injury in rat renal cortical slices exposed to CER.

Discussion of the role of the extracellular signal-regulated kinase-phospholipase A2 pathway in production of reactive oxygen species in Alzheimer's disease

In this paper we show that exposure of a rat brain synaptosome fraction to the amyloid beta peptide fragment betaA(25-35), but not the inverted peptide betaA(35-25), stimulated production of reactive oxygen species (ROS) in a concentration- and time-dependent manner. The ROS formation was attenuated by the tyrosine kinase inhibitor genistein, the mitogen-activated protein kinase inhibitor U0126, and the phospholipase A2 (PLA2) inhibitor 7,7-dimethyl-(5Z,8Z)-eicosadienoic acid. This strongly suggests that betaA(25-35) stimulated ROS production through an extracellular signal-regulated kinase-PLA2-dependent pathway. The interaction between these enzymes and their possible involvement in free radical formation in Alzheimer's disease are discussed.

Phosphorylation of P42/P44 MAP kinase and DNA fragmentation in the rat perforant pathway stimulation model of limbic epilepsy

The intracellular signaling pathways associated with neuronal injury after perforant pathway stimulation of the rodent hippocampus have not been examined. To determine whether activation of the p42/p44 (Erk1/2) MAP kinase (MAPK) phosphorylation cascade is linked to neuronal injury after perforant pathway stimulation (PPS), we stained for phosphorylated Erk1/2 (P-Erk1/2) and for DNA fragmentation, a marker of cell death after PPS. Eighteen Sprague-Dawley rats underwent PPS for 6 (n=6), 12 (n=6), or 24 (n=6) h and were sacrificed either immediately (n=9) or 48 h (n=9) after stimulation. Sham-operated non-stimulated control animals (n=2) and control animals receiving low frequency stimulation only (n=4) were also examined. Brain sections were stained for DNA fragmentation and P-Erk1/2. DNA fragmentation was evident only in granule cells and CA3 pyramidal cells of the stimulated side 48 h after 24 h of PPS. PPS resulted in robust phosphorylation of Erk1/2 that displayed a stereotyped timecourse, appearing first in hilar neurons on the ipsilateral side and later in hilar neurons, granule cells, hippocampal pyramidal and non-neuronal cell populations on both the stimulated and contralateral sides. Both Erk1/2 phosphorylation and DNA fragmentation show definite and reproducible staining patterns after PPS that vary based on duration of stimulation. Populations displaying Erk1/2 activation appeared to differ from those showing DNA fragmentation and neuronal injury.

Intravenous administration of MEK inhibitor U0126 affords brain protection against forebrain ischemia and focal cerebral ischemia

Brain subjected to acute ischemic attack caused by an arterial blockage needs immediate arterial recanalization. However, restoration of cerebral blood flow can cause tissue injury, which is termed reperfusion injury. It is important to inhibit reperfusion injury to achieve greater brain protection. Because oxidative stress has been shown to activate mitogen-activated protein kinases (MAPKs), and because oxidative stress contributes to reperfusion injury, MAPK may be a potential target to inhibit reperfusion injury after brain ischemia. Here, we demonstrate that reperfusion after forebrain ischemia dramatically increases phosphorylation level of extracellular signal-regulated kinase 2 (ERK2) in the gerbil hippocampus. In addition, i.v. administration of U0126 (100-200 mg/kg), a specific inhibitor of MEK (MAPK/ERK kinase), protects the hippocampus against forebrain ischemia. Moreover, treatment with U0126 at 3 h after ischemia significantly reduces infarct volume after transient (3 h) focal cerebral ischemia in mice. This protection is accompanied by reduced phosphorylation level of ERK2, substrates for MEK, in the damaged brain areas. Furthermore, U0126 protects mouse primary cultured cortical neurons against oxygen deprivation for 9 h as well as nitric oxide toxicity. These results provide further evidence for the role of MEK/ERK activation in brain injury resulting from ischemia/reperfusion, and indicate that MEK inhibition may increase the resistance of tissue to ischemic injury.

Transient cerebral ischemia increases tyrosine phosphorylation of the synaptic RAS-GTPase activating protein, SynGAP

Cerebral ischemia results in activation of the mitogen-activated protein kinase pathway and increased tyrosine phosphorylation of proteins associated with postsynaptic densities (PSDs). The authors investigated the possible relation between these events by determining the effect of ischemia on tyrosine phosphorylation of the brain-specific, PSD-enriched, Ras-GTPase activating protein, SynGAP. Transient (15 minutes) global ischemia was produced in rats by 4-vessel occlusion and PSDs prepared from forebrains immediately after ischemia or at 20 minutes, 1 hour, or 24 hours of reperfusion. Tyrosine phosphorylation of SynGAP was elevated relative to sham-operated controls by 20 minutes of reperfusion and remained elevated for at least 24 hours. Tyrosine phosphorylation of SynGAP also increased in CA1 and CA3/DG subfields of the hippocampus. Enhanced tyrosine phosphorylation of SynGAP was not accompanied by a change in PSD RasGAP activity. SynGAP bound to the SH2 domains of Src and Fyn in a tyrosine phosphorylation-dependent fashion, and this interaction increased after ischemia. SynGAP binds to the PDZ domains of PSD-95/SAP90 and coimmunoprecipitated with PSD-95. The coimmunoprecipitation of SynGAP with PSD-95 decreased after ischemia. The results indicate that changes in the properties and interactions of SynGAP may be involved in the neuropathology of ischemia.

Effects of riluzole on N-methyl-D-aspartate-induced tyrosine phosphorylation in the rat hippocampus

Since increased tyrosine phosphorylation has been observed in response to brain ischemia, we investigated whether riluzole (an inhibitor of glutamate neurotransmission with neuroprotective properties) affects tyrosine phosphorylation stimulated by N-methyl-D-aspartate (NMDA) in rat hippocampal slices. Riluzole produced an extremely potent concentration-related inhibition of NMDA (1 mM)-stimulated protein tyrosine phosphorylation (IC(50)=0.5+/-0.03 microM, mean+/-S.D.), but failed to affect that evoked by phorbol 12-myristate 13-acetate (PMA, an activator of protein kinase C, 0.1 and 1 microM). These results suggest that inhibition of tyrosine phosphorylation may contribute to the neuroprotective effects of riluzole against excitotoxic injury.

Extracellular signal-regulated kinase 1/2 activation in hippocampus after cerebral ischemia may not interfere with postischemic cell death

To investigate the effect of the activation of extracellular signal-regulated kinase 1/2 (ERK1/2) on cerebral ischemic injury, temporospatial alterations of active (diphosphorylated) ERK1/2 immunoreactivity in hippocampus was examined. Western blot showed that diphosphorylated ERK1/2 were decreased at 10 min of cerebral ischemia but increased rapidly (within 2 min) and transiently (within 4 h) during reperfusion. Immunohistochemistry showed that little diphosphorylated ERK1/2 immunoreactivity was seen in CA1 pyramidal cell bodies after ischemia, while strong immunoreactivity were seen in neuronal bodies in CA3/DG and in fiber systems in both CA1 and CA3 regions. Cerebral ventricular infusion of PD98059, a specific inhibitor of ERK kinase, completely prevented ERK1/2 activation after ischemia but had no effect on the survival of pyramidal cells in CA1 subfield. The results suggest that ERK1/2 activation in hippocampus after brain ischemia may not interfere with the postischemic cell death in CA1 region.

Phosphorylation of extracellular signal-regulated kinase after transient cerebral ischemia in hyperglycemic rats

The present study was undertaken to investigate whether extracellular signal-regulated kinase (ERK) was involved in mediating hyperglycemia-exaggerated cerebral ischemic damage. Phosphorylation of ERK 1/2 was studied by immunocytochemistry and by Western blot analyses. Rats were subjected to 15 min of forebrain ischemia, followed by 0.5, 1, and 3 h of reperfusion under normoglycemic and hyperglycemic conditions. The results showed that in normoglycemic animals, moderate phosphorylation of ERK 1/2 was transiently induced after 0.5 h of recovery in cingulate cortex and in dentate gyrus, returning to control values thereafter. In hyperglycemic animals, phosphorylation of ERK 1/2 was markedly increased in the cingulate cortex and dentate gyrus after 0.5 h of recovery, the increases being sustained for at least 3 h after reperfusion. Hyperglycemia also induced phosphorylation of ERK 1/2 in the hippocampal CA3 sector but not in the CA1 area. Thus, the distribution of phospho-ERK 1/2 coincides with hyperglycemia-recruited damage structures. The results suggest that hyperglycemia may influence the outcome of an ischemic insult by modulating signal transduction pathways involving ERK 1/2.

Involvement of mitogen-activated protein kinase in peroxynitrite-induced cell death of human neuroblastoma SH-SY5Y cells

We have investigated the activation of mitogen-activated protein kinase (MAP kinase) in relation to cell death induced by peroxynitrite in human neuroblastoma SH-SY5Y cells. Exposure of the cells to peroxynitrite caused transient increase in MAP kinase activity, and resulted in cell death. PD98059, a selective inhibitor of MAP kinase kinase, reduced peroxynitrite-induced cell death. These results suggest that the activation of MAP kinase may be involved in cell death induced by peroxynitrite.

Mitochondrial ATP production is necessary for activation of the extracellular-signal-regulated kinases during ischaemia/reperfusion in rat myocyte-derived H9c2 cells

To search for the stimuli involved in activating the mitogen-activated protein kinases (MAPKs) during ischaemia and reperfusion, we simulated the event in a system in vitro conducive to continuous and non-invasive measurements of several major perturbations that occur at the time: O(2) tension, mitochondrial respiration and energy status. Using H9c2 cells (a clonal line derived from rat heart), we found that activation of the extracellular signal-regulated MAPKs (ERKs) on reoxygenation was abolished if the mitochondria were inhibited prior to and during reoxygenation. Re-introduction of O(2) per se is therefore not sufficient to activate the ERKs. Recovery and maintenance of cellular ATP levels by mitochondrial respiration is necessary, although ATP recovery alone is not sufficient. ERK activation by H(2)O(2), but not phorbol esters, was also sensitive to mitochondrial inhibition. Thus, reoxygenation and H(2)O(2)-mediated oxidative stress share a mechanism of ERK activation that is ATP- or mitochondrion-dependent, and this common feature suggests that the reoxygenation response is mediated by reactive oxygen species. A correlation between ERK activity and ATP levels was also found during the anoxic phase of ischaemia, an effect that was not due to substrate limitation for the kinases. Our results reveal the importance of cellular metabolism in ERK activation, and introduce ATP as a novel participant in the mechanisms underlying the ERK cascade.

Alteration of MAP kinase pathways after transient forebrain ischemia

Extracellular regulated kinase (ERK) transduce growth factor signals while c-Jun NH(2)-terminal kinase (JNK) delivers stress signals into the nuclei for regulation of gene expression. These signaling pathways were studied by laser-scanning confocal microcopy and Western blot analysis using phospho-specific antibodies on rat brains that were subjected to 15 minutes transient forebrain ischemia followed by varied periods of reperfusion. Extracellular regulated kinase was activated at 30 minutes and 4 hours of reperfusion in the nuclei and dendrites of surviving dentate gyrus (DG) cells, but not in dying CA1 neurons after ischemia. Tyrosine phosphorylation of Trk kinase, an ERK upstream growth factor receptor, was elevated in the DG tissue, and to a lesser extent in the CA1 region. In addition, phosphorylation of activating transcription factor-2 (ATF-2) and c-Jun was selectively increased in CA1 dying neurons during the late period of reperfusion. These findings suggested that the Trk-ERK signaling pathway might be neuroprotective for dentate granule cells. The activation of ATF-2 and c-Jun pathways in the late period of reperfusion in CA1 dying neurons might reflect damage signals in these neurons. These results suggested that the lack of protective signals acting in concert with the presence of damage signals in CA1 neurons after ischemia might contribute to delayed neuronal death after transient forebrain ischemia.

The role of complement anaphylatoxin C5a in neurodegeneration: implications in Alzheimer's disease

There is evidence that the complement system, a major component of inflammatory responses, may play an important role in neurodegenerative conditions such as Alzheimer's disease (AD). Work from our lab demonstrated that mice genetically deficient in the complement component C5 are more susceptible to hippocampal excitotoxic lesions (Pasinetti et al., 1996) and that the C5-derived ana;hylatoxin C5a may protect against excitotoxicity in vitro and in vivo (Osaka et al., 1999). Potential mechanisms identified in C5a-mediated neuroprotection include activation of mitogen activated protein (MAP)-kinase (Osaka et al., 1998; Osaka et al., 1999). This novel neuroprotective role of C5a complicates current theories that complement proteins augment beta-amyloid (Abeta) toxicity in AD. In view of the fact that the complement system represents a target for therapeutic interventions in AD, further characterization of the complex role of complement proteins is essential. Towards this aim, we have characterized a transgenic C5a receptor (C5aR) knockout (KO) mouse. Recent studies in the lab using C5aR-KO mice show that disruption of C5aR alters calcium calmodulin kinase (CaM-KII) signal transduction in brain cells. We are presently using C5aR-KO mice to study the role of C5a in caspase mediated apoptotic neuronal death. In this review we will attempt to delineate possible neuroprotective roles for C5a in mechanisms of neurotoxicity pertaining to AD.

Diphosphorylation of extracellular signal-regulated kinases and c-Jun N-terminal protein kinases in brain ischemic tolerance in rat

Extracellular signal-regulated kinases (ERKs) and c-Jun N-terminal protein kinases (JNKs) activation in brain ischemic tolerance were examined by Western immunoblot. ERK but not JNK diphosphorylation (activation) were increased after preconditioning ischemia. The increased JNK1 but not ERK diphosphorylation after lethal ischemia was eliminated by pretreatment with preconditioning ischemia. The results suggest that the elimination of JNK1 activation after lethal ischemia by preconditioning ischemia may be one of the important protective mechanisms in ischemic tolerance, and ERKs activation may be involved in the induction of the protective responses.

Altered association of protein tyrosine kinases with postsynaptic densities after transient cerebral ischemia in the rat brain

Transient cerebral ischemia results in an increase in the tyrosine phosphorylation of proteins associated with postsynaptic densities (PSDs). The authors investigated the possible mechanisms behind this increase by analyzing isolated PSDs for protein tyrosine kinase activity and for the presence of specific tyrosine kinases. Transient (15 minutes) global ischemia was produced in adult rats by four-vessel occlusion, and PSDs were isolated immediately after ischemia or after 20 minutes or 6 hours of reperfusion. Tyrosine phosphorylation of several PSD proteins, including the N-methyl-D-aspartate (NMDA) receptor subunits NR2A and NR2B, was enhanced relative to shams after 20 minutes of reperfusion and underwent a further increase between 20 minutes and 6 hours. The ability of intrinsic PSD tyrosine kinase to phosphorylate PSD proteins, including the NMDA receptor, increased threefold after ischemia. Whereas PSD-associated proline-rich tyrosine kinase 2 (PYK2) and gp145TrkB were elevated immediately after the ischemic event, increases in Src and Fyn were not apparent until 6 hours of reperfusion. The level of PSD-associated pp125FAK decreased after ischemia. The results demonstrate that ischemia results in selective changes in the association of protein tyrosine kinases with the PSD which may account for ischemia-induced increases in the tyrosine phosphorylation of PSD proteins.

Persistent CREB phosphorylation with protection of hippocampal CA1 pyramidal neurons following temporary occlusion of the middle cerebral artery in the rat

Phosphorylation of the DNA-binding transcription factor, cyclic AMP response element binding protein (CREB), was immunohistochemically examined in rat brain hippocampal CA1 in order to examine the ischemic vulnerability of this region from the viewpoint of CREB activation. The rat brain had been subjected to 90-min focal ischemia followed by various periods of recirculation. Focal ischemia was induced by occlusion of the middle cerebral artery using the intraluminal suture method. CA1 pyramidal neurons in the sham animals showed definite immunoreactivity with anti-CREB antibody, which binds to both unphosphorylated and phosphorylated CREB, while reactivity with anti-phosphorylated CREB antibody was barely detectable in these neurons. In contrast, at 3.5 h of recirculation, a significant increase in the number of phosphorylated CREB-positive neurons was noted in the CA1 on both sides, and the increase continued until 48 h of recirculation with a tendency for gradual decline. At each period, the ischemic side showed a more marked increase in the number of immunoreactive cells as compared to the nonischemic side. Cresyl violet staining revealed CA1 pyramidal neurons to be maintained intact until 14 day of recirculation, at which time CREB phosphorylation has returned to the control level. Transient global ischemia is known to induce only mild CREB phosphorylation in the CA1 followed by a frank neuronal loss in this region. These data suggest that CREB phosphorylation can be persistently activated in CA1 neurons after focal ischemia and that this phenomenon may be closely associated with protection of these neurons.

Involvement of extracellular signal-regulated protein kinase in gliosis induced during recovery from metabolic inhibition

Brain reperfusion may be of particular importance in the etiology of periventricular leukomalacia, of which the common findings are gliosis and ventricular dilatation. To investigate the mechanism of this pathogenesis, we used a metabolic inhibition (MI) model using cyanide plus deoxyglucose treatment of cultured glia isolated from fetal rat brain and examined the activity of extracellular signal-regulated protein kinase (ERK) during MI and also during the recovery from MI of 30 min. ERK activation was stimulated during MI and the recovery from MI. The time course and extent of activation of ERK during MI and the recovery from MI, however, were distinctly different. Activation of ERK was stimulated within 5 min of MI and declined thereafter. Activation of ERK was sustained during the recovery phase from MI and the extent of the activation was much greater than that during MI. Pretreatment with EGTA to eliminate extracellular Ca(2+), or with APV, an NMDA receptor antagonist, to inhibit Ca(2+) influx through the NMDA receptor, attenuated the activation of ERK. Moreover, pretreatment with PMA to downregulate PKC abolished the activation of ERK. PD98059, an inhibitor of ERK kinase, attenuated the cell proliferation induced by MI followed by recovery from MI. These results suggest that ERK is involved in gliosis during the recovery phase from MI and may play a role in the etiology of periventricular leukomalacia.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

The topography and subcellular distribution of mitogen-activated protein kinase kinase1 (MEK1) in adult rat brain and differentiating PC12 cells

Mitogen-activated protein kinase signal transduction pathway involved in the regulation of proliferation and differentiation of various mammalian cells consists of a sequential activation of three protein kinases, Raf, mitogen-activated protein kinase kinase, and mitogen-activated protein kinase. These kinases are highly expressed in brain and play an important role in neuronal signalling. In this study, to further characterize mitogen-activated protein kinase signalling pathway in brain, we have elucidated the topography and subcellular distribution of mitogen-activated protein kinase kinasel in adult rat brain and differentiating PC12 cells. Our immunohistochemical data indicate that mitogen-activated protein kinase kinase1 is widely distributed throughout the brain and expressed prominently in cortex, hippocampus, brainstem, hypothalamus and cerebellum. In these areas of brain mitogen-activated protein kinase kinasel is exclusively neuronal in origin and is localized within perikarya and dendrites. Confocal microscopy data has determined that a portion of mitogen-activated protein kinase kinase1 in rat brain is co-localized with microtubules. This co-localization was observed only within neuritic shaft and cilia of ventricular ependymal cells. In nerve growth factor-induced differentiating PC12 cells, mitogen-activated protein kinase kinase1 displays co-localization with microtubules within proximal regions of neuritic shafts and their junctions with the cell somas. From bovine brain extract, mitogen-activated protein kinase kinasel co-purifies with microtubules. In vitro kinase assay detected mitogen-activated protein kinase kinase1 activity within purified microtubules. These observations indicate that mitogen-activated protein kinase kinase1 is associated with microtubules within some specialized compartments of the brain and microtubule-associated mitogen-activated protein kinase kinase1 is catalytically active.

Activation of the extracellular signal-regulated protein kinase cascade in the hippocampal CA1 region in a rat model of global cerebral ischemic preconditioning

A short period of sublethal preconditioning ischemia (3 min) followed by two days of reperfusion provides almost complete protection against ischemic cell death induced by a second (9 min) lethal ischemic episode. Here, we have investigated the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase, two kinases known to activate gene transcription and to be of importance for cell survival, after sublethal preconditioning ischemia in the rat hippocampal CA1 region. The activation levels of these two kinases were also studied after a second ischemic episode both in preconditioned and nonconditioned brains. An increased phosphorylation of the extracellular signal-regulated protein kinase kinase was found in neuronal cell bodies, particularly in the nucleus, 30 min, 4 h and two days of reperfusion after preconditioning ischemia. Two days after preconditioning ischemia both extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase were markedly phosphorylated. During the early reperfusion period (30 min) after the second ischemic insult the phosphorylation levels of these two kinases were increased in both nonconditioned and preconditioned brains. In the late reperfusion time (one day), the phosphorylation levels of the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase were decreased in preconditioned brains, but remained elevated in nonconditioned brains. We conclude that phosphorylation of the extracellular signal-regulated protein kinase kinase and extracellular signal-regulated protein kinase after sublethal ischemia correlates with the neuroprotection induced by preconditioning, possibly by transcriptional activation of neuroprotective genes. Also, preconditioning enhances normalization of the disturbed cell signaling through the extracellular signal-regulated protein kinase cascade induced by lethal ischemia.

A simple in vitro model of ischemia based on hippocampal slice cultures and propidium iodide fluorescence

This protocol describes a model of cerebral ischemia based on organotypic hippocampal slice cultures and quantitative assessment of cell death by use of propidium iodide and image analysis. The cultures were made from rat hippocampal slices that were obtained at postnatal day 4-7 and allowed to develop for >14 days in vitro. For induction of 'in vitro ischemia', the cultures were washed in glucose free buffer and the culture chamber flooded with a nitrogen/carbon dioxide mixture until the oxygen concentration was <1.0%. The cultures were exposed to this atmosphere for 30-35 min, washed in serum-free medium, and returned to ordinary growth medium. After 24 h, dead cells were quantified by use of propidium iodide. The cell death resulting from the oxygen/glucose deprivation was largely confined to the CA1 region and was blocked by NMDA-receptor antagonists but not by antagonists to AMPA-receptors or metabotropic glutamate receptors. The type of cell death was judged to be necrotic, based on ultrastructural observations. The oxygen/glucose deprived cultures exhibited increased phosphorylation of the MAP kinase cascade. This activation of the MAP kinase cascade was blocked by NMDA-receptor antagonists. The in vitro model described in the present report is simple to use and reproduces many features of in vivo ischemia, including the preferential vulnerability of CA1 cells. The model should be suited to analyses of the mechanisms underlying the regionally selective cell death in the hippocampus and ischemic cell death in general.

FAK and PYK2/CAKbeta in the nervous system: a link between neuronal activity, plasticity and survival?

A major aim of neurobiology today is to improve understanding of the signaling pathways that couple rapid events, such as the action potential and neurotransmitter release, to long-lasting changes in synaptic strength and increased neuronal survival. These adaptations involve interactions of neurons with other cells and with the extracellular matrix. They use, in part, the same molecular machinery that controls adhesion, motility or survival in non-neuronal cells. This machinery includes two homologous non-receptor tyrosine kinases, FAK and PYK2/CAKbeta, and the associated SRC-family tyrosine kinases. Specific brain isoforms of FAK with distinct properties are regulated by neurotransmitters, whereas PYK2/CAKbeta is highly sensitive to depolarization. The multiplicity of the pathways that can be activated by these tyrosine kinases indicates their importance in signal transduction in the adult brain.

ERK2 activation by homocysteine in vascular smooth muscle cells

Homocysteine at abnormally high levels is an independent risk factor for atherosclerosis and may be a key factor in atherogenesis. Since homocysteine (Hcys) has been shown to promote cell proliferation and induction of the gene transcription factor c-fos in vascular smooth muscle cells (VSMCs), effects which can be mediated by MAP kinase, we hypothesized that homocysteine activates a MAP kinase-dependent signal transduction pathway. In this study, we find that homocysteine transiently activates MAP kinase (ERK2 isoform) in cultured VSMCs from chick embryos. Homocysteine activation of ERK2 is dose-dependent with an EC50 of approximately 500 nM and blocked by the MAP/Erk kinase (MEK) inhibitor PD98059. VSMC embryonic lineage is another determinant of homocysteine sensitivity. These findings demonstrate that homocysteine activates the MAP kinase signal transduction pathway and thus support the hypothesis that homocysteine may promote atherosclerosis by stimulation of growth promoting signal transduction pathways.

Regional selective neuronal degeneration after protein phosphatase inhibition in hippocampal slice cultures: evidence for a MAP kinase-dependent mechanism

The regional selectivity and mechanisms underlying the toxicity of the serine/threonine protein phosphatase inhibitor okadaic acid (OA) were investigated in hippocampal slice cultures. Image analysis of propidium iodide-labeled cultures revealed that okadaic acid caused a dose- and time-dependent injury to hippocampal neurons. Pyramidal cells in the CA3 region and granule cells in the dentate gyrus were much more sensitive to okadaic acid than the pyramidal cells in the CA1 region. Electron microscopy revealed ultrastructural changes in the pyramidal cells that were not consistent with an apoptotic process. Treatment with okadaic acid led to a rapid and sustained tyrosine phosphorylation of the mitogen-activated protein kinases ERK1 and ERK2 (p44/42(mapk)). The phosphorylation was markedly reduced after treatment of the cultures with the microbial alkaloid K-252a (a nonselective protein kinase inhibitor) or the MAP kinase kinase (MEK1/2) inhibitor PD98059. K-252a and PD98059 also ameliorated the okadaic acid-induced cell death. Inhibitors of protein kinase C, Ca2+/calmodulin-dependent protein kinase II, or tyrosine kinase were ineffective. These results indicate that sustained activation of the MAP kinase pathway, as seen after e.g., ischemia, may selectively harm specific subsets of neurons. The susceptibility to MAP kinase activation of the CA3 pyramidal cells and dentate granule cells may provide insight into the observed relationship between cerebral ischemia and dementia in Alzheimer's disease.

Inhibition of the p44/42 MAP kinase pathway protects hippocampal neurons in a cell-culture model of seizure activity

Excessive release of glutamate and the subsequent influx of calcium are associated with a number of neurological insults that result in neuronal death. The calcium-activated intracellular signaling pathways responsible for this excitotoxic injury are largely unknown. Here, we report that PD098059, a selective inhibitor of the calcium-activated p44/42 mitogen-activated protein kinase (MAP kinase) pathway, reduces neuronal death in a cell-culture model of seizure activity. Dissociated hippocampal neurons grown chronically in the presence of kynurenate, a broad spectrum glutamate-receptor antagonist, and elevated amounts of magnesium exhibit intense seizure-like activity after the removal of these blockers of excitatory synaptic transmission. A 30-min removal of the blockers produced extensive neuronal death within 24 h as assayed by the uptake of trypan blue and the release of lactate dehydrogenase. Phospho-p44/42 MAP kinase immunoreactivity after 30 min of seizure-like activity was present in many neuronal somata and dendrites as well as some synaptic terminals, consistent with both the presynaptic and postsynaptic effects of this pathway. The addition of PD098059 (40 microM; EC50 = 10 microM) during a 30-min washout of synaptic blockers inhibited the phosphorylation of p44/42 MAP kinase and reduced both the trypan-blue staining (n = 13) and the release of lactate dehydrogenase (n = 16) by 73% +/- 18% and 75% +/- 19% (mean +/- SD), respectively. The observed neuroprotection could be caused by an effect of PD098059 on seizure-like events or on downstream signaling pathways activated by the seizure-like events. Either possibility suggests a heretofore unknown function for the p44/42 MAP kinase pathway in neurons.

Cell cycle-related gene expression in the adult rat brain: selective induction of cyclin G1 and p21WAF1/CIP1 in neurons following focal cerebral ischemia

The present studies were initiated to investigate whether p53 transactivated target genes are induced in a rat model of focal cerebral ischemia. Therefore, we applied in situ hybridization, immunocytochemistry and western blotting to study the temporal and spatial expression of p53 and its transcriptional targets Bax, p21 and cyclin G1 following permanent middle cerebral artery occlusion in the rat. Cyclin G1 immunoreactivity was constitutively expressed in the nuclei of cells in the choroid plexus and ependymal cell layer and in the cytoplasm of cell bodies and dendrites of pyramidal neurons of the cerebral cortex. Cyclin G1 messenger RNA and protein levels transiently increased to 150% of contralateral levels in neurons of the ipsilateral frontal and parietal cortex and striatum 3 h following middle cerebral artery occlusion. A low level of constitutively expressed p21 messenger RNA and protein was found in nuclei of cells in the choroid plexus, oligodendrocytes and neurons. p21 messenger RNA and protein levels gradually increased to 250% and 140% of contralateral levels in areas bordering the infarct core up to 6 h following middle cerebral artery occlusion. In contrast, p53 and Bax messenger RNA and protein levels, and protein levels of p27, cyclin-dependent kinase 5, p35 and cyclin E decreased in the infarct core and border areas with time after middle cerebral artery occlusion. The selective up-regulation of cyclin G1 and p21 in neurons in the border zone of a focal ischemic infarct indicates their involvement in an adaptive response to ischemic injury. The possible participation of cyclin G1 and p21 in a signal transduction pathway associated with ischemia-induced cellular stress is discussed.

Role of MAP kinase in neurons

Extracellular stimuli such as neurotransmitters, neurotrophins, and growth factors in the brain regulate critical cellular events, including synaptic transmission, neuronal plasticity, morphological differentiation and survival. Although many such stimuli trigger Ser/Thr-kinase and tyrosine-kinase cascades, the extracellular signal-regulated kinases, ERK1 and ERK2, prototypic members of the mitogen-activated protein (MAP) kinase family, are most attractive candidates among protein kinases that mediate morphological differentiation and promote survival in neurons. ERK1 and ERK2 are abundant in the central nervous system (CNS) and are activated during various physiological and pathological events such as brain ischemia and epilepsy. In cultured hippocampal neurons, simulation of glutamate receptors can activate ERK signaling, for which elevation of intracellular Ca2+ is required. In addition, brain-derived neurotrophic factor and growth factors also induce the ERK signaling and here, receptor-coupled tyrosine kinase activation has an association. We describe herein intracellular cascades of ERK signaling through neurotransmitters and neurotrophic factors. Putative functional implications of ERK and other MAP-kinase family members in the central nervous system are give attention.

Reduction of tyrosine kinase activity and protein tyrosine dephosphorylation by anoxic stimulation in vitro

Tyrosine-specific protein phosphorylation has been recently implicated in mediating pathological changes associated with cerebral ischemia. In the present study, acute hypoxia/ischemia (anoxia) was simulated in vitro by incubating rat hippocampal slices in glucose-free artificial cerebrospinal fluid saturated with 95% N2/5% CO2. A marked decrease in the level of tyrosine phosphorylation of many protein bands compared with the control was observed. Immunoprecipitation and western blot confirmed that the NR2A/2B subunits of the N-methyl-D-aspartate receptors are among the dephosphorylated proteins. Maximal dephosphorylation of bands corresponding to NR2A/2B was reached after 10 min, and no recovery was observed even after 1 h in normal, oxygenated artificial cerebrospinal fluid. The effect was partially blocked by dephostatin, a membrane-permeable inhibitor of protein tyrosine phosphatases, but was not affected by the presence of glutamate receptor antagonists, or by removing extracellular Ca2+ or chelating intracellular Ca2+. Enzyme assay showed that anoxic stimulation resulted in a selective reduction in protein tyrosine kinase activity without affecting protein tyrosine phosphatase activity. Thus the present work suggests that anoxic stimulation produces a selective inhibition of protein tyrosine kinase activity leading to tyrosine-dephosphorylation of several proteins including the N-methyl-D-aspartate receptors. The underlying mechanism may involve a novel signal transduction pathway, which may protect neurons from degeneration during ischemic stress.

Human immunodeficiency virus type 1 and its coat protein gp120 induce apoptosis and activate JNK and ERK mitogen-activated protein kinases in human neurons

Detection of apoptotic neurons and microglial cells in the brains of human immunodeficiency virus type 1 (HIV-1)-infected patients has suggested that programmed cell death may be implicated in the physiopathology of HIV-1 encephalopathy. To analyze in vitro the intracellular signals induced by HIV-1 in human neurons and the associated neuronal death, we tested cultured human central nervous system (CNS) cells for apoptosis induced by HIV-1 and gp120 and for signaling pathways activated by gp120. HIV-1 and gp120 induced apoptosis of neurons and microglial cells but not of astrocytes or transformed microglial cells. Gp120 activated c-Jun N-terminal kinase (JNK) and p42 extracellular-regulated kinase (ERK) in primary CNS cells, with an early peak of activation at 2 to 5 minutes that was not present when pure microglial or astrocyte cultures were tested, followed by a late and sustained activation (10 and 60 minutes) in primary and enriched glial cell cultures as well as in transformed microglial cells. This demonstrates that gp120 could be an effector of HIV-1-induced apoptosis in the CNS and act directly on neuronal and glial cells.

Cyclin-dependent protein kinase 5 activity increases in rat brain following ischemia

Cyclin-dependent kinase 5 (CDK5) is the 34 kDa catalytic subunit of a recently characterized neuronal cdc2-like protein kinase which appears to be involved in regulation of the neurocytoskeleton. Using the rat postdecapitative model, the effect of brain ischemia on histone H1 and tau protein CDK5 phosphorylating activity was examined. Histone H1 kinase activity increased in both cytosolic and particulate fractions of the hippocampus and neocortex after 5 min and 15 min of ischemia, then declined to control levels. CDK5 tau protein phosphorylating activity increased after 15 min ischemia; however, no electrophoretic shifts or changes in radiodensity of the tau bands were observed autoradiographically. On Western blot analysis, the CDK5 protein band did not change after 25 min ischemia, despite the increase and subsequent decline in enzyme activity. These data demonstrate a postischemic increase in CDK5 activity, an associated increase in CDK5 tau phosphorylating activity and a decline in activity in the absence of massive proteolysis. CDK5 appears to play a role in the events associated with neuronal response to ischemic injury.

Induction of the dual specificity phosphatase PAC1 in rat brain following seizure activity

Recurrent seizure activity leads to delayed neuronal death as well as to inflammatory responses involving microglia in hippocampal subfields CA1, CA3 and CA4. Since mitogen activated protein (MAP) kinases control neuronal apoptosis and trigger generation of inflammatory cytokines, their activation state could determine seizure-related brain damage. PAC1 is a dual specificity protein phosphatase inactivating MAP kinases which we have found to be undetectable in normal brain. Despite this, kainic acid-induced seizure activity lead to rapid (approximately 3 h) but transient appearance of PAC1 mRNA in granule cells of the dentate gyrus as well as in pyramidal CA1 neurons. This pattern changed with time and after 2-3 days PAC1 was induced in dying CA1 and CA3 neurons. At this time PAC1 mRNA was also expressed in white matter microglia as well as in microglia invading the damaged hippocampus. PAC1 may play an important role controlling MAP kinase involvement in both neuronal death and neuro-inflammation following excitotoxic damage.

DNA scission after focal brain ischemia. Temporal differences in two species

BACKGROUND AND PURPOSE

Species- and model-dependent differences in cell response to focal brain ischemia may underlie differences in adhesion receptor expression. The aim of this study was to quantitatively evaluate the spatial and temporal distribution of dUTP incorporation into damaged DNA, as an indicator of ischemic injury, in the corpus striatum.

METHODS

Cerebral ischemia was produced in 16 nonhuman primates and 19 rats by occluding the middle cerebral artery (MCA:O) with reperfusion for various periods. In situ dUTP was incorporated into cells with DNA damage by terminal deoxynucleotidyl transferase (TdT), DNA polymerase I, or the Klenow fragment of DNA polymerase. Dual immunolabeling experiments with immunoprobes against neuronal, vascular, or glial marker proteins were performed.

RESULTS

Significant topographical differences in dUTP between the two species were seen. In both models the TdT and polymerase I regions changed characteristically during focal ischemia. The number and density of dUTP-labeled cells increased with time from MCA:O and were dramatically different between the species (2P < .001). By 2 hours of ischemia, the density of dUTP label was 48.8 +/- 10.3 cells/mm2 in the primate and 2.4 +/- 0.8 cells/mm2 in the rat (2P < .05), but these values became nearly identical by 24 hours of reperfusion. In the primate, 80.0 +/- 6.6% of labeled cells displayed microtubule-associated protein-2 antigen (at 2-hour MCA:O), while 1.8 +/- 0.5% were associated with microvessels at 24 hours of reperfusion.

CONCLUSIONS

In situ detection of DNA damage, accomplished by three methods, reveals distinct temporal, topographical, and density differences in ischemic injury to cells in the primate and the rat corpus striatum as a result of MCA:O.

Delayed neuronal death in ischemic hippocampus involves stimulation of protein tyrosine phosphorylation

Glutamate triggers neuronal degeneration after ischemia-reperfusion in the brain. However, the details of intracellular signal transduction that propagates cell death remain unknown. The present work investigated whether protein tyrosine phosphorylation mediates neuronal death in the ischemic brain. Transient forebrain ischemia for 5-10 min in Mongolian gerbils or intoxication with the glutamate analogue kainic acid (12 mg/kg) in Sprague-Dawley rats caused neuronal death selectively in the hippocampus 2-4 days or 1 day later, respectively. Under these conditions, 160-, 115-, 105-, 92-, and 85-kDa proteins showed a significant increase in tyrosyl residue phosphorylation selectively in the hippocampus 3-12 h after ischemia or 4-8 h after kainic acid-induced seizures. Tyrosine kinases, including pp60c-src, were activated without a change of tyrosine phosphatases. Administration of radicicol, a selective inhibitor of tyrosine kinases, attenuated stimulation of tyrosine phosphorylation and hippocampal degeneration after ischemia or kainic acid injection. The results suggest that protein tyrosine phosphorylation might propagate delayed neuronal death in the mature hippocampus through glutamate overload after ischemia-reperfusion.