Activation of ERK and Akt signaling in focal cerebral ischemia: modulation by TGF-alpha and involvement of NMDA receptor

RNF144a induces ERK-dependent cell death under oxidative stress via downregulation of vaccinia-related kinase 3

Vaccinia-related kinase 3 (VRK3) has been reported to be a negative regulator of ERK (ERK1 and ERK2; also known as MAPK3 and MAPK1, respectively) that protects cells from persistent ERK activation and inhibits ERK-dependent apoptosis. Here we report that the E3 ubiquitin-protein ligase RNF144a promotes the degradation of VRK3 via polyubiquitylation and thus affects VRK3-mediated ERK activity. Under oxidative stress, VRK3 migrates from the nucleus to the cytoplasm, which increases its chance of interacting with RNF144a, thereby promoting the degradation of VRK3. Overexpression of RNF144a increases ERK activity via downregulation of VRK3 and promotes ERK-dependent apoptosis. In contrast, depletion of RNF144a increases the protein level of VRK3 and protects cells from excessive ERK activity. These findings suggest that VRK3 protects cells by suppressing oxidative stress-induced ERK, and that RNF144a sensitively regulates this process.

TGFα preserves oligodendrocyte lineage cells and improves white matter integrity after cerebral ischemia

Transforming growth factor α (TGF-α) has been reported to play important roles in neurogenesis and angiogenesis in the injured brain. The present study characterizes a novel role for TGFα in oligodendrocyte lineage cell survival and white matter integrity after ischemic stroke. Three days after transient (60 min) middle cerebral artery occlusion (tMCAO), TGFα expression was significantly increased in microglia/macrophages and neurons. Expression of the receptor of TGFα-epidermal growth factor receptor (EGFR)-was increased in glial cells after ischemia, including in oligodendrocyte lineage cells. TGFα knockout enlarged brain infarct volumes and exacerbated cell death in oligodendrocyte precursor cells (OPCs) and oligodendrocytes three days after tMCAO. TGFα-deficient mice displayed long-term exacerbation of sensorimotor deficits after tMCAO, and these functional impairments were accompanied by loss of white matter integrity and impaired oligodendrocyte replacement. In vitro studies confirmed that 5 or 10 ng/mL TGFα directly protected OPCs and oligodendrocytes against oxygen and glucose deprivation (OGD)-induced cell death, but exerted no effects on OPC differentiation. Further studies identified STAT3 as a key transcription factor mediating the effects of TGFα on OPCs and oligodendrocytes. In conclusion, TGFα provides potent oligodendrocyte protection against cerebral ischemia, thereby maintaining white matter integrity and improving neurological recovery after stroke.

Progesterone Protects Prefrontal Cortex in Rat Model of Permanent Bilateral Common Carotid Occlusion via Progesterone Receptors and Akt/Erk/eNOS

Sustained activation of pro-apoptotic signaling due to a sudden and prolonged disturbance of cerebral blood circulation governs the neurodegenerative processes in prefrontal cortex (PFC) of rats whose common carotid arteries are permanently occluded. The adequate neuroprotective therapy should minimize the activation of toxicity pathways and increase the activity of endogenous protective mechanisms. Several neuroprotectants have been proposed, including progesterone (P₄). However, the underlying mechanism of its action in PFC following permanent bilateral occlusion of common carotid arteries is not completely investigated. We, thus herein, tested the impact of post-ischemic P₄ treatment (1.7 mg/kg for seven consecutive days) on previously reported aberrant neuronal morphology and amount of DNA fragmentation, as well as the expression of progesterone receptors along with the key elements of Akt/Erk/eNOS signal transduction pathway (Bax, Bcl-2, cytochrome C, caspase 3, PARP, and the level of nitric oxide). The obtained results indicate that potential amelioration of histological changes in PFC might be associated with the absence of activation of Bax/caspase 3 signaling cascade and the decline of DNA fragmentation. The study also provides the evidence that P₄ treatment in repeated regiment of administration might be effective in neuronal protection against ischemic insult due to re-establishment of the compromised action of Akt/Erk/eNOS-mediated signaling pathway and the upregulation of progesterone receptors.

NMDA receptor-driven calcium influx promotes ischemic human cardiomyocyte apoptosis through a p38 MAPK-mediated mechanism

N-methyl-D-aspartate receptor (NMDAR) activity plays a key role in cerebral ischemia. Although NMDAR is also expressed in cardiomyocytes, little research has been performed on NMDAR activity in myocardial ischemia. Here, using an in vitro oxygen-glucose deprivation (OGD) cardiomyocyte model, we evaluated the effects of NMDAR activity upon calcium influx, viability, apoptosis, and investigated the roles of several key mitogen-activated protein kinases (MAPKs). Primary human neonatal cardiomyocytes were cultured under OGD conditions to mimic in vivo ischemic conditions. Enhancing NMDAR activity via NMDA significantly promoted calcium influx, decreased cell viability, increased apoptosis, and enhanced p38 MAPK phosphorylation in OGD cardiomyocytes (all P < 0.05). These effects were rescued by several calcium-channel blockers (ie, MK-801, La³⁺ , Gap26 peptide, 18β-glycyrrhetinic acid) but most potently rescued via the NMDAR-specific antagonist MK-801 or removal of extracellular free calcium (all P < 0.05). Knocking-down p38 MAPK activity by small-molecule inhibition or genetic methods significantly increased cell viability and reduced apoptosis (all P < 0.05). Enhancing p38 MAPK activity abolished MK-801's apoptosis-reducing effects in a p38 MAPK-dependent manner. In conclusion, NMDAR-driven calcium influx promotes apoptosis in ischemic human cardiomyocytes, an effect which can be attributed to enhanced p38 MAPK activity.

Hepatoprotective effects of limb ischemic post-conditioning in hepatic ischemic rat model and liver cancer patients via PI3K/ERK pathways

The most effective way of treating liver cancer is surgical resection, which usually requires blocking the hepatic portal circulation, and may result in hepatic ischemia-reperfusion injury (HIRI). It is of paramount importance to control HIRI for liver cancer surgical resection. In this study, a 70% ischemia-reperfusion (I/R) model of rat liver was established, and the protective effect and mechanism of limb ischemic post-conditioning (LIPOC) on HIRI was investigated. We show that LIPOC has a protective effect on hepatic ischemia-reperfusion injury in rats, which reduces the elimination of superoxide dismutase, thereby increasing oxygen free radical scavenging, decreasing lipid peroxidation, inhibiting neutrophil aggregation, as well as reducing TNFα, IL1β, and other inflammatory cytokines. In addition, LIPOC inhibited the apoptosis of hepatocytes induced by I/R injury, and decreased the Bax/Bcl-2 ratio. Furthermore, LIPOC promoted the phosphorylation of Akt and ERK1/2. The use of PI3K inhibitor LY294002 and ERK1/2 blocker PD98059 inhibited the phosphorylation of Akt and ERK1/2 caused by LIPOC and abolished the injury protection of liver I/R. Moreover, through 16 cases of hepatocellular carcinoma resections, we found that short-term LIPOC treatment significantly suppressed the elevated alanine aminotransferase, aspartic transaminase, and total bilirubin in the early post-operation of liver resection, and reduced reperfusion injury to the ischemic liver. In summary, our study demonstrates that LIPOC could be an effective method for HIRI in the clinical implementation of liver resection and uncovers the potential mechanism of LIPOC in the protective effects of HIRI.

Topiramate mitigates 3-nitropropionic acid-induced striatal neurotoxicity via modulation of AMPA receptors

Prevalence of glutamate receptor subunit 2 (GluR2)-lacking alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors is a hallmark of excitotoxicity-related neurodegenerative diseases. Topiramate (TPM) is a structurally novel anticonvulsant with a well-known modulatory effects on AMPA/kainate subtypes of glutamate receptors. The present study aimed at investigating the neuroprotective potential of TPM on 3-nitropropionic acid (3-NP)-induced striatal neurodegeneration and Huntington's disease-like symptoms. Rats were injected with 3-NP (10 mg/kg/i.p.) for 14 days. TPM (50 mg/kg/p.o.) was given once a day, 1 h before 3-NP. TPM amended 3-NP induced changes in neurobehavioral performance, striatal neurotransmitters levels and histopathological injury. 3-NP control rats showed a significant ablation in the mRNA expression of Ca²⁺-impermeable Glu2R subunit along with an elevation in its regulatory protein (protein interacting with C kinase-1) PICK1, an effect that was largely reversed by TPM. TPM in addition, enhanced the phosphorylation of the protein kinase B/glycogen synthase kinase-3β/cAMP response element binding protein (Akt/GSK-3β/CREB) cue. Moreover, improvement in oxidative status, suppression of caspase-3 activity and restoration of striatal BDNF were noticed following treatment with TPM. The current study revealed that TPM boosted the neuroprotective (Akt/GSK-3β/CREB) pathway by its negative modulatory effect on AMPA glutamate receptors as well as its direct antioxidant property.

Angelica sinensis Exerts Angiogenic and Anti-apoptotic Effects Against Cerebral Ischemia–Reperfusion Injury by Activating p38MAPK/HIF-1α/VEGF-A Signaling in Rats

This study evaluated the effects of Angelica sinensis extract [Dang Gui (DG)] administered before 60[Formula: see text]min of middle cerebral artery occlusion followed by 3[Formula: see text]d of reperfusion and investigated the involvement of mitogen-activated protein kinase (MAPK)/hypoxia-inducible factor (HIF)-1[Formula: see text] signaling in the cortical ischemic penumbra. DG was intraperitoneally administered at a dose of 0.25[Formula: see text]g/kg (DG-0.25g), 0.5[Formula: see text]g/kg (DG-0.5g), or 1[Formula: see text]g/kg (DG-1g) 30[Formula: see text]min before the onset of cerebral ischemia. Our study results revealed that DG-0.5g and DG-1g pretreatment effectively attenuated cerebral infarct and improved neurological deficits. DG-0.5g and DG-1g pretreatment significantly downregulated glial fibrillary acidic protein (GFAP), cytochrome c, and cleaved caspase-3 expression and upregulated phospho-p38 MAPK (p-p38 MAPK)/p38 MAPK, phospho-cAMP response element-binding protein (p-CREB)/CREB, cytosolic and mitochondrial phospho-Bad (p-Bad)/Bad ratios, and HIF-1[Formula: see text], vascular endothelial growth factor-A (VEGF-A), phospho-90 kDa ribosomal S6 kinase (p-p90RSK), and von Willebrand factor (vWF) expression in the cortical ischemic penumbra. Pretreatment with SB203580, a p38 MAPK inhibitor, dramatically abrogated the upregulating effects of DG-1g on p-p38 MAPK/p38 MAPK, p-CREB/CREB, and p-Bad/Bad ratios and HIF-1[Formula: see text], VEGF-A, and vWF expression and the downregulating effects of DG-1g on GFAP, cytochrome c, cleaved caspase-3, and cerebral infarction. DG-0.5g and DG-1g pretreatment provided neuroprotective effects against astrocyte-mediated cerebral infarction by activating angiogenic and anti-apoptotic signaling. Moreover, the angiogenic and anti-apoptotic effects of DG pretreatment can be attributed to the activation of p38 MAPK/HIF-1[Formula: see text]/VEGF-A/vWF signaling and p38 MAPK/HIF-1[Formula: see text]/VEGF-A/p-Bad-related regulation of cytochrome c/caspase-3 signaling, respectively, in the cortical ischemic penumbra 3[Formula: see text]d after reperfusion.

[Inhibitory effect of apatinib on HCT-116 cells and its mechanism]

OBJECTIVE

To investigate the inhibitory effects of apatinib on colorectal carcinoma HCT-116 cells in vitro and the signaling pathways involved.

METHODS

The cytotoxicity of different concentrations (0, 0.5, 1, 1.5, and 2 µmol/L) of apatinib in HCT-116 cells was assessed by MTT assay, using capecitabine as the positive control. The apoptosis rate of apatinib-treated HCT-116 cells was detected using flow cytometry, and the expressions of Bcl-2, Bax, and caspase-3 were determined with quantitative real-time PCR and Western blotting. The effect of apatinib on the expressions of Akt, pAkt, Erk1/2 and pErk1/2 in HCT-116 cells was evaluated using Western blotting.

RESULTS

Apatinib significantly inhibited the proliferation of HCT-116 cells in a concentration-dependent manner with an IC₅₀ value of 1.335 µmol/L. Flow cytometric analysis showed that apatinib significantly increased the apoptotic rate of HCT-116 cells dose-dependently. Apatinib induced the expression of the pro-apoptotic genes Bax and caspase-3 at both the mRNA and protein levels while inhibited the expression of the anti- apoptotic gene Bcl-2. The expressions of p-Akt and p-Erk1/2 were decreased in HCT-116 cells after apatinib treatment, but the total protein levels did not undergo obvious changes.

CONCLUSION

Apatinib inhibits the proliferation and induces apoptosis of HCT-116 cells by suppressing the phosphorylation of Erk1/2 and Akt in the MAPK/Erk and PI3K/Akt signaling pathways.

Enriched Environment Enhances Poststroke Neurological Function Recovery on Rat: Involvement of p-ERK1/2

BACKGROUND

Increasing evidence shows that exposure to an enriched environment (EE) after cerebral ischemia or reperfusion injury is neuroprotective in animal models, including that EE enhances functional recovery after ischemic stroke. However, the mechanism underlying this effect remains unclear. To clarify this critical issue, the current study investigated the effects of EE on the role of extracellular signal-regulated kinase (ERK) after cerebral ischemia or reperfusion injury of rat.

METHODS

Adult rats were subjected to ischemia induced by middle cerebral artery occlusion (MCAO) followed by reperfusion. Ladder walking task and limb-use asymmetry task were used to test the recovery of rat behavior on postoperative days 1, 3, 5, 7, 14 and days 3, 7, 14, respectively. On the eighth day after MCAO, infarct volume was assessed by 2,3,5-triphenyltetrazolium chloride staining. Expressions of phosphorylated ERK1/2 (p-ERK1/2) and total ERK1/2 were examined by western blot, and electron microscopy was used to evaluate the astrocytes morphology surround in the perivascular 14 days after MCAO.

RESULTS

EE improves the recovery of coordination and integration of motor movements on rats after cerebral ischemia or reperfusion injury. EE downregulates the level of p-ERK1/2 in the rat cortex after cerebral ischemia or reperfusion injury. Furthermore, EE reduces astrocytic swelling and injury.

CONCLUSIONS

These findings suggest that EE could promote rehabilitation after ischemia via regulation of p-ERK1/2 expression, which may provide a therapeutic approach for cerebral ischemia or reperfusion injury. The suppression of postischemic astrocytic swelling in the brain of the ischemic rats through the intervention of EE would be one of the underlying mechanisms in the protective effect of cerebral ischemia.

Repeated Estradiol Treatment Attenuates Chronic Cerebral Hypoperfusion-Induced Neurodegeneration in Rat Hippocampus

Although a substantial number of pre-clinical and experimental studies have investigated effects of 17β-estradiol, its precise molecular mechanism of action in the early state of chronic cerebral hypoperfusion remains controversial. The present study attempted to verify whether post-ischemic estradiol treatment (33.3 μg/kg for seven consecutive days) affects previously reported number of hippocampal apoptotic cells and amount of DNA fragmentation characteristic for apoptosis as well as the expression of key elements within synaptosomal Akt and Erk signal transduction pathways (NF-κB, Bax, Bcl-2, cytochrome C, caspase 3, and PARP). Additionally, alterations of aforementioned molecules linked to protection in various neurodegenerative disorders were monitored in the cytosolic, mitochondrial, and nuclear fractions associating investigated kinases and NF-κB with gene expression of their downstream effectors-Bcl-2, Bax, and caspase 3. The results revealed that an initial increase in the number of apoptotic cells and amount of DNA fragmentation induced by chronic cerebral hypoperfusion was significantly reduced by 17β-estradiol. In synaptic regions, an altered profile with respect to the protein expression of Bcl-2 and phosphorylated Akt was detected, although the level of other examined proteins was not modified. In other investigated sub-cellular fractions, 17β-estradiol elicited phosphorylation and translocation of Akt and Erk along with modulation of the expression of their subsequent effectors. Our findings support the concept that repeated post-ischemic 17β-estradiol treatment attenuates neurodegeneration induced by chronic cerebral hypoperfusion in hippocampus through the activation of investigated kinases and regulation of their downstream molecules in sub-cellular manner indicating a time window and regime of its administration as a valid therapeutic intervention.

Genistein attenuates brain damage induced by transient cerebral ischemia through up-regulation of ERK activity in ovariectomized mice

Stroke has severe consequences in postmenopausal women. As replacement therapy of estrogen have various adverse effects and the undermined outcomes. Genistein, a natural phytoestrogen, has been suggested to be a potential neuroprotective agent for such stroke patients. However, the role of genistein and its underlying mechanism in ovariectomized mice has not yet been evaluated. In the present study, ovariectomized mice were treated with genistein (10 mg/kg) or vehicle daily for two weeks before developing transient cerebral ischemia (middle cerebral artery occlusion). The neurological manifestation was evaluated, and infarct volumes were demonstrated by 2,3,5-triphenyltetrazolium chloride staining at 24 h after reperfusion. In addition, phosphorylation of extracellular signal-regulated kinase (ERK) was detected by Western blotting and immunofluorescence staining, and cellular apoptosis was evaluated in the ischemic penumbra. We found that treatment with genistein reduced infarct volumes, improved neurological outcomes and attenuated cellular apoptosis at 24 h after reperfusion. ERK1/2 showed increased phosphorylation by genistein treatment after reperfusion, and an ERK1/2 inhibitor U0126 abolished this protective effect of genistein in terms of infarct volumes, neurological scores and cellular apoptosis. Our findings indicate that treatment with genistein can reduce the severity of subsequent stroke episodes, and that this beneficial function is associated with ERK activation.

Small interfering RNA directed against CTMP reduces acute traumatic brain injury in a mouse model by activating Akt

OBJECTIVE

Protein kinase B (PKB/Akt), which is phosphorylated and activated by upstream activators, exerts critical neuroprotective effects by phosphorylating downstream targets after traumatic brain injury (TBI). Studies on the regulation of Akt will be crucial for our understanding of neuronal survival. The goal of this study is to investigate the effects of carboxyl-terminal modulator protein (CTMP) on phosphorylation of Akt and neurological function in a mouse model of TBI.

METHODS

Traumatic brain injury in mice was performed by a controlled cortical impact device. The expression of Akt, phospho-Akt, and CTMP was examined in the injured cortices by immunohistochemistry and Western blot analysis. To determine the effects of CTMP, small interfering RNAs (siRNAs) directed against CTMP were injected in mice with TBI, and the expression of phosphorylated Akt and neurological function were evaluated.

RESULTS

Phospho-Akt significantly increased at 4 hours post-TBI in the nucleus (P < 0.01) and remained at high levels until 72 hours after TBI, as shown by Western blot analysis. In the cytosol, the expression of phospho-Akt reached its peak at 4 hours post-TBI, but decreased markedly at 24 hours and maintained below pre-TBI levels until 72 hours post-TBI. Interestingly, the expression of CTMP significantly increased 4 hours after TBI (P < 0.01) and sustained those levels until 72 hours without dramatic changes. Treatment with CTMP siRNA effectively augmented the phosphorylation of Akt and significantly improved the neurological functional recovery up to 28 days post-TBI.

CONCLUSION

We conclude that Akt is phosphorylated and translocated to nucleus after TBI to exert neuroprotective effects. However, CTMP is simultaneously triggered to inhibit the phosphorylation of Akt. Inhibition of CTMP by siRNA improves the recovery of neurological functions after TBI.

PRAS40 plays a pivotal role in protecting against stroke by linking the Akt and mTOR pathways

The proline-rich Akt substrate of 40kDa (PRAS40) protein is not only a substrate of the protein kinase Akt but also a component of the mTOR complex 1 (mTORC1), thus it links the Akt and the mTOR pathways. We investigated the potential protective role of PRAS40 in cerebral ischemia and its underlying mechanisms by using rats with lentiviral over-expression of PRAS40 and mice with PRAS40 gene knockout (PRAS40 KO). Our results show that gene transfer of PRAS40 reduced infarction size in rats by promoting phosphorylation of Akt, FKHR (FOXO1), PRAS40, and mTOR. In contrast, PRAS40 KO increased infarction size. Although the PRAS40 KO under normal condition did not alter baseline levels of phosphorylated proteins in the Akt and mTOR pathways, PRAS40 KO that underwent stroke exhibited reduced protein levels of p-S6K and p-S6 in the mTOR pathway but not p-Akt, or p-PTEN in the Akt pathway. Furthermore, co-immunoprecipitation suggests that there were less interactive effects between Akt and mTOR in the PRAS40 KO. In conclusion, PRAS40 appears to reduce brain injury by converting cell signaling from Akt to mTOR.

Akt and mTOR mediate programmed necrosis in neurons

Necroptosis is a newly described form of regulated necrosis that contributes to neuronal death in experimental models of stroke and brain trauma. Although much work has been done elucidating initiating mechanisms, signaling events governing necroptosis remain largely unexplored. Akt is known to inhibit apoptotic neuronal cell death. Mechanistic target of rapamycin (mTOR) is a downstream effector of Akt that controls protein synthesis. We previously reported that dual inhibition of Akt and mTOR reduced acute cell death and improved long term cognitive deficits after controlled-cortical impact in mice. These findings raised the possibility that Akt/mTOR might regulate necroptosis. To test this hypothesis, we induced necroptosis in the hippocampal neuronal cell line HT22 using concomitant treatment with tumor necrosis factor α (TNFα) and the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. TNFα/zVAD treatment induced cell death within 4 h. Cell death was preceded by RIPK1–RIPK3–pAkt assembly, and phosphorylation of Thr-308 and Thr473 of AKT and its direct substrate glycogen synthase kinase-3β, as well as mTOR and its direct substrate S6 ribosomal protein (S6), suggesting activation of Akt/mTOR pathways. Pretreatment with Akt inhibitor viii and rapamycin inhibited Akt and S6 phosphorylation events, mitochondrial reactive oxygen species production, and necroptosis by over 50% without affecting RIPK1–RIPK3 complex assembly. These data were confirmed using small inhibitory ribonucleic acid-mediated knockdown of AKT1/2 and mTOR. All of the aforementioned biochemical events were inhibited by necrostatin-1, including Akt and mTOR phosphorylation, generation of oxidative stress, and RIPK1–RIPK3–pAkt complex assembly. The data suggest a novel, heretofore unexpected role for Akt and mTOR downstream of RIPK1 activation in neuronal cell death.

Activation of Akt/GSK-3beta/beta-catenin signaling pathway is involved in survival of neurons after traumatic brain injury in rats

OBJECTIVE

Apoptotic cell death is an important factor influencing the prognosis after traumatic brain injury (TBI). Akt/GSK-3beta/beta-catenin signaling plays a critical role in the apoptosis of neurons in several models of neurodegeneration. The goal of this study was to determine if the mechanism of cell survival mediated by the Akt/GSK-3beta/beta-catenin pathway is involved in a rat model of TBI.

METHODS

TBI was performed by a controlled cortical impact device. Expression of Akt, phospho-Akt, GSK-3beta, phospho-GSK-3beta, beta-catenin, phospho-beta-catenin were examined by immunohistochemistry and Western blot analysis. Double immunofluorenscent staining was used to observe the neuronal expression of the aforementioned subtrates. Terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling (TUNEL) staining was performed to identify apoptosis.

RESULTS

Western blot analysis showed that phospho-Akt significantly increased at 4 hours post-TBI, but decreased after 72 hours post-TBI. Phospho-GSK-3beta - phosphorylated by phospho-Akt - slightly increased at 4 hours post-TBI and peaked at 72 hours post-TBI. These changes in Phospho-GSK-3beta expression were accompanied by a marked increase in expression of phospho-beta-catenin at 4 hours post-TBI which was sustained until 7 days post-TBI. Double staining of phospho-Akt and NeuN revealed the colocalization of phospho-Akt positive cells and neuronal cells. In addition, double staining of phospho-Akt and TUNEL showed no colocalization of phospho-Akt cells and TUNEL-positive cells.

CONCLUSION

Phosphorylation of Akt (Ser473) and GSK3beta (Ser9) was accelerated in the injured cortex, and involved in the neuronal survival after TBI. Moreover, neuroprotection of beta-catenin against ischemia was partly mediated by enhanced and persistent activation of the Akt/GSK3beta signaling pathway.

Opiate drug use and the pathophysiology of neuroAIDS

Opiate abuse and HIV-1 have been described as interrelated epidemics, and even in the advent of combined anti-retroviral therapy, the additional abuse of opiates appears to result in greater neurologic and cognitive deficits. The central nervous system (CNS) is particularly vulnerable to interactive opiate-HIV-1 effects, in part because of the unique responses of microglia and astroglia. Although neurons are principally responsible for behavior and cognition, HIV-1 infection and replication in the brain is largely limited to microglia, while astroglia and perhaps glial progenitors can be latently infected. Thus, neuronal dysfunction and injury result from cellular and viral toxins originating from HIV-1 infected/exposed glia. Importantly, subsets of glial cells including oligodendrocytes, as well as neurons, express µ-opioid receptors and therefore can be direct targets for heroin and morphine (the major metabolite of heroin in the CNS), which preferentially activate µ-opioid receptors. This review highlights findings that neuroAIDS is a glially driven disease, and that opiate abuse may act at multiple glial-cell types to further compromise neuron function and survival. The ongoing, reactive cross-talk between opiate drug and HIV-1 co-exposed microglia and astroglia appears to exacerbate critical proinflammatory and excitotoxic events leading to neuron dysfunction, injury, and potentially death. Opiates enhance synaptodendritic damage and a loss of synaptic connectivity, which is viewed as the substrate of cognitive deficits. We especially emphasize that opioid signaling and interactions with HIV-1 are contextual, differing among cell types, and even within subsets of the same cell type. For example, astroglia even within a single brain region are heterogeneous in their expression of µ-, δ-, and κ-opioid receptors, as well as CXCR4 and CCR5, and Toll-like receptors. Thus, defining the distinct targets engaged by opiates in each cell type, and among brain regions, is critical to an understanding of how opiate abuse exacerbates neuroAIDS.

Phosphorylated mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2 may not always represent its kinase activity in a rat model of focal cerebral ischemia with or without ischemic preconditioning

The extracellular signal-regulated kinase (ERK) 1/2 protein requires a dual phosphorylation at conserved threonine and tyrosine residues to be fully activated under normal physiological conditions. Thus, ERK1/2 kinase activity is often defined by the quantity of phosphorylated kinase. However, this may not accurately represent its true activity under certain pathological conditions. We investigated whether ERK1/2 kinase activity is proportional to its phosphorylation state in a rat focal ischemia model with and without rapid ischemic preconditioning. We showed that phosphorylated-ERK1/2 protein levels were increased 2.6±0.07-fold, and ERK1/2 kinase activity was increased 10.6±1.9-fold in animals receiving ischemic preconditioning alone without test ischemia compared with sham group (P<0.05, n=6/group), suggesting that phosphorylated-ERK1/2 protein levels represent its kinase activity under these conditions. However, preconditioning plus test ischemia robustly blocked ERK1/2 kinase activity, whereas it increased phosphorylated-ERK1/2 protein levels beyond those receiving test ischemia alone, suggesting that phosphorylated-ERK1/2 protein levels were not representative of actual kinase activity in this pathological condition. In conclusion, protein phosphorylation levels of ERK1/2 do not always correspond to kinase activity, thus, measuring the true kinase activity is essential.

Induction of COX-2 enzyme and down-regulation of COX-1 expression by lipopolysaccharide (LPS) control prostaglandin E2 production in astrocytes

Pathological conditions and pro-inflammatory stimuli in the brain induce cyclooxygenase-2 (COX-2), a key enzyme in arachidonic acid metabolism mediating the production of prostanoids that, among other actions, have strong vasoactive properties. Although low basal cerebral COX-2 expression has been reported, COX-2 is strongly induced by pro-inflammatory challenges, whereas COX-1 is constitutively expressed. However, the contribution of these enzymes in prostanoid formation varies depending on the stimuli and cell type. Astrocyte feet surround cerebral microvessels and release molecules that can trigger vascular responses. Here, we investigate the regulation of COX-2 induction and its role in prostanoid generation after a pro-inflammatory challenge with the bacterial lipopolysaccharide (LPS) in astroglia. Intracerebral administration of LPS in rodents induced strong COX-2 expression mainly in astroglia and microglia, whereas COX-1 expression was predominant in microglia and did not increase. In cultured astrocytes, LPS strongly induced COX-2 and microsomal prostaglandin-E(2) (PGE(2)) synthase-1, mediated by the MyD88-dependent NFκB pathway and influenced by mitogen-activated protein kinase pathways. Studies in COX-deficient cells and using COX inhibitors demonstrated that COX-2 mediated the high production of PGE(2) and, to a lesser extent, other prostanoids after LPS. In contrast, LPS down-regulated COX-1 in an MyD88-dependent fashion, and COX-1 deficiency increased PGE(2) production after LPS. The results show that astrocytes respond to LPS by a COX-2-dependent production of prostanoids, mainly vasoactive PGE(2), and suggest that the coordinated down-regulation of COX-1 facilitates PGE(2) production after TLR-4 activation. These effects might induce cerebral blood flow responses to brain inflammation.

Experimental evidence of Ginkgo biloba extract EGB as a neuroprotective agent in ischemia stroke rats

EGb761 is a standard extract of Ginkgo biloba, which is a kind of traditional Chinese herbs that has widely used in clinic treatment of stroke in China. However, its effects against ischemic stroke have not been evaluated comprehensively and its neuroprotective mechanism has not really been explored. In the present study, magnetic resonance diffusion-weighted imaging (DWI), neurological behavior and TTC staining were used to evaluate the therapeutic effect of EGb761 in rat ischemic models. Additionally, Western blot and immunohistochemistry were performed to measure the phosphorylations of cAMP response element binding protein (CREB) and Akt as well as the expression of brain-derived neurotrophic factor (BDNF) in rat brains. The results showed that Ginkgo biloba extract injection significantly increased the apparent diffusion coefficient (ADC) value and average diffusion coefficient (DCavg) value both in the peripheral zone and central zone, improved behavior scores, as well as enhanced the phosphorylations of AKT, CREB and the expression of BDNF in the brains. All these data demonstrate that EGb761 had significant therapeutic effects on ischemic stroke and it perhaps worked through activating the Akt-CREB-BDNF pathway.

Melatonin combats molecular terrorism at the mitochondrial level

The intracellular environmental is a hostile one. Free radicals and related oxygen and nitrogen-based oxidizing agents persistently pulverize and damage molecules in the vicinity of where they are formed. The mitochondria especially are subjected to frequent and abundant oxidative abuse. The carnage that is left in the wake of these oxygen and nitrogen-related reactants is referred to as oxidative damage or oxidative stress. When mitochondrial electron transport complex inhibitors are used, e.g., rotenone, 1-methyl-1-phenyl-1,2,3,6-tetrahydropyridine, 3-nitropropionic acid or cyanide, pandemonium breaks loose within mitochondria as electron leakage leads to the generation of massive amounts of free radicals and related toxicants. The resulting oxidative stress initiates a series of events that leads to cellular apoptosis. To alleviate mitochondrial destruction and the associated cellular implosion, the cell has at its disposal a variety of free radical scavengers and antioxidants. Among these are melatonin and its metabolites. While melatonin stimulates several antioxidative enzymes it, as well as its metabolites (cyclic 3-hydroxymelatonin, N¹-acetyl-N²-formyl-5-methoxykynuramine and N¹-acetyl-5-methoxykynuramine), likewise effectively neutralize free radicals. The resulting cascade of reactions greatly magnifies melatonin's efficacy in reducing oxidative stress and apoptosis even in the presence of mitochondrial electron transport inhibitors. The actions of melatonin at the mitochondrial level are a consequence of melatonin and/or any of its metabolites. Thus, the molecular terrorism meted out by reactive oxygen and nitrogen species is held in check by melatonin and its derivatives.

WITHDRAWN: Comprehensive evaluation of neuroprotective effects of Ginkgo biloba extract EGB against ischemic stroke

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Growth factors improve neurogenesis and outcome after focal cerebral ischemia

Stem cells have been proposed as a new form of cell-based therapy in a variety of disorders, including acute and degenerative brain diseases. Endogenous neural stem cells (eNSC) reside in the subventricular zone and in the subgranular zone of the hippocampus. eNSC are capable of self-renewal and differentiation into functional glia and neurons. Unfortunately, spontaneous brain regeneration is inefficient for clinically significant improvement following brain injury. However, eNSC responses may be augmented considerably by perturbing the pathways governing cell proliferation, migration and differentiation by application of exogenous growth factors. Importantly, current evidence suggests that such perturbations may lead to better functional outcome after stroke. This article summarizes the progress made in this field.

Akt1 gene deletion and stroke

Activation of Akt has been implicated as a major contributor to neuronal survival after an ischemic insult. Numerous neuroprotective agents have been shown to augment Akt activity, suggesting that this protein represents a major mechanism of cellular salvage after injury. Estrogen is known to augment Akt, but the possibility that Akt plays a differential role in the male and female brain has yet to be evaluated. In this study, we employed both pharmacological and genetic approaches to investigate the role of Akt in stroke. Utilizing a focal stroke model we show that deletion of the Akt1 isoform does not affect stroke outcome in either male or female mice. Akt1 deficient mice had equivalent levels of phosphorylated Akt (p-Akt) when compared to their WT controls following stroke suggesting that alternative isoforms can compensate for Akt1 loss. Secondly, estrogen's neuroprotective effect is maintained in Akt1(-/-) mice and estrogen exposure did not enhance p-Akt levels in WT female mice. Thirdly, we show that inhibiting Akt using the direct pan-Akt inhibitor triciribine has no effect on stroke outcome despite dramatic reductions in p-Akt. Our study demonstrates the limitations of genetic mouse models and suggests that the importance of Akt to ischemic outcome remains unclear.

Neuroprotection and free radical scavenging effects of Osmanthus fragrans

The ethanol extract of dried flowers Osmanthus fragrans (OFE) was assessed for free radical scavenging effects measured by the bleaching of the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical, scavenging of the hydroxyl anion, investigation of the ferric reducing/antioxidant power (FRAP) and lipid-peroxidation inhibition in rat tissues. OFE contained a high amount of total flavonoid and polyphenol. OFE presented the effects in the metal reducing power, FRAP assay with IC(50) values of 0.23 microg/ml, and 7.74 microg/ml, respectively. OFE presented similar activities toward the DPPH and hydroxyl anion scavenging ability with IC(50) values of 10 microg/ml. OFE with IC(50 )values between 46 and 97 microg/ml inhibited lipid peroxidation initiated by ferrous chloride in rat brain, liver, heart and kidney mitochodrias. Moreover, the neuroprotective activity of OFE was investigated under different insults (glutamate, arachidonic acid, and 6-hydroxydopamine) in Wistar rat primary cortical neurons. OFE with EC(50 )values between 66 and 165 microg/ml attenuated the neurotoxicity on MTT and LDH assays. In addition, the AKT protein expression of excitotoxicity and oxidative stress was displayed by western blotting analysis. OFE could up-regulate the glutamate and 6-OHDA decreased AKT expression. This is the first demonstration of the neuroprotective, free radical scavenging and anti-oxidative effects of O. fragrans.

Constitutively active calcineurin mediates delayed neuronal death through Fas-ligand expression via activation of NFAT and FKHR transcriptional activities in mouse brain ischemia

We recently demonstrated that a constitutively active form of calcineurin (CaN) is generated by calpain-mediated limited proteolysis following brain ischemia. The calpain-induced CaN activation mediated delayed neuronal death through translocation of nuclear factor of activated T-cells (NFAT) into nuclei after brain ischemia. We also previously demonstrated that activation of forkhead in rhabdomyosarcoma (FKHR), a forkhead transcription factor and substrate of protein kinase-B (Akt), mediated ischemia-induced neuronal death through Fas-ligand expression in gerbil hippocampus. FKHR activation occurred through decreased Akt activity and concomitant dephosphorylation mediated by undefined phosphatases. In this study, we show that phosphorylated Ser-256 of FKHR is dephosphorylated by constitutively active CaN and that in turn FKHR forms a complex with CaN that is translocated into nuclei after brain ischemia. After nuclear translocation of NFAT and FKHR, both NFAT and FKHR stimulated expression of Fas-ligand by binding to its promoter region. Consistent with activation of the Fas-ligand promoter by FKHR dephosphorylation, Fas-ligand expression increased 2 days after ischemia/reperfusion, and treatment with the CaN inhibitor FK506 inhibited that expression. These results suggest that FKHR is a downstream target of CaN and that constitutively active CaN mediates delayed neuronal death through Fas-ligand expression via up-regulation of both NFAT and FKHR transcriptional activity in brain ischemia.

Kainate induces AKT, ERK and cdk5/GSK3beta pathway deregulation, phosphorylates tau protein in mouse hippocampus

Acute treatment with kainate 30 mg/kg (KA) produced behavioral alterations and reactive gliosis. However, it did not produce major death of mouse hippocampal neurons, indicating that concentrations were not cytotoxic. KA caused rapid and temporal Erk phosphorylation (at 6h) and Akt dephosphorylation (1-3 days). Concomitantly, the activation of GSK3beta was increased 1-3 days after KA. After 7 days, a reduction in GSK3beta activation was observed. Caspase-3 activity increased, but to a lesser extent than calpain activation (measured by fluorimetry and calpain-cleaved alpha-spectrin). As calpain is involved in cdk5 activation, and cdk5 is related to GSK3beta, the cdk5/p25 pathway was examined. Results showed that the p25/p35 ratio in KA-injected mice for 3 days was 73.6% higher than control levels. However, no changes in cdk5 expression were detected. Both Western blot and immunohistochemistry against p-Tau(Thr(231)) indicated an increase at this phosphorylated site of tau protein. Indeed an increase in p-Tau(Ser(199)) and p-Tau(Ser(396)) was observed by Western blot. Our results demonstrate that tau hyperphosphorylation, induced by KA, is due to an increase in GSK3beta/cdk5 activity in combination with an inactivation of Akt. This indicates that the calpain/cdk5 pathway for tau phosphorylation has a potential role in delayed apoptotic death evoked by excitotoxicity. Moreover, the subsequent activation of caspase and calpain proteases leads to dephosphorylation of tau, thus increasing microtubular destructuration. Taken together, our results provide new insights in the activation of several kinase-pathways implicated in cytoskeletal alterations that are a common feature of neurodegenerative diseases.

Apoptosis: Future Targets for Neuroprotective Strategies

Focal permanent or transient cerebral artery occlusion produces massive cell death in the central core of the infarction, whereas in the peripheral zone (penumbra) nerve cells are subjected to various determining survival and death signals. Cell death in the core of the infarction and in the adult brain is usually considered a passive phenomenon, although events largely depend on the partial or complete disruption of crucial metabolic pathways. Cell death in the penumbra is currently considered an active process largely dependent on the activation of cell death programs leading to apoptosis. Yet cell death in the penumbra includes apoptosis, necrosis, intermediate and other forms of cell death. A rather simplistic view implies poor prospects regarding cell survival in the core of the infarction and therapeutic expectations in the control of cell death and cell survival in the penumbra. However, the capacity for neuroprotection depends on multiple factors, primarily the use of the appropriate agent, at the appropriate time and during the appropriate interval. Understanding the mechanisms commanding cell death and survival area is as important as delimiting the therapeutic time window and the facility of a drug to effectively impact on specific targets. Moreover, the detrimental effects of homeostasis and the activation of multiple pathways with opposing signals following ischemic stroke indicate that better outcome probably does not depend on a single compound but on several drugs acting in combination at the optimal time in a particular patient.

Akt contributes to neuroprotection by hypothermia against cerebral ischemia in rats

Activation of the Akt/protein kinase B (PKB) kinase pathway can be neuroprotective after stroke. Akt is activated by growth factors via a phosphorylation-dependent pathway involving the kinases phosphoinositide 3 (PI3) kinase and phosphoinositide-dependent protein kinase-1 (PDK1) and is negatively regulated by phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Akt kinase blocks apoptosis by phosphorylating the substrates forkhead transcription factor (FKHR) and glycogen synthase kinase 3beta (GSK3beta). We found that intra-ischemic hypothermia (30 degrees C) reduced infarct size and improved functional outcomes up to 2 months. Changes in phosphorylation levels of Akt, as measured by Western blots and immunostaining, differed from levels of Akt activity measured in an in vitro assay in normothermic animals. Hypothermia blocked most of these changes and maintained Akt activity. Inhibition of PI3/Akt enlarged infarct size in hypothermic animals. Hypothermia improved phosphorylation of PDK1, PTEN, and FKHR. Hypothermia did not improve GSK3beta (Ser9) phosphorylation but blocked the nuclear translocation of phosphorylated beta-catenin (Ser33/37/Thr41) downstream of GSK3beta. Phosphorylation levels of PTEN, Akt, and Akt substrate decreased before apoptotic cytochrome c release and degradation of microtubule-associated protein-2, a marker of neuronal survival. Hypothermia may protect from ischemic damage in part by preserving Akt activity and attenuating the apoptotic effects of PTEN, PDK1, and FKHR.

Lead neurotoxicity: From exposure to molecular effects

The effects of lead (Pb(2+)) on human health have been recognized since antiquity. However, it was not until the 1970s that seminal epidemiological studies provided evidence on the effects of Pb(2+) intoxication on cognitive function in children. During the last two decades, advances in behavioral, cellular and molecular neuroscience have provided the necessary experimental tools to begin deciphering the many and complex effects of Pb(2+) on neuronal processes and cell types that are essential for synaptic plasticity and learning and memory in the mammalian brain. In this review, we concentrate our efforts on the effects of Pb(2+) on glutamatergic synapses and specifically on the accumulating evidence that the N-methyl-D-aspartate type of excitatory amino acid receptor (NMDAR) is a direct target for Pb(2+) effects in the brain. Our working hypothesis is that disruption of the ontogenetically defined pattern of NMDAR subunit expression and NMDAR-mediated calcium signaling in glutamatergic synapses is a principal mechanism for Pb(2+)-induced deficits in synaptic plasticity and in learning and memory documented in animal models of Pb(2+) neurotoxicity. We provide an introductory overview of the magnitude of the problem of Pb(2+) exposure to bring forth the reality that childhood Pb(2+) intoxication remains a major public health problem not only in the United States but worldwide. Finally, the latest research offers some hope that the devastating effects of childhood Pb(2+) intoxication in a child's ability to learn may be reversible if the appropriate stimulatory environment is provided.

Tissue-plasminogen activator-induced ischemic brain injury is reversed by melatonin: role of iNOS and Akt

In vivo studies showed that tissue-plasminogen activator (t-PA) may aggravate neuronal injury after focal cerebral ischemia. We hypothesized that t-PA impairs survival-promoting cell signaling in the ischemic brain, which may be reversed by a neuroprotectant, i.e. melatonin. We examined the effects of t-PA (10 mg/kg, i.v.), administered alone or in combination with melatonin (4 mg/kg, i.p.), on ischemic injury, inducible nitric oxide synthase (iNOS) expression as well as Akt, Bcl-X(L) and caspase-3 signaling following 90 min of intraluminal middle cerebral artery (MCA) occlusion in mice. t-PA, delivered immediately after reperfusion onset, increased infarct volume at 24 hr after MCA occlusion, in accordance with previous findings. Melatonin reduced infarct size when administered alone and reversed the t-PA-induced brain injury. Immunohistochemical studies showed that t-PA treatment was associated with an accumulation of iNOS positive cells in ischemic brain areas, which was abolished after co-delivery of melatonin. Western blots revealed that t-PA decreased phosphorylated Akt levels, but did not influence Bcl-X(L) expression and caspase-3 activity in ischemic brain lysates. Co-treatment with melatonin restored phosphorylated Akt levels, increased Bcl-X(L) expression and reduced caspase-3 activity. We provide evidence that t-PA-induced brain injury is accompanied by an activation of iNOS and inhibition of phosphatidylinositol-3 kinase/Akt. That melatonin reversed these signaling changes and the t-PA-induced brain injury makes this indole attractive as an add-on treatment with thrombolytics.

D-aspartate modulates transcriptional activity in Harderian gland of frog,Rana esculenta: Morphological and molecular evidence

In the green frog, Rana esculenta, a substantial amount of D-aspartate (D-Asp) is found endogenously within the Harderian gland (HG) following its synthesis from L-aspartate (L-Asp) by an aspartate racemase. The frog HG is an orbital seromucoid gland that displays seasonal changes in secretory activity. Our in vivo experiments, consisting of i.p. injection of 2.0 mumol/g b.w. D-Asp in frogs collected during two periods of differing glandular activity (high or medium-low secretory activity), revealed that HG can to take up and accumulate D-Asp and that this amino acid may modulate the exocrine secretion through a kinase pathway. At a time when the gland shows relatively low secretory activity, i.p. administration of D-Asp rapidly induced activation of ERK1 and an increase in cells active in RNA synthesis. This increase in transcriptional activity was followed by a significant increase in mucous secretion. By contrast, administration of exogenous D-Asp when HG was showing high activity rapidly induced inhibition of both ERK1 and transcriptional activity. Since D-Asp is known to be recognized by receptors for N-methyl-D-aspartic acid (NMDA), it is possible that in the HG, D-Asp mediated NMDA activation may enhance the kinase pathway. The above activation of opposing stimulatory and inhibitory processes could reflect different levels of NMDA-receptor activity, which could vary as a function of the level of gland activity. This study provides the first evidence of a role for this excitatory amino acid in exocrine secretion. The effects of D-Asp in HG appear to be specific since they were not seen in frogs treated with other D- or L-amino acids with known excitatory effects on neurosecretion.

Signal transduction pathways involved in melatonin-induced neuroprotection after focal cerebral ischemia in mice

Because of its favorable action profile in humans, melatonin is a particularly interesting candidate as a neuroprotectant in acute ischemic stroke. Until now, the signaling mechanisms mediating melatonin's neuroprotective actions remained essentially uninvestigated. Herein, we examined the effects of melatonin, administered either orally for 9 wk as a stroke prophylactic (4 mg/kg/day) or intraperitoneally immediately after reperfusion onset (4 mg/kg), on the activation of signal transduction pathways in mice submitted to 90 min of intraluminal middle cerebral artery occlusion, followed by 24 hr of reperfusion. In these studies, melatonin significantly reduced ischemic infarct size by approximately 30-35%, as compared with animals receiving diluent (sham) treatment, independent of whether the indole was administered prior to or after ischemia. Under both conditions, animals receiving melatonin exhibited elevated phosphorylated Akt levels in their brains, as determined by Western blots. Additionally, phosphorylation levels of mitogen-activated protein kinase/extracellular-regulated kinase (ERK)-1/-2 and Jun kinase (JNK)-1/-2 were increased following prophylactic, but not acute, melatonin treatment. Our data suggest a role of phosphatidyl inositol-3 kinase/Akt signaling in acute melatonin-induced neuroprotection, while ERK-1/-2 and/or JNK-1/-2 rather appear to be involved in melatonin's long-term effects.

Lead stimulates ERK1/2 and p38MAPK phosphorylation in the hippocampus of immature rats

Lead (Pb(2+)) is widely recognized as a neurotoxicant whose mechanisms of action are not completely established. We have previously demonstrated that Pb(2+) can activate the p38(MAPK) pathway and increase the phosphorylation of Hsp27 in bovine adrenal chromaffin cells and human SH SY5Y cells over a short incubation period (1 h). In the present work we analyzed the effects of Pb(2+) administered in vivo on the level and the phosphorylation state of ERK1/2 and p38(MAPK) in the hippocampus of immature rats. Rats were treated with lead acetate (2, 8 or 12 mg/kg, i.p.) or saline (control) over the 8th to 12th postnatal days, and hippocampal slices were prepared on the 14th day. The Pb(2+) level in the lead-treated animals increased 2.5-6-fold in the blood (3.0-6.0 microg/dl) and 2.0-3.0-fold in the forebrain (78-103 ng/g wet weight), compared to control (saline). The phosphorylation of both ERK1/2 and p38(MAPK) was significantly increased by prior exposure to Pb(2+) in vivo. In in vitro experiments, hippocampal slices from 14-day-old rats were exposed to Pb(2+) (1-10 microM) for 1 and 3 h. There were no changes in the phosphorylation state of ERK and p38(MAPK) for 1-h incubation, whereas a significant increase of ERK1/2 and p38(MAPK) phosphorylation by Pb(2+) (5 microM) was observed for the 3-h incubation. Cell viability measured using MTT was not modified in any of the conditions tested. These results indicate that the phosphorylation of hippocampal ERK1/2 and p38(MAPK) is stimulated by lead in a period of rapid brain development, an effect that may underlie, at least in part, the neurotoxicty elicited by this metal.

Transforming growth factor-alpha attenuates N-methyl-D-aspartic acid toxicity in cortical cultures by preventing protein synthesis inhibition through an Erk1/2-dependent mechanism

Transforming growth factor-alpha (TGF-alpha), a ligand of the epidermal growth factor receptor, reduces the infarct size after focal cerebral ischemia in rat, but the molecular basis underlying the protection is unknown. Excitotoxicity and global inhibition of translation are acknowledged to contribute significantly to the ischemic damage. Here we studied whether TGF-alpha can rescue neurons from excitotoxicity in vitro and how it affects calcium homeostasis, protein synthesis, and the associated Akt and extracellular signal-regulated kinase 1/2 (Erk1/2) intracellular signaling pathways in mixed neuron-glia cortical cultures. We found that 100 ng/ml TGF-alpha attenuated neuronal cell death induced by a 30-min exposure to 35 microM N-methyl-D-aspartic acid (NMDA) (as it reduced lactate dehydrogenase release, propidium iodide staining, and caspase-3 activation) and decreased the elevation of intracellular Ca2+ elicited by NMDA. TGF-alpha induced a prompt and sustained phosphorylation of Erk1/2 and prevented the loss of Akt-P induced by NMDA 3 h after exposure. The protective effect of TGF-alpha was completely prevented by PD 98059, an inhibitor of the Erk1/2 pathway. Studies of incorporation of [3H]leucine into proteins showed that NMDA decreased the rate of protein synthesis, and TGF-alpha attenuated this effect. TGF-alpha stimulated the phosphorylation of the eukaryotic initiation factor 4E (eIF4E) but did not affect eIF2 alpha, two proteins involved in translation regulation. PD 98059 abrogated the TGF-alpha effect on eIF4E. Our data demonstrate that TGF-alpha exerts a neuroprotective action against NMDA toxicity, in which Erk1/2 activation plays a key role, and suggest that the underlying mechanisms involve recovery of translation inhibition, mediated at least in part by eIF4E phosphorylation.