Comparative study of survival signal withdrawal- and 4-hydroxynonenal-induced cell death in cerebellar granule cells

Effects of Pituitary Adenylate Cyclase Activating Polypeptide on Cell Death

Pituitary adenylate cyclase activating polypeptide (PACAP) was first isolated as a hypothalamic peptide based on its efficacy to increase adenylate cyclase (AC) activity. It has a widespread distribution throughout the body including the nervous system and peripheral organs, where PACAP exerts protective effects both in vivo and in vitro through its anti-apoptotic, anti-inflammatory, and antioxidant functions. The aim of the present paper was to review the currently available literature regarding the effects of PACAP on cell death in vitro in neural and non-neural cells. Among others, its effect on apoptosis can be detected in cerebellar granule cells against different toxic stimuli. Different neural cell types from the cerebral cortex are also prevented from cell death. PACAP also shows effects on cell death in cells belonging to the peripheral nervous system and protects both neural and non-neural cells of sensory organs. In addition, cell survival-promoting effect can be observed in different peripheral organ systems including cardiovascular, immune, respiratory, gastrointestinal, urinary, and reproductive systems. The studies summarized here indicate its noteworthy effect on cell death in different in vitro models, suggesting PACAP’s potential therapeutic usage in several pathological conditions.

Toll-like Receptor 4 Signaling is Critical for the Adaptive Cellular Stress Response Effects Induced by Intermittent Fasting in the Mouse Brain

Among different kinds of dietary energy restriction, intermittent fasting (IF) has been considered a dietary regimen which causes a mild stress to the organism. IF can stimulate proteins and signaling pathways related to cell stress that can culminate in the increase of the body resistance to severe stress conditions. Energy intake reduction induced by IF can induce modulation of receptors, kinases, and phosphatases, which in turn can modulate the activation of transcription factors such as NF-E2-related factor 2 (NRF2) and cAMP response element-binding (CREB) which regulate the transcription of genes related to the translation of proteins such as growth factors: brain-derived neurotrophic factor (BDNF), chaperone proteins: heat shock proteins (HSP), and so on. It has been shown that toll-like receptors (TLRs) are important molecules in innate immune response which are present not only in the periphery but also in neurons and glial cells. In central nervous system, TLRs can exert functions related to set up responses to infection, as well as influence neural progenitor cell proliferation and differentiation, being involved in cognitive parameters such as learning and memory. Little is known about the involvement of TLR4 on the beneficial effects induced by IF protocol. The present work investigated the effects of IF on memory and on the signaling mechanisms associated with NRF2 and CREB in Tlr4 knockout mice. The results suggest that TLR4 participates in the modulatory effects of IF on oxidative stress levels, on the transcription factors CREB and NRF2, and on BDNF and HSP90 expressions in hippocampus.

Therapeutic potential of PACAP for neurodegenerative diseases

Pituitary adenylate cyclase activating polypeptide (PACAP) is widely expressed in the central and peripheral nervous system. PACAP can initiate multiple signaling pathways through binding with three class B G-protein coupled receptors, PAC1, VPAC1 and VPAC2. Previous studies have revealed numerous biological activities of PACAP in the nervous system. PACAP acts as a neurotransmitter, neuromodulator and neurotrophic factor. Recently, its neuroprotective potential has been demonstrated in numerous in vitro and in vivo studies. Furthermore, evidence suggests that PACAP might move across the blood-brain barrier in amounts sufficient to affect the brain functions. Therefore, PACAP has been examined as a potential therapeutic method for neurodegenerative diseases. The present review summarizes the recent findings with special focus on the models of Alzheimer's disease (AD) and Parkinson's disease (PD). Based on these observations, the administered PACAP inhibits pathological processes in models of AD and PD, and alleviates clinical symptoms. It thus offers a novel therapeutic approach for the treatment of AD and PD.

Reactive oxygen/nitrogen species and their functional correlations in neurodegenerative diseases

The continuous production and efflux of reactive oxygen/nitrogen species from endogenous and exogenous sources can damage biological molecules and initiate a cascade of events. Mitochondria are pivotal in controlling cell survival and death. Cumulative oxidative stress, disrupted mitochondrial respiration, and mitochondrial damage are related with various neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and others. Biochemical cascades of apoptosis are mediated in signaling molecules, including protein kinases and transcription factors. The expressions in the pro-apoptotic signal transduction networks may indeed promote cell death and degeneration in brain cells. The regulation of that protein phosphorylation by kinases and phosphatases is emerging as a prerequisite mechanism in the control of the apoptotic cell death program. In this review, we attempt to put forth the evidence for possible mechanistic explanations for involvement of free radicals in the pathogenesis of neurodegenerative diseases.

Resveratrol restores Nrf2 level and prevents ethanol-induced toxic effects in the cerebellum of a rodent model of fetal alcohol spectrum disorders

In humans, ethanol exposure during pregnancy produces a wide range of abnormalities in infants collectively known as fetal alcohol spectrum disorders (FASD). Neuronal malformations in FASD manifest as postnatal behavioral and functional disturbances. The cerebellum is particularly sensitive to ethanol during development. In a rodent model of FASD, high doses of ethanol (blood ethanol concentration 80 mM) induces neuronal cell death in the cerebellum. However, information on potential agent(s) that may protect the cerebellum against the toxic effects of ethanol is lacking. Growing evidence suggests that a polyphenolic compound, resveratrol, has antioxidant and neuroprotective properties. Here we studied whether resveratrol (3,5,4'-trihydroxy-trans-stilbene), a phytoalexin found in red grapes and blueberries, protects the cerebellar granule neurons against ethanol-induced cell death. In the present study, we showed that administration of resveratrol (100 mg/kg) to postnatal day 7 rat pups prevents ethanol-induced apoptosis by scavenging reactive oxygen species in the external granule layer of the cerebellum and increases the survival of cerebellar granule cells. It restores ethanol-induced changes in the level of transcription factor nuclear factor-erythroid derived 2-like 2 (nfe2l2, also known as Nrf2) in the nucleus. This in turn retains the expression and activity of its downstream gene targets such as NADPH quinine oxidoreductase 1 and superoxide dismutase in cerebellum of ethanol-exposed pups. These studies indicate that resveratrol exhibits neuroprotective effects in cerebellum by acting at redox regulating proteins in a rodent model of FASD.

Past, present and future therapeutics for cerebellar ataxias

Cerebellar ataxias are a group of disabling neurological disorders. Patients exhibit a cerebellar syndrome and can also present with extra-cerebellar deficits, namely pigmentary retinopathy, extrapyramidal movement disorders, pyramidal signs, cortical symptoms (seizures, cognitive impairment/behavioural symptoms), and peripheral neuropathy. Recently, deficits in cognitive operations have been unraveled. Cerebellar ataxias are heterogeneous both at the phenotypic and genotypic point of view. Therapeutical trials performed during these last 4 decades have failed in most cases, in particular because drugs were not targeting a deleterious pathway, but were given to counteract putative defects in neurotransmission. The identification of the causative mutations of many hereditary ataxias, the development of relevant animal models and the recent identifications of the molecular mechanisms underlying ataxias are impacting on the development of new drugs. We provide an overview of the pharmacological treatments currently used in the clinical practice and we discuss the drugs under development.

Distribution and functional characterization of pituitary adenylate cyclase-activating polypeptide receptors in the brain of non-human primates

The distribution and density of pituitary adenylate cyclase-activating polypeptide (PACAP) binding sites have been investigated in the brain of the primates Jacchus callithrix (marmoset) and Macaca fascicularis (macaque) using [(125)I]-PACAP27 as a radioligand. PACAP binding sites were widely expressed in the brain of these two species with particularly high densities in the septum, hypothalamus and habenula. A moderate density of recognition sites was seen in all subdivisions of the cerebral cortex with a heterogenous distribution, the highest concentrations occurring in layers I and VI while the underlying white matter was almost devoid of binding sites. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed intense expression of the mRNAs encoding the short and hop-1 variants of pituitary adenylate cyclase-activating polypeptide-specific receptor (PAC1-R) in the cortex of both marmoset and macaque, whereas vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide mutual receptor, subtype 1 (VPAC1-R) and vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide mutual receptor, subtype 2 (VPAC2-R) mRNAs were expressed at a much lower level. In situ hybridization histochemistry showed intense expression of PAC1-R and weak expression of VPAC1-R mRNAs in layer IV of the cerebral cortex. Incubation of cortical tissue slices with PACAP induced a dose-dependent stimulation of cyclic AMP formation, indicating that PACAP binding sites correspond to functional receptors. Moreover, treatment of primate cortical slices with 100 nM PACAP significantly reduced the activity of caspase-3, a key enzyme of the apoptotic cascade. The present results indicate that PACAP should exert the same neuroprotective effect in the brain of primates as in rodents and suggest that PAC1-R agonists may have a therapeutic value to prevent neuronal cell death after stroke or in specific neurodegenerative diseases.

Neurotrophic effects of PACAP in the cerebellar cortex

In the rodent cerebellum, PACAP is expressed by Purkinje neurons and PAC1 receptors are present on granule cells during both the development period and in adulthood. Treatment of granule neurons with PACAP inhibits proliferation, slows migration, promotes survival and induces differentiation. PACAP also protects cerebellar granule cells against the deleterious effects of neurotoxic agents. Most of the neurotrophic effects of PACAP are mediated through the cAMP/PKA signaling pathway and often involve the ERK MAPkinase. Caspase-3 is one of the key enzymes implicated in the neuroprotective action of PACAP but PACAP also inhibits caspase-9 activity and increases Bcl-2 expression. PACAP and functional PAC1 receptors are expressed in the monkey and human cerebellar cortex with a pattern of expression very similar to that described in rodents, suggesting that PACAP could also exert neurodevelopmental and neuroprotective functions in the cerebellum of primates including human.

N-acetylcysteine and neurodegenerative diseases: basic and clinical pharmacology

Increasing lines of evidence suggest a key role of oxidative stress in neurodegenerative diseases. Alzheimer's disease, Parkinson's disease, myoclonus epilepsy of the Unverricht-Lundborg type, spinocerebellar degeneration, tardive dyskinesia and Down's syndrome have been associated with several mitochondrial alterations. Oxidative stress can decrease cellular bioenergetic capacity, which will then increase the generation of reactive oxygen species resulting in cellular damage and programmed cell death. First, this review examines the mechanisms of action of N-acetylcysteine (NAC), an antioxidant and a free radical-scavenging agent that increases intracellular GSH, at the cellular level. NAC can act as a precursor for glutathione synthesis as well as a stimulator of the cytosolic enzymes involved in glutathione regeneration. The chemical properties of NAC include redox interactions, particularly with other members of the group XIV elements (selenium, etc.) and ebselen, a lipid-soluble seleno-organic compound. Second, NAC has been shown to protect against oxidative stress-induced neuronal death in cultured granule neurons. Recent findings on the protective effect of NAC against 4-hydroxynonenal (HNE)-induced toxicity in cerebellar granule neurons are summarized. Finally, the protective pharmacokinetics of NAC in humans and the possible usefulness of NAC for the treatment of neurodegenerative diseases are discussed with reference to basic and clinical studies.

N-Acetylcysteine and ebselen but not nifedipine protected cerebellar granule neurons against 4-hydroxynonenal-induced neuronal death

4-Hydroxynonenal (HNE), an aldehydic product of membrane lipid peroxidation, has been shown to induce neurotoxicity in various types of neurons. To clarify the mechanisms underlying HNE-induced neurotoxicity, the effects of antioxidants (N-acetylcysteine (NAC) and ebselen with or without NAC pretreatment) and Ca(2+)-related reagents were examined in cerebellar granule neurons. The decreases in neuronal survival and mitochondrial membrane potential induced by HNE were suppressed by pretreatment with NAC at concentrations of 500 and 1000 microM. HNE-induced protein modification and reactive oxygen species generation were also suppressed by pretreatment with NAC at 1000 microM. Although simultaneous application of ebselen (10 microM) did not protect against HNE-induced neurotoxicity, it completely suppressed HNE-induced injury after pretreatment with NAC at 300 microM. HNE increased [Ca(2+)](i) levels, and this increase was significantly attenuated by simultaneous application of nifedipine (10 microM) or EGTA (1000 microM), but not by MK-801 or CNQX. However, none of these Ca(2+)-related reagents was able to prevent HNE-induced neuronal death or mitochondrial injury. These results suggest that pretreatment with a low concentration of NAC dramatically potentiates the neuroprotective activity of ebselen, and that HNE-induced increase in [Ca(2+)](i) is not involved in HNE-induced neuronal death in cerebellar granule neurons.

N-acetylcysteine selectively protects cerebellar granule cells from 4-hydroxynonenal-induced cell death

4-hydroxynonenal (HNE), an aldehydic product of membrane lipid peroxidation, has been shown to induce neurotoxicity accompanied by multiple events. To clarify mechanisms of neuroprotective compounds on HNE-induced toxicity, the protective effects of N-acetylcysteine (NAC), alpha-tocopherol (TOC), ebselen and S-allyl-L-cysteine (SAC) were compared in cerebellar granule neurons. The decrease in MTT reduction induced by HNE was significantly suppressed by pretreatment of the neurons with 1000 microM NAC or 10 and 100 microM TOC; however, lactate dehydrogenase (LDH) release and propidium iodide (PI) fluorescence studies revealed that neuronal death was suppressed by NAC but not by TOC. Treatment of these neurons with HNE resulted in a drastic reduction of mitochondrial membrane potential, and this reduction was also prevented by NAC but not by TOC. Ebselen and SAC, a garlic compound, were unable to protect these neurons against HNE-induced toxicity. Pretreatment with NAC also prevented HNE-induced depletion of intracellular glutathione (GSH) levels in these neurons. These results suggest that NAC, but not other antioxidants such as TOC, SAC and ebselen, exerts significant protective effects against HNE-induced neuronal death in cerebellar granule neurons, and that this neuroprotective effect is due, at least in part, to preservation of mitochondrial membrane potential and intracellular GSH levels.

Functional repression of cAMP response element in 6-hydroxydopamine-treated neuronal cells

Impaired survival signaling may represent a central mechanism in neurodegeneration. 6-Hydroxydopamine (6-OHDA) is an oxidative neurotoxin used to injure catecholaminergic cells of the central and peripheral nervous systems. Although 6-OHDA elicits phosphorylation of several kinases, downstream transcriptional effects that influence neuronal cell death are less defined. The cAMP response element (CRE) is present in the promoter sequences of several important neuronal survival factors. Treatment of catecholaminergic neuronal cell lines (B65 and SH-SY5Y) with 6-OHDA resulted in repression of basal CRE transactivation. Message levels of CRE-driven genes such as brain-derived neurotrophic factor and the survival factor Bcl-2 were decreased in 6-OHDA-treated cells, but message levels of genes lacking CRE sequences were not affected. Repression of CRE could be reversed by delayed treatment with cAMP several hours after initiation of 6-OHDA injury. Furthermore, restoration of CRE-driven transcription was associated with significant neuroprotection. In contrast to observations in other model systems, the mechanism of CRE repression did not involve decreased phosphorylation of its binding protein CREB. Instead, total CREB and phospho-CREB (pCREB) were increased in the cytoplasm and decreased in the nucleus of 6-OHDA-treated cells. 6-OHDA also decreased nuclear pCREB in dopaminergic neurons of primary mouse midbrain cultures. Co-treatment with cAMP promoted/restored nuclear localization of pCREB in both immortalized and primary culture systems. Increased cytoplasmic pCREB was observed in degenerating human Parkinson/Lewy body disease substantia nigra neurons but not in age-matched controls. Notably, cytoplasmic accumulation of activated upstream CREB kinases has been observed previously in both 6-OHDA-treated cells and degenerating human neurons, supporting a potential role for impaired nuclear import of phosphorylated signaling proteins.

Pituitary adenylate cyclase activating polypeptide protects cardiomyocytes against oxidative stress-induced apoptosis

Pituitary adenylate cyclase activating polypeptide (PACAP) has well-known neuroprotective effects, and one of the main factors leading to neuroprotection seems to be its anti-apoptotic effects. The peptide and its receptors are present also in the heart, but whether PACAP can be protective in cardiomyocytes, is not known. Therefore, the aim of the present study was to investigate the effects of PACAP on oxidative stress-induced apoptosis in cardiomyocytes. Our results show that PACAP increased cell viability by attenuating H2O2-induced apoptosis in a cardiac myocyte culture. PACAP also decreased caspase-3 activity and increased the expression of the anti-apoptotic markers Bcl-2 and phospho-Bad. These effects of PACAP were counteracted by the PACAP antagonist PACAP6-38. In summary, our results show that PACAP is able to attenuate oxidative stress-induced cardiomyocyte apoptosis.

Identification and Characterization of Survival-Related Gene, a Novel Cell Survival Gene Controlling Apoptosis and Tumorigenesis

Apoptosis plays a critical role in cellular homeostasis during development, immune responses, and tumorigenesis. Recent studies have identified a number of genes that control this process. We report here our identification of a novel cell survival-related gene (SRG) from a human expression cDNA library by functional cloning. SRG shows no significant nucleotide sequence homology to any known genes in the Genbank. Our fluorescence in situ hybridization analysis has estimated that SRG is located at 1p36, agreeing with the location at 1p36.22 in the human genome sequence. SRG encodes a putative protein of 172 amino acids, which is mainly located in the perinuclear region. Northern blotting analysis indicates that SRG is highly expressed in many human cancer cell lines although it is low in most tissues except liver and placenta. To investigate the function of SRG in apoptosis, we transfected SRG cDNA into BAF/BO3 and B16/F0 cells and induced apoptosis by cytokine/serum deprivation. We found that SRG-transfected cells are resistant to apoptosis induced by cytokine/serum deprivation. In addition, mice bearing SRG-transfected melanoma had more tumor formation and larger tumor growth. Melanoma transfected with antisense SRG showed significantly less tumor formation and smaller tumor growth. Interestingly, mouse SRG gene was also identified on chromosome 4 and blocking SRG expression with small interfering RNA promoted serum deprivation-induced apoptosis of NIH3T3 cells. Our results show that SRG is a novel cell survival gene that critically controls apoptosis and tumor formation.

CREB mediates ERK-induced survival of mouse renal tubular cells after oxidant stress

BACKGROUND

We showed that extracellular signal-regulated protein kinase (ERK) is prosurvival during oxidant stress both in the kidney and in cultured mouse proximal tubule (TKPTS) cells and demonstrated concomitant activation of ERK as well as the cyclic adenosine monophosphate (cAMP)-responsive element binding protein (CREB), during survival in vitro. We now show that CREB is a necessary prosurvival target of ERK.

METHODS

Ischemia/reperfusion (I/R) injury was induced in 129Sv mice. Oxidant stress was induced by hydrogen peroxide (H(2)O(2)) in TKPTS cells. Activation of CREB was determined by immunohistochemistry and Western blotting. Inhibition and activation of CREB was achieved by mutant or activated CREB-containing adenoviruses in vitro. The effects of oxidant stress on cell survival, CREB binding, and CREB-mediated transcription was determined by cell counting, gelshift analysis, and luciferase assay, respectively.

RESULTS

I/R activates CREB in the surviving distal nephron segments of the kidney. Inhibition of ERK and CREB abrogates survival after 0.5 mmol/L H(2)O(2) treatment, while overexpression of CREB ameliorates necrotic death caused by 1 mmol/L H(2)O(2). Inhibition of ERK also inhibited CREB activation. Binding of phosphorylated CREB to a CREB oligonucleotide was significantly increased after 0.5 mmol/L H(2)O(2) but decreased after 1 mmol/L H(2)O(2). Similarly, CREB-mediated transcription was significantly increased after 0.5 mmol/L H(2)O(2) treatment, while 1 mmol/L H(2)O(2) inhibited it. Interestingly, transcription from the CREB-driven bcl-2 promoter was unchanged after 0.5 mmol/L but decreased after 1 mmol/L H(2)O(2) treatment in agreement with Western blot studies.

CONCLUSION

We show that survival during oxidant stress is mediated through CREB and identification of its downstream targets will reveal important survival pathways.

Distinct nuclear factor-kappaB/Rel proteins have opposing modulatory effects in glutamate-induced cell death in HT22 cells

Members of the nuclear factor-kappaB (NF-kappaB)/Rel family (p50, p52, p65 (RelA), RelB and c-Rel) is sequestered in the cytoplasm through its tight association with the inhibitor of NF-kappaB (IkappaB). NF-kappaB has been shown to function as key regulators of either cell death or survival in neurons after activation of the cells by various extracellular signals. In the study presented here, we investigated whether the selective activation of diverse NF-kappaB/Rel family members in HT22 cells might lead to distinct effects on glutamate-induced cell death. Exposing HT22 cells to glutamate, which blocks cystine uptake into the cells via inhibition of the glutamate-cystine antiporter, resulted in a transient activation of IkappaB and NF-kappaB/Rel and caused delayed cell death. Aspirin, which has been shown to block phosphorylation of the IkappaB component of the cytoplasmic NF-kappaB complex, significantly suppressed glutamate-induced cell death, whereas the NF-kappaB decoy oligonucleotide potentiated it. The inhibition of NF-kappaB/Rel protein expression by antisense oligonucleotides showed that p65 is involved in glutamate-mediated cell death, whereas p50 is involved in inhibitory pathways of the cell death. These findings suggest that in HT22 cells, the balance between promoting and presenting cell death to glutamate-induced oxidative stress relies on the activation of distinct NF-kappaB proteins.

Effects of PACAP on in vitro and in vivo neuronal cell death, platelet aggregation, and production of reactive oxygen radicals

Pituitary adenylate cyclase activating polypeptide (PACAP) exerts neuroprotective effects in various in vitro and in vivo models of cerebral pathologies. It has been shown that PACAP protects neurons in rat models of both global and focal ischemia. In the present study, we investigated factors that may play a role in the neuroprotective effects of PACAP. PACAP strongly reduced the anisomycin-induced apoptosis of PC12 cells, which was abolished in a PKA-deficient PC12 cell line (A126). This effect was also observed in vivo, in permanent occlusion of the middle cerebral artery, where the number of TUNEL-positive neurons was significantly reduced in the ischemic core of PACAP-treated animals. Our results show that PACAP has a minor antioxidant effect in a non-cellular in vitro system, and has considerable antioxidant effects in an in vitro red blood cell filtration model. PACAP had no effect on platelet aggregation induced by collagen, ADP or epinephrine. Our results demonstrate that the effects of PACAP on delayed neuronal death may play a significant role in the reduction of the infarct size in vivo, but the antioxidant effect could only be observed at concentrations higher than that used in the model of focal ischemia.

4-Hydroxynonenal modulates the long-term potentiation induced by L-type Ca2+ channel activation in the rat dentate gyrus in vitro

Increased oxyradical production and membrane lipid peroxidation (MLP) occur under physiological and degenerative conditions in neurons. We investigated whether 4-hydroxynonenal (4HN), one of the membrane lipid peroxidation products, affects long-term potentiation (LTP) in the rat dentate gyrus in vitro. Treatment of hippocampal slices with 4HN (10 microM) enhanced LTP without affecting basal evoked potentials. The enhancement was completely inhibited by 2 microM nifedipine, a blocker of L-type Ca2+ channels. In cultured dentate gyrus neurons, treatment of the cells with 4HN for 24 h resulted in a significant amount of cell death that was detoxified by glutathione, whereas short-term treatment with 4HN (< or = 6 h) had no effect. Nifedipine partially but significantly suppressed the 4HN-induced cell death. These results suggest that 4HN modulates LTP and induces delayed cell death through L-type Ca2+ channel activation in the dentate gyrus. 4HN thereby plays an important role in both physiological and pathophysiological events in the hippocampus.

Modulation of voltage-gated Ca2+ current by 4-hydroxynonenal in dentate granule cells

Although recent studies have suggested that dentate granule cells play a key role in hippocampal functions, electrophysiological properties in these cells have not been sufficiently explored. In the present study, modification of voltage-gated Ca2+ channels by 4-hydroxynonenal (4HN), a major aldehydic product of membrane lipid peroxidation, in cultured dentate granule cells was examined using the whole-cell patch clamp technique. When whole-cell voltage clamp was applied, the cells exhibited a high-voltage-activated Ca2+ current, which was totally sensitive to 30 microM Cd2+ and partially sensitive to 2 microM nifedipine. 4HN enhanced the Ca2+ current in these cells. When L-type Ca2+ channels were blocked by application of nifedipine, the enhancement was completely canceled, whereas application of omega-conotoxin-GVIA or omega-agatoxin-IVA, blockers of N- and P/Q-type Ca2+ channels, respectively, had no effect. These results suggest that 4HN modulates L-type Ca2+ channels in the dentate granule cells, and thereby plays a role in the physiological and pathophysiological responses of these cells to oxidative stress.

Hydrogen peroxide modulates whole cell Ca2+ currents through L-type channels in cultured rat dentate granule cells

Modification of voltage-gated Ca(2+) channels by hydrogen peroxide, a membrane-permeable form of reactive oxygen species, in cultured dentate granule cells was examined using the whole cell patch clamp technique. Pretreatment with hydrogen peroxide (1 and 10 microM) for 2 h enhanced the Ca(2+) current without affecting its voltage dependence. The enhancement was completely cancelled by 1 mM glutathione, an antioxidant, and 2 microM nifedipine, an L-type Ca(2+) channel blocker. In contrast, the enhancement of the Ca(2+) current was not mimicked by pretreatment with 10 microg/ml tunicamycin, an endoplasmic reticulum stressor. These results suggest that oxidative stress induced by hydrogen peroxide selectively regulates the activity of L-type Ca(2+) channels.

S-allyl-L-cysteine selectively protects cultured rat hippocampal neurons from amyloid beta-protein- and tunicamycin-induced neuronal death

S-allyl-L-cysteine (SAC), one of the organosulfur compounds found in aged garlic extract, has been shown to possess various biological effects including neurotrophic activity. In our previous experiments, we found that SAC could protect against amyloid beta-protein (Abeta)- and tunicamycin-induced cell death in differentiated PC12 cells. In the study described here, we characterized the neuronal death induced by Abeta, 4-hydroxynonenal (HNE), tunicamycin, and trophic factor deprivation, and investigated whether and how SAC could prevent this in cultured rat hippocampal neurons. Treatment with SAC protected these cells against Abeta- and tunicamycin-induced neuronal death, which is mediated predominantly through caspase-12-dependent pathway in a concentration-dependent manner. In contrast, it afforded no protection against HNE- and trophic factor-deprivation-induced cell death, which has been shown to be mediated by caspase-3-dependent pathway. SAC also attenuated the Abeta-induced increase of intracellular reactive oxygen species in hippocampal neurons. SAC had no effect on Abeta-induced cell death in cultured cerebellar granule neurons, which was prevented by a caspase-3 inhibitor. These results suggest that SAC could protect against the neuronal cell death that is triggered by ER dysfunction in the hippocampus, and that it has no effect on neuronal cell death that is dependent upon the caspase-3 mediated pathway.

Neurotoxicity induced by amyloid beta-peptide and ibotenic acid in organotypic hippocampal cultures: protection by S-allyl-L-cysteine, a garlic compound

We have assessed amyloid-beta (Abeta)-induced neurotoxicity, with and without added ibotenic acid (IBO), a potent N-methyl-D-aspartate (NMDA) agonist, in an organotypic hippocampal slice culture (OHC). In the OHC, there was little neurotoxicity after treatment with Abeta(25-35) (25 or 50 microM) alone for 48 h. However, with IBO alone neuronal death was observed in the pyramidal cell layer at low concentrations, and there was dramatic neuronal death at concentrations of 65 microM or more. When Abeta was combined with IBO (Abeta+IBO) there was more intense cell death than with IBO alone. S-Allyl-L-cysteine (SAC), one of the organosulfur compounds having a thioallyl group in aged garlic extract, was shown to protect the hippocampal neurons in the CA3 area and the dentate gyrus (DG) from the cell death induced by Abeta+IBO with no change in the CA1 area. Although L-glutamate (500 microM) potentiated the degree of IBO-induced neuronal death, it attenuated the Abeta+IBO-induced neuronal death in both the CA3 area and the DG with no obvious effect on the CA1 area. These results suggest that Abeta+IBO induces extensive neuronal death, and that SAC and L-glutamate protect cells from death in specific areas of the hippocampus. In addition, inhibition using a pan-caspase inhibitor, z-VAD-fmk, only provided partial protection from Abeta+IBO-induced toxicity for the neurons in the CA3 area. These results suggest that multiple mechanisms may be involved in Abeta+IBO-induced neuronal death in the OHC.

Protective effect of S-allyl-L-cysteine, a garlic compound, on amyloid beta-protein-induced cell death in nerve growth factor-differentiated PC12 cells

Aged garlic extract (AGE) contains several neuroactive compounds, including S-allyl-L-cysteine (SAC) and allixin. We characterized cell death induced by amyloid beta-protein (Abeta), 4-hydroxynonenal (HNE), tunicamycin, an endoplasmic reticulum (ER) stressor, or trophic factor deprivation, and investigated whether and how SAC could prevent this in nerve growth factor (NGF)-differentiated PC12 cells, a model of neuronal cells. Exposure of the cells to amyloid beta-protein(1-40) (Abeta(1-40)) decreased the extent of [3-(4,5)-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium (MTT) reduction activity and loss of neuronal integrity, but these effects were not prevented by Ac-DEVD-CHO, a caspase-3 inhibitor. Simultaneously applied SAC protected the cells against Abeta-induced cell death in a concentration-dependent manner. It also protected them against tunicamycin-induced neuronal death. In contrast, it afforded no protection against cell death induced by HNE and trophic factor deprivation, which is mediated by a caspase-3-dependent pathway. These results suggest that SAC may selectively protect cell death induced by Abeta and tunicamycin, which may be triggered by ER dysfunction in NGF-differentiated PC12 cells.

Oxidative stress-mediated down-regulation of bcl-2 promoter in hippocampal neurons

Generation of oxidative stress/reactive oxygen species (ROS) is one of the causes of neuronal apoptosis. We have examined the effects of ROS at the transcriptional level in an immortalized hippocampal neuronal cell line (H19-7) and in rat primary hippocampal neurons. Treatment of H19-7 cells with hydrogen peroxide (150 micro m) resulted in a 40% decrease in Bcl-2 protein and a parallel decrease in bcl-2 mRNA levels. H19-7 cells overexpressing bcl-2 were found to be resistant to ROS-induced apoptosis. We had previously shown that bcl-2 promoter activity is positively regulated by the transcription factor cyclic AMP response element binding protein (CREB) in neurons. In the present study, we demonstrate that ROS decreases the activity of luciferase reporter gene driven by a cyclic AMP response element site containing bcl-2 promoter. Exposure of neurons to ROS for 6 h resulted in basal and fibroblast growth factor-2-stimulated phosphorylation/activation of CREB. Chronic 24 h treatment with ROS led to a significant (p < 0.01) decrease in CREB protein and CREB mRNA levels. Adenoviral overexpression of wild type CREB in H19-7 cells resulted in significant (p < 0.01) protection against ROS-induced apoptosis through up-regulation of Bcl-2 expression whereas dominant negative CREB exaggerated the injury. These findings demonstrate that loss of CREB function contributes to oxidative stress-induced neuronal dysfunction.

Analysis of the PC12 cell transcriptome after differentiation with pituitary adenylate cyclase-activating polypeptide (PACAP)

Pituitary adenylate cyclase-activating polypeptide (PACAP) promotes neurite outgrowth and inhibits proliferation of rat pheochromocytoma (PC12) cells. Characterizing the PACAP-differentiated PC12 cell transcriptome should provide genetic insight into how these processes occur in these cells, and in neuronal precursors in vivo. For this purpose, RNA samples were collected from PC12 cells before or after a 6-h treatment with PACAP, from which a labeled cDNA was hybridized to a high-density cDNA array containing 15 365 genes. The genomic response to PACAP involves at least 73 genes. Among the genes differentially expressed in the presence of PACAP, 71% were up regulated, and 29% down regulated, 2-fold or more. Sixty-six percent of the messages affected by PACAP code for functionally categorized proteins, most not previously known to be regulated during PC12 cell differentiation. PACAP has been shown to induce PC12 cell neurite outgrowth through the mitogen-activated protein kinase kinase (MEK) pathway independently of protein kinase A (PKA). Therefore treatments were conducted in the absence or presence of the PKA inhibitor H89, or the MEK inhibitor U0126 in order to identify subsets of genes involved in specific aspects of PC12 cell differentiation. Co-treatment of PC12 cells with PACAP plus H89 revealed a cluster of five genes specifically regulated through the PKA pathway and co-treatment of the cells with PACAP and U0126 revealed a cluster of 13 messages specifically activated through the MEK pathway. Many of the known genes regulated by PACAP have been associated with neuritogenesis (i.e. villin 2 or annexin A2) or cell growth (i.e. growth arrest specific 1 or cyclin B2). Thus, some of the expressed sequence tags (ESTs) that exhibit the same regulation pattern (i.e. AU016391 or AW552690) may also be involved in the neuritogenic and anti-mitogenic effects of PACAP in PC12 cells. Among the 73 PACAP regulated genes, 10 are disqualified on pharmacological grounds as actors in PACAP-mediated neurite outgrowth or growth arrest, leaving 63 new PACAP-regulated genes implicated in neuronal differentiation. Thirteen of these are candidates for mediating ERK-dependent neurite outgrowth, and 47 are possibly involved in the ERK-independent growth arrest induced by PACAP.

Transfection of mGSTA4 in HL-60 cells protects against 4-hydroxynonenal-induced apoptosis by inhibiting JNK-mediated signaling

The mammalian alpha-class glutathione S-transferase (GST) isozymes mGSTA4-4, rGSTA4-4, and hGSTA4-4 are known to utilize 4-hydroxynonenal (4HNE) as a preferred substrate. During the present studies, we have examined the effect of transfecting human myeloid HL-60 cells with mGSTA4, on 4-HNE-induced apoptosis and the associated signaling mechanisms. Results of these studies show that treatment of the wild-type or vector-only-transfected HL-60 cells with 20 microM 4-HNE caused apoptosis within 2 h. The cells transfected with mGSTA4 did not undergo apoptosis under these conditions even after 4 h. In the wild-type and vector-transfected cells, apoptosis was preceded by JNK activation and c-Jun phosphorylation within 30 min, and an increase in AP-1 binding within 2 h of treatment with 20 microM 4-HNE. In mGSTA4-transfected cells, JNK activation and c-Jun phosphorylation were observed after 1 h, and increased AP-1 binding was observed after 8 h under these conditions. In the control cells, 20 microM 4-HNE caused caspase 3 activation and poly(ADP-ribose) polymerase cleavage within 2 h, while in mGSTA4-transfected cells, a lesser degree of these effects was observed even after 8 h. Transfection with mGSTA4 also provided protection to the cells from 4-HNE and doxorubicin cytotoxicity (1.6- and 2.6-fold, respectively). These results show that 4-HNE mediates apoptosis through its effects on JNK and caspase 3, and that 4-HNE metabolizing GST isozyme(s) may be important in the regulation of this pathway of oxidative-stress-induced apoptosis.