The Ras-ERK pathway is required for the induction of neuronal nitric oxide synthase in differentiating PC12 cells

Nitric oxide and sex differences in dendritic branching and arborization

Nitric oxide (NO) is an important signaling molecule with many functions in the nervous system. Derived from the enzymatic conversion of arginine by several nitric oxide synthases (NOS), NO plays significant roles in neuronal developmental events such as the establishment of dendritic branching or arbors. A brief summary of the discovery, molecular biology, and chemistry of NO, and a description of important NO-mediated signal transduction pathways with emphasis on the role for NO in the development of dendritic branching during neurodevelopment are presented. Important sex differences in neuronal nitric oxide synthase expression during neuronal development are considered. Finally, a survey of endogenous and exogenous substances that disrupt dendritic patterning is presented with particular emphasis on how these molecules may drive NO-mediated sex differences in dendritic branching.

Vasoinhibin Suppresses Nerve Growth Factor-Induced Differentiation and Survival of PC12 Pheochromocytoma Cells

BACKGROUND

Vasoinhibin, a protein derived from prolactin, regulates various vascular functions including endothelial cell survival. Of note, vasoinhibin is present in the central nervous system, where it triggers neuroendocrine and behavioral responses to stress. Moreover, vasoinhibin compromises nerve growth factor (NGF)-induced neurite outgrowth in primary sensory neurons of the peripheral nervous system. Nonetheless, information on the functions of vasoinhibin in developing neurons remains limited. The present study explored whether vasoinhibin affects the neurotrophic actions of NGF by measuring the cell differentiation and survival of PC12 pheochromocytoma cells.

METHODS

The effects of recombinant or lentiviral vector-transduced human vasoinhibin were tested on differentiating PC12 cells. Neurite outgrowth was quantified by measuring their length and density. The MTT assay was employed to assess cell viability, and ELISA was used to quantify DNA fragmentation as an index of apoptosis. Phosphorylated Akt and ERK1/2 were analyzed by Western blotting.

RESULTS

The addition of a human recombinant vasoinhibin, and the transduction of a lentiviral vector carrying a human vasoinhibin sequence, significantly reduced NGF-induced neurite outgrowth, cell survival, and phosphorylation of Akt and ERK1/2, and increased DNA fragmentation and caspase 3 activation in PC12 cells.

CONCLUSIONS

Vasoinhibin downregulates NGF-induced differentiation and survival of PC12 cells, blocking tropomyosin receptor kinase A-triggered signaling pathways and increasing apoptosis. These results establish that vasoinhibin interaction with NGF and other neurotrophins may be critical in mediating pathways involved in neuronal survival and differentiation.

Cyclosporin A attenuating morphine tolerance through inhibiting NO/ERK signaling pathway in human glioblastoma cell line: the involvement of calcineurin

Cyclosporin A (CsA) is known to have an immunosuppressive action. However, it is also attracting attention due to its effects on the nervous system, such as inhibiting the development and expression of morphine-induced tolerance and dependence through unknown mechanisms. It has been shown that CsA modulates the nitric oxide (NO) synthesis and extracellular signal-regulated kinases (ERK) activation, which are potentially involved in signaling pathways in morphine-induced tolerance in cellular models. Therefore, the current study was designed to evaluate the modulatory role of CsA on the MOR tolerance, by targeting the downstream signaling pathway of NO and ERK using an in vitro model. For this purpose, T98G cells were pretreated with CsA, calcineurin autoinhibitory peptide (CAIP), and N^G-nitro-l-arginine methyl ester (L-NAME) 30 min before 18 h exposure to MOR. Then, we analyzed the intracellular cyclic adenosine monophosphate (cAMP) levels and also the expression of phosphorylated ERK and nitric oxide synthase (nNOS) proteins. Our results showed that CsA (1 nM, 10 nM, and 100 nM) and CAIP (50 µM) have significantly reduced cAMP and nitrite levels as compared to MOR-treated (2.5 µM) T98G cells. This clearly revealed the attenuation of MOR tolerance by CsA. The expression of nNOS and p-ERK proteins were down-regulated when the T98G cells were pretreated with CsA (1 nM, 10 nM, and 100 nM), CAIP (50 µM), and L-NAME (0.1 mM) as compared to MOR. In conclusion, the CsA pretreatment had a modulatory role in MOR-induced tolerance, which was possibly mediated through NO/ERK signaling pathway.

Mechanisms involved in glucocorticoid induction of pituitary GH expression during embryonic development

Glucocorticoid hormones are involved in functional differentiation of GH-producing somatotrophs. Glucocorticoid treatment prematurely induces GH expression in mammals and birds in a process requiring protein synthesis and Rat sarcoma (Ras) signaling. The objective of this study was to investigate mechanisms through which glucocorticoids initiate GH expression during embryogenesis, taking advantage of the unique properties of chicken embryos as a developmental model. We determined that stimulation of GH expression occurred through transcriptional activation of GH, rather than enhancement of mRNA stability, and this process requires histone deacetylase activity. Through pharmacological inhibition, we identified the ERK1/2 pathway as a likely downstream Ras effector necessary for glucocorticoid stimulation of GH. However, we also found that chronic activation of ERK1/2 activity with a constitutively active mutant or stimulatory ligand reduced initiation of GH expression by glucocorticoid treatment. Corticosterone treatment of cultured embryonic pituitary cells increased ERK1/2 activity in an apparent cyclical manner, with a rapid increase within 5 minutes, followed by a reduction to near-basal levels at 3 hours, and a subsequent increase again at 6 hours. Therefore, we conclude that ERK1/2 signaling must be strictly controlled for maximal glucocorticoid induction of GH to occur. These results are the first in any species to demonstrate that Ras- and ERK1/2-mediated transcriptional events requiring histone deacetylase activity are involved in glucocorticoid induction of pituitary GH during embryonic development. This report increases our understanding of the molecular mechanisms underlying glucocorticoid recruitment of somatotrophs during embryogenesis and should provide insight into glucocorticoid-induced developmental changes in other tissues and cell types.

Neuronal nitric oxide synthase, as a downstream signaling molecule of c‑jun, regulates the survival of differentiated PC12 cells

The high expression of c-jun and neuronal nitric oxide synthase (nNOS) generally occurs in neurons following the generation of various animal models of central neuronal diseases. However, the mechanism between them in neuronal disease remains to be elucidated. Our previous studies demonstrated that the expression of c‑jun always occurs prior to expression of nNOS in motoneuron injuries and suppression of c‑jun expression by c‑jun siRNA decreased nNOS expression in differentiated PC12 cells. The present study aimed to examine whether there was an association of up and downstream regulation or crosstalk between c‑jun and nNOS in neurons. Using a culture of differentiated PC12 cells in vitro, the expression of nNOS and c-jun in cells was investigated by immunofluorescence. The nNOS inhibitor 7‑nitroindazole (7‑NI) was used in differentiated PC12 cells to downregulate the expression of nNOS. The optimal concentration of 7‑NI on the viability and survival of cultured differentiated PC12 cells was selected using a 3‑(4,5-dimethylthiazol-2-yl)‑2,5-diphenyltetrazolium assay and the effects of 7‑NI on the activity of constitutive nitric oxide synthase (cNOS) in differentiated PC12 cells were determined using a NOS Activity Detection kit. The effects of 7‑NI on the gene expression of nNOS and c‑jun were detected by western blot analysis. The results from the immunofluorescence demonstrated that the c‑jun and nNOS protein were constantly expressed in PC12 cells. The cell viability of differentiated PC12 cells were significantly inhibited by treatment with 200 and 400 µmol/l 7‑NI, and the expression levels of the nNOS protein were significantly inhibited by treatment with 200 µmol/l 7‑NI. However, 7‑NI had no significant effect on the protein expression level of c‑jun and the total activities of cNOS. Based on our previous studies, which revealed that the nNOS gene was a downstream signaling molecule of the JNK/c‑jun signaling pathway in cultured neurons, the expression of nNOS downstream was able to be regulated by c‑jun which was the upstream molecule. Therefore, these results indicated that the association between them involved up and downregulation instead of crosstalk.

Nitrosative/oxidative stress conditions regulate thioredoxin-interacting protein (TXNIP) expression and thioredoxin-1 (TRX-1) nuclear localization

Thioredoxin (TRX-1) is a multifunctional protein that controls the redox status of other proteins. TRX-1 can be found in the extracellular milieu, cytoplasm and nucleus, and it has distinct functions in each environment. Previously, we studied the intracellular localization of TRX-1 and its relationship with the activation of the p21Ras - ERK1/2 MAP Kinases signaling pathway. In situations where this pathway was activated by stress conditions evoked by a nitrosothiol, S-nitroso-N-acetylpenicillamine (SNAP), TRX-1 accumulated in the nuclear compartment due to nitrosylation of p21Ras and activation of downstream ERK1/2 MAP kinases. Presently, we demonstrate that ERK1/2 MAP Kinases activation and spatial distribution within cells trigger TRX-1 nuclear translocation through down-regulation of the physiological inhibitor of TRX-1, Thioredoxin Interacting Protein (TXNIP). Once activated by the oxidants, SNAP and H₂O₂, the ERK1/2 MAP kinases migrate to the nucleus. This is correlated with down-regulation of TXNIP. In the presence of the MEK inhibitors (PD98059 or UO126), or in cells transfected with the Protein Enriched in Astrocytes (PEA-15), a cytoplasmic anchor of ERK1/2 MAP kinases, TRX-1 nuclear migration and TXNIP down-regulation are no longer observed in cells exposed to oxidants. On the other hand, over-expression of TXNIP abolishes nuclear migration of TRX-1 under nitrosative/oxidative stress conditions, whereas gene silencing of TXNIP facilitates nuclear migration even in the absence of stress conditions. Studies based on the TXNIP promoter support this regulation. In conclusion, changes in TRX-1 compartmentalization under nitrosative/oxidative stress conditions are dependent on the expression levels of TXNIP, which are regulated by cellular compartmentalization and activation of the ERK1/2 MAP kinases.

Nitric oxide synthase mediates PC12 differentiation induced by the surface topography of nanostructured TiO2

Background

Substrate nanoscale topography influences cell proliferation and differentiation through mechanisms that are at present poorly understood. In particular the molecular mechanism through which cells 'sense’ and adapt to the substrate and activate specific intracellular signals, influencing cells survival and behavior, remains to be clarified.

Results

To characterize these processes at the molecular level we studied the differentiation of PC12 cells on nanostructured TiO₂ films obtained by supersonic cluster beam deposition.

Our findings indicate that, in PC12 cells grown without Nerve Growth Factor (NGF), the roughness of nanostructured TiO₂ triggers neuritogenesis by activating the expression of nitric oxide synthase (NOS) and the phospho-extracellular signal-regulated kinase 1/2 (pERK1/2) signaling. Differentiation is associated with an increase in protein nitration as observed in PC12 cells grown on flat surfaces in the presence of NGF. We demonstrate that cell differentiation and protein nitration induced by topography are not specific for PC12 cells but can be regarded as generalized effects produced by the substrate on different neuronal-like cell types, as shown by growing the human neuroblastoma SH-SY5Y cell line on nanostructured TiO₂.

Conclusion

Our data provide the evidence that the nitric oxide (NO) signal cascade is involved in the differentiation process induced by nanotopography, adding new information on the mechanism and proteins involved in the neuritogenesis triggered by the surface properties.

Nerve growth factor reduces myocardial ischemia/reperfusion injury in rat hearts

BACKGROUND

Nerve growth factor (NGF) is a neurotrophin that supports the survival and differentiation of sympathetic neurons, and its increased expression after myocardial infarct was correlated with cardiac sympathetic hyperinnervation and arrhythmias. However, it is unclear whether NGF protects the heart during infarct. In this study, we sought to address this issue in rat heart exposed to ischemia/reperfusion injury (IRI).

METHODS

NGF was administered intravenously (IV), 15 min before ischemia, at different concentrations in the absence or presence of inhibitors of phosphatidylinositol-3 kinase (PI3K) or nitric oxide synthase (NOS) in different groups of rats (n=6) with left coronary occlusion for 30 min followed by 120-min reperfusion. The area at risk and infarct to risk ratios were determined from sections stained with 1% 2,3,5-triphenylterazolium chloride.

RESULTS

NGF treatment at doses of 0.015-15 μg/kg, with an optimal dose of 0.15 μg/kg given IV before ischemia, reduced the infarct size from about 60% at the area of risk to about 25%, indicating cardioprotection by about 60%. The infarct-sparing effects of NGF were partially abolished by the inhibition of PI3K and NOS using wortmannin and N(G)-monomethyl-l-arginine, respectively.

CONCLUSIONS

We have demonstrated for the first time that NGF attenuates myocardial infarct damage in an in vivo rat model of myocardial regional IRI. This cardioprotective effect is proposed to be related to the activities of PI3K and NOS. This suggests that NGF has a potential therapeutic role in the treatment of IRI.

Sodium nitroprusside, a nitric oxide donor, fails to bypass the block of neuronal differentiation in PC12 cells imposed by a dominant negative Ras protein

Nitric oxide (NO) is a mediator of a diverse array of inter- and intracellular signal transduction processes. The aim of the present study was to analyze its possible role as a second messenger in the process of neuronal differentiation of PC12 pheochromocytoma cells. Upon NGF treatment wildtype PC12 cells stop dividing and develop neurites. In contrast, a PC12 subclone (designated M-M17-26) expressing a dominant-negative mutant Ras protein keeps proliferating and fails to grow neurites after NGF treatment. Sodium nitroprusside (SNP), an NO donor, was found to induce the p53 protein and to inhibit proliferation of both PC12 and M-M17-26 cells, but failed to induce neuronal differentiation in these cell lines. Key signaling pathways (the ERK and Akt pathways) were also not affected by SNP treatment, and the phosphorylation of CREB transcription factor was only slightly stimulated. It is thus concluded from the results presented in this paper that NO is unable to activate signaling proteins acting downstream or independent of Ras that are required for neuronal differentiation.

Suppression of c-jun influences nNOS expression in differentiated PC12 cells

In various animal models of central neuronal diseases, both c-jun and nNOS genes are expressed inside injured neurons; however, the mechanism of these two genes in neuronal diseases remains uncertain. Our previous studies have shown that c-jun expression always occurs prior to expression of nNOS in motoneuron injuries. We aimed to determine whether there is a correlation between c-jun and nNOS, and whether the crosstalk between these two genes regulated the pathological progression of injury-induced neuronal degeneration. In the present study, we used the neuron-like differentiated PC12 cells, which express c-jun and nNOS, to examine whether c-jun is the upstream molecule modulating nNOS expression. The c-jun small interfering RNAs (c-jun siRNA) were transfected into PC12 cells and cells were treated for 72 h in vitro. Western blotting and immunofluorescence were used to check the protein levels and the expression of c-jun and nNOS in differentiated PC12 cells. The results from the immunofluorescence experiments showed that the c-jun and nNOS proteins were co-expressed in the differentiated PC12 cells. The results from the western blotting experiments revealed that the protein levels of c-jun were significantly decreased by c-jun siRNA. Moreover, the nNOS protein levels were also downregulated in differentiated PC12 cells following c-jun siRNA treatment. The present study found that siRNA used against c-jun not only knocked down c-jun, but also downregulated the nNOS protein expression in differentiated PC12 cells. These results indicate that there is a functional relationship between c-jun and nNOS in differentiated PC12 cells.

Regulation of nitric oxide production in snail (Lymnaea stagnalis) defence cells: a role for PKC and ERK signalling pathways

BACKGROUND INFORMATION

Nitric oxide (NO) is an important molecule in innate immune responses. In molluscs NO is produced by mobile defence cells called haemocytes; however, the molecular mechanisms that regulate NO production in these cells is poorly understood. The present study focused on the role of cell signalling pathways in NO production by primary haemocytes from the snail Lymnaea stagnalis.

RESULTS

When haemocytes were challenged with PMA (10 microM) or the beta-1,3-glucan laminarin (10 mg/ml), an 8-fold and 4-fold increase in NO production were observed after 60 min respectively. Moreover, the NOS (NO synthase) inhibitors L-NAME (N(G)-nitro-L-arginine methyl ester) and L-NMMA (N(G)-monomethyl-L-arginine) were found to block laminarin- and PMA-induced NO synthesis. Treatment of haemocytes with PMA or laminarin also increased the phosphorylation (activation) status of PKC (protein kinase C). When haemocytes were preincubated with PKC inhibitors (calphostin C or GF109203X) or inhibitors of the ERK (extracellular-signal-regulated kinase) pathway (PD98059 or U0126) prior to challenge, significant reductions in PKC and ERK phosphorylation and NO production were observed following exposure to laminarin or PMA. The greatest effect on NO production was seen with GF109203X and U0126, with PMA-induced NO production inhibited by 94% and 87% and laminarin-induced NO production by 50% and 91% respectively.

CONCLUSIONS

These data suggest that ERK and PKC comprise part of the signalling machinery that regulates NOS activation and subsequent production of NO in molluscan haemocytes. To our knowledge, this is the first report that shows a role for these signalling proteins in the generation of NO in invertebrate defence cells.

Nitric oxide activates Nrf2 through S-nitrosylation of Keap1 in PC12 cells

Nitric oxide (NO) exerts bifunctional effects on cell survival. While a high concentration of NO is cytotoxic, a relatively low concentration of NO promotes cytoprotection and cell survival. However, the molecular mechanism underlying the cytoprotective effect of NO remains poorly understood. One of the transcription factors that confer cellular protection against oxidative stress is NF-E2-related factor 2 (Nrf2), which is sequestered in the cytoplasm by forming an inactive complex with Klech-like ECH-associated protein 1 (Keap1). Previous studies suggested that various stimuli could induce the dissociation of Nrf2 from Keap1 in cytosol and/or promote its nuclear translocation by activating several upstream kinases. NO-mediated thiol modification in Keap1 has also been proposed as a possible mechanism of Nrf2 activation. Since NO can modify the function or activity of target proteins through S-nitrosylation of cysteine, we attempted to investigate whether the cytoprotective effect of NO is mediated through Nrf2 activation by directly modifying cysteine residues of Keap1. Our present study reveals that treatment of rat pheochromocytoma (PC12) cells with an NO donor S-nitroso-N-acetylpenicillamine (SNAP) induced nuclear translocation and DNA binding of Nrf2. Under the same experimental conditions, there was NO-mediated S-nitrosylation of Keap1 observed, which coincided with the Nrf2 activation. Moreover, SNAP treatment caused phosphorylation of Nrf2, and pharmacological inhibition of protein kinase C (PKC) abolished the phosphorylation and nuclear localization of Nrf2. In conclusion, NO can activate Nrf2 by S-nitrosylation of Keap1 and alternatively by PKC-catalyzed phosphorylation of Nrf2 in PC12 cells.

Leukemia inhibitory factor regulates trafficking of T-type Ca2+ channels

Neuropoietic cytokines such as ciliary neurotrophic factor (CNTF) and leukemia inhibitory factor (LIF) stimulate the functional expression of T-type Ca(2+) channels in developing sensory neurons. However, the molecular and cellular mechanisms involved in the cytokine-evoked membrane expression of T-type Ca(2+) channels are not fully understood. In this study we investigated the role of LIF in promoting the trafficking of T-type Ca(2+) channels in a heterologous expression system. Our results demonstrate that transfection of HEK-293 cells with the rat green fluorescent protein (GFP)-tagged T-type Ca(2+) channel α(1H)-subunit resulted in the generation of transient Ca(2+) currents. Overnight treatment of α(1H)-GFP-transfected cells with LIF caused a significant increase in the functional expression of T-type Ca(2+) channels as indicated by changes in current density. LIF also evoked a significant increase in membrane fluorescence compared with untreated cells. Disruption of the Golgi apparatus with brefeldin A inhibited the stimulatory effect of LIF, indicating that protein trafficking regulates the functional expression of T-type Ca(2+) channels. Trafficking of α(1H)-GFP was also disrupted by cotransfection of HEK-293 cells with the dominant-negative form of ADP-ribosylation factor (ARF)1 but not ARF6, suggesting that ARF1 regulates the LIF-evoked membrane trafficking of α(1H)-GFP subunits. Trafficking of T-type Ca(2+) channels required transient activation of the JAK and ERK signaling pathways since stimulation of HEK-293 cells with LIF evoked a considerable increase in the phosphorylation of the downstream JAK targets STAT3 and ERK. Pretreatment of HEK-293 cells with the JAK inhibitor P6 or the ERK inhibitor U0126 blocked ERK phosphorylation. Both P6 and U0126 also inhibited the stimulatory effect of LIF on T-type Ca(2+) channel expression. These findings demonstrate that cytokines like LIF promote the trafficking of T-type Ca(2+) channels.

Extracellular signal-regulated kinase 1/2 plays a pro-life role in experimental brain stem death via MAPK signal-interacting kinase at rostral ventrolateral medulla

BACKGROUND

As the origin of a life-and-death signal detected from systemic arterial pressure, which sequentially increases (pro-life) and decreases (pro-death) to reflect progressive dysfunction of central cardiovascular regulation during the advancement towards brain stem death in critically ill patients, the rostral ventrolateral medulla (RVLM) is a suitable neural substrate for mechanistic delineation of this fatal phenomenon. The present study assessed the hypothesis that extracellular signal-regulated kinase 1/2 (ERK1/2), a member of the mitogen-activated protein kinases (MAPKs) that is important for cell survival and is activated specifically by MAPK kinase 1/2 (MEK1/2), plays a pro-life role in RVLM during brain stem death. We further delineated the participation of MAPK signal-interacting kinase (MNK), a novel substrate of ERK in this process.

METHODS

An experimental model of brain stem death that employed microinjection of the organophosphate insecticide mevinphos (Mev; 10 nmol) bilaterally into RVLM of Sprague-Dawley rats was used, in conjunction with cardiovascular, pharmacological and biochemical evaluations.

RESULTS

Results from ELISA showed that whereas the total ERK1/2 was not affected, augmented phosphorylation of ERK1/2 at Thr202 and Tyr204 in RVLM occurred preferentially during the pro-life phase of experimental brain stem death. Furthermore, pretreatment by microinjection into the bilateral RVLM of a specific ERK2 inhibitor, ERK activation inhibitor peptide II (1 nmol); a specific MEK1/2 inhibitor, U0126 (5 pmol); or a specific MNK1/2 inhibitor, CGP57380 (5 pmol) exacerbated the hypotension and blunted the augmented life-and-death signals exhibited during the pro-life phase. Those pretreatments also blocked the upregulated nitric oxide synthase I (NOS I)/protein kinase G (PKG) signaling, the pro-life cascade that sustains central cardiovascular regulatory functions during experimental brain stem death.

CONCLUSIONS

Our results demonstrated that activation of MEK1/2, ERK1/2 and MNK1/2 in RVLM plays a preferential pro-life role by sustaining the central cardiovascular regulatory machinery during brain stem death via upregulation of NOS I/PKG signaling cascade in RVLM.

Neurotrophins regulate bone marrow stromal cell IL-6 expression through the MAPK pathway

BACKGROUND

The host's response to infection is characterized by altered levels of neurotrophins and an influx of inflammatory cells to sites of injured tissue. Progenitor cells that give rise to the differentiated cellular mediators of inflammation are derived from bone marrow progenitor cells where their development is regulated, in part, by cues from bone marrow stromal cells (BMSC). As such, alteration of BMSC function in response to elevated systemic mediators has the potential to alter their function in biologically relevant ways, including downstream alteration of cytokine production that influences hematopoietic development.

METHODOLOGY/PRINCIPAL FINDINGS

In the current study we investigated BMSC neurotrophin receptor expression by flow cytometric analysis to determine differences in expression as well as potential to respond to NGF or BDNF. Intracellular signaling subsequent to neurotrophin stimulation of BMSC was analyzed by western blot, microarray analysis, confocal microscopy and real-time PCR. Analysis of BMSC Interleukin-6 (IL-6) expression was completed using ELISA and real-time PCR.

CONCLUSION

BMSC established from different individuals had distinct expression profiles of the neurotrophin receptors, TrkA, TrkB, TrkC, and p75(NTR). These receptors were functional, demonstrated by an increase in Akt-phosphorylation following BMSC exposure to recombinant NGF or BDNF. Neurotrophin stimulation of BMSC resulted in increased IL-6 gene and protein expression which required activation of ERK and p38 MAPK signaling, but was not mediated by the NFkappaB pathway. BMSC response to neurotrophins, including the up-regulation of IL-6, may alter their support of hematopoiesis and regulate the availability of inflammatory cells for migration to sites of injury or infection. As such, these studies are relevant to the growing appreciation of the interplay between neurotropic mediators and the regulation of hematopoiesis.

Insulin/IGF-I and related signaling pathways regulate aging in nondividing cells: from yeast to the mammalian brain

Mutations that reduce glucose or insulin/insulin-like growth factor-I (IGF-I) signaling increase longevity in organisms ranging from yeast to mammals. Over the past 10 years, several studies confirmed this conserved molecular strategy of longevity regulation, and many more have been added to the complex mosaic that links stress resistance and aging. In this review, we will analyze the similarities that have emerged over the last decade between longevity regulatory pathways in organisms ranging from yeast, nematodes, and fruit flies to mice. We will focus on the role of yeast signal transduction proteins Ras, Tor, Sch9, Sir2, their homologs in higher organisms, and their association to oxidative stress and protective systems. We will discuss how the “molecular strategy” responsible for life span extension in response to dietary and genetic manipulations appears to be remarkably conserved in various organisms and cells, including neuronal cells in different organisms. Taken together, these studies indicate that simple model systems will contribute to our comprehension of aging of the mammalian nervous system and will stimulate novel neurotherapeutic strategies in humans.

Differential central NOS-NO signaling underlies clonidine exacerbation of ethanol-evoked behavioral impairment

BACKGROUND

The molecular mechanisms that underlie clonidine exacerbation of behavioral impairment caused by ethanol are not fully known. We tested the hypothesis that nitric oxide synthase (NOS)-derived nitric oxide (NO) signaling in the locus coeruleus (LC) is implicated in this phenomenon.

METHODS

Male Sprague-Dawley rats with intracisternal (i.c.) and jugular vein cannulae implanted 6 days earlier were tested for drug-induced behavioral impairment. The latter was assessed as the duration of loss of righting reflex (LORR) and rotorod performance every 15 minutes until the rat recovered to the baseline walk criterion (180 seconds). In a separate cohort, we measured p-neuronal NOS (nNOS), p-endothelial NOS (eNOS), and p-ERK1/2 in the LC following drug treatment, vehicle, or NOS inhibitor.

RESULTS

Rats that received clonidine [60 Ig/kg, i.v. (intravenous)] followed by ethanol (1 or 1.5 g/kg, i.v.) exhibited synergistic impairment of rotorod performance. Intracisternal pretreatment with nonselective NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 0.5 mg) or selective nNOS inhibitor N-propyl-L-arginine (1 microg) exacerbated the impairment of rotorod performance caused by clonidine-ethanol combination. Exacerbation of behavioral impairment was caused by L-NAME enhancement of the effect of ethanol, not clonidine. L-NAME did not influence blood ethanol levels; thus, the interaction was pharmacodynamic. LORR caused by clonidine (60 microg/kg, i.v.)-ethanol (1 g/kg, i.v.) combination was abolished by selective inhibition of central eNOS (L-NIO, 10 microg i.c.) but not by nNOS inhibition under the same conditions. Western blot analyses complemented the pharmacological evidence by demonstrating that clonidine-ethanol combination inhibits phosphorylation (activation) of nNOS (p-nNOS) and increases the level of phosphorylated eNOS (p-eNOS) in the LC; the change in p-nNOS was paralleled by similar change in LC p-ERK1/2. NOS inhibitors alone did not affect the level of nitrate/nitrite, p-nNOS, p-eNOS, or p-ERK1/2 in the LC.

CONCLUSIONS

Alterations in NOS-derived NO in the LC underlie clonidine-ethanol induced behavioral impairment. A decrease in nNOS activity, due at least partly to a reduction in nNOS phosphorylation, mediates rotorod impairment, while enhanced eNOS activity contributes to LORR, elicited by clonidine-ethanol combination.

Nitric oxide-cGMP signaling regulates axonal elongation during optic nerve regeneration in the goldfish in vitro and in vivo

Nitric oxide (NO) signaling results in both neurotoxic and neuroprotective effects in CNS and PNS neurons, respectively, after nerve lesioning. We investigated the role of NO signaling on optic nerve regeneration in the goldfish (Carassius auratus). NADPH diaphorase staining revealed that nitric oxide synthase (NOS) activity was up-regulated primarily in the retinal ganglion cells (RGCs) 5-40 days after axotomy. Levels of neuronal NOS (nNOS) mRNA and protein also increased in the RGCs alone during this period. This period (5-40 days) overlapped with the process of axonal elongation during regeneration of the goldfish optic nerve. Therefore, we evaluated the effect of NO signaling molecules upon neurite outgrowth from adult goldfish axotomized RGCs in culture. NO donors and dibutyryl cGMP increased neurite outgrowth dose-dependently. In contrast, a nNOS inhibitor and small interfering RNA, specific for the nNOS gene, suppressed neurite outgrowth from the injured RGCs. Intra-ocular dibutyryl cGMP promoted the axonal regeneration from injured RGCs in vivo. None of these molecules had an effect on cell death/survival in this culture system. This is the first report showing that NO-cGMP signaling pathway through nNOS activation is involved in neuroregeneration in fish CNS neurons after nerve lesioning.

CNTF-evoked activation of JAK and ERK mediates the functional expression of T-type Ca2+ channels in chicken nodose neurons

Culture of chicken nodose neurons with CNTF but not BDNF causes a significant increase in T-type Ca(2+) channel expression. CNTF-induced channel expression requires 12 h stimulation to reach maximal expression and is not affected by inhibition of protein synthesis, suggesting the involvement of a post-translational mechanism. In this study, we have investigated the biochemical mechanism responsible for the CNTF-dependent stimulation of T-type channel expression in nodose neurons. Stimulation of nodose neurons with CNTF evoked a considerable increase in signal transducer and activator of transcription (STAT3) and extracellular signal-regulated kinase (ERK) phosphorylation. CNTF-evoked ERK phosphorylation was transient whereas BDNF-evoked activation of ERK was sustained. Pre-treatment of nodose neurons with the Janus tyrosine kinase (JAK) inhibitor P6 blocked STAT3 and ERK phosphorylation, whereas the ERK inhibitor U0126 prevented ERK activation but not STAT3 phosphorylation. Both P6 and U0126 inhibited the stimulatory effect of CNTF on T-type channel expression. Inhibition of STAT3 activation by the selective blocker stattic has no effect on ERK phosphorylation and T-type channel expression. These results indicate that CNTF-evoked stimulation of T-type Ca(2+) channel expression in chicken nodose neurons requires JAK-dependent ERK signaling. A cardiac tissue extract derived from E20 chicken heart was also effective in promoting T-type Ca(2+) channel expression and STAT3 and ERK phosphorylation. The ability of the heart extract to stimulate JAK/STAT and ERK activation was developmentally regulated. These findings provide further support to the idea that CNTF or a CNTF-like factor mediates normal expression of T-type channels.

Extrinsic regulation of T-type Ca(2+) channel expression in chick nodose ganglion neurons

Functional expression of T-type Ca(2+) channels is developmentally regulated in chick nodose neurons. In this study we have tested the hypothesis that extrinsic factors regulate the expression of T-type Ca(2+) channels in vitro. Voltage-gated Ca(2+) currents were measured using whole-cell patch clamp recordings in E7 nodose neurons cultured under various conditions. Culture of E7 nodose neurons for 48 h with a heart extract induced the expression of T-type Ca(2+) channels without any significant effect on HVA currents. T-type Ca(2+) channel expression was not stimulated by survival promoting factors such as BDNF. The stimulatory effect of heart extract was mediated by a heat-labile, trypsin-sensitive factor. Various hematopoietic cytokines including CNTF and LIF mimic the stimulatory effect of heart extract on T-type Ca(2+) channel expression. The stimulatory effect of heart extract and CNTF requires at least 12 h continuous exposure to reach maximal expression and is not altered by culture of nodose neurons with the protein synthesis inhibitor anisomycin, suggesting that T-type Ca(2+) channel expression is regulated by a posttranslational mechanism. Disruption of the Golgi apparatus with brefeldin-A inhibits the stimulatory effect of heart extract and CNTF suggesting that protein trafficking regulates the functional expression of T-type Ca(2+) channels. Heart extract- or CNTF-evoked stimulation of T-type Ca(2+) channel expression is blocked by the Jak/STAT and MAP kinase blockers, AG490 and U0126, respectively. This study provides new insights into the electrical differentiation of placode-derived sensory neurons and the role of extrinsic factors in regulating the functional expression of Ca(2+) channels.

Nitric oxide signaling participates in norepinephrine-induced activity of neuronal intracellular survival pathways

Much evidence has gathered that nitric oxide (NO) signaling, via cGMP-dependent mechanisms, may activate pro-survival pathways in hippocampal neurons and inhibit apoptosis. Past research has revealed that the enhancement of monoaminergic neurotransmission via exercise or treatment with antidepressant medications leads to an enhanced expression of brain-derived neurotrophic factor (BDNF). In isolated hippocampal neurons, norepinephrine (NE) application also increases the immunoreactivity of BDNF and several pro-survival signaling molecules. The data herein support the possibility that NO signaling plays an important role in enhancing neurotrophin expression and activation of the pro-survival phosphatidylinositol 3' kinase (PI-3K) pathway stimulated by NE. In isolated hippocampal neurons, the NO donor, sodium nitroprusside, increases BDNF, PI-3K, and phospho-ERK1 immunoreactivity. Specific inhibitors of the NO system suggest that NE-induced increases in hippocampal BDNF and the PI-3K pathway, but not stimulation of the MAPK pathway, depend upon NO signaling. In addition, inhibiting cGMP suggest that the effects of NE on BDNF immunoreactivity and Akt phosphorylation are also cGMP-dependent. Finally, the application of l-NAME to hippocampal neurons increases cell death. This is the first study of its kind demonstrating the involvement of NE-induced pro-survival signaling in three distinct signaling pathways: PI-3K, MAPK, and NO/cGMP. Possible mechanisms are discussed in light of the results.

Nerve growth factor induces endothelial cell invasion and cord formation by promoting matrix metalloproteinase-2 expression through the phosphatidylinositol 3-kinase/Akt signaling pathway and AP-2 transcription factor

Nerve growth factor (NGF) is a well characterized neurotrophic agonist in the nervous system that triggers angiogenesis. In this study, we investigated the signaling mechanisms involved in NGF-induced angiogenesis. NGF stimulated endothelial cell invasion and cord formation on Matrigel in vitro but had marginal effect on proliferation and migration of these cells. NGF stimulated matrix metalloproteinase (MMP)-2 mRNA expression and protein secretion in human umbilical vein endothelial cells. Using synthetic and endogenous inhibitors of MMP-2 and MMP-2 small interfering RNA suppressed NGF-induced invasion and cord formation. We demonstrated that NGF-induced MMP-2 secretion, invasion, and cord formation are regulated via activation of the NGF receptor, TrkA, phosphatidylinositol 3-kinase (PI3K), and Akt using various pharmacological inhibitors. Specifically, NGF enhanced TrkA phosphorylation, PI3K activity, and Akt phosphorylation. Introduction of NGF-neutralizing antibodies, dominant-negative Akt, or wild-type PTEN effectively inhibited NGF-induced MMP-2 secretion and cord formation. Deletion and site-directed mutagenesis analysis of the MMP-2 promoter demonstrated that the AP-2-binding site is critical for NGF-induced MMP-2 promoter activity. NGF increased the DNA binding activity of AP-2, which was suppressed by inhibitors of TrkA and PI3K. Furthermore, transfection of AP-2 small interfering RNA effectively blocked NGF-induced MMP-2 secretion and cord formation. Finally, NGF promoted neovessel formation in Matrigel plugs in vivo, which was significantly inhibited by K252a and LY294002, but it failed to promote angiogenesis using MMP-2 knock-out mice. Our data collectively suggest that NGF stimulates endothelial cell invasion and cord formation by augmenting MMP-2 via the PI3K/Akt signaling pathway and AP-2 transcription factor, which may be responsible for triggering angiogenesis.

Role of MAPKs in angiotensin II-induced steroidogenesis in rat glomerulosa cells

Angiotensin II is one of the most important stimuli of rat adrenal glomerulosa cells, stimulating both steroid secretion and growth. In a previous report, we had shown that Ang II promotes cellular hypertrophy, but not proliferation, in rat adrenal glomerulosa cells maintained in primary culture for 3 days. The inhibition of proliferation and stimulation of hypertrophy induced by Ang II involves both p42/p44(mapk) and p38 MAPK activation. The increase in cell protein content induced by Ang II entails formation of a cortical actin ring and Rac-dependent activation of p42/p44(mapk) and p38 MAPK. The present study summarizes these results and provides evidences that Ang II-induced activation of p42/p44(mapk) and p38 MAPK are implicated in aldosterone secretion by enhancing expression of specific steroidogenic proteins such as StAR and 3beta-HSD.

Dp71ab/DAPs complex composition changes during the differentiation process in PC12 cells

PC12 cells express different Dp71 isoforms originated from alternative splicing; one of them, Dp71ab lacks exons 71 and 78. To gain insight into the function of Dp71 isoforms we identified dystrophin associated proteins (DAPs) that associate in vivo with Dp71ab during nerve growth factor (NGF) induced differentiation of PC12 cells. DAPs expression was analyzed by RT-PCR, Western blot and indirect immunofluorescence, showing the presence of each mRNA and protein corresponding to alpha-, beta-, gamma-, delta-, and epsilon-sarcoglycans as well as zeta-sarcoglycan mRNA. Western blot analysis also revealed the expression of beta-dystroglycan, alpha1-syntrophin, alpha1-, and beta-dystrobrevins. We have established that Dp71ab forms a complex with beta-dystroglycan, alpha1-syntrophin, beta-dystrobrevin, and alpha-, beta- and gamma-sarcoglycans in undifferentiated PC12 cells. In differentiated PC12 cells, the complex composition changes since Dp71ab associates only with beta-dystroglycan, alpha1-syntrophin, beta-dystrobrevin, and delta-sarcoglycan. Interestingly, neuronal nitric oxide synthase associates with the Dp71ab/DAPs complex during NGF treatment, raising the possibility that Dp71ab may be involved in signal transduction events during neuronal differentiation.

A novel pathway for transcriptional regulation of alpha-synuclein

Alpha-synuclein is an abundant neuronal protein that has been linked to both normal synaptic function and neurodegeneration--in particular, Parkinson's disease (PD). Uncovering mechanisms that control alpha-synuclein transcription is therefore critical for PD pathogenesis and synaptic function. We previously reported that in PC12 cells and primary neurons, alpha-synuclein is transcriptionally up-regulated after application of growth factors. In the current work we have characterized the pathway involved in this regulation in PC12 cells. The MAP/ERK pathway, and in particular Ras, is both sufficient and necessary for the NGF and basic fibroblast growth factor (bFGF) -mediated response. Significantly, response elements for this pathway, including a putative occult promoter, lie within intron 1, a hitherto unappreciated regulatory region of the gene that may be utilized in this or other settings. The PI3 kinase pathway is also involved in alpha-synuclein regulation, but response elements for this pathway appear to lie primarily outside of intron 1. These findings indicate that NGF- and bFGF-mediated signal transduction via the MAP/ERK and PI3 kinase pathways, and in part via regulatory regions within intron 1, may be involved in alpha-synuclein transcriptional regulation. Targeting of these pathways may serve to modulate alpha-synuclein so that it achieves desirable levels within neuronal cells.

Nitric oxide induces thioredoxin-1 nuclear translocation: Possible association with the p21Ras survival pathway

One of the major redox-regulating molecules with thiol reducing activity is thioredoxin-1 (TRX-1). TRX-1 is a multifunctional protein that exists in the extracellular millieu, cytoplasm, and nucleus, and has a distinct role in each environment. It is well known that TRX-1 promptly migrates to the nuclear compartment in cells exposed to oxidants. However, the intracellular location of TRX-1 in cells exposed to nitrosothiols has not been investigated. Here, we demonstrated that the exposure of HeLa cells to increasing concentrations of the nitrosothiol S-nitroso-N-acetylpenicillamine (SNAP) promoted TRX-1 nuclear accumulation. The SNAP-induced TRX-1 translocation to the nucleus was inhibited by FPTIII, a selective inhibitor of p21Ras. Furthermore, TRX-1 migration was attenuated in cells stably transfected with NO insensitive p21Ras (p21(RasC118S)). Downstream to p21Ras, the MAP Kinases ERK1/2 were activated by SNAP under conditions that promote TRX-1 nuclear translocation. Inhibition of MEK prevented SNAP-stimulated ERK1/2 activation and TRX-1 nuclear migration. In addition, cells treated with p21Ras or MEK inhibitor showed increased susceptibility to cell death induced by SNAP. In conclusion, our observations suggest that the nuclear translocation of TRX-1 is induced by SNAP involving p21Ras survival pathway.

Up-regulation of cytosolic phospholipase A2α expression by N,N-diethyldithiocarbamate in PC12 cells; involvement of reactive oxygen species and nitric oxide

Disulfiram (an alcohol-aversive drug) and related compounds are known to provoke several side effects involving behavioral and neurological complications. N,N-diethyldithiocarbamate (DDC) is considered as one of the main toxic species of disulfiram and acts as an inhibitor of superoxide dismutase. Since arachidonic acid (AA) formation is regulated by reactive oxygen species (ROS) and related to toxicity in neuronal cells, we investigated the effects of DDC on AA release and expression of the alpha type of cytosolic phospholipase A(2) (cPLA(2)alpha) in PC12 cells. Treatment with 80-120 microM DDC that causes a moderate increase in ROS levels without cell toxicity stimulated cPLA(2)alpha mRNA and its protein expression. The expression was mediated by extracellular-signal-regulated kinase (ERK1/2), one of the mitogen-activated protein kinases. Treatment with N(G) nitro-L-arginine methyl ester (an inhibitor of nitric oxide synthase, 1 mM) and oxy-hemoglobin (a scavenger of nitric oxide, 2 mg/mL) abolished the DDC-induced responses (ERK1/2 phosphorylation and cPLA(2)alpha expression). We also showed DDC-induced up-regulation of the mRNA expression of lipocortin 1, an inhibitor of PLA(2). Furthermore, DDC treatment of the cells enhanced Ca(2+)-ionophore-induced AA release in 30 min, although the effect was limited. Changes in AA metabolism in DDC-treated cells may have a potential role in mediating neurotoxic actions of disulfiram. In this study, we show the first to demonstrate the up-regulation of cPLA(2)alpha expression by DDC treatment in neuronal cells.

Cross talk between nitric oxide and ERK1/2 signaling pathway in the spinal cord mediates naloxone-precipitated withdrawal in morphine-dependent rats

Our recent study has shown activation of spinal extracellular signal-regulated kinase-1 and -2 (ERK1/2), a member of the mitogen-activated protein kinase (MAPK) family, contributes to naloxone-precipitated withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats. However, the mechanism and significance of the spinal ERK1/2 activation during morphine dependence and withdrawal remain unknown. In this study, we reported that intrathecal (i.t.) pretreatment with either the non-selective nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), neuronal NOS (nNOS) inhibitor 7-nitro indazole (7-NI), or the inducible NOS (iNOS) inhibitor aminoguanidine (AG), could reduce morphine withdrawal-induced increase of phospho-ERK1/2 (pERK1/2) expression in the rat spinal cord. On the other hand, attenuation of the spinal ERK phosphorylation by the MAPK kinase (MEK) inhibitor U0126 also could inhibit the increase of nNOS and iNOS expression in the spinal cord of morphine withdrawal rats. Inhibitory expression of pERK1/2 by i.t. NOS inhibitor L-NAME, 7-NI or AG and of nNOS and iNOS by i.t. U0126 in the spinal cord were accompanied by decreased scores of morphine withdrawal and the inhibited spinal Fos protein (a maker for neuronal excitation or activation) expression induced by morphine withdrawal. These findings suggest cross talk between nitric oxide (NO) and the ERK1/2 signaling pathway mediates morphine withdrawal and withdrawal-induced spinal neuronal sensitization in morphine-dependent rats.

Fundamental role of nitric oxide in neuritogenesis of PC12h cells

1 We investigated the neuritogenic action of nitric oxide (NO)-generating agents and their mechanisms of action in a subclone of rat pheochromocytoma, PC12h cells. 2 NO donors such as sodium nitroprusside (SNP, 0.05-1 microM), NOR1 (5-100 microM), NOR2 (5-20 microM), NOR3 (5-20 microM), NOR4 (5-100 microM), or S-nitroso-N-acetyl-DL-penicillamine (SNAP, 10-100 microM) significantly induced neurite outgrowth. 3 NOR4-induced neurite outgrowth was accompanied by expression of neurofilament 200 kDa subunit (NF200) protein, an axonal marker, and was significantly inhibited by an NO scavenger, a soluble GC inhibitor, and a PKG inhibitor: 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide (carboxy-PTIO, 20-100 microM), 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one (ODQ, 100 microM) and KT5823 (0.2-1 microM), respectively. 4 The intracellular cGMP concentration of cells was markedly increased by treatment with NOR4 (100 microM). 5 A mitogen-activated protein kinase (MAPK) kinase inhibitor, PD98059 (10-50 microM), abolished the NOR4-induced neurite outgrowth. In agreement with this observation, NOR4 did phosphorylate extracellular signal-regulated kinase (ERK) 1 and 2, substrates of MAPK kinase. 6 A membrane-permeable cGMP analog, 8-Br-cGMP (1 mM) also induced significant neurite outgrowth. The 8-Br-cGMP-induced neurite outgrowth was almost completely inhibited by both KT5823 (0.5 microM) and PD98059 (50 microM). Moreover, sustained ERK phosphorylation was observed in the 8-Br-cGMP-treated PC12h cells. 7 These results suggest that NO itself has the ability to induce neurite outgrowth and that NO-induced ERK activation involves the NO-cGMP-PKG signaling pathway in PC12h cells.

Tellurium Compound AS101 Induces PC12 Differentiation and Rescues the Neurons from Apoptotic Death

Parkinson's disease is characterized by the loss of dopaminergic neurons in the substantia nigra (SN). Studies show that anti-apoptotic and neurotrophic agents are suitable candidates to prevent delayed cell death and/or restore neural function. Here we present the nontoxic immunomodulating compound AS101, which has the ability to induce neurite outgrowth and neural differentiation in PC12 cells. The present study shows that components of the ras signaling pathway are crucial for AS101-induced PC12 differentiation. These include p21ras and its downstream effectors, c-raf-1 and MEK, as well as PI3K. Moreover, these components mediate AS101-induced upregulation of p21waf, which is obligatory for AS101-induced PC12 differentiation. Furthermore, nitric oxide plays a significant role in these AS101 activities. Finally, we show that AS101 prevents apoptosis of NGF-differentiated PC12 cells after NGF withdrawal. Taken together, these results suggest that AS101 induces PC12 cell differentiation and survival by activating the ras-ERK1/2 and ras-PI3K signal transduction pathways, as well as inducing NO production. Our findings may be important in understanding the regulation of survival/apoptosis of neurons deprived of neurotropic support. Futhermore the data propose that AS101 may have clinical potential in the treatment of neurodegenerative disorders like Parkinson's disease.

Nerve growth factor-induced expression of the GTP cyclohydrolase I gene via Ras/MEK pathway in PC12D cells

Neurotrophins are essential for the development and survival of the catecholaminergic neurons. GTP cyclohydrolase I (GCH) is the first and rate-limiting enzyme in the biosynthesis of 5,6,7,8-tertahydrobiopterin (BH4), the required cofactor for tyrosine hydroxylase. Previously, we reported that TH requires the Ras/mitogen-activated protein kinase kinase (MEK) pathway for its induction by nerve growth factor (NGF). Here, we examined intracellular signals required for NGF-induced expression of the GCH gene in PC12D cells. The activity of GCH was increased up to 5-fold after the NGF treatment, and the increase was repressed by pretreatment with U0126, an MEK1/2 inhibitor, but not with protein kinase A (PKA), phosphoinositide 3-kinase (PI3K), p38 mitogen-activated protein kinase (MAPK), and c-Jun NH2-terminal kinase (JNK) inhibitors. Induction of GCH mRNA by NGF was also abolished by pretreatment with U0126. The human GCH promoter activity was significantly enhanced by NGF treatment. Deletion analysis showed that the 465-bp 5'-flanking region is responsible for NGF-enhanced promoter activity. These data suggest that the Ras-MEK pathway is required for coordinate expression of the GCH and TH genes induced by neurotrophins.

Differences in neuritogenic response to nitric oxide in PC12 and PC12h cells

We have demonstrated that a natural iridoid compound, genipin, induces neurite outgrowth through the nitric oxide (NO)-cGMP-protein kinase G signaling pathway in PC12h cells. PC12 cells, the parental cell line of PC12h cells, have been shown to carry out neurite extension that accompanies NO production in response to nerve growth factor (NGF). This neurite outgrowth was significantly inhibited by NG-nitro-L-arginine methyl ester (L-NAME), an NO synthase inhibitor, in both PC12 and PC12h cells, suggesting that the neuritogenesis is NO-dependent in both cells. In this report, we investigated whether genipin also induces neurite outgrowth in PC12 cells in order to determine the NO-dependent neurotrophic action of genipin in more than just one cell type. Genipin induced marked neurite outgrowth in PC12h cells but not in PC12 cells. The genipin-induced neurite outgrowth was significantly inhibited by L-NAME in PC12h cells. An NO donor, NOR4, also significantly induced neurite outgrowth in a concentration-dependent manner in PC12h cells but not in PC12 cells. On the other hand, NGF-primed PC12 cells exhibited significant neurite extension, which was inhibited by L-NAME, in response to genipin. Interestingly, NGF-primed PC12 cells responded to NOR4 extending neurites and expressed detectable neuronal NO synthase protein which is not detected in naive PC12 cells. These results suggest that genipin exerts a neuritogenic action on neuronal cells which are responsive to NO itself. Furthermore, the results also suggest that PC12h cells are more suitable for the study of NO-dependent neuronal function than PC12 cells which were not responsive to NO.

Effects of the JNK inhibitor anthra[1,9-cd]pyrazol-6(2H)-one (SP-600125) on soluble guanylyl cyclase alpha1 gene regulation and cGMP synthesis

The decreased expression of the nitric oxide (NO) receptor, soluble guanylyl cyclase (sGC), occurs in response to multiple stimuli in vivo and in cell culture and correlates with various disease states such as hypertension, inflammation, and neurodegenerative disorders. The ability to understand and modulate sGC expression and cGMP levels in any of these conditions could be a valuable therapeutic tool. We demonstrate herein that the c-Jun NH2-terminal kinase JNK II inhibitor anthra[1,9-cd]pyrazol-6(2H)-one (SP-600125) completely blocked the decreased expression of sGCalpha1-subunit mRNA by nerve growth factor (NGF) in PC12 cells. Inhibitors of the ERK and p38 MAPK pathways, PD-98059 and SB-203580, had no effect. SP-600125 also inhibited the NGF-mediated decrease in the expression of sGCalpha1 protein as well as sGC activity in PC12 cells. Other experiments revealed that decreased sGCalpha1 mRNA expression through a cAMP-mediated pathway, using forskolin, was not blocked by SP-600125. We also demonstrate that TNF-alpha/IL-1beta stimulation of rat fetal lung (RFL-6) fibroblast cells resulted in sGCalpha1 mRNA inhibition, which was blocked by SP-600125. Expression of a constitutively active JNKK2-JNK1 fusion protein in RFL-6 cells caused endogenous sGCalpha1 mRNA levels to decrease, while a constitutively active ERK2 protein had no effect. Collectively, these data demonstrate that SP-600125 may influence the intracellular levels of the sGCalpha1-subunit in certain cell types and may implicate a role for c-Jun kinase in the regulation of sGCalpha1 expression.

Regulation of cholinergic gene expression by nerve growth factor depends on the phosphatidylinositol-3'-kinase pathway

Nerve growth factor (NGF) exerts anti-apoptotic, trophic and differentiating actions on sympathetic neurons and cholinergic cells of the basal forebrain and activates the expression of genes regulating the synthesis and storage of the neurotransmitter acetylcholine (ACh). We have been studying the intracellular signaling pathways involved in this process. Although, in the rat pheochromocytoma cell line PC12, NGF strongly activates the mitogen-activated protein kinase (MAPK) pathway, prolonged inhibition of MAPK kinase (MEK) activity by PD98059 or U0126 did not affect the ability of NGF to up-regulate choline acetyltransferase (ChAT) or to increase intracellular ACh levels. In contrast, the treatment with the phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002, but not with its inactive analogue LY303511, completely abolished the NGF-induced production of ACh. Inhibition of PI3K also eliminated the NGF effect on the intracellular ACh level in primary cultures of septal neurons from E18 mouse embryos. Blocking the PI3K pathway prevented the activation of cholinergic gene expression, as demonstrated in RT/PCR assays and in transient transfections of PC12 cells with cholinergic locus promoter-luciferase reporter constructs. These results indicate that the PI3K pathway, but not the MEK/MAPK pathway, is the mediator of NGF-induced cholinergic differentiation.

Sargaquinoic acid supports the survival of neuronal PC12D cells in a nerve growth factor-independent manner

Sargaquinoic acid (designated previously as MC14) was isolated from a marine brown alga Sargassum macrocarpum, and has been found to possess a novel nerve growth factor (NGF)-dependent neurite outgrowth promoting activity in PC12D cells. In this study, we explored the neuroprotective effects of MC14 in terms of its survival supporting, antioxidant and neurite-regenerating activities under NGF deficient or deprived conditions. Intriguingly, MC14 did not only promote the NGF-induced survival support on neuronal PC12D cells, but also significantly abated neuronal PC12D cell death even in the absence of NGF. The pharmacological inhibition of phosphatidylinositol-3 kinase (PI3K) by wortmannin significantly suppressed the survival supporting activity of MC14, whereas the NGF receptor (tyrosine kinase A or TrkA) inhibitor K252a showed no detectable effect on MC14 activity. These results demonstrate that MC14 supports survival of neuronal PC12D cells in an NGF-independent manner, and that PI3K may be required for the neuroprotective activity of MC14. In addition, we have shown that MC14 markedly enhanced neurite-regeneration and protected PC12D cells from hydrogen peroxide (H(2)O(2))-induced oxidative stress. These pharmacological features suggest that MC14 may be a potentially important neuroprotective agent.

Nerve growth factor-induced up-regulation of cytosolic phospholipase A2alpha level in rat PC12 cells

Nerve growth factor (NGF) regulates various types of gene transcription in neurons. One of the cytosolic phospholipase A(2)s, cPLA(2)alpha, which preferentially cleaves phospholipids at the sn-2 position to arachidonic acid (AA), is involved in neuronal responses including survival. We investigated the effect of NGF on cPLA(2)alpha expression and its signaling pathways in PC12 cells, which differentiate into neuronal-like cells with neurites by NGF treatment. Treatment with NGF increased cPLA(2)alpha mRNA level after 4h and its protein level 24h after NGF addition. The NGF-induced increase in cPLA(2)alpha mRNA was inhibited by actinomycin D. NGF caused phosphorylation of mitogen-activated protein kinases (MAPKs); sustained phosphorylation of extracellular-regulated kinases (ERK1/2) and transient phosphorylation of p38 MAPK. NGF responses (cPLA(2)alpha mRNA and its protein) were inhibited by selective inhibitors for the ERK1/2 pathway, p38 MAPK and c-Jun NH(2)-terminal kinase. Epidermal growth factor, which transiently activates ERK1/2, did not modify cPLA(2)alpha expression. Although phorbol 12-myristate 13-acetate, an activator of protein kinase C (PKC), alone showed no effect, NGF-induced cPLA(2)alpha mRNA expression decreased due to the inhibition of PKC. These findings suggest that NGF-induced cPLA(2)alpha expression is regulated by gene transcription via the ERK1/2, p38 MAPK and PKC pathways in PC12 cells.

Elucidation of molecular events leading to neutrophil apoptosis following phagocytosis: cross-talk between caspase 8, reactive oxygen species, and MAPK/ERK activation

Phagocytosis of complement-opsonized targets is a primary function of neutrophils at sites of inflammation, and the clearance of neutrophils that have phagocytosed microbes is important for the resolution of inflammation. Our previous work suggests that phagocytosis leads to rapid neutrophil apoptosis that is inhibited by antibody to the beta2 integrin, Mac-1, and requires NADPH oxidase-derived reactive oxygen species (ROS) generated during phagocytosis. Here we report that phagocytosis-induced cell death (PICD) does not occur in Mac-1-deficient murine neutrophils, suggesting that PICD proceeds through a bona fide Mac-1-dependent pathway. A sustained, intracellular oxidative burst is associated with PICD. Furthermore, PICD does not require traditional death receptors, Fas, or tumor necrosis factor (TNF) receptor. TNF but not Fas synergizes with phagocytosis to enhance significantly PICD by increasing the oxidative burst, and this is Mac-1-dependent. Phagocytosis-induced ROS promote cleavage/activation of caspases 8 and 3, key players in most extrinsic ("death receptor") mediated pathways of apoptosis, and caspases 8 and 3 but not caspase 9/mitochondria, are required for PICD. This suggests that ROS target the extrinsic versus the intrinsic ("stress stimulus") apoptotic pathway. Phagocytosis also triggers a competing MAPK/ERK-dependent survival pathway that provides resistance to PICD likely by down-regulating caspase 8 activation. The anti-apoptotic factor granulocyte-macrophage colony-stimulating factor (GM-CSF) significantly enhances ROS generation associated with phagocytosis. Despite this, it completely suppresses PICD by sustaining ERK activation and inhibiting caspase 8 activation in phagocytosing neutrophils. Together, these studies suggest that Mac-1-mediated phagocytosis promotes apoptosis through a caspase 8/3-dependent pathway that is modulated by NADPH oxidase-generated ROS and MAPK/ERK. Moreover, TNF and GM-CSF, likely encountered by phagocytosing neutrophils at inflammatory sites, exploit pro-(ROS) and anti-apoptotic (ERK) signals triggered by phagocytosis to promote or suppress PICD, respectively, and thus modulate the fate of phagocytosing neutrophils.

ERK, JNK, and p38 MAP kinases differentially regulate proliferation and migration of phenotypically distinct smooth muscle cell subtypes

Proliferation and migration of vascular smooth muscle cells (SMCs) are important processes involved in the pathogenesis of vascular disorders such as atherosclerosis and post-angioplasty restenosis. Here we demonstrate that proliferation and migration of specific SMC subtypes is mitogen-activated protein (MAP) kinase-dependent. WKY12-22 SMCs derived from the aortae of 12 day-old pup rats proliferate and migrate faster than WKY3M-22 SMCs derived from the aortae of adult rats. WKY12-22 and WKY3M-22 cells equally expressed the active forms of phospho (Thr(183)/Tyr(185))-c-Jun N-terminal kinase (JNK) and phospho (Tyr(182))-p38, whereas the activity of extracellular signal-regulated kinase (ERK) was greater in WKY12-22 cells compared with WKY3M-22 cells. Proliferation of both SMC subtypes was attenuated by PD98059, SP600125 and SB202190, inhibitors of ERK, JNK, and p38, respectively. However, inhibition of PD98059 had a more profound effect on WKY12-22 SMCs. Furthermore, migration of WKY12-22 and WKY3M-22 cells was inhibited by SP600125 and SB202190, however, PD98059 failed to influence migration of either SMC subtype. Hence, migration of both SMC subtypes is JNK- and p38-dependent, but not ERK-dependent. These findings demonstrate that SMC heterogeneity is mediated, at least in part, by the activity of specific MAP kinase subtypes.

Intraluminal pressure increases vascular neuronal nitric oxide synthase expression

BACKGROUND

Development of high blood pressure (BP) is associated with an increased expression of neuronal nitric oxide synthase (nNOS) in vascular smooth muscle cells.

METHODS

We investigated whether or not changes in intraluminal pressure affect nNOS expression in carotid arteries of normotensive rats. Expression of nNOS and other NOS isoforms was determined by Western blot analysis in rat carotid arteries maintained up to 24 h at different levels of intraluminal pressure in an organ culture system.

RESULTS

Expression of nNOS in arteries exposed to 80 mmHg was stable for the duration of the experiment. Increasing intraluminal pressure to 200 mmHg transiently augmented nNOS expression at 9 h, both in intact arteries and in arteries where the endothelium and the adventitia were removed. The expression of endothelial NOS (eNOS) was also augmented under similar experimental conditions, but only after 24 h exposure. The ERK1/2 kinase cascade inhibitor PD 98059 significantly impaired the expression of nNOS in arteries exposed to 200 mmHg for 9 h. However, the angiotensin AT(1) antagonist candesartan and the angiotensin converting enzyme inhibitor perindoprilat did not have any effect under the same experimental conditions. Finally, the preferential nNOS inhibitor S-methyl-L-thiocitrulline significantly augmented the contraction evoked by angiotensin II in arteries exposed to 200 mmHg, but not in those maintained at 80 mmHg intraluminal pressure for 9 h.

CONCLUSION

These results show that transmural pressure increases nNOS expression and NO release in rat smooth muscle cells by a mechanism involving the mitogen-activated protein kinase pathway, but independent from the local formation of angiotensin II.

Effect of thyroid hormone responsive protein (THRP) expression on PC12 cell survival

The thyroid hormone responsive protein (THRP) is a novel gene product that remains responsive to thyroid hormone in the cerebral cortex of adult rats. The biological effects of THRP are currently unknown. Since thyroid hormones (TH) are known to cause cell death in primary neuronal cultures, the effect of exogenous THRP expression on PC12 cell viability was investigated. Co-transfection of the THRP expression plasmid with the selectable marker pSV2neo resulted in a lower number of surviving PC12 cells compared to transfection with pSV2neo and the empty vector, pSVL. Similar results were observed when PC12 cells were transfected with the plasmid pCMV. SPORT beta-gal with and without pSVL-THRP. However, expression of exogenous THRP in the colonic epithelial cell line Caco-2 and the glial cell line U251 had no effect on cell viability. Coexpression of THRP with either the wild-type (WT)-c-Abl or a kinase-defective mutant c-Abl (K290R) did not alter the cell viability changes induced by THRP alone. Under these experimental conditions the predominant form of cell death was necrosis as evidenced by in situ analyses, such as terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end labeling (TUNEL) and staining with membrane permeating and non-permeating nuclear dyes, Hoechst 33342 and propidium iodide respectively. In addition cell cycle arrest induced by THRP was demonstrated by reduced (3)H-thymidine incorporation into cellular DNA. The number of PC12 cells treated with 10(-7) M of l-3, 5, 3'-triiodothyronine (T(3)) was significantly reduced after the fourth day of culture. Treatment of the cells with T(3 )resulted in a dose dependent induction of THRP mRNA. It is concluded that: (1). THRP expression induces PC12 cell death; (2). under these experimental conditions the form of cell death is predominantly necrosis although cell cycle arrest may also occur; (3). the effect of THRP on cell viability is not modulated by c-Abl tyrosine kinase; and (4). the effect of T(3 )treatment on PC12 cell survival may be mediated by THRP.

Reactive oxygen species-mediated regulation of eNOS and iNOS expression in multicellular prostate tumor spheroids

Nitric oxide (NO) generated by either endothelial nitric oxide synthase (eNOS) or inducible nitric oxide synthase (iNOS) may be involved in prostate tumorigenesis through the inhibition of reactive oxygen species (ROS)-induced apoptosis. Multicellular DU-145 prostate tumor spheroids endogenously generated NO that paralleled the production of ROS. With increasing spheroid size, eNOS expression was downregulated, whereas an upregulation of iNOS expression was observed. In parallel, NO generation declined, as evaluated by the NO indicator diaminofluorescein-2 diacetate (DAF-2DA), suggesting that NO generation in DU-145 tumor spheroids is mainly mediated by eNOS. Elevation of ROS by treatment of tumor spheroids with either buthionine sulfoximine (BSO) or hydrogen peroxide resulted in upregulation of eNOS, whereas iNOS was downregulated. Furthermore, eNOS expression was increased by epidermal growth factor (EGF) in a redox-sensitive manner. Upregulation of eNOS after treatment with hydrogen peroxide was apparently transduced through receptor tyrosine kinase signaling pathways since it was abolished by the protein kinase C (PKC) inhibitor bisindolylmaleimide-1 (BIM-1), the p21(ras) inhibitor S-trans-trans-farnesylthiosalicylic acid (FTS), the c-Raf inhibitor ZM 336372 and PD98059, which inhibits ERK1/2 activation. Endogenous NO may serve to escape from oxidative stress-induced apoptosis since treatment of tumor spheroids with the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl imidazoline-1-oxyl 3-oxide (carboxy-PTIO) as well as the NO synthase inhibitor N-omega-amino-L-arginine (L-NAA) increased cleaved caspase-3. Consequently, lowering intracellular NO levels with either L-NAA or PTIO significantly raised ROS levels, indicating that endogenously generated NO may play a role as a ROS scavenger, thereby protecting exponentially growing tumor spheroids from ROS-induced apoptosis.

Involvement of nitric oxide in glucose toxicity on differentiated PC12 cells: prevention of glucose toxicity by tetrahydrobiopterin, a cofactor for nitric oxide synthase

Effects of high concentrations of glucose on cell survival of differentiated PC12 cells were examined. Seven day-culture with D-glucose (9.0-27.0 mg/ml as 2-6-fold of the optimal level) induced cell death in a dose-related manner but 3-day culture with high concentrations of glucose had no effect on cell viability. L-glucose had no effect on viability of PC12 cells, suggesting that D-glucose toxicity was independent of its osmolarity effect. Seven-day culture with D-glucose (13.5 mg/ml as 3-fold of the optimal level) increased nitric oxide metabolites (NOx) in the culture medium. Glucose-induced increase in NOx was eliminated by 0.1 mM L-nitro-arginine methylester (L-NAME), a nitric oxide synthase (NOS) inhibitor. Intracellular Ca(2+) concentration was increased by D-glucose in a dose-related manner, suggesting that D-glucose activated NOS by increasing intracellular Ca(2+) concentration in PC12 cells. Glucose-induced cell death was blunted by 0.1 mM L-NAME, showing that nitric oxide (NO) was involved in the glucose toxicity to PC12 cells. Tetrahydrobiopterin (BH(4)), a cofactor for NOS, attenuated both glucose-induced cell death and NOx production at 1 microM but not at 10 microM. The effects of BH(4) on glucose-induced cell death and NOx production were not mimicked by reducing agents such as ascorbate and cysteine. These results taken together suggest that high concentrations of glucose induced cell death via NO production and that low concentration of BH(4) had a protective effect against glucose neurotoxicity in differentiated PC12 cells.

Role of phosphatidylinositide 3-kinase in brain-derived neurotrophic factor-induced DARPP-32 expression in medium size spiny neurons in vitro

Brain-derived neurotrophic factor (BDNF) regulates several properties of striatal dopaminoceptive medium-sized spiny neurons (MSNs) in vivo and in vitro, including expression levels of DARPP-32 (dopamine and cyclic adenosine 3',5'-monophosphate-regulated phosphoprotein, 32 kDa). DARPP-32 is expressed in 96% of the MSNs, and is a key modulator of dopamine actions. We investigated the intracellular signal transduction pathways activated by BDNF in MSNs and via which BDNF induces DARPP-32 expression. We found that phosphorylation of the cyclic AMP response element binding protein (CREB) is only transiently increased following stimulation of MSNs by BDNF, whereas increased phosphorylation of the extracellular signal regulated kinases 1 and 2 (Erk1/2) and Akt is sustained for longer than 4 h. Treatment of cultures with inhibitors of mitogen-activated protein kinase kinase (MEK) or phosphatidylinositide 3-kinase (PI3K) showed that the majority of the BDNF-induced increase in DARPP-32 requires the PI3K pathway. We also found that inhibition of PI3K reduces BDNF-induced Erk phosphorylation, indicating that cross-talk between these pathways may play a prominent role in MSNs.