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Signaling pathways mediating a selective induction of nitric oxide synthase II by tumor necrosis factor alpha in nerve growth factor-responsive cells.
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PMID:  16144552     Owner:  NLM     Status:  PubMed-not-MEDLINE    
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BACKGROUND: Inflammation and oxidative stress play a critical role in neurodegeneration associated with acute and chronic insults of the nervous system. Notably, affected neurons are often responsive to and dependent on trophic factors such as nerve growth factor (NGF). We previously showed in NGF-responsive PC12 cells that tumor necrosis factor alpha (TNFalpha) and NGF synergistically induce the expression of the free-radical producing enzyme inducible nitric oxide synthase (iNOS). We proposed that NGF-responsive neurons might be selectively exposed to iNOS-mediated oxidative damage as a consequence of elevated TNFalpha levels. With the aim of identifying possible therapeutic targets, in the present study we investigated the signaling pathways involved in NGF/TNFalpha-promoted iNOS induction. METHODS: Western blotting, RT-PCR, transcription factor-specific reporter gene systems, mutant cells lacking the low affinity p75NTR NGF receptor and transfections of TNFalpha/NGF chimeric receptors were used to investigate signalling events associated with NGF/TNFalpha-promoted iNOS induction in PC12 cells. RESULTS: Our results show that iNOS expression resulting from NGF/TNFalpha combined treatment can be elicited in PC12 cells. Mutant PC12 cells lacking p75NTR did not respond, suggesting that p75NTR is required to mediate iNOS expression. Furthermore, cells transfected with chimeric TNFalpha/NGF receptors demonstrated that the simultaneous presence of both p75NTR and TrkA signaling is necessary to synergize with TNFalpha to mediate iNOS expression. Lastly, our data show that NGF/TNFalpha-promoted iNOS induction requires activation of the transcription factor nuclear factor kappa B (NF-kappaB). CONCLUSION: Collectively, our in vitro model suggests that cells bearing both the high and low affinity NGF receptors may display increased sensitivity to TNFalpha in terms of iNOS expression and therefore be selectively at risk during acute (e.g. neurotrauma) or chronic (e.g. neurodegenerative diseases) conditions where high levels of pro-inflammatory cytokines in the nervous system occur pathologically. Our results also suggest that modulation of NFkappaB-promoted transcription of selective genes could serve as a potential therapeutic target to prevent neuroinflammation-induced neuronal damage.
Authors:
Michael S Thomas; Wenru Zhang; Paivi M Jordan; H Uri Saragovi; Giulio Taglialatela
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Type:  Journal Article     Date:  2005-09-06
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Title:  Journal of neuroinflammation     Volume:  2     ISSN:  1742-2094     ISO Abbreviation:  -     Publication Date:  2005 Sep 
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Created Date:  2005-10-06     Completed Date:  2005-10-24     Revised Date:  2009-11-18    
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Nlm Unique ID:  101222974     Medline TA:  J Neuroinflammation     Country:  England    
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Languages:  eng     Pagination:  19     Citation Subset:  -    
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Department of Neuroscience and Cell Biology, The University of Texas Medical Branch, Galveston, Texas, USA. msthomas@utmb.edu
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Journal ID (nlm-ta): J Neuroinflammation
ISSN: 1742-2094
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open-access: This is an Open Access article distributed under the terms of the Creative Commons Attribution License (), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Received Day: 10 Month: 3 Year: 2005
Accepted Day: 6 Month: 9 Year: 2005
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DOI: 10.1186/1742-2094-2-19

Signaling pathways mediating a selective induction of nitric oxide synthase II by tumor necrosis factor alpha in nerve growth factor-responsive cells
Michael S Thomas1 Email: msthomas@utmb.edu
WenRu Zhang1 Email: wezhang@utmb.edu
Paivi M Jordan1 Email: pmroozen@utmb.edu
H Uri Saragovi2 Email: uri.saragovi@mcgill.ca
Giulio Taglialatela1 Email: gtaglial@utmb.edu
1Department of Neuroscience and Cell Biology, the University of Texas Medical Branch at Galveston, Texas - USA
2Department of Pharmacology and Therapeutics, McGill University, Montreal, QC, Canada

Background

Neuroinflammation is thought to play a prominent role in neurodegeneration associated with a variety of acute and chronic insults in both the central (CNS) and peripheral (PNS) nervous system [1,2]. Examples of neurotraumatic or neurodegenerative conditions where the occurrence or role of neuroinflammation has been documented include peripheral nerve injury [3-6], acute and chronic spinal cord injury [7-11], traumatic brain injury [12-14], stroke [15-17], amyotrophic lateral sclerosis (ALS, [18-20] and Alzheimer Disease (AD, [21-24].

Neurons susceptible to neuroinflammatory insults are often dependent for their survival on target derived neurotrophic factors such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) or glia-derived neurotrophic factor (GDNF). The same neurodegenerative conditions have also been associated with the presence of damaging high levels of free radical species leading to pathological oxidative stress [25]. For example, inflammatory involvement in AD pathogenesis has been proposed partly based on observations of increased levels of the pro-inflammatory cytokines tumor necrosis factor alpha (TNF?) and interleukin-1 beta (IL-1?) in cerebrospinal fluid and brain cortex of AD patients [26,27]. Additionally, among the most affected neurons in AD are the basal forebrain cholinergic neurons (BFCN, [28-30]), which rely upon trophic support by target-derived NGF [31,32]. Furthermore, there is strong evidence for the presence of oxidative damage in the AD brain [33-36]. Similarly, neuronal damage following acute spinal cord injury or peripheral nerve injury has been shown to involve a neuroinflammatory as well as oxidative stress component [1,8,10,11,37-39], and traumatic head injury is also known to be associated with increased circulating concentrations of inflammatory cytokines and reduced numbers of basal forebrain cholinergic neurons [13,40-42].

Thus, there seems to be an intimate relationship between pro-inflammatory cytokines, oxidative stress and trophic factors that underscores the neuropathological consequences of extrinsic (e.g. traumatic) or intrinsic (e.g. disease-related) injury to the nervous system. Our previous work has shown that in NGF-responsive rat pheochromocytoma (PC12) cells TNF? induces expression of the free radical nitric oxide (NO) synthesizing enzyme NOS II (iNOS) only in the presence of NGF acting through its high affinity receptor TrkA [43]. Indeed, perturbed levels of NOS and NO-derived oxidative damage have been reported in both acute and chronic neurodegenerative conditions [25], including spinal cord injury [44-46], stroke [47,48] and AD [49-53]. However, TNF? alone has not been shown to be an effective inducer of human iNOS promoter activity [54] or of rat cortical iNOS expression when administered intracerebroventricularly [55]. Nonetheless, TNF? has been shown to contribute to the death of NGF-dependent neurons in vitro [56] and in vivo [57,58]. Therefore, our previous results suggest the attractive idea that one mechanism through which increased levels of TNF? affect certain trophic factor-responsive neurons may involve NO-derived oxidative damage brought about by a synergistic induction of iNOS. Understanding the molecular mechanisms mediating the synergistic NGF/TNF?-promoted induction of iNOS may thus provide novel therapeutic targets for the prevention of certain neurodegenerative events associated with acute or chronic injury of the nervous system.

Here we report that a reversible expression of iNOS, produced in PC12 cells by simultaneous exposure to NGF and TNF?, requires the simultaneous presence of both the low-affinity p75NTR and the high-affinity TrkA NGF receptors. Furthermore, using specific inhibitors and a reporter gene assay, we show that such synergistic effect of the combined NGF/TNF? treatment is mediated by the transcription factor nuclear factor kappa B (NF-?B).


Methods
Materials

All routine reagents and chemicals were obtained from Sigma-Aldrich (St Louis, MO, USA), except where noted otherwise. Recombinant human and rat TNF and rat IGF were obtained from R&D Systems, Minneapolis, MN, USA, purified mouse NGF from Harlan Bioproducts, Indianapolis, IN, USA, and pyrrolidine dithiocarmbamate (PDTC), the octapeptide proteasome inhibitor (PSI), PD98059, K252a and 1400 W from Calbiochem, San Diego, CA, USA.

Clonal cell lines

Stock cultures of rat pheochromocytoma cells (PC12; a kind gift of Dr. Lloyd Greene, Columbia University, New York, NY, USA) and PC12 cells lacking the low affinity p75NTR NGF receptor were maintained in 75 cm2 tissue culture flasks in 10 ml RPMI-1640 culture medium supplemented with 5% heat inactivated fetal bovine serum in a humidified cell incubator at 37?C kept at a 5% CO2 atmosphere. Half of the medium was replaced every other day and the cells were split once a week to maintain cell viability.

Expression vectors

Transient transfection of cells was performed by a liposomal packaging system. Briefly, 1.2 pmol of expression vector were mixed with DMRIE-C (Life Technologies, Carlsbad, CA, USA) in a 1:3 DNA to liposome ratio. The DNA/liposomes were diluted in 400 ?l serum free transfection medium (Optimem) and then added to approximately 100,000 cells in a 12 well cell culture plate. The cells were allowed to take up the liposomal DNA for 3 hours before being washed and returned to cell culture medium. Cells were allowed to recover for 24 hours before any treatments. The cDNA coding for chimeric proteins bearing the extracellular domain of the TNFR1 receptor and the transmembrane and cytosolic domains of the NGF receptors (either p75NTR or TrkA) was a kind gift from Dr. Eric Shooter and prepared as described [77], (Stanford University, Palo Alto, Ca, USA). The p-SEAP expression vector, containing the SEAP gene under NF-kB, AP1 or CRE enhancer control, was purchased from Clontech (Palo Alto, CA, USA). Conditioned medium from cells transfected with the SEAP reporter vectors was assayed for alkaline phosphatase by sampling the medium and using the chemiluminescent Great EscAPe SEAP assay (Clontech, Palo Alto, CA, USA), according to manufacturer's instructions.

Western blot analysis

Cells were lysed using an SDS-based lysis buffer (2% SDS, 5 mM EDTA, 50 mM Tris, 1 mM each of DTT, PMSF and protease inhibitor cocktail). Following an ice-cold PBS wash, cells were lysed with SDS lysis buffer and the sonicated briefly before clarifying by centrifugation at 20,000 g for 20 minutes at 4?C. After centrifugation the supernatant was collected and protein content was measured using the standard BCA protein assay (Pierce, Rockford, IL, USA). Protein extracts (40 ?g) were diluted in 6X sample buffer and loaded onto a 6% SDS-polyacrylamide gel. Gels were run for one hour at 100 V and then were transferred to a nitrocellulose membrane overnight at 25 V. All incubations were at room temperature in 0.5% Tween in Tris buffered saline (TTBS). The membranes were blocked for one hour in 5% milk in TTBS. Primary monoclonal anti-iNOS (Signal Transduction Laboratories, San Diego, CA, USA) or polyclonal anti-TNFR1 (Santa Cruz Biotechnology, Santa Cruz, CA, USA) were diluted in 2.5% milk in TTBS at 1:1000 and membranes were incubated with the antibody for one hour at room temperature. Membranes were washed three times for ten minutes each in TTBS before incubating for one hour with a horseradish-peroxidase secondary antibody (BioRad, Hercules, CA, USA) at 1:7500 in 2.5% milk in TTBS. Finally, membranes were washed again in TTBS three times for ten minutes each. Immunoreactive bands were visualized by a chemiluminescent western blot detection kit (Amersham Biosciences, Piscatay, NJ, USA) according to manufacturer's instructions. Images were captured using a 12 bit monochrome camera (UVP, Upland, CA, USA).

Reverse transcriptase polymerase chain reaction assay

Total RNA was extracted with Trizol Extraction Kit (Gibco BRL, San Diego, CA, USA) according to manufacturer's instructions. One ?g of total RNA from each sample was applied to Ready-to-go RT-PCR Beads (Amersham Biosciences, Piscatay, NJ, USA) and used to complete the amplification protocol according to manufacturer's instructions. Primer sequences for rat iNOS were as follows; forward 5'-CAC GGA GAA CAG AGT TGG-3' and reverse 5'-GGA ACA CAG TAA TGG CCG ACC-3'. Amplified samples were run on agarose gels and stained with ethidium bromide. Images were captured using a 12 bit monochrome camera (UVP, Upland, CA, USA).

Flow cytometry

One ?g of antibody against TrkA or p75NTR (Santa Cruz Biotechnology, Santa Cruz, CA, USA) was labeled with Zenon Rabbit IgG labeling kit from Molecular Probes (Eugene, OR) according to manufacturer's instructions and incubated for 1 hr with the cells in suspension. After incubation, labeled cells were visualized and quantified using a Becton Dickinson FACS Vantage Flow Cytometer set at appropriate instrument parameters.

Statistical analysis

Where appropriate, data were expressed as mean +/- standard error of the mean (S.E.M.), and analyzed by student unpaired two-tailed t test with significance set at p < 0.05.


Results
Combined NGF and TNF? induce iNOS message and protein

The upper panel of figure 1 shows a western blot detecting iNOS in PC12 cells treated simultaneously with 10 ng/ml NGF and 10 ng/ml TNF? in the presence or absence of 50 nM K252a, an inhibitor of phosphorylative events associated with tyrosine kinase receptor activation that has been shown to block the function of the high affinity NGF receptor TrkA [61]. There was a marked induction of iNOS expression only in cells simultaneously treated with NGF and TNF?, while neither treatment alone elicited any effect. Furthermore, K252a completely abolished NGF/TNF?-promoted iNOS induction, suggesting that TrkA function is essential to mediate it. As shown in the lower panel of figure 1, along with increased protein levels there was also an induction of iNOS mRNA in PC12 cells treated with NGF and TNF? but not in cells treated with either factor alone.

NGF and TNF? are both required for sustained iNOS expression

Figure 2A shows western blots detecting iNOS in cells treated with increasing concentrations of NGF (top panel) or TNF? (bottom panel), in the presence or absence of a fixed amount of TNF? or NGF, respectively. Either factor was ineffective when added alone at any of the concentrations tested. However, there was a marked dose-response increase in iNOS expression when increasing concentrations of NGF or TNF? were added in the presence of a fixed amount of TNF? or NGF, respectively. Figure 2B shows a representative western blot detecting iNOS expression in cells continuously treated with NGF and TNF? as compared to cells in which the combined treatment was withdrawn after 24 hr. The expression of iNOS returned to basal, undetectable, levels between 24 and 48 hr after withdrawal of both TNF? and NGF. Furthermore, as shown in figure 2C, withdrawal of either NGF or TNF? alone was sufficient to abolish iNOS expression induced by the combined treatment, both at the protein (top panel) and mRNA level (bottom panel). To exclude the involvement of unknown serum factors, NGF/TNF?-promoted induction of iNOS was determined in cells cultured for 24 hr in serum free or in defined medium N2 (Figure 2D). There was a detectable iNOS induction in both serum free- and defined medium-cultured cells, although much reduced in serum free conditions, which is predictable as PC12 cells do not survive for longer periods of time (24?48 hrs) in the absence of serum or N2 supplements. Since insulin is present in both serum and the N2 supplement, and can activate the insulin-like growth factor (IGF) receptor, we asked whether TNF? may synergize with IGF, which is also present in serum, to induce iNOS expression. The results shown in Figure 2E indicate that this is not the case.

TNF?/NGF-mediated iNOS expression is independent of NOS enzymatic activity

In order to determine whether the enzymatic activity of iNOS may play a role in sustaining TNF?/NGF-promoted signaling we pretreated PC12 cells with two NOS inhibitors prior to TNF?/NGF tretament. Pretreatment with N(G)-nitro-L-arginine methyl ester (L-NAME) did not affect expression of iNOS induced by the NGF/ TNF? combined treatment (Figure 3A). The same result was observed if a more specific inhibitor of iNOS (1400 W) was used instead of L-NAME (Figure 3B). Concentrations of 1400 W used here have been previously shown to be effective in inhibiting selectively iNOS activity in PC12 cells by others [78]. These results suggest that sustained iNOS expression in response of the combined NGF/TNF? treatment is independent of NOS enzymatic activity.

NGF/TNF? promoted iNOS induction requires the transcription factor NF-?B

Figure 4 shows results from PC12 cells transiently transfected with a secreted alkaline phosphatase reporter gene construct (SEAP) promoted by enhancer sequences specific for nuclear factor kappa B (NF-?B), activator protein 1 (AP-1), cAMP-responsive element (CRE) or Tal (non-inducible control). Twenty-four hr after transfection cells were treated with 10 ng/ml each of TNF? and NGF (alone or combined) and SEAP released in the culture medium (an index of endogenous transcription factor activation) was assayed 3 hr and 12 hr later. At 3 hr, cells treated with TNF? showed a significant increase in NF-?B activity but not AP-1 or CRE. Cells treated with NGF alone showed at 3 hr no significant increase in NF-?B, AP1 or CRE activity. When cells were exposed to the combined NGF/ TNF? treatment, there was a robust increase in NF-?B activity that was significantly higher than the response induced by the individual treatment with TNF?. On the other hand, neither AP-1 nor CRE activity were significantly affected by the combined NGF/ TNF? treatment. At 12 hr, both TNF? and NGF/TNF? combined treatments significantly increased NF-?B activity, but were not statistically significantly different. NGF-treated cells showed a significant increase in AP-1 and CRE activity at 12 hr, while NF-?B activity was not affected. As a result, there was also a significant increase in AP-1 and CRE activity elicited by the NGF/TNF? combined treatment at 12 hr. Neither NGF nor TNF? (alone or combined) elicited any effect on the control reporter construct Tal, either at 3 or 12 hr.

Involvement of NF-?B was further explored by determining the extent to which pharmacological inhibition of NF-?B would block NGF/TNF?-promoted iNOS induction in PC12 cells. As shown in figure 5A, treatment of PC12 cells with either pyrrolidine di-thio-carbamate (PDTC) or the octapeptide proteasome inhibitor PSI (two effective NF-?B inhibitors that have distinct mechanisms of action [8,63-65], completely abolished NGF/ TNF?-promoted iNOS induction. In this experiment, PD98059, a selective MAPK inhibitor, was used as a negative control. Both NF-?B inhibitors effectively blocked NF-?B-mediated transcriptional activity as determined by SEAP reporter gene assay (Figure 5B), whereas PD98059 had no effect. However, PD98059 completely blocked NGF-promoted neurite outgrowth (Figure 5C), an event that in PC12 cells is dependent on MAPK activation [66]. Furthermore, consistent with the results reported in Figure 4, inhibition of NOS activity by L-NAME did not affect NF?B activation by NGF/TNF? combined treatment (Figure 5D).

NGF/TNF?-promoted iNOS induction requires the simultaneous presence of both the p75NTR and TrkA NGF receptors

Next, we subcloned a PC12 mutant cell line (PC12p75NTR (-)) that lacks p75NTR expression while retaining TrkA at levels comparable with wild type PC12 cells (Figure 6A). NF-?B activity was not significantly increased by the NGF/TNF? combined treatment over the levels induced by TNF? alone in PC12p75NTR (-) (Figure 6B). Consistent with this finding, PC12p75NTR (-) cells exposed to the combined NGF/TNF? treatment did not show any induction of iNOS expression as compared to the parent cell line (Figure 6C). It is important to note that the PC12p75NTR (-) cells used here express TNF? receptor type 1 (TNFR1) at levels comparable (or even higher) than wild type PC12 cells (Figure 6D). Therefore lack of iNOS induction by the NGF/TNF? combined treatment in these cells cannot be ascribed to lack of TNF? responsiveness (as can also be appreciated by the NF?B response induced by TNF? alone shown in figure 6B).

The results obtained in PC12p75NTR(-) would suggest that p75NTR is essential to mediate iNOS induction by the combined TNF?/NGF treatment while the results obtained using K252a (Figure 1) would suggest a prominent role for TrkA. In order to ultimately ascertain the relative role of the two NGF receptors in mediating TNF?/NGF-promoted iNOS induction we made use of PC12 cells transiently transfected with expression vectors coding for chimeric TNF?/NGF receptors constructed as described by Rovelli et al. [77]. These constructs bear the ligand binding domain from the human TNFR1 and the signal transduction domain from rat NGF receptors, either TrkA or p75NTR. Previously, it has been shown that transfection with these chimeras allows for TNF-promoted NGF signaling [77]. Figure 7 shows a western blot detecting iNOS in PC12 cells individually or simultaneously transfected with chimeric TNF? receptors bearing the intracellular domain of p75NTR (p55/p75NTR) or TrkA (p55/TrkA). Transfected cells were then treated either with TNF? and NGF alone, or with both TNF? and NGF. As expected, the combined TNF?/NGF treatment induced a robust expression of iNOS in these PC12 cells, regardless of the presence of any transfected expression vector. As also expected, NGF alone did not elicit iNOS expression in any of the transfected cells. Similarly, TNF? alone did not induce iNOS in cells transfected with either p55/p75NTR or p55/TrkA chimeric receptors. However, TNF? promptly induced iNOS expression in cells transfected with both p55/p75NTR and p55/TrkA chimeric receptors.


Discussion

The work presented here stems from our original observation that iNOS expression and subsequent NO production can be synergistically induced by NGF and TNF? in a TrkA-dependent manner in PC12 cells [43]. Our present results investigated the signalling pathways involved. Since we consistently observed a higher iNOS expression if NGF is added simultaneously to TNF?, we propose that iNOS expression was induced selectively in NGF-responsive cells. These results do not allow us to rule out the possibility that intermediate factors induced by TNF? or NGF may play a role in sensitizing indirectly cells to NGF or TNF?, respectively. However, the results shown in Figure 2 seem to exclude such a possibility. Indeed, while withdrawal of NGF and/or TNF? allows for a prompt ablation of iNOS expression (Figure 2B), neither NGF nor TNF? alone is sufficient to sustain iNOS expression following withdrawal of TNF? or NGF (Figure 2C). These observations suggest that the simultaneous and continuous presence of both factors is required to sustain iNOS induction/expression and that cell sensitization through a priming mechanism seems unlikely. Nonetheless, other researchers have attributed increased TNF? toxicity in PC12 cells to NGF-induced differentiation [67]. However, our results seem to exclude that differentiation of PC12 cells may have played a role. First, in our experimental conditions iNOS expression occurs as early as 3 hr after the exposure to the combined NGF/TNF? treatment [43], earlier than any morphological differentiation induced by NGF. Second, while blockade of NGF-induced differentiation by the MAPK inhibitor PD98059 (Figure 5C, [68]) had no effect on NGF/TNF?-promoted iNOS expression (Figure 5A), blockade of NF?B did not affect NGF-induced differentiation (Figure 5C) but completely inhibited iNOS expression.

In the present study we also report that induction and maintenance of iNOS expression by the combined NGF/TNF? treatment requires continuous de novo iNOS mRNA synthesis, presumably due to transcription factor regulation. Indeed, abolishing iNOS enzymatic activity had no effect on NGF/TNF?-promoted iNOS induction (Figure 4A,B). Therefore, the involvement of positive feedback due to NO seems unlikely. On the other hand, analysis of transcriptional activity of NF-?B, AP-1 and CRE revealed that NF-?B most likely mediates synergistic iNOS induction by TNF? and NGF. Since iNOS induction can be observed as early as 3 hr after NGF/TNF? combined treatment in PC12 cells [43], the results shown in figure 5 suggest that NF-?B is the only transcription factor among those tested here that is responsive to the simultaneous treatment with TNF? and NGF in a fashion consistent with induction of iNOS expression. In fact, while TNF? alone induced NF?B at 3 hr, this induction was significantly lower than the one promoted by the combined NGF/TNF? treatment. Whether the extent to which NF?B is activated or whether qualitative differences in NF?B subunit composition in response to TNF? as compared to NGF/TNF? treatment may play a role in inducing iNOS expression remains to be established. Nonetheless, inhibition of NF-?B completely inhibited iNOS induction while inhibition of MAPK was ineffective (Figure 5A). Lastly, inhibition of NOS activity failed to block NGF/TNF?-promoted NF?B activation, thus further supporting the idea that targeting NO may acutely ameliorate associated oxidative stress, but could not represent the most comprehensive approach to achieve a long term correction of these events.

Previous studies indicated that NGF can induce NF-?B by acting through the low affinity p75NTR receptor [70]. Thus, involvement of NF-?B in mediating NGF/TNF? combined effects would suggest a role for p75NTR. Indeed, we found that mutant PC12 cells that lack expression of the p75NTR receptor failed to respond in terms of iNOS expression when simultaneously treated with NGF and TNF?. Consistent with this finding, in PC12 cell mutants lacking p75NTR expression NF-?B activity was not induced by the combined NGF/TNF? treatment above the levels observed in cells treated with TNF? alone (Figure 6B).

That PC12 cells bearing only the TrkA receptor failed to respond the combined NGF/TNF? treatment suggests that signaling from p75NTR in combination with TNF? is necessary to induce iNOS expression. On the other hand, our previous work illustrated the importance of TrkA-associated signaling in mediating NGF/TNF?-promoted induction of iNOS [43] (see also figure 1). These results are only apparently in contrast. Indeed, in an admittedly artificial system making use of chimeric constructs we observed that only in the presence of both TNF?-responsive NGF receptor signaling can TNF? promote iNOS expression when added alone. Whether this is a consequence of simultaneous but independent signaling of both types of NGF receptors [79] or recruitment of intracellular signalling elements uniquely driven by the simultaneous activation of both NGF receptors' signaling domains remains to be investigated. On the other hand, these results exclude the possibility that the combined action of TNF? and NGF may derive from yet undescribed interaction(s) of the extracellular domains of their respective receptors following ligand binding.

Thus, our combined results would indicate that there exists a specific pathway involving NF-?B and requiring the simultaneous expression or both types of NGF receptors that is synergistically induced by TNF? and NGF to promote expression of iNOS. This is of particular interest given that neuron types expressing both TrkA and p75NTR receptors are limited and known to be affected in neurodegenerative conditions where neuroinflammation and pro-inflammatory cytokines have been shown to play a significant role. Notably, simultaneous expression of TrkA and p75NTR in the CNS is mostly restricted to the BFCN that are known to be particularly affected in AD. Indeed, others have also described signaling pathways that require the simultaneous expression of both TrkA and p75NTR [71,72] as well as the convergence of TrkA and p75NTR-mediated signaling impinging upon NF-?B [73]. Recent reports in neurons of TNF-promoted signaling occurring selectively in the presence of the glutamate agonist NMDA [4] illustrate the importance of considering the signaling "context" when studying the effects of cytokine treatment.

Overall, our data indicate the possibility that a convergence between NGF-promoted trophic signaling and TNF? could selectively endanger NGF-responsive neurons under conditions of neuroinflammation because of a synergistic action between TNF? and NGF to induce iNOS expression. For example, TNF? overexpressing transgenic mice show selective neurodegeneration of NGF-responsive basal forebrain cholinergic neurons [57] and direct TNF? administration in the brain of mice results in an impairment of basal forebrain cholinergic function [58]. However, whether induction of iNOS and subsequent oxidative damage may play a role in these two models remains to be determined [80].


Conclusion

TNF? and NGF, via concerted signaling events involving NF?B transcriptional activity and targeting NGF-responsive cells bearing both the high and low affinity NGF receptors, converge to stimulate de novo transcription of iNOS. Our present results are relevant to neurodegenerative conditions such as AD [22,74], stroke [17,75], ALS [20,76] and spinal chord injury [8,10] where neuroinflammation and high levels of pro-inflammatory cytokines have been shown to play a significant role and proposed as therapeutic targets.


List of Abbreviations

AraC, cytosine ?-D-arabinofuranoside; AD, Alzheimers disease; BDNF, brain derived neurotrophic factor; BFCN, basal forebrain cholinergic neurons; CNS, central nervous system; CRE, cyclic-AMP response element; GDNF, glial derived neurotrophic factor; IGF, insulin-like growth factor; IL-1?, interleukin-1beta; iNOS, inducible nitric oxide synthase; MAPK, mitogen activated protein kinase; NF-?B, nuclear factor kappa B; NGF, nerve growth factor; NO, nitric oxide; nNOS, neuronal nitric oxide synthase; NTR, neurotrophin receptor; PC12, pheochromocytoma; PCN, penicillin; PDTC, pyrrolidinedithyocarbamate; PSI, proteosome inhibitor; SDS, sodium dodecylsulfate; SEAP, secreted alkaline phosphatase; S.E.M, standard error of the mean; Strep, streptomycin; TNF?, tumor necrosis factor alpha; TrkA, troponin-like receptor kinase A; TTBS, tris-buffered saline with tween 20;


Competing interests

The author(s) declare they have no competing interests.


Authors' contributions

MST participated in the conception and design of the study, carried out the bulk of experiments, performed data analysis, and drafted the manuscript. PMJ participated in study design especially with regards to the IGF experiments. WZ participated in study design and coordination and provided the expertise for RTPCR and withdrawal experiments. HUS sub-cloned the PC12p75NTR(-) cells and participated in study design and result interpretation of experiments involving these cells. GT participated in conception, study design, coordination and helped to draft and review the manuscript. All authors read and approved the final manuscript.


Acknowledgements

This work was supported in part by a research development grant by the UTMB Sealy Endowed Fund for Biomedical Research. Michael Thomas is supported by an NIEHS training grant pre-doctoral fellowship from T32 ES007254 and the UTMB Sealy Center for Aging pre-doctoral fellowship.


References
Floyd RA. Neuroinflammatory processes are important in neurodegenerative diseases: an hypothesis to explain the increased formation of reactive oxygen and nitrogen species as major factors involved in neurodegenerative disease developmentFree Radic Biol Med 1999;26:1346–55. [pmid: 10381209] [doi: 10.1016/S0891-5849(98)00293-7]
McGeer PL,McGeer EG. Innate immunity, local inflammation, and degenerative diseaseSci Aging Knowledge Environ 2002;2002:re3. [pmid: 14602998]
Creange A,Lefaucheur JP,Authier FJ,Gherardi RK. Cytokines and peripheral neuropathiesRevue Neurologique 1998;154:208–216. [pmid: 9773044]
Sung YJ,Ambron RT. Pathways that elicit long-term changes in gene expression in nociceptive neurons following nerve injury: contributions to neuropathic painNeurol Res 2004;26:195–203. [pmid: 15072639] [doi: 10.1179/016164104225013761]
Chandross KJ. Nerve injury and inflammatory cytokines modulate gap junctions in the peripheral nervous systemGlia 1998;24:21–31. [pmid: 9700486] [doi: 10.1002/(SICI)1098-1136(199809)24:1<21::AID-GLIA3>3.0.CO;2-3]
Stoll G,Jander S,Myers RR. Degeneration and regeneration of the peripheral nervous system: from Augustus Waller's observations to neuroinflammationJ Peripher Nerv Syst 2002;7:13–27. [pmid: 11939348] [doi: 10.1046/j.1529-8027.2002.02002.x]
Norenberg MD,Smith J,Marcillo A. The pathology of human spinal cord injury: defining the problemsJ Neurotrauma 2004;21:429–40. [pmid: 15115592] [doi: 10.1089/089771504323004575]
La Rosa G,Cardali S,Genovese T,Conti A,Di Paola R,La Torre D,Cacciola F,Cuzzocrea S. Inhibition of the nuclear factor-kappaB activation with pyrrolidine dithiocarbamate attenuating inflammation and oxidative stress after experimental spinal cord trauma in ratsJ Neurosurg Spine 2004;1:311–21. [pmid: 15478370]
Popovich PG,Jones TB. Manipulating neuroinflammatory reactions in the injured spinal cord: back to basicsTrends Pharmacol Sci 2003;24:13–7. [pmid: 12498725] [doi: 10.1016/S0165-6147(02)00006-8]
Hausmann ON. Post-traumatic inflammation following spinal cord injurySpinal Cord 2003;41:369–78. [pmid: 12815368] [doi: 10.1038/sj.sc.3101483]
Bareyre FM,Schwab ME. Inflammation, degeneration and regeneration in the injured spinal cord: insights from DNA microarraysTrends Neurosci 2003;26:555–63. [pmid: 14522149] [doi: 10.1016/j.tins.2003.08.004]
Bayir H,Kochanek PM,Clark RS. Traumatic brain injury in infants and children: mechanisms of secondary damage and treatment in the intensive care unitCrit Care Clin 2003;19:529–49. [pmid: 12848319] [doi: 10.1016/S0749-0704(03)00014-9]
Morganti-Kossmann MC,Rancan M,Stahel PF,Kossmann T. Inflammatory response in acute traumatic brain injury: a double-edged swordCurr Opin Crit Care 2002;8:101–5. [pmid: 12386508] [doi: 10.1097/00075198-200204000-00002]
Lenzlinger PM,Morganti-Kossmann MC,Laurer HL,McIntosh TK. The duality of the inflammatory response to traumatic brain injuryMol Neurobiol 2001;24:169–81. [pmid: 11831551] [doi: 10.1385/MN:24:1-3:169]
Sundararajan S,Landreth GE. Antiinflammatory properties of PPARgamma agonists following ischemiaDrug News Perspect 2004;17:229–36. [pmid: 15334171] [doi: 10.1358/dnp.2004.17.4.829049]
Dirnagl U. Inflammation in stroke: the good, the bad, and the unknownErnst Schering Res Found Workshop 2004:87–99. [pmid: 15032055]
Danton GH,Dietrich WD. Inflammatory mechanisms after ischemia and strokeJ Neuropathol Exp Neurol 2003;62:127–36. [pmid: 12578222]
Consilvio C,Vincent AM,Feldman EL. Neuroinflammation, COX-2, and ALS ? a dual role?Exp Neurol 2004;187:1–10. [pmid: 15081582] [doi: 10.1016/j.expneurol.2003.12.009]
Pompl PN,Ho L,Bianchi M,McManus T,Qin W,Pasinetti GM. A therapeutic role for cyclooxygenase-2 inhibitors in a transgenic mouse model of amyotrophic lateral sclerosisFaseb J 2003;17:725–7. [pmid: 12586733]
McGeer PL,McGeer EG. Inflammatory processes in amyotrophic lateral sclerosisMuscle Nerve 2002;26:459–70. [pmid: 12362410] [doi: 10.1002/mus.10191]
Cacquevel M,Lebeurrier N,Cheenne S,Vivien D. Cytokines in neuroinflammation and Alzheimer's diseaseCurr Drug Targets 2004;5:529–34. [pmid: 15270199] [doi: 10.2174/1389450043345308]
McGeer EG,McGeer PL. Inflammatory processes in Alzheimer's diseaseProg Neuropsychopharmacol Biol Psychiatry 2003;27:741–9. [pmid: 12921904] [doi: 10.1016/S0278-5846(03)00124-6]
Gupta A,Pansari K. Inflammation and Alzheimer's diseaseInt J Clin Pract 2003;57:36–9. [pmid: 12587940]
McGeer PL,McGeer EG. Local neuroinflammation and the progression of Alzheimer's diseaseJ Neurovirol 2002;8:529–38. [pmid: 12476347] [doi: 10.1080/13550280290100969]
Emerit J,Edeas M,Bricaire F. Neurodegenerative diseases and oxidative stressBiomed Pharmacother 2004;58:39–46. [pmid: 14739060] [doi: 10.1016/j.biopha.2003.11.004]
Tarkowski E,Liljeroth AM,Minthon L,Tarkowski A,Wallin A,Blennow K. Cerebral pattern of pro- and anti-inflammatory cytokines in dementiasBrain Res Bull 2003;61:255–60. [pmid: 12909295] [doi: 10.1016/S0361-9230(03)00088-1]
Tarkowski E,Andreasen N,Tarkowski A,Blennow K. Intrathecal inflammation precedes development of Alzheimer's diseaseJ Neurol Neurosurg Psychiatry 2003;74:1200–5. [pmid: 12933918] [doi: 10.1136/jnnp.74.9.1200]
McGeer PL,McGeer EG,Suzuki J,Dolman CE,Nagai T. Aging, Alzheimer's disease, and the cholinergic system of the basal forebrainNeurology 1984;34:741–5. [pmid: 6539435]
Rinne JO,Paljarvi L,Rinne UK. Neuronal size and density in the nucleus basalis of Meynert in Alzheimer's diseaseJ Neurol Sci 1987;79:67–76. [pmid: 3612173] [doi: 10.1016/0022-510X(87)90260-7]
Vogels OJ,Broere CA,ter Laak HJ,ten Donkelaar HJ,Nieuwenhuys R,Schulte BP. Cell loss and shrinkage in the nucleus basalis Meynert complex in Alzheimer's diseaseNeurobiology of Aging 1990;11:3–13. [pmid: 2183081] [doi: 10.1016/0197-4580(90)90056-6]
Hefti F. Nerve growth factor promotes survival of septal cholinergic neurons after fimbrial transectionsJ Neurosci 1986;6:2155–62. [pmid: 3746405]
Hartikka J,Hefti F. Development of septal cholinergic neurons in culture: plating density and glial cells modulate effects of NGF on survival, fiber growth, and expression of transmitter-specific enzymesJ Neurosci 1988;8:2967–85. [pmid: 2842468]
Perry G,Castellani RJ,Smith MA,Harris PL,Kubat Z,Ghanbari K,Jones PK,Cordone G,Tabaton M,Wolozin B,et al. Oxidative damage in the olfactory system in Alzheimer's diseaseActa Neuropathol (Berl) 2003;106:552–6. [pmid: 12955399] [doi: 10.1007/s00401-003-0761-7]
Butterfield DA,Boyd-Kimball D,Castegna A. Proteomics in Alzheimer's disease: insights into potential mechanisms of neurodegenerationJ Neurochem 2003;86:1313–27. [pmid: 12950441] [doi: 10.1046/j.1471-4159.2003.01948.x]
Giasson BI,Ischiropoulos H,Lee VM,Trojanowski JQ. The relationship between oxidative/nitrative stress and pathological inclusions in Alzheimer's and Parkinson's diseasesFree Radic Biol Med 2002;32:1264–75. [pmid: 12057764] [doi: 10.1016/S0891-5849(02)00804-3]
Perry G,Nunomura A,Hirai K,Takeda A,Aliev G,Smith MA. Oxidative damage in Alzheimer's disease: the metabolic dimensionInt J Dev Neurosci 2000;18:417–21. [pmid: 10817925] [doi: 10.1016/S0736-5748(00)00006-X]
Gold BG,Udina E,Bourdette D,Navarro X. Neuroregenerative and neuroprotective actions of neuroimmunophilin compounds in traumatic and inflammatory neuropathiesNeurol Res 2004;26:371–80. [pmid: 15198862] [doi: 10.1179/016164104225013734]
Rogerio F,Teixeira SA,de Rezende AC,de Sa RC,de Souza Queiroz L,De Nucci G,Muscara MN,Langone F. Superoxide dismutase isoforms 1 and 2 in lumbar spinal cord of neonatal rats after sciatic nerve transection and melatonin treatmentBrain Res Dev Brain Res 2005;154:217–25. [pmid: 15707675] [doi: 10.1016/j.devbrainres.2004.10.017]
Kim HK,Park SK,Zhou JL,Taglialatela G,Chung K,Coggeshall RE,Chung JM. Reactive oxygen species (ROS) play an important role in a rat model of neuropathic painPain 2004;111:116–24. [pmid: 15327815] [doi: 10.1016/j.pain.2004.06.008]
van Beek J,Elward K,Gasque P. Activation of complement in the central nervous system: roles in neurodegeneration and neuroprotectionAnn N Y Acad Sci 2003;992:56–71. [pmid: 12794047]
Murdoch I,Perry EK,Court JA,Graham DI,Dewar D. Cortical cholinergic dysfunction after human head injuryJ Neurotrauma 1998;15:295–305. [pmid: 9605345]
Murdoch I,Nicoll JA,Graham DI,Dewar D. Nucleus basalis of Meynert pathology in the human brain after fatal head injuryJ Neurotrauma 2002;19:279–84. [pmid: 11898797] [doi: 10.1089/08977150252807018]
Macdonald NJ,Taglialatela G. Tumor necrosis factor alpha and nerve growth factor synergistically induce iNOS in pheochromocytoma cellsNeuroreport 2000;11:3453–3456. [pmid: 11095498]
Isaksson J,Farooque M,Olsson Y. Improved functional outcome after spinal cord injury in iNOS-deficient miceSpinal Cord. 2004
Urushitani M,Shimohama S,Kihara T,Sawada H,Akaike A,Ibi M,Inoue R,Kitamura Y,Taniguchi T,Kimura J. Mechanism of selective motor neuronal death after exposure of spinal cord to glutamate: Involvement of glutamate induced nitric oxide in motor neuron toxicity and nonmotor neuron protectionAnnals of Neurology 1998;44:796–807. [pmid: 9818936] [doi: 10.1002/ana.410440514]
Diaz-Ruiz A,Ibarra A,Perez-Severiano F,Guizar-Sahagun G,Grijalva I,Rios C. Constitutive and inducible nitric oxide synthase activities after spinal cord contusion in ratsNeurosci Lett 2002;319:129–32. [pmid: 11834310] [doi: 10.1016/S0304-3940(01)02540-X]
Parmentier-Batteur S,Bohme GA,Lerouet D,Zhou-Ding L,Beray V,Margaill I,Plotkine M. Antisense oligodeoxynucleotide to inducible nitric oxide synthase protects against transient focal cerebral ischemia-induced brain injuryJournal of Cerebral Blood Flow & Metabolism 2001;21:15–21. [pmid: 11149663] [doi: 10.1097/00004647-200101000-00003]
Sarchielli P,Galli F,Floridi A,Gallai V. Relevance of protein nitration in brain injury: a key pathophysiological mechanism in neurodegenerative, autoimmune, or inflammatory CNS diseases and strokeAmino Acids 2003;25:427–36. [pmid: 14661102] [doi: 10.1007/s00726-003-0028-6]
Luth HJ,Munch G,Arendt T. Aberrant expression of NOS isoforms in Alzheimer's disease is structurally related to nitrotyrosine formationBrain Res 2002;953:135–43. [pmid: 12384247] [doi: 10.1016/S0006-8993(02)03280-8]
Luth HJ. Expression of endothelial and inducible NOS-isoforms is increased in Alzheimer's disease, in APP23 transgenic mice and after experimental brain lesion in rat: evidence for an induction by amyloid pathologyBrain Research 2001;913:57–67. [pmid: 11532247] [doi: 10.1016/S0006-8993(01)02758-5]
Law A,Gauthier S,Quirion R. Say NO to Alzheimer's disease: the putative links between nitric oxide and dementia of the Alzheimer's typeBrain Res Brain Res Rev 2001;35:73–96. [pmid: 11245887] [doi: 10.1016/S0165-0173(00)00051-5]
de la Monte SM,Lu BX,Sohn YK,Etienne D,Kraft J,Ganju N,Wands JR. Aberrant expression of nitric oxide synthase III in Alzheimer's disease: relevance to cerebral vasculopathy and neurodegenerationNeurobiology of Aging 2000;21:309–19. [pmid: 10867216] [doi: 10.1016/S0197-4580(99)00108-6]
Lee S,Zhao ML,Hirano A,Dickson D. Inducible nitric oxide synthase immunoreactivity in the Alzheimer disease hippocampus: association with Hirano bodies, neurofibrillary tangles, and senile plaquesJournal of Neuropathology and Experimental Neurology 1999;58:1163–1169. [pmid: 10560659]
Darville MI,Eizirik DL. Regulation by cytokines of the inducible nitric oxide synthase promoter in insulin-producing cellsDiabetologia 1998;41:1101–8. [pmid: 9754830] [doi: 10.1007/s001250051036]
Kong GY,Peng ZC,Costanzo C,Kristensson K,Bentivoglio M. Inducible nitric oxide synthase expression elicited in the mouse brain by inflammatory mediators circulating in the cerebrospinal fluidBrain Res 2000;878:105–18. [pmid: 10996141] [doi: 10.1016/S0006-8993(00)02716-5]
Barker V,Middleton G,Davey F,Davies AM. TNFalpha contributes to the death of NGF-dependent neurons during developmentNature Neuroscience 2001;4:1194–8. [pmid: 11685224] [doi: 10.1038/nn755]
Aloe L,Fiore M,Probert L,Turrini P,Tirassa P. Overexpression of tumour necrosis factor alpha in the brain of transgenic mice differentially alters nerve growth factor levels and choline acetyltransferase activityCytokine 1999;11:45–54. [pmid: 10080878] [doi: 10.1006/cyto.1998.0397]
Wenk GL,McGann K,Hauss-Wegrzyniak B,Rosi S. The toxicity of tumor necrosis factor-alpha upon cholinergic neurons within the nucleus basalis and the role of norepinephrine in the regulation of inflammation: implications for alzheimer's diseaseNeuroscience 2003;121:719–29. [pmid: 14568031] [doi: 10.1016/S0306-4522(03)00545-1]
Kiss JZ,Wang C,Olive S,Rougon G,Lang J,Baetens D,Harry D,Pralong WF. Activity-dependent mobilization of the adhesion molecule polysialic NCAM to the cell surface of neurons and endocrine cellsEmbo J 1994;13:5284–92. [pmid: 7957094]
Stoppini L,Buchs PA,Muller D. A simple method for organotypic cultures of nervous tissueJournal of Neuroscience Methods 1991;37:173–82. [pmid: 1715499] [doi: 10.1016/0165-0270(91)90128-M]
Ohmichi M,Decker SJ,Pang L,Saltiel AR. Inhibition of the cellular actions of nerve growth factor by staurosporine and K252A results from the attenuation of the activity of the trk tyrosine kinaseBiochemistry 1992;31:4034–9. [pmid: 1314657] [doi: 10.1021/bi00131a019]
Pappas TC,Decorti F,Macdonald NJ,Neet KE,Taglialatela G. Tumour necrosis factor-alpha- vs. growth factor deprivation-promoted cell death: different receptor requirements for mediating nerve growth factor-promoted rescueAging Cell 2003;2:83–92. [pmid: 12882321] [doi: 10.1046/j.1474-9728.2003.00039.x]
Taglialatela G,Robinson R,Perez-Polo JR. Inhibition of nuclear factor kappa B (NFkappaB) activity induces nerve growth factor-resistant apoptosis in PC12 cellsJournal of Neuroscience Research 1997;47:155–62. [pmid: 9008146] [doi: 10.1002/(SICI)1097-4547(19970115)47:2<155::AID-JNR4>3.0.CO;2-E]
Taglialatela G,Kaufmann JA,Trevino A,Perez-Polo JR. Central nervous system DNA fragmentation induced by the inhibition of nuclear factor kappa BNeuroreport 1998;9:489–93. [pmid: 9512395]
Traenckner EB,Wilk S,Baeuerle PA. A proteasome inhibitor prevents activation of NF-kappa B and stabilizes a newly phosphorylated form of I kappa B-alpha that is still bound to NF-kappa BEmbo J 1994;13:5433–41. [pmid: 7957109]
Pang L,Sawada T,Decker SJ,Saltiel AR. Inhibition of MAP kinase kinase blocks the differentiation of PC-12 cells induced by nerve growth factorJournal of Biological Chemistry 1995;270:13585–8. [pmid: 7775407] [doi: 10.1074/jbc.270.36.21040]
Mielke K,Herdegen T. Fatal shift of signal transduction is an integral part of neuronal differentiation: JNKs realize TNFalpha-mediated apoptosis in neuronlike, but not naive, PC12 cellsMol Cell Neurosci 2002;20:211–24. [pmid: 12093155] [doi: 10.1006/mcne.2002.1132]
Morooka T,Nishida E. Requirement of P38 Mitogen-Activated Protein Kinase For Neuronal Differentiation in Pc12 CellsJournal of Biological Chemistry 1998;273:24285–24288. [pmid: 9733710] [doi: 10.1074/jbc.273.38.24285]
Perez-Polo JR,Foreman PJ,Jackson GR,Shan D,Taglialatela G,Thorpe LW,Werrbach-Perez K. Nerve growth factor and neuronal cell deathMolecular Neurobiology 1990;4:57–91. [pmid: 2076219]
Carter BD,Kaltschmidt C,Kaltschmidt B,Offenhauser N,Bohm-Matthaei R,Baeuerle PA,Barde YA. Selective activation of NF-kappa B by nerve growth factor through the neurotrophin receptor p75 [see comments]Science 1996;272:542–5. [pmid: 8614802]
Lad SP,Peterson DA,Bradshaw RA,Neet KE. Individual and combined effects of TrkA and p75NTR nerve growth factor receptors. A role for the high affinity receptor siteJ Biol Chem 2003;278:24808–17. [pmid: 12702729] [doi: 10.1074/jbc.M212270200]
Szutowicz A,Madziar B,Pawelczyk T,Tomaszewicz M,Bielarczyk H. Effects of NGF on acetylcholine, acetyl-CoA metabolism, and viability of differentiated and non-differentiated cholinergic neuroblastoma cellsJ Neurochem 2004;90:952–61. [pmid: 15287901] [doi: 10.1111/j.1471-4159.2004.02556.x]
Foehr ED,Lin X,O'Mahony A,Geleziunas R,Bradshaw RA,Greene WC. NF-kappa B signaling promotes both cell survival and neurite process formation in nerve growth factor-stimulated PC12 cellsJ Neurosci 2000;20:7556–63. [pmid: 11027214]
Hoozemans JJ,Veerhuis R,Rozemuller AJ,Eikelenboom P. Non-steroidal anti-inflammatory drugs and cyclooxygenase in Alzheimer's diseaseCurr Drug Targets 2003;4:461–8. [pmid: 12866660] [doi: 10.2174/1389450033490902]
Barone FC,Parsons AA. Therapeutic potential of anti-inflammatory drugs in focal strokeExpert Opin Investig Drugs 2000;9:2281–306. [pmid: 11060807] [doi: 10.1517/13543784.9.10.2281]
Weydt P,Weiss MD,Moller T,Carter GT. Neuro-inflammation as a therapeutic target in amyotrophic lateral sclerosisCurr Opin Investig Drugs 2002;3:1720–4. [pmid: 12528305]
Rovelli G,Heller RA,Canossa M,Shooter EM. Chimeric tumor necrosis factor-TrkA receptors reveal that ligand-dependent activation of the TrkA tyrosine kinase is sufficient for differentiation and survival of PC12 cellsProc Natl Acad Sci U S A 1993;90:8717–8721. [pmid: 7690970]
Jiang H,Koubi D,Zhang L,Kuo J,Rodriguez AI,Jackson Hunter T,et al. Inhibitors of iNOS protects PC12 cells against the apoptosis induced by oxygen and glucose deprivationNeuroscience Letters 2005;375:59–63. [pmid: 15664123] [doi: 10.1016/j.neulet.2004.10.067]
Woo SB,Page J,Saragovi HU,Neet KE. Binding of nerve growth factor (NGF) to Trk receptor chimerasFaseb Journal 2004;18:C273.
Floden AM,Li SS,Combs CK. beta-Amyloid-stimulated microglia induce neuron death via synergistic stimulation of tumor necrosis factor alpha and NMDA receptorsJournal of Neuroscience 2005;25:2566–2575. [pmid: 15758166] [doi: 10.1523/JNEUROSCI.4998-04.2005]

Figures

[Figure ID: F1]
Figure 1 

A: (Top) Western blot analysis detecting the presence of iNOS in 40 ?g total protein extracts from PC12 cells treated for 24 hr with 10 ng/ml NGF and 10 ng/ml TNF , individually or combined (Both), in the presence of 50 nM of the receptor tyrosine kinase inhibitor K252a. Positive control (Pos) is 4 ?g of total protein extracts from mouse macrophages. (Bottom) RT-PCR detecting iNOS mRNA in PC12 cells treated for 24 hr with 10 ng/ml NGF and 10 ng/ml TNF , individually or combined (Both) compared to untreated cells (Cont). Internal PCR controls lacking reverse transcriptase (RT-) were performed on each sample as shown. Results shown are representative of 3 replicate experiments.



[Figure ID: F2]
Figure 2 

A: Western blots detecting iNOS in total protein extracts from PC12 cells treated for 24 hr with increasing concentrations of NGF in the presence or absence of 10 ng/ml TNF? (Top) or treated with increasing concentrations of TNF? in the presence or absence of 25 ng/ml NGF (Bottom). Positive control (Pos) is 4 ?g of total protein extracts from mouse macrophages. Results shown are representative of 2 replicate experiments. B: Western blot analysis detecting iNOS in total protein extracts from PC12 cells simultaneously pre-treated with 10 ng/ml NGF and 10 ng/ml TNF?. At 24 hr treatment was withdrawn and the presence of iNOS was determined 24, 48, and 72 hr thereafter. Results shown are representative of 3 replicate experiments. C: Western blot analysis (Top) and RT-PCR (Bottom) detecting iNOS protein and mRNA in total protein extracts and total RNA from PC12 cells simultaneously pre-treated for 24 hr with 10 ng/ml NGF and 10 ng/ml TNF? (Both). After 24 hr, treatment was withdrawn and replaced with either NGF or TNF? alone or with both and iNOS expression determined 24 hr thereafter. Results shown are representative of 2 replicate experiments. D: Western blot detecting iNOS in total protein extracts from PC12 cells simultaneously treated for 24 hr with 10 ng/ml NGF and 10 ng/ml TNF? in medium containing serum, in serum free medium (SF) or in defined medium (N2). Results shown are representative of 3 replicate experiments. E: Western blot analysis detecting the presence of iNOS in total protein extracts from PC12 cells treated for 72 hr with 100 ng/ml IGF and 10 ng/ml TNF , individually or combined, as compared to cells simultaneously treated with 10 ng/ml NGF and 10 ng/ml TNF? or untreated controls (Cont). Results shown are representative of 4 replicate experiments.



[Figure ID: F3]
Figure 3 

A: Western blot detecting iNOS in total protein extracts from PC12 cells treated for 24 hr with 10 ng/ml NGF and 10 ng/ml TNF?, either individually or simultaneously (Both). Cells were pretreated with vehicle or 0.5 ?M of the generic NOS inhibitor L-NAME. Positive control (Pos) is 4 ?g of total protein extracts from mouse macrophages. Results shown are representative of 3 replicate experiments. B: Western blot detecting iNOS in total protein extracts from PC12 cells simultaneously treated with 10 ng/ml NGF and 10 ng/ml TNF? (Both), in the presence or absence of a pre-treatment with varying concentrations of the iNOS-specific inhibitor 1400 W. Results shown are representative of 4 replicate experiments.



[Figure ID: F4]
Figure 4 

Detection of SEAP in the culture medium of PC12 cells transfected with a SEAP reporter gene construct under the transcriptional control of enhancers specific for NF-?B, AP-1 or CRE. pTal is the non-enhanced control SEAP reporter vector. Twenty-four hr after transfection, cells were treated with vehicle (Control), 10 ng/ml NGF, 10 ng/ml TNF? or NGF plus TNF? (Both) and the presence of SEAP in the culture medium assayed 3 hr (Top) or 12 hr (Bottom) thereafter. Results are normalized to control cells in each transfection group (N = 3). * and #: p < 0.05 vs. control and TNF?-alone, respectively (two-tailed unpaired Student's t-test). Results shown are representative of 3 replicate experiments.



[Figure ID: F5]
Figure 5 

A: Western blot detecting iNOS in PC12 cells simultaneously treated with 10 ng/ml NGF and 10 ng/ml TNF? for 24 hr. Thirty minutes before NGF/ TNF? treatment cells were pre-treated with 10 ?M pyrrolidinedithyocarbamate (PDTC), 2 ?M of a oligopeptide proteosome inhibitor (PSI) or 10 ?M of a MAPK inhibitor (PD98059). Results shown are representative of 2 replicate experiments. B: SEAP release in the culture medium of PC12 cells transfected for 24 hr with an NF-?B-sensitive SEAP reporter gene construct and treated for 12 hr with vehicle (Control), 10 ng/ml NGF, 10 ng/ml TNF? or NGF plus TNF? in the presence of 10 ?M PD98059, 10 ?M PDTC or 2 ?M PSI. Data are shown as mean ? S.E.M. from 3 independent replicate experiments. * and #: p < 0.05 vs. control or TNF?-alone cells, respectively (two-tailed unpaired Student's t-test). C: Representative photomicrographs of PC12 cells treated for 48 hr with 10 ng/ml NGF in the presence or absence of 10 ?M PD98059 or 2 ?M PDTC. D: NF?B transcriptional activity (as measured by a transiently transfected SEAP reporter vector) in PC12 cells treated for 24 hr with 10 ng/ml NGF, 10 ng/ml TNF? or NGF plus TNF? (Both) in the presence of 0.5 ?M L-NAME. Data are shown as mean ? S.E.M. from 3 independent replicate experiments. * and #: p < 0.05 vs. control or TNF?-alone cells, respectively (two-tailed unpaired Student's t-test).



[Figure ID: F6]
Figure 6 

A: Graph depicting the percentage of TrkA- or p75NTR- immunopositive cells in wild type (wt)PC12 cells and PC12 cell mutants lacking the low affinity NGF receptor (PC12p75NTR(-)) from flow cytometry data. Results shown are representative of 3 replicate flow cytometry experiments on the same cell line. B: SEAP release in the culture medium of PC12p75NTR (-) cells transfected for 24 hr with an NF-?B-sensitive SEAP reporter gene construct and treated for 12 hr with vehicle (Cont), 10 ng/ml NGF, 10 ng/ml TNF? or NGF plus TNF? (Both). Data are shown as mean ? S.E.M. from 3 independent replicate experiments. * : p < 0.05 vs. control or NGF-alone cells (two-tailed unpaired Student's t-test). C: Western blot detecting the presence of iNOS in wtPC12 cells and PC12p75NTR (-) cells treated for 24 hr with vehicle (Cont), 10 ng/ml NGF, 10 ng/ml TNF? or NGF plus TNF? (Both). Membrane was re-probed for ?-actin (lower panel) to control for equal protein loading. Positive control (Pos) is 4 ?g of total protein extracts from mouse macrophages. Results shown are representative of 4 replicate experiments. D: Western blot detecting the presence of TNFR-I in total protein extracts from wtPC12 cells and PC12p75NTR (-) cells. Twenty ?g of total protein extracts from rat dorsal root ganglia (DRG) were used as a positive control.



[Figure ID: F7]
Figure 7 

Western blot detecting iNOS in 40 ?g total protein extracts from PC12 cells treated for 24 hr with 10 ng/ml human TNF?, 10 ng/ml NGF, or both. Twenty-four hr before treatment, cells were transfected with either an empty vector or expression vectors for chimeric receptor proteins bearing the human TNFR1 ligand binding domains and the intracellular domain of either rat p75NTR or TrkA NGF receptors (p75NTR, TrkA or p75NTR+TrkA). Positive control (Pos) is 40 ?g of total protein extract from wild type PC12 cells treated with both rat TNF? and NGF. Membrane was re-probed for ?-actin (lower panel) to control for equal protein loading and is representative from 3 independent transfections and treatments.



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