Inhibition of extracellular signal-regulated kinase 1/2 augments nitric oxide production in lipopolysaccharide-stimulated RAW264.7 macrophage cells

Cellular study of the LPS-induced osteoclastic multinucleated cell formation from RAW264.7 cells

Despite the response to the receptor activator of nuclear factor κ-Β ligand (RANKL), a study has reported that lipopolysaccharide (LPS) could induce RAW264.7 linage osteoclastic differentiation. However, on the contrary, another study recently showed that the LPS-induced multinuclear cells from RAW264.7 did not express osteoclastic functions. Interestingly, in our previous study, we found that RAW264.7 cells pretreated with 10 ng LPS plus macrophage-colony stimulating factor did not show any effects for enhancing RANKL-induced osteoclastic cell differentiation. Therefore, in our current study, we aim to investigate the oteoclastogesis induction ability and efficacy of LPS in the RAW264.7 cell line and relevant molecular signaling. The osteoclastogenic activity of LPS-treated RAW264.7 linage was studied by bone resorption pits and fibrous actin study. Besides that, through polymerase chain reaction and western blot, we showed that the transcriptional factor c-Fos and Nfatc1 might be associated with LPS-induced osteoclastogenesis. Overall, the results of our current study showed positive proof for osteoclast generation from LPS-independent treatment, as well as established an optimal and efficient method for this process.

Falcarindiol inhibits LPS-induced inflammation via attenuating MAPK and JAK-STAT signaling pathways in murine macrophage RAW 264.7 cells

Falcarindiol (FAD) is a natural polyacetylene compound found rich in many plants of the Umbelliferae family. Previously, we isolated FAD from the rhizome of Cnidium officinale Makino, which belongs to the Umbelliferae family and found it to have a significant inhibitory effect on lipopolysaccharide (LPS)-induced production of nitric oxide, a pro-inflammatory molecule in murine macrophage RAW 264.7 cells. In this study, we investigated its effect on the expression of other major pro-inflammatory molecules as well as the mechanism underlying these effects. Pre-treatment of RAW 264.7 cells with FAD suppressed LPS-stimulated mRNA expression of inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNFα), interleukin-6 (IL-6), and interleukin-1 beta (IL-1β) and thereby reduced the respective protein levels. Mechanistic studies demonstrated that FAD attenuated the LPS-induced activation of JNK, ERK, STAT1, and STAT3 signaling molecules. Moreover, we found that FAD did not influence LPS-induced activation of p38 and NFκB signaling pathways. Collectively, this study provides evidence that FAD inhibits the production of major pro-inflammatory molecules in LPS-challenged murine macrophages via suppression of JNK, ERK, and STAT signaling pathways.

The Peptidylarginine Deiminase Inhibitor Cl-Amidine Suppresses Inducible Nitric Oxide Synthase Expression in Dendritic Cells

The conversion of peptidylarginine into peptidylcitrulline by calcium-dependent peptidylarginine deiminases (PADs) has been implicated in the pathogenesis of a number of diseases, identifying PADs as therapeutic targets for various diseases. The PAD inhibitor Cl-amidine ameliorates the disease course, severity, and clinical manifestation in multiple disease models, and it also modulates dendritic cell (DC) functions such as cytokine production, antigen presentation, and T cell proliferation. The beneficial effects of Cl-amidine make it an attractive compound for PAD-targeting therapeutic strategies in inflammatory diseases. Here, we found that Cl-amidine inhibited nitric oxide (NO) generation in a time- and dose-dependent manner in maturing DCs activated by lipopolysaccharide (LPS). This suppression of NO generation was independent of changes in NO synthase (NOS) enzyme activity levels but was instead dependent on changes in inducible NO synthase (iNOS) transcription and expression levels. Several upstream signaling pathways for iNOS expression, including the mitogen-activated protein kinase, nuclear factor-κB p65 (NF-κB p65), and hypoxia-inducible factor 1 pathways, were not affected by Cl-amidine. By contrast, the LPS-induced signal transducer and the activator of transcription (STAT) phosphorylation and activator protein-1 (AP-1) transcriptional activities (c-Fos, JunD, and phosphorylated c-Jun) were decreased in Cl-amidine-treated DCs. Inhibition of Janus kinase/STAT signaling dramatically suppressed iNOS expression and NO production, whereas AP-1 inhibition had no effect. These results indicate that Cl-amidine-inhibited STAT activation may suppress iNOS expression. Additionally, we found mildly reduced cyclooxygenase-2 expression and prostaglandin E2 production in Cl-amidine-treated DCs. Our findings indicate that Cl-amidine acts as a novel suppressor of iNOS expression, suggesting that Cl-amidine has the potential to ameliorate the effects of excessive iNOS/NO-linked immune responses.

Lipopolysaccharide enhances interferon-γ-induced nitric oxide (NO) production in murine vascular endothelial cells via augmentation of interferon regulatory factor-1 activation

Lipopolysaccharide (LPS) enhances the production of nitric oxide (NO) in interferon (IFN)-γstimulated vascular endothelial cells. We studied the mechanism by which LPS enhances IFN-γ-induced NO production by using the murine vascular endothelial cell line, END-D. LPS enhanced IFN-γinduced NO production via augmented expression of inducible type NO synthase (iNOS) mRNA. LPS significantly augmented the activation of interferon regulatory factor (IRF)-1 in IFN-γ-stimulated END-D cells, although it did not affect the activation of either MyD88-dependent nuclear factor (NF)-κB or MyD88-independent IRF-3. SB203580, an inhibitor of p38 mitogen-activated protein kinase (MAPK), prevented the nuclear translocation of IRF-1 in LPS and IFN-γ-stimulated END-D cells, and inhibited the iNOS expression and NO production in those cells. Therefore, it is proposed that LPS enhanced NO production in IFN-γ-stimulated END-D cells via augmenting p38 MAPKmediated IRF-1 activation.

Nucleotide receptor P2RX7 stimulation enhances LPS-induced interferon-β production in murine macrophages

Stimulation of P2RX(7) with extracellular ATP potentiates numerous LPS-induced proinflammatory events, including cytokine induction in macrophages, but the molecular mechanisms underlying this process are not well defined. Although P2RX(7) ligation has been proposed to activate several transcription factors, many of the LPS-induced mediators affected by P2RX(7) activation are not induced by P2RX(7) agonists alone, suggesting a complementary role for P2RX(7) in transcriptional regulation. Type I IFN production, whose expression is tightly controlled by multiple transcription factors that form an enhanceosome, is critical for resistance against LPS-containing bacteria. The effect of purinergic receptor signaling on LPS-dependent type I IFN is unknown and would be of great relevance to a diverse array of inflammatory conditions. The present study demonstrates that stimulation of macrophages with P2RX(7) agonists substantially enhances LPS-induced IFN-β expression, and this enhancement is ablated in macrophages that do not express functional P2RX(7) or when the MAPK MEK1/2 pathways are inhibited. Potentiation of LPS-induced IFN-β expression following P2RX(7) stimulation is likely transcriptionally regulated, as this enhancement is observed at the IFN-β promoter level. Furthermore, P2RX(7) stimulation is able to increase the phosphorylation and subsequent IFN-β promoter occupancy of IRF-3, a transcription factor that is critical for IFN-β transcription by TLR agonists. This newly discovered role for P2RX(7) in IFN regulation may have implications in antimicrobial defense, which has been linked to P2RX(7) activation in other studies.

Extracellular signal-regulated kinase (ERK) is involved in LPS-induced disturbances in intestinal motility

BACKGROUND

Lipopolysaccharide (LPS) is a causative agent of sepsis. A relationship has been described between LPS, free radicals, and cyclooxygenase-2 (COX-2). Here, we investigate the role of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinases (MAPK) in the effect of LPS on intestinal motility, oxidative stress status, and COX-2 expression.

METHODS

Rabbits were injected with (i) saline, (ii) LPS, (iii) U0126, an ERK MAPK inhibitor, or (iv) U0126+LPS. Duodenal contractility was studied in an organ bath with acetylcholine, prostaglandin E(2), and KCl added. Neuromuscular function was assessed by electrical field stimulation (EFS). Neurotransmitter blockers were used to study the EFS-elicited contractile response. The formation of products of oxidative damage to proteins (carbonyls), lipids, [malondialdehyde (MDA), and 4-hydroxyalkenals (4-HDA)] was quantified in plasma and intestine. The protein expression of phospho-ERK (p-ERK), total ERK, and COX-2 in the intestine was measured by western blot, and p-ERK was localized by immunohistochemistry.

KEY RESULTS

Acetylcholine, prostaglandin E(2), and KCl-induced contractions decreased with LPS. Electrical field stimulation induced a neurogenic contraction that was reduced by LPS. Lipopolysaccharide increased p-ERK and COX-2 expression and the levels of carbonyls and MDA+4-HDA. U0126 blocked the effect of LPS on acetylcholine, prostaglandin E(2), KCl, and EFS-induced contractions, the levels of carbonyls and MDA+4-HDA and p-ERK and COX-2 expression. Phospho-ERK was detected mostly in the neurons of the myenteric and submucosal ganglia.

CONCLUSIONS & INFERENCES

We can suggest that ERK is involved in the mechanism of action of LPS in the intestine.

M. bovis BCG induced expression of COX-2 involves nitric oxide-dependent and -independent signaling pathways

In a multifaceted immunity to mycobacterial infection, induced expression of cyclooxygenase-2 (COX-2) by Mycobacterium bovis bacillus Calmette-Guerin (BCG) may act as an important influencing factor for the effective host immunity. We here demonstrate that M. bovis BCG-triggered TLR2-dependent signaling leads to COX-2 and PGE2 expression in vitro in macrophages and in vivo in mice. Further, the presence of PGE2 could be demonstrated in sera or cerebrospinal fluid of tuberculosis patients. The induced COX-2 expression in macrophages is dependent on NF-kappaB activation, which is mediated by inducible NO synthase (iNOS)/NO-dependent participation of the members of Notch1-PI-3K signaling cascades as well as iNOS-independent activation of ERK1/2 and p38 MAPKs. Inhibition of iNOS activity abrogated the M. bovis BCG ability to trigger the generation of Notch1 intracellular domain (NICD), a marker for Notch1 signaling activation, as well as activation of the PI-3K signaling cascade. On the contrary, treatment of macrophages with 3-morpholinosydnonimine, a NO donor, resulted in a rapid increase in generation of NICD, activation of PI-3K pathway, as well as the expression of COX-2. Stable expression of NICD in RAW 264.7 macrophages resulted in augmented expression of COX-2. Further, signaling perturbations suggested the involvement of the cross-talk of Notch1 with members with the PI-3K signaling cascade. These results implicate the dichotomous nature of TLR2 signaling during M. bovis BCG-triggered expression of COX-2. In this perspective, we propose the involvement of iNOS/NO as one of the obligatory, early, proximal signaling events during M. bovis BCG-induced COX-2 expression in macrophages.

Hydrogen peroxide induces the production of tumor necrosis factor-alpha in RAW 264.7 macrophage cells via activation of p38 and stress-activated protein kinase

The effect of hydrogen peroxide (H(2)O(2)) on production of tumor necrosis factor (TNF)-alpha was examined in RAW 264.7 murine macrophage cells. H(2)O( 2) led to production of TNF-alpha up to 24 h after the treatment, but not nitric oxide in RAW 264.7 cells. H(2)O(2) induced TNF-alpha production in mouse peritoneal macrophages as well as RAW 264.7 cells. The H(2)O(2)induced TNF-alpha production was prevented by inhibitors of p38 and stress-activated protein kinase (SAPK/JNK), and H(2)O( 2) induced the phosphorylation of p38 and SAPK. Further, H(2)O( 2) significantly augmented the AP-1 activity, but not nuclear factor (NF)-kappaB activity in RAW 264.7 cells. A high level of intracellular reactive oxygen radicals (ROS) was detected in H(2)O(2)-exposed RAW 264.7 cells. Ebselen, a cell permeable antioxidant, prevented the H( 2)O(2)-induced TNFalpha production. H(2)O(2) significantly enhanced lipopolysaccharide (LPS)-induced TNF-alpha production. Therefore, H( 2) O(2) was suggested to induce TNF-alpha production in macrophages via activating p38 and SAPK/JNK as oxidative stress-related signal pathways.

Lysophosphatidic acid inhibits bacterial endotoxin-induced pro-inflammatory response: potential anti-inflammatory signaling pathways

Previous studies have demonstrated that heterotrimeric guanine nucleotide-binding regulatory (Gi) protein-deficient mice exhibit augmented inflammatory responses to lipopolysaccharide (LPS). These findings suggest that Gi protein agonists will suppress LPS-induced inflammatory gene expression. Lysophosphatidic acid (LPA) activates G protein-coupled receptors leading to Gi protein activation. We hypothesized that LPA will inhibit LPS-induced inflammatory responses through activation of Gi-coupled anti-inflammatory signaling pathways. We examined the anti-inflammatory effect of LPA on LPS responses both in vivo and in vitro in CD-1 mice. The mice were injected intravenously with LPA (10 mg/kg) followed by intraperitoneal injection of LPS (75 mg/kg for survival and 25 mg/kg for other studies). LPA significantly increased the mice survival to endotoxemia (P < 0.05). LPA injection reduced LPS-induced plasma TNF-alpha production (69 +/- 6%, P < 0.05) and myeloperoxidase (MPO) activity in lung (33 +/- 9%, P < 0.05) as compared to vehicle injection. LPS-induced plasma IL-6 was unchanged by LPA. In vitro studies with peritoneal macrophages paralleled results from in vivo studies. LPA (1 and 10 microM) significantly inhibited LPS-induced TNFalpha production (61 +/- 9% and 72 +/- 9%, respectively, P < 0.05) but not IL-6. We further demonstrated that the anti-inflammatory effect of LPA was reversed by ERK 1/2 and phosphatase inhibitors, suggesting that ERK 1/2 pathway and serine/threonine phosphatases are involved. Inhibition of phosphatidylinositol 3 (PI3) kinase signaling pathways also partially reversed the LPA anti-inflammatory response. However, LPA did not alter NFkappaB and peroxisome proliferator-activated receptor gamma (PPARgamma) activation. Inhibitors of PPARgamma did not alter LPA-induced inhibition of LPS signaling. These studies demonstrate that LPA has significant anti-inflammatory activities involving activation of ERK 1/2, serine/threonine phosphatases, and PI3 kinase signaling pathways.

Differential modulatory effects of annexin 1 on nitric oxide synthase induction by lipopolysaccharide in macrophages

Annexin-1 (ANXA1) is a glucocorticoid-regulated protein that modulates the effects of bacterial lipopolysaccharide (LPS) on macrophages. Exogenous administration of peptides derived from the N-terminus of ANXA1 reduces LPS-stimulated inducible nitric oxide synthase (iNOS) expression, but the effects of altering the endogenous expression of this protein are unclear. We transfected RAW264.7 murine macrophage-like cell lines to over-express constitutively ANXA1 and investigated whether this protein modulates the induction of iNOS, cyclooxygenase-2 (COX-2) and tumour necrosis factor-alpha (TNF-alpha) in response to LPS. In contrast to exogenous administration of N-terminal peptides, endogenous over-expression of ANXA1 results in up-regulation of LPS-induced iNOS protein expression and activity. However, levels of iNOS mRNA are unchanged. ANXA1 has no effect on COX-2 or TNF-alpha production in response to LPS. In experiments to investigate the mechanisms underlying these phenomena we observed that activation of signalling proteins classically associated with iNOS transcription was unaffected. Over-expression of ANXA1 constitutively activates extracellular signal regulated kinase (ERK)-1 and ERK-2, components of a signalling pathway not previously recognized as regulating LPS-induced iNOS expression. Inhibition of ERK activity, by the inhibitor U0126, reduced LPS-induced iNOS expression in our cell lines. Over-expression of ANXA1 also modified LPS-induced phosphorylation of the ERK-regulated translational regulation factor eukaryotic initiation factor 4E. Our data suggest that ANXA1 may modify iNOS levels by post-transcriptional mechanisms. Thus differential effects on iNOS expression in macrophages are seen when comparing acute administration of ANXA1 peptides versus the chronic endogenous over-expression of ANXA1.