Tumor necrosis factor-α enhances hyperbaric oxygen-induced visfatin expression via JNK pathway in human coronary arterial endothelial cells

Background  

Visfatin, a adipocytokine with insulin-mimetic effect, plays a role in endothelial angiogenesis. Hyperbaric oxygen (HBO) has been used in medical practice. However, the molecular mechanism of beneficial effects of HBO is poorly understood. We sought to investigate the cellular and molecular mechanisms of regulation of visfatin by HBO in human coronary arterial endothelial cells (CAECs).     

Proinflammatory cytokines tumor necrosis factor-α and interferon-γ modulate epithelial barrier function in Madin-Darby canine kidney cells through mitogen activated protein kinase signaling

Background  

The tight junction is a dynamic structure that is regulated by a number of cellular signaling processes. Occludin, claudin-1, claudin-2 and claudin-3 are integral membrane proteins found in the tight junction of MDCK cells. These proteins are restricted to this region of the membrane by a complex array of intracellular proteins which are tethered to the cytoskeleton. Alteration of these tight junction protein complexes during pathological events leads to impaired epithelial barrier function that perturbs water and electrolyte homeostasis. We examined MDCK cell barrier function in response to challenge by the proinflammatory cytokines tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ).     

Gender difference in tumor necrosis factor-α production in human neutrophils stimulated by lipopolysaccharide and interferon-γ

The gender difference in tumor necrosis factor-α (TNF-α) production in human neutrophils stimulated by lipopolysaccharide (LPS) and interferon-γ (IFN-γ) was explored by using peripheral blood neutrophils from young men and women. As compared with female neutrophils, male neutrophils released greater amounts of TNF-α, and exhibited stronger activation of mitogen-activated protein kinases and phosphatidylinositol 3-kinase in response to LPS stimulation. LPS-induced TNF-α production was markedly enhanced by pretreatment of cells with IFN-γ, and IFN-γ-mediated priming in male neutrophils was significantly greater than that in female neutrophils. Male neutrophils showed higher expression of TLR4, but not IFN-γ receptors, than female neutrophils, and its expression was increased by stimulation with IFN-γ or IFN-γ plus LPS. These findings indicate that male neutrophils show higher responsiveness to stimulation with LPS and IFN-γ than female neutrophils, and suggest that the gender difference in neutrophil responsiveness to LPS and IFN-γ is partly responsible for that in the outcome of sepsis, in which premenopausal women show a favorable prognosis as compared with men.     

Hydrogen sulfide attenuated tumor necrosis factor-α-induced inflammatory signaling and dysfunction in vascular endothelial cells

Background

Hydrogen sulfide (H₂S), the third physiologically relevant gaseous molecule, is recognized increasingly as an anti-inflammatory mediator in various inflammatory conditions. Herein, we explored the effects and mechanisms of sodium hydrosulfide (NaHS, a H₂S donor) on tumor necrosis factor (TNF)-α-induced human umbilical vein endothelial cells (HUVEC) dysfunction.

Methodology and Principal Findings

Application of NaHS concentration-dependently suppressed TNF-α-induced mRNA and proteins expressions of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), mRNA expression of P-selectin and E-selectin as well as U937 monocytes adhesion to HUVEC. Western blot analysis revealed that the expression of the cytoprotective enzyme, heme oxygenase-1 (HO-1), was induced and coincident with the anti-inflammatory action of NaHS. Furthermore, TNF-α-induced NF-κB activation assessed by IκBα degradation and p65 phosphorylation and nuclear translocation and ROS production were diminished in cells subjected to treatment with NaHS.

Significance

H₂S can exert an anti-inflammatory effect in endothelial cells through a mechanism that involves the up-regulation of HO-1.     

Hypoxia inducing factor-1α regulates tumor necrosis factor-related apoptosis-inducing ligand sensitivity in tumor cells exposed to hypoxia

Hypoxia is a common environmental stress. Particularly, the center of rapidly-growing solid tumors is easily exposed to hypoxic conditions. Hypoxia is well known to attenuate the therapeutic response to radio and chemotherapies including tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) protein. HIF-1α is a critical mediator of the hypoxic response. However, little is known about the function of hypoxia-inducible factor-1α (HIF-1α) on hypoxic inhibition of TRAIL-mediated apoptosis. In this study, we investigated whether hypoxic inhibition of TRAIL-mediated apoptosis can be regulated by modulating HIF-1α protein. Hypoxia- and DEF-induced HIF-1α activation inhibited the TRAIL-mediated apoptosis in SK-N-SH, HeLa, A549 and SNU-638 cells. And also, HIF-1α inactivating reagents including DOX increased the sensitivity to TRAIL protein in tumor cells exposed to hypoxia. Furthermore, knock-down of HIF-1α using lentiviral RNA interference sensitized tumor cells to TRAIL-mediated cell death under hypoxic condition. Taken together, these results indicate that HIF-1α inactivation increased TRAIL sensitivity in hypoxia-induced TRAIL-resistant tumor cells and also suggest that HIF-1α inhibitors may have benefits in combination therapy with TRAIL against hypoxic tumor cells.     

Synergistic activity of interleukin-17 and tumor necrosis factor-α enhances oxidative stress-mediated oligodendrocyte apoptosis

Th1 cytokine-induced loss of oligodendrocytes (OLs) is associated with axonal loss in CNS demyelinating diseases such as multiple sclerosis (MS)that contributes to neurological disabilities in affected individuals. Recent studies indicated that, in addition to Th1-phenotype cytokines including tumor necrosis factor (TNF)-α, Th17 phenotype cytokine, interleukin (IL)-17 also involved in the development of MS. In this study, we investigated the direct effect of IL-17 on the survival of OLs in the presence of TNF-α and individually in vitro settings. Our findings suggest that IL-17 alone, however, was not able to affect the survival of OLs, but it exacerbates the TNF-α-induced OL apoptosis as compared with individual TNF-α treatment. This effect of cytokines was ascribed to an inhibition of cell-survival mechanisms, co-localization of Bid/Bax proteins in the mitochondrial membrane and caspase 8 activation mediated release of apoptosis inducing factor from mitochondria in treated OLs. In addition, cytokine treatment disturbed the mitochondrial membrane potential in OLs with corresponding increase in the generation of reactive oxygen species, which were attenuated by N-acetyl cysteine treatment. In addition, combining of these cytokines induced cell-cycle arrest at G1/S phases in OL-like cells and inhibited the maturation of OL progenitor cells that was attenuated by peroxisome proliferator-activated receptor-γ/-β agonists. Collectively, these data provide initial evidence that IL-17 exacerbates TNF-α-induced OL loss and inhibits the differentiation of OL progenitor cells suggesting that antioxidant- or peroxisome proliferator-activated receptor agonist-based therapies have potential to limit CNS demyelination in MS or other related demyelinating disorders.     

A complex interaction between Wnt signaling and TNF-α in nucleus pulposus cells

Introduction

Increased expression of the proinflammatory cytokine TNF-α in intervertebral discs (IVDs) leads to inflammation, which results in progressive IVD degeneration. We have previously reported that activation of Wnt-β-catenin (hereafter called Wnt) signaling suppresses the proliferation of nucleus pulposus cells and induces cell senescence, suggesting that Wnt signaling triggers the process of degeneration of the IVD. However, it is not known whether cross talk between TNF-α and Wnt signaling plays a role in the regulation of nucleus pulposus cells. The goal of the present study was to examine the effect of the interaction between Wnt signaling and the proinflammatory cytokine TNF-α in nucleus pulposus cells.

Methods

Cells isolated from rat nucleus pulposus regions of IVDs were cultured in monolayers, and the expression and promoter activity of Wnt signaling and TNF-α were evaluated. We also examined whether the inhibition of Wnt signaling using cotransfection with Dickkopf (DKK) isoforms and Sclerostin (SOST) could block the effects of pathological TNF-α expression in nucleus pulposus cells.

Results

TNF-α stimulated the expression and promoter activity of Wnt signaling in nucleus pulposus cells. In addition, the activation of Wnt signaling by 6-bromoindirubin-3′-oxime (BIO), which is a selective inhibitor of glycogen synthase kinase 3 (GSK-3) activity that activates Wnt signaling, increased TNF-α expression and promoter activity. Conversely, the suppression of TNF-α promoter activity using a β-catenin small interfering RNA was evident. Moreover, transfection with DKK-3, DKK-4, or SOST, which are inhibitors of Wnt signaling, blocked Wnt signaling-mediated TNF-α activation; these effects were not observed for DKK-1 or DKK-2.

Conclusions

Here, we have demonstrated that Wnt signaling regulates TNF-α and that Wnt signaling and TNF-α form a positive-feedback loop in nucleus pulposus cells. The results of the present study provide in vitro evidence that activation of Wnt signaling upregulates the TNF-α expression and might cause the degeneration of nucleus pulposus cells. We speculate that blocking this pathway might protect nucleus pulposus cells against degeneration.     

Retinoic acid increases hypoxia-inducible factor-1α through intracrine prostaglandin E2 signaling in human renal proximal tubular cells HK-2

We have previously shown in HK-2 cells that ATRA (all-trans-retinoic acid) up-regulates HIF-1α (hypoxia-inducible factor-1α) in normoxia, which results in increased production of renal protector VEGF-A (vascular endothelial growth factor-A). Here we investigated the role of COXs (cyclooxygenases) in these effects and we found that, i) ATRA increased the expression of COX-1 and COX-2 mRNA and protein and the intracellular levels (but not the extracellular ones) of PGE₂. Furthermore, inhibitors of COX isoenzymes blocked ATRA-induced increase in intracellular PGE₂, HIF-1α up-regulation and increased VEGF-A production. Immunofluorescence analysis found intracellular staining for EP1-4 receptors (PGE₂ receptors). These results indicated that COX activity is critical for ATRA-induced HIF-1α up-regulation and suggested that intracellular PGE₂ could mediate the effects of ATRA; ii) Treatment with PGE₂ analog 16,16-dimethyl-PGE₂ resulted in up-regulation of HIF-1α and antagonists of EP1-4 receptors inhibited 16,16-dimethyl-PGE₂- and ATRA-induced HIF-1α up-regulation. These results confirmed that PGE₂ mediates the effects of ATRA on HIF-1α expression; iii) Prostaglandin uptake transporter inhibitor bromocresol green blocked the increase in HIF-1α expression induced by PGE₂ or by PGE₂-increasing cytokine interleukin-1β, but not by ATRA. Therefore only intracellular PGE₂ is able to increase HIF-1α expression. In conclusion, intracellular PGE₂ increases HIF-1α expression and mediates ATRA-induced HIF-1α up-regulation.     

In vitro induction of tumor necrosis factor-α by ochratoxin A (OTA) from rat liver: role of Kupffer cells

Tumor necrosis factor-α (TNF-α) is released from blood-free perfused rat liver by the fungal metabolite ochratoxin A. Here we have identified Kupffer cells as the sole source of OTA-mediated cytokine release. If single cell preparation of Kupffer cells, hepatocytes, or sinusoidal endothelial cells were prepared from rat livers, only Kupffer cells released TNF-α upon incubation with 2.5 μmol/l OTA. OTA failed to induce TNF-α release in the blood-free perfused isolated rat liver when Kupffer cells were blockedin vitro by 15 μmol/l gadolinium chloride. When rats were pretreatedin vivo with the Kupffer cell depleting clodronate liposomes, OTA-mediated TNF-α release was abrogated in the isolated perfused liver model.     

Activation of Wnt11 by transforming growth factor-β drives mesenchymal gene expression through non-canonical Wnt protein signaling in renal epithelial cells

Transforming growth factor β1 (TGF-β) promotes renal interstitial fibrosis in vivo and the expression of mesenchymal genes in vitro; however, most of its direct targets in epithelial cells are still elusive. In a screen for genes directly activated by TGF-β, we found that components of the Wnt signaling pathway, especially Wnt11, were targets of activation by TGF-β and Smad3 in primary renal epithelial cells. In gain and loss of function experiments, Wnt11 mediated the actions of TGF-β through enhanced activation of mesenchymal marker genes, such as Zeb1, Snail1, Pai1, and αSMA, without affecting Smad3 phosphorylation. Inhibition of Wnt11 by receptor knockdown or treatment with Wnt inhibitors limited the effects of TGF-β on gene expression. We found no evidence that Wnt11 activated the canonical Wnt signaling pathway in renal epithelial cells; rather, the function of Wnt11 was mediated by the c-Jun N-terminal kinase (JNK) pathway. Consistent with the in vitro results, all the TGF-β, Wnt11, and JNK targets were activated in a unilateral ureteral obstruction (UUO) model of renal fibrosis in vivo. Our findings demonstrated cooperativity among the TGF-β, Wnt11, and JNK signaling pathways and suggest new targets for anti-fibrotic therapy in renal tissue.     

Myostatin induces tumor necrosis factor-α expression in rheumatoid arthritis synovial fibroblasts through the PI3K–Akt signaling pathway

In rheumatoid arthritis (RA), a chronic inflammatory disease, loss of muscle mass is an important contributor to the loss of muscle strength in RA patients. Myostatin, a myokine involved in the process of muscle hypertrophy and myogenesis, enhances osteoclast differentiation and inflammation. Here, we investigated the mechanisms of myostatin in RA synovial inflammation. We found a positive correlation between myostatin and tumor necrosis factor-α (TNF-α), a well-known proinflammatory cytokine, in RA synovial tissue. Our in vitro results also showed that myostatin dose-dependently induced TNF-α expression through the phosphatidylinositol 3-kinase (PI3K)–Akt–AP-1 signaling pathway. Myostatin treatment of human MH7A cells stimulated AP-1-induced luciferase activity and activation of the c-Jun binding site on the TNF-α promoter. Our results indicated that myostatin increases TNF-α expression via the PI3K–Akt–AP-1 signaling pathway in human RA synovial fibroblasts. Myostatin appears to be a promising target in RA therapy.