Tumor necrosis factor-α as a therapeutic target for diabetic nephropathy

Activation of innate immunity with the subsequent development of a chronic low-grade inflammatory response is now recognized as a critical factor in the pathogenesis of diabetes mellitus and diabetic complications, including diabetic nephropathy. In the setting of diabetic nephropathy, there is now evidence of the relevant contribution of pro-inflammatory cytokines, with special participation of tumor necrosis factor-α (TNF-α). This new pathogenic perspective leads to new therapeutic implications derived from modulation of inflammation and inflammatory cytokines. Experimental studies have shown the beneficial renal actions derived from TNF-α inhibition with the use of soluble TNF-α receptor fusion proteins, chimeric monoclonal antibodies and pentoxifylline (PTF). Clinical application of this strategy is nowadays limited to PTF administration, which has demonstrated significant beneficial effects in patients with diabetic nephropathy. Overall, these studies indicate that inhibition of TNF-α might be an efficacious treatment for renal disease secondary to diabetes mellitus.     

Tumor necrosis factor-α and transforming growth factor-β1 facilitate differentiation and proliferation of tendon-derived stem cells in vitro

Objectives

To investigate the effects of tumor necrosis factor-α (TNF-α) and transforming growth factor-β1 (TGF-β1) on the proliferation and differentiation of tendon-derived stem cells (TDSC).

Results

TNF-α inhibits the proliferation and tenogenic/osteogenic differentiation of TDSC but, after simultaneous or sequential treatment with TGF-β1 and TNF-α, the expression of tenogenic/osteogenic-related marker and proliferation of TDSC was significantly increased. During these processes, Smad2/3 and Smad1/5/8 were highly phosphorylated, meaning that the TGF-β and BMP signaling pathways were highly activated. Further study revealed that the expression of Inhibitor-Smad appeared to be negatively correlated to the proliferation and differentiation of TDSC.

Conclusions

Combining the use of TNF-α and TGF-β1 could improve the proliferation and differentiation of TDSC in vitro, and the expression of I-Smad is negatively correlated with TDSC proliferation and differentiation.

     

Tumor necrosis factor-α signaling in nonalcoholic steatohepatitis and targeted therapies

Nonalcoholic steatohepatitis (NASH), an inflammatory subtype of nonalcoholic fatty liver disease, is featured by significantly elevated levels of various proinflammatory cytokines. Among numerous proinflammatory factors that contribute to NASH pathogenesis, the secreted protein, tumor necrosis factor-alpha (TNF-α), plays an essential role in multiple facets of NASH progression and is therefore considered as a potential therapeutic target. In this review, we will first systematically describe the preclinical studies on the biochemical function of TNF-α and its intracellular downstream signaling mechanisms through its receptors. Moreover, we extensively discuss its functions in regulating inflammation, cell death, and fibrosis of liver cells in the pathogenesis of NASH, and the molecular mechanism that TNF-α expression is regulated by NF-κB and other upstream master regulators during NASH progression. As TNF-α is one of the causal factors that remarkably contributes to NASH progression, combination of therapeutic modalities, including TNF-α-based therapies may lead to the resolution of NASH via multiple pathways and thus generate clinical benefits. For translational studies, we summarize recent advances in strategies targeting TNF-α and its signaling pathway, which paves the way for potential therapeutic treatments for NASH in the future.     

Tumor necrosis factor-α gene promoter polymorphism in coal worker' pneumoconiosis

Tumor necrosis factor-alpha (TNF-) is believed to play a central role in the pathogenesis of pneumoconiosis. TNF2, a polymorphism in the TNF- gene promoter, has been associated with an increase in TNF- production and airway inflammation. To investigate the frequency of TNF2 in patients who have coal workers' pneumoconiosis (CWP) and to determine whether it is associated with development of a large opacity in CWP, we investigated the expression of the TNF2 allele in 80 patients who had CWP and in 54 healthy controls using restriction fragment length polymorphism (RFLP). Compared to controls (10.2%), the frequency of the TNF2 allele was greater in the CWP patients (20.6%). Furthermore, the TNF2 allele was very common in patients who had a large opacity (28.2%) in comparison with 13.4% in those with simple CWP. From these data, we suggest that the TNF2 allele is associated with the development of a large opacity in CWP.     

Tumor necrosis factor-α stimulation endothelial-to-mesenchymal transition during cardiac fibrosis via endothelin-1 signaling

Cardiac fibrosis is an important pathological change after myocardial infarction (MI). High concentration of tumor necrosis factor-α (TNF-α) contributes to cardiac fibrosis, and TNF-α has been demonstrated to be involved in transforming growth factor-β1-induced endothelial-to-mesenchymal transition (EndMT). However, the role and molecular mechanisms of TNF-α during cardiac fibrosis remain largely unexplored. In this study, we demonstrated that TNF-α and endothelin-1 (ET-1) were upregulated in cardiac fibrosis after MI, and genes associated with EndMT were also upregulated. An in vitro model of EndMT demonstrated that TNF-α promoted EndMT by upregulation of vimentin and α-smooth muscle actin, and which strongly increased ET-1 expression. ET-1 promoted TNF-α-induced expression of gene program through phosphorylation levels of SMAD family member 2, while subsequent inhibition of ET-1 almost abolished the effect of TNF-α during the process of EndMT. In summary, these findings demonstrated that ET-1 is involved in the EndMT induced by TNF-α during cardiac fibrosis.     

Tumor necrosis factor-α accelerates apoptosis of steatotic hepatocytes from a murine model of non-alcoholic fatty liver disease

Non-alcoholic steatohepatitis (NASH) develops in a subset of patients with non-alcoholic fatty liver disease (NAFLD), but the exact mechanisms involved in the progression of NAFLD to NASH remain poorly understood. We investigated the role of tumor necrosis factor-α (TNF-α) in the apoptosis of hepatocytes that is related to the severity of NASH. We separated primary hepatocytes from the NAFLD liver caused by a high-fat diet. The production of intracellular reactive oxygen species was increased in steatotic hepatocytes, which were also sensitive to TNF-α. This factor induced significant apoptosis through the signal-regulating kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK) pathway. We describe here a novel culture model of steatotic hepatocytes separated from the NAFLD liver, and demonstrate that TNF-α induces their apoptosis in vitro.     

Tumor necrosis factor-α regulates distinct molecular pathways and gene networks in cultured skeletal muscle cells

Background

Skeletal muscle wasting is a debilitating consequence of large number of disease states and conditions. Tumor necrosis factor-α (TNF-α) is one of the most important muscle-wasting cytokine, elevated levels of which cause significant muscular abnormalities. However, the underpinning molecular mechanisms by which TNF-α causes skeletal muscle wasting are less well-understood.

Methodology/Principal Findings

We have used microarray, quantitative real-time PCR (QRT-PCR), Western blot, and bioinformatics tools to study the effects of TNF-α on various molecular pathways and gene networks in C2C12 cells (a mouse myoblastic cell line). Microarray analyses of C2C12 myotubes treated with TNF-α (10 ng/ml) for 18h showed differential expression of a number of genes involved in distinct molecular pathways. The genes involved in nuclear factor-kappa B (NF-kappaB) signaling, 26s proteasome pathway, Notch1 signaling, and chemokine networks are the most important ones affected by TNF-α. The expression of some of the genes in microarray dataset showed good correlation in independent QRT-PCR and Western blot assays. Analysis of TNF-treated myotubes showed that TNF-α augments the activity of both canonical and alternative NF-κB signaling pathways in myotubes. Bioinformatics analyses of microarray dataset revealed that TNF-α affects the activity of several important pathways including those involved in oxidative stress, hepatic fibrosis, mitochondrial dysfunction, cholesterol biosynthesis, and TGF-β signaling. Furthermore, TNF-α was found to affect the gene networks related to drug metabolism, cell cycle, cancer, neurological disease, organismal injury, and abnormalities in myotubes.

Conclusions

TNF-α regulates the expression of multiple genes involved in various toxic pathways which may be responsible for TNF-induced muscle loss in catabolic conditions. Our study suggests that TNF-α activates both canonical and alternative NF-κB signaling pathways in a time-dependent manner in skeletal muscle cells. The study provides novel insight into the mechanisms of action of TNF-α in skeletal muscle cells.     

Tumor necrosis factor-α can induce Langhans-type multinucleated giant cell formation derived from myeloid dendritic cells

The formation of the rich cellular features of MGCs, where the nuclei are arranged circularly at the periphery of the cell (morphologically epithelioid; Langhans-type), is assumed to be associated with any granulomatous disease. The mechanism by which TNF controls the formation of human MGCs in vitro was investigated, focusing on the effect of the TNF-neutralizing antibody. Peripheral blood monocytes were isolated with mAb-coated immunologic magnetic beads and cultured for 10 days in the presence of 20 ng/mL GM-CSF and 10 ng/mL IL-4. These cells were further incubated in the presence of TNF-α with/without its blockade antibodies for 14 days. Myeloid DCs can be generated from peripheral blood monocytes, and both IL-4 and GM-CSF can provide sufficient stimulus for their differentiation. The formation of MGC can be induced in the presence of TNF-α. This reaction was prohibited by the presence of the TNF-neutralizing antibody but not by the presence of anti-TNF receptor II antibody. The activation of Rho and focal adhesion kinases induced by TNF-α stimulation might be linked to cell assembling and the formation of Langhans-type MGCs. MGCs can produce only small amounts of superoxide anions compared to isolated macrophages such as myeloid DCs.     

Tumor necrosis factor-α exerts interleukin-6-dependent and -independent effects on cultured skeletal muscle cells

In vivo studies have shown that cancer-associated skeletal muscle wasting (cachexia) is mediated by two cytokines, tumor necrosis factor-α (TNF) and interleukin-6 (IL-6). It has been unclear from these studies whether TNF exerts direct effects on skeletal muscle and/or whether these effects are mediated via IL-6. Previous studies from our laboratory have shown that TNF induces IL-6 mRNA expression in cultured skeletal muscle cells. To further investigate the relationship between TNF and IL-6, the effects of TNF and IL-6 on protein and DNA dynamics in murine C2C12 skeletal myotube cultures were determined. At 1000 U/ml, TNF induced 30% increases in protein and DNA content. The effects of TNF on protein accumulation were inhibited by aphidicolin, an inhibitor of DNA synthesis. IL-6 mimicked the effects of TNF on C2C12 cultures, inducing a 32% increase in protein accumulation and a 71% increase in the rate of protein synthesis. IL-6 also decreased expression of mRNA for several proteolytic system components, including ubiquitin 2.4 kb (51%) and 1.2 kb (63%), cathepsin B (39%) and m-calpain (47%), indicating that IL-6 acts on both protein synthesis and degradation. Incubation of murine C2C12 myotube cultures with TNF (1000 U/ml) in the presence of a polyclonal mouse anti-IL-6 antibody resulted in an abolishment of the effects of TNF on protein synthesis, but did not inhibit TNF-induced stimulation of DNA synthesis. These findings indicate that the effects of TNF on muscle protein synthesis are mediated by IL-6, but that TNF exerts IL-6-independent effects on proliferation of murine skeletal myoblasts.     

Leucine-rich glioma inactivated 3 and tumor necrosis factor-α regulate mutually through NF-κB

Leucine-rich glioma inactivated 3 (LGI3) is a secreted protein member of LGI family. We previously reported that LGI3 increased in obese adipose tissues and suppressed adipogenesis through its receptor, ADAM23. We proposed that LGI3 may be a pro-inflammatory adipokine secreted predominantly by preadipocytes and macrophages. In this study, we showed that LGI3 and tumor necrosis factor-α (TNF-α) upregulated each other in 3T3-L1 cells. Treatment of 3T3-L1 preadipocytes with LGI3 protein increased TNF-α mRNA and protein. LGI3 treatment led to NF-κB activation and binding to an NF-κB binding site (−523 to −514) in TNF-α promoter. TNF-α treatment increased mRNA and protein expression of LGI3 and ADAM23. TNF-α increased NF-κB binding to a predicted binding site (−40 to −31) in LGI3 promoter. High fat diet-fed mice showed that LGI3 and TNF-α were increased and colocalized in adipose tissue inflammation. Taken together, these results suggested that mutual upregulation of LGI3 and TNF-α may play a role in adipose tissue inflammation in obesity.     

Tumour necrosis factor-α gene polymorphisms in asbestos-induced diseases

Background: Tumour necrosis factor (TNF)-α influences the pathogenesis of lung fibrosis and carcinogenesis in normal cells. Polymorphisms of this gene have been suggested to be associated with susceptibility to lung diseases.

Methods: Association studies were performed in German subjects, using control subjects (n?=?177), pulmonary fibrosis patients (n?=?612) and bronchial carcinoma patients (n?=?374).

Results: Compared with a healthy (control) group, a significant result could be obtained for the asbestosis (patient) group (crude odds ratio (OR_crude)?=?1.57; 95% confidence interval (CI) 1.05–2.36; p?=?0.03), especially with severe lung asbestosis (OR_crude?=?4.15; 95% CI 1.06–16.16; p?=?0.04). A significant association was revealed when comparing asbestosis patients (OR_crude?=?4.08; 95% CI 1.53–10.54; p?=?0.004 and OR_adjusted?=?3.89; 95% CI 1.49–10.17; p?=?0.006) with asbestos-induced lung cancer patients.

Conclusion: The results confirm the hypothesis that TNF-α polymorphisms are associated with asbestos-induced fibrotic or malignant lung diseases in Germans.     

Proinflammatory macrophages impair skeletal muscle differentiation in obesity through secretion of tumor necrosis factor-α via sustained activation of p38 mitogen-activated protein kinase

Obesity is associated with skeletal muscle loss and impaired myogenesis. Increased infiltration of proinflammatory macrophages in skeletal muscle is noted in obesity and is associated with muscle insulin resistance. However, whether the infiltrated macrophages can contribute to obesity-induced muscle loss is unclear. In this study, we investigate macrophage and muscle differentiation markers in the quadriceps (QC), gastrocnemius, tibia anterior, and soleus muscles from obese mice that were fed a high-fat diet for 16 weeks. Then, we examined the effect and mediator of macrophage-secreted factors on myoblast differentiation in vitro. We found markedly increased levels of proinflammatory macrophage markers (F4/80 and CD11c) in the QC muscle compared with the other three muscle groups. Consistent with the increased levels of proinflammatory macrophage infiltration, the QC muscle also showed a significant reduction in the expression of muscle differentiation makers MYOD1 and myosin heavy chain. In in vitro studies, treatment of C2C12 myoblasts with Raw 264.7 macrophage-conditioned medium (CM) significantly promoted cell proliferation and inhibited myoblast differentiation. Neutralization of tumor necrosis factor α (TNF-α) in Raw 264.7 macrophage CM reversed the reduction of myoblast differentiation. Finally, we found that both macrophage CM and TNF-α induced sustained activation of p38 mitogen-activated protein kinase (MAPK) in C2C12 myoblasts. Together, our findings suggest that the increased infiltration of proinflammatory macrophages could contribute toward obesity-induced muscle loss by secreting inflammatory cytokine TNF-α via the p38 MAPK signaling pathway.     

Tumor necrosis factor-α converting enzyme (TACE) increases RANKL expression in osteoblasts and serves as a potential biomarker of periodontitis

Periodontitis is a very prevalent disease. Therefore, biomarkers for the early and standard diagnoses of periodontitis are urgently needed. TACE is a membrane-bound metalloprotease. Although a recent study suggested that TACE levels in GCF are elevated during periodontal disease, the levels of TACE in GCF at different stages of chronic periodontitis have not been determined. Here, we analyzed the protein levels of TACE in GCF from periodontal disease subjects and confirmed that the protein levels of TACE were higher in the moderate periodontitis groups. TACE is known to be a NF-κB ligand that stimulates RANKL secretion in osteoblasts. To understand the effects of TACE on RANKL and OPG in osteoblasts, we treated MG63 cells with TACE. We observed an increase in RANKL protein expression but a decrease in OPG protein expression. Our data suggest that TACE can induce RANKL expression and promote osteoclastogenesis, thus worsening the outcome of periodontitis.     

Tumor necrosis factor-α in macrophages of heart,liver, kidney,and in the pituitary gland

The relationship between myonuclear number, cellular size, succinate dehydrogenase activity, and myosin type was examined in single fiber segments (n=54; 9±3 mm long) mechanically dissected from soleus and plantaris muscles of adult rats. One end of each fiber segment was stained for DNA before quantitative photometric analysis of succinate dehydrogenase activity; the other end was double immunolabelled with fast and slow myosin heavy chain monoclonal antibodies. Mean±S.D. cytoplasmic volume/myonucleus ratio was higher in fast and slow plantaris fibers (112±69 vs. 34±21x10³ m³) than fast and slow soleus fibers (40±20 vs. 30±14x10³ m³), respectively. Slow fibers always had small volumes/myonucleus, regardless of fiber diameter, succinate dehydrogenase activity, or muscle of origin. In contrast, smaller diameter (<70 m) fast soleus and plantaris fibers with high succinate dehydrogenase activity appeared to have low volumes/myonucleus while larger diameter (>70 m) fast fibers with low succinate dehydrogenase activity always had large volume/myonucleus. Slow soleus fibers had significantly greater numbers of myonuclei/mm than did either fast soleus or fast plantaris fibers (116±51 vs. 55±22 and 44±23), respectively. These data suggest that the myonuclear domain is more limited in slow than fast fibers and in the fibers with a high, compared to a low, oxidative metabolic capability.     

Tumor necrosis factor-α gene promoter −308 and −238 polymorphisms and its serum level in psoriasis

BackgroundPsoriasis is a chronic, immune-mediated, inflammatory skin disease affecting genetically predisposed individuals and requiring long-term treatment. The etiology of psoriasis is not fully understood. This article aimed to determine association between genetic polymorphisms in tumor necrosis factor-α (TNF -α) promoter ?308 (rs1800629) and ?238 (rs 361,525) and its serum level in psoriasis patients.MethodsThe study was conducted on 70 patients with psoriasis and 70 age and sex-matched, healthy individuals. All patients were subjected to history taking and complete medical examination. The polymorphisms of TNF -α promoter gene ?308 (rs1800629) and ?238 (rs 361,525) were detected by real time PCR and Serum levels of TNF -α were measured by ELISA technique.ResultsAG polymorphism and A allele of TNF-α ?238 G/A (rs 361,525) were significantly more in patients than controls, whereas AG polymorphism and A allele of TNF-α ?308 G/A (rs1800629) were significantly more in controls than patients. There were significant high levels of TNF-α in serum of patients in comparison to controls.ConclusionsThe AG polymorphism and A allele of TNF-α ?238G/A (rs 361,525) may act as a risk factor for occurrence of psoriasis, whereas AG polymorphism and A allele of TNF-α ?308G/A (rs1800629) may have protective role. There is pivotal role of TNF-α as a pro-inflammatory mediator in pathogenesis of psoriasis.