Two tumour necrosis factor receptors: structure and function

Role of TNF-α in human female reproduction

TNF-α is a highly versatile cytokine, playing an important role in both apoptosis and inflammation, which is central to reproduction. It belongs to the Th1 type of cytokines. Thus, TNF-α is a proinflammatory cytokine and is involved during follicle development and ovulation, corpus luteum formation and regression and cyclic endometrium function. It has been postulated to be detrimental to the survival of the conceptus due to apoptosis of human primary villous trophoblast cells, leading to miscarriage. However, TNF-α may have a dual role in early pregnancy. Hormonally regulated uterine TNF-α in the mother is probably essential for trophoblast cell invasion, while increased production of TNF-α by maternal macrophages may facilitate labor. The current knowledge on the role of TNF-α and its receptors in the female reproduction is described in this review.

Differential modulation of TNF-alpha-induced apoptosis by Neisseria meningitidis

Infections by Neisseria meningitidis show duality between frequent asymptomatic carriage and occasional life-threatening disease. Bacterial and host factors involved in this balance are not fully understood. Cytopathic effects and cell damage may prelude to pathogenesis of isolates belonging to hyper-invasive lineages. We aimed to analyze cell–bacteria interactions using both pathogenic and carriage meningococcal isolates. Several pathogenic isolates of the ST-11 clonal complex and carriage isolates were used to infect human epithelial cells. Cytopathic effect was determined and apoptosis was scored using several methods (FITC-Annexin V staining followed by FACS analysis, caspase assays and DNA fragmentation). Only pathogenic isolates were able to induce apoptosis in human epithelial cells, mainly by lipooligosaccharide (endotoxin). Bioactive TNF-α is only detected when cells were infected by pathogenic isolates. At the opposite, carriage isolates seem to provoke shedding of the TNF-α receptor I (TNF-RI) from the surface that protect cells from apoptosis by chelating TNF-α. Ability to induce apoptosis and inflammation may represent major traits in the pathogenesis of N. meningitidis. However, our data strongly suggest that carriage isolates of meningococci reduce inflammatory response and apoptosis induction, resulting in the protection of their ecological niche at the human nasopharynx.

Acquisition of Neisseria meningitidis often leads to asymptomatic colonization (carriage) and rarely results in invasive disease associated with tissue injury. The reasons that make disease-associated isolates (pathogenic isolates) but not asymptomatic carriage isolates able to invade the host to establish disease are not understood. Isolates belonging to the ST-11 clonal complex are most frequently associated with the disease and rarely found in carriers. These hyper-invasive isolates may be able to induce cytopathic effects in target cells. We aimed to investigate the cytopathic effect of meningococcal isolates on epithelial cells using both ST-11 pathogenic isolates and carriage isolates. We showed that cytopathic effects were strongly associated with pathogenic isolates and infected cells exhibited features of apoptosis. This effect is mainly mediated by bacterial endotoxin (lipooligosaccharide) and involved an autocrine signaling mechanism of secreted TNF-α through its receptor TNF-RI. In contrast, carriage isolates down-regulate TNF-RI on the surface of infected cells by increasing TNF-RI shedding into the medium. We suggest that chelating secreted TNF-α protects cells from apoptosis. Our results unravel a differential modulation of TNF-α signaling by meningococcal isolates leading to cell survival or death and would therefore contribute to better understanding of the duality between carriage and invasiveness.

Influence of testosterone and a novel SARM on gene expression in whole blood of Macaca fascicularis

Anabolic hormones, including testosterone, have been suggested as a therapy for aging-related conditions, such as osteoporosis and sarcopenia. These therapies are sometimes associated with severe androgenic side effects. A promising alternative to testosterone replacement therapy are selective androgen receptor modulators (SARMs). SARMs have the potential to mimic the desirable central and peripheral androgenic anabolic effects of testosterone without having its side effects. In this study we evaluated the effects of LGD2941, in comparison to testosterone, on mRNA expression of selected target genes in whole blood in an non-human model. The regulated genes can act as potential blood biomarker candidates in future studies with AR ligands. Cynomolgus monkeys (Macaca fascicularis) were treated either with testosterone or LGD2941 for 90 days in order to compare their effects on mRNA expression in blood. Blood samples were taken before SARM application, on day 16 and on day 90 of treatment. Gene expression of 37 candidate genes was measured using quantitative real-time RT-PCR (qRT-PCR) technology. Our study shows that both testosterone and LGD2941 influence mRNA expression of 6 selected genes out of 37 in whole blood. The apoptosis regulators CD30L, Fas, TNFR1 and TNFR2 and the interleukins IL-12B and IL-15 showed significant changes in gene expression between control and the treatment groups and represent potential biomarkers for androgen receptor ligands in whole blood.

Increased soluble tumor necrosis factor-alpha receptors in patients with major depressive disorder

AIM

Several lines of evidence suggest that major depressive disorder is associated with an inflammatory status. Tumor necrosis factor-alpha has been investigated as a potential molecular target in mood disorders. Tumor necrosis factor-alpha exerts its activity through binding to specific cell membrane receptors named as TNFR1 and TNFR2. The aim of the present study was to investigate soluble plasma TNFR1 (sTNFR1) and TNFR2 levels (sTNFR2) in major depressive disorder patients.

METHODS

Female outpatients with major depressive disorder (n = 30) were compared with a healthy control group (n = 19). Severity of depressive symptoms was evaluated on Beck Depression Inventory; post-traumatic stress disorder (PTSD) symptoms were evaluated on PTSD Checklist-Civilian Version; and childhood abuse and neglect on the Childhood Trauma Questionnaire. Plasma tumor necrosis factor-alpha and its soluble receptors were measured by ELISA.

RESULTS

Patients had no changes in tumor necrosis factor-alpha concentrations but did have increased sTNFR1 (P < 0.001) and sTNFR2 (P < 0.001) levels compared to controls. Plasma level of sTNFR1 was positively predicted by age (B = 0.25, P = 0.05) and PTSD-like symptoms (B = 0.41, P = 0.002) and plasma levels of sTNFR2 by depression severity (B = 0.67, P < 0.001).

CONCLUSIONS

Soluble tumor necrosis factor-alpha receptors could be reliable markers of inflammatory activity in major depression.

TNF-alpha and its inhibitors in cancer

Tumor necrosis factor (TNF)-alpha is implicated in the same time in apoptosis and in cell proliferation. TNF-alpha not only acts as pro-inflammatory cytokine conducing to wide spectrum of human diseases including inflammatory diseases, but can also induce tumor development. The molecular mechanisms of TNF-alpha functions have been intensively investigated. In this review we covered TNF-alpha, the molecule, its signaling pathway, and its therapeutic functions. We provide a particular insight in its paradoxical role in tumor promotion and in its use as anti-tumor agent. This review considers also the recent findings regarding TNF-alpha inhibitors, their pharmacokinetics, and their pharmacodynamics. Six TNF-alpha inhibitors have been considered here: Infliximab, Adalimumab, Golimumab, CDP870, CDP571, Etanercept, and Thalidomide. We discussed the clinical relevance of their functions in treatment of several diseases such as advanced inflammatory rheumatic and bowel disease, with a focus in cancer treatment. Targeting TNF-alpha by these drugs has many side effects like malignancies development, and the long-term sequels are not very well explored. Their efficacy and their safety were discussed, underscoring the necessity of close patients monitoring and of their caution use.

Protein kinase Cepsilon inhibits UVR-induced expression of FADD, an adaptor protein, linked to both Fas- and TNFR1-mediated apoptosis

Protein kinase C (PKC)epsilon overexpression in FVB/N transgenic mice sensitized skin to UVR-induced development of squamous cell carcinomas and suppressed formation of sunburn cells, which are DNA-damaged keratinocytes undergoing apoptosis. Here, we elucidated the mechanisms associated with the inhibition of UVR-induced appearance of sunburn cells in PKCepsilon transgenic mice. We found that the inhibition of UVR-induced sunburn cell formation in PKCepsilon transgenic mice may be the result of the inhibition of the expression of Fas, Fas ligand, and the mammalian death adaptor protein termed Fas-associated with death domain (FADD). The adaptor protein FADD is the key component of the death-inducing signaling complex of both Fas and tumor necrosis factor receptor 1. A decreased expression of epidermal FADD was observed after a single UVR exposure. However, a complete loss of FADD expression was found after four (Monday, Wednesday, Friday, and Monday) repeated UVR exposures. FADD transmits apoptotic signals from death receptors to the downstream initiator caspase-8 and connects to the mitochondrial intrinsic apoptotic signal transduction pathway by the cleavage of Bid, a Bcl-2 family member. PKCepsilon-mediated loss of FADD expression inhibited UVR signals to the activation of both extrinsic and intrinsic apoptotic pathways.

Insulin sensitivity in African-American and white women: association with inflammation

Whether the contribution of inflammation to risk for chronic metabolic disease differs with ethnicity is not known. The objective of this study was to determine: (i) whether ethnic differences exist in markers of inflammation and (ii) whether lower insulin sensitivity among African Americans vs. whites is due to greater inflammatory status. Subjects were African-American (n = 108) and white (n = 105) women, BMI 27-30 kg/m(2). Insulin sensitivity was assessed with intravenous glucose tolerance test and minimal modeling; fat distribution with computed tomography; body composition with dual-energy X-ray absorptiometry; markers of inflammation (tumor necrosis factor (TNF)-alpha, soluble tumor necrosis factor receptor (sTNFR)-1, sTNFR-2, C-reactive protein (CRP), and interleukin (IL)-6) with enzyme-linked immunosorbent assay (ELISA). Whites had greater intra-abdominal adipose tissue (IAAT), insulin sensitivity, and concentrations of TNF-alpha, sTNFR-1, and sTNFR-2 than African Americans. Greater TNF-alpha in whites vs. African Americans was attributed to greater IAAT in whites. Among whites, but not African Americans, CRP was independently and inversely associated with insulin sensitivity, after adjusting for IAAT (r = -0.29 P < 0.05, and r = -0.13 P = 0.53, respectively). Insulin sensitivity remained lower in African Americans after adjusting for CRP (P < 0.001). In conclusion, greater IAAT among whites may be associated with greater inflammation. Insulin sensitivity was lower among African Americans, independent of obesity, fat distribution, and inflammation.

The type 1 TNF receptor and its associated adapter protein, FAN, are required for TNFalpha-induced sickness behavior

RATIONALE

During the course of an infection, the pro-inflammatory cytokine tumor necrosis factor alpha (TNFalpha) acts in the brain to trigger development of behavioral responses, collectively termed sickness behavior. Biological activities of TNFalpha can be mediated by TNF receptor type 1 (TNF-R1) and type 2 (TNF-R2). TNFalpha activates neutral sphingomyelinase through the TNF-R1 adapter protein FAN (factor associated with neutral sphingomyelinase activation), but a behavioral role of FAN in the brain has never been reported.

OBJECTIVES

We hypothesized that TNFalpha-induced sickness behavior requires TNF-R1 and that FAN is a necessary component for this response.

MATERIALS AND METHODS

We determined the role of brain TNF-R1 in sickness behavior by administering an optimal amount of TNFalpha intracerebroventricularly (i.c.v., 50 ng/mouse) to wild-type (WT), TNF-R1-, TNF-R2-, and FAN-deficient mice. Sickness was assessed by decreased social exploration of a novel juvenile, induction of immobility, and loss of body weight.

RESULTS

TNF-R1-deficient mice were resistant to the sickness-inducing properties of i.c.v. TNFalpha, whereas both TNF-R2-deficient and WT mice were fully responsive. Furthermore, the complete absence of TNFalpha-induced sickness behavior in FAN-deficient mice provided in vivo evidence that FAN-dependent TNF-R1 signaling is critical for this central action of TNFalpha.

CONCLUSIONS

This is the first report to demonstrate that TNFalpha-induced sickness behavior is fully mediated by TNF-R1 and that the adaptor protein FAN is a necessary intracellular intermediate for sickness behavior.

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced chemokine release in both TRAIL-resistant and TRAIL-sensitive cells via nuclear factor kappa B

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in a variety of tumour cells, but not in most normal cells, and has attracted considerable attention for its potential use in cancer therapy. Recently, increasing evidence has shown that TRAIL is involved in inflammation, although much of this evidence is controversial. In this article, it is shown that TRAIL induces CXCL2, CCL4 and CCL20 secretion in a nuclear factor kappa B-dependent manner. The dominant negative constructs of tumour necrosis factor receptor-associated death domain protein (TRADD) and tumour necrosis factor receptor-associated factor 2 are unable to block TRAIL-induced chemokine up-regulation, and the dominant negative construct of TRADD may even enhance TRAIL-triggered signals. Using small interfering RNA, receptor interacting protein has been demonstrated to be essential for TRAIL-induced chemokine release. Furthermore, it has been demonstrated that p38 mitogen-activated protein kinase is involved in TRAIL-induced chemokine release without any effects on nuclear factor kappa B activation, suggesting that some unknown transcription factors may be activated by TRAIL. Using a xenograft tumour model, it has been illustrated that TRAIL can also induce chemokine release in vivo. Although these chemokines induced by TRAIL are inflammatory chemokines, their functions are not restricted to inflammation and require further examination. Our results indicate that attention should be paid to the side-effects of TRAIL treatment, not only in TRAIL-resistant but also in TRAIL-sensitive tumour cells.

Cytokines and myelination in the central nervous system

Myelin abnormalities that reflect damage to developing and mature brains are often found in neurological diseases with evidence of inflammatory infiltration and microglial activation. Many cytokines are virtually undetectable in the uninflamed central nervous system (CNS), so that their rapid induction and sustained elevation in immune and glial cells contributes to dysregulation of the inflammatory response and neural cell homeostasis. This results in aberrant neural cell development, cytotoxicity, and loss of the primary myelin-producing cells of the CNS, the oligodendrocytes. This article provides an overview of cytokine and chemokine activity in the CNS with relevance to clinical conditions of neonatal and adult demyelinating disease, brain trauma, and mental disorders with observed white matter defects. Experimental models that mimic human disease have been developed in order to study pathogenic and therapeutic mechanisms, but have shown mixed success in clinical application. However, genetically altered animals, and models of CNS inflammation and demyelination, have offered great insight into the complexities of neuroimmune interactions that impact oligodendrocyte function. The intracellular signaling pathways of selected cytokines have also been highlighted to illustrate current knowledge of receptor-mediated events. By learning to interpret the actions of cytokines and by improving methods to target appropriate predictors of disease risk selectively, a more comprehensive understanding of altered immunoregulation will aid in the development of advanced treatment options for patients with inflammatory white matter disorders.

Tumor necrosis factor receptor 1 induces interleukin-6 upregulation through NF-kappaB in a rat neuropathic pain model

Peripheral nerve injury resulting in neuropathic pain induces the upregulation of interleukin (IL)-6 and tumor necrosis factor-alpha, which binds to tumor necrosis factor receptor 1 (TNFR1) and induces NF-kappaB and p38 MAPK activation in the spinal cord and dorsal root ganglia (DRG). We here investigated whether TNFR1 regulates IL-6 expression through NF-kappaB or p38 MAPK activations in the spinal cord and DRG in rats with chronic constriction injury (CCI) of the sciatic nerve. Intrathecal treatment with a TNFR1 antisense oligonucleotide (ASO) significantly inhibited CCI-elevated IKKs phosphorylation, IkB-alpha degradation, the nuclear translocation, phosphorylation, and DNA-binding activity of NF-kappaB, p38 MAPK activation, and IL-6 mRNA and protein expression in the spinal cord and DRG. Interestingly, CCI remarkably elevated IKKalpha and p65 phosphorylations in the spinal cord rather than in the DRG. In addition, NF-kappaB decoy, but not p38 MAPK inhibitor, SB203580 reduced CCI-elevated IL-6 expression in the spinal cord and DRG. Therefore, these data suggest that TNFR1 induces IL-6 upregulation and neuropathic pain through NF-kappaB, but not p38 MAPK activation in the spinal cord and DRG and that the NF-kappaB/IL-6 pathways in the DRG may be less dependent on TNFR1 than the spinal cord pathway.

Cytokine mRNA expression in painful radiculopathy

Inflammatory cytokines contribute to lumbar radiculopathy. Regulation of cytokines for transient cervical injuries, with or without longer-lasting inflammation, remains to be defined. The C7 root in the rat underwent compression (10gf), chromic gut suture exposure (chr), or their combination (10gf+chr). Ipsilateral C7 spinal cord and dorsal root ganglia (DRG) were harvested at 1 hour after injury for real-time PCR analysis of IL-1beta, IL-6, and TNF-alpha. Cytokine mRNA increased after all 3 injuries. TNF-alpha mRNA in the DRG was significantly increased over sham after 10gf+chr (P = .026). Spinal IL-1beta was significantly increased over sham after 10gf and 10gf+chr (P < .024); IL-6 was significantly increased after 10gf+chr (P < .024). In separate studies, the soluble TNF-alpha receptor was administered at injury and again at 6 hours in all injury paradigms. Allodynia was assessed and tissue samples were harvested for cytokine PCR. Allodynia significantly decreased with receptor administration for 10gf and 10gf+chr (P < .005). Treatment also significantly decreased IL-1beta and TNF-alpha mRNA in the DRG for 10gf+chr (P < .028) at day 1. Results indicate an acute, robust cytokine response in cervical nerve root injury with varying patterns, dependent on injury type, and that early increases in TNF-alpha mRNA in the DRG may drive pain-related signaling for transient cervical injuries.

PERSPECTIVE

Inflammatory cytokine mRNA in the DRG and spinal cord are defined after painful cervical nerve root injury. Studies describe a role for TNF-alpha in mediating behavioral sensitivity and inflammatory cytokines in transient painful radiculopathy. Results outline an early response of inflammatory cytokine upregulation in cervical pain.

New aspects concerning ulcerative colitis and colonic carcinoma: analysis of levels of neuropeptides, neurotrophins, and TNFalpha/TNF receptor in plasma and mucosa in parallel with histological evaluation of the intestine

BACKGROUND

The levels of neuropeptides, neurotrophins, and TNFalpha (TNFalpha)/TNF receptor in plasma and mucosa for patients with ulcerative colitis (UC) and colonic carcinoma, and concerning plasma also for healthy controls, were examined. Moreover, the relationships between the different substances and the influence of mucosal derangement on the levels were analyzed.

METHODS

The levels of VIP, SP, CGRP, BDNF, NGF, and TNFalpha/TNF receptor 1 were measured using ELISA/EIA.

RESULTS

Patients with UC demonstrated the highest levels of all analyzed substances in plasma, with the exception of BDNF. However, there were differences within the UC group, patients treated with corticosteroids, and/or nonsteroid antiinflammatory/immunosuppressive treatment having higher plasma levels than those not given these treatments. Patients with colonic carcinoma showed higher SP and TNF receptor 1 levels in plasma compared to healthy controls. Concerning mucosa, the levels of almost all analyzed substances were elevated for patients with UC compared to noncancerous mucosa of colonic carcinoma patients. There were correlations between many of the substances in both plasma and mucosa, especially concerning the 3 neuropeptides examined. There were also marked associations with mucosa derangement.

CONCLUSIONS

Via analysis of correlations for the respective patients and via comparisons between the different patient groups, new and original information was obtained. Interestingly, the degree of mucosal affection was markedly correlated with tissue levels of the substances and the treatments were found to be of importance concerning plasma but not tissue levels of these. Combined plasma analysis of neuropeptides, neurotrophins, and TNF receptor 1 may help to distinguish UC and colonic carcinoma patients.

The role of TNF-alpha receptors p55 and p75 in acute myocardial ischemia/reperfusion injury and late preconditioning

The specific role of TNF-alpha receptors I (TNFR-I, p55) and II (TNFR-II, p75) in myocardial ischemic injury remains unclear. Using genetically engineered mice, we examined the relative effects of TNF-alpha signaling via p55 and p75 in acute myocardial ischemia/reperfusion injury under basal conditions and in late preconditioning (PC). Wild-type (WT) (C57BL/6 and B6,129) mice and mice lacking TNF-alpha (TNF-alpha(-/-)), p55 (p55(-/-)), p75 (p75(-/-)), or both receptors (p55(-/-)/p75(-/-)) underwent 30 min of coronary occlusion and 24 h of reperfusion with or without six cycles of 4-min coronary occlusion/4-min reperfusion (O/R) 24 h earlier (ischemic PC). Six cycles of O/R reduced infarct size 24 h later in WT mice, indicating a late PC effect. This late PC-induced infarct-sparing effect was abolished not only in TNF-alpha(-/-) and p55(-/-)/p75(-/-) mice, but also in p55(-/-) and p75(-/-) mice, indicating that TNF-alpha signaling via both p55 and p75 is necessary for the development of protection. In nonpreconditioned TNF-alpha(-/-), p55(-/-)/p75(-/-), and p75(-/-) mice, infarct size was similar to strain-matched WT mice. In contrast, infarct size in nonpreconditioned p55(-/-) mice was reduced compared with nonpreconditioned WT mice. We conclude that (i) unopposed p75 signaling (in the absence of p55) reduces infarct size following acute ischemia/reperfusion injury in naive myocardium, whereas unopposed p55 signaling (in the absence of p75) has no effect; and (ii) the development of the infarct-sparing effects of the late phase of PC requires nonredundant signaling via both p55 and p75 receptors. These findings reveal a fundamental, heretofore unrecognized, difference between the two TNF-alpha receptors in the setting of myocardial ischemia/reperfusion injury: that is, both p55 and p75 are necessary for the development of protection during late PC, but only signaling via p75 is protective in nonpreconditioned myocardium.

Selective stimulation of either tumor necrosis factor receptor differentially induces pain behavior in vivo and ectopic activity in sensory neurons in vitro

Recent studies suggest that tumor necrosis factor-alpha (TNF) sensitizes primary afferent neurons, and thus facilitates neuropathic pain. Here, we separately examined the roles of tumor necrosis factor receptor (TNFR) 1 and 2 by parallel in vivo and in vitro paradigms using proteins that selectively activate TNFR1 or TNFR2 (R1 and R2). In vivo, intrathecally injected R1, but not R2 slightly reduced mechanical and thermal withdrawal thresholds in rats, whereas co-injection resulted in robust, at least additive pain-associated behavior. In vitro, the electrophysiological responses of dorsal root ganglia (DRG) from rats with spinal nerve ligation were measured utilizing single-fiber recordings of teased dorsal root filaments. In naïve DRG, only R1 (10-1000 pg/ml) induced firing in Ass- and Adelta-fibers, whereas R2 had no effect. In injured DRG, both R1 and R2 at significantly lower concentrations (1 pg/ml) increased discharge rates of Adelta-fibers. Most interesting, in adjacent uninjured DRG, R2 and not R1, increased ectopic activity in both Ass- and Adelta-fibers. We conclude that TNFR1 may be predominantly involved in the excitation of sensory neurons and induction of pain behavior in the absence of nerve injury, TNFR2 may contribute in the presence of TNFR1 activation. Importantly, the effects of individually applied R1 and R2 on injured and adjacent uninjured fibers imply that the role of TNFR2 in the excitation of sensory neurons increases after injury.

Biology of TNFalpha and IL-10, and their imbalance in heart failure

Our understanding of the multiple in vivo functions of the proinflammatory cytokine, tumor necrosis factor (TNFalpha), is advancing at a rapid pace. In addition to its antitumor effects, overproduction of TNFalpha provokes tissue injury and organ failure. TNFalpha has also been shown to be cardiodepressant and responsible for various cardiovascular complications. It appears that still much needs to be learned for a full comprehension of the role of TNFalpha in heart biology. Another cytokine, interleukin-10 (IL-10), has been shown to have anti-inflammatory properties. It is suggested to counterbalance many adverse effects of TNFalpha. IL-10 suppresses the production of TNFalpha and many other proinflammatory cytokines. TNFalpha-induced oxidative stress is also known to be mitigated by IL-10. Moreover, improvement in cardiac function after treatment with various drugs is also shown to be associated with an increase in IL-10 content. Based on the data reviewed in here, it is suggested that an optimal balance between IL-10 and TNFalpha may be a new therapeutic strategy for a healthier heart.

TNFR1 promotes tumor necrosis factor-mediated mouse colon epithelial cell survival through RAF activation of NF-kappaB

Tumor necrosis factor (TNF) is a therapeutic target in the treatment of inflammatory bowel disease; however, the exact role of TNF signaling in the colon epithelium remains unclear. We demonstrate that TNF activation of TNF receptor (R)1 stimulates both pro- and anti-apoptotic signaling pathways in the colon epithelium; however, TNFR1 protects against colon epithelial cell apoptosis following TNF exposure. To investigate anti-apoptotic signaling pathways downstream of TNFR1, we generated an intestinal epithelium-specific Raf knock-out mouse and identified Raf kinase as a key regulator of colon epithelial cell survival in response to TNF. Surprisingly, Raf promotes NF-kappaB p65 phosphorylation, independent of MEK signaling, to support cell survival. Taken together, these data demonstrate a novel pathway in which Raf promotes colon epithelial cell survival through NF-kappaB downstream of TNFR1 activation. Thus, further understanding of colon epithelial cell-specific TNFR signaling may result in the identification of new targets for inflammatory bowel disease treatment and define novel mediators of colitis-associated cancer.

Plasma elevations of tumor necrosis factor-receptor-1 at day 7 postallogeneic transplant correlate with graft-versus-host disease severity and overall survival in pediatric patients

Tumor necrosis factor-alpha (TNF-alpha) is known to play a role in the pathogenesis of graft-versus-host disease (GVHD), a cause of significant morbidity and treatment-related mortality (TRM) after allogeneic hematopoietic stem cell transplantation (HCT). We measured the concentration of TNF-Receptor-1 (TNFR1) in the plasma of HCT recipients as a surrogate marker for TNF-alpha both prior to transplant and at day 7 in 82 children who underwent a myeloablative allogeneic HCT at the University of Michigan between 2000 and 2005. GVHD grade II-IV developed in 39% of patients at a median of 20 days after HCT. Increases in TNFR1 level at day 7 post-HCT, expressed as ratios compared to pretransplant baseline, correlated with the severity of GVHD (P = .02). In addition, day 7 TNFR1 ratios >2.5 baseline were associated with inferior 1-year overall survival (OS 51% versus 74%, P = .04). As an individual biomarker, TNFR1 lacks sufficient precision to be used as a predictor for the development of GVHD. However, increases in the concentration of TNFR1, which are detectable up to 2 weeks in advance of clinical manifestations of GVHD, correlate with survival in pediatric HCT patients.

Tumor necrosis factor inhibits ligand-stimulated EGF receptor activation through a TNF receptor 1-dependent mechanism

Tumor necrosis factor (TNF) and epidermal growth factor (EGF) are key regulators in the intricate balance maintaining intestinal homeostasis. Previous work from our laboratory shows that TNF attenuates ligand-driven EGF receptor (EGFR) phosphorylation in intestinal epithelial cells. To identify the mechanisms underlying this effect, we examined EGFR phosphorylation in cells lacking individual TNF receptors. TNF attenuated EGF-stimulated EGFR phosphorylation in wild-type and TNFR2(-/-), but not TNFR1(-/-), mouse colon epithelial (MCE) cells. Reexpression of wild-type TNFR1 in TNFR1(-/-) MCE cells rescued TNF-induced EGFR inhibition, but expression of TNFR1 deletion mutant constructs lacking the death domain (DD) of TNFR1 did not, implicating this domain in EGFR downregulation. Blockade of p38 MAPK, but not MEK, activation of ERK rescued EGF-stimulated phosphorylation in the presence of TNF, consistent with the ability of TNFR1 to stimulate p38 phosphorylation. TNF promoted p38-dependent EGFR internalization in MCE cells, suggesting that desensitization is achieved by reducing receptor accessible to ligand. Taken together, these data indicate that TNF activates TNFR1 by DD- and p38-dependent mechanisms to promote EGFR internalization, with potential impact on EGF-induced proliferation and migration key processes that promote healing in inflammatory intestinal diseases.

P55 tumour necrosis factor receptor in bone marrow-derived cells promotes atherosclerosis development in low-density lipoprotein receptor knock-out mice

AIMS

Tumour necrosis factor (TNF) is a pivotal pro-inflammatory cytokine with a clear pathogenic role in many chronic inflammatory diseases, and p55 TNF receptor (TNFR) mediates the majority of TNF responses. The aim of the current study was to investigate the role of p55 TNFR expression in bone marrow-derived cells, in atherosclerotic lesion development.

METHODS AND RESULTS

Irradiated low-density lipoprotein receptor knock-out mice were reconstituted with either p55 TNFR knock-out or control haematopoietic stem cells to generate chimeras deficient or wild-type for p55 TNFR specifically in bone marrow-derived cells, including macrophages. Upon high fat feeding, p55 TNFR knock-out transplanted mice developed smaller atherosclerotic lesions. These lesions were characterized by the presence of smaller foam cells and a reduced macrophage foam cell area. They did not differ in other compositional characteristics as determined by quantification of inflammatory T-cell and neutrophil influx, apoptotic and necrotic cell death, and collagen content. In vitro studies confirmed a significant defect in modified lipoprotein endocytosis by p55 TNFR knock-out macrophages due to reduced scavenger receptor class A expression. Interestingly, plasma cytokine/chemokine profile analysis indicated that monocyte chemoattractant protein-1 (MCP-1) levels, a major chemokine involved in atherogenesis, were consistently and significantly lower in p55 TNFR knock-out transplanted mice compared with controls, before and after high fat feeding.

CONCLUSION

p55 TNFR expression in bone marrow-derived cells contributes to the development of atherosclerosis by enhancing lesional foam cell formation and by promoting the expression of pro-atherosclerotic chemokines such as MCP-1.

Tumor necrosis factor p55 and p75 receptors are involved in chemical-induced apoptosis of dentate granule neurons

Localized tumor necrosis factor-alpha (TNFalpha) elevation has diverse effects in brain injury often attributed to signaling via TNFp55 or TNFp75 receptors. Both dentate granule cells and CA pyramidal cells express TNF receptors (TNFR) at low levels in a punctate pattern. Using a model to induce selective death of dentate granule cells (trimethyltin; 2 mg/kg, i.p.), neuronal apoptosis [terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ end labeling, active caspase 3 (AC3)] was accompanied by amoeboid microglia and elevated TNFalpha mRNA levels. TNFp55R (55 kDa type-1 TNFR) and TNFp75R (75 kDa type-2 TNFR) immunoreactivity in AC3(+) neurons displayed a pattern suggestive of receptor internalization and a temporal sequence of expression of TNFp55R followed by TNFp75R associated with the progression of apoptosis. A distinct ramified microglia response occurred around CA1 neurons and healthy dentate neurons that displayed an increase in the normal punctate pattern of TNFRs. Neuronal damage was decreased with i.c.v. injection of TNFalpha antibody and in TNFp55R-/-p75R-/- mice that showed higher constitutive mRNA levels for interleukin (IL-1alpha), macrophage inflammatory protein 1-alpha (MIP-1alpha), TNFalpha, transforming growth factor beta1, Fas, and TNFRSF6-assoicated via death domain (FADD). TNFp75R-/- mice showed exacerbated injury and elevated mRNA levels for IL-1alpha, MIP-1alpha, and TNFalpha. In TNFp55R-/- mice, constitutive mRNA levels for TNFalpha, IL-6, caspase 8, FADD, and Fas-associated phosphatase were higher; IL-1alpha, MIP-1alpha, and transforming growth factor beta1 lower. The mice displayed exacerbated neuronal death, delayed microglia response, increased FADD and TNFp75R mRNA levels, and co-expression of TNFp75R in AC3(+) neurons. The data demonstrate TNFR-mediated apoptotic death of dentate granule neurons utilizing both TNFRs and suggest a TNFp75R-mediated apoptosis in the absence of normal TNFp55R activity.

Mechanisms for cytotoxic effects of anti-tumor necrosis factor agents on transmembrane tumor necrosis factor alpha-expressing cells: comparison among infliximab, etanercept, and adalimumab

OBJECTIVE

Three anti-tumor necrosis factor alpha (anti-TNFalpha) agents have been proved to be effective for rheumatoid arthritis (RA) and other inflammatory disorders. Infliximab and adalimumab have been generated as anti-TNFalpha monoclonal antibodies, while etanercept is engineered from human type II TNF receptors. In spite of all 3 agents' equal efficacy for RA, both infliximab and adalimumab are effective for other diseases such as Crohn's disease and Wegener's granulomatosis, while etanercept is not. We undertook this study to understand the different clinical effects of these anti-TNFalpha agents by analyzing their biologic activities on transmembrane TNFalpha.

METHODS

Jurkat T cells stably expressing an uncleavable form of transmembrane TNFalpha were used for the following studies: 1) flow cytometric analysis of binding activities of anti-TNF agents to cell surface transmembrane TNFalpha, 2) complement-dependent cytotoxicity (CDC), 3) antibody-dependent cell-mediated cytotoxicity (ADCC) by using peripheral blood mononuclear cells, and 4) outside-to-inside (reverse) signal transduction through transmembrane TNFalpha estimated by apoptosis and cell cycle analysis using flow cytometry.

RESULTS

All of the anti-TNFalpha agents bound to transmembrane TNFalpha. Infliximab and adalimumab exerted almost equal CDC activities, while etanercept showed considerably lower activity. ADCC activities were almost equal among these 3 agents. Adalimumab and infliximab induced apoptosis and cell cycle arrest in transmembrane TNFalpha-expressing Jurkat T cells, reflecting an outside-to-inside signal transduction through transmembrane TNFalpha.

CONCLUSION

Three different anti-TNF agents showed different biologic effects on transmembrane TNFalpha. This finding suggests that CDC and outside-to-inside signals by anti-TNFalpha antibodies may explain the successful clinical efficacy of adalimumab and infliximab in Crohn's disease and Wegener's granulomatosis.

Endogenous tumor necrosis factor alpha (TNFalpha) requires TNF receptor type 2 to generate heat hyperalgesia in a mouse cancer model

To provide a tool to investigate the mechanisms inducing and maintaining cancer-related pain and hyperalgesia, a soft tissue tumor/metastasis model was developed that is applicable in C57BL/6J wild-type and transgenic mice. We show that the experimental tumor-induced heat hyperalgesia and nociceptor sensitization were prevented by systemic treatment with the tumor necrosis factor alpha (TNFalpha) antagonist etanercept. In naive mice, exogenous TNFalpha evoked heat hyperalgesia in vivo and sensitized nociceptive nerve fibers to heat in vitro. TNFalpha enhanced the expression of the nociceptor-specific heat transducer ion channel transient receptor potential vanilloid 1 (TRPV1) and increased the amplitudes of capsaicin and heat-activated ionic currents via p38/MAP (mitogen-activated protein) kinase and PKC (protein kinase C). Deletion of the tumor necrosis factor receptor type 2 (TNFR2) gene attenuated heat hyperalgesia and prevented TRPV1 upregulation in tumor-bearing mice, whereas TNFR1 gene deletion played a minor role. We propose endogenous TNFalpha as a key player in cancer-related heat hyperalgesia and nociceptor sensitization that generates TRPV1 upregulation and sensitization via TNFR2.

Change in plasma tumor necrosis factor receptor 1 levels in the first week after myeloablative allogeneic transplantation correlates with severity and incidence of GVHD and survival

Acute graft-versus-host disease (GVHD) remains a significant cause of mortality after hematopoietic cell transplantation (HCT). Tumor necrosis factor-alpha (TNF-alpha) mediates GVHD by amplifying donor immune responses to host tissues and by direct toxicity to target organs. We measured TNF receptor 1 (TNFR1) as a surrogate marker for TNF-alpha in 438 recipients of myeloablative HCT before transplantation and at day 7 after transplantation. Increases in TNFR1 levels more than or equal to 2.5 baseline correlated with eventual development of GVHD grade 2 to 4 (58% vs 32%, P < .001) and with treatment-related mortality (39% vs 17%, P < .001). In a multivariate analysis including age, degree of HLA match, donor type, recipient and donor sex, disease, and status at HCT, the increase in TNFR1 level at day 7 remained a significant predictor for outcome. Measurement of TNFR1 levels early after transplantation provides independent information in advance of important clinical outcomes, such as GVHD and death.

Turmeric-based diet can delay apoptosis without modulating NF-kappaB in unilateral ureteral obstruction in rats

The unilateral ureteral obstruction (UUO) model of renal injury in rat is characterized by nuclear factor kappaB (NF-kappaB) activation and tumour necrosis factor alpha (TNF-alpha) production, which induces apoptosis via activation of caspase 8 resulting in cell death. Curcumin, the major component found in turmeric spice, has been reported to provide protection against fibrosis and apoptosis elicited by UUO. This study examined the effects of a turmeric-based diet (5% w/w) on the apoptotic pathway induced by UUO in rats after 30 days of ligation. Administration of a turmeric-based diet demonstrated a significant decrease (P<0.05) in mRNA expression of TNF-alpha and caspase 8, but not NF-kappaB, expression, which may contribute to the protective role of the turmeric-based diet. We conclude that a turmeric-based diet can delay apoptosis without modulating NF-kappaB, so as not to sensitize the mesangial cells to the apoptotic stimuli.

Tumor necrosis factor-alpha-induced sickness behavior is impaired by central administration of an inhibitor of c-jun N-terminal kinase

RATIONALE

Tumor necrosis factor-alpha (TNFalpha) acts within the brain to induce sickness behavior, but the molecular mechanisms are still unknown. TNFalpha binding induces receptor trimerization, activation of c-Jun N-terminal kinase (JNK), and induction of downstream transcription factors.

OBJECTIVES

We hypothesized that TNFalpha-induced sickness behavior can be blocked by a novel JNK inhibitor.

METHODS

To test this idea, we used a bipartite protein consisting of a ten-amino-acid sequence of the trans-activating domain of the viral TAT protein (D-TAT) linked to a 19-amino-acid peptide that specifically inhibits JNK activation (D-JNKI-1). C57BL/6J mice were pre-treated intracerebroventricularly (i.c.v.) with D-JNKI-1 or the control peptide containing only the protein transduction domain, D-TAT. Mice were then injected centrally with an optimal amount of TNFalpha (50 ng/mouse) to induce sickness behavior. Sickness was assessed as a decrease in social exploration of a novel juvenile, an increase in duration of immobility and loss of body weight.

RESULTS

Pre-treatment with D-JNKI-1 (10 ng/mouse), but not D-TAT, significantly inhibited all three indices of sickness induced by central TNFalpha.

CONCLUSIONS

These findings demonstrate that D-JNKI-1 can abrogate TNFalpha-induced sickness behavior and suggest a potential therapeutic target for treating major depressive disorders that develop on a background of cytokine-induced sickness behavior.

Genes and structure of selected cytokines involved in pathogenesis of psoriasis

Psoriasis is a common skin disease involving 1-4% of human population worldwide, of strong genetic background. The following cytokines are directly involved in psoriasis: TNF, IL-1, IL-2, IL-6, IL-7, IL-8, IL-15, IL-18, IL-19, IL-20, IL-23 whereas IL-4, IL-10, IL-12 as well as IL-11, IL-17 and IFN-gamma are rather indirectly engaged. This work is a review of some genetic factors and structure of selected cytokines and receptors and their genes location.

Epigallocatechin-3-O-gallate inhibits TNFalpha-induced monocyte chemotactic protein-1 production from vascular endothelial cells

Monocyte chemotactic protein-1 (MCP-1) plays a pivotal role in the recruitment of monocytes and thus in the development of inflammatory cardiovascular diseases. Epigallocatechin-3-O-gallate (EGCG), the major catechin derived from green tea, has multiple beneficial effects to reduce cardiovascular disease but the effects of EGCG on vascular endothelial MCP-1 production is not known. In this study, we investigated the mechanisms by which EGCG may inhibit tumor necrosis factor-alpha (TNFalpha)-induced MCP-1 production in bovine coronary artery endothelial cells. TNFalpha increased MCP-1 production in both a concentration and time-dependent manner. Inhibitors of phosphatidylinositol-3-OH kinase (PI-3 kinase), LY294002 and wortmannin, decreased TNFalpha-induced MCP-1 production. EGCG prevented TNFalpha-mediated MCP-1 production and reduced phosphorylation of Akt (Ser473). In addition, EGCG attenuated TNFalpha mediated down-regulation of TNFalpha receptor 1 (TNFR1), but not TNFR2. In conclusion, EGCG inhibited TNFalpha-induced MCP-1 production. Moreover, EGCG inhibited Akt phosphorylation as well as TNF activation of TNFR1, which subsequently resulted in reduced MCP-1 production. These data provide a novel mechanism where the green tea flavonoid, EGCG, could provide direct vascular benefits in inflammatory cardiovascular diseases.

EAPF/Phafin-2, a novel endoplasmic reticulum-associated protein, facilitates TNF-alpha-triggered cellular apoptosis through endoplasmic reticulum-mitochondrial apoptotic pathway

We recently identified the Phafin protein family, whose members all contain an N-terminal PH domain (pleckstrin homology) and a C-terminal FYVE (Fab1, YGLO23, Vps27, and EEA1) domain. LAPF (lysosome-associated apoptosis-inducing protein containing PH and FYVE domains, also known as Phafin-1), as one representative member of this new family, has been shown to be able to initiate caspase-independent apoptosis through lysosomal-mitochondrial apoptotic pathway. Here, we describe the cloning and functional characterization of another Phafin member, EAPF (endoplasmic reticulum-associated apoptosis-involved protein containing PH and FYVE domains)/Phafin-2. Overexpression of EAPF/Phafin-2 enhances the sensitivity of L929 and MCF-7 cells to TNF-alpha-induced apoptosis, concomitant with its partial translocation to endoplasmic reticulum (ER). Both the PH and the FYVE domains contribute to the ER translocation of EAPF/Phafin-2 as well as EAPF/Phafin-2-enhanced apoptosis. Knockdown of mouse and human EAPF/Phafin-2 expression protects L929 cells and MCF-7 cells from TNF-alpha-induced apoptosis, respectively. We demonstrate that EAPF/Phafin-2 induces a much sharper and more rapid Ca2+ influx triggered by TNF-alpha and Ca2+ release ER contributes to the enhancement of EAPF/Phafin-2 in TNF-induced apoptosis. EAPF/Phafin-2 increases the activity of caspase 12, suggesting that EAPF/Phafin-2 is involved in ER-related apoptotic pathway. Overexpression of EAPF/Phafin-2 also enhances TNF-alpha-induced activity of caspase 3 (but not caspase 8 or 9), and promotes TNF-alpha-triggered mitochondrial membrane permeabilization (MMP) in L929 cells, including dissipation of mitochondrial membrane potential and release of AIF. Besides, EAPF/Phafin-2 also suppresses the unfolded protein response by inhibiting phosphorylation of eIF2alpha. Therefore, our results demonstrate that EAPF/Phafin-2 facilitates TNF-alpha-induced cellular apoptosis through an ER-mitochondrial apoptotic pathway, which may improve our understanding of drug-induced cancer cell death and cancer chemotherapy.

Effects of three anti-TNF-alpha drugs: etanercept, infliximab and pirfenidone on release of TNF-alpha in medium and TNF-alpha associated with the cell in vitro

Tumor necrosis factor-alpha (TNF-alpha) is a vital component of the inflammatory process and its aberrant over-expression has been linked to numerous disease states. New treatment strategies have sought to reduce circulating TNF-alpha, either with neutralizing anti-TNF-alpha binding proteins such as etanercept or via drugs that inhibit de novo TNF-alpha synthesis like pirfenidone. In the present study, we examined the effects of both classes of drugs on secreted and cell-associated TNF-alpha produced by THP-1 cells. All of the tested drugs significantly reduced secreted levels of bioactive TNF-alpha following stimulation with LPS as measured by bioassay. However, etanercept-treated cells had approximately six-fold higher levels of cell-associated TNF-alpha compared with that of the LPS-alone treatment group. Surprisingly, LPS+infliximab treated cells did not increase cell-associated TNF-alpha relative to the LPS-alone treatment. Pirfenidone significantly reduced both secreted and cell-associated TNF-alpha levels. These drug-related differences in cell-associated TNF-alpha may have broad implications in the future for the therapeutic uses of anti-TNF-alpha drugs in the management of TNF-alpha diseases.

Peripheral blood and bone marrow TNF and TNF receptors in early and advanced stages of B-CLL in correlation with ZAP-70 protein and CD38 antigen

The aim of the study was to evaluate TNF and TNF receptor levels in peripheral blood (PB) and bone marrow (BM) in correlation with clinical and laboratory parameters of B-CLL patients. TNF concentration was significantly higher in BM than in PB. In B-CLL patients elevated TNF and sTNF-RII plasma levels had a high correlation with adverse prognostic factors such as ZAP-70 and CD38. Moreover, the percentage of TNF-producing T cells was significantly higher in ZAP-70-positive comparing to ZAP-70-negative patients. TNF and sTNF-RII plasma levels were higher in the group of patients requiring treatment comparing to the patients who did not.

The role of TNF-alpha in Trichuris muris infection I: influence of TNF-alpha receptor usage, gender and IL-13

Th1 and Th2 responses to the gut-dwelling nematode Trichuris muris have been well established in mouse models of infection, with Th2 responses clearly playing an important role in resistance. TNF-alpha has previously been shown to play an undefined role in resistance, although it is not a typical Th2 cytokine. However, the relative importance of the two TNF-alpha receptors, p55 and p75, has not previously been investigated. We demonstrate that p55 is the dominant TNF-alpha receptor during T. muris infection as p55-/- mice are more susceptible to infection than p75-/- mice. Moreover, p75 clearly plays a role in negatively regulating TNF-alpha. We also demonstrate that a gender difference influences the immune response of p55-/- and p75-/- mice in response to T. muris infection, with female mice fully expelling by day 35 post-infection (p.i.) and male mice harbouring chronic infections. Further, this gender difference can be reversed with recombinant IL-13 (rIL-13) in male gene-deficient mice or IL-13R2.Fc treatment in female gene-deficient mice.

Dopamine induces TNFalpha and TNF-R1 expression in SH-SY5Y human neuroblastoma cells

Cytotoxic concentrations of dopamine (100-500 microM DA) induce expression of tumour necrosis factor receptor-1 (TNF-R1) and tumour necrosis factor-alpha (TNFalpha) in SH-SY5Y human neuroblastoma cells. TNFalpha expression is dose-dependent and can also be detected after 6-hydroxydopamine (6-OHDA) or 1-methyl-4-phenylpyridinium iodide (MPP) treatment. The expression of TNF-R1 is also dose-dependent, but was not observed in 6-OHDA or MPP-treatment. Cells not expressing TNF-R1 were insensitive to TNFalpha, whereas those treated with DA showed a further decrease in viability when subsequently treated with TNFalpha. Thus, DA treatment confers sensitivity to TNFalpha. The decrease of cell viability caused by DA was in part prevented by neutralizing TNFalpha with anti-TNFalpha. As TNF-R1 is increased in substantia nigra of Parkinsonian brains, we suggest that nonvesiculated DA might also play a role in inducing TNF-R1 expression and predispose the neuron to the action of cytokines released in a microglia-mediated inflammatory response.

SCHOOL model and new targeting strategies

Protein-protein interactions play a central role in biological processes and thus are an appealing target for innovative drug design a nd development. They can be targeted bysmall molecule inhibitors, peptides and peptidomimetics, which represent an alternative to protein therapeutics that carry many disadvantages. In this chapter, I describe specific protein-protein interactions suggested by a novel model of immune signaling, the Signaling Chain HOmoOLigomerization (SCHOOL) model, to be critical for cell activation mediated by multichain immune recognition receptors (MIRRs) expressed on different cells of the hematopoietic system. Unraveling a long-standing mystery of MIRR triggering and transmembrane signaling, the SCHOOL model reveals the intrareceptor transmembrane interactions and interreceptor cytoplasmic homointeractions as universal therapeutic targets for a diverse variety of disorders mediated by immune cells. Further, assuming that the general principles underlying MIRR-mediated transmembrane signaling mechanisms are similar, the SCHOOL model can be applied to any particular receptor of the MIRR family. Thus, an important application of the SCHOOL model is that global therapeutic strategies targeting key protein-protein interactions involved in MIRR triggering and transmembrane signal transduction may be used to treat a diverse set of immune-mediated diseases. This assumes that clinical knowledge and therapeutic strategies can be transferred between seemingly disparate disorders, such as T-cell-mediated skin diseases and platelet disorders, or combined to develop novel pharmacological approaches. Intriguingly, the SCHOOL model unravels the molecular mechanisms underlying ability of different human viruses such as human immunodeficiency virus, cytomegalovirus and severe acute respiratory syndrome coronavirus to modulate and/or escape the host immune response. It also demonstrates how the lessons learned from viral pathogenesis can be used practically for rational drug design. Application of this model to platelet collagen receptor signaling has already led to the development of a novel concept of platelet inhibition and the invention of new platelet inhibitors, thus proving the suggested hypothesis and highlighting the importance and broad perspectives of the SCHOOL model in the development of new targeting strategies.

Importance of pericytes and mechanisms of pericyte loss during diabetes retinopathy

Pericytes are distinctive regulators of angiogenesis and are adumbrated to provide vessel stability and control of endothelial proliferation. The present article spotlights the persona of pericytes in physiological angiogenesis, recruitment of pericytes and different mechanisms of pericyte depletion. Developing retina appears particularly dependent on pericytes, and pericyte loss is considered as hallmark of early diabetic retinopathies. Several factors are contemplated to be engaged in pericyte conscription including angiopoietin-1 and its receptor tyrosine kinase Tie-2, vascular endothelial growth factor-A and its receptor flk-1 and the platelet-derived growth factor PDGF-B/PDGF-beta system. At present, the mechanisms by which diabetes persuade apoptosis in the retinal microvasculature remain indecisive, albeit oxidative stress, formation of advanced glycation end products , upregulation of protein kinase C, increased polyol pathway flux and focal leukostasis may be important. In this context, accelerated microvascular cell death may become a constructive surrogate end-point in pharmacological studies of experimental diabetic.

Tumor necrosis factor-alpha from macrophages enhances LPS-induced clara cell expression of keratinocyte-derived chemokine

Tumor necrosis factor (TNF)-alpha is a cytokine produced by alveolar macrophages in response to LPS in the lung. Clara cells are bronchiolar epithelial cells that produce a variety of proinflammatory cytokines in response to LPS but not to TNF-alpha. In this study, we examined whether TNF-alpha affects Clara cell cytokine production in the setting of LPS stimulation. Using a transformed murine Clara cell line (C22), we observed that both LPS and TNF-alpha induced production of keratinocyte-derived chemokine (KC) and monocyte chemoattractant protein (MCP)-1. We also found that simultaneous LPS and TNF-alpha stimulation is synergistic for KC production, but additive for MCP-1 production. By using a Transwell coculture system of RAW264.7 macrophages and Clara cells isolated from C57Bl/6 mice, we found that macrophages produce a soluble factor that enhances Clara cell KC production in response to LPS. Cocultures of Clara cells from mice deficient in TNF-alpha receptors with RAW264.7 macrophages demonstrated that the effect of macrophages on Clara cells is mediated primarily via TNF-alpha. To determine whether these findings occur in vivo, we treated wild-type and TNF receptor-deficient mice intratracheally with LPS and examined the expression of KC. LPS-treated, TNF receptor-deficient mice showed much less KC mRNA in airway epithelial cells compared with wild-type mice. In contrast, a similar number of KC-expressing cells was seen in the lung periphery. Thus, upregulation of KC by Clara cells in the setting of LPS stimulation is largely dependent on TNF-alpha originating from alveolar macrophages. These findings shed light on macrophage-Clara cell interactions in regulating the pulmonary inflammatory response to LPS.

Elevated NF-kappaB responses and FLIP levels in leukemic but not normal lymphocytes: reduction by salicylate allows TNF-induced apoptosis

As its name suggests, tumor necrosis factor (TNF) is known to induce cytotoxicity in a wide variety of tumor cells and cell lines. However, its use as a chemotherapeutic drug has been limited by its deleterious side effects of systemic shock and widespread inflammatory responses. Some nonsteroidal antiinflammatory drugs, such as sodium salicylate, have been shown to have a chemopreventive role in certain forms of cancer. Here, we reveal that sodium salicylate selectively enhances the apoptotic effects of TNF in human erythroleukemia cells but does not affect primary human lymphocytes or monocytes. Sodium salicylate did not affect the intracellular distribution of TNF receptors (TNFRs) but stimulated cell surface TNFR2 shedding. Erythroleukemia cells were shown to possess markedly greater basal NF-kappaB responses and elevated Fas-associated protein with death domain-like IL-1 converting enzyme (FLIP) levels. Sodium salicylate achieved its effects by reducing the elevated NF-kappaB responsiveness and FLIP levels and restoring the apoptotic response of TNF rather than the proliferative/proinflammatory effects of the cytokine in these cancer cells. Inhibition of NF-kappaB or FLIP levels in human erythroleukemia cells by pharmacological or molecular-biological means also resulted in switching the character of these cells from a TNF-responsive proliferative phenotype into an apoptotic one. These findings expose that the enhanced proliferative nature of human leukemia cells is caused by elevated NF-kappaB and FLIP responses and basal levels, reversible by sodium salicylate to allow greater apoptotic responsiveness of cytotoxic stimuli such as TNF. Such findings provide insight into the molecular mechanisms by which human leukemia cells can switch from a proliferative into an apoptotic phenotype.

PtdIns(4,5)P-restricted plasma membrane localization of FAN is involved in TNF-induced actin reorganization

The WD-repeat protein factor associated with nSMase activity (FAN) is a member of the family of TNF receptor adaptor proteins that are coupled to specific signaling cascades. However, the precise functional involvement of FAN in specific cellular TNF responses remain unclear. Here, we report the involvement of FAN in TNF-induced actin reorganization and filopodia formation mediated by activation of Cdc42. The pleckstrin-homology (PH) domain of FAN specifically binds to phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P), which targets FAN to the plasma membrane. Site-specific mutagenesis revealed that the ability of FAN to mediate filopodia formation was blunted either by the destruction of the PtdIns(4,5)P binding motif, or by the disruption of intramolecular interactions between the PH domain and the adjacent beige and Chediak-Higashi (BEACH) domain. Furthermore, FAN was shown to interact with the actin cytoskeleton in TNF-stimulated cells via direct filamentous actin (F-actin) binding. The results of this study suggest that PH-mediated plasma membrane targeting of FAN is critically involved in TNF-induced Cdc42 activation and cytoskeleton reorganization.

Differential expression and role of p21cip/waf1 and p27kip1 in TNF-alpha-induced inhibition of proliferation in human glioma cells

Background

The role of TNF-α in affecting the fate of tumors is controversial, while some studies have reported apoptotic or necrotic effects of TNF-α, others provide evidence that endogenous TNF-α promotes growth and development of tumors. Understanding the mechanism(s) of TNF-α mediated growth arrest will be important in unraveling the contribution of tissue associated macrophages in tumor resistance. The aim of this study was to investigate the role of Cyclin Dependent Kinase Inhibitors (CDKI) – p21^cip/waf1 and p27^kip1 in TNF-α mediated responses in context with p53 and activation of NF-κB and Akt pathways. The study was done with human glioma cell lines -LN-18 and LN-229 cells, using monolayer cultures and Multicellular Spheroids (MCS) as in vitro models.

Results

TNF-α induced inhibition of proliferation and enhanced the expression of p21^cip/waf1 and p27^kip1 in LN-18 cells. p21 was induced on exposure to TNF-α, localized exclusively in the nucleus and functioned as an inhibitor of cell cycle but not as an antiapoptotic protein. In contrast, p27 was constitutively expressed, localized predominantly in the cytoplasm and was not involved in arrest of proliferation. Our data using IκBα mutant LN-18 cells and PI3K/Akt inhibitor-LY294002 revealed that the expression of p21 is regulated by NF-κB. Loss of IκBα function in LN-229 cells (p53 positive) did not influence TNF-α induced accumulation of pp53 (Ser-20 p53) suggesting that p53 was not down stream of NF-κB. Spheroidogenesis enhanced p27 expression and p21 induced by TNF-α was significantly increased in the MCS compared to monolayers.

Conclusion

This study demarcates the functional roles for CDKIs-p21^cip/waf1 and p27^kip1 during TNF-α stimulated responses in LN-18 glioma cells. Our findings provide evidence that TNF-α-induced p21 might be regulated by NF-κB or p53 independently. p21 functions as an inhibitor of cell proliferation and does not have a direct role in rendering the cells resistant to TNF-α mediated cytotoxicity.

RANKL-stimulated TNFα production in osteoclast precursor cells promotes osteoclastogenesis by modulating RANK signaling pathways

Although TNFalpha is known to be an important factor for bone resorption, particularly in inflammatory bone diseases, the relevance between RANKL and TNFalpha in osteoclastogenesis remains unclear. In this study we examined the mechanism of TNFalpha induced osteoclastogenesis and its downstream signaling. We show that osteoclastogenesis is suppressed by anti-TNFalpha- and anti-TNF receptor type I (TNFRI)-antibodies and in TNFalpha- and TNFRI-deficient mice using in vitro culture systems: (1) co-culture of mouse spleen derived osteoclast precursor cells (pOCs) with osteoblasts, (2) pure pOC culture and (3) RAW264.7 cells in presence of RANKL. Furthermore, TNFalpha production in pOCs was stimulated by RANKL. Endogenous TNFalpha in pOCs induced c-Fos and NFATc1. Expression rates of NFATc1 and c-Fos were significantly decreased in TNFalpha- and TNFRI-deficient pOCs during osteoclastogenesis. These results indicate that TNFalpha is induced by RANKL in pOCs and serves as an autocrine factor promoting osteoclastogenesis through c-Fos and NFATc1 activation.

TNFalpha-induced sickness behavior in mice with functional 55 kD TNF receptors is blocked by central IGF-I

A variety of pathogenic insults cause synthesis of tumor necrosis factor (TNF)alpha in the brain, resulting in sickness behavior. Here we used TNF-receptor (TNF-R)2-deficient and wild-type mice to demonstrate that the reduction in social exploration of a novel juvenile, the increase in immobility and the loss of body weight caused by central TNFalpha (i.c.v., 50 ng/mouse) are blocked by central pre-treatment with the multifunctional peptide, insulin-like growth factor (IGF-I; i.c.v., 300 ng/mouse). These results establish that sickness behavior induced by central TNFalpha via the TNF-R1 (p55) is directly opposed by IGF-I in the brain.

Aloe emodin inhibits the cytotoxic action of tumor necrosis factor

We demonstrate the capacity of an herbal anthraquinone aloe emodin to reduce the cytotoxicity of the proinflammatory cytokine tumor necrosis factor (TNF) towards L929 mouse fibrosarcoma and U251 human glioma cell lines. Aloe emodin inhibited both TNF-induced cell necrosis and apoptosis, but it did not reduce cell death induced by UV radiation or hydrogen peroxide. Aloe emodin inhibited both basal and TNF-triggered activation of extracellular signal-regulated kinase (ERK), and a selective blockade of ERK activation mimicked the cytoprotective action of the drug. On the other hand, aloe emodin did not affect TNF-induced activation of p38 mitogen-activated protein kinase or generation of reactive oxygen species. The combination of aloe emodin and TNF caused an intracellular appearance of acidified autophagic vesicles, and the inhibition of autophagy with bafilomycin or 3-methyladenine efficiently blocked the cytoprotective action of aloe emodin. These data indicate that aloe emodin could prevent TNF-triggered cell death through mechanisms involving induction of autophagy and blockade of ERK activation.