Involvement of the membrane form of tumour necrosis factor-alpha in lipopolysaccharide-induced priming of mouse peritoneal macrophages for enhanced nitric oxide response to lipopolysaccharide

MicroRNA in TLR signaling and endotoxin tolerance

Toll-like receptors (TLRs) in innate immune cells are the prime cellular sensors for microbial components. TLR activation leads to the production of proinflammatory mediators and thus TLR signaling must be properly regulated by various mechanisms to maintain homeostasis. TLR4-ligand lipopolysaccharide (LPS)-induced tolerance or cross-tolerance is one such mechanism, and it plays an important role in innate immunity. Tolerance is established and sustained by the activity of the microRNA miR-146a, which is known to target key elements of the myeloid differentiation factor 88 (MyD88) signaling pathway, including IL-1 receptor-associated kinase (IRAK1), IRAK2 and tumor-necrosis factor (TNF) receptor-associated factor 6 (TRAF6). In this review, we comprehensively examine the TLR signaling involved in innate immunity, with special focus on LPS-induced tolerance. The function of TLR ligand-induced microRNAs, including miR-146a, miR-155 and miR-132, in regulating inflammatory mediators, and their impact on the immune system and human diseases, are discussed. Modulation of these microRNAs may affect TLR pathway activation and help to develop therapeutics against inflammatory diseases.

TNFR1 upregulation mediates tolerance after brain ischemic preconditioning

A short ischemic event (ischemic preconditioning (IPC)) can result in subsequent resistance to severe ischemic injury (ischemic tolerance (IT)). The expression and neuroprotective role of tumor necrosis factor (TNF-alpha) have been described in models of IPC and we have showed the participation of its processing enzyme, the TNF-alpha convertase enzyme (TACE) in this process. We have now decided to explore the expression and localization of TNF receptors (TNFR) as well as other signalling mechanisms involved in IT. A period of 10 mins of temporary middle cerebral artery occlusion (tMCAO) was used for focal IPC. To evaluate the ability of IPC to produce IT, permanent MCAO was performed 48 hours after IPC. Ischemic preconditioning produced a reduction in infarct volume, as we showed previously. Ischemic preconditioning caused upregulation of neuronal TNFR1 that was reduced by the selective TACE inhibitor BB1101. Intracerebral administration of TNFR1 antisense oligodeoxynucleotide, which caused a reduction in TNFR1 expression, inhibited the IPC-induced protective effect, showing that TNFR1 upregulation is implicated in IT. Moreover, treatment with BB1101, TNFR1 antisense and lactacystin-a specific proteasome inhibitor-blocked IPC-induced NF-kappaB. Immunohistochemical studies showed the expression of TACE and TNFR1 in neurons. In summary, these data show that IPC produces neuronal upregulation of TACE and TNFR1, and that the pathway TACE/TNF-alpha/TNFR1/NF-kappaB is involved in IT.

Thymocyte depletion during acuteTrypanosoma cruziinfection in C57BL/6 mice is partly reverted by lipopolysaccharide pretreatment

Infection with Trypanosoma cruzi in C57BL/6 mice leads to a progressive fatal disease accompanied by thymocyte depletion, which is not related with a higher parasite burden but with increased serum levels of tumour necrosis factor alpha (TNF- alpha). Because this situation may result from an excessive inflammatory syndrome, mice were now given anti-TNF-alpha mAbs throughout their acute infection, or subjected to a LPS desensitization protocol before parasite challenge. Treatment with anti-TNF-alpha mAbs failed to ameliorate thymocyte depletion but shortened survival time and increased parasite load. Pretreatment with LPS (desensitization followed by a sublethal LPS dose) prolonged survival time with a trend to reduce parasitemias and TNF-alpha serum concentrations. Given that pentoxifylline (PTx) interferes with in vitro LPS tolerance, experiments by administering PTx in combination with the tolerance-inducing LPS doses were also performed. Such schedule significantly reduced mortality, TNF-alpha and IL-6 serum concentrations, and CD4+ CD8+ thymocyte loss. LPS pretreatment allowed a better infection control and protected from the accompanying tissue damage.

In vitro ischemic tolerance involves upregulation of glutamate transport partly mediated by the TACE/ADAM17-tumor necrosis factor-alpha pathway

A short ischemic event [ischemic preconditioning (IPC)] can result in a subsequent resistance to severe ischemic injury (ischemic tolerance). Although tumor necrosis factor-alpha (TNF-alpha) contributes to the brain damage found after cerebral ischemia, its expression and neuroprotective role in models of IPC have also been described. Regarding the role of TNF-alpha convertase (TACE/ADAM17), we have recently shown its upregulation in rat brain after IPC induced by transient middle cerebral artery occlusion and that subsequent TNF-alpha release accounts for at least part of the neuroprotection found in this model. We have now used an in vitro model of IPC using rat cortical cultures exposed to sublethal oxygen-glucose deprivation (OGD) to investigate TACE expression and activity after IPC and the subsequent mechanisms of ischemic tolerance. OGD-induced cell death was significantly reduced in cells exposed to IPC by sublethal OGD 24 hr before, an effect that was inhibited by the TACE inhibitor BB3103 (1 microm) and anti-TNF-alpha antibody (2 microg/ml) and that was mimicked by TNF-alpha (10 pg/ml) preincubation. Western blot analysis showed that TACE expression is increased after IPC. IPC caused TNF-alpha release, an effect that was blocked by the selective TACE inhibitor BB-3103. In addition, IPC diminished the increase in extracellular glutamate caused by OGD and increased cellular glutamate uptake and expression of EAAT2 and EAAT3 glutamate transporters; however, only EAAT3 upregulation was mediated by increased TNF-alpha. These data demonstrate that neuroprotection induced by IPC involves upregulation of glutamate uptake partly mediated by TACE overexpression.

TACE/ADAM17-TNF-alpha pathway in rat cortical cultures after exposure to oxygen-glucose deprivation or glutamate

The role of the tumor necrosis factor (TNF)-alpha convertase (TACE/ADAM17) in the adult nervous system remains poorly understood. The authors have previously demonstrated that TACE is upregulated in rat forebrain slices exposed to oxygen-glucose deprivation (OGD). They have now used rat mixed cortical cultures exposed to OGD or glutamate to study (1) TACE expression and localization, and (2) the effects of TNF-alpha release on cell viability. OGD-or glutamate-caused TNF-alpha release, an effect that was blocked by the TACE inhibitor BB3103 (BB) (0.1-1 micromol/L; control: 1.67 +/- 0.59; OGD: 6.59 +/- 1.52; glutamate: 3.38 +/- 0.66; OGD +/- BB0.1: 3.23 +/- 0.67; OGD +/- BB1: 1.33 +/- 0.22 pg/mL, n = 6, P < 0.05). Assay of TACE activity as well as Western blot showed that TACE expression is increased in OGD-or glutamate-exposed cells. In control cultures, TACE immunoreactivity was present in some microglial cells, whereas, after OGD or glutamate, TACE immunostaining appeared in most microglial cells and in some astrocytes. Conversely, BB3103 (0.1 micromol/L) caused apoptosis after glutamate exposure as shown by annexin and Hoechst 33342 staining and caspase-3 activity, an effect mimicked by the proteasome inhibitor MG-132 (caspase activity: glutamate: 5.1 +/- 0.1; glutamate + BB: 7.8 +/- 0.8; glutamate + MG: 11.9 +/- 0.5 pmol. min(-1) mg(-1) protein, n = 4, P < 0.05), suggesting that translocation of the transcription factor NF-kappaB mediates TNF-alpha-induced antiapoptotic effect. Taken together, these data demonstrate that, in rat mixed neuronal-glial cortical cultures exposed to OGD or glutamate, (1) TACE/ADAM17 activity accounts for the majority of TNF-alpha shedding, (2) an increase in glial TACE expression contributes to the rise in TNF-alpha, and (3) TNF-alpha release in this setting inhibits apoptosis via activation of the transcription factor NF-kappaB.

Priming and activation of mouse macrophages by trehalose 6,6'-dicorynomycolate vesicles from Corynebacterium glutamicum

Vesicles consisting of pure trehalose dicorynomycolate (TDCM), the corynebacterial analog of the most studied mycobacterial glycolipid 'cord factor', were isolated from Corynebacterium glutamicum cells by mild detergent treatment; these induced in vivo a macrophage priming similar to that obtained with mycobacterial-derived trehalose dimycolate. In vitro, both TDCM and bacterial lipopolysaccharide (LPS) induced in macrophages the production of nitric oxide (NO) and tumor necrosis factor-alpha (TNF-alpha), endotoxin tolerance, and were primed for an enhanced secondary NO response to LPS. Interferon-gamma pretreatment did not influence the LPS-induced TNF-alpha response, but considerably increased the TDCM-induced response.

TGFbeta1 stimulates the secretion of matrix metalloproteinase 2 (MMP2) and the invasive behavior in human ovarian cancer cells, which is suppressed by MMP inhibitor BB3103

The present study investigated the modulatory role of transforming growth factor beta 1 (TGFbeta1) on the secretion of matrix metalloproteinases (MMPs) and tested whether the altered secretion of MMPs could directly affect the invasive behavior of ovarian cancer cells. To this aim, human ovarian cancer SKOV3 cells were treated once with vehicle or various concentrations of TGFbeta1 for 24 h. Gelatinase activities in conditioned media were analyzed by zymography and densitometry. TGFbeta1 dose-dependently stimulated the secretion of a 68-kDa gelatinase, which was characterized as an MMP because its activity was inhibited by a metalloproteinase inhibitor 1,10-phenanthroline, and by a synthetic MMP inhibitor BB3103. In addition, we used aminophenylmercuric acetate (APMA) to activate latent gelatinases. APMA time-dependently decreased the activity of 68-kDa gelatinase, and increased the activities of 64- and 62-kDa gelatinolytic bands. The 68-kDa gelatinase was further characterized as MMP2 (gelatinase A) by immunoblotting analysis. We then tested TGFbeta1 effect on the invasive potential of SKOV3 cells as assessed by the migration ability through reconstituted basement membrane, and further investigated whether TGFbeta1 may act through modulating the MMP activity to affect ovarian cancer cell invasion. The results show that TGFbeta1 stimulated the invasive behavior of SKOV3 cells, and that MMP inhibitor BB3103 abrogated this effect of TGFbeta1. In conclusion, this study indicates that TGFbeta1 may act partly through stimulating the secretion of MMP in promoting the invasive behavior of human ovarian cancer cells. Furthermore, this work supports the idea that specific MMP inhibitors of the hydroxamate class could be therapeutically useful in controlling cancer cell invasion/metastasis.

Combination therapy including pentoxifylline for entero-Behçet's disease

Behçet's disease is a chronic relapsing vasculitis characterized by recurrent aphthous oral and genital ulcerations with uveitis. Multiple organs can be involved. Entero-Behçet's disease is often uncontrollable, relapsing, and can cause acute intestinal bleeding or perforation. We utilized a combination therapy including 600 mg of pentoxifylline per day, in two doses, to treat three female patients and observed the subsequent changes in clinical symptoms, serum C reactive protein levels, and endoscopic findings. In all three patients, clinical symptoms as well as serum C reactive protein levels improved immediately. Endoscopically, lower intestinal lesions were significantly reduced or healed in all of them. Combination therapy including pentoxifylline appears to be clinically effective in the patients with entero-Behçet's disease.

Up-regulation of TNF-alpha convertase (TACE/ADAM17) after oxygen-glucose deprivation in rat forebrain slices

Tumour necrosis factor-alpha (TNF-alpha) is a major immunomodulatory and proinflammatory cytokine which is shed in its soluble form by a membrane-anchored zinc protease, identified as a disintegrin and metalloproteinase (ADAM) called TNF-alpha convertase (TACE; ADAM17). The role of this protease in the adult nervous system remains poorly understood. During cerebral ischemia and subsequent reperfusion, expression and release of TNF-alpha have been shown. We have investigated the expression and activity of TACE in an in vitro model of brain ischemia consisting of rat forebrain slices exposed to oxygen-glucose deprivation (OGD). OGD caused the release of TNF-alpha, an effect which was inhibited by a hydroxamate-based metalloprotease inhibitor, BB-3103, with an IC(50) of 0.1 microM, suggesting that TNF-alpha release results selectively from TACE activity. Assay of TACE enzymatic activity on a fluorescein-labelled peptide spanning the cleavage site in pro-TNF-alpha, as well as Western blot and RT-PCR analyses showed that TACE is present in control forebrain and, more interestingly, that TACE expression is increased in OGD-exposed tissue. TACE enzymatic activity from OGD-exposed slices was significantly inhibited by cycloheximide, suggesting that de novo synthesis of TACE contributes to TNF-alpha release after ischaemia. Moreover, it was also inhibited by bisindolylmaleimide I, indicating that TACE activity is regulated by PKC. These findings posed the question of what was its function therein. Among other actions, TNF-alpha has been described to be involved in the expression of inducible nitric oxide synthase (iNOS), a high-output NOS isoform associated to cellular damage, but the link between TNF-alpha release after brain ischaemia and iNOS expression in this condition has not been shown. We have now found that iNOS expression in OGD-subjected brain slices is inhibited by BB-3103 at concentrations below 1 microM, indicating that shedding of TNF-alpha by TACE plays a necessary part in the induction of this NOS isoenzyme after OGD. Taken together, these data demonstrate that (1) TACE/ADAM17 activity accounts for the majority of TNF-alpha shedding after OGD in rat forebrain slices, (2) an increase in TACE expression contributes, at least in part, to the rise in TNF-alpha after OGD and (3) iNOS expression in OGD-subjected brain slices results from TACE activity and subsequent increase in TNF-alpha levels.

Endocytosis of uncleaved tumor necrosis factor-alpha in macrophages

Activated monocytes and macrophages secrete the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). TNF-alpha is produced as a 26 kd transmembrane protein that is cleaved to release a 17 kd soluble protein. TNF-alpha in both forms is biologically active. The intracellular trafficking of membrane-associated TNF-alpha in lipopolysaccharide-activated mouse macrophages was assessed after treatment with the metalloprotease inhibitor BB-3103, which prevents the cleavage of pro-TNF-alpha. Immunoprecipitation and immunofluorescence studies showed sustained expression of cell-associated TNF-alpha in the presence of the inhibitor. Cell immunoreactivity and surface biotinylation revealed that uncleaved TNF-alpha accumulated on the cell surface and was endocytosed, appearing in intracellular vesicles. Perturbation of post-Golgi traffic blocked the surface expression of 26 kd TNF-alpha. Tracking a bolus of TNF-alpha over time in cycloheximide-treated cells confirmed that uncleaved TNF-alpha is first transported to the cell surface and subsequently endocytosed. Vesicular structures immunoreactive for TNF-alpha were identified as endosomes by double labeling. The secretory and membrane-associated endocytic trafficking of TNF-alpha provides a mechanism for modulating the quantity of biologically active 26 kd TNF-alpha expressed on macrophages, allowing regulation of paracrine and autocrine responses.

Differential regulation of protein tyrosine kinase on free radical production, granule enzyme release, and cytokine synthesis by activated murine peritoneal macrophages

The present study examined the regulatory effect of tyrosine kinase inhibitors (genistein, tyrphostin, and 2,5-dihydroxycinnamate) on the free radical production, granule enzyme release, and synthesis of interleukin (IL)-8 and granulocyte macrophage-colony stimulating factor (GM-CSF) in murine peritoneal macrophages exposed to different stimulators [10 ng/mL of IL-1, 1 microgram/mL of lipopolysaccharide (LPS), and 1 microM N-formyl-methionyl-leucyl-phenylalanine (fMLP)]. Protein tyrosine kinase (PTK) inhibitors attenuated the stimulated superoxide, hydrogen peroxide, and nitric oxide production in macrophages stimulated with IL-1, LPS, or fMLP. N,N-Dimethylsphingosine (DMS) alone stimulated superoxide and hydrogen peroxide production by intact macrophages, but at 45 microM the stimulatory effect on superoxide production was not found. In contrast, DMS attenuated nitric oxide production by macrophages. High concentrations of DMS, tyrphostin, and 2,5-dihydroxycinnamate showed cytotoxic effects. PTK inhibitors did not exhibit a significant effect on granule enzyme release induced by IL-1, whereas they attenuated the effect of LPS and fMLP on degranulation. Genistein and tyrphostin decreased the production of IL-8 and GM-CSF in macrophages activated by IL-1, whereas 2,5-dihydroxycinnamate did not affect it. The results suggest that tyrosine kinases exposed to IL-1, LPS, and fMLP may exert different modulatory actions on macrophage responses. The IL-1-activated macrophage responses, particularly degranulation, appear to be differently regulated by tyrosine kinases compared with the responses activated by LPS and fMLP.

Differential expression of inducible nitric oxide synthase gene by alveolar and peritoneal macrophages in lipopolysaccharide-hyporesponsive C3H/HeJ mice

In lipopolysaccharide (LPS)-hyporesponsive C3H/HeJ mice, alveolar macrophages (AMphi) produce much more tumour necrosis factor-alpha than peritoneal macrophages (PMphi) when stimulated with LPS (10 microgram/ml), but the induction of inducible nitric oxide synthase (iNOS) gene expression and production of nitric oxide (NO) in AMphi are not found. In the present study, we determined the induction of iNOS gene expression, using semi-quantitative reverse transcription-polymerase chain reaction, and the release of NO in AMphi and PMphi from C3H/HeJ and C3H/HeN mice. The results showed the induction of iNOS mRNA accumulation in a dose-dependent manner by LPS alone or in combination with interferon-gamma in both macrophages. The effects of the stimuli on iNOS gene expression and NO production were significantly higher in AMphi than in the PMphi of C3H/HeJ mice. The response of macrophages from C3H/HeN mice was similar to those from C3H/HeJ mice, but the difference of iNOS gene expression between AMphi and PMphi in C3H/HeN mice was not as striking as in C3H/HeJ mice. The results show that the iNOS gene expression and NO production were activated differently in AMphi and PMphi and suggest that the functional properties of macrophages isolated from distinct origins are different.

Fas ligand is present in tumors of the Ewing's sarcoma family and is cleaved into a soluble form by a metalloproteinase

Fas ligand (FasL) exists in transmembrane and soluble forms and induces apoptosis on cross-linking with the Fas receptor. We evaluated the biological significance of FasL and Fas in 61 tumor tissues and 9 cell lines of the Ewing's sarcoma family of tumors (ESFT). FasL was present in 62.5% and Fas in 79.4% of primary ESFT. Metastatic tumors had higher expression of FasL (95%), suggesting association with a metastatic phenotype. FasL was detected in the cytoplasm and membrane of ESFT cells by immunofluorescence. Western blotting revealed transmembrane and soluble FasL in cytosolic extracts and soluble FasL in conditioned media. Both transmembrane and soluble FasL induced apoptosis of Fas-sensitive Jurkat cells in co-culture experiments with ESFT cells or their media. Treatment with phenanthroline and the synthetic metalloproteinase inhibitor BB-3103 reduced the levels of soluble FasL in the media, suggesting that in ESFT, FasL is processed by a metalloproteinase and released in the extracellular milieu. The released soluble FasL may serve to attack cells of the immune system and/or interfere with the binding of transmembrane FasL with Fas, and results in down-regulation of transmembrane FasL. Synthetic metalloproteinase inhibitors may modify the ratio of transmembrane to soluble FasL.

TGF-beta plays a key role in morphogenesis of the pancreatic islets of Langerhans by controlling the activity of the matrix metalloproteinase MMP-2

Islets of Langerhans are microorgans scattered throughout the pancreas, and are responsible for synthesizing and secreting pancreatic hormones. While progress has recently been made concerning cell differentiation of the islets of Langerhans, the mechanism controlling islet morphogenesis is not known. It is thought that these islets are formed by mature cell association, first differentiating in the primitive pancreatic epithelium, then migrating in the extracellular matrix, and finally associating into islets of Langerhans. This mechanism suggests that the extracellular matrix has to be degraded for proper islet morphogenesis. We demonstrated in the present study that during rat pancreatic development, matrix metalloproteinase 2 (MMP-2) is activated in vivo between E17 and E19 when islet morphogenesis occurs. We next demonstrated that when E12.5 pancreatic epithelia develop in vitro, MMP-2 is activated in an in vitro model that recapitulates endocrine pancreas development (Miralles, F., P. Czernichow, and R. Scharfmann. 1998. Development. 125: 1017-1024). On the other hand, islet morphogenesis was impaired when MMP-2 activity was inhibited. We next demonstrated that exogenous TGF-beta1 positively controls both islet morphogenesis and MMP-2 activity. Finally, we demonstrated that both islet morphogenesis and MMP-2 activation were abolished in the presence of a pan-specific TGF-beta neutralizing antibody. Taken together, these observations demonstrate that in vitro, TGF-beta is a key activator of pancreatic MMP-2, and that MMP-2 activity is necessary for islet morphogenesis.

Regulation of CD95 (Apo-1/Fas) ligand and receptor expression in human embryonal carcinoma cells by interferon gamma and all-trans retinoic acid

Expression of CD95 (Apo-1/Fas) ligand and its two receptor isoforms, in response to all-trans retinoic acid and interferon gamma (IFNgamma), was analyzed atthe mRNA and protein levels in human Tera-2 embryonal carcinoma cells. Exposure of Tera-2 cells to all-trans retinoic acid for up to 16 days led to a decrease of CD95 ligand expression when compared to the control conditions, whereas expression of both CD95 isoforms increased. These changes were functionally significant since Tera-2 cells treated with all-trans retinoic acid for six to 16 days were more susceptible to CD95-mediated apoptosis. On the other hand, Tera-2 cells lost their capacity to induce apoptosis in CD95 receptor bearing Jurkat T lymphocytes after six days of incubation with all-trans retinoic acid. When Tera-2 cells were treated with IFNgamma, expression of CD95 ligand and both CD95 receptor isoforms increased within 24 hours. Tera-2 cells were then more susceptible to CD95 mediated apoptosis but also killed more CD95 receptor bearing Jurkat T lymphocytes via CD95 ligation compared to the control conditions. The results are indicative of differential regulation of CD95-mediated apoptosis by all-trans retinoic acid and IFNgamma in Tera-2 embryonal carcinoma cells, with likely impact on antitumor immunity.