CD40-40L Signaling in Vascular Inflammation

Anthrax lethal toxin enhances IkappaB kinase activation and differentially regulates pro-inflammatory genes in human endothelium

Anthrax lethal toxin (LT) was previously shown to enhance transcriptional activity of NF-kappaB in tumor necrosis factor-alpha-activated primary human endothelial cells. Here we show that this LT-mediated increase in NF-kappaB activation is associated with the enhanced degradation of the inhibitory proteins IkappaBalpha and IkappaBbeta but not IkappaBepsilon. Moreover, this was accompanied by enhanced activation of the IkappaB kinase complex (IKK), which is responsible for targeting IkappaB proteins for degradation. Importantly, LT enhancement of IkappaBalpha degradation was completely blocked by a selective IKKbeta inhibitor, whereas IkappaBbeta degradation was attenuated, suggesting a mechanistic link. Consistent with the above data, LT-cotreated cells show elevated phosphorylation of two IKK substrates, IkappaBalpha and p65, both of which were blocked by incubation with the IKKbeta inhibitor. Consistent with NF-kappaB activation, LT increased transcription of the NF-kappaB regulated gene CD40. Conversely, LT inhibited transcription of another NF-kappaB-regulated gene, CCL2. This inhibition was linked to the LT-mediated suppression of another CCL2-regulating transcription factor, AP-1 (activator protein-1). These data suggest that LT-mediated enhancement of NF-kappaB is IKK-dependent, but importantly, the net effect of LT on the transcription of proinflammatory genes is driven by the cumulative effect of LT on the particular set of transcription factors that regulate a given promoter. Together, these findings provide new mechanistic insight on how LT may disrupt the host response to anthrax.

Increased IkappaB alpha expression is essential for the tolerogenic property of TGF-beta-exposed APCs

IkappaB alpha is an inhibitor of the transcriptional factor NF-kappaB, and it is an essential component of the signaling pathways that lead to expression of inflammatory molecules. These include cytokines and costimulatory molecules associated with antigen presentation in an inflammatory immune response. In this study, we report that antigen-presenting cells exposed to TGF-beta induce peripheral tolerance by increasing IkappaB alpha expression. Exposure of antigen presenting cells (APCs) to TGF-beta is known to impair their ability to secrete IL-12, and such impairment correlated with reduced NF-kappaB activity as indicated by significantly reduced nuclear levels of p50, an essential subunit of NF-kappaB for IL-12 transcription. Blockade of increased nuclear IkappaB alpha in APCs by expression of small interfering RNA molecules (siRNAs) targeting IkappaB alpha transcripts prevented IL-12 impairment and the decline in nuclear p50 levels. Furthermore, such IkappaB alpha blockade also interfered with the tolerogenic property of TGF-beta-exposed APCs. However, increased expression of IkappaB alpha in APCs, independent of TGF-beta exposure, reduced nuclear p50 levels and permitted tolerance induction by APCs. Thus, our findings attribute a direct and significant role to IkappaB alpha in the tolerogenic potential of APCs. Increased IkappaB alpha expression in APCs may therefore offer a therapeutic approach to achieve antigen-specific immunomodulation.

Suramin inhibits the CD40-CD154 costimulatory interaction: a possible mechanism for immunosuppressive effects

Suramin is a symmetric polysulfonated naphthylamine-benzamide urea derivative approved for the treatment of trypanosomiasis and onchocerciasis and a known P2 (ATP/UTP purine receptor) antagonist. Here, we report its ability to inhibit the important CD40-CD154 costi-mulatory interaction required for T cell activation and the development of an effective immune response. In vitro, it inhibited the binding of both human and murine CD154 (CD40L) to their receptor (CD40) even in the presence of protein-containing media and prevented the CD154-induced proliferation of human B cells as well as the corresponding increase in surface expression of CD86, CD80, CD40, and MHC class II in a concentration-dependent manner. Furthermore, in isolated human islets, it also decreased the CD154-induced release of inflammatory cytokines such as IFN-g, interleukin-6 (IL-6), and IL-8. Suramin was selected for investigation because it has been reported to be an inhibitor of the interaction of TNF-a with its receptor and CD154 is a member of the TNF-family. However, it turned out to be a considerably, about 30-fold, more effective inhibitor of the CD40-CD154 protein-protein interaction than of the corresponding TNF interaction. Its median inhibitory concentration (IC50 50 mM) is somewhat higher than for the P2-receptor, but well within the range of its therapeutic concentration levels. Suramin shows considerable polypharmacology, but its interference with the positive costimulatory interaction might provide a possible, not yet identified mechanism for its ability to suppress T cell activity and induce immunosuppression, which might also have limited its clinical usefulness in the treatment of AIDS and cancer.

CD40-CD40 ligand interactions in oxidative stress, inflammation and vascular disease

CD40 ligand (CD40L) and its receptor CD40 participate in numerous inflammatory pathways that contribute to multiple pathophysiological processes. A role for CD40-CD40L interactions has been identified in atherosclerosis, and such interactions are known to destabilize atherosclerotic plaques by inducing the expression of cytokines, chemokines, growth factors, matrix metalloproteinases and pro-coagulant factors. The CD40-CD40L interaction has also been implicated in immune system disorders. Recent studies have suggested that CD40-CD40L interactions regulate oxidative stress and affect various signaling pathways in both the immunological and cardiovascular systems. Here, we discuss the emerging role of CD40-CD40L-mediated processes in oxidative stress, inflammatory pathways and vascular diseases. Understanding the roles and regulation of CD40-CD40L-mediated oxidative signaling in immune and non-immune cells could facilitate the development of therapeutics targeting diverse inflammatory diseases.

Soluble CD40 ligand induces endothelial dysfunction in human and porcine coronary artery endothelial cells

The purpose of this study was to determine the effects and mechanisms of sCD40L on endothelial dysfunction in both human coronary artery endothelial cells (HCAECs) and porcine coronary artery rings. HCAECs treated with sCD40L showed significant reductions of endothelial nitric oxide synthase (eNOS) mRNA and protein levels, eNOS mRNA stability, eNOS enzyme activity, and cellular NO levels, whereas superoxide anion (O(2)(-)) production was significantly increased. sCD40L enhanced eNOS mRNA 3'UTR binding to cytoplasmic molecules and induced a unique expression pattern of 95 microRNAs. sCD40L significantly decreased mitochondrial membrane potential, and catalase and SOD activities, whereas it increased NADPH oxidase (NOX) activity. sCD40L increased phosphorylation of MAPKs p38 and ERK1/2 as well as IkappaBalpha and enhanced NF-kappaB nuclear translocation. In porcine coronary arteries, sCD40L significantly decreased endothelium-dependent vasorelaxation and eNOS mRNA levels, whereas it increased O(2)(-) levels. Antioxidant seleno-l-methionine; chemical inhibitors of p38, ERK1/2, and mitochondrial complex II; as well as dominant negative mutant forms of IkappaBalpha and NOX4 effectively blocked sCD40L-induced eNOS down-regulation in HCAECs. Thus, sCD40L reduces eNOS levels, whereas it increases oxidative stress through the unique molecular mechanisms involving eNOS mRNA stability, 3'UTR-binding molecules, microRNAs, mitochondrial function, ROS-related enzymes, p38, ERK1/2, and NF-kappaB signal pathways in endothelial cells.

Future innovations in anti-platelet therapies

Platelets have long been recognized to be of central importance in haemostasis, but their participation in pathological conditions such as thrombosis, atherosclerosis and inflammation is now also well established. The platelet has therefore become a key target in therapies to combat cardiovascular disease. Anti-platelet therapies are used widely, but current approaches lack efficacy in a proportion of patients, and are associated with side effects including problem bleeding. In the last decade, substantial progress has been made in understanding the regulation of platelet function, including the characterization of new ligands, platelet-specific receptors and cell signalling pathways. It is anticipated this progress will impact positively on the future innovations towards more effective and safer anti-platelet agents. In this review, the mechanisms of platelet regulation and current anti-platelet therapies are introduced, and strong, and some more speculative, potential candidate target molecules for future anti-platelet drug development are discussed.

Nitrotyrosine promotes human aortic smooth muscle cell migration through oxidative stress and ERK1/2 activation

Nitrotyrosine is a new biomarker of atherosclerosis and inflammation. The objective of this study was to determine the direct effects of free nitrotyrosine on human aortic smooth muscle cell (AoSMC) migration and molecular mechanisms. By a modified Boyden chamber assay, nitrotyrosine significantly increased AoSMC migration in a concentration-dependent manner. For example, nitrotyrosine at 300 nM increased AoSMC migration up to 152% compared with l-tyrosine-treated control cells (P<0.01). Cell wound healing assay confirmed this effect. Nitrotyrosine significantly increased the expression of some key cell migration-related molecules including PDGF receptor-B, matrix metalloproteinase 2 (MMP2) and integrins alphaV and beta3 at both mRNA and protein levels in AoSMC (P<0.01). In addition, nitrotyrosine increased reactive oxygen species (ROS) production in AoSMC by staining with fluorescent dye DCFHDA. Furthermore, nitrotyrosine induced transient phosphorylation of ERK2 by Bio-Plex luminex immunoassay and western blot analysis. AoSMC were able to uptake nitrotyrosine. Antioxidants including seleno-l-methionine and superoxide dismutase mimetic (MnTBAP) as well as ERK1/2 inhibitor PD98059 effectively blocked the promoting effect of nitrotyrosine on AoSMC migration and the mRNA expression of above cell migration-related molecules. Thus, nitrotyrosine directly increases AoSMC migration in vitro and the expression of migration-related molecules through overproduction of ROS and activation of ERK1/2 pathway. Nitrotyrosine may contribute to cardiovascular pathogenesis.

In vitro model of platelet-endothelial activation due to cigarette smoke under cardiovascular circulation conditions

Cigarette smoke has been shown to increase platelet activation and endothelial cell (EC) adhesion molecule expression. In the present study, we utilized a hemodynamic shearing device (HSD) to investigate the above effects in vitro in a combined system of platelets and cultured HUVECs (Human Umblical Vein ECs) under physiological shear stress. We investigated the alteration of E-selectin expression on ECs upon exposure to: (1) platelets and nicotine-free smoke extract (NFE), (2) platelets alone, (3) NFE alone, under physiological shear stress. We additionally confirmed the protective effect of nicotine on platelet activation. We found that: (i) surface expression of E-selectin on ECs was significantly increased upon simultaneous exposure of ECs and platelets to NFE relative to exposure of ECs to either platelets or NFE alone (p < 0.05). (ii) Platelet activation was significantly increased in the presence of NFE (p < 0.05). (iii) Nicotine (200 nM) when added to NFE, significantly reduced platelet activation due to NFE (p < 0.05), an effect additionally confirmed by conventional cigarette extracts which contain nicotine (p < 0.05). We therefore conclude that: (a) NFE and platelets additively increase EC E-selectin surface expression, and (b) nicotine modulates platelet activation regardless of ECs.

Premature labor: a state of platelet activation?

OBJECTIVE

This study was undertaken to determine whether premature labor is associated with changes in the maternal plasma concentration of soluble CD40 ligand (sCD40L), a marker of platelet activation.

METHODS

A cross-sectional study included patients in the following groups: 1) non-pregnant (n=21); 2) normal pregnancy (n=71); 3) normal pregnancy at term with (n=67) and without labor (n=88); 4) preterm labor (PTL) with intact membranes (n=136) that was divided into the following sub-groups: 4a) PTL who delivered at term (n=49); 4b) PTL without intra-amniotic infection and/or inflammation (IAI) who delivered preterm (n=54); and 4c) PTL with IAI who delivered preterm (n=33). sCD40L concentrations were measured by ELISA.

RESULTS

The median maternal plasma sCD40L concentration was higher in pregnant than non-pregnant women (P=0.017). Patients with PTL had a higher median maternal plasma sCD40L concentration than women with normal pregnancies, regardless of the presence or absence of IAI and gestational age at delivery (P<0.001 for all comparisons). IAI was not associated with a higher median maternal plasma concentration of sCD40L.

CONCLUSIONS

Normal pregnancy is a state in which there is a physiologic increase of sCD40L. PTL was associated with an increased median maternal plasma sCD40L concentration that could not be accounted for by IAI. Thus, our findings suggest that platelet activation occurs during an episode of preterm labor.