Signal transduction pathways activated in endothelial cells following infection with Chlamydia pneumoniae

Chlamydia pneumoniae is an important respiratory pathogen. Recently, its presence has been demonstrated in atherosclerotic lesions. In this study, we characterized C. pneumoniae-mediated activation of endothelial cells and demonstrated an enhanced expression of endothelial adhesion molecules followed by subsequent rolling, adhesion, and transmigration of leukocytes (monocytes, granulocytes). These effects were blocked by mAbs against endothelial and/or leukocyte adhesion molecules (beta1 and beta2 integrins). Additionally, activation of different signal transduction pathways in C. pneumoniae-infected endothelial cells was shown: protein tyrosine phosphorylation, up-regulation of phosphorylated p42/p44 mitogen-activated protein kinase, and NF-kappaB activation/translocation occurred within 10-15 min. Increased mRNA and surface expression of E-selectin, ICAM-1, and VCAM-1 were noted within hours. Thus, C. pneumoniae triggers a cascade of events that could lead to endothelial activation, inflammation, and thrombosis, which in turn may result in or may promote atherosclerosis.     

FK506 suppresses E-selectin, ICAM-1 and VCAM-1 expression on vascular endothelial cells by inhibiting tumor necrosis factor alpha secretion from peripheral blood mononuclear cells

FK506 suppresses activation of T cells; however, it down-regulates E-selectin, ICAM-1 and VCAM-1 expression in inflamed tissues. In this study, we investigated the effect of FK506 on expression of those adhesion molecules on human vascular endothelial cells (HMVEC). Culture supernatant from peripheral blood mononuclear cells (PBMC) stimulated with anti-CD3 plus anti-CD2 antibodies effectively induced the expression of E-selectin, ICAM-1 and VCAM-1 on HMVEC, and treatment with FK506 down-regulated their expression. Culture supernatant contained tumor necrosis factor (TNF) alpha and interleukin (IL)-1beta, which effectively induced adhesion molecules, and FK506 suppressed both cytokine secretions. TNFalpha content in culture supernatant was parallel to the induction of adhesion molecules by the culture supernatant. IL-1beta content was not enough to induce those adhesion molecules. Anti-TNFalpha antibody completely inhibited those expressions. FK506 did not inhibit either TNFalpha- or IL-1beta-induced expression of adhesion molecules, or viability of HMVEC. These results indicate that FK506 suppresses migration of inflammatory cells through the inhibition of TNFalpha secretion from leukocytes.     

Effects of 17beta-estradiol on growth and apoptosis in human vascular endothelial cells: influence of mechanical strain and tumor necrosis factor-alpha

Vascular endothelial cell (EC) integrity is key to arterial health; endothelial dysfunction is linked to atherogenesis. Atherosclerosis shows a male preponderance, possibly related to the protective effect of estrogens in women. This study examined the effect of estrogens on growth, apoptosis and adhesion molecule expression in cultured human EC. The effects of 17beta-estradiol (E2) were studied in human umbilical vein endothelial cells (HUVEC) under normal culture conditions, and following exposure to cyclic mechanical strain or tumor necrosis factor alpha (TNFalpha). E2 enhanced HUVEC growth in serum-enriched media, in a concentration-dependent manner. This up-regulation of EC growth by E2 was associated with an increase in telomerase activity, assessed by PCR-based TRAP analysis. Cyclic strain enhanced [(3)H]-thymidine incorporation into DNA, and increased activation of mitogen-activated protein (MAP) kinase ERK1/2 and expression of early growth genes (Egr-1 and Sp-1); E2 attenuated the strain-induced ERK1/2 activation but not the early growth gene expression or DNA synthesis. TNFalpha (20 ng/mL) induced apoptosis in HUVEC, causing a decrease in DNA synthesis, increase in floating and Annexin-V-stained cell numbers, and morphological changes. TNFalpha also upregulated ERK1/2 activity and expression of adhesion molecules (ICAM-1, VCAM-1 and E-selectin). E2 significantly attenuated the effects of TNFalpha on ERK1/2 activity, apoptosis, and E-selectin expression in the cells. Thus, estradiol enhances growth and reduces TNFalpha-induced apoptosis in EC; enhanced EC growth may be mediated via upregulation of telomerase activity. These effects are possible cellular mechanisms underlying female gender-associated cardiovascular protection.     

Simvastatin modulates TNFalpha-induced adhesion molecules expression in human endothelial cells

Adhesion and transendothelial migration of leukocytes into the vascular wall is a crucial step in atherogenesis. Expression of cell adhesion molecules by endothelial cells plays a leading role in this process. We investigated the effect of simvastatin, an inhibitor of HMG-CoA reductase administered to reduce plasma levels of LDL-cholesterol, on the expression of vascular cell adhesion molecule-1 (VCAM-1) and intracellular cell adhesion molecule-1 (ICAM-1) by human umbilical vein endothelial cells (HUVEC) stimulated with tumor necrosis factor alpha (TNFalpha). We found the expression to be significantly inhibited by the drug in a time and concentration-dependent manner and to a greater extent in the case of VCAM-1 as compared with ICAM-1. In TNFalpha-stimulated HUVEC, simvastatin decreased VCAM-1 and ICAM-1 mRNA levels, inhibited TNFalpha-induced activation of nuclear factor kappaB (NF-kappaB) and enhanced expression of peroxisome proliferator-activated receptor alpha (PPARalpha). These effects were associated with reduction of adherence of monocytes and lymphocytes to HUVEC. The present findings suggest that the benefits of statins in vascular disease may include the inhibition of expression of VCAM-1 and ICAM-1 through effects on NF-kappaB.     

Respiratory syncytial virus infection of human lung endothelial cells enhances selectively intercellular adhesion molecule-1 expression

Respiratory syncytial virus (RSV) is worldwide the most frequent cause of bronchiolitis and pneumonia in infants requiring hospitalization. In the present study, we supply evidence that human lung microvascular endothelial cells, human pulmonary lung aorta endothelial cells, and HUVEC are target cells for productive RSV infection. All three RSV-infected endothelial cell types showed an enhanced cell surface expression of ICAM-1 (CD54), which increased in a time- and RSV-dose-dependent manner. By using noninfectious RSV particles we verified that replication of RSV is a prerequisite for the increase of ICAM-1 cell surface expression. The up-regulated ICAM-1 expression pattern correlated with an increased cellular ICAM-1 mRNA amount. In contrast to ICAM-1, a de novo expression of VCAM-1 (CD106) was only observed on RSV-infected HUVEC. Neither P-selectin (CD62P) nor E-selectin (CD62E) was up-regulated by RSV on human endothelial cells. Additional experiments performed with neutralizing Abs specific for IL-1alpha, IL-1beta, IL-6, and TNF-alpha, respectively, excluded an autocrine mechanism responsible for the observed ICAM-1 up-regulation. The virus-induced ICAM-1 up-regulation was dependent on protein kinase C and A, PI3K, and p38 MAPK activity. Adhesion experiments using polymorphonuclear neutrophil granulocytes (PMN) verified an increased ICAM-1-dependent adhesion rate of PMN cocultured with RSV-infected endothelial cells. Furthermore, the increased adhesiveness resulted in an enhanced transmigration rate of PMN. Our in vitro data suggest that human lung endothelial cells are target cells for RSV infection and that ICAM-1 up-regulated on RSV-infected endothelial cells might contribute to the enhanced accumulation of PMN into the bronchoalveolar space.     

Butyrate inhibits cytokine-induced VCAM-1 and ICAM-1 expression in cultured endothelial cells: the role of NF-kappaB and PPARalpha

Adhesion and migration of leukocytes into the surrounding tissues is a crucial step in inflammation, immunity, and atherogenesis. Expression of cell adhesion molecules by endothelial cells plays a leading role in this process. Butyrate, a natural short-chain fatty acid produced by bacterial fermentation of dietary fiber, has been attributed with anti-inflammatory activity in inflammatory bowel disease. Butyrate in vitro is active in colonocytes and several other cell types. We have studied the effect of butyrate on expression of endothelial leukocyte adhesion molecules by cytokine-stimulated human umbilical vein endothelial cells (HUVEC). Pretreatment of HUVEC with butyrate-inhibited tumor necrosis factor-alpha (TNFalpha)-induced expression of vascular cell adhesion molecule-1 (VCAM-1) and intracellular cell adhesion molecule-1 (ICAM-1) in a time and concentration-dependent manner. Butyrate at 10 mM/L inhibited interleukin-1 (IL-1)-stimulated VCAM-1 and ICAM-1 expression. The effect of butyrate on cytokine-stimulated VCAM-1 expression was more pronounced than in the case of ICAM-1. Butyrate decreased TNFalpha-induced expression of mRNA for VCAM-1 and ICAM-1. Suppressed expression of VCAM-1 and ICAM-1 was associated with reduced adherence of monocytes and lymphocytes to cytokine-stimulated HUVEC. Butyrate inhibited TNFalpha-induced activation of nuclear factor-kappaB (NF-kappaB) in HUVEC. Finally, butyrate enhanced peroxisome proliferator-activated receptor-alpha (PPARalpha) expression in HUVEC. These results demonstrate that butyrate may have anti-inflammatory properties not only in colonocytes but also in endothelial cells. The anti-inflammatory and (perhaps) antiatherogenic properties of butyrate may partly be attributed to an effect on activation of NF-kappaB and PPARalpha and to the associated expression of VCAM-1 and ICAM-1. The present findings support further investigations on the therapeutic benefits of butyrate in several pathological events involving leukocyte recruitment.     

Interferon-gamma synergises with tumour necrosis factor and lymphotoxin-alpha to enhance the mRNA and protein expression of adhesion molecules in mouse brain endothelial cells

Changes to the cerebral microvasculature are evident during cerebral malaria (CM). Activation of the endothelium is likely to be due to the actions of cytokines, circulating levels of which are elevated during CM. Endothelial cells are known to up-regulate the expression of cellular adhesion molecules, which can lead to cellular sequestration and obstruction of vessels. However, it is unknown whether cytokines synergise in the up-regulation of the adhesion molecules involved in CM. In this study, the mRNA and/or protein expression of the adhesion molecules vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), P-selectin and E-Selectin were examined in a mouse brain endothelial cell line. Endothelial cells were stimulated with interferon-gamma (IFN-gamma), tumour necrosis factor (TNF) and lymphotoxin-alpha (LT-alpha), alone or in combination. The expression of ICAM-1, VCAM-1, P-selectin and E-Selectin mRNA in mouse brain endothelial cells by TNF and/or LT-alpha was found to be significantly enhanced in the presence of IFN-gamma. The same synergistic effect was found when analyzing ICAM-1 protein expression in cytokine stimulated mouse brain endothelial cells. The findings show that cytokines can synergise to influence gene expression and protein expression in a mouse brain endothelial cell line.     

Rapid up-regulation of alpha4 integrin-mediated leukocyte adhesion by transforming growth factor-beta1

The alpha4 integrins (alpha4beta1 and alpha4beta7) are cell surface heterodimers expressed mostly on leukocytes that mediate cell-cell and cell-extracellular matrix adhesion. A characteristic feature of alpha4 integrins is that their adhesive activity can be subjected to rapid modulation during the process of cell migration. Herein, we show that transforming growth factor-beta1 (TGF-beta1) rapidly (0.5-5 min) and transiently up-regulated alpha4 integrin-dependent adhesion of different human leukocyte cell lines and human peripheral blood lymphocytes (PBLs) to their ligands vascular cell adhesion molecule-1 (VCAM-1) and connecting segment-1/fibronectin. In addition, TGF-beta1 enhanced the alpha4 integrin-mediated adhesion of PBLs to tumor necrosis factor-alpha-treated human umbilical vein endothelial cells, indicating the stimulation of alpha4beta1/VCAM-1 interaction. Although TGF-beta1 rapidly activated the small GTPase RhoA and the p38 mitogen-activated protein kinase, enhanced adhesion did not require activation of both signaling molecules. Instead, polymerization of actin cytoskeleton triggered by TGF-beta1 was necessary for alpha4 integrin-dependent up-regulated adhesion, and elevation of intracellular cAMP opposed this up-regulation. Moreover, TGF-beta1 further increased cell adhesion mediated by alpha4 integrins in response to the chemokine stromal cell-derived factor-1alpha. These data suggest that TGF-beta1 can potentially contribute to cell migration by dynamically regulating cell adhesion mediated by alpha4 integrins.     

Monocyte adhesion to xenogeneic endothelium during laminar flow is dependent on alpha-Gal-mediated monocyte activation

Monocytes are the predominant inflammatory cell recruited to xenografts and participate in delayed xenograft rejection. In contrast to allogeneic leukocytes that require up-regulation of endothelial adhesion molecules to adhere and emigrate into effector tissues, we demonstrate that human monocytes adhere rapidly to unstimulated xenogeneic endothelial cells. The major xenoantigen galactosealpha(1,3)galactosebeta(1,4)GlcNAc-R (alpha-gal) is abundantly expressed on xenogeneic endothelium. We have identified a putative receptor for alpha-gal on human monocytes that is a member of the C-type family of lectin receptors. Monocyte arrest under physiological flow conditions is regulated by alpha-gal, because cleavage or blockade results in a dramatic reduction in monocyte adhesion. Recruitment of human monocytes to unactivated xenogeneic endothelial cells requires both alpha(4) and beta(2) integrins on the monocyte; binding of alpha-gal to monocytes results in rapid activation of beta(2), but not alpha(4), integrins. Thus, activation of monocyte beta(2) integrins by alpha-gal expressed on xenogeneic endothelium provides a mechanism that may explain the dramatic accumulation of monocytes in vivo.     

The dynamics of gene expression in human lung microvascular endothelial cells after stimulation with inflammatory cytokines

Vascular endothelium plays an essential role in the pathogenesis of vasoocclusion. The changes in the endothelial cell function can be triggered by changes in gene expression caused by interaction with cytokines and blood cells. Using cDNA arrays, we have recently reported complex patterns of gene expression after stimulation of endothelial cells with TNFalpha and IL-1beta. Better understanding of the time course of gene expression changes, their concentration dependence and reversibility after withdrawal of the offending cytokine is essential for successful prevention and therapy of vasoocclusion. Here we present a detailed study of the concentration dependence and time course of gene expression in endothelial cells after their exposure to TNFalpha and IL-1beta. We focus on the adhesion molecules (VCAM-1, ICAM-1, E-selectin) and cytokines (IL-6, GCP-2, MCP-1) that are likely to contribute to vasoocclusion. We report differences in the time course and intensity of their expression and in their response to TNFalpha and IL-1beta stimulation. We demonstrate that expression of the studied genes is upregulated by low TNFalpha concentrations that better reflect the TNFalpha levels detected in the plasma of patients developing vasoocclusion. These results help to understand the changes in the endothelium and to design rational prevention and therapy of vasoocclusion.     

A novel Mutein of TNFalpha Containing the Arg-Gly-Asp Sequence Shows Reduced Toxicity in Intestine

The effects of human tumour necrosis factor-alpha (TNFalpha), or its mutein (F4168) having the cell adhesive Arg-Gly-Asp sequence at the N-terminus, on intestinal injury, were examined. Histopathological examination revealed that an intravenous injection of TNFalpha resulted in marked haemorrhage or oedema in the caecum of rats, whereas F4168 showed no such effects even at the same therapeutic dose. Moreover, the number of neutrophils that adhered to endothelial cells or infiltrated the mucosal tissue was much higher after TNFalpha injection compared with F4168 in vivo. The enhanced adhesion of neutrophils on to human umbilical vein endothelial cells also occurred when the latter were pre-stimulated with TNFalpha but not with F4168 in vitro. The expression of the cell adhesion molecules including endothelial leukocyte adhesion molecule-1 or intercellular adhesion molecule-1 on F4168- stimulated human umbilical vein endothelial ceils was significantly lower than that stimulated with TNFalpha. These results suggest that the Arg-Gly-Asp sequence introduced into the TNFalpha molecule abrogates the side effect of this cytokine such as tissue injury or shock, and that F4168 could be useful for systemic therapy.