Category: Important Info

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Activation of the Phosphatidylinositol 3-Kinase/Protein Kinase Akt Pathway Mediates Nitric Oxide-Induced Endothelial Cell Migration and Angiogenesis

To test the hypothesis that the phosphatidylinositol 3-kinase (PI3 kinase)/protein kinase Akt signaling pathway is involved in nitric oxide (NO)-induced endothelial cell migration and angiogenesis, we treated human and bovine endothelial cells with NO donors, S-nitroso-l-glutathione (GSNO) and S-nitroso-N-penicillamine (SNAP). Both GSNO and SNAP increased Akt phosphorylation and activity, which were blocked by cotreatment with the PI3 kinase inhibitor wortmannin. The mechanism was due to the activation of soluble guanylyl cyclase because 8-bromo-cyclic GMP activated PI3 kinase and the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-α]quinoxalin-1-one (ODQ) blocked NO-induced PI3 kinase activity. Indeed, transfection with adenovirus containing endothelial cell NO synthase (eNOS) or protein kinase G (PKG) increased endothelial cell migration, which was inhibited by cotransfection with a dominant-negative mutant of PI3 kinase (dnPI3 kinase). In a rat model of hind limb ischemia, adenovirus-mediated delivery of human eNOS cDNA in adductor muscles resulted in time-dependent expression of recombinant eNOS, which was accompanied by significant increases in regional blood perfusion and capillary density. Coinjection of adenovirus carrying dnPI3 kinase abolished neovascularization in ischemic hind limb induced by eNOS gene transfer. These findings indicate that NO promotes endothelial cell migration and neovascularization via cGMP-dependent activation of PI3 kinase and suggest that this pathway is important in mediating NO-induced angiogenesis.

http://mcb.asm.org/content/23/16/5726.full

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Thioredoxin, a Redox Enzyme Released in Infection and Inflammation, Is a Unique Chemoattractant for Neutrophils, Monocytes, and T Cells

Thioredoxin (Trx) is a ubiquitous intracellular protein disulfide oxidoreductase with a CXXC active site that can be released by various cell types upon activation. We show here that Trx is chemotactic for monocytes, polymorphonuclear leukocytes, and T lymphocytes, both in vitro in the standard micro Boyden chamber migration assay and in vivo in the mouse air pouch model. The potency of the chemotactic action of Trx for all leukocyte populations is in the nanomolar range, comparable with that of known chemokines. However, Trx does not increase intracellular Ca2+ and its activity is not inhibited by pertussis toxin. Thus, the chemotactic action of Trx differs from that of known chemokines in that it is G protein independent. Mutation of the active site cysteines resulted in loss of chemotactic activity, suggesting that the latter is mediated by the enzyme activity of Trx. Trx also accounted for part of the chemotactic activity released by human T lymphotropic virus (HTLV)-1–infected cells, which was inhibited by incubation with anti-Trx antibody. Since Trx production is induced by oxidants, it represents a link between oxidative stress and inflammation that is of particular interest because circulating Trx levels are elevated in inflammatory diseases and HIV infection.

http://jem.rupress.org/content/189/11/1783.long

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BLTR mediates leukotriene B(4)-induced chemotaxis and adhesion and plays a dominant role in eosinophil accumulation in a murine model of peritonitis.

Leukotriene B(4) (LTB(4)) is a potent chemoattractant active on multiple leukocytes, including neutrophils, macrophages, and eosinophils, and is implicated in the pathogenesis of a variety of inflammatory processes. A seven transmembrane-spanning, G protein-coupled receptor, called BLTR (LTB(4) receptor), has recently been identified as an LTB(4) receptor. To determine if BLTR is the sole receptor mediating LTB(4)-induced leukocyte activation and to determine the role of LTB(4) and BLTR in regulating leukocyte function in inflammation in vivo, we generated a BLTR-deficient mouse by targeted gene disruption. This mouse reveals that BLTR alone is responsible for LTB(4)-mediated leukocyte calcium flux, chemotaxis, and firm adhesion to endothelium in vivo. Furthermore, despite the apparent functional redundancy with other chemoattractant-receptor pairs in vitro, LTB(4) and BLTR play an important role in the recruitment and/or retention of leukocytes, particularly eosinophils, to the inflamed peritoneum in vivo. These studies demonstrate that BLTR is the key receptor that mediates LTB(4)-induced leukocyte activation and establishes a model to decipher the functional roles of BLTR and LTB(4) in vivo.

http://jem.rupress.org/content/192/3/439.long

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Functional Characterization of Human Receptors for Short Chain Fatty Acids and Their Role in Polymorphonuclear Cell Activation

Short chain fatty acids (SCFAs), including acetate, propionate, and butyrate, are produced at high concentration by bacteria in the gut and subsequently released in the bloodstream. Basal acetate concentrations in the blood (about 100 μm) can further increase to millimolar concentrations following alcohol intake. It was known previously that SCFAs can activate leukocytes, particularly neutrophils. In the present work, we have identified two previously orphan G protein-coupled receptors, GPR41 and GPR43, as receptors for SCFAs. Propionate was the most potent agonist for both GPR41 and GPR43. Acetate was more selective for GPR43, whereas butyrate and isobutyrate were more active on GPR41. The two receptors were coupled to inositol 1,4,5-trisphosphate formation, intracellular Ca2+ release, ERK1/2 activation, and inhibition of cAMP accumulation. They exhibited, however, a differential coupling to G proteins; GPR41 coupled exclusively though the Pertussis toxin-sensitive Gi/o family, whereas GPR43 displayed a dual coupling through Gi/o and Pertussis toxin-insensitive Gq protein families. The broad expression profile of GPR41 in a number of tissues does not allow us to infer clear hypotheses regarding its biological functions. In contrast, the highly selective expression of GPR43 in leukocytes, particularly polymorphonuclear cells, suggests a role in the recruitment of these cell populations toward sites of bacterial infection. The pharmacology of GPR43 matches indeed the effects of SCFAs on neutrophils, in terms of intracellular Ca2+ release and chemotaxis. Such a neutrophil-specific SCFA receptor is potentially involved in the development of a variety of diseases characterized by either excessive or inefficient neutrophil recruitment and activation, such as inflammatory bowel diseases or alcoholism-associated immune depression. GPR43 might therefore constitute a target allowing us to modulate immune responses in these pathological situations.

http://www.jbc.org/content/278/28/25481.long

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Cadmium Induces Interleukin-8 in Alveolar Epithelial Type II Cells (A549)

Cadmium (Cd) is a contaminant in cigarette smoke and may play an important role in the pathogenesis of smoking-related emphysema. It is reported that repeated Cd exposure causes emphysema after neutrophil infiltration in the rat lung. Interleukin-8 (IL-8) is a major neutrophil chemotactic factor commonly involved in a variety of pulmonary disorders including emphysema. The aim of this study is to elucidate the effect of Cd on IL-8 production of alveolar epithelial type II cells, using the A549 cell line. We used 1–100 mM of cadmium chloride (CdCl2) to stimulate the cells for a 48 h period. IL-8 production (2957 ± 137 pg/mL) without any cytotoxic effect was observed in the cell supernatants after 24 h exposure to 50 mM CdCl2. The Cd-removed supernatant caused neutrophil chemotaxis and was inhibited by the anti-IL-8 antibody.

Cd-induced IL-8 was inhibited by EDTA, and the inhibition was blocked by copper (II) chloride. The addition of anti-interleukin-1b or tumor necrosis factor-a antibodies did not diminish IL-8 release induced by Cd. These results suggest that Cd increases the production of IL-8 without any cytotoxic effect in alveolar epithelial cells, which may be an important factor in the developmental process of cigarette smoking-related emphysema.

pdf at: lib.med.tottori-u.ac.jp/yam/bef_41/yam40-1/fukuda/fukuda.pdf

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Decreased neutrophil function as a cause of retained placenta in dairy cattle.

It is unclear why some cows fail to expel the placenta following calving. One theory suggests the fetal placenta must be recognized as “foreign” tissue and rejected by the immune system after parturition to cause expulsion of the placenta. We hypothesized that impaired neutrophil function causes retained placenta (RP). We examined the ability of neutrophils to recognize fetal cotyledon tissue as assessed by a chemotaxis assay, which utilized a placental homogenate obtained from a spontaneously expelled placenta as the chemoattractant. Neutrophil killing ability was also estimated by determining myeloperoxidase activity in isolated neutrophils. Blood samples were obtained from 142 periparturient dairy cattle in two herds. Twenty cattle developed RP (14.1%). Neutrophils isolated from blood of cows with RP had significantly lower neutrophil function in both assays before calving, and this impaired function lasted for 1 to 2 wk after parturition. The addition of antibody directed against interleukin-8 (IL-8) to the cotyledon preparation used as a chemoattractant inhibited chemotaxis by 41%, suggesting that one of the chemoattractants present in the cotyledon at parturition is IL-8. At calving, plasma IL-8 concentration was lower in RP cows (51 +/- 12 pg/ml) than in cows expelling the placenta normally (134 +/- 11 pg/ml). From these data, we suggest that neutrophil function is a determining factor for the development of RP in dairy cattle. Also, depressed production of IL-8 may be a factor affecting neutrophil function in cows developing RP.

pdf available at: ddr.nal.usda.gov/bitstream/10113/13056/1/IND23327452.pdf

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Homocysteine induces monocyte chemoattractant protein-1 expression by activating NF-kappaB in THP-1 macrophages.

Homocysteinemia is an independent risk factor for cardiovascular disorders. The recruitment of monocytes is an important event in atherogenesis. Monocyte chemoattractant protein-1 (MCP-1) is a potent chemokine that stimulates monocyte migration into the intima of arterial walls. The objective of the present study was to investigate the effect of homocysteine on MCP-1 expression in macrophages and the underlying mechanism of such effect. Human monocytic cell (THP-1)-derived macrophages were incubated with homocysteine. By nuclease protection assay and ELISA, homocysteine (0.05-0.2 mM) was shown to significantly enhance the expression of MCP-1 mRNA (up to 2.6-fold) and protein (up to 4.8-fold) in these cells. Homocysteine-induced MCP-1 expression resulted in increased monocyte chemotaxis. The increase in MCP-1 expression was associated with activation of nuclear factor (NF)-kappaB due to increased phosphorylation of the inhibitory protein (IkappaB-alpha) as well as reduced expression of IkappaB-alpha mRNA in homocysteine-treated cells. In conclusion, our results demonstrate that homocysteine, at pathological concentration, stimulates MCP-1 expression in THP-1 macrophages via NF-kappaB activation.

http://ajpheart.physiology.org/content/280/6/H2840.long

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Angiotensin II stimulates migration of retinal microvascular pericytes: involvement of TGF-beta and PDGF-BB.

We studied the promigratory effect of angiotensin II (ANG II) on cultured bovine retinal microvascular pericytes. ANG II stimulated migration of pericytes by 86% at 10(-8) M, but this effect was lost at 10(-4) M. Migratory responses were inhibited by the ANG II type 1 (AT(1)) receptor antagonist losartan but not by PD-123319, an AT(2) antagonist. Addition of PD-123319 to the 10(-4) M ANG II dose restored migratory responses. The promigratory effect of ANG II (10(-7) M) was reduced by 59% in absence of gradient. Although ANG II augmented the latent matrix metalloproteinase-2 (MMP-2) activity of the pericyte by 35%, it also doubled tissue inhibitors of MMPs. ANG II-induced migration was not altered by a broad-spectrum MMP inhibitor (GM6001); it was inhibited by ~50% by antibodies against transforming growth factor (TGF)-beta(1/2/3) and was abolished by antibodies against platelet-derived growth factor (PDGF)-BB. We conclude that ANG II induces chemotactic responses on retinal microvascular pericytes acting through the AT(1) receptor. This effect is opposed by the AT(2) receptor. ANG II-induced chemotaxis is mediated by PDGF-BB and involves TGF-beta, but it is independent of MMP activity. It is also independent of vascular endothelial growth factor (VEGF) because VEGF did not stimulate pericyte migration. ANG II can contribute to the regulation of retinal neovascularization by stimulating pericyte migration.

link to pdf at: ajpheart.physiology.org/content/282/2/H739.full.pdf

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CXC Chemokine Receptor 5 Expression Defines Follicular Homing T Cells with B Cell Helper Function

Leukocyte traffic through secondary lymphoid tissues is finely tuned by chemokines. We have studied the functional properties of a human T cell subset marked by the expression of CXC chemokine receptor 5 (CXCR5). Memory but not naive T cells from tonsils are CXCR5+ and migrate in response to the B cell–attracting chemokine 1 (BCA-1), which is selectively expressed by reticular cells and blood vessels within B cell follicles. Tonsillar CXCR5+ T cells do not respond to other chemokines present in secondary lymphoid tissues, including secondary lymphoid tissue chemokine (SLC), EBV-induced molecule 1 ligand chemokine (ELC), and stromal cell–derived factor 1 (SDF-1). The involvement of tonsillar CXCR5+ T cells in humoral immune responses is suggested by their localization in the mantle and light zone germinal centers of B cell follicles and by the concomitant expression of activation and costimulatory markers, including CD69, HLA-DR, and inducible costimulator (ICOS). Peripheral blood CXCR5+ T cells also belong to the CD4+ memory T cell subset but, in contrast to tonsillar cells, are in a resting state and migrate weakly to chemokines. CXCR5+ T cells are very inefficient in the production of cytokines but potently induce antibody production during coculture with B cells. These properties portray CXCR5+ T cells as a distinct memory T cell subset with B cell helper function, designated here as follicular B helper T cells (TFH).

http://jem.rupress.org/content/192/11/1553.long

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Insulin-like Growth Factor-I-induced Migration of Melanoma Cells Is Mediated by Interleukin-8 Induction

Successive events of growth factor-induced autocrine and paracrine activation promote tumor growth and metastasis. Insulin-like growth factor-I (IGF-I) stimulates melanoma cells to grow, survive, and migrate. Interleukin-8 (IL-8) is produced by melanoma cells and has been correlated with melanoma metastasis, but the biological functions of this cytokine have not been elucidated. We show here that IGF-I-induced migration of melanoma cells could be inhibited by neutralizing antibody against IL-8. IGF-I overexpression induced IL-8 production in melanoma cells, especially in biologically early melanomas by accelerating its transcription rate via activation of mitogen-activated protein kinase pathway. IGF-I treatment phosphorylated c-Jun and stimulated the binding of AP-1 but not NF-{kappa}B to the IL-8 promoter. These data identify IL-8 as a new target of IGF-I in melanoma and suggest that some of the biological functions of IGF-I are mediated by IL-8.

http://cgd.aacrjournals.org/cgi/content/full/13/2/87