Signaling from the brink of danger.
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Dendritic Cells↗
Biomedical subjects
S T Grey
Publications and source records attributed to S T Grey.
A20 inhibits cytokine-induced apoptosis and nuclear factor kappaB-dependent gene activation in islets.
Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease resulting from apoptotic destruction of beta cells in the islets of Langerhans. Low expression of antioxidants and a predilection to produce nitric oxide (NO) have been shown to underscore beta cell apoptosis. With this perspective in mind, we questioned whether beta cells could mount an induced protective response to inflammation. Here we show that human and rat islets can be induced to rapidly express the antiapoptotic gene A20 after interleukin (IL)-1beta activation. Overexpression of A20 by means of adenovirus-mediated gene transfer protects islets from IL-1beta and interferon gamma-induced apoptosis. The cytoprotective effect of A20 against apoptosis correlates with and is dependent on the abrogation of cytokine-induced NO production. The inhibitory effect of A20 on cytokine-stimulated NO production is due to transcriptional blockade of inducible NO synthase (iNOS) induction; A20 inhibits the activation of the transcription factor nuclear factor kappaB at a level upstream of IkappaBalpha degradation. These data demonstrate a dual antiapoptotic and antiinflammatory function for A20 in beta cells. This qualifies A20 as part of the physiological cytoprotective response of islets. We propose that A20 may have therapeutic potential as a gene therapy candidate to achieve successful islet transplantation and the cure of IDDM.
Adenoviridae↗
Extracellular ATP and ADP activate transcription factor NF-kappa B and induce endothelial cell apoptosis.
Inflammation within the vasculature is associated with endothelial cell (EC) perturbation, loss of vascular ATP-diphosphohydrolase activity, and platelet microthrombus formation with release of ATP and ADP into the micro-environment. The nature and effects of purinergic stimulation of EC under these circumstances remain largely undetermined. ATP and ADP activated EC transcribed mRNA from certain transcription factor NF-kappa B target genes and expressed E-selectin protein on cell membranes. Band shift analysis and reporter assays confirmed the activation of NF-kappa B in response to both ATP and ADP. Apoptosis was shown to occur in response to purinergic signaling, potentially through the activation of P2z/P2x7 receptors. Induction of EC activation responses and apoptosis in response to stimulation with ATP and ADP is associated with activation of NF-kappa B.
Adenosine Diphosphate↗
Expression of human thrombomodulin cofactor activity in porcine endothelial cells.
BACKGROUND: Xenograft rejection may predispose to vascular thrombosis because of putative cross-species' functional incompatibilities between natural anticoagulants present on the donor endothelium and host activated coagulation factors. For example, porcine thrombomodulin expressed on porcine aortic endothelial cells (PAEC) does not provide the expected thrombomodulin (TM)-cofactor activity for human protein C in the presence of human thrombin. In addition, TM may be down-regulated after cellular activation. Our aim was to express human TM cofactor activity in PAEC and to study the proinflammatory effect of tumor necrosis factor-alpha (TNF-alpha) on stable expressed human thrombomodulin in vitro. METHODS AND RESULTS: Retroviral transduction of PAEC with the gene encoding for human thrombomodulin (hTM) resulted in expression of high levels of specific TM cofactor activity on PAEC (0.62 microg/ml activated protein C/10(5) cells). High-level expression of hTM resulted in a 620-fold higher activation of human protein C in the presence of human thrombin when compared with mock-transduced PAEC (0.0001 microg/ml/10(5) cells; P<0.001). Transduced PAEC expressing hTM also bound more human thrombin than control PAEC, as determined by inhibition of thrombin-induced platelet activation (P<0.05). We noted that exposure to TNF-alpha significantly reduced exogenous hTM cofactor activity on transduced PAEC in a time- and dose-dependent fashion; this occurred despite the relatively stable expression of hTM mRNA and hTM antigen in these cells. Treatment of transduced PAEC with selected antioxidants could protect against the loss of hTM cofactor activity directly associated with the oxidative stress induced by TNF-alpha activation responses. CONCLUSIONS: Our data show that the functional deficiency of the anticoagulant protein C pathway in PAEC may be corrected by viral transduction of these cells. As analysis of the hTM function showed modulation under conditions of cellular activation, we suggest that expression of hTM mutants resistant to oxidation may have greater therapeutic utility in the genetic modification of porcine xenografts.
Animals↗
A20 inhibits NF-kappaB activation in endothelial cells without sensitizing to tumor necrosis factor-mediated apoptosis.
Expression of the NF-kappaB-dependent gene A20 in endothelial cells (EC) inhibits tumor necrosis factor (TNF)-mediated apoptosis in the presence of cycloheximide and acts upstream of IkappaBalpha degradation to block activation of NF-kappaB. Although inhibition of NF-kappaB by IkappaBalpha renders cells susceptible to TNF-induced apoptosis, we show that when A20 and IkappaBalpha are coexpressed, the effect of A20 predominates in that EC are rescued from TNF-mediated apoptosis. These findings place A20 in the category of "protective" genes that are induced in response to inflammatory stimuli to protect EC from unfettered activation and from undergoing apoptosis even when NF-kappaB is blocked. From a therapeutic perspective, genetic engineering of EC to express an NF-kappaB inhibitor such as A20 offers the mean of achieving an anti-inflammatory effect without sensitizing the cells to TNF-mediated apoptosis.
Adenoviridae↗
Differential effect of tumor necrosis factor-alpha on thrombomodulin gene expression by human monocytoid (THP-1) cell versus endothelial cells.
Human mononuclear phagocytes (MO) express a functional form of thrombomodulin (TM), the anticoagulant molecule typically considered purely in the context of regulation of conversion of protein C (PC) to activated PC (aPC) by thrombin-bound TM at the endothelial cell surface. We have been interested in the anti-inflammatory actions of aPC, including its ability to suppress MO production of multiple pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1), leading us to consider whether MO surface expression of TM and resultant local aPC generation, might contribute to autoregulation of MO activation at sites of inflammation involving thrombin and fibrin formation. Since TNF-alpha and IL-1 are known to downregulate endothelial expression of TM, this study investigated the effects of TNF-alpha on production of TM by the monocytic leukemic cell line, THP-1. THP-1 cells display many monocyte-like properties, providing a convenient source for biochemical and molecular studies. Western blotting of lysates of THP-1 cells versus cultured human umbilical vein endothelial cells showed that after 24 h of stimulation, TNF-alpha decreased TM protein expression in endothelial but not THP-1 cells and comparable responses were noted by flow cytometry. Subsequent Northern blot analysis showed that at 24 h, TNF-alpha diminished TM steady state mRNA in endothelial but not THP-1 cells, although Northern analysis of the kinetics of TM steady state mRNA did show a rapid and transient modulation by TNF-alpha at 2 h of stimulation, which was confirmed by nuclear run-on analysis of the effect of TNF-alpha on TM gene transcription rates in THP-1 cells, analysis of protein expression by flow cytometry and Western blotting showed similar effects. In contrast to the divergent effects of TNF-alpha on THP-1 vs endothelial cells, agonists such as cyclic adenosine monophosphate (c-AMP) and phorbol ester (PMA) had comparable effects on THP-1 and endothelial cells, resulting in parallel increases or decreases in TM mRNA and protein expression, respectively. Hence, there is a 'split' in the nature of endothelial vs THP-1 cellular responses to TNF-alpha as compared to non-inflammatory stimuli, suggesting cell-specific differences in regulation of the TM promoter. We conclude that in contrast to its effects on TM expression by endothelial cells, exposure of THP-1 cells to TNF-alpha causes a rapid and transient decrease in TM mRNA production which is followed by sustained and high level expression, supporting the concept that MO expression of TM may contribute to regulation of MO activation and cytokine production at inflammatory sites.
Cell Line↗
Expression of heme oxygenase-1 can determine cardiac xenograft survival.
The rejection of concordant xenografts, such as mouse-to-rat cardiac xenografts, is very similar to the delayed rejection of porcine-to-primate discordant xenografts. In concordant models, this type of rejection is prevented by brief complement inhibition by cobra venom factor (CVF) and sustained T-cell immunosuppression by cyclosporin A (CyA). Mouse hearts that survive indefinitely in rats treated with CVF plus CyA express the anti-inflammatory gene heme oxygenase-1 (HO-1) in their endothelial cells and smooth muscle cells. The anti-inflammatory properties of HO-1 are thought to rely on the ability of this enzyme to degrade heme and generate bilirubin, free iron and carbon monoxide. Bilirubin is a potent anti-oxidant, free iron upregulates the transcription of the cytoprotective gene, ferritin, and carbon monoxide is thought to be essential in regulating vascular relaxation in a manner similar to nitric oxide. We show here that the expression of the HO-1 gene is functionally associated with xenograft survival, and that rapid expression of HO-1 in cardiac xenografts can be essential to ensure long-term xenograft survival.
Animals↗
Xenogeneic endothelial cells activate human prothrombin.
BACKGROUND: Delayed xenograft rejection is characterized by platelet activation and fibrin deposition and is thought to occur independently of complement activation. We have therefore investigated the potential for xenogeneic endothelial cells (EC) to regulate the conversion of prothrombin to thrombin, a central component of the final common pathway of coagulation and an important platelet agonist. METHODS AND RESULTS: Quiescent porcine aortic EC (PAEC) were found to convert high levels of human prothrombin to thrombin (0.234+/-0.019 IU/ml) when compared with human aortic EC (0.017+/-0 IU/ml, 30-min time point, chromogenic assay; P<0.001). PAEC activation by human complement resulted in comparable levels of thrombin generation. Prothrombin conversion by PAEC as determined by generation of F1+2 (1.909+/-0.119 nmol/L) and formation of thrombin-antithrombin III complexes (125.611+/-6.373 microg/L) was significantly greater than the matched human aortic EC values (F1+2: 1.539+/-0.03 nmol/L, P<0.001; thrombin-antithrombin III: 1.833+/-0.104 microg/L, P<0.001). Sequential analysis of prothrombin activation by PAEC indicated generation of the intermediate meizothrombin followed by autolytically accelerated thrombin formation. Subsequent experiments established important cross-species' incompatibilities with respect to porcine thrombomodulin interaction with human thrombin and protein C in that PAEC had a reduced capacity to generate activated human protein C in vitro. CONCLUSION: These observations indicate a potentially important molecular barrier involving blood coagulation that may impact on the planned clinical application of porcine transgenic organs.
Animals↗
A physiologic anti-inflammatory pathway based on thrombomodulin expression and generation of activated protein C by human mononuclear phagocytes.
The endothelial molecule thrombomodulin (TM) regulates hemostasis by binding thrombin and promoting conversion of protein C to activated protein C (aPC). Apart from its anticoagulant actions, aPC modulates mononuclear phagocyte (M phi) activation, including TNF-alpha production, indicating interrelationships of the coagulation and immune systems. While the endothelium is considered to be the prime regulator of aPC generation, TM recently has been identified M phi and neutrophils. This study analyzes TM membrane expression by human blood monocytes, alveolar macrophages, and U937 cells cultured in the presence of various stimuli. All except U937 cell expressed high levels of surface TM. Surprisingly, stimulation with LPS or TNF-alpha further up-regulated TM expression by M phi, whereas cultured endothelial cells (EC) showed decreased TM expression. However, noninflammatory stimuli induced qualitatively similar changes in M phi and EC; all-trans retinoic acid and prostaglandin E up-regulated surface TM, and PMA decreased TM expression. Changes in M phi TM expression were accompanied by alteration in functional activity. Thus, LPS increased the TM cofactor activity of THP-1 cells by 27 +/- 6.9% (p < 0.05), and PMA decreased their cofactor activity by 53.2 +/- 11.5% (p < 0.05).In addition, in vivo relevance was demonstrated by the presence of TM on intragraft inflammatory M phi during cardiac rejection, whereas adjacent EC lacked TM expression. These studies demonstrate that expression of TM on human M phi is regulated differently to EC with respect to inflammatory stimuli, suggesting the potential for extravascular M phi to promote local production of aPC.
Anti-Inflammatory Agents↗
Binding of activated protein C to a specific receptor on human mononuclear phagocytes inhibits intracellular calcium signaling and monocyte-dependent proliferative responses.
Upon activation, mononuclear phagocytes (Mphi) play key roles in the development of septic shock and multiple host immune responses, but details of the regulation of Mphi activation are little understood. We recently showed that the physiologic anticoagulant molecule, activated protein C (APC), blocks responses of human blood Mphi, alveolar Mphi, or THP-1 cells induced by LPS, IFN-gamma, or PMA, including TNF-alpha production and down-regulation of several LPS binding-related proteins. We now report a possible mechanism of action through inhibition of the rapid intracellular calcium signaling that occurs at the onset of Mphi activation, and characterization of a specific Mphi receptor for APC. Flow cytometry studies using Fluo-3 showed that Mph activation by Fc-receptor cross-linking or rIFN-gamma caused a rapid increase in free intracellular calcium, a primary event in multiple signal transduction pathways, which was blocked by pretreatment with APC. Consistent with this, addition of APC inhibited PHA-induced T cell proliferation in a dose- and time-dependent manner. Peak suppression (> 70%) required addition of APC within the first hour of 72 hr cocultures of Mphi and lymphocytes, and proliferative responses were not restored by addition of IL-2 or TNF-alpha. Biochemical studies showed that 125I-labeled APC bound specifically to M phi in a time-dependent and saturable manner. Scatchard analysis indicated there were 180,690 binding sites for APC per cell, which were of high affinity (Kd value of 12.9 mM). Binding of 125I-APC was doubled by activation of Mphi with LPS, and bound APC was not displaced by the zymogen, protein C (PC), or by enzymatically inactive (diisopropyl fluorophosphate- or PPACK-treated) APC, indicating an absolute requirement for the active site of APC in its binding to Mphi. APC binding was blocked by a polyclonal Ab to human PC/APC, but not by protein S, factor Va or Xa, or a polyclonal antithrombomodulin antibody. When 125I-APC was crosslinked to its receptor, immunoprecipitated and analyzed by SDS-PAGE under reducing conditions, a covalent complex (110-115 kD) of 125I-APC (62 kD) and its receptor was seen. In addition, a Mphi membrane protein of 50-55 kD, as determined by SDS-PAGE, was affinity-purified using an APC-Affigel column, and confirmed by ligand binding. Taken together, our findings document the presence of a M phi surface receptor for APC, which appears distinct from a recently described endothelial receptor for PC and APC, and which may be involved in the inhibitory effects of APC on activation of human Mphi, including Mphi-dependent T cell proliferation.
Calcium↗
Selective inhibitory effects of the anticoagulant activated protein C on the responses of human mononuclear phagocytes to LPS, IFN-gamma, or phorbol ester.
Recent studies have shown that infusion of the anticoagulant protein, activated protein C (APC), can ameliorate many of the systemic effects of endotoxemia in experimental animals, although the mechanisms in this action are unknown. We investigated the effects of APC on the responses of blood monocytes, alveolar macrophages, and cells of the monocyte line, THP-1, to stimulation in vitro by LPS, IFN-gamma, or PMA. Mononuclear phagocyte (MO) activation was associated with rapid production of TNF-alpha, down-regulation of the glycophosphatidylinositol-linked protein CD14 (the key MO receptor for complexes of LPS and LPS-binding protein responsible for intracellular signaling), and down-regulation of the related LPS-binding proteins CD11b and CD18. Addition of APC, but not the zymogen, PC, or active site-blocked APC, inhibited selected MO responses involving the CD14-dependent LPS-induced pathway of MO activation, or activation induced by IFN-gamma or PMA. Thus, APC inhibited the production of TNF-alpha and prevented down-regulation of membrane CD11b, CD14, and CD18, but had no effect on up-regulation of MHC class II, ICAM-1, or IL-2R, down-regulation of MO expression of another glycophosphatidylinositol-linked protein, CD59, or production of reactive oxygen intermediates. These data show that APC inhibits host cytokine production but maintains MO responses associated with adhesion, phagocytosis, and killing of Gram-negative bacteria, such that use of APC may be a logical and potent adjunctive therapy in select inflammatory diseases involving MO activation and damaging host cytokine overproduction.
Antigens, CD↗
Cellular immune responses in the skin of sheep infected with larvae of Lucilia cuprina, the sheep blowfly.
Cellular immune responses were observed in the skin of sheep after primary and secondary infection with sheep blowfly (Lucilia cuprina) larvae. Both primary and secondary infections resulted in a massive cellular infiltration within 48 h of wound initiation, with the majority of cells having the CD45 phenotype. Neutrophils comprised the major cell type at the skin surface. In the dermis, the number of CD4+ T helper, gamma delta-TCR+ cells and T19+ (CD4-, CD8-) T cells also increased significantly in skin during both primary and secondary infections compared with control sites. However, there was no significant difference in the numbers of these cells between primary and secondary infections. An increase in the expression of the CD1 antigen on Langerhans/dendritic cells was observed, along with an apparent increase in the number of these cells in secondary lesions, with the majority of the cells being concentrated in the upper dermis and epidermis. While there was no increase in mast cells, eosinophils increased significantly during infection compared with control sites. The cellular infiltration observed following primary and secondary infections suggests polyclonal activation of T cells and their selective recruitment to the lesion site.
Animals↗
Adenovirus-mediated gene transfer of A20 in murine islets inhibits Fas-induced apoptosis.
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Adenoviridae↗
Adenovirus-mediated gene transfer of the anti-apoptotic protein A20 in rodent islets inhibits IL-1 beta-induced NO release.
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Adenoviridae↗
A novel function for A20 in smooth muscle cells: inhibition of activation and proliferation.
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Animals↗