Lipopolysaccharide Activates Caspase-1 (Interleukin-1–Converting Enzyme) in Cultured Monocytic and Endothelial Cells

Sirtuins and chemokines as markers of replicative and induced senescence of human endotheliocytes

Background. One of the factors of the pathogenesis of atherosclerosis and other cardiovascular diseases is induced endothelial senescence. In this regard, the urgent task of molecular biology and medicine is the search for molecules that affect the process of vascular endotheliocytes senescence.The aim. To assess the expression of Sirt-1,3,6 and chemokines IL-4, CXCL11 in the replicative and induced senescence of human endotheliocytes.Materials and methods. The study was conducted on the primary culture of isolated human umbilical vein endothelial cells (HUVECs). HUVECs were cultured under conditions of replicative (natural) and lipopolysaccharide induced senescence.Results. The synthesis of Sirt-1,3,6, IL-4 and CXCL11 was evaluated using western blot analysis. We revealed a decrease in Sirt-1,3,6 synthesis by 1.6–1.8 times (р < 0.05) in the conditions of HUVEC replicative senescence. Induced senescence of endotheliocytes is characterized by a more pronounced decrease (1.7–3.4 times; р < 0.05) in the Sirt-1,3,6 synthesis. CXCL11 synthesis increases by 1.4 times (р < 0.05) in replicative and by 3.4 times (р < 0.05) in induced HUVEC senescence. IL-4 synthesis increases by 4.7 times in conditions of induced HUVEC senescence and doesn’t have changes in replicative senescence of endotheliocytes.Conclusion. These data obtained indicate that sirtuins and chemokines play an important role in the development of endothelial dysfunction observed in natural and induced senescence.

Induction of proinflammatory cytokines and caspase-1 by leptin in monocyte/macrophages from holstein cows

The proliferation of peripheral blood mononuclear cells (PBMC) containing both monocyte/macrophages and T lymphocytes increased after treatment with T-cell mitogen (concanavalin A: Con A). PBMC treated with either leptin alone or combination of leptin and ConA showed enhanced proliferative activity by 10-40%, compared with those treated with ConA alone. In contrast, isolated T lymphocytes treated with leptin and ConA showed lowered proliferative activity than the ConA-treated alone, indicating that leptin induced production of some cytokines from monocyte/macrophages, that subsequently resulted in enhancement of T lymphocytes proliferation in PBMC. Among the cytokines examined, monocyte/monocytes constitutively expressed interleukin (IL)-1beta, IL-12p35, IL-18 mRNA, and faintly expressed tumor necrosis factor (TNF)-alpha and IL-12p40 mRNA. Leptin treatment augmented the monocyte/macrophages mRNA expression of only TNF-alpha and IL-12p40 to comparable levels of cells treated with lipopolysaccharide (LPS). However, leptin treatment increased monocyte/macrophages production of IL-1beta as well as TNF-alpha, and induced the mRNA expression of caspase-1, which is shown to mediate the conversion of latent pro-IL-1beta and pro-IL-18 to active forms. These results suggest that leptin directly acts on monocyte/macrophages to produce factors that induce T lymphocytes proliferation such as IL-12p35/p40 complex through IL-12p40 induction and IL-1beta/IL-18 production through caspase-1 induction.

Adenosine A2A-receptor stimulation inhibits lipopolysaccharide-induced interleukin-18 production in monocytes

Adenosine inhibited interleukin (IL)-18 production in lipopolysaccharide (LPS)-stimulated monocytes. The action of adenosine was antagonized by an adenosine A2A-receptor (A2AR) antagonist and was mimicked by an A2AR agonist, suggesting that the stimulation of A2AR may be involved in the actions of adenosine. On the other hand, the stimulation of A1R and A3R inhibited the actions of A2AR stimulation, whereas the stimulation of A2BR had no effect on them. Activation of A2AR is known to increase cyclic adenosine monophosphate (cAMP) levels and to activate protein kinase A (PKA). A PKA inhibitor prevented the actions of A2AR stimulation, indicating that the action mechanism of A2AR stimulation may be via the activation of the cAMP/PKA pathway.

alpha7 Nicotinic acetylcholine receptor stimulation inhibits lipopolysaccharide-induced interleukin-18 and -12 production in monocytes

Nicotine inhibited interleukin (IL)-18 and -12 production in lipopolysaccharide (LPS)-stimulated monocytes, and the action of nicotine was antagonized by a non-selective and a selective alpha7 nicotinic acetylcholine receptor (alpha7-nAChR) antagonist, suggesting that the stimulation of alpha7-nAChR may be involved in the action of nicotine. Nicotine is reported to induce prostaglandin E(2) (PGE(2)) production in monocytes through the up-regulation of cyclooxygenase (COX)-2 expression. PGE(2) is known to increase cAMP levels and to activate protein kinase A (PKA). COX-2 and PKA inhibitors prevented the action of nicotine, indicating that the mechanism of action of nicotine may be via endogenous PGE(2) production.

Evidence for nucleotide receptor modulation of cross talk between MAP kinase and NF-kappa B signaling pathways in murine RAW 264.7 macrophages

Extracellular nucleotides such as ATP are present in abundance at sites of inflammation and tissue damage, and these agents exert a potent modulatory effect on macrophage/monocyte function via the nucleotide receptor P2X(7). In this regard, after exposure to bacterial LPS, P2X(7) activation augments expression of the inducible nitric oxide (NO) synthase and production of NO in macrophages. Because P2X(7) has been reported to stimulate certain members of the MAP kinase family (ERK1/2) and can enhance the DNA-binding activity of NF-kappa B, we tested the hypothesis that LPS and nucleotides regulate NF-kappa B-dependent inflammatory events via cross talk with MAPK-associated pathways. In this regard, the present studies revealed that cotreatment of macrophages with LPS and the P2X(7)-selective ligand 2'-3'-O-(4-benzoylbenzoyl)adenosine 5'-triphosphate (BzATP) results in the cooperative activation of NF-kappa B DNA-binding activity and a sustained attenuation of levels of the NF-kappa B inhibitory protein I kappa B alpha. Interestingly, a persistent reduction in I kappa B alpha levels is also observed when the MEK1/2 inhibitor U0126 is coadministered with LPS, suggesting that components of the MEK/ERK pathway are involved in regulating I kappa B alpha protein expression and/or turnover. The observation that U0126 and BzATP exhibit overlapping actions with respect to LPS-induced changes in I kappa B alpha levels is supported by the finding that Ras activation, which is upstream of MEK/ERK activation, is reduced upon macrophage cotreatment with BzATP and LPS compared with the effects of BzATP treatment alone. These data are consistent with the concept that the Ras/MEK/ERK pathways are involved in regulating NF-kappa B/I kappa B-dependent inflammatory mediator production and suggest a previously unidentified mechanism by which nucleotides can modulate LPS-induced action via cross talk between NF-kappa B and Ras/MEK/MAPK-associated pathways.

Lipopolysaccharide Inhibits TNF-Induced Apoptosis: Role of Nuclear Factor-κB Activation and Reactive Oxygen Intermediates

LPS, a component of the cell wall in Gram-negative bacteria, induces inflammation and septic shock syndrome by stimulating various inflammatory cytokines including TNF. How LPS affects the TNF-mediated cellular responses, however, is not understood. In this study, the effect of LPS on TNF-mediated apoptosis in human histiocytic lymphoma U-937 cells was investigated. We found that treatment of cells with LPS completely abolished TNF-mediated cytotoxicity and activation of caspase-3. LPS-chelating antibiotic, polymyxin B, suppressed the antiapoptotic activity, indicating the specificity of the effect. Within minutes, LPS through CD14 induced the activation of NF-κB, degradation of IκBα (inhibitory subunit of NF-κB) and IκBβ, and nuclear translocation of p65. An antioxidant, pyrrolidine dithiocarbamate, which blocked LPS-induced NF-κB activation, also abolished the antiapoptotic effects of LPS at the same time. Besides TNF, the apoptosis induced by taxol and okadaic acid was also sensitive to LPS-induced NF-κB activation, whereas that induced by H2O2, doxorubicin, daunomycin, vincristine, and vinblastine was NF-κB insensitive. Tumor cells that constitutively expressed NF-κB also showed resistance to the apoptotic effects of TNF, taxol, and okadaic acid, but sensitivity to all other agents, indicating the critical role of NF-κB in blocking apoptosis induced by certain agents. Overall, these results indicate that LPS induces resistance to the apoptotic effects of TNF and other agents, and that NF-κB activation, whether induced or constitutive, inhibits this apoptosis.

Lipopolysaccharide Induces the Antiapoptotic Molecules, A1 and A20, in Microvascular Endothelial Cells

The effect of lipopolysaccharide (LPS) on endothelial cells is a key component of the inflammatory response seen in Gram-negative sepsis. LPS does not cause death of cultured human endothelial cells. However, when the expression of new proteins is inhibited by cycloheximide, microvascular endothelial cells in culture undergo apoptosis. This finding suggests that LPS induces apoptotic and antiapoptotic pathways, with the antiapoptotic response being dependent on the synthesis of new proteins. Concurrent activation of apoptotic and antiapoptotic pathways has previously been documented for tumor necrosis factor (TNF). In the case of TNF, the antiapoptotic signal has been attributed to at least two cytoprotective proteins: the Bcl-2 homologue, A1, and the zinc-finger protein, A20. In this study, we demonstrate that both these molecules are induced in microvascular endothelial cells by LPS. Enforced overexpression of either A1 or A20 inhibits LPS and cycloheximide-initiated apoptosis. Induction of A1 and A20 does not require synthesis of intermediary proteins, but is dependent on the presence of soluble CD14. In addition, we show that inhibition of signaling by the transcription factor, NF-κB, blocks accumulation of A1 and A20 mRNA. Taken together, our findings suggest that LPS directly induces expression of the cytoprotective proteins, A1 and A20, via a CD14-dependent pathway requiring activation of NF-κB.

© 1998 by The American Society of Hematology.