490 research outputs found
Cross-talk between the signals hypoxia and glucose at the glucose response element of the L-type pyruvate kinase gene
No full textThe signals oxygen and glucose play an important role in metabolism, angiogenesis, tumorigenesis, and embryonic development. Little is known about an interaction of these two signals. We demonstrate here the cross-talk between oxygen and glucose in the regulation of L-type pyruvate kinase (L-PK) gene expression in the liver. In the liver the periportal to perivenous drop in O-2 tension was proposed to be an endocrine key regulator for the zonated gene expression. In primary rat hepatocyte cultures the expression of the L-PK gene on mRNA and on protein level was induced by venous pO(2), whereas its glucose-dependent induction occurred predominantly under arterial pO(2). It was shown by transient transfection of L-PK promoter luciferase and glucose response element (Glc(PK)RE) SV40 promoter luciferase gene constructs that the modulation by O-2 of the glucose-dependent induction occurred at the Glc(PK)RE in the L-PK gene promoter. The reduction of the glucose-dependent induction of the L-PK gene expression under venous pO(2) appeared to be mediated via an interference between hypoxia inducible factor-1 (HIF-1) and upstream stimulating factor at the Glc(PK)RE. The glucose response element also functioned as an hypoxia response element which was confirmed in cotransfection assays with Glc(PK)RE luciferase gene constructs and HIF-1 alpha expression vectors. Furthermore, it was found by gel shift and supershift assay that HIF-1 alpha and USF-1 or USF-2 could bind to the Glc(PK)RE. Our findings implicate that the cross-talk between oxygen and glucose might have a fundamental role in the regulation of several physiological and pathophysiological processes
Re-evaluation of thin layer chromatography as an alternative method for the quantification of prostaglandins from rat Kupffer cells
No full textIn contrast to conventionally used inummoassays, thin layer chromatography (TLC)-by prelabeling of cells with radioactive arachidonic acid (AA)-allows to differentiate between cellularly built and added prostanoids and thus to investigate feedback effects of prostanoids on their own release. PGD(2), TXB2 and PGE(2) released from zymosan-stimulated Kupffer cells were separated with distinct R-F-values, corresponding to those of the pure substances. Quantification of PGD(2) and PGE(2) gave comparable results with TLC and immunoassays, but measurement in the presence of added prostanoids was only possible with TLC. Moreover TLC was superior to immunoassays in having a longer linear range while being comparably sensitive. Cellularly built TXB2 in its radioactively labeled form was not detectable by TLC. Inhibition of TXB2 release by externally added AA or technical artifacts were excluded, suggesting that the cellular AA-pools used for prostaglandin and thromboxane synthesis differ in their accessibility for added AA. Thus, TLC is a simple, sensitive and precise method for the quantification of cellularly built prostaglandins but not of thromboxane even in the presence of added prostanoids. (c) 2004 Elsevier Inc. All rights reserved
Inhibition of prostaglandin D-2 clearance in rat hepatocytes by the thromboxane receptor antagonists daltroban and ifetroban and the thromboxane synthase inhibitor furegrelate
No full textProstanoids, i.e. prostaglandins and thromboxane, regulate liver-specific functions both in homeostasis and during defense reactions. For example, prostanoids are released from Kupffer cells, the resident liver macrophages, in response to the inflammatory mediator anaphylatoxin C5a, and mediate an enhanced glucose output from hepatocytes as energy supply. In perfused rat livers, the thromboxane receptor antagonist daltroban enhanced C5a-induced prostanoid overflow and reduced glucose output. It was the aim of this study to elucidate whether daltroban interfered with prostanoid release from Kupffer cells or prostanoid clearance by hepatocytes, and/or whether it directly influenced prostanoid-dependent glucose metabolism in these cells. In perfused rat livers, daltroban enhanced prostaglandin (PG)D, overflow not only after infusion of C5a (15-fold), but also after PGD(2) (10-fold). Neither daltroban nor another receptor antagonist, ifetroban, or the thromboxane synthase inhibitor furegrelate enhanced prostanoid release from Kupffer cells. In contrast, all inhibitors reduced clearance, i.e. uptake and degradation, of PGD2 by hepatocytes: within 5 min uptake of 1 nmol/L PGD(2) was reduced from 43 +/- 5 fmol (controls) to 22 +/- 6 fmol (daltroban), 24 +/- 6 fmol (ifetroban) and 21 +/- 6 fmol (furegrelate). PGD(2) in the medium was reduced to 39 +/- 7% in the controls, but remained at 93 +/- 9%, 93 +/- 11% and 60 +/- 3% in the presence of the inhibitors. PGD(2)-dependent glucose output in the perfused liver or activation of glycogen phosphorylase in isolated hepatocytes remained unaffected by daltroban. These data clearly demonstrate that the thromboxane-inhibitors reduced PGD(2) clearance by hepatocytes, presumably by inhibition of prostanoid transport into the cells. In contrast, they did not interfere with PGD(2)-dependent glucose metabolism, suggesting an independent mechanism for the inhibition of glucose output from the liver. (C) 2003 Elsevier Inc. All rights reserved
Signaling cross-talk between hypoxia and glucose via hypoxia-inducible factor 1 and glucose response elements
No full textThe substrates oxygen and glucose are important for the appropriate regulation of metabolism, angiogenesis, tumorigenesis and embryonic development. The knowledge about an interaction between these two signals is limited. We demonstrated that the regulation of glucagon receptor, insulin receptor and L-type pyruvate kinase (L-PK) gene expression in liver is dependent upon a cross-talk between oxygen and glucose. The periportal to perivenous drop in O-2 tension was proposed to be an endocrine key regulator for the zonated gene expression in liver. In primary rat hepatocyte cultures, the expression of the glucagon receptor and the L-PK mRNA was maximally induced by glucose under arterial pO(2) whereas the insulin receptor was maximally induced under perivenous pO(2). It was demonstrated for the L-PK gene that the modulation by O-2 of the glucose-dependent induction occured at the glucose-responsive element (Glc(PK)RE) in the L-PK gene promoter. The reduction of the glucose-dependent induction of the L-PK gene expression under venous pO(2) appeared to be mediated via an interference between hypoxia-inducible factor I (HIF-1) and the glucose-responsive transcription factors at the Glc(PK)RE. The glucose response element (GlcRE) also functioned as a hypoxia response element and, vice versa, a hypoxia-responsive element was functioning as a GlcRE. Thus, our findings implicate that the cross-talk between oxygen and glucose might have a fundamental role in the regulation of several physiological and pathophysiological processes. (C) 2002 Elsevier Science Inc. All rights reserved
Functions of anaphylatoxin C5a in rat liver: direct and indirect actions on nonparenchymal and parenchymal cells
No full textGrowing evidence obtained in recent years indicates that anaphylatoxin C5a receptors (C5aR) are not restricted to myeloid cells but are also expressed on nonmyeloid cells in different tissues such as brain, lung, skin and liver. In contrast to its well-defined systemic functions, the actions of anaphylatoxins in these organs are poorly characterized. The liver can be a primary target organ for the C5a anaphylatoxin since the liver is directly connected to the gut, via the mesenteric veins and portal vein which is a main source of complement activating lipopolysaccharides (LPS). In the normal rat liver, the C5aR is only expressed by nonparenchymal cells, i.e. strongly by Kupffer cells (KC) and hepatic stellate cells (HSC) and weakly by sinusoidal endothelial cells (SEC), bur not expressed by the parenchymal hepatocytes (HC). Accordingly, direct effects of C5a were only found in the C5aR-expressing KC and HSC: C5a induced thr release of prostanoids from KC and HSC and enhanced the UPS-dependent release of interleukin-6 from KC, These soluble mediators indirectly influenced effector functions of the C5aR-free HC. C5a enhanced the glycogen phosphorylase activity and thus the glucose output from HC indirectly via prostanoids released from KC and HSC. Glucose can serve as an energy substrate as well as an electron donor for the synthesis of reactive oxygen intermediates by KC. Moreover, C5a also enhanced transcription of the gene for the type-2 acute phase protein alpha (2)-macroglobulin in HC indirectly by increasing LPS-dependent IL-6 release from KC. Under pathological conditions. C5aR was found to be upregulated in various organs including the liver. Simulation of inflammatory conditions by treatment of rats with IL-6, a main inflammatory mediator in the liver, caused a de novo expression of functional C5aR in HC. In livers of IL-6-treated rats, C5a initiated glucose output from HC and perhaps other HC-specific defense reactions directly without the intervention of soluble mediators from nonparenchymal cells. (C) 2001 Elsevier Science B.V, All rights reserved
Inhibition by prostaglandin E-2 of anaphylatoxin C5a - but not zymosan-induced prostanoid release from rat Kupffer cells
No full textThe proinflammatory anaphylatoxin C5a induces the release of prostanoids, le, prostaglandins (PG) and thromboxane (TX), from the resident liver macrophages (Kupffer cells [KC]). Because KC themselves express prostanoid receptors, prostanoids-besides having paracrine functions-might regulate their own release in an autocrine loop. So far, such a possible feedback regulation has not been investigated systematically, probably because of methodological difficulties to measure newly synthesized prostanoids in the presence of added prostanoids. Here, after prelabeling of phospholipids with [C-14]arachidonate, cellularly formed [C-14] prostanoids were determined in the presence of added unlabelled prostanoids by thin layer chromatography. In cultured KC, recombinant rat C5a (rrC5a) rapidly increased PGD(2), PGE(2), and TXA(2) release, which was strongly reduced by PGE(2), but neither by PGD(2) nor by the TXA(2) analog U46619. The inhibitory effect of PGE(2) was mimicked by cAMP, indicating that the G(s)-coupled PGE(2) receptors type 2 or 4 were involved. Zymosan also enhanced prostanoid release from KC, but with slightly slower kinetics; this action was neither inhibited by PGE2 nor by cAMP. Also in perfused rat livers, rrC5a enhanced prostanoid release from KC as shown by prostanoid overflow and thereby indirectly increased glucose output from hepatocytes. Again, PGE(2), but not PGD(2), inhibited rrC5a-elicited prostanoid overflow. This resulted in a complete inhibition of rrC5a-incluced, prostanoid-mediated glucose output. Thus, PGE2 can inhibit specifically the C5a-induced prostanoid release from KC via a feedback mechanism and thereby limit prostanoid-mediated hepatocellular defense reactions, eg, glucose release
Anaphylatoxin C5a actions in rat liver: Synergistic enhancement by C5a of lipopolysaccharide-dependent alpha(2)-macroglobulin gene expression in hepatocytes via IL-6 release from Kupffer cells
No full textThe effects of the anaphylatoxins C5a and C3a on the liver are only poorly characterized in contrast to their well known systemic actions. Recently, it has been demonstrated that the anaphylatoxin C5a enhanced glucose output from hepatocytes (HC) indirectly via prostanoid release from Kupffer cells (KC). In the present study, it is shown that recombinant rat C5a (rrC5a), together with LPS, activated the gene of the acute phase protein alpha (2)-macroglobulin (alpha (2)MG) in HC also indirectly via IL-6 release from KC. RrC5a alone increased neither IL-6 mRNA in nor IL-6 release from KC, whereas LPS alone did so. However, rrC5a synergistically enhanced the LPS-dependent increase in IL-6 mRNA and IL-6 release. Only rIL-6, but not TNF-alpha or IL-1 beta, enhanced a2MG mRNA in HC. In line with the actions of rrC5a and LPS on KC, conditioned medium of KC stimulated only with rrC5a did not increase alpha (2)MG mRNA in HC. However, medium of KC stimulated with rrC5a plus LPS induced alpha (2)MG mRNA expression in HC more strongly than medium from cells stimulated only with LPS; thus, C5a acted synergistically with LPS. The stimulatory effects of KC-conditioned medium could partially be inhibited by a neutralizing anti-IL-6 All, indicating that KC-derived IL-6 was a major mediator in C5a- plus LPS-elicited alpha (2)MG gene expression. These results suggest that C5a, besides enhancing glucose output via prostanoids, is involved in the initiation of the acute phase response in HC via proinflammatory cytokines from KC. This provides evidence for another important function of C5a in the regulation of hepatocellular defense reactions
Inhibition by prostaglandin E-2 of anaphylatoxin C5a - but not zymosan-induced prostanoid release from rat Kupffer cells
No full textThe proinflammatory anaphylatoxin C5a induces the release of prostanoids, le, prostaglandins (PG) and thromboxane (TX), from the resident liver macrophages (Kupffer cells [KC]). Because KC themselves express prostanoid receptors, prostanoids-besides having paracrine functions-might regulate their own release in an autocrine loop. So far, such a possible feedback regulation has not been investigated systematically, probably because of methodological difficulties to measure newly synthesized prostanoids in the presence of added prostanoids. Here, after prelabeling of phospholipids with [C-14]arachidonate, cellularly formed [C-14] prostanoids were determined in the presence of added unlabelled prostanoids by thin layer chromatography. In cultured KC, recombinant rat C5a (rrC5a) rapidly increased PGD(2), PGE(2), and TXA(2) release, which was strongly reduced by PGE(2), but neither by PGD(2) nor by the TXA(2) analog U46619. The inhibitory effect of PGE(2) was mimicked by cAMP, indicating that the G(s)-coupled PGE(2) receptors type 2 or 4 were involved. Zymosan also enhanced prostanoid release from KC, but with slightly slower kinetics; this action was neither inhibited by PGE2 nor by cAMP. Also in perfused rat livers, rrC5a enhanced prostanoid release from KC as shown by prostanoid overflow and thereby indirectly increased glucose output from hepatocytes. Again, PGE(2), but not PGD(2), inhibited rrC5a-elicited prostanoid overflow. This resulted in a complete inhibition of rrC5a-incluced, prostanoid-mediated glucose output. Thus, PGE2 can inhibit specifically the C5a-induced prostanoid release from KC via a feedback mechanism and thereby limit prostanoid-mediated hepatocellular defense reactions, eg, glucose release
Induction of anaphylatoxin C5a receptors in rat hepatocytes by lipopolysaccharide in vivo: Mediation by interleukin-6 from Kupffer cells
No full textBackground & Aims: In normal rat liver, anaphylatoxin C5a induces glucose output from hepatocytes indirectly via prostanoids released from Kupffer cells. Correspondingly, it was found that hepatocytes, in contrast to Kupffer cells, did not express C5a receptors. Lipopolysaccharide (LPS) has been reported to enhance C5a receptor expression in murine livers. This might be the result of de novo expression in hepatocytes. Methods: C5a receptor expression was Investigated in hepatocytes after in vivo treatment of rats with LPS and in vitro stimulation of isolated cells with LPS and proinflammatory cytokines on messenger RNA (mRNA) and protein level, and functionally in isolated epatocytes and perfused liver. Results: In vivo treatment of rats with LPS induced C5a receptor mRNA and protein in hepatocytes with a maximum after 8-10 hours. At this time-point, C5a directly activated glycogen phosphorylase in isolated hepatocytes and enhanced glucose output in perfused livers without the involvement of prostanoids. LPS failed to induce C5a receptors in cultured hepatocytes in vitro, whereas interleukin (IL) 6 and IL-1beta, which are known to be released from Kupffer cells on stimulation with LPS, did so, In cocultures of hepatocytes with Kupffer cells, LPS induced C5a receptors in hepatocytes in an IL-6-dependent manner. Conclusions: Thus, IL-6 from Kupffer cells appears to be the main mediator of LPS-Induced de novo expression of C5a receptors in hepatocytes
Ludovicus Jungermannus ...
No full textBotanico: Jungermann, Ludwig.
Titolo sul recto, dove comapre anche la nota manoscritta: Jungermann.
1 incisione ; 216 x 165 mm.
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