- Medizin (6) (remove)
- 5-Lipoxygenase contributes to PPAR [gamma] activation in macrophages in response to apoptotic cells (2012)
- Background: One hallmark contributing to immune suppression during the late phase of sepsis is macrophage polarization to an anti-inflammatory phenotype upon contact with apoptotic cells (AC). Taking the important role of the nuclear receptor PPARγ for this phenotype switch into consideration, it remains elusive how AC activate PPARγ in macrophages. Therefore, we were interested to characterize the underlying principle. Methods: Apoptosis was induced by treatment of Jurkat T cells for 3 hours with 0.5 μg/ml staurosporine. Necrotic cells (NC) were prepared by heating cells for 20 minutes to 65°C. PPARγ activation was followed by stably transducing RAW264.7 macrophages with a vector encoding the red fluorescent protein mRuby after PPARγ binding to 4 × PPRE sites downstream of the reporter gene sequence. This readout was established by treatment with the PPARγ agonist rosiglitazone (1 μM) and AC (5:1). Twenty-four hours after stimulation, mRuby expression was analysed by fluorescence microscopy. Lipid rafts of AC, NC, as well as living cells (LC) were enriched by sucrose gradient centrifugation. Fractions were analysed for lipid raft-associated marker proteins. Lipid rafts were incubated with transduced RAW264.7 macrophages as described above. 5-Lipoxygenase (5-LO) involvement was verified by pharmacological inhibition (MK-866, 1 μM) and overexpression. Results: Assuming that the molecule responsible for PPARγ activation in macrophages is localized in the cell membrane of AC, most probably associated to lipid rafts, we isolated lipid rafts from AC, NC and LC. Mass spectrometric analysis of lipid rafts of AC showed the expression of 5-LO, whereas lipid rafts of LC did not. Moreover, incubating macrophages with lipid rafts of AC induced mRuby expression. In contrast, lipid rafts of NC and LC did not. To verify the involvement of 5-LO in activating PPARγ in macrophages, Jurkat T cells were incubated for 30 minutes with the 5-LO inhibitor MK-866 (1 μM) before apoptosis induction. In line with our hypothesis, these AC did not induce mRuby expression. Finally, although living Jurkat T cells overexpressing 5-LO did not activate PPARγ in macrophages, mRuby expression was significantly increased when AC were generated from 5-LO overexpressing compared with wild-type Jurkat cells. Conclusion: Our results suggest that induction of apoptosis activates 5-LO, localizing to lipid rafts, necessary for PPARγ activation in macrophages. Therefore, it will be challenging to determine whether 5-LO activity in AC, generated from other cell types, correlates with PPARγ activation, contributing to an immune-suppressed phenotype in macrophages.
- Selective non-steroidal glucocorticoid receptor agonists attenuate inflammation but do not impair intestinal epithelial cell restitution in vitro (2012)
- Introduction: Despite the excellent anti-inflammatory and immunosuppressive action of glucocorticoids (GCs), their use for the treatment of inflammatory bowel disease (IBD) still carries significant risks in terms of frequently occurring severe side effects, such as the impairment of intestinal tissue repair. The recently-introduced selective glucocorticoid receptor (GR) agonists (SEGRAs) offer anti-inflammatory action comparable to that of common GCs, but with a reduced side effect profile. Methods: The in vitro effects of the non-steroidal SEGRAs Compound A (CpdA) and ZK216348, were investigated in intestinal epithelial cells and compared to those of Dexamethasone (Dex). GR translocation was shown by immunfluorescence and Western blot analysis. Trans-repressive effects were studied by means of NF-κB/p65 activity and IL-8 levels, trans-activation potency by reporter gene assay. Flow cytometry was used to assess apoptosis of cells exposed to SEGRAs. The effects on IEC-6 and HaCaT cell restitution were determined using an in vitro wound healing model, cell proliferation by BrdU assay. In addition, influences on the TGF-β- or EGF/ERK1/2/MAPK-pathway were evaluated by reporter gene assay, Western blot and qPCR analysis. Results: Dex, CpdA and ZK216348 were found to be functional GR agonists. In terms of trans-repression, CpdA and ZK216348 effectively inhibited NF-κB activity and IL-8 secretion, but showed less trans-activation potency. Furthermore, unlike SEGRAs, Dex caused a dose-dependent inhibition of cell restitution with no effect on cell proliferation. These differences in epithelial restitution were TGF-β-independent but Dex inhibited the EGF/ERK1/2/MAPK-pathway important for intestinal epithelial wound healing by induction of MKP-1 and Annexin-1 which was not affected by CpdA or ZK216348. Conclusion: Collectively, our results indicate that, while their anti-inflammatory activity is comparable to Dex, SEGRAs show fewer side effects with respect to wound healing. The fact that SEGRAs did not have a similar effect on cell restitution might be due to a different modulation of EGF/ERK1/2 MAPK signalling.
- 5-Lipoxygenase: underappreciated role of a pro-inflammatory enzyme in tumorigenesis (2010)
- Leukotrienes constitute a group of bioactive lipids generated by the 5-lipoxygenase (5-LO) pathway. An increasing body of evidence supports an acute role for 5-LO products already during the earliest stages of pancreatic, prostate, and colorectal carcinogenesis. Several pieces of experimental data form the basis for this hypothesis and suggest a correlation between 5-LO expression and tumor cell viability. First, several independent studies documented an overexpression of 5-LO in primary tumor cells as well as in established cancer cell lines. Second, addition of 5-LO products to cultured tumor cells also led to increased cell proliferation and activation of anti-apoptotic signaling pathways. 5-LO antisense technology approaches demonstrated impaired tumor cell growth due to reduction of 5-LO expression. Lastly, pharmacological inhibition of 5-LO potently suppressed tumor cell growth by inducing cell cycle arrest and triggering cell death via the intrinsic apoptotic pathway. However, the documented strong cytotoxic off-target effects of 5-LO inhibitors, in combination with the relatively high concentrations of 5-LO products needed to achieve mitogenic effects in cell culture assays, raise concern over the assignment of the cause, and question the relationship between 5-LO products and tumorigenesis. Keywords: leukotriene, apoptosis, cell proliferation, mitogenic effects, cytotoxicity
- Peroxisome Proliferator-Activated Receptor alpha (PPAR alpha) down-regulation in cystic fibrosis lymphocytes (2006)
- Background PPARs exhibit anti-inflammatory capacities and are potential modulators of the inflammatory response. We hypothesized that their expression and/or function may be altered in cystic fibrosis (CF), a disorder characterized by an excessive host inflammatory response. Methods PPARα, β and γ mRNA levels were measured in peripheral blood cells of CF patients and healthy subjects via RT-PCR. PPARα protein expression and subcellular localization was determined via western blot and immunofluorescence, respectively. The activity of PPARα was analyzed by gel shift assay. Results In lymphocytes, the expression of PPARα mRNA, but not of PPARβ, was reduced (-37%; p < 0.002) in CF patients compared with healthy persons and was therefore further analyzed. A similar reduction of PPARα was observed at protein level (-26%; p < 0.05). The transcription factor was mainly expressed in the cytosol of lymphocytes, with low expression in the nucleus. Moreover, DNA binding activity of the transcription factor was 36% less in lymphocytes of patients (p < 0.01). For PPARα and PPARβ mRNA expression in monocytes and neutrophils, no significant differences were observed between CF patients and healthy persons. In all cells, PPARγ mRNA levels were below the detection limit. Conclusion Lymphocytes are important regulators of the inflammatory response by releasing cytokines and antibodies. The diminished lymphocytic expression and activity of PPARα may therefore contribute to the inflammatory processes that are observed in CF.
- Wie sekundäre Pflanzeninhaltsstoffe uns vor Krankheiten schützen : von molekularen Wirkmechanismen zu neuen Medikamenten (2006)
- Wirkungen von Heilpflanzen, Gewürzen, Tees und Lebensmitteln werden in der Naturheilkunde seit der Antike genutzt. Pharmakologisch wirksam sind in der Regel nur die sekundären Pflanzeninhaltsstoffe. Diese in den oft aus vielen Bestandteilen zusammengesetzten Naturstoffen aufzuspüren und ihren molekularbiologischen Wirkungsmechanismus im Körper aufzuklären, ist das Ziel eines Forschungsnetzwerks am Frankfurter ZAFES (Zentrum für Arzneimittelforschung, -Entwicklung und -Sicherheit). So konnten Pharmazeuten und Kliniker gemeinsam herausfinden, wie ein Bestandteil des Rotweins, das Resveratrol, vor Darmkrebs schützt. Die Inhaltsstoffe von Salbei und Rosmarin bieten vielversprechende Ausgangspunkte für neue Medikamente gegen Altersdiabetes. Weihrauch, Myrte und Johanniskraut enthalten Wirkstoffe, die Schlüsselenzyme für Entzündungsreaktionen – etwa bei rheumatischen Beschwerden – hemmen.
- Trichostatin A induces 5-lipoxygenase promoter activity and mRNA expression via inhibition of histone deacetylase 2 and 3 (2012)
- The 5-lipoxygenase (5-LO) is the key enzyme in the formation of leukotrienes. We have previously shown that the histone deacetylase (HDAC) inhibitor trichostatin A (TSA) activates 5-LO transcription via recruitment of Sp1, Sp3 and RNA polymerase II to the proximal promoter. To identify the HDACs involved in the regulation of 5-LO promoter activity isoform-specific HDAC inhibitors were applied. 5-LO promoter activity and mRNA expression were up-regulated by the class I HDAC inhibitors apicidin and MS-275 but not by class II inhibitors. Knockdown of HDAC 1, 2 and 3 revealed that HDAC2 and HDAC3 but not HDAC1 is involved in the up-regulation of 5-LO mRNA expression. To analyse the chromatin modifications at the 5-LO promoter associated with HDAC inhibition, the time course of 5-LO mRNA induction by trichostatin A was investigated and the concomitant changes in histone modifications at the 5-LO promoter in HL-60, U937 and Mono Mac6 cells were determined. Chromatin immunoprecipitation analysis revealed that trichostatin A increases acetylation of histones H3 and H4 at the 5-LO core promoter in HL-60 and U937 cells whereas no significant changes were observed in Mono Mac6 cells. The appearance of H3 and H4 acetylation preceded the 5-LO mRNA induction whereas in all three cell lines, induction of 5-LO mRNA expression correlated with histone H3 lysine 4 trimethylation (H3K4me3), a marker for transcriptional activity of gene promoters.