Refine
Year of publication
Document Type
- Article (97)
Language
- English (97)
Has Fulltext
- yes (97)
Is part of the Bibliography
- no (97)
Keywords
- inflammation (16)
- macrophage (14)
- cancer (7)
- breast cancer (6)
- macrophages (6)
- apoptosis (5)
- macrophage polarization (5)
- sphingosine-1-phosphate (5)
- hypoxia (4)
- lipocalin-2 (4)
Institute
- Medizin (95)
- Sonderforschungsbereiche / Forschungskollegs (36)
- Biochemie und Chemie (13)
- Zentrum für Arzneimittelforschung, Entwicklung und Sicherheit (6)
- Biochemie, Chemie und Pharmazie (3)
- Exzellenzcluster Makromolekulare Komplexe (2)
- Pharmazie (2)
- Biowissenschaften (1)
- Buchmann Institut für Molekulare Lebenswissenschaften (BMLS) (1)
- Institut für Ökologie, Evolution und Diversität (1)
Macrophages ingesting apoptotic cells attenuate inflammatory responses, such as reactive oxygen species (ROS) generation. In atherosclerosis, ongoing inflammation and accumulation of apoptotic/necrotic material are observed, suggesting defects of phagocytes in recognizing or responding to dying cells. Modified lipoproteins such as oxidized LDL (oxLDL) are known to promote inflammation and to interfere with apoptotic cell clearance. Here, we studied the impact of cells exposed to oxLDL on their ability to interfere with the oxidative burst in phagocytes. In contrast to apoptotic cells, cells dying in response to or in the presence of oxLDL failed to suppress ROS generation despite efficiently being taken up by phagocytes. In addition, apoptotic cells, but not oxLDL-treated cells, inhibited phosphorylation of extracellular signal-regulated kinase, which is important for NADPH oxidase activation. oxLDL treatment did not interfere with activation of the antiinflammatory transcriptional regulator peroxisome proliferator-activated receptor gamma by apoptotic cells. Moreover, cells exposed to oxLDL failed to suppress lipopolysaccharide- induced proinflammatory cytokine expression, whereas apoptotic cells attenuated these phagocyte responses. Thus, the presence of oxLDL during cell death impaired the ability of apoptotic cells to act antiinflammatory with regard to oxidative burst inhibition and cytokine expression in phagocytes.
Bacterial and fungal toll-like receptor activation elicits type I IFN responses in mast cells
(2021)
Next to their role in IgE-mediated allergic diseases and in promoting inflammation, mast cells also have antiinflammatory functions. They release pro- as well as antiinflammatory mediators, depending on the biological setting. Here we aimed to better understand the role of mast cells during the resolution phase of a local inflammation induced with the Toll-like receptor (TLR)-2 agonist zymosan. Multiple sequential immunohistology combined with a statistical neighborhood analysis showed that mast cells are located in a predominantly antiinflammatory microenvironment during resolution of inflammation and that mast cell-deficiency causes decreased efferocytosis in the resolution phase. Accordingly, FACS analysis showed decreased phagocytosis of zymosan and neutrophils by macrophages in mast cell-deficient mice. mRNA sequencing using zymosan-induced bone marrow-derived mast cells (BMMC) revealed a strong type I interferon (IFN) response, which is known to enhance phagocytosis by macrophages. Both, zymosan and lipopolysaccharides (LPS) induced IFN-β synthesis in BMMCs in similar amounts as in bone marrow derived macrophages. IFN-β was expressed by mast cells in paws from naïve mice and during zymosan-induced inflammation. As described for macrophages the release of type I IFNs from mast cells depended on TLR internalization and endosome acidification. In conclusion, mast cells are able to produce several mediators including IFN-β, which are alone or in combination with each other able to regulate the phagocytotic activity of macrophages during resolution of inflammation.
The sphingolipid sphingosine-1-phosphate (S1P) emerges as an important regulator of immunity, mainly by signaling through a family of five specific G protein-coupled receptors (S1PR1–5). While S1P signaling generally has the potential to affect not only trafficking but also differentiation, activation, and survival of a diverse range of immune cells, the specific outcome depends on the S1P receptor repertoire expressed on a given cell. Among the S1PRs, S1PR4 is specifically abundant in immune cells, suggesting a major role of the S1P/S1PR4 axis in immunity. Recent studies indeed highlight its role in activation of immune cells, differentiation, and, potentially, trafficking. In this review, we summarize the emerging data that support a major role of S1PR4 in modulating immunity in humans and mice and discuss therapeutic implications.
The activation of the transcription factor NF-E2-related factor 2 (Nrf2) maintains cellular homeostasis in response to oxidative stress by the regulation of multiple cytoprotective genes. Without stressors, the activity of Nrf2 is inhibited by its interaction with the Keap1 (kelch-like ECH-associated protein 1). Here, we describe (3S)-1-[4-[(2,3,5,6-tetramethylphenyl) sulfonylamino]-1-naphthyl]pyrrolidine-3-carboxylic acid (RA839), a small molecule that binds noncovalently to the Nrf2-interacting kelch domain of Keap1 with a Kd of ∼6 μm, as demonstrated by x-ray co-crystallization and isothermal titration calorimetry. Whole genome DNA arrays showed that at 10 μm RA839 significantly regulated 105 probe sets in bone marrow-derived macrophages. Canonical pathway mapping of these probe sets revealed an activation of pathways linked with Nrf2 signaling. These pathways were also activated after the activation of Nrf2 by the silencing of Keap1 expression. RA839 regulated only two genes in Nrf2 knock-out macrophages. Similar to the activation of Nrf2 by either silencing of Keap1 expression or by the reactive compound 2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid methyl ester (CDDO-Me), RA839 prevented the induction of both inducible nitric-oxide synthase expression and nitric oxide release in response to lipopolysaccharides in macrophages. In mice, RA839 acutely induced Nrf2 target gene expression in liver. RA839 is a selective inhibitor of the Keap1/Nrf2 interaction and a useful tool compound to study the biology of Nrf2.
Hypoxia poses a stress to cells and decreases mitochondrial respiration, in part by electron transport chain (ETC) complex reorganization. While metabolism under acute hypoxia is well characterized, alterations under chronic hypoxia largely remain unexplored. We followed oxygen consumption rates in THP-1 monocytes during acute (16 h) and chronic (72 h) hypoxia, compared to normoxia, to analyze the electron flows associated with glycolysis, glutamine, and fatty acid oxidation. Oxygen consumption under acute hypoxia predominantly demanded pyruvate, while under chronic hypoxia, fatty acid- and glutamine-oxidation dominated. Chronic hypoxia also elevated electron-transferring flavoproteins (ETF), and the knockdown of ETF–ubiquinone oxidoreductase lowered mitochondrial respiration under chronic hypoxia. Metabolomics revealed an increase in citrate under chronic hypoxia, which implied glutamine processing to α-ketoglutarate and citrate. Expression regulation of enzymes involved in this metabolic shunting corroborated this assumption. Moreover, the expression of acetyl-CoA carboxylase 1 increased, thus pointing to fatty acid synthesis under chronic hypoxia. Cells lacking complex I, which experienced a markedly impaired respiration under normoxia, also shifted their metabolism to fatty acid-dependent synthesis and usage. Taken together, we provide evidence that chronic hypoxia fuels the ETC via ETFs, increasing fatty acid production and consumption via the glutamine-citrate-fatty acid axis.
The translation inhibitor and tumor suppressor Pdcd4 was reported to be lost in various tumors and put forward as prognostic marker in tumorigenesis. Decreased Pdcd4 protein stability due to PI3K-mTOR-p70S6K1 dependent phosphorylation of Pdcd4 followed by β-TrCP1-mediated ubiquitination, and proteasomal destruction of the protein was characterized as a major mechanism contributing to the loss of Pdcd4 expression in tumors. In an attempt to identify stabilizers of Pdcd4, we used a luciferase-based high-throughput compatible cellular assay to monitor phosphorylation-dependent proteasomal degradation of Pdcd4 in response to mitogen stimulation. Following a screen of approximately 2000 compounds, we identified 1,2-bis(4-chlorophenyl)disulfide as a novel Pdcd4 stabilizer. To determine an initial structure-activity relationship, we used 3 additional compounds, synthesized according to previous reports, and 2 commercially available compounds for further testing, in which either the linker between the aryls was modified (compounds 2–4) or the chlorine residues were replaced by groups with different electronic properties (compounds 5 and 6). We observed that those compounds with alterations in the sulfide linker completely lost the Pdcd4 stabilizing potential. In contrast, modifications in the chlorine residues showed only minor effects on the Pdcd4 stabilizing activity. A reporter with a mutated phospho-degron verified the specificity of the compounds for stabilizing the Pdcd4 reporter. Interestingly, the active diaryl disulfides inhibited proliferation and viability at concentrations where they stabilized Pdcd4, suggesting that Pdcd4 stabilization might contribute to the anti-proliferative properties. Finally, computational modelling indicated that the flexibility of the disulfide linker might be necessary to exert the biological functions of the compounds, as the inactive compound appeared to be energetically more restricted.
Natural Killer T cells (NKT cells) are emerging as critical regulators of pro- and anti-tumor immunity, both at baseline and in therapeutic settings. While type I NKT cells can promote anti-tumor immunity, their activity in the tumor microenvironment may be limited by negative regulators such as inhibitory immune checkpoints. We observed dominant expression of B- and T-lymphocyte attenuator (BTLA) on type I NKT cells in polyoma middle T oncogene-driven (PyMT) murine autochthonous mammary tumors. Other immune checkpoint receptors, such as programmed cell death 1 (PD-1) were equally distributed among T cell populations. Interference with BTLA using neutralizing antibodies limited tumor growth and pulmonary metastasis in the PyMT model in a therapeutic setting, correlating with an increase in type I NKT cells and expression of cytotoxic marker genes. While therapeutic application of an anti-PD-1 antibody increased the number of CD8+ cytotoxic T cells and elevated IL-12 expression, tumor control was not established. Expression of ZBTB16, the lineage-determining transcription factor of type I NKT cells, was correlated with a favorable patient prognosis in the METABRIC dataset, and BTLA levels were instrumental to further distinguish prognosis in patents with high ZBTB16 expression. Taken together, these data support a role of BTLA on type I NKT cells in limiting anti-tumor immunity.
Macrophages acquire anti-inflammatory and proresolving functions to facilitate resolution of inflammation and promote tissue repair. While alternatively activated macrophages (AAMs), also referred to as M2 macrophages, polarized by type 2 (Th2) cytokines IL-4 or IL-13 contribute to the suppression of inflammatory responses and play a pivotal role in wound healing, contemporaneous exposure to apoptotic cells (ACs) potentiates the expression of anti-inflammatory and tissue repair genes. Given that liver X receptors (LXRs), which coordinate sterol metabolism and immune cell function, play an essential role in the clearance of ACs, we investigated whether LXR activation following engulfment of ACs selectively potentiates the expression of Th2 cytokine-dependent genes in primary human AAMs. We show that AC uptake simultaneously upregulates LXR-dependent, but suppresses SREBP-2-dependent gene expression in macrophages, which are both prevented by inhibiting Niemann–Pick C1 (NPC1)-mediated sterol transport from lysosomes. Concurrently, macrophages accumulate sterol biosynthetic intermediates desmosterol, lathosterol, lanosterol, and dihydrolanosterol but not cholesterol-derived oxysterols. Using global transcriptome analysis, we identify anti-inflammatory and proresolving genes including interleukin-1 receptor antagonist (IL1RN) and arachidonate 15-lipoxygenase (ALOX15) whose expression are selectively potentiated in macrophages upon concomitant exposure to ACs or LXR agonist T0901317 (T09) and Th2 cytokines. We show priming macrophages via LXR activation enhances the cellular capacity to synthesize inflammation-suppressing specialized proresolving mediator (SPM) precursors 15-HETE and 17-HDHA as well as resolvin D5. Silencing LXRα and LXRβ in macrophages attenuates the potentiation of ALOX15 expression by concomitant stimulation of ACs or T09 and IL-13. Collectively, we identify a previously unrecognized mechanism of regulation whereby LXR integrates AC uptake to selectively shape Th2-dependent gene expression in AAMs.
In cells the interorganelle communication comprises vesicular and non-vesicular mechanisms. Non-vesicular material transfer predominantly takes place at regions of close organelle apposition termed membrane contact sites and is facilitated by a growing number of specialized proteins. Contacts of the endoplasmic reticulum (ER) and mitochondria are now recognized to be essential for diverse biological processes such as calcium homeostasis, phospholipid biosynthesis, apoptosis, and autophagy. In addition to these universal roles, ER-mitochondria communication serves also cell type-specific functions. In this review, we summarize the current knowledge on ER-mitochondria contacts in cells of the innate immune system, especially in macrophages. We discuss ER- mitochondria communication in the context of macrophage fatty acid metabolism linked to inflammatory and ER stress responses, its roles in apoptotic cell engulfment, activation of the inflammasome, and antiviral defense.