Der Mechanismus der Phorbolester-induzierten Ras-Aktivierung in COS7-Zellen

Die als binärer molekularer Schalter in der Zelle vorkommende kleine GTPase Ras wird durch eine Vielzahl extra- und intrazellularer Stimuli und ihre Analoga aktiviert. Es wurde in verschiedenen Veröffentlichungen angedeutet, dass eines dieser Analoga, der Phorbolester 12-O-Tetradecanoylphorbol-13-Acetat (TPA), zur HB-EGF-Freisetzung, Transaktivierung des EGF-Rezeptors und daraufhin via Shc zur Ras-Aktivierung in COS7-Zellen führt. In der vorliegenden Dissertation konnte jedoch demonstriert werden, dass dieses Szenario sich in diesen Zellen nicht abspielt und die TPA-induzierte Ras-Aktivierung über einen anderen Signalweg als den postulierten verläuft. Möglicherweise vermittelt in COS7-Zellen der phosphorylierte Ras-Guaninnukleotid-Austauschfaktor Sos die Ras-Aktivierung nach TPA-Behandlung. Abschliessend konnte in dieser Arbeit gezeigt werden, dass die Phorbolester-ausgelöste Transaktivierung vom EGF-Rezeptor die Phosphorylierung von Serin 473 an der Proteinkinase Akt vermittelt

A human macrophage – hepatocyte co-culture model for comparative studies of infection and replication of Francisella tularensis LVS strain and subspecies holarctica and mediasiatica

Detection of intracellular LPS in macrophage / hepatocyte co-cultures infected with LVS (open bars), spp. holarctica (grey filled bars) or spp. mediasiatica (black filled bars) and untreated control (hatched bars). A) Different amounts of macrophages in the co-culture were tested (6, 12 and 22 % of macrophages on total cell count). Flow cytometric detection of intracellular LPS in macrophages (MFI mean fluorescence intensity); B-D) percentage of remaining detectable macrophages after infection of the co-cultures with B) 6 % macrophages/94 % hepatocytes, C) 12 % macrophages/ 88 % hepatocytes and D) 22 % macrophages/ 88 % hepatocytes 72 h post infection. (TIF 32735 kb

Monocytes of patients with familial hypercholesterolemia show alterations in cholesterol metabolism

<p>Abstract</p> <p>Background</p> <p>Elevated plasma cholesterol promotes the formation of atherosclerotic lesions in which monocyte-derived lipid-laden macrophages are frequently found. To analyze, if circulating monocytes already show increased lipid content and differences in lipoprotein metabolism, we compared monocytes from patients with Familial Hypercholesterolemia (FH) with those from healthy individuals.</p> <p>Methods</p> <p>Cholesterol and oxidized cholesterol metabolite serum levels of FH and of healthy, gender/age matched control subjects were measured by combined gas chromatography – mass spectroscopy. Monocytes from patients with FH and from healthy subjects were isolated by antibody-assisted density centrifugation. Gene expression profiles of isolated monocytes were measured using Affymetrix HG-U 133 Plus 2.0 microarrays. We compared monocyte gene expression profiles from FH patients with healthy controls using a Welch T-test with correction for multiple testing (p < 0.05; Benjamini Hochberg correction, False Discovery Rate = 0.05). The differential expression of FH associated genes was validated at the mRNA level by qRT-PCR and/or at the protein level by Western Blot or flow cytometry. Functional validation of monocyte scavenger receptor activities were done by binding assays and dose/time dependent uptake analysis using native and oxidized LDL.</p> <p>Results</p> <p>Using microarray analysis we found in FH patients a significant up-regulation of 1,617 genes and a down-regulation of 701 genes compared to monocytes from healthy individuals. These include genes of proteins that are involved in the uptake, biosynthesis, disposition, and cellular efflux of cholesterol. In addition, plasma from FH patients contains elevated amounts of sterols and oxysterols. An increased uptake of oxidized as well as of native LDL by FH monocytes combined with a down-regulation of NPC1 and ABCA1 explains the lipid accumulation observed in these cells.</p> <p>Conclusion</p> <p>Our data demonstrate that circulating FH monocytes show differences in cell physiology that may contribute to the early onset of atherosclerosis in this disease.</p

Ras activation in response to lysophosphatidic acid requires a permissive input from the epidermal growth factor receptor.

The topology of the signalling pathway linking the G-protein-coupled receptor agonist lysophosphatidic acid (LPA) to extracellular-signal-regulated kinase activation remains undeciphered. In the present study, we report that analysis of LPA signals at the level of Ras-GTP formation and Ras nucleotide exchange discriminates true mediatory signals from permissive activities that do not participate in signal relay. Hence, whereas pertussis toxin (PTX) treatment impairs stimulation of nucleotide exchange, epidermal growth factor receptor (EGFR) inhibition does not compromise LPA-induced acceleration of nucleotide exchange, but instead attenuates basal nucleotide turnover on Ras. Our data indicate that LPA activation of Ras proceeds via PTX-sensitive G(i/o)-proteins and requires a permissive input from basal EGFR activity

Evaluation of drug-induced liver toxicity of trovafloxacin and levofloxacin in a human microphysiological liver model

Abstract Drug-induced liver injury induced by already approved substances is a major threat to human patients, potentially resulting in drug withdrawal and substantial loss of financial resources in the pharmaceutical industry. Trovafloxacin, a broad-spectrum fluoroquinolone, was found to have unexpected side effects of severe hepatotoxicity, which was not detected by preclinical testing. To address the limitations of current drug testing strategies mainly involving 2D cell cultures and animal testing, a three-dimensional microphysiological model of the human liver containing expandable human liver sinusoidal endothelial cells, monocyte-derived macrophages and differentiated HepaRG cells was utilized to investigate the toxicity of trovafloxacin and compared it to the structurally-related non-toxic drug levofloxacin. In the model, trovafloxacin elicited vascular and hepatocellular toxicity associated with pro-inflammatory cytokine release already at clinically relevant concentrations, whereas levofloxacin did not provoke tissue injury. Similar to in vivo, cytokine secretion was dependent on a multicellular immune response, highlighting the potential of the complex microphysiological liver model for reliably detecting drug-related cytotoxicity in preclinical testing. Moreover, hepatic glutathione depletion and mitochondrial ROS formation were elucidated as intrinsic toxicity mechanisms contributing to trovafloxacin toxicity

Thermo-responsive cell culture carrier: Effects on macrophage functionality and detachment efficiency

Harvesting cultivated macrophages for tissue engineering purposes by enzymatic digestion of cell adhesion molecules can potentially result in unintended activation, altered function, or behavior of these cells. Thermo-responsive polymer is a promising tool that allows for gentle macrophage detachment without artificial activation prior to subculture within engineered tissue constructs. We therefore characterized different species of thermo-responsive polymers for their suitability as cell substrate and to mediate gentle macrophage detachment by temperature shift. Primary human monocyte- and THP-1-derived macrophages were cultured on thermo-responsive polymers and characterized for phagocytosis and cytokine secretion in response to lipopolysaccharide stimulation. We found that both cell types differentially respond in dependence of culture and stimulation on thermo-responsive polymers. In contrast to THP-1 macrophages, primary monocyte–derived macrophages showed no signs of impaired viability, artificial activation, or altered functionality due to culture on thermo-responsive polymers compared to conventional cell culture. Our study demonstrates that along with commercially available UpCell carriers, two other thermo-responsive polymers based on poly(vinyl methyl ether) blends are attractive candidates for differentiation and gentle detachment of primary monocyte–derived macrophages. In summary, we observed similar functionality and viability of primary monocyte–derived macrophages cultured on thermo-responsive polymers compared to standard cell culture surfaces. While this first generation of custom-made thermo-responsive polymers does not yet outperform standard culture approaches, our results are very promising and provide the basis for exploiting the unique advantages offered by custom-made thermo-responsive polymers to further improve macrophage culture and recovery in the future, including the covalent binding of signaling molecules and the reduction of centrifugation and washing steps. Optimizing these and other benefits of thermo-responsive polymers could greatly improve the culture of macrophages for tissue engineering applications

Live-cell imaging of endogenous Ras-GTP illustrates predominant Ras activation at the plasma membrane

Ras-GTP imaging studies using the Ras-binding domain (RBD) of the Ras effector c-Raf as a reporter for overexpressed Ras have produced discrepant results about the possible activation of Ras at the Golgi apparatus. We report that RBD oligomerization provides probes for visualization of endogenous Ras-GTP, obviating Ras overexpression and the side effects derived thereof. RBD oligomerization results in tenacious binding to Ras-GTP and interruption of Ras signalling. Trimeric RBD probes fused to green fluorescent protein report agonist-induced endogenous Ras activation at the plasma membrane (PM) of COS-7, PC12 and Jurkat cells, but do not accumulate at the Golgi. PM illumination is exacerbated by Ras overexpression and its sensitivity to dominant-negative RasS17N and pharmacological manipulations matches Ras-GTP formation assessed biochemically. Our data illustrate that endogenous Golgi-located Ras is not under the control of growth factors and argue for the PM as the predominant site of agonist-induced Ras activation