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Cyclic adenosine monophosphate (cAMP), the ubiquitous second messenger produced upon stimulation of GPCRs which couple to the stimulatory GS protein, orchestrates an array of physiological processes including cardiac function, neuronal plasticity, immune responses, cellular proliferation and apoptosis. By interacting with various effector proteins, among others protein kinase A (PKA) and exchange proteins directly activated by cAMP (Epac), it triggers signaling cascades for the cellular response. Although the functional outcomes of GSPCR-activation are very diverse depending on the extracellular stimulus, they are all mediated exclusively by this single second messenger. Thus, the question arises how specificity in such responses may be attained. A hypothesis to explain signaling specificity is that cellular signaling architecture, and thus precise operation of cAMP in space and time would appear to be essential to achieve signaling specificity. Compartments with elevated cAMP levels would allow specific signal relay from receptors to effectors within a micro- or nanometer range, setting the molecular basis for signaling specificity. Although the paradigm of signaling compartmentation gains continuous recognition and is thoroughly being investigated, the molecular composition of such compartments and how they are maintained remains to be elucidated. In addition, such compartments would require very restricted diffusion of cAMP, but all direct measurements have indicated that it can diffuse in cells almost freely.
In this work, we present the identification and characterize of a cAMP signaling compartment at a GSPCR. We created a Förster resonance energy transfer (FRET)-based receptor-sensor conjugate, allowing us to study cAMP dynamics in direct vicinity of the human glucagone-like peptide 1 receptor (hGLP1R). Additional targeting of analogous sensors to the plasma membrane and the cytosol enables assessment of cAMP dynamics in different subcellular regions. We compare both basal and stimulated cAMP levels and study cAMP crosstalk of different receptors. With the design of novel receptor nanorulers up to 60nm in length, which allow mapping cAMP levels in nanometer distance from the hGLP1R, we identify a cAMP nanodomain surrounding it. Further, we show that phosphodiesterases (PDEs), the only enzymes known to degrade cAMP, are decisive in constraining cAMP diffusion into the cytosol thereby maintaining a cAMP gradient. Following the discovery of this nanodomain, we sought to investigate whether downstream effectors such as PKA are present and active within the domain, additionally studying the role of A-kinase anchoring proteins (AKAPs) in targeting PKA to the receptor compartment. We demonstrate that GLP1-produced cAMP signals translate into local nanodomain-restricted PKA phosphorylation and determine that AKAP-tethering is essential for nanodomain PKA.
Taken together, our results provide evidence for the existence of a dynamic, receptor associated cAMP nanodomain and give prospect for which key proteins are likely to be involved in its formation. These conditions would allow cAMP to exert its function in a spatially and temporally restricted manner, setting the basis for a cell to achieve signaling specificity. Understanding the molecular mechanism of cAMP signaling would allow modulation and thus regulation of GPCR signaling, taking advantage of it for pharmacological treatment.
G-protein-coupled receptors (GPCRs) represent one of the most important classes of drug targets. The discovery of new GCPR therapeutics would greatly benefit from the development of a generalizable high-throughput assay to directly monitor their activation or de-activation. Here we screened a variety of labels inserted into the third intracellular loop and the C-terminus of the alpha(2 Lambda)-adrenergic receptor and used fluorescence (FRET) and bioluminescence resonance energy transfer (BRET) to monitor ligand-binding and activation dynamics. We then developed a universal intramolecular BRET receptor sensor design to quantify efficacy and potency of GPCR ligands in intact cells and real time. We demonstrate the transferability of the sensor design by cloning beta(2)-adrenergic and PTH1-receptor BRET sensors and monitored their efficacy and potency. For all biosensors, the Z factors were well above 0.5 showing the suitability of such design for microtiter plate assays. This technology will aid the identification of novel types of GPCR ligands.
Patienten mit arterieller Hypertonie haben ein erhöhtes Risiko eine Tumorerkrankung, insbesondere Nierenzellkarzinome, zu entwickeln. Die arterielle Hypertonie ist über die Entstehung von oxidativem Stress mit der Entwicklung von DNA-Schäden verknüpft, wobei ein hochreguliertes Renin-Angiotensin-Aldosteron-System (RAAS) eine entscheidende Rolle einnimmt. Das Ziel dieser Arbeit war es zum einen Hypertoniker (HypAll) und gesunde Kontrollen und zum anderen gut (HypGut) und schlecht (HypSch) eingestellte Hypertoniker unter Berücksichtigung der eingenommenen Antihypertensiva bezüglich ihrer Level an oxidativem Stress und DNA-Schäden zu vergleichen. Zusätzlich erfolgte im Rahmen einer Längsschnittanalyse der intraindividuelle Vergleich unter den Hypertonikern. Hierfür erfolgte die Bestimmung von SHp, D-ROM und 3-Nitrotyrosin als Marker für oxidativen Stress im Plasma, von 8-oxodG, 15-F2t-Isoprostan und Malondialdehyd als Marker für oxidativen Stress im Urin und von γ-H2AX und Mikrokernen als Marker für DNA-Schäden in Lymphozyten.
Dabei konnte ein erhöhter oxidativer Stress in der HypAll-Gruppe verglichen zu den Kontrollen anhand aller Marker für oxidativen Stress mit Ausnahme von Malondialdehyd festgestellt werden. Nach Altersadjustierung zeigte sich dieser Gruppenunterschied nur noch für die Proteinstressmarker SHp und 3-Nitrotyrosin signifikant. Bezüglich der Marker für DNA-Schäden ergab sich kein Unterschied zwischen HypAll und Kontrollen. Ebenso zeigte sich kein signifikanter Unterschied in den Leveln für oxidativen Stress und DNA-Schäden zwischen der HypGut- und HypSch-Gruppe. Zuletzt konnte im Rahmen der Längsschnittstudie ein positiver Zusammenhang zwischen der Entwicklung des Blutdrucks und des oxidativen Stresses anhand der Veränderung von D-ROM und des systolischen Blutdrucks beobachtet werden.
Die teils nicht-signifikanten und teils mangelnden Unterschiede zwischen HypAll und Kontrollen sowie zwischen HypGut und HypSch sind am ehesten durch das besondere Patientengut, welches sich auch grundlegend von dem anderer vergleichbarer Studien unterscheidet, erklärbar. Die Patienten mit therapieresistenter Hypertonie (TRH) zeichnen sich durch eine langjährige Einnahme zahlreicher Antihypertensiva aus. Diese, insbesondere die RAAS-wirksamen, besitzen eine über die reine Blutdrucksenkung hinausgehende antioxidative und antigenotoxische Wirkung, welche vermutlich zu einer Angleichung der Level für oxidativen Stress und DNA-Schäden geführt hat.
Um die Dynamik der Biomarker und den Einfluss der Antihypertensiva auf oxidativen Stress und DNA-Schäden besser zu verstehen, sind weitere Studien über einen längeren Beobachtungszeitraum sowie mit zusätzlich therapienaiven Hypertonikern sinnvoll. Die weitere Erforschung von Biomarkern, um sie im klinischen Alltag zur Verbesserung der Patientenbehandlung einsetzen zu können, ist notwendig.
Pyridoxal 5′‐phosphate (PLP) is an essential cofactor for neurotransmitter metabolism. Pyridoxal phosphatase (PDXP) deficiency in mice increases PLP and γ‐aminobutyric acid levels in the brain, yet how PDXP is regulated is unclear. Here, we identify the Ca\(^{2+}\)‐ and integrin‐binding protein 1 (CIB1) as a PDXP interactor by yeast two‐hybrid screening and find a calmodulin (CaM)‐binding motif that overlaps with the PDXP‐CIB1 interaction site. Pulldown and crosslinking assays with purified proteins demonstrate that PDXP directly binds to CIB1 or CaM. CIB1 or CaM does not alter PDXP phosphatase activity. However, elevated Ca\(^{2+}\) concentrations promote CaM binding and, thereby, diminish CIB1 binding to PDXP, as both interactors bind in a mutually exclusive way. Hence, the PDXP‐CIB1 complex may functionally differ from the PDXP‐Ca\(^{2+}\)‐CaM complex.
Pyrrolizidinalkaloide (PA) sind sekundäre Pflanzenstoffe, welche über Nahrungsmittel in den menschlichen Organismus gelangen können. Zahlreiche Studien belegen, dass PA in der Leber verstoffwechselt und dabei in aktive genotoxische Metabolite umgewandelt werden. Diese verursachen vor allem in der Leber zelluläre Schäden, was sich klinisch in Form einer hepatischen venösen okklusiven Leberkrankheit, aber auch in der Entstehung von Tumoren zeigt. Die vorliegende Arbeit testet das genotoxische Potential der drei PA Lasiocarpin, Senecionin und Seneciphyllin anhand der Leberzelllinie Huh6 mit Hilfe des Mikrokerntests. Darüber hinaus wird die Wirkung von Lasiocarpin auf den intrazellulären Glutathion-Gehalt, die Superoxidproduktion und das mitochondriale Membranpotential analysiert. Zudem werden sowohl der eventuell negative Einfluss einer Glutathion Depletion, als auch die möglicherweise schützenden Effekte des pflanzlichen Antioxidans Delphinidin in Bezug auf die Genotoxizität von Lasiocarpin untersucht. Es konnte gezeigt werden, dass alle drei ausgewählten PA einen signifikanten Anstieg der Mikrokernfrequenz bewirken.Unsere Messungen zeigten für Lasiocarpin eine dezente Reduktion des Glutathion Gehalts. Dagegen führte eine Glutathion-Depletion in den Huh6 Zellen zu keiner Steigerung der Genotoxizität von Lasiocarpin. In Kombination mit dem Antioxidans Delphinidin zeigte sich für Lasiocarpin eine signifikante Reduktion der Mikrokernfrequenz. Abschließend ist anzumerken, dass in Zukunft vor allem die Wechselwirkung der PA untereinander und mit anderen (Pflanzen-)bestandteilen für eine verbesserte Risikoabschätzung der PA-Exposition untersucht werden sollte.
Hormones are essential components in the body and their imbalance leads to pathological consequences. T2DM, insulin resistance and obesity are the most commonly occurring lifestyle diseases in the past decade. Also, an increased cancer incidence has been strongly associated with obese and T2DM patients.
Therefore, our aim was to study the influence of high insulin levels in accumulating DNA damage in in vitro models and patients, through the induction of oxidative stress. The primary goal of this study was to analyze the genotoxicity induced by the combined action of two endogenous hormones (insulin and adrenaline) with in vitro models, through the induction of micronuclei and to see if they cause an additive increase in genomic damage. This is important for multifactorial diseases having high levels of more than one hormone, such as metabolic syndrome and conditions with multiple pathologies (e.g., T2DM along with high stress levels).
Furthermore, the combination of insulin and the pharmacological inhibition of the tumor suppressor gene: PTEN, was to be tested in in vitro models for their genotoxic effect and oxidative stress inducing potential. As the tumor suppressor gene: PTEN is downregulated in PTEN associated syndromes and when presented along with T2DM and insulin resistance, this may increase the potential to accumulate genomic damage.
The consequences of insulin action were to be further elucidated by following GFP-expressing cells in live cell-imaging to observe the ability of insulin, to induce micronuclei and replicative stress. Finally, the detrimental potential of high insulin levels in obese patients with hyperinsulinemia and pre-diabetes was to be studied by analyzing markers of oxidative stress and genomic damage. In summary, the intention of this work was to understand the effects of high insulin levels in in vitro and in patients to understand its relevance for the development of genomic instability and thus an elevated cancer risk.
Schicksal von Mikrokernen bzw. mikrokernhaltigen Zellen und Bedeutung von Mikrokernen als Biomarker
(2021)
Mikrokerne sind als wichtiger Biomarker in der Gentoxizitätsforschung seit langer Zeit etabliert und ihre Bildung ist mechanistisch gut verstanden, wohingegen das Mikrokernschicksal und die genaue Funktion von Mikrokernen in der Kanzerogenese unzureichend erforscht sind. Um das Schicksal von Mikrokernen und mikrokernhaltigen Zellen über einen längeren Zeitraum zu untersuchen, wurden HeLa-Zellen, die mit einem GFP-markierten Histon H2B transfiziert worden sind, mittels Lebendzellmikroskopie nach Behandlung mit verschiedenen gentoxischen Agenzien für 96 h untersucht. Parameter wie die Mitose- oder Zelltodrate wurden dabei ebenso wie das Schicksal der Mikrokerne dokumentiert. Während Persistenz und Reinkorporation von Mikrokernen häufig beobachtet wurden, waren Degradation und Auswurf von Mikrokernen selten bis gar nicht zu sehen. Auch konnte ein Teil der mikrokernhaltigen Zellen über mehrere Zellteilungen persistieren und proliferieren, wodurch die in Mikrokernen manifestierte chromosomale Instabilität unverändert bleiben kann. Ein eindeutiger Substanzeinfluss auf das Mikrokernschicksal konnte nicht ausgemacht werden. Extrusion sollte weiterhin durch Behandlung mit Hydroxyurea oder Cytochalasin B in Kombination mit gentoxischer Behandlung induziert werden, es wurde jedoch kein Effekt auf die Extrusionsrate beobachtet. Degradation wurde mittels γH2AX-Antikörperfärbung und transduziertem dsRed-markierten Autophagiemarker LC3B in HeLa-H2B-GFP-Zellen untersucht. Trotz erhöhter DNA-Degradation in Mikrokernen wurde nur selten eine Ko-Lokalisierung mit LC3B beobachtet. Dafür gab es in HeLa-H2B-GFP-Zellen, die zusätzlich mit dsRed markierten Kernmembranmarker Lamin B1 transduziert worden sind, Anzeichen für eine eingeschränkte Mikrokernmembranintegrität. Weiterhin wurden Zytokinese-Block Mikrokerntests nach Behandlung mit Thebain mit und ohne metabolische Aktivierung sowie Celecoxib und Celecoxibderivaten durchgeführt. Hierbei wurde nach Thebainbehandlung nur ohne metabolische Aktivierung und bei Anwesenheit von Zytotoxizität mehr Mikrokerne gefunden, während nach Behandlung mit Celecoxib und Celecoxibderivaten kein Anstieg beobachtet wurde. Zusätzlich wurde der Einfluss durch neurodegenerative Veränderungen auf Mundschleimhautzellen in zwei großen Kohorten untersucht, wobei keine Effekte auf die Häufigkeit von Mikrokernen oder mikrokernhaltigen Zellen zugeordnet werden konnten, während es teilweise bei Parametern, die auf Zytotoxizität hindeuten, zu Veränderungen kam. Es konnte insgesamt gezeigt werden, dass Mikrokerne und mikrokernhaltige Zellen zusätzlich zu ihrer Funktion als Biomarker über wenigstens mehrere Zellteilungen bestehen bleiben können. Auf diese Weise können sie z. B. über Chromothripsis zu einer beschleunigten Kanzerogenese führen, was zu einer schlechten Prognose für Krebspatienten führen kann.
Long-term fate of etoposide-induced micronuclei and micronucleated cells in Hela-H2B-GFP cells
(2020)
Micronuclei are small nuclear cellular structures containing whole chromosomes or chromosomal fragments. While there is a lot of information available about the origin and formation of micronuclei, less is known about the fate of micronuclei and micronucleated cells. Possible fates include extrusion, degradation, reincorporation and persistence. Live cell imaging was performed to quantitatively analyse the fates of micronuclei and micronucleated cells occurring in vitro. Imaging was conducted for up to 96 h in HeLa-H2B-GFP cells treated with 0.5, 1 and 2 µg/ml etoposide. While a minority of micronuclei was reincorporated into the main nucleus during mitosis, the majority of micronuclei persisted without any alterations. Degradation and extrusion were observed rarely or never. The presence of micronuclei affected the proliferation of the daughter cells and also had an influence on cell death rates. Mitotic errors were found to be clearly increased in micronucleus-containing cells. The results show that micronuclei and micronucleated cells can, although delayed in cell cycle, sustain for multiple divisions.
Cyclisches Adenosinmonophosphat ist ein ubiquitärer zweiter Botenstoff zahlreicher Signalwege im menschlichen Körper. Auf eine Vielzahl verschiedenster extrazellulärer Signale folgt jedoch eine Erhöhung desselben intrazellulären Botenstoffs - cAMP. Nichtsdestotrotz schafft es die Zelle, Signalspezifität aufrecht zu erhalten. Ein anerkanntes, wenn auch bisher unverstandenes Modell, um dieses zu ermöglichen, ist das Prinzip der Kompartimentierung. Die Zelle besitzt demnach Areale verschieden hoher cAMP-Konzentrationen, welche lokal begrenzt einzelne Signalkaskaden beeinflussen und somit eine differenzierte Signalübertragung ermöglichen. Eine mögliche Ursache für die Ausbildung solcher Bereiche geringerer cAMP- Konzentrationen (hier als Domänen bezeichnet), ist die hydrolytische Aktivität von Phosphodiesterasen (PDEs), welche als einzige Enzyme die Fähigkeiten besitzen, cAMP zu degradieren.
In dieser Arbeit wird der Einfluss der cAMP-Hydrolyse verschiedener PDEs auf die Größe dieser Domänen evaluiert und mit denen der PDE4A1 verglichen, welche bereits durch unsere Arbeitsgruppe aufgrund ihrer Größe als Nanodomänen definiert wurden. Der Fokus wird dabei auf den Einfluss von kinetischen Eigenschaften der Phosphodiesterasen gelegt. So werden eine PDE mit hoher Umsatzgeschwindigkeit (PDE2A3) und eine PDE mit hoher Substrataffinität (PDE8A1) verglichen. Mithilfe sogenannter Linker, Abstandshaltern definierter Länge, werden zusätzlich die Nanodomänen ausgemessen, um einen direkten Zusammenhang zwischen Größe und kinetischer Eigenschaft anzugeben. Die Zusammenschau der Ergebnisse zeigt, dass die maximale Umsatzgeschwindigkeit der Phosphodiesterasen direkt mit der Größe der Nanodomänen korreliert.
Durch den unmittelbaren Vergleich der gesamten PDE mit ihrer katalytischen Domäne wird zusätzlich der Einfluss von regulatorischen Domänen evaluiert. Es wird gezeigt, dass diese cAMP-Gradienten modulieren können. Bei der PDE2A3 geschieht die Modulation u.a. durch Stimulation mit cGMP, welche höchstwahrscheinlich dosisabhängig ist und somit graduell verläuft. Hiermit präsentieren sich die Domänen als dynamische Bereiche, d.h. sie können in ihrer Ausprägung reguliert werden. In dieser Arbeit wird die Hypothese bestätigt, dass Phosphodiesterasen eine wichtige Rolle in der Kompartimentierung von cAMP spielen, die Gruppe jedoch inhomogener ist, als bislang angenommen. Die Gradienten-Bildung lässt sich nicht bei jeder Phosphodiesterase darstellen (PDE8A1). Einige Phosphodiesterasen (PDE2A3) jedoch bilden Kompartimente, die durch externe Stimuli in ihrer Größe reguliert werden können.
Die Arbeit legt den Grundstein zur breiteren Charakterisierung des spezifischen Einflusses weiterer PDEs auf cAMP-Kompartimentierung, welches nicht nur das Verständnis der Kompartimentierungs-Strategien voranbringt, sondern auch essentiell für das Verständnis der Pathophysiologie zahlreicher Krankheitsbilder, aber auch für das Verständnis bereits angewandter aber auch potentiell neuer Medikamente ist.
Aims Acute myocardial infarction (MI) is the major cause of chronic heart failure. The activity of blood coagulation factor XIII (FXIIIa) plays an important role in rodents as a healing factor after MI, whereas its role in healing and remodelling processes in humans remains unclear. We prospectively evaluated the relevance of FXIIIa after acute MI as a potential early prognostic marker for adequate healing.
Methods and results This monocentric prospective cohort study investigated cardiac remodelling in patients with ST-elevation MI and followed them up for 1 year. Serum FXIIIa was serially assessed during the first 9 days after MI and after 2, 6, and 12 months. Cardiac magnetic resonance imaging was performed within 4 days after MI (Scan 1), after 7 to 9 days (Scan 2), and after 12 months (Scan 3). The FXIII valine-to-leucine (V34L) single-nucleotide polymorphism rs5985 was genotyped. One hundred forty-six patients were investigated (mean age 58 ± 11 years, 13% women). Median FXIIIa was 118 % (quartiles, 102–132%) and dropped to a trough on the second day after MI: 109%(98–109%; P < 0.001). FXIIIa recovered slowly over time, reaching the baseline level after 2 to 6 months and surpassed baseline levels only after 12 months: 124 % (110–142%). The development of FXIIIa after MI was independent of the genotype. FXIIIa on Day 2 was strongly and inversely associated with the relative size of MI in Scan 1 (Spearman’s ρ = –0.31; P = 0.01) and Scan 3 (ρ = –0.39; P < 0.01) and positively associated with left ventricular ejection fraction: ρ = 0.32 (P < 0.01) and ρ = 0.24 (P = 0.04), respectively.
Conclusions FXIII activity after MI is highly dynamic, exhibiting a significant decline in the early healing period, with reconstitution 6 months later. Depressed FXIIIa early after MI predicted a greater size of MI and lower left ventricular ejection fraction after 1 year. The clinical relevance of these findings awaits to be tested in a randomized trial.
Aims
Chronic heart failure (CHF) can be caused by autoantibodies stimulating the heart via binding to first and/or second extracellular loops of cardiac β1-adrenoceptors. Allosteric receptor activation depends on conformational features of the autoantibody binding site. Elucidating these features will pave the way for the development of specific diagnostics and therapeutics. Our aim was (i) to fine-map the conformational epitope within the second extracellular loop of the human β\(_1\)-adrenoceptor (β1ECII) that is targeted by stimulating β\(_1\)-receptor (auto)antibodies and (ii) to generate competitive cyclopeptide inhibitors of allosteric receptor activation, which faithfully conserve the conformational auto-epitope.
Methods and results
Non-conserved amino acids within the β\(_1\)EC\(_{II}\) loop (compared with the amino acids constituting the ECII loop of the β\(_2\)-adrenoceptor) were one by one replaced with alanine; potential intra-loop disulfide bridges were probed by cysteine–serine exchanges. Effects on antibody binding and allosteric receptor activation were assessed (i) by (auto)antibody neutralization using cyclopeptides mimicking β1ECII ± the above replacements, and (ii) by (auto)antibody stimulation of human β\(_1\)-adrenoceptors bearing corresponding point mutations. With the use of stimulating β\(_1\)-receptor (auto)antibodies raised in mice, rats, or rabbits and isolated from exemplary dilated cardiomyopathy patients, our series of experiments unmasked two features of the β\(_1\)EC\(_{II}\) loop essential for (auto)antibody binding and allosteric receptor activation: (i) the NDPK\(^{211–214}\) motif and (ii) the intra-loop disulfide bond C\(^{209}\)↔C\(^{215}\). Of note, aberrant intra-loop disulfide bond C\(^{209}\)↔C\(^{216}\) almost fully disrupted the functional auto-epitope in cyclopeptides.
Conclusions
The conformational auto-epitope targeted by cardio-pathogenic β\(_1\)-receptor autoantibodies is faithfully conserved in cyclopeptide homologues of the β\(_1\)EC\(_{II}\) loop bearing the NDPK\(^{211–214}\) motif and the C\(^{209}\)↔C\(^{215}\) bridge while lacking cysteine C216. Such molecules provide promising tools for novel diagnostic and therapeutic approaches in β\(_1\)-autoantibodypositive CHF.
Neurodegenerative diseases show an increase in prevalence and incidence, with the most prominent example being Alzheimer's disease. DNA damage has been suggested to play a role in the pathogenesis, but the exact mechanisms remain elusive. We enrolled 425 participants with and without neurodegenerative diseases and analyzed DNA damage in the form of micronuclei in buccal mucosa samples. In addition, other parameters such as binucleated cells, karyolytic cells, and karyorrhectic cells were quantified. No relevant differences in DNA damage and cytotoxicity markers were observed in patients compared to healthy participants. Furthermore, other parameters such as lifestyle factors and diseases were also investigated. Overall, this study could not identify a direct link between changes in buccal cells and neurogenerative diseases, but highlights the influence of lifestyle factors and diseases on the human buccal cytome.
Metabolism and signaling of cytokinins was first established in plants, followed by cytokinin discoveries in all kingdoms of life. However, understanding of their role in mammalian cells is still scarce. Kinetin is a cytokinin that mitigates the effects of oxidative stress in mammalian cells. The effective concentrations of exogenously applied kinetin in invoking various cellular responses are not well standardized. Likewise, the metabolism of kinetin and its cellular targets within the mammalian cells are still not well studied. Applying vitality tests as well as comet assays under normal and hyper-oxidative states, our analysis suggests that kinetin concentrations of 500 nM and above cause cytotoxicity as well as genotoxicity in various cell types. However, concentrations below 100 nM do not cause any toxicity, rather in this range kinetin counteracts oxidative burst and cytotoxicity. We focus here on these effects. To get insights into the cellular targets of kinetin mediating these pro-survival functions and protective effects we applied structural and computational approaches on two previously testified targets for these effects. Our analysis deciphers vital residues in adenine phosphoribosyltransferase (APRT) and adenosine receptor (A2A-R) that facilitate the binding of kinetin to these two important human cellular proteins. We finally discuss how the therapeutic potential of kinetin against oxidative stress helps in various pathophysiological conditions.
Aims
Volume overload (VO) and pressure overload (PO) induce differential cardiac remodelling responses including distinct signalling pathways. Extracellular signal‐regulated kinases 1 and 2 (ERK1/2), key signalling components in the mitogen‐activated protein kinase (MAPK) pathways, modulate cardiac remodelling during pressure overload (PO). This study aimed to assess their role in VO‐induced cardiac remodelling as this was unknown.
Methods and results
Aortocaval fistula (Shunt) surgery was performed in mice to induce cardiac VO. Two weeks of Shunt caused a significant reduction of cardiac ERK1/2 activation in wild type (WT) mice as indicated by decreased phosphorylation of the TEY (Thr‐Glu‐Tyr) motif (−28% as compared with Sham controls, P < 0.05). Phosphorylation of other MAPKs was unaffected. For further assessment, transgenic mice with cardiomyocyte‐specific ERK2 overexpression (ERK2tg) were studied. At baseline, cardiac ERK1/2 phosphorylation in ERK2tg mice remained unchanged compared with WT littermates, and no overt cardiac phenotype was observed; however, cardiac expression of the atrial natriuretic peptide was increased on messenger RNA (3.6‐fold, P < 0.05) and protein level (3.1‐fold, P < 0.05). Following Shunt, left ventricular dilation and hypertrophy were similar in ERK2tg mice and WT littermates. Left ventricular function was maintained, and changes in gene expression indicated reactivation of the foetal gene program in both genotypes. No differences in cardiac fibrosis and kinase activation was found amongst all experimental groups, whereas apoptosis was similarly increased through Shunt in ERK2tg and WT mice.
Conclusions
VO‐induced eccentric hypertrophy is associated with reduced cardiac ERK1/2 activation in vivo. Cardiomyocyte‐specific overexpression of ERK2, however, does not alter cardiac remodelling during VO. Future studies need to define the pathophysiological relevance of decreased ERK1/2 signalling during VO.
Die extrazellulär Signal-regulierten Kinasen 1 und 2 (ERK1/2) spielen eine zentrale Rolle bei der Vermittlung kardialer Hypertrophie und dem Zellüberleben. Hypertrophe Stimuli aktivieren ERK1/2, triggern deren Dimerisierung und in der Folge die ERK188-Autophosphorylierung. Diese neu entdeckte Autophosphorylierung ist eine Voraussetzung für den nukleären Import von ERK1/2 und führt zum Entstehen pathologischer kardialer Hypertrophie. Da das Dimer Interface von ERK eine mögliche Zielstruktur darstellt, um selektiv die nukleären Signalwege von ERK zu unterbrechen, wurde untersucht, ob man mit Hemmung der ERK-Dimerisierung eine therapeutische Möglichkeit hat, um pathologische kardiale Hypertrophie zu verhindern. Dazu wurden verschiedene ERK2 Mutanten und Peptide generiert, um die ERK-Dimerisierung zu verhindern. Die Effekte dieser Konstrukte auf die ERK-Dimerisierung und den Kernimport wurden in verschiedenen Zelltypen mittels Fluoreszenzmikroskopie, Co-Immunopräzipitationen und Duolink proximity ligation assays getestet. Es konnte gezeigt werden, dass die Peptide effektiv die ERK-ERK Interaktion nach Stimulation mit Phenylephrin und/oder Carbachol verhindern. Zusätzlich reduzierten die Peptide ERKT188-Phosphorylierung und in der Folge den ERK-Import in den Nukleus und Kardiomyozytenhypertrophie. Normale ERK-Aktivierung wurde jedoch durch die Peptide nicht verhindert. Insgesamt konnte gezeigt werden, dass das ERK-Dimer Interface eine wertvolle Zielstruktur ist, mit dem man nukleäre ERK1/2 Signalwege selektiv unterbrechen und damit effektiv Kardiomyozytenwachstum reduzieren kann, ohne gleichzeitig das Zellüberleben zu gefährden.
ERK1/2 are known key players in the pathophysiology of heart failure, but the members of the ERK cascade, in particular Raf1, can also protect the heart from cell death and ischemic injury. An additional autophosphorylation (ERK1 at Thr208, ERK2 at Thr188) empowers ERK1/2 translocation to the nucleus and phosphorylation of nuclear targets which take part in the development of cardiac hypertrophy. Thereby, targeting this additional phosphorylation is a promising pharmacological approach.
In this thesis, an in silico model of ERK cascade in the cardiomyocyte is introduced. The model is a semi-quantitive model and its behavior was tested with different softwares (SQUAD and CellNetAnalyzer). Different phosphorylation states of ERK1/2 as well as different stimuli can be reproduced. The different types of stimuli include hypertrophic as well as non-hypertrophic stimuli. With the introduced in-silico model time courses and synergistic as well as antagonistic receptor stimuli combinations can be predicted. The simulated time courses were experimentally validated. SQUAD was mainly used to make predictions about time courses and thresholds, whereas CNA was used to analyze steady states and feedback loops.
Furthermore, new targets of ERK1/2 which partially contribute, also in the formation of cardiac hypertrophy, were identified and the most promising of them were illuminated. Important further targets are Caspase 8, GAB2, Mxi-2, SMAD2, FHL2 and SPIN90.
Cardiomyocyte gene expression data sets were analyzed to verify involved components and to find further significantly altered genes after induced hypertrophy with TAC (transverse aortic constriction). Changes in the ultrastructure of the cardiomyocyte are the final result of induced hypertrophy.
A new cyclic dipeptide, petrocidin A (\(\textbf{1}\)), along with three known compounds—2,3-dihydroxybenzoic acid (\(\textbf{2}\)), 2,3-dihydroxybenzamide (\(\textbf{3}\)), and maltol (\(\textbf{4}\))—were isolated from the solid culture of \(Streptomyces\) sp. SBT348. The strain \(Streptomyces\) sp. SBT348 had been prioritized in a strain collection of 64 sponge-associated actinomycetes based on its distinct metabolomic profile using liquid chromatography/high-resolution mass spectrometry (LC-HRMS) and nuclear magnetic resonance (NMR). The absolute configuration of all α-amino acids was determined by HPLC analysis after derivatization with Marfey’s reagent and comparison with commercially available reference amino acids. Structure elucidation was pursued in the presented study by mass spectrometry and NMR spectral data. Petrocidin A (\(\textbf{1}\)) and 2,3-dihydroxybenzamide (\(\textbf{3}\)) exhibited significant cytotoxicity towards the human promyelocytic HL-60 and the human colon adenocarcinoma HT-29 cell lines. These results demonstrated the potential of sponge-associated actinomycetes for the discovery of novel and pharmacologically active natural products.
Mammalian phosphoglycolate phosphatase (PGP) is thought to target phosphoglycolate, a 2-deoxyribose fragment derived from the repair of oxidative DNA lesions. However, the physiological role of this activity and the biological function of the DNA damage product phosphoglycolate is unknown. We now show that knockin replacement of murine Pgp with its phosphatase-inactive Pgp\(^{D34N}\) mutant is embryonically lethal due to intrauterine growth arrest and developmental delay in midgestation. PGP inactivation attenuated triosephosphate isomerase activity, increased triglyceride levels at the expense of the cellular phosphatidylcholine content, and inhibited cell proliferation. These effects were prevented under hypoxic conditions or by blocking phosphoglycolate release from damaged DNA. Thus, PGP is essential to sustain cell proliferation in the presence of oxygen. Collectively, our findings reveal a previously unknown mechanism coupling a DNA damage repair product to the control of intermediary metabolism and cell proliferation.
Cholesterol-dependent cytolysins (CDCs) are protein toxins that originate from Gram-positive bacteria and contribute substantially to their pathogenicity. CDCs bind membrane cholesterol and build prepores and lytic pores. Some effects of the toxins are observed in non-lytic concentrations. Two pathogens, \(Streptococcus\) \(pneumoniae\) and \(Listeria\) \(monocytogenes\), cause fatal bacterial meningitis, and both produce toxins of the CDC family—pneumolysin and listeriolysin O, respectively. It has been demonstrated that pneumolysin produces dendritic varicosities (dendrite swellings) and dendritic spine collapse in the mouse neocortex, followed by synaptic loss and astrocyte cell shape remodeling without elevated cell death. We utilized primary glial cultures and acute mouse brain slices to examine the neuropathological effects of listeriolysin O and to compare it to pneumolysin with identical hemolytic activity. In cultures, listeriolysin O permeabilized cells slower than pneumolysin did but still initiated non-lytic astrocytic cell shape changes, just as pneumolysin did. In an acute brain slice culture system, listeriolysin O produced dendritic varicosities in an NMDA-dependent manner but failed to cause dendritic spine collapse and cortical astrocyte reorganization. Thus, listeriolysin O demonstrated slower cell permeabilization and milder glial cell remodeling ability than did pneumolysin and lacked dendritic spine collapse capacity but exhibited equivalent dendritic pathology.
Functional selectivity of G-protein-coupled receptors is believed to originate from ligand-specific conformations that activate only subsets of signaling effectors. In this study, to identify molecular motifs playing important roles in transducing ligand binding into distinct signaling responses, we combined in silico evolutionary lineage analysis and structure-guided site-directed mutagenesis with large-scale functional signaling characterization and non-negative matrix factorization clustering of signaling profiles. Clustering based on the signaling profiles of 28 variants of the β\(_2\)-adrenergic receptor reveals three clearly distinct phenotypical clusters, showing selective impairments of either the Gi or βarrestin/endocytosis pathways with no effect on Gs activation. Robustness of the results is confirmed using simulation-based error propagation. The structural changes resulting from functionally biasing mutations centered around the DRY, NPxxY, and PIF motifs, selectively linking these micro-switches to unique signaling profiles. Our data identify different receptor regions that are important for the stabilization of distinct conformations underlying functional selectivity.