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Necroptosis is an immunogenic form of programmed cell death characterized by plasma membrane accumulation of activated mixed lineage kinase domain-like (MLKL) that eventually leads to membrane disruption and release of danger-associated molecular patterns (DAMPs). Necroptotic cell death is tightly controlled by checkpoints, including compartmentalization as well as post-translational modifications (PTMs), like phosphorylation and ubiquitination of receptor-interacting protein kinase (RIPK) 1, RIPK3 and MLKL. Removal of plasma membrane-located activated MLKL via endocytosis or exocytosis can counteract necroptosis, but up till now, the exact mechanisms by which necroptosis is regulated downstream of MLKL activation and oligomerization are not fully understood.
Ubiquitination is a key post-translational modification that regulates various cellular processes including cell survival and cell death signaling via ubiquitination of RIPK1, RIPK3 and MLKL. M1-linked (linear) poly-ubiquitination is mediated exclusively by the linear ubiquitin chain assembly complex (LUBAC) which critically regulates cell fate and immune signaling via death receptors such as TNF receptor 1 (TNFR1).
In this study, we demonstrate that M1 poly-Ubiquitin (poly-Ub) increases during necroptosis which can be blocked by inhibition of LUBAC activity with the small-molecule HOIL-1-interacting protein (HOIP) inhibitor HOIPIN-8 or by loss of LUBAC catalytic subunit HOIP. Intriguingly, HOIPIN-8, as well as the HOIP inhibitor gliotoxin, and HOIP knockdown effectively prevent TNFα/smac mimetic/zVAD.fmk-induced necroptotic cell death in cells of human origin, without affecting necroptotic RIPK1 and RIPK3 phosphorylation, necrosome formation and oligomerization of phosphorylated MLKL. We demonstrate that HOIPIN-8 treatment inhibits MLKL translocation to intracellular membranes and accumulation in plasma membrane hotspots as well as MLKL exocytosis. We further confirm that HOIPIN-8 treatment suppresses necroptotic cell death in primary human pancreatic organoids (hPOs). Using time-lapse imaging and live/dead staining, we demonstrate loss of organoid structure and hPO cell death induced by smac mimetics and caspase inhibitors, thus providing a novel platform to investigate necroptosis in near physiological settings. Inhibition of LUBAC activity with HOIPIN-8 prevents hPO collapse and extends cell viability. Of note, loss of the M1 Ub-targeting deubiquitinating enzymes (DUBs) OTU DUB with linear linkage specificity (OTULIN) and cylindromatosis (CYLD) in human cell lines does not affect necroptosis induction and HOIPIN-8-mediated rescue of necroptosis. Intriguingly, inhibition of LUBAC activity with HOIPIN-8 does not block necroptotic cell death in murine cell lines.
Using massive analyses of cDNA ends (MACE)-seq-based global transcriptome analysis we confirm that necroptosis induces a pro-inflammatory cytokine profile which is dependent on LUBAC function and necroptotic signaling. Loss of LUBAC activity prevents the MLKL-dependent production and release of pro-inflammatory cytokines and chemokines.
Finally, we identify Flotillin-1 and -2 (FLOT1/2) as putative targets of necroptosis-induced M1 poly-Ub. Ubiquitin-binding in ABIN and NEMO (UBAN)-based pulldowns of M1 poly-ubiquitinated proteins revealed enrichment of FLOTs after necroptosis induction which is dependent on LUBAC activity and can be blocked with necroptosis inhibitors Nec-1s, GSK’872 and NSA, targeting RIPK1, RIPK3 and MLKL, respectively. Of note, loss of FLOT1/2 potentiates necroptosis suppression induced by LUBAC inhibition with HOIPIN-8.
Together, these findings identify LUBAC-mediated M1 poly-Ub as an important mediator of necroptosis and identify FLOTs as novel putative targets of LUBAC-mediated M1 poly-Ub during necroptosis. In addition, by modeling necroptosis in primary human organoids, we further expand the spectrum of experimental models to study necroptosis in human cellular settings.
Formulation scientists have developed a toolkit of strategies that can improve the solubility and subsequent bioavailability of poorly soluble candidates. Amorphous formulations are especially appealing due to the significant improvement in solubility the amorphous form can provide, but must be stabilized for effective performance (Timpe, 2007).
2. The Importance of Drug Polymer Interactions in Precipitation Inhibition
Polymeric “precipitation inhibitors” have seen widespread usage in the literature (Warren, 2010). The precipitation inhibition effect of polymers on precipitations is related to interference with nucleation and crystal growth (Xu, 2013). Many techniques have been reported in the literature to predict these interactions, however, they are not suitable to screening due to API and time resources required, which are not amenable to early stage pharmaceutical development.
3. Mesoporous Silica: An Emerging Formulation Technology
Mesoporous silicon dioxide has emerged in recent years as a new option for stabilizing the amorphous form. Upon impregnation of the silica with a concentrated drug solution, the drug can be molecularly adsorbed and locally and sterically confined, preventing recrystallization (Ditzinger, 2018). Upon administration of mesoporous silica formulations to the body the amorphous formulation generates supersaturation which must be stabilized using precipitation inhibitors (Guzman, 2007).
4. Co-incorporation: A New Method to Combine Precipitation Inhibitors with Mesoporous Silica
There has been no systematic study of how best to incorporate precipitation inhibitors into mesoporous silica formulations. The current standard practice involves combining inhibitors in a physical mixture with the drug-loaded silica, either by pestle and mortar or overhead stirring. Due to the lack of a defined protocol, there is uncertainty about how reliably the precipitation inhibitor is combined with the drug-loaded silica on a batch to batch basis. In this work, a novel co-incorporated formulation of glibenclamide and the precipitation inhibitor, HPMCAS, onto mesoporous silica was described. By co-incorporating the precipitation inhibitor, the formulation significantly outperformed the commonly applied simple physical blend due to the formation of drug-polymer interactions in the solid state.
5. In Silico Pharmaceutics: A New Method to Select Precipitation Inhibitors for Mesoporous Silica
An approach that can incorporate understanding of the drug-polymer interactions with a quick and efficient screening process would be very useful. The COnductor like Screening MOdel for Real Solvents (COSMO-RS) is a quantum mechanical theory, which can be used to derive thermodynamic properties of interest. (Klamt, 1993, 1995, 2003). We proposed excess mixing enthalpies of drug and polymer could be calculated using the COSMO-RS theory. This new approach was applied to screen precipitation inhibitors for three model compounds, all of which showed a strong positive correlation between the rank assigned based on the calculated free enthalpy of mixing and the overall formulation performance.
6. Conclusion
This body of work aimed to improve the processes underpinning the design and development of mesoporous silica with precipitation inhibitors. Firstly, this involved two extensive literature reviews in the area of solubility enhancement formulation technologies and precipitation inhibition. Secondly, a mechanistic rational and experimental approach was developed to improve the formulation of precipitation inhibitors with mesoporous silica, the “co-incorporation” approach significantly improved process efficiency and formulation performance. Finally, combining insights from the aforementioned review, and learnings from the mechanistic analysis of the “co-incorporation” approach, an in silico screening protocol was developed to calculate the enthalpy of interaction between drug and polymer, to identify the most optimal precipitation inhibitor for a given formulation.
Die 5 Lipoxygenase (5 LO) ist das Schlüsselenzym in der Synthese von Leukotrienen. Sie wird auf transkriptioneller und posttranskriptioneller Ebene reguliert. Die Differenzierung myeloider Zelllinien mit 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) und transformierendem Wachstumsfaktor beta (TGFbeta) führt zu einer Erhöhung der 5 LO mRNA-, Protein-Bildung und der zellulären Enzymaktivität. Hier wurde gezeigt, dass dabei reife, nicht jedoch prä-mRNA der 5 LO im Zytosol und im Zellkern stark angereichert wird und dass beide Agentien in die mRNA-Prozessierung eigreifen. Obwohl die Bindung von VDR-Retinoid-X-Rezeptor (RXR)-Heterodimeren an Bindungsstellen im 5 LO-Promotor mittels DNAseI-Footprinting und EMSAs nachgewiesen wurde, konnten Reportergene unter der Kontrolle des 5 LO-Promotors in transienten und stabilen Transfektionen durch 1,25(OH)2D3/TGFbeta nicht stimuliert werden. Offensichtlich wird die Induktion der Expression der 5 LO durch 1,25(OH)2D3/TGFbeta durch Elemente außerhalb des Promotors vermittelt. In transienten Transfektionen führte der Einbau der kodierenden Sequenz der 5 LO in Luziferase-Plasmide bei Cotransfektion von VDR/RXR zu einer 5 fachen Induktion der Reportergen-Aktivität durch 1,25(OH)2D3/TGFbeta, was durch zusätzlichen Einbau der letzten vier Introns auf eine 13-fache Erhöhung gesteigert wurde. Der VDR zeigte einen Ligand-unabhängigen Effekt. Diese Reportergen-Effekte waren promotorunabhängig und von der kodierenden Sequenz gesteuert. RT-PCR-Analyse wies auf eine Deletion von Teilen der kodierenden Sequenz im Laufe der mRNA-Prozessierung hin, was durch 1,25(OH)2D3/TGFbeta verhindert wird. Auch Cotransfektion der TGFbeta-Effektoren Smads 3/4 führte in Abhängigkeit von der kodierenden Sequenz und in geringerem Maße von der 3'-UTR und den Introns J M, aber unabhängig vom Promotor, zu einer starken Erhöhung der Reportergenaktivität. Die 5 LO-Expression wird in den untersuchten Zellen vermutlich durch posttranskriptionelle Prozesse (Splicing, mRNA-Reifung) herunterreguliert, während 1,25(OH)2D3/TGFbeta die Expression der 5 LO durch eine Gegenregulation zu erhöhen, an der Komplexe beteiligt sind, die vermutlich Smads, VDR-RXR-Dimere, andere Transkriptionsfaktoren, Coaktivatoren, RNA-Polymerase II und Splicing-Faktoren enthalten. Hyperacetylierung des 5 LO-Promoters durch Inkubation mit mit dem Histondeacetylase-Inhibitor TsA führte zu einer transkriptionellen Aktivierung. Die kodierende Sequenz (und die Introns) wirkt diesem Effekt vermutlich durch die Rekrutierung von HDACs an VDR oder Smads, die direkt oder indirekt an die kodierende Region binden, entgegen.
The RAF family of kinases constitutes the members A, B and CRAF. They mediate RAS signaling by linking it to the MEK/ERK transduction module, which regulates cellular processes such as cell proliferation, migration, survival and cell death. As the RAS/RAF/MEK/ERK (MAPK) pathway is found to be activated in human cancers, the RAF kinases have been exploited as valuable therapeutic targets and RAF inhibitors show promising results in the clinic, esp. with tumors harboring an activating BRAFV600E mutation. However, RAF inhibitors paradoxically accelerate metastasis in RAS mutant and BRAF wildtype tumors. They also become ineffective over time in BRAFV600E tumors because of reactivation of downstream mitogen-activated protein kinase (MAPK) signaling by promoting RAF dimerization. Aims of the present work were 1) to investigate the role of ARAF kinase in the paradoxical activation of the enzymatic cascade by RAF inhibitors downstream of mutated RAS and 2) to study the consequences of the loss of ARAF function on signal transduction in vitro and in vivo (nude mice). We have engineered several cell lines that would allow the study of basal and RAF inhibitor induced effects on MAPK activation, tumor cell migration and invasion.
In summary, we were able to show that the RAF isoform ARAF has an obligatory role in promoting MAPK activity and tumor cell invasion in a cell type dependent manner. In these cell types, ARAF depletion prevented the activation of MAPK kinase 1 (MEK1) and extracellular signal-regulated kinase 1 and 2 (ERK1/2) and led to a significant decrease of protrusions growing out of tumor cell spheroids in a three-dimensional (3D) culture that were otherwise induced by BRAFV600E-specific or BRAF/CRAF inhibitors (GDC-0879 and sorafenib, respectively). RAF inhibitors stimulated homodimerization of ARAF and heteromerization of BRAF with CRAF and the scaffolding protein KSR1. However, induced oligomerization was not sufficient to activate MAPK signaling if ARAF was depleted. By employing full length recombinant kinases, we were able to show for the first time that the three RAF isoforms competed for the binding to MEK1. In cell culture models, the overexpression of dimer-deficient ARAF mutants impaired the interaction between ARAF and endogenous MEK1 and thus prevented the subsequent phosphorylation of MEK1 and ERK1/2. Our findings reveal a new role for ARAF in directly activating the MAPK cascade through homodimerization and thereby promoting tumor cell invasion, suggesting the conserved RAF-dimer interface as a target for RAS- and RAF mediated cancer therapy.
Collectively, we provide evidence for the dual role ARAF plays in controlling MAPK signaling and cancer as loss of ARAF promoted strong lung metastasis formation in nude mice. Preliminary data describing the underlying mechanisms behind ARAF-regulated metastases have been presented and discussed.
Bewegung und sportliche Aktivität fördern die Gesundheit des Organismus und senken das Risiko chronischer Krankheiten. Sie bewirken dabei eine Vielzahl von physiologischen und biochemischen Veränderungen in der Skelettmuskulatur, insbesondere Muskelfasertyp-Transformation, Änderungen des Muskelmetabolismus und der Angiogenese. Unter basalen Bedingungen spielen reactive oxygen species (ROS) eine essentielle Rolle für die normale Muskelfunktion. Die Sport-induzierte Produktion von ROS erweist sich als wichtige physiologische Funktion für die Regulierung der Muskelkraft und der Anpassungsreaktion der Muskelfasern auf das Training. Eine der wichtigsten Quellen von ROS im kardiovaskulären System sowie in der Skelettmuskulatur ist die Familie der NADPH-Oxidasen (Nox). Im Unterschied zu anderen NADPHOxidasen ist Nox4 konstitutiv aktiv und produziert Wasserstoffperoxid (H2O2), welches in diversen zellulären Signalkaskaden involviert ist. Gleichzeitig gibt es zahlreiche Hinweise, dass Nox4 über die ROS-Produktion an Sport-induzierten Anpassungsprozessen in Skelettmuskeln beteiligt ist. Vor diesem Hintergrund wurde die Hypothese aufgestellt, dass Nox4 die Sport-induzierte Transformation von langsam- zu schnellkontrahierenden Muskelfasern, die Änderungen des Muskelstoffwechsels sowie die Sport-induzierte und die retinale Angiogenese beeinflusst. Die Untersuchung der Sportinduzierten Fasertyptransformation zeigte, dass die relative Zusammensetzung der Muskelfasern in Nox4-Knockout- und Wildtyp-Mäusen sehr ähnlich und somit von Nox4 unabhängig war. Obwohl das Training die Expression von PGC1α und GLUT4 sowie die AMPK-Aktivierung steigerte, hatte Nox4 nur eine geringe, nicht konstitutive Auswirkung auf den Muskelmetabolismus. Außerdem zeigte die vorliegende Studie, dass Nox4 die Sport-induzierte Angiogenese fördert. Nox4 führte zu einer erhöhten Stretch- und Hypoxie-induzierten Expression von VEGF in Myoblasten, die aus C2C12-Zellen und Satellitenzellen differenziert wurden. Als Folge des Nox4-Knockouts wurde nicht nur eine Reduktion der VEGF-Expression, sondern auch eine Steigerung der Expression von Angiopoietin 1 (Ang1) nachgewiesen, welches die Sport-induzierte Angiogenese hemmte. Das Fehlen von Nox4 schützte außerdem vor der retinalen Neoangiogenese und trug zu einer schnelleren Heilung nach der Oxygen-inducedretinopathy (OIR) bei, indem das Netzwerk neuer Gefäße mittels Ang1 stabilisiert wurde. Somit führt Nox4 zur Sport- und Hypoxie-induzierten Angiogenese durch einen Doppelmechanismus der Induktion und Aufrechterhaltung der VEGF Expression und der Hemmung von Ang1.
This thesis presents experimental studies of proton capture and fragmentation reactions with heavy-ion storage rings. In one experiment, the 96Ru(p, γ)97Rh cross sections near the Gamow window have been measured at the ESR of GSI. In the other experiment, the measurement of the fragmentation yields has been carried out at the CSRe of IMP.
It is essential to determine the cross sections of (γ, p) or (p, γ) reactions for p-process network calculations. However, only very few of the required cross sections have been measured and thus most of them rely solely on Hauser-Feshbach model predictions. The predictions of the model have always very large uncertainties because of the not well-known input parameters. These parameters can be constrained by experiments. Compared to the traditional activation technique, a novel method using a storage ring has been developed to measure the cross sections of (p, γ) reactions in inverse kinematics.
This proton capture experiment has been performed at the ESR, where the circulating 96Ru44+ ions interacted with a hydrogen gas target at 9, 10 and 11 MeV/u. The nuclear reaction products of (p, p), (p, α), (p, n) and (p, γ) reactions were registered by position sensitive detectors. A Geant4 simulation code has been developed to distinguish the (p, γ) reaction products unambiguously from the background reactions. In this work, a relative normalization method has been utilized to accurately determine the cross sections of the (p, γ) reaction. The 96Ru(p, γ)97Rh cross section in the Gamow window of the p process is sensitive to two parameters, i.e., the γ-ray strength function and the optical model potential, while it is mainly sensitive to the γ-ray strength function in the energy region of our experiment. Therefore, our experimental (p, γ) cross sections near 10 MeV/u have been used to directly constrain the γ-ray strength function used in the model. Furthermore, the proton potential has also been constrained by combining our results with additional experimental data for this reaction in the lower energy region. The constrained model has been used to calculate the reaction rate over a wide temperature range, which is an extremely important input for astrophysical calculations.
The yields of fragments produced by 78Kr fragmentation reactions have been measured at the CSRe for the Tz = −1/2 and Tz = 1/2 nuclei along or close to the paths of αp- and rp-processes. The measured yields present a significant odd-even staggering effect for Tz = −1/2 nuclides but they are small for Tz = 1/2 nuclides.
The magnitude of this effect for four consecutive yields has been quantified using a third-order difference formula. It is found that the largest odd-even staggering is reached near the closed shells Z = 20 and Z = 28. Our experimental results could also compared with the data from other experiments with different projectile-target combinations. All these experimental data strongly support the closed shells Z = 20 and Z = 28 for the Tz = −1/2 nuclei.
Bacteria are highly organized organisms which are able to adapt to and propagate under a multitude of environmental conditions. Propagation hereby requires reliable chromosome replication and segregation which has to occur cooperatively with other cellular processes such as transcription, translation or signaling. Several mechanisms were proposed for segregation of the Escherichia coli (E. coli) chromosome, for example a mitotic-like active segregation model or entropy-based passive chromosome segregation. Another segregation model suggests coupled transcription, translation and insertion of membrane proteins (termed "transertion"), which links the replicating chromosome (nucleoid) to the growing cell cylinder.
Fluorescence microscopy was widely used to provide evidence for a distinct segregation model. However, the dynamic nature of bacterial chromosomes, the small bacterial size and the optical resolution limit of ~ 200-300 nm impair unveiling the underlying mechanisms. With the emergence of super-resolution fluorescence microscopy techniques and advanced labeling methods, a new toolbox became available enabling scientists to visualize biomolecules and cellular processes in unprecedented detail. Single-molecule localization microscopy (SMLM) represents a set of super-resolution microscopy techniques which relies on the temporal separation of the fluorescence signal and detection of single fluorophores. Separation can be achieved using photoactivatable or -convertible fluorescent proteins (FPs) in photoactivated localization microscopy (PALM), photoswitchable organic dyes in direct stochastic optical reconstruction microscopy (dSTORM) or dynamically binding fluorescent probes in point accumulation for imaging in nanoscale topography (PAINT). In all these techniques, the fluorescence emission pattern of single fluorophores is spatially localized with nanometer-precision. An artificial image is finally reconstructed from the coordinates of all single fluorophores detected. This provides a spatial resolution of ~ 20 nm, which is perfectly suited to investigate cellular processes in bacteria. In this thesis, different SMLM techniques were applied to study fundamental processes in E. coli. This includes determination of protein copy numbers and distributions as well as the nanoscale organization of nucleic acids and lipids.
A novel labeling approach was applied and used for super-resolution imaging of the E. coli nucleoid. It is based on the incorporation of the modified thymidine analogue 5-ethynyl-2’- deoxyuridine (EdU) into the replicating chromosome. Azide-functionalized organic fluorophores can be covalently attached to the ethynyl group of incorporated EdU bases using a copper-catalyzed "click chemistry" reaction. Under the investigated growth condition, E. coli cells exhibited overlapping replication cycles, which is commonly referred to as multi-fork replication and enables cells to divide faster than they can replicate the entire chromosome. dSTORM imaging of such labeled nucleoids revealed chromosome features with diameters of 50 - 200 nm, representing highly condensed DNA filaments. Sorting single E. coli cells by length allowed visualizing structural changes of the nucleoid throughout the cell cycle. Replicating nucleoids segregated and expanded along the bacterial long axis, while constantly covering the entire width of the cell. Measuring cell and nucleoid length revealed a relative nucleoid expansion rate of 78 ± 6 %. At the same time, nucleoids populated 63 ± 8 % of the cell length, almost exclusively being localized to the cylindrical part of the cell. This value was hence normalized to the cylindrical fraction of the cell, yielding a value of 79 ± 10 % (nucleoid-populated fraction of the cell cylinder), which is in good agreement with the observed relative nucleoid expansion rate. These results therefore support a growth-mediated segregation model, in which the chromosome is anchored to the inner membrane and passively segregated into the prospective daughter cells upon cell growth. 3-dimensional dSTORM imaging of labeled nucleoids confirmed that compacted nucleoids helically wrap along the inner membrane. Similar results were obtained by imaging orthogonally aligned E. coli cells using a holographic optical tweezer approach.
In order to visualize particular proteins together with the nucleoid, several correlative imaging workflows were established, facilitating multi-color SMLM imaging in single E. coli cells. These workflows bypass prior limitations of SMLM, including destruction of FPs by reactive oxygen species in copper-catalyzed click reactions or incompatibility of PALM imaging with dSTORM imaging buffers. A sequential SMLM imaging routine was developed which is based on postlabeling and retrieval of previously imaged cells. Optimal imaging conditions can be maintained for each fluorophore, enabling to extract quantitative information from PALM measurements while correlating the protein distribution to the nucleoid ultrastructure within the highly resolved cell envelope. Applying this workflow to an E. coli strain carrying a chromosomal rpoC - photoactivatable mCherry (PAmCh) fusion, transcribing RNA polymerase (RNAP) was found to be localized on the surface of nucleoids, where active genes are exposed towards the cytosol. During growth in nutrient-rich medium, the majority of RNAP molecules was bound to the chromosome, thus ensuring that the RNAP pool is equally distributed to the daughter cells upon cell division. This work represented the first triple-color SMLM study performed in E. coli cells. ...
Redox homeostasis must be kept in balance for an intact redox signaling, which is necessary to control neuronal pathways such as growth cone pathfinding, synaptic plasticity and transmission (Oswald, Garnham, Sweeney, & Landgraf, 2018).
Nucleoredoxin (NXN) is an oxidoreductase and thioredoxin-like protein holding two conserved cysteine residues in its structure (Funato & Miki, 2007), which are essential for its redox-regulating functionality. The function of NXN in neurons is still less well studied. But the expression of NXN in neurons, which was confirmed through analyzing adult NXN-LacZ reporter mice, suggested a dominant functional role in neuronal pathways. Initial experiments revealed calcium-calmodulin-dependent kinase 2 a (Camk2a) as a potential interaction partner through a Yeast-2-Hybrid screen (not shown) which is the major protein to induce synaptic plasticity during neuronal activity. Therefore, neuronal expression of NXN and the potential interaction with Camk2a prompted us to investigate deeper into the neuronal pathway. The goal of this work was to confirm the interaction of Camk2a and NXN with further experiments and to characterize behavior of mice carrying a neuronal NXN deletion. To achieve a pan-neuronal depletion of NXN expression in our mouse model, we used the Cre/loxP system with a NestinCre driver. We did not achieve the expected complete deletion of NXN due to unknown compensatory mechanisms. Nevertheless, the partial deletion of NXN in our transgenic mouse model prevented embryonic lethality as occurring in complete NXN knockout mice (Funato et al., 2010). The interaction of Camk2a and NXN was confirmed through proximity ligation assay (PLA) and immunofluorescence staining of primary cortical neurons.
Investigations of the functional interaction revealed a lower redox-sensitivity of Camk2a activity in NXN-deficient brain samples. Additionally, the respiratory activity was significantly reduced in mitochondria of NXN deficient mouse brain pointing to possible dysfunctional mitochondria which is also observed in various neurodegenerative diseases, e.g.: Alzheimer, Parkinson, and Huntington disease (Norat et al., 2020). Unexpectedly, behavioral studies revealed only a subtle effect of the pan-neuronal NXN-deficiency. Significant differences between genotypes were found at the reduction of exploratory behavior and a reduced motivation for the voluntary wheel running in NesNXN-/- mice, which is normally seen as a joyful and rewarding activity. The observed behavior of NesNXN-/- mice potentially results from interaction mechanisms of NXN with Camk2a, as well as decreased oxidation of
Camk2a and further unidentified target proteins of NXN.
Conclusively, function of NXN was revealed as a non-essential redox modulator of Camk2a in neurons. The behavioral phenotype of NesNXN-/- mice is probably compensated through unknown mechanisms. Redox signaling of Camk2a in neurons is regulated through various components such as TXN or GSH, which can backup each other (Branco et al., 2017; Ren et al., 2017). NXN is an additional but not essential regulator.
Most of the elements heavier than iron are produced through neutron capture reactions in the s- and r -process. The overall path of the s-process is well understood and can be accurately reproduced in network simulations. However, there are still some neutron capture reactions of unstable nuclei involved in the s-process, which were not yet measured due to the difficulty in producing suitable targets. In those cases, theoretical models have to be used to estimate the missing cross section.
One example is the branching point nucleus 86Rb, whose neutron capture cross section cannot be directly measured due to its short half life of 18.86 days. It is, however, also possible to measure its inverse, the 87Rb(g,n) reaction in order to obtain the 86Rb(n,g) cross section through the principle of detailed balance.
Natural rubidium was irradiated with a quasi-monoenergetic photon beam in the energy range between 10.7 MeV and 16 MeV in order to investigate the photo-dissociation cross section of 87Rb. The results are presented in this thesis. Not only the total cross section of 87Rb(g,n), but also the partial production cross section of the ground and isomeric state of 84Rb through the 85Rb(g,n) reaction was measured.
Not all isotopes can be reached via neutron capture reaction, and are therefore bypassed by the s- and r -process. These 35 proton-rich isotopes are called p-nuclei and are produced in the γ-process by a chain of photo-disintegration reactions in Type II supernovae. Network calculations of Type II supernova show that the γ-process can explain the production of most p-nuclei, but some – especially 92/94Mo and 96/98Ru – are heavily underproduced. While this could be the result of deficiencies in the corresponding stellar models or insufficient knowledge of the involved reaction rates, it is also possible that the missing p-nuclei are synthesized in other production scenarios.
An alternative scenario for 92Mo is the production via a chain of proton capture reactions in Type Ia supernovae. One important reaction in this chain is the 90Zr(p,g) reaction. The reaction cross section was already measured several times, but the results were inconclusive. In the present work, the 90 Zr(p,g) reaction was measured using the in-beam gamma-ray spectroscopy technique and the discrepancies between the data sets could be largely explained.
Die nach dem Verfall des Moskauer Imperiums innerhalb der nordatlantischen Allianz entstandene Diskussion über eine eigenständigere europäische Sicherheitspolitik ist nicht neu. Ist diese Diskussion heute jedoch eingebunden in eine generelle Debatte über die künftigen sicherheitspolitischen Strukturen und einer stärkeren organisatorischen Verflechtung beispielsweise von Vereinten Nationen, Europäischer Union, OSZE und NATO, so stand in den späten fünfziger und frühen sechziger Jahren vor allem die Frage einer verstärkten politischen Konsultation und Kooperation innerhalb des Bündnisses und damit verbunden die Teilhabe der (kontinental-)europäischen Mitglieder der Atlantischen Allianz am nuklearen Entscheidungsprozeß auf der Tagesordnung. Dahinter stand die zwiespältige europäische Besorgnis, die USA könnten sich entweder mit Moskau einigen und ihre Streitkräfte in Europa reduzieren oder ganz abziehen, oder aber sie würden bleiben und die europäischen Staaten dominieren. Für beide Fälle wollten die Europäer, unter ihnen in vorderster Linie Bundeskanzler Konrad Adenauer und - als Sonderfall - Charles de Gaulle, Vorsorge treffen, wobei die nukleare Partizipation als Königsweg zu Macht und Einfluß in der Allianz galt. Die amerikanische Regierung hingegen war stets an einer stärkeren Teilung der Verteidigungslasten interessiert, ohne aber ihren Einfluß aufgeben oder von den Verbündeten zu abhängig werden zu wollen. Zur Vertrauensbildung und engeren Anbindung war Washington hierbei auch zu Zugeständnissen in der Teilhabe an der nuklearen Verfügungsgewalt bereit, womit jedoch möglichst neue nationale Nuklearstreitmächte vermieden werden sollten. ...