Modelle zur Beschreibung der Auswirkungen von Grenzflächenunordnung auf den Spintransport durch einen antiferromagnetischen Isolator.
pAntiferromagnetische Isolatoren (AFIs) haben mehrere Eigenschaften, die nützlich für Anwendungen in der Spintronik sein können: das Fehlen joulscher Wärme beim Spintransport, ihre schnellere Dynamik im Vergleich zu ferromagnetischen Isolatoren (FI) und die fehlende Kopplung an Magnetfelder. Aktuelle Experimente zeigen zudem, dass eine dünne AFI-Schicht den Spintransport vom FI Yttrium-Eisen-Granat (YIG) zu einem Metall wie Platin verbessern kann.pDer Kopplungsmechanismus an den Grenzflächen ist in bisherigen Modellen jedoch noch nicht detailliert untersucht worden. Die Wechselwirkung zwischen den zwei Seiten der Grenzschicht wurde durch einen effektiven Parameter in den Modellen beschrieben. Allerdings weisen experimentellen Ergebnisse, insbesondere die Varianz von Probe zu Probe und die Tatsache, dass mit polykristallinen AFI Schichten bisher der stärkste Spintransport erreicht wurde, darauf hin, dass die genaue Beschaffenheit der AFI Schicht- und bei sehr dünnen Schichten heißt das insbesondere die Beschaffenheit der Grenzfläche - den Spintransport mitbestimmen. Die Beschaffenheit der Grenzschicht lässt sich dabei nicht mit einem einzelnen Parameter beschreiben.Die zentrale Frage des hier vorgeschlagenen Projekts ist, ob Unordnung an der Grenzschicht den Spintransport behindert oder unterstützt.Konkret untersucht werden sollenp(i) die Richtungsabhängigkeit des Spintransports in AFIs, insbesondere in NiO,p(ii) ein Modell, welches die Rauheit der Grenzfläche, durch eine Grenzflächen-Austauschwechselwirkung mit zufälligen Anteilen darstellt, undp(iii) die Streuung an Kristalldefekten.pZur Berechnung des Spinstroms durch die Grenzflächen, auch in höherer als erster Ordnung in der Grenzflächenkopplung, wird der Formalismus der Greenschen Funktionen auf magnonischen Transport im AFI erweitern werden. Die Übertragung von Methoden, die für den elektrischen Transport durch raue Grenzflächen entwickelt wurden, werden die Berücksichtigung der Unordnung an den AFI-Grenzflächen ermöglichen.pEine erfolgreiche Bearbeitung des Projekts wird in wichtige Erkenntnisse über die Kopplung an der Grenzfläche resultieren. Daraus werden Empfehlungen für die Präparation der entsprechenden Grenzflächen im Experimente folgen, da die Auswirkung etwa von der Rauheit der Grenzfläche auf den Spintransport bekannt sein werden. Darüber hinaus wird eine theoretische Methode zur Verfügung stehen, mit der weitere Berechnungen zu Spintransport in AFIs oder in mehrlagigen Systemen durchgeführt werden können, z. Bsp. solche, die Quanteneffekte beim magnonischen Spintransport untersuchen wollen.
- AG Belzig (Theoretische Physik mit SP Quantentransport)
|(2023): Protectiveness of NAM-based hazard assessment : which testing scope is required? Alternatives to Animal Experimentation : ALTEX. Springer Spektrum. ISSN 1868-596X. eISSN 1868-8551. Available under: doi: 10.14573/altex.2309081
Hazard assessment (HA) requires toxicity tests to allow deriving protective points of departure (PoDs) for risk assessment irrespective of a compound’s mode of action (MoA). The scope of in vitro test batteries (ivTB) thereby necessitated for systemic toxicity is still unclear. We explored the protectiveness regarding systemic toxicity of an ivTB with a scope, which was guided by previous findings from rodent studies, where examining six main targets, including liver and kidney, was sufficient to predict the guideline scope-based PoD with high probability. The ivTB comprises human in vitro models representing liver, kidney, lung and the neuronal system covering transcriptome, mitochondrial dysfunction and neuronal outgrowth. Additionally, 32 CALUX®- and 10 HepG2 BAC-GFP reporters cover a broad range of disturbance mechanisms. Eight compounds were chosen for causing adverse effects such as immunotoxicity or anemia in vivo, i.e., effects not directly covered by assays in the ivTB. PoDs derived from the ivTB and from oral repeated dose studies in rodents were extrapolated to maximum unbound plasma concentrations for comparison. The ivTB-based PoDs were one to five orders of magnitude lower than in vivo PoDs for six of eight compounds, implying that they were protective. The extent of in vitro response varied across test compounds. Especially for hematotoxic substances, the ivTB showed either no response or only cytotoxicity. Assays better capturing this type of hazard would be needed to complement the ivTB. This study highlights the potentially broad applicability of ivTBs for deriving protective PoDs of compounds with unknown MoA.
|(2021): Comparing in vitro human liver models to in vivo human liver using RNA-Seq Archives of Toxicology. Springer. 2021, 95(2), pp. 573-589. ISSN 0340-5761. eISSN 1432-0738. Available under: doi: 10.1007/s00204-020-02937-6
The liver plays an important role in xenobiotic metabolism and represents a primary target for toxic substances. Many different in vitro cell models have been developed in the past decades. In this study, we used RNA-sequencing (RNA-Seq) to analyze the following human in vitro liver cell models in comparison to human liver tissue: cancer-derived cell lines (HepG2, HepaRG 3D), induced pluripotent stem cell-derived hepatocyte-like cells (iPSC-HLCs), cancerous human liver-derived assays (hPCLiS, human precision cut liver slices), non-cancerous human liver-derived assays (PHH, primary human hepatocytes) and 3D liver microtissues. First, using CellNet, we analyzed whether these liver in vitro cell models were indeed classified as liver, based on their baseline expression profile and gene regulatory networks (GRN). More comprehensive analyses using non-differentially expressed genes (non-DEGs) and differential transcript usage (DTU) were applied to assess the coverage for important liver pathways. Through different analyses, we noticed that 3D liver microtissues exhibited a high similarity with in vivo liver, in terms of CellNet (C/T score: 0.98), non-DEGs (10,363) and pathway coverage (highest for 19 out of 20 liver specific pathways shown) at the beginning of the incubation period (0 h) followed by a decrease during long-term incubation for 168 and 336 h. PHH also showed a high degree of similarity with human liver tissue and allowed stable conditions for a short-term cultivation period of 24 h. Using the same metrics, HepG2 cells illustrated the lowest similarity (C/T: 0.51, non-DEGs: 5623, and pathways coverage: least for 7 out of 20) with human liver tissue. The HepG2 are widely used in hepatotoxicity studies, however, due to their lower similarity, they should be used with caution. HepaRG models, iPSC-HLCs, and hPCLiS ranged clearly behind microtissues and PHH but showed higher similarity to human liver tissue than HepG2 cells. In conclusion, this study offers a resource of RNA-Seq data of several biological replicates of human liver cell models in vitro compared to human liver tissue.
|(2018): Prevention of neuronal apoptosis by astrocytes through thiol-mediated stress response modulation and accelerated recovery from proteotoxic stress Cell Death & Differentiation. 2018, 25(12), pp. 2101-2117. ISSN 1350-9047. eISSN 1476-5403. Available under: doi: 10.1038/s41418-018-0229-x
Prevention of neuronal apoptosis by astrocytes through thiol-mediated stress response modulation and accelerated recovery from proteotoxic stress
The development of drugs directly interfering with neurodegeneration has proven to be astonishingly difficult. Alternative therapeutic approaches could result from a better understanding of the supportive function of glial cells for stressed neurons. Therefore, here, we investigated the mechanisms involved in the endogenous neuro-defensive activity of astrocytes. A well-established model of postmitotic human dopaminergic neurons (LUHMES cells) was used in the absence ('LUHMES' mono-culture) or presence ('co-culture') of astrocytes. Inhibition of the LUHMES proteasome led to proteotoxic (protein aggregates; ATF-4 induction) and oxidative (GSH-depletion; NRF-2 induction) stress, followed by neuronal apoptosis. The presence of astrocytes attenuated the neuronal stress response, and drastically reduced neurodegeneration. A similar difference between LUHMES mono- and co-cultures was observed, when proteotoxic and oxidative stress was triggered indirectly by inhibitors of mitochondrial function (rotenone, MPP+). Human and murine astrocytes continuously released glutathione (GSH) into the medium, and transfer of glia-conditioned medium was sufficient to rescue LUHMES, unless it was depleted for GSH. Also, direct addition of GSH to LUHMES rescued the neurons from inhibition of the proteasome. Both astrocytes and GSH blunted the neuronal ATF-4 response and similarly upregulated NRF-1/NFE2L1, a transcription factor counter-regulating neuronal proteotoxic stress. Astrocyte co-culture also helped to recover the neurons' ability to degrade aggregated poly-ubiquitinated proteins. Overexpression of NRF-1 attenuated the toxicity of proteasome inhibition, while knockdown increased toxicity. Thus, astrocytic thiol supply increased neuronal resilience to various proteotoxic stressors by simultaneously attenuating cell death-related stress responses, and enhancing the recovery from proteotoxic stress through upregulation of NRF-1.
|(2018): Stage-specific metabolic features of differentiating neurons : Implications for toxicant sensitivity Toxicology and Applied Pharmacology. 2018, 354, pp. 64-80. ISSN 0041-008X. eISSN 1096-0333. Available under: doi: 10.1016/j.taap.2017.12.013
Stage-specific metabolic features of differentiating neurons : Implications for toxicant sensitivity
Developmental neurotoxicity (DNT) may be induced when chemicals disturb a key neurodevelopmental process, and many tests focus on this type of toxicity. Alternatively, DNT may occur when chemicals are cytotoxic only during a specific neurodevelopmental stage. The toxicant sensitivity is affected by the expression of toxicant targets and by resilience factors. Although cellular metabolism plays an important role, little is known how it changes during human neurogenesis, and how potential alterations affect toxicant sensitivity of mature vs. immature neurons. We used immature (d0) and mature (d6) LUHMES cells (dopaminergic human neurons) to provide initial answers to these questions. Transcriptome profiling and characterization of energy metabolism suggested a switch from predominantly glycolytic energy generation to a more pronounced contribution of the tricarboxylic acid cycle (TCA) during neuronal maturation. Therefore, we used pulsed stable isotope-resolved metabolomics (pSIRM) to determine intracellular metabolite pool sizes (concentrations), and isotopically non-stationary 13C-metabolic flux analysis (INST 13C-MFA) to calculate metabolic fluxes. We found that d0 cells mainly use glutamine to fuel the TCA. Furthermore, they rely on extracellular pyruvate to allow continuous growth. This metabolic situation does not allow for mitochondrial or glycolytic spare capacity, i.e. the ability to adapt energy generation to altered needs. Accordingly, neuronal precursor cells displayed a higher sensitivity to several mitochondrial toxicants than mature neurons differentiated from them. In summary, this study shows that precursor cells lose their glutamine dependency during differentiation while they gain flexibility of energy generation and thereby increase their resistance to low concentrations of mitochondrial toxicants.
|(2017): Good cell culture practice for stem cells and stem-cell-derived models Alternatives to Animal Experimentation : ALTEX. 2017, 34(1), pp. 95-132. ISSN 0946-7785. eISSN 1868-8551. Available under: doi: 10.14573/altex.1607121
The first guidance on Good Cell Culture Practice dates back to 2005. This document expands this to aspects of quality assurance for in vitro cell culture focusing on the increasingly diverse cell types and culture formats used in research, product development, testing and manufacture of biotechnology products and cell-based medicines. It provides a set of basic principles of best practice which can be used in training new personnel, reviewing and improving local procedures, and helping to assure standard practices and conditions for the comparison of data between laboratories and experimentation performed at different times. This includes recommendations for the documentation and reporting of culture conditions. It is intended as guidance, which will facilitate the generation of reliable data from cell culture systems, but is not intended to conflict with local or higher level legislation or regulatory requirements. It may not be possible to meet all recommendations in this guidance for practical, legal or other reasons. However, when necessary to divert from the principles of GCCP, the risk of decreasing the quality of work and safety of laboratory staff should be addressed and any conclusions or alternative approaches justified. This workshop report is considered as a first step toward a revised GCCP 2.0.
|(2016): Astrocyte differentiation of human pluripotent stem cells: new tools for neurological disorder research Frontiers in cellular neuroscience. 2016, 10, 215. eISSN 1662-5102. Available under: doi: 10.3389/fncel.2016.00215
Astrocyte differentiation of human pluripotent stem cells: new tools for neurological disorder research
Astrocytes have a central role in brain development and function, and so have gained increasing attention over the past two decades. Consequently, our knowledge about their origin, differentiation and function has increased significantly, with new research showing that astrocytes cultured alone or co-cultured with neurons have the potential to improve our understanding of various central nervous system diseases, such as amyotrophic lateral sclerosis, Alzheimer's disease, or Alexander disease. The generation of astrocytes derived from pluripotent stem cells (PSCs) opens up a new area for studying neurologic diseases in vitro; these models could be exploited to identify and validate potential drugs by detecting adverse effects in the early stages of drug development. However, as it is now known that a range of astrocyte populations exist in the brain, it will be important in vitro to develop standardized protocols for the in vitro generation of astrocyte subsets with defined maturity status and phenotypic properties. This will then open new possibilities for co-cultures with neurons and the generation of neural organoids for research purposes. The aim of this review article is to compare and summarize the currently available protocols and their strategies to generate human astrocytes from PSCs. Furthermore, we discuss the potential role of human-induced PSCs derived astrocytes in disease modeling.
|(2016): Analysis of Draize eye irritation testing and its prediction by mining publicly available 2008-2014 REACH data Alternatives to Animal Experimentation : ALTEX. 2016, 33(2), pp. 123-134. ISSN 0946-7785. eISSN 1868-8551. Available under: doi: 10.14573/altex.1510053
Analysis of Draize eye irritation testing and its prediction by mining publicly available 2008-2014 REACH data
Public data from ECHA online dossiers on 9,801 substances encompassing 326,749 experimental key studies and additional information on classification and labeling were made computable. Eye irritation hazard, for which the rabbit Draize eye test still represents the reference method, was analyzed. Dossiers contained 9,782 Draize eye studies on 3,420 unique substances, indicating frequent retesting of substances. This allowed assessment of the test's reproducibility test based on all substances tested more than once. There was a 10% chance of a non-irritant evaluation given after a prior severe-irritant result as given by UN GHS classification criteria. The most reproducible outcomes were the results negative (94% reproducible) and severe eye irritant (73% reproducible). To evaluate whether other GHS categorizations predict eye irritation we built a dataset of 5,629 substances (1,931 'irritant' and 3,698 'non-irritant'). The two best decision trees with up to three other GHS classifications resulted in balanced accuracies of 68% and 73%, i.e., in the rank order of the Draize rabbit eye test itself, but both use inhalation toxicity data ("May cause respiratory irritation"), which is not typically available. Next, a dataset of 929 substances with at least one Draize study was mapped to PubChem to compute chemical similarity using 2D conformational fingerprints and Tanimoto similarity. Using a minimum similarity of 0.7 and simple classification by the closest chemical neighbor resulted in balanced accuracy from 73% over 737 substances to 100% at a threshold of 0.975 over 41 substances. This represents a strong support of read-across and (Q)SAR approaches in this area.
|01.03.2019 – 28.02.2022