122 research outputs found
Bildungsmechanismus und physiologische Relevanz supramolekularer Proteincluster des Amyloid Precursor Protein APP in der Zellmembran
Proteine in biologischen Membranen sind in der Regel heterogen in Domänen organisiert. Die Mechanismen dieser Segregation in Membranproteincluster unterschiedlicher Zusammensetzung sind noch immer unverstanden. Auch das Amyloid Precursor Protein APP bildet Proteincluster in der Plasmamembran, welche die Endozytose von APP in das frĂźhe Endosomenkompartiment begĂźnstigen kĂśnnen. Dies ist von besonderer Bedeutung, da APP nach seiner Internalisierung durch proteolytische Prozessierung u.a. in das Aβ-Peptid gespalten wird. Dieses Peptid kann entweder in seiner aggregierten Form, den sogenannten amyloiden Plaques, oder als lĂśsliches Oligomer der AuslĂśser neurodegenerativer Veränderungen bei der Alzheimerschen Demenz sein. Der eigentliche Bildungsmechanismus der plasmalemmalen APP-Cluster ist ungeklärt. In dieser Arbeit wurde daher der APP-Clustermechanismus systematisch unter Anwendung verschiedener Mikroskopiemethoden untersucht. Es konnte gezeigt werden, dass APP in der Plasmamembran hauptsächlich Ăźber seine extrazelluläre Domäne aggregiert. Dabei haben die Glykokalyx und der Glykosylierungsstatus von APP keinen Einfluss auf die Clusterbildung. Auch eine sterische Hinderung oder Friktion der groĂen Ektodomäne mit der umgebenden Zellmatrix konnte als Ursache fĂźr die Proteinaggregation ausgeschlossen werden. Vielmehr wurde in dieser Arbeit eine fundamentale Rolle der fĂźnf ersten Aminosäuren DAEFR in der N-terminalen Aβ-Region bei der lateralen Organisation von APP in Proteincluster entdeckt. Diese fĂźnf Aminosäuren stellen eine notwendige Bedingung fĂźr die Bildung von Proteinclustern dar. Des Weiteren konnte gezeigt werden, dass stabile APP-Cluster eine notwendige Voraussetzung fĂźr den Aufenthalt von APP in Clathrinmembrandomänen und somit auch fĂźr die Endozytose von APP sind. Die in dieser Arbeit vorgelegten Daten beschreiben eine bisher unbekannte physiologische Funktion der N-terminalen Aβ-Sequenz bei der Regulation der Clusterbildung und der Endozytose von APP. Da nach der Internalisierung in das frĂźhe Endosomenkompartiment das Aβ-Peptid durch proteolytische Spaltung entsteht, steuert die Aβ-Region im intakten Protein folglich die Prozessierung zum neurotoxischen Aβ-Peptid. Deshalb wurde in dieser Arbeit ein vollkommen neuer Therapieansatz fĂźr die Alzheimersche Erkrankung diskutiert, der darauf beruht, die Clusterbildung durch an die extrazelluläre Aβ-Region bindende MolekĂźle zu stĂśren
CDKN2BAS is associated with periodontitis in different European populations and is activated by bacterial infection
Epidemiological studies have indicated a relationship between coronary heart disease (CHD) and periodontitis. Recently, CDKN2BAS was reported as a shared genetic risk factor of CHD and aggressive periodontitis (AgP), but the causative variant has remained unknown. To identify and validate risk variants in different European populations, we first explored 150 kb of the genetic region of CDKN2BAS including the adjacent genes CDKN2A and CDKN2B, covering 51 tagging single nucleotide polymorphisms (tagSNPs) in AgP and chronic periodontitis (CP) in individuals of Dutch origin (n=313). In a second step, we tested the significant SNP associations in an independent AgP and CP population of German origin (n=1264). For the tagSNPs rs1360590, rs3217992, and rs518394, we could validate the associations with AgP before and after adjustment for the covariates smoking, gender and diabetes, with SNP rs3217992 being the most significant (OR 1.48, 95% CI 1.19 to 1.85; p=0.0004). We further showed in vivo gene expression of CDKN2BAS, CDKN2A, CDKN2B, and CDK4 in healthy and inflamed gingival epithelium (GE) and connective tissue (CT), and detected a significantly higher expression of CDKN2BAS in healthy CT compared to GE (p=0.004). After 24 h of stimulation with Porphyromonas gingivalis in Streptococcus gordonii pre-treated gingival fibroblast (HGF) and cultured gingival epithelial cells (GECs), we observed a 25-fold and fourfold increase of CDKN2BAS gene expression in HGFs (p=0.003) and GECs (p=0.004), respectively. Considering the global importance of CDKN2BAS in the disease risk of CHD, this observation supports the theory of inflammatory components in the disease physiology of CHD
Role of NOD2/CARD15 in coronary heart disease
<p>Abstract</p> <p>Background:</p> <p>Bacterial DNA has been repeatedly detected in atheromatous lesions of coronary heart disease (CHD) patients. Phylogenetic signatures in the atheroma lesions that are similar to those of bacterial biofilms on human barrier organs, including the respiratory or gastrointestinal tract, raise the question of a defective barrier function in CHD. NOD2 plays a major role in defense against bacterial invasion. Genetic variation in the <it>CARD15 </it>gene, which encodes NOD2, was previously shown to result in a barrier defect that causes chronic inflammatory disorders (e.g. Crohn disease). In the present study, we investigated the possible involvement of NOD2/<it>CARD15 </it>in the pathology of CHD by <it>i) </it>analyzing the local expression of NOD2 in atherectomy versus healthy tissue (n = 5 each) using histochemical immunofluorescence and <it>ii) </it>by testing the three major functional <it>CARD15 </it>variants (R702W, G908R and 1007fs) for association with early-onset CHD in 900 German patients and 632 healthy controls.</p> <p>Results:</p> <p>In atherectomy tissue of CHD patients, NOD2 was detected in inflammatory cells at the luminal sides of the lesions. However, the allele and genotype frequencies of the three major <it>CARD15 </it>polymorphisms did not differ between CHD patients and controls.</p> <p>Conclusion:</p> <p>The NOD2 up-regulation in atheroma lesions indicates an involvement of this protein in the pathology of CHD. Although NOD2 could be important in local immune response mechanisms, none of the analyzed <it>CARD15 </it>variants seem to play a significant role in the etiology of CHD.</p
Oomycete small RNAs bind to the plant RNA-induced silencing complex for virulence
The exchange of small RNAs (sRNAs) between hosts and pathogens can lead to gene silencing in the recipient organism, a mechanism termed cross-kingdom RNAi (ck-RNAi). While fungal sRNAs promoting virulence are established, the significance of ck-RNAi in distinct plant pathogens is not clear. Here, we describe that sRNAs of the pathogen Hyaloperonospora arabidopsidis, which represents the kingdom of oomycetes and is phylogenetically distant from fungi, employ the host plant's Argonaute (AGO)/RNA-induced silencing complex for virulence. To demonstrate H. arabidopsidis sRNA (HpasRNA) functionality in ck-RNAi, we designed a novel CRISPR endoribonuclease Csy4/GUS reporter that enabled in situ visualization of HpasRNA-induced target suppression in Arabidopsis. The significant role of HpasRNAs together with AtAGO1 in virulence was revealed in plant atagol mutants and by transgenic Arabidopsis expressing a short-tandem-target-mimic to block HpasRNAs, that both exhibited enhanced resistance. HpasRNA-targeted plant genes contributed to host immunity, as Arabidopsis gene knockout mutants displayed quantitatively enhanced susceptibility
Sensing dot with high output swing for scalable baseband readout of spin qubits
A key requirement for quantum computing, in particular for a scalable quantum
computing architecture, is a fast and high-fidelity qubit readout. For
semiconductor based qubits, one limiting factor is the output swing of the
charge sensor. We demonstrate GaAs and Si/SiGe asymmetric sensing dots (ASDs),
which exceed the response of a conventional charge sensing dot by more than ten
times, resulting in a boosted output swing of . This
substantially improved output signal is due to a device design with a strongly
decoupled drain reservoir from the sensor dot, mitigating negative feedback
effects of conventional sensors. The large output signal eases the use of very
low-power readout amplifiers in close proximity to the qubit and will thus
render true scalable qubit architectures with semiconductor based qubits
possible in the future.Comment: 8 pages, 7 figure
Tailoring potentials by simulation-aided design of gate layouts for spin qubit applications
Gate-layouts of spin qubit devices are commonly adapted from previous
successful devices. As qubit numbers and the device complexity increase,
modelling new device layouts and optimizing for yield and performance becomes
necessary. Simulation tools from advanced semiconductor industry need to be
adapted for smaller structure sizes and electron numbers. Here, we present a
general approach for electrostatically modelling new spin qubit device layouts,
considering gate voltages, heterostructures, reservoirs and an applied
source-drain bias. Exemplified by a specific potential, we study the influence
of each parameter. We verify our model by indirectly probing the potential
landscape of two design implementations through transport measurements. We use
the simulations to identify critical design areas and optimize for robustness
with regard to influence and resolution limits of the fabrication process.Comment: 10 pages, 6 figure
Inference with Artificial Neural Networks on Analog Neuromorphic Hardware
The neuromorphic BrainScaleS-2 ASIC comprises mixed-signal neurons and
synapse circuits as well as two versatile digital microprocessors. Primarily
designed to emulate spiking neural networks, the system can also operate in a
vector-matrix multiplication and accumulation mode for artificial neural
networks. Analog multiplication is carried out in the synapse circuits, while
the results are accumulated on the neurons' membrane capacitors. Designed as an
analog, in-memory computing device, it promises high energy efficiency.
Fixed-pattern noise and trial-to-trial variations, however, require the
implemented networks to cope with a certain level of perturbations. Further
limitations are imposed by the digital resolution of the input values (5 bit),
matrix weights (6 bit) and resulting neuron activations (8 bit). In this paper,
we discuss BrainScaleS-2 as an analog inference accelerator and present
calibration as well as optimization strategies, highlighting the advantages of
training with hardware in the loop. Among other benchmarks, we classify the
MNIST handwritten digits dataset using a two-dimensional convolution and two
dense layers. We reach 98.0% test accuracy, closely matching the performance of
the same network evaluated in software
CDKN2BAS is associated with periodontitis in different European populations and is activated by bacterial infection
Epidemiological studies have indicated a relationship between coronary heart disease (CHD) and periodontitis. Recently, CDKN2BAS was reported as a shared genetic risk factor of CHD and aggressive periodontitis (AgP), but the causative variant has remained unknown. To identify and validate risk variants in different European populations, we first explored 150 kb of the genetic region of CDKN2BAS including the adjacent genes CDKN2A and CDKN2B, covering 51 tagging single nucleotide polymorphisms (tagSNPs) in AgP and chronic periodontitis (CP) in individuals of Dutch origin (n=313). In a second step, we tested the significant SNP associations in an independent AgP and CP population of German origin (n=1264). For the tagSNPs rs1360590, rs3217992, and rs518394, we could validate the associations with AgP before and after adjustment for the covariates smoking, gender and diabetes, with SNP rs3217992 being the most significant (OR 1.48, 95% CI 1.19 to 1.85; p=0.0004). We further showed in vivo gene expression of CDKN2BAS, CDKN2A, CDKN2B, and CDK4 in healthy and inflamed gingival epithelium (GE) and connective tissue (CT), and detected a significantly higher expression of CDKN2BAS in healthy CT compared to GE (p=0.004). After 24 h of stimulation with Porphyromonas gingivalis in Streptococcus gordonii pre-treated gingival fibroblast (HGF) and cultured gingival epithelial cells (GECs), we observed a 25-fold and fourfold increase of CDKN2BAS gene expression in HGFs (p=0.003) and GECs (p=0.004), respectively. Considering the global importance of CDKN2BAS in the disease risk of CHD, this observation supports the theory of inflammatory components in the disease physiology of CHD
Enhanced Gilbert Damping in Thin Ferromagnetic Films
Using a scattering matrix approach, the precession of the magnetization of a
ferromagnet is shown to transfer spins into adjacent normal metal layers. This
``pumping'' of spins slows down the precession corresponding to an enhanced
Gilbert damping factor in the Landau-Lifshitz equation. The damping is
expressed in terms of the scattering matrix of the ferromagnet-normal metal
interface, which is accessible to model and first-principles calculations. Our
estimates for permalloy thin films explain the trends observed in recent
experiments.Comment: 1 figur
Low-frequency spin qubit energy splitting noise in highly purified 28Si/SiGe
We identify the dominant source for low-frequency spin qubit splitting noise in a highly isotopically-purified silicon device with an embedded nanomagnet and a spin echo decay time Techo2â=â128âÂľs. The power spectral density (PSD) of the charge noise explains both, the clear transition from a 1/f2- to a 1/f-dependence of the splitting noise PSD as well as the experimental observation of a decreasing time-ensemble spin dephasing time, from Tâ2ââ20âÂľs, with increasing measurement time over several hours. Despite their strong hyperfine contact interaction, the few 73Ge nuclei overlapping with the quantum dot in the barrier do not limit Tâ2, likely because their dynamics is frozen on a few hours measurement scale. We conclude that charge noise and the design of the gradient magnetic field are the key to further improve the qubit fidelity in isotopically purified 28Si/SiGe
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