Knockdown of Amyloid Precursor Protein in Zebrafish Causes Defects in Motor Axon Outgrowth

Amyloid precursor protein (APP) plays a pivotal role in Alzheimer’s disease (AD) pathogenesis, but its normal physiological functions are less clear. Combined deletion of the APP and APP-like protein 2 (APLP2) genes in mice results in post-natal lethality, suggesting that APP performs an essential, if redundant, function during embryogenesis. We previously showed that injection of antisense morpholino to reduce APP levels in zebrafish embryos caused convergent-extension defects. Here we report that a reduction in APP levels causes defective axonal outgrowth of facial branchiomotor and spinal motor neurons, which involves disorganized axonal cytoskeletal elements. The defective outgrowth is caused in a cell-autonomous manner and both extracellular and intracellular domains of human APP are required to rescue the defective phenotype. Interestingly, wild-type human APP rescues the defective phenotype but APPswe mutation, which causes familial AD, does not. Our results show that the zebrafish model provides a powerful system to delineate APP functions in vivo and to study the biological effects of APP mutations

Free Energy Simulations of a GTPase: GTP and GDP Binding to Archaeal Initiation Factor 2

International audienceArchaeal initiation factor 2 (aIF2) is a protein involved in the initiation of protein biosynthesis. In its GTP-bound, "ON" conformation, aIF2 binds an initiator tRNA and carries it to the ribosome. In its GDP-bound, "OFF" conformation, it dissociates from tRNA. To understand the specific binding of GTP and GDP and its dependence on the ON or OFF conformational state of aIF2, molecular dynamics free energy simulations (MDFE) are a tool of choice. However, the validity of the computed free energies depends on the simulation model, including the force field and the boundary conditions, and on the extent of conformational sampling in the simulations. aIF2 and other GTPases present specific difficulties; in particular, the nucleotide ligand coordinates a divalent Mg(2+) ion, which can polarize the electronic distribution of its environment. Thus, a force field with an explicit treatment of electronic polarizability could be necessary, rather than a simpler, fixed charge force field. Here, we begin by comparing a fixed charge force field to quantum chemical calculations and experiment for Mg(2+):phosphate binding in solution, with the force field giving large errors. Next, we consider GTP and GDP bound to aIF2 and we compare two fixed charge force fields to the recent, polarizable, AMOEBA force field, extended here in a simple, approximate manner to include GTP. We focus on a quantity that approximates the free energy to change GTP into GDP. Despite the errors seen for Mg(2+):phosphate binding in solution, we observe a substantial cancellation of errors when we compare the free energy change in the protein to that in solution, or when we compare the protein ON and OFF states. Finally, we have used the fixed charge force field to perform MDFE simulations and alchemically transform GTP into GDP in the protein and in solution. With a total of about 200 ns of molecular dynamics, we obtain good convergence and a reasonable statistical uncertainty, comparable to the force field uncertainty, and somewhat lower than the predicted GTP/GDP binding free energy differences. The sign and magnitudes of the differences can thus be interpreted at a semiquantitative level, and are found to be consistent with the experimental binding preferences of ON- and OFF-aIF2

Increased Secreted Amyloid Precursor Protein-α (sAPPα) in Severe Autism: Proposal of a Specific, Anabolic Pathway and Putative Biomarker

Autism is a neurodevelopmental disorder characterized by deficits in verbal communication, social interactions, and the presence of repetitive, stereotyped and compulsive behaviors. Excessive early brain growth is found commonly in some patients and may contribute to disease phenotype. Reports of increased levels of brain-derived neurotrophic factor (BDNF) and other neurotrophic-like factors in autistic neonates suggest that enhanced anabolic activity in CNS mediates this overgrowth effect. We have shown previously that in a subset of patients with severe autism and aggression, plasma levels of the secreted amyloid-β (Aβ) precursor protein-alpha form (sAPPα) were significantly elevated relative to controls and patients with mild-to-moderate autism. Here we further tested the hypothesis that levels of sAPPα and sAPPβ (proteolytic cleavage products of APP by α- and β-secretase, respectively) are deranged in autism and may contribute to an anabolic environment leading to brain overgrowth. We measured plasma levels of sAPPα, sAPPβ, Aβ peptides and BDNF by corresponding ELISA in a well characterized set of subjects. We included for analysis 18 control, 6 mild-to-moderate, and 15 severely autistic patient plasma samples. We have observed that sAPPα levels are increased and BDNF levels decreased in the plasma of patients with severe autism as compared to controls. Further, we show that Aβ1-40, Aβ1-42, and sAPPβ levels are significantly decreased in the plasma of patients with severe autism. These findings do not extend to patients with mild-to-moderate autism, providing a biochemical correlate of phenotypic severity. Taken together, this study provides evidence that sAPPα levels are generally elevated in severe autism and suggests that these patients may have aberrant non-amyloidogenic processing of APP

Effect of rapid thermal annealing on texture and properties of pulsed laser deposited zinc oxide thin films

A comparative study on the properties of pulsed laser deposited ZnO thin films as a function of rapid thermal annealing temperature (Ta) is presented. Grazing incidence x-ray diffraction pattern reveals that preferred orientation of the films changes from (002) to (103) as Ta varies from 500 to 800 1C. A clear correlation between grain morphology and texture formation is noticed. Photoluminescence spectra of all films show a strong near-band-edge ultraviolet (UV) emission and the UV emission intensity increases with Ta. Simultaneously, a weak and broad green emission centered at 505 nm corresponds to oxygen vacancies also emerged in the films annealed at TaZ600 1C. A significant hysteresis behavior is observed in current–voltage characteristics and attributed to trapping/ de-trapping driven effect. It is shown that high resistance state is dominated by space charge limited currents and low resistance state is governed by both Pool–Frenkel (2–5 V) and Schottky emission (0–2 V).This study has been partially funded by: (i) FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) under the projects PTDC/FIS/098943/2008 and PEST-C/FIS/UI607/2011; (ii) European COST Actions MP0901-NanoTP and MP0903-NanoAlloy. We acknowledge the Synchrotron Light Source ANKA for provision of beamtime at the PDIFF beamline and financial support for our participation at the experiments under proposal MNT-123. The authors K.C.S. and K.K. are grateful for financial support through the FCT grants SFRH/BPD/68489/2010 and SFRH/BPD/87215/2012 respectively. The authors would also like to thank Engineer Jose Santos for technical support at Thin Film Laboratory

Structural mechanism of the ATP-induced dissociation of rigor myosin from actin

Myosin is a true nanomachine, which produces mechanical force from ATP hydrolysis by cyclically interacting with actin filaments in a four-step cycle. The principle underlying each step is that structural changes in separate regions of the protein must be mechanically coupled. The step in which myosin dissociates from tightly bound actin (the rigor state) is triggered by the 30 Å distant binding of ATP. Large conformational differences between the crystal structures make it difficult to perceive the coupling mechanism. Energetically accessible transition pathways computed at atomic detail reveal a simple coupling mechanism for the reciprocal binding of ATP and actin

High-performance ferroelectric-dielectric multilayered thin films for energy storage capacitors

Herein, the effect of the insertion of a thin dielectric HfO2:Al2O3 (HAO) layer at different positions in the Pt/0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BCZT)/Au structure on the energy storage performance of the capacitors is investigated. A high storage performance is achieved through the insertion of a HAO layer between BCZT and Au layers. The insertion of the dielectric layer causes a depolarization field which results in a high linearity hysteresis loop with low energy dissipation. The Pt/BCZT/HAO/ Au capacitors show an impressive energy storage density of 99.8 J cm−3 and efficiency of 71.0%, at an applied electric field of 750 kV cm−1. Further, no significant change in the energy storage properties is observed after passing 108 switching cycles through the capacitor. The presence of resistive switching (RS) in leakage current characteristics confirms the strong charge coupling between ferroelectric and insulator layers. The same trend of the RS ratio and the energy storage performance with the variation of the architecture of the devices suggests that the energy storage properties can be improved through the charge coupling between the layers. By combining ferroelectrics and dielectrics into one single structure, the proposed strategy provides an efficient way for developing highly efficient energy storage capacitors.This work was supported by: i) the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding Contract UID/FIS/04650/2013 and ii) the Project Norte-070124FEDER-000070 Nanomateriais Multifuncionais. Part of this work was carried out with the support of the Karlsruhe Nano Micro Facility (KNMF), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT), under the proposal 2017-017-017030. J.P.B.S. is grateful for financial support through the FCT Grant No. SFRH/ BPD/92896/2013. K.C.S. acknowledges UGC and DST-SERB, Govt. of India for the funds through Grant Nos. F.4-5(59-FRP/2014(BSR)) and ECR/2017/000068, respectively. The authors would also like to thank Engineer José Santos for the technical support at the Thin Films Laboratory (Univ. Minho).info:eu-repo/semantics/publishedVersio

Ferroelectric switching behavior of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films

The effect of pulse amplitude on the ferroelectric and switching properties of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films has been studied. The structural and morphological analysis revealed that the films had a well crystallized perovskite phase and grain size of about 30-40 nm. A well saturated P-E hysteresis loop was observed with a remnant polarization (Pr) approximate to 4.8 mu C/cm(2) and a coercive field approximate to 100 kV/cm at a frequency of 1 kHz. The P-r has been found to be decreased only 4.3% after passing 8.0 x 10(8) cycles. The analysis of switching response with nucleation limited switching model reveals that characteristic switching time (t(0)) variance is due to the random distribution of the local electric fields. The peak value of polarization current and t(0) exhibits exponential dependence on reciprocal of pulse amplitude. (C) 2012 Elsevier B. V. All rights reserved.The author J.P.B.S. thanks FCT for the financial support (grant SFRH/BD/44861/2008). K. C. S thanks to FCT for Postdoc grant (SFRH/BPD/68489/2010) S. A. S. R. thanks FCT for the financial support (grant SFRH/BD/30531/2006). JMS thanks FCT for the financial support (grant SFRH/BPD/64850/2009)

Oxygen partial pressure effect on structural and electrical behavior of pulsed laser deposited Zn0.98Co0.02O thin films

Thin Zn0.98Co0.02O films were grown by pulsed laser deposition at different oxygen partial pressure (PO2) and its influence on their structural and electrical properties was investigated. Raman and photoluminescence studies revealed that zinc interstitial defects significantly decreased with increase of PO2. Complex impedance spectroscopy has been made to elucidate conduction mechanism and electronic relaxation process in Zn0.98Co0.02O films. Resistivity/impedance in the films grown at 0.1 mbar decreased as the temperature increases while the films grown at 0.01 and 0.001 mbar have shown opposite trend. The change in resistivity/impedance with temperature in the films grown at low and high PO2 is attributed to annihilation of defects and thermal activation of free carriers respectively. The relaxation time in the films grown at low PO2 increases with the temperature. It exhibits an exponential dependence on the inverse temperature with three different slopes. The corresponding energies estimated from Arrhenius type relation are very close to the energies for electronic relaxation of zinc interstitials, zinc antisities and oxygen vacancies respectively. Impedance analysis and current–voltage characteristics suggest that the resistivity of Zn0.98Co0.02O films is mainly due to bulk effect of the films.Fundação para a Ciência e a Tecnologia (FCT