Dieter Fischer

Dynamic DNA methylation programs persistent adverse effects of early-life stress

Adverse early life events can induce long-lasting changes in physiology and behavior. We found that early-life stress (ELS) in mice caused enduring hypersecretion of corticosterone and alterations in passive stress coping and memory. This phenotype was accompanied by a persistent increase in arginine vasopressin (AVP) expression in neurons of the hypothalamic paraventricular nucleus and was reversed by an AVP receptor antagonist. Altered Avp expression was associated with sustained DNA hypomethylation of an important regulatory region that resisted age-related drifts in methylation and centered on those CpG residues that serve as DNA-binding sites for the methyl CpG–binding protein 2 (MeCP2). We found that neuronal activity controlled the ability of MeCP2 to regulate activity-dependent transcription of the Avp gene and induced epigenetic marking. Thus, ELS can dynamically control DNA methylation in postmitotic neurons to generate stable changes in Avp expression that trigger neuroendocrine and behavioral alterations that are frequent features in depression.

Subtle shifts in the ratio between pro- and antiapoptotic molecules after activation of corticosteroid receptors decide neuronal fate

Glucocorticoid receptor (GR) activation induces apoptosis of granule cells in the hippocampus. In contrast, neuroprotection is seen after mineralocor‐ticoid receptor (MR) activation. To date there is no in vivo evidence for direct interactions between corticosteroids and any of the key regulatory molecules of programmed cell death. In this report, we show that the opposing actions of MR and GR on neuronal survival result from their ability to differentially influence the expression of members of the bcl‐2 gene family; specifically, in the rat hippocampus, activation of GR induces cell death by increasing the ratio of the pro‐apoptotic molecule Bax relative to the antiapoptotic molecules Bcl‐2 or Bcl‐xL; the opposite effect is observed after stimulation of MR. The same results were obtained in both young and aged animals; however, older subjects (which were more susceptible to GR‐mediated apoptosis) tended to express the antiapoptotic genes more robustly. Using a loss‐of‐function mouse model, we corroborated the observations made in the rat, demonstrating Bax to be essential in the GR‐mediated cell death‐signaling cascade. In addition, we show that GR activation increases and MR activation decreases levels of the tumor suppressor protein p53 (a direct transcriptional regulator of bax and bcl‐2 genes), thus providing new information on the early genetic events linking corticosteroid receptors with apoptosis in the nervous system.—Almeida, O. F. X., Condé, G. L., Crochemore, C., Demeneix, B. A., Fischer, D., Hassan, A. H. S., Meyer, M., Holsboer, F., Michaelidis, T. M. Subtle shifts in the ratio between pro‐ and antiapoptotic molecules after activation of corticosteroid receptors decide neuronal fate. FASEB J. 14, 779–790 (2000)

Enhancement of p53 activity and inhibition of neural cell proliferation by glucocorticoid receptor activation

In analyzing the molecular mechanisms underlying glucocorticoid‐induced apoptosis in neural cells, we observed that dexamethasone, by activating glucocorticoid receptors, causes arrest of HT‐22 cells in the G1 phase of the cell cycle; upon withdrawal of the agonist, cells resume proliferation. Our investigations revealed that glucocorticoid treatment, although having no effects on endogenous p53 protein stability, induces rapid translocation of p53 to the nucleus and enhances its transcriptional activity. Consistently, transfection studies with p53‐responsive promoters revealed a substantial stimulation of the trans‐activation potential of exogenous p53 by dexamethasone. Cells arrested in G1 failed to show signs of apoptosis even after overexpression of p53. Although dexamethasone induced transcription of the proapoptotic gene bax, there was no increase of Bax protein levels. We conclude that glucocorticoid receptor‐induced neural cell cycle arrest is associated with an increase in nuclear translocation and transcriptional activity of p53, and suggest that potentiation of p53 may serve as a brake on cell proliferation and may prime cells for differentiation or death induced by other signals.—Crochemore, C., Michaelidis, T. M., Fischer, D., Loeffler, J.‐P., Almeida, O. F. X. Enhancement of p53 activity and inhibition of neural cell proliferation by glucocorticoid receptor activation. FASEB J. 16, 761–770 (2002)

Insidious adrenocortical insufficiency underlies neuroendocrine dysregulation in TIF-2 deficient mice.

The transcription‐intermediary‐factor‐2 (TIF‐2) is a coactivator of the glucocorticoid receptor (GR), and its disruption would be expected to influence glucocorticoid‐mediated control of the hypothalamopituitary‐adrenal (HPA) axis. Here, we show that its targeted deletion in mice is associated with altered expression of several glucocorticoid‐dependent components of HPA regulation (e.g., corticotropin‐releasing hormone, vasopressin, ACTH, glucocorticoid receptors), suggestive of hyperactivity under basal conditions. At the same time, TIF‐2‐/‐mice display significantly lower basal corticosterone levels and a sluggish and blunted initial secretory response to brief emotional and prolonged physical stress. Subsequent analysis revealed this discrepancy to result from pronounced aberrations in the structure and function of the adrenal gland, including the cytoarchitectural organization of the zona fasciculata and basal and stress‐induced expression of key elements of steroid hormone synthesis, such as the steroidogenic acute regulatory (StAR) protein and 3β‐hydroxysteroid dehydrogenase (3(‐HSD). In addition, altered expression levels of two nuclear receptors, DAX‐1 and steroidogenic factor 1 (SF‐1), in the adrenal cortex strengthen the view that TIF‐2 deletion disrupts adrenocortical development and steroid biosynthesis. Thus, hyperactivity of the hypothalamo‐pituitary unit is ascribed to insidious adrenal insufficiency and impaired glucocorticoid feedback. Patchev, A. V., Fischer, D., Wolf, S. S., Götz, F., Gehin, M., Chambon, P., Patchev, V. K., and Almeida O. F. X. Insidious adrenocortical insufficiency underlies neuroendocrine dysregulation in TIF‐2 deficient mice. FASEB J. 21, 231–238 (2007)

Structural evolution of magnesium difluoride: from an amorphous deposit to a new polymorph

The structural evolution of magnesium difluoride from an amorphous deposit has been investigated by in situ powder X-ray diffraction (XRPD) and transmission electron microscopy (TEM). Crystalline MgF(2) was evaporated at different temperatures, which define the vapor pressures in the range from 4.7 × 10(-3) to 1.6 × 10(-1) mbar, and deposited onto various substrates. The temperature of the substrate was systematically varied from -228 to 25 °C. Magnesium difluoride was obtained as an amorphous sample when deposited on a substrate kept at a temperature below -100 °C. Upon warming, the deposit transforms via the CaCl(2) type of structure (β-MgF(2), at 70 °C) into the stable rutile type (α-MgF(2), 250 °C) by a displacive order-disorder phase transition. The new β-MgF(2) polymorph was refined assuming the orthorhombic CaCl(2) type of structure (Pnnm, No. 58) with the lattice constants a = 4.592(1) Å, b = 4.938(3) Å, and c = 2.959(3) Å. When deposited above -50 °C, samples crystallize directly in the rutile structure.

Highly Luminescent Thin Films of the Dense Framework 3∞[EuIm2] with Switchable Transparency Formed by Scanning Femtosecond‐Pulse Laser Deposition

Highly luminescent switchable thin films of the dense framework ∞(3)[EuIm2] were deposited by a scanning laser ablation technique using a femtosecond laser. The films can be controlled in terms of film thickness and amount of material deposited such that the material properties of the bulk material are retained on the nanometer scale. Polycrystalline films are formed that can be switched between transparent at visible light and nontransparent at UV light due to the intrinsic luminescence of the hybrid material, expanding the concept of smart films. The new femtosecond pulsed laser deposition method also provides a novel approach for coatings with framework compounds and coordination polymers.

Experimental and theoretical study on Raman spectra of magnesium fluoride clusters and solids.

In this study, the Raman and IR spectra of a large number of isomers of MgF(2) clusters and of possible bulk polymorphs of MgF(2) are calculated and compared with experimental data observed using a low-temperature atom beam deposition. The bulk polymorphs were taken from earlier work, while the cluster modifications for the neutral (MgF(2))(n) (n = 1-10) clusters and charged clusters (up to the trimer anion and cation, (Mg(3)F(7))(-) and (Mg(3)F(5))(+), respectively) are determined in the present work by global energy landscape explorations using simulated annealing. These theoretical calculations are complemented by an experimental study on both the vapor phase and the deposited films of MgF(2), which are generated in a low-temperature atom beam deposition setup for the synthesis of MgF(2) bulk phases. The MgF(2) vapor and film are characterized via Raman spectroscopy of the MgF(2) gas phase species embedded in an Ar-matrix and of the MgF(2)-films deposited onto a cooled substrate, respectively. We find that, in the vapor phase, there are monomers and dimers and charged species to be present in our experimental setup. Furthermore, the results suggest that in the amorphous bulk MgF(2), rutile-like domains are present and MgF(2) clusters similar to those in the matrix. Finally, peaks at about 800 cm(-1), which are in the same range as the A(g) modes of clusters with dangling fluorine atoms connected to three-coordinated Mg atoms, indicate that such dangling bonds are also present in amorphous MgF(2).

A new pulsed laser deposition technique: Scanning multi-component pulsed laser deposition method

The scanning multi-component pulsed laser deposition (PLD) method realizes uniform depositions of desired coatings by a modified pulsed laser deposition process, preferably with a femto-second laser-system. Multi-component coatings (single or multilayered) are thus deposited onto substrates via laser induced ablation of segmented targets. This is achieved via horizontal line-scanning of a focused laser beam over a uniformly moving targets surface. This process allows to deposit the desired composition of the coating simultaneously, starting from the different segments of the target and adjusting the scan line as a function of target geometry. The sequence and thickness of multilayers can easily be adjusted by target architecture and motion, enabling inter/intra layer concentration gradients and thus functional gradient coatings. This new, simple PLD method enables the achievement of uniform, large-area coatings. Case studies were performed with segmented targets containing aluminum, titanium, and niobium. Under the laser irradiation conditions applied, all three metals were uniformly ablated. The elemental composition within the rough coatings obtained was fixed by the scanned area to Ti-Al-Nb = 1:1:1. Crystalline aluminum, titanium, and niobium were found to coexist side by side at room temperature within the substrate, without alloy formation up to 600 °C.

Investigation of structural relations among the compounds in the ICSD using geometry based comparison techniques

We investigate the structural relations among the inorganic crystalline compounds listed in the ICSD using a geometry based similarity criterion. Using MYSQL-language based codes together with the structure comparison algorithm CMPZ, we classify the ordered crystalline structures contained in the ICSD into structure families, and explore the relations among these structures and structure families.

Theoretical and Experimental Exploration of the Energy Landscape of LiI

The prediction of the existence and stability of (meta)-stable phases in a chemical system is realized via a two-step process: identification of structure candidates through global exploration of the classical empirical energy landscape, followed by a local optimization of the candidates on ab-initio level employing a heuristic algorithm. From the computed energy/volume curves, one can then calculate the thermodynamically stable phase at a given pressure and the transition pressures among the phases. In order to gain insight into the kinetic stability of the structure candidates, one computes estimates of the energy and enthalpy barriers around the structures with the so-called threshold algorithm, yielding a tree graph representation of the chemical system. In this work we perform a theoretical and experimental study of the LiI energy landscape. We determine the structure candidates, construct the tree graph representation and compute the abinitio energy/volume curves for the hypothetical structures. We find that the thermodynamically preferred modifications at standard pressure should exhibit the rock salt and the wurtzite structure, respectively. In order to validate our predictions by experiments, we have employed the newly developed ´Low-Temperature - Atomic Beam Deposition` (LT-ABD) technique, which allows to disperse the components of the desired product at an atomic level and in an appropriate ratio. After depositing LiI at T = 77 K, the first crystallization occurs at T » 173 K in the wurtzite-type structure followed by a transition to the more stable rock salt-type structure at T » 273 K. At room temperature only the cubic phase remains.