Showing papers by "University of Göttingen published in 2001"

Sustained excitability elevations induced by transcranial DC motor cortex stimulation in humans

Abstract: The authors show that in the human transcranial direct current stimulation is able to induce sustained cortical excitability elevations. As revealed by transcranial magnetic stimulation, motor cortical excitability increased approximately 150% above baseline for up to 90 minutes after the end of stimulation. The feasibility of inducing long-lasting excitability modulations in a noninvasive, painless, and reversible way makes this technique a potentially valuable tool in neuroplasticity modulation.

Erythropoietin prevents neuronal apoptosis after cerebral ischemia and metabolic stress

Abstract: Erythropoietin (EPO) promotes neuronal survival after hypoxia and other metabolic insults by largely unknown mechanisms. Apoptosis and necrosis have been proposed as mechanisms of cellular demise, and either could be the target of actions of EPO. This study evaluates whether antiapoptotic mechanisms can account for the neuroprotective actions of EPO. Systemic administration of EPO (5,000 units/kg of body weight, i.p.) after middle-cerebral artery occlusion in rats dramatically reduces the volume of infarction 24 h later, in concert with an almost complete reduction in the number of terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling of neurons within the ischemic penumbra. In both pure and mixed neuronal cultures, EPO (0.1–10 units/ml) also inhibits apoptosis induced by serum deprivation or kainic acid exposure. Protection requires pretreatment, consistent with the induction of a gene expression program, and is sustained for 3 days without the continued presence of EPO. EPO (0.3 units/ml) also protects hippocampal neurons against hypoxia-induced neuronal death through activation of extracellular signal-regulated kinases and protein kinase Akt-1/protein kinase B. The action of EPO is not limited to directly promoting cell survival, as EPO is trophic but not mitogenic in cultured neuronal cells. These data suggest that inhibition of neuronal apoptosis underlies short latency protective effects of EPO after cerebral ischemia and other brain injuries. The neurotrophic actions suggest there may be longer-latency effects as well. Evaluation of EPO, a compound established as clinically safe, as neuroprotective therapy in acute brain injury is further supported.

Productivity overshadows temperature in determining soil and ecosystem respiration across European forests

Abstract: Summary This paper presents CO2 flux data from 18 forest ecosystems, studied in the European Union funded EUROFLUX project. Overall, mean annual gross primary productivity (GPP, the total amount of carbon (C) fixed during photosynthesis) of these forests was 1380 ± 330 gC m−2 y−1 (mean ±SD). On average, 80% of GPP was respired by autotrophs and heterotrophs and released back into the atmosphere (total ecosystem respiration, TER = 1100 ± 260 gC m−2 y−1). Mean annual soil respiration (SR) was 760 ± 340 gC m−2 y−1 (55% of GPP and 69% of TER). Among the investigated forests, large differences were observed in annual SR and TER that were not correlated with mean annual temperature. However, a significant correlation was observed between annual SR and TER and GPP among the relatively undisturbed forests. On the assumption that (i) root respiration is constrained by the allocation of photosynthates to the roots, which is coupled to productivity, and that (ii) the largest fraction of heterotrophic soil respiration originates from decomposition of young organic matter (leaves, fine roots), whose availability also depends on primary productivity, it is hypothesized that differences in SR among forests are likely to depend more on productivity than on temperature. At sites where soil disturbance has occurred (e.g. ploughing, drainage), soil espiration was a larger component of the ecosystem C budget and deviated from the relationship between annual SR (and TER) and GPP observed among the less-disturbed forests. At one particular forest, carbon losses from the soil were so large, that in some years the site became a net source of carbon to the atmosphere. Excluding the disturbed sites from the present analysis reduced mean SR to 660 ± 290 gC m−2 y−1, representing 49% of GPP and 63% of TER in the relatively undisturbed forest ecosystems.

Cadmium-induced changes in antioxidative systems, hydrogen peroxide content, and differentiation in Scots pine roots.

Abstract: To investigate whether Cd induces common plant defense pathways or unspecific necrosis, the temporal sequence of physiological reactions, including hydrogen peroxide (H(2)O(2)) production, changes in ascorbate-glutathione-related antioxidant systems, secondary metabolism (peroxidases, phenolics, and lignification), and developmental changes, was characterized in roots of hydroponically grown Scots pine (Pinus sylvestris) seedlings. Cd (50 microM, 6 h) initially increased superoxide dismutase, inhibited the systems involved in H(2)O(2) removal (glutathione/glutathione reductase, catalase [CAT], and ascorbate peroxidase [APX]), and caused H(2)O(2) accumulation. Elongation of the roots was completely inhibited within 12 h. After 24 h, glutathione reductase activities recovered to control levels; APX and CAT were stimulated by factors of 5.5 and 1.5. Cell death was increased. After 48 h, nonspecific peroxidases and lignification were increased, and APX and CAT activities were decreased. Histochemical analysis showed that soluble phenolics accumulated in the cytosol of Cd-treated roots but lignification was confined to newly formed protoxylem elements, which were found in the region of the root tip that normally constitutes the elongation zone. Roots exposed to 5 microM Cd showed less pronounced responses and only a small decrease in the elongation rate. These results suggest that in cells challenged by Cd at concentrations exceeding the detoxification capacity, H(2)O(2) accumulated because of an imbalance of redox systems. This, in turn, may have triggered the developmental program leading to xylogenesis. In conclusion, Cd did not cause necrotic injury in root tips but appeared to expedite differentiation, thus leading to accelerated aging.

A novel approach to temporary stenting: degradable cardiovascular stents produced from corrodible metal—results 6–18 months after implantation into New Zealand white rabbits

Abstract: OBJECTIVE To determine whether corrodible materials may be safely used as biodegradable cardiovascular implants. DESIGN Corrodible iron stents (> 99.8% iron) were produced from pure iron and laser cut with a stent design similar to a commercially available permanent stent (PUVA-AS16). A total of 16 NOR-I stents were implanted into the native descending aorta of 16 New Zealand white rabbits (mean luminal diameter at the implantation site 3.4 mm, balloon diameter to vessel diameter ratio 1.13). RESULTS No thromboembolic complications and no adverse events occurred during the follow up of 6–18 months. All stents were patent at repeat angiography after 6 (n = 9), 12 (n = 5), and 18 months (n = 2) with no significant neointimal proliferation, no pronounced inflammatory response, and no systemic toxicity. CONCLUSIONS This initial in vivo experience suggests that degradable iron stents can be safely implanted without significant obstruction of the stented vessel caused by inflammation, neointimal proliferation, or thrombotic events.

Pin1 is overexpressed in breast cancer and cooperates with Ras signaling in increasing the transcriptional activity of c-Jun towards cyclin D1

Abstract: Phosphorylation on serines or threonines preceding proline (Ser/Thr-Pro) is a major signaling mechanism. The conformation of a subset of phosphorylated Ser/Thr-Pro motifs is regulated by the prolyl isomerase Pin1. Inhibition of Pin1 induces apoptosis and may also contribute to neuronal death in Alzheimer's disease. However, little is known about the role of Pin1 in cancer or in modulating transcription factor activity. Here we report that Pin1 is strikingly overexpressed in human breast cancers, and that its levels correlate with cyclin D1 levels in tumors. Overexpression of Pin1 increases cellular cyclin D1 protein and activates its promoter. Furthermore, Pin1 binds c-Jun that is phosphorylated on Ser63/73-Pro motifs by activated JNK or oncogenic Ras. Moreover, Pin1 cooperates with either activated Ras or JNK to increase transcriptional activity of c-Jun towards the cyclin D1 promoter. Thus, Pin1 is up-regulated in human tumors and cooperates with Ras signaling in increasing c-Jun transcriptional activity towards cyclin D1. Given the crucial roles of Ras signaling and cyclin D1 overexpression in oncogenesis, our results suggest that overexpression of Pin1 may promote tumor growth.

Crystal structures of complexes of the small ribosomal subunit with tetracycline, edeine and IF3

Abstract: The small ribosomal subunit is responsible for the decoding of genetic information and plays a key role in the initiation of protein synthesis. We analyzed by X-ray crystallography the structures of three different complexes of the small ribosomal subunit of Thermus thermophilus with the A-site inhibitor tetracycline, the universal initiation inhibitor edeine and the C-terminal domain of the translation initiation factor IF3. The crystal structure analysis of the complex with tetracycline revealed the functionally important site responsible for the blockage of the A-site. Five additional tetracycline sites resolve most of the controversial biochemical data on the location of tetracycline. The interaction of edeine with the small subunit indicates its role in inhibiting initiation and shows its involvement with P-site tRNA. The location of the C-terminal domain of IF3, at the solvent side of the platform, sheds light on the formation of the initiation complex, and implies that the anti-association activity of IF3 is due to its influence on the conformational dynamics of the small ribosomal subunit.

Photosynthesis-induced biofilm calcification and calcium concentrations in Phanerozoic oceans.

Abstract: Photosynthetic carbon assimilation is commonly invoked as the cause of calcium carbonate precipitation in cyanobacterial biofilms that results in the formation of calcareous stromatolites. However, biofilm calcification patterns in recent lakes and simulation of photosynthetically induced rise in calcium carbonate supersaturation demonstrate that this mechanism applies only in settings low in dissolved inorganic carbon and high in calcium. Taking into account paleo-partial pressure curves for carbon dioxide, we show that Phanerozoic oceans sustaining calcified cyanobacteria must have had considerably higher calcium concentrations than oceans of today. In turn, the enigmatic lack of calcified cyanobacteria in stromatolite-bearing Precambrian sequences can now be explained as a result of high dissolved inorganic carbon concentrations.

CYP2D6 and CYP2C19 genotype-based dose recommendations for antidepressants: a first step towards subpopulation-specific dosages.

Abstract: CYP2D6 and CYP2C19 genotype-based dose recommendations for antidepressants: A first step towards subpopulation specific dosages.

Crystal structure of an initiation factor bound to the 30S ribosomal subunit.

Abstract: Initiation of translation at the correct position on messenger RNA is essential for accurate protein synthesis. In prokaryotes, this process requires three initiation factors: IF1, IF2, and IF3. Here we report the crystal structure of a complex of IF1 and the 30S ribosomal subunit. Binding of IF1 occludes the ribosomal A site and flips out the functionally important bases A1492 and A1493 from helix 44 of 16S RNA, burying them in pockets in IF1. The binding of IF1 causes long-range changes in the conformation of H44 and leads to movement of the domains of 30S with respect to each other. The structure explains how localized changes at the ribosomal A site lead to global alterations in the conformation of the 30S subunit.

Blood vessel maturation in a 3-dimensional spheroidal coculture model: direct contact with smooth muscle cells regulates endothelial cell quiescence and abrogates VEGF responsiveness

Abstract: Paracrine interactions between endothelial cells (EC) and mural cells act as critical regulators of vessel wall assembly, vessel maturation and define a plasticity window for vascular remodeling. The present study was aimed at studying blood vessel maturation processes in a novel 3-dimensional spheroidal coculture system of EC and smooth muscle cells (SMC). Coculture spheroids differentiate spontaneously in a calcium-dependent manner to organize into a core of SMC and a surface layer of EC, thus mimicking the physiological assembly of blood vessels with surface lining EC and underlying mural cells. Coculture of EC with SMC induces a mature, quiescent EC phenotype as evidenced by 1) a significant increase in the number of junctional complexes of the EC surface layer, 2) a down-regulation of PDGF-B expression by cocultured EC, and 3) an increased resistance of EC to undergo apoptosis. Furthermore, EC cocultured with SMC become refractory to stimulation with VEGF (lack of CD34 expression on VEGF stimulation; inability to form capillary-like sprouts in a VEGF-dependent manner in a 3-dimensional in gel angiogenesis assay). In contrast, costimulation with VEGF and Ang-2 induced sprouting angiogenesis originating from coculture spheroids consistent with a model of Ang-2-mediated vessel destabilization resulting in VEGF responsiveness. Ang-2 on its own was able to stimulate endothelial cells in the absence of Ang-1 producing SMC, inducing lateral sheet migration as well as in gel sprouting angiogenesis. Taken together, the data establish the spheroidal EC/SMC system as a powerful cell culture model to study paracrine interactions in the vessel wall and provide functional evidence for smooth muscle cell-mediated quiescence effects on endothelial cells.

Thermophilic adaptation of proteins.

Abstract: Hyperthermophilic organisms optimally grow close to the boiling point of water. As a consequence, their macromolecules must be much more thermostable than those from mesophilic species. Here, proteins from hyperthermophiles and mesophiles are compared with respect to their thermodynamic and kinetic stabilities. The known differences in amino acid sequences and three-dimensional structures between intrinsically thermostable and thermolabile proteins will be summarized, and the crucial role of electrostatic interactions for protein stability at high temperatures will be highlighted. Successful attempts to increase the thermostability of proteins, which were either based on rational design or on directed evolution, are presented. The relationship between high thermo-stability of enzymes from hyperthermophiles and their low catalytic activity at room temperature is discussed. Not all proteins from hyperthermophiles are thermostable enough to retain their structures and functions at the high physiological temperatures. It will be shown how this shortcoming can be surpassed by extrinsic factors such as large molecular chaperones and small compatible solutes. Finally, the potential of thermostable enzymes for biotechnology is discussed.

Erythropoietin and erythropoietin receptor in human ischemic/hypoxic brain

Abstract: Using immunohistochemistry, expression of erythropoietin (EPO), a hypoxia-inducible neuroprotective factor, and its receptor (EPOR) were investigated in human brain tissue after ischemia/hypoxia. Autopsy brains of neuropathologically normal subjects were compared to those with ischemic infarcts or hypoxic damage. In normal brain, weak EPO/EPOR immunoreactivity was mainly neuronal. In fresh infarcts, EPO immunoreactivity appeared in vascular endothelium, EPOR in microvessels and neuronal fibers. In older infarcts reactive astrocytes exhibited EPO/EPOR immunoreactivity. Acute hypoxic brain damage was associated with vascular EPO expression, older hypoxic damage with EPO/EPOR immunoreactivity in reactive astrocytes. The pronounced up-regulation of EPO/EPOR in human ischemic/hypoxic brains underlines their role as an endogenous neuroprotective system and suggests a novel therapeutic potential in cerebrovascular disease for EPO, a clinically well-characterized and safe compound.

Complementation cloning identifies CDG-IIc, a new type of congenital disorders of glycosylation, as a GDP-fucose transporter deficiency.

Abstract: Congenital disorders of glycosylation (CDG) comprise a rapidly growing group of inherited disorders in which glycosylation of glycoproteins is defective due to mutations in genes required for the assembly of lipid-linked oligosaccharides, their transfer to nascent glycoproteins (CDG-I) or the processing of protein-bound glycans1,2 (CDG-II). Previously' a defect in the GDP-fucose import into the lumen of the Golgi was identified in a person with CDG (A.C.) with a general deficiency of fucosyl residues in glycoproteins3. This patient presents the clinical features of leukocyte adhesion deficiency type II (LAD II) including mental retardation, short stature, facial stigmata, and recurrent bacterial peripheral infections with persistently elevated peripheral leukocytes4,5,6,7. Using a fucose-specific, lectin-staining procedure for detection of fucosylated glycoproteins and a retroviral cDNA library, we isolated a cDNA complementing the fucosylation defect in the patient's fibroblasts. The cDNA encodes a highly hydrophobic protein of 364 amino acids with multiple putative transmembrane domains. Restoration of GDP-fucose import activity in Golgi-enriched vesicles from the patient's fibroblasts verified the GDP-fucose transporter activity of this protein. We identified two missense mutations in the GDP-fucose transporter cDNA of patient A.C. and of two other people with LAD II. Thus complementation cloning allowed us to identify the human GDP-fucose transporter cDNA and GDP-fucose transporter deficiency as a cause for a new type of CDG. Following the recent recommendations2,8 for the nomenclature for CDG, this new type is classified as CDG-IIc (formerly LAD II).

Direct, high-resolution measurement of furrow stiffening during division of adherent cells.

Abstract: It is unclear whether cell division is driven by cortical relaxation outside the equatorial region or cortical contractility within the developing furrow alone. To approach this question, a technique is required that can monitor spatially-resolved changes in cortical stiffness with good time resolution. We employed atomic force microscopy (AFM), in force-mapping mode, to track dynamic changes in the stiffness of the cortex of adherent cultured cells along a single scan-line during M phase, from metaphase to cytokinesis. Video microscopy, which we used to correlate the AFM data with mitotic events identified by light microscopy, indicated that the AFM force-mapping technique does not perturb dividing cells. Here we show that cortical stiffening occurs over the equatorial region about 160 seconds before any furrow appears, and that this stiffening markedly increases as the furrow starts. By contrast, polar relaxation of cells does not seem to be an obligatory event for cell division to occur.

Renal Fibrosis: Collagen Composition and Assembly Regulates Epithelial-Mesenchymal Transdifferentiation

Abstract: Type IV collagen is a major component of basement membranes and it provides structural and functional support to various cell types. Type IV collagen exists in a highly complex suprastructure form and recent studies implicate that protomer (the trimeric building unit of type IV collagen) assembly is mediated by the NC1 domain present in the C-terminus of each collagen α-chain polypeptide. Here we show that type IV collagen contributes to the maintenance of the epithelial phenotype of proximal tubular epithelial cells, whereas type I collagen promotes epithelial-to-mesenchymal transdifferentiation (EMT). In addition, the recombinant human α1NC1 domain inhibits assembly of type IV collagen NC1 hexamers and potentially disrupts the deposition of type IV collagen, facilitating EMT in vitro. Inhibition of type IV collagen assembly by the α1NC1 domain up-regulates the production of transforming growth factor-β1 in proximal tubular epithelial cells, an inducer of EMT. These results strongly suggest that basement membrane architecture is pivotal for the maintenance of epithelial phenotype and that changes in basement membrane architecture potentially lead to up-regulation of transforming growth factor-β1, which contributes to EMT during renal fibrosis.

The Origin, Formation and Developmental Significance of the Epicardium: A Review

Abstract: Questions on the embryonic origin and developmental significance of the epicardium did not receive much recognition for more than a century. It was generally thought that the epicardium was derived from the outermost layer of the primitive myocardium of the early embryonic heart tube. During the past few years, however, there has been an increasing interest in the development of the epicardium. This was caused by a series of new embryological data. The first data showed that the epicardium did not derive from the primitive myocardium but from a primarily extracardiac primordium, called the proepicardial serosa. Subsequent data then suggested that the proepicardial serosa and the newly formed epicardium provided nearly all cellular elements of the subepicardial and intermyocardial connective tissue, and of the coronary vasculature. Recent data even suggest important modulatory roles of the epicardium and of other proepicardium-derived cells in the differentiation of the embryonic myocardium and cardiac conduction system. The present paper reviews our current knowledge on the origin and embryonic development of the epicardium.

Discoidin domain receptor 1 tyrosine kinase has an essential role in mammary gland development.

Abstract: Various types of collagen have been identified as potential ligands for the two mammalian discoidin domain receptor tyrosine kinases, DDR1 and DDR2. Here, we used a recombinant fusion protein between the extracellular domain of DDR1 and alkaline phosphatase to detect specific receptor binding sites during mouse development. Major sites of DDR1-binding activity, indicative of ligand expression, were found in skeletal bones, the skin, and the urogenital tract. Ligand expression in the uterus during implantation and in the mammary gland during pregnancy colocalized with the expression of the DDR1 receptor. The generation of DDR1-null mice by gene targeting yielded homozygous mutant animals that were viable but smaller in size than control littermates. The majority of mutant females were unable to bear offspring due to a lack of proper blastocyst implantation into the uterine wall. When implantation did occur, the mutant females were unable to lactate. Histological analysis showed that the alveolar epithelium failed to secrete milk proteins into the lumen of the mammary gland. The lactational defect appears to be caused by hyperproliferation and abnormal branching of mammary ducts. These results suggest that DDR1 is a key mediator of the stromal-epithelial interaction during ductal morphogenesis in the mammary gland.

Mitochondrial ATP-sensitive potassium channels inhibit apoptosis induced by oxidative stress in cardiac cells

Abstract: Mitochondria can either enhance or suppress cell death. Cytochrome c release from mitochondria and depolarization of the mitochondrial membrane potential (DeltaPsi) are crucial events in triggering apoptosis. In contrast, activation of mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels prevents lethal ischemic injury in vivo, implicating these channels as key players in the process of ischemic preconditioning. We probed the relationship between mitoK(ATP) channels and apoptosis in cultured neonatal rat cardiac ventricular myocytes. Incubation with 200 micromol/L hydrogen peroxide induced TUNEL positivity, cytochrome c translocation, caspase-3 activation, poly(ADP-ribose) polymerase cleavage, and dissipation of DeltaPsi. Pharmacological opening of mitoK(ATP) channels by diazoxide (100 micromol/L) preserved mitochondrial integrity and suppressed all markers of apoptosis. Diazoxide prevented DeltaPsi depolarization in a concentration-dependent manner (EC(50) approximately 40 micromol/L, with saturation by 100 micromol/L), as shown by both flow cytometry and quantitative image analysis of cells stained with fluorescent DeltaPsi indicators. These cytoprotective effects of diazoxide were reproduced by pinacidil, another mitoK(ATP) agonist, and blocked by the mitoK(ATP) channel antagonist 5-hydroxydecanoate (500 micromol/L). Our findings identify a novel mitochondrial pathway that is protective against apoptosis. The results also pinpoint mitoK(ATP) channels as logical therapeutic targets in diseases of enhanced apoptosis and oxidative stress.