Biomedical subjects

Y Yang

Publications and source records attributed to Y Yang.

At least 1,135 records · Page 63Linked to original sources

PubMed1995

Crystal structure of thioltransferase at 2.2 A resolution.

We report here the first three-dimensional structure of a mammalian thioltransferase as determined by single crystal X-ray crystallography at 2.2 A resolution. The protein is known for its thiol-redox properties and dehydroascorbate reductase activity. Recombinant pig liver thioltransferase expressed in Escherichia coli was crystallized in its oxidized form by vapor diffusion technique. The structure was determined by multiple isomorphous replacement method using four heavy-atom derivatives. The protein folds into an alpha/beta structure with a four-stranded mixed beta-sheet in the core, flanked on either side by helices. The fold is similar to that found in other thiol-redox proteins, viz. E. coli thioredoxin and bacteriophage T4 glutaredoxin, and thus seems to be conserved in these functionally related proteins. The active site disulfide (Cys 22-Cys 25) is located on a protrusion on the molecular surface. Cys 22, which is known to have an abnormally low pKa of 3.8, is accessible from the exterior of the molecule. Pro 70, which is in close proximity to the disulfide bridge, assumes a conserved cis-peptide configuration. Mutational data available on the protein are in agreement with the three-dimensional structure.

Animals↗

PubMed1995

Liquid chromatography/mass spectrometry with collision-induced dissociation of arachidonic acid metabolites derivatized with aminobenzenesulphonic acid.

A fused-silica capillary high-performance liquid chromatography column (i.d. 0.25 mm) packed with octadecylsilane-bonded silica has been used on-line with continuous-flow negative-ion fast-atom bombardment (FAB) mass spectrometry for the separation and structural analysis of series of fatty acids and arachidonic acid metabolites derivatized with 4-aminobenzenesulphonic acid. Negative-ion FAB spectra of the derivatized lipids showed strong [M-H] pseudomolecular ions. Collision-induced dissociation of these anions produced structurally informative daughter ions, arising from charge-remote fragmentations.

Arachidonic Acids↗

PubMed1995

Frontal lobe degeneration of non-Alzheimer type and Pick's atrophy: lumping or splitting?

We report six cases of presenile (five) and senile (one) progressive dementia with a mild-to-marked frontal or frontotemporal atrophy and ventricular dilation (Frontal Lobe Degeneration [FLD]). The most prominent microscopic features were layer-dependent neuronal depletion of the cortex, spongiosis, and cortical and subcortical gliosis. Five cases showed additional degeneration of the S. nigra, and two also had motor neuron disease. Despite the absence of Pick cells and bodies, such cases have many features in common with Pick atrophy. Because Pick cells and bodies are inconstantly occurring features in otherwise typical cases of Pick atrophy, they cannot be regarded as inevitable markers of the latter. In our opinion, cases with mild frontal or frontotemporal atrophy as described herein and by others match the grades 1 and 2 in terms of Schneider's classification of Pick atrophy [37]. As long as the etiology of both Pick atrophy and the so-called FLD is unknown, and we finally have to follow morphological criteria for classification, there is apparently no convincing reason to introduce a separate category, such as FLD or FTA, for the cases with moderate or mild frontal atrophy and dementia of frontal lobe type, which can be sufficiently classified with the Pick spectrum of lobar atrophy.

Adult↗

PubMed1995

Study on three dimensional reconstruction of transesophageal echocardiographic images.

Using biplane transesophageal echocardiography and the concept of three dimensional transthoracic echocardiography, we performed three dimensional reconstruction of transesophageal images of various clinicopathologic cases, including atrial septal defect, mitral stenosis, mitral valve prolapse and pulmonary stenosis. The hardware equipment and image processing flow chart of three dimensional reconstruction of transesophageal echocardiographic images are described. Our present study indicates that three dimensional reconstruction of transesophageal echocardiographic images could display multi-regional three dimensional structures of heart and great vessels, including superior vena cava, ascending aorta, right ventricular outflow tract, pulmonary artery and left heart, with clear, visual and stereoscopic imaging. The regional structures could be displayed at different levels of stereo-anatomic-sections and in different orientations of rotating stereo-images, which could provide accurate three dimensional anatomical information for cardiac stereo-morphological study and definition of spatial location and size of cardiac abnormalities.

Adolescent↗

PubMed1995

Left coronary artery fistula identified by color Doppler flow imaging.

Coronary artery fistula (CAF) is an abnormal communication between a coronary artery and a cardiac chamber, great vessel, or other vascular structures. The presence of the fistula is usually identified by angiography. In this paper, the diagnosis of left coronary artery-right ventricle fistula was made by color Doppler before angiography? and it was confirmed by surgery. Color Doppler flow imaging is a non-invasive method which can reveal the proximal dilatation, the course and the draining site of CAF.

Child↗

PubMed1995

Computer simulations of human lung structures for medical applications.

Knowledge of the structure of the human lung has salient health effects applications. The clinical issues encompass: (1) aerosol therapy, the targeted delivery of inhaled particles to enhance the efficacies of pharmacologic drugs; and (2) nuclear medicine, where planar gamma camera imaging, Single Photon Emission Computer Tomography (SPECT) and Positron Emission Tomography (PET) assess the distribution patterns of radiolabeled diagnostic particles and gases. If the resolution of such images could be enhanced, medical regimens would greatly benefit. Therefore, the focused objective of our work was to develop 3-D mathematical descriptions of the complex airway networks within the lung. A Silicon Graphics workstation was used to depict the daedal structures. The computer-generated color illustrations presented herein are intended to complement medical investigation. They will assist the clinician by serving as templates for the lung and, thereby, providing a real basis for the analysis of relatively abstract images. The illustrations identify individual airways and could be of great importance to physicians in the treatment of airway diseases occurring at well defined locations (e.g. bronchogenic carcinomas). To demonstrate that computers can be actively integrated into medical research and practice we have addressed SPECT images of a subject. Computer templates will aid future clinical investigators in two major ways: (1) the interpretation of a planar gamma camera, SPECT and PET images; and (2) the design of drug testing protocols using inhalation exposures. Considering their usefulness for demonstration, the lung simulations have the potential of playing a substantive role in education.

Administration, Inhalation↗

PubMed1995

Computer model of human lung morphology to complement SPECT analyses.

Aerosol therapy protocols could be improved if inhaled pharmacologic drugs were selectively deposited within the human lung. The targeted delivery to specific sites, such as receptors and sensitive airway cells, would enhance the efficacies of airborne pharmaceuticals. The high spatial discrimination of deposition patterns of inhaled particles can be determined via Single Photon Emission Computer Tomography (SPECT). However, major problems continue to compromise SPECT protocols. Our work focuses on two issues: how can the spatial discrimination be improved; and how are the images to be interpreted? We present a methodology, described by a mathematical model and supercomputer code, for systematically slicing through the human lung in a prescribed manner that is conducive to implementation into SPECT analyses. The lung is divided into concentric shells, or annuli, and the airway generation-by-generation composition of the respective shells determined. This identification was accomplished by superimposing the new shell structure with the 3-D branching network presented by Martonen et al. [23]. Perhaps the key aspect of the model-code is that the supercomputer is instructed to determine the 3-D spatial coordinates of each of the airways (over 16 million) of the lung with respect to the clinician-selected contours of shells within the lung.

Administration, Inhalation↗

PubMed1995

Anions and the anomalous gel filtration behavior of notexin and scutoxin.

Based on their mol. wts, notexin and scutoxin elute later than expected from gel filtration columns in multiple peaks [Francis et al. (1991) Toxicon 29, 85-96]. Notexins present in these peaks have identical amino acid sequences and unmodified amino acid side-chains. Scutoxin is an isoform of notexin which contains arginine at position 16 and glutamate at position 82. Like notexin, it also elutes in different fractions on a gel filtration column, yet the fractions show identical amino acid sequence. This perplexing chromatographic behavior appears to be caused by the association of these proteins with different anions, since dissolving notexin in buffers containing different anions produces up to a 30% change in elution volume. Certain anions promote an apparent reduction in the interaction of notexin with gel filtration matrix, hence earlier elution. These anions include citrate, 3-phosphoglycerate and 2-phosphoglycerate, which also inhibit the PLA2 activity of notexin. However, even under conditions which minimize protein-matrix interaction the toxins elute later than expected based on their mol. wt.

Amino Acid Sequence↗

PubMed1995

On the accuracy of surface reconstruction from disparity interpolation.

Observers viewed flashed random-dot stereograms depicting a pair of long, narrow, curved ribbons of textured surface defined by a Gabor function in disparity. Observers judged the location of the peak of the depth profile of one ribbon relative to that of the other. In one ribbon, disparity changed smoothly while in the other disparity was periodically sampled. Up to a limiting sampling period, disparity interpolation produced accurate surface reconstruction, but beyond that performance deteriorated rapidly. This interpolation limit depended on surface orientation (vertical vs horizontal) and disparity sign, but not Gabor spatial frequency.

Depth Perception↗

PubMed1995

Cytokine regulation of HLA-G expression in human trophoblast cell lines.

HLA class I genes are differentially expressed among subpopulations of cells in first trimester human placentas. In this study, HLA class I protein was detected in extravillous cytotrophoblast cells by immunohistochemistry using the monoclonal antibody W6/32. In the same trophoblast subpopulation, class Ib proteins were identified with two monoclonal antibodies, 87G (anti-HLA-G) and 131 (anti-HLA-A/G) and class Ia protein was detected with the monoclonal antibody, 4E (anti-HLA-B/C). All of the antibodies also identified antigens on the human trophoblast-derived choriocarcinoma cell line, JEG-3. Therefore, the JEG-3 cells were used as a model system to study cytokine regulation of HLA-G in trophoblast cells. Northern blot hybridization studies showed that interferons (IFN-alpha, IFN-beta, IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) modestly enhanced steady state levels of HLA-G mRNA. Yet analysis of HLA-G protein by immunocytochemistry and flow cytometry failed to identify any changes in intracellular or membrane expression of HLA-G protein following cytokine treatment. Resistance to upregulation of HLA class I antigens was not a general feature of JEG-3 cells; IFNs enhanced expression of HLA-B/C as well as HLA class I light chain, beta 2-microglobulin. HLA null Jar choriocarcinoma cells did not contain HLA-G mRNA or antigen and exposure to cytokines had no effect on HLA-G. The results of this study are consistent with the postulate that trophoblast cell expression of HLA-G is stringently regulated and is controlled in part by post-transcriptional mechanisms.

Cell Line↗

PubMed1995

A group of Giardia lamblia variant-specific surface protein (VSP) genes with nearly identical 5' regions.

The surfaces of Giardia lamblia trophozoites contain one of a set of variant-specific surface proteins. The genes encoding these proteins are highly conserved at the 3' terminus, but frequently demonstrate little similarity in the remainder of the coding region. This report describes a family of vsp genes highly similar to a repeat-containing vsp gene (vspC5) at the 5' coding and flanking regions, but which diverge abruptly from vspC5 in the first repeat and do not themselves contain full copies of the repeat. This observation suggests the possibility that recombination among different vsp genes may have played a role in development of the vsp gene repertoire.

Amino Acid Sequence↗

PubMed1995

Role of basic residues in the proteolytic activation of Sendai virus fusion glycoprotein.

Cleavage activation of the Sendai virus (Fushimi strain) fusion (F) protein was analyzed by site-directed mutagenesis of the amino acids proximal to the highly conserved fusion peptide. In addition, the functional properties of the wild-type and mutant proteins were examined to determine their ability to elicit the formation of syncytia when co-expressed with the hemagglutinin-neuraminidase (HN) glycoprotein. Viral genes were expressed from recombinant T7 transcription vectors (pT7/T3 plasmids) containing F or HN genes, after transfection into cells previously infected with a recombinant vaccinia virus expressing T7 RNA polymerase (vTF7-3). The wild-type F protein sequence (112VPQSRF) which contains a monobasic cleavage activation site was altered to include a tribasic, 112VPRKRF (mB3), or a pentabasic sequence, 112RRRKRF (mB5) adjacent to the fusion peptide. Although addition of basic residues to the normal protein sequence resulted in enhanced cleavage activation of the mB3 and mB5 proteins, only the mB5 protein was able to induce syncytia formation in CV-1 or HeLa T4 cells. Further analysis by the introduction of acidic residues upstream of the cleavage activation site was performed to determine whether increased hydrophilicity of the surrounding residues might contribute to cleavage activation. The mutants examined, mAcB1 (104NDDEENAGVPQSRF), mAcB3 (104NDDEENAGVPRKRF), and mAcB5 (104NDDEENAGRRRKRF) all contained DEE in replacement for the wild-type TTQ sequence (104NDTTQNAGVPQSRF). Analysis showed that only mAcB3 was efficiently cleaved by the endogenous cellular proteases, while mAcB1 was minimally cleaved, and mAcB5 not at all. Consequently, only the mAcB3 mutant was able to support fusion of CV-1 or HeLa T4 cells when co-expressed with HN.

Amino Acid Sequence↗

PubMed1995

Conformational changes of active sites during refolding of urea-denatured creatine kinase.

The course of the recovery of the active site conformation during refolding of urea-denatured creatine kinase (ATP:creatine N-phosphotransferase, EC 2.7.3.2) has been studied. The recovery of the active site conformation has been followed by changes in probe fluorescence of active site of the enzyme labeled by o-phthaldehyde and has been shown to be a triphasic process. A comparison of the rate constants for the conformational recovery of the active site with those for the recovery of enzyme catalytic activity shows that these are synchronized. The results obtained show clearly that, although recovery of partial activity and conformation of the active site occur in reactions with nearly the same rate as those of the refolding processes observed, the complete recovery of the enzyme activity and the active site conformation can only be obtained long after any detectable conformational change of whole enzyme molecule.

Animals↗

PubMed1995

Effects of localized bending on DNA supercoiling.

The DNA double helix is straight only in the idealized case. In reality, it bends, twists and stretches in response to local base sequence and to specific interactions with proteins and other bound ligands. Naturally occurring bends appear to promote the assembly of nucleosomes, and in some cases can effectively replace regulatory DNA-binding proteins in vivo. Recently, a computational method known as 'finite element analysis', which is used routinely by engineers to analyse the stability of buildings and bridges, has been applied to the quantitative assessment of natural curvature in supercoiled DNA structures, providing new insight into the relationship between local, sequence-dependent features and the overall topology of these chains.

Computer Simulation↗

PubMed1995

Gene therapy in a xenograft model of cystic fibrosis lung corrects chloride transport more effectively than the sodium defect.

We have developed a model of gene therapy for cystic fibrosis (CF) lung disease, based on growth of human CF bronchial xenografts in nu/nu mice. We now report an evaluation of the primary abnormalities in CF lung epithelia--defective Cl secretion and Na hyperabsorption--in xenografts following adenovirus-mediated gene transfer. In vivo infection of CF xenografts with a cystic fibrosis transmembrane regulator (CFTR) recombinant adenovirus, at a multiplicity of infection equal to 100, was sufficient to reconstitute near normal levels of cAMP-stimulated Cl transport, despite transducing only 5% of cells in the pseudostratified epithelium. Correction in sodium hyperabsorption was partial and variable. These experiments define aspects of adenovirus-mediated gene therapy relevant to CF protocols based on intrapulmonary genetic reconstitution.

Absorption↗

PubMed1995

Recombinant IL-12 prevents formation of blocking IgA antibodies to recombinant adenovirus and allows repeated gene therapy to mouse lung.

Enthusiasm for the use of recombinant adenoviruses in gene therapy has been tempered by the problematic immune responses that develop to the virus and virus-infected cells. Humoral immune responses to the input viral proteins generate neutralizing antibodies that thwart attempts to effectively administer the therapy more than once. Previous studies in murine models of gene therapy for cystic fibrosis (CF) have shown that the formation of adenoviral antibodies of the IgA subtype, a process that is dependent on T helper cells of the TH2 subset, contributes to a block in gene transfer that occurs following a second administration of virus. We show in this report that coadministration of interferon-gamma (IFN-gamma) (or interleukin-12, which activates TH1 cells to secrete IFN-gamma) with the recombinant adenovirus into the airway of C57BL/6 mice diminishes the activation of TH2 cells and formation of neutralizing antibody, allowing for efficient readministration of recombinant virus. This suggests a strategy for gene therapy of CF in which administration of a short-acting immune modulator at the time of gene therapy may be sufficient to overcome the problems of humoral immunity.

Adenoviridae↗

PubMed1995

Sequential requirement of hepatocyte growth factor and neuregulin in the morphogenesis and differentiation of the mammary gland.

We have examined the role of two mesenchymal ligands of epithelial tyrosine kinase receptors in mouse mammary gland morphogenesis. In organ cultures of mammary glands, hepatocyte growth factor (HGF, scatter factor) promoted branching of the ductal trees but inhibited the production of secretory proteins. Neuregulin (NRG, neu differentiation factor) stimulated lobulo-alveolar budding and the production of milk proteins. These functional effects are paralleled by the expression of the two factors in vivo: HGF is produced in mesenchymal cells during ductal branching in the virgin animal; NRG is expressed in the mesenchyme during lobulo-alveolar development at pregnancy. The receptors of HGF and NRG (c-met, c-erbB3, and c-erbB4), which are expressed in the epithelial cells, are not regulated. In organ culture, branching morphogenesis and lobulo-alveolar differentiation of the mammary gland could be abolished by blocking expression of endogenous HGF and NRG by the respective antisense oligonucleotides; in antisense oligonucleotide-treated glands, morphogenesis could again be induced by the addition of recombinant HGF and NRG. We thus show that two major postnatal morphogenic periods of mammary gland development are dependent on sequential mesenchymal-epithelial interactions mediated by HGF and NRG.

Animals↗

PubMed1995

The spatial accuracy of cellular dose estimates obtained from 3D reconstructed serial tissue autoradiographs.

In order to better predict and understand the effects of radiopharmaceuticals used for therapy, it is necessary to determine more accurately the radiation absorbed dose to cells in tissue. Using thin-section autoradiography, the spatial distribution of sources relative to the cells can be obtained from a single section with micrometre resolution. By collecting and analysing serial sections, the 3D microscopic distribution of radionuclide relative to the cellular histology, and therefore the dose rate distribution, can be established. In this paper, a method of 3D reconstruction of serial sections is proposed, and measurements are reported of (i) the accuracy and reproducibility of quantitative autoradiography and (ii) the spatial precision with which tissue features from one section can be related to adjacent sections. Uncertainties in the activity determination for the specimen result from activity losses during tissue processing (4-11%), and the variation of grain count per unit activity between batches of serial sections (6-25%). Correlation of the section activity to grain count densities showed deviations ranging from 6-34%. The spatial alignment uncertainties were assessed using nylon fibre fiduciary markers incorporated into the tissue block, and compared to those for alignment based on internal tissue landmarks. The standard deviation for the variation in nylon fibre fiduciary alignment was measured to be 41 microns cm-1, compared to 69 microns cm-1 when internal tissue histology landmarks were used. In addition, tissue shrinkage during histological processing of up to 10% was observed. The implications of these measured activity and spatial distribution uncertainties upon the estimate of cellular dose rate distribution depends upon the range of the radiation emissions. For long-range beta particles, uncertainties in both the activity and spatial distribution translate linearly to the uncertainty in dose rate of < 15%. For short-range emitters (< 100 microns), such as alpha particle sources, the magnitude of the uncertainty in serial section alignment is comparable with the particle track length. Under these circumstances, dosimetric errors are introduced in proportion to the serial section alignment inaccuracy.

Animals↗