Search PubMed⌕ Search

Biomedical subjects

Y Xia

Publications and source records attributed to Y Xia.

At least 109 records · Page 6Linked to original sources
PubMed2000

The mechanism of apoptosis in human platelets during storage.

BACKGROUND: Although it is usually involved only in nucleated cells (NCs), artificially enucleated cells also lose viability by a programmed process of cell death called apoptosis. Because platelets undergo loss of viability during storage, an attempt was made to determine whether platelets contained the apoptotic mechanisms and whether it was activated during platelet storage. STUDY DESIGN AND METHODS: Platelet viability was measured by reduction of a tetrazolium dye (MTS) and annexin V binding. Members of the death receptor, caspase, and Bcl-2 families were detected by RNase protection assay and Western blotting. Caspase 3 activation was measured by enzyme and Western blot assays and by cleavage of gelsolin. RESULTS: After 5 days of storage under standard blood banking conditions, platelets display biochemical signs of apoptosis by losing MTS activity and increasing the amount of phosphatidylserine on their surface. The mRNA and the proenzyme for several members of the caspase, death receptor, and Bcl-2 families are expressed at high levels in platelets. An increase in caspase 3 activity and the amount of the biologically active p17 subunit of active caspase 3 were observed to coincide with the appearance of apoptotic markers during storage. These effects were not due to platelet activation. The caspase 3 substrate, gelsolin, began to undergo proteolysis after 3 to 4 days of storage, and the addition of the caspase inhibitor z-VAD-fmt substantially inhibited this process. CONCLUSION: Platelets contain many of the components of the apoptotic mechanism and show activation of caspase 3 and consequent cleavage of gelsolin during storage, independent of platelet activation. Evaluation of the mechanism of apoptosis in platelets may provide a basis for developing novel strategies to enhance platelet viability during storage.

Apoptosis↗
PubMed2000

Magic-angle effect in magnetic resonance imaging of articular cartilage: a review.

RATIONALE AND OBJECTIVES: The laminar appearance of articular cartilage in magnetic resonance (MR) images has been a source of confusion, especially concerning the number, intensity, thickness, and origin of the layers. The laminar appearance is associated with the magic-angle effect in the MR imaging (MRI) of articular cartilage. METHODS: This article introduces the topic with background information about cartilage and the magic-angle effect and then reviews the literature about the magic-angle effect. The review concludes with a brief discussion of the future directions of study and the potential clinical relevance of the laminae in MR images of articular cartilage. CONCLUSIONS: The magic-angle effect is commonly seen in MR images of several tissues. The direct cause of the laminar appearance of articular cartilage is the T2 relaxation anisotropy in the tissue, which is closely linked to the structure of the collagen fibers, their orientation in the magnetic field, and the water-proteoglycan interaction that amplifies the prevailing orientation of the collagen fiber network. The laminar appearance of cartilage has an intrinsic spatial heterogeneity over the two-dimensional joint surface, which leads to inconsistencies in the reported total number of cartilage laminae and the laminar patterns observable in MRI, depending on where the sample was taken. Two additional thin, low-intensity laminae may also be visible at the boundaries of the cartilage with fluid and with bone; whether these boundary laminae are identified and counted with the others may introduce inconsistency in the results reported by various researchers.

Cartilage, Articular↗
PubMed2000

Effect of respiratory muscle training on GLUT-4 in the sheep diaphragm.

PURPOSE: Endurance exercise training is associated with enhanced glucose uptake and hence improvement in carbohydrate metabolism. Glucose transport (GLUT) membrane proteins are regulated by a variety of physiological stimuli, including exercise. In limb muscle, both acute exercise and endurance training enhance the expression of the skeletal muscle transporter, GLUT-4. The purpose of this study is to determine whether chronic loading enhances GLUT-4 expression in the diaphragm. METHODS: The effect of chronic inspiratory flow resistive (IFR) loading on diaphragm GLUT-4 was studied in a model of respiratory muscle endurance training in sheep. IFR loads (resistance 50-100 cm H2O x L(-1) x s(-1)) were maintained for 3 h x d(-1), 5-6 d x wk(-1) for 3 wk. Loading was adjusted so that PaO2 was >60 Torr and PaCO2 <45 Torr in room air. Six untrained sheep were used as controls. GLUT-4 protein and mRNA were analyzed by Western and Northern analysis respectively. RESULTS: GLUT-4 protein levels were two-fold greater in trained animals when compared with controls (P < 0.01). GLUT-4 mRNA levels in the trained muscles was not significantly different from controls. CONCLUSIONS: We conclude that in the sheep diaphragm, chronic IFR loading increases GLUT-4 protein levels. This increase may be one of the mechanisms contributing to the improved respiratory muscle endurance previously demonstrated in this animal model of respiratory muscle training.

Animals↗
PubMed2000

Cellular mechanisms for diminished scarring with aging.

The study of an age-dependent spectrum of scar formation is driven by the desire to understand and recapitulate scarless healing. Although focus in the past has been directed toward scarring in the fetus, less exuberant scarring is a common clinical observation in the elderly. Cell turnover is a major contributor to the development of scar tissue and is governed by the proliferative and apoptotic cellular fractions within a healing wound. We hypothesize that the balance between cell proliferation and apoptosis during late stages of excisional wound healing is, at least in part, responsible for age-related variations in scarring potential. Full-thickness 7-mm ulcers (four per ear), exposing bare cartilage, were made on the inner surface of the ear on 12 young and 12 aged New Zealand White rabbits. Analyses were performed at days 15, 21, and 28 postwounding. A previously described Scar Elevation Index was derived from histomorphometric analysis, along with the quantification of epithelial ingrowth and total cellularity. Apoptotic cellular fractions were derived from TdT-mediated dUTP nick end-labeling assay-stained histologic sections; proliferative fractions were derived from proliferating cell nuclear antigen-labeled serial sections. Young rabbits demonstrated significantly greater scar elevation/area. Apoptosis was strongly associated with progress of epithelialization in both groups. Significantly higher proliferative indices were seen in the young and were sustained through day 28, by which time levels had substantially declined in the aged. No differences in apoptotic indices were demonstrated between groups at any time point. The clinical observation of less exuberant scarring with aging is supported by this animal model. Apoptosis follows the progression of epithelialization but does not appear to independently influence scar morphology. A diminished proliferative response during later stages of healing is an important contributing mechanism for the decrease in scar formation seen in the elderly.

Age Factors↗
PubMed2000

Activation tagging in Arabidopsis.

Activation tagging using T-DNA vectors that contain multimerized transcriptional enhancers from the cauliflower mosaic virus (CaMV) 35S gene has been applied to Arabidopsis plants. New activation-tagging vectors that confer resistance to the antibiotic kanamycin or the herbicide glufosinate have been used to generate several tens of thousands of transformed plants. From these, over 30 dominant mutants with various phenotypes have been isolated. Analysis of a subset of mutants has shown that overexpressed genes are almost always found immediately adjacent to the inserted CaMV 35S enhancers, at distances ranging from 380 bp to 3.6 kb. In at least one case, the CaMV 35S enhancers led primarily to an enhancement of the endogenous expression pattern rather than to constitutive ectopic expression, suggesting that the CaMV 35S enhancers used here act differently than the complete CaMV 35S promoter. This has important implications for the spectrum of genes that will be discovered by this method.

Arabidopsis↗
PubMed2000

Activation tagging identifies a conserved MYB regulator of phenylpropanoid biosynthesis.

Plants produce a wide array of natural products, many of which are likely to be useful bioactive structures. Unfortunately, these complex natural products usually occur at very low abundance and with restricted tissue distribution, thereby hindering their evaluation. Here, we report a novel approach for enhancing the accumulation of natural products based on activation tagging by Agrobacterium-mediated transformation with a T-DNA that carries cauliflower mosaic virus 35S enhancer sequences at its right border. Among approximately 5000 Arabidopsis activation-tagged lines, we found a plant that exhibited intense purple pigmentation in many vegetative organs throughout development. This upregulation of pigmentation reflected a dominant mutation that resulted in massive activation of phenylpropanoid biosynthetic genes and enhanced accumulation of lignin, hydroxycinnamic acid esters, and flavonoids, including various anthocyanins that were responsible for the purple color. These phenotypes, caused by insertion of the viral enhancer sequences adjacent to an MYB transcription factor gene, indicate that activation tagging can overcome the stringent genetic controls regulating the accumulation of specific natural products during plant development. Our findings suggest a functional genomics approach to the biotechnological evaluation of phytochemical biodiversity through the generation of massively enriched tissue sources for drug screening and for isolating underlying regulatory and biosynthetic genes.

Amino Acid Sequence↗
PubMed2000

Synergistic interaction of MEK kinase 2, c-Jun N-terminal kinase (JNK) kinase 2, and JNK1 results in efficient and specific JNK1 activation.

Mitogen-activated protein kinases (MAPKs) are activated through cascades or modules consisting of a MAPK, a MAPK kinase (MAPKK), and a MAPKK kinase (MAPKKK). Investigating the molecular basis of activation of the c-Jun N-terminal kinase (JNK) subgroup of MAPK by the MAPKKK MEKK2, we found that strong and specific JNK1 activation by MEKK2 was mediated by the MAPKK JNK kinase 2 (JNKK2) rather than by JNKK1 through formation of a tripartite complex consisting of MEKK2, JNKK2, and JNK1. No scaffold protein was required for the MEKK2-JNKK2-JNK1 tripartite-complex formation. Expression of JNK1, JNKK2, and MEKK2 significantly augmented the coprecipitation of, respectively, MEKK2-JNKK2, MEKK2-JNK1, and JNKK2-JNK1, indicating that the interaction of MEKK2, JNKK2, and JNK1 is synergistic. Finally, the JNK1 was activated more efficiently in the MEKK2-JNKK2-JNK1 complex than was the JNK1 excluded from the complex. Thus, formation of a signaling complex through synergistic interaction of a MAPKKK, a MAPKK, and a MAPK molecule like MEKK2-JNKK2-JNK1 is likely to be responsible for the efficient, specific flow of information via MAPK cascades.

Animals↗
PubMed2000

Clostridium difficile toxin A excites enteric neurones and suppresses sympathetic neurotransmission in the guinea pig.

BACKGROUND AND AIMS: Evidence suggests that the intestinal actions of Clostridium difficile toxin A-stimulation of secretion and motility, and an acute inflammatory response-have a neurally mediated component. METHODS: Direct intracellular electrophysiological recording of electrical and synaptic behaviour in enteric neurones was performed in the submucous plexus of guinea pig small intestine during exposure to the toxin. RESULTS: Application of toxin A affected both the electrical behaviour of the neuronal cell bodies and inhibitory noradrenergic neurotransmission to the cell bodies. Altered electrical behaviour included depolarisation and increased excitability. Tetrodotoxin or a histamine H(2) receptor antagonist did not affect the depolarisation evoked by toxin A. Failure of the histamine antagonist to suppress the actions of toxin A is evidence that its actions were not mediated by degranulation of intramural mast cells. The action of toxin A on neurotransmission was suppression of inhibitory postsynaptic potentials evoked in the neuronal cell bodies by stimulation of sympathetic nerve fibres that synapsed with the cell bodies. The inhibitory postsynaptic potentials were mediated by norepinephrine (noradrenaline) acting at postsynaptic alpha adrenoceptors on the cell bodies. Hyperpolarising responses evoked in the cell bodies by micropressure application of norepinephrine were unaffected by toxin A. This fulfils criteria for a presynaptic inhibitory action of toxin A to suppress release of norepinephrine from sympathetic postganglionic axons. CONCLUSIONS: Results suggest that the neural component of the action of toxin A involves both direct excitation of enteric neurones and suppression of norepinephrine release from postganglionic sympathetic nerve fibres in the enteric nervous system.

Animals↗
PubMed2000

Probing structure-function relationships of the DNA polymerase alpha-associated zinc-finger protein using computational approaches.

We present the application of a method for protein structure prediction to aid the determination of structure-function relationships by experiment. The structure prediction method was rigourously tested by making blind predictions at the third meeting on the Critical Assessment of Protein Structure methods (CASP3). The method is a combined hierarchical approach involving exhaustive enumeration of all possible folds of a small protein sequence on a tetrahedral lattice. A set of filters, primarily in the form of discriminatory functions, are applied to these conformations. As the filters are applied, greater detail is added to the models resulting in a handful of all-atom "final" conformations. Encouraged by the results at CASP3, we used our approach to help solve a practical biological problem: the prediction of the structure and function of the 67-residue C-terminal zinc-finger region of the DNA polymerase alpha-associated zinc-finger (PAZ) protein. We discuss how the prediction points to a novel function relative to the sequence homologs, in conjunction with evidence from experiment, and how the predicted structure is guiding further experimental studies. This work represents a move from the theoretical realm to actual application of structure prediction methods for gaining unique insight to guide experimental biologists.

Amino Acid Sequence↗
PubMed2000

Heparin-binding EGF-like growth factor contributes to reduced glomerular filtration rate during glomerulonephritis in rats.

Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a member of the epidermal growth factor (EGF) family, is expressed during inflammatory and pathological conditions. We have cloned the rat HB-EGF and followed the expression of HB-EGF in rat kidneys treated with anti- glomerular basement membrane (anti-GBM) antibody (Ab) to induce glomerulonephritis (GN). We observed glomerular HB-EGF mRNA and protein within 30 minutes of Ab administration and showed by in situ hybridization that glomerular HB-EGF mRNA expression was predominantly in mesangial and epithelial cells. Expression of HB-EGF correlated with the onset of decreased renal function in this model. To test the direct effect of HB-EGF on renal function, we infused the renal cortex with active rHB-EGF, prepared from transfected Drosophila melanogaster cells. This treatment induced a significant decrease in single nephron GFR (SNGFR), single nephron plasma flow, and glomerular ultrafiltration coefficient and an increase in the glomerular capillary hydrostatic pressure gradient. In addition, anti-HB-EGF Ab administered just before anti-GBM Ab blocked the fall in SNGFR and GFR at 90 minutes without any change in the glomerular histologic response. These studies suggest that HB-EGF expressed early in the anti-GBM Ab GN model contributes to the observed acute glomerular hemodynamic alterations.

Animals↗
PubMed2000

Associations of apolipoprotein E concentration and polymorphism with lipids and apolipoprotein levels in Chinese from Beijing and Shanghai.

The association of apolipoprotein E concentration and common polymorphism (codons 112/158) with lipid and apolipoprotein concentrations was studied in two Chinese healthy population samples from Beijing (n=99) and Shanghai (n=67). Body mass index and apolipoproteins E and AI and triglyceride concentrations were significantly different between the two populations (0.001<p<0.05), but apolipoprotein E common allele frequencies were not significantly different. Apolipoprotein E concentration was independently associated with apolipoproteins B and AI, total cholesterol and triglyceride concentrations in the Beijing group, but only with total cholesterol and apolipoprotein AI concentrations in the Shanghai group. Apolipoprotein E polymorphism was significantly associated with apolipoproteins E and AI, and triglyceride concentrations in the Beijing subjects (0.001<p<0.01), whereas apolipoprotein E polymorphism was significantly related only to apolipoprotein E concentration in the Shanghai group (p<0.001). This preliminary study with a limited number of subjects shows that the relations between both apolipoprotein E genotypes and concentration with lipid traits are not the same in the two studied Chinese populations.

Adolescent↗
PubMed2000

Effect of irrigation on the efficacy of insecticides for controlling two species of mole crickets (Orthoptera: Gryllotalpidae) on golf courses.

Effects of irrigation regimen, quantity, and timing on the efficacy of three insecticides for controlling nymphs of the southern mole cricket, Scapteriscus borellii Giglio-Tos, and the tawny mole cricket, Scapteriscus vicinus Scudder, were studied on golf courses in 1997, 1998, and 1999. Two irrigation regimen tests using two rates of bifenthrin and lambda-cyhalothrin produced inconclusive results. Mole cricket damage ratings after the applications of bifenthrin (60 g [AI]/ha) and lambda-cyhalothrin (76 g [AI]/ha) were not significantly different among the four irrigation regimens (non-irrigation, irrigation before treatment, irrigation after treatment, and irrigation before and after treatment). Mole cricket damage rating after the application of bifenthrin (120 g [AI]/ha) under irrigation before and after irrigation was significantly better than those under other irrigation regimens at 14 and 21 d after treatment (DAT). Different irrigation quantity and irrigation timing (after insecticide treatment) did not significantly affect the performance of imidacloprid (434 g [AI]/ha) in the 1998 tests. However, the results from the 1999 test indicated that mole cricket damage ratings from the imidacloprid-treated plots were significantly different between 2 and 0.5 cm irrigation water after treatment at 21 and 28 DAT. Application of bifenthrin at a rate of 120 g (AI)/ha with 0.5 cm of irrigation water after treatment resulted in significantly lower mole cricket damage ratings than those of 1.0 and 2.0 cm of irrigation water after treatment at 30 DAT only in the 1998 test. Bifenthrin with irrigation at 1 h after insecticide treatment provided better mole cricket control than that of irrigation at 5 min after treatment at 30 DAT only in the 1998 test. Mole cricket damage ratings after application of bifenthrin were not significantly different between either irrigation quantity treatment or irrigation timing treatment in the 1999 tests. Possible effects of application timing, environmental conditions, irrigation practice, and insecticide physical properties on the results are discussed.

Agriculture↗
PubMed2000

The platelet thrombopoietin receptor number and function are markedly decreased in patients with essential thrombocythaemia.

Essential thrombocythaemia (ET) is a relatively common myeloproliferative disorder characterized by an elevated platelet count. As thrombopoietin (TPO) and the TPO receptor (c-mpl) regulate platelet production in normal physiology, their role in ET was investigated. A well-characterized cohort of 23 ET patients was evaluated and followed for 3 years. The TPO levels in these ET patients (189 +/- 131 pg/ml) were the same as in normal subjects (179 +/- 112 pg/ml) and TPO was not produced by ET platelets. There were 5.6 +/- 5.5 TPO binding sites/ET platelet vs. 56 +/- 17 TPO binding sites/normal platelet and this was associated in ET patients with normal-sized platelet c-mpl protein and mRNA, but a 10-fold reduction in platelet c-mpl mRNA. The K(d) for the TPO receptor on ET platelets was 66 +/- 30 pmol/l vs. 163 +/- 31 pmol/l on normal platelets, but the c-mpl cDNA had a normal nucleic acid sequence. The decreased number of ET platelet TPO receptors resulted in a fourfold decrease in the platelet-dependent TPO clearance (0.30 +/- 0.14 ml/h/10(9) ET platelets vs. 1.24 +/- 0.38 ml/h/10(9) normal platelets) at a time when the platelet count in ET patients was 2.7-fold above normal. The fourfold decrease in the TPO clearance, elevated platelet mass and resulting normal total TPO clearance explain the normal TPO levels. These results also suggest that the thrombocytosis in ET may be attributed to an alteration of the normal feedback interaction between TPO and its receptor and not as a result of any defect in the structure of TPO or c-mpl.

Adult↗
PubMed2000

[Effect of foliar leaching on growth and mineral nutrition of maize under NaCl stress].

The impact of foliar leaching on growth and mineral nutrition maize under NaCl stress was investigated. The results showed that there was no difference in biomass between leaching and control treatments under low NaCl stress (0 and 50 mmol.L-1), but under high NaCl stress (100 and 200 mmol.L-1), the biomass of leaching treatment was higher, with a better at pH 3.5 than at pH 7.0. The shoot K+ content in leaching treatments was higher than that of control under no NaCl stress, but lower under 200 mmol.L-1 NaCl stress. Shoot Na+ content of leaching treatments was lower than that of control under high NaCl stress, and shoot Ca2+ and Mg2+ contents of leaching treatments were higher under no NaCl stress. Root K+, Na+, Ca2+ and Mg2+ content and relative water content of leaching treatments had no significant changes, compared with those of control. It was suggested that foliar leaching could alleviate harmful degree of maize under serious salt stress, which was related with the decrease of shoot Na+ content by foliar leaching.

Minerals↗
PubMed2000

[Purification and characterization of cuticle-degrading protease from entomopathogenic fungus, Metarhizium anisopliae].

The cuticle-degrading proteases from entomopathogensis fungus, Melarhizium anisopliae, were induced by adding cicada exuviae, colloidal chitin, shrimp cuticle, maggot cuticle, horsefly cuticle and silkworm chrysalis cuticle into minimal medium. After ultrafiltration, Ultrogel AcA 54 column and IEF, a protease designated as MAP-21 with Mr 27 kD, and pI 7.6 were purified. It was shown that the recognition site of MAP-21 was Arg, PMSF and TLCK could inhibited the activity of this protease, indicating that there were Ser and His residues in the active center. The inhibitors to trypsin, leupeptin antipain and STI also repressed the activity of MAP-21, while chymostatin, TPCK and elastatinal TEI were shown no inhibition to its activity, demonstrating that, MAP-21 was a trypsin-like protease. Other properties of MAP-21 were also reported.

Enzyme Induction↗
PubMed2000

[Cloning of a new catechol 1,2-dioxygenase gene (tfd C) from Plesiomonas and its expression in the E. coli].

A new catechol-1,2-dioxygenase gene (tfd C) was cloned from the Plesiomonas using the PCR method. Primers were designed according to the reported sequence of Catechol-1,2-dioxygenase (C120) gene from Alcaligenes eutroplus. The amplified fragment contained a 765 bp open reading frame (ORF), encoding a protein of 255 amino acids. The new tfd C gene shared a high homology with the one cloned from Alcaligenes eutroplus, showing only one base difference at 693 site (C-->A) and consequently one amino acid difference at 228 site (P-->T). The ORF was cloned to the plasmid pBluescriptII KS, which was transferred to E. coli JM109 and a positive clone, pBt2G, was then selected. A significant activity of C120 was detected in the positive clone. When the ORF was cloned to the plasmid pET-30a, which was transferred to E. coli BL21(DE3) plysS, the expected 33 kD protein was detected from a positive clone, pET30A, by SDS-PAGE. The C120 is a key enzyme in degrading aromatic pollutants in the environment. In order to use plants to degrade aromatic pollutants, the gene will be introduced into the turfgrass. To express the gene properly in plants, its translation initiation codon was modified from GTG to ATG. A similar activity of C120 was obtained following the modification.

Amino Acid Sequence↗
PubMed2000

[Synthesis of droloxifene citrate and its new bioactivity].

AIM: To investigate a feasible synthetic procedure of droloxifene and study on its new bioactivities. METHODS AND RESULTS: Droloxifene was synthesized using methoxybenzene and phenylacetic acid as starting materials, via Friedel-Crafts acylation, alkylation, demethylation, etherification, Grignard addition, elimination-dehydration, conversing configuration and forming citrate, totally 8 steps, overall yield 14.7% (9.2%). By pharmacological test, droloxifene citrate shows two new bioactivities: (1) obvious effect on reversing the MDR of K562/A02 cells and modulating mdrl, GST pi and TopoII alpha expression. (2) inducing apoptosis in cultured rat luteal cell. CONCLUSION: The improved synthetic procedure is shorter than the reported method by two steps and has advantages of simple separation, purification and conversion of configuration; easily available starting materials and reagents; concise operation. Two new bioactivities on reversing MDR and inducing apoptosis of luteal cell offered a clue in new drugs research and widened clinic application of droloxifene.

Animals↗