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Y Luo

Publications and source records attributed to Y Luo.

At least 163 records · Page 9Linked to original sources
PubMed2000

Crystallization and preliminary X-ray diffraction studies of human epidermal growth factor.

Human epidermal growth factor (hEGF), a 6.2 kDa protein of 53 amino acids with three internal disulfide bridges, has been crystallized by the hanging-drop method. hEGF crystallizes in space group P3(1)21 (or P3(2)21) using MgCl(2) as precipitant, with unit-cell parameters a = b = 61.4, c = 87.0 A. Another type of crystal, obtained using NaCl as precipitant, belongs to a tetragonal point group and has unit-cell dimensions a = b = 102.5, c = 166.6 A. The trigonal crystals with the smaller unit cell diffract X-rays better and a native data set from a single crystal has been collected to 3.0 A resolution.

Crystallization↗
PubMed2000

Crystal structures of two mutants (K206Q, H207E) of the N-lobe of human transferrin with increased affinity for iron.

The X-ray crystallographic structures of two mutants (K206Q and H207E) of the N-lobe of human transferrin (hTF/2N) have been determined to high resolution (1.8 and 2.0 A, respectively). Both mutant proteins bind iron with greater affinity than native hTF/2N. The structures of the K206Q and H207E mutants show interactions (both H-bonding and electrostatic) that stabilize the interaction of Lys296 in the closed conformation, thereby stabilizing the iron bound forms.

Amino Acid Substitution↗
PubMed2000

Sialylation of the host receptor may modulate entry of demyelinating persistent Theiler's virus.

Theiler's murine encephalomyelitis virus (TMEV) is a picornavirus of the Cardiovirus genus. Certain strains of TMEV may cause a chronic demyelinating disease, which is very similar to multiple sclerosis in humans, associated with a persistent viral infection in the mouse central nervous system (CNS). Other strains of TMEV only cause an acute infection without persistence in the CNS. It has been shown that sialic acid is a receptor moiety only for the persistent TMEV strains and not for the nonpersistent strains. We report the effect of sialylation on cell surface on entry and the complex structure of DA virus, a persistent TMEV, and the receptor moiety mimic, sialyllactose, refined to a resolution of 3.0 A. The ligand binds to a pocket on the viral surface, composed mainly of the amino acid residues from capsid protein VP2 puff B, in the vicinity of the VP1 loop and VP3 C terminus. The interaction of the receptor moiety with the persistent DA strain provides new understanding for the demyelinating persistent infection in the mouse CNS by TMEV.

Animals↗
PubMed2000

1999 George Lyman Duff memorial lecture: lipid transfer proteins, HDL metabolism, and atherogenesis.

Plasma high density lipoprotein (HDL) levels show an inverse relationship to atherogenesis, in part reflecting the role of HDL in mediating reverse cholesterol transport. The transfer of HDL cholesterol to the liver involves 3 catabolic pathways: the indirect, cholesteryl ester transfer protein (CETP)-mediated pathway, the selective uptake (scavenger receptor BI) pathway, and a particulate HDL uptake pathway. The functions of the lipid transfer proteins (CETP and phospholipid transfer protein) in HDL metabolism have been elucidated by genetic approaches in humans and mice. Human CETP deficiency is associated with increased HDL levels but appears to increase coronary artery disease risk. Phospholipid transfer protein deficiency, produced by gene knockout in mice, results in decreased HDL levels, reflecting decreased transfer of phospholipids from triglyceride-rich lipoproteins into HDL. Obese (ob/ob) mice have markedly increased HDL levels and represent an interesting model of defective HDL catabolism in the liver. In hepatocytes of wild-type mice, there is extensive uptake and resecretion of HDL and selective uptake of cholesteryl ester from HDL during recycling. In ob/ob mice, these processes are defective, suggesting that HDL recycling plays an important role in holo-HDL catabolism, selective uptake, and the determination of plasma HDL levels.

Animals↗
PubMed2000

Sterol upregulation of human CETP expression in vitro and in transgenic mice by an LXR element.

The cholesterol ester transfer protein (CETP) facilitates the transfer of HDL cholesterol esters from plasma to the liver. Transgenic mice expressing human CETP, controlled by its natural flanking region, increase expression of this gene in response to hypercholesterolemia. We established a CETP promoter-luciferase reporter assay in differentiated 3T3-L1 adipocytes to map the sterol upregulatory element. Promoter mutagenesis suggested that a direct repeat of a nuclear receptor binding sequence separated by 4 nucleotides (DR4 element, -384 to -399) was responsible for this activity. Using mice carrying normal or mutated promoter sequences, we confirmed the importance of this element for gene induction by dietary sterol. A gel retardation complex containing LXR/RXR was identified using the CETP DR4 element and adipocyte nuclear extracts. Both LXRalpha/RXRalpha and LXRbeta/RXRalpha transactivated the CETP promoter via its DR4 element in a sterol-responsive fashion. Thus, the positive sterol response of the CETP gene is mediated by a nuclear receptor binding site that is activated by LXRs. That Cyp7a, the rate-limiting enzyme for conversion of cholesterol into bile acids in the liver, is also regulated by LXRalpha suggests that this class of nuclear receptor coordinates the regulation of HDL cholesterol ester catabolism and bile acid synthesis in the liver.

3T3 Cells↗
PubMed2000

Animal models in xenotransplantation.

The severe shortage of donor organs has provided a strong impetus to push the investigation into the use of animal organs for humans. Xenotransplantation will not only benefit patients, but also represents a unique and potentially profitable business opportunity. However, there are many barriers to successful clinical xenotransplantation, including immunological barriers, physiological incompatibility, zoonosis and ethical concerns. This overview will focus on currently available animal models used in attempts to break through the immunological barriers to xenotransplantation. There are many advantages to using small animal, namely rodent, models in xenotransplantation research. For example, the use of the mouse model allows the use of knockout mice and careful dissection of rejection mechanisms at the molecular level. The following models can be used to study hyperacute rejection (HAR): guinea-pig-to-rat, mouse-to-rabbit, guinea-pig-to-mouse, rat-to-presensitised mouse and rat-to-alpha-Gal knockout mouse. The hamster-to-rat, mouse-to-rat and rat-to-mouse models are commonly used to study acute vascular rejection. Large animal models are complex and expensive, but they are more relevant to clinical xenotransplantation. Based on experiments using transgenic pig-to-primate models, HAR can be overcome. However, acute vascular rejection remains a major barrier at the present time. A pig cartilage-to-monkey model has been developed to study chronic rejection. Other novel models such as pig venous segment-to-monkey model and rat-to-primate model may represent viable options to study immunological barriers following xenotransplantation. Like many other medical breakthroughs, animal research will continue to make enormous contributions towards the eventual success of xenotransplantation.

Animals↗
PubMed2000

Determinants of the apoptotic response to lysosomal photodamage.

Studies with mouse leukemia L1210 cells revealed that selective lysosomal photodamage caused by any of three photosensitizing agents was followed by a gradual loss of the mitochondrial membrane potential (delta psi m), release of cytochrome c into the cytosol, increased DEVDase activity (a measure of levels of caspase-3) and a limited apoptotic response. Similar effects were observed in the murine hepatoma 1c1c7 cell line. Immunofluorescence techniques employing 1c1c7 cells demonstrated the immediate release of the lysosomal enzyme cathepsin B following lysosomal photodamage. These studies suggest that the cytotoxic effects of lysosomal photodamage are initiated by released lysosomal proteases that either directly and/or indirectly activate caspases as a consequence of the induction of mitochondrial damage.

Animals↗
PubMed2000

Pharmacokinetics of penicillin G procaine versus penicillin G potassium and procaine hydrochloride in horses.

OBJECTIVE: To compare the pharmacokinetics of penicillin G and procaine in racehorses following i.m. administration of penicillin G procaine (PGP) with pharmacokinetics following i.m. administration of penicillin G potassium and procaine hydrochloride (PH). ANIMALS: 6 healthy adult mares. PROCEDURE: Horses were treated with PGP (22,000 units of penicillin G/kg of body weight, i.m.) and with penicillin G potassium (22,000 U/kg, i.m.) and PH (1.55 mg/kg, i.m.). A minimum of 3 weeks was allowed to elapse between drug treatments. Plasma and urine penicillin G and procaine concentrations were measured by use of high-pressure liquid chromatography. RESULTS: Median elimination phase half-lives of penicillin G were 24.7 and 12.9 hours, respectively, after administration of PGP and penicillin G potassium. Plasma penicillin G concentration 24 hours after administration of penicillin G potassium and PH was not significantly different from concentration 24 hours after administration of PGP. Median elimination phase half-life of procaine following administration of PGP (15.6 hours) was significantly longer than value obtained after administration of penicillin G potassium and PH (1 hour). CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that i.m. administration of penicillin G potassium will result in plasma penicillin G concentrations for 24 hours after drug administration comparable to those obtained with administration of PGP Clearance of procaine from plasma following administration of penicillin G potassium and PH was rapid, compared with clearance following administration of PGP.

Animals↗
PubMed2000

Fas ligand expression and apoptosis in primary rat hepatocytes induced by lipopolysaccharide.

OBJECTIVE: To study hepatocyte apoptosis induced by lipopolysaccharide (LPS) directly and indirectly, and to elucidate the mechanisms of liver damage in endotoxemia. METHODS: Rat hepatocytes were isolated using collagenase perfusion, and cultured in RPMI 1640 medium. After 24h or 48 h of LPS treatment at various concentrations (1, 5, 10 mug/ml), membrane-bound Fas ligand (mFasL) expression in hepatocytes was determined by immunocytochemistry, and apoptosis was detected by TUNEL. In another set of experiments it was examined whether LPS-treated hepatocytes and its supernatants can stimulate apoptosis in LPS-untreated hepatocytes. RESULTS: LPS markedly stimulated mFasL expression and apoptosis in hepatocytes in a dose and time (24-48 h) dependent manner. In the co-culture system LPS-treated hepatocytes significantly induced LPS-untreated hepatocyte apoptosis. In contrast, there was no apoptotic cells observed in the supernatant stimulation system. CONCLUSION: LPS not only directly causes hepatocyte apoptosis, but also indirectly induces apoptosis of LPS-untreated hepatocytes by way of stimulating mFasL expression in hepatocytes.

Animals↗
PubMed2000

SEMA3A regulates developing sensory projections in the chicken spinal cord.

The present study explores the role of SEMA3A (collapsin-1) in the temporal and spatial regulation of developing sensory projections in the chick spinal cord. During development, SEMA3A mRNA (SEMA3A) is first expressed throughout the spinal gray matter, but disappears from the dorsal region when small caliber (trkA(+)) sensory axon collaterals first grow into the dorsal horn. In explant cultures of spinal cord segments with attached sensory ganglia, the spatial extent of SEMA3A expression varied in different explants, but in each case the growth of trkA(+) sensory collaterals was largely excluded from areas of SEMA3A expression. To test if SEMA3A had a direct effect on sensory axon growth, we injected recombinant protein into the explants before placing them in culture. Increased levels of SEMA3A substantially reduced the ingrowth of trkA(+) axons, whereas trkC(+) axon collaterals were not affected. Consistent with the insensitivity of trkC(+) collaterals to SEMA3A, these collaterals did not express neuropilin-1, a receptor for SEMA3A. The inhibitory effects of SEMA3A on trkA(+) axons within the spinal cord suggests that the fall in SEMA3A expression in the dorsal horn may contribute to the initiation of growth of these axons into gray matter. In addition, the observation that trkA(+) axons frequently grew close to but rarely over areas of SEMA3A expression suggests that semaphorin may act principally as a short-range guidance cue within the spinal cord.

Afferent Pathways↗
PubMed2000

Clinical evaluation of polyacid-modified resin composite posterior restorations: one-year results.

OBJECTIVE: The aim of this investigation was to evaluate the clinical performance of a new compomer restorative system, Dyract AP, placed in combination with Non-Rinse Conditioner and Prime & Bond NT in permanent posterior teeth. METHOD AND MATERIALS: Fifty Class II and 41 Class I restorations were placed in 39 patients by 1 dentist. The restorations were evaluated directly, with modified US Public Health Service criteria, and indirectly, with color slides and polyvinyl siloxane impressions, at baseline and 6 months and 1 year after placement. Preoperative and 1-year postoperative bitewing radiographs were also taken. RESULTS: All 82 restorations available for 1-year evaluation were in situ. No postoperative sensitivity or pulpal problems were reported. Four Class II restorations (4.9%) failed because of partial fracture or recurrent caries. The percentages of Alfa score for each criterion were color match, 95.1%; marginal discoloration, 57.3%; marginal integrity, 35.4%; anatomic form, 98.8%; and surface texture, 91.5%. The average wear rate of Dyract AP was low (18.5 +/- 11.7 microns at 6 months and 35.7 +/- 13.6 microns at 12 months). CONCLUSION: The excellent handling characteristics, the good clinical performance, and the improved wear resistance suggest that this compomer will provide reliable direct tooth-colored restorations in stress-bearing areas.

Acid Etching, Dental↗
PubMed2000

[Ecological process of vegetation restoration in Caragana mirophylla sand-fixing area].

The occurrence and development of artificial vegetation after mobile sandy dunes being fixed by adopting straw check combining with seeding Caragana microphylla were studied. Especially the process of species invasion and the changes of community structure in 35 years were analyzed in detail. The results showed that the species richness of artificial community of C. microphylla increased, from 5 species (in 2 years) to 23 species in 35 years. In the structure concerning plant lifeform, therophytes were in dominant position, while the ratio of therophytes to all plant species had a tendency of decrease. The rates of species number and the quantity of hemicryptophytes and geocryptophytes increased gradually. Species diversity and community evenness indexes increased and ecological dominance index decreased gradually. The similarity index of the artificial plant community to natural one increased with age. The changes of physical and chemical property of soil were also discussed.

China↗
PubMed2000

Molecular and immunohistochemical study of the inactivation of the p16 gene in primary hepatocellular carcinoma.

OBJECTIVE: To determine whether p16 gene is involved in the genesis of primary hepatocellular carcinoma (HCC). METHODS: Twenty-five HCC tumor samples with corresponding non-tumor liver tissue specimens were examined for p16 gene alterations. The identification of deletion of exon 1 and exon 2 in p16 gene was performed using comparative multiplex polymerase chain reaction (PCR) analysis. The point mutation of exon 2 in p16 gene was investigated by single strand conformational polymorphism (SSCP) analysis, and the status of p16 gene methylation was screened using a PCR based methylation analysis. 35 parafin-embedded specimens of HCC with corresponding non-tumor liver tissues, including the 25 cases described above for screening p16 gene alterations, were investigated for p16 protein expression using immunohistochemical analysis. RESULTS: Among 25 cases, 2 homozygous deletions and 1 hemizygous deletion were found in HCC samples. No point mutation was identified in the remaining 22 tumor samples without p16 gene deletions. Hypermethylation was detected in 24% (6/25) of tumor samples. However, the corresponding non-tumor liver tissue specimens were always unmethylated at the p16 locus. Loss of p16 protein expression occurred in 16 of 35 (45.7%) tumor samples, and all the non-tumor liver tissue specimens showed positive p16 staining. For the 25 cases examined for p16 gene alterations, the loss of p16 protein expression was observed in all tumors with p16 gene alterations and also in 3 tumors without p16 gene alterations. CONCLUSION: Inactivation of the p16 gene may play an important role in the genesis of primary hepatocellular carcinoma.

Carcinoma, Hepatocellular↗
PubMed2000

[Aberrant expression of MUC2 and MUC3 genes in gastric carcinoma and its significance].

OBJECTIVES: To explore the clinicopathological significance of the expression of MUC2 (mucin 2) and MUC3 (mucin 3) genes in tissues of the normal gastric mucosa, intestinal metaplasia (IM) and gastric carcinoma. METHODS: MUC2 and MUC3 apomucins were detected by immunohistochemistry; MUC2 and MUC3 mRNAs were detected by in situ hybridization. RESULTS: In the normal stomach, antibody detecting MUC2 apomucin and oligonucleotide probe detecting MUC2 mRNA were not reactive with mucus-producing cells in the superficial epithelium and neck, which were weakly reactive with antibody and probe detecting MUC3. In the duodenum, MUC2 apomucin and mRNA were found at the peri- and supranuclear area of goblet cells, but MUC3 apomucin and mRNA were at the cytoplasm of goblet cells and columnar cells. MUC2 and MUC3 apomucins and its mRNAs were found in 85.2%, 88.9% and 31.6%; 57.1% of specimens of IM, 67.4%, 66.7% and 57.9%, 43.6% of specimens of gastric carcinoma. There were no associations between expressions of MUC2 and MUC3 genes and different types of IM. Patients with moderate/well differentiation had higher proportion of MUC2 apomucin expression than those with poor differentiation (P < 0.05), and patients with positive staining of MUC3 apomucin in the cancerous tissues had higher proportions of metastasis of lymph nodes (P < 0.01), serosal invasion (P < 0.05) and clinical stages III-IV (P < 0.05). CONCLUSIONS: MUC2 and MUC3 genes are mainly expressed in the mucosa of the duodenum, and marked expression is seen during the neoplastic transformation of stomach mucosa. MUC3 apomucin might have a poor prognostic significance.

Adult↗