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Biomedical subjects

Z Jia

Publications and source records attributed to Z Jia.

At least 19 recordsLinked to original sources
PubMed2006

Expression of the novel co-stimulatory molecule B7-H4 by renal tubular epithelial cells.

Crosstalk between T cells and renal tubular epithelial cells (TECs) in the pathogenesis of tubular lesions, the most important sign of progressive renal diseases, has not been clarified. Previous work has shown that TECs harbor co-stimulatory signals that promote T-cell activation, which induces tubular lesions. Nevertheless, the expression and functional role of B7-H4, a recently identified co-stimulatory ligand of the B7 superfamily, in pathologic human kidneys is unclear. We investigated the expression of B7-H4 on cryostat renal biopsies from patients with idiopathic membranous nephropathy (n=20), immunoglobulin A nephropathy (n=19), lupus nephritis (n=16), and acute renal allograft rejection (n=15) using immunohistochemistry. In addition, we also analyzed TEC-associated B7-H4 in the regulation of T-cell activation. Immunohistological staining revealed that B7-H4 antigen is restricted to tubular epithelium and that the protein is prominent in sections with severe tubular lesions, although no correlation was observed between tubular B7-H4 expression and levels of serum creatinine, serum urea nitrogen concentration, and 24-h proteinuria in each type of nephropathy. In vitro, mixed lymphocyte reactions revealed that TEC-related B7-H4 promotes cytokine (interleukin-2 and interferon-gamma) production and proliferation of co-cultured T cells. Interestingly, the secretion of interleukin-2 by C10 T cell hybridomas also increased when C10 cells were co-cultured with the B7-H4-transgenic murine TEC line, 3M-1-secreting tubular epithelial cells (MCT) in the presence of the antigen hen egg lysozyme. Our results clearly show that TEC-associated B7-H4 induces T-cell activation and we propose that B7-H4 is a potential activator that promotes tubular lesion.

Animals↗
PubMed2006

Enhanced magnetic properties of self-assembled FePt nanoparticles with MnO shell.

Self-assembled FePt/MnO nanoparticles with different morphology and size were synthesized with a polyol process. With the MnO coating, FePt nanoparticles exhibit a high blocking temperature and magnetic moment. The low-temperature hysteresis loop of FePt nanoparticles can be shifted through the AFM pinning of the MnO shell. The aggregation of FePt nanoparticles during the L10 phase transformation can be significantly decreased by coating with the MnO shell.

Iron↗
PubMed2006

Polymorphism of HLA class II genes in Miao and Yao nationalities of Southwest China.

In the present study, the polymorphism of human leucocyte antigen class II genes was investigated by the sequence-based typing method in two Chinese populations: the Miaos (n = 85) from Guizhou province and the Yaos (n = 66) from Yunnan province. These two populations exhibited certain similarity in their allelic distributions. Among 24 DRB1 alleles detected, DRB1*150101, DRB1*140101, DRB1*160201 and DRB1*090102 in Miao and DRB1*120201, DRB1*140101, DRB1*150101 and DRB1*090102 in Yao were highly predominant. Sixteen DQB1 alleles in total were found in these two populations among which DQB1*050201, DQB1*060101/060103 and DQB1*030101/0309 in both Miao and Yao and DQB1*050301 in Yao were commonly observed. In the 13 DPB1 alleles detected, the most frequent allele was DPB1*0501 in Miao and Yao followed by DPB1*02 and DPB1*1301. Frequent comparisons with other Chinese populations suggested the southern Chinese feature for both the Miao and Yao nationalities.

Alleles↗
PubMed2006

Cyclooxygenase-2 plays an essential part in cardioprotection of delayed phase of recombinant human erythropoietin preconditioning in rats.

AIMS: To study the cardioprotection of recombinant human erythropoietin (rhEPO) preconditioning (EPC) and to investigate the role and possible mechanism of cyclooxygenase (COX)-2 in the delayed phase of EPC. METHODS: In phase 1, myocardial ischaemia reperfusion (I-R) rat model was established by 30 minutes ligation of left descending coronary and three hours of reperfusion. Rats were given 0.9% saline solution or rhEPO 24 hours before I-R protocol. COX-2 selective inhibitor celecoxib was given for further investigation of the cardioprotection of EPC. At the end of I-R protocol, infarct sizes were measured and ultrastructural organisations were studied. In phase 2, myocardial COX-2 mRNA expressions and prostaglandins (PGs) contents were studied in different groups after euthanasia. RESULTS: It was found that EPC could elicit potent cardioprotection against I-R injury, shown by reduction of infarct size and improvement of ultrastructural organisation; whereas administration of celecoxib resulted in complete loss of this protection. EPC resulted in robust increase in COX-2 mRNA and PGs levels that were also abrogated by celecoxib. CONCLUSIONS: COX-2 plays an essential part in cardioprotection of the delayed phase of EPC in rats, which might be related to actions of PGE(2) or PGI(2), or both.

Animals↗
PubMed2005

Application of direct covalent molecular assembly in the fabrication of polyimide ultrathin films.

Ultrathin films were fabricated using synthesized hydroxyl polyimide (HPI) in a layer-by-layer fashion on amine-terminated substrates of silicon, quartz, and gold. The interlayer linkages were established by using terephthaloyl chloride as a bridging agent to form ester groups between HPI layers. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis absorption spectroscopy, atomic force microscopy, ellipsometry, and electrochemical impedance spectroscopy were employed to study the interfacial chemistry, stepwise growth, morphology, thickness, optical property, and insulation behavior of the assembled film. The films show excellent stability and strength, which can be attributed to the covalent interlayer linkage.

Journal Article↗
PubMed2003

A second binding site revealed by C-terminal truncation of calpain small subunit, a penta-EF-hand protein.

The subunits in calpain and in the related penta-EF-hand (PEF) proteins are bound through contacts between the unpaired EF-hand 5 from each subunit. To study subunit binding further, a tetra-EF-hand 18 kDa N- and C-terminally truncated form of the calpain small subunit was prepared (18k). This protein does not combine with the calpain large subunit to form active calpain, but forms homodimers in solution, as shown by ultracentrifugation. The X-ray structure of the 18k protein in the presence of cadmium was solved to a resolution of 2.0 A. The structure of the monomer is almost identical to the known structure of the calpain small subunit, but the 18k protein forms an oligomer in the crystal by the use of two binding sites. One of these sites is an artefact arising from the C-terminal truncation, but the other is a naturally occurring site that is fully exposed to water in intact purified calpain. The characteristics of this site suggest that it may be important in binding other protein modulators involved in the regulation of calpain and of PEF proteins.

Binding Sites↗
PubMed2003

HLA-DRB1, DQB1 and DPB1 polymorphism in the Naxi ethnic group of South-western China.

Polymorphism of HLA-DRB1, DQB1 and DPB1 was revealed with a sequencing-based typing (SBT) method in unrelated healthy volunteers from the Naxi ethnic group. Among the 43 DRB1 alleles detected, the most common allele was DRB1*12021 with a frequency of 17%, followed by DRB1*08032, DRB1*09012 and DRB1*1404 with frequencies of 8.5%, 7.4% and 7.4%, respectively. Among 23 DQB1 alleles detected, the most frequent DQB1 allele was DQB1*03011/0309 (21.9%), followed by DQB1*0502 (16.4%) and DQB1*05031 (9.6%). For the DPB1 locus, the most common alleles were DPB1*0501 (25.5%), DPB1*0402 (14.6%) and DPB1*02012 (12.0%). The most common DRB1-DQB1-DPB1 haplotype was DRB1*1404-DQB1*05031-DPB1*0402 with a frequency of 5.26%, followed by the DRB1*08032-DQB1*06011-DPB1*1301 (3.51%). The distribution characteristics of the HLA class II alleles revealed that the Naxi ethnic group belonged to the Southern group of Chinese.

Alleles↗
PubMed2002

A novel DRB1*09 allelic sequence in the Jing ethnic minority of China.

A new DRB1 allele, DRB1*0902, has been identified in an individual of the Jing ethnic minority. Its sequence was confirmed by sequencing of PCR products and clones. This allele differed by three nucleotides from DRB1*09012 at positions 157, 161 and 166, and resulted in amino acid motif substitution from VAES to DAEY.

Amino Acid Motifs↗
PubMed2001

The receptor tyrosine kinase EphB2 regulates NMDA-dependent synaptic function.

Members of the Eph family of receptor tyrosine kinases control many aspects of cellular interactions during development, including axon guidance. Here, we demonstrate that EphB2 also regulates postnatal synaptic function in the mammalian CNS. Mice lacking the EphB2 intracellular kinase domain showed wild-type levels of LTP, whereas mice lacking the entire EphB2 receptor had reduced LTP at hippocampal CA1 and dentate gyrus synapses. Synaptic NMDA-mediated current was reduced in dentate granule neurons in EphB2 null mice, as was synaptically localized NR1 as revealed by immunogold localization. Finally, we show that EphB2 is upregulated in hippocampal pyramidal neurons in vitro and in vivo by stimuli known to induce changes in synaptic structure. Together, these data demonstrate that EphB2 plays an important role in regulating synaptic function.

Animals↗
PubMed2001

Structure of protein tyrosine phosphatase 1B in complex with inhibitors bearing two phosphotyrosine mimetics.

Protein tyrosine phosphatases (PTPases) are signal-transducing enzymes that dephosphorylate intracellular proteins that have phosphorylated tyrosine residues. It has been demonstrated that protein tyrosine phosphatase 1B (PTP1B) is an attractive therapeutic target because of its involvement in regulating insulin sensitivity (Elcheby et al. Science 1999, 283, 1544-1548). The identification of a second binding site in PTP1B (Puius et al., Proc. Natl. Acad. Sci. U.S.A.1997, 94, 13420-13425) suggests a new strategy for inhibitor design, where appropriate compounds may be made to simultaneously occupy both binding sites to gain much higher affinity and selectivity. To test this hypothesis and gain further insights into the structural basis of inhibitor binding, we have determined the crystal structure of PTP1B complexed with two non-peptidyl inhibitors, 4 and 5, both of which contain two aryl difluoromethylenephosphonic acid groups, a nonhydrolyzable phosphate mimetic. The structures were determined and refined to 2.35 and 2.50 A resolution, respectively. Although one of the inhibitors seems to have satisfied the perceived requirement for dual binding, it did not bind both the active site and the adjacent noncatalytic binding site as expected. The second or distal phosphonate group instead extends into the solvent and makes water-mediated interactions with Arg-47. The selectivity of the more potent of these two inhibitors, as well as four other inhibitors bearing two such phosphate mimetics for PTP1B versus seven other PTPases, was examined. In general, selectivity was modest to good when compared to PTPases Cdc25a, PTPmeg-1, PTPbeta, and CD45. However, selectivity was generally poor when compared to other PTPases such as SHP-1, SHP-2, and especially TCPTP, for which almost no selectivity was found. The implications these results have concerning the utility of dual-binding inhibitors are discussed.

Binding Sites↗
PubMed2001

Dissociation and aggregation of calpain in the presence of calcium.

Calpain is a heterodimeric Ca(2+)-dependent cysteine protease consisting of a large (80 kDa) catalytic subunit and a small (28 kDa) regulatory subunit. The effects of Ca(2+) on the enzyme include activation, aggregation, and autolysis. They may also include subunit dissociation, which has been the subject of some debate. Using the inactive C105S-80k/21k form of calpain to eliminate autolysis, we have studied its disassociation and aggregation in the presence of Ca(2+) and the inhibition of its aggregation by means of crystallization, light scattering, and sedimentation. Aggregation, as assessed by light scattering, depended on the ionic strength and pH of the buffer, on the Ca(2+) concentration, and on the presence or absence of calpastatin. At low ionic strength, calpain aggregated rapidly in the presence of Ca(2+), but this was fully reversible by EDTA. With Ca(2+) in 0.2 m NaCl, no aggregation was visible but ultracentrifugation showed that a mixture of soluble high molecular weight complexes was present. Calpastatin prevented aggregation, leading instead to the formation of a calpastatin-calpain complex. Crystallization in the presence of Ca(2+) gave rise to crystals mixed with an amorphous precipitate. The crystals contained only the small subunit, thereby demonstrating subunit dissociation, and the precipitate was highly enriched in the large subunit. Reversible dissociation in the presence of Ca(2+) was also unequivocally demonstrated by the exchange of slightly different small subunits between mu-calpain and m-calpain. We conclude that subunit dissociation is a dynamic process and is not complete in most buffer conditions unless driven by factors such as crystal formation or autolysis of active enzymes. Exposure of the hydrophobic dimerization surface following subunit dissociation may be the main factor responsible for Ca(2+)-induced aggregation of calpain. It is likely that dissociation serves as an early step in calpain activation by releasing the constraints upon protease domain I.

Animals↗
PubMed2001

Efficient antitumor immunity derived from maturation of dendritic cells that had phagocytosed apoptotic/necrotic tumor cells.

Dendritic cells (DCs) that acquired antigen from apoptotic tumor cells are able to induce major histocompatibility complex (MHC) class I-restricted cytotoxic T lymphocytes and antitumor immunity. In the present study, we investigated the efficiency of antitumor immunity derived from DCs that had phagocytosed apoptotic/necrotic BL6-10 melanoma cells compared with that of DCs pulsed with the tumor mTRP2 peptide. Our data showed that phagocytosis of apoptotic/necrotic tumor cells resulted in maturation of DCs with up-regulated expression of proinflammatory cytokines [interleukin (IL)-1beta, IL-6, tumor necrosis factor-alpha, interferon-gamma and granulocyte-macrophage colony-stimulating factor], chemokines (MIP-1alpha, MIP-1beta and MIP-2), the CC chemokine receptor CCR7 and the cell surface molecules (MHC class II, CD11b, CD40 and CD86), and down-regulated expression of the CC chemokine receptors CCR2 and CCR5. These mature DCs displayed enhanced migration toward the CC chemokine MIP-3beta in a chemotaxis assay in vitro and to the regional lymph nodes in an animal model in vivo. Our data also showed that vaccination with DCs that had phagocytosed apoptotic/necrotic BL6-10 cells was able to (i) more strongly stimulate allogeneic T-cell proliferation in vitro, (ii) induce an in vivo Th1-type immune response leading to more efficient tumor-specific cytotoxic CD8(+) T-cell-mediated immunity and (iii) eradicate lung metastases in all 6 vaccinated mice compared with mice vaccinated with DCs pulsed with the tumor mTRP2 peptide, in which lung metastases were reduced (mean number of 16 per mouse) but not completely eradicated. Therefore, DCs that had phagocytosed apoptotic/necrotic tumor cells appear to offer new strategies in DC cancer vaccines.

Animals↗
PubMed2001

Crystal structure of an aldehyde reductase Y50F mutant-NADP complex and its implications for substrate binding.

Pig aldehyde reductase containing the active site mutation tyrosine(50) to phenylalanine has been crystallized in the presence of the cofactor NADP(H) to a resolution of 2.2 A. This structure clearly shows loss of the tyrosine hydroxyl group and no other significant perturbations compared with previously determined structures. The mutant binds cofactor (both oxidized and reduced) more tightly than the wild-type enzyme but shows a complete lack of binding of the aldehyde reductase inhibitor barbitone, as determined by fluorescence titrations. Numerous attempts at preparing a ternary complex with a range of small aldehyde substrates were unsuccessful. This result, in addition to the inability of the mutant protein to bind the inhibitor, provides strong evidence for the proposal that the tyrosine hydroxyl group is essential for substrate binding in addition to catalysis.

Alcohol Oxidoreductases↗
PubMed2001

Synthesis and antibacterial activities of quaternary ammonium salt of chitosan.

Chitosan derivatives with quaternary ammonium salt, such as N,N,N-trimethyl chitosan, N-N-propyl-N,N-dimethyl chitosan and N-furfuryl-N,N-dimethyl chitosan were prepared using different 96% deacetylated chitosan of M(v) 2.14x10(5), 1.9x10(4), 7.8x10(3). Amino groups on chitosan react with aldehydes to from a Schiff base intermediate. Quaternized chitosan were obtained by reaction of a Schiff base with methyl iodide. The yields, degree of quaternization and water-solubility of quaternized chitosan were influenced by the molecular weight of the chitosan sample. The antibacterial activities of quaternized chitosan against Escherichia coli were explored by calculation of the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) in water, 0.25 and 0.50% acetic acid medium. Results show the antibacterial activities of quaternized chitosan against E. coli is related to its molecular weight. Antibacterial activities of quaternized chitosan in acetic acid medium is stronger than that in water. Their antibacterial activities is increased as the concentration of acetic acid is increased. It was also found that the antibacterial activity of quaternized chitosan against E. coli is stronger than that of chitosan.

Alkylation↗
PubMed2001

Cloning and characterization of a novel variant of rat GABA(B)R1 with a truncated C-terminus.

The gamma-aminobutyric acid B receptor (GABA(B)R) belong to the G-protein-coupled receptor superfamily and has been identified as a mediator in the transmission of slow inhibitory neurotransmission in the mammalian central nervous system. Two types of GABA(B)R have been cloned, GABA(B)R1 and R2. GABA(B)R2 is co-expressed with GABA(B)R1 in many brain regions and inwardly rectifying potassium channels are activated by GABA(B)R agonists only upon co-expression of GABA(B)R1 with GABA(B)R2. Several splice variants of GABA(B)R1 receptors have been cloned from rat brain library. Using a rat hippocampal cDNA library, we have isolated a novel cDNA clone of GABA(B) receptor containing an insert of 124 bp between exon 3 and exon 4. This insert occurred between the regions encoding the Sushi domain and leucine binding protein (LBP)-like domain. The insert and subsequent frame shift generated a cDNA that codes for a truncated polypeptide of 239 amino acids lacking the C-terminus. Analysis of the deduced amino acid sequence of the new cDNA clone, termed GABA(B)R1g, showed that it was identical to the first 157 amino acids of GABA(B)R1a, but diverged thereafter. The C-terminal region of GABA(B)R1g contained two cysteine residues. GABA(B)R1g was expressed in both brain and peripheral tissues. Northern blot analysis demonstrated that two transcripts (4.5 kb and 4.0 kb) exist in hippocampus. In addition, studies of hippocampus in developing animals indicated that the expression of GABA(B)R1g is maximal at postnatal day four. GABA(B)R1g could be generated by alternative splicing of the GABA(B)R1 gene.

Alternative Splicing↗
PubMed2001

Gamma-hydroxybutyric acid-induced absence seizures in GluR2 null mutant mice.

In this electrophysiological study, we examined the susceptibility of GluR2 mutant null mice to absence seizures in comparison with wild-type controls. The prodrug of (GHB), gamma-butyrolactone (GBL) was given systemically to induce the absence seizures. We also tested the severity and duration of the seizure activity in this model. The results showed that the latency from GBL administration to onset of seizure was significantly prolonged in GluR2(-/-) mice when compared to GluR2(+/+) mice. The duration of spike-and-wave discharges (SWD) was also significantly decreased in the GluR2(-/-) mice. Ninety minutes following GBL administration, wild-type animals continued to exhibit intermittent SWD bursts while GluR2(-/-) mice had returned to baseline. These data suggest that the GluR2 subunit may be involved in the initiation and maintenance of absence seizures induced by GBL.

Animals↗
PubMed2001

Cloning and tissue distribution of a novel isoform of the rat GABA(B)R1 receptor subunit.

We have identified a novel splice variant of the metabotropic GABA(B) receptor (R) subunit I, designated GABA(B)R1f, from a rat hippocampus cDNA library screen. GABA(B)R1f shares sequence homology with rat GABA(B)R1a, with the exception of an in-frame deletion of exon 4, resulting in a 21 bp deletion in the coding sequence of the N-terminal extracellular domain. In addition, GABA(B)R1f also contains a 93 bp in-frame insertion in a region of the sequence corresponding to the second extracellular loop and the fifth transmembrane domain, similar to that found in rat GABA(B)R1c. While being ubiquitously (but variably) expressed, reverse-transcription polymerase chain reaction analysis revealed the GABA(B)R1f isoform to be most prevalent in peripheral vs central tissues, suggesting a potential role for this novel isoform in either the mediation of inhibitory transmission in these various tissues, or in as yet defined actions unrelated to central synaptic regulatory mechanisms attributable to GABA(B)R.

Alternative Splicing↗