Biomedical subjects

B Lu

Publications and source records attributed to B Lu.

At least 127 records · Page 7Linked to original sources

PubMed1999

Differential effects of GDNF and BDNF on cultured ventral mesencephalic neurons.

Previous studies have shown that brain derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) can enhance the survival of dopaminergic neurons in the ventral mesencephalon (VM). Here we compared several non-survival functions of the two factors in VM neurons in culture. We found that both BDNF and GDNF elicited an increase in the depolarization-induced release of dopamine, but had no effect on GABA release, in the VM cultures. BDNF, but not GDNF, significantly enhanced the expression of the calcium binding protein calbindin and synaptic protein SNAP25. In contrast, treatment of the cultures with GDNF, but not BDNF, elicited a marked fasciculation of the processes of the VM neurons. Thus, although both act on VM neurons, BDNF and GDNF have distinct functions.

Actins↗

PubMed1999

Targeted disruption of migration inhibitory factor gene reveals its critical role in sepsis.

To study the biologic role of migration inhibitory factor (MIF), a pleiotropic cytokine, we generated a mouse strain lacking MIF by gene targeting in embryonic stem cells. Analysis of the role of MIF during sepsis showed that MIF-/- mice were resistant to the lethal effects of high dose bacterial lipopolysaccharide (LPS), or Staphylococcus aureus enterotoxin B (SEB) with D-galactosamine and had lower plasma levels of tumor necrosis factor alpha (TNF-alpha) than did wild-type mice, but normal levels of interleukin (IL)-6 and IL-10. When stimulated with LPS and interferon gamma, macrophages from MIF-/- mice showed diminished production of TNF-alpha, normal IL-6 and IL-12, and increased production of nitric oxide. MIF-/- animals cleared gram-negative bacteria Pseudomonas aeruginosa instilled into the trachea better than did wild-type mice and had diminished neutrophil accumulation in their bronchoalveolar fluid compared to the wild-type mice. Thioglycollate elicited peritoneal exudates in uninfected MIF-/- mice, but showed normal neutrophil accumulation. Finally, the findings of enhanced resistance to P. aeruginosa and resistance to endotoxin-induced lethal shock suggest that the counteraction or neutralization of MIF may serve as an adjunct therapy in sepsis.

Animals↗

PubMed1999

Structure and function of the murine chemokine receptor CXCR3.

The gene encoding the murine homologue of human CXCR3 exists in a single copy consisting of two exons with an intron interrupting the coding sequence between nucleotides 10 and 11. The deduced amino acid sequence is 86% identical to the predicted human sequence. Murine CXCR3 mRNA is detectable in bone marrow cells cultured in the presence of IL-2 but not unstimulated cells. It is also detectable at low abundance in normal mouse spleen, lymph node, mammary gland, and thymus. Transfection of murine CXCR3 in murine pre-B lymphocyte line (CXCR3++/L1.2) conferred binding of the ligands IP10, ITAC and Mig with K(D)'s of 1.35 +/- 0.56, 1.41 +/- 0.20, and 11.65 +/- 0.90 nM, respectively. Lower affinity binding was observed for several beta or CC chemokines (eotaxin, MCP-3, MIP3alpha and SLC/6Ckine/Exodus 2). ITAC, IP10 and Mig induced chemotaxis with an order of potency ITAC > IP10 = Mig. The chemokines also increased intracellular calcium concentration and were variably desensitized to repeated agonist stimulation. The hierarchy for cross- desensitization was ITAC > Mig > IP10. Thus, while Mig, ITAC and IP10 all act on the same receptor for binding and agonist stimulation, they may interact with different receptor conformational isoforms to produce divergent responses.

Amino Acid Sequence↗

PubMed1999

Development of an extremely wear-resistant ultra high molecular weight polyethylene for total hip replacements.

Osteolysis induced by ultra high molecular weight polyethylene wear debris is one of the primary factors limiting the lifespan of total hip replacements. Crosslinking polyethylene is known to improve its wear resistance in certain industrial applications, and crosslinked polyethylene acetabular cups have shown improved wear resistance in two clinical studies. In the present study, crosslinked polyethylene cups were produced by two methods. Chemically crosslinked cups were produced by mixing a peroxide with ultra high molecular weight polyethylene powder and then molding the cups directly to shape. Radiation-crosslinked cups were produced by exposing conventional extruded ultra high molecular weight polyethylene bar stock to gamma radiation at various doses from 3.3 to 100 Mrad (1 Mrad = 10 kGy), remelting the bars to extinguish residual free radicals (i.e., to minimize long-term oxidation), and then machining the cups by conventional techniques. In hip-joint simulator tests lasting as long as 5 million cycles, both types of cross-linked cups exhibited dramatically improved resistance to wear. Artificial aging of the cups by heating for 30 days in air at 80 degrees C induced oxidation of the chemically crosslinked cups. However, a chemically crosslinked cup that was aged 2.7 years at room temperature had very little oxidation. Thus, whether substantial oxidation of chemically crosslinked polyethylene would occur at body temperature remains unclear. The radiation-crosslinked remelted cups exhibited excellent resistance to oxidation. Because crosslinking can reduce the ultimate tensile strength, fatigue strength, and elongation to failure of ultra high molecular weight polyethylene, the optimal crosslinking dose provides a balance between these physical properties and the wear resistance of the implant and might substantially reduce the incidence of wear-induced osteolysis with total hip replacements.

Arthroplasty, Replacement, Hip↗

PubMed1999

Molecular cloning and characterization of the canine prostaglandin E receptor EP2 subtype.

Prostaglandin E2 (PGE2) binds to four G-protein coupled cell surface receptors (EP1-EP4) and has been implicated as a local mediator of bone anabolism via a cyclic AMP mediated pathway following activation of the EP2 and/or EP4 receptor subtype. A canine kidney cDNA library was screened using a human EP2 probe, and a clone with an open reading frame of 1083 bp, potentially encoding a protein of 361 amino acids, was characterized. This open reading frame has 89% identity to the human EP2 cDNA at the nucleotide level and 87% identity at the predicted protein level. Scatchard analysis of a CHO cell line stably transfected with canine EP2 yielded a dissociation constant of 22 nM for PGE2. Competition binding studies, using 3H-PGE2 as ligand, demonstrated specific displacement by PGE2, Prostaglandin E1, Prostaglandin A3, and butaprost (an EP2 selective ligand), but not by ligands with selectivity for the related DP, FP, IP, or TP receptors. Specific ligand binding also resulted in increased levels of cAMP in EP2 transfected cells with no evidence of short-term, ligand-induced desensitization. Northern blot analysis revealed two transcripts of 3300 and 2400 bp in canine lung, and reverse-transcription polymerase chain reaction showed expression in all tissues examined. Southern blot analysis suggests the presence of a single-copy gene for EP2 in the dog.

Amino Acid Sequence↗

PubMed1999

Expression of C5a receptor in mouse brain: role in signal transduction and neurodegeneration.

In this study we explored the potential role of the complement derived anaphylatoxin C5a and the expression of its receptor in mouse brain. Using in situ hybridization, we found that C5a receptor messenger RNA is expressed in mouse brain. In response to intraventricular kainic acid injection, there was marked increase in the C5a receptor messenger RNA expression, particularly in hippocampal formation and cerebral cortex. C5a ligand-binding autoradiography confirmed the functional expression and elevation of the C5a receptor post-lesioning. The expression of C5a receptor messenger RNA in brain was confirmed by northern blot hybridization of total RNA from neuronal and glial cells in vitro. Based on these findings we explored the role of C5a in mechanisms of signal transduction in brain cells. Treatment of primary cultures of mouse astrocytes with human recombinant C5a resulted in the activation of mitogen-activated extracellular signal-regulated protein kinase. This response appeared to be mediated by the C5a receptor since astrocyte cultures derived from C5a receptor knockout mice were not responsive to the treatment. Understanding the regulation of C5a receptor in brain and mechanisms by which pro-inflammatory C5a modulates specific signal transduction pathways in brain cells is crucial to studies of inflammatory mechanisms in neurodegeneration.

Animals↗

PubMed1999

Differential signaling of glial cell line-derived neurothrophic factor and brain-derived neurotrophic factor in cultured ventral mesencephalic neurons.

In the ventral mesencephalon, two neurotrophic factors, brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor, have been shown previously to have similar effects on the survival of dopaminergic neurons. Here, we compared the signaling mechanisms for brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor, focusing on the mitogen-associated protein kinase and the transcription factor cyclic-AMP responsive element-binding protein. Double-staining experiments indicated that many neurons co-expressed the receptors for glial cell line-derived neurotrophic factor and brain-derived neurotrophic factor, c-RET and TrkB, suggesting that they are responsive to both brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor. Although both brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor induced a rapid phosphorylation of mitogen-associated protein kinase and cyclic-AMP, responsive element-binding protein, there were significant differences in the kinetics and pharmacology of the phosphorylation. The phosphorylation of mitogen-associated protein kinase by glial cell line-derived neurotrophic factor was transient; within 2 h, the level of mitogen-associated protein kinase phosphorylation returned to baseline. In contrast, the effect of brain-derived neurotrophic factor was long lasting; the mitogen-associated protein kinase remained phosphorylated for up to 4 h after brain-derived neurotrophic factor treatment. PD098059, a specific inhibitor for mitogen-associated protein kinase kinase, completely blocked the glial cell line-derived neurotrophic factor signaling through mitogen-associated protein kinase, but had no effect on brain-derived neurotrophic factor-induced mitogen-associated protein kinase phosphorylation. Both brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor induced the phosphorylation of cyclic-AMP responsive element-binding protein in the nuclei of ventral mesencephalon neurons. However, PD098059 blocked the cyclic-AMP responsive element-binding protein phosphorylation induced by glial cell line-derived neurotrophic factor, but not that by brain-derived neurotrophic factor. These results indicate that, although both brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor act on ventral mesencephalon neurons, the two factors have different signaling mechanisms, which may mediate their distinctive biological functions.

Animals↗

PubMed1999

Modes of protein movement that lead to the asymmetric localization of partner of Numb during Drosophila neuroblast division.

Partner of Numb (Pon) colocalizes with the determinant Numb and is required for its proper asymmetric localization in Drosophila. How the asymmetric localization of Pon is accomplished is not well understood. Here, we show that Pon localization takes place at the protein level and that its C-terminal region is necessary and sufficient for asymmetric localization. Fusion of the Pon localization domain with green fluorescent protein (GFP) allowed monitoring of the localization process in living embryos. Upon a neuroblast's entry into mitosis, Pon is recruited from the cytoplasm to the cortex. Cortically recruited Pon can move apically or basally within the two-dimensional confines of the cortex. This movement can occur when myosin motor activity is inhibited. However, the restriction of Pon to the basal cortex requires both actomyosin and Inscuteable.

Animals↗

PubMed1999

Targeted deletion of the neutral endopeptidase gene alters ventilatory responses to acute hypoxia in mice.

Neutral endopeptidase (NEP) is one of the major endopeptidases responsible for the inactivation of substance P in the carotid body, a neurotransmitter shown to be important in the transduction of hypoxic stimuli. Ventilatory responses to acute hypoxia were measured by indirect plethysmography in unanesthetized, unrestrained wild-type mice and in mice in which the NEP gene was deleted (NEP -/-). Ventilation was measured while the animals breathed room air: 12% O(2) in N(2) and 8% O(2) in N(2). Deletion of the NEP gene caused marked alterations in both the magnitude and composition of the hypoxic ventilatory response to both 8% O(2) in N(2) and 12% O(2) in N(2), compared with the wild-type mice (C57BL/6J) on the same genetic background as the NEP -/- mice. Treatment of C57BL/6J mice with thiorphan, a NEP inhibitor, resulted in a greater ventilatory response to 8% O(2) because of a significantly greater shortening of expiratory time. The results of these studies demonstrate that NEP plays an important role in modifying the expression of the ventilatory response to acute hypoxia.

Acute Disease↗

PubMed1999

Increased activator protein-1 DNA binding and c-Jun NH2-terminal kinase activity in human breast tumors with acquired tamoxifen resistance.

Human breast tumors that are initially responsive to tamoxifen (TAM) eventually relapse during treatment. Estrogen receptor (ER) expression and function are often preserved in these tumors, and clinical evidence suggests that this relapse may be related to TAM's known agonistic properties. ER can interact with the activator protein-1 (AP-1) transcription factor complex through protein-protein interactions that are independent of ER DNA binding and, in certain ER-positive cells, this may allow TAM to exert an agonist response on AP-1-regulated genes. We, therefore, assessed both AP-1 DNA binding and the known AP-1 activating enzyme, c-Jun NH2-terminal kinase (JNK), in a panel of 30 ER-positive primary human breast tumors with acquired TAM resistance, as compared to a matched panel of 27 untreated control ER-positive breast tumors and a separate control set of 14 primary tumors, which included 7 ER-positive tumors that were growth-arrested by 3 months of preoperative TAM. AP-1 DNA binding activity was measured from cryopreserved tumor extracts using a labeled oligonucleotide probe containing a consensus AP-1 response element by electrophoretic mobility shift assay. JNK was first extracted from the tumor lysates by incubation over a Sepharose-bound c-Jun(1-89) fusion protein, and its activity was then measured by chemiluminescent Western blot by detection of the phosphorylated product using a phospho-Jun(Ser-63)-specific primary antibody. The set of control ER-positive breast tumors growth arrested by TAM showed no significant difference from untreated control tumors in their AP-1 DNA binding and JNK activities. In contrast, there was a significant (P < 0.001) increase in mean AP-1 DNA binding activity for the panel of ER-positive TAM-resistant (TAM-R) tumors as compared to its matched control panel of untreated tumors. Mean JNK activity in the TAM-R tumors was also significantly higher than that found in the untreated tumors (P = 0.038). Overall, there was no significant correlation between JNK activity and AP-1 DNA binding; however, regression analysis showed that, for any given level of JNK activity, the TAM-R tumors possessed a 3.5-fold increase in AP-1 DNA binding activity as compared to the untreated tumors. These findings indicate that, when compared to untreated ER-positive primary breast tumors, TAM-R tumors demonstrate significantly increased levels of AP-1 DNA binding and JNK activity, consistent with experimental models suggesting that TAM-stimulated ER-positive tumor growth may be mediated by enhanced AP-1 transcriptional activity. These observations support the need for further evaluation of these markers in breast tumors as predictors of TAM resistance.

Aged↗

PubMed1999

[Experimental study of osseointegrated dental implants placed into fresh extraction sockets in dogs].

OBJECTIVE: To investigate the better way in treating bone defects around implants. METHODS: 12 mongrel dogs, pure titanium implants were immediately inserted in the mesial roots of the second, third and fourth mandibular premolar sockets. The defects around implants were separately filled with demineralized freeze-dried bone allograft (DFDBA), demineralized freeze-dried allocancellous in combination with bBMP (bBMP compound bone) and nothing. RESULTS: Histologic observation showed that bone defects around implants were substituted by new bone in DFDBA group at 12 weeks and in bBMP compound bone group at 8 weeks, and also the osseointegration were obtained between implants and bone, but bone defects were only filled about 3/5 in no graft group at 12 weeks. CONCLUSION: Immediate implants could obtain good osseointegration if the defects around implants were treated properly and the right technique was used, and also the use of bBMP compound bone could promote obviously bone formation in defects around implants.

Animals↗

PubMed1999

[Measurement and research of posterior chamber intraocular lens tilt and decentration in vivo].

OBJECTIVE: To observe the situation of implanted lenses in vivid eyes and postoperative visual acuity affected by the lens tilt and decentration. METHODS: 64 eyes underwent extracapsular cataract extraction with posterior chamber lens implantation. Postoperatively, the lens tilt was measured by means of the 3(rd) and 4(th) Purkinje images, and the decentration of lenses was measured on the anterior segment photographs taken with a fundus camera. RESULTS: The mean tilt was (6.95 +/- 2.46) degree, and the mean decentration, (0.66 +/- 0.28) mm. There were a significant differences in the tilt and decentration between the symmetrical bag/bag and asymmetrical bag/sulcus group (P < 0.001). Bag/bag group without tear had less average decentration 0.32 mm. When tilt was more than 9.65 degrees and decentration was more than 1.02 mm, the symptom such as glare or monocular diplopia was obvious. CONCLUSIONS: These results indicate that in the bag without tear, the lenses have a perfect stability and consistent centration, and the tilt and decentration of the implanted lens affect postoperative visual quality in varying degrees.

Adult↗

PubMed1999

[Activation of G protein on the membrane of TCS-sensitive cells].

Trichosanthin (TCS), a Type I Ribosome Inactivating Protein isolated from the root tuber of Trichosanthes Kirilowii M. has various biological activities including abortion induction, anti-tumor and anti-HIV. The mechanism of TCS specifically killing sensitive cells has not been studied clearly. In this study, we initially found that there exists TCS-affinity molecule on Syncytiotrophoblast cells and Jar cells. Furthermore, by [35S]GTP gamma S Binding Assay, we find that TCS can activate G protein on the membrane of TCS-sensitive cells. These results indicate that on the membrane of TCS-sensitive cells exists TCS-specific receptor.

Cell Membrane↗

PubMed1999

[Ultra trace determination of platinum, palladium, gold and rhodium in minerals].

Our work studied the minerals dissolved in aqua regia. The trace Pt(II), Pd(II) Au (III) and Rh(I) complexes were loaded by the mixed carbon powder which carried diphenyl thiourea when aqua regia or hydrochloric acid media as well as stannous chloride were present. We added some carbon powder in ashen loader and determined the elements with atomic emission spectrometry. The determination sensitivity counted with 10 grams of samples is 1 x 10(-9). The RSD for 0.05 x 10(-6) standard Pt, Pd, Au and Rh solutions are 6.0%, 5.1%, 8.5% and 11.4%, respectively. The method is simple and operation is easy. The results satisfy our requirement.

English Abstract↗

PubMed1998

Oxidant stress impaired DNA-binding of estrogen receptor from human breast cancer.

Full-length (67 kDa) immunoreactive estrogen receptor (ER) extracted from a third of untreated ER-positive primary breast tumors appears unable to bind to its cognate estrogen response element (ERE). We have observed partial reversibility of this ER DNA-binding defect upon treatment of these tumor extracts with excess thiol reducing agent (DTT), suggesting that ER DNA-binding is subject to redox modulation as is reported for other zinc-finger proteins and transcriptional activators. Treatment of recombinant ER DNA-binding domain (ER-DBD) or ER-enriched extracts from CHO(ER) and MCF-7 cells with thiol-reacting oxidants (diamide, iodosobenzoate, H2O2) or alkylator (iodoacetamide) produces a dose-dependent loss in ER DNA-binding capacity. Thiol-specific oxidative loss in ER DNA-binding is fully reversible by DTT reduction, unlike the defect caused by thiol-specific alkylation. Circular dichroism spectrometry shows that both forms of treatment substantially modify ER secondary structure, inducing loss of alpha-helical content within the ER-DBD that is reversible after thiol oxidation but not after thiol alkylation. Oxidant (H2O2, menadione) exposure of cultured CHO(ER) or MCF-7 cells impairs the ability of endogenous ER to bind DNA and transactivate an ER-responsive reporter gene (ERE-tk-CAT), demonstrating that extracellular redox stress can modulate intracellular ER function. Since these thiol-specific oxidant and alkylator treatments have no significant effect on either recombinant ER ligand-binding or intracellular immunoreactive ER content, our findings suggest that DNA-binding and transactivation are the most sensitive intracellular ER functions impaired by oxidant stress in some ER-positive human breast tumors.

Alkylating Agents↗

PubMed1998

Partner of Numb colocalizes with Numb during mitosis and directs Numb asymmetric localization in Drosophila neural and muscle progenitors.

During mitosis of multiple types of precursor cells in Drosophila, Numb is asymmetrically distributed between the two daughter cells and confers distinct daughter cell fates. Here we report the identification of a novel gene product, Partner of Numb (PON), based on its physical interaction with Numb. PON is asymmetrically localized during mitosis and colocalizes with Numb. Loss of pon function disrupts Numb localization in muscle progenitors and delays Numb crescent formation in neural precursors. Moreover, ectopically expressed PON responds to the apical-basal polarity of epithelial cells and is sufficient to localize Numb basally. We propose that PON is one component of a multimolecular machinery that localizes Numb by responding to polarity cues conserved in neural precursors and epithelial cells.

Amino Acid Sequence↗

PubMed1998

Coat protein interactions involved in tobacco mosaic tobamovirus cross-protection.

To investigate the molecular role of the tobacco mosaic tobamovirus (TMV) coat protein (CP) in conferring cross-protection, a potato X potexvirus (PVX) vector (S. Chapman, Plant J. 2, 549-557, 1992) was used to systemically express a set of TMV mutant CPs in Nicotiana benthamiana prior to challenge inoculation with TMV. PVX-expressed wild-type TMV CP delayed TMV accumulation for up to 2 weeks compared to unprotected plants or plants preinfected with the unmodified PVX vector. Similar delays in TMV accumulation were obtained using TMV CPs that were deficient in virion formation but competent to assemble into helical aggregates. In contrast, TMV CPs that were incapable of helical aggregation or unable to bind viral RNA did not delay the accumulation of TMV. Furthermore, TMV CPs with enhanced intersubunit interactions that favor helical aggregation produced significantly greater delays in the accumulation of challenge TMV than obtained from the wild-type CP. Thus the capabilities of TMV CP to interact with viral RNA and self-associate in a helical fashion appear to be essential to its ability to confer protection. Taken together, these findings support a model for CP-mediated resistance in which the protecting CP recoats the challenge virus RNA as it disassembles.

Capsid Proteins↗

PubMed1998

Presynaptic modulation of synaptic transmission and plasticity by brain-derived neurotrophic factor in the developing hippocampus.

In addition to the regulation of neuronal survival and differentiation, neurotrophins may play a role in synapse development and plasticity. Application of brain-derived neurotrophic factor (BDNF) promotes long-term potentiation (LTP) in CA1 synapses of neonatal hippocampus, which otherwise exhibit only short-term potentiation. This is attributable, at least in part, to an attenuation of the synaptic fatigue induced by high-frequency stimulation (HFS). However, the prevention of synaptic fatigue by BDNF could be mediated by an attenuation of synaptic vesicle depletion from presynaptic terminals and/or a reduction of the desensitization of postsynaptic receptors. Here we provide evidence supporting a presynaptic effect of BDNF. The effect of BDNF on synaptic fatigue depended on the stimulation frequency, not on the stimulus duration nor on the number of stimulation pulses. BDNF was only effective when the synapses were stimulated at frequencies >50 Hz. Treatment with BDNF also potentiated paired-pulse facilitation (PPF), a parameter reflecting changes in the properties of presynaptic terminals. This effect of BDNF was restricted only to PPF elicited with interpulse intervals </=20 msec. Changes in the extracellular calcium concentration altered the magnitude of the BDNF effect on PPF and synaptic responses to HFS, suggesting that BDNF regulates neurotransmitter release. When the desensitization of glutamate receptors was blocked by cyclothiazide or aniracetam, the BDNF potentiation of the synaptic responses to HFS was unaltered. Taken together, these results suggest that BDNF acts presynaptically. When two pathways in the same slice were monitored simultaneously, BDNF treatment potentiated the tetanized pathway without affecting the synaptic efficacy of the untetanized pathway. The selective potentiation of high-frequency transmission by BDNF appears to contribute directly to the effect of BDNF on LTP rather than indirectly by inducing the release of additional diffusible factors. The preferential potentiation of highly active synapses by BDNF may have implications in the Hebbian mechanism of synaptic plasticity.

Animals↗