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Biomedical subjects

C Wang

Publications and source records attributed to C Wang.

At least 109 records · Page 6Linked to original sources
PubMed2002

Adaptation to chronic PCP results in hyperfunctional NMDA and hypofunctional GABA(A) synaptic receptors.

Schizophrenia is currently thought to be associated with a hypoglutamatergic state that is mimicked by acute phencyclidine (PCP), an antagonist of the N-methyl-D-aspartate (NMDA) receptor subtype. In this study we tested the hypothesis that chronic treatment of rats with this antagonist may be a more appropriate animal model than acute exposure since it could result in adaptive synaptic responses that would model certain aspects of the schizophrenic state in humans. In vitro intracellular electrophysiological recordings employing brain slices from rats treated chronically in vivo with PCP demonstrated that chronic PCP caused a substantial increase in synaptic responses mediated by NMDA receptors without any significant changes in alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate-mediated synaptic responses. At the same time, GABA(A) receptor-mediated inhibitory responses were depressed significantly. Pharmacological and paired-pulse facilitation experiments demonstrated that these adaptive responses following chronic PCP administration were not the result of altered glutamate or GABA release. Immunoblot analyses suggest that the hyperfunctional NMDA response is at least partially mediated by an increased synthesis of NR1 and NR2A subunits as well as a change in the subunit stoichiometry of the NMDA receptor. This change in receptor composition was also supported by pharmacological experiments with a subunit selective NMDA antagonist. Our data support a reconsideration of NMDA and GABA(A) receptor responsiveness following a chronic, not acute, exposure to PCP and the adaptations that persist after such a regimen.

Animals↗
PubMed2002

Rapid distributed fronto-parieto-occipital processing stages during working memory in humans.

Cortical potentials were recorded from implanted electrodes during a difficult working memory task requiring rapid storage, modification and retrieval of multiple memoranda. Synchronous event-related potentials were generated in distributed occipital, parietal, Rolandic and prefrontal sites beginning approximately 130 ms after stimulus onset and continuing for >500 ms. Coherent phase-locked, event-related oscillations supported interaction between these dorsal stream structures throughout the task period. The Rolandic structures generated early as well as sustained potentials to sensory stimuli in the absence of movement. Activation peaks and phase lags between synaptic populations suggested that perceptual processing occurred exclusively in the visual association cortex from approximately 90 to 130 ms, with its results projected to fronto-parietal areas for interpretation from approximately 130 to 280 ms. The direction of interaction then appeared to reverse from approximately 300 to 400 ms, consistent with mental arithmetic being performed by fronto-parietal areas operating upon a visual scratch pad in the dorsolateral occipital cortex. A second reversal, from approximately 420 to 600 ms, may have represented an updating of memoranda stored in fronto-parietal sites. Lateralized perisylvian oscillations suggested an articulatory loop. Anterior cingulate activity was evoked by feedback signals indicating errors. These results indicate how a fronto-centro-parietal 'central executive' might interact with an occipital visual scratch pad, perisylvian articulatory loop and limbic monitor to implement the sequential stages of a complex mental operation.

Adolescent↗
PubMed2002

Leaf area dynamics of a boreal black spruce fire chronosequence.

Specific leaf area (SLA) and leaf area index (LAI) were estimated using site-specific allometric equations for a boreal black spruce (Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada. Stands ranged from 3 to 131 years in age and had soils that were categorized as well or poorly drained. The goals of the study were to: (i) measure SLA for the dominant tree and understory species of boreal black spruce-dominated stands, and examine the effect of various biophysical conditions on SLA; and (ii) examine leaf area dynamics of both understory and overstory for well- and poorly drained stands in the chronosequence. Overall, average SLA values for black spruce (n = 215), jack pine (Pinus banksiana Lamb., n = 72) and trembling aspen (Populus tremuloides Michx., n = 27) were 5.82 +/- 1.91, 5.76 +/- 1.91 and 17.42 +/- 2.21 m2 x kg-1, respectively. Foliage age, stand age, vertical position in the canopy and soil drainage had significant effects on SLA. Black spruce dominated overstory LAI in the older stands. Well-drained stands had significantly higher overstory LAI (P < 0.001), but lower understory LAI (P = 0.022), than poorly drained stands. Overstory LAI was negligible in the recent (3-12 years old) burn sites and highest in the 70-year-old burn site (6.8 and 3.0 in the well- and poorly drained stands, respectively), declining significantly (by 30-50%) from this peak in the oldest stands. Understory leaf area represented a significant portion (> 40%) of total leaf area in all stands except the oldest.

Ecosystem↗
PubMed2002

Levonorgestrel implants (Norplant II) for male contraception clinical trials: combination with transdermal and injectable testosterone.

Recent studies demonstrate that combinations of androgens and progestagens are highly effective in the suppression of spermatogenesis in normal volunteers. To test whether progestagen and androgen delivery systems designed to produce steady serum levels will be as effective as other androgen plus progestagen combinations, we compared Norplant II and testosterone (T) transdermal patch to T patch alone on the suppression of spermatogenesis in normal men. Thirty-nine healthy male volunteers (age, 20-45 yr) were randomly assigned to one of two groups. Group 1 (n = 19) received two transdermal T patches daily (Testoderm TTS, each patch designed to deliver about 5 mg/d T) alone, and group 2 (n = 20) received combined Norplant II [Jadelle, four capsules delivering approximately 160 microg/d levonorgestrel (LNG)] plus T patch. Neither of these regimens were very effective, with suppression of spermatogenesis to severe oligozoospermia occurring in less than 60% of subjects. We then expanded the study to include two more groups to determine whether T patch or Norplant II was the main factor causing the inadequate suppression of spermatogenesis. Another 29 subjects were randomized to one of two groups. Group 3 (n = 15) received oral LNG (125 microg/d) plus T patch, and group 4 (n = 14) received Norplant II plus T enanthate (TE) injection (100 mg/wk i.m.). After a pretreatment phase of 4 wk, all subjects received treatment for 24 wk, followed by a recovery period of 12-24 wk. Steady-state serum LNG levels (800-1200 pmol/liter) were achieved from wk 3-24 after Norplant II insertion and decreased rapidly after the removal of the implants at wk 24. Trough serum LNG levels after oral LNG administration were at a comparable range (940-1300 pmol/liter). Azoospermia was achieved in 24%, 35%, 33%, and 93%, and severe oligozoospermia (<1 x 10(6)/ml) developed in 24%, 60%, 42%, and 100% of the subjects in groups 1, 2, 3, and 4, respectively, during treatment phase. All subjects in the Norplant II plus TE groups had persistent sperm concentrations less than 3 x 10(6)/ml from wk 12 until the end of treatment. Concomitant with the marked suppression of spermatogenesis in the Norplant II plus TE group, serum FSH and LH levels were most decreased in this group compared with all other groups. In the T patch-only group, serum SHBG was not suppressed, and total serum T was higher than baseline levels. In the other three groups administered progestagens, serum SHBGs were significantly suppressed, and serum total T remained similar to baseline levels. Serum free T levels were not changed in any group. Except for a suppression of serum high-density lipoprotein cholesterol, there was no significant change in weight, hematocrit, clinical chemistry, or prostate-specific antigen levels in any of the treatment groups. Although more efficacious than T patch alone, Norplant II or oral LNG plus T patch was not as effective in suppressing spermatogenesis to severe oligo- or azoospermia as in previous reports using oral LNG plus TE. This relative lesser efficacy occurred despite the achievement of serum LNG levels by Norplant II that were equivalent to those reported after administration of oral LNG. Substituting the transdermal T delivery system with TE injections resulted in very effective suppression of sperm output. The difference in spermatogenesis suppression of these combined regimens is likely due to less T delivered by the transdermal patch compared with the TE weekly injections. We conclude that Norplant II implants plus TE 100 mg/wk were very efficient in suppressing spermatogenesis to a level acceptable for contraceptive efficacy. This study demonstrates that the dose or route of administration of androgens is critical for sperm suppression in combined androgen-progestagen regimens for hormonal male contraception.

Administration, Cutaneous↗
PubMed2001

[A epidemiological survey and management analysis of asthma among employees of 6 chemical plants in Beijing area].

OBJECTIVE: To estimate the prevalence and to evaluate the current status for management of asthma among employees in chemical plants in Beijing area. METHODS: A general survey was conducted among 12694 employees in 6 large chemical plants in Beijing area by face to face interview and physical examination. RESULTS: The prevalence of asthma was 1.13% (143/12694), 1.09% (78/7164) for male and 1.18% (65/5530) for female. The incidence of asthma was different among various chemical plants. 91.61% of the patients had received drug therapy in acute exacerbation stage, however, only 8.39% of them persevered drug therapy in remission stage. CONCLUSION: Atopy and exposure to some chemical substances are risk factors for asthma. Treatment of asthma among this population by far fails to accord with the demands of the recommeded regimen for asthma.

Adult↗
PubMed2001

Crystal structure of Sar1-GDP at 1.7 A resolution and the role of the NH2 terminus in ER export.

The Sar1 GTPase is an essential component of COPII vesicle coats involved in export of cargo from the ER. We report the 1.7-A structure of Sar1 and find that consistent with the sequence divergence of Sar1 from Arf family GTPases, Sar1 is structurally distinct. In particular, we show that the Sar1 NH2 terminus contains two regions: an NH2-terminal extension containing an evolutionary conserved hydrophobic motif that facilitates membrane recruitment and activation by the mammalian Sec12 guanine nucleotide exchange factor, and an alpha1' amphipathic helix that contributes to interaction with the Sec23/24 complex that is responsible for cargo selection during ER export. We propose that the hydrophobic Sar1 NH2-terminal activation/recruitment motif, in conjunction with the alpha1' helix, mediates the initial steps in COPII coat assembly for export from the ER.

Animals↗
PubMed2001

Conformational and functional significance of residue proline 17 in chicken muscle adenylate kinase.

The effect of mutation proline 17 on the multiple conformations and catalytic function in chicken muscle adenylate kinase (AK) has been studied. The substitution of proline 17 with glycine or valine altered the distribution of multiple conformations. Compared with the wild-type enzyme, the P17G and P17V mutants contained decreased fraction of minor conformer from 18% to 9% and 11%, respectively. Due to the mutation, the enzyme showed lower secondary structural content, poorer affinity to substrates or substrate analogues, and reduced catalytic efficiency. The results revealed the significance of proline 17 in the conformation and function of AK.

Adenosine Diphosphate↗
PubMed2001

Crystallization and preliminary X-ray diffraction analysis of the 10 kDa C-terminal subdomain of 70 kDa heat-shock cognate protein.

The 70 kDa heat-shock cognate protein (Hsc70) is a cytosolic molecular chaperone. It is composed of a 44 kDa N-terminal nucleotide-binding domain, an 18 kDa peptide-binding subdomain and a 10 kDa C-terminal subdomain. Single crystals of recombinant 10 kDa subdomain of rat Hsc70 have been obtained using ammonium sulfate as a precipitant at room temperature. The crystals diffract beyond 3.5 A using a synchrotron-radiation source at a wavelength of 1.0 A. The crystals belong to the hexagonal space group P6(1)22 or P6(5)22, with unit-cell parameters a = b = 119.0, c = 166.4 A.

Animals↗
PubMed2001

Human erythrocyte pyruvate kinase: characterization of the recombinant enzyme and a mutant form (R510Q) causing nonspherocytic hemolytic anemia.

Human erythrocyte pyruvate kinase plays an important role in erythrocyte metabolism. Mutation on the gene results in pyruvate kinase deficiency and is an important cause of hereditary nonspherocytic hemolytic anemia. Because of difficulties in isolating the mutant enzymes from patients, these mutations have not been fully studied. In this study, a complementary DNA (cDNA) encoding the human erythrocyte pyruvate kinase was generated. The cDNA was cloned into several expression vectors, and the protein was expressed and purified. The tetrameric protein exhibited properties characteristic of authentic human erythrocyte pyruvate kinase, including response to substrate, phosphoenolpyruvate, activation by fructose 1,6-bisphosphate, and inhibition by adenosine triphosphate (ATP). The N-terminal segment of the protein was highly susceptible to proteolysis, but only 2 of the 4 subunits were cleaved and lacked 47 N-terminal amino acid residues. A mutant protein, R510Q, which is the most frequently occurring mutation among Northern European population, was also generated and purified. The mutant protein retained its binding capacity to and could be activated by fructose 1,6-bisphosphate and showed similar kinetics toward phosphoenolpyruvate and adenosine diphosphate as for the wild-type enzyme. Conversely, the mutant protein has a dramatically decreased stability toward heat and is more susceptible to ATP inhibition. The enzyme instability decreases the enzyme level in the cell, accounting for the clinically observed "pyruvate kinase deficiency" of patients who are homozygous for this mutation. This study provides the first detailed functional characterization of human erythrocyte pyruvate kinase. These findings will allow the establishment of a fine correlation between molecular abnormalities and the clinical expression of the disease.

Adenosine Triphosphate↗
PubMed2001

[Application of plasma radio frequency at low temperature in treatment of snoring and obstructive sleep apnea syndrome: a pilot study].

OBJECTIVE: To explore the effect of plasma radiofrequency at low temperature in treatment of snoring and obstructive sleep apnea syndrome (OSAS). METHODS: Plastic surgery of uvula and soft palate was performed by plasma radiofrequency at low temperature under local anaesthesia in out-patient department among 12 patients with simple snoring and 47 patients with OSA (42 males and 17 females with the average age of 40.2 +/- 7.2 years). Nocturnal polysomnography was performed before and after operation. The patients were followed up for 4 to 8 weeks after operation. RESULTS: Clinical symptoms improved significantly after four to eight weeks. The free margin of soft palate was elevated, the uvula was shortened, and the volume of tonsils was reduced remarkably. The pharyngeal space was expanded significantly. No bleeding, choke, open rhinolalia and cicatricial stricture occurred during and after operation. Mean AHI of 47 OSA patients decreased from 18.1 +/- 7.3 to 6.9 +/- 5.4 (P < 0.02), mean lowest SaO2 increased from 82.1% +/- 6.7% to 86.7% +/- 3.3% (P < 0.05). The percentage of slow wave sleep in total sleep time increased from 3.0 +/- 2.7% to 10.4 +/- 3.6% ( P < 0.05). In general, 49 patients were with excellent curative effect, 8 with good effect, and 2 needed oral appliance to release the base of tongue. Conclusion Snoring and mild and moderate obstructive sleep apnea can be significantly improved by using radiofrequency ablation at least on a short-term basis. This treatment can be administered as an outpatient procedure without complications related to speech, taste or swallowing.

Adult↗
PubMed2001

The role of backbone motions in ligand binding to the c-Src SH3 domain.

The Src homology 3 (SH3) domain of pp60(c-src) (Src) plays dual roles in signal transduction, through stabilizing the repressed form of the Src kinase and through mediating the formation of activated signaling complexes. Transition of the Src SH3 domain between a variety of binding partners during progression through the cell cycle requires adjustment of a delicate free energy balance. Although numerous structural and functional studies of SH3 have provided an in-depth understanding of structural determinants for binding, the origins of binding energy in SH3-ligand interactions are not fully understood. Considering only the protein-ligand interface, the observed favorable change in standard enthalpy (DeltaH=-9.1 kcal/mol) and unfavorable change in standard entropy (TDeltaS=-2.7 kcal/mol) upon binding the proline-rich ligand RLP2 (RALPPLPRY) are inconsistent with the predominantly hydrophobic interaction surface. To investigate possible origins of ligand binding energy, backbone dynamics of free and RLP2-bound SH3 were performed via (15)N NMR relaxation and hydrogen-deuterium (H/(2)H) exchange measurements. On the ps-ns time scale, assuming uncorrelated motions, ligand binding results in a significant reduction in backbone entropy (-1.5(+/-0.6) kcal/mol). Binding also suppresses motions on the micros-ms time scale, which may additionally contribute to an unfavorable change in entropy. A large increase in protection from H/(2)H exchange is observed upon ligand binding, providing evidence for entropy loss due to motions on longer time scales, and supporting the notion that stabilization of pre-existing conformations within a native state ensemble is a fundamental paradigm for ligand binding. Observed changes in motion on all three time scales occur at locations both near and remote from the protein-ligand interface. The propagation of ligand binding interactions across the SH3 domain has potential consequences in target selection through altering both free energy and geometry in intact Src, and suggests that looking beyond the protein-ligand interface is essential in understanding ligand binding energetics.

Animals↗
PubMed2001

Different combinations of the heat-shock cognate protein 70 (hsc70) C-terminal functional groups are utilized to interact with distinct tetratricopeptide repeat-containing proteins.

A group of tetratricopeptide repeat (TPR)-containing proteins has been shown to interact with the C-terminal domain of the 70 kDa heat-shock cognate protein (hsc70). In the present study, the effect of the TPR-containing proteins, including the C-terminus of hsc70-interacting protein (CHIP), TPR1 and human glutamine-rich TPR-containing protein (hSGT), on refolding of luciferase by DnaJ and hsc70 was investigated. These proteins inhibited the restoration of luciferase activity by the chaperones. The inhibitory effect exerted by TPR1 and hSGT depended upon their binding to hsc70. However, the interaction with hsc70 did not appear to be required for the inhibition of luciferase refolding by CHIP. We also demonstrate that the peptide, GPTIEEVD, corresponding to the C-terminal end of hsc70, abolished the association of [(3)H]hsc70 with CHIP, TPR1 and hSGT. This implied that the GPTIEEVD motif of hsc70 was responsible for interacting with these TPR-containing proteins. However, the GGXP-repeats (where X is any aliphatic residue), another C-terminal conserved motif of vertebrate hsc70s, were not essential for interacting with the TPR-containing proteins. On the basis of mutagenesis studies, it was clear that a unique combination of the functional groups in the GPTIEEVD motif were utilized to interact with each TPR-containing protein, suggesting that inhibitors can be designed and used to elucidate the functional role of these interactions.

Amino Acid Motifs↗
PubMed2001

Rudimentary TCR signaling triggers default IL-10 secretion by human Th1 cells.

Understanding the process of inducing T cell activation has been hampered by the complex interactions between APC and inflammatory Th1 cells. To dissociate Ag-specific signaling through the TCR from costimulatory signaling, rTCR ligands (RTL) containing the alpha1 and beta1 domains of HLA-DR2b (DRA*0101:DRB1*1501) covalently linked with either the myelin basic protein peptide 85-99 (RTL303) or CABL-b3a2 (RTL311) peptides were constructed to provide a minimal ligand for peptide-specific TCRs. When incubated with peptide-specific Th1 cell clones in the absence of APC or costimulatory molecules, only the cognate RTL induced partial activation through the TCR. This partial activation included rapid TCR zeta-chain phosphorylation, calcium mobilization, and reduced extracellular signal-related kinase activity, as well as IL-10 production, but not proliferation or other obvious phenotypic changes. On restimulation with APC/peptide, the RTL-pretreated Th1 clones had reduced proliferation and secreted less IFN-gamma; IL-10 production persisted. These findings reveal for the first time the rudimentary signaling pattern delivered by initial engagement of the external TCR interface, which is further supplemented by coactivation molecules. Activation with RTLs provides a novel strategy for generating autoantigen-specific bystander suppression useful for treatment of complex autoimmune diseases.

Calcium Signaling↗
PubMed2001

Decreased glutamate receptor 2 expression and enhanced epileptogenesis in immature rat hippocampus after perinatal hypoxia-induced seizures.

Hypoxic encephalopathy is the most common cause of neonatal seizures and can lead to chronic epilepsy. In rats at postnatal days 10-12 (P10-12), global hypoxia induces spontaneous seizures and chronically decreases seizure threshold, thus mimicking clinical aspects of neonatal hypoxia. We have shown previously that the acute and chronic epileptogenic effects of hypoxia are age-dependent and require AMPA receptor activation. In this study, we aimed to determine whether hypoxia-induced seizures and epileptogenesis are associated with maturational and seizure-induced changes in AMPA receptor composition and function. Northern and Western blots indicated that glutamate receptor 2 (GluR2) mRNA and protein expression were significantly lower in neocortex and hippocampus at P10-12 compared with adult. After hypoxia-induced seizures at P10, GluR2 mRNA was significantly decreased within 48 hr, and GluR2 protein was significantly decreased within 96 hr. AMPA-induced Co(2+) uptake by neurons in hippocampal slices indicated higher expression of Ca(2+)-permeable AMPA receptors in immature pyramidal neurons compared with adult. In slices obtained 96 hr after hypoxia-induced seizures, AMPA-induced Co(2+) uptake was significantly increased compared with age-matched controls, and field recordings revealed increased tetanus-induced afterdischarges that could be kindled in the absence of NMDA receptor activation. In situ end labeling showed no acute or delayed cell death after hypoxia-induced seizures. Our results indicate that susceptibility to hypoxia-induced seizures occurs during a developmental stage in which the expression of Ca(2+)-permeable AMPA receptors is relatively high. Furthermore, perinatal hypoxia-induced seizures induce increased expression of Ca(2+)-permeable AMPA receptors and an increased capacity for AMPA receptor-mediated epileptogenesis without inducing cell death.

Aging↗
PubMed2001

Enrichment during transdominant genetic experiments using a flow sorter.

BACKGROUND: Flow cytometry, in combination with retroviral expression libraries, is a powerful tool for genetic experimentation in mammalian cells. Expression libraries are transduced into cells engineered with a fluorescent reporter. Sorting for either bright or dim cells allows enrichment for specific inhibitors that alter reporter activity. This strategy has been used to isolate peptides and RNAs that either activate or suppress defined biochemical pathways. METHODS: Several variables contribute to the enrichment process: (1) the background of the fluorescence bioassay; (2) the mean fluorescence ratio between the induced and noninduced reporter cell populations; (3) the genetic penetrance, or strength, of the inhibitor; and (4) the multiplicity of infection (MOI). An experimental and theoretical analysis, including computer modeling, of these issues in the context of a mammalian cell bioassay was undertaken. RESULTS: MOI measurements were shown to be problematic. High MOI had little effect on enrichment early in the cycling process but a significant effect at later stages. Penetrance and background were critical throughout the process. Enrichments within about twofold of the theoretical maximum were observed. CONCLUSIONS: Caution should be exercised in MOI determination because of the danger of significant underestimation. High MOI is potentially advantageous early in the selection process but hinders enrichment in the later rounds. Modeling shows that MOI, assay background and clone penetrance are the principal variables that determine the success of transdominant selections by FACS.

Animals↗
PubMed2001

Ligand-independent activation of oestrogen receptor alpha by caveolin-1.

Expression of caveolin-1 in the human mammary adenocarcinoma cell line MCF-7 causes ligand-independent concentration of oestrogen receptor alpha (ERalpha) in the nucleus, and potentiates ligand-independent and ligand-dependent transcription from an oestrogen response element-driven reporter gene. Furthermore, caveolin-1 co-immunoprecipitates with ERalpha [Schlegel, Wang, Katzenellenbogen, Pestell and Lisanti (1999) J. Biol. Chem. 274, 33551-33556]. In the present study we show that caveolin-1 binds directly to ERalpha. This interaction is mediated by residues 82-101 of caveolin-1 (i.e. the caveolin scaffolding domain) and residues 1-282 of ERalpha. The caveolin-binding domain of ERalpha includes the ligand-independent transactivation domain, activation function (AF)-1, but lacks the hormone-binding domain and the ligand-gated transactivation domain, AF-2. In co-transfection studies, caveolin-1 potentiates the transcriptional activation of ERalpha(1-282), a truncation mutant that has intact AF-1 and DNA-binding domains. Since AF-1 activity is regulated largely by phosphorylation we determined that co-expression with caveolin-1 increased the basal phosphorylation of ERalpha(1-282), but blocked the epidermal growth factor-dependent increase in phosphorylation. Indeed, caveolin-1 interacted with and potentiated the transactivation of an ERalpha mutant that cannot be phosphorylated by extracellular signal-regulated kinase (ERK)1/2 [ERalpha(Ser(118)-->Ala)]. Thus caveolin-1 is a novel ERalpha regulator that drives ERK1/2-independent phosphorylation and activation of AF-1.

Animals↗