Biomedical subjects

Jie Liu

Publications and source records attributed to Jie Liu.

At least 73 records · Page 4Linked to original sources

PubMed2006

Generating suspended single-walled carbon nanotubes across a large surface area via patterning self-assembled catalyst-containing block copolymer thin films.

Using self-assembled block copolymers as templates, catalytically active nanostructures with controlled size and space have been produced. A self-assembled polystyrene-b-polyferrocenylsilane thin film and monolayer of surface micelles of cobalt-complexed polystyrene-b-poly(2-vinylpyridine) are fully compatible with novolac-based conventional photoresists. Combining bottom-up self-assembly of catalyst-containing block copolymers with top-down microfabrication processing, plateaus covered with arrays of catalytically active nanostructures have been generated. Spatially selective growth of suspended single-walled carbon nanotubes over a large surface area has been achieved. Greatly enhanced Raman signals have been detected from the suspended tubes. This facile method of creating highly ordered catalyst nanostructures on top of posts enables the rational synthesis of suspended carbon nanotubes, thus facilitating the study of CNT properties by optical methods and enabling the fabrication of devices based on suspended CNTs.

Letter↗

PubMed2006

Investigation of differentially expressed proteins in rat gastrocnemius muscle during denervation-reinnervation.

To have a better insight into the molecular events involved in denervation-induced atrophy and reinnervation-induced regeneration of skeletal muscles, it is important to investigate the changes in expression levels of a great multitude of muscle proteins during the process of denervation-reinnervation. In this study, we employed an experimental model of rat sciatic nerve crush to examine the differentially expressed proteins in the rat gastrocnemius muscle at different time points (0, 1, 2, 3, 4 weeks) after sciatic nerve crush by using two-dimensional gel electrophoresis (2-DE) followed by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS), collectively referred to as the modern proteomic analysis. The results showed that 16 proteins in the rat gastrocnemius muscle exhibited two distinct types of change pattern in their relative abundance: (1) The relative expression levels of 11 proteins (including alpha actin, myosin heavy chain, etc.) were decreased either within 1 or 2 weeks post-sciatic nerve injury, followed by restoration during the ensuing days until 4 weeks. (2) The other 5 proteins (including alpha enolase, beta enolase, signal peptide peptidase-like 3, etc.) displayed an up-regulation in their relative expression levels within 1 week following sciatic nerve injury, and a subsequent gradual decrease in their relative expression levels until 4 weeks. Moreover, the significance of the changes in expression levels of the 16 proteins during denervation-reinnervation has been selectively discussed.

Animals↗

PubMed2006

RPA, a class II ARFGAP protein, activates ARF1 and U5 and plays a role in root hair development in Arabidopsis.

The polar growth of plant cells depends on the secretion of a large amount of membrane and cell wall materials at the growing tip to sustain rapid growth. Small GTP-binding proteins, such as Rho-related GTPases from plants and ADP-ribosylation factors (ARFs), have been shown to play important roles in polar growth via regulating intracellular membrane trafficking. To investigate the role of membrane trafficking in plant development, a Dissociation insertion line that disrupted a putative ARF GTPase-activating protein (ARFGAP) gene, AT2G35210, was identified in Arabidopsis (Arabidopsis thaliana). Phenotypic analysis showed that the mutant seedlings developed isotropically expanded, short, and branched root hairs. Pollen germination in vitro indicated that the pollen tube growth rate was slightly affected in the mutant. AT2G35210 is specifically expressed in roots, pollen grains, and pollen tubes; therefore, it is designated as ROOT AND POLLEN ARFGAP (RPA). RPA encodes a protein with an N-terminal ARFGAP domain. Subcellular localization experiments showed that RPA is localized at the Golgi complexes via its 79 C-terminal amino acids. We further showed that RPA possesses ARF GTPase-activating activity and specifically activates Arabidopsis ARF1 and ARF1-like protein U5 in vitro. Furthermore, RPA complemented Saccharomyces cerevisiae glo3Delta gcs1Delta double mutant, which suggested that RPA functions as an ARFGAP during vesicle transport between the Golgi and the endoplasmic reticulum. Together, we demonstrated that RPA plays a role in root hair and pollen tube growth, most likely through the regulation of Arabidopsis ARF1 and ARF1-like protein U5 activity.

ADP-Ribosylation Factor 1↗

PubMed2006

Structure and catalytic properties of magnesia-supported copper salts of molybdovanadophosphoric acid.

The structure and stability of magnesia-supported copper salts of molybdovanadophosphoric acid (Cu(2)PMo(11)VO(40)) were characterized by different techniques. The catalyst was prepared in ethanol by impregnation because this solvent does not hurt texture of the water-sensitive MgO and Cu(2)PMo(11)VO(40). The Keggin-type structure compound may be degraded partially to form oligomerized polyoxometalate when supported on MgO. However, the oligomers can rebuild as the Keggin structure again after thermal treatment in air or during the reaction. Meanwhile, the V atoms migrate out of the Keggin structure to form a lacunary structure, as observed by Fourier transform IR spectroscopy. Moreover, the presence of Cu(2+) as a countercation showed an affirmative influence on the migration of V atoms, and the active sites derived from the lacunary species generated after release of V from the Keggin anion. The electron paramagnetic resonance data imply that V(5+) autoreduces to V(4+) in the fresh catalyst, and during the catalytic reaction a large number of V(4+) ions are produced, which enhance the formation of O(2-) vacancies around the metal atoms. These oxygen vacancies may also improve the reoxidation function of the catalyst. This behavior is correlated to higher catalytic properties of this catalyst. The oxidative dehydrogenation of hexanol to hexanal was studied over this catalyst. After reaction at 553.2 K for 50 h, catalytic properties did not decrease and exhibited higher selectivity (>96.0%) toward hexanal.

Journal Article↗

PubMed2006

Carbon nanotubes with small and tunable diameters from poly(ferrocenylsilane)-block-polysiloxane diblock copolymers.

Iron-containing nanostructures produced from various self-assembled poly(ferrocenylsilane)-block-polysiloxane thin films are catalytically active for the initiation and growth of high density, small diameter carbon nanotubes (CNTs). Moreover, the tube diameter and density can be tuned by adjusting the chain lengths of the block copolymer. Iron-containing nanostructures from poly(ferrocenylmethylethylsilane)-b-poly(methylvinylsiloxane) polymer with 25 repeat units of an iron-containing segment and 265 repeat units of a non-iron-containing segment are able to produce CNTs with diameters around or less than 1 nm. Lithographically selective growth of CNTs across a large surface area has been demonstrated using this polymer system. Under the same growth condition, it has been found that the yield of defect-free CNTs varies with the size of the catalytically active nanostructures, which are dictated by the chain lengths of the two blocks. This result indicates that, for a specific-sized catalyst nanocluster, a unique set of growth conditions is required for synthesizing high yield, defect-free CNTs. This finding further addresses the importance of using uniform-sized catalyst-containing nanostructures for consistently achieving high-yield and high-quality CNTs with a minimum number of defects and amount of amorphous carbon.

Journal Article↗

PubMed2006

Study on improving the turbidity measurement of the absolute coagulation rate constant.

The existing theories dealing with the evaluation of the absolute coagulation rate constant by turbidity measurement were experimentally tested for different particle-sized (radius = a) suspensions at incident wavelengths (lambda) ranging from near-infrared to ultraviolet light. When the size parameter alpha = 2pi a/lambda > 3, the rate constant data from previous theories for fixed-sized particles show significant inconsistencies at different light wavelengths. We attribute this problem to the imperfection of these theories in describing the light scattering from doublets through their evaluation of the extinction cross section. The evaluations of the rate constants by all previous theories become untenable as the size parameter increases and therefore hampers the applicable range of the turbidity measurement. By using the T-matrix method, we present a robust solution for evaluating the extinction cross section of doublets formed in the aggregation. Our experiments show that this new approach is effective in extending the applicability range of the turbidity methodology and increasing measurement accuracy.

Models, Chemical↗

PubMed2006

Enhanced urinary bladder and liver carcinogenesis in male CD1 mice exposed to transplacental inorganic arsenic and postnatal diethylstilbestrol or tamoxifen.

Pregnant CD1 mice received 85 ppm arsenite in the drinking water from gestation day 8 to 18, groups (n = 35) of male offspring were subsequently injected on postpartum days 1 through 5 with diethylstilbestrol (DES; 2 microg/pup/day) or tamoxifen (TAM; 10 microg/pup/day), and tumor formation was assessed over 90 weeks. Arsenic alone increased hepatocellular carcinoma (14%), adenoma (23%) and total tumors (31%) compared to control (0, 2 and 2%, respectively). Arsenic alone also increased lung adenocarcinoma, adrenal cortical adenoma and renal cystic tubular hyperplasia compared to control. Compared to arsenic alone, arsenic plus DES increased liver tumor incidence in mice at risk 2.2-fold and increased liver tumor multiplicity (tumors/liver) 1.8-fold. The treatments alone did not impact urinary bladder carcinogenesis, but arsenic plus TAM significantly increased formation of urinary bladder transitional cell tumors (papilloma and carcinoma; 13%) compared to control (0%). Urinary bladder proliferative lesions (combined tumors and hyperplasia) were also increased by arsenic plus TAM (40%) or arsenic plus DES (43%) compared to control (0%) or the treatments alone. Urinary bladder proliferative lesions occurred in the absence of any evidence of uroepithelial cytotoxic lesions. Urinary bladder lesions and hepatocellular carcinoma induced by arsenic plus TAM and/or DES overexpressed estrogen receptor-alpha, indicating that aberrant estrogen signaling may have been a factor in the enhanced carcinogenic response. Thus, in male CD1 mice, gestational arsenic exposure alone induced liver adenoma and carcinoma, lung adenocarcinoma, adrenal adenoma and renal cystic hyperplasia. Furthermore, DES enhanced transplacental arsenic-induced hepatocarcinogenesis. In utero arsenic also initiated urinary bladder tumor formation when followed by postnatal TAM and uroepithelial proliferative lesions when followed by TAM or DES.

Animals↗

PubMed2006

WNK1 kinase isoform switch regulates renal potassium excretion.

Members of the WNK family of serine/threonine kinases have been implicated as important modulators of salt homeostasis, regulating the balance between renal sodium reabsorption and potassium excretion. Gain-of-expression mutations in the WNK1 gene uncouple Na(+) and K(+) balance and cause a familial disorder of diminished renal potassium excretion, excessive sodium retention, and hypertension (pseudohypoaldosteronism type II or Gordon's syndrome). Alternative splicing of the WNK1 gene produces a kidney-specific short form of WNK1 (KS-WNK1) and a more ubiquitous long form (L-WNK1), but it is not clear how either of these isoforms influence renal potassium excretion. Here we demonstrate that KS-WNK1 and L-WNK1 converge in a pathway to regulate the renal outer-medullary K(+) channel, Kir1.1. Reconstitution studies in Xenopus oocytes reveal that L-WNK1 significantly inhibits Kir1.1 by reducing cell surface localization of the channel. A catalytically inactive L-WNK1 mutant has no inhibitory effect on Kir1.1, indicating that channel inhibition depends on kinase activity. KS-WNK1, lacking an intact kinase domain, does not directly alter Kir1.1. Instead, KS-WNK1 negatively regulates L-WNK1 to release Kir1.1 from inhibition. Acute dietary potassium loading increases the relative abundance of KS-WNK1 to L-WNK1 transcript and protein in the kidney, indicating that physiologic up-regulation of Kir1.1 activity involves a WNK1 isoform switch and KS-WNK1-mediated release from L-WNK1 inhibition. Thus, these observations provide evidence for the physiological regulation of Na(+) and K(+) balance by a kinase isoform switch mechanism.

Animals↗

PubMed2006

Comparison of tricuspid inflow and superior vena caval Doppler velocities in acute simulated hypovolemia: new non-invasive indices for evaluating right ventricular preload.

BACKGROUND: Assessment of cardiac preload is important for clinical management of some emergencies related to hypovolemia. Effects of acute simulated hypovolemia on Doppler blood flow velocity indices of tricuspid valve (TV) and superior vena cava (SVC) were investigated in order to find sensitive Doppler indices for predicting right ventricular preload. METHODS: Doppler flow patterns of SVC and TV in 12 healthy young men were examined by transthoracic echocardiography (TTE) during graded lower body negative pressure (LBNP) of up to -60 mm Hg which simulated acute hypovolemia. Peak velocities of all waves and their related ratios (SVC S/D and tricuspid E/A) were measured, calculated and statistically analyzed. RESULTS: Except for the velocity of tricuspid A wave, velocities of all waves and their related ratios declined during volume decentralization. Of all indices measured, the peak velocities of S wave and AR wave in SVC correlated most strongly with levels of LBNP (r = -0.744 and -0.771, p < 0.001). CONCLUSION: The S and AR velocities are of good values in assessing right ventricular preload. Monitoring SVC flow may provide a relatively noninvasive means to assess direct changes in right ventricular preload.

Adult↗

PubMed2006

Quantum resonance and antiresonance for a periodically kicked Bose-Einstein condensate in a one-dimensional box.

We investigate the quantum dynamics of a periodically kicked Bose-Einstein condensate (BEC) confined in a one-dimensional (1D) box both numerically and theoretically, emphasizing on the phenomena of quantum resonance and antiresonance. The quantum resonant behavior of BEC is different from the single particle case but the antiresonance condition (Tau = 2pi and alpha = 0) is not affected by the atomic interaction. For the antiresonance case, the nonlinearity (atom interaction) causes the transition between oscillation and quantum beating. For the quantum resonance case, because of the coherence of BEC, the energy increase is oscillating and the rate is dramatically affected by the many-body interaction. We also discuss the relation between the quantum resonant behavior and the Kolmogorov-Arnold-Moser (KAM) or non-KAM property of the corresponding classical system.

Journal Article↗

PubMed2006

Arsenicals in maternal and fetal mouse tissues after gestational exposure to arsenite.

Exposure of pregnant C3H/HeNCR mice to 42.5- or 85-ppm of arsenic as sodium arsenite in drinking water between days 8 and 18 of gestation markedly increases tumor incidence in their offspring. In the work reported here, distribution of inorganic arsenic and its metabolites, methyl arsenic and dimethyl arsenic, were determined in maternal and fetal tissues collected on gestational day 18 of these exposure regimens. Tissues were collected from three females and from associated fetuses exposed to each dosage level. Concentrations of total speciated arsenic (sum of inorganic, methyl, and dimethyl arsenic) were higher in maternal tissues than in placenta and fetal tissues; total speciated arsenic concentration in placenta exceeded those in fetal tissues. Significant dosage-dependent (42.5 ppm versus 85 ppm of arsenite in drinking water) differences were found in total speciated arsenic concentrations in maternal lung (p<0.01) and liver (p<0.001). Total speciated arsenic concentrations did not differ significantly between dosage levels for maternal blood or for fetal lung, liver, and blood, or for placenta. Percentages of inorganic, methyl, or dimethyl arsenic in maternal or fetal tissues were not dosage-dependent. Over the range of total speciated arsenic concentrations in most maternal and fetal tissues, dimethyl arsenic was the most abundant arsenical. However, in maternal liver at the highest total speciated arsenic concentration, inorganic arsenic was the most abundant arsenical, suggesting that a high tissue burden of arsenic affected formation or retention of methylated species in this organ. Tissue concentration-dependent processes could affect kinetics of transfer of inorganic arsenic or its metabolites from mother to fetus.

Animals↗

PubMed2006

Mechanism of presynaptic filament stabilization by the bacteriophage T4 UvsY recombination mediator protein.

UvsY is the recombination mediator protein (RMP) of bacteriophage T4, which promotes homologous recombination by facilitating presynaptic filament assembly. The results of previous studies suggest that UvsY promotes the assembly of presynaptic filaments in part by stabilizing interactions between T4 UvsX recombinase and single-stranded DNA (ssDNA). To test this hypothesis, we studied the interactions of UvsX and UvsY with a fluorescein-derivatized oligonucleotide. This assay distinguishes between bipartite UvsX- or UvsY-ssDNA and tripartite UvsX-UvsY-ssDNA complex formation via differential fluorescence quenching effects. Salt stabilities of the three complexes were measured at equilibrium in the presence and absence of various nucleotide ligands of the UvsX protein and also under steady-state conditions for UvsX-catalyzed ssDNA-dependent ATP hydrolysis. The results demonstrate that UvsY globally stabilizes UvsX-ssDNA complexes, consistent with an increase in the apparent equilibrium binding affinity, K(ss)omega, of the UvsX-ssDNA interactions. The UvsY-mediated affinity increase is observed at equilibrium in the presence of ADP, ATPgammaS, or in the absence of the nucleotide and also at steady-state in the presence of ATP. Intriguingly, the stabilizing effects of UvsY and ATPgammaS on UvsX-ssDNA interactions are synergistic, indicating nonredundant mechanisms for UvsX-ssDNA complex stabilization by RMP versus nucleoside triphosphate effectors. Experiments with UvsY missense mutants defective in ssDNA binding demonstrate that UvsY-ssDNA interactions are of major importance in stabilizing UvsX-ssDNA complexes, whereas UvsY-UvsX protein-protein interactions provide residual stabilization energy. Together, the data is consistent with a mechanism in which UvsY stabilizes presynaptic filaments by organizing the ssDNA lattice into a structure that is favorable for UvsX-ssDNA interactions.

Adenine Nucleotides↗

PubMed2006

Fabrication of ordered catalytically active nanoparticles derived from block copolymer micelle templates for controllable synthesis of single-walled carbon nanotubes.

We report the use of the block copolymer micelle approach to produce various transition metal nanoparticles such as iron, cobalt, and nickel with precisely controlled size and spacing. These uniformly sized catalyst nanoparticles derived from the block copolymer micelle approach have enabled the synthesis of carbon nanotubes (CNTs) with narrow size distribution. Because of the excellent film forming ability of the polymeric material, metal-bearing surface micelles produced from the solution micelles can be distributed uniformly on a surface, resulting in evenly dispersed catalyst nanoparticles. As a result, high quality and uniformly distributed CNTs have been synthesized. Spatially selective growth of CNTs from a lithographically patterned metal-bearing micelle film has been achieved. The polymer template approach can potentially be extended to synthesize single-metallic and bimetallic catalytically active nanoparticles with uniform size and spacing and is fully compatible with conventional lithographic process. Additionally, catalyst nanoparticles produced from this method do not coalesce at high growth temperature. All these attributes make this approach a promising fabrication pathway for controllable synthesis of CNTs.

Journal Article↗

PubMed2006

Genetic diseases associated with heterotrimeric G proteins.

Heterotrimeric G proteins couple receptors for diverse extracellular signals to effector enzymes or ion channels. Each G protein comprises a specific alpha-subunit and a tightly bound betagamma dimer. Several human disorders that result from genetic G-protein abnormalities involve the imprinted GNAS gene, which encodes Gs alpha, the ubiquitously expressed alpha-subunit that couples receptors to adenylyl cyclase and cAMP generation. Loss-of-function and gain-of-function mutations, in addition to imprinting defects, of this gene lead to diverse clinical phenotypes. Mutations of GNAT1 and GNAT2, which encode the retinal G proteins (transducins), are rare causes of specific congenital visual defects. Common polymorphisms of the GNAS and GNB3 (which encodes Gbeta3) genes have been associated with multigenic disorders (e.g. hypertension and metabolic syndrome). To date, no other G proteins have been implicated directly in human disease.

Chromogranins↗

PubMed2006

Identification of protease-sensitive sites in Human Endothelial-Monocyte Activating Polypeptide II protein.

The cleaved approximately 22-kDa form of Endothelial-Monocyte Activating Polypeptide [mature (m)EMAP II] functions as a potent inhibitor of tumor growth. Although the anti-tumor effect of mEMAP II has been described, little is known regarding the cleavage of mEMAP II from its precursor form (pEMAP II). We determined that pEMAP II is expressed at the cell membrane surface and proteinases MMP-9, elastase, and cathepsin L release protein fragments consistent with mEMAP II molecular mass. MMP-9 and elastase generate a approximately 25-26 kDa spanning fragments, while cathepsin L generates a approximately 22 kDa fragment. Although several fragments are processed from pEMAP II within a 44 AA residue stretch, cathepsin L cleaves pEMAP II within 4 amino acids of the determined N-terminal sequence, suggesting that this region is sensitive to proteinases.

Amino Acid Sequence↗

PubMed2006

Reverse of NK cytolysis resistance of type II cytokine predominant-human tumor cells.

Tumor cells suppress host immunity by secreting soluble factors, among which cytokines play important roles. Type I cytokine mRNA levels (IL-2 and IFNgamma) and type II cytokine mRNA levels (IL-4, IL-10 and IL-13) of twenty tumor cell lines and fresh tumor tissues from fifteen patients with colorectal cancer were examined by RT-PCR method. Upon analysis, tumor cells showed type II predominance and were resistant to NK cytolysis. In order to reverse the type II predominant status, type I cytokines (IL-2 or IFNgamma) and/or anti-type II cytokine antibody (IL-10 mAb) were used in an in vitro study. By this shifting treatment, type II cytokine mRNA levels of these tumor cells were decreased, moreover, the sensitivity to natural cytolysis of these cells was then significantly increased. Thus, tumor-induced type II cytokine dominance is possibly to be shifted into type I status, which benefits the anti-tumor natural immunity.

Adenocarcinoma↗

PubMed2006

Guided growth of nanoscale conducting polymer structures on surface-functionalized nanopatterns.

We describe an electrochemical method of directly growing conducting polymer nanostructures between metal electrodes with the geometry controlled by hydrophilic/hydrophobic patterns. The surface patterning can be achieved by a large number of lithographic methods such as AFM, electron-beam, elastomeric microprinting, and photolithography and is compatible with industrial semiconductor fabrication processes. Conducting polymer structures so formed have good alignment compared to bulk synthesis and are grown in place between electrodes. Polypyrrole field effect transistors have been produced using this method. Electrical measurements show conductivity strongly dependent on the presence of anionic dopant species during growth. Devices grown with a high concentration of dopant show metallic behavior, while those with less doping behave as p-type semiconductors.

Journal Article↗

PubMed2006

Molecular mechanism of distorted iron regulation in the blood-CSF barrier and regional blood-brain barrier following in vivo subchronic manganese exposure.

Previous studies in this laboratory indicated that manganese (Mn) exposure in vitro increases the expression of transferrin receptor (TfR) by enhancing the binding of iron regulatory proteins (IRPs) to iron responsive element-containing RNA. The current study further tested the hypothesis that in vivo exposure to Mn increased TfR expression at both blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCB), which contributes to altered iron (Fe) homeostasis in the CSF. Groups of rats (10-11 each) received oral gavages at doses of 5 mg Mn/kg or 15 mg Mn/kg as MnCl(2) once daily for 30 days. Blood, CSF, and choroid plexus were collected and brain capillary fractions were separated from the regional parenchyma. Metal analyses showed that oral Mn exposure decreased concentrations of Fe in serum (-66%) but increased Fe in the CSF (+167%). Gel shift assay showed that Mn caused a dose-dependent increase of binding of IRP1 to iron responsive element-containing RNA in BCB in the choroid plexus (+70%), in regional BBB of capillaries of striatum (+39%), hippocampus (+56%), frontal cortex (+49%), and in brain parenchyma of striatum (+67%), hippocampus (+39%) and cerebellum (+28%). Real-time RT-PCR demonstrated that Mn exposure significantly increased the expression of TfR mRNA in choroid plexus and striatum with concomitant reduction in the expression of ferritin (Ft) mRNA. Collectively, these data indicate that in vivo Mn exposure results in Fe redistribution in body fluids through regulating the expression of TfR and ferritin at BCB and selected regional BBB. The disrupted Fe transport by brain barriers may underlie the distorted Fe homeostasis in the CSF.

Animals↗