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Biomedical subjects

Xu Li

Publications and source records attributed to Xu Li.

At least 73 records · Page 4Linked to original sources
PubMed2005

Levels of mTOR and its downstream targets 4E-BP1, eEF2, and eEF2 kinase in relationships with tau in Alzheimer's disease brain.

The pathogenesis of formation of neurofibrillary tangles (NFTs) in Alzheimer's disease (AD) brains is unknown. One of the possibilities might be that translation of tau mRNA is aberrantly regulated in AD brains. In the current study, levels of various translation control elements including total and phosphorylated (p) forms of mammalian target of rapamycin (mTOR), eukaryotic initiation factor 4E binding protein 1 (4E-BP1), eukaryotic elongation factor 2 (eEF2), and eEF2 kinase were investigated in relationship with tau in homogenates of the medial temporal cortex from 20 AD and 10 control brains. We found that levels of p-mTOR (Ser2481), and p-4E-BP1 (Thr70 and Ser65) dramatically increase in AD, and are positively significantly correlated with total tau and p-tau. Levels of p-eEF2K were significantly increased, and total eEF2 significantly decreased in AD, when compared to controls. The changes of p-mTOR (2481), p-4E-BP1, and p-eEF2 were immunohistochemically confirmed to be in neurons of AD brains. This suggested that there are obvious abnormalities of elements related with translation control in AD brain and their aberrant changes may up-regulate the translation of tau mRNA, contributing to hyperphosphorylated tau accumulation in NFT-bearing neurons.

Adaptor Proteins, Signal Transducing↗
PubMed2005

[Aldosterone stimulating PDGF-B expression in HSC via activation of EGR-1].

OBJECTIVE: It is known that intrahepatic renin-angiotensin-aldosterone system (RAAS) plays a key role in liver fibrogenesis. Aldosterone (Aldo), the principal effector molecule of the RAAS, exerts local effects on cell growth and fibrogenesis. However, the signal transduction mechanisms underlying the effects of Aldo on hepatic fibrogenesis remain to be fully elucidated. The present study aims to investigate the signal transduction mechanism underlying the effects of Aldo on extracellular signal-regulated kinase 1/2 (ERK1/2), early growth response-1 (EGR-1) and on the platelet-derived growth factor-B (PDGF-B). METHODS: In vitro, hepatic stellate cell (HSC)-T6 cell line was treated with Aldo for 10 min, 0.5 h, 1 h, 2 h and 3 h. Protein expression of phospho-p42/44 was detected by Western blot. In addition, HSC-T6 were preincubated for 1 h or not at all with U0126 (an inhibitor of the MAPK/ERK kinase), and antioxidant-N-acetylcysteine (NAC) prior to exposure to Aldo for the indicated times. Protein expressions of phospho-p42/44 and PDGF-B were measured by Western blot. DNA biding activity of EGR-1 was analyzed by electrophoretic gel mobility shift assay (EMSA). By means of immunohistochemistry, expression of PDGF-B was detected. RESULTS: Aldo induced phospho-p42/44 expression could be abrogated by U0126; NAC did not inhibit phospho-p42/44 expression. Gel shift study showed that stimulation of HSC by Aldo markedly increased the EGR-1 DNA binding activity, which was abrogated by U0126, reaching a maximum at 60 minutes, and then declined progressively. NAC did not reduce the EGR-1 activity. Aldo increased the PDGF-B protein level in HSC, which was not attenuated by NAC and U0126. CONCLUSIONS: Stimulation of HSC by Aldo results in activation of EGR-1 via ERK1/2 pathway, leading to up-regulation of PDGF-B expression.

Aldosterone↗
PubMed2005

[Effects of Danshen injection on the reserve of tissue plasminogen activator and nitric oxide in endothelium and vasodilatation in diabetic patients].

OBJECTIVE: To investigate the effects of Danshen Injection on the reserve of tissue plasminogen activator and nitric oxide in endothelium and vasodilatation in diabetic patients. METHODS: 32 patients and 16 normal individuals were enrolled into this study. The capacity of vascular endothelium to release tPA and NO was examined by venous occlusion of the upper arm. Brachial artery diameter was measured at baseline, during post occlusion reactive hyperemia (flow-mediated endothelium-dependent), and after sublingual nitroglycerol administration (endothelium-independent). Vasodilation was expressed as the percentage changes relative to the baseline diameter, while endothelial tPA and NO release was expressed as the percentage change relative to the baseline tPA and NO levels. Thickness of the intima of carotid artery was measured using ultrasound imaging. RESULTS: There was no significant difference in eudothelum-independent vasodilation between the controls and diabetes. However, significant reduction in endothelium-dependent vasodilation, endothelial NO release and tPA release (P <0.05, or P <0.01) were found in diabetes compared with the controls and the reduction was lower in diabetes with hypertension than that in diabetes without it. At the same time, there was no difference in intimamedial thickness of the carotid artery between two groups, although the carotid artery in the diabetes without hypertension was much thicker than that in the control. But that in the diabetes with hypertension had significant difference compared with that in the control. CONCLUSION: Danshen Injection may improve the above-mentioned marks. And it may increase the endothelium-dependent vasodilation and endothelial tPA and NO release and improve the vascular disease in patients with diabetes mellitus.

Adult↗
PubMed2005

[Construction, structure prediction and phylogenetic analysis of murine scFv gene against human cervical cancer].

AIM: To construct the gene of murine single-chain Fv fragment (scFv) against human cervical cancer and to predict the physical and chemical characteristics, secondary structure, tertiary structure and the molecular evolution of the scFv using computer-assisted modeling. METHODS: The variable region gene of the heavy and light chains were amplified respectively using recombinant DNA techniques from CSA125 hybridoma cells that can secret monoclonal antibodies with high activity and specificity against human cervical cancer. These two fragments were then spliced together through a flexible linker to scFv against human cervical cancer by using splicing overlap extension (SOE) PCR. The scFv gene, named CSAs-1, was cloned into the vector pMD18-T. The physical and chemical characteristics secondary and tertiary structure and the phylogenetic tree were predicted using Internet and corresponding softwares. RESULTS: The whole scFv gene was cloned successfully and encoded 278 amino acids. Theoretically, the CSAs-1 scFv was relative molecular masses 28,800, the isoelectric point (pI) was 7.215. PHDsec indicated that CSAs-1 was alpha+beta globin. There were many protein kinase C phosphorylation sites and casein kinase II phosphorylation sites in the V(H) and V(L) domains. The computer graphic modeling indicated the linker was isolated from V(H) and V(L). The V(L), as well as the V(H), was involved in composing the hydrophobic "pocket" which was beneficial to the antigen binding. Phylogenetic tree analysis indicated that V(H) genes from various vertebrate species formed three clusters that corresponded to three V(H) groups and that V(L) sequences from each species had a level of diversity similar to that of their V(H) genes. CSAs-1 V regions belong to A group. CONCLUSION: The construction and analysis of a molecular model of scFv laid the foundation for the further research into genetic engineering antibody and the mechanism of antigen-antibody interaction.

Animals↗
PubMed2005

Middle and long-term clinical outcomes of patients with regional hepatolithiasis after subcutaneous tunnel and hepatocholangioplasty with utilization of the gallbladder.

BACKGROUND: Roux-en-Y choledochojejunostomy is routinely performed in patients with regional hepatolithiasis. However, some of these patients, who have a normal gallbladder and normal Oddi's sphincter, are unnecessarily undergoing bilio-intestinal drainage. Alternatively, reconstruction can be achieved by subcutaneous tunnel and hepatocholangioplasty with the utilization of the gallbladder (STHG). This method is effective to potential endoscopic tunnel and intervention during follow-up, and prevention of reflux cholangitis as well as the disorders of the GI tract. METHODS: The middle and long-term complications of 46 patients who underwent STHG were analyzed. With B-ultrasonography and biochemical assay, the contraction and concentration function of the gallbladder were also studied. RESULTS: Follow-up showed that all patients survived with a relatively normal life. One patient experienced right epigastric pain, chills and fever because of a stone which impacted in the left hepatic bile duct. Another patient had cholangitis because of biliary ascariasis. The two patients were treated by endoscopic therapy within the subcutaneous gallbladder under local anesthesia. CONCLUSIONS: This operation not only keeps the normal physical functional of the gallbladder, Oddi's sphincter and gastrointestinal tract, but also prevents reflux cholangitis and the disorder of the digestive tract. Hence STHG is a novel operation dealing with regional hepatolithiasis.

Adult↗
PubMed2005

[Aldosterone stimulates alpha1-(1) procollagen mRNA expression in HSC via activation of ERK1/2 and AP-1].

OBJECTIVE: It has been known that the intrahepatic renin-angiotensin-aldosterone system (RAAS) plays a key role in the fibrogenesis in livers. Aldosterone (Aldo), the principal effector molecule of the RAAS, exerts local effects on cell growth and fibrogenesis. However, the signal transduction mechanisms underlying the effects of Aldo on hepatic fibrogenesis remain to be fully elucidated. The present study aims to investigate the signal transduction mechanism underlying the effects of Aldo on the signal passageway of active protein-1 (AP-1). METHODS: In vitro, HSCs-T6 cell line was treated with Aldo for 10 min, 30 min, 60 min, 120 min and 180 min, and protein expression of Phospho-P42/44 was detected by Western blot. In addition, HSCs-T6 cell line was preincubated for 60 min or not with U0126 (an inhibitor of the MAPK/ERK kinase), and also with antioxidant-N-acetylcysteine (NAC) prior to exposure to Aldo for the indicated times. Protein expression of Phospho-P42/44 was measured by Western blot. DNA biding activity of AP-1 was analyzed by electrophoretic gel mobility shift assay (EMSA). By means of RT-PCR, expression of alpha1(1) procollagen mRNA was detected. RESULTS: Aldo stimulated HSC via extracellular signal-regulated kinase (ERK1/2) pathway. Time course experiments showed that Aldo induced Phospho-P42/44 expression, which was abrogated by U0126, reaching a maximum at 10 minutes, and then declined progressively. NAC inhibited the Phospho-P42/44 expression. EMSA showed that stimulation of HSC by Aldo markedly increased AP-1 DNA binding activity. U0126 markedly reduced AP-1 DNA binding activity induced by Aldo; NAC partly decreased AP-1 activity induced by Aldo. Aldo up-regulated expression of alpha1(1) procollagen mRNA, which was attenuated by U0126 and NAC. CONCLUSION: Stimulation of HSC by Aldo results in activation of AP-1 via ERK1/2 pathway, leading to up-regulation of AP-1 target gene alpha1(1) procollagen mRNA expression.

Aldosterone↗
PubMed2005

[Synthesis, characterization and evaluation of octadecyl ester-bonded monolithic column].

An ester-bonded monolithic silica column for reversed-phase high performance liquid chromatography was synthesized by reacting stearic acid with gamma-glycidoxypropyltrimethoxysilane and coupling the intermediate product onto monolithic silica column. Characterization of the prepared column was carried out with Fourier transformation infrared spectrometry and elemental analysis. The chromatographic properties of the packing were evaluated by using benzene, biphenyl, and anthracene as samples and methanol-water as binary mobile phase. The column back-pressure and separation effect were also evaluated for fast separation. The results show that the stationary phase has satisfactory chromatographic properties and resists hydrolysis between pH = 2 - 8, and it can be used for the fast-separation of solutes efficiently.

Anthracenes↗
PubMed2004

Equiphase-sphere approximation for light scattering by stochastically inhomogeneous microparticles.

We report the development and validation of the equiphase-sphere (EPS) approximation for calculating the total-scattering cross-section (TSCS) spectra of inhomogeneous microparticles having complex interior structures. We show that this closed-form, analytical approximation can accurately model the TSCS of randomly inhomogeneous spherical particles having internal refractive index variations with geometrical scales spanning from nanometers (i.e., subwavelength) to microns (i.e., suprawavelength). Moreover, we derive an easy-to-use criterion for the range of validity of the EPS approximation in modeling TSCS of inhomogeneous particles. The work discussed in this paper may positively impact tissue optical imaging and diagnostic applications.

Journal Article↗
PubMed2004

Characterization of the heptad repeat regions, HR1 and HR2, and design of a fusion core structure model of the spike protein from severe acute respiratory syndrome (SARS) coronavirus.

Severe acute respiratory syndrome coronavirus (SARS-CoV) is a newly emergent virus responsible for a worldwide epidemic in 2003. The coronavirus spike proteins belong to class I fusion proteins, and are characterized by the existence of two heptad repeat (HR) regions, HR1 and HR2. The HR1 region in coronaviruses is predicted to be considerably longer than that in other type I virus fusion proteins. Therefore the exact binding sequence to HR2 from the HR1 is not clear. In this study, we defined the region of HR1 that binds to HR2 by a series of biochemical and biophysical measures. Subsequently the defined HR1 (902-952) and HR2 (1145-1184) chains, which are different from previously defined binding regions, were linked together by a flexible linker to form a single-chain construct, 2-Helix. This protein was expressed in Escherichia coli and forms a typical six-helix coiled coil bundle. Highly conserved HR regions between mouse hepatitis virus (MHV) and SARS-CoV spike proteins suggest a similar three-dimensional structure for the two fusion cores. Here, we constructed a homology model for SARS coronavirus fusion core based on our biochemical analysis and determined the MHV fusion core structure. We also propose an important target site for fusion inhibitor design and several strategies, which have been successfully used in fusion inhibitor design for human immunodeficiency virus (HIV), for the treatment of SARS infection.

Amino Acid Sequence↗
PubMed2004

Crystallization and preliminary crystallographic analysis of the fusion core of the spike protein of the murine coronavirus mouse hepatitis virus (MHV).

Crystals of a 2-Helix fusion-core construct of MHV spike protein (commonly referred to as E2) have been grown at 291 K using PEG 4000 as precipitant. The diffraction pattern of the crystal extends to 2.8 A resolution at 100 K in-house. Furthermore, a selenomethionine (SeMet) derivative of MHV spike protein fusion core has been overexpressed and purified. The derivative crystals were obtained under similar conditions and three different wavelength data sets were collected to 2.4 A resolution from a single derivative crystal at BSRF (Beijing Synchrotron Radiation Facility). The crystals have unit-cell parameters a = b = 48.3, c = 199.6 A, alpha = beta = 90, gamma = 120 degrees and belong to space group R3. Assuming the presence of two molecules in the asymmetric unit, the solvent content is calculated to be about 46%.

Amino Acid Sequence↗
PubMed2004

Phosphorylated eukaryotic translation factor 4E is elevated in Alzheimer brain.

Eukaryotic translation factor 4E (eIF4E) plays a key role in regulating protein translation. It was thought that in order to maintain neuronal functions, tau protein is continuously generated to compensate those being hyperphosphorylated and compromised in its ability to promote and maintain microtubule assembly in Alzheimer's disease. If eIF4E is involved in tau mRNA translation, level of eIF4E phosphorylation should be changed. In the current study, we found a dramatic increase of phosphorylated eIF4E in Alzheimer's disease, especially in those cases with late stages of neurofibrillary changes. Level of eIF4E phosphorylation is significantly correlated with total- and Alzheimer hyperphosphorylated taus. These data suggest that the increase of eIF4E phosphorylation is involved in formation of Alzheimer neurofibrillary changes.

Aged↗
PubMed2004

Analysis of bacterial adhesion using a gradient force analysis method and colloid probe atomic force microscopy.

The atomic force microscope (AFM) has been used to examine the stickiness of bacteria on the basis of the analysis of approach and retraction force curves between the AFM tip and the bacterial surface. One difficulty in analyzing approach curve data is that the distance between the AFM tip and the surface of the bacterium is difficult to define. The exact distances are difficult to determine because the surface of the bacterium deforms during force imaging, producing a highly nonlinear region in the approach curve. In this study, AFM approach and retraction curves were obtained using a colloid probe AFM for three strains of Escherichia coli (D21, D21f2, and JM109). These strains differed in their relative adhesion to glass surfaces, on the basis of measurements of sticking coefficients in packed bed flow through column tests. A gradient force curve analysis method was developed to model the interactions between the colloid probe and a surface. Gradient analysis of the approach curve revealed four different regions of colloid-surface interactions during the approach and contact of the probe with the bacterial surface: a noninteraction region, a noncontact phase, a contact phase, and a constant compliance region. The noncontact phase, which ranged from 28 to 59 nm for the three bacterial strains, was hypothesized to arise primarily from steric repulsion of the colloid by extracellular polymers on the bacterial surface. The contact phase, spanning 59-113 nm, was believed to arise from the initial pressure of the colloid on the outer membrane of the cell. The constant compliance region likely reflected the response of the colloid probe to the stiff peptidoglycan layer that confers strength and rigidity to gram negative bacteria. It was shown that the sticking coefficients reported for the three E. coli strains were correlated with the length of the noncontact phase but not the properties of the other phases. Sticking coefficients were also not correlated with any parameters determined from retraction force curves such as pull-off distances or separation energies. These results show that gradient analysis is useful for studying the contribution of the length of the exopolymers on the cell surface to bacterial adhesion to glass surfaces.

Algorithms↗
PubMed2004

Equiphase-sphere approximation for analysis of light scattering by arbitrarily shaped nonspherical particles.

We extend the previously proposed concept of equiphase sphere (EPS) to analyze light-scattering properties of arbitrarily shaped particles. Our analyses based on the Wentzel-Kramers-Brillouin technique and numerical studies based on the finite-difference time-domain method demonstrate that a wide range of irregularly shaped particles can be approximated as their equivalent equiphase ellipsoids to determine their total scattering cross-section (TSCS) spectra. As a result, a simple expression given by the EPS approximation can be used to calculate the TSCS spectra of these particles. We find that the accuracy of the EPS approximation is influenced by both the magnitude and the geometric scale of the surface perturbation of the particle, and we derive validity conditions of the EPS approximation to guide the practical application of this method.

Journal Article↗
PubMed2004

Analytical techniques for addressing forward and inverse problems of light scattering by irregularly shaped particles.

Understanding light scattering by nonspherical particles is crucial in modeling the transport of light in realistic structures such as biological tissues. We report the application of novel analytical approaches based on modified Wentzel-Kramers-Brillouin and equiphase-sphere methods that facilitate accurate characterization of light scattering by a wide range of irregularly shaped dielectric particles. We also demonstrate that these approaches have the potential to address the inverse-scattering problem by means of a spectral analysis of the total scattering cross section of arbitrarily shaped particles.

Algorithms↗
PubMed2004

Crystallization and preliminary crystallographic analysis of the fusion core from two new zoonotic paramyxoviruses, Nipah virus and Hendra virus.

Highly conserved heptad-repeat (HR1 and HR2) regions in class I viral fusion (F) proteins, including the F protein from paramyxovirus, interact with each other post-fusion to form a six-helix bundle called a fusion core. Crystals of the fusion core of Nipah virus have been grown at 291 K using PEG 4000 as precipitant. The diffraction pattern of the crystal extends to 2.1 angstroms resolution at 100 K in-house. The crystals have unit-cell parameters a = 31.664, b = 31.725, c = 51.256 angstroms, alpha = 80.706, beta = 86.343, gamma = 65.812 degrees and belong to space group P1. Crystals of the fusion core of Hendra virus have also been grown at 291 K using PEG 4000 as precipitant. The diffraction pattern of the crystal extends to 2.0 angstroms resolution at 100 K in-house. A selenomethionine (SeMet) derivative of the HeV fusion core was overexpressed using the same Escherichia coli expression system and purified. The derivative crystals were obtained under similar conditions and three different wavelength data sets were collected to 2.0 angstroms resolution from the derivative crystal at BSRF (Beijing Synchrotron Radiation Facility). The crystals have unit-cell parameters a = 31.997, b = 31.970, c = 53.865 angstroms, alpha = 85.990, beta = 85.842, gamma = 68.245 degrees and belong to space group P1.

Crystallization↗
PubMed2004

Structural basis for coronavirus-mediated membrane fusion. Crystal structure of mouse hepatitis virus spike protein fusion core.

The surface transmembrane glycoprotein is responsible for mediating virion attachment to cell and subsequent virus-cell membrane fusion. However, the molecular mechanisms for the viral entry of coronaviruses remain poorly understood. The crystal structure of the fusion core of mouse hepatitis virus S protein, which represents the first fusion core structure of any coronavirus, reveals a central hydrophobic coiled coil trimer surrounded by three helices in an oblique, antiparallel manner. This structure shares significant similarity with both the low pH-induced conformation of influenza hemagglutinin and fusion core of HIV gp41, indicating that the structure represents a fusion-active state formed after several conformational changes. Our results also indicate that the mechanisms for the viral fusion of coronaviruses are similar to those of influenza virus and HIV. The coiled coil structure has unique features, which are different from other viral fusion cores. Highly conserved heptad repeat 1 (HR1) and HR2 regions in coronavirus spike proteins indicate a similar three-dimensional structure among these fusion cores and common mechanisms for the viral fusion. We have proposed the binding regions of HR1 and HR2 of other coronaviruses and a structure model of their fusion core based on our mouse hepatitis virus fusion core structure and sequence alignment. Drug discovery strategies aimed at inhibiting viral entry by blocking hairpin formation may be applied to the inhibition of a number of emerging infectious diseases, including severe acute respiratory syndrome.

Amino Acid Motifs↗