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Lei Liu

Publications and source records attributed to Lei Liu.

At least 37 records · Page 2Linked to original sources
PubMed2006

S-nitrosylating agents: a novel class of compounds that increase cystic fibrosis transmembrane conductance regulator expression and maturation in epithelial cells.

The endogenous bronchodilator, S-nitrosoglutathione (GSNO), increases expression, maturation, and function of both the wild-type and the DeltaF508 mutant of the cystic fibrosis transmembrane conductance regulatory protein (CFTR). Though transcriptional mechanisms of action have been identified, GSNO seems also to have post-transcriptional effects on CFTR maturation. Here, we report that 1) GSNO is only one of a class of S-nitrosylating agents that, at low micromolar concentrations, increase DeltaF508 and wild-type CFTR expression and maturation; 2) NO itself (at these concentrations) and 8-bromocyclic GMP are minimally active on CFTR; 3) a novel agent, S-nitrosoglutathione diethyl ester, bypasses the need for GSNO bioactivation by gamma-glutamyl transpeptidase to increase CFTR maturation; 4) surprisingly, expression-but not S-nitrosylation-of cysteine string proteins (Csp) 1 and 2 is increased by GSNO; 5) the effect of GSNO to increase full maturation of wild-type CFTR is inhibited by Csp silencing (si)RNA; 6) proteins relevant to CFTR trafficking are SNO-modified, and SNO proteins traffic through the endoplasmic reticulum (ER) and Golgi after GSNO exposure; and 7) GSNO alters the interactions of DeltaF508 CFTR with Csp and Hsc70 in the ER and Golgi. These data suggest that GSNO is one of a class of S-nitrosylating agents that act independently of the classic NO radical/cyclic GMP pathway to increase CFTR expression and maturation. They also suggest that the effect of GSNO is dependent on Csp and on intracellular SNO trafficking. We speculate that these data will be of relevance to the development of NO donor-based therapies for CF.

Cell Differentiation↗
PubMed2006

Significant effects of phosphorylation on relative stabilities of DNA and RNA sugar radicals: remarkably high susceptibility of h-2' abstraction in RNA.

The roles of nucleic acid radicals in DNA and RNA damage cannot be properly understood in the absence of knowledge of the C-H bond strengths depicting the energy cost to generate each of these radicals. However, previous theoretical studies on the relative energies of different nucleic acid radicals are not fully convincing mainly because of the use of oversimplified model compounds. In the present study we chose nucleoside 3',5'-bisphosphates as model compounds for DNA and RNA, in which the effects of both the nucleobase and phosphorylation were taken into consideration. Using the newly developed ONIOM-G3B3 methods, we calculated the gas-phase bond dissociation enthalpies and solution-phase bond dissociation free energies of all the carbohydrate C-H bonds in the model compounds. It was found that the monoanionic phosphate group (OPO3H-) was a better radical stabilization group than the OH group by 1.3 kcal/mol, whereas the neutral phosphate group (OPO3H2) was a significantly worse radical stabilization group than OH by 4.4 kcal/mol. Due to these reasons, the relative thermodynamic susceptibility of H-abstraction from deoxyribonucleotides and ribonucleotides varied considerably depending on the phosphorylation state and the charge carried by the phosphate groups. Strikingly, the bond dissociation free energy of C2'-H in ribonucleotides was dramatically lower than that of all the other C-H bonds by 5-6 kcal/mol regardless of the phosphorylation state and the charge carried by the phosphate group. This explained the previous experimental finding that radiation damage of RNA occurs mainly via H-abstraction at H-2'. A model study suggested that the strength of the hydrogen bonding interaction between the 2'-OH and 3-phosphate groups should dramatically increase from ribonucleoside 3',5'-bisphosphate to its C2' radical. The strengthened hydrogen bonding stabilized the C2' radical, rendering the C2'-H bond of RNA extraordinarily vulnerable to H-abstraction.

Carbohydrates↗
PubMed2006

U1-like snRNAs lacking complementarity to canonical 5' splice sites.

We have detected a surprising heterogeneity among human spliceosomal U1 small nuclear RNA (snRNA). Most interestingly, we have identified three U1 snRNA variants that lack complementarity to the canonical 5' splice site (5'SS) GU dinucleotide. Furthermore, we have observed heterogeneity among the identified variant U1 snRNA genes caused by single nucleotide polymorphism (SNP). The identified snRNAs were ubiquitously expressed in a variety of human tissues representing different stages of development and displayed features of functional spliceosomal snRNAs, i.e., trimethylated cap structures, association with Sm proteins and presence in nuclear RNA-protein complexes. The unanticipated heterogeneity among spliceosomal snRNAs could contribute to the complexity of vertebrates by expanding the coding capacity of their genomes.

Base Pairing↗
PubMed2006

Configuration-dependent interface charge transfer at a molecule-metal junction.

The role of the molecule-metal interface is a key issue in molecular electronics. Interface charge transfer processes for 4-fluorobenzenethiol monolayers with different molecular orientations on Au(111) were studied by resonant photoemission spectroscopy. The electrons excited into the LUMO or LUMO+1 are strongly localized for the molecules standing up on Au(111). In contrast, an ultrafast charge transfer process was observed for the molecules lying down on Au(111). This configuration-dependent ultrafast electron transfer is dominated by an adiabatic mechanism and directly reflects the delocalization of the molecular orbitals for molecules lying down on Au(111). Theoretical calculations confirm that the molecular orbitals indeed experience a localization-delocalization transition resulting from hybridization between the molecular orbitals and metal surface. Such an orientation-dependent transition could be harnessed in molecular devices that switch via charge transfer when the molecular orientation is made to change.

Journal Article↗
PubMed2006

N,N-dimethyl-beta-alanine as an inexpensive and efficient ligand for palladium-catalyzed Heck reaction.

N,N-Dimethyl-beta-alanine was found to be a more powerful phosphine-free ligand than the previously reported ligand, N,N-dimethylglycine, in the Pd-catalyzed Heck reaction for a variety of aryl bromides, aryl iodides, and activated aryl chlorides with a practical turnover number of 10(3). Both kinetic and theoretical studies suggested that N,N-dimethyl-beta-alanine led to faster oxidative addition of an aryl halide to Pd than N,N-dimethylglycine. [reaction: see text]

Catalysis↗
PubMed2006

Low ligand loading, highly enantioselective addition of phenylacetylene to aromatic ketones catalyzed by Schiff-base amino alcohols.

[reaction: see text] Schiff-base amino alcohols 7a,b derived from L-phenylglycine through three simple steps are found to be highly effective for the enantioselective addition of phenylacetylene to aromatic ketones. When the loading of 7b was 1 mol %, an ee value of up to 95% was obtained. However, when 7b was lowered to 0.1 mol %, a high ee value of 85% was still achieved. A practical solution to synthesize the optically active tertiary propargylic alcohols was described.

Journal Article↗
PubMed2006

Pluripotency potential of human adipose-derived stem cells marked with exogenous green fluorescent protein.

Musculoskeletal tissues regeneration requires rapid expansion of seeding cells both in vitro and in vivo while maintaining their multilineage differentiation ability. Human adipose-derived stem cells (ASCs) are considered to contain multipotent mesenchymal stem cells. Monolayer cultures of human ASCs were isolated from human lipoaspirates and passaged 3 times and then infected with replication-incompetent adenoviral vectors carrying green fluorescent protein (Ad/GFP) genes. Then, Ad/GFP infected human ASCs were transferred to osteogenic, chondrogenic, adipogenic, and myogenic medium. The morphological characterization of induced cells was observed using phase-contrast microscopy and fluorescence microscopy. The expression of marker proteins or genes was measured by immunocytochemical and RT-PCR analysis. Osteopontin (OPN), and osteocalcin (OCN) were positive in osteogenic lineages, aggrecan and SOX9 were positive in chondrogenic ones, peroxisome proliferator-activated receptor (PPAR-gamma2) and lipoprotein lipase (LPL) were positive in adipogenic ones, and myogenin and myod1 was positive in myogenic ones. At the same time, the results of fluorescence microscopic imaging proved that the high level of GFP expression during ASCs differentiation maintained stable nearly 2 months. So the exogenous GFP and multilineage potential of human ASCs had no severe influences on each other. Since the human ASCs can be easily obtained and abundant, it is proposed that they may be promising candidate cells for further studies on tissue engineering. Imaging with expression of GFP facilitates the research on ASCs physiological behavior and application in tissue engineering during differentiation both in vitro and in vivo.

Adenoviridae↗
PubMed2006

Quantum-chemical predictions of redox potentials of organic anions in dimethyl sulfoxide and reevaluation of bond dissociation enthalpies measured by the electrochemical methods.

A first-principle theoretical protocol was developed that could predict the absolute pK(a) values of over 250 structurally unrelated compounds in DMSO with a precision of 1.4 pK(a) units. On this basis we developed the first theoretical protocol that could predict the standard redox potentials of over 250 structurally unrelated organic anions in DMSO with a precision of 0.11 V. Using the two new protocols we systematically reevaluated the bond dissociation enthalpies (BDEs) measured previously by the electrochemical methods. It was confirmed that for most compounds the empirical equation (BDE = 1.37 pK(HA) + 23.1E(o) + constant) was valid. The constant in this equation was determined to be 74.0 kcal/mol, compared to 73.3 kcal/mol previously reported. Nevertheless, for a few compounds the empirical equation could not be used because the solvation energy changed dramatically during the bond cleavage, which resulted from the extraordinary change of dipole moment during the reaction. In addition, we found 40 compounds (mostly oximes and amides) for which the experimental values were questionable by over 5 kcal/mol. Further analyses revealed that all these questionable BDEs could be explained by one of the three following reasons: (1) the experimental pK(a) value is questionable; (2) the experimental redox potential is questionable; (3) the solvent effect cannot be neglected. Thus, by developing practical theoretical methods and utilizing them to solve realistic problems, we hope to demonstrate that ab initio theoretical methods can now be developed to make not only reliable, but also useful, predictions for solution-phase organic chemistry.

Anions↗
PubMed2006

Exploring photosynthesis evolution by comparative analysis of metabolic networks between chloroplasts and photosynthetic bacteria.

BACKGROUND: Chloroplasts descended from cyanobacteria and have a drastically reduced genome following an endosymbiotic event. Many genes of the ancestral cyanobacterial genome have been transferred to the plant nuclear genome by horizontal gene transfer. However, a selective set of metabolism pathways is maintained in chloroplasts using both chloroplast genome encoded and nuclear genome encoded enzymes. As an organelle specialized for carrying out photosynthesis, does the chloroplast metabolic network have properties adapted for higher efficiency of photosynthesis? We compared metabolic network properties of chloroplasts and prokaryotic photosynthetic organisms, mostly cyanobacteria, based on metabolic maps derived from genome data to identify features of chloroplast network properties that are different from cyanobacteria and to analyze possible functional significance of those features. RESULTS: The properties of the entire metabolic network and the sub-network that consists of reactions directly connected to the Calvin Cycle have been analyzed using hypergraph representation. Results showed that the whole metabolic networks in chloroplast and cyanobacteria both possess small-world network properties. Although the number of compounds and reactions in chloroplasts is less than that in cyanobacteria, the chloroplast's metabolic network has longer average path length, a larger diameter, and is Calvin Cycle -centered, indicating an overall less-dense network structure with specific and local high density areas in chloroplasts. Moreover, chloroplast metabolic network exhibits a better modular organization than cyanobacterial ones. Enzymes involved in the same metabolic processes tend to cluster into the same module in chloroplasts. CONCLUSION: In summary, the differences in metabolic network properties may reflect the evolutionary changes during endosymbiosis that led to the improvement of the photosynthesis efficiency in higher plants. Our findings are consistent with the notion that since the light energy absorption, transfer and conversion is highly efficient even in photosynthetic bacteria, the further improvements in photosynthetic efficiency in higher plants may rely on changes in metabolic network properties.

Arabidopsis↗
PubMed2006

Demecolcine-induced enucleation of sheep meiotically maturing oocytes.

The objective of this study was to investigate the possible effect of demecolcine, a microtubule-disrupting reagent, on induced enucleation (IE) of sheep meiotically maturing oocytes. Immunofluorescent staining with anti-tubulin antibodies was used to examine the spindle status of the oocytes. When the oocytes with intact germinal vesicles (GV) were cultured in the medium containing various concentrations of demecolcine (0.01 to 0.4 microg.mL-1) for 20 to 22 h, the spindle microtubule organization and first polar body (PB1) extrusion were inhibited by demecolcine in a dose-dependent manner. The highest IE rate (58.1%) was from the treatment with 0.04 microg.mL-1 demecolcine. Demecolcine treatment applied after germinal vesicle breakdown (GVBD) or at metaphase (M) yielded a PB1 extrusion rate and IE efficiency similar to the treatment applied at the onset of maturation. Analysis by immunofluorescence showed that both nonspindle microtubules and spindle microtubules were significantly disorganized by demecolcine. Combination treatment with demecolcine and cycloheximide (CHX) or 6-dimethylaminopurine (6-DMAP) led to single pronuclear formation rather than PB1 extrusion. When demecolcine-treated oocytes were transferred into demecolcine-free medium, the ability to extrude PB1 was quickly restored and a 72.1% IE rate was obtained following such treatment. These results demonstrate that demecolcine can be used as a potential reagent for induced enucleation of sheep meiotically maturing oocytes and may greatly facilitate research in nuclear transfer.

Animals↗
PubMed2006

The gene ncgl2918 encodes a novel maleylpyruvate isomerase that needs mycothiol as cofactor and links mycothiol biosynthesis and gentisate assimilation in Corynebacterium glutamicum.

Data mining of the Corynebacterium glutamicum genome identified 4 genes analogous to the mshA, mshB, mshC, and mshD genes that are involved in biosynthesis of mycothiol in Mycobacterium tuberculosis and Mycobacterium smegmatis. Individual deletion of these genes was carried out in this study. Mutants mshC- and mshD- lost the ability to produce mycothiol, but mutant mshB- produced mycothiol as the wild type did. The phenotypes of mutants mshC- and mshD- were the same as the wild type when grown in LB or BHIS media, but mutants mshC- and mshD- were not able to grow in mineral medium with gentisate or 3-hydroxybenzoate as carbon sources. C. glutamicum assimilated gentisate and 3-hydroxybenzoate via a glutathione-independent gentisate pathway. In this study it was found that the maleylpyruvate isomerase, which catalyzes the conversion of maleylpyruvate into fumarylpyruvate in the glutathione-independent gentisate pathway, needed mycothiol as a cofactor. This mycothiol-dependent maleylpyruvate isomerase gene (ncgl2918) was cloned, actively expressed, and purified from Escherichia coli. The purified mycothiol-dependent isomerase is a monomer of 34 kDa. The apparent Km and Vmax values for maleylpyruvate were determined to be 148.4 +/- 11.9 microM and 1520 +/- 57.4 micromol/min/mg, respectively (mycothiol concentration, 2.5 microM). Previous studies had shown that mycothiol played roles in detoxification of oxidative chemicals and antibiotics in streptomycetes and mycobacteria. To our knowledge, this is the first demonstration that mycothiol is essential for growth of C. glutamicum with gentisate or 3-hydroxybenzoate as carbon sources and the first characterization of a mycothiol-dependent maleylpyruvate isomerase.

Amino Acid Sequence↗
PubMed2006

Multilineage differentiation of adipose-derived stromal cells from GFP transgenic mice.

Functional engineering of musculoskeletal tissues generally involves rapid expansion of progenitor cells in vitro while retaining their potential for further differentiation and then induction in specific culture conditions. The autologous adipose-derived stromal cells (ASCs) are considered to contain pluripotent mesenchymal stem cells. Imaging with expression of green fluorescent protein (GFP) facilitates the detailed research on ASCs physiological behavior during differentiation into a variety of cell lineages both in vitro and in vivo. In this study, we aimed to confirm the trans-germ plasticity of homogeneously marked ASCs from GFP transgenic mice. Simultaneously, the term and intensity of GFP expression in ASCs were also focused on during variant inductions, when cells were incubated with multiple growth factors and adjuvant. ASCs were harvested from inguinal fat pads of transgenic nude mice, passaged 3 times in monolayer cultures, and then transferred to osteogenic, adipogenic, neurogenic, and myogenic medium. The morphological characterization of inductive cells was observed using phase-contrast microscopy and histological staining such as alizarin red for mineralization nodules and oil red O for lipid accumulation. The expression of marker genes or proteins was measured using RT-PCR and immunocytochemical analysis. Collagen type I, osteopontin (OPN), and osteocalcin (OCN) were positive in osteogenic lineages, peroxisome proliferator-activated receptor(PPAR)-gamma2 and lipoprotein lipase (LPL) were positive in adipogenic ones, glial fibrillary acidic protein (GFAP) and neuron-specific enolase (NSE) were positive in neurogenic ones, and alpha-smooth muscle actin (alpha-SMA) was positive in myogenic ones. Moreover, the results of fluorescence microscopic imaging suggested that there was no significant decline of GFP expression during ASCs differentiation and the level of GFP maintained stable till differentiated ASCs showed apoptotic phenotype. So the endogenous GFP and multilineage potential of transgenic ASCs had no influences on each other. Since the population of GFP ASCs can be easily identified, it is proposed that they may be promising candidate seed cells for further studies on ASCs tissue engineering, especially the study on engineered tissues formed in vivo.

Adipogenesis↗
PubMed2006

Effects of acute topiramate dosing on methamphetamine-induced subjective mood.

Clinical studies have shown that topiramate, a sulphamate-substituted fructopyranose derivative, might be an efficacious treatment for alcohol dependence, smoking cessation within an alcohol-dependent population, and cocaine dependence. Mechanistically, topiramate's therapeutic effects have been hypothesized to be due to inhibition of cortico-mesolimbic dopamine function, the primary substrate that governs the acquisition, maintenance, and reinstatement of goal-directed behaviour towards seeking abused drugs. Predicated on this hypothesis, we tested in 10 methamphetamine-dependent individuals (three females) whether low- or high-dose (15 or 30 mg i.v.) methamphetamine-induced positive subjective effects and reinforcement can be antagonized by low- or high-dose (100 or 200 mg orally) topiramate using a placebo-controlled, cross-over, factorial design. Methamphetamine administration was associated with orderly, prototypical, and significant increases on measures of stimulation, euphoria, craving, and reinforcement; however, some dysphoric symptoms also emerged. Topiramate alone showed a non-significant trend towards mild reductions in positive mood and reinforcement; yet topiramate appeared to accentuate the appreciation of methamphetamine-induced stimulation and euphoria significantly, but not craving or reinforcement. The experimental combination of topiramate and methamphetamine appeared to be safe and well tolerated, with few adverse events. Acute dosing with up to 200 mg topiramate appears to enhance, rather than attenuate, the positive subjective effects of methamphetamine. Perhaps this indicates a partial inhibition of methamphetamine's reinforcing effects. Thus, testing chronically administered or higher doses, or both, of topiramate would be necessary to determine conclusively whether or not it can attenuate the positive subjective and reinforcing effects of methamphetamine.

Adult↗
PubMed2006

In silico discovery of human natural antisense transcripts.

BACKGROUND: Several high-throughput searches for potential natural antisense transcripts (NATs) have been performed recently, but most of the reports were focused on cis type. A thorough in silico analysis of human transcripts will help expand our knowledge of NATs. RESULTS: We have identified 568 NATs from human RefSeq RNA sequences. Among them, 403 NATs are reported for the first time, and at least 157 novel NATs are trans type. According to the pairing region of a sense and antisense RNA pair, hNATs are divided into 6 classes, of which about 87% involve 5' or 3' UTR sequences, supporting the regulatory role of UTRs. Among a total of 535 NAT pairs related with splice variants, 77.4% (414/535) have their pairing regions affected or completely eliminated by alternative splicing, suggesting significant relationship of alternative splicing and antisense-directed regulation. The extensive occurrence of splice variants in hNATs and other multiple pairing patterns results in a one-to-many relationship, allowing the formation of complex regulation networks. Based on microarray data from Stanford Microarray Database, two hNAT pairs were found to display significant inverse expression patterns before and after insulin injection. CONCLUSION: NATs might carry out more extensive and complex functions than previously thought. Combined with endogenous micro RNAs, hNATs could be regarded as a special group of transcripts contributing to the complex regulation networks.

Algorithms↗
PubMed2006

Measurement of intraocular pressure after LASIK by dynamic contour tonometry.

Changes of corneal properties induced by laser in situ keratomileusis (LASIK) results in low inaccurate intraocular pressure (IOP) readings by Goldmann applanation tonometry (GAT). Before and after LASIK, the applied value of IOP, measured by dynamic contour tonometry (DCT) in comparison to GAT, was evaluated. Before and 1, 4 weeks after LASIK, the IOP in 30 cases (60 eyes) was measured by GAT and DCT respectively. The obtained results were statistically processed by SPSS11.5 statistical software. The results showed that central corneal thickness (CCT) could affect GAT measurements but not DCT measurements. The comparison of IOP one and 4 weeks after LASIK revealed that the readings from GAT was separately decreased by 5.00 +/- 1.12 and 5.45 +/- 1.13 mmHg as compared with those before LASIK, while those from DCT had no significant difference. It was concluded that LASIK-induced changes of CCT could influence the accuracy of GAT measurements, but had no influence on those from DCT. DCT was more beneficial to the measurements of IOP in normal eyes and those subject to LASIK surgery.

Adult↗
PubMed2006

Correcting the corneal power measurements after myopic laser in situ keratomileusis.

To describe and evaluate a refraction-derived method and a clinically derived method to calculate the correct corneal power for intraocular lens (IOL) power calculations after laser in situ keratomileusis (LASIK) and to compare the results to the commonly used history-derived method. Retrospective analysis were conducted in consecutive case from clinical practice. For each patient, we established the pre-LASIK and post-LASIK spectacle refraction, the pre-LASIK (K(pre)) and post-LASIK K readings (K(post)). We then calculated the pre- and post-LASIK refraction at the cornmeal plane and the amount of correction obtained by the refraction surgery (deltaSEQco). The cases were divided into two groups. Group I was used to derive two formulas. The values obtained with the two methods were compared with the K by history-derived method (K(c.hd) in group II to validate the results. The K values calculated by using the refraction-derived method (K(c.rd)) and the K values calculated using the clinically derived method (K(c.cd)) correlated highly with K(c.hd). The correct corneal power for intraocular lens (IOL) power calculations after LASIK can use refraction-derived method and clinically derived method instead of history-derived method when some refractive parameters are not available.

Adolescent↗