Biomedical subjects

Liang Li

Publications and source records attributed to Liang Li.

At least 145 records · Page 8Linked to original sources

PubMed2003

The biochemistry and physiology of metallic fluoride: action, mechanism, and implications.

Fluoride is a well-known G protein activator. Activation of heterotrimeric GTP-binding proteins by fluoride requires trace amounts of Al3+ or Be2+ ions. AlFx mimics a gamma-phosphate at its transition state in a Galpha protein and is therefore able to inhibit its GTPase activity. AlFx also forms complexes with small GTP-binding proteins in the presence of their GTPase-activating proteins (GAP). As phosphate analogs, AlFx or BeFx affect the activity of a variety of phosphoryl transfer enzymes. Most of these enzymes are fundamentally important in cell signal transduction or energy metabolism. Al3+ and F- tend to form stable complexes in aqueous solution. The exact structure and concentration of AlFx depend on the pH and the amount of F- and Al3+ in the solution. Humans are exposed to both F and Al. It is possible that Al-F complexes may be formed in vivo, or formed in vitro prior to their intake by humans. Al-F complexes may play physiological or pathological roles in bone biology, fluorosis, neurotoxicity, and oral diseases such as dental caries and periodontal disease. The aim of this review is to discuss the basic chemical, biochemical, and toxicological properties of metallic fluoride, to explore its potential physiological and clinical implications.

Aluminum Compounds↗

PubMed2003

Notch activity in neural cells triggered by a mutant allele with altered glycosylation.

The receptor protein Notch is inactive in neural precursor cells despite neighboring cells expressing ligands. We investigated specification of the R8 neural photoreceptor cells that initiate differentiation of each Drosophila ommatidium. The ligand Delta was required in R8 cells themselves, consistent with a lateral inhibitor function for Delta. By contrast, Delta expressed in cells adjacent to R8 could not activate Notch in R8 cells. The split mutation of Notch was found to activate signaling in R8 precursor cells, blocking differentiation and leading to altered development and neural cell death. split did not affect other, inductive functions of Notch. The Ile578-->Thr578 substitution responsible for the split mutation introduced a new site for O-fucosylation on EGF repeat 14 of the Notch extracellular domain. The O-fucose monosaccharide did not require extension by Fringe to confer the phenotype. Our results suggest functional differences between Notch in neural and non-neural cells. R8 precursor cells are protected from lateral inhibition by Delta. The protection is affected by modifications of a particular EGF repeat in the Notch extracellular domain. These results suggest that the pattern of neurogenesis is determined by blocking Notch signaling, as well as by activating Notch signaling.

Animals↗

PubMed2003

[The effect of mechanical stimulation on the expression of alpha 2, beta 1, beta 3 integrins and the proliferation, synthetic function in rat osteoblasts].

The purpose of this paper is to investigate the probable molecular mechanism in mechano-transduction of the regulation of integrins and the effects of cyclic biaxial mechanical strain on proliferation and synthetic function in the osteoblasts isolated from 3-month-old female Sprague-Dawley (SD) rats. The osteoblasts were cultured in F-12 medium contained with 10% fetal bovine serum(FBS) and grown to subconfluency in Flexercell type I dishes in a humidified incubator with 5% CO2 and 95% air at 37 degrees C. Mechanical strains were applied to the cells for periods of 30 min, 2, 4 and 8 hours every day, lasting 2 days. The amplitude of mechanical strain applied to the cells were 400, 1,000 and 4,000 mu strain respectively, at a frequency of one hertz(1 Hz). Unstrained cells were used as control. The expression of integrins alpha 2, beta 1, beta 3 on the membrane of osteoblasts and proliferation activity of osteoblasts were studied with Flow Cytometry(FCM). The content of osteocalcin, carboxyterminal propeptide of type-I procollage(PICP), total protein secreted by osteoblastes were detected with the isotope labelling method. The results showed that there are actual expressions of integrins alpha 2, beta 1, beta 3 on the membrane of osteoblasts without mechanical strain and that the expression of integrins beta 1 is highest. The mechanical strain increased the expression of integrins alpha 2, beta 1, beta 3 on the membrane of osteoblasts, but the strain-related up-regulation of expression of integrins alpha 2, beta 1, beta 3 are different in various amplitude and different duration of mechanical stains. The up-regulation of expression of integrins beta 3 is most sensitive to mechanical strain. The up-regulation of expression of integrins alpha 2, beta 1, beta 3 is higher at 4,000 mu strain than at 400, 1,000 mu strain. The mechanical strain can elevate the proliferation activity and the synthetic function of osteoblast at 400, 1,000 mu strain. However, the mechanical strain increased significant the proliferation in the osteoblasts and suppressed obviously the synthetic function in the osteoblasts. In the present study, the reaction of the osteoblasts in 3 month-old rat to the mechanical stimulation suggested that 1) expressions of integrins alpha 2, beta 1, beta 3 were increased in a amplitude of strain-dependent manner; 2) the changes of expression of integrins alpha 2, beta 1, beta 3 relate close to the changes of the proliferation and synthetic function of the osteoblasts. Low amplitude of strain can increase the proliferation and the synthetic function of the osteoblasts along with up-regulation of expression of integrins alpha 2, beta 1, beta 3; while higher amplitude of strain elevated significantly the proliferation of osteoblasts and suppressed obviously the synthetic function of the osteoblasts along with up-regulation of expression of integrins alpha 2, beta 1, beta 3. The amplitude of 4,000 mu strain is an optimal amplitude as stimulus for up-regulation of expression of integrins alpha 2, beta 1, beta 3 on the membrane of osteoblasts and increase the proliferation activity, but decrease the synthetic function of osteoblasts in the present study. Accordingly it indicates that integrins have a important role in regulation of signal transduction pathway in osteoblasts as a result of mechanical strain.

Animals↗

PubMed2003

Exploration of the functional proteome: lessons from lipid rafts.

Lipid rafts are liquid-ordered cholesterol and glycolipid-enriched membrane microdomains that act as sorting devices for the accumulation of acylated signaling molecules. Lipid rafts are implicated in receptor signaling, protein and membrane trafficking, cytoskeletal re-organization and the entry of infectious organisms into cells. Several recent studies have investigated the composition of the lipid raft proteome by mass spectrometry. Here, those studies and the insights they afford into raft function are reviewed. Lipid rafts contain hydrophobic proteins, posing problems of isolation, recovery and analysis. Recent advances in proteome preparation that extend the boundaries of protein detection in lipid rafts are described and their implications for the exploration of the functional proteome are discussed.

Humans↗

PubMed2003

[Advances in the applications of DNA chips and proteomics approaches for neurosciences].

DNA chips and proteomics are two of the recently developed high-throughput technologies that allow us to simultaneously analyze the expression levels of multiple genes and the interactions of their products in the brain. Their applications in neuroscience provide us with the unprecedented opportunities for understanding of the brain. A typical gene chip experiment contains a series of steps, including preparations (or purchase) of DNA chips, target DNA and probes, hybridization of chips with target DNA, chip scanning, and imaging analysis. The technologies in proteomics are more complicated, which comprise of three main aspects of technologies: protein isolation, identification and bioinformatic analysis of data. If protein isolation is based on 2-D, it includes the preparation of protein sample, 2-D, staining gels, spot excision, proteolysis, mass spectrometry of purified protein and finally undergoing bioinformatic analysis. Here we review the two technologies with emphasis on their applications in neurosciences. The challenges, advantages and disadvantages of the two techniques, and perspectives for their developments are discussed.

Animals↗

PubMed2003

[Nitric oxide production and expression of cytokines by macrophages infected by M. tuberculosis H(37)R(v)].

OBJECTIVE: To study nitric oxide (NO) production and cytokine expression by macrophages infected by M. tuberculosis H(37)R(v), and to compare the difference between dead and live M. tuberculosis in the induction of immune responses, and thus to show if dead bacteria could be a possible candidate for new vaccines. METHODS: Reverse transcription-polymerase chain reaction (RT-PCR) and ELISA were used to measure the production of NO and cytokines in macrophages infected by H(37)R(v). RESULTS: Macrophages infected by viable M. tuberculosis produced more NO, IL-1, IL-12, IL-18, TNF-alpha and inducible nitric oxide synthases (iNOS), as compared with macrophages infected by dead bacteria. The number of bacteria was also an important factor determining the production of NO and cytokines. CONCLUSIONS: Viable M. tuberculosis H(37)R(v) can induce the activation of macrophages and the production of more NO and cytokines which play important roles in the host immune response. Heat-killed M. tuberculosis H(37)R(v) failed to induce activation of macrophages and the production of NO and cytokines, which makes it unlikely to be a candidate for vaccine development.

Cells, Cultured↗

PubMed2003

[Effect of aging on the ability of growth and differentiation of rat bone marrow stromal cells].

OBJECTIVE: To measure the osteogenesis and adipogenesis potentiality of rat marrow stromal cells (MSCs) derived from 3, 6, 9, 12-month-old doner rats. METHODS: Rat MSCs were induced to osteoblast or adipocyte by osteogenic inducer or adipogenic inducer. In different times, 3 and 12-month-old rat MSCs were observed by histochemistry staining; the mRNA level of type I collagen and lipoprotein lipase of 3, 6, 9, 12-month-old rat MSCs were measured by RT-PCR. RESULTS: The expression of alkaline phosphatase (ALP) of the control group and induced group of 12-month old rat MSCs was less than that of 3-month old rat MSCs after 1-week osteogenic induction. 12 days later, calcification was observed in 3-month old group. Lipid droplets occurred in the cells of 12-month old group after 2-day adipogenic induction, while these droplets occurred after 3-day or 4-day induction in 3-month old group. The mRNA level of type I collagen decreased with the increase of age. The mRNA level of lipoprotein lipase of younger rats was lower than that of older rats. Both of the changes were more significantly with the increase of the induction time. CONCLUSIONS: With the increase of age, the ability of osteogenesis of rat MSCs decreased, but the ability of adipogenesis increased.

Adipose Tissue↗

PubMed2003

[Contraction peculiarity of the muscles that control the moving of the jaw of rat in different growing time].

OBJECTIVE: This study was aimed to evaluate the effect of functional change in oral cavity on the contraction peculiarity of the muscles that control the moving of the jaw in different time of growth. METHODS: Fifteen male Wistar rats 4, 6 and 8 weeks old were used in this experiment. After deep anesthesia, the masseter muscles(MM), digastric muscles(DM) and lateral pterygoid muscles(LPM) were stimulated in the apartment made by the present authors. The curves that express the relations of force with electric stimulation were recorded, and the relationships between the speed and force of twitch were analyzed. RESULTS: The maximal forces of twitch of the 8-week-old rats' MM, DM, LPM were 61.7 +/- 14.4 g, 86.4 +/- 25.1 g and 175.3 +/- 39.4 g respectively. When a single electric stimulus stimulated the muscles, the speed of twitch increased with the growth of the rats. As for MM and LPM, the speed markedly increased with the growing of rats from 4 weeks old to 6 weeks old; as for DM, it increased in rats growing from 6 weeks old to 8 weeks old. CONCLUSION: The quickest time of growth of the muscles that control the moving of the jaw of rat is a period from 6 weeks to 8 weeks old and the forces of contraction and twitch increase markedly.

Animals↗

PubMed2003

[A system applying cyclic biaxial mechanical strain to cultured cells].

To study the response of cultured cells to the cyclical biaxial biomechanical strain, a system was made according to the principle of Winston. The system was made of culture dish, pressure cavity and step motor. The culture dishes were made of polymethyl methacrylate and the bottom of the culture dishes were made of silicone rubber membrane. When the diameter of the silicone rubber tube and the distance between rollers and curvilinear plate changed, the pressure in the pressure cavity changed and the strain of the membrane changed from 0 to 4%. When the roll of the step motor changed, the frequency of the strain changed from 0.1 to 5 Hz.

Animals↗

PubMed2003

[Identification of differentially expressed genes in Lin-CD34- and Lin-CD34+ cells].

OBJECTIVE: To identify genes that differentially expressed in Lin(-)CD(34)(-) and Lin(-)CD(34)(+) cells. METHODS: With Lin(-)CD(34)(-) cells as tester and Lin(-)CD(34)(+) cells as driver, cDNA subtractive library for Lin(-)CD(34)(-) cells was constructed using suppression subtractive hybridization technique. Part of clones in the library were sequenced and the homologue analysis was conducted against the DNA database in GenBank. RESULTS: 593 clones containing an average of 300 - 500 bp insert were identified. Of them, 53 randomly selected ESTs were sequenced. Homologue analysis revealed that 37 ESTs represented 10 known genes, and the other 16 ESTs represented 4 novel sequences. CONCLUSION: Part of specifically expressed genes in Lin(-)CD(34)(-) cells were identified, which maybe related to Lin(-)CD(34)(-) cells' specific characteristics.

Antigens, CD34↗

PubMed2003

[Effect of Tpo and/or IL-11 gene modified stromal cells on the expansion of CD34+ CD38- hematopoietic primitive progenitor cells].

OBJECTIVE: To investigate the effects of Tpo and/or IL-11 gene modified stromal cells on the expansion of CD(34)(+) hematopoietic stem/progenitor cells in cord blood. METHODS: Retroviral vectors containing Tpo or IL-11 gene were constructed and used to transfect the stromal cell line HFCL. Tpo and/or IL-11 mRNA was assayed by Northern blot. Non-modified stromal cells were used, CD(34)(+) hematopoietic stem/progenitor cells from cord blood were expanded on gene-modified stromal cells for 7 days. The phenotype of CD(34)(+)CD(38)(-) primitive progenitors was detected by flow cytometry. RESULTS: HFCL expressed Tpo and/or IL-11 mRNA after transfected by the retroviral vectors. The percentages of CD(34)(+)CD(38)(-) primitive progenitors in the cultures of Tpo, IL-11 and Tpo + IL-11 modified HFCL were (1.8 +/- 0.24)%, (1.62 +/- 0.23)%, and (2.45 +/- 0.28)%, respectively, which were higher than that in the control [(0.8 +/- 0.23)%]. CONCLUSION: The stromal cells modified by Tpo and/or IL-11 gene were able to enhance ex vivo expansion of CD(34)(+) and CD(34)(+)CD(38)(-) hematopoietic stem/progenitor cells from cord blood.

ADP-ribosyl Cyclase↗

PubMed2003

[Studies on chemical constituents from the stems of Schisandra sphaerandra].

OBJECTIVE: To investigate the chemical constituents from the stems of Schisandra sphaerandra. METHOD: Compounds were isolated from ethanolic extract of the titled herb by silica gel column chromatography, and their structures were elucidated by physical and chemical evidences and spectroscopic analysis. RESULT: 12 compounds were obtained and identified as wuweizisu C (1), ganwuweizic acid (2), nigranoic acid (3), catechin (4), 2 alpha,24-dihytroxyursolic acid. (5), 3 beta-O-acetylursolic acid (6), ursolic acid (7), slyceryl 26-hydroxyhexacosanoate (8), slyceryl hexacosanoate (9), fat acids (10), beta-sitosterol (11), daucosterol (12), respectirely. CONCLUSION: Three pentacyclic triterpene carboxylic acid (5-7) were isolated from Schisandreae for the first time.

Plant Stems↗

PubMed2003

[Effect of xue hanjing oral fluid on mice immunological function].

OBJECTIVE: To observe effect of Xue Hanjing oral fluid on mice immunological function. METHOD: The weight of thymus gland and spleen and the function of abdominal cavity macrophage were measured. Production of the hemolysin antibody, the immunoglobulin of blood serum and complement and the proliferation of T lymphocytes were observed respectively by means of microblood, immune-turbidimetry and MTT staining. RESULT: Xue Hanjing oral fluid could enhance index of the thymus gland and spleen and the phago-percent of abdominal cavity macrophage, increase the immunoglobulin of blood serum(IgG and IgM), and accelerate production of the hemolysin antibody and the proliferation of T lymphocytes. CONCLUSIONS: Xue Hanjing oral can reinforce immunological function in mice.

Adjuvants, Immunologic↗

PubMed2002

Low-mass proteome analysis based on liquid chromatography fractionation, nanoliter protein concentration/digestion, and microspot matrix-assisted laser desorption ionization mass spectrometry.

HPLC fractionation combined with mass spectrometry can become a powerful tool for analyzing the proteome in the mass range below 15 kDa where efficient protein separation by gel electrophoresis can be difficult. For sensitive and high-resolution separation of the low-mass proteome, the use of analytical rather than preparative HPLC columns is preferred. However, individual fractions collected by a conventional HPLC separation usually contain a small amount of proteins whose concentrations may not be sufficiently high for subsequent enzyme digestion and protein identification by mass spectrometry. In this work, we present a high sensitivity nanoliter sample handling technique to analyze proteins fractionated by HPLC. In this technique, an individual HPLC fraction in hundreds of microliter volume is pre-concentrated to several microliters. About 700 pl of the pre-concentrated fraction is then drawn into a 20-microm I.D. capillary and dried in a small region near the capillary's entrance. This process can be repeated many times to concentrate a sufficient amount of protein to the small region of the capillary. After protein concentration, protein digestion is achieved by drawing 1 nl of chemical or enzymatic reagent into the capillary and placing it in the same region where the dried protein sits. The resulting peptides are then deposited onto a microspot in a MALDI probe for mass analysis. The performance of this technique is demonstrated with the use of a standard protein solution. This technique is applied to the identification of low-mass proteins separated by HPLC from a complex mixture of an E. coli extract.

Amino Acid Sequence↗

PubMed2002

The dentate gyrus neurogenesis: a therapeutic target for Alzheimer's disease.

Neurogenesis persists in the aged human dentate gyrus but its role and regulation in pathological conditions such as Alzheimer's disease (AD), where the neurotrophic environment is changed, are poorly understood. In this study we investigated the effect of changes in the neurotrophic environment on neurogenesis in cultured rat hippocampal progenitors and in normal adult rats as models. In hippocampal progenitor cells from adult rats, fibroblast growth factor-2 (FGF-2) dose-dependently decreased microtubule-associated protein 2 and increased tau levels, indicating an FGF-2-induced dendrite to axon polarity shift. Cerebrolysin, a neurotrophic drug which has been shown to improve cognition and mood of AD patients, was found to increase neuron-like differentiated adult rat hippocampal progenitors in culture both by reducing apoptosis and by counteracting the FGF-2-induced polarity shift. Intraperitoneal administration of Cerebrolysin enhanced dentate gyrus neurogenesis and maze performance of 8- to 12-month-old female rats. These studies suggest that AD pathogenesis might involve an abnormally elevated FGF-2-associated dysregulation of dentate gyrus neurogenesis, especially neuronal polarity and that the neurogenesis pathology is a promising therapeutic target for this disease.

Alzheimer Disease↗

PubMed2002

Enhancement of electrically evoked startle-like responses by tetanic stimulation of the superior colliculus.

Single-pulse unilateral electrical stimulation of either the amygdala or the inferior colliculus elicited startle-like responses in chloral hydrate anesthetized rats. EMG responses to intracranial stimulation were recorded from the anterior biceps femoris muscles. The EMG responses were generally enhanced following unilateral tetanic stimulation of the deep layers of the superior colliculus, but the enhancement was stronger for amygdala sites than inferior colliculus sites. The enhancement of EMG responses to ipsilateral amygdala stimulation was much larger than that for contralateral amygdala stimulation and that for ipsilateral inferior colliculus stimulation. The enhancement of EMG responses to contralateral inferior colliculus stimulation was not significant. The present study provides a motor-output model for studying plasticity in the neural pathways mediating startle facilitation.

Amygdala↗

PubMed2002

Metal powder substrate-assisted laser desorption/ionization mass spectrometry for polyethylene analysis.

Polyethylene is one of the most important industrial polymers and is also one of the most challenging polymers to be characterized by mass spectrometry. We have developed a substrate-assisted laser desorption/ionization (LDI) mass spectrometric method for polyethylene analysis. In this method, cobalt, copper, nickel, or iron metal powders are used as a sample substrate and silver nitrate is used as the cationization reagent. Using a conventional UV LDI time-of-flight mass spectrometer, intact oligomer ions having masses up to 5000 u can be detected. Cobalt is found to produce spectra with the highest signal-to-noise ratio and the lowest level of fragmentation. Cobalt powder size is shown to have some effect on the spectra produced. The best results are obtained with the use of cobalt powders with diameters ranging from 30 to 100 microm. Fragmentation cannot be totally eliminated, but the fragment ion peaks can be readily discerned from the intact polyethylene ions in the substrate-assisted LDI spectrum. Thus, the average molecular masses of low-mass polyethylene samples can be determined by using this method. A rapid heating model is used to account for the effectiveness of using the coarse metal powders to assist the analysis of intact polyethylene molecules by LDI.

Journal Article↗

PubMed2002

Mass spectrometric methods for generation of protein mass database used for bacterial identification.

The availability of a suitable database is critical in a proteomic approach for bacterial identification by mass spectrometry (MS). The major limitation of the present public proteome database is the lack of extensive low-mass bacterial protein entries with masses experimentally verified for most bacteria. Here, we present a method based on mass spectrometry to create protein mass tables specifically tailored for bacterial identification. Several issues related to the detection of bacterial proteins for the purpose of database creation are addressed. Three species of bacteria, namely, Escherichia coli, Bacillus megaterium, and Citrobacter freundii, which can be found in the ambient environment, were chosen for this study. Direct matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS analysis of each bacterial extract reveals 20-29 protein components in the mass range from 2000 to 20,000 Da. HPLC fractionation of bacterial extracts followed by off-line MALDI-TOF analysis of individual fractions detects 156-423 components. Analysis of the extracts by HPLC/electrospray ionization MS shows the number of detectable proteins in the range of 46-59. Although a number of components were common to the three detection schemes employed, some unique components were found using each of these techniques. In addition, for E. coli where a large proteome database exists in the public domain, a number of masses detected by the mass spectrometric methods do not match with the proteome database. Compared to the public proteome database, the mass tables generated in this work are demonstrated to be more useful for bacterial identification in an application where the bacteria of interest have limited protein entries in the public database. The implication of this work for future development of a comprehensive mass database is discussed.

Bacteria↗