Biomedical subjects

L Li

Publications and source records attributed to L Li.

At least 559 records · Page 31Linked to original sources

PubMed2000

Creating a protein-based element of inheritance.

Proteins capable of self-perpetuating changes in conformation and function (known as prions) can serve as genetic elements. To test whether novel prions could be created by recombinant methods, a yeast prion determinant was fused to the rat glucocorticoid receptor. The fusion protein existed in different heritable functional states, switched between states at a low spontaneous rate, and could be induced to switch by experimental manipulations. The complete change in phenotype achieved by transferring a prion determinant from one protein to another confirms the protein-only nature of prion inheritance and establishes a mechanism for engineering heritable changes in phenotype that should be broadly applicable.

Animals↗

PubMed2000

The chsA gene from Aspergillus nidulans is necessary for maximal conidiation.

A fragment from the open reading frame of the cloned chsA gene from Aspergillus nidulans was deleted and replaced with the argB gene. The resulting construct was used to replace the wild-type chsA gene in an argB deletion strain. The growth and morphology of the vegetative hyphae from the resulting chsA disruptant strain were indistinguishable from those of a wild-type strain but the chitin content of the hyphae from the disruptant was reduced to approximately 90% of that of wild-type. The disruptant showed reduced ability to produce the asexual spores (conidia) that are formed by differentiated aerial hyphae called conidiophores. The ability to form undifferentiated aerial hyphae was not impaired in the disruptant. The conidiophores and conidia produced by the disruptant were indistinguishable from those of wild-type. Conidium formation by the disruptant grown on a variety of media was reduced to about 30% of the wild-type. A chsE null strain did not show a defect in conidiation but a strain in which both chsA and chsE were inactivated produced about 3% of the conidia of wild-type. That finding supports the hypothesis that chsA and chsE encode a partially redundant function necessary for conidiophore development.

Aspergillus nidulans↗

PubMed2000

Pan-neural Prospero terminates cell proliferation during Drosophila neurogenesis.

Organogenesis requires coordination between developmental specific regulators and genes governing cell proliferation. Here we show that Drosophila prospero encodes a critical regulator of the transition from mitotically active cells to terminal differentiated neurons. Loss of pros results in aberrant expression of multiple cell-cycle regulatory genes and ectopic mitotic activity. In contrast, ectopic pros expression causes transcriptional suppression of multiple cell-cycle regulatory genes and premature termination of cell division. pros activity, hence, provides a critical regulatory link between neuronal lineage development and transcriptional regulation of cell cycle regulatory genes.

Animals↗

PubMed2000

SNIP, a novel SNAP-25-interacting protein implicated in regulated exocytosis.

Synaptosome-associated protein of 25 kDa (SNAP-25) is a presynaptic membrane protein that has been clearly implicated in membrane fusion in both developing and mature neurons, although its mechanisms of action are unclear. We have now identified a novel SNAP-25-interacting protein named SNIP. SNIP is a hydrophilic, 145-kDa protein that comprises two predicted coiled-coil domains, two highly charged regions, and two proline-rich domains with multiple PPXY and PXXP motifs. SNIP is selectively expressed in brain where it co-distributes with SNAP-25 in most brain regions. Biochemical studies have revealed that SNIP is tightly associated with the brain cytoskeleton. Subcellular fractionation and immunofluorescence localization studies have demonstrated that SNIP co-localizes with SNAP-25 as well as the cortical actin cytoskeleton, suggesting that SNIP serves as a linker protein connecting SNAP-25 to the submembranous cytoskeleton. By using deletion analysis, we have mapped the binding domains of SNIP and SNAP-25, and we have demonstrated that the SNIP-SNAP-25 association is mediated via coiled-coil interactions. Moreover, we have shown that overexpression of SNIP or its SNAP-25-interacting domain inhibits Ca(2+)-dependent exocytosis from PC12 cells. These results indicate that SNIP is involved in regulation of neurosecretion, perhaps via its interaction with SNAP-25 and the cytoskeleton.

Adaptor Proteins, Vesicular Transport↗

PubMed2000

Thromboxane A(2) regulation of endothelial cell migration, angiogenesis, and tumor metastasis.

Prostaglandin endoperoxide H synthases and their arachidonate products have been implicated in modulating angiogenesis during tumor growth and chronic inflammation. Here we report the involvement of thromboxane A(2), a downstream metabolite of prostaglandin H synthase, in angiogenesis. A TXA(2) mimetic, U46619, stimulated endothelial cell migration. Angiogenic basic fibroblast growth factor (bFGF) or vascular endothelial growth factor (VEGF) increased TXA(2) synthesis in endothelial cells three- to fivefold. Inhibition of TXA(2) synthesis with furegrelate or CI reduced HUVEC migration stimulated by VEGF or bFGF. A TXA(2) receptor antagonist, SQ29,548, inhibited VEGF- or bFGF-stimulated endothelial cell migration. In vivo, CI inhibited bFGF-induced angiogenesis. Finally, development of lung metastasis in C57Bl/6J mice intravenously injected with Lewis lung carcinoma or B16a cells was significantly inhibited by thromboxane synthase inhibitors, CI or furegrelate sodium. Our data demonstrate the involvement of TXA(2) in angiogenesis and development of tumor metastasis.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed2000

Hyperglycemia triggers massive neutrophil deposition in brain following transient ischemia in rats.

Myeloperoxidase (MPO) immunohistochemistry was used to ascertain the role of polymorphonuclear leukocytes in hyperglycemia-induced accentuation of brain injury after transient ischemia. Rats received 12.5 min of normothermic global cerebral ischemia by bilateral carotid occlusion plus hypotension. Hyperglycemia was induced before ischemia by intraperitoneal dextrose administration. Quantitative MPO immunohistochemistry was performed at 24 h and 3 days postischemia. Brains of normoglycemic-ischemic animals contained almost no MPO activity. By contrast, striking numbers of MPO-positive cells were present in brains studied 24 h after hyperglycemic ischemia, both within pial and parenchymal vessels and within the parenchyma. MPO deposition tended to subside at 3 days. These results indicate that hyperglycemia triggers the early, massive deposition of neutrophils in the postischemic brain--an event that may contribute to exacerbation of injury.

Animals↗

PubMed2000

Characterization, chromosomal localization, and the complete 30-kb DNA sequence of the human Jagged2 (JAG2) gene.

The genomic sequence of the human Jagged2 (JAG2) gene, which encodes a ligand for the Notch receptors, was determined. The 30-kb DNA sequence spanning the JAG2 gene contains 26 exons and a putative promoter region. Several potential binding sites for transcription factors, including NF-kappab, E47, E12, E2F, Ets-1, MyoD, and OCT-1, were found in the human JAG2 promoter region. The JAG2 gene was also mapped to the chromosomal region 14q32 using fluorescence in situ hybridization.

Base Sequence↗

PubMed2000

Azimuthal directional sensitivity of prepulse inhibition of the pinna startle reflex in decerebrate rats.

Previous studies have indicated that the auditory midbrain, the inferior colliculus, is important for both sound localization and mediation of prepulse inhibition of the startle reflex. The present study investigated the azimuthal directional sensitivity of prepulse inhibition of the pinna startle reflex in decerebrate rats. The pinna startle reflex was measured by recording multi-unit action potentials from the cervicoauricular muscles. The startling noise burst (94 dB SPL) was produced by a stationary speaker at 0 degrees azimuth, and the non-startling prepulse noise burst (46 dB SPL) was produced by a movable speaker whose direction was changed in the frontal azimuthal plane. The interval between the onset of the prepulse sound and the onset of the startling sound was 100 ms. The pinna reflex to the startling sound was strongly inhibited by the prepulse sound, and the inhibited startle response exhibited a flat azimuthal directional curve. In addition to further confirming that the neural pathways mediating prepulse inhibition are located in the brainstem, the present results indicate that interaural disparities of binaural inputs used for sound localization are not capable of modulating prepulse inhibition of the startle reflex.

Acoustic Stimulation↗

PubMed2000

Cell-dependent mechanisms restrict the HIV type 1 coreceptor activity of US28, a chemokine receptor homolog encoded by human cytomegalovirus.

Several members of the chemokine receptor family are used together with CD4 for HIV-1 entry into target cells. The human cytomegalovirus US28 gene encodes a chemokine receptor homolog that has been reported to function as an HIV-1 coreceptor. However, studies of US28 have given conflicting results regarding its ability to mediate HIV-1 entry. We examined the ability of US28 to function as an HIV-1 coreceptor in various cell lines and found that its coreceptor activity is highly cell dependent. US28 could function as a coreceptor for HIV-1 entry in HeLa and U87 cells but not in COS-1 and Cf2Th cells. In COS-1 cells, US28 was expressed on the cell surface and could mediate cell-cell fusion with HIV-1 Env-expressing cells, suggesting that the block to infection may result from a defect in virus internalization or postentry steps. In Cf2Th cells, US28 was expressed at high levels intracellularly but was not transported to the cell surface. The block in US28 coreceptor function in COS-1 and Cf2Th cells was coreceptor dependent, since CCR5, CXCR4, and other coreceptors can mediate HIV-1 entry in these cell lines. HIV-1 viruses pseudotyped with the MuLV or VSV Env entered and replicated at similar efficiency in COS-1 and U87 cells in single-cycle infections, suggesting that postentry and other early events in the HIV-1 life cycle are not intrinsically inefficient in COS-1 cells. These results identify two distinct mechanisms that can restrict the HIV-1 coreceptor activity of US28 in a cell- and coreceptor-dependent manner, and help to explain the existing controversy regarding the ability of US28 to mediate HIV-1 entry.

Animals↗

PubMed2000

Distinct role of follicular dendritic cells and T cells in the proliferation, differentiation, and apoptosis of a centroblast cell line, L3055.

Germinal center (GC) B cells undergo complex interactions with follicular dendritic cells (FDC) and T cells in the course of differentiation into memory B and plasma cells. To delineate the individual roles of FDC and T cells at each stage of GC B cell differentiation at the clonal level and to analyze the signals involved, we adopted a unique experimental model using an FDC line, HK, and a lymphoma cell line, L3055, that resembles centroblasts. A detailed phenotypic analysis revealed L3055 cells to be a clonal population originating from the GC. Like freshly isolated centroblasts, L3055 cells underwent spontaneous apoptosis when cultured in the absence of fresh FDC or HK cells. L3055 cells proliferated continuously in the presence of HK cells, while they differentiated into a population with the phenotype of centrocytes after stimulation with CD40 ligand (CD40L) and IL-4. The CD40L-stimulated L3055 cells underwent CD95-mediated apoptosis, which was reminiscent of the feature of CD40L-stimulated tonsillar GC B cells. In contrast to HK cells that did not protect L3055 cells from anti-Ig killing, CD40L plus IL-2, IL-4, and IL-10 prevented anti-Ig-induced apoptosis. These experimental results demonstrate a distinct function of FDC and activated T cells, in that FDC provide signals for rapid proliferation of centroblasts, whereas T cells confer signals for differentiation of centroblasts into centrocytes and resistance to B cell receptor-mediated apoptosis. T cells collaborate with FDC in the protection and expansion of the Ag-specific GC B cells.

Adolescent↗

PubMed2000

Decrease in phorbol ester-induced potentiation of noradrenaline release in synapsin I-deficient mice.

Synapsin I is involved in regulating amino acid neurotransmitter release, but has a less clear role in noradrenergic nerve terminals. To better understand the role of synapsin I in the function of noradrenergic nerve terminals, we compared noradrenaline release in wild-type and synapsin I-deficient mice. No difference was found in the accumulation or in the Ca(2+)-independent release of [(3)H]noradrenaline in cerebrocortical synaptosomes from wild-type and synapsin I-deficient mice. Synaptosomes lacking synapsin I also displayed no gross alterations in either the time course or the Ca(2+)-dependency of [(3)H]noradrenaline release when stimulated by depolarizing secretagogues or ionophore treatment. In wild-type synaptosomes, activation of protein kinase C by phorbol ester treatment resulted in a Ca(2+)-dependent increase in [(3)H]noradrenaline release evoked by depolarizing secretagogues and ionophore treatment. The phorbol ester-mediated enhancement of [(3)H]noradrenaline release evoked by depolarizing secretagogues, but not by ionophore treatment, was greatly reduced in synapsin I-deficient synaptosomes. These results indicate that synapsin I plays a role in regulating noradrenaline release.

Animals↗

PubMed2000

Improving signal to background ratio for on-the-fly fluorescence lifetime detection in capillary electrophoresis.

On-the-fly fluorescence lifetime detection (OFLD) in capillary electrophoresis (CE) was previously demonstrated using a commercial multiharmonic Fourier transform (MHF) spectrofluorometer interfaced to a commercial CE system. This paper discusses optimization of the interface design for minimization of background fluorescence and scattered light, thereby maximizing the signal-to-background ratio (S/B) of the dynamic measurement. Strategies included using various combinations of optical filters including a holographic filter and longpass or bandpass filters, tilting the capillary relative to the incident laser beam, employing a confocal design and adding an iris to remove out-of-focus light, using a microscope objective in the emission beam to increase the collection efficiency, and using square instead of ciruclar capillary columns. Significant improvements in S/B for on-column, on-the-fly detection of fluorescein in CE were achieved with most modifications.

Electrophoresis, Capillary↗

PubMed2000

Effects of matrix-assisted laser desorption/ionization experimental conditions on quantitative compositional analysis of ethylene oxide/propylene oxide copolymers.

Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has the potential to become a valuable tool for the compositional analysis of copolymers. For a copolymer composed of structurally very similar building blocks with minor chain length changes, one would expect the relative peak intensities observed in the MALDI mass spectra to reflect its composition, at least within a narrow mass range. However, we show that variations in experimental conditions in MALDI can have a significant effect on the mass spectral appearance of a copolymer. The effects of concentration, laser power, type of matrices and solvents on mass spectra of an ethylene oxide/propylene oxide copolymer are illustrated. These somewhat surprising results show that great care needs to be exercised when interpreting copolymer spectra for compositional analysis, even for copolymers with structurally similar monomers. This work also points out that further studies are needed to better understand and optimize spectral acquisition conditions for reliable copolymer compositional analysis by MALDI.

Epoxy Compounds↗

PubMed2000

Human albumin solution for resuscitation and volume expansion in critically ill patients. The Albumin Reviewers.

BACKGROUND: Human albumin solutions are used in a range of medical and surgical problems. Licensed indications are the emergency treatment of shock and other conditions where restoration of blood volume is urgent, burns, and hypoproteinaemia. Human albumin solutions are more expensive than other colloids and crystalloids. OBJECTIVES: To quantify the effect on mortality of human albumin and plasma protein fraction (PPF) administration in the management of critically ill patients. SEARCH STRATEGY: We searched the Cochrane Injuries Group trials register, Cochrane Controlled Trials Register, Medline, Embase and BIDS Index to Scientific and Technical Proceedings. Reference lists of trials and review articles were checked, and authors of identified trials were contacted. The search was last updated in November 1999. SELECTION CRITERIA: Randomised controlled trials comparing albumin/PPF with no albumin/PPF, or with a crystalloid solution, in critically ill patients with hypovolaemia, burns or hypoalbuminaemia. DATA COLLECTION AND ANALYSIS: We collected data on the participants, albumin solution used, mortality at the end of follow up, and quality of allocation concealment. Analysis was stratified according to patient type. We assessed publication bias using the regression test for funnel plot asymmetry. MAIN RESULTS: We found 30 trials meeting the inclusion criteria and reporting death as an outcome. There were 156 deaths among 1419 trial participants. For each patient category the risk of death in the albumin treated group was higher than in the comparison group. For hypovolaemia the relative risk of death following albumin administration was 1.46 (95% confidence interval 0.97 to 2.22), for burns the relative risk was 2.40 (1.11 to 5.19), and for hypoalbuminaemia the relative risk was 1.69 (1.07 to 2.67). The pooled relative risk of death with albumin administration was 1.68 (1.26 to 2.23). Overall, the risk of death in patients receiving albumin was 14% compared to 8% in the control groups, an increase in the risk of death of 6% (3% to 9%). These data suggest that for every 17 critically ill patients treated with albumin there is one additional death. REVIEWER'S CONCLUSIONS: There is no evidence that albumin administration reduces the risk of death in critically ill patients with hypovolaemia, burns or hypoalbuminaemia, and a strong suggestion that it may increase the risk of death. These data suggest that the use of human albumin in critically ill patients should be urgently reviewed and that it should not be used outside the context of a rigorously conducted randomised controlled trial.

Blood Proteins↗

PubMed2000

Regulation of CD27 expression in the course of germinal center B cell differentiation: the pivotal role of IL-10.

The molecules of the TNF superfamily and their receptors play crucial roles in the humoral immune response. In view of the powerful effects on germinal center (GC) B cell differentiation, the expression of these molecules should be tightly regulated. In this study, we have undertaken a detailed analysis of the regulation of CD27 expression following the differentiation of GC B cells supported by a follicular dendritic cell line. We show that CD27 is differentially expressed on B cell subpopulations at different stages of differentiation. Naive B cells are virtually negative but plasma cells generated in vivo are strongly positive for CD27 expression. GC B cells that exhibit a moderate expression of CD27 remarkably up-regulate the expression levels of this molecule when they differentiate into plasma cells, which is induced by IL-10. The up-regulation of CD27 expression correlates with that of CD38. Therefore, high expression of CD27 molecules emerges as a specific marker for plasma cells. Our results suggest an important role for CD27 in the differentiation of GC B cells into plasma cells. Evaluation of CD27 expression levels may be of a clinical significance in assessment of B cell maturation in immunocompromised patients.

Animals↗

PubMed2000

A therapeutic human anti-idiotypic antibody mimics CD55 in three distinct regions.

The human anti-idiotypic antibody 105AD7 was isolated from a colorectal cancer patient receiving the anti-tumor antibody 791T/36 for radioimmuno-scintigraphy of liver metastases. We have mapped the binding site of 791T/36 to the first two small consensus repeat (SCR) domains of the complement regulatory protein (CD55) that is overexpressed by a wide range of solid tumors. Cloning of both antigen and anti-idiotype has identified the molecular basis of their mimicry. Amino acid homology has been identified between three complementarity-determining regions of 105AD7 and three regions of CD55 within the first two SCR domains. 791T/36 and anti-anti-idiotypic (Ab3) polyclonal antibodies raised against 105AD7 showed specific binding to these peptides. The antibodies were also found to bind synergistically to combinations of these peptides, indicating cooperativity between the peptides in stabilizing antibody binding. This also implies that the contact face on both CD55 antigen and 105AD7 is generated by the cooperation of several peptides positioned on two domains in each protein. Thus a human monoclonal anti-idiotypic antibody generated by a cancer patient is able to show both amino acid and structural homology with the complement regulatory protein CD55. These findings help identify the mechanism by which a human anti-idiotypic antibody is able to mimic a tumor-associated antigen and stimulate anti-tumor B and T cell responses.

Adenocarcinoma↗

PubMed2000

fMRI of visual system activation in the conscious rabbit.

A conscious rabbit preparation developed for fMRI, and the results from visual stimulation studies at a 4.7T magnetic field are described. The rabbit is ideal for these experiments because of its natural tolerance for restraint. High spatial and temporal resolution magnetic resonance images, without movement artifacts, were obtained during long periods of restraint. Functional activation in primary visual cortex and lateral geniculate nucleus (LGN) were reproducibly observed in response to light stimulus. In comparison to existing anesthetized animal models, a functional response free of the anesthetic modulation can be recorded with the new approach. The conscious animal model can be applied to functional studies of sensory systems, learning and memory, and drug-induced cerebral activation.

Animals↗

PubMed2000

Attenuation of neurodegeneration-relevant modifications of brain proteins by dietary soy.

Epidemiological studies show that postmenopausal women who undertake estrogen-replacement therapy have significantly lower risk for the onset of Alzheimer's disease (AD) than women who do not. Animal behavior studies have shown that ovariectomy results in the development of cognitive dysfunction that is prevented by estrogen-replacement, suggesting that normal mammalian cognitive function is impaired by estrogen reduction. Soy isoflavones in particular genistein have been demonstrated to have weak and selective estrogenic actions in various models of human chronic diseases. A hallmark of several human dementias including AD and fronto temporal dementia with Parkinsonism on chromosome 17 (FTDP-17) is the hyperphosphorylation of the microtubule-associated protein tau. Preliminary experiments are discussed here which show that isoflavones delivered in a soy protein matrix attenuated selected AD-relevant tau phosphorylations in a primate model of menopause. The rationale is discussed for the use of soy-based foods for protection against postmenopausal neurodegeneration.

Alzheimer Disease↗