Biomedical subjects

Liping Ma

Publications and source records attributed to Liping Ma.

9 recordsLinked to original sources

PubMed2006

Aluminum tolerance of two wheat cultivars (Brevor and Atlas66) in relation to their rhizosphere pH and organic acids exuded from roots.

Phytotoxicity of aluminum (Al) has become a serious problem in inhibiting plant growth on acid soils. Under Al stress, the changes of rhizosphere pH, root elongation, absorption of Al by wheat roots, organic acids exuded from roots, and some main factors related to Al-tolerant mechanisms have been studied using hydroponics, fluorescence spectrophotometry, and high performance liquid chromatography (HPLC). Two wheat cultivars, Brevor and Atlas66, differing in Al tolerance are chosen in the study. Accordingly, the rhizosphere pH has a positive effect on Al tolerance. Atlas66 (Al-tolerant) has higher capability to maintain high rhizosphere pH than Brevor (Al-sensitive) does. High pH can reduce Al3+ activity and toxicity, and increase the efficiency of exuding organic acids from the roots. More inhibition of root elongation has been found in Brevor because of the exposure of roots to Al3+ solution at low pH. Brevor accumulate more Al in roots than Atlas66 even at higher pH. Al-induced exudation of malic and citric acids has been found in Atlas66 roots, while no Al-induced organic acids have been found in Brevor. These results indicate that the Al-induced secretion of organic acids from Atlas66 roots has a positive correlation with Al tolerance. Comprehensive treatment of Al3+ and H+ indicates that wheat is adversely influenced by excess Al3+, rather than low pH.

Aluminum↗

PubMed2006

Comprehensive evaluation of solution nuclear magnetic resonance spectroscopy sample preparation for helical integral membrane proteins.

The preparation of high quality samples is a critical challenge for the structural characterization of helical integral membrane proteins. Solving the structures of this diverse class of proteins by solution nuclear magnetic resonance spectroscopy (NMR) requires that well-resolved 2D 1H/15N chemical shift correlation spectra be obtained. Acquiring these spectra demands the production of samples with high levels of purity and excellent homogeneity throughout the sample. In addition, high yields of isotopically enriched protein and efficient purification protocols are required. We describe two robust sample preparation methods for preparing high quality, homogeneous samples of helical integral membrane proteins. These sample preparation protocols have been combined with screens for detergents and sample conditions leading to the efficient production of samples suitable for solution NMR spectroscopy. We have examined 18 helical integral membrane proteins, ranging in size from approximately 9 kDa to 29 kDa with 1-4 transmembrane helices, originating from a number of bacterial and viral genomes. 2D 1H/15N chemical shift correlation spectra acquired for each protein demonstrate well-resolved resonances, and >90% detection of the predicted resonances. These results indicate that with proper sample preparation, high quality solution NMR spectra of helical integral membrane proteins can be obtained greatly enhancing the probability for structural characterization of these important proteins.

Carbon Isotopes↗

PubMed2006

Dopamine promotes the survival of embryonic striatal cells: involvement of superoxide and endogenous NADPH oxidase.

The dopaminergic system appears early in mammalian brain development, and a neurodevelopmental role for dopamine (DA) has been suggested. In the present study, we found that DA markedly promoted the survival of embryonic striatal cells in cultures. The failure of DA receptor antagonists to block this survival-promoting effect and the capability of S-apomorphine, which is devoid of DA receptor agonist activity but possesses antioxidative activity as R-apomorphine and DA, to completely mimic this effect suggested that DA receptor activation was not required in the survival-promoting effect elicited by DA, and its antioxidative activity might be involved. Moreover, it was found that mRNA of NADPH oxidase was expressed in the embryonic striatum. Furthermore, DPI or apocynin, NADPH oxidase inhibitors, promoted the survival of embryonic striatal cells. Addition of either DA or DPI into striatal cell cultures decreased the superoxide level. These results indicate that the mechanisms underlying the neuroprotective effects of DA were likely associated with its antioxidative activity. NADPH oxidase might contribute, at least in part, to ROS generation.

Animals↗

PubMed2006

Expression of trophinin and bystin identifies distinct cell types in the germinal zones of adult rat brain.

In the adult brain, the subventricular zone (SVZ) is one of the regions where active neurogenesis occurs. Relatively few specific markers are available to distinguish different types of cells in the SVZ and rostral migratory stream (RMS) of adult brain. Here, we showed that trophinin and bystin, both of which are required for early embryo implantation during development, were expressed in the SVZ and RMS of the adult rat brain, but not in the brain of embryos and early postnatal animals. Trophinin-expressing cells were immunopositive for both Ki-67 and nestin in the SVZ. Some of the trophinin-positive cells did not express either the type A cell marker polysialylated weakly adhesive form of the neural cell adhesion molecule (PSA-NCAM) or the type B cell marker glial fibrillary acidic protein (GFAP). Double-label immunohistochemistry revealed that bystin-positive cells co-expressed GFAP, Ki-67 and nestin, but not PSA-NCAM, suggesting that they are likely type B cells. Intracerebroventricular infusion of cytosine-beta-d-arabiofuranoside (Ara-C) eliminated trophinin-positive cells in the SVZ. Following its depletion, however, the remaining bystin-positive cells continued to divide and generate actively dividing trophinin-positive cells that were negative for PSA-NCAM, leading to reconstruction of SVZ network. These characteristics indicate that this subset of trophinin-positive cells in the SVZ is type C cells. Conversely in the RMS, trophinin co-localized with nestin and PSA-NCAM, suggesting that it is expressed in neuroblasts. Cultured neural precursor cells derived from the adult SVZ also expressed both trophinin and bystin. These findings provide insight into the molecular basis of adult neurogenesis in the SVZ and RMS.

Age Factors↗

PubMed2006

Fas-mediated apoptosis in cholangiocarcinoma cells is enhanced by 3,3'-diindolylmethane through inhibition of AKT signaling and FLICE-like inhibitory protein.

Stimulation of Fas-mediated apoptosis has been promoted as a potential therapy for many cancers, including cholangiocarcinoma. We have previously reported that Fas-resistant, but not Fas-sensitive, cholangiocarcinoma cells are tumorigenic in nude mice. The present studies sought to identify molecular targets that promote Fas-mediated apoptosis in cholangiocarcinoma. We found that Fas-resistant cholangiocarcinoma cells exhibited increased constitutive phosphorylation of AKT compared with Fas-sensitive cells. Increased phosphorylation of AKT was also demonstrated in human cholangiocarcinoma tumors and was evident in a mouse xenograft cholangiocarcinoma model. Furthermore, we found that 3,3'-diindolylmethane (DIM), a vegetable autolysis product, promoted Fas-mediated apoptosis of cholangiocarcinoma cells. DIM inhibited phosphorylation of AKT and activation of FLICE-like-inhibitory-protein (FLIP). Inhibition of phosphatidylinositol 3-kinase/AKT decreased FLIP activation and promoted Fas-mediated apoptosis. By contrast, adenovirus-mediated constitutively activated AKT protected cholangiocarcinoma cells from Fas-mediated apoptosis. Decreased activation of extracellular signal-regulated kinase and nuclear factor-kappaB and increased activation of caspase-3, -8, and -9 were associated with inhibition of AKT and FLIP. These results support AKT and FLIP as potential molecular targets and DIM as a potent compound for cholangiocarcinoma intervention.

Adenoviridae↗

PubMed2005

A novel dileucine lysosomal-sorting-signal mediates intracellular EGF-receptor retention independently of protein ubiquitylation.

One of the main goals of this study was to understand the relationship between an epidermal growth factor (EGF) receptor dileucine (LL)-motif (679-LL) required for lysosomal sorting and the protein ubiquitin ligase CBL. We show that receptors containing 679-AA (di-alanine) substitutions that are defective for ligand-induced degradation nevertheless bind CBL and undergo reversible protein ubiquitylation similar to wild-type receptors. We also demonstrate that 679-LL but not CBL is required for EGF receptor downregulation by an endosomal membrane protein encoded by human adenoviruses that uncouples internalization from post-endocytic sorting to lysosomes. 679-LL is necessary for endosomal retention as well as degradation by the adenovirus protein, and is also transferable to reporter molecules. Using NMR spectroscopy, we show that peptides with wild-type 679-LL or mutant 679-AA sequences both exhibit alpha-helical structural propensities but that this structure is not stable in water. A similar analysis carried out in hydrophobic media showed that the alpha-helical structure of the wild-type peptide is stabilized by specific interactions mediated by side-chains in both leucine residues. This structure distinguishes 679-LL from other dileucine-based sorting-signals with obligatory amino-terminal acidic residues that are recognized in the form of an extended beta or beta-like conformation. Taken together, these data show that 679-LL is an alpha-helical stabilizing motif that regulates a predominant step during lysosomal sorting, involving intracellular retention under both sub-saturating and saturating conditions.

Adenoviridae↗

PubMed2005

Expression of the p75 neurotrophin receptor in acute leukaemia.

The dLNGFR is a cytoplasmically deleted form of the low-affinity nerve growth factor receptor (LNGFR, also known as p75NTR). Recently, we observed a myeloid leukaemia in mice transplanted with dLNGFR-modified bone marrow cells. Retroviral-mediated expression of dLNGFR was suspected to contribute to the murine leukaemia. This led us to investigate the expression of p75NTR in human leukaemia. Expression of p75NTR was observed in nine of 119 (8%) adult patients with acute leukaemia by flow cytometry analysis, particularly in acute lymphoblastic leukaemia (26%). These results support further detailed analyses of neurotrophin receptors and downstream signalling pathways in haematological malignancies.

Adult↗

PubMed2004

Programmable polymer thin film and non-volatile memory device.

Building on the success of organic electronic devices, such as light-emitting diodes and field-effect transistors, procedures for fabricating non-volatile organic memory devices are now being explored. Here, we demonstrate a novel organic memory device fabricated by solution processing. Programmable electrical bistability was observed in a device made from a polystyrene film containing gold nanoparticles and 8-hydroxyquinoline sandwiched between two metal electrodes. The as-prepared device, which is in a low-conductivity state, displays an abrupt transition to a high-conductivity state under an external bias of 2.8 V. These two states differ in conductivity by about four orders of magnitude. Applying a negative bias of 1.8 V causes the device to return to the low-conductivity state. The electronic transition is attributed to the electric-field-induced charge transfer between the gold nanoparticles and 8-hydroxyquinoline. The transition from the low- to the high-conductivity state takes place in nanoseconds, and is non-volatile, indicating that the device may be used for low-cost, high-density memory storage.

Electric Conductivity↗

PubMed2003

Ventilation of wards and nosocomial outbreak of severe acute respiratory syndrome among healthcare workers.

OBJECTIVE: To identify valid measures for preventing outbreaks of severe acute respiratory syndrome (SARS) among protected healthcare workers in isolation units. METHODS: Architectural factors, admitted SARS cases and infection of healthcare workers in different isolation wards between January 30 and March 30, 2003 were analyzed. RESULTS: Four types of isolation wards were analyzed, including the ward where the thirty-first bed was located on the twelfth floor, the laminar flow ward in the Intensive Care Unit where the tenth bed was located on the fifteenth floor, the ward where the twenty-seventh bed was located on the thirteenth floor of the Lingnan Building, and thirty wards on the fourteenth to eighteenth floors of the Zhongshan Building. The ratios (m(2)/m(3)) of the area of the ventilation windows to the volume of the rooms were 0, 0, 1:95 and 1:40, respectively. Numbers of SARS cases in the wards mentioned above were 1, 1, 1 and 96, respectively. Total times of hospitalization were 43, 168, 110 and 1272 hours, respectively. The infection rates of the healthcare workers in the areas mentioned above were 73.2%, 32.1%, 27.5% and 1.7%, respectively. The difference in the infection rates was of statistical significance. CONCLUSIONS: Isolating SARS cases in wards with good ventilation could reduce the viral load of the ward and might be the key to preventing outbreaks of SARS among healthcare workers along with strict personal protection measures in isolation units.

Adult↗