尼群地平对实验性糖尿病大鼠心肌收缩性的影响

腹腔注射链脲佐霉素（６５ｍｇ／ｋｇ）诱发Ｗｉｓｔａｒ大鼠糖尿病。糖尿病发病４周后,向饲料中加尼群地平（３０ｍｇ·ｋｇ－１·ｄ－１）。结果表明,糖尿病４周时大鼠心室舒张功能首先受损,８周后心室舒张和收缩功能均明显受累。尼群地平处理对糖尿病大鼠的心肌收缩性有一定的改善作用。提示尼群地平对大鼠糖尿病性心肌病有一定有益作用。     

The quorum-sensing system in a plant bacterium Mesorhizobium huakuii affects growth rate and symbiotic nodulation

Mesorhizobium huakuii is a free-living bacterium which is capable of establishing a specific symbiotic relationship with Astragalus sinicus, an important winter green manure widely used in Eastern Asia, allowing for nitrogen fixing during this process. Previous studies demonstrate that M.␣huakuii produces quorum-sensing molecules at high cell density and quorum sensing plays a role in biofilm formations. In this study, we isolated and characterized two quorum-sensing deficient mutants in M. huakuii. Analysis of the flanking region of transposon insertions indicated that autoinducer synthase related genes are not homologous to acyl homoserine lactone (AHL) synthase genes that are shared among many Gram-negative bacteria, but related to peptide synthesis, indicating that M. huakuii quorum-sensing signals are distinct from AHLs. Compared with the wild-type strains, these quorum-sensing deficient mutants promoted their growth rate and were defective in nodule formation on host plants, indicative of a critical role of quorum sensing in M.␣huakuii during the host–bacterium symbiotic interaction.Yijing Gao and Zengtao Zhong contributed equally to this work.     

Isolation and characterization of a bacterial strain of the genus Ochrobactrum with methyl parathion mineralizing activity

AIMS: To isolate and characterize a methyl parathion (MP)-mineralizing bacterium, and to elucidate the degradative pathway of MP and localize the responsible degrading genes. METHODS AND RESULTS: A bacterial strain, designated B2, capable of mineralizing MP was isolated from the MP-polluted soil. Analysis of the 16S rRNA gene sequence and phenotypic analysis suggested that strain B2 had a close relationship with Ochrobactrum anthropi. B2 could totally degrade MP and four metabolites [p-nitrophenol (PNP), 4-nitrocatechol (4-NC), 1,2,4-benzenetriol (BT) and hydroquinone (HQ)] were identified by HPLC and gas chromatography-mass spectrometry analyses. Plasmid curing of strain B2 resulted in the loss of ability of B2 to degrade PNP, but not the ability to hydrolyse MP. CONCLUSIONS: Ochrobactrum sp. B2 can mineralize MP rapidly via PNP, 4-NC, BT and HQ pathway. B2 harbours a plasmid encoding the ability to degrade PNP, while MP-hydrolysing activity is encoded on the bacterial chromosome. SIGNIFICANCE AND IMPACT OF THE STUDY: This new bacterial strain (B2) capable of mineralizing MP will be useful in a pure-culture remediation process of organophosphate pesticides and their metabolites such as nitroaromatics.     

Nutritional Energy Stimulates NAD+ Production to Promote Tankyrase-Mediated PARsylation in Insulinoma Cells

The poly-ADP-ribosylation (PARsylation) activity of tankyrase (TNKS) regulates diverse physiological processes including energy metabolism and wnt/β-catenin signaling. This TNKS activity uses NAD⁺ as a co-substrate to post-translationally modify various acceptor proteins including TNKS itself. PARsylation by TNKS often tags the acceptors for ubiquitination and proteasomal degradation. Whether this TNKS activity is regulated by physiological changes in NAD⁺ levels or, more broadly, in cellular energy charge has not been investigated. Because the NAD⁺ biosynthetic enzyme nicotinamide phosphoribosyltransferase (NAMPT) in vitro is robustly potentiated by ATP, we hypothesized that nutritional energy might stimulate cellular NAMPT to produce NAD⁺ and thereby augment TNKS catalysis. Using insulin-secreting cells as a model, we showed that glucose indeed stimulates the autoPARsylation of TNKS and consequently its turnover by the ubiquitin-proteasomal system. This glucose effect on TNKS is mediated primarily by NAD⁺ since it is mirrored by the NAD⁺ precursor nicotinamide mononucleotide (NMN), and is blunted by the NAMPT inhibitor FK866. The TNKS-destabilizing effect of glucose is shared by other metabolic fuels including pyruvate and amino acids. NAD⁺ flux analysis showed that glucose and nutrients, by increasing ATP, stimulate NAMPT-mediated NAD⁺ production to expand NAD⁺ stores. Collectively our data uncover a metabolic pathway whereby nutritional energy augments NAD⁺ production to drive the PARsylating activity of TNKS, leading to autoPARsylation-dependent degradation of the TNKS protein. The modulation of TNKS catalytic activity and protein abundance by cellular energy charge could potentially impose a nutritional control on the many processes that TNKS regulates through PARsylation. More broadly, the stimulation of NAD⁺ production by ATP suggests that nutritional energy may enhance the functions of other NAD⁺-driven enzymes including sirtuins.     

Overexpression of Smad7 suppressed ROS/MMP9-dependent collagen synthesis through regulation of heme oxygenase-1

We previously reported that AngiotensinII receptor blocker effectively inhibited TGF-β1-mediated epithelial-to-mesenchymal transition progress through regulating Smad7. However, the underlying mechanism by which Smad7 exerted in regulating MMP9 and fibrogenic response has not been fully elucidated. In the current study, we proved that NADPH p47^phox-dependent reactive oxygen species (ROS) production contributed to MMP9 activation and collagen expression, which was suppressed by transfecting pcDNA3–Smad7 in cardiac fibroblasts. The effect of Smad7 overexpression on MMP9 activity and collagen expression was further reversed by adding H₂O₂ (10 μmol/L). In contrast, knockdown of Smad7 caused the enhanced collagen synthesis in cardiac fibroblasts, which was also reversed by treating cells with a ROS inhibitor, YCG063 (2 μmol/L). Further investigation showed that Smad7 regulated NADPH-mediated ROS production through activating Heme oxygenase-1 (HO-1). Meanwhile, the intercellular level of bilirubin (product of hemin) and nitric oxide (NO) in cell supernatant were not significantly increased in cells treated with AngII or transfected with Smad7. Knockdown of HO-1 in Smad7-overexpressed cardiac fibroblasts or cells pretreated with SnPP IX, a competitive inhibitor of HO-1 activity, resulted in increased productions of ROS and NADPH p47^phox, and abolished the inhibitory effects of Smad7 on MMP9 activity and collagen expression. Our results indicated that HO-1 might be critically involved in Smad7-mediated regulation of MMP9 activity and fibrogenic genes expression via antagonizing the enhanced myocardial oxidative stress.     

Modulate the phase transition temperature of hydrogels with both thermosensitivity and biodegradability

The synthesis and characterization of thermoresponsive hydrogels on the basis of N-isoproplyarylamide (NIPAAm) and acrylamide (AAm) copolymers crosslinked with a novel biodegradable crosslinker (PEG-co-PLA) were carried out in this study. Swelling measurement results demonstrated that four gels of PNAM5, PNAM10, PNAM12 and PNAM15 are thermoresponsive. The equilibrium swelling ratio and degradation of the hydrogels strongly depend on hydrogels composition. The morphology of the hydrogels was observed by scanning electron microscopy (SEM), and their thermal property was characterized by differential scanning calorimetry (DSC). The results show that the proportion of AAm in the copolymer has notable effect on the low critical solution temperature (LCST) of the hydrogel. When the molar ratio of AAm to NIPAAm was increased from 1:10 to 3:10 the LCST of the copolymer increased from 39.7 to 64.2 °C. The compression modulus of PNAM15 is of the highest among other hydrogels, because PNAM15 hydrogel has a more compact structure.