Hepcidin protects against lipopolysaccharide-induced liver injury in a mouse model of obstructive jaundice

Obstructive jaundice (OJ) increases the risk of liver injury and sepsis, leading to increased mortality. Cholestatic liver injury is associated with a downregulation of hepcidin expression levels. In fact, hepcidin has an important antimicrobial effect, especially against Escherichia coli. It is unknown whether supplementing recombinant hepcidin is effective in alleviating cholestasis-induced liver injury and mortality in mice with superimposed sepsis. A mouse model of cholestasis was developed using extrahepatic bile duct ligation for 3 days. In addition, sepsis due to E. coli 0111:B4 lipopolysaccharide (LPS) was induced in the model. The serum levels of total bilirubin, AST, ALT, and LDH and the mRNA levels of IL-1β, TNF-α, and MCP-1 in the liver were significantly higher in the OJ mice receiving LPS than in the sham-operated mice receiving LPS. Compared to the OJ mice receiving LPS, the hepcidin-pretreated OJ mice receiving LPS showed a significant decrease in the above mentioned parameters, as well as a reversal in the downregulation of LC3B-II and upregulation of cleaved caspase-3; this, in turn, led to significantly decreased lethality in 24h. In conclusion, these results indicate that hepcidin pretreatment significantly reduced hepatic proinflammatory cytokine expression and liver injury, leading to reduced early lethality in OJ mice receiving LPS. Enhanced autophagy and reduced apoptosis may account for the protective effects of hepcidin.     

High-throughput comparison of gene fitness among related bacteria

ABSTRACT: BACKGROUND: The contribution of a gene to the fitness of a bacterium can be assayed by whether and to what degree the bacterium tolerates transposon insertions in that gene. We use this fact to compare the fitness of syntenic homologous genes among related Salmonella strains to reveal differences not apparent at the gene sequence level. RESULTS: A transposon Tn5 derivative was used to construct mutants in Salmonella Typhimurium ATCC14028 (STM1) and Salmonella Typhi Ty2 (STY1), which were then grown in rich media. The locations of 234,152 and 53,556 integration sites, respectively, were mapped by sequencing. These data were compared to similar data available for a different Ty2 strain (STY2) and essential genes identified in E. coli K-12 (ECO). Of 277 genes considered essential in ECO, all had syntenic homologs in STM1, STY1, and STY2, and all but nine genes were either devoid of Tn insertions or had very few. For three of these nine genes, part of the annotated gene lacked Tn integrations (yejM, ftsN and murB). At least one of the other six genes, trpS, had a potentially functionally redundant gene encoded elsewhere in Salmonella but not in ECO. An additional 165 genes were almost entirely devoid of transposon integrations in all three Salmonella strains examined, including many genes associated with protein and DNA synthesis. Four of these genes (STM14_1498.L, STM14_2872, STM14_3360.RJ, and STM14_5442) are not found in E. coli. Notable differences in the extent of gene selection were also observed among the three different Salmonella isolates. Mutations in hns, for example, were selected against in STM1 but not in the two STY strains, which have a defect in rpoS rendering hns nonessential. CONCLUSIONS: Comparisons among transposon integration profiles from different members of a species and among related species, all grown in similar conditions, identify differences in gene fitness among syntenic homologous genes. Further differences in fitness profiles among shared genes can be expected in other selective environments, with potential relevance for comparative systems biology.     

Nitrite oxidation in the Namibian oxygen minimum zone

Nitrite oxidation is the second step of nitrification. It is the primary source of oceanic nitrate, the predominant form of bioavailable nitrogen in the ocean. Despite its obvious importance, nitrite oxidation has rarely been investigated in marine settings. We determined nitrite oxidation rates directly in ¹⁵N-incubation experiments and compared the rates with those of nitrate reduction to nitrite, ammonia oxidation, anammox, denitrification, as well as dissimilatory nitrate/nitrite reduction to ammonium in the Namibian oxygen minimum zone (OMZ). Nitrite oxidation (⩽372 nM NO₂⁻ d⁻¹) was detected throughout the OMZ even when in situ oxygen concentrations were low to non-detectable. Nitrite oxidation rates often exceeded ammonia oxidation rates, whereas nitrate reduction served as an alternative and significant source of nitrite. Nitrite oxidation and anammox co-occurred in these oxygen-deficient waters, suggesting that nitrite-oxidizing bacteria (NOB) likely compete with anammox bacteria for nitrite when substrate availability became low. Among all of the known NOB genera targeted via catalyzed reporter deposition fluorescence in situ hybridization, only Nitrospina and Nitrococcus were detectable in the Namibian OMZ samples investigated. These NOB were abundant throughout the OMZ and contributed up to ∼9% of total microbial community. Our combined results reveal that a considerable fraction of the recently recycled nitrogen or reduced NO₃⁻ was re-oxidized back to NO₃⁻ via nitrite oxidation, instead of being lost from the system through the anammox or denitrification pathways.     

The sushi domains of secreted GABA(B1) isoforms selectively impair GABA(B) heteroreceptor function

GABA(B) receptors are the G-protein-coupled receptors for gamma-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the brain. GABA(B) receptors are promising drug targets for a wide spectrum of psychiatric and neurological disorders. Receptor subtypes exhibit no pharmacological differences and are based on the subunit isoforms GABA(B1a) and GABA(B1b). GABA(B1a) differs from GABA(B1b) in its ectodomain by the presence of a pair of conserved protein binding motifs, the sushi domains (SDs). Previous work showed that selectively GABA(B1a) contributes to heteroreceptors at glutamatergic terminals, whereas both GABA(B1a) and GABA(B1b) contribute to autoreceptors at GABAergic terminals or to postsynaptic receptors. Here, we describe GABA(B1j), a secreted GABA(B1) isoform comprising the two SDs. We show that the two SDs, when expressed as a soluble protein, bind to neuronal membranes with low nanomolar affinity. Soluble SD protein, when added at nanomolar concentrations to dissociated hippocampal neurons or to acute hippocampal slices, impairs the inhibitory effect of GABA(B) heteroreceptors on evoked and spontaneous glutamate release. In contrast, soluble SD protein neither impairs the activity of GABA(B) autoreceptors nor impairs the activity of postsynaptic GABA(B) receptors. We propose that soluble SD protein scavenges an extracellular binding partner that retains GABA(B1a)-containing heteroreceptors in proximity of the presynaptic release machinery. Soluble GABA(B1) isoforms like GABA(B1j) may therefore act as dominant-negative inhibitors of heteroreceptors and control the level of GABA(B)-mediated inhibition at glutamatergic terminals. Of importance for drug discovery, our data also demonstrate that it is possible to selectively impair GABA(B) heteroreceptors by targeting their SDs.     

Cholangiocyte expression of alpha2beta1-integrin confers susceptibility to rotavirus-induced experimental biliary atresia

Inoculation of BALB/c mice with rhesus rotavirus (RRV) in the newborn period results in biliary epithelial cell (cholangiocyte) infection and the murine model of biliary atresia. Rotavirus infection of a cell requires attachment, which is governed in part by cell-surface expression of integrins such as alpha2beta1. We hypothesized that cholangiocytes were susceptible to RRV infection because they express alpha2beta1. RRV attachment and replication was measured in cell lines derived from cholangiocytes and hepatocytes. Flow cytometry was performed on these cell lines to determine whether alpha2beta1 was present. Cholangiocytes were blocked with natural ligands, a monoclonal antibody, or small interfering RNA against the alpha2-subunit and were infected with RRV. The extrahepatic biliary tract of newborn mice was screened for the expression of the alpha2beta1-integrin. Newborn mice were pretreated with a monoclonal antibody against the alpha2-subunit and were inoculated with RRV. RRV attached and replicated significantly better in cholangiocytes than in hepatocytes. Cholangiocytes, but not hepatocytes, expressed alpha2beta1 in vitro and in vivo. Blocking assays led to a significant reduction in attachment and yield of virus in RRV-infected cholangiocytes. Pretreatment of newborn pups with an anti-alpha2 monoclonal antibody reduced the ability of RRV to cause biliary atresia in mice. Cell-surface expression of the alpha2beta1-integrin plays a role in the mechanism that confers cholangiocyte susceptibility to RRV infection.     

松墨天牛成虫头部感受器超微结构的观察

扫描电镜观察表明 ,松墨天牛MonochamusalternatusHope成虫头部存在 1 1种感受器。触角有 8种 ,下颚须和下唇须有 6种。栓锥感受器Ⅰ型、毛形感受器Ⅰ型及刺形感受器为触角、下颚须和下唇须共有。触角特有栓锥感受器Ⅱ型、毛形感受器Ⅱ型、锥形感受器以及柱形感受器Ⅰ型和Ⅱ型。下颚须及下唇须特有钟形感受器、坛形感受器和板形感受器。松墨天牛成虫触角感受器在种类、数量和分布上存在性别差异 ,雌雄虫的下颚须和下唇须感受器数量有所不同。