Autolysis-mediated membrane vesicle formation in Bacillus subtilis

It is known that Bacillus subtilis releases membrane vesicles (MVs) during the SOS response, which is associated with cell lysis triggered by the PBSX prophage-encoded cell-lytic enzymes XhlAB and XlyA. In this study, we demonstrate that MVs are released under various stress conditions: sucrose fatty acid ester (SFE; surfactant) treatment, cold shock, starvation, and oxygen deficiency. B. subtilis possesses four major host-encoded cell wall-lytic enzymes (autolysins; LytC, LytD, LytE, and LytF). Deletions of the autolysin genes abolished autolysis and the consequent MV production under these stress conditions. In contrast, deletions of xhlAB and xlyA had no effect on autolysis-triggered MV biogenesis, indicating that autolysis is a novel and prophage-independent pathway for MV production in B. subtilis. Moreover, we found that the cell lysis induced by the surfactant treatment was effectively neutralized by the addition of exogenous purified MVs. This result suggests that the MVs can serve as a decoy for the cellular membrane to protect the living cells in the culture from membrane damage by the surfactant. Our results indicate a positive effect of B. subtilis MVs on cell viability and provide new insight into the biological importance of the autolysis phenomenon in B. subtilis.     

HLA-DQB1*03 Confers Susceptibility to Chronic Hepatitis C in Japanese: A Genome-Wide Association Study

Hepatitis C virus (HCV) establishes a chronic infection in 70-80% of infected individuals. Many researchers have examined the effect of human leukocyte antigen (HLA) on viral persistence because of its critical role in the immune response against exposure to HCV, but almost all studies have proven to be inconclusive. To identify genetic risk factors for chronic HCV infection, we analyzed 458,207 single nucleotide polymorphisms (SNPs) in 481 chronic HCV patients and 2,963 controls in a Japanese cohort. Next, we performed a replication study with an independent panel of 4,358 cases and 1,114 controls. We further confirmed the association in 1,379 cases and 25,817 controls. In the GWAS phase, we found 17 SNPs that showed suggestive association (P < 1 × 10^-5). After the first replication study, we found one intronic SNP in the HLA-DQ locus associated with chronic HCV infection, and when we combined the two studies, the association reached the level of genome-wide significance. In the second replication study, we again confirmed the association (P _combined = 3.59 × 10⁻¹⁶, odds ratio [OR] = 0.79). Subsequent analysis revealed another SNP, rs1130380, with a stronger association (OR=0.72). This nucleotide substitution causes an amino acid substitution (R55P) in the HLA-DQB1 protein specific to the DQB1*03 allele, which is common worldwide. In addition, we confirmed an association with the previously reported IFNL3-IFNL4 locus and propose that the effect of DQB1*03 on HCV persistence might be affected by the IFNL4 polymorphism. Our findings suggest that a common amino acid substitution in HLA-DQB1 affects susceptibility to chronic infection with HCV in the Japanese population and may not be independent of the IFNL4 genotype.     

Why do ants shift their foraging from extrafloral nectar to aphid honeydew?

When aphids parasitize plants with extrafloral nectaries (EFNs) and aphid colony size is small, ants frequently use EFNs but hardly tend aphids. However, as the aphid colony size increases, ants stop using EFNs and strengthen their associations with aphids. Although the shift in ant behavior is important for determining the dynamics of the ant–plant–aphid interaction, it is not known why this shift occurs. Here, we test two hypotheses to explain the mechanism responsible for this behavioral shift: (1) Extrafloral nectar secretion changes in response to aphid herbivory, or (2) plants do not change extrafloral nectar secretion, but the total reward to ants from aphids will exceed that from EFNs above a certain aphid colony size. To judge which mechanism is plausible, we investigated secretion patterns of extrafloral nectar produced by plants with and without aphids, compared the amount of sugar supplied by EFNs and aphids, and examined whether extrafloral nectar or honeydew was more attractive to ants. Our results show that there was no inducible extrafloral secretion in response to aphid herbivory, but the sugar concentration in extrafloral nectar was higher than in honeydew, and more ant workers were attracted to an artificial extrafloral nectar solution than to an artificial aphid honeydew solution. These results indicate that extrafloral nectar is a more attractive reward than aphid honeydew per unit volume. However, even an aphid colony containing only two individuals can supply a greater reward to ants than EFNs. This suggests that the ant behavioral shift may be explained by the second hypothesis.     

Novel mutations of CDKN1C in Japanese patients with Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is an imprinting-related human disease that is characterized by macrosomia, macroglossia, abdominal wall defects, and variable minor features. BWS is caused by several genetic/epigenetic alterations, such as loss of methylation at KvDMR1, gain of methylation at H19-DMR, paternal uniparental disomy of chromosome 11, CDKN1C mutations, and structural abnormalities of chromosome 11. CDKN1C is an imprinted gene with maternal preferential expression, encoding for a cyclin-dependent kinase (CDK) inhibitor. Mutations in CDKN1C are found in 40 % of familial BWS cases with dominant maternal transmission and in ~5 % of sporadic cases. In this study, we searched for CDKN1C mutations in 37 BWS cases that had no evidence for other alterations. We found five mutations—four novel and one known—from a total of six patients. Four were maternally inherited and one was a de novo mutation. Two frame-shift mutations and one nonsense mutation abolished the QT domain, containing a PCNA-binding domain and a nuclear localization signal. Two missense mutations occurred in the CDK inhibitory domain, diminishing its inhibitory function. The above-mentioned mutations were predicted by in silico analysis to lead to loss of function; therefore, we strongly suspect that such anomalies are causative in the etiology of BWS.     

ESA Hyporesponsiveness Is Associated with Adverse Events in Maintenance Hemodialysis (MHD) Patients,But Not with Iron Storage

Objective

It has been reported that hyporesponsiveness to erythropoiesis-stimulating agent (ESA) is associated with adverse events in patients on maintenance hemodialysis (MHD). However, it has not been determined whether higher iron storage is associated with an improved response, including better survival, to ESA.

Design and Method

We measured serum ferritin, hemoglobin (Hb), and transferrin saturation (TSAT) levels every three months for two years in 1,095 MHD patients. The weekly dose of ESA to Hb ratio was also calculated as an index of ESA responsiveness (ERI).

Results

A significant correlation (p<0.001, R = 0.89) between ferritin and Hb was only observed in the patients with ferritin levels <50 ng/mL. High-dose (≥50 mg/week) intravenous iron administration, female sex, low serum albumin, and angiotensin-converting enzyme inhibitor/angiotensin receptor blocker use were significant predictors of a high ERI value (>280); however, serum ferritin and TSAT levels did not predict a higher ERI. In the time-dependent Cox hazard model, the risk for a composite event in the patients with a high ERI (≥280) and a high ferritin level (≥100 ng/mL) was significantly greater (hazard ratio [HR], 2.09, P = 0.033) than that for patients with a high ERI and a low ferritin (<100 ng/mL) level.

Conclusion

Hb was dependent upon ferritin levels in patients with ferritin levels <50 ng/mL but not in patients with ferritin levels ≥50 ng/mL. Patients with hyporesponsiveness to ESA had a greater risk of composite events, but ERI was unrelated to iron storage.     

Transcriptional suppression of nephrin in podocytes by macrophages: roles of inflammatory cytokines and involvement of the PI3K/Akt pathway

Expression of nephrin, a crucial component of the glomerular slit diaphragm, is downregulated in patients with proteinuric glomerular diseases. Using conditionally immortalized reporter podocytes, we found that bystander macrophages as well as macrophage-derived cytokines IL-1beta and TNF-alpha markedly suppressed activity of the nephrin gene promoter in podocytes. The cytokine-initiated repression was reversible, observed on both basal and inducible expression, independent of Wilms' tumor suppressor WT1, and caused in part via activation of the phosphatidylinositol-3-kinase/Akt pathway. These results indicated a novel mechanism by which activated macrophages participate in the induction of proteinuria in glomerular diseases.     

Rapid, transient induction of ER stress in the liver and kidney after acute exposure to heavy metal: evidence from transgenic sensor mice

Endoplasmic reticulum (ER) stress-responsive alkaline phosphatase (ES-TRAP) serves as a sensitive indicator for ER stress. In response to heavy metals including cadmium, nickel and cobalt, hepatocytes and renal tubular cells expressing ES-TRAP exhibited ER stress and decreased ES-TRAP activity. In ES-TRAP transgenic mice, acute exposure to cadmium showed rapid, transient decreases in the activity of serum ES-TRAP. It was inversely correlated with the induction of endogenous ER stress markers in the liver and kidney. Our result provides first evidence for the acute, reversible induction of ER stress in vivo after exposure to heavy metal.     

Specific role of the truncated betaIV-spectrin Sigma6 in sodium channel clustering at axon initial segments and nodes of ranvier

At axon initial segments and nodes of Ranvier in neurons, the spectrin membrane skeleton plays roles in physically stabilizing the plasma membrane integrity and in clustering voltage-gated sodium channels for proper conduction of the action potential. betaIV-Spectrin, an essential component of the membrane skeleton at these sites, has an N-terminal-truncated isoform, Sigma6, which is expressed at much higher levels than the full-length isoform Sigma1. To investigate the role of betaIV-spectrin Sigma6, we generated Sigma1-deficient mice with a normal level of Sigma6 expression (Sigma1(-/-) mice), and compared their phenotypes with those of previously generated mice lacking both Sigma1 and Sigma6(Sigma1Sigma6(-/-) mice). The gross neurological defects observed in Sigma1Sigma6(-/-) mice, such as hindleg contraction, were apparently ameliorated in Sigma1(-/-) mice. At cellular levels, Sigma1Sigma6(-/-) and Sigma1(-/-) neurons similarly exhibited waving and swelling of the plasma membrane at axon initial segments and nodes of Ranvier. By contrast, the levels of ankyrin G and voltage-gated sodium channels at these sites, which are significantly reduced in Sigma1Sigma6(-/-) mice, were substantially recovered in Sigma1(-/-) mice. We conclude that the truncated betaIV-spectrin isoform Sigma6 plays a specific role in clustering voltage-gated sodium channels, whereas it is dispensable for membrane stabilization at axon initial segments and nodes of Ranvier.