Homeostatic generation of reactive oxygen species protects the zebrafish liver from steatosis.

UNLABELLED: Nonalcoholic fatty liver disease is the most common liver disease in both adults and children. The earliest stage of this disease is hepatic steatosis, in which triglycerides are deposited as cytoplasmic lipid droplets in hepatocytes. Through a forward genetic approach in zebrafish, we found that guanosine monophosphate (GMP) synthetase mutant larvae develop hepatic steatosis. We further demonstrate that activity of the small GTPase Rac1 and Rac1-mediated production of reactive oxygen species (ROS) are down-regulated in GMP synthetase mutant larvae. Inhibition of Rac1 activity or ROS production in wild-type larvae by small molecule inhibitors was sufficient to induce hepatic steatosis. More conclusively, treating larvae with hydrogen peroxide, a diffusible ROS that has been implicated as a signaling molecule, alleviated hepatic steatosis in both GMP synthetase mutant and Rac1 inhibitor-treated larvae, indicating that homeostatic production of ROS is required to prevent hepatic steatosis. We further found that ROS positively regulate the expression of the triglyceride hydrolase gene, which is responsible for the mobilization of stored triglycerides in hepatocytes. Consistently, inhibition of triglyceride hydrolase activity in wild-type larvae by a small molecule inhibitor was sufficient to induce hepatic steatosis. CONCLUSION: De novo GMP synthesis influences the activation of the small GTPase Rac1, which controls hepatic lipid dynamics through ROS-mediated regulation of triglyceride hydrolase expression in hepatocytes.

Mutation of zebrafish Snapc4 is associated with loss of the intrahepatic biliary network.

Biliary epithelial cells line the intrahepatic biliary network, a complex three-dimensional network of conduits. The loss of differentiated biliary epithelial cells is the primary cause of many congenital liver diseases. We identified a zebrafish snapc4 (small nuclear RNA-activating complex polypeptide 4) mutant in which biliary epithelial cells initially differentiate but subsequently disappear. In these snapc4 mutant larvae, biliary epithelial cells undergo apoptosis, leading to degeneration of the intrahepatic biliary network. Consequently, in snapc4 mutant larvae, biliary transport of ingested fluorescent lipids to the gallbladder is blocked. Snapc4 is the largest subunit of a protein complex that regulates small nuclear RNA (snRNA) transcription. The snapc4(s445) mutation causes a truncation of the C-terminus, thereby deleting the domain responsible for a specific interaction with Snapc2, a vertebrate specific subunit of the SNAP complex. This mutation leads to a hypomorphic phenotype, as only a subset of snRNA transcripts are quantitatively altered in snapc4(s445) mutant larvae. snapc2 knockdown also disrupts the intrahepatic biliary network in a similar fashion as in snapc4(s445) mutant larvae. These data indicate that the physical interaction between Snapc2 and Snapc4 is important for the expression of a subset of snRNAs and biliary epithelial cell survival in zebrafish.

Impact of vancomycin-resistant enterococcal bacteremia on outcome during acute myeloid leukemia induction therapy.

This study aimed to identify the rate and impact of vancomycin-resistant enterococcal (VRE) bacteremia in patients with acute myeloid leukemia (AML) receiving induction chemotherapy (IC). Thirty-seven (10.6%) of 350 patients had VRE bacteremia during IC, with increasing rates of VRE bacteremia over the course of the study period. The overall complete remission (CR) rate for the cohort was 73%, and there was no difference in CR rate between the VRE bacteremia and non-VRE bacteremia cohorts (70% vs. 73%, p = 0.70). Unadjusted median overall survival (OS) was 12.8 months, and differed significantly between those with and without VRE bacteremia (7.1 months vs. 13.1 months, respectively; p = 0.03). The presence of VRE bacteremia during IC for AML was independently associated with increased all-cause mortality (hazard ratio 1.72, 95% confidence interval 1.13-2.63, p = 0.01).