Adipose-specific deletion of autophagy-related gene 7 (atg7) in mice reveals a role in adipogenesis.

White adipocytes have a unique structure in which nearly the entire cell volume is occupied by one large lipid droplet. However, the molecular and cellular processes involved in the cytoplasmic remodeling necessary to create this structure are poorly defined. Autophagy is a membrane trafficking process leading to lysosomal degradation. Here, we investigated the effect of the deletion of an essential autophagy gene, autophagy-related gene 7 (atg7), on adipogenesis. A mouse model with a targeted deletion of atg7 in adipose tissue was generated. The mutant mice were slim and contained only 20% of the mass of white adipose tissue (WAT) found in wild-type mice. Interestingly, approximately 50% of the mutant white adipocytes were multilocular. The mutant white adipocytes were smaller with a larger volume of cytosol and contained more mitochondria. These cells exhibited altered fatty acid metabolism with increased rates of beta-oxidation and reduced rates of hormone-induced lipolysis. Consistently, the mutant mice had lower fed plasma concentrations of fatty acids and the levels decreased at faster rates upon insulin stimuli. These mutant mice exhibited increased insulin sensitivity. The mutant mice also exhibited markedly decreased plasma concentrations of leptin but not adiponectin, lower plasma concentrations of triglyceride and cholesterol, and they had higher levels of basal physical activity. Strikingly, these mutant mice were resistant to high-fat-diet-induced obesity. Taken together, our results indicate that atg7, and by inference autophagy, plays an important role in normal adipogenesis and that inhibition of autophagy by disrupting the atg7 gene has a unique anti-obesity and insulin sensitization effect.

N-Glycosylation-dependent block is a novel mechanism for drug-induced cardiac arrhythmia.

Voltage-gated potassium channels formed with the cardiac subunit HERG and a polymorphic variant of MinK-related peptide 1 (MiRP1) exhibit increased susceptibility to the antibiotic sulfamethoxazole (SMX) compared with channels formed with wild-type (WT) subunits. Here the molecular bases for SMX high-affinity block are investigated. The polymorphism causes a benign T to A amino acid mutation at position 8 (T8A) that destroys an N-glycosylation site of MiRP1. In vitro disruption of glycosylation by mutagenesis or in vivo by treatment with neuraminidase is associated with increased susceptibility to SMX and to other elementary agents such as divalent cations. Defective glycosylation does not affect the ability of T8A to form stable complexes with HERG, but rather it increases drug susceptibility through structural modifications in the channel complex. We conclude that N-glycosylation may play a key role in the etiology of life-threatening arrhythmia.

Targeted deletion of autophagy-related 5 (atg5) impairs adipogenesis in a cellular model and in mice.

Mammalian white adipocytes have a unique structure in which nearly the entire cell volume is occupied by a single large lipid droplet, while the surrounding cytoplasm occupies minimal space. The massive cytoplasmic remodeling processes involved in the formation of this unique cellular structure are poorly defined. Autophagy is a membrane trafficking process leading to lysosomal degradation of cytoplasmic components. Here, we investigated the functional role of atg5, a gene encoding an essential protein required for autophagy, in adipocyte differentiation in a cellular model and in mice. Massive autophagy was activated when wild-type primary mouse embryonic fibroblasts (MEFs) were induced for adipocyte differentiation. Importantly, the autophagy deficient primary atg5(-/-) MEFs exhibited dramatically reduced efficiency in adipogenesis. Time-lapse microscopy revealed that atg5(-/-) MEFs initially appeared to differentiate normally; however, a majority of the differentiating atg5(-/-) cells ultimately failed to undergo further morphological transformation and eventually died, likely through apoptosis. Consistent with these in vitro results, histological analysis revealed that the atg5(-/-) late-stage embryos and neonatal pups had much less subcutaneous perilipin A-positive adipocytes. Consistently, when treated with chloroquine, a functional inhibitor of autophagy, wild-type MEFs exhibited drastically reduced efficiency of adipocyte differentiation. Taken together, these findings demonstrated that Atg5 is involved in normal adipocyte differentiation, suggesting an important role of autophagy in adipogenesis.