Early atherogenesis and visceral fat in obese adolescents.

BACKGROUND/OBJECTIVES: Little information is available as to the cause of increased thickening of the intima-media of the carotid artery (cIMT) in the pediatric population. Therefore, cIMT was compared in obese adolescents and normal-weight controls, and associations between cIMT and lipid and non-lipid cardiovascular risk factors were assessed. SUBJECTS/METHODS: Subjects included 61 obese non-diabetic male and female volunteers aged 12-18 years inclusive with a body mass index (BMI) >95th percentile for age and 2-h blood glucose <200 mg dl(-1) matched to 25 normal-weight control volunteers with normal glucose levels. Each subject underwent a 2-h glucose tolerance test and measurement of hemoglobin A1c, ultrasensitive C-reactive protein, fasting insulin, blood lipids, visceral, subcutaneous abdominal and hepatic fat, and cIMT. RESULTS: Maximum cIMT was 0.647±0.075 mm in the obese subjects versus 0.579±0.027 mm in normal-weight controls (P<0.001). There was no difference in maximum cIMT between male and female subjects. There were significant correlations between maximum cIMT and BMI z-score, 2-h glucose, fasting insulin, homeostasis model assessment (HOMA), total low-density lipoprotein (LDL) cholesterol, very LDL cholesterol, high-density lipoprotein (HDL) cholesterol, HDL2 cholesterol, HDL3 cholesterol, triglycerides, remnant lipoprotein cholesterol, intermediate-density lipoprotein cholesterol, lipoprotein(a), apoprotein B100, abdominal subcutaneous fat volume, visceral fat volume and hepatic phase difference. On multiple regression analysis, visceral fat was the most significant predictor of maximum cIMT. Two-hour blood glucose, HOMA and systolic blood pressure were also significant predictors of maximum cIMT. CONCLUSIONS: cIMT was increased in the obese adolescents compared with the normal-weight-matched controls. Visceral fat was a key predictor of arterial wall thickening in these subjects. The results suggest that the focus of cardiovascular disease prevention in the adolescent obese should be visceral obesity, and not blood lipids or lipid subclasses.

Mechanism of mammalian mitochondrial DNA replication: import of mitochondrial transcription factor A into isolated mitochondria stimulates 7S DNA synthesis.

The light strand promoter of mammalian mitochondrial DNA gives rise to a primary transcript, but also to the RNA primer necessary for initiation of replication and 7S DNA synthesis as well as 7S RNA. Here we have studied the turnover of 7S DNA in isolated rat liver mitochondria and whether import of mitochondrial transcription factor A (mtTFA), which is necessary for transcription initiation, increases its rate of synthesis. 7S DNA was present as two species, probably due to two different sites of RNA-DNA transition. Time course and pulse-chase experiments showed that the half-life of this DNA is approximately 45 min. Import of mtTFA, produced in vitro, into the mitochondrial matrix in stoichiometric amounts significantly increased the rate of 7S DNA formation. We conclude that isolated rat liver mitochondria faithfully synthesize and degrade 7S DNA and that increased matrix levels of mtTFA are sufficient to increase its rate of synthesis, strongly supporting the hypothesis that this process is transcription primed.

Assembly and clustering of acetylcholine receptors containing GFP-tagged epsilon or gamma subunits: selective targeting to the neuromuscular junction in vivo.

Acetylcholine receptor (AChR) gamma and epsilon subunits were tagged by green fluorescent protein (GFP) to analyse assembly and targeting in live muscle fibers at the neuromuscular junction. N- or C-terminal fusion polypeptides showed no fluorescence upon transfection of HEK cells. When GFP was inserted into the cytoplasmic loop connecting putative transmembrane regions M3 and M4, the gamma/GFP and epsilon/GFP subunits were fluorescent and formed together with the alpha, beta, and delta subunits GFP-tagged AChR complexes that were integrated into the plasma membrane. As the AChR were also clustered by rapsyn, the results indicate that the cytoplasmatic domains of the gamma and epsilon subunits may not be required for assembly and rapsyn-dependent clustering. The gamma/GFP and epsilon/GFP subunit-containing receptors were expressed in X. laevis oocytes and have affinities for acetylcholine similar to that of the wild-type receptors. Direct gene transfer into single muscle fibers reveals that gamma/GFP or epsilon/GFP polypeptides are expressed at the site of injection and are transported within the endoplasmatic reticulum. When reaching subsynaptic regions, both gamma/GFP or epsilon/GFP subunits compete with endogenous epsilon subunits to assemble GFP-tagged receptors, which are selectively targeted to the postsynaptic membrane.