Normal thyroid thermogenesis but reduced viability and adiposity in mice lacking the mitochondrial glycerol phosphate dehydrogenase

The mitochondrial glycerol phosphate dehydrogenase (mGPD) is important for metabolism of glycerol phosphate for gluconeogenesis or energy production and has been implicated in thermogenesis induced by cold and thyroid hormone treatment. mGPD in combination with the cytosolic glycerol phosphate dehydrogenase (cGPD) is proposed to form the glycerol phosphate shuttle, catalyzing the interconversion of dihydroxyacetone phosphate and glycerol phosphate with net oxidation of cytosolic NADH. We made a targeted deletion in Gdm1 and produced mice lacking mGPD. On a C57BL/6J background these mice showed a 50% reduction in viability compared with wild-type littermates. Uncoupling protein-1 mRNA levels in brown adipose tissue did not differ between mGPD knockout and control pups, suggesting normal thermogenesis. Pups lacking mGPD had decreased liver ATP and slightly increased liver glycerol phosphate. In contrast, liver and muscle metabolites were normal in adult animals. Adult mGPD knockout animals had a normal cold tolerance, normal circadian rhythm in body temperature, and demonstrated a normal temperature increase in response to thyroid hormone. However, they were found to have a lower body mass index, a 40% reduction in the weight of white adipose tissue, and a slightly lower fasting blood glucose than controls. The phenotype may be secondary to consequences of the obligatory production of cytosolic NADH from glycerol metabolism in the mGPD knockout animal. We conclude that, although mGPD is not essential for thyroid thermogenesis, variations in its function affect viability and adiposity in mice.     

Mechanism of insulin resistance in A-ZIP/F-1 fatless mice

Insulin resistance is a major factor in the pathogenesis of type 2 diabetes and may be related to alterations in fat metabolism. Fatless mice have been created using dominant-negative protein (A-ZIP/F-1) targeted gene expression in the adipocyte and shown to develop diabetes. To understand the mechanism responsible for the insulin resistance in these mice, we conducted hyperinsulinemic-euglycemic clamps in awake fatless and wild type littermates before the development of diabetes and examined insulin action and signaling in muscle and liver. We found the fatless mice to be severely insulin-resistant, which could be attributed to defects in insulin action in muscle and liver. Both of these abnormalities were associated with defects in insulin activation of insulin receptor substrate-1 and -2-associated phosphatidylinositol 3-kinase activity and a 2-fold increase in muscle and liver triglyceride content. We also show that upon transplantation of fat tissue into these mice, triglyceride content in muscle and liver returned to normal as does insulin signaling and action. In conclusion, these results suggest that the development of insulin resistance in type 2 diabetes may be due to alterations in the partitioning of fat between the adipocyte and muscle/liver leading to accumulation of triglyceride in the latter tissues with subsequent impairment of insulin signaling and action.     

The design and synthesis of potent, selective benzodiazepine sulfonamide bombesin receptor subtype 3 (BRS-3) agonists with an increased barrier of atropisomerization

Bombesin receptor subtype 3 (BRS-3) is an orphan G-protein coupled receptor expressed primarily in the hypothalamus which plays a role in the onset of both diabetes and obesity. We report herein our progress made towards identifying a potent, selective bombesin receptor subtype-3 (BRS-3) agonist related to the previously described MK-7725(1) Chobanian et al. (2012) that would prevent atropisomerization through the increase of steric bulk at the C-2 position. This would thereby make clinical development of this class of compounds more cost effective by inhibiting racemization which can occur over long periods of time at room/elevated temperature.     

A guide to analysis of mouse energy metabolism

We present a consolidated view of the complexity and challenges of designing studies for measurement of energy metabolism in mouse models, including a practical guide to the assessment of energy expenditure, energy intake and body composition and statistical analysis thereof. We hope this guide will facilitate comparisons across studies and minimize spurious interpretations of data. We recommend that division of energy expenditure data by either body weight or lean body weight and that presentation of group effects as histograms should be replaced by plotting individual data and analyzing both group and body-composition effects using analysis of covariance (ANCOVA).     

PHOSPHONOACETATE DERIVATIVES OF OLIGODEOXYRIBONUCLEOTIDES

Abstract

A deoxyribodinucleotide phosphonoacetate derivative has been prepared, separated into individual diastereomers, and incorporated into oligodeoxyribonucleotides possessing alternating phosphodiester and phosphonoacetate backbone linkages. The hybridization properties and enzymatic stabilities of these oligonucleotides have been studied.     

Growth of Venezuelan Equine Encephalomyelitis Virus in Human Diploid Cell Strain WI-38

We demonstrated that Venezuelan equine encephalomyelitis (VEE) virus replicated in and adapted rapidly to human diploid cell strain WI-38. Peak titers of approximately 10(9.8) mouse intracerebral 50% lethal doses were obtained at low passage levels in Eagles basal medium supplemented with calf serum. VEE virus replicated poorly in serum-free medium. Propagation of VEE virus was accompanied by the production of hemagglutinin and cytopathogenic effects.     

Nifedipine loaded chitosan microspheres: characterization of internal structure

In the present investigation, a simple technique was employed to obtain cross-sections of unloaded and nifedipine loaded chitosan microspheres. Microspheres, adhering to a polymerized resin block, were cut with an ultramicrotome and viewed with a scanning electron microscope. Unloaded microspheres exhibited a uniform dense matrix structure while crystals of nifedipine were clearly visible in the drug-loaded microspheres. At 2% drug loading, however, no crystals could be seen in the microspheres indicating that either the drug was molecularly dispersed or dissolved in the matrix at this concentration. This was confirmed by powder X-ray diffractometry studies where no peak due to crystalline nifedipine was observed. At high Span 85 concentration (1.5% w/v), the external surface of the microspheres collapsed, but the internal structure remained dense. When the drug was dispersed in the chitosan solution with stirring during preparation, the entrapment was good and the shape of the crystals was changed. The internal structure of the microspheres following dissolution exhibited the presence of pores.     

The fat and thin of lipin

Mutations in the Lpin1 gene (encoding lipin) cause the lipodystrophy (adipose tissue deficiency) of the fld mouse, but the underlying mechanism has been unclear. In this issue of Cell Metabolism, Phan and Reue (2005) show that overexpression of lipin in either muscle or adipose tissue increases adiposity. Interestingly, mice overexpressing lipin in muscle are insulin resistant, while those overexpressing lipin in adipose tissue are insulin sensitive.     

Melanin in <Emphasis Type="Italic">Fonsecaea pedrosoi</Emphasis>: a trap for oxidative radicals

Background  

The pathogenic fungus Fonsecaea pedrosoi constitutively produces the pigment melanin, an important virulence factor in fungi. Melanin is incorporated in the cell wall structure and provides chemical and physical protection for the fungus.