The effects of weight cycling on lifespan in male C57BL/6J mice.

OBJECTIVE: With the increasing rates of obesity, many people diet in an attempt to lose weight. As weight loss is seldom maintained in a single effort, weight cycling is a common occurrence. Unfortunately, reports from clinical studies that have attempted to determine the effect of weight cycling on mortality are in disagreement, and to date, no controlled animal study has been performed to assess the impact of weight cycling on longevity. Therefore, our objective was to determine whether weight cycling altered lifespan in mice that experienced repeated weight gain and weight loss throughout their lives. METHODS: Male C57BL/6J mice were placed on one of three lifelong diets: a low-fat (LF) diet, a high-fat (HF) diet or a cycled diet in which the mice alternated between 4 weeks on the LF diet and 4 weeks on the HF diet. Body weight, body composition, several blood parameters and lifespan were assessed. RESULTS: Cycling between the HF and LF diet resulted in large fluctuations in body weight and fat mass. These gains and losses corresponded to significant increases and decreases, respectively, in leptin, resistin, GIP, IGF-1, glucose, insulin and glucose tolerance. Surprisingly, weight cycled mice had no significant difference in lifespan (801±45 days) as compared to LF-fed controls (828±74 days), despite being overweight and eating a HF diet for half of their lives. In contrast, the HF-fed group experienced a significant decrease in lifespan (544±73 days) compared with LF-fed controls and cycled mice. CONCLUSIONS: This is the first controlled mouse study to demonstrate the effect of lifelong weight cycling on longevity. The act of repeatedly gaining and losing weight, in itself, did not decrease lifespan and was more beneficial than remaining obese.

Growth hormone improves body composition, fasting blood glucose, glucose tolerance and liver triacylglycerol in a mouse model of diet-induced obesity and type 2 diabetes.

AIMS/HYPOTHESIS: Growth hormone has been used experimentally in two studies to treat individuals with type 2 diabetes, with both reporting beneficial effects on glucose metabolism. However, concerns over potential diabetogenic actions of growth hormone complicate its anticipated use to treat type 2 diabetes. Thus, an animal model of type 2 diabetes could help evaluate the effects of growth hormone for treating this condition. METHODS: Male C57BL/6J mice were placed on a high-fat diet to induce obesity and type 2 diabetes. Starting at 16 weeks of age, mice were treated once daily for 6 weeks with one of four different doses of growth hormone. Body weight, body composition, fasting blood glucose, insulin, glucose tolerance, liver triacylglycerol, tissue weights and blood chemistries were determined. RESULTS: Body composition measurements revealed a dose-dependent decrease in fat and an increase in lean mass. Analysis of fat loss by depot revealed that subcutaneous and mesenteric fat was the most sensitive to growth hormone treatment. In addition, growth hormone treatment resulted in improvement in glucose metabolism, with the highest dose normalising glucose, glucose tolerance and liver triacylglycerol. In contrast, insulin levels were not altered by the treatment, nor did organ weights change. However, fasting plasma leptin and resistin were significantly decreased after growth hormone treatment. CONCLUSIONS/INTERPRETATION: Growth hormone therapy improves glucose metabolism in this mouse model of obesity and type 2 diabetes, providing a means to explore the molecular mechanism(s) of this treatment.

Oligomeric structure of hepatic lipase: evidence from a novel epitope tag technique.

The subunit structure of purified rHL (rHL) was determined by gel filtration chromatography, density gradient ultracentrifugation studies and a novel approach using epitope-tagged rHL. By gel filtration studies, native rHL had an apparent molecular weight of 179 kDa whereas enzyme treated with 6 M guanidine hydrochloride (GuHCl) for 22 h at room temperature gave a protein peak at 76 kDa. Using milder conditions for denaturation of rHL, such as 1 M GuHCl for 2 h, rHL eluted in two distinct peaks, one at 179 kDa and the other at 76 kDa. In addition, both protein peaks produced under mild denaturing conditions possessed detectable catalytic activity. Consistent with studies on lipoprotein lipase, the denatured rHL eluted from heparin-Sepharose at a lower salt concentration of 0.42 M NaCl than the native rHL which eluted at 0.72 M NaCl. By density gradient ultracentrifugation studies, the estimated molecular weight of native rHL was determined to be 113 kDa. Together, the data suggest that native rHL exists as a dimer that can be denatured into monomers by GuHCl and that a fraction of the denatured enzyme has detectable enzyme activity. To confirm these results, we designed two different rHL constructs that were epitope-tagged with either the myc or flag epitope and transfected them into 293 cells. The addition of the tag was shown not to alter enzyme secretion rate or specific activity of the lipase. Partially purified lipase from media of cotransfected cells was used to establish a dimer assay which employed a sandwich ELISA. This assay firmly established the presence of a rHL species which contained both the myc and flag tags, supporting an oligomeric subunit structure for rHL. Furthermore, the data using the epitope-tagged enzyme shows that this method could be a useful tool not only in identifying the region of the lipase responsible for dimer formation but also to study other protein-protein interactions.

Chronic changes in peripheral growth hormone levels do not affect ghrelin stomach mRNA expression and serum ghrelin levels in three transgenic mouse models.

Ghrelin is an endogenous ligand for the growth hormone secretagogue (GHS) receptor. Ghrelin is involved in feeding behaviour and is a potent stimulator of GH release. Chronically increased GH concentrations are known to negatively regulate the pituitary GHS receptor. This study tested whether chronic changes in peripheral GH levels/action affect ghrelin mRNA expression and circulating concentrations of ghrelin. Stomach ghrelin mRNA expression and serum concentrations of ghrelin were measured in three groups of transgenic mice and the respective control animals: group 1, GH-receptor gene disrupted mice (GHR/KO); group 2, mice expressing bovine GH (bGH); and group 3, mice expressing GH-antagonist (GHA). Ghrelin mRNA expression in the stomach, pituitary and hypothalamus of young adult male rats were measured using reverse-transcription-polymerase chain reaction. Ghrelin mRNA expression levels were approximately 3000-fold higher in rat stomach than in rat pituitary. Ghrelin mRNA expression in rat hypothalamus was below the detection limits of our assay. Stomach ghrelin mRNA expression, as well as serum concentrations of ghrelin, did not change significantly in any of the three mouse groups compared to the respective control group. These data support previous observations that the stomach is the main source of circulating ghrelin, and also indicate that stomach ghrelin mRNA expression and serum concentrations of ghrelin are not affected by chronic changes in peripheral GH/insulin-like growth factor-I levels/action.

[Anatomical heterogeneity in the proteome of human subcutaneous adipose tissue]. / El proteoma del tejido adiposo subcutáneo muestra heterogeneidad anatómica.

BACKGROUND: Human subcutaneous (SQ) white adipose tissue (WAT) can vary according to its anatomical location, with subsequent differences in its proteomic profile. PATIENTS AND METHODS: SQ-WAT aspirates were obtained from six overweight (BMI>25kg/m(2)) women who underwent extensive liposuction. SQ-WAT was removed from six different locations (upper abdominal, lower abdominal, thigh, back, flank, and hip), and the protein profiles were determined by two-dimensional gel electrophoresis. In addition, the proteomic profiles of upper abdominal and hip SQ-WAT were subjected to further analysis, comparing samples obtained from two layers of WAT (deep and superficial). RESULTS: Twenty one protein spots showed differential intensities among the six defined anatomical locations, and 14 between the superficial and the deep layer. Among the proteins identified were, vimentin (structural protein), heat-shock proteins (HSPs), superoxide-dismutase (stress-resistance/chaperones), fatty-acid-binding protein (FABP) 4, and alpha-enolase (lipid and carbohydrate metabolism), and ATP-synthase (energy production). Among the WAT samples analyzed, the back sub-depot showed significant differences in the levels of selected proteins when compared to the other locations, with lower level of expression of several proteins involved in energy production and metabolism (ATP-synthase, alpha-enolase, HSPs and FABP-4). CONCLUSIONS: The levels of several proteins in human SQ-WAT are not homogeneous between different WAT depots. These changes suggest the existence of inherent functional differences in subcutaneous fat depending upon its anatomical location. Thus, caution must be used when extrapolating data from one subcutaneous WAT region to other depots.

The use of proteomics to study infectious diseases.

Technology surrounding genomics, or the study of an organism's genome and its gene use, has advanced rapidly resulting in an abundance of readily available genomic data. Although genomics is extremely valuable, proteins are ultimately responsible for controlling most aspects of cellular function. The field of proteomics, or the study of the full array of proteins produced by an organism, has become the premier arena for the identification and characterization of proteins. Yet the task of characterizing a proteomic profile is more complex, in part because many unique proteins can be produced by the same gene product and because proteins have more diverse chemical structures making sequencing and identification more difficult. Proteomic profiles of a particular organism, tissue or cell are influenced by a variety of environmental stimuli, including those brought on by infectious disease. The intent of this review is to highlight applications of proteomics used in the study of pathogenesis, etiology and pathology of infectious disorders. While many infectious agents have been the target of proteomic studies, this review will focus on those infectious diseases which rank among the highest in worldwide mortalities, such as HIV/AIDS, tuberculosis, malaria, measles, and hepatitis.

Heparan sulfate proteoglycans are primarily responsible for the maintenance of enzyme activity, binding, and degradation of lipoprotein lipase in Chinese hamster ovary cells.

Various aspects of lipoprotein lipase (LPL) metabolism, including cell surface binding, degradation, and enzymatic activity, were compared between Chinese hamster ovary (CHO) cells and two distinct proteoglycan-deficient CHO cell lines. The contribution of low density lipoprotein receptor-related protein in binding LPL was also analyzed by the use of a 39-kDa receptor-associated protein expressed as a glutathione S-transferase fusion protein (GST-RAP). Equilibrium binding data with 125I-LPL revealed the presence of a class of high affinity binding sites with a KD of 7.8 nM in CHO cells, whereas no high affinity binding was observed for proteoglycan-deficient cells. The high affinity binding of LPL in CHO cells appeared to be concentrated in cell surface projections and was not effectively inhibited by GST-RAP. Moreover, degradation of endogenous and exogenous LPL was significantly greater in control CHO cells than in proteoglycan-deficient cells. Degradation of LPL in CHO cells was not affected by GST-RAP, suggesting that proteoglycans and not low density lipoprotein receptor-related protein are responsible for the majority of binding and degradation of LPL in these cells. Our data also show that proteoglycan binding is not essential for the assembly of active LPL homodimers, although proteoglycan binding controls the distribution of LPL activity. Furthermore, LPL produced by CHO cells was more stable than LPL produced by proteoglycan-deficient cells.

Genetics and molecular biology of hepatic lipase.

Hepatic lipase is emerging as a major factor in the control of HDL metabolism. Hepatic lipase plays a central role in the hydrolysis of HDL2 triglycerides and phospholipids and in the concomitant apolipoprotein A-I efflux from this density class. New data suggest that allelic variation at the hepatic lipase gene locus accounts for 25% of the total variability in HDL cholesterol. Recent information suggests that this lipase may enhance the uptake of lipoproteins by cell surface receptors.

Site-directed mutagenesis of a putative heparin binding domain of avian lipoprotein lipase.

Lipoprotein lipase (LPL) binds to heparin and heparan sulfate proteoglycans. We have employed site-directed mutagenesis to dissect one of the proposed heparin binding domains of avian LPL, which contains the sequence Arg-Lys-Asn-Arg (amino acids 281-284). Various single, double, and triple mutants of chicken LPL were constructed in order to alter the positive charge of this region. The mutant and wild-type cDNAs were subcloned into an expression vector, pRc/CMV, and expressed in Chinese hamster ovary cells. In general, the LPL mutants with a decrease in regional positive charge showed a decrease in affinity for heparin and heparan sulfate proteoglycans. The greatest effect was seen with the triple mutant, LPL 5G, in which all of the positively charged amino acids were altered to neutral residues. On a heparin-Sepharose column, LPL 5G eluted at 0.96 M NaCl compared with 1.35 M for wild-type LPL. This mutant also had the lowest specific activity with 1.5 mu eq fatty acid/micrograms/h for the cell-associated pool and with no detectable activity in the media. Wild-type cells, however, produced a lipase with a specific activity of 12.4 and 13.1 mu eq fatty acid/micrograms/h for cell-associated and media lipase pools, respectively. LPL 5G also showed a decrease in affinity for the heparan sulfate proteoglycans on the cell surface of Chinese hamster ovary cells. In conclusion, the region of avian LPL between Arg281 and Arg284 does appear to be involved in heparin-binding; however, additional regions must be involved since binding was not completely abolished. In addition, specific activity of the cell-associated and secreted LPL is correlated to affinity of the enzyme for heparan sulfate chains.

Binding of hepatic lipase to heparin. Identification of specific heparin-binding residues in two distinct positive charge clusters.

The interaction of hepatic lipase (HL) with heparan sulfate is critical to the function of this enzyme. The primary amino acid sequence of HL was compared to that of lipoprotein lipase (LPL), a related enzyme that possesses several putative heparin-binding domains. Of the three putative heparin-binding clusters of LPL (J. Biol. Chem. 1994. 269: 4626-4633; J. Lipid Res. 1998. 39: 1310-1315), one was conserved in HL (Cluster 1; residues Lys 297-Arg 300 in rat HL) and two were partially conserved (Cluster 2; residues Asp 307-Phe 320, and Cluster 4; residues Lys 337, and Thr 432-Arg 443). Mutants of HL were generated in which potential heparin-binding residues within Clusters 1 and 4 were changed to Asn. Two chimeras in which the LPL heparin-binding sequences of Clusters 2 and 4 were substituted for the analogous HL sequences were also constructed. These mutants were expressed in Chinese hamster ovary (CHO) cells and assayed for heparin-binding ability using heparin-Sepharose chromatography and a CHO cell-binding assay. The results suggest that residues within the homologous Cluster 1 region (Lys 297, Lys 298, and Arg 300), as well as some residues in the partially conserved Cluster 4 region (Lys 337, Lys 436, and Arg 443), are involved in the heparin binding of hepatic lipase. In the cell-binding assay, heparan sulfate-binding affinity equal to that of LPL was seen for the RHL chimera mutant that possessed the Cluster 4 sequence of LPL. Mutation of Cluster 1 residues of HL resulted in a major reduction in heparin binding ability as seen in both the cell-binding assay and the heparin-Sepharose elution profile. These results suggest that Cluster 1, the N-terminal heparin-binding domain, is of primary significance in RHL. This is different for LPL: mutations in the C-terminal binding domain (Cluster 4) cause a more significant shift in the salt required for elution from heparin-Sepharose than mutations in the N-terminal domain (Cluster 1).