Differential Response of Obese Gene Expression from Fasting in Bovine Adipose Tissues

To understand the molecular mechanism for intramuscular fat deposition, the expression of the obese gene was examined in response to fasting. Food deprivation for 48 h induced a decrease in the level of obese mRNA in pooled adipose tissues (abdominal, perirenal, subcutaneous, intermuscular and intramuscular). The expression of obese mRNA was examined for individual adipose tissue from several fat depots. It was highly expressed in perirenal adipose tissue, but fasting did not affect its expression level in this tissue. Moderate levels were detected in subcutaneous and intermuscular adipose tissues, and a fasting-induced decrease in obese mRNA was apparent in these tissues. The expression level of the obese gene in intramuscular adipose tissue was very low and did not respond to fasting.     

Differential response of obese gene expression from fasting in bovine adipose tissues

To understand the molecular mechanism for intramuscular fat deposition, the expression of the obese gene was examined in response to fasting. Food deprivation for 48 h induced a decrease in the level of obese mRNA in pooled adipose tissues (abdominal, perirenal, subcutaneous, intermuscular and intramuscular). The expression of obese mRNA was examined for individual adipose tissue from several fat depots. It was highly expressed in perirenal adipose tissue, but fasting did not affect its expression level in this tissue. Moderate levels were detected in subcutaneous and intermuscular adipose tissues, and a fasting-induced decrease in obese mRNA was apparent in these tissues. The expression level of the obese gene in intramuscular adipose tissue was very low and did not respond to fasting.     

Nutritional regulation of adipose tissue apolipoprotein E expression

Apolipoprotein E (apoE) is a multifunctional protein that is highly expressed in human and murine adipose tissue. Endogenous adipocyte apoE expression influences adipocyte triglyceride turnover and modulates the expression of genes involved in lipid synthesis and oxidation. We now demonstrate the regulation of adipose tissue apoE expression by nutritional status in lean and obese mice. Obesity induced by high-fat diet, or by hyperphagia in ob/ob mice, produces significant reduction of adipose tissue apoE expression at the protein and messenger RNA level. Fasting in C57BL/6J mice for 24 h significantly increased apoE protein and messenger RNA levels. In ob/ob mice, transplantation of adipose tissue from lean littermate controls to restore circulating leptin levels produced significant weight loss over 12 wk and also produced an increase in adipose tissue apoE expression. The increase in adipose tissue apoE expression in this model, however, did not require leptin. Adipose tissue apoE was also significantly increased in ob/ob mice after a 48-h fast or after 7 days of caloric restriction. In summary, obesity suppresses adipose tissue apoE expression, whereas fasting or weight loss increases it. From our previous observations, these changes in adipose tissue apoE expression will have significant impact on adipose tissue lipid flux and lipoprotein metabolism. Furthermore, these results suggest adipose tissue apoE participates in defending adipose tissue and organismal energy homeostasis in response to nutritional perturbation.     

Adipose tissue regeneration in 6-month-old and adult rabbits following lipectomy

The effects of surgical ablation of adipose tissue were studied in male New Zealand rabbits. They were lipectomized or sham-operated either at 6 or 12 months, ages at which size and number of adipocytes are, respectively, stabilized in this species. The lipectomized animals were subjected to removal of about 80% of the perirenal and omental and to the totality of the dorsoscapular and inguinal fat tissues. Approximately 35 and 48% of the total body fat were, thus, surgically removed, respectively, in 6- and 12-month-old rabbits. All rabbits were killed 3 months after surgery and were carefully dissected. There was no significant difference in food consumption and body weight gain between lipectomized and sham-operated rabbits. Surgical removal of dorsoscapular, inguinal, and omental fat did not lead to regeneration whereas regeneration of the perirenal fat was substantial. At sacrifice the perirenal weight reached approximately 55% of the initial weight. Regeneration of perirenal adipose tissue in adults proceeded at roughly the same rate as after lipectomy in younger rabbits. These results suggest that adipose tissue regeneration in the rabbit is site dependent.     

Hormonal control of net glucose-stimulated lipogenesis during transition from brown to white adipose tissue in the goat

Perinatal (1-2 days of age) and one-month-old (24-32 days of age) male goats were used to investigate the effect of age and long-term culture (24 h) of perirenal and omental adipose explants in the presence of insulin, cortisol and bovine somatotropin (alone or in different combinations) on net glucose-stimulated lipogenesis (NGSL, i.e. the rate of lipogenesis in the presence of glucose minus the rate of lipogenesis in the absence of glucose) in the absence and in the presence of catecholamines in acute incubations (2 h). Mean values of NGSL in both freshly prepared and cultured explants were consistently lower in perinatal than in one-month-old goats. Cortisol alone decreased and combinations of insulin plus cortisol increased NGSL in perirenal explants of one-month-old animals. When perirenal explants from these one-month-old goats were cultured in the presence of insulin plus cortisol plus bovine somatotropin, the rates of lipogenesis were lower than those in cultures with insulin plus cortisol. No such effects of these hormones were noted in omental explants of both perinatal and one-month-old animals. In freshly prepared perirenal and omental explants, the rates of NGSL were inhibited by isoprenaline in tissues of both groups of animals and by noradrenaline in omental tissues of animals of the older group only. The mean values of NGSL in cultured explants of perinatal animals were not affected by noradrenaline. Isoprenaline inhibited NGSL in omental but not in perirenal tissue. In older animals the rates of NGSL were decreased by both noradrenaline and isoprenaline in perirenal and omental adipose tissues. Isoprenaline was more effective than noradrenaline in perirenal adipose tissue.     

Molecular characterization of lipoprotein lipase, hepatic lipase and pancreatic lipase genes: effects of fasting and refeeding on their gene expression in red sea bream Pagrus major

To investigate the nutritional regulation of lipid metabolism in fish, molecular characterization of lipases was conducted in red sea bream Pagrus major, and the effects of fasting and refeeding on their gene expression was examined. Together with data from a previous study, a total of four lipase genes were identified and characterized as lipoprotein lipase (LPL), hepatic lipase (HL) and pancreatic lipase (PL). These four lipase genes, termed LPL1, LPL2, HL and PL, share a high degree of similarity. LPL1 and LPL2 genes were expressed in various tissues including adipose tissue, gill, heart and hepatopancreas. HL gene was exclusively expressed in hepatopancreas. PL gene expression was detected in hepatopancreas and adipose tissue. Red sea bream LPL1 and LPL2 gene expression levels in hepatopancreas were increased during 48 h of fasting and decreased after refeeding, whereas no significant change in the expression levels of LPL1 and LPL2 was observed in adipose tissue, indicating that LPL1 and LPL2 gene expression is regulated in a tissue-specific manner in response to the nutritional state of fish. HL and PL gene expression was not affected by fasting and refeeding. The results of this study suggested that LPL, HL and PL gene expression is under different regulatory mechanisms in red sea bream with respect to the tissue-specificities and their nutritional regulation.     

Expression of Class III facilitative glucose transporter genes (GLUT-10 and GLUT-12) in mouse and human adipose tissues

We have examined whether GLUT-10 and GLUT-12, members of the Class III group of the recently expanded family of facilitative glucose transporters, are expressed in adipose tissues. The mouse GLUT-12 gene, located on chromosome 10, comprises at least five exons and encodes a 622 amino acid protein exhibiting 83% sequence identity and 91% sequence similarity to human GLUT-12. Expression of the GLUT-12 gene was evident in all the major mouse adipose tissue depots (epididymal, perirenal, mesenteric, omental, and subcutaneous white; interscapular brown). The GLUT-10 gene is also expressed in mouse adipose tissues and as with GLUT-12 expression occurred in the mature adipocytes as well as the stromal vascular cells. 3T3-L1 adipocytes express GLUT-10, but not GLUT-12, and expression of GLUT-12 was not induced by insulin or glucose. Both GLUT-10 and GLUT-12 expression was also found in human adipose tissue (subcutaneous and omental) and SGBS adipocytes. It is concluded that white fat expresses a wide range of facilitative glucose transporters.     

Resistin concentrations in murine adipose tissue and serum measured by a new enzyme immunoassay

Objective: In an attempt to clarify the conflicting data on resistin mRNA expression and protein analysis by western blotting in adipose tissue and serum, we developed a sensitive enzyme‐linked immunosorbent assay (ELISA) for direct measurement of mouse resistin. Research Methods and Procedures: We developed polyclonal antibodies directed to the N (21 to 40) and C (79 to 91) termini of mouse resistin. Then, affinity‐purified anti‐C‐terminal resistin immunoglobin G (IgG) was biotinylated. ELISA was based on the sandwiching of antigen between antibody IgG coated on polystyrene plates and biotinylated antibody IgG. The bound biotinylated antibody was quantified with streptavidin‐linked horseradish peroxidase. Results: New ELISA can measure a concentration as low as 0.5 ng/mL of recombinant mouse resistin and is sensitive and specific enough to measure resistin protein in various adipose tissues and in sera. In normal mice, decreases in resistin concentrations in both white adipose tissue and serum were age dependent during 6 to 24 weeks of development. Resistin concentrations were significantly higher in omental adipose tissue in comparison with perirenal and abdominal adipose tissues and were 2‐ to 5‐fold higher in females than males during the growth period. ob/ob mice had significantly lower resistin concentrations than the control mice in both sera and the white adipose tissues, particularly in the omental fat. The treatment by testosterone, but not progesterone or β‐estradiol, in cultured adipocytes reduces resistin protein levels in a dose‐dependent manner. Discussion: New sensitive ELISA for mouse resistin clarified that the resistin concentrations in normal mice were markedly elevated in the omental adipose depots as compared with the perirenal and abdominal adipocyte depots and significantly elevated compared with adipose tissues in genetically obese mice.     

Sex-dependent effects of neonatal maternal deprivation on endocannabinoid levels in the adipose tissue: influence of diet

Maternal deprivation (MD) during neonatal life has diverse long-term effects, including modification of metabolism. We have previously reported that MD modifies the metabolic response to high-fat diet (HFD) intake, with this response being different between males and females, while previous studies indicate that in mice with HFD-induced obesity, endocannabinoid (EC) levels are markedly altered in various brown and white adipose tissue depots. Here, we analyzed the effects of MD (24 h at postnatal day 9), alone or in combination with a HFD from weaning until the end of the experiment in Wistar rats of both sexes. Brown and white perirenal and subcutaneous adipose tissues were collected and the levels of anandamide (AEA), 2-arachidonoylglycerol (2-AG), palmitoylethanolamide (PEA), and oleoylethanolamide (OEA) were determined. In males, MD increased the content of OEA in brown and 2-AG in subcutaneous adipose tissues, while in females the content of 2-AG was increased in perirenal fat. Moreover, in females, MD decreased AEA and OEA levels in perirenal and subcutaneous adipose tissues, respectively. HFD decreased the content of 2-AG in brown fat of both sexes and OEA in brown and subcutaneous adipose tissue of control females. In contrast, in subcutaneous fat, HFD increased AEA levels in MD males and OEA levels in control and MD males. The present results show for the first time that MD and HFD induce sex-dependent effects on the main ECs, AEA, and 2-AG, and of AEA-related mediators, OEA and PEA, in the rat brown and white (visceral and subcutaneous) adipose tissues.     

Ketone body synthesis from leucine by adipose tissue from different sites in the rat

Leucine is catabolized to ketone bodies in adipose tissue, but the contribution of this output to overall ketone metabolism is not known. The intent of the present study was to determine the capacity of different adipose tissues to synthesize ketone bodies from leucine. The amino acid was readily converted into acetoacetate in epididymal, perirenal, and omental fat tissues. In rats fed ad libitum, the rate of acetoacetate synthesis in omental fat (about 2 mumol g tissue-1h-1) was at least 8 times higher than in epididymal or perirenal fat. In omental fat, the rates of acetoacetate formation from alpha-ketoisocaproic acid were 47-55% lower than from leucine at all concentrations examined. There was no significant synthesis of beta-hydroxybutyrate from leucine or alpha-ketoisocaproic acid. After oxidative decarboxylation, a greater proportion (about three-fourths) of leucine in omental fat was metabolized to acetoacetate than to CO2 production through the Krebs cycle. Although addition of glucose, pyruvate, or carnitine did not affect the production of acetoacetate, fasting for 24 h stimulated acetoacetate synthesis from leucine and alpha-ketoisocaproic acid in omental fat. The high rate of leucine conversion to acetoacetate in omental fat was related to high activities of leucine aminotransferase and branched-chain alpha-keto acid dehydrogenase. Moreover, protein content and cytochrome c oxidase activity of omental mitochondria were, respectively, 13 and 12 times higher than in epididymal mitochondria. In contrast, fat content of epididymal adipose tissue was 21 times that of omental adipose tissue. Epididymal depot consisted of 2.0% protein and 75.8% fat, whereas omental depot contains 17.2% protein and 3.6% fat, resembling that of liver and muscle. The results suggest that the high ketogenic capacity of omental fat stems in part from an augmented mitochondrial mass and high activity of branched-chain alpha-keto acid dehydrogenase.     

Response of leptin mRNA to 24-h food deprivation and refeeding is influenced by age in rats

To obtain an insight into the influence of aging on leptin gene expression, the responses of leptin mRNA in retroperitoneal and epididymal adipose tissues and plasma leptin concentrations to 24-h food deprivation and refeeding were examined in 2-, 10- and 24-month-old normal rats. The basal level of leptin gene expression in retroperitoneal adipose tissue was significantly higher in 10- and 24-month-old rats than that in 2-month-old rats, while the level in epididymal adipose tissue was highest in 10-month-old rats for all three age groups. The basal concentrations of plasma leptin was significantly higher in 10- and 24-month-old rats than those in 2-month-old rats. The 24-h food deprivation was followed by a significant reduction in leptin mRNA expression in both retorperitoneal and epididymal adipose tissues for all three age groups. The leptin gene expression was restored to control levels 24 h following refeeding in the 2- and 10-month-old rats, but failed to be restored in the 24-month-old rats. In addition, the time course of recovery for leptin mRNA expression by refeeding to the control levels differed between the retroperitoneal and the epididymal adipose tissue in 2- and 10-month-old rats. The concentrations of plasma leptin 24 h following refeeding were compatible with the leptin mRNA levels in adipose tissues in three age groups. These results suggest that the expression of the leptin gene in response to food-deprivation and refeeding is influenced by an animal's age and that this expression is different for different regions of white adipose tissue.     

Insulin regulates hepatic leptin receptor expression in early lactating dairy cows

Energy balance controls the expression of the leptin receptor (Lepr) in the ruminant hypothalamus but whether similar regulation occurs in peripheral tissues is unknown. To address this issue, we measured Lepr expression in the liver and adipose tissue of dairy cows during the transition from late pregnancy (LP) to early lactation (EL). This period is characterized by the development of a profound state of energy insufficiency and is associated with reduced plasma insulin and leptin and with increased plasma growth hormone. Hepatic expression of the short (Lepr-a) and long (Lepr-b) isoforms was 40% higher during EL (8 days postpartum) than LP (30 days prepartum). A similar effect was observed when negative energy balance was induced in nonpregnant, late-lactation dairy cows by food restriction, implicating energy insufficiency as a specific cause in EL. The stimulation of hepatic Lepr expression was reversed after a 48-h period of hyperinsulinemic euglycemia in EL. Changes in hepatic Lepr expression during chronic elevation of plasma leptin in EL or plasma growth hormone in nonpregnant, late-lactation cows did not support a role for these hormones in mediating the effects of energy insufficiency on hepatic Lepr expression. In adipose tissue, Lepr expression was increased 10-fold during the transition from LP to EL. Overall, these data indicate that hypoinsulinemia is partly responsible for the induction of Lepr expression in the liver, and perhaps adipose tissue, of energy-deficient dairy cows.     

In vivo development of adipose tissue following implantation of lipid-depleted cultured adipocyte

The monolayer culture of isolated and disaggregated adipocytes from rat omental and perirenal sites, gave rise to a population of fibroblast-like cells, usually devoid of lipid inclusion. Similar fibroblast-like cells have been obtained in cultures of adipose tissue stromal cells and are thought to be undifferentiated adipocyte stem cells. Although the adipocyte-derived fibroblasts were morphologically indistinguishable from culture-derived fibroblasts of other origins, upon autoimplantation into the splenic bed they regained the lipid inclusion and developed again into adipose tissue. The findings suggest that the transformation of adipose cells into fibroblast-like cells is reversible modulation and not a dedifferentiation into the adipose tissue stem cell. This work also substantiates the increasingly recognized heterogeneity of fibroblasts.     

FGF21 mediates the lipid metabolism response to amino acid starvation

Lipogenic gene expression in liver is repressed in mice upon leucine deprivation. The hormone fibroblast growth factor 21 (FGF21), which is critical to the adaptive metabolic response to starvation, is also induced under amino acid deprivation. Upon leucine deprivation, we found that FGF21 is needed to repress expression of lipogenic genes in liver and white adipose tissue, and stimulate phosphorylation of hormone-sensitive lipase in white adipose tissue. The increased expression of Ucp1 in brown adipose tissue under these circumstances is also impaired in FGF21-deficient mice. Our results demonstrate the important role of FGF21 in the regulation of lipid metabolism during amino acid starvation.     

Distribution and quantification of β-3 adrenergic receptor in tissues of sheep

The β-3 adrenergic receptor (ADRB3) is a G-protein coupled receptor involved in regulating lipolysis, as part of homeostatic regulation. In this study, South African Mutton Merino and Shanxi Dam Line were used to study the distribution and quantification of ADRB3 in adipose (subcutaneous, omental, retroperitoneal, mesenteric and perirenal fat) and non-adipose (heart, liver, spleen, lung and kidney) tissues of sheep. The protein was determined by immunohistochemical technique and by mRNA abundance via real-time polymerase chain reaction. ADRB3 was detected in all studied tissues with abundance in adipose tissues higher than in non-adipose tissues (P < 0.001). For adipose tissues, greater expression was found in deep deposits such as great omental and retroperitoneal fat than in subcutaneous fat (P < 0.05). Significant differences (P < 0.05) both for mRNA and for protein expression also existed between the two sheep flocks. These findings are consistent with the known function of ADRB3 in mediating lipolysis and homeostasis in adipose tissues.