Sequential changes in the expression of genes involved in lipid metabolism in adipose tissue and liver in response to fasting

Fasting/refeeding: an experimental model to study the impact of early thermal manipulation on hepatic metabolism in mule ducks

An increase in egg incubation temperature was previously shown to enhance the metabolism of mule ducks and increase liver fattening after overfeeding, through a metabolic programming mechanism. Here, we examined whether fasting (F) followed by refeeding (RF) in 11-wk-old mule ducks could become an accelerated model to study the mechanisms of metabolic programming following embryonic thermal manipulation. This study investigated the hepatic response of mule ducks subjected to 23 h of fasting and 1 h of refeeding, in control or thermally programmed animals (with an increase of 1°C, 16 h per day from days 13 to 27 of embryogenesis). Liver weight and energy composition, hepatocyte structure, plasma parameters, and gene expression levels were measured at 1, 2, and 4 h after RF. All these parameters were strongly affected by RF, whereas significant impacts of embryonic programming were measured in cell size (+1 µm on average), lipid composition (+4.2% of saturated fatty acids 4 h after the meal), and relative gene expressions (including HK1, SCD1, ELOVL6, and FASN). In addition to confirming previously identified molecular targets of thermal manipulation, this study revealed new ones, thanks to kinetic sampling after RF. Finally, the detailed description of the impact of the F/RF challenge on the liver structure, composition, and gene expression, but also on plasma parameters allowed us to draw a parallel with these same traits measured during overfeeding. This comparative analysis suggests that this protocol could become a pertinent model to study the mechanisms involved in embryonic liver thermal programming, without overfeeding.

Chronic high-fat feeding and prolonged fasting in liver-specific ANGPTL4 knockout mice

Obesity is associated with dyslipidemia, ectopic lipid deposition, and insulin resistance. In mice, the global or adipose-specific loss of function of the protein angiopoietin-like 4 (ANGPTL4) leads to decreased plasma triglyceride levels, enhanced adipose triglyceride uptake, and protection from high-fat diet (HFD)-induced glucose intolerance. ANGPTL4 is also expressed highly in the liver, but the role of liver-derived ANGPTL4 is unclear. The goal of this study was to determine the contribution of hepatocyte ANGPTL4 to triglyceride and glucose homeostasis in mice during a high-fat diet challenge. We generated hepatocyte-specific ANGPTL4 deficient (Angptl4^LivKO) mice, fed them a 60% kcal/fat diet (HFD) for 6 mo and assessed triglyceride, liver, and glucose metabolic phenotypes. We also explored the effects of prolonged fasting on Angptl4^LivKO mice. The loss of hepatocyte-derived ANGPTL4 led to no major changes in triglyceride partitioning or lipoprotein lipase activity compared with control mice. Interestingly, although there was no difference in fasting plasma triglyceride levels after a 6 h fast, after an 18-h fast, normal chow diet-fed Angptl4^LivKO mice had lower triglyceride levels than control mice. On a HFD, Angptl4^LivKO mice initially showed no difference in glucose tolerance and insulin sensitivity, but improved glucose tolerance emerged in these mice after 6 mo on HFD. Our data suggest that hepatocyte ANGPTL4 does not directly regulate triglyceride partitioning, but that loss of liver-derived ANGPTL4 may be protective from HFD-induced glucose intolerance and influence plasma triglyceride (TG) metabolism during prolonged fasting.NEW & NOTEWORTHY1) Angiopoietin-like 4 deficiency in hepatocytes (Angptl4^LivKO) does not improve triglyceride phenotypes during high-fat feeding. 2) Angptl4^LivKO mice have improved glucose tolerance after chronic high-fat diet. 3) Angptl4^LivKO mice have decreased fasting plasma triglyceride levels after an 18-h fast, but not after a 6-h fast.

Peroxisomes as cellular adaptors to metabolic and environmental stress

Peroxisomes are involved in multiple metabolic processes, including fatty acid oxidation, ether lipid synthesis, and reactive oxygen species (ROS) metabolism. Recent studies suggest that peroxisomes are critical mediators of cellular responses to various forms of stress, including oxidative stress, hypoxia, starvation, cold exposure, and noise. As dynamic organelles, peroxisomes can modulate their proliferation, morphology, and movement within cells, and engage in crosstalk with other organelles in response to external cues. Although peroxisome-derived hydrogen peroxide has a key role in cellular signaling related to stress, emerging studies suggest that other products of peroxisomal metabolism, such as acetyl-CoA and ether lipids, are also important for metabolic adaptation to stress. Here, we review molecular mechanisms through which peroxisomes regulate metabolic and environmental stress.

Lampaya Medicinalis Phil. decreases lipid-induced triglyceride accumulation and proinflammatory markers in human hepatocytes and fat body of Drosophila melanogaster

BACKGROUND

Excess hepatic triglyceride (TG) accumulation (steatosis) commonly observed in obesity, may lead to non-alcoholic fatty liver disease (NAFLD). Altered regulation of intracellular lipid droplets (LD) and TG metabolism, as well as activation of JNK-mediated proinflammatory pathways may trigger liver steatosis-related disorders. Drosophila melanogaster is an animal model used for studying obesity and its associated disorders. In Drosophila, lipids and glycogen are stored in the fat body (FB), which resembles mammalian adipose tissue and liver. Dietary oversupply leads to obesity-related disorders, which are characterized by FB dysfunction. Infusions of Lampaya medicinalis Phil. (Verbenaceae) are used in folk medicine of Chile to counteract inflammatory diseases. Hydroethanolic extract of lampaya (HEL) contains considerable amounts of flavonoids that may explain its anti-inflammatory effect.

METHODS

We studied whether HEL affects palmitic acid (PA, C16:0) and oleic acid (OA; C18:1)-induced TG accumulation and proinflammatory marker content in HepG2 hepatocytes as well as impaired lipid storage and proinflammatory molecule expression in Drosophila melanogaster fed a high-fat diet (HFD).

RESULTS

In HepG2 hepatocytes, exposure to OA/PA elevated TG content, FABP4, ATGL and DGAT2 expression, and the JNK proinflammatory pathway, as well as TNF-α and IL-6 production, while diminished FAS expression. These effects were prevented by HEL co-treatment. In Drosophila larvae fed a HFD, HEL prevented TG accumulation and downregulated proinflammatory JNK pathway activation.

CONCLUSION

HEL effect counteracting OA/PA- and HFD-induced lipid accumulation and proinflammatory marker expression in HepG2 hepatocytes and Drosophila larvae may represent a preventive approach against hepatic steatosis and inflammation, associated to obesity and NAFLD.

Effects of dietary conjugated linoleic acid on metabolic status, BW and expression of genes related to lipid metabolism in adipose tissue of dairy cows during peripartum

Conjugated linoleic acid (CLA) dietary supplementation reduces milk fat content and yield, but its effects on lipid metabolism and energy status remain controversial. The objective of this study was to investigate the effects of dietary CLA on adipose tissue (AT) mRNA abundance of genes related to lipid metabolism, plasma indicators of metabolic status, body condition score (BCS) and BW changes in dairy cows. Sixteen multiparous Holstein cows (3.2 ± 1.4 lactations, 615 ± 15 kg BW) were randomly assigned to treatments: 1) CLA; rumen-protected CLA (75 g/d) or 2) Control; equivalent amount of rumen inert fatty acid (FA) as the previous diet (78 g/d), from -20.2 ± 3.2 (mean ± SEM) to 21d relative to calving (d 0). Subcutaneous AT was biopsied from the tail-head region at d 21 to determine the mRNA abundance of genes related to lipid metabolism. Blood samples were collected at -20.2 ± 3.2, 0, 7, 14 and 21d relative to calving to determine plasma non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHBA), insulin and glucose. Conjugated linoleic acid decreased milk fat yield and milk fat content by 15 and 16%, respectively. Cows fed CLA had lower plasma NEFA and BHBA and greater glucose and insulin concentrations (P < 0.05). Mean BCS at 21d postpartum was greater (P < 0.01; 2.89 vs 2.25), and BCS loss from the day of enrollment to 21d postpartum was reduced (P < 0.01; -0.13 vs -0.64) in the CLA group. The expression of acylcoenzyme A oxidase, carnitine palmitoyltransferase 1A, hormone-sensitive lipase, β2 adrenergic receptor and acetyl-CoA carboxylase was downregulated by CLA supplementation, whereas the expression of sterol regulatory element binding protein, lipoprotein lipase and peroxisome proliferator-activated receptor gamma was upregulated (P < 0.01). In summary, CLA-supplemented cows showed signs of better metabolic status and less severe fat mobilization. Moreover, CLA increased mRNA abundance of genes related to lipogenesis and decreased mRNA abundance of genes related to FA oxidation and lipolysis in the AT of dairy cows during early lactation.

High-protein diet more effectively reduces hepatic fat than low-protein diet despite lower autophagy and FGF21 levels

BACKGROUND AND AIMS

Non-alcoholic fatty liver disease (NAFLD) is becoming increasingly prevalent and nutrition intervention remains the most important therapeutic approach for NAFLD. Our aim was to investigate whether low- (LP) or high-protein (HP) diets are more effective in reducing liver fat and reversing NAFLD and which mechanisms are involved.

METHODS

19 participants with morbid obesity undergoing bariatric surgery were randomized into two hypocaloric (1500-1600 kcal/day) diet groups, a low protein (10E% protein) and a high protein (30E% protein), for three weeks prior to surgery. Intrahepatic lipid levels (IHL) and serum fibroblast growth factor 21 (FGF21) were measured before and after the dietary intervention. Autophagy flux, histology, mitochondrial activity and gene expression analyses were performed in liver samples collected during surgery.

RESULTS

IHL levels decreased by 42.6% in the HP group, but were not significantly changed in the LP group despite similar weight loss. Hepatic autophagy flux and serum FGF21 increased by 66.7% and 42.2%, respectively, after 3 weeks in the LP group only. Expression levels of fat uptake and lipid biosynthesis genes were lower in the HP group compared with those in the LP group. RNA-seq analysis revealed lower activity of inflammatory pathways upon HP diet. Hepatic mitochondrial activity and expression of β-oxidation genes did not increase in the HP group.

CONCLUSIONS

HP diet more effectively reduces hepatic fat than LP diet despite of lower autophagy and FGF21. Our data suggest that liver fat reduction upon HP diets result primarily from suppression of fat uptake and lipid biosynthesis.

Evaluating the appropriate oral lipid tolerance test model for investigating plasma triglyceride elevation in mice

The oral lipid tolerance test (OLTT) has been known to assess intestinal fat metabolism and whole-body lipid metabolism, but rodent models for OLTT are not yet established. Differences in OLTT methodology preclude the generation of definitive results, which may cause some confusion about the anti-hypertriglyceridemia effects of the test materials. To standardize and generate more appropriate methodology for the OLTT, we examined the effects of mice strain, dietary lipid sources, fasting period, and gender on lipid-induced hypertriglyceridemia in mice. First, lipid-induced hypertriglyceridemia was more strongly observed in male ddY mice than in C57BL/6N or ICR mice. Second, the administration of olive and soybean oils remarkably represented lipid-induced hypertriglyceridemia. Third, fasting period before the OLTT largely affected the plasma triglyceride elevation. Fasting for 12 h, but less than 48 h, provoked lipid-induced hypertriglyceridemia. Fourth, we explored the suppressive effects of epigallocatechin gallate (EGCG), a green tea polyphenol, on lipid-induced hypertriglyceridemia. The administration of 100 mg/kg of EGCG suppressed lipid-induced hypertriglyceridemia and intestinal lipase activity. Fifth, EGCG-induced suppressive effects were observed after lipid-induced hypertriglyceridemia was observed in male mice, but not in female mice. Lastly, lipid-induced hypertriglyceridemia could be more effectively induced in mice fed a high-fat diet for 1 week before the OLTT. These findings indicate that male ddY mice after 12 h fasting displayed marked lipid-induced hypertriglyceridemia in response to soybean oil. Hence, the defined experiment condition may be a more appropriate OLTT model for evaluating lipid-induced hypertriglyceridemia.

Identification and characterization of two isoforms of acyl-coenzyme A oxidase 1 gene and their expression in fasting-induced grass carp Ctenopharyngodon idella adipocyte lipolysis

Acyl-coenzyme A oxidases 1 (ACOX1) is the first rate-limiting enzyme responsible for peroxisomal β-oxidation. In the present study, two mRNA variants, ACOX1a and ACOX1b, transcribed from a single gene, were for the first time isolated and characterized from grass carp Ctenopharyngodon idella, both encoding putative peptides of 660 amino acids. Analysis of the exon-intron structures clarified that grass carp ACOX1a and ACOX1b comprise 14 coding exons and correspond to 3a and 3b isoforms of exon 3 splicing variants. Both ACOX1a and ACOX1b mRNAs were expressed in a wide range of tissues, but the abundance of each ACOX1 mRNA showed the tissue-dependent expression patterns. Time-course analysis of ACOX1 expressions indicated that the level of ACOX1a mRNA reached an almost maximal level at day 2, while that of ACOX1b mRNA reached an almost maximal level at day 8 during grass carp primary preadipocyte differentiation. In fasting-induced adipocyte lipolysis, only ACOX1a showed a significant increase in adipocyte, indicating that two ACOX1 isoforms may serve somewhat different roles in the peroxisomal β-oxidation. These results suggested that grass carp ACOX1a and ACOX1b were differently modulated by fasting in adipocyte. In addition, we found that mitochondrial β-oxidation might dominate at the early stage of fasting in adipocytes, indicating that mitochondria and peroxisomes might possess different capacities in fasting-induced adipocytes fatty acid oxidation.

Insulin and β-adrenergic receptors mediate lipolytic and anti-lipolytic signalling that is not altered by type 2 diabetes in human adipocytes

Control of fatty acid storage and release in adipose tissue is fundamental in energy homeostasis and the development of obesity and type 2 diabetes. We here take the whole signalling network into account to identify how insulin and β-adrenergic stimulation in concert controls lipolysis in mature subcutaneous adipocytes obtained from non-diabetic and, in parallel, type 2 diabetic women. We report that, and show how, the anti-lipolytic effect of insulin can be fully explained by protein kinase B (PKB/Akt)-dependent activation of the phosphodiesterase PDE3B. Through the same PKB-dependent pathway β-adrenergic receptor signalling, via cAMP and PI3Kα, is anti-lipolytic and inhibits its own stimulation of lipolysis by 50%. Through this pathway both insulin and β-adrenergic signalling control phosphorylation of FOXO1. The dose–response of lipolysis is bell-shaped, such that insulin is anti-lipolytic at low concentrations, but at higher concentrations of insulin lipolysis was increasingly restored due to inhibition of PDE3B. The control of lipolysis was not altered in adipocytes from diabetic individuals. However, the release of fatty acids was increased by 50% in diabetes due to reduced reesterification of lipolytically liberated fatty acids. In conclusion, our results reveal mechanisms of control by insulin and β-adrenergic stimulation — in human adipocytes — that define a network of checks and balances ensuring robust control to secure uninterrupted supply of fatty acids without reaching concentrations that put cellular integrity at risk. Moreover, our results define how selective insulin resistance leave lipolytic control by insulin unaltered in diabetes, while the fatty acid release is substantially increased.

Dietary squid paste supplementation promotes feed intake via brain-gut dynamic response in Chinese soft-shelled turtle Pelodiscus sinensis

Background

As the primary source of protein for aquaculture, fishmeal has reached the extremity of sustainable development, our previous studies have proven that rice protein concentrate and squid paste are outstanding protein source and stimulant for Pelodiscus sinensis. However, little attention has been given to the molecular mechanism of the appetite modulated by the dietary nutrient factor, especially for a reptile. Thus, the present study aimed to evaluate feed intake and brain-gut dynamic responses to dietary rice protein concentrate and squid paste in Chinese soft-shelled turtle Pelodiscus sinensis.

Methods

Three isonitrogenous and isoenergetic practical diets were formulated including 60% fishmeal (CT), 42% fishmeal + 18% rice protein concentrate (RP) and 42% fishmeal + 18% rice protein concentrate + 1% squid paste (RPS), respectively. Microcapsule lysine was supplemented in RP and RPS diets to balance the amino acid profile. Turtles (initial weight 30.65 ± 0.97 g) were fed three times daily to apparent satiation. After the 8-week feeding trial, the turtles were exposed to 48h food deprivation, then the dynamic expression of the orexigenic and anorexigenic peptides were measured.

Results

The results showed that no significant effect was observed on feed intake when fishmeal was replaced by rice protein concentrate (P = 0.421), while significantly improved feed intake was found by squid paste supplemented (P = 0.02). The mRNA expression of anorexigenic peptides, such as leptin receptor, insulin receptor, pro-opiomelanocortin, cocaine and amphetamine-regulated transcript, cholecystokinin (and its receptor) and glucagon-like peptide-1 receptor in the brain increased significantly at 3 h past feeding (P < 0.05), and then decreased. Nevertheless, neuropeptide Y and peptide YY mRNA expression showed the valley at 3h and peak at 12h past feeding. Intestinal cholecystokinin receptor and glucagon-like peptide-1 receptor mRNA expression showed no difference during the postprandial time (P > 0.05). The results suggested that squid paste is an outstanding stimulant for Pelodiscus sinensis. Furthermore, the orexigenic and anorexigenic peptides evaluated here might play an essential role in short-term fasting to this species, of which the dynamic expression levels were regulated by squid paste.

Comparative Analysis of the Preventive Effects of Canagliflozin, a Sodium-Glucose Co-Transporter-2 Inhibitor, on Body Weight Gain Between Oral Gavage and Dietary Administration by Focusing on Fatty Acid Metabolism

PURPOSE

Sodium-glucose co-transporter-2 (SGLT2) inhibitors have various pleiotropic effects, including body weight reduction, and therefore have the potential to be used in various applications. However, such effects have not been fully investigated; thus, non-clinical studies using animal models are needed. In animal experiments, SGLT2 inhibitors are usually administered by oral or dietary methods. However, the detailed characteristics of these dosing methods, especially to induce their pleiotropic effects, have not been reported. Therefore, we compared the preventive effects of canagliflozin, an SGLT2 inhibitor, on body weight gain following oral gavage and dietary administration methods in a mouse model of diet-induced obesity.

METHODS

Canagliflozin was dosed by oral gavage or dietary administration for 9 weeks to 6-week-old C57BL/6N mice fed a high-fat diet, and parameters related to obesity were evaluated.

RESULTS

The suppression of body weight gain, fat mass, and hepatic lipid content was observed following both dosing methods, whereas the effect on body weight tended to be stronger in the dietary administration group. In adipose tissue, fatty acid synthase expression was significantly decreased in the dietary administration group, and its expression was significantly correlated with fat mass. However, the expression of genes related to fatty acid oxidation was unchanged, indicating that the preventive effect on body weight gain was mediated mainly through the suppression of lipid synthesis rather than the promotion of lipid oxidation.

CONCLUSION

Canagliflozin prevented body weight gain through the suppression of lipid synthesis via both dosing methods, although there were some differences in the efficacy. The findings of our study can help to identify new mechanisms of action of SGLT2 inhibitors and potential applications.

Maternal Overfeeding during Lactation Impairs the Metabolic Response to Fed/Fasting Changing Conditions in the Postweaning Offspring

SCOPE

The metabolic response to fed/fasting changing conditions at early age in rats with different predisposition to obesity-related alterations due to maternal conditions during the perinatal period is studied.

METHODS AND RESULTS

Offspring of dams made obese by a cafeteria diet and moved to a normal-fat diet 1 month before gestation (O-PCaf, with an apparently normal phenotype in adulthood), and offspring of cafeteria diet-fed dams during lactation (O-CAF, with a thin-outside-fat inside phenotype), together with the offspring of control dams (O-C), are studied at early age. Fasting is associated with downregulation of lipogenesis-related genes in liver and rpWAT, and upregulation of genes related to lipolysis and fatty acid uptake in rpWAT in O-C animals. The response to fed/fasting conditions is impaired in O-CAF, but not in O-PCaf animals. The fasting-induced increase in the expression of Prkaa1 in liver and rpWAT, and the corresponding increase of hepatic AMPKα1 protein levels of O-C animals are attenuated in O-CAF rats, while no alterations are found in O-PCaf animals versus controls.

CONCLUSION

Maternal intake of a cafeteria diet during lactation causes early alterations in the offspring, impairing their metabolic flexibility in response to fed/fasting changing conditions, which may contribute to hindering energy homeostasis maintenance.

Muscarinic Agonist Ameliorates Insulin Secretion in Wfs1-Deficient Mice

OBJECTIVES

Similar to patients with Wolfram syndrome and to heterozygous Wolframin1 (Wfs1) mutation carriers, Wfs1-deficient mice exhibit impaired glucose tolerance and lower plasma insulin levels. Muscarinic receptor 3 agonists have previously been shown to potentiate glucose-stimulated insulin secretion. Therefore, the aim of this study was to investigate insulin-secretion dynamics in Wfs1-deficient mice and evaluate carbachol, muscarinic agonist and the ability to ameliorate the insulin secretion deficits caused by the Wfs1 mutation.

METHODS

Wild-type Wfs1 heterozygous and Wfs1 mutant mice were used. Blood glucose was measured after glucose and carbachol administration. Insulin secretion was measured from serum using ELISA.

RESULTS

Glucose administration causes hyperglycemia in Wfs1-deficient mice due to decreased insulin secretion. This deficit is abolished by administration of the muscarinic agonist carbachol.

CONCLUSIONS

Activation of the muscarinic pathway to potentiate insulin secretion may present a target to manage diabetes resulting from Wfs1 deficiency.

Modifying the Dietary Carbohydrate-to-Protein Ratio Alters the Postprandial Macronutrient Oxidation Pattern in Liver of AMPK-Deficient Mice

Background: Hepatic AMP-activated kinase (AMPK) activity is sensitive to the dietary carbohydrate-to-protein ratio. However, the role of AMPK in metabolic adaptations to variations in dietary macronutrients remains poorly understood.Objective: The objective of this study was to determine the role of hepatic AMPK in the adaptation of energy metabolism in response to modulation of the dietary carbohydrate-to-protein ratio.Methods: Male 7-wk-old wild-type (WT) and liver AMPK-deficient (knockout) mice were fed either a normal-protein and normal-carbohydrate diet (NP-NC; 14% protein, 76% carbohydrate on an energy basis), a low-protein and high-carbohydrate diet (LP-HC; 5% protein, 85% carbohydrate), or a high-protein and low-carbohydrate diet (HP-LC; 55% protein, 35% carbohydrate) for 3 wk. During this period, after an overnight fast, metabolic parameters were measured and indirect calorimetry was performed in mice during the first hours after refeeding a 1-g calibrated meal of their own diet in order to investigate lipid and carbohydrate metabolism.Results: Knockout mice fed an LP-HC or HP-LC meal exhibited 24% and 8% lower amplitudes in meal-induced carbohydrate and lipid oxidation changes. By contrast, knockout mice fed an NP-NC meal displayed normal carbohydrate and lipid oxidation profiles. These mice exhibited a transient increase in hepatic triglycerides and a decrease in hepatic glycogen. These changes were associated with a 650% higher secretion of fibroblast growth factor 21 (FGF21) 2 h after refeeding.Conclusions: The consequences of hepatic AMPK deletion depend on the dietary carbohydrate-to-protein ratio. In mice fed the NP-NC diet, deletion of AMPK in the liver led to an adaptation of liver metabolism resulting in increased secretion of FGF21. These changes possibly compensated for the absence of hepatic AMPK, as these mice exhibited normal postprandial changes in carbohydrate and lipid oxidation. By contrast, in mice fed the LP-HC and HP-LC diets, the lack of adjustment in liver metabolism in knockout mice resulted in a metabolic inflexibility, leading to a reduced amplitude of meal-induced changes in carbohydrate and lipid oxidation.

Angiopoietin-like 4 directs uptake of dietary fat away from adipose during fasting

Objective

Angiopoietin-like 4 (ANGPTL4) is a fasting-induced inhibitor of lipoprotein lipase (LPL) and a regulator of plasma triglyceride metabolism. Here, we examined the kinetics of Angptl4 induction and tested the hypothesis that ANGPTL4 functions physiologically to reduce triglyceride delivery to adipose tissue during nutrient deprivation.

Methods

Gene expression, LPL activity, and triglyceride uptake were examined in fasted and fed wild-type and Angptl4^−/− mice.

Results

Angptl4 was strongly induced early in fasting, and this induction was suppressed in mice with access to food during the light cycle. Fasted Angptl4^−/− mice manifested increased LPL activity and triglyceride uptake in adipose tissue compared to wild-type mice.

Conclusions

Angptl4 is induced early in fasting to divert uptake of fatty acids and triglycerides away from adipose tissues.

•Angptl4 is induced within the first few hours of fasting.

•Angptl4 expression is driven by fasting rather than circadian rhythms.

•Fasted Angptl4^−/− mice have increased triglyceride uptake in adipose tissue.

•Angptl4^−/− mice also have increased LPL activity specifically in adipose tissue.

•Data support a model where ANGPTL4 acts locally in adipose during fasting.

The effects of dietary macronutrient composition on lipid metabolism-associated factor gene expression in the adipose tissue of chickens are influenced by fasting and refeeding

Background

Broiler chickens are compulsive feeders that become obese as juveniles and are thus a unique model for metabolic disorders in humans. However, little is known about the relationship between dietary composition, fasting and refeeding and adipose tissue physiology in chicks. Our objective was to determine how dietary macronutrient composition and fasting and refeeding affect chick adipose physiology during the early post-hatch period.

Methods

Chicks were fed one of three isocaloric diets after hatch: high-carbohydrate (HC; control), high-fat (HF; 30% of ME from soybean oil) or high-protein (HP; 25% vs. 22% crude protein). At 4 days post-hatch, chicks were fed (continuous ad libitum access to food), fasted (3 h food withdrawal), or refed (fasted for 3 h and refed for 1 h). Subcutaneous, clavicular, and abdominal adipose tissue was collected for histological analysis and to measure gene expression, and plasma to measure non-esterified fatty acid (NEFA) concentrations (n = 6–10 per group).

Results

Adipose tissue weights were reduced in chicks that were fed the HP diet and adipocyte diameter was greater in the adipose tissue of chicks that ate the HF diet. Consumption of diets differing in protein and fat content also affected gene expression; mRNAs encoding fatty acid binding protein 4 and a lipolytic enzyme, monoglyceride lipase, were greater in chicks fed the HC and HF than HP diet in all three adipose tissue depots. Fasting influenced gene expression in a depot-dependent manner, where most fasting and refeeding-induced changes were observed in the clavicular fat of chicks that consumed the HC diet. Fasting increased plasma NEFA concentrations in chicks fed the HC and HP diets.

Conclusions

The decreased adipose tissue deposition in chicks fed the HP diet is likely explained by decreased rates of adipogenesis. Consumption of the HF diet was associated with greater adipose tissue deposition and larger adipocytes, likely as a result of greater rates of adipocyte hypertrophy. The depot-dependent effects of diet and fasting on gene expression may help explain mechanisms underlying metabolic distinctions among subcutaneous and visceral fat depots in humans.

Impact of polyunsaturated and saturated fat overfeeding on the DNA-methylation pattern in human adipose tissue: a randomized controlled trial

Background: Dietary fat composition can affect ectopic lipid accumulation and, thereby, insulin resistance. Diets that are high in saturated fatty acids (SFAs) or polyunsaturated fatty acids (PUFAs) have different metabolic responses.Objective: We investigated whether the epigenome of human adipose tissue is affected differently by dietary fat composition and general overfeeding in a randomized trial.Design: We studied the effects of 7 wk of excessive SFA (n = 17) or PUFA (n = 14) intake (+750 kcal/d) on the DNA methylation of ∼450,000 sites in human subcutaneous adipose tissue. Both diets resulted in similar body weight increases. We also combined the data from the 2 groups to examine the overall effect of overfeeding on the DNA methylation in adipose tissue.Results: The DNA methylation of 4875 Cytosine-phosphate-guanine (CpG) sites was affected differently between the 2 diets. Furthermore, both the SFA and PUFA diets increased the mean degree of DNA methylation in adipose tissue, particularly in promoter regions. However, although the mean methylation was changed in 1797 genes [e.g., alpha-ketoglutarate dependent dioxygenase (FTO), interleukin 6 (IL6), insulin receptor (INSR), neuronal growth regulator 1 (NEGR1), and proopiomelanocortin (POMC)] by PUFAs, only 125 genes [e.g., adiponectin, C1Q and collagen domain containing (ADIPOQ)] were changed by SFA overfeeding. In addition, the SFA diet significantly altered the expression of 28 transcripts [e.g., acyl-CoA oxidase 1 (ACOX1) and FAT atypical cadherin 1 (FAT1)], whereas the PUFA diet did not significantly affect gene expression. When the data from the 2 diet groups were combined, the mean methylation of 1444 genes, including fatty acid binding protein 1 (FABP1), fatty acid binding protein 2 (FABP2), melanocortin 2 receptor (MC2R), MC3R, PPARG coactivator 1 α (PPARGC1A), and tumor necrosis factor (TNF), was changed in adipose tissue by overfeeding. Moreover, the baseline DNA methylation of 12 CpG sites that was annotated to 9 genes [e.g., mitogen-activated protein kinase 7 (MAPK7), melanin concentrating hormone receptor 1 (MCHR1), and splicing factor SWAP homolog (SFRS8)] was associated with the degree of weight increase in response to extra energy intake.Conclusions: SFA overfeeding and PUFA overfeeding induce distinct epigenetic changes in human adipose tissue. In addition, we present data that suggest that baseline DNA methylation can predict weight increase in response to overfeeding in humans. This trial was registered at clinicaltrials.gov as NCT01427140.

Response of genes involved in lipid metabolism in rat epididymal white adipose tissue to different fasting conditions after long-term fructose consumption

There has been much concern regarding the dietary fructose contributes to the development of metabolic syndrome. High-fructose diet changes the expression of genes involved in lipid metabolism. Levels of a number of hepatic lipogenic enzymes are increased by a high-carbohydrate diet in fasted-refed model rats/mice. Both the white adipose tissue (WAT) and the liver play a key role in the maintenance of nutrient homeostasis. Here, the aim of this study was to analyze the expression of key genes related to lipid metabolism in epididymal WAT (eWAT) in response to different fasting condition after long-term chronic fructose consumption. Rats were fed standard chow supplemented with 10% w/v fructose solution for 5 weeks, and killed after chow-fasting and fructose withdrawal (fasting) or chow-fasting and continued fructose (fructose alone) for 14 h. Blood parameters and the expression of genes involved in fatty acid synthesis (ChREBP, SREBP-1c, FAS, SCD1), triglyceride biosynthesis (DGAT-1, DGAT-2) and lipid mobilization (ATGL, HSL) in eWAT were analyzed. In addition, mRNA levels of PPAR-γ, CD36 and LPL were also detected. As expected, fructose alone increased the mRNA expression of FAS, SCD1, and correspondingly decreased ATGL and HSL mRNA levels. However, ChREBP, DGAT-2, ATGL and HSL mRNA levels restored near to normal while FAS and SCD1 tend to basic level under fasting condition. The mRNA expression of SREBP-1c, PPAR-γ and LPL did not changed at any situations but CD36 mRNA decreased remarkably in fructose alone group. In conclusion, these findings demonstrate that genes involved in lipid metabolism in rat eWAT are varied in response to different fasting conditions after long-term fructose consumption.

Gene expression modulation of lipid and central energetic metabolism related genes by high-fat diet intake in the main homeostatic tissues

HF diet feeding affects the energy balance by transcriptional metabolic adaptations, based in direct gene expression modulation, perinatal programing and transcriptional factor regulation, which could be affected by the animal model, gender or period of dietary treatment.

Whole Blood RNA as a Source of Transcript-Based Nutrition- and Metabolic Health-Related Biomarkers

Blood cells are receiving an increasing attention as an easily accessible source of transcript-based biomarkers. We studied the feasibility of using mouse whole blood RNA in this context. Several paradigms were studied: (i) metabolism-related transcripts known to be affected in rat tissues and peripheral blood mononuclear cells (PBMC) by fasting and upon the development of high fat diet (HFD)-induced overweight were assessed in whole blood RNA of fasted rats and mice and of HFD-fed mice; (ii) retinoic acid (RA)-responsive genes in tissues were assessed in whole blood RNA of control and RA-treated mice; (iii) lipid metabolism-related transcripts previously identified in PBMC as potential biomarkers of metabolic health in a rat model were assessed in whole blood in an independent model, namely retinoblastoma haploinsufficient (Rb^+/-) mice. Blood was collected and stored in RNAlater^® at -80°C until analysis of selected transcripts by real-time RT-PCR. Comparable changes with fasting were detected in the expression of lipid metabolism-related genes when RNA from either PBMC or whole blood of rats or mice was used. HFD-induced excess body weight and fat mass associated with expected changes in the expression of metabolism-related genes in whole blood of mice. Changes in gene expression in whole blood of RA-treated mice reproduced known transcriptional actions of RA in hepatocytes and adipocytes. Reduced expression of Fasn, Lrp1, Rxrb and Sorl1 could be validated as early biomarkers of metabolic health in young Rb^+/- mice using whole blood RNA. Altogether, these results support the use of whole blood RNA in studies aimed at identifying blood transcript-based biomarkers of nutritional/metabolic status or metabolic health. Results also support reduced expression of Fasn, Lrp1, Rxrb and Sorl1 in blood cells at young age as potential biomarkers of metabolic robustness.

Effect of feeding restriction on growth and dressing percentages in Mexican hairless pig

Twenty-four male Mexican hairless pigs, weighing 16 ± 1.12 kg, were used to evaluate growth performance and carcass yield in pigs fed 2 (L), 3 (M) and 4 (H) times the Metabolizable Energy (ME) required for maintenance. The pigs were assigned randomly to two experimental rearing systems (indoors and outdoors). They were fed daily according to their respective feeding regimen (FR). The indoor pigs were fed ad libitum with chopped star grass forage (Cynodon nlemfuensis). The outdoor pigs had access during 16 h to a paddock of star grass. The pigs were slaughtered when they achieve 70 kg of live weight. No significant differences between indoors and outdoors were observed in any of the variables evaluated (P > 0.05). A significant reduction of daily live weight gain (P < 0.05) was observed conforming to FR reductions (0.501, 0.438 and 0.300 kg/day for H, M and L, respectively). Days to achieve 70 kg of live weight increase (P < 0.05) as FR reduces (110, 124 and 180 days for H, M and L, respectively) were recorded. Forage consumption in pigs reared indoors reduces (P < 0.05) conforming to FR increases (0.092, 0.121 and 0.307 kg DM/day for H, M and L respectively). Fat carcass yield reduces significantly (P < 0.05) according FR reductions (24.5, 22.8 y 18.9 kg, for H, M and L respectively). Also, carcass meat yield was higher (P < 0.05) in pigs from L regimen (25.0 kg) than in pigs from M and H regimen (22.0 and 22.8 kg, respectively). Results obtained indicate a reduction in daily live weight gain conforming to daily feed intake reductions; however, improvement in carcass meat yield, accompanied with a reduction in carcass fat yield, was observed.

Agaricus brasiliensis (sun mushroom) affects the expression of genes related to cholesterol homeostasis

PURPOSE

The sun mushroom (Agaricus brasiliensis) is considered a major source of bioactive compounds with potential health benefits. Mushrooms typically act as lipid-lowering agents; however, little is known about the mechanisms of action of A. brasiliensis in biological systems. This study aimed to determine the underlying mechanism involved in the cholesterol-lowering effect of A. brasiliensis through the assessment of fecal and serum lipid profiles in addition to gene expression analysis of specific transcription factors, enzymes, and transporters involved in cholesterol homeostasis.

METHODS

Twenty-four albino Fischer rats approximately 90 days old, with an average weight of 205 g, were divided into four groups of 6 each and fed a standard AIN-93 M diet (C), hypercholesterolemic diet (H), hypercholesterolemic diet +1 % A. brasiliensis (HAb), or hypercholesterolemic diet +0.008 % simvastatin (HS) for 6 weeks. Simvastatin was used as a positive control, as it is a typical drug prescribed for lipid disorders. Subsequently, blood, liver, and feces samples were collected for lipid profile and quantitative real-time polymerase chain reaction gene expression analyses.

RESULTS

Diet supplementation with A. brasiliensis significantly improved serum lipid profiles, comparable to the effect observed for simvastatin. In addition, A. brasiliensis dietary supplementation markedly promoted fecal cholesterol excretion. Increased expression of 7α-hydroxylase (CYP7A1), ATP-binding cassette subfamily G-transporters (ABCG5/G8), and low-density lipoprotein receptor (LDLR) was observed following A. brasiliensis administration.

CONCLUSIONS

Our results suggest that consumption of A. brasiliensis improves the serum lipid profile in hypercholesterolemic rats by modulating the expression of key genes involved in hepatic cholesterol metabolism.

Leptin Effect on Acetylation and Phosphorylation of Pgc1α in Muscle Cells Associated With Ampk and Akt Activation in High-Glucose Medium

Leptin is crucial in energy metabolism, including muscle regulation. Peroxisome proliferator activated receptor gamma co-activator 1α (PGC1α) orchestrates energy metabolism and is tightly controlled by post-translational covalent modifications such as phosphorylation and acetylation. We aimed to further the knowledge of PGC1α control by leptin (at physiological levels) in muscle cells by time-sequentially analysing the activation of AMP activated protein kinase (AMPK), P38 mitogen-activated protein kinase (P38 MAPK) and Akt (Protein kinase B)--all known to phosphorylate PGC1α and to be involved in the regulation of its acetylation status--in C2C12 myotubes placed in a high-glucose serum-free medium. We also studied the protein levels of PGC1α, Sirtuin 1, adiponectin, COX IV, mitofusin 2 (Mfn2), and pyruvate dehydrogenase kinase 4 (PDK4). Our main findings suggest an important role of leptin regulating AMPK and Akt phosphorylation, Mfn2 induction and PGC1α acetylation status, with the novelty that the latter in transitorily increased in response to leptin, an effect dependent, at least in part, on AMPK regulation. These post-translational reversible changes in PGC1α in response to leptin, especially the increase in acetylation status, may be related to the physiological role of the hormone in modulating muscle cell response to the physiological/nutritional status.

Autonomic nervous system-mediated effects of galanin-like peptide on lipid metabolism in liver and adipose tissue

Galanin-like peptide (GALP) is a neuropeptide involved in the regulation of feeding behavior and energy metabolism in mammals. While a weight loss effect of GALP has been reported, its effects on lipid metabolism have not been investigated. The aim of this study was to determine if GALP regulates lipid metabolism in liver and adipose tissue via an action on the sympathetic nervous system. The respiratory exchange ratio of mice administered GALP intracerebroventricularly was lower than that of saline-treated animals, and fatty acid oxidation-related gene mRNA levels were increased in the liver. Even though the respiratory exchange ratio was reduced by GALP, this change was not significant when mice were treated with the sympatholytic drug, guanethidine. Lipolysis-related gene mRNA levels were increased in the adipose tissue of GALP-treated mice compared with saline-treated animals. These results show that GALP stimulates fatty acid β-oxidation in liver and lipolysis in adipose tissue, and suggest that the anti-obesity effect of GALP may be due to anorexigenic actions and improvement of lipid metabolism in peripheral tissues via the sympathetic nervous system.

Adipokinetic hormone receptor gene identification and its role in triacylglycerol metabolism in the blood-sucking insect Rhodnius prolixus

Adipokinetic hormone (AKH) has been associated with the control of energy metabolism in a large number of arthropod species due to its role on the stimulation of lipid, carbohydrate and amino acid mobilization/release. In the insect Rhodnius prolixus, a vector of Chagas' disease, triacylglycerol (TAG) stores must be mobilized to sustain the metabolic requirements during moments of exercise or starvation. Besides the recent identification of the R. prolixus AKH peptide, other components required for the AKH signaling cascade and its mode of action remain uncharacterized in this insect. In the present study, we identified and investigated the expression profile of the gene encoding the AKH receptor of R. prolixus (RhoprAkhr). This gene is highly conserved in comparison to other sequences already described and its transcript is abundant in the fat body and the flight muscle of the kissing bug. Moreover, RhoprAkhr expression is induced in the fat body at moments of increased TAG mobilization; the knockdown of this gene resulted in TAG accumulation both in fat body and flight muscle after starvation. The inhibition of Rhopr-AKHR transcription as well as the treatment of insects with the peptide Rhopr-AKH in its synthetic form altered the transcript levels of two genes involved in lipid metabolism, the acyl-CoA-binding protein-1 (RhoprAcbp1) and the mitochondrial glycerol-3-phosphate acyltransferase-1 (RhoprGpat1). These results indicate that the AKH receptor is regulated at transcriptional level and is required for TAG mobilization under starvation. In addition to the classical view of AKH as a direct regulator of enzymatic activity, we propose here that AKH signaling may account for the regulation of nutrient metabolism by affecting the expression profile of target genes.

Amelioration of palmitate-induced metabolic dysfunction in L6 muscle cells expressing low levels of receptor-interacting protein 140

We have shown that reduced expression of receptor-interacting protein 140 (RIP140) alters the regulation of fatty-acid (FA) oxidation in muscle. To determine whether a high level of FA availability alters the effects of RIP140 on metabolic regulation, L6 myotubes were transfected with or without RNA interference oligonucleotide sequences to reduce RIP140 expression, and then incubated with high levels of palmitic acid, with or without insulin. High levels of palmitate reduced basal (53%-58%) and insulin-treated (24%-44%) FA uptake and oxidation, and increased basal glucose uptake (88%). In cells incubated with high levels of palmitate, low RIP140 increased basal FA uptake and insulin-treated FA oxidation and glucose uptake, and decreased basal glucose uptake and insulin-treated FA uptake. Under basal conditions, low RIP140 increased the mRNA content of FAT/CD36 (159%) and COX4 (61%), as well as the protein content of Nur77 (68%), whereas the mRNA expression of FGF21 (50%) was decreased, as was the protein content of CPT1b (35%) and FGF21 (44%). Under insulin-treated conditions, low RIP140 expression increased the mRNA content of MCAD (84%) and Nur77 (84%), as well as the protein content of Nur77 (23%). Thus, a low level of RIP140 restores the rates of FA uptake in the basal state, in part via a reduction in upstream insulin signaling. Our data also indicate that the protein expression of Nur77 may be modulated by RIP140 when muscle cells are metabolically challenged by high levels of palmitate.

Fish oil decreases hepatic lipogenic genes in rats fasted and refed on a high fructose diet

Fasting and then refeeding on a high-carbohydrate diet increases serum and hepatic triacylglycerol (TAG) concentrations compared to standard diets. Fructose is a lipogenic monosaccharide which stimulates de novo fatty acid synthesis. Omega-3 (n-3) fatty acids stimulate hepatic β-oxidation, partitioning fatty acids away from TAG synthesis. This study investigated whether dietary n-3 fatty acids from fish oil (FO) improve the hepatic lipid metabolic response seen in rats fasted and then refed on a high-fructose diet. During the post-prandial (fed) period, rats fed a FO rich diet showed an increase in hepatic peroxisome proliferator-activated receptor α (PPAR-α) gene expression and decreased expression of carbohydrate responsive element binding protein (ChREBP), fatty acid synthase (FAS) and microsomal triglyceride transfer protein (MTTP). Feeding a FO rich diet for 7 days prior to 48 h of fasting resulted in lower hepatic TAG, lower PPAR-α expression and maintenance of hepatic n-3 fatty acid content. Refeeding on a high fructose diet promoted an increase in hepatic and serum TAG and in hepatic PPAR-α, ChREBP and MTTP expression. FO did not prevent the increase in serum and hepatic TAG after fructose refeeding, but did decrease hepatic expression of lipogenic genes and increased the n-3 fatty acid content of the liver. n-3 Fatty acids can modify some components of the hepatic lipid metabolic response to later feeding with a high fructose diet.

ATGL-catalyzed lipolysis regulates SIRT1 to control PGC-1α/PPAR-α signaling

Sirtuin 1 (SIRT1), an NAD(+)-dependent protein deacetylase, regulates a host of target proteins, including peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α (PGC-1α), a transcriptional coregulator that binds to numerous transcription factors in response to deacetylation to promote mitochondrial biogenesis and oxidative metabolism. Our laboratory and others have shown that adipose triglyceride lipase (ATGL) increases the activity of the nuclear receptor PPAR-α, a PGC-1α binding partner, to promote fatty acid oxidation. Fatty acids bind and activate PPAR-α; therefore, it has been presumed that fatty acids derived from ATGL-catalyzed lipolysis act as PPAR-α ligands. We provide an alternate mechanism that links ATGL to PPAR-α signaling. We show that SIRT1 deacetylase activity is positively regulated by ATGL to promote PGC-1α signaling. In addition, ATGL mediates the effects of β-adrenergic signaling on SIRT1 activity, and PGC-1α and PPAR-α target gene expression independent of changes in NAD(+). Moreover, SIRT1 is required for the induction of PGC-1α/PPAR-α target genes and oxidative metabolism in response to increased ATGL-mediated lipolysis. Taken together, this work identifies SIRT1 as a critical node that links β-adrenergic signaling and lipolysis to changes in the transcriptional regulation of oxidative metabolism.

Sub-chronically exposing mice to a polycyclic aromatic hydrocarbon increases lipid accumulation in their livers

The potential for exposing humans and wildlife to environmental polycyclic aromatic hydrocarbons (PAHs) has increased. Risk assessments describing how PAHs disturb lipid metabolism and induce hepatotoxicity have only received limited attention. In the present study, seven-week-old male ICR mice received intraperitoneal injections of 0, 0.01, 0.1 or 1mg/kg body weight 3-methylcholanthrene (3MC) per week for 10 weeks. A high-fat diet was provided during the exposure. Histopathological lipid accumulation and lipid metabolism-related genes were measured. We observed that sub-chronic 3MC exposure significantly increased lipid droplet and triacylglycerol (TG) levels in the livers. A low dose of 3MC activated the aryl hydrocarbon receptor, which negatively regulated lipid synthesis in the livers. The primary genes including acetyl-CoA carboxylase (Acc), fatty acid synthase (Fas) and stearoyl-CoA desaturase 1 (Scd1) decreased significantly when compared with those in the control group, indicating that de novo fatty acid synthesis in the hepatocytes was significantly inhibited by the sub-chronic 3MC exposure. However, the free fatty acid (FFA) synthesis in the adipose tissue was greatly enhanced by up-regulating the expression of peroxisome proliferator-activated receptor γ (PPARγ) and sterol regulatory element binding protein-1c (SREBP1C) and target genes including Acc, Fas and Scd1. The synthesized FFA was released into the blood and then transported into the liver by the up-regulation of Fat and Fatp2, which resulted in the gradual accumulation of lipids in the liver. In conclusion, histological examinations and molecular level analyses highlighted the development of lipid accumulation and confirmed that 3MC significantly impaired lipid metabolism in mice.

Exacerbated oxidative stress in the fasting liver according to fuel partitioning

Complete starvation may prove lethal due to excessive loss of body proteins. However, it is still not completely understood whether responses to food deprivation are time-dependently induced or triggered in relation with the successive phases of protein sparing and wasting that characterize prolonged fasting. As the liver has a wide range of vital functions, we examined the hepatic regulatory mechanisms elicited during prolonged fasting. We showed that fasting-induced transcriptome/proteome changes occur in close relation with fuel partitioning, independently of ATP levels. Omics data suggesting a worsening of oxidative stress during the proteolytic stage of fasting were further validated using biochemical assays. Low levels of antioxidant factors were indeed paralleled by their decreased activity that could be impaired by low NADPH levels. Oxidative damage to lipids and proteins was accordingly increased only during late fasting. At this stage, the gene/protein expression of several chaperones was also repressed. Together with the impairment of metabolic achievements, a vicious cycle involving protein misfolding and oxidative stress could jeopardize liver function when the proteolytic stage of fasting is reached. Thus, monitoring of liver impairments should help to better manage or treat catabolic and/or oxidative stress conditions, such as ageing and degeneration.

Impact of fasting time on hepatic lipid metabolism in nutritional animal studies

Many animal studies on improvement of lipid metabolism, using dietary components, fast the animals on the final day of the feeding. Although fasting has a significant impact on lipid metabolism, its time-dependent influence is not fully understood. We examined the effects of several fasting times on lipid metabolism. Rats fed with a semisynthetic diet for 2 wk were killed after 0 (9:00 am), 6 (7:00 am-1:00 pm), 9 (0:00 am-9:00 am), and 13 h (8:00 pm-9:00 am) of fasting. Compared to the 0 h group, marked reduction of liver weight and hepatic triacylglycerol content was observed in the 9 and 13 h groups. Activities of hepatic enzymes involved in fatty acid synthesis gradually decreased during fasting. In contrast, drastic time-dependent reduction of gene expression, of the enzymes, was observed. Expression of carnitine palmitoyltransferase mRNA was higher in the fasting groups than in the 0 h group. Our study showed that fasting has a significant impact on several parameters related to lipid metabolism in rat liver.

Liver but not adipose tissue is responsive to the pattern of enteral feeding

Nutritional support is an important aspect of medical care, providing calories to patients with compromised nutrient intake. Metabolism has a diurnal pattern, responding to the light cycle and food intake, which in turn can drive changes in liver and adipose tissue metabolism. In this study, we assessed the response of liver and white adipose tissue (WAT) to different feeding patterns under nutritional support (total enteral nutrition or TEN). Mice received continuous isocaloric TEN for 10 days or equal calories of chow once a day (Ch). TEN was given either at a constant (CN, same infusion rate during 24 h) or variable rate (VN, 80% of calories fed at night, 20% at day). Hepatic lipogenesis and carbohydrate-responsive element-binding protein (ChREBP) expression increased in parallel with the diurnal feeding pattern. Relative to Ch, both patterns of enteral feeding increased adiposity. This increase was not associated with enhanced lipogenic gene expression in WAT; moreover, lipogenesis was unaffected by the feeding pattern. Surprisingly, leptin and adiponectin expression increased. Moreover, nutritional support markedly increased hepatic and adipose FGF21 expression in CN and VN, despite being considered a fasting hormone. In summary, liver but not WAT, respond to the pattern of feeding. While hepatic lipid metabolism adapts to the pattern of nutrient availability, WAT does not. Moreover, sustained delivery of nutrients in an isocaloric diet can cause adiposity without the proinflammatory state observed in hypercaloric feeding. Thus, the liver but not adipose tissue is responsive to the pattern of feeding behavior.

Identification and characterization of genes that control fat deposition in chickens

BACKGROUND

Fat deposits in chickens contribute significantly to meat quality attributes such as juiciness, flavor, taste and other organoleptic properties. The quantity of fat deposited increases faster and earlier in the fast-growing chickens than in slow-growing chickens. In this study, Affymetrix Genechip® Chicken Genome Arrays 32773 transcripts were used to compare gene expression profiles in liver and hypothalamus tissues of fast-growing and slow-growing chicken at 8 wk of age. Real-time RT-PCR was used to validate the differential expression of genes selected from the microarray analysis. The mRNA expression of the genes was further examined in fat tissues. The association of single nucleotide polymorphisms of four lipid-related genes with fat traits was examined in a F2 resource population.

RESULTS

Four hundred genes in the liver tissues and 220 genes hypothalamus tissues, respectively, were identified to be differentially expressed in fast-growing chickens and slow-growing chickens. Expression levels of genes for lipid metabolism (SULT1B1, ACSBG2, PNPLA3, LPL, AOAH) carbohydrate metabolism (MGAT4B, XYLB, GBE1, PGM1, HKDC1)cholesttrol biosynthesis (FDPS, LSS, HMGCR, NSDHL, DHCR24, IDI1, ME1) HSD17B7 and other reaction or processes (CYP1A4, CYP1A1, AKR1B1, CYP4V2, DDO) were higher in the fast-growing White Recessive Rock chickens than in the slow-growing Xinghua chickens. On the other hand, expression levels of genes associated with multicellular organism development, immune response, DNA integration, melanin biosynthetic process, muscle organ development and oxidation-reduction (FRZB, DMD, FUT8, CYP2C45, DHRSX, and CYP2C18) and with glycol-metabolism (GCNT2, ELOVL 6, and FASN), were higher in the XH chickens than in the fast-growing chickens. RT-PCR validated high expression levels of nine out of 12 genes in fat tissues. The G1257069A and T1247123C of the ACSBG2 gene were significantly associated with abdominal fat weight. The G4928024A of the FASN gene were significantly associated with fat bandwidth, and abdominal fat percentage. The C4930169T of the FASN gene was associated with abdominal fat weight while the A59539099G of the ELOVL 6 was significantly associated with subcutaneous fat. The A8378815G of the DDT was associated with fat band width.

CONCLUSION

The differences in fat deposition were reflected with differential gene expressions in fast and slow growing chickens.

Effect of dietary lipid structure in early postnatal life on mouse adipose tissue development and function in adulthood

Obese individuals have more (hyperplastic) and larger (hypertrophic) adipocytes in their white adipose tissue (WAT) than normal-weight individuals. The difference in cell number emerges early in childhood, suggesting that this is a critical period for being susceptible to obesity. Breast-feeding has been shown to be protective against obesity, and we have previously shown in mice that the physical structure of lipids in human milk may contribute to this protective effect. In the present study, we investigated how differences in the physical structure of lipids in the early diet may modulate adipose tissue development. Male mice were fed a diet containing control infant milk formula (Control IMF; Danone Research) or Nuturis® (Concept IMF with large phospholipid-coated lipid droplets; Danone Research) from postnatal day (PN)16 to 42. Subsequently, mice were challenged with a moderate Western-style diet (WSD) until PN98, and body composition was monitored by dual-energy X-ray absorptiometry. Epididymal WAT was analysed for adipocyte size, number and gene expression of metabolic transcription factors. Early Concept IMF exposure reduced fat accumulation during the WSD challenge by 30 % compared with the Control IMF. It reduced adipocyte size without affecting adipocyte number in adult mice. The Concept IMF decreased the expression of PPARγ, CCAAT/enhancer-binding protein and retinoid X receptor α in WAT in adulthood, key regulators of metabolic activity. In conclusion, Concept IMF exposure in early life reduced susceptibility to obesity in adult life, by preventing adipocyte hypertrophia upon adult dietary challenge without affecting adipogenesis. These data emphasise the importance of the physical properties of dietary lipids in early life in obesity risk later in life.

Autofluorescence imaging of living pancreatic islets reveals fibroblast growth factor-21 (FGF21)-induced metabolism

Fibroblast growth factor-21 (FGF21) has therapeutic potential for metabolic syndrome due to positive effects on fatty acid metabolism in liver and white adipose tissue. FGF21 also improves pancreatic islet survival in excess palmitate; however, much less is known about FGF21-induced metabolism in this tissue. We first confirmed FGF21-dependent activity in islets by identifying expression of the cognate coreceptor Klothoβ, and by measuring a ligand-stimulated decrease in acetyl-CoA carboxylase expression. To further reveal the effect of FGF21 on metabolism, we employed a unique combination of two-photon and confocal autofluorescence imaging of the NAD(P)H and mitochondrial NADH responses while holding living islets stationary in a microfluidic device. These responses were further correlated to mitochondrial membrane potential and insulin secretion. Glucose-stimulated responses were relatively unchanged by FGF21. In contrast, responses to glucose in the presence of palmitate were significantly reduced compared to controls showing diminished NAD(P)H, mitochondrial NADH, mitochondrial membrane potential, and insulin secretion. Consistent with the glucose-stimulated responses being smaller due to continued fatty acid oxidation, mitochondrial membrane potential was increased in FGF21-treated islets by using the fatty acid transport inhibitor etomoxir. Citrate-stimulated NADPH responses were also significantly larger in FGF21-treated islets suggesting preference for citrate cycling rather than acetyl-CoA carboxylase-dependent fatty acid synthesis. Overall, these data show a reduction in palmitate-induced potentiation of glucose-stimulated metabolism and insulin secretion in FGF21-treated islets, and establish the use of autofluorescence imaging and microfluidic devices to investigate cell metabolism in a limited amount of living tissue.

Effects of short-term refeeding on the expression of genes involved in lipid metabolism in chicks (Gallus gallus)

The aim of this study was to analyze the expression patterns of key genes involved in lipid metabolism in response to feeding in chicks. A total of 18 thirteen day-old male chicks were fasted for 12h. The mRNA levels of the genes in the liver and white adipose tissue were analyzed after 0, 2, and 4h of refeeding. The mRNA levels of sterol regulatory element-binding protein (SREBP) 1, liver X receptor α, peroxisome proliferator-activated receptor (PPAR) γ, acetyl-CoA carboxylase α and fatty acid synthase were significantly increased after 2h of refeeding. In contrast, the mRNA levels of PPARα and carnitine palmitoyltransferase 1a were significantly decreased after 2h of refeeding. The mRNA level of acyl-CoA oxidase was significantly decreased after 4h of refeeding. The mRNA levels of cholesterol metabolism-related genes such as SREBP2 and 3-hydroxy-3-methylglutaryl-CoA reductase were significantly increased after 2h of refeeding. In the white adipose tissue, the mRNA level of PPARγ was significantly increased after 2h of refeeding, whereas the mRNA level of adipose triglyceride lipase was significantly decreased after 4h of refeeding. These results demonstrated that expression of lipid metabolism-related genes is regulated by short-term refeeding in chicks.

Effects of short term fasting on the expression of genes involved in lipid metabolism in chicks

The aim of this study was to analyze the expression patterns of key genes involved in lipid metabolism in response to short term fasting in chicks (Gallus gallus). The mRNA level of the genes was analyzed after 0, 2, and 4 h of fasting in the liver and white adipose tissue. In the liver, the mRNA level of peroxisome proliferator-activated receptor α was significantly increased after 2 h of fasting. The mRNA levels of carnitine palmitoyltransferase 1a and acyl-CoA oxidase were significantly increased after 4 h of fasting. In contrast, the mRNA levels of sterol regulatory element-binding protein 1, acetyl-CoA carboxylase α, and fatty acid synthase were significantly decreased after 4 h of fasting. The mRNA levels of cholesterol metabolism-related genes such as 3-hydroxy-3-methylglutaryl-CoA reductase and cholesterol 7α-hydroxylase were significantly decreased after 4 h of fasting. In the white adipose tissue, the mRNA level of adipose triglyceride lipase was significantly increased after 4 h of fasting. In contrast, the mRNA levels of peroxisome proliferator-activated receptor γ and lipoprotein lipase were significantly decreased after 4 h of fasting. These results demonstrated that the gene expression of lipid metabolism-related genes is regulated by short term fasting in both the liver and WAT in chicks.

Protective effect of FGF21 on type 1 diabetes-induced testicular apoptotic cell death probably via both mitochondrial- and endoplasmic reticulum stress-dependent pathways in the mouse model

Fibroblast growth factor 21 (FGF21) is a novel member identified and was reported to express predominantly in pancreas, liver and adipose tissue, and relatively less in other organs, such as the testis. However, the role of FGF21 in the testis has never been addressed. The present study examined FGF21 expression at mRNA level by real-time RT-PCR assay in the testis of fasting and non-fasting mice or mice with type 1 diabetes that was induced with streptozotocin. We also examined the effect of Fgf21 gene deletion or supplementation of the exogenous FGF21 on the testicular apoptotic cell death spontaneously or induced by type 1 diabetes in FGF21 knockout (FGF21-KO) mice. Deletion of Fgf21 gene does not affect testicular cell proliferation, but significantly increases the spontaneous incidence of testicular TUNEL positive cells with increases in the Bax/Bcl2 expression ratio and apoptosis-inducing factor (AIF) expression. Diabetes induced significant increases in testicular TUNEL positive cells, Bax/Bcl2 expression ratio, AIF expression, CHOP and cleaved caspase-12 expression, and oxidative damage, but did not change the expression of cleaved caspase-3 and caspase-8. Deletion of Fgf21 gene also significantly enhances diabetes-induced TUNEL positive cells along with the increased expression of Bax/Bcl2 ratio, AIF, CHOP, cleaved caspase-12, and oxidative damage, which was significantly prevented by the supplementation of exogenous FGF21. These results suggest that Fgf21 gene may involve in maintaining normal spermatogenesis and also protect the germ cells from diabetes-induced apoptotic cell death probably via the prevention of diabetes-induced oxidative damage.

Peripheral blood mononuclear cells: a potential source of homeostatic imbalance markers associated with obesity development

Peripheral blood mononuclear cells (PBMC) have a great potential for nutrition and obesity studies. PBMC reflect the nutritional response of key organs involved in energy homeostasis maintenance, which is altered in the obese state. Here, we aimed to determine the usefulness of PBMC as a source of early markers of obesity. To that purpose, we analysed whether PBMC could reflect the insensitivity to changes in feeding conditions associated with obesity during the development of this pathology. Expression of key genes central to energy metabolism was measured by Q-PCR in PBMC samples of normoweight (control) and cafeteria-fed (obese) rats in feeding, fasting and refeeding conditions. Samples were obtained monthly from 2 (beginning of cafeteria diet-feeding) to 6 months of age. In general terms, expression of genes related to fatty acid synthesis (Fasn, Srebp1) and adipogenesis (Pparg) decreased with fasting and increased with refeeding. Conversely, the expression of a key gene regulating beta-oxidation (Cpt1a) and the gene for an orexigenic neuropeptide (Npy)-in accordance with their metabolic role-increased with fasting and decreased with refeeding. This expression pattern disappeared in obese rats, in which insensitivity to feeding conditions was observed after only 1 month of cafeteria diet-feeding. Thus, during development, PBMC accurately reflect nutritional regulation of energy homeostasic genes and the insensitivity to feeding associated with obesity, even in the earlier stages with a low degree of overweight. For this reason, this set of blood cells could constitute a potential source of biomarkers of early homeostatic imbalance which would be useful in nutrition studies that could help prevent the occurrence of obesity.