Intermittent fasting up-regulates Fsp27/Cidec gene expression in white adipose tissue

Gene network based analysis identifies a coexpression module involved in regulating plasma lipids with high-fat diet response

Plasma lipids are modulated by gene variants and many environmental factors, including diet-associated weight gain. However, understanding how these factors jointly interact to influence molecular networks that regulate plasma lipid levels is limited. Here, we took advantage of the BXD recombinant inbred family of mice to query weight gain as an environmental stressor on plasma lipids. Coexpression networks were examined in both nonobese and obese livers, and a network was identified that specifically responded to the obesogenic diet. This obesity-associated module was significantly associated with plasma lipid levels and enriched with genes known to have functions related to inflammation and lipid homeostasis. We identified key drivers of the module, including Cidec, Cidea, Pparg, Cd36, and Apoa4. The Pparg emerged as a potential master regulator of the module as it can directly target 19 of the top 30 hub genes. Importantly, activation of this module is causally linked to lipid metabolism in humans, as illustrated by correlation analysis and inverse-variance weighed Mendelian randomization. Our findings provide novel insights into gene-by-environment interactions for plasma lipid metabolism that may ultimately contribute to new biomarkers, better diagnostics, and improved approaches to prevent or treat dyslipidemia in patients.

The Health-Promoting Effects and the Mechanism of Intermittent Fasting

Intermittent fasting (IF) is an eating pattern in which individuals go extended periods with little or no energy intake after consuming regular food in intervening periods. IF has several health-promoting effects. It can effectively reduce weight, fasting insulin levels, and blood glucose levels. It can also increase the antitumor activity of medicines and cause improvement in the case of neurological diseases, such as memory deficit, to achieve enhanced metabolic function and prolonged longevity. Additionally, IF activates several biological pathways to induce autophagy, encourages cell renewal, prevents cancer cells from multiplying and spreading, and delays senescence. However, IF has specific adverse effects and limitations when it comes to people of a particular age and gender. Hence, a more systematic study on the health-promoting effects and safety of IF is needed. This article reviewed the research on the health-promoting effects of IF, providing a theoretical basis, direction for subsequent basic research, and information related to the clinical application of IF.

AMPK-PPARγ-Cidec Axis Drives the Fasting-Induced Lipid Droplet Aggregation in the Liver of Obese Mice

Intermittent fasting is one of the most common clinical treatments for the obesity, a main risk factor of the metabolic syndrome which can lead to a variety of diseases. Fasting-induced fat mobilization alters the metabolic state of lipid in the liver, predisposing to increase the hepatic lipid droplet aggregation and triglyceride levels. However, the underlying mechanisms regarding the lipid droplet aggregation in the liver after fasting remains elusive. Here, we report that a lipid droplet surface binding protein Cidec (cell death inducing DFFA like effector C) is activated by AMPK to regulate the hepatic lipid droplet fusion following fasting in obese mice. Specifically, we found that lipid droplets were significantly aggregated in the liver of high-fat-diet and ob/ob mice after 16 and 24 h of fasting, accompanied by the dramatically up-regulated expression of Cidec. Consistently, overexpression of Cidec in the AML12 cells resulted in the intracellular lipid droplet aggregation. Furthermore, we showed that fasting caused the up-regulated expression of AMPK, which in turn activated the transcription of Cidec through the transcription factor PPARγ. Altogether, our observations reveal that fasting-induced hepatic lipid droplet aggregation is mediated by the AMPK-activated expression of Cidec via PPARγ, extending our understanding about the molecular mechanism of the impact of fasting on the obesity and providing potential targets for the treatment of human obesity.

CIDEC silencing attenuates diabetic nephropathy via inhibiting apoptosis and promoting autophagy

OBJECTIVE

The role of cell death-inducing DFF45-like effector C (CIDEC) in insulin resistance has been established, and it is considered to be an important trigger factor for the progression of diabetic nephropathy (DN). We intend to explore whether CIDEC plays an important role in the regulation of DN and its potential mechanism.

METHODS

High-fat diet and low dose streptozotocin were used to establish type 2 diabetic rat model. We investigate the role of CIDEC in the pathogenesis and process of DN through histopathological analysis, western blot and gene silencing. Meanwhile, the effect of CIDEC on renal tubular epithelial cells stimulated by high glucose was also verified.

RESULTS

DM group exhibited glucose and lipid metabolic disturbance, with hypertrophy of kidneys, damaged renal function, increased apoptosis, decreased autophagy, glomerulosclerosis and interstitial fibrosis. CIDEC gene silencing improved metabolic disorder and insulin resistance, alleviated renal hypertrophy and renal function damage, decreased glomerular and tubular apoptosis, increased autophagy and inhibited renal fibrosis. At the cellular level, high glucose stimulation increased CIDEC expression in renal tubular epithelial cells, accompanied by increased apoptosis and decreased autophagy. CIDEC gene silencing can improve autophagy and reduce apoptosis. At the molecular level, CIDEC gene silencing also decreased the expression of early growth response factor (EGR)1 and increased the expression of adipose triglyceride lipase (ATGL).

CONCLUSION

CIDEC gene silencing may delay the progression of DN by restoring autophagy activity and inhibiting apoptosis with the participation of EGR1and ATGL.

Tetrahydroxanthohumol, a xanthohumol derivative, attenuates high-fat diet-induced hepatic steatosis by antagonizing PPARγ

We previously reported xanthohumol (XN), and its synthetic derivative tetrahydro-XN (TXN), attenuates high-fat diet (HFD)-induced obesity and metabolic syndrome in C57Bl/6J mice. The objective of the current study was to determine the effect of XN and TXN on lipid accumulation in the liver. Non-supplemented mice were unable to adapt their caloric intake to 60% HFD, resulting in obesity and hepatic steatosis; however, TXN reduced weight gain and decreased hepatic steatosis. Liver transcriptomics indicated that TXN might antagonize lipogenic PPARγ actions in vivo. XN and TXN inhibited rosiglitazone-induced 3T3-L1 cell differentiation concomitant with decreased expression of lipogenesis-related genes. A peroxisome proliferator activated receptor gamma (PPARγ) competitive binding assay showed that XN and TXN bind to PPARγ with an IC50 similar to pioglitazone and 8-10 times stronger than oleate. Molecular docking simulations demonstrated that XN and TXN bind in the PPARγ ligand-binding domain pocket. Our findings are consistent with XN and TXN acting as antagonists of PPARγ.

The role and its mechanism of intermittent fasting in tumors: friend or foe?

Intermittent fasting (IF) is becoming a prevailing topic worldwide, as it can cause changes in the body’s energy metabolism processes, improve health, and affect the progression of many diseases, particularly in the circumstance of oncology. Recent research has shown that IF can alter the energy metabolism of tumor cells, thereby inhibiting tumor growth and improving antitumor immune responses. Furthermore, IF can increase cancer sensitivity to chemotherapy and radiotherapy and reduce the side effects of these traditional anticancer treatments. IF is therefore emerging as a promising approach to clinical cancer treatment. However, the balance between long-term benefits of IF compared with the harm from insufficient caloric intake is not well understood. In this article, we review the role of IF in tumorigenesis and tumor therapy, and discuss some scientific problems that remain to be clarified, which might provide some assistance in the application of IF in clinical tumor therapy.

Peroxisome Proliferator-Activated Receptors and Caloric Restriction-Common Pathways Affecting Metabolism, Health, and Longevity

Caloric restriction (CR) is a traditional but scientifically verified approach to promoting health and increasing lifespan. CR exerts its effects through multiple molecular pathways that trigger major metabolic adaptations. It influences key nutrient and energy-sensing pathways including mammalian target of rapamycin, Sirtuin 1, AMP-activated protein kinase, and insulin signaling, ultimately resulting in reductions in basic metabolic rate, inflammation, and oxidative stress, as well as increased autophagy and mitochondrial efficiency. CR shares multiple overlapping pathways with peroxisome proliferator-activated receptors (PPARs), particularly in energy metabolism and inflammation. Consequently, several lines of evidence suggest that PPARs might be indispensable for beneficial outcomes related to CR. In this review, we present the available evidence for the interconnection between CR and PPARs, highlighting their shared pathways and analyzing their interaction. We also discuss the possible contributions of PPARs to the effects of CR on whole organism outcomes.

Intermittent Fasting for Twelve Weeks Leads to Increases in Fat Mass and Hyperinsulinemia in Young Female Wistar Rats

Fasting is known to cause physiological changes in the endocrine pancreas, including decreased insulin secretion and increased reactive oxygen species (ROS) production. However, there is no consensus about the long-term effects of intermittent fasting (IF), which can involve up to 24 hours of fasting interspersed with normal feeding days. In the present study, we analyzed the effects of alternate-day IF for 12 weeks in a developing and healthy organism. Female 30-day-old Wistar rats were randomly divided into two groups: control, with free access to standard rodent chow; and IF, subjected to 24-hour fasts intercalated with 24-hours of free access to the same chow. Alternate-day IF decreased weight gain and food intake. Surprisingly, IF also elevated plasma insulin concentrations, both at baseline and after glucose administration collected during oGTT. After 12 weeks of dietary intervention, pancreatic islets displayed increased ROS production and apoptosis. Despite their lower body weight, IF animals had increased fat reserves and decreased muscle mass. Taken together, these findings suggest that alternate-day IF promote β -cell dysfunction, especially in developing animals. More long-term research is necessary to define the best IF protocol to reduce side effects.

CIDEA and CIDEC are regulated by CREB and are not induced during fasting in grass carp Ctenopharyngodon idella adipocytes

Cell death-inducing DNA fragmentation factor 45-like effector family proteins, including CIDEA, CIDEB and CIDEC, play an important role in energy metabolism. In the present study, CIDEA, CIDEB and CIDEC cDNAs were firstly isolated and characterized from grass carp Ctenopharyngodon idella, encoding peptides of 205, 208 and 238 amino acids, respectively. Analysis of the exon-intron structures clarified that grass carp CIDEA, CIDEB and CIDEC consisted of 5 coding exons, 5 coding exons and 6 coding exons, respectively, which is similar with human and mouse. Both CIDE family genes mRNAs were expressed in a wide range of tissues, but the abundance of each CIDE family gene mRNA showed the tissue-dependent expression patterns. Time-course analysis of CIDE family expressions indicated that their expression were enhanced significantly from day 0 to day 8 after differentiation. Forskolin caused an increase in CIDEA and CIDEC expression, and the effects were attenuated by treatment with CREB inhibitor, revealing that CIDEA and CIDEC are regulated by CREB. Further study found that CIDEA and CIDEC mRNA levels did not show significant changes during fasting. These results provide the groundwork to elucidate the gene structure and physiological function of CIDE family in fish.

Effect of Intermittent Energy Restriction on Flow Mediated Dilatation, a Measure of Endothelial Function: A Short Report

Intermittent energy restriction is a popular alternative to daily energy restriction for weight loss; however, it is unknown if endothelial function, a risk factor for cardiovascular disease, is altered by periods of severe energy restriction. The objective of the study was to determine the impact of two consecutive very low energy intake days, which is the core component of the 5:2 intermittent energy restriction diet strategy, on endothelial function compared to consecutive ad libitum eating days. The secondary objective was to explore the effects of these dietary conditions on fasting glucose concentrations. This was a 4-week randomized, single-blinded, crossover study of 35 participants. Participants consumed a very low energy diet (500 calories for women, 600 calories for men) on two consecutive days per week and 5 days of habitual eating. In weeks 3 and 4 of the trial, participants had measurements of flow mediated dilatation (FMD) and blood samples taken following either 2 habitual eating days or 2 energy restricted days in a randomized order. FMD values were not different after the two eating states (8.6% vs. 8.3%, p = 0.7). All other outcome variables were unchanged. Endothelial function, as measured by flow mediated dilatation, was not altered by two consecutive very low energy intake days. Further investigations assessing the impact in specific population groups as well as different testing conditions would be beneficial.

Intermittent Fasting with or without Exercise Prevents Weight Gain and Improves Lipids in Diet-Induced Obese Mice

Intermittent fasting (IF) and high intensity interval training (HIIT) are effective lifestyle interventions for improving body composition and overall health. However, the long-term effects of IF and potential synergistic effects of combining IF with exercise are unclear. The purpose of the study was to investigate the long-term effects of IF, with or without HIIT, on body composition and markers of metabolic health in diet-induced obese mice. In a randosmised, controlled design, 8-week-old C57BL/6 mice (males (n = 39) and females (n = 49)) were fed a high fat (HF) and sugar (S) water diet (30% (w/v)) for 24-weeks but were separated into five groups at 12-weeks: (1) 'obese' baseline control (OBC); (2) no intervention (CON); (3) intermittent fasting (IF); (4) high intensity intermittent exercise (HIIT) and (5) combination of dietary and exercise intervention (IF + HIIT). Body composition, strength and blood variables were measured at 0, 10 and/or 12-weeks. Intermittent fasting with or without HIIT resulted in significantly less weight gain, fat mass accumulation and reduced serum low density lipoproteins (LDL) levels compared to HIIT and CON male mice (p < 0.05). The results suggest that IF, with or without HIIT, can be an effective strategy for weight gain prevention despite concurrently consuming a high fat and sugar diet.

Effects of intermittent fasting and chronic swimming exercise on body composition and lipid metabolism

Intermittent fasting protocol (IFP) has been suggested as a strategy to change body metabolism and improve health. The effects of IFP seem to be similar to aerobic exercise, having a hormetic adaptation according to intensity and frequency. However, the effects of combining both interventions are still unknown. Therefore, the aim of the present study was to evaluate the effects of IFP with and without endurance-exercise training on body composition, food behavior, and lipid metabolism. Twenty-week-old Wistar rats were kept under an inverted circadian cycle of 12 h with water ad libitum and assigned to 4 different groups: control group (ad libitum feeding and sedentary), exercise group (ad libitum feeding and endurance training), intermittent fasting group (IF; intermittent fasting and sedentary), and intermittent fasting and exercise group (IFEX; intermittent fasting and endurance training). After 6 weeks, the body weight of IF and IFEX animals decreased without changes in food consumption. Yet, the body composition between the 2 groups was different, with the IFEX animals containing higher total protein and lower total fat content than the IF animals. The IFEX group also showed increases in total high-density lipoprotein cholesterol and increased intramuscular lipid content. The amount of brown adipose tissue was higher in IF and IFEX groups; however, the IFEX group showed higher expression levels of uncoupling protein 1 in this tissue, indicating a greater thermogenesis. The IFP combined with endurance training is an efficient method for decreasing body mass and altering fat metabolism, without inflicting losses in protein content.

Potential Benefits and Harms of Intermittent Energy Restriction and Intermittent Fasting Amongst Obese, Overweight and Normal Weight Subjects-A Narrative Review of Human and Animal Evidence

Intermittent energy restriction (IER) has become popular as a means of weight control amongst people who are overweight and obese, and is also undertaken by normal weight people hoping spells of marked energy restriction will optimise their health. This review summarises randomised comparisons of intermittent and isoenergetic continuous energy restriction for weight loss to manage overweight and obesity. It also summarises the potential beneficial or adverse effects of IER on body composition, adipose stores and metabolic effects from human studies, including studies amongst normal weight subjects and relevant animal experimentation. Six small short term (<6 month) studies amongst overweight or obese individuals indicate that intermittent energy restriction is equal to continuous restriction for weight loss, with one study reporting greater reductions in body fat, and two studies reporting greater reductions in HOMA insulin resistance in response to IER, with no obvious evidence of harm. Studies amongst normal weight subjects and different animal models highlight the potential beneficial and adverse effects of intermittent compared to continuous energy restriction on ectopic and visceral fat stores, adipocyte size, insulin resistance, and metabolic flexibility. The longer term benefits or harms of IER amongst people who are overweight or obese, and particularly amongst normal weight subjects, is not known and is a priority for further investigation.

Nutrition, insulin resistance and dysfunctional adipose tissue determine the different components of metabolic syndrome

Obesity is an excessive accumulation of body fat that may be harmful to health. Today, obesity is a major public health problem, affecting in greater or lesser proportion all demographic groups. Obesity is estimated by body mass index (BMI) in a clinical setting, but BMI reports neither body composition nor the location of excess body fat. Deaths from cardiovascular diseases, cancer and diabetes accounted for approximately 65% of all deaths, and adiposity and mainly abdominal adiposity are associated with all these disorders. Adipose tissue could expand to inflexibility levels. Then, adiposity is associated with a state of low-grade chronic inflammation, with increased tumor necrosis factor-α and interleukin-6 release, which interfere with adipose cell differentiation, and the action pattern of adiponectin and leptin until the adipose tissue begins to be dysfunctional. In this state the subject presents insulin resistance and hyperinsulinemia, probably the first step of a dysfunctional metabolic system. Subsequent to central obesity, insulin resistance, hyperglycemia, hypertriglyceridemia, hypoalphalipoproteinemia, hypertension and fatty liver are grouped in the so-called metabolic syndrome (MetS). In subjects with MetS an energy balance is critical to maintain a healthy body weight, mainly limiting the intake of high energy density foods (fat). However, high-carbohydrate rich (CHO) diets increase postprandial peaks of insulin and glucose. Triglyceride-rich lipoproteins are also increased, which interferes with reverse cholesterol transport lowering high-density lipoprotein cholesterol. In addition, CHO-rich diets could move fat from peripheral to central deposits and reduce adiponectin activity in peripheral adipose tissue. All these are improved with monounsaturated fatty acid-rich diets. Lastly, increased portions of ω-3 and ω-6 fatty acids also decrease triglyceride levels, and complement the healthy diet that is recommended in patients with MetS.

The role of expression imbalance between adipose synthesis and storage mediated by PPAR-γ/FSP27 in the formation of insulin resistance in catch up growth

Background

Catch up growth (CUG) motivated by under-nutrition can lead to insulin resistance (IR) and visceral fat over-accumulation. However, the precise mechanisms on IR induced by adipose tissue changes during CUG remain unresolved.

Methods

Experimental rats were divided into three groups: normal chow group, catch up growth group and resveratrol administrated group. The whole experiment was carried out in four stages: 4, 6, 8 and 12 weeks.

Peroxisome-proliferator activated receptor gamma (PPAR-γ) and fat-specific protein 27 (FSP27) expression level in epididymal adipose tissues (EAT) and subcutaneous adipose tissues (SAT) were detected along with other IR indicators.

Results

Calorie restriction (CR) significantly increased PPAR-γ expression in EAT while decreased FSP27 expression. During re-feeding, both of the expression of PPAR-γ and FSP27 increased, even FSP27 returned to normal level when CUG for 4 weeks. Although PPAR-γ expression declined slightly at 8 weeks, it was still much stronger than normal chow groups. However, no changes were seen in SAT. Relative insufficiency of FSP27 expression in EAT results in a decrease in lipid storage capacity, causing a series of path physiological changes that led to the formation of IR. Resveratrol inhibited the expression of PPAR-γ and promoted FSP27 expression, thus fundamentally improving IR.

Conclusions

The imbalance between adipose synthesis and storage mediated by PPAR-γ / FSP27 in the EAT plays a pivotal role in the formation of IR during CUG. Resveratrol can correct fat formation and storage imbalance status by up-regulating FSP27 and down-regulating PPAR-γ expression level, ameliorating insulin sensitivity.

Intermittent fasting favored the resolution of Salmonella typhimurium infection in middle-aged BALB/c mice

Intermittent fasting (IF) reportedly increases resistance and intestinal IgA response to Salmonella typhimurium infection in mature mice. The aim of this study was to explore the effect of aging on the aforementioned improved immune response found with IF. Middle-aged male BALB/c mice were submitted to IF or ad libitum (AL) feeding for 40 weeks and then orally infected with S. typhimurium. Thereafter, infected animals were all fed AL (to maximize their viability) until sacrifice on day 7 or 14 post-infection. We evaluated body weight, bacterial load (in feces, Peyer's patches, spleen and liver), total and specific intestinal IgA, lamina propria IgA+ plasma cells, plasma corticosterone, and messenger RNA (mRNA) expression of α-chain, J-chain, and the polymeric immunoglobulin receptor (pIgR) in liver and intestinal mucosa. In comparison with the infected AL counterpart, the infected IF group (long-term IF followed by post-infection AL feeding) generally had lower intestinal and systemic bacterial loads as well as higher total IgA on both post-infection days. Both infected groups showed no differences in corticosterone levels, body weight, or food and caloric intake. The increase in intestinal IgA was associated with enhanced pIgR mRNA expression in the intestine (day 7) and liver. Thus, to maintain body weight and caloric intake, IF elicited metabolic signals that possibly induced the increased hepatic and intestinal pIgR mRNA expression found. The increase in IgA probably resulted from intestinal IgA transcytosis via pIgR. This IgA response along with phagocyte-induced killing of bacteria in systemic organs (not measured) may explain the resolution of the S. typhimurium infection.

Central obesity and altered peripheral adipose tissue gene expression characterize the NAFLD patient with insulin resistance: Role of nutrition and insulin challenge

OBJECTIVE

Insulin resistance (IR) and white adipose tissue (WAT) dysfunction frequently are associated with nonalcoholic fatty liver disease (NAFLD); however, the pathogenic mechanisms contributing to their clustering are not well defined. The aim of this study was to define some nutritional, anthropometric, metabolic, and genetic mechanisms contributing to their clustering.

METHODS

Forty-five (20 men, 25 women) patients (age 45.7 ± 11.1 y) with recent diagnosis of NAFLD were grouped according to IR state. Energy balance was assessed using a food questionnaire and indirect calorimetry, and body composition with anthropometry and dual-energy x-ray absorptiometry. Biochemical and hormonal parameters combined with adipose tissue gene expression were determined. Microarray analysis of gene expression was performed in a subset of WAT samples from IR patients (n = 9), in the fasted state, after specific test meals (monounsaturated fatty acid [MUFA], saturated fat [SAT], and carbohydrate-rich) and after being challenged with insulin.

RESULTS

IR patients exhibited higher trunk fat to leg fat ratio (P < 0.05) and had a higher ratio of SAT/MUFA fat intake (P < 0.05) than insulin-sensitive (IS) individuals. Deposition of fat in the trunk but not in the leg was directly related to liver enzyme levels (P < 0.05). IR patients also had lower adiponectin serum levels and leptin (LEP) mRNA expression in WAT compared with IS patients (P < 0.01 and P < 0.05, respectively). Microarray analysis after insulin challenge confirmed that insulin treatment induces the expression of PPARG gene and LEP and decreases GCGR gene (P < 0.05 for all) in WAT. No changes in these genes were observed in the postprandial state induced after the acute effect of specific diets.

CONCLUSIONS

Patients exhibiting NAFLD and IR had preferential central fat deposition directly related to their serum alanine aminotransferase levels. These patients showed peripheral adipose tissue dysfunction and exhibited inappropriately low LEP biosynthesis that could be partially restored after anabolic conditions induced by insulin signaling.

Circulating leptin levels do not reflect the amount of body fat in the dunlin Calidris alpina during migration

Leptin is a peptide hormone that plays an important role in the regulation of energy homeostasis. Studies in mammals have shown that circulating leptin levels reflect adiposity and that this adipocyte-derived cytokine acts as an afferent satiety signal to the brain, decreasing food intake and increasing energy expenditure. Since leptin has been found in the liver and adipose tissue of migratory birds that are able to accumulate fat reserves as endogenous fuel for flight, we hypothesized that individuals with higher fat score would have higher plasma leptin levels, as it had been found previously in mammals. The aim of this study was to determine if circulating leptin levels correlate with the amount of body fat in a migratory bird, the dunlin Calidris alpina. Adult dunlins were caught during autumn migration on the Baltic coast, and their fat score was determined. Blood samples from 150 birds were used to assess the levels of circulating leptin. We did not find any statistical differences between dunlins with various fat scores. In fact, plasma leptin levels tended to be lower in fat birds than in lean individuals. Our data indicate that in wild birds in migration mode leptin does not reflect the amount of accumulated fat. It suggests that leptin in birds during migration is neither involved in the regulation of energy homeostasis nor acts as a signal to control the amount of body fat.

Intermittent fasting: a dietary intervention for prevention of diabetes and cardiovascular disease?

Intermittent fasting, in which individuals fast on consecutive or alternate days, has been reported to facilitate weight loss and improve cardiovascular risk. This review evaluates the various approaches to intermittent fasting and examines the advantages and limitations for use of this approach in the treatment of obesity and type 2 diabetes.

Fsp27/CIDEC is a CREB target gene induced during early fasting in liver and regulated by FA oxidation rate

FSP27 [cell death-inducing DFFA-like effector c (CIDEC) in humans] is a protein associated with lipid droplets that downregulates the fatty acid oxidation (FAO) rate when it is overexpressed. However, little is known about its physiological role in liver. Here, we show that fasting regulates liver expression of Fsp27 in a time-dependent manner. Thus, during the initial stages of fasting, a maximal induction of 800-fold was achieved, whereas during the later phase of fasting, Fsp27 expression decreased. The early response to fasting can be explained by a canonical PKA-CREB-CRTC2 signaling pathway because: i) CIDEC expression was induced by forskolin, ii) Fsp27 promoter activity was increased by CREB, and iii) Fsp27 expression was upregulated in the liver of Sirt1 knockout animals. Interestingly, pharmacological (etomoxir) or genetic (Hmgcs2 interference) inhibition of the FAO rate increases the in vivo expression of Fsp27 during fasting. Similarly, CIDEC expression was upregulated in HepG2 cells by either etomoxir or HMGCS2 interference. Our data indicate that there is a kinetic mechanism of autoregulation between short- and long-term fasting, by which free FAs delivered to the liver during early fasting are accumulated/exported by FSP27/CIDEC, whereas over longer periods of fasting, they are degraded in the mitochondria through the carnitine palmitoyl transferase system.