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

Induction of the Lipid Droplet Formation Genes in Steatohepatitis Mice by Embryo/Postnatal Nutrient Environment Is Associated with Histone Acetylation around the Genes

Recently, we have demonstrated that mice, cultured embryos in α-minimum essential medium (αMEM) and subsequent fed a high-fat, high-sugar diet, developed steatohepatitis. In this study, we investigated using these samples whether the expression of lipid droplet formation genes in the liver is higher in MEM mice, whether these expressions are regulated by histone acetylation, writers/readers of histone acetylation, and the transcriptional factors of endoplasmic reticulum stress. Mice were produced by two-cell embryos in αMEM or standard potassium simplex-optimized medium (control) in vitro for 48 h, and implanted into an oviduct for spontaneous delivery. MEM and control-mice were fed a high-fat, high-sugar diet for 18 wk, and then liver samples were collected and analyzed by histology, qRT-PCR, and chromatin immunoprecipitation assay. Gene expression of Cidea, Cidec, and Plin4 were higher in MEM mice and histone H3K9 acetylation, BRD4, and CBP were higher in MEM mice than in control mice around those genes. However, the binding of endoplasmic reticulum stress-related transcription factors (ATF4, CHOP and C/EBPα) around those genes in the liver, was not clearly differed between MEM mice and control mice. The increased expression of Cidea, Cidec and Plin4 in the liver, accompanied by the development of steatohepatitis in mice induced is positively associated with increased histone H3K9 acetylation and CBP and BRD4 binding around these genes.

FOXO1 represses PPARα-Mediated induction of FGF21 gene expression

Fibroblast growth factor 21 (FGF21) has emerged as a metabolic regulator that exerts potent anti-diabetic and lipid-lowering effects in animal models of obesity and type 2 diabetes, showing a protective role in fatty liver disease and hepatocellular carcinoma progression. Hepatic expression of FGF21 is regulated by PPARα and is induced by fasting. Ablation of FoxO1 in liver has been shown to increase FGF21 expression in hyperglycemia. To better understand the role of FOXO1 in the regulation of FGF21 expression we have modified HepG2 human hepatoma cells to overexpress FoxO1 and PPARα. Here we show that FoxO1 represses PPARα-mediated FGF21 induction, and that the repression acts on the FGF21 gene promoter without affecting other PPARα target genes. Additionally, we demonstrate that FoxO1 physically interacts with PPARα and that FoxO1/3/4 depletion in skeletal muscle contributes to increased Fgf21 tissue levels. Taken together, these data indicate that FOXO1 is a PPARα-interacting protein that antagonizes PPARα activity on the FGF21 promoter. Because other PPARα target genes remained unaffected, these results suggest a highly specific mechanism implicated in FGF21 regulation. We conclude that FGF21 can be specifically modulated by FOXO1 in a PPARα-dependent manner.

PPARγ lipodystrophy mutants reveal intermolecular interactions required for enhancer activation

Peroxisome proliferator-activated receptor γ (PPARγ) is the master regulator of adipocyte differentiation, and mutations that interfere with its function cause lipodystrophy. PPARγ is a highly modular protein, and structural studies indicate that PPARγ domains engage in several intra- and inter-molecular interactions. How these interactions modulate PPARγ's ability to activate target genes in a cellular context is currently poorly understood. Here we take advantage of two previously uncharacterized lipodystrophy mutations, R212Q and E379K, that are predicted to interfere with the interaction of the hinge of PPARγ with DNA and with the interaction of PPARγ ligand binding domain (LBD) with the DNA-binding domain (DBD) of the retinoid X receptor, respectively. Using biochemical and genome-wide approaches we show that these mutations impair PPARγ function on an overlapping subset of target enhancers. The hinge region-DNA interaction appears mostly important for binding and remodelling of target enhancers in inaccessible chromatin, whereas the PPARγ-LBD:RXR-DBD interface stabilizes the PPARγ:RXR:DNA ternary complex. Our data demonstrate how in-depth analyses of lipodystrophy mutants can unravel molecular mechanisms of PPARγ function.

MicroRNAs and Circular RNAs in Lipoprotein Metabolism

PURPOSE OF REVIEW

Non-coding RNAs (ncRNAs) including microRNAs (miRNAs) and circular RNAs (circRNAs) are pivotal regulators of mRNA and protein expression that critically contribute to cardiovascular pathophysiology. Although little is known about the origin and function of such ncRNAs, they have been suggested as promising biomarkers with powerful therapeutic value in cardiovascular disease (CVD). In this review, we summarize the most recent findings on ncRNAs biology and their implication on cholesterol homeostasis and lipoprotein metabolism that highlight novel therapeutic avenues for treating dyslipidemia and atherosclerosis.

RECENT FINDINGS

Clinical and experimental studies have elucidated the underlying effects that specific miRNAs impose both directly and indirectly regulating circulating high-density lipoprotein (HDL), low-density lipoprotein (LDL), and very low-density lipoprotein (VLDL) metabolism and cardiovascular risk. Some of these relevant miRNAs include miR-148a, miR-128-1, miR-483, miR-520d, miR-224, miR-30c, miR-122, miR-33, miR-144, and miR-34. circRNAs are known to participate in a variety of physiological and pathological processes due to their abundance in tissues and their stage-specific expression activation. Recent studies have proven that circRNAs may be considered targets of CVD as well. Some of these cirRNAs are circ-0092317, circ_0003546, circ_0028198, and cirFASN that have been suggested to be strongly involved in lipoprotein metabolism; however, their relevance in CVD is still unknown. MicroRNA and cirRNAs have been proposed as powerful therapeutic targets for treating cardiometabolic disorders including atherosclerosis. Here, we discuss the recent findings in the field of lipid and lipoprotein metabolism underscoring the novel mechanisms by which some of these ncRNAs influence lipoprotein metabolism and CVD.

Lyophilized Maqui (Aristotelia chilensis) Berry Administration Suppresses High-Fat Diet-Induced Liver Lipogenesis through the Induction of the Nuclear Corepressor SMILE

The liver is one of the first organs affected by accumulated ectopic lipids. Increased de novo lipogenesis and excessive triglyceride accumulation in the liver are hallmarks of nonalcoholic fatty liver disease (NAFLD) and are strongly associated with obesity, insulin resistance, and type 2 diabetes. Maqui dietary supplemented diet-induced obese mice showed better insulin response and decreased weight gain. We previously described that these positive effects of maqui are partially due to an induction of a brown-like phenotype in subcutaneous white adipose tissue that correlated with a differential expression of Chrebp target genes. In this work, we aimed to deepen the molecular mechanisms underlying the impact of maqui on the onset and development of the obese phenotype and insulin resistance focusing on liver metabolism. Our results showed that maqui supplementation decreased hepatic steatosis caused by a high-fat diet. Changes in the metabolic profile include a downregulation of the lipogenic liver X receptor (LXR) target genes and of fatty acid oxidation gene expression together with an increase in the expression of small heterodimer partner interacting leucine zipper protein (Smile), a corepressor of the nuclear receptor family. Our data suggest that maqui supplementation regulates lipid handling in liver to counteract the metabolic impact of a high-fat diet.

Lipid Droplet Contact Sites in Health and Disease

After having been disregarded for a long time as inert fat drops, lipid droplets (LDs) are now recognized as ubiquitous cellular organelles with key functions in lipid biology and beyond. The identification of abundant LD contact sites, places at which LDs are physically attached to other organelles, has uncovered an unexpected level of communication between LDs and the rest of the cell. In recent years, many disease factors mutated in hereditary disorders have been recognized as LD contact site proteins. Furthermore, LD contact sites are dramatically rearranged in response to infections with intracellular pathogens, as well as under pathological metabolic conditions such as hepatic steatosis. Collectively, it is emerging that LD-organelle contacts are important players in development and progression of disease.

Eicosapentaenoic acid-enriched phospholipids suppressed lipid accumulation by specific inhibition of lipid droplet-associated protein FSP27 in mice

BACKGROUND

Sea cucumber is a rich source of eicosapentaenoic acid in the form of eicosapentaenoic acid-enriched phospholipids (EPA-PL). It is known to be efficacious in preventing obesity. However, few studies have focused on the role of EPA-PL in inhibiting lipid accumulation by lipid droplets (LDs). This study first investigated the effect of EPA-PL from sea cucumber on the formation of LDs and the underlying mechanism in C57BL/6J mice. The mice were randomly divided into two groups and treated for 8 weeks or 3, 7, and 14 days with either (i) a high-sucrose diet (model group), (ii) a high-sucrose diet plus 2% EPA-PL (EPA-PL group).

RESULTS

Eight-week EPA-PL supplementation significantly reduced lipid accumulation and LD size in liver and white adipose tissue (WAT), which was accompanied by the decreased expression of LDs-associated protein FSP27. A 3-day EPA-PL treatment suppressed the mRNA expression of Fsp27. The mRNA level of Fsp27 reached its 'normal level' after withdrawing EPA-PL for 7 days, suggesting that EPA-PL might serve as a rapid regulator of FSP27. Furthermore, EPA-PL increased the expression of lipolysis genes Hsl and Atgl accompanied by the regulation of Pparγ in WAT.

CONCLUSIONS

Dietary EPA-PL from sea cucumber (Cucumaria frondosa) protected against lipid accumulation by regulating LDs-associated protein FSP27, which might provide novel evidence for the anti-obesity action of EPA-PL. © 2020 Society of Chemical Industry.

Pgc1a is responsible for the sex differences in hepatic Cidec/Fsp27β mRNA expression in hepatic steatosis of mice fed a Western diet

Hepatic fat-specific protein 27 [cell death-inducing DNA fragmentation effector protein C (Cidec)/Fsp27] mRNA levels have been associated with hepatic lipid droplet extent under certain circumstances. To address its hepatic expression under different dietary conditions and in both sexes, apolipoprotein E (Apoe)-deficient mice were subjected to different experimental conditions for 11 wk to test the influence of cholesterol, Western diet, squalene, oleanolic acid, sex, and surgical castration on Cidec/Fsp27 mRNA expression. Dietary cholesterol increased hepatic Cidec/Fsp27β expression, an effect that was suppressed when cholesterol was combined with saturated fat as represented by Western diet feeding. Using the latter diet, neither oleanolic acid nor squalene modified its expression. Females showed lower levels of hepatic Cidec/Fsp27β expression than males when they were fed Western diets, a result that was translated into a lesser amount of CIDEC/FSP27 protein in lipid droplets and microsomes. This was also confirmed in low-density lipoprotein receptor (Ldlr)-deficient mice. Incubation with estradiol resulted in decreased Cidec/Fsp27β expression in AML12 cells. Whereas male surgical castration did not modify the expression, ovariectomized females did show increased levels compared with control females. Females also showed increased expression of peroxisome proliferator-activated receptor-γ coactivator 1-α (Pgc1a), suppressed by ovariectomy, and the values were significantly and inversely associated with those of Cidec/Fsp27β. When Pgc1a-deficient mice were used, the sex differences in Cidec/Fsp27β expression disappeared. Therefore, hepatic Cidec/Fsp27β expression has a complex regulation influenced by diet and sex hormonal milieu. The mRNA sex differences are controlled by Pgc1a.

Fat-specific protein 27b is regulated by hepatic peroxisome proliferator-activated receptor γ in hepatic steatosis

The fat-specific protein 27 gene (Fsp27) belongs to the cell death-inducing DNA fragmentation factor 45-like effector family. Fsp27 is highly expressed in adipose tissue and fatty liver. In adipocytes, FSP27 localizes to the membrane of lipid droplets and promotes lipid droplet hypertrophy. Recently, FSP27 was shown to consist of two isoforms, FSP27α and FSP27β. Previously, we demonstrated that Fsp27a is directly regulated by peroxisome proliferator-activated receptor γ (PPARγ) in fatty livers of genetically obese leptin deficient ob/ob mice and that Fsp27b may potentially be regulated by different factors transcriptionally as they both have a different promoter region. Thus, the aim of the present study was to elucidate whether Fsp27b is regulated by PPARγ in fatty liver. Fsp27a and Fsp27b were markedly induced in fatty liver of ob/ob mice compared with those in the normal liver. However, both Fsp27a/b were expressed at markedly lower levels in liver-specific PPARγ knockout mice with an ob/ob background. Further, the PPAR response element (PPRE) for the PPARγ-dependent promotion of Fsp27b promotor activity was revealed at position -1,163/-1,151 from the transcriptional start site (+1). Interestingly, the cis-element responsible for the PPARγ-dependent induction of Fsp27b was the same as that responsible for PPARγ-dependent induction of Fsp27a. These results suggest that PPARγ regulates not only Fsp27a but also Fsp27b in fatty liver of ob/ob mice through a common PPRE.

New Insights into Apolipoprotein A5 and the Modulation of Human Adipose-derived Mesenchymal Stem Cells Adipogenesis

Background:

The hallmark of obesity is the excessive accumulation of triglyceride (TG) in adipose tissue. Apolipoprotein A5 (ApoA5) has been shown to influence the prevalence and pathogenesis of obesity. However, the underlying mechanisms remain to be clarified.

Methods:

Human adipose-derived mesenchymal stem cells (AMSCs) were treated with 600 ng/ml human recombinant ApoA5 protein. The effect of ApoA5 on intracellular TG content and adipogenic related factors expression were determined. Furthermore, the effect of ApoA5 on CIDE-C expression was also observed.

Results:

During the process of adipogenesis, ApoA5 treatment reduced the intracellular accumulation of lipid droplets and the TG levels; meanwhile, ApoA5 down-regulated the expression levels of adipogenic related factors, including CCAAT enhancer-binding proteins α/β (C/EBPα/β), fatty acid synthetase (FAS), and fatty acid-binding protein 4 (FABP4). Furthermore, the suppression of adipogenesis by ApoA5 was mediated through the inhibition of CIDE-C expression, an important factor which promotes the process of adipogenesis. However, over-expressing intracellular CIDE-C could lead to the loss-of-function of ApoA5 in inhibiting AMSCs adipogenesis.

Conclusions:

In conclusion, ApoA5 inhibits the adipogenic process of AMSCs through, at least partly, down-regulating CIDE-C expression. The present study provides novel mechanisms whereby ApoA5 prevents obesity via AMSCs in humans.

Fasting reveals largely intact systemic lipid mobilization mechanisms in respiratory chain complex III deficient mice

Mice homozygous for the human GRACILE syndrome mutation (Bcs1l^c.A232G) display decreased respiratory chain complex III activity, liver dysfunction, hypoglycemia, rapid loss of white adipose tissue and early death. To assess the underlying mechanism of the lipodystrophy in homozygous mice (Bcs1l^p.S78G), these and wild-type control mice were subjected to a short 4-hour fast. The homozygotes had low baseline blood glucose values, but a similar decrease in response to fasting as in wild-type mice, resulting in hypoglycemia in the majority. Despite the already depleted glycogen and increased triacylglycerol content in the mutant livers, the mice responded to fasting by further depletion and increase, respectively. Increased plasma free fatty acids (FAs) upon fasting suggested normal capacity for mobilization of lipids from white adipose tissue into circulation. Strikingly, however, serum glycerol concentration was not increased concomitantly with free FAs, suggesting its rapid uptake into the liver and utilization for fuel or gluconeogenesis in the mutants. The mutant hepatocyte mitochondria were capable of responding to fasting by appropriate morphological changes, as analyzed by electron microscopy, and by increasing respiration. Mutants showed increased hepatic gene expression of major metabolic controllers typically associated with fasting response (Ppargc1a, Fgf21, Cd36) already in the fed state, suggesting a chronic starvation-like metabolic condition. Despite this, the mutant mice responded largely normally to fasting by increasing hepatic respiration and switching to FA utilization, indicating that the mechanisms driving these adaptations are not compromised by the CIII dysfunction. SUMMARY STATEMENT: Bcs1l mutant mice with severe CIII deficiency, energy deprivation and post-weaning lipolysis respond to fasting similarly to wild-type mice, suggesting largely normal systemic lipid mobilization and utilization mechanisms.

FSP27 and Links to Obesity and Diabetes Mellitus

PURPOSE OF REVIEW

Obesity is a pandemic, yet preventable healthcare problem. Insulin resistance, diabetes mellitus, dyslipidemia, and cardiovascular complications are core manifestation of obesity. While adipose tissue is a primary site of energy storage, it is also an endocrine organ, secreting a large number of adipokines and cytokines. Nonetheless in obesity, the secretion of cytokines and free fatty acids increases significantly and is associated with the degree of adiposity and insulin resistance. Fat-specific protein 27 (FSP27) has emerged as one of the major proteins that promote physiological storage of fat in adipose tissue.

RECENT FINDINGS

Review of number of recent findings suggests that FSP27 plays a crucial role in physiological storage of fat within the adipose tissue especially in humans. However, in disease conditions such as obesity, FSP27 may contribute to ectopic fat accumulation in non-adipose tissue. More studies are required to highlight the tissue-specific role of FSP27, especially in humans.

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.

CIDE Proteins in Human Health and Disease

Cell death-Inducing DNA Fragmentation Factor Alpha (DFFA)-like Effector (CIDE) proteins have emerged as lipid droplet-associated proteins that regulate fat metabolism. There are three members in the CIDE protein family—CIDEA, CIDEB, and CIDEC (also known as fat-specific protein 27 (FSP27)). CIDEA and FSP27 are primarily expressed in adipose tissue, while CIDEB is expressed in the liver. Originally, based upon their homology with DNA fragmentation factors, these proteins were identified as apoptotic proteins. However, recent studies have changed the perception of these proteins, redefining them as regulators of lipid droplet dynamics and fat metabolism, which contribute to a healthy metabolic phenotype in humans. Despite various studies in humans and gene-targeting studies in mice, the physiological roles of CIDE proteins remains elusive. This review will summarize the known physiological role and metabolic pathways regulated by the CIDE proteins in human health and disease.

Fat-specific protein 27 is a novel target gene of liver X receptor α

Fat-specific protein 27 (FSP27) is highly expressed in the fatty liver of genetically obese ob/ob mice and promotes hepatic triglyceride (TG) accumulation. The nuclear hormone receptor liver X receptor α (LXRα) also plays a critical role in the control of TG levels in the liver. The present study demonstrated transcriptional regulation of Fsp27a and Fsp27b genes by LXRα. Treatment with the LXR ligand T0901317 markedly increased Fsp27a and Fsp27b mRNAs in wild-type C57BL/6J and ob/ob mouse livers. A reporter assay indicated that two LXR-responsive elements (LXREs) are necessary for LXRα-dependent induction of Fsp27a and Fsp27b promoter activities. Furthermore, the LXRα/retinoid X receptor α complex is capable of directly binding to the two LXREs both in vitro and in vivo. These results suggest that LXRα positively regulates Fsp27a and Fsp27b expression through two functional LXREs. Fsp27a/b are novel LXR target genes in the ob/ob fatty liver.

Therapeutic silencing of FSP27 reduces the progression of atherosclerosis in Ldlr-/- mice

Background and aims

Obesity, hepatosteatosis, and hypertriglyceridemia are components of the metabolic syndrome and independent risk factors for cardiovascular disease. The lipid droplet-associated protein CIDEC (cell death-inducing DFFA-like effector C), known in mice as FSP27 (fat-specific protein 27), plays a key role in maintaining triacylglyceride (TAG) homeostasis in adipose tissue and liver, and controls circulating TAG levels in mice. Importantly, mutations and SNPs in CIDEC are associated with dyslipidemia and altered metabolic function in humans. Here we tested whether systemic silencing of Fsp27 using antisense oligonucleotides (ASOs) was atheroprotective in LDL receptor knock-out (Ldlr^−/−) mice.

Methods

Atheroprone Ldlr^−/− mice were fed a high-fat, high-cholesterol diet for 12 weeks while simultaneously dosed with saline, ASO-ctrl, or ASO-Fsp27.

Results

Data show that, compared to control treatments, silencing Fsp27 significantly reduced body weight gain and visceral adiposity, prevented diet-induced hypertriglyceridemia, and reduced athero-sclerotic lesion size both in en face aortas and in the aortic root.

Conclusions

Our findings suggest that therapeutic silencing of Fsp27 with ASOs may be beneficial in the prevention and management of atherogenic disease in patients with metabolic syndrome.

Cidec differentially regulates lipid deposition and secretion through two tissue-specific isoforms

Lipid metabolism has important roles in animal growth, development, and reproduction. As a regulator of lipid metabolism, CIDEc promotes unilocular development of lipid droplets and stimulates intracellular lipid deposition, and has two isoforms, CIDEc-l and CIDEc-s. CIDEc-l has ten more N-terminal amino acids than CIDEc-s. However, the functions of two isoforms are largely unknown. In this study, the expression profiles of two isoforms in Bama pigs differed, with cidec-l dominant in the liver and small intestine, and cidec-s dominant in muscle and adipose tissue. Fasting and consuming a high-fat diet resulted in changes in the expression of the two isoforms that were closely related to changes in blood and muscle triglyceride (TG) concentrations. Comparison of gene expression and TG concentration suggested that CIDEc-l accelerated lipid secretion and that CIDEc-s promoted lipid deposition, implying that the two isoforms had different functions. Study In vitro confirmed that CIDEc-s stimulated lipid deposition in C2C12 muscle cells and CIDEc-l promoted lipid secretion in HepG2 liver cells. The results showed that two tissue-specific CIDEc isoforms had different roles in lipid deposition and secretion. They may be potential targets for regulation of fat content.

Global Analysis of Plasma Lipids Identifies Liver-Derived Acylcarnitines as a Fuel Source for Brown Fat Thermogenesis

Cold-induced thermogenesis is an energy-demanding process that protects endotherms against a reduction in ambient temperature. Using non-targeted liquid chromatography-mass spectrometry-based lipidomics, we identified elevated levels of plasma acylcarnitines in response to the cold. We found that the liver undergoes a metabolic switch to provide fuel for brown fat thermogenesis by producing acylcarnitines. Cold stimulates white adipocytes to release free fatty acids that activate the nuclear receptor HNF4α, which is required for acylcarnitine production in the liver and adaptive thermogenesis. Once in circulation, acylcarnitines are transported to brown adipose tissue, while uptake into white adipose tissue and liver is blocked. Finally, a bolus of L-carnitine or palmitoylcarnitine rescues the cold sensitivity seen with aging. Our data highlight an elegant mechanism whereby white adipose tissue provides long-chain fatty acids for hepatic carnitilation to generate plasma acylcarnitines as a fuel source for peripheral tissues in mice.

Insulin Represses Fasting-Induced Expression of Hepatic Fat-Specific Protein 27

The fat-specific protein 27 (Fsp27) gene belongs to the cell death-inducing DNA fragmentation factor 45-like effector family. Fsp27 is highly expressed in adipose tissue as well as the fatty liver of ob/ob mice. Fsp27 is directly regulated by the peroxisome proliferator-activated receptor γ (PPARγ) in livers of genetically obese leptin deficient ob/ob mice. In the present study, Fsp27 was markedly induced by 24 h fasting in genetically normal mouse livers and repressed by refeeding a high sucrose diet. In contrast with the liver, Fsp27 expression was decreased in adipose tissue by fasting and increased by refeeding. Interestingly, fasting-induced Fsp27 liver expression was independent of PPARγ. Moreover, Fsp27 expression was induced in the insulin-depleted livers of streptozotocin-treated mice. Finally, Fsp27 expression was repressed by direct injection of glucose or insulin in fasting mice. These results suggest that insulin represses Fsp27 expression in the fasting liver.

A Systems Biology Approach Using Transcriptomic Data Reveals Genes and Pathways in Porcine Skeletal Muscle Affected by Dietary Lysine

Nine crossbred finishing barrows (body weight 94.4 ± 6.7 kg) randomly assigned to three dietary treatments were used to investigate the effects of dietary lysine on muscle growth related metabolic and signaling pathways. Muscle samples were collected from the longissimus dorsi of individual pigs after feeding the lysine-deficient (4.30 g/kg), lysine-adequate (7.10 g/kg), or lysine-excess (9.80 g/kg) diet for five weeks, and the total RNA was extracted afterwards. Affymetrix Porcine Gene 1.0 ST Array was used to quantify the expression levels of 19,211 genes. Statistical ANOVA analysis of the microarray data showed that 674 transcripts were differentially expressed (at p ≤ 0.05 level); 60 out of 131 transcripts (at p ≤ 0.01 level) were annotated in the NetAffx database. Ingenuity pathway analysis showed that dietary lysine deficiency may lead to: (1) increased muscle protein degradation via the ubiquitination pathway as indicated by the up-regulated DNAJA1, HSP90AB1 and UBE2B mRNA; (2) reduced muscle protein synthesis via the up-regulated RND3 and ZIC1 mRNA; (3) increased serine and glycine synthesis via the up-regulated PHGDH and PSPH mRNA; and (4) increased lipid accumulation via the up-regulated ME1, SCD, and CIDEC mRNA. Dietary lysine excess may lead to: (1) decreased muscle protein degradation via the down-regulated DNAJA1, HSP90AA1, HSPH1, and UBE2D3 mRNA; and (2) reduced lipid biosynthesis via the down-regulated CFD and ME1 mRNA. Collectively, dietary lysine may function as a signaling molecule to regulate protein turnover and lipid metabolism in the skeletal muscle of finishing pigs.

Therapeutic silencing of fat-specific protein 27 improves glycemic control in mouse models of obesity and insulin resistance

Obesity is a component of the metabolic syndrome, mechanistically linked to diabetes, fatty liver disease, and cardiovascular disease. Proteins that regulate the metabolic fate of intracellular lipid droplets are potential therapeutic candidates to treat obesity and its related consequences. CIDEC (cell death-inducing DFFA-like effector C), also known in mice as Fsp27 (fat-specific protein 27), is a lipid droplet-associated protein that prevents lipid mobilization and promotes intracellular lipid storage. The consequences of complete loss of FSP27 on hepatic metabolism and on insulin resistance are controversial, as both healthy and deleterious lipodystrophic phenotypes have been reported in Fsp27^−/− mice. To test whether therapeutic silencing of Fsp27 might be useful to improve obesity, fatty liver, and glycemic control, we used antisense oligonucleotides (ASOs) in both nutritional (high-fat diet) and genetic (leptin-deficient ob/ob) mouse models of obesity, hyperglycemia, and hepatosteatosis. We show that partial silencing Fsp27 in either model results in the robust decrease in visceral fat, improved insulin sensitivity and whole-body glycemic control, and tissue-specific changes in transcripts controlling lipid oxidation and synthesis. These data suggest that partial reduction of FSP27 activity (e.g., using ASOs) might be exploited therapeutically in insulin-resistant obese or overweight patients.

Bile acid receptor agonists INT747 and INT777 decrease oestrogen deficiency-related postmenopausal obesity and hepatic steatosis in mice

Menopause is often followed by obesity and, related to this, non-alcoholic fatty liver disease (NAFLD). Two bile acid (BA) receptors, farnesoid X receptor (FXR) and G-protein-coupled receptor TGR5, have emerged as putative therapeutic targets for obesity and NAFLD.

AIM OF THIS STUDY

to evaluate the efficacy of selective agonists INT747/obeticholic acid (FXR) and INT777 (TGR5) as novel treatments for the metabolic effects of oestrogen deficiency. Ovariectomized (OVX) or sham-operated (SHAM) mice were fed a high-fat diet (HFD) for 5weeks. During the last 4weeks two groups of OVX and SHAM mice received either INT747- or INT777-supplemented HFD. OVX mice had significantly higher bodyweight gain than SHAM mice, which was attenuated by INT747- or INT777-treatment. No significant changes in food intake or physical activity were found. OVX mice had significantly lower energy expenditure than SHAM mice; INT747- and INT777-treated OVX mice had intermediate energy expenditure. Liver triglyceride and cholesterol content was significantly increased in OVX compared to SHAM mice, which was normalized by INT747- or INT777-treatment. Significant changes in metabolic gene expression were found in liver (Cpt1, Acox1), muscle (Ucp3, Pdk4, Cpt1, Acox1, Fasn, Fgf21), brown adipocytes (Dio2) and white adipocytes (c/EBPα, Pparγ, Adipoq). For the first time, expression of FXR and induction of its target gene Pltp1 was shown in skeletal muscle. BA receptor agonists are suitable therapeutics to correct postmenopausal metabolic changes in an OVX mouse model. Potential mechanisms include increased energy expenditure and changes in expression patterns of key metabolic genes in liver, muscle and adipose tissues.

Alcohol and fat promote steatohepatitis: a critical role for fat-specific protein 27/CIDEC

Alcoholic liver disease (ALD) is a major public health problem worldwide and is the leading cause of end-stage liver disease. While the ultimate control of ALD will require the prevention of alcohol abuse, better understanding of the mechanisms of alcohol-induced liver injury may lead to treatments of fatty liver, alcoholic hepatitis, and prevention or delay of occurrence of cirrhosis. The elucidation and the discovery of several new concepts in ALD pathogenesis have raised our understanding on the complex mechanisms and the potential in developing the new strategies for therapeutic benefits. In this review, we provide the most up-to-date information on the basic molecular mechanisms focusing on the role of fat-specific protein 27/CIDEC in the pathogenesis of ALD.

β2-Adrenergic receptor ablation modulates hepatic lipid accumulation and glucose tolerance in aging mice

Catecholamines acting through β-adrenergic receptors (β(1)-, β(2)-, β(3)-AR subtypes) modulate important biological responses in various tissues. Our previous studies suggest a role for increased hepatic β-AR-mediated signaling during aging as a mediator of hepatic steatosis, liver glucose output, and insulin resistance in rodents. In the current study, we have utilized β(2)-AR knockout (KO) and wildtype (WT) control mice to define further the role of β(2)-AR signaling during aging on lipid and glucose metabolism. Our results demonstrate for the first time that age-related increases in hepatic triglyceride accumulation and body weight are attenuated upon β(2)-AR ablation. Although no differences in plasma triglyceride, non-esterified fatty acids or insulin levels were detected between old WT and KO animals, an age-associated increase in hepatic expression of lipid homeostasis regulator Cidea was significantly reduced in old KO mice. Interestingly, we also observed a shift from reduced glucose tolerance in young adult KO animals to significantly improved glucose tolerance in old KO when compared to age-matched WT mice. These results provide evidence for an important role played by β(2)-ARs in the regulation of lipid and glucose metabolism during aging. The effect of β(2)-AR ablation on caloric intake during aging is currently not known and requires investigation. Future studies are also warranted to delineate the β(2)-AR-mediated mechanisms involved in the control of lipid and glucose homeostasis, especially in the context of a growing aging population.

Differential Roles of Cell Death-inducing DNA Fragmentation Factor-α-like Effector (CIDE) Proteins in Promoting Lipid Droplet Fusion and Growth in Subpopulations of Hepatocytes

Lipid droplets (LDs) are dynamic subcellular organelles whose growth is closely linked to obesity and hepatic steatosis. Cell death-inducing DNA fragmentation factor-α-like effector (CIDE) proteins, including Cidea, Cideb, and Cidec (also called Fsp27), play important roles in lipid metabolism. Cidea and Cidec are LD-associated proteins that promote atypical LD fusion in adipocytes. Here, we find that CIDE proteins are all localized to LD-LD contact sites (LDCSs) and promote lipid transfer, LD fusion, and growth in hepatocytes. We have identified two types of hepatocytes, one with small LDs (small LD-containing hepatocytes, SLHs) and one with large LDs (large LD-containing hepatocytes, LLHs) in the liver. Cideb is localized to LDCSs and promotes lipid exchange and LD fusion in both SLHs and LLHs, whereas Cidea and Cidec are specifically localized to the LDCSs and promote lipid exchange and LD fusion in LLHs. Cideb-deficient SLHs have reduced LD sizes and lower lipid exchange activities. Fasting dramatically induces the expression of Cidea/Cidec and increases the percentage of LLHs in the liver. The majority of the hepatocytes from the liver of obese mice are Cidea/Cidec-positive LLHs. Knocking down Cidea or Cidec significantly reduced lipid storage in the livers of obese animals. Our data reveal that CIDE proteins play differential roles in promoting LD fusion and lipid storage; Cideb promotes lipid storage under normal diet conditions, whereas Cidea and Cidec are responsible for liver steatosis under fasting and obese conditions.

CIDEC/FSP27 is regulated by peroxisome proliferator-activated receptor alpha and plays a critical role in fasting- and diet-induced hepatosteatosis

The cell death-inducing DNA fragmentation factor alpha-like effector c (CIDEC; also known in rodents as FSP27 or fat-specific protein 27) is a lipid droplet-associated protein that promotes intracellular triglyceride (TAG) storage. CIDEC/Fsp27 is highly expressed in adipose tissue, but undetectable in normal liver. However, its hepatic expression rises during fasting or under genetic or diet-induced hepatosteatosis in both mice and patients. Herein, we demonstrate that CIDEC/Fsp27 is a direct transcriptional target of the nuclear receptor PPARα (peroxisome proliferator-activated receptor alpha) in both mouse and human hepatocytes, and that preventing Fsp27 induction accelerates PPARα-stimulated fatty acid oxidation. We show that adenoviral-mediated silencing of hepatic Fsp27 abolishes fasting-induced liver steatosis in the absence of changes in plasma lipids. Finally, we report that anti-Fsp27 short hairpin RNA and PPARα agonists synergize to ameliorate hepatosteatosis in mice fed a high fat diet.

CONCLUSIONS

Together, our data highlight the physiological importance of CIDEC/Fsp27 in TAG homeostasis under both physiological and pathological liver steatosis. Our results also suggest that patients taking fibrates likely have elevated levels of hepatic CIDEC, which may limit the efficient mobilization and catabolism of hepatic TAGs.

Transcriptional activation of Fsp27 by the liver-enriched transcription factor CREBH promotes lipid droplet growth and hepatic steatosis

Fat-specific protein 27 (Fsp27) is a lipid droplet-associated protein that promotes lipid droplet (LD) growth and triglyceride (TG) storage in white adipocytes. Fsp27 is also highly expressed in the steatotic liver and contributes to TG accumulation. In this study we discovered that the liver produces Fsp27β, an alternative Fsp27 isoform, which contains 10 additional amino acids at the N-terminus of the original Fsp27 (Fsp27α). White adipose tissue (WAT) and the liver specifically expressed Fsp27α and Fsp27β transcripts, respectively, which were driven by distinct promoters. The Fsp27β promoter was activated by the liver-enriched transcription factor cyclic-AMP-responsive-element-binding protein H (CREBH) but not by peroxisome proliferator-activated receptor gamma (PPARγ), which activated the Fsp27α promoter. Enforced expression of the constitutively active CREBH strongly induced Fsp27β and the human ortholog CIDEC2 in mouse hepatocytes and HepG2 cells, respectively. In contrast, loss of CREBH decreased hepatic Fsp27β in fasted mice, suggesting that CREBH plays a critical role in Fsp27β expression in the liver. Similar to Fsp27α, Fsp27β localized on the surface of lipid droplets and suppressed lipolysis. Consequently, enforced expression of Fsp27β or CREBH promoted lipid droplet enlargement and TG accumulation in the liver.

CONCLUSION

The CREBH-Fsp27β axis is important for regulating lipid droplet dynamics and TG storage in the liver.

Cytochrome P450 1B1: An unexpected modulator of liver fatty acid homeostasis

Cytochrome P450 1b1 (Cyp1b1) expression is absent in mouse hepatocytes, but present in liver endothelia and activated stellate cells. Increased expression during adipogenesis suggests a role of Cyp1b1 metabolism in fatty acid homeostasis. Wild-type C57BL/6j (WT) and Cyp1b1-null (Cyp1b1-ko) mice were provided low or high fat diets (LFD and HFD, respectively). Cyp1b1-deletion suppressed HFD-induced obesity, improved glucose tolerance and prevented liver steatosis. Suppression of lipid droplets in sinusoidal hepatocytes, concomitant with enhanced glycogen granules, was a consistent feature of Cyp1b1-ko mice. Cyp1b1 deletion altered the in vivo expression of 560 liver genes, including suppression of PPARγ, stearoyl CoA desaturase 1 (Scd1) and many genes stimulated by PPARα, each consistent with this switch in energy storage mechanism. Ligand activation of PPARα in Cyp1b1-ko mice by WY-14643 was, nevertheless, effective. Seventeen gene changes in Cyp1b1-ko mice correspond to mouse transgenic expression that attenuated diet-induced diabetes. The absence of Cyp1b1 in mouse hepatocytes indicates participation in energy homeostasis through extra-hepatocyte signaling. Extensive sexual dimorphism in hepatic gene expression suggests a developmental impact of estrogen metabolism by Cyp1b1. Suppression of Scd1 and increased leptin turnover support enhanced leptin participation from the hypothalamus. Cyp1b1-mediated effects on vascular cells may underlie these changes.

Impact of nutrients on circadian rhythmicity

The suprachiasmatic nucleus (SCN) in the mammalian hypothalamus functions as an endogenous pacemaker that generates and maintains circadian rhythms throughout the body. Next to this central clock, peripheral oscillators exist in almost all mammalian tissues. Whereas the SCN is mainly entrained to the environment by light, peripheral clocks are entrained by various factors, of which feeding/fasting is the most important. Desynchronization between the central and peripheral clocks by, for instance, altered timing of food intake can lead to uncoupling of peripheral clocks from the central pacemaker and is, in humans, related to the development of metabolic disorders, including obesity and Type 2 diabetes. Diets high in fat or sugar have been shown to alter circadian clock function. This review discusses the recent findings concerning the influence of nutrients, in particular fatty acids and glucose, on behavioral and molecular circadian rhythms and will summarize critical studies describing putative mechanisms by which these nutrients are able to alter normal circadian rhythmicity, in the SCN, in non-SCN brain areas, as well as in peripheral organs. As the effects of fat and sugar on the clock could be through alterations in energy status, the role of specific nutrient sensors will be outlined, as well as the molecular studies linking these components to metabolism. Understanding the impact of specific macronutrients on the circadian clock will allow for guidance toward the composition and timing of meals optimal for physiological health, as well as putative therapeutic targets to regulate the molecular clock.

Regulation of FSP27 protein stability by AMPK and HSC70

Fat-specific protein 27 (FSP27) plays a pivotal role in controlling the formation of large lipid droplet and energy metabolism. The cellular levels of FSP27 are tightly regulated through the proteasomal ubiquitin-mediated degradation. However, the upstream signals that trigger FSP27 degradation and the underlying mechanism(s) have yet to be identified. Here we show that AMP-activated protein kinase (AMPK) activation by AICAR (5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide) or phenformin induced the ubiquitination of FSP27 and promoted its degradation in 3T3-L1 adipocytes. The levels of FSP27 protein could be maintained by either knocking down AMPKα1 or blocking proteasomal pathway. Moreover, AICAR treatment induced multilocularization of LDs in 3T3-L1 adipocytes, reminiscent of the morphological changes in cells depleted of FSP27. Furthermore, mass spectrometry-based proteomic analysis identified heat shock cognate 70 (HSC70) as a novel binding protein of FSP27. The specific interaction was confirmed by co-immunoprecipitation of both ectopically expressed and endogenous proteins. Importantly, knockdown of HSC70 by small interference RNA resulted in increased half-life of FSP27 in cells treated with a protein synthesis inhibitor cycloheximide (CHX) or AICAR. However, silencing of the E3 ubiquitin ligase CHIP (COOH terminus of HSC70-interacting protein) failed to alter the stability of FSP27 protein under both conditions. Taken together, our data indicate that AMPK is a negative regulator of FSP27 stability through the proteasomal ubiquitin-dependent protein catabolic process. Promotion of FSP27 degradation may be an important factor responsible for the beneficial effect of AMPK activators on energy metabolism.

Expression of hepatic fat-specific protein 27 depends on the specific etiology of fatty liver

Fat-specific protein 27 gene (FSP27), isolated by screening for genes specifically expressed in fully differentiated mouse adipocytes, belongs to the cell death-inducing DNA fragmentation factor, alpha subunit-like effector family. FSP27 is induced in not only adipose tissue but also the liver of ob/ob mice, and it promotes the development of fatty liver. The FSP27 gene is expressed in a fatty liver-specific manner and is not detected in the normal mouse liver. FSP27 expression is directly regulated by the induction of the hepatic peroxisome proliferator-activated receptor γ (PPARγ) in ob/ob fatty liver. In the present study, expression of hepatic FSP27 mRNA was determined in non-genetic fatty liver models. The FSP27 gene was markedly induced in the high-fat- or methionine- and choline-deficient (MCD) diet-induced fatty liver, but it was not elevated in alcohol-induced fatty liver. Interestingly, the induction of FSP27 mRNA due to the MCD diet was independent of PPARγ levels and completely absent in the liver from PPARγ-null mice. These results suggest that FSP27 mRNA expression in the liver depends on the etiology of fatty liver.

Recent insights into the molecular pathophysiology of lipid droplet formation in hepatocytes

Triacyglycerols are a major energy reserve of the body and are normally stored in adipose tissue as lipid droplets (LDs). The liver, however, stores energy as glycogen and digested triglycerides in the form of fatty acids. In stressed condition such as obesity, imbalanced nutrition and drug induced liver injury hepatocytes accumulate excess lipids in the form of LDs whose prolonged storage leads to disease conditions most notably non-alcoholic fatty liver disease (NAFLD). Fatty liver disease has become a major health burden with more than 90% of obese, nearly 70% of overweight and about 25% of normal weight patients being affected. Notably, research in recent years has shown LD as highly dynamic organelles for maintaining lipid homeostasis through fat storage, protein sorting and other molecular events studied in adipocytes and other cells of living organisms. This review focuses on the molecular events of LD formation in hepatocytes and the importance of cross talk between different cell types and their signalling in NAFLD as to provide a perspective on molecular mechanisms as well as possibilities for different therapeutic intervention strategies.