Hormonal regulation of stearoyl coenzyme-A desaturase 1 activity and gene expression in primary cultures of chicken hepatocytes

Therapeutic potential of oleic acid supplementation in myotonic dystrophy muscle cell models

BACKGROUND

We recently reported that upregulation of Musashi 2 (MSI2) protein in the rare neuromuscular disease myotonic dystrophy type 1 contributes to the hyperactivation of the muscle catabolic processes autophagy and UPS through a reduction in miR-7 levels. Because oleic acid (OA) is a known allosteric regulator of MSI2 activity in the biogenesis of miR-7, here we sought to evaluate endogenous levels of this fatty acid and its therapeutic potential in rescuing cell differentiation phenotypes in vitro. In this work, four muscle cell lines derived from DM1 patients were treated with OA for 24 h, and autophagy and muscle differentiation parameters were analyzed.

RESULTS

We demonstrate a reduction of OA levels in different cell models of the disease. OA supplementation rescued disease-related phenotypes such as fusion index, myotube diameter, and repressed autophagy. This involved inhibiting MSI2 regulation of direct molecular target miR-7 since OA isoschizomer, elaidic acid (EA) could not cause the same rescues. Reduction of OA levels seems to stem from impaired biogenesis since levels of the enzyme stearoyl-CoA desaturase 1 (SCD1), responsible for converting stearic acid to oleic acid, are decreased in DM1 and correlate with OA amounts.

CONCLUSIONS

For the first time in DM1, we describe a fatty acid metabolism impairment that originated, at least in part, from a decrease in SCD1. Because OA allosterically inhibits MSI2 binding to molecular targets, reduced OA levels synergize with the overexpression of MSI2 and contribute to the MSI2 > miR-7 > autophagy axis that we proposed to explain the muscle atrophy phenotype.

A nutrigenomics approach to study the effects of ω-3 fatty acids in laying hens under physiological stress

Supplement of ω-3 fatty acids can decrease the harmful effects of stress. However, the potential molecular mechanisms that are modulated by dietary ω-3 fatty acids in laying hens under stress remain unknown. Hence, RNA-sequencing (RNA-Seq) technology was used to gain new insights into different gene expression profiles and potential pathways involved in response to stress in the liver of 35-week-old Lohmann LSL-Lite laying hens supplemented with ω-3. Three groups including control (non-stress), stress, and stress_ω-3 fatty acids (three layers per each group) were applied. A total of 1,321 genes were detected as differentially expressed genes of which 701, 1,049, and 86 DEGs belonged to stress vs. control, stress_ω-3 vs. control, and stress vs. stress_ω-3 pairwise comparisons, respectively. Gene ontology and KEGG pathway analysis indicated that the DEGs were enriched in particular regulation of steroid and cholesterol biosynthetic process, fatty acid degradation, AMPK signaling pathway, fatty acid biosynthesis, and immune response. Our data represented a promising approach regarding the importance of ω-3 as anxiolytic and anti-stress. In this context, UNC13B and ADRA1B genes were downregulated in the stress_ω-3 group compared to the stress group, which are associated with decreased activity of glutamatergic stimulatory neurons and probably play important role in facilitating the response to stress. This study extends the current understanding of the liver transcriptome response to physiological stress, and provides new insights into the molecular responses to stress in laying hens fed a diet supplemented with ω-3 fatty acids.

Liraglutide Lowers Palmitoleate Levels in Type 2 Diabetes. A Post Hoc Analysis of the LIRAFLAME Randomized Placebo-Controlled Trial

Background

Liraglutide is a glucose-lowering medication used to treat type 2 diabetes and obesity. It is a GLP-1 receptor agonist with downstream metabolic changes beyond the incretin system, such as reducing the risk of cardiovascular complications. The understanding of these changes is critical for improving treatment outcomes. Herein, we present a post hoc experimental analysis using metabolomic phenotyping to discover molecular mecphanisms in response to liraglutide.

Method

Plasma samples were obtained from The LiraFlame Study (ClinicalTrials.gov identifier: NCT03449654), a randomized double-blinded placebo-controlled clinical trial, including 102 participants with type 2 diabetes randomized to either liraglutide or placebo treatment for 26 weeks. Mass spectrometry-based metabolomics analyses were carried out on samples from baseline and the end of the trial. Metabolites (n=114) were categorized into pathways and linear mixed models were constructed to evaluate the association between changes in metabolites and liraglutide treatment.

Results

We found the free fatty acid palmitoleate was significantly reduced in the liraglutide group compared to placebo (adjusted for multiple testing p-value = 0.04). The activity of stearoyl-CoA desaturase-1 (SCD1), the rate limiting enzyme for converting palmitate into palmitoleate, was found significantly downregulated by liraglutide treatment compared to placebo (p-value = 0.01). These metabolic changes have demonstrated to be linked to insulin sensitivity and cardiovascular health.

Transcriptome profile of liver at different physiological stages reveals potential mode for lipid metabolism in laying hens

Background

Liver is an important metabolic organ that plays a critical role in lipid synthesis, degradation, and transport; however, the molecular regulatory mechanisms of lipid metabolism remain unclear in chicken. In this study, RNA-Seq technology was used to investigate differences in expression profiles of hepatic lipid metabolism-related genes and associated pathways between juvenile and laying hens. The study aimed to broaden the understanding of liver lipid metabolism in chicken, and thereby to help improve laying performance in the poultry industry.

Results

RNA-Seq analysis was carried out on total RNA harvested from the liver of juvenile (n = 3) and laying (n = 3) hens. Compared with juvenile hens, 2567 differentially expressed genes (1082 up-regulated and 1485 down-regulated) with P ≤ 0.05 were obtained in laying hens, and 960 of these genes were significantly differentially expressed (SDE) at a false discovery rate (FDR) of ≤0.05 and fold-change ≥2 or ≤0.5. In addition, most of the 198 SDE novel genes (91 up-regulated and 107 down-regulated) were discovered highly expressed, and 332 SDE isoforms were identified. Gene ontology (GO) enrichment and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis showed that the SDE genes were most enrichment in steroid biosynthesis, PPAR signaling pathway, biosynthesis of unsaturated fatty acids, glycerophospholipid metabolism, three amino acid pathways, and pyruvate metabolism (P ≤ 0.05). The top significantly enriched GO terms among the SDE genes included lipid biosynthesis, cholesterol and sterol metabolic, and oxidation reduction, indicating that principal lipogenesis occurred in the liver of laying hens.

Conclusions

This study suggests that the majority of changes at the transcriptome level in laying hen liver were closely related to fat metabolism. Some of the SDE uncharacterized novel genes and alternative splicing isoforms that were detected might also take part in lipid metabolism, although this needs further investigation. This study provides valuable information about the expression profiles of mRNAs from chicken liver, and in-depth functional investigations of these mRNAs could provide new insights into the molecular networks of lipid metabolism in chicken liver.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1943-0) contains supplementary material, which is available to authorized users.

Phosphorylation of sterol regulatory element binding protein-1a by protein kinase A (PKA) regulates transcriptional activity

The counter-regulatory hormone glucagon inhibits lipogenesis via downregulation of sterol regulatory element binding protein 1 (SREBP-1). The effect of glucagon is mediated via protein kinase A (PKA). To determine if SREBP-1 is a direct phosphorylation target of PKA, we conducted mass spectrometry analysis of recombinant n-terminal SREBP-1a following PKA treatment in vitro. This analysis identified serines 331/332 as bona-fide phosphorylation targets of PKA. To determine the functional consequences of phosphorylation at these sites, we constructed mammalian expression vector for both nSREBP-1a and 1c isoforms in which the candidate PKA phosphorylation sites were mutated to active phosphomimetic or non-phosphorylatable amino acids. The transcriptional activity of SREBP was reduced by the phosphomimetic mutation of S332 of nSREBP-1a and the corresponding serine (S308) of nSREBP-1c. This site is a strong candidate for mediating the negative regulatory effect of glucagon on SREBP-1 and lipogenesis.

cDNA cloning and the response to overfeeding in the expression of stearoyl-CoA desaturase 1 gene in Landes goose

Stearoyl-CoA desaturase 1 (SCD1) is a rate limiting enzyme in the biosynthesis of monounsaturated fatty acids. It has been cloned from several species: Rattus norvegicus, Mus musculus, Homo Sapiens and Gallus gallus, but not from Anser anser. This study was conducted to isolate the SCD1 cDNA sequence and investigate the effect of overfeeding on SCD1 gene tissue expression in Landes goose. The complete cDNA is 3294 bp in length, with an ORF of 1.083 bp encoding a predicted polypeptide of 360 amino acids and 5'/3'-UTR of 74 and 2137 bp, respectively. Quantitative real time PCR (qPCR) was used to examine SCD1 expression in heart, liver, spleen, lung, kidney, gizzard, glandular stomach, intestine, crureus, pectoral muscle, hypothalamus and adipose tissue (abdominal fat) in both the overfed and control group. SCD1 mRNA was highly expressed in goose fatty liver, and the expression levels of SCD1 in liver and fat of overfeeding group were more than double that of the control group. During the overfeeding period, SCD1 expression in liver and adipose tissue reached the highest level after 70 days, but declined at 79 days. In the control group, after fasting 24h, the expression level of SCD1 gene in tissues declined sharply. However, SCD1 gene expression in hypothalamus was unaffected. The results of this study provide a theoretical basis to study the relationship between SCD1 gene expression and the formation of fatty liver of Landes goose in response to overfeeding.

Fatty acid composition of adipose tissue triglycerides after weight loss and weight maintenance: the DIOGENES study

Fatty acid composition of adipose tissue changes with weight loss. Palmitoleic acid as a possible marker of endogenous lipogenesis or its functions as a lipokine are under debate. Objective was to assess the predictive role of adipose triglycerides fatty acids in weight maintenance in participants of the DIOGENES dietary intervention study. After an 8-week low calorie diet (LCD) subjects with > 8 % weight loss were randomized to 5 ad libitum weight maintenance diets for 6 months: low protein (P)/low glycemic index (GI) (LP/LGI), low P/high GI (LP/HGI), high P/low GI (HP/LGI), high P/high GI (HP/HGI), and a control diet. Fatty acid composition in adipose tissue triglycerides was determined by gas chromatography in 195 subjects before the LCD (baseline), after LCD and weight maintenance. Weight change after the maintenance phase was positively correlated with baseline adipose palmitoleic (16:1n-7), myristoleic (14:1n-5) and trans-palmitoleic acid (16:1n-7t). Negative correlation was found with baseline oleic acid (18:1n-9). Lower baseline monounsaturated fatty acids (14:1n-5, 16:1n-7 and trans 16:1n-7) in adipose tissue triglycerides predict better weight maintenance. Lower oleic acid predicts lower weight decrease. These findings suggest a specific role of monounsaturated fatty acids in weight management and as weight change predictors.

Regulator of sex-limitation KRAB zinc finger proteins modulate sex-dependent and -independent liver metabolism

Krüppel-related zinc finger proteins (KRAB-zfps) comprise the largest mammalian transcription factor family, but their specific functions are largely unknown. Two KRAB-zfps, regulator of sex-limitation (Rsl) 1 and Rsl2, repress expression of the mouse sex-limited protein (Slp) gene, the hallmark of Rsl activity, as well as some other male-predominant liver genes. This phenotype suggests Rsl modifies sex-specific transcription. The scope of Rsl control was determined by expression profiling of liver RNA from wild-type (wt), rsl, and transgenic mice with hepatic overexpression of Rsl1 or Rsl2. About 7.5% of the liver transcriptome was Rsl-responsive. More genes in males than females were affected by the loss of Rsl (e.g., in rsl mice), whereas Rsl overexpression altered more transcripts in females than males. Rsl dramatically repressed some female-predominant genes, but most were modestly (1.25- to 2-fold) influenced. In males, most Rsl-responsive genes unexpectedly expressed at lower levels in rsl than wt, suggesting not all are direct targets of Rsl repression. Gene Ontology analysis showed Rsl targets enriched in pathways of cholesterol, steroid, and lipid metabolism, linking Rsl to energy balance. In accord with this, blood glucose levels were less in male rsl than wt mice, and less responsive to fasting and refeeding. rsl mice were also leaner than wt, consistent with their hepatic regulation of phosphoenolpyruvate carboxykinase 1 and stearoyl-Coenzyme A desaturase 1. Altogether, Rsl's effect on sexually dimorphic and metabolically sensitive liver gene expression suggests a role for KRAB-zfps as broad genetic modulators of individual adaptation.

Dehydroepiandrosterone activates cyclic adenosine 3',5'-monophosphate/protein kinase A signalling and suppresses sterol regulatory element-binding protein-1 expression in cultured primary chicken hepatocytes

Dehydroepiandrosterone (DHEA), a steroid hormone that is secreted by the adrenal cortex in mammals, has an array of biological actions, including inhibition of fat synthesis, decreasing the number of adipocytes, and a reduction in mammalian metabolic efficiency. Recent studies showed that DHEA may decrease fat deposition in poultry, but the mechanism of action is unclear. In the present study, we demonstrate that DHEA stimulates intracellular cyclic adenosine 3',5'-monophosphate (cAMP) accumulation in chicken hepatocytes during a 30 min incubation period. Increases in intracellular cAMP are evoked by as low as 0.1 microm-DHEA. The cAMP induced by DHEA, while suppressing cAMP-specific phosphodiesterase activity, also activates cAMP-dependent protein kinase A (PKA) in chicken hepatocytes. In addition, the activation of PKA leads to down-regulation of sterol regulatory element-binding protein-1 (SREBP-1). These findings demonstrate that direct action by DHEA leads to activation of the cAMP/PKA signalling system in the modulation of lipid metabolism by repressing SREBP-1, thereby providing a novel explanation for some of the underlying effects proposed for DHEA in the prevention of fat deposition in poultry.

The mechanism mediating the activation of acetyl-coenzyme A carboxylase-alpha gene transcription by the liver X receptor agonist T0-901317

In birds and mammals, agonists of the liver X receptor (LXR) increase the expression of enzymes that make up the fatty acid synthesis pathway. Here, we investigate the mechanism by which the synthetic LXR agonist, T0-901317, increases the transcription of the acetyl-coenzyme A carboxylase-alpha (ACC alpha) gene in chick embryo hepatocyte cultures. Transfection analyses demonstrate that activation of ACC alpha transcription by T0-901317 is mediated by a cis-acting regulatory unit (-101 to -71 bp) that is composed of a liver X receptor response element (LXRE) and a sterol-regulatory element (SRE). The SRE enhances the ability of the LXRE to activate ACC alpha transcription in the presence of T0-901317. Treating hepatocytes with T0-901317 increases the concentration of mature sterol-regulatory element binding protein-1 (SREBP-1) in the nucleus and the acetylation of histone H3 and histone H4 at the ACC alpha LXR response unit. These results indicate that T0-901317 increases hepatic ACC alpha transcription by directly activating LXR*retinoid X receptor (RXR) heterodimers and by increasing the activity of an accessory transcription factor (SREBP-1) that enhances ligand induced-LXR*RXR activity.

The Role of Glucagon in Regulating Chicken Hepatic Malic Enzyme and Histidase Messenger Ribonucleic Acid Expression In Response to an Increase in Dietary Protein Intake

Increased dietary protein intake rapidly (3 h) decreases hepatic malic enzyme and increases hepatic histidase mRNA expression in broiler chicks. A series of experiments was conducted to determine the role that glucagon or a specific mixture of dietary amino acids might have in regulating the rapid changes in mRNA expression of these enzymes, when dietary protein intake is increased. Three hours after the injection of glucagon (240 microg/kg of BW) into the brachial vein of broiler chicks, hepatic malic enzyme mRNA expression was significantly lower and hepatic histidase mRNA expression was significantly greater than the level detected in saline-injected chicks. In addition, broiler chicks fed a high (40 g/ 100 g of diet) protein diet had significantly higher plasma glucagon levels at 1 and 3 h after initial access to this diet than broiler chicks fed a basal (22 g/100 g of diet) protein diet. The plasma glucagon concentration, however, was not different between the chicks fed the 2 dietary protein levels at 2 h after the initial access to the 2 diets. When a mixture of indispensable or dispensable amino acids was added to the basal diet to equal the concentrations of the individual indispensable or dispensable amino acids in the high protein diet, hepatic mRNA expression of malic enzyme and histidase were intermediate to the expression found in chicks fed the basal and high protein diet. The results indicate that glucagon may mediate the changes in the mRNA expression of malic enzyme and histidase in response to dietary protein intake and that total amino acid intake rather than the ingestion of specific amino acids regulates the mRNA expression of malic enzyme and histidase in chicks.

Sterol regulatory element-binding protein 1 is negatively modulated by PKA phosphorylation

Sterol regulatory element-binding protein (SREBP)-1a and -1c are key transcription factors that regulate lipid biosynthesis in cells. We identified that Ser338 located at the NH2 terminus of SREBP-1a is a PKA phosphorylation site in vitro and in HepG2 cells. PKA phosphorylation of this site attenuated DNA occupancy, as revealed by chromatin immunoprecipitation assay, and the ensuing transactivation. In contrast, replacing Ser with Ala [SREBP-1a(N)-S338A] increased transactivation. Although it forms heterodimers with the wild-type SREBP-1a(N) or S338A but not a homodimer with itself, SREBP-1a(N)-S338D (replacing Ser with Asp) decreased DNA binding. Ser314 of SREBP-1c, the counterpart of SREBP-1a Ser338, was also phosphorylated by PKA. Accordingly, the adenovirus-mediated expression of SREBP-1c(N)-S314D in HepG2 cells retarded lipogenesis. Our results indicate that the cAMP-PKA pathway, by phosphorylating SREBP-1, may modulate lipid metabolism in liver cell lines.

Protective effects of antioxidant vitamins on Aroclor 1254-induced toxicity in cultured chicken embryo hepatocytes

Primary culture of chicken embryo hepatocytes (CEHs) was established to reveal toxicity of polychlorinated biphenyls (PCBs) and attenuating effects of antioxidants vitamin E (VE), vitamin C (VC) and vitamin A (VA) on PCBs-induced cytotoxicity. CEHs were dispersed from 14-day-old chicken embryo livers and exposed to Aroclor 1254 (A1254) in the range of 0.1-10 microg/ml, A1254 (10 microg/ml) and each vitamin (10 microg/ml) for 24 h. Cell viability was evaluated by determinations of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and lactate dehydrogenase (LDH) leakage. The antioxidant status, namely cellular lipid peroxidation, was evaluated by measuring the thiobarbituric acid reactive substances (TBARS) and glutathion (GSH) levels and superoxide dismutase (SOD) activities. The cultured CEHs maintained normal polygonal cell shape and formed confluent monolayer after 24-h culture. A1254 (10 microg/ml) caused irreversible damage to cell membrane integrity and induced cell death in a dose-dependent manner. It induced increased TBARS production, decreased SOD activity and GSH concentration. VE, VC and VA alone or combinations of VE+VC and VE+VA significantly attenuated A1254-induced toxic effects, which suggested that lipid peroxidation was involved in the sequence of events leading to A1254-induced damage or death of the cultured CEHs. These results indicated that CEHs in serum-free culture represented a suitable model for rapid toxicity assessment of environmental pollutants such as PCBs in a visible manner. Antioxidant vitamins displayed protective effects on CEHs from A1254-induced damage through preventing lipid peroxidation.

Coordinated upregulation of oxidative pathways and downregulation of lipid biosynthesis underlie obesity resistance in perilipin knockout mice: a microarray gene expression profile

Obesity is a major risk factor for diabetes and heart disease. We previously reported that the inactivation of the gene for perilipin (plin), an adipocyte lipid droplet surface protein, produced lean and obesity-resistant mice. To dissect the underlying mechanisms involved, we used oligonucleotide microarrays to analyze the gene-expression profile of white adipose tissue (WAT), liver, heart, skeletal muscle, and kidney of plin(-/-) and plin(+/+) mice. As compared with wild-type littermates, the WAT of plin(-/-) mice had 270 and 543 transcripts that were significantly up- or downregulated. There was a coordinated upregulation of genes involved in beta-oxidation, the Krebs cycle, and the electron transport chain concomitant with a downregulation of genes involved in lipid biosynthesis. There was also a significant downregulation of the stearoyl CoA desaturase-1 gene, which has been associated with obesity resistance. Thus, in response to the constitutive activation of lipolysis associated with absence of perilipin, WAT activated pathways to rid itself of the products of lipolysis and activated pathways of energy expenditure that contribute to the observed obesity resistance. The biochemical pathways involved in obesity resistance in plin(-/-) mice identified in this study may represent potential targets for the treatment of obesity.

Melanin-concentrating hormone is a critical mediator of the leptin-deficient phenotype

Energy homeostasis is regulated by a complex network involving peripheral and central signals that determine food intake and energy expenditure. Melanin-concentrating hormone (MCH) plays an essential role in this process. Animals treated with MCH develop hyperphagia and obesity. Ablation of the prepro-MCH gene leads to a lean phenotype, as does ablation of the rodent MCH receptor, MCHR-1. MCH is overexpressed in the leptin-deficient ob/ob mouse, and we hypothesized that ablation of MCH in this animal would lead to attenuation of its obese phenotype. Compared with ob/ob animals, mice lacking both leptin and MCH (double null) had a dramatic reduction in body fat. Surprisingly, the hyperphagia of the ob/ob mouse was unaffected. Instead, leanness was secondary to a marked increase in energy expenditure resulting from both increased resting energy expenditure and locomotor activity. Furthermore, double-null mice showed improvements in other parameters impaired in ob/ob mice. Compared with ob/ob mice, double-null animals had increased basal body temperature, improved response to cold exposure, lower plasma glucocorticoid levels, improved glucose tolerance, and reduced expression of stearoyl-CoA desaturase 1 (SCD-1). These results highlight the importance of MCH in integration of energy homeostasis downstream of leptin and, in particular, the role of MCH in regulation of energy expenditure.

Recent insights into stearoyl-CoA desaturase-1

PURPOSE OF REVIEW

Stearoyl-Coenzyme A (CoA) desaturase is a central lipogenic enzyme catalyzing the synthesis of monounsaturated fatty acids - mainly oleate (C(18:1)). Oleate is the most abundant monounsaturated fatty acid in dietary fat and is therefore readily available. Why, then, is stearoyl-CoA desaturase a highly regulated enzyme? This review summarizes the recent and timely advances concerning the important role of stearoyl-CoA desaturase in metabolism.

RECENT FINDINGS

Recent findings using mice that have a naturally occurring mutation in the SCD1 gene isoform as well as a mouse model with a targeted disruption of the stearoyl-CoA desaturase gene-1 (SCD1-/-) have revealed the role of de-novo synthesized oleate and thus the physiological importance of SCD1 expression. In the highlighted references, it is shown that the SCD1-/- mice have reduced body adiposity, increased insulin sensitivity, and are resistant to diet-induced obesity. The expression of several genes of lipid oxidation is upregulated, whereas lipid synthesis genes are downregulated. SCD1 was also found to be a component of the novel metabolic response to the hormone leptin.

SUMMARY

SCD1, therefore, appears to be an important metabolic control point, and inhibition of its expression could be of benefit for the treatment of obesity, diabetes and other metabolic diseases.

Feed restriction significantly alters lipogenic gene expression in broiler breeder chickens

Broiler breeder pullets were divided into two groups at 21 wk of age. One group was given free access to feed (ad libitum) and the other fed a limited amount of feed (restricted). At 22 wk, all birds were photostimulated and maintained throughout an egg-laying cycle ending at 36 wk. Samples of liver and abdominal fat pad were collected just before photostimulation (prelight), after photostimulation at first egg and at peak egg production (plateau). Hepatic expression of sterol regulatory element binding protein-1, ATP-citrate lyase, fatty acid synthase, malic enzyme, acetyl-CoA carboxylase and stearoyl-CoA (Delta9) desaturase 1 genes in ad libitum birds declined from their highest levels just before photostimulation as the birds came into and maintained egg production. In contrast, the restricted birds had significant (P < 0.05) increases in the expression of these genes after photostimulation at first egg with a subsequent decline as they reached peak egg production. Hepatic expression of fatty acid binding protein, VLDL apolipoprotein (apoVLDL-II) and apoB genes increased significantly (P < 0.05) in both ad libitum and restricted breeders after photostimulation, whereas apoA1 gene expression declined during this time. Abdominal fat pad weights were significantly (P < 0.05) higher in the ad libitum compared with restricted birds after photostimulation. Lipoprotein lipase in this tissue showed a pattern of expression similar to that observed for the hepatic lipogenic enzyme genes. In conclusion, feed restriction during the pullet-to-breeder transition period significantly (P < 0.05) altered hepatic lipogenic gene expression in broiler breeders.

Effects of sterculic acid on stearoyl-CoA desaturase in differentiating 3T3-L1 adipocytes

The effects of sterculic acid on cell size, adiposity, and fatty acid composition of differentiating 3T3-L1 adipocytes are correlated with stearoyl-CoA desaturase (SCD) expression (mRNA and protein levels) and enzyme activity. Fluorescence-activated cell scanning (FACS) analysis showed that adipocytes differentiated with methylisobutylxanthine, dexamethasone, and insulin (MDI) plus 100 microM sterculic acid comprised a population of predominantly large cells with reduced adiposity compared to MDI-treated cells. Although both groups had similar amounts of total fat, their fatty acid profiles were strikingly different: MDI-treated cells had high levels of the unsaturated palmitoleic (Delta(9)-16:1) and oleic (Delta(9)-18:1) acids, whereas the cells cultured with MDI plus sterculic acid accumulated palmitic (16:0) and stearic (18:0) acids together with a marked reduction in Delta(9)-16:1. Although the cells treated with MDI plus sterculic acid had similar levels of scd1 and scd2 mRNAs and antibody-detectable SCD protein as the MDI-treated cells, the SCD enzyme activity was inhibited more than 90%. The accumulation of 16:0 and 18:0, together with normal levels of fatty acid synthase (FAS) and aP2 mRNAs, shows that de novo synthesis and elongation of fatty acids, as well as cell differentiation, were not affected by sterculic acid. Because of the increase in cell size in the sterculic acid-treated cells, the insulin-stimulated 2-deoxyglucose (2-DOG) uptake was determined. Compared to MDI-treated cells, the 2-DOG uptake in the cells treated with sterculic acid was not affected. These results indicate that sterculic acid directly inhibits SCD activity, possibly by a turnover-dependent reaction, without affecting the processes required for adipocyte differentiation, scd gene expression or SCD protein translation.

Stearoyl coenzyme A desaturase 1 expression and activity are increased in the liver during iron overload

In humans, hepatic iron overload can lead to hepatocellular carcinoma development. Iron related dysregulation of hepatic genes could play a role in this phenomenon. We previously found that the carbonyl-iron overloaded mouse was a useful model to study the mechanisms involved in the development of hepatic lesions related to iron excess. The aim of the present study was to identify hepatic genes overexpressed in conditions of iron overload by using this model. A suppressive subtractive hybridization was performed between hepatic mRNAs extracted from control and 3% carbonyl-iron overloaded mice during 8 months. This methodology allowed us to identify stearoyl coenzyme A desaturase 1 (SCD1) mRNA overexpression in the liver of iron loaded mice. The corresponding enzymatic activity was also found to be significantly increased. In addition, we demonstrated that both SCD1 mRNA expression and activity were increased in another iron overload model in mice obtained by a single iron-dextran subcutaneous injection. Moreover, we found, in both models, that SCD1 mRNA was not only influenced by the quantity of iron in the liver but also by the duration of iron overload since SCD1 mRNA upregulation was not detected in earlier stages of iron overload. In addition, we found that cellular repartition likely influenced SCD1 mRNA expression. In conclusion, we demonstrated that iron excess in the liver induced both the expression of SCD1 mRNA and its corresponding enzymatic activity. The level and duration of iron overload, as well as cellular repartition of iron excess in the liver likely play a role in this induction. The fact that the expression and activity of SCD1, an enzyme adding a double bound into saturated fatty acids, are induced in two models of iron overload in mice leads to the conclusion that iron excess in the liver may enhance the biosynthesis of unsaturated fatty acids.

Effects of polyunsaturated fatty acids and clofibrate on chicken stearoyl-coA desaturase 1 gene expression

In chicken, adiposity is influenced by hepatic stearoyl-CoA desaturase (SCD) 1. This gene is up-regulated by low-fat high-carbohydrate diet and down-regulated by addition of polyunsaturated fatty acids (PUFA). In this study, we present evidence for an inhibition of chicken SCD1 expression by PUFA using reporter gene constructs in transient transfection assays. This inhibition does not involve the peroxisome proliferator-activated receptor pathway, in contrast with what has been observed in rodents. We were able to localise a PUFA as well as an insulin response element within the -372/+125 bp region of the promoter. Sequence analyses of this region allowed identification of several cis-regulatory elements: A sterol regulatory element (SRE) and a juxtaposed NF-Y element which have been shown to be involved in the regulation of mouse SCD genes by PUFA. In addition, we identified an overlapping Sp1/USF motif, which was described to play a role in insulin/glucose and PUFA regulation of fatty synthase, ATP-citrate-lyase, and leptin genes. These data provide the first characterisation of the chicken SCD1 promoter and putative cis-sequences involved in the regulation of this gene by PUFA and insulin.