Desaturase Gene Expression Research Articles

Up-regulated expression of desaturase genes of Mucor rouxii in response to low temperature associates with pre-existing cellular fatty acid constituents

Transcriptional response of desaturase genes to low temperature was investigated in the dimorphic fungus Mucor rouxii. The two morphological forms of M. rouxii, yeast-like and mycelial cells containing different fatty acid profiles were shifted from 30 to 10°C. Both cultures exhibited significantly altered fatty acid composition, whose content in polyunsaturated fatty acids increased as consequence of the temperature shift and was accompanied by a reduction of C18:1Δ(9) about 2 h after the temperature shift. These changes were particularly significant in phosphatidylcholine and phosphatidylethanolamine fractions. Moreover, the fatty acid profiles of monoacylglycerol and diacylglycerol were also modulated in response to the lower temperature of incubation. The changes of membrane lipids of M. rouxii were due to the cold-induced expression of Δ(9)-, Δ(12)- and Δ(6)-desaturase genes. Although the mRNA levels of the three desaturases were transiently induced by lowering the temperature, the pre-existing composition of fatty acid profiles of mycelial and yeast-like forms of M. rouxii may have lead to different expression profiles of desaturase genes that modified their membrane physical state under cold shock. While expression of Δ(12)-desaturase gene contributed mainly to cold acclimation of mycelia, Δ(9)-desaturase expression was the main transcript identified in the yeast-like culture after temperature shift.

Key role of the ERK1/2 MAPK pathway in the transcriptional regulation of the stearoyl-CoA desaturase (SCD1) gene expression in response to leptin

Stearoyl-CoA Desaturase-1 (SCD1) is the rate limiting enzyme catalyzing the synthesis of monounsaturated fatty acids. Variation of SCD1 activity and the ratio of saturated to unsaturated fatty acids have been implicated in a variety of diseases including obesity, type II diabetes and cancers. In liver, many factors regulate SCD1 expression including dietary and hormonal factors such as insulin and leptin. We previously showed in hepatic cells that insulin acts through the PI3K and mTOR pathways to upregulate SCD1 expression. In the present study, using HepG2 cells, we characterized the signaling pathway mediating the leptin inhibitory response on SCD1 gene expression. We showed that leptin inhibits SCD1 at the transcriptional level. Inhibition of the ERK1/2 MAPK pathway with the PD98059 reverses the effect of leptin on SCD1 expression. Our data also demonstrated that the effect of leptin is entirely independent of the effect of insulin. Using the pharmaceutical inhibitors Ag490 and SL0101, we showed that the inhibitory effect of leptin is also mediated by the Janus Kinase 2 (Jak2) and p90RSK. EMSA and transfection experiments suggest a key role for the Sp1 transcription factor, which in turn may compete for the binding of other transcription factors such as AP-1, leading to the inhibition of SCD1 transcription. Taken together, our observations showed that, independently of insulin action, leptin exerts an inhibitory effect on SCD1 transcription via a signaling pathway implicating Jak2, ERK1/2, and p90RSK which probably targets the downstream transcription factor Sp1 on the SCD1 promoter.

Role of fatty acid elongases in determination of de novo synthesized monounsaturated fatty acid species

Enhanced production of monounsaturated fatty acids (FA) derived from carbohydrate-enriched diets has been implicated in the development of obesity and insulin resistance. The FA elongases Elovl-5 and Elovl-6 are regulated by nutrient and hormone status, and have been shown using intact yeast and mammalian microsome fractions to be involved in the synthesis of monounsaturated FAs (MUFA). Herein, targeted knockdown and overexpression of Elovl-5 or Elovl-6 was used to determine their roles in de novo synthesis of specific MUFA species in mammalian cells. Treatment of rat insulinoma (INS)-1 cells with elevated glucose increased de novo FA synthesis and the ratio of MUFAs to saturated FAs. Elovl-5 knockdown decreased elongation of 16:1,n-7. Elovl-5 overexpression increased synthesis of 18:1,n-7; however, this increase was dependent on stearoyl-CoA desaturase-driven 16:1,n-7 availability. Knockdown of Elovl-6 decreased elongation of 16:0 and 16:1,n-7, resulting in accumulation of 16:1,n-7. Elovl-6 overexpression preferentially drove synthesis of 16:0 elongation products 18:0 and 18:1,n-9 but not 18:1,n-7. These findings demonstrate that coordinated induction of FA elongase and desaturase activity is required for balanced synthesis of specific n-7 versus n-9 MUFA species. Given the relative abundance of 16:0 to 16:1,n-7 and the specificity of Elovl-6 for 16:0, Elovl-6 is a major elongase for 18:1,n-9 production.

Omega-3 long chain fatty acid synthesis is regulated more by substrate levels than gene expression

The conversion of linoleic acid (LA) and alpha-linolenic acid (ALA) to long chain polyunsaturated fatty acids (LCPUFA) is known to involve desaturation and elongation steps. Although there is evidence that genes for these steps can be regulated by extremes of dietary PUFA, the degree to which there is meaningful regulation of LCPUFA levels in tissues by diet as a result of changes in expression of desaturase and elongase genes is unclear. In this study, we tested the effect of increasing ALA levels in diets of rats from 0.2% to 2.9% energy (en) against a constant LA level (1%en) on plasma and liver phospholipid LCPUFA content together with the expression of hepatic genes involved in PUFA metabolism, the desaturases FADS1 and FADS2, the elongases ELOV2 and ELOV5, and the transcription factors sterol regulatory element-binding protein-1c (SREBP-1c) and peroxisome proliferator-activated receptor alpha (PPARα). The levels of plasma and liver eicosapentaenoic acid (EPA) and docosapentaenoic acid (DPA) increased in proportion to dietary ALA whereas docosahexaenoic acid (DHA) increased only up to 1%en ALA. A low PUFA (0.4%en) reference diet stimulated the expression of delta 6 desaturase (FADS2) and elongase 2 (ELOVL2) when compared to higher PUFA diets. There was, however, no difference in the expression of any of the genes in rats, which were fed diets containing between 0.2%en and 2.9%en ALA and mRNA expression was unrelated to tissue/plasma LCPUFA content. These data suggest that the endogenous synthesis of n−3 LCPUFA from the precursor ALA is regulated independently of changes in the expression of the synthetic enzymes or regulatory transcription factor, and provides evidence that n−3 LCPUFA synthesis is regulated more by substrate competition for existing enzymes than by an increase in their mRNA expression.

The GmFAD7 gene family from soybean: identification of novel genes and tissue-specific conformations of the FAD7 enzyme involved in desaturase activity

The FAD7 gene encodes a ω3 fatty acid desaturase which catalyses the production of trienoic fatty acids (TAs) in plant chloroplasts. A novel GmFAD7 gene (named GmFAD7-2) has been identified in soybean, with high homology to the previously annotated GmFAD7 gene. Genomic sequencing analysis together with searches at the soybean genome database further confirmed that both GmFAD7 genes were located in two different loci within the soybean genome, suggesting that the soybean ω3 plastidial desaturase FAD7 is encoded by two different paralogous genes. Both GmFAD7-1 and GmFAD7-2 genes were expressed in all soybean tissues examined, displaying their highest mRNA accumulation in leaves. This expression profile contrasted with GmFAD3A and GmFAD3B mRNA accumulation, which was very low in this tissue. These results suggested a concerted control of plastidial and reticular ω3 desaturase gene expression in soybean mature leaves. Analysis of GmFAD7 protein distribution in different soybean tissues showed that, in mature leaves, two bands were detected, coincident with the higher expression level of both GmFAD7 genes and the highest 18:3 fatty acid accumulation. By contrast, in seeds, where FAD7 activity is low, specific GmFAD7 protein conformations were observed. These GmFAD7 protein conformations were affected in vitro by changes in the redox conditions of thiol groups and iron availability. These results suggest the existence of tissue-specific post-translational regulatory mechanisms affecting the distribution and conformation of the FAD7 enzymes related with the control of its activity.

Key role of the ERK1/2 MAPK pathway in the transcriptional regulation of the Stearoyl-CoA Desaturase (SCD1) gene expression in response to leptin

Stearoyl-CoA Desaturase-1 (SCD1) is the rate limiting enzyme catalyzing the synthesis of monounsaturated fatty acids. Variation of SCD1 activity and the ratio of saturated to unsaturated fatty acids have been implicated in a variety of diseases including obesity, type II diabetes and cancers. In liver, many factors regulate SCD1 expression including dietary and hormonal factors such as insulin and leptin. We previously showed in hepatic cells that insulin acts through the PI3K and mTOR pathways to upregulate SCD1 expression. In the present study, using HepG2 cells, we characterized the signaling pathway mediating the leptin inhibitory response on SCD1 gene expression. We showed that leptin inhibits SCD1 at the transcriptional level. Inhibition of the ERK1/2 MAPK pathway with the PD98059 reverses the effect of leptin on SCD1 expression. Our data also demonstrated that the effect of leptin is entirely independent of the effect of insulin. Using the pharmaceutical inhibitors Ag490 and SL0101, we showed that the inhibitory effect of leptin is also mediated by the Janus Kinase 2 (Jak2) and p90RSK. EMSA and transfection experiments suggest a key role for the Sp1 transcription factor, which in turn may compete for the binding of other transcription factors such as AP-1, leading to the inhibition of SCD1 transcription. Taken together, our observations showed that, independently of insulin action, leptin exerts an inhibitory effect on SCD1 transcription via a signaling pathway implicating Jak2, ERK1/2, and p90RSK which probably targets the downstream transcription factor Sp1 on the SCD1 promoter.

Remodeling of Retinal Fatty Acids in an Animal Model of Diabetes

OBJECTIVEThe results of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications cohort study revealed a strong association between dyslipidemia and the development of diabetic retinopathy. However, there are no experimental data on retinal fatty acid metabolism in diabetes. This study determined retinal-specific fatty acid metabolism in control and diabetic animals.RESEARCH DESIGN AND METHODSTissue gene and protein expression profiles were determined by quantitative RT-PCR and Western blot in control and streptozotocin-induced diabetic rats at 3–6 weeks of diabetes. Fatty acid profiles were assessed by reverse-phase high-performance liquid chromatography, and phospholipid analysis was performed by nano-electrospray ionization tandem mass spectrometry.RESULTSWe found a dramatic difference between retinal and liver elongase and desaturase profiles with high elongase and low desaturase gene expression in the retina compared with liver. Elovl4, an elongase expressed in the retina but not in the liver, showed the greatest expression level among retinal elongases, followed by Elovl2, Elovl1, and Elovl6. Importantly, early-stage diabetes induced a marked decrease in retinal expression levels of Elovl4, Elovl2, and Elovl6. Diabetes-induced downregulation of retinal elongases translated into a significant decrease in total retinal docosahexaenoic acid, as well as decreased incorporation of very-long-chain polyunsaturated fatty acids (PUFAs), particularly 32:6n3, into retinal phosphatidylcholine. This decrease in n3 PUFAs was coupled with inflammatory status in diabetic retina, reflected by an increase in gene expression of proinflammatory markers interleukin-6, vascular endothelial growth factor, and intercellular adhesion molecule-1.CONCLUSIONSThis is the first comprehensive study demonstrating diabetes-induced changes in retinal fatty acid metabolism. Normalization of retinal fatty acid levels by dietary means or/and modulating expression of elongases could represent a potential therapeutic target for diabetes-induced retinal inflammation.

Expression Analysis Identifies FAD2-2 as the Olive Oleate Desaturase Gene Mainly Responsible for the Linoleic Acid Content in Virgin Olive Oil

The effect of ripening stage and water regimen on oleate desaturase gene expression levels in the fruit of different olive ( Olea europaea L.) varieties was investigated to elucidate the contribution of each to the linoleic acid content in virgin olive oil. To this end, fatty acid analysis and quantitative real time PCR were performed using distinct olive tissues and different developmental stages from the Picual and Arbequina cultivars. The results showed that the olive FAD2-1, FAD2-2, and FAD6 genes were spatial and temporally regulated. In addition, the data indicated that FAD2-2 seems to be the main gene responsible for the linoleic acid content in the olive fruit mesocarp tissue. This conclusion was also confirmed when the study was extended to Hojiblanca, Picudo, and Manzanilla varieties. With regard to the water regimen, unlike the Picual cultivar, a small increase of linoleic acid was observed in the Arbequina variety cultivated with irrigation, which correlated well with the increase detected for the FAD2-2 gene expression level. All of these data strongly suggest that FAD2-2 is the main gene that determines the linoleic acid content in the virgin olive oil.

Whole-body synthesis-secretion rates of long-chain n-3 PUFAs from circulating unesterified α-linolenic acid in unanesthetized rats

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), long-chain n-3 PUFAs important for brain and heart function, can be obtained from dietary fish products or by liver synthesis from alpha-linolenic acid (alpha-LNA). Their daily human dietary requirements are not clear, and their liver synthesis rates in humans and nonhumans are unknown. We estimated whole-body (presumably liver) synthesis rates in unanesthetized rats by infusing [U-(13)C]alpha-LNA intravenously for 2 h and measuring labeled and unlabeled n-3 PUFA in arterial plasma using negative chemical ionization GC-MS. Newly synthesized esterified [(13)C]DHA, [(13)C]EPA, and [(13)C]docosapentaenoic acid (DPA) appeared in arterial plasma after 60 min of infusion, then their concentrations rose in an S-shaped manner. Esterified concentration x plasma volume data were fit with a sigmoidal equation, whose peak first derivatives provided synthesis rates of unlabeled EPA, DPA, and DHA equal to 8.40, 6.27, and 9.84 mumol/day, respectively. The DHA synthesis rate exceeded the published daily rat brain DHA consumption rate by 30-fold, suggesting that liver synthesis from alpha-LNA could maintain brain DHA homeostasis were DHA absent from the diet. This stable isotope infusion method could be used to quantify whole-body DHA synthesis rates in human subjects.

Physiological roles of fatty acyl desaturases and elongases in marine fish: Characterisation of cDNAs of fatty acyl Δ6 desaturase and elovl5 elongase of cobia ( Rachycentron canadum)

In the present paper, we investigated the expression of fatty acyl desaturase and elongase genes in a marine teleost, cobia, a species of great interest due to its considerable aquaculture potential. A cDNA was cloned that, when expressed in yeast, was shown to result in desaturation of 18:3 n−3 and 18:2 n−6, indicating that it coded for a Δ6 desaturase enzyme. Very low desaturation of 20:4 n−3 and 20:3 n−6 indicated only trace Δ5 activity. Another cloned cDNA enabled elongation of 18:4 n−3, 18:3 n−6, 20:5 n−3 and 20:4 n−6 in the yeast expression system, indicating that it had C18–20 and C20–22 elongase activity. Sequence comparison and phylogenetic analysis confirmed that it was homologous to human ELOVL5 elongase. However, the cobia Elovl5 elongase also had low activity toward C24 HUFA. The cobia Δ6 desaturase had a preference for 18:3 n−3, but the elongase was generally equally active with both n−3 and n−6 substrates. Expression of both genes was 1–2 orders of magnitude greater in brain than other tissues suggesting an important role, possibly to ensure sufficient docosahexaenoic acid (DHA, 22:6 n−3) synthesis in neural tissues through elongation and desaturation of eicosapentaenoic acid (EPA; 20:5 n−3).

The effects of 2-bromopalmitate on the fatty acid composition in differentiating adipocytes of red sea bream (Pagrus major)

To determine whether external factors affect the adipogenic function of fish adipocytes, the effects of 2-bromopalmitate (a PPAR agonist) on the fatty acid composition in differentiating adipocytes of red sea bream were investigated in vitro. In the presence of 2-bromopalmitate, the red sea bream adipocytes were differentiated and the effects on the fatty acid composition and the adipogenic gene expression were analyzed. With the level of 2-bromopalmitate, the content of 16:1n-7, a delta-9 desaturation product, increased in association with the increase in a stearoyl CoA desaturase (SCD) gene expression level while the triglyceride accumulation was not affected. Subsequently, the effects on the bioconversion of the n-3 and n-6 fatty acids, which are main series of dietary essential fatty acids, were examined. In the presence of 300 microM of 18:3n-3 or 18:2n-6, red sea bream stromal-vascular cells accumulated the lipid in the cytoplasm within 3 days by the fatty acid uptake with the increase of corresponding fatty acid contents. Furthermore, in both the 18:3n-3 and 18:2n-6 stored cells, the products of delta-6 desaturation (18:4n-3 and 18:3n-6, respectively) and C(18-20) elongation (20:3n-3 and 20:2n-6, respectively) were detected. However, neither the delta-6 desatutration nor C(18-20) elongation of 18:3n-3 and 18:2n-6 were enhanced by 2-bromopalmitate treatment. In conclusion, the results indicate that the adipocyte function in fish, e.g. adipogenic gene expression and fatty acid composition, can be modified by external factors and a main effect of 2-bromopalmitate is the increase in the content of delta-9 desaturation product by stimulating the SCD gene expression.

Effect of level of eicosapentaenoic acid on the transcriptional regulation of Δ-9 desaturase using a novel in vitro bovine intramuscular adipocyte cell culture model

Ruminant fat is often perceived as having a negative impact on human health; however, the composition of the fat is under complex biochemical control and can be improved through strategic manipulation of the animal’s diet. There were two major objectives of this study, namely (i) to develop and validate a primary bovine intramuscular adipocyte cell line and (ii) to examine the effect of eicosapentaenoic acid (EPA) on the transcriptional regulation of Δ-9 desaturasein vitro using the novel cell line. Intramuscular adipose tissue was obtained from the Musculus longissimus thoracis of a beef heifer. Mature adipocytes were isolated and cultured, and subsequently harvested and evaluated for lipid accumulation and the expression of genes regulating key functional adipocyte protein markers at passages 10, 20 and 30. Isolated cells were shown to accumulate lipid in culture over time. Fatty acid analysis by gas chromatography was carried out at passage 30. Thirteen fatty acids ranging from tetradecanoic acid (C14:0) to the polyunsaturated fatty acid, docosahexaenoic acid (C22:6), were easily detected and measured. High-quality total RNA was isolated from adipocytes and the expression of peroxisome proliferator-activated receptor-γ, fatty acid synthase, fatty acid-binding protein-4, adipocyte lipid-binding protein, CD36, Δ-9 desaturase, sterol regulatory element-binding protein (SREBP), microsomal triglyceride transfer protein and leptin genes were identified by reverse transcriptase-PCR and sequence analysis. Expression of the negative control, liver-specific hepatocyte nuclear factor-1alpha, was not detected. Adipocytes were subsequently incubated in medium containing 0, 50 or 100 μM EPA for 24 h. Increasing the EPA concentration of the culture media led to a linear increase in adipocyte EPA concentration (P < 0.01). Expression of Δ-9 desaturase mRNA was decreased five- and seven-fold, respectively, following 50 and 100 μM EPA incubation compared to the control. Gene expression of SREBP-1c was decreased by 6- and 18-fold in cells supplemented with 50 and 100 μM EPA, respectively, compared to the control. Regression analysis showed a negative linear relationship between EPA concentration and the gene expression of both Δ-9 desaturase (P < 0.001) and SREBP-1c (P < 0.001), while a significant positive relationship was observed between Δ-9 desaturase and SREBP-1c gene expression (P < 0.001). This is the first report demonstrating that EPA treatment of bovine intramuscular adipocyte cells decreased gene expression of both Δ-9 desaturase and SREBP-1cin vitro. The bovine adipocyte cell line developed here is an important resource for future studies facilitating less-expensive, rapid screening of research hypotheses and circumventing the limitations associated with the use of experimental animals including cost, inter-animal variation, pre-experimental management and ethics.

Omega-3 fatty acid desaturase ( FAD3, FAD7, FAD8) gene expression and linolenic acid content in cowpea leaves submitted to drought and after rehydration

Membrane polyunsaturated fatty acids (PUFA) and particularly linolenic acid (18:3, LA) are known to be implicated in plant tolerance to low temperature. Their role in resistance to drought is much less investigated. In this work, three full-length cDNAs corresponding to omega-3 fatty acid desaturases: fad3 (endoplasmic reticulum), fad7 and fad8 (chloroplastic) were isolated from Vigna unguiculata leaves. Two cowpea cultivars, one drought-tolerant, EPACE-1, and one drought-susceptible, 1183, were compared in terms of fad isoform gene expression and leaf LA contents in plants submitted to water stress followed by rehydration. In EPACE-1, LA content in the main leaf polar lipids increased in response to mild water deficit. Severe water deficits induced a decrease in MGDG LA content while those of PC and DGDG continued to increase. Variations in FAD gene expression, matched those in LA contents. In 1183, LA contents decreased in all lipid classes in response to water stress, as did FAD3 and FAD8 gene expression levels. Rehydration after a moderate water stress induced stimulation mostly in FAD3 gene expression in both cvs. LA contents were equivalent to control levels in EPACE-1. In 1183, they were back to control levels in PC shortly after rehydration but remained low in galactolipids. These results suggested that omega-3 FAD activities were involved in the increase in leaf membrane unsaturation, in the drought tolerant plants whereas the sensitive plants lost PUFAs in response to the treatment. The significance of this discrepancy between the two cvs. in terms of adaptation to drought is discussed.

Cellular regulation of bovine intramuscular adipose tissue development and composition12

It is well documented that grain feeding stimulates adipogenesis in beef cattle, whereas pasture feeding depresses the development of adipose tissues, including intramuscular (i.m.) adipose tissue. Additionally, production practices that depress adipocyte differentiation also limit the synthesis of MUFA. Marbling scores and MUFA increase in parallel suggesting that stearoyl-coenzyme A desaturase (SCD) gene expression is closely associated with and necessary for marbling adipocyte differentiation. Similarly, marbling scores and fatty acid indices of SCD activity are depressed in response to dietary vitamin A restriction. In bovine preadipocytes, vitamins A and D both decrease glycerol-3-phosphate dehydrogenase (GPDH) activity, an index of adipocyte differentiation, whereas incubation of bovine preadipocytes with l-ascorbic acid-2-phosphate increases GPDH activity. Exposing bovine preadipocytes to zinc also stimulates adipogenesis, putatively by inhibiting nitric oxide (NO) production. However, incubation of bovine preadipocytes with arginine, a biological precursor of NO, strongly promotes differentiation in concert with increased SCD expression. This suggests that the effect of either arginine or zinc on adipogenesis is independent of NO synthesis in bovine preadipocytes. Enhanced expression of SCD is associated with a greater accumulation of MUFA both in bovine preadipocyte cultures and during development in growing steers. In bovine preadipocytes, trans-10, cis-12 CLA strongly depresses adipocyte differentiation and SCD gene expression, thereby reducing MUFA concentrations. The bovine preadipocyte culture studies suggest that any production practice that elevates vitamins A or D or trans-10, cis-12 CLA in bovine adipose tissue will reduce i.m. adipose tissue development. Conversely, supplementation with vitamin C or zinc may promote the development of i.m. adipose tissue.

Atorvastatin Decreases Stearoyl‐CoA Desaturase Gene Expression in THP‐1 Macrophages Incubated with Oxidized LDL

Statins, inhibitors of HMG-CoA reductase, reduce plasma low-density lipoprotein (LDL) cholesterol levels decreasing the incidence of coronary events. However, the observed benefit of statins appears to extend beyond their lipid-lowering effects. Previous studies by our group have demonstrated that atorvastatin in oxidized LDL incubated macrophages modifies the gene expression profile of certain enzymes involved in fatty acid metabolism, mainly stearoyl-CoA desaturase (SCD). SCD is a rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids and its expression is mediated by sterol regulatory element-binding protein-1 (SREBP-1). The aim of this study was to determine whether atorvastatin might affect the fatty acid composition in macrophages and if their SCD gene expression profile could explain this effect. Therefore, THP-1 macrophages were treated with atorvastatin and native or oxidized LDL, their fatty acid composition was determined by gas-chromatography, and the SCD and SREBP-1 gene expression profile was analysed using quantitative RT-PCR. We found that atorvastatin reduces the percentage of palmitoleic and oleic acids in THP-1 cells incubated with oxLDL, which could be explained by the inhibition of SCD and SREBP-1 gene expression. The observed results were reversed when mevalonate was added to THP-1 macrophages. This would suggest that inhibition of SCD in THP-1 macrophages incubated with oxLDL and the change in fatty acid composition is an important effect of atorvastatin.

Effect of level and duration of dietary n-3 polyunsaturated fatty acid supplementation on the transcriptional regulation of Δ9-desaturase in muscle of beef cattle1

The objective of this study was to examine the effect of level and duration of feeding of an n-3 PUFA-enriched fish oil (FO) supplement in combination with soybean oil (SO) on the transcriptional regulation of Delta(9)-desaturase gene expression in bovine muscle. Beef bulls (n = 40) were assigned to 1 of 4 iso-lipid and isonitrogenous concentrate diets fed for ad libitum intake for a 100-d finishing period. Concentrates were supplemented with one of the following: 1) 6% SO (CON); 2) 6% SO + 1% FO (FO1); 3) 6% SO + 2% FO (FO2); or 4) 8% palmitic acid for the first 50 d and 6% SO + 2% FO for the second 50 d [FO2(50)]. Samples of LM were harvested and concentrations of fatty acids were measured. Total RNA was isolated and the gene expression of Delta(9)-desaturase was determined. The mRNA expression of putative regulators of Delta(9)-desaturase gene expression, sterol regulatory element binding protein-1c (SREBP-1c) and peroxisome proliferator activated receptor-alpha (PPAR-alpha), were also measured in the CON and FO2 groups. Expression of mRNA for Delta(9)-desaturase was decreased (P < 0.05) 2.6-, 4.4-, and 4.9-fold in FO1, FO2(50), and FO2 compared with CON, respectively. Expression of Delta(9)-desaturase mRNA tended to be reduced (P = 0.09) by increasing FO from 1 to 2%, but was not affected by duration of supplementation (P > 0.24). Expression of mRNA for SREBP-1c was decreased 2-fold in FO2 compared with CON (P < 0.05), whereas expression of PPAR-alpha was not affected (P > 0.30). There was a positive relationship between Delta(9)-desaturase and SREBP-1c gene expression (P < 0.01), but the expression of both genes was negatively related to tissue concentrations of n-3 PUFA (P < 0.05) and positively related to concentration of n-6 PUFA (P < 0.01). Simultaneous enhancement of tissue concentrations of CLA and n-3 PUFA concentrations in bovine muscle may be hindered by negative interactions between n-3 PUFA and Delta(9)-desaturase gene expression, possibly mediated through reduced expression of SREBP-1c.

Sesamin Increases Alpha‐Linolenic Acid Conversion to Docosahexaenoic Acid in Atlantic Salmon (Salmo salar L.) Hepatocytes: Role of Altered Gene Expression

In vitro cultivated Atlantic salmon (Salmo salar L.), hepatocytes were incubated without or with a mixture of sesamin and episesamin in order to test for possible effects on lipid metabolism. Sesamin/episesamin exposure (0.05 mM, final concentration) led to increased elongation and desaturation of (14)C 18:3n-3 to docosahexaenoic acid ((14)C 22:6n-3, DHA, P < 0.01) and down regulated gene expression of Delta6 and Delta5 desaturases compared to control treatment. Sesamin/episesamin further increased the hepatocytes capacity for fatty acid beta-oxidation of (14)C 18:3n-3 (P < 0.01) to the (14)C acid soluble products, acetate, malate and oxaloacetate, in agreement with an increased gene expression of carnitine palmitoyltransferase I. Also the gene expression of cluster of differentiation 36 was upregulated and the expression of scavenger receptor type B, peroxisome proliferator-activated receptors alpha and gamma were downregulated. The amount of triacylglycerols secreted by the cells tended to be lower in the sesamin/episesamin incubated hepatocytes than the control cells. This study shows that sesamin has favourable effects on lipid metabolism leading to increased level of DHA, which may be of interest for aquaculture use.

Olanzapine appears to increase the expression of fatty acid synthase (FASN) and stearoyl-CoA desaturase (SCD) genes

Olanzapine appears to increase the expression of fatty acid synthase (FASN) and stearoyl-CoA desaturase (SCD) genes

Olanzapine appears to increase the expression of fatty acid synthase (FASN) and stearoyl-CoA desaturase (SCD) genes

Olanzapine appears to increase the expression of fatty acid synthase (FASN) and stearoyl-CoA desaturase (SCD) genes

Δ6-Desaturase (FADS2) deficiency unveils the role of ω3- and ω6-polyunsaturated fatty acids

Mammalian cell viability is dependent on the supply of the essential fatty acids (EFAs) linoleic and alpha-linolenic acid. EFAs are converted into omega3- and omega6-polyunsaturated fatty acids (PUFAs), which are essential constituents of membrane phospholipids and precursors of eicosanoids, anandamide and docosanoids. Whether EFAs, PUFAs and eicosanoids are essential for cell viability has remained elusive. Here, we show that deletion of delta6-fatty acid desaturase (FADS2) gene expression in the mouse abolishes the initial step in the enzymatic cascade of PUFA synthesis. The lack of PUFAs and eicosanoids does not impair the normal viability and lifespan of male and female fads2 -/- mice, but causes sterility. We further provide the molecular evidence for a pivotal role of PUFA-substituted membrane phospholipids in Sertoli cell polarity and blood-testis barrier, and the gap junction network between granulosa cells of ovarian follicles. The fads2 -/- mouse is an auxotrophic mutant. It is anticipated that FADS2 will become a major focus in membrane, haemostasis, inflammation and atherosclerosis research.