Rate Of Lipogenesis Research Articles

Intestinal Lipid Handling

Objective— Animal models have evidenced the role of intestinal triglyceride-rich lipoprotein overproduction in dyslipidemia. However, few studies have confronted this issue in humans and disclosed the intrinsic mechanisms. This work aimed to establish whether intestinal insulin resistance modifies lipid and lipoprotein homeostasis in the intestine of obese subjects. Approach and Results— Duodenal specimens obtained from 20 obese subjects undergoing bariatric surgery were paired for age, sex, and body mass index with or without insulin resistance, as defined by the homeostasis model assessment of insulin resistance. Insulin signaling, biomarkers of inflammation and oxidative stress, and lipoprotein assembly were assessed. The intestine of insulin-resistant subjects showed defects in insulin signaling as demonstrated by reduced protein kinase B phosphorylation and increased p38 mitogen-activated protein kinase phosphorylation, likely as the result of high oxidative stress (evidenced by malondialdehyde and conjugated dienes) and inflammation (highlighted by nuclear factor-κB, tumor necrosis factor-α, interleukin-6, intercellular adhesion molecule-1, and cyclooxygenase-2). Enhanced de novo lipogenesis rate and apolipoprotein B-48 biogenesis along with exaggerated triglyceride-rich lipoprotein production were observed, concomitantly with the high expression levels of liver and intestinal fatty acid–binding proteins and microsomal transfer protein. The presence of an aberrant intracellular cholesterol transport/metabolism was also suggested by the reduced expression of ATP-binding cassette A1 transporter and proprotein convertase subtilisin/kexin type 9. Conclusions— According to the present data, the small intestine may be classified as an insulin-sensitive tissue. Dysregulation of intestinal insulin signaling, possibly triggered by oxidative stress and inflammation, was associated with exaggerated lipogenesis and lipoprotein synthesis, which may represent a key mechanism for atherogenic dyslipidemia in patients with metabolic syndrome.

A systems approach to determine the effect of changes in gene expression in adipose tissue on productive and reproductive efficiency in dairy cattle

In order to assess the patterns of metabolism that affect efficiency, an existing mechanistic metabolic model of dairy cows (Molly) was expanded to include transcriptional control of metabolism in adipose tissue and reproductive processes. Our objective was to test the effects of changes in gene transcription in adipose tissue on patterns of metabolism, reproductive processes and efficiency. The model describes the substrate sensitivity and maximum velocity for lipogenesis, esterification and lipolysis. Data were collected from first and second parity cows from various studies, and included nutrient intake, milk component output, changes in adipose tissue lipid, visceral and body protein and lipid, and metabolism rates in adipose tissue and gene transcription. The lipogenic pathways were primarily controlled by transcriptional changes, whereas lipolysis varied primarily by post-translational control. We used the difference in transcriptional and post-translational metabolic control to alter Vmax and Ks for lipogenesis and lipolysis; in addition, we modelled a range of energy costs for ion transport and protein turnover in liver, muscle and adipose tissues. Changing rates of lipogenesis and lipolysis (~four-fold) did not affect milk production or feed intake, but altered maintenance costs, fat accretion, energetic efficiency and reproduction. Increases in lipogenesis decreased postpartum interval to first ovulation; increases in rates of lipolysis increased the interval. Changes in metabolic rate from changing either adipose tissue metabolism or rate of ion transport and protein turnover affected rates of oestrogen and progesterone degradation, which affected follicular growth and corpus luteum function. This model may be used to help interpret genomic and transcriptomic data to pinpoint the most effective ways to select and manage for changes in productive and reproductive efficiency.

Differential effects of high-carbohydrate and high-fat diets on hepatic lipogenesis in rats

Hepatic fatty acid synthesis is influenced by several nutritional and hormonal factors. In this study, we have investigated the effects of distinct experimental diets enriched in carbohydrate or in fat on hepatic lipogenesis. Male Wistar rats were divided into four groups and fed distinct experimental diets enriched in carbohydrates (70% w/w) or in fat (20 and 35% w/w). Activity and expression of the mitochondrial citrate carrier and of the cytosolic enzymes acetyl-CoA carboxylase and fatty acid synthetase were analyzed through the study with assessments at 0, 1, 2, 4, and 6 weeks. Liver lipids and plasma levels of lipids, glucose, and insulin were assayed in parallel. Whereas the high-carbohydrate diet moderately stimulated hepatic lipogenesis, a strong inhibition of this anabolic pathway was found in animals fed high-fat diets. This inhibition was time-dependent and concentration-dependent. Moreover, whereas the high-carbohydrate diet induced an increase in plasma triglycerides, the high-fat diets determined an accumulation of triglycerides in liver. An increase in the plasmatic levels of glucose and insulin was observed in all cases. The excess of sucrose in the diet is converted into fat that is distributed by bloodstream in the organism in the form of circulating triglycerides. On the other hand, a high amount of dietary fat caused a strong inhibition of lipogenesis and a concomitant increase in the level of hepatic lipids, thereby highlighting, in these conditions, the role of liver as a reservoir of exogenous fat.

Effects of small interfering RNA-mediated hepatic glucagon receptor inhibition on lipid metabolism in db/db mice

Hepatic glucose overproduction is a major characteristic of type 2 diabetes. Because glucagon is a key regulator for glucose homeostasis, antagonizing the glucagon receptor (GCGR) is a possible therapeutic strategy for the treatment of diabetes mellitus. To study the effect of hepatic GCGR inhibition on the regulation of lipid metabolism, we generated siRNA-mediated GCGR knockdown (si-GCGR) in the db/db mouse. The hepatic knockdown of GCGR markedly reduced plasma glucose levels; however, total plasma cholesterol was increased. The detailed lipid analysis showed an increase in the LDL fraction, and no change in VLDL HDL fractions. Further studies showed that the increase in LDL was the result of over-expression of hepatic lipogenic genes and elevated de novo lipid synthesis. Inhibition of hepatic glucagon signaling via siRNA-mediated GCGR knockdown had an effect on both glucose and lipid metabolism in db/db mice.

Short‐term high‐fat diet impairs regulation of hepatic lipogenesis in rats

Chronic high‐fat intake can produce obesity, fatty liver, and insulin resistance in rodents. We have found that a long‐term (>; 10 wk) high‐fat diet impairs the induction of SREBP‐1c and lipogenic enzymes by carbohydrate feeding. The present study investigated the early effects of the same diet on male Sprague Dawley rats consuming either a low‐fat (LF, 15%kcal, N=6) or a high‐fat (HF, 55% N=6) diet ad libitum for 1 wk. Although body weights were similar, HF rats had higher body fat (p< 0.02), liver lipid concentration (p< 0.02), and HOMA (p< 0.05 ) than LF rats. Analysis of liver samples collected from either 24 h food deprived rats or rats refed a high‐carbohydrate (55% kcal) diet for 16 hr, showed that refeeding increased mRNA for SREBP‐1c (10X), Acetyl CoA Carboxylase (7X), Fatty Acid Synthase (40X) and Pyruvate Kinase (6X) in LF, but only by 1.5 ‐ 3X in HF livers. Despite similar plasma insulin responses, LF showed greater feeding‐induced increases than HF in hepatic mTORC1 activity (increased p‐S6/total S6), and SREBP‐1c maturation, both mediators of insulin‐stimulated lipogenesis. Refeeding increased Fatty Acid Synthase protein content similarly in HF and LF at wk1, but did not do so at wk 10. These findings show that even short‐term HF diets impair early events in carbohydrate‐induced hepatic lipogenesis. NIH 1SC3GM086298

The deficit of lipid in cultured cells contrasted with clinical lipidomics

Cells grown in culture are frequently employed to model lipid metabolism in vivo. There are reasons of convenience for this but examination of the lipidome of cultured cells and their metabolic responses to lipid supplementation give cause to indicate disparity with their counterparts in living animals. The reason is mainly that homeostatic regulation is exercised in animals supplied with an adequate diet in which the adipose tissue and liver represent plentiful sources of lipid integrated via inter-organ collaboration and able to buffer transient fluctuations in dietary lipid and essential fatty acids (EFAs). Moreover, conventional culture media are generally deficient in total lipids as well as essential EFAs. Cultured cells exposed to high glucose concentrations and lipid deficit typically manifest accelerated rates of lipogenesis evidenced by high rates of de novo FA biosynthesis. A more realistic model may be obtained by increasing supplements of lipid especially enriched in essential EFAs in the growth medium. Increasing concentrations of ω3 FAs, in particular, attenuate the rate of de novo lipogenesis. The improvement of cell culture models for pharmacological screening of drug-candidates targeting lipid or glucose metabolism is highlighted.

Regulation of bovine adipose tissue metabolism during lactation. 7. Metabolism and gene expression as a function of genetic merit and dietary energy intake

The regulation of adipose tissue metabolism is critical to the efficient establishment and support of lactation, through both energy supply and several endocrine and cytokine factors. We still lack detailed knowledge of the role of transcription and posttranslational regulation of metabolic flux. We need to quantitatively understand the genetic and environmental (primarily dietary) regulation of adipose tissue to help improve productive efficiency. Therefore, objectives of this project were to help define mechanisms of adipose tissue responses to lactation and energy deficit, including changes in gene expression and their relation to changes in metabolic flux and production. A total of 48 cows were selected for genetic merit based on sire predicted transmitting ability of milk. From 21d prepartum to 60d in milk (DIM), cows were fed to energy requirements or to 90% of energy requirements, with content of protein, vitamins, and minerals balanced to be the same for both treatments. Adipose tissue biopsies were taken at 21 and 7d prepartum and 7, 28, and 56 DIM to determine rates of lipogenesis and lipolysis, and to measure gene expression of proteins controlling lipolysis. The cows on the restricted diet consumed 12% less feed prepartum and 16% less feed postpartum and dietary energy restriction decreased milk production. The slowest rates of lipogenesis occurred at 7 and 28 DIM; higher-merit cows had faster rates of lipogenesis at 7 DIM but slower rates than lower-merit cows at 28 DIM. Energy restriction decreased lipogenesis. Basal and isoproterenol lipolysis increased with higher milk production and was relatively unaffected by dietary energy intake. The expression of genes controlling lipolysis were not affected by lactation and were slightly increased by dietary restriction, but were not well related to rates of lipolysis. These data confirm and extend previous work that regulation of adipose tissue metabolism in lactation is a function of both diet and genetic merit and is controlled by multiple mechanisms including gene transcription and posttranslational protein modifications.

Change in subcutaneous adipose tissue metabolism and gene network expression during the transition period in dairy cows, including differences due to sire genetic merit

Adipose metabolism is an essential contributor to the efficiency of milk production, and metabolism is controlled by several mechanisms, including gene expression of critical proteins; therefore, the objective of this study was to determine how lactational state and the genetic merit of dairy cattle affects adipose tissue (AT) metabolism and mRNA expression of genes known to control metabolism. Animals of high (HGM) and low genetic merit (LGM) were fed to requirements, and weekly dry matter intake, milk production, blood glucose, and nonesterified fatty acids were measured. Subcutaneous AT biopsies were collected at −21, 7, 28 and 56 d in milk (DIM). The mRNA expression of genes coding for lipogenic enzymes [phosphoenolpyruvate carboxykinase 1 (soluble) (PCK1), fatty acid synthase (FASN), diacylglycerol O-acyltransferase 2 (DGAT2), and stearoyl-coenzyme A desaturase (SCD)], transcription regulators [peroxisome proliferator-activated receptor γ (PPARG), thyroid hormone responsive (THRSP), wingless-type MMTV integration site family, member 10B (WNT10B), sterol regulatory element binding transcription factor 1 (SREBF1), and adiponectin (ADIPOQ)], lipolytic enzymes [hormone-sensitive lipase (LIPE), patatin-like phospholipase domain containing 2 (PNPLA2), monoglyceride lipase (MGLL), adrenoceptor β-2 (ADRB2), adipose differentiation-related protein (ADFP), and α-β-hydrolase domain containing 5 (ABHD5)], and genes controlling the sensing of intracellular energy [phosphodiesterase 3A (PDE3A); PDE3B; protein kinase, AMP-activated, α-1 catalytic subunit (PRKAA1); PRKAA2; and growth hormone receptor (GHR)] was measured. Dry matter intake, blood glucose, and nonesterified fatty acid concentrations did not differ between genetic merit groups. Milk production was greater for HGM cows from 6 to 8 wk postpartum. As expected, the rates of lipogenesis decreased in early lactation, whereas stimulated lipolysis increased. At 7 DIM, lipogenesis in HGM cows increased as a function of substrate availability (0.5, 1, 2, 3, 4, or 8mM acetic acid), whereas the response in LGM cows was much less pronounced. However, the lipogenic response at 28 DIM reversed and rates were greater in tissue from LGM than HGM cows. Peak lipolytic response, regardless of DIM, was observed at the lowest dose of isoproterenol (10−8M), and −21d tissue had a greater lipolysis rate than tissue at 7, 28, and 56d. In HGM compared with LGM cows, stimulated lipolysis at 7 and 28 DIM was greater but peaked at 10−7M isoproterenol, suggesting differences in tissue responsiveness due to genetic merit. Regardless of genetic merit, the expression of lipogenic genes decreased markedly in early lactation, whereas those controlling lipolysis stayed similar or decreased slightly. Cows of HGM had lower expression of lipogenic genes after parturition and through 56 DIM. In contrast, the expression of most of the lipolytic enzymes, receptors and proteins was similar in all cows pre- and postpartum. These results confirm that gene transcription is a major control mechanism for AT lipogenesis during early lactation, but that control of lipolysis is likely primarily by posttranslational mechanisms.

Methyl-β-cyclodextrin alters adipokine gene expression and glucose metabolism in swine adipose tissue

This study was designed to determine whether methyl-β-cyclodextrin (MCD) can substitute for albumin in incubation medium for neonatal swine adipose tissue explants, or whether MCD affects metabolism and cytokine expression. Subcutaneous adipose tissue explants (100 ± 10 mg) were prepared from 21-day-old pigs. Explants were incubated in medium 199 supplemented with 25 mM HEPES, 1.0 nM insulin at 37°C. The medium also contained bovine serum albumin (BSA) or MCD at 0%, 0.05%, 0.1%, 0.2% or 0.3%. Tissue explants were treated with these media for 1 h and then switched to the same basal incubation medium containing 0.05% BSA. Explants were removed from basal medium at 2 or 8 h of incubation, and real-time PCR was performed to assess expression of tumor necrosis α (TNF) and interleukin 6 (IL6), acetyl CoA carboxylase (ACAC) and fatty acid synthase (FASN). Alternatively, rates of 14C-glucose oxidation and lipogenesis were monitored ± insulin (100 nM), following MCD treatment. Incubation with BSA had minimal effects on gene expression or adipose tissue metabolism, only producing a doubling in TNF mRNA abundance (P < 0.01). Treatment with MCD increased TNF mRNA abundance by eightfold (P < 0.009), whereas IL6 gene expression increased a 100-fold (P < 0.001) with a suppression in ACAC and FASN expression (P < 0.01). This was paralleled by MCD inhibition of insulin-stimulated glucose oxidation and lipogenesis (P < 0.001). Addition of a TNF antibody to the incubation medium alleviated this inhibition of insulin-stimulated glucose metabolism by ∼30% (P < 0.05).

Differential expression of L-FABP and L-BABP between fat and lean chickens

Liver fatty acid-binding protein (L-FABP) and liver bile acid-binding protein (L-BABP), in the liver intra-cytoplasm of chicken, are members of the fatty acid-binding protein subfamily. This study was designed to analyze and compare L-FABP and L-BABP expression levels between fat and lean lines in chicken liver tissue, and to determine the relationship between their expression and lipid metabolism. Real-time polymerase chain reaction (PCR) and Western blotting were used to detect the mRNA and protein expression in liver tissue between the lean and fat lines. Real-time PCR showed that L-FABP mRNA expression in fat male chickens was higher than that in lean male chickens at 2, 3, 4, 5, 6, and 10 weeks of age (P < 0.05), and L-BABP mRNA expression in fat male chickens was higher than that in lean male chickens at 1, 2, 3, 4, 8, and 10 weeks of age (P < 0.05). Western blotting showed that the L-FABP protein expression in fat male chickens was higher than that in lean male chickens at 3, 5, 6, and 7 weeks of age (P < 0.05), and L-BABP protein expression in fat male chickens was higher than that in lean male chickens at 3, 4, 5, and 6 weeks of age (P < 0.05). These results suggested that chicken L-FABP and L-BABP affect abdominal fat deposition through differences in their expression level, and the possible mechanism is that a high expression level of L-FABP and L-BABP leads to a high lipogenesis rate and, ultimately, to lipid deposition.

The strange and critical intersection of hepatitis C and lipoprotein metabolism: “C-zing” the oil

Since its discovery in 1989, a substantial amount of research has emerged regarding the close association of hepatitis C virus (HCV) replication and hepatic lipoprotein metabolism. Even before the identification of the HCV virus, a link to fat metabolism was suspected based on clinical observations regarding steatosis as a common feature of what used to be known as “non-A, non-B hepatitis.”1 This relationship was later extended in studies that revealed that HCV-infected patients with steatosis often lack common risk factors for fatty liver, such as obesity.2 These early observations, along with subsequent studies that identified circulating viral particles in low-density, more-buoyant plasma fractions (partitioned with plasma centrifugation in sucrose or iodixanol gradients), fueled a now extensive and growing body of literature on this key aspect of HCV replication.3 Investigations performed over the past 23 years have defined replicative pathways of HCV involving mechanisms and biochemical pathways right out of the “play book” of fatty liver disease (FLD).

Palmitoleic (16:1 cis‐9) and cis‐Vaccenic (18:1 cis‐11) Acid Alter Lipogenesis in Bovine Adipocyte Cultures

Our objectives were to: (1) confirm elongation products of palmitoleic acid (16:1 cis-9) elongation in vitro using stable isotopes and (2) evaluate if exogenous supplementation of palmitoleic acid, elongation products, or both are responsible for decreased desaturation and lipogenesis rates observed with palmitoleic acid supplementation in bovine adipocytes. Stromal vascular cultures were isolated from adipose tissue of two beef carcasses, allowed to reach confluence, held for 2 days, and differentiated with a standard hormone cocktail (day 0). On day 2, secondary differentiation media containing 1 of 4 fatty acid treatments [0 μM fatty acid (control), or 150 μM palmitic (16:0), palmitoleic, or cis-vaccenic (18:1 cis-11)] was added for 4 days. On day 6, cells were incubated with [(13)C] 16:1, [(13)C] 2, or [(13)C] 18:0 to estimate elongation, lipogenic, and desaturation rates using gas chromatography-mass spectrometry. Enrichment of [(13)C] 18:1 cis-11 confirmed 18:1 cis-11 is an elongation product of 16:1. Additionally, [(13)C] label was seen in 20:1 cis-13 and cis-9, cis-11 CLA. Synthesis of [(13)C] 16:0 from [(13)C] 2 was reduced (P < 0.05) in palmitoleic acid and cis-vaccenic acid-treated compared with control cells following 36 h incubation. By 12 h of [(13)C] 18:0 incubation, cells supplemented with palmitoleic acid had reduced (P < 0.05) [(13)C] 18:1 cis-9 compared with all other treatments. Gene expression and fatty acid results support isotopic data for lipogenesis and desaturation. Therefore, palmitoleic acid is actively elongated in vitro and its elongation product, cis-vaccenic acid, can also reduce lipogenesis. However, inhibition of desaturation can be directly attributed to palmitoleic acid and not its elongation products, 18:1 cis-11 or 20:1 cis-13.

겨우살이 Lectin이 흰쥐의 혈청지질 및 간조직에 미치는 영향

본 연구에서 국내산 겨우살이 lectin이 흰쥐 간의 지방형성에 미치는 영향을 알아보기 위해 혈청 내 지질 함량을 측정하였고, 이를 확인하고자 간조직의 지방형성 변화를 조사하였다. 렉틴의 분리는 sephadex G-150로 여과 및 sepharose 4B affinity chromatography 로 정제하였다. <TEX>$CCl_4$</TEX>를 복강 내에 투여시 72시간 경과 후 혈청 총cholesterol 및 triglyceride는 정상군 및 olive oil 투여군에 비해 유의하게 증가하였으며, lectin과 <TEX>$CCl_4$</TEX>를 동시 투여 하였을 때는 유의한 감소를 나타내였다. 흰쥐 간의 조직학적 관찰은 <TEX>$CCl_4$</TEX>투여군은 정상군 및 olive oil 투여군에 비해 지방변화 및 간세포 내에 많은 대소의 cytoplasmic vacuole가 보였으나, <TEX>$CCl_4$</TEX>와 lectin을 동시 투여시는 <TEX>$CCl_4$</TEX> 투여군에 비해 cytoplasmic vacuole은 현저히 감소하였고, 이에 비례하여 혈청 cholesterol 및 triglyceride 측정치가 현저히 감소하는 결과를 나타내었다. 이상의 결과를 볼때 흰쥐에서 lectin이 혈청 지질을 감소시키거나 또는 조직학적 관찰에서 간조직의 지질형성을 억제시키는 효과가 있는 것으로 확인되었다. This study was carried out to investigate effect of serum lipid and liver tissue in lectin from Viscum album on rats. The lectin was purified by sepharose 4B affinity chromatography and gel filtration using sephadex G-150 with plant material from Viscum album. After 72 h of <TEX>$CCl_4$</TEX> injection, there was a significant increase in serum total cholesterol and triglycerige levels relative to the control group. However, treatment of both Viscum album and purified lectin were significantly decreased lipid parameters against the <TEX>$CCl_4$</TEX>-induced. Histological observation of the liver section of rats challenged with <TEX>$CCl_4$</TEX> produced a marked increase of cytoplasmic vacuoles in number, while rats administered olive oil alone did not alter the normal hepatic architecture. Histological observation of the liver section in rats treated 72 h with either Viscum album purified lectin or <TEX>$CCl_4$</TEX>-induced liver lipogenesis showed decreased numbers of cytoplasmic vaculoes and necrotic cells. These results suggest that Viscum album lectin has a significantly decreased lipid in serum or histological observation of the liver section decreased in lipogenesis in rats.

Supplemental palmitoleic (C16:1 cis-9) acid reduces lipogenesis and desaturation in bovine adipocyte cultures1

Our objective was to determine if palmitoleic (C16:1 cis-9) acid supplementation to primary bovine adipocytes regulates lipogenic gene expression and rates of lipogenesis. Stromal vascular cells were isolated from subcutaneous and intermuscular fat, propagated, and frozen for use in this study. Cells were passaged 4 times, allowed to reach confluence, held for 2 d, and then differentiated with a standard hormone cocktail (d 0). At d 2, secondary differentiation media containing 1 of 4 concentrations of palmitoleic acid (0, 50, 150, or 300 μM) were added for 10 d. Cells were harvested on d 6 and 12 to assess fatty acid concentrations and gene expression. In addition, (13)C2 and (13)C18:0 stable isotopes were added on d 6 to measure lipogenesis and desaturase activity, respectively. Concentrations of C16:1 and total fatty acids increased (P < 0.05) linearly in response to palmitoleic acid supplement. Concentrations of C18:1 cis-11 and C20:1 cis-13 also increased (P < 0.01) in response to supplementation, suggesting elongation of palmitoleic acid in vitro. Concentrations of C16:1, C18:1 cis-11, and total fatty acids were also greater (P < 0.05) at d 12 compared with d 6. In contrast, C16:0, C18:0, and C18:1 cis-9 concentrations decreased (P < 0.05) in response to palmitoleic acid supplementation and were not affected (P > 0.05) by harvest day. The ratio of C18:1 cis-9/C18:0 and fractional synthetic rate (FSR) of desaturation decreased (P < 0.05) in response to increasing palmitoleic acid supplementation. In addition, FSR of lipogenesis was reduced (P < 0.05) in palmitoleic acid-treated cells. Messenger RNA abundance as determined by real-time quantitative PCR for stearoyl-CoA desaturase 1 (SCD1), fatty acid synthase (FASN), and elongase protein 6 (ELOVL6) genes were reduced (P < 0.05) by palmitoleic acid supplementation. Expression of a β-oxidation gene, carnitine palmitoyltransferase 1A (CPT1A), was upregulated (P < 0.05) with palmitoleic acid supplementation in a dose-responsive manner. Supplementation of palmitoleic acid to bovine adipocytes results in increased incorporation of this fatty acid and its elongation products into the adipocyte, which downregulates SCD1, FASN, and ELOVL6 to decrease lipogenesis and upregulates CPT1A, potentially increasing β-oxidation. These results suggest that palmitoleic acid, an end product of desaturation, can act as a regulator of lipogenesis, desaturation, and β-oxidation in bovine adipocytes.

Role of temperature on lipid/fatty acid composition in Pacific cod (Gadus macrocephalus) eggs and unfed larvae

During early development, oviparous fish species must use finite lipid and fatty acid (FA) reserves for both catabolism and structural components. In cold environments, developing fish have the additional constraint of maintaining membrane fluidity for metabolic efficiency (homeoviscous adaptation), resulting in further demand on lower melting point FAs like n-3 polyunsaturated fatty acids (PUFAs). To examine whether marine fish embryos physiologically adapt to changing temperature environments, we incubated Pacific cod (Gadus macrocephalus) eggs at 5 temperatures (0, 2, 4, 6, and 8 °C) in the laboratory and sampled them repeatedly during development to measure changes in lipid/FA composition. Pacific cod embryos increased n-3 PUFA content during the egg stage in all temperature treatments, with the possible exception of 0 °C, where poor survival and hatch success limited our ability for continued sampling. At the beginning of the hatch cycle, free-swimming embryos shifted from lipogenesis to lipid catabolism. The rates of lipogenesis and catabolism were temperature dependent, and the distinct increase in unsaturated fatty acids at temperatures <8 °C was consistent with homeoviscous adaptation theory. However, with the possible exception of embryos at 0 °C, the relative amounts of essential fatty acids (e.g., EPA, DHA, AA) were conserved in a similar manner across incubation temperatures. Collectively, these data suggest Pacific cod are capable of homeoviscous adaptation but cannot tolerate temperatures approaching 0 °C despite their possible ability to biosynthesize PUFAs from other energetic sources.

StearoylCoA Desaturase-5: A Novel Regulator of Neuronal Cell Proliferation and Differentiation

Recent studies have demonstrated that human stearoylCoA desaturase-1 (SCD1), a Δ9-desaturase that converts saturated fatty acids (SFA) into monounsaturated fatty acids, controls the rate of lipogenesis, cell proliferation and tumorigenic capacity in cancer cells. However, the biological function of stearoylCoA desaturase-5 (SCD5), a second isoform of human SCD that is highly expressed in brain, as well as its potential role in human disease, remains unknown. In this study we report that the constitutive overexpression of human SCD5 in mouse Neuro2a cells, a widely used cell model of neuronal growth and differentiation, displayed a greater n-7 MUFA-to-SFA ratio in cell lipids compared to empty-vector transfected cells (controls). De novo synthesis of phosphatidylcholine and cholesterolesters was increased whereas phosphatidylethanolamine and triacylglycerol formation was reduced in SCD5-expressing cells with respect to their controls, suggesting a differential use of SCD5 products for lipogenic reactions. We also observed that SCD5 expression markedly accelerated the rate of cell proliferation and suppressed the induction of neurite outgrowth, a typical marker of neuronal differentiation, by retinoic acid indicating that the desaturase plays a key role in the mechanisms of cell division and differentiation. Critical signal transduction pathways that are known to modulate these processes, such epidermal growth factor receptor (EGFR)Akt/ERK and Wnt, were affected by SCD5 expression. Epidermal growth factor-induced phosphorylation of EGFR, Akt and ERK was markedly blunted in SCD5-expressing cells. Furthermore, the activity of canonical Wnt was reduced whereas the non-canonical Wnt was increased by the presence of SCD5 activity. Finally, SCD5 expression increased the secretion of recombinant Wnt5a, a non-canonical Wnt, whereas it reduced the cellular and secreted levels of canonical Wnt7b. Our data suggest that, by a coordinated modulation of key lipogenic pathways and transduction signaling cascades, SCD5 participates in the regulation of neuronal cell growth and differentiation.

Food restriction and refeeding induces changes in lipid pathways and fat deposition in the adipose and hepatic tissues in rats with diet‐induced obesity

The aim of this study was to determine the effects of successive cycles of a moderately restrictive diet and refeeding with a high-fat diet on the metabolism of the adipose and hepatic tissues of obese rats. Rats were assigned to the following groups: a chow diet; a high-fat diet; a moderate caloric restriction; or a moderate caloric restriction plus refeeding. Some animals in each group were given [1-(14)C]triolein intragastrically, while others received an intraperitoneal injection of 3 mCi (3)H(2)O. All animals were killed by decapitation. The retroperitoneal, visceral epididymal and omental white adipose tissues, brown adipose tissue, liver and blood were immediately removed. The lipid uptake from the diet, in vivo rate of lipogenesis, percentage of fat, lipid profile and leptin concentration were analysed. The high-fat diet promoted an increase in fatty liver (P ≤ 0.05), adiposity mass (P ≤ 0.05) and the plasma concentration of leptin (P ≤ 0.05) and a decreased lipid uptake in white adipose tissue depots (P ≤ 0.05) in relation to the chow diet. The moderate caloric restriction did not reverse the changes promoted by the high-fat diet but induced a small decrease in adiposity, which was reversed after refeeding, and the animals maintained a dyslipidaemic profile and high fat deposition in the liver. We can conclude that the high-fat diet and subsequent moderate caloric restriction plus refeeding increased the risks of developing visceral obesity, dyslipidaemia and non-alcoholic fatty liver disease, which suggests that this type of experimental protocol can be used to study mechanisms related to the metabolic syndrome.

A soyabean diet does not modify the activity of brown adipose tissue but alters the rate of lipolysis in the retroperitoneal white adipose tissue of male rats recovering from early-life malnutrition

Nutritional recovery with a soyabean diet decreases body and fat weights when compared with a casein diet. We investigated whether the reduced adiposity observed in rats recovering from early-life malnutrition with a soyabean diet results from alterations in lipid metabolism in white adipose tissue (WAT) and/or brown adipose tissue (BAT). Male rats from mothers fed either 17 or 6% protein during pregnancy and lactation were maintained on 17% casein (CC and LC groups), 17% soyabean (CS and LS groups) or 6% casein (LL group) diets over 60d. The rats maintained on a soyabean diet had similar relative food intakes, but lower body and retroperitoneal WAT weights and a reduced lipid content in the retroperitoneal WAT. The insulin levels were lower in the recovered rats and were elevated in those fed a soyabean diet. Serum T3 concentration and uncoupling protein 1 content in the BAT were decreased in the recovered rats. The thermogenic capacity of the BAT was not affected by the soyabean diet. The lipogenesis rate in the retroperitoneal WAT was similar in all of the groups except for the LL group, which had exacerbated lipogenesis. The enhancement of the lipolysis rate by isoproterenol was decreased in white adipocytes from the soyabean-recovered rats and was elevated in adipocytes from the soyabean-control rats. Thus, in animals maintained on a soyabean diet, the proportions of fat deposits are determined by the lipolysis rate, which differs depending on the previous nutritional status.

A palatable hyperlipidic diet causes obesity and affects brain glucose metabolism in rats

BackgroundWe have previously shown that either the continuous intake of a palatable hyperlipidic diet (H) or the alternation of chow (C) and an H diet (CH regimen) induced obesity in rats. Here, we investigated whether the time of the start and duration of these feeding regimens are relevant and whether they affect brain glucose metabolism.MethodsMale Wistar rats received C, H, or CH diets during various periods of their life spans: days 30-60, days 30-90, or days 60-90. Experiments were performed the 60th or the 90th day of life. Rats were killed by decapitation. The glucose, insulin, leptin plasma concentration, and lipid content of the carcasses were determined. The brain was sliced and incubated with or without insulin for the analysis of glucose uptake, oxidation, and the conversion of [1-14C]-glucose to lipids.ResultsThe relative carcass lipid content increased in all of the H and CH groups, and the H30-60 and H30-90 groups had the highest levels. Groups H30-60, H30-90, CH30-60, and CH30-90 exhibited a higher serum glucose level. Serum leptin increased in all H groups and in the CH60-90 and CH30-90 groups. Serum insulin was elevated in the H30-60, H60-90, CH60-90, CH30-90 groups. Basal brain glucose consumption and hypothalamic insulin receptor density were lower only in the CH30-60 group. The rate of brain lipogenesis was increased in the H30-90 and CH30-90 groups.ConclusionThese findings indicate that both H and CH diet regimens increased body adiposity independent treatment and the age at which treatment was started, whereas these diets caused hyperglycemia and affected brain metabolism when started at an early age.

Increased Lipogenesis and Stearate Accelerate Vascular Calcification in Calcifying Vascular Cells

Vascular calcification is recognized as an independent predictor of cardiovascular mortality, particularly in subjects with chronic kidney disease. However, the pathways by which dysregulation of lipid and mineral metabolism simultaneously occur in this particular population remain unclear. We have shown that activation of the farnesoid X receptor (FXR) blocks mineralization of bovine calcifying vascular cells (CVCs) and in ApoE knock-out mice with 5/6 nephrectomy. In contrast to FXR, this study showed that liver X receptor (LXR) activation by LXR agonists and adenovirus-mediated LXR overexpression by VP16-LXRα and VP16-LXRβ accelerated mineralization of CVCs. Conversely, LXR inhibition by dominant negative (DN) forms of LXRα and LXRβ reduced calcium content in CVCs. The regulation of mineralization by FXR and LXR agonists was highly correlated with changes in lipid accumulation, fatty acid synthesis, and the expression of sterol regulatory element binding protein-1 (SREBP-1). The rate of lipogenesis in CVCs through the SREBP-1c dependent pathway was reduced by FXR activation, but increased by LXR activation. SREBP-1c overexpression augmented mineralization in CVCs, whereas SREBP-1c DN inhibited alkaline phosphatase activity and mineralization induced by LXR agonists. LXR and SREBP-1c activations increased, whereas FXR activation decreased, saturated and monounsaturated fatty acids derived from lipogenesis. In addition, we found that stearate markedly promoted mineralization of CVCs as compared with other fatty acids. Furthermore, inhibition of either acetyl-CoA carboxylase or acyl-CoA synthetase reduced mineralization of CVCs, whereas inhibition of stearoyl-CoA desaturase induced mineralization. Therefore, a stearate metabolite derived from lipogenesis might be a risk factor for the development of vascular calcification.