Role of stearoyl-coenzyme A desaturase in regulating lipid metabolism

Susceptibility to gold nanoparticle-induced hepatotoxicity is enhanced in a mouse model of nonalcoholic steatohepatitis

Although the safety of gold nanoparticle (AuNP) use is of growing concern, most toxicity studies of AuNPs had focused on their chemical characteristics, including their physical dimensions, surface chemistry, and shape. The present study examined the susceptibility of rodents with healthy or damaged livers to AuNP-induced hepatotoxicity. To induce a model of liver injury, mice were fed a methionine- and choline-deficient (MCD) diet for 4 weeks. Sizes and biodistribution of 15-nm PEGylated AuNPs were analyzed by transmission electron microscopy. Levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were estimated with an automatic chemical analyzer, and liver sections were subjected to pathological examination. Activities of antioxidant enzymes were determined by biochemical assay. Lateral tail vein injection of MCD diet-fed mice with 5 mg kg(-1) AuNPs significantly elevated the serum ALT and AST levels compared to MCD diet-fed mice injected with mPEG (methylpolyethylene glycol). Similarly, severe hepatic cell damage, acute inflammation, and increased apoptosis and reactive oxygen species (ROS) production were observed in the livers of AuNP-injected mice on the MCD diet; these liver injuries were attenuated in mice fed a normal chow diet. The results suggest that AuNPs display toxicity in a stressed liver environment by stimulating the inflammatory response and accelerating stress-induced apoptosis. These conclusions may point to the importance of considering health conditions, including liver damage, in medical applications of AuNPs.

Daily intake of cod or salmon for 2 weeks decreases the 18:1n-9/18:0 ratio and serum triacylglycerols in healthy subjects

Intake of fish and omega-3 (n-3) fatty acids is associated with a reduced concentration of plasma triacylglycerols (TAG) but the mechanisms are not fully clarified. Stearoyl-CoA desaturase-1 (SCD1) activity, governing TAG synthesis, is affected by n-3 fatty acids. Peripheral blood mononuclear cells (PBMC) display expression of genes involved in lipid metabolism. The aim of the present study was to estimate whether intake of lean and fatty fish would influence n-3 fatty acids composition in plasma phospholipids (PL), serum TAG, 18:1n-9/18:0 ratio in plasma PL, as well as PBMC gene expression of SCD1 and fatty acid synthase (FAS). Healthy males and females (n = 30), aged 20-40, consumed either 150 g of cod, salmon, or potato (control) daily for 15 days. During intervention docosahexaenoic acid (DHA, 22:6n-3) increased in the cod group (P < 0.05), while TAG concentration decreased (P < 0.05). In the salmon group both eicosapentaenoic acid (EPA, 20:5n-3) and DHA increased (P < 0.05) whereas TAG concentration and the 18:1n-9/18:0 ratio decreased (P < 0.05). Reduction of the 18:1n-9/18:0 ratio was associated with a corresponding lowering of TAG (P < 0.05) and an increase in EPA and DHA (P < 0.05). The mRNA levels of SCD1 and FAS in PBMC were not significantly altered after intake of cod or salmon when compared with the control group. In conclusion, both lean and fatty fish may lower TAG, possibly by reducing the 18:1n-9/18:0 ratio related to allosteric inhibition of SCD1 activity, rather than by influencing the synthesis of enzyme protein.

Genetic variation in stearoyl-CoA desaturase 1 is associated with metabolic syndrome prevalence in Costa Rican adults

Stearoyl-CoA desaturase 1 (SCD1) activity, a key regulator of lipid metabolism, may be associated with the development of metabolic syndrome (MetS). We examined the association of genetic variation in the SCD1 gene with the occurrence of MetS and its five components in a population of Costa Rican adults (n = 2152; mean age, 58 y; range, 18-86 y). Associations of tag single nucleotide polymorphisms (tagSNP) of the SCD1 gene with prevalence of MetS and its five components were analyzed by use of log-Poisson models with robust variance estimates and linear regression models, respectively. The likelihood ratio was used to test potential gene-fatty acid interactive effects with adipose tissue α-linolenic acid. One tagSNP (rs1502593) was significantly associated with an increased prevalence of MetS in the total study sample. Compared with the common homozygous CC genotype, the CT and TT genotypes for rs1502593 were associated with higher prevalence ratios (PR) of MetS for CT vs. CC: [PR = 1.22 (95% CI = 1.03, 1.44)] and for TT vs. CC [PR = 1.24 (95% CI = 1.01, 1.52)]. Among women, we observed borderline positive associations between systolic blood pressure and fasting blood sugar levels and rs1502593 (P = 0.05 and 0.06). Compared to the common haplotype (frequency ≥ 5%) with no minor alleles of SCD1 tagSNP, the other two observed common haplotypes carrying the rs1502593 minor allele were significantly associated with elevated prevalence of MetS. No gene-fatty acid interactive effects were observed. Our results suggest that genetic variation in the SCD1 gene may play a role in the development of MetS.

Wheel running prevents the accumulation of monounsaturated fatty acids in the liver of ovariectomized mice by attenuating changes in SCD-1 content

Decreases in female sex steroids enhance the accumulation of visceral fat mass, leading to a predisposition to developing metabolic diseases. The purpose of this study was to determine whether loss of ovarian function alters the amount and (or) the fatty acid (FA) composition of triacylglycerol (TAG) levels in the liver of ovary-intact (SHAM) or ovariectomized (OVX) mice. We also sought to determine whether voluntary wheel running could attenuate the associated changes in the liver. Twenty-two C57/BL6 female mice were divided into 2 groups (SHAM, OVX) and were then subdivided into sedentary and exercising groups (SHAM-Sed, SHAM-Ex, OVX-Sed, OVX-Ex). Visceral fat mass significantly increased in the OVX-Sed animals; however, the effect was attenuated in the OVX-Ex animals. Total hepatic TAG content did not significantly increase in the OVX-Sed animals; however, SHAM-Ex and OVX-Ex animals demonstrated significant decreases in TAG levels. A significant increase in the FA desaturase index (18:1/18:0 and 16:1/16:0) was detected in the OVX-Sed animals compared with all other groups, which corresponded to increases in stearoyl-CoA desaturase (SCD-1) content. These results indicate that loss of ovarian function alters FA composition of hepatic TAG mediated by increases in SCD-1. These data indicate that female sex steroids influence lipid metabolism in the liver and provide important insight concerning the influence of exercise on hepatic function.

Protease-activated receptor 1 and hematopoietic cell tissue factor are required for hepatic steatosis in mice fed a Western diet

Nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of obesity and metabolic syndrome and contributes to increased risk of cardiovascular disease and liver-related morbidity and mortality. Indeed, obese patients with metabolic syndrome generate greater amounts of thrombin, an indication of coagulation cascade activation. However, the role of the coagulation cascade in Western diet-induced NAFLD has not been investigated. Using an established mouse model of Western diet-induced NAFLD, we tested whether the thrombin receptor protease-activated receptor 1 (PAR-1) and hematopoietic cell-derived tissue factor (TF) contribute to hepatic steatosis. In association with hepatic steatosis, plasma thrombin-antithrombin levels and hepatic fibrin deposition increased significantly in C57Bl/6J mice fed a Western diet for 3 months. PAR-1 deficiency reduced hepatic inflammation, particularly monocyte chemoattractant protein-1 expression and macrophage accumulation. In addition, PAR-1 deficiency was associated with reduced steatosis in mice fed a Western diet, including reduced liver triglyceride accumulation and CD36 expression. Similar to PAR-1 deficiency, hematopoietic cell TF deficiency was associated with reduced inflammation and reduced steatosis in livers of low-density lipoprotein receptor-deficient mice fed a Western diet. Moreover, hematopoietic cell TF deficiency reduced hepatic fibrin deposition. These studies indicate that PAR-1 and hematopoietic cell TF are required for liver inflammation and steatosis in mice fed a Western diet.

Aryl hydrocarbon receptor-mediated induction of Stearoyl-CoA desaturase 1 alters hepatic fatty acid composition in TCDD-elicited steatosis

2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD) induces hepatic dyslipidemia mediated by the aryl hydrocarbon receptor (AhR). Stearoyl-CoA desaturase 1 (Scd1) performs the rate-limiting step in monounsaturated fatty acid (MUFA) synthesis, desaturating 16:0 and 18:0 into 16:1n7 and 18:1n9, respectively. To further examine the role of Scd1 in TCDD-induced hepatotoxicity, comparative studies were performed in Scd1(+/+) and Scd1(-/-) mice treated with 30 μg/kg TCDD. TCDD induced Scd1 activity, protein, and messenger RNA (mRNA) levels approximately twofold. In Scd1(+/+) mice, hepatic effects were marked by increased vacuolization and inflammation and a 3.5-fold increase in serum alanine aminotransferase (ALT) levels. Hepatic triglycerides (TRGs) were induced 3.9-fold and lipid profiling by gas chromatography-mass spectroscopy measured a 1.9-fold increase in fatty acid (FA) levels, consistent with the induction of lipid transport genes. Induction of Scd1 altered FA composition by decreasing saturated fatty acid (SFA) molar ratios 8% and increasing MUFA molar ratios 9%. Furthermore, ChIP-chip analysis revealed AhR enrichment (up to 5.7-fold), and computational analysis identified 16 putative functional dioxin response elements (DREs) within Scd1 genomic loci. Band shift assays confirmed AhR binding with select DREs. In Scd1(-/-) mice, TCDD induced minimal hepatic vacuolization and inflammation, while serum ALT levels remained unchanged. Although Scd1 deficiency attenuated TCDD-induced TRG accumulation, overall FA levels remained unchanged compared with Scd1(+/+) mice. In Scd1(-/-) mice, TCDD induced SFA ratios 8%, reduced MUFA ratios 13%, and induced polyunsaturated fatty acid ratios 5% relative to treated Scd1(+/+) mice. Collectively, these results suggest that AhR regulation of Scd1 not only alters lipid composition but also contributes to the hepatotoxicity of TCDD.

Dietary conjugated linoleic Acid and hepatic steatosis: species-specific effects on liver and adipose lipid metabolism and gene expression

Objective. To summarize the recent studies on effect of conjugated linoleic acid (CLA) on hepatic steatosis and hepatic and adipose lipid metabolism highlighting the potential regulatory mechanisms. Methods. Sixty-four published experiments were summarized in which trans-10, cis-12 CLA was fed either alone or in combination with other CLA isomers to mice, rats, hamsters, and humans were compared. Summary and Conclusions. Dietary trans-10, cis-12 CLA induces a severe hepatic steatosis in mice with a more muted response in other species. Regardless of species, when hepatic steatosis was present, a concurrent decrease in body adiposity was observed, suggesting that hepatic lipid accumulation is a result of uptake of mobilized fatty acids (FA) from adipose tissue and the liver's inability to sufficiently increase FA oxidation and export of synthesized triglycerides. The potential role of liver FA composition, insulin secretion and sensitivity, adipokine, and inflammatory responses are discussed as potential mechanisms behind CLA-induced hepatic steatosis.

New insights from rodent models of fatty liver disease

Rodent models of fatty liver disease are essential research tools that provide a window into disease pathogenesis and a testing ground for prevention and treatment. Models come in many varieties involving dietary and genetic manipulations, and sometimes both. High-energy diets that induce obesity do not uniformly cause fatty liver disease; this has prompted close scrutiny of specific macronutrients and nutrient combinations to determine which have the greatest potential for hepatotoxicity. At the same time, diets that do not cause obesity or the metabolic syndrome but do cause severe steatohepatitis have been exploited to study factors important to progressive liver injury, including cell death, oxidative stress, and immune activation. Rodents with a genetic predisposition to overeating offer yet another model in which to explore the evolution of fatty liver disease. In some animals that overeat, steatohepatitis can develop even without resorting to a high-energy diet. Importantly, these models and others have been used to document that aerobic exercise can prevent or reduce fatty liver disease. This review focuses primarily on lessons learned about steatohepatitis from manipulations of diet and eating behavior. Numerous additional insights about hepatic lipid metabolism, which have been gained from genetically engineered mice, are also mentioned.

Hepatic fatty acid partitioning

PURPOSE OF REVIEW

A net retention of triacylglycerol within the liver is a prerequisite for the development of nonalcoholic fatty liver disease. The accumulation of liver fat reflects an imbalance between fatty acid input and disposal. Here we summarize recent research into understanding the fate of fatty acids within the hepatocyte.

RECENT FINDINGS

Several recent studies have elucidated the contribution of different sources of fatty acids to liver fat and to plasma triacylglycerol. Some recent studies have suggested that, contrary to expectations, hepatic fatty acid oxidation is upregulated in insulin-resistant individuals. A recent observation shows the potential importance of fatty acid transformation, especially desaturation, to determination of metabolic fate. These studies highlight our lack of understanding of the regulation of metabolic partitioning of fatty acids within the human liver.

SUMMARY

The regulation of hepatic fatty acid partitioning involves many factors; not least insulin. Insulin undoubtedly regulates the supply of fatty acids to the liver from adipose tissue; however, whether insulin has a direct intrahepatic effect on hepatic fatty acid partitioning, in humans, remains unclear. The transformation of fatty acids, by desaturases, may have an important role in aiding the disposal of saturated fatty acids via oxidative pathways. Factors that upregulate hepatic fatty acid oxidation need to be elucidated.

Metabolic changes in skin caused by Scd1 deficiency: a focus on retinol metabolism

We previously reported that mice with skin-specific deletion of stearoyl-CoA desaturase-1 (Scd1) recapitulated the skin phenotype and hypermetabolism observed in mice with a whole-body deletion of Scd1. In this study, we first performed a diet-induced obesity experiment at thermoneutral temperature (33°C) and found that skin-specific Scd1 knockout (SKO) mice still remain resistant to obesity. To elucidate the metabolic changes in the skin that contribute to the obesity resistance and skin phenotype, we performed microarray analysis of skin gene expression in male SKO and control mice fed a standard rodent diet. We identified an extraordinary number of differentially expressed genes that support the previously documented histological observations of sebaceous gland hypoplasia, inflammation and epidermal hyperplasia in SKO mice. Additionally, transcript levels were reduced in skin of SKO mice for genes involved in fatty acid synthesis, elongation and desaturation, which may be attributed to decreased abundance of key transcription factors including SREBP1c, ChREBP and LXRα. Conversely, genes involved in cholesterol synthesis were increased, suggesting an imbalance between skin fatty acid and cholesterol synthesis. Unexpectedly, we observed a robust elevation in skin retinol, retinoic acid and retinoic acid-induced genes in SKO mice. Furthermore, SEB-1 sebocytes treated with retinol and SCD inhibitor also display an elevation in retinoic acid-induced genes. These results highlight the importance of monounsaturated fatty acid synthesis for maintaining retinol homeostasis and point to disturbed retinol metabolism as a novel contributor to the Scd1 deficiency-induced skin phenotype.

Increased elongase 6 and Δ9-desaturase activity are associated with n-7 and n-9 fatty acid changes in cystic fibrosis

Patients with cystic fibrosis, caused by mutations in CFTR, exhibit specific and consistent alterations in the levels of particular unsaturated fatty acids compared with healthy controls. Evidence suggests that these changes may play a role in the pathogenesis of this disease. Among these abnormalities are increases in the levels of n-7 and n-9 fatty acids, particularly palmitoleate (16:1n-7), oleate (18:1n-9), and eicosatrienoate or mead acid (20:3n-9). The underlying mechanisms of these particular changes are unknown, but similar changes in the n-3 and n-6 fatty acid families have been correlated with increased expression of fatty acid metabolic enzymes. This study demonstrated that cystic fibrosis cells in culture exhibit increased metabolism along the metabolic pathways leading to 16:1n-7, 18:1n-9, and 20:3n-9 compared with wild-type cells. Furthermore, these changes are accompanied by increased expression of the enzymes that produce these fatty acids, namely Δ5, Δ6, and Δ9 desaturases and elongases 5 and 6. Taken together, these findings suggest that fatty acid abnormalities of the n-7 and n-9 series in cystic fibrosis are as a result, at least in part, of increased expression and activity of these metabolic enzymes in CFTR-mutated cells.

Dietary cystine level affects metabolic rate and glycaemic control in adult mice

Plasma total cysteine (tCys) is strongly and independently associated with obesity in large human cohorts, but whether the association is causal is unknown. Dietary cyst(e)ine increases weight gain in some rodent models. We investigated the body composition, metabolic rate and metabolic phenotype of mature C3H/HeH mice assigned to low-cystine (LC) or high-cystine (HC) diets for 12 weeks.

Compared to LC mice, HC mice gained more weight (P=.004 for 12-week weight gain %), with increased fat mass and lean mass, and lowered O₂ consumption and CO₂ production by calorimetry. The HC mice had 30% increase in intestinal fat/body weight % (P=.003) and ∼twofold elevated hepatic triglycerides (P=.046), with increased expression of hepatic lipogenic factors, peroxisome proliferator-activated receptor-γ and sterol regulatory element binding protein-1. Gene expression of both basal and catecholamine-stimulated lipolytic enzymes, adipose triglyceride lipase and hormone-sensitive lipase was inhibited in HC mice adipose tissue. The HC mice also had elevated fasting glucose (7.0 vs. 4.5 mmol/L, P<.001) and a greater area under the curve (P<.001) in intraperitoneal glucose tolerance tests, with enhanced expression of the negative regulator of insulin signaling, protein tyrosine phosphatase-1B, in liver and adipose tissue.

Overall, high cystine intake promotes adiposity and an adverse metabolic phenotype in mice, indicating that the positive association of plasma tCys with obesity in humans may be causal.

Metformin inhibits nuclear receptor TR4-mediated hepatic stearoyl-CoA desaturase 1 gene expression with altered insulin sensitivity

OBJECTIVE

TR4 is a nuclear receptor without clear pathophysiological roles. We investigated the roles of hepatic TR4 in the regulation of lipogenesis and insulin sensitivity in vivo and in vitro.

RESEARCH DESIGN AND METHODS

TR4 activity and phosphorylation assays were carried out using hepatocytes and various TR4 wild-type and mutant constructs. Liver tissues from TR4 knockout, C57BL/6, and db/db mice were examined to investigate TR4 target gene stearoyl-CoA desaturase (SCD) 1 regulation.

RESULTS

TR4 transactivation is inhibited via phosphorylation by metformin-induced AMP-activated protein kinase (AMPK) at the amino acid serine 351, which results in the suppression of SCD1 gene expression. Additional mechanistic dissection finds TR4-transactivated SCD1 promoter activity via direct binding to the TR4-responsive element located at -243 to -255 on the promoter region. The pathophysiological consequences of the metformin→AMPK→TR4→SCD1 pathway are examined via TR4 knockout mice and primary hepatocytes with either knockdown or overexpression of TR4. The results show that the suppression of SCD1 via loss of TR4 resulted in reduced fat mass and increased insulin sensitivity with increased β-oxidation and decreased lipogenic gene expression.

CONCLUSIONS

The pathway from metformin→AMPK→TR4→SCD1→insulin sensitivity suggests that TR4 may function as an important modulator to control lipid metabolism, which sheds light on the use of small molecules to modulate TR4 activity as a new alternative approach to battle the metabolic syndrome.

Isocaloric intake of a high-fat diet modifies adiposity and lipid handling in a sex dependent manner in rats

Background

High-fat (HF) diet feeding usually leads to hyperphagia and body weight gain, but macronutrient proportions in the diet can modulate energy intake and fat deposition. The mechanisms of fat accumulation and mobilization may differ significantly between depots, and gender can also influence these differences.

Aim

To investigate, in rats of both sexes, the effect of an isocaloric intake of a diet with an unbalanced proportion of macronutrients on fatty acid composition of visceral and subcutaneous adipose tissues and how this is influenced by both dietary fatty acids and levels of proteins involved in tissue lipid handling.

Methods

Eight-week-old Wistar rats of both sexes were fed a control diet (3% w/w fat) or high-fat diet (30% w/w fat) for 14 weeks. Fatty acid composition was analyzed by gas-chromatography and levels of LPL, HSL, α2-AR, β3-AR, PKA and CPT1 were determined by Western blot.

Results

The HF diet did not induce hyperphagia or body weight gain, but promoted an increase of adiposity index only in male rats. HF diet produced an increase of the proportion of MUFA and a decrease in that of PUFA in both adipose depots and in both sexes. The levels of proteins involved in the adrenergic control of the lipolytic pathway increased in the gonadal fat of HF females, whereas LPL levels increased in the inguinal fat of HF males and decreased in that of females.

Conclusion

Sexual dimorphism in adiposity index reflects a differential sex response to dietary fatty acid content and could be related to the levels of the proteins involved in tissue lipid management.

Molecular cloning and expression analysis of a delta 6-fatty acid desaturase gene from Rhizopus stolonifer strain YF6 which can accumulate high levels of gamma-linolenic acid

The delta 6-desaturase gene was cloned from Rhizopus stolonifer, which could accumulate up to 49% of gamma-linolenic acid (GLA, C18:3 Δ(6,9,12)) to the total fatty acids. The cloned DNA contains a 1,380 bp open reading frame encoding a protein of 460 amino acids, which showed high similarity to those of fungal delta 6-desaturases with three conserved histidine-rich motifs and HPGG motif. Notably, this deduced sequence had a shorter C-terminus. Results demonstrated that the cDNA sequence exhibited delta 6-desaturase activity by accumulation of about 22.4 % of GLA to the total fatty acids in the recombinant Pichia pastoris strain GS115.

Increased lipogenesis, induced by AKT-mTORC1-RPS6 signaling, promotes development of human hepatocellular carcinoma

BACKGROUND & AIMS

De novo lipogenesis is believed to be involved in oncogenesis. We investigated the role of aberrant lipid biosynthesis in the pathogenesis of human hepatocellular carcinoma (HCC).

METHODS

We evaluated expression of enzymes that regulate lipogenesis in human normal liver tissues and HCC and surrounding, nontumor, liver tissues from patients using real-time reverse transcription polymerase chain reaction, immunoblotting, immunohistochemistry, and biochemical assays. Effects of lipogenic enzymes on human HCC cell lines were evaluated using inhibitors and overexpression experiments. The lipogenic role of the proto-oncogene AKT was assessed in vitro and in vivo.

RESULTS

In human liver samples, de novo lipogenesis was progressively induced from nontumorous liver tissue toward the HCC. Extent of aberrant lipogenesis correlated with clinical aggressiveness, activation of the AKT-mammalian target of rapamycin signaling pathway, and suppression of adenosine monophosphate-activated protein kinases. In HCC cell lines, the AKT-mammalian target of rapamycin complex 1-ribosomal protein S6 pathway promoted lipogenesis via transcriptional and post-transcriptional mechanisms that included inhibition of fatty acid synthase ubiquitination by the USP2a de-ubiquitinase and disruption of the SREBP1 and SREBP2 degradation complexes. Suppression of the genes adenosine triphosphate citrate lyase, acetyl-CoA carboxylase, fatty acid synthase, stearoyl-CoA desaturase 1, or sterol regulatory element-binding protein 1, which are involved in lipogenesis, reduced proliferation, and survival of HCC cell lines and AKT-dependent cell proliferation. Overexpression of an activated form of AKT in livers of mice induced lipogenesis and tumor development.

CONCLUSIONS

De novo lipogenesis has pathogenic and prognostic significance for HCC. Inhibitors of lipogenic signaling, including those that inhibit the AKT pathway, might be useful as therapeutics for patients with liver cancer.

Stimulation of lipogenesis as well as fatty acid oxidation protects against palmitate-induced INS-1 beta-cell death

Saturated fatty acids are generally cytotoxic to β-cells. Accumulation of lipid intermediates and subsequent activation of lipid-mediated signals has been suggested to play a role in fatty acid-induced toxicity. To determine the effects of lipid metabolism in fatty acid-induced toxicity, lipid metabolism was modulated by up- and down-regulation of a lipogenic or fatty acid oxidation pathway, and the effects of various modulators on palmitate (PA)-induced INS-1 β-cell death were then evaluated. Treatment with the liver X receptor agonist T0901317 reduced PA-induced INS-1 cell death, regardless of its enhanced lipogenic activity. Furthermore, transient expression of a lipogenic transcription factor sterol regulatory element binding protein-1c (SREBP-1c) was also protective against PA-induced cytotoxicity. In contrast, knockdown of SREBP-1c or glycerol-3-phosphate acyltransferase 1 significantly augmented PA-induced cell death and reduced T0901317-induced protective effects. Conversely, T0901317 increased carnitine PA transferease-1 (CPT-1) expression and augmented PA oxidation. CPT-1 inhibitor etomoxir or CPT-1 knockdown augmented PA-induced cell death and reduced T0901317-induced protective effects, whereas the peroxisome proliferator-activated receptor (PPAR)-α agonist bezafibrate reduced PA-induced toxicity. In particular, T0901317 reduced the levels of PA-induced endoplasmic reticulum (ER) stress markers, including phospho-eukaryotic initiation factor-2α, phospho-C-Jun N terminal kinase, and CCAAT/enhancer-binding protein homologous protein. In contrast, knockdown of SREBP-1c or glycerol-3-phosphate acyltransferase 1 augmented PA-induced ER stress responses. Results of these experiments suggested that stimulation of lipid metabolism, including lipogenesis and fatty acid oxidation, protected β-cells from PA-induced lipotoxicity and that protection through enhanced lipogenesis was likely due to reduced ER stress.

Global gene expression profiles of subcutaneous adipose and muscle from glucose-tolerant, insulin-sensitive, and insulin-resistant individuals matched for BMI

OBJECTIVE

To determine altered gene expression profiles in subcutaneous adipose and skeletal muscle from nondiabetic, insulin-resistant individuals compared with insulin-sensitive individuals matched for BMI.

RESEARCH DESIGN AND METHODS

A total of 62 nondiabetic individuals were chosen for extremes of insulin sensitivity (31 insulin-resistant and 31 insulin-sensitive subjects; 40 were European American and 22 were African American) and matched for age and obesity measures. Global gene expression profiles were determined and compared between ethnic groups and between insulin-resistant and insulin-sensitive participants individually and using gene-set enrichment analysis.

RESULTS

African American and European American subjects differed in 58 muscle and 140 adipose genes, including many inflammatory and metabolically important genes. Peroxisome proliferator-activated receptor γ cofactor 1A (PPARGC1A) was 1.75-fold reduced with insulin resistance in muscle, and fatty acid and lipid metabolism and oxidoreductase activity also were downregulated. Unexpected categories included ubiquitination, citrullination, and protein degradation. In adipose, highly represented categories included lipid and fatty acid metabolism, insulin action, and cell-cycle regulation. Inflammatory genes were increased in European American subjects and were among the top Kyoto Encyclopedia of Genes and Genomes pathways on gene-set enrichment analysis. FADS1, VEGFA, PTPN3, KLF15, PER3, STEAP4, and AGTR1 were among genes expressed differentially in both adipose and muscle.

CONCLUSIONS

Adipose tissue gene expression showed more differences between insulin-resistant versus insulin-sensitive groups than the expression of genes in muscle. We confirm the role of PPARGC1A in muscle and show some support for inflammation in adipose from European American subjects but find prominent roles for lipid metabolism in insulin sensitivity independent of obesity in both tissues.

Fatty acid bile acid conjugate inhibits hepatic stearoyl coenzyme A desaturase and is non-atherogenic

BACKGROUND AND AIMS

Suppression of stearoyl-coenzyme A desaturase (SCD) activity leads to reduction of obesity, fatty liver as well as of insulin resistance. It was, however, recently reported to enhance atherogenesis. The aim of the present study was to investigate whether inhibition of SCD by Aramchol, a fatty acid bile conjugate with known hypocholesterolemic effects, will affect atherogenesis and how.

METHODS

Aramchol was tested in vitro in cultured cells and in vivo in rodents.

RESULTS

Aramchol, at very low concentrations, reduced SCD activity in liver microsomes of mice. Aramchol enhanced cholesterol efflux from macrophages more than twofold. In vivo it increased fecal sterol output and decreased markedly plasma cholesterol levels in mice. In ApoE(-/-), LDRL(-/-) and C57Bl6 mice, the effects of Aramchol on atherogenesis were non-atherogenic.

CONCLUSIONS

Aramchol reduces SCD activity and is non-atherogenic. It may offer a means to obtain the desirable hepatic metabolic effects of SCD inhibition without the deleterious atherogenic effect.

The fatty acid desaturation index of blood lipids, as a biomarker of hepatic stearoyl-CoA desaturase expression, is a predictive factor of breast cancer risk

PURPOSE OF REVIEW

This review summarizes epidemiological data linking the fatty acid desaturation index measured in blood lipids, as a biomarker of hepatic stearoyl-CoA desaturase activity, the key enzyme involved in the synthesis of monounsaturated fatty acids from saturated fatty acids, to breast cancer risk. The biological plausibility of this association is discussed.

RECENT FINDINGS

Epidemiological cohort studies reported an association between a high saturated to monounsaturated fatty acid ratio measured in blood lipids, indicating low stearoyl-CoA desaturase-1 activity, and decreased breast cancer risk. The suppression of stearoyl-CoA desaturase expression reduces cancer cell proliferation and in-vitro invasiveness, and dramatically impairs tumor formation and growth. These effects could not be overcome by supplying exogenous monounsaturated fatty acids.

SUMMARY

Epidemiological findings, in accordance with experimental data, suggested that decreased hepatic stearoyl-CoA desaturase expression/activity may be related to decreased risk of breast cancer.

Depression and altered serum lipids in cynomolgus monkeys consuming a Western diet

Research over the past 15 years has suggested a high comorbidity of depression and coronary heart disease (CHD). However the mechanisms responsible for this relationship are poorly understood. This study was designed to examine the relationships between depressive behaviors and concentrations of circulating lipids and lipid signaling molecules that may be common to both CHD and depression in a cohort of cynomolgus monkeys (Macaca fascicularis) consuming a 'Western' diet, enriched with saturated fat and cholesterol. Socially-housed adult female cynomolgus monkeys (n=36) were fed the Western diet for 27 months and depressive behavior was recorded weekly. Body weight, body mass index and circulating cholesterol profiles were measured in all animals, and fatty acids (FA) and FA-based signaling molecules were measured in the 6 least and 6 most depressed monkeys. Monkeys consuming the Western diet exhibited a broad range of percent time spent in depressive behavior. The percent time spent depressed was positively correlated with total plasma and LDL cholesterol and negatively correlated with HDL cholesterol. Despite being leaner, depressed monkeys had higher concentrations of monounsaturated fats (C16:1 and C17:1), a higher ω6/ω3 polyunsaturated fatty acid (PUFA) ratio and higher concentrations of omega-6 (ω6) PUFAs, particularly C18:2ω6 and C20:3ω6. FA ratios suggest that stearoyl CoA desaturase 1 activity was increased in depressed monkeys. Depressed female cynomolgus monkeys had elevated concentrations of serum lipids and lipid signaling molecules that are typically associated with obesity, insulin resistance and cardiovascular disease, which may account in part for the comorbidity of depression and CHD.

Stearoyl CoA desaturase 1: role in cellular inflammation and stress

Stearoyl CoA desaturase 1 (SCD1) catalyzes the rate-limiting step in the production of MUFA that are major components of tissue lipids. Alteration in SCD1 expression changes the fatty acid profile of these lipids and produces diverse effects on cellular function. High SCD1 expression is correlated with metabolic diseases such as obesity and insulin resistance, whereas low levels are protective against these metabolic disturbances. However, SCD1 is also involved in the regulation of inflammation and stress in distinct cell types, including β-cells, adipocytes, macrophages, endothelial cells, and myocytes. Furthermore, complete loss of SCD1 expression has been implicated in liver dysfunction and several inflammatory diseases such as dermatitis, atherosclerosis, and intestinal colitis. Thus, normal cellular function requires the expression of SCD1 to be tightly controlled. This review summarizes the current understanding of the role of SCD1 in modulating inflammation and stress.

Adipose tissue palmitoleic acid and obesity in humans: does it behave as a lipokine?

BACKGROUND

Animal models have shown that adipose-derived palmitoleic acid may serve as a lipokine that contributes to resistance to diet-induced obesity. Studies in humans have evaluated only plasma palmitoleic acid concentrations, which reflect stearoyl-coenzyme A desaturase 1 (SCD1) activity in the liver and are associated with increased risk of obesity. These apparent opposite effects of palmitoleic acid deserve further research in humans. Because carbohydrate intake can increase hepatic SCD1 activity, it could be used as a stratifying variable to disentangle the effects of adipose tissue SCD1 compared with the effects of liver SCD1 activity on obesity.

OBJECTIVE

We examined whether the effects of adipose tissue palmitoleic acid and SCD1 activity were associated with decreased obesity prevalence and whether this association was modified by carbohydrate intake.

DESIGN

Prevalence ratios (PRs) of obesity [body mass index (in kg/m²) > 30] were examined in a cross-sectional study in 1926 adults in Costa Rica. Two desaturation indexes (16:1/16:0 and 18:1/18:0) were used as surrogate measures of adipose tissue SCD1 activity.

RESULTS

We observed a positive association between adipose tissue palmitoleic acid concentrations and obesity (PR for lowest compared with highest quintiles of palmitoleic acid: 2.27; 95% CI: 1.52, 3.38; P for trend < 0.0001). A significant association was also observed between obesity and adipose desaturation indexes. The association between adipose tissue palmitoleic acid concentrations and obesity was attenuated in persons with low carbohydrate intake.

CONCLUSIONS

There is no direct evidence that adipose tissue palmitoleic acid behaves as a lipokine to reduce obesity occurrence in humans. However, the attenuation of the association by low carbohydrate intake warrants further research on adipose-derived palmitoleic acid and obesity risk.

Thermogenesis and related metabolic targets in anti-diabetic therapy

Exercise, together with a low-energy diet, is the first-line treatment for type 2 diabetes type 2 diabetes . Exercise improves insulin sensitivity insulin sensitivity by increasing the number or function of muscle mitochondria mitochondria and the capacity for aerobic metabolism, all of which are low in many insulin-resistant subjects. Cannabinoid 1-receptor antagonists and β-adrenoceptor agonists improve insulin sensitivity in humans and promote fat oxidation in rodents independently of reduced food intake. Current drugs for the treatment of diabetes are not, however, noted for their ability to increase fat oxidation, although the thiazolidinediones increase the capacity for fat oxidation in skeletal muscle, whilst paradoxically increasing weight gain.There are a number of targets for anti-diabetic drugs that may improve insulin sensitivity insulin sensitivity by increasing the capacity for fat oxidation. Their mechanisms of action are linked, notably through AMP-activated protein kinase, adiponectin, and the sympathetic nervous system. If ligands for these targets have obvious acute thermogenic activity, it is often because they increase sympathetic activity. This promotes fuel mobilisation, as well as fuel oxidation. When thermogenesis thermogenesis is not obvious, researchers often argue that it has occurred by using the inappropriate device of treating animals for days or weeks until there is weight (mainly fat) loss and then expressing energy expenditure energy expenditure relative to body weight. In reality, thermogenesis may have occurred, but it is too small to detect, and this device distracts us from really appreciating why insulin sensitivity has improved. This is that by increasing fatty acid oxidation fatty acid oxidation more than fatty acid supply, drugs lower the concentrations of fatty acid metabolites that cause insulin resistance. Insulin sensitivity improves long before any anti-obesity effect can be detected.

A mouse macrophage lipidome

We report the lipidomic response of the murine macrophage RAW cell line to Kdo(2)-lipid A, the active component of an inflammatory lipopolysaccharide functioning as a selective TLR4 agonist and compactin, a statin inhibitor of cholesterol biosynthesis. Analyses of lipid molecular species by dynamic quantitative mass spectrometry and concomitant transcriptomic measurements define the lipidome and demonstrate immediate responses in fatty acid metabolism represented by increases in eicosanoid synthesis and delayed responses characterized by sphingolipid and sterol biosynthesis. Lipid remodeling of glycerolipids, glycerophospholipids, and prenols also take place, indicating that activation of the innate immune system by inflammatory mediators leads to alterations in a majority of mammalian lipid categories, including unanticipated effects of a statin drug. Our studies provide a systems-level view of lipid metabolism and reveal significant connections between lipid and cell signaling and biochemical pathways that contribute to innate immune responses and to pharmacological perturbations.

Greater dietary fat oxidation in obese compared with lean men: an adaptive mechanism to prevent liver fat accumulation?

Liver fat represents a balance between input, secretion, and oxidation of fatty acids. As humans spend the majority of a 24-h period in a postprandial state, dietary fatty acids make an important contribution to liver fat metabolism. We compared hepatic fatty acid partitioning in healthy lean (n = 9) and abdominally obese (n = 10) males over 24 h. Volunteers received three mixed meals adjusted for basal metabolic rate. U-13C-labeled fatty acids were incorporated into the meals, and [2H2]palmitate was infused intravenously to distinguish between sources of fatty acids incorporated into VLDL-TG. Immunoaffinity chromatography was used to isolate VLDL-TG of hepatic origin. Liver and whole body fatty acid oxidation was assessed by isotopic enrichment of 3-hydoxybutyrate and breath CO2. We found a similar contribution of dietary fatty acids to VLDL-TG in the two groups over 24 h. The contribution of fatty acids from splanchnic sources was higher (P < 0.05) in the abdominally obese group. Ketogenesis occurred to a significantly greater extent in abdominally obese compared with lean males, largely due to lessened downregulation of postprandial ketogenesis (P < 0.001). The appearance of 13C in breath CO2 was also greater (P < 0.001) in abdominally obese compared with lean men. Hepatic elongation and desaturation of palmitic acid were higher (P < 0.05) in abdominally obese than in lean males. Oxidation of dietary fatty acids and hepatic desaturation and elongation of palmitic acid occurred to a greater extent in abdominally obese men. These alterations may represent further pathways for redirection of fatty acids into export from the liver or oxidation to prevent liver fat accumulation.

Cysteine supplementation reverses methionine restriction effects on rat adiposity: significance of stearoyl-coenzyme A desaturase

Stearoyl-CoA desaturase-1 (SCD1) is a key enzyme in fatty acid and energy metabolism, but little is known about its nutritional regulation. Dietary methionine restriction in rats decreases hepatic Scd1 mRNA and protein, increases energy expenditure, and decreases fat-pad mass/body-weight% (FM/BW%). In humans, plasma concentrations of the methionine product, cysteine, are associated with obesity. To determine which consequences of methionine-restriction are mediated by decreased cysteine availability, we monitored obesity-related variables in 4 dietary groups for 12 weeks: control-fed (CF), methionine-restricted (MR), MR supplemented with 0.5% l-cysteine (MR+Cys) and CF+Cys rats. MR lowered weight gain and FM/BW% despite higher food intake/weight than CF, and lowered serum cysteine. Hepatic Scd1 expression was decreased, with decreased serum SCD1 activity indices (calculated from serum fatty acid profile), decreased serum insulin, leptin and triglycerides, and higher adiponectin. Cysteine supplementation (MR+Cys) essentially reversed all these phenotypes and raised serum cysteine but not methionine to CF levels. Adding extra cysteine to control diet (CF+Cys) increased serum taurine but did not affect serum cysteine, lipids, proteins, or total weight gain. FM/BW% and serum leptin were modestly decreased. Our results indicate that anti-obesity effects of MR are caused by low cysteine and that dietary sulfur amino acid composition contributes to SCD1 regulation.

Dietary fat intake promotes the development of hepatic steatosis independently from excess caloric consumption in a murine model

Nonalcoholic fatty liver disease results from overconsumption and is a significant and increasing cause of liver failure. The type of diet that is conducive to the development of this disease has not been established, and evidence-based treatment options are currently lacking. We hypothesized that the onset of hepatic steatosis is linked to the consumption of a diet with a high fat content, rather than related to excess caloric intake. In addition, we also hypothesized that fully manifested hepatic steatosis could be reversed by reducing the fat percentage in the diet of obese mice. C57BL/6J male mice were fed either a purified rodent diet containing 10% fat or a diet with 60% of calories derived from fat. A pair-feeding design was used to distinguish the effects of dietary fat content and caloric intake on dietary-induced hepatic lipid accumulation and associated injury. Livers were analyzed by quantitative reverse transcriptase polymerase chain reaction for lipid metabolism-related gene expression. After 9 weeks, mice on the 60%-fat diet exhibited more weight gain, insulin resistance, and hepatic steatosis compared with mice on a 10%-fat diet with equal caloric intake. Furthermore, mice with established metabolic syndrome at 9 weeks showed reversal of hepatic steatosis, insulin resistance, and obesity when switched to a 10%-fat diet for an additional 9 weeks, independent of caloric intake. Quantitative reverse transcriptase polymerase chain reaction revealed that transcripts related to both de novo lipogenesis and increased uptake of free fatty acids were significantly up-regulated in mice pair-fed a 60%-fat diet compared with 10%-fat-fed animals. Dietary fat content, independent from caloric intake, is a crucial factor in the development of hepatic steatosis, obesity, and insulin resistance in the C57BL/6J diet-induced obesity model caused by increased uptake of free fatty acids and de novo lipogenesis. In addition, once established, all these features of the metabolic syndrome can be successfully reversed after switching obese mice to a diet low in fat. Low-fat diets deserve attention in the investigation of a potential treatment of patients with nonalcoholic fatty liver disease.

Adipose-specific deletion of stearoyl-CoA desaturase 1 up-regulates the glucose transporter GLUT1 in adipose tissue

Stearoyl-CoA desaturase 1 (SCD1) deficiency protects mice from diet-induced obesity and insulin resistance. To understand the tissue-specific role of SCD1 in energy homeostasis, we have generated mice with an adipose-specific knockout of Scd1 (AKO), and report here that SCD1 deficiency increases GLUT1 expression in adipose tissue of AKO mice, but not global SCD1 knockout (GKO) mice. In 3T3-L1 adipocytes treated with an SCD inhibitor, basal glucose uptake and the cellular expression of GLUT1 were significantly increased while GLUT4 expression remained unchanged. Consistently, adipose-specific SCD1 knockout (AKO) mice had significantly elevated GLUT1 expression, but not GLUT4, in white adipose tissue compared to Lox counterparts. Concurrently, adiponectin expression was significantly diminished, whereas TNF-alpha expression was elevated. In contrast, in adipose tissue of GKO mice, GLUT4 and adiponectin expression were significantly elevated with lowered TNF-alpha expression and little change in GLUT1 expression, suggesting a differential responsiveness of adipose tissue to global- or adipose-specific SCD1 deletion. Taken together, these results indicate that adipose-specific deletion of SCD1 induces GLUT1 up-regulation in adipose tissue, associated with decreased adiponectin and increased TNF-alpha production, and suggest that GLUT1 may play a critical role in controlling glucose homeostasis of adipose tissue in adipose-specific SCD1-deficient conditions.

Conserved role of SIRT1 orthologs in fasting-dependent inhibition of the lipid/cholesterol regulator SREBP

The sterol regulatory element-binding protein (SREBP) transcription factor family is a critical regulator of lipid and sterol homeostasis in eukaryotes. In mammals, SREBPs are highly active in the fed state to promote the expression of lipogenic and cholesterogenic genes and facilitate fat storage. During fasting, SREBP-dependent lipid/cholesterol synthesis is rapidly diminished in the mouse liver; however, the mechanism has remained incompletely understood. Moreover, the evolutionary conservation of fasting regulation of SREBP-dependent programs of gene expression and control of lipid homeostasis has been unclear. We demonstrate here a conserved role for orthologs of the NAD(+)-dependent deacetylase SIRT1 in metazoans in down-regulation of SREBP orthologs during fasting, resulting in inhibition of lipid synthesis and fat storage. Our data reveal that SIRT1 can directly deacetylate SREBP, and modulation of SIRT1 activity results in changes in SREBP ubiquitination, protein stability, and target gene expression. In addition, chemical activators of SIRT1 inhibit SREBP target gene expression in vitro and in vivo, correlating with decreased hepatic lipid and cholesterol levels and attenuated liver steatosis in diet-induced and genetically obese mice. We conclude that SIRT1 orthologs play a critical role in controlling SREBP-dependent gene regulation governing lipid/cholesterol homeostasis in metazoans in response to fasting cues. These findings may have important biomedical implications for the treatment of metabolic disorders associated with aberrant lipid/cholesterol homeostasis, including metabolic syndrome and atherosclerosis.

Methionine restriction effects on mitochondrial biogenesis and aerobic capacity in white adipose tissue, liver, and skeletal muscle of F344 rats

Methionine restriction increases life span in rats and mice and reduces age-related accretion of adipose tissue in Fischer 344 rats. Recent reports have shown that adipose tissue mitochondrial content and function are associated with adiposity; therefore, the expression of genes involved in mitochondrial biogenesis and oxidative capacity was examined in white adipose tissue, liver, and skeletal muscle from Fischer 344 rats fed control (0.86% methionine) or methionine-restricted (0.17% methionine) diets for 3 months. Methionine restriction induced transcriptional changes of peroxisome proliferator-activated receptors, peroxisome proliferator-activated receptor coactivators 1alpha and 1beta, and some of their known target genes in all of these tissues. In addition, tissue-specific responses were elicited at the protein level. In inguinal adipose tissue, methionine restriction increased protein levels of peroxisome proliferator-activated receptor and peroxisome proliferator-activated receptor coactivator target genes. It also induced mitochondrial DNA copy number, suggesting mitochondrial biogenesis and corresponding with the up-regulation of citrate synthase activity. In contrast, methionine restriction induced changes in mitochondrial glycerol-3-phosphate dehydrogenase activity and stearoyl-coenzyme A desaturase 1 protein levels only in liver and uncoupling protein 3 and cytochrome c oxidase subunit IV protein levels only in skeletal muscle. No increase in mitochondrial DNA copy number was observed in liver and skeletal muscle despite an increase in mitochondrial citrate synthase activity. The results indicate that adiposity resistance in methionine-restricted rats is associated with mitochondrial biogenesis in inguinal adipose tissue and increased mitochondrial aerobic capacity in liver and skeletal muscle.

Glucolipotoxicity alters lipid partitioning and causes mitochondrial dysfunction, cholesterol, and ceramide deposition and reactive oxygen species production in INS832/13 ss-cells

Elevated glucose and saturated fatty acids synergize in inducing apoptosis in INS832/13 cells and in human islet cells. In order to gain insight into the molecular mechanism(s) of glucolipotoxicity (Gltox), gene profiling and metabolic analyses were performed in INS832/13 cells cultured at 5 or 20 mm glucose in the absence or presence of palmitate. Expression changes were observed for transcripts involved in mitochondrial, lipid, and glucose metabolism. At 24 h after Gltox, increased expression of lipid partitioning genes suggested a promotion of fatty acid esterification and reduced lipid oxidation/detoxification, whereas changes in the expression of energy metabolism genes suggested mitochondrial dysfunction. These changes were associated with decreased glucose-induced insulin secretion, total insulin content, ATP levels, AMP-kinase activity, mitochondrial membrane potential and fat oxidation, unchanged de novo fatty acid synthesis, and increased reactive oxygen species, cholesterol, ceramide, and triglyceride levels. However, the synergy between elevated glucose and palmitate to cause ss-cell toxicity in term of apoptosis and reduced glucose-induced insulin secretion only correlated with triglyceride and ceramide depositions. Overexpression of endoplasmic reticulum glycerol-3-phosphate acyl transferase to enhance lipid esterification amplified Gltox at intermediate glucose (11 mm), whereas reducing acetyl-coenzyme A carboxylase 1 expression by small interfering RNA to shift lipid partitioning to fat oxidation reduced Gltox. The results suggest that Gltox entails alterations in lipid partitioning, sterol and ceramide accumulation, mitochondrial dysfunction, and reactive oxygen species production, all contributing to altering ss-cell function. The data also suggest that the early promotion of lipid esterification processes is instrumental in the Gltox process.

Genetic variation in lipid desaturases and its impact on the development of human disease

Perturbations in lipid metabolism characterize many of the chronic diseases currently plaguing our society, such as obesity, diabetes, and cardiovascular disease. Thus interventions that target plasma lipid levels remain a primary goal to manage these diseases. The determinants of plasma lipid levels are multi-factorial, consisting of both genetic and lifestyle components. Recent evidence indicates that fatty acid desaturases have an important role in defining plasma and tissue lipid profiles. This review will highlight the current state-of-knowledge regarding three desaturases (Scd-1, Fads1 and Fads2) and their potential roles in disease onset and development. Although research in rodent models has provided invaluable insight into the regulation and functions of these desaturases, the extent to which murine research can be translated to humans remains unclear. Evidence emerging from human-based research demonstrates that genetic variation in human desaturase genes affects enzyme activity and, consequently, disease risk factors. Moreover, this genetic variation may have a trans-generational effect via breastfeeding. Therefore inter-individual variation in desaturase function is attributed to both genetic and lifestyle components. As such, population-based research regarding the role of desaturases on disease risk is challenged by this complex gene-lifestyle paradigm. Unravelling the contribution of each component is paramount for understanding the inter-individual variation that exists in plasma lipid profiles, and will provide crucial information to develop personalized strategies to improve health management.

Muscle transcriptomic profiles in pigs with divergent phenotypes for fatness traits

BACKGROUND

Selection for increasing intramuscular fat content would definitively improve the palatability and juiciness of pig meat as well as the sensorial and organoleptic properties of cured products. However, evidences obtained in human and model organisms suggest that high levels of intramuscular fat might alter muscle lipid and carbohydrate metabolism. We have analysed this issue by determining the transcriptomic profiles of Duroc pigs with divergent phenotypes for 13 fatness traits. The strong aptitude of Duroc pigs to have high levels of intramuscular fat makes them a valuable model to analyse the mechanisms that regulate muscle lipid metabolism, an issue with evident implications in the elucidation of the genetic basis of human metabolic diseases such as obesity and insulin resistance.

RESULTS

Muscle gene expression profiles of 68 Duroc pigs belonging to two groups (HIGH and LOW) with extreme phenotypes for lipid deposition and composition traits have been analysed. Microarray and quantitative PCR analysis showed that genes related to fatty acid uptake, lipogenesis and triacylglycerol synthesis were upregulated in the muscle tissue of HIGH pigs, which are fatter and have higher amounts of intramuscular fat than their LOW counterparts. Paradoxically, lipolytic genes also showed increased mRNA levels in the HIGH group suggesting the existence of a cycle where triacylglycerols are continuously synthesized and degraded. Several genes related to the insulin-signalling pathway, that is usually impaired in obese humans, were also upregulated. Finally, genes related to antigen-processing and presentation were downregulated in the HIGH group.

CONCLUSION

Our data suggest that selection for increasing intramuscular fat content in pigs would lead to a shift but not a disruption of the metabolic homeostasis of muscle cells. Future studies on the post-translational changes affecting protein activity or expression as well as information about protein location within the cell would be needed to to elucidate the effects of lipid deposition on muscle metabolism in pigs.

Characterizing human adipose tissue lipids by long echo time 1H-MRS in vivo at 1.5 Tesla: validation by gas chromatography

The aim of this study was to investigate the use of (1)H-MRS with various echo times to characterize subcutaneous human adipose tissue (SAT) triglyceride composition and to validate the findings with fatty acid (FA) analysis of SAT biopsies by gas chromatography (GC). (1)H-MRS spectra were acquired with a 1.5 Tesla clinical imager from the SAT of 17 healthy volunteers, with 10 undergoing SAT biopsy. Spectra were localized with PRESS and a series of echo times; 30, 50, 80, 135, 200, 300 and 540 ms were acquired with TR = 3000 ms. Prior knowledge from phantom measurements was used to construct AMARES fitting models for the lipid spectra. SAT FA composition were compared with serum lipid levels and subject characteristics in 17 subjects.Long TE (135, 200 ms) spectra corresponded better with the GC data than short TE (30, 50 ms) spectra. TE = 135 ms was found optimal for determining diallylic content (R = 0.952, p < 0.001) and TE = 200 ms was optimal for determining olefinic content (R = 0.800, p < 0.01). The improved performance of long TE spectra is a result of an improved baseline and better peak separation, due to J-modulation and suppression of water. The peak position of the diallylic resonance correlated with the average double bond content of polyunsatured fatty acids with R = 0.899 (p < 0.005). The apparent T(2) of the methylene resonance displayed relatively small inter-individual variation, 88.1 +/- 1.1 ms (mean +/- SD). The outer methyl triplet line of omega-3 PUFA at 1.08 ppm could be readily detected and quantitated from spectra obtained at TE = 540. The omega-3 resonance correlated with the omega-3 content determined by GC with R = 0.737 (p < 0.05, n = 8). Age correlated significantly with SAT diallylic content (R = 0.569, p = 0.017, n = 17), but serum lipid levels showed no apparent relation to SAT FA composition. We conclude that long TE (1)H-MRS provides a robust non-invasive method for characterizing adipose tissue triglycerides in vivo.

Decrease in membrane phospholipid unsaturation induces unfolded protein response

Various kinds of fatty acids are distributed in membrane phospholipids in mammalian cells and tissues. The degree of fatty acid unsaturation in membrane phospholipids affects many membrane-associated functions and can be influenced by diet and by altered activities of lipid-metabolizing enzymes such as fatty acid desaturases. However, little is known about how mammalian cells respond to changes in phospholipid fatty acid composition. In this study we showed that stearoyl-CoA desaturase 1 (SCD1) knockdown increased the amount of saturated fatty acids and decreased that of monounsaturated fatty acids in phospholipids without affecting the amount or the composition of free fatty acid and induced unfolded protein response (UPR), evidenced by increased expression of C/EBP homologous protein (CHOP) and glucose-regulated protein 78 (GRP78) mRNAs and splicing of Xbox-binding protein 1 (XBP1) mRNA. SCD1 knockdown-induced UPR was rescued by various unsaturated fatty acids and was enhanced by saturated fatty acid. Lysophosphatidylcholine acyltransferase 3 (LPCAT3), which incorporates preferentially polyunsaturated fatty acids into phosphatidylcholine, was up-regulated in SCD1 knockdown cells. Knockdown of LPCAT3 synergistically enhanced UPR with SCD1 knockdown. Finally we showed that palmitic acid-induced UPR was significantly enhanced by LPCAT3 knockdown as well as SCD1 knockdown. These results suggest that a decrease in membrane phospholipid unsaturation induces UPR.

Genetics and beyond--the transcriptome of human monocytes and disease susceptibility

Background

Variability of gene expression in human may link gene sequence variability and phenotypes; however, non-genetic variations, alone or in combination with genetics, may also influence expression traits and have a critical role in physiological and disease processes.

Methodology/Principal Findings

To get better insight into the overall variability of gene expression, we assessed the transcriptome of circulating monocytes, a key cell involved in immunity-related diseases and atherosclerosis, in 1,490 unrelated individuals and investigated its association with >675,000 SNPs and 10 common cardiovascular risk factors. Out of 12,808 expressed genes, 2,745 expression quantitative trait loci were detected (P<5.78×10⁻¹²), most of them (90%) being cis-modulated. Extensive analyses showed that associations identified by genome-wide association studies of lipids, body mass index or blood pressure were rarely compatible with a mediation by monocyte expression level at the locus. At a study-wide level (P<3.9×10⁻⁷), 1,662 expression traits (13.0%) were significantly associated with at least one risk factor. Genome-wide interaction analyses suggested that genetic variability and risk factors mostly acted additively on gene expression. Because of the structure of correlation among expression traits, the variability of risk factors could be characterized by a limited set of independent gene expressions which may have biological and clinical relevance. For example expression traits associated with cigarette smoking were more strongly associated with carotid atherosclerosis than smoking itself.

Conclusions/Significance

This study demonstrates that the monocyte transcriptome is a potent integrator of genetic and non-genetic influences of relevance for disease pathophysiology and risk assessment.

Plasma and erythrocyte fatty acid patterns in patients with recurrent depression: a matched case-control study

Background

The polyunsaturated fatty acid (PUFA) composition of (nerve) cell membranes may be involved in the pathophysiology of depression. Studies so far, focussed mainly on omega-3 and omega-6 PUFAs. In the present study, saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and PUFAs of the omega-3, -6 and -9 series in plasma and erythrocytes of patients with recurrent major depressive disorder (MDD-R) were compared with controls.

Methodology and Principal Findings

We carried out a case-control study. The sample consisted of 137 patients with MDD-R and 65 matched non-depressed controls. In plasma and erythrocytes of patients with MDD-R the concentrations of most of the SFAs and MUFAs, and additionally erythrocyte PUFAs, all with a chain length >20 carbon (C) atoms, were significantly lower than in the controls. In contrast, the concentrations of most of the shorter chain members (≤18C) of the SFAs and MUFAs were significantly higher in the patients. Estimated activities of several elongases in plasma of patients were significantly altered, whereas delta-9 desaturase activity for C14∶0 and C18∶0 was significantly higher.

Conclusions/Significance

The fatty acid status of patients with MDD-R not only differs with regard to omega-3 and omega-6 PUFAs, but also concerns other fatty acids. These alterations may be due to: differences in diet, changes in synthesizing enzyme activities, higher levels of chronic (oxidative) stress but may also result from adaptive strategies by providing protection against enhanced oxidative stress and production of free radicals.