Human fatty acid synthase mRNA: tissue distribution, genetic mapping, and kinetics of decay after glucose deprivation

Fatty acid synthase (FASN) signalome: A molecular guide for precision oncology

The initial excitement generated more than two decades ago by the discovery of drugs targeting fatty acid synthase (FASN)-catalyzed de novo lipogenesis for cancer therapy was short-lived. However, the advent of the first clinical-grade FASN inhibitor (TVB-2640; denifanstat), which is currently being studied in various phase II trials, and the exciting advances in understanding the FASN signalome are fueling a renewed interest in FASN-targeted strategies for the treatment and prevention of cancer. Here, we provide a detailed overview of how FASN can drive phenotypic plasticity and cell fate decisions, mitochondrial regulation of cell death, immune escape and organ-specific metastatic potential. We then present a variety of FASN-targeted therapeutic approaches that address the major challenges facing FASN therapy. These include limitations of current FASN inhibitors and the lack of precision tools to maximize the therapeutic potential of FASN inhibitors in the clinic. Rethinking the role of FASN as a signal transducer in cancer pathogenesis may provide molecularly driven strategies to optimize FASN as a long-awaited target for cancer therapeutics.

Proteolytic activation of fatty acid synthase signals pan-stress resolution

Chronic stress and inflammation are both outcomes and major drivers of many human diseases. Sustained responsiveness despite mitigation suggests a failure to sense resolution of the stressor. Here we show that a proteolytic cleavage event of fatty acid synthase (FASN) activates a global cue for stress resolution in Caenorhabditis elegans. FASN is well established for biosynthesis of the fatty acid palmitate. Our results demonstrate FASN promoting an anti-inflammatory profile apart from palmitate synthesis. Redox-dependent proteolysis of limited amounts of FASN by caspase activates a C-terminal fragment sufficient to downregulate multiple aspects of stress responsiveness, including gene expression, metabolic programs and lipid droplets. The FASN C-terminal fragment signals stress resolution in a cell non-autonomous manner. Consistent with these findings, FASN processing is also seen in well-fed but not fasted male mouse liver. As downregulation of stress responses is critical to health, our findings provide a potential pathway to control diverse aspects of stress responses.

Review of Eukaryote Cellular Membrane Lipid Composition, with Special Attention to the Fatty Acids

Biological membranes, primarily composed of lipids, envelop each living cell. The intricate composition and organization of membrane lipids, including the variety of fatty acids they encompass, serve a dynamic role in sustaining cellular structural integrity and functionality. Typically, modifications in lipid composition coincide with consequential alterations in universally significant signaling pathways. Exploring the various fatty acids, which serve as the foundational building blocks of membrane lipids, provides crucial insights into the underlying mechanisms governing a myriad of cellular processes, such as membrane fluidity, protein trafficking, signal transduction, intercellular communication, and the etiology of certain metabolic disorders. Furthermore, comprehending how alterations in the lipid composition, especially concerning the fatty acid profile, either contribute to or prevent the onset of pathological conditions stands as a compelling area of research. Hence, this review aims to meticulously introduce the intricacies of membrane lipids and their constituent fatty acids in a healthy organism, thereby illuminating their remarkable diversity and profound influence on cellular function. Furthermore, this review aspires to highlight some potential therapeutic targets for various pathological conditions that may be ameliorated through dietary fatty acid supplements. The initial section of this review expounds on the eukaryotic biomembranes and their complex lipids. Subsequent sections provide insights into the synthesis, membrane incorporation, and distribution of fatty acids across various fractions of membrane lipids. The last section highlights the functional significance of membrane-associated fatty acids and their innate capacity to shape the various cellular physiological responses.

Druggable Metabolic Vulnerabilities Are Exposed and Masked during Progression to Castration Resistant Prostate Cancer

There is an urgent need for exploring new actionable targets other than androgen receptor to improve outcome from lethal castration-resistant prostate cancer. Tumor metabolism has reemerged as a hallmark of cancer that drives and supports oncogenesis. In this regard, it is important to understand the relationship between distinctive metabolic features, androgen receptor signaling, genetic drivers in prostate cancer, and the tumor microenvironment (symbiotic and competitive metabolic interactions) to identify metabolic vulnerabilities. We explore the links between metabolism and gene regulation, and thus the unique metabolic signatures that define the malignant phenotypes at given stages of prostate tumor progression. We also provide an overview of current metabolism-based pharmacological strategies to be developed or repurposed for metabolism-based therapeutics for castration-resistant prostate cancer.

Hesperidin and Naringin Improve Broiler Meat Fatty Acid Profile and Modulate the Expression of Genes Involved in Fatty Acid β-oxidation and Antioxidant Defense in a Dose Dependent Manner

The beneficial properties of the flavanones hesperidin and naringin as feed additives in poultry have lately been under investigation. In broilers, both flavanones have been shown to exhibit antioxidant properties while their individual effects on fatty acid (FA) composition and the underlying molecular mechanisms of their activity have not been explored. Here, we studied their effects on broiler meats' FA profiles and on the expression of genes related to lipid metabolism, antioxidant defense and anti-inflammatory function. The experimental design comprised six treatment groups of broilers, each supplemented from day 11 until slaughter at 42 days with hesperidin, naringin or vitamin E, as follows: the E1 group received 0.75 g of hesperidin per kg of feed, E2 received 1.5 g hesperidin/kg feed, N1 received 0.75 g naringin/kg feed, N2 received 1.5 g naringin/kg feed, vitamin E (VE) received 0.2 g a-tocopheryl acetate/kg feed, and the control group was not provided with a supplemented feed. The VE treatment group served as a positive control for antioxidant activity. An analysis of the FA profiles of the abdominal adipose tissue (fat pad), major pectoralis (breast) and biceps femoris (thigh) muscles showed that both hesperidin and naringin had significant effects on saturated FA (SFA), polyunsaturated FA (PUFA) and omega n-6 content. Both compounds reduced SFA and increased PUFA and n-6 content, as well as reducing the atherogenicity and thrombogenicity indices in the breast muscle and fat pad. The effects on the thigh muscle were limited. An analysis of gene expression in the liver revealed that naringin significantly increased peroxisome proliferator-activated receptor alpha (PPARα), Acyl-CoA oxidase 1 (ACOX1) and glutathione disulfide reductase (GSR) expression. In the breast muscle, both hesperidin and naringin increased fatty acid synthase (FASN) expression and hesperidin increased the expression of adiponectin. In brief, both hesperidin and naringin supplementation beneficially affected FA profiles in the breast meat and fat pad of broiler chicken. These effects could be attributed to an increase in FA β-oxidation since the increased expression of related genes (PPARα and ACOX1) was observed in the liver. Furthermore, the antioxidant activity of hesperidin and naringin previously observed in the meat of broilers could be attributed, at least partly, to the regulation of antioxidant defense genes, as evidenced by the increased GSR expression in response to naringin supplementation.

Type I fatty acid synthase trapped in the octanoyl-bound state

De novo fatty acid biosynthesis in humans is accomplished by a multidomain protein, the Type I fatty acid synthase (FAS). Although ubiquitously expressed in all tissues, fatty acid synthesis is not essential in normal healthy cells due to sufficient supply with fatty acids by the diet. However, FAS is overexpressed in cancer cells and correlates with tumor malignancy, which makes FAS an attractive selective therapeutic target in tumorigenesis. Herein, we present a crystal structure of the condensing part of murine FAS, highly homologous to human FAS, with octanoyl moieties covalently bound to the transferase (MAT—malonyl‐/acetyltransferase) and the condensation (KS—β‐ketoacyl synthase) domain. The MAT domain binds the octanoyl moiety in a novel (unique) conformation, which reflects the pronounced conformational dynamics of the substrate‐binding site responsible for the MAT substrate promiscuity. In contrast, the KS binding pocket just subtly adapts to the octanoyl moiety upon substrate binding. Besides the rigid domain structure, we found a positive cooperative effect in the substrate binding of the KS domain by a comprehensive enzyme kinetic study. These structural and mechanistic findings contribute significantly to our understanding of the mode of action of FAS and may guide future rational inhibitor designs.

Fatty Acid Synthase: An Emerging Target in Cancer

In recent years, lipid metabolism has garnered significant attention as it provides the necessary building blocks required to sustain tumor growth and serves as an alternative fuel source for ATP generation. Fatty acid synthase (FASN) functions as a central regulator of lipid metabolism and plays a critical role in the growth and survival of tumors with lipogenic phenotypes. Accumulating evidence has shown that it is capable of rewiring tumor cells for greater energy flexibility to attain their high energy requirements. This multi-enzyme protein is capable of modulating the function of subcellular organelles for optimal function under different conditions. Apart from lipid metabolism, FASN has functional roles in other cellular processes such as glycolysis and amino acid metabolism. These pivotal roles of FASN in lipid metabolism make it an attractive target in the clinic with several new inhibitors currently being tested in early clinical trials. This article aims to present the current evidence on the emergence of FASN as a target in human malignancies.

Variation in the Fatty Acid Synthase Gene (FASN) and Its Association with Milk Traits in Gannan Yaks

Fatty acid synthase (FASN) is an enzyme involved in the synthesis of fatty acids (FA) and plays a central role in de novo lipogenesis in mammals. This study was conducted to ascertain the relative level of expression of the FASN gene (FASN) in tissues from the yak (Bos grunniens), and to search for variation in two regions of yak FASN using polymerase chain reaction single-stranded conformational polymorphism (PCR-SSCP) analyses; it also ascertains whether that variation is associated with yak milk traits. The gene was found to be expressed in twelve tissues, with the highest expression detected in the mammary gland, followed by subcutaneous fat tissue. Two regions of the gene were analyzed in 290 Gannan yaks: A region spanning exon 24-intron 24 and a region spanning exon 34. These regions both produced two PCR-SSCP patterns, which, upon sequencing, represented different DNA sequences. This sequence variation resulted from the presence of three nucleotide substitutions: c.4296+38C/T (intron 24), c.5884A/G, and c.5903G/A, both located in exon 34. The exon 34 substitutions would result in the amino acid substitutions p.Thr1962Ala and p.Gly1968Glu if expressed. Four haplotypes spanning from the exon 24-intron 24 region to exon 34 were identified. Of these, two were common (A₁-A₂ and B₁-A₂), and two were rare (A₁-B₂ and B₁-B₂) in the yaks investigated. The presence of A₁-A₂ was associated with an increase in milk fat content (p = 0.050) and total milk solid content (p = 0.037), while diplotype A₁-A₂/B₁-A₂ had a higher milk fat content (p = 0.038) than the other diplotypes. This study suggests that further characterization of the FASN gene might provide for an improved understanding of milk traits in yaks.

Fatty acid synthase downregulation contributes to acute lung injury in murine diet-induced obesity

The prevalence of obesity is rising worldwide and obese patients comprise a specific population in the intensive care unit. Acute respiratory distress syndrome (ARDS) incidence is increased in obese patients. Exposure of rodents to hyperoxia mimics many of the features of ARDS. In this report, we demonstrate that high fat diet induced obesity increases the severity of hyperoxic acute lung injury in mice in part by altering fatty acid synthase (FASN) levels in the lung. Obese mice exposed to hyperoxia had significantly reduced survival and increased lung damage. Transcriptomic analysis of lung homogenates identified Fasn as one of the most significantly altered mitochondrial associated genes in mice receiving 60% compared to 10% fat diet. FASN protein levels in the lung of high fat diet mice were lower by immunoblotting and immunohistochemistry. Depletion of FASN in type II alveolar epithelial cells resulted in altered mitochondrial bioenergetics and more severe lung injury with hyperoxic exposure, even upon the administration of a 60% fat diet. This is the first study to show that a high fat diet leads to altered FASN expression in the lung and that both a high fat diet and reduced FASN expression in alveolar epithelial cells promote lung injury.

Circulating serum fatty acid synthase is elevated in patients with diabetes and carotid artery stenosis and is LDL-associated

BACKGROUND AND AIMS

Diabetes is an independent risk factor for carotid artery stenosis (CAS). Fatty acid synthase (FAS), an essential de novo lipogenesis enzyme, has increased activity in the setting of diabetes that leads to altered lipid metabolism. Circulating FAS (cFAS) was recently observed in the blood of patients with hyperinsulinemia and cancer. We thought to evaluate the origin of cFAS and its role in diabetes-associated CAS.

METHODS

Patients with diabetes and no diabetes, undergoing carotid endarterectomy (CEA) for CAS, were prospectively enrolled for collection of plaque and fasting serum. FPLC was used to purify lipoprotein fractions, and ELISA was used to quantify cFAS content and activity. Immunoprecipitation (IP) was used to evaluate the affinity of cFAS to LDL-ApoB.

RESULTS

Patients with CAS had higher cFAS activity (p < 0.01), and patients with diabetes had higher cFAS activity than patients with no diabetes (p < 0.05). cFAS activity correlated with serum glucose (p = 0.03, r² = 0.35), and cFAS content trended with plaque FAS content (p = 0.06, r² = 0.69). cFAS was predominantly in LDL cholesterol fractions of patients with CAS (p < 0.001), and IP of cFAS demonstrated pulldown of ApoB. Similar to patients with diabetes, db/db mice had highest levels of serum cFAS (p < 0.01), and fasL^-/- (tissue-specific liver knockdown of FAS) mice had the lowest levels of cFAS (p < 0.001).

CONCLUSIONS

Serum cFAS is higher in patients with diabetes and CAS, appears to originate from the liver, and is LDL cholesterol associated. We postulate that LDL may be serving as a carrier for cFAS that contributes to atheroprogression in carotid arteries of patients with diabetes.

Clove extract functions as a natural fatty acid synthesis inhibitor and prevents obesity in a mouse model

Numerous medicinal plants have been reported to prevent various chronic diseases.

Identification of a novel 11β-HSD1 inhibitor from a high-throughput screen of natural product extracts

Selective inhibitors of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) have considerable potential as a treatment for metabolic syndrome including type 2 diabetes mellitus and obesity. To identify 11β-HSD1 inhibitors, we conducted high-throughput screening (HTS) of active natural product extracts from the Korea Chemical Bank, including Tanshinone I, Tanshinone IIA, and flavanone derivatives, and 2- and 3-phenyl-4H-chromen-4-one. Then Tanshinone IIA and its derivatives were targeted for the development of a lead compound according to the HTS results. However, the mechanism for anti-adipogenic effect through 11β-HSD1 enzyme inhibition by Tanshinone IIA is not clear. Tanshinone IIA (2a) concentration-dependently inhibited 11β-HSD1 activity in human and mouse 11β-HSD1 overexpressed cells and 3T3-L1 adipocytes. Tanshinone IIA (2a) also inhibited 11β-HSD1 enzyme activities in murine liver and fats. Furthermore, Tanshinone IIA (2a)-suppressed adipocyte differentiation of cortisone-induced adipogenesis in 3T3-L1 cells was associated with the suppression of the cortisone-induced adipogenesis-specific markers mRNA and protein expression. In 3T3-L1 preadipocytes, Tanshinone IIA (2a)-inhibited cortisone induced reactive oxygen species formation in a concentration-dependent manner. Thus, these results support the therapeutic potential of Tanshinone IIA (2a) as a 11β-HSD1 inhibitor in metabolic syndrome patients.

Genetic diversity analysis of buffalo fatty acid synthase (FASN) gene and its differential expression among bovines

Fatty Acid Synthase (FASN) gene seems to be structurally and functionally different in bovines in view of their distinctive fatty acid synthesis process. Structural variation and differential expression of FASN gene is reported in buffalo (Bubalus bubalis), a bovine species close to cattle, in this study. Amino acid sequence and phylogenetic analysis of functionally important thioesterase (TE) domain of FASN revealed its conserved nature across mammals. Amino acid residues at TE domain, responsible for substrate binding and processing, were found to be invariant in all the mammalian species. A total of seven polymorphic nucleotide sites, including two in coding region of TE domain were identified across the 10 buffalo populations of riverine and swamp types. G and C alleles were found almost fixed at g18996 and g19056 loci, respectively in riverine buffaloes. Principal component analysis of three SNPs (g18433, g18996 and g19056) revealed distinct classification of riverine and swamp buffalo populations. Reverse Transcription-PCR amplification of mRNA corresponding to exon 8-10 region of buffalo FASN helped in identification of two transcript variants; one transcript of 565 nucleotides and another alternate transcript of 207 nucleotides, seems to have arisen through alternative splicing. Both the transcripts were found to be expressed in most of the vital tissues of buffalo with the highest expression in mammary gland. Semi-quantitative and real-time expression analysis across 13 different buffalo tissues revealed its highest expression in lactating mammary gland. When compared, expression of FASN was also found to be higher in liver, adipose and skeletal muscle of buffalo tissues, than cattle. However, the FASN expression was highest in adipose among the three tissues in both the species. Results indicate structural and functional distinctiveness of bovine FASN. Presence of alternate splicing in buffalo FASN also seems to be a unique phenomenon to the bovines, probably associated with mRNA based regulation of the biological functions of FASN in these species.

Fatty acid synthase is required for mammary gland development and milk production during lactation

The mammary gland is one of the few adult tissues that strongly induce de novo fatty acid synthesis upon physiological stimulation, suggesting that fatty acid is important for milk production during lactation. The committed enzyme to perform this function is fatty acid synthase (FASN). To determine whether de novo fatty acid synthesis is obligatory or dietary fat is sufficient for mammary gland development and function during lactation, Fasn was specifically knocked out in mouse mammary epithelial cells. We found that deletion of Fasn hindered the development and induced the premature involution of the lactating mammary gland and significantly decreased medium- and long-chain fatty acids and total fatty acid contents in the milk. Consequently, pups nursing from Fasn knockout mothers experienced growth retardation and preweanling death, which was rescued by cross-fostering pups to a lactating wild-type mother. These results demonstrate that FASN is essential for the development, functional competence, and maintenance of the lactating mammary gland.

Extra fructose in the growth medium fuels lipogenesis of adipocytes

Fructose in excessive amounts exerts negative effects on insulin sensitivity, blood pressure, and liver metabolism. These adverse outcomes were attributed to its disturbances of key metabolic pathways in the liver. Recently, possible consequences of high fructose levels directly on adipocytes in vivo have been considered. We have cultured adipocytes in growth media containing 1 g/L fructose additionally to glucose and monitored the cells fate. Cells developed lipid vesicles much earlier with fructose and showed altered kinetics of the expression of mRNAs involved in lipogenesis and hexose uptake. Adiponectin secretion, too, peaked earlier in fructose containing media than in media with glucose only. From these data it can be speculated that similar effects of fructose containing diets happen in vivo also. Apart from toxic action on liver cells, adipocytes might be stimulated to take up extra fructose and generate new lipid vesicles, further dysregulating energy homeostasis.

Fatty acid metabolism: Implications for diet, genetic variation, and disease

Cultures across the globe, especially Western societies, are burdened by chronic diseases such as obesity, metabolic syndrome, cardiovascular disease, and cancer. Several factors, including diet, genetics, and sedentary lifestyle, are suspected culprits to the development and progression of these health maladies. Fatty acids are primary constituents of cellular physiology. Humans can acquire fatty acids by de novo synthesis from carbohydrate or protein sources or by dietary consumption. Importantly, regulation of their metabolism is critical to sustain balanced homeostasis, and perturbations of such can lead to the development of disease. Here, we review de novo and dietary fatty acid metabolism and highlight recent advances in our understanding of the relationship between dietary influences and genetic variation in fatty acid metabolism and their role in chronic diseases.

Plasma fatty acid composition in patients with pancreatic cancer: correlations to clinical parameters

Pancreatic cancer (PC) ranks as the fourth cause of cancer-related deaths in the Czech Republic. Evidence exists that deregulation of fatty acid (FA) metabolism is connected with some malignancies; therefore, we decided to analyze FA profile in plasma lipid classes in patients with PC with relation to tumor staging, nutritional status, and survival. The study included 84 patients (47 males, 37 females) with PC and 68 controls (36 males, 32 females). FA patterns were analyzed in plasma lipid classes by gas-chromatography. We observed increased proportion of total monounsaturated FA (MUFA) in PC group in all plasma lipid classes. These changes were connected with increased Δ9-desaturase (SCD1) and Δ5-desaturase indices. Correlations of dihomo-γ-linolenic acid (DHGLA) with these variables were opposite. Longer survival of patients was connected with higher content of EPA, DHA, and with lower SCD1 index, respectively. Plasma phospholipid proportions of α-linolenic acid, DHGLA, EPA, and n-3 polyunsaturated fatty acids displayed negative trend with tumor staging. Plasma lipid FA pattern in PC patients resulted from decreased dietary fat intake and increased de novo synthesis of FA with transformation into MUFA. Changes in FA profile implicated some pathophysiological mechanisms responsible for disturbed FA metabolism in PC and importance of appropriate nutritional support.

Lipids and prostate cancer

The role of lipid metabolism has gained particular interest in prostate cancer research. A large body of literature has outlined the unique upregulation of de novo lipid synthesis in prostate cancer. Concordant with this lipogenic phenotype is a metabolic shift, in which cancer cells use alternative enzymes and pathways to facilitate the production of fatty acids. These newly synthesized lipids may support a number of cellular processes to promote cancer cell proliferation and survival. Hence, de novo lipogenesis is under intense investigation as a therapeutic target. Epidemiologic studies suggest dietary fat may also contribute to prostate cancer; however, whether dietary lipids and de novo synthesized lipids are differentially metabolized remains unclear. Here, we highlight the lipogenic nature of prostate cancer, especially the promotion of de novo lipid synthesis, and the significance of various dietary lipids in prostate cancer development and progression.

Blockade of fatty acid synthase triggers significant apoptosis in mantle cell lymphoma

Fatty acid synthase (FASN), a key player in the de novo synthetic pathway of long-chain fatty acids, has been shown to contribute to the tumorigenesis in various types of solid tumors. We here report that FASN is highly and consistently expressed in mantle cell lymphoma (MCL), an aggressive form of B-cell lymphoid malignancy. Specifically, the expression of FASN was detectable in all four MCL cell lines and 15 tumors examined. In contrast, benign lymphoid tissues and peripheral blood mononuclear cells from normal donors were negative. Treatment of MCL cell lines with orlistat, a FASN inhibitor, resulted in significant apoptosis. Knockdown of FASN expression using siRNA, which also significantly decreased the growth of MCL cells, led to a dramatic decrease in the cyclin D1 level. β-catenin, which has been previously reported to be upregulated in a subset of MCL tumors, contributed to the high level of FASN in MCL cells, Interesting, siRNA knock-down of FASN in turn down-regulated β-catenin. In conclusion, our data supports the concept that FASN contributes to the pathogenesis of MCL, by collaborating with β-catenin. In view of its high and consistent expression in MCL, FASN inhibitors may hold promises for treating MCL.

Fatty acid synthase and liver triglyceride metabolism: housekeeper or messenger?

Fatty acid synthase (FAS) catalyzes the de novo synthesis of fatty acids. In the liver, FAS has long been categorized as a housekeeping protein, producing fat for storage of energy when nutrients are present in excess. Most previous studies of FAS regulation have focused on the control of gene expression. However, recent findings suggest that hepatic FAS may also be involved in signaling processes that include activation of peroxisome proliferator-activated receptor α (PPARα). Moreover, reports of rapid alterations in FAS activity as well as findings of post-translational modifications of the FAS protein support the notion that dynamic events in addition to transcription impact FAS regulation. These results indicate that FAS enzyme activity can impact liver physiology through signaling as well as energy storage and that its regulation may be complex. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

Macrophage fatty-acid synthase deficiency decreases diet-induced atherosclerosis

Fatty acid metabolism is perturbed in atherosclerotic lesions, but whether it affects lesion formation is unknown. To determine whether fatty acid synthesis affects atherosclerosis, we inactivated fatty-acid synthase (FAS) in macrophages of apoE-deficient mice. Serum lipids, body weight, and glucose metabolism were the same in FAS knock-out in macrophages (FASKOM) and control mice, but blood pressure was lower in FASKOM animals. Atherosclerotic extent was decreased 20-40% in different aortic regions of FASKOM as compared with control mice on Western diets. Foam cell formation was diminished in FASKOM as compared with wild type macrophages due to increased apoAI-specific cholesterol efflux and decreased uptake of oxidized low density lipoprotein. Expression of the anti-atherogenic nuclear receptor liver X receptor alpha (LXRalpha; Nr1h3) and its downstream targets, including Abca1, were increased in FASKOM macrophages, whereas expression of the potentially pro-atherogenic type B scavenger receptor CD36 was decreased. Peroxisome proliferator-activated receptor alpha (PPARalpha) target gene expression was decreased in FASKOM macrophages. PPARalpha agonist treatment of FASKOM and wild type macrophages normalized PPARalpha target gene expression as well as Nr1h3 (LXRalpha). Atherosclerotic lesions were more extensive when apoE null mice were transplanted with LXRalpha-deficient/FAS-deficient bone marrow as compared with LXRalpha-replete/FAS-deficient marrow, consistent with anti-atherogenic effects of LXRalpha in the context of FAS deficiency. These results show that macrophage FAS deficiency decreases atherosclerosis through induction of LXRalpha and suggest that FAS, which is induced by LXRalpha, may generate regulatory lipids that cause feedback inhibition of LXRalpha in macrophages.

A new targeting approach for breast cancer gene therapy using the human fatty acid synthase promoter

Gene therapy with adenoviral vectors is a promising new approach for the treatment of refractory advanced breast cancer. Strategies to restrict adenoviral-mediated therapeutic gene expression are important to avoid harming normal cells. Fatty acid synthase (FAS) is overexpressed in several human cancers. FAS is highly expressed in infiltrating breast cancer tissue, and always associated with malignant phenotypes and poor prognosis. In this study, expression of the FAS was evaluated in three breast cancer cell lines. A 680 bp-FAS promoter was cloned and its transcriptional activity was analyzed in breast cancer cell lines. We made a recombinant adenovirus construct carrying herpes simplex virus thymidine kinase (HSV-TK) driven by human FAS promoter (Ad-FAS-TK) and analyzed its target cytotoxicity in vitro and in vivo against human breast cancer cells combined with prodrug ganciclovir (GCV). The results show that the expression of FAS varies in the three breast cancer cell lines examined (respectively, SK-Br3>MCF-7>MDA-MB-231), but FAS promoter can initiate relative high transcriptional activities in all three kinds of cancer cells while little in normal fibroblast cells. Furthermore, FAS promoter can drive the therapeutic gene in a wider range of human breast cancers than cerbB2 promoter and exhibit a stronger activity than midkine (MK) promoter. Combination of Ad-FAS-TK and GCV treatment exhibited strong-targeted cytotoxic effect on breast cancer cells but showed little activity in normal fibroblast cells. The tumorigenic capability of breast cancer cells treated with Ad-FAS-TK/GCV was completely inhibited in vitro and in vivo assays. In conclusion, adenoviral-mediated suicide gene therapy controlled by tumor associated-FAS promoter can induce specific cytotoxic effect on human breast cancer cells in vitro and in vivo. So it is a promising target for the development of gene therapy against breast cancers.

The effect of dietary carbohydrate on genes for fatty acid synthase and inflammatory cytokines in adipose tissues from lean and obese subjects

BACKGROUND

Hepatic de novo lipogenesis (DNL) is markedly stimulated in humans by low-fat diets enriched in simple sugars. However, the dietary responsiveness of the key enzyme controlling DNL in human adipose tissue, fatty acid synthase (FAS), is uncertain.

HYPOTHESIS

Adipose tissue mRNA for FAS is increased in lean and obese subjects when hepatic DNL is elevated by a eucaloric, low-fat, high-sugar diet.

DESIGN

Twelve lean and seven obese volunteers were given two eucaloric diets (10% vs. 30% fat; 75% vs. 55% carbohydrate; sugar/starch 60/40) each for 2 weeks by a random-order cross-over design. FAS mRNA in abdominal and gluteal adipose tissues was compared to hepatic DNL measured in serum by isotopic and nonisotopic methods. Adipose tissue mRNA for tumor necrosis factor-alpha and IL-6, which are inflammatory cytokines that modulate DNL, was also assayed.

RESULTS

The low-fat high-sugar diet induced a 4-fold increase in maximum hepatic DNL (P<.001) but only a 1.3-fold increase in adipose tissue FAS mRNA (P=.029) and no change in cytokine mRNA. There was a borderline significant positive correlation between changes in FAS mRNA and hepatic DNL (P=.039). Compared to lean subjects, obese subjects had lower levels of FAS mRNA and higher levels of cytokine mRNA (P<.001).

CONCLUSIONS

The results suggest that key elements of human adipose tissue DNL are less responsive to dietary carbohydrate than is hepatic DNL and may be regulated by diet-independent factors. Irrespective of diet, there is reduced expression of the FAS gene and increased expression of cytokine genes in adipose tissues of obese subjects.

Fatty acid synthase gene expression in human adipose tissue: association with obesity and type 2 diabetes

AIMS/HYPOTHESIS

Increased expression and activity of the lipogenic pathways in adipose tissue may contribute to the development of obesity. As a central enzyme in lipogenesis, the gene encoding fatty acid synthase (FASN) was identified as a candidate gene for determining body fat. In the present study we tested the hypothesis that increased FASN expression links metabolic alterations of excess energy intake, including hyperinsulinaemia, dyslipidaemia and altered adipokine profile to increased body fat mass.

SUBJECTS AND METHODS

In paired samples of visceral and subcutaneous adipose tissue from 196 participants (lean or obese), we investigated whether FASN mRNA expression (assessed by PCR) in adipose tissue is increased in obesity and related to visceral fat accumulation, measures of insulin sensitivity (euglycaemic-hyperinsulinaemic clamp) and glucose metabolism.

RESULTS

FASN mRNA expression was increased by 1.7-fold in visceral vs subcutaneous fat. Visceral adipose tissue FASN expression was correlated with FASN protein levels, subcutaneous FASN expression, visceral fat area, fasting plasma insulin, serum concentrations of IL-6, leptin and retinol-binding protein 4 (RBP4), and inversely with measures of insulin sensitivity, independently of age, sex and BMI. Moreover, we found significant correlations between FASN expression and markers of renal function, including serum creatinine and urinary albumin excretion.

CONCLUSIONS/INTERPRETATION

Increased FASN gene expression in adipose tissue is linked to visceral fat accumulation, impaired insulin sensitivity, increased circulating fasting insulin, IL-6, leptin and RBP4, suggesting an important role of lipogenic pathways in the causal relationship between consequences of excess energy intake and the development of obesity and type 2 diabetes.

Hypothalamic fatty acid metabolism: a housekeeping pathway that regulates food intake

The hypothalamus is a specialized area in the brain that integrates the control of energy homeostasis. More than 70 years ago, it was proposed that the central nervous system sensed circulating levels of metabolites such as glucose, lipids and amino acids and modified feeding according to the levels of those molecules. This led to the formulation of the Glucostatic, Lipostatic and Aminostatic Hypotheses. It has taken almost that much time to demonstrate that circulating long-chain fatty acids act as signals of nutrient surplus in the hypothalamus. Moreover, pharmacological and/or genetic inhibition of fatty acid synthase, AMP-activated protein kinase and carnitine palmitoyltransferase 1 results in profound decrease in feeding and body weight in rodents. The molecular mechanism behind these actions depends on changes in the cellular pool of malonyl-CoA and fatty acyl-CoAs. Current evidence also suggests that this pathway may play a major role in the physiological regulation of feeding, by integrating hormonal and nutrient-derived signals in the hypothalamus. Here, we summarize what is known about hypothalamic fatty acid metabolism and feeding control and provide future directions for research. Understanding these molecular mechanisms could provide new targets for the treatment of obesity and related disorders.

The lipogenic enzymes DGAT1, FAS, and LPL in adipose tissue: effects of obesity, insulin resistance, and TZD treatment

Acyl-coenzyme A:diacylglycerol transferase (DGAT), fatty acid synthetase (FAS), and LPL are three enzymes important in adipose tissue triglyceride accumulation. To study the relationship of DGAT1, FAS, and LPL with insulin, we examined adipose mRNA expression of these genes in subjects with a wide range of insulin sensitivity (SI). DGAT1 and FAS (but not LPL) expression were strongly correlated with SI. In addition, the expression of DGAT1 and FAS (but not LPL) were higher in normal glucose-tolerant subjects compared with subjects with impaired glucose tolerance (IGT) (P < 0.005). To study the effects of insulin sensitizers, subjects with IGT were treated with pioglitazone or metformin for 10 weeks, and lipogenic enzymes were measured in adipose tissue. After pioglitazone treatment, DGAT1 expression was increased by 33 +/- 10% (P < 0.05) and FAS expression increased by 63 +/- 8% (P < 0.05); however, LPL expression was not altered. DGAT1, FAS, and LPL mRNA expression were not significantly changed after metformin treatment. The treatment of mice with rosiglitazone also resulted in an increase in adipose expression of DGAT1 by 2- to 3-fold, as did the treatment of 3T3 F442A adipocytes in vitro with thiazolidinediones. These data support a more global concept suggesting that adipose lipid storage functions to prevent peripheral lipotoxicity.

Tanis: a link between type 2 diabetes and inflammation?

Here we describe a novel protein, which we have named Tanis, that is implicated in type 2 diabetes and inflammation. In Psammomys obesus, a unique polygenic animal model of type 2 diabetes and the metabolic syndrome, Tanis is expressed in the liver in inverse proportion to circulating glucose (P = 0.010) and insulin levels (P = 0.004) and in direct proportion with plasma triglyceride concentrations (P = 0.007). Hepatic Tanis gene expression was markedly increased (3.1-fold) after a 24-h fast in diabetic but not in nondiabetic P. obesus. In addition, glucose inhibited Tanis gene expression in cultured hepatocytes (P = 0.006) as well as in several other cell types (P = 0.001-0.011). Thus, Tanis seems to be regulated by glucose and is dysregulated in the diabetic state. Yeast-2 hybrid screening identified serum amyloid A (SAA), an acute-phase inflammatory response protein, as an interacting protein of Tanis, and this was confirmed by Biacore experiments. SAA and other acute-phase proteins have been the focus of recent attention as risk factors for cardiovascular disease, and we contend that Tanis and its interaction with SAA may provide a mechanistic link among type 2 diabetes, inflammation, and cardiovascular disease.

A link between diabetes and atherosclerosis: Glucose regulates expression of CD36 at the level of translation

Both the risk and the rate of development of atherosclerosis are increased in diabetics, but the mechanisms involved are unknown. Here we report a glucose-mediated increase in CD36 mRNA translation efficiency that results in increased expression of the macrophage scavenger receptor CD36. Expression of CD36 was increased in endarterectomy lesions from patients with a history of hyperglycemia. Macrophages that were differentiated from human peripheral blood monocytes in the presence of high glucose concentrations showed increased expression of cell-surface CD36 secondary to an increase in translational efficiency of CD36 mRNA. We obtained similar data from primary cells isolated from human vascular lesions, and we found that glucose sensitivity is a function of ribosomal reinitiation following translation of an upstream open reading frame (uORF). Increased translation of macrophage CD36 transcript under high glucose conditions provides a mechanism for accelerated atherosclerosis in diabetics.

Fatty acid synthase is expressed mainly in adult hormone-sensitive cells or cells with high lipid metabolism and in proliferating fetal cells

Animal fatty acid synthase (FAS) is a homodimer protein which synthesizes long-chain fatty acids and is rich in liver, brain, breast, and lung. However, the precise cellular localization of FAS in human tissues has not been elucidated. Immunohistochemistry with a new antibody to human FAS revealed that in adult human tissues FAS is distributed mainly in cells with high lipid metabolism (adipocytes, corpus luteum, hepatocytes, sebaceous glands, and Type II alveolar cells), in hormone-sensitive cells (anterior pituitary, apocrine gland, breast, endometrium, prostate, seminal vesicle, and adrenal cortex), and in a subset of epithelial cells of duodenum and stomach, colon absorptive cells, cerebral neurons, basket cells of cerebellum, decidua, uroepithelium, and epidymis. In fetal cells at 20 weeks of gestation, FAS was mainly present in proliferative epithelial cells of the digestive and respiratory systems, proximal renal tubules, adrenocortical cells, and mesenchymal and hematolymphoid cells. Staining was significant in nonproliferating cells, as observed in adult, and in sympathetic ganglion cells, Leidig cells of testis, and Langhans cells of chorionic villi. FAS is maintained in hormone-sensitive cells and/or cells active in lipid metabolism in the adult and is expressed in proliferating cells in the fetus, suggesting active fatty acid synthesis for energy utilization or membrane lipids.

Exercise attenuates nuclear protein binding to gene regulatory sequences of hepatic fatty acid synthase

The effect of an acute bout of exhaustive exercise on hepatic fatty acid synthase (FAS) gene expression was examined in rats. Female Sprague-Dawley rats (age 8 wk) were fasted for 48 h (F, n = 6), or fasted, refed a high-fructose diet for 6 h, and killed at rest (R, n = 6) or killed after running on a treadmill at 27 m/min and 5% grade for 88 +/- 7 min (E, n = 6). Gel mobility shift assay indicated that R rats had twofold higher liver nuclear protein binding to oligonucleotides corresponding to the insulin responsive sequence (-71/-50) and carbohydrate response element (+283/+303) on the FAS promoter, compared with F rats. Exercise severely attenuated this binding in liver nuclear extracts to the levels seen in F rats. Competition and supershift experiments revealed that the bound protein complexes contained the upstream stimulatory factors. Nuclear run-on experiment revealed a 49-fold increase in transcription rate of the FAS gene in R vs. F rats, whereas exercise suppressed the transcription rate. FAS mRNA abundance and FAS enzyme activity were dramatically increased with refeeding but were unaltered by exercise. The results reveal that dietary induction of hepatic FAS is stimulated by increased nuclear protein binding to insulin responsive sequence and carbohydrate response element, whereas exhaustive exercise attenuates the binding, which may precede downregulation of FAS mRNA and enzyme synthesis reported in our previous work (M. A. Griffiths, R. Fiebig, M. T. Gore, D. H. Baker, K. Esser, L. Oscai, and L. L. Ji. J. Nutr. 126, 1959-1971, 1996).

Insulin increases fatty acid synthase gene transcription in human adipocytes

The purpose of this study was to investigate the molecular mechanism whereby insulin increases expression of a key de novo lipogenic gene, fatty acid synthase (FAS), in cultured human adipocytes and hepatoma cells. RNA isolated from cultured adipocytes or from Hep G2 cells treated with or without insulin (20 nM) was analyzed. In addition, run-on transcription assays and measurements of RNA half-life were performed to determine the controlled step in FAS gene regulation by insulin. We demonstrated that FAS mRNA was expressed in both Hep G2 cells and human adipocytes. Insulin induced an approximately five- and three-fold increase in FAS mRNA content in adipocytes and hepatoma cells, respectively. Similar regulation of FAS was observed in adipocytes from lean and obese human subjects. Furthermore, we demonstrated that the induction of human FAS expression by insulin was due to increased transcription rate of the FAS gene in human adipocytes, whereas mRNA stabilization accounted for increased FAS mRNA content in hepatoma cells. In conclusion, we report here for the first time expression of human FAS mRNA and its specific transcriptional induction by insulin in cultured human adipocytes.

Properties and purification of a glucose-inducible human fatty acid synthase mRNA-binding protein

Glucose stabilizes the mRNA for human fatty acid synthase (FAS), an enzyme relevant to diverse human disorders, including hyperlipidemia, obesity, and malignancy. To determine the underlying mechanisms, RNA gel mobility shift assays were used to demonstrate that human Hep G2 cells contain a cytoplasmic factor that binds specifically to the 3'-terminus of the human FAS mRNA. D-Glucose increased RNA-binding activity by 2.02-fold (P = 0.0033), with activity peaking 3 h after glucose feeding. Boiling or treatment of extracts with proteinase K abolished binding. Ultraviolet cross-linking of the FAS mRNA-binding factor followed by SDS-PAGE resolved a proteinase K-sensitive band with an apparent molecular mass of 178 +/- 7 kDa. The protein was purified to homogeneity using nondenaturing polyacrylamide gels as an affinity matrix. Acid phosphatase treatment of the protein prevented binding to the FAS mRNA, but binding activity was unaffected by modification of sulfhydryl groups and was not Mg2+ or Ca2+ dependent. Deletion and RNase T1 mapping localized the binding site of the protein to 37 nucleotides characterized by the repetitive motif ACCCC and found within the first 65 bases of the 3'-UTR. Hybridization of the FAS transcript with an oligonucleotide antisense to this sequence abolished binding. These findings indicate that a 178-kDa glucose-inducible phosphoprotein binds to an (ACCCC)n-containing sequence in the 3'-UTR of the FAS mRNA within the same time frame that glucose stabilizes the FAS message. This protein may participate in the posttranscriptional control of FAS gene expression.

Characterization of the chicken fatty acid synthase gene 5' part and promoter region

Fatty acid synthase activity has been shown to be regulated mainly at the transcriptional level under both dietary and hormonal influences. As a first step towards elucidating the factors involved, we isolated and characterized chicken genomic clones encompassing the 5' part of the chicken fatty acid synthase gene and its flanking region. The entire region of the cloned DNA spans 30 kb, and the first three exons of the gene were mapped to a 6.3-kb genomic fragment. The transcription initiation site was determined after subcloning the cDNA which encodes the 5' end of the mRNA. The first exon, which was 129 bp long, was located approximately 5.3 kb upstream of the second exon, which contained the start codon. In the 5' flanking region, putative TATA and CAAT boxes were located 30 and 92 bp, respectively, upstream of the transcription initiation site. The 5' flanking region contained numerous sequences corresponding to consensus binding sites for transcription factors. Various lengths of flanking sequences extending up to 1028 bp upstream of the transcription initiation site and containing 100 bp of the first exon were linked to the bacterial chloramphenicol acetyltransferase gene; in this study, these constructs were analyzed in transient transfection assays in human hepatoma cells. The proximal 125-bp sequence upstream of the transcription start site was shown to be a basal promoter. The cloning and characterization of the chicken fatty-acid synthase gene provides some further insight into the regulation of fatty acid synthesis in birds as compared to mammals.

Essential amino acids regulate fatty acid synthase expression through an uncharged transfer RNA-dependent mechanism

To better understand the regulation of gene expression by amino acids, we studied the effects of these macronutrients on fatty acid synthase (FAS), an enzyme crucial for energy storage. When HepG2 cells were fed serum-free media selectively deficient in each amino acid, the omission of any single classic essential amino acid as well as Arg or His (essential in some rapidly growing cells) resulted in FAS mRNA levels that were about half of those in complete medium. Control message levels were unaffected and omission of nonessential amino acids did not alter FAS expression. FAS mRNA levels peaked 12-16 h after feeding complete and Ser (nonessential)-deficient media but did not increase in cells fed Lys (essential)-deficient medium. With Lys, FAS mRNA increased over the physiologic concentration range of 15-150 microM, and low concentrations of lysine decreased FAS but not apoB protein mass. Transcription inhibitors mimicked treatment with Lys-deficient media, and nuclear run-off assays showed that Lys-deficient media abolished FAS but not apoB transcription. After treatment with Lys-deficient media, the intracellular Lys pool was rapidly depleted in association with an increase of uncharged (deacylated) tRNA Lys from < 1 to 64% of available tRNA Lys. Even in the presence of the essential amino acid His, increasing the level of uncharged tRNA His with histidinol, a competitive inhibitor of the histidinyl-tRNA synthetase, blocked FAS expression. Tyrosinol treatment did not alter FAS mRNA levels. These results suggest that essential amino acids regulate FAS expression by altering uncharged tRNA levels, a novel mechanism for nutrient control of gene expression in mammalian cells.