Summary PPARα is activated by drugs to treat human disorders of lipid metabolism. Its endogenous ligand is unknown. PPARα-dependent gene expression is impaired with inactivation of fatty acid synthase (FAS), suggesting that FAS is involved in generation of a PPARα ligand. Here we demonstrate the FAS-dependent presence of a phospholipid bound to PPARα isolated from mouse liver. Binding was increased under conditions that induce FAS activity and displaced by systemic injection of a PPARα agonist. Mass spectrometry identified the species as 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine (16:0/18:1-GPC). Knockdown of CEPT1, required for phosphatidylcholine synthesis, suppressed PPARα-dependent gene expression. Interaction of 16:0/18:1-GPC with the PPARα ligand binding domain and co-activator peptide motifs was comparable to PPARα agonists, but interactions with PPARδ were weak and none were detected with PPARγ. Portal vein infusion of 16:0/18:1-GPC induced PPARα-dependent gene expression and decreased hepatic steatosis. These data suggest that 16:0/18:1-GPC is a physiologically relevant endogenous PPARα ligand.
SUMMARY De novo lipogenesis in adipocytes, especially with high fat feeding, is poorly understood. We demonstrate that an adipocyte lipogenic pathway encompassing fatty acid synthase (FAS) and PexRAP (Peroxisomal Reductase Activating PPARγ) modulates endogenous PPARγ activation and adiposity. Mice lacking FAS in adult adipose tissue manifested increased energy expenditure, increased brown fat-like adipocytes in subcutaneous adipose tissue, and resistance to diet-induced obesity. FAS knockdown in embryonic fibroblasts decreased PPARγ transcriptional activity and adipogenesis. FAS-dependent alkyl ether phosphatidylcholine species were associated with PPARγ and treatment of 3T3-L1 cells with one such ether lipid increased PPARγ transcriptional activity. PexRAP, a protein required for alkyl ether lipid synthesis, was associated with peroxisomes and induced during adipogenesis. PexRAP knockdown in cells decreased PPARγ transcriptional activity and adipogenesis. PexRAP knockdown in mice decreased expression of PPARγ–dependent genes and reduced diet-induced adiposity. These findings suggest that inhibiting PexRAP or related lipogenic enzymes could treat obesity and diabetes.
Central nervous system control of energy balance affects susceptibility to obesity and diabetes, but how fatty acids, malonyl-CoA, and other metabolites act at this site to alter metabolism is poorly understood. Pharmacological inhibition of fatty acid synthase (FAS), rate limiting for de novo lipogenesis, decreases appetite independently of leptin but also promotes weight loss through activities unrelated to FAS inhibition. Here we report that the conditional genetic inactivation of FAS in pancreatic β cells and hypothalamus produced lean, hypophagic mice with increased physical activity and impaired hypothalamic PPARα signaling. Administration of a PPARα agonist into the hypothalamus increased PPARα target genes and normalized food intake. Inactivation of β cell FAS enzyme activity had no effect on islet function in culture or in vivo. These results suggest a critical role for brain FAS in the regulation of not only feeding, but also physical activity, effects that appear to be mediated through the provision of ligands generated by FAS to PPARα. Thus, 2 diametrically opposed proteins, FAS (induced by feeding) and PPARα (induced by starvation), unexpectedly form an integrative sensory module in the central nervous system to orchestrate energy balance. IntroductionHigher organisms adapt to changes in energy needs by assimilating peripheral hormonal and nutritional cues and integrating them in the central nervous system (1, 2). Even subtle defects in this system have deleterious consequences since modest excess weight in humans is associated with increased mortality (3, 4). The most thermodynamically efficient strategy for weight loss is appetite suppression, a difficult goal given the diversity of factors regulating food intake, ranging from amines and peptides to metabolites and fatty acids (reviewed in ref. 5).Fatty acid metabolism affects feeding behavior. Malonyl-CoA, an intermediary substrate controlling fatty acid flux, and carnitine palmitoyltransferase-1 (CPT-1), which allows fatty acids access to mitochondria for β-oxidation, have been independently implicated in regulating appetite (6, 7). Pharmacological inhibition of fatty acid synthase (FAS), the multifunctional enzyme that utilizes malonyl-CoA for the first committed step in fatty acid biosynthesis (8), with the compound C75 produces anorexia and weight loss in mice in the setting of increased malonyl-CoA (9). However, recent studies indicate that these effects on malonyl-CoA alone may not be sufficient to induce anorexia, as C75 also has an impact on the sympathetic nervous system and metabolic mediators, including PPARα and PPARγ coactivator-1 α (PGC1α) (10, 11). In addition,
Dietary fat promotes pathological insulin resistance through chronic inflammation1–3. Macrophage inactivation of inflammatory proteins improves diet-induced diabetes4, but how nutrient-dense diets induce diabetes is unknown5. Membrane lipids affect the innate immune response6, which requires domains7 that influence high-fat diet (HFD)-induced chronic inflammation8,9 and alter cell function based on phospholipid composition10. Endogenous fatty acid synthesis, mediated by fatty acid synthase (FAS)11, affects membrane composition. Here we show that macrophage FAS is indispensable for dietinduced inflammation. Deleting FAS in macrophages prevents diet-induced insulin resistance, adipose macrophage recruitment, and chronic inflammation in mice. FAS deficiency alters membrane order and composition, impairing retention of plasma membrane cholesterol, as well as disrupting Rho GTPase trafficking required for cell adhesion, migration, and activation. Expressing a constitutively active Rho GTPase restored inflammatory signaling. Exogenous palmitate partitioned to different pools than endogenous lipids and did not rescue inflammatory signaling. However, exogenous cholesterol as well as other planar sterols rescued signaling, and exogenous cholesterol restored FAS-induced perturbations in membrane order. Endogenous fat production in macrophages is necessary for exogenous fat-induced insulin resistance by creating a receptive environment at the plasma membrane for assembly of cholesterol-dependent signaling networks.
This Mini-Review summarizes the historic developments and technological achievements in the biotechnological production of glutathione in the past 30 years. Glutathione is the most abundant non-protein thiol compound present in living organisms. It is used as a pharmaceutical compound and can be used in food additives and the cosmetic industries. Glutathione can be produced using enzymatic methods in the presence of ATP and its three precursor amino acids (L-glutamic acid, L-cysteine, glycine). Alternatively, glutathione can be produced by direct fermentative methods using sugar as a starting material. In the latter method, Saccharomyces cerevisiae and Candida utilis are currently used to produce glutathione on an industrial scale. At the molecular level, the genes gshA and gshB, which encode the enzymes gamma-glutamylcysteine synthetase and glutathione synthetase, respectively, have been cloned from Escherichia coli and over-expressed in E. coli, S. cerevisiae, and Lactococcus lactis. It is anticipated that, with the design and/or discovery of novel producers, the biotechnological production of glutathione will be further improved to expand the application range of this physiologically and medically important tripeptide.
Hemorrhagic shock (HS) due to major trauma and surgery predisposes the host to the development of systemic inflammatory response syndrome (SIRS) including acute lung injury (ALI) through activating and exaggerating the innate immune response. IL-1β is a crucial pro-inflammatory cytokine that contributes to the development of SIRS and ALI. Lung endothelial cells (EC) are one important source of IL-1β, and the production of active IL-1β is controlled by the inflammasome. In this study, we addressed the mechanism underlying HS activation of the inflammasome in lung EC. We show that high mobility group box 1 (HMGB1) acting through TLR4, and a synergistic collaboration with TLR2 and RAGE signaling, mediates HS-induced activation of EC NAD(P)H oxidase. In turn, reactive oxygen species (ROS) derived from NAD(P)H oxidase promote the association of thioredoxin-interacting protein (TXNIP) with the Nod-like receptor protein NLRP3 and subsequently induce inflammasome activation and IL-1β secretion from the EC. We also show that neutrophil-derived ROS play a role in enhancing EC NAD(P)H oxidase activation, and therefore an amplified inflammasome activation in response to HS. The present study explores a novel mechanism underlying HS activation of EC inflammasome and, thus, presents a potential therapeutic target for SIRS and ALI induced after HS.
Exogenous dietary fat can induce obesity and promote diabetes, but endogenous fat production is not thought to affect skeletal muscle insulin resistance, an antecedent of metabolic disease. Unexpectedly, the lipogenic enzyme fatty acid synthase (FAS) was increased in the skeletal muscle of mice with diet-induced obesity and insulin resistance. Skeletal muscle-specific inactivation of FAS protected mice from insulin resistance without altering adiposity, specific inflammatory mediators of insulin signaling, or skeletal muscle levels of diacylglycerol or ceramide. Increased insulin sensitivity despite high-fat feeding was driven by activation of AMPK without affecting AMP content or the AMP/ATP ratio in resting skeletal muscle. AMPK was induced by elevated cytosolic calcium caused by impaired sarco/endoplasmic reticulum calcium ATPase (SERCA) activity due to altered phospholipid composition of the sarcoplasmic reticulum (SR), but came at the expense of decreased muscle strength. Thus, inhibition of skeletal muscle FAS prevents obesity-associated diabetes in mice, but also causes muscle weakness, which suggests that mammals have retained the capacity for lipogenesis in muscle to preserve physical performance in the setting of disrupted metabolic homeostasis.
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