Anabolic Lipid Metabolism Research Articles

Increasing Energetic Demands on Photoreceptors in Diabetes Corrects Retinal Lipid Dysmetabolism and Reduces Subsequent Microvascular Damage

Mechanisms responsible for the pathogenesis of diabetic retinal disease remain incompletely understood, but they likely involve multiple cellular targets, including photoreceptors. Evidence suggests that dysregulated de novo lipogenesis in photoreceptors is a critical early target of diabetes. Following on this observation, the present study aimed to determine whether two interventions shown to improve diabetic retinopathy in mice-pharmacologic visual cycle inhibition and prolonged dark adaptation-reduce photoreceptor anabolic lipid metabolism. Elevated retinal lipid biosynthetic signaling was observed in two mouse models of diabetes, with both models showing reduced retinal AMP-activated kinase (AMPK) signaling, elevated acetyl CoA carboxylase (ACC) signaling, and increased activity of fatty acid synthase, which promotes lipotoxicity in photoreceptors. Although retinal AMPK-ACC axis signaling was dependent on systemic glucose fluctuations in healthy animals, mice with diabetes lacked such regulation. Visual cycle inhibition and prolonged dark adaptation reversed abnormal retinal AMPK-ACC signaling in mice with diabetes. Although visual cycle inhibition reduced the severity of diabetic retinopathy in control mice, as assessed by retinal capillary atrophy, this intervention was ineffective in fatty acid synthase gain-of-function mice. These results suggest that early diabetic retinopathy is characterized by glucose-driven elevations in retinal lipid biosynthetic activity, and that two interventions known to increase photoreceptor glucose demands alleviate disease by reversing these signals.

Enzyme-Catalyzed Hydrogen-Deuterium Exchange between Environmental Pollutants and Enzyme-Regulated Endogenous Metabolites.

Environmental pollutants can disrupt the homeostasis of endogenous metabolites in organisms, leading to metabolic disorders and syndromes. However, it remains highly challenging to efficiently screen for critical biological molecules affected by environmental pollutants. Herein, we found that enzyme could catalyze hydrogen-deuterium (H-D) exchange between a deuterium-labeled environmental pollutant [D38-bis(2-ethylhexyl) phthalate (D38-DEHP)] and several groups of enzyme-regulated metabolites [cardiolipins (CLs), monolysocardiolipins (MLCLs), phospholipids (PLs), and lysophospholipids (LPLs)]. A high-throughput scanning identified the D-labeled endogenous metabolites in a simple enzyme [phospholipase A2 (PLA2)], enzyme mixtures (liver microsomes), and living organisms (zebrafish embryos) exposed to D38-DEHP. Mass fragmentation and structural analyses showed that similar positions were D-labeled in the CLs, MLCLs, PLs, and LPLs, and this labeling was not attributable to natural metabolic transformations of D38-DEHP or incorporation of its D-labeled side chains. Molecular docking and competitive binding analyses revealed that DEHP competed with D-labeled lipids for binding to the active site of PLA2, and this process mediated H-D exchange. Moreover, competitive binding of DEHP against biotransformation enzymes could interfere with catabolic or anabolic lipid metabolism and thereby affect the concentrations of endogenous metabolites. Our findings provide a tool for discovering more molecular targets that complement the known toxic endpoints of metabolic disruptors.

Gochujang Consumption Prevents Metabolic Syndrome in a High-Fat Diet Induced Obese Mouse Model

High-fat and high-salt diets are risk factors for metabolic syndrome development. However, gochujang, which has a high salt content, possesses antiobesity properties in cell and animal models. We aimed to evaluate the effects of Sunchang traditional and modern factory produced gochujang on metabolic syndrome factors in high-fat diet (HFD)-induced obese mice. For 14 weeks, 4-week-old C57BL/6J male mice were separated into five groups and fed a normal diet (ND), a high-fat diet only (HD), a HD with salt (SALT), a HD with traditional Sunchang gochujang (TS), and HD with modern factory made Sunchang gochujang (FS). Compared to HD and SALT groups, the gochujang groups had lower body weight, blood leptin, and insulin levels with reduced Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) index and improved serum and liver lipid profiles. In addition, gochujang supplemented groups exhibited a significant reduction in mRNA expression of anabolic lipid metabolism related factors; PPARγ, CEBPα, and FABP4, and a significant increase in mRNA expression of energy expenditure-related factors; PPARα and CPT1. Protein expressions of SREBP1 were downregulated in the gochujang fed groups. TS and FS intakes improved obesity in HFD-induced obese mice. Compared to the gochujang groups, the SALT group did not exhibit any of those benefits suggesting that the high salt content of gochujang has different effects compared with added salt alone. Our findings provide evidence that gochujang could be a functional food to attenuate metabolic syndrome.

Traditional Sunchang Gochujang Attenuates Obesity in High-Fat Diet Induced Obese Mice

ObjectivesObesity is a major global health crisis. High fat diet (HFD) and salt intake have been linked to leptin resistance and obesity. Korea has lower obesity prevalence relative to other countries, although Koreans consume various fermented substances containing high salt, such as gochujang and doenjang amongst others. This phenomenon is defined as “the Korean paradox”. Gochujang is a Korean fermented pepper paste that contains high amount of salt. Therefore, we aimed to evaluate the anti-obesity potential of traditional gochujang on HFD-induced obese mice by comparing its effects with HFD and HFD containing same amount of salt from traditional gochujang.Methods4 weeks old C57BL/6J male mice were divided into 4 groups and fed a normal diet (ND), HFD (HD), HFD + salt (SALT) and HFD + traditional sunchang gochujang (TS) diets for 14 weeks. Biochemical analyses of serum, liver, and brown and epididymal fat tissues were performed to assess metabolic changes and obesity-related markers. The expressions of mRNA and protein involved in obesity, lipogenesis, adipogenesis and energy expenditure were evaluated from liver, brown and epididymal fat tissues by qPCR and western blot.ResultsTS supplementation significantly reduced obesity in HFD-induced obese mice. Compared to HD, TS had a lower body weight (24%), reduced serum leptin and insulin levels and improved serum and liver lipid profiles. Compared to HD and SALT groups, TS group had a significant reduction of mRNA and protein expressions associated with anabolic lipid metabolism including leptin, PPARγ, CEBPα, FAS, and ACC, while showing significant increase of adiponectin and energy expenditure-related mRNA, such as PPARα and CPT1.ConclusionsTS ameliorates obesity in HFD-induced obese mice by boosting leptin levels and inhibiting the adipogenesis and lipogenesis. Also, SALT group did not show any improvements compared with TS group. These observations imply that high salt content of TS is not a problematic feature. Our findings prove “the Korean paradox” of gochujang and anti-obesity effects of traditional gochujang, proposing the possibility of the traditional gochujang as a functional food against obesity.Funding SourcesMinistry of Agriculture, Food and Rural Affairs and partly Korea Agro-Fisheries and Food trade corporation.

Innate immune signaling in Drosophila shifts anabolic lipid metabolism from triglyceride storage to phospholipid synthesis to support immune function

During infection, cellular resources are allocated toward the metabolically-demanding processes of synthesizing and secreting effector proteins that neutralize and kill invading pathogens. In Drosophila, these effectors are antimicrobial peptides (AMPs) that are produced in the fat body, an organ that also serves as a major lipid storage depot. Here we asked how activation of Toll signaling in the larval fat body perturbs lipid homeostasis to understand how cells meet the metabolic demands of the immune response. We find that genetic or physiological activation of fat body Toll signaling leads to a tissue-autonomous reduction in triglyceride storage that is paralleled by decreased transcript levels of the DGAT homolog midway, which carries out the final step of triglyceride synthesis. In contrast, Kennedy pathway enzymes that synthesize membrane phospholipids are induced. Mass spectrometry analysis revealed elevated levels of major phosphatidylcholine and phosphatidylethanolamine species in fat bodies with active Toll signaling. The ER stress mediator Xbp1 contributed to the Toll-dependent induction of Kennedy pathway enzymes, which was blunted by deleting AMP genes, thereby reducing secretory demand elicited by Toll activation. Consistent with ER stress induction, ER volume is expanded in fat body cells with active Toll signaling, as determined by transmission electron microscopy. A major functional consequence of reduced Kennedy pathway induction is an impaired immune response to bacterial infection. Our results establish that Toll signaling induces a shift in anabolic lipid metabolism to favor phospholipid synthesis and ER expansion that may serve the immediate demand for AMP synthesis and secretion but with the long-term consequence of insufficient nutrient storage.

Abstract 2967: Pancreatic cancer cell growth requires lipids released by tumor-induced stroma autophagy

Abstract Pancreatic ductal adenocarcinoma (PDAC) is non-resectable in the majority of patients and highly resistant to chemotherapy, resulting in a poor survival. The tumor microenvironment and hypoxia are important modifiers of cancer progression in PDAC. Understanding the metabolic vulnerabilities of PDAC in the harsh tumor microenvironment may lead to novel therapeutic approaches with improved clinical efficacy. First, we found that PDAC cells showed beneficial effects of co-cultured stroma cells, but only under lipid-free serum conditions. To study the metabolic crosstalk between cancer cells and stroma in more detail, we performed an untargeted metabolomic screen of PDAC cells and fibroblasts co-cultured in normoxia and hypoxia, and performed RNA-seq profiling in parallel. We found that stromal cells are metabolically more responsive to co-culture than cancer cells. PDAC cells induce catabolic carbohydrate and protein metabolism in stromal cells, particularly in hypoxia. In contrast, 13C-based metabolic flux assays demonstrated that stromal cells display enhanced anabolic lipid metabolism in co-culture with PDAC cells. Furthermore, de novo synthesized 13C-labeled fatty acids in stromal cells were taken up by PDAC cells. In particular, PDAC cells showed extensive scavenging of lysophospholipids (lyso-PLs) from the culture medium, which was increased in co-culture under hypoxic conditions. These data were confirmed by analyzing portal vein plasma samples isolated from pancreatic cancer patients before and after surgery. In addition, we found metabolites and expression levels of metabolic enzymes from the glycerophospholipid pathway to be enriched in PDAC cells in co-culture and hypoxia. By using fibroblasts, human pancreatic stellate cells and patient-derived cancer-associated fibroblasts (CAFs), we demonstrate direct transfer of lyso-PLs from stromal to PDAC cells via lipid droplets. The transfer of lyso-PLs was abrogated by pharmacological inhibitors of autophagy, or by siRNA-mediated knockdown of autophagy genes in stromal and tumor cells. These data suggest that PDAC cells cause stroma cells to undergo autophagy, and reprogram stroma metabolism to obtain complex lipid species for their metabolic needs in the lipid-starved tumor microenvironment. Citation Format: Petrus R. De Jong, Sean-Luc Shanahan, Morgan A. Brand, Alejandro D. Campos, Anagha Srirangam, Nikolas Marino, Claudia P. Miller, Olga Zagnitko, Adam D. Richardson, David A. Scott, Brian P. James, Andrew P. Hodges, Ally Perlina, Alexey M. Eroshin, Randall French, Malene Hansen, Sally A. Litherland, Andrew M. Lowy, J. Pablo Arnoletti, Garth Powis. Pancreatic cancer cell growth requires lipids released by tumor-induced stroma autophagy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2967. doi:10.1158/1538-7445.AM2017-2967

ABCD2 identifies a subclass of peroxisomes in mouse adipose tissue

ATP-binding cassette transporter D2 (D2) is an ABC half transporter that is thought to promote the transport of very long-chain fatty acyl-CoAs into peroxisomes. Both D2 and peroxisomes increase during adipogenesis. Although peroxisomes are essential to both catabolic and anabolic lipid metabolism, their function, and that of D2, in adipose tissues remain largely unknown. Here, we investigated the D2 localization and the proteome of D2-containing organelles, in adipose tissue. Centrifugation of mouse adipose homogenates generated a fraction enriched with D2, but deficient in peroxisome markers including catalase, PEX19, and ABCD3 (D3). Electron microscopic imaging of this fraction confirmed the presence of D2 protein on an organelle with a dense matrix and a diameter of ∼200nm, the typical structure and size of a microperoxisome. D2 and PEX19 antibodies recognized distinct structures in mouse adipose. Immunoisolation of the D2-containing compartment confirmed the scarcity of PEX19 and proteomic profiling revealed the presence of proteins associated with peroxisome, endoplasmic reticulum (ER), and mitochondria. D2 is localized to a distinct class of peroxisomes that lack many peroxisome proteins, and may associate physically with mitochondria and the ER.

Postprandial Hepatic Lipid Metabolism Requires Signaling through Akt2 Independent of the Transcription Factors FoxA2, FoxO1, and SREBP1c

Under conditions of obesity and insulin resistance, the serine/threonine protein kinase Akt/PKB is required for lipid accumulation in liver. Two forkhead transcription factors, FoxA2 and FoxO1, have been suggested to function downstream of and to be negatively regulated by Akt and are proposed as key determinants of hepatic triglyceride content. In this study, we utilize genetic loss of function experiments to show that constitutive activation of neither FoxA2 nor FoxO1 can account for the protection from steatosis afforded by deletion of Akt2 in liver. Rather, another downstream target positively regulated by Akt, the mTORC1 complex, is required invivo for de novo lipogenesis and Srebp1c expression. Nonetheless, activation of mTORC1 and SREBP1c is not sufficient to drive postprandial lipogenesis in the absence of Akt2. These data show that insulin signaling through Akt2 promotes anabolic lipid metabolism independent of Foxa2 or FoxO1 and through pathways additional to the mTORC1-dependent activation of SREBP1c.

The effect of ractopamine hydrochloride on gene expression in adipose tissues of finishing pigs1

The long-term effect of feeding the catecholamine analog ractopamine (RAC; ractopamine hydrochloride, Elanco Animal Health, Indianapolis, IN) on the expression of genes involved in energy and lipid metabolism in subcutaneous adipose tissue was studied. Large White pigs (84 kg) were fed corn- and soybean meal-based diets supplemented with 0, 20, or 60 mg/kg of RAC for 14, 28, or 42 d. Expression (mRNA abundance) in adipose tissue of sterol regulatory binding protein-1 (SREBP-1), PPARα, PPARγ2, fatty acid synthase (FAS), glucose transporter 4 (GLUT4), and stearoyl-CoA desaturase was determined by Northern blotting. Feed intakes did not differ, and RAC (20 and 60 mg/kg) improved BW gain at d 14, 28, and 42 (P < 0.05) and increased loin eye area (measured on d 42 only; P < 0.05). Expression of SREBP-1 and PPARγ2 declined (P < 0.05) with RAC by d 28 and 42, whereas expression of PPARα was increased (P < 0.05) on d 14, 28, and 42. After 14 d, expression of FAS and GLUT4 was decreased (P < 0.05) with 60 mg/kg of RAC, whereas both RAC concentrations attenuated FAS expression on d 28 and 42. Overall, adipose tissue stearoyl-CoA desaturase expression was not affected by RAC but showed somewhat less expression (P < 0.15) on d 28 at 60 mg/kg of RAC. Although prolonged, chronic RAC feeding most likely downregulates adipose tissue membrane β-adrenergic receptors, mRNA abundances of anabolic lipid metabolism transcription factors, glucose transporters, and enzymes (SREBP-1, PPARγ2, FAS, GLUT4) were still attenuated up to d 42. Conversely, a transcription factor related to oxidative metabolism expression (PPARα) was enhanced. We conclude that even after 42 d, RAC still decreased expression of lipogenic genes in adipose tissue by yet undefined cyclic adenosine monophosphate-directed mechanisms, but in contemporary lean pigs, this effect is likely of limited practical significance.

The regulation of hepatic metabolism by insulin

Central to the signaling cascade by which insulin regulates metabolism in liver, muscle and adipose tissue is the serine/threonine protein kinase Akt, also known as Protein Kinase B. Each of the three Akt family members has distinct roles in normal physiology. The isoform specificity in hepatic metabolism is evident in liver, in that Akt2 deletion abrogates control of lipogenic gene expression, but insulin is still capable of regulating the genes encoding gluconeogenic proteins. Most impressively, deletion of Akt2 selectively in the liver leads to marked abnormalities in anabolic lipid metabolism, whereas glucose metabolism is relatively normal. Deletion of both Akt2 genes results in significant glucose intolerance. The phenotype of livers deficient in Akt2, which are protected from accumulation of fat in the liver, support the hypothesis insulin resistance under pathological conditions is “selective”, retaining the ability of insulin to regulate anabolic lipid pathways while losing suppression of hepatic glucose output.

Regulation of Fat Cell Mass by Insulin in Drosophila melanogaster

A phylogenetically conserved response to nutritional abundance is an increase in insulin signaling, which initiates a set of biological responses dependent on the species. Consequences of augmented insulin signaling include developmental progression, cell and organ growth, and the storage of carbohydrates and lipids. Here, we address the evolutionary origins of insulin's positive effects on anabolic lipid metabolism by selectively modulating insulin signaling in the fat body of the fruit fly, Drosophila melanogaster. Analogous to the actions of insulin in higher vertebrates, those in Drosophila include expansion of the insect fat cell mass both by increasing the adipocyte number and by promoting lipid accumulation. The ability of insulin to accomplish the former depends on its capacity to bring about phosphorylation and inhibition of the transcription factor Drosophila FOXO (dFOXO) and the serine/threonine protein kinase shaggy, the fly ortholog of glycogen synthase kinase 3 (GSK3). Increasing the amount of triglyceride per cell also depends on the phosphorylation of shaggy but is independent of dFOXO. Thus, the findings of this study provide evidence that the control of fat mass by insulin is a conserved process and place dFOXO and shaggy/GSK3 downstream of the insulin receptor in controlling adipocyte cell number and triglyceride storage, respectively.

17β-Estradiol inhibits 11β-hydroxysteroid dehydrogenase type 1 activity in rodent adipocytes

17Beta-estradiol (E(2)) serves as an anti-obesity steroid; however, the mechanism underlying this effect has not been fully clarified. The effect of E(2) on adipocytes opposes that of glucocorticoids, which potentiate adipogenesis and anabolic lipid metabolism. The key to the intracellular activation of glucocorticoid in adipocytes is 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), which catalyses the production of active glucocorticoids (cortisol in humans and corticosterone in rodents) from inactive 11-keto steroids (cortisone in humans and 11-dehydrocorticosterone in rodents). Using differentiated 3T3-L1 adipocytes, we showed that E(2) inhibited 11beta-HSD1 activity. Estrogen receptor (ER) antagonists, ICI-182 780 and tamoxifen, failed to reverse this inhibition. A significant inhibitory effect of E(2) on 11beta-HSD1 activity was observed within 5-10 min. Furthermore, acetylation or alpha-epimerization of 17-hydroxy group of E(2) attenuated the inhibitory effect on 11beta-HSD1. These results indicate that the inhibition of 11beta-HSD1 by E(2) depends on neither an ER-dependent route, transcriptional pathway nor non-specific fashion. Hexose-6-phosphate dehydrogenase, which provides the cofactor NADPH for full activation of 11beta-HSD1, was unaffected by E(2). A kinetic study revealed that E(2) acted as a non-competitive inhibitor of 11beta-HSD1. The inhibitory effect of E(2) on 11beta-HSD1 was reproduced in adipocytes isolated from rat mesenteric fat depots. This is the first demonstration that E(2) inhibits 11beta-HSD1, thereby providing a novel insight into the anti-obesity mechanism of estrogen.

Adipose tissue beta-adrenergic and A1 adenosine receptors in suckling pigs.

During the first few weeks after birth, major changes occur in porcine adipocyte lipid metabolism. Two of the important receptors controlling lipid metabolism in adipocytes are the beta-adrenergic receptors (betaAR) and the A1 adenosine receptors (A1R). To gain insight into the role of these receptors in modulating neonatal adipocyte lipid metabolism, we measured receptor affinity and number in suckling pigs. Adipose tissue from crossbred (X-Bred) and genetically obese suckling pigs at 0, 3, 10, and 17 d of age was used to prepare crude membranes. The betaAR and A1R number and affinity were measured in membranes by equilibrium saturation binding with radioligands. Obese pigs were smaller than X-Bred pigs (average weight = 1.62 and 2.43 kg for obese and X-Bred, respectively; P < .01). Osmium-fixed adipocytes were larger in obese pigs than in X-Bred pigs (average cell diameter = 34.4 and 30.1 microm for obese and X-Bred, respectively; P < .01). In the obese and X-Bred pigs, the affinity of the betaAR for iodocyanopindolol was greater (lower Kd) at 17 d than at the younger ages (average Kd = 177 pM at 17 d compared with > 330 pM at younger ages; age effect P < .01). The pattern for the betaAR number was complex; the lowest receptor number was at 10 d of age in obese and X-Bred pigs (average number = 41 at 10 d compared with > 65 fmol/mg protein at older and younger ages; age effect P = .03). The higher betaAR Kd and the lower receptor number in younger animals suggest less regulation by physiologic concentrations of epinephrine and norepinephrine. This would allow greater anabolic lipid metabolism to proceed during the neonatal period, when adipocytes increase four- to sixfold in volume. There were no measurable A1R at any of these early ages; thus, adenosine control mechanisms to counteract the betaAR and provide negative controls to lipid accretion are not operable in suckling pigs.